Provenance of fine-grained sediments in the inner shelf of the Korea Strait (South Sea), Korea

NASA Astrophysics Data System (ADS)

Um, In kwon; Choi, Man Sik; Bae, Sung Ho; Song, Yunho; Kong, Gee Soo

2017-12-01

Major metals (Al, Fe, Mg, and Ti), trace metals (Li, Cs, Sc, and Rb), and rare earth elements (REEs) in the fine-grained sediments (< 15 μm) of the central South Sea mud (CSSM) were analyzed to determine the sediment provenance. The spatial distribution of the analyzed elements showed a clear separation between the western (W-CSSM) and eastern (E-CSSM) regions of the CSSM. Concentrations of Fe, Ti, Mg, Sc, and REEs were higher in the WCSSM, whereas concentrations of Al, Cs, Li, and Rb were higher in the E-CSSM. Unlike the ratios of trace metals ((Cs+Sc)/Li and Rb/Li), REEs could not be used to track the provenance of fine-grained sediments because of a grain size effect. The mixing relationships of the provenance indicators showed that the fine-grained sediments of the CSSM comprise a mixture of the sediments discharged from the Seomjin River (SRS) and sediments eroded and transported from the Heuksan mud belt (HMBS) area by the Korean Coastal Current. Sediments originating from the HMB were deposited mostly in the W-CSSM, whereas those from the Seomjin River were deposited mostly in the E-CSSM. This study indicated that sediments from Chinese rivers as well as the Geum River are important even in the inner shelf of the South Sea of Korea.

Provenance of Fine-grained Sediments in the Inner Shelf of the Korea Strait (South Sea), Korea

NASA Astrophysics Data System (ADS)

Um, In kwon; Choi, Man Sik; Bae, Sung Ho; Song, Yunho; Kong, Gee Soo

2018-03-01

Major metals (Al, Fe, Mg, and Ti), trace metals (Li, Cs, Sc, and Rb), and rare earth elements (REEs) in the fine-grained sediments (< 15 μm) of the central South Sea mud (CSSM) were analyzed to determine the sediment provenance. The spatial distribution of the analyzed elements showed a clear separation between the western (W-CSSM) and eastern (E-CSSM) regions of the CSSM. Concentrations of Fe, Ti, Mg, Sc, and REEs were higher in the WCSSM, whereas concentrations of Al, Cs, Li, and Rb were higher in the E-CSSM. Unlike the ratios of trace metals ((Cs+Sc)/Li and Rb/Li), REEs could not be used to track the provenance of fine-grained sediments because of a grain size effect. The mixing relationships of the provenance indicators showed that the fine-grained sediments of the CSSM comprise a mixture of the sediments discharged from the Seomjin River (SRS) and sediments eroded and transported from the Heuksan mud belt (HMBS) area by the Korean Coastal Current. Sediments originating from the HMB were deposited mostly in the W-CSSM, whereas those from the Seomjin River were deposited mostly in the E-CSSM. This study indicated that sediments from Chinese rivers as well as the Geum River are important even in the inner shelf of the South Sea of Korea.

Seafloor environments within the Boston Harbor- Massachusetts Bay sedimentary system: A regional synthesis

USGS Publications Warehouse

Knebel, H.J.; Circe, R.C.

1995-01-01

Modern seafloor sedimentary environments within the glaciated, topographically complex Boston Harbor and Massachusetts Bay area have been interpreted and mapped from an extensive collection of sidescan sonar records and supplemental marine geologic data. Three categories of environments are present that reflect the dominant long-term processes of erosion or nondeposition, deposition, and sediment reworking. (1) Environments of erosion or nondeposition comprise exposures of bedrock, glacial drift, coarse lag deposits, and possibly coastal plain rocks that contain sediments (where present) ranging from boulder fields to gravelly sands and occur in areas of relatively strong currents. (2) Environments of deposition contain fine-grained sediments ranging from muddy sands to muds that have accumulated in areas of predominantly weak bottom currents. (3) Environments of sediment reworking contain patches with textures ranging from sandy gravels to muds that have been produced by a combination of erosion and deposition in areas with variable bottom currents. The distribution of sedimentary environments across the Boston Harbor-Massachusetts Bay area is extremely patchy. Locally, this patchiness is due either to modifications of bottom-current strength (caused by the irregular topography and differences in water depth) or to small-scale changes in the supply of fine-grained sediments. Regional patchiness, however, reflects differences in geologic and oceanographic conditions among the estuarine, inner shelf, and basinal parts of the sedimentary system. The estuarine part of the system (Boston Harbor) is a depositional trap for fine-grained sediments because it is protected from large waves, has generally weak and variable tidal currents, and receives a large supply of fine grained detritus from natural and anthropogenic sources. The inner shelf, on the other hand, is largely an area of erosion or nondeposition due to sediment removal and redistribution during past sea-level changes, to sediment resuspension and winnowing by modern waves and currents, and to an inadequate supply of fine-grained sediments. The basinal part of the system (Stellwagen Basin) is mainly a tranquil depositional environment in which fine-grained sediments from several potential sources settle through the water column and accumulate under weak bottom currents. This study indicates areas within the Boston Harbor-Massachusetts Bay sedimentary system where fine-grained sediments and associated contaminants are likely to be either moved or deposited. It also provides a guide to the locations and variability of benthic habitats.

Geochemical evidence for the provenance of aeolian deposits in the Qaidam Basin, Tibetan Plateau

NASA Astrophysics Data System (ADS)

Du, Shisong; Wu, Yongqiu; Tan, Lihua

2018-06-01

The main purpose of this study is to analyse the material source of different grain-size components of dune sand in the Qaidam Basin. We determined the trace and rare earth element (REE) compositions and Sr-Nd isotopic compositions of the coarse (75-500 μm) and fine (<75 μm) fractions of surface sediment samples. The comparison of the immobile trace element and REE compositions, Sr-Nd isotopic compositions and multidimensional scaling (MDS) results of the dune sands with those of different types of sediments in potential source areas revealed the following information. (1) The fine- and coarse-grained fractions of dune sands in the Qaidam Basin exhibit distinctly different elemental concentrations, elemental patterns and characteristic parameters of REE. Moreover, Sr-Nd isotopic differences also exist between different grain-size fractions of aeolian sand, which means that different grain-size fractions of these dune sands have different source areas. (2) The geochemical characteristics of the coarse particles of dune sand exhibit obvious regional heterogeneity and generally record a local origin derived from local fluvial sediments and alluvial/proluvial sediments. The coarse- and fine-grained dune sand in the southern Qaidam Basin mainly came from Kunlun Mountains, whereas the coarse- and fine-grained dune sand in the northeastern Qaidam Basin mainly came from Qilian Mountains. (3) The fine-grained fractions of sediments throughout the entire Qaidam Basin may have been affected by the input of foreign materials from the Tarim Basin.

The response of excess 230Th and extraterrestrial 3He to sediment redistribution at the Blake Ridge, western North Atlantic

NASA Astrophysics Data System (ADS)

McGee, David; Marcantonio, Franco; McManus, Jerry F.; Winckler, Gisela

2010-10-01

The constant-flux proxies excess 230Th ( 230Th xs) and extraterrestrial 3He ( 3He ET) are commonly used to calculate sedimentary mass accumulation rates and to quantify lateral advection of sediment at core sites. In settings with significant lateral input or removal of sediment, these calculations depend on the assumption that concentrations of 230Th xs and 3He ET are the same in both advected sediment and sediment falling through the water column above the core site. Sediment redistribution is known to fractionate grain sizes, preferentially transporting fine grains; though relatively few studies have examined the grain size distribution of 230Th xs and 3He ET, presently available data indicate that both are concentrated in fine grains, suggesting that fractionation during advection may bias accumulation rate and lateral advection estimates based on these proxies. In this study, we evaluate the behavior of 230Th xs and 3He ET in Holocene and last glacial samples from two cores from the Blake Ridge, a drift deposit in the western North Atlantic. At the end of the last glacial period, both cores received large amounts of laterally transported sediment enriched in fine-grained material. We find that accumulation rates calculated by normalization to 230Th and 3He are internally consistent despite large spatial and temporal differences in sediment advection. Our analyses of grain size fractions indicate that ~ 70% of 3He ET-bearing grains are in the < 20 μm fraction, with roughly equal amounts in the < 4 and 4-20 μm fractions. 230Th xs is concentrated in <4-μm grains relative to 4- to 20-μm grains by approximately a factor of 2 in Holocene samples and by a much larger factor (averaging a factor of 10) in glacial samples. Despite these enrichments of both constant-flux proxies in fine particles, the fidelity of 230Th- and 3He-based accumulation rate estimates appears to be preserved even in settings with extreme sediment redistribution, perhaps due to the cohesive behavior of fine particles in marine settings.

Transport of fine sediment over a coarse, immobile riverbed

USGS Publications Warehouse

Grams, Paul E.; Wilcock, Peter R.

2014-01-01

Sediment transport in cobble-boulder rivers consists mostly of fine sediment moving over a coarse, immobile bed. Transport rate depends on several interrelated factors: boundary shear stress, the grain size and volume of fine sediment, and the configuration of fine sediment into interstitial deposits and bed forms. Existing models do not incorporate all of these factors. Approaches that partition stress face a daunting challenge because most of the boundary shear is exerted on immobile grains. We present an alternative approach that divides the bed into sand patches and interstitial deposits and is well constrained by two clear end-member cases: full sand cover and absence of sand. Entrainment from sand patches is a function of their aerial coverage. Entrainment from interstices among immobile grains is a function of sand elevation relative to the size of the immobile grains. The bed-sand coverage function is used to predict the ratio of the rate of entrainment from a partially covered bed to the rate of entrainment from a completely sand-covered bed, which is determined using a standard sand transport model. We implement the bed-sand coverage function in a morphodynamic routing model and test it against observations of sand bed elevation and suspended sand concentration for conditions of nonuniform fine sediment transport in a large flume with steady uniform flow over immobile hemispheres. The results suggest that this approach may provide a simple and robust method for predicting the transport and migration of fine sediment through rivers with coarse, immobile beds.

Morphology and processes associated with the accumulation of the fine-grained sediment deposit on the southern New England shelf

USGS Publications Warehouse

Twichell, David C.; McClennen, Charles E.; Butman, Bradford

1981-01-01

A 13,000 km2 area of the southern New England Continental Shelf which is covered by anomalously fine-grained sediment has been surveyed by means of high-resolution, seismic-reflection and side-scan sonar techniques to map its morphology and structure, and a near-bottom instrument system contributed to understanding present activity of the deposit. Seismic-reflection profiles show that the fine-grained deposit, which is as much as 13 m thick, has accumulated during the last transgression because it rests on a reflector that is geomorphically similar to and continuous with the Holocene transgressive sand sheet still exposed on the shelf to the west. The ridge and swale topography comprising the sand sheet on the shelf off New Jersey and Long Island are relict in origin as these same features are found buried under the fine sediment deposit. Southwestward migrating megaripples observed on the sonographs in the eastern part of the deposit are evidence that sediment is still actively accumulating in this area. In the western part of the deposit, where surface sediment is composed of silt plus clay, evidence of present sediment mobility consists of changes in the near-bottom, suspended-matter concentrations primarily associated with storms. Nantucket Shoals and Georges Bank are thought to be the sources for the fine-textured sediment. Storms and strong tidal currents in these shoal areas may still erode available fine-grained material, which then is transported westward by the mean drift to the southern New England Shelf, where a comparatively tranquil environment permits deposition of the fine material.

Spatial Statistics of Deep-Water Ambient Noise; Dispersion Relations for Sound Waves and Shear Waves

DTIC Science & Technology

2014-09-30

marine sediments. New focus is on very fine- grained sediments (silt and clay ). OBJECTIVES 1) The scientific objective of the deep-water ambient...density, grain size and overburden pressure. A new focus is on the inter-particle cohesive forces in silts and clays and their role in controlling wave...algebraic expressions. The GS theory is the basis for new research on very fine-grained sediments (silts and clays ), in which inter-granular cohesion is

Tephra Sedimentation from a Short-term Wind-affected Volcanic Plume of the 8 October 2016 Aso Nakadake Eruption, Japan

NASA Astrophysics Data System (ADS)

Tsuji, T.; Nishizaka, N.; Onishi, K.

2017-12-01

Sedimentation processes during explosive volcanic eruptions can be constrained based on detailed analysis of grain-size variation of tephra deposits. Especially, an accurate description of the amount of fine particles has also significant implications for the assessment of specific tephra hazards. Grain size studies for single short-term eruption has advantage to contribute understanding the sedimentation processes because it is simple compared to long-lasting eruption. The 2016 Aso Nakadake eruption, Japan represents an ideal for the study of short-term eruptions thanks to an accurate investigation. Then, we investigate the grain size variation with distance from the vent and sedimentological features of the deposit to discuss the sedimentation processes of the tephra fragments. The eruption provided pyroclastic flow deposit and fallout tephra which distributed NE to ENE direction from the vent. The deposits between 4 and 20 km from vent consist of fine-coated lapilli to coarse ash, ash pellet and mud droplet in ascending degree. The samples are lapilli-bearing within 20 km from vent and those outside of 20 km mainly consist of ash particles. Detailed analyses of individual samples highlight a rapid decay of maximum and mean grain size for the deposit from proximal to distal. The decay trend of maximum grain-size is approximated by three segments of exponential curves with two breaks-in-slope at 10 and 40 km from vent. Most of the sampled deposits are characterized by bimodal grain-size distributions, with the modes of the coarse subpopulation decreasing with distance from vent and those of the fine subpopulation being mostly stable. The fine subpopulation has been interpreted as being mostly associated with size-selective sedimentation processes (e.g., particle aggregation) confirmed by the existence of fine-coated particles, ash pellet and mud droplet. As the fine-coated particles generally have a higher terminal velocity than the individual constituent particles, those could be related with the rapid decrease of maximum grain-size with distance from vent at proximal area. Further detail grain-size analyses and theoretical studies can be contributed to understand the effect of fine ash aggregation on sedimentation processes quantitatively.

Nearshore disposal of fine-grained sediment in a high-energy environment: Santa Cruz Harbor case study

USGS Publications Warehouse

Cronin, Katherine; van Ormondt, Maarten; Storlazzi, Curt D.; Presto, Katherine; Tonnon, Pieter K.; Rosati, Julie D.; Wang, Ping; Roberts, Tiffany M.

2011-01-01

Current regulations in California prohibit the disposal of more than 20% fine-grained sediment in the coastal zone; this threshold is currently being investigated to determine if this environmental regulation can be improved upon. A field monitoring and numerical modeling experiment took place late 2 009 to determine the fate of fine-grained dredge disposal material from Santa Cruz Harbor, California, U.S.A. A multi-nested, hydrodynamic-sediment transport modeling approach was used to simulate the direction and dispersal of the dredge plume. Result s show that the direction and dispersal of the plume was influenced by the wave  climate, a large proportion of which moved in a easterly direction during wave events. Therefore it is vitally important to accurately simulate the tides, waves, currents, temperature and salinity when modeling the dispersal of the fine-grained dredge plume. 

The dynamics of fine-grain sediment dredged from Santa Cruz Harbor

USGS Publications Warehouse

Storlazzi, Curt D.; Conaway, Christopher H.; Presto, M. Katherine; Logan, Joshua B.; Cronin, Katherine; van Ormondt, Maarten; Lescinski, Jamie; Harden, E. Lynne; Lacy, Jessica R.; Tonnon, Pieter K.

2011-01-01

In the fall and early winter of 2009, a demonstration project was done at Santa Cruz Harbor, California, to determine if 450 m3/day of predominantly (71 percent) mud-sized sediment could be dredged from the inner portion of the harbor and discharged to the coastal ocean without significant impacts to the beach and inner shelf. During the project, more than 7600 m3 of sediment (~5400 m3 of fine-grain material) was dredged during 17 days and discharged approximately 60 m offshore of the harbor at a depth of 2 m on the inner shelf. The U.S. Geological Survey's Pacific Coastal and Marine Science Center was funded by the U.S. Army Corps of Engineers and the Santa Cruz Port District to do an integrated mapping and process study to investigate the fate of the mud-sized sediment dredged from the inner portion of Santa Cruz Harbor and to determine if any of the fine-grain material settled out on the shoreline and/or inner shelf during the fall and early winter of 2009. This was done by collecting highresolution oceanographic and sediment geochemical measurements along the shoreline and on the continental shelf of northern Monterey Bay to monitor the fine-grain sediment dredged from Santa Cruz Harbor and discharged onto the inner shelf. These in place measurements, in conjunction with beach, water column, and seabed surveys, were used as boundary and calibration information for a three-dimensional numerical circulation and sediment dynamics model to better understand the fate of the fine-grain sediment dredged from Santa Cruz Harbor and the potential consequences of disposing this type of material on the beach and on the northern Monterey Bay continental shelf.

Grain size statistics and depositional pattern of the Ecca Group sandstones, Karoo Supergroup in the Eastern Cape Province, South Africa

NASA Astrophysics Data System (ADS)

Baiyegunhi, Christopher; Liu, Kuiwu; Gwavava, Oswald

2017-11-01

Grain size analysis is a vital sedimentological tool used to unravel the hydrodynamic conditions, mode of transportation and deposition of detrital sediments. In this study, detailed grain-size analysis was carried out on thirty-five sandstone samples from the Ecca Group in the Eastern Cape Province of South Africa. Grain-size statistical parameters, bivariate analysis, linear discriminate functions, Passega diagrams and log-probability curves were used to reveal the depositional processes, sedimentation mechanisms, hydrodynamic energy conditions and to discriminate different depositional environments. The grain-size parameters show that most of the sandstones are very fine to fine grained, moderately well sorted, mostly near-symmetrical and mesokurtic in nature. The abundance of very fine to fine grained sandstones indicate the dominance of low energy environment. The bivariate plots show that the samples are mostly grouped, except for the Prince Albert samples that show scattered trend, which is due to the either mixture of two modes in equal proportion in bimodal sediments or good sorting in unimodal sediments. The linear discriminant function analysis is dominantly indicative of turbidity current deposits under shallow marine environments for samples from the Prince Albert, Collingham and Ripon Formations, while those samples from the Fort Brown Formation are lacustrine or deltaic deposits. The C-M plots indicated that the sediments were deposited mainly by suspension and saltation, and graded suspension. Visher diagrams show that saltation is the major process of transportation, followed by suspension.

Variations in grain-scale sediment structure and entrainment force in a gravel-bed channel as a function of fine sediment content and morphological location

NASA Astrophysics Data System (ADS)

Voepel, Hal; Ahmed, Sharif; Hodge, Rebecca; Leyland, Julian; Sear, David

2017-04-01

One of the major causes of uncertainty in estimates of bedload transport rates in gravel-bed rivers is a lack of understanding of grain-scale sediment structure, and the impact that this structure has on the force required to entrain sediment. There are at least two factors that standard entrainment models do not consider. The first is the way in which the spatial arrangement and orientation of grains and the resultant forces varies throughout a channel and over time, ways that have yet to be fully quantified. The second is that sediment entrainment is a 3D process, yet calculations of entrainment thresholds for sediment grains are typically based on 2D diagrams where we calculate static moments of force vectors about a pivot angle, represented as a single point rather than as a more realistic axis of rotation. Our research addresses these limitations by quantifying variations in 3D sediment structure and entrainment force requirements across two key parameters: morphological location within a riffle-pool sequence (reflecting variation in hydraulic conditions), and the fine sediment content of the gravel-bed (sand and clay). We report results from a series of flume experiments in which we water-worked a gravel-bed with a riffle-pool morphology containing varying amounts of fine sediment. After each experimental run intact samples of the bed at different locations were extracted and the internal structure of the bed was measured using non-destructive, micro-focus X-ray computed tomography (CT) imaging. The CT images were processed to measure the properties of individual grains, including volume, center of mass, dimension, and contact points. From these data we were able to quantify the sediment structure and entrainment force requirements through measurement of 3D metrics including grain pivot angles, grain exposure and protrusion. Comparison of the metrics across different morphological locations and fine sediment content demonstrates how these factors affect the bed structure and entrainment force requirement. These results have implications for the development of sediment entrainment models for gravel-bed rivers. Keywords: fluvial sediment, geomorphology, entrainment models, X-ray computed tomography, 3D imaging, vector mechanics

K/Ar Dating of Fine Grained Sediments Near Prydz Bay, Antarctica: East Antarctic Ice Sheet Behavior During the Middle-Miocene Climate Transition

NASA Astrophysics Data System (ADS)

Duchesne, A. E.; Pierce, E. L.; Williams, T.; Hemming, S. R.; Johnson, D. L.; May, T.; Gombiner, J.; Torfstein, A.

2012-12-01

¶ The Middle Miocene Climate Transition (MMCT) (~14 Ma) represents a time of major East Antarctic Ice-Sheet (EAIS) expansion, with research suggesting major global sea level fall on the order of ~60 meters (John et al., 2011, EPSL). Ocean Drilling Program (ODP) core data from Site 1165B near Prydz Bay shows an influx of cobbles deposited ~13.8-13.5 Ma, representing a sudden burst of ice-rafted detritus (IRD) during the MMCT. Based on 40Ar/39Ar dating of hornblendes and/or biotite grains, 5 of 6 dated pebbles from a companion study show Wilkes Land origins, indicating transport from over 1500 kilometers away. However, samples throughout this time interval have an anomalously low abundance of sand, thus we seek to understand the sedimentary processes that led to the deposition of these isolated dropstones in a fine matrix through provenance studies of the core's terrigenous fine fraction. Geochemical provenance studies of the terrigenous fraction of marine sediments can aid in identifying past dynamic EAIS behavior; the few outcrops available on the continent provide specific rock characterizations and age constraints from which cored marine sediments can then be matched to using established radiogenic isotope techniques. Here we apply the K/Ar dating method as a provenance tool for identifying the source area(s) of fine-grained terrigenous sediments (<63 μm) deposited during the MMCT. ¶ After source area characterization, we find that the fine-grained sediments from the mid-Miocene show a mixture of both local Prydz Bay sourcing (~400 Ma signature) and Wilkes Land provenance (~900 Ma signature). While locally-derived Prydz Bay sediments are likely to have been delivered via meltwater from ice and deposited as hemipelagic sediments (with some possible bottom current modification, as this is a drift site), sediments sourced from Wilkes Land required transport via large icebergs. Future work will involve further provenance determination on both the fine-grained sediments and the abundant dropstones deposited at ODP Site 1165B during the MMCT. We anticipate that the use of the K/Ar radiometric dating technique as a proxy for the study of glacially transported fine-grained terrigenous materials will enable future Antarctic provenance research and further aid in providing insight into past EAIS behavior.; ODP Core 34X from Site 1165B

Basis for paleoenvironmental interpretation of magnetic properties of sediment from Upper Klamath Lake (Oregon): Effects of weathering and mineralogical sorting

USGS Publications Warehouse

Rosenbaum, J.G.; Reynolds, R.L.

2004-01-01

Studies of magnetic properties enable reconstruction of environmental conditions that affected magnetic minerals incorporated in sediments from Upper Klamath Lake. Analyses of stream sediment samples from throughout the catchment of Upper Klamath Lake show that alteration of Fe-oxide minerals during subaerial chemical weathering of basic volcanic rocks has significantly changed magnetic properties of surficial deposits. Titanomagnetite, which is abundant both as phenocrysts and as microcrystals in fresh volcanic rocks, is progressively destroyed during weathering. Because fine-grained magnetite is readily altered due to large surface-to-volume ratios, weathering causes an increase in average magnetic grain size as well as reduction in the quantity of titanomagnetite both absolutely and relative to hematite. Hydrodynamic mineralogical sorting also produces differences in magnetic properties among rock and mineral grains of differing sizes. Importantly, removal of coarse silicate and Fe-oxide grains by sorting concentrated extremely fine-grained magnetite in the resulting sediment. The effects of weathering and sorting of minerals cannot be completely separated. These processes combine to produce the magnetic properties of a non-glacial lithic component of Upper Klamath Lake sediments, which is characterized by relatively low magnetite content and coarse magnetic grain size. Hydrodynamic sorting alone causes significant differences between the magnetic properties of glacial flour in lake sediments and of fresh volcanic rocks in the catchment. In comparison to source volcanic rocks, glacial flour in the lake sediment is highly enriched in extremely fine-grained magnetite.

Sources of fine sediment stored in agricultural lowland streams, Midwest, USA

NASA Astrophysics Data System (ADS)

Lamba, Jasmeet; Thompson, A. M.; Karthikeyan, K. G.; Fitzpatrick, Faith A.

2015-05-01

Agricultural activities can accelerate the offsite transport of productive soil from fields leading to stream water quality degradation. Identification of the nature and relative contribution of different sources to fine-grained sediment (e.g., silts, clays) in streams is important to effectively focus agricultural best management practices in watersheds. Sediment fingerprinting techniques through the use of geochemical tracers are commonly used to differentiate relative contribution from various sources. Research was conducted in lowland streams in the Pleasant Valley watershed in South Central Wisconsin (USA) to identify provenance of fine-grained sediment deposits and evaluate the impact of land use on relative contributions from the following potential sources: cropland, pasture, woodland, and eroding stream banks. Results show that both agriculture (croplands and pastures) and eroding stream banks are primary sources to fine sediment deposits on the stream bed with contributions ranging from 19 to 100% and 0 to 81%, respectively. The increase in area under agricultural land use within a subwatershed results in greater contribution from agriculture (R2 = 0.846, p = 0.0034). Relative contributions from eroding stream banks increased with increasing area under grasslands and woodlands within a subwatershed (R2 = 0.814, p = 0.0055). Subwatersheds with greater mass of fine sediment deposited on the stream bed per unit area should be prioritized for best management practices. The conservation practices should be targeted to stream banks or croplands depending on the dominant source of fine sediment within a subwatershed. Site specific changes in relative contributions from different sources to fine-grained sediment in this watershed highlights the complexities involved in sediment transport dynamics. The nested sampling sites helped determine that sediment dynamics at the subwatershed scale need to be considered for application of targeted conservation techniques.

Sources of fine sediment stored in agricultural lowland streams, Midwest, USA

USGS Publications Warehouse

Lamba, Jasmeet; Thompson, Anita M.; Karthikeyan, K.G.; Fitzpatrick, Faith A.

2015-01-01

Agricultural activities can accelerate the offsite transport of productive soil from fields leading to stream water quality degradation. Identification of the nature and relative contribution of different sources to fine-grained sediment (e.g., silts, clays) in streams is important to effectively focus agricultural best management practices in watersheds. Sediment fingerprinting techniques through the use of geochemical tracers are commonly used to differentiate relative contribution from various sources. Research was conducted in lowland streams in the Pleasant Valley watershed in South Central Wisconsin (USA) to identify provenance of fine-grained sediment deposits and evaluate the impact of land use on relative contributions from the following potential sources: cropland, pasture, woodland, and eroding stream banks. Results show that both agriculture (croplands and pastures) and eroding stream banks are primary sources to fine sediment deposits on the stream bed with contributions ranging from 19 to 100% and 0 to 81%, respectively. The increase in area under agricultural land use within a subwatershed results in greater contribution from agriculture (R2 = 0.846, p = 0.0034). Relative contributions from eroding stream banks increased with increasing area under grasslands and woodlands within a subwatershed (R2 = 0.814, p = 0.0055). Subwatersheds with greater mass of fine sediment deposited on the stream bed per unit area should be prioritized for best management practices. The conservation practices should be targeted to stream banks or croplands depending on the dominant source of fine sediment within a subwatershed. Site specific changes in relative contributions from different sources to fine-grained sediment in this watershed highlights the complexities involved in sediment transport dynamics. The nested sampling sites helped determine that sediment dynamics at the subwatershed scale need to be considered for application of targeted conservation techniques.

Major, trace and REE geochemistry of recent sediments from lower Catumbela River (Angola)

NASA Astrophysics Data System (ADS)

Vinha, Manuela; Silva, M. G.; Cabral Pinto, Marina M. S.; Carvalho, Paula Cristina S.

2016-03-01

The mineralogy, texture, major, trace and rare earth elements, from recent sediment samples collected in the lower Catumbela River, were analysed in this study to characterize and discuss the factors controlling its geochemistry and provide data that can be used as tracers of Catumbela River inputs to the Angolan continental shelf. The sediments are mainly sands and silty-sands, but sandy-silt also occurs and the mineralogy is composed of quartz, feldspar, phyllosilicates, magnetite, ilmenite and also carbonates when the river crosses limestones and marls in the downstream sector. The hydraulic sorting originates magnetite-ilmenite and REE-enriched minerals placers. The mineralogy of the sediments is controlled by the source rocks and the degree of chemical weathering is lower than erosion. The texture is mainly controlled by location. There is enrichment in all the analysed trace elements in the fine grained, clay minerals and Fe-oxy-hydroxides rich sediments, compared to the coarse grained and quartz plus feldspar rich ones. The coarse grained sediments (without the placers) are impoverished in ΣREE when compared with UCC and NASC compositions, while the fine grained sediments have ΣREE contents similar to UCC and NASC. The placers have ΣREE contents up to 959.59 mg/kg. The source composition is the dominant factor controlling the REE geochemistry of the analysed sediments as there is no difference in the (La/Yb)N, (La/Sm)N and (Gd/Yb)N ratios in coarse and fine grained sediments. The sorting of magnetite, ilmenite, zircon, throrite, thorianite, rutile and titanite explain the HREE/LREE enriched patterns of the coarse grained sediments.

Quantification of Fine-grained Sediment Concentration in the Aquatic Environment Using Optical and Acoustic Sensors: Insight from Lab Experiments

NASA Astrophysics Data System (ADS)

Xu, K.; Champagne, B. N.

2017-12-01

The transport of sediment in the coastal zone and continental shelf is highly impacted by fluvial and oceanographic dynamics. In Louisiana, the Mississippi River delivers a bulk of water, sediment, and nutrients to the coast. However, coastal land loss highlights the importance of the sediment deposited at the mouth of the river. Sediment is the foundation to build land and suspended sediment concentration (SSC) tracks the delivery, deposition, and erosion of sediment. On a more applicable scale, variables such as SSC can be used to calculate sediment transport flux, an important parameter for projects such as sediment diversions and barrier island restoration. In order to rely on suspended sediment concentration (SSC) as continuous data, lab experiments are needed to establish the relationship between turbidity and SSC. Factors such as sensor type (optical or acoustic) and grain size (coarse or fine) can greatly impact the estimated SSC. In this study, fine-grained sediment was collected from multiple sites in coastal Louisiana and used to calibrate both optical backscatter (OBS) and acoustic backscatter (ABS) sensors to establish the relationship between sensor type and accuracy of the SSC estimation. Multiple grain-size analyses using a Laser Diffraction Particle Size Analyzer helped determine the effects of sensor accuracy regarding grain size. The results of these experiments were combined in order to establish the calibration curves of SSC. Our results indicated that the OBS-3A sensor's turbidity data were more correlated with the SSC than the OBS-5+'s data. Possible explanations for this could be due to differences between the instruments' measuring ranges and their sensitivity to various grain sizes. This technology development has a broad impact to the studies of sediment delivery, transport, and deposition in multiple types of coastal protection and restoration projects.

Polychaete Tubes, Turbulence, and Erosion of Fine-Grained Sediment

NASA Astrophysics Data System (ADS)

Kincke-Tootle, A.; Frank, D. P.; Briggs, K. B.; Calantoni, J.

2016-02-01

The role of polychaete tubes protruding through the benthic boundary layer in promoting or hindering erosion of fine-grained sediment was examined in laboratory experiments. Diver core samples of the top 10cm of sediment were collected west of Trinity Shoal off the Louisiana coast in 10-m depth. Diver cores were used in laboratory experiments conducted in a unidirectional flume. Tubes that were constructed by polychaetes, which comprised 70% of the species from the study area, were inserted into the core sediment surface. The sediment cores were then placed in the 2-m long test section of a small oscillatory flow tunnel and high-speed, stereo particle image velocimetry was used to determine the 2-dimensional, 3-component fluid velocity at high temporal (100 Hz) and spatial (< 1mm vector spacing) resolution. The tubes that protruded above the boundary layer allowed vortices to be initiated. Tubes are made up of shell fragments and fine-grained sediment, allowing for some rigidity and resistance to the flow. Rigidity determines the resistance causing small-scale eddies to form. The small-scale turbulence incited scour erosion, allowing fine-grained particles to be suspended into the water and in some cases coarser particles to be mobilized. Less-rigid tubes succumb to the shear stress, inhibit the formation of small-scale eddies, limit sediment erodibility, and increase the critical shear stress of the sediment. Discussion will focus on a modification to the critical Shields parameter to account for the effects of benthic biological activity.

Evaluation of a fine sediment removal tool in spring-fed and snowmelt driven streams

USGS Publications Warehouse

Sepulveda, Adam; Layhee, Megan J.; Sutphin, Zach; Sechrist, Juddson D.

2015-01-01

The accumulation of fine-grained sediments impairs the structure and function of streams, so removing fine sediments may be required to achieve restoration objectives. There has been little work on methods of removing excess sediment or on the efficacy of the methods. We used a 4-year before-after-control-impact design in southeastern Idaho streams to test a fine sediment removal system (FSRS) manufactured by Streamside Environmental LLC. The FSRS agitates fine sediment in the substrate with clean pump water and then vacuums the sediment out of the stream with a second pump. Our objectives were: 1) to test if the FSRS can selectively remove fine sediment; 2) to monitor the bio-physical responses in FSRS treated and downstream waters; and 3) to compare the bio-physical responses to the FSRS in spring-fed and snowmelt driven stream reaches. The FSRS removed ~ 14 metric tons of sediment from the two treated reaches. More than 90% of this sediment was < 2 mm, indicating that the FSRS selected for fine sediment in both stream types. Sustained effects of removing this sediment were confined to substrate improvements in treated reaches. Embeddedness in the spring-fed reach decreased and subsurface grain size in spring-fed and snowmelt driven reaches increased. We did not detect any sustained invertebrate or fish responses in treated reaches or any detrimental bio-physical responses in downstream waters. These results indicate that the FSRS reduced fine sediment levels but sediment removal did not reverse the impacts of sediment accumulation to stream biota within our monitoring time frame.

Controlling factors of stratigraphic occurrences of fine-grained turbidites: Examples from the Japanese waters

NASA Astrophysics Data System (ADS)

Ikehara, K.

2017-12-01

Fine-grained turbidite has been used for subaqueous paleoseismology, and has been recognized from shallow- to deep-water environments around the Japanese islands. Stratigraphic occurrence of fine-grained turbidites in the deepest Beppu Bay, south Japan, with its water depth of 75 m suggest clear influence of sea-level changes. Turbidite frequency was high during the post glacial sea-level rising and last 2.7 ka, and was low during the Holocene maximum sea-level highstand (5.3-2.7 ka). Retreat and progress of coastal delta front of the nearby river might affect the sediment supply to the deepest basin. On the other hand, fine-grained turbidites found in the forearc basins ( 3500 and 4500 m in water depths) and trench floor ( 6000 m in water depth) along the southern Ryukyu arc have no clear relation with sea-level changes. Sediment and bathymetric characteristics suggest that origin of these fine-grained turbidites is Taiwan. Remarkable tectonic uplift of Taiwanese coast with small mountainous rivers and narrow shelf may produce the continuous supply of fine-grained turbidites in this area. The Japan Trench floor composes of a series of small basins reflecting subducting horst-graben structure of the Pacific Plate. Each small basin acts as a natural sediment trap receiving the earthquake-induced turbidity currents. Thick fine-grained turbidites are also occurred in the small basins in the Japan Trench floor ( 7500 m in water depth). These are most likely induced by huge earthquakes along the Japan Trench. Thus, their stratigraphic occurrences might have close relation with recurrence of huge earthquakes in the past.

Experimental study of the effect of grain sizes in a bimodal mixture on bed slope, bed texture, and the transition to washload

NASA Astrophysics Data System (ADS)

Hill, Kimberly M.; Gaffney, John; Baumgardner, Sarah; Wilcock, Peter; Paola, Chris

2017-01-01

When fine sediment is added to a coarse-grained system, the mobility and composition of the bed can change dramatically. We conducted a series of flume experiments to determine how the size of fine particles introduced to an active gravel bed influences the mobility and composition of the bed. We initiated our experiments using a constant water discharge and feed rate of gravel. After the system reached steady state, we doubled the feed rate by supplying a second sediment of equal or lesser size, creating size ratios from 1:1 to 1:150. As we decreased the relative size of the fine particles, the system transitioned among three regimes: (1) For particle size ratios close to one, the bed slope increased to transport the additional load of similar-sized particles. The bed surface remained planar and unchanged. (2) For intermediate particle size ratios, the bed slope decreased with the additional fines. The bed surface became patchy with regions of fine and coarse grains. (3) For the largest particle size ratios (the smallest fines), the bed slope remained relatively unchanged. The subsurface became clogged with fine sediment, but fine particles were not present in the surface layer. This third regime constitutes washload, defined by those fractions that do not affect bed-material transport conditions. Our results indicate washload should be defined in terms of three conditions: small grain size relative to that of the bed material, full suspension based on the Rouse number, and a small rate of fine sediment supply relative to transport capacity.

Rare earth elements in the phosphatic-enriched sediment of the Peru shelf

USGS Publications Warehouse

Piper, D.Z.; Baedecker, P.A.; Crock, J.G.; Burnett, W.C.; Loebner, B.J.

1988-01-01

Apatite-enriched materials from the Peru shelf have been analyzed for their major oxide and rare earth element (REE) concentrations. The samples consist of (1) the fine fraction of sediment, mostly clay material, (2) phosphatic pellets and fish debris, which are dispersed throughout the fine-grained sediment, (3) tabular-shaped phosphatic crusts, which occur within the uppermost few centimeters of sediment, and (4) phosphatic nodules, which occur on the seafloor. The bulk REE concentrations of the concretions suggest that these elements are partitioned between the enclosed detrital material and the apatite fraction. Analysis of the fine-grained sediment with which the samples are associated suggested that this detrital fraction in the concretions should have shale REE values; the analysis of the fish debris suggested that the apatite fraction might have seawater values. The seawater contribution of REE's is negligible in the nodules and crust, in which the apatite occurs as a fine-grained interstitial cement. That is, the concentration of REE's and the REE patterns are predominantly a function of the amount of enclosed fine-grained sediment. By contrast, the REE pattern of the pelletal apatite suggests a seawater source and the absolute REE concentrations are relatively high. The REE P2O5 ratios of the apatite fraction of these samples thus vary from approximately zero (in the case of the crust and nodules) to as much as approximately 1.2 ?? 10-3 (in the case of the pellets). The range of this ratio suggests that rather subtle variations in the depositional environment might cause a significant variation in the REE content of this authigenic fraction of the sediment. Pelletal glauconite was also recovered from one sediment core. Its REE concentrations closely resemble those of the fish debris. ?? 1988.

Evolution of Fine-Grained Channel Margin Deposits behind Large Woody Debris in an Experimental Gravel-Bed Flume

NASA Astrophysics Data System (ADS)

ONeill, B.; Marks, S.; Skalak, K.; Puleo, J. A.; Wilcock, P. R.; Pizzuto, J. E.

2014-12-01

Fine grained channel margin (FGCM) deposits of the South River, Virginia sequester a substantial volume of fine-grained sediment behind large woody debris (LWD). FGCM deposits were created in a laboratory setting meant to simulate the South River environment using a recirculating flume (15m long by 0.6m wide) with a fixed gravel bed and adjustable slope (set to 0.0067) to determine how fine sediment is transported and deposited behind LWD. Two model LWD structures were placed 3.7 m apart on opposite sides of the flume. A wire mesh screen with attached wooden dowels simulated LWD with an upstream facing rootwad. Six experiments with three different discharge rates, each with low and high sediment concentrations, were run. Suspended sediment was very fine grained (median grain size of 3 phi) and well sorted (0.45 phi) sand. Upstream of the wood, water depths averaged about 0.08m, velocities averaged about 0.3 m/s, and Froude numbers averaged around 0.3. Downstream of the first LWD structure, velocities were reduced tenfold. Small amounts of sediment passed through the rootwad and fell out of suspension in the area of reduced flow behind LWD, but most of the sediment was carried around the LWD by the main flow and then behind the LWD by a recirculating eddy current. Upstream migrating dunes formed behind LWD due to recirculating flow, similar to reattachment bars documented in bedrock canyon rivers partially obstructed by debouching debris fans. These upstream migrating dunes began at the reattachment point and merged with deposits formed from sediment transported through the rootwad. Downstream migrating dunes formed along the channel margin behind the LWD, downstream of the reattachment point. FGCM deposits were about 3 m long, with average widths of about 0.8 m. Greater sediment concentration created thicker FGCM deposits, and higher flows eroded the sides of the deposits, reducing their widths.

TOC as a regional sediment conditionindicator: Parsing effects of grain size and organic content

EPA Science Inventory

TOC content of sediments is often used as an indicator of benthic condition. Percent TOC is generally positively correlated with sediment percent fines. While sediment grain size may have impacts on benthic organisms independent of organic content, it is often not explicitly co...

TOC as a regional sediment condition indicator: Parsing effects of grain size and organic content

EPA Science Inventory

TOC content of sediments is often used as an indicator of benthic condition. Percent TOC is generally positively correlated with sediment percent fines. While sediment grain size may have impacts on benthic organisms independent of organic content, it is often not explicitly co...

Microbial acetogenesis as a source of organic acids in ancient Atlantic Coastal Plain sediments

USGS Publications Warehouse

Chapelle, F.H.; Bradley, P.M.

1996-01-01

Field and laboratory evidence shows that deeply buried (90-888 m) fine-grained sediments of the Atlantic Coastal Plain contain viable acetogenic microorganisms, and that these microorganisms actively produce organic acids. Concentrations of formate, acetate, and propionate in pore waters extracted from fine-grained sediments ranged from 50 ??M to 5 mM and were much higher than in adjacent pore waters associated with sandy sediments (<2 ??M). Laboratory studies showed that asceptically cored fine-grained sediments incubated under a H2 atmosphere produced formate and acetate, and that H14CO-3 was converted to 14C-acetate and 14C-formate over time. An enrichment culture of these acetogenic microorganisms was recovered from one long-term incubation that showed the presence of several morphologically distinct gram-positive, rod-shaped bacteria. These microorganisms were capable of growth under autotrophic (H2 + CO2), heterotrophic (syringate), and mixotrophic (H2 + CO2 + syringate) conditions. These results suggest that microbial acetogenesis, rather than abiotic processes, is the most important organic acid-producing mechanism during low-temperature (???30 ??C) diagenesis of Atlantic Coastal Plain sediments.

MAHLI at the Rocknest sand shadow: Science and science-enabling activities

NASA Astrophysics Data System (ADS)

Minitti, M. E.; Kah, L. C.; Yingst, R. A.; Edgett, K. S.; Anderson, R. C.; Beegle, L. W.; Carsten, J. L.; Deen, R. G.; Goetz, W.; Hardgrove, C.; Harker, D. E.; Herkenhoff, K. E.; Hurowitz, J. A.; Jandura, L.; Kennedy, M. R.; Kocurek, G.; Krezoski, G. M.; Kuhn, S. R.; Limonadi, D.; Lipkaman, L.; Madsen, M. B.; Olson, T. S.; Robinson, M. L.; Rowland, S. K.; Rubin, D. M.; Seybold, C.; Schieber, J.; Schmidt, M.; Sumner, D. Y.; Tompkins, V. V.; Van Beek, J. K.; Van Beek, T.

2013-11-01

Martian solar days 57-100, the Mars Science Laboratory Curiosity rover acquired and processed a solid (sediment) sample and analyzed its mineralogy and geochemistry with the Chemistry and Mineralogy and Sample Analysis at Mars instruments. An aeolian deposit—herein referred to as the Rocknest sand shadow—was inferred to represent a global average soil composition and selected for study to facilitate integration of analytical results with observations from earlier missions. During first-time activities, the Mars Hand Lens Imager (MAHLI) was used to support both science and engineering activities related to sample assessment, collection, and delivery. Here we report on MAHLI activities that directly supported sample analysis and provide MAHLI observations regarding the grain-scale characteristics of the Rocknest sand shadow. MAHLI imaging confirms that the Rocknest sand shadow is one of a family of bimodal aeolian accumulations on Mars—similar to the coarse-grained ripples interrogated by the Mars Exploration Rovers Spirit and Opportunity—in which a surface veneer of coarse-grained sediment stabilizes predominantly fine-grained sediment of the deposit interior. The similarity in grain size distribution of these geographically disparate deposits support the widespread occurrence of bimodal aeolian transport on Mars. We suggest that preservation of bimodal aeolian deposits may be characteristic of regions of active deflation, where winnowing of the fine-sediment fraction results in a relatively low sediment load and a preferential increase in the coarse-grained fraction of the sediment load. The compositional similarity of Martian aeolian deposits supports the potential for global redistribution of fine-grained components, combined with potential local contributions.

Can coarse surface layers in gravel-bedded rivers be mobilized by finer gravel bedload?

NASA Astrophysics Data System (ADS)

Venditti, J. G.; Dietrich, W. E.; Nelson, P. A.; Wydzga, M. A.; Fadde, J.; Sklar, L.

2005-12-01

In response to reductions in sediment supply, gravel-bed rivers undergo a coarsening of the sediments that comprise the river's bed and, over some longer time scale, a river's grade may also be reduced as sediments are depleted from upstream reaches. Coarse, degraded river reaches are commonly observed downstream of dams across the Western United States. Following dam closure, these riverbeds become immobile under the altered flow and sediment supply regimes, leading to a reduction in the available salmon spawning and rearing habitat. Gravel augmentation to these streams is now common practice. This augmentation is typically seen as resurfacing the static coarse bed. As an alternative, we propose that the addition of appropriately finer gravels to these channels may be capable of mobilizing an otherwise immobile coarse surface layer, creating the potential to release fine material trapped beneath the surface. A series of laboratory experiments are being undertaken to test this hypothesis in a 30 m long and 0.86 m wide gravel-bedded flume channel using a constant discharge and a unimodal bed sediment with a median grain size of 8 mm and no sand present. The channel width-to-depth ratio of ~4 suppresses the development of lateral topography and allows us to focus on grain-to-grain interactions. Experiments proceed by maintaining a constant sediment feed until an equilibrium grade and transport rate are established, starving the flume of sediment for at least 24 hours, and then adding narrowly graded gravel over a period of one to two hours at a rate that is ~4x the bedload rate observed prior to terminating the sediment supply. The bed prior to sediment addition has an armor median grain size that is typically twice that of the subsurface and feed size distribution. The volume and median grain size of the resulting pulses are varied. Pulses move downstream rapidly with well-defined fronts in the form of bedload sheets and cause peaks in the sediment flux approximately equal to the supply rate. Once the pulse has passed through the flume, bedload flux rapidly drops to background values, leaving few introduced grains on the bed. When the sediment feed is the median grain size of the subsurface bed material mixture, few armor grains are mobilized, although there is some exchange between the surface and bedload. Pulses composed of the fine tail of the surface grain size distribution are capable of mobilizing all grain sizes in the armor (including the largest grains) as finer bedload fills the interstices of the coarse surface layer. This suggests that gravel augmentation using fine gravel may provide an effective means of improving bed mobility conditions. Further experiments are underway to explore the effects of repeated fine gravel addition on bed state.

Geochemical evidence for modern sediment accumulation on the continental shelf off southern New England

USGS Publications Warehouse

Bothner, Michael H.; Spiker, E. C.; Johnson, P. P.; Rendigs, R. R.; Aruscavage, P. J.

1981-01-01

An area of fine-grained sediment approximately 170 km x 74 km in size, located in water depths between 60 m and 150 m, south of Martha's Vineyard, Mass., is a site of modern sediment deposition. The 14C ages systematically increase with sediment depth from about 1,300 years B.P. at the surface to 8,000-10,000 years B.P. at the depth of maximum core penetration. The old age for the surface sediments probably results from a combination of deposition of old carbon and faunal mixing. In the finest sediments, the sedimentation rates were approximately 130 cm/1,000 yrs when deposition began and have decreased to about 25 cm/1,000 yrs. The decreasing sedimentation rate reflects a diminishing source of fine sediments, which presumably came from the Georges Bank and Nantucket Shoals area. Inventories of excess 210Pb in undisturbed cores average 70 dpm/cm2 (disintegrations per minute per square centimeter), more than two times higher than the flux of 210Pb from the atmosphere and from 226Ra decay in the overlying water. This additional influx of 210Pb either must be with new fine-grained sediment material or from solutions that are stripped of their 210Pb by particulates in the bottom nepheloid layer. Stable Pb concentrations in surface sediments are about 28 ppm, as much as two times higher than concentrations at depth. The high accumulation rates, 210Pb inventories, and trace-metal profiles imply that this area is a modern sink for fine-grained sediments and for pollutants associated with particulate matter in the water column. To our knowledge, this is the only site of present-day natural deposition on the Continental Shelf off the eastern United States, exclusive of the Gulf of Maine. Because the net currents on the outer half of this Continental Shelf flow from northeast to southwest, this fine-grained deposit may receive its sediments and possible contaminants from the Nantucket Shoals and Georges Bank regions.

Bed-sediment grain-size and morphologic data from Suisun, Grizzly, and Honker Bays, CA, 1998-2002

USGS Publications Warehouse

Hampton, Margaret A.; Snyder, Noah P.; Chin, John L.; Allison, Dan W.; Rubin, David M.

2003-01-01

The USGS Place Based Studies Program for San Francisco Bay investigates this sensitive estuarine system to aid in resource management. As part of the inter-disciplinary research program, the USGS collected side-scan sonar data and bed-sediment samples from north San Francisco Bay to characterize bed-sediment texture and investigate temporal trends in sedimentation. The study area is located in central California and consists of Suisun Bay, and Grizzly and Honker Bays, sub-embayments of Suisun Bay. During the study (1998-2002), the USGS collected three side-scan sonar data sets and approximately 300 sediment samples. The side-scan data revealed predominantly fine-grained material on the bayfloor. We also mapped five different bottom types from the data set, categorized as featureless, furrows, sand waves, machine-made, and miscellaneous. We performed detailed grain-size and statistical analyses on the sediment samples. Overall, we found that grain size ranged from clay to fine sand, with the coarsest material in the channels and finer material located in the shallow bays. Grain-size analyses revealed high spatial variability in size distributions in the channel areas. In contrast, the shallow regions exhibited low spatial variability and consistent sediment size over time.

Can Wet Rocky Granular Flows Become Debris Flows Due to Fine Sediment Production by Abrasion?

NASA Astrophysics Data System (ADS)

Arabnia, O.; Sklar, L. S.; Bianchi, G.; Mclaughlin, M. K.

2015-12-01

Debris flows are rapid mass movements in which elevated pore pressures are sustained by a viscous fluid matrix with high concentrations of fine sediments. Debris flows may form from coarse-grained wet granular flows as fine sediments are entrained from hillslope and channel material. Here we investigate whether abrasion of the rocks within a granular flow can produce sufficient fine sediments to create debris flows. To test this hypothesis experimentally, we used a set of 4 rotating drums ranging from 0.2 to 4.0 m diameter. Each drum has vanes along the boundary ensure shearing within the flow. Shear rate was varied by changing drum rotational velocity to maintain a constant Froude Number across drums. Initial runs used angular clasts of granodiorite with a tensile strength of 7.6 MPa, with well-sorted coarse particle size distributions linearly scaled with drum radius. The fluid was initially clear water, which rapidly acquired fine-grained wear products. After each 250 m tangential distance, we measured the particle size distributions, and then returned all water and sediment to the drums for subsequent runs. We calculate particle wear rates using statistics of size and mass distributions, and by fitting the Sternberg equation to the rate of mass loss from the size fraction > 2mm. Abundant fine sediments were produced in the experiments, but very little change in the median grain size was detected. This appears to be due to clast rounding, as evidenced by a decrease in the number of stable equilibrium resting points. We find that the growth in the fine sediment concentration in the fluid scales with unit drum power. This relationship can be used to estimate fine sediment production rates in the field. We explore this approach at Inyo Creek, a steep catchment in the Sierra Nevada, California. There, a significant debris flow occurred in July 2013, which originated as a coarse-grained wet granular flow. We use surveys to estimate flow depth and velocity where super-elevation occurred, to calculate a unit power of 4.5 KW/m2. From this we predict that 14% of the coarse mass is converted to fine sediment by abrasion per km. At that rate, the increase in fines concentration may have been sufficient to cause a wet granular flow to evolve into a debris flow within the first 1 km of its > 4km travel distance.

Effects of salinity and particle concentration on sediment hydrodynamics and critical bed-shear-stress for erosion of fine grained sediments used in wetland restoration projects

NASA Astrophysics Data System (ADS)

Ghose-Hajra, M.; McCorquodale, A.; Mattson, G.; Jerolleman, D.; Filostrat, J.

2015-03-01

Sea-level rise, the increasing number and intensity of storms, oil and groundwater extraction, and coastal land subsidence are putting people and property at risk along Louisiana's coast, with major implications for human safety and economic health of coastal areas. A major goal towards re-establishing a healthy and sustainable coastal ecosystem has been to rebuild Louisiana's disappearing wetlands with fine grained sediments that are dredged or diverted from nearby rivers, channels and lakes to build land in open water areas. A thorough geo-hydrodynamic characterization of the deposited sediments is important in the correct design and a more realistic outcome assessment of the long-term performance measures for ongoing coastal restoration projects. This paper evaluates the effects of salinity and solid particle concentration on the re-suspension characteristics of fine-grained dredged sediments obtained from multiple geographic locations along the Gulf coast. The critical bed-shear-stress for erosion has been evaluated as a function of sedimentation time. The sediment hydrodynamic properties obtained from the laboratory testing were used in a numerical coastal sediment distribution model to aid in evaluating sediment diversions from the Mississippi River into Breton Sound and Barataria Bay.

Fine-grained channel margin (FGCM) deposits conditioned by Large Woody Debris (LWD) in a gravel-bed river

NASA Astrophysics Data System (ADS)

Skalak, K. J.; Pizzuto, J. E.

2006-12-01

The purpose of this research is to examine the origin, occurrence, persistence, residence time and general significance of fine-grained channel margin storage in South River, a steep gravel-bedded stream in western Virginia. Fine-grained channel margin (FGCM) deposits in this study refers to specific in-channel deposits of mud and sand. These deposits occur primarily in the margins and near-banks regions of the channel. Fine- grained sediment storage in the near-bank regions is a result of reduced velocity caused by the bank obstructions. Nearly all of these obstructions consist of LWD accumulations in the channel. Storage occurs in four different geomorphic settings: 1) long pooled sections caused by bedrock or old mill dams, 2) the upstream ends of pools in channel margins with LWD accumulations, 3) bank obstructions usually caused by trees, 4) side channel backwaters where flow separates around islands. In approximately 38 km of river, there is 3000 m3 of fine-grained sediment stored in these features. The channel stores approximately 15 percent its total annual suspended load as fine-grained channel margin deposits. Consequently, these features represent a significant component of an annual sediment budget for this river. On average, the FGCM deposits are about 35 cm deep, 20 m long, and 4 m wide. They average 30 percent mud, 68 percent sand, and 2 percent gravel. These deposits have been cored and analyzed for Hg, grain size, loss-on-ignition, and bomb radiocarbon. Results from bomb radiocarbon analysis indicate that these features have an average age of 13 years. High Hg concentrations in fish tissue are an ongoing problem along South River, further motivating detailed study of these deposits.

The coevolution of bed roughness, grain clustering, surface armoring, hydraulic roughness, and sediment transport rate in experimental coarse alluvial channels: implications for long-term effects of gravel augmentation

NASA Astrophysics Data System (ADS)

Johnson, J. P.; Aronovitz, A. C.

2012-12-01

We conducted laboratory flume experiments to quantify changes in multiple factors leading to mountain river bed stability (i.e., minimal bed changes in space and time), and to understand how stable beds respond to perturbations in sediment supply. Experiments were run in a small flume 4 m long by 0.1 m wide. We imposed an initial well-graded size distribution of sediment (from coarse sand to up to 4 cm clasts), a steady water discharge (0.9 L/s), and initial bed surface slopes (8% and 12%). We measured outlet sediment flux and size distribution, bed topography and surface size distributions, and water depths; from these we calculated total shear stress, form drag and skin friction stress partitioning, and hydraulic roughness. The bed was initially allowed to stabilize with no imposed upstream sediment flux. This stabilization occurred due to significant changes in all of the factors listed in the title, and resulted in incipient step-pool like bed morphologies. In addition, this study was designed to explore possible long-term effects of gravel augmentation on mountain channel morphology and surface grain size. While the short-term goal of gravel augmentation is usually to cause fining of surface sediment patches, we find that the long-term effects may be opposite. We perturbed the stabilized channels by temporarily imposing an upstream sediment flux of the finest sediment size fraction (sand to granules). Median surface sizes initially decreased due to fine sediment deposition, although transport rates of intermediate-sized grains increased. When the fine sediment supply was stopped, beds evolved to be both rougher and coarser than they had been previously, because the largest grains remained on the bed but intermediate-sized grains were preferentially transported out, leaving higher fractions of larger grains on the surface. Existing models for mixed grain size transport actually predict changes in mobilization reasonably well, but do not explicity account for surface roughness evolution. Our results indicate a nonlinear relationship between surface median grain size and bed roughness.

Distribution and transport of sediment-bound metal contaminants in the rio grande de tarcoles, costa rica (Central America)

USGS Publications Warehouse

Fuller, C.C.; Davis, J.A.; Cain, D.J.; Lamothe, P.J.; Fries Fernandez, T.L.G.; Vargas, J.A.; Murillo, M.M.

1990-01-01

A reconnaissance survey of the extent of metal contamination in the Rio Grande de Tarcoles river system of Costa Rica indicated high levels of chromium (Cr) in the fine-grain bed sediments (83 times Cr background or 3000->5000 ??g/g). In the main channel of the river downstream of the San Jose urban area, Cr contamination in sediments was 4-6 times background and remained relatively constant over 50 km to the mouth of the river. Sediment from a mangrove swamp at the river mouth had Cr levels 2-3 times above background. Similar patterns of dilution were observed for lead (Pb) and zinc (Zn) sediment contamination, although the contamination levels were lower. The high affinity of Cr towards particulate phases, probably as Cr(III), allows the use of Cr contamination levels for delineating regions of deposition of fine-grained sediments and dilution of particle associated contaminants during transport and deposition.A reconnaissance survey of the extent of metal contamination in the Rio Grande de Tarcoles river system of Costa Rica indicated high levels of chromium (Cr) in the fine-grain bed sediments (83 times Cr background or 3000->5000 ??g/g). In the main channel of the river downstream of the San Jose urban area, Cr contamination in sediments was 4-6 times background and remained relatively constant over 50 km to the mouth of the river. Sediments from a mangrove swamp at the river mouth had Cr levels 2-3 times above background. Similar patterns of dilution were observed for lead (Pb) and zinc (Zn) sediment contamination, although the contamination levels were lower. The high affinity of Cr towards particulate phases, probably as Cr(III), allows the use of Cr contamination levels for delineating regions of deposition of fine-grained sediments and dilution of particle associated contaminants during transport and deposition.

Rare earth element compositions of core sediments from the shelf of the South Sea, Korea: Their controls and origins

NASA Astrophysics Data System (ADS)

Jung, Hoi-Soo; Lim, Dhongil; Choi, Jin-Yong; Yoo, Hae-Soo; Rho, Kyung-Chan; Lee, Hyun-Bok

2012-10-01

Rare earth elements (REEs) of bulk sediments and heavy mineral samples of core sediments from the South Sea shelf, Korea, were analyzed to determine the constraints on REE concentrations and distribution patterns as well as to investigate their potential applicability for discriminating sediment provenance. Bulk sediment REEs showed large variation in concentrations and distribution patterns primarily due to grain size and carbonate dilution effects, as well as due to an abundance of heavy minerals. In the fine sandy sediments (cores EZ02-15 and 19), in particular, heavy minerals (primarily monazite and titanite/sphene) largely influenced REE compositions. Upper continental crust-normalized REE patterns of these sand-dominated sediments are characterized by enriched light REEs (LREEs), because of inclusion of heavy minerals with very high concentrations in LREEs. Notably, such a strong LREE enrichment is also observed in Korean river sediments. So, a great care must be taken when using the REE concentrations and distribution patterns of sandy and coarse silty shelf sediments as a proxy for discriminating sediment provenance. In the fine-grained muddy sediments with low heavy mineral abundance, in contrast, REE fractionation ratios and their UCC-normalized patterns seem to be reliable proxies for assessing sediment provenance. The resultant sediment origin suggested a long lateral transportation of some fine-grained Chinese river sediments (probably the Changjiang River) to the South Sea of Korea across the shelf of the northern East China Sea.

Geomorphic field experiment to quantify grain size and biotic influence on riverbed sedimentation dynamics in a dry-season reservoir, Russian River, CA

NASA Astrophysics Data System (ADS)

Florsheim, J. L.; Ulrich, C.; Hubbard, S. S.; Borglin, S. E.; Rosenberry, D. O.

2013-12-01

An important problem in geomorphology is to differentiate between abiotic and biotic fine sediment deposition on coarse gravel river beds because of the potential for fine sediment to infiltrate and clog the pore space between gravel clasts. Infiltration of fines into gravel substrate is significant because it may reduce permeability; therefore, differentiation of abiotic vs. biotic sediment helps in understanding the causes of such changes. We conducted a geomorphic field experiment during May to November 2012 in the Russian River near Wohler, CA, to quantify biotic influence on riverbed sedimentation in a small temporary reservoir. The reservoir is formed upstream of a small dam inflated during the dry season to enhance water supply pumping from the aquifer below the channel; however, some flow is maintained in the reservoir to facilitate fish outmigration. In the Russian River field area, sediment transport dynamics during storm flows prior to dam inflation created an alternate bar-riffle complex with a coarser gravel surface layer over the relatively finer gravel subsurface. The objective of our work was to link grain size distribution and topographic variation to biotic and abiotic sediment deposition dynamics in this field setting where the summertime dam annually increases flow depth and inundates the bar surfaces. The field experiment investigated fine sediment deposition over the coarser surface sediment on two impounded bars upstream of the reservoir during an approximately five month period when the temporary dam was inflated. The approach included high resolution field surveys of topography, grain size sampling and sediment traps on channel bars, and laboratory analyses of grain size distributions and loss on ignition (LOI) to determine biotic content. Sediment traps were installed at six sites on bars to measure sediment deposited during the period of impoundment. Preliminary results show that fine sediment deposition occurred at all of the sample sites, and is spatially variable--likely influenced by topographic differences that moderate flow over the bars. Traps initially filled with coarse gravel from the bar's surface trapped more fine sediment than traps initially filled with material from the bar's subsurface sediment, suggesting that a gravel bar's armor layer may enhance the source of material available to infiltrate into the channel substrate. LOI analysis indicates that both surface and subsurface samples have organic content ranging between 2 and 4%, following winter storm flows prior to impoundment. In contrast, samples collected after the 5-month impoundment have higher organic content ranging between 5 and 11%. This work aids in differentiating between abiotic and biotic fine sediment deposition in order to understand their relative potential for clogging gravel substrate.

Magnetic fingerprint of the sediment load in a meander bend section of the Seine River (France)

NASA Astrophysics Data System (ADS)

Kayvantash, D.; Cojan, I.; Kissel, C.; Franke, C.

2017-06-01

This study aims to evaluate the potential of magnetic methods to determine the composition of the sediment load in a cross section of an unmanaged meander in the upstream stretch of the Seine River (Marnay-sur-Seine). Suspended particulate matter (SPM) was collected based on a regular sampling scheme along a cross section of the river, at two different depth levels: during a low-water stage (May 2014) and a high-water stage (February 2015). Riverbed sediments (RBS) were collected during the low-water stage and supplementary samples were taken from the outer and inner banks. Magnetic properties of the dry bulk SPM and sieved RBS and bank sediments were analysed. After characterizing the main magnetic carrier as magnetite, hysteresis parameters were measured, giving access to the grain size and the concentration of these magnetite particles. The results combined with sedimentary grain size data were compared to the three-dimensional velocity profile of the river flow. In the RBS where the magnetic grain size is rather uniform, the concentration of magnetite is inversely proportional to the mean grain size of the total sediment indicating that magnetite is strongly associated with the fine sedimentary fraction. The same pattern is observed in the samples from the outer and inner banks. During the low-water stage, the uniformly fine SPM grain size distribution characterizes the wash load. The magnetic fraction is also relatively fine (within the pseudo single domain range) with concentration similar to that of the fine RBS fraction. During the high-water stage, SPM samples correspond to mixtures of wash load and resuspended sediment from the bedload and riverbanks. Here, the grain size distribution is heterogeneous across the section showing coarser particles compared to those in the low-water stage and more varying magnetite concentrations while the magnetic grain size is like that of the low-water stage. The magnetite concentration in the high-water SPM can be modelled based on a mixing of the magnetite concentrations of the different grain size fractions, thus quantifying the impact of resuspension in the cross section.

Sedimentary controls on modern sand grain coat formation

NASA Astrophysics Data System (ADS)

Dowey, Patrick J.; Worden, Richard H.; Utley, James; Hodgson, David M.

2017-05-01

Coated sand grains can influence reservoir quality evolution during sandstone diagenesis. Porosity can be reduced and fluid flow restricted where grain coats encroach into pore space. Conversely pore-lining grain coats can restrict the growth of pore-filling quartz cement in deeply buried sandstones, and thus can result in unusually high porosity in deeply buried sandstones. Being able to predict the distribution of coated sand grains within petroleum reservoirs is thus important to help find good reservoir quality. Here we report a modern analogue study of 12 sediment cores from the Anllóns Estuary, Galicia, NW Spain, collected from a range of sub-environments, to help develop an understanding of the occurrence and distribution of coated grains. The cores were described for grain size, bioturbation and sedimentary structures, and then sub-sampled for electron and light microscopy, laser granulometry, and X-ray diffraction analysis. The Anllóns Estuary is sand-dominated with intertidal sand flats and saltmarsh environments at the margins; there is a shallowing/fining-upwards trend in the estuary-fill succession. Grain coats are present in nearly every sample analysed; they are between 1 μm and 100 μm thick and typically lack internal organisation. The extent of grain coat coverage can exceed 25% in some samples with coverage highest in the top 20 cm of cores. Samples from muddy intertidal flat and the muddy saltmarsh environments, close to the margins of the estuary, have the highest coat coverage (mean coat coverage of 20.2% and 21.3%, respectively). The lowest mean coat coverage occurs in the sandy saltmarsh (10.4%), beyond the upper tidal limit and sandy intertidal flat environments (8.4%), close to the main estuary channel. Mean coat coverage correlates with the concentration of clay fraction. The primary controls on the distribution of fine-grained sediment, and therefore grain coat distribution, are primary sediment transport and deposition processes that concentrate the clay fraction in the sediment towards the margins of the estuary. Bioturbation and clay illuviation/mechanical infiltration are secondary processes that may redistribute fine-grained sediment and produce grain coats. Here we have shown that detrital grain coats are more likely in marginal environments of ancient estuary-fills, which are typically found in the fining-upward part of progradational successions.

Vertical migration of fine-grained sediments from interior to surface of seabed driven by seepage flows-`sub-bottom sediment pump action'

NASA Astrophysics Data System (ADS)

Zhang, Shaotong; Jia, Yonggang; Wen, Mingzheng; Wang, Zhenhao; Zhang, Yaqi; Zhu, Chaoqi; Li, Bowen; Liu, Xiaolei

2017-02-01

A scientific hypothesis is proposed and preliminarily verified in this paper: under the driving of seepage flows, there might be a vertical migration of fine-grained soil particles from interior to surface of seabed, which is defined as `sub-bottom sediment pump action' in this paper. Field experiments were performed twice on the intertidal flat of the Yellow River delta to study this process via both trapping the pumped materials and recording the pore pressures in the substrate. Experimental results are quite interesting as we did observe yellow slurry which is mainly composed of fine-grained soil particles appearing on the seabed surface; seepage gradients were also detected in the intertidal flat, under the action of tides and small wind waves. Preliminary conclusions are that `sediment pump' occurs when seepage force exceeds a certain threshold: firstly, it is big enough to disconnect the soil particles from the soil skeleton; secondly, the degree of seabed fluidization or bioturbation is big enough to provide preferred paths for the detached materials to migrate upwards. Then they would be firstly pumped from interior to the surface of seabed and then easily re-suspended into overlying water column. Influential factors of `sediment pump' are determined as hydrodynamics (wave energy), degree of consolidation, index of bioturbation (permeability) and content of fine-grained materials (sedimentary age). This new perspective of `sediment pump' may provide some implications for the mechanism interpretation of several unclear geological phenomena in the Yellow River delta area.

Response of the Indian Creek alluvial fan, Nevada, to glacial-interglacial climate change

NASA Astrophysics Data System (ADS)

D'Arcy, Mitch; Roda-Boluda, Duna; Whittaker, Alexander; Brooke, Sam

2017-04-01

Alluvial fans have been shown to record signals of glacial-interglacial climate changes. Specifically, it has been suggested that their down-system grain size fining patterns may record changes in sediment flux. However, very few field studies have tested this because they require (i) robust fan chronologies, (ii) constraints on basin subsidence and 3D fan geometry, and (iii) a suitable model for inverting grain size fining for sediment flux. Here, we present a case study from the fluvially-dominated Indian Creek fan system in Fish Lake Valley, Nevada, which satisfies these criteria. We measure grain size fining patterns on a surface dating to the mid-glacial period ˜71 kyr ago, and a surface dating to the Holocene, which between them represent an overall warming (˜3 ˚ C) and drying (˜30%) of the regional climate. We use constraints on basin subsidence and a self-similar model of grain size fining to reconstruct sediment fluxes to the alluvial fan during the time periods captured by the two surfaces. Our results indicate a decline in sediment flux of ˜38% between the deposition of the ˜71 kyr and Holocene surfaces, implying significant sensitivity to climatic forcing over time periods of >10 kyr. This could represent a decrease in catchment erosion rates and/or a decrease in sediment export as the climate dried. Our results offer quantitative new constraints on how simple landscapes react to known glacial-interglacial climate shifts.

Methane gas hydrate effect on sediment acoustic and strength properties

USGS Publications Warehouse

Winters, W.J.; Waite, W.F.; Mason, D.H.; Gilbert, L.Y.; Pecher, I.A.

2007-01-01

To improve our understanding of the interaction of methane gas hydrate with host sediment, we studied: (1) the effects of gas hydrate and ice on acoustic velocity in different sediment types, (2) effect of different hydrate formation mechanisms on measured acoustic properties (3) dependence of shear strength on pore space contents, and (4) pore pressure effects during undrained shear.A wide range in acoustic p-wave velocities (Vp) were measured in coarse-grained sediment for different pore space occupants. Vp ranged from less than 1 km/s for gas-charged sediment to 1.77–1.94 km/s for water-saturated sediment, 2.91–4.00 km/s for sediment with varying degrees of hydrate saturation, and 3.88–4.33 km/s for frozen sediment. Vp measured in fine-grained sediment containing gas hydrate was substantially lower (1.97 km/s). Acoustic models based on measured Vp indicate that hydrate which formed in high gas flux environments can cement coarse-grained sediment, whereas hydrate formed from methane dissolved in the pore fluid may not.The presence of gas hydrate and other solid pore-filling material, such as ice, increased the sediment shear strength. The magnitude of that increase is related to the amount of hydrate in the pore space and cementation characteristics between the hydrate and sediment grains. We have found, that for consolidation stresses associated with the upper several hundred meters of sub-bottom depth, pore pressures decreased during shear in coarse-grained sediment containing gas hydrate, whereas pore pressure in fine-grained sediment typically increased during shear. The presence of free gas in pore spaces damped pore pressure response during shear and reduced the strengthening effect of gas hydrate in sands.

Surface Sediment Geochemistry in and around the Hudson Shelf Valley Offshore of New York

NASA Astrophysics Data System (ADS)

Mecray, E. L.; ten Brink, M. B.; Butman, B.; Denny, J.; Murray, R. W.

2001-05-01

The Hudson Shelf Valley, an ancient submerged portion of the Hudson River, extends across the continental shelf offshore of New York and New Jersey. Between 1959 and 1987, the area near the head of the valley was used for disposal of approximately 1.20 x 108 m3 of dredged material and sewage sludge. The distribution of metal concentrations and sediment characteristics were used to investigate the transport and fate of the sediments and their associated contaminants. Surface (0-2cm) sediments collected at 440 stations throughout the New York Bight between 1993 and 1998 were used to establish the regional distribution of pollutant metals, grain size, organic carbon, and Clostridium perfringens spores. Sediments in the New York Bight are generally sandy, however fine-grained sediments are found in the axis of the Valley. Statistical methods identified common sources and chemical mobility within groups of anthropogenic and naturally-occurring elements. High metal concentrations, fine-grained sediments, and higher organic carbon concentrations co-occur in depo-centers within the Valley. Normalization of the metal concentrations to these factors shows higher metal concentrations on the fine-grained particles in sandy areas of the Bight, particularly along the southern shore of Long Island. These distributions have implications for evaluating the impact of the mass distribution for contaminated metals in different habitats and areas. Decreasing concentrations of pollutants with time are observed, reflecting reduced contaminant loading in the upper region of the Valley; however, concentrations are still above natural background levels.

The effects of sediment and mercury mobilization in the South Yuba River and Humbug Creek Confluence Area, Nevada County, California: Concentrations, speciation, and environmental fate-Part 1: Field characterization

USGS Publications Warehouse

Fleck, Jacob A.; Alpers, Charles N.; Marvin-DiPasquale, Mark; Hothem, Roger L.; Wright, Scott A.; Ellett, Kevin; Beaulieu, Elizabeth; Agee, Jennifer L.; Kakouros, Evangelos; Kieu, Le H.; Eberl, Dennis D.; Blum, Alex E.; May, Jason T.

2011-01-01

Millions of pounds of mercury (Hg) were deposited in the river and stream channels of the Sierra Nevada from placer and hard-rock mining operations in the late 1800s and early 1900s. The resulting contaminated sediments are relatively harmless when buried and isolated from the overlying aquatic environment. The entrained Hg in the sediment constitutes a potential risk to human and ecosystem health should it be reintroduced to the actively cycling portion of the aquatic system, where it can become methylated and subsequently bioaccumulated in the food web. Each year, sediment is mobilized within these fluvial systems during high stormflows, transporting hundreds of tons of Hg-laden sediment downstream. The State of California and resource-management agencies, including the Bureau of Land Management (BLM) and the U.S. Forest Service, are concerned about additional disturbances, such as from suction gold dredging activities, which have the potential to mobilize Hg associated with buried sediment layers elevated in Hg that are otherwise likely to remain buried under normal storm conditions. The BLM initiated a study looking at the feasibility of removing Hg-contaminated sediment at the confluence of the South Yuba River and Humbug Creek in the northern Sierra Nevada of California by using standard suction-dredge technology. Additionally, the California State Water Resources Control Board (SWRCB) supported a comprehensive characterization of the intended dredge site. Together, the BLM and SWRCB supported a comprehensive characterization of Hg contamination at the site and the potential effects of sediment disturbance at locations with historical hydraulic mining debris on downstream environments. The comprehensive study consisted of two primary components: field studies and laboratory experiments. The field component, described in this report, had several study elements: 1) a preliminary, small-scale, in-stream dredge test; 2) comprehensive characterization of grain size distribution, Hg speciation, and mineralogy of bed and suspended sediment; 3) a determination of the past and current sources of sediment in the study area; 4) an assessment of Hg bioaccumulation in the local invertebrate population; and 5) a comparison of potential Hg transport caused 2 by natural storm disturbances with potential Hg mobilization caused by suction dredging as a method of Hg removal at the study site. The laboratory component of the study assessed the potential influenc of the disturbance of Hg-contaminated sediment through experiments designed to simulate in-stream transport, deposition, and potential methylation of Hg, described in a companion report (see Marvin-DiPasquale and others, 2010). Results of the field studies indicate that the fine-grained fraction (silt-clay, less than 0.063 millimeters) contains the greatest concentration of Hg in contaminated sediment. Because the fine-grained fraction is the most susceptible to long-range fluvial transport, disturbance of Hg-contaminated sediment is likely to increase the concentration and load of Hg in downstream waters. The preliminary, small-scale dredge test showed an increase in the concentration of fine particles and Hg in the water column caused by the dredge activity, despite relatively low concentrations of fine particles and Hg (about 300 nanograms per gram) at the dredge site. Characterization of sediment from two test pits and other sites in the vicinity of the confluence of the South Yuba River and Humbug Creek revealed a highly variable distribution of fine- and coarse-grained sediment. The highest levels of Hg contamination (up to 14,000 ng/g) were associated with the fine-grained fraction of sediment from the bedrock contact zone of Pit 2, a horizon which also yielded grains of gold and gold-Hg amalgam. A closed-circuit tank experiment with a venturi dredge at the base of Pit 1, in a gravel bar within the South Yuba River, resulted in fine-grained suspended sediment remaining in sus

Clay-mineral suites, sources, and inferred dispersal routes: Southern California continental shelf

USGS Publications Warehouse

Hein, J.R.; Dowling, J.S.; Schuetze, A.; Lee, H.J.

2003-01-01

Clay mineralogy is useful in determining the distribution, sources, and dispersal routes of fine-grained sediments. In addition, clay minerals, especially smectite, may control the degree to which contaminants are adsorbed by the sediment. We analyzed 250 shelf sediment samples, 24 river-suspended-sediment samples, and 12 river-bed samples for clay-mineral contents in the Southern California Borderland from Point Conception to the Mexico border. In addition, six samples were analyzed from the Palos Verdes Headland in order to characterize the clay minerals contributed to the offshore from that point source. The <2 ??m-size fraction was isolated, Mg-saturated, and glycolated before analysis by X-ray diffraction. Semi-quantitative percentages of smectite, illite, and kaolinite plus chlorite were calculated using peak areas and standard weighting factors. Most fine-grained sediment is supplied to the shelf by rivers during major winter storms, especially during El Nin??o years. The largest sediment fluxes to the region are from the Santa Ynez and Santa Clara Rivers, which drain the Transverse Ranges. The mean clay-mineral suite for the entire shelf sediment data set (26% smectite, 50% illite, 24% kaolinite+chlorite) is closely comparable to that for the mean of all the rivers (31% smectite, 49% illite, 20% kaolinite+chlorite), indicating that the main source of shelf fine-grained sediments is the adjacent rivers. However, regional variations do exist and the shelf is divided into four provinces with characteristic clay-mineral suites. The means of the clay-mineral suites of the two southernmost provinces are within analytical error of the mineral suites of adjacent rivers. The next province to the north includes Santa Monica Bay and has a suite of clay minerals derived from mixing of fine-grained sediments from several sources, both from the north and south. The northernmost province clay-mineral suite matches moderately well that of the adjacent rivers, but does indicate some mixing from sources in adjacent provinces.

Sediment provenance and paleoenvironmental changes in the northwestern shelf mud area of the South China Sea since the mid-Holocene

NASA Astrophysics Data System (ADS)

Xu, Fangjian; Hu, Bangqi; Dou, Yanguang; Liu, Xiting; Wan, Shiming; Xu, Zhaokai; Tian, Xu; Liu, Zhaoqing; Yin, Xuebo; Li, Anchun

2017-07-01

The late Quaternary paleoceanography and paleoenvironment of the South China Sea (SCS) have been well reconstructed over the last decade. In contrast, the provenance of the terrigenous sediments that have accumulated in the northwestern continental shelf mud area remains enigmatic. This study investigated the provenance of these sediments and the paleoenvironmental changes archived in Core X2 via the analysis of geochemical elements, grain size, and accelerator mass spectrometry (AMS) 14C ages. Based on the upper continental crust (UCC)-normalized REE patterns and REE fractionation parameters, southwestern and western Taiwanese rivers and the Pearl River were identified as the main sources of the fine-grained sediment deposited in the northwestern shelf mud area off Hainan Island. This finding further confirms the long-distance transport (> 1000 km) of fine-grained sediment from Taiwanese rivers to the northern SCS shelf and slope. Obvious changes in the grain size and Chemical Index of Alteration (CIA) record occurred at approximately 4.0 cal kyr BP and were likely caused by increased Hainan Island inputs due to sea level changes.

Hydraulic conductivity of the streambed, east branch Grand Calumet River, northern Lake County, Indiana

USGS Publications Warehouse

Duwelius, R.F.

1996-01-01

The hydraulic conductivity of the streambed generally was dependant on the type of sediments in the part of the streambed that was tested. Although most of the streambed contained soft, fine-grained sediments, parts of the streambed also contained fill materials including coal, cinders, and concrete and asphalt rubble. The highest values of horizontal hydraulic conductivity generally were calculated from data collected at locations where the streambed contained fill materials, particularly concrete and asphalt rubble. Horizontal hydraulic conductivities determined for 11 hydraulic tests in predominantly fill materials ranged from 1.2x1O+1 to 1.2x1O+3 feet per day and averaged 5.6x1O+2 feet per day. The lowest values of horizontal hydraulic conductivity were calculated from data collected at locations where the streambed contained fine-grained sediments. Horizontal hydraulic conductivities determined for 36 hydraulic tests in predominantly fine-grained sediments ranged from 1.Ox1O-2 to 2.4x1O+2 feet per day and averaged 1.5x1O+1 feet per day.

Fine Sediment Residency in Streambeds in Southeastern Australia.

NASA Astrophysics Data System (ADS)

Croke, J. C.; Thompson, C. J.; Rhodes, E.

2007-12-01

A detailed understanding of channel forming and maintenance processes in streams requires some measurement and/or prediction of bed load transport and sediment mobility. Traditional field based measurements of such processes are often problematic due to the high discharge characteristics of upland streams. In part to compensate for such difficulties, empirical flow competence equations have also been developed to predict armour or bedform stabilising grain mobility. These equations have been applied to individual reaches to predict the entrainment of a threshold grain size and the vertical extent of flushing. In cobble- and boulder-bed channels the threshold grain size relates to the size of the bedform stabilising grains (eg. D84, D90). This then allows some prediction of when transport of the matrix material occurs. The application of Optically Stimulated Luminescence (OSL) dating is considered here as an alternative and innovative way to determine fine sediment residency times in stream beds. Age estimates derived from the technique are used to assist in calibrating sediment entrainment models to specific channel types and hydrological regimes. The results from a one-dimensional HEC-RAS model indicate that recurrence interval floods exceeding bankfull up to 13 years are competent to mobilise the maximum overlying surface grain sizes at the sites. OSL minimum age model results of well bleached quartz in the fine matrix particles are in general agreement with selected competence equation predictions. The apparent long (100-1400y) burial age of most of the mineral quartz suggests that competent flows are not able to flush all subsurface fine-bed material. Maximum bed load exchange (flushing) depth was limited to twice the depth of the overlying D90 grain size. Application of OSL in this study provides important insight into the nature of matrix material storage and flushing in mountain streams.

Plutonium isotopes offer an alternative approach to establishing chronological profiles in coarse sediments

NASA Astrophysics Data System (ADS)

Pondell, C.; Kuehl, S. A.; Canuel, E. A.

2016-12-01

There are several methodologies used to determine chronologies for sediments deposited within the past 100 years, including 210Pb and 137Cs radioisotopes and organic and inorganic contaminants. These techniques are quite effective in fine sediments, which generally have a high affinity for metals and organic compounds. However, the application of these chronological tools becomes limited in systems where coarse sediments accumulate. Englebright Lake is an impoundment in northern California where sediment accumulation is characterized by a combination of fine and coarse sediments. This combination of sediment grain size complicated chronological analysis using the more traditional 137Cs chronological approach. This study established a chronology of these sediments using 239+240Pu isotopes. While most of the 249+240Pu activity was measured in the fine grain size fraction (<63 microns), up to 25% of the plutonium activity was detected in the coarse size fractions of sediments from Englebright Lake. Profiles of 239+240Pu were similar to available 137Cs profiles, verifying the application of plutonium isotopes for determining sediment chronologies and expanding the established geochronology for Englebright Lake sediments. This study of sediment accumulation in Englebright Lake demonstrates the application of plutonium isotopes in establishing chronologies in coarse sediments and highlights the potential for plutonium to offer new insights into patterns of coarse sediment accumulation.

Impacts of Colonial Deforestation on Sediment Organic Carbon Fluxes and Budget Using Black Carbon Chronology: Waiapu Continental Shelf, New Zealand

NASA Astrophysics Data System (ADS)

Wadman, H. M.; Canuel, E. A.; Bauer, J. E.; McNinch, J. E.

2009-12-01

Small, mountainous rivers deliver a disproportionate amount of sediment and associated organic matter to coastal regions globally. The Waiapu River, North Island, New Zealand, is characterized by one of the highest sediment yields on earth, providing a model system for studying episodic delivery and preservation of sedimentary organic matter in an energetic, aggradational setting. Hyperpycnal plumes provide the primary mode of sediment delivery, depositing fine-grained sediment as flood layers on the inner shelf. Severe erosion following colonial-era (~1890-1920) slash and burn deforestation increased the sediment yield to the shelf 4- to 5-fold relative to previous levels. Colonial catchment-wide burning also produced black carbon (BC), which may be used to establish chronological control in the heterogeneous inner shelf sediments that are not easily dateable using traditional techniques. While recent work indicates that these inner shelf flood layers sequester ~16-34% of the total fine-grained sediment budget, comparable to the amount preserved on the mid-outer shelf, little is understood about the organic matter associated with these inner shelf sediments. High-resolution seismic reflection data were used to select four representative cores to characterize total sedimentary BC, total organic carbon (TOC) and total nitrogen (TN) sequestered in the inner shelf fine-grained sediments. Soot and graphitic BC (SGBC) was quantified using chemo-thermal oxidation (CTO-375), while coarse-grained BC (CGBC) was quantified using traditional point-counting methodologies. SGBC weight percentages ranged from ~0.01-0.07, and peaked at ~150cm depth in all four cores. This interval corresponds to peak abundance of CGBC as well. The ~150cm interval is interpreted to represent the height of colonial slash and burn deforestation, and is further supported by fining-upward sequences in all of the cores as well as by multiple 14C dates. Overall, SGBC represented an average of 29% (range 7-75%) of the TOC throughout the cores, with the highest levels found in the deforestation layer at ~150cm (average 44%, range 30-75%). A secondary increase in % SGBC was found in the upper 50cm of the cores and is interpreted as increasing global BC production by diesel combustion in the 1970s. TOC and TN weight percentages associated with the fine-sediment fraction did not differ markedly above and below the deforestation layer. TOC and TN associated with the bulk sediment, however, did show increases in weight percent above ~150cm. This suggests that either 1) increases in fine-grained sedimentary organic material associated with the recent increase in sediment yield have been effectively remineralized, or 2) sedimentary organic matter is bimodal in origin (recent plant material vs. ancient, bedrock-derived carbon), and size-related variations in catchment and burial dynamics are influencing the fate of the different size fractions of organic material.

OSL dating of fine-grained quartz from Holocene Yangtze delta sediments

NASA Astrophysics Data System (ADS)

Sugisaki, S.; Buylaert, J. P.; Murray, A. S.; Tada, R.; Zheng, H.; Ke, W.; Saito, K.; Irino, T.; Chao, L.; Shiyi, L.; Uchida, M.

2014-12-01

Flood events in the Yangtze River are associated with variation in East Asian Summer Monsoon (EASM) precipitation. Understanding the frequency and scale of the EASM precipitation during the Holocene is a key to understanding the mechanism and cyclicity of floods and droughts. Because about 70% of the annual discharge occurs during the flood season, the Yangtze delta sediments provide a good archive of EASM precipitation. In this study, we investigate the possibility of applying OSL dating to establishing high-resolution chronologies for the Yangtze delta sediment cores YD13-1H and G3. The objectives of this study are: (1) test whether fine grained quartz in present day suspended particle matter (SPM) is fully bleached or reset before deposition, (2) where possible, test quartz fine- and coarse-grain OSL dating against radiocarbon shell ages, (3) interpret the sediment transport processes through the differential bleaching of quartz and feldspar OSL signals. We show that the SPM collected from the surface water column of the Yangtze River during the flood season is well-bleached (offset ~60 years). Fine-grained pro-delta sediments are thus potentially a good dosimeter for OSL dating. OSL ages sediment cores indicate a pronounced change in sedimentation rate at ~6 ka and ~2ka. These events are consistent with what is known of the evolution of the Yangtze catchment and delta. The delta began to build at ~6 ka (Zhao et al., 1979), and human activities increased significantly in the catchment at ~2ka　(Chen et al., 1985). It is however surprising that the entire top 9 m of sediment only records these two events. The question of whether significant deposition was limited to 2 ka and 6 ka, or whether the record has been disturbed by erosion/reworking remains. These issues are discussed in terms of the reliability of the quartz OSL ages, the degree of bleaching by comparison with polymineral OSL signals, and the relationship of the OSL ages to the sedimentary record.

Seafloor environments in Cape Cod Bay, a large coastal embayment

USGS Publications Warehouse

Knebel, H.J.; Rendigs, R. R.; List, J.H.; Signell, R.P.

1996-01-01

Cape Cod Bay is a glacial, semi-enclosed embayment that has a patchy distribution of modern seafloor sedimentary environments of erosion or nondeposition, deposition, and sediment reworking. Sidescan-sonar records and supplemental bathymetric, sedimentary, subbottom, and physical- oceanographic data indicate that the characteristics and distribution of these three categories of bottom environments are controlled by a combination of geologic and oceanographic processes that range from episodic to long-term and from regional to local. (1) Environments of erosion or nondeposition comprise exposares of bedrock, glacial drift, and coarse lag deposits that contain sediments (where present) ranging from boulder fields to gravelly coarse-to-medium sands. These environments are dominant on the shallow margins of the bay (water depths <30 m) where they reflect sediment resuspension, winnowing, and transport during modern northerly storms. (2) Environments of deposition are blanketed by fine-grained sediments ranging from muds to muddy fine sands. These environments are dominant across the floor of the central basin (water depths= 30-60 m) where fine- grained sediments (derived from regional and local sources and emplaced primarily during episodic wind- and density-driven flow) settle through the water column and accumulate under weak bottom currents during nonstorm conditions. (3) Environments of sediment reworking contain patches with diverse textures ranging from gravelly sands to muds. These environments occupy much of the transitional slopes between the margins and the basin floor and reflect a combination of erosion and deposition. The patchy distribution of sedimentary environments within the bay reflects not only regional changes in processes between the margins and the basin but local changes within each part of the bay as well. Small-scale patchiness is caused by local changes in the strengths of wave- and wind-driven currents and (on the margins) by local variations in the supply of fine-grained sediments. This study indicates areas within Cape Cod Bay where fine-grained sediments and associated contaminants are likely to be either moved or deposited. It also provides a guide to the locations and variability of benthic habitats.

Seafloor environments in Cape Cod Bay, a large coastal embayment

USGS Publications Warehouse

Knebel, H.J.; Rendigs, R. R.; List, J.H.; Signell, Richard P.

1996-01-01

Cape Cod Bay is a glacial, semi-enclosed embayment that has a patchy distribution of modern seafloor sedimentary environments of erosion or nondeposition, deposition, and sediment reworking. Sidescan-sonar records and supplemental bathymetric, sedimentary, subbottom, and physical-oceanographic data indicate that the characteristics and distribution of these three categories of bottom environments are controlled by a combination of geologic and oceanographic processes that range from episodic to long-term and from regional to local. (1) Environments of erosion or nondeposition comprise exposures of bedrock, glacial drift, and coarse lag deposits that contain sediments (where present) ranging from boulder fields to gravelly coarse-to-medium sands. These environments are dominant on the shallow margins of the bay (water depths < 30 m) where they reflect sediment resuspension, winnowing, and transport during modern northerly storms. (2) Environments of deposition are blanketed by fine-grained sediments ranging from muds to muddy fine sands. These environments are dominant across the floor of the central basin (water depths = 30–60 m) where fine-grained sediments (derived from regional and local sources and emplaced primarily during episodic wind- and density-driven flow) settle through the water column and accumulate under weak bottom currents during nonstorm conditions. (3) Environments of sediment reworking contain patches with diverse textures ranging from gravelly sands to muds. These environments occupy much of the transitional slopes between the margins and the basin floor and reflect a combination of erosion and deposition.The patchy distribution of sedimentary environments within the bay reflects not only regional changes in processes between the margins and the basin but local changes within each part of the bay as well. Small-scale patchiness is caused by local changes in the strengths of wave- and wind-driven currents and (on the margins) by local variations in the supply of fine-grained sediments.This study indicates areas within Cape Cod Bay where fine-grained sediments and associated contaminants are likely to be either moved or deposited. It also provides a guide to the locations and variability of benthic habitats.

Sedimentological downstream effects of dam failure and the role of sediment connectivity: a case study from the Bohemian Massif, Austria

NASA Astrophysics Data System (ADS)

Wurster, Maria-Theresia; Weigelhofer, Gabriele; Pichler-Scheder, Christian; Hein, Thomas; Pöppl, Ronald

2017-04-01

Sediment connectivity describes the potential for sediment transport through catchment systems, further defining locality and characteristics of sedimentation in river channels. Dams generally decrease sediment connectivity and act as temporary sediment sinks. When dams are removed these sediments are being reworked and released downstream. During dam restoration works along a small-sized stream in the Bohemian Massif of Austria in December 2015 a dam failure occurred which led to the entrainment of several tons of fine-grained reservoir sediments further entering and depositing in the downstream channel reaches, located in the Thayatal National Park. Aiming to remove these fine sediment deposits the National Park Authority decided to initiate a flushing event in April 2016. The main aim of the present study was to investigate the effects of dam failure-induced fine sediment release and reservoir flushing on downstream bed sediment characteristics by applying geomorphological mapping (incl. volumetric surveys) and sedimentological analyses (freeze-core sampling and granulometry), further discussing the role of in-channel sediment connectivity. The obtained results have shown that immediately after the dam failure event a total of ca. 18 m3 of fine-grained sediments have accumulated as in-channel sediment bars which were primarily formed in zones of low longitudinal connectivity (e.g. in the backwater areas of woody debris jams, or at slip-off bank locations). The flushing event has been shown to have caused remobilization and downstream translocation of these deposits, further reducing their total volume by approx. 60%. The results of the granulometric analyses of the freeze-core samples have revealed fine sediment accumulation and storage in the upper parts of the channel bed, having further increased after the flushing event. Additionally, effects on chemical conditions and invertebrate community have been observed. These observations clearly indicate a significant influence of vertical connectivity conditions on in-channel fine sediment storage.

The Shale Gas potential of Lower Carboniferous Sediments in Germany

NASA Astrophysics Data System (ADS)

Kerschke, D.; Mihailovic, A.; Schulz, H., -M.; Horsfield, B.

2012-04-01

Organic-rich Carboniferous sediments are proven source rocks for conventional gas systems in NW Europe and are likely gas shale candidates. Within the framework of GeoEnergie, an initiative to strengthen scientific excellence, funded by the German Ministry of Education and Research (BMBF), the influence of palaeogeography and basin dynamics on sedimentology and diagenesis is being investigated. Our aim is to unravel the evolution of shale gas-relevant properties which control gas prospectivity and production parameters like porosity, brittleness, etc. for the Lower Carboniferous in Germany. Northern Germany is underlain by thick, mudstone-bearing Carboniferous successions with a wide range of thermal maturities. Some of these mudstone horizons are rich in organic carbon which is either of marine and/or terrigenous origin. During the Carboniferous deposition of fine-grained, TOC-rich basinal sediments changed into shallow marine to paralic siliciclastic sediments (carbonates during the Lower Carboniferous) in the north, and grade into coarse-grained sediments close to the uprising Variscan mountains in the south. As a result different architectural elements including TOC-rich fine-grained sediments like basinal shales, fine-grained parts of turbidites, and shallow marine mudstones occur in both the Lower and the Upper Carboniferous section. A high shale gas potential occurs in basinal shales of Namurian age with marine organic material and TOC contents of up to 8 % (Rhenish Alum Shales). Such sediments with thermal maturities between 1.3 to 3.0 % vitrinite reflectance and sufficient quartz contents occur in wide areas of present-day Central European Basins System (CEBS), and are at favourable depth for shale gas exploration predominantly along the southern CEBS margin.

Sources of fine-grained sediment in the Linganore Creek watershed, Frederick and Carroll Counties, Maryland, 2008-10

USGS Publications Warehouse

Gellis, Allen C.; Noe, Gregory B.; Clune, John W.; Myers, Michael K.; Hupp, Cliff R.; Schenk, Edward R.; Schwarz, Gregory E.

2015-01-01

Management implications of this study indicate that both agriculture and streambanks are important sources of sediment in Linganore Creek where the delivery of agriculture sediment was 4 percent and the delivery of streambank sediment was 44 percent. Fourth order streambanks, on average, had the highest rates of bank erosion. Combining the sediment fingerprinting and sediment budget results indicates that 96 percent of the eroded fine-grained sediment from agriculture went into storage. Flood plains and ponds are effective storage sites of sediment in the Linganore Creek watershed. Flood plains stored 8 percent of all eroded sediment with 4th and 5th order flood plains, on average, storing the most sediment. Small ponds in the Linganore Creek watershed, which drained 16 percent of the total watershed area, stored 15 percent of all eroded sediment. Channel beds were relatively stable with the greatest erosion generally occurring in 4th and 5th order streams.

Sedimentation in Hot Creek in vicinity of Hot Creek Fish Hatchery, Mono County, California

USGS Publications Warehouse

Burkham, D.E.

1978-01-01

An accumulation of fine-grained sediment in Hot Creek downstream from Hot Creek Fish Hatchery, Mono County, Calif., created concern that the site may be deteriorating as a habitat for trout. The accumulation is a phenomenon that probably occurs naturally in the problem reach. Fluctuation in the weather probably is the basic cause of the deposition of fine-grained sediment that has occurred since about 1970. Man 's activities and the Hot Creek Fish Hatchery may have contributed to the problem; the significance of these factors, however, probably was magnified because of drought conditions in 1975-77. (Woodard-USGS)

Sediment tracing in the upper Hunter catchment using elemental and mineralogical compositions: Implications for catchment-scale suspended sediment (dis)connectivity and management

NASA Astrophysics Data System (ADS)

Fryirs, Kirstie; Gore, Damian

2013-07-01

River bed colmation layers clog the interstices of gravel-bed rivers, impeding the vertical exchange of water and nutrients that drives ecosystem function in the hyporheic zone. In catchments where fine-grained sediment supply has increased since human disturbance, understanding sediment provenance and the (dis)connectivity of supply allows practitioners to target sediment source problems and treat them within catchment management plans. Release of alluvial fine-grained sediment from channel bank erosion since European settlement has resulted in the formation of a colmation layer along the upper Hunter River at Muswellbrook, eastern Australia. X-ray fluorescence spectrometry (XRF) and X-ray diffractometry (XRD) are used to determine the elemental and mineralogical signatures of colmation layer and floodplain sediment sources across this 4480 km2 catchment. This sediment tracing technique is used to construct a picture of how suspended sediment supply and (dis)connectivity operates in this catchment. In this system, the primary source areas are subcatchments in which sediments are stored largely in partly confined floodplain pockets, but from which sediment supply is unimpeded and directly connected to the receiving reach. Subcatchments in which alluvial sediment storage is significant — and which contain large, laterally unconfined valleys — are essentially 'switched off' or disconnected from the receiving reach. This is because large sediment sinks act to trap fine-grained sediment before it reaches the receiving reach, forming a buffer along the sediment conveyor belt. Given the age structure of floodplains in the receiving reach, this pattern of source area contributions and (dis)connectivity must have occurred throughout the Holocene.

The relationship of lithology and watershed characteristics to fine sediment deposition in streams of the Oregon coast range.

PubMed

Sable, K A; Wohl, E

2006-05-01

Lithology is one of many factors influencing the amount, grain size distribution, and location of fine sediment deposition on the bed of mountain stream channels. In the Oregon Coast Range, 18 pool-riffle stream reaches with similar slope and intact riparian area and relatively unaffected by logjams were surveyed for assessment of fine sediment deposition. Half of the streams were in watersheds underlain by relatively erodible sandstone. The other half were underlain by a more resistant basalt. Channel morphology, hydraulic variables, particle size, relative pool volume of fine sediment (V*), and wood characteristics were measured in the streams. A significantly higher amount of fine sediment was deposited in the sandstone channels than in the basalt channels, as indicated by V*. Grab samples of sediment from pools also were significantly finer grained in the sandstone channels. Geographic information systems (GIS) software was used to derive several variables that might correlate with fine sediment deposition. These variables were combined with those derived from field data to create multiple linear regression models to be used for further exploration of the type and relative influence of factors affecting fine sediment deposition. Lithology appeared to be significant in some of these models, but usually was not the primary driver. The results from these models indicate that V* at the reach scale is best explained by stream power per unit area and by the volume of wood perpendicular to the flow per channel area (R(2) = 0.46). Findings show that V* is best explained using only watershed scale variables, including negative correlations with relief ratio and basin precipitation index, and positive correlations with maximum slope and circularity.

Contaminant distribution and accumulation in the surface sediments of Long Island Sound

USGS Publications Warehouse

Mecray, E.L.; Buchholtz ten Brink, Marilyn R.

2000-01-01

The distribution of contaminants in surface sediments has been measured and mapped as part of a U.S. Geological Survey study of the sediment quality and dynamics of Long Island Sound. Surface samples from 219 stations were analyzed for trace (Ag, Ba, Cd, Cr, Cu, Hg, Ni, Pb, V, Zn and Zr) and major (Al, Fe, Mn, Ca, and Ti) elements, grain size, and Clostridium perfringens spores. Principal Components Analysis was used to identify metals that may covary as a function of common sources or geochemistry. The metallic elements generally have higher concentrations in fine-grained deposits, and their transport and depositional patterns mimic those of small particles. Fine-grained particles are remobilized and transported from areas of high bottom energy and deposited in less dynamic regions of the Sound. Metal concentrations in bottom sediments are high in the western part of the Sound and low in the bottom-scoured regions of the eastern Sound. The sediment chemistry was compared to model results (Signell et al., 1998) and maps of sedimentary environments (Knebel et al., 1999) to better understand the processes responsible for contaminant distribution across the Sound. Metal concentrations were normalized to grain-size and the resulting ratios are uniform in the depositional basins of the Sound and show residual signals in the eastern end as well as in some local areas. The preferential transport of fine-grained material from regions of high bottom stress is probably the dominant factor controlling the metal concentrations in different regions of Long Island Sound. This physical redistribution has implications for environmental management in the region.

Trace elements and organic compounds in bed sediment from selected streams in southern Louisiana, 1998

USGS Publications Warehouse

Skrobialowski, Stanley C.

2002-01-01

Bed-sediment samples from 21 selected streams in southern Louisiana were collected and analyzed for the presence of trace elements and organic compounds during 1998 as part of the U.S. Geological Survey National Water-Quality Assessment Program. Concentrations of selected trace elements and organic compounds were compared on the basis of sediment-quality criteria, land use, and grain size; concentrations of selected trace elements also were compared with concentrations from previous studies. Concentrations of seven selected trace elements and 21 organic compounds were evaluated with sediment-quality criteria established by the Canadian Council of Ministers of the Environment. Concentrations of selected trace elements and organic compounds were highest at sites draining urban and agricultural areas and may result from cumulative effects of relatively high percentages of fine-grained material, iron, and organic material. Concentrations exceeding sediment-quality criteria for the protection of aquatic life occurred most frequently at Bayou Grosse Tete at Rosedale and Bayou Lafourche below weir at Thibodaux. Exceedance of Interim Sediment Quality Guidelines occurred most frequently for arsenic and chromium. Trace-element concentrations in fine-grained samples were compared with concentrations in bulk samples and were determined to be significantly different, and concentrations were generally higher in finegrained sediment. Shapiro-Wilk, paired t-test, and Wilcoxon rank sum statistical procedures, with an alpha of 0.05, were used to compare concentrations of 21 trace elements, total organic carbon, and total carbon in finegrained and bulk sediment samples for 19 sites. Significant differences were determined between fine-grained and bulk sediment samples for aluminum, barium, beryllium, chromium, copper, iron, lithium, nickel, phosphorus, selenium, titanium, and zinc concentrations. Of 133 paired concentrations, 69 percent were greater in fine-grained samples, and 23 percent were greater in bulk samples. Comparisons with data from previous studies indicate increases by more than 20 percent in concentrations of antimony at Bayou Lafourche below weir at Thibodaux, arsenic and chromium at Tickfaw River at Liverpool, lead at Bayou Lafourche below weir at Thibodaux, and zinc at Bayou Lafourche below weir at Thibodaux and Vermilion River at Perry. Historic comparisons also indicate decreases by more than 20 percent in concentrations of chromium at Bayou des Cannes near Eunice and mercury at Mermentau River at Mermentau.

Abrasion and Fragmentation Processes in Marly Sediment Transport

NASA Astrophysics Data System (ADS)

Le Bouteiller, C.; Naaim, F.; Mathys, N.; Lave, J.; Kaitna, R.

2009-04-01

In the highly erosive marly catchments of Draix (Southern Alps, France), downstream fining of sediments has been observed and can not be explained by selective sorting. Moreover, high concentrations of suspended fine sediment (up to 800 g/L) are measured during flood events in these basins. These observations lead to the hypothesis that abrasion and fragmentation of marly sediments during transport play an important role in the production of fine sediments. Several experiments are conducted in order to quantify these processes: material from the river bed is introduced into the water flow in a circular flume as well as in a large scale rotating drum. Abrasion rates range from 5 to 15%/km, depending on the lithology: marls from the upper basin are more erosive than those from the lower basin. Modifications of grain size distribution in the rough fraction are also observed. Field measurements are also conducted. Downstream of the main marly sediment sources, the river bed is composed of marls and limestone pebbles. We have sampled the river bed for analysis of grain size distribution and lithology. First results show a decrease of the proportion of marls along the river bed. This is in accordance with the high erosion rates observed in our laboratory experiments. Further investigations are planned in order to study more precisely marl grain size distribution, especially in the finer fraction.

A Manual to Identify Sources of Fluvial Sediment | Science ...

EPA Pesticide Factsheets

Sedimentation is one of the main causes of stream/river aquatic life use impairments in R3. Currently states lack standard guidance on appropriate tools available to quantify sediment sources and develop sediment budgets in TMDL Development. Methods for distinguishing sediment types for TMDL development will focus stream restoration and soil conservation efforts in strategic locations in a watershed and may better target appropriate BMPs to achieve sediment load reductions. Properly identifying sediment sources in a TMDL will also help focus NPDES permitting, stream restoration activities and other TMDL implementation efforts. This project will focus on developing a framework that will be published as a guidance document that outlines steps and approaches to identify the significant sources of fine-grained sediment in 303D listed watersheds. In this framework, the sediment-fingerprinting and sediment budget approaches will be emphasized. This project will focus on developing a framework that will be published as a guidance document that outlines steps and approaches to identify the significant sources of fine-grained sediment in 303D listed watersheds. In this framework, the sediment-fingerprinting and sediment budget approaches will be emphasized.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Steinen, R.; Tennet, P.

Fine-grained sediments present in Florida Bay, the inner reef tract of Florida, and the Great Bahama Bank are formed by three processes. The sediments differ primarily in the amount of 4-{mu}m-long aragonite needles that comprise the sediment, but also in the amount of aragonite. Florida Bay muds are composed primarily of equant 1 {mu}m grains; less than 20% are needles. The fine-grained fraction from the inner reef tract of Florida contains more aragonite needles than Florida Bay muds. Some samples contain nearly 90% needles, whereas samples, from adjacent localities contain only 50%. Sediment from both areas is deposited and mixedmore » by bioturbation on the deltas at tidal passes through the Florida Keys. The amount of needle sediment diminishes rapidly away from the tidal passes in Florida Bay. The fine-grained fraction on the Great Bahama Bank is dominated by 4-{mu}m-long needles of aragonite but may contain fragments and whole tests of foraminifers. In general, the more abundant the aragonite-needle content is in any of the sediment, the greater the aragonite content of that sediment. The three main processes responsible for mud production on the Florida-Bahama Platform are (1) disintegration of skeletal encrustations, mainly red algae and spirobid worm tubules, on Thalassia grass blades; (2) postmortem disaggregation of aragonite needles from green algae; and (3) direct precipitation of aragonite and Mg-calcite from supersaturated marine waters. Where sufficient nutrients exist in the water column, such as in Florida Bay, mud production is dominated by the epibionts on the Thalassia grass community. Less nutrients in the water column of the inner reef tract results in fewer encrustations.« less

Fine-grained suspended sediment source identification for the Kharaa River basin, northern Mongolia

NASA Astrophysics Data System (ADS)

Rode, Michael; Theuring, Philipp; Collins, Adrian L.

2015-04-01

Fine sediment inputs into river systems can be a major source of nutrients and heavy metals and have a strong impact on the water quality and ecosystem functions of rivers and lakes, including those in semiarid regions. However, little is known to date about the spatial distribution of sediment sources in most large scale river basins in Central Asia. Accordingly, a sediment source fingerprinting technique was used to assess the spatial sources of fine-grained (<10 microns) sediment in the 15 000 km2 Kharaa River basin in northern Mongolia. Five field sampling campaigns in late summer 2009, and spring and late summer in both 2010 and 2011, were conducted directly after high water flows, to collect an overall total of 900 sediment samples. The work used a statistical approach for sediment source discrimination with geochemical composite fingerprints based on a new Genetic Algorithm (GA)-driven Discriminant Function Analysis, the Kruskal-Wallis H-test and Principal Component Analysis. The composite fingerprints were subsequently used for numerical mass balance modelling with uncertainty analysis. The contributions of the individual sub-catchment spatial sediment sources varied from 6.4% (the headwater sub-catchment of Sugnugur Gol) to 36.2% (the Kharaa II sub-catchment in the middle reaches of the study basin) with the pattern generally showing higher contributions from the sub-catchments in the middle, rather than the upstream, portions of the study area. The importance of riverbank erosion was shown to increase from upstream to midstream tributaries. The source tracing procedure provides results in reasonable accordance with previous findings in the study region and demonstrates the general applicability and associated uncertainties of an approach for fine-grained sediment source investigation in large scale semi-arid catchments. The combined application of source fingerprinting and catchment modelling approaches can be used to assess whether tracing estimates are credible and in combination such approaches provide a basis for making sediment source apportionment more compelling to catchment stakeholders and managers.

Effects of suspended sediment concentration and grain size on three optical turbidity sensors

USGS Publications Warehouse

Merten, Gustavo Henrique; Capel, Paul D.; Minella, Jean P.G.

2014-01-01

Purpose: Optical turbidity sensors have been successfully used to determine suspended sediment flux in rivers, assuming the relation between the turbidity signal and suspended sediment concentration (SSC) has been appropriately calibrated. Sediment size, shape and colour affect turbidity and are important to incorporate into the calibration process. Materials and methods: This study evaluates the effect of SSC and particle size (i.e. medium sand, fine sand, very fine sand, and fines (silt + clay)) on the sensitivity of the turbidity signal. Three different turbidity sensors were used, with photo detectors positioned at 90 and 180 degrees relative to the axis of incident light. Five different sediment ratios of sand:fines (0:100, 25:75, 50:50, 75:25 and 100:0) were also evaluated for a single SSC (1000 mg l-1). Results and discussion: The photo detectors positioned at 90 degrees were more sensitive than sensor positioned at 180 degrees in reading a wide variety of grain size particles. On average for the three turbidity sensors, the sensitivity for fines were 170, 40, and 4 times greater than sensitivities for medium sand, fine sand, and very fine sand, respectively. For an SSC of 1000 mg l-1 with the treatments composed of different proportions of sand and fines, the presence of sand in the mixture linearly reduced the turbidity signal. Conclusions: The results indicate that calibration of the turbidity signal should be carried out in situ and that the attenuation of the turbidity signal due to sand can be corrected, as long as the proportion of sand in the SSC can be estimated.

Testing short-range migration of microbial methane as a hydrate formation mechanism: Results from Andaman Sea and Kumano Basin drill sites and global implications

NASA Astrophysics Data System (ADS)

Malinverno, Alberto; Goldberg, David S.

2015-07-01

Methane gas hydrates in marine sediments often concentrate in coarse-grained layers surrounded by fine-grained marine muds that are hydrate-free. Methane in these hydrate deposits is typically microbial, and must have migrated from its source as the coarse-grained sediments contain little or no organic matter. In "long-range" migration, fluid flow through permeable layers transports methane from deeper sources into the gas hydrate stability zone (GHSZ). In "short-range" migration, microbial methane is generated within the GHSZ in fine-grained sediments, where small pore sizes inhibit hydrate formation. Dissolved methane can then diffuse into adjacent sand layers, where pore size does not restrict hydrate formation and hydrates can accumulate. Short-range migration has been used to explain hydrate accumulations in sand layers observed in drill sites on the northern Cascadia margin and in the Gulf of Mexico. Here we test the feasibility of short-range migration in two additional locations, where gas hydrates have been found in coarse-grained volcanic ash layers (Site NGHP-01-17, Andaman Sea, Indian Ocean) and turbidite sand beds (Site IODP-C0002, Kumano forearc basin, Nankai Trough, western Pacific). We apply reaction-transport modeling to calculate dissolved methane concentration and gas hydrate amounts resulting from microbial methane generated within the GHSZ. Model results show that short-range migration of microbial methane can explain the overall amounts of methane hydrate observed at the two sites. Short-range migration has been shown to be feasible in diverse margin environments and is likely to be a widespread methane transport mechanism in gas hydrate systems. It only requires a small amount of organic carbon and sediment sequences consisting of thin coarse-grained layers that can concentrate microbial methane generated within thick fine-grained sediment beds; these conditions are common along continental margins around the globe.

Particle sorting during sediment redistribution processes and the effect on 230Th-normalized mass accumulation rates

NASA Astrophysics Data System (ADS)

Marcantonio, Franco; Lyle, Mitchell; Ibrahim, Rami

2014-08-01

The 230Th method of determining mass accumulation rates (MARs) assumes that little to no fractionation occurs during sediment redistribution processes at the seafloor. We examine 230Th inventories in radiocarbon-dated multicore sediments from paired winnowed and focused sites at Cocos and Carnegie Ridges, Panama Basin. Radiocarbon-derived sand MARs, which likely represent the vertical rain of particles poorly transported by bottom currents, are similar at each of the paired sites but are different using 230Th normalization. 230Th-normalized MARs are about 60% lower at focused sites and likely underestimate vertical MARs, while the reverse is true for winnowed sites. We hypothesize that size fractionation occurs most frequently at lower current velocities, resulting in the coarse fraction being left behind and primarily the fine 230Th-rich grains being transported downslope. 230Th-normalization works well for recording fine-grained (detrital and opal), but not coarse-grained (carbonate), fluxes in regions that have undergone sediment redistribution.

Investigating selective transport and abrasion on an alluvial fan using quantitative grain size and shape analysis

NASA Astrophysics Data System (ADS)

Litwin, K. L.; Jerolmack, D. J.

2011-12-01

Selective sorting and abrasion are the two major fluvial processes that are attributed to the downstream fining of sediments in rivers and alluvial fans. Selective transport is the process by which smaller grains are preferentially transported downstream while larger grains are deposited closer to the source. Abrasion is defined by the production of fine sediments and sand that occurs by saltation of gravel, where particle-to-particle collisions supply the energy required to break apart grains. We hypothesize that abrasion results in the gradual fining of large grains and the production of fine sands and silts, while sorting accounts for the differences in transport of these two grain-size fractions produced from abrasion, thereby creating the abrupt gravel-sand transition observed in many channel systems. In this research, we explore both selective transport and abrasion processes on the Dog Canyon alluvial fan near Alamogordo, New Mexico. We complete an extensive grain size analysis down the main channel of the fan employing an image-based technique that utilizes an autocorrelation process. We also characterize changes in grain shape using standard shape parameters, as well as Fourier analysis, which allows the study of contributions of grain roughness on a variety of length scales. Sorting appears to dominate the upper portion of the fan; the grain-size distribution narrows moving downstream until reaching a point of equal mobility, at which point sorting ceases. Abrasion exerts a subtle but persistent effect on grains during transport down the fan. Shape analysis reveals that particles become more rounded by the removal of small-scale textural features, a process that is expected to only modestly influence grain size of gravel, but should produce significant quantities of sand. This study provides a better understanding of the importance of grain abrasion and sorting on the downstream fining of channel grains in an alluvial fan, as well as an improved knowledge about the abrupt gravel-sand transition observed in a majority of alluvial fans.

Sources and distribution of yttrium and rare earth elements in surface sediments from Tagus estuary, Portugal.

PubMed

Brito, Pedro; Prego, Ricardo; Mil-Homens, Mário; Caçador, Isabel; Caetano, Miguel

2018-04-15

The distribution and sources of yttrium and rare-earth elements (YREE) in surface sediments were studied on 78 samples collected in the Tagus estuary (SW Portugal, SW Europe). Yttrium and total REE contents ranged from 2.4 to 32mg·kg -1 and 18 to 210mg·kg -1 , respectively, and exhibited significant correlations with sediment grain-size, Al, Fe, Mg and Mn, suggesting a preferential association to fine-grained material (e.g. aluminosilicates but also Al hydroxides and Fe oxyhydroxides). The PAAS (Post-Archean Australian Shale) normalized patterns display three distinct YREE fractionation pattern groups along the Tagus estuary: a first group, characterized by medium to coarse-grained material, a depleted and almost flat PAAS-normalized pattern, with a positive anomaly of Eu, representing one of the lithogenic components; a second group, characterized mainly by fine-grained sediment, with higher shale-normalized ratios and an enrichment of LREE relative to HREE, associated with waste water treatment plant (WWTP) outfalls, located in the northern margin; and, a third group, of fine-grained material, marked by a significant enrichment of Y, a depletion of Ce and an enrichment of HREE over LREE, located near an inactive chemical-industrial complex (e.g. pyrite roast plant, chemical and phosphorous fertilizer industries), in the southern margin. The data allow the quantification of the YREE contents and its spatial distribution in the surface sediments of the Tagus estuary, identifying the main potential sources and confirming the use of rare earth elements as tracers of anthropogenic activities in highly hydrodynamic estuaries. Copyright © 2017 Elsevier B.V. All rights reserved.

Modeling the formation of methane hydrate-bearing intervals in fine-grained sediments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Malinverno, Alberto; Cook, Ann; Daigle, Hugh

Sediment grain size exerts a fundamental control on how methane hydrates are distributed within the pore space. Fine-grained muds are the predominant sediments in continental margins, and hydrates in these sediments have often been observed in semi-vertical veins and fractures. In several instances, these hydrate veins/fractures are found in discrete depth intervals a few tens meters thick within the gas hydrate stability zone (GHSZ) surrounded by hydrate-free sediments above and below. As they are not obviously connected with free gas occurring beneath the base of the GHSZ, these isolated hydrate-bearing intervals have been interpreted as formed by microbial methane generatedmore » in situ. To investigate further the formation of these hydrate deposits, we applied a time-dependent advection-diffusion-reaction model that includes the effects of sedimentation, solute diffusion, and microbial methane generation. The microbial methane generation term depends on the amount of metabolizable organic carbon deposited at the seafloor, which is degraded at a prescribed rate resulting in methane formation beneath the sulfate reduction zone. In the model, methane hydrate precipitates once the dissolved methane concentration is greater than solubility, or hydrate dissolves if concentration goes below solubility. If the deposition of organic carbon at the seafloor is kept constant in time, we found that the predicted amounts of hydrate formed in discrete intervals within the GHSZ are much less than those estimated from observations. We then investigated the effect of temporal variations in the deposition of organic carbon. If greater amounts of organic carbon are deposited during some time interval, methane generation is enhanced during burial in the corresponding sediment interval. With variations in organic carbon deposition that are consistent with observations in continental margin sediments, we were able to reproduce the methane hydrate contents estimated in discrete depth intervals. Our results support the suggestion that in situ microbial methane generation is the source for hydrates within fine-grained sediments.« less

Physical and chemical effects of grain aggregates on the Palos Verdes margin, southern California

USGS Publications Warehouse

Drake, D.E.; Eganhouse, R.; McArthur, W.

2002-01-01

Large discharges of wastewater and particulate matter from the outfalls of the Los Angeles County Sanitation Districts onto the Palos Verdes shelf since 1937 have produced an effluent-affected sediment deposit characterized by low bulk density, elevated organic matter content, and a high percentage of fine silt and clay particles relative to underlying native sands and sandy silts. Comparison of the results of grain-size analyses using a gentle wet-sieving technique that preserves certain grain aggregates to the results of standard size analyses of disaggregated particles shows that high percentages (up to 50%) of the silt and clay fractions of the effluent-affected mud are incorporated in aggregates having intermediate diameters in the fine-to-medium sand size range (63-500 ??m), Scanning electron microscope images of the aggregates show that they are predominantly oval fecal pellets or irregularly shaped fragments of pellets. Deposit-feeding polychaete worms such as Capitella sp. and Mediomastus sp., abundant in the mud-rich effluent-affected sediment on Palos Verdes shelf, are probably responsible for most of the grain aggregates through fecal pellet production. Particle settling rates and densities, and the concentrations of organic carbon and p,p???-DDE, a metabolite of the hydrophobic pesticide DDT, were determined for seven grain-size fractions in the effluent-affected sediment. Fecal pellet grain densities ranged from about 1.2 to 1.5 g/cc, and their average settling rates were reduced to the equivalent of about one phi size relative to spherical quartz grains of the same diameter. However, repackaging of fine silt and clay grains into the sand-sized fecal pellets causes an effective settling rate increase of up to 3 orders of magnitude for the smallest particles incorporated in the pellets. Moreover, organic carbon and p,p???-DDE exhibit a bimodal distribution with relatively high concentrations in the finest size fraction (0-20 ??m), as expected, and a second concentration peak associated with the sand-sized fecal pellets. The repackaging of fine-grained particles along with their adsorbed chemical compounds into relatively fast-settling pellets has important implications for the mobilization and transport of the sediment and the desorption of chemicals from grain surfaces. ?? 2002 Published by Elsevier Science Ltd.

A visual basic program to generate sediment grain-size statistics and to extrapolate particle distributions

USGS Publications Warehouse

Poppe, L.J.; Eliason, A.H.; Hastings, M.E.

2004-01-01

Measures that describe and summarize sediment grain-size distributions are important to geologists because of the large amount of information contained in textural data sets. Statistical methods are usually employed to simplify the necessary comparisons among samples and quantify the observed differences. The two statistical methods most commonly used by sedimentologists to describe particle distributions are mathematical moments (Krumbein and Pettijohn, 1938) and inclusive graphics (Folk, 1974). The choice of which of these statistical measures to use is typically governed by the amount of data available (Royse, 1970). If the entire distribution is known, the method of moments may be used; if the next to last accumulated percent is greater than 95, inclusive graphics statistics can be generated. Unfortunately, earlier programs designed to describe sediment grain-size distributions statistically do not run in a Windows environment, do not allow extrapolation of the distribution's tails, or do not generate both moment and graphic statistics (Kane and Hubert, 1963; Collias et al., 1963; Schlee and Webster, 1967; Poppe et al., 2000)1.Owing to analytical limitations, electro-resistance multichannel particle-size analyzers, such as Coulter Counters, commonly truncate the tails of the fine-fraction part of grain-size distributions. These devices do not detect fine clay in the 0.6–0.1 μm range (part of the 11-phi and all of the 12-phi and 13-phi fractions). Although size analyses performed down to 0.6 μm microns are adequate for most freshwater and near shore marine sediments, samples from many deeper water marine environments (e.g. rise and abyssal plain) may contain significant material in the fine clay fraction, and these analyses benefit from extrapolation.The program (GSSTAT) described herein generates statistics to characterize sediment grain-size distributions and can extrapolate the fine-grained end of the particle distribution. It is written in Microsoft Visual Basic 6.0 and provides a window to facilitate program execution. The input for the sediment fractions is weight percentages in whole-phi notation (Krumbein, 1934; Inman, 1952), and the program permits the user to select output in either method of moments or inclusive graphics statistics (Fig. 1). Users select options primarily with mouse-click events, or through interactive dialogue boxes.

Sediment distribution and hydrologic conditions of the Potomac aquifer in Virginia and parts of Maryland and North Carolina

USGS Publications Warehouse

McFarland, Randolph E.

2013-01-01

Sediments of the heavily used Potomac aquifer broadly contrast across major structural features of the Atlantic Coastal Plain Physiographic Province in eastern Virginia and adjacent parts of Maryland and North Carolina. Thicknesses and relative dominance of the highly interbedded fluvial sediments vary regionally. Vertical intervals in boreholes of coarse-grained sediment commonly targeted for completion of water-supply wells are thickest and most widespread across the central and southern parts of the Virginia Coastal Plain. Designated as the Norfolk arch depositional subarea, the entire sediment thickness here functions hydraulically as a single interconnected aquifer. By contrast, coarse-grained sediment intervals are thinner and less widespread across the northern part of the Virginia Coastal Plain and into southern Maryland, designated as the Salisbury embayment depositional subarea. Fine-grained intervals that are generally avoided for completion of water-supply wells are increasingly thick and widespread northward. Fine-grained intervals collectively as thick as several hundred feet comprise two continuous confining units that hydraulically separate three vertically spaced subaquifers. The subaquifers are continuous northward but merge southward into the single undivided Potomac aquifer. Lastly, far southeastern Virginia and northeastern North Carolina are designated as the Albemarle embayment depositional subarea, where both coarse- and fine-grained intervals are of only moderate thickness. The entire sediment thickness functions hydraulically as a single interconnected aquifer. A substantial hydrologic separation from overlying aquifers is imposed by the upper Cenomanian confining unit. Potomac aquifer sediments were deposited by a fluvial depositional complex spanning the Virginia Coastal Plain approximately 100 to 145 million years ago. Westward, persistently uplifted granite and gneiss source rocks sustained a supply of coarse-grained sand and gravel. Immature, high-gradient braided streams deposited longitudinal bars and channel fills across the Norfolk arch subarea. By contrast, across the Salisbury and Albemarle embayment subareas, mature, medium- to low-gradient meandering streams deposited medium- to coarse-grained channel fills and point bars segregated from fine-grained overbank deposits. The Virginia depositional complex merged northward across the Salisbury embayment subarea with another complex in Maryland. Here, additional sediments were received from schist source rocks that underwent three cycles of initial uplift and rapid erosion followed by crustal stability and erosional leveling. Because of the predominance of coarse-grained sediments, transmissivity, hydraulic conductivity, and regional velocities of lateral flow through the Potomac aquifer are greatest across the Norfolk arch depositional subarea, but decrease progressively northward with increasingly fine-grained sediments. Confining units hydraulically separate the Potomac aquifer from overlying aquifers, as indicated by large vertical hydraulic gradients. By contrast, most of the Potomac aquifer internally functions hydraulically as a single interconnected aquifer, as indicated by uniformly small vertical gradients. Most fine-grained sediments within the aquifer do not hydraulically separate overlying and underlying coarse-grained sediments. Across the Salisbury embayment depositional subarea, however, hydraulic separation among the vertically spaced subaquifers is imposed by the intervening confining units. The Potomac aquifer is the largest and most heavily used source of groundwater in the Virginia Coastal Plain. Water-level declines as great as 200 feet create the potential for saltwater intrusion. Conventional stratigraphic correlation has been generally ineffective at accurately characterizing complexly distributed fluvial sediments that compose the Potomac aquifer. Consequently, the aquifer’s internal hydraulic connectivity and overall hydrologic function have not been well understood. Water-supply planning and development efforts have been hampered, and interpretations of regulatory criteria for allowable water-level declines have been ambiguous. An investigation undertaken during 2010–11 by the U.S. Geological Survey, in cooperation with the Virginia Department of Environmental Quality, provides a comprehensive regional description of the spatial distribution of Potomac aquifer sediments and their relation to hydrologic conditions. Altitudes and thicknesses of 2,725 vertical sediment intervals represent the spatial distribution of Potomac aquifer sediments in the Virginia Coastal Plain and adjacent parts of Maryland and North Carolina. Sediment intervals are designated as either dominantly coarse or fine grained and were determined by interpretation of geophysical logs and ancillary information from 456 boreholes. Sediment-interval and borehole summary statistical data indicate regional trends in sediment lithology and stratigraphic continuity, upon which three structurally based and hydrologically distinct sediment depositional subareas are designated. Broad patterns of sediment deposition over time are inferred from published sediment pollen-age data. Discrepancies in previously drawn hydrostratigraphic relations between southeastern Virginia and northeastern North Carolina are partly resolved based on borehole geophysical logs and a recently documented geologic map and corehole. A conceptual model theorizes the depositional history of the sediments and geologically accounts for their distribution. Documented pumping tests of the Potomac aquifer at 197 locations produced 336 values of transmissivity and 127 values of storativity. Based on effective aquifer thicknesses, 296 values of sediment hydraulic conductivity and 113 values of sediment specific storage are calculated. Vertical hydraulic gradients are calculated from 9,479 pairs of water levels measured between November 17, 1953, and October 4, 2011, in 129 closely spaced pairs of wells. Borehole sediment-interval and related data provide a means to achieve high yielding production wells in the Potomac aquifer by site-specific targeting of drilling operations toward water-bearing coarse-grained sand and gravel. Advance knowledge of the potential of different parts of the aquifer also aids in planning optimal groundwater-development areas. Depositional subareas further provide a possible context for resource management. Current (2013) regulatory limits on water-level declines are relative to top surfaces of subdivided upper, middle, and lower Potomac aquifers across the entire Virginia Coastal Plain, but have the potential to exceed the same limit relative to a single undivided Potomac aquifer. By contrast, designation of the sediments as a single aquifer in the Norfolk arch and Albemarle embayment subareas—and as a series of vertically spaced subaquifers and intervening confining units in the Salisbury embayment subarea—best reflects understanding of the Potomac aquifer and can avoid the potential for excessive water-level declines. Simulation modeling to evaluate effects of groundwater withdrawals could be designed similarly, including vertical discretization and (or) zonation of the Potomac aquifer based on depositional subareas and a geostatistical distribution of aquifer properties derived from borehole sediment-interval data. Further resource-management information needs extend beyond the developed part of the Potomac aquifer, particularly across the Northern Neck and Middle Peninsula where only the shallowest part of the aquifer is known, and include structural aspects such as faults, basement bedrock, and the Chesapeake Bay impact crater.

Environmental Support for High Frequency Acoustic Measurements at NOSC (Naval Ocean Systems Center) Oceanographic Tower, 26 April-7 May 1982. Part 1. Sediment Geoacoustic Properties

DTIC Science & Technology

1983-06-01

surrounding the tripod (cores 14, 15, 16) were moderately to moderately well-sorted, fine-skewed, platykurtic to mesokurtic coarse grained sands, The...side of the interface. mrt Sediments throughout the 18 cm length of core 7 were moderately sorted, very finely-skewed, platykurtic to mesokurtic

Late Noachian fluvial erosion on Mars: Cumulative water volumes required to carve the valley networks and grain size of bed-sediment

NASA Astrophysics Data System (ADS)

Rosenberg, Eliott N.; Head, James W., III

2015-11-01

Our goal is to quantify the cumulative water volume that was required to carve the Late Noachian valley networks on Mars. We employ an improved methodology in which fluid/sediment flux ratios are based on empirical data, not assumed. We use a large quantity of data from terrestrial rivers to assess the variability of actual fluid/sediment flux sediment ratios. We find the flow depth by using an empirical relationship to estimate the fluid flux from the estimated channel width, and then using estimated grain sizes (theoretical sediment grain size predictions and comparison with observations by the Curiosity rover) to find the flow depth to which the resulting fluid flux corresponds. Assuming that the valley networks contained alluvial bed rivers, we find, from their current slopes and widths, that the onset of suspended transport occurs near the sand-gravel boundary. Thus, any bed sediment must have been fine gravel or coarser, whereas fine sediment would be carried downstream. Subsequent to the cessation of fluvial activity, aeolian processes have partially redistributed fine-grain particles in the valleys, often forming dunes. It seems likely that the dominant bed sediment size was near the threshold for suspension, and assuming that this was the case could make our final results underestimates, which is the same tendency that our other assumptions have. Making this assumption, we find a global equivalent layer (GEL) of 3-100 m of water to be the most probable cumulative volume that passed through the valley networks. This value is similar to the ∼34 m water GEL currently on the surface and in the near-surface in the form of ice. Note that the amount of water required to carve the valley networks could represent the same water recycled through a surface valley network hydrological system many times in separate or continuous precipitation/runoff/collection/evaporation/precipitation cycles.

Volcanic ash in surficial sediments of the Kodiak shelf - An indicator of sediment dispersal patterns

USGS Publications Warehouse

Hampton, M.A.; Bouma, A.H.; Frost, T.P.; Colburn, I.P.

1979-01-01

Surficial sediments of the Kodiak shelf, Gulf of Alaska, contain various amounts of volcanic ash whose physical properties indicate that it originated from the 1912 Katmai eruption. The distribution of ash is related to the shelf physiography and represents redistribution by oceanic circulation rather than the original depositional pattern from the volcanic event. The ash distribution can be used, in conjunction with the distribution of grain sizes, as an indicator of present-day sediment dispersal patterns on the shelf. No significant modern input of sediment is occurring on the Kodiak shelf, which is mostly covered by Pleistocene glacial deposits. Coarse-grained sediments on flat portions of shallow banks apparently are being winnowed, with the removed ash-rich fine material being deposited in shallow depressions on the banks and in three of the four major troughs that cut transversely across the shelf. The other major trough seems to be experiencing a relatively high-energy current regime, with little deposition of fine material. ?? 1979.

Sediment production from forest road surfaces.

Treesearch

Leslie Reid; T. Dunne

2011-01-01

Erosion on roads is an important source of fine-grained sediment in streams draining logged basins of the Pacific Northwest. Runoff rates and sediment concentrations from 10 road segments subject to a variety of traffic levels were monitored to produce sediment rating curves and unit hydrographs for different use levels and types of surfaces. These relationships are...

Fine-Grained Turbidites: Facies, Attributes and Process Implications

NASA Astrophysics Data System (ADS)

Stow, Dorrik; Omoniyi, Bayonle

2016-04-01

Within turbidite systems, fine-grained sediments are still the poor relation and sport several contrasting facies models linked to process of deposition. These are volumetrically the dominant facies in deepwater and, from a resource perspective, they form important marginal and tight reservoirs, and have great potential for unconventional shale gas, source rocks and seals. They are also significant hosts of metals and rare earth elements. Based on a large number of studies of modern, ancient and subsurface systems, including 1000s of metres of section logging, we define the principal genetic elements of fine-grained deepwater facies, present a new synthesis of facies models and their sedimentary attributes. The principal architectural elements include: non-channelised slope-aprons, channel-fill, channel levee and overbank, turbidite lobes, mass-transport deposits, contourite drifts, basin sheets and drapes. These comprise a variable intercalation of fine-grained facies - thin-bedded and very thin-bedded turbidites, contourites, hemipelagites and pelagites - and associated coarse-grained facies. Characteristic attributes used to discriminate between these different elements are: facies and facies associations; sand-shale ratio, sand and shale geometry and dimensions, sand connectivity; sediment texture and small-scale sedimentary structures; sediment fabric and microfabric; and small-scale vertical sequences of bed thickness. To some extent, we can relate facies and attribute characteristics to different depositional environments. We identify four distinct facies models: (a) silt-laminated mud turbidites, (b) siliciclastic mud turbidites, (c) carbonate mud turbidites, (d) disorganized silty-mud turbidites, and (e) hemiturbidites. Within the grainsize-velocity matrix turbidite plot, these all fall within the region of mean size < 0.063mm, maximum grainsize (one percentile) <0.2mm, and depositional velocity 0.1-0.5 m/s. Silt-laminated turbidites and many mud turbidites reflect uniform, steady flow characteristics and a depositional sorting mechanism for silt-clay separation; whereas disorganized turbidites reflect an unsteady flow type, either as a short-lived surge or as a mud-contaminated mid-flow. Fine-grained carbonate turbidites show certain distinctive characteristics linked to the different dynamic behaviour of fine carbonate material. Hemiturbidites are the result of long-distance transport and an upward buoyancy mechanism during deposition.

Phase transition behavior of sediment transport at the sand-mud interface, across scales from flumes to the large rivers

NASA Astrophysics Data System (ADS)

Ma, H.; Nittrouer, J. A.; Wu, B.; Zhang, Y.; Mohrig, D. C.; Lamb, M. P.; Wang, Y.; Fu, X.; Moodie, A. J.; Naito, K.; Parker, G.

2017-12-01

Sediment dispersal and deposition creates deltaic landscapes, establishes coastlines, and produces fertile floodplains, all of which serve as critical landforms inhabited by a large proportion of humankind. If poorly managed, sediment loads in these environments can elevate and clog channels, thereby enhancing hazards such as severe flooding. Predictive descriptions of sediment loads, however, are not well constrained, especially for fine-grained (silt and very-fine sand) dispersal systems, which often include river deltas and coastlines. Here, we show efforts to collect and analyze an extensive sediment load database for fine-grained channels, spanning from small flume experiments to large rivers, in order to evaluate the nature of sediment flux. Our analyses determined that sediment transport exhibits two distinct transport phases, separated by a discontinuous transition, whereby sediment flux differs by one to two orders of magnitude. It is determined that the transition responds to the bed material grain size, and we propose a phase diagram based on this metric alone. These findings help elucidate why previous theories of sediment transport at the sand-silt interface, which are typically continuous, are not able to give satisfactory predictions across different scales and environments. Our work serves to help evaluate anthropic influences on rivers, deltas, and coastlines, and can be applied to better constrain sediment flux of paleo-fluvial systems found on Earth and Mars. For example, in situ measurements of sediment flux for the silty-sandy bed of the lower Yellow River, China, validate the aforementioned phase transition behavior, and illustrate that the channel resides near the transition of high to low efficiency transport modes. Recent dam construction and resulting downstream coarsening of the bed via armoring, however, might lead to the unintended consequence of enhancing flood risk by driving the system to a low efficiency transport mode with high resistance to sediment-laden flow, which in turn will elevate the water stage under the same flood discharge.

Investigating the influence of lithologic heterogeneity on gas hydrate formation and methane recycling at the base of the gas hydrate stability zone in channelized systems

NASA Astrophysics Data System (ADS)

Daigle, H.; Nole, M.; Cook, A.; Malinverno, A.

2017-12-01

In marine environments, gas hydrate preferentially accumulates in coarse-grained sediments. At the meso- to micro-scale, however, hydrate distribution in these coarse-grained units is often heterogeneous. We employ a methane hydrate reservoir simulator coupling heat and mass transfer as well as capillary effects to investigate how capillary controls on methane solubility affect gas and hydrate accumulations in reservoirs characterized by graded bedding and alternating sequences of coarse-grained sands and fine-grained silt and clay. Simulations bury a channelized reservoir unit encased in homogeneous, fine-grained material characterized by small pores (150 nm) and low permeability ( 1 md in the absence of hydrate). Pore sizes within each reservoir bed between vary between coarse sand and fine silt. Sands have a median pore size of 35 microns and a lognormal pore size distribution. We also investigate how the amount of labile organic carbon (LOC) affects hydrate growth due to microbial methanogenesis within the sediments. In a diffusion-dominated system, methane movies into reservoir layers along spatial gradients in dissolved methane concentration. Hydrate grows in such a way as to minimize these concentration gradients by accumulating slower in finer-grained reservoir layers and faster in coarser-grained layers. Channelized, fining-upwards sediment bodies accumulate hydrate first along their outer surfaces and thence inward from top to bottom. If LOC is present in thin beds within the channel, higher saturations of hydrate will be distributed more homogeneously throughout the unit. When buried beneath the GHSZ, gas recycling can occur only if enough hydrate is present to form a connected gas phase upon dissociation. Simulations indicate that this is difficult to achieve for diffusion-dominated systems, especially those with thick GHSZs and/or small amounts of LOC. However, capillary-driven fracturing behavior may be more prevalent in settings with thick GHSZs.

Investigating the influence of lithologic heterogeneity on gas hydrate formation and methane recycling at the base of the gas hydrate stability zone in channelized systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Daigle, Hugh; Nole, Michael; Cook, Ann

In marine environments, gas hydrate preferentially accumulates in coarse-grained sediments. At the meso- to micro-scale, however, hydrate distribution in these coarse-grained units is often heterogeneous. We employ a methane hydrate reservoir simulator coupling heat and mass transfer as well as capillary effects to investigate how capillary controls on methane solubility affect gas and hydrate accumulations in reservoirs characterized by graded bedding and alternating sequences of coarse-grained sands and fine-grained silt and clay. Simulations bury a channelized reservoir unit encased in homogeneous, fine-grained material characterized by small pores (150 nm) and low permeability (~1 md in the absence of hydrate). Poremore » sizes within each reservoir bed between vary between coarse sand and fine silt. Sands have a median pore size of 35 microns and a lognormal pore size distribution. We also investigate how the amount of labile organic carbon (LOC) affects hydrate growth due to microbial methanogenesis within the sediments. In a diffusion-dominated system, methane movies into reservoir layers along spatial gradients in dissolved methane concentration. Hydrate grows in such a way as to minimize these concentration gradients by accumulating slower in finer-grained reservoir layers and faster in coarser-grained layers. Channelized, fining-upwards sediment bodies accumulate hydrate first along their outer surfaces and thence inward from top to bottom. If LOC is present in thin beds within the channel, higher saturations of hydrate will be distributed more homogeneously throughout the unit. When buried beneath the GHSZ, gas recycling can occur only if enough hydrate is present to form a connected gas phase upon dissociation. Simulations indicate that this is difficult to achieve for diffusion-dominated systems, especially those with thick GHSZs and/or small amounts of LOC. However, capillary-driven fracturing behavior may be more prevalent in settings with thick GHSZs.« less

Hydraulic evolution of high-density turbidity currents from the Brushy Canyon Formation, Eddy County, New Mexico inferred by comparison to settling and sorting experiments

NASA Astrophysics Data System (ADS)

Motanated, Kannipa; Tice, Michael M.

2016-05-01

Hydraulic transformations in turbidity currents are commonly driven by or reflected in changes in suspended sediment concentrations, but changes preceding transformations can be difficult to diagnose because they do not produce qualitative changes in resultant deposits. This study integrates particle settling experiments and in situ detection of hydraulically contrasting particles in turbidites in order to infer changes in suspended sediment concentration during deposition of massive (Bouma Ta) sandstone divisions. Because grains of contrasting density are differentially sorted during hindered settling from dense suspensions, relative grading patterns can be used to estimate suspended sediment concentrations and interpret hydraulic evolution of the depositing turbidity currents. Differential settling of dense particles (aluminum ballotini) through suspensions of hydraulically coarser light particles (silica ballotini) with volumetric concentration, Cv, were studied in a thin vessel by using particle-image-velocimetry. At high Cv, aluminum particles were less retarded than co-sedimenting silica particles, and effectively settled as hydraulically coarser grains. This was because particles were entrained into clusters dominated by the settling behavior of the silica particles. Terminal settling velocities of both particles converged at Cv ≥ 25%, and particle sorting was diminished. The results of settling experiments were applied to understand settling of analogous feldspar and zircon grains in natural turbidity flows. Distributions of light and heavy mineral grains in massive sandstones, Bouma Ta divisions, of turbidites from the Middle Permian Brushy Canyon Formation were observed in situ by X-ray fluorescence microscopy (μXRF). Hydraulic sorting of these grains resulted in characteristic patterns of zirconium abundance that decreased from base to top within Ta divisions. These profiles resulted from upward fining of zircon grains with respect to co-occurring feldspar grains. Although calculated settling velocity distributions for zircon grains in structureless sandstones were slower than those for feldspar grains at infinite dilution, calculated settling velocity distributions for zircon and feldspar grains in overlying black siltstone layers were identical. This evidence suggests that these sandstone divisions were deposited from hyperconcentrated suspensions where particle segregation was diminished and hydraulically fine grains were entrained with hydraulically coarse particles. Hydraulic fining of zircon grains during deposition implies that the suspended sediment concentration at the bases of turbidity currents increased even as the overall current evolved toward lower density as reflected by cessation of Ta deposition and by hydraulic equivalence of zircon and feldspar grains in overlying low-density turbiditic siltstones. This evolution likely resulted from volumetric collapse of the turbidity currents.

A method for the concentration of fine-grained rutile (TiO2) from sediment and sedimentary rocks by chemical leaching

USGS Publications Warehouse

Commeau, Judith A.; Valentine, Page C.

1991-01-01

Most of the sample analyzed by the method described were marine muds collected from the Gulf of Maine (Valentine and Commeau, 1990). The silt and clay fraction (up to 99 wt% of the sediment) is composed of clay minerals (chiefly illite-mica and chlorite), silt-size quartz and feldspar, and small crystals (2-12 um) of rutile and hematite. The bulk sediment samples contained an average of 2 to 3 wt percent CaCO3. Tiher samples analyzed include red and gray Carboniferous and Triassic sandstones and siltstones exposed around the Bay of Fundy region and Paleozoic sandstones, siltstones, and shales from northern Maine and New Brunswick. These rocks are probable sources for the fine-grained rutile found in the Gulf of Maine.

Ar-Ar Ages of Detrital Hornblendes from Glacial Sediments of the North Sea Trough Mouth Fan

NASA Astrophysics Data System (ADS)

Hemming, S. R.; Haflidason, H.; Sejrup, H. P.

2007-12-01

Determining the relative timing of major iceberg calving from different ice sheet margins around the North Atlantic remains an important goal that will lead to a better understanding of causes and consequences of rapid climate variability during the last glacial period. Characterization of the composition of potential contributors is a necessary step towards this goal. The North Sea trough mouth fan is one of the largest glaciogenic debris flow complexes in the North Atlantic/Arctic region, with an approximate area of 142,000 square km (King et al., 1998, Marine Geology v. 152, pp. 217-246; Nygard et al., 2007, Geology, pp. 395-398). The large ice stream trough crosses the shelf along the southern margin of Norway. The crystalline rocks along the southern margin of Norway are Grenville (approximately 1 Ga old orogen). We undertook a study of the Ar-Ar age populations of individual detrital hornblende grains from a sediment sample of the glacigenic debris lobe created during the last phases of the last glacial maximum from the North Sea trough mouth fan. The goal is to test the hypothesis that the ice stream that fed this fan is the source of abundant Grenville age grains found on Bjorn drift site ODP984, at times when North American Grenville sources are not found in the North Atlantic ice rafted detritus belt (Hemming et al., 2005, AGU Spring meeting, PP23A-04). Hornblende grains from North Sea TMF core NH071-B01\\SC1 (1) (63.24N, 3.36E, 1049m) have a dominant age population of Grenville (921 Ma, 19 of 48 grains) with subordinate populations of 1108 Ma (n=3) and 1779 Ma (n=4). Accordingly they lend support to the hypothesis that this ice stream could be the source of IRD on the Bjorn drift. These results could additionally shed light on the pathways of fine grain sediment transport to the Bjorn drift which would contribute a better understanding of sediment processes in the region. For example, the provenance implied for the IRD by the Ar-Ar hornblende ages is consistent with that implied by the Nd isotope data from fine grained sediments reported for glacial intervals by DePaolo et al. (2006, EPSL, v. 298, pp. 394- 410). It is well known that much of the debris carried by icebergs is fine grained, and thus this provenance match suggests that it is likely that much of the fine grained material may also be carried to this site by icebergs.

Experimental Simulations of Methane Gas Migration through Water-Saturated Sediment Cores

NASA Astrophysics Data System (ADS)

Choi, J.; Seol, Y.; Rosenbaum, E. J.

2010-12-01

Previous numerical simulations (Jaines and Juanes, 2009) showed that modes of gas migration would mainly be determined by grain size; capillary invasion preferably occurring in coarse-grained sediments vs. fracturing dominantly in fine-grained sediments. This study was intended to experimentally simulate preferential modes of gas migration in various water-saturated sediment cores. The cores compacted in the laboratory include a silica sand core (mean size of 180 μm), a silica silt core (1.7 μm), and a kaolin clay core (1.0 μm). Methane gas was injected into the core placed within an x-ray-transparent pressure vessel, which was under continuous x-ray computed tomography (CT) scanning with controlled radial (σr), axial (σa), and pore pressures (P). The CT image analysis reveals that, under the radial effective stress (σr') of 0.69 MPa and the axial effective stress (σa') of 1.31 MPa, fracturings by methane gas injection occur in both silt and clay cores. Fracturing initiates at the capillary pressure (Pc) of ~ 0.41 MPa and ~ 2.41 MPa for silt and clay cores, respectively. Fracturing appears as irregular fracture-networks consisting of nearly invisibly-fine multiple fractures, longitudinally-oriented round tube-shape conduits, or fine fractures branching off from the large conduits. However, for the sand core, only capillary invasion was observed at or above 0.034 MPa of capillary pressure under the confining pressure condition of σr' = 1.38 MPa and σa' = 2.62 MPa. Compared to the numerical predictions under similar confining pressure conditions, fracturing occurs with relatively larger grain sizes, which may result from lower grain-contact compression and friction caused by loose compaction and flexible lateral boundary employed in the experiment.

MODELLING SEDIMENT TRANSPORT FOR THE LAKE MICHIGAN MASS BALANCE PROJECT

EPA Science Inventory

A sediment transport model is one component of the overall ensemble of models being developed for the Lake Michigan Mass Balance. The SEDZL model is being applied to simulate the fine-grained sediment transport in Lake Michigan for the 1982-1983 and 1994-1995 periods. Model perf...

Evaluating process origins of sand-dominated fluvial stratigraphy

NASA Astrophysics Data System (ADS)

Chamberlin, E.; Hajek, E. A.

2015-12-01

Sand-dominated fluvial stratigraphy is often interpreted as indicating times of relatively slow subsidence because of the assumption that fine sediment (silt and clay) is reworked or bypassed during periods of low accommodation. However, sand-dominated successions may instead represent proximal, coarse-grained reaches of paleo-river basins and/or fluvial systems with a sandy sediment supply. Differentiating between these cases is critical for accurately interpreting mass-extraction profiles, basin-subsidence rates, and paleo-river avulsion and migration behavior from ancient fluvial deposits. We explore the degree to which sand-rich accumulations reflect supply-driven progradation or accommodation-limited reworking, by re-evaluating the Castlegate Sandstone (Utah, USA) and the upper Williams Fork Formation (Colorado, USA) - two Upper Cretaceous sandy fluvial deposits previously interpreted as having formed during periods of relatively low accommodation. Both units comprise amalgamated channel and bar deposits with minor intra-channel and overbank mudstones. To constrain relative reworking, we quantify the preservation of bar deposits in each unit using detailed facies and channel-deposit mapping, and compare bar-deposit preservation to expected preservation statistics generated with object-based models spanning a range of boundary conditions. To estimate the grain-size distribution of paleo-sediment input, we leverage results of experimental work that shows both bed-material deposits and accumulations on the downstream side of bars ("interbar fines") sample suspended and wash loads of active flows. We measure grain-size distributions of bar deposits and interbar fines to reconstruct the relative sandiness of paleo-sediment supplies for both systems. By using these novel approaches to test whether sand-rich fluvial deposits reflect river systems with accommodation-limited reworking and/or particularly sand-rich sediment loads, we can gain insight into large-scale downstream-fining and mass-extraction trends in basins with limited exposure.

Organochlorine pesticide residues in bed sediments of the San Joaquin River, California

USGS Publications Warehouse

Gilliom, Robert J.; Clifton, Daphne G.

1990-01-01

Bed sediments of the San Joaquin River and its tributaries were sampled during October 7–11, 1985, and analyzed for organochiorine pesticide residues in order to determine their areal distribution and to evaluate and prioritize needs for further study. Residues of DDD, DDE, DDT, and dieldrin are widespread in the fine-grained bed sediments of the San Joaquin River and its tributaries despite little or no use of these pesticides for more than 15 years. The San Joaquin River has among the highest bed-sediment concentrations of DDD, DDE, DDT, and dieldrin residues of major rivers in the United States. Concentrations of all four pesticides were correlated with each other and with the amount of organic carbon and fine-grained particles in the bed sediments. The highest concentrations occurred in bed sediments of westside tributary streams. Potential tributary loads of DDD, DDE, DDT, and dieldrin to the San Joaquin River were computed from bed-sediment concentrations and data on streamfiow and suspended-sediment concentration in order to identify the general magnitude of differences between streams and to determine study priorities. The estimated loads indicate that the most important sources of residues during the study period were Salt Slough because of a high load of fine sediment, and Newman Wasteway, Orestimba Creek, and Hospital Creek because of high bed-sediment concentrations. Generally, the highest estimated loads of DDD, DDE, DDT, and dieldrin were in Orestimba and Hospital Creeks.

Revisiting the effects of hydrodynamic sorting and sedimentary recycling on chemical weathering indices

NASA Astrophysics Data System (ADS)

Guo, Yulong; Yang, Shouye; Su, Ni; Li, Chao; Yin, Ping; Wang, Zhongbo

2018-04-01

Although the proxies based on elemental geochemistry of siliciclastic sediments have been well developed to indicate the intensity of chemical weathering in various catchments, their geological indications and limitations, and especially how the differentiation of minerals and sediment grain size influences the applications of these proxies needs more clarification. This paper investigates the interactive effects of weathering, hydraulic sorting and sedimentary recycling on river sediment chemistry, and further validates the application of various weathering indices by measuring mineralogical and geochemical compositions of bank sediments and suspended particulate matters (SPMs) from five rivers in East China bearing various sizes, geologic settings and climatic regimes. For a specific river, the silicate weathering intensity registered in the fine SPMs is systematically stronger than that in the coarse-grained bank sediments. Most of the weathering indices not only reflect the integrated weathering history of various catchments but also depend on hydraulic sorting effect during sediment transport and depositional processes. The correlation between CIA (chemical index of alteration) and WIP (weathering index of Parker) offers an approach to predict the weathering trends of the fine SPMs, coarse bank sediments and recycled sediments under the influence of quartz dilution. To minimize the effects of hydrodynamic sorting and sedimentary recycling, we suggest that the fine sediments (e.g. SPMs and <2 μm fraction of bank sediments) in rivers can better reflect the average of present-day weathering crust in catchments and the weathered terrigenous materials into marginal seas and oceans.

Identification of magnetic minerals in the fine-grain sediment on the Bengawan Solo River

NASA Astrophysics Data System (ADS)

Purnama, B.; Kusuma, R.; Legowo, B.; Suharyana; Wijayanta, A. T.

2018-03-01

The magnetic mineral content in the fine sediment of Bengawan Solo River is discussed. The fine sediment is obtained on the upper part of the tributary of Bengawan Solo River. Magnetic minerals are separated using permanent magnets. Furthermore the magnetic minerals are overnight dried using oven at 100°C. FTIR characterization indicate that the magnetic minerals in the fine sediment of Bengawan Solo River have the same characteristics as minerals in Cilacap and Purwokerto areas. Magnetic minerals are estimated to form at wave number k = 569.03 cm-1. This hematite content increase to 70.67% after anealling treatment at 600°C for 4 hours in atmosphere condition. This result is interesting because the heating process increases the hematite content. Within results, the magnetic properties of the sample will change.

Using lake sediments from Buarvatnet to reconstruct multiple episodic events found at Folgefonn Peninsula, Norway

NASA Astrophysics Data System (ADS)

Roethe, T.; Bakke, J.; Støren, E.

2016-12-01

Here we present work in progress from Buarvatnet at the Folgefonn Peninsula, located on the west coast of Norway. Earlier work from Buarvatnet indicated several distinct spikes in the Silica count rates, detected by the ITRAX surface XRF-scanner. However, the process behind these distinct spikes was not understood. The arrival of high-resolution and innovative instruments at EARTHLAB, in particular the computed tomography (CT) scanner and grain Morphometer, have the potential to get a process-based understanding of these distinct layers and unravel the frequency and timing of such events. Multiple sediment cores were retrieved using a modified piston corer and a Uwitech corer from Buarvatnet. The sediments have been analysed using a multi-proxy approach and the analyses included magnetic properties, loss-on-ignition, dry bulk density, grain size/shape, geochemical analysis (XRF scanning) and CT-scanning. Accurate age-control will be achieved through 210Pb dating of the top-most sediments and 14C dating of terrestrial macrofossils. The lithostratigraphy of the 3.6 m long master sediment core from Buarvatnet is divided into three distinct units. The lower most unit ( 87 cm) is massive with fine-grained greyish sediments, most likely representing the deglaciation of the area. A 224 cm long unit is found above, characterised as dark brown gyttja with multiple thin layers (sub-mm to cm thick) of fine grained sediments. Also in this unit is two distinct sub-units showing a finer upwards sequence. At top, a gradual transition from dark brown gyttja to grey fine-grained sediments is found in the upper-most 19 cm of the sediment core. In total 16 distinct layers is found in the gyttja sequence, including the two sub-units, based on the lithostratigraphy and the prelimnary results from the magnetic, physical and geochemical properties. A preliminary hypothesis is that these distinct layers are due to outburst floods from a glacier-dammed lake upstream from Buarvatnet. In such a scenario, a bedrock threshold dams the meltwater from the retreating glacier and an outburst flood is triggered when the glacier calves or advances into the lake. Understanding the processes behind the multiple events is therefore important in order to highlight the potential hazards in rapid outburst floods in a warming world.

Modeling the Formation of Hydrate-Filled Veins in Fine-Grained Sediments from in Situ Microbial Methane

NASA Astrophysics Data System (ADS)

Malinverno, A.; Cook, A.; Daigle, H.

2016-12-01

Continental margin sediments are dominantly fine-grained silt and clay, and methane hydrates in these sediments are often found in semi-vertical veins and fractures. In several instances, these hydrate veins occupy discrete depth intervals that are a few tens of meters thick and are surrounded by hydrate-free sediments. As they are not connected with gas sources beneath the base of the gas hydrate stability zone (GHSZ), these isolated hydrate-bearing intervals have been interpreted as formed by in situ microbial methane. To investigate the formation of these hydrate deposits, we applied a time-dependent advection-diffusion-reaction model that includes the effects of sedimentation, compaction, solute diffusion, and microbial methane generation. Microbial methane generation depends on the amount of metabolizable organic carbon deposited at the seafloor, whose progressive degradation produces methane beneath the sulfate reduction zone. If the amount of organic carbon entering the methanogenic zone is kept constant in time, we found that the computed amounts of hydrate formed in discrete intervals within the GHSZ are well below those estimated from observations. On the other hand, if the deposition of organic carbon is higher in a given time interval, methane generation during burial is more intense in the corresponding sediment interval, resulting in enhanced hydrate formation. With variations in organic carbon deposition comparable to those generally observed in continental margins, our model was able to reproduce the methane hydrate contents that were estimated from drilling. These results support the suggestion that in situ microbial generation associated with transient organic carbon deposition is the source of methane that forms isolated intervals of hydrate-filled veins in fine-grained sediments.

Modeling the Formation of Hydrate-Filled Veins in Fine-Grained Sediments from in Situ Microbial Methane

DOE Office of Scientific and Technical Information (OSTI.GOV)

Malinverno, Alberto; Cook, Ann; Daigle, Hugh

Continental margin sediments are dominantly fine-grained silt and clay, and methane hydrates in these sediments are often found in semi-vertical veins and fractures. In several instances, these hydrate veins occupy discrete depth intervals that are a few tens of meters thick and are surrounded by hydrate-free sediments. As they are not connected with gas sources beneath the base of the gas hydrate stability zone (GHSZ), these isolated hydrate-bearing intervals have been interpreted as formed by in situ microbial methane. To investigate the formation of these hydrate deposits, we applied a time-dependent advection-diffusion-reaction model that includes the effects of sedimentation, compaction,more » solute diffusion, and microbial methane generation. Microbial methane generation depends on the amount of metabolizable organic carbon deposited at the seafloor, whose progressive degradation produces methane beneath the sulfate reduction zone. If the amount of organic carbon entering the methanogenic zone is kept constant in time, we found that the computed amounts of hydrate formed in discrete intervals within the GHSZ are well below those estimated from observations. On the other hand, if the deposition of organic carbon is higher in a given time interval, methane generation during burial is more intense in the corresponding sediment interval, resulting in enhanced hydrate formation. With variations in organic carbon deposition comparable to those generally observed in continental margins, our model was able to reproduce the methane hydrate contents that were estimated from drilling. These results support the suggestion that in situ microbial generation associated with transient organic carbon deposition is the source of methane that forms isolated intervals of hydrate-filled veins in fine-grained sediments.« less

Sedimentation and remobilization of radiocesium in the coastal area of Ibaraki, 70 km south of the Fukushima Dai-ichi Nuclear Power Plant.

PubMed

Otosaka, Shigeyoshi; Kobayashi, Takuya

2013-07-01

Sedimentation and remobilization processes of radiocesium were investigated from time-series observations at nine stations in the coastal area of Ibaraki, 70-110 km south of the Fukushima Dai-ichi Nuclear Power Plant (1FNPP). Sediment samples were collected four times between June 2011 and January 2012, and concentrations of radiocesium as well as sediment properties such as grain size and elemental compositions were analyzed. Cumulative inventory of (137)Cs in sediment (0-10 cm) ranged between 4 × 10(3) and 3 × 10(4) Bq/m(2) as of January 2012. This amount was generally higher at stations nearer 1FNPP and has remained at the same level since August 2011. From these results, it can be inferred that dissolved radiocesium advected southward from the region adjacent to the 1FNPP and was deposited to the sediment of the study area in the early stage after the accident. The incorporation of radiocesium into sediments was almost irreversible, and higher concentrations of (137)Cs were obtained from the finer-grained fraction of sediments. In the northern offshore stations, resuspension of the fine-grained sediments formed a high-turbidity layer 10-20 m above the seabed. These results indicate that radiocesium-enriched fine particles were transported from the coast to offshore regions through the bottom high-turbidity layer.

Acoustics of marine sediment under compaction: binary grain-size model and viscoelastic extension of Biot's theory.

PubMed

Leurer, Klaus C; Brown, Colin

2008-04-01

This paper presents a model of acoustic wave propagation in unconsolidated marine sediment, including compaction, using a concept of a simplified sediment structure, modeled as a binary grain-size sphere pack. Compressional- and shear-wave velocities and attenuation follow from a combination of Biot's model, used as the general framework, and two viscoelastic extensions resulting in complex grain and frame moduli, respectively. An effective-grain model accounts for the viscoelasticity arising from local fluid flow in expandable clay minerals in clay-bearing sediments. A viscoelastic-contact model describes local fluid flow at the grain contacts. Porosity, density, and the structural Biot parameters (permeability, pore size, structure factor) as a function of pressure follow from the binary model, so that the remaining input parameters to the acoustic model consist solely of the mass fractions and the known mechanical properties of each constituent (e.g., carbonates, sand, clay, and expandable clay) of the sediment, effective pressure, or depth, and the environmental parameters (water depth, salinity, temperature). Velocity and attenuation as a function of pressure from the model are in good agreement with data on coarse- and fine-grained unconsolidated marine sediments.

Hydrate Formation in Gas-Rich Marine Sediments: A Grain-Scale Model

NASA Astrophysics Data System (ADS)

Holtzman, R.; Juanes, R.

2009-12-01

We present a grain-scale model of marine sediment, which couples solid- and multiphase fluid-mechanics together with hydrate kinetics. The model is applied to investigate the spatial distribution of the different methane phases - gas and hydrate - within the hydrate stability zone. Sediment samples are generated from three-dimensional packs of spherical grains, mapping the void space into a pore network by tessellation. Gas invasion into the water-saturated sample is simulated by invasion-percolation, coupled with a discrete element method that resolves the grain mechanics. The coupled model accounts for forces exerted by the fluids, including cohesion associated with gas-brine surface tension. Hydrate growth is represented by a hydrate film along the gas-brine interface, which increases sediment cohesion by cementing the grain contacts. Our model of hydrate growth includes the possible rupture of the hydrate layer, which leads to the creation of new gas-water interface. In previous work, we have shown that fine-grained sediments (FGS) exhibit greater tendency to fracture, whereas capillary invasion is the preferred mode of methane gas transport in coarse-grained sediments (CGS). The gas invasion pattern has profound consequences on the hydrate distribution: a larger area-to-volume ratio of the gas cluster leads to a larger drop in gas pressure inside the growing hydrate shell, causing it to rupture. Repeated cycles of imbibition and hydrate growth accompanied by trapping of gas allow us to determine the distribution of hydrate and gas within the sediment as a function of time. Our pore-scale model suggests that, even when film rupture takes place, the conversion of gas to hydrate is slow. This explains two common field observations: the coexistence of gas and hydrate within the hydrate stability zone in CGS, and the high methane fluxes through fracture conduits in FGS. These results demonstrate the importance of accounting for the strong coupling among multiphase flow, sediment mechanics, and hydrate formation. Our model explains the remarkable differences in hydrate distribution and saturation between fine- and coarse-grained sediments, and promotes the quantitative understanding of the role of methane hydrate in seafloor stability and the global carbon cycle, including the size of the hydrate energy resource, and estimates of methane fluxes into the ocean and the atmosphere.

Sediment dynamics and the burial and exhumation of bedrock reefs along an emergent coastline as elucidated by repetitive sonar surveys: Northern Monterey Bay, CA

USGS Publications Warehouse

Storlazzi, C.D.; Fregoso, T.A.; Golden, N.E.; Finlayson, D.P.

2011-01-01

Two high-resolution bathymetric and acoustic backscatter sonar surveys were conducted along the energetic emergent inner shelf of northern Monterey Bay, CA, USA, in the fall of 2005 and the spring of 2006 to determine the impact of winter storm waves, beach erosion, and river floods on biologically-important siliclastic bedrock reef habitats. The surveys extended from water depths of 4 m to 22 m and covered an area of 3.14 km2, 45.8% of which was bedrock, gravel, and coarse-grained sand and 54.2% was fine-grained sand. Our analyses of the bathymetric and acoustic backscatter data demonstrates that during the 6 months between surveys, 11.4% of the study area was buried by fine-grained sand while erosion resulted in the exposure of bedrock or coarse-grained sand over 26.5% of the study area. The probability of burial decreased with increasing water depth and rugosity; the probability of exhumation increased with increasing wave-induced near-bed shear stress, seabed slope and rugosity. Much of the detected change was at the boundary between bedrock and unconsolidated sediment due to sedimentation and erosion burying or exhuming bedrock, respectively. In a number of cases, however, the change in seabed character was apparently due to changes in sediment grain size when scour exposed what appeared to be an underlying coarser-grained lag or the burial of coarser-grained sand and gravel by fine-grained sand. These findings suggest that, in some places, (a) burial and exhumation of nearshore bedrock reefs along rocky, energetic inner shelves occurs over seasonal timescales and appears related to intrinsic factors such as seabed morphology and extrinsic factors such as wave forces, and (b) single acoustic surveys typically employed for geologic characterization and/or habitat mapping may not adequately characterize the geomorphologic and sedimentologic nature of these types of environments that typify most of the Pacific Ocean and up to 50% of the world's coastlines.

Influence of a dam on fine-sediment storage in a canyon river

USGS Publications Warehouse

Hazel, J.E.; Topping, D.J.; Schmidt, J.C.; Kaplinski, M.

2006-01-01

Glen Canyon Dam has caused a fundamental change in the distribution of fine sediment storage in the 99-km reach of the Colorado River in Marble Canyon, Grand Canyon National Park, Arizona. The two major storage sites for fine sediment (i.e., sand and finer material) in this canyon river are lateral recirculation eddies and the main-channel bed. We use a combination of methods, including direct measurement of sediment storage change, measurements of sediment flux, and comparison of the grain size of sediment found in different storage sites relative to the supply and that in transport, in order to evaluate the change in both the volume and location of sediment storage. The analysis shows that the bed of the main channel was an important storage environment for fine sediment in the predam era. In years of large seasonal accumulation, approximately 50% of the fine sediment supplied to the reach from upstream sources was stored on the main-channel bed. In contrast, sediment budgets constructed for two short-duration, high experimental releases from Glen Canyon Dam indicate that approximately 90% of the sediment discharge from the reach during each release was derived from eddy storage, rather than from sandy deposits on the main-channel bed. These results indicate that the majority of the fine sediment in Marble Canyon is now stored in eddies, even though they occupy a small percentage (???17%) of the total river area. Because of a 95% reduction in the supply of fine sediment to Marble Canyon, future high releases without significant input of tributary sediment will potentially erode sediment from long-term eddy storage, resulting in continued degradation in Marble Canyon. Copyright 2006 by the American Geophysical Union.

Linking Monsoon Activity with River-Derived Sediment Deposition in the northern South China Sea

NASA Astrophysics Data System (ADS)

Ge, Q.; Xue, Z. G.; Liu, P.; Chu, F.

2016-02-01

Sediments retrieved from a gravity core were analyzed to examine the connection between East Asian Monsoon (EAM) and river-derived sediment deposition on the continental slope in the South China Sea since the Last Glacial Maximum. Combined clay mineralogy and grain size index analysis provided evidence of the sources of fine-grained sediment as well as for rebuilding the history of paleo-EAM. A shift of sediment source from the Pearl River to southwestern Taiwanese rivers was identified during the Holocene. The 4-8μm grain size fraction, as an environmental sensitive component and thus the EAM proxy, indicated the local deposition environment is mainly controlled by sea-level variations. And during the Holocene, the East Asian summer monsoon exhibited an in-phase relationship with East Asian winter monsoon, both following variations of the insolation intensity.

INTERREGIONAL COMPARISONS OF SEDIMENT MICROBIAL RESPIRATION IN STREAMS

EPA Science Inventory

The rate of microbial respiration on fine-grained stream sediments was measured at 369 first to fourth-order streams in the Central Appalachians, Colorado's Southern Rockies, and California's Central Valley in 1994 and 1995. Study streams were randomly selected from the USEPA's ...

Estimation of sediment sources using selected chemical tracers in the Perry lake basin, Kansas, USA

USGS Publications Warehouse

Juracek, K.E.; Ziegler, A.C.

2009-01-01

The ability to achieve meaningful decreases in sediment loads to reservoirs requires a determination of the relative importance of sediment sources within the contributing basins. In an investigation of sources of fine-grained sediment (clay and silt) within the Perry Lake Basin in northeast Kansas, representative samples of channel-bank sources, surface-soil sources (cropland and grassland), and reservoir bottom sediment were collected, chemically analyzed, and compared. The samples were sieved to isolate the <63 ?? m fraction and analyzed for selected nutrients (total nitrogen and total phosphorus), organic and total carbon, 25 trace elements, and the radionuclide cesium-137 (137Cs). On the basis of substantial and consistent compositional differences among the source types, total nitrogen (TN), total phosphorus (TP), total organic carbon (TOC), and 137Cs were selected for use in the estimation of sediment sources. To further account for differences in particle-size composition between the sources and the reservoir bottom sediment, constituent ratio and clay-normalization techniques were used. Computed ratios included TOC to TN, TOC to TP, and TN to TP. Constituent concentrations (TN, TP, TOC) and activities (137Cs) were normalized by dividing by the percentage of clay. Thus, the sediment-source estimations involved the use of seven sediment-source indicators. Within the Perry Lake Basin, the consensus of the seven indicators was that both channel-bank and surface-soil sources were important in the Atchison County Lake and Banner Creek Reservoir subbasins, whereas channel-bank sources were dominant in the Mission Lake subbasin. On the sole basis of 137Cs activity, surface-soil sources contributed the most fine-grained sediment to Atchison County Lake, and channel-bank sources contributed the most fine-grained sediment to Banner Creek Reservoir and Mission Lake. Both the seven-indicator consensus and 137Cs indicated that channel-bank sources were dominant for Perry Lake and that channel-bank sources increased in importance with distance downstream in the basin. ?? 2009 International Research and Training Centre on Erosion and Sedimentation and the World Association for Sedimentation and Erosion Research.

Seasonal variations in the characteristics of superficial sediments in a macrotidal estuary (the Seine inlet, France)

NASA Astrophysics Data System (ADS)

Lesourd, S.; Lesueur, P.; Brun-Cottan, J. C.; Garnaud, S.; Poupinet, N.

2003-09-01

Seasonal variations in the sedimentary regime in the mouth of the Seine river, a macrotidal estuary, are described for a 3-year period. The aim of this study is to characterize and to understand the main governing mechanisms, using data from more than a thousand of superficial sediment grab samples or box cores gathered throughout the study period. Analyses of lithofacies and rheological properties were carried out. The distribution of sediments is governed by seasonal meteorological variations. The surface covered by mud reaches a maximum (40% of the total mouth area) during winter. After the winter, the soft mud deposits are progressively redistributed throughout the whole estuary area and onto the shelf. During the lowest freshwater flow at the end of summer, the fine-grained sediments cover less than 20% of the river mouth area. These seasonal variations mainly depend on the river discharge intensity, but are also linked to wave activity. In the study area, the amount of fine-grained deposits after high river flow periods depends on (1) volume of mud erodable within the estuary, (2) the duration of the flood tidal influx, and (3) the duration preceding the particular annual high river flow. During the last decades, filling of the estuary upstream from Honfleur has led to a downstream shift of the fine-grained sediment deposition area; following this, the present-day mud deposition area is in the open part of the estuary, in the subtidal shallow area. Subsequently, fresh mud deposits undergo intense hydrodynamical and meteorological effects, and are partly reworked by waves and tidal currents effects. In this study, it is shown that the behaviour of suspended matter and of superficial sediments is strongly influenced by short but intense events including high river flows and gales.

The impact of disposal of fine-grained sediments from maintenance dredging works on SPM concentration and fluid mud in and outside the harbor of Zeebrugge

NASA Astrophysics Data System (ADS)

Fettweis, Michael; Baeye, Matthias; Cardoso, Claudio; Dujardin, Arvid; Lauwaert, Brigitte; Van den Eynde, Dries; Van Hoestenberghe, Thomas; Vanlede, Joris; Van Poucke, Luc; Velez, Carlos; Martens, Chantal

2016-11-01

The amount of sediments to be dredged and disposed depends to a large part on the suspended particulate matter (SPM) concentration. Tidal, meteorological, climatological, and seasonal forcings have an influence on the horizontal and vertical distribution of the SPM in the water column and on the bed and control the inflow of fine-grained sediments towards harbors and navigation channels. About 3 million tons (dry matter) per year of mainly fine-grained sediments is dredged in the port of Zeebrugge and is disposed on a nearby disposal site. The disposed sediments are quickly resuspended and transported away from the site. The hypothesis is that a significant part of the disposed sediments recirculates back to the dredging places and that a relocation of the disposal site to another location at equal distance to the dredging area would reduce this recirculation. In order to validate the hypothesis, a 1-year field study was set up in 2013-2014. During 1 month, the dredged material was disposed at a new site. Variations in SPM concentration were related to tides, storms, seasonal changes, and human impacts. In the high-turbidity Belgian near-shore area, the natural forcings are responsible for the major variability in the SPM concentration signal, while disposal has only a smaller influence. The conclusion from the measurements is that the SPM concentration decreases after relocation of the disposal site but indicate stronger (first half of field experiment) or weaker (second half of field experiment) effects that are, however, supported by the environmental conditions. The results of the field study may have consequences on the management of disposal operations as the effectiveness of the disposal site depends on environmental conditions, which are inherently associated with chaotic behavior.

A 2D Micromodel Study of Fines Migration and Clogging Behavior in Porous Media: Implications of Fines on Methane Extraction from Hydrate-Bearing Sediments

NASA Astrophysics Data System (ADS)

Cao, S. C.; Jang, J.; Waite, W. F.; Jafari, M.; Jung, J.

2017-12-01

Fine-grained sediment, or "fines," exist nearly ubiquitously in natural sediment, even in the predominantly coarse-grained sediments that host gas hydrates. Fines within these sandy sediments can play a crucial role during gas hydrate production activities. During methane extraction, several processes can alter the mobility and clogging potential of fines: 1) fluid flow as the formation is depressurized to release methane from hydrate; 2) pore-fluid chemistry shifts as pore-fluid brine freshens due to pure water released from dissociating hydrate; 3) the presence of a moving gas/water interface as gas evolves from dissociating hydrate and moves through the reservoir toward the production well. To evaluate fines migration and clogging behavior changes resulting from methane gas production and pore-water freshening during hydrate dissociation, 2D micromodel experiments have been conducted on a selection of pure fines, pore-fluids, and micromodel pore-throat sizes. Additionally, tests have been run with and without an invading gas phase (CO2) to test the significance of a moving meniscus on fines mobility and clogging. The endmember fine particles chosen for this research include silica silt, mica, calcium carbonate, diatoms, kaolinite, illite, and bentonite (primarily made of montmorillonite). The pore fluids include deionized water, sodium chloride brine (2M concentration), and kerosene. The microfluidic pore models, used as porous media analogs, were fabricated with pore-throat widths of 40, 60, and 100 µm. Results from this research show that in addition to the expected dependence of clogging on the ratio of particle-to-pore-throat size, pore-fluid chemistry is also a significant factor because the interaction between a particular type of fine and pore fluid influences that fine's capacity to cluster, clump together and effectively increase its particle "size" relative to the pore-throat width. The presence of a moving gas/fluid meniscus increases the clogging potential regardless of fine type as the advancing meniscus tends to gather and concentrate the fines. Results show the need to identify both the type and concentration of fines prior to evaluating whether a system's clogging potential will increase or decrease as pore waters freshen during methane extraction from hydrate.

Sedimentation processes in a coral reef embayment: Hanalei Bay, Kauai

USGS Publications Warehouse

Storlazzi, C.D.; Field, M.E.; Bothner, Michael H.; Presto, M.K.; Draut, A.E.

2009-01-01

Oceanographic measurements and sediment samples were collected during the summer of 2006 as part of a multi-year study of coastal circulation and the fate of terrigenous sediment on coral reefs in Hanalei Bay, Kauai. The goal of this study was to better understand sediment dynamics in a coral reef-lined embayment where winds, ocean surface waves, and river floods are important processes. During a summer period that was marked by two wave events and one river flood, we documented significant differences in sediment trap collection rates and the composition, grain size, and magnitude of sediment transported in the bay. Sediment trap collection rates were well correlated with combined wave-current near-bed shear stresses during the non-flood periods but were not correlated during the flood. The flood's delivery of fine-grained sediment to the bay initially caused high turbidity and sediment collection rates off the river mouth but the plume dispersed relatively quickly. Over the next month, the flood deposit was reworked by mild waves and currents and the fine-grained terrestrial sediment was advected around the bay and collected in sediment traps away from the river mouth, long after the turbid surface plume was gone. The reworked flood deposits, due to their longer duration of influence and proximity to the seabed, appear to pose a greater long-term impact to benthic coral reef communities than the flood plumes themselves. The results presented here display how spatial and temporal differences in hydrodynamic processes, which result from variations in reef morphology and orientation, cause substantial variations in the deposition, residence time, resuspension, and advection of both reef-derived and fluvial sediment over relatively short spatial scales in a coral reef embayment.

Microbial colonization and degradation of polyethylene and biodegradable plastic bags in temperate fine-grained organic-rich marine sediments.

PubMed

Nauendorf, Alice; Krause, Stefan; Bigalke, Nikolaus K; Gorb, Elena V; Gorb, Stanislav N; Haeckel, Matthias; Wahl, Martin; Treude, Tina

2016-02-15

To date, the longevity of plastic litter at the sea floor is poorly constrained. The present study compares colonization and biodegradation of plastic bags by aerobic and anaerobic benthic microbes in temperate fine-grained organic-rich marine sediments. Samples of polyethylene and biodegradable plastic carrier bags were incubated in natural oxic and anoxic sediments from Eckernförde Bay (Western Baltic Sea) for 98 days. Analyses included (1) microbial colonization rates on the bags, (2) examination of the surface structure, wettability, and chemistry, and (3) mass loss of the samples during incubation. On average, biodegradable plastic bags were colonized five times higher by aerobic and eight times higher by anaerobic microbes than polyethylene bags. Both types of bags showed no sign of biodegradation during this study. Therefore, marine sediment in temperate coastal zones may represent a long-term sink for plastic litter and also supposedly compostable material. Copyright © 2016 Elsevier Ltd. All rights reserved.

Suspended sediment and turbidity after road construction/improvement and forest harvest in streams of the Trask River Watershed Study, Oregon

Treesearch

Ivan Arismendi; Jeremiah D. Groom; Maryanne Reiter; Sherri L. Johnson; Liz Dent; Mark Meleason; Alba Argerich; Arne E. Skaugset

2017-01-01

Transport of fine-grained sediment from unpaved forest roads into streams is a concern due to the potential negative effects of additional suspended sediment on aquatic ecosystems. Here we compared turbidity and suspended sediment concentration (SSC) dynamics in five nonfish bearing coastal Oregon streams above and below road crossings, during three consecutive time...

Bottom-boundary-layer measurements on the continental shelf off the Ebro River, Spain

USGS Publications Warehouse

Cacchione, D.A.; Drake, D.E.; Losada, M.A.; Medina, R.

1990-01-01

Measurements of currents, waves and light transmission obtained with an instrumented bottom tripod (GEOPROBE) were used in conjunction with a theoretical bottom-boundary-layer model for waves and currents to investigate sediment transport on the continental shelf south of the Ebro River Delta, Spain. The current data show that over a 48-day period during the fall of 1984, the average transport at 1 m above the seabed was alongshelf and slightly offshore toward the south-southwest at about 2 cm/s. A weak storm passed through the region during this period and caused elevated wave and current speeds near the bed. The bottom-boundary-layer model predicted correspondingly higher combined wave and current bottom shear velocities at this time, but the GEOPROBE optical data indicate that little to no resuspension occurred. This result suggests that the fine-grained bottom sediment, which has a clay component of 80%, behaves cohesively and is more difficult to resuspend than noncohesive materials of similar size. Model computations also indicate that noncohesive very fine sand in shallow water (20 m deep) was resuspended and transported mainly as bedload during this storm. Fine-grained materials in shallow water that are resuspended and transported as suspended load into deeper water probably account for the slight increase in sediment concentration at the GEOPROBE sensors during the waning stages of the storm. The bottom-boundary-layer data suggest that the belt of fine-grained bottom sediment that extends along the shelf toward the southwest is deposited during prolonged periods of low energy and southwestward bottom flow. This pattern is augmented by enhanced resuspension and transport toward the southwest during storms. ?? 1990.

Quantifying alluvial fan sensitivity to climate in Death Valley, California, from field observations and numerical models

NASA Astrophysics Data System (ADS)

Brooke, Sam; Whittaker, Alexander; Armitage, John; D'Arcy, Mitch; Watkins, Stephen

2017-04-01

A quantitative understanding of landscape sensitivity to climate change remains a key challenge in the Earth Sciences. The stream-flow deposits of coupled catchment-fan systems offer one way to decode past changes in external boundary conditions as they comprise simple, closed systems that can be represented effectively by numerical models. Here we combine the collection and analysis of grain size data on well-dated alluvial fan surfaces in Death Valley, USA, with numerical modelling to address the extent to which sediment routing systems record high-frequency, high-magnitude climate change. We compile a new database of Holocene and Late-Pleistocene grain size trends from 11 alluvial fans in Death Valley, capturing high-resolution grain size data ranging from the Recent to 100 kyr in age. We hypothesise the observed changes in average surface grain size and fining rate over time are a record of landscape response to glacial-interglacial climatic forcing. With this data we are in a unique position to test the predictions of landscape evolution models and evaluate the extent to which climate change has influenced the volume and calibre of sediment deposited on alluvial fans. To gain insight into our field data and study area, we employ an appropriately-scaled catchment-fan model that calculates an eroded volumetric sediment budget to be deposited in a subsiding basin according to mass balance where grain size trends are predicted by a self-similarity fining model. We use the model to compare predicted trends in alluvial fan stratigraphy as a function of boundary condition change for a range of model parameters and input grain size distributions. Subsequently, we perturb our model with a plausible glacial-interglacial magnitude precipitation change to estimate the requisite sediment flux needed to generate observed field grain size trends in Death Valley. Modelled fluxes are then compared with independent measurements of sediment supply over time. Our results constitute one of the first attempts to combine the detailed collection of alluvial fan grain size data in time and space with coupled catchment-fan models, affording us the means to evaluate how well field and model data can be reconciled for simple sediment routing systems.

Fine Sediment Erosion and Transport to the Near Coastal Zone from Watersheds of St. Thomas, USVI

NASA Astrophysics Data System (ADS)

Benoit, G.; Xuan, Z.

2014-12-01

The US Virgin Islands' landscape is characterized by steep slopes and short distances from ridge peaks to fringing reefs. Fine-grained sediments eroded from predominantly thin soils may be transported rapidly by streams (locally called guts) to the sea and cause stress to corals. We have studied erosion and transport processes on St Thomas by three methods: (1) continuous monitoring of suspended matter in one of the island's few perennial streams, Dorothea Gut, (2) measurement of 137Cs inventories in soil cores taken across the landscape, and (3) evaluation of sediment captured in most of the island's coastal ponds, through which a significant portion of runoff must pass. We find that, for areas that have not been recently disturbed, watersheds retain fine sediments surprisingly well. On the other hand, small patches of land, like building lots that have been recently disturbed and poorly managed, can produce disproportionate amounts of fine sediment. These results differ somewhat from nearby St John, USVI, where unpaved roads are the major source of eroded sediments.

Incorporation of Fine-Grained Sediment Erodibility Measurements into Sediment Transport Modeling, Capitol Lake, Washington

USGS Publications Warehouse

Stevens, Andrew W.; Gelfenbaum, Guy; Elias, Edwin; Jones, Craig

2008-01-01

Capitol Lake was created in 1951 with the construction of a concrete dam and control gate that prevented salt-water intrusion into the newly formed lake and regulated flow of the Deschutes River into southern Puget Sound. Physical processes associated with the former tidally dominated estuary were altered, and the dam structure itself likely caused an increase in retention of sediment flowing into the lake from the Deschutes River. Several efforts to manage sediment accumulation in the lake, including dredging and the construction of sediment traps upriver, failed to stop the lake from filling with sediment. The Deschutes Estuary Feasibility Study (DEFS) was carried out to evaluate the possibility of removing the dam and restoring estuarine processes as an alternative ongoing lake management. An important component of DEFS was the creation of a hydrodynamic and sediment transport model of the restored Deschutes Estuary. Results from model simulations indicated that estuarine processes would be restored under each of four restoration alternatives, and that over time, the restored estuary would have morphological features similar to the predam estuary. The model also predicted that after dam-removal, a large portion of the sediment eroded from the lake bottom would be deposited near the Port of Olympia and a marina located in lower Budd Inlet seaward of the present dam. The volume of sediment transported downstream was a critical piece of information that managers needed to estimate the total cost of the proposed restoration project. However, the ability of the model to predict the magnitude of sediment transport in general and, in particular, the volume of sediment deposition in the port and marina was limited by a lack of information on the erodibility of fine-grained sediments in Capitol Lake. Cores at several sites throughout Capitol Lake were collected between October 31 and November 1, 2007. The erodibility of sediments in the cores was later determined in the lab with Sedflume, an apparatus for measuring sediment erosion-parameters. In this report, we present results of the characterization of fine-grained sediment erodibility within Capitol Lake. The erodibility data were incorporated into the previously developed hydrodynamic and sediment transport model. Model simulations using the measured erodibility parameters were conducted to provide more robust estimates of the overall magnitudes and spatial patterns of sediment transport resulting from restoration of the Deschutes Estuary.

Sedimentary environments within a glaciated estuarine-inner shelf system: Boston Harbor and Massachusetts Bay

USGS Publications Warehouse

Knebel, H.J.

1993-01-01

Three modern sedimentary environments have been identified and mapped across the glaciated Boston Harbor estuary and adjacent inner shelf of Massachusetts Bay by means of an extensive set of sidescan sonar records and supplemental bathymetric, sedimentary, subbottom and bottom-current data. 1. (1) Environments of erosion and nondeposition appear on the sonographs either as patterns with isolated reflections (caused by outcrops of bedrock, glacial drift, and coastal plain rocks) or as patterns of strong backscatter (caused by coarse-grained lag deposits). Sediments in these environments range from boulder fields to gravelly sands with megaripples. Inside the harbor, areas of erosion or nondeposition are found primarily near mainland and insular shores and within constricted tidal channels, whereas, on the shelf, they are present over extensive areas of hummocky topography near the coast and atop local bathymetric highs offshore. 2. (2) Environments of sediment reworking are characterized on the sonographs by patterns with patches of strong to weak backscatter caused by a combination of erosional and depositional processes. These environments have diverse grain sizes that range from sandy gravels to muds. Within the harbor, the locations of reworked sediments are uncorrelated with the bottom topography, but, on the shelf, they are found on the lower flanks of bathymetric highs, within broad lows and in relatively deep water (30-50 m). 3. (3) Environments of deposition are depicted on the sonographs as uniform patterns of weak backscatter. These areas contain relatively fine-grained muddy sands and muds. Inside the harbor, depositional environments are found over extensive subtidal flats and within sheltered depressions, whereas, on the shelf, they are restricted to broad lows mainly in deep water. The extreme patchiness of modern sedimentary environments within the Boston Harbor-Massachusetts Bay system reflects the interaction between the irregular bottom topography and both geologic and oceanographic processes. The estuarine part of the system is an effective trap for fine-grained detritus because of its protected nature, low wave climate, and large supply of sediments. The open shelf, however, is largely mantled by winnowed and sorted sediments as a result of erosion during past sea-level fluctuations, sediment resuspension and transport by modern waves and currents, and a spatially variable supply of fine-grained sediments.

Interpreting Hydraulic Conditions from Morphology, Sedimentology, and Grain Size of Sand Bars in the Colorado River in Grand Canyon

NASA Astrophysics Data System (ADS)

Rubin, D. M.; Topping, D. J.; Schmidt, J. C.; Grams, P. E.; Buscombe, D.; East, A. E.; Wright, S. A.

2015-12-01

During three decades of research on sand bars and sediment transport in the Colorado River in Grand Canyon, we have collected unprecedented quantities of data on bar morphology, sedimentary structures, grain size of sand on the riverbed (~40,000 measurements), grain size of sand in flood deposits (dozens of vertical grain-size profiles), and time series of suspended sediment concentration and grain size (more than 3 million measurements using acoustic and laser-diffraction instruments sampling every 15 minutes at several locations). These data, which include measurements of flow and suspended sediment as well as sediment within the deposits, show that grain size within flood deposits generally coarsens or fines proportionally to the grain size of sediment that was in suspension when the beds were deposited. The inverse problem of calculating changing flow conditions from a vertical profile of grain size within a deposit is difficult because at least two processes can cause similar changes. For example, upward coarsening in a deposit can result from either an increase in discharge of the flow (causing coarser sand to be transported to the depositional site), or from winnowing of the upstream supply of sand (causing suspended sand to coarsen because a greater proportion of the bed that is supplying sediment is covered with coarse grains). These two processes can be easy to distinguish where suspended-sediment observations are available: flow-regulated changes cause concentration and grain size of sand in suspension to be positively correlated, whereas changes in supply can cause concentration and grain size of sand in suspension to be negatively correlated. The latter case (supply regulation) is more typical of flood deposits in Grand Canyon.

Cyclicity and reservoir properties of Lower-Middle Miocene sediments of South Kirinsk oil and gas field

NASA Astrophysics Data System (ADS)

Kurdina, Nadezhda

2017-04-01

Exploration and additional exploration of oil and gas fields, connected with lithological traps, include the spreading forecast of sedimentary bodies with reservoir and seal properties. Genetic identification and forecast of geological bodies are possible in case of large-scale studies, based on the study of cyclicity, structural and textural features of rocks, their composition, lithofacies and depositional environments. Porosity and permeability evaluation of different reservoir groups is also an important part. Such studies have been successfully completed for productive terrigenous Dagi sediments (Lower-Middle Miocene) of the north-eastern shelf of Sakhalin. In order to identify distribution of Dagi reservoirs with different properties in section, core material of the one well of South Kirinsk field has been studied (depth interval from 2902,4 to 2810,5 m). Productive Dagi deposits are represented by gray-colored sandstones with subordinate siltstones and claystones (total thickness 90,5 m). Analysis of cyclicity is based on the concepts of Vassoevich (1977), who considered cycles as geological body, which is the physical result of processes that took place during the sedimentation cycle. Well section was divided into I-X units with different composition and set of genetic features due to layered core description and elementary cyclites identification. According to description of thin sections and results of cylindrical samples porosity and permeability studies five groups of reservoirs were determined. There are coarse-grained and fine-coarse-grained sandstones, fine-grained sandstones, fine-grained silty sandstones, sandy siltstones and siltstones. It was found, in Dagi section there is interval of fine-coarse-grained and coarse-grained sandstones with high petrophysical properties: permeability 3000 mD, porosity more than 25%, but rocks with such properties spread locally and their total thickness is 6 meters only. This interval was described in the IV unit. In the IV unit lower cyclites elements consist of conglomerates and upper by above-mentioned sandstones. The appearance of conglomerates indicates a coastal-marine depositional environment. The most widely spread reservoir type of Dagi section is fine-grained sandstones and fine-grained silty sandstones with porosity value 22-24% and permeability 100-500 mD. They present the lower elements of cyclites in I, II, VII and VIII units. These sandstones contain fragments of pelecypods shells and marks of bioturbation. There are long (up to 1 m) vertical burrows, which means shallow basin and a weak hydrodynamics. The most clayey section parts (units V and VI) that are presented by wavy-horizontal interlayering of clayey siltstones and clayey-silty rocks contain reservoirs but of poorer petrophysical properties. Sandy siltstones with 14-23% porosity and permeability value 1-10 mD. In general, units V and VI are characterized by conditions of active hydrodynamic and sandy siltstones appearance - with additional supply of sediments with temporary flows. Presence of different reservoir groups in Dagi section is controlled by sedimentation factors and reflects succession of vertical genetic series. According to the preliminary assessment, rocks accumulated predominantly in coastal-marine and shallow-marine environment. Frequent change of lithotypes in Dagi section in well 5 of South Kirinsk field indicates significant changes of depositional environment whose diagnostic and identification are an integral part of the field exploration works.

Impacts of geochemical and environmental factors on seasonal variation of heavy metals in a coastal lagoon Yucatan, Mexico.

PubMed

Arcega-Cabrera, F; Garza-Pérez, R; Noreña-Barroso, E; Oceguera-Vargas, I

2015-01-01

This study investigated the influence of geochemical and environmental factors on seasonal variation in metals in Yucatan's Chelem lagoon. Anthropogenic activities discharge non-treated wastewater directly into it with detrimental environmental consequences. Accordingly, this study established the spatial and temporal patterns of fine grain sediments and concentrations of heavy metals. Multivariate analyses showed fine grain facies deposition, transition sites dominated by fine grain transport, and fine grain erosion sites. Spatial and temporal variations of heavy metals concentration were significant for Cd, Cu, Cr, and Pb. As, Cd, and Sn were as much as 12 times higher than SQuiRTs standards (Buchman 2008). The results indicate that aquifer water is bringing metals from relatively far inland and releasing them into the lagoon. Thus, it appears that the contamination of this lagoon is highly complex and must take into account systemic connections with inland anthropogenic activates and pollution, as well as local factors.

Temporal fluctuations in grain size, organic materials and iron concentrations in intertidal surface sediment of San Francisco Bay

USGS Publications Warehouse

Thomson-Becker, E. A.; Luoma, S.N.

1985-01-01

The physical and chemical characteristics of the oxidized surface sediment in an estuary fluctuate temporally in response to physical forces and apparently-fluctuating inputs. These characteristics, which include grain size and concentrations of organic materials and iron, will influence both trace-metal geochemistry and bioavailability. Temporal trends in the abundance of fine particles, total organic carbon content (TOC), absorbance of extractable organic material (EOM), and concentration of extractable iron in the sediment of San Francisco Bay were assessed using data sets containing approximately monthly samples for periods of two to seven years. Changes in wind velocity and runoff result in monthly changes in the abundance of fine particles in the intertidal zone. Fine-grained particles are most abundant in the late fall/early winter when runoff is elevated and wind velocities are low; particles are coarser in the summer when runoff is low and wind velocities are consistently high. Throughout the bay, TOC is linearly related to fine particle abundance (r = 0.61). Temporal variability occurs in this relationship, as particles are poor in TOC relative to percent of fine particles in the early rainy season. Iron-poor particles also appear to enter the estuary during high runoff periods; while iron is enriched on particle surfaces in the summer. Concentrations of extractable iron and absorbance of EOM vary strongly from year to year. Highest absorbances of EOM occurred in the first year following the drought in 1976-77, and in 1982 and 1983 when river discharge was unusually high. Extractable-iron concentrations were also highest in 1976-77, but were very low in 1982 and 1983. ?? 1985 Dr W. Junk Publishers.

Quantifying In Situ Metal and Organic Contaminant Mobility in Marine Sediments

DTIC Science & Technology

2009-01-01

and west of Ford Island, within the Pearl Harbor Naval Base. Sediments are fine grain silts and clays of basaltic origins and contain various... fiber filters for organics), and check valves (Figure 8) connected to synchronized parallel rotary valves connected to the collection chamber. Samples

LABORATORY EVALUATION OF METHODS TO SEPARATE FINE GRAINED SEDIMENT FROM STORM WATER

EPA Science Inventory

A literature survey had been conducted by the St. Anthony Falls Hydraulic laboratory to assess various methods for separation of sediment from storm water at construction sites. Two methods have shown some promise in this application, and a research program was initiated with the...

AN EVALUATION OF ELECTRODE INSERTION TECHNIQUES FOR MEASUREMENT OF REDOX POTENTIAL IN ESTUARINE SEDIMENTS

EPA Science Inventory

Eh measurements by electrodes are commonly used to characterize redox status of sediments in freshwater, marine and estuarine studies, due to the relative ease and rapidity of data collection. In our studies of fine-grained estuarine seabeds, we observed that Eh values measured i...

Individual and cumulative effects of agriculture, forestry and metal mining activities on the metal and phosphorus content of fluvial fine-grained sediment; Quesnel River Basin, British Columbia, Canada.

PubMed

Smith, Tyler B; Owens, Philip N

2014-10-15

The impact of agriculture, forestry and metal mining on the quality of fine-grained sediment (<63 μm) was investigated in the Quesnel River Basin (QRB) (~11,500 km(2)) in British Columbia, Canada. Samples of fine-grained sediment were collected monthly during the snow-free season in 2008 using time-integrated samplers at replicate sites representative of agriculture, forestry and mining activities in the basin (i.e. "impacted" sites). Samples were also collected from replicate reference sites and also from the main stem of the Quesnel River at the downstream confluence with the Fraser River. Generally, metal(loid) and phosphorus (P) concentrations for "impacted" sites were greater than for reference sites. Furthermore, concentrations of copper (forestry and mining sites), manganese (agriculture and forestry sites) and selenium (agriculture, forestry and mining sites) exceeded upper sediment quality guideline (SQG) thresholds. These results suggest that agriculture, forestry and metal mining activities are having an influence on the concentrations of sediment-associated metal(loid)s and P in the Quesnel basin. Metal(loid) and P concentrations of sediment collected from the downstream site were not significantly greater than values for the reference sites, and were typically lower than the values for the impacted sites. This suggests that the cumulative effects of agriculture, forestry and mining activities in the QRB are presently not having a measureable effect at the river basin-scale. The lack of a cumulative effect at the basin-scale is thought to reflect: (i) the relatively recent occurrence of land use disturbances in this basin; (ii) the dominance of sediment contributions from natural forest and agriculture; and (iii) the potential for storage of contaminants on floodplains and other storage elements between the locations of disturbance activities and the downstream sampling site, which may be attenuating the disturbance signal. Copyright © 2014 Elsevier B.V. All rights reserved.

The Role of Authigenic Volcanic Ash in Marine Sediment

NASA Astrophysics Data System (ADS)

Scudder, R.; McKinley, C. C.; Thomas, D. J.; Murray, R. W.

2016-12-01

Marine sediments are a fundamental archive of the history of weathering and erosion, biological productivity, volcanic activity, patterns of deep-water formation and circulation, and a multitude of other earth, ocean, and atmosphere processes. In particular, the record and consequences of volcanic eruptions have long fascinated humanity. Volcanic ash layers are often visually stunning, and can have thicknesses of 10s of cm or more. While the ash layer records are of great importance by themselves, we are missing a key piece of information-that of the very fined grained size fractions. Dispersed ash is the very fine grained-component that has either been mixed into the bulk sediment by bioturbation, or is deposited from subaqueous eruptions, erosion of terrestrial deposits, general input during time periods of elevated global volcanism, or other mechanisms, plays an important role in the marine sediment. The presence of dispersed ash in the marine record has previously been relatively over-looked as it is difficult to identify petrographically due to its commonly extremely fine grain size and/or alteration to authigenic clay. The dispersed ash, either altered or unaltered, is extremely difficult to differentiate from detrital/terrigenous/authigenic clay, as they are all "aluminosilicates". Here we apply a combined geochemical, isotopic, and statistical technique that enables us to resolve volcanic from detrital terrigenous inputs at DSDP/ODP/IODP sites from both the Brazil Margin and the Northwest Pacific Oceans. Incorporating the combined geochemical/statistical techniques with radiogenic isotope records allows us to address paleoceanographic questions in addition to studies of the effect of sediment fluxes on carbon cycling, the relationship between volcanic ash and biological productivity of the open ocean and nutrient availability for subseafloor microbial life.

A new model evaluating Holocene sediment dynamics: Insights from a mixed carbonate-siliciclastic lagoon (Bora Bora, Society Islands, French Polynesia, South Pacific)

NASA Astrophysics Data System (ADS)

Isaack, Anja; Gischler, Eberhard; Hudson, J. Harold; Anselmetti, Flavio S.; Lohner, Andreas; Vogel, Hendrik; Garbode, Eva; Camoin, Gilbert F.

2016-08-01

Mixed carbonate-siliciclastic lagoons of barrier reefs provide great potential as sedimentary archives focusing on paleoenvironmental and paleoclimatic changes as well as on event deposition. Sediment sources include lagoonal carbonate production, the marginal reef and the volcanic hinterland. Mixed carbonate-siliciclastic continent-attached coastal lagoons have been intensively studied, however, their isolated oceanic counterparts have been widely disregarded. Here, we present a new model of Holocene sediment dynamics in the barrier-reef lagoon of Bora Bora based on sedimentological, paleontological, geochronological and geochemical data. The lagoonal succession started with a Pleistocene soil representing the Lowstand Systems Tract. As the rising Holocene sea inundated the carbonate platform, peat accumulated locally 10,650-9400 years BP. Mixed carbonate-siliciclastic sedimentation started ca. 8700-5500 years BP and represents the Transgressive Systems Tract. During that time, sediments were characterized by relatively coarse grain size and contained high amounts of terrestrial material from the volcanic hinterland as well as carbonate sediments mainly produced within the lagoon. Siliciclastic content decreases throughout the Holocene. After the rising sea had reached its modern level, sand aprons formed between reef crest and lagoon creating transport pathways for reef-derived material leading to carbonate-dominated sedimentation ca. 6000-3000 years BP during the Highstand Systems Tract. However, mainly fine material was transported and accumulated in the lagoon while coarser grains were retained on the prograding sand apron. From ca. 4500-500 years BP, significant variations in grain-size, total organic carbon as indicator for primary productivity, Ca and Cl element intensities as qualitative indicators for carbonate availability and lagoonal salinity are seen. Such patterns could indicate event (re-)deposition and correlate with contemporaneous event deposits found in the lagoon of nearby Tahaa, which are supposed to be induced by elevated cyclone activity. Correspondingly, enhanced erosion and run-off from the volcanic hinterland as well as lower lagoonal salinity would be associated with intense rainfall during repeated cyclone landfall. Increased amounts of coarse-grained sediment from marginal reef areas would be transported into the lagoon. However, Ti/Ca and Fe/Ca ratios as proxies for terrigenous sediment delivery have incessantly declined since the mid-Holocene. Also, benthic foraminiferal faunas do not validate reef-to-lagoon transport of sediment. Alternatively, the apparent onset of higher hydrodynamic energy conditions can be explained by more permanent southeast trade winds and higher-than-present sea level, which are supposed for the mid-late Holocene in the south Pacific. Sustained winds would have flushed higher amounts of open ocean water into the lagoon enhancing primary productivity and the amount of pelagic organisms within the lagoon while lowering lagoonal salinity. We propose the shift towards coarser-grained sedimentation patterns during the mid-late Holocene to reflect sediment-load shedding of sand aprons due to oversteepening of slopes at sand apron/lagoon edges during times of stronger trades and higher-than-present sea level of the Highstand Systems Tract, which led to redeposition of sediment even within the lagoon center. Modern conditions including a sea-level fall to modern level were reached ca. 1000 years BP, and lagoonal infill has been determined to a large part by fine-grained carbonate-dominated sediments produced within the lagoon and derived from the marignal reef. Infill of lagoonal accommodation space via sand aprons is estimated to be up to six times higher than infill by lagoonal background sedimentation and emphasizes the importance of the progradation of sand aprons. Contrary to the commonly supposed assumption that coarse-grained sediment layers within fine-grained lagoonal successions represent overwash events induced by storms or periods of higher storm activity, we postulate a new model of long-term lagoonal sediment dynamics including sea level, climatic change and geomorphological variation of the barrier reef lagoon.

Importance of geology to fisheries management: Examples from the northeastern Gulf of Mexico

USGS Publications Warehouse

Scanlon, Kathryn M.; Koenig, C.C.; Coleman, F.C.; Miller, M.

2003-01-01

Seafloor mapping of shelf-edge habitats in the northeastern Gulf of Mexico demonstrates how sidescan-sonar imagery, seismic-reflection profiling, video data, geologic mapping, sediment sampling, and understanding the regional geologic history can enhance, support, and guide traditional fisheries research and management. New data from the Madison Swanson and Steamboat Lumps Marine Reserves reveal complex benthic habitats consisting of high-relief calcareous pinnacles, low-relief karstic hardbottom, rocky outcrops several kilometers in length, and variable thickness of fine-grained and apparently mobile coarse-grained sediments. Our data also show that certain fish alter the landscape by clearing sediment from hardbottom areas (e.g., red grouper Epinephelus morio) and by burrowing extensively in fine-grained sediment (e.g., tilefish Lopholatilus chamaeleonticeps). The seafloor imagery and geologic maps show that (a) sea level fluctuations played a dominant role in the development of the present-day regional geology, and (b) habitats (and benthic communities) are tied closely to geologic character. Understanding the geologic setting allowed for efficient and representative sampling of the biology. The geologic data can be used to set meaningful boundaries for fishery reserves and to help predict habitats in areas that are not well mapped. This interdisciplinary work added value to traditional research disciplines by providing management with integrated tools to make better decisions. 

Braided fluvial sedimentation in the lower paleozoic cape basin, South Africa

NASA Astrophysics Data System (ADS)

Vos, Richard G.; Tankard, Anthony J.

1981-07-01

Lower Paleozoic braided stream deposits from the Piekenier Formation in the Cape Province, South Africa, provide information on lateral and vertical facies variability in an alluvial plain complex influenced by a moderate to high runoff. Four braided stream facies are recognized on the basis of distinct lithologies and assemblages of sedimentary structures. A lower facies, dominated by upward-fining conglomerate to sandstone and mudstone channel fill sequences, is interpreted as a middle to lower alluvial plain deposit with significant suspended load sedimentation in areas of moderate to low gradients. These deposits are succeeded by longitudinal conglomerate bars which are attributed to middle to upper alluvial plain sedimentation with steeper gradients. This facies is in turn overlain by braid bar complexes of large-scale transverse to linguoid dunes consisting of coarse-grained pebbly sandstones with conglomerate lenses. These bar complexes are compared with environments of the Recent Platte River. They represent a middle to lower alluvial plain facies with moderate gradients and no significant suspended load sedimentation or vegetation to stabilize channels. These bar complexes interfinger basinward with plane bedded medium to coarse-grained sandstones interpreted as sheet flood deposits over the distal portions of an alluvial plain with low gradients and lacking fine-grained detritus or vegetation.

Geochemistry and magnetic sediment distribution at the western boundary upwelling system of southwest Atlantic

NASA Astrophysics Data System (ADS)

Cruz, Anna P. S.; Barbosa, Catia F.; Ayres-Neto, Arthur; Munayco, Pablo; Scorzelli, Rosa B.; Amorim, Nívea Santos; Albuquerque, Ana L. S.; Seoane, José C. S.

2018-02-01

In order to investigate the chemical and magnetic characteristics of sediments of the western boundary upwelling system of Southwest Atlantic we analyzed magnetic susceptibility, grain size distribution, total organic carbon, heavy mineral abundance, Fe associated with Mössbauer spectra, and Fe and Mn of pore water to evaluate the deposition patterns of sediments. Four box-cores were collected along a cross-shelf transect. Brazil Current and coastal plume exert a primary control at the inner and outer shelf cores, which exhibited similar depositional patterns characterized by a high abundance of heavy minerals (mean 0.21% and 0.08%, respectively) and very fine sand, whereas middle shelf cores presented low abundances of heavy minerals (mean 0.03%) and medium silt. The inner shelf was dominated by sub-angular grains, while in middle and outer shelf cores well-rounded grains were found. The increasing Fe3+:Fe2+ ratio from the inner to the outer shelf reflects farther distance to the sediment source. The outer shelf presented well-rounded minerals, indicating abrasive processes as a result of transport by the Brazil Current from the source areas. In the middle shelf, cold-water intrusion of the South Atlantic Central Water contributes to the primary productivity, resulting in higher deposition of fine sediment and organic carbon accumulation. The high input of organic carbon and the decreased grain size are indicative of changes in the hydrodynamics and primary productivity fueled by the western boundary upwelling system, which promotes loss of magnetization due to the induction of diagenesis of iron oxide minerals.

The distribution of sediments grain size along the depth in source of the Yangtze River, Tibetan Plateau, China

NASA Astrophysics Data System (ADS)

Zhou, Y.; Yao, S.; Zhou, S.; Liu, X.; Yan, X.; Lu, J.

2017-12-01

Sediment was the one result of river process, in alluvial rive, it can reflect the hydrodynamic characteristic, even the hydrology and climate. In the source region of the Yangtze River with few human activities, The Qumalai Reach of the Tongtianhe River was selected to research the distribution of sediments grain size along the depth. The vertical drilling tools were used to obtain 7 boreholes along the river cross section, and the sedimentary cores were made analysis of stratification and granularity. The results show: The sediments are dominated by sand and grail, the sediment transport capacity of river sources is strong; the grain size frequency distribution curve with 2 3 kurtosis, main peak is sharp, it is typical deposit sediment of the suspended load; The grain size coarsen from the stream terrace to the main channel, sediment transport capacity of main stream is bigger; There are several coarse and fine sediments layers in the sedimentary core of the terrace and flood plain, medium diameters of each layer are various from 0.4mm to 80mm, different layer with different grain size can reflect the different hydrodynamic characteristic of each historical period. This result can provide the original data and enlightenment to support the research for historical river process and hydrology so much as the climate change.

Fine-grained sediment storage conditioned by Large Woody Debris in a gravel-bed river

NASA Astrophysics Data System (ADS)

Skalak, K. J.; Narinesingh, P.; Pizzuto, J. E.

2006-05-01

The purposes of this study are 1) to determine the quantity of mud and sand stored in the channel margins and near-bank regions of South River, a steep gravel-bedded stream in western Virginia, and 2) to understand the geomorphic and hydrologic processes that control the erosion and deposition of these fine-grained deposits. The volume of storage in these deposits is equivalent to about 5-10 percent of the river's annual suspended sediment load. Sediment storage in the near-bank regions is a result of reduced velocity caused by the bank obstructions. Storage occurs in four different geomorphic settings: 1) long pooled sections caused by bedrock or old mill dams, 2) regions downstream of riffles in channel margins with LWD accumulations, 3) bank obstructions usually caused by trees, 4) side channel backwaters where flow separates around islands. Most storage occurs in regions downstream of riffles (approximately 44 percent of the total). Long pooled sections account for roughly 37 percent of the total storage, bank obstructions account for 13 percent, and backwaters account for roughly 6 percent. In approximately 17 km of river, there are 38 separate fine-grained deposits (total volume more than 1600 m3). On average, these deposits are about 35 cm deep, 20 m long, and 4 m wide. They average 30 percent mud, 68 percent sand, and 2 percent gravel. These deposits have been cored and analyzed for Hg, grain size, loss-on-ignition, and bomb radiocarbon. High Hg concentrations in fish tissue are an ongoing problem along South River, further motivating detailed study of these deposits.

Pacing of deep marine sedimentation in the middle Eocene synorogenic Ainsa Basin, Spanish Pyrenees: deconvolving a 6myr record of tectonic and climate controls

NASA Astrophysics Data System (ADS)

Mac Niocaill, C.; Cantalejo, B.; Pickering, K. T.; Grant, M.; Johansen, K.

2016-12-01

The Middle Eocene thrust-top Ainsa Basin of Northern Spain preserves world-class exposures of deep-marine submarine fan and related deposits. Detailed paleomagnetic, micropaleontologic, and time-series analysis enable us to deconvolve, for the first time in any ancient deep-marine basin worldwide, both the pacing on deposition of the fine-grained interfan sediments and the main sandbodies (submarine fans) through the history of the deep-marine basin. Our magnetostratigraphy and faunal constraints provide a chronological framework for sedimentation in the basin. We use time-series analysis of a range of geochemical and sedimentologic data to identify likely climatic signals in the sedimentary archive. This has enabled us to test the likely importance of climate versus tectonics in controlling deposition. We show that the fine-grained interfan sedimentation preserves a dominant Milankovitch-like cyclicity, whereas the sandbodies (fans) reflect a complex interplay of controls such as tectonics and climate in the sediment source area, including shallow-marine staging areas for sediment redeposition into deeper water. These results not only provide critical information about the timing of substantial coarse clastic delivery into the Ainsa Basin but also give constraints on sediment flux over a 6 Myr window.

Quantifying sediment dynamics on alluvial fans, Iglesia basin, south Central Argentine Andes

NASA Astrophysics Data System (ADS)

Harries, Rebekah; Kirstein, Linda; Whittaker, Alex; Attal, Mikael; Peralta, Silvio

2017-04-01

Qualitative interpretations of environmental change drawn from alluvial fan stratigraphy typically tie the deposition of greater volumes of coarser sediment to wetter climatic periods. For example, step changes in sediment flux and discharge associated with glacial-interglacial cycles are often linked to the progradation and back stepping of a fan's toe (Harvey et al, 2002). Indeed, more recent quantitative stratigraphic models demonstrate changes in the volume and calibre of sediment fluxed from an uplifted catchment can produce predictable shifts in the rate at which fluvial deposits fine downstream (Duller et al. 2010, Armitage et al. 2011). These interpretations, however, make three important assumptions: 1) the volume and calibre of the sediment transferred from an eroding mountain belt to a depositional basin is directly related to climate through some value of time-averaged discharge or catchment wetness; 2) lateral sources of sediment, such as tributaries, do not significantly influence the pattern of deposition in a basin and, similarly, 3) the reworking of older fan surfaces is minimal and does not impact the depositional pattern of younger deposits. Here we demonstrate each of these assumptions underestimates the importance of variance in transportable grain sizes in influencing the local and basin-wide deposited grain size trends. Using the Iglesia basin in the Argentine south Central Andes as a natural laboratory, we compare three large, adjacent, alluvial fan systems whose catchments experience the same background tectonic and climatic forcing. We find regional climate forcing is not expressed uniformly in the downstream grain size fining rates of their modern systems. Furthermore, we observe the variance in transportable grain sizes supplied from each primary catchment and the variance of material introduced by tributaries and fan surfaces downstream can act as first order controls on the rate of downstream fining. We also raise the importance of considering factors such as climate storminess and degree of glacial cover in having a dominant control on the variance of sediment released. These findings have significant implications for our ability to invert the fluvial stratigraphy for climatically driven changes in discharge and highlight a need to quantify the impact of sediment dynamics on modern systems so that we may better understand the limitations in applying quantitative models to ancient stratigraphy.

A three-dimensional stratigraphic model for aggrading submarine channels based on laboratory experiments, numerical modeling, and sediment cores

NASA Astrophysics Data System (ADS)

Limaye, A. B.; Komatsu, Y.; Suzuki, K.; Paola, C.

2017-12-01

Turbidity currents deliver clastic sediment from continental margins to the deep ocean, and are the main driver of landscape and stratigraphic evolution in many low-relief, submarine environments. The sedimentary architecture of turbidites—including the spatial organization of coarse and fine sediments—is closely related to the aggradation, scour, and lateral shifting of channels. Seismic stratigraphy indicates that submarine, meandering channels often aggrade rapidly relative to lateral shifting, and develop channel sand bodies with high vertical connectivity. In comparison, the stratigraphic architecture developed by submarine, braided is relatively uncertain. We present a new stratigraphic model for submarine braided channels that integrates predictions from laboratory experiments and flow modeling with constraints from sediment cores. In the laboratory experiments, a saline density current developed subaqueous channels in plastic sediment. The channels aggraded to form a deposit with a vertical scale of approximately five channel depths. We collected topography data during aggradation to (1) establish relative stratigraphic age, and (2) estimate the sorting patterns of a hypothetical grain size distribution. We applied a numerical flow model to each topographic surface and used modeled flow depth as a proxy for relative grain size. We then conditioned the resulting stratigraphic model to observed grain size distributions using sediment core data from the Nankai Trough, offshore Japan. Using this stratigraphic model, we establish new, quantitative predictions for the two- and three-dimensional connectivity of coarse sediment as a function of fine-sediment fraction. Using this case study as an example, we will highlight outstanding challenges in relating the evolution of low-relief landscapes to the stratigraphic record.

Application of ground-penetrating-radar methods in hydrogeologic studies

USGS Publications Warehouse

Beres, Milan; Haeni, F.P.

1991-01-01

A ground-penetrating-radar system was used to study selected stratified-drift deposits in Connecticut. Ground-penetrating radar is a surface-geophysical method that depends on the emission, transmission, reflection, and reception of an electromagnetic pulse and can produce continuous high-resolution profiles of the subsurface rapidly and efficiently. Traverse locations on land included a well field in the town of Mansfield, a sand and gravel pit and a farm overlying a potential aquifer in the town of Coventry, and Haddam Meadows State Park in the town of Haddam. Traverse locations on water included the Willimantic River in Coventry and Mansfield Hollow Lake in Mansfield. The penetration depth of the radar signal ranged from about 20 feet in fine-grained glaciolacustrine sediments to about 70 feet in coarse sand and gravel. Some land records in coarse-grained sediments show a distinct, continuous reflection from the water table about 5 to 11 feet below land surface. Parallel reflectors on the records are interpreted as fine-grained sediments. Hummocky or chaotic reflectors are interpreted as cross-bedded or coarse-grained sediments. Other features observed on some of the radar records include the till and bedrock surface. Records collected on water had distinct water-bottom multiples (more than one reflection) and diffraction patterns from boulders. The interpretation of the radar records, which required little or no processing, was verified by using lithologic logs from test holes located along some of the land traverses and near the water traverses.

SEDIMENT MICROBIAL RESPIRATION IN A SYNOPTIC SURVEY OF MID-ATLANTIC REGION STREAMS

EPA Science Inventory

l. The rate of microbial respiration on fine-grained stream sediments was measured at 196 first-to third-order sites in the mid-Atlantic region of the United States.2. Sample collection took place between April and July in 1993, 1994 and 1995.3. Study streams were randomly sele...

Fate and effects of picric acid and 2,6-DNT in marine environments: toxicity of degradation products.

PubMed

Nipper, Marion; Carr, R Scott; Biedenbach, James M; Hooten, Russell L; Miller, Karen

2005-11-01

The toxicity of transformation products of 2,6-dinitrotoluene (2,6-DNT) and 2,4,6-trinitrophenol (picric acid) were assessed in spiked sandy and fine-grained marine sediments and in seawater. Toxicity of pore water from sediments spiked with 2,6-DNT decreased for the macro-alga, Ulva fasciata, zoospores as biotransformation proceeded, but increased for the copepod, Schizopera knabeni, nauplii. The primary biotransformation product of 2,6-DNT, 2-amino-6-nitrotoluene, was also more toxic than the parent compound to copepod nauplii, but not to alga zoospores, in spiked seawater tests. Two biotransformation products of picric acid, picramic acid and 2,4-DNP, were more toxic than their parent compound. Porewater toxicity from picric acid-spiked sediments decreased significantly at the end of six-months incubation. Fine-grained sediment spiked with either ordnance compound had lower toxicity than its sandy counterpart after six months, suggesting faster microbial transformation in the former and production of less toxic products. Photo-transformation of 2,6-DNT in seawater resulted in a reduction in toxicity.

Recent Innovations in Monitoring Suspended-Sediment Mass Balance of the Colorado River Ecosystem Below Glen Canyon Dam: A laser-Based Approach

NASA Astrophysics Data System (ADS)

Melis, T. S.; Topping, D. J.; Rubin, D. M.; Agrawal, Y. C.

2002-12-01

Intensive monitoring of suspended-sediment in the Colorado River ecosystem below Glen Canyon Dam is a priority for environmental management. Historically, the program has been logistically complicated, costly and limited in spatial and temporal resolution. These elements have contributed to relatively large uncertainties in mass-balance estimates of sediment export. To improve mass-balance estimates, the Grand Canyon Monitoring and Research Center is field testing new and existing technologies to develop a continuous suspended-sediment transport protocol. A recent innovation includes use of optical forward-scattering instruments, LISST, in combination with programmable pumping samplers. The LISST-100 (Laser In-Situ Scattering and Transmissometry) is both a particle-size analyzer (size range 2.5 to 500 microns) and a transmissometer capable of measuring variable concentrations, depending on particle size. A second innovation, the LISST-25X, is a recently developed variation of the instrumentation that allows sand to be measured separately from finer particles. This is achieved by use of shaped focal plane detectors that compute 2 distinct weighted sums of angular scattering by suspended particles. The LISST-25X currently collects volume-concentration and grain size (Sauter-mean-diameter) data for suspended particles at four sites below the dam. Unit values are derived by averaging 1000 individual measurements every 15-minutes (sampling about 1.1 liters of water per hour). The volume-to-mass conversion is made once average particle density has been gravimetrically determined through conventional methods. During high-concentration conditions, laser-transmission values (T) can fall outside of the user-defined minimal threshold (20

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gustavson, T.C.; Holliday, V.T.

Eolian sediments have accumulated as non-glacigenic loess and thin sand sheets on the Central and Southern High Plains grasslands of Texas and new mexico since the late Miocene. Locally as much as 110 m of eolian sediments with numerous paleosols are preserved in the Quaternary Blackwater Draw formation and the upper part of the Miocene-Pleiocene Ogallala formation. These sediments and paleosols, which cover more than 130,000 km{sup 2}, are similar to recent surface sediments and soils and record a long period of episodic eolian transport and sedimentation, and pedogenesis on a stable low-relief grass-covered landscape. Eolian sections, which comprise themore » fine sand to coarse silt lithofacies of the Ogallala formation, and the very fine to fine sand and sandy mud lithofacies of the Blackwater Draw formation, generally lack primary sedimentary structures. Grain size of Ogallala sediments decreases from west to east and grain size of Blackwater Draw sediments decreases from southwest to northeast. Soil horizonation is well developed in most sections, and buried calcic and argillic horizons are common. Calcic horizons are characterized by sharply increased CaCO{sub 3} content in the form of filaments, nodules, and petrocalcic horizons (calcretes). Argillic horizons are characterized by increased illuvial clay, pedogenic structure, and darker reddish hues. Rhizocretions are common locally. Open root tubules, which are typically less than 1 mm in diameter and characteristic of small plants like grasses, are present in all Ogallala and Blackwater Draw eolian sediments. Paleosols preserved in eolian sediments of the High Plains reflect periods of sedimentation followed by episodes of landscape stability and pedogenesis, and negligible sedimentation. Episodes of sedimentation and soil development likely resulted from cyclic decreases and increases in available moisture and vegetative cover. Eolian sediments were eroded and transported eastward during dry periods when vegetation was sparse in source areas, such as the western High Plains and the Pecos Valley. During humid periods more abundant vegetation probably protected source areas from deflation, and resulted in landscape stability across the High Plains.« less

Toxicological and chemical assessment of ordnance compounds in marine sediments and porewaters

USGS Publications Warehouse

Nipper, M.; Carr, R.S.; Biedenbach, J.M.; Hooten, R.L.; Miller, K.

2002-01-01

Toxicological and chemical studies were performed with a silty and a sandy marine sediment spiked with 2,6-dinitrotoluene (2,6-DNT), 2,4,6-trinitrophenylmethylnitramine (tetryl), or 2,4,6-trinitrophenol (picric acid). Whole sediment toxicity was analyzed by the 10-day survival test with the amphipod Ampelisca abdita, and porewater toxicity tests assessed macro-algae (Ulva fasciata) zoospore germination and germling growth, sea urchin (Arbacia punctulata) embryological development, and polychaete (Dinophilus gyrociliatus) survival and reproduction. Whole sediments spiked with 2,6-DNT were not toxic to amphipods. The fine-grained sediment spiked with tetryl was also not acutely toxic. The tetryl and picric acid LC50 values in the sandy sediment were 3.24 and 144 mg/kg dry weight, respectively. The fine-grained sediment spiked with picric acid generated a U-shaped concentration-response curve in the amphipod test, with increased survival both in the lowest and highest concentration. Grain-size distribution and organic carbon content strongly influenced the behavior of ordnance compounds in spiked sediments. Very low concentrations were measured in some of the treatments and irreversible binding and biodegradation are suggested as the processes responsible for the low measurements. Porewater toxicity varied with its sedimentary origin and with ordnance compound. The sea urchin embryological development test tended to be the least sensitive. Tetryl was the most toxic chemical in all porewater tests, and picric acid the least toxic. Samples spiked with 2,6-DNT contained a degradation product identified as 2-methyl-3-nitroaniline (also known as 2-amino-6-nitrotoluene), and unidentified peaks, possibly degradation products, were also seen in some of the picric acid- and tetryl-spiked samples. Degradation products may have played a role in observed toxicity. ?? 2002 Elsevier Science Ltd. All rights reserved.

Coevolution of bed surface patchiness and channel morphology: 1. Mechanisms of forced patch formation

USGS Publications Warehouse

Nelson, Peter A.; McDonald, Richard R.; Nelson, Jonathan M.; Dietrich, William E.

2015-01-01

Riverbeds frequently display a spatial structure where the sediment mixture composing the channel bed has been sorted into discrete patches of similar grain size. Even though patches are a fundamental feature in gravel bed rivers, we have little understanding of how patches form, evolve, and interact. Here we present a two-dimensional morphodynamic model that is used to examine in greater detail the mechanisms responsible for the development of forced bed surface patches and the coevolution of bed morphology and bed surface patchiness. The model computes the depth-averaged channel hydrodynamics, mixed-grain-size sediment transport, and bed evolution by coupling the river morphodynamic model Flow and Sediment Transport with Morphological Evolution of Channels (FaSTMECH) with a transport relation for gravel mixtures and the mixed-grain-size Exner equation using the active layer assumption. To test the model, we use it to simulate a flume experiment in which the bed developed a sequence of alternate bars and temporally and spatially persistent forced patches with a general pattern of coarse bar tops and fine pools. Cross-stream sediment flux causes sediment to be exported off of bars and imported into pools at a rate that balances downstream gradients in the streamwise sediment transport rate, allowing quasi-steady bar-pool topography to persist. The relative importance of lateral gravitational forces on the cross-stream component of sediment transport is a primary control on the amplitude of the bars. Because boundary shear stress declines as flow shoals over the bars, the lateral sediment transport is increasingly size selective and leads to the development of coarse bar tops and fine pools.

Fine-grained sediment spatial distribution on the basis of a geostatistical analysis: Example of the eastern Bay of the Seine (France)

NASA Astrophysics Data System (ADS)

Méar, Y.; Poizot, E.; Murat, A.; Lesueur, P.; Thomas, M.

2006-12-01

The eastern Bay of the Seine (English Channel) was the subject in 1991 of a sampling survey of superficial sediments. Geostatistic tools were used to examine the complexity of the spatial distribution of the fine-grained fraction (<50 μm). A central depocentre of fine sediments (i.e. content up to 50%) oriented in a NW-SE direction in a muddy coastal strip, in a very high energy hydrodynamical situation due to storm swells and its megatidal setting, is for the first time recognised and discussed. Within this sedimentary unit, the distribution of the fine fraction is very heterogeneous, with mud patches of less than 4000 m diameter; the boundary between these mud patches and their substratum is very sharp. The distribution of this fine fraction appears to be controlled by an anticyclonic eddy located off the Pays de Caux. Under the influence of this, the suspended material expelled from the Seine estuary moves along the coast and swings off Antifer harbour, towards the NW. It is trapped within this eddy because of the settling of suspended particulate matter. Both at a general scale and a local scale the morphology (whether inherited or due to modern processes) has a strong influence on the spatial distribution of the fine fraction. At the general scale, the basin-like shape of the area facilitates the silting, and the presence of the submarine dunes, called "Ridins d'Antifer", clearly determines the northern limit of the muddy zone. At a local scale, the same influence is obvious: paleovalleys trap the fine sediments, whereas isolated sand dunes and ripples limit the silting. This duality of role of the morphology is therefore one of the reasons why the muddy surface is extremely heterogeneous spatially. The presence of an important population of suspension feeding echinoderm, the brittle-star Ophiothrix fragilis Abildgaard, has led to a local increase in the silting, and to the modification of the physicochemical and sedimentological parameters. A complex relationship is shown to occur between the amount of fine fraction and the number of brittle-stars (ind. m -2). Classical statistical methods are not appropriate to study the spatial distribution of the mud fraction, because the spatial component of the percentage of the distribution is not integrated in the analysis. On the other hand, this is the main property of the geostatistic concepts. The use of geostatistic tools within a strict and clearly identified procedure enables the proposal of an accurate cartography. Further application of the proposed protocol (based on a semivariographic study and a conditional simulation interpolation) for surficial sediments mapping will help explain spatial and temporal variations of fine-grained fraction. Then assessments of sedimentation and erosion stages allow highlighting signature of environmental processes.

Generation and fate of glacial sediments in the central Transantarctic Mountains based on radiogenic isotopes and implications for reconstructing past ice dynamics

NASA Astrophysics Data System (ADS)

Farmer, G. Lang; Licht, Kathy J.

2016-10-01

The Nd, Sr and Pb isotopic compositions of glacial tills from the Byrd and Nimrod Glaciers in the central Transantarctic Mountains (TAM) in East Antarctica were obtained to assess the sources of detritus transported by these ice masses. Tills from lateral moraines along the entire extent of both glaciers have isotopic compositions consistent with their derivation predominately from erosion of adjacent bedrock. Fine- (<63μ) and coarser-grained (0.5 mm-2 mm) sediment from these tills have identical isotopic characteristics, indicating that fine-grained detritus is the product of further comminution of coarser sediments. Comparison of present-day till isotopic data to existing data from fine-grained LGM tills in the central Ross Sea confirm that these were deposited from East Antarctic ice that expanded through the TAM and indicates that the LGM sediments are mixtures of detritus eroded along the entire path of ice transiting the TAM. If specific lithologies were preferentially eroded as ice passed through the TAM, it is not clearly evident in the Ross Sea till isotopic compositions. Our data do demonstrate, however, that glacial tills generated from erosion of inboard regions of the mountain belt yield sediment with a larger component of 560 Ma to 600 Ma detrital zircons and lower average εNd(0) values (<-5) than that produced further downstream. As a result, past retreat of ice grounding-lines up the narrow valleys of the TAM resulting in active erosion of inboard region should recognizable in glacial sediments deposited in the Ross Sea and so provide a means to identify times when the East Antarctic ice sheet was smaller than today. This study highlights both the value and necessity of utilizing multiple provenance methods in evaluating glacial erosion and transport when reconstructing past ice sheet dynamics.

Impact evaluation of the industrial activities in the Bay of Bakar (Adriatic Sea, Croatia): recent benthic foraminifera and heavy metals.

PubMed

Popadić, Adriana; Vidović, Jelena; Cosović, Vlasta; Medaković, Davorin; Dolenec, Matej; Felja, Igor

2013-11-15

The Bay of Bakar is one of the most heavily polluted bays at the Eastern Adriatic. Three major industrial companies potentially endanger the bay. The concentration of major, minor and trace elements in surface sediments from thirteen stations was discussed in relation to the sediment type and foraminiferal assemblages. The distribution of major elements in the bay is influenced by geological nature of surroundings. Heavy metal distribution depends on pollution sources and on amount of mud fraction: fine-grained sediments are enriched by them in comparison with coarse-grained ones. Different sediment quality criteria complicate the pollution assessment in the bay. Heavy metal concentrations generally fall into allowed depositional values for marine environments; only area in front of the coke plant and the City of Bakar harbor is heavily polluted. Stress-tolerant foraminiferal species dominate at stations with higher concentrations of heavy metals and coarse-grained sediments consist of larger number of epifaunal taxa. Copyright © 2013 Elsevier Ltd. All rights reserved.

Transport of suspended and bedload sediment at eight stations in the Coeur d'Alene River basin, Idaho

USGS Publications Warehouse

Clark, Greg M.; Woods, Paul F.

2000-01-01

At most of the stations, and at the stream discharges sampled, the bedload was primarily composed of material greater than 2 millimeters in diameter, the break between sand and gravel. A predominance of sand-sized bedload was noted at only a few stations, and generally only during low stream discharge. The particle-size distribution of bedload sediment at most stations became proportionately coarser as stream discharge increased. During the peak of snowmelt runoff for water years 1999 and 2000, gravel-sized material between 2 and 64 millimeters in diameter comprised more than 70 percent of the bedload transport at most stations. However, at the station on the Coeur d’Alene River at Rose Lake, the bedload was predominantly composed of fine-grained material of less than 1 millimeter in diameter for all measured stream discharges. The slow water velocities at Rose Lake accounted for the predominance of fine-grained sediment transport.

Concentrations and Distribution of Slag-Related Trace Elements and Mercury in Fine-Grained Beach and Bed Sediments of Lake Roosevelt, Washington, April-May 2001

USGS Publications Warehouse

Majewski, Michael S.; Kahle, Sue C.; Ebbert, James C.; Josberger, Edward G.

2003-01-01

A series of studies have documented elevated concentrations of trace elements such as arsenic, cadmium, copper, lead, mercury, and zinc in the water, bed sediment, or fish of Lake Roosevelt and the upstream reach of the Columbia River. Elevated concentrations of some trace elements in this region are largely attributable to the transport of slag and metallurgical waste discharged into the Columbia River from a smelter in Canada. Although most recent studies have focused on contamination levels in water, bed sediment, and fish, there is growing concern in the region over the potential threat of airborne contaminants to human health. In response to these concerns, the U.S. Geological Survey conducted an assessment of trace-element concentrations in the relatively shallow fine-grained sediment along the shore of Lake Roosevelt that is exposed annually during periods of reservoir drawdown. During each winter and spring, the water level of Lake Roosevelt is lowered as much as about 80 feet to provide space to capture high river flows from spring runoff, exposing vast expanses of lake-bottom sediment for a period of several months. Upon drying, these exposed areas provide an extremely large source for wind-blown dust. This study concluded that trace elements associated with slag and metallurgical waste are present in the fine-grained fraction (less than 63 micrometers) of bed sediments along the length of Lake Roosevelt, and as such, could be components of the airborne dust resulting from exposure, drying, and wind mobilization of the sediments exposed during the annual drawdowns of the reservoir. Trace-element concentrations in the surficial bed sediment varied, but the major components in slag?arsenic, cadmium, copper, lead, and zinc?showed generally pronounced gradients of decreasing concentrations from near the International Border to the Grand Coulee Dam. The results of this study provide base-line information needed to plan and conduct air monitoring of trace elements in wind-blown dust along Lake Roosevelt.

Analyses and descriptions of geochemical samples from the Rich Mountain Roadless Area, Fannin and Gilmer counties, Georgia

USGS Publications Warehouse

Sears, C.M.; Foose, M.P.; Day, G.W.; Ericksen, M.S.

1983-01-01

Semi-quantitative spectrographic analyses for 31 elements on rock, soil, fine-grained stream sediment, bulk stream sediment, and panned stream sediment samples collected in the Rich Mountain Roadless Area, Fannin and Gilmer Counties, Georgia, are reported here. Atomic absorption analyses for gold and fluorometric analyses for uranium are also reported. Brief descriptions of all rock samples analyzed are included.

Distribution and grain-size partitioning of metals in bovfom sediments of an experimentally acidified Wisconsin lake

USGS Publications Warehouse

Elder, John F.

2007-01-01

A study of concentrations and distribution of major and trace elements in surficial bottom sediments of Little Rock Lake in northern Wisconsin included examination of spatial variation and grain-size effects. No significant differences with respect to metal distribution in sediments were observed between the two basins of the lake, despite the experimental acidification of one of the basins from pH 6.1 to 4.6. The concentrations of most elements in the lake sediments were generally similar to soil concentrations in the area and were well below sediment quality criteria. Two exceptions were lead and zinc, whose concentrations in July 1990 exceeded the criteria of 50 μg/g and 100 μg/g, respectively, in both littoral and pelagic sediments. Concentrations of some elements, particularly Cu, Pb, and Zn, increased along transects from nearshore to midlake, following a similar gradient of sedimentary organic carbon. In contrast, Mn, Fe, and alkali/alkaline-earth elements were at maximum concentrations in nearshore sediments. These elements are less likely to partition to organic particles, and their distribution is more dependent on mineralogical composition, grain size, and other factors. Element concentrations varied among different sediment grain-size fractions, although a simple inverse relation to grain size was not observed. Fe, Mn, Pb, and Zn were more concentrated in a grain-size range 20–60 tm than in either the very fine or the coarse fractions, possibly because of the aggregation of smaller particles cemented together by organic and Fe/Mn hydrous-oxide coatings.

Impact of early diagenesis and bulk particle grain size distribution on estimates of relative geomagnetic palaeointensity variations in sediments from Lama Lake, northern Central Siberia

NASA Astrophysics Data System (ADS)

Nowaczyk, Norbert R.; Harwart, Stefanie; Melles, Martin

2001-04-01

High-resolution analyses of rock magnetic and sedimentological parameters were conducted on an 11m long sediment core from Lama Lake, Northern Siberia, which encompasses the late Pleistocene and the Holocene epochs. The results reveal a strong link between the median grain size of the magnetic particles, identified as magnetite, and the oxidation state of the sediment. Reducing conditions associated with a relative high total organic carbon (TOC) content of the sediment characterize the upper 7m of the core (~Holocene), and these have led to a partial dissolution of detrital magnetite grains, and a homogenization of grain-size-related rock magnetic parameters. The anoxic sediments are characterized by significantly larger median magnetic grain sizes, as indicated, for example, by lower median destructive fields of the natural remanent magnetization (MDFNRM) and lower ratios of saturation remanence to saturation magnetization (MSR/MS). Consequently, estimates of relative geomagnetic palaeointensity variations yielded large amplitude shifts associated with anoxic/oxic boundaries. Despite the partial reductive dissolution of magnetic particles within the anoxic section, and consequent minimal variations in magnetic concentration and grain size, palaeointensity estimates for this part of the core were still lithologically distorted by the effects of particle size (and subsidiary TOC) variations. Anomalously high values coincide with an interval of significantly more fine-grained sediment, which is also associated with a decrease in TOC content, which may thus imply a decreased level of magnetite dissolution in this interval. Calculation of relative palaeointensity estimates therefore seems to be compromised by a combined effect of shifts in the particle size distribution of the bulk sediment and by partial magnetite dissolution varying in association with the TOC content of the sediment.

Geologic map of the Mound Spring quadrangle, Nye and Clark Counties, Nevada, and Inyo County, California

USGS Publications Warehouse

Lundstrom, Scott C.; Mahan, Shannon; Blakely, Richard J.; Paces, James B.; Young, Owen D.; Workman, Jeremiah B.; Dixon, Gary L.

2003-01-01

The Mound Spring quadrangle, the southwestern-most 7.5' quadrangle of the area of the Las Vegas 1:100,000-scale quadrangle, is entirely within the Pahrump Valley, spanning the Nevada/California State line. New geologic mapping of the predominantly Quaternary materials is combined with new studies of gravity and geochronology in this quadrangle. Eleven predominantly fine-grained units are delineated, including playa sediment, dune sand, and deposits associated with several cycles of past groundwater discharge and distal fan sedimentation. These units are intercalated with 5 predominantly coarse-grained alluvial-fan and wash gravel units mainly derived from the Spring Mountains. The gravel units are distinguished on the basis of soil development and associated surficial characteristics. Thermoluminescence and U-series geochronology constrain most of the units to the Holocene and late and middle Pleistocene. Deposits of late Pleistocene groundwater discharge in the northeast part of the quadrangle are associated with a down-to-the-southwest fault zone that is expressed by surface fault scarps and a steep gravity gradient. The gravity field also defines a northwest-trending uplift along the State line, in which the oldest sediments are poorly exposed. About 2 km to the northeast a prominent southwest-facing erosional escarpment is formed by resistant beds in middle Pleistocene fine-grained sediments that dip northeast away from the uplift. These sediments include cycles of groundwater discharge that were probably caused by upwelling of southwesterly groundwater flow that encountered the horst.

Microstructural and petrophysical characterization of a "structurally oversimplified" fault zone in poorly lithified sands: evidence for a coseismic rupture?

NASA Astrophysics Data System (ADS)

Balsamo, Fabrizio; Storti, Fabrizio

2010-05-01

We studied an extensional fault zone developed in poorly lithified, quartz-rich high porosity sandy sediments of the seismically active Crotone basin (southern Italy). The fault zone cuts across interlayered fine- to coarse-grained sands and consists of a cm-thick, discrete fault core embedded in virtually undeformed wall sediments. Consequently, it can be described as "structurally oversimplified" due to the lack of footwall and hanging wall damage zones. We acquired microstructural, grain size, grain shape, porosity, mineralogical and permeability data to investigate the influence of initial sedimentological characteristics of sands on the final faulted granular products and related hydrologic properties. Faulting evolves by a general grain size and porosity reduction with a combination of intragranular fracturing, spalling, and flaking of grain edges, irrespective of grain mineralogy. The dominance of cataclasis, also confirmed by fractal dimensions >2.6, is generally not expected at a deformation depth <1 km. Coarse-grained sand shows a much higher comminution intensity, grain shape variations and permeability drop than fine-grained sands. This is because coarser aggregates have (i) fewer grain-to-grain contacts for a given area, which results in higher stress concentration at contact points, and (ii) a higher probability of pre-existing intragranular microstructural defects that result in a lower grain strength. The peculiar structural architecture, the dominance of cataclasis over non-destructive particulate flow, and the compositional variations of clay minerals in the fault core, strongly suggest that the studied fault zone developed by a coseismic rupture.

Watershed export of fine sediment, organic carbon, and chlorophyll-a to Chesapeake Bay: Spatial and temporal patterns in 1984-2016.

PubMed

Zhang, Qian; Blomquist, Joel D

2018-04-01

Chesapeake Bay has long experienced nutrient enrichment and water clarity deterioration. This study provides new quantification of loads and yields for sediment (fine and coarse grained), organic carbon (total, dissolved, and particulate), and chlorophyll-a from the monitored nontidal Chesapeake Bay watershed (MNTCBW), all of which are expected to drive estuarine water clarity. We conducted an integrated analysis of nine major tributaries to the Bay to understand spatial and temporal export patterns over the last thirty years (1984-2016). In terms of spatial pattern, export of these constituents from the MNTCBW was strongly dominated (~90%) by the three largest tributaries (i.e., Susquehanna, Potomac, and James). Among the nine tributaries, the ranking of constituent export generally follows the order of their watershed sizes, with other factors such as land use and reservoir playing important roles in some exceptions. In terms of partitioning, suspended sediment (SS) export was dominated by fine-grained sediment (SS fine ) in all nine tributaries; overall, ~90% of the MNTCBW SS is SS fine . Total organic carbon (TOC) export was dominated by dissolved organic carbon (DOC) in all tributaries except Potomac River; overall, ~60% of the MNTCBW TOC is DOC. A comparison with literature shows that the MNTCBW SS and TOC yields were ~80% and ~60% of the respective medians of worldwide watersheds. In terms of temporal pattern, flow-normalized yields from the MNTCBW show overall increases in SS (both long-term [1984-2016] and short-term [2004-2016]), SS fine (long-term and short-term), TOC (long-term), and chlorophyll-a (short-term). The rises in SS, SS fine , and TOC were largely driven by Susquehanna River where Conowingo Reservoir's trapping efficiency has greatly diminished in the last twenty years. Overall, these new results on the status and trends of sediment, organic carbon, and chlorophyll-a provide the foundation for building potential linkages between riverine inputs and estuarine water clarity patterns. Copyright © 2017 The Authors. Published by Elsevier B.V. All rights reserved.

Debris flow rheology: Experimental analysis of fine-grained slurries

USGS Publications Warehouse

Major, Jon J.; Pierson, Thomas C.

1992-01-01

The rheology of slurries consisting of ≤2-mm sediment from a natural debris flow deposit was measured using a wide-gap concentric-cylinder viscometer. The influence of sediment concentration and size and distribution of grains on the bulk rheological behavior of the slurries was evaluated at concentrations ranging from 0.44 to 0.66. The slurries exhibit diverse rheological behavior. At shear rates above 5 s−1 the behavior approaches that of a Bingham material; below 5 s−1, sand exerts more influence and slurry behavior deviates from the Bingham idealization. Sand grain interactions dominate the mechanical behavior when sand concentration exceeds 0.2; transient fluctuations in measured torque, time-dependent decay of torque, and hysteresis effects are observed. Grain rubbing, interlocking, and collision cause changes in packing density, particle distribution, grain orientation, and formation and destruction of grain clusters, which may explain the observed behavior. Yield strength and plastic viscosity exhibit order-of-magnitude variation when sediment concentration changes as little as 2–4%. Owing to these complexities, it is unlikely that debris flows can be characterized by a single rheological model.

Morphodynamic Modeling of the Lower Yellow River, China: Flux (Equilibrium) Form or Entrainment (Nonequilibrium) Form of Sediment Mass Conservation?

NASA Astrophysics Data System (ADS)

An, C.; Parker, G.; Ma, H.; Naito, K.; Moodie, A. J.; Fu, X.

2017-12-01

Models of river morphodynamics consist of three elements: (1) a treatment of flow hydraulics, (2) a formulation relating some aspect of sediment transport to flow hydraulics, and (3) a description of sediment conservation. In the case of unidirectional river flow, the Exner equation of sediment conservation is commonly described in terms of a flux-based formulation, in which bed elevation variation is related to the streamwise gradient of sediment transport rate. An alternate formulation of the Exner equation, however, is the entrainment-based formulation in which bed elevation variation is related to the difference between the entrainment rate of bed sediment into suspension and the deposition rate of suspended sediment onto the bed. In the flux-based formulation, sediment transport is regarded to be in a local equilibrium state (i.e., sediment transport rate locally equals sediment transport capacity). However, the entrainment-based formulation does not require this constraint; the sediment transport rate may lag in space and time behind the changing flow conditions. In modeling the fine-grained Lower Yellow River, it is usual to treat sediment conservation in terms of an entrainment-based (nonequilibrium) rather than a flux-based (equilibrium) formulation with the consideration that fine-grained sediment may be entrained at one place but deposited only at some distant location downstream. However, the differences in prediction between the two formulations are still not well known, and the entrainment formulation may not always be necessary for the Lower Yellow River. Here we study this problem by comparing the results of flux-based and entrainment-based morphodynamics under conditions typical of the Yellow River, using sediment transport equations specifically designed for the Lower Yellow River. We find, somewhat unexpectedly, that in a treatment of a 200-km reach using uniform sediment, there is little difference between the two formulations unless the sediment fall velocity is arbitrarily greatly reduced. A consideration of sediment mixtures, however, shows that the two formulations give very different patterns of grain sorting. We explain this in terms of the structures of the two Exner equations for sediment mixtures, and define conditions for applicability of each formulation.

How Can We Look for Fossils on Mars?

NASA Astrophysics Data System (ADS)

McMahon, S.; Bosak, T.; Grotzinger, J. P.; Briggs, D. E. G.; Hurowitz, J.; Tosca, N.; Petroff, A.; Summons, R. E.; Weiss, B. P.

2018-04-01

Mars 2020 should target fine-grained sediments, which on Earth preserve biosignatures more reliably and consistently than other settings identified on Mars. Taphonomic experiments will show how oxychlorine compounds may affect preservation.

Inference of lithologic distributions in an alluvial aquifer using airborne transient electromagnetic surveys

USGS Publications Warehouse

Dickinson, Jesse; Pool, D.R.; Groom, R.W.; Davis, L.J.

2010-01-01

An airborne transient electromagnetic (TEM) survey was completed in the Upper San Pedro Basin in southeastern Arizona to map resistivity distributions within the alluvial aquifer. This investigation evaluated the utility of 1D vertical resistivity models of the TEM data to infer lithologic distributions in an alluvial aquifer. Comparisons of the resistivity values and layers in the 1D resistivity models of airborne TEM data to 1D resistivity models of ground TEM data, borehole resistivity logs, and lithologic descriptions in drill logs indicated that the airborne TEM identified thick conductive fine-grained sediments that result in semiconfined groundwater conditions. One-dimensional models of ground-based TEM surveys and subsurface lithology at three sites were used to determine starting models and constraints to invert airborne TEM data using a constrained Marquardt-styleunderparameterized method. A maximum structural resolution of six layers underlain by a half-space was determined from the resistivity structure of the 1D models of the ground TEM data. The 1D resistivity models of the airborne TEM data compared well with the control data to depths of approximately 100 m in areas of thick conductive silt and clay and to depths of 200 m in areas of resistive sand and gravel. Comparison of a 3D interpolation of the 1D resistivity models to drill logs indicated resistive (mean of 65 ohm-m ) coarse-grained sediments along basin margins and conductive (mean of 8 ohm-m ) fine-grained sediments at the basin center. Extents of hydrologically significant thick silt and clay were well mapped by the 1D resistivity models of airborne TEM data. Areas of uncertain lithology remain below conductive fine-grained sediments where the 1D resistivity structure is not resolved: in areas where multiple lithologies have similar resistivity values and in areas of high salinity.

Variations in sedimentological properties in Lake Challa, East Africa: Understanding the source to sink processes

NASA Astrophysics Data System (ADS)

Meyer, Inka; Eloy, Jonas; Verschuren, Dirk; De Batist, Marc

2016-04-01

The clastic mineral fraction of lacustrine sediments has been proven to provide valuable information about sedimentation dynamics within a lake, and it can be used to define distinct terrestrial source areas and transport mechanisms from source to sink. Down-core variation in the properties of the clastic mineral fraction yields indications for changes in terrestrial sediment sources over time. However, in order to use terrestrial proxies in palaeo-environmental reconstruction, we have to understand and quantify the modern conditions of sediment provenance and deposition at the study site. In this study we present data on grain-size distribution, mineralogy and particle shape of the clastic mineral component of lacustrine sediments from Lake Challa, a small freshwater lake of volcanic origin, located on the eastern slope of Mt. Kilimanjaro. Situated close to the equator, it contains a uniquely long and continuous sediment sequence allowing the study of inter-hemispheric climate dynamics. The finely laminated profundal sediments of Lake Challa are characterized by a fine-grained texture and are mainly composed of organic matter, biogenic silica and authigenic carbonate, with a relatively minor component of detrital mineral that can either originate from erosion of the steep volcanic crater walls or was mobilized by wind from unvegetated areas of the surrounding scrub savannah landscape. In order to distinguish between these two sources of terrestrial sediment input (i.e., local run-off versus distant aeolian) into Lake Challa, and to map out differences in sediment properties, samples were investigated from profundal surface sediments and short cores, as well as on-shore soils from several locations around the lake and from beyond the crater catchment. Variation in grain-size distribution and mineralogy can be linked to distinct terrestrial sources, whereas the shape of single particles gives additional information about transport dynamics. In future, the results from this study will be applied to the down-core record of Lake Challa to reconstruct climate-driven changes in terrigenous sediment input over time.

Mechanical and chemical compaction in fine-grained shallow-water limestones.

USGS Publications Warehouse

Shinn, E.A.; Robbin, D.M.

1983-01-01

Significant mechanical compaction resulted from pressures simulating less than 305 m of burial. Increasing loads to an equivalent of more than 3400 m did not significantly increase compaction or reduce sediment core length. Chemical compaction (pressure dissolution) was detected only in sediment cores compacted to pressures greater than 3400 m of burial. These short-term experiments suggest that chemical compaction would begin at much shallower depths given geologic time. Compaction experiments that caused chemical compaction lend support to the well-established hypothesis; that cement required to produce a low-porosity/low-permeability fine-grained limestone is derived internally. Dissolution, ion diffusion, and reprecipitation are considered the most likely processes for creating significant thicknesses of dense limestone in the geologic record. Continuation of chemical compaction after significant porosity reduction necessitates expulsion of connate fluids, possibly including hydrocarbons. -from Authors

Continental sedimentary processes decouple Nd and Hf isotopes

NASA Astrophysics Data System (ADS)

Garçon, Marion; Chauvel, Catherine; France-Lanord, Christian; Huyghe, Pascale; Lavé, Jérôme

2013-11-01

The neodymium and hafnium isotopic compositions of most crustal and mantle rocks correlate to form the "Terrestrial Array". However, it is now well established that whereas coarse detrital sediments follow this trend, fine-grained oceanic sediments have high Hf ratios relative to their Nd isotopic ratios. It remains uncertain whether this "decoupling" of the two isotopic systems only occurs in the oceanic environment or if it is induced by sedimentary processes in continental settings. In this study, the hafnium and neodymium isotopic compositions of sediments in large rivers is expressly used to constrain the behavior of the two isotopic systems during erosion and sediment transport from continent to ocean. We report major and trace element concentrations together with Nd and Hf isotopic compositions of bedloads, suspended loads and river banks from the Ganges River and its tributaries draining the Himalayan Range i.e. the Karnali, the Narayani, the Kosi and the Marsyandi Rivers. The sample set includes sediments sampled within the Himalayan Range in Nepal, at the Himalayan mountain front, and also downstream on the floodplain and at the outflow of the Ganges in Bangladesh. Results show that hydrodynamic sorting of minerals explains the entire Hf isotopic range, i.e. more than 10 εHf units, observed in the river sediments but does not affect the Nd isotopic composition. Bedloads and bank sediments have systematically lower εHf values than suspended loads sampled at the same location. Coarse-grained sediments lie below or on the Terrestrial Array in an εHf vs. εNd diagram. In contrast, fine-grained sediments, including most of the suspended loads, deviate from the Terrestrial Array toward higher εHf relative to their εNd, as is the case for oceanic terrigenous clays. The observed Nd-Hf decoupling is explained by mineralogical sorting processes that enrich bottom sediments in coarse and dense minerals, including unradiogenic zircons, while surface sediments are enriched in fine material with radiogenic Hf signatures. The data also show that Nd-Hf isotopic decoupling increases with sediment transport in the floodplain to reach its maximum at the river mouth. This implies that the Nd-Hf isotopic decoupling observed in worldwide oceanic clays and river sediments is likely to have the same origin. Finally, we estimated the Nd-Hf isotopic composition of the present-day mantle if oceanic sediments had never been subducted and conclude that the addition of oceanic sediments with their anomalous Nd-Hf isotopic compositions has slowly shifted the composition of the Earth's mantle towards more radiogenic Hf values through time.

Classification of gravity-flow deposits and their significance for unconventional petroleum exploration, with a case study from the Triassic Yanchang Formation (southern Ordos Basin, China)

NASA Astrophysics Data System (ADS)

Fan, Aiping; Yang, Renchao; (Tom) van Loon, A. J.; Yin, Wei; Han, Zuozhen; Zavala, Carlos

2018-08-01

The ongoing exploration for shale oil and gas has focused sedimentological research on the transport and deposition mechanisms of fine-grained sediments, and more specifically on fine-grained mass-flow deposits. It appears, however, that no easily applicable classification scheme for gravity-flow deposits exists, and that such classifications almost exclusively deal with sandy and coarser sediments. Since the lack of a good classification system for fine-grained gravity flow deposits hampers scientific communication and understanding, we propose a classification scheme on the basis of the mud content in combination with the presumed transport mechanism. This results in twelve types of gravity-flow deposits. In order to show the practical applicability of this classification system, we apply it to the Triassic lacustrine Yanchang Formation in the southern Ordos Basin (China), which contains numerous slumps, debris-flows deposits, turbidites and hyperpycnites. The slumps and debrites occur mostly close to a delta front, and the turbidites and hyperpycnites extend over large areas from the delta slopes into the basin plain. The case study shows that (1) mud cannot only be transported but also deposited under active hydrodynamic conditions; (2) fine-grained gravity-flow constitute a significant part of the lacustrine mudstones and shales; (3) muddy gravity flows are important for the transport and deposition of clastic particles, clay minerals and organic matter, and thus are important mechanisms involved in the generation of hydrocarbons, also largely determining the reservoir capability for unconventional petroleum.

Morphobathymetric analysis of the large fine-grained sediment waves over the Gulf of Valencia continental slope (NW Mediterranean)

NASA Astrophysics Data System (ADS)

Ribó, Marta; Puig, Pere; Muñoz, Araceli; Lo Iacono, Claudio; Masqué, Pere; Palanques, Albert; Acosta, Juan; Guillén, Jorge; Gómez Ballesteros, María

2016-01-01

Detailed analysis of recently acquired swath bathymetry, together with high-resolution seismic profiles and bottom sediment samples, revealed the presence of large-scale fine-grained sediment waves over the Gulf of Valencia continental slope. As many other deep-water sediment waves, these features were previously attributed to gravitational slope failure, related to creep-like deformation, and are here reinterpreted as sediment wave fields extending from 250 m depth to the continental rise, at 850 m depth. Geometric parameters were computed from the high-resolution multibeam dataset. Sediment wave lengths range between 500 and 1000 m, and maximum wave heights of up to 50 m are found on the upper slope, decreasing downslope to minimum values of 2 m high. Sediment waves on the lower part of the slope are quasi-stationary vertically accreting, whereas they show an upslope migrating pattern from the mid-slope to the upper part of the continental slope. High-resolution seismic profiles show continuous internal reflectors, with sediment waves merging down-section and sediment wave packages decreasing in thickness downslope. These sediment packages are thicker on the crest of each individual sediment wave and thinner on the downslope flank. 210Pb analyses conducted on sediment cores collected over the sediment wave fields also indicate slightly higher sediment accumulation rates on the wave crests. Sediment wave formation processes have been inferred from contemporary hydrodynamic observations, which reveal the presence of near-inertial internal waves interacting with the Gulf of Valencia continental slope. Internal wave activity is suggested to be the preferential mechanism for the transport and deposition of sediment, and the maintenance of the observed sediment wave fields.

Rare earth element fingerprints in Korean coastal bay sediments: Association with provenance discrimination

NASA Astrophysics Data System (ADS)

Kang, Jeongwon; Woo, Han Jun; Jang, Seok; Jeong, Kap-Sik; Jung, Hoi-Soo; Hwang, Ha Gi; Lee, Jun-Ho; Cho, Jin Hyung

2016-09-01

Rare earth elements (REEs: La-Lu) in surface sediments collected from the mouth and middle tidal flats of Gomso Bay, South Korea, in August 2011 and May 2012 were analyzed to investigate the fine-grained sediment provenance. The upper continental crust (UCC)-normalized light REEs (LREEs: La to Nd) were more enriched than the middle REEs (MREEs: Sm to Dy) and heavy REEs (HREEs: Ho to Lu), resulting in large (La/Yb)UCC (1.9 ± 0.4) to (Gd/Yb)UCC (1.4 ± 0.2) ratios. The monthly (La/Yb)UCC values differed between the mouth and middle tidal flats due to deposition of fine-grained sediments that originated from distant rivers (the Geum and Yeongsan) and the Jujin Stream, located on the southern shore of the inner bay. We observed relative reductions in the (La/Yb)UCC value and REE content in the sediments from the mouth of the bay compared with those from Jujin Stream sediments. Confined to the middle tidal flat around the KH Line of Jujin Stream, the sediments, most enriched in LREEs but depleted in Eu, were distributed in August as strong Jujin Stream runs. Here, we suggest that an increase in LREE/HREE and decrease in MREE/LREE ratios can be used as a proxy to identify the Jujin Stream provenance in mixed riverine sediments and to trace Jujin Stream sediments within the Gomso Bay tidal flat, especially in the summer rainy season.

Fine-grained sediment gravity flow deposits induced by flood and lake slope failure events: examples of lacustrine varved sediments in Japan

NASA Astrophysics Data System (ADS)

Ishihara, Yoshiro; Sasaki, Yasunori; Sasaki, Hana; Onishi, Yuri

2016-04-01

Fine-grained sediment gravity flow deposits induced by flood and lake slope failure events are frequently intercalated in lacustrine successions. When sediment gravity flow deposits are present in varved sediments, it is suggested that they provide valuable information about sediment gravity flows, because they can easily trace laterally and can give the magnitude of erosion and recurrence interval of events. In addition, because large sedimentary bodies of stacked sediment gravity flow deposits in varved sediments of a calm lake are not suggested, a relatively simple depositional environment is expected. In the present study, we analysed sedimentary facies of sediment gravity flow deposits in varved lacustrine diatomites in the Middle Pleistocene Hiruzenbara and Miyajima formations in Japan, and concluded a depositional model of the lacustrine sediment gravity flow deposits. Varved diatomites: The Hiruzenbara Fm., a dammed lake fill as foots of Hiruzen Volcanos, is deposited during an interglacial period during MIS12 to 15. Varves of ca. 8000 yr were measured in a 20 m intercalating flood and lake slope failure-induced sediment gravity flow deposits. The Miyajima Fm., distributed in a paleo-caldera lake in NE Japan, includes many sediment gravity flow deposits possibly originated from fandeltas around the lake. These formations have differences in their depositional setting; the Hiruzebara Fm. was deposited in a large lake basin, whereas the Miyajima Fm. was deposited in a relatively small basin. Because of the depositional setting, intercalation of volcaniclastics is dominant in the Miyajima Fm. Lacustrine sediment gravity flow deposits: Sediment gravity flow deposits in both formations can be classified into flood- and lake slope failure-induced types based on the sedimentary facies. Composites of the both types are also found. Flood-induced types comprise fine-grained silts dominated by carbonaceous fragments, whereas lake slope failure-induced types are dominated by rip-up clasts of diatomite. The former is well continued in outcrops; however, the thickness of the latter is changeable and the lower contact is erosive. In the Hirzenbara Fm., flood-induced type includes epiphytic diatom valves as river inflows, whereas slope failure-induced type is composed of diatom valves of varved diatomite. Flood-induced types are suggested to be classified into hyperpycnal flow and hypopycnal flow types with regard to the presence of basal erosion. On the other hand, slope failure-induced types can be interpreted as debris flow deposits occurred in the lakes. Differences in the two types are also shown as bed-thickness frequency distributions indicating event magnitude.

Sources and ages of fine-grained sediment to streams using fallout radionuclides in the Midwestern United States

USGS Publications Warehouse

Gellis, Allen; Fuller, Christopher C.; Van Metre, Peter C.

2017-01-01

Fallout radionuclides, 7Be and 210Pbex, sampled in bed sediment for 99 watersheds in the Midwestern region of the United States and in 15 samples of suspended sediment from 3 of these watersheds were used to partition upland from channel sources and to estimate the age or the time since the surface-derived portion of sediment was on the land surface (0–∼1 year). Channel sources dominate: 78 of the 99 bed material sites (79%) have >50% channel-derived sediment, and 9 of the 15 suspended-sediment samples (60%) have >50% channel-derived sediment. 7Be was detected in 82 bed sediment samples and all 15 suspended-sediment samples. The surface-derived portion of 54 of the 80 (68%) streams with detectable 7Be and 210Pbex were ≤ 100 days old and the surface-derived portion of all suspended-sediment samples were ≤ 100 days old, indicating that surface-derived fine-grained sediment moves rapidly though these systems. The concentrations of two hydrophobic pesticides–DDE and bifenthrin–are correlated with the proportion of surface-derived sediment, indicating a link between geomorphic processes and particle-associated contaminants in streams. Urban areas had the highest pesticide concentrations and the largest percentage of surface-derived sediment. Although the percentage of surface-derived sediment is less than channel sources at most of the study sites, the relatively young age of the surface-derived sediment might indicate that management actions to reduce sediment contamination where the land surface is an important source could have noticeable effects.

Processes Controlling Transfer of Fine-Grained Sediment in Tidal Systems Spanning a Range of Fluvial Influence

DTIC Science & Technology

2012-09-30

understand how the delicate balance of ebb and flood sediment fluxes is maintained to create tidal flat and mangrove complexes, and distributary shoals and...and the subaqueous delta on the inner continental shelf, and sediment sinks within vegetated/ mangrove shoreline complexes. Our overall hypothesis...on Mangrove /Vegetated Intertidal Areas. Along the main stem tidal river and in the offshore banks may be shorelines lined with vegetation ( mangroves

Particle Size Characteristics of Fluvial Suspended Sediment in Proglacial Streams, King George Island, South Shetland Island

NASA Astrophysics Data System (ADS)

Szymczak, Ewa

2017-12-01

In this study, the characterization of particle size distribution of suspended sediment that is transported by streams (Ornithologist Creek, Ecology Glacier Creeks, Petrified Forest Creek, Czech Creek, Vanishing Creek, Italian Creek) in the area of the Arctowski Polish Antarctic Station is presented. During the first period of the summer season, the aforementioned streams are supplied by the melting snow fields, while later on, by thawing permafrost. The water samples were collected from the streams at monthly intervals during the Antarctic summer season (January - March) of 2016. The particle size distribution was measured in the laboratory with a LISST-25X laser diffraction particle size analyser. According to Sequoia Scientific Inc., LISST-25X can measure particle sizes (Sauter Mean Diameter) between 2.50 and 500 μm. The results of particle size measurements were analysed in relation to flow velocity (0.18-0.89 m/s), the cross-sectional parameters of the streams, suspended sediment concentration (0.06-167.22 mg/dm3) and the content of particulate organic matter (9.8-84.85%). Overall, the mean particle size ranged from 28.8 to 136 μm. The grain size of well-sorted sediments ranged from 0.076 to 0.57, with the skewness and kurtosis values varying from -0.1 to 0.4, and from 0.67 to 1.3, respectively. Based on the particle size characteristics of suspended sediment, the streams were divided into two groups. For most of the streams, the sediment was very well sorted, while fine sand and very fine sand were dominant fractions displaying symmetric and platykurtic distributions, respectively. Only in two streams, the suspended sediment consisted of silt-size grains, well or moderately well sorted, with coarse-skewness and mostly mesokurtic distribution. The C-M chart suggested that the transportation processes of suspended sediment included the suspended mode only. The grain-size distribution of suspended sediment was mainly influenced by the stream runoff, surface sediment type and biological processes.

Assessing grain-size correspondence between flow and deposits of controlled floods in the Colorado River, USA

USGS Publications Warehouse

Draut, Amy; Rubin, David M.

2013-01-01

Flood-deposited sediment has been used to decipher environmental parameters such as variability in watershed sediment supply, paleoflood hydrology, and channel morphology. It is not well known, however, how accurately the deposits reflect sedimentary processes within the flow, and hence what sampling intensity is needed to decipher records of recent or long-past conditions. We examine these problems using deposits from dam-regulated floods in the Colorado River corridor through Marble Canyon–Grand Canyon, Arizona, U.S.A., in which steady-peaked floods represent a simple end-member case. For these simple floods, most deposits show inverse grading that reflects coarsening suspended sediment (a result of fine-sediment-supply limitation), but there is enough eddy-scale variability that some profiles show normal grading that did not reflect grain-size evolution in the flow as a whole. To infer systemwide grain-size evolution in modern or ancient depositional systems requires sampling enough deposit profiles that the standard error of the mean of grain-size-change measurements becomes small relative to the magnitude of observed changes. For simple, steady-peaked floods, 5–10 profiles or fewer may suffice to characterize grain-size trends robustly, but many more samples may be needed from deposits with greater variability in their grain-size evolution.

Phreatomagmatic eruptions through unconsolidated coastal plain sequences, Maungataketake, Auckland Volcanic Field (New Zealand)

NASA Astrophysics Data System (ADS)

Agustín-Flores, Javier; Németh, Károly; Cronin, Shane J.; Lindsay, Jan M.; Kereszturi, Gábor; Brand, Brittany D.; Smith, Ian E. M.

2014-04-01

Maungataketake is a monogenetic basaltic volcano formed at ~ 85-89 ka in the southern part of the Auckland Volcanic Field (AVF), New Zealand. It comprises a basal 1100-m diameter tuff ring, with a central scoria/spatter cone and lava flows. The tuff ring was formed under hydrogeological and geographic conditions very similar to the present. The tuff records numerous density stratified, wet base surges that radiated outward up to 1 km, decelerating rapidly and becoming less turbulent with distance. The pyroclastic units dominantly comprise fine-grained expelled grains from various sedimentary deposits beneath the volcano mixed with a minor component of juvenile pyroclasts (~ 35 vol.%). Subtle lateral changes relate to deceleration with distance and vertical transformations are minor, pointing to stable explosion depths and conditions, with gradual transitions between units and no evidence for eruptive pauses. This volcano formed within and on ~ 60 m-thick Plio/Pleistocene, poorly consolidated, highly permeable shelly sands and silts (Kaawa Formation) capped by near-impermeable, water-saturated muds (Tauranga Group). These sediments rest on moderately consolidated Miocene-aged permeable turbiditic sandstones and siltstones (Waitemata Group). Magma-water fuelled thermohydraulic explosions remained in the shallow sedimentary layers, excavating fine-grained sediments without brittle fragmentation required. On the whole, the resulting cool, wet pyroclastic density currents were of low energy. The unconsolidated shallow sediments deformed to accommodate rapidly rising magma, leading to development of complex sill-like bodies and a range of magma-water contact conditions at any time. The weak saturated sediments were also readily liquefied to provide an enduring supply of water and fine sediment to the explosion loci. Changes in magma flux and/or subsequent stabilisation of the conduit area by a lava ring-barrier led to ensuing Strombolian and fire-fountaining eruption phases. Future eruptions in littoral environments around Auckland are likely to be of this type, producing base surges that rapidly decrease in energy over short runout distances (~ 1 km).

Short Term Sediment Exchange Between Marshes and Bays Using Beryllium-7 as a Tracer, Fourleague Bay, Louisiana.

NASA Astrophysics Data System (ADS)

Restreppo, G. A.; Bentley, S. J.; Xu, K.; Wang, J.

2016-12-01

Modern delta models focus on the availability and exchange of coarse sediment as one of the major factors of deltaic growth or decay. Fine-grained sediment exchange within a river's delta is relatively poorly understood, as is the impact that this exchange has on land building and land loss. To better understand the dynamics of fine grain sediment exchange between river mouth, adjacent bays, and marshland, sediment cores from Fourleague Bay, LA, were collected and analyzed for 7Be, a naturally occurring radioisotope that serves as a marker for recently deposited sediment. Time-series push cores were collected every two months at ten sites, five located across a longitudinal transect in the middle bay and five located along adjacent marshes, from May 2015 to May 2016. All sites fall within 11 to 28 km of the Atchafalaya Delta, along a gradient extending towards the open ocean. Cores were extruded in 2 cm intervals, dried, ground, and analyzed via gamma spectrometry for the presence of 7Be. Inventories of 7Be were then calculated and used to determine bimonthly sedimentation rates over the course twelve months. Sediment deposition on the bay floor and marsh surface were then compared to Atchafalaya River discharge, wind speed and direction, and wave action. Preliminary results indicate patterns of initial fluvial sediment transfer from river to bay floor, then bay floor to marsh surface, with decreasing fluvial influence towards the open ocean. Sediment transport from bay to marsh appears to be coupled with meteorological forcing that induces bay-floor sediment resuspension and the flooding of marsh surfaces. This indirect mechanism of fluvial sediment supply to wetland surfaces may extend the region of influence for sediment delivery from man-made river-sediment diversions.

A geochronologic framework for the Ziegler Reservoir fossil site, Snowmass Village, Colorado

USGS Publications Warehouse

Mahan, Shannon; Gray, Harrison J.; Pigati, Jeffrey S.; Wilson, Jim; Lifton, Nathaniel A.; Paces, James B.; Blaauw, Maarten

2014-01-01

The Ziegler Reservoir fossil site near Snowmass Village, Colorado, provides a unique opportunity to reconstruct high-altitude paleoenvironmental conditions in the Rocky Mountains during the last interglacial period. We used four different techniques to establish a chronological framework for the site. Radiocarbon dating of lake organics, bone collagen, and shell carbonate, and in situ cosmogenic 10Be and 26Al ages on a boulder on the crest of a moraine that impounded the lake suggest that the ages of the sediments that hosted the fossils are between ~ 140 ka and > 45 ka. Uranium-series ages of vertebrate remains generally fall within these bounds, but extremely low uranium concentrations and evidence of open-system behavior limit their utility. Optically stimulated luminescence (OSL) ages (n = 18) obtained from fine-grained quartz maintain stratigraphic order, were replicable, and provide reliable ages for the lake sediments. Analysis of the equivalent dose (DE) dispersion of the OSL samples showed that the sediments were fully bleached prior to deposition and low scatter suggests that eolian processes were likely the dominant transport mechanism for fine-grained sediments into the lake. The resulting ages show that the fossil-bearing sediments span the latest part of marine isotope stage (MIS) 6, all of MIS 5 and MIS 4, and the earliest part of MIS 3.

Strontium isotope record of seasonal scale variations in sediment sources and accumulation in low-energy, subtidal areas of the lower Hudson River estuary

USGS Publications Warehouse

Smith, J.P.; Bullen, T.D.; Brabander, D.J.; Olsen, C.R.

2009-01-01

Strontium isotope (87Sr/86Sr) profiles in sediment cores collected from two subtidal harbor slips in the lower Hudson River estuary in October 2001 exhibit regular patterns of variability with depth. Using additional evidence from sediment Ca/Sr ratios, 137Cs activity and Al, carbonate (CaCO3), and organic carbon (OCsed) concentration profiles, it can be shown that the observed variability reflects differences in the relative input and trapping of fine-grained sediment from seaward sources vs. landward sources linked to seasonal-scale changes in freshwater flow. During high flow conditions, the geochemical data indicate that most of the fine-grained sediments trapped in the estuary are newly eroded basin materials. During lower (base) flow conditions, a higher fraction of mature materials from seaward sources with higher carbonate content is trapped in the lower estuary. Results show that high-resolution, multi-geochemical tracer approaches utilizing strontium isotope ratios (87Sr/86Sr) can distinguish sediment sources and constrain seasonal scale variations in sediment trapping and accumulation in dynamic estuarine environments. Low-energy, subtidal areas such as those in this study are important sinks for metastable, short-to-medium time scale sediment accumulation. These results also show that these same areas can serve as natural recorders of physical, chemical, and biological processes that affect particle and particle-associated material dynamics over seasonal-to-yearly time scales. ?? 2009.

Guidelines for collecting and processing samples of stream bed sediment for analysis of trace elements and organic contaminants for the National Water-Quality Assessment Program

USGS Publications Warehouse

Shelton, Larry R.; Capel, Paul D.

1994-01-01

A major component of the U.S. Geological Survey's National Water-Quality Assessment program is to assess the occurrence and distribution of trace elements and organic contaminants in streams. The first phase of the strategy for the assessment is to analyze samples of bed sediments from depositional zones. Fine-grained particles deposited in these zones are natural accumulators of trace elements and hydrophobic organic compounds. For the information to be comparable among studies in many different parts of the Nation, strategies for selecting stream sites and depositional zones are critical. Fine-grained surficial sediments are obtained from several depositional zones within a stream reach and composited to yield a sample representing average conditions. Sample collection and processing must be done consistently and by procedures specifically designed to separate the fine material into fractions that yield uncontaminated samples for trace-level analytes in the laboratory. Special coring samplers and other instruments made of Teflon are used for collection. Samples are processed through a 2.0-millimeter stainless-steel mesh sieve for organic contaminate analysis and a 63-micrometer nylon-cloth sieve for trace-element analysis. Quality assurance is maintained by strict collection and processing procedures, duplicate samplings, and a rigid cleaning procedure.

Texture development in naturally compacted and experimentally deformed silty clay sediments from the Nankai Trench and Forearc, Japan

NASA Astrophysics Data System (ADS)

Schumann, Kai; Stipp, Michael; Leiss, Bernd; Behrmann, Jan H.

2014-12-01

The petrophysical properties of fine-grained marine sediments to a large extent depend on the microstructure and crystallographic preferred orientations (CPOs). In this contribution we show that Rietveld-based synchrotron texture analysis is a new and valuable tool to quantify textures of water-saturated fine-grained phyllosilicate-rich sediments, and assess the effects of compaction and tectonic deformation. We studied the CPO of compositionally almost homogeneous silty clay drillcore samples from the Nankai Accretionary Prism slope and the incoming Philippine Sea plate, offshore SW Japan. Basal planes of phyllosilicates show bedding-parallel alignment increasing with drillhole depth, thus reflecting progressive burial and compaction. In some samples calcite and albite display a CPO due to crystallographically controlled non-isometric grain shapes, or nannofossil tests. Consolidated-undrained experimental deformation of a suite of thirteen samples from the prism slope shows that the CPOs of phyllosilicate and calcite basal planes develop normal to the experimental shortening axis. There is at least a qualitative relation between CPO intensity and strain magnitude. Scanning electron micrographs show concurrent evolution of preferred orientations of micropores and detrital illite flakes normal to axial shortening. This indicates that the microfabrics are sensitive strain gauges, and contribute to anisotropic physical properties along with the CPO.

Detrital magnetization of laboratory-redeposited sediments

NASA Astrophysics Data System (ADS)

Valet, Jean-Pierre; Tanty, Cyrielle; Carlut, Julie

2017-07-01

We conducted several redeposition experiments in laboratory using natural and artificial sediments in order to investigate the role of grain size and lithology on sedimentary remanence acquisition. The role of grain size was investigated by using sorted sediment from natural turbidites. Taking advantage of the magnetic grain size distribution within turbidites, we compared redeposition experiments performed with coarse magnetic grains taken from the bottom layers of a turbidite with fine grains from the upper layers of the same turbidite. In order to document the magnetization acquired for increasing sediment concentrations that is analogous to increasing depth in the sediment column, the samples were frozen at temperatures between -5 and -10 °C. Magnetization acquisition behaved similarly in both situations, so that little smearing of the palaeomagnetic signal should be linked to grain size variability within this context. Other series of experiments were aimed at investigating the influence of lithology. We used clay or carbonated sediments that were combined with magnetic separates from basaltic rocks or with single-domain biogenic magnetite. The experiments revealed that the magnetization responded differently with clay and carbonates. Clay rapidly inhibited alignment of magnetic grains at low concentrations and, therefore, significant magnetization lock-in occurred despite large water contents, perhaps even within the bioturbated layer. Extension of the process over a deeper interval contributes to smear the geomagnetic signal and therefore to alter the palaeomagnetic record. In carbonates, the magnetization was acquired within a narrow window of 45-50 per cent sediment concentration, therefore, little smearing of the geomagnetic signal can be expected. Finally, experiments on carbonate sediments and biogenic magnetite with increasing field intensities indicate that magnetization acquisition is linear with respect to field intensity. Altogether, the results suggest that sediments with dominant carbonate content should be favoured for records of geomagnetic field changes provided that the minor clay fraction does not vary excessively. They confirm the advantage of using cultures of magnetotactic bacteria for redeposition experiments.

Sediment sorting at a side channel bifurcation

NASA Astrophysics Data System (ADS)

van Denderen, Pepijn; Schielen, Ralph; Hulscher, Suzanne

2017-04-01

Side channels have been constructed to reduce the flood risk and to increase the ecological value of the river. In various Dutch side channels large aggradation in these channels occurred after construction. Measurements show that the grain size of the deposited sediment in the side channel is smaller than the grain size found on the bed of the main channel. This suggest that sorting occurs at the bifurcation of the side channel. The objective is to reproduce with a 2D morphological model the fining of the bed in the side channel and to study the effect of the sediment sorting on morphodynamic development of the side channel. We use a 2D Delft3D model with two sediment fractions. The first fraction corresponds with the grain size that can be found on the bed of the main channel and the second fraction corresponds with the grain size found in the side channel. With the numerical model we compute several side channel configurations in which we vary the length and the width of the side channel, and the curvature of the upstream channel. From these computations we can derive the equilibrium state and the time scale of the morphodynamic development of the side channel. Preliminary results show that even when a simple sediment transport relation is used, like Engelund & Hansen, more fine sediment enters the side channel than coarse sediment. This is as expected, and is probably related to the bed slope effects which are a function of the Shields parameter. It is expected that by adding a sill at the entrance of the side channel the slope effect increases. This might reduce the amount of coarse sediment which enters the side channel even more. It is unclear whether the model used is able to reproduce the effect of such a sill correctly as modelling a sill and reproducing the correct hydrodynamic and morphodynamic behaviour is not straightforward in a 2D model. Acknowledgements: This research is funded by STW, part of the Dutch Organization for Scientific Research under grant number P12-P14 (RiverCare Perspective Programme) project number 13516.

The contribution of sediment from forested areas of the Chesapeake Bay Watershed

NASA Astrophysics Data System (ADS)

Gellis, A.; Brakebill, J.

2012-12-01

Fine-grained sediment is a major pollutant in the Chesapeake Bay and its receiving waters. Sediment budget studies have been conducted in small basins draining to the Bay over the last decade to understand the important sources of fine-grained sediment, quantify erosion rates, and determine sediment yields. Sediment budget approaches include modeling (SPARROW), sediment fingerprinting, and quantifying upland rates of erosion (Cesium-137). SPARROW model results indicate that forests deliver between 2 to 8% of the total sediment to the Bay. Sediment-fingerprinting results from small watershed studies indicate that forests contribute between 13 to 29 % of the sediment. The Cesium-137 technique was used to quantify soil redistribution (erosion and deposition) rates for forested areas in the Linganore Creek (146 km2) watershed which drains the Piedmont Physiographic Province. Average forest erosion rates measured in 2009 for Linganore Creek using Cesium-137 were 2.6 t/ha/yr. With 27% of the Linganore Creek watershed in forest, over 10,300 may be eroded off of forested lands which is more than the average annual suspended-sediment load (8,050 Mg/yr) in Linganore Creek, indicating that much of the eroded forest sediment goes in storage. Most of the forested areas in the Chesapeake Bay watershed were cut down for agriculture between the time of European colonization and the early 20th Century. In the late 20th century forested lands show an increase in areal extent. Although studies have not been conducted to understand why these secondary growth forests are eroding, it may involve that these forests have not fully recovered from deforestation. Soil profiles are thin, and runoff and sediment relations may have been altered, leading to high rates of erosion.

Holocene water mass history off NE Greenland - A first high-resolution sediment record from the western Fram Strait

NASA Astrophysics Data System (ADS)

Zehnich, Marc; Palme, Tina; Spielhagen, Robert F.; Hass, H. Christian; Bauch, Henning A.

2017-04-01

While the Holocene history of the eastern Fram Strait seems well investigated, no high-resolution paleoenvironmental records were available from the western Fram Strait so far. A new sedimentary record, obtained during expedition PS93.1 (2015) of RV Polarstern on the outermost NE Greenland shelf, allows for the first time to reconstruct Holocene changes in near-surface salinities, temperature, stratification and water masses (polar waters vs. Atlantic Water), potentially related to variations of the freshwater and sea ice export from the Arctic Ocean. The 260 cm long sedimentary record from site PS93/025 (80.5°N, 8.5°W) was investigated for sediment composition, foraminifer contents, grain size variations (sortable silt) and the isotopic composition of planktic foraminifers. Radiocarbon datings reveal an age of 10.2 cal-ka for the core base and continuous sedimentation throughout most of the Holocene. The sediments are generally very fine-grained (<2% sand). The grain size record reveals a fining-upwards trend and sediments from <6.5 cal-ka consist of <0.5% coarse fraction. A comparison of foraminifer and coarse fraction abundances shows strong similarities. Apparently the contribution of coarse terrestrial material from iceberg transport was extremely low throughout the last 10.2 cal-ka. Foraminifer abundances (both planktic and benthic) are high in Early Holocene sediments until ca. 7 cal-ka and decrease rapidly thereafter. This is interpreted to reflect a relatively strong advection of Atlantic Water to the NW Fram Strait, which correlates well with similar findings on the eastern side of the Arctic Gateway. Sortable silt grain sizes are high (27-32 µm) in the older part of the record and gradually decrease between 7 cal-ka and 4 cal-ka. After ca. 4 cal-ka, sortable silt shows values of 20-22 µm and little variation. Considering also the grain-size distribution curves, we propose a decline of bottom current velocities on the outer NE Greenland shelf after 7 cal-ka, related to a decrease of Atlantic Water advection. These preliminary results reveal a strong coupling of Holocene environments on both sides of the Fram Strait.

Trace metal pollution assessment in the surface sediments of nearshore area, off Calicut, southwest coast of India.

PubMed

Srinivas, Reji; Shynu, R; Sreeraj, M K; Ramachandran, K K

2017-07-15

Metal concentrations (Al, Cr, Ni, Cu, Zn, and Pb), grain size, and total organic carbon content in 29 surface sediment samples from the nearshore area off Calicut were analyzed to determine their distribution and pollution status. Surface sediments were dominantly silts with low percentage of clay and sand at nearshore and offshore areas. The mean metal concentrations were in the following order: Cr>Ni>Zn>Pb>Cu. The enrichment factor and geo-accumulation index of metals suggest that the surface sediments were not polluted by Zn and moderately polluted by Cu and Ni. By contrast, Cr and Pb showed significant enrichment levels. Results from a multivariate statistical analysis suggested that the spatial enrichment of these heavy metals was related to sediment type. Thus, the sediment distribution and their metal enrichment were mainly controlled by local hydrodynamic conditions that caused the winnowing of fine-grained sediments. Copyright © 2017. Published by Elsevier Ltd.

Settling velocities of fine suspended particles in the Changjiang Estuary, China

USGS Publications Warehouse

Shi, Z.; Zhou, H.J.; Eittreim, S.L.; Winterwerp, J.C.

2003-01-01

Point-sampled suspended sediment concentration profiles (grain size largely < 32 ??m) were measured in August 1978, April 1990, and May 1990 in the Changjiang Estuary. They were selectively fit with the Rouse equation in order to calculate the median settling velocities ws,50 of fine suspended particles in the Changjiang Estuary, East China Sea. Calculated settling velocities ranged from 0.4 to 4.1 mm s-1. Furthermore, ws values increased with the mean concentration C?? of sediment in suspension. The best-fit equation for the field settling velocity of fine particles in the Changjiang Estuary can be expressed by the power law: ws = 2.37 C??0.84 (r2 < 0.3). ?? 2003 Elsevier Ltd. All rights reserved.

Degradation of picric acid and 2,6-DNT in marine sediments and waters: The role of microbial activity and ultra-violet exposure

USGS Publications Warehouse

Nipper, Marion; Qian, Yaorong; Carr, R. Scott; Miller, Karen

2004-01-01

Bio- and photo-transformation of two munitions and explosives of concern, 2,6-dinitrotoluene (2,6-DNT) and 2,4,6-trinitrophenol (picric acid) were assessed in spiked marine sediments and water. A sandy and a fine-grained sediment, with 0.25% and 1.1% total organic carbon, respectively, were used for biotransformation assessments at 10 and 20 °C. Sterilized sediments were used as controls for biotic vs. abiotic transformation. Transformation products were analyzed by HPLC, GC/MS and LC/MS. Biotransformation in sediments started soon after the initial contact of the chemicals with the sediments and proceeded for several months, with rates in the following sequence: fine-grain at 20 °C > fine-grain at 10 °C > sand at 20 °C > sand at 10 °C. The biotransformation paths seemed to be similar for all conditions. The major biotransformation product of 2,6-DNT was 2-amino-6-nitrotoluene (2-A-6-NT). 2-Nitrotoluene (2-NT) and other minor components, including N,N-dimethyl-3-nitroaniline, benzene nitrile, methylamino-2-nitrosophenol and diaminophenol, were also identified. After more prolonged incubation these chemicals were replaced by high molecular weight polymers. Several breakdown products of picric acid were identified by GC/MS, including 2,4-dinitrophenol, amino dinitrophenols, 3,4-diamino phenol, amino nitrophenol and nitro diaminophenol. Photo-transformation of 2,6-DNT and picric acid in seawater was assessed under simulated solar radiation (SSR). No significant photolysis of picric acid in seawater was observed for up to 47 days, but photo-transformation of 2,6-DNT began soon after the initial exposure to SSR, with 89% being photo-transformed in 24 h and none remaining after 72 h. High molecular weight chemicals were generated, with mass spectra ranging from molecular weight 200–500 compared to 182 for DNT, and the color of the stock solution changed from clear to orange. Complexity of the mass spectra and mass differences among fragments suggest that multiple polymers were produced and were co-eluting during the LC/MS analyses.

Degradation of picric acid and 2,6-DNT in marine sediments and waters: the role of microbial activity and ultra-violet exposure.

PubMed

Nipper, Marion; Qian, Yaorong; Carr, R Scott; Miller, Karen

2004-08-01

Bio- and photo-transformation of two munitions and explosives of concern, 2,6-dinitrotoluene (2,6-DNT) and 2,4,6-trinitrophenol (picric acid) were assessed in spiked marine sediments and water. A sandy and a fine-grained sediment, with 0.25% and 1.1% total organic carbon, respectively, were used for biotransformation assessments at 10 and 20 degrees C. Sterilized sediments were used as controls for biotic vs. abiotic transformation. Transformation products were analyzed by HPLC, GC/MS and LC/MS. Biotransformation in sediments started soon after the initial contact of the chemicals with the sediments and proceeded for several months, with rates in the following sequence: fine-grain at 20 degrees C > fine-grain at 10 degrees C > sand at 20 degrees C > sand at 10 degrees C. The biotransformation paths seemed to be similar for all conditions. The major biotransformation product of 2,6-DNT was 2-amino-6-nitrotoluene (2-A-6-NT). 2-Nitrotoluene (2-NT) and other minor components, including N,N-dimethyl-3-nitroaniline, benzene nitrile, methylamino-2-nitrosophenol and diaminophenol, were also identified. After more prolonged incubation these chemicals were replaced by high molecular weight polymers. Several breakdown products of picric acid were identified by GC/MS, including 2,4-dinitrophenol, amino dinitrophenols, 3,4-diamino phenol, amino nitrophenol and nitro diaminophenol. Photo-transformation of 2,6-DNT and picric acid in seawater was assessed under simulated solar radiation (SSR). No significant photolysis of picric acid in seawater was observed for up to 47 days, but photo-transformation of 2,6-DNT began soon after the initial exposure to SSR, with 89% being photo-transformed in 24 h and none remaining after 72 h. High molecular weight chemicals were generated, with mass spectra ranging from molecular weight 200-500 compared to 182 for DNT, and the color of the stock solution changed from clear to orange. Complexity of the mass spectra and mass differences among fragments suggest that multiple polymers were produced and were co-eluting during the LC/MS analyses.

Regional distribution patterns of chemical parameters in surface sediments of the south-western Baltic Sea and their possible causes

NASA Astrophysics Data System (ADS)

Leipe, T.; Naumann, M.; Tauber, F.; Radtke, H.; Friedland, R.; Hiller, A.; Arz, H. W.

2017-12-01

This study presents selected results of a sediment geochemical mapping program of German territorial waters in the south-western Baltic Sea. The field work was conducted mainly during the early 2000s. Due to the strong variability of sediment types in the study area, it was decided to separate and analyse the fine fraction (<63 μm, mud) from more than 600 surficial samples, combined with recalculations for the bulk sediment. For the contents of total organic carbon (TOC) and selected elements (P, Hg), the regional distribution maps show strong differences between the analysed fine fraction and the recalculated total sediment. Seeing that mud contents vary strongly between 0 and 100%, this can be explained by the well-known grain-size effect. To avoid (or at least minimise) this effect, further interpretations were based on the data for the fine fraction alone. Lateral transport from the large Oder River estuary combined with high abundances and activities of benthic fauna on the shallow-water Oder Bank (well sorted fine sand) could be some main causes for hotspots identified in the fine-fraction element distribution. The regional pattern of primary production as the main driver of nutrient element fixation (C, N, P, Si) was found to be only weakly correlated with, for example, the TOC distribution in the fine fraction. This implies that, besides surface sediment dynamics, local conditions (e.g. benthic secondary production) also have strong impacts. To the best of the authors' knowledge, there is no comparable study with geochemical analyses of the fine fraction of marine sediments to this extent (13,600 km2) and coverage (between 600 and 800 data points) in the Baltic Sea. This aspect proved pivotal in confidently pinpointing geochemical "anomalies" in surface sediments of the south-western Baltic Sea.

Reconstruction of sediment transport pathways in modern microtidal sand flat by multiple classification analysis

NASA Astrophysics Data System (ADS)

Yamashita, S.; Nakajo, T.; Naruse, H.

2009-12-01

In this study, we statistically classified the grain size distribution of the bottom surface sediment on a microtidal sand flat to analyze the depositional processes of the sediment. Multiple classification analysis revealed that two types of sediment populations exist in the bottom surface sediment. Then, we employed the sediment trend model developed by Gao and Collins (1992) for the estimation of sediment transport pathways. As a result, we found that statistical discrimination of the bottom surface sediment provides useful information for the sediment trend model while dealing with various types of sediment transport processes. The microtidal sand flat along the Kushida River estuary, Ise Bay, central Japan, was investigated, and 102 bottom surface sediment samples were obtained. Then, their grain size distribution patterns were measured by the settling tube method, and each grain size distribution parameter (mud and gravel contents, mean grain size, coefficient of variance (CV), skewness, kurtosis, 5, 25, 50, 75, and 95 percentile) was calculated. Here, CV is the normalized sorting value divided by the mean grain size. Two classical statistical methods—principal component analysis (PCA) and fuzzy cluster analysis—were applied. The results of PCA showed that the bottom surface sediment of the study area is mainly characterized by grain size (mean grain size and 5-95 percentile) and the CV value, indicating predominantly large absolute values of factor loadings in primal component (PC) 1. PC1 is interpreted as being indicative of the grain-size trend, in which a finer grain-size distribution indicates better size sorting. The frequency distribution of PC1 has a bimodal shape and suggests the existence of two types of sediment populations. Therefore, we applied fuzzy cluster analysis, the results of which revealed two groupings of the sediment (Cluster 1 and Cluster 2). Cluster 1 shows a lower value of PC1, indicating coarse and poorly sorted sediments. Cluster 1 sediments are distributed around the branched channel from Kushida River and show an expanding distribution from the river mouth toward the northeast direction. Cluster 2 shows a higher value of PC1, indicating fine and well-sorted sediments; this cluster is distributed in a distant area from the river mouth, including the offshore region. Therefore, Cluster 1 and Cluster 2 are interpreted as being deposited by fluvial and wave processes, respectively. Finally, on the basis of this distribution pattern, the sediment trend model was applied in areas dominated separately by fluvial and wave processes. Resultant sediment transport patterns showed good agreement with those obtained by field observations. The results of this study provide an important insight into the numerical models of sediment transport.

Magnetic properties of sediments in cores from the Mandovi estuary, western India: Inferences on provenance and pollution.

PubMed

Prajith, A; Rao, V Purnachandra; Kessarkar, Pratima M

2015-10-15

Magnetic properties of sediments were investigated in 7 gravity cores recovered along a transect of the Mandovi estuary, western India to understand their provenance and pollution. The maximum magnetic susceptibility of sediments was at least 6 times higher in the upper/middle estuary than in lower estuary/bay. The χfd% and χARM/SIRM of sediments indicated coarse, multi-domain and pseudo-single domain magnetic grains, resembling ore material in the upper/middle estuary and coarse stable single domain (SSD) to fine SSD grains in the lower estuary/bay. Mineralogy parameters indicated hematite and goethite-dominated sediments in the upper/middle estuary and magnetite-dominated sediments in the lower estuary/bay. Two sediment types were discernible because of deposition of abundant ore material in the upper/middle estuary and detrital sediment in the lower estuary/bay. The enrichment factor and Index of geo-accumulation of metals indicated significant to strong pollution with respect to Fe and Mn in sediments from the upper/middle estuary. Copyright © 2015 Elsevier Ltd. All rights reserved.

Distribution of surficial sediment in Long Island Sound and adjacent waters: Texture and total organic carbon

USGS Publications Warehouse

Poppe, L.J.; Knebel, H.J.; Mlodzinska, Z.J.; Hastings, M.E.; Seekins, B.A.

2000-01-01

The surficial sediment distribution within Long Island Sound has been mapped and described using bottom samples, photography, and sidescan sonar, combined with information from the geologic literature. The distributions of sediment type and total organic carbon (TOC) reveal several broad trends that are largely related to the sea-floor geology, the bathymetry, and the effects of modern tidal- and wind-driven currents. Sediment types are most heterogeneous in bathymetrically complex and shallow nearshore areas; the heterogeneity diminishes and the texture fines with decreasing bottom-current energy. Lag deposits of gravel and gravelly sand dominate the surficial sediment texture in areas where bottom currents are the strongest (such as where tidal flow is constricted) and where glacial till crops out at the sea floor. Sand is the dominant sediment type in areas characterized by active sediment transport and in shallow areas affected by fine-grained winnowing. Silty sand and sand-silt-clay mark transitions within the basin from higher- to lower-energy environments, suggesting a diminished hydraulic ability to sort and transport sediment. Clayey silt and silty clay are the dominant sediment types accumulating in the central and western basins and in other areas characterized by long-term depositional environments. The amount of TOC in the sediments of Long Island Sound varies inversely with sediment grain size. Concentrations average more than 1.9% (dry weight) in clayey silt, but are less than 0.4% in sand. Generally, values for TOC increase both toward the west in the Sound and from the shallow margins to the deeper parts of the basin floor. Our data also suggest that TOC concentrations can vary seasonally.

Correlating field and laboratory rates of particle abrasion, Rio Medio, Sangre de Cristo Mountains, New Mexico

NASA Astrophysics Data System (ADS)

Polito, P. J.; Sklar, L. S.

2006-12-01

River bed sediments commonly fine downstream due to a combination of particle abrasion, selective transport of finer grains, and fining of the local sediment supply from hillslopes and tributaries. Particle abrasion rates can be directly measured in the laboratory using tumbling barrels and annular flumes, however, scaling experimental particle abrasion rates to the field has proven difficult due to the confounding effects of selective transport and local supply variations. Here we attempt to correlate laboratory and field rates of particle abrasion in a field setting where these confounding effects can be controlled. The Rio Medio, which flows westward from the crest of the Sangre de Cristo Mountains in north central New Mexico, is one of several streams studied by John P. Miller in the early 1960's. Several kilometers downstream of its headwaters, the river crosses the Picuris-Pecos fault. Upstream of the fault the river receives quartzite, sandstone and shale clasts from the Ortega Formation, while downstream sediments are supplied by the Embudo Granite. Because the upstream lithologies are not resupplied downstream of the fault, any observed fining of these clasts should be due only to abrasion and selective transport. We hypothesize that we can account for the effects of selective transport by comparing relative fining rates for the different upstream lithologies from both the field and a laboratory tumbler. By correlating laboratory abrasion rates with rock strength, we can predict the relative fining rates due solely to abrasion expected in the field; differences between the predicted and observed fining rates could then be attributed to selective transport. We used point counts to measure bed surface sediment grain size distributions at 15 locations along a 25 kilometer reach of the Rio Medio, beginning just downstream of the fault and ending upstream of a developed area with disturbed channel conditions. We recorded intermediate particle diameter as well as lithologic composition for 100 clasts at each location. To better characterize the size distribution of poorly represented lithologies we also measured every grain we could find of these minority lithologies within a one square meter area on adjacent bar top surfaces. At each sampling site we also measured channel gradient, and bank-full width and depth. We collected gravel samples for laboratory tumbling experiments and larger bedrock blocks from which we extracted cores for the Brazilian tensile splitting strength test. Preliminary results show very rapid fining of the weak sedimentary rocks downstream of the fault, much less rapid fining of the quartzite and a net downstream coarsening of the granitic sediments, which dominate the bed in the downstream end of the study reach. This enigmatic downstream coarsening may be a legacy of Pliestocene glaciation, which is evident in the landscape upstream of the fault. Outburst floods or debris flows from upstream moraines may have delivered large quantities of coarse sediments to downstream reaches, which are now relatively immobile. Despite these complications, the Rio Medio site may yet provide sufficient information to test our proposed method for scaling laboratory particle abrasion rates to the field.

Dynamics of sediments along with their core properties in the Monastir-Bekalta coastline (Tunisia, Central Mediterranean)

NASA Astrophysics Data System (ADS)

Khiari, Nouha; Atoui, Abdelfattah; Khalil, Nadia; Charef, Abdelkrim; Aleya, Lotfi

2017-10-01

The authors report on two campaigns of high-resolution samplings along the shores of Monastir Bay in Tunisia: the first being a study of sediment dynamics, grain size and mineral composition in surface sediment, and the second, eight months later, using four sediment cores to study grain-size distribution in bottom sediments. Particle size analysis of superficial sediment shows that the sand in shallow depths is characterized by S-shaped curves, indicating a certain degree of agitation, possible transport by rip currents near the bottom and hyperbolic curves illustrating heterogeneity of sand stock. The sediments settle in a relatively calm environment. Along the bay shore (from 0 to 2 m depth), the bottom is covered by medium sand. Sediment transport is noted along the coast; from north to south and from south to north, caused by longshore drift and a rip current in the middle of the bay. These two currents are generated by wind and swell, especially by north to northeast waves which transport the finest sediment. Particle size analysis of bottom sediment indicates a mean grain size ranging from coarse to very fine sands while vertical distribution of grain size tends to decrease from surface to depth. The increase in particle size of sediment cores may be due to the coexistence of terrigenous inputs along with the sedimentary transit parallel to the coast due to the effect of longshore drift. Mineralogical analysis shows that Monastir's coastal sands and bottom sediment are composed of quartz, calcite, magnesium calcite, aragonite and hematite. The existence of a low energy zone with potential to accumulate pollutants indicates that managerial action is necessary to help preserve Monastir Bay.

Pizza or Pancake? Formation Models of Gas Escape Biosignatures in Terrestrial and Martian Sediments

NASA Astrophysics Data System (ADS)

Bonaccorsi, R.; Fairen, A. G.; Baker, L.; McKay, C. P.; Willson, D.

2016-05-01

Fine-grained sedimentary hollowed structures were imaged in Gale Crater, but no biomarkers identified to support biology. Our observation-based (gas escape) terrestrial model could inform on possible martian paleoenvironments at time of formation.

Effect of grain-coating mineralogy on nitrate and sulfate storage in the unsaturated zone

USGS Publications Warehouse

Reilly, T.J.; Fishman, N.S.; Baehr, A.L.

2009-01-01

Unsaturated-zone sediments and the chemistry of shallow groundwater underlying a small (???8-km2) watershed were studied to identify the mechanisms responsible for anion storage within the Miocene Bridgeton Formation and weathered Coastal Plain deposits in southern New Jersey. Lower unsaturated-zone sediments and shallow groundwater samples were collected and concentrations of selected ions (including NO3- and SO42-) from 11 locations were determined. Grain size, sorting, and color of the lower unsaturated-zone sediments were determined and the mineralogy of these grains and the composition of coatings were analyzed by petrographic examination, scanning electron microscopy and energy dispersive analysis of x-rays, and quantitative whole-rock x-ray diffraction. The sediment grains, largely quartz and chert (80-94% w/w), are coated with a very fine-grained (<20 ??m), complex mixture of kaolinite, halloysite, goethite, and possibly gibbsite and lepidocrocite. The mineral coatings are present as an open fabric, resulting in a large surface area in contact with pore water. Significant correlations between the amount of goethite in the grain coatings and the concentration of sediment-bound SO42- were observed, indicative of anion sorption. Other mineral-chemical relations indicate that negatively charged surfaces and competition with SO 42- results in exclusion of NO3- from inner sphere exchange sites. The observed NO3- storage may be a result of matrix forces within the grain coatings and outer sphere complexation. The results of this study indicate that the mineralogy of grain coatings can have demonstrable effects on the storage of NO 3- and SO42- in the unsaturated zone. ?? Soil Science Society of America. All rights reserved.

Sediment source fingerprinting as an aid to catchment management: A review of the current state of knowledge and a methodological decision-tree for end-users

USGS Publications Warehouse

Collins, A.L; Pulley, S.; Foster, I.D.L; Gellis, Allen; Porto, P.; Horowitz, A.J.

2017-01-01

The growing awareness of the environmental significance of fine-grained sediment fluxes through catchment systems continues to underscore the need for reliable information on the principal sources of this material. Source estimates are difficult to obtain using traditional monitoring techniques, but sediment source fingerprinting or tracing procedures, have emerged as a potentially valuable alternative. Despite the rapidly increasing numbers of studies reporting the use of sediment source fingerprinting, several key challenges and uncertainties continue to hamper consensus among the international scientific community on key components of the existing methodological procedures. Accordingly, this contribution reviews and presents recent developments for several key aspects of fingerprinting, namely: sediment source classification, catchment source and target sediment sampling, tracer selection, grain size issues, tracer conservatism, source apportionment modelling, and assessment of source predictions using artificial mixtures. Finally, a decision-tree representing the current state of knowledge is presented, to guide end-users in applying the fingerprinting approach.

In situ acoustic and laboratory ultrasonic sound speed and attenuation measured in heterogeneous soft seabed sediments: Eel River shelf, California

USGS Publications Warehouse

Gorgas, T.J.; Wilkens, R.H.; Fu, S.S.; Neil, Frazer L.; Richardson, M.D.; Briggs, K.B.; Lee, H.

2002-01-01

We compared in situ and laboratory velocity and attenuation values measured in seafloor sediments from the shallow water delta of the Eel River, California. This region receives a substantial volume of fluvial sediment that is discharged annually onto the shelf. Additionally, a high input of fluvial sediments during storms generates flood deposits that are characterized by thin beds of variable grain-sizes between the 40- and 90-m isobaths. The main objectives of this study were (1) to investigate signatures of seafloor processes on geoacoustic and physical properties, and (2) to evaluate differences between geoacoustic parameters measured in situ at acoustic (7.5 kHz) and in the laboratory at ultrasonic (400 kHz) frequencies. The in situ acoustic measurements were conducted between 60 and 100 m of water depth. Wet-bulk density and porosity profiles were obtained to 1.15 m below seafloor (m bsf) using gravity cores of the mostly cohesive fine-grained sediments across- and along-shelf. Physical and geoacoustic properties from six selected sites obtained on the Eel margin revealed the following. (1) Sound speed and wet-bulk density strongly correlated in most cases. (2) Sediment compaction with depth generally led to increased sound speed and density, while porosity and in situ attenuation values decreased. (3) Sound speed was higher in coarser- than in finer-grained sediments, on a maximum average by 80 m s-1. (4) In coarse-grained sediments sound speed was higher in the laboratory (1560 m s-1) than in situ (1520 m s-1). In contrast, average ultrasonic and in situ sound speed in fine-grained sediments showed only little differences (both approximately 1480 m s-1). (5) Greater attenuation was commonly measured in the laboratory (0.4 and 0.8 dB m-1 kHz-1) than in situ (0.02 and 0.65 dB m-1 kHz-1), and remained almost constant below 0.4 m bsf. We attributed discrepancies between laboratory ultrasonic and in situ acoustic measurements to a frequency dependence of velocity and attenuation. In addition, laboratory attenuation was most likely enhanced due to scattering of sound waves at heterogeneities that were on the scale of ultrasonic wavelengths. In contrast, high in situ attenuation values were linked to stratigraphic scattering at thin-bed layers that form along with flood deposits. ?? 2002 Published by Elsevier Science B.V.

Carbonate apron models: Alternatives to the submarine fan model for paleoenvironmental analysis and hydrocarbon exploration

USGS Publications Warehouse

Mullins, H.T.; Cook, H.E.

1986-01-01

Sediment gravity flow deposition along the deep-water flanks of carbonate platforms typically does not produce submarine fans. Rather, wedge-shaped carbonate aprons develop parallel to the adjacent shelf/slope break. The major difference between submarine fans and carbonate aprons is a point source with channelized sedimentation on fans, versus a line source with sheet-flow sedimentation on aprons. Two types of carbonate aprons may develop. Along relatively gentle (< 4??) platform-margin slopes, aprons form immediately adjacent to the shallow-water platform and are referred to as carbonate slope aprons. Along relatively steep (4-15??) platform margin slopes, redeposited limestones accumulate in a base-of-slope setting, by-passing an upper slope via a multitude of small submarine canyons, and are referred to as carbonate base-of-slope aprons. Both apron types are further subdivided into inner and outer facies belts. Inner apron sediments consist of thick, mud-supported conglomerates and megabreccias (Facies F) as well as thick, coarse-grained turbidites (Facies A) interbedded with subordinate amounts of fine-grained, peri-platform ooze (Facies G). Outer apron sediments consist of thinner, grain-supported conglomerates and turbidites (Facies A) as well as classical turbidites (Facies C) with recognizable Bouma divisions, interbedded with approximately equal proportions of peri-platform ooze (Facies G). Seaward, aprons grade laterally into basinal facies of thin, base-cut-out carbonate turbidites (Facies D) that are subordinate to peri-platform oozes (Facies G). Carbonate base-of-slope aprons grade shelfward into an upper slope facies of fine-grained peri-platform ooze (Facies G) cut by numerous small canyons that are filled with coarse debris, as well as intraformational truncation surfaces which result from submarine sliding. In contrast, slope aprons grade shelfward immediately into shoal-water, platform-margin facies without an intervening by-pass slope. The two carbonate apron models presented here offer alternatives to the submarine-fan model for paleoenvironmental analysis and hydrocarbon exploration for mass-transported carbonate facies. ?? 1986.

Effects of soil conditions on survival and growth of black willow cuttings.

PubMed

Schaff, Steven D; Pezeshki, S Reza; Shields, F Douglas

2003-06-01

Current streambank restoration efforts focus on providing bank stability, enhancing water quality, and improving woody habitat using native vegetation rather than traditional engineering techniques. However, in most cases harsh site conditions limit restoration success. A two-year field study was conducted at Twentymile Creek, in northern Mississippi, investigating edaphic factors governing the survival of black willow (Salix nigra) cuttings used for streambank restoration. Low height growth, above-ground biomass production, and average leaf area were observed in willow cuttings grown in plots subjected to moisture deficits. However, sediment texture emerged as the dominant factor determining willow post growth, health, and survival. Shoot biomass, leaf biomass, and total above-ground biomass were 15-, 10-, and 14-fold greater for large willow cuttings (posts) grown in plots with sandy sediments relative to those grown in plots with similar moisture and soil redox potential but with silt and clay sediments. Average leaf size, average leaf mass and specific leaf area were all lower in fine textured plots. Under moisture conditions present at our sites, coarse-grained sediment (sand) was more conducive to willow growth, biomass production, and survival than were fine-grained sediments (silt/clay). Our results strongly suggest that soil texture and moisture conditions can determine restoration success. Therefore, it is critical that site conditions are factored into the selection of project locations prior to the initiation of willow planting restoration projects.

Distribution and Phase Association of Some Major and Trace Elements in the Arabian Gulf Sediments

NASA Astrophysics Data System (ADS)

Basaham, A. S.; El-Sayed, M. A.

1998-02-01

Twenty-four sediment samples were collected from the Arabian Gulf (ROPME Sea) and analysed for their grain size distribution and carbonate contents as well as the major elements Ca, Mg, Fe and Al and macro and trace elements Mn, Sr, Ba, Zn, Cu, Cr, V, Ni and Hg. Concentration of trace elements are found comparable to previous data published for samples taken before and after the Gulf War, and reflect the natural background level. Grain size analyses, aluminium and carbonate measurements support the presence of two major sediment types: (1) a terrigenous, fine-grained and Al rich type predominating along the Iranian side; and (2) a coarse-grained and carbonate rich type predominating along the Arabian side of the Gulf. Investigation of the correlation of the elements analysed with the sediment type indicates that they could be grouped under two distinct associations: (1) carbonate association including Ca and Sr; and (2) terrigenous association comprising Al, Fe, Mg, Ba, Mn, Zn, Cu, Cr, V, Ni and Hg. Element/Al ratios calculated for the mud non-carbonate fraction indicate that the Euphrates and Tigris rivers have minor importance as sediment sources to the Gulf. Most of the elements have exceptionally high aluminium ratios in sediments containing more than 85-90% carbonate. These sediments are restricted to the southern and south-eastern part of the area where depth is shallow and temperature and salinity are high. Both biological accumulation and chemical and biochemical coprecipitation could be responsible for this anomaly.

Effects of coarse woody debris and its removal on a channel affected by the 1980 eruption of Mount St. Helens, Washington

Treesearch

Thomas E. Lisle

1995-01-01

Abstract - During the May 18, 1980, eruption of Mount St. Helens, Washington, a pyroclastic surge introduced large volumes of coarse woody debris (CWD) and fine grained sediment to Clearwater Creek, approximately 15 km northeast of the summit. Effects of controlled CWD removal on sediment storage, substrate, and pool frequency and volume were measured in four reaches,...

Clay mineral distribution and provenance in the Heuksan mud belt, Yellow Sea

NASA Astrophysics Data System (ADS)

Cho, Hyen Goo; Kim, Soon-Oh; Kwak, Kyeong Yoon; Choi, Hunsoo; Khim, Boo-Keun

2015-12-01

The Heuksan mud belt (HMB), located in the southeastern Yellow Sea, runs parallel to the southwest coast of Korea. In this study, the distribution and relative contribution of four major clay minerals are investigated using 101 surface sediment samples collected in the course of KIOST (2001, 2010, 2011) and KIGAM (2012) cruises, as well as 33 river sediment samples (four from the Huanghe River, three from the Changjiang River, and 26 from Korean rivers) in order to clarify the provenance of fine-grained sediments in the HMB. Based on this currently largest and most robust dataset available for interpretation, the clay mineral assemblages of the fine-grained sediments in the HMB are found to be on average composed of 64.7% illite, 17.9% chlorite, 11.4% kaolinite, and 5.9% smectite. Overall, the clay mineral assemblages are similar in both the northern and the southern parts of the HMB, although smectite seems to be relatively enriched in the southern part, whereas kaolinite is slightly more dominant in the northern part. This clearly indicates that the clays are mostly derived from Korean rivers and, in the southern part of the HMB, partly also from the Huanghe River in China. The new data thus confirm and strengthen the tentative interpretation of some earlier work based on a more limited dataset.

Mesozoic (Lower Jurassic) red stromatactis limestones from the Southern Alps (Arzo, Switzerland): calcite mineral authigenesis and syneresis-type deformation

NASA Astrophysics Data System (ADS)

Neuweiler, Fritz; Bernoulli, Daniel

2005-02-01

The Broccatello lithological unit (Lower Jurassic, Hettangian to lower parts of Upper Sinemurian) near the village of Arzo (southern Alps, southern Switzerland) is a mound-shaped carbonate deposit that contains patches of red stromatactis limestone. Within the largely bioclastic Broccatello unit, the stromatactis limestone is distinguished by its early-diagenetic cavity system, a relatively fine-grained texture, and an in-situ assemblage of calcified siliceous sponges (various demosponges and hexactinellids). A complex shallow subsurface diagenetic pathway can be reconstructed from sediment petrography in combination with comparative geochemical analysis (carbon and oxygen isotopes; trace and rare earth elements, REE + Y). This pathway includes organic matter transformation, aragonite and skeletal opal dissolution, patchy calcification and lithification, sediment shrinkage, sagging and collapse, partial REE remobilization, and multiple sediment infiltration. These processes occurred under normal-marine, essentially oxic conditions and were independent from local, recurring syn-sedimentary faulting. It is concluded that the stromatactis results from a combination of calcite mineral authigenesis and syneresis-type deformation. The natural stromatactis phenomenon may thus be best explained by maturation processes of particulate polymer gels expected to form in fine-grained carbonate sediments in the shallow subsurface. Conditions favorable for the evolution of stromatactis appear to be particularly frequent during drowning of tropical or subtropical carbonate platforms.

Fluvial gravel stabilization by net-spinning Hydropsychid caddisflies: exploring the magnitude and geographic scope of ecosystem engineering effect and evaluating resistance to anthropogenic stresses

NASA Astrophysics Data System (ADS)

Daniels, M.; Albertson, L.; Sklar, L. S.; Tumolo, B.; Mclaughlin, M. K.

2017-12-01

Several studies have demonstrated the substantial effects that organisms can have on earth surface processes. Known as ecosystem engineers, in streams these organisms maintain, modify, or create physical habitat structure by influencing fluvial processes such as gravel movement, fine sediment deposition and bank erosion. However, the ecology of ecosystem engineers and the magnitude of ecosystem engineering effects in a world increasingly influence by anthropogenically-driven changes is not well understood. Here we present a synthesis of research findings on the potential gravel stabilization effects of Hydropsychid caddisflies, a globally distributed group of net-spinning insects that live in the benthic substrate of most freshwater streams. Hydropsychid caddisflies act as ecosystem engineers because these silk structures can fundamentally alter sediment transport conditions, including sediment stability and flow currents. The silk nets spun by these insects attach gravel grains to one another, increasing the shear stress required to initiate grain entrainment. In a series of independent laboratory experiments, we investigate the gravel size fractions most affected by these silk attachments. We also investigate the role of anthropogenic environmental stresses on ecosystem engineering potential by assessing the impact of two common stressors, high fine sediment loads and stream drying, on silk structures. Finally, an extensive field survey of grain size and Hydropsychid caddisfly population densities informs a watershed-scale network model of Hydropsychid caddisfly gravel stabilizing potential. Our findings provide some of the first evidence that caddisfly silk may be a biological structure that is resilient to various forms of human-mediated stress and that the effects of animal ecosystem engineers are underappreciated as an agent of resistance and recovery for aquatic communities experiencing changes in sediment loads and hydrologic regimes.

The 1845 Hekla eruption: Grain-size characteristics of a tephra layer

NASA Astrophysics Data System (ADS)

Gudnason, Jonas; Thordarson, Thor; Houghton, Bruce F.; Larsen, Gudrun

2018-01-01

The 1845 eruption is commonly viewed as a typical Hekla eruption. It is a key event in the eruptive history of the volcano, as it is one of the best documented Hekla eruptions, in terms of contemporary accounts and observations. The eruption started on 2 September 1845 with an intense, hour long explosive Plinian phase that passed into effusive activity, ending on the 16 March 1846. The amount of tephra produced in the opening phase was 0.13 km3/7.5 × 1010 kg. The total grain-size distribution of the deposit is bimodal with a dominant coarse mode at - 2.5 φ (5.6 mm) and a broad finer mode at 3 to 4.5 φ (0.125 to 0.045 mm). At individual sites, the grain-size distribution of the tephra from the Plinian opening phase is also commonly (not always) bimodal. Deconvolved grain-size distributions exhibit distinctly different sedimentation patterns of the coarse and fine subpopulations. The lapilli-dominated subpopulation fines rapidly with transport, while the ash-dominated subpopulation shows less changes with distance, indicating premature sedimentation of fines by aggregation from the 1845 volcanic plume. Tephra deposition was to the ESE of the volcano from a 19 km (a.s.l.) high eruption plume. The plume front travelled at speeds of 16-19 m s- 1. Reports of ash deposition onto ships near the Faroe and Shetland Islands, 700 to 1100 km away from Hekla, demonstrate that even moderate-sized Hekla eruptions can affect very large parts of European air-space.

Shoreline erosion and decadal sediment accumulation in the Tar-Pamlico estuary, North Carolina, USA: A source-to-sink analysis

NASA Astrophysics Data System (ADS)

Eulie, Devon O.; Corbett, D. Reide; Walsh, J. P.

2018-03-01

Estuaries contain vital habitats and it is important to understand how these areas respond to human activities and natural processes such as sea-level rise and wave attack. As estuarine shorelines erode or become modified with hard structures, there is potential for significantly altering the availability of sediment and the filling of coastal systems. This study used a source-to-sink approach and quantified rates of shoreline erosion in the Tar-Pamlico sub-estuary, a tributary of the larger Albemarle-Pamlico Estuarine System (APES). The average shoreline change rate (SCR) determined using an end-point method was -0.5 ± 0.9 m yr-1 for the Tar-Pamlico. Incorporating bulk density estimates, this contributes 0.6 × 105 tons of fine sediment to the system annually, or after accounting for fluvial input, about 40% of the total sediment supply to the sub-estuary. The role of the Tar-Pamlico as a sink for these sediments was addressed using the radionuclide tracers 210Pb and 137Cs. Radionuclide activities and sediment accumulation rates identified several depositional regions, in particular in the middle of the estuary. Linear sediment accumulation rates ranged from 0.10 ± 0.02 to 0.38 ± 0.02 g cm-2 yr-1, and total storage of fine sediment in the system was 1.6 × 105 t yr-1. It was not possible to confidently discern a change in the rate of shoreline erosion or seabed accumulation. A preliminary budget for fine sediments (grain-size <63 μm) was then calculated to compare erosional sources with sedimentary sinks. Almost all (∼93.0%) of the fine sediment entering the system was accumulated and stored, while only about 7.0% was exported to Pamlico Sound.

Physical processes dominate in shaping invertebrate assemblages in reef-associated sediments of an exposed Hawaiian coast

USGS Publications Warehouse

DeFelice, R.C.; Parrish, J.D.

2001-01-01

The invertebrate assemblages in sediments bordering exposed fringing reefs at Hanalei Bay, Kauai, Hawaii, were examined during July to September 1994. Densities of invertebrate animals larger than 0.5 mm in sediments of the bay ranged from counts of 10 260 m-2 in the fine carbonate sands of the central bay to 870 m-2 in the habitat dominated by terrigenous silt near the reef edge close to the Hanalei river mouth. Similar sediment types supported broadly similar infaunal communities. Within the primarily carbonate sediments, mean grain size and wave exposure appear to have an important influence on the community. Taxonomic richness, number of individuals, and diversity showed significant negative relationships with exposure to wave energy (as estimated by sand ripple wavelength). The number of individuals was also significantly correlated with mean grain size. Overall, polychaetes and small crustaceans were numerically dominant among the major taxonomic groups investigated. Macrophagous and microphagous polychaetes had significant, but opposite, associations with grain size. In addition, microphagous polychaetes were significantly negatively correlated with wave exposure. No habitat variable measured could explain the variation in percent composition of crustaceans or echinoderms in the sedimentary habitats. The percentage of gastropods in the community was significantly negatively correlated with grain size, grain-size standard deviation and exposure, and positively with percent organic carbon. Bivalves were significantly positively associated with depth and grain size. These strong relationships imply that, in Hanalei Bay, physical processes are especially important in influencing assemblage structure, and that community structure and composition vary continuously along environmental gradients.

Sediment Connectivity and Transport Pathways in Tidal Inlets: a Conceptual Framework with Application to Ameland Inlet

NASA Astrophysics Data System (ADS)

Pearson, S.; van Prooijen, B. C.; Zheng Bing, W.; Bak, J.

2017-12-01

Predicting the response of tidal inlets and adjacent coastlines to sea level rise and anthropogenic interventions (e.g. sand nourishments) requires understanding of sediment transport pathways. These pathways are strongly dependent on hydrodynamic forcing, grain size, underlying morphology, and the timescale considered. To map and describe these pathways, we considered the concept of sediment connectivity, which quantifies the degree to which sediment transport pathways link sources to receptors. In this study we established a framework for understanding sediment transport pathways in coastal environments, using Ameland Inlet in the Dutch Wadden Sea as a basis. We used the Delft3D morphodynamic model to assess the fate of sediment as it moved between specific morphological units defined in the model domain. Simulation data was synthesized in a graphical network and then graph theory used to analyze connectivity at different space and time scales. At decadal time scales, fine and very fine sand (<250μm) have greater connectivity with receptor areas further away from their sources. Conversely, medium sand (>250μm) shows lower connectivity, even in more energetic areas. Greater sediment connectivity was found under the influence of wind and waves when compared to purely tidal forcing. Connectivity shows considerable spatial variation in cross shore and alongshore directions, depending on proximity to the inlet and dominant wave direction. Furthermore, connectivity generally increases at longer timescales. Asymmetries in connectivity (i.e. unidirectional transport) can be used to explain long-term erosional or depositional trends. As such, an understanding of sediment connectivity as a function of grain size could yield useful insights for resolving sediment transport pathways and the fate of a nourishment in coastal environments.

Ecological and taphonomical influences on coccoliths in surface sediments in the shelf of the Yellow and East China Seas

NASA Astrophysics Data System (ADS)

Jin, Xiaobo; Liu, Chuanlian

2017-05-01

Coccoliths, combined with sediment grain size, carbonate calcium and organic matters content, were analyzed to assess the ecological and taphonomical influences on coccolith distribution patterns in surface sediments in the continental shelf of the Yellow and East China Seas. Coccolith abundances ranged from 0 to 2.08×109 coccoliths g-1 sediment. The increasing abundance from the coastal inner shelf to the seaward middle shelf generally reflects the ecological fact that living coccolithophores are more abundant in the mesotrophic shelf waters than in the eutrophic coastal waters, although their deposits are still controlled by taphonomical effects, such as bottom (tidal) currents and calcite preservation conditions. Most abundant coccoliths are found in the fine-grained sediments of southwestern Cheju Island, where both ecology and taphonomy favor coccolith preservation. Still, large densities of coccoliths (>108 coccoliths g-1 sediment) are also found in coarse-grained relict sediments in the middle shelf. Coccolith assemblages were predominated by Gephyrocapsa oceanica and Emiliania huxleyi. The relative abundance of E. huxleyi, in addition to ecological reasons, may relate to selective post-mortem dissolution, since small E. huxleyi coccoliths are more susceptible to dissolution. Coccolith calcite has minor contributions (<1% to 12%) to total sediment CaCO3, and the main parts are attributed to terrigenous CaCO3 debris and relict shell fragments.

Geohydrology of the Valley-Fill Aquifer in the Norwich-Oxford-Brisben Area, Chenango County, New York

USGS Publications Warehouse

Hetcher, Kari K.; Miller, Todd S.; Garry, James D.; Reynolds, Richard J.

2003-01-01

This set of maps and geohydrologic sections depicts the geology and hydrology of aquifers in the 21.9-square-mile reach of the Chenango River valley between Brisben and North Norwich, N.Y. This report depicts the principal geographic features of the study area; locations of domestic, commercial, and municipal wells from which data were obtained to construct water-table and saturated-thickness maps and five geohydrologic sections; surficial geology; water-table altitude; generalized saturated thickness of the unconfined (water-table) aquifer; generalized thickness of the discontinuous series of confined aquifers; and five geohydrologic sections, all of which are in the northern part of the study area.The unconsolidated material in the Chenango River valley consists primarily of three types of deposits: (1) glaciofluvial material consisting of stratified coarse-grained sediment (sand and gravel) that was deposited by meltwater streams flowing above, below, or next to a glacier; (2) glaciolacustrine material consisting of stratified fine-grained sediment (very fine sand, silt, and clay) that was deposited in lakes that formed at the front of a glacier; and (3) recent alluvial material consisting of stratified fine-to-medium grained sediment (fine-to-medium sand and silt) that was deposited on flood plains.The water-table map was compiled from water-level data obtained from wells completed in the unconfined aquifer, and from altitudes of stream and river surfaces indicated on 1:24,000-scale topographic maps. Depth to the water table ranged from less than 5 feet below land surface near major streams to more than 75 feet on some of the kame terraces along the valley walls. Saturated thickness of the unconfined aquifer ranged from less than 1 foot near Norwich to more than 200 feet at a kame delta north of Oxford.A discontinuous series of confined aquifers is present throughout much of the Chenango River valley north of Oxford. These aquifers consist of kame deposits, eskers, and subglacial outwash sand and gravel deposits that are overlain and confined by lacustrine fine sand, silt, and clay. The saturated thickness of these aquifers is as much as 150 feet near North Norwich.

New Support for Hypotheses of an Ancient Ocean on Mars

NASA Technical Reports Server (NTRS)

Oehler, Dorothy Z.; Allen, Carlton C.

2013-01-01

A new analog for the giant polygons in the Chryse-Acidalia area suggests that those features may have formed in a major body of water - likely a Late Hesperian to Early Amazonian ocean. This analog -terrestrial polygons in subsea, passive margin basins derives from 3D seismic data that show similar-scale, polygonal fault systems in the subsurface of more than 50 terrestrial offshore basins. The terrestrial and martian polygons share similar sizes, basin-wide distributions, tectonic settings, and association with expected fine-grained sediments. Late Hesperian deposition from outflow floods may have triggered formation of these polygons, by providing thick, rapidly-deposited, fine-grained sediments necessary for polygonal fracturing. The restriction of densely occurring polygons to elevations below approx. -4000 m to -4100 m supports inferences that a body of water controlled their formation. Those same elevations appear to restrict occurrence of polygons in Utopia Planitia, suggesting that this analog may apply also to Utopia and that similar processes may have occurred across the martian lowlands.

Biostratinomic processes for the development of mud-cast logs in Carboniferous and Holocene swamps

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gastaldo, R.A.; Demko, T.M.; Liu, Yuejin

1989-08-01

Prostrate trees are common features of fossil forest litters, and are frequently preserved as mud-casts. Specimens of Carboniferous mud-cast trees and a mud-filled incipient cast of a Holocene Taxodium have been investigated to determine the biostratinomic processes responsible for their formation. These processes are complex. Hollowing of tree trunks may take place during life or by degradation after death. Once the trunk has fallen, the hollow cavity is supported by surrounding wood and/or bark tissues and acts as a conduit for sediment-laden waters. Leaf litter may be preserved on bedding surfaces. The infilling sequence of horizontal, parallel bedded, fine-grained sedimentmore » is deposited from suspended load during multiple overbank flooding events. These results differ from experimentally produced pith casts in which the sediment grain size is of fine sand. In Holocene specimens, alluvial mud within the log may provide a substrate for infaunal invertebrates. No evidence of infaunal burrowing in Carboniferous analogues exists.« less

Martian crater degradation by eolian processes: Analogy with the Rio Cuarto Crater Field, Argentina

NASA Technical Reports Server (NTRS)

Grant, J. A.; Schultz, P. H.

1993-01-01

Numerous degraded and rimless craters occur across broad areas of the Martian surface that are mantled by thick, unconformable deposits. These regions include Arabia, Mesogaea, Electris, Tempe, the interior and surface to the northwest of Isidis Basin, southern Ismenius Lacus, and the polar layered terrains. Occurrence of the deposits and low regional thermal inertias indicate that at least some accumulated fine-grained sediment (effective particle diameters of 0.1-0.5 mm or coarse silt to medium sand) to a thickness of 100's to 1000's of meters. Most unconformable deposits experienced some eolian modification that may be recent in some locales. Despite the presence of these deposits, simple eolian deposition appears incapable of creating the numerous degraded and rimless craters occurring within their limits. Nevertheless, terrestrial analyses of the Rio Cuario craters formed into loessoid deposits demonstrates that eolian redistribution of fine-grained sediment in and around craters produces degraded morphologies that are analogous to some found in mantled regions on Mars.

A comparison of instrumental dewatering methods for the separation and concentration of suspended sediment for subsequent trace element analysis

USGS Publications Warehouse

Horowitz, A.J.; Elrick, K.A.; Hooper, R.C.

1989-01-01

The continuous-flow centrifuges can process whole water at an influent feed rate of 41 per minute; however, when suspended sediment concentrations are low (<30 mg l-1), when small volumes of whole water are to be processed (30 to 401), or when suspended sediment mean grain size is very fine (<10 ??m), influent feed rates of 21 per minute may be more efficient. Tangential-flow filtration can be used to process samples at the rate of 11 per minute. -from Authors

Textural characteristics and sedimentary environment of sediment at eroded and deposited regions in the severely eroded coastline of Batu Pahat, Malaysia.

PubMed

Wan Mohtar, Wan Hanna Melini; Nawang, Siti Aminah Bassa; Abdul Maulud, Khairul Nizam; Benson, Yannie Anak; Azhary, Wan Ahmad Hafiz Wan Mohamed

2017-11-15

This study investigates the textural characteristics of sediments collected at eroded and deposited areas of highly severed eroded coastline of Batu Pahat, Malaysia. Samples were taken from systematically selected 23 locations along the 67km stretch of coastline and are extended to the fluvial sediments of the main river of Batu Pahat. Grain size distribution analysis was conducted to identify its textural characteristics and associated sedimentary transport behaviours. Sediments obtained along the coastline were fine-grained material with averaged mean size of 7.25 ϕ, poorly sorted, positively skewed and has wide distributions. Samples from eroded and deposition regions displayed no distinctive characteristics and exhibited similar profiles. The high energy condition transported the sediments as suspension, mostly as pelagic and the sediments were deposited as shallow marine and agitated deposits. The fluvial sediments of up to 3km into the river have particularly similar profile of textural characteristics with the neighbouring marine sediments from the river mouth. Profiles were similar with marine sediments about 3km opposite the main current and can go up to 10km along the current of Malacca Straits. Copyright © 2017 Elsevier B.V. All rights reserved.

Palaeoenvironments and palaeotectonics of the arid to hyperarid intracontinental latest Permian- late Triassic Solway basin (U.K.)

NASA Astrophysics Data System (ADS)

Brookfield, Michael E.

2008-10-01

The late Permian to late Triassic sediments of the Solway Basin consist of an originally flat-lying, laterally persistent and consistent succession of mature, dominantly fine-grained red clastics laid down in part of a very large intracontinental basin. The complete absence of body or trace fossils or palaeosols indicates a very arid (hyperarid) depositional environment for most of the sediments. At the base of the succession, thin regolith breccias and sandstones rest unconformably on basement and early Permian rift clastics. Overlying gypsiferous red silty mudstones, very fine sandstones and thick gypsum were deposited in either a playa lake or in a hypersaline estuary, and their margins. These pass upwards into thick-bedded, multi-storied, fine- to very fine-grained red quartzo-felspathic and sublithic arenites in which even medium sand is rare despite channels with clay pebbles up to 30 cm in diameter. Above, thick trough cross-bedded and parallel laminated fine-grained aeolian sandstones (deposited in extensive barchanoid dune complexes) pass up into very thick, multicoloured mudstones, and gypsum deposited in marginal marine or lacustrine sabkha environments. The latter pass up into marine Lower Jurassic shales and limestones. Thirteen non-marine clastic lithofacies are arranged into five main lithofacies associations whose facies architecture is reconstructed where possible by analysis of large exposures. The five associations can be compared with the desert pavement, arid ephemeral stream, sabkha, saline lake and aeolian sand dune environments of the arid to hyperarid areas of existing intracontinental basins such as Lake Eyre and Lake Chad. The accommodation space in such basins is controlled by gradual tectonic subsidence moderated by large fluctuations in shallow lake extent (caused by climatic change and local variation) and this promotes a large-scale layer-cake stratigraphy as exemplified in the Solway basin. Here, the dominant fine-grained mature sandstones above the local basal reg breccias suggest water-reworking of wind-transported sediment, as in the northern part of the Lake Chad basin. Growth faulting occurs in places in the Solway basin, caused by underlying evaporite movement, but these faults did not significantly affect pre-late Triassic sedimentation and did not expose pre-Permian units above the basal breccias. There is no evidence of post-early Permian rifting anywhere during deposition of the late Permian to middle Triassic British succession although the succession is often interpreted with a rift-basin model. The arid to hyperarid palaeoclimate changed little during deposition of the Solway basin succession, in contrast to Lakes Eyre and Chad: and this is attributed to tectonic and palaeolatitude stability. Unlike the later Mesozoic- Cenozoic, only limited plate movements took place during the Triassic in western Europe, palaeolatitude changed little, and the Solway Basin remained in the northern latitudinal desert belt from early to mid-Triassic times. However, the influence of the early Triassic impoverished biota on environmental interpretations needs further study.

Beneficial reuse of fly ashes in geotechnical engineering with physicochemical and electron microscopic methods.

DOT National Transportation Integrated Search

2013-06-01

The sedimentation behavior of fine grained soil is largely dependent on its pore fluid chemistry. Physicochemical properties of the : pore fluid, such as ionic strength and pH, could greatly influence the micro structure of kaolinite which in turn in...

Numerical modelling of fine-grained sediments remobilization in heavily polluted streams. Case study: Elbe and Bílina River, Czech Republic.

NASA Astrophysics Data System (ADS)

Kaiglová, Jana; Langhammer, Jakub; Jiřinec, Petr; Janský, Bohumír; Chalupová, Dagmar

2014-05-01

The study aimed to estimate remobilization of channel and riparian cohesive sediment of streams, heavily polluted by industrial emmissions. There were analyzed four stream stretches in Czech Republic: (1) Elbe River from Usti nad Labem to the boundary with Germany; (2) Bílina river, draining industrial and mining areas of Northwest Bohemia; (3) Midstream reach of Czech Elbe by the confluence with Vltava river, affected by chemical industry and (4) fluvial lakes in the riparian zone of Czech Elbe river downstream of Pardubice burdened by old loads from heavy chemical industry. Sediments of clay and silt character bedded in the riparian water-courses are regarded heavily polluted by wide range of toxic matters. In the sediment samples, there were found elevated concentrations of persistent organic matters (DDT, PCB, HCH, Fluoranthen), Heavy metals (Hg, As, Cd), and others. The pollution in sediment is resulting from the unregulated heavy industrial production in the area in the second half of 20th century during the socialistic regime in Czech republic that still play an important role in Elbe river water quality. The main goal of the study was to evaluate the risk of remobilization of polluted sediments by the assessment of discharge (values and return periods), initiating remobilization of sediment from the river bed. The modeling stems on basic assumption, that once the sediment is elevated from the bed, it could be transported far downstream in the form of suspended load. The evaluation was made on the basis of numerical hydrodynamic calculation coupled with sediment transport model. The MIKE by DHI modelling software with different levels of schematization was used according the flow conditions and available data sources. For 50 km stretch of Bílina river the 1D schematization (MIKE 11) was selected as the discharges driving remobilization were expected within the extent of channel capacity due to the stream regulation. For the lower and middle course of Elbe river and the riparian sediment evaluation the 2D schematization (MIKE 21 C) was selected. It enabled to distinguish flow characteristics in the zone with complicated hydrodynamic conditions. The risk of remobilization of fine-grained sediments was evaluated in order to define a threshold discharge value after that the spreading of pollution can be expected. The major contribution of the study, realized in the framework of international iniciative ELSA was the identification of threshold values for potential remobilization of sediment burdened by old loads in different environments. These threshold values are important information for identification and mitigation of risks related with old loads and hydrological extremes. From methodological point of view the study verified validity of applied distinct approaches for fine-grained sediment remobilization assessment and identified limits for their application. Key words: sediment, remobilization, old loads, modelling, hydrodynamics, Elbe river

Measuring Density Stratification and Understanding its Impact on Sediment Transport in Fine-grained Rivers, Based on Observations from the Lower Yellow River, China

NASA Astrophysics Data System (ADS)

Moodie, A. J.; Nittrouer, J. A.; Ma, H.; Lamb, M. P.; Carlson, B.; Kineke, G. C.; Parker, G.

2017-12-01

High concentrations of suspended sediment in channelized fluid flow produces density stratification that can alter the turbulent flow structure, thus limiting fluid momentum redistribution and affecting sediment transport capacity. A low channel-bed slope and large flow depth are hypothesized to be additional important factors contributing to density stratification. However, there are limited observations of density stratification in large rivers, especially those that carry significant fluxes of mud, and so the conditions leading to the development of density stratification are poorly constrained. The Yellow River, China, is a fine-grained and low-sloping river that maintains some of the highest suspended sediment concentrations in large rivers worldwide, making it an ideal natural laboratory for studying density stratification and its impact on sediment transport. Suspended sediment samples from the lower Yellow River, collected over a range of discharge conditions, produced sediment concentration profiles that are used in conjunction with velocity profiles to determine the threshold shear velocity for density stratification effects to develop. Comparing measured and predicted concentration and velocity profiles demonstrates that, there is no significant density stratification for base flow conditions; however, above a shear velocity value of 0.05 m/s, there is a progressive offset between the measured and predicted profiles, indicating that density stratification is increasingly important with higher shear stress values. The analyses further indicate that sediment entrainment from the bed and sediment diffusivity within the water column are significantly impacted by density stratification, suggesting that shear stress and sediment transport rates are inhibited by the development of density stratification. Near-bed concentration measurements are used to assess a stress-to-entrainment relationship, accounting for density stratification. These measurements are being used to refine relations for sediment entrainment and sediment flux in sandy and muddy, lowland rivers and deltas.

Quaternary Turbidite Sedimentation in the Moresby Trough, Preliminary Observations from the Papua New Guinea S2S Study Area

NASA Astrophysics Data System (ADS)

Bentley, S. J.; Muhammad, Z.; Dickens, J.; Droxler, A.; Peterson, L.; Opdyke, B.

2004-12-01

Multicores and jumbo piston cores were collected from the Moresby Trough from the R/V Melville in March-April 204 to study patterns of off-shelf sediment flux from the Gulf of Papua to the deep sea over Pleistocene-Holocene timescales. The Moresby Trough represents the primary deep-sea sediment conduit linking the Source to Sink Gulf of Papua study area to the north with the Coral Sea Basin to the south. Core locations were navigated from the surface using dynamic positioning and multibeam bathymetric mosaics collected during the cruise. Selected cores have been analyzed using a multi-sensor core logger, X-radiography, granulometry, and Pb-210 geochronology. Most piston cores collected from the Moresby Trough contain abundant mafic sandy turbidites overlain by fine-grained hemipelagic deposits 1-2 m thick. X-radiographs of multicores reveal mostly bioturbated hemipelagics. However, one core, MV25-0403-24MC, was collected from the axis of a primary channel, and contains at least two fine-grained turbidites within the upper 0.5 m of sediment. The uppermost turbidite contains low but uniform activities of excess Pb-210, and may have been 15-20 cm thick at the time of deposition (i.e., before subsequent disruption by bioturbation), based on fabric and radiochemical evidence. Application of a simple box-model for physical mixing (i.e., during the flow) and subsequent decay suggests that the uppermost turbidite was deposited 70-120 years before present. Bioturbation has since reworked about 60% of the bed, suggesting that such beds will only escape destruction by bioturbation if they are > 10 cm thick, and are deposited more frequently than once per century. Based on these observations, we suggest that gravity flows are presently active in the Moresby trough, and may account for a significant fraction of the hemipelagic drape present in channel systems. However, fabric evidence for these thin, fine-grained beds may be obscured by subsequent bioturbation. Also, at some point in the past, possibly at the onset of the Holocene Transgression, the character of sediment flux to the Moresby Trough shifted from sandy mafic-rich sandy turbidity currents to much finer sediments, delivered downslope by both benthic flows and vertical flux through the water column.

Sediment source fingerprinting as an aid to catchment management: A review of the current state of knowledge and a methodological decision-tree for end-users.

PubMed

Collins, A L; Pulley, S; Foster, I D L; Gellis, A; Porto, P; Horowitz, A J

2017-06-01

The growing awareness of the environmental significance of fine-grained sediment fluxes through catchment systems continues to underscore the need for reliable information on the principal sources of this material. Source estimates are difficult to obtain using traditional monitoring techniques, but sediment source fingerprinting or tracing procedures, have emerged as a potentially valuable alternative. Despite the rapidly increasing numbers of studies reporting the use of sediment source fingerprinting, several key challenges and uncertainties continue to hamper consensus among the international scientific community on key components of the existing methodological procedures. Accordingly, this contribution reviews and presents recent developments for several key aspects of fingerprinting, namely: sediment source classification, catchment source and target sediment sampling, tracer selection, grain size issues, tracer conservatism, source apportionment modelling, and assessment of source predictions using artificial mixtures. Finally, a decision-tree representing the current state of knowledge is presented, to guide end-users in applying the fingerprinting approach. Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.

Diagenesis in subrecent marine sediments in the Eastern Scheldt, Southwest Netherlands

NASA Astrophysics Data System (ADS)

Oenema, O.

The diagenesis in fine-grained sediments from a 300 to 400-years-old Dunkirk deposit, exposed on the intertidal flat, was studied at a site in the Eastern Scheldt. A new in situ pore water sampling technique that allowed repeated sampling at exactly the same place was used to monitor the seasonal fluctuations in interstitial water composition. Concentrations of organic carbon (1.5 to 2%), nitrogen (C/N = 19), phosphorus (500 μg·g -1) and manganese (250 μg·g -1) in the subrecent anoxic sediments were low, probably because they had already been depleted during earlier stages of diagenesis. Rates of organic carbon mineralization by sulphate reduction (0.1 Mole·m -2·y -1) and rates of nutrient regeneration were 1 to 2 orders of magnitude lower than in recent fine-grained sediments elsewhere in the Eastern Scheldt. Pore water NH 4+ and ΣPO 4 concentrations were controlled by mineralization, uptake by Zostera noltii and sediment-seawater exchange. During the summer the uptake exceeded the mineralization rate at 0 to 5 cm. Mineralization and diffusional processes dominated the changes in the NH 4+ and ΣPO 4 profiles in the other seasons. Dissolved manganese and iron concentrations showed a typical subsurface maximum at 0 to 3 cm, and low (<5 μMole) concentrations below this depth. Dissolved iron concentrations were probably controlled by the solubility of iron sulphides, and manganese probably by the solubility of Mn, Ca-carbonate.

Accumulation of trace elements, pesticides, and polychlorinated biphenyls in sediments and the clam Corbicula manilensis of the Apalachicola River, Florida

USGS Publications Warehouse

Elder, J.F.; Mattraw, H.C.

1984-01-01

A survey of trace element and synthetic organic compound concentrations in botton materials was conducted on the Apalachichola River in northwest Florida in 1979-80 as part of the Apalachicola River Quality Assessment. Substances analyzed included trace elements (predominantly heavy metals), organochlorine insecticides, organophosphorus insecticides, chlorinated phenoxy-acid herbicides, and polychlorinated biphenyls (PCBs). Three kinds of materials were surveyed: fine-grained sediments, whole-body tissue of the Asiatic clam Corbicula manilensis, and bottom-load organic detritus. No hazardous levels of any of the substances were found. Concentrations in the fine-grained sediments and clams were generally at least ten times lower than maximum limits considered safe for biota of aquatic systems. A comparison of trace-substance data from the Apalachicola River with data from Lake Seminole (upstream) and Apalachicola Bay (downstream) showed lower concentrations in riverine clams. Sediment concentrations in all parts of the system were comparable. Most trace substances in the Apalachicola River enter the river from the upstream part of the basin (the Chattahoochee and Flint Rivers in Georgia and Alabama) and from nonpoint sources throughout the basin. There are no major point discharges along the Apalachicola. Trend analysis was limited by the scope of the study, but did not reveal any spatial or temporal trends in concentrations of any of the substances analyzed. Concentrations of organic compounds and most metals in Corbicula manilensis did not correlate with those in sediments.

Changes to channel sediments resulting from complex human impacts in a gravel-bed river, Polish Carpathians

NASA Astrophysics Data System (ADS)

Zawiejska, Joanna; Wyżga, Bartłomiej; Hajdukiewicz, Hanna; Radecki-Pawlik, Artur; Mikuś, Paweł

2016-04-01

During the second half of the twentieth century, many sections of the Czarny Dunajec River, Polish Carpathians, were considerably modified by channelization as well as gravel-mining and the resultant channel incision (up to 3.5 m). This paper examines changes to the longitudinal pattern of grain size and sorting of bed material in an 18-km-long river reach. Surface bed-material grain size was established on 47 gravel bars and compared with a reference downstream fining trend of bar sediments derived from the sites with average river width and a vertically stable channel. Contrary to expectations, the extraction of cobbles from the channel bed in the upper part of the study reach, conducted in the past decades, has resulted in the marked coarsening of bed material in this river section. The extraction facilitated entrainment of exposed finer grains and has led to rapid bed degradation, whereas the concentration of flood flows in the increasingly deep and narrow channel has increased their competence and enabled a delivery of the coarse particles previously typical of the upstream reach. The middle section of the study reach, channelized to prevent sediment delivery to a downstream reservoir, now transfers the bed material flushed out from the incising upstream section. With considerably increased transport capacity of the river and with sediment delivery from bank erosion eliminated by bank reinforcements, bar sediments in the channelized section are typified by increased size of the finer fraction and better-than-average sorting. In the wide, multi-thread channel in the lower part of the reach, low unit stream power and high channel-form roughness facilitate sediment deposition and are reflected in relatively fine grades of bar gravels. The study showed that selective extraction of larger particles from the channel bed leads to channel incision at and upstream of the mining site. However, unlike bulk gravel mining, selective extraction does not result in sediment deficit downstream as large volumes of finer bed material are flushed out from the incising channel section. Grain-size analyses of bulk gravels and measurements of 100 coarsest particles within the channel sediment ranging in age from 5200 years BP to the present, performed in this deeply incised section, indicated that grain size of channel sediments changed relatively little since mid-Holocene to the 1960s, but has increased rapidly over the last half-century as a result of human interventions and rapidly progressing channel incision. This study was performed within the scope of the Research Project DEC-2013/09/B/ST10/00056 financed by the National Science Centre of Poland.

Lower Cretaceous smarl turbidites of the Argo Abyssal Plain, Indian Ocean

USGS Publications Warehouse

Dumoulin, Julie A.; Stewart, Sondra K.; Kennett, Diana; Mazzullo, Elsa K.

1992-01-01

Sediments recovered during Ocean Drilling Program (ODP) Leg 123 from the Argo Abyssal Plain (AAP) consist largely of turbidites derived from the adjacent Australian continental margin. The oldest abundant turbidites are Valanginian-Aptian in age and have a mixed (smarl) composition; they contain subequal amounts of calcareous and siliceous biogenic components, as well as clay and lesser quartz. Most are thin-bedded, fine sand to mud-sized, and best described by Stow and Piper's model (1984) for fine-grained biogenic turbidites. Thicker (to 3 m), coarser-grained (medium-to-coarse sand-sized) turbidites fit Bouma's model (1962) for sandy turbidites; these generally are base-cut-out (BCDE, BDE) sequences, with B-division parallel lamination as the dominant structure. Parallel laminae most commonly concentrate quartz and/or calcispheres vs. lithic clasts or clay, but distinctive millimeter to centimeter-thick, radiolarian-rich laminae occur in both fine and coarse-grained Valanginian-Hauterivian turbidites.AAP turbidites were derived from relatively deep parts of the continental margin (outer shelf, slope, or rise) that lay below the photic zone, but above the calcite compensation depth (CCD). Biogenic components are largely pelagic (calcispheres, foraminifers, radiolarians, nannofossils); lesser benthic foraminifers are characteristic of deep-water (abyssal to bathyal) environments. Abundant nonbiogenic components are mostly clay and clay clasts; smectite is the dominant clay species, and indicates a volcanogenic provenance, most likely the Triassic-Jurassic volcanic suite exposed along the northern Exmouth Plateau.Lower Cretaceous smarl turbidites were generated during eustatic lowstands and may have reached the abyssal plain via Swan Canyon, a submarine canyon thought to have formed during the Late Jurassic. In contrast to younger AAP turbidites, however, Lower Cretaceous turbidites are relatively fine-grained and do not contain notably older reworked fossils. Early in its history, the northwest Australian margin provided mainly contemporaneous slope sediment to the AAP; marginal basins adjacent to the continent trapped most terrigenous detritus, and pronounced canyon incisement did not occur until Late Cretaceous and, especially, Cenozoic time.

Fractionation of surface sediment fines based on a coupled sieve-SPLITT (split flow thin cell) method.

PubMed

Coppola, Laurent; Gustafsson, Orjan; Andersson, Per; Axelsson, Pär

2005-05-01

In traditional sediment grain-size separation using sieve technique, the bulk of the organic matter passes through the smallest mesh size (generally 38 microm) and is not further fractionated. In this study, a common sieve separation has therefore been coupled with an extra high capacity split flow thin cell fractionation (EHC-SPLITT) instrument to separate the bulk surface sediment not only into size-based sieve fractions (> 100, 63-100, 38-63 and < 38 microm) but particularly to further fractionate hydrodynamically the fine fraction (< 38 microm) using the EHC-SPLITT. Compared to the few previous studies using a smaller high capacity (HC) SPLITT cell, the EHC-SPLITT evaluated in detail here has several advantages (e.g., 23 times higher throughput and allowance for large particle diameters). First, the EHC-SPLITT was calibrated with particle standards. Then, its ability to fractionate fine surface sediments hydrodynamically was demonstrated with material from biogeochemically distinct regimes using two cutoff velocities (1 and 6 m d(-1)). The results from particle standards indicated a good agreement between theory and experiment and a satisfactory mass recovery for the sieve-SPLITT method (80-97%) was observed for sediment samples. The mass distributions revealed that particles < 38 microm were predominant (70-90%), indicating the large need for a technique such as the EHC-SPLITT to further fractionate the fine particles. There were clearly different compositions in the EHC-SPLITT-mediated sub-fractions of the sediment fines as indicated by analyses of organic and inorganic parameters (POC, Si, Fe and Al). The EHC-SPLITT technique has the potential to provide information of great utility to studies of benthic boundary layer transport and off-shelf export and how such processes fractionate geochemical signals.

Coupled changes in sand grain size and sand transport driven by changes in the upstream supply of sand in the Colorado River: relative importance of changes in bed-sand grain size and bed-sand area

USGS Publications Warehouse

Topping, D.J.; Rubin, D.M.; Melis, T.S.

2007-01-01

Sand transport in the Colorado River in Marble and Grand canyons was naturally limited by the upstream supply of sand. Prior to the 1963 closure of Glen Canyon Dam, the river exhibited the following four effects of sand supply limitation: (1) hysteresis in sediment concentration, (2) hysteresis in sediment grain size coupled to the hysteresis in sediment concentration, (3) production of inversely graded flood deposits, and (4) development or modification of a lag between the time of a flood peak and the time of either maximum or minimum (depending on reach geometry) bed elevation. Construction and operation of the dam has enhanced the degree to which the first two of these four effects are evident, and has not affected the degree to which the last two effects of sand supply limitation are evident in the Colorado River in Marble and Grand canyons. The first three of the effects involve coupled changes in suspended-sand concentration and grain size that are controlled by changes in the upstream supply of sand. During tributary floods, sand on the bed of the Colorado River fines; this causes the suspended sand to fine and the suspended-sand concentration to increase, even when the discharge of water remains constant. Subsequently, the bed is winnowed of finer sand, the suspended sand coarsens, and the suspended-sand concentration decreases independently of discharge. Also associated with these changes in sand supply are changes in the fraction of the bed that is covered by sand. Thus, suspended-sand concentration in the Colorado River is likely regulated by both changes in the bed-sand grain size and changes in the bed-sand area. A physically based flow and suspended-sediment transport model is developed, tested, and applied to data from the Colorado River to evaluate the relative importance of changes in the bed-sand grain size and changes in the bed-sand area in regulating suspended-sand concentration. Although the model was developed using approximations for steady, uniform flow, and other simplifications that are not met in the Colorado River, the results nevertheless support the idea that changes in bed-sand grain size are much more important than changes in bed-sand area in regulating the concentration of suspended sand.

Sequence stratigraphy of the lower Upper Cretaceous Elbtal Group (Saxony, Germany): new data from Middle Cenomanian-Upper Turonian outcrops and boreholes

NASA Astrophysics Data System (ADS)

Richardt, Nadine; Wilmsen, Markus

2013-04-01

The formations of the Saxonian Cretaceous have been combined in the so-called Elbtal Group. Their sedimentation took place in a terrestrial to neritic environment palaeogeographically located between the Mid-European Island (MEI) in the SW and the Lusatian Massif in the NE. The through extended from the narrow marine strait of Saxony into the broad Bohemian Cretaceous Basin (Czech Republic) further to the SE. Deposition has been dominated by marine siliciclastics that accumulated on a graded shelf with basically three main facies zones: the coarse-grained nearshore zone ("Küstensandsteinzone"), the transitional zone ("Faziesübergangszone") and the fine-grained marly offshore facies zone ("Plänerfazies"). In general, transgression proceeded in late Early Cenomanian times from the N. Relictic remains of these marine bioclastic conglomerates (Meißen Formation) only occur in the northwesternmost area of the basin around Meißen and are related to the highstand of the depositional sequence Cenomanian 3 (DS Ce 3). After a short stratigraphic gap, onlap continued in the Middle Cenomanian with the following Niederschöna Formation consisting of coarse-grained braided river deposits at the base grading via carbonaceous point-bar cycles of a meandering river system into bioturbated, partly cross-bedded estuarine sediments toward the top. These sediments record DS Ce 4 and are capped by a paleosol. Sedimentation of DS Ce 5 started with a renewed transgressional pulse initiating the Late Cenomanian. The strata consist of bioturbated, cross-bedded predominantly fine- to medium-grained quartz sandstones with some shell-rich horizons corresponding to the Oberhäslich Formation. The unconformably overlying DS Tu 1 comprises the uppermost Cenomanian Dölzschen Formation and the Lower Turonian part of the Schmilka Formation. The onset of this depositional sequence is marked by a major transgression ("plenus Transgression) drowning the remaining pre-transgression topography (onlap of Dölzschen Formation onto basement highs). The lowermost Turonian "Lohmgrund Marl" defines the base of the Schmilka Formation changing gradually into strongly bioturbated, silty Pläner and coarsening upward into moderately bioturbated, thick-bedded-massive, mainly fine-grained quartz sandstones with occasional clayey or silty layers, shell-rich horizons and sparse wood remains. After an interruption in sedimentation indicated by a root horizon or a conspicuous erosional surface, the Schmilka Formation continues with similar lithology into the early Middle Turonian. It is replaced up-section by the overlying Middle-Upper Turonian Postelwitz Formation, characterized by decreasing thickness of bedding and stronger sedimentary variability (grain size, bioturbation, glauconite and fossil content), including the intercalation of thick units of silty Pläner. The lithological variations of sandy and Pläner intervals nicely reflect the Middle-Late Turonian sea-level changes of DS Tu 2 (early Middle Turonian), DS Tu 3 (late Middle-earliest Late Turonian) and DS Tu 4 (early Late-mid-Late Turonian): Pläner units represent transgressive and highstand conditions, sand packages late highstand as well as falling and lowstand systems tracts. A major mid-Late Turonian sea-level fall is indicated in the upper Postelwitz Formation, initiating DS Tu 5 (Late Turonian) with a strongly basin-ward prograding unit of coarse-grained sandstone. The following transgression culminated in a prominent maximum flooding interval represented by the intercalation of a clayey-fine-grained regional marker bed, forming the base of the Schrammstein Formation (thick-bedded, unfossiliferous medium- to coarse-grained quartz sandstones). In conclusion, all depositional sequences of Middle Cenomanian-Late Turonian age and their bounding unconformities (sequence boundaries SB Ce 4 and 5, SB Tu 1-4) reported from coeval sections around the MEI (e. g., Münsterland Creatceous Basin, Lower Saxonian and Danubian Cretaceous) and other Cretaceous basins in the Tethyan region (e. g., Egypt) are also developed in the Saxonian Cretaceous, supporting eustatic sea-level changes as main triggers for the sequence stratigraphic architecture of the Elbtal Group.

Temporal changes in physical, chemical and biological sediment parameters in a tropical estuary after mangrove deforestation

NASA Astrophysics Data System (ADS)

Ellegaard, Marianne; Nguyen, Ngoc Tuong Giang; Andersen, Thorbjørn Joest; Michelsen, Anders; Nguyen, Ngoc Lam; Doan, Nhu Hai; Kristensen, Erik; Weckström, Kaarina; Son, Tong Phuoc Hoang; Lund-Hansen, Lars Chresten

2014-04-01

Dated sediment cores taken near the head and mouth of a tropical estuary, Nha-Phu/Binh Cang, in south central Viet Nam were analyzed for changes over time in physical, chemical and biological proxies potentially influenced by removal of the mangrove forest lining the estuary. A time-series of satellite images was obtained, which showed that the depletion of the mangrove forest at the head of the estuary was relatively recent. Most of the area was converted into aquaculture ponds, mainly in the late 1990's. The sediment record showed a clear increase in sedimentation rate at the head of the estuary at the time of mangrove deforestation and a change in diatom assemblages in the core from the mouth of the estuary indicating an increase in the water column turbidity of the entire estuary at the time of the mangrove deforestation. The proportion of fine-grained sediment and the δ13C signal both increased with distance from the head of the estuary while the carbon content decreased. The nitrogen content and the δ15N signal were more or less constant throughout the estuary. The proportion of fine-grained material and the chemical proxies were more or less stable over time in the core from the mouth while they varied synchronously over time in the core from the head of the estuary. The sediment proxies combined show that mangrove deforestation had large effects on the estuary with regard to both the physical and chemical environment with implications for the biological functioning.

Oceanographic controls over sediment water content: northern Bermuda rise

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baker, M.; Laine, E.P.

1985-01-01

Cores taken from the plateaus of Northern Bermuda Rise show that the region is underlain at depths of 1-5 m by a 1-3 m thick layer of hemipelagic lutites with anomalously high water contents. The lack of visually apparent textural and lithological changes in this extremely fine grained sediment rule out these common causes for variation in water content. The water content averages 175% within this layer and 100% immediately above and below it. This is an increase of 9.5% in porosity. The high water content sediment is confined to a period between 12 and 16 ka. Current work onmore » the mineralogy of the sediments which comprise this layer suggest two oceanographic factors that may have influenced its formation. A meltwater spike associated with deglaciation may have altered the ecological conditions above the thermocline sufficiently to promote the increased production of radiolaria, resulting in the deposition of silica enriched sediment on the sea floor. A combination of textural and perhaps chemical factors caused by the silica enrichment may have influenced the increase in water content. Intensified bottom currents at this time also may have eroded smectite rich sediments from exposures of Neogene age and deposited them on the plateaus. An increase in smectite would increase the water content due to the extremely fine grain size and the chemistry of the clay. Thus, the lateral continuity and isochroniety of this layer, combined with its mineralogical characteristics suggests that oceanographic changes can influence water content and perhaps other geotechnical properties on a regional scale.« less

Flow and sand transport over an immobile gravel bed.

USDA-ARS?s Scientific Manuscript database

Many dams in the USA and elsewhere have exceeded their design life and are being considered for remediation or removal, which will result in the reintroduction of fine sediments, often into coarse grained armored substrates, downstream of dams. The deposition of sand in the interstices of the grave...

Sampling interval analysis and CDF generation for grain-scale gravel bed topography

USDA-ARS?s Scientific Manuscript database

In river hydraulics, there is a continuing need for characterizing bed elevations to arrive at quantitative roughness measures that can be used in predicting flow depth and for improved prediction of fine-sediment transport over and through coarse beds. Recently published prediction methods require...

Using the Fish Larvae and Egg Exposure System (FLEES) to Generate Effects Data for Informing Environmental Windows

DTIC Science & Technology

2017-03-01

complete a specific part of its life cycle due to resuspended sediment. However, there is limited information concerning species-specific biological...and to determine its effects on the early life stages of aquatic organisms. Studies using FLEES use fine-grained sediment particles which are most...the dredge to areas where the critical life stages of the species of concern may be exposed. Target endpoints were project specific, including

Protecting Secure Facilities From Underground Intrusion Using Seismic/Acoustic Sensor Arrays

DTIC Science & Technology

2009-08-01

the upper 6 meters of sediments were deposited as part of a delta during a time of higher sea level, when low-gradient rivers carried fine-grained...geological site characterization and stratigraphy and sedimentation processes. Dr. Jason R. McKenna is a geophysicist at the United States Army Engineer...doctrine is being revised to address the engineer force structure at all levels to ensure that emerging lessons learned from Iraq and Afghanistan are

Field observations of bed shear stress and sediment resuspension on continental shelves, Alaska and California

USGS Publications Warehouse

Drake, D.E.; Cacchione, D.A.

1986-01-01

Bed shear stress was estimated using wave and current measurements obtained with the GEOPROBE bottom-tripod system during resuspension events in Norton Sound, Alaska, and on the northern California shelf. The boundary-layer model of Grant and Madsen (1979, Journal of Geophysical Research, 84, 1797-1808) was used to compute the bed shear stress under combined wave-generated and quasi-steady currents. Resuspension events were identified by sudden, large increases in light scattering at 1.9 m above the sea floor. The shear-stress values were used to compute the Shields parameter (??). The results for Norton Sound are in excellent agreement with the Shields threshold criterion; the data for the California shelf plot somewhat above the Shields threshold curve, though generally within the scatter envelope. Although the surface sediments in each area contain substantial fine-grained fractions (mean diameters were 0.007 cm in Norton Sound and 0.002 cm on the California shelf), the results do not indicate significant cohesion, because the sediment was entrained at bed shear-stress values close to those predicted by the modified Shields curve for cohesionless fine-grained particles. We suspect that frequent wave stirring and observed plowing of the surface sediment by benthonic animals maintain a high water content and contribute to the ease with which these materials are resuspended. ?? 1986.

What does it take to turn a rock into a badlands material?

NASA Astrophysics Data System (ADS)

Kasanin-Grubin, Milica; Nadal Romero, Estela; Della Seta, Marta; Martinez-Murillo, Juan F.

2016-04-01

Badlands can develop under different climatic conditions ranging from arid to humid on materials that have a complex combination of physico-chemical properties. The aim of this study is to determine the critical material properties for badland development based on current knowledge and new data. For that purpose we analyzed, both using the existing and new data, the importance of the distribution of grain size, mineralogical composition, and physico-chemical properties. Generally, the badland materials are most commonly described as "fine - grained" however, the size of the dominant grain fractions is not the solely important parameter. We argue that there is a critical amount of each size fraction (sand, silt and clay) that makes these materials susceptible to erosion. Furthermore, sorting of the material is an important factor in material susceptibility to erosion. The well-sorted fine sediments are generally considered as materials prone to disintegration and piping, while sediments with a large range of sizes and higher degree of packing are more resistant. However, poorly sorted sediments can also be very erodible and are found in badlands. Besides quartz, feldspar and carbonates, clay minerals are always present in badland materials and these minerals are crucial for badland development.The dominant clay mineral determines the behaviour of badland material, regarding swelling/shrinking, dispersion and crust development. Previous studies have shown that pH, SAR (sodium adsorption ratio), TDS (total dissolved salts), PS (percentage of sodium) and ESP (exchangeable sodium percentage) are distinctive parameters for both eroded and non-eroded slopes in badlands. Furthermore, our findings prove that content of organic carbon (Corg) is also a very important parameter and that materials with high SAR are less dispersive if the Corg is above 3%. In conclusion, this study shows that there are a number of thresholds regarding grain size, mineralogical composition and physico-chemical parameters that have to be met to make sediment a badland material.

Settling equivalence of detrital minerals and grain-size dependence of sediment composition

NASA Astrophysics Data System (ADS)

Garzanti, Eduardo; Andò, Sergio; Vezzoli, Giovanni

2008-08-01

This study discusses the laws which govern sediment deposition, and consequently determine size-dependent compositional variability. A theoretical approach is substantiated by robust datasets on major Alpine, Himalayan, and African sedimentary systems. Integrated (bulk-petrography, heavy-mineral, X-ray powder diffraction) multiple-window analyses at 0.25ϕ to 0.50ϕ sieve interval of eighty-five fluvial, beach, and eolian-dune samples, ranging from very fine silt to coarse sand, document homologous intrasample compositional trends, revealed by systematic concentration of denser grains in finer-grained fractions (“size-density sorting”). These trends are explained by the settling-equivalence principle, stating that detrital minerals are deposited together if their settling velocity is the same. Settling of silt is chiefly resisted by fluid viscosity, and Stokes' law predicts that size differences between detrital minerals in ϕ units (“size shifts”) are half the difference between the logarithms of their submerged densities. Settling of pebbles is chiefly resisted by turbulence effects, and the Impact law predicts double size shifts than Stokes' law. Settling of sand is resisted by both viscosity and turbulence, the settling-equivalence formula is complex, and size shifts increase - with increasing settling velocity and grain size - from those predicted by Stokes' law to those predicted by the Impact law. In wind-laid sands, size shifts match those predicted by the Impact law; size-density sorting is thus greater than in water-laid fine sands. New analytical, graphical, and statistical techniques for rigorous settling-equivalence analysis of terrigenous sediments are illustrated. Deviations associated with non-spherical shape, density anomalies, inheritance from source rocks, or mixing of detrital species with contrasting provenance and different size distribution are also tentatively assessed. Such integrated theoretical and experimental approach allows us to mathematically predict intrasample compositional variability of water-laid and wind-laid sediments, once the density of detrital components is known.

Environmental controls on photosynthetic microbial mat distribution and morphogenesis on a 3.42 Ga clastic-starved platform.

PubMed

Tice, Michael M

2009-12-01

Three morphotypes of microbial mats are preserved in rocks deposited in shallow-water facies of the 3.42 Ga Buck Reef chert (BRC). Morphotype alpha consists of fine anastomosing and bifurcating carbonaceous laminations, which loosely drape underlying detrital grains or form silica-filled lenses. Morphotype beta consists of meshes of fine carbonaceous strands intergrown with detrital grains and dark laminations, which loosely drape coarse detrital grains. Morphotype gamma consists of fine, even carbonaceous laminations that tightly drape underlying detrital grains. Preservation of nearly uncompacted mat morphologies and detrital grains deposited during mat growth within a well-characterized sedimentary unit makes quantitative correlation between morphology and paleoenvironment possible. All mats are preserved in the shallowest-water interval of those rocks deposited below normal wave base and above storm wave base. This interval is bounded below by a transgressive lag formed during regional flooding and above by a small condensed section that marks a local relative sea-level maximum. Restriction of all mat morphotypes to the shallowest interval of the storm-active layer in the BRC ocean reinforces previous interpretations that these mats were constructed primarily by photosynthetic organisms. Morphotypes alpha and beta dominate the lower half of this interval and grew during deposition of relatively coarse detrital carbonaceous grains, while morphotype gamma dominates the upper half and grew during deposition of fine detrital carbonaceous grains. The observed mat distribution suggests that either light intensity or, more likely, small variations in ambient current energy acted as a first-order control on mat morphotype distribution. These results demonstrate significant environmental control on biological morphogenetic processes independent of influences from siliciclastic sedimentation.

Numerical Model of Channel and Aquatic Habitat Response to Sediment Pulses in Mountain Rivers of Central Idaho

NASA Astrophysics Data System (ADS)

Lewicki, M.; Buffington, J. M.; Thurow, R. F.; Isaak, D. J.

2006-12-01

Mountain rivers in central Idaho receive pulsed sediment inputs from a variety of mass wasting processes (side-slope landslides, rockfalls, and tributary debris flows). Tributary debris flows and hyperconcentrated flows are particularly common due to winter "rain-on-snow" events and summer thunderstorms, the effects of which are amplified by frequent wildfire and resultant changes in vegetation, soil characteristics, and basin hydrology. Tributary confluences in the study area are commonly characterized by debris fans built by these repeated sediment pulses, providing long-term controls on channel slope, hydraulics and sediment transport capacity in the mainstem channel network. These long-term impacts are magnified during debris-flow events, which deliver additional sediment and wood debris to the fan and may block the mainstem river. These changes in physical conditions also influence local and downstream habitat for aquatic species, and can impact local human infrastructure (roads, bridges). Here, we conduct numerical simulations using a modified version of Cui's [2005] network routing model to examine bedload transport and debris-fan evolution in medium- sized watersheds (65-570 km2) of south-central Idaho. We test and calibrate the model using data from a series of postfire debris-flow events that occurred from 2003-4. We investigate model sensitivity to different controlling factors (location of the pulse within the stream network, volume of the pulse, and size distribution of the input material). We predict that on decadal time scales, sediment pulses cause a local coarsening of the channel bed in the vicinity of the sediment input, and a wave of downstream fining over several kilometers of the river (as long as the pulse material is not coarser than the stream bed itself). The grain-size distribution of the pulse influences its rate of erosion, the rate and magnitude of downstream fining, and the time required for system recovery. The effects of textural fining on spawning habitat depend on the size of sediment in the wave relative to that of the downstream channel; fining can improve spawning habitat availability in channels that are otherwise too coarse, or degrade habitat availability in finer-grained channels. Despite the perceived negative effects of sediment pulses, they can be important sources of gravel and wood debris, creating downstream spawning sites and productive wood-forced habitats. Field observations illustrate that opportunistic salmonids will spawn along the margins of recently deposited debris fans, emphasizing the biological value of such disturbances and the plasticity of salmonids to natural disturbances.

Distribution of Trichloroethylene and Geologic Controls on Contaminant Pathways near the Royal River, McKin Superfund Site Area, Gray, Maine

USGS Publications Warehouse

Lyford, Forest P.; Flight, L.E.; Stone, Janet Radway; Clifford, Scott

1999-01-01

Vapor-diffusion samplers were used in the autumn of 1997 to determine the lateral extent and distribution of concentrations of a trichloroethylene (TCE) plume in the ground-water discharge area near the McKin Superfund Site, Gray, Maine. Analyses of vapor in the samplers identified a plume about 800 feet wide entering the river near Boiling Springs, an area of ground-water discharge on the flood plain of the Royal River. The highest observed concentration of TCE in vapor was in an area of sand boils on the western bank of the river and about 200 feet downstream from Boiling Springs. Previous studies showed that most of the TCE load in the river originated in the area of the sand boils. In general, highest concentrations were observed on the western side of the river on the upgradient side of the plume, but TCE also was detected at numerous locations in the center and eastern bank of the river. The TCE plume discharges to the river where fine-grained glaciomarine sediments of the Presumpscot Formation are absent and where coarse-grained facies of buried glaciomarine fan deposits provide a pathway for ground-water flow. Based on results of analyses of vapor-diffusion samples and other previous studies, the plume appears to pass under and beyond the river near Boiling Springs and along the river for about 300 feet downstream from the sand boils. A coarse-grained, organic-rich layer at the base of the alluvial flood plain sediments is confined by overlying fine-grained alluvial sediments and may provide a conduit for ground-water leaking upward from buried glaciomarine fan deposits.

Exploring Regolith Depth and Cycling on Mars

NASA Astrophysics Data System (ADS)

Fassett, C.; Needham, D. H.; Watters, W. A.; Hundal, C.

2017-12-01

Regolith or loose sediment is ubiquitous on the surface of Mars, but our understanding of how this fragmental layer forms and evolves with time is limited. In particular, how regolith thickness varies spatially on Mars is not well known. A common perspective is to start from the canonical model for lunar regolith, which is not unreasonable, given that both Mars and the Moon are heavily cratered surfaces. However, this lunar-like paradigm is not supported by observations of Mars from recent missions. On Mars, bedrock exposures are more common and bedrock is generally closer to the surface than on the Moon, and the processes modifying the regolith differ substantially on the two bodies. Moreover, boulders on the Moon have much shorter lifetimes than on Mars, so boulders are much less common on the lunar surface. The sediment transport processes infilling craters differs dramatically on these two bodies as well. On Mars, fine-grained sediment is efficiently transported (advectively) by wind and trapped in craters rapidly after they form. Lateral transport of lunar regolith is comparatively inefficient and dominated by slow impact-driven (diffusive) transport of regolith. The goal of this contribution is to discuss observational constraints on Mars' regolith depth, and to place observations into a model for Mars landform evolution and regolith cycle. Our operating hypothesis is that the inter-crater surface on Mars is comparatively starved of fine-grained sediment (compared to the Moon), because transport and trapping of fines in craters out-competes physical weathering. Moreover, thick sedimentary bodies on Mars often get (weakly) cemented and lithified due to interactions with fluids, even in the most recent, Amazonian epoch. This is consistent with what is observed at the MER and MSL landing sites and what is known from the SNC meteorites.

A review of the geologic framework of the Long Island Sound Basin, with some observations relating to postglacial sedimentation

USGS Publications Warehouse

Lewis, Ralph S.; DiGiacomo-Cohen, Mary

2000-01-01

Most of the papers in this thematic section present regional perspectives that build on more than 100 years of geologic investigation in Long Island Sound. When viewed collectively, a common theme emerges in these works. The major geologic components of the Long Island Sound basin (bedrock, buried coastal-plain strata, recessional moraines, glacial-lake deposits, and the remains of a large marine delta) interact with the water body to affect the way the modern sedimentary system functions.Previous work, along with our present knowledge of the geologic framework of the Long Island Sound basin, is comprehensively reviewed with this theme in mind. Aspects of the crystalline bedrock, and the deltaic deposits associated with glacial Lake Connecticut, are examined with respect to their influence on sedimentation along the Connecticut coast and in the northern and western Sound. We also discuss the influence of the glacial drift that mantles the coastal-plain remnant along the north shore of Long Island and in the southern Sound.A total of approximately 22.7 billion m3 of marine sediment has accumulated in the Long Island Sound basin. A significant portion (44%) of the fine-grained marine section in the central and western basins was redistributed there from the eastern Sound, as tidal scour removed slightly over 5 billion m3 (5.3 X 1012 kg) of fine material from glacial lake and early-marine deposits east of the Connecticut River. The remainder of the estimated 1.2 X 1013 kg of fine-grained marine sediment that now resides in the central and western Sound can be accounted for by riverine input over the past 13.5 ka.

Repeated sedimentation and exposure of glacial Lake Missoula sediments: A lake-level history at Garden Gulch, Montana, USA

NASA Astrophysics Data System (ADS)

Smith, Larry N.

2017-01-01

Glaciolacustrine sediments record lake transgression, regression, and subaerial modification of the silty lake-bottom of glacial Lake Missoula in the Clark Fork River valley. The sequence preserved at Garden Gulch, MT documents lake-level fluctuations at >65% of its full-pool volume. Twelve sedimentary cycles fine upwards from (1) very fine-grained sandy silt to (2) silt with climbing ripples to (3) rhythmically laminated silt and some clay. The cycles are fine-grained turbidites capped locally by thin layers of angular gravel derived from local bedrock outcrops. The gravels appear to be the toes of mass wasting lobes carried onto the exposed lakebed surface during repeated lake-level lowerings. Periglacial wedges, small rotational faults, involutions, and clastic dikes deform the tops of eleven cycles. The wedges are 10-30 cm wide, penetrate 30-70 cm deep, are spaced <1 m apart, and contain vertically oriented gravel and massive to laminated sediment. Wedges split and taper in plan view. A few thin silt-filled dikes, which branch and taper downwards from wedges, are interpreted as filled frost cracks. One 10-20 cm-wide sand-filled dike protrudes upward from a sand bed; it is interpreted as a liquefaction feature consistent with a filling and draining lake. The deformed cycle tops preserve evidence of periglacial cold, subaerial exposure, seasonal frost heave, and the incipient formation of sorted polygons. The lowest five cycles are thicker and display more periglacial modification at their tops than the upper seven cycles. The Garden Gulch section may represent as few as seven and as many as twelve substantial fillings and partial to complete drainings of glacial Lake Missoula.

Wave- and tidally-driven flow and sediment flux across a fringing coral reef: Southern Molokai, Hawaii

USGS Publications Warehouse

Storlazzi, C.D.; Ogston, A.S.; Bothner, Michael H.; Field, M.E.; Presto, M.K.

2004-01-01

The fringing coral reef off the south coast of Molokai, Hawaii is currently being studied as part of a US Geological Survey (USGS) multi-disciplinary project that focuses on geologic and oceanographic processes that affect coral reef systems. For this investigation, four instrument packages were deployed across the fringing coral reef during the summer of 2001 to understand the processes governing fine-grained terrestrial sediment suspension on the shallow reef flat (h=1m) and its advection across the reef crest and onto the deeper fore reef. The time-series measurements suggest the following conceptual model of water and fine-grained sediment transport across the reef: Relatively cool, clear water flows up onto the reef flat during flooding tides. At high tide, more deep-water wave energy is able to propagate onto the reef flat and larger Trade wind-driven waves can develop on the reef flat, thereby increasing sediment suspension. Trade wind-driven surface currents and wave breaking at the reef crest cause setup of water on the reef flat, further increasing the water depth and enhancing the development of depth-limited waves and sediment suspension. As the tide ebbs, the water and associated suspended sediment on the reef flat drains off the reef flat and is advected offshore and to the west by Trade wind- and tidally- driven currents. Observations on the fore reef show relatively high turbidity throughout the water column during the ebb tide. It therefore appears that high suspended sediment concentrations on the deeper fore reef, where active coral growth is at a maximum, are dynamically linked to processes on the muddy, shallow reef flat.

Assessment of the performance of numerical modeling in reproducing a replenishment of sediments in a water-worked channel

NASA Astrophysics Data System (ADS)

Juez, C.; Battisacco, E.; Schleiss, A. J.; Franca, M. J.

2016-06-01

The artificial replenishment of sediment is used as a method to re-establish sediment continuity downstream of a dam. However, the impact of this technique on the hydraulics conditions, and resulting bed morphology, is yet to be understood. Several numerical tools have been developed during last years for modeling sediment transport and morphology evolution which can be used for this application. These models range from 1D to 3D approaches: the first being over simplistic for the simulation of such a complex geometry; the latter requires often a prohibitive computational effort. However, 2D models are computationally efficient and in these cases may already provide sufficiently accurate predictions of the morphology evolution caused by the sediment replenishment in a river. Here, the 2D shallow water equations in combination with the Exner equation are solved by means of a weak-coupled strategy. The classical friction approach considered for reproducing the bed channel roughness has been modified to take into account the morphological effect of replenishment which provokes a channel bed fining. Computational outcomes are compared with four sets of experimental data obtained from several replenishment configurations studied in the laboratory. The experiments differ in terms of placement volume and configuration. A set of analysis parameters is proposed for the experimental-numerical comparison, with particular attention to the spreading, covered surface and travel distance of placed replenishment grains. The numerical tool is reliable in reproducing the overall tendency shown by the experimental data. The effect of fining roughness is better reproduced with the approach herein proposed. However, it is also highlighted that the sediment clusters found in the experiment are not well numerically reproduced in the regions of the channel with a limited number of sediment grains.

Visual classification of very fine-grained sediments: Evaluation through univariate and multivariate statistics

USGS Publications Warehouse

Hohn, M. Ed; Nuhfer, E.B.; Vinopal, R.J.; Klanderman, D.S.

1980-01-01

Classifying very fine-grained rocks through fabric elements provides information about depositional environments, but is subject to the biases of visual taxonomy. To evaluate the statistical significance of an empirical classification of very fine-grained rocks, samples from Devonian shales in four cored wells in West Virginia and Virginia were measured for 15 variables: quartz, illite, pyrite and expandable clays determined by X-ray diffraction; total sulfur, organic content, inorganic carbon, matrix density, bulk density, porosity, silt, as well as density, sonic travel time, resistivity, and ??-ray response measured from well logs. The four lithologic types comprised: (1) sharply banded shale, (2) thinly laminated shale, (3) lenticularly laminated shale, and (4) nonbanded shale. Univariate and multivariate analyses of variance showed that the lithologic classification reflects significant differences for the variables measured, difference that can be detected independently of stratigraphic effects. Little-known statistical methods found useful in this work included: the multivariate analysis of variance with more than one effect, simultaneous plotting of samples and variables on canonical variates, and the use of parametric ANOVA and MANOVA on ranked data. ?? 1980 Plenum Publishing Corporation.

Grain-size analysis and sediment dynamics of hurricane-induced event beds in a coastal New England pond

NASA Astrophysics Data System (ADS)

Castagno, K. A.; Ruehr, S. A.; Donnelly, J. P.; Woodruff, J. D.

2017-12-01

Coastal populations have grown increasingly susceptible to the impacts of tropical cyclone events as they grow in size, wealth, and infrastructure. Changes in tropical cyclone frequency and intensity, augmented by a changing climate, pose an increasing threat of property damage and loss of life. Reconstructions of intense-hurricane landfalls from a series of southeastern New England sediment cores identify a series of events spanning the past 2,000 years. Though the frequency of these landfalls is well constrained, the intensity of these storms, particularly those for which no historical record exists, is not. This study analyzes the grain-size distribution of major storm event beds along a transect of sediment cores from a kettle pond in Falmouth, MA. The grain-size distribution of each event is determined using an image processing, size, and shape analyzer. The depositional patterns and changes in grain-size distribution in these fine-grained systems may both spatially and temporally reveal characteristics of both storm intensity and the nature of sediment deposition. An inverse-modeling technique using this kind of grain-size analysis to determine past storm intensity has been explored in back-barrier lagoon systems in the Caribbean, but limited research has assessed its utility to assess deposits from back-barrier ponds in the northeastern United States. Increases in hurricane intensity may be closely tied to increases in sea surface temperature. As such, research into these prehistoric intervals of increased frequency and/or intensity provides important insight into the current and future hurricane risks facing coastal communities in New England.

Grain size associations of branched tetraether lipids in soils and riverbank sediments: influence of hydrodynamic sorting processes

NASA Astrophysics Data System (ADS)

Peterse, Francien; Eglinton, Timothy I.

2017-06-01

We analyzed the abundance and distribution of branched glycerol dialkyl glycerol tetraethers (brGDGTs) in grain size fractions of 7 globally distributed river flank sediments and catchment soils in order to determine if and how the initial soil-brGDGT signature is influenced by hydrodynamic sorting upon entering a river and during subsequent transport from land to sea. BrGDGTs are hypothesized to form associations with high-surface-area fine-grained minerals in soils. Such associations, if maintained during transport, may impart resistance to degradation and promote downstream transport, reducing potential interferences by aquatic brGDGTs. We find that brGDGTs are indeed primarily associated with organic carbon (OC) bound to the clay-silt fraction (<63μm) in both soils and river sediments, and that these associations appear to be maintained during river transport. However, the relative distribution of individual brGDGTs among size fractions is relatively uniform, suggesting that brGDGTs are well mixed in river sediments and that OC-mineral associations are continuously renewed. Consequently, the brGDGT signature finally stored in continental margin sediments appears insensitive to differential particle transport processes. Nevertheless, the lower (upstream) temperature signal generally reflected by brGDGTs in river sediments may also be explained by a contribution of in situ produced brGDGTs leading to an underestimation of reconstructed air temperatures.

Sediment size of surface floodplain sediments along a large lowland river

NASA Astrophysics Data System (ADS)

Swanson, K. M.; Day, G.; Dietrich, W. E.

2007-12-01

Data on size distribution of surface sediment across a floodplain should place important constraints of modeling of floodplain deposition. Diffusive or advective models would predict that, generally, grain size should decrease away from channel banks. Variations in grain size downstream along floodplains may depend on downstream fining of river bed material, exchange rate with river banks and net deposition onto the floodplain. Here we report detailed grain size analyses taken from 17 floodplain transects along 450 km (along channel distance) reach of the middle Fly River, Papua New Guinea. Field studies have documented a systematic change in floodplain characteristics downstream from forested, more topographically elevated and topography bounded by an actively shifting mainstem channel to a downstream swamp grass, low elevation topography along which the river meanders are currently stagnant. Frequency and duration of flooding increase downstream. Flooding occurs both by overbank flows and by injections of floodwaters up tributary and tie channels connected to the mainstem. Previous studies show that about 40% of the total discharge of water passes across the floodplain, and, correspondingly, about 40% of the total load is deposited on the plain - decreasing exponentially from channel bank. We find that floodplain sediment is most sandy at the channel bank. Grain size rapidly declines away from the bank, but surprisingly two trends were also observed. A relatively short distance from the bank the surface material is finest, but with further distance from the bank (out to greater than 1 km from the 250 m wide channel) clay content decreases and silt content increases. The changes are small but repeated at most of the transects. The second trend is that bank material fines downstream, corresponding to a downstream finding bed material, but once away from the bank, there is a weak tendency for a given distance away from the bank the floodplain surface deposits to slightly coarsen downstream. We also find that sand is present (about 4%) in these surface sediments out to 1 km from the channel bank. These trends are not consistent with simple lateral transport models, and other factors, including effects of flocculation, local flow patterns, and possibly dry season wind effects may matter.

Sedimentation Investigation at Masirah Island, Oman.

DTIC Science & Technology

1983-11-01

source of fine-graine"’ rJ-.e.i _. BAt Is .iA Anchorage t-e botton is gravel and coarse sand. C’. rrents are so swift there, fine meterial will not settle...stable and with the proposed pier (a gravity structure to -3 m MLW) and the new intake groin, it will likely remain stable in the future. The volume of...US-BUILT SALTWATER INTAKE GROIN. This shore-normal gravity structure, which affects adjacent shores in .alythe same manner a groin would, was completed

Only pick the right grains: Modelling the bias due to subjective grain-size interval selection for chronometric and fingerprinting approaches.

NASA Astrophysics Data System (ADS)

Dietze, Michael; Fuchs, Margret; Kreutzer, Sebastian

2016-04-01

Many modern approaches of radiometric dating or geochemical fingerprinting rely on sampling sedimentary deposits. A key assumption of most concepts is that the extracted grain-size fraction of the sampled sediment adequately represents the actual process to be dated or the source area to be fingerprinted. However, these assumptions are not always well constrained. Rather, they have to align with arbitrary, method-determined size intervals, such as "coarse grain" or "fine grain" with partly even different definitions. Such arbitrary intervals violate principal process-based concepts of sediment transport and can thus introduce significant bias to the analysis outcome (i.e., a deviation of the measured from the true value). We present a flexible numerical framework (numOlum) for the statistical programming language R that allows quantifying the bias due to any given analysis size interval for different types of sediment deposits. This framework is applied to synthetic samples from the realms of luminescence dating and geochemical fingerprinting, i.e. a virtual reworked loess section. We show independent validation data from artificially dosed and subsequently mixed grain-size proportions and we present a statistical approach (end-member modelling analysis, EMMA) that allows accounting for the effect of measuring the compound dosimetric history or geochemical composition of a sample. EMMA separates polymodal grain-size distributions into the underlying transport process-related distributions and their contribution to each sample. These underlying distributions can then be used to adjust grain-size preparation intervals to minimise the incorporation of "undesired" grain-size fractions.

Age determination and provenance of sandy sediments possibly hosting gas hydrate in the eastern margin of Japan Sea

NASA Astrophysics Data System (ADS)

Uchida, T.; Takashima, I.; Sasaki, S.; Matsumoto, R.

2012-12-01

In 2010 the MD179 project was undertaken by the Marion Dufresne aiming at recovery of deep seated gas and gas hydrate, methane induced carbonate, and deep sediments in order to develop the geologic model of gas hydrate accumulation and evaluate the possible environmental impact of gas hydrate for the last glacial-interglacial cycles. Sediment samples below the seafloor were obtained in the Umitaka Spur, Joetsu Channel, Toyama Trough, Japan Basin, Nishi Tsugaru and Okushiri Ridge areas by the cruise. Small amounts of sandy sediment have been retrieved as thin intercalations in Pleistocene and Holocene silty layers, where trace fossils and strong bioturbations are commonly observed. Those sandy sediments consist of very fine- to fine-grained sand grains, and are sometimes tuffaceous. Pore-size distribution measurements and thin-section observations of these arenite sands were carried out, which indicates that porosities of silty sediments are around 50 % but those of arenites range from 42 to 52 %, of which mean pore sizes and permeabilities are larger than those of silty sediments. These coarser sediments might have been transported approximately around 3 to 30 ka according to the tephra ages, where supplying sediments might have not been abundant due to sea level fluctuation during the Pleistocene ice age. While the presence of gas hydrate in intergranular pores of arenite sands has not been confirmed, the soupy occurrence in recovered sediments may strongly indicate the presence of gas hydrate filling the intergranular pore system of arenite sands that is called pore-space hydrates. They have been recognized till now in the Mallik as well as in the Nankai Trough areas, which are considered to be common even in the subsurface sandy sediments at the eastern margin of Japan Sea. Time of deposition of coarse-grained sediments can be recognized by the thermoluminescence (TL) dating method. The TL dating works on the principle that materials containing naturally occurring radioactive isotopes such as uranium, thorium or potassium are subject to low levels of radiation. Measurements of TL dating have been completed only for seven samples, which indicate 48 to 980 ka in age. Additionally they usually provide information about the provenance and the sedimentary paleoenvironment when the sediments deposited. The TL emission spectra along temperature increase from 100 to 400 degree C are divided into two types; the unimodal type and the bimodal type, which may indicate the histories of sediment transportation and their provenances. This study was performed as a part of the MH21 Research Consortium on methane hydrate in Japan.

Hyporheic zone as a bioreactor: sediment heterogeneity influencing biogeochemical processes

NASA Astrophysics Data System (ADS)

Perujo, Nuria; Romani, Anna M.; Sanchez-Vila, Xavier

2017-04-01

Mediterranean fluvial systems are characterized by frequent periods of low flow or even drought. During low flow periods, water from wastewater treatment plants (WWTPs) is proportionally large in fluvial systems. River water might be vertically transported through the hyporheic zone, and then porous medium acts as a complementary treatment system since, as water infiltrates, a suite of biogeochemical processes occurs. Subsurface sediment heterogeneity plays an important role since it influences the interstitial fluxes of the medium and drives biomass growing, determining biogeochemical reactions. In this study, WWTP water was continuously infiltrated for 3 months through two porous medium tanks: one consisting of 40 cm of fine sediment (homogeneous); and another comprised of two layers of different grain size sediments (heterogeneous), 20 cm of coarse sediment in the upper part and 20 cm of fine one in the bottom. Several hydrological, physicochemical and biological parameters were measured periodically (weekly at the start of the experiment and biweekly at the end). Analysed parameters include dissolved nitrogen, phosphorus, organic carbon, and oxygen all measured at the surface, and at 5, 20 and 40 cm depth. Variations in hydraulic conductivity with time were evaluated. Sediment samples were also analysed at three depths (surface, 20 and 40 cm) to determine bacterial density, chlorophyll content, extracellular polymeric substances, and biofilm function (extracellular enzyme activities and carbon substrate utilization profiles). Preliminary results suggest hydraulic conductivity to be the main driver of the differences in the biogeochemical processes occurring in the subsurface. At the heterogeneous tank, a low nutrient reduction throughout the whole medium is measured. In this medium, high hydraulic conductivity allows for a large amount of infiltrating water, but with a small residence time. Since some biological processes are largely time-dependent, small water residence time results in low nutrient reduction. Moreover, high nitrification and low ammonium concentration in the interface of the two grain-size layers are measured, probably related to high dissolved oxygen concentration at the coarse-fine sediment interface, further promoting accumulation of bacteria and algae. In contrast, the homogeneous tank shows low dissolved oxygen values and high denitrification in depth which could be related to lower overall hydraulic conductivity, as compared to the heterogeneous tank. The preliminary analysis of our results indicates a key role of hydraulic conductivity on biogeochemical processes in the porous medium but, at the same time that it is strongly interacting with sediment grain-size distribution and the development of biofilm. The final scope of this study is to know the interactions between physicochemical and biological components in sediments in order to understand in detail the biogeochemical processes occurring.

'Berries' and Rock Share Common Origins

NASA Technical Reports Server (NTRS)

2004-01-01

This false-color composite image, taken at a region of the rock outcrop dubbed 'Shoemaker's Patio' near the Mars Exploration Rover Opportunity's landing site, shows finely layered sediments, which have been accentuated by erosion. The sphere-like grains or 'blueberries' distributed throughout the outcrop can be seen lining up with individual layers. This observation indicates that the spherules are geologic features called concretions, which form in pre-existing wet sediments. Other sphere-like grains, such as impact spherules or volcanic lapilli (fragments of material etween 2 and 64 millimeters or .08 and 2.5 inches in maximum dimension that are ejected from a volcano) are thought to be deposited with sediments and thus would form layers distinct from those of the rocks. This image was captured by the rover's panoramic camera on the 50th martian day, or sol, of the mission. Data from the camera's infrared, green and violet filters were used to create this false-color picture.

One-dimensional pore pressure diffusion of different grain-fluid mixtures

NASA Astrophysics Data System (ADS)

von der Thannen, Magdalena; Kaitna, Roland

2015-04-01

During the release and the flow of fully saturated debris, non-hydrostatic fluid pressure can build up and probably dissipate during the event. This excess fluid pressure has a strong influence on the flow and deposition behaviour of debris flows. Therefore, we investigate the influence of mixture composition on the dissipation of non-hydrostatic fluid pressures. For this we use a cylindrical pipe of acrylic glass with installed pore water pressure sensors in different heights and measure the evolution of the pore water pressure over time. Several mixtures with variable content of fine sediment (silt and clay) and variable content of coarse sediment (with fixed relative fractions of grains between 2 and 32 mm) are tested. For the fines two types of clay (smectite and kaolinite) and loam (Stoober Lehm) are used. The analysis is based on the one-dimensional consolidation theory which uses a diffusion coefficient D to model the decay of excess fluid pressure over time. Starting from artificially induced super-hydrostatic fluid pressures, we find dissipation coefficients ranging from 10-5 m²/s for liquid mixtures to 10-8 m²/s for viscous mixtures. The results for kaolinite and smectite are quite similar. For our limited number of mixtures the effect of fines content is more pronounced than the effect of different amounts of coarse particles.

Tsunami sediments and their grain size characteristics

NASA Astrophysics Data System (ADS)

Sulastya Putra, Purna

2018-02-01

Characteristics of tsunami deposits are very complex as the deposition by tsunami is very complex processes. The grain size characteristics of tsunami deposits are simply generalized no matter the local condition in which the deposition took place. The general characteristics are fining upward and landward, poor sorting, and the grain size distribution is not unimodal. Here I review the grain size characteristics of tsunami deposit in various environments: swale, coastal marsh and lagoon/lake. Review results show that although there are similar characters in some environments and cases, but in detail the characteristics in each environment can be distinguished; therefore, the tsunami deposit in each environment has its own characteristic. The local geological and geomorphological condition of the environment may greatly affect the grain size characteristics.

Physical properties of muddy sediments from French Guiana

NASA Astrophysics Data System (ADS)

Caillaud, J.; Lesourd, L.; Philippe, S.; Gontharet, S.; Sarrazin, M.; Gardel, A.

2017-01-01

The North West migration of long and discontinuous mud banks along the French Guiana coast has been extensively studied during the past years, in particular with a large-scale vision, which consequently has integrated morpho and hydrodynamic data. The aims of the present paper were to use intrinsic sediment properties (grain-size, mineralogy, concentration, and cohesion) to (1) highlight the sedimentary conditions during the consolidation processes from fluid deposit to vegetation development, and (2) verify the apparent homogeneously derived sedimentary facies. Two intertidal transects, Macouria and Cayenne, were compared from the coast to offshore. Their altitude averages of 1 m and 2.8 m above mean sea level, respectively, were different enough to compare the influence of the hydrodynamic impact and emersion time on their sediment properties. The latter, i.e. grain size distribution, mineralogical content, mud concentration, and shear strength (cohesion), were determined from sampled surface sediments (first cm) and along sediment cores (20-30 cm depth) from each transect. A specific X-ray technique was applied to the whole core to differentiate clearly its thin layers. On both intertidal sites, the grain size dominated by the fine silt fraction (2-20 μm) and the bulk mineralogy characterized by five major minerals (quartz, feldspars, chlorite, illite, and kaolinite) appeared homogeneous along both transects and cores. In spite of this apparent uniformity of particle size and mineralogical parameters, as well as for visual observation along the core, high precision X-rays still showed a cyclic sedimentation at a micro-scale level. This cyclicity with intercalation of fine layers was related to distinct dynamic deposits marked by both tidal processes and hydrodynamic factors (swell propagation). The cohesion and concentration results were dependent on the topography, where high topography was characterized by sediments with high cohesion and concentration values, and vice versa. A comparison between these two parameters was done to define critical limits between soft and stiff muds, as well as unvegetated and colonized muds. The favorable intrinsic sedimentary properties for consolidation and colonization were also discussed according to the field observations and bibliographic data.

Variations of sediment toxicity in a tidal estuary: a case study of the South Passage, Changjiang (Yangtze) Estuary.

PubMed

Gao, Jinjuan; Shi, Huahong; Dai, Zhijun; Mei, Xuefei

2015-06-01

Sediments in estuaries, especially those containing a large reservoir of contaminants released from urban and industrial activities, have had great impacts on benthic fauna and associated species. A better understanding of the toxicity of contaminants in estuarine sediments is of great significance to ecological assessments. Here, based on the collected sediments from neap to spring tides in the South Passage, Changjiang Estuary, the toxicity of the sediments was first studied using the frog embryo teratogenesis assay-Xenopus (FETAX). The results showed that the extracts of estuarine sediments induced multiple malformations in the embryos and that the phenotypes of malformation had two distinct patterns of variations corresponding to the tidal cycles. The phenotypes in the first pattern were dominated by hypopigmentation and edema of the heart, and the pattern was mainly controlled by fine-grained fractions. The phenotypes in the second pattern were dominated by edema of the heart and enlarged proctodeum, and it was mostly controlled by coarse-grain fractions. The sediment toxicity was higher during the spring and flood tides, which may be influenced by the grain size and sediment resuspension. Furthermore, obvious periodicities existed in the changes of the percentages of hatching (14-16 h and 6 h), enlarged proctodeum (15-18 h), and bent tail (5-7 h) due to the influence of tidal cycles. Moreover, our results also suggested that FETAX is an appropriate cost-effective biological monitoring tool to assess estuarine ecological health in contaminated sediments. Copyright © 2015 Elsevier Ltd. All rights reserved.

Resistivity profiling for mapping gravel layers that may control contaminant migration at the Amargosa Desert Research Site, Nevada

USGS Publications Warehouse

Lucius, Jeffrey E.; Abraham, Jared D.; Burton, Bethany L.

2008-01-01

Gaseous contaminants, including CFC 113, chloroform, and tritiated compounds, move preferentially in unsaturated subsurface gravel layers away from disposal trenches at a closed low-level radioactive waste-disposal facility in the Amargosa Desert about 17 kilometers south of Beatty, Nevada. Two distinct gravel layers are involved in contaminant transport: a thin, shallow layer between about 0.5 and 2.2 meters below the surface and a layer of variable thickness between about 15 and 30 meters below land surface. From 2003 to 2005, the U.S. Geological Survey used multielectrode DC and AC resistivity surveys to map these gravel layers. Previous core sampling indicates the fine-grained sediments generally have higher water content than the gravel layers or the sediments near the surface. The relatively higher electrical resistivity of the dry gravel layers, compared to that of the surrounding finer sediments, makes the gravel readily mappable using electrical resistivity profiling. The upper gravel layer is not easily distinguished from the very dry, fine-grained deposits at the surface. Two-dimensional resistivity models, however, clearly identify the resistive lower gravel layer, which is continuous near the facility except to the southeast. Multielectrode resistivity surveys provide a practical noninvasive method to image hydrogeologic features in the arid environment of the Amargosa Desert.

Rock magnetic and geochemical analyses of surface sediment characteristics in deep ocean environments: A case study across the Ryukyu Trench

NASA Astrophysics Data System (ADS)

Kawamura, N.; Kawamura, K.; Ishikawa, N.

2008-03-01

Magnetic minerals in marine sediments are often dissolved or formed with burial depth, thereby masking the primary natural remanent magnetization and paleoclimate signals. In order to clarify the present sedimentary environment and the progressive changes with burial depth in the magnetic properties, we studied seven cores collected from the Ryukyu Trench, southwest Japan. Magnetic properties, organic geochemistry, and interstitial water chemistry of seven cores are described. Bottom water conditions at the landward slope, trench floor, and seaward slope are relatively suboxic, anoxic, and oxic, respectively. The grain size of the sediments become gradually finer with the distance from Okinawa Island and finer with increasing water depth. The magnetic carriers in the sediments are predominantly magnetite and maghemized magnetite, with minor amounts of hematite. In the topmost sediments from the landward slope, magnetic minerals are diluted by terrigenous materials and microfossils. The downcore variations in magnetic properties and geochemical data provided evidence for the dissolution of fine-grained magnetite with burial depth under an anoxic condition.

Compiling and Mapping Global Permeability of the Unconsolidated and Consolidated Earth: GLobal HYdrogeology MaPS 2.0 (GLHYMPS 2.0)

NASA Astrophysics Data System (ADS)

Huscroft, Jordan; Gleeson, Tom; Hartmann, Jens; Börker, Janine

2018-02-01

The spatial distribution of subsurface parameters such as permeability are increasingly relevant for regional to global climate, land surface, and hydrologic models that are integrating groundwater dynamics and interactions. Despite the large fraction of unconsolidated sediments on Earth's surface with a wide range of permeability values, current global, high-resolution permeability maps distinguish solely fine-grained and coarse-grained unconsolidated sediments. Representative permeability values are derived for a wide variety of unconsolidated sediments and applied to a new global map of unconsolidated sediments to produce the first geologically constrained, two-layer global map of shallower and deeper permeability. The new mean logarithmic permeability of the Earth's surface is -12.7 ± 1.7 m2 being 1 order of magnitude higher than that derived from previous maps, which is consistent with the dominance of the coarser sediments. The new data set will benefit a variety of scientific applications including the next generation of climate, land surface, and hydrology models at regional to global scales.

Particle sorting in Filter Porous Media and in Sediment Transport: A Numerical and Experimental Study

NASA Astrophysics Data System (ADS)

Glascoe, L. G.; Ezzedine, S. M.; Kanarska, Y.; Lomov, I. N.; Antoun, T.; Smith, J.; Hall, R.; Woodson, S.

2014-12-01

Understanding the flow of fines, particulate sorting in porous media and fractured media during sediment transport is significant for industrial, environmental, geotechnical and petroleum technologies to name a few. For example, the safety of dam structures requires the characterization of the granular filter ability to capture fine-soil particles and prevent erosion failure in the event of an interfacial dislocation. Granular filters are one of the most important protective design elements of large embankment dams. In case of cracking and erosion, if the filter is capable of retaining the eroded fine particles, then the crack will seal and the dam safety will be ensured. Here we develop and apply a numerical tool to thoroughly investigate the migration of fines in granular filters at the grain scale. The numerical code solves the incompressible Navier-Stokes equations and uses a Lagrange multiplier technique. The numerical code is validated to experiments conducted at the USACE and ERDC. These laboratory experiments on soil transport and trapping in granular media are performed in constant-head flow chamber filled with the filter media. Numerical solutions are compared to experimentally measured flow rates, pressure changes and base particle distributions in the filter layer and show good qualitative and quantitative agreement. To further the understanding of the soil transport in granular filters, we investigated the sensitivity of the particle clogging mechanism to various parameters such as particle size ratio, the magnitude of hydraulic gradient, particle concentration, and grain-to-grain contact properties. We found that for intermediate particle size ratios, the high flow rates and low friction lead to deeper intrusion (or erosion) depths. We also found that the damage tends to be shallower and less severe with decreasing flow rate, increasing friction and concentration of suspended particles. We have extended these results to more realistic heterogeneous population particulates for sediment transport. This work performed under the auspices of the US DOE by LLNL under Contract DE-AC52-07NA27344 and was sponsored by the Department of Homeland Security, Science and Technology Directorate, Homeland Security Advanced Research Projects Agency.

Modern sedimentation processes in a wave-dominated coastal embayment: Espírito Santo Bay, southeast Brazil

NASA Astrophysics Data System (ADS)

Bastos, Alex Cardoso; Costa Moscon, Daphnne Moraes; Carmo, Dannilo; Neto, José Antonio Baptista; da Silva Quaresma, Valéria

2015-02-01

Sediment dynamics in wave-dominated coastal embayments are generally controlled by seasonal meteorological conditions, storms having a particularly strong influence. In the present study, such hydrodynamic processes and associated deposits have been investigated in a coastal embayment located along the southeast coast of Brazil, i.e. Espírito Santo Bay, in the winter (June/July) of 2008. The bay has undergone a series of human interventions that have altered the local hydrodynamic processes and, consequently, the sediment transport patterns. Facies distribution and sediment dynamics were examined by acoustic seabed mapping, sediment and core sampling, hydrodynamic measurements and sand transport modelling. The results show that sediment distribution can be described in terms of nearshore and offshore zones. The offshore bay sector is predominantly composed of "palimpsest" lithoclastic medium-coarse sands deposited in the course of the early Holocene transgression that peaked about 5,000 years ago. In the inner bay or nearshore zone (up to depths of 4-8 m), these older transgressive deposits are today overlain by a thin (up to 30-cm-thick) and partly patchy blanket of younger regressive fine sand/muddy fine sands. Both coarse- and fine-grained facies are being reworked during high-energy events (Hs>1.5 m) when fine sediment is resuspended, weak tide-induced drift currents causing the sand patches to be displaced. The coarser sediment, by contrast, is mobilized as bedload to produce wave ripples with spacings of up to 1.2 m. These processes lead to a sharp spatial delimitation between a fine sand/mud facies and a rippled coarse sand facies. The fine sand patches have a relief of about 20-30 cm and reveal a typical internal tempestite depositional sequence. Fair-weather wave-induced sediment transport (Hs<1 m), supported by weak tidal currents, seems to only affect the fine sediment facies. Sediment dynamics in Espírito Santo Bay is thus essentially controlled by wave action during storms, tidal currents playing a very subordinate role. Anthropogenic changes due to the construction of a port at the entrance of the bay have not only produced erosion along the beach, but could also explain the occurrence of sand patches concentrated in the north-eastern part of the bay. Because storm-induced deposits of the type observed in this study have an inherently patchy distribution, this feature needs to be taken into consideration when interpreting the rock record in terms of modern analogues.

Why consider subseabed disposal of high-level nuclear waste

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heath, G. R.; Hollister, C. D.; Anderson, D. R.

1980-01-01

Large areas of the deep seabed warrant assessment as potential disposal sites for high-level radioactive waste because: (1) they are far from seismically and tectonically active lithospheric plate boundaries; (2) they are far from active or young volcanos; (3) they contain thick layers of very uniform fine-grained clays; (4) they are devoid of natural resources likely to be exploited in the forseeable future; (5) the geologic and oceanographic processes governing the deposition of sediments in such areas are well understood, and are remarkably insensitive to past oceanographic and climatic changes; and (6) sedmentary records of tens of millions of yearsmore » of slow, uninterrupted deposition of fine grained clay support predictions of the future stability of such sites. Data accumulated to date on the permeability, ion-retardation properties, and mechanical strength of pelagic clay sediments indicate that they can act as a primary barrier to the escape of buried nuclides. Work in progress should determine within the current decade whether subseabed disposal is environmentally acceptable and technically feasible, as well as address the legal, political and social issues raised by this new concept.« less

On a grain of sand - a microhabitat for the opportunistic agglutinated foraminifera Hemisphaerammina apta n. sp., from the early Eocene Arctic Ocean

NASA Astrophysics Data System (ADS)

McNeil, David H.; Neville, Lisa A.

2018-02-01

Hemisphaerammina apta n. sp. is an attached monothalamous agglutinated foraminifera discovered in shelf sediments of the early Eocene Arctic Ocean. It is a simple yet distinctive component of the endemic agglutinated foraminiferal assemblage that colonized the Arctic Ocean after the microfaunal turnover caused by the Paleocene-Eocene Thermal Maximum. Associated foraminifera are characterized by a high percentage of monothalamous species (up to 60 %) and are entirely agglutinated indicating a brackish (mesohaline) early Eocene Arctic Ocean. Hemisphaerammina apta occurs exclusively as individuals attached to fine detrital grains (0.2 to 1.8 mm) of sediment. It is a small species (0.06 to 0.2 mm in diameter), fine-grained, with a low hemispherical profile, no floor across the attachment area, no substantive marginal flange, no internal structures, and no aperture. Lacking an aperture, it apparently propagated and fed through minute (micrometre-sized) interstitial pores in the test wall. Attachment surfaces vary from concave to convex and rough to smooth. Grains for attachment are diverse in shape and type but are predominantly of quartz and chert. The presence of H. apta in the early Eocene was an opportunistic response to an environment with an active hydrological system (storm events). Attachment to grains of sand would provide a more stable base on a sea floor winnowed by storm-generated currents. Active transport is indicated by the relative abundance of reworked foraminifera mixed with in situ species. Contemporaneous reworking and colonization by H. apta is suggested by its attachment to a reworked specimen of Cretaceous foraminifera.

Kinematics of Cone-In-Cone Growth, with Implications for Timing and Formation Mechanism

NASA Astrophysics Data System (ADS)

Hooker, J. N.; Cartwright, J. A.

2015-12-01

Cone-in-cone is an enigmatic structure. Similar to many fibrous calcite veins, cone-in-cone is generally formed of calcite and present in bedding-parallel vein-like accumulations within fine-grained rocks. Unlike most fibrous veins, cone-in-cone contains conical inclusions of host-rock material, creating nested, parallel cones throughout. A long-debated aspect of cone-in-cone structures is whether the calcite precipitated with its conical form (primary cone-in-cone), or whether the cones formed afterwards (secondary cone-in-cone). Trace dolomite within a calcite cone-in-cone structure from the Cretaceous of Jordan supports the primary hypothesis. The host sediment is a siliceous mud containing abundant rhombohedral dolomite grains. Dolomite rhombohedra are also distributed throughout the cone-in-cone. The rhombohedra within the cones are randomly oriented yet locally have dolomite overgrowths having boundaries that are aligned with calcite fibers. Evidence that dolomite co-precipitated with calcite, and did not replace calcite, includes (i) preferential downward extension of dolomite overgrowths, in the presumed growth-direction of the cone-in-cone, and (ii) planar, vertical borders between dolomite crystals and calcite fibers. Because dolomite overgrows host-sediment rhombohedra and forms fibers within the cones, it follows that the host-sediment was included within the growing cone-in-cone as the calcite precipitated, and not afterward. The host-sediment was not injected into the cone-in-cone along fractures, as the secondary-origin hypothesis suggests. This finding implies that cone-in-cone in general does not form over multiple stages, and thus has greater potential to preserve the chemical signature of its original precipitation. Because cone-in-cone likely forms before complete lithification of the host, and because the calcite displaces the host material against gravity, this chemical signature can preserve information about early overpressures in fine-grained sediments.

Sediment-hosted contaminants and distribution patterns in the Mississippi and Atchafalaya River Deltas

USGS Publications Warehouse

Flocks, James G.; Kindinger, Jack G.; Ferina, Nicholas; Dreher, Chandra

2002-01-01

The Mississippi and Atchafalaya Rivers transport very large amounts of bedload and suspended sediments to the deltaic and coastal environments of the northern Gulf of Mexico. Absorbed onto these sediments are contaminants that may be detrimental to the environment. To adequately assess the impact of these contaminants it is first necessary to develop an understanding of sediment distribution patterns in these deltaic systems. The distribution patterns are defined by deltaic progradational cycles. Once these patterns are identified, the natural and industrial contaminant inventories and their depositional histories can be reconstructed. Delta progradation is a function of sediment discharge, as well as channel and receiving-basin dimensions. Fluvial energy controls the sediment distribution pattern, resulting in a coarse grained or sandy framework, infilled with finer grained material occupying the overbank, interdistributary bays, wetlands and abandoned channels. It has been shown that these fine-grained sediments can carry contaminants through absorption and intern them in the sediment column or redistribute them depending on progradation or degradation of the delta deposit. Sediment distribution patterns in delta complexes can be determined through high-resolution geophysical surveys and groundtruthed with direct sampling. In the Atchafalaya and Mississippi deltas, remote sensing using High-Resolution Single-Channel Seismic Profiling (HRSP) and Sidescan Sonar was correlated to 20-ft vibracores to develop a near-surface geologic framework that identifies variability in recent sediment distribution patterns. The surveys identified bedload sand waves, abandoned-channel back-fill, prodelta and distributary mouth bars within the most recently active portions of the deltas. These depositional features respond to changes in deltaic processes and through their response may intern or transport absorbed contaminants. Characterizing these features provides insight into the fate of sediment-hosted contaminants.

Modeling Sediment Bypassing around Rocky Headlands

NASA Astrophysics Data System (ADS)

George, D. A.; Largier, J. L.; Pasternack, G. B.; Erikson, L. H.; Storlazzi, C. D.; Barnard, P.

2016-12-01

Sediment bypassing rocky headlands remains understudied despite the importance of characterizing littoral processes and sediment budgets for erosion abatement, climate change adaptation, and beach management. This study was developed to identify controlling factors on and the mechanisms supporting sediment bypassing. Sediment flux around four idealized rocky headlands was investigated using the hydrodynamic model Delft3D and spectral wave model SWAN. The experimental design involved 120 simulations to explore the influence of headland morphology, substrate composition, sediment grain size, and oceanographic forcing. Headlands represented sizes and shapes found in natural settings, grain sizes ranged from fine to medium sand, and substrates from sandy beds to offshore bedrock reefs. The oceanography included a constructed representative tide, an alongshore background current, and four wave conditions derived from observational records in the eastern Pacific Ocean. A bypassing ratio was developed for alongshore flux between upstream and downstream cross-shore transects to determine the degree of blockage by a headland. Results showed that northwesterly oblique large waves (Hs = 7 m, Tp = 16 s) generated the most flux around headlands, whereas directly incident waves blocked flux across a headland apex. The headland shape heavily influenced the sediment fate by changing the relative angle between the shoreline and the incident waves. The bypassing ratio characterized each headland's capacity to allow alongshore flux under different wave conditions. All headlands may allow flux, although larger ones block sediment more effectively, promoting their ability to be littoral cell boundaries compared to smaller headlands. The controlling factors on sediment bypassing were determined to be wave angle, shape and size of the headland, and sediment grain size. This novel numerical modeling study advances headland modeling from the generic realm to broadly applicable classes of headlands and encourages further investigation into the mechanics of sediment bypassing.

Controls on sediment entrainment shear stress determined from X-Ray CT scans and a 3D moment-balance model

NASA Astrophysics Data System (ADS)

Hodge, R. A.; Voepel, H.; Leyland, J.; Sear, D. A.; Ahmed, S. I.

2017-12-01

The shear stress at which a grain is entrained is determined by the balance between the applied fluid forces, and the resisting forces of the grain. Recent research has tended to focus on the applied fluid forces; calculating the resisting forces requires measurement of the geometry of in-situ sediment grains which has previously been very difficult to measure. We have used CT scanning to measure the grain geometry of in-situ water-worked grains, and from these data have calculated metrics that are relevant to grain entrainment. We use these metrics to parameterise a new, fully 3D, moment-balance model of grain entrainment. Inputs to the model are grain dimensions, exposed area, elevation relative to the velocity profile, the location of grain-grain contact points, and contact area with fine matrix sediment. The new CT data and model mean that assumptions of previous grain-entrainment models (e.g. spherical grains, 1D measurements of protrusion, entrainment in the downstream direction) are no longer necessary. The model calculates the critical shear stress for each possible set of contact points, and outputs the lowest value. Consequently, metrics including pivot angle and the direction of grain entrainment are now model outputs, rather than having to be pre-determined. We use the CT data and model to calculate the critical shear stress of 1092 in-situ grains from baskets that were buried and water-worked in a flume prior to scanning. We find that there is no consistent relationship between relative grain size (D/D50) and pivot angle, whereas there is a negative relationship between D/D50 and protrusion. Out of all measured metrics, critical shear stress is most strongly controlled by protrusion. This finding suggests that grain-scale topographic data could be used to estimate grain protrusion and hence improve estimates of critical shear stress.

Quantifying Grain-Size Variability of Metal Pollutants in Road-Deposited Sediments Using the Coefficient of Variation

PubMed Central

Wang, Xiaoxue; Li, Xuyong

2017-01-01

Particle grain size is an important indicator for the variability in physical characteristics and pollutants composition of road-deposited sediments (RDS). Quantitative assessment of the grain-size variability in RDS amount, metal concentration, metal load and GSFLoad is essential to elimination of the uncertainty it causes in estimation of RDS emission load and formulation of control strategies. In this study, grain-size variability was explored and quantified using the coefficient of variation (Cv) of the particle size compositions, metal concentrations, metal loads, and GSFLoad values in RDS. Several trends in grain-size variability of RDS were identified: (i) the medium class (105–450 µm) variability in terms of particle size composition, metal loads, and GSFLoad values in RDS was smaller than the fine (<105 µm) and coarse (450–2000 µm) class; (ii) The grain-size variability in terms of metal concentrations increased as the particle size increased, while the metal concentrations decreased; (iii) When compared to the Lorenz coefficient (Lc), the Cv was similarly effective at describing the grain-size variability, whereas it is simpler to calculate because it did not require the data to be pre-processed. The results of this study will facilitate identification of the uncertainty in modelling RDS caused by grain-size class variability. PMID:28788078

Time-integrated sampling of fluvial suspended sediment: a simple methodology for small catchments

NASA Astrophysics Data System (ADS)

Phillips, J. M.; Russell, M. A.; Walling, D. E.

2000-10-01

Fine-grained (<62·5 µm) suspended sediment transport is a key component of the geochemical flux in most fluvial systems. The highly episodic nature of suspended sediment transport imposes a significant constraint on the design of sampling strategies aimed at characterizing the biogeochemical properties of such sediment. A simple sediment sampler, utilizing ambient flow to induce sedimentation by settling, is described. The sampler can be deployed unattended in small streams to collect time-integrated suspended sediment samples. In laboratory tests involving chemically dispersed sediment, the sampler collected a maximum of 71% of the input sample mass. However, under natural conditions, the existence of composite particles or flocs can be expected to increase significantly the trapping efficiency. Field trials confirmed that the particle size composition and total carbon content of the sediment collected by the sampler were representative statistically of the ambient suspended sediment.

Sedimentary and pore water geochemistry linked to deglaciation and postglacial development of Lake Vättern, Sweden

NASA Astrophysics Data System (ADS)

Swärd, Henrik; O´Regan, Matt; Kylander, Malin; Greenwood, Sarah; Mörth, Magnus; Jakobsson, Martin

2017-04-01

Lake Vättern, in south central Sweden, underwent profound environmental changes during the Late Weichselian deglaciation of Fennoscandia. It evolved from (i) a sub/proglacial lake situated at the westernmost rim of the Baltic Ice Lake (BIL) into (ii) a brackish to marine phase where the Vättern basin was a part of the Yoldia Sea connecting the North and Baltic Seas, and finally to (iii) a freshwater basin as isostatic rebound following deglaciation led to its isolation. The sedimentary and pore water geochemical signatures associated with these dramatic environmental changes were investigated in a 74 m composite sediment core from southern Lake Vättern. This was accomplished using high-resolution X-ray fluorescence measurements of elemental data along with discrete measurements of total organic carbon (TOC), δ13C, mineralogical composition (XRD) and pore water chemistry. Proglacial sediments in Lake Vättern are devoid of organic matter, and show cyclic trends in elemental data, grain size and mineralogy. These are interpreted as varved sediments whose thickness decreases upcore from decimeters to millimeters. The coarse grained varves are enriched in Ca, Si, Zr and Sr and contain calcite while the fine grained varves are enriched in K, Rb, Ti and Fe and lack calcite. Overall, the presence of calcite is limited to the proglacial sediments and reflected in the elemental data by an abrupt decrease of Ca at the (i)/(ii) transition. This suggests a glacial/glaciofluvial origin for the calcite, likely eroded from local limestones that borders the lake basin in the northeast. The saline incursion at the beginning of phase (ii) is evident in pore water chemistry by a significant increase of the major sea water species (Cl, Na, Mg, K and Ca) but is not clearly seen in the sedimentary geochemistry. Increased biological production in and around the lake during stage (iii) is strongly reflected in sedimentary geochemistry showing decreasing detrital inputs, increasing TOC and δ13C signals and a mineralogical composition that resembles the fine grained varves of the proglacial sediments, but with a more intense quartz signal. Furthermore, pore water profiles show substantial increase in the concentration of redox sensitive species (Fe, Mn and P) indicating anoxic biodegradation in the sediments.

Texture and depositional history of near-surface alluvial deposits in the central part of the western San Joaquin Valley, California

USGS Publications Warehouse

Laudon, Julie; Belitz, Kenneth

1989-01-01

Saline conditions and associated high levels of selenium and other soluble trace elements in soil, shallow ground water, and agricultural drain water of the western San Joaquin Valley, California, have prompted a study of the texture of near-surface alluvial deposits in the central part of the western valley. Texture is characterized by the percentage of coarse-grained sediment present within a specified subsurface depth interval and is used as a basis for mapping the upper 50 feet of deposits. Resulting quantitative descriptions of the deposits are used to interpret the late Quaternary history of the area. Three hydrogeologic units--Coast Range alluvium, flood-basin deposits, and Sierran sand--can be recognized in the upper 50 feet of deposits in the central part of the western San Joaquin Valley. The upper 30 feet of Coast Range alluvium and the adjacent 5 to 35 feet of flood-basin deposits are predominantly fine grained. These fine-grained Coast Range deposits are underlain by coarse-grained channel deposits. The fine-grained flood basin deposits are underlain by coarse-grained Sierran sand. The extent and orientation of channel deposits below 20 feet in the Coast Range alluvium indicate that streams draining the Coast Range may have been tributary to the axial stream that deposited the Sierran sand and that streamflow may have been to the southeast. The fining-upward stratigraphic sequence in the upper 50 feet of deposits and the headward retreat of tributary stream channels from the valley trough with time support a recent hypothesis of climatic control of alluviation in the western San Joaquin Valley.

Fish as major carbonate mud producers and missing components of the tropical carbonate factory

USGS Publications Warehouse

Perry, C.T.; Salter, M.A.; Harborne, A.R.; Crowley, S.F.; Jelks, H.L.; Wilson, R.W.

2011-01-01

Carbonate mud is a major constituent of recent marine carbonate sediments and of ancient limestones, which contain unique records of changes in ocean chemistry and climate shifts in the geological past. However, the origin of carbonate mud is controversial and often problematic to resolve. Here we show that tropical marine fish produce and excrete various forms of precipitated (nonskeletal) calcium carbonate from their guts ("low" and "high" Mg-calcite and aragonite), but that very fine-grained (mostly <2 ??m) high Mg-calcite crystallites (i.e., >4 mole % MgCO3) are their dominant excretory product. Crystallites from fish are morphologically diverse and species-specific, but all are unique relative to previously known biogenic and abiotic sources of carbonate within open marine systems. Using site specific fish biomass and carbonate excretion rate data we estimate that fish produce ???6.1 ?? 106 kg CaCO3/year across the Bahamian archipelago, all as mud-grade (the <63 ??m fraction) carbonate and thus as a potential sediment constituent. Estimated contributions from fish to total carbonate mud production average ???14% overall, and exceed 70% in specific habitats. Critically, we also document the widespread presence of these distinctive fish-derived carbonates in the finest sediment fractions from all habitat types in the Bahamas, demonstrating that these carbonates have direct relevance to contemporary carbonate sediment budgets. Fish thus represent a hitherto unrecognized but significant source of fine-grained carbonate sediment, the discovery of which has direct application to the conceptual ideas of how marine carbonate factories function both today and in the past.

Fish as major carbonate mud producers and missing components of the tropical carbonate factory

USGS Publications Warehouse

Perry, Chris T.; Salter, Michael A.; Harborne, Alastair R.; Crowley, Stephen F.; Jelks, Howard L.; Wilson, Rod W.

2011-01-01

Carbonate mud is a major constituent of recent marine carbonate sediments and of ancient limestones, which contain unique records of changes in ocean chemistry and climate shifts in the geological past. However, the origin of carbonate mud is controversial and often problematic to resolve. Here we show that tropical marine fish produce and excrete various forms of precipitated (nonskeletal) calcium carbonate from their guts ("low" and "high" Mg-calcite and aragonite), but that very fine-grained (mostly 4 mole % MgCO3) are their dominant excretory product. Crystallites from fish are morphologically diverse and species-specific, but all are unique relative to previously known biogenic and abiotic sources of carbonate within open marine systems. Using site specific fish biomass and carbonate excretion rate data we estimate that fish produce ~6.1 x 106 kg CaCO3/year across the Bahamian archipelago, all as mud-grade (the <63 μm fraction) carbonate and thus as a potential sediment constituent. Estimated contributions from fish to total carbonate mud production average ~14% overall, and exceed 70% in specific habitats. Critically, we also document the widespread presence of these distinctive fish-derived carbonates in the finest sediment fractions from all habitat types in the Bahamas, demonstrating that these carbonates have direct relevance to contemporary carbonate sediment budgets. Fish thus represent a hitherto unrecognized but significant source of fine-grained carbonate sediment, the discovery of which has direct application to the conceptual ideas of how marine carbonate factories function both today and in the past.

A new Late Weichselian and Holocene marine chronology for the western Svalbard slope 30,000-0 cal years BP

NASA Astrophysics Data System (ADS)

Jessen, Simon P.; Rasmussen, Tine L.; Nielsen, Tove; Solheim, Anders

2010-05-01

Data have been compiled from eleven sediment cores from 76° to 80°N on the western Svalbard slope. The cores are from water depths between 630 and 1880 m and show clear similarities in lithology and magnetic susceptibility. All cores penetrated into mass transported sediments from glacigenic debris flow events and turbidity flow events. The mass transport probably occurred when the ice reached the shelf edge. The deposits date between 24,080 ± 150 and 23,550 ± 185 calibrated (cal) years BP. The records also include laminated, fine grained sediments interpreted as deposits from sediment-laden meltwater plumes dated between 14,780 ± 220 and 14,300 ± 260 cal years BP. In Holocene sediments a diatom-rich fine grained layer dates 10,100 ± 150 to 9840 ± 200 cal years BP. The eleven cores have been stacked into one record with absolute age control from 35 AMS 14C dates. Together with oxygen isotope stratigraphy and contents of ice rafted detritus the stacked record provides a useful chronology tool for cores on the western Svalbard slope. Our study improves the age control of earlier well documented glacial events and shows that the maximum glacial state and the onset of the deglaciation both occurred 2500-3000 years earlier than previously reconstructed for the western Svalbard margin. The results indicate that during the last 30,000 years advance and retreat of the Svalbard-Barents Sea Ice Sheet was closely linked to the flow of Atlantic Water and Polar Water over the margin.

Suspended sediment and turbidity after road construction/improvement and forest harvest in streams of the Trask River Watershed Study, Oregon

NASA Astrophysics Data System (ADS)

Arismendi, Ivan; Groom, Jeremiah D.; Reiter, Maryanne; Johnson, Sherri L.; Dent, Liz; Meleason, Mark; Argerich, Alba; Skaugset, Arne E.

2017-08-01

Transport of fine-grained sediment from unpaved forest roads into streams is a concern due to the potential negative effects of additional suspended sediment on aquatic ecosystems. Here we compared turbidity and suspended sediment concentration (SSC) dynamics in five nonfish bearing coastal Oregon streams above and below road crossings, during three consecutive time periods ("before", "after road construction/improvement", and "after forest harvest and hauling"). We hypothesized that the combined effects of road construction/improvement and the hauling following forest harvest would increase turbidity and SSC in these streams. We tested whether the differences between paired samples from above and below road crossing exceeded various biological thresholds, using literature values of biological responses to increases in SSC and turbidity. Overall, we found minimal increases of both turbidity and SSC after road improvement, forest harvest, and hauling. Because flow is often used as a surrogate for turbidity or SSC we examined these relationships using data from locations above road crossings that were unaffected by roads or forest harvest and hauling. In addition, we examined the association between turbidity and SSC for these background locations. We found a positive, but in some cases weak association between flow and turbidity, and between flow and SSC; the relationship between turbidity and SSC was more robust, but also inconsistent among sites over time. In these low order streams, the concentrations and transport of suspended sediment seems to be highly influenced by the variability of local conditions. Our study provides an expanded understanding of current forest road management practice effects on fine-grained sediment in streams and introduces alternative metrics using multiple thresholds to evaluate potential indicators of biological relevance.

Processes controlling the remobilization of surficial sediment and formation of sedimentary furrows in north-central Long Island Sound

USGS Publications Warehouse

Poppe, L.J.; Knebel, H.J.; Lewis, R.S.; DiGiacomo-Cohen, M. L.

2002-01-01

Sidescan sonar, bathymetric, subbottom, and bottom-photographic surveys and sediment sampling have improved our understanding of the processes that control the complex distribution of bottom sediments and benthic habitats in Long Island Sound. Although the deeper (>20 m) waters of the central Sound are long-term depositional areas characterized by relatively weak bottom-current regimes, our data reveal the localized presence of sedimentary furrows. These erosional bedforms occur in fine-grained cohesive sediments (silts and clayey silts), trend east-northeast, are irregularly spaced, and have indistinct troughs with gently sloping walls. The average width and relief of the furrows is 9.2 m and 0.4 m, respectively. The furrows average about 206 m long, but range in length from 30 m to over 1,300 m. Longitudinal ripples, bioturbation, and nutclam shell debris are common within the furrows. Although many of the furrows appear to end by gradually narrowing, some furrows show a "tuning fork" joining pattern. Most of these junctions open toward the east, indicating net westward sediment transport. However, a few junctions open toward the west suggesting that oscillating tidal currents are the dominant mechanism controlling furrow formation. Sedimentary furrows and longitudinal ripples typically form in environments which have recurring, directionally stable, and occasionally strong currents. The elongate geometry and regional bathymetry of Long Island Sound combine to constrain the dominant tidal and storm currents to east-west flow directions and permit the development of these bedforms. Through resuspension due to biological activity and the subsequent development of erosional bedforms, fine-grained cohesive sediment can be remobilized and made available for transport farther westward into the estuary.

Processes controlling the remobilization of surficial sediment and formation of sedimentary furrows in North-Central Long Island Sound

USGS Publications Warehouse

Poppe, L.J.; Knebel, H.J.; Lewis, R.S.; DiGiacomo-Cohen, M. L.

2002-01-01

Sidescan sonar, bathymetric, subbottom, and bottom-photographic surveys and sediment sampling have improved our understanding of the processes that control the complex distribution of bottom sediments and benthic habitats in Long Island Sound. Although the deeper (>20 m) waters of the central Sound are long-term depositional areas characterized by relatively weak bottom-current regimes, our data reveal the localized presence of sedimentary furrows. These erosional bedforms occur in fine-grained cohesive sediments (silts and clayey silts), trend east-northeast, are irregularly spaced, and have indistinct troughs with gently sloping walls. The average width and relief of the furrows is 9.2 m and 0.4 m, respectively. The furrows average about 206 m long, but range in length from 30 m to over 1,300 m. Longitudinal ripples, bioturbation, and nutclam shell debris are common within the furrows. Although many of the furrows appear to end by gradually narrowing, some furrows show a "tuning fork" joining pattern. Most of these junctions open toward the east, indicating net westward sediment transport. However, a few junctions open toward the west suggesting that oscillating tidal currents are the dominant mechanism controlling furrow formation. Sedimentary furrows and longitudinal ripples typically form in environments which have recurring, directionally stable, and occasionally strong currents. The elongate geometry and regional bathymetry of Long Island Sound combine to constrain the dominant tidal and storm currents to east-west flow directions and permit the development of these bedforms. Through resuspension due to biological activity and the subsequent development of erosional bedforms, fine-grained cohesive sediment can be remobilized and made available for transport farther westward into the estuary.

Geoacoustic Characterization of the Mud Drape at the New England Mud Patch

NASA Astrophysics Data System (ADS)

Reed, A. H.

2016-02-01

The New England Mud Patch is an extensive deposit of fine-grained sediments that extends from an area south of Cape Cod, MA to south of Montauk Point Long Island, NY out on the continental shelf in water depths of 60 to 90 meters. The mud patch has a remarkable accumulation of up to a 13 meter thick sequence of mud that overlays a transgressive surface of Pleistocene Age and then thins out on the periphery where surficial sediments convert from mud to sand and sand/gravel. The deposit likely accumulated in this region due to the coalescing of shelf currents that had oppositional flow. This work focuses on a section of the mud patch that is centered over the thickest portion of mud and extends east-west for 30 km and north south for 10 km. Gravity cores were collected throughout this region and the cores penetrated the upper 2-4 m of mud at 28 different sites with multiple cores collected in several locations. The mud thickness in these regions exceeded the core barrel length, therefore the cores did not penetrate into the basal sand sediment layer, a relict transgressional horizon, which displays prominently in the acoustic data for this selected region. These cores were evaluated for compressional sound speed (averaging 1480 m/s) and density (1580 kg/m3) and found to be largely homogeneous and similar throughout the study area. The largest source of inhomogeneity was due to dispersed shell hash and disarticulated bivalves, but these inclusions represent minor components in the total sediment volume. The overlying sediment that characterizes the New England Mud Patch can be readily classified as mud, silty mud, or sandy-silty mud. This fine-grained sediment deposit reflects upon the low-energy nature of the hydrodynamics within this region.

Identifying the source of fluvial terrace deposits using XRF scanning and Canonical Discriminant Analysis: A case study of the Chihshang terraces, eastern Taiwan

NASA Astrophysics Data System (ADS)

Chang, Queenie; Lee, Jian-Cheng; Hunag, Jyh-Jaan; Wei, Kuo-Yen; Chen, Yue-Gau; Byrne, Timothy B.

2018-05-01

The source of fluvial deposits in terraces provides important information about the catchment fluvial processes and landform evolution. In this study, we propose a novel approach that combines high-resolution Itrax-XRF scanning and Canonical Discriminant Analysis (CDA) to identify the source of fine-grained fluvial terrace deposits. We apply this approach to a group of terraces that are located on the hanging wall of the Chihshang Fault in eastern Taiwan with two possible sources, the Coastal Range on the east and the Central Range on the west. Our results of standard samples from the two potential sources show distinct ranges of canonical variables, which provided a better separation ability than individual chemical elements. We then tested the possibility of using this approach by applying it to several samples with known sediment sources and obtain positive results. Applying this same approach to the fine-grained sediments in Chihshang terraces indicates that they are mostly composed of Coastal Range material but also contain some inputs from the Central Range. In two lowest terraces T1 and T2, the fine-grained deposits show significant Central Range component. For terrace T4, the results show less Central Range input and a trend of decreasing Central Range influences up section. The Coastal Range material becomes dominant in the two highest terraces T7 and T10. Sediments in terrace T5 appear to have been potentially altered by post-deposition chemical alteration processes and are not included in the analysis. Our results show that the change in source material in the terraces deposits was relatively gradual rather than the sharp changes suggested by the composition of the gravels and conglomerates. We suggest that this change in sources is related to the change in dominant fluvial processes that controlled by the tectonic activity.

Giant polygons and mounds in the lowlands of Mars: signatures of an ancient ocean?

PubMed

Oehler, Dorothy Z; Allen, Carlton C

2012-06-01

This paper presents the hypothesis that the well-known giant polygons and bright mounds of the martian lowlands may be related to a common process-a process of fluid expulsion that results from burial of fine-grained sediments beneath a body of water. Specifically, we hypothesize that giant polygons and mounds in Chryse and Acidalia Planitiae are analogous to kilometer-scale polygons and mud volcanoes in terrestrial, marine basins and that the co-occurrence of masses of these features in Chryse and Acidalia may be the signature of sedimentary processes in an ancient martian ocean. We base this hypothesis on recent data from both Earth and Mars. On Earth, 3-D seismic data illustrate kilometer-scale polygons that may be analogous to the giant polygons on Mars. The terrestrial polygons form in fine-grained sediments that have been deposited and buried in passive-margin, marine settings. These polygons are thought to result from compaction/dewatering, and they are commonly associated with fluid expulsion features, such as mud volcanoes. On Mars, in Chryse and Acidalia Planitiae, orbital data demonstrate that giant polygons and mounds have overlapping spatial distributions. There, each set of features occurs within a geological setting that is seemingly analogous to that of the terrestrial, kilometer-scale polygons (broad basin of deposition, predicted fine-grained sediments, and lack of significant horizontal stress). Regionally, the martian polygons and mounds both show a correlation to elevation, as if their formation were related to past water levels. Although these observations are based on older data with incomplete coverage, a similar correlation to elevation has been established in one local area studied in detail with newer higher-resolution data. Further mapping with the latest data sets should more clearly elucidate the relationship(s) of the polygons and mounds to elevation over the entire Chryse-Acidalia region and thereby provide more insight into this hypothesis.

Evidence from the Seychelles of Last Interglacial Sea Level Oscillations

NASA Astrophysics Data System (ADS)

Vyverberg, K.; Dutton, A.; Dechnik, B.; Webster, J.; Zwartz, D.

2014-12-01

Several studies indicate that sea level oscillated during Marine Isotope Stage (MIS) 5e, but the details of these scenarios, including the number of sea level oscillations, are still debated. We lack a detailed understanding of the sensitivity of the large polar ice sheets to changes in temperature that could result in eustatic sea level oscillations. Because the Seychelles are located far from the margins of the Last Glacial Maximum northern hemisphere ice sheets, they have not been subjected to glacial isostatic adjustment, and have been tectonically stable since the Last Interglacial period; therefore, they provide a robust record of eustatic sea level during MIS 5e. All of the outcrops we examined contain unconformities and/or sharp transitions between facies, though the nature of these boundaries varies between sites. In some outcrops we observed a hardground comprising fine-grained, mollusc-rich sediment layer between distinct generations of in situ coralgal framework. In one outcrop, this succession was observed twice, where two generations of reef growth were each capped by a strongly indurated fine-grained, mollusc-rich sediment layer. At the site with the greatest vertical extent of outcrop, there is a marked difference in the taxonomic composition of the coral community above and below an unconformable surface, but the indurated fine-grained, sediment layer observed elsewhere was absent. Most of the other outcrops we studied contained a common succession of facies from in situ reef units overlain by cemented coral rubble. In two dated outcrops, the age of corals above and below the rubble layer are the same age. The hardgrounds and rubble layers may represent ephemeral exposure of the reef units during two drops in sea level. The inference of multiple meter-scale oscillations during the MIS 5e highstand indicates a more dynamic cryosphere than the present interglacial, although the climatic threshold for more volatile polar ice sheets is not yet clear.

Petrophysical Properties Of Sandy Sediments Possibly Hosting Gas Hydrate In The Eastern Margin Of Japan Sea

NASA Astrophysics Data System (ADS)

Uchida, T.; Takashima, I.; Sunaga, H.; Sasaki, S.; Matsumoto, R.

2011-12-01

In 2010 the MD179 project was undertaken by the Marion Dufresne aiming at recovery of deep seated gas and gas hydrate, methane induced carbonate, and deep sediments older than 300 ka in order to develop geologic model of gas hydrate accumulation and evaluate the possible environmental impact of gas hydrate for the last glacial-interglacial cycles. Sediment samples below the seafloor were obtained in the Umitaka Spur, Joetsu Channel, Toyama Trough, Japan Basin, Nishi Tsugaru and Okushiri Ridge areas by the MD179 cruise. Small amounts of sandy sediment have been retrieved as thin intercalations in Pleistocene and Holocene silty layers, where trace fossils and strong bioturbations are commonly observed. Those sandy sediments consist of very fine- to fine-grained sand grains, and are sometimes tuffaceous. Pore-size distribution measurements and thin-section observations of these arenite sands were undertaken, which indicatesd that porosities of muddy sediments are around 50 % but those of arenites range from 42 to 52 %, of which mean pore sizes and permeabilities are larger than those of siltstones and mudstones. These coarser sediments might have been transported approximately around 3 to 30 ka, where supplying sediments may not be abundant due to sea level fluctuation during the Pleistocene ice age. While the presence of gas hydrate in intergranular pores of arenite sands has not been confirmed, the soupy occurrence in recovered sediments may strongly indicate the presence of gas hydrate filling the intergranular pore system of arenite sands that is called pore-space hydrates. They have been recognized till now in the Mallik as well as in the Nankai Trough areas, which are considered to be very common even in the subsurface sandy sediments at the eastern margin of Japan Sea. Concentration of gas hydrate may need primary intergranular pores large enough to occur within a host sediment that may be arenite sand without matrix grains deposited in the sedimentary environment such as deep sea channels. The geological modeling of the gas hydrate formation and evolution system is concerned for energy resource potential in the Japan Sea as well as the Nankai Trough areas. Time of deposition of coarse-grained sediments can be recognized by the thermoluminescence (TL) dating method. TL dating works on the principle that materials containing naturally occurring radioactive isotopes such as uranium, thorium or potassium are subject to low levels of radiation. In mineral crystals, this leads to ionization of the atoms in the host material and freed electrons may become trapped in structural defects or holes in the mineral crystal lattice. These electrons can be released by heating under controlled conditions, and an emission of light occurs which is the basis of TL dating. Additionally they usually provide information about the provenance and the paleoenvironment when the sediments deposited. This study was performed as a part of the MH21 Research Consortium on methane hydrate in Japan.

Modern sedimentation patterns in Potter Cove, King George Island, Antarctica

NASA Astrophysics Data System (ADS)

Hass, H. Christian; Kuhn, Gerhard; Wölfl, Anne-Cathrin; Wittenberg, Nina; Betzler, Christian

2013-04-01

IMCOAST among a number of other initiatives investigates the modern and the late Holocene environmental development of south King George Island with a strong emphasis on Maxwell Bay and its tributary fjord Potter Cove (maximum water depth: about 200 m). In this part of the project we aim at reconstructing the modern sediment distribution in the inner part of Potter Cove using an acoustic ground discrimination system (RoxAnn) and more than136 ground-truth samples. Over the past 20 years the air temperatures in the immediate working area increased by more than 0.6 K (Schloss et al. 2012) which is less than in other parts of the West Antarctic Peninsula (WAP) but it is still in the range of the recovery of temperatures from the Little Ice Age maximum to the beginning of the 20th century. Potter Cove is a small fjord characterized by a series of moraine ridges produced by a tidewater glacier (Fourcade Glacier). Presumably, the farthest moraine is not much older than about 500 years (LIA maximum), hence the sediment cover is rather thin as evidenced by high resolution seismic data. Since a few years at least the better part of the tidewater glacier retreated onto the island's mainland. It is suggested that such a fundamental change in the fjord's physiography has also changed sedimentation patterns in the area. Potter Cove is characterized by silty-clayey sediments in the deeper inner parts of the cove. Sediments are coarser (fine to coarse sands and boulders) in the shallower areas; they also coarsen from the innermost basin to the mouth of the fjord. Textural structures follow the seabed morphology, i.e. small v-shaped passages through the moraine ridges. The glacier still produces large amounts of turbid melt waters that enter the cove at various places. We presume that very fine-grained sediments fall out from the meltwater plumes and are distributed by mid-depth or even bottom currents, thus suggesting an anti-estuarine circulation pattern. Older sediments that are more distal to the glacier front and sediments in shallower places (e.g. on top of the moraine ridges) become increasingly overprinted by coarser sediments from the shallow areas of the fjord. These areas are prone to wave induced winnowing effects as well as disturbances by ploughing icebergs. It can be concluded that coarsening of the fjord sediments will continue while the supply of fine-grained meltwater sediments might cease due to exhaustion of the reservoirs.

Formation of natural gas hydrates in marine sediments. Gas hydrate growth and stability conditioned by host sediment properties

USGS Publications Warehouse

Clennell, M.B.; Henry, P.; Hovland, M.; Booth, J.S.; Winters, W.J.; Thomas, M.

2000-01-01

The stability conditions of submarine gas hydrates (methane clathrates) are largely dictated by pressure, temperature, gas composition, and pore water salinity. However, the physical properties and surface chemistry of the host sediments also affect the thermodynamic state, growth kinetics, spatial distributions, and growth forms of clathrates. Our model presumes that gas hydrate behaves in a way analogous to ice in the pores of a freezing soil, where capillary forces influence the energy balance. Hydrate growth is inhibited within fine-grained sediments because of the excess internal phase pressure of small crystals with high surface curvature that coexist with liquid water in small pores. Therefore, the base of gas hydrate stability in a sequence of fine sediments is predicted by our model to occur at a lower temperature, and so nearer to the seabed than would be calculated from bulk thermodynamic equilibrium. The growth forms commonly observed in hydrate samples recovered from marine sediments (nodules, sheets, and lenses in muds; cements in sand and ash layers) can be explained by a requirement to minimize the excess of mechanical and surface energy in the system.

Colorado River sediment transport: 1. Natural sediment supply limitation and the influence of Glen Canyon Dam

USGS Publications Warehouse

Topping, David J.; Rubin, David M.; Vierra, L.E.

2000-01-01

Analyses of flow, sediment‐transport, bed‐topographic, and sedimentologic data suggest that before the closure of Glen Canyon Dam in 1963, the Colorado River in Marble and Grand Canyons was annually supply‐limited with respect to fine sediment (i.e., sand and finer material). Furthermore, these analyses suggest that the predam river in Glen Canyon was not supply‐limited to the same degree and that the degree of annual supply limitation increased near the head of Marble Canyon. The predam Colorado River in Grand Canyon displays evidence of four effects of supply limitation: (1) seasonal hysteresis in sediment concentration, (2) seasonal hysteresis in sediment grain size coupled to the seasonal hysteresis in sediment concentration, (3) production of inversely graded flood deposits, and (4∥ development or modification of a lag between the time of a flood peak and the time of either maximum or minimum (depending on reach geometry) bed elevation. Analyses of sediment budgets provide additional support for the interpretation that the predam river was annually supply‐limited with respect to fine sediment, but it was not supply‐limited with respect to fine sediment during all seasons. In the average predam year, sand would accumulate and be stored in Marble Canyon and upper Grand Canyon for 9 months of the year (from July through March) when flows were dominantly below 200–300 m3/s; this stored sand was then eroded during April through June when flows were typically higher. After closure of Glen Canyon Dam, because of the large magnitudes of the uncertainties in the sediment budget, no season of substantial sand accumulation is evident. Because most flows in the postdam river exceed 200–300 m3/s, substantial sand accumulation in the postdam river is unlikely.

3.5-D model of sediment age and grain size for the Northern Gulf of Aqaba-Elat (Red Sea) using submarine cores

NASA Astrophysics Data System (ADS)

Kanari, Mor; Ben-Avraham, Zvi; Tibor, Gideon; Goodman Tchernov, Beverly N.; Bookman, Revital; Taha, Nimer; Marco, Shmuel

2016-04-01

The Northern Gulf of Aqaba-Elat (NGAE) is the northeast extension of the Red Sea, located at the southernmost part of the Dead Sea Fault, at the transition zone between the deep en-echelon submarine basins of the Red Sea and the shallow continental basins of the Arava Valley (Israel and Jordan). We aim to characterize the top sedimentary cover across the NGAE in order to check the effect of tectonics on the sedimentary column, using high resolution grain size data and radiocarbon dating of core sediments. We analyzed 11 piston cores and 9 short cores: high resolution grain-size and radiocarbon age determinations were used to compile a 3.5-D (3.5 dimensional) model of age-depth-grain size for the top 3-5 meters of the NGAE. Two general trends of the grain size spatial distribution are observed: grains are coarsest at the NE corner of the NGAE (Aqaba coastline) and grow finer with the distance to the west on the shelf and with the distance from shore to the south. Long- and short-term accumulation rates were compiled for the entire NGAE, demonstrating a distinct E-W trend on the shelf and a NNE-SSW trend in the deep basin. The 3.5-D age-depth-grain size model conforms to- and validates the tectonic structure of the shelf detailed by previous authors. We suggest that the impact of tectonic structure of the shelf is highly significant in terms of spatial variations across the shelf, both in age of the sediment and its grain size characteristics. The temporal-spatial distribution of the grain size in the deep basin of the NGAE reveals a correlation between sediment age, dominant grain size and active tectonics: fine-grain, old sediment in the margins (Late Pleistocene, as old as >40 ka on the west margin; Early Holocene, as old as 7.5 ka, on the east margin), and Late Pleistocene sediment farther south from the dominant active diagonal fault which underlies the Elat Canyon. Young coarse sediment is present in the middle of the basin, where most of the active sediment transportation (and tectonic activity) take place. The dominant sedimentary activity follows the migration of the active tectonic fault segments from east to west between 40 ka to present. We observe focusing of turbidites to the location of the dominant active tectonic fault. A spatial/temporal evolutionary model is presented for the sedimentary processes of the NGAE since 40 ka to present, suggesting three phases of development: (a) Late Pleistocene 40 to 12 ka; (b) Early to Mid-Holocene 12 to 5-4 ka; (c) Late Holocene 5-4 ka to present.

Implications of tidally-varying bed stress and intermittent estuarine stratification on fine-sediment dynamics through the Mekong's tidal river to estuarine reach

NASA Astrophysics Data System (ADS)

McLachlan, R. L.; Ogston, A. S.; Allison, M. A.

2017-09-01

River gauging stations are often located upriver of tidal propagation where sediment transport processes and storage are impacted by widely varying ratios of marine to freshwater influence. These impacts are not yet thoroughly understood. Therefore, sediment fluxes measured at these stations may not be suitable for predicting changes to coastal morphology. To characterize sediment transport dynamics in this understudied zone, flow velocity, salinity, and suspended-sediment properties (concentration, size, and settling velocity) were measured within the tidal Sông Hậu distributary of the lower Mekong River, Vietnam. Fine-sediment aggregation, settling, and trapping rates were promoted by seasonal and tidal fluctuations in near-bed shear stress as well as the intermittent presence of a salt wedge and estuary turbidity maximum. Beginning in the tidal river, fine-grained particles were aggregated in freshwater. Then, in the interface zone between the tidal river and estuary, impeded near-bed shear stress and particle flux convergence promoted settling and trapping. Finally, in the estuary, sediment retention was further encouraged by stratification and estuarine circulation which protected the bed against particle resuspension and enhanced particle aggregation. These patterns promote mud export ( 1.7 t s-1) from the entire study area in the high-discharge season when fluvial processes dominate and mud import ( 0.25 t s-1) into the estuary and interface zone in the low-discharge season when estuarine processes dominate. Within the lower region of the distributaries, morphological change in the form of channel abandonment was found to be promoted within minor distributaries by feedbacks between channel depth, vertical mixing, and aggregate trapping. In effect, this field study sheds light on the sediment trapping capabilities of the tidal river - estuary interface zone, a relatively understudied region upstream of where traditional concepts place sites of deposition, and predicts how fine-sediment dynamics and morphology of large tropical deltas such as the Mekong will respond to changing fluvial and marine influences in the future.

Bed Sediment Monitoring of Multiple Contiguous Small Dam Removals

NASA Astrophysics Data System (ADS)

Galster, J. C.; Wyrick, J. R.

2010-12-01

Dam removal is crucial for reconnecting river habitats, restoring passage of fish and other aquatic organisms, and restoring the free flow of water and sediment. However, removal of obsolete dams is often resisted due to concerns of releasing sediment and initiating channel instability. Two dams on the Musconetcong River in northern New Jersey have been removed as part of a watershed-wide effort to remove or breach all major obstructions to restore the river to its original free-flowing state. The two dams were consecutively situated 1 kilometer apart and their removals provided an opportunity to study the geomorphic response in the form of bed elevation changes and sediment size through pre- and post-removal monitoring. Initial geomorphic surveys of the riverbed in the vicinity of and between the two dams have shown areas of erosion and deposition. These surveys have established a set of control points along the river channel between the two dams, and confirm the downstream movement of a sediment plume and localized areas of erosion. At the upstream dam, comparisons pre- and post-dam removal surveys show greater than 100 cubic meters of sediment being both eroded and deposited within the site. Most but not all of the erosion occurred around the newly exposed sediment bar upstream of the former dam, where the thalweg has reestablished itself following the dam’s removal. Areas that were excavated during removal have experienced deposition. Most of the deposition occurred downstream and on the left-hand bank. Due to the two low flow culverts in the former dam, a mid-channel sediment bar formed but has subsequently eroded. At the downstream dam site, erosion has removed up to 1.1 m of sediment from the bed in places while depositing up to 0.5 m sediment in others. As sediment from the former impoundment migrated through the project site, areas excavated during the removal became areas of deposition following the removal, and; alternately, areas in the channel margins where sediments were placed experienced gradual erosion. Grain size analysis shows a coarsening of the riverbed over the first nine months since removal. Grain size analyses were done upstream and downstream of the dam sites as well as at two locations between the sites. Pebble counts were completed using the random walk method at each of the six sites. The largest change in grain sizes at the four sites occurred upstream of the downstream dam site, where there was a significant coarsening of the sediment from October 2008 to June 2009. This has most likely occurred from the increase in energy upstream of the dam post-removal, which has transported many of the fine-grained sediments downstream. Downstream of this dam site sediment size has not significantly changed, suggesting that the fine sediments have been transported downstream far enough to leave the site. Surveys of the channel thalweg above and below both dams also show a pulse of sediment migrating slowing from the uppermost impoundment areas. Long-term monitoring of the channel thalweg may reveal reach-level changes in channel slope.

Magnetic Mineralogy as Indicator of dry Conditions in Lacustrine Sediments From Santa María del Oro, Nayarit, Central Mexico

NASA Astrophysics Data System (ADS)

Ortega, B.; Vazquez, G.; Rodriguez, A.

2007-05-01

Combined magnetic and geochemical analysis were conducted on laminated sediments from Santa Maria del Oro, a crater lake in Nayarit (Mexico), to build up a model of paleoenvironmental conditions for the late Holocene. The occurrence of a severe drought at the end of the archeological Classic period (100 - 900 AD) has been documented in sites of central Mexico (Zirahuen lake and Lerma basin), the Gulf of Mexico coast (Los Tuxtlas) and the Yucatan peninsula. The effects of this climatic event are considered to have stressed the social and political situation in the Yucatan area and other sites in Mesoamerica, and resulted in the "collapse" of the Maya civilization. Santa Maria del Oro sediments between ca. 600 - 1140 AD are characterized by repeated sequences of ocher silt laminae with high inorganic carbon content, authigenic siderite, and low concentration of SD magnetic minerals, followed upward by an increase of concentrations of fine grained SD and SP ferrimagnetic minerals in brown silt laminae. This sequence is considered to represent dissolution-precipitation cycles of magnetic minerals in low erosion, concentrated waters and anoxic water-sediment interface environments. Dissolution of magnetite occurs in reductive conditions, which are considered as warmer and dryer periods. Above the ocher silt, precipitation of fine grained magnetite occurs when conditions change to oxic environments. Ostracode C and O isotopy document a negative precipitation/evaporation balance during this time period.

Cohesive and mixed sediment in the Regional Ocean Modeling System (ROMS v3.6) implemented in the Coupled Ocean-Atmosphere-Wave-Sediment Transport Modeling System (COAWST r1234)

NASA Astrophysics Data System (ADS)

Sherwood, Christopher R.; Aretxabaleta, Alfredo L.; Harris, Courtney K.; Rinehimer, J. Paul; Verney, Romaric; Ferré, Bénédicte

2018-05-01

We describe and demonstrate algorithms for treating cohesive and mixed sediment that have been added to the Regional Ocean Modeling System (ROMS version 3.6), as implemented in the Coupled Ocean-Atmosphere-Wave-Sediment Transport Modeling System (COAWST Subversion repository revision 1234). These include the following: floc dynamics (aggregation and disaggregation in the water column); changes in floc characteristics in the seabed; erosion and deposition of cohesive and mixed (combination of cohesive and non-cohesive) sediment; and biodiffusive mixing of bed sediment. These routines supplement existing non-cohesive sediment modules, thereby increasing our ability to model fine-grained and mixed-sediment environments. Additionally, we describe changes to the sediment bed layering scheme that improve the fidelity of the modeled stratigraphic record. Finally, we provide examples of these modules implemented in idealized test cases and a realistic application.

Infilling of the Hudson River Estuary During the Late Holocene (3000ka to Present): Implications for Estuarine Stratigraphic Models

NASA Astrophysics Data System (ADS)

McHugh, C. M.; Pekar, S. F.; Ryan, W. B.; Carbotte, S.; Bell, R.; Burckle, L.

2002-12-01

Estuaries are widely preserved in the geologic record and the estuarine fill, contained between non-marine sediment, provides an excellent temporal marker for continental margin studies. Estuarine stratigraphic models have provided a framework within which to interpret the estuarine fill. However, estuarine systems differ greatly in the shape of their valleys, the tectonic boundaries they cross, and in sediment supply so that their position in the geologic record may be out of sequence with that predicted by the models. New insights into estuarine systems and models are provided by the Hudson River Estuary (HRE; New York State) based on >150 cores and grab sediment samples and acoustic images documenting in great detail how the HRE filled its earlier excavated valley during the latest Holocene (3ka to present). Radiocarbon and 137-Cs radioisotope ages, borehole, and core data document the sedimentation patterns of the estuary. Diatom assemblages provide estimates of the shallowing-upwards of the estuary as its basin filled with sediments. The three areas of the stratigraphic model present in the HRE, include zones formed within inner fluvial and outer marine areas, (containing coarse-grained, sands and gravels), and a central area (containing fine-grained, silts and clays), that are nearly filled with little room for sediments to accumulate at or near sea-level. This has resulted in sedimentary bypass for almost the entire length the estuary. South of Kingston, fine-grained sediments have ceased accumulating when the bottom approaches wave base. Upstream from Kingston, final filling occurs as sediments fill in the remaining accommodation, forming islands. This should result in the export of sediment to the coastal zone. Instead, localized areas of sediment trapping still exist, which are related to the Hudson Valley Highlands and to the location of the estuarine turbidity maximum that hold large volumes of sediment. As a result minor volumes of Recent sediment are accumulating in coastal bays (Sandy Hook, New Jersey) and on the inner shelf, and sediment export to the Hudson Shelf Valley on the mid-shelf is nearly non-existent, with sediments dated at 14ka from 14-C on the outer shelf. Additionally, anthropogenic activities (construction of bridges and dredging) alter sedimentation patterns in the estuary leading to continued localized erosion and deposition. For example, sediment export onto the shelf is taking place, not by natural processes but by dredging. The variability documented for the HRE indicates that although estuarine and stratigraphic models provide a framework for continental margin studies, the models need to be interpreted, taking into consideration these factors.

Multielement chemical and statistical analyses from a uranium hydrogeochemical and stream-sediment survey in and near the Elkhorn Mountains, Jefferson County, Montana; Part II, Stream sediments

USGS Publications Warehouse

Suits, V.J.; Wenrich, K.J.

1982-01-01

Fifty-two stream-sediment samples, collected from an area south of Helena, Jefferson County, Montana, were sieved into two size fractions (50 ppm for the fine fraction) were encountered in samples from the Warm Springs Creek drainage area, along Prickly Pear Creek near Welmer and Golconda Creeks and along Muskrat Creek. All groups showed a significant correlation at the 99 percent confidence level (r between 0.73 and 0.77) between U and Th. Uranium was found to correlate significantly only with Th (as mentioned above) and with -Ni in the fine fraction of the volcanics group. U correlates significantly with -Al2O3, Ba, organic C, -K2O, -Sr and Y in both size fractions for the Boulder batholith. Correlations between U and each of several elements differ for the fine and coarse fractions of the Boulder batholith group, suggesting that the U distribution in these stream sediments is in large part controlled by grain size. Correlations were found between U and CaO, Cr, Fe203, -Na2O, Sc, -SiO2, TiO2, Yb and Zr in the coarse fraction but not in the fine fraction. U correlates weakly (to the 90% confidence level, crc<.37) with -Co and -Cu in the fine but not the coarse fraction. These results are compared to a previous study in the northern Absaroka mountains. Correlation coefficients between all other elements determined from these samples are also shown in Tables 12 to 15.

An historical assessment of trace metal accumulation in Lake Champlain, Vermont

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mecray, E.L.; King, J.W.

1993-03-01

The Lake Champlain watershed, with its increased land use, shoreline development, and population, is being threatened by pollutants in the water column and bottom sediments. A comprehensive study is currently being conducted to characterize the bottom sediments of the lake for toxicity and to reconstruct the history of pollutant inputs. Surface sediment samples were collected from 30 stations and analyzed for metal (Cu, Zn, Cr, Pb, Ni, Mn, Fe, Cd, Al, and Ag) concentrations to determine the contaminated regions of the lake. Once the contaminated regions were determined, a Nemesis corer was used to retrieve sediments cores averaging 1 metermore » in length from 10 sites within Lake Champlain. Grain size and metal analyses were conducted at one and two cm intervals down the cores. Grain size data, in combination with metal and radiometric stratigraphy, can serve as an indicator of changing land use in the watershed. The grain size in some cores has a fining upward trend indicating increased land use and soil erosion. Downcore variations in metal concentrations reveal two different regimes. The concentration at depth remain consistently low and are inferred to correspond with the natural background levels. In contrast, the upper section of the cores show abrupt increases in metal concentrations which are attributed to increased anthropogenic inputs. Radiometric ([sup 210] and [sup 137]Cs) and pollen chronostratigraphy of these cores indicates that the increased metal concentrations and the changes in grain size recorded in the upper most sediments is related to increased human disturbance beginning in the late 18th and early 19th centuries. This study demonstrates that the historical record of pollution inputs to Lake Champlain can be reconstructed from the sediment sequences.« less

Bathymetry, substrate and circulation in Westcott Bay, San Juan Islands, Washington

USGS Publications Warehouse

Grossman, Eric E.; Stevens, Andrew W.; Curran, Chris; Smith, Collin; Schwartz, Andrew

2007-01-01

Nearshore bathymetry, substrate type, and circulation patterns in Westcott Bay, San Juan Islands, Washington, were mapped using two acoustic sonar systems, video and direct sampling of seafloor sediments. The goal of the project was to characterize nearshore habitat and conditions influencing eelgrass (Z. marina) where extensive loss has occurred since 1995. A principal hypothesis for the loss of eelgrass is a recent decrease in light availability for eelgrass growth due to increase in turbidity associated with either an increase in fine sedimentation or biological productivity within the bay. To explore sources for this fine sediment and turbidity, a dual-frequency Biosonics sonar operating at 200 and 430 kHz was used to map seafloor depth, morphology and vegetation along 69 linear kilometers of the bay. The higher frequency 430 kHz system also provided information on particulate concentrations in the water column. A boat-mounted 600 kHz RDI Acoustic Doppler Current Profiler (ADCP) was used to map current velocity and direction and water column backscatter intensity along another 29 km, with select measurements made to characterize variations in circulation with tides. An underwater video camera was deployed to ground-truth acoustic data. Seventy one sediment samples were collected to quantify sediment grain size distributions across Westcott Bay. Sediment samples were analyzed for grain size at the Western Coastal and Marine Geology Team sediment laboratory in Menlo Park, Calif. These data reveal that the seafloor near the entrance to Westcott Bay is rocky with a complex morphology and covered with dense and diverse benthic vegetation. Current velocities were also measured to be highest at the entrance and along a deep channel extending 1 km into the bay. The substrate is increasingly comprised of finer sediments with distance into Westcott Bay where current velocities are lower. This report describes the data collected and preliminary findings of USGS Cruise B-6-07-PS conducted between May 31, 2007 and June 5, 2007.

Numerical experiments on breaking waves on contrasting beaches using a two-phase flow approach

NASA Astrophysics Data System (ADS)

Bakhtyar, R.; Barry, D. A.; Kees, C. E.

2012-11-01

A mechanistic understanding of beach environments needs to account for interactions of oceanic forcing and beach materials, in particular the role of waves on the evolution of the beach profile. A fully coupled two-phase flow model was used to simulate nearshore fluid-sediment turbulent flow in the cross-shore direction. It includes the Reynolds-Averaged Navier-Stokes equations and turbulent stress closures for each phase, and accounts for inter-granular stresses. The model has previously been validated using laboratory-scale data, so the results are likely more reliable for that scale. It was used to simulate wave breaking and the ensuing hydrodynamics and sediment transport processes in the surf/swash zones. Numerical experiments were conducted to investigate the effects of varying beach and wave characteristics (e.g., beach slope, sediment grain size, wave periods and heights) on the foreshore profile changes. Spilling and plunging breakers occur on dissipative and intermediate beaches, respectively. The impact of these wave/beach types on nearshore zone hydrodynamics and beach morphology was determined. The numerical results showed that turbulent kinetic energy, sediment concentrations and transport rate are greater on intermediate than on dissipative beaches. The results confirmed that wave energy, beach grain size and bed slope are main factors for sediment transport and beach morphodynamics. The location of the maximum sediment transport is near the breaking point for both beach types. Coarse- and fine-sand beaches differ significantly in their erosive characteristics (e.g., foreshore profile evolutions are erosive and accretionary on the fine and coarse sand beaches, respectively). In addition, a new parameter (based on main driving factors) is proposed that can characterize the sediment transport in the surf and swash zones. The results are consistent with existing physical observations, suggesting that the two-phase flow model is suitable for the simulation of hyper-concentrated mixed water-sediment flows in the nearshore. The model thus has potential as a useful tool for investigating interactions between nearshore hydrodynamics and beach morphology.

The mid-Holocene to present large-scale morphodynamic and coupled fluvial-tidal sedimentologic evolution of the Lower Columbia River, WA/OR, USA

NASA Astrophysics Data System (ADS)

Prokocki, E.; Best, J.; Ashworth, P. J.; Parsons, D. R.; Sambrook Smith, G.; Nicholas, A. P.; Simpson, C.; Wang, H.; Sandbach, S.; Keevil, C.

2015-12-01

Optically stimulated luminescence (OSL) dating of four deep sediment cores (≤ 20m depth), in conjunction with shallow vibracores (≤ 6m depth), obtained from mid-channel bars in the lower Columbia River (LCR), USA, provides new insights into the mid-Holocene to present geomorphic and coupled sedimentological evolution of the LCR fluvial-tidal zone. These data reveal that the relatively coarse-grained basal sediments of mid-channel bars positioned across the LCR tidal-fluvial hydraulic regime were deposited at c. 2.5 to 2.0 ka, and not at c. 8.0 ka as previously reported. Thus, these younger depositional ages of basal sediments relative to previous studies coupled with the overall sedimentary architecture of these bars, and the absence of a temporal lag in the timing of basal sedimentation between bars located from river kilometer 51.1 to 29.3, challenges existing models that these bars represent: (a) estuarine tidal-bars, or (b) bay-head deltaic deposits. Within the context of post glacial Holocene sea-level rise, our results suggest these bars represent vertical construction of a LCR fluvial top-set from c. 2.5- 2.0 ka to the present, as the regional rate of sea-level rise slowed to ≤ 1.4 mmyr-1. Within this geomorphic context, two tidal-fluvial sedimentological signatures can be identified: (i) in the downstream direction, basal bar deposits incorporate a larger percentage of finer-grained interbeds, and (ii) vertically stacked silt/very-fine sand draped current ripple cross-laminae become prevalent from approximately 5 m in depth to the bar surfaces. The preservation of finer-grained interbeds within basal bar deposits is reasoned to be caused by the flocculation and settling of suspended sediment enhanced by the turbidity maximum. The stacked draped current ripple cross-laminae are interpreted to result from tidal-currents generating asymmetric current ripples that were draped by fine-sediment entrained by wind-waves, which fell-out of suspension during reduced wave activity, slackwater intervals, and periods when the turbidity maximum was active.

Carbon Characteristics and Biogeochemical Processes of Uranium Accumulating Organic Matter Rich Sediments in the Upper Colorado River Basin

NASA Astrophysics Data System (ADS)

Boye, K.; Noel, V.; Tfaily, M. M.; Dam, W. L.; Bargar, J.; Fendorf, S. E.

2015-12-01

Uranium plume persistence in groundwater aquifers is a problem on several former ore processing sites on floodplains in the upper Colorado River Basin. Earlier observations by our group and others at the Old Rifle Site, CO, have noted that U concentrations are highest in organic rich, fine-grained, and, therefore, diffusion limited sediment material. Due to the constantly evolving depositional environments of floodplains, surficial organic matter may become buried at various stages of decomposition, through sudden events such as overbank flooding and through the slower progression of river meandering. This creates a discontinuous subsurface distribution of organic-rich sediments, which are hotspots for microbial activity and thereby central to the subsurface cycling of contaminants (e.g. U) and biologically relevant elements (e.g. C, N, P, Fe). However, the organic matter itself is poorly characterized. Consequently, little is known about its relevance in driving biogeochemical processes that control U fate and transport in the subsurface. In an investigation of soil/sediment cores from five former uranium ore processing sites on floodplains distributed across the Upper Colorado River Basin we confirmed consistent co-enrichment of U with organic-rich layers in all profiles. However, using C K-edge X-ray Absorption Spectroscopy (XAS) coupled with Fourier-Transformed Ion-Cyclotron-Resonance Mass-Spectroscopy (FT-ICR-MS) on bulk sediments and density-separated organic matter fractions, we did not detect any chemical difference in the organic rich sediments compared to the surrounding coarser-grained aquifer material within the same profile, even though there were differences in organic matter composition between the 5 sites. This suggests that U retention and reduction to U(IV) is independent of C chemical composition on the bulk scale. Instead it appears to be the abundance of organic matter in combination with a limited O2 supply in the fine-grained material that stimulate anaerobic microbial processes responsible for U enrichment. Thus, the chemical composition of organic matter is subordinate to the physical environment and total organic matter content in controlling U reduction and retention processes.

Fine-Grained Sediments; an Annotated Bibliography on Their Dynamic Behavior in Aquatic Systems.

DTIC Science & Technology

1987-09-01

rates would be in- creased less than 15 percent at Moon Island reach and Cow Point, Aberdeen, and South Aberdeen reaches; unchanged in the Crossover... Holstein takes place under influence of the supply of mud by the river Elbe and by erosion of older Holocene deposits on the flats in front of the

A multifaceted approach to prioritize and design bank stabilization measures along the Big Sioux River, South Dakota, USA

USDA-ARS?s Scientific Manuscript database

A multifaceted approach was used to manage fine-grained sediment loadings from river bank erosion along the Big Sioux River between Dell Rapids and Sioux Falls, South Dakota, USA. Simulations with the RVR Meander and CONCEPTS river-morphodynamics computer models were conducted to identify stream-ban...

Geomorphic responses to large check-dam removal on a mountain river in Taiwan

NASA Astrophysics Data System (ADS)

Wang, H.; Stark, C. P.; Cook, K. L.; Kuo, W.

2011-12-01

Dam removal has become an important aspect of river restoration in recent years, but studies documenting the physical and ecological response to dam removal are still lacking - particularly in mountain rivers and following major floods. This presentation documents the recent removal of a large dam on a coarse-grained, steep (an order of magnitude greater than on the Marmot) mountain channel in Taiwan. The Chijiawan river, a tributary of the Tachia River draining a 1236 km2 watershed, is the only habitat in Taiwan of the endangered Formosan landlocked salmon. The habitat of this fish has been cut significantly since the 1960s following construction of check dams designed to prevent reservoir sedimentation downstream. The largest and lowermost barrier on Chijiawan creek is the 15m high, "No. 1 Check Dam" built in 1971. Forty years later, in early 2011, the sediment wedge behind the dam had reached an estimated 0.2 million m3 and the dam toe had been scoured about 4m below its foundation, posing a serious risk of dam failure. For these reasons, the Shei-Pa National Park removed the dam in late May 2011. To monitor the response of the river to dam removal, we installed video cameras, time-lapse cameras, stage recorders, and turbidity sensors, conducted surveys of grain size distributions and longitudinal profiles, and carried out repeat photography. Channel changes were greatest immediately following removal as a result of the high stream power, steep energy slope, and unconsolidated alluvial fill behind the dam. Headcut propagation caused immediate removal of the sand-grade sediment and progressive channel widening. One month after dam removal, a minor flood event excavated a big wedge of sediment from the impoundment. Most of the subsequent downstream deposition occurred within 500m of the dam, with alluviation reaching up to 0.5m in places. Two months after dam removal, erosion had propagated 300m upstream into the impounded sediment along a bed profile of gradient at 1.4% at a headcut with a local gradient of 5.1%. The change in grain size was a fining of the sediment at the two downstream sites and a slight coarsening at the upstream site from April 2010 to July 2011. This is likely due to the increase in energy upstream of the dam post-removal, which has transported the fine-grained sediments downstream. As the river adjusts over coming months and years, we anticipate that observations such as these will help generate an important resource for all those concerned with dam removal and river restoration.

Suspended sediment dynamics in a large-scale turbidity current: Direct measurements from the deep-water Congo Canyon

NASA Astrophysics Data System (ADS)

Simmons, S.; Azpiroz, M.; Cartigny, M.; Clare, M. A.; Parsons, D. R.; Sumner, E.; Talling, P. J.

2016-12-01

Turbidity currents that transport sediment to the deep ocean deposit a greater volume of sediment than any other process on Earth. To date, only a handful of studies have directly measured turbidity currents, with flow durations ranging from a few minutes to a few hours. Our understanding of turbidity current dynamics is therefore largely derived from scaled laboratory experiments and numerical modelling. Recent years have seen the first field-scale measurements of depth-resolved velocity profiles, but sediment concentration (a key parameter for turbidity currents) remains elusive. Here, we present high resolution measurements of deep-water turbidity currents from the Congo Canyon; one of the world's largest submarine canyons. Direct measurements using acoustic Doppler current profilers (ADCPs) show that flows can last for many days, rather than hours as seen elsewhere, and provide the first quantification of concentration and grain size within deep-water turbidity currents.Velocity and backscatter were measured at 5 second intervals by an ADCP suspended 80 m above the canyon floor, at 2000 m water depth. A novel inversion method using multiple ADCP frequencies enabled quantification of sediment concentration and grain size within the flows. We identify high concentrations of coarse sediment within a thin frontal cell, which outruns a thicker, trailing body. Thus, the flows grow in length while propagating down-canyon. This is distinct from classical models and other field-scale measurements of turbidity currents. The slow-moving body is dominated by suspended fine-grained sediment. The body mixes with the surrounding fluid leaving diffuse clouds of sediment that persist for days after initial entrainment. Ambient tidal flow also controls the mixing within the body and the surrounding fluid. Our results provide a new quantification of suspended sediment within flows and the interaction with the surrounding fluid.

Contrasting mercury and manganese deposition in a mangrove-dominated estuary (Guaratuba Bay, Brazil)

NASA Astrophysics Data System (ADS)

Sanders, C. J.; Santos, I. R.; Silva-Filho, E. V.; Patchineelam, S. R.

2008-08-01

Sediment cores were taken at seven sites along the mangrove-bound Guaratuba Bay estuary (southern Brazil), with the purpose of assessing conditions controlling Hg deposition along a horizontal estuarine sediment gradient. The data suggest contrasting depositional patterns for Hg and Mn in this relatively pristine setting. Total Hg contents of bulk sediments ranged from 12 to 36 ng/g along the estuary, the highest values being found in muddier organic-rich sediments of the upper estuary (the corresponding mud gradient is 12 to 42 wt.%, and the organic matter gradient 4 to 10 wt.%). Thus, the deposition of fine sediments relatively enriched in mercury occurs primarily in closer proximity to the freshwater source. The data also indicate a reverse gradient in reactive Mn contents, ranging from 29 to 81 μg/g, and increasing seaward. This implies that reactive Mn is mobilized from fine-grained reducing mangrove forest sediments in the upper estuary, and deposited downstream in sandier, oxygen-rich nearshore sediments. These results suggest that mangrove-surrounded estuaries may act as barriers to mercury transport to coastal waters, but as a source of manganese. The present findings also imply that reactive Mn may be used as an indication of Hg depositional patterns in other similar coastal sedimentary settings.

Shallow marine event sedimentation in a volcanic arc-related setting: The Ordovician Suri Formation, Famatina range, northwest Argentina

USGS Publications Warehouse

Mangano, M.G.; Buatois, L.A.

1996-01-01

The Loma del Kilome??tro Member of the Lower Ordovician Suri Formation records arc-related shelf sedimentation in the Famatina Basin of northwest Argentina. Nine facies, grouped into three facies assemblages, are recognized. Facies assemblage 1 [massive and parallel-laminated mudstones (facies A) locally punctuated by normally graded or parallel-laminated silty sandstones (facies B] records deposition from suspension fall-out and episodic storm-induced turbidity currents in an outer shelf setting. Facies assemblage 2 [massive and parallel-laminated mudstones (facies A) interbedded with rippled-top very fine-grained sandstones (facies D)] is interpreted as the product of background sedimentation alternating with distal storm events in a middle shelf environment. Facies assemblage 3 [normally graded coarse to fine-grained sandstones (facies C); parallel-laminated to low angle cross-stratified sandstones (facies E); hummocky cross-stratified sandstones and siltstones (facies F); interstratified fine-grained sandstones and mudstones (facies G); massive muddy siltstones and sandstones (facies H); tuffaceous sandstones (facies I); and interbedded thin units of massive and parallel-laminated mudstones (facies A)] is thought to represent volcaniclastic mass flow and storm deposition coupled with subordinated suspension fall-out in an inner-shelf to lower-shoreface setting. The Loma del Kilo??metro Member records regressive-transgressive sedimentation in a storm- and mass flow-dominated high-gradient shelf. Volcano-tectonic activity was the important control on shelf morphology, while relative sea-level change influenced sedimentation. The lower part of the succession is attributed to mud blanketing during high stand and volcanic quiescence. Progradation of the inner shelf to lower shoreface facies assemblage in the middle part represents an abrupt basinward shoreline migration. An erosive-based, non-volcaniclastic, turbidite unit at the base of this package suggests a sea level fall. Pyroclastic detritus, andesites, and a non-volcanic terrain were eroded and their detritus was transported basinward and redeposited by sediment gravity flows during the low stand. The local coexistence of juvenile pyroclastic detritus and fossils suggests reworking of rare ash-falls. The upper part of the Loma del Kilo??metre Member records a transgression with no evidence of contemporaneous volcanism. Biostratinomic, paleoecologic, and ichnologic analyses support this paleoenvironmental interpretations and provide independent evidence for the dominance of episodic sedimentation in an arc-related shallow marine setting. Fossil concentrations were mainly formed by event processes, such as storms and volcaniclastic mass flows. High depositional rates inhibited formation of sediment-starved biogenic concentrations. Collectively, trace fossils belong to the Cruziana ichnofacies. Low diversity, scarcity, and presence of relatively simple forms indicate benthic activity under stressful conditions, most probably linked to high sedimentation rates. Contrasting sedimentary dynamics between 'normal shelves' and their volcaniclastic counterparts produce distinct and particular signatures in the stratigraphic record. Arc-related shelves are typified by event deposition with significant participation of sediment gravity flows, relatively high sedimentation rates, textural and mineralogical immaturity of sediments, scarcity and low diversity of trace fossils, and dominance of transported and reworked faunal assemblages genetically related to episodic processes.

Sediment characteristics and provenance of the Taiwan Shoal in the southern Taiwan Strait

NASA Astrophysics Data System (ADS)

Koo, W. S.; Lin, A. T.; Kuo, L. W.; Lee, Y. H.

2016-12-01

The Taiwan Shoal in the southern Taiwan Strait exhibits a lobe-shaped shallow water area, with a depth less than around 40 m and an area approximately of 13,000 km2. The Shoal consists of relict sediments remnant from deltaic deposits during the last glacial period and associated with the paleo-Min River. We collected seafloor sediments in and around the Taiwan Shoal to study the sediment characteristics and provenance of the Shoal as well as Taiwanese river sediments to characterize sediment sourced from southern Taiwan. Our results help to understand possible sediment delivery pathways in a source-to-sink context from the southern Taiwan Strait to the northern South China Sea. The method of X-ray diffraction is used to identify mineral compositions for muds and mineral compositions are examined under polarized microscope for sands. Zircon grains are separated from heavy minerals for U-Pb dating in order to understand the sediment source terranes. Sediments of the Taiwan Shoal are mostly tawny-colored, medium to coarse-grained sands with abundant shell fragments and shallow-water benthic foraminifera. Sediments to the south of the Taiwan Shoal and in the outer shelf consist of dark brown-colored and fine-grained sands with rare shell fragments. Siliciclastic compositions of the Taiwan Shoal sediments are mostly quartz. The second abundant composition is rock fragments with more occurrences near the Chinese coastline and the Penghu archipelago. Slate fragments are found to occur near Taiwan, especially in the Penghu Channel area. Clay minerals from the Penghu Channels and south of the Taiwan Shoal are dominated by illite and chlorite with minor smectite and kaolinite. The sediment colors and mineral species are very different for the sediments of the Taiwan Shoal and outer shelf, revealing that these two areas featuring different oceanographic processes and sediment provenance.

Insight into the geology of the East Antarctic hinterland: a study of sediment inclusions from ice cores of the Lake Vostok borehole

USGS Publications Warehouse

Leitchenkov, G.L.; Belyatsky, B.V.; Rodionov, N.V.; Sergeev, S.A.

2007-01-01

refrozen from the lake water. This ice layer contains random sediment inclusions, eight of which have been studied using state-of the-art analytical techniques. Six inclusions comprise soft aggregates consisting mainly of clay-mica minerals and micron-sized quartz grains while two others are solid clasts of fine-grained cemented rocks. The largest rock clast consists of poorly-rounded quartz and minor amounts of accessory minerals and is classified as quartzose siltstone. More than twenty grains of zircon and monazite have been identified in this siltstone and dated by SIMS SHRIMP-II. Two age clusters have been recognized for these detrital grains, in the ranges 0.8−1.2 Ga and 1.6−1.8 Ga. The compositions of the rock clasts suggest that the bedrock situated to the west of Lake Vostok is sedimentary. The age data on the detrital accessory minerals suggest that the provenance of these sedimentary rocks − the Gamburtsev Mountains and Vostok Subglacial Highlands, is mainly represented by Paleoproterozoic and MesoproterozoicNeoproterozoic crustal provinces

Holocene sedimentation and coastal wetlands response to rising sea level at the Aucilla river mouth, a low energy coast in the Big Bend area of Florida

USGS Publications Warehouse

Garrett, Connie; Hertler, Heidi; Hoenstine, Ronald; Highley, Brad

1993-01-01

The shallow dip of the Florida carbonate platform results in low wave energy on Florida ???Big Bend??? coasts. Therefore sedimentation is dominated by river-and tidal-hydrodynamics near the Aucilla River mouth. Where present, Holocene sediments are thin and unconformably overlie Oligocene-aged Suwannee Limestone. The oldest unlithified sediments include reworked carbonate rubble with clay and wood fragments (seven thousand years old or less, based on wood radio-carbon dating). Although this basal sequence is observed in most areas, the sediments that overlie it vary. Sediment sequences from the outer littoral to submarine environments include organic-rich sands, oyster biotherm remains, and cleaner sands with organic-filled burrows. Inner littoral (salt-marsh) sequences generally consist of sandy, fining-upwards sequences in which dry weights of fine-grained clastics and organic components increase up-sequence at similar rates. Offshore sediments preserve greatly attenuated fluvial and salt-marsh facies, if these facies are preserved at all. With sea-level rise, erosion can result from insufficient sediment supply and down-cutting by tidal currents (Dolotov, 1992; and Dalrymple et al., 1992). Dolotov (1992) attributes displacement of original coastal stratigraphy to insufficient sediments for beach profile maintenance, while Dalrymple et al. (1992) attribute erosional truncation (ravinement) or complete removal of portions of typical estuarine sequences to headward migration of tidal channels.

Early Diagenesis of Subseafloor Sandy Sediments Closely Related to Gas Hydrate Occurrences and Their Provenances in the Eastern Margin of Japan Sea

NASA Astrophysics Data System (ADS)

Uchida, T.; Sakai, H.; Horiuchi, S.; Matsumoto, R.

2015-12-01

A lot of effort have been put into recovering gas hydrate, methane induced carbonate, and associated sediments in order to develop the geologic model of gas hydrate accumulation and evaluate its possible environmental impact for the last glacial-interglacial cycles. Having investigated gas hydrate occurrences in the eastern margin of Japan Sea revealed wide distributions of chimney-shape gas hydrate concentrations beneath the seafloor, confirmed off Shimane and off Akita/Yamagata as well as off Joetsu (Niigata), which are quite different from the occurrences of pore space hydrate filling intergranular pore systems of sands recognized in Nankai Trough, Mallik and other sites. Many sediment samples have been obtained below from the Umitaka Spur, Joetsu Channel, Toyama Trough, Mogami Trough and Okushiri Ridge areas. Small amounts of sandy sediment have been retrieved as thin intercalations in Holocene and Pleistocene silty/muddy layers, where trace fossils and strong bioturbations are commonly observed. Sandy sediments consist of very fine- to fine-grained sand grains, and are sometimes tuffaceous. Pore-size distribution measurements and thin-section observations of these sands were carried out, which indicate that porosities of silty sediments are around 50 % but those of arenites range from 42 to 52 %, of which mean pore sizes and permeabilities are larger than those of silty sediments. These coarser sediments might have been transported approximately around 3 to 30 ka due to the tephra ages, where supplying sediments might be abundant due to sea level fluctuation during the Pleistocene ice age. Sandy sediments contain not only detrital quartz and feldspar but mafic minerals (pyroxene, amphibole and mica), contents of which may indicate their provenances. Silty/muddy sediments usually contain diatom tests, foraminifers and framboidal pyrites, and, in particular, the shapes of diatom are usually various, dominantly fragmental and infrequently preserved. It is remarked that physical diagenesis proceeds first due to mechanical compaction, whereas chemical diagenesis advances very slowly in early diagenesis. This study was performed as a part of the MH21 Research Consortium on methane hydrate in Japan and the METI project entitled "FY2014 promoting research and development on methane hydrate."

Lake Sediment Particle Size Analysis for Holocene Paleoenvironmental Study of Steens Mountain, Eastern Oregon

NASA Astrophysics Data System (ADS)

Morris, J.; Stoner, J. S.; Reilly, B. T.; Hatfield, R. G.; Konyndyk, D.; Abbott, M. B.; Finkenbinder, M. S.; Hillman, A. L.

2016-12-01

In order to better understand climate trends in the late Pleistocene and Holocene in southeast Oregon, we present a sedimentological analysis of Fish Lake, Harney County, Oregon. Fish Lake (42° 44' 15" N, 118° 38' 57" W, 2,246.7 m) sits on the west slope of Steens Mountain, a fault-block mountain of Miocene basalt, adjacent to a glacial moraine. The present environment is high desert with sub alpine steppe vegetation, receiving approximately 12" of precipitation annually. The lake was cored in August 2013 with a series of overlapping drives, correlated by six distinct tephra and magnetic susceptibility. The composite section provides a 7.5 m continuous record of at least the last 13 ka, constrained by an age model built with 13 terrestrial macrofossil 14C dates. The recovered sediments, consisting of fine terrigenous and biogenous material in varying proportions, were analyzed with computed tomography (CT) scans, x-ray fluorescence (XRF) scans, magnetic measurements, loss on ignition (LOI), and sediment grain-size. CT and LOI data reveal a low density, high organic interval in the early Holocene ( 8.5-11 ka) with relatively coarse and well-sorted grain-size, suggesting an extended period of low lake level and low precipitation. Sediment grain-sizes are variable through the middle and late Holocene with high amplitude longer period features from 3 ka to the present. We investigate these grain-size fluctuations in the context of regional Holocene records.

Seabed maps showing topography, ruggedness, backscatter intensity, sediment mobility, and the distribution of geologic substrates in Quadrangle 6 of the Stellwagen Bank National Marine Sanctuary Region offshore of Boston, Massachusetts

USGS Publications Warehouse

Valentine, Page C.; Gallea, Leslie B.

2015-11-10

The U.S. Geological Survey (USGS), in cooperation with the National Oceanic and Atmospheric Administration's National Marine Sanctuary Program, has conducted seabed mapping and related research in the Stellwagen Bank National Marine Sanctuary (SBNMS) region since 1993. The area is approximately 3,700 square kilometers (km2) and is subdivided into 18 quadrangles. Seven maps, at a scale of 1:25,000, of quadrangle 6 (211 km2) depict seabed topography, backscatter, ruggedness, geology, substrate mobility, mud content, and areas dominated by fine-grained or coarse-grained sand. Interpretations of bathymetric and seabed backscatter imagery, photographs, video, and grain-size analyses were used to create the geology-based maps. In all, data from 420 stations were analyzed, including sediment samples from 325 locations. The seabed geology map shows the distribution of 10 substrate types ranging from boulder ridges to immobile, muddy sand to mobile, rippled sand. Mapped substrate types are defined on the basis of sediment grain-size composition, surface morphology, sediment layering, the mobility or immobility of substrate surfaces, and water depth range. This map series is intended to portray the major geological elements (substrates, topographic features, processes) of environments within quadrangle 6. Additionally, these maps will be the basis for the study of the ecological requirements of invertebrate and vertebrate species that utilize these substrates and guide seabed management in the region.

Quantifying the in-channel retention of cohesive sediments during artificial flood events using FTIR-DRIFT spectrometry

NASA Astrophysics Data System (ADS)

Kurtenbach, A.; Gallé, T.; Buis, K.; de Sutter, R.; Troch, P.; Eisold, B.; Bierl, R.; Symader, W.

2010-05-01

Cohesive sediments control river ecosystem quality both as a transport medium for contaminants and as clogging material of stream bottom habitats. However, experimental field studies with fine-grained sediments in fluvial systems are rather scarce owing to the lack of adequate tracers and detection methods. As a result, current modelling approaches only insufficiently describe hydrodynamic transport and depositional behaviour of fine-grained sediments in rivers. We adopted two strategies to specifically study cohesive sediment dynamics in natural systems under defined boundary conditions. First, artificial floods were generated in the Olewiger Bach basin (24 km²), a mid-mountain gravel bed river, in order to characterise the in-channel fine sediment dynamics on their own. The advantage of these artificial flood waves lies in the selective control on some governing processes by experimental design. Second, fine sediment transport and deposition during these controlled reservoir releases were analysed by introducing the clay mineral kaolinite as a fine particle tracer, whose concentration was measured by Fourier transform infrared spectroscopy (FTIR) in diffuse reflectance mode (DRIFT). The DRIFT technique offers some important advantages such as the ability to assess both mineral and organic structures in aquatic particles, good sensitivity and high throughput (Gallé et al. 2004). Our laboratory tests confirm that FTIR-DRIFT spectrometry is capable of detecting the kaolinite tracer even in low percentage solid concentrations. The mass balance of the injected kaolinite for near bank-full artificial floods showed that, in spite of the very fine material and the non-stationary boundary conditions, over 50 percent of the tracer could be retained over a flow length of only 500 m. By combining fine particulate and natural dissolved tracers (e.g. dissolved organic carbon, DOC) we were able to identify the hyporheic zone as a potential short-term retention and storage zone for the introduced kaolinite. Thus, hyporheic exchange and/or deposition losses in riverine dead and channel periphery zones are significant determinants for the mass balance of cohesive particles during floods. Within a multidisciplinary research group, accentuating the relevance and interaction of hydraulic, groundwater, biogeochemical and ecological processes, we will model the kaolinite retention dynamics. This will be performed with the STRIVE-package (STReam-RIVer Ecosystem) developed in the modelling platform "FEMME" (http://www.nioo.knaw.nl/projects/femme). FEMME (a Flexible Environment for Mathematically Modelling the Environment) takes care of the basic necessities for dynamic ecological modelling along with other facilities (calibration, validation, sensitivity analysis, output formulation etc.). It supports a modular structure, facilitating an easy implementation or exchange of submodels to build ecosystem models of different complexity. STRIVE is such a package devoted to model stream or river ecosystems by linking different submodels (e.g. hydraulic and solute/particle transport modules, hyporheic zone module, groundwater module etc.) to integrate and study process interactions and the role of lateral exchanges with adjacent subsystems. A brief overview concerning this modelling environment and its adaptation on the Olewiger Bach system will be outlined. References Gallé, T., Van Lagen, B., Kurtenbach, A., Bierl, R. (2004): An FTIR-DRIFT Study on River Sediment Particle Structure: Implications for Biofilm Dynamics and Pollutant Binding. - Environmental Science and Technology, 38, 4496-4502.

Holocene reworking of a sand sheet in the Merrimack Embayment, Western Gulf of Maine

USGS Publications Warehouse

Hein, C.J.; FitzGerald, D.M.; Barnhardt, W.

2007-01-01

Recent bathymetric, backscatter, and seafloor sediment samples demonstrate that a large sand sheet was formed in the inner shelf by the reworking of the Merrimack River lowstand delta (deposited 12 kya; currently at 45 m depth) and braid plain during the Holocene transgression. Asymmetric bedforms and distinct grain size distributions suggest the sand sheet is actively being reworked by inner-shelf processes. Bottom sediments range from silty sand at the submerged delta to coarse sand and fine gravel in the innermost shelf (depth: 10-50 m). Coarse-grained sand comprises an expansive (32 km2 ) featureless sand sheet centered off the Merrimack River. Fine-grained sand discontinuously overlies this sand sheet in many locations and forms long wavelength (100 – 800 m), low amplitude (1-2 m), asymmetrical bedforms. Sets of these bedforms are oriented from slightly oblique offshore to onshore; several bedform sets are located within 1 km and oriented orthogonally to one another. Along the paleo-delta front north-northwest oriented bedforms are dominant. Inshore of these features, the bedforms become more closely spaced and have orientations to the west and westsouthwest. Preliminary data suggest that the combined forcings of instantaneous storm-wave generated shear stress and storm-induced currents associated with high energy northeast storm events may be responsible for sand sheet reworking and bedform development.

Preservation of primary porosity in the Neogene clastic reservoirs of the Surma Basin, Bangladesh

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ferdous, H.S.; Renaut, R.W.

1996-01-01

The Surma Basin is a Tertiary sub-basin within the greater Bengal Basin, in N.E. Bangladesh. The Neogene sequence ([approximately]17 km thick) contains the producing hydrocarbon reservoirs with proven gas reserves. These sediments are alternating coarse and fine clastics, representing a complex interfingering of deltaic and marine subenvironments, with the former dominating. The principal reservoir facies are distributary channel-fill sandstones in a lower delta-plain setting. Kailashtila, Beanibazar and Rashidpur, located in anticlinal structures, are major hydrocarbon-producing fields in the E. Surma Basin. Petrographic analysis shows that primary intergranular porosity mainly controls the reservoir quality of these Neogene sands, which occur atmore » a depth of [approximately]3000 m. Most samples show primary pores with about 20% porosity and permeabilities of about 200 mD. The preservation of a higher proportion of primary pores in fine to medium grained sandstones is a result of (1) moderate compaction resulting from overpressuring caused by a higher rate of subsidence and sedimentation, (2) weak cementation, and (3) a general lack of deleterious clays and the presence of some grain-rimming chlorites. The general absence of long and sutured grain contacts also supports these observations. Some of the existing literature suggests that secondary pores are dominant in the Neogene sandy reservoirs of the Bengal Basin; however, they contribute little ([approximately]2%) to the total porosity in the Surma Basin.« less

Preservation of primary porosity in the Neogene clastic reservoirs of the Surma Basin, Bangladesh

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ferdous, H.S.; Renaut, R.W.

1996-12-31

The Surma Basin is a Tertiary sub-basin within the greater Bengal Basin, in N.E. Bangladesh. The Neogene sequence ({approximately}17 km thick) contains the producing hydrocarbon reservoirs with proven gas reserves. These sediments are alternating coarse and fine clastics, representing a complex interfingering of deltaic and marine subenvironments, with the former dominating. The principal reservoir facies are distributary channel-fill sandstones in a lower delta-plain setting. Kailashtila, Beanibazar and Rashidpur, located in anticlinal structures, are major hydrocarbon-producing fields in the E. Surma Basin. Petrographic analysis shows that primary intergranular porosity mainly controls the reservoir quality of these Neogene sands, which occur atmore » a depth of {approximately}3000 m. Most samples show primary pores with about 20% porosity and permeabilities of about 200 mD. The preservation of a higher proportion of primary pores in fine to medium grained sandstones is a result of (1) moderate compaction resulting from overpressuring caused by a higher rate of subsidence and sedimentation, (2) weak cementation, and (3) a general lack of deleterious clays and the presence of some grain-rimming chlorites. The general absence of long and sutured grain contacts also supports these observations. Some of the existing literature suggests that secondary pores are dominant in the Neogene sandy reservoirs of the Bengal Basin; however, they contribute little ({approximately}2%) to the total porosity in the Surma Basin.« less

Experimental tsunami deposits: Linking hydrodynamics to sediment entrainment, advection lengths and downstream fining

NASA Astrophysics Data System (ADS)

Johnson, Joel P. L.; Delbecq, Katie; Kim, Wonsuck; Mohrig, David

2016-01-01

A goal of paleotsunami research is to quantitatively reconstruct wave hydraulics from sediment deposits in order to better understand coastal hazards. Simple models have been proposed to predict wave heights and velocities, based largely on deposit grain size distributions (GSDs). Although seemingly consistent with some recent tsunamis, little independent data exist to test these equations. We conducted laboratory experiments to evaluate inversion assumptions and uncertainties. A computer-controlled lift gate instantaneously released 6.5 m3 of water into a 32 m flume with shallow ponded water, creating a hydraulic bore that transported sand from an upstream source dune. Differences in initial GSDs and ponded water depths influenced entrainment, transport, and deposition. While the source dune sand was fully suspendable based on size alone, experimental tsunamis produced deposits dominated by bed load sand transport in the upstream 1/3 of the flume and suspension-dominated transport downstream. The suspension deposits exhibited downstream fining and thinning. At 95% confidence, a published advection-settling model predicts time-averaged flow depths to approximately a factor of two, and time-averaged downstream flow velocities to within a factor of 1.5. Finally, reasonable scaling is found between flume and field cases by comparing flow depths, inundation distances, Froude numbers, Rouse numbers and grain size trends in suspension-dominated tsunami deposits, justifying laboratory study of sediment transport and deposition by tsunamis.

Single-Grain OSL Dating of Early Middle Palaeolithic Deposits at Cuesta de la Bajada, Ebro Basin, Spain

NASA Astrophysics Data System (ADS)

Arnold, L. J.; Demuro, M.; Santonja, M.; Perez-Gonzalez, A.

2012-12-01

The open-air site of Cuesta de la Bajada comprises a 2-2.5 m-thick sequence of fluvial-lacustrine sediments inset into the +50-60 m terrace deposits preserved along the south-eastern margins of the Alfambra river valley, Teruel, Spain. The main archaeological horizons lie ~20 m above the present-day river level and consists of an upward-fining sequence of massive fluvial silts and fine sands with dispersed gravels, detritic marls and shales that collectively overlie a series of planar bedded fluvial gravels. These units have yielded ~3000 lithic artefacts displaying reduction techniques characteristic of an early Middle Palaeolithic techno-complex, as well as a multitude of faunal remains indicative of a late Middle Pleistocene origin. The paucity of open-air Palaeolithic sites in the interior eastern sector of the Iberian Peninsula, and the relatively low number of documented early Middle Palaeolithic archives in this region, means that Cuesta de la Bajada is of key importance for understanding the coexistence/transition of Iberian Acheulean and Mousterian techno-complexes during the Middle Pleistocene period. Establishing reliable absolute chronologies at Cuesta de la Bajada remains essential for understanding the regional significance of this site. In an attempt to redress the existing chronological uncertainty we are undertaking an interdisciplinary dating study of the Middle Palaeolithic deposits using OSL dating, ESR/U-series dating of teeth and ESR dating of sedimentary quartz. Here we present results obtained using quartz single-grain OSL dating of 4 samples collected from a 7 m vertical profile bracketing the archaeological horizons. 2 samples were collected from the archaeology-bearing silt and fine sand horizons, while the remaining samples were obtained from well-bedded fine-sands and silts 3.5 m above and 3 m below the main excavation. The measured quartz grains are characterised by relatively bright OSL signals and typically display dose-response curves with very high saturation limits. The latter offers the advantage of extending the age range over which single-grain techniques can be applied in this Middle Pleistocene context. Dose-recovery tests performed at high doses of 470 Gy yielded accurate equivalent dose (De) results with low overdispersion, providing reasonable confidence in the chosen measurement conditions. 3 of the samples display single-grain De distributions with low levels of dispersion indicating that the sediments were adequately bleached prior to burial and remained undisturbed thereafter. The fourth sample displays higher De dispersion and a younger subpopulation of grains, which could be explained by beta-dose heterogeneity associated with interspersed gravels within the basal archaeological horizon. We apply various statistical age models to derive final chronologies and compare the resultant single-grain ages with those obtained using different absolute dating methods. We also report on experiments performed using 'synthetic multi-grain aliquots' created from the single-grain De datasets, and discuss their implications for the reliability of multi-grain OSL dating techniques in this context.

Single-grain OSL dating of Early Middle Palaeolithic deposits at Cuesta de la Bajada, Ebro Basin, Spain

NASA Astrophysics Data System (ADS)

Arnold, Lee; Demuro, Martina; Santonja, Manuel; Perez-Gonzalez, Alfredo; Pares, Josep

2013-04-01

The open-air site of Cuesta de la Bajada comprises a 2-2.5 m-thick sequence of fluvial-lacustrine sediments inset into the +50-60 m terrace deposits preserved along the south-eastern margins of the Alfambra river valley, Teruel, Spain. The main archaeological horizons lie ~20 m above the present-day river level and consists of an upward-fining sequence of massive fluvial silts and fine sands with dispersed gravels, detritic marls and shales that collectively overlie a series of planar bedded fluvial gravels. These units have yielded ~3000 lithic artefacts displaying reduction techniques characteristic of an early Middle Palaeolithic techno-complex, as well as a multitude of faunal remains indicative of a late Middle Pleistocene origin. The paucity of open-air Palaeolithic sites in the interior eastern sector of the Iberian Peninsula, and the relatively low number of documented early Middle Palaeolithic archives in this region, means that Cuesta de la Bajada is of key importance for understanding the coexistence/transition of Iberian Acheulean and Mousterian techno-complexes during the Middle Pleistocene period. Establishing reliable absolute chronologies at Cuesta de la Bajada remains essential for understanding the regional significance of this site. In an attempt to redress the existing chronological uncertainty we are undertaking an interdisciplinary dating study of the Middle Palaeolithic deposits using OSL dating, ESR/U-series dating of teeth and ESR dating of sedimentary quartz. Here we present results obtained using quartz single-grain OSL dating of 4 samples collected from a 7 m vertical profile bracketing the archaeological horizons. 2 samples were collected from the archaeology-bearing silt and fine sand horizons, while the remaining samples were obtained from well-bedded fine-sands and silts 3.5 m above and 3 m below the main excavation. The measured quartz grains are characterised by relatively bright OSL signals and typically display dose-response curves with very high saturation limits. The latter offers the advantage of extending the age range over which single-grain techniques can be applied in this Middle Pleistocene context. Dose-recovery tests performed at high doses of 470 Gy yielded accurate equivalent dose (De) results with low overdispersion, providing reasonable confidence in the chosen measurement conditions. Three of the samples display single-grain De distributions with low levels of dispersion indicating that the sediments were adequately bleached prior to burial and remained undisturbed thereafter. The fourth sample displays higher De dispersion and a younger subpopulation of grains, which could be explained by beta-dose heterogeneity associated with interspersed gravels within the basal archaeological horizon. We apply various statistical age models to derive final chronologies and compare the resultant single-grain ages with those obtained using different absolute dating methods. We also report on experiments performed using 'synthetic multi-grain aliquots' created from the single-grain De datasets, and discuss their implications for the reliability of multi-grain OSL dating techniques in this context.

Water-quality, bed-sediment, and biological data (October 2012 through September 2013) and statistical summaries of data for streams in the Clark Fork Basin, Montana

USGS Publications Warehouse

Dodge, Kent A.; Hornberger, Michelle I.; Dyke, Jessica

2014-01-01

This report presents the analytical results and quality-assurance data for water-quality, bed-sediment, and biota samples collected at sites from October 2012 through September 2013. Water-quality data include concentrations of selected major ions, trace elements, and suspended sediment. Turbidity and dissolved organic carbon were analyzed for water samples collected at the four sites where seasonal daily values of turbidity were being determined. Daily values of mean suspended-sediment concentration and suspended-sediment discharge were determined for four sites. Bed-sediment data include trace-element concentrations in the fine-grained fraction. Biological data include trace-element concentrations in whole-body tissue of aquatic benthic insects. Statistical sum-maries of water-quality, bed-sediment, and biological data for sites in the upper Clark Fork Basin are provided for the period of record.

Water-quality, bed-sediment, and biological data (October 2013 through September 2014) and statistical summaries of data for streams in the Clark Fork Basin, Montana

USGS Publications Warehouse

Dodge, Kent A.; Hornberger, Michelle I.

2015-12-24

This report presents the analytical results and qualityassurance data for water-quality, bed-sediment, and biota samples collected at sites from October 2013 through September 2014. Water-quality data include concentrations of selected major ions, trace elements, and suspended sediment. At 12 sites, dissolved organic carbon and turbidity samples were collected. In addition, nitrogen (nitrate plus nitrite) samples were collected at two sites. Daily values of mean suspended-sediment concentration and suspended-sediment discharge were determined for four sites. Seasonal daily values of turbidity were determined for four sites. Bed-sediment data include trace-ele­ment concentrations in the fine-grained fraction. Biological data include trace-element concentrations in wholebody tissue of aquatic benthic insects. Statistical summaries of water-quality, bed-sediment, and biological data for sites in the upper Clark Fork Basin are provided for the period of record.

Magnetic study of turbidites

NASA Astrophysics Data System (ADS)

Tanty, Cyrielle; Valet, Jean Pierre; Carlut, Julie

2015-04-01

Turbidites induce sedimentary reworking and re-deposition caused by tsunami, earthquake, volcanic processes, and other catastrophic events. They result from rapid depositional processes and are thus considered not being pertinent for comparison with pelagic sediments. Turbidites are evidently ruled out from paleomagnetic records dealing with time-series. Consequently, no attention has ever been paid to the magnetization of turbidites which is fully justified if the high level of turbulence governing the depositional processes influences the acquisition of magnetization. In certain conditions like channeled turbidity currents, levees of sediment are generated and then associated with relatively calm although very fast redeposition processes. Such conditions will thus govern the subsequent acquisition of magnetization through mechanical lock-in of the magnetic grains. This situation is actually quite similar to what happens during the experiences of artificial redeposition that are conducted in laboratory. Therefore, combining laboratory experiments and studies of natural turbidites could reveal important information on the processes involved in the acquisition of magnetization, especially if the comparison with the overlying hemipelagic sediments does not show any striking difference. We will present the results of magnetic measurements performed on four different and relatively recent turbidites. We selected different origins associated either with spillover of channeled turbidity currents or with co-seismic faulting. Each event is characterized by a different thickness (ten to few tens of cm), lithology and mean granulometry (few tens of μm to hundreds of μm). We have carried out measurements of magnetic susceptibility, magnetic remanence, anisotropy of magnetic susceptibility (AMS) and we also scrutinize the evolution of various rock magnetic parameters (ARM, IRM, S ratio, magnetic grain sizes, hysteresis parameters…). The magnetic characteristics of the turbiditic levels have been compared with those of the surrounding hemipelagic sediments. In all cases, the magnetization of remanence reflect the expected field direction at the site location without significant change in direction inside the turbiditic levels. This is an indication that magnetization acquisition likely obeys the same rules as for slowly deposited hemipelagic sediments. As expected there is a grain size grading with relatively coarse sediment at the bottom and fine-grained sediment at the top, similarly to what is observed with laboratory redeposited sediments and thus further justify the comparison. Surprisingly, in most cases the magnetic grain sizes follow a similar pattern, which would imply that magnetic grains were not clustered inside sedimentary particles, otherwise we would expect a different relationship.

Fish as major carbonate mud producers and missing components of the tropical carbonate factory

PubMed Central

Perry, Chris T.; Salter, Michael A.; Harborne, Alastair R.; Crowley, Stephen F.; Jelks, Howard L.; Wilson, Rod W.

2011-01-01

Carbonate mud is a major constituent of recent marine carbonate sediments and of ancient limestones, which contain unique records of changes in ocean chemistry and climate shifts in the geological past. However, the origin of carbonate mud is controversial and often problematic to resolve. Here we show that tropical marine fish produce and excrete various forms of precipitated (nonskeletal) calcium carbonate from their guts (“low” and “high” Mg-calcite and aragonite), but that very fine-grained (mostly < 2 μm) high Mg-calcite crystallites (i.e., MgCO3) are their dominant excretory product. Crystallites from fish are morphologically diverse and species-specific, but all are unique relative to previously known biogenic and abiotic sources of carbonate within open marine systems. Using site specific fish biomass and carbonate excretion rate data we estimate that fish produce ∼6.1 × 106 kg CaCO3/year across the Bahamian archipelago, all as mud-grade (the < 63 μm fraction) carbonate and thus as a potential sediment constituent. Estimated contributions from fish to total carbonate mud production average ∼14% overall, and exceed 70% in specific habitats. Critically, we also document the widespread presence of these distinctive fish-derived carbonates in the finest sediment fractions from all habitat types in the Bahamas, demonstrating that these carbonates have direct relevance to contemporary carbonate sediment budgets. Fish thus represent a hitherto unrecognized but significant source of fine-grained carbonate sediment, the discovery of which has direct application to the conceptual ideas of how marine carbonate factories function both today and in the past. PMID:21368155

Mixing of biogenic siliceous and terrigenous clastic sediments: South Belridge field and Beta field, California

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schwartz, D.E.

1990-05-01

The intermixing and interbedding of biogenically derived siliceous sediment with terrigenous clastic sediment in reservoirs of upper Miocene age provides both reservoir rock and seal and influences productivity by affecting porosity and permeability. Miocene reservoirs commonly contain either biogenic-dominated cyclic diatomite, porcelanite, or chert (classic Monterey Formation) or clastic-dominated submarine fan sequences with interbedded or intermixed siliceous members of biogenic origin. Biogenic-clastic cycles, 30-180 ft thick, at South Belridge field were formed by episodic influx of clastic sediment from distant submarine fans mixing with slowly accumulating diatomaceous ooze. The cycles consist of basal silt and pelletized massive diatomaceous mudstone, overlainmore » by burrowed, faintly bedded clayey diatomite and topped by laminated diatomite. Cycle tops have higher porosity and permeability, lower grain density, and higher oil saturation than clay and silt-rich portions of the cycles. Submarine fan sediments forming reservoirs at the Beta field are comprised of interbedded sands and silts deposited in a channelized middle fan to outer fan setting. Individual turbidites display fining-upward sequences, with oil-bearing sands capped by wet micaceous silts. Average sands are moderately to poorly sorted, fine- to medium-grained arkosic arenites. Sands contain pore-filling carbonate and porcelaneous cements. Porcelaneous cement consists of a mixture of opal-A, opal-CT, and chert with montmorillonite and minor zeolite. This cement is an authigenic material precipitated in intergranular pore space. The origin of the opal is biogenic, with recrystallization of diatom frustules (opal-A) into opal-CT lepispheres and quartz crystals. Porcelaneous cement comprises 4-21% of the bulk volume of the rock. Seventy percent of the bulk volume of the cement is micropore space.« less

Characterizing wave- and current- induced bottom shear stress: U.S. middle Atlantic continental shelf

USGS Publications Warehouse

Dalyander, P. Soupy; Butman, Bradford; Sherwood, Christopher R.; Signell, Richard P.; Wilkin, John L.

2013-01-01

Waves and currents create bottom shear stress, a force at the seabed that influences sediment texture distribution, micro-topography, habitat, and anthropogenic use. This paper presents a methodology for assessing the magnitude, variability, and driving mechanisms of bottom stress and resultant sediment mobility on regional scales using numerical model output. The analysis was applied to the Middle Atlantic Bight (MAB), off the U.S. East Coast, and identified a tidally-dominated shallow region with relatively high stress southeast of Massachusetts over Nantucket Shoals, where sediment mobility thresholds are exceeded over 50% of the time; a coastal band extending offshore to about 30 m water depth dominated by waves, where mobility occurs more than 20% of the time; and a quiescent low stress region southeast of Long Island, approximately coincident with an area of fine-grained sediments called the “Mud Patch”. The regional high in stress and mobility over Nantucket Shoals supports the hypothesis that fine grain sediment winnowed away in this region maintains the Mud Patch to the southwest. The analysis identified waves as the driving mechanism for stress throughout most of the MAB, excluding Nantucket Shoals and sheltered coastal bays where tides dominate; however, the relative dominance of low-frequency events varied regionally, and increased southward toward Cape Hatteras. The correlation between wave stress and local wind stress was lowest in the central MAB, indicating a relatively high contribution of swell to bottom stress in this area, rather than locally generated waves. Accurate prediction of the wave energy spectrum was critical to produce good estimates of bottom shear stress, which was sensitive to energy in the long period waves.

Connectivity of earthquake-triggered landslides with the fluvial network: Implications for landslide sediment transport after the 2008 Wenchuan earthquake

NASA Astrophysics Data System (ADS)

Li, Gen; West, A. Joshua; Densmore, Alexander L.; Hammond, Douglas E.; Jin, Zhangdong; Zhang, Fei; Wang, Jin; Hilton, Robert G.

2016-04-01

Evaluating the influence of earthquakes on erosion, landscape evolution, and sediment-related hazards requires understanding fluvial transport of material liberated in earthquake-triggered landslides. The location of landslides relative to river channels is expected to play an important role in postearthquake sediment dynamics. In this study, we assess the position of landslides triggered by the Mw 7.9 Wenchuan earthquake, aiming to understand the relationship between landslides and the fluvial network of the steep Longmen Shan mountain range. Combining a landslide inventory map and geomorphic analysis, we quantify landslide-channel connectivity in terms of the number of landslides, landslide area, and landslide volume estimated from scaling relationships. We observe a strong spatial variability in landslide-channel connectivity, with volumetric connectivity (ξ) ranging from ~20% to ~90% for different catchments. This variability is linked to topographic effects that set local channel densities, seismic effects (including seismogenic faulting) that regulate landslide size, and substrate effects that may influence both channelization and landslide size. Altogether, we estimate that the volume of landslides connected to channels comprises 43 + 9/-7% of the total coseismic landslide volume. Following the Wenchuan earthquake, fine-grained (<~0.25 mm) suspended sediment yield across the Longmen Shan catchments is positively correlated to catchment-wide landslide density, but this correlation is statistically indistinguishable whether or not connectivity is considered. The weaker-than-expected influence of connectivity on suspended sediment yield may be related to mobilization of fine-grained landslide material that resides in hillslope domains, i.e., not directly connected to river channels. In contrast, transport of the coarser fraction (which makes up >90% of the total landslide volume) may be more significantly affected by landslide locations.

Spatio-temporal distribution and environmental risk of sedimentary heavy metals in the Yangtze River Estuary and its adjacent areas.

PubMed

Chen, Bin; Liu, Jian; Qiu, Jiandong; Zhang, Xilin; Wang, Shuang; Liu, Jinqing

2017-03-15

Twenty-five surface sediments and one sediment core sample were collected from the study area. Grain size, major elements, and heavy metals were determined. The content of fine-grained sediments (silt and clay), as well as the concentrations of major elements and heavy metals, showed seaward decreasing trends, with high content in the coastal areas of the East China Sea (ECS) and south west of Jeju Island. Low enrichment factor (EF) and geoaccumulation index (Igeo) values were found, indicating that the ecological risk of heavy metals was low. The EF values obtained from the high-resolution sedimentary records of heavy metals in the Yangtze River Estuary could be divided into Stage 1 (1950s to the late 1970s) and Stage 2 (late 1970s to the current sampling day), which coincided with economic development of the Yangtze River Basin, implementation of environmental protection, and impoundment of the Three Gorges Dam. Copyright © 2016. Published by Elsevier Ltd.

Geologic implications of gas hydrates in the offshore of India: Krishna-Godavari Basin, Mahanadi Basin, Andaman Sea, Kerala-Konkan Basin

USGS Publications Warehouse

Kumar, Pushpendra; Collett, Timothy S.; Boswell, Ray; Cochran, James R.; Lall, Malcolm; Mazumdar, Aninda; Ramana, Mangipudi Venkata; Ramprasad, Tammisetti; Riedel, Michael; Sain, Kalachand; Sathe, Arun Vasant; Vishwanath, Krishna; Yadav, U.S.

2014-01-01

NGHP-01 yielded evidence of gas hydrate from downhole log and core data obtained from all the sites in the Krishna–Godavari Basin, the Mahanadi Basin, and in the Andaman Sea. The site drilled in the Kerala–Konkan Basin during NGHP-01 did not yield any evidence of gas hydrate. Most of the downhole log-inferred gas hydrate and core-recovered gas hydrate were characterized as either fracture-filling in clay-dominated sediments or as pore-filling or grain-displacement particles disseminated in both fine- and coarse-grained sediments. Geochemical analyses of gases obtained from sediment cores recovered during NGHP-01 indicated that the gas in most all of the hydrates in the offshore of India is derived from microbial sources; only one site in the Andaman Sea exhibited limited evidence of a thermogenic gas source. The gas hydrate petroleum system concept has been used to effectively characterize the geologic controls on the occurrence of gas hydrates in the offshore of India.

Characterization of bottom sediments in the Río de la Plata estuary

NASA Astrophysics Data System (ADS)

Simionato, Claudia G.; Moreira, Diego

2016-04-01

Bottom sediments and surface water samples were collected in the intermediate and outer Río de la Plata Estuary during 2009-2010, in six repeated cruises, with 26 stations each. Samples were processed for grain size using a laser particle size analyzer, and water and organic matter contents. The aim of this work is to analyze this data set to provide a comprehensive and objective characterization of the bottom sediments distribution, to study their composition and to progress in the construction of a conceptual model of the involved physical mechanisms. Principal Components Analysis is applied to the bottom sediments size histograms to investigate the spatial patterns. Variations in grain-size parameters contain information on possible sediment transport patterns, which were analyzed by means of trend vectors. Sediments show a gradational arrangement of textures, sand dominant at the head, silt in the intermediate estuary and clayey silt and clay at its mouth; textures become progressively more poorly sorted offshore, and the water and organic matter contents increase. And seem to be strongly related to the geometry and the hydrodynamics. Along the Northern coast of the intermediate estuary, well sorted medium and fine silt predominates, whereas in the Southern coast, coarser and less sorted silt prevails, due to differences in tidal currents and/or in water pathways. Around Barra del Indio, clay prevails over silt and sand, and the water and organic matter contents reach a maximum, probably due flocculation, and the reduction of the currents. Immediately seawards the salt wedge, net transport reverses its direction and well sorted coarser sand from the adjacent shelf dominates. Relict sediment is observed around the Santa Lucía River, consisting of poorly sorted fine silt and clay. The inferred net transport suggests convergence at the Barra del Indio shoal, which is consistent with the constant growing of the banks.

Including Deposition Rate in Models of Cosmogenic Nuclide Accumulation in Fluvial Sediments to Improve Terrace Abandonment Ages

NASA Astrophysics Data System (ADS)

Norton, K. P.; Wang, N.; Van Dissen, R. J.; Little, T.

2017-12-01

Fluvial sediments are archives of the erosional, transport, and depositional processes occurring in the catchment. Terraces become robust markers for geomorphic analysis if their time of abandonment can be determined. Methods such as OSL can determine burial ages for fine grained sediments within the terrace fill but may not be directly related to the terrace abandonment age. Cosmogenic nuclides can be used to determine exposure ages for geologically young terraces but the surface being dated may have been subsequently eroded and the material itself may have been deposited with an inherited nuclide concentration. To deal with this problem, many researchers collect multiple samples with depth to model the depth-dependent nuclide concentration to help constrain inheritance and post-depositional erosion. It is often, however, assumed that the entire sediment pile accumulated instantaneously. In this submission, we present the results of a depth profile model that incorporates sediment accumulation rate to improve terrace age estimates. We test this model on fault-offset river terraces near Kaikoura, New Zealand. We measured depth profiles of OSL ages and cosmogenic nuclide concentrations of two late Quaternary terraces that are offset by up to 800 m across the Kekerengu Fault. OSL ages and dated tephras in the overlying loess provide minimum age constraints for both terraces while OSL ages of fine-grained sediments within the fill provide depositional ages. The predicted sedimentation rates for the terraces are as high as 0.5m/yr, consistent with geologically instantaneous deposition. Modelled abandonment ages from cosmogenic nuclides for the terraces are consistent with OSL and tephra constraints at 9.7 +/- 3.8 ka and 30.4 +/- 2.1 ka, respectively. These terrace abandonment ages yield dextral slip rates of 18.5-20.5 mm/yr and 25-28 mm/yr, respectively, consistent with the rapid slip rate on the adjacent Hope Fault.

Effect of sediment size on bioleaching of heavy metals from contaminated sediments of Izmir Inner Bay.

PubMed

Guven, Duyusen E; Akinci, Gorkem

2013-09-01

The effect of sediment size on metals bioleaching from bay sediments was investigated by using fine (< 45 microm), medium (45-300 microm), and coarse (300-2000 microm) size fractions of a sediment sample contaminated with Cr, Cu, Pb, and Zn. Chemical speciation of the metals in bulk and size fractions of sediment were studied before and after bioleaching. Microbial activity was provided with mixed cultures of Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxidans. The bioleaching process was carried out in flask experiments for 48 days, by using 5% (W/V) of solid concentration in suspension. Bioleaching was found to be efficient for the removal of selected heavy metals from every size fraction of sediments, where the experiments with the smaller particles resulted in the highest solubilization ratios. At the end of the experimental period, Cr, Cu, Pb and Zn were solubilized to the ratios of 68%, 88%, 72%, and 91% from the fine sediment, respectively. Higher removal efficiencies can be explained by the larger surface area provided by the smaller particles. The changes in the chemical forms of metals were determined and most of the metal releases were observed from the reducible and organic fractions independent from grain size. Higher concentrations were monitored in the residual fraction after bioleaching period, suggesting they are trapped in this fraction, and cannot be solubilized under natural conditions.

Regional Supplement to the Corps of Engineers Wetland Delineation Manual: Caribbean Islands Region (Version 2.0)

DTIC Science & Technology

2011-05-01

are dominant in two or more strata should be counted two or more times in the dominance test. Procedure for Selecting Dominant Species by the 50/20...Sediment deposits are thin layers or coatings of fine-grained mineral material (e.g., silt or clay) or organic matter (e.g., pollen ), sometimes mixed

First-order Description of the Mechanical Fracture Behavior of Fine-Grained Surficial Marine Sediments During Gas Bubble Growth

DTIC Science & Technology

2010-01-01

Mechanical analysis of idealized shallow hydraulic fracture, / Geotech . Geoenviron. Eng., 128, 488-495, doi:10.1061/ (ASCE) 1090-0241 (2002) 128:6(488...F. Chiu, and H.-J. Chai (2007), Experimental study on fracture behavior of a silty clay, Geotech . Test. J., 30, 1-9, doi: I0.1520/GTJI00715

Iron Fertilization and Productivity in the Panama Basin

NASA Astrophysics Data System (ADS)

Loveley, M. R.; Marcantonio, F.; Lyle, M. W.; Hertzberg, J. E.

2016-12-01

The Panama Basin, located in the Eastern Equatorial Pacific, is a high-nutrient low-chlorophyll zone (HNLC). HNLC zones are thought to be iron limited, and thus have low rates of primary productivity. Iron can be delivered to the ocean by continental dust, and times of increased dust flux are thought to be correlated with increased productivity. However, few studies have addressed the relationship between dust flux and primary productivity in the Panama Basin. We use xs230Th-derived 232Th accumulation rates as a dust flux proxy, and excess Ba, and authigenic U to reconstruct primary productivity in the basin. We focus on these proxies' differences between glacial and interglacial times for the last five marine isotope stages, during which glacial times are dustier. Our study involves two marine sediment cores, one retrieved from the northern part of the Panama Basin at the Cocos Ridge, (MV1014-01-"8JC", 6° 14.0'N 86° 2.6' W, 1993 m depth), and one from the southern part of the basin at the Carnegie Ridge, (MV1014-02-"17JC" 0° 10.8'S 85° 52.0' W, 2846 m depth). Both cores record high sedimentation rates (between 4 and 20 cm kyr-1) which allow us to present a high-resolution study of the basin. However, sediment focusing and the preferential transport of fine grained material have been identified in these cores. In the Panama Basin, the lithogenic dust fraction is part of the fine fraction (<4 µm) influenced by sediment focusing. Our recent research has shown that 230Th-normalized MARs of the fine-grained fraction remain relatively unaffected by the redistribution process. Our preliminary findings show that dust flux may not have played a major role in influencing primary productivity during glacial periods in the Panama Basin. Other factors, such as nutrient consumption or nutrient supply from upwelled deep water, may have had a more dominant role during these times.

Vertical hydraulic conductivity measurements in the Denver Basin, Colorado

USGS Publications Warehouse

Barkmann, P.E.

2004-01-01

The Denver Basin is a structural basin on the eastern flank of the Rocky Mountain Front Range, Colorado, containing approximately 3000 ft of sediments that hold a critical groundwater resource supplying many thousands of households with water. Managing this groundwater resource requires understanding how water gets into and moves through water-bearing layers in a complex multiple-layered sedimentary sequence. The Denver Basin aquifer system consists of permeable sandstone interbedded with impermeable shale that has been subdivided into four principle aquifers named, in ascending order, the Laramie-Fox Hills, Arapahoe, Denver, and Dawson aquifers. Although shale can dominate the stratigraphic interval containing the aquifers, there is very little empirical data regarding the hydrogeologic properties of the shale layers that control groundwater flow in the basin. The amount of water that flows vertically within the basin is limited by the vertical hydraulic conductivity through the confining shale layers. Low vertical flow volumes translate to low natural recharge rates and can have a profound negative impact on long-term well yields and the economic viability of utilizing the resource. To date, direct measurements of vertical hydraulic conductivity from cores of fine-grained sediments have been published from only five locations; and the data span a wide range from 1??10-3 to 1??10-11 cm/sec. This range may be attributable, in part, to differences in sample handling and analytical methods; however, it may also reflect subtle differences in the lithologic characteristics of the fine-grained sediments such as grain-size, clay mineralogy, and compaction that relate to position in the basin. These limited data certainly call for the collection of additional data.

Sedimentology and geochemistry of surface sediments, outer continental shelf, southern Bering Sea

USGS Publications Warehouse

Gardner, J.V.; Dean, W.E.; Vallier, T.L.

1980-01-01

Present-day sediment dynamics, combined with lowerings of sea level during the Pleistocene, have created a mixture of sediments on the outer continental shelf of the southern Bering Sea that was derived from the Alaskan Mainland, the Aleutian Islands, and the Pribilof ridge. Concentrations of finer-grained, higher-organic sediments in the region of the St. George basin have further modified regional distribution patterns of sediment composition. Q-mode factor analysis of 58 variables related to sediment size and composition - including content of major, minor, and trace elements, heavy and light minerals, and clay minerals - reveals three dominant associations of sediment: 1. (1) The most significant contribution, forming a coarse-grained sediment scattered over most of the shelf consists of felsic sediment derived from the generally quartz-rich rocks of the Alaskan mainland. This sediment contains relatively high concentrations of Si, Ba, Rb, quartz, garnet, epidote, metamorphic rock fragments, potassium feldspar, and illite. 2. (2) The next most important group, superimposed on the felsic group consists of andesitic sediment derived from the Aleutian Islands. This more mafic sediment contains relatively high concentrations of Na, Ca, Ti, Sr, V, Mn, Cu, Fe, Al, Co, Zn, Y, Yb, Ga, volcanic rock fragments, glass, clinopyroxene, smectite, and vermiculite. 3. (3) A local group of basaltic sediment, derived from rocks of the Pribilof Islands, is a subgroup of the Aleutian andesite group. Accumulation of fine-grained sediment in St. George basin has created a sediment group containing relatively high concentrations of C, S, U, Li, B, Zr, Ga, Hg, silt, and clay. Sediment of the Aleutian andesite group exhibits a strong gradient, or "plume", with concentrations decreasing away from Unimak Pass and toward St. George basin. The absence of present-day currents sufficient to move even clay-size material as well as the presence of Bering submarine canyon between the Aleutian Islands and the outer continental shelf and slope, indicates that Holocene sediment dynamics cannot be used to explain the observed distribution of surface sediment derived from the Aleutian Islands. We suggest that this pattern is relict and resulted from sediment dynamics during lower sea levels of the Pleistocene. ?? 1980.

Grain velocity of bedload movement in an armored non-uniform mobile bed

NASA Astrophysics Data System (ADS)

Liu, C.

2015-12-01

The velocity of bedload particles, which directly reflects the interaction between flow and sediment, is one of the important parameters to predict sediment transport rate, is also one of the fundamental problems for sediment transport. Many excellent works have been accomplished in this filed. However, the existing researches are mostly based on the artificial fixed bed, few moveable bed studies are focus on uniform sediment bed, these boundary conditions are different from a real river. In this research, an experiment on non-uniform sediment with an armored, moveable bed were carried out in a flume, the range of bed material is from 0.2mm to 20mm. With a special hanging glass and illumination system, the motion particles in the bed were clearly shoot on top of the flume by a video camera, avoiding the interference of waves at the flow surface. The speed of the camera is 50 frames per second. About 7000 unique coordinates of moving particles were determined from 3000 frames of successive pictures, the particle velocity of longitudinal and crosswise directions were obtained from the coordinates. The results show that, the probability density distribution of grain velocities of both directions are similar to that in the uniform sediment, which have an exponent decay trend, whereas the value of cross velocity of particles is clearly greater than that in the uniform sediment condition. Negative particle velocity was recognized in the experiment, it is shown that these negative may occur at two conditions, one is the backflow of fine particles behind the coarser particles, and the other is a state of movement change, such as a particle from static state to motion or vice versa. Furthermore, the particle movement was strongly affected by the arrangement of local coarse particles. The influence of coarser particles to the movement of fine particles also identified by two opposite effects, one is the acceleration effects in a 'tunnel' between pair of series particles, the other is the deceleration effects out of the tunnel, or fine particles captured by the backwater flow just behind a coarse particle. In addition, ensemble particle velocity in the armored bed is distinctly less than which in the fixed bed and uniform bed condition with same particle Reynolds number and Shields parameter. (Supported by(2012BAB04B01;NSFC(11472310))

In-situ geophysical measurements in marine sediments: Applications in seafloor acoustics and paleoceanography

NASA Astrophysics Data System (ADS)

Gorgas, Thomas Joerg

Acoustic in-situ sound speeds and attenuation were measured on the Eel River shelf, CA, with the Acoustic Lance between 5 and 15 kHz to 2.0 meters below seafloor (mbsf). A comparison with laboratory ultrasonic geoacoustic data obtained at 400 kHz on cored sediments showed faster in-situ and ultrasonic sound speeds in coarse-grained deposits in water depths to 60 m than in fine-grained deposits below that contour line. Ultrasonic attenuation was often greater than in-situ values and remained almost constant below 0.4 mbsf in these heterogeneous deposits. In-situ attenuation decreased with depth. These observations partly agree with results from other field studies, and with theoretical models that incorporate intergranular friction and dispersion from viscosity as main controls on acoustic wave propagation in marine sediments. Deviations among in-situ and laboratory acoustic data from the Eel Margin with theoretical studies were linked to scattering effects. Acoustic Lance was also deployed in homogeneous, fine-grained sediments on the inner shelf of SE Korea, where free gas was identified in late-September, but not in mid-September 1999. Free gas was evidenced by an abrupt decrease of in-situ sound speed and by characteristic changes in acoustic waveforms. These results suggest the presence of a gassy sediment layer as shallow as 2 mbsf along the 70 m bathymetry line, and was attributed to a variable abundance of free gas on short-term and/or small-regional scales on the SE Korea shelf. Bulk density variations in marine sediments obtained along the Walvis Ridge/Basin, SW Africa, at Ocean Drilling Program (ODP) Sites 1081 to 1084 were spectral-analyzed to compute high-resolution sedimentation rates (SRs) in both the time- and age domains by correctly identifying Milankovitch cycles (MCs). SRs for the ODP sites yielded age-depth models that often correlate positively with biostratigraphic data and with organic mass accumulation rates (MAR Corg), a proxy for productivity, and negatively with Sea Surface Temperatures (SSTs), a proxy for wind strength. These results suggest that strong amplitudes of all main MCs existed for periods of high SRs and high MAR Corg and low SSTs, indicating a positive link between wind stress, upwelling vigor, productivity and insolation patterns in this area.

Architectural elements from Lower Proterozoic braid-delta and high-energy tidal flat deposits in the Magaliesberg Formation, Transvaal Supergroup, South Africa

NASA Astrophysics Data System (ADS)

Eriksson, Patrick G.; Reczko, Boris F. F.; Jaco Boshoff, A.; Schreiber, Ute M.; Van der Neut, Markus; Snyman, Carel P.

1995-06-01

Three architectural elements are identified in the Lower Proterozoic Magaliesberg Formation (Pretoria Group, Transvaal Supergroup) of the Kaapvaal craton, South Africa: (1) medium- to coarse-grained sandstone sheets; (2) fine- to medium-grained sandstone sheets; and (3) mudrock elements. Both sandstone sheet elements are characterised by horizontal lamination and planar cross-bedding, with lesser trough cross-bedding, channel-fills and wave ripples, as well as minor desiccated mudrock partings, double-crested and flat-topped ripples. Due to the local unimodal palaeocurrent patterns in the medium- to coarse-grained sandstone sheets, they are interpreted as ephemeral braid-delta deposits, which were subjected to minor marine reworking. The predominantly bimodal to polymodal palaeocurrent trends in the fine- to medium-grained sandstone sheets are inferred to reflect high-energy macrotidal processes and more complete reworking of braid-delta sands. The suspension deposits of mudrocks point to either braid-delta channel abandonment, or uppermost tidal flat sedimentation. The depositional model comprises ephemeral braid-delta systems which debouched into a high-energy peritidal environment, around the margins of a shallow epeiric sea on the Kaapvaal craton. Braid-delta and tidal channel dynamics are inferred to have been similar. Fine material in the Magaliesberg Formation peritidal complexes indicates that extensive aeolian removal of clay does not seem applicable to this example of the early Proterozoic.

Stratigraphy and sedimentation of Mississippian Ste. Genevieve-Cedar Bluff interval, Southwestern Indiana

DOE Office of Scientific and Technical Information (OSTI.GOV)

Breedon, D.; Droste, J.B.; Murray, H.H.

1983-09-01

The Ste. Genevieve Limestone and Cedar Bluff Group of Mississippian age, both important sources of hydrocarbons in the Illinois basin, were traced from a subsurface stratigraphic section in White County, Illinois (described by Swan in 1963, across Gibson and Daviess Counties, Indiana, using electric logs and sample descriptions from 84 wells. The Ste. Genevieve Limestone is subdivided into four members and the Cedar Bluff Group into three formations. Six cross sections and nine isopach maps based on 300 wells show that these units comprise a succession of alternating fine- and coarse-grained carbonate rocks with only minor interruptions of sandstone andmore » shale. Two complete coarsening-upward cycles are apparent, and a third cycle is incomplete. Each cycle consists of a lower sequence of lime mudstones and wackestones, and an upper sequence of oolitic and skeletal grainstones. These cycles are the record of successive shoaling-upward cycles of sedimentation on a shallow marine platform. The lower mudstone-wackestone sequence represents deposition in a shallow subtidal environment, and the upper oolitic-skeletal grainstone unit represents development of oolite shoals and tidal channels in very shallow waters. Terrigenous clastic sediments brought into the basin by the Michigan river periodically encroached into the marine environment. Dolomitization of the fine-grained carbonate sediments is largely restricted to areas which are overlain by oolitic grainstones. In eastern Daviess County, indentification of the individual stratigraphic units in this interval is somewhat tenuous, but tracing the units from eastern Illinois into Indiana made correlation and identification of the individual stratigraphic units possible by using electric logs and sample descriptions.« less

Structural equation modelling reveals factors regulating surface sediment organic carbon content and CO2 efflux in a subtropical mangrove.

PubMed

Ouyang, Xiaoguang; Lee, Shing Yip; Connolly, Rod M

2017-02-01

Mangroves are blue carbon ecosystems that sequester significant carbon but release CO 2 , and to a lesser extent CH 4, from the sediment through oxidation of organic carbon or from overlying water when flooded. Previous studies, e.g. Leopold et al. (2015), have investigated sediment organic carbon (SOC) content and CO 2 flux separately, but could not provide a holistic perspective for both components of blue carbon. Based on field data from a mangrove in southeast Queensland, Australia, we used a structural equation model to elucidate (1) the biotic and abiotic drivers of surface SOC (10cm) and sediment CO 2 flux; (2) the effect of SOC on sediment CO 2 flux; and (3) the covariation among the environmental drivers assessed. Sediment water content, the percentage of fine-grained sediment (<63μm), surface sediment chlorophyll and light condition collectively drive sediment CO 2 flux, explaining 41% of their variation. Sediment water content, the percentage of fine sediment, season, landform setting, mangrove species, sediment salinity and chlorophyll collectively drive surface SOC, explaining 93% of its variance. Sediment water content and the percentage of fine sediment have a negative impact on sediment CO 2 flux but a positive effect on surface SOC content, while sediment chlorophyll is a positive driver of both. Surface SOC was significantly higher in Avicennia marina (2994±186gm -2 , mean±SD) than in Rhizophora stylosa (2383±209gm -2 ). SOC was significantly higher in winter (2771±192gm -2 ) than in summer (2599±211gm -2 ). SOC significantly increased from creek-side (865±89gm -2 ) through mid (3298±137gm -2 ) to landward (3933±138gm -2 ) locations. Sediment salinity was a positive driver of SOC. Sediment CO 2 flux without the influence of biogenic structures (crab burrows, aerial roots) averaged 15.4mmolm -2 d -1 in A. marina stands under dark conditions, lower than the global average dark flux (61mmolm -2 d -1 ) for mangroves. Copyright © 2016 Elsevier B.V. All rights reserved.

Gas hydrate characterization and grain-scale imaging of recovered cores from the Mount Elbert Gas Hydrate Stratigraphic Test Well, Alaska North Slope

USGS Publications Warehouse

Stern, Laura A.; Lorenson, T.D.; Pinkston, John C.

2011-01-01

Using cryogenic scanning electron microscopy (CSEM), powder X-ray diffraction, and gas chromatography methods, we investigated the physical states, grain characteristics, gas composition, and methane isotopic composition of two gas-hydrate-bearing sections of core recovered from the BPXA–DOE–USGS Mount Elbert Gas Hydrate Stratigraphic Test Well situated on the Alaska North Slope. The well was continuously cored from 606.5 m to 760.1 m depth, and sections investigated here were retrieved from 619.9 m and 661.0 m depth. X-ray analysis and imaging of the sediment phase in both sections shows it consists of a predominantly fine-grained and well-sorted quartz sand with lesser amounts of feldspar, muscovite, and minor clays. Cryogenic SEM shows the gas-hydrate phase forming primarily as a pore-filling material between the sediment grains at approximately 70–75% saturation, and more sporadically as thin veins typically several tens of microns in diameter. Pore throat diameters vary, but commonly range 20–120 microns. Gas chromatography analyses of the hydrate-forming gas show that it is comprised of mainly methane (>99.9%), indicating that the gas hydrate is structure I. Here we report on the distribution and articulation of the gas-hydrate phase within the cores, the grain morphology of the hydrate, the composition of the sediment host, and the composition of the hydrate-forming gas.

Gas hydrate characterization and grain-scale imaging of recovered cores from the Mount Elbert Gas Hydrate Stratigraphic Test Well, Alaska North Slope

USGS Publications Warehouse

Stern, L.A.; Lorenson, T.D.; Pinkston, J.C.

2011-01-01

Using cryogenic scanning electron microscopy (CSEM), powder X-ray diffraction, and gas chromatography methods, we investigated the physical states, grain characteristics, gas composition, and methane isotopic composition of two gas-hydrate-bearing sections of core recovered from the BPXA-DOE-USGS Mount Elbert Gas Hydrate Stratigraphic Test Well situated on the Alaska North Slope. The well was continuously cored from 606.5. m to 760.1. m depth, and sections investigated here were retrieved from 619.9. m and 661.0. m depth. X-ray analysis and imaging of the sediment phase in both sections shows it consists of a predominantly fine-grained and well-sorted quartz sand with lesser amounts of feldspar, muscovite, and minor clays. Cryogenic SEM shows the gas-hydrate phase forming primarily as a pore-filling material between the sediment grains at approximately 70-75% saturation, and more sporadically as thin veins typically several tens of microns in diameter. Pore throat diameters vary, but commonly range 20-120 microns. Gas chromatography analyses of the hydrate-forming gas show that it is comprised of mainly methane (>99.9%), indicating that the gas hydrate is structure I. Here we report on the distribution and articulation of the gas-hydrate phase within the cores, the grain morphology of the hydrate, the composition of the sediment host, and the composition of the hydrate-forming gas. ?? 2009.

Large-scale dam removal on the Elwha River, Washington, USA: source-to-sink sediment budget and synthesis

USGS Publications Warehouse

Warrick, Jonathan A.; Bountry, Jennifer A.; East, Amy E.; Magirl, Christopher S.; Randle, Timothy J.; Gelfenbaum, Guy R.; Ritchie, Andrew C.; Pess, George R.; Leung, Vivian; Duda, Jeff J.

2015-01-01

Understanding landscape responses to sediment supply changes constitutes a fundamental part of many problems in geomorphology, but opportunities to study such processes at field scales are rare. The phased removal of two large dams on the Elwha River, Washington, exposed 21 ± 3 million m3, or ~ 30 million tonnes (t), of sediment that had been deposited in the two former reservoirs, allowing a comprehensive investigation of watershed and coastal responses to a substantial increase in sediment supply. Here we provide a source-to-sink sediment budget of this sediment release during the first two years of the project (September 2011–September 2013) and synthesize the geomorphic changes that occurred to downstream fluvial and coastal landforms. Owing to the phased removal of each dam, the release of sediment to the river was a function of the amount of dam structure removed, the progradation of reservoir delta sediments, exposure of more cohesive lakebed sediment, and the hydrologic conditions of the river. The greatest downstream geomorphic effects were observed after water bodies of both reservoirs were fully drained and fine (silt and clay) and coarse (sand and gravel) sediments were spilling past the former dam sites. After both dams were spilling fine and coarse sediments, river suspended-sediment concentrations were commonly several thousand mg/L with ~ 50% sand during moderate and high river flow. At the same time, a sand and gravel sediment wave dispersed down the river channel, filling channel pools and floodplain channels, aggrading much of the river channel by ~ 1 m, reducing river channel sediment grain sizes by ~ 16-fold, and depositing ~ 2.2 million m3 of sand and gravel on the seafloor offshore of the river mouth. The total sediment budget during the first two years revealed that the vast majority (~ 90%) of the sediment released from the former reservoirs to the river passed through the fluvial system and was discharged to the coastal waters, where slightly less than half of the sediment was deposited in the river-mouth delta. Although most of the measured fluvial and coastal deposition was sand-sized and coarser (> 0.063 mm), significant mud deposition was observed in and around the mainstem river channel and on the seafloor. Woody debris, ranging from millimeter-size particles to old-growth trees and stumps, was also introduced to fluvial and coastal landforms during the dam removals. At the end of our two-year study, Elwha Dam was completely removed, Glines Canyon Dam had been 75% removed (full removal was completed 2014), and ~ 65% of the combined reservoir sediment masses—including ~ 8 Mt of fine-grained and ~ 12 Mt of coarse-grained sediment—remained within the former reservoirs. Reservoir sediment will continue to be released to the Elwha River following our two-year study owing to a ~ 16 m base level drop during the final removal of Glines Canyon Dam and to erosion from floods with larger magnitudes than occurred during our study. Comparisons with a geomorphic synthesis of small dam removals suggest that the rate of sediment erosion as a percent of storage was greater in the Elwha River during the first two years of the project than in the other systems. Comparisons with other Pacific Northwest dam removals suggest that these steep, high-energy rivers have enough stream power to export volumes of sediment deposited over several decades in only months to a few years. These results should assist with predicting and characterizing landscape responses to future dam removals and other perturbations to fluvial and coastal sediment budgets.

[Analysis of particle size characteristics of road sediments in Beijing Olympic Park].

PubMed

Li, Hai-yan; Shi, An-bang; Qu, Yang-sheng; Yue, Jing-lin

2014-09-01

Particle size analysis of road sediment collected in October and November in Beijing Olympic Park indicates that most of the sediments are 76-830 μm; the grain size of the sediments in the area of large population flow is mainly coarse but the grain size in the area of large traffic volume is fine relatively while most of the sediments are <300 p.m. Moreover, sediments of size range <300 μm can be easily accumulated on the road with moderate traffic density. The results demonstrate that the effect of pedestrian flow on the composition of the particles is unobvious and the main influences are the traffic density, extensive construction. With the length of dry period increasing, the content of sediments of size range >300 μm decreases and the content of sediments of size range < 150 μm increases, however, the change of the content of sediments of size range 150-300 μm is not obvious. The results indicate that the effectiveness of the road sediment removal depends on the length of dry period, and the accumulation of different size particles varies differently under the different dry days. Compared with the stone road, surface particles can accumulate on the asphalt road more easily as the accumulation of particles is affected by the road material significantly. Therefore, to reduce the urban surface water pollution, it is necessary to improve the design of park road such as using the stone road, which can decrease the roughness of the road.

Sediment concentrations, flow conditions, and downstream evolution of two turbidity currents, Monterey Canyon, USA

USGS Publications Warehouse

Xu, Jingping; Octavio E. Sequeiros,; Noble, Marlene A.

2014-01-01

The capacity of turbidity currents to carry sand and coarser sediment from shallow to deep regions in the submarine environment has attracted the attention of researchers from different disciplines. Yet not only are field measurements of oceanic turbidity currents a rare achievement, but also the data that have been collected consist mostly of velocity records with very limited or no suspended sediment concentration or grain size distribution data. This work focuses on two turbidity currents measured in Monterey Canyon in 2002 with emphasis on suspended sediment from unique samples collected within the body of these currents. It is shown that concentration and grain size of the suspended material, primarily controlled by the source of the gravity flows and their interaction with bed material, play a significant role in shaping the characteristics of the turbidity currents as they travel down the canyon. Before the flows reach their normal or quasi-steady state, which is defined by bed slope, bed roughness, and suspended grain size, they might pass through a preliminary adjustment stage where they are subject to capacity-driven deposition, and release heavy material in excess. Flows composed of fine (silt/clay) sediments tend to be thicker than those with sands. The measured velocity and concentration data confirm that flow patterns differ between the front and body of turbidity currents and that, even after reaching normal state, the flow regime can be radically disrupted by abrupt changes in canyon morphology.

Submarine landslides triggered by destabilization of high-saturation hydrate anomalies

NASA Astrophysics Data System (ADS)

Handwerger, Alexander L.; Rempel, Alan W.; Skarbek, Rob M.

2017-07-01

Submarine landslides occur along continental margins at depths that often intersect the gas hydrate stability zone, prompting suggestions that slope stability may be affected by perturbations that arise from changes in hydrate stability. Here we develop a numerical model to identify the conditions under which the destabilization of hydrates results in slope failure. Specifically, we focus on high-saturation hydrate anomalies at fine-grained to coarse-grained stratigraphic boundaries that can transmit bridging stresses that decrease the effective stress at sediment contacts and disrupt normal sediment consolidation. We evaluate slope stability before and after hydrate destabilization. Hydrate anomalies act to significantly increase the overall slope stability due to large increases in effective cohesion. However, when hydrate anomalies destabilize there is a loss of cohesion and increase in effective stress that causes the sediment grains to rapidly consolidate and generate pore pressures that can either trigger immediate slope failure or weaken the surrounding sediment until the pore pressure diffuses away. In cases where failure does not occur, the sediment can remain weakened for months. In cases where failure does occur, we quantify landslide dynamics using a rate and state frictional model and find that landslides can display either slow or dynamic (i.e., catastrophic) motion depending on the rate-dependent properties, size of the stress perturbation, and the size of the slip patch relative to a critical nucleation length scale. Our results illustrate the fundamental mechanisms through which the destabilization of gas hydrates can pose a significant geohazard.

Late Holocene climate dynamics: A high-resolution sediment core from Maxwell Bay, South Shetland Islands, Antarctica

NASA Astrophysics Data System (ADS)

Hass, H. C.; Kuhn, G.; Monien, P.; Brumsack, H.

2009-12-01

Presently, the Antarctic Peninsula belongs to the fastest warming regions on Earth. Meltwater discharge increases, glaciers retreat and as a consequence the coastal ecosystems change at an ever-increasing pace. The goal of our study is to reconstruct the timing and impact of historical climate phases such as the Medieval Warm Period (MWP) and the Little Ice Age (LIA) as analogs for the recent climate development, and to identify the marine sedimentary processes affected by the changing climate. We present results from a 928 cm long gravity core from Maxwell Bay, King George Island, Antarctica. The core spans the past c. 1700 years. Sedimentation at the core site is governed by sediments from the tributary fjords entering Maxwell Bay, namely Potter and Marian coves and Collins Harbor. There are two sediment classes: Class 1 is characterized by two grain-size subpopulations. The coarser one represents the bedload fraction, whereas the finer one is interpreted to represent meltwater-induced suspension load. Since meltwater is restricted to the summer season, it is suggested that Class 1 sediments characterize periods of intense summer-meltwater production and thus, warmer climate phases. Class 2 samples show the same coarse grain-size mode but they lack the fine subpopulation. We suggest that these sediments indicate less intense summer-meltwater production and thus colder climatic conditions. The mean grain size suggests that average bottom current speeds were slightly higher during colder climate phases than during the warmer phases. Bioproduction at the core location and in the sediment source areas as reflected by bio-productivity proxies (TOC, bio-opal) is not always positively related to climate since warm-phase meltwater discharge adversely affects bioproduction through light attenuation by turbid waters. Furthermore, during warmer phases the TOC signal becomes diluted due to increased deposition of terrigenous fine sediment. Comparison with Antarctic, hemispherical, and global temperature reconstructions reveals clear signals of the MWP, the LIA and the post-LIA climate recovery. Class 1 sediments dominate the warmer MWP, Class 2 sediments dominate the colder LIA. The Maxwell Bay record shows climate signals that are partly unique to either one of the hemispheres. Thus, it resembles best the global temperature reconstruction. Apparently, the MWP started earlier in the Southern Hemisphere (SH) than in the Northern Hemisphere suggesting that the source for the warming might also be in the SH. In contrast to the MWP the timing of the LIA appears to be largely synchronous between the hemispheres. Generally finer sediments clearly mark the end of the LIA. however no stronger meltwater influence can be detected; the conditions of the AD 1970s resemble those at the beginning of the MWP. Changing sedimentation processes cannot be detected in the Maxwell Bay record until AD 1975.

Depositional and Structural Controls on the Evolution of the Gas Hydrate Petroleum System in Green Canyon 955, Gulf of Mexico

NASA Astrophysics Data System (ADS)

Haines, S. S.; Hart, P. E.; Collett, T. S.; Weimer, P.; Shedd, W. W.; Frye, M.; Boswell, R.

2016-12-01

The depositional, erosional, and deformational history at Green Canyon 955 (GC955), Gulf of Mexico, provides insight into the reservoir characteristics and the gas and gas hydrate petroleum system at this established research site. Using high-resolution 2D seismic data, industry 3D seismic data, and borehole logs, we have refined our knowledge of the area's geologic history. Following extended fine-grained deposition (while the primary sediment input was hundreds of km to the east), channel/levee activity shifted to the area of GC955 approximately 500 kya. The initial resulting deposits include sand-rich proximal levee packages, readily identifiable in high-resolution seismic images, and limited channel deposits. The levee deposits occur in discrete "pods", the result of intermingled deposition and erosion. Subsequently, salt diapirism initiated a period of uplift and caused channel activity to shift a few kilometers eastward. Pelagic deposition was followed by a mix of fine-grained sediments and limited sandy strata deposited in a distal levee and/or fan environment. Channel features from this time period are evident east of GC955, but the available data suggest that these were mainly erosional, with minimal sand deposition. Salt-driven structural deformation created a multi-kilometer-scale east-west graben and normal faults. These extensional faults facilitated upward migration of gas from deeper in the system, ultimately leading to creation of several gas chimneys. The presence of free gas at the location of well GC955-Q indicates that the fine-grained unit overlying the main reservoir provides a good seal, consistent with pelagic deposition. The absence of free gas at well GC955-H, coupled with the presence of ongoing chimney-related gas flow nearby, indicates that this seal can be broken where the pelagic unit is cut by the large-throw graben faults. Reservoir connectivity within the levee deposit "pods" is likely, based on established characteristics of levee reservoirs. Connectivity between pods is uncertain, but gas/hydrate distribution suggests at least some compartmentalization. The character of borehole logs and of seismic reflections from the top of the main reservoir may indicate a fining-upward sediment distribution that likely controls the presence of gas hydrate.

Carbon Dynamics Along a Temperate Fjord-Head Delta: Linkages With Carbon Burial in Fjords

NASA Astrophysics Data System (ADS)

Cui, Xingqian; Bianchi, Thomas S.; Kenney, William F.; Wang, Jiaze; Curtis, Jason H.; Xu, Kehui; Savage, Candida

2017-12-01

We used seven 210Pb-dated sediment cores from the Gaer Arm in the Doubtful Sound fjord complex, Fiordland, New Zealand to evaluate organic carbon (OC) dynamics in a temperate fjord-head delta. The highly dynamic spatial features of this delta were clearly evident in the observed sediment properties such as mass accumulation rates that varied by a factor of 14, sediment grain size by a factor 5, and sedimentary OC content by a factor 6. Low lignin concentrations (e.g., 2.95 mg (100 mg OC)-1) and syringic/vanillic ratios of lignin phenols (S/V; e.g., 0.44) at the upper deltaic stations were representative of substantial autochthonous OC contributions to delta sediments. Significantly higher acid/aldehyde ratios of vanillic phenols [(Ad/Al)v] at the deltaic stations (0.45-0.82) than the surface grabs (0.26-0.30) indicated rapid degradation of OC within the delta. Despite being a "hot spot" for OC oxidation, the delta likely improves OC preservation in the adjacent fjord by filtering out coarse-grained particles and exporting fine-grained particles to fjord sediments. Our results showed that fjord-head deltas can influence sedimentation and OC dynamics in select regions of fjords and thus warrant more examination of fjord-head processes, particularly in areas where they are expanding. In particular, as Earth warms and glaciers retreat, the newly exposed fjord-head platforms in high-latitude environments may evolve into similar "hot spots" of OC oxidation, thereby altering the dynamics of OC burial in these systems.

Enhancing mud supply from the Lower Missouri River to the Mississippi River Delta USA: Dam bypassing and coastal restoration

NASA Astrophysics Data System (ADS)

Kemp, G. Paul; Day, John W.; Rogers, J. David; Giosan, Liviu; Peyronnin, Natalie

2016-12-01

Sand transport to the Mississippi River Delta (MRD) remains sufficient to build wetlands in shallow, sheltered coastal bays fed by engineered diversions on the Mississippi River (MR) and its Atchafalaya River (AR) distributary. But suspended mud (silt & clay) flux to the coast has dropped from a mean of 390 Mt y-1 in the early 1950s, to 100 Mt y-1 since 1970. This fine-grained sediment travels deeper into receiving estuarine basins and plays a critical role in sustaining existing marshes. Virtually all of the 300 Mt y-1 of missing mud once flowed from the Missouri River (MOR) Basin before nearly 100 dams were built as part of the Pick-Sloan water development project. About 100 Mt y-1 is now intercepted by main-stem Upper MOR dams closed in 1953. But the remaining 200 Mt y-1 is trapped by impoundments built on tributaries to the Lower MOR in the 1950s and 1960s. Sediment flux during the post-dam high MOR discharge years of 1973, 1993 and 2011 approached pre-dam levels when tributaries to the Lower MOR, including the Platte and Kansas Rivers, contributed to flood flows. West bank tributaries drain a vast, arid part of the Great Plains, while those entering from the east bank traverse the lowlands of the MOR floodplain. Both provinces are dominated by highly erodible loess soils. Staunching the continued decline in MR fine-grained sediment flux has assumed greater importance now that engineered diversions are being built to reconnect the Lowermost MR to the MRD. Tributary dam bypassing in the Lower MOR basin could increase mud supply to the MRD by 100-200 Mt y-1 within 1-2 decades. Such emergency measures to save the MRD are compatible with objectives of the Missouri River Restoration and Platte River Recovery Programs to restore MOR riparian habitat for endangered species. Rapid mobilization to shunt fine-grained sediments past as many as 50 Lower MOR tributary dams in several U.S. states will undoubtedly require as much regional coordination and funding in the 21st century as the monumental effort it took to build the dams in the last century.

In Situ Sedimentological Evidence for Climate Change in Early Mars Provided by the Curiosity Rover in Gale Crater

NASA Astrophysics Data System (ADS)

Heydari, Ezat; Fairen, Alberto G.

2016-10-01

The Striated formation is one of the rock units that was deposited in Gale crater, Mars, during the Late Noachian to Hesperian time (4.2 to 3.6 billion years ago). It crops out for 3 km along the Curiosity's traverse. The Striated formation strikes N65○E and has a depositional dip of 10○ - 20○ to SE. It consists of 500 m to 1000 m of highly rhythmic layers each 1 m to 4 m in thickness. Study of MAHLI and MastCam images provided by the Curiosity Rover indicates that layers form fining-upward cycles consisting of thick-bedded to massive conglomerate at the base that grades upward to thinly bedded conglomerate, then to pebbly sandstone, and topped by laminated, fine grained sandstone. Layers show slump folds, soft sediment deformation, and cross-beddings.The highly rhythmic occurrence and the fining-upward grain size characteristic indicate that each layer within the Striated formation is a coarse-grained turbidite: a type of rock that forms when sediments move down-hill by gravity-driven turbidity flows and deposit in deep waters. We propose that turbidite layers of the Striated formation are related to delivery of sediments to Gale crater by megafloods through its northern rim. Upon entering Gale crater, sediments moved down-hill and deposited as turbidite layers when the crater may have been filled to the rim with water. About 1000 to 3000 turbidite layers are present suggesting the occurrences of as many megafloods during hothouse climatic intervals when Mars was warmer than the Present and had plenty of liquid water. Floods were generated by one or a combination of the following processes: (1) torrential rain along the margins of Mars's Northern Ocean, 500 km to 1000 km to the north, (2) rapid melting of ice in highland areas, and (3) tsunamis formed by impacts on the Northern Ocean. Cold and/or dry climate of icehouse intervals may have followed each warming episode. Mars's climate forcing mechanism and periodicities of climate change are not clear at this point. However, the highly regular and rhythmic nature of turbidite layers point to an orbital triggering mechanism, possibly driven by changes in obliquity.

Hydrate-Bearing Clayey Sediments: Morphology, Physical Properties, Production and Engineering/Geological Implications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dai, Sheng; Santamarina, J. Carlos

Fine-grained sediments host more than 90 percent of global gas hydrate accumulation. However, hydrate formation in clay-dominated sediments is less understood and characterized than other types of hydrate occurrence. There is an inadequate understanding of hydrate formation mechanisms, segregation structures, hydrate lens topology, system connectivity, and physical macro-scale properties of clay-dominated hydrate-bearing sediments. This situation hinders further analyses of the global carbon budget as well as engineering challenges/solutions related to hydrate instability and production. This project studies hydrate-bearing clay-dominated sediments with emphasis on the enhanced fundamental understanding of hydrate formation and resulting morphology, the development laboratory techniques to emulate naturalmore » hydrate formations, the assessment of analytical tools to predict physical properties, the evaluation of engineering and geological implications, and the advanced understanding of gas production potential from finegrained sediments.« less

Colorado River sediment transport: 2. Systematic bed‐elevation and grain‐size effects of sand supply limitation

USGS Publications Warehouse

Topping, David J.; Rubin, David M.; Nelson, Jonathan M.; Kinzel, Paul J.; Corson, Ingrid C.

2000-01-01

The Colorado River in Marble and Grand Canyons displays evidence of annual supply limitation with respect to sand both prior to [Topping et al, this issue] and after the closure of Glen Canyon Dam in 1963. Systematic changes in bed elevation and systematic coupled changes in suspended‐sand concentration and grain size result from this supply limitation. During floods, sand supply limitation either causes or modifies a lag between the time of maximum discharge and the time of either maximum or minimum (depending on reach geometry) bed elevation. If, at a cross section where the bed aggrades with increasing flow, the maximum bed elevation is observed to lead the peak or the receding limb of a flood, then this observed response of the bed is due to sand supply limitation. Sand supply limitation also leads to the systematic evolution of sand grain size (both on the bed and in suspension) in the Colorado River. Sand input during a tributary flood travels down the Colorado River as an elongating sediment wave, with the finest sizes (because of their lower settling velocities) traveling the fastest. As the fine front of a sediment wave arrives at a given location, the bed fines and suspended‐sand concentrations increase in response to the enhanced upstream supply of finer sand. Then, as the front of the sediment wave passes that location, the bed is winnowed and suspended‐sand concentrations decrease in response to the depletion of the upstream supply of finer sand. The grain‐size effects of depletion of the upstream sand supply are most obvious during periods of higher dam releases (e.g., the 1996 flood experiment and the 1997 test flow). Because of substantial changes in the grain‐size distribution of the bed, stable relationships between the discharge of water and sand‐transport rates (i.e., stable sand rating curves) are precluded. Sand budgets in a supply‐limited river like the Colorado River can only be constructed through inclusion of the physical processes that couple changes in bed‐sediment grain size to changes in sand‐transport rates.

Chemical composition of sediments from White Sea, Russian Arctic

NASA Astrophysics Data System (ADS)

Gamza, Olga; Shevchenko, Vladimir; Novigatsky, Aleksandr

2010-05-01

The White Sea, the only Russian inland sea, is located on the north of outlying districts of the European part of Russia, belongs to Arctic Ocean. Area of water of sea occupies about 90 tousend square kilometers. The sea can be divided into some general parts: neck, funnel, basin and 4 Bays: Dvina Bay, Kandalaksha Bay, Mezen Bay and Onega Bay. The purpose of this work was geochemical mapping of the surface sediments of this area. The main tasks were: compilation data base of element composition of the surface sediments, geochemical mapping of each element, research of the anormal concentration of elements on the surface. To detect the content of chemical elements several methods were used: atomic absorption spectrometry (P.P. Shirshov Institute of Oceanology); neutron activation analysis (Vernadsky Institute of Geochemistry and Analytical Chemistry), total and organic carbon analysis, photometric method to detection Si, Al, P (P.P. Shirshov Institute of Oceanology). Bulk composition is one of the fundamental characteristics of sediments and bottom deposites of modern basins. Coarse-grained sediments with portion of pelitic component <50% is spread on the shallow area (Kandalaksha Bay), in areas with high hydrodynamic activity of near-bottom water. Under the conditions of their low activity, fine-grained facies are common(>80%). Character of elements distribution correlates with facial distribution of sediments from White Sea. According to litologic description, bottom surface of Dvina Bay is practically everywhere covered by layer of fine-grained sand. In the border area between Dvina Bay and White Sea basin on terraced subwater slope aleurite politic silts are abundant. They tend to exhange down the slope to clay silts. In Onega Bay fractions of non-deposition are observed. They are characterized by wide spread of thin blanket poorgraded sediments, which are likely to be relic. Relief of Kandalakscha Bay bottom is presented as alternation of abyssal fosses (near 300 m) with silles and elevations (<20 m), and also numerous islands. Thus variety of sediment composition is observed here - from rules and gravels to fine-grained clay silts [1]. The map of distribution of chemical elements was created by using bulk composition data with the help of program ArcView. Mn distribution in sedimentation mass is largely determed by influence of redox diagenesis. Reactive form of Mn dominates over less moving, litogenic form in sedimation mass of White Sea. Litogenic form remains in sediment, reactive form moves into silt near-bottom water, resulting Mn migration both in sediment and near-bottom layer of marine water. Mn oxidizes on the contact with oxygen of marine water and alters into insoluble form MnO2, causing Mn enrichment of surface layer of sediments. Highly movable silt deposit MnO2 and enriched by Mn suspension are moved by underflow and accumulate in bottom depressions and in central part of the sea, which is quite wide from both places of original sedimentation and run off sources [2]. Thus, the interrelation between granulometric composition of sediment and materials concentration can be shown by the example of Mn. Local conditions, leading to accumulation of clastic components, are: 1. Rise of content in sand owning to separation of heavy minerals 2. Rise of content in surface, mainly sandy clay sediments owning to presence of concretions 3. Rise of content in lower bunches roof owning to diagenetic contraction. Authors thank academic Lisitsyn for encourage, Andrey Apletalin for valuable help, and everybody, who helped in field and laboratory research of the White sea sediments. Work was being done under the auspices of Russian foundation of basic research (grants 09-05-10081, 09-05-00658 and 08-05-00860), RSA presidiums program of 17 fundamental researches (project 17.1). References: 1.Kuzmina T., Lein A., Lutchsheva L., Murdmaa I., Novigatsky A., Shevchenko V. Chemical composition of White Sea's sediments // Litology and mineral deposits . 2009. - № 2. - P 115-132. 2.Nevessky E., Medvedev V. , Kalinenko V. White sea, sedimentation and holocoen developmental history. - Moscow.: Nauka, 1977. - 236 p. 3.White Sea and it water collection affected by climatic and antropogenic factors. / under the editorship of Terzhevik A., Filatov N. - Petrozavodsk.: Karelsky nauchny centr RAN, 2007. - 335p

Surficial geology of the sea floor in west-central Long Island Sound as shown by sidescan-sonar imagery

USGS Publications Warehouse

McMullen, K.Y.; Poppe, L.J.; DiGiacomo-Cohen, M. L.; Moser, M.S.; Christman, E.B.

2005-01-01

We used sidescan-sonar imagery detailing almost 300 km2 of the sea floor in west-central Long Island Sound in conjunction with bathymetry, sediment samples, bottom video, and seismic data to interpret the area's surficial geology. The distribution of sediments and sedimentary environments interpreted from these data sets represents the Quaternary geology, regional bathymetry, and effects of modern tidal- and wave-driven currents. Four distinct sedimentary environments consisting of 1) fine-grained deposition, 2) sorting and reworking, 3) coarse-grained bedload transport, and 4) erosion or nondeposition, were identified and mapped. Relatively low-energy environments prevail where deposition of clayey silts occurs in deeper water throughout the central part of the study area, and in the protected areas of the far northeastern corner. As low-energy environments transition to relatively high-energy environments, sorting and reworking of sand, silty sand, and sand-silt-clay takes place on the flanks of the shoals and over smaller bathymetric highs. Environments of coarse-grained bedload transport, distinguished by sandy sediments with current-derived bedforms, are located on an unnamed shoal in the northwestern part of the study area and directly to the south of this on Stratford Shoal. High-energy conditions are reflected by environments of erosion or nondeposition, which occur on bathymetric highs where gravel and gravelly sediments are present.

The timing of sediment transport down Monterey Submarine Canyon, offshore California

USGS Publications Warehouse

Stevens, Thomas; Paull, Charles K.; Ussler, William III; McGann, Mary; Buylaert, Jan-Pieter; Lundsten, Eve M.

2013-01-01

While submarine canyons are the major conduits through which sediments are transported from the continents out into the deep sea, the time it takes for sediment to pass down through a submarine canyon system is poorly constrained. Here we report on the first study to couple optically stimulated luminescence (OSL) ages of quartz sand deposits and accelerator mass spectrometry 14C ages measured on benthic foraminifera to examine the timing of sediment transport through the axial channel of Monterey Submarine Canyon and Fan, offshore California. The OSL ages date the timing of sediment entry into the canyon head while the 14C ages of benthic foraminifera record the deposition of hemipelagic sediments that bound the sand horizons. We use both single-grain and small (∼2 mm area) single-aliquot regeneration approaches on vibracore samples from fining-upward sequences at various water depths to demonstrate relatively rapid, decadal-scale sand transport to at least 1.1 km depth and more variable decadal- to millennial-scale transport to a least 3.5 km depth on the fan. Significant differences between the time sand was last exposed at the canyon head (OSL age) and the timing of deposition of the sand (from 14C ages of benthic foraminifera in bracketing hemipelagic sediments) are interpreted as indicating that the sand does not pass through the entire canyon instantly in large individual events, but rather moves multiple times before emerging onto the fan. The increased spread in single-grain OSL dates with water depth provides evidence of mixing and temporary storage of sediment as it moves through the canyon system. The ages also indicate that the frequency of sediment transport events decreases with distance down the canyon channel system. The amalgamated sands near the canyon head yield OSL ages that are consistent with a sub-decadal recurrence frequency while the fining-upward sand sequences on the fan indicate that the channel is still experiencing events with a 150–250 year recurrence frequency out to 3.5 km water depths.    

Pocomoke Sound Sedimentary and Ecosystem History

USGS Publications Warehouse

Cronin, Thomas M.

2004-01-01

Summary of Results: Pocomoke Sound Sediment and Sediment Processes Transport of sediment from coastal marshes. Analyses of pollen and foraminifera from surface sediments in Pocomoke Sound suggest that neither the upstream forested wetlands nor coastal marshes bordering the sound have contributed appreciably to particulate matter in the 10- to 1000-micron size range that is currently being deposited in the sound. Sediment processes derived from short-lived isotope. Analyses of beryllium-7, cesium-137 and lead-210 and redox sensitive elements from Pocomoke sediments showed that there has been a significant increase in anthropogenic elements since the late 1940's when the Delmarva Peninsula became more accessible from the Baltimore-Washington region. Cesium-137 was found to be a useful tool to determine changes in sedimentation within the system. Three major stages of sedimentation occurred. Before 1950, the system was equilibrium with the agriculture activity in the watershed, whereas urbanization and agricultural activity changes during and immediately preceding World War II resulted in increased sediment flux. Around 1970, the sediment flux diminished and there was an apparent increase in bank erosion sediment to the deeper parts of the system. Rates of sediment deposition. Radiocarbon, lead-210, and pollen dating of sediment cores from Pocomoke Sound indicate relatively continuous deposition of fine-grained sediments in the main Pocomoke channel at > ~7 m water depths. Mean sediment accumulation rates during the past few centuries were relatively high (>1 cm yr -1 ). The ages of coarser-grained sediments (sands) blanketing the shallow (4.0 cm yr -1 ) at most sites throughout the Sound in post-Colonial time. These results confirm those from other regions of the bay that land-clearance increased the flux of river-borne sediment to certain r

Sediment balance of intertidal mudflats in a macrotidal estuary

NASA Astrophysics Data System (ADS)

lafite, R.; Deloffre, J.; Lemoine, M.

2012-12-01

Intertidal area contributes widely to fine-grained sediment balance in estuarine environments. Their sedimentary dynamics is controlled by several forcing parameters including tidal range, river flow and swell, affected by human activities such as dredging, construction or vessels traffic leading to modify sediment transport pattern. Although the estuarine hydrodynamics is well documented, the link between forcing parameters and these sedimentary processes is weakly understood. One of the main reasons is the difficulty to integrate spatial (from the fluvial to the estuary mouth) and temporal (from swell in seconds to pluriannual river flow variability) patterns. This study achieved on intertidal mudflats distributed along the macrotidal Seine estuary (France) aims (i) to quantify the impact of forcing parameters on each intertidal area respect to its longitudinal position in the estuarine system and (ii) to assess the fine-grained sediment budget at estuarine scale. The Seine estuary is a macrotidal estuary developed over 160 km up the upstream limit of tidal wave penetration. With an average river flow of 450m3.s-1, 80% of the Suspended Particles Matter (SPM) annual flux is discharged during the flood period. In the downstream part, the Seine estuary Turbidity Maximum (TM) is the SPM stock located near the mouth. During their transfer toward the sea, the fine particles can be trapped in (i) the intertidal mudflats; preferential areas characterized by low hydrodynamics and generally sheltered of the tidal dominant flow, the main tidal current the Seine River and (ii) the TM. The Seine estuary is an anthropic estuary in order to secure navigation: one consequence of these developments is the tidal bore disappearance. Along the macrotidal Seine estuary hydrodynamics features and sedimentary fluxes were followed during at least 1 year using respectively Acoustic Doppler Velocimeter, Optical BackScatter and altimeter. Results in the fluvial estuary enhance the role of hydrological cycle that lead to (i) an increased mean water level and (ii) provide SPM from the continental area. This feature leads to significant accretion over intertidal area. In the middle and marine estuary the TM is the main SPM supplier. In these parts of the estuary deposition over these intertidal area is driven by (i) tidal cycle in particular fortnightly cycle link to maximum TM resuspension during (strongest) spring tide and (ii) TM location controlled by river inflow that varies following an annual and inter-annual variability. Outside sedimentation period, the erosion is driven by the combination of (i) progressive erosion driven by fortnightly cycle and (ii) sudden erosion controlled either by wave or boat generated waves respectively at the mouth and in the middle/upper estuary. This last is reinforced by the rheological characteristics of deposit that correspond to fluid/low consolidated mud. During most of the year, the Seine estuary mudflats record an erosion pattern. Significant and intensive sedimentation only occurs few days per year. This pattern is linked to highly variable hydrodynamics conditions (bottom shear stress ranging from 0.5 to 5 N.m-2) that control the sediment supply availability. In this infilling macrotidal anthropized system mudflats are close to equilibrium with an annual rate ranging between +/- 5cm.yrs-1: they act as temporal storage area of fined-grained sediments.

Spatial variability in the abundance, composition, and age of organic matter in surficial sediments of the East China Sea

NASA Astrophysics Data System (ADS)

Wu, Ying; Eglinton, Timothy; Yang, Liyang; Deng, Bing; Montluçon, Daniel; Zhang, Jing

2013-12-01

the sources and fate of organic matter (OM) sequestered in continental margin sediments is of importance because the mode and efficiency of OM burial impact the carbon cycle and the regulation of atmospheric CO2 over long time scales. We carried out molecular (lignin-derived phenols from CuO oxidation), elemental, isotopic (δ13C, Δ14C), and sedimentological (grain size and mineral surface area) analyses in order to examine spatial variability in the abundance, source, age of surface sediments of the East China Sea. Higher terrigenous organic matter values were found in the main accumulating areas of fluvial sediments, including the Changjiang (Yangtze) Estuary and Zhejiang-Fujian coastal zone. Isotopic and biomarker data suggest that the sedimentary OM in the inner shelf region was dominated by aged (Δ14C = -423 ± 42‰) but relatively lignin-rich OM (Λ = 0.94 ± 0.57 mg/100 mg OC) associated with fine-grained sediments, suggesting important contributions from soils. In contrast, samples from the outer shelf, while of similar age (Δ14 C = -450 ± 99‰), are lignin poor (Λ = 0.25 ± 0.14 mg/100 mg OC) and associated with coarse-grained material. Regional variation of lignin phenols and OM ages indicates that OM content is fundamentally controlled by hydrodynamic sorting (especially, sediment redistribution and winnowing) and in situ primary production. Selective sorption of acid to aldehyde in clay fraction also modified the ratios of lignin phenols. The burial of lignin in East China Sea is estimated to be relatively efficient, possibly as a consequence of terrigenous OM recalcitrance and/or relatively high sedimentation rates in the Changjiang Estuary and the adjacent Zhejing-Fujian mud belt.

How Is Topographic Simplicity Maintained in Ephemeral, Dryland Channels?

NASA Astrophysics Data System (ADS)

Singer, M. B.; Michaelides, K.

2014-12-01

Topography in river channels reflects the time integral of streamflow-driven sediment flux mass balance. In dryland basins, infrequent and spatially heterogeneous rainfall generates a nonuniform sediment supply to ephemeral channels from hillslopes, and this sediment is subsequently sorted by spatially and temporally discontinuous channel flow. Paradoxically, the time integral of these interactions tends to produce simple topography, manifest in straight longitudinal profiles and symmetrical cross sections, which are distinct from bed morphology in perennial channels, but the controlling processes are unclear. We present a set of numerical modeling experiments based on field measurements and scenarios of uniform/nonuniform streamflow to investigate ephemeral channel bed-material flux and net sediment accumulation behavior in response to variations in channel hydrology, width, and grain size distribution. Coupled with variations in valley and channel width and frequent, yet discontinuous hillslope supply of coarse sediment, bed material becomes weakly sorted into coarse and fine sections that then affect rates of channel Qs. We identify three sediment transport thresholds relevant to poorly armored, dryland channels: 1) a low critical value required to entrain any grain sizes from the bed; 2) a value of ~4.5τ*c needed to move all grain sizes within a cross section with equal mobility; and 3) a value of ~50τ*c required to entrain gravel at nearly equivalent rates at all sections along a reach. The latter represents the 'geomorphically effective' event, which resets channel topography. We show that spatially variable flow below ~50τ*c creates and subsequently destroys incipient topography along ephemeral reaches and that large flood events above this threshold apparently dampen fluctuations in longitudinal sediment flux and thus smooth incipient channel bar forms. Both processes contribute to the maintenance of topographic simplicity in ephemeral dryland channels.

Grain Size Biasing of 230Th-derived Focusing Factors in the Panama Basin

NASA Astrophysics Data System (ADS)

Loveley, M. R.; Marcantonio, F.; Lyle, M. W.; Ibrahim, R.; Wang, J. K.; Hertzberg, J. E.

2014-12-01

In this study, we attempt to understand how differing grain size classes in Panama Basin sediments may create biasing of 230Th as a constant-flux proxy. Greater amounts of 230Th are contained in fine grained particles, which, if fractionated from coarser grained counterparts may lead to biasing of 230Th-derived mass accumulation rates (MARs) and sediment focusing factors. We examined sediments that span the past 25 kyr from four new sediment cores retrieved from two different localities close to the ridges that bound the Panama Basin. Each locality contained paired sites that were seismically interpreted to have undergone sediment redistribution, i.e., thick focused sites versus thin winnowed sites. Two sediment cores were retrieved from the northern part of the Panama basin, Cocos Ridge, (MV1014-01-"4JC", 5° 44.7'N 85° 45.5' W, 1730 m depth; MV1014-01-"8JC", 6° 14.0'N 86° 2.6' W, 1993 m depth), and two were retrieved from the southern part of the basin, Carnegie Ridge, (MV1014-02-"11JC", 0° 41.6'S 85° 20.0' W, 2452 m depth; MV1014-02-"17JC" 0° 10.8'S 85° 52.0' W, 2846 m depth). Cores 4JC and 11JC lie closer to the ridge tops of the Cocos and Carnegie Ridges, respectively, and have thin sediment drapes, while deeper cores, 8JC (Cocos) and 17JC (Carnegie), have thicker sediment drapes and lie downslope from the ridge top cores. Age-model-derived sand MARs, which likely represent the vertical rain of particles that cannot be transported by bottom currents, are similar at each of the paired sites in Holocene and glacial time slices. However, 230Th-normalized MARs are about 50% lower, on average at each of the paired sites during the same time slices. Both Holocene and glacial samples from "thin" cores (4,11JC) contain, surprisingly, significant amounts (up to 50%) of the 230Th within the coarse grained (>63 μm) fraction which makes up 40-70% of the bulk samples analyzed. On the contrary, Holocene and glacial samples from "thick" cores, (8,17JC), contain the greatest amounts of 230Th (up to 49%) in the finest grain-sized fraction (<4μm), which makes up 26-40% of the bulk samples analyzed. Although, redistribution of sediment has taken place, our analysis indicates that 230Th-derived focusing factors are being overestimated at thick sites and underestimated at thin sites.

Turbulent behaviour of non-cohesive sediment gravity flows at unexpectedly high flow density

NASA Astrophysics Data System (ADS)

Baker, Megan; Baas, Jaco H.; Malarkey, Jonathan; Kane, Ian

2016-04-01

Experimental lock exchange-type turbidity currents laden with non-cohesive silica-flour were found to be highly dynamic at remarkably high suspended sediment concentrations. These experiments were conducted to produce sediment gravity flows of volumetric concentrations ranging from 1% to 52%, to study how changes in suspended sediment concentration affects the head velocities and run-out distances of these flows, in natural seawater. Increasing the volumetric concentration of suspended silica-flour, C, up to C = 46%, within the flows led to a progressive increase in the maximum head velocity. This relationship suggests that suspended sediment concentration intensifies the density difference between the turbulent suspension and the ambient water, which drives the flow, even if almost half of the available space is occupied by sediment particles. However, from C = 46% to C = 52% a rapid reduction in the maximum head velocity was measured. It is inferred that at C = 46%, friction from grain-to-grain interactions begins to attenuate turbulence within the flows. At C > 46%, the frictional stresses become progressively more dominant over the turbulent forces and excess density, thus producing lower maximum head velocities. This grain interaction process started to rapidly reduce the run-out distance of the silica-flour flows at equally high concentrations of C ≥ 47%. All flows with C < 47% reflected off the end of the 5-m long tank, but the head velocities gradually reduced along the tank. Bagnold (1954, 1963) estimated that, for sand flows, grain-to-grain interactions start to become important in modulating turbulence at C > 9%. Yet, the critical flow concentration at which turbulence modulation commenced for these silica-flour laden flows appeared to be much higher. We suggest that Bagnold's 9% criterion cannot be applied to flows that carry fine-grained sediment, because turbulent forces are more important than dispersive forces, and frictional forces start to affect the flows only at concentrations just below the cubic packing density of spheres of C = 52%. These experimental results also imply that natural flows may be able to transport vast volumes of non-cohesive sediment with relative ease, especially considering that the experimental flows moved on a horizontal slope. References Bagnold, R. A. (1954). Experiments on a Gravity-Free Dispersion of Large Solid Spheres in Newtonian Fluid under Shear. Proceedings of the Royal Society series A: Mathematical, Physical and Engineering Sciences, 225(1160), 49-63. Bagnold, R. A. (1963). Beach and nearshore processes: Part 1. Mechanics of marine sedimentation. In: Hill, M. N. (Ed.) The Earth Beneath the Sea, vol. 3. Wiley-Interscience, London, 507-533.

Structural and Lithologic Characterization of the SAFOD Pilot Hole and Phase One Main Hole

NASA Astrophysics Data System (ADS)

Barton, D. C.; Bradbury, K.; Solum, J. G.; Evans, J. P.

2005-12-01

Petrological and microstructural analyses of drill cuttings were conducted for the San Andreas Fault Observatory at Depth (SAFOD) Pilot Hole and Main Hole projects. Grain mounts were produced at ~30 m (100 ft) intervals from drill cuttings collected from the Pilot Hole to a depth of 2164 m (7100 ft) and from Phase 1 of the SAFOD main hole to a depth of 3067 m (10062 ft). . Thin-section grain mount analysis included identification of mineral composition, alteration, and deformation within individual grains, measured at .5 mm increments on an equally spaced, 300 point grid pattern. Lithologic features in the Quaternary/Tertiary deposits from 30 - 640 m (100-2100 ft) in the Pilot Hole, and 670 - 792 m (2200 - 2600 ft) in the Phase 1 main hole, include fine-grained, thinly bedded sediments with clasts of fine-grained volcanic groundmass. Preliminary grain mount analysis from 1920 - 3067 m (6300 - 10062) in the Phase 1 main hole, indicates a sedimentary sequence consisting of fine-grained lithic fragments of very fine-grained shale. Deformation mechanisms observed within the cuttings of granitic rocks from 914 - 1860 m (3000 - 6100 ft.) include intracrystalline plasticity and cataclasis. Intracrystalline plastic deformation within quartz and feldspar grains is indicated by undulatory extinction, ribbon grains, chessboard patterns, and deformation twins and lamellae. Cataclastic deformation is characterized by intra- and intergranular microfractures, angular grains, gouge zones, iron-oxide banding, and comminution. Mineral and cataclasite abundances were plotted as a function of weight percent vs. depth. Plots of quartz and feldspar abundances are also correlated with XRD weight percent data from 1160 - 1890 m (3800 - 6200 ft.) in the granitic and granodioritic sequences of the Phase 1 main hole. Regions of the both of the drill holes with cataclasite abundances ranging from 20 - 30 wt% are interpreted as shear zones. Shear zones identified in this study from 1150 - 1420 m (3773 - 4659 ft.) in the Pilot Hole occur in the same location as shear zones recognized by Boness and Zoback (2004) using borehole geophysical data. These shear zones may possibly be correlated to shear zones identified in the Phase I main hole from 1615 - 2012 m (5300 - 6600 ft). If this is the case, it can be explained by steeply dipping subsidiary fault zones, likely associated with the San Andreas Fault system.

The Devil is in the Details: Using X-Ray Computed Tomography to Develop Accurate 3D Grain Characteristics and Bed Structure Metrics for Gravel Bed Rivers

NASA Astrophysics Data System (ADS)

Voepel, H.; Hodge, R. A.; Leyland, J.; Sear, D. A.; Ahmed, S. I.

2014-12-01

Uncertainty for bedload estimates in gravel bed rivers is largely driven by our inability to characterize the arrangement and orientation of the sediment grains within the bed. The characteristics of the surface structure are produced by the water working of grains, which leads to structural differences in bedforms through differential patterns of grain sorting, packing, imbrication, mortaring and degree of bed armoring. Until recently the technical and logistical difficulties of characterizing the arrangement of sediment in 3D have prohibited a full understanding of how grains interact with stream flow and the feedback mechanisms that exist. Micro-focus X-ray CT has been used for non-destructive 3D imaging of grains within a series of intact sections of river bed taken from key morphological units (see Figure 1). Volume, center of mass, points of contact, protrusion and spatial orientation of individual surface grains are derived from these 3D images, which in turn, facilitates estimates of 3D static force properties at the grain-scale such as pivoting angles, buoyancy and gravity forces, and grain exposure. By aggregating representative samples of grain-scale properties of localized interacting sediment into overall metrics, we can compare and contrast bed stability at a macro-scale with respect to stream bed morphology. Understanding differences in bed stability through representative metrics derived at the grain-scale will ultimately lead to improved bedload estimates with reduced uncertainty and increased understanding of interactions between grain-scale properties on channel morphology. Figure 1. CT-Scans of a water worked gravel-filled pot. a. 3D rendered scan showing the outer mesh, and b. the same pot with the mesh removed. c. vertical change in porosity of the gravels sampled in 5mm volumes. Values are typical of those measured in the field and lab. d. 2-D slices through the gravels at 20% depth from surface (porosity = 0.35), and e. 75% depth from surface (porosity = 0.24), showing the presence of fine sediments 'mortaring' the larger gravels. f. shows a longitudinal slide from which pivot angle measurements can be determined for contact points between particles. g. Example of two particle extraction from the CT scan showing how particle contact areas can be measured (dark area).

Laminar laboratory rivers

NASA Astrophysics Data System (ADS)

Seizilles, Grégoire; Devauchelle, Olivier; Lajeunesse, Éric; Métivier, François

2014-05-01

A viscous fluid flowing over fine plastic grains spontaneously channelizes into a few centimeters-wide river. After reaching its equilibrium shape, this stable laboratory flume is able to carry a steady load of sediments, like many alluvial rivers. When the sediment discharge vanishes, the river size, shape and slope fit the threshold theory proposed by Glover and Florey (1951), which assumes that the Shields parameter is critical on the channel bed. As the sediment discharge is increased, the river widens and flattens. Surprisingly, the aspect ratio of its cross section depends on the sediment discharge only, regardless of the water discharge. We propose a theoretical interpretation of these findings based on the balance between gravity, which pulls particles towards the center of the channel, and the diffusion of bedload particles, which pushes them away from areas of intense bedload.

From deposition to erosion: Spatial and temporal variability of sediment sources, storage, and transport in a small agricultural watershed

USGS Publications Warehouse

Florsheim, J.L.; Pellerin, B.A.; Oh, N.H.; Ohara, N.; Bachand, P.A.M.; Bachand, Sandra M.; Bergamaschi, B.A.; Hernes, P.J.; Kavvas, M.L.

2011-01-01

The spatial and temporal variability of sediment sources, storage, and transport were investigated in a small agricultural watershed draining the Coast Ranges and Sacramento Valley in central California. Results of field, laboratory, and historical data analysis in the Willow Slough fluvial system document changes that transformed a transport-limited depositional system to an effective erosion and transport system, despite a large sediment supply. These changes were caused by a combination of factors: (i) an increase in transport capacity, and (ii) hydrologic alteration. Alteration of the riparian zone and drainage network pattern during the past ~ 150 years included a twofold increase in straightened channel segments along with a baselevel change from excavation that increased slope, and increased sediment transport capacity by ~ 7%. Hydrologic alteration from irrigation water contributions also increased transport capacity, by extending the period with potential for sediment transport and erosion by ~ 6 months/year. Field measurements document Quaternary Alluvium as a modern source of fine sediment with grain size distributions characterized by 5 to 40% fine material. About 60% of an upland and 30% of a lowland study reach incised into this deposit exhibit bank erosion. During this study, the wet 2006 and relatively dry 2007 water years exhibited a range of total annual suspended sediment load spanning two orders of magnitude: ~ 108,500 kg/km2/year during 2006 and 5,950 kg/km2/year during 2007, only 5% of that during the previous year. Regional implications of this work are illustrated by the potential for a small tributary such as Willow Slough to contribute sediment – whereas large dams limit sediment supply from larger tributaries – to the Sacramento River and San Francisco Bay Delta and Estuary. This work is relevant to lowland agricultural river–floodplain systems globally in efforts to restore aquatic and riparian functions and where water quality management includes reducing fine sediment contributions that can couple with other pollutants.

U.S. Geological Survey Quality-Assurance Project for Sediment Analysis

USGS Publications Warehouse

Gordon, John D.; Newland, Carla

2000-01-01

Introduction Sediment is derived primarily from natural weathering of rock and is an assemblage of individual mineral grains that are then deposited by some physical agent, such as water, wind, ice, or gravity (Fetter, 1988). The U.S. Geological Survey (USGS) samples sediments and collects data on the amount of sediment in selected waterways. The most pressing sediment-related problems are associated with environmental questions, such as the transport and fate of attached pollutants, effects of sediment on aquatic biota and their habitats, and effects on sediment transport from land-use changes. Current (2000) sediment issues require that sediment studies address multiple objectives in water-resources management (Koltun and others, 1997). To support sediment research, the USGS operates laboratories for the analysis of the physical characteristics of sediment. Sediment laboratories producing data for the USGS have two principal functions: (1) the determination of suspended-sediment concentration in samples and (2) the determination of sand/fine separations. The reliability of these determinations and the usefulness of the data are dependent on the accuracy and reliability of the laboratory analyses (Guy, 1969).

Assessment of Dredged Material Toxicity in San Francisco Bay

DTIC Science & Technology

1990-11-01

reference sediment. When compared to the fine-grain Sequim Bay refer- ence material, no statistically significant mortalities were detected. R...Oakland Harbor. Sequim Bay material was used as the refer- ence. The hierarchy of interspecific sensitivity was oyster larvae > juvenile sand dabs...in San Francisco Bay 6. AUTHOR(S) Thomas M. Dillon, David W. Moore 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) - 8. PERFORMING ORGANIZATION

Workshop and Conference on Clay Microstructure: The Microstructure of Fine-Grained Terrigenous Marine Sediments - From Muds to Shale Held in Stennis, Mississippi on October 4-7, 1988

DTIC Science & Technology

1988-10-07

from experiments on wet clay minerals by using the EC technique.(3,4) Layer lattice image of fully hydrated tubular halloysite could be clearly observed...in wet air environment. Tubular and spherical halloysite and their hydrazine complexes were observed both in wet air and in vacuum, and their

Organic carbon accumulation and preservation in surface sediments on the Peru margin

USGS Publications Warehouse

Arthur, M.A.; Dean, W.E.; Laarkamp, K.

1998-01-01

Concentrations and characteristics of organic matter in surface sediments deposited under an intense oxygen-minimum zone on the Peru margin were studied in samples from deck-deployed box cores and push cores acquired by submersible on two transects spanning depths of 75 to 1000 m at 12??and 13.5??S. The source of organic matter to the seafloor in these areas is almost entirely marine material as confirmed by the narrow range of ??13C of organic carbon obtained in the present study (-20.3 to -21.6???; PDB) and the lack of any relationship between pyrolysis hydrogen index and carbon isotope composition. Organic carbon contents are highest (up to 16%) on the slope at depths between 75 and 350 m in sediments deposited under intermediate water masses with low dissolved oxygen concentrations (< 5 ??mol/kg). Even at these low concentrations of dissolved oxygen, however, the surface sediments that were recovered from these depths are dominantly unlaminated. Strong currents (up to 30 cm/s) associated with the poleward-flowing Peru Undercurrent were measured at depths between 160 and 300 m on both transects. The seafloor in this range of water depths is characterized by bedforms stabilized by bacterial mats, extensive authigenic mineral crusts, and (or) thick organic flocs. Constant advection of dissolved oxygen, although in low concentrations, active resuspension of surficial organic matter, activity of organisms, and transport of fine-grained sediment to and from more oxygenated zones all contribute to greater degradation and poorer initial preservation of organic matter than might be expected under oxygen-deficient conditions. Dissolved-oxygen concentrations ultimately may be the dominant affect on organic matter characteristics, but reworking of fine-grained sediment and organic matter by strong bottom currents and redeposition on the seafloor in areas of lower energy also exert important controls on organic carbon concentration and degree of oxidation in this region.

The silicon isotopic composition of fine-grained river sediments and its relation to climate and lithology

NASA Astrophysics Data System (ADS)

Bayon, G.; Delvigne, C.; Ponzevera, E.; Borges, A. V.; Darchambeau, F.; De Deckker, P.; Lambert, T.; Monin, L.; Toucanne, S.; André, L.

2018-05-01

The δ30Si stable isotopic composition of silicon in soils and fine-grained sediments can provide insights into weathering processes on continents, with important implications on the Si budget of modern and past oceans. To further constrain the factors controlling the distribution of Si isotopes in sediments, we have analysed a large number (n = 50) of separate size-fractions of sediments and suspended particulate materials collected near the mouth of rivers worldwide. This includes some of the world's largest rivers (e.g. Amazon, Congo, Mackenzie, Mississippi, Murray-Darling, Nile, Yangtze) and rivers from the case study areas of the Congo River Basin and Northern Ireland. Silt-size fractions exhibit a mean Si isotopic composition (δ30Si = -0.21 ± 0.19‰; 2 s.d.) similar to that previously inferred for the upper continental crust. In contrast, clay-size fractions display a much larger range of δ30Si values from -0.11‰ to -2.16‰, which yield a global δ30Siclay of -0.57 ± 0.60‰ (2 s.d.) representative of the mean composition of the average weathered continental crust. Overall, these new data show that the Si isotopic signature transported by river clays is controlled by the degree of chemical weathering, as inferred from strong relationships with Al/Si ratios. At a global scale, the clay-bound Si isotopic composition of the world's largest river systems demonstrates a link with climate, defining a general correlation with mean annual temperature (MAT) in corresponding drainage basins. While the distribution of Si isotopes in river sediments also appears to be influenced by the tectonic setting, lithological effects and sediment recycling from former sedimentary cycles, our results pave the way for their use as paleo-weathering and paleo-climate proxies in the sedimentary record.

Potential sources of hydrogel stabilization of Florida Bay lime mud sediments and implications for organic matter preservation

USGS Publications Warehouse

Louda, J.W.; Loitz, J.W.; Melisiotis, A.; Orem, W.H.

2004-01-01

The fine grained carbonate mud sediments of central Florida Bay are resuspended quite easily. However, this disturbance is usually limited to the surficial ('floc') layer, as the underlying sediments appear to be stabilized by an hydrogelation involving the bulk organic matter. That gelation has occurred within these sediments is suggested from their physical behavior and an observed mathematical relationship between the percentages of organic carbon (C org) and water. Specifically, when extruded from a core barrel, the sediment maintains its integrity and has the consistency of a fine spackling compound. However, upon homogenization, as with a stirring rod prior to sieving, these sediments break into two distinct phases, 1/2-2/3 milky water and 1/3-1/2 sediment grains, by volume. The relationship observed between Corg and water was modeled as both linear (% water = (0.0777) Corg + 0.2984, R2 = 0.8664) and logarithmic (% water = 0.2489 Ln Corg + 0.2842, R2 = 0.9455) functions. As this relationship tends to be asymptotic at higher Corg (>3.5% dry)/water values (>60%) and given an higher correlation, the relationship appears better modeled as a logarithmic function. Values of C org from 1.2 to over 6.5%dry wt. and water contents from 30 to over 70%wt. were observed. The calculated intercept revealed that, without organic carbon (viz. hydrogel formation), these carbonates would likely contain only ???30% water by weight ('m' from linear model). This gelation is proposed to involve exopolymeric substances (EPS), likely polysaccharides, derived from diatoms and cyanobacteria of the microphytobenthos. A cyanobacterial-diatomaceous biofilm/mat underlain by purple sulfur bacteria was shown, by pigment based chemotaxonomy, to form the main components of the microphytobenthos. Additional water column detrital biomass, also mainly cyanobacteria and diatoms, is admixed with the living microphytobenthos in a flocculent/nephloid layer above the sediments prior to final incorporation into the gel-stabilized sediment column. Loss of seagrass cover appears to have allowed higher energy wave induced effects to reach the water-(nephloid)-sediment interface and increase overall turbidity in the bay. The effects of these gelatinized organics upon sediment stability, pore water chemistry and dissolved species flux in/out of the sediments are discussed as areas for future research which takes this (hydro-) gelation phenomenon into account.

The clay mineral and Sr-Nd isotopic composition for fine-grained fraction of sediments from northwestern South China Sea: implications for sediment provenance

NASA Astrophysics Data System (ADS)

Cai, G.

2013-12-01

*Guanqiang Cai caiguanqiang@sina.com Guangzhou Marine Geological Survey, Guangzhou, 510760, P.R. China As the largest marginal sea in the western pacific, the South China Sea (SCS) receives large amount of terrigenous material annually through numerous rivers from surrounding continents and islands, which make it as the good place for the study of source to sink process. Yet few studies put emphasis on the northwestern continental shelf and slope in the SCS, even though most of the detrital materials derived from the Red River and Hainan Island are deposited in this area, and northwestern shelf plays a significant role in directly linking the South China, the Indochina and the South China Sea and thus controlling the source to sink process of terrestrial sediment. We presented the clay mineral and Sr-Nd isotopic composition of fine-grained fraction for sediments from northwestern SCS, in order to identify sediment source and transportation. The results show that the clay mineral of northwestern SCS sediments are mainly illite (30%~59%), smectite (20%~40%) and kaolinite (8%~35%), with minor chlorite. The illite chemical index varies between 0.19 and 0.75 with an average of 0.49, indicating an intensive hydrolysis in the source region. The 87Sr/86Sr ratios of sediments range from 0.716288 to 0.734416 (average of 0.724659), and ɛ Nd(0) values range from -10.31 to -11.62 (average of -10.93), which suggest that the source rocks of these sediments are derived from continental crust. The Hainan Island is an important source for sediments deposited in the nearshore and western shelf, especially for illite, kaolinite and smectite clay minerals. Furthermore, the relatively high contents of kaolinite and smectite in sediments from eastern shelf and southern slope of Hainan Island are also controlled by the supply of terrigenous materials from Hainan, which cannot be resulted from sedimentary differentiation of the Pearl and Red river sediments. And the correlation analysis between smectite and Sr-Nd isotopic ratios imply that the smectite in sediments mainly come from chemical weathering products of old continental crust, rather than volcanic rocks of Luzon island.

Environmental process descriptors for TNT, TNT-related compounds and picric acid in marine sediment slurries.

PubMed

Yost, Sally L; Pennington, Judith C; Brannon, James M; Hayes, Charolett A

2007-08-01

Process descriptors were determined for picric acid, TNT, and the TNT-related compounds 2,4DNT, 2,6DNT, 2ADNT, 4ADNT, 2,4DANT, 2,6DANT, TNB and DNB in marine sediment slurries. Three marine sediments of various physical characteristics (particle size ranging from 15 to >90% fines and total organic carbon ranging from <0.10 to 3.60%) were kept in suspension with 20ppt saline water. Concentrations of TNT and its related compounds decreased immediately upon contact with the marine sediment slurries, with aqueous concentrations slowly declining throughout the remaining test period. Sediment-water partition coefficients could not be determined for these compounds since solution phase concentrations were unstable. Kinetic rates and half-lives were influenced by the sediment properties, with the finer grained, higher organic carbon sediment being the most reactive. Aqueous concentrations of picric acid were very stable, demonstrating little partitioning to the sediments. Degradation to picramic acid was minimal, exhibiting concentrations at or just above the detection limit.

Size segregation in bedload sediment transport at the particle scale

NASA Astrophysics Data System (ADS)

Frey, P.; Martin, T.

2011-12-01

Bedload, the larger material that is transported in stream channels, has major consequences, for the management of water resources, for environmental sustainability, and for flooding alleviation. Most particularly, in mountains, steep slopes drive intense transport of a wide range of grain sizes. Our ability to compute local and even bulk quantities such as the sediment flux in rivers is poor. One important reason is that grain-grain interactions in stream channels may have been neglected. An arguably most important difficulty pertains to the very wide range of grain size leading to grain size sorting or segregation. This phenomenon largely modifies fluxes and results in patterns that can be seen ubiquitously in nature such as armoring or downstream fining. Most studies have concerned the spontaneous percolation of fine grains into immobile gravels, because of implications for salmonid spawning beds, or stratigraphical interpretation. However when the substrate is moving, the segregation process is different as statistically void openings permit downward percolation of larger particles. This process also named "kinetic sieving" has been studied in industrial contexts where segregation of granular or powder materials is often non-desirable. We present an experimental study of two-size mixtures of coarse spherical glass beads entrained by a shallow turbulent and supercritical water flow down a steep channel with a mobile bed. The particle diameters were 4 and 6mm, the channel width 6.5mm and the channel inclination ranged from 7.5 to 12.5%. The water flow rate and the particle rate were kept constant at the upstream entrance. First only the coarser particle rate was input and adjusted to obtain bed load equilibrium, that is, neither bed degradation nor aggradation over sufficiently long time intervals. Then a low rate of smaller particles (about 1% of the total sediment rate) was introduced to study the spatial and temporal evolution of segregating smaller particles. Flows were filmed from the side by a high-speed camera. Using image processing algorithms made it possible to determine the position, velocity and trajectory of both smaller and coarser particles. After a certain time, a quasi-continuous area of smaller beads developed under moving and above quasi-immobile coarser beads (see figure). Results include the time evolution of segregating smaller beads, assessment of percolation velocity and streamwise and vertical velocity depth profiles.

Attrition in the kimberlite system

NASA Astrophysics Data System (ADS)

Jones, Thomas J.; Russell, James K.

2018-05-01

The sustained transportation of particles in a suspension commonly results in particle attrition leading to grain size reduction and shape modification. Particle attrition is a well-studied phenomenon that has mainly focussed on sediments produced in aeolian or fluvial environments. Here, we present analogue experiments designed to explore processes of attrition in the kimberlite system; we focus on olivine as it is the most abundant constituent of kimberlite. The attrition experiments on olivine use separate experimental set-ups to approximate two natural environments relevant to kimberlites. Tumbling mill experiments feature a low energy system supporting near continual particle-particle contact and are relevant to re-sedimentation and dispersal processes. Experiments performed in a fluidized particle bed constitute a substantially higher energy environment pertinent to kimberlite ascent and eruption. The run-products of each experiment are analysed for grain size reduction and shape modification and these data are used to elucidate the rates and extents of olivine attrition as a function of time and energy. Lastly, we model the two experimental datasets with an empirical rate equation that describes the production of daughter products (fines) with time. Both datasets approach a fines production limit, or plateau, at long particle residence times; the fluidized system is much more efficient producing a substantially higher fines content and reaches the plateau faster. Our experimental results and models provide a way to forensically examine a wide range of processes relevant to kimberlite on the basis of olivine size and shape properties.

Rare earth elements in fine-grained sediments of major rivers from the high-standing island of Taiwan

NASA Astrophysics Data System (ADS)

Li, Chuan-Shun; Shi, Xue-Fa; Kao, Shuh-Ji; Liu, Yan-Guang; Lyu, Hua-Hua; Zou, Jian-Jun; Liu, Sheng-Fa; Qiao, Shu-Qing

2013-06-01

Thirty-eight sediment samples from 15 primary rivers on Taiwan were retrieved to characterize the rare earth element (REE) signature of fluvial fine sediment sources. Compared to the three large rivers on the Chinese mainland, distinct differences were observed in the REE contents, upper continental crust normalized patterns and fractionation factors of the sediment samples. The average REE concentrations of the Taiwanese river sediments are higher than those of the Changjiang and Huanghe, but lower than the Zhujiang. Light rare earth elements (LREEs) are enriched relative to heavy rare earth elements (HREEs) with ratios from 7.48 to 13.03. We found that the variations in (La/Lu)UCC-(Gd/Lu)UCC and (La/Yb)UCC-(Gd/Yb)UCC are good proxies for tracing the source sediments of Taiwanese and Chinese rivers due to their distinguishable values. Our analyses indicate that the REE compositions of Taiwanese river sediments were primarily determined by the properties of the bedrock, and the intensity of chemical weathering in the drainage areas. The relatively high relief and heavy rainfall also have caused the REEs in the fluvial sediments from Taiwan to be transported to the estuaries down rivers from the mountains, and in turn delivered nearly coincidently to the adjacent seas by currents and waves. Our studies suggest that the REE patterns of the river sediments from Taiwan are distinguishable from those from the other sources of sediments transported into the adjacent seas, and therefore are useful proxies for tracing the provenances and dispersal patterns of sediments, as well as paleoenvironmental changes in the marginal seas.

Evaluating porewater polycyclic aromatic hydrocarbon-related toxicity at a contaminated sediment site using a spiked field-sediment approach.

PubMed

Hartzell, Sharon E; Unger, Michael A; Vadas, George G; Yonkos, Lance T

2018-03-01

Although the complexity of contaminant mixtures in sediments can confound the identification of causative agents of adverse biological response, understanding the contaminant(s) of primary concern at impacted sites is critical to sound environmental management and remediation. In the present study, a stock mixture of 18 polycyclic aromatic hydrocarbon (PAH) compounds was prepared to reflect the variety and relative proportions of PAHs measured in surface sediment samples collected from discrete areas of a historically contaminated industrial estuary. This site-specific PAH stock mixture was spiked into nontoxic in-system and out-of-system field-collected reference sediments in dilution series spanning the range of previously measured total PAH concentrations from the region. Spiked sediments were evaluated in 10-d Leptocheirus plumulosus tests to determine whether toxicity in laboratory-created PAH concentrations was similar to the toxicity found in field-collected samples with equivalent PAH concentrations. The results show that toxicity of contaminated sediments was not explained by PAH exposure, while indicating that toxicity in spiked in-system (fine grain, high total organic carbon [TOC]) and out-of-system (course grain, low TOC) sediments was better explained by porewater PAH concentrations, measured using an antibody-based biosensor that quantified 3- to 5-ring PAHs, than total sediment PAH concentrations. The study demonstrates the application of site-specific spiking experiments to evaluate sediment toxicity at sites with complex mixtures of multiple contaminant classes and the utility of the PAH biosensor for rapid sediment-independent porewater PAH analysis. Environ Toxicol Chem 2018;37:893-902. © 2017 SETAC. © 2017 SETAC.

Characteristic sediment and water column chlorophyll-a in the sea cucumber’s Paracaudina sp. habitat on the Kenjeran Water, Surabaya

NASA Astrophysics Data System (ADS)

Widianingsih, W.; Zaenuri, M.; Anggoro, S.; Kusumaningrum, H. P.; Hartati, R.

2018-03-01

The study of characteristic sediment and water column chlorophyll-a has an important role in the sea cucumber habitat. Sediment chlorophyll-a represents a productivity primer for the benthic community. This research has a purpose to investigate characteristic sediment and water column chlorophyll-a on the Kenjeran water, Surabaya. Sediment samples were collected by the ekman grab for analysis, grain size and nutrient. The sample for sediment chlorophyll-a was taken by core sampler. The water samples were taken with Nansen Bottles. According to the research result, the values of sediment chlorophyll-a at station 10, 11 and 12 were higher than the other stations. In contrast, the value of chlorophyll-a in the column water had almost the same value for each station. The sediment chlorophyll-a value on clay and silt sediment type was higher than the fine sand and coarse sediment type. The suitable habitat characteristic for Paracaudina sp. was clay and silt sediment with sediment chlorophyll concentration ranging from 347.82 mg·m-2 to 1135.52 mg·m-2.

Off shore wind farms change the benthic pelagic coupling in the Belgian Part of the North Sea

NASA Astrophysics Data System (ADS)

Vanaverbeke, Jan; Coates, Delphine; Braeckman, Ulrike; Soetaert, Karline; Moens, Tom

2016-04-01

Since Europe enforced renewable energy target figures upon its member states through the implementation of two main European Directives 11 2001/77/EC and 2009/28/EC, the development of offshore wind farms (OWF) has accelerated. Belgium installed OWFs on sandbanks, characterized by permeable sediments, low in organic matter content and a species-poor macrofaunal community with species occurring in low densities. A detailed monitoring campaign in the immediate vicinity of a wind turbine (1-200m), revealed a significant decrease in median grain size and permeability, coinciding with a 6-fold increase in organic matter content. The observed fining of the sediment is explained by an altered benthic-pelagic coupling in the area. The wind turbines are colonized by an abundant fouling community producing high amounts of detritus and faeces, a continuous additional source of organic matter. The changes in sediment composition, and the availability of additional organic matter resulted in drastic increase in macrofaunal densities (from 1390 ind m-2 to 18600 ind m-2), and a change from a species-poor community to a species-rich community dominated by the ecosystem engineer Lanice conchilega. Large densities of L. conchilega, as observed in our samples, are known to trap fine material from the water column, which can result in a further decrease of sediment permeability in the vicinity of the wind turbines. A preliminary experiment, where permeable sediments were subjected to artificial fining, showed a decreased penetration depth of advective water currents and a reduced trapping of diatoms by the sediment in finer sediments. Additionally, sediment community oxygen consumption rates, and efflux of NH4+ from the sediment, measured after a simulated phytoplankton bloom, decreased significantly when sediment permeability was reduced. We hypothesize that the combination of the altered macrofaunal community composition, together with the changes in the physical properties of the sediment matrix, will lead to a change in the biogeochemical properties of the sediment: highly reactive permeable sediments, poor in organic matter will shift towards sediment where organic matter will accumulate. Degradation of organic matter will then no longer be governed by physical processes, but mediated by biological processes (bioturbation, bio-irrigation).

Biostratigraphic, chronostratigraphic, and stratigraphic sequence analysis of Lower Tertiary marine sediments of Alabama for indicators of sea-level change

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thompson, P.R.; Baum, G.R.

1991-03-01

Early Eocene to late Oligocene marine sedimentary units in southwestern Alabama were sampled at closely spaced intervals to derive a precise time-stratigraphic framework and to determine the paleoecological and mineralogical responses to fluctuations in sea level. Paleontologic control consisted of planktonic, smaller and larger benthonic foraminifera, calcareous nannofossils, dinoflagellates, and megafossils. Paleomagnetic reversals were delineated in two boreholes which, when supplemented by strontium isotope dates and the biostratigraphic control, provided a robust in situ chronostratigraphy for the Gulf Coast lower Tertiary. Paleoecologic trends in regression and transgression can be clearly correlated across major regional facies changes. Using the chronostratigraphy developedmore » here, the second-, third-, and fourth-orders of Vail's global sea-level cycles can be recognized and demonstrate the influence of sea-level change on sedimentation. Stratigraphic systems tracts (SSTs) and bounding surfaces in outcrop were determined by lithologic variations and paleoecologic trends, and additionally by gamma logs in the cores. The lower sequence boundary occurs at a contact where an older, relatively fine-grained, deep-water, fossiliferous unit was abruptly succeeded by a coarse-grained, shallow-water, poorly fossiliferous unit. The transgressive surface occurs at the base of a fining- and deepening-upwards unit that was commonly glauconitic and very fossiliferous. Transgression culminated with a pulse of planktonic microfossils in a bed having reduced clastic sedimentation; on the log the surface of maximum starvation was marked by a gamma spike.« less

A two-dimensional spectrum analysis for sedimentation velocity experiments of mixtures with heterogeneity in molecular weight and shape.

PubMed

Brookes, Emre; Cao, Weiming; Demeler, Borries

2010-02-01

We report a model-independent analysis approach for fitting sedimentation velocity data which permits simultaneous determination of shape and molecular weight distributions for mono- and polydisperse solutions of macromolecules. Our approach allows for heterogeneity in the frictional domain, providing a more faithful description of the experimental data for cases where frictional ratios are not identical for all components. Because of increased accuracy in the frictional properties of each component, our method also provides more reliable molecular weight distributions in the general case. The method is based on a fine grained two-dimensional grid search over s and f/f (0), where the grid is a linear combination of whole boundary models represented by finite element solutions of the Lamm equation with sedimentation and diffusion parameters corresponding to the grid points. A Monte Carlo approach is used to characterize confidence limits for the determined solutes. Computational algorithms addressing the very large memory needs for a fine grained search are discussed. The method is suitable for globally fitting multi-speed experiments, and constraints based on prior knowledge about the experimental system can be imposed. Time- and radially invariant noise can be eliminated. Serial and parallel implementations of the method are presented. We demonstrate with simulated and experimental data of known composition that our method provides superior accuracy and lower variance fits to experimental data compared to other methods in use today, and show that it can be used to identify modes of aggregation and slow polymerization.

Salmon Spawning Effects on Streambed Stability

NASA Astrophysics Data System (ADS)

Buxton, T. H.; Buffington, J. M.; Yager, E.; Fremier, A. K.; Hassan, M. A.

2014-12-01

Female salmon build nests ("redds") in streambeds to protect their eggs from predation and damage by bed scour. During spawning, streambed material is mixed, fine sediment is winnowed downstream, and sediment is moved into a tailspill mound resembling the shape of a dune. Redd surfaces are coarser and better sorted than unspawned beds, which is thought to increase redd stability because larger grains are heavier and harder to move and sorting leads to higher friction angles for grain mobility. However, spawning also loosens sediment and creates topography that accelerates flow, both of which may increase particle mobility. We address factors controlling the relative stability of redds and unspawned beds using simulated salmon redds and water worked ("unspawned") beds composed of mixed-grain surfaces in a laboratory flume. Results show that simulated spawning lowered packing resistance to particle mobility on redds by an average of 32-39% compared to unspawned beds. Reductions in packing were sufficient to counter the higher inherent stability of relatively coarse, well sorted grains on redds, overall reducing critical shear stress by 8-20% relative to unspawned beds. In addition, boundary shear stress was 13-41% higher on redds due to flow convergence over the tailspill structure. Finally, redd instability relative to unspawned beds was observed in visual measurements of grain mobility, where bed-averaged shear stress was 22% lower at incipient motion and 29% lower at the discharge that mobilized all grain sizes on redds. Results of these complementary observations, along with sediment mass transport rates being nearly five times higher on a redd than an unspawned bed, indicate that redds are unstable compared to unspawned beds. Given these findings, further research is needed to investigate linkages between spawning disturbance and streambed mobility that may affect salmon reproduction in streams, and to assess whether a certain level of bed disturbance from spawning is required to restore ecosystem functions in streams with threatened populations of salmon.

Shelf mud fields formation within historical times: examples from offshore the Gironde estuary, France

NASA Astrophysics Data System (ADS)

Lesueur, P.; Tastet, J. P.; Marambat, L.

1996-12-01

The Gironde shelf mud fields are distinctive morpho-sedimentary units that overlap the sands and gravels covering the North Aquitaine continental shelf (France). The muddy deposits are located offshore of the two main channels of the Gironde mouth, the West-Gironde mud patch (WGMP) and South-Gironde mud patch (SGMP). Fine-grained sediments originate in the Gironde, especially during river floods, and a smaller part of silty and shelly fine sand has its origin in the sandy covering of the inner shelf, during periods of high-energy (i.e. storms). The stratigraphy of these muddy deposits has been revised, using 14C dates and palynological analyses from cores. The results do not agree with previous estimates, of 10,000 or 7000 BP, for the age of the deposits. The deposition of the Aquitaine shelf mud fields is not linked to the postglacial transgression. The substrate has formed between 2000 and 5000 BP. Some shells from the lower part of the muddy sediments have been dated at 1000 or 1100 BP (SGMP) and 500-600 BP (WGMP). Pollen analyses confirm they formed after 2000 BP. The oldest muds were deposited in the Subatlantic period, and evidence of human activities (such as clearance and agriculture) are conspicuous. Some palynological markers provide evidence of Roman colonization at about 2000 BP. Causes of deferred settling of the muds have been sought through variations in the rate of escape of Gironde suspended matter. This depends on the infilling and the morphological changes within the estuary since the post-Holocene stillstand and the increase of sediment supply resulting from soil erosion within the catchment area. The latest link to climatic fluctuations, and intensive human activities that have occurred during the last thousand years, are suspected to have been influential. However, the various events were concomitant and are difficult to separate. Comparison between cores suggests that at first there was a concentration of sedimentation at the site of the SGMP and in the inner zone of the WGMP. However, later, recent fine-grained sedimentation was concentrated on the outer zone of the WGMP, as testified by the preponderance of pollen that records the afforestation of Les Landes (mid-19th century). The sedimentation rates are variable and range between 1 and 4 mm y -1.

Early Diagenetic Changes of Sediment Pore Properties Beneath the Seafloor and Their Contributions to Gas Hydrate Concentration in the Eastern Margin of Japan Sea

NASA Astrophysics Data System (ADS)

Uchida, T.; Horiuchi, S.; Kato, Y.; Matsumoto, R.

2014-12-01

Recently many of the chimney-shape gas hydrate concentrated beneath the seafloor have been confirmed off Shimane and off Akita as well as off Joetsu in the eastern margin of Japan Sea, which are quite different from the occurrences of pore space hydrate filling the intergranular pore system of sands recognized in Nankai Trough, Mallik and other sites. Sediment samples below the seafloor were retrieved in 2010 up to 40 m long at the Umitaka Spur, Joetsu Channel, Toyama Trough, Japan Basin, Nishi Tsugaru and Okushiri Ridge areas. Small amounts of sandy sediment have been retrieved as thin intercalations in Pleistocene and Holocene muddy layers transported approximately around 3 to 30 ka according to the tephra ages, where supplying sediments might have not been abundant due to sea level fluctuation during the Pleistocene ice age. It is important to clarify the relationship between burial depths and absolute porosities of the argillaceous sediments in relation to early diagenesis. Macroscopic observations and descriptions, measurements of porosity and permeability, SEM (scanning electron microscope) observations, and X-ray diffraction analyses have been performed. They consist of silt- to clay-grained particles, and they sometimes contain very fine- to medium-grained thin sandy layers. Average porosities of these fine-grained sediments are 50 % in all study areas, which quickly reduce from 60% to less than 50% within 10 meters and gradually decrease to the depth. However, mean pore sizes in the Nishi Tsugaru are around 1000 nm while 100 nm in the other areas, which tend to decrease with depth. It is suggested that repacking of the muddy particles gradually advances by mechanical compaction, which may crucially influence permeability. They usually contain much opal-A, quartz, feldspar, illite and smectite that do not change definitely with depth. By optical and microscopic observations, diatom tests, foraminifers and framboidal pyrites are commonly observed, and, in particular, the shapes of diatom are usually various, dominantly fragmental and infrequently preserved. It is remarked that physical diagenesis proceeds first due to mechanical compaction, whereas chemical diagenesis advances very slowly in early diagenesis. This study was performed as a part of the MH21 Research Consortium on methane hydrate in Japan.

Depositional processes of alluvial fans along the Hilina Pali fault scarp, Island of Hawaii

NASA Astrophysics Data System (ADS)

Morgan, Alexander M.; Craddock, Robert A.

2017-11-01

A series of previously unstudied alluvial fans are actively forming along the Hilina Pali escarpment on the south flank of Kīlauea volcano on the Island of Hawaii. These fans are characterized by their steep slopes, coarse grain sizes, and lobate surface morphology. Fans are fed by bedrock channels that drain from the Ka'ū Desert, but sediment is mostly sourced from deeply eroded alcoves carved into the Hilina Pali. Examination of recent deposits indicates that the fans are dominantly constructed from gravel and larger sized sediment. Flow discharges calculated using field measurements of channel geometries and the Manning equation indicate that events inducing sediment transport are of high magnitude and occur during high intensity precipitation events, including Kona storms. The fans along the Hilina Pali appear to be a rare example of fans formed predominately from sieve lobe deposition owing to the area's high slopes, high discharge, coarse bedload, and limited supply of fine-grained sediment. Given such conditions, sieve lobe deposition can form large lobes consisting of boulder-sized material, which may have implications for the identification of depositional processes when interpreting the stratigraphic record.

Are polygonal faults the keystone for better understanding the timing of fluid migration in sedimentary basins?

NASA Astrophysics Data System (ADS)

Gay, Aurélien

2017-06-01

The initial sediment lithification starts with complex interactions involving minerals, surface water, decomposing organic matter and living organisms. This is the eogenesis domain (0 to 2 km below the seafloor) in which the sediments are subject to physical, chemical and mechanical transformations defining the early fabric of rocks. This interval is intensively prospected for its energy/mining resources (hydrocarbons, metal deposits, geothermal energy). In most basins worldwide it is composed of very fine-grained sediments and it is supposed to play the role of a seal for fluids migration. However, it is affected by polygonal faulting due to a volume loss during burial by contraction of clay sediments with a high smectite content. This process is of high interest for fractured reservoirs and/or cover integrity but it is not well constrained giving an uncertainty as this interval can either promote the migration of deeper fluids and the mineralized fluids intensifies diagenesis in the fracture planes, rendering this interval all the more impermeable. The next challenge will be to define where, when and how does this polygonal fault interval occur and this can only be done by understanding the behavior of clay grains and fluids during early burial.

Distribution, behavior, and transport of inorganic and methylmercury in a high gradient stream

USGS Publications Warehouse

Flanders, J.R.; Turner, R.R.; Morrison, T.; Jensen, R.; Pizzuto, J.; Skalak, K.; Stahl, R.

2010-01-01

Concentrations of Hg remain elevated in physical and biological media of the South River (Virginia, USA), despite the cessation of the industrial use of Hg in its watershed nearly six decades ago, and physical characteristics that would not seem to favor Hg(II)-methylation. A 3-a study of inorganic Hg (IHg) and methylmercury (MeHg) was conducted in physical media (soil, sediment, surface water, porewater and soil/sediment extracts) to identify non-point sources, transport mechanisms, and potential controls on Hg(II)-methylation. Data collected from surface water and sediment indicate that the majority of the non-point sources of IHg to the South River are within the first 14. km downstream from the historic point source. Partitioning data indicate that particle bound IHg is introduced in this reach, releasing dissolved and colloidal bound IHg, which is transported downstream. Extraction experiments revealed that floodplain soils released a higher fraction of their IHg content in aqueous extractions than fine-grained sediment (FGS). Based on ultrafiltration [<5000 nominal molecular weight cutoff (NMWC)] the majority of soil IHg released was colloidal in nature, providing evidence for the continued evolution of IHg for Hg(II)-methylation from soil. Strong seasonal patterns in MeHg concentrations were observed in surface water and sediment. The highest concentrations of MeHg in surface water were observed at moderate temperatures, suggesting that other factors limit net Hg(II)-methylation. Seasonal changes in sediment organic content and the fraction of 1. N KOH-extractable THg were also observed and may be important factors in controlling net Hg(II)-methylation rates. Sulfate concentrations in surface water are low and the evidence suggests that Fe reduction may be an important Hg(II)-methylation process. The highest sediment MeHg concentrations were observed in habitats with large amounts of FGS, which are more prevalent in the upper half of the study area due to the lower hydrologic gradient and agricultural impacts. Past and present land use practices and other geomorphologic controls contribute to the erosion of banks and accumulation of fine-grained sediment in this section of the river, acting as sources of IHg. ?? 2010 Elsevier Ltd.

Mercury in Sediments From the Long Island Sound Region

NASA Astrophysics Data System (ADS)

Varekamp, J. C.; Lauriat, K.; Zierzow, T.; Buchholtz ten Brink, M.; Mecray, E.

2001-05-01

About 400 surface and core sediment samples from a sampling grid in Long Island Sound (LIS) were analyzed for mercury, Clostridium perfringens with many other chemical and physical parameters. About 16 cores from coastal salt marshes in Connecticut were analyzed as well. The Hg concentrations in LIS surface sediments vary between 30 and 650 ppb, with the highest values in the western end of LIS. The trend of increasing Hg to the west correlates with increasing abundances of fine-grained sediment and C-org. Normalization of the Hg data on mean grainsize or C-org contents still show an east-west trend. Data from the "12 mile sewage dump site" in the New York Bight area provide a linear relationship between C. perfringens and Hg. Using that relationship, we obtain that many LIS samples have 10-50 percent sewage-derived Hg, with values up to 70 percent in the extreme west. The remaining Hg is largely imported with fine-grained sediment from the surrounding watersheds, which is a focussed flux of the integrated regional atmospheric Hg deposition and point source mercury. The Housatonic River is an important source of mercury, with up to 5 ppm Hg in the river bed sediment. The Still River, a tributary of the Housatonic River, has sediments that carry up to 15 ppm Hg, and we surmise that the hatting industry of Danbury (CT) was an important Hg source. The in situ atmospheric deposition of Hg on LIS is only a small part of the overall LIS Hg sediment budget. Core data from LIS and surrounding marshes show contamination profiles with background values at 50-100 ppb Hg and peak values in the 200-500 range, with values up to 1200 ppb Hg at the mouth of the Housatonic River. Many cores show a decline in Hg concentrations in the upper 10-15 cm (last 40 years), whereas the C. perfringens concentrations increase exponentially towards the surface. The onset of Hg contamination coincides with the first elevated C. perfringens levels, indicating an anthropogenic origin for the Hg contamination.

Giant weathering pits in the Entrada Sandstone, southeastern Utah: Preliminary findings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Netoff, D.I.; Shroba, R.R.

Giant weathering pits formed in outcrops of the lower Entrada Sandstone slickrock of Jurassic age are present in two areas in the Glen Canyon region of arid southeastern Utah. The pits are far larger than any previously described in the geologic literature. The pits near Cookie Jar Butte are commonly cylindrical, typically have low width-to-depth ratios (1.5--3.6), and have a depth of closure of as much as 18 m. There are no obvious lithologic or structural controls that determine their shape or location. Many of the pits at Rock Creek Bay are elongate; several of them have long axes inmore » excess of 53 m, and the longest one is 74 m. Many of the pit walls are breached at the top, and the depth of closure is generally less than 6 m. The shapes of these pits are influenced by point orientation and pit coalescence. Thin-section analyses of near-surface sandstone cores taken near Cookie Jar Butte from pit walls, floors, and rims reveal no significant diagenetic alteration of the fine-grained to very fine frained quartzose sandstone (quartz arenite). Quartz grains appear fresh, and feldspar grains are only slightly weathered. The cement between the grains is mostly CaCO[sub 3]. In several of the pits in both areas sandy sediment veneers the bedrock floor. This sediment is similar in character to the adjacent sandstone and is probably locally derived. Possible origins of the giant pits include various physical, chemical, and biological weathering processes that initiate pit development, followed by excavation by plunge-pool action, wind deflation, dissolution, and piping. Preliminary field and laboratory data do not clearly identify and single process of group of processes that account for pit development.« less

Linking basin-scale and pore-scale gas hydrate distribution patterns in diffusion-dominated marine hydrate systems: DIFFUSION-DRIVEN HYDRATE GROWTH IN SANDS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nole, Michael; Daigle, Hugh; Cook, Ann E.

The goal of this study is to computationally determine the potential distribution patterns of diffusion-driven methane hydrate accumulations in coarse-grained marine sediments. Diffusion of dissolved methane in marine gas hydrate systems has been proposed as a potential transport mechanism through which large concentrations of hydrate can preferentially accumulate in coarse-grained sediments over geologic time. Using one-dimensional compositional reservoir simulations, we examine hydrate distribution patterns at the scale of individual sand layers (1 to 20 m thick) that are deposited between microbially active fine-grained material buried through the gas hydrate stability zone (GHSZ). We then extrapolate to two- dimensional and basin-scalemore » three-dimensional simulations, where we model dipping sands and multilayered systems. We find that properties of a sand layer including pore size distribution, layer thickness, dip, and proximity to other layers in multilayered systems all exert control on diffusive methane fluxes toward and within a sand, which in turn impact the distribution of hydrate throughout a sand unit. In all of these simulations, we incorporate data on physical properties and sand layer geometries from the Terrebonne Basin gas hydrate system in the Gulf of Mexico. We demonstrate that diffusion can generate high hydrate saturations (upward of 90%) at the edges of thin sands at shallow depths within the GHSZ, but that it is ineffective at producing high hydrate saturations throughout thick (greater than 10 m) sands buried deep within the GHSZ. As a result, we find that hydrate in fine-grained material can preserve high hydrate saturations in nearby thin sands with burial.« less

Linking basin-scale and pore-scale gas hydrate distribution patterns in diffusion-dominated marine hydrate systems: DIFFUSION-DRIVEN HYDRATE GROWTH IN SANDS

DOE PAGES

Nole, Michael; Daigle, Hugh; Cook, Ann E.; ...

2017-02-01

The goal of this study is to computationally determine the potential distribution patterns of diffusion-driven methane hydrate accumulations in coarse-grained marine sediments. Diffusion of dissolved methane in marine gas hydrate systems has been proposed as a potential transport mechanism through which large concentrations of hydrate can preferentially accumulate in coarse-grained sediments over geologic time. Using one-dimensional compositional reservoir simulations, we examine hydrate distribution patterns at the scale of individual sand layers (1 to 20 m thick) that are deposited between microbially active fine-grained material buried through the gas hydrate stability zone (GHSZ). We then extrapolate to two- dimensional and basin-scalemore » three-dimensional simulations, where we model dipping sands and multilayered systems. We find that properties of a sand layer including pore size distribution, layer thickness, dip, and proximity to other layers in multilayered systems all exert control on diffusive methane fluxes toward and within a sand, which in turn impact the distribution of hydrate throughout a sand unit. In all of these simulations, we incorporate data on physical properties and sand layer geometries from the Terrebonne Basin gas hydrate system in the Gulf of Mexico. We demonstrate that diffusion can generate high hydrate saturations (upward of 90%) at the edges of thin sands at shallow depths within the GHSZ, but that it is ineffective at producing high hydrate saturations throughout thick (greater than 10 m) sands buried deep within the GHSZ. As a result, we find that hydrate in fine-grained material can preserve high hydrate saturations in nearby thin sands with burial.« less

Open-water and under-ice seasonal variations in trace element content and physicochemical associations in fluvial bed sediment.

PubMed

Doig, Lorne E; Carr, Meghan K; Meissner, Anna G N; Jardine, Tim D; Jones, Paul D; Bharadwaj, Lalita; Lindenschmidt, Karl-Erich

2017-11-01

Across the circumpolar world, intensive anthropogenic activities in the southern reaches of many large, northward-flowing rivers can cause sediment contamination in the downstream depositional environment. The influence of ice cover on concentrations of inorganic contaminants in bed sediment (i.e., sediment quality) is unknown in these rivers, where winter is the dominant season. A geomorphic response unit approach was used to select hydraulically diverse sampling sites across a northern test-case system, the Slave River and delta (Northwest Territories, Canada). Surface sediment samples (top 1 cm) were collected from 6 predefined geomorphic response units (12 sites) to assess the relationships between bed sediment physicochemistry (particle size distribution and total organic carbon content) and trace element content (mercury and 18 other trace elements) during open-water conditions. A subset of sites was resampled under-ice to assess the influence of season on these relationships and on total trace element content. Concentrations of the majority of trace elements were strongly correlated with percent fines and proxies for grain size (aluminum and iron), with similar trace element grain size/grain size proxy relationships between seasons. However, finer materials were deposited under ice with associated increases in sediment total organic carbon content and the concentrations of most trace elements investigated. The geomorphic response unit approach was effective at identifying diverse hydrological environments for sampling prior to field operations. Our data demonstrate the need for under-ice sampling to confirm year-round consistency in trace element-geochemical relationships in fluvial systems and to define the upper extremes of these relationships. Whether contaminated or not, under-ice bed sediment can represent a "worst-case" scenario in terms of trace element concentrations and exposure for sediment-associated organisms in northern fluvial systems. Environ Toxicol Chem 2017;36:2916-2924. © 2017 SETAC. © 2017 SETAC.

Sedimentological Properties of Natural Gas Hydrates-Bearing Sands in the Nankai Trough and Mallik Areas

NASA Astrophysics Data System (ADS)

Uchida, T.; Tsuji, T.; Waseda, A.

2009-12-01

The Nankai Trough parallels the Japanese Island, where extensive BSRs have been interpreted from seismic reflection records. High resolution seismic surveys have definitely indicated gas hydrate distributions, and drilling the MITI Nankai Trough wells in 2000 and the METI Tokai-oki to Kumano-nada wells in 2004 have revealed subsurface gas hydrate in the eastern part of Nankai Trough. In 1998 and 2002 Mallik wells were drilled at Mackenzie Delta in the Canadian Arctic that also clarified the characteristics of gas hydrate-dominant sandy layers at depths from 890 to 1110 m beneath the permafrost zone. During the field operations, the LWD and wire-line well log data were continuously obtained and plenty of gas hydrate-bearing sand cores were recovered. Subsequence sedimentological and geochemical analyses performed on those core samples revealed the crucial geologic controls on the formation and preservation of natural gas hydrate in sediments. Pore-space gas hydrates reside in sandy sediments mostly filling intergranular porosity. Pore waters chloride anomalies, core temperature depression and core observations on visible gas hydrates confirm the presence of pore-space gas hydrates within moderate to thick sandy layers, typically 10 cm to a meter thick. Sediment porosities and pore-size distributions were obtained by mercury porosimetry, which indicate that porosities of gas hydrate-bearing sandy strata are approximately 45 %. According to grain size distribution curves, gas hydrate is dominant in fine- to very fine-grained sandy strata. Gas hydrate saturations are typically up to 80 % in pore volume throughout most of the hydrate-dominant sandy layers, which are estimated by well log analyses as well as pore water chloride anomalies. It is necessary for investigating subsurface fluid flow behaviors to evaluate both porosity and permeability of gas hydrate-bearing sandy sediments, and the measurements of water permeability for them indicated that highly saturated sands should have permeability of 1 x 10-15 to 5 x 10-15 m2 (1 to 5 millidarcies). Most of gas hydrates fill the intergranular pore systems of sandy layers, which are derived from the sedimentary facies such as channels and crevasse splay/levee deposits. It is remarked that those sandy strata are usually composed of arenite sands with matrix-free intergranular pore systems. Gas hydrates are less frequently found in fine-grained sediments such as siltstone and mudstone from overbank deposits. Methane gas accumulation and original pore space large enough to occur within host sediments may be required for forming highly saturated gas hydrate in pore system. The distribution of a porous and coarser-grained host rock should be one of the important factors to control the occurrence of gas hydrate, as well as physicochemical conditions. This appears to be a similar mode for conventional oil and gas accumulations, and this knowledge is important to predicting the location of other hydrate deposits and their eventual energy resource. This study was performed as a part of the MH21 Research Consortium on methane hydrate in Japan.

A kinetic model that explains the dependence of magnetic susceptibility of sediment on grain size and organic matter content in transitional marine environments. Testing case studies in estuarine-like environments of NW Iberia

NASA Astrophysics Data System (ADS)

Rey, D.; Mohamed, K. J.; Andrade, A.; Rubio, B.; Bernabeu, A. M.

2017-12-01

The wide use of magnetic proxies to study pollution, sedimentological processes, and environmental and paleoclimatic changes is currently limited by the lack of transference functions that closely correlate with the unmeasurable variables. Among them, magnetic susceptibility (MS) is the oldest and most popular, but have yet to live up to its expectations. This paper explores and quantifies how MS values of surficial sediments in transitional environments depends on grain size and on what can be said about the spatial distribution of hydrodynamic forces and the potential modulation of MS by sediment and organic matter provenances. The concentration of (oxyhydr)oxides in sands (d50 > 63 microns) is primarily controlled by their degree of dilution in the diamagnetic framework, which is larger for coarser grainsizes. In contrast, the concentration of (oxyhydr)oxides in muddy sediments is controlled by their dissolution rate during very early diagenesis, which is controlled by their content in organic matter (TOC), inversely dependent of grainsize. The balance between both components results in the study area in sands of d50 = 68 microns displaying the maximum MS values. The influence of organic matter on the dissolution of magnetite in surficial sediments can be quantified using a simple kinetic model. The model reveals the existence of a negative exponential relationship between magnetic susceptibility and grain size, that depends on the TOC of the fine-grained fraction. The model accurately predicts that a TOC increase of 0.35% results in a 50% reduction in the concentration of magnetite in the sediments of the Ría the Muros. We have also encountered this relationship not universal in this form, as its quantification is strongly modulated by coarse sediment mineralogy, TOC lability and by other factors such as wave climate, depth, and sediment oxygenation. Better understanding and quantification of the role that TOC, hydrodynamics, and changes in the geochemical environment have on the surface and downcore evolution of magnetic properties is useful to correctly interpret magnetic properties as proxies for pollutants, sedimentological processes, and environmental and paleoclimatic changes.

What multi-beam bathymetric data can tell about morphodynamics and sediment transport in an estuarine environment?

NASA Astrophysics Data System (ADS)

Winterscheid, Axel; Reiß, Marcel

2017-04-01

The Elbe River Estuary is one of the most important waterways for commercial shipping in Europe. It connects the North Sea with the Port of Hamburg located about 100 km inlands. To secure navigation, the Federal Waterways and Shipping Administration (WSV) is operating a fleet of survey vessels all equipped with a multi-beam echo sounder controlling the required water depths. Beyond navigational purposes, this monitoring is creating a comprehensive and ever-growing data base, which can be used for a consistent morphodynamical description of the river bed. The history of multi-beam records in the Elbe River Estuary reaches back to 2008. At particular river sections where large amounts of fine grained sediments accumulate surveys are taken biweekly; at other sections there are monthly surveys. Locally, sedimentation rates of up to 12 cm per day have been observed within the fairway. The time series of multiple multi-beam records have been analyzed with a particular focus on morphodynamics and sedimentation rates. Here we compare the morphodynamical characteristics of two river sections. The first section is located at the downstream end of the estuarine turbidity zone near the city of Cuxhaven; the second section is located 50 km away at the upstream end of the turbidity zone near the city of Hamburg. These two sections have been selected because in both the morphology of the river bed and the sedimentation processes are strongly influenced by the presence of fine grained sediments. The results show that changing sedimentation rates in both sections are conditioned by different site specific factors, e.g. the dynamic shifting of the turbidity zone along the estuary, which is resulting in a temporarily higher availability of suspended sediments and more intense sedimentation rates in the upper part of the estuary and the respective section. In contrast, in the downstream located river section more intense sedimentation rates could be related to periods of strong north-western wind conditions causing increased water levels and higher wave loads on the adjacent wadden areas of the German Bight. These processes were formerly inferred from theory and numerical studies but could not so far be supported on the basis of direct measurements due to a lack of continuous data records on sedimentation rates with a sufficiently high spatial and temporal resolution.

Modern pollen deposition in Long Island Sound

USGS Publications Warehouse

Beuning, Kristina R.M.; Fransen, Lindsey; Nakityo, Berna; Mecray, Ellen L.; Buchholtz ten Brink, Marilyn R.

2000-01-01

Palynological analyses of 20 surface sediment samples collected from Long Island Sound show a pollen assemblage dominated by Carya, Betula, Pinus, Quercus, Tsuga, and Ambrosia, as is consistent with the regional vegetation. No trends in relative abundance of these pollen types occur either from west to east or associated with modern riverine inputs throughout the basin. Despite the large-scale, long-term removal of fine-grained sediment from winnowed portions of the eastern Sound, the composition of the pollen and spore component of the sedimentary matrix conforms to a basin-wide homogeneous signal. These results strongly support the use of select regional palynological boundaries as chronostratigraphic tools to provide a framework for interpretation of the late glacial and Holocene history of the Long Island Sound basin sediments.

Clay, Water, and Salt: Controls on the Permeability of Fine-Grained Sedimentary Rocks.

PubMed

Bourg, Ian C; Ajo-Franklin, Jonathan B

2017-09-19

The ability to predict the permeability of fine-grained soils, sediments, and sedimentary rocks is a fundamental challenge in the geosciences with potentially transformative implications in subsurface hydrology. In particular, fine-grained sedimentary rocks (shale, mudstone) constitute about two-thirds of the sedimentary rock mass and play important roles in three energy technologies: petroleum geology, geologic carbon sequestration, and radioactive waste management. The problem is a challenging one that requires understanding the properties of complex natural porous media on several length scales. One inherent length scale, referred to hereafter as the mesoscale, is associated with the assemblages of large grains of quartz, feldspar, and carbonates over distances of tens of micrometers. Its importance is highlighted by the existence of a threshold in the core scale mechanical properties and regional scale energy uses of shale formations at a clay content X clay ≈ 1/3, as predicted by an ideal packing model where a fine-grained clay matrix fills the gaps between the larger grains. A second important length scale, referred to hereafter as the nanoscale, is associated with the aggregation and swelling of clay particles (in particular, smectite clay minerals) over distances of tens of nanometers. Mesoscale phenomena that influence permeability are primarily mechanical and include, for example, the ability of contacts between large grains to prevent the compaction of the clay matrix. Nanoscale phenomena that influence permeability tend to be chemomechanical in nature, because they involve strong impacts of aqueous chemistry on clay swelling. The second length scale remains much less well characterized than the first, because of the inherent challenges associated with the study of strongly coupled nanoscale phenomena. Advanced models of the nanoscale properties of fine-grained media rely predominantly on the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, a mean field theory of colloidal interactions that accurately predicts clay swelling in a narrow range of conditions (low salinity, low compaction, Na + counterion). An important feature of clay swelling that is not predicted by these models is the coexistence, in most conditions of aqueous chemistry and dry bulk density, of two types of pores between parallel smectite particles: mesopores with a pore width of >3 nm that are controlled by long-range interactions (the osmotic swelling regime) and nanopores with a pore width <1 nm that are controlled by short-range interactions (the crystalline swelling regime). Nanogeochemical characterization and simulation techniques, including coarse-grained and all-atom molecular dynamics simulations, hold significant promise for the development of advanced constitutive relations that predict this coexistence and its dependence on aqueous chemistry.

Surface processes in an active rift setting: a source to sink approach from the Sperchios delta, central Greece

NASA Astrophysics Data System (ADS)

Pechlivanidou, Sofia; Cowie, Patience; Gawthorpe, Rob

2015-04-01

This study presents an integrated source to sink approach to understand the controls on the distribution of sediments source areas, sediment routing and downstream fining in the Sperchios rift system, central Greece. The Sperchios Rift forms an active half-graben basin, which is controlled by major NW-SE trending faults. Detailed sedimentological analysis (grain size, macro/micro faunal, geochemical and mineral magnetic analysis) in conjunction with 14C age constraints reveal the stratigraphic evolution of the Sperchios delta, located at the eastern part of the rift, including the presence of a Holocene transgressive - regressive wedge overlying Late Pleistocene alluvial deposits. The process-based stratigraphic model SedFlux2D is used to simulate the delta evolution and model scenarios are compared with the measured data. A series of sensitivity tests are used to explore uncertainties associated with variations in sediment supply, tectonic subsidence rate, and Holocene relative sea level. We discuss the effects of the major controls, in particular the rate of relative sea-level rise and tectonic subsidence rate, on accommodation creation and thus delta architecture in this active rift setting during the Holocene. The transition from transgression to regression is found to be mainly controlled by the slowing rate of relative sea level rise that occurred approximately 5500 kyrs ago. Finally, we compare the sediment volumes and grain size variations preserved in the Sperchios delta to onshore erosion rates inferred from data collected on bedrock erodibility, measurements of downstream fining, as well as stream-power/transport capacity for both transverse and axial drainage networks. This comparison, when combined with information on relative uplift/subsidence patterns due to active extensional tectonics, allows us to develop a semi-quantitative, process-based source-to-sink model for this area.

Cold-water coral habitats of Rockall and Porcupine Bank, NE Atlantic Ocean: Sedimentary facies and benthic foraminiferal assemblages

NASA Astrophysics Data System (ADS)

Smeulders, G. G. B.; Koho, K. A.; de Stigter, H. C.; Mienis, F.; de Haas, H.; van Weering, T. C. E.

2014-01-01

The extent of the cold-water coral mounds in the modern ocean basins has been recently revealed by new state-of-the-art equipment. However, not much is known about their geological extent or development through time. In the facies model presented here seven different types of seabed substrate are distinguished, which may be used for reconstruction of fossil coral habitats. The studied substrates include: off-mound settings, (foram) sands, hardgrounds, dead coral debris, and substrates characterized by a variable density of living coral framework. Whereas sediment characteristics only provide a basis for distinguishing on- and off-mound habitats and the loci of most prolific coral growth, benthic foraminiferal assemblages are the key to identifying different mound substrates in more detail. Specific foraminiferal assemblages are distinguished that are characteristic of these specific environments. Assemblages from off-mound settings are dominated by (attached) epifaunal species such as Cibicides refulgens and Cibicides variabilis. The attached epibenthic species Discanomalina coronata is also common in off-mound sediments, but it is most abundant where hardgrounds have formed. In contrast, the settings with coral debris or living corals attract shallow infaunal species that are associated with more fine-grained soft sediments. The typical ‘living coral assemblage' is composed of Cassidulina obtusa, Bulimina marginata, and Cassidulina laevigata. The abundance of these species shows an almost linear increase with the density of the living coral cover. The benthic foraminifera encountered from off-mound to top-mound settings appear to represent a gradient of decreasing current intensity and availability of suspended food particles, and increasing availability of organic matter associated with fine-grained sediment trapped in between coral framework.

Rock magnetic and geochemical evidence for authigenic magnetite formation via iron reduction in coal-bearing sediments offshore Shimokita Peninsula, Japan (IODP Site C0020)

NASA Astrophysics Data System (ADS)

Phillips, Stephen C.; Johnson, Joel E.; Clyde, William C.; Setera, Jacob B.; Maxbauer, Daniel P.; Severmann, Silke; Riedinger, Natascha

2017-06-01

Sediments recovered at Integrated Ocean Drilling Program (IODP) Site C0020, in a fore-arc basin offshore Shimokita Peninsula, Japan, include numerous coal beds (0.3-7 m thick) that are associated with a transition from a terrestrial to marine depositional environment. Within the primary coal-bearing unit (˜2 km depth below seafloor) there are sharp increases in magnetic susceptibility in close proximity to the coal beds, superimposed on a background of consistently low magnetic susceptibility throughout the remainder of the recovered stratigraphic sequence. We investigate the source of the magnetic susceptibility variability and characterize the dominant magnetic assemblage throughout the entire cored record, using isothermal remanent magnetization (IRM), thermal demagnetization, anhysteretic remanent magnetization (ARM), iron speciation, and iron isotopes. Magnetic mineral assemblages in all samples are dominated by very low-coercivity minerals with unblocking temperatures between 350 and 580°C that are interpreted to be magnetite. Samples with lower unblocking temperatures (300-400°C), higher ARM, higher-frequency dependence, and isotopically heavy δ56Fe across a range of lithologies in the coal-bearing unit (between 1925 and 1995 mbsf) indicate the presence of fine-grained authigenic magnetite. We suggest that iron-reducing bacteria facilitated the production of fine-grained magnetite within the coal-bearing unit during burial and interaction with pore waters. The coal/peat acted as a source of electron donors during burial, mediated by humic acids, to supply iron-reducing bacteria in the surrounding siliciclastic sediments. These results indicate that coal-bearing sediments may play an important role in iron cycling in subsiding peat environments and if buried deeply through time, within the subsequent deep biosphere.

Chemo-stratigraphy in the Murray Formation Using ChemCam

NASA Astrophysics Data System (ADS)

Blaney, D. L.; Anderson, R. B.; Bridges, N.; Bridges, J.; Calef, F. J., III; Clegg, S. M.; Le Deit, L.; Fisk, M. R.; Forni, O.; Gasnault, O.; Kah, L. C.; Kronyak, R. E.; Lanza, N.; Lasue, J.; Mangold, N.; Maurice, S.; Milliken, R.; Ming, D. W.; Nachon, M.; Newsom, H. E.; Rapin, W.; Stack, K.; Sumner, D. Y.; Wiens, R. C.

2015-12-01

Curiosity has completed a detailed chemo-stratigraphy analysis at the Pahrump exposure of the Murray formation. In total >570 chemical measurements and supporting remote micro images to classify texturally were collected. Chemical trends with both stratigraphic position and with texture were evaluated. From these data emerges a complex aqueous history where sediments have interacted with fluids with variable chemistry in distinct episodes. The ChemCam data collected at the nearby "Garden City" (GC) vein complex provides constraints on the chemical evolution of the Pahrump. GC is thought be stratigraphically above the Pahrump outcrop. Fluids producing the veins likely also migrated through the Pahrump sediments. Multiple episodes of fluids are evident at GC, forming distinct Ca sulfate, F-rich, enhanced MgO, and FeO-rich veins. These different fluid chemistries could be the result of distinct fluids migrating through the section from a distance with a pre-established chemical signature, fluids locally evolved from water rock interactions, or both. Texturally rocks have been classified into two distinct categories: fine grained or as cross-bedded sandstones. The sandstones have significantly lower SiO2, Al2O3, and K2O and higher FeO, and CaO. Fine grained rocks have further been sub-classified as resistant and recessive with other textural features such as laminations and pits noted.The strongest chemical trend in the fine-grained sandstones shows enhancements in MgO and FeO in erosion-resistant materials compared to fine grained recessive units, suggesting that increased abundance of Mg- and/or iron-rich cements may provide additional strength. The MgO and FeO variations with texture are independent of stratigraphic locations (e.g resistant material at both the bottom and top of the outcrop both are enhanced in MgO and FeO). The presence of the GC MgO and FeO rich veins provides additional evidence for fluids rich in these elements were present in the outcrop. Other elemental trends results including SiO2, Al2O3, K2O and Na2O will be explored in addition to key trace element signatures such as Li, Cr and F to understand the chemical evolution of the outcrop.

Methane hydrate formation in turbidite sediments of northern Cascadia, IODP Expedition 311

USGS Publications Warehouse

Torres, M.E.; Trehu, A.M.; Cespedes, N.; Kastner, M.; Wortmann, U.G.; Kim, J.-H.; Long, P.; Malinverno, A.; Pohlman, J.W.; Riedel, M.; Collett, T.

2008-01-01

Expedition 311 of the Integrated Ocean Drilling Program (IODP) to northern Cascadia recovered gas-hydrate bearing sediments along a SW-NE transect from the first ridge of the accretionary margin to the eastward limit of gas-hydrate stability. In this study we contrast the gas gas-hydrate distribution from two sites drilled ~ 8??km apart in different tectonic settings. At Site U1325, drilled on a depositional basin with nearly horizontal sedimentary sequences, the gas-hydrate distribution shows a trend of increasing saturation toward the base of gas-hydrate stability, consistent with several model simulations in the literature. Site U1326 was drilled on an uplifted ridge characterized by faulting, which has likely experienced some mass wasting events. Here the gas hydrate does not show a clear depth-distribution trend, the highest gas-hydrate saturation occurs well within the gas-hydrate stability zone at the shallow depth of ~ 49??mbsf. Sediments at both sites are characterized by abundant coarse-grained (sand) layers up to 23??cm in thickness, and are interspaced within fine-grained (clay and silty clay) detrital sediments. The gas-hydrate distribution is punctuated by localized depth intervals of high gas-hydrate saturation, which preferentially occur in the coarse-grained horizons and occupy up to 60% of the pore space at Site U1325 and > 80% at Site U1326. Detailed analyses of contiguous samples of different lithologies show that when enough methane is present, about 90% of the variance in gas-hydrate saturation can be explained by the sand (> 63????m) content of the sediments. The variability in gas-hydrate occupancy of sandy horizons at Site U1326 reflects an insufficient methane supply to the sediment section between 190 and 245??mbsf. ?? 2008 Elsevier B.V.

Settling characteristics of fine-grained sediments used in Louisiana coastal land building and restoration projects

NASA Astrophysics Data System (ADS)

Ghose Hajra, M.

2016-02-01

Coastal property development, sea level rise, geologic subsidence, loss of barrier islands, increasing number and intensity of coastal storms and other factors have resulted in water quality degradation, wetlands loss, reduced storm and surge protection, ground settlement, and other challenges in coastal areas throughout the world. One of the goals towards reestablishing a healthy coastal ecosystem is to rebuild wetlands with river diversion or sediment conveyance projects that optimally manage and allocate sediments, minimally impact native flora and fauna, and positively affect the water quality. Engineering properties and material characteristics of the dredged material and foundation soils are input parameters in several mathematical models used to predict the long term behavior of the dredged material and foundation soil. Therefore, proper characterization of the dredged material and foundation soils is of utmost importance in the correct design of a coastal restoration and land reclamation project. The sedimentation and consolidation characteristics of the dredged material as well as their effects on the time rate of settlement of the suspended solid particles and underlying foundation soil depend, among other factors, on the (a) grain size distribution of the dredged material, (b) salinity (fresh, brackish, or saltwater environment) of the composite slurry, and (c) concentration of the solid particles in the slurry. This paper will present the results from column settling tests and self-weight consolidation tests performed on dredged samples obtained from actual restoration projects in Louisiana. The effects of salinity, grain size distribution, and initial particle concentration on the sedimentation and consolidation parameters of the dredged material will also be discussed.

Geology of the Holocene surficial uranium deposit of the north fork of Flodelle Creek, northeastern Washington ( USA).

USGS Publications Warehouse

Johnson, S.Y.; Otton, J.K.; Macke, D.L.

1987-01-01

The N fork of Flodelle Creek drainage basin in NE Washington contains the first surficial U deposit to be mined in the US. The U was leached from granitic bedrock and fixed in organic-rich pond sediments. The distribution of these pond sediments and, therefore, the U has been strongly influenced by relict glacial topography, slope proceses, and beaver activity. Ponds in the drainage basin have been sinks for fine-grained, organic-rich sediments. These organic-rich sediments provide a suitable geochemical environment for precipitation and adsorption of uranium leached from granitic bedrock into ground, spring, and surface waters. Processes of pond formation have thus been important in the development of surficial U deposits in the N fork of Flodelle Creek drainage basin and may have similar significance in other areas.-from Authors

Early Depositional History of the Eocene Izu-Bonin Mariana Arc, Western Pacific Ocean

NASA Astrophysics Data System (ADS)

Waldman, R.; Marsaglia, K. M.; Tepley, F. J., III

2015-12-01

Expedition 351 of the International Ocean Discovery Program cored an Eocene section at Site U1438 in the Philippine Sea that provides insight into the early history of the Izu-Bonin arc. Subduction here is hypothesized to have initiated spontaneously, leaving a characteristic depositional sequence of post-subduction-initiation localized extension and volcanism. We conducted detailed macroscopic and microscopic study of the cores of the lowermost 100m of volcaniclastic and sedimentary rocks (Unit IV) directly overlying subduction initiation igneous basement, to identify depositional facies and trends. We subdivided Unit IV into three subunits based on lithologic characteristics. Transitions between the subunits are relatively abrupt, occurring within the length of a single core. The lowermost subunit (IVA) consists of 4 meters of laminated pelagic claystone with thin beds of graded volcaniclastic siltstone, and fine-grained tuff laminae composed of plagioclase feldspar and green-brown amphibole. The middle subunit (IVB) comprises 51 meters of texturally variable, thick-bedded, coarse-grained gravity flow deposits. These are composed of volcaniclastic sandstone and conglomerate containing glassy and tachylitic volcanic grains as well as sedimentary lithic fragments, along with traces of shallow-water carbonate bioclasts. Subunit IVB sediments are poorer in feldspar than IVA and contain only trace amphibole. They show variable grain rounding and an upsection increase in vitric components. Tachylite grains range from sub-angular to well rounded throughout, and other volcanic grain types show upward increases in angularity and vesicularity. The abrupt transition from pelagic sediments in subunit IVA to shallow-water-sourced gravity flows in subunit IVB suggests a rapid emergence of shallow-water to subaerial volcanic center early in the arc's development. The upper part of subunit IVB also contains igneous intrusions, providing possible evidence for more proximal volcanism at the site. Subunit IVC consists of 46 meters of fine-grained turbidites composed of tuffaceous siltstone, along with radiolarian mudstone and vitric tuff layers. Ongoing studies of the volcanic components will provide additional insight into the source(s) of volcanics throughout the arc's early development.

Grain size controls on sediment supply from debris-mantled dryland hillslopes

NASA Astrophysics Data System (ADS)

Michaelides, K.

2011-12-01

Debris-mantled hillslopes are common in arid and semiarid environments where low rates of chemical weathering give rise to thin, non-cohesive soils mantled with a layer of coarse rock fragments derived from weathered bedrock that can reach boulder size. The grain size distributions (GSDs) on the surface of these hillslopes interact with different magnitudes and frequencies of runoff-producing rainfall events that selectively transport grain sizes of different classes depending on flow, grain position on the slope, and hillslope attributes. Sediment transport over many runoff events determines sediment delivery to the slope base, which ultimately modifies the GSD of valley floors. The relationship between hillslope attributes and sediment flux forms the basis of geomorphic transport laws used to model the topographic evolution of drainage basins over >104 y timescales, but the specific responses of sediment flux across the hillslope and the corresponding changes in GSDs to individual storm events are poorly understood. Sheetwash erosion of coarse fragments presents a particular set of conditions for sediment transport that is poorly resolved in current models. A particle-based model for sheetwash sediment transport on debris-mantled hillslopes was developed within a rainfall-runoff model. The rainfall-runoff model produces spatial values of flow depth and velocity which are used to drive a particle-by-particle force-balance model derived from first principles for grain sizes > 1 mm. Particles on the hillslope surface are represented explicitly and can be composed of mixed grain sizes of any distribution or of uniform sizes of any diameter. The model resolves all the forces on each particle at each time and space step based on the flow hydraulics acting on them, so no assumptions are made about incipient motion using Shield's criterion. This research examines how the interplay between hillslope GSD, hillslope attributes (gradient and length) and runoff characteristics, determine sediment transport dynamics and net flux, GSD supplied to the slope base and the changes in GSD on the hillslope. The results show a strong control of initial hillslope GSD on flux characteristics: (1) GSD controls the degree of non-linearity in the relationship between sediment flux and hillslope gradient. (2) Grain size uniformity controls the degree and form of non-linearity in the relationship between sediment flux and gradient. (3) Over multiple runoff events, slopes coarsen - steeper slopes become coarser than shallow slopes. For individual events, changes in GSD on the slope depend on the magnitude and duration of the runoff event and can result in variable coarsening and fining on different parts of the slope. (4) The GSD of sediment delivered to the slope base is dependent on the hillslope GSD and the hillslope attributes and runoff characteristics. For most runoff events, the GSD of fluxed sediment is finer than the hillslope GSD except for extreme runoff events on very steep slopes with intermediate GSD (not extremely coarse). These findings provide insights into hillslope responses to climatic forcing and have theoretical implications for modeling hillslope evolution in drylands.

Inorganic geochemistry of surface sediments of the Ebro shelf and slope, northwestern Mediterranean

USGS Publications Warehouse

Gardner, J.V.; Dean, W.E.; Alonso, B.

1990-01-01

Distributions of major, minor, and trace elements in surface sediment of the continental shelf and upper slope of the northeastern Spanish continental margin reflect the influences of discharge from the Ebro River and changes in eustatic sea levels. Multivariate factor analysis of sediment geochemistry was used to identify five groupings of samples (factors) on the shelf and slope. The first factor is an aluminosilicate factor that represents detrital clastic material. The second factor is a highly variable amount of excess SiO2 and probably represents a quartz residuum originating from winnowing of relict detrital sediments. A carbonate factor (Factor 3) has no positive correlation with other geochemical parameters but is associated with the sand-size fraction. The carbonate in these sediments consists of a mixture of biogenic calcite and angular to subangular detrital grains. Organic carbon is associated with the aluminosilicate factor (Factor 1) but also factors out by itself (Factor 4); this suggests that there may be two sources of organic matter, terrestrial and marine. The fifth factor comprises upper slope sediments that contain high concentrations of manganese. The most likely explanation for these high manganese concentrations is precipitation of Mn oxyhydroxides at the interface between Mn-rich, oxygen-deficient, intermediate waters and oxygenated surface waters. During eustatic low sea levels of the glacial Pleistocene, the Ebro Delta built across the outer continental shelf and deposited sediment with fairly high contents of organic carbon and continental components. The period of marine transgression from eustatic low (glacial) to eustatic high (interglacial) sea levels was characterized by erosion of the outer shelf delta and surficial shelf sediments and the transport of sediment across the slope within numerous canyons. Once eustatic high sea level was reached, delta progradation resumed on the inner shelf. Today, coarse-grained sediment (silt and sand) is transported to the continental shelf by Ebro River and is distributed along the inner shelf by currents generated by dominant northeasterly winds. Clay-size material is deposited on the mid- and outer-shelf. However, erosion and delta progradation during the last glacial period, and fine-grained Holocene sedimentation, have probably produced a distribution of sediment on a diachronous surface. ?? 1990.

Magnetic Signature of Glacial Flour in Sediments From Bear Lake, Utah/Idaho

NASA Astrophysics Data System (ADS)

Rosenbaum, J. G.; Dean, W. E.; Colman, S. M.; Reynolds, R. L.

2002-12-01

Variations in magnetic properties within an interval of Bear Lake sediments correlative with oxygen isotope stage 2 (OIS 2) and OIS 3 provide a record of glacial flour production for the Uinta Mountains. Like sediments of the same age from Upper Klamath Lake (OR), these Bear Lake sediments have high magnetic susceptibilities (MS) relative to non-glacial-age sediments and contain well-defined millennial-scale variations in magnetic properties. In contrast to glacial flour derived from volcanic rocks surrounding Upper Klamath Lake, glacial flour derived from the Uinta Mountains and deposited in Bear Lake by the Bear River has low magnetite content but high hematite content. The relatively low MS values of younger and older non-glacial-age sediments are due entirely to dilution by non-magnetic endogenic carbonate and to the effects of sulfidic alteration of detrital Fe-oxides. Analysis of samples from streams entering Bear Lake and from along the course of the Bear River demonstrates that, in comparison to other areas of the catchment, sediment derived from the Uinta Mountains is rich in hematite (high HIRM) and aluminum, and poor in magnetite (low MS) and titanium. Within the glacial-age lake sediments, there are strong positive correlations among HIRM, Al/Ti, and fine sediment grain size. MS varies inversely with theses three variables. These relations indicate that the observed millennial-scale variations in magnetic and chemical properties arise from varying proportions of two detrital components: (1) very fine-grained glacial flour derived from Proterozoic metasedimentary rocks in the Uinta Mountains and characterized by high HIRM and low MS, and (2) somewhat coarser material, characterized by higher MS and lower HIRM, derived from widespread sedimentary rocks along the course of the Bear River and around Bear Lake. Measurement of glacial flour incorporated in lake sediments can provide a continuous history of alpine glaciation, because the rate of accumulation of glacial flour probably varies closely with the areal extent of glaciation. In the absence of post-depositional alteration of magnetic minerals, magnetic measurements can provide a highly sensitive tool for assessing variations in glacial flour content if glacial and non-glacial materials have contrasting magnetic properties. For Bear Lake, the required contrast is produced by differences in bedrock underlying glaciated and unglaciated areas.

Sediment grain-size characteristics and relevant correlations to the aeolian environment in China's eastern desert region.

PubMed

Zhang, Chunlai; Shen, Yaping; Li, Qing; Jia, Wenru; Li, Jiao; Wang, Xuesong

2018-06-15

To identify characteristics of aeolian activity and the aeolian environment in China's eastern desert region, this study collected surface sediment samples from the main desert and sandy lands in this region: the Hobq Desert and the Mu Us, Otindag, Horqin, and Hulunbuir sandy lands. We analyzed the grain-size characteristics and their relationships to three key environmental indicators: drift potential, the dune mobility index, and vegetation cover. The main sediment components are fine to medium sands, with poor (Hulunbuir) to moderate (all other areas) sorting, of unimodal to bimodal distribution. This suggests that improved sorting is accomplished by the loss of both relatively coarser and finer grains. Since 2000, China's eastern desert region has generally experienced low wind energy environmental conditions, resulting in decreased dune activity. In the Hobq Desert, however, the dry climate and sparse vegetation, in conjunction with the most widely distributed mobile dune area in the eastern desert region, have led to frequent and intense aeolian activity, including wind erosion, sand transport, and deposition, resulting in conditions for good sediment sorting. In the Mu Us, Otindag, and Horqin sandy lands, mosaic distribution has resulted from wind erosion-dominated and deposition-dominated aeolian environments. In the Hulunbuir Sandy Land, high precipitation, low temperatures, and steppe vegetation have resulted in well-developed soils; however, strong winds and flat terrain have created an aeolian environment dominated by wind erosion. Copyright © 2018. Published by Elsevier B.V.

Dispersal of fine sediment in nearshore coastal waters

USGS Publications Warehouse

Warrick, Jonathan A.

2013-01-01

Fine sediment (silt and clay) plays an important role in the physical, ecological, and environmental conditions of coastal systems, yet little is known about the dispersal and fate of fine sediment across coastal margin settings outside of river mouths. Here I provide simple physical scaling and detailed monitoring of a beach nourishment project near Imperial Beach, California, with a high portion of fines (40% silt and clay by weight). These results provide insights into the pathways and residence times of fine sediment transport across a wave-dominated coastal margin. Monitoring of the project used physical, optical, acoustic, and remote sensing techniques to track the fine portion of the nourishment sediment. The initial transport of fine sediment from the beach was influenced strongly by longshore currents of the surf zone that were established in response to the approach angles of the waves. The mean residence time of fine sediment in the surf zone—once it was suspended—was approximately 1 hour, and rapid decreases in surf zone fine sediment concentrations along the beach resulted from mixing and offshore transport in turbid rip heads. For example, during a day with oblique wave directions and surf zone longshore currents of approximately 25 cm/s, the offshore losses of fine sediment in rips resulted in a 95% reduction in alongshore surf zone fine sediment flux within 1 km of the nourishment site. However, because of the direct placement of nourishment sediment on the beach, fine suspended-sediment concentrations in the swash zone remained elevated for several days after nourishment, while fine sediment was winnowed from the beach. Once offshore of the surf zone, fine sediment settled downward in the water column and was observed to transport along and across the inner shelf. Vertically sheared currents influenced the directions and rates of fine sediment transport on the shelf. Sedimentation of fine sediment was greatest on the seafloor directly offshore of the nourishment site. However, a mass balance of sediment suggests that the majority of the fine sediment moved far away (over 2 km) from the nourishment site or to water depths greater than 10 m, where fine sediment represents a substantial portion of the bed material. Thus, the fate of fine sediment in nearshore waters was influenced strongly by wave conditions, surf zone and rip current transport, and the vertical density and flow conditions of coastal waters.

Sediment-phosphorus dynamics can shift aquatic ecology and cause downstream legacy effects after wildfire in large river systems.

PubMed

Emelko, Monica B; Stone, Micheal; Silins, Uldis; Allin, Don; Collins, Adrian L; Williams, Chris H S; Martens, Amanda M; Bladon, Kevin D

2016-03-01

Global increases in the occurrence of large, severe wildfires in forested watersheds threaten drinking water supplies and aquatic ecology. Wildfire effects on water quality, particularly nutrient levels and forms, can be significant. The longevity and downstream propagation of these effects as well as the geochemical mechanisms regulating them remain largely undocumented at larger river basin scales. Here, phosphorus (P) speciation and sorption behavior of suspended sediment were examined in two river basins impacted by a severe wildfire in southern Alberta, Canada. Fine-grained suspended sediments (<125 μm) were sampled continuously during ice-free conditions over a two-year period (2009-2010), 6 and 7 years after the wildfire. Suspended sediment samples were collected from upstream reference (unburned) river reaches, multiple tributaries within the burned areas, and from reaches downstream of the burned areas, in the Crowsnest and Castle River basins. Total particulate phosphorus (TPP) and particulate phosphorus forms (nonapatite inorganic P, apatite P, organic P), and the equilibrium phosphorus concentration (EPC0 ) of suspended sediment were assessed. Concentrations of TPP and the EPC0 were significantly higher downstream of wildfire-impacted areas compared to reference (unburned) upstream river reaches. Sediments from the burned tributary inputs contained higher levels of bioavailable particulate P (NAIP) - these effects were also observed downstream at larger river basin scales. The release of bioavailable P from postfire, P-enriched fine sediment is a key mechanism causing these effects in gravel-bed rivers at larger basin scales. Wildfire-associated increases in NAIP and the EPC0 persisted 6 and 7 years after wildfire. Accordingly, this work demonstrated that fine sediment in gravel-bed rivers is a significant, long-term source of in-stream bioavailable P that contributes to a legacy of wildfire impacts on downstream water quality, aquatic ecology, and drinking water treatability. © 2015 John Wiley & Sons Ltd.

The influence of particles recycling on the geochemistry of sediments in a large tropical dam lake in the Amazonian region, Brazil

NASA Astrophysics Data System (ADS)

Fonseca, Rita; Pinho, Catarina; Oliveira, Manuela

2016-12-01

As a result of over-erosion of soils, the fine particles, which contain the majority of nutrients, are easily washed away from soils, which become deficient in a host of components, accumulating in lakes. On one hand, the accumulation of nutrients-rich sediments are a problem, as they affect the quality of the overlying water and decrease the water storage capacity of the system; on the other hand, sediments may constitute an important resource, as they are often extremely rich in organic and inorganic nutrients in readily available forms. In the framework of an extensive work on the use of rock related materials to enhance the fertility of impoverish soils, this study aimed to evaluate the role on the nutrients cycle, of particles recycling processes from the watershed to the bottom of a large dam reservoir, at a wet tropical region under high weathering conditions. The study focus on the mineralogical transformations that clay particles undergo from the soils of the drainage basin to their final deposition within the reservoir and their influence in terms of the geochemical characteristics of sediments. We studied the bottom sediments that accumulate in two distinct seasonal periods in Tucuruí reservoir, located in the Amazonian Basin, Brazil, and soils from its drainage basin. The surface layers of sediments in twenty sampling points with variable depths, are representative of the different morphological sections of the reservoir. Nineteen soil samples, representing the main soil classes, were collected near the margins of the reservoir. Sediments and soils were subjected to the same array of physical, mineralogical and geochemical analyses: (1) texture, (2) characterization and semi-quantification of the clay fraction mineralogy and (3) geochemical analysis of the total concentration of major elements, organic compounds (organic C and nitrogen), soluble fractions of nutrients (P and K), exchangeable fractions (cation exchange capacity, exchangeable bases and acidity) and pH(H2O). There is a remarkable homogeneity in the sedimentary distribution along the reservoir in terms of the texture and mineralogy of the clay fraction and of the chemistry of the total, soluble and exchangeable phases. These observations contrast with the physical, morphological and chemical heterogeneity of the soils and the setting lithology. Most of the sediments has a higher contribution of fine-grained material and the mineralogy of the clay fraction is dominated by kaolinite in soils and kaolinite and illite in sediments, followed by lesser amounts of gibbsite, goethite, and metahaloisite and by small/vestigial contents of chlorite and smectite. The sediments are mainly inherited from the watershed but there exist marked differences between the accumulated sediments and their parent materials. These differences mainly come from the selective erosion of fine-grained particles and the extreme climatic conditions which enhance complex transformations of mineralogical and chemical nature. Compared with the parental soils, the reservoir sediments show the following differences: (1) enrichment in fine-grained and less dense inorganic particles, (2) aggradative mineralogical transformations, including enrichment in clay minerals with higher cationic adsorption and exchange capacity, (3) degradation of the crystalline structure of Fe- and Al-oxides (goethite, gibbsite), (4) increase in easily leached elements (Mg, Ca, P, K, Na) and decrease in chemically less mobile elements (Si, Fe) and (5) higher contents of organic carbon, nitrogen, and soluble forms of P and K, mainly concentrated in the clay fraction. These transformations are extremely important in the nutrients cycle, denoting that sediments represent an efficient sink for nutrients from the over-erosion of soils. Mineral and organic compounds can permanently or temporarily sequester these nutrients, recycling them and enhancing their availability through the slow release of components from relatively loose crystal structures. These processes can easily explain the enrichment in soluble and exchangeable forms of elements such as P, K, Ca or Mg. This study conclude that the particles recycling in a large tropical dam reservoir which receives high fluxes of allochthonous nutrients, has an important role in the good quality of sediments for agricultural use and in the profitable use of this technology to recover depleted soils in remediation projects in regions near large hydroelectric plants.

The Halekulani Sand Channel and Makua Shelf sediment deposits: Are they a sand resource for replenishing Waikiki's beaches?

USGS Publications Warehouse

Hampton, M.A.; Fletcher, C. H.; Barry, J.H.; Lemmo, S.J.; ,

2000-01-01

The Halekulani Sand Channel and the Makua Shelf off the south shore of Oahu contain at least 1.3 million m3 of sediment that is a possible resource for nourishing degraded sections of Waikiki Beach. A sidescan sonar survey indicates continuous sediment cover within the channel and on the shelf, and samples from the top and bottom of vibracores from the channel and shelf contain from 29% to 77% of grains between 0 to 2.5 phi (1 to 0.177 mm), the size range of four samples from Waikiki Beach. Compositional analyses indicate high variability, but the vibracore samples normally have relatively high Halimeda content compared to beach sand samples. Laboratory tests show a positive correlation of abrasion with Halimeda content, suggesting that the offshore sediment would abrade more than beach sediment under nearshore wave action. The common gray color of the offshore sediment can be aesthetically undesirable for sand on popular tourist beaches such as Waikiki; however, visual observation of native beach sand indicates that a significant component of gray color is endemic to many Hawaiian beaches. The gray color was removed in the laboratory by soaking in heated hydrogen peroxide. The geological properties of the offshore sediment indicate potential as a resource for beach nourishment, but industrial treatment might be necessary to remove excess fine and coarse grains, and possibly the gray color. Further, the abrasion potential might have to be considered in calculating beach sand losses over time.

Results of geophysical surveys of glacial deposits near a former waste-disposal site, Nashua, New Hampshire

USGS Publications Warehouse

Ayotte, Joseph D.; Dorgan, Tracy H.

1995-01-01

Geophysical investigations were done near a former waste-disposal site in Nashua, New Hampshire to determine the thickness and infer hydraulic characteristics of the glacial sediments that underlie the area. Approximately 5 miles of ground- penetrating radar (GPR) data were collected in the study area by use of dual-80 Megahertz antennas. Three distinct radar-reflection signatures were evident from the data and are interpreted to represent (1) glacial lake-bottom sediments, (2) coarse sand and gravel and (or) sandy glacial till, and (3) bedrock. The GPR signal penetrated as much as 70 feet of sediment in coarse-grained areas, but penetration depth was generally less than 40 feet in extensive areas of fine-grained deposits. Geologic features were evident in many of the profiles. Glacial-lake-bottom sediments were the most common features identified. Other features include deltas deposited in glacial Lake Nashua and lobate fans of sediment deposited subaqueously at the distal end of deltaic sediments. Cross-bedded sands were often identifiable in the deltaic sediments. Seismic-refraction data were also collected at five of the GPR data sites. In most cases, depths to the water table and to the till and (or) bedrock surface indicated by the seismic-refraction data compared favorably with depths calculated from the GPR data. Test holes were drilled at three locations to determine the true depths to radar reflectors and to determine the types of geologic material represented by the various reflectors.

Fluvial sediment in the environment: a national challenge

USGS Publications Warehouse

Larsen, Matthew C.; Gellis, Allen C.; Glysson, G. Douglas; Gray, John R.; Horowitz, Arthur J.

2010-01-01

Sediment and sediment-associated constituents can contribute substantially to water-quality impairment. In the past, sediment was viewed mainly as an engineering problem that affected reservoir storage capacity, shipping channel maintenance, and bridge scour, as well as the loss of agricultural soil. Sediment is now recognized as a major cause of aquatic system degradation in many rivers and streams as a result of light attenuation, loss of spawning substrate due to fine-grained sediment infilling, reduction in primary productivity, decreases in biotic diversity, and effects from sediment-associated chemical constituents. Recent advances in sediment measurement, assessment, source-identification, and analytical protocols provide new capabilities to quantify sediment and solid-phase chemical fluxes in aquatic systems. Developing, maintaining, and augmenting current sediment- and water-quality-monitoring networks is essential for determining the health of U.S. waterways and for evaluating the effectiveness of management actions in reducing sediment-related problems. The application of new scientific capabilities that address the adverse effects of sediment and sediment- associated constituents represents a major step in managing the Nation’s water quality. A robust Federal, national-scale eff rt, in collaboration with vested stakeholders, is needed to address these sediment-related water-quality issues across the United States.

Uppermost impact fallback layer in the Bosumtwi crater (Ghana): Mineralogy, geochemistry, and comparison with Ivory Coast tektites

NASA Astrophysics Data System (ADS)

Koeberl, Christian; Brandstätter, Franz; Glass, Billy P.; Hecht, Lutz; Mader, Dieter; Reimold, Wolf Uwe

In 2004, an International Continental Scientific Drilling Program (ICDP) drilling project at the Bosumtwi impact crater, Ghana (10.5 km in diameter, 1.07 Myr old), was performed to study the sediments that fill the lake as well as the underlying impactites. In one (LB-05) of 16 cores drilled into the lake sediments, the zone between the impact breccias and the post-impact sediments was penetrated, preserving the final, fine-grained impact fallback layer. This ~30 cm thick layer contains in the top 10 cm “accretionary” lapilli, microtektite-like glass spherules, and shocked quartz grains. Glass particles -- mostly of splash form less than 1 mm size -- make up the bulk of the grains (~70-78% by number) in the coarser size fraction (>125 μm) of the top of the fallback layer. About one-third of all quartz grains in the uppermost part of the layer are shocked, with planar deformation features (PDFs); almost half of these grains are highly shocked, with 3 or more sets of PDFs. K-feldspar grains also occur and some show shock deformation. The abundance of shocked quartz grains and the average shock level as indicated by the number of sets of PDFs, for both quartz and K-feldspar, decrease with depth into the layer. The well-preserved glass spherules and fragments are chemically rather homogeneous within each particle, and also show relatively small variations between the various particles. On average, the composition of the fallback spherules from core LB-5B is very similar to the composition of Ivory Coast tektites and microtektites, with the exception of CaO contents, which are about 1.5 to 2 times higher in the fallback spherules. This is a rare case in which the uppermost fallback layer and the transition to the post-impact sediments has been preserved in an impact structure; its presence indicates that the impactite sequence at Bosumtwi is complete and that Bosumtwi is a very well-preserved impact crater.

Methane Hydrate Formation from Enhanced Organic Carbon Burial During Glacial Lowstands: Examples from the Gulf of Mexico

NASA Astrophysics Data System (ADS)

Malinverno, A.; Cook, A.; Daigle, H.; Oryan, B.

2017-12-01

Methane hydrates in fine-grained marine sediments are often found within veins and fractures occupying discrete depth intervals that are surrounded by hydrate-free sediments. As they are not connected with gas sources beneath the base of the methane hydrate stability zone (MHSZ), these isolated hydrate-bearing intervals have been interpreted as formed by in situ microbial methane. We investigate here the hypothesis that these hydrate deposits form in sediments that were deposited during glacial lowstands and contain higher amounts of labile particulate organic carbon (POC), leading to enhanced microbial methanogenesis. During Pleistocene lowstands, river loads are deposited near the steep top of the continental slope and turbidity currents transport organic-rich, fine-grained sediments to deep waters. Faster sedimentation rates during glacial periods result in better preservation of POC because of decreased exposure times to oxic conditions. The net result is that more labile POC enters the methanogenic zone and more methane is generated in these sediments. To test this hypothesis, we apply an advection-diffusion-reaction model with a time-dependent deposition of labile POC at the seafloor controlled by glacioeustatic sea level variations in the last 250 kyr. The model is run for parameters estimated at three sites drilled by the 2009 Gulf of Mexico Joint Industry Project: Walker Ridge in the Terrebonne Basin (WR313-G and WR313-H) and Green Canyon near the canyon embayment into the Sigsbee Escarpment (GC955-H). In the model, gas hydrate forms in sediments with higher labile POC content deposited during the glacial cycle between 230 and 130 kyr (marine isotope stages 6 and 7). The corresponding depth intervals in the three sites contain hydrates, as shown by high bulk electrical resistivities and resistive subvertical fracture fills. This match supports the hypothesis that enhanced POC burial during glacial lowstands can result in hydrate formation from in situ microbial methanogenesis. Our results have implications for carbon cycling during glacial/interglacial cycles and for hydrate accumulation in the MHSZ. In particular, once hydrate-bearing intervals formed during glacial periods are buried beneath the MHSZ and dissociate, gas bubbles can rise and recycle microbial methane into the MHSZ.

Sediment carbon fate in phreatic karst (Part 1): Conceptual model development

NASA Astrophysics Data System (ADS)

Husic, A.; Fox, J.; Agouridis, C.; Currens, J.; Ford, W.; Taylor, C.

2017-06-01

Recent research has paid increased attention to quantifying the fate of carbon pools within fluvial networks, but few, if any, studies consider the fate of sediment organic carbon in fluviokarst systems despite that karst landscapes cover 12% of the earth's land surface. The authors develop a conceptual model of sediment carbon fate in karst terrain with specific emphasis upon phreatic karst conduits, i.e., those located below the groundwater table that have the potential to trap surface-derived sediment and turnover carbon. To assist with their conceptual model development, the authors study a phreatic system and apply a mixture of methods traditional and novel to karst studies, including electrical resistivity imaging, well drilling, instantaneous velocimetry, dye tracing, stage recording, discrete and continuous sediment and water quality sampling, and elemental and stable carbon isotope fingerprinting. Results show that the sediment transport carrying capacity of the phreatic karst water is orders of magnitude less than surface streams during storm-activated periods promoting deposition of fine sediments in the phreatic karst. However, the sediment transport carrying capacity is sustained long after the hydrologic event has ended leading to sediment resuspension and prolonged transport. The surficial fine grained laminae occurs in the subsurface karst system; but unlike surface streams, the light-limited conditions of the subsurface karst promotes constant heterotrophy leading to carbon turnover. The coupling of the hydrological processes leads to a conceptual model that frames phreatic karst as a biologically active conveyor of sediment carbon that recharges degraded organic carbon back to surface streams. For example, fluvial sediment is estimated to lose 30% of its organic carbon by mass during a one year temporary residence within the phreatic karst. It is recommended that scientists consider karst pathways when attempting to estimate organic matter stocks and carbon transformation in fluvial networks.

Controls on the abruptness of gravel-sand transitions

NASA Astrophysics Data System (ADS)

Venditti, J. G.; Church, M. A.; Lamb, M. P.; Domarad, N.; Rennie, C. D.

2014-12-01

As gravel-bedded rivers fine downstream, they characteristically exhibit an abrupt transition from gravel- to sand-bed. This is the only abrupt transition in grain-size that occurs in the fluvial system and has attracted considerable attention. A number of competing theories have been proposed to account for the abruptness of the transition, including base-level control, attrition of ~10mm gravel to produce sand, and sediment sorting processes. The prevailing theory for the emergence of abrupt transitions is size selective sorting of bimodal sediment wherein gravel deposits due to downstream declining shear stress, fining the bedload until a sand-bed emerges. We explored this hypothesis by examining grain-size, shear stress, gravel mobility and sand suspension thresholds through the gravel-sand transition (GST) of the Fraser River, British Columbia. The Fraser GST is an arrested gravel wedge with patches of gravel downstream of the wedge forming a diffuse extension. There is an abrupt change in bed slope through the transition that leads to an abrupt change in shear stress. The GST, bed-slope change and backwater caused by the ocean are all coincident spatially, which enhances the sharpness of the GST. Interestingly, the bimodal reach of the river occurs downstream of the GST and exhibits no downstream gradients in shear stress, suspended sediment flux, gravel mobility or sand suspension thresholds. This calls into question the prevailing theory for the emergence of an abrupt GST by size selective sorting. We provide evidence, both empirical and theoretical, that suggests the emergence of an abrupt GST is caused by rapid deposition of sand when fine gravel deposits. We argue that the emergence of gravel-sand transitions is a consequence of gravel-bedded rivers adopting a steeper slope than sand-bedded rivers. The abruptness arises because the bed slope required to convey the gravel load fixes the distal location of a terminal gravel wedge, and once the river has lost the capacity to carry the gravel mixture, the river adopts the lower slope required to pass the sand load. Progressive downstream fining of a gravel-sand mixture is not a necessary condition for the emergence of a gravel-sand transition.

Estimating floodplain sedimentation in the Laguna de Santa Rosa, Sonoma County, CA

USGS Publications Warehouse

Curtis, Jennifer A.; Flint, Lorraine E.; Hupp, Cliff R.

2013-01-01

We present a conceptual and analytical framework for predicting the spatial distribution of floodplain sedimentation for the Laguna de Santa Rosa, Sonoma County, CA. We assess the role of the floodplain as a sink for fine-grained sediment and investigate concerns regarding the potential loss of flood storage capacity due to historic sedimentation. We characterized the spatial distribution of sedimentation during a post-flood survey and developed a spatially distributed sediment deposition potential map that highlights zones of floodplain sedimentation. The sediment deposition potential map, built using raster files that describe the spatial distribution of relevant hydrologic and landscape variables, was calibrated using 2 years of measured overbank sedimentation data and verified using longer-term rates determined using dendrochronology. The calibrated floodplain deposition potential relation was used to estimate an average annual floodplain sedimentation rate (3.6 mm/year) for the ~11 km2 floodplain. This study documents the development of a conceptual model of overbank sedimentation, describes a methodology to estimate the potential for various parts of a floodplain complex to accumulate sediment over time, and provides estimates of short and long-term overbank sedimentation rates that can be used for ecosystem management and prioritization of restoration activities.

Settling speeds on flocs in fresh water and seawater

NASA Astrophysics Data System (ADS)

Burban, Pierre-Yves; Xu, Yao-Jun; McNeil, Joe; Lick, Wilbert

1990-10-01

The settling speeds of floes of fine-grained, natural sediments approximately 10-200 μm in diameter have been measured in both fresh water and seawater. These floes were formed at fluid shears of 100, 200, and 400 s-1 and at sediment concentrations of 10, 100, and 400 mg/L, values typical of conditions in the near-shore areas of lakes and oceans, especially during storm conditions. It is demonstrated that the settling speed of a floe is a strong function of fluid shear and sediment concentration as well as of the diameter of the floe, but it is a weak function of salinity. For the same diameter and salinity, floes produced at the lower fluid shears and sediment concentrations have lower settling speeds than do floes produced at higher fluid shears and sediment concentrations. If the conditions of fluid shear and sediment concentration under which the floes were produced are unknown or ignored, it is shown that the settling speed of a floe is a weak function of diameter and salinity.

Gravity flows associated with flood events and carbon burial: Taiwan as instructional source area.

PubMed

Liu, James T; Kao, Shuh-Ji; Huh, Chih-An; Hung, Chin-Chang

2013-01-01

Taiwan's unique setting allows it to release disproportionately large quantities of fluvial sediment into diverse dispersal systems around the island. Earthquakes, lithology, topography, cyclone-induced rainfall, and human disturbance play major roles in the catchment dynamics. Deep landslides dominate the sediment-removal process on land, giving fluvial sediment distinct geochemical signals. Extreme conditions in river runoff, sediment load, nearshore waves and currents, and the formation of gravity flows during typhoon events can be observed within short distances. Segregation of fresh biomass and clastic sediment occurs during the marine transport process, yet turbidity currents in the Gaoping Submarine Canyon carry woody debris. Strong currents in the slope and back-arc basin of the Okinawa Trough disperse fine-grained sediments rapidly and widely. Temporal deposition and remobilization may occur when the shallow Taiwan Strait acts as a receptacle. Taiwan can therefore serve as a demonstration of the episodic aspect of the source-to-sink pathway to both the coastal and deep-ocean environments.

Beaver dams and channel sediment dynamics on Odell Creek, Centennial Valley, Montana, USA

NASA Astrophysics Data System (ADS)

Levine, Rebekah; Meyer, Grant A.

2014-01-01

Beaver dams in streams are generally considered to increase bed elevation through in-channel sediment storage, thus, reintroductions of beaver are increasingly employed as a restoration tool to repair incised stream channels. Here we consider hydrologic and geomorphic characteristics of the study stream in relation to in-channel sediment storage promoted by beaver dams. We also document the persistence of sediment in the channel following breaching of dams. Nine reaches, containing 46 cross-sections, were investigated on Odell Creek at Red Rock Lakes National Wildlife Refuge, Centennial Valley, Montana. Odell Creek has a snowmelt-dominated hydrograph and peak flows between 2 and 10 m3 s- 1. Odell Creek flows down a fluvial fan with a decreasing gradient (0.018-0.004), but is confined between terraces along most of its length, and displays a mostly single-thread, variably sinuous channel. The study reaches represent the overall downstream decrease in gradient and sediment size, and include three stages of beaver damming: (1) active; (2) built and breached in the last decade; and (3) undammed. In-channel sediment characteristics and storage were investigated using pebble counts, fine-sediment depth measurements, sediment mapping and surveys of dam breaches. Upstream of dams, deposition of fine (≤ 2 mm) sediment is promoted by reduced water surface slope, shear stress and velocity, with volumes ranging from 48 to 182 m3. High flows, however, can readily transport suspended sediment over active dams. Variations in bed-sediment texture and channel morphology associated with active dams create substantial discontinuities in downstream trends and add to overall channel heterogeneity. Observations of abandoned dam sites and dam breaches revealed that most sediment stored above beaver dams is quickly evacuated following a breach. Nonetheless, dam remnants trap some sediment, promote meandering and facilitate floodplain development. Persistence of beaver dam sediment within the main channel on Odell Creek is limited by frequent breaching (< 1-5 years), so in-channel sediment storage because of damming has not caused measurable channel aggradation over the study period. Enhanced overbank flow by dams, however, likely increases fine-grained floodplain sedimentation and riparian habitat. Contrasts between beaver-damming impacts on Odell Creek and other stream systems of different scales suggest a high sensitivity to hydrologic, geomorphic, and environmental controls, complicating predictions of the longer-term effects of beaver restoration.

Characterization of geologic deposits in the vicinity of US Ecology, Amargosa Basin, southern Nevada

USGS Publications Warehouse

Taylor, Emily M.

2010-01-01

Multiple approaches have been applied to better understand the characteristics of geologic units exposed at the surface and buried at depth in the vicinity of US Ecology (USE), a low-level commercial waste site in the northern Amargosa Desert, Nevada. Techniques include surficial geologic mapping and interpretation of the subsurface using borehole data. Dated deposits at depth were used to estimate rates of sediment accumulation. The subsurface lithologies have been modeled in three dimensions. Lithologic cross sections have been created from the three-dimensional model and have been compared to resistivity data at the same location. Where deposits appear offset, a fault was suspected. Global Positioning System elevation transects were measured and trenches were excavated to locate a strand of the Carrara Fault. The presence of the fault helps to better understand the shape of the potentiometric surface. These data will be used to better understand the hydrologic parameters controlling the containment of the waste at US Ecology.Quaternary geologic units exposed at the surface, in the vicinity of US Ecology, are derived from the alluvium shed off the adjacent range front and the Amargosa River. These deposits vary from modern to early Pleistocene in age. At depth, heterogeneous sands and gravel occur. Observed in deep trenches and boreholes, the subsurface deposits are characterized as fining-upward sequence of sediment from 5- to 8-meters thick. No volcanic units or fine-grained playa deposits were described in the boreholes to a depth of 200 meters. Based on Infrared Stimulated Luminescence dated core samples, short-term rates of sediment accumulation (<70,000 years) are an average of 2.7 millimeters per year, however, long-term rates (<3,900,000 years) are orders of magnitude less. Resistivity data, when compared to lithologic cross sections, generally are consistent with lithology grain size and probable soil carbonate accumulations. Surface resistivity displays a fining-upward sequence of sediments at the surface with a soil carbonate imprint. Finally, trenching north of US Ecology successfully exposed offset Quaternary deposits on a splay of the Carrara Fault. Holocene deposits do not appear to be faulted, however, a fault zone does intersect middle and late Pleistocene aged units.

Modern sedimentary facies, depositional environments, and major controlling processes on an arid siliciclastic coast, Al qahmah, SE Red Sea, Saudi Arabia

NASA Astrophysics Data System (ADS)

Nabhan, Abdullah I.; Yang, Wan

2018-04-01

The facies and environments along the arid siliciclastic coast of Red Sea in Al Qahmah, Saudi Arabia are studied to establish a depositional model for interpretation of ancient rocks deposited in rift settings. Field and petrographic studies of 151 sediment samples in an area of 20 km2 define seven main facies types: beach, washover fan, tidal channel, dune, sabkha, delta, and wadi (seasonal stream). The wadi and delta facies are composed of poorly to moderately well-sorted, gravelly, medium-to-fine sands. Delta-front sands are redistributed by southward longshore currents to form a beach. Beach facies is composed of well-to-moderately sorted fine sands with minor gravels, which contain high concentrations of magnetite, ilmenite, garnet, pyroxene, amphibole, epidote, titanite, and apatite grains, indicating strong winnowing. Crabs and other burrowers destroy primary sedimentary structures and mix sediments in foreshore and backshore of the beaches. Wind and storm surge rework foreshore and backshore sediments to form washover fans. Sabkha facies occurs extensively in supratidal depressions behind beach, are flooded by rainstorms and spring tide, and capped by a 5-cm-thick crust composed of interlaminated halite, quartz, albite, minor gypsum and biotite, and rarely calcium carbonate. Halite occurs as thin sheets and gypsum as nodules with a chicken-wire structure. Clastic fraction in sabkha sediments ranges from coarse silt to coarse sand with moderate sorting, and is transported by currents and wind. Tidal inlets and tidal creeks assume abandoned wadis and are filled by muddy sand. Sand dunes and sand sheets are 1-7 m high and widely distributed due to variable wind directions. Fine-grained dune sands are moderately well sorted, whereas sheet sands are coarser and poorly sorted due to vegetation baffling. Most eolian sands are sourced from beach deposits. This suite of complex riverine, wave, tidal, wind, chemical, and biological processes form the facies mosaic along the arid Al Qahmah coast, which is strongly affected by climate-driven evaporation and wind action.

Millennial-scale record of overwash deposits preserved within lagoon sediments from the Arabian Peninsula

NASA Astrophysics Data System (ADS)

Griffis, A. M.; Jessica, P.; Reinhardt, E. G.; Kosciuch, T. J.; Kovacs, S. E.; Hoffmann, G.

2017-12-01

Coastlines along the Arabian Sea are susceptible to tsunami-related inundation due to their proximity to the Makran Subduction Zone (MSZ). This subduction zone has seen decades of low intensity events, but has historically produced large tsunamigenic-earthquakes that have impacted the 100 million people living along the Arabian Sea. One major problem in assessing the seismic risk of the MSZ is that the historical record of events are spatially and temporally limited and rely heavily on eye witness accounts. This hinders our ability to forecast the potential magnitude and recurrence intervals of earthquakes and tsunamis that can be expected in the future. Sediments deposited by paleotsunamis are useful as they expand the decadal record of events to include millennial timescales that more accurately capture the full range of magnitudes and recurrence intervals. On November 28, 1945 a 8.1 Mw earthquake originating from the MSZ generated a tsunami inundating coastlines along the Arabian Sea with wave heights up to 13m. At Sur, a small village on the northeastern coastline of Oman, the tsunami deposited a laterally continuous shell-rich layer within a 12 km2 lagoon. This layer contained distinctive taphonomic assemblages of foraminifera and bivalves. Below the 1945 shelly deposit at Sur Lagoon, seven anomalous sand layers were found preserved within fine-grained lagoonal sediment. These layers of medium-coarse sands range in thickness from 5 to 35 cm and are separated by sandy-mud sediment. Grain size analysis shows that these anomalously coarse layers are followed by an abrupt return to lagoonal mud. The sand layers have features consistent with the 1945 tsunami deposit such as fining upward trends, sharp basal contact, and marine foraminifera (e.g., Amphistegina sp., planktics). In contrast, the surrounding lagoon deposits are generally massive, finer in grain size, and contain foraminiferal species typically found in shallow quiescent coastal environments (e.g., Ammonia tepida, miliolids). We have attributed these seven marine sand layers to tsunami overwash deposition. Preliminary radiocarbon dating of articulated bivalve shells establish a late Holocene age range for the tsunami sand layers with ongoing analyses further constraining timings leading to assessing relative magnitudes of past events.

Downstream lightening and upward heavying, sorting of sediments of uniform grain size but differing in density

NASA Astrophysics Data System (ADS)

Viparelli, E.; Solari, L.; Hill, K. M.

2014-12-01

Downstream fining, i.e. the tendency for a gradual decrease in grain size in the downstream direction, has been observed and studied in alluvial rivers and in laboratory flumes. Laboratory experiments and field observations show that the vertical sorting pattern over a small Gilbert delta front is characterized by an upward fining profile, with preferential deposition of coarse particles in the lowermost part of the deposit. The present work is an attempt to answer the following questions. Are there analogous sorting patterns in mixtures of sediment particles having the same grain size but differing density? To investigate this, we performed experiments at the Hydrosystems Laboratory at the University of Illinois at Urbana-Champaign. During the experiments a Gilbert delta formed and migrated downstream allowing for the study of transport and sorting processes on the surface and within the deposit. The experimental results show 1) preferential deposition of heavy particles in the upstream part of the deposit associated with a pattern of "downstream lightening"; and 2) a vertical sorting pattern over the delta front characterized by a pattern of "upward heavying" with preferential deposition of light particles in the lowermost part of the deposit. The observed downstream lightening is analogous of the downstream fining with preferential deposition of heavy (coarse) particles in the upstream part of the deposit. The observed upward heavying was unexpected because, considering the particle mass alone, the heavy (coarse) particles should have been preferentially deposited in the lowermost part of the deposit. Further, the application of classical fractional bedload transport relations suggests that in the case of mixtures of particles of uniform size and different densities equal mobility is not approached. We hypothesize that granular physics mechanisms traditionally associated with sheared granular flows may be responsible for the observed upward heavying and for the deviation from equal mobility.

Gas hydrate reservoirs and gas migration mechanisms in the Terrebonne Basin, Gulf of Mexico

DOE PAGES

Hillman, Jess I. T.; Cook, Ann E.; Daigle, Hugh; ...

2017-07-27

Here, the interactions of microbial methane generation in fine-grained clay-rich sediments, methane migration, and gas hydrate accumulation in coarse-grained, sand-rich sediments are not yet fully understood. The Terrebonne Basin in the northern Gulf of Mexico provides an ideal setting to investigate the migration of methane resulting in the formation of hydrate in thin sand units interbedded with fractured muds. Using 3D seismic and well log data, we have identified several previously unidentified hydrate bearing units in the Terrebonne Basin. Two units are >100 m- thick fine-grained clay-rich units where gas hydrate occurs in near-vertical fractures. In some locations, these fine-grainedmore » units lack fracture features, and they contain 1-4-m thick hydrate bearing-sands. In addition, several other thin sand units were identified that contain gas hydrate, including one sand that was intersected by a well at the location of a discontinuous bottom-simulating reflector. Using correlation of well log data to seismic data, we have mapped and described these new units in detail across the extent of the available data, allowing us to determine the variation of seismic amplitudes and investigate the distribution of free gas and/or hydrate. We present several potential source-reservoir scenarios between the thick fractured mud units and thin hydrate bearing sands. We observe that hydrate preferentially forms within thin sand layers rather than fractures when sands are present in larger marine mud units. Based on regional mapping showing the patchy lateral extent of the thin sand layers, we propose that diffusive methane migration or short-migration of microbially generated methane from the marine mud units led to the formation of hydrate in these thin sands, as discontinuous sands would not be conducive to long-range migration of methane from deeper reservoirs.« less

Sequence of structures in fine-grained turbidites: Comparison of recent deep-sea and ancient flysch sediments

NASA Astrophysics Data System (ADS)

Stow, Dorrik A. V.; Shanmugam, Ganapathy

1980-01-01

A comparative study of the sequence of sedimentary structures in ancient and modern fine-grained turbidites is made in three contrasting areas. They are (1) Holocene and Pleistocene deep-sea muds of the Nova Scotian Slope and Rise, (2) Middle Ordovician Sevier Shale of the Valley and Ridge Province of the Southern Appalachians, and (3) Cambro-Ordovician Halifax Slate of the Meguma Group in Nova Scotia. A standard sequence of structures is proposed for fine-grained turbidites. The complete sequence has nine sub-divisions that are here termed T 0 to T 8. "The lower subdivision (T 0) comprises a silt lamina which has a sharp, scoured and load-cast base, internal parallel-lamination and cross-lamination, and a sharp current-lineated or wavy surface with 'fading-ripples' (= Type C etc. …)." (= Type C ripple-drift cross-lamination, Jopling and Walker, 1968). The overlying sequence shows textural and compositional grading through alternating silt and mud laminae. A convolute-laminated sub-division (T 1) is overlain by low-amplitude climbing ripples (T 2), thin regular laminae (T 3), thin indistinct laminae (T 4), and thin wipsy or convolute laminae (T 5). The topmost three divisions, graded mud (T 6), ungraded mud (T 7) and bioturbated mud (T 8), do not have silt laminae but rare patchy silt lenses and silt pseudonodules and a thin zone of micro-burrowing near the upper surface. The proposed sequence is analogous to the Bouma (1962) structural scheme for sandy turbidites and is approximately equivalent to Bouma's (C)DE divisions. The repetition of partial sequences characterizes different parts of the slope/base-of-slope/basin plain environment, and represents deposition from different stages of evolution of a large, muddy, turbidity flow. Microstructural detail and sequence are well preserved in ancient and even slightly metamorphosed sediments. Their recognition is important for determining depositional processes and for palaeoenvironmental interpretation.

Gas hydrate reservoirs and gas migration mechanisms in the Terrebonne Basin, Gulf of Mexico

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hillman, Jess I. T.; Cook, Ann E.; Daigle, Hugh

Here, the interactions of microbial methane generation in fine-grained clay-rich sediments, methane migration, and gas hydrate accumulation in coarse-grained, sand-rich sediments are not yet fully understood. The Terrebonne Basin in the northern Gulf of Mexico provides an ideal setting to investigate the migration of methane resulting in the formation of hydrate in thin sand units interbedded with fractured muds. Using 3D seismic and well log data, we have identified several previously unidentified hydrate bearing units in the Terrebonne Basin. Two units are >100 m- thick fine-grained clay-rich units where gas hydrate occurs in near-vertical fractures. In some locations, these fine-grainedmore » units lack fracture features, and they contain 1-4-m thick hydrate bearing-sands. In addition, several other thin sand units were identified that contain gas hydrate, including one sand that was intersected by a well at the location of a discontinuous bottom-simulating reflector. Using correlation of well log data to seismic data, we have mapped and described these new units in detail across the extent of the available data, allowing us to determine the variation of seismic amplitudes and investigate the distribution of free gas and/or hydrate. We present several potential source-reservoir scenarios between the thick fractured mud units and thin hydrate bearing sands. We observe that hydrate preferentially forms within thin sand layers rather than fractures when sands are present in larger marine mud units. Based on regional mapping showing the patchy lateral extent of the thin sand layers, we propose that diffusive methane migration or short-migration of microbially generated methane from the marine mud units led to the formation of hydrate in these thin sands, as discontinuous sands would not be conducive to long-range migration of methane from deeper reservoirs.« less

Slope-apron deposition in an ordovician arc-related setting: The Vuelta de Las Tolas Member (Suri Formation), Famatina Basin, northwest Argentina

USGS Publications Warehouse

Mangano, M.G.; Buatois, L.A.

1997-01-01

The Ordovician Suri Formation is part of the infill of the Famatina Basin of northwest Argentina, which formed in an active setting along the western margin of early Paleozoic Gondwana. The lower part of this formation, the Vuelta de Las Tolas Member, records sedimentation on a slope apron formed in an intra-arc basin situated on a flooded continental arc platform. The coincidence of a thick Arenig-Llanvirn sedimentary succession and volcanic-plutonic arc rocks suggests an extensional or transtensional arc setting, and is consistent with evidence of an extensional regime within the volcanic arc in the northern Puna region. The studied stratigraphic sections consist of volcanic rocks and six sedimentary facies. The facies can be clustered into four facies associations. Association 1, composed of facies A (laminated siltstones and mudstones) and B (massive mudstones and siltstones), is interpreted to have accumulated from silty-muddy high-and low-density turbidity currents and highly fluid, silty debris flows, with subsequent reworking by bottom currents, and to a lesser extent, hemipelagic suspension in an open-slope setting. Facies association 2 is dominated by facies C (current-rippled siltstones) strata. These deposits are interpreted to record overbank sedimentation from fine-grained turbidity currents. Facies E (matrix-supported volcanic breccias) interbedded with andesitic lava units comprises facies association 3. Deposition was contemporaneous with subaqueous volcanic activity, and accumulated from cohesive debris flows in a coarse-grained wedge at the base of slope. Facies association 4 is typified by facies D (vitric fine-grained sandstones and siltstones) and F (channelized and graded volcanic conglomerates and breccias) deposits. These strata commonly display thinning-and fining-upward trends, indicating sedimentation from highly-concentrated volcaniclastic turbidity currents in a channelized system. The general characteristics of these deposits of fresh pyroclastic detritus suggest that their accumulation was contemporaneous with, or post-dated shallow-water or subaereal explosive volcanism. The Vuelta de Las Tolas Member tends to show an overall random facies patterns reflecting the strong influence of non-cyclical episodic processes related to arc volcanism and slope sedimentation. The scarcity of resident ichnofaunas and the presence of thick packages of uniform mudstones suggest deposition under oxygen-depleted conditions in a topographically confined, ponded sub-basin. Interbasinal correlations favor comparison with Middle Arenig slope-apron successions formed in the northern Puna Basin and suggest a southward prolongation of the Arenig volcanic arc.

Monitoring strategies associated with the controlled drawdown of a hydropower reservoir

NASA Astrophysics Data System (ADS)

Hauer, Christoph; Haimann, Marlene; Habersack, Helmut; Haun, Stefan; Hammer, Andreas; Schletterer, Martin

2017-04-01

Reservoirs are important in context of an increased demand on renewable energy and water for irrigation and drinking water purposes. Thus reservoir management is an important task. Beside the technical and the economically feasibility ecological factors are important issues. Thus, an integrative monitoring concept was developed and applied during a controlled drawdown of the Gepatsch reservoir in the Austrian Alps.The controlled drawdown (December 2015 - March 2016) was done slowly, with the consequence of moderatesuspended sediment concentrations (SSCs) in the downstream Inn river. The water was released through the penstock towards the turbines and directly into the Inn River. However, to limit the erosional impact on turbines only one Twin-Pelton turbines was operated during the controlled drawdown. The monitoring program itself was subdivided into monitoring of the sediments in the penstock to determine the amount and the composition of sediments which were sluiced through the turbine, monitoring of the turbine itself to quantify the damages of the turbine and a monitoring related to SSCs in the downstream river reach. In order to detect possible changes, measured discharge and turbidity values were examined. In addition, the flow velocity was modelled (1D). The goal was to monitor the observed peaks concerning their temporal shift and to draw conclusions on the storage capacity of fine sediments in the river substrate. Moreover, detailed fine sediment depositions on gravel bars along the Inn river were monitored and the grain size distribution of the river bed was determined. The monitoring started already in April / November 2015 with the aim to survey and analyses the turbidity, suspended load and fine sediment deposits on gravel bars along the River Inn as well as its biota (macroinvertebrates and fish) for "undisturbed" conditions. The SSCs were measured in a pre-analysis and during the drawdown itself in the penstock and in the outlet channel with turbidity meters, a LISST-StreamSide and a Coriolis Flow Density Meter. In addition gravimetric samples were collected on a daily basis, where subsequently the SSC and the particle size distribution were quantified in the laboratory. The material erosion of the Pelton runner, which was used during the drawdown, was measured in equal intervals to obtain a relationship between the turbine damage and the suspended sediment emission on the turbine. Concerning the studies on fine sediment deposits on gravel bars only four gravel bars showed statistically significant changes comparing the surface deposits before and after the controlled drawdown. Therefore the assumption that an increase in deposited sediments is coupled with a high rate of turbidity did not appear. The changes in river bed composition by freeze-cores delivered additional information on the fine sediment dynamics. High turbidity values resulted in a higher share of fine particles in the vertical stratigraphy especially at the first sampling sites downstream of the power plant. The same effect was monitored concerning an increase of overlaying sediments on the gravel bars. The developed integrative monitoring concept for the controlled drawdown of the Gepatsch reservoir, including continuous and periodical measurements, was a novel reach-scale approach to integrate hydrology, erosional aspects of sediments on turbines, fine sediment transport dynamics and variability in the river, and determination of ecological impacts.

An Alternative to Channel-Centered Views of the Landscape for Understanding Modern Streams in the Mid-Atlantic Piedmont Region, Eastern USA

NASA Astrophysics Data System (ADS)

Merritts, D. J.; Walter, R. C.; Rahnis, M. A.; Oberholtzer, W.

2008-12-01

Stream channels generally are the focus of conceptual models of valley bottom geomorphology. The channel-centered model prevalent in the tectonically inactive eastern U. S. invokes meandering stream channels migrating laterally across valley floors, eroding one bank while depositing relatively coarse sediment in point bars on the other. According to this model, overbank deposition during flooding deposits a veneer of fine sediment over the gravel substrate. Erosion is considered normal, and the net volume of sediment is relatively constant with time. A dramatic change in conditions-land-clearing during European settlement--led to widespread aggradation on valley bottoms. This historic sedimentation was incorporated in the channel-centered view by assuming that meandering streams were overwhelmed by the increased sediment load and rapidly aggraded vertically. Later, elevated stream channels cut through these deposits because of decreased sediment supply and increased stormwater runoff accompanying urbanization. This view can be traced to early ideas of stream equilibrium in which incoming sediment supply and runoff determine stream-channel form. We propose a different conceptual model. Our trenching and field work along hundreds of km of stream length in the mid-Atlantic Piedmont reveal no point bars prior to European settlement. Instead, a polygenetic valley-bottom landscape underlies the drape of historic sediment. The planar surface of this veneer gives the appearance of a broad floodplain generated by long-term meandering and overbank deposition, but the "floodplain" is a recent aggradational surface from regional base-level rise due to thousands of early American dams that spanned valley bottoms. As modern streams incise into the historic fine-grained slackwater sediment, they expose organic-rich hydric soils along original valley bottom centers; talus, colluvium, bedrock, and saprolite with forest soils along valley margins; and weathered Pleistocene (and older) alluvial fans and fan pediments at tributary confluences. Two-dimensional views along incised stream banks give the appearance of overbank sediment atop stream bed gravel, but the fine- grained bank (1-5 m) is mostly the result of slackwater sedimentation from damming, whereas the underlying gravel polygenetic in origin. The gravel is Pleistocene or older in age, and not the result of active stream channel migration and point-bar formation during the Holocene. The Holocene warm period was dominated by valley-bottom stability and widespread wetland formation, fostered by beaver activity. Modern stream channel forms are largely the result of incision and bank erosion in response to dam breaching and base- level fall, not hydraulic adjustment to prevailing (or changed) supplies of sediment and water. Rather, channel dimensions are controlled by thickness of historic sediment (i.e., dam height and distance upstream of dam) and depth of incision. Changes in slope (i.e., rapid base-level fall), rather than changes in sediment supply and runoff, are powerful determinants of modern channel forms, and there are no pre-settlement forms for comparison. At present, there is an "impedance mismatch" between those with channel-centered views and those who view the deeply weathered mid-Atlantic landscape as the result of hundreds of thousands to millions of years of slow landscape evolution.

Surface sediment remobilization triggered by earthquakes in the Nankai forearc region

NASA Astrophysics Data System (ADS)

Okutsu, N.; Ashi, J.; Yamaguchi, A.; Irino, T.; Ikehara, K.; Kanamatsu, T.; Suganuma, Y.; Murayama, M.

2017-12-01

Submarine landslides triggered by earthquakes generate turbidity currents (e.g. Piper et al., 1988; 1999). Recently several studies report that the remobilization of the surface sediment triggered by earthquakes can also generate turbidity currents. However, studies that proposed such process are still limited (e.g. Ikehara et al., 2016; Mchugh et al., 2016; Moernaut et al., 2017). The purpose of this study is to examine those sedimentary processes in the Nankai forearc region, SW Japan using sedimentary records. We collected 46 cm-long multiple core (MC01) and a 6.7 m-long piston core (PC03) from the small basin during the R/V Shinsei Maru KS-14-8 cruise. The small confined basin, which is our study site, block the paths of direct sediment supply from river-submarine canyon system. The sampling site is located at the ENE-WSW elongated basin between the accretionary prism and the forearc basin off Kumano without direct sediment supply from river-submarine canyon system. The basin exhibits a confined basin that captures almost of sediments supplied from outside. Core samples are mainly composed of silty clay or very fine sand. Cs-137 measurement conducted on a MC01 core shows constantly high value at the upper 17 cm section and no detection below it. Moreover, the sedimentary structure is similar to fine-grained turbidite described by Stow and Shanmgam (1980), we interpret the upper 17 cm of MC01 as muddy turbidite. Grain size distribution and magnetic susceptibility also agree to this interpretation. Rapid sediment deposition after 1950 is assumed and the most likely event is the 2004 off Kii peninsula earthquakes (Mw=6.6-7.4). By calculation from extent of provenance area, which are estimated by paleocurrent analysis and bathymetric map, and thickness of turbidite layer we conclude that surface 1 cm of slope sediments may be remobilized by the 2004 earthquakes. Muddy turbidites are also identified in a PC03 core. The radiocarbon age gap of 170 years obtained around 2 mbsf of PC03 core also indicates similar sedimentary process. However, we also obtained large age gap in a thick turbidite layer, indicating remobilization of deeper sediments by landslide. Our results revealed that the studied basin recorded various scales and styles of sediment remobilizations by earthquake shakings.

Mesophotic coral ecosystems under anthropogenic stress: a case study at Ponce, Puerto Rico

NASA Astrophysics Data System (ADS)

Appeldoorn, Richard; Ballantine, David; Bejarano, Ivonne; Carlo, Milton; Nemeth, Michael; Otero, Ernesto; Pagan, Francisco; Ruiz, Hector; Schizas, Nikolaos; Sherman, Clark; Weil, Ernesto

2016-03-01

Mesophotic coral ecosystems (MCEs) were compared between La Parguera and Ponce, off the south coast of Puerto Rico. In contrast to La Parguera, Ponce has a narrow insular shelf and hosts several river outlets, a commercial port, a regional sewage treatment plant with associated deep water outfall, and three deep dredge disposal sites. Off Ponce, MCEs receive higher (16×) rates of sedimentation than off La Parguera, a less impacted site. The most impacted sites were located offshore of Cayo Ratones and are in or down-current and in close proximity to one of the dredge disposal sites. There, MCEs are characterized by a steep, irregular, rocky slope with a cover of fine-grained, dark brown sediment, which increases with depth. At shallower depths, scattered rocky outcroppings are colonized by sponges, black corals and algae. The sediment cover contains two to three times the terrigenous content and a significantly higher percentage of the fine-grained fraction than off La Parguera. Thirteen remotely operated vehicle (ROV) dives east and west of Ponce showed that the deepest depth at which corals were observed increased with distance from Cayo Ratones and did not approach depths observed off La Parguera except at the eastern-most (up-current) site, Caja de Muertos, which was also significantly further offshore. Benthic communities off Caja de Muertos were comparable to those at La Parguera, while off Cayo Ratones, there were no mesophotic corals and sparse development of other benthic macrobiota except sponges. Management authorities should include MCEs when assessing potential impacts from anthropogenic activities and take the necessary steps to reduce local threats.

Atmospheric dust in modern soil on aeolian sandstone, Colorado Plateau (USA): Variation with landscape position and contribution to potential plant nutrients

USGS Publications Warehouse

Reynolds, R.; Neff, J.; Reheis, M.; Lamothe, P.

2006-01-01

Rock-derived nutrients in soils originate from both local bedrock and atmospheric dust, including dust from far-distant sources. Distinction between fine particles derived from local bedrock and from dust provides better understanding of the landscape-scale distribution and abundance of soil nutrients. Sandy surficial deposits over dominantly sandstone substrates, covering vast upland areas of the central Colorado Plateau, typically contain 5-40% silt plus clay, depending on geomorphic setting and slope (excluding drainages and depressions). Aeolian dust in these deposits is indicated by the presence of titanium-bearing magnetite grains that are absent in the sedimentary rocks of the region. Thus, contents of far-traveled aeolian dust can be estimated from magnetic properties that primarily reflect magnetite content, such as isothermal remanent magnetization (IRM). Isothermal remanent magnetization was measured on bulk sediment samples taken along two transects in surficial sediment down gentle slopes away from sandstone headwalls. One transect was in undisturbed surficial sediment, the other in a setting that was grazed by domestic livestock until 1974. Calculation of far-traveled dust contents of the surficial deposits is based on measurements of the magnetic properties of rock, surficial deposits, and modern dust using a binary mixing model. At the undisturbed site, IRM-based calculations show a systematic down-slope increase in aeolian dust (ranging from 2% to 18% of the surface soil mass), similar to the down-slope increase in total fines (18-39% of surface soil mass). A combination of winnowing by wind during the past and down-slope movement of sediment likely accounts for the modern distribution of aeolian dust and associated nutrients. At the previously grazed site, dust also increases down slope (5-11%) in sediment with corresponding abundances of 13-25% fines. Estimates of the contributions of aeolian dust to the total soil nutrients range widely, depending on assumptions about grain-size partitioning of potential nutrients in weathered bedrock. Nevertheless, aeolian dust is important for this setting, contributing roughly 40-80% of the rock-derived nutrient stocks (P, K, Na, Mn, Zn, and Fe) in uppermost soil over most of the sampled slope at the undisturbed site, which shows no evidence of recent wind erosion. ?? 2005 Elsevier B.V. All rights reserved.

Hydraulic, geomorphic, and trout habitat conditions of the Lake Fork of the Gunnison River in Hinsdale County, Lake City, Colorado, Water Years 2010-2011

USGS Publications Warehouse

Williams, Cory A.; Richards, Rodney J.; Schaffrath, Keelin R.

2015-01-01

Sediment mobility is an important process for flushing fine sediments from within the gravel frameworks. Evaluations of channel and flow characteristics at cross-section locations 2–8 show a range of streambed mobility. In general, boundary shear stress and streambed mobility increase with increases in streamflow. Within the cross sections, the greatest boundary shear stress occurs towards the center of the channel. Reach-scale assessment of sediment mobility in the lower reach shows increased streambed mobility. This is due in part to smaller grain sizes in the lower reach, but may also reflect the greater extent of channel alterations, specifically the temporary berms constructed by CDOT in the late 1980s and 1990s, present in this reach.

Organic matter degradation in surface sediments of the Changjiang estuary: Evidence from amino acids.

PubMed

Wang, Kui; Chen, Jianfang; Jin, Haiyan; Li, Hongliang; Zhang, Weiyan

2018-05-12

Organic matter degradation is a key component of the processes of carbon preservation and burial in seafloor sediments. The aim of this study was to explore organic matter degradation state within the open-shelf Changjiang Estuary of the East China Sea, using an amino acids-based degradation index (DI) in conjunction with information about organic matter source (marine versus terrestrial), bottom water oxygenation state, and sediment grain size. The relative molar percentages of 17 individual amino acids (characterized using principal component analysis) in surface sediments indicate that organic matter is degraded to varying extents across the estuary seabed. Sediments with DI >0 (relatively labile) were found mostly within a coastal hypoxic area. Sediments of DI less than -1 (relatively refractory) were found near the Changjiang River mouth and the northern and southern parts of the central shelf. We consider DI to be a more reliable indicator of degradation than simple ratios of AAs. DI was inversely correlated with the proportion of terrestrial organic material (F t ) in the sediments, indicating that relatively fresh/labile organic matter was generally associated with marine sources. DI was significantly correlated with F t and bottom water apparent oxygen utilization (AOU bot ) together. The parameter DI and the (labile) amino acid tyrosine were highest in hypoxic areas, suggesting the presence of relatively fresh organic matter, probably due to a combination of marine-source inputs and better preservation of organic matter in the silt and clay sediments of these areas (as compared to sandy sediments). Less degraded organic matter with high amino acids was also favorable to benthic animals. Overall, sedimentary estuarine organic matter was least degraded in areas characterized by marine sources of organic matter, low-oxygen conditions, and fine-grained sediments. Copyright © 2018 Elsevier B.V. All rights reserved.

Clay Mineralogy of AN Alluvial Aquifer in a Mountainous, Semiarid Terrain, AN Example from Rifle, Colorado

NASA Astrophysics Data System (ADS)

Elliott, W. C.; Lim, D.; Zaunbrecher, L. K.; Pickering, R. A.; Williams, K. H.; Navarre-Sitchler, A.; Long, P. E.; Noel, V.; Bargar, J.; Qafoku, N. P.

2015-12-01

Alluvial sediments deposited along the Colorado River corridor in the semi-arid regions of central to western Colorado can be important hosts for legacy contamination including U, V, As and Se. These alluvial sediments host aquifers which are thought to provide important "hot spots" and "hot moments" for microbiological activity controlling organic carbon processing and fluxes in the subsurface. Relatively little is known about the clay mineralogy of these alluvial aquifers and the parent alluvial sediments in spite of the fact that they commonly include lenses of silt-clay materials. These lenses are typically more reduced than coarser grained materials, but zones of reduced and more oxidized materials are present in these alluvial aquifer sediments. The clay mineralogy of the non-reduced parent alluvial sediments of the alluvial aquifer located in Rifle, CO (USA) is composed of chlorite, smectite, illite, kaolinite and quartz. The clay mineralogy of non-reduced fine-grained materials at Rifle are composed of the same suite of minerals found in the sediments plus a vermiculite-smectite intergrade that occurs near the bottom of the aquifer near the top of the Wasatch Formation. The clay mineral assemblages of the system reflect the mineralogically immature character of the source sediments. These assemblages are consistent with sediments and soils that formed in a moderately low rainfall climate and suggestive of minimal transport of the alluvial sediments from their source areas. Chlorite, smectite, smectite-vermiculite intergrade, and illite are the likely phases involved in the sorption of organic carbon and related microbial redox transformations of metals in these sediments. Both the occurrence and abundance of chlorite, smectite-vermiculite, illite and smectite can therefore exert an important control on the contaminant fluxes and are important determinants of biogeofacies in mountainous, semiarid terrains.

Sea-floor geology in central Rhode Island Sound south of Sakonnet Point, Rhode Island

USGS Publications Warehouse

McMullen, K.Y.; Poppe, L.J.; Ackerman, S.D.; Worley, C.R.; Nadeau, M.A.; Van Hoy, M. V.

2012-01-01

The U.S. Geological Survey (USGS) and the National Oceanic and Atmospheric Administration (NOAA) are working together to study the sea floor along the northeastern coast of the United States. NOAA collected multibeam-echosounder data during hydrographic survey H11995 in a 63-square-kilometer area in central Rhode Island Sound, south of Sakonnet Point, Rhode Island. The USGS collected sediment samples, bottom video, and still photographs from 27 stations in this study area to verify an interpretation of the bathymetric data. Collected data are used to map areas of scour depressions and erosional outliers, megaripples, boulders, and relatively undisturbed modern marine sediments. In general, much of the eastern part of the study area, a submerged segment of the Harbor Hill-Roanoke Point-Charlestown-Buzzards Bay moraine, is bouldery. Bottom photography shows boulders are generally encrusted with hydrozoans, algae, and anemone. Scour depressions, presumably formed by long-period storm waves, and erosional outliers of Holocene sediments dominate the western part of the study area and several large areas in the east. The scour depressions tend to have coarser grained sediment than intervening erosional outliers. The coarseness likely creates turbulence in the water over these areas, which prevents fine-grained sediment deposition. Several small areas of megaripples are visible in the bathymetry data in the west. Other sandy areas are typically rippled, with burrows, worm tubes, and starfish present.

Glacial Cycles Influence Marine Methane Hydrate Formation

NASA Astrophysics Data System (ADS)

Malinverno, A.; Cook, A. E.; Daigle, H.; Oryan, B.

2018-01-01

Methane hydrates in fine-grained continental slope sediments often occupy isolated depth intervals surrounded by hydrate-free sediments. As they are not connected to deep gas sources, these hydrate deposits have been interpreted as sourced by in situ microbial methane. We investigate here the hypothesis that these isolated hydrate accumulations form preferentially in sediments deposited during Pleistocene glacial lowstands that contain relatively large amounts of labile particulate organic carbon, leading to enhanced microbial methanogenesis. To test this hypothesis, we apply an advection-diffusion-reaction model with a time-dependent organic carbon deposition controlled by glacioeustatic sea level variations. In the model, hydrate forms in sediments with greater organic carbon content deposited during the penultimate glacial cycle ( 120-240 ka). The model predictions match hydrate-bearing intervals detected in three sites drilled on the northern Gulf of Mexico continental slope, supporting the hypothesis of hydrate formation driven by enhanced organic carbon burial during glacial lowstands.

Estuarine sediment transport by gravity-driven movement of the nepheloid layer, Long Island Sound

USGS Publications Warehouse

Poppe, L.J.; McMullen, K.Y.; Williams, S.J.; Crocker, J.M.; Doran, E.F.

2008-01-01

Interpretation of sidescan-sonar imagery provides evidence that down-slope gravity-driven movement of the nepheloid layer constitutes an important mode of transporting sediment into the basins of north-central Long Island Sound, a major US East Coast estuary. In the Western Basin, this transport mechanism has formed dendritic drainage systems characterized by branching patterns of low backscatter on the seafloor that exceed 7.4 km in length and progressively widen down-slope, reaching widths of over 0.6 km at their southern distal ends. Although much smaller, dendritic patterns of similar morphology are also present in the northwestern part of the Central Basin. Because many contaminants display affinities for adsorption onto fine-grained sediments, and because the Sound is affected by seasonal hypoxia, mechanisms and dispersal pathways by which inorganic and organic sediments are remobilized and transported impact the eventual fate of the contaminants and environmental health of the estuary. 

Determining sources of deep-sea mud by organic matter signatures in the Sunda trench and Aceh basin off Sumatra

NASA Astrophysics Data System (ADS)

Omura, Akiko; Ikehara, Ken; Arai, Kohsaku; Udrekh

2017-12-01

The content, optically determined properties, and stable isotope composition of organic carbon in fine-grained sediment cores were analyzed to investigate the origins of deep-sea sediments deposited in the Aceh forearc basin and on the Sunda trench floor off Sumatra from the late Pleistocene to the Holocene. In the Aceh basin, the depositional frequency of turbidite mud decreased as sea level rose during the deglaciation. The terrigenous organic carbon content was high at the end of the last glacial period, whereas during the deglaciation most of the organic carbon was of marine origin. In the Sunda trench, the Holocene turbidites consisted of remobilized slope sediments from two different sources: sediments derived from the old Bengal/Nicobar fan included thermally matured organic fragments, whereas those derived from the trench slope contained little terrigenous organic carbon.

Accumulation of COGEMA-La Hague-derived reprocessing wastes in French salt marsh sediments.

PubMed

Cundy, Andrew B; Croudace, Ian W; Warwick, Phillip E; Oh, Jung-Suk; Haslett, Simon K

2002-12-01

Over the past five decades, authorized low-level discharges from coastal nuclear facilities have released significant quantities of artificial radionuclides into the marine environment. In northwest Europe, the majority of the total discharge has derived from nuclear reprocessing activities at Sellafield in the United Kingdom and COGEMA-La Hague in France. At the Sellafield site, a significant amount of the discharges has been trapped in offshore fine sediment deposits, and notably in local coastal and estuarine sediments, and much research has been focused on understanding the distribution, accumulation, and reworking of long-lived radionuclides in these deposits. In contrast, there are few high-resolution published data on the vertical distribution of radionuclides in fine-grained estuarine sediments near, and downstream of, COGEMA-La Hague. This paper therefore examines the vertical distribution of a range of anthropogenic radionuclides in dated salt marsh cores from two estuaries, one adjacent to, and the other downstream of, the COGEMA-La Hague discharge point (the Havre de Carteret at Barneville-Carteret and the Baie de Somme, respectively). The radionuclides examined show a vertical distribution which predominantly reflects variations in input from COGEMA-La Hague (albeit much more clearly at Barneville-Carteret than at the Baie de Somme site), and Pu isotopic ratios are consistent with a La Hague, rather than weapons' fallout, source. Because of sediment mixing, the marshes apparently retain an integrated record of the La Hague discharges, rather than an exact reproduction of the discharge history. Sorption of radionuclides increases in the order 90Sr < 137Cs < 60Co < 239,240Pu, which is consistent with Kd values reported in the literature. In general, the radionuclide activities observed at the sites studied are low (particularly in comparison with salt marsh sediments near the Sellafield facility), but are similar to those found in areas of fine sedimentation in the central Channel. These marshes are not major sinks for discharged reprocessing wastes.

Evidence of repeated wildfires prior to human occupation on San Nicolas Island, California

USGS Publications Warehouse

Pigati, Jeffrey S.; McGeehin, John P.; Skipp, Gary L.; Muhs, Daniel R.

2014-01-01

Understanding how early humans on the California Channel Islands might have changed local fire regimes requires a baseline knowledge of the frequency of natural wildfires on the islands prior to human occupation. A sedimentary sequence that was recently discovered in a small canyon on San Nicolas Island contains evidence of at least 24 burn events that date to between ~37 and 25 ka (thousands of calibrated 14C years before present), well before humans entered North America. The evidence includes abundant macroscopic charcoal, blackened sediments, and discrete packages of oxidized, reddish-brown sediments that are similar in appearance to sedimentary features called “fire areas” on Santa Rosa Island and elsewhere. Massive fine-grained sediments that contain the burn evidence are interpreted as sheetwash deposits and are interbedded with coarse-grained, clast-supported alluvial sediments and matrix supported sands, pebbles, and cobbles that represent localized debris flows. These sedimentary sequences suggest that the catchment area above our study site underwent multiple cycles of relative quiescence that were interrupted by fire and followed by slope instability and mass wasting events. Our 14C-based chronology dates these cycles to well before the arrival of humans on the Channel Islands and shows that natural wildfires occurred here, at a minimum, every 300–500 years prior to human occupation.

The role of large woody debris in modulating the dispersal of a post-fire sediment pulse

NASA Astrophysics Data System (ADS)

Short, Lauren E.; Gabet, Emmanuel J.; Hoffman, Daniel F.

2015-10-01

In 2001, a series of post-fire debris flows brought 30,000 m3 of sediment, deposited as fans, to the narrow valley floor of Sleeping Child Creek in western Montana (USA). In 2005, pebble-counts and surveys of the channel in proximity to six of the debris flow fans documented a regular sequence of fine-grained aggradation upstream of the fans, incision through the fans, and coarse-grained aggradation downstream of the fans. These measurements were repeated in 2012. We found that the delivery of large woody debris (LWD) over the intervening 7 years has been a dominant factor in the disposition of the debris-flow material. The amount of LWD in the study reach has increased by as much as 50% in the areas with a high burn severity, leading to the formation of large logjams that interrupt the flow of sediment along the streambed. Nearly all of the surveyed reaches have aggraded since 2005, including those that had initially begun incising through the debris flow deposits, and the streambed has become generally finer. We hypothesize that, over the next few decades, debris flow sediment not colonized and anchored by riparian vegetation will trickle out of the affected reaches as the logjams slowly degrade.

Muddy marine sediments are gels

NASA Astrophysics Data System (ADS)

Dorgan, K. M.; Clemo, W. C.; Barry, M. A.; Johnson, B.

2016-02-01

Marine sediments cover 70% of the earth's surface, are important sites of carbon burial and nutrient regeneration, and provide habitat for diverse and abundant infaunal communities. The majority of these sediments are muds, in which bioturbation affects sediment structure and geochemical gradients. How infaunal activites result in particle mixing depends on the mechanical properties of muddy sediments. At the scale of burrowing animals, muds are elastic solids. Animals move through these elastic muds by extending crack-shaped burrows by fracture. The underlying mechanism driving this elasticity, however, has not been explicitly illustrated. Here, we test the hypothesis that the elastic behavior of muddy sediments is disrupted by removal of organic material by measuring fracture toughness and stiffness of manipulated and control sediments. Our results indicate that the mechanical responses of sediments to forces are governed by the muco-polymeric matrix of organic material. Similar effects of organic material oxidation were not observed in sands, indicating a clear mechanical distinction between fine- and coarse-grained sediments. Muddy sediments are gels, not fluids or granular materials, and models of how sediments respond to forces imposed by, e.g., organisms, gases, and ambient water should explicitly consider the role of organic material.

Oceanographic controls on sedimentary and geochemical facies on the Peru outer shelf and upper slope

USGS Publications Warehouse

Arthur, Michael A.; Dean, Walter E.

2013-01-01

Concentrations and characteristics of organic matter in surface sediments deposited under an intense oxygen-minimum zone (OMZ) on the Peru margin were mapped and studied in samples from deck-deployed box cores and push cores acquired by submersible on two east-west transects spanning depths of 75 to 1,000 meters (m) at 12°S and 13.5°S. On the basis of sampling and analyses of the top 1–2 centimeters (cm) of available cores, three main belts of sediments were identified on each transect with increasing depth: (1) muds rich in organic carbon (OC); (2) authigenic phosphatic mineral crusts and pavements; and (3) glaucony facies.Sediments rich in OC on the 12°S transect were mainly located on the outer shelf and upper slope (150–350 m), but they occurred in much shallower water (approximately 100 m) on the 13.5°S transect. The organic matter is almost entirely marine as confirmed by Rock-Eval pyrolysis and isotopic composition of OC. Concentrations of OC are highest (up to 18 percent) in sediments within the OMZ where dissolved oxygen (DO) concentrations are <5 micromoles per kilogram (μM). Even at these low concentrations of DO, however, the surface sediments from within the OMZ are dominantly unlaminated. Concentrations of DO may have the dominant effect on organic matter characteristics, but reworking of fine-grained sediment and organic matter by strong bottom currents with velocities as high as 30 centimeters per second (cm/s) on the slope between 150 and 300 m and redeposition on the seafloor in areas of lower energy and higher DO concentration also exert important controls on OC concentration and degree of oxidation in this region.Phosphate-rich sediments and crusts occurred at depths of about 300 to 550 m on both transects. Nodular crusts of sediment cemented by carbonate-fluorapatite (CFA; phosphorite) or dolomite form within the OMZ. These phosphorite crusts evolve through cementation from light olive-green, stiff but friable, phosphatized claystone “protocrusts” through dense, dark phosphorite crusts, cemented breccias, and pavements. The degree of phosphatization and thickness of the crusts depend on the rates of sediment supply and on the strength and frequency of currents that re-expose crusts on the seafloor. Phosphorite crusts and pavements on the Peru margin can only become buried and incorporated into the geologic record once bottom currents slacken sufficiently to allow fine-grained sediment to accumulate.Glaucony-rich surface sediments, relatively undiluted by other components, were found mainly in deeper water on the 13.5°S transect (750 m to at least 1,067 m). These sediments consist almost entirely of sand-size glaucony pellets. These widespread glaucony sands formed in place and were then concentrated and reworked by strong currents that winnowed away the fine-grained matrix. Although the glaucony occurs in sand-size pellets, the pellets are made up of aggregates of authigenic, platy, micaceous clay minerals. Glaucony is predominantly a potassium (K), sodium (Na), iron (Fe), magnesium (Mg) aluminosilicate with an approximate formula of (K,Na)(Fe3+,Al,Mg)2(Si,Al)4O10(OH)2. The glaucony on the 13.5°S transect forms by alteration of one or more original “framework” minerals (carbonate and [or] aluminosilicates) to form pellital aggregates of Fe-, K-, and Mg-rich clay minerals. Because Fe, K, and Mg are derived from seawater, sedimentation rates must be extremely slow in order for the original framework minerals to remain in contact with seawater. The close association of glaucony and phosphorite indicates a delicate balance between the slightly oxidizing conditions at the base of the OMZ that form glaucony and the slightly reducing conditions that mobilize iron and phosphate to form phosphorite.

Aquatic vegetation and trophic condition of Cape Cod (Massachusetts, U.S.A.) kettle ponds

USGS Publications Warehouse

Roman, C.T.; Barrett, N.E.; Portnoy, J.W.

2001-01-01

The species composition and relative abundance of aquatic macrophytes was evaluated in five Cape Cod, Massachusetts, freshwater kettle ponds, representing a range of trophic conditions from oligotrophic to eutrophic. At each pond, aquatic vegetation and environmental variables (slope, water depth, sediment bulk density, sediment grain size, sediment organic content and porewater inorganic nutrients) were measured along five transects extending perpendicular to the shoreline from the upland border into the pond. Based on a variety of multivariate methods, including Detrended Correspondence Analysis (DCA), an indirect gradient analysis technique, and Canonical Correspondence Analysis (CCA), a direct gradient approach, it was determined that the eutrophic Herring Pond was dominated by floating aquatic vegetation (Brasenia schreberi, Nymphoides cordata, Nymphaea odorata), and the algal stonewort, Nitella. Partial CCA suggested that high porewater PO4-P concentrations and fine-grained sediments strongly influenced the vegetation of this eutrophic pond. In contrast, vegetation of the oligotrophic Duck Pond was sparse, contained no floating aquatics, and was dominated by emergent plants. Low porewater nutrients, low sediment organic content, high water clarity and low pH (4.8) best defined the environmental characteristics of this oligotrophic pond. Gull Pond, with inorganic nitrogen-enriched sediments, also exhibited a flora quite different from the oligotrophic Duck Pond. The species composition and relative abundance of aquatic macrophytes provide good indicators of the trophic status of freshwater ponds and should be incorporated into long-term monitoring programs aimed at detecting responses to anthropogenically-derived nutrient loading.

Aquatic vegetation and trophic condition of Cape Cod (Massachusetts, USA) kettle ponds

USGS Publications Warehouse

Roman, C.T.; Barrett, N.E.; Portnoy, J.W.

2001-01-01

The species composition and relative abundance of aquatic macrophytes was evaluated in five Cape Cod, Massachusetts, freshwater kettle ponds, representing a range of trophic conditions from oligotrophic to eutrophic. At each pond, aquatic vegetation and environmental variables (slope, water depth, sediment bulk density, sediment grain size, sediment organic content and porewater inorganic nutrients) were measured along five transects extending perpendicular to the shoreline from the upland border into the pond. Based on a variety of multivariate methods, including Detrended Correspondence Analysis (DCA), an indirect gradient analysis technique, and Canonical Correspondence Analysis (CCA), a direct gradient approach, it was determined that the eutrophic Herring Pond was dominated by floating aquatic vegetation (Brasenia schreberi, Nymphoides cordata, Nymphaea odorata), and the algal stonewort, Nitella. Partial CCA suggested that high porewater PO4-P concentrations and fine-grained sediments strongly influenced the vegetation of this eutrophic pond. In contrast, vegetation of the oligotrophic Duck Pond was sparse, contained no floating aquatics, and was dominated by emergent plants. Low porewater nutrients, low sediment organic content, high water clarity and low pH (4.8) best defined the environmental characteristics of this oligotrophic pond. Gull Pond, with inorganic nitrogen-enriched sediments, also exhibited a flora quite different from the oligotrophic Duck Pond. The species composition and relative abundance of aquatic macrophytes provide good indicators of the trophic status of freshwater ponds and should be incorporated into long-term monitoring programs aimed at detecting responses to anthropogenically-derived nutrient loading.

Relationships of flour solvent retention capacity, secondary structure and rheological properties with the cookie making characteristics of wheat cultivars.

PubMed

Kaur, Amritpal; Singh, Narpinder; Kaur, Seeratpreet; Ahlawat, Arvind Kumar; Singh, Anju Mahendru

2014-09-01

The relationships of grain, flour solvent retention capacity (SRC) and dough rheological properties with the cookie making properties of wheat cultivars were evaluated. Cultivars with higher proportion of intermolecular-β-sheets+antiparallel β sheets and lower α-helix had greater gluten strength. The grain weight and diameter positively correlated with the proportion of fine particles and the cookie spread factor (SF) and negatively to the grain hardness (GH) and Na2CO3 SRC. The SF was higher in the flour with a higher amount of fine particle and with a lower Na2CO3 SRC and dough stability (DS). The breaking strength (BS) of cookies was positively correlated to lactic acid (LA) SRC, DS, peak time, sedimentation value (SV), G' and G″. Na2CO3 SRC and GH were strongly correlated. The gluten performance index showed a strong positive correlation with SV, DS, G' and G″. The water absorption had a significant positive correlation with sucrose SRC and LASRC. Cultivars with higher GH produced higher amount of coarse particles in flours that had higher Na2CO3 SRC and lower cookie SF. Copyright © 2014 Elsevier Ltd. All rights reserved.

Luminescence signal profiling: a new proxy for sedimentologically "invisible" marine Mass Transport Deposits (MTDs)

NASA Astrophysics Data System (ADS)

López, Gloria I.; Bialik, Or; Waldmann, Nicolas

2017-04-01

When dealing with fine-grained, organic-rich, colour-monotone, underwater marine sediment cores retrieved from the continental shelf or slope, the initial visual impression, upon split-opening the vessels, is often of a "disappointing" homogeneous, monotonous, continuous archive. Only after thorough, micro- to macro-scale, multi-parameter investigations the sediment reveals its treasures, initially by performing some measurements on the intact core itself, hence depicting for the first time its contents, and subsequently by carrying out the destructive, multi-proxy sample-based analyses. Usually, routine Multi-Sensor Core Logger (MSCL) measurements of petrophysical parameters (e.g. magnetic susceptibility, density, P-Wave velocity) on un-split sediment cores are the first undertaken while still on-board in the field or back at the laboratory. Less often done, but equally valuable, are continuous X-Ray and CT scan imaging of the same intact archives. Upon splitting, routine granulometry, micro- and macro-fossil and invertebrate identification, total organic / inorganic carbon content (TOC / TIC), amid other analyses take place. The geochronology component is also established usually by AMS 14C on selected organic-rich units, and less common is Optically Stimulated Luminescence (OSL) dating used on the coarser-grained, siliciclastic layers. A relatively new tool used in Luminescence, the Portable OSL Reader, employed to rapidly assess the luminescence signal of untreated poly-mineral samples to assist with targeted field sampling for full OSL dating, was used for the first time in marine sediment cores as a novel petrophysical characterization tool with astonishing results. In this study, two 2 m-long underwater piston sediment cores recovered from 200 m depths on the continental shelf off-southern Israel, were subjected to pulsed-photon stimulation (PPSL) obtaining favourable luminescence signals along their entire lengths. Astoundingly, luminescence signals were obtained on both, already split-opened cores. Both cores depicted the monotonous characteristics of homogeneousness down-core as per most of the results obtained from the non-destructive and destructive tests. One of the cores showed several small higher energy events, including a Mass Transport Deposit (MTD) within its first 10 cm, only fully visible on the CT scan imaging, the PPSL profile and particle size distribution plot. This initial investigation demonstrates the feasibility and usefulness of luminescence profiling as a new sedimentological and petrophysical proxy to better visualize homogeneous yet complex, fine-grained, underwater archives. Moreover, it helps to understand the continuity of the stratigraphy and linearity of deposition of the sediment, besides assisting on the estimation of relative ages provided that good OSL ages are obtained throughout the recovered archive.

Modeling the effect of dune sorting on the river long profile

NASA Astrophysics Data System (ADS)

Blom, A.

2012-12-01

River dunes, which occur in low slope sand bed and sand-gravel bed rivers, generally show a downward coarsening pattern due to grain flows down their avalanche lee faces. These grain flows cause coarse particles to preferentially deposit at lower elevations of the lee face, while fines show a preference for its upper elevations. Before considering the effect of this dune sorting mechanism on the river long profile, let us first have a look at some general trends along the river profile. Tributaries increasing the river's water discharge in streamwise direction also cause a streamwise increase in flow depth. As under subcritical conditions mean dune height generally increases with increasing flow depth, the dune height shows a streamwise increase, as well. This means that also the standard deviation of bedform height increases in streamwise direction, as in earlier work it was found that the standard deviation of bedform height linearly increases with an increasing mean value of bedform height. As a result of this streamwise increase in standard deviation of dune height, the above-mentioned dune sorting then results in a loss of coarse particles to the lower elevations of the bed that are less and even rarely exposed to the flow. This loss of coarse particles to lower elevations thus increases the rate of fining in streamwise direction. As finer material is more easily transported downstream than coarser material, a smaller bed slope is required to transport the same amount of sediment downstream. This means that dune sorting adds to river profile concavity, compared to the combined effect of abrasion, selective transport and tributaries. A Hirano-type mass conservation model is presented that deals with dune sorting. The model includes two active layers: a bedform layer representing the sediment in the bedforms and a coarse layer representing the coarse and less mobile sediment underneath migrating bedforms. The exposure of the coarse layer is governed by the rate of sediment supply from upstream. By definition the sum of the exposure of both layers equals unity. The model accounts for vertical sediment fluxes due to grain flows down the bedform lee face and the formation of a less mobile coarse layer. The model with its vertical sediment fluxes is validated against earlier flume experiments. It deals well with the transition between a plane bed and a bedform-dominated bed. Applying the model to field scale confirms that dune sorting increases river profile concavity.

Uranium in Surface Waters and Sediments Affected by Historical Mining in the Denver West 1:100,000 Quadrangle, Colorado

USGS Publications Warehouse

Zielinski, Robert A.; Otton, James K.; Schumann, R. Randall; Wirt, Laurie

2008-01-01

Geochemical sampling of 82 stream waters and 87 stream sediments within mountainous areas immediately west of Denver, Colorado, was conducted by the U.S. Geological Survey in October 1994. The primary purpose was to evaluate regionally the effects of geology and past mining on the concentration and distribution of uranium. The study area contains uranium- and thorium-rich bedrock, numerous noneconomic occurrences of uranium minerals, and several uranium deposits of variable size and production history. During the sampling period, local streams had low discharge and were more susceptible to uranium-bearing acid drainage originating from historical mines of base- and precious-metal sulfides. Results indicated that the spatial distribution of Precambrian granites and metamorphic rocks strongly influences the concentration of uranium in stream sediments. Within-stream transport increases the dispersion of uranium- and thorium rich mineral grains derived primarily from granitic source rocks. Dissolved uranium occurs predominantly as uranyl carbonate complexes, and concentrations ranged from less than 1 to 65 micrograms per liter. Most values were less than 5 micrograms per liter, which is less than the current drinking water standard of 30 micrograms per liter and much less than locally applied aquatic-life toxicity standards of several hundred micrograms per liter. In local streams that are affected by uranium-bearing acid mine drainage, dissolved uranium is moderated by dilution and sorptive uptake by stream sediments. Sorbents include mineral alteration products and chemical precipitates of iron- and aluminum-oxyhydroxides, which form where acid drainage enters streams and is neutralized. Suspended uranium is relatively abundant in some stream segments affected by nearby acid drainage, which likely represents mobilization of these chemical precipitates. The 234U/238U activity ratio of acid drainage (0.95-1.0) is distinct from that of local surface waters (more than 1.05), and this distinctive isotopic composition may be preserved in iron-oxyhydroxide precipitates of acid drainage origin. The study area includes a particularly large vein-type uranium deposit (Schwartzwalder mine) with past uranium production. Stream water and sediment collected downstream from the mine's surface operations have locally anomalous concentrations of uranium. Fine-grained sediments downstream from the mine contain rare minute particles (10-20 micrometers) of uraninite, which is unstable in a stream environment and thus probably of recent origin related to mining. Additional rare particles of very fine grained (less than 5 micrometer) barite likely entered the stream as discharge from settling ponds in which barite precipitation was formerly used to scavenge dissolved radium from mine effluent.

Niger River Discharge and the Connection to the West African Monsoon Over the Last 25 kyr

NASA Astrophysics Data System (ADS)

Patten, J.; Marcantonio, F.; Slowey, N. C.; Schmidt, M. W.; Parker, A. O.; Thomas, D. J.

2016-12-01

The intensity of the West African monsoon is directly tied to the shifting of the Inter-Tropical Convergence Zone and global-scale climate variability. As the West African monsoon varies through time, it affects the precipitation that occurs within the Niger River basin and the Niger River's discharge into the eastern equatorial Atlantic Ocean. The accumulation of marine sediments on the continental slope offshore of the Niger Delta reflects these processes. We seek to better understand how related environmental processes have varied as climate and sea level changed during the latter part of the last glacial-interglacial cycle. Here we present results from our ongoing investigation of sediments collected offshore of the Niger Delta that reflect such changes. The concentrations of 230Th, 232Th, and 234U in the sediments have been measured and combined with ages from radiocarbon dates and planktonic foraminiferal δ18O stratigraphies to estimate how the rate of sediment accumulation has varied through time. This record is considered together with measurements of sediment CaCO3 content and grain-size distribution to better understand the relative importance of environmental processes that control the flux of sediments and thorium to the seafloor - scavenging by particles settling through the water column versus the transport of sediments downslope by turbidity flows. We present xs230Th-derived 232Th fluxes that we suggest approximate the amount of fine-grained detrital material delivered from the Niger River to our sites. We anticipate that the importance of these competing processes will vary as climate/sea-level change influences the flux of sediments from the Niger River and the transport of these sediments to the slope.

Sediment transport monitoring for sustainable hydropower development

NASA Astrophysics Data System (ADS)

Rüther, Nils; Guerrero, Massimo; Stokseth, Siri

2015-04-01

Due to the increasing demand of CO2 neutral energy not only in Europe but also in World, a relatively large amount of new hydro power plants (HPP) are built. In addition, will existing ones refurbished and renewed in order to run them more cost effective. A huge thread to HPPs is incoming sediments in suspension from the rivers upstream. The sediments settle in the reservoir and reduce the effective head and volume and reduce consequently the life time of the reservoir. In addition are the fine sediments causing severe damages to turbines and infrastructure of a HPP. For estimating the amount of incoming sediments in suspension and therefore planning efficient counter measures, it is essential to monitor the rivers within the catchment of the HPP for suspended sediments. This work is considerably time consuming and requires highly educated personnel and is therefore expensive. Consequently will this study present a method to measure suspended sediment concentrations and their grain size distribution with a dual frequency acoustic Doppler current profiler (ADCP). This method is more cost effective and reliable in comparison to traditional measurement methods. Having more detailed information about the sediments being transported in a river, the hydro power plant can be planned, built, and operated much more efficiently and sustainable. The two horizontal ADCPs are installed at a measurement cross section in the Devoll river in Albania. To verify the new method, the suspended load concentrations will be monitored also in the traditional ways at the same cross sections. It is planned to install turbidity measurement devices included with an automatic sampling devices. It is also planned to use an optical in situ measurement device (LISST SL by Sequoia Inc.) to have detailed information of sediment concentration and grain sizes over the depth.

Geochemical record of Holocene to Recent sedimentation on the Western Indus continental shelf, Arabian Sea

NASA Astrophysics Data System (ADS)

Limmer, David R.; BöNing, Philipp; Giosan, Liviu; Ponton, Camilo; KöHler, Cornelia M.; Cooper, Matthew J.; Tabrez, Ali R.; Clift, Peter D.

2012-01-01

We present a multiproxy geochemical analysis of two cores recovered from the Indus Shelf spanning the Early Holocene to Recent (<14 ka). Indus-23 is located close to the modern Indus River, while Indus-10 is positioned ˜100 km further west. The Holocene transgression at Indus-10 was over a surface that was strongly weathered during the last glacial sea level lowstand. Lower Holocene sediments at Indus-10 have higherɛNdvalues compared to those at the river mouth indicating some sediment supply from the Makran coast, either during the deposition or via reworking of older sediments outcropping on the shelf. Sediment transport from Makran occurred during transgressive intervals when sea level crossed the mid shelf. The sediment flux from non-Indus sources to Indus-10 peaked between 11 ka and 8 ka. A hiatus at Indus-23 from 8 ka until 1.3 ka indicates non-deposition or erosion of existing Indus Shelf sequences. HigherɛNdvalues seen on the shelf compared to the delta imply reworking of older delta sediments in building Holocene clinoforms. Chemical Index of Alteration (CIA), Mg/Al and Sr isotopes are all affected by erosion of detrital carbonate, which reduced through the Holocene. K/Al data suggest that silicate weathering peaked ca. 4-6 ka and was higher at Indus-10 compared to Indus-23. Fine-grained sediments that make up the shelf have geochemical signatures that are different from the coarser grained bulk sediments measured in the delta plain. The Indus Shelf data highlight the complexity of reconstructing records of continental erosion and provenance in marine settings.

Fine particles on mars: Observations with the viking 1 lander cameras

USGS Publications Warehouse

Mutch, T.A.; Arvidson, R. E.; Binder, A.B.; Huck, F.O.; Levinthal, E.C.; Liebes, S.; Morris, E.C.; Nummedal, D.; Pollack, James B.; Sagan, C.

1976-01-01

Drifts of fine-grained sediment are present in the vicinity of the Viking 1 lander. Many drifts occur in the lees of large boulders. Morphologic analysis indicates that the last dynamic event was one of general deflation for at least some drifts. Particle cohesion implies that there is a distinct small-particle upturn in the threshold velocity-particle size curve; the apparent absence of the most easily moved particles (150 micrometers in diameter) may be due to their preferential transport to other regions or their preferential collisional destruction. A twilight rescan with lander cameras indicates a substantial amount of red dust with mean radius on the order of 1 micrometer in the atmosphere.

Fine particles on Mars: observations with the viking 1 lander cameras.

PubMed

Mutch, T A; Arvidson, R E; Binder, A B; Huck, F O; Levinthal, E C; Liebes, S; Morris, E C; Nummedal, D; Pollack, J B; Sagan, C

1976-10-01

Drifts of fine-grained sediment are present in the vicinity of the Viking 1 lander. Many drifts occur in the lees of large boulders. Morphologic analysis indicates that the last dynamic event was one of general deflation for at least some drifts. Particle cohesion implies that there is a distinct small-particle upturn in the threshold velocity-particle size curve; the apparent absence of the most easily moved particles (150 micrometers in diameter) may be due to their preferential transport to other regions or their preferential collisional destruction. A twilight rescan with lander cameras indicates a substantial amount of red dust with mean radius on the order of 1 micrometer in the atmosphere.

Epiphytic calcium carbonate production and facies development within sub-tropical seagrass beds, Inhaca Island, Mozambique

NASA Astrophysics Data System (ADS)

Perry, C. T.; Beavington-Penney, S. J.

2005-02-01

Seagrass beds have been widely recognised as playing an important role in influencing carbonate sediment facies development. This reflects their role not only as facilitators of fine sediment settling and stabilisation, but also as substrates for epiphytic organisms that, after death, contribute skeletal carbonate to the sediment substrate. In low latitude (reef-related) settings, epiphytic carbonate production rates are often high and this, in combination with the trapping of carbonate mud produced by a range of associated calcareous algal species, typically results in the development of carbonate mud-rich facies. Whilst such environments, and their associated sediment substrates, have been widely documented, studies of seagrass facies in marginal (sub-tropical/warm temperate) marine settings have not been conducted from a sedimentological perspective. This study determines rates of epiphytic carbonate production on two seagrass species Thalassodendron ciliatum and Thalassia hemprichii, and examines seagrass sediment facies from a sub-tropical reef-related environment in southern Mozambique. Dense seagrass beds colonise primarily siliciclastic sediment substrates and are characterised by low rates of epiphytic carbonate production (mean: 43.9 g CaCO 3 m -2 year -1 for T. ciliatum, and 33.4 g CaCO 3 m -2 year -1 for T. hemprichii). Epiphytic encrusters are dominated by thin, monostromatic layers of the crustose coralline red algae Hydrolithon farinosum, along with rotaliid smaller benthic foraminifera (including Asterorotalia cf. gaimardi and Spirillina sp.) and the soritid Peneroplis sp., as well as rare encrusting acervulinid foraminifera, serpulids and bryozoans. Epiphytic calcium carbonate production rates are therefore low and this is reflected in the low (<15%) carbonate content of the seagrass sediments, as well as the low (<1%) sediment fine (<63 μm size fraction) content. This study suggests that mud-rich sediment facies do not necessarily develop in conjunction with seagrass beds and that mud-poor facies may develop in some seagrass-colonised environments. At these sites (sub-tropical and siliciclastic-sediment dominated) this is suggested to reflect both the low levels of epiphytic and benthic algal carbonate mud production as well as a net outflux of fine-grained sediment due to tidal current-induced sediment resuspension. In keeping with carbonate facies generally there are thus likely to be latitude and environment-related shifts in the composition and character of seagrass related sediment facies.

Age, distribution, and significance within a sediment budget, of in-channel depositional surfaces in the Normanby River, Queensland, Australia

NASA Astrophysics Data System (ADS)

Pietsch, T. J.; Brooks, A. P.; Spencer, J.; Olley, J. M.; Borombovits, D.

2015-06-01

We present the results of investigations into alluvial deposition in the catchment of the Normanby River, which flows into Princess Charlotte Bay (PCB) in the northern part of the Great Barrier Reef Lagoon. Our focus is on the fine fraction (< ~ 63 μm) of alluvial deposits that sit above the sand and gravel bars of the channel floor, but below the expansive flat surface generally referred to as the floodplain. Variously described as benches, bank attached bars or inset or inner floodplains, these more or less flat-lying surfaces within the macro-channel have hitherto received little attention in sediment budgeting models. We use high resolution LiDAR based mapping combined with optical dating of exposures cut into these in-channel deposits to compare their aggradation rates with those found in other depositional zones in the catchment, namely the floodplain and coastal plain. In total 59 single grain OSL dates were produced across 21 stratigraphic profiles at 14 sites distributed though the 24 226 km2 catchment. In-channel storage in these inset features is a significant component of the contemporary fine sediment budget (i.e. recent decades/last century), annually equivalent to more than 50% of the volume entering the channel network from hillslopes and subsoil sources. Therefore, at the very least, in-channel storage of fine material needs to be incorporated into sediment budgeting exercises. Furthermore, deposition within the channel has occurred in multiple locations coincident in time with accelerated sediment production following European settlement. Generally, this has occurred on a subset of the features we have examined here, namely linear bench features low in the channel. This suggests that accelerated aggradation on in-channel depositional surfaces has been in part a response to accelerated erosion within the catchment. The entire contribution of ~ 370 kilotonnes per annum of fine sediment estimated to have been produced by alluvial gully erosion over the last ~ 100 years can be accounted for by that stored as in-channel alluvium. These features therefore can play an important role in mitigating the impact on the receiving water of accelerated erosion.

NEW TOOLS FOR STREAM MORPHO-DYNAMIC MODELING (Invited)

NASA Astrophysics Data System (ADS)

Tonina, D.; McKean, J. A.; Maturana, O. R.; Luce, C.; Buffington, J. M.

2009-12-01

Morphological evolution of streambeds and sediment transport in streams has been typically studied in long reaches using one-dimensional models, due partly to the lack of accurate and easy-to-acquire river bathymetry. The Experimental Advanced Airborne Research Lidar (EAARL) allows simultaneous surveying in both aquatic and terrestrial domains quickly and remotely. However, its usefulness to define boundary conditions for morpho-dynamic models has not yet been tested. We first evaluated EAARL accuracy and then used the data to model fine sediment transport in gravel bed rivers. A random vertical error, modeled as a Normal distribution with zero mean and 10 cm standard deviation, was introduced to bathymetric point cloud data in an EAARL survey. Comparison of water elevations and velocity and shear stress distributions among simulations with and without these random bathymetric errors showed little effect on model predictions. This result allowed us to use EAARL data to model the effects of chronic and acute loads of fine-grained sediment on riverine ecosystems, river morphology, and bed evolution. The simulations were done with the Multidimensional Surface Water Model System (MD-SWMS, USGS). We added a new sand conservation model and the two-class sediment transport equation of Wilcock and Kenworthy [2002, WRR] to MD-SWMS. Simulations show patterns of fine sediment transport and deposition along meandering and straight stream reaches, and the impact of sudden inputs of fine sediment on salmonid spawning sites. Initial results illustrate the sensitivity of sand transport to flow characteristics. At a base flow of 1 m3/sec, sand moves only a few tens-of-meters from the point source during a 4-month model period. Over the same time interval a constant bankfull flow of 6 m3/sec removes all of the sand from the source area; the sand migrates in distinct waves through the 0.5 km-long model reach and we predict all salmon spawning sites in the reach would be contaminated with sand. Chronic inputs, which may come from human activities, seem to have a more persistent impact on streambed habitat quality than pulsed inputs, which may stem from wild fires and other natural disturbances.

Runoff of particle bound pollutants from urban impervious surfaces studied by analysis of sediments from stormwater traps.

PubMed

Jartun, Morten; Ottesen, Rolf Tore; Steinnes, Eiliv; Volden, Tore

2008-06-25

Runoff sediments from 68 small stormwater traps around the harbor of urban Bergen, Norway, were sampled and the concentrations of polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), heavy metals, and total organic carbon (TOC) were determined in addition to grain size. Our study provides empirical data from a large area in the interface between the urban and marine environment, studying the active transport of pollutants from land-based sources. The results of the analyses clearly demonstrate the importance of the urban environment representing a variety of contamination sources, and that stormwater runoff is an important dispersion mechanism of toxic pollutants. The concentrations of different pollutants in urban runoff sediments show that there are several active pollution sources supplying the sewage systems with PCBs, PAHs and heavy metals such as lead (Pb), zinc (Zn) and cadmium (Cd). The concentration of PCB7 in the urban runoff sediments ranged between < 0.0004 and 0.704 mg/kg. For PAH16, the concentration range was < 0.2-80 mg/kg, whereas the concentration ranges of Pb, Zn and Cd were 9-675, 51.3-4670 and 0.02-11.1 mg/kg respectively. Grain size distribution in 21 selected samples varied from a median particle diameter of 13 to 646 microm. However, several samples had very fine-grained particles even up to the 90 percentile of the samples, making them available for stormwater dispersion in suspended form. The sampling approach proposed in this paper will provide environmental authorities with a useful tool to examine ongoing urban contamination of harbors and similar recipients.

Iron and nutrient content of wind-erodible sediment in the ephemeral river valleys of Namibia

NASA Astrophysics Data System (ADS)

Dansie, A. P.; Wiggs, G. F. S.; Thomas, D. S. G.

2017-08-01

Research concerning the global distribution of aeolian dust sources has principally focussed on salt/clay pan and desiccated lacustrine emission areas. In southern Africa such sources are identified as Etosha Pan in northern Namibia and Makgadikgadi Pans in northern Botswana. Dust emitting from ephemeral river valleys, however, has been largely overlooked. Rivers are known nutrient transport pathways and the flooding regimes of ephemeral river valleys frequently replenish stores of fine sediment which, on drying, can become susceptible to aeolian erosion. Such airborne sediment may be nutrient rich and thus be significant for the fertilisation of marine waters once deposited. This study investigates the dust source sediments from three ephemeral river valleys in Namibia in terms of their particle size distribution and their concentrations of bioavailable N, P and Fe. We compare the nutrient content of these sediments from the ephemeral river valleys to those collected from Etosha and Makgadikgadi Pans and consider their relative ocean fertilising potential. Our results show that the ephemeral river valleys contain fine grained sediment similar in physical character to Etosha and Makgadikgadi Pans yet they have up to 43 times greater concentrations of bioavailable iron and enriched N and P macronutrients that are each important for ocean fertilisation. The known dust-emitting river valleys of Namibia may therefore be contributing a greater fertilisation role in the adjacent marine system than previously considered, and not-yet investigated. Given this finding a re-assessment of the potential role of ephemeral river valleys in providing nutrient-rich sediment into the aeolian and marine systems in other dryland areas is necessary.

Impact of laver treatment practices on the geoenvironmental properties of sediments in the Ariake Sea.

PubMed

Du, Yan Jun; Hayashi, Shigenori; Shen, Shui-Long

2014-04-15

Since the 1970s, the catch of Tairagi and Agemaki shellfish that inhabit the shallow sediments of the Ariake Sea of Japan has fallen dramatically. This is partly accounted for by the Isahaya land reclamation dike project and by the increasingly frequent local red tides. A recent survey of local fisherman suggested that the decline in the shellfish harvest may also be due to the practice of laver treatment in the tidal flats of the Ariake Sea. We carried out field and laboratory investigations to determine whether the practice changes the geoenvironmental properties of the fine-grained sediments in the tidal flats. There were notable changes in the salt concentration, pH, and sulfide content between the sediments exposed to a laver treating agent and those without laver treatment. Based on these differences, we identified potential mechanisms by which the laver treating agent was transported into the sediments and influenced the sulfide levels. Copyright © 2014 Elsevier Ltd. All rights reserved.

The persistence and character of stranded oil on coarse-sediment beaches.

PubMed

Owens, Edward H; Taylor, Elliott; Humphrey, Blair

2008-01-01

Small amounts of oil that can persist for decades in the intertidal zone of coarse-sediment beaches have been documented in a few well-studied cases. Oil that survives attenuation over the short-term (weeks to months) will persist until there is a change in the environmental conditions, as might occur where there is a seasonal storm-wave climate or as a beach undergoes long-term (erosional) changes. Oil residues can persist on the beach surface as tar mats, asphalt-like pavements, or as veneers on sediment particles or hard surfaces. Subsurface oil residues can persist in similar forms or as fill or partial fill of the pore spaces between coarse-sediment particles. Oil penetrates until it reaches fine-grained sediment, the water table, bedrock, or other penetration-limiting layers. Amounts of persistent oil are very small fractions of the volumes that were originally stranded and these protected residues can continue to biodegrade as they become thinner and more discontinuous.

Suspended Sediment Load and Sediment Yield During Floods and Snowmelt Runoff In The Rio Cordon (northeastern Italy)

NASA Astrophysics Data System (ADS)

Lenzi, M. A.

Suspended sediment transport in high mountain streams display a grater time-space variability and a shorter duration (normally concentrated during the snowmelt period and the duration time of single floods) than in larger lowland rivers. Suspended sedi- ment load and sediment yield were analysed in a small, high-gradient stream of East- ern Italian Alps which was instrumented to measure in continuous water discharge and sediment transport. The research was conducted in the Rio Cordon, a 5 Km2 small catchment of the Dolomites. The ratio of suspended to total sediment yield and the re- lations between sediment concentration and water discharge were analysed for eleven floods which occurred from 1991 to 2001. Different patterns of hysteresis in the re- lation between suspended sediment and discharge were related to types and locations of active sediment sources. The within-storm variation of particle size of suspended sediment during a mayor flood (September 1994, 30 years

Comparison of the physical and geotechnical properties of gas-hydrate-bearing sediments from offshore India and other gas-hydrate-reservoir systems

USGS Publications Warehouse

Winters, William J.; Wilcox-Cline, R.W.; Long, P.; Dewri, S.K.; Kumar, P.; Stern, Laura A.; Kerr, Laura A.

2014-01-01

The sediment characteristics of hydrate-bearing reservoirs profoundly affect the formation, distribution, and morphology of gas hydrate. The presence and type of gas, porewater chemistry, fluid migration, and subbottom temperature may govern the hydrate formation process, but it is the host sediment that commonly dictates final hydrate habit, and whether hydrate may be economically developed.In this paper, the physical properties of hydrate-bearing regions offshore eastern India (Krishna-Godavari and Mahanadi Basins) and the Andaman Islands, determined from Expedition NGHP-01 cores, are compared to each other, well logs, and published results of other hydrate reservoirs. Properties from the hydrate-free Kerala-Konkan basin off the west coast of India are also presented. Coarser-grained reservoirs (permafrost-related and marine) may contain high gas-hydrate-pore saturations, while finer-grained reservoirs may contain low-saturation disseminated or more complex gas-hydrates, including nodules, layers, and high-angle planar and rotational veins. However, even in these fine-grained sediments, gas hydrate preferentially forms in coarser sediment or fractures, when present. The presence of hydrate in conjunction with other geologic processes may be responsible for sediment porosity being nearly uniform for almost 500 m off the Andaman Islands.Properties of individual NGHP-01 wells and regional trends are discussed in detail. However, comparison of marine and permafrost-related Arctic reservoirs provides insight into the inter-relationships and common traits between physical properties and the morphology of gas-hydrate reservoirs regardless of location. Extrapolation of properties from one location to another also enhances our understanding of gas-hydrate reservoir systems. Grain size and porosity effects on permeability are critical, both locally to trap gas and regionally to provide fluid flow to hydrate reservoirs. Index properties corroborate more advanced consolidation and triaxial strength test results and can be used for predicting behavior in other NGHP-01 regions. Pseudo-overconsolidation is present near the seafloor and is underlain by underconsolidation at depth at some NGHP-01 locations.

Spatial Statistics of Deep-Water Ambient Noise; Dispersion Relations for Sound Waves and Shear Waves

DTIC Science & Technology

2015-09-30

propagation in very fine-grained sediments (silt and clay ). OBJECTIVES 1) The scientific objective of the deep-water ambient noise research is to...forces in silts and clays and the role they play in controlling wave speeds and attenuations. On a 2 quantum mechanical level, these forces are... clays . APPROACH 1) Deep-water ambient noise Three deep-diving, autonomous instrument platforms, known as Deep Sound I, II, & III, have been

Terrestrial Analogs for Clay Minerals at Yellowknife Bay, Gale Crater, Mars

NASA Technical Reports Server (NTRS)

Treiman, Allan H; Morris, Richard V.; Bristow, Thomas; Ming, Douglas W.; Achillies, Cherie; Bish, David L.; Blake, David; Vaniman, David; Chipera, Steve

2013-01-01

Sediments of the Sheepbed unit, Gale Crater, were analyzed by the CheMin X-ray diffraction instrument on the Curiosity Rover. The sediments consist of typical basalt minerals (Fe-forsterite, augite, pigeonite, plagioclase), as well as Fe oxide/hydroxides, Fesulfides, amorphous material, and a phyllosilicate. The phyllosilicate has a broad 001 peak at approx 1.0 nm, consistent with a poorly ordered smectite. However, in the absence of diagnostic tests possible on Earth, its identity is not clear. The position of the 06L diffraction band is generally used to distinguish dioctahedral from trioctahedral smectite, but it is beyond CheMin's range of 2 Theta. The measured position of the 02L diffraction band (approx 22.5deg 2 Theta by CheMin), implies that the smectite is trioctahedral. The exact position and shape of the 02L band is determined by the cations in the 'M' sites of the smectite; to constrain those cations, we sought analogs among terrestrial smectites, emphasizing those developed from basaltic precursors. A potential analog for the Sheepbed smectite is 'griffithite,' a variety of trioctahedral smectite in altered basalt of the Topanga formation, Griffith Park, Los Angeles. 'Griffithite' has an 02L diffraction band that is close in position and shape to that of the Sheepbed smectite, although 'griffithite' has a very sharp 001 peak, indicating a high degree of layer ordering not seen in the Sheepbed smectite. A typical chemical formula for 'griffithite,' determined by electron microprobe, is (Ca0.59 Na0.03) (Mg4.28 Fe1.83) (Si6.64 Al1.36) O20 (OH)4, normalized to Si+Al=8. This formula is consistent with a fully trioctahedral Fe-Mg smectite with Ca and Na as interlayer cations. In the Topanga basalt, four types of 'griffithite' are present: fine-grained, filling cracks and vesicles; coarse-grained, filling vesicles; coarse-grained, replacing olivine phenocrysts; and coarse-grained, replacing glassy mesostasis. The fine-grained 'griffithite' formed first, and the last three varieties may be contemporaneous. One sample shows agate (alpha- quartz) that was precipitated between the episodes of deposition of the fine-grained and coarse-grained 'griffithite.' 'Griffithite' is not unique as a possible terrestrial analog - some clay minerals from the Doushantou formation, China, have similar 02L diffraction bands, and many basalts contain smectites in vesicles and as replacements after olivine. Similar trioctahedral smectites occur also in the nakhlite martian meteorites - as veinlets and replacements of olivine. By understanding the formation of these terrestrial clays, we hope to constrain the nature and mechanism of formation of the Sheepbed clay mineral.

Measuring the fraction of pool volume filled with fine sediment

Treesearch

Sue Hilton; Thomas E. Lisle

1993-01-01

The fraction of pool volume filled with fine sediment (usually fine sand to medium gravel) can be a useful index of the sediment supply and substrate habitat of gravel-bed channels. It can be used to evaluate and monitor channel condition and to detect and evaluate sediment sources. This fraction (V*) is the ratio of fine-sediment volume to pool water volume plus fine-...

Structural and Stratigraphic Controls on Methane Hydrate occurrence and distribution: Gulf of Mexico, Walker Ridge 313 and Green Canyon 955: Final Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jaiswal, Priyank

The goal of this project was to determine structural and stratigraphic controls on hydrate occurrence and distribution in Green Canyon (GC) 955 and Walker Ridge (WR) 313 blocks using seismic and well data. Gas hydrate was discovered in these blocks in coarse- and fine-grained sediments during the 2009 Joint Industrial project (JIP) Leg 11 drilling expedition. Although the immediate interest of the exploration community is exclusively hydrate which is present in coarse–grained sediments, factors that control hydrate and free gas distribution in the two blocks and whether coarse and fine-grained hydrate-bearing units are related in any manner, formed the coremore » of this research. The project spanned from 10/01/2012 to 07/31/2016. In the project, in both the leased blocks, the interval spanning the gas hydrate stability zone (GHSZ) was characterized using a joint analysis of sparse Ocean Bottom Seismic (OBS) and dense, surface–towed multichannel seismic (MCS) data. The project team had the luxury of calibrating their results with two well logs. Advance processing methods such as depth migration and full-waveform inversion (FWI) were used for seismic data analysis. Hydrate quantification was achieved through interpretation of the FWI velocity field using appropriate rock physics models at both blocks. The seismic modeling/inversion methodology (common to both GC955 and WR313 blocks) was as follows. First, the MCS data were depth migrated using a P-wave velocity (VP) model constructed using inversion of reflection arrival times of a few (four in both cases) key horizons carefully picked in the OBS data to farthest possible offsets. Then, the resolution of the traveltime VP model was improved to wavelength scale by inverting OBS gathers up to the highest frequency possible (21.75 Hz for GC955 and 17.5 for WR313) using FWI. Finally, the hydrate saturation (or the volume fraction) was estimated at the well location assuming one of the other hydrate morphology (filling the primary or the secondary porosity) was extrapolated out from the wells using the FWI VP as a guide. General outcomes were as follows. First and foremost, an imaging methodology using sparse seismic data, which is easily replicable at other sites with similar datasets, has been demonstrated. The end product of this methodology at both the leased blocks is quantitative estimates of hydrate distribution. Second, at both locations there is strong evidence that the base of the GHSZ, which does not appear as a clear Bottom Simulating Reflection (BSR), manifests in the VP perturbations created by FWI, suggesting that FWI is sensitive to subtle compositional changes in shallow sediments and establishes it as a valuable tool for investigations of hydrate-bearing basins. Third, through joint interpretation of the depth migrated image and the FWI VP model, how structure and stratigraphy jointly determine hydrate and free gas distribution in both blocks could be clearly visualized. The joint interpretation also suggests that the coarse and fine grained hydrate-bearing sediments at both leased are connected. Site specific results, in addition to general results, are as follows. At GC955 the overlying fine-grained hydrate-bearing unit could have been sourced from the underlying hydrate coarse-grained channel-levee complex through a chimney feature. The channel-levee system at GC955 is compartmentalized by faults, of which only a few may be impermeable. Although compartmentalized, the channel-levee system in the GC955 as a whole might be in communication except selected zones. At WR313 the overlying fine-grained fracture-filled hydrate unit appears to be sourced from below the GHSZ. The reason that only a particular fine-grained unit has hydrate, despite having lower porosity that the bounding units, could be the presence of secondary porosity (such as those formed from clay dewatering under compaction). In conclusion, the project was a pioneering effort in in joint analysis of OBS and MCS datasets for advancing the knowledge about a hydrate and free–gas system dynamics using advanced processing methods such as FWI and depth migration. Results obtained in this project can greatly advance the tools and techniques used for delineating specific hydrate prospects. Results obtained in this project can also be seamlessly incorporated into other DOE funded project on modeling the potential productivity and commercial viability of hydrate from sand-dominated reservoirs. The OBS and MCS data in this project were acquired in 2012 (after the JIP II drilling) by the USGS and therefore the results are a posteriori. Nonetheless, the seismic inversion workflow established through this project can be used to generate various what-if quantification scenarios even in absence of logs and serve as a valuable tool for guiding drilling operations. Results from this project can augment other DOE sponsored projects on determining the commercial viability of methane production from the Gulf of Mexico.« less

Sediment texture and metal contamination in the Venice Lagoon (Italy): A snapshot before the installation of the MOSE system

NASA Astrophysics Data System (ADS)

Zonta, Roberto; Botter, Margherita; Cassin, Daniele; Bellucci, Luca Giorgio; Pini, Roberto; Dominik, Janusz

2018-05-01

Sediments of the Venice Lagoon down to 50 cm depth were investigated to assess sediment texture and metal contamination status, before the construction and activation of the MOSE system, which is intended to prevent the periodical flood events affecting the lagoon and the city of Venice. 380 cores were collected in shallow-water areas of the lagoon, and analysed along their vertical profile to determine grain-size distribution and concentrations of some major and trace elements (Al, As, Cr, Cu, Fe, Hg, Mn, Ni, Pb and Zn), total carbon and organic carbon. Radionuclide analyses (137Cs, 210Pb) were performed on 15 cores in an attempt to establish sediment chronology and determine radionuclide inventories in erosional and depositional areas. On the whole-lagoon scale, strong depletion of particles <31 μm in diameter (from medium silt to clay fractions) was observed in sediments down to 10 cm depth in comparison to deeper layers. This depletion characterised both erosional and depositional areas, and may be caused by increased water dynamics and resuspension of sediment due to anthropogenic activities. The apparent sediment accumulation rate determined with 210Pbxs in depositional areas was estimated at 0.2-0.4 cm y-1. In the majority of cores, 210Pbxs inventories were lower than expected from atmospheric fallout, suggesting its export along with fine particles. The different sediment characteristics in terms of grain-size distribution and organic carbon content observed in the upper layer with respect to the deeper ones reflect the modification of the sedimentary balance in recent years. The loss of fine particles, even from sediments in depositional areas of the northern part of the lagoon, may herald changes in local sediment texture leading to a further depletion of morphodiversity, which in turn may lead to the reduction or loss of important lagoon habitats. On the whole-lagoon scale, the prevalently lithogenic elements (Al, As, Cr, Fe, Mn, Ni) decreased towards the top of the cores, reflecting the depletion of fine particles in the upper sediment layer due to winnowing in non-confined lagoon areas. In contrast, partly anthropogenic elements (Cu, Hg, Pb, Zn) increased up to the subsurface sediment layers (5-10 and/or 10-20 cm) as an effect of increasing pollutant inputs until a certain time in the past. Enrichment Factors (EF) were calculated from 9 cores, comparing concentrations in the "pre-industrial" (>100 years ago) and recent (surface layer, 0-5 cm) sediments. The mostly lithogenic elements were not enriched (EF ˜ 1), whereas the partly anthropogenic elements showed slight (Cu and Pb, EF ˜ 1.2) to significant (Hg and Zn, EF ˜ 2) enrichment. The shallow waters on the landward side (particularly close to freshwater inputs), the area nearby the industrial district of Porto Marghera and a small zone adjacent to the city of Chioggia were identified as the main pollutant accumulation sites. Mercury was the only element potentially harmful for aquatic life. Its concentration in the biologically active surface sediment layer (0-5 cm) exceeded the NOAA Effects Range-Median (ERM) value in 27% of samples, corresponding to 20% of the shallow-water surface area. The collected data set represents a valuable reference for monitoring the impact of the construction and operation of the MOSE system on the sediment features of the Venice Lagoon.

Offshore gas hydrate sample database with an overview and preliminary analysis

USGS Publications Warehouse

Booth, James S.; Rowe, Mary M.; Fisher, Kathleen M.

1996-01-01

Synopsis -- A database of offshore gas hydrate samples was constructed from published observations and measurements. More than 90 samples from 15 distinct regions are represented in 13 data categories. This database has permitted preliminary description of gas hydrate (chiefly methane hydrate) tendencies and associations with respect to their geological environment. Gas hydrates have been recovered from offshore sediment worldwide and from total depths (water depth plus subseabed depth) ranging from 500 m to nearly 6,000 m. Samples have come from subbottom depths ranging from 0 to 400 m. Various physiographic provinces are represented in the data set including second order landforms such as continental margins and deep-sea trenches, and third order forms such as submarine canyons, continental slopes, continental margin ridges and intraslope basins. There is a clear association between fault zones and other manifestations of local, tectonic-related processes, and hydrate-bearing sediment. Samples of gas hydrate frequently consist of individual grains or particles. These types of hydrates are often further described as inclusions or disseminated in the sediment. Moreover, hydrates occur as a cement, as nodules, or as layers (mostly laminae) or in veins. The preponderance of hydrates that could be characterized as 2- dimensional (planar) were associated with fine sediment, either as intercalated layers or in fractures. Hydrate cements were commonly associated with coarser sediment. Hydrates have been found in association with grain sizes ranging from clay through gravel. More hydrates are associated with the more abundant finer-grained sediment than with coarser sediment, and many were discovered in the presence of both fine (silt and clay) and coarse sediment. The thickness of hydrate zones (i. e., sections of hydrate-bearing sediment) varies from a few centimeters to as much as 30 m. In contrast, the thickness of layers of pure hydrate or the dimensions of individual hydrate grains were most often characterized in terms of millimeters or centimeters, although a pure hydrate layer discovered in the Middle America Trench off Guatemala was as much as 3-4-m-thick. The data suggest that grains, or thin veins or laminae of pure gas hydrate may be ubiquitous in many hydrate zones but that typically they may only comprise a minor component of the thicker zones. In more than 80 percent of the hydrate samples the methane was of biogenic origin. The methane in the remainder was either classified as (or may be at least part) thermogenic. Each site where thermogenic gas was identified is characterized by faults or other manifestions of a dynamic geological environment (e.g., diapirs, mud volcanoes, gas seeps). Every sample in the database came from within the zone of theoretical methane hydrate stability, as determined on the basis of assumed regional pressure and temperature gradients. Most show that they were situated --- expressed in terms of depth --- well above the phase boundary and about 70% of the samples were located more than 100 m above the assumed regional position of that boundary. The calculated subseabed positions of the phase boundaries and the BSRs (bottom simulating reflector) are essentially identical. This may be taken as general corroboration of the regional phase boundary calculations and the concept of the BSR. Three provocative aspects of marine gas hydrates have been disclosed by the database: gas hydrates are frequently situated at much shallower subseabed depths than the assumed contemporary position of the regional phase boundary hydrates are often found in areas typified by faults or other indicators of a dynamic geological environment zones of gas hydrate-bearing sediment tend to be tens of centimeters to tens of meters thick but the hydrate within the thicker zones tends to be only a minor constituent. Whether existing as dispersed particles, cements, or pure layers or vein

Suspended sediments of the modern Amazon and Orinoco rivers

USGS Publications Warehouse

Meade, R.H.

1994-01-01

The Amazon and Orinoco Rivers are massive transcontinental conveyance systems for suspended sediment. They derive about 90% of their sediment from the Andes that support their western headwaters, transport it for thousands of kilometers across the breadth of the continent and deposit it in the coastal zones of the Atlantic. At their points of maximum suspended-sediment discharge, the Amazon transports an average of 1100-1300 ?? 106 tons per year and the Orinoco transports about 150 ?? 106 tons per year. Relations of sediment discharge to water discharge are complicated by unusual patterns of seasonal storage and remobilization, increased storage and reduced transport of sediment in the middle Orinoco during periods of peak water discharge, and storage of suspended sediment in the lower Amazon during rising discharge and resuspension during falling discharge. Spatial distributions of suspended sediment in cross-sections of both rivers are typically heterogeneous, not only in the vertical sense but also in the lateral. The cross-channel mixing of tributary inputs into the mainstem waters is a slow process that requires several hundred kilometers of downriver transport to complete. Considerable fine-grained sediment is exchanged between rivers and floodplains by the combination of overbank deposition and bank erosion. ?? 1994.

In-stream wetlands and their significance for channel filling and the catchment sediment budget, Jugiong Creek, New South Wales

NASA Astrophysics Data System (ADS)

Zierholz, C.; Prosser, I. P.; Fogarty, P. J.; Rustomji, P.

2001-06-01

Evidence is presented here of recent and extensive infilling of the incised channel network of the Jugiong Creek catchment, SE Australia. The present channel network resulted from widespread stream and gully incision in the period between 1880 and 1920. Our survey shows that gully floors have been colonised extensively by emergent macrophyte vegetation since before 1944, forming continuous, dense, in-stream wetlands, which now cover 25% of the channel network in the 2175 km 2 catchment and have so far trapped almost 2,000,000 t of nutrient-enriched, fine sediments. This mass of sediments represents the equivalent of 4.7 years of annual sediment production across the catchment and in some tributaries, more than 20 years of annual yield is stored within in-stream wetlands. Previous work on the late Quaternary stratigraphy of the region has shown that there were repeated phases of channel incision in the past following which the channels quickly stabilised by natural means and then filled with fine-grained sediment to the point of channel extinction, creating unchannelled swampy valley floors. The current formation and spread of in-stream wetlands is interpreted to be the onset of the next infill phase but it is not known whether present conditions will allow complete channel filling and reformation of the pre-existing swampy valley floors. Nevertheless, further spread of in-stream wetlands is likely to increase the sediment trapping capacity and further reduce the discharge of sediments and nutrients into the Murrumbidgee River. The in-stream wetlands may provide a significant capacity to buffer erosion from gullied catchments of considerable size (up to 300 km 2) as an adjunct to current riparian management options. They may also assist the recovery of sediment-impacted channels downstream.

Greigite as a marker of paleo sulphate methane transition zone (SMTZ) in cold seep environment of Krishna-Godavari (KG) Basin, Bay of Bengal, India.

NASA Astrophysics Data System (ADS)

B, F. K.; Dewangan, P.; Usapkar, A.; Mazumdar, A.; Kocherla, M.; Tammisetti, R.; Khalap, S. T.; Satelkar, N. P.; Mehrtens, T.; Rosenauer, A.

2014-12-01

Rockmagnetic results and electron microscopic observations on a sediment core retrieved from a proven cold seep environment of Krishna-Godavari (KG) Basin revealed an anomalously magnetically enhanced zone (17 - 23 mbsf) below the present-day SMTZ in the KG offshore basin. This zone is characterized by higher SIRM / k, kARM / SIRM and kfd % values indicating the presence of fine grained superparamagnetic (SP) sized ferrimagnetic iron sulphides minerals such as greigite formed due to anaerobic oxidation of methane (AOM). Identification of such mineral phases and understanding the mechanism of their formation and preservation is of vital importance which could provide better understanding of the geochemical processes on the paleo - SMTZ. Magnetic concentrates extracted from this zone were characterised by transmission electron microscopy and energy dispersive X- ray spectrometry. We observed two possible occurrences of magnetic phases within this sediment depths 17 - 23 mbsf. (a) authigenically formed SP sized ferrimagnetic inclusions of magnetite, pyrite and greigite within matrix of host siliceous grain, (b) poorly crystallized fine-grained magnetite with ill defined grain boundary possibily formed extracellulary by magnetotactic bacterias through biologically-induced mineralization. High methane fluxes as observed in this basin provides suitable environment for the formation of greigite in the vicinity of SMTZ. We hypothesize that due to availability of residual iron and low supply of hydrogen sulphide caused by downwards diffusion lead to preservation of greigite. The occurence of greigite as inclusion within the host silicate matrix might explain its preservation in this zone in spite of intense pyritization. The greigite would otherwise be converted to stable-form pyrite. It is challenging to explain the origin of biologically produced magnetite within 17 - 23 mbsf as it is expected to dissolve in this zone due to intense pyritization.

Primary factors affecting water quality and quantity in four watersheds in Eastern Puerto Rico

USGS Publications Warehouse

Murphy, Sheila F.; Stallard, Robert F.

2009-01-01

As part of the U.S. Geological Survey (USGS) Water, Energy, and Biogeochemical Budgets (WEBB) program, four small watersheds in eastern Puerto Rico were monitored to identify and evaluate the effects of geology, landcover, atmospheric deposition, and other factors on stream water quality and quantity. Two catchments are located on coarse-grained granitic plutonic rocks, which weather to quartz- and clay-rich, sandy soils, and two are located on fine-grained volcanic rocks and volcaniclastic sediments, which weather to quartz-poor, fine-grained soils. These differing soil materials result in different hydrologic regimes. Soils on the granitic rocks have greater permeability than those developed on the volcaniclastic rocks, allowing more water infiltration and potentially greater landslide erosion rates. For each bedrock type, one catchment was covered with mature rainforest, and the other catchment was affected by agricultural practices typical of eastern Puerto Rico. These practices led to the erosion of much of the original surface soil in the agricultural watersheds, which introduced large quantities of sediment to stream channels. The agricultural watersheds are undergoing natural reforestation, like much of Puerto Rico. Eastern Puerto Rico receives large atmospheric inputs of marine salts, pollutants from the Northern Hemisphere, and Saharan Desert dust. Marine salts contribute over 80 percent of the ionic charge in precipitation, with peak inputs in January. Intense storms, mostly hurricanes, are associated with exceptionally high chloride concentrations in stream waters. Temperate pollution contributes nitrate, ammonia, and sulfate, with maximum inputs during northern cold fronts in January, April, and May. Pollution inputs have increased through time. Desert dust peaks in June and July, during times of maximum dust transport from the Saharan Desert across the Atlantic Ocean.

Contourite drifts on early passive margins as an indicator of established lithospheric breakup

NASA Astrophysics Data System (ADS)

Soares, Duarte M.; Alves, Tiago M.; Terrinha, Pedro

2014-09-01

The Albian-Cenomanian breakup sequence (BS) offshore Northwest Iberia is mapped, described and characterised for the first time in terms of its seismic and depositional facies. The interpreted dataset comprises a large grid of regional (2D) seismic-reflection profiles, complemented by Industry and ODP/DSDP borehole data. Within the BS are observed distinct seismic facies that reflect the presence of: (a) black shales and fine-grained turbidites, (b) mass-transport deposits (MTDs) and coarse-grained turbidites, and (c) contourite drifts. Borehole data show that these depositional systems developed as mixed carbonate-siliciclastic sediments proximally, and as organic-carbon-rich mudstones (black shales) distally on the Northwest Iberia margin. MTDs and turbidites tend to occur on the continental slope, frequently in association with large-scale olistostromes. Distally, these change into interbedded fine-grained turbidites and black shales showing widespread evidence of deep-water current activity towards the top of the BS. Current activity is expressed by intra-BS erosional surfaces and sediment drifts. The results in this paper are important as they demonstrate that contourite drifts are ubiquitous features in the study area after Aptian-Albian lithospheric breakup. Therefore, we interpret the recognition of contourite drifts in Northwest Iberia as having significant palaeogeographic implications. Contourite drifts materialise the onset of important deep-water circulation marking the establishment of oceanic gateways between two fully separated continental margins. As a corollary, we postulate the generation of deep-water geostrophic currents to have had significant impact on North Atlantic climate and ocean circulation during the Albian-Cenomanian, with the record of such impacts being preserved in the contourite drifts analysed in this work.

Rocky Mountain Tertiary coal-basin models and their applicability to some world basins

USGS Publications Warehouse

Flores, R.M.

1989-01-01

Tertiary intermontane basins in the Rocky Mountain region of the United States contain large amounts of coal resources. The first major type of Tertiary coal basin is closed and lake-dominated, either mud-rich (e.g., North Park Basin, Colorado) or mud plus carbonate (e.g., Medicine Lodge Basin, Montana), which are both infilled by deltas. The second major type of Tertiary coal basin is open and characterized by a preponderance of sediments that were deposited by flow-through fluvial systems (e.g., Raton Basin, Colorado and New Mexico, and Powder River Basin, Wyoming and Montana). The setting for the formation of these coals varies with the type of basin sedimentation, paleotectonism, and paleoclimate. The mud-rich lake-dominated closed basin (transpressional paleotectonism and warm, humid paleoclimate), where infilled by sandy "Gilbert-type" deltas, contains thick coals (low ash and low sulfur) formed in swamps of the prograding fluvial systems. The mud- and carbonate-rich lake-dominated closed basin is infilled by carbonate precipitates plus coarse-grained fan deltas and fine-grained deltas. Here, thin coals (high ash and high sulfur) formed in swamps of the fine-grained deltas. The coarse-clastic, open basins (compressional paleotectonism and warm, paratropical paleoclimate) associated with flow-through fluvial systems contain moderately to anomalously thick coals (high to low ash and low sulfur) formed in swamps developed in intermittently abandoned portions of the fluvial systems. These coal development patterns from the Tertiary Rocky Mountain basins, although occurring in completely different paleotectonic settings, are similar to that found in the Tertiary, Cretaceous, and Permian intermontane coal basins in China, New Zealand, and India. ?? 1989.

Temporal and spatial variability of the sediment grain-size distribution on the Eel shelf: The flood layer of 1995

USGS Publications Warehouse

Drake, D.E.

1999-01-01

Sediment grain-size characteristics observed on the Eel shelf have been analyzed using a wet-sieving technique that minimizes breakage of aggregates. At several sites on the 70-m isobath north of the river, where a 1995 flood layer attained a maximum thickness of about 9 cm, replicate box cores were collected on seven cruises during February 1995 to January 1997. These samples provide a unique opportunity to follow the evolution of a flood layer over a two-year period as it was modified and gradually buried. One month after the flood, a layer of tan-colored, high-porosity sediment with up to 96% of its particles in the size range of 0-20 ??m had accumulated on the central part of the shelf, 7-30 km north of the river and principally between the 50-m and 90-m isobaths. Substantial coarsening of this layer occurred between February 1995 and May 1995, particularly along the southern and the landward edge of the deposit in water depths of <70 m. The early stage of coarsening was probably caused by physical reworking of the surface 0.5-cm of the deposit and by addition of new sediment from shallower regions of the shelf. Temporal changes in inventories of several grain-size fractions show that physical processes continued to add coarse sediment to the flood layer after May 1995, but the large increases in thickness of the surface mixed layer could only be attributed to bioturbation by a recovering, or seasonally fluctuating, benthic community. The 1995 flood layer has evolved from exhibiting limited variability and normal grading (i:e., upward fining) to a layer that (1) shows significant spatial variability on scales from centimeters to 10's of meters, (2) is substantially coarser owing to additions of sediment from the inner shelf, (3) is inversely graded (i.e., coarsens upward), and (4) is intensely bioturbated to depths of 4-5 cm.

Gas Hydrate Petroleum System Analysis

NASA Astrophysics Data System (ADS)

Collett, T. S.

2012-12-01

In a gas hydrate petroleum system, the individual factors that contribute to the formation of gas hydrate accumulations, such as (1) gas hydrate pressure-temperature stability conditions, (2) gas source, (3) gas migration, and (4) the growth of the gas hydrate in suitable host sediment can identified and quantified. The study of know and inferred gas hydrate accumulations reveal the occurrence of concentrated gas hydrate is mostly controlled by the presence of fractures and/or coarser grained sediments. Field studies have concluded that hydrate grows preferentially in coarse-grained sediments because lower capillary pressures in these sediments permit the migration of gas and nucleation of hydrate. Due to the relatively distal nature of the deep marine geologic settings, the overall abundance of sand within the shallow geologic section is usually low. However, drilling projects in the offshore of Japan, Korea, and in the Gulf of Mexico has revealed the occurrence of significant hydrate-bearing sand reservoirs. The 1999/2000 Japan Nankai Trough drilling confirmed occurrence of hydrate-bearing sand-rich intervals (interpreted as turbidite fan deposits). Gas hydrate was determined to fill the pore spaces in these deposits, reaching saturations up to 80% in some layers. A multi-well drilling program titled "METI Toaki-oki to Kumano-nada" also identified sand-rich reservoirs with pore-filling hydrate. The recovered hydrate-bearing sand layers were described as very-fine- to fine-grained turbidite sand layers measuring from several centimeters up to a meter thick. However, the gross thickness of the hydrate-bearing sand layers were up to 50 m. In 2010, the Republic of Korea conducted the Second Ulleung Basin Gas Hydrate (UBGH2) Drilling Expedition. Seismic data clearly showed the development of a thick, potential basin wide, sedimentary sections characterized by mostly debris flows. The downhole LWD logs and core data from Site UBGH2-5 reveal that each debris flows is characterized by basal silt- to sand-rich clay dominated stratigraphic units. The upper most debris flow at Site UBGH2-5 extends into the overlying gas hydrate stability zone and IR core scans indicate that this section contains some amount of gas hydrate. The UBGH2 LWD and coring program also confirmed the occurrence of numerous volcaniclastic and siliciclastic sand reservoirs that were deposited as part of local to basin-wide turbidite events. Gas hydrate saturations within the turbidite sands ranged between 60-80 percent. In 2009, the Gulf of Mexico (GOM) Joint Industry Project (JIP) drilled seven wells at three sites, finding gas hydrate at high concentration in sands in four wells, with suspected gas hydrate at low to moderate saturations in two other wells. In the northern GOM, high sedimentation rates in conjunction with salt tectonism, has promoted the formation of complex seafloor topography. As a result, coarse-grained deposition can occur as gravity-driven sedimentation traversing the slope within intra-slope "ponded" accommodation spaces.

Long-term erosion rates of Panamanian drainage basins determined using in situ 10Be

NASA Astrophysics Data System (ADS)

Gonzalez, Veronica Sosa; Bierman, Paul R.; Nichols, Kyle K.; Rood, Dylan H.

2016-12-01

Erosion rates of tropical landscapes are poorly known. Using measurements of in situ-produced 10Be in quartz extracted from river and landslide sediment samples, we calculate long-term erosion rates for many physiographic regions of Panama. We collected river sediment samples from a wide variety of watersheds (n = 35), and then quantified 24 landscape-scale variables (physiographic, climatic, seismic, geologic, and land-use proxies) for each watershed before determining the relationship between these variables and long-term erosion rates using linear regression, multiple regression, and analysis of variance (ANOVA). We also used grain-size-specific 10Be analysis to infer the effect of landslides on the concentration of 10Be in fluvial sediment and thus on erosion rates. Cosmogenic 10Be-inferred, background erosion rates in Panama range from 26 to 595 m My- 1, with an arithmetic average of 201 m My- 1, and an area-weighted average of 144 m My- 1. The strongest and most significant relationship in the dataset was between erosion rate and silicate weathering rate, the mass of material leaving the basin in solution. None of the topographic variables showed a significant relationship with erosion rate at the 95% significance level; we observed weak but significant correlation between erosion rates and several climatic variables related to precipitation and temperature. On average, erosion rates in Panama are higher than other cosmogenically-derived erosion rates in tropical climates including those from Puerto Rico, Madagascar, Australia and Sri Lanka, likely the result of Panama's active tectonic setting and thus high rates of seismicity and uplift. Contemporary sediment yield and cosmogenically-derived erosion rates for three of the rivers we studied are similar, suggesting that human activities are not increasing sediment yield above long-term erosion rate averages in Panama. 10Be concentration is inversely proportional to grain size in landslide and fluvial samples from Panama; finer grain sizes from landslide material have lower 10Be concentration than fine-grained fluvial sediment. Large grains from both landslide and stream sediments have similarly low 10Be concentrations. These data suggest that fluvial gravel is delivered to the channel by landslides whereas sand is preferentially delivered by soil creep and bank collapse. Furthermore, the difference in 10Be concentration in sand-sized material delivered by soil creep and that delivered by landsliding suggests that the frequency and intensity of landslides influence basin scale erosion rates.

Advances in Holocene mountain geomorphology inspired by sediment budget methodology

NASA Astrophysics Data System (ADS)

Slaymaker, Olav; Souch, Catherine; Menounos, Brian; Filippelli, Gabriel

2003-09-01

The sediment budget, which links sediment sources to sediment sinks with hydroclimatic and weathering processes mediating the response, is applied to the analysis of sediments in three alpine lakes in British Columbia. We provide two ways of using the sediment budget as an integrating device in the interpretation of mountain geomorphology. These approaches differ in their resolution and ability to budget the major components of the fine-sediment cascade in glaciated environments. Taken together, they provide an integrated index of landscape change over the Holocene. The first example compares the hydroclimatic controls of lake sedimentation for the last 600 years (A.D. 1370-1998) preserved in varved sediments from two of the lake basins. This hydroclimatological approach incorporates contemporary monitoring, air photo analysis, and detailed stratigraphy of sedimentation events within a single varve to infer the timing, sources, and preferred pathways of fine-grained sediments reaching the lake basins. The results indicate that glaciers, hillslope, and channel instability within the major subbasins are the principal sediment sources to the lake basins. Transitory sediment storage of glacially derived sediments within the channels is believed to modulate the episodic and more frequent delivery of sediments from adjacent hillslope and fluvial storage sites and direct routing of glacial rock flour during years of prolonged glacial melt. The second example, relying on the phosphorus geochemistry of sediments in an alpine lake basin, considers the evolution of phosphorus forms (from mineral to occluded and organic fractions) as a function of the soil development, inherent slope instability, and repeated cycles of glaciation and neoglaciation over the Holocene. This geochemical approach demonstrates that both neoglaciation and full glaciation have essentially zeroed the system in such a way that a high proportion of mineral phosphorus remains in the present lake sediments and the bioavailability of phosphorus (a key to ecosystem development) is low. Both examples illustrate the importance of variable sediment sources; the seasonality, frequency, and magnitude of sediment transfers; and the profound influence of ice cover over contemporary, neoglacial and Pleistocene time scales. They also signal the value of including both clastic and dissolved components in the sediment budget.

A survey of benthic sediment contaminants in reaches of the Columbia River Estuary based on channel sedimentation characteristics.

PubMed

Counihan, Timothy D; Waite, Ian R; Nilsen, Elena B; Hardiman, Jill M; Elias, Edwin; Gelfenbaum, Guy; Zaugg, Steven D

2014-06-15

While previous studies have documented contaminants in fish, sediments, water, and wildlife, few specifics are known about the spatial distribution of contaminants in the Columbia River Estuary (CRE). Our study goal was to characterize sediment contaminant detections and concentrations in reaches of the CRE that were concurrently being sampled to assess contaminants in water, invertebrates, fish, and osprey (Pandion haliaetus) eggs. Our objectives were to develop a survey design based on sedimentation characteristics and then assess whether sediment grain size, total organic carbon (TOC), and contaminant concentrations and detections varied between areas with different sedimentation characteristics. We used a sediment transport model to predict sedimentation characteristics of three 16km river reaches in the CRE. We then compartmentalized the modeled change in bed mass after a two week simulation to define sampling strata with depositional, stable, or erosional conditions. We collected and analyzed bottom sediments to assess whether substrate composition, organic matter composition, and contaminant concentrations and detections varied among strata within and between the reaches. We observed differences in grain size fractions between strata within and between reaches. We found that the fine sediment fraction was positively correlated with TOC. Contaminant concentrations were statistically different between depositional vs. erosional strata for the industrial compounds, personal care products and polycyclic aromatic hydrocarbons class (Indus-PCP-PAH). We also observed significant differences between strata in the number of detections of Indus-PCP-PAH (depositional vs. erosional; stable vs. erosional) and for the flame retardants, polychlorinated biphenyls, and pesticides class (depositional vs. erosional, depositional vs. stable). When we estimated mean contaminant concentrations by reach, we observed higher contaminant concentrations in the furthest downstream reach with a decreasing trend in the two upstream reaches. Contaminant survey designs that account for sedimentation characteristics could increase the probability that sampling is allocated to areas likely to be contaminated. Published by Elsevier B.V.

A survey of benthic sediment contaminants in reaches of the Columbia River Estuary based on channel sedimentation characteristics

USGS Publications Warehouse

Counihan, Timothy D.; Waite, Ian R.; Nilsen, Elena B.; Hardiman, Jill M.; Elias, Edwin; Gelfenbaum, Guy; Zaugg, Steven D.

2014-01-01

While previous studies have documented contaminants in fish, sediments, water, and wildlife, few specifics are known about the spatial distribution of contaminants in the Columbia River Estuary (CRE). Our study goal was to characterize sediment contaminant detections and concentrations in reaches of the CRE that were concurrently being sampled to assess contaminants in water, invertebrates, fish, and osprey (Pandion haliaetus) eggs. Our objectives were to develop a survey design based on sedimentation characteristics and then assess whether sediment grain size, total organic carbon (TOC), and contaminant concentrations and detections varied between areas with different sedimentation characteristics. We used a sediment transport model to predict sedimentation characteristics of three 16 km river reaches in the CRE. We then compartmentalized the modeled change in bed mass after a two week simulation to define sampling strata with depositional, stable, or erosional conditions. We collected and analyzed bottom sediments to assess whether substrate composition, organic matter composition, and contaminant concentrations and detections varied among strata within and between the reaches. We observed differences in grain size fractions between strata within and between reaches. We found that the fine sediment fraction was positively correlated with TOC. Contaminant concentrations were statistically different between depositional vs. erosional strata for the industrial compounds, personal care products and polycyclic aromatic hydrocarbons class (Indus–PCP–PAH). We also observed significant differences between strata in the number of detections of Indus–PCP–PAH (depositional vs. erosional; stable vs. erosional) and for the flame retardants, polychlorinated biphenyls, and pesticides class (depositional vs. erosional, depositional vs. stable). When we estimated mean contaminant concentrations by reach, we observed higher contaminant concentrations in the furthest downstream reach with a decreasing trend in the two upstream reaches. Contaminant survey designs that account for sedimentation characteristics could increase the probability that sampling is allocated to areas likely to be contaminated.