California State Waters Map Series: Drakes Bay and vicinity, California

USGS Publications Warehouse

Watt, Janet T.; Dartnell, Peter; Golden, Nadine E.; Greene, H. Gary; Erdey, Mercedes D.; Cochrane, Guy R.; Johnson, Samuel Y.; Hartwell, Stephen R.; Kvitek, Rikk G.; Manson, Michael W.; Endris, Charles A.; Dieter, Bryan E.; Sliter, Ray W.; Krigsman, Lisa M.; Lowe, Erik N.; Chinn, John L.; Watt, Janet T.; Cochran, Susan A.

2015-01-01

Sediment transport in the map area largely is controlled by surface waves and tidal currents in the nearshore and, at depths greater than 20 to 30 m, by tidal and subtidal currents. In the map area, nearshore littoral drift of sand and coarse sediment is to the south, owing to the dominant west-northwest swell direction, and scour from large waves and tidal currents removes and redistributes sediment over large areas of the inner shelf. Tidal currents are particularly strong over the shelf in the map area, and they dominate the current regime in the nearshore. Further offshore, bottom currents generally flow to the northwest, distributing finer grained sediment accordingly.

Effects of grain size, mineralogy, and acid-extractable grain coatings on the distribution of the fallout radionuclides 7Be, 10Be, 137Cs, and 210Pb in river sediment

NASA Astrophysics Data System (ADS)

Singleton, Adrian A.; Schmidt, Amanda H.; Bierman, Paul R.; Rood, Dylan H.; Neilson, Thomas B.; Greene, Emily Sophie; Bower, Jennifer A.; Perdrial, Nicolas

2017-01-01

Grain-size dependencies in fallout radionuclide activity have been attributed to either increase in specific surface area in finer grain sizes or differing mineralogical abundances in different grain sizes. Here, we consider a third possibility, that the concentration and composition of grain coatings, where fallout radionuclides reside, controls their activity in fluvial sediment. We evaluated these three possible explanations in two experiments: (1) we examined the effect of sediment grain size, mineralogy, and composition of the acid-extractable materials on the distribution of 7Be, 10Be, 137Cs, and unsupported 210Pb in detrital sediment samples collected from rivers in China and the United States, and (2) we periodically monitored 7Be, 137Cs, and 210Pb retention in samples of known composition exposed to natural fallout in Ohio, USA for 294 days. Acid-extractable materials (made up predominately of Fe, Mn, Al, and Ca from secondary minerals and grain coatings produced during pedogenesis) are positively related to the abundance of fallout radionuclides in our sediment samples. Grain-size dependency of fallout radionuclide concentrations was significant in detrital sediment samples, but not in samples exposed to fallout under controlled conditions. Mineralogy had a large effect on 7Be and 210Pb retention in samples exposed to fallout, suggesting that sieving sediments to a single grain size or using specific surface area-based correction terms may not completely control for preferential distribution of these nuclides. We conclude that time-dependent geochemical, pedogenic, and sedimentary processes together result in the observed differences in nuclide distribution between different grain sizes and substrate compositions. These findings likely explain variability of measured nuclide activities in river networks that exceeds the variability introduced by analytical techniques as well as spatial and temporal differences in erosion rates and processes. In short, we suggest that presence and amount of pedogenic grain coatings is more important than either specific surface area or surface charge in setting the distribution of fallout radionuclides.

Magnetic and mineralogical properties of central Baffin Bay sediments since the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Simon, Q.; St-Onge, G.; Hillaire-Marcel, C.

2011-12-01

Magnetic and mineralogical properties of terrigenous sediments from the deep central Baffin Bay (HU2008-029-016PC - 70°46,14N/-64°65,77W - 2063 m) were analyzed as a means of linking sedimentological changes to ice-margin dynamics along the surrounding coastlines of W. Greenland, E. Baffin Island and N.E. Ellesmere Island since the Last Glacial Maximum (LGM). A chronology based on relative paleointensity (RPI) and secular variation (PSV) in sections where magnetism properties were suitable has been set. The age-model yields a low mean sedimentation rate varying between 4 - 8 cm/kyr along the core and illustrates a significant increase during Termination 1. Carbonate content increases drastically from 16 ka due to increasing supplies of dolomitic material from dolostone rocks outcropping in the Canadian Arctic Archipelago and associated with inputs from the Innuitian Ice Sheet margin. The magnetic properties demonstrate major changes during the deglaciation and especially during Heinrich event 1 (H1), the Younger Dryas (YD) and throughout the Holocene. Very low median destructive field (MDF) of the natural remanent magnetization (NRM) values are observed during the 11.5 - 12.6 ka (YD) and 14.8 - 16 (H1) ka intervals, and are reflecting coarser magnetic grains. Similarly, the kARM/kLF grain-size ratio shows coarser magnetic grain size during the H1 and YD intervals, and finer magnetic grains during the LGM (19 - 22 ka). During the LGM, "glacial flour" formed by mechanical grinding of rocks by ice sheets released finer magnetic grains from lateral source (e.g., Greenland continental shelf). On the contrary, during the YD and H1 periods, icebergs released coarser magnetic grains from a northern source (axial source). The Holocene is marked by the highest median destructive field (MDF) and ARM20mT/ARM0mT values of the core, indicating an increased proportion of finer magnetic grains during this interval. Together with the large increase in the silt fraction, these different proxies tend to demonstrate the establishment of the modern Baffin Bay oceanic circulation that followed the deglaciation and the opening of Lancaster Sound, Jones Sound and Nares Strait, and the onset of the Western Greenland Current. These data provide strong marine evidence of 1) increasing supplies of sedimentary material coming from the rapid retreat of ice streams in the northern part of Baffin Bay starting at 16 ka and 2) the ice-margin dynamics (Innuitian vs. Greenland ice sheets) since the LGM. The study enables to document these sedimentological changes with regard to regional and Northern Hemisphere climatic variability, and highlights the importance of Baffin Bay for the establishment of modern oceanic circulation.

Sea-floor geology in northeastern Block Island Sound, Rhode Island

USGS Publications Warehouse

McMullen, Kate Y.; Poppe, Lawrence J.; Ackerman, Seth D.; Blackwood, Dann S.; Lewit, P.G.; Parker, Castle E.

2013-01-01

Multibeam-echosounder and sidescan-sonar data collected by the National Oceanic and Atmospheric Administration in northeastern Block Island Sound, combined with sediment samples and bottom photography collected by the U.S. Geological Survey, are used to interpret sea-floor features and sedimentary environments in this 52-square-kilometer-area offshore Rhode Island. Boulders, which are often overgrown with sessile fauna and flora, are mostly in water depths shallower than 20 meters. They are probably part of the southern flank of the Harbor Hill-Roanoke Point-Charlestown-Buzzards Bay moraine, deposited about 18,000 years ago. Scour depressions, areas of the sea floor with a coarser grained, rippled surface lying about 0.5 meter below the finer grained, surrounding sea floor, along with erosional outliers within the depressions are in a band near shore and also offshore in deep parts of the study area. Textural and bathymetric differences between areas of scour depressions and the surrounding sea floor or erosional outliers stand out in the sidescan-sonar imagery with sharp tonal contrasts. Also visible in the sidescan-sonar imagery are broad, low-profile bedforms with coarser grained troughs and finer grained crests.

Nesting ecology of Podocnemis expansa (Schweigger, 1812) and Podocnemis unifilis (Troschel, 1848) (Testudines, Podocnemididae) in the Javaés River, Brazil.

PubMed

Ferreira Júnior, P D; Castro, P T A

2010-02-01

Nest site has influence on incubation duration and hatching success of two Neotropical turtles, the giant Amazon River turtle (Podocnemis expansa) and yellow-spotted side-neck turtle (Podocnemis unifilis--'Tracajá'). The 2000 and 2001 nesting seasons have been monitored at the Javaés River in Bananal Island, Brazil. Although they nest on the same beaches, there is a separation of the nesting areas of P unifilis and P. expansa nests on the upper parts of the beach. The incubation duration for P. expansa is influenced by the nesting period, the height of the nest from the river, the clutch size, and the grain size in the site of the nest. Nests of Podocnemis expansa placed in coarse sediments have shorter incubation duration than those placed in finer sediments. The hatching success in P. expansa is influenced by grain size, incubation duration, and nesting period. The grain size is negatively correlated with hatching success, indicating that the nests situated in finer-grained sand have better chances of successful egg hatching than those in coarser-grained sand. Nests of the end of the reproductive season have lower hatching success and incubation duration than those at the start of the season. For P. unifilis, the nesting period and nest depth influence the incubation duration; moreover, the river dynamics significantly affect the hatching success. The oscillation of the river level and the moment of initial increase, the height of the nest from the river level, and the nesting period are all decisive components for hatching success. The results of this research show the importance of protecting areas with great geological diversity, wherein the features of the environment can affect the microenvironment of nests, with consequences on incubation duration and hatching success.

Climate signals in Late Holocene sediments from Maxwell Bay and English Strait (South Shetland Islands, Antarctica)

NASA Astrophysics Data System (ADS)

Hass, H. Christian; Schröder, Simon; Kuhn, Gerhard

2017-04-01

Climate fluctuations of the past two millennia such as the Little Ice Age and the Medieval Warm Period are reported mainly from the Northern Hemisphere. Evidence from Antarctica is comparably sparse and reveals regional and temporal differences, which are particularly evident at the western and eastern sides of the Antarctic Peninsula. High-resolution coastal-marine sediment cores from the northernmost tip of the West Antarctic Peninsula reveal periods dominated by finer sediments between periods that lack the finer sediment component. In Maxwell Bay this fine sediment (grain size mode around 16 µm) has been traced back to sediment related to the occurrence of glacial meltwater. It was found in sheltered places and meltwater creeks of Potter Cove, a small tributary fjord to Maxwell Bay. In the sediment core this sediment occurs predominantly between 600 and 1250 AD (Medieval Warm Period) whereas it is only sparsely affecting the record between 1450 and 1900 AD (Little Ice Age). The temporal pattern is very similar to global-temperature reconstructions and even resembles temperature reconstructions from the Northern Hemisphere. To avoid local effects that may occur in Maxwell Bay more sediment cores were taken from bays and straits further south of King George Island during Cruise PS97 of RV "Polarstern" in 2016. A core from English Strait reveals completely different sedimentary conditions with no detectable meltwater signal (16 µm). However, the mean grain size record resembles that of the cores from Maxwell Bay. The lack of a clear-cut meltwater sediment class as it occurs further north is likely the result of a much smaller hinterland (Greenwich and Robert islands) when compared to Maxwell Bay between Nelson Island and the much bigger King George Island where glaciers and ice sheets discharge large quantities of very turbid meltwater directly into the bay. It is concluded that during the warmer climate periods a large amount of meltwater was released along the NW Antarctic Peninsula. The related plume sediments were distributed downstream to overprint coastal sediments even though the amount was likely not sufficient to produce a discrete sediment class.

Grain size and shape evolution of experimentally deformed sediments: the role of slip rate

NASA Astrophysics Data System (ADS)

Balsamo, Fabrizio; Storti, Fabrizio; De Paola, Nicola

2016-04-01

Sediment deformation within fault zones occurs with a broad spectrum of mechanisms which, in turn, depend on intrinsic material properties (porosity, grain size and shape, etc.) and external factors (burial depth, fluid pressure, stress configuration, etc.). Fieldworks and laboratory measurements conducted in the last years in sediments faulted at shallow depth showed that cataclasis and grain size reduction can occur very close to the Earth surface (<1-2 km), and that fault displacement is one of the parameters controlling the amount of grain size, shape, and microtextural modifications in fault cores. In this contribution, we present a new set of microstructural observations combined with grain size and shape distribution data obtained from quart-feldspatic loose sediments (mean grain diameter 0.2 mm) experimentally deformed at different slip rates from subseismic (0.01 mm/s, 0.1 mm/s, 1 mm/s, 1 cm/s, and 10 cm/s) to coseismic slip rates (1 m/s). The experiments were originally performed at sigma n=14 MPa, with the same amount of slip (1.3 m), to constrain the frictional properties of such sediments at shallow confining pressures (<1 km). After the experiments, the granular materials deformed in the 0.1-1 mm-thick slip zones were prepared for both grain size distribution analyses and microstructural and textural analyses in thin sections. Grain size distribution analyses were obtained with a Malvern Mastersizer 3000 particle size laser-diffraction analyser, whereas grain shape data (angularity) were obtained by using image analysis technique on selected SEM-photomicrographs. Microstructural observations were performed at different scales with a standard optical microscope and with a SEM. Results indicate that mean grain diameter progressively decreases with increasing slip rates up to ~20-30 m, and that granulometric curves systematically modify as well, shifting toward finer grain sizes. Obtained fractal dimensions (D) indicate that D increases from ~2.3 up to >3 moving from subseismic to coseismic slip rates. Grain angularity also changes with increasing slip rates, being particles more smoothed and rounded in sediments deformed at coseismic slip rates. As a whole, our results indicate that both grain size and shape distributions of experimentally deformed sediments progressively changes from subseismic to coseismic slip rate, thus helping to understand the deformation mechanisms in natural fault zones and to predict frictional and permeability properties of faults affecting shallow sediments.

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.

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.

Composition of conglomerates analyzed by the Curiosity rover: Implications for Gale Crater crust and sediment sources

DOE PAGES

Mangold, N.; Thompson, L. M.; Forni, O.; ...

2016-03-16

The Curiosity rover has analyzed various detrital sedimentary rocks at Gale Crater, among which fluvial and lacustrine rocks are predominant. Conglomerates correspond both to the coarsest sediments analyzed and the least modified by chemical alteration, enabling us to link their chemistry to that of source rocks on the Gale Crater rims. Here, we report the results of six conglomerate targets analyzed by Alpha-Particle X-ray Spectrometer and 40 analyzed by ChemCam. The bulk chemistry derived by both instruments suggests two distinct end-members for the conglomerate compositions. The first group (Darwin type) is typical of conglomerates analyzed before sol 540; it hasmore » a felsic alkali-rich composition, with a Na 2O/K 2O > 5. The second group (Kimberley type) is typical of conglomerates analyzed between sols 540 and 670 in the vicinity of the Kimberley waypoint; it has an alkali-rich potassic composition with Na 2O/K 2O < 2. The variety of chemistry and igneous textures (when identifiable) of individual clasts suggest that each conglomerate type is a mixture of multiple source rocks. Conglomerate compositions are in agreement with most of the felsic alkali-rich float rock compositions analyzed in the hummocky plains. The average composition of conglomerates can be taken as a proxy of the average igneous crust composition at Gale Crater. Finally, the differences between the composition of conglomerates and that of finer-grained detrital sediments analyzed by the rover suggest modifications by diagenetic processes (especially for Mg enrichments in fine-grained rocks), physical sorting, and mixing with finer-grained material of different composition.« less

Grain-size distribution and selected major and trace element concentrations in bed-sediment cores from the Lower Granite Reservoir and Snake and Clearwater Rivers, eastern Washington and northern Idaho, 2010

USGS Publications Warehouse

Braun, Christopher L.; Wilson, Jennifer T.; Van Metre, Peter C.; Weakland, Rhonda J.; Fosness, Ryan L.; Williams, Marshall L.

2012-01-01

Fifty subsamples from 15 cores were analyzed for major and trace elements. Concentrations of trace elements were low, with respect to sediment quality guidelines, in most cores. Typically, major and trace element concentrations were lower in the subsamples collected from the Snake River compared to those collected from the Clearwater River, the confluence of the Snake and Clearwater Rivers, and Lower Granite Reservoir. Generally, lower concentrations of major and trace elements were associated with coarser sediments (larger than 0.0625 millimeter) and higher concentrations of major and trace elements were associated with finer sediments (smaller than 0.0625 millimeter).

The Grain-size Patchiness of Braided Gravel-Bed Streams: Example of the Urumqi River (northeast Tian Shan, China)

NASA Astrophysics Data System (ADS)

Guerit, L.; Barrier, L.; Narteau, C.; Métivier, F.; Liu, Y.; Lajeunesse, E.; Gayer, E.; Malverti, L.; Meunier, P.; Ye, B.

2012-04-01

In gravel-beds rivers, sediments are sorted into patches of different grain-sizes. For single-thread streams, it has long been shown that this local granulometric sorting is closely linked to the channel morpho-sedimentary elements. For braided streams, this relation is still unclear. In such rivers, many observations of vertical sediment sorting has led to the definition of a surface and a subsurface layers. Because of this common stratification, methods for sampling gravel-bed rivers have been divided in two families. The surface layer is generally sampled by surface methods and the subsurface layer by volumetric methods. Yet, the equivalency between the two kind of techniques is still a key question. In this study, we characterized the grain-size distribution of the surface layer of the Urumqi River, a shallow braided gravel-bed river in China, by surface-count (Wolman grid-by-number) and volumetric (sieve-by-weight) sampling methods. An analysis of two large samples (212 grains and 3226 kg) show that these two methods are equivalent to characterize the river-bed surface layer. Then, we looked at the grain-size distributions of the river-bed morpho-sedimentary elements: (1) chutes at flow constrictions, which pass downstream to (2) anabranches and (3) bars at flow expansions. Using both sampling methods, we measured the diameter of more than 2300 grains and weight more than 6000 kg of grains larger than 4 mm. Our results show that the three morpho-sedimentary elements correspond only to two kinds of grain-size patches: (1) chutes composed of one coarse-grained top layer lying on finer deposits, and (2) anabranches and bars made up of finer-grained deposits more homogeneous in depth. On the basis of these quantitative observations, together with the concave or convex morphology of the different elements, we propose that chute patches form by erosion and transit with size-selective entrainment, whereas anabranch and bar patches rather develop and migrate by transit and deposition. These patch features may be typical of shallow braided gravel-bed rivers and should be considered in future works about on bedload transport processes and their geomorphologic and stratigraphic results.

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.

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.

The importance of both geological and pedological processes in control of grain size and sedimentation rates in Peoria Loess

USGS Publications Warehouse

Wang, Hongfang; Mason, J.A.; Balsam, W.L.

2006-01-01

The loess-paleosol succession in the Peoria Loess in southern Illinois is characterized as alternating loess layers and weathering bands, known as paleosol A horizons. The fast loess accumulation during the late Wisconsin glaciation interacted with the incipient pedogenesis and caused unclear boundaries of loess-paleosol alternations in soil horizonation and mineralogy. Parameters of grain size distribution, sedimentation rate, matrix carbonate content and diffuse reflectance (i.e. soil colors and iron oxides) are used in this paper to discuss the geological and pedological influences for the Peoria Loess in Keller Farm section in southern Illinois. The multi-proxy analysis revealed that many paleosol A horizons, defined by the diffuse reflectance variability, contain finer-grained materials with a relatively higher sedimentation rate. It suggests that glaciofluvial sediments were available in the source areas for uploading eolian dust during the temporary ice sheet retreats. The denser vegetation and wetter surface soils on the loess deposit area could increase the dust trapping efficiency and caused a greater accumulation rate of loess deposits. The coarser-grained materials and slower sedimentation rate are often found in loess layers. It suggests that strong surface winds transported the coarser-grained materials from local dust sources and sparse vegetation and dry surface soils reduced the dust trapping efficiency during the ice sheet readvance. The strong interactions between the geological and pedological processes played an important role on the loess-paleosol alternations in southern Illinois during the late Wisconsin glaciation. ?? 2006 Elsevier B.V. All rights reserved.

Stochastic Modelling of the Hydraulic Anisotropy of Ash Impoundment Sediment

NASA Astrophysics Data System (ADS)

Slávik, Ivan

2017-12-01

In the case reported here the impoundments of a 400 MW coal heated power plant with an annual production of about 1.5 million tons of fuel ash are of the cross-valley type, operated by the simple and cheap „upstream method”. The aim of the research was to determine overall and local values of the permeability in horizontal as well as in vertical direction and the anisotropy of the thin-layered sedimented ash. The coal ashes are hydraulically transported through pipelines in form of a slurry and periodically floated on the beach of the impoundment. The ashes are deposited in the form of a thin-layered sediment, with random alternation of layers with a coarser or finer granularity. The ash impoundment sediment is anthropogenic sediment with horizontally laminated texture. Therefore, the sediment is anisotropic from the viewpoint of water seepage. The knowledge of the permeability and the seepage anisotropy of the sediment is a basic requirement for the design of an appropriate dewatering system. The seepage anisotropy of the ash sediment has been checked by means of stochastic modelling, based on the correlation between the effective grain diameter and the coefficient of permeability of the ash: the effective grain diameter and the thickness of individual layers have been proposed to be random events.

Bottom currents and sediment waves on a shallow carbonate shelf, Northern Carnarvon Basin, Australia

NASA Astrophysics Data System (ADS)

Belde, Johannes; Reuning, Lars; Back, Stefan

2017-04-01

The modern seafloor of the Australian Northwest Shelf between Exmouth and Dampier was analyzed for large scale sedimentary bedforms on 3D seismic reflection data. The Carnarvon MegaSurvey of Petroleum Geo-Services (PGS), a merged dataset of multiple industrial 3D seismic reflection surveys with a total size of 49,717 km2, offers an extensive view of the continental shelf, slope and rise of the Northern Carnarvon Basin. Over the shelf two fields of large scale sediment waves were observed in water depths between 55-130 m, where the seafloor may be influenced by different processes including internal waves, tides and storms. Based on the dimensions and orientations of the sediment waves the dominant direction and approximate strength of local bottom currents could be estimated. Information on local sediment grain-size distribution was provided by the auSEABED database allowing a classification of the observed sediment waves into sand- or mudwaves. The first sediment wave field is positioned northwest of the Montebello Islands where the shelf is comparatively narrow and local sediment is mainly sand-sized. It most likely formed by increased bottom currents induced by the diversion of tidal flows around the islands. The second sediment wave field is located north of the Serrurier and Bessieres Islands within a local seafloor depression. Local sediments are poorly sorted, containing significant amounts of mud and gravel in addition to the mainly sand-sized grains. The coarser sediment fraction could have been reworked to sandwaves by cyclone-induced bottom currents. Alternatively, the finer sediment fraction could form mudwaves shaped by less energetic along-slope oriented currents in the topographic depression. The sediment waves consist partially of carbonate grains such as ooids and peloids that formed in shallow water during initial stages of the post glacial sea-level rise. These stranded carbonate grains thus formed in a different environment than the sediment waves in which they were redeposited. In fossil examples of similar high-energy ramp systems this possible out-of-equilibrium relationship between grains and bedforms has to be taken into account for the interpretation of the depositional environment.

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.

Distribution, sources and contamination assessment of heavy metals in surface sediments of the South Yellow Sea and northern part of the East China Sea.

PubMed

Lu, Jian; Li, Anchun; Huang, Peng

2017-11-15

Surface sediment samples collected from the South Yellow Sea and northern part of the East China Sea during spring and autumn, respectively, were analyzed for grain size, aluminum, and heavy metals (Cr, Ni, Cu, Zn, and Pb) to evaluate heavy metal levels and the contamination status. The results showed that all of the heavy metal concentrations met the standard criteria of the Chinese National Standard Criteria for Marine Sediment Quality. Both the EFs and a multivariate analysis (PCA) indicated that Cr, Ni, Cu, and Zn were mainly from natural contributions, while Pb was influenced by anthropogenic inputs, especially during autumn. The geoaccumulation index of Pb near the mouth of the Yangtze River suggested that the pollution degree in autumn was heavier than that in spring, which might be caused by the greater river discharge in summer and more heavy metal adsorption with finer grain sizes. Copyright © 2017 Elsevier Ltd. All rights reserved.

Littoral transport in the surf zone elucidated by an Eulerian sediment tracer.

USGS Publications Warehouse

Duane, D.B.; James, W.R.

1980-01-01

An Eulerian, or time integration, sand tracer experiment was designed and carried out in the surf zone near Pt. Mugu, California on April 19, 1972. Data indicate that conditions of stationarity and finite boundaries required for proper application of Eulerian tracer theory exist for short time periods in the surf zone. Grain counts suggest time required for tracer sand to attain equilibrium concentration is on the order of 30-60 minutes. Grain counts also indicate transport (discharge) was strongly dependent upon grain size, with the maximum rate occurring in the size 2.5-2.75 phi, decreasing to both finer and coarser sizes. The measured instantaneous transport was at the annual rate of 2.4 x 106 m3/yr.- Authors

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.

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.

Glacial-interglacial climate changes recorded by debris flow fan deposits, Owens Valley, California

NASA Astrophysics Data System (ADS)

D'Arcy, Mitch; Roda-Boluda, Duna C.; Whittaker, Alexander C.

2017-08-01

It is hotly debated whether and how climate changes are recorded by terrestrial stratigraphy. Basin sediments produced by catchment-alluvial fan systems may record past climate over a variety of timescales, and could offer unique information about how climate controls sedimentation. Unfortunately, there are fundamental uncertainties about how climatic variables such as rainfall and temperature translate into sedimentological signals. Here, we examine 35 debris flow fan surfaces in Owens Valley, California, that record deposition throughout the past 125,000 years, during which climate has varied significantly. We show that the last full glacial-interglacial cycle is recorded with high fidelity by the grain size distributions of the debris flow deposits. These flows transported finer sediment during the cooler glacial climate, and became systematically coarser-grained as the climate warmed and dried. We explore the physical mechanisms that might explain this signal, and rule out changes in sediment supply through time. Instead, we propose that grain size records past changes in storm intensity, which is responsible for debris flow initiation in this area and is decoupled from average rainfall rates. This is supported by an exponential Clausius-Clapeyron-style scaling between grain size and temperature, and also reconciles with climate dynamics and the initiation of debris flows. The fact that these alluvial fans exhibit a strong, sustained sensitivity to orbital climate changes sheds new light on how eroding landscapes and their sedimentary products respond to climatic forcing. Finally, our findings highlight the importance of threshold-controlled events, such as storms and debris flows, in driving erosion and sedimentation at the Earth's surface in response to climate change.

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.

Archaeological Investigations at Sites 45-OK-287 and 45-OK-288, Chief Joseph Dam Project, Washington.

DTIC Science & Technology

1984-01-01

marks and evidence of burning by element ........ ........................ . 258 xviii .. . - ... ., ." xvii LIST OF PLATES Plate 1-1. 45-OK-287: view...which the site is located, and glaclotacustrlne sediments of two ages exposed In the opposite bank. The lowest major terrace the river cut In the...the site were exposed in fewer excavation units, but they have a finer grain size and greater proportion of angular cobbles, deriving from the bedrock

Modes of sediment transport in channelized water flows with ramifications to the erosion of the Martian outflow channels

NASA Technical Reports Server (NTRS)

Komar, P. D.

1980-01-01

The paper discusses application to Martian water flows of the criteria that determine which grain-size ranges are transported as bed load, suspension, and wash load. The results show nearly all sand-sized material and finer would have been transported as wash load and that basalt pebbles and even cobbles could have been transported at rapid rates of suspension. An analysis of the threshold of sediment motion on Mars further indicates that the flows would have been highly competent, the larger flows having been able to transport boulder-sized material. Comparisons with terrestrial rivers which transport hyperconcentration levels of sediments suggest that the Martian water flows could have achieved sediment concentrations up to 70% in weight. Although it is possible that flows could have picked up enough sediment to convert to pseudolaminar mud flows, they probably remained at hyperconcentration levels and fully turbulent in flow character.

A conceptual review of regional-scale controls on the composition of clastic sediment and the co-evolution of continental blocks and their sedimentary cover.

PubMed

Cox, R; Lowe, D R

1995-01-02

Both sediment recycling and first-cycle input influence the composition of clastic material in sedimentary systems. This paper examines conceptually the roles played by these processes in governing the composition of clastic sediment on a regional scale by outlining the expected effects on sediment composition of protracted sediment recycling and of continuous first-cycle input on a maturing continental block. Generally speaking, long-term recycling tends to enrich sediments in the most chemically and mechanically stable components: quartz in the sand and silt size fractions, and illite among the clay minerals. Sandstones trend towards pure quartz arenites, and mudrocks become more potassic and aluminous. The average grain size of clastic sediment decreases by a combination of progressive attrition of sand grains and ongoing breakdown of primary silicate minerals to finer-grained clay minerals and oxides. Sandstones derived by continuous first-cycle input from an evolving continental crustal source also become increasingly rich in quartz, but in addition become more feldspathic as the proportion of granitic material in the upper continental crust increases during crustal stabilization. Associated mudrocks also become richer in potassium and aluminum, but will have higher K2O/Al2O3 ratios than recycled muds. The average grain size of the sediment may increase with time as the proportion of sand-prone granitic source rocks increases at the expense of more mud-prone volcanic sources. In general, except in instances where chemical weathering is extreme, first-cycle sediments lack the compositional maturity of recycled detritus, and are characterized by the presence of a variety of primary silicate minerals. Sedimentary systems are not usually completely dominated by either recycling or first-cycle detritus. Generally, however, sedimentary systems associated with the earliest phases of formation and accretion of continental crust are characterized by first-cycle input from igneous and metamorphic rocks, whereas those associated with more mature cratons tend to be dominated by recycled sedimentary material.

Archaeological Investigations at Sites 45-OK-287 and 45-OK-288, Chief Joseph Dam Project, Washington.

DTIC Science & Technology

1984-01-01

Table C-1. Distribution of butchering marks and evidence of burning by element .. ....... ....... ....... .. 258 xvii9. LIST OF PLATES Plate 1-1. 45-OK...the vicinity of the Omak Trench. Till forms the terrace on which the site Is located, and glaclolacustrIne sediments of two ! -ages exposed In the...the site were exposed In fewer excavation units, but they have a finer grain size and greater proportion of angular cobbles, deriving from the bedrock

Sedimentary Biosignatures of Social Organization in Cone-Forming Filamentous Bacteria

NASA Astrophysics Data System (ADS)

Tice, M. M.; Gong, J.; Zeng, Z.; Sneed, J.; Wehner, M.; Sparks, D. W.

2013-12-01

Conical mats consisting of centimeter-scale steep-sided cones growing above flat basal films form some of the most distinctive fossil microbial communities in the geologic record. Cones have been hypothesized to form by the initially random motion of filamentous bacteria into small tangled clumps followed by the phototactic motion of the same bacteria up resulting slopes. More recent models of cone development suggest that they form in response to growth in stagnant fluids where diffusion limits exchange of nutrients and wastes with the environment. Determining the biological and environmental factors that promote cone formation will be important for interpreting the geological record of fossil mats and stromatolites, on Earth and potentially on Mars. Here we report the results of new experiments demonstrating complex social organization of cone-forming communities and a novel biosignature of the growth of such communities on sandy sediments, as well as detection of that biosignature in 3.2 Ga fossil mats of the Moodies Group (Barberton greenstone belt, South Africa). In order to investigate the processes involved in cone formation, we grew cultures of a filamentous cyanobacterium originally isolated from tufted cones in Yellowstone National Park, Montana, U.S.A. (Leptolyngbya sp. Y-WT-2000 Cl 1). During early mat development, filaments coat sand grain surfaces and aggregate into ~100-μm-long tufts, or mutually aligned bundles of filaments. Tufts are highly motile, bridging sand grains and merging to form larger tufts. After 10-14 days of growth, tufts aggregate during the early morning into centers composed of many tufts that wave vertically and along the sand surface. Centers move across the sediment surface during the middle of the day and merge along bridging tufts. These bridges transmit force to the underlying sediment and are capable of rolling sand grains. At this stage, mats are composed of small mobile centers that disperse along streams of co-moving bacteria during the evening. This diel cycle, together with preferential movement of relatively coarse sand grains that protrude above surrounding finer grains, efficiently sorts the underlying sediment such that mature mats are composed of large stabilized centers resting on small piles of coarser sand. Because these cone-forming mats sort sand grains by applying a shear stress at the sediment surface, growth of similar bacteria on sand surfaces should result in the preferential aggregation of equant coarse light mineral grains into cones and the formation of finer heavy mineral lags in interconical spaces. We observe these patterns of sorting by grain size, aspect ratio, and density around cones in Moodies Group fossil mats. These patterns could not have been produced by hydraulic sorting alone, and instead suggest the following conclusions. Cone-constructing Moodies microorganisms were 1) filamentous, 2) moved by gliding motility, and 3) moved as socially organized groups. In addition, it seems probable that these organisms 4) periodically reversed the direction of their movement on a time scale much more rapid than the time between deposition of sand beds, possibly as part of a diel cycle.

Response of bed surface patchiness to reductions in sediment supply

NASA Astrophysics Data System (ADS)

Nelson, Peter A.; Venditti, Jeremy G.; Dietrich, William E.; Kirchner, James W.; Ikeda, Hiroshi; Iseya, Fujiko; Sklar, Leonard S.

2009-06-01

River beds are often arranged into patches of similar grain size and sorting. Patches can be distinguished into "free patches," which are zones of sorted material that move freely, such as bed load sheets; "forced patches," which are areas of sorting forced by topographic controls; and "fixed patches" of bed material rendered immobile through localized coarsening that remain fairly persistent through time. Two sets of flume experiments (one using bimodal, sand-rich sediment and the other using unimodal, sand-free sediment) are used to explore how fixed and free patches respond to stepwise reductions in sediment supply. At high sediment supply, migrating bed load sheets formed even in unimodal, sand-free sediment, yet grain interactions visibly played a central role in their formation. In both sets of experiments, reductions in supply led to the development of fixed coarse patches, which expanded at the expense of finer, more mobile patches, narrowing the zone of active bed load transport and leading to the eventual disappearance of migrating bed load sheets. Reductions in sediment supply decreased the migration rate of bed load sheets and increased the spacing between successive sheets. One-dimensional morphodynamic models of river channel beds generally are not designed to capture the observed variability, but should be capable of capturing the time-averaged character of the channel. When applied to our experiments, a 1-D morphodynamic model (RTe-bookAgDegNormGravMixPW.xls) predicted the bed load flux well, but overpredicted slope changes and was unable to predict the substantial variability in bed load flux (and load grain size) because of the migration of mobile patches. Our results suggest that (1) the distribution of free and fixed patches is primarily a function of sediment supply, (2) the dynamics of bed load sheets are primarily scaled by sediment supply, (3) channels with reduced sediment supply may inherently be unable to transport sediment uniformly across their width, and (4) cross-stream variability in shear stress and grain size can produce potentially large errors in width-averaged sediment flux calculations.

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.

Variability of in situ sediment strength and pore pressure behavior of tidal estuary surface sediments

NASA Astrophysics Data System (ADS)

Lucking, Greg; Stark, Nina; Lippmann, Thomas; Smyth, Stephen

2017-10-01

Tidal estuaries feature spatially and temporally varying sediment dynamics and characteristics. Particularly, the variability of geotechnical sediment parameters is still poorly understood, limiting the prediction of long-term sediment stability and dynamics. This paper presents results from an in situ investigation of surficial sediments (≤50 cm) in a tidal estuary in New Hampshire (USA), using a portable free fall penetrometer. The aim is to investigate variations in sediment strength and pore pressure behavior with regard to sediment type and seabed morphology. The study also provides a detailed analysis of high velocity impact pore pressure data to derive information about sediment type and permeability. The penetrometer was deployed 227 times, and the findings are correlated to 78 sediment samples. Differences in sediment strength and type were found when transitioning from tidal flats to the deeper channels. Finer-grained sediments located predominantly on the tidal flats appeared well consolidated with noticeable and spatially consistent sediment strength (reflected in an estimate of quasi-static bearing capacity qsbcmax 10 kPa). Sediments with higher sand content (>75%) showed more variations in strength relating to differences in gradation, and likely represent loose and poorly consolidated sands (qsbcmax 10-55 kPa). The rate at which the recorded excess pore pressures approached equilibrium after penetration was classified and related to sediment type. The data indicate that the development of excess pore pressures upon impact and during penetration may provide additional insight into the nature and layering of bed material, such as identifying a desiccated or over-consolidated dilative surficial layer. In summary, with varying sediment grain size distributions, bulk densities and morphology, sediment strength and pore pressure behavior can vary significantly within a tidal estuary.

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.

Network-scale dynamics of sediment mixtures: how do tectonics affect surface bed texture and channel slope?

NASA Astrophysics Data System (ADS)

Gasparini, N. M.; Bras, R. L.; Tucker, G. E.

2003-04-01

An alluvial channel's slope and bed texture are intimately linked. Along with fluvial discharge, these variables are the key players in setting alluvial transport rates. We know that both channel slope and mean grain size usually decrease downstream, but how sensitive are these variables to tectonic changes? Are basin concavity and downstream fining drastically disrupted during transitions from one tectonic regime to another? We explore these questions using the CHILD numerical landscape evolution model to generate alluvial networks composed of a sand and gravel mixture. The steady-state and transient patterns of both channel slope and sediment texture are investigated. The steady-state patterns in slope and sediment texture are verified independently by solving the erosion equations under equilibrium conditions, i.e. the case when the erosion rate is equal to the uplift rate across the entire landscape. The inclusion of surface texture as a free parameter (as opposed to just channel slope) leads to some surprising results. In all cases, an increase in uplift rate results in channel beds which are finer at equilibrium (for a given drainage area). Higher uplift rates imply larger equilibrium transport rates; this leads to finer channels that have a smaller critical shear stress to entrain material, and therefore more material can be transported for a given discharge (and channel slope). Changes in equilibrium slopes are less intuitive. An increase in uplift rates can cause channel slopes to increase, remain the same, or decrease, depending on model parameter values. In the surprising case in which equilibrium channel slopes decrease with increasing uplift rates, we suggest that surface texture changes more than compensate for the required increase in transport rates, causing channel slopes to decrease. These results highlight the important role of sediment grain size in determining transport rates and caution us against ignoring this important variable in fluvial networks.

The Importance of Actualistic Source-to-Sink Sand Provenance Studies in Illuminating the Nature of Ancient Fluvial Systems From the Deep-Marine Clastic Successions They Sourced

NASA Astrophysics Data System (ADS)

Marsaglia, K. M.; Parra, J. G.; Dawson, S.

2006-12-01

Successions of gravity-flow deposits in deep-marine fan systems have the potential to record the evolution of their fluvial source region as well as specific tectonic, climatic, eustatic and anthropogenic events. Deciphering these signals involves the description and quantification of key sediment attributes such as fan volume, the rate of sediment accumulation, the frequency of depositional events, sediment texture, and sediment composition. Sediment composition/provenance provides insight into the nature of the fluvial source, including drainage basin geology and drainage development. For example, Marsaglia et al. (1995) demonstrated a connection between source river lengthening owing to eustatic change and sand composition in Quaternary turbidite successions of the Santa Barbara Basin at Ocean Drilling Program (ODP) Site 893. In contrast, longer-term compositional trends recognized in the Mesozoic to Cenozoic rift-to-drift successions cored by various ODP legs on the North Atlantic margins are more likely associated with continental margin drainage development and fluvial system evolution (Marsaglia et al., in press). These two connections between sink and source were made possible by well-documented petrologic data sets for both modern onshore fluvial systems and older offshore deep-marine successions, but in each case different workers collected the onshore and offshore data sets. In the Waipaoa River Sedimentary System of North Island, New Zealand we have taken a different, more holistic approach, with a limited and linked group of researchers and sample data base covering the complete system. The study area is an active forearc margin characterized by uplifted and deformed sedimentary successions and periodic input of arc-derived ash. Recently, the modern onshore system has been thoroughly documented via studies of the petrology of outcropping Mesozoic to Cenozoic units, fluvial terrace deposits, and modern fluvial sediments (e.g., James et al., in press). Now we are building on that data set and moving from source-to-sink to trace sandy sediment through the system out onto the shelf and slope where it has been encountered in shallow cores. Lessons learned onshore, such as a distinct compositional dependence on grain size and the relationships of bedrock geology to certain sand grain types, also apply to these offshore core samples. Many of the sandy intervals are largely composed of reworked tephra from Taupo eruptions, whereas quartz and feldspar dominate finer sand samples. Lithic-dominated sands are less common and coarser grained. Isolated greywacke gravel clasts indicate that at some point coarse sediment "leaked" into the basin from the south. The volumetric importance of this extrabasinal input can be assessed by looking at the types and proportions of lithic fragments within the finer sand fraction.

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.

Can we use only Grain Size Data for Paleo-Flow Reconstructions?

NASA Astrophysics Data System (ADS)

Perillo, M. M.; Pohl, F.; Eggenhuisen, J. T.; Fedele, J.; Hoyal, D. C. J. D.; Mohrig, D. C.

2015-12-01

Paleo-flow and paleo-environmental reconstruction from ancient deposits is a critical task for earth surface scientists interested in the sedimentary record. Forming processes are commonly interpreted from the architectural characteristics of sedimentary deposits using quantitative relationships derived from experiments or geomorphic studies. However, very little attention has been paid to the equivalent problem at the scale of micro-facies: can we interpret the conditions at the time of sediment accumulation from grain size information in a small sample? Here we investigate the use of grain size distributions alone to reconstruct the flow conditions based on a set of experiments conducted in a 2D flume tank in the Eurotank facilities at Utrecht University. The experiments are designed for the examination of grain size distributions within sediments which were deposited by flows with known conditions (e.g. velocity, turbulence, shear velocity, concentration). By changing the slope of the flume tank we were able to create a range of flows from strongly depositional (depletive) to bypassing. Inspired by Eastwood et al (2012), we propose a working methodology to link the grain size distribution of the deposit to flow conditions. Our method utilizes the following empiric relations: i) the finer fraction of the deposit was deposited while most of that range surpass the Bagnold (1966)'s suspension threshold (shear velocity υ* approx. 3 times the settling velocity ωs); ii) the mean fraction was at incipient suspension stage (υ* ~ ωs); iii) the finer portion of the coarser grains were at bedload/saltation stage, where u* is approx. υ*c (critical shear velocity for initiation of motion); and iv) the coarser portion of the coarser grains were at creep-bedload stage, where υ* is approx. 0.7υ*c . We test whether this set of rules can be applied to the probability distribution function of deposit grainsize in an inversion that converges on a single value for the shear velocity, and whether this inverted shear velocity is in accordance with the experimental flow conditions. Preliminary application of this method to outcrop work will be given. Bagnold, R. (1966), U. S. Geol. Surv. Prof. Pap., 422-I, 37 pp. Eastwood, E. N., G. Kocurek, D. Mohrig, and T. Swanson (2012), J. Geophys. Res., 117, F03035, doi:10.1029/2012JF002368.

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.

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.

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.

Low Albedo Surfaces and Eolian Sediment: Mars Orbiter Camera Views of Western Arabia Terra Craters and Wind Streaks

NASA Technical Reports Server (NTRS)

Edgett, Kenneth S.

2001-01-01

High spatial resolution (1.5 to 12 m/pixel) Mars Global Surveyor Mars Orbiter Camera images obtained September 1997 through June 2001 indicate that the large, dark wind streaks of western Arabia Terra each originate at a barchan dune field on a crater floor. The streaks consist of a relatively thin coating of sediment deflated from the dune fields and their vicinity. This sediment drapes a previous mantle that more thickly covers nearly all of western Arabia Terra. No dunes or eolian bedforms are found within the dark wind streaks, nor do any of the intracrater dunes climb up crater walls to provide sand to the wind streaks. The relations between dunes, wind streak, and subjacent terrain imply that dark-toned grains finer than those which comprise the dunes are lifted into suspension and carried out of the craters to be deposited on the adjacent terrain. Such grains are most likely in the silt size range (3.9-62.5 micrometers). The streaks change in terms of extent, relative albedo, and surface pattern over periods measured in years, but very little evidence for recent eolian activity (dust plumes, storms, dune movement) has been observed.

Spatial distribution and ecological risk assessment of heavy metals in coastal surface sediments in the Hebei Province offshore area, Bohai Sea, China

USGS Publications Warehouse

Ding, Xigui; Ye, Siyuan; Yuan, Hongming; Krauss, Ken W.

2018-01-01

Seven hundred and nine surface sediment samples, along with deeper sediment samples, were collected from Hebei Province along the coastal section of the Bohai Sea, China, and analyzed for grain size, concentrations of organic carbon (Corg) and heavy metals (Cu, Pb, Zn, Cr, Cd, As, and Hg). Results indicated that the average concentrations in the sediments were 16.1 mg/kg (Cu), 19.4 mg/kg (Pb), 50 mg/kg (Zn), 48.8 mg/kg (Cr), 0.1 mg/kg (Cd), 8.4 mg/kg (As), and 20.3 μg/kg (Hg). These concentrations generally met the China Marine Sediment Quality criteria. However, both pollution assessments indicated moderate to strong Cd and Hg contamination in the study area. The potential ecological risk index suggested that the combined ecological risk of the seven studied metals may be low, but that 24.5% of the sites, where sediments were more finer and higher in Corg concentration, had high ecological risk in Hg and Cd pollution.

Algal Turf Sediments and Sediment Production by Parrotfishes across the Continental Shelf of the Northern Great Barrier Reef

PubMed Central

Goatley, Christopher H. R.; Bellwood, David R.

2017-01-01

Sediments are found in the epilithic algal matrix (EAM) of all coral reefs and play important roles in ecological processes. Although we have some understanding of patterns of EAM sediments across individual reefs, our knowledge of patterns across broader spatial scales is limited. We used an underwater vacuum sampler to quantify patterns in two of the most ecologically relevant factors of EAM sediments across the Great Barrier Reef: total load and grain size distribution. We compare these patterns with rates of sediment production and reworking by parrotfishes to gain insights into the potential contribution of parrotfishes to EAM sediments. Inner-shelf reef EAMs had the highest sediment loads with a mean of 864.1 g m-2, compared to 126.8 g m-2 and 287.4 g m-2 on mid- and outer-shelf reefs, respectively. High sediment loads were expected on inner-shelf reefs due to their proximity to the mainland, however, terrigenous siliceous sediments only accounted for 13–24% of total mass. On inner-shelf reef crests parrotfishes would take three months to produce the equivalent mass of sediment found in the EAM. On the outer-shelf it would take just three days, suggesting that inner-shelf EAMs are characterised by low rates of sediment turnover. By contrast, on-reef sediment production by parrotfishes is high on outer-shelf crests. However, exposure to oceanic swells means that much of this production is likely to be lost. Hydrodynamic activity also appears to structure sediment patterns at within-reef scales, with coarser sediments (> 250 μm) typifying exposed reef crest EAMs, and finer sediments (< 250 μm) typifying sheltered back-reef EAMs. As both the load and grain size of EAM sediments mediate a number of important ecological processes on coral reefs, the observed sediment gradients are likely to play a key role in the structure and function of the associated coral reef communities. PMID:28122042

An optical age chronology of late Quaternary extreme fluvial events recorded in Ugandan dambo soils

USGS Publications Warehouse

Mahan, S.A.; Brown, D.J.

2007-01-01

There is little geochonological data on sedimentation in dambos (seasonally saturated, channel-less valley floors) found throughout Central and Southern Africa. Radiocarbon dating is problematic for dambos due to (i) oxidation of organic materials during dry seasons; and (ii) the potential for contemporary biological contamination of near-surface sediments. However, for luminescence dating the equatorial site and semi-arid climate facilitate grain bleaching, while the gentle terrain ensures shallow water columns, low turbidity, and relatively long surface exposures for transported grains prior to deposition and burial. For this study, we focused on dating sandy strata (indicative of high-energy fluvial events) at various positions and depths within a second-order dambo in central Uganda. Blue-light quartz optically stimulated luminescences (OSL) ages were compared with infrared stimulated luminescence (IRSL) and thermoluminescence (TL) ages from finer grains in the same sample. A total of 8 samples were dated, with 6 intervals obtained at ???35, 33, 16, 10.4, 8.4, and 5.9 ka. In general, luminescence ages were stratigraphically, geomorphically and ordinally consistent and most blue-light OSL ages could be correlated with well-dated climatic events registered either in Greenland ice cores or Lake Victoria sediments. Based upon OSL age correlations, we theorize that extreme fluvial dambo events occur primarily during relatively wet periods, often preceding humid-to-arid transitions. The optical ages reported in this study provide the first detailed chronology of dambo sedimentation, and we anticipate that further dambo work could provide a wealth of information on the paleohydrology of Central and Southern Africa. ?? 2006 Elsevier Ltd. All rights reserved.

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

Mexican Ridges passive margin foldbelt of western Gulf of Mexico detached along the top of an extensive, Oligocene mass transport complex

NASA Astrophysics Data System (ADS)

Fick, A.; Mann, P.

2016-12-01

The Mexican Ridges fold-thrust belt (MRFTB) is a 110-210-km-wide and 500-600-km long passive margin, deep-water fold belt fringing the eastern Mexico continental shelf and deepwater western Gulf of Mexico (WGOM). Previous workers determined: 1) that the MRFTB formed in response to multiple gravity sliding events along multiple, Paleogene shale horizons during the Neogene and 2) that down-dip, east-west shortening ranges from 12-22 km in the deep western GOM basin is paired with updip extension of 9-10 km along the Mexican shelf. We have used a grid of 9,440 km's of 2D seismic lines tied to 2 wells to better constrain the detachment underlying the MRFTB. In the northern fold belt, fault detachment and detachment folds in the competent Neogene stratigraphy are cored by a ductile wedge of finer-grained Oligocene sediment ranging in thickness from 0-900 meters. The wedge covers approximately 81,750 km2 and extends 300 kilometers from its onlap onto the Eocene shelf to its downdip pinchout in the deepwater GOM basin. Previous workers have interpreted the Oligocene strata coring the folds to be composed of finer grained sediments with some chaotic seismic facies or homogeneous shales but have not mapped this detachment surface in detail. Our new 2D seismic reflection data tied to wells shows that the basal detachment of the MRFTB is a thickening-landward, wedge of stacked, fine-grained mass transport complexes (MTCs). This Oligocene aged MTC has experienced significant internal deformation in the proximal shelf area while its depositional facies are well preserved in the more distal deepwater areas of the GOM. Elevated pore and fluid pressure in the MTC complex may have contributed to its role as a regional detachment underlying the Mexican Ridges fold-thrust belt along with defining the regional, lobate geometry of the MRFTB.

Hydrological regime as key to the morpho-texture and activity of braided streams

NASA Astrophysics Data System (ADS)

Storz-Peretz, Y.; Laronne, J. B.

2012-04-01

Braided streams are a common fluvial pattern in different climates. However, studies of gravel braided streams have mainly been conducted in humid braided systems or in flume simulations thereof, leaving arid braided streams scarcely investigated. Dryland rivers have bare catchments, rapid flow recession and unarmoured channel beds which are responsible for very high bedload discharges, thereby increasing the likelihood for braiding. Our main objective is to characterize the morpho-texture of the main morphological elements - mid-channel bars, chutes and anabranches (braid-cells) in the dryland braided system and compare them to their humid counterparts. Selected areas of the dryland braided Wadis Ze'elim, Rahaf and Roded in the SE hyper-arid Israel were measured, as were La-Bleone river in the French pre-alps along with the Saisera and Cimoliana rivers in NE Italy representing humid braided systems. Terrestrial Laser Scanning (TLS) of morphological units produced point clouds from which high resolution accurate Digital Elevation Models (DEMs) were extracted. Active braid cells in humid environments were also surveyed by electronic theodolite. Roughness and upper tail Grain Size Distribution (GSD) quantiles were derived from the scanned point clouds or from Wolman sampling. Results indicate that dryland anabranches tend to be finer-grained and less armoured than the bars, contrary to the humid braided systems, where the main or larger anabranches are coarser-grained and more armoured than the bars. Chutes are commonly similar or coarser-grained than the bars they dissect, in accordance with their steeper gradients due to the considerable relief of the bar-anabranch. The morpho-texture displayed in the steep braided Saisera River, located in the Italian Dolomites having the highest annual precipitation, has similarity to that of the dryland braided channels. In drylands coarse gravel is deposited mainly as bars due to the high flux of bedload, whereas the rapid flow recession is responsible for deposition of finer sediment with minimal winnowing in the branch channels. Therefore, channels are finer-grained than the bars. This process is associated with the mid-channel deposition of central bars. However, the steeper chutes and coarser anabranches are associated with erosive braiding processes, such as chute cutoffs and multiple bar dissection, allowing winnowing to occur also during rapid recession. Hence coarser-grained anabranches in drylands are essentially chutes. Lengthy flow recession in humid braided channels allows winnowing of fines, thereby generating armored channels, the finer sedimentary particles often deposited downstream as unit bars. Therefore, channels are coarser-grained than the bars they surround. Even though the steep Saisera is in a humid region, its hydrological regime is ephemeral with rapid and short recessions, responsible for a morpho-texture similar to that of dryland braided streams. Hence, the hydrologic regimen is a key to understanding the morpho-textural character of braided channels and for the higher activity of the ephemeral unarmoured channels in sub-barful events compared to their humid counterparts.

Geophysical bed sediment characterization of the Androscoggin River from the former Chlor-Alkali Facility Superfund Site, Berlin, New Hampshire, to the state border with Maine, August 2009

USGS Publications Warehouse

Degnan, James R.; Teeple, Andrew; Johnston, Craig M.; Marvin-DiPasquale, Mark C.; Luce, Darryl

2011-01-01

The former Chlor-Alkali Facility in Berlin, New Hampshire, was listed on the U.S. Environmental Protection Agency National Priorities List in 2005 as a Superfund site. The Chlor-Alkali Facility lies on the east bank of the Androscoggin River. Elemental mercury currently discharges from that bank into the Androscoggin River. The nature, extent, and the speciation of mercury and the production of methyl mercury contamination in the adjacent Androscoggin River is the subject of continuing investigations. The U.S. Geological Survey, in cooperation with Region I of the U.S. Environmental Protection Agency, used geophysical methods to determine the distribution, thickness, and physical properties of sediments in the Androscoggin River channel at a small area of an upstream reference reach and downstream from the site to the New Hampshire–Maine State border. Separate reaches of the Androscoggin River in the study area were surveyed with surface geophysical methods including ground-penetrating radar and step-frequency electromagnetics. Results were processed to assess sediment characteristics including grain size, electrical conductivity, and pore-water specific conductance. Specific conductance measured during surface- and pore-water sampling was used to help interpret the results of the geophysical surveys. The electrical resistivity of sediment samples was measured in the laboratory with intact pore water for comparison with survey results. In some instances, anthropogenic features and land uses, such as roads and power lines affected the detection of riverbed properties using geophysical methods; when this occurred, the data were removed. Through combining results, detailed riverbed sediment characterizations were made. Results from ground-penetrating radar surveys were used to image and measure the depth to the riverbed, depth to buried riverbeds, riverbed thickness and to interpret material-type variations in terms of relative grain size. Fifty two percent of the riverbed in the study area was covered with gravel and finer sediments. The electrically resistive river water and sediment in this study area were conducive to the penetration of the ground-penetrating radar and step-frequency electromagnetic signals and allowed for effective sediment characterization by geophysical methods. The reach between the former Chlor-Alkali Facility and the Riverside Dam, had small areas of fine sediment (estimated 11 percent of riverbed area), found on the upstream left bank and the downstream right bank, with an electromagnetic conductivity (31.4 millisiemens per meter (mS/m) maximum) that was higher than the upstream reference reach. The greatest electromagnetic conductivity (195 mS/m), pore-water specific conductance (324 mS/m) and lab measured sediment conductivity of (76.8 mS/m, measured with a direct-current resistivity test box) in the study were measured approximately 1 mile (mi) downstream of the site from a sandbar on the left bank. Reaches adjacent to and within 2 mi downstream from the site had elevated electromagnetic conductivity despite having lower estimated percentages of riverbed area covered in sediment (11, 25, and 61 percent, respectively) than the reference reach (97). Typically finer grained sediment with similar mineralogy will be more conductive. The Shelburne Reservoir is approximately 8 mi downstream from the site had the second greatest pore-water specific conductance measured, 45.8 mS/m. Many of the locations with the largest step-frequency electromagnetic values have not been sampled for pore water and sediment.

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.

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.

Testing Models of Modern Glacial Erosion of the St. Elias Mountains, Alaska Using Marine Sediment Provenance

NASA Astrophysics Data System (ADS)

Penkrot, M. L.; Jaeger, J. M.; Loss, D. P.; Bruand, E.

2015-12-01

The glaciated coastal St. Elias Range in Alaska is a primary site to examine climate-tectonic interactions. Work has primarily focused on the Bering-Bagley and Malaspina-Seward ice fields, utilizing detrital and bedrock zircon and apatite geochronology to examine local exhumation and glacial erosion (Berger et al., 2008; Enkelmann et al., 2009; Headly et al., 2013). These studies argue for specific regions of tectonically focused or climatically widespread glacial erosion. Analyzed zircon and apatite grains are sand size, however glacial erosion favors the production of finer-grained sediments. This study focuses on the geochemical provenance of the silt-size fraction (15-63μm) of surface sediments collected throughout the Gulf of Alaska (GOA) seaward of the Bering and Malaspina glaciers to test if the exhumation patterns observed in zircon and apatites are also applicable for the silt size fraction. Onshore bedrock Al-normalized elemental data were used to delineate sediment sources, and a subset of provenance-applicable elements was chosen. Detrital thermochronologic data suggest that sediment produced by the Bagley/Bering system is derived from bedrock on the windward side with input from the Chugach Metamorphic Complex (CMC) underlying the Bagley only during glacial surge events (Headly et al., 2013). Geochemical observations of GOA silt deposited during the 1994-95 surge event confirm input of CMC sediment (elevated in Cr, Ni, Sc, Sr, depleted in Hf, Pb and Rb relative to Kultieth and Poul Creek formations). We also observe a windward-side sediment source (Kultieth and Poul Creek). It is hypothesized that the sediment carried by the Malaspina is primarily from CMC rock underlying the Seward ice field mixed with Yakataga formation rock that underlies the Seward throat (Headly et al., 2013). Geochemical observations of GOA silt support this hypothesis.

The Role of Source Material in Basin Sedimentation, as Illustrated within Eureka Valley, Death Valley National Park, CA.

NASA Astrophysics Data System (ADS)

Lawson, M. J.; Yin, A.; Rhodes, E. J.

2015-12-01

Steep landscapes are known to provide sediment to sink regions, but often petrological factors can dominate basin sedimentation. Within Eureka Valley, in northwestern Death Valley National Park, normal faulting has exposed a steep cliff face on the western margin of the Last Chance range with four kilometers of vertical relief from the valley floor and an angle of repose of nearly 38 degrees. The cliff face is composed of Cambrian limestone and dolomite, including the Bonanza King, Carrara and Wood Canyon formations. Interacting with local normal faulting, these units preferentially break off the cliff face in coherent blocks, which result in landslide deposits rather than as finer grained material found within the basin. The valley is well known for a large sand dune, which derives its sediment from distal sources to the north, instead of from the adjacent Last Chance Range cliff face. During the Holocene, sediment is sourced primary from the northerly Willow Wash and Cucomungo canyon, a relatively small drainage (less than 80 km2) within the Sylvan Mountains. Within this drainage, the Jurassic quartz monzonite of Beer Creek is heavily fractured due to motion of the Fish Valley Lake - Death Valley fault zone. Thus, the quartz monzonite is more easily eroded than the well-consolidated limestone and dolomite that forms the Last Change Range cliff face. As well, the resultant eroded material is smaller grained, and thus more easily transported than the limestone. Consequently, this work highlights an excellent example of the strong influence that source material can have on basin sedimentation.

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.

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.

Origin of intraformational folds in the Jurassic Todilto Limestone, Ambrosia Lake uranium mining district, McKinley and Valencia counties, New Mexico

USGS Publications Warehouse

Green, M.W.

1982-01-01

The Todilto Limestone of Middle Jurassic age in the Ambrosia Lake uranium mining district of McKinley and Valencia Counties, New Mexico, is the host formation for numerous small- to medium-sized uranium deposits in joints, shear zones, and fractures within small- to large-scale intraformational folds. The folds probably were formed as a result of differential sediment loading when eolian sand dunes of the overlying Summerville Formation of Middle Jurassic age migrated over soft, chemically precipitated, lime muds of the Todilto shortly after their deposition in a regressive, mixed fresh and saline lacustrine or marine environment of deposition. Encroachment of Summerville eolian dunes over soft Todilto lime muds was apparently a local phenomenon and was restricted to postulated beltlike zones which trended radially across the Todilto coastline toward the receding body of water. Intraformational folding is believed to be confined to the pathways of individual eolian dunes or clusters of dunes within the dune belts. During the process of sediment loading by migrating sand dunes, layers of Todilto lime mud were differentially compacted, contorted, and dewatered, producing both small- and large-scale plastic deformation structures, including convolute laminations, mounds, rolls, folds, and small anticlines and synclines. With continued compaction and dewatering, the mud, in localized areas, reached a point of desaturation at which sediment plasticity was lost. Prolonged loading by overlying dune sands thus caused faulting, shearing, fracturing, and jointing of contorted limestone beds. These areas or zones of deformation within the limestone became the preferred sites of epigenetic uranium mineralization because of the induced transmissivity created by sediment rupture. Along most of the prograding Todilto coastline, adjacent to the eolian dune belts, both interdune and coastal sabkha environments dominated during Todilto-Summerville time. Sediments in coastal areas consisted mainly of clay, silt, sandy silt, and very fine-grained sand, which was apparently derived from the winnowing of the finer grained fraction of sediment from adjacent dune fields during periods of eolian activity. Most of the sabkha sediments were probably carried in airborne suspension to the low-lying, ground-water-saturated coastal areas, where they were deposited as relatively uniform blanket-like layers. Deposition of sabkha deposits was apparently slow and uniform over most of the Todilto coastal areas and crested only small-scale deformation features in underlying Todilto rocks. Large-scale deformation features and uranium deposits are both notably absent in the Todilto where it is overlain by finer textured sabkha deposits in the Summerville.

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.

Spatial distribution and ecological risk assessment of heavy metals in coastal surface sediments in the Hebei Province offshore area, Bohai Sea, China.

PubMed

Ding, Xigui; Ye, Siyuan; Yuan, Hongming; Krauss, Ken W

2018-06-01

Seven hundred and nine surface sediment samples, along with deeper sediment samples, were collected from Hebei Province along the coastal section of the Bohai Sea, China, and analyzed for grain size, concentrations of organic carbon (Corg) and heavy metals (Cu, Pb, Zn, Cr, Cd, As, and Hg). Results indicated that the average concentrations in the sediments were 16.1 mg/kg (Cu), 19.4 mg/kg (Pb), 50 mg/kg (Zn), 48.8 mg/kg (Cr), 0.1 mg/kg (Cd), 8.4 mg/kg (As), and 20.3 μg/kg (Hg). These concentrations generally met the China Marine Sediment Quality criteria. However, both pollution assessments indicated moderate to strong Cd and Hg contamination in the study area. The potential ecological risk index suggested that the combined ecological risk of the seven studied metals may be low, but that 24.5% of the sites, where sediments were finer and higher in Corg concentration, had high ecological risk in Hg and Cd pollution. Copyright © 2018 Elsevier Ltd. All rights reserved.

Debris flows in Grand Canyon National Park, Arizona: magnitude, frequency and effects on the Colorado River

USGS Publications Warehouse

Melis, Theodre S.; Webb, Robert H.; ,

1993-01-01

Debris flows are recurrent sediment-transport processes in 525 tributaries of the Colorado River in Grand Canyon. Arizona. Initiated by slope failures in bedrock and (or) colluvium during intense rainfall, Grand Canyon debris flows are high-magnitude, short-duration floods. Debris flows in these tributaries transport very large boulders into the river where they accumulate on debris fans and form rapids. The frequency of debris flows range from less than 1 per century to 10 or more per century in these tributaries. Before regulation by Glen Canyon Dam in 1963, high-magnitude floods on the Colorado River reworked debris fans by eroding all particles except large boulders. Because flow regulation has substantially decreased the river's competence, debris flows occurring after 1963 have increased accumulation of finer-grained sediments on debris fans and in rapids.

Analysis of Long Wave Infrared (LWIR) Soil Data to Predict Reflectance Response

DTIC Science & Technology

2009-08-01

Aridisol red-orange sandy soil 6% x 16% 61 12% smectite Aridisol grey calcareous silty soil x 19% 49 22% smectite ...trace 16% 59 20% smectite ; grain size analysis of fraction finer than 2 mm indicates 35% finer than 20 micrometer (12% finer than 5 micrometer...Entisol red-orange sandy loam/alluvium see comment 8% x 10% 72 7% smectite ; 47% finer than 20 μm (22% finer than 5 μm) Entisol sandy

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.

Sediment Carbon Accumulation in Southern Latitude Saltmarsh Communities of Tasmania, Australia.

PubMed

Ellison, Joanna C; Beasy, Kim M

2018-05-02

Carbon sequestration values of wetlands are greatest in their sediments. Northern hemisphere research dominates the earlier saltmarsh carbon sequestration literature, recently augmented by analyses across mainland Australia where species assemblages, catchment histories and environmental settings differ. No previous assessment has been made for Tasmania. Carbon stores and accumulation rates in saltmarsh sediments of the Rubicon estuary, Tasmania, were investigated. Carbon was determined from sediment cores by Elemental Analyser, combined with analysis of organic content and bulk density. Carbon accumulation was determined using short-term and long-term sediment accretion indicators. Results showed carbon densities to be lower than global averages, with variation found between carbon stores of native and introduced species zones. Cores from introduced Spartina anglica indicated a trend of higher sediment carbon percentages relative to cores from native saltmarsh Juncus kraussii and Sarcocornia quinqueflora , and in finer grain sizes. Sediment carbon stock of 30 cm depths was 49.5 Mg C ha −1 for native saltmarsh and 55.5 Mg C ha −1 for Spartina . Carbon percentages were low owing to high catchment inorganic sediment yields, however carbon accumulation rates were similar to global averages, particularly under Spartina . Covering 85% of saltmarsh area in the estuary, Spartina contributes the majority to carbon stores, potentially indicating a previously unrecognized value for this invasive species in Australia.

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.

Wave Glider Monitoring of Sediment Transport and Dredge Plumes in a Shallow Marine Sandbank Environment.

PubMed

Van Lancker, Vera; Baeye, Matthias

2015-01-01

As human pressure on the marine environment increases, safeguarding healthy and productive seas increasingly necessitates integrated, time- and cost-effective environmental monitoring. Employment of a Wave Glider proved very useful for the study of sediment transport in a shallow sandbank area in the Belgian part of the North Sea. During 22 days, data on surface and water-column currents and turbidity were recorded along 39 loops around an aggregate-extraction site. Correlation with wave and tidal-amplitude data allowed the quantification of current- and wave-induced advection and resuspension, important background information to assess dredging impacts. Important anomalies in suspended particulate matter concentrations in the water column suggested dredging-induced overflow of sediments in the near field (i.e., dynamic plume), and settling of finer-grained material in the far field (i.e., passive plume). Capturing the latter is a successful outcome to this experiment, since the location of dispersion and settling of a passive plume is highly dependent on the ruling hydro-meteorological conditions and thus difficult to predict. Deposition of the observed sediment plumes may cause habitat changes in the long-term.

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.

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.

Paleo-environmental Setting of the Murray Formation of Aeolis Mons, Gale Crater, Mars, as Explored by the Curiosity Rover

NASA Astrophysics Data System (ADS)

Lewis, K. W.; Fedo, C.; Grotzinger, J. P.; Gupta, S.; Stein, N.; Rivera-Hernandez, F.; Watkins, J. A.; Banham, S.; Edgett, K. S.; Minitti, M. E.; Schieber, J.; Edgar, L. A.; Siebach, K. L.; Stack, K.; Newsom, H. E.; House, C. H.; Sumner, D. Y.; Vasavada, A. R.

2017-12-01

Since landing, the Mars Science Laboratory Curiosity rover climbed 300 meters in elevation from the floor of north Gale crater up the lower northwest flank of Aeolis Mons ("Mount Sharp"). Nearly 200 meters of this ascent was accomplished in the 1.5 years alone, as the rover was driven up-section through the sedimentary rocks of the informally designated "Murray" formation. This unit comprises a large fraction of the lower strata of Mt. Sharp along the rover traverse. Our exploration of the Murray formation reveals a diverse suite of fine-grained facies. Grain sizes range from finer grains than can be resolved by the MAHLI imager (particles <62.5 microns) up to medium sand; the finer fraction comprises the bulk of the stratigraphy. Layering occurs at a range of scales; the majority is expressed as parallel laminae of mm-scale. Some sandy stratigraphic intervals exhibit cross-stratification at ripple (cm) and dune (m and larger) scales; the inferred bedforms are consistent with a range of subaqueous and aeolian depositional settings. Diagenetic features include locally variable occurrences of concretions and near-ubiquitous Ca-sulfate veins; these attest to extended interaction of the sediment with aqueous fluids in the subsurface. As a whole, the sedimentary facies of the Murray formation have been interpreted to record a predominately lacustrine paleo-environment, with likely subaerial aeolian and fluvial intervals. Further exploration, including the campaign at the hematite-bearing Vera Rubin Ridge, continues to reveal the complex and long-lived depositional history of the Gale crater basin.

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

Characteristics and origin of Earth-mounds on the Eastern Snake River Plain, Idaho

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

Tullis, J.A.

1995-09-01

Earth-mounds are common features on the Eastern Snake River Plain, Idaho. The mounds are typically round or oval in plan view, <0.5 m in height, and from 8 to 14 m in diameter. They are found on flat and sloped surfaces, and appear less frequently in lowland areas. The mounds have formed on deposits of multiple sedimentary environments. Those studied included alluvial gravel terraces along the Big Lost River (late Pleistocene/early Holocene age), alluvial fan segments on the flanks of the Lost River Range (Bull Lake and Pinedale age equivalents), and loess/slopewash sediments overlying basalt flows. Backhoe trenches were dugmore » to allow characterization of stratigraphy and soil development. Each mound has features unique to the depositional and pedogenic history of the site; however, there are common elements to all mounds that are linked to the history of mound formation. Each mound has a {open_quotes}floor{close_quotes} of a sediment or basement rock of significantly different hydraulic conductivity than the overlying sediment. These paleosurfaces are overlain by finer-grained sediments, typically loess or flood-overbank deposits. Mounds formed in environments where a sufficient thickness of fine-grained sediment held pore water in a system open to the migration to a freezing front. Heaving of the sediment occurred by the growth of ice lenses. Mound formation occurred at the end of the Late Pleistocene or early in the Holocene, and was followed by pedogenesis. Soils in the mounds were subsequently altered by bioturbation, buried by eolian deposition, and eroded by slopewash runoff. These secondary processes played a significant role in maintaining or increasing the mound/intermound relief.« less

Application of sedimentary-structure interpretation to geoarchaeological investigations in the Colorado River Corridor, Grand Canyon, Arizona, USA

USGS Publications Warehouse

Draut, A.E.; Rubin, D.M.; Dierker, J.L.; Fairley, H.C.; Griffiths, R.E.; Hazel, J.E.; Hunter, R.E.; Kohl, K.; Leap, L.M.; Nials, F.L.; Topping, D.J.; Yeatts, M.

2008-01-01

We present a detailed geoarchaeological study of landscape processes that affected prehistoric formation and modern preservation of archaeological sites in three areas of the Colorado River corridor in Grand Canyon, Arizona, USA. The methods used in this case study can be applied to any locality containing unaltered, non-pedogenic sediments and, thus, are particularly relevant to geoarchaeology in arid regions. Resolving the interaction of fluvial, aeolian, and local runoff processes in an arid-land river corridor is important because the archaeological record in arid lands tends to be concentrated along river corridors. This study uses sedimentary structures and particle-size distributions to interpret landscape processes; these methods are commonplace in sedimentology but prove also to be valuable, though less utilized, in geoarchaeology and geomorphology. In this bedrock canyon, the proportion of fluvial sediment generally decreases with distance away from the river as aeolian, slope-wash, colluvial, and debris-flow sediments become more dominant. We describe a new facies consisting of 'flood couplets' that include a lower, fine-grained fluvial component and an upper, coarser, unit that reflects subaerial reworking at the land surface between flood events. Grain-size distributions of strata that lack original sedimentary structures are useful within this river corridor to distinguish aeolian deposits from finer-grained fluvial deposits that pre-date the influence of the upstream Glen Canyon Dam on the Colorado River. Identification of past geomorphic settings is critical for understanding the history and preservation of archaeologically significant areas, and for determining the sensitivity of archaeological sites to dam operations. Most archaeological sites in the areas studied were formed on fluvial deposits, with aeolian deposition acting as an important preservation agent during the past millennium. Therefore, the absence of sediment-rich floods in this regulated river, which formerly deposited large fluvial sandbars from which aeolian sediment was derived, has substantially altered processes by which the prehistoric, inhabited landscape formed, and has also reduced the preservation potential of many significant cultural sites.

Loess as a Quaternary paleoenvironmental indicator

USGS Publications Warehouse

Muhs, Daniel R.; Prins, M.A.; Machalett, B.

2014-01-01

Loess is aeolian sediment that is dominated by silt-sized particles. Unlike either coarser dune sand or finer-grained, long-range-transported dust, loess is relatively poorly sorted, reflecting a combination of transport processes, including saltation, low suspension, and high suspension. Loess can be readily identified in the field; deposits range in thickness from a few centimeters to many tens of meters, and are found over large areas of Eurasia, South and North America (Fig. 1), and smaller areas of New Zealand, Australia, Africa and the Middle East. Loess covers approximately 10% of the Earth’s land surface and is therefore one of the most important terrestrial archives of paleoenvironmental change during the Quaternary. In many regions, loess sections consist of deposits of mostly unaltered sediment with intercalated paleosols. Paleosols represent periods of landscape stability when loess deposition ceased altogether, or at least slowed significantly. Loess can be dated directly using luminescence, radiocarbon, and amino acid geochronology methods.

Magnetic properties of sediments from Ocean Drilling Program sites 1109, 1115, and 1118 (Leg 180), Woodlark Basin (Papua New Guinea)

NASA Astrophysics Data System (ADS)

Ishikawa, N.; Frost, G. M.

2002-09-01

Latest Miocene-Pleistocene synrift sediments at Ocean Drilling Program sites 1109, 1115, and 1118 (Leg 180), located on the hanging wall margin north of the Moresby fault in the Woodlark Basin, showed variations in magnetic parameters carried by magnetite and maghemite related to sedimentation process in the basin. At sites 1109 and 1115, an increase in the sedimentation rate at 3.8 Ma was accompanied by the deposition of sediments with low ferrimagnetic mineral concentrations. An increase in the ferrimagnetic mineral concentrations occurred between 3.4 Ma and 3.2 Ma at the three sites. The onset age of the change became younger with distance from the subsidence center of the basin near the Moresby fault: 3.4 Ma at Site 1118, 3.3 Ma at Site 1109, and 3.2 Ma at Site 1115, which implies a northward onlapping of sediments with high ferrimagnetic mineral concentration. Sediments with finer-grained ferrimagnetic minerals were deposited between 2.3 and 2.0 Ma at sites 1118 and 1109 and later, 2.8 Ma at Site 1115 during a period of a low sedimentation rate. The upper parts of sites 1109 and 1115 had a diamagnetic contribution, which is attributed to relatively high concentrations of diamagnetic pelagic materials at a low sedimentation rate associated with the low frequency of turbidites.

Source, transport and fluxes of Amazon River particulate organic carbon: Insights from river sediment depth-profiles

NASA Astrophysics Data System (ADS)

Bouchez, Julien; Galy, Valier; Hilton, Robert G.; Gaillardet, Jérôme; Moreira-Turcq, Patricia; Pérez, Marcela Andrea; France-Lanord, Christian; Maurice, Laurence

2014-05-01

In order to reveal particulate organic carbon (POC) source and mode of transport in the largest river basin on Earth, we sampled the main sediment-laden tributaries of the Amazon system (Solimões, Madeira and Amazon) during two sampling campaigns, following vertical depth-profiles. This sampling technique takes advantage of hydrodynamic sorting to access the full range of solid erosion products transported by the river. Using the Al/Si ratio of the river sediments as a proxy for grain size, we find a general increase in POC content with Al/Si, as sediments become finer. However, the sample set shows marked variability in the POC content for a given Al/Si ratio, with the Madeira River having lower POC content across the measured range in Al/Si. The POC content is not strongly related to the specific surface area (SSA) of the suspended load, and bed sediments have a much lower POC/SSA ratio. These data suggest that SSA exerts a significant, yet partial, control on POC transport in Amazon River suspended sediment. We suggest that the role of clay mineralogy, discrete POC particles and rock-derived POC warrant further attention in order to fully understand POC transport in large rivers.

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.

Non-Fluvial Controls of Erosion, Sediment Transport and Fluvial Morphology in a mid-Atlantic Piedmont Watershed, White Clay Creek, Pennsylvania, U.S.A.

NASA Astrophysics Data System (ADS)

McCarthy, K.; Affinito, R. A.; Pizzuto, J. E.; Stotts, S.; Henry, T.; Krauthauser, M.; O'Neal, M. A.

2017-12-01

Quantifying contemporary sediment budgets is essential for restoration and ecosystem management of mid-Atlantic watersheds, but relevant processes and controls are poorly understood. In the 153 km2 White Clay Creek watershed in southeastern Pennsylvania, longitudinal profiles reflect migration of knickpoints though bedrock over Quaternary timescales. In bank exposures along stream valleys, saprolite, bedrock, and matrix-supported cobbly and bouldery diamicton (likely colluvial) commonly underlie finer-grained clay, silt, sand, and gravel deposits of valley floor depositional environments. Overbank sedimentation rates were quantified by measuring the thickness of sediment deposited over the roots of floodplain trees. The sampled trees range in age from 25-270 years with median sediment accumulation rates of approximately 2 mm/yr (range 0-10 mm/yr). Rates of bank retreat (measured from historical aerial imagery or root-exposure dendrochronology) vary from 6-36 cm/yr, with median rates of 10 cm/yr. While bank erosion rates are subject to a variety of controls, including channel curvature, the density of riparian trees, and freeze-thaw processes, the strongest influence appears to be the grain size and thickness of bouldery diamicton exposed along the toes of retreating banks. Cobbles and boulders supplied by eroding diamicton also mantle the bed of the channel, such that 33- 80% of the bed material remains immobile at bankfull stage. A conceptual model of fluvial processes and sediment budgets for these channels must account for the watershed's history of changing climate, tectonics, and land use, requiring mapping of bedrock, colluvium, former mill dam sediments, and other non-alluvial deposits and controls. Efforts to apply hydraulic geometry principles (requiring a precise adjustment to contemporary hydraulic and sediment regime) or to treat these channels as traditional "threshold" rivers are unlikely to be successful.

Numerical Model of Turbulence, Sediment Transport, and Sediment Cover in a Large Canyon-Bound River

NASA Astrophysics Data System (ADS)

Alvarez, L. V.; Schmeeckle, M. W.

2013-12-01

The Colorado River in Grand Canyon is confined by bedrock and coarse-grained sediments. Finer grain sizes are supply limited, and sandbars primarily occur in lateral separation eddies downstream of coarse-grained tributary debris fans. These sandbars are important resources for native fish, recreational boaters, and as a source of aeolian transport preventing the erosion of archaeological resources by gully extension. Relatively accurate prediction of deposition and, especially, erosion of these sandbar beaches has proven difficult using two- and three-dimensional, time-averaged morphodynamic models. We present a parallelized, three-dimensional, turbulence-resolving model using the Detached-Eddy Simulation (DES) technique. DES is a hybrid large eddy simulation (LES) and Reynolds-averaged Navier Stokes (RANS). RANS is applied to the near-bed grid cells, where grid resolution is not sufficient to fully resolve wall turbulence. LES is applied further from the bed and banks. We utilize the Spalart-Allmaras one equation turbulence closure with a rough wall extension. The model resolves large-scale turbulence using DES and simultaneously integrates the suspended sediment advection-diffusion equation. The Smith and McLean suspended sediment boundary condition is used to calculate the upward and downward settling of sediment fluxes in the grid cells attached to the bed. The model calculates the entrainment of five grain sizes at every time step using a mixing layer model. Where the mixing layer depth becomes zero, the net entrainment is zero or negative. As such, the model is able to predict the exposure and burial of bedrock and coarse-grained surfaces by fine-grained sediments. A separate program was written to automatically construct the computational domain between the water surface and a triangulated surface of a digital elevation model of the given river reach. Model results compare favorably with ADCP measurements of flow taken on the Colorado River in Grand Canyon during the High Flow Experiment (HFE) of 2008. The model accurately reproduces the size and position of the major recirculation currents, and the error in velocity magnitude was found to be less than 17% or 0.22 m/s absolute error. The mean deviation of the direction of velocity with respect to the measured velocity was found to be 20 degrees. Large-scale turbulence structures with vorticity predominantly in the vertical direction are produced at the shear layer between the main channel and the separation zone. However, these structures rapidly become three-dimensional with no preferred orientation of vorticity. Surprisingly, cross-stream velocities, into the main recirculation zone just upstream of the point of reattachment and out of the main recirculation region just downstream of the point of separation, are highest near the bed. Lateral separation eddies are more efficient at storing and exporting sediment than previously modeled. The input of sediment to the eddy recirculation zone occurs near the reattachment zone and is relatively continuous in time. While, the export of sediment to the main channel by the return current occurs in pulses. Pulsation of the strength of the return current becomes a key factor to determine the rates of erosion and deposition in the main recirculation zone.

Authigenic vivianite in Potomac River sediments: control by ferric oxy-hydroxides.

USGS Publications Warehouse

Hearn, P.P.; Parkhurst, D.L.; Callender, E.

1983-01-01

Sand-size aggregates of vivianite crystals occur in the uppermost sediments of the Potomac River estuary immediately downstream from the outfall of a sewage treatment plant at the southernmost boundary of the District of Columbia, USA. They are most abundant in a small area of coarse sand (dredge spoil) which contrasts with the adjacent, much finer sediments. The sewage outfall supplies both reducing conditions and abundant phosphate. Analyses and calculations indicate that the pore waters in all the adjacent sediments are supersaturated with respect to vivianite. Its concentration in the coarse sand is attributed to the absence there of amorphous ferric oxyhydroxides, which are present in the finer sediments and preferentially absorb the phosphate ion. -H.R.B.

The perfect debris flow? Aggregated results from 28 large-scale experiments

USGS Publications Warehouse

Iverson, Richard M.; Logan, Matthew; LaHusen, Richard G.; Berti, Matteo

2010-01-01

Aggregation of data collected in 28 controlled experiments reveals reproducible debris-flow behavior that provides a clear target for model tests. In each experiment ∼10 m3 of unsorted, water-saturated sediment composed mostly of sand and gravel discharged from behind a gate, descended a steep, 95-m flume, and formed a deposit on a nearly horizontal runout surface. Experiment subsets were distinguished by differing basal boundary conditions (1 versus 16 mm roughness heights) and sediment mud contents (1 versus 7 percent dry weight). Sensor measurements of evolving flow thicknesses, basal normal stresses, and basal pore fluid pressures demonstrate that debris flows in all subsets developed dilated, coarse-grained, high-friction snouts, followed by bodies of nearly liquefied, finer-grained debris. Mud enhanced flow mobility by maintaining high pore pressures in flow bodies, and bed roughness reduced flow speeds but not distances of flow runout. Roughness had these effects because it promoted debris agitation and grain-size segregation, and thereby aided growth of lateral levees that channelized flow. Grain-size segregation also contributed to development of ubiquitous roll waves, which had diverse amplitudes exhibiting fractal number-size distributions. Despite the influence of these waves and other sources of dispersion, the aggregated data have well-defined patterns that help constrain individual terms in a depth-averaged debris-flow model. The patterns imply that local flow resistance evolved together with global flow dynamics, contradicting the hypothesis that any consistent rheology applied. We infer that new evolution equations, not new rheologies, are needed to explain how characteristic debris-flow behavior emerges from the interactions of debris constituents.

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.

Reconstructing Tsunami Flow Speed from Sedimentary Deposits

NASA Astrophysics Data System (ADS)

Jaffe, B. E.; Gelfenbaum, G. R.

2014-12-01

Paleotsunami deposits contain information about the flow that created them that can be used to reconstruct tsunami flow speed and thereby improving assessment of tsunami hazard. We applied an inverse tsunami sediment transport model to sandy deposits near Sendai Airport, Japan, that formed during the 11 March 2011 Tohoku-oki tsunami to test model performance and explore the spatial variations in tsunami flow speed. The inverse model assumes the amount of suspended sediment in the water column is in equilibrium with local flow speed and that sediment transport convergences, primarily from bedload transport, do not contribute significantly to formation of the portion of the deposit we identify as formed by sediment settling out of suspension. We interpret massive or inversely graded intervals as forming from sediment transport convergences and do not model them. Sediment falling out of suspension forms a specific type of normal grading, termed 'suspension' grading, where the entire grain size distribution shifts to finer sizes higher up in a deposit. Suspension grading is often observed in deposits of high-energy flows, including turbidity currents and tsunamis. The inverse model calculates tsunami flow speed from the thickness and bulk grain size of a suspension-graded interval. We identified 24 suspension-graded intervals from 7 trenches located near the Sendai Airport from ~250-1350 m inland from the shoreline. Flow speeds were highest ~500 m from the shoreline, landward of the forested sand dunes where the tsunami encountered lower roughness in a low-lying area as it traveled downslope. Modeled tsunami flow speeds range from 2.2 to 9.0 m/s. Tsunami flow speeds are sensitive to roughness, which is unfortunately poorly constrained. Flow speed calculated by the inverse model was similar to those calculated from video taken from a helicopter about 1-2 km inland. Deposit reconstructions of suspension-graded intervals reproduced observed upward shifts in grain size distributions reasonably well. As approaches to estimating paleo-roughness improve, the flow speed and size of paleotsunamis will be better understood and the ability to assess tsunami hazard from paleotsunami deposits will improve.

Wave Glider Monitoring of Sediment Transport and Dredge Plumes in a Shallow Marine Sandbank Environment

PubMed Central

Van Lancker, Vera; Baeye, Matthias

2015-01-01

As human pressure on the marine environment increases, safeguarding healthy and productive seas increasingly necessitates integrated, time- and cost-effective environmental monitoring. Employment of a Wave Glider proved very useful for the study of sediment transport in a shallow sandbank area in the Belgian part of the North Sea. During 22 days, data on surface and water-column currents and turbidity were recorded along 39 loops around an aggregate-extraction site. Correlation with wave and tidal-amplitude data allowed the quantification of current- and wave-induced advection and resuspension, important background information to assess dredging impacts. Important anomalies in suspended particulate matter concentrations in the water column suggested dredging-induced overflow of sediments in the near field (i.e., dynamic plume), and settling of finer-grained material in the far field (i.e., passive plume). Capturing the latter is a successful outcome to this experiment, since the location of dispersion and settling of a passive plume is highly dependent on the ruling hydro-meteorological conditions and thus difficult to predict. Deposition of the observed sediment plumes may cause habitat changes in the long-term. PMID:26070156

Current and sea-level signals in periplatform ooze (Neogene, Maldives, Indian Ocean)

NASA Astrophysics Data System (ADS)

Betzler, Christian; Lüdmann, Thomas; Hübscher, Christian; Fürstenau, Jörn

2013-05-01

Periplatform ooze is an admixture of pelagic carbonate and sediment derived from neritic carbonate platforms. Compositional variations of periplatform ooze allow the reconstruction of past sea-level changes. Periplatform ooze formed during sea-level highstands is finer grained and richer in aragonite through the elevated input of material from the flooded platform compared to periplatform ooze formed during the episodes of lowered sea level. In many cases, however, the sea floor around carbonate platforms is subjected to bottom currents which are expected to affect sediment composition, i.e. through winnowing of the fine fraction. The interaction of sea-level driven highstand shedding and current impact on the formation of periplatform ooze has hitherto not been analyzed. To test if a sea-level driven input signal in periplatform ooze is influenced or even distorted by changing current activity, an integrated study using seismic, hydroacoustic and sedimentological data has been performed on periplatform ooze deposited in the Inner Sea of the Maldives. The Miocene to Pleistocene succession of drift deposits is subdivided into nine units; limits of seismostratigraphic units correspond to changes or turnarounds in grain size trends in cores recovered at ODP Site 716 and NEOMA Site 1143. For the Pleistocene it can be shown how changes in grain size occur in concert with sea-level changes and changes of the monsoonal system, which is thought to be a major driver of bottom currents in the Maldives. A clear highstand shedding pattern only appears in the data at a time of relaxation of monsoonal strength during the last 315 ky. Results imply (1) that drift sediments provide a potential target for analyzing past changes in oceanic currents and (2) that the ooze composition bears a mixed signal of input and physical winnowing at the sea floor.

Lunar soil: Size distribution and mineralogical constituents

USGS Publications Warehouse

Duke, M.B.; Woo, C.C.; Bird, M.L.; Sellers, G.A.; Finkelman, R.B.

1970-01-01

The lunar soil collected by Apollo 11 consists primarily of submillimeter material and is finer in grain size than soil previously recorded photographically by Surveyor experiments. The main constituents are fine-grained to glassy rocks of basaltic affinity and coherent breccia of undetermined origin. Dark glass, containing abundant nickel-iron spheres, coats many rocks, mineral, and breccia fragments. Several types of homogeneous glass occur as fragments and spheres. Colorless spheres, probably an exotic component, are abundant in the fraction finer than 20 microns.

Intercomparison of textural parameters of intertidal sediments generated by different statistical procedures, and implications for a unifying descriptive nomenclature

NASA Astrophysics Data System (ADS)

Fan, Daidu; Tu, Junbiao; Cai, Guofu; Shang, Shuai

2015-06-01

Grain-size analysis is a basic routine in sedimentology and related fields, but diverse methods of sample collection, processing and statistical analysis often make direct comparisons and interpretations difficult or even impossible. In this paper, 586 published grain-size datasets from the Qiantang Estuary (East China Sea) sampled and analyzed by the same procedures were merged and their textural parameters calculated by a percentile and two moment methods. The aim was to explore which of the statistical procedures performed best in the discrimination of three distinct sedimentary units on the tidal flats of the middle Qiantang Estuary. A Gaussian curve-fitting method served to simulate mixtures of two normal populations having different modal sizes, sorting values and size distributions, enabling a better understanding of the impact of finer tail components on textural parameters, as well as the proposal of a unifying descriptive nomenclature. The results show that percentile and moment procedures yield almost identical results for mean grain size, and that sorting values are also highly correlated. However, more complex relationships exist between percentile and moment skewness (kurtosis), changing from positive to negative correlations when the proportions of the finer populations decrease below 35% (10%). This change results from the overweighting of tail components in moment statistics, which stands in sharp contrast to the underweighting or complete amputation of small tail components by the percentile procedure. Intercomparisons of bivariate plots suggest an advantage of the Friedman & Johnson moment procedure over the McManus moment method in terms of the description of grain-size distributions, and over the percentile method by virtue of a greater sensitivity to small variations in tail components. The textural parameter scalings of Folk & Ward were translated into their Friedman & Johnson moment counterparts by application of mathematical functions derived by regression analysis of measured and modeled grain-size data, or by determining the abscissa values of intersections between auxiliary lines running parallel to the x-axis and vertical lines corresponding to the descriptive percentile limits along the ordinate of representative bivariate plots. Twofold limits were extrapolated for the moment statistics in relation to single descriptive terms in the cases of skewness and kurtosis by considering both positive and negative correlations between percentile and moment statistics. The extrapolated descriptive scalings were further validated by examining entire size-frequency distributions simulated by mixing two normal populations of designated modal size and sorting values, but varying in mixing ratios. These were found to match well in most of the proposed scalings, although platykurtic and very platykurtic categories were questionable when the proportion of the finer population was below 5%. Irrespective of the statistical procedure, descriptive nomenclatures should therefore be cautiously used when tail components contribute less than 5% to grain-size distributions.

Design and maintenance of a network for collecting high-resolution suspended-sediment data at remote locations on rivers, with examples from the Colorado River

USGS Publications Warehouse

Griffiths, Ronald E.; Topping, David J.; Andrews, Timothy; Bennett, Glenn E.; Sabol, Thomas A.; Melis, Theodore S.

2012-01-01

Management of sand and finer sediment in fluvial settings has become increasingly important for reasons ranging from endangered-species habitat to transport of sediment-associated contaminants. In all rivers, some fraction of the suspended load is transported as washload, and some as suspended bed material. Typically, the washload is composed of silt-and-clay-size sediment, and the suspended bed material is composed of sand-size sediment. In most rivers, as a result of changes in the upstream supply of silt and clay, large, systematic changes in the concentration of the washload occur over time, independent of changes in water discharge. Recent work has shown that large, systematic, discharge-independent changes in the concentration of the suspended bed material are also present in many rivers. In bedrock canyon rivers, such as the Colorado River in Grand Canyon National Park, changes in the upstream tributary supply of sand may cause large changes in the grain-size distribution of the bed sand, resulting in changes in both the concentration and grain-size distribution of the sand in suspension. Large discharge-independent changes in suspended-sand concentration coupled to discharge-independent changes in the grain-size distribution of the suspended sand are not unique to bedrock canyon rivers, but also occur in large alluvial rivers, such as the Mississippi River. These systematic changes in either suspended-silt-and-clay concentration or suspended-sand concentration may not be detectable by using conventional equal-discharge- or equal-width-increment measurements, which may be too infrequently collected relative to the time scale over which these changes in the sediment load are occurring. Furthermore, because large discharge-independent changes in both suspended-silt-and-clay and suspended-sand concentration are possible in many rivers, methods using water discharge as a proxy for suspended-sediment concentration (such as sediment rating curves) may not produce sufficiently accurate estimates of sediment loads. Finally, conventional suspended-sediment measurements are both labor and cost intensive and may not be possible at the resolution required to resolve discharge-independent changes in suspended-sediment concentration, especially in more remote locations. For these reasons, the U.S. Geological Survey has pursued the use of surrogate technologies (such as acoustic and laser diffraction) for providing higher-resolution measurements of suspended-sediment concentration and grain size than are possible by using conventional suspended-sediment measurements alone. These factors prompted the U.S. Geological Survey's Grand Canyon Monitoring and Research Center to design and construct a network to automatically measure suspended-sediment transport at 15-minute intervals by using acoustic and laser-diffraction surrogate technologies at remote locations along the Colorado River within Marble and Grand Canyons in Grand Canyon National Park. Because of the remoteness of the Colorado River in this reach, this network also included the design of a broadband satellite-telemetry system to communicate with the instruments deployed at each station in this network. Although the sediment-transport monitoring network described in this report was developed for the Colorado River in Grand Canyon National Park, the design of this network can easily be adapted for use on other rivers, no matter how remote. In the Colorado River case-study example described in this report, suspended-sediment concentration and grain size are measured at five remote stations. At each of these stations, surrogate measurements of suspended-sediment concentration and grain size are made at 15-minute intervals using an array of different single-frequency acoustic-Doppler side-looking profilers. Laser-diffraction instruments are also used at two of these stations to measure both suspended-sediment concentrations and grain-size distributions. Cross-section calibrations of these instruments have been constructed and verified by using either equal-discharge-increment (EDI) or equal-width-increment (EWI) measurements of the velocity-weighted suspended-sediment concentration and grain-size distribution. The suspended-silt-and-clay concentration parts of these calibration relations have also included information from EDI- or EWI-calibrated samples collected by automatic pump samplers. Three of the monitoring stations are equipped with two-way satellite broadband telemetry systems that operate once a day to remotely monitor and program the instruments and download data. Data from these stations are typically downloaded twice per month; data from stations without satellite-telemetry systems are downloaded during site visits, which occur every 2 months or semiannually, depending on the remoteness of the site. Upon downloading and processing, suspended-silt-and-clay concentration, suspended-sand concentration, and suspended-sand median grain size are posted on the World Wide Web. Satellite telemetry in combination with the high-resolution sediment surrogate measurements can generate near-real-time suspended-sediment-concentration and grain-size data (limited only by the time required to download the instruments and process the data). The approach for measuring suspended-sediment concentration and grain size using this monitoring network is more practical, and can be done at a much lower cost and with higher temporal resolution, than any other method.

Climate change in southern Illinois, USA, based on the age and δ13C of organic matter in cave sediments

USGS Publications Warehouse

Panno, Samuel V.; Curry, B. Brandon; Wang, Hongfang; Hackley, Keith C.; Liu, Chao-Li; Lundstrom, Craig; Zhou, Juanzuo

2004-01-01

Matrix-supported diamicton and uniform to laminated, silty, fine-grained sediment deposited from about 42,500 to 27,600 cal yr B.P. under slackwater conditions nearly filled two caves in southwestern Illinois. At some point, most of the sediment was flushed from the caves and from about 22,700 to 4000 cal yr B.P., floods deposited a drape of sandy and silty sediment on remnant slackwater successions, cobbly alluvium, and bedrock (especially from 7700 to 4000 cal yr B.P.). Clay mineral analyses of the slackwater cave sediment reveal a provenance of chiefly Petersburg Silt, a smectite- and illite-rich proglacial lacustrine unit present in the overlying Illinois Episode glacial succession. Today, remnants of the ancient subterranean slackwater deposits nearly fill several secondary passages and, in at least two locations, cover a cobble-mantled strath terrace 1.3 to 1.5 m above active stream channels. Slumping and sinkhole formation appear to have been important mechanisms for deposition of the ancient subterranean deposits. Slumping of these surficial deposits and associated vegetation can occur along the flanks of sinkholes (in addition to sinkhole formation) and enter caves; however, the finer organics, some of them comminuted during transport into the caves, become part of the cave alluvium. This finer organic fraction is the modern analog of the humified organic matter disseminated in slackwater sediment dated in this investigation by radiocarbon methods. Twenty-four 14C ages on humified organic matter provide chronologic control. The ??13C values of the organic matter reflect the proportion of C4-type to C3-type vegetation growing in and around swallets and sinkholes at the time of redeposition. Drought-tolerant C4-type vegetation was more prevalent relative to C3-type vegetation from 42,500 to 31,200 cal yr B.P. compared to conditions from 28,800 cal yr B.P. to the present. The ??13C values are consistent with the results from other investigations of speleothems and organic matter from loessial paleosols. ?? 2004 University of Washington. All rights reserved.

Deciphering Depositional Signals in the Bed-Scale Stratigraphic Record of Submarine Channels

NASA Astrophysics Data System (ADS)

Sylvester, Z.; Covault, J. A.

2017-12-01

Submarine channels are important conduits of sediment transfer from rivers and shallow-marine settings into the deep sea. As such, the stratigraphic record of submarine-channel systems can store signals of past climate- and other environmental changes in their upstream sediment-source areas. This record is highly fragmented as channels are primarily locations of sediment bypass; channelized turbidity currents are likely to leave a more complete record in areas away from and above the thalweg. However, the link between the thick-bedded axial channel deposits that record a small number of flows and the much larger number of thin-bedded turbidites forming terrace- and levee deposits is poorly understood. We have developed a relatively simple two-dimensional model that, given a number of input flow parameters (mean velocity, grain size, duration of deposition, flow thickness), predicts the thickness and composition of the turbidite that is left behind in the channel and in the overbank areas. The model is based on a Rouse-type suspended sediment concentration profile and the Garcia-Parker entrainment function. In the vertical direction, turbidites tend to rapidly become thinner and finer-grained with height above thalweg, due to decreasing concentration. High near-thalweg concentrations result in thick axial beds. However, an increase in flow velocity can result in high entrainment and no deposition at the bottom of the channel, yet a thin layer of sand and mud is still deposited higher up on the channel bank. If channel thalwegs are largely in a bypass condition, relatively minor velocity fluctuations result in a few occasionally preserved thick beds in the axis, and numerous thin turbidites - and a more complete record - on the channel banks. We use near-seafloor data from the Niger Delta slope and an optimization algorithm to show how our model can be used to invert for likely flow parameters and match the bed thickness and grain size of 100 turbidites observed in a core taken from a slope channel terrace.

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

Brown, Christopher F.; Icenhower, Jonathan P.; Um, Wooyong

Geochemical tests provide evidence for the transit of a plume of caustic waste solution through the sediment column at the Hanford 241-B and -BX Tank Farms. Direct-push samples recovered from boreholes surrounding Tanks 241-B-110 and 241-BX-102 and related waste transfer lines and diversion boxes included sediments typical of those previously recovered from other localities on the Hanford Site. The Hanford formation sediments are dominantly quartzo-feldspathic sands strewn with lithic fragments, displaying a range of particle size distributions and sorting characteristics. Some moderately well-sorted, fine-grained lithologies are interpreted as lenticular bodies irregularly dispersed in coarser-grained, more poorly sorted sediments. Tier Imore » tests conducted on the vadose zone sediments revealed an inverse correlation between moisture content and sediment size fraction (i.e., there is greater moisture content in finer-grained sediments). The Tier I tests also showed that the pore water solutions were likely sodium-rich, moderately saline, and possessed higher pH values than background (untainted) sediments. These data are characteristic of sediments that have encountered sodium-rich, saline, caustic waste solution, as documented in other reports at other suspect contamination sites around Hanford. Analyses of solutions from 1:1 water extracts reveal relatively balanced cation and anion concentrations, indicating that most of the geochemical species have been accounted for. The water extract data for affected sediments also indicate unusually high concentrations of aluminum, iron, and phosphorus. The relatively high concentrations of aluminum and iron may be the result of dissolution of secondary amorphous phases that precipitated after a reactive plume partially dissolved aluminum- and iron-bearing phases as it migrated through the sediment column. On the other hand, the presence of elevated concentrations of phosphorous may be the tell-tale signature of wastes derived from the bismuth phosphate separation process. Elements typically mobile in the geosphere, such as technetium-99, are present at either low concentrations or are below the analytical detection limit. However, we expect that the mobile elements would be present mainly along a narrow plume front, and if this front had passed deeper into the sediment profile than depths sampled, the retention of these elements would be minor. On the other hand for the direct push sediments from around BX Tank Farm, uranium-238 was detected in nearly all sediment specimens (by acid extract experiments) at concentrations above the natural crustal average (0.763 pCi/g), and we also detected the presence of several anthropogenic radioisotopes, such as cobalt-60, cesium-137, europium-154, and europium-155 (by gamma energy analysis). These data are direct confirmation of contamination of the sediments.« less

Geomorphological palaeoenvironments of the Sneeuberg Range, Great Karoo, South Africa

NASA Astrophysics Data System (ADS)

Holmes, P. J.; Boardman, J.; Parsons, A. J.; Marker, M. E.

2003-12-01

Sedimentary sequences within headwater valleys on the landward side of the Great Escarpment of South Africa are elucidated and their significance as indicators of environmental change is assessed. This study focuses on the Sneeuberg Range, the most prominent mountain range in the semi-arid central Great Karoo. Valley fills of a hitherto unrecognised complexity and of a greater age than any previously recorded in the central Great Karoo are reported. Three phases of deposition spanning the Late Pleistocene up to the present are documented from sites where gully erosion has incised the valley fills. The earliest depositional phase is represented by deeply weathered, calcretised gravel deposits, which probably were emplaced by debris flow and fluvial processes in the form of a fan. These deposits subsequently were buried by finer grained, largely unconsolidated sediment, with much of this emplacement occurring during the Holocene. There is evidence for phases of landscape stability and instability within this facies. Finally, sheetwash has removed fine-grained sediments from valley flanks and has deposited it either on valley bottoms, or in presently active gullies. This process appears to be ongoing, and is the subject of current investigation. The sedimentary deposits are interpreted as representing a wide range of palaeoenvironmental conditions that have prevailed within the central Great Karoo since the penultimate glaciation. Copyright

Geologic investigation of Playa Lakes, Tonopah Test Range, Nevada : data report.

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

Rautman, Christopher Arthur

Subsurface geological investigations have been conducted at two large playa lakes at the Tonopah Test Range in central Nevada. These characterization activities were intended to provide basic stratigraphic-framework information regarding the lateral distribution of ''hard'' and ''soft'' sedimentary materials for use in defining suitable target regions for penetration testing. Both downhole geophysical measurements and macroscopic lithilogic descriptions were used as a surrogate for quantitative mechanical-strength properties, although some quantitative laboratory strength measurements were obtained as well. Both rotary (71) and core (19) holes on a systematic grid were drilled in the southern half of the Main Lake; drill hole spacingsmore » are 300 ft north-south and 500-ft east-west. The drilled region overlaps a previous cone-penetrometer survey that also addressed the distribution of hard and soft material. Holes were drilled to a depth of 40 ft and logged using both geologic examination and down-hole geophysical surveying. The data identify a large complex of very coarse-grained sediment (clasts up to 8 mm) with interbedded finer-grained sands, silts and clays, underlying a fairly uniform layer of silty clay 6 to 12 ft thick. Geophysical densities of the course-grained materials exceed 2.0 g/cm{sup 2}, and this petrophysical value appears to be a valid discriminator of hard vs. soft sediments in the subsurface. Thirty-four holes, including both core and rotary drilling, were drilled on a portion of the much larger Antelope Lake. A set of pre-drilling geophysical surveys, including time-domain electromagnetic methods, galvanic resistivity soundings, and terrain-conductivity surveying, was used to identify the gross distribution of conductive and resistive facies with respect to the present lake outline. Conductive areas were postulated to represent softer, clay-rich sediments with larger amounts of contained conductive ground water. Initial drilling, consisting of cored drill holes to 100-ft (33-m) depth, confirmed both the specific surface geophysical measurements and the more general geophysical model of the subsurface lake facies. Good agreement of conductive regions with drill holes containing little to no coarse-grained sediments was observed, and vice-versa. A second phase of grid drilling on approximately 300-ft (100-m) centers was targeted a delineating a region of sufficient size containing essentially no coarse-grained ''hard'' material. Such a region was identified in the southwestern portion of Antelope Lake.« less

Storm-generated Holocene and historical floods in the Manawatu River, New Zealand

NASA Astrophysics Data System (ADS)

Fuller, Ian C.; Macklin, Mark G.; Toonen, Willem H. J.; Holt, Katherine A.

2018-06-01

This paper reports the first reconstruction of storm-generated late Holocene and historical river floods in the North Island of New Zealand. The sedimentary infills of nine palaeochannels were studied in the lower alluvial reaches of the Manawatu River. Floods in these palaeochannels were recorded as a series of sand-rich units set within finer-grained fills. Flood chronologies were constrained using a combination of radiocarbon dating, documentary sources, geochemical markers, and palynological information. Flood units were sedimentologically and geochemically characterised using high resolution ITRAX™ X-Ray Fluorescence (XRF) core scanning and laser diffraction grain-size analysis. The longest palaeoflood record extends back ca.3000 years. The temporal resolution and length of the Manawatu record reflects accommodation space for fluvial deposits, channel dynamics and mobility, and high sediment supply. Floods that occurred in the Manawatu during the mid-1800s at the time of European land clearance and in the first decade of the twentieth century appear to be among the largest recorded in the last 3000 years.

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.

Layered Outcrops in Gusev Crater

NASA Technical Reports Server (NTRS)

2004-01-01

NASA's Mars Exploration Rover Spirit collected data on morphology, composition, and mineralogy of a rock nicknamed 'Tetl' using the microscopic imager, the alpha particle X-ray spectrometer, and the Moessbauer spectrometer before moving on. Scientists are discussing a suggestion that this rock outcrop and others on the 'West Spur' of the 'Columbia Hills' in Gusev Crater on Mars may contain evidence of graded bedding, in which alternate layers of sediment are either coarser or finer depending on the turbulence of the processes that deposited them. Such layers could be deposited by water circulating in rivers or lakes, volcanic ash settling on the surface, wind carrying fine-grained sediments, or a combination of these processes. This view is a mosaic of images that Spirit took with its microscopic imager on the rover's 272nd and 273rd martian days, or sols (Oct. 7 and 8, 2004). It has been enhanced to bring out details in the shadows without washing out sunlit areas. The section of rock shown here is approximately 17 centimeters (6.7 inches) wide.

Biogenic silica from the BDP93 drill site and adjacent areas of the Selenga Delta, Lake Baikal, Siberia

USGS Publications Warehouse

Colman, Steven M.; Peck, John A.; Hatton, Josephine; Karabanov, Eugene B.; King, John W.

1999-01-01

Biogenic silica contents of sediments on the lower Selenga Delta and Buguldeika saddle in Lake Baikal show distinct fluctuations that reflect changes in diatom productivity, and ultimately, climate. The pattern of the upper 50 m of the section, dating from about 334 ka, is similar to that of the marine oxygen-isotope record, increasingly so as the younger sediments become progressively finer grained and less locally derived with time. The last two interglaciations are marked by biogenic silica abundances similar to those of the Holocene. The equivalent of marine oxygen-isotope stage 3 is distinctly intermediate in character between full glacial and full interglacial biogenic silica values. Following near-zero values during the last glacial maximum, biogenic silica began to increase at about 13 ka. The rise in biogenic silica to Holocene values was interrupted by an abrupt decrease during Younger Dryas time, about 11 to 10 14C ka.

Past environmental/climatic changes in the northern part of the South China Sea, input from multi-proxy analysis of core MD12-3432

NASA Astrophysics Data System (ADS)

Chen, Quan; Kissel, Catherine; Liu, Zhifei

2017-04-01

In the South China Sea, the magnetic component of marine sediment is a powerful recorder of paleoenvironmental changes linked to the regional and global climate. Based on the knowledge of the sedimentary signature of the potential sources for terrigenous sediments, the composition of marine sediments can be used to decipher the different mechanisms, forcing, and transport vectors. We report here the analysis of the magnetic properties combined with sortable silt and clay mineralogy of a 51 m long sedimentary sequence retrieved from the northern South China Sea and covering the last 400 ka. Magnetic minerals with different coercivities (magnetite, pyrrhotite and hematite) are mixed in the sequence and their relative concentration varies with time. Glacial low sea-levels reduce the land-site distance and they are illlustrated by higher concentrations in magnetites and iron-sulfides (pyrrhotite) related to the sediments previously deposited on the continental shelf and re-worked by the river. This is accompanied by increasing kaolinite content within the clay assemblage (Pearl River signature) and by coarser grains. Superimposed to this eccentricity periodicity, hematite content and smectite/(illite+chlorite) ratio present a predominant precession periodicity synchronous with the northern hemisphere summer insolation changes and therefore with that of the East Asian summer monsoon. Events of high hematite content, in phase with finer grains, coincide with precession lows, while smectite/(illite+chlorite) ratio is maximum during precession highs. Knowing that smectite is mainly produced by contemporaneous chemical weathering intensity in Luzon, we use the smectite/(illite+chlorite) ratio as a tracer for increasing weathering rate in Luzon, in turn related to enhanced East Asian summer monsoon. Hematite is not produced in large amount on adjacent lands and its association with fine sediment grains suggests that its periodic supply is related to the eolian dust transported from the Central China deserts to the studied site. Higher hematite content at this latitude may therefore be used as a tracer for weak East Asian summer monsoon intensity.

Relation of sortable silt grain-size to deep-sea current speeds: Calibration of the 'Mud Current Meter'

NASA Astrophysics Data System (ADS)

McCave, I. N.; Thornalley, D. J. R.; Hall, I. R.

2017-09-01

Fine grain-size parameters have been used for inference of palaeoflow speeds of near-bottom currents in the deep-sea. The basic idea stems from observations of varying sediment size parameters on a continental margin with a gradient from slower flow speeds at shallower depths to faster at deeper. In the deep-sea, size-sorting occurs during deposition after benthic storm resuspension events. At flow speeds below 10-15 cm s-1 mean grain-size in the terrigenous non-cohesive 'sortable silt' range (denoted by SS bar , mean of 10-63 μm) is controlled by selective deposition, whereas above that range removal of finer material by winnowing is also argued to play a role. A calibration of the SS bar grain-size flow speed proxy based on sediment samples taken adjacent to sites of long-term current meters set within 100 m of the sea bed for more than a year is presented here. Grain-size has been measured by either Sedigraph or Coulter Counter, in some cases both, between which there is an excellent correlation for SS bar (r = 0.96). Size-speed data indicate calibration relationships with an overall sensitivity of 1.36 ± 0.19 cm s-1/μm. A calibration line comprising 12 points including 9 from the Iceland overflow region is well defined, but at least two other smaller groups (Weddell/Scotia Sea and NW Atlantic continental rise/Rockall Trough) are fitted by sub-parallel lines with a smaller constant. This suggests a possible influence of the calibre of material supplied to the site of deposition (not the initial source supply) which, if depleted in very coarse silt (31-63 μm), would limit SS bar to smaller values for a given speed than with a broader size-spectrum supply. Local calibrations, or a core-top grain-size and local flow speed, are thus necessary to infer absolute speeds from grain-size. The trend of the calibrations diverges markedly from the slope of experimental critical erosion and deposition flow speeds versus grain-size, making it unlikely that the SS bar (or any deposit size for that matter) is simply predicted by the deposition threshold. A more probable control is the rate of deposition of the different size fractions under changing flows over several tens of years (the typical averaging period of a centimetre of deposited sediment). This suggestion is supported by a simple depositional model for which the deposited SS bar is calculated from measured currents with a size-varying depositional threshold. More surficial sediment samples taken near long-term current meter sites are needed to make calibrations more robust and explore regional differences.

Stages of rootless cone formation observed within the Raudhólar cone group, Iceland

NASA Astrophysics Data System (ADS)

Fitch, E. P.; Hamilton, C.; Fagents, S. A.; Thordarson, T.

2013-12-01

Secondary (rootless) cones form when lava interacts explosively with water contained in the substrate, and represent a largely degassed, end-member system that can elucidate mechanisms of magma-water interactions in the absence of primary degassing-induced fragmentation. Rootless cones are well documented in Iceland. The Raudhólar rootless cone group, located within the ~5200-year-old Ellidaá lava flow on the south-eastern outskirts of Reykjavík, was extensively quarried during the Second World War and now provides excellent cross-sections through the tephra sequences. Taking advantage of this exposure, we performed detailed stratigraphic, grain-size, and componentry analyses, which suggest that the energetics of rootless explosions vary substantially during cone formation. The lower unit contains the most substrate sediment and is characterized by dilute pyroclastic density current deposits. The middle unit is dominated by a succession of bed-pairs, each containing a finer-grained lower layer and coarser-grained upper layer. In the upper unit, the succession grades into a welded section that caps the cone. The abundance of substrate sediment generally decreases upwards within the cone, which suggests that the efficiency of lava-substrate mixing decreased with time. In addition, clast size generally increases upwards within the cone, implying that the fragmentation energy also decreased as the rootless eruption progressed. Both lines of evidence suggest that the explosions decreased in intensity with time, likely due to the depletion of available groundwater. However, alternating fine- and coarse-grained beds imply cycles of increased and decreased fragmentation efficiency, which we attribute to groundwater recharge and depletion during the event. Therefore, this study presents a detailed look at rootless cone formation and provides the foundation for future work on this important, yet understudied, system.

Modern process study on Chen Co and Ranwu Lake of Tibetan Plateau

NASA Astrophysics Data System (ADS)

Ju, J.

2013-12-01

Lakes are important junctions of geospheres. There are many lakes distributed on the Tibetan Plateau (TP). Lake sediment is one of the important media for retrieving the past environmental changes. Because of the uniqueness of environment of the TP, sediment, water and ecological system in lakes has local characteristic inevitably. Modern process research on different lakes will benefit interpreting the proxies more accurately. The development of observation station makes the observation and sampling more convenient. Modern process of lakes can be fulfilled in two ways, spatial or seasonal variation study, with a same aim finding out the dominant factors controlling the variations. Chen Co is a closed lake locating at inland area of southern Tibet. Ranwu Lake is an open lake locating at outflow area of SE Tibet. In this study, I studied the spatial and (or) seasonal variation of lake water and sediment in the two distinct types of lakes to make clear the mechanism of modern process. Particular attention was given to the pattern and degree of influence of rivers supplied by glaciers on lakes. Preliminary conclusions are outlined as follow: (1) In the lakes with glacier melt supplying rivers, the patterns of supply of the rivers to the lake are different. In close lake Chen Co, the influence of glacier melt is mainly reflected in the south lake area. In the open lake Ranwu Lake, the influence is comprehensive and direct. This difference influencing patterns how the lake sediments reflected the glacier melt under the past environmental changes. (2) The supply of Kaluxiong Qu River, supplied mainly by glacier melt, to Chen co has North-South difference: more directly to south lake area, reflecting by lower value of conductivity and pH, finer grain size and west to east transporting trend, greater deposition rate, more allogenic fine sediments, not obvious biological and endogenic deposition there. This enlightens the site selection for lake cores and interpretation of proxies in lake sediments. (3) The nutritional status of lake water was controlled by temperature, salinity by lake level. Carbonate deposition was influenced by biological factor clearly, but also influenced by under-water terrain and depth. (4) Paleo-lacustrine sediments have certain impact to modern sediment, reflecting the finer grain size and more chemical constituents of clay minerals in the ricver mouth of the southern river. (5) For Ranwu Lake, next to the oceanic glaciers, glacier melt influenced the lake more directly, which can be illustrated by the Quchi River dominating a lot of aspects of Ranwu Lake, including the water level, seasonal and spatial water temperate, conductivity, pH value, and even the chlorophyll content. Depositional flux analysis detected by sediment traps found that the fluxes decreasing from upper lake to the lower lake and greater flux in summer than other seasons, reflecting the dominant influence of Quchi River on the lake. (6) Analysis for the dust flux detected by a dust collector found that the greatest flux happened in winter and spring, with the flux 3~4 more than other seasons.

Use of the Cone Penetration Testing (CPT) method to interpret late Quaternary tide-dominated successions: A case study from the eastern China coastal plain

NASA Astrophysics Data System (ADS)

Zhang, Xia; Lin, Chun-Ming; Dalrymple, Robert W.; Gao, Shu; Canas, Daniel T.

2018-06-01

We evaluate the applicability of cone penetration testing (CPT), calibrated using adjacent cores, as a tool for the sedimentological and stratigraphic examination of late Quaternary tide-dominated successions in the eastern China coastal plain. The results indicate that the sedimentary facies and sequence-stratigraphic surfaces can be readily distinguished using CPT profiles in the Qiantang River incised-valley system because of their distinctive mechanical behavior. The lithologic character of the various facies, which is controlled mainly by sediment supply, dynamic processes and post-depositional diagenesis, is the key factor affecting how well the CPT technique works. Within this particular macrotidal environment, which is dominated by non-cohesive sand and silt in the tidal channels, the accumulation of fluid mud is rare. Consequently, the tidal-channel deposits exhibit the geotechnical properties of coarse-grained sediments, and can be easily distinguished from the mud-dominated facies. However, in the nearby Changjiang delta system which is characterized by very high suspended-sediment concentrations and an abundance of fine-grained cohesive sediments, the presence of channel-bottom fluid muds makes it difficult to recognize channel deposits, because of the lack of a sharp lithologic contrast at their base. Consequently, the CPT method might not be as universally effective in tide-dominated systems as it appears to be in wave-dominated settings. Care is needed in the interpretation of the results from tide-dominated successions because of the widespread presence of fluid muds, the heterolithic nature of tidal deposits, the rheological similarity between adjacent facies, and the averaging of geotechnical properties between the alternating finer and coarser layers.

Character, distribution, and ecological significance of storm wave-induced scour in Rhode Island Sound, USA

USGS Publications Warehouse

McMullen, Katherine Y.; Poppe, Lawrence J.; Parker, Castle E.

2015-01-01

Multibeam bathymetry, collected during NOAA hydrographic surveys in 2008 and 2009, is coupled with USGS data from sampling and photographic stations to map the seabed morphology and composition of Rhode Island Sound along the US Atlantic coast, and to provide information on sediment transport and benthic habitats. Patchworks of scour depressions cover large areas on seaward-facing slopes and bathymetric highs in the sound. These depressions average 0.5-0.8 m deep and occur in water depths reaching as much as 42 m. They have relatively steep well-defined sides and coarser-grained floors, and vary strongly in shape, size, and configuration. Some individual scour depressions have apparently expanded to combine with adjacent depressions, forming larger eroded areas that commonly contain outliers of the original seafloor sediments. Where cobbles and scattered boulders are present on the depression floors, the muddy Holocene sands have been completely removed and the winnowed relict Pleistocene deposits exposed. Low tidal-current velocities and the lack of obstacle marks suggest that bidirectional tidal currents alone are not capable of forming these features. These depressions are formed and maintained under high-energy shelf conditions owing to repetitive cyclic loading imposed by high-amplitude, long-period, storm-driven waves that reduce the effective shear strength of the sediment, cause resuspension, and expose the suspended sediments to erosion by wind-driven and tidal currents. Because epifauna dominate on gravel floors of the depressions and infauna are prevalent in the finer-grained Holocene deposits, it is concluded that the resultant close juxtaposition of silty sand-, sand-, and gravel-dependent communities promotes regional faunal complexity. These findings expand on earlier interpretations, documenting how storm wave-induced scour produces sorted bedforms that control much of the benthic geologic and biologic diversity in Rhode Island Sound.

Effects of sandfish (Holothuria scabra) removal on shallow-water sediments in Fiji.

PubMed

Lee, Steven; Ford, Amanda K; Mangubhai, Sangeeta; Wild, Christian; Ferse, Sebastian C A

2018-01-01

Sea cucumbers play an important role in the recycling and remineralization of organic matter (OM) in reef sands through feeding, excretion, and bioturbation processes. Growing demand from Asian markets has driven the overexploitation of these animals globally. The implications of sea cucumber fisheries for shallow coastal ecosystems and their management remain poorly understood. To address this knowledge gap, the current study manipulated densities of Holothuria scabra within enclosures on a reef flat in Fiji, between August 2015 and February 2016, to study the effects of sea cucumber removal on sedimentary function as a biocatalytic filter system. Three treatments were investigated: (i) high density (350 g m -2 wet weight; ca . 15 individuals); (ii) natural density (60 g m -2 ; ca . 3 individuals); and (iii) exclusion (0 g m -2 ). Quantity of sediment reworked through ingestion by H. scabra , grain size distribution, O 2 penetration depth, and sedimentary oxygen consumption (SOC) were quantified within each treatment. Findings revealed that the natural population of H. scabra at the study site can rework ca . 10,590 kg dry sediment 1,000 m -2 year -1 ; more than twice the turnover rate recorded for H. atra and Stichopus chloronotus . There was a shift towards finer fraction grains in the high treatment. In the exclusion treatment, the O 2 penetration depth decreased by 63% following a 6 °C increase in water temperature over the course of two months, while in the high treatment no such change was observed. SOC rates increased ca . two-fold in the exclusion treatment within the first month, and were consistently higher than in the high treatment. These results suggest that the removal of sea cucumbers can reduce the capacity of sediments to buffer OM pulses, impeding the function and productivity of shallow coastal ecosystems.

Effects of sandfish (Holothuria scabra) removal on shallow-water sediments in Fiji

PubMed Central

Ford, Amanda K.; Mangubhai, Sangeeta; Wild, Christian; Ferse, Sebastian C.A.

2018-01-01

Sea cucumbers play an important role in the recycling and remineralization of organic matter (OM) in reef sands through feeding, excretion, and bioturbation processes. Growing demand from Asian markets has driven the overexploitation of these animals globally. The implications of sea cucumber fisheries for shallow coastal ecosystems and their management remain poorly understood. To address this knowledge gap, the current study manipulated densities of Holothuria scabra within enclosures on a reef flat in Fiji, between August 2015 and February 2016, to study the effects of sea cucumber removal on sedimentary function as a biocatalytic filter system. Three treatments were investigated: (i) high density (350 g m−2 wet weight; ca. 15 individuals); (ii) natural density (60 g m−2; ca. 3 individuals); and (iii) exclusion (0 g m−2). Quantity of sediment reworked through ingestion by H. scabra, grain size distribution, O2 penetration depth, and sedimentary oxygen consumption (SOC) were quantified within each treatment. Findings revealed that the natural population of H. scabra at the study site can rework ca. 10,590 kg dry sediment 1,000 m−2 year−1; more than twice the turnover rate recorded for H. atra and Stichopus chloronotus. There was a shift towards finer fraction grains in the high treatment. In the exclusion treatment, the O2 penetration depth decreased by 63% following a 6 °C increase in water temperature over the course of two months, while in the high treatment no such change was observed. SOC rates increased ca. two-fold in the exclusion treatment within the first month, and were consistently higher than in the high treatment. These results suggest that the removal of sea cucumbers can reduce the capacity of sediments to buffer OM pulses, impeding the function and productivity of shallow coastal ecosystems. PMID:29796344

Sediment dynamics in the lower Mekong River: Transition from tidal river to estuary

NASA Astrophysics Data System (ADS)

Nowacki, Daniel J.; Ogston, Andrea S.; Nittrouer, Charles A.; Fricke, Aaron T.; Van, Pham Dang Tri

2015-09-01

A better understanding of flow and sediment dynamics in the lowermost portions of large-tropical rivers is essential to constraining estimates of worldwide sediment delivery to the ocean. Flow velocity, salinity, and suspended-sediment concentration were measured for 25 h at three cross sections in the tidal Song Hau distributary of the Mekong River, Vietnam. Two campaigns took place during comparatively high-seasonal and low-seasonal discharge, and estuarine conditions varied dramatically between them. The system transitioned from a tidal river with ephemeral presence of a salt wedge during high flow to a partially mixed estuary during low flow. The changing freshwater input, sediment sources, and estuarine characteristics resulted in seaward sediment export during high flow and landward import during low flow. The Dinh An channel of the Song Hau distributary exported sediment to the coast at a rate of about 1 t s-1 during high flow and imported sediment in a spatially varying manner at approximately 0.3 t s-1 during low flow. Scaling these values results in a yearly Mekong sediment discharge estimate about 65% smaller than a generally accepted estimate of 110 Mt yr-1, although the limited temporal and spatial nature of this study implies a relatively high degree of uncertainty for the new estimate. Fluvial advection of sediment was primarily responsible for the high-flow sediment export. Exchange-flow and tidal processes, including local resuspension, were principally responsible for the low-flow import. The resulting bed-sediment grain size was coarser and more variable during high flow and finer during low, and the residual flow patterns support the maintenance of mid-channel islands. This article was corrected on 7 OCT 2015. See the end of the full text for details.

Let's Bet on Sediments! Hudson Canyon Cruise--Grades 9-12. Focus: Sediments of Hudson Canyon.

ERIC Educational Resources Information Center

National Oceanic and Atmospheric Administration (DOC), Rockville, MD.

These activities are designed to teach about the sediments of Hudson Canyon. Students investigate and analyze the patterns of sedimentation in the Hudson Canyon, observe how heavier particles sink faster than finer particles, and learn that submarine landslides are avalanches of sediment in deep ocean canyons. The activity provides learning…

Background radioactivity in sediments near Los Alamos, New Mexico.

PubMed

McLin, Stephen G

2004-07-26

River and reservoir sediments have been collected annually by Los Alamos National Laboratory since 1974 and 1979, respectively. These background samples are collected from five river stations and four reservoirs located throughout northern New Mexico and southern Colorado. Analyses include 3H, 90Sr, 137Cs, total U, 238Pu, 239,240Pu, 241Am, gross alpha, gross beta, and gross gamma radioactivity. Surprisingly, there are no federal or state regulatory standards in the USA that specify how to compute background radioactivity values on sediments. Hence, the sample median (or 0.50 quantile) is proposed for this background because it reflects central data tendency and is distribution-free. Estimates for the upper limit of background radioactivity on river and reservoir sediments are made for sampled analytes using the 0.95 quantile (two-tail). These analyses also show that seven of ten analytes from reservoir sediments are normally distributed, or are normally distributed after a logarithmic or square root transformation. However, only three of ten analytes from river sediments are similarly distributed. In addition, isotope ratios for 137Cs/238Pu, 137Cs/239,240Pu, and 239,240Pu/238Pu from reservoir sediments are independent of clay content, total organic carbon/specific surface area (TOC/SSA) and cation exchange capacity/specific surface area (CEC/SSA) ratios. These TOC/SSA and CEC/SSA ratios reflect sediment organic carbon and surface charge densities that are associated with radionuclide absorption, adsorption, and ion exchange reactions on clay mineral structures. These latter ratio values greatly exceed the availability of background radionuclides in the environment, and insure that measured background levels are a maximum. Since finer-grained reservoir sediments contain larger clay-sized fractions compared to coarser river sediments, they show higher background levels for most analytes. Furthermore, radioactivity values on reservoir sediments have remained relatively constant since the early 1980s. These results suggest that clay contents in terrestrial sediments are often more important at concentrating background radionuclides than many other environmental factors, including geology, climate and vegetation. Hence, reservoirs and floodplains represent ideal radionuclide sampling locations because fine-grained materials are more easily trapped here. Ultimately, most of these differences still reflect spatial and temporal variability originating from global atmospheric nuclear weapons testing and disintegration of nuclear-powered satellites upon atmospheric reentry. Copyright 2004 Elsevier B.V.

Stratigraphy and paleoenvironment of Miocene phosphatic rocks in the East San Francisco Bay region, California

USGS Publications Warehouse

Hill, James M.

1979-01-01

A stratigraphic study of the Monterey Group in the East San Francisco Bay Region, California, indicates that a depositional basin began to subside in early to middle Miocene time. The Miocene sea transgressed from the west or southwest, and the area subsided to a possible water depth of 500 to 2,500 m. The Monterey Group within the study area is a time-transgressive sequence of six sandstone and shale formations. Stratigraphic cycles of interbedded sandstone and shale formations are related to the amount of terrigenous sediment input into the basin as well as the depositional environment. During periods of low terrigenous sedimentation, biogenetic sedimentation in the form of diatomite layers were interbedded with hemipelagic muds and thin turbidite sands. These diatom-rich sediments were probably deposited within the upper bathyal zone (180 to 500 m) and, during lithification, diagenetically altered to form siliceous shales and cherts. As terrigenous sedimentation increased, probably due to periodic uplift east of the study area, biogenetic sedimentation was masked until finer grained sediment at a lower rate of deposition reoccurred. As the basin filled and a higher energy environment prevailed; coarse-grained sediment was again deposited until a lower energy environment resumed. Three types of inorganic phosphate are present within the study area: nodular, Pelletal, and pebbles of sandy phosphatic mudstone. The nodular phosphate is associated with the siliceous shale formations and formed within diatomite layers before compaction and lithification. The other two types of phosphate are found within the sandstone formations and probably originated in a shallower, higher energy environment than the siliceous shales. Faulting was active during middle to late Miocene time. The change in stratigraphic thickness across the Mission fault is 350 m which may approximate the vertical (?) displacement along this fault. This displacement took place in middle to upper Miocene time and apparently caused erosion of the upper formations of the Monterey Group on the west side of the Mission fault before the Briones Formation was deposited in late Miocene time. Depositional thinning of the Monterey Group in the southern portion of the study area may imply that the Hayward and Calaveras faults were also active at this time.

Aeolian Environments of Iceland

NASA Astrophysics Data System (ADS)

Arnalds, Olafur; Olafsson, Haraldur; Dagsson Waldhauserová, Pavla

2017-04-01

Iceland has the largest area of volcaniclastic sandy desert on Earth or 22,000 km2. The sand has been mostly produced by glacio-fluvial processes, leaving behind fine-grained unstable sediments which are later re-distributed by repeated aeolian events. Volcanic eruptions add to this pool of unstable sediments, often from subglacial eruptions. Icelandic desert surfaces are divided into sand fields, sandy lavas and sandy lag gravel, each with separate aeolian surface characteristics such as threshold velocities. Storms are frequent due to Iceland's location on the North Atlantic Storm track. Dry winds occur on the leeward sides of mountains and glaciers, in spite of the high moisture content of the Atlantic cyclones. Surface winds often move hundreds to more than 1000 kg m-1 per annum, and more than 10,000 kg m-1 have been measured in a single storm. Desertification occurs when aeolian processes push sand fronts and have thus destroyed many previously fully vegetated ecosystems since the time of the settlement of Iceland in the late ninth century. There are about 135 dust events per annum, ranging from minor storms to >300,000 t of dust emitted in single storms. Dust can be generated from all the major sandy areas of Iceland; however the amount of finer particles that become dust varies with the surfaces. There are areas that produce more dust by far compared to the general sandy deserts; they have therefore been termed "dust plume areas" or "dust hot-spots". They are characterized by repeated charging of fine sediments with a relatively high proportion of finer (silty) materials which, upon repeated wind erosion become sorted downwind from the sources with loss of silt (dust) and an increasing saltation component (sand). Dust production is on the order of 30-40 million tons annually, some travelling over 1000 km and deposited on land and sea. Dust deposited on deserts tends to be re-suspended during subsequent storms. High PM10 concentrations occur during major dust storms. They are more frequent in the wake of volcanic eruptions, such as after the Eyjafjallajökull 2010 eruption. Airborne dust affects human health, with negative effects enhanced by the tubular morphology of the grains, and the basaltic composition with its high metal content. Dust deposition on snow and glaciers intensifies melting. Moreover, the dust production probably also influences atmospheric conditions and parameters that affect climate change.

Effect of Particle and Carbide Grain Sizes on a HVOAF WC-Co-Cr Coating for the Future Application on Internal Surfaces: Microstructure and Wear

NASA Astrophysics Data System (ADS)

Pulsford, J.; Kamnis, S.; Murray, J.; Bai, M.; Hussain, T.

2018-01-01

The use of nanoscale WC grain or finer feedstock particles is a possible method of improving the performance of WC-Co-Cr coatings. Finer powders are being pursued for the development of coating internal surfaces, as less thermal energy is required to melt the finer powder compared to coarse powders, permitting spraying at smaller standoff distances. Three WC-10Co-4Cr coatings, with two different powder particle sizes and two different carbide grain sizes, were sprayed using a high velocity oxy-air fuel (HVOAF) thermal spray system developed by Castolin Eutectic-Monitor Coatings Ltd., UK. Powder and coating microstructures were characterized using XRD and SEM. Fracture toughness and dry sliding wear performance at three loads were investigated using a ball-on-disk tribometer with a WC-Co counterbody. It was found that the finer powder produced the coating with the highest microhardness, but its fracture toughness was reduced due to increased decarburization compared to the other powders. The sprayed nanostructured powder had the lowest microhardness and fracture toughness of all materials tested. Unlubricated sliding wear testing at the lowest load showed the nanostructured coating performed best; however, at the highest load this coating showed the highest specific wear rates with the other two powders performing to a similar, better standard.

Influence of geomorphic setting on sedimentation of two adjacent alpine lakes, Triglav Lakes Valley (Julian Alps, NW Slovenia)

NASA Astrophysics Data System (ADS)

Smuc, Andrej; Skabene, Dragomir; Muri, Gregor; Vreča, Polona; Jaćimović, Radojko; Čermelj, Branko; Turšič, Janja

2013-04-01

The Triglav Lakes Valley is elongated, 7km long depression, located high (at places over 2000 m.a.s.l.) in the central part of the Julian Alps (NW Slovenia). It hosts 6 small isolated lakes that formed due to the combination of Neogene tectonic and Pleistocene glaciation. The study is focused on the 5th and 6th Triglav Valley Lakes that characterize lower part of the valley. The lakes are located so close to each other that they are even connected in times of high water. Thus, they share the same bedrock geology, are subjected to the same climatic forcing and share similar vegetation communities. Despite their proximity, the lakes differ in their hydrologic and geomorphic setting. The lakes have no permanent surface tributaries; however 5th is fed periodically, at times of high water level, by the Močivec spring, while additional water flows from the swamp area near its northern shore. An underground spring on the eastern side of 5th represents the lake's only permanent freshwater inflow, while drainage takes place to the west via a small ponor. 6th has only one weak underground spring on the eastern side of the lake. Water levels may fluctuate between 2 and 3 m. Additionally, the lakes have different configuration of lakes shores; the northern shores of the 5th lake are low-angle soil and debris covered plateau, while southern shores of the 5th lake and shores of the 6th lake are represented by heavily karstified carbonate base rock and covered partly by trees. The detailed sedimentary analysis of the lakes record showed some similarities, but also some significant differences. Sediments of both lakes are represented by fine-grained turbidity current deposits that are transported from lake shores during snow melt or storms. The grain-size and sedimentary rates of the lakes are however markedly different. The 5th lake has coarser grained sediments, with mean ranging from 46 to 60 µm and records higher sedimentation rates of ~0,57 cm/year, compared to the 6th lake that has sediments with mean of 23-36 µm and sedimentation rate of 0,34 cm/year. The mineralogical composition of the lake sediments is similar. Calcite predominates strongly, comprising more than 77% of total minerals, while dolomite and quartz are rare. We attributed discrepancies in sedimentary record to different hydrologic and geomorphic setting of the lakes. The northern shores of the 5th lake contribute more and coarser grained eroded material to the lake. It is evident that the 5th lake functions as a sink for coarser and heavier mineral components, leaving only finer, suspended grain portion to be transported into the 6th lake when lakes are connected during periods of high water levels.

Spectral slope variations for OSIRIS-REx target Asteroid (101955) Bennu: Possible evidence for a fine-grained regolith equatorial ridge

NASA Astrophysics Data System (ADS)

Binzel, Richard P.; DeMeo, Francesca E.; Burt, Brian J.; Cloutis, Edward A.; Rozitis, Ben; Burbine, Thomas H.; Campins, Humberto; Clark, Beth Ellen; Emery, Joshua P.; Hergenrother, Carl W.; Howell, Ellen S.; Lauretta, Dante S.; Nolan, Michael C.; Mansfield, Megan; Pietrasz, Valerie; Polishook, David; Scheeres, Daniel J.

2015-08-01

Ongoing spectroscopic reconnaissance of the OSIRIS-REx target Asteroid (101955) Bennu was performed in July 2011 and May 2012. Near-infrared spectra taken during these apparitions display slightly more positive ("redder") spectral slopes than most previously reported measurements. While observational systematic effects can produce such slope changes, and these effects cannot be ruled out, we entertain the hypothesis that the measurements are correct. Under this assumption, we present laboratory measurements investigating a plausible explanation that positive spectral slopes indicate a finer grain size for the most directly observed sub-Earth region on the asteroid. In all cases, the positive spectral slopes correspond to sub-Earth latitudes nearest to the equatorial ridge of Bennu. If confirmed by OSIRIS-REx in situ observations, one possible physical implication is that if the equatorial ridge is created by regolith migration during episodes of rapid rotation, that migration is most strongly dominated by finer grain material. Alternatively, after formation of the ridge (by regolith of any size distribution), larger-sized equatorial material may be more subject to loss due to centrifugal acceleration relative to finer grain material, where cohesive forces can preferentially retain the finest fraction (Rozitis, B., Maclennan, E., Emery, J.P. [2014]. Nature 512, 174-176).

Arsenic associations in sediments from shallow aquifers of northwestern Hetao Basin, Inner Mongolia

USGS Publications Warehouse

Deng, Y.; Wang, Y.; Ma, T.; Yang, H.; He, J.

2011-01-01

Understanding the mechanism of arsenic mobilization from sediments to groundwater is important for water quality management in areas of endemic arsenic poisoning, such as the Hetao Basin in Inner Mongolia, northern China. Aquifer geochemistry was characterized at three field sites (SH, HF, TYS) in Hangjinhouqi County of northwestern Hetao Basin. The results of bulk geochemistry analysis of sediment samples indicated that total As concentrations have a range of 6. 8-58. 5 mg/kg, with a median of 14. 4 mg/kg. The highest As concentrations were found at 15-25 m depth. In the meanwhile, the range of As concentration in the sediments from background borehole is 3-21. 8 mg/kg, with a median value of 9 mg/kg. The As sediments concentrations with depth from the SH borehole were correlated with the contents of Fe, Sb, B, V, total C and total S. Generally, the abundance of elements varied with grain size, with higher concentrations in finer fractions of the sediments. Distinct lithology profile and different geochemical characteristics of aquifer sediments indicate the sediments are associated with different sources and diverse sedimentary environments. Up to one third of arsenic in the sediments could be extracted by ammonium oxalate, suggesting that Fe oxyhydroxides may be the major sink of As in the aquifer. Sequential extraction results indicate that arsenic occurs as strongly adsorbed on and/or co-precipitated with amorphous Fe oxyhydroxides in sediments accounting for 35 and 20%, respectively, of the total contents of arsenic. The release of As into groundwater may occur by desorption from the mineral surface driven by reductive dissolution of the Fe oxide minerals. Furthermore, small proportions of As associated with iron sulfides occur in the reductive sediments. ?? 2011 Springer-Verlag.

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.

Resuspension of sediment, a new approach for remediation of contaminated sediment.

PubMed

Pourabadehei, Mehdi; Mulligan, Catherine N

2016-06-01

Natural events and anthropogenic activities are the reasons of undesirable resuspension of contaminated sediments in aquatic environment. Uncontrolled resuspension could remobilize weakly bound heavy metals into overlying water and pose a potential risk to aquatic ecosystem. Shallow harbours, with contaminated sediments are subjected to the risk of uncontrolled resuspension. Remediation of sediments in these areas cannot be performed by conventional in situ methods (e.g. capping with or without reactive amendment). Ex situ remediation also requires dredging of sediment, which could increase the risk of spreading contaminants. Alternatively, the resuspension technique was introduced to address these issues. The concept of the resuspension method is that finer sediments have a greater tendency to adsorb the contamination. Therefore, finer sediments, believed carry more concentration of contaminants, were targeted for removal from aquatic environment by a suspension mechanism in a confined water column. The objective of this study was to evaluate the feasibility of the resuspension technique as a new approach for remediation of contaminated sediment and a viable option to reduce the risk of remobilization of contaminants in harbours due to an undesirable resuspension event. Unlike the common in situ techniques, the resuspension method could successfully reduce the total concentration of contaminants in almost all samples below the probable effect level (PEL) with no significant change in the quality of overlying water. The results indicated that removal efficiency could be drastically enhanced for metals in sediment with a higher enrichment factor. Moreover, availability of metals (e.g. Cd and Pb) with a high concentration in labile fractions was higher in finer sediments with a high enrichment factor. Consequently, removal of contaminants from sediment through the resuspension method could reduce the risk of mobility and availability of metals under changing environmental conditions. Potential dredging in harbours could be performed safer and more cost-effective afterward. Copyright © 2016 Elsevier Ltd. All rights reserved.

The physics of debris flows

NASA Astrophysics Data System (ADS)

Iverson, Richard M.

1997-08-01

Recent advances in theory and experimentation motivate a thorough reassessment of the physics of debris flows. Analyses of flows of dry, granular solids and solid-fluid mixtures provide a foundation for a comprehensive debris flow theory, and experiments provide data that reveal the strengths and limitations of theoretical models. Both debris flow materials and dry granular materials can sustain shear stresses while remaining static; both can deform in a slow, tranquil mode characterized by enduring, frictional grain contacts; and both can flow in a more rapid, agitated mode characterized by brief, inelastic grain collisions. In debris flows, however, pore fluid that is highly viscous and nearly incompressible, composed of water with suspended silt and clay, can strongly mediate intergranular friction and collisions. Grain friction, grain collisions, and viscous fluid flow may transfer significant momentum simultaneously. Both the vibrational kinetic energy of solid grains (measured by a quantity termed the granular temperature) and the pressure of the intervening pore fluid facilitate motion of grains past one another, thereby enhancing debris flow mobility. Granular temperature arises from conversion of flow translational energy to grain vibrational energy, a process that depends on shear rates, grain properties, boundary conditions, and the ambient fluid viscosity and pressure. Pore fluid pressures that exceed static equilibrium pressures result from local or global debris contraction. Like larger, natural debris flows, experimental debris flows of ˜10 m³ of poorly sorted, water-saturated sediment invariably move as an unsteady surge or series of surges. Measurements at the base of experimental flows show that coarse-grained surge fronts have little or no pore fluid pressure. In contrast, finer-grained, thoroughly saturated debris behind surge fronts is nearly liquefied by high pore pressure, which persists owing to the great compressibility and moderate permeability of the debris. Realistic models of debris flows therefore require equations that simulate inertial motion of surges in which high-resistance fronts dominated by solid forces impede the motion of low-resistance tails more strongly influenced by fluid forces. Furthermore, because debris flows characteristically originate as nearly rigid sediment masses, transform at least partly to liquefied flows, and then transform again to nearly rigid deposits, acceptable models must simulate an evolution of material behavior without invoking preternatural changes in material properties. A simple model that satisfies most of these criteria uses depth-averaged equations of motion patterned after those of the Savage-Hutter theory for gravity-driven flow of dry granular masses but generalized to include the effects of viscous pore fluid with varying pressure. These equations can describe a spectrum of debris flow behaviors intermediate between those of wet rock avalanches and sediment-laden water floods. With appropriate pore pressure distributions the equations yield numerical solutions that successfully predict unsteady, nonuniform motion of experimental debris flows.

The physics of debris flows

USGS Publications Warehouse

Iverson, R.M.

1997-01-01

Recent advances in theory and experimentation motivate a thorough reassessment of the physics of debris flows. Analyses of flows of dry, granular solids and solid-fluid mixtures provide a foundation for a comprehensive debris flow theory, and experiments provide data that reveal the strengths and limitations of theoretical models. Both debris flow materials and dry granular materials can sustain shear stresses while remaining static; both can deform in a slow, tranquil mode characterized by enduring, frictional grain contacts; and both can flow in a more rapid, agitated mode characterized by brief, inelastic grain collisions. In debris flows, however, pore fluid that is highly viscous and nearly incompressible, composed of water with suspended silt and clay, can strongly mediate intergranular friction and collisions. Grain friction, grain collisions, and viscous fluid flow may transfer significant momentum simultaneously. Both the vibrational kinetic energy of solid grains (measured by a quantity termed the granular temperature) and the pressure of the intervening pore fluid facilitate motion of grains past one another, thereby enhancing debris flow mobility. Granular temperature arises from conversion of flow translational energy to grain vibrational energy, a process that depends on shear rates, grain properties, boundary conditions, and the ambient fluid viscosity and pressure. Pore fluid pressures that exceed static equilibrium pressures result from local or global debris contraction. Like larger, natural debris flows, experimental debris flows of ???10 m3 of poorly sorted, water-saturated sediment invariably move as an unsteady surge or series of surges. Measurements at the base of experimental flows show that coarse-grained surge fronts have little or no pore fluid pressure. In contrast, finer-grained, thoroughly saturated debris behind surge fronts is nearly liquefied by high pore pressure, which persists owing to the great compressibility and moderate permeability of the debris. Realistic models of debris flows therefore require equations that simulate inertial motion of surges in which high-resistance fronts dominated by solid forces impede the motion of low-resistance tails more strongly influenced by fluid forces. Furthermore, because debris flows characteristically originate as nearly rigid sediment masses, transform at least partly to liquefied flows, and then transform again to nearly rigid deposits, acceptable models must simulate an evolution of material behavior without invoking preternatural changes in material properties. A simple model that satisfies most of these criteria uses depth-averaged equations of motion patterned after those of the Savage-Hutter theory for gravity-driven flow of dry granular masses but generalized to include the effects of viscous pore fluid with varying pressure. These equations can describe a spectrum of debris flow behaviors intermediate between those of wet rock avalanches and sediment-laden water floods. With appropriate pore pressure distributions the equations yield numerical solutions that successfully predict unsteady, nonuniform motion of experimental debris flows.

Depth and substrate as determinants of distribution of juvenile flathead sole (Hippoglossoides elassodon) and rock sole (Pleuronectes bilineatus), in Kachemak Bay, Alaska

USGS Publications Warehouse

Abookire, Alisa A.; Norcross, Brenda L.

1998-01-01

Three transects in Kachemak Bay, Alaska, were sampled in September 1994, May and August 1995, and February, May, and August 1996. Juvenile flathead sole, Hippoglossoides elassodon, and rock sole, Pleuronectes bilineatus, were the most abundant flatfishes, comprising 65-85% of all fiatfishes captured at any period. Collections of fish and sediments were made at regular depth contour intervals of l0 m. Habitat distribution was described by depth at 10 m increments and sediment percent weights of gravel, sand, and mud. Year-round habitat of flathead sole age-0 was primarily from 40 to 60 m, and age-1 habitat was primarily from 40 to 80 m. Summer habitat of rock sole age-0 and -1 was from 10 to 30 m, and in winter they moved offshore to depths of up to 150 m. Both age classes of flathead sole were most abundant on mixed mud sediments, while age-1 were also in high abundance on muddy sand sediments. Rock sole age-0 and -1 were most abundant on sand, though age-1 were also found on a variety of sediments both finer and coarser grained than sand. Flathead sole and rock sole had distinctive depth and sediment habitats. When habitat overlap occurred between the species, it was most often due to rock sole moving offshore in the winter. Abundances were not significantly different among seasons for age-1 flatfishes.

Impacts of dredged-material disposal on the coastal soft-bottom macrofauna, Saronikos Gulf, Greece.

PubMed

Katsiaras, N; Simboura, N; Tsangaris, C; Hatzianestis, I; Pavlidou, A; Kapsimalis, V

2015-03-01

Dredged sediments derived by the low course and estuary of the metropolitan river of Athens (Kifissos River) were dumped every day for 21 months to an open-sea site in the Saronikos Gulf. The spoil-ground and surrounding area was monitored prior, during and post to dumping for 24 months, over 6-month intervals. Dumping significantly changed the granulometry of the pre-existing superficial sediments to finer-grained only in the spoil ground and increased the sediment contamination load (aliphatic, polycyclic aromatic hydrocarbons and heavy metals) throughout the study area. Microtox® SPT showed that sediment toxicity levels were high at almost all sampling stations. During dumping, burial of natural soft-bottom habitats degraded severely the communities of the spoil-ground resulting in an almost azoic state, as well as significantly declined the species number and abundance of benthic communities in locations up to 3.2 km away from the spoil-ground, due to dispersion of the spoil and smothering. Benthic indices on the surrounding sites were significantly correlated with hydrocarbon concentrations and sediment toxicity levels. Post to dumping, the macrofauna communities of the spoil-ground were still significantly degraded, but the surrounding areas showed patterns of recovery. However, the high concentrations of aliphatic, polycyclic aromatic hydrocarbons and levels of toxicity persisted in the sediments after the ceasing of dumping operations in the study area, implying the ecological hazard imposed on the area. Copyright © 2014 Elsevier B.V. All rights reserved.

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.

Geochemical data for mercury, methylmercury, and other constituents in sediments from Englebright Lake, California, 2002

USGS Publications Warehouse

Alpers, Charles N.; Hunerlach, Michael P.; Marvin-DePasquale, Mark C.; Antweiler, Ronald C.; Lasorsa, Brenda K.; De Wild, John F.; Snyder, Noah P.

2006-01-01

Deep coring penetrated the full thickness of material deposited after 1940 at six locations in the reservoir; the cores reached a maximum depth of 32.8 meters below the reservoir floor. At the three deep coring sites closest to Englebright Dam, concentrations of HgT (dry basis) were consistently in the range of 100 to 500 ng/g (nanogram per gram), in sediment dominantly of silt size (median grain size of 0.004 to 0.063 mm [millimeter]). At the deep coring sites located farther upstream, the upper parts of the profile had lower concentrations of HgT, generally ranging from 2 to 100 ng/g, in sediment dominantly of sand size (median grain size from 0.063 to 2 mm). The lower part of the vertical profiles at three upstream coring sites had higher concentrations of HgT than the upper and middle parts of these profiles, and had finer median grain size. The highest median concentration of MeHg (1.1 ng/g) was in the top 2 cm (centimeter) of the shallow box cores. This vertical interval also had the highest value of the ratio of MeHg to HgT, 0.41 percent. Median concentrations of MeHg and median values of MeHg/HgT decreased systematically with depth from 0-4 to 4-8 to 8-12 cm in the shallow cores. However, similar systematic decreases were not observed at the meter scale in the deep cores of the MEM (MEthylMercury) series. The overall median of the ratio MeHg/HgT in the deep cores was 0.25 percent, not much less than the overall median value for the shallow cores (0.33 percent). Mercury-203 radiotracer divalent inorganic mercury (203Hg(II)) was used to determine microbial mercury-methylation potential rates for 11 samples collected from three reservoir locations and various depths in the sediment profile. For the five shallow mercury-methylation subsamples, ancillary geochemical parameters were assayed, including microbial sulfate reduction rates, sulfur speciation (sediment acid volatile sulfide, total reduced sulfur, and pore-water sulfate), iron speciation (sediment acid extractable iron(II), amorphous iron(III), crystalline iron(III) and pore-water iron(II)), pore-water chloride and dissolved organic carbon, and pH, oxidation-reduction potential (Eh) and whole-sediment organic content. The highest potential rates of microbial mercury methylation were measured in shallow (0 to 8 cm depth) sediments (5 to 30 nanograms of mercury per gram dry sediment per day), whereas potential rates for subsamples collected from depths greater than 500 cm were consistently below the detection limit of the radiotracer method (< 0.02 nanogram of mercury per gram dry sediment per day). Chemical analyses of trace and major elements in bed sediment are presented for 202 samples from deep cores from five locations in Englebright Lake. The mean values and standard deviations for selected trace elements were as follows (in micrograms per gram): antimony, 2.4 ? 1.6; arsenic, 69 ? 48; chromium, 134 ? 23; lead, 33 ? 25; and nickel, 87 ? 24. Concentrated samples of heavy-mineral grains, prepared using nine large-volume composite samples from

Monitoring fluvial erosion of the Oso landslide, Washington, using repeat Structure-from-Motion photogrammetry

NASA Astrophysics Data System (ADS)

Anderson, S. W.; Magirl, C. S.; Keith, M. K.

2015-12-01

On March 22, 2014, the Oso landslide, located in northwestern Washington State, catastrophically mobilized about 8 million m3 of mixed glacial sediment, creating a valley-wide blockage that impounded the North Fork Stillaguamish River to a height of 8 m. The river overtopped the landslide blockage within several days and incised a new channel through predominately fine-grained, cohesive glaciolacustrine sediment in the center of the deposit. Our research focuses on the evolution of this new channel. Using a consumer-grade digital camera mounted on a fixed wing-aircraft, we used structure-from-motion (SfM) photogrammetry to produce 25 cm digital elevation models (DEMs) of the channel at one-month intervals between November 2014 and July 2015. A large RTK GPS validation dataset and inter-survey comparisons documents sub-decimeter vertical and horizontal accuracies. In combination with aerial lidar surveys acquired in March and April 2014, this dataset provides a uniquely resolved look at the erosion of a landslide dam. The newly-formed channel incised rapidly, lowering to within a meter of its pre-slide elevation by May 2014 despite modest flows. During high flows of the 2014-2015 winter flood season, erosion was dominated by channel widening of tens of meters with an overall stable planform. Incision fully returned the channel to pre-slide elevations by December 2014. A total of 510,000 +/- 50,000 m3 of material was eroded between March 2014 and July 2015, split evenly between the initial period of incision and the later period of widening. Sediment yield and channel morphology showed asymptotic trends towards stability. Measurements of deposit bulk density and grain size allowed conversion of volumetric sediment yields to mass yields by size classes. Over the 16 months after the slide, the river eroded about 0.82 +/- 0.1 Mt of sediment, of which 0.78 Mt was finer than 2mm. This yield agrees within 15% of an independent estimate based on concurrent sediment gaging in the reach, and represents about 400% of the background sediment yield over that same period.

Species distribution model transferability and model grain size - finer may not always be better.

PubMed

Manzoor, Syed Amir; Griffiths, Geoffrey; Lukac, Martin

2018-05-08

Species distribution models have been used to predict the distribution of invasive species for conservation planning. Understanding spatial transferability of niche predictions is critical to promote species-habitat conservation and forecasting areas vulnerable to invasion. Grain size of predictor variables is an important factor affecting the accuracy and transferability of species distribution models. Choice of grain size is often dependent on the type of predictor variables used and the selection of predictors sometimes rely on data availability. This study employed the MAXENT species distribution model to investigate the effect of the grain size on model transferability for an invasive plant species. We modelled the distribution of Rhododendron ponticum in Wales, U.K. and tested model performance and transferability by varying grain size (50 m, 300 m, and 1 km). MAXENT-based models are sensitive to grain size and selection of variables. We found that over-reliance on the commonly used bioclimatic variables may lead to less accurate models as it often compromises the finer grain size of biophysical variables which may be more important determinants of species distribution at small spatial scales. Model accuracy is likely to increase with decreasing grain size. However, successful model transferability may require optimization of model grain size.

A Composite Medium Approximation for Moisture Tension-Dependent Anisotropy in Unsaturated Layered Sediments

NASA Astrophysics Data System (ADS)

Pruess, K.

2001-12-01

Sedimentary formations often have a layered structure in which hydrogeologic properties have substantially larger correlation length in the bedding plane than perpendicular to it. Laboratory and field experiments and observations have shown that even small-scale layering, down to millimeter-size laminations, can substantially alter and impede the downward migration of infiltrating liquids, while enhancing lateral flow. The fundamental mechanism is that of a capillary barrier: at increasingly negative moisture tension (capillary suction pressure), coarse-grained layers with large pores desaturate more quickly than finer-grained media. This strongly reduces the hydraulic conductivity of the coarser (higher saturated hydraulic conductivity) layers, which then act as barriers to downward flow, forcing water to accumulate and spread near the bottom of the overlying finer-grained material. We present a "composite medium approximation" (COMA) for anisotropic flow behavior on a typical grid block scale (0.1 - 1 m or larger) in finite-difference models. On this scale the medium is conceptualized as consisting of homogeneous horizontal layers with uniform thickness, and capillary equilibrium is assumed to prevail locally. Directionally-dependent relative permeabilities are obtained by considering horizontal flow to proceed via "conductors in parallel," while vertical flow involves "resistors in series." The model is formulated for the general case of N layers, and implementation of a simplified two-layer (fine-coarse) approximation in the multiphase flow simulator TOUGH2 is described. The accuracy of COMA is evaluated by comparing numerical simulations of plume migration in 1-D and 2-D unsaturated flow with results of fine-grid simulations in which all layers are discretized explicitly. Applications to water seepage and solute transport at the Hanford site are also described. This work was supported by the U.S. Department of Energy under Contract No. DE-AC03-76SF00098 through Memorandum Purchase Order 248861-A-B2 between Pacific Northwest National Laboratory and Lawrence Berkeley National Laboratory.

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.

Grain size dependent magnetic discrimination of Iceland and South Greenland terrestrial sediments in the northern North Atlantic sediment record

NASA Astrophysics Data System (ADS)

Hatfield, Robert G.; Stoner, Joseph S.; Reilly, Brendan T.; Tepley, Frank J.; Wheeler, Benjamin H.; Housen, Bernard A.

2017-09-01

We use isothermal and temperature dependent in-field and magnetic remanence methods together with electron microscopy to characterize different sieved size fractions from terrestrial sediments collected in Iceland and southern Greenland. The magnetic fraction of Greenland silts (3-63 μm) and sands (>63 μm) is primarily composed of near-stoichiometric magnetite that may be oxidized in the finer clay (<3 μm) fractions. In contrast, all Icelandic fractions dominantly contain titanomagnetite of a range of compositions. Ferrimagnetic minerals preferentially reside in the silt-size fraction and exist as fine single-domain (SD) and pseudo-single-domain (PSD) size inclusions in Iceland samples, in contrast to coarser PSD and multi-domain (MD) discrete magnetites from southern Greenland. We demonstrate the potential of using magnetic properties of the silt fraction for source unmixing by creating known endmember mixtures and by using naturally mixed marine sediments from the Eirik Ridge south of Greenland. We develop a novel approach to ferrimagnetic source unmixing by using low temperature magnetic susceptibility curves that are sensitive to the different crystallinity and cation substitution characteristics of the different source regions. Covariation of these properties with hysteresis parameters suggests sediment source changes have driven the magnetic mineral variations observed in Eirik Ridge sediments since the last glacial maximum. These observations assist the development of a routine method and interpretative framework to quantitatively determine provenance in a geologically realistic and meaningful way and assess how different processes combine to drive magnetic variation in the North Atlantic sediment record.

Trace metal accumulation in sediments and benthic macroinvertebrates before and after maintenance of a constructed wetland.

PubMed

O'Connor, Thomas P; Muthukrishnan, Swarna; Barshatzky, Kristen; Wallace, William

2012-04-01

Stormwater best management practices (BMPs) require regular maintenance. The impact on trace metal concentrations in a constructed stormwater wetland BMP on Staten Island, New York, was investigated by analyzing sediment concentrations and tissue residues of the dominant macroinvertebrates (Tubifex tubifex) prior and subsequent to maintenance. Trace metal concentrations were assessed using standard serial extraction (for sediment) and acid digestion (for tissue burdens) techniques, followed by quantitative determination using graphite furnace atomic absorption spectrometry and inductively coupled plasma optical emission spectrometry, respectively. The results suggest that disturbance of sediment during maintenance of the BMP resulted in an increase in the most mobile fraction of trace metals, especially those associated with finer grained sediments (< 63 tm), and as a consequence, measured metal concentrations in macroinvertebrates increased. Regressions of a subset of metal concentrations (copper, lead, and zinc) in sediment and the macroinvertebrate tissue burden samples generally increased as a result of maintenance. A follow-up sampling event 9 months after maintenance demonstrated that the most readily available form of trace metal in the BMP was reduced, which supports (1) long-term sequestration of metals in the BMP and (2) that elevated bioavailability following maintenance was potentially a transient feature of the disturbance. This study suggests that in the long-term, performing sediment removal might help reduce bioavailability of trace metal concentrations in both the BMP and the receiving water to which a BMP discharges. However, alternative practices might need to be implemented to reduce trace metal bioavailability in the short-term.

Computer programs for computing particle-size statistics of fluvial sediments

USGS Publications Warehouse

Stevens, H.H.; Hubbell, D.W.

1986-01-01

Two versions of computer programs for inputing data and computing particle-size statistics of fluvial sediments are presented. The FORTRAN 77 language versions are for use on the Prime computer, and the BASIC language versions are for use on microcomputers. The size-statistics program compute Inman, Trask , and Folk statistical parameters from phi values and sizes determined for 10 specified percent-finer values from inputed size and percent-finer data. The program also determines the percentage gravel, sand, silt, and clay, and the Meyer-Peter effective diameter. Documentation and listings for both versions of the programs are included. (Author 's abstract)

Large-scale dam removal on the Elwha River, Washington, USA: river channel and floodplain geomorphic change

USGS Publications Warehouse

East, Amy E.; Pess, George R.; Bountry, Jennifer A.; Magirl, Christopher S.; Ritchie, Andrew C.; Logan, Joshua; Randle, Timothy J.; Mastin, Mark C.; Minear, Justin T.; Duda, Jeffrey J.; Liermann, Martin C.; McHenry, Michael L.; Beechie, Timothy J.; Shafroth, Patrick B.

2015-01-01

As 10.5 million t (7.1 million m3) of sediment was released from two former reservoirs, downstream dispersion of a sediment wave caused widespread bed aggradation of ~ 1 m (greater where pools filled), changed the river from pool–riffle to braided morphology, and decreased the slope of the lowermost river. The newly deposited sediment, which was finer than most of the pre-dam-removal bed, formed new bars (largely pebble, granule, and sand material), prompting aggradational channel avulsion that increased the channel braiding index by almost 50%. As a result of mainstem bed aggradation, floodplain channels received flow and accumulated new sediment even during low to moderate flow conditions. The river system showed a two- to tenfold greater geomorphic response to dam removal (in terms of bed elevation change magnitude) than it had to a 40-year flood event four years before dam removal. Two years after dam removal began, as the river had started to incise through deposits of the initial sediment wave, ~ 1.2 million t of new sediment (~ 10% of the amount released from the two reservoirs) was stored along 18 river km of the mainstem channel and 25 km of floodplain channels. The Elwha River thus was able to transport most of the released sediment to the river mouth. The geomorphic alterations and changing bed sediment grain size along the Elwha River have important ecological implications, affecting aquatic habitat structure, benthic fauna, salmonid fish spawning and rearing potential, and riparian vegetation. The response of the river to dam removal represents a unique opportunity to observe and quantify fundamental geomorphic processes associated with a massive sediment influx, and also provides important lessons for future river-restoration endeavors.

Late Cretaceous to Miocene phosphatic sediments in the Georges Bank Basin, U.S. North Atlantic outer continental shelf

USGS Publications Warehouse

Poppe, L.J.; Manheim, F. T.; Popenoe, P.

1992-01-01

Phosphorite and phosphatic sediments are present in the Georges Bank Basin in marine, Late Cretaceous to Miocene strata equivalent to the Dawson Canyon Formation and Banquereau Formation of offshore Nova Scotia. The Late Cretaceous to Paleocene phosphorite occurs predominantely as sand- and gravel-sized pellets and as cement in conglomeratic aggregates. The Eocene and Miocene phosphate occurs mainly as fine-very fine sand-size spheroidal-avoidal pellets in unconsolidated clayey silts. The older phosphorites form intraformational conglomerates that are the result of a winnowed finer-grained matrix, leaving lag deposits of phosphorite. We present evidence that most of the Eocene and Miocene phosphate is primary and formed during marine trangressions. Our observations extend the geographic and temporal limits of the major phosphogenic system of the Western North Atlantic northward and through time. However, compared to the well-known phosphorite deposits along the southeastern margin of the U.S.A., these northern deposits are not of commercial scale due to a high terrigenous input and the lack of a mechanism capable of driving persistant upwelling. ?? 1992.

The role of autochthonous organic matter in radioactive cesium accumulation to riverine fine sediments.

PubMed

Fujii, Manabu; Ono, Keisuke; Yoshimura, Chihiro; Miyamoto, Manami

2018-06-15

Anthropogenically released radioactive cesium (RCs) poses serious ecological and environmental concerns given its persistency in the environment. Although accumulation of RCs in aqueous and sedimentary environments is often reported to associate with organic matter (OM), the mechanisms responsible remain unclear. Here, we investigated RCs in fine sediments along the Abukuma River, the largest river near the Fukushima Daiichi Nuclear Power Plant, 1.5-4 years after the accident. Measuring the density-separated sediment fractions with a broad range of OM content (%) indicated that the RCs concentration (Bq·kg -1 ) is positively correlated with OM content for intermediate-density fractions in which OM is primarily characterized by autochthonous origin. This relationship, however, did not hold for light-density fractions containing a high proportion of large-size allochthonous OM. Furthermore, H 2 O 2 -assisted OM digestion and amorphous material dissolution treatments resulted in only a minor reduction in sedimentary RCs. These results along with the fact that sediments with high autochthonous OM content showed high specific surface area indicated that RCs is tightly associated with finer-grained and chemically non-labile inorganic fractions concurrently resident with autochthonous OM. Overall, our findings highlight that autochthonous OM exerts a significant control on the accumulation, transport, and fate of RCs in aqueous and sedimentary environments. Copyright © 2018 Elsevier Ltd. All rights reserved.

Sediment Transport During Three Controlled-Flood Experiments on the Colorado River Downstream from Glen Canyon Dam, with Implications for Eddy-Sandbar Deposition in Grand Canyon National Park

USGS Publications Warehouse

Topping, David J.; Rubin, David M.; Grams, Paul E.; Griffiths, Ronald E.; Sabol, Thomas A.; Voichick, Nicholas; Tusso, Robert B.; Vanaman, Karen M.; McDonald, Richard R.

2010-01-01

Three large-scale field experiments were conducted on the Colorado River downstream from Glen Canyon Dam in 1996, 2004, and 2008 to evaluate whether artificial (that is, controlled) floods released from the dam could be used in conjunction with the sand supplied by downstream tributaries to rebuild and sustainably maintain eddy sandbars in the river in Grand Canyon National Park. Higher suspended-sand concentrations during a controlled flood will lead to greater eddy-sandbar deposition rates. During each controlled flood experiment, sediment-transport and bed-sediment data were collected to evaluate sediment-supply effects on sandbar deposition. Data collection substantially increased in spatial and temporal density with each subsequent experiment. The suspended- and bed-sediment data collected during all three controlled-flood experiments are presented and analyzed in this report. Analysis of these data indicate that in designing the hydrograph of a controlled flood that is optimized for sandbar deposition in a given reach of the Colorado River, both the magnitude and the grain size of the sand supply must be considered. Because of the opposing physical effects of bed-sand area and bed-sand grain size in regulating suspended-sand concentration, larger amounts of coarser sand on the bed can lead to lower suspended-sand concentrations, and thus lower rates of sandbar deposition, during a controlled flood than can lesser amounts of finer sand on the bed. Although suspended-sand concentrations were higher at all study sites during the 2008 controlled-flood experiment (CFE) than during either the 1996 or 2004 CFEs, these higher concentrations were likely associated with more sand on the bed of the Colorado River in only lower Glen Canyon. More sand was likely present on the bed of the river in Grand Canyon during the 1996 CFE than during either the 2004 or 2008 CFEs. The question still remains as to whether sandbars can be sustained in the Colorado River in Grand Canyon National Park through use of controlled floods in conjunction with typical amounts and grain sizes of sand supplied by the tributaries that enter the Colorado River downstream from Glen Canyon Dam.

Laboratory evaluation of the Sequoia Scientific LISST-ABS acoustic backscatter sediment sensor

USGS Publications Warehouse

Snazelle, Teri T.

2017-12-18

Sequoia Scientific’s LISST-ABS is an acoustic backscatter sensor designed to measure suspended-sediment concentration at a point source. Three LISST-ABS were evaluated at the U.S. Geological Survey (USGS) Hydrologic Instrumentation Facility (HIF). Serial numbers 6010, 6039, and 6058 were assessed for accuracy in solutions with varying particle-size distributions and for the effect of temperature on sensor accuracy. Certified sediment samples composed of different ranges of particle size were purchased from Powder Technology Inc. These sediment samples were 30–80-micron (µm) Arizona Test Dust; less than 22-µm ISO 12103-1, A1 Ultrafine Test Dust; and 149-µm MIL-STD 810E Silica Dust. The sensor was able to accurately measure suspended-sediment concentration when calibrated with sediment of the same particle-size distribution as the measured. Overall testing demonstrated that sensors calibrated with finer sized sediments overdetect sediment concentrations with coarser sized sediments, and sensors calibrated with coarser sized sediments do not detect increases in sediment concentrations from small and fine sediments. These test results are not unexpected for an acoustic-backscatter device and stress the need for using accurate site-specific particle-size distributions during sensor calibration. When calibrated for ultrafine dust with a less than 22-µm particle size (silt) and with the Arizona Test Dust with a 30–80-µm range, the data from sensor 6039 were biased high when fractions of the coarser (149-µm) Silica Dust were added. Data from sensor 6058 showed similar results with an elevated response to coarser material when calibrated with a finer particle-size distribution and a lack of detection when subjected to finer particle-size sediment. Sensor 6010 was also tested for the effect of dissimilar particle size during the calibration and showed little effect. Subsequent testing revealed problems with this sensor, including an inadequate temperature compensation, making this data questionable. The sensor was replaced by Sequoia Scientific with serial number 6039. Results from the extended temperature testing showed proper temperature compensation for sensor 6039, and results from the dissimilar calibration/testing particle-size distribution closely corroborated the results from sensor 6058.

Reconstructing a sediment pulse: Modeling the effect of placer mining on Fraser River, Canada

NASA Astrophysics Data System (ADS)

Ferguson, R. I.; Church, M.; Rennie, C. D.; Venditti, J. G.

2015-07-01

Gold mining along 525 km of the Fraser River between 1858 and 1909 added an estimated 1.1 × 108 t of tailings, half gravel and the rest finer, to the river's natural sediment load. We simulate the response using a 1-D multigrain size morphodynamic model. Since premining conditions are unknown and modern data are insufficient for tuning the process representation, we devised a novel modeling strategy which may be useful in other data-poor applications. We start the model from a smoothed version of the modern longitudinal profile with bed grain size distributions optimized to match alternative assumptions about natural sediment supply and compare runs that include mining with control runs that can be used to quantify the effects of deficiencies in process representation and initialization. Simulations with an appropriate choice of natural supply rate closely match the best available test data, which consist of a detailed 1952-1999 gravel budget for the distal part of the model domain. The simulations suggest that the main response to mining was rapid bed fining, which allowed a major increase in bed load transport rate with only slight (~0.1 m) mean aggradation within the mining region and most of the excess sediment exported well beyond the mountain front within the mining period or soon afterward. We compare this pattern of response by a large, powerful river with previous case studies of river adjustment to sediment supply change.

The erosion of the beaches on the coast of Alicante: Study of the mechanisms of weathering by accelerated laboratory tests.

PubMed

López, I; López, M; Aragonés, L; García-Barba, J; López, M P; Sánchez, I

2016-10-01

One of the main problems that coasts around the world present, is the regression and erosion of beaches. However, the factors involved in these processes are unclear. In this study, the influence of sediment erosion on beach regression has been analysed. In order to do that, a three-step investigation has been carried out. Firstly, coastline variations of four Spanish beaches have been analysed. Secondly, a study on sediment position along the beach profile has been developed. Finally, the process that beach sediments undergo along the surf zone when they are hit by the incident waves has been simulated by an accelerated particle weathering test. Samples of sand and shells were subjected to this accelerated particle weathering test. Results were supplemented with those from carbonate content test, XRD, SEM and granulometric analysis. Results shows a cross-shore classification of sediments along the beach profile in which finer particles move beyond offshore limit. Besides, it was observed that sediment erosion process is divided into three sages: i) particles wear due to crashes ii) dissolution of the carbonate fraction, and iii) breakage and separation of mineral and carbonate parts of particles. All these processes lead to a reduction of particle size. The mechanism responsible of beach erosion would consist of multiples and continuous particle location exchanges along the beach profile as a consequence of grain-size decrease due to erosion. Copyright © 2016 Elsevier B.V. All rights reserved.

Sea-Floor Character and Sedimentary Processes in the Vicinity of Woods Hole, Massachusetts

USGS Publications Warehouse

Poppe, Lawrence J.; McMullen, Katherine Y.; Foster, David S.; Blackwood, Dann S.; Williams, S. Jeffress; Ackerman, Seth D.; Barnum, Steven R.; Brennan, Rick T.

2008-01-01

Continuous-coverage multibeam bathymetric models and sidescan-sonar imagery have been verified with high-resolution seismic-reflection profiles, sediment sampling, and bottom photography. Together these data layers provide detailed base maps that yield topographic, compositional, and environmental perspectives of the sea floor in the vicinity of Woods Hole, an important harbor and major passage between the Elizabeth Islands and Cape Cod, Massachusetts. Tidally dominated high-energy environments within Woods Hole have prevented deposition of Holocene marine sediments, exposed underlying glacial drift of the Buzzards Bay moraine, and winnowed finer grained sediments, leaving lag deposits of boulders and gravel. These conditions have also enlarged and preserved depressions in the moraine surface that were originally kettle holes and formed ebb-tidal deltas at the entrances to passages. Fields of transverse and barchanoid sand waves dominate across the southern part of the study area in Vineyard Sound, where benthic environments are characterized by processes associated with coarse-bedload transport. Transverse sand waves dominate near shoals where sediment supply is greater and have asymmetries that indicate that the shoals are shaped and maintained by clockwise gyres of net sediment transport. Barchanoid sand waves, which are most common where Holocene sediments are thinner, commonly align into elongate fields that have smaller isolated waves concentrated at the eastern ends and that progressively widen and have waveforms that increase in amplitude, wavelength, and complexity westward. The northern, protected parts of the Little and Inner Harbors are characterized by muddy sediment and processes associated with deposition. A pockmark field in Little Harbor and the muddy, organic-rich sediments that form a scarp along the edge of Parker Flat are evidence for the presence of submerged marsh deposits formed during the Holocene rise in sea level.

Characterisation of organic matter source and sediment distribution in Ashtamudi Estuary, southern India

NASA Astrophysics Data System (ADS)

Kumar, Prem; Ankit, Yadav; Mishra, Praveen K.; Jha, Deepak Kumar; Anoop, Ambili

2017-04-01

In the present study we have focussed on the surface sediments of Ashtamudi Estuary (southern India) to understand (i) the fate and sources of organic matter by investigating lipid biomarker (n-alkanes) distribution in modern sediments and vegetation samples and (ii) the processes controlling the sediment distribution into the lake basin using end-member modelling approach. The sediment n-alkanes from the Ashtamudi Estuary exhibit a pronounced odd over even predominance with maxima at C29 and C31 chain length indicative of a dominant terrestrial contribution. A number of n-alkane indices have been calculated to illustrate the variability in space by considering separately the river dominated northern reaches and tidal influenced southern part of Ashtamudi Estuary. The highest terrigenous organic contents were found in sediments from the river and upper bay sites, with smaller contributions to the lower parts of the estuary. The Paq and TAR (terrigenous/aquatic ratio) indices demonstrate maximum aquatic productivity (plankton growth and submerged macrophytes) in the tidal dominated region of the Ashtamudi Estuary. The carbon preference index (CPI) and average chain length (ACL) provide evidence for high petrogenic organic inputs in the tidal zone, whereas dominant biogenic contribution have been observed in the riverine zone. In addition, the end member modeling of the grain size distribution of the surface sediment samples enabled us to decipher significant sedimentological processes affecting the sediment distribution in the estuarine settings. The end-member distribution showing highest loading with the coarser fraction is maximum where estuary debouches into the sea. However, the samples near the mouth of the river shows finer fraction of the end-member.

Investigations of Sediment Transportation, Middle Loup River at Dunning, Nebraska: With Application of Data from Turbulence Flume

USGS Publications Warehouse

Hubbell, David Wellington; Matejka, Donald Quintin

1959-01-01

An investigation of fluvial sediments of the Middle Loup River at Dunning, Nebr., was begun in 1946 and expanded in 1949 to provide information on sediment transportation. Construction of an artificial turbulence flume at which the total sediment discharge of the Middle Loup River at Dunning, Nebr., could be measured with suspended-sediment sampling equipment was completed in 1949. Since that time. measurements have been made at the turbulence flume and at several selected sections in a reach upstream and downstream from the flume. The Middle Loup River upstream from Dunning traverses the sandhills region of north-central Nebraska and has a drainage area of approximately 1,760 square miles. The sandhills are underlain by the Ogallala formation of Tertiary age and are mantled by loess and dune sand. The topography is characterized by northwest-trending sand dunes, which are stabilized by grass cover. The valley floor upstream from Dunning is generally about half a mile wide, is about 80 feet lower than the uplands, and is composed of sand that was mostly stream deposited. The channel is defined by low banks. Bank erosion is prevalent and is the source of most of the sediment load. The flow originates mostly from ground-water accretion and varies between about 200 and 600 cfs (cubic feet per second). Measured suspended-sediment loads vary from about 200 to 2,000 tons per day, of which about 20 percent is finer than 0.062 millimeter and 100 percent is finer than 0.50 millimeter. Total sediment discharges vary from about 500 to 3,500 tons per day, of which about 10 percent is finer than 0.062 millimeter, about 90 percent is finer than 0.50 millimeter, and about 98 percent is finer than 2.0 millimeters. The measured suspended-sediment discharge in the reach near Dunning averages about one-half of the total sediment discharge as measured at the turbulence flume. This report contains information collected during the period October 1, 1948, to September 30, 1952. The information includes sediment discharges; particle-size analyses of total load, of measured suspended sediment, and of bed material; water discharges and other hydraulic data for the turbulence flume and the selected sections. Sediment discharges have been computed with several different formulas, and insofar as possible, each computed load has been compared with data from the turbulence flume. Sediment discharges computed with the Einstein procedure did not agree well, in general, with comparable measured loads. However, a satisfactory representative cross section for the reach could not be determined with the cross sections that were selected for this investigation. If the computed cross section was narrower and deeper than a representative cross section for the reach, computed loads were high; and if the computed cross section was wider and shallower than a representative cross section for the reach, computed loads were low. Total sediment discharges computed with the modified Einstein procedure compared very well with the loads of individual size ranges and the measured total loads at the turbulence flume. Sediment discharges computed with the Straub equation averaged about twice the measured total sediment discharge at the turbulence flume. Bed-load discharges computed with the Kalinske equation were of about the right magnitude; however, high computed loads were associated with low total loads, low unmeasured loads, and low concentrations of measured suspended sediment coarser than 0.125 millimeter. Bed-load discharges computed with the Schoklitsch equation seemed somewhat high; about one-third of the computed loads were slightly higher than comparable unmeasured loads. Although, in general, high computed discharges with the Schoklitsch equation were associated with high measured total loads, high unmeasured loads, and high concentrations of measured suspended sediment coarser than 0.125 millimeter, the trend was not consistent. Bed-load discharges computed

Breakup and reestablishment of the armour layer in a large gravel-bed river below dams: The lower Ebro

NASA Astrophysics Data System (ADS)

Vericat, Damia; Batalla, Ramon J.; Garcia, Celso

2006-06-01

Changes in armour layer during floods under supply limited conditions are little known. This paper describes the breakup and the reestablishment of the bed armour layer in the regulated gravel-bed Ebro River during a flooding period. The study was conducted over a 28-km study reach from 2002 to 2004. The surface, subsurface and bed load grain size distribution constitute the bases for the analysis of bed-armouring dynamics. The results indicate that the magnitude of floods controlled the degree of armouring of the river bed. The initial mean armouring ratio was 2.3, with maximum values reaching 4.4. Floods in the winter of 2002-2003 ( Q8) caused the breakup of the armour layer in several sections. This resulted in the erratic bed load pattern observed during the December 2002 flushing flow and in the increase in bed load transport during successive events. Most grain size classes were entrained and transported, causing river bed incision. The mean armouring ratio decreased to 1.9. In contrast, during low magnitude floods in 2003-2004 ( Q2), the coarsest fractions (64 mm) did not take part in the bed load while finer particles were winnowed, thus surface deposits coarsened. As a result, the armour layer was reestablished (i.e., the mean armouring ratio increased to 2.3), and the supply of subsurface sediment decreased. The supply and transport of bed material appear to be in balance in the river reach immediately below the dam. In contrast, the transport of medium and finer size classes in the downstream reaches was higher than their supply from upstream, a phenomenon that progressively reduced their availability in the river bed surface, hence the armour layer reworking.

Identification and assessment of groundwater flow and storage components of the relict Schöneben Rock Glacier, Niedere Tauern Range, Eastern Alps (Austria)

NASA Astrophysics Data System (ADS)

Winkler, Gerfried; Wagner, Thomas; Pauritsch, Marcus; Birk, Steffen; Kellerer-Pirklbauer, Andreas; Benischke, Ralf; Leis, Albrecht; Morawetz, Rainer; Schreilechner, Marcellus G.; Hergarten, Stefan

2016-06-01

More than 2,600 relict rock glaciers are known in the Austrian Alps but the knowledge of their hydraulic properties is severely limited. The relict Schöneben Rock Glacier (Niedere Tauern Range, Austria), with an extension of 0.17 km2, was investigated based on spring data (2006-2014) and seismic refraction survey. Spring-discharge hydrographs and natural and artificial tracer data suggest a heterogeneous aquifer with a layered internal structure for the relict rock glacier. The discharge behavior exhibits a fast and a delayed flow component. The spring discharge responds to recharge events within a few hours but a mean residence time of several months can also be observed. The internal structure of the rock glacier (up to several tens of meters thick) consists of: an upper blocky layer with a few meters of thickness, which lacks fine-grained sediments; a main middle layer with coarse and finer-grained sediments, allowing for fast flow; and an approximately 10-m-thick basal till layer as the main aquifer body responsible for the base flow. The base-flow component is controlled by (fine) sandy to silty sediments with low hydraulic conductivity and high storage capacity, exhibiting a difference in hydraulic conductivity to the upper layer of about three orders of magnitude. The high storage capacity of relict rock glaciers has an impact on water resources management in alpine catchments and potentially regulates the risk of natural hazards such as floods and related debris flows. Thus, the results highlight the importance of such aquifer systems in alpine catchments.

Preferential Flow Paths and Recirculation-Disrupting Jets in the Leeside of Self-Forming Coarse-Grained Laboratory Bedforms

NASA Astrophysics Data System (ADS)

Lichtner, D.; Christensen, K. T.; Best, J.; Blois, G.

2014-12-01

Exchange of fluid in the near-subsurface of a streambed is influenced by turbulence in the free flow, as well as by bed topography and permeability. Macro-roughness elements such as bedforms are known to produce pressure gradients that drive fluid into the streambed on their stoss sides and out of the bed on their lee sides. To study the modification of the near-bed flow field by self-forming permeable bedforms, laboratory experiments were conducted in a 5 mm wide flume filled with 1.3 mm glass beads. The narrow width of the flume permitted detailed examination of the fluid exiting the bed immediately downstream of a bedform. Dense 2-D velocity field measurements were gathered using particle image velocimetry (PIV). In up to 8% of instantaneous PIV realizations, the flow at the near-bed presented a component perpendicular to the streambed, indicating flow across the interface. At the downstream side of the bedform, such flow disrupted the mean recirculation pattern that is typically observed in finer sediment beds. It is hypothesized that the coarse grain size and the resulting high bed permeability promote such near-surface jet events. A qualitative analysis of raw image frames indicated that an in-place jostling of sediment is associated with these jets thus suggesting that subsurface flow may be characterized by impulsive events. These observations are relevant to hyporheic exchange rates in coarse sediments and can have strong morphodynamic implications as they can explain the lack of ripples and characteristics of dunes in high permeability gravels. Overall, further study of the flow structure over highly permeable streambeds is needed to understand subsurface exchange and bedform initiation.

Tectonic Processes Along the Southeastern Margin of Alaska - The Neogene Sedimentary Record: Yakataga Formation, St. Elias Mountains

NASA Astrophysics Data System (ADS)

Witmer, J. W.; Ridgway, K. D.; Brennan, P. R.; Arnaud, E.; Pavlis, T.

2008-12-01

Neogene collision of the Yakutat microplate with the southern Alaskan continental margin is associated with extreme rates of exhumation and erosion of the St. Elias Mountains. The exhumation and the concurrent development of temperate glaciers are recorded in the ~5000 m of sedimentary strata of the Yakataga Formation. We present new data from measured stratigraphic sections that document along-strike and temporal changes within the Yakataga Formation along this collisional margin during Miocene to Pleistocene time. In the eastern part of our study area, the Yakataga Formation consists of lenticular sandstone and conglomerate facies associated with fan-delta depositional environments that are overlain by thick-bedded glaciomarine strata. These strata grade to finer-grained sandstone and convoluted mudstone typical of marine shelf environments in the central part of our study area. Along strike in the westernmost part of our study area the Yakataga Formation is interpreted to be laterally equivalent to Neogene strata of the Redwood Formation. These strata include thick-bedded, macrofossil-rich sandstone, well-rounded conglomerate, and thin-bedded mudstone facies that are characteristic of nearshore and shelf depositional environments. These sediments were likely sourced by fluvial systems along the continental margin that served as the backstop for Neogene collision. Preliminary compositional data also suggest that the Redwood Formation was derived from a different source than the Yakataga Formation. Along-strike changes in structural configuration of the Yakataga Formation are also observed. In the easternmost part of our study area adjacent to the Dangerous River zone (DRZ), a possible remnant strike-slip fault system, unconformities between the Yakataga Formation and underlying strata require erosion of 1000s of meters of missing Eocene-Miocene strata. We interpret this part of the mountain range to have undergone the greatest amount of Neogene exhumation. In the central part of the study area, the Yakataga Formation is exposed in a series of growth folds and megachannels that have been incorporated into a southward-propagating thrust belt as sediment was transported westward away from the exhuming St. Elias Range. To the west, more complete stratigraphic sections and finer-grained lithofacies suggest relatively less syndepositional deformation during the deposition of the Yakataga Formation. From a stratigraphic perspective, the DRZ appears to have focused deformation, exhumation, development of temperate glaciers, and westward transport of sediment during deposition of the Yakataga Formation. The westward changes in lithofacies and deformation within the Yakataga Formation are interpreted as products of progressive oblique collision of the Yakutat microplate to the southeastern Alaskan continental margin. New U-Pb detrital zircon geochronologic data from the Yakataga Formation and older underlying strata demonstrate minimal changes in provenance from Eocene to Pleistocene time. We interpret these data to reflect recycling of sediment within the collisional zone.

CROSS-SHORE TRANSPORT OF BIMODAL SANDS.

USGS Publications Warehouse

Richmond, Bruce M.; Sallenger,, Asbury H.; Edge, Billy L.

1985-01-01

Foreshore sediment level and sediment size were monitored as part of an extensive nearshore processes experiment - DUCK 82. Changes in foreshore texture were compared with computed values of onshore transported material based on current measurements from the surf zone and sediment transport theory. Preliminary results indicate reasonable agreement between predicted size of sediment transported onshore and beach texture changes. It is also demonstrated that coarse sediment may move onshore while finer material may simultaneously move offshore. Refs.

Process recognition in multi-element soil and stream-sediment geochemical data

USGS Publications Warehouse

Grunsky, E.C.; Drew, L.J.; Sutphin, D.M.

2009-01-01

Stream-sediment and soil geochemical data from the Upper and Lower Coastal Plains of South Carolina (USA) were studied to determine relationships between soils and stream sediments. From multi-element associations, characteristic compositions were determined for both media. Primary associations of elements reflect mineralogy, including heavy minerals, carbonates and clays, and the effects of groundwater. The effects of groundwater on element concentrations are more evident in soils than stream sediments. A "winnowing index" was created using ratios of Th to Al that revealed differing erosional and depositional environments. Both soils and stream sediments from the Upper and Lower Coastal Plains show derivation from similar materials and subsequent similar multi-element relationships, but have some distinct differences. In the Lower Coastal Plain, soils have high values of elements concentrated in heavy minerals (Ce, Y, Th) that grade into high values of elements concentrated into finer-grain-size, lower-density materials, primarily comprised of carbonates and feldspar minerals (Mg, Ca, Na, K, Al). These gradational trends in mineralogy and geochemistry are inferred to reflect reworking of materials during marine transgressions and regressions. Upper Coastal Plain stream-sediment geochemistry shows a higher winnowing index relative to soil geochemistry. A comparison of the 4 media (Upper Coastal Plain soils and stream sediments and Lower Coastal Plain soils and stream sediments) shows that Upper Coastal Plain stream sediments have a higher winnowing index and a higher concentration of elements contained within heavy minerals, whereas Lower Coastal Plain stream sediments show a strong correlation between elements typically contained within clays. It is not possible to calculate a functional relationship between stream sediment-soil compositions for all elements due to the complex history of weathering, deposition, reworking and re-deposition. However, depending on the spatial separation of the stream-sediment and soil samples, some elements are more highly correlated than others. Crown Copyright ?? 2009.

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.

Seismic reflection and vibracoring studies of the continental shelf offshore central and western Long Island, New York

USGS Publications Warehouse

Kelly, W.M.; Albanese, J.R.; Coch, N.K.; Harsch, A.A.

1999-01-01

The ridge-and-swale topography on the continental shelf south of Fire Island, New York, is characterized by northeast-trending linear shoals that are shore attached and shore oblique on the inner shelf and isolated and shore parallel on the middle shelf. High-resolution seismic reflection profiles show that the ridges and swales occur independent of, and are not controlled by, the presence of internal structures (for example, filled tidal inlet channels, paleobarrier strata) or underlying structure (for example, high-relief Cretaceous unconformity). Grab samples of surficial sediments on the shelf south of Fire Island average 98% sand. Locally, benthic fauna increase silt and clay content through fecal pellet production or increase the content of gravel-size material by contribution of their fragmented shell remains. Surficial sand on the ridges is unimodal at 0.33 mm (medium sand, about 50 mesh), and surficial sand in troughs is bimodal at 0.33 mm and 0.15 mm (fine sand, about 100 mesh). In addition to seismic studies, 26 vibracores were recovered from the continental shelf in state and federal waters from south of Rockaway and Long Beaches, Long Island, New York. Stratigraphic and sedimentological data gleaned from these cores were used to outline the geologic framework in the study area. A variety of sedimentary features were noted in the cores, including burrow-mottled sections of sand in a finer silty-sand, rhythmic lamination of sand and silty-sand that reflect cyclic changes in sediment transport, layers of shell hash and shells that probably represent tempestites, and changes from dark color to light color in the sediments that probably represent changes in the oxidation-reduction conditions in the area with time. The stratigraphic units identified are an upper, generally oxidized, nearshore facies, an underlying fine- to medium-sand and silty-clay unit considered to be an estuarine facies, and a lower, coarse-grained deeply oxidized, cross-laminated pre-Holocene unit. Grain-size analysis shows that medium- to fine-grained sand makes up most (68-99%) of the surficial sediments. Gravel exists in trace amounts up to 19%. Silt ranges between 3% and 42% and clay ranges from 1% to 10%.The ridge-and-swale topography on the continental shelf south of Fire Island, New York, is characterized by northeast-trending linear shoals that are shore attached and shore oblique on the inner shelf and isolated and shore parallel on the middle shelf. High-resolution seismic reflection profiles show that the ridges and swales occur independent of, and are not controlled by, the presence of internal structures (for example, filled tidal inlet channels, paleobarrier strata) or underlying structure (for example, high-relief Cretaceous unconformity). Grab samples of surficial sediments on the shelf south of Fire Island average 98% sand. Locally, benthic fauna increase silt and clay content through fecal pellet production or increase the content of gravel-size material by contribution of their fragmented shell remains. Surficial sand on the ridges is unimodal at 0.33 mm (medium sand, about 50 mesh), and surficial sand in troughts is bimodal at 0.33 mm and 0.15 mm (fine sand, about 100 mesh). In addition to seismic studies, 26 vibracores were recovered from the continental shelf in state and federal waters from south of Rockaway and Long Beaches, Long Island, New York. Stratigraphic and sedimentological data gleaned from these cores were used to outline the geologic framework in the study area. A variety of sedimentary features were noted in the cores, including burrow-mottled sections of sand in a finer silty-sand, rhythmic lamination of sand and silty-sand that reflect cyclic changes in sediment transport, layers of shell hash and shells that probably represent tempestites, and changes from dark color to light color in the sediments that probably represent changes in the oxidation-reduction conditions in the area with time. The stratigraphic un

Aeolian transport of biota with dust: A wind tunnel experiment

NASA Astrophysics Data System (ADS)

Rivas, J. A., Jr.; Gill, T. E.; Van Pelt, R. S.; Walsh, E.

2015-12-01

Ephemeral wetlands are ideal sources for dust emission, as well as repositories for dormant stages of aquatic invertebrates. An important component of invertebrate dispersal and colonization to new areas is the ability to be entrained into the atmosphere. Aquatic invertebrate eggs fall within the size of dust and sand grains (30-600μm), are less dense and aerodynamically shaped. We have shown previously that aquatic invertebrates can be dispersed long distances in dust storms but the extent of transport of taxa based on diapausing egg size/morphology has not been investigated. Here, we control the wind erosion process in a wind tunnel to test entrainment of diapausing stages of brine shrimp, clam shrimp, tadpole shrimp, fairy shrimp, Daphnia, and the rotifers Brachionus plicatilis and B. calyciflorus into the air by saltation. Diapausing eggs were mixed with sterilized wind-erodible soil. The soil/egg mixture was moistened with distilled water and air dried to form a crust. Dust was generated in a wind tunnel by releasing sand grains that act as saltator material similar to wind-entrained natural sands. Maximum wind velocity was 10m/s and entrained particles were sampled through an isokinetic horizontal intake opening. Aeolian sediment was collected from three points in the system; transfer section for coarse sediment, the pan subtending a settling chamber for finer saltation-sized sediment, and two paper filters for suspension-sized sediment. Samples were then passed through 250 and 350 μm sieves to remove abrader sand and rehydrated with various sterile media depending on the type of organism. We retrieved viable brine, fairy, and tadpole shrimp, ostracods, Daphnia, and diapausing eggs of the rotifers after hydration. This experiment demonstrates that resting stages of many invertebrates can be wind-eroded due to size and egg morphology and remain viable under controlled conditions mimicking dust emission.

Influence of permeability on nanoscale zero-valent iron particle transport in saturated homogeneous and heterogeneous porous media.

PubMed

Strutz, Tessa J; Hornbruch, Götz; Dahmke, Andreas; Köber, Ralf

2016-09-01

Nanoscale zero-valent iron (NZVI) particles can be used for in situ groundwater remediation. The spatial particle distribution plays a very important role in successful and efficient remediation, especially in heterogeneous systems. Initial sand permeability (k 0) influences on spatial particle distributions were investigated and quantified in homogeneous and heterogeneous systems within the presented study. Four homogeneously filled column experiments and a heterogeneously filled tank experiment, using different median sand grain diameters (d 50), were performed to determine if NZVI particles were transported into finer sand where contaminants could be trapped. More NZVI particle retention, less particle transport, and faster decrease in k were observed in the column studies using finer sands than in those using coarser sands, reflecting a function of k 0. In heterogeneous media, NZVI particles were initially transported and deposited in coarse sand areas. Increasing the retained NZVI mass (decreasing k in particle deposition areas) caused NZVI particles to also be transported into finer sand areas, forming an area with a relatively homogeneous particle distribution and converged k values despite the different grain sizes present. The deposited-particle surface area contribution to the increasing of the matrix surface area (θ) was one to two orders of magnitude higher for finer than coarser sand. The dependency of θ on d 50 presumably affects simulated k changes and NZVI distributions in numerical simulations of NZVI injections into heterogeneous aquifers. The results implied that NZVI can in principle also penetrate finer layers.

Mineral resource of the month: Pumice and pumicite

USGS Publications Warehouse

Crangle, Robert

2015-01-01

Pumice is an extrusive igneous volcanic rock formed through the rapid cooling of air-pocketed lava, which results in a low-density, high-porosity rock. Fine-grained pumice, or pumicite, is defined as minute grains, flakes, threads or shards of volcanic glass, with a size finer than 4 millimeters. 

Effect of flour particle size on microstructural, rheological and physico-sensory characteristics of bread and south Indian parotta.

PubMed

Sakhare, Suresh D; Inamdar, Aashitosh A; Soumya, C; Indrani, D; Rao, G Venkateswara

2014-12-01

Wheat flour fractioned by sieving into four different particle size fractions namely finer fractions (<75 and 75-118 μm), coarser fractions (118-150 and >150 μm) were analyzed for their chemical, rheological, bread & parotta making characteristics. The finer fractions had lower ash, higher dry gluten, damaged starch and sodium dodecysulphate (SDS)-sedimentation value than the coarser fractions. The flour from finer fractions gave bread with best sensory and textural attributes. The parottas from finer fractions showed significantly higher sensory scores for colour, texture, layers, mouthfeel and overall quality score than the coarser fractions. In the micrograph of finer flour fractions, higher number of loosened single starch granules than the aggregates of starch and protein matrix were seen as compared to coarser fractions. These studies indicate that the flour from the finer fractions produce higher quality bread, parotta owing to the presence of higher damaged starch content, quantity and quality of protein in these fractions than coarser fractions.

Holocene facies analysis of the sedimentary record with anthropogenic impacts in the Ria de Vigo (NW Spain)

NASA Astrophysics Data System (ADS)

Rubio, B.; Garcia-Gil, S.; Vilas, F.; Garcia, A.

2004-05-01

The Ria de Vigo constitutes the southernmost ria of the Rias Bajas. The reconnaisance studies of this ria indicate a heterogeneous distribution of both terrigenous and carbonate sediments with a major axial deposit of cohesive sediments. These fine sediments are relatively rich in organic matter, particularly in the inner part of the ria. This is the result of a progressive change in hydrodynamic conditions along the ria. The outer parts are affected by severe storms in winter and by upwelling processes in summer, whilst the inner parts have an estuarine character throughout the year. The upwelling produces a marked increase in the biological productivity in the Ria and, consequently, these sediments have typically very high contents of organic matter. In recent years, increasing interest has been shown in the levels of heavy metals in sediments of the Galician Rias. Particularly, some of these studies showed a higher concentration of heavy metals in the muddiest surficial sediments in the Ria de Vigo. However, and despite of the important human and industrial settlement in the Galician rias, knowledge about the evolution of historical contamination along the Holocene sedimentary record is scarce. In order to ascertain this evolution have been selected 8 gravity corer located along the axial part of the ria. This evaluation was focused on the muddy sediments of the axial part of the ria due to the dependence of metal levels on grain size, resulting from the association of metals with the finer particles, as it has been demonstrated by previous studies in the ria. On these sediments, the combination of geochemical, mineralogical and sedimentological data, facies interpretations (obtained from x-ray radiography), and their integration with high resolution seismic data (Uniboom and 3.5 Khz subbottom profiler) have allowed to establish the evolution of certain heavy metals (Zn, Cu and Pb) along the Holocene recent sedimentary record in the Ria de Vigo. Sediments in the outer ria are comprised by muddy sands showing a very slight enrichment in certain heavy metals in the upper sediments. Contrary to facies in the outer ria sediments, facies in the inner ria comprises finer organic-rich sediments. These are related to the presence of biodeposits produced by mussel rafts and to a higher anthropogenic influence due to industrial activity. Both influences are notably reflected in the Cu, Zn and Pb vertical profiles, increasing markedly the levels of these metals in the uppermost 0.15 m of sediments. Diagenetic recycling may contribute to the enhancement of trace metal concentrations in the upper sediments of inner cores and also this is related to a higher content of organic carbon in these sediments. Results obtained in this ria constitutes a good reference to study other rias and coastal areas of the Iberian Atlantic margin. This work was funded by projects REN2003-02822 MAR, REN2003-03233 MAR, VEM2003-20093-C03-03 of the Spanish MCYT and PGDIT03RMA30101PR of the Galician Government (XUGA). Contribution No 302 XM2 group.

A brittle to ductile transition in NiAl of a critical grain size

NASA Technical Reports Server (NTRS)

Schulson, E. M.; Barker, D. R.

1983-01-01

Tensile tests have been carried out on the strongly ordered B2 aluminide NiAl at 400 C to investigate the effect of the grain size on the ductility of the material. It is found that the ductility is very low and essentially independent of the grain size for aggregates of grains larger than about 20 microns; for finer-grained aggregates, the ductility increases sharply with decreasing grain size. Thus, NiAl exhibits a critical grain size below which polycrystalline aggregates are ductile in tension. For all grain sizes, fracture occurs in a brittle manner through a combination of intergranular decohesion and transgranular cleavage.

Sentence-Level Attachment Prediction

NASA Astrophysics Data System (ADS)

Albakour, M.-Dyaa; Kruschwitz, Udo; Lucas, Simon

Attachment prediction is the task of automatically identifying email messages that should contain an attachment. This can be useful to tackle the problem of sending out emails but forgetting to include the relevant attachment (something that happens all too often). A common Information Retrieval (IR) approach in analyzing documents such as emails is to treat the entire document as a bag of words. Here we propose a finer-grained analysis to address the problem. We aim at identifying individual sentences within an email that refer to an attachment. If we detect any such sentence, we predict that the email should have an attachment. Using part of the Enron corpus for evaluation we find that our finer-grained approach outperforms previously reported document-level attachment prediction in similar evaluation settings.

Falling-stream turbidimeter as a means of measuring sediment concentrations in streams

USGS Publications Warehouse

Guy, Harold P.; Olson, Richard C.

1972-01-01

The ratio of suspended-sediment concentration to the square root of the median particle size of sand-sized sediments was found to be a useful parameter for elimination of the effect of particle size in the relative transparency-concentration relationships. Thus it was possible to evaluate the effect of the different type of sediment on the relative transparency independent of particle size. The use of this parameter to eliminate the effect of particle size was unsuccessful for finer sediments. -

The need to consider temporal variability when modelling exchange at the sediment-water interface

USGS Publications Warehouse

Rosenberry, Donald O.

2011-01-01

Most conceptual or numerical models of flows and processes at the sediment-water interface assume steady-state conditions and do not consider temporal variability. The steady-state assumption is required because temporal variability, if quantified at all, is usually determined on a seasonal or inter-annual scale. In order to design models that can incorporate finer-scale temporal resolution we first need to measure variability at a finer scale. Automated seepage meters that can measure flow across the sediment-water interface with temporal resolution of seconds to minutes were used in a variety of settings to characterize seepage response to rainfall, wind, and evapotranspiration. Results indicate that instantaneous seepage fluxes can be much larger than values commonly reported in the literature, although seepage does not always respond to hydrological processes. Additional study is needed to understand the reasons for the wide range and types of responses to these hydrologic and atmospheric events.

Sedimentary and geochemical conditions in the "Helgoland Mud Area" (SE North Sea) during the past 1000 years

NASA Astrophysics Data System (ADS)

Hass, H. Christian; Kuhn, Gerhard

2017-04-01

Helgoland is a small rocky island in the German Bight with an exposed rocky shore. The working area, SE of Helgoland, is a halotectonic depression filled with muddy sediment. Earlier studies suggest that this depression became rapidly filled with muddy sediments likely originating from the Elbe river that changed its bed eastwards in the course of the rising sealevel during the Late Holocene. Today, the water depth is between 20 and 30 m. A RoxAnn acoustic ground discrimination unit and shallow seismics together with seafloor sampling were applied to analyze the recent sedimentary conditions. Five sediment cores spanning the past millennium were investigated to reconstruct the sedimentary conditions through time. In addition one core was geochemically investigated using an XRF scanning device. Today, the area is about 500 km2 large characterized mostly by muddy, fine-skewed sediment. Its soft and smooth surface forms a clear contrast to the surrounding sandy areas that reveal typically rippled surfaces. The grain-size records show medium silt during the later part of the Medieval Warm Period (MWP, until the 14th century AD), followed by coarse silt during the Little Ice Age (LIA, until c. 1900 AD) and again finer sediments during the 20th century AD. The changes in grain size likely mirror calmer weather conditions during the MWP and the increased frequency and strength of severe storms during the LIA. This includes a calmer period during the Maunder Sun-Spot Minimum (around AD 1700) that was most likely supported by an increased number of negative NAO situations. Among the elements investigated in Core HE215/4-2 the contents of the heavy metals Pb and Zn show two- and threefold increases starting already between 1600 and 1700 AD. Mining and extended metal production in the Oberharz Mountains in northern Germany became a blooming industry during the 17th century AD. It can be speculated that signals of this early industrialization were also transported into the North Sea via the Elbe and Weser rivers.

Characterisation of bed sediments and suspension of the river Po (Italy) during normal and high flow conditions.

PubMed

Davide, Vignati; Pardos, Michel; Diserens, Jérôme; Ugazio, Giancarlo; Thomas, Richard; Dominik, Janusz

2003-07-01

Grain-size distribution, major elements, nutrients and trace metals were determined in bed sediments and suspension collected at 10 representative sites along the river Po under normal and high flow conditions. Grain-size distribution and major element composition of suspension highlighted the presence of two distinct particle populations in the upper-middle Po (coarser particles, lower carbonate content) and in the lower Po (finer particles, higher carbonate content). This change partly reflects the geological differences between the two parts of the basin, and also the presence of a hydroelectric power plant at Isola Serafini (Piacenza). With respect to environmental quality issues, bed sediments and suspension provide similar results. A moderate nutrient pollution is found in all but the uppermost parts of the river basin, while the most significant inputs of trace metals appear to originate from the urban areas of Turin and Milan. Calculation of sediment enrichment factors identifies Cd, Cu, Hg and Zn as the most impacted elements by human activities. On the other hand, the high levels of Ni and Cr throughout the river seem to derive mainly from the presence of basic rocks in the upper and middle parts of the basin. Both nutrient and trace metal particulate concentrations substantially decrease under high flow conditions possibly due to "flushing" of contaminated bed sediments and resuspension of coarser material. Under normal flow conditions, water hydrochemistry and concentrations of some elements (As, Ca, Cr, Cu, K, Mg, Mn, Na, Ni, and Pb) in the dissolved phase (<0.45 microm) were also determined. Calculation of trace metals partition coefficients shows that the relative importance of the particulate and water phases varies in response to water hydrochemistry and suspended solid content, but that most elements achieve a conditional equilibrium in the lower stretches of the river Po. These results are the first of this kind reported for the whole river course and highlight the factors and mechanisms controlling the origin, mobility and fate of nutrients and trace metals in the river Po.

High-resolution rock-magnetic variability in shallow marine sediment: a sensitive paleoclimatic metronome

NASA Astrophysics Data System (ADS)

Arai, Kohsaku; Sakai, Hideo; Konishi, Kenji

1997-05-01

An outer shelf deposit in central Japan centered on the Olduvai normal polarity event in the reversed Matuyama chron reveals a close correlation of both the magnetic susceptibility and remanent intensity with the sedimentary cyclicities apparent in lithologies and molluscan assemblages. Two sedimentary cycles are characterized by distinctly similar, but double-peaked magnetic cyclicities. The rock-magnetic variability is primarily attributed to the relative abundance of terrigenous magnetic minerals, and the double peak of the variability is characterized by the concentration of finer-grained magnetic minerals. The concentration is suspected to be controlled by both climatic change and shifting proximity of the shoreline as a function of rise and fall of the sea level due to glacio-eustasy. Rock-magnetic study reveals the record of a 21 ka period of orbital precession cycles within the sedimentary cyclicity attributable to a 41 ka period of orbital obliquity forcing.

Are catchment-wide erosion rates really "Catchment-Wide"? Effects of grain size on erosion rates determined from 10Be

NASA Astrophysics Data System (ADS)

Reitz, M. A.; Seeber, L.; Schaefer, J. M.; Ferguson, E. K.

2012-12-01

Early studies pioneering the method for catchment wide erosion rates by measuring 10Be in alluvial sediment were taken at river mouths and used the sand size grain fraction from the riverbeds in order to average upstream erosion rates and measure erosion patterns. Finer particles (<0.0625 mm) were excluded to reduce the possibility of a wind-blown component of sediment and coarser particles (>2 mm) were excluded to better approximate erosion from the entire upstream catchment area (coarse grains are generally found near the source). Now that the sensitivity of 10Be measurements is rapidly increasing, we can precisely measure erosion rates from rivers eroding active tectonic regions. These active regions create higher energy drainage systems that erode faster and carry coarser sediment. In these settings, does the sand-sized fraction fully capture the average erosion of the upstream drainage area? Or does a different grain size fraction provide a more accurate measure of upstream erosion? During a study of the Neto River in Calabria, southern Italy, we took 8 samples along the length of the river, focusing on collecting samples just below confluences with major tributaries, in order to use the high-resolution erosion rate data to constrain tectonic motion. The samples we measured were sieved to either a 0.125 mm - 0.710 mm fraction or the 0.125 mm - 4 mm fraction (depending on how much of the former was available). After measuring these 8 samples for 10Be and determining erosion rates, we used the approach by Granger et al. [1996] to calculate the subcatchment erosion rates between each sample point. In the subcatchments of the river where we used grain sizes up to 4 mm, we measured very low 10Be concentrations (corresponding to high erosion rates) and calculated nonsensical subcatchment erosion rates (i.e. negative rates). We, therefore, hypothesize that the coarser grain sizes we included are preferentially sampling a smaller upstream area, and not the entire upstream catchment, which is assumed when measurements are based solely on the sand sized fraction. To test this hypothesis, we used samples with a variety of grain sizes from the Shillong Plateau. We sieved 5 samples into three grain size fractions: 0.125 mm - 710 mm, 710 mm - 4 mm, and >4 mm and measured 10Be concentrations in each fraction. Although there is some variation in the grain size fraction that yields the highest erosion rate, generally, the coarser grain size fractions have higher erosion rates. More significant are the results when calculating the subcatchment erosion rates, which suggest that even medium sized grains (710 mm - 4 mm) are sampling an area smaller than the entire upstream area; this finding is consistent with the nonsensical results from the Neto River study. This result has numerous implications for the interpretations of 10Be erosion rates: most importantly, an alluvial sample may not be averaging the entire upstream area, even when using the sand size fraction - resulting erosion rates more pertinent for that sample point rather than the entire catchment.

Controlling factors of recent clastic coastal sediments (Viransehir, Mersin bay, S Turkey)

NASA Astrophysics Data System (ADS)

Gül, Murat; Özbek, Ahmet; Kurt, Mehmet Ali; Zorlu, Kemal

2009-04-01

The Plio-Quaternary conglomeratic sets within the marine environment of the Viranşehir coast (W Mersin, S Turkey) are responsible for the evolution of sandy and gravely beaches due to their control on various factors such as sea floor irregularity, wave energy, and organic activity. The conglomeratic sets close to the shoreline (50-150 cm) act as wave breakers, creating hard substratum and high energy, well-oxygenated environment for organisms like Patella sp., Phoronida worms and Brachidontes pharaonis (Fischer P. 1870). The boring activities of these organisms have disintegrated the sandy matrix of these sets. Finer-grained matrix sediments have been transported to the interset and open sea, while cobble-pebbles have been carried landwards and have created imbricated gravely beach deposits without matrix. Sandy beach is evolving where the conglomeratic sets away from the shoreline (5.0-10.0 m). In this example, sets form a bar; causing fivefold division as backshore, berm, surf zone, bar and offshore from land to sea. Poorly sorted, cobbles-pebbles cobbles and pebbles are found associated with the high-energy environments of bars, whilst well-sorted sands are observed in low energetic environments on shore. The sets and recent shell fragments are the main sources of coastal sediments in Viranşehir. However, the amount of shell fragments decrease towards the active river mouth. This is due to sediment and fresh water influx from the river causing deteriorated temperature, salinity and light penetration of the marine environment resulting in less organic diversity.

Granulometric selectivity in Liza ramado and potential contamination resulting from heavy metal load in feeding areas

NASA Astrophysics Data System (ADS)

Pedro, Sílvia; Canastreiro, Vera; Caçador, Isabel; Pereira, Eduarda; Duarte, Armando C.; Raposo de Almeida, Pedro

2008-11-01

The stomach contents of thin-lipped grey mullets Liza ramado were analysed in terms of granulometric composition and compared to the sediment of potential feeding areas in the Tagus estuary. Total organic matter (TOM) content and heavy metal content were determined in the surface sediment of three areas and eight trace elements were quantified: Cd, Co, Cr, Cu, Hg, Ni, Pb and Zn. The three sampled areas did not differ in TOM; and the heavy metal content was below Effects Range-Low level for most elements. The mean observed concentrations were present in the following sequence: Zn > Pb > Cr > Cu ≈ Ni > Co > Cd > Hg. Stomach contents granulometric composition provided information about the feeding selectivity of the mullets. Sediment fractions with particle size between 20 and 50 μm are preferred, independently of the fishes' length. Smaller standard length (SL) fishes have a higher positive selection of fine grained sediments than those with a larger SL. Finer fractions usually have higher concentration of heavy metals, which makes younger specimens of the thin-lipped grey mullet potentially more exposed to heavy metal load in the estuary. Metal concentration was not independent from the sampling point, presenting higher values near the margins and the estuary tidal drainage system. This means that during the first period of each tidal cycle, the mullets will feed first on the most contaminated areas, as a consequence of their movement following the rising tide to feed on previously exposed areas.

Optical and thermoluminescence dating of Middle Stone Age and Kintampo bearing sediments at Birimi, a multi-component archaeological site in Ghana

NASA Astrophysics Data System (ADS)

Quickert, Nicole A.; Godfrey-Smith, Dorothy I.; Casey, Joanna L.

2003-05-01

We report the first luminescence ages for the archeological and geological sediments forming the substrate of the Birimi archaeological site in the Northern Region of Ghana. The site's significance rests on the fact that it contains a rich collection of artifact assemblages representative of three distinct cultures, and that, on the basis of artifact typology, the earliest assemblage is diagnostic of the Middle Stone Age (MSA) . In situ occurrences of MSA artifacts are found at over 1 m below today's surface. They are overlain by a ceramic-rich complex of a sedentary or semi-sendentary Later Stone Age culture known as the Kintampo. The western half of the site is dominated by the industrial remains of Iron Age smelting activity. Elemental, mineralogical, and sedimentological analysis of the cultural and sub-cultural sedimentary horizons at the site revealed at least three distinct lithostratigraphic units. The quartz sediments are derived from the sandstone of the Gambaga escarpment, mass wasted and accreted fluvially at a rate of 3.2 cm/ka, forming a wide terrace at Birimi. Silts and finer fractions derive from windblown dust, likely from White Volta River and granitic sources to the north. Soil forming processes and wide fluctuations in moisture have progressively reduced the sediments at depth to the resistant quartz and kaolinite, with rich iron oxide coatings, and created two ironstone horizons composed of goethite-cemented quartz nodules. Multiple aliquot green-light stimulated optical ages for 125-150 μm quartz grains yielded ages of 23.6±2.9 and 40.8±11.8 ka for the MSA-bearing sediments, and 58.4±15.3 ka for the base of the terrace. Radiocarbon ages on charcoal from Kintampo-bearing units are 3.36-3.83 ka cal BP, and are supported by thermoluminescence (TL) ages on pottery sherds and burnt house daub fragments of this cultural complex. A 0.4 ka age on sediment from the site's surface confirms that the quartz zeroes well when exposed to natural light. Sediments bearing the Kintampo artifacts, however, yielded ages of 7.8-16.9 ka. These ages were obtained on sediments from large pits, some over 50 cm deep, and they deviate only slightly from the ages expected for naturally aggraded sediments at these depths. We conclude, therefore, that extensive digging of pits by the Kintampo dwellers was followed by rapid refilling, and that the bulk mobilization of the matrix did not permit the sedimentary quartz grains to experience any appreciable zeroing at that time.

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.

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

Rock-magnetic changes with reduction diagenesis in Japan Sea sediments and preservation of geomagnetic secular variation in inclination during the last 30,000 years

NASA Astrophysics Data System (ADS)

Yamazaki, T.; Abdeldayem, A. L.; Ikehara, K.

2003-06-01

A rock-magnetic and paleomagnetic study was conducted on a sediment core of about 4.4 m long taken from the northeastern part of the Japan Sea. The core covers the last about 30 kyrs, which was dated by nineteen radiocarbon (14C) ages. Remanent magnetization is carried dominantly by magnetite. Reductive dissolution of magnetic minerals occurs between 1.2 and 1.6 m in depth (about 5-8 ka in age). A rapid downcore decrease of anhysteretic remanent magnetization (ARM) begins at the shallowest depth. Saturation isothermal remanent magnetization (SIRM) follows, and a decrease of magnetic susceptibility (k) takes place at the deepest. Within this zone, coercivity of natural remanent magnetization (NRM) and the ratios of ARM to k and SIRM to k also decreases with depth. These observations indicate that finer magnetic grains were lost earlier than larger grains. A decrease of S ratios, wasp-waisted hysteresis curves, and a deviation from a mixing trend of single-domain and multi-domain grains in a Day plot occur as the dissolution proceeds, which suggests that high coercivity minerals like hematite are more resistive to dissolution than low coercivity minerals like magnetite. The start of the dissolution at 1.2 m in depth is synchronous with increases in organic-carbon and total-sulfur contents, but the horizon does not coincide with the present Fe-redox boundary at about 0.02 m below the sediment-water interface. From low-temperature magnetometry, it is estimated that magnetites with maghemite skin are reduced to pure magnetites prior to dissolution. There is no evidence for precipitation of secondary magnetic phases and acquisition of chemical remanent magnetization (CRM). Neither pyrrhotite nor greigite was detected. Information of paleomagnetic directions have survived the reductive dissolution. Inclination variations of this core resembles closely to the secular variation records available around Japan. Well-dated records older than 10 ka are still very rare, and hence our new record could be useful for establishing regional secular variations.

Nontoxic chemical process for in situ permeability enhancement and accelerated decontamination of fine-grain subsurface sediments

DOEpatents

Kansa, E.J.; Wijesinghe, A.M.; Viani, B.E.

1997-01-14

The remediation of heterogeneous subsurfaces is extremely time consuming and expensive with current and developing technologies. Although such technologies can adequately remove contaminants in the high hydraulic conductivity, coarse-grained sediments, they cannot access the contaminated low hydraulic conductivity fine-grained sediments. The slow bleed of contaminants from the fine-grained sediments is the primary reason why subsurface remediation is so time-consuming and expensive. This invention addresses the problem of remediating contaminated fine-grained sediments. It is intended that, in the future, a heterogeneous site be treated by a hybrid process that first remediates the high hydraulic conductivity, coarse-grained sediments, to be followed by the process, described in this invention, to treat the contaminated low hydraulic conductivity fine-grained sediments. The invention uses cationic flocculants and organic solvents to collapse the swelling negative double layer surrounding water saturated clay particles, causing a flocculated, cracked clay structure. The modification of the clay fabric in fine-grained sediments dramatically increases the hydraulic conductivity of previously very tight clays many orders of magnitude. 8 figs.

Nontoxic chemical process for in situ permeability enhancement and accelerated decontamination of fine-grain subsurface sediments

DOEpatents

Kansa, Edward J.; Wijesinghe, Ananda M.; Viani, Brian E.

1997-01-01

The remediation of heterogeneous subsurfaces is extremely time consuming and expensive with current and developing technologies. Although such technologies can adequately remove contaminants in the high hydraulic conductivity, coarse-grained sediments, they cannot access the contaminated low hydraulic conductivity fine-grained sediments. The slow bleed of contaminants from the fine-grained sediments is the primary reason why subsurface remediation is so time-consuming and expensive. This invention addresses the problem of remediating contaminated fine-grained sediments. It is intended that, in the future, a heterogeneous site be treated by a hybrid process that first remediates the high hydraulic conductivity, coarse-grained sediments, to be followed by the process, described in this invention, to treat the contaminated low hydraulic conductivity fine-grained sediments. The invention uses cationic flocculents and organic solvents to collapse the swelling negative double layer surrounding water saturated clay particles, causing a flocculated, cracked clay structure. The modification of the clay fabric in fine-grained sediments dramatically increases the hydraulic conductivity of previously very tight clays many orders of magnitude.

Long-term sand supply to Coachella Valley Fringe-toed Lizard Habitat in the Northern Coachella Valley, California

USGS Publications Warehouse

Griffiths, Peter G.; Webb, Robert H.; Lancaster, Nicholas; Kaehler, Charles A.; Lundstrom, Scott C.

2002-01-01

The Coachella Valley fringe-toed lizard (Uma inornata) is a federally listed threatened species that inhabits active sand dunes in the vicinity of Palm Springs, California. The Whitewater Floodplain and Willow Hole Reserves provide some of the primary remaining habitat for this species. The sediment-delivery system that creates these active sand dunes consists of fluvial depositional areas fed episodically by ephemeral streams. Finer fluvial sediments (typically sand size and finer) are mobilized in a largely unidirectional wind field associated with strong westerly winds through San Gorgonio Pass. The fluvial depositional areas are primarily associated with floodplains of the Whitewater?San Gorgonio Rivers and Mission Creek?Morongo Wash; other small drainages also contribute fluvial sediment to the eolian system. The eolian dunes are transitory as a result of unidirectional sand movement from the depositional areas, which are recharged with fine-grained sediment only during episodic floods that typically occur during El Ni?o years. Eolian sand moves primarily from west to east through the study area; the period of maximum eolian activity is April through June. Wind speed varies diurnally, with maximum velocities typically occurring during the afternoon. Development of alluvial fans, alteration of stream channels by channelization, in-stream gravel mining, and construction of infiltration galleries were thought to reduce the amount of fluvial sediment reaching the depositional areas upwind of Uma habitat. Also, the presence of roadways, railroads, and housing developments was thought to disrupt or redirect eolian sand movement. Most of the sediment yield to the fluvial system is generated in higher elevation areas with little or no development, and sediment yield is affected primarily by climatic fluctuations and rural land use, particularly livestock grazing and wildfire. Channelization benefits sediment delivery to the depositional plains upwind of the reserves by minimizing in-channel sediment storage on the alluvial fans. The post-development annual sediment yield to the Whitewater and Mission Creek?Morongo Wash depositional areas are 3.5 and 1.5 million ft3/yr, respectively, covering each depositional area to a depth of 0.2 to 0.4 in. Given existing sand-transport rates, this material could be depleted by eolian processes in 8 to 16 months, a rate consistent with the presence of persistent sand dunes. However, these depletion times are likely minimum estimates, as some eolian sand is seen to persist in the immediate vicinity of depositional areas for longer time periods. Transport rates may be reduced by the presence of vegetation and other windbreaks. Because they are perpendicular to prevailing winds, the infiltration galleries on Whitewater River trap fluvial and eolian sediment, reducing sediment availability. Also, the presence of the railroad and Interstate 10 redirect eolian sand movement to the southeast along their corridors,potentially eliminating the Whitewater depositional area as a sand source for the Willow Hole Reserve. Using directional wind data, we discuss the potential for eolian sand transport from the Mission Creek?Morongo Wash depositional area to Willow Hole.

Stratigraphy and paleogeographic significance of a Late Pennsylvanian to Early Permian channeled slope sequence in the Darwin Basin, southern Darwin Hills, east-central California

USGS Publications Warehouse

Stevens, Calvin H.; Stone, Paul; Magginetti, Robert T.; Ritter, Scott M.

2015-01-01

The complex stratigraphy of late Paleozoic rocks in the southern Darwin Hills consists of regionally extensive Mississippian and Early to Middle Pennsylvanian rocks overlain by latest Pennsylvanian to Early Permian rocks, herein called the Darwin Hills sequence. Deposition of this latter sequence marked the beginning of the Darwin Basin. In Mississippian time, a carbonate platform prograded westward over slightly older slope deposits. In the Late Mississippian this platform was exposed to erosion and siliciclastic sediments were deposited. In Early to Middle Pennsylvanian time the area subsided, forming a west-facing ramp that was subjected to deformation and erosion in Middle or early Late Pennsylvanian time. Later this area was tilted westward and deep-water sediments were deposited on this slope. In latest Pennsylvanian to earliest Permian time, a major channel was cut through the older Pennsylvanian rocks and into the Upper Mississippian strata. This channel was gradually filled with increasingly finer grained, deep-water sediment as the area evolved into a basin floor by Early Permian (Sakmarian) time. Expansion of the Darwin Basin in Artinskian time led to a second phase of deposition represented by strata of the regionally extensive Darwin Canyon Formation. The geology in this small area thus documents tectonic events occurring during the early development of the Darwin Basin.

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).

Palaeoclimatic implications of aeolian sediments on the Miaodao Islands, Bohai Sea, East China, based on OSL dating and proxies

NASA Astrophysics Data System (ADS)

Xu, Shujian; Ding, Xinchao; Yu, Lupeng; Ni, Zhichao

2015-12-01

The loess-paleosol sequences in Shandong Province, East China, is an important aeolian archive, which can provide information for aeolian activity, palaeoclimatic change and sea level change in eastern coast of China since the last interglacial period. However, for so long, most of the studies about loess have been focused on the Chinese Loess Plateau, remaining many questions and disputes about the loess in East China. The Xianjingyuan (XJY) section on the TIA, Bohai Sea, is a representative aeolian section for islands off the eastern coast of China. In this study, optically stimulated luminescence (OSL) dating, particle size and magnetic susceptibility were applied to date and analysis the loess-paleosol sequences in this section. The results show that: (1) The OSL ages at the depths of 0.8 m, 2.5 m, and 3.9 m are 12.6 ± 1.0 ka, 19.2 ± 1.1 ka and 56.9 ± 2.6 ka, respectively, and the loess started to accumulate at ca. 86.5 ka according to the depositional rates (2) The loess accumulated mainly during the Marine Isotope Stage (MIS) 2, i.e., Last glacial maximum and deglaciation, MIS4 and MIS3b with higher depositional rate, coarser grain size, and higher magnetic susceptibility; while paleosol mainly developed during MIS3a, MIS3c and MIS5 with lower depositional rate, finer grain size and lower magnetic susceptibility. (3) The palaeoclimatic changes and aeolian sediments evolution were mainly controlled by the changes of East Asian summer monsoon and sea levels.

High-resolution paleoclimate records of Holocene hydroclimatic variability in the Eastern Colombian Andes from Lago de Tota

NASA Astrophysics Data System (ADS)

Ahmed, M. N.; Bird, B. W.; Escobar, J.; Polissar, P. J.

2017-12-01

The Northern Hemisphere (NH) South American Monsoon (SAM) is a significant source of precipitation for the North Andes (north of 0˚) and has major control over regional hydroclimate variability. Holocene-length histories of NH SAM variability are few compared to the Southern Hemisphere (SH), limiting understanding of how these systems are connected on orbital and shorter timescales. Here, we present multi-proxy lake-sediment-based paleoclimate and paleohydrologic reconstructions from Lago de Tota, Colombia, using sedimentological, geochemical and leaf-wax hydrogen isotopic indicators from radiometically dated cores. The results indicate periods of wet and dry climate phases during the past 9000 BP with an average Holocene sedimentation rate 33cm/kyr. An increase in total organic matter (TOM) content and finer grain-size distributions was observed from 8000 to 3200 BP, suggesting a period of high lake level. This was followed by lower TOM and coarser grain sizes, suggesting lower lake levels from 3200 BP to the present. Although Tota's lake level pattern is antiphased with other lake level reconstructions from the NH and SH Andes, it is consistent with hypothesized changes in atmospheric convection over the Andes during the Holocene and the way in which they would be modified by the so-called dry island effect in the Colombian Andes. This suggests that a common forcing mechanism can be invoked to explain differing millennial-scale Andean hydroclimate changes, namely atmospheric convection. Orbital and Pacific atmosphere-forcing are therefore likely to have played a significant role in driving pan-Andean hydroclimate variability based on their inter-hemispheric influence on Andean convection.

Monitoring bedload entrainment and transport in snowmelt-dominated forest streams of the Columbia Mountains, Canada

NASA Astrophysics Data System (ADS)

Green, Kim; Brardinoni, Francesco; Alila, Younes

2014-05-01

We monitor bedload transport and water discharge at six stations in two forested headwater streams of the Columbia Mountains, Canada. The monitoring network of sediment traps is designed to examine the effects of channel bed texture, and the influence of alluvial (i.e., step pools, and riffle pools) and semi-alluvial morphologies (i.e., boulder cascades and forced step pools) on bedload entrainment and transport. Results suggest that patterns of bedload entrainment are influenced by flow resistance while the value of the critical dimensionless shear stress for mobilization of the surface D50 varies due to channel gradient, grain sheltering effects and, to a less extent, flow resistance. Regardless of channel morphology we observe: (i) equal-threshold entrainment for all mobile grains in channels with high grain and/or form resistance; and (ii) initial equal-threshold entrainment of calibers ≤ 22mm, and subsequent size-selective entrainment of coarser material in channels with low form resistance (e.g. riffle pool). Scaled fractional analysis reveals that in reaches with high flow resistance most bedload transport occurs in partial mobility fashion relative to the available bed material and that only material finer than 16mm attains full mobility during over-bank flows. Equal mobility transport for a wider range of grain sizes is achieved in reaches with reduced flow resistance. Evaluation of bedload rating curves across sites identifies that grain effects predominate with respect to bedload flux whereas morphological effects (i.e. form resistance) play a secondary role. Application of selected empirical formulae developed in steep alpine channels present variable success in predicting transport rates in the study reaches.

Record of late Pleistocene glaciation and deglaciation in the southern Cascade Range. I. Petrological evidence from lacustrine sediment in Upper Klamath Lake, southern Oregon

USGS Publications Warehouse

Reynolds, R.L.; Rosenbaum, J.G.; Rapp, J.; Kerwin, M.W.; Bradbury, J.P.; Colman, S.; Adam, D.

2004-01-01

Petrological and textural properties of lacustrine sediments from Upper Klamath Lake, Oregon, reflect changing input volumes of glacial flour and thus reveal a detailed glacial history for the southern Cascade Range between about 37 and 15 ka. Magnetic properties vary as a result of mixing different amounts of the highly magnetic, glacially generated detritus with less magnetic, more weathered detritus derived from unglaciated parts of the large catchment. Evidence that the magnetic properties record glacial flour input is based mainly on the strong correlation between bulk sediment particle size and parameters that measure the magnetite content and magnetic mineral freshness. High magnetization corresponds to relatively fine particle size and lower magnetization to coarser particle size. This relation is not found in the Buck Lake core in a nearby, unglaciated catchment. Angular silt-sized volcanic rock fragments containing unaltered magnetite dominate the magnetic fraction in the late Pleistocene sediments but are absent in younger, low magnetization sediments. The finer grained, highly magnetic sediments contain high proportions of planktic diatoms indicative of cold, oligotrophic limnic conditions. Sediment with lower magnetite content contains populations of diatoms indicative of warmer, eutrophic limnic conditions. During the latter part of oxygen isotope stage 3 (about 37-25 ka), the magnetic properties record millennial-scale variations in glacial-flour content. The input of glacial flour was uniformly high during the Last Glacial Maximum, between about 21 and 16 ka. At about 16 ka, magnetite input, both absolute and relative to hematite, decreased abruptly, reflecting a rapid decline in glacially derived detritus. The decrease in magnetite transport into the lake preceded declines in pollen from both grass and sagebrush. A more gradual decrease in heavy mineral content over this interval records sediment starvation with the growth of marshes at the margins of the lake and dilution of detrital material by biogenic silica and other organic matter.

Influence of Si and N additions on structure and phase stability of Ge(2)Sb(2)Te(5) thin films.

PubMed

Kölpin, Helmut; Music, Denis; Laptyeva, Galyna; Ghadimi, Reza; Merget, Florian; Richter, Silvia; Mykhaylonka, Ruslàn; Mayer, Joachim; Schneider, Jochen M

2009-10-28

The influence of Si and N in Ge(2)Sb(2)Te(5) (space group [Formula: see text]) on structure and phase stability thereof was studied experimentally by thin film growth and characterization as well as theoretically by ab initio calculations. It was found that Si and N most probably accumulate in the amorphous matrix embedding Ge(2)Sb(2)Te(5) grains. The incorporation of Si and N in these samples causes an increase of the crystallization temperature and the formation of finer grains. N is more efficient in increasing the crystallization temperature and in reducing the grain size than Si which can be understood based on the bonding analysis. The incorporation of both Si and N in Ge(2)Sb(2)Te(5) is energetically unfavourable, leading to finer grains and larger crystallization temperatures. While in the case of Si additions no significant changes in bonding are observed, N additions appear to enable the formation of strong Te-N bonds in the amorphous matrix, which are shown to be almost twice as strong as the strongest bonds in unalloyed Ge(2)Sb(2)Te(5).

Enhanced Hydrogen Transport over Palladium Ultrathin Films through Surface Nanostructure Engineering.

PubMed

Abate, Salvatore; Giorgianni, Gianfranco; Gentiluomo, Serena; Centi, Gabriele; Perathoner, Siglinda

2015-11-01

Palladium ultrathin films (around 2 μm) with different surface nanostructures are characterized by TEM, SEM, AFM, and temperature programmed reduction (TPR), and evaluated in terms of H2 permeability and H2-N2 separation. A change in the characteristics of Pd seeds by controlled oxidation-reduction treatments produces films with the same thickness, but different surface and bulk nanostructure. In particular, the films have finer and more homogeneous Pd grains, which results in lower surface roughness. Although all samples show high permeo-selectivity to H2 , the samples with finer grains exhibit enhanced permeance and lower activation energy for H2 transport. The analysis of the data suggests that grain boundaries between the Pd grains at the surface favor H2 transfer from surface to subsurface. Thus, the surface nanostructure plays a relevant role in enhancing the transport of H2 over the Pd ultrathin film, which is an important aspect to develop improved membranes that function at low temperatures and toward new integrated process architectures in H2 and syngas production with enhanced sustainability. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Direct sampling during multiple sediment density flows reveals dynamic sediment transport and depositional environment in Monterey submarine canyon

NASA Astrophysics Data System (ADS)

Maier, K. L.; Gales, J. A.; Paull, C. K.; Gwiazda, R.; Rosenberger, K. J.; McGann, M.; Lundsten, E. M.; Anderson, K.; Talling, P.; Xu, J.; Parsons, D. R.; Barry, J.; Simmons, S.; Clare, M. A.; Carvajal, C.; Wolfson-Schwehr, M.; Sumner, E.; Cartigny, M.

2017-12-01

Sediment density flows were directly sampled with a coupled sediment trap-ADCP-instrument mooring array to evaluate the character and frequency of turbidity current events through Monterey Canyon, offshore California. This novel experiment aimed to provide links between globally significant sediment density flow processes and their resulting deposits. Eight to ten Anderson sediment traps were repeatedly deployed at 10 to 300 meters above the seafloor on six moorings anchored at 290 to 1850 meters water depth in the Monterey Canyon axial channel during 6-month deployments (October 2015 - April 2017). Anderson sediment traps include a funnel and intervalometer (discs released at set time intervals) above a meter-long tube, which preserves fine-scale stratigraphy and chronology. Photographs, multi-sensor logs, CT scans, and grain size analyses reveal layers from multiple sediment density flow events that carried sediment ranging from fine sand to granules. More sediment accumulation from sediment density flows, and from between flows, occurred in the upper canyon ( 300 - 800 m water depth) compared to the lower canyon ( 1300 - 1850 m water depth). Sediment accumulated in the traps during sediment density flows is sandy and becomes finer down-canyon. In the lower canyon where sediment directly sampled from density flows are clearly distinguished within the trap tubes, sands have sharp basal contacts, normal grading, and muddy tops that exhibit late-stage pulses. In at least two of the sediment density flows, the simultaneous low velocity and high backscatter measured by the ADCPs suggest that the trap only captured the collapsing end of a sediment density flow event. In the upper canyon, accumulation between sediment density flow events is twice as fast compared to the lower canyon; it is characterized by sub-cm-scale layers in muddy sediment that appear to have accumulated with daily to sub-daily frequency, likely related to known internal tidal dynamics also measured in the experiment. The comprehensive scale of the Monterey Coordinated Canyon Experiment allows us to integrate sediment traps with ADCP instrument data and seafloor core samples, which provides important new data to constrain how, when, and what sediment is transported through submarine canyons and how this is archived in seafloor deposits.

Effect of the resuspension technique on distribution of the heavy metals in sediment and suspended particulate matter.

PubMed

Pourabadehei, Mehdi; Mulligan, Catherine N

2016-06-01

Harbour areas play important roles in the economy worldwide. Human activities, however, in those areas, generate contamination, which mostly accumulates in sediments. On the other hand, harbour areas have been facing deposition of significant amounts of sediment each year. As a consequence, shallowness and accumulation of contaminants in sediment become challenging issues in harbours. Among the various management options for remediation of contaminated sediments in harbours, resuspension technique was introduced as a new approach to address those issues. The concept of the resuspension method is that finer sediments have a greater tendency to adsorb the contamination. Therefore, removing the finer sediments instead of dredging the whole contaminated area is the main goal of the resuspension technique. The objective of this paper was to evaluate the effect of the resuspension method on reducing the concentration of contamination and distribution of heavy metals in sediment and suspended particulate matter. The resuspension method was successful in reducing the concentration of seven selected heavy metals (Cr, Ni, Cu, Zn, As, Cd and Pb) by removing just 4% of the contaminated sediment. The contamination intensity in the sediment, presented by geoaccumulation index, was reduced for Cd and Pb as the main contaminants by 26 and 28 percent and the rest of the selected heavy metals returned to the natural level. The results of the sequential extraction tests and enrichment factor implied that the resuspension technique is capable of decreasing the risk of remobilization of heavy metals in the aquatic ecosystem. Copyright © 2016 Elsevier Ltd. All rights reserved.

Fine-grained sediment dispersal along the California coast

USGS Publications Warehouse

Warrick, Jonathan A.; Storlazzi, Curt D.

2013-01-01

Fine-grained sediment (silt and clay) enters coastal waters from rivers, eroding coastal bluffs, resuspension of seabed sediment, and human activities such as dredging and beach nourishment. The amount of sediment in coastal waters is an important factor in ocean ecosystem health, but little information exists on both the natural and human-driven magnitudes of fine-grained sediment delivery to the coastal zone, its residence time there, and its transport out of the system—information upon which to base environmental assessments. To help fill these information gaps, the U.S. Geological Survey has partnered with Federal, State, and local agencies to monitor fine-grained sediment dispersal patterns and fate in the coastal regions of California. Results of these studies suggest that the waves and currents of many of the nearshore coastal settings of California are adequately energetic to transport fine-grained sediment quickly through coastal systems. These findings will help with the management and regulation of fine-grained sediment along the U.S. west coast.

Volumetric analysis of a New England barrier system using ground-penetrating-radar and coring techniques

USGS Publications Warehouse

Van Heteren, S.; FitzGerald, D.M.; Barber, D.C.; Kelley, J.T.; Belknap, D.F.

1996-01-01

Ground-penetrating-radar (GPR) profiles calibrated with core data allow accurate assessments of coastal barrier volumes. We applied this procedure successfully to the barrier system along Saco Bay, Maine (USA), as part of a sediment-budget study that focused on present-day sand volumes in various coastal, shoreface, and inner-shelf lith-osomes, and on sand fluxes that have affected the volume or distribution of sand in these sediment bodies through time. On GPR profiles, the components of the barrier lithosome are readily differentiated from other facies, except where the radar signal is attenuated by brackish or salty groundwater. Significant differences between dielectric properties of the barrier lithosome and other units commonly result in strong boundary reflectors. The mostly sandy barrier sediments allow deep penetration of GPR waves, in contrast to finer-grained strata and till-covered bedrock. Within the Saco Bay barrier system, 22 ??3 x 106 m3 of sediment are unevenly distributed. Two-thirds of the total barrier volume is contained within the northern and southern ends of the study area, in the Pine Point spit and the Ferry Beach/Goosefare complex, respectively. The central area around Old Orchard Beach is locally covered by only a thin veneer of barrier sand, averaging <3 m, that unconformably overlies shallow pre-Holocene facies. The prominence of barrier-spit facies and the distribution pattern of back-barrier sediments indicate that a high degree of segmentation, governed by antecedent topography, has affected the development of the Saco Bay barrier system. The present-day configuration of the barrier and back-barrier region along Saco Bay, however, conceals much of its early compartmentalized character.

Identification and Characterization of Intercritical Heat-Affected Zone in As-Welded Grade 91 Weldment

NASA Astrophysics Data System (ADS)

Wang, Yiyu; Kannan, Rangasayee; Li, Leijun

2016-12-01

A metallurgical method is proposed for locating the intercritical heat-affected zone in the as-welded Grade 91 steel. New austenitic grains, preferentially formed along the original prior austenite grain boundaries, are characterized to contain finer M23C6 carbides and higher strain levels than the original prior austenite grains. Kurdjumov-Sachs Group 1 variant pairs, with a low misorientation of 7 deg within a martensitic block, are identified as the dominant variants in the new PAGs.

The BMPix and PEAK Tools: New Methods for Automated Laminae Recognition and Counting - Application to Glacial Varves From Antarctic Marine Sediment

NASA Astrophysics Data System (ADS)

Weber, M. E.; Reichelt, L.; Kuhn, G.; Thurow, J. W.; Ricken, W.

2009-12-01

We present software-based tools for rapid and quantitative detection of sediment lamination. The BMPix tool extracts color and gray-scale curves from images at ultrahigh (pixel) resolution. The PEAK tool uses the gray-scale curve and performs, for the first time, fully automated counting of laminae based on three methods. The maximum count algorithm counts every bright peak of a couplet of two laminae (annual resolution) in a Gaussian smoothed gray-scale curve. The zero-crossing algorithm counts every positive and negative halfway-passage of the gray-scale curve through a wide moving average. Hence, the record is separated into bright and dark intervals (seasonal resolution). The same is true for the frequency truncation method, which uses Fourier transformation to decompose the gray-scale curve into its frequency components, before positive and negative passages are count. We applied the new methods successfully to tree rings and to well-dated and already manually counted marine varves from Saanich Inlet before we adopted the tools to rather complex marine laminae from the Antarctic continental margin. In combination with AMS14C dating, we found convincing evidence that the laminations from three Weddell Sea sites represent true varves that were deposited on sediment ridges over several millennia during the last glacial maximum (LGM). There are apparently two seasonal layers of terrigenous composition, a coarser-grained bright layer, and a finer-grained dark layer. The new tools offer several advantages over previous tools. The counting procedures are based on a moving average generated from gray-scale curves instead of manual counting. Hence, results are highly objective and rely on reproducible mathematical criteria. Since PEAK associates counts with a specific depth, the thickness of each year or each season is also measured which is an important prerequisite for later spectral analysis. Since all information required to conduct the analysis is displayed graphically, interactive optimization of the counting algorithms can be achieved quickly and conveniently.

A long record of extreme wave events in coastal Lake Hamana, Japan

NASA Astrophysics Data System (ADS)

Boes, Evelien; Yokoyama, Yusuke; Schmidt, Sabine; Riedesel, Svenja; Fujiwara, Osamu; Nakamura, Atsunori; Garrett, Ed; Heyvaert, Vanessa; Brückner, Helmut; De Batist, Marc

2017-04-01

Coastal Lake Hamana is located near the convergent tectonic boundary of the Nankai-Suruga Trough, along which the Philippine Sea slab is subducted underneath the Eurasian Plate, giving rise to repeated tsunamigenic megathrust earthquakes (Mw ≥ 8). A good understanding of the earthquake- and tsunami-triggering mechanisms is crucial in order to better estimate the complexity of seismic risks. Thanks to its accommodation space, Lake Hamana may represent a good archive for past events, such as tsunamis and tropical storms (typhoons), also referred to as "extreme wave" events. Characteristic event layers, consisting of sediment entrained by these extreme waves and their backwash, are witnesses of past marine incursions. By applying a broad range of surveying methods (reflection-seismic profiling, gravity coring, piston coring), sedimentological analyses (CT-scanning, XRF-scanning, multi-sensor core logging, grain size, microfossils etc.) and dating techniques (210Pb/137Cs, 14C, OSL, tephrochronology), we attempt to trace extreme wave event deposits in a multiproxy approach. Seismic imagery shows a vertical stacking of stronger reflectors, interpreted to be coarser-grained sheets deposited by highly energetic waves. Systematic sampling of lake bottom sediments along a transect from ocean-proximal to ocean-distal sites enables us to evaluate vertical and lateral changes in stratigraphy. Ocean-proximal, we observe a sequence of eight sandy units separated by silty background sediments, up to a depth of 8 m into the lake bottom. These sand layers quickly thin out and become finer-grained land-inward. Seismic-to-core correlations show a good fit between the occurrence of strong reflectors and sandy deposits, hence confirming presumptions based on acoustic imagery alone. Sand-rich intervals typically display a higher magnetic susceptibility, density and stronger X-ray attenuation. However, based on textural and structural differences, we can make the distinction between different types of sand units: i) massive to layered sands with a sharp, erosive lower contact, ii) thin, discontinuous sand lenses with a sharp lower contact and iii) inter-fingered sand-rich and silt-rich intervals with a gradual lower contact. Variability in appearance suggests a variety in triggering events too, going from tsunamis, over storm surges (typhoons) to the impact of sea-level changes on the interaction between tidal delta and lacustrine sedimentation. Preliminary dating (210Pb/137Cs) results in sedimentation rates of 0.4 cm/yr for the last 100-150 yr. Two closely-spaced tephra layers are tentatively linked with the reported Osawa Fuji scoria (3090 BP) and Kawago-daira pumice (3150 BP). However, more absolute ages (14C and OSL) are essential in order to obtain an accurate age-depth model and to position events in time. We are proceeding with the age determination of event sand beds based on single-grain OSL dating of feldspars. Whereas quartz appeared to be not suitable for dating, research in onshore archives close to Lake Hamana already proved the suitability of the IRSL50 signal of feldspar.

Variations in fluvial deposition on an alluvial plain: an example from the Tongue River Member of the Fort Union Formation (Paleocene), southeastern Powder River Basin, Wyoming, U.S.A.

USGS Publications Warehouse

Johnson, E.A.; Pierce, F.W.

1990-01-01

The Tongue River Member of the Paleocene Fort Union Formation is an important coal-bearing sedimentary unit in the Powder River Basin of Wyoming and Montana. We studied the depositional environments of a portion of this member at three sites 20 km apart in the southeastern part of the basin. Six lithofacies are recognized that we assign to five depositional facies categorized as either channel or interchannel-wetlands environments. (1) Type A sandstone is cross stratified and occurs as lenticular bodies with concave-upward basal surfaces; these bodies are assigned to the channel facies interpreted to be the product of low-sinuosity streams. (2) Type B sandstone occurs in parallel-bedded units containing mudrock partings and fossil plant debris; these units constitute the levee facies. (3) Type C sandstone typically lacks internal structure and occurs as tabular bodies separating finer grained deposits; these bodies represent the crevasse-splay facies. (4) Gray mudrock is generally nonlaminated and contains ironstone concretions; these deposits constitute the floodplain facies. (5) Carbonaceous shale and coal are assigned to the swamp facies. We recognize two styles of stream deposition in our study area. Laterally continuous complexes of single and multistoried channel bodies occur at our middle study site and we interpret these to be the deposits of sandy braided stream systems. In the two adjacent study sites, single and multistoried channel bodies are isolated in a matrix of finer-grained interchannel sediment suggesting deposition by anastomosed streams. A depositional model for our study area contains northwest-trending braided stream systems. Avulsions of these systems created anastomosed streams that flowed into adjacent interchannel areas. We propose that during late Paleocene a broad alluvial plain existed on the southeastern flank of the Powder River Basin. The braided streams that crossed this surface were tributaries to a northward-flowing, basin-axis trunk stream that existed to the west. ?? 1990.

On the surface roughness of a braidplain in an Alpine proglacial area

NASA Astrophysics Data System (ADS)

Baewert, H.; Morche, D.; Culha, C.

2014-12-01

Surface roughness is a crucial parameter of studies concerning (paleo) flood peak discharge estimation and related factors (cf. stream power). Usually, the analysis requires preliminary knowledge of grain size distribution of the study site. However, in some cases this is impractical, especially when investigating large areas, or even impossible due to inaccessibility. In addition, the particles in the channel are usually hidden by other particles or incorporated into finer sediment. Therefore, removing particles from the channel bottom is not suitable, because it falsifies the results. Here, the application of noninvasive terrestrial laser scanning (TLS) offers new possibilities. The indirect recording of the surface leads to a significant reduction of the workload. Furthermore, form roughness and burial/imbrication are taken into account. However, there are some disadvantages in using TLS. The resolution of the TLS data is a limiting factor when defining surface roughness, because coarseness at finer detail will not be captured at lower resolution (Baewert et al. 2014). There are numerous other factors, which may alter the results. We would like to further understand how the noise associated with TLS data alters the outcome and whether the interpolation method has an influence. This study focuses on the latter two issues. For this purpose, a braidplain in the forefield of the glacier Gepatschferner in Austria was surveyed using a terrestrial laser scanner. The images were taken from different angles and with different resolutions. Subsequently, the outliers are removed from the point cloud in order to investigate the influence of the noise. Thinning the point cloud is another method used to understand the effects of the point density. References Baewert, H., Bimböse, M., Bryk, A., Rascher, E., Schmidt, K.-H. & Morche, D. (2014): Roughness determination of coarse grained alpine river bed surfaces using Terrestrial Laser Scanning data. - Zeitschrift für Geomorphologie N.F. 58(1): 81-95. Doi: 10.1127/0372-8854/2013/S-00127 .

Mediterranean undercurrent sandy contourites, Gulf of Cadiz, Spain

USGS Publications Warehouse

Hans, Nelson C.; Baraza, J.; Maldonado, A.

1993-01-01

The Pliocene-Quaternary pattern of contourite deposits on the eastern Gulf of Cadiz continental slope results from an interaction between linear diapiric ridges that are perpendicular to slope contours and the Mediterranean undercurrent that has flowed northwestward parallel to the slope contours and down valleys between the ridges since the late Miocene opening of the Strait of Gibraltar. Coincident with the northwestward decrease in undercurrent speeds from the Strait there is the following northwestward gradation of sediment facies associations: (1) upper slope facies, (2) sand dune facies on the upstream mid-slope terrace, (3) large mud wave facies on the lower slope, (4) sediment drift facies banked against the diapiric ridges, and (5) valley facies between the ridges. The southeastern sediment drift facies closest to Gibraltar contains medium-fine sand beds interbedded with mud. The adjacent valley floor facies is composed of gravelly, shelly coarse to medium sand lags and large sand dunes on the valley margins. Compared to this, the northwestern drift contains coarse silt interbeds and the adjacent valley floors exhibit small to medium sand dunes of fine sand. Further northwestward, sediment drift grades to biogenous silt near the Faro Drift at the Portuguese border. Because of the complex pattern of contour-parallel and valley-perpendicular flow paths of the Mediterranean undercurrent, the larger-scale bedforms and coarser-grained sediment of valley facies trend perpendicular to the smaller-scale bedforms and finer-grained contourite deposits of adjacent sediment drift facies. The bottom-current deposits of valleys and the contourites of the Cadiz slope intervalley areas are distinct from turbidite systems. The valley sequences are not aggradational like turbidite channel-levee complexes, but typically exhibit bedrock walls against ridges, extensive scour and fill into adjacent contourites, transverse bedform fields and bioclastic lag deposits. Both valley and contourite deposits exhibit reverse graded bedding and sharp upper bed contacts in coarse-grained layers, low deposition rates, and a regional pattern of bedform zones, textural variation, and compositional gradation. The surface sandy contourite layer of 0.2-1.2 m thickness that covers the Gulf of Cadiz slope has formed during the present Holocene high sea level because high sea level results in maximum water depth over the Gibraltar sill and full development of the Mediterranean undercurrent. The late Pleistocene age of the mud underlying the surface sand sheet correlates with the age of the last sea-level lowstand and apparent weak Mediterranean undercurrent development. Thus, the cyclic deposition of sand or mud layers and contourite or drape sequences appear to be related to late Pliocene and Quaternary sea-level changes and Mediterranean water circulation patterns. Since its Pliocene origin, the contourite sequence has had low deposition rates of < 5 cm/1000y on the upper slope and < 13 cm/1000y in the middle slope sediment drift. ?? 1993.

Sedimentation in a Submarine Seamount Apron at Site U1431, International Ocean Discovery Program Expedition 349, South China Sea

NASA Astrophysics Data System (ADS)

Dadd, K. A.; Clift, P. D.; Hyun, S.; Jiang, T.; Liu, Z.

2014-12-01

International Ocean Discovery Program (IODP) Expedition 349 Site U1431 is located near the relict spreading ridge in the East Subbasin of the South China Sea. Holes at this site were drilled close to seamounts and intersected the volcaniclastic apron. Volcaniclastic breccia and sandstone at Site U1431 are dated as late middle Miocene to early late Miocene (~8-13 Ma), suggesting a 5 m.y. duration of seamount volcanism. The apron is approximately 200 m thick and is sandwiched between non-volcaniclastic units that represent the background sedimentation. These comprise dark greenish gray clay, silt, and nannofossil ooze interpreted as turbidite and hemipelagic deposits that accumulated at abyssal water depths. At its base, the seamount sequence begins with dark greenish gray sandstone, siltstone, and claystone in upward fining sequences interpreted as turbidites intercalated with minor intervals of volcaniclastic breccia. Upsection the number and thickness of breccia layers increases with some beds up to 4.8 m and possibly 14.5 m thick. The breccia is typically massive, ungraded, and poorly sorted with angular to subangular basaltic clasts, as well as minor reworked subrounded calcareous mudstone, mudstone, and sandstone clasts. Basaltic clasts include nonvesicular aphyric basalt, sparsely vesicular aphyric basalt, highly vesicular aphyric basalt, and nonvesicular glassy basalt. Mudstone clasts are clay rich and contain foraminifer fossils. The matrix comprises up to 40% of the breccia beds and is a mix of clay, finer grained altered basalt clasts, and mafic vitroclasts with rare foraminifer fossils. Some layers have calcite cement between clasts. Volcaniclastic sandstone and claystone cycles interbedded with the breccia layers have current ripples and parallel laminations indicative of high-energy flow conditions during sedimentation. The breccia beds were most likely deposited as a series of debris flows or grain flows. This interpretation is supported by their massive structure, poor sorting, and reverse-graded bases. The upper part of the apron grades back into the background clay, silt and nannofossil ooze sedimentation with minor volcaniclastic sand and silt.

Physical and thermal properties of mud-dominant sediment from the Joetsu Basin in the eastern margin of the Japan Sea

NASA Astrophysics Data System (ADS)

Goto, Shusaku; Yamano, Makoto; Morita, Sumito; Kanamatsu, Toshiya; Hachikubo, Akihiro; Kataoka, Satsuki; Tanahashi, Manabu; Matsumoto, Ryo

2017-12-01

Physical properties (bulk density and porosity) and thermal properties (thermal conductivity, heat capacity, specific heat, and thermal diffusivity) of sediment are crucial parameters for basin modeling. We measured these physical and thermal properties for mud-dominant sediment recovered from the Joetsu Basin, in the eastern margin of the Japan Sea. To determine thermal conductivity, heat capacity, and thermal diffusivity, the dual-needle probe method was applied. Grain density and grain thermal properties for the mud-dominant sediment were estimated from the measured physical and thermal properties by applying existing models of physical and thermal properties of sediment. We suggest that the grain density, grain thermal conductivity, and grain thermal diffusivity depend on the sediment mineral composition. Conversely, the grain heat capacity and grain specific heat showed hardly any dependency on the mineral composition. We propose empirical formulae for the relationships between: thermal diffusivity and thermal conductivity, and heat capacity and thermal conductivity for the sediment in the Joetsu Basin. These relationships are different from those for mud-dominant sediment in the eastern flank of the Juan de Fuca Ridge presented in previous work, suggesting a difference in mineral composition, probably mainly in the amount of quartz, between the sediments in that area and the Joetsu Basin. Similar studies in several areas of sediments with various mineral compositions would enhance knowledge of the influence of mineral composition.

Ice rafting of fine-grained sediment, a sorting and transport mechanism, Beaufort Sea, Alaska.

USGS Publications Warehouse

Barnes, P.W.; Reimnitz, E.; Fox, D.

1982-01-01

The presence of turbid, sediment-rich fast ice in the Arctic is a major factor affecting transport of fine-grained sediment. Observers have documented the widespread, sporadic occurrence of sediment- rich fast ice in both the Beaufort and Bering Seas. The occurrence of sediment in only the upper part of the seasonal fast ice indicates that sediment-rich ice forms early during ice growth. The most likely mechanism requires resuspension of nearshore bottom sediment during storms, accompanied by formation of frazil ice and subsequent lateral advection before the fast ice is stabilized. We estimate that the sediment incorporated in the Beaufort ice canopy formed a significant proportion of the seasonal influx of terrigenous fine-grained sediment. The dominance of fine-grained sediment suggests that in the Arctic and sub-Arctic these size fractions may be ice rafted in greater volumes than the coarse fraction of traditionally recognized ice-rafted sediment. -from Authors

Macrophytes: ecosystem engineers in UK urban rivers

NASA Astrophysics Data System (ADS)

Gibbs, H.; Gurnell, A.; Heppell, K.; Spencer, K.

2012-04-01

Macrophytes act as ecosystem engineers within river channels in that they have the ability to cause geomorphological and ecological change. They induce reductions in flow velocity and associated sediment accumulation, and their system of underground roots and rhizomes also reinforces the accumulated sediment reducing sediment erosion and resuspension and creating habitats. As sediments, particularly finer-grained, store contaminants including metals, this engineering means that in the specific context of urban rivers where sediments are more likely to be contaminated, macrophytes trap and hold contaminated sediments creating a potentially important sink of metals. However, depending on the ability for the macrophyte to reinforce the sediment and reduce erosion and resuspension, there is the potential for the sink to turn in to a source and metals to be released in to the overlying water. This research therefore looks at the ecosystem engineering ability of common macrophytes in UK urban rivers by looking at: (i) the effect upon flow velocity and sediment accumulation of Sparganium erectum (branched bur-reed); (ii) the sediment reinforcement ability of both S. erectum, Typha latifolia (bulrush) and Phalaris arundinacea (reed canary grass); and, (iii) the storage of metals within the sediment, overlying water and the macrophytes. Research was undertaken on the River Blackwater, an urban river in Surrey, UK which has extensive macrophyte growth. Flow velocity measurements and fine sediment depths were recorded both within and outside of dense stands of S. erectum. The uprooting resistance (as an indicator of sediment reinforcement) was measured for three species: S. erectum, T. latifolia and P. arundinacea. Additionally, some preliminary sampling was undertaken of the sediment, overlying water and the macrophytes to determine metal storage. Lower flow velocities and greater volumes of fine sediment were recorded within the stands of S. erectum as opposed to the adjacent areas of open channel with minimal macrophyte growth. Uprooting resistances were considerable and differences were found both between species and over the annual growth cycle. T. latifolia showed the greatest uprooting resistance and P. arundinacea the lowest uprooting resistance. Maximum uprooting resistance for all species was in June. The sampled sediments were found to be a store of metals. For all macrophyte species, the below-ground tissues (roots and rhizomes) generally had greater metal concentrations than above-ground tissues (stem and leafs). The results from this research will help inform the use of macrophytes in the management of sediment-contaminated urban rivers.

Hysteretic sediment fluxes in rainfall-driven soil erosion

NASA Astrophysics Data System (ADS)

Cheraghi, Mohsen; Jomaa, Seifeddine; Sander, Graham C.; Barry, D. Andrew

2017-04-01

Hysteresis patterns of different sediment particle sizes were studied via a detailed laboratory study and modelling. Seven continuous rainfall events with stepwise- varying rainfall intensities (30, 37.5, 45, 60, 45, 37.5 and 30 mm h-1, each 20 min duration) were conducted using a 5-m × 2-m erosion flume. Flow rates and sediment concentration data were measured using flume discharge samples, and interpreted using the Hairsine and Rose (HR) soil erosion model. The total sediment concentration and concentrations of seven particle size classes (< 2, 2-20, 20-50, 50-100, 100-315, 315-1000 and > 1000 μm) were measured. For the total eroded soil and the finer particle sizes (< 2, 2-20 and 20-50 μm), there was a clockwise pattern in the sediment concentration versus discharge curves. However, as the particle size increased, concentrations tended to vary linearly with discharge. The HR model predictions for the total eroded soil and the finer particle size classes (up to 100 μm) were in good agreement with the experimental results. For the larger particles, the model provided qualitative agreement with the measurements but concentration values were different. In agreement with previous investigations using the HR model, these differences were attributed to the HR model's assumption of suspended sediment flow, which does not account for saltation and rolling motions. Keywords: Hysteresis effects, Sediment transport, Flume experiment, Splash soil erosion, Hairsine and Rose model, Particle Swarm Optimization.

Underwater microscope for measuring spatial and temporal changes in bed-sediment grain size

USGS Publications Warehouse

Rubin, David M.; Chezar, Henry; Harney, Jodi N.; Topping, David J.; Melis, Theodore S.; Sherwood, Christopher R.

2007-01-01

For more than a century, studies of sedimentology and sediment transport have measured bed-sediment grain size by collecting samples and transporting them back to the laboratory for grain-size analysis. This process is slow and expensive. Moreover, most sampling systems are not selective enough to sample only the surficial grains that interact with the flow; samples typically include sediment from at least a few centimeters beneath the bed surface. New hardware and software are available for in situ measurement of grain size. The new technology permits rapid measurement of surficial bed sediment. Here we describe several systems we have deployed by boat, by hand, and by tripod in rivers, oceans, and on beaches.

Underwater Microscope for Measuring Spatial and Temporal Changes in Bed-Sediment Grain Size

USGS Publications Warehouse

Rubin, David M.; Chezar, Henry; Harney, Jodi N.; Topping, David J.; Melis, Theodore S.; Sherwood, Christopher R.

2006-01-01

For more than a century, studies of sedimentology and sediment transport have measured bed-sediment grain size by collecting samples and transporting them back to the lab for grain-size analysis. This process is slow and expensive. Moreover, most sampling systems are not selective enough to sample only the surficial grains that interact with the flow; samples typically include sediment from at least a few centimeters beneath the bed surface. New hardware and software are available for in-situ measurement of grain size. The new technology permits rapid measurement of surficial bed sediment. Here we describe several systems we have deployed by boat, by hand, and by tripod in rivers, oceans, and on beaches.

Incision and Landsliding Lead to Coupled Increase in Sediment Flux and Grain Size Export

NASA Astrophysics Data System (ADS)

Roda-Boluda, D. C.; Brooke, S.; D'Arcy, M. K.; Whittaker, A. C.; Armitage, J. J.

2017-12-01

The rates and grain sizes of sediment fluxes modulate the dynamics and timing of landscape response to tectonics, and dictate the depositional patterns of sediment in basins. Over the last decades, we have gained a good quantitative understanding on how sediment flux and grain size may affect incision and basin stratigraphy. However, we comparably still have limited knowledge on how these variables change with varying tectonic rates. To address this question, we have studied 152 catchments along 8 normal fault-bounded ranges in southern Italy, which are affected by varying fault slip rates and experiencing a transient response to tectonics. Using a data set of 38 new and published 10Be erosion rates, we calibrate a sediment flux predictive equation (BQART), in order to estimate catchment sediment fluxes. We demonstrate that long-term sediment flux is governed by fault slip rates and the tectonically-controlled transient incision, and that sediment flux estimates from the BQART, steady-state assumptions, and incised volumes are highly correlated. This is supported by our 10Be erosion rates, which are controlled by fault slip and incision rates, and the associated landsliding. Based on a new landslide inventory, we show that erosion rate differences are likely due to differences in incision-related landslide activity across these catchments, and that landslides are a major component of sediment fluxes. From a data set of >13000 grain size counts on hillslope grain size supply and fluvial sediment at catchment outlets, we observe that landslides deliver material 20-200% coarser than other sediment sources, and that this coarse supply has an impact on the grain size distributions being exported from the catchments. Combining our sediment flux and grain size data sets, we are able to show that for our catchments, and potentially also for any areas that respond to changes in climate or tectonics via enhanced landsliding, sediment flux and grain size export increase concomitantly and scale non-linearly. Finally, we explore the consequences that this coupled sediment flux and grain size increase may have on basin stratigraphy, and we show that it has a significant effect on amplifying gravel front progradation.

Seafloor studies of Mamala Bay, Honolulu, Hawaii

USGS Publications Warehouse

Torresan, Michael E.

No comprehensive study of the effects of disposal of dredge spoils has been conducted to determine if the environment has suffered. The U.S. Army Corps of Engineers (USACE) has regularly dredged the shipping channels of Honolulu Harbor and Pearl Harbor for commercial and military purposes. The 5-year frequency for new dredging activity has led to the formation of extensive offshore wide deposits of relatively coarse sediments being created in a sedimentary environment that naturally collects much finer-grained materials. At the same time, the rapid growth of Honolulu and its suburban region over the past 3 decades has added nutrient-enriched sewage outfall to the artificially-heavy sediment load. The combined effects of dredge-spoil disposal and contaminant loads are not well-documented, and are poorly understood. The U.S. Geological Survey (USGS) began a comprehensive study to characterize the seafloor of Mamala Bay.In 1993, the USGS initiated a program sponsored by the USACE and the U.S. Environmental Protection Agency that produced a detailed map of the seafloor, especially of the distribution of dredge spoils, and a preliminary analysis of the environmental effects of dredge-spoils disposal and the chemical effects of the introduction of nutrient-rich outfall. Part of the work would involve sediment sampling, biological testing, and evaluation. Of particular interest is tissue sampling and analysis of endemic shrimp to determine the rates of absorption of toxic elements, such as heavy metals, that are easily brought into the food chain.

Evaluation of the ecological effects of heavy metals on the assemblages of benthic foraminifera of the canals of Aveiro (Portugal)

NASA Astrophysics Data System (ADS)

Martins, V.; da Silva, E. Ferreira; Sequeira, C.; Rocha, F.; Duarte, A. C.

2010-04-01

Aveiro is a town with 80,000 inhabitants situated in the central west coast of Portugal. It is located at the centre of the Ria de Aveiro, a coastal lagoon that functions as a multi-estuarine area. This town is crossed by several canals which are connected with lagoon channels through canal locks. The operation of the canal locks influences the hydro dynamism in Aveiro's canal and this and other human activities have left a sedimentary record. The study of these records was based on the sediments grain size and composition, mineralogy (by XRD techniques), geochemical (by ICP-MS), total organic carbon (TOC), and microfaunal (benthic foraminifera) content in 15 grab-samples collected in 2006 in Aveiro's canal. The total elemental concentrations evaluated by total digestion of the sediment fraction <2000 μm revealed the presence of "hot spots" of pollution caused by heavy metal contaminants in some Aveiro canals, related to legacies of past industrial activities. These "hot spots" have, for instance, higher available concentrations of Al, Cd, Co, Cu, Fe, Pb, Mn and Zn (evaluated by sequential chemical extractions) and are located in Paraíso, Alboi, Botirões and Cojo Canals, at sites where the sediments are finer and richer in TOC. Abiotic and biotic variables submitted to principal component analysis and cluster analysis highlights the hydrodynamics and human effects on the system and the negative influence of pollutants on the benthic organisms (foraminifera).

Evaluation of Bajo Blanco Sandbar as a Potential Beach Nourishment Borrow Site for Eroding Beaches in Rincon, Puerto Rico

NASA Astrophysics Data System (ADS)

Rojas, C. A.; Canals, M.

2016-02-01

The municipality of Rincón, Puerto Rico is recognized for its world-class surfing beaches. Unfortunately, the coast from Punta Higüero to Punta Cadena in Rincón is experiencing long-term erosion (Thieler 2007), which has caused the destruction of many beachfront homes and hotels and had negative impacts on the local tourism-driven economy. The purpose of this project is to evaluate whether the nearby Bajo Blanco sandbar, located just offshore of these eroded beaches, could be used as a possible beach nourishment borrow site. A high-resolution bathymetric survey of Bajo Blanco sandbar was conducted along with a grain size analysis to compare the grain size distribution of the Bajo Blanco sandbar with the sediment properties of the eroded beaches. It was found that the sediment from Bajo Blanco is finer yet may be suitable as beach fill material for these beaches according to Dean's overfill ratio. Compatibility analysis suggests a total volume of sandbar sediment of approximately 685,555 cubic meters to allow successful beach equilibrium. To evaluate the potential effects of the sand extraction on the nearshore wave climate, numerical simulations were performed using the spectral wave model of the USACE Coastal Modeling System (CMS-Wave). Wave model results for several dredging scenarios suggest that wave energy flux concentrates around the shoal causing an increase in wave height at the northern and southern edges of the shoal. Therefore, conservation of energy leads to a reduction of wave energy flux shoreward of the shoal, causing a shadow of reduced wave height. In addition, the Tres Palmas Marine reserve is located just north of Bajo Blanco sandbar and features some of the healthiest Elkorn Corals in the Caribbean. To avoid excessive sedimentation of these reefs during dredging activities, the Particle Tracking Module (PTM), integrated in the Surface-water Modeling System (SMS), was used to evaluate the Lagrangian particle transport processes along Bajo Blanco under various wave conditions. Results suggest that dredging operations be conducted during small to moderate wave events, since the wave-induced currents related to these events force sediment particles to advect south and thus away from the Tres Palmas Marine Reserve.

The development of the Ganges-Brahmaputra tidal delta plain: construction to maintenance phase changes in platform and channel morphology

NASA Astrophysics Data System (ADS)

Wilson, C.; Goodbred, S. L., Jr.; Hale, R. P.; Bain, R. L.

2016-12-01

The lower Ganges-Brahmaputra (G-B) delta can be divided into the fluvial-tidal river mouth and distributaries under active construction by the G-B rivers, and the distal tidally maintained deltaplain. In the active river-mouth, distributaries have constructed 5,000 km2 of large, coalescing islands that define the prograding coastline and subaerial-delta front. Although seasonal riverbank erosion is common, the area as a whole has gained land, primarily via horizontal and vertical accretion of intertidal mudflats and seaward progradation of emergent, tidally-elongated sandy channel-mouth bars. An analysis of historical imagery within the active river mouth shows larger and higher order channels form as merging bars and shoal-islands constrict distributary channels, while lower order creeks emerge secondarily, presumably as flow on shoaling intertidal mudflats becomes channelized and mangrove vegetation takes hold. With waning fluvial input (occurring from major distributary migration or avulsion), tidal and marine processes exhibit a stronger control on sediment transport and distribution, as is happening in the downdrift areas of the G-B tidal delta plain. The relatively pristine Sundarbans mangrove forest covers 4,100 km2 along the coast, while 11,200 km2 of the lower tidal delta plain is densely inhabited (population density up to 1,000/km2) and embanked for agricultural purposes. Although considered moribund or abandoned from direct fluvial sediment input, distal portions of the tidal delta are connected to the sediment transport system by its dense network of tidal channels. The subaerial landscape that was initially constructed by the point-sourced input of coarser-grained fluvial sediment from the mainstem rivers is thereafter maintained predominantly by onshore tidal sediment transport of finer-grained silt, and we observe accretion rates as high as 2-4 cm/y supported on the mangrove platform during the monsoon season. The tidal channels show evidence of some migration since the mid-1800s (Allison, 1998); however, there appears to be little evidence of net infilling or widening in coastal areas (<50 km from the Bay of Bengal). In contrast, we show interior areas have chronic siltation over the past 50 years due to anthropogenically modified changes in the tidal prism from poldering.

Temporal variability and memory in sediment transport in an experimental step-pool channel

NASA Astrophysics Data System (ADS)

Saletti, Matteo; Molnar, Peter; Zimmermann, André; Hassan, Marwan A.; Church, Michael

2015-11-01

Temporal dynamics of sediment transport in steep channels using two experiments performed in a steep flume (8%) with natural sediment composed of 12 grain sizes are studied. High-resolution (1 s) time series of sediment transport were measured for individual grain-size classes at the outlet of the flume for different combinations of sediment input rates and flow discharges. Our aim in this paper is to quantify (a) the relation of discharge and sediment transport and (b) the nature and strength of memory in grain-size-dependent transport. None of the simple statistical descriptors of sediment transport (mean, extreme values, and quantiles) display a clear relation with water discharge, in fact a large variability between discharge and sediment transport is observed. Instantaneous transport rates have probability density functions with heavy tails. Bed load bursts have a coarser grain-size distribution than that of the entire experiment. We quantify the strength and nature of memory in sediment transport rates by estimating the Hurst exponent and the autocorrelation coefficient of the time series for different grain sizes. Our results show the presence of the Hurst phenomenon in transport rates, indicating long-term memory which is grain-size dependent. The short-term memory in coarse grain transport increases with temporal aggregation and this reveals the importance of the sampling duration of bed load transport rates in natural streams, especially for large fractions.

Rainfall-runoff properties of tephra: Simulated effects of grain-size and antecedent rainfall

NASA Astrophysics Data System (ADS)

Jones, Robbie; Thomas, Robert E.; Peakall, Jeff; Manville, Vern

2017-04-01

Rain-triggered lahars (RTLs) are a significant and often persistent secondary volcanic hazard at many volcanoes around the world. Rainfall on unconsolidated volcaniclastic material is the primary initiation mechanism of RTLs: the resultant flows have the potential for large runout distances (> 100 km) and present a substantial hazard to downstream infrastructure and communities. RTLs are frequently anticipated in the aftermath of eruptions, but the pattern, timing and scale of lahars varies on an eruption-by-eruption and even catchment-by-catchment basis. This variability is driven by a set of local factors including the grain size distribution, thickness, stratigraphy and spatial distribution of source material in addition to topography, vegetation coverage and rainfall conditions. These factors are often qualitatively discussed in RTL studies based on post-eruption lahar observations or instrumental detections. Conversely, this study aims to move towards a quantitative assessment of RTL hazard in order to facilitate RTL predictions and forecasts based on constrained rainfall, grain size distribution and isopach data. Calibrated simulated rainfall and laboratory-constructed tephra beds are used within a repeatable experimental set-up to isolate the effects of individual parameters and to examine runoff and infiltration processes from analogous RTL source conditions. Laboratory experiments show that increased antecedent rainfall and finer-grained surface tephra individually increase runoff rates and decrease runoff lag times, while a combination of these factors produces a compound effect. These impacts are driven by increased residual moisture content and decreased permeability due to surface sealing, and have previously been inferred from downstream observations of lahars but not identified at source. Water and sediment transport mechanisms differ based on surface grain size distribution: a fine-grained surface layer displayed airborne remobilisation, accretionary pellet formation, rapid surface sealing and infiltration-excess overland flow generation whilst a coarse surface layer demonstrated exclusively rainsplash-driven particle detachment throughout the rainfall simulations. This experimental protocol has the potential to quantitatively examine the effects of a variety of individual parameters in RTL initiation under controlled conditions.

Provenance and depositional environment of epi-shelf lake sediment from Schirmacher Oasis, East Antarctica, vis-à-vis scanning electron microscopy of quartz grain, size distribution and chemical parameters

NASA Astrophysics Data System (ADS)

Shrivastava, Prakash K.; Asthana, Rajesh; Roy, Sandip K.; Swain, Ashit K.; Dharwadkar, Amit

2012-07-01

The scientific study of quartz grains is a powerful tool in deciphering the depositional environment and mode of transportation of sediments, and ultimately the origin and classification of sediments. Surface microfeatures, angularity, chemical features, and grain-size analysis of quartz grains, collectively reveal the sedimentary and physicochemical processes that acted on the grains during different stages of their geological history. Here, we apply scanning electron microscopic (SEM) analysis to evaluating the sedimentary provenance, modes of transport, weathering characteristics, alteration, and sedimentary environment of selected detrital quartz grains from the peripheral part of two epi-shelf lakes (ESL-1 and ESL-2) of the Schirmacher Oasis of East Antarctica. Our study reveals that different styles of physical weathering, erosive signatures, and chemical precipitation variably affected these quartz grains before final deposition as lake sediments. Statistical analysis (central tendencies, sorting, skewness, and kurtosis) indicates that these quartz-bearing sediments are poorly sorted glaciofluvial sediments. Saltation and suspension seem to have been the two dominant modes of transportation, and chemical analysis of these sediments indicates a gneissic provenance.

Grain Size Distribution in Mudstones: A Question of Nature vs. Nurture

NASA Astrophysics Data System (ADS)

Schieber, J.

2011-12-01

Grain size distribution in mudstones is affected by the composition of the source material, the processes of transport and deposition, and post-depositional diagenetic modification. With regard to source, it does make a difference whether for example a slate belt is eroded vs a stable craton. The former setting tends to provide a broad range of detrital quartz in the sub 62 micron size range in addition to clays and greenschist grade rock fragments, whereas the latter may be biased towards coarser quartz silt (30-60 microns), in addition to clays and mica flakes. In flume experiments, when fine grained materials are transported in turbulent flows at velocities that allow floccules to transfer to bedload, a systematic shift of grain size distribution towards an increasingly finer grained suspended load is observed as velocity is lowered. This implies that the bedload floccules are initially constructed of only the coarsest clay particles at high velocities, and that finer clay particles become incorporated into floccules as velocity is lowered. Implications for the rock record are that clay beds deposited from decelerating flows should show subtle internal grading of coarser clay particles; and that clay beds deposited from continuous fast flows should show a uniform distribution of coarse clays. Still water settled clays should show a well developed lower (coarser) and upper (finer) subdivision. A final complication arises when diagenetic processes, such as the dissolution of biogenic silica, give rise to diagenetic quartz grains in the silt to sand size range. This diagenetic silica precipitates in fossil cavities and pore spaces of uncompacted muds, and on casual inspection can be mistaken for detrital quartz. In distal mudstone successions close to 100 % of "apparent" quartz silt can be of that origin, and reworking by bottom currents can further enhance a detrital perception by producing rippled and laminated silt beds. Although understanding how size distributions in mudstones evolve is considered central to problems in hillslope, fluvial, aeolian, coastal, and submarine systems, one can not simply measure distributions and hope to arrive at an answer. The complex origins of mudstones are reflected in their very broad compositional range, and multiple overprinted processes have to be considered in order to make sense out of observed grain size distributions.

Comparisons of Unconsolidated Sediments Analyzed by APXS (MSL-Curiosity) within Gale Crater, Mars: Soils, Sands of the Barchan and Linear Dunes of the Active Bagnold Dune Field, and Ripple-field Sands.

NASA Astrophysics Data System (ADS)

Thompson, L. M.; O'Connell-Cooper, C.; Spray, J. G.; Gellert, R.; Boyd, N. I.; Desouza, E.

2017-12-01

The MSL-APXS has analyzed a variety of unconsolidated sediments within the Gale impact crater, including soils, sands from barchan [High, Namib dunes], and linear dunes [Nathan Bridges, Mount Desert dunes], within the active Bagnold dune field, and sands from two smaller ripple fields ("mega-ripples"). The Gale "soils" (unsorted, unconsolidated sediments, ranging from fine-grained particles (including dust) to coarser "pebbly" material [>2 mm]), are, to a large degree, similar to Martian basaltic soils quantified by APXS, at Gusev crater (MER-A_Spirit) and Meridiani Planum (MER-B_Opportunity). Some local contributions are indicated by, for example, the enriched K levels (relative to a martian average basaltic soil [ABS]) within coarser Gale soil samples, and a Cr, Mn, Fe enrichment within finer-grained samples. Sands (grain size 62 µm to 2 mm) of the Bagnold dunes, generally, exhibit elevated Mg and Ni, indicating enrichment from olivine and pyroxene, but depleted S, Cl and Zn, indicating high activity levels and low dust. Compositional differences, related both to position within a dune (i.e., crest versus off-crest sand), and type of dune (linear versus barchan), are identified. Off-crest sands have Na, Al, Si, K, P contents similar to (or slightly depleted, relative to) the ABS, enrichment in Mg, and low dust content, whilst crest sands contain very high Mg and Ni (relative to the ABS), low felsic elemental concentrations and very low dust content. Cr is significantly enriched (and, to a lesser degree, Mn, Fe, Ti) in the off-crest sands of the linear dunes. In contrast, barchan dunes off-crest sands have Cr, Mn, Fe, and Ti abundances similar to those in the Gale soils. Additionally, Ni concentrations in barchan dunes off-crest sands are enriched relative to the linear dunes. Analyses from a small, isolated "mega-ripple" reveal a composition similar to that of the Gale soils, including a high dust content. The second mega-ripple, within a larger ripple field, is broadly similar in composition to the active dune sands, with low dust, and elevated Mg and Ni. The compositional differences between sand bodies indicate the influence of ongoing eolian sorting processes. Further, the Cr enrichment (found in most Gale sediments, most notably the linear dunes off-crest sands) reinforces evidence of local contributions.

Quality-assurance plan for the analysis of fluvial sediment by the U.S. Geological Survey Kentucky Water Science Center Sediment Laboratory

USGS Publications Warehouse

Shreve, Elizabeth A.; Downs, Aimee C.

2005-01-01

This report describes laboratory procedures used by the U.S. Geological Survey Kentucky Water Science Center Sediment Laboratory for the processing and analysis of fluvial-sediment samples for concentration of sand and finer material. The report details the processing of a sediment sample through the laboratory from receiving the sediment sample, through the analytical process, to compiling results of the requested analysis. Procedures for preserving sample integrity, calibrating and maintaining of laboratory and field instruments and equipment, analyzing samples, internal quality assurance and quality control, and validity of the sediment-analysis results also are described. The report includes a list of references cited and a glossary of sediment and quality-assurance terms.

Sediment transport under wave groups: Relative importance between nonlinear waveshape and nonlinear boundary layer streaming

USGS Publications Warehouse

Yu, X.; Hsu, T.-J.; Hanes, D.M.

2010-01-01

Sediment transport under nonlinear waves in a predominately sheet flow condition is investigated using a two-phase model. Specifically, we study the relative importance between the nonlinear waveshape and nonlinear boundary layer streaming on cross-shore sand transport. Terms in the governing equations because of the nonlinear boundary layer process are included in this one-dimensional vertical (1DV) model by simplifying the two-dimensional vertical (2DV) ensemble-averaged two-phase equations with the assumption that waves propagate without changing their form. The model is first driven by measured time series of near-bed flow velocity because of a wave group during the SISTEX99 large wave flume experiment and validated with the measured sand concentration in the sheet flow layer. Additional studies are then carried out by including and excluding the nonlinear boundary layer terms. It is found that for the grain diameter (0.24 mm) and high-velocity skewness wave condition considered here, nonlinear waveshape (e.g., skewness) is the dominant mechanism causing net onshore transport and nonlinear boundary layer streaming effect only causes an additional 36% onshore transport. However, for conditions of relatively low-wave skewness and a stronger offshore directed current, nonlinear boundary layer streaming plays a more critical role in determining the net transport. Numerical experiments further suggest that the nonlinear boundary layer streaming effect becomes increasingly important for finer grain. When the numerical model is driven by measured near-bed flow velocity in a more realistic surf zone setting, model results suggest nonlinear boundary layer processes may nearly double the onshore transport purely because of nonlinear waveshape. Copyright 2010 by the American Geophysical Union.

A regional view of urban sedimentary basins in Northern California based on oil industry compressional-wave velocity and density logs

USGS Publications Warehouse

Brocher, T.M.

2005-01-01

Compressional-wave (sonic) and density logs from 119 oil test wells provide knowledge of the physical properties and impedance contrasts within urban sedimentary basins in northern California, which is needed to better understand basin amplification. These wire-line logs provide estimates of sonic velocities and densities for primarily Upper Cretaceous to Pliocene clastic rocks between 0.1 - and 5.6-km depth to an average depth of 1.8 km. Regional differences in the sonic velocities and densities in these basins largely 1reflect variations in the lithology, depth of burial, porosity, and grain size of the strata, but not necessarily formation age. For example, Miocene basin filling strata west of the Calaveras Fault exhibit higher sonic velocities and densities than older but finer-grained and/or higher-porosity rocks of the Upper Cretaceous Great Valley Sequence. As another example, hard Eocene sandstones west of the San Andreas Fault have much higher impedances than Eocene strata, mainly higher-porosity sandstones and shales, located to the east of this fault, and approach those expected for Franciscan Complex basement rocks. Basement penetrations define large impedence contrasts at the sediment/basement contact along the margins of several basins, where Quaternary, Pliocene, and even Miocene deposits directly overlie Franciscan or Salinian basement rocks at depths as much as 1.7 km. In contrast, in the deepest, geographic centers of the basins, such logs exhibit only a modest impedance contrast at the sediment/basement contact at depths exceeding 2 km. Prominent (up to 1 km/sec) and thick (up to several hundred meters) velocity and density reversals in the logs refute the common assumption that velocities and densities increase monotonically with depth.

Hydrodynamic and sedimentological controls governing formation of fluvial levees

NASA Astrophysics Data System (ADS)

Johnston, G. H.; Edmonds, D. A.; David, S. R.; Czuba, J. A.

2017-12-01

Fluvial levees are familiar features found on the margins of river channels, yet we know little about what controls their presence, height, and shape. These attributes of levees are important because they control sediment transfer from channel to floodplain and flooding patterns along a river system. Despite the familiarity and importance of levees, there is a surprising lack of basic geomorphic data on fluvial levees. Because of this we seek to understand: 1) where along rivers do levees tend to occur?; 2) what geomorphic and hydrodynamic variables control cross-sectional shape of levees? We address these questions by extracting levee shape from LiDAR data and by collecting hydrodynamic and sedimentological data from reaches of the Tippecanoe River, the White River, and the Muscatatuck River, Indiana, USA. Fluvial levees are extracted from a 1.5-m resolution LiDAR bare surface model and compared to hydrological, sedimentological, and geomorphological data from USGS stream gages. We digitized banklines and extracted levee cross-sections to calculate levee slope, taper, height, e-folding length, and e-folding width. To answer the research questions, we performed a multivariable regression between the independent variables—channel geometry, sediment grain size and concentration, flooding conditions, and slope—and the dependent levee variables. We find considerable variation in levee presence and shape in our field data. On the Muscatatuck River levees occur on 30% of the banks compared to 10% on the White River. Moreover, levees on the Muscatatuck are on average 3 times wider than the White River. This is consistent with the observation that the Muscatatuck is finer-grained compared to the White River and points to sedimentology being an important control on levee geomorphology. Future work includes building a morphodynamic model to understand how different hydrodynamic and geomorphic conditions control levee geometry.

Straight from the source's mouth; a quantitative study of grain-size export for an entire active rift, the Corinth Rift, central Greece

NASA Astrophysics Data System (ADS)

Watkins, Stephen E.; Whittaker, Alexander C.; Bell, Rebecca E.; Brooke, Sam A. S.; McNeill, Lisa C.; Gawthorpe, Robert L.

2017-04-01

The volumes, grain sizes and characteristics of sediment supplied from source catchments fundamentally controls basin stratigraphy. However, to date, few studies have constrained sediment budgets, including grain size, released into an active rift basin at a regional scale. The Gulf of Corinth, central Greece, is one of the most rapidly extending rifts in the world, with geodetic measurements of 5 mm/yr in the East to 15 mm/yr in the West. It has well-constrained climatic and tectonic boundary conditions and bedrock lithologies are well-characterised. It is therefore an ideal natural laboratory to study the grain-size export for a rift. In the field, we visited the river mouths of 49 catchments draining into the Corinth Gulf, which in total drain 83% of the rift. At each site, hydraulic geometries, surface grain-size of channel bars and full-weighted grain-size distributions of river sediment were obtained. The surface grain-size was measured using the Wolman point count method and the full-weighted grain-size distribution of the bedload by in-situ sieving. In total, approximately 17,000 point counts and 3 tonnes of sediment were processed. The grain-size distributions show an overall increase from East to West on the southern coast of the gulf, with largest grain-sizes exported from the Western rift catchments. D84 ranges from 20 to 110 mm, however 50% of D84 grain-sizes are less than 40 mm. Subsequently, we derived the full Holocene sediment budget for the Corinth Gulf by combining our grain size data with catchment sediment fluxes, constrained using the BQART model and calibrated to known Holocene sediment volumes in the basin from seismic data (c.f. Watkins et al., in review). This is the first time such a budget has been derived for the Corinth Rift. Finally, our estimates of sediment budgets and grain sizes were compared to regional uplift constraints, fault distributions, slip rates and lithology to identify the relative importance of these controls on sediment supply to the basin.

Sediment transport processes in the Pearl River Estuary as revealed by grain-size end-member modeling and sediment trend analysis

NASA Astrophysics Data System (ADS)

Li, Tao; Li, Tuan-Jie

2018-04-01

The analysis of grain-size distribution enables us to decipher sediment transport processes and understand the causal relations between dynamic processes and grain-size distributions. In the present study, grain sizes were measured from surface sediments collected in the Pearl River Estuary and its adjacent coastal areas. End-member modeling analysis attempts to unmix the grain sizes into geologically meaningful populations. Six grain-size end-members were identified. Their dominant modes are 0 Φ, 1.5 Φ, 2.75 Φ, 4.5 Φ, 7 Φ, and 8 Φ, corresponding to coarse sand, medium sand, fine sand, very coarse silt, silt, and clay, respectively. The spatial distributions of the six end-members are influenced by sediment transport and depositional processes. The two coarsest end-members (coarse sand and medium sand) may reflect relict sediments deposited during the last glacial period. The fine sand end-member would be difficult to transport under fair weather conditions, and likely indicates storm deposits. The three remaining fine-grained end-members (very coarse silt, silt, and clay) are recognized as suspended particles transported by saltwater intrusion via the flood tidal current, the Guangdong Coastal Current, and riverine outflow. The grain-size trend analysis shows distinct transport patterns for the three fine-grained end-members. The landward transport of the very coarse silt end-member occurs in the eastern part of the estuary, the seaward transport of the silt end-member occurs in the western part, and the east-west transport of the clay end-member occurs in the coastal areas. The results show that grain-size end-member modeling analysis in combination with sediment trend analysis help to better understand sediment transport patterns and the associated transport mechanisms.

Secure and private sensing for driver authentication and transportation safety : final report.

DOT National Transportation Integrated Search

2017-08-01

Recent technology trends have allowed affordable and efficient collection of driver data. This has enabled a variety of potential applications, including more accurate pricing determinations for insurance and finer grained traffic planning for improv...

Investigations of grain size dependent sediment transport phenomena on multiple scales

NASA Astrophysics Data System (ADS)

Thaxton, Christopher S.

Sediment transport processes in coastal and fluvial environments resulting from disturbances such as urbanization, mining, agriculture, military operations, and climatic change have significant impact on local, regional, and global environments. Primarily, these impacts include the erosion and deposition of sediment, channel network modification, reduction in downstream water quality, and the delivery of chemical contaminants. The scale and spatial distribution of these effects are largely attributable to the size distribution of the sediment grains that become eligible for transport. An improved understanding of advective and diffusive grain-size dependent sediment transport phenomena will lead to the development of more accurate predictive models and more effective control measures. To this end, three studies were performed that investigated grain-size dependent sediment transport on three different scales. Discrete particle computer simulations of sheet flow bedload transport on the scale of 0.1--100 millimeters were performed on a heterogeneous population of grains of various grain sizes. The relative transport rates and diffusivities of grains under both oscillatory and uniform, steady flow conditions were quantified. These findings suggest that boundary layer formalisms should describe surface roughness through a representative grain size that is functionally dependent on the applied flow parameters. On the scale of 1--10m, experiments were performed to quantify the hydrodynamics and sediment capture efficiency of various baffles installed in a sediment retention pond, a commonly used sedimentation control measure in watershed applications. Analysis indicates that an optimum sediment capture effectiveness may be achieved based on baffle permeability, pond geometry and flow rate. Finally, on the scale of 10--1,000m, a distributed, bivariate watershed terain evolution module was developed within GRASS GIS. Simulation results for variable grain sizes and for distributed rainfall infiltration and land cover matched observations. Although a unique set of governing equations applies to each scale, an improved physics-based understanding of small and medium scale behavior may yield more accurate parameterization of key variables used in large scale predictive models.

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.

Analysis of Fluvial Bed Sediments Along the Apalachicola River, Florida through Field Reconnaissance Studies

NASA Astrophysics Data System (ADS)

Passeri, D.; Hagen, S. C.; Daranpob, A.; Smar, D. E.

2011-12-01

River competence is an important parameter in understanding sediment transport in fluvial systems. Competence is defined as the measure of a stream's ability to transport a certain maximum grain size of sediment. Studies have shown that bed sediment particle size in rivers and streams tends to vary spatially along the direction of stream flow. Over a river section several reaches long, variability of sediment particle sizes can be seen, often becoming finer downstream. This phenomenon is attributed to mechanisms such as local control of stream gradient, coarse tributary sediment supply or particle breakdown. Average particle size may also be smaller in tributary sections of rivers due to river morphology. The relationship between river mean velocity and particle size that can be transported has also been explored. The Hjulstrom curve classifies this relationship by relating particle size to velocity, dividing the regions of sedimentation, transportation, and erosion. The curve can also be used to find values such as the critical erosion velocity (the velocity required to transport particles of various sizes in suspension) and settling velocity (the velocity at which particles of a given size become too heavy to be transported and fall out of suspension, consequently causing deposition). The purpose of this research is to explore the principles of river competence through field reconnaissance collection and laboratory analysis of fluvial sediment core samples along the Apalachicola River, FL and its distributaries. Sediment core samples were collected in the wetlands and estuarine regions of the Apalachicola River. Sieve and hydrometer analyses were performed to determine the spatial distribution of particle sizes along the river. An existing high resolution hydrodynamic model of the study domain was used to simulate tides and generate river velocities. The Hjulstrom curve and the generated river velocities were used to define whether sediment was being transported, eroded or deposited at the different locations in the river and its distributaries. Parameters such as critical erosion velocity and settling velocity were also calculated to describe sediment transport along the channel. This research provides a better understanding of the fluvial geomorphic system, particularly sediment transport in channels. It also provides excellent validation data for future sediment transport studies in similar fluvial study domains.

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.

Recent Compositional Trends within the Murray Formation, Gale Crater, Mars, as seen by APXS: Implications for Sedimentary, Diagenetic and Alteration History.

NASA Astrophysics Data System (ADS)

Thompson, L. M.; Yen, A.; Spray, J. G.; Johnson, J. R.; Fraeman, A. A.; Berger, J. A.; Gellert, R.; Boyd, N.; Desouza, E.; O'Connell-Cooper, C.; VanBommel, S.

2017-12-01

The >230 m thick Murray Formation is the lower-most unit of the Mount Sharp Group, and interpreted as primarily lacustrine. Representative mudstone, siltstone and fine sandstone targets, encountered above -4330 m elevation, trend to lower Si, Al, Ti, Cr and Ca, and higher Fe, Mn, Zn, P and Mg than the Murray below. Less common, distinctive, coarser grained sandstone lenses tend to exhibit slightly different compositions to the more typical Murray but, overall, show similar elemental trends with elevation, albeit exaggerated. This suggests that the variations observed with elevation in Al, Ti, Cr, K, Fe, Mn, Zn and P within both the coarser sandstones and finer grained Murray are the result of diagenetic and/or alteration processes rather than provenance or physical sedimentary processes such as sorting. This is supported by the chemistry of obvious diagenetic, dark grey nodules, and other potential diagenetic/alteration features within this section, which show variations in the same element concentrations (i.e., P, Mn, Fe, Zn, Mg, Ca and S), distinct from diagenetic features lower down in the stratigraphy, indicating mobility of these elements within this section and changing fluid chemistry. Trends in FeO/MnO generally mimic the presence of ferric absorption features observed in visible/near infrared passive spectra from the ChemCam instrument and from CRISM orbital data, which may be consistent with changes in redox conditions as we climb up section towards Vera Rubin Ridge (Hematite Ridge). Layer-parallel CaSO4 is also common, and not observed below -4330 m. This may represent syndepositional evaporite layers, or late bedding/laminae parallel veins emplaced after lithification, in conjunction with cross-cutting veins. The overall differences in composition between the sandstone targets and finer grained Murray are attributed to distinct provenances and/or sorting during transport. We will discuss the implications of the trends and composition of the Murray above -4330 m elevation and how this pertains to the history and evolution of the Murray Formation as a whole, climatic conditions during the formation of the Murray and the nature of Gale crater lake. Also, what do the trends imply about how circulating fluids have evolved within the Murray sediments and pH, redox, salinity conditions of these fluids?

Seabed texture and composition changes offshore of Port Royal Sound, South Carolina before and after the dredging for beach nourishment

NASA Astrophysics Data System (ADS)

Xu, Kehui; Sanger, Denise; Riekerk, George; Crowe, Stacie; Van Dolah, Robert F.; Wren, P. Ansley; Ma, Yanxia

2014-08-01

Beach nourishment has been a strategy widely used to slow down coastal erosion in many beaches around the world. The dredging of sand at the borrow site, however, can have complicated physical, geological and ecological impacts. Our current knowledge is insufficient to make accurate predictions of sediment infilling in many dredging pits due to lack of detailed sediment data. Two sites in the sandy shoal southeast of Port Royal Sound (PRS) of South Carolina, USA, were sampled 8 times from April 2010 to March 2013; one site (defined as 'borrow site') was 2 km offshore and used as the dredging site for beach nourishment of nearby Hilton Head Island in Beaufort County, South Carolina, and the other site (defined as 'reference site') was 10 km offshore and not directly impacted by the dredging. A total of 184 surficial sediment samples were collected randomly at two sites during 8 sampling periods. Most sediments were fine sand, with an average grain size of 2.3 phi and an organic matter content less than 2%. After the dredging in December 2011-January 2012, sediments at the borrow site became finer, changing from 1.0 phi to 2.3 phi, and carbonate content decreased from 10% to 4%; changes in mud content and organic matter were small. Compared with the reference site, the borrow site experienced larger variations in mud and carbonate content. An additional 228 sub-samples were gathered from small cores collected at 5 fixed stations in the borrow site and 1 fixed station at the reference site 0, 3, 6, 9, and 12 months after the dredging; these down-core sub-samples were divided into 1-cm slices and analyzed using a laser diffraction particle size analyzer. Most cores were uniform vertically and consisted of fine sand with well to moderately well sorting and nearly symmetrical averaged skewness. Based on the analysis of grain size populations, 2 phi- and 3 phi-sized sediments were the most dynamic sand fractions in PRS. Mud deposition on shoals offshore of PRS presumably happens when offshore mud transport is prevalent and there is a following rapid sand accumulation to bury the mud. However, in this borrow site there was very little accumulation of mud. This will allow the site to be used in future nourishment projects presuming no accumulation of mud occurs in the future.

Modern and relict sedimentary systems of the semi-arid continental shelf in NE Brazil

NASA Astrophysics Data System (ADS)

Ximenes Neto, Antonio Rodrigues; Morais, Jáder Onofre de; Ciarlini, Clairton

2018-07-01

This paper describes the carbonate-siliciclastic system of the equatorial continental shelf of NE Brazil (East Ceará) based on X-ray fluorescence (XRF), grain size, CaCO3, shallow seismic and remotely operated vehicle (ROV) analyses. Data were obtained for two sectors: 1) Halimeda Bank (HB), inner shelf (-12 m), and 2) transverse profile (TP), inner to outer shelf-upper slope (-5 to -100 m). In total, 72 samples were collected, and 29 km of seismic lines (HB) and ROV profiles (HB and TP) were surveyed. The main chemical elements were Ca and Si (93%). These elements occur in two types of shallow marine sediments: carbonate (mainly autochthonous) and siliciclastics (terrigenous/allochthonous/relict). With respect to the chemical elements, a strong negative correlation was observed between calcareous (Ca and Sr) and siliciclastic (Si, Al, and K) components. Strontium does not always show a strong positive correlation with Ca. The average CaCO3 contents of 81% and 91% were determined for the HB and TP, respectively. The profiles show a predominance of carbonate sediments; however, the HB demonstrates a greater continental influence (inner shelf). The grain size presents a prevalence of sand (82%) in relation to gravel (18%). This particle size variation is mainly due to the breakdown of Halimeda nodules, siliciclastic sediments in the finer fraction (>2.5Φ), and the presence of gravel with iron coating (relict). Two types of echo-characters have been identified. Both are associated with the large presence of carbonate sediments. Echo I shows the bottom surface with continuity in the sub-bottom without a subsurface reflector. Echo II presents a discontinuous subsurface reflector. The ROV allowed the observation of algae patches in higher floors and gravelly and sandy bioclastics in the lowest sectors. Large patches of calcareous green algae, Halimeda, occur in the inner shelf below the 15 m isobath, mainly due to the semi-arid climate (weak sediment supply from the mainland), geographical position (equatorial) and oceanographic conditions (hydrodynamic and biogeochemistry). It has been concluded that the seafloor of the semi-arid continental shelf of East Ceará (NE Brazil) shows modern predominance of carbonate deposition based on the lack of contaminants, geochemical purity of carbonate sediments, and high percentage of CaCO3. The conditions for exploitation in the intermediate sector are provided. However, it would be ideal to perform punctual extraction and analyze the resilience and regeneration of Halimeda incrassata and the consequences for fisheries (important economic resource of the region).

Preliminary assessment of aggradation potential in the North Fork Stillaguamish River downstream of the State Route 530 landslide near Oso, Washington

USGS Publications Warehouse

Magirl, Christopher S.; Keith, Mackenzie K.; Anderson, Scott W.; O'Connor, Jim; Robert Aldrich,; Mastin, Mark C.

2015-12-28

On March 22, 2014, the State Route 530 Landslide near Oso, Washington, traveled almost 2 kilometers (km), destroyed more than 40 structures, and impounded the North Fork Stillaguamish River to a depth of 8 meters (m) and volume of 3.3×106 cubic meters (m3). The landslide killed 43 people. After overtopping and establishing a new channel through the landslide, the river incised into the landslide deposit over the course of 10 weeks draining the impoundment lake and mobilizing an estimated 280,000±56,000 m3 of predominantly sand-sized and finer sediment. During the first 4 weeks after the landslide, this eroded sediment caused downstream riverbed aggradation of 1–2 m within 1 km of the landslide and 0.4 m aggradation at Whitman Road Bridge, 3.5 km downstream. Winter high flows in 2014–15 were anticipated to mobilize an additional 220,000±44,000 m3 of sediment, potentially causing additional aggradation and exacerbating flood risk downstream of the landslide. Analysis of unit stream power and bed-material transport capacity along 35 km of the river corridor indicated that most fine-grained sediment will transport out of the North Fork Stillaguamish River, although some localized additional aggradation was possible. This new aggradation was not likely to exceed 0.1 m except in reaches within a few kilometers downstream of the landslide, where additional aggradation of up to 0.5 m is possible. Alternative river response scenarios, including continued mass wasting from the landslide scarp, major channel migration or avulsion, or the formation of large downstream wood jams, although unlikely, could result in reaches of significant local aggradation or channel change.

The exceptional sediment load of fine-grained dispersal systems: Example of the Yellow River, China.

PubMed

Ma, Hongbo; Nittrouer, Jeffrey A; Naito, Kensuke; Fu, Xudong; Zhang, Yuanfeng; Moodie, Andrew J; Wang, Yuanjian; Wu, Baosheng; Parker, Gary

2017-05-01

Sedimentary dispersal systems with fine-grained beds are common, yet the physics of sediment movement within them remains poorly constrained. We analyze sediment transport data for the best-documented, fine-grained river worldwide, the Huanghe (Yellow River) of China, where sediment flux is underpredicted by an order of magnitude according to well-accepted sediment transport relations. Our theoretical framework, bolstered by field observations, demonstrates that the Huanghe tends toward upper-stage plane bed, yielding minimal form drag, thus markedly enhancing sediment transport efficiency. We present a sediment transport formulation applicable to all river systems with silt to coarse-sand beds. This formulation demonstrates a remarkably sensitive dependence on grain size within a certain narrow range and therefore has special relevance to silt-sand fluvial systems, particularly those affected by dams.

The exceptional sediment load of fine-grained dispersal systems: Example of the Yellow River, China

PubMed Central

Ma, Hongbo; Nittrouer, Jeffrey A.; Naito, Kensuke; Fu, Xudong; Zhang, Yuanfeng; Moodie, Andrew J.; Wang, Yuanjian; Wu, Baosheng; Parker, Gary

2017-01-01

Sedimentary dispersal systems with fine-grained beds are common, yet the physics of sediment movement within them remains poorly constrained. We analyze sediment transport data for the best-documented, fine-grained river worldwide, the Huanghe (Yellow River) of China, where sediment flux is underpredicted by an order of magnitude according to well-accepted sediment transport relations. Our theoretical framework, bolstered by field observations, demonstrates that the Huanghe tends toward upper-stage plane bed, yielding minimal form drag, thus markedly enhancing sediment transport efficiency. We present a sediment transport formulation applicable to all river systems with silt to coarse-sand beds. This formulation demonstrates a remarkably sensitive dependence on grain size within a certain narrow range and therefore has special relevance to silt-sand fluvial systems, particularly those affected by dams. PMID:28508078

Microstructural and mechanical evolution during deformation and annealing of poly-phase marbles - constraints from laboratory experiments and field observations

NASA Astrophysics Data System (ADS)

Austin, N. J.; Evans, B.; Dresen, G. H.; Rybacki, E.

2009-12-01

Deformed rocks commonly consist of several mineral phases, each with dramatically different mechanical properties. In both naturally and experimentally deformed rocks, deformation mechanisms and, in turn, strength, are commonly investigated by analyzing microstructural elements such as crystallographic preferred orientation (CPO) and recrystallized grain size. Here, we investigated the effect of variations in the volume fraction and the geometry of rigid second phases on the strength and evolution of CPO and grain size of synthetic calcite rocks. Experiments using triaxial compression and torsional loading were conducted at 1023 K and equivalent strain rates between ~2e-6 and 1e-3 s-1. The second phases in these synthetic assemblages are rigid carbon spheres or splinters with known particle size distributions and geometries, which are chemically inert at our experimental conditions. Under hydrostatic conditions, the addition of as little as 1 vol.% carbon spheres poisons normal grain growth. Shape is also important: for an equivalent volume fraction and grain dimension, carbon splinters result in a finer calcite grain size than carbon spheres. In samples deformed at “high” strain rates, or which have “large” mean free spacing of the pinning phase, the final recrystallized grain size is well explained by competing grain growth and grain size reduction processes, where the grain-size reduction rate is determined by the rate that mechanical work is done during deformation. In these samples, the final grain size is finer than in samples heat-treated hydrostatically for equivalent durations. The addition of 1 vol.% spheres to calcite has little effect on either the strength or CPO development. Adding 10 vol.% splinters increases the strength at low strains and low strain rates, but has little effect on the strength at high strains and/or high strain rates, compared to pure samples. A CPO similar to that in pure samples is observed, although the intensity is reduced in samples containing 10 vol.% splinters. When 10 vol.% spheres are added to calcite, the strength of the aggregate is reduced, and a distinct and strong CPO develops. Viscoplastic self consistent calculations were used to model the evolution of CPO in these materials, and these suggest a variation in the activity of the various slip systems within pure samples and those containing 10 vol.% spheres. The applicability of these laboratory observations has been tested with field-based observations made in the Morcles Nappe (Swiss Helvetic Alps). In the Morcles Nappe, calcite grain size becomes progressively finer as the thrust contact is approached, and there is a concomitant increase in CPO intensity, with the strongest CPO’s in the finest-grained, quartz-rich limestones, nearest the thrust contact, which are interpreted to have been deformed to the highest strains. Thus, our laboratory results may be used to provide insight into the distribution of strain observed in natural shear zones.

Sediment delivery after a wildfire

USGS Publications Warehouse

Reneau, Steven L.; Katzman, D.; Kuyumjian, G.A.; Lavine, A.; Malmon, D.V.

2007-01-01

We use a record of sedimentation a small reservoir within the Cerro Grande burn area, New Mexico, to document postfire delivery of ash, other fine-grained sediment carried in suspension within floods, and coarse-grained sediment transported as bedload over a five-year period. Ash content of sediment layers is estimated using fallout 137Cs as a tracer, and ash concentrations are shown to rapidly decrease through a series of moderate-intensity convective storms in the first rainy season after the fire. Over 90% of the ash was delivered to the reservoir in the first year, and ash concentrations in suspended sediment were negligible after the second year. Delivery of the remainder of the fine sediment also declined rapidly after the first year despite the occurrence of higher-intensity storms in the second year. Fine sediment loads after five years remained significantly above prefire averages. Deposition of coarse-grained sediment was irregular in time and was associated with transport by snowmelt runoff of sediment stored along the upstream channel during short-duration summer floods. Coarse sediment delivery in the first four years was strongly correlated with snowmelt volume, suggesting a transport-limited system with abundant available sediment. Transport rates of coarse sediment declined in the fifth year, consistent with a transition to a more stable channel as the accessible sediment supply was depleted and the channel bed coarsened. Maximum impacts from ash and other fine-grained sediment therefore occurred soon after the fire, whereas the downstream impacts from coarse-grained sediment were attenuated by the more gradual process of bedload sediment transport. ?? 2007 Geological Society of America.

Geoacoustic provinces and physical properties of surface sediments in the southern part of the East Sea, Korea

NASA Astrophysics Data System (ADS)

Kim, Sora; Bahk, Jang-Jun; Kim, Daechoul; Lee, Gwang Soo; Kim, Seong-Pil

2017-04-01

A total of 288 piston and box core samples were collected and analyzed to characterize the physical properties and geoacoustic provinces of surficial sediments in the southern part of the East Sea. Based on in-situ condition sound velocity (converted laboratory sound velocity to in-situ condition sound velocity) and sediment properties (sediment textures and physical properties), the study area was divided into eight provinces (Province IA, IB, IC, II, III, IV, VA, and VB) : (1) Province IA : hemi-pelagic mud partially mixed with intermittent sandy sediments originating from the outer shelf due to slide/slump or mass flows (in-situ condition sound velocity: 1439 m/s, mean grain size: 8.5Φ, bulk density: 1.24 g/cm3,and porosity: 84%); (2) Province IB : Holocene muddy sediments are dominant, but in some area that is influenced by the surrounding land and coast (in-situ condition sound velocity: 1448 m/s, mean grain size: 8.3Φ, bulk density: 1.32 g/cm3, and porosity: 79%); (3) Province IC : muddy sediments that were deposited during the Holocene (in-situ condition sound velocity: 1457 m/s, mean grain size: 7.8Φ, bulk density: 1.36 g/cm3, and porosity: 78%); (4) Province II : mixed recent and relict sediments (in-situ condition sound velocity: 1493 m/s, mean grain size: 5.9Φ, bulk density: 1.53 g/cm3, and porosity: 68%); (5) Province III (Pohang) : there is a mixture of muddy sediments and sandy sediments and sediments from Hyeongsan River are mostly deposited (in-situ condition sound velocity: 1586 m/s, mean grain size: 4.1Φ, bulk density: 1.74 g/cm3, and porosity: 57%); (6) Province IV : coarse-grained relict sediments formed during the Pleistocene (in-situ condition sound velocity: 1572 m/s, mean grain size: 4.1Φ, bulk density: 1.76 g/cm3, and porosity: 55%); (7) Province VA : relict sand with some gravel, show marked differences from the area in which muddy sediments are deposited (in-situ condition sound velocity: 1662 m/s, mean grain size: 3.3Φ, bulk density: 1.82 g/cm3, and porosity: 51%), and (8) Province VB : similar to but coarser sediments than Province IV (in-situ condition sound velocity: 1667 m/s, mean grain size: 3.2Φ, bulk density: 1.87 g/cm3, and porosity: 46%). The in-situ condition sound velocity, mean grain size, and bulk density increased from Province IA to Province VB, whereas the porosity and water content decrease. Variability of the physical and acoustic properties tended to follow the general of the mean grain size. The classification of each province using the in-situ condition sound velocity corrected with the temperature and sediment type provides a better reflection of the sediment properties and sedimentary environment.

Bed structure and bedload transport: Sediment grain reorientation in response to high and low flows in an experimental flume

NASA Astrophysics Data System (ADS)

Gurer, M.; Sullivan, S.; Masteller, C.

2016-12-01

Bedload is a regime of sediment transport that occurs when particles roll, hop, or bounce downstream. This mode of transport represents an important portion of the sediment load in a gravel river. Despite numerous studies focused on bedload transport, it still remains difficult to predict accurately due to the complex arrangement of riverbed particles. The formation of gravel clusters, stones being imbricated, or streamlined, and other interlocked arrangements, as well as grains armoring the bed, all tend to stabilize gravel channels and decrease bed mobility. Typically, the development of bed structure usually occurs as sediment moves downstream. However, it is unclear that gravel bed structure can be developed during weaker flows that do not generate significant sediment transport. We examine how individual sediment grains reorient themselves during low flow conditions, in the absence of sediment transport, and during high flow conditions, as bedload transport occurs. We then perform flume experiments where we expose a gravel bed to varying durations of low flow and raise the water level, simulating a flood and transporting sediment. We also compare the long-axis orientations of grains before and after each low flow period and transport. We find that sediment grains reorient themselves differently during low and high flows. During low flow, grains appear to reorient themselves with the long-axes towards cross-stream direction, or perpendicular to the flow, with longer duration flows resulting in more pronounced cross-stream orientation. During high flow, grains orient themselves with their long-axes facing downstream or parallel to the flow, similar to imbricated grains observed in the sedimentary record. Further, when transport occurs, we find that median grain orientation is strongly correlated with bedload transport rates (R^2 = 0.98). We also observe that median grain orientations more perpendicular to downstream flow result in reduced transport rates. This new result suggests that the low flow reorientation of grains perpendicular to downstream flow drives observed differences in bedload transport during high flows. We conclude that low flow periods are important for the creation of bed structure and the stabilization of gravel river channels.

Chromium in urban sediment particulates: an integrated micro-chemical and XANES study

NASA Astrophysics Data System (ADS)

Taylor, Kevin; Byrne, Patrick; Hudson-Edwards, Karen

2015-04-01

Chromium is generally common within the urban sediment cascade as a result of abundant industrial and transport-related sources. The risks that Cr-bearing particles pose to ecosystems and humans depend on the solid phase chemical speciation of Cr in the particles. In this study, we use bulk chemical digests, sequential chemical extraction analysis, electron microscopy, electron microprobe and microfocus XANES analysis to describe the solid-phase speciation of Cr in urban particulate matter from both aquatic sediment and road dust sediment (RDS) in Manchester, UK. Cr-bearing grains within RDS are predominantly iron oxide grains, commonly of goethite or haematite mineralogy, but Cr-bearing silicate glass grains are also present. Iron oxide glass grains most likely have sorbed Cr, and derive from the rusting of Cr-steel particles from vehicles. Electron microprobe analysis indicates concentrations of Cr up to 3200 μg/g in these grains, and XANES analysis indicates that Cr(III) is the dominant oxidation state, with some trace amounts of Cr(VI). Cr-bearing grains within aquatic sediments are dominated by alumino-silicate glass grains derived from industrial waste. These grains contain Cr-rich areas with up to 19% Cr2O3 and XANES analysis indicates that Cr is present as Cr(III). The dominance of Cr(III) in these urban particulate grains suggests limited bioavailability or toxicity. However, the presence within two markedly different grain types (iron oxides and silicate glasses) indicates that the long-term geochemical behaviour and environmental risk of RDS and the aquatic sediments studied are likely to be quite different. These findings highlight the importance of understanding sources of metal contaminants in urban environments and the geochemical processes that affect their transfer through the urban sediment cascade and the wider river basin.

Variations in Grain-Scale Sediment Structure in a Gravel-Bed Channel as a Function of Fine Sediment Content and Morphological Location

NASA Astrophysics Data System (ADS)

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

2016-12-01

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 bed stability. Furthermore, grain-scale structure varies throughout a channel and over time in ways that have not been fully quantified. Our research aims to quantify variations in sediment structure caused by two key variables; 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. The fine sediment content of the bed was incrementally increased over a series of runs from gravel only, to coarse sand, fine sand and two concentrations of clay. 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 through metrics including measurement of grain pivot angles, grain exposure and protrusion, and vertical variation in bed porosity and fine sediment content. Metrics derived from the CT data were verified using data from grain counts and tilt-table measurements on co-located samples. Comparison of the metrics across different morphological locations and fine sediment content demonstrates how these factors affect the bed structure. These results have implications for the development of sediment entrainment models for gravel bed rivers.

Comparison of sediment grain size characteristics on nourished and un-nourished estuarine beaches and impacts on horseshoe crab habitat, Delaware Bay, New Jersey

USGS Publications Warehouse

Jackson, N.L.; Smith, D.R.; Nordstrom, K.F.

2005-01-01

This study was undertaken to determine whether nourished and un-nourished estuarine beaches have conspicuous differences in sediment size and sorting that could affect their value as habitat for horseshoe crabs. Comparisons are made of beach profiles and sediment samples gathered at 0.15 m and 0.30 m depths on the backshore, at spring tide elevation, neap tide elevation, and the lower foreshore on 5 un-nourished and 3 nourished beaches in Delaware Bay, where tidal range is <2.0 m. The backshore is at least 0.5 m higher on the recently nourished beaches than on a nearby un-nourished beach reworked by storm waves. Nourishing these beaches to elevations higher than natural overwash heights will restrict natural evolution of the upper beach. Sediments at spring tide elevation on un-nourished sites average 0.72 mm in diameter at 0.15 m depth and 0.67 mm at 0.30 m depth.The similarity in size implies a relatively deep active layer in the zone of maximum cut and fill associated with cyclic profile change during low frequency, high magnitude storms. Sedimentary changes at neap tide elevation may be influenced more by depth of activation by waves than by cycles of deposition and erosion. Sediment at 0.15 m depth at spring and neap locations on the foreshore of nourished beaches is finer (0.51 mm) and better sorted (0.82 phi) than at 0.30 m depth (0.91 mm, 1.38 phi), implying that waves have not reworked the deeper sediments. Differences in sediment characteristics at depth may persist on eroding nourished beaches, where unreworked fill is close to the surface. Sediment texture influences horseshoe crab egg viability and development. Lower rates of water movement through the foreshore and greater thickness of the capillary fringe on nourished sites suggests that greater moisture retention will occur where horseshoe crabs bury eggs and may provide more favorable conditions for egg development, but the depth of these conditions will not be great on a recently nourished beach. ?? 2005 Gebru??der Borntraeger.

Textural and geochemical characteristics of marine sediments in the SW Gulf of Mexico: implications for source and seasonal change.

PubMed

Rosales-Hoz, Leticia; Carranza-Edwards, Arturo; Martinez-Serrano, Raymundo G; Alatorre, Miguel Angel; Armstrong-Altrin, John S

2015-04-01

Two oceanographic cruises were taken during the winter (SAV I, November and December 2007) and summer (SAV II, July and August 2008) across the mouth of the Papaloapan River in the Gulf of Mexico. Surficial sediment samples were collected from shallow (16-30 m), intermediate (30 to 80 m), and deeper areas (≥300 m). Shallow water sediments are coarser, better-sorted, and primarily composed of sands during the winter, while those found in the summer are finer. At depths greater than 30 m, sediments are primarily fine-grained no matter the season. Major element analysis from shallow areas indicates higher SiO2 concentrations during the windy season with negative correlation against Al2O3 during both seasons, following the respective abundances of sand and muds. High organic carbon content was observed in shallow areas during the summer. Trace metals V, Ni, Cu, Zn, Pb, Li, Cr, Co, and Ba were evaluated. The first six metals showed higher average concentration in the deeper areas, although the highest values at some individual sampling sites for Cr, Co, Cu, and Ba were observed in the coastal area. Factor and cluster analysis were used to explain the sediment distribution pattern and the factors that determine the sediment characteristics within the study area. In shallow areas, four clusters were observed during the winter and five during the summer. The geochemical characteristics of the samples in each cluster suggest association with fluvial sediment input, textural characteristics, heavy minerals, and Cu and Ba concentration. To evaluate the variations in heavy metal concentration, metal enrichment factors (EFs) were calculated. Enrichment in V, Cr, Co, Zn, Ba, and Pb was detected at certain sites, whereas Cu behaved differently. The distribution of Cu enrichment suggests that it may be of natural origin, associated with the lithology of the volcanic continental area. The minor enrichment observed for other elements may be associated with river discharge. According to sediment quality guidelines, trace metal concentrations of Cu, Pb, and Zn present occasional risks to aquatic organisms.

Particle size distribution of typical ceramic raw materials by laser granulometry

NASA Technical Reports Server (NTRS)

Wojnarovitsne, I. H.; Lenkel, M.

1984-01-01

The principles of the method are explained and the working of the CILAS 715 laser granulometer is described. The particle size distributions of milled glazes, quartz, feldspar and china clay were determined by this instrument and by Andreasen sedimentation. The agreement was good for isometric particles, but the china clay appears finer by sedimentation, because the platelets arrange themselves horizontally during sedimentation, while in the laser granulometer preferred orientation is prevented by circulation between the sample holder and the vibrated and stirred reservoir of the slip.

Swash mark and grain flow

USGS Publications Warehouse

Sallenger,, Asbury H.

1981-01-01

Swash marks composed entirely of coarse sand are commonly found on coarse-sand beaches. These swash marks are 10 to 30 centimeters in width and a few millimeters to one centimeter in height. Previous observations, mostly on finer-sand beaches, indicate swash marks are seldom over a few millimeters in height and are commonly composed of material readily floated by surface tension (e.g., mica flakes and shell fragments). Swash marks composed of coarse sand have both fining seaward and fining with depth trends in grain size. Apparently, the leading margin of a wave upwash drives a highly concentrated flow of grains in which both grain size and grain velocity decrease with depth. Therefore, large grains are transported at greater velocities than are smaller grains. Thus, at the maximum advance of an upwash, a swash mark is deposited which has the observed fining seaward and fining with depth trends in grain size.

Grain-scale supercharging and breakdown on airless regoliths

NASA Astrophysics Data System (ADS)

Zimmerman, M. I.; Farrell, W. M.; Hartzell, C. M.; Wang, X.; Horanyi, M.; Hurley, D. M.; Hibbitts, K.

2016-10-01

Interactions of the solar wind and emitted photoelectrons with airless bodies have been studied extensively. However, the details of how charged particles interact with the regolith at the scale of a single grain have remained largely uncharacterized. Recent efforts have focused upon determining total surface charge under photoemission and solar wind bombardment and the associated electric field and potential. In this work, theory and simulations are used to show that grain-grain charge differences can exceed classical sheath predictions by several orders of magnitude, sometimes reaching dielectric breakdown levels. Temperature-dependent electrical conductivity works against supercharging by allowing current to leak through individual grains; the balance between internal conduction and surface charging controls the maximum possible grain-to-grain electric field. Understanding the finer details of regolith grain charging, conductive equilibrium, and dielectric breakdown will improve future numerical studies of space weathering and dust levitation on airless bodies.

Grain-Scale Supercharging and Breakdown on Airless Regoliths

NASA Technical Reports Server (NTRS)

Zimmerman, M. I.; Farrell, W. M.; Hartzell, C.M.; Wang, X.; Horanyi, M.; Hurley, D. M.; Hibbitts, K.

2016-01-01

Interactions of the solar wind and emitted photoelectrons with airless bodies have been studied extensively. However, the details of how charged particles interact with the regolith at the scale of a single grain have remained largely uncharacterized. Recent efforts have focused upon determining total surface charge under photoemission and solar wind bombardment and the associated electric field and potential. In this work, theory and simulations are used to show that grain-grain charge differences can exceed classical sheath predictions by several orders of magnitude, sometimes reaching dielectric breakdown levels. Temperature-dependent electrical conductivity works against supercharging by allowing current to leak through individual grains; the balance between internal conduction and surface charging controls the maximum possible grain-to-grain electric field. Understanding the finer details of regolith grain charging, conductive equilibrium, and dielectric breakdown will improve future numerical studies of space weathering and dust levitation on airless bodies.

Rheology of water and ammonia-water ices

NASA Technical Reports Server (NTRS)

Goldsby, D. L.; Kohlstedt, D. L.; Durham, W. B.

1993-01-01

Creep experiments on fine-grained water and ammonia-water ices have been performed at one atmosphere and high confining pressure in order to develop constitutive relationships necessary to model tectonic processes and interpret surface features of icy moons of the outer solar system. The present series of experiments explores the effects of temperature, strain rate, grain size, and melt fraction on creep strength. In general, creep strength decreases with increasing temperature, decreasing strain rate, and increasing melt fraction. A transition from dislocation creep to diffusion creep occurs at finer grain sizes, higher temperatures, and lower strain rates.

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.

Geochemical and Sedimentological Records of Late Quaternary Climate Change, Lake Tanganyika, Tropical East Africa

NASA Astrophysics Data System (ADS)

Felton, A. A.; Russell, J. M.; Cohen, A. S.; Baker, M. E.; McGlue, M. M.; Lezzar, K. E.

2005-12-01

We have analyzed piston core records from Lake Tanganyika (western Tanzania, East African Rift Valley) to investigate possible signals of tropical paleoclimate change during the Late Quaternary. Long paleoclimate records from East Africa are of importance for understanding climatic processes such as the role of solar variability in regulating tropical climates at Milankovitch time scales, and the relationship between abrupt climate changes, migration of Intertropical Convergence Zone, and regional climate variability (Nicholson, 2000). However, records of pre-Holocene climate variability from tropical African lakes (>25ka) are still quite rare. Long records from Lake Tanganyika are of particular interest given the lake's antiquity and its demonstrated potential for producing high resolution (frequently annually laminated) sedimentary records (Cohen et al., 1993). We analyzed physical properties, grain size, total organic carbon, major, minor and trace element variability, and biogenic silica data for a 7.75 m core from the Kalya slope and horst region of central Lake Tanganyika at 640m water depth. Nine 14C dates provide an age model for the core, which spans ~62 cal kyr. Elemental concentrations preserved in Lake Tanganyika sediments record variability in deposition and runoff into the lake basin. Under conditions of rapid erosion, exposure and rapid weathering of bedrock has been shown to generate high concentrations of original silicate minerals enriched in soluble cations such as sodium and potassium, elements that are also biologically conservative. Prior to 40ka cal yr. core sediments are characterized by high magnetic susceptibility, intermediate levels of organic carbon, low to intermediate levels of biogenic silica, and fine grain size, indicative of relatively high precipitation. There is a profound decrease in magnetic susceptibility, a decrease in organic carbon and an increase in grain size at 40ka cal yr, which persists until ~16ka cal yr. Seismic reflection profiles demonstrate the existence of paleodeltas at ~360m below modern lake level that may have formed during this period, although it is unclear whether this deposit represents a Late Quaternary (OIS 2) or earlier (OIS 6) event. Maximum aridity occurred at about 20-20.5ka cal yr, consist with earlier interpretations of lake lowstands (Gasse et al., 1989, Scholz et al., 1997). The late Pleistocene and earliest Holocene sediments in our record are characterized by generally rising magnetic susceptibility, declining organic carbon and biogenic silica, and finer grain size. However during this period there are marked fluctuations in magnetic susceptibility and biogenic silica at millennial time-scales. These indicate intervals of fluctuating precipitation, productivity, and possibly windiness and are particularly prominent during the Pleistocene-Holocene transition. Massive clays, rising magnetic susceptibility, low biogenic silica and low organic carbon mark the early Holocene, indicative of increased rainfall during a regionally wet interval. These sediments are capped by a laminated ooze, indicative of drier conditions and a more stratified water body.

IRD evidence for Heinrich Events H1 and H2 on the NJ Margin

NASA Astrophysics Data System (ADS)

Christensen, B. A.; Calabrese, J.; O'Neill, C.; Goff, J. A.

2011-12-01

Recent seismic reflection studies suggest icebergs grounded on the late Pleistocene New Jersey margin (Goff and Austin, 2009) during Heinrich events H1 (~17 cal Ka), H2 (~23 cal Ka), H3 (~30 cal Ka) and H4 (~37 cal Ka). We tested this hypothesis by analyzing sediments on the upper NJ continental slope, near the area where icebergs were found. Ocean Drilling Program Site 1073A is located at 39°13.5214'N, 72°16.5461'W in 639 m water depth. The greater water depth increases the likelihood of preservation and improves the stratigraphic control. We obtained elemental measurements for Site 1073A Cores 1-6 using the X-ray Fluorescence (XRF) Core Scanner at the MARUM IODP core repository, University of Bremen. Cores were scanned at 10kV and 30kV to obtain a full suite of elements for analysis, with XRF data collected between 1 and 10 cm intervals. The values are reported in areas for the elements and were then converted to elemental ratios (Ca/Sr, Si/Sr, K/Al, and Si/Ti) for analysis. The origin of a Heinrich layer within an IRD belt can be identified by geochemical measures along with magnetic susceptibility and the presence of detrital materials that reflect its provenance (Hemming, 2004). Following analyses for Atlantic Ocean IRD by Hodell et al. (2008), higher Si/Sr values indicate abundant detrital silicates and low biogenic carbonate. Abundant detrital carbonate is identified by higher Ca/Sr values. K/Al may be used as a proxy for weathered matter being deposited and is a good indicator of terrigenous material (Yarincik, 2000). Si/Ti ratios may be used as a proxy for organic and siliceous productivity (Agnihotri, 2008). The elemental analysis was ground-truthed with grain size analysis at 10 cm intervals. Grain size analysis reveals large particles in a finer matrix at 123 cm and 284 cm. We interpret these as IRD. A linear sedimentation age model places the IRD around the time of Heinrich events H1 and H2. Age control is provided for the late Pleistocene principally by radiocarbon methods (McHugh and Olsson, 2002); however, the age model is not unequivocal so we present results for a few interpretations (linear sedimentation rates, and modeled). Nonetheless, the IRD is consistent with the timing of H1 and H2. While the IRD are obvious from the grain size analysis, we were not able to identify IRD from XRF elemental analyses. This may because the sediments are derived locally rather than transported from the higher latitudes, rendering IRD identification a function of grain size (anomalously large particles in a marine setting) rather than geochemistry. Alternatively, the particles were not close enough to the surface to impact the XRF response. This study provides further evidence for the presence of icebergs on the late Pleistocene NJ margin.

Seismic wave velocity of hydrate-bearing fine-grained sediments sampled from the Ulleung basin in East Sea, Korea

NASA Astrophysics Data System (ADS)

Kim, H.; Kwon, T.; Cho, G.

2012-12-01

Synthesizing gas hydrate in a fine-grained natural seabed sediment sample, mainly composed of silty-to-clayey soils, has been hardly attempted due to the low permeability. It has been known that hydrate loci in pore spaces and heterogeneity of hydrate growth in core-scale play a critical role in determining physical properties of hydrate-bearing sediments. In the presented study, we attempted to identify the effect of hydrate growth morphology on seismic velocities in natural fine-grained sediments sampled from the Ulleung Basin in East Sea. We synthesized CO2 hydrate in clayey silt sediments in an instrumented oedometric cell and measured seismic velocities during hydrate formation and loading processes. Herein, we present the experiment results on P-wave and S-wave velocities of gas hydrate-bearing fine-grained sediments. It is found that the geophysical properties of gas hydrate-bearing sediments are governed by hydrate saturation and effective stress as well as morphological feature of hydrate formation in sediments.

Lasting Impact of a Tsunami Event on Sediment-Organism Interactions in the Ocean

NASA Astrophysics Data System (ADS)

Seike, Koji; Sassa, Shinji; Shirai, Kotaro; Kubota, Kaoru

2018-02-01

Although tsunami sedimentation is a short-term phenomenon, it may control the long-term benthic environment by altering seafloor surface characteristics such as topography and grain-size composition. By analyzing sediment cores, we investigated the long-term effect of the 2011 tsunami generated by the Tohoku Earthquake off the Pacific coast of Japan on sediment mixing (bioturbation) by an important ecosystem engineer, the heart urchin Echinocardium cordatum. Recent tsunami deposits allow accurate estimation of the depth of current bioturbation by E. cordatum, because there are no preexisting burrows in the sediments. The in situ hardness of the substrate decreased significantly with increasing abundance of E. cordatum, suggesting that echinoid bioturbation softens the seafloor sediment. Sediment-core analysis revealed that this echinoid rarely burrows into the coarser-grained (medium-grained to coarse-grained) sandy layer deposited by the 2011 tsunami; thus, the vertical grain-size distribution resulting from tsunami sedimentation controls the depth of E. cordatum bioturbation. As sandy tsunami layers are preserved in the seafloor substrate, their restriction on bioturbation continues for an extended period. The results demonstrate that understanding the effects on seafloor processes of extreme natural events that occur on geological timescales, including tsunami events, is important in revealing continuing interactions between seafloor sediments and marine benthic invertebrates.

What controls the location of sediment cover in bedrock-alluvial channels?

NASA Astrophysics Data System (ADS)

Hodge, R. A.; Hoey, T.

2016-12-01

The extent of sediment cover in a bedrock alluvial channel is a key factor in understanding the processes within these channels, and hence how they evolve over time. However, sediment cover is typically quantified as a single value, with little consideration as to where that sediment is located on the bed. The spatial location of the cover is important because sediment grains typically move between sediment patches, hence sediment transport lengths are controlled by inter-patch distances. Furthermore, the location of sediment cover affects its stability, with patches in deep hollows likely to be more stable that isolated grains on flat bedrock surfaces. We present data that attempts to identify the key factors affecting the location and stability of sediment cover. Field data were collected from rivers with c.10-30% sediment cover. Froude-scaled flume experiments were undertaken using a 3D printed 1:10 scale replica of one of the field sites, Trout Beck. In the flume, we undertook two sets of experiments: 1) spatially-distributed hydraulic measurements at a range of discharges; and 2) pulses of sediment input at a constant discharge, and the subjected to an increasing discharge in order to identify the discharge needed to remove the sediment patches. We found that local topography was an important control on sediment patch location, but that the additional influence of hydraulics means that sediment patches do not just fill the bed from the lowest elevations. The extent to which topography was important also depended on the size of the sediment pulse, with larger sediment pulses being stabilised by grain-grain and grain-flow interactions and less influenced by the bed topography. These results are consistent with field data where the geometry of the patches reflects bed topography.

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.

Dating Saharan dust deposits on Lanzarote (Canary Islands) by luminescence dating techniques and their implication for palaeoclimate reconstruction of NW Africa

NASA Astrophysics Data System (ADS)

von Suchodoletz, H.; Fuchs, M.; ZöLler, L.

2008-02-01

Lava flow dammed valleys (Vegas) on Lanzarote (Canary Islands) represent unique sediment traps, filled with autochthonous volcanic material and allochthonous Saharan dust. These sediments and the intercalated palaeosoil sediments document past environmental change of the last glacial-interglacial cycles, both on Lanzarote and in NW Africa. A reliable chronology must be established to use these sediment archives for palaeoclimate reconstructions. Owing to the lack of organic material and the limiting time range of the 14C-dating method, luminescence dating is the most promising method for these sediments. However, the fluvio-eolian character of these sediments is a major problem for luminescence dating, because these sediments are prone to insufficient resetting of the parent luminescence signal (bleaching) prior to sedimentation. To check for the best age estimates, we compare the bleaching behavior of (1) different grain sizes (coarse- versus fine-grain quartz OSL) and (2) different minerals (fine-grain feldspar IRSL versus fine-grain quartz OSL). The results show that owing to its bleaching characteristics, quartz is the preferable mineral for luminescence dating. On the basis of the fine- and coarse-grain quartz OSL age estimates, a chronostratigraphy up to 100 ka could be established. Beyond this age limit for OSL quartz, the chronostratigraphy could be extended up to 180 ka by correlating the vega sediments with dated marine sediment archives.

Fluidization of host sediments and its impacts on peperites-forming processes, the Cretaceous Buan Volcanics, Korea

NASA Astrophysics Data System (ADS)

Kwon, Chang Woo; Gihm, Yong Sik

2017-07-01

In the Cretaceous Buan Volcanics (SW Korea), blocky and fluidal peperites are developed in a bed of poorly sorted, massive pumiceous lapilli tuff (hot sediments) as a result of the vertical to subvertical intrusion of the trachyandesitic dikes into the bed. Blocky peperites are composed of polyhedral or platy juvenile clasts with a jigsaw-crack texture. Fluidal peperites are characterized by fluidal or globular juvenile clasts with irregular or ragged margins. The blocky peperites are ubiquitous in the host sediments, whereas the fluidal peperites only occur in fine-grained zone (well sorted fine to very fine ash) that are aligned parallel to the dike margin. The development of the fine-grained zone within the poorly sorted host sediments is interpreted to form by grain size segregation caused by upward moving pore water (fluidization) that has resulted from heat transfer from intruding magma toward the waterlogged host sediments during intrusion. With the release of pore water and the selective entrainment of fine-grained ash, the fine-grained zone formed within the host sediments. Subsequent interactions between the fine-grained zone and the intruding magma resulted in ductile deformation of the magma, which generated fluidal peperites. Outside the fine-grained zone, because of the relative deficiency of both pore water and fine-grained ash, intruding magma fragmented in a brittle manner, resulting in the formation of blocky peperites. The results of this study suggest that redistribution of constituent particles (ash) and interstitial fluids during fluidization resulted in heterogeneous physical conditions of the host sediments, which influenced peperite-forming processes.

Effects of sediment supply on surface textures of gravel-bed rivers

Treesearch

John M. Buffington; David R. Montgomery

1999-01-01

Using previously published data from flume studies, we test a new approach for quantifying the effects of sediment supply (i.e., bed material supply) on surface grain size of equilibrium gravel channels. Textural response to sediment supply is evaluated relative to a theoretical prediction of competent median grain size (D’50). We find that surface median grain size (...

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.

Effects of sediment supply on surface textures of gravel‐bed rivers

USGS Publications Warehouse

Buffington, John M.; Montgomery, David R.

1999-01-01

Using previously published data from flume studies, we test a new approach for quantifying the effects of sediment supply (i.e., bed material supply) on surface grain size of equilibrium gravel channels. Textural response to sediment supply is evaluated relative to a theoretical prediction of competent median grain size (D50′). We find that surface median grain size (D50) varies inversely with sediment supply rate and systematically approaches the competent value (D50′) at low equilibrium transport rates. Furthermore, equilibrium transport rate is a power function of the difference between applied and critical shear stresses and is therefore a power function of the difference between competent and observed median grain sizes (D50′ and D50). Consequently, we propose that the difference between predicted and observed median grain sizes can be used to determine sediment supply rate in equilibrium channels. Our analysis framework collapses data from different studies toward a single relationship between sediment supply rate and surface grain size. While the approach appears promising, we caution that it has been tested only on a limited set of laboratory data and a narrow range of channel conditions.

Impact of pore-water freshening on clays and the compressibility of hydrate-bearing reservoirs during production

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

Jang, Junbong; Cao, Shuang; Waite, William

Gas production efficiency from natural hydrate-bearing sediments depends in part on geotechnical properties of fine-grained materials, which are ubiquitous even in sandy hydrate-bearing sediments. The responses of fine-grained material to pore fluid chemistry changes due to freshening during hydrate dissociation could alter critical sediment characteristics during gas production activities. We investigate the electrical sensitivity of fine grains to pore fluid freshening and the implications of freshening on sediment compression and recompression parameters.

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...

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

The effects of surface finish and grain size on the strength of sintered silicon carbide

NASA Technical Reports Server (NTRS)

You, Y. H.; Kim, Y. W.; Lee, J. G.; Kim, C. H.

1985-01-01

The effects of surface treatment and microstructure, especially abnormal grain growth, on the strength of sintered SiC were studied. The surfaces of sintered SiC were treated with 400, 800 and 1200 grit diamond wheels. Grain growth was induced by increasing the sintering times at 2050 C. The beta to alpha transformation occurred during the sintering of beta-phase starting materials and was often accompanied by abnormal grain growth. The overall strength distributions were established using Weibull statistics. The strength of the sintered SiC is limited by extrinsic surface flaws in normal-sintered specimens. The finer the surface finish and grain size, the higher the strength. But the strength of abnormal sintering specimens is limited by the abnormally grown large tabular grains. The Weibull modulus increases with decreasing grain size and decreasing grit size for grinding.

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.

Where Light Meets Dark

NASA Technical Reports Server (NTRS)

2004-01-01

[figure removed for brevity, see original site] Figure 1 (close-up)

This panoramic camera image of the soil target whimsically called 'Neopolitan' from the Mars Exploration Rover Opportunity's 'Eagle Crater' soil survey highlights the border between two different soil types - a lighter, finer-grained unit to the left and a darker, coarser-grained to the right. Scientists are pondering the unusually distinct border between these different soil types. To the lower left and partially hidden by the shadow of the mast is an airbag bounce mark.

Controls on alluvial fan long-profiles

USGS Publications Warehouse

Stock, J.D.; Schmidt, K.M.; Miller, D.M.

2008-01-01

Water and debris flows exiting confined valleys have a tendency to deposit sediment on steep fans. On alluvial fans where water transport of gravel predominates, channel slopes tend to decrease downfan from ???0.10-0.04 to ???0.01 across wide ranges of climate and tectonism. Some have argued that this pattern reflects grain-size fining downfan such that higher threshold slopes are required just to entrain coarser particles in the waters of the upper fan, whereas lower slopes are required to entrain finer grains downfan (threshold hypothesis). An older hypothesis is that slope is adjusted to transport the supplied sediment load, which decreases downfan as deposition occurs (transport hypothesis). We have begun to test these hypotheses for alluvial fan long-profiles using detailed hydraulic and particle-size data in sediment transport models. On four alluvial fans in the western U.S., we find that channel hydraulic radiiare largely 0.5-0.9 m at fan heads, decreasing to 0.1-0.2 m at distal margins. We find that median gravel diameter does not change systematically along the upper 60%-80% of active fan channels as slope declines, so downstream gravel fining cannot explain most of the observed channel slope reduction. However, as slope declines, channel-bed sand cover increases systematically downfan from areal fractions of <20% above fan heads to distal fan values in excess of 70%. As a result, entrainment thresholds for bed material might decrease systematically downfan, leading to lower slopes. However, current models of this effect alone tend to underpredict downfan slope changes. This is likely due to off-channel gravel deposition. Calculations that match observed fan long-profiles require an exponential decline in gravel transport rate, so that on some fans approximately half of the load must be deposited off channel every -0.20-1.4 km downfan. This leads us to hypothesize that some alluvial fan long-proffies are statements about the rate of overbank deposition of coarse particles downfan, a process for which there is currently no mechanistic theory. ?? 2007 Geological Society of America.

Petrography, mineralogy, and geochemistry of deep gravelly sands in the Eyreville B core, Chesapeake Bay impact structure

USGS Publications Warehouse

Bartosova, Katerina; Gier, Susanne; Horton, J. Wright; Koeberl, Christian; Mader, Dieter; Dypvik, Henning

2010-01-01

The ICDP–USGS Eyreville drill cores in the Chesapeake Bay impact structure reached a total depth of 1766 m and comprise (from the bottom upwards) basement-derived schists and granites/pegmatites, impact breccias, mostly poorly lithified gravelly sand and crystalline blocks, a granitic slab, sedimentary breccias, and postimpact sediments. The gravelly sand and crystalline block section forms an approximately 26 m thick interval that includes an amphibolite block and boulders of cataclastic gneiss and suevite. Three gravelly sands (basal, middle, and upper) are distinguished within this interval. The gravelly sands are poorly sorted, clast supported, and generally massive, but crude size-sorting and subtle, discontinuous layers occur locally. Quartz and K-feldspar are the main sand-size minerals and smectite and kaolinite are the principal clay minerals. Other mineral grains occur only in accessory amounts and lithic clasts are sparse (only a few vol%). The gravelly sands are silica rich (~80 wt% SiO2). Trends with depth include a slight decrease in SiO2 and slight increase in Fe2O3. The basal gravelly sand (below the cataclasite boulder) has a lower SiO2 content, less K-feldspar, and more mica than the higher sands, and it contains more lithic clasts and melt particles that are probably reworked from the underlying suevite. The middle gravelly sand (below the amphibolite block) is finer-grained, contains more abundant clay minerals, and displays more variable chemical compositions than upper gravelly sand (above the block). Our mineralogical and geochemical results suggest that the gravelly sands are avalanche deposits derived probably from the nonmarine Potomac Formation in the lower part of the target sediment layer, in contrast to polymict diamictons higher in the core that have been interpreted as ocean-resurge debris flows, which is in agreement with previous interpretations. The mineralogy and geochemistry of the gravelly sands are typical for a passive continental margin source. There is no discernible mixing with marine sediments (no glauconite or Paleogene marine microfossils noted) during the impact remobilization and redeposition. The unshocked amphibolite block and cataclasite boulder might have originated from the outer parts of the transient crater.

Clear as Mud: Changes in Paleoshelf Environments and Deposition Rates at Medford, New Jersey during the Paleocene-Eocene Thermal Maximum

NASA Astrophysics Data System (ADS)

Podrecca, L.; Miller, K. G.; Wright, J. D.; Browning, J. V.; Emge, T.

2017-12-01

The Paleocene-Eocene boundary marks a time of swift global climatic change. Constraining the timeframe of this event is a first order question necessary for ascertaining the origin of the event and the potential for its use as an analog for modern climate change. The New Jersey shelf sediments of the Marlboro Formation records this time period with exceptionally thick (5-15m) records of the period of global low carbon isotopic values ("the core") which requires minimum sedimentation rates of 10's cm/kyr. Rhythmic layers have been previously reported from Wilson Lake & Millville, NJ (IODP Leg 174AX). These structures coined "laminae couplets" consist of semi-periodic 1-2mm thick raised laminations separated by matrix of varying width (averaging 1.8cm). These have been dismissed as artifacts of drilling "biscuits". We report here on a series of shallow auger cores drilled on a transect at Medford, NJ, without using drilling fluid. These cores also show a similar set of structures on the 2cm scale verifying that they are primary depositional features. The mm width laminae in the auger core show remarkable swelling within minutes of splitting. XRD, XRF, bulk carbonate geochemistry, and grain size analysis have been determined at regular depth intervals throughout the core. We have analyzed differences in these parameters between the laminae and interbedded matrix material, as well as across the transect as a whole. In general, the Marlboro formation at this updip location consists of micaceous, lignitic, very clayey silt (mean size 6 micrometers) with occasional organic debris indicating proximal deposition from a fluvial system. Paleodepth of 40m and normal marine salinities are estimated using a paleoslope model and the presence of common though not abundant planktonic foraminifera. We discuss a model of deposition for the Marlboro Formation as fluid mud (nearbed suspension flows) associated with the "Appalachian Amazon" alluding toward the finer grained inter-laminae representing settling events. These may be either hemipelagics associated with episodic flood events or seasonal periods of in-river sediment discharge and the benthic salinity front.

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.

Discrimination of fine-grained sediment provenance using geochemical elements on the inner shelf of the Korean Strait (South Sea), Korea

NASA Astrophysics Data System (ADS)

Um, I. K.; Choi, M. S.

2017-12-01

The central South Sea mud (CSSM) is located between the Heuksan mud belt (HMB) in the Yellow Sea and Korea Strait shelf mud (KSSM) in the East Sea and developed along the eastward transport pathway in the South Sea. Major elements (Al, Fe, Mg, and Ti), trace elements (Li, Cs, Sc, and Rb), and rare earth elements (REEs) in the fine-grained sediments (<15 μm) of thirty-two surface sediment samples on the CSSM were analyzed to determine the fine-grained sediment provenance. The spatial distribution of the analyzed elements showed a clear separation of the western (W-CSSM) and eastern (E-CSSM) regions of the CSSM. Concentrations of Fe, Ti, Mg, Sc, and REEs were higher in the W-CSSM, whereas concentrations of Al, Cs, Li, and Rb were higher in the E-CSSM. The ratios of trace metals ((Cs+Sc)/Li and Rb/Li) can be successfully used as a provenance indicator in the study area but REEs compositions 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

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.

[Spatial change of the grain-size of aeolian sediments in Qira oasis-desert ecotone, Northwest China].

PubMed

Lin, Yong Chong; Xu, Li Shuai

2017-04-18

In order to understand the environmental influence of oasis-desert ecotone to oasis ecological system, we comparatively analyzed the grain size characteristics of various aeolian sediments, including the sediments in oasis-desert ecotone, shelterbelt and the inside oasis and in Qira River valley. The results showed that the grain size characteristics (including grain-size distribution curve, grain size parameters, and content of different size classes) of sediments in the oasis-desert ecotone were consistent along the prevailing wind direction with a grain-size range of 0.3-200 μm and modal size of 67 μm. All of the sediments were good sorting and mainly composed of suspension components and saltation components, but not denatured saltation and creeping components (>200 μm). They were typically aeolian deposits being short-range transported. The grain sizes of sediments in oasis-desert ecotone were smaller than that in the material sources of Qira River valley and desert (0.3-800 μm), but very similar to those of the modern aeolian deposits in oasis-desert ecotone, shelterbelt and the inside oasis. The denatured saltation and creep components (>200 μm) were suppressed to transport into oasis-desert ecotone because of the high vegetation cover in oasis-desert ecotone. Therefore, like the shelterbelts, the oasis-desert ecotone could also block the invasion of desert. They safeguarded the oasis ecological environment together.

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.

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.

Origin and depositional environment of fine-grained sediments since the last glacial maximum in the southeastern Yellow Sea: evidence from rare earth elements

NASA Astrophysics Data System (ADS)

Um, In Kwon; Choi, Man Sik; Lee, Gwang Soo; Chang, Tae Soo

2015-12-01

Despite the well-reconstructed seismic stratigraphy of the Holocene mud deposit in the southeastern Yellow Sea, known as the Heuksan mud belt (HMB), the provenances of these sediments and their depositional environments are unclear, especially for the fine-grained sediments. According to seismic data (extracted from another article in this special issue), the HMB comprises several sedimentary units deposited since the last glacial maximum. Based on analytical results on rare earth elements, fine-grained sediments in all sedimentary units can be interpreted as mixtures of sediments discharged from Chinese and Korean rivers. The proportions of fine-grained sediments from Chinese rivers (74.5 to 80.0%) were constant and higher than those from Korean rivers in all units. This fact demonstrates that all units have the same fine-grained sediment provenance: units III-b and III-a, located in the middle and northern parts of the HMB and directly deposited from Chinese rivers during the sea-level lowstand, could be the sediment source for units II-b and II-a. Unit I, while ambiguous, is of mixed origin combining reworked sediments from nearby mud deposits and Changjiang River-borne material with those of the Keum River. The results of this study indicate that at least 18.6% of bulk sediments in the HMB clearly originate from Chinese rivers, despite its location close to the southwestern coast of Korea.

Sediment supply as a driver of river evolution in the Amazon Basin

NASA Astrophysics Data System (ADS)

Ahmed, Joshua; Constantine, José Antonio; Dunne, Thomas; Legleiter, Carl; Lazarus, Eli D.

2015-04-01

The Amazon represents the only large river basin in the world where there is a sufficient range of sediment supplies and a lack of engineering controls to assess how sediment supply drives the evolution of meandering rivers. Despite recent analytical advances (Asahi et al., 2013; Pittaluga and Seminara, 2011), modern theory does not yet identify or explain the effects of externally imposed sediment supplies, a fundamental river characteristic, on meandering river evolution. These sediment supplies would be radically reduced by the construction of large dams proposed for the Amazon Basin (Finer and Jenkins, 2012). Here, we demonstrate that the sediment loads imposed by their respective drainage basins determine planform changes in lowland rivers across the Amazon. Our analysis, based on Landsat image sequences, indicates that rivers with high sediment loads draining the Andes and associated foreland basin experience annual migration rates that are on average four times faster than rivers with lower sediment loads draining the Central Amazon Trough and shields. Incidents of meander cutoff also occur more frequently along the rivers of the Andes and foreland basin, where the number of oxbows in the floodplains is more than twice that observed in the floodplains of the Central Amazon Trough and shields. Our results, which cannot be explained by differences in channel slope or hydrology, highlight the importance of sediment supply in modulating the ability of meandering alluvial rivers to reshape the floodplain environment through river migration. Asahi, K., Shimizu, Y., Nelson, J., Parker, G., 2013. Numerical simulation of river meandering with self-evolving banks. Journal of Geophysical Research: Earth Surface, 118(4), 2013JF002752. Finer, M., Jenkins, C.N., 2012. Proliferation of hydroelectric dams in the Andean Amazon and implications for Andes-Amazon connectivity. PLOS One, 7(4), e35126. Pittaluga, M.B., Seminara, G., 2011. Nonlinearity and unsteadiness in river meandering: a review of progress in theory and modelling. Earth Surface Processes and Landforms, 36(1), 20-38.

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.

A Cognitive Diagnosis Model for Continuous Response

ERIC Educational Resources Information Center

Minchen, Nathan D.; de la Torre, Jimmy; Liu, Ying

2017-01-01

Nondichotomous response models have been of greater interest in recent years due to the increasing use of different scoring methods and various performance measures. As an important alternative to dichotomous scoring, the use of continuous response formats has been found in the literature. To assess finer-grained skills or attributes and to…

Modeling Diagnostic Assessments with Bayesian Networks

ERIC Educational Resources Information Center

Almond, Russell G.; DiBello, Louis V.; Moulder, Brad; Zapata-Rivera, Juan-Diego

2007-01-01

This paper defines Bayesian network models and examines their applications to IRT-based cognitive diagnostic modeling. These models are especially suited to building inference engines designed to be synchronous with the finer grained student models that arise in skills diagnostic assessment. Aspects of the theory and use of Bayesian network models…

Relationships between Student Cognitions and Their Effects on Study Strategies

ERIC Educational Resources Information Center

Ferla, Johan; Valcke, Martin; Schuyten, Gilberte

2008-01-01

Using Vermunt's model [Vermunt, J. D. (1998). "The regulation of constructive learning processes". "British Journal of Educational Psychology", 68, 149-171] of self-regulated learning as a conceptual framework, this study aims to contribute to the development of finer grained models of higher education students' learning by (1) investigating…

Stratigraphy and depositional sequences of the US Atlantic shelf and slope

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

Poag, C.W.; Valentine, P.C.

1985-01-01

Litho-, bio-, and seismostratigraphic analyses of Georges Bank basin, Baltimore Canyon trough, and Blake Plateau basin reveal common aspects of stratigraphic framework and depositional history. Synrift graben-fill is inferred to be chiefly coarse terrigenous siliciclastics of Triassic-Early Jurassic age, as thick as 5 km. Following widespread erosion, restricted marine carbonates and evaporites formed initial post-rift deposits during an Early-Middle Jurassic transition to sea floor spreading. As sea floor spreading proceeded, shallow-water limestones and shelf-edge reefs built up, culminating in a discontinuous, margin-rimming reefal bank during the Late Jurassic-Early Cretaceous. During the Early Cretaceous, thick siliciclastics buried the shelf-edge barrier northmore » of Cape Hatteras, whereas shallow-water carbonates persisted in the Blake Plateau basin. Late Cretaceous deposits became increasingly finer-grained as they accumulated beneath a deepening shelf-sea; maximum thickness is more than 2 km. Cretaceous deposition was terminated by marginwide erosion and followed by widespread carbonate deposition in the Paleogene. Neogene and Quaternary deposition was chiefly siliciclastic, characterized by deltaic progradation. Cenozoic sediment thickness reaches 2 km in the Baltimore Canyon trough.« less

Are grain packing and flow turbulence the keys to predicting bedload transport in steep streams? (Invited)

NASA Astrophysics Data System (ADS)

Yager, E.; Monsalve Sepulveda, A.; Smith, H. J.; Badoux, A.

2013-12-01

Bedload transport rates in steep mountain channels are often over-predicted by orders of magnitude, which has been attributed to a range of processes from grain jamming, roughness drag, changes in fluid turbulence and a limited upstream sediment supply. We hypothesize that such poor predictions occur in part because the grain-scale mechanics (turbulence, particle arrangements) of sediment transport are not well understood or incorporated into simplified reach-averaged calculations. To better quantify how turbulence impacts sediment movement, we measured detailed flow velocities and forces at the onset of motion of a single test grain with a fixed pocket geometry in laboratory flume experiments. Of all measured parameters (e.g. flow velocity, shear stress), the local fluid drag force had the highest statistical correlation with grain motion. Use of flow velocity or shear stress to estimate sediment transport may therefore result in erroneous predictions given their relatively low correlation to the onset of sediment motion. To further understand the role of grain arrangement on bedload transport, we measured in situ grain resisting forces to motion (using a force sensor) for a range of grain sizes and patch classes in the Erlenbach torrent, Switzerland (10% gradient). Such forces varied by over two orders of magnitude for a given grain weight and were statistically greater than those calculated using empirical equations for the friction angle. In addition, when normalized by the grain weight, the resisting forces declined with higher grain protrusion above the surrounding bed sediment. Therefore, resisting forces from grain packing and interlocking are substantial and depend on the amount of grain burial. The onset of motion may be considerably under-estimated when calculated solely from measured grain sizes and friction angles. These packing forces may partly explain why critical Shields stresses are higher in steep channels. Such flow and grain parameters also spatially vary in steep streams because of boulder steps and patches of different grain size distributions. To determine if this spatial variation is important for bedload transport, we incorporated probability density functions of flow turbulence and patch grain size distributions into a simple bedload transport equation. Predicted bedload fluxes were significantly improved when distributions of these parameters, rather than single reach-averaged values, were used.

Can glacial shearing of sediment reset the signal used for luminescence dating?

NASA Astrophysics Data System (ADS)

Bateman, Mark D.; Swift, Darrel A.; Piotrowski, Jan A.; Rhodes, Edward J.; Damsgaard, Anders

2018-04-01

Understanding the geomorphology left by waxing and waning of former glaciers and ice sheets during the late Quaternary has been the focus of much research. This has been hampered by the difficulty in dating such features. Luminescence has the potential to be applied to glacial sediments but requires signal resetting prior to burial in order to provide accurate ages. This paper explores the possibility that, rather than relying on light to reset the luminescence signal, glacial processes underneath ice might cause resetting. Experiments were conducted on a ring-shear machine set up to replicate subglacial conditions and simulate the shearing that can occur within subglacial sediments. Luminescence measurement at the single grain level indicates that a number (albeit small) of zero-dosed grains were produced and that these increased in abundance with distance travelled within the shearing zone. Observed changes in grain shape characteristics with increasing shear distance indicate the presence of localised high pressure grain-to-grain stresses caused by grain bridges. This appears to explain why some grains became zeroed whilst others retained their palaeodose. Based on the observed experimental trend, it is thought that localised grain stress is a viable luminescence resetting mechanism. As such relatively short shearing distances might be sufficient to reset a small proportion of the luminescence signal within subglacial sediments. Dating of previously avoided subglacial sediments may therefore be possible.

Predictive modelling of grain-size distributions from marine electromagnetic profiling data using end-member analysis and a radial basis function network

NASA Astrophysics Data System (ADS)

Baasch, B.; Müller, H.; von Dobeneck, T.

2018-07-01

In this work, we present a new methodology to predict grain-size distributions from geophysical data. Specifically, electric conductivity and magnetic susceptibility of seafloor sediments recovered from electromagnetic profiling data are used to predict grain-size distributions along shelf-wide survey lines. Field data from the NW Iberian shelf are investigated and reveal a strong relation between the electromagnetic properties and grain-size distribution. The here presented workflow combines unsupervised and supervised machine-learning techniques. Non-negative matrix factorization is used to determine grain-size end-members from sediment surface samples. Four end-members were found, which well represent the variety of sediments in the study area. A radial basis function network modified for prediction of compositional data is then used to estimate the abundances of these end-members from the electromagnetic properties. The end-members together with their predicted abundances are finally back transformed to grain-size distributions. A minimum spatial variation constraint is implemented in the training of the network to avoid overfitting and to respect the spatial distribution of sediment patterns. The predicted models are tested via leave-one-out cross-validation revealing high prediction accuracy with coefficients of determination (R2) between 0.76 and 0.89. The predicted grain-size distributions represent the well-known sediment facies and patterns on the NW Iberian shelf and provide new insights into their distribution, transition and dynamics. This study suggests that electromagnetic benthic profiling in combination with machine learning techniques is a powerful tool to estimate grain-size distribution of marine sediments.

Predictive modelling of grain size distributions from marine electromagnetic profiling data using end-member analysis and a radial basis function network

NASA Astrophysics Data System (ADS)

Baasch, B.; M"uller, H.; von Dobeneck, T.

2018-04-01

In this work we present a new methodology to predict grain-size distributions from geophysical data. Specifically, electric conductivity and magnetic susceptibility of seafloor sediments recovered from electromagnetic profiling data are used to predict grain-size distributions along shelf-wide survey lines. Field data from the NW Iberian shelf are investigated and reveal a strong relation between the electromagnetic properties and grain-size distribution. The here presented workflow combines unsupervised and supervised machine learning techniques. Nonnegative matrix factorisation is used to determine grain-size end-members from sediment surface samples. Four end-members were found which well represent the variety of sediments in the study area. A radial-basis function network modified for prediction of compositional data is then used to estimate the abundances of these end-members from the electromagnetic properties. The end-members together with their predicted abundances are finally back transformed to grain-size distributions. A minimum spatial variation constraint is implemented in the training of the network to avoid overfitting and to respect the spatial distribution of sediment patterns. The predicted models are tested via leave-one-out cross-validation revealing high prediction accuracy with coefficients of determination (R2) between 0.76 and 0.89. The predicted grain-size distributions represent the well-known sediment facies and patterns on the NW Iberian shelf and provide new insights into their distribution, transition and dynamics. This study suggests that electromagnetic benthic profiling in combination with machine learning techniques is a powerful tool to estimate grain-size distribution of marine sediments.

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.

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.

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.

Inverse modelling of fluvial sediment connectivity identifies characteristics and spatial distribution of sediment sources in a large river network.

NASA Astrophysics Data System (ADS)

Schmitt, R. J. P.; Bizzi, S.; Kondolf, G. M.; Rubin, Z.; Castelletti, A.

2016-12-01

Field and laboratory evidence indicates that the spatial distribution of transport in both alluvial and bedrock rivers is an adaptation to sediment supply. Sediment supply, in turn, depends on spatial distribution and properties (e.g., grain sizes and supply rates) of individual sediment sources. Analyzing the distribution of transport capacity in a river network could hence clarify the spatial distribution and properties of sediment sources. Yet, challenges include a) identifying magnitude and spatial distribution of transport capacity for each of multiple grain sizes being simultaneously transported, and b) estimating source grain sizes and supply rates, both at network scales. Herein, we approach the problem of identifying the spatial distribution of sediment sources and the resulting network sediment fluxes in a major, poorly monitored tributary (80,000 km2) of the Mekong. Therefore, we apply the CASCADE modeling framework (Schmitt et al. (2016)). CASCADE calculates transport capacities and sediment fluxes for multiple grainsizes on the network scale based on remotely-sensed morphology and modelled hydrology. CASCADE is run in an inverse Monte Carlo approach for 7500 random initializations of source grain sizes. In all runs, supply of each source is inferred from the minimum downstream transport capacity for the source grain size. Results for each realization are compared to sparse available sedimentary records. Only 1 % of initializations reproduced the sedimentary record. Results for these realizations revealed a spatial pattern in source supply rates, grain sizes, and network sediment fluxes that correlated well with map-derived patterns in lithology and river-morphology. Hence, we propose that observable river hydro-morphology contains information on upstream source properties that can be back-calculated using an inverse modeling approach. Such an approach could be coupled to more detailed models of hillslope processes in future to derive integrated models of hillslope production and fluvial transport processes, which is particularly useful to identify sediment provenance in poorly monitored river basins.

Microplastics in the Mediterranean Sea: Deposition in coastal shallow sediments, spatial variation and preferential grain size.

PubMed

Alomar, Carme; Estarellas, Fernando; Deudero, Salud

2016-04-01

Marine litter loads in sea compartments are an emergent issue due to their ecological and biological consequences. This study addresses microplastic quantification and morphological description to test spatial differences along an anthropogenic gradient of coastal shallow sediments and further on to evaluate the preferential deposition of microplastics in a given sediment grain fraction. Sediments from Marine Protected Areas (MPAs) contained the highest concentrations of microplastics (MPs): up to 0.90 ± 0.10 MPs/g suggesting the transfer of microplastics from source areas to endpoint areas. In addition, a high proportion of microplastic filaments were found close to populated areas whereas fragment type microplastics were more common in MPAs. There was no clear trend between sediment grain size and microplastic deposition in sediments, although microplastics were always present in two grain size fractions: 2 mm > x > 1 mm and 1 mm > x 0.5 mm. Copyright © 2016 Elsevier Ltd. All rights reserved.

Signal or noise? Separating grain size-dependent Nd isotope variability from provenance shifts in Indus delta sediments, Pakistan

NASA Astrophysics Data System (ADS)

Jonell, T. N.; Li, Y.; Blusztajn, J.; Giosan, L.; Clift, P. D.

2017-12-01

Rare earth element (REE) radioisotope systems, such as neodymium (Nd), have been traditionally used as powerful tracers of source provenance, chemical weathering intensity, and sedimentary processes over geologic timescales. More recently, the effects of physical fractionation (hydraulic sorting) of sediments during transport have called into question the utility of Nd isotopes as a provenance tool. Is source terrane Nd provenance resolvable if sediment transport strongly induces noise? Can grain-size sorting effects be quantified? This study works to address such questions by utilizing grain size analysis, trace element geochemistry, and Nd isotope geochemistry of bulk and grain-size fractions (<63μm, 63-125 μm, 125-250 μm) from the Indus delta of Pakistan. Here we evaluate how grain size effects drive Nd isotope variability and further resolve the total uncertainties associated with Nd isotope compositions of bulk sediments. Results from the Indus delta indicate bulk sediment ɛNd compositions are most similar to the <63 µm fraction as a result of strong mineralogical control on bulk compositions by silt- to clay-sized monazite and/or allanite. Replicate analyses determine that the best reproducibility (± 0.15 ɛNd points) is observed in the 125-250 µm fraction. The bulk and finest fractions display the worst reproducibility (±0.3 ɛNd points). Standard deviations (2σ) indicate that bulk sediment uncertainties are no more than ±1.0 ɛNd points. This argues that excursions of ≥1.0 ɛNd points in any bulk Indus delta sediments must in part reflect an external shift in provenance irrespective of sample composition, grain size, and grain size distribution. Sample standard deviations (2s) estimate that any terrigenous bulk sediment composition should vary no greater than ±1.1 ɛNd points if provenance remains constant. Findings from this study indicate that although there are grain-size dependent Nd isotope effects, they are minimal in the Indus delta such that resolvable provenance-driven trends can be identified in bulk sediment ɛNd compositions over the last 20 k.y., and that overall provenance trends remain consistent with previous findings.

Marine sedimentary provenance evidence for massive discharges of icebergs from the Aurora and Wilkes sub-glacial basins

NASA Astrophysics Data System (ADS)

Pierce, E. L.; Williams, T.; van de Flierdt, T.; Hemming, S. R.; Brachfeld, S. A.; Goldstein, S. L.

2010-12-01

Understanding the evolution of the East Antarctic Ice Sheet (EAIS) is a fundamental goal in the field of paleoclimate today. Given the current and projected state of global warming, it is important to know how an ice sheet that holds over 50 m of sea-level has behaved under warmer conditions in the past. Despite the fact that over 98% of the East Antarctica continent is covered by thick (2.1 km on average) ice, the chronological characterization of glaciogenic detrital hornblende grains has been proven an excellent provenance tool in the investigation of the source areas for ice rafted detritus around Antarctica (Roy et al., 2007, Chem. Geo.). A circum-Antarctica core-top survey of Ar-Ar ages in hornblende grains demonstrates that East Antarctica can be simply divided into several sectors that correspond to modern ice divides and published geochronological evidence from sparse outcrops around the margins of the continent. Williams et al., (2010, EPSL) found evidence in ice rafted detritus layers in ODP Site 1165 from the Wilde drift off Prydz Bay for large discharges of icebergs from the Adélie and Wilkes Land coasts occurring during the late Miocene and early Pliocene. Sourcing from the Adélie and Wilkes Land coasts requires iceberg transport more than 1500 km around the Antarctic perimeter, and this is therefore evidence for massive discharges of icebergs from these sectors. In the Aurora and Wilkes Basins in these sectors, the ice sheet is grounded well below sea level, and is therefore thought to be potentially unstable under warmer conditions. Such long distant transport of sediments with distinctive sources is reminiscent of Heinrich Events in the North Atlantic. A model often invoked as the cause of these events is the collapse and retreat of ice-streams, which leads to massive discharges of icebergs, laden with sediment, into the ocean. The importance of this interpretation, if true, has led us to make more detailed studies of Quaternary sediments from the Adélie and Wilkes Land coasts as well as glaciogenic sediments throughout the Cenozoic in Prydz Bay. We will present Ar-Ar ages of detrital hornblende and biotite grains (>150 µm), as well as epsilon-Nd values measured on the terrigenous fine fraction (<63 µm), from 9 marine sediment cores along the Adélie and Wilkes Land coasts of East Antarctica (95° to 165°E), and compare them and proximal Prydz Bay data with IRD layers in ODP Site 1165. We have also compared the Ar-Ar biotite age populations from the same IRD layers in ODP site 1165 that Williams et al., (2010, EPSL) examined to explore the use of Ar-Ar biotite ages as a tracer of IRD; given the high K content in biotite, it may be possible to use the 63-150 µm fraction for provenance studies which may be particularly useful for tracing sources of IRD into the Southern Ocean where IRD abundances are low and thus grain sizes tend to be finer. The combined application of these tracers will allow interpretation of the average crust formation age of the sources, as well as provide information on major tectonothermal pulses and cooling through approximately 300°C.

Petrology and provenance of Upper Cretaceous Sandstone, southern San Rafael Mountains, Santa Barbara County, California

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

Toyne, C.D.

1987-05-01

Petrologic analysis of 24 medium to coarse-grained sandstone samples, collected from a 2950-m submarine fan complex of late Campanian-early Maestrichtian age exposed within Mono Creek Canyon, reveal commonly calcite cemented, poorly sorted, subangular biotic arkoses. Framework averages 86.0%. Matrix - primarily detrital quartz, feldspar, and lithic fragments finer than 0.03 mm and mechanically and chemically altered phyllosilicates and labile aphanites - averages 8.9%. Calcite cement averages 4.2%. Porosity averages 0.9%. Gazzi-Dickinson point counts of 400 framework grains per slide yield modal averages of Q/sub 37.7/ F/sub 49.8/ L/sub 12.5/; Qm/sub 27.4/ F/sub 49.8/ Lt/sub 22.8/; Qm/sub 35.6/ P/sub 43.7/ K/submore » 20.7/; and Qp/sub 49.4/ Lv/sub 22.1/ Ls/sub 28.5/. P/F averages 0.68, Lv/L averages 0.45, Qp/Q averages 0.27, and detrital phyllosilicate, predominantly biotite, averages 5.7% of total framework. Neither primary nor secondary parameters vary systematically with stratigraphic position. Miscellaneous constituents average 1.3% of framework and include epidote, garnet, amphibole, pyroxene, zircon, and tourmaline as well as carbonaceous blebs, opaque minerals, and unidentifiable lithic fragments. Separate analysis of 100 medium sized quartz grains per slide indicates a mean population of 63.0% non-undulatory monocrystalline quartz, 9.1% undulatory monocrystalline quartz, 10.1% polycrystalline quartz of 2 to 3 crystals, and 17.9% polycrystalline quartz composed of more than 3 crystals. Modal data, plotted upon provenance discrimination diagrams, indicate a plutonic provenance transitional between a dissected magmatic arc and uplifted basement terrane. Paleocurrent data, neglecting possible clockwise rotation, indicate sediment transport from the north.« less

Vegetation and climate history during the last millennium derived from Anggertu Lake, Tengger Desert

NASA Astrophysics Data System (ADS)

Duan, F.; An, C.; Zhao, Y.; Wang, W.; Cao, Z.

2017-12-01

Studying the climate changes during the last millennium can help us to understand current relationship between human-social activities and natural environment changes, and improve projections of future climate. Pollen assemblages, loss-on-ignition (LOIorg at 550 °C) and grain size data collected from sediment core (AGE15A) from the center of Anggertu lake (eastern Tengger Desert, Inner Mongolia) are presented to reconstruct regional vegetation and climate history during the last millennium. Results show that: 1) desert or desert steppe dominated by Artemisia and Amaranthaceae expanded around this region during the period of 988 1437 A.D., indicating a generally dry climate condition with two short humid periods (1003 1082 A.D. and 1388 1437 A.D). These two wet periods are characterized by relatively high vegetation cover and bio-productivity, reflected by high pollen concentrations and LOIorg. Increase in the steppe or meadow vegetation communities (Poaceae, Cyperaceae) and vegetation cover during the period of 1437 2015 A.D. suggest a wetting trend, as also indicated by gradually finer grain size. The relatively high LOI indicate a high bio-productivity during this interval. And then unstable lacustrine environment was found with frequent fluctuations in pollen concentration and grain size since 1842 A.D.. 2) This study recorded a relatively dry Medieval Warm Period (MWP; 1082 1388 A.D.) and a wet Little Ice Age (LIA; 1437 1842 A.D.), which is generally consistent with climate characteristics in arid central Asia (ACA). 3) Increased Amaranthaceae and high abundance of Poaceae were related to overgrazing and agricultural activities at that time to some extent. Thus vegetation evolution of the lake region was influenced by human activities and climate changes.

Sedimentary deposits study of the 2006 Java tsunami, in Pangandaran, West Java (preliminary result)

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

Maemunah, Imun, E-mail: imun-m2001@yahoo.com; Institute Technology of Bandung; Suparka, Emmy, E-mail: emmy@gc.itb.ac.id

The 2006 Java Earthquake (Mw 7.2) has generated a tsunami that reached Pangandaran coastal plain with 9.7 m above sea level height of wave. In 2014 we examined the tsunami deposit exposed in shallow trenches along a∼300 m at 5 transect from shoreline to inland on Karapyak and Madasari, Pangandaran. We documented stratigraphically and sedimentologically, the characteristics of Java Tsunami deposit on Karapyak and Madasari and compared both sediments. In local farmland a moderately-sorted, brown soil is buried by a poorly-sorted, grey, medium-grained sand-sheet. The tsunami deposit was distinguished from the underlying soil by a pronounced increase in grain size that becomesmore » finner upwards and landwards. Decreasing concentration of coarse size particles with distance toward inland are in agreement with grain size analysis. The thickest tsunami deposit is about 25 cm found at 84 m from shoreline in Madasari and about 15 cm found at 80 m from shoreline in Karapyak. The thickness of tsunami deposits in some transect become thinner landward but in some other transect lack a consistent suggested strongly affected by local topography. Tsunami deposits at Karapyak and Madasari show many similarities. Both deposits consist of coarse sand that sharply overlies a finer sandy soil. The presence mud drapes and other sedimentary structure like graded bedding, massive beds, mud clasts in many locations shows a dynamics process of tsunami waves. The imbrication coarse and shell fragments of the 2006 Java, tsunami deposits also provide information about the curent direction, allowing us to distinguish run up deposits from backwash deposits.« less

Land-Marine Paleoseismic Integration for the Northern Cascadia Margin, USA

NASA Astrophysics Data System (ADS)

Goldfinger, C.; Galer, S.; Beeson, J. W.; Hamilton, T. S.; Black, B.; Romsos, C. G.; Nelson, C. H.; Morey, A. E.

2015-12-01

New and archive cores (N=70), bathymetric, backscatter and sub-bottom data from the Washington margin reveal patterns of Holocene sediment transport and deposition. Barkley, Nitinat, Juan de Fuca (JDF), Quillayute, Grays, Guide, and Willapa Canyons each have different post-glacial mechanisms of loading and dispersal of sediment via turbidity currents. In high-stand conditions, the northern canyons, Barkley, Nitinat, JDF, and Quillayute are mostly relict systems. The remaining canyons, Quinault, Grays, Guide, and Willapa, are recharged to varying degrees by northward transport of Columbia River derived sediment. All systems are nonetheless active conduits for turbidity currents during the Holocene. Sedimentologic and CT analyses, supported by radiocarbon ages, micropaleontology, and the Mazama Ash show that the Holocene sedimentary sequence consists of a series of sand to mud turbidites in the active portions of all systems, interbedded with hemipelagic sediment. The relict systems are finer grained, commonly not visually detected, with Holocene turbidite counts the same as recharged systems. Use of 1960's core sketches (Atwater) fails to capture the full record, as noted by Barnard (1973). Hydrodynamic models and heavy mineral distributions show that the northern canyon systems (Barkley, Nitinat, JDF, Quillayute) are independent of the southern systems, (Quinault, Guide, Grays, Willapa) during the Holocene. Best fitting flow inversions suggest turbidity currents range in height from 80-170 m, consistent with earlier work and backscatter observations. Mass balancing suggests sediment supplied to the slope canyons and abyssal channels is 4-6 times greater than supplied by recharge to the canyon heads by external sources, strongly indicating autogenic sourcing by earthquakes. Turbidite deposition off Washington is not very sensitive to either sediment supply or slope angle. Lithostratigraphic correlation and age models of Holocene turbidite sequences suggests deposition of ~ 20 Holocene turbidites in most parts of the Canyon systems, with little variation. The explanation most consistent with the data is triggering by a series of 18-20 Holocene earthquakes, in agreement temporal and lithostratigraphic linkages to new marine sites in Canada, as well and land paleoseismic data.

Characterizing Feedbacks Between Environmental Forcing and Sediment Characteristics in Fluvial and Coastal Systems

NASA Astrophysics Data System (ADS)

Feehan, S.; Ruggiero, P.; Hempel, L. A.; Anderson, D. L.; Cohn, N.

2016-12-01

Characterizing Feedbacks Between Environmental Forcing and Sediment Characteristics in Fluvial and Coastal Systems American Geophysical Union, 2016 Fall Meeting: San Francisco, CA Authors: Scott Feehan, Peter Ruggiero, Laura Hempel, and Dylan Anderson Linking transport processes and sediment characteristics within different environments along the source to sink continuum provides critical insight into the dominant feedbacks between grain size distributions and morphological evolution. This research is focused on evaluating differences in sediment size distributions across both fluvial and coastal environments in the U.S. Pacific Northwest. The Cascades' high relief is characterized by diverse flow regimes with high peak/flashy flows and sub-threshold flows occurring in relative proximity and one of the most energetic wave climates in the world. Combining analyses of both fluvial and coastal environments provides a broader understanding of the dominant forces driving differences between each system's grain size distributions, sediment transport processes, and resultant evolution. We consider sediment samples taken during a large-scale flume experiment that simulated floods representative of both high/flashy peak flows analogous to runoff dominated rivers and sub-threshold flows, analogous to spring-fed rivers. High discharge flows resulted in narrower grain size distributions while low flows where less skewed. Relative sediment size showed clear dependence on distance from source and the environments' dominant fluid motion. Grain size distributions and sediment transport rates were also quantified in both wave dominated nearshore and aeolian dominated backshore portions of Long Beach Peninsula, Washington during SEDEX2, the Sandbar-aEolian-Dune EXchange Experiment of summer 2016. The distributions showed spatial patterns in mean grain size, skewness, and kurtosis dependent on the dominant sediment transport process. The feedback between these grain size distributions and the predominant driver of sediment transport controls the potential for geomorphic change on societally relevant time scales in multiple settings.

Pyroclastic Activity at Home Plate in Gusev Crater, Mars

NASA Technical Reports Server (NTRS)

Squyres, S. W.; Aharonson, O.; Clark, B. S.; Cohen, B.; Crumpler, L.; deSouza, P. A.; Farrand, W. H.; Gellert, R.; Grant, J.; Grotzinger, J. P.;

Pyroclastic activity at home plate in Gusev crater, Mars

USGS Publications Warehouse

Squyres, S. W.; Aharonson, O.; Clark, B. C.; Cohen, B. A.; Crumpler, L.; de Souza, P.A.; Farrand, W. H.; Gellert, Ralf; Grant, J.; Grotzinger, J.P.; Haldemann, A.F.C.; Johnson, J. R.; Klingelhofer, G.; Lewis, K.W.; Li, R.; McCoy, T.; McEwen, A.S.; McSween, H.Y.; Ming, D. W.; Moore, Johnnie N.; Morris, R.V.; Parker, T.J.; Rice, J. W.; Ruff, S.; Schmidt, M.; Schroder, C.; Soderblom, L.A.; Yen, A.

2007-01-01

Home Plate is a layered plateau in Gusev crater on Mars. It is composed of clastic rocks of moderately altered alkali basalt composition, enriched in some highly volatile elements. A coarse-grained lower unit lies under a finer-grained upper unit. Textural observations indicate that the lower strata were emplaced in an explosive event, and geochemical considerations favor an explosive volcanic origin over an impact origin. The lower unit likely represents accumulation of pyroclastic materials, whereas the upper unit may represent eolian reworking of the same pyroclastic materials.

Effects of fluidization of the host sediment on peperite textures: A field example from the Cretaceous Buan Volcanics, SW Korea

NASA Astrophysics Data System (ADS)

Gihm, Yong Sik; Kwon, Chang Woo

2017-04-01

In the Cretaceous Buan Volcanics (SW Korea), blocky and fluidal peperites are hosted in a massive pumiceous lapilli tuff intruded by intermediate dikes. Blocky peperites, the most abundant species, are characterized by polyhedral or platy juvenile clasts and a jigsaw-crack texture. Fluidal peperites occur only along dike margins, where the host sediments are composed of well sorted, fine to very fine ash (fine-grained zone), and are characterized by fluidal or globular juvenile clasts with irregular or ragged margins. The fine-grained zone is interpreted to form by grain size segregation caused by upward moving pore water (fluidization) that has resulted from heat transfer from intruding magma toward waterlogged host sediments during intrusion. With the release of pore water and the selective entrainment of fine-grained ash, fine-grained zones formed within the host sediments. Subsequent interactions between the fine-grained zone and the intruding magma resulted in ductile deformation of the magma before fragmentation, which generated fluidal peperites. Outside the fine-grained zone, intruding magma fragmented in a brittle manner because of the relative deficiency of both pore water and fine-grained ash, resulting in the formation of blocky peperites. The results of this study suggest that redistribution of constituent particles (ash) and interstitial fluids during fluidization resulted in heterogeneous physical conditions of the host sediments, which influenced peperite-forming processes, as reflected by the different peperite textures.

Earth Observations taken by the Expedition 22 Crew

NASA Image and Video Library

2009-12-01

ISS022-E-005258 (1 Dec. 2009) --- This detailed hand-held digital camera?s image recorded from the International Space Station highlights sand dunes in the Fachi-Bilma erg, or sand sea, which is part of the central eastern Tenere Desert. The Tenere occupies much of southeastern Niger and is considered to be part of the larger Sahara Desert that stretches across northern Africa. Much of the Sahara is comprised of ergs ? with an area of approximately 150,000 square kilometers, the Fachi-Bilma is one of the larger sand seas. Two major types of dunes are visible in the image. Large, roughly north-south oriented transverse dunes fill the image frame. This type of dune tends to form at roughly right angles to the dominant northeasterly winds. The dune crests are marked in this image by darker, steeper sand accumulations that cast shadows. The lighter-toned zones between are lower interdune ?flats?. The large dunes appear to be highly symmetrical with regard to their crests. This suggests that the crest sediments are coarser, preventing the formation of a steeper slip face on the downwind side of the dune by wind-driven motion of similarly-sized sand grains. According to NASA scientists, this particular form of transverse dune is known as a zibar, and is thought to form by winnowing of smaller sand grains by the wind, leaving the coarser grains to form dune crests. A second set of thin linear dunes oriented at roughly right angles to the zibar dunes appears to be formed on the larger landforms and is therefore a younger landscape feature. These dunes appear to be forming from finer grains in the same wind field as the larger zibars. The image was taken with digital still camera fitted with a 400 mm lens, and is provided by the ISS Crew Earth Observations experiment and Image Science & Analysis Laboratory, Johnson Space Center.

A Review of distribution and quantity of lingering subsurface oil from the Exxon Valdez Oil Spill

NASA Astrophysics Data System (ADS)

Nixon, Zachary; Michel, Jacqueline

2018-01-01

Remaining lingering subsurface oil residues from the Exxon Valdez oil spill (EVOS) are, at present, patchily distributed across the geologically complex and spatially extensive shorelines of Prince William Sound and the Gulf of Alaska. We review and synthesize previous literature describing the causal geomorphic and physical mechanisms for persistence of oil in the intertidal subsurface sediments of these areas. We also summarize previous sampling and modeling efforts, and refine previously presented models with additional data to characterize the present-day linear and areal spatial extent, and quantity of lingering subsurface oil. In the weeks after the spill in March of 1989, approximately 17,750 t of oil were stranded along impacted shorelines, and by October of 1992, only 2% of the mass of spilled oil was estimated to remain in intertidal areas. We estimate that lingering subsurface residues, generally between 5 and 20 cm thick and sequestered below 10-20 cm of clean sediment, are present over 30 ha of intertidal area, along 11.4 km of shoreline, and represent approximately 227 t or 0.6% of the total mass of spilled oil. These residues are typically located in finer-grained sand and gravel sediments, often under an armor of cobble- or boulder-sized clasts, in areas with limited groundwater flow and porosity. Persistence of these residues is correlated with heavy initial oil loading together with localized sheltering from physical disturbance such as wave energy within the beach face. While no longer generally bioavailable and increasingly chemically weathered, present removal rates for these remaining subsurface oil residues have slowed to nearly zero. The only remaining plausible removal mechanisms will operate over time scales of decades.

Thoughts on Scale

ERIC Educational Resources Information Center

Schoenfeld, Alan H.

2015-01-01

This essay reflects on the challenges of thinking about scale--of making sense of phenomena such as continuous professional development (CPD) at the system level, while holding on to detail at the finer grain size(s) of implementation. The stimuli for my reflections are three diverse studies of attempts at scale--an attempt to use ideas related to…

Textual and Discoursal Resources Used in the Essay Genre in Sociology and English

ERIC Educational Resources Information Center

Bruce, Ian

2010-01-01

Research that has examined university assignment writing has varied from large-scale, inventorial surveys across disciplines to more specific, finer-grained analyses of the assignment requirements of specific disciplines. However, while such research has involved surveys of the views and expectations of faculty or the analysis of assignment tasks,…

Influence of thermo-mechanical treatment in ferritic phase field on microstructure and mechanical properties of reduced activation ferritic-martensitic steel

NASA Astrophysics Data System (ADS)

Prakash; Vanaja, J.; Laha, K.; Nageswara Rao, G. V. S.

2018-03-01

The present study focuses on the evaluation of microstructure and mechanical properties of reduced activation ferritic-martensitic (RAFM) steel (9Cr-1W-0.06Ta) subjected to thermo-mechanical treatment (TMT) in ferritic phase field. The results obtained were compared with the steel in conventional normalised plus tempered (N+T) condition. The microstructure of the steel in N+T and TMT conditions was assessed by optical and scanning electron microscopes. Hardness, tensile and creep studies were carried out and the results were correlated with the microstructural studies. While the TMT processed steel resulted in coarser prior austenite grains and exhibited ferritic microstructure with large distribution of fine M23C6 and MX precipitates, the N+T steel reveals tempered martensitic structure with finer prior austenitic grains with coarser M23C6 and MX precipitates. Although ferritic structure is present in TMT processed steel, it exhibits better tensile and creep rupture strengths than N+T steel due to the presence of increased dislocation density and finer distribution of precipitates.

The Effects of Atmosphere on the Sintering of Ultrafine-Grained Tungsten with Ti

NASA Astrophysics Data System (ADS)

Ren, Chai; Koopman, Mark; Fang, Z. Zak; Zhang, Huan

2016-11-01

Tungsten (W) is a brittle material at room temperature making it very difficult to fabricate. Although the lack of ductility remains a difficult challenge, nano-sized and ultrafine-grained (UFG) structures offer the potential to overcome tungsten's room-temperature brittleness. One way to manufacture UFG W is to compact and sinter nano-sized W powder. It is challenging, however, to control grain growth during sintering. As one method to inhibit grain growth, the effect of Ti-based additives on the densification and grain growth of nano-W powders was investigated in this study. Addition of 1% Ti into tungsten led to more than a 63% decrease in average grain size of sintered samples at comparable density levels. It was found that sintering in Ar yielded a finer grain size than sintering in H2 at similar densities. The active diffusion mechanisms during sintering were different for W-1% Ti nano powders sintered in Ar and H2.

Evaluation of CAESAR-Lisflood as a tool for modelling river channel change and floodplain sediment residence times.

NASA Astrophysics Data System (ADS)

Feeney, Christopher; Smith, Hugh; Chiverrell, Richard; Hooke, Janet; Cooper, James

2017-04-01

Sediment residence time represents the duration of particle storage, from initial deposition to remobilisation, within reservoirs such as floodplains. Residence time influences rates of downstream redistribution of sediment and associated contaminants and is a useful indicator of landform stability and hence, preservation potential of alluvial archives of environmental change. River channel change controls residence times, reworking sediments via lateral migration, avulsion and incision through floodplain deposits. As reworking progresses, the floodplain age distribution is 'updated', reflecting the time since 'older' sediments were removed and replaced with 'younger' ones. The relationship between ages and the spatial extents they occupy can be used to estimate the average floodplain sediment residence times. While dating techniques, historic maps and remote sensing can reconstruct age distributions from historic reworking, modelling provides advantages, including: i) capturing detailed river channel changes and resulting floodplain ages over longer timescales and higher resolutions than from historic mapping, and ii) control over inputs to simulate hypothetical scenarios to investigate the effects of different environmental drivers on residence times. CAESAR-Lisflood is a landform evolution model capable of simulating variable channel width, divergent flow, and both braided and meandering planforms. However, the model's ability to accurately simulate channel changes requires evaluation if it is to be useful for quantitative evaluation of floodplain sediment residence times. This study aims to simulate recent historic river channel changes along ten 1 km reaches in northern England. Simulation periods were defined by available overlapping historic map and mean daily flow datasets, ranging 27-39 years. LiDAR-derived 2 m DEMs were modified to smooth out present-day channels and burn in historic channel locations. To reduce run times, DEMs were resampled to coarser resolutions based on the size of the channel and historic rate of lateral channel migration. Separate pre-defined coarse and finer channel bed and floodplain grain size distributions were used, respectively, in combination with constructed reach DEMs for model simulations. Calibration was performed by modifying selected parameters to obtain best fits between observed and modelled channel planforms. Initial simulations suggest the model can broadly reproduce observed planform change and is comparable in terms of channel sinuosities and the mean radius of curvature. As such, CAESAR-Lisflood may provide a useful tool for evaluating floodplain sediment residence times under environmental change scenarios.

Determination of the effects of fine-grained sediment and other limiting variables on trout habitat for selected streams in Wisconsin

USGS Publications Warehouse

Scudder, Barbara C.; Selbig, J.W.; Waschbusch, R.J.

2000-01-01

Two Habitat Suitability Index (HSI) models, developed by the U.S. Fish and Wildlife Service, were used to evaluate the effects of fine-grained (less than 2 millimeters) sediment on brook trout (Salvelinusfontinalis, Mitchill) and brown trout (Salmo trutta, Linnaeus) in 11 streams in west-central and southwestern Wisconsin. Our results indicated that fine-grained sediment limited brook trout habitat in 8 of 11 streams and brown trout habitat in only one stream. Lack of winter and escape cover for fry was the primary limiting variable for brown trout at 61 percent of the sites, and this factor also limited brook trout at several stations. Pool area or quality, in stream cover, streambank vegetation for erosion control, minimum flow, thalweg depth maximum, water temperature, spawning substrate, riffle dominant substrate, and dissolved oxygen also were limiting to trout in the study streams. Brook trout appeared to be more sensitive to the effects of fine-grained sediment than brown trout. The models for brook trout and brown trout appeared to be useful and objective screening tools for identifying variables limiting trout habitat in these streams. The models predicted that reduction in the amount of fine-grained sediment would improve brook trout habitat. These models may be valuable for establishing instream sediment-reduction goals; however, the decrease in sediment delivery needed to meet these goals cannot be estimated without quantitative data on land use practices and their effects on sediment delivery and retention by streams.

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.

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

Temporal pattern and memory in sediment transport in an experimental step-pool channel

NASA Astrophysics Data System (ADS)

Saletti, Matteo; Molnar, Peter; Zimmermann, André; Hassan, Marwan A.; Church, Michael; Burlando, Paolo

2015-04-01

In this work we study the complex dynamics of sediment transport and bed morphology in steep streams, using a dataset of experiments performed in a steep flume with natural sediment. High-resolution (1 sec) time series of sediment transport were measured for individual size classes at the outlet of the flume for different combinations of sediment input rates, discharges, and flume slopes. The data show that the relation between instantaneous discharge and sediment transport exhibits large variability on different levels. After dividing the time series into segments of constant water discharge, we quantify the statistical properties of transport rates by fitting the data with a Generalized Extreme Value distribution, whose 3 parameters are related to the average sediment flux. We analyze separately extreme events of transport rate in terms of their fractional composition; if only events of high magnitude are considered, coarse grains become the predominant component of the total sediment yield. We quantify the memory in grain size dependent sediment transport with variance scaling and autocorrelation analyses; more specifically, we study how the variance changes with different aggregation scales and how the autocorrelation coefficient changes with different time lags. Our results show that there is a tendency to an infinite memory regime in transport rate signals, which is limited by the intermittency of the largest fractions. Moreover, the structure of memory is both grain size-dependent and magnitude-dependent: temporal autocorrelation is stronger for small grain size fractions and when the average sediment transport rate is large. The short-term memory in coarse grain transport increases with temporal aggregation and this reveals the importance of the sampling frequency of bedload transport rates in natural streams, especially for large fractions.

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.

Grain Refinement of AZ31 Magnesium Alloy Weldments by AC Pulsing Technique

NASA Astrophysics Data System (ADS)

Kishore Babu, N.; Cross, C. E.

2012-11-01

The current study has investigated the influence of alternating current pulsing on the structure and mechanical properties of AZ31 magnesium alloy gas tungsten arc (GTA) weldments. Autogenous full penetration bead-on-plate GTA welds were made under a variety of conditions including variable polarity (VP), variable polarity mixed (VPM), alternating current (AC), and alternating current pulsing (ACPC). AC pulsing resulted in significant refinement of weld metal when compared with the unpulsed conditions. AC pulsing leads to relatively finer and more equiaxed grain structure in GTA welds. In contrast, VP, VPM, and AC welding resulted in predominantly columnar grain structures. The reason for this grain refinement may be attributed to the periodic variations in temperature gradient and solidification rate associated with pulsing as well as weld pool oscillation observed in the ACPC welds. The observed grain refinement was shown to result in an appreciable increase in fusion zone hardness, tensile strength, and ductility.

Influence of a Brazilian sewage outfall on the toxicity and contamination of adjacent sediments

USGS Publications Warehouse

Abessa, D.M.S.; Carr, R.S.; Rachid, B.R.F.; Sousa, E.C.P.M.; Hortelani, M.A.; Sarkis, J.E.

2005-01-01

The submarine sewage outfall of Santos (SSOS) is situated in the Santos Bay (São Paulo, Brazil) and is potentially a significant source of contaminants to the adjacent marine ecosystem. The present study aimed to assess the influence of SSOS on the sediment toxicity and contamination at Santos Bay. At the disposal site, sediments tended to be finer, organically richer and exhibited higher levels of surfactants and metals, sometimes exceeding the “Threshold Effect Level” values. The SSOS influence was more evident toward the East, where the sediments exhibited higher levels of TOC, total S and metals during the summer 2000 sampling campaign. Sediment toxicity to amphipods was consistently detected in four of the five stations studied. Amphipod survival tended to correlate negatively to Hg, total N and % mud. This work provides evidence that the SSOS discharge affects the quality of sediments from Santos Bay, and that control procedures are warranted.

Does Silicate Weathering of Loess Affect Atmospheric CO2?

NASA Astrophysics Data System (ADS)

Anderson, S. P.

2002-12-01

Weathering of glacial loess may be a significant, yet unrecognized, component of the carbon cycle. Glaciers produce fine-grained sediment, exposing vast amounts of mineral surface area to weathering processes, yet silicate mineral weathering rates at glacier beds and of glacial till are not high. Thus, despite the tremendous potential for glaciers to influence global weathering rates and atmospheric CO2 levels, this effect has not been demonstrated. Loess, comprised of silt-clay sizes, may be the key glacial deposit in which silicate weathering rates are high. Loess is transported by wind off braid plains of rivers, and deposited broadly (order 100 km from the source) in vegetated areas. Both the fine grain size, and hence large mineral surface area, and presence of vegetation should render loess deposits highly susceptible to silicate weathering. These deposits effectively extend the geochemical impact of glaciation in time and space, and bring rock flour into conditions conducive to chemical weathering. A simple 1-d model of silicate weathering fluxes from a soil profile demonstrates the potential of loess deposition to enhance CO2 consumption. At each time step, computed mineral dissolution (using anorthite and field-based rate constants) modifies the size of mineral grains within the soil. In the case of a stable soil surface, this results in a gradual decline in weathering fluxes and CO2 consumption through time, as finer grain sizes dissolve away. Computed weathering fluxes for a typical loess, with an initial mean grain size of 25 μm, are an order of magnitude greater than fluxes from a non-loess soil that differs only in having a mean grain size of 320 μm. High weathering fluxes are maintained through time if loess is continually deposited. Deposition rates as low as 0.01 mm/yr (one loess grain thickness per year) can lead to a doubling of CO2 consumption rates within 5 ka. These results suggest that even modest loess deposition rates can significantly increase CO2 consumption rates due to silicate weathering in soils. Thick loess deposits cover 5-10% of the global land surface, and loess deposits too thin to be included in global inventories cover a much greater area. Loess deposition and weathering over timescales greater than the duration of glaciation must be considered in models of atmospheric CO2 variation.

Effects of moisture and grain size on the mechanisms of rainsplash transport

NASA Astrophysics Data System (ADS)

Taube, S. R.; Furbish, D. J.

2010-12-01

Desert shrubs accumulate soil mounds beneath their canopies through rainsplash transport. Previous studies of this process have suggested that there is a preferential concentration of smaller grain sizes closer to the base of the shrub, based on the idea that smaller material is more readily splashed inward beneath the shrub. However, our studies have shown that there are two mechanisms of ejection of the grains with moist soil conditions, each preferentially moving either large or small grain sizes. Larger grains tend to be launched from grain-to-grain collisions following drop impact and travel as individual grains. Smaller grains appear to clump together and move as a single large "grain". The medium-sized grains generally had a greater travel distance than the very large or very small grains, potentially because they involve both modes of transport with a greater effective transfer of energy from the raindrop to the grains. The average travel distance is greatest near 100 microns, which is reflected by the data of Leguedois, et al. (2005). Experiments using high-speed imaging reveals that there is a marked difference between the mechanism of transport when the sediment grains are dry versus when they are moist. The dry grains are rapidly deposited about the impact site with a small proportion moving far from the site. However, moist grains tend to clump together to form “blobs” of water and sediment. Immediately after impact, the drop creates a water corona with entrained sediment, which then contracts into water-sediment blobs that are rocketed outwards from the impact, leaving little to no grain mass near the impact site. Varying degrees of moisture content appeared to have little influence on grain dispersal, leading us to believe that once the soil material is moist (but not saturated), its splash behavior is mostly related to details of the drop corona.

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.

Deposition and deformation of fluvial-lacustrine sediments of the Upper Triassic-Lower Jurassic Whitmore Point Member, Moenave Formation, northern Arizona

NASA Astrophysics Data System (ADS)

Tanner, Lawrence H.; Lucas, Spencer G.

2010-01-01

The stratigraphic section of the Upper Triassic-Lower Jurassic Whitmore Point Member of the Moenave Formation at Potter Canyon, Arizona, comprises c. 26 m of gray to black shales and red mudstones interbedded with mainly sheet-like siltstones and sandstones. These strata represent deposition from suspension and sheetflow processes in shallow, perennial meromictic to ephemeral lakes, and on dry mudflats of the terminal floodout of the northward-flowing Moenave stream system. The lakes were small, as indicated by the lack of shoreline features and limited evidence for deltas. Changes in base level, likely forced by climate change, drove the variations between mudflat and perennial lacustrine conditions. Lenticular sandstones that occur across the outcrop face in the same stratigraphic interval in the lower part of the sequence represent the bedload fill of channels incised into a coarsening-upward lacustrine sequence following a fall in base level. These sandstones are distinctive for the common presence of over-steepened bedding, dewatering structures, and less commonly, folding. Deformation of these sandstones is interpreted as aseismic due to the lack of features typically associated with seismicity, such as fault-graded bedding, diapirs, brecciated fabrics and clastic dikes. Rapid deposition of the sands on a fluid-rich substrate produced a reverse density gradient that destabilized, and potentially fluidized the underlying, finer-grained sediments. This destabilization allowed synsedimentary subsidence of most of the channel sands, accompanied by longitudinal rotation and/or ductile deformation of the sand bodies.

How does sediment affect the hydraulics of bedrock-alluvial rivers?

NASA Astrophysics Data System (ADS)

Hodge, Rebecca; Hoey, Trevor; Maniatis, George; Leprêtre, Emilie

2016-04-01

Relationships between flow, sediment transport and channel morphology are relatively well established in coarse-grained alluvial channels. Developing equivalent relationships for bedrock-alluvial channels is complicated by the two different components that comprise the channel morphology: bedrock and sediment. These two components usually have very different response times to hydraulic forcing, meaning that the bedrock morphology may be inherited from previous conditions. The influence of changing sediment cover on channel morphology and roughness will depend on the relative magnitudes of the sediment size and the spatial variations in bedrock elevation. We report results from experiments in a 0.9m wide flume designed to quantify the interactions between flow and sediment patch morphology using two contrasting bedrock topographies. The first topography is a plane bed with sand-scale roughness, and the second is a 1:10 scale, 3D printed, model of a bedrock channel with spatially variable roughness (standard deviation of elevations = 12 mm in the flume). In all experiments, a sediment pulse was added to the flume (D50 between 7 and 15 mm) and sediment patches were allowed to stabilise under constant flow conditions. The flow was then incrementally increased in order to identify the discharges at which sediment patches and isolated grains were eroded. In the plane bed experiments ˜20% sediment cover is sufficient to alter the channel hydraulics through the increased roughness of the bed; this impact is expressed as the increased discharge at which isolated grains are entrained. In the scaled bed experiments, partial sediment cover decreased local flow velocities on a relatively smooth area of the bed. At the scale of the entire channel, the bed morphology, and the hydraulics induced by it, was a primary control on sediment cover stability at lower sediment inputs. At higher inputs, where sediment infilled the local bed topography, patches were relatively more stable, suggesting an increased impact on the hydraulics and the role of grain-grain interactions. We draw together these experiments using a theoretical framework to express the impact of sediment cover on channel roughness and hence hydraulics.

Exploring the persistence of sorted bedforms on the inner-shelf of Wrightsville Beach, North Carolina

USGS Publications Warehouse

Gutierrez, Ben; Voulgaris, George; Thieler, E. Robert

2005-01-01

Geological studies offshore of Wrightsville Beach, North Carolina reveal subtle large-scale regions of coarse sand with gravel and shell hash (widths between 100 and 200 m and negative relief of ∼1 m) that trend obliquely to the coast. It was previously suggested that these regions serve as conduits for sand exchange between the shoreface and inner shelf during storm-associated downwelling. Consequently they were classified as rippled scour depressions. More recently, the role of alongshore flows and self-organization as a result of inhibited settling of fine sand has been discussed. In this study, 45 days of near-bed current measurements were analyzed using benthic boundary layer and sediment transport models to examine the role of along- and cross-shore flows in driving sediment transport at this site. The wind climate was found to be a dominant influence on near-bed flows. Six distinct sediment transport events were recognized. During these events, sediment transport models show that bedload transport is directed mainly in the cross-shore direction, while suspended sediments are directed alongshore to the southwest. Current observations during these sediment transport events provide no evidence of cross-shore sediment transport caused by steady downwelling currents. Instead, benthic boundary layer model results are used to show that differences in bed roughness between the coarse areas of the seabed within the “rippled scour depressions” and the finer areas of the inner shelf are more pronounced during increasingly energetic wave and current conditions. The enhanced difference in roughness results in increased turbulence intensities over coarse regions inhibiting the deposition of the fine sand that is resuspended over the shelf during these events relative to finer areas over the shelf. Findings from this study contribute to explaining the observed long-term persistence of these features.

Determination of grain-size characteristics from electromagnetic seabed mapping data: A NW Iberian shelf study

NASA Astrophysics Data System (ADS)

Baasch, Benjamin; Müller, Hendrik; von Dobeneck, Tilo; Oberle, Ferdinand K. J.

2017-05-01

The electric conductivity and magnetic susceptibility of sediments are fundamental parameters in environmental geophysics. Both can be derived from marine electromagnetic profiling, a novel, fast and non-invasive seafloor mapping technique. Here we present statistical evidence that electric conductivity and magnetic susceptibility can help to determine physical grain-size characteristics (size, sorting and mud content) of marine surficial sediments. Electromagnetic data acquired with the bottom-towed electromagnetic profiler MARUM NERIDIS III were analysed and compared with grain size data from 33 samples across the NW Iberian continental shelf. A negative correlation between mean grain size and conductivity (R=-0.79) as well as mean grain size and susceptibility (R=-0.78) was found. Simple and multiple linear regression analyses were carried out to predict mean grain size, mud content and the standard deviation of the grain-size distribution from conductivity and susceptibility. The comparison of both methods showed that multiple linear regression models predict the grain-size distribution characteristics better than the simple models. This exemplary study demonstrates that electromagnetic benthic profiling is capable to estimate mean grain size, sorting and mud content of marine surficial sediments at a very high significance level. Transfer functions can be calibrated using grains-size data from a few reference samples and extrapolated along shelf-wide survey lines. This study suggests that electromagnetic benthic profiling should play a larger role for coastal zone management, seafloor contamination and sediment provenance studies in worldwide continental shelf systems.

Granular avalanches on the Moon: Mass-wasting conditions, processes, and features

NASA Astrophysics Data System (ADS)

Kokelaar, B. P.; Bahia, R. S.; Joy, K. H.; Viroulet, S.; Gray, J. M. N. T.

2017-09-01

Seven lunar crater sites of granular avalanches are studied utilizing high-resolution images (0.42-1.3 m/pixel) from the Lunar Reconnaissance Orbiter Camera; one, in Kepler crater, is examined in detail. All the sites are slopes of debris extensively aggraded by frictional freezing at their dynamic angle of repose, four in craters formed in basaltic mare and three in the anorthositic highlands. Diverse styles of mass wasting occur, and three types of dry-debris flow deposit are recognized: (1) multiple channel-and-lobe type, with coarse-grained levees and lobate terminations that impound finer debris, (2) single-surge polylobate type, with subparallel arrays of lobes and fingers with segregated coarse-grained margins, and (3) multiple-ribbon type, with tracks reflecting reworked substrate, minor levees, and no coarse terminations. The latter type results from propagation of granular erosion-deposition waves down slopes dominantly of fine regolith, and it is the first recognized natural example. Dimensions, architectures, and granular segregation styles of the two coarse-grained deposit types are like those formed in natural and experimental avalanches on Earth, although the timescale of motion differs due to the reduced gravity. Influences of reduced gravity and fine-grained regolith on dynamics of granular flow and deposition appear slight, but we distinguish, for the first time, extensive remobilization of coarse talus by inundation with finer debris. The (few) sites show no clear difference attributable to the contrasting mare basalt and highland megaregolith host rocks and their fragmentation. This lunar study offers a benchmarking of deposit types that can be attributed to formation without influence of liquid or gas.

Fine-grained policy control in U.S. Army Research Laboratory (ARL) multimodal signatures database

NASA Astrophysics Data System (ADS)

Bennett, Kelly; Grueneberg, Keith; Wood, David; Calo, Seraphin

2014-06-01

The U.S. Army Research Laboratory (ARL) Multimodal Signatures Database (MMSDB) consists of a number of colocated relational databases representing a collection of data from various sensors. Role-based access to this data is granted to external organizations such as DoD contractors and other government agencies through a client Web portal. In the current MMSDB system, access control is only at the database and firewall level. In order to offer finer grained security, changes to existing user profile schemas and authentication mechanisms are usually needed. In this paper, we describe a software middleware architecture and implementation that allows fine-grained access control to the MMSDB at a dataset, table, and row level. Result sets from MMSDB queries issued in the client portal are filtered with the use of a policy enforcement proxy, with minimal changes to the existing client software and database. Before resulting data is returned to the client, policies are evaluated to determine if the user or role is authorized to access the data. Policies can be authored to filter data at the row, table or column level of a result set. The system uses various technologies developed in the International Technology Alliance in Network and Information Science (ITA) for policy-controlled information sharing and dissemination1. Use of the Policy Management Library provides a mechanism for the management and evaluation of policies to support finer grained access to the data in the MMSDB system. The GaianDB is a policy-enabled, federated database that acts as a proxy between the client application and the MMSDB system.

Bed Surface Adjustments to Spatially Variable Flow in Low Relative Submergence Regimes

NASA Astrophysics Data System (ADS)

Monsalve, A.; Yager, E. M.

2017-11-01

In mountainous rivers, large relatively immobile grains partly control the local and reach-averaged flow hydraulics and sediment fluxes. When the flow depth is similar to the size of these grains (low relative submergence), heterogeneous flow structures and plunging flow cause spatial distributions of bed surface elevations, textures, and sedimentation rates. To explore how the bed surface responds to these flow variations we conducted a set of experiments in which we varied the relative submergence of staggered hemispheres (simulated large boulders) between runs. All experiments had the same average sediment transport capacity, upstream sediment supply, and initial bed thickness and grain size distribution. We combined our laboratory measurements with a 3-D flow model to obtain the detailed flow structure around the hemispheres. The local bed shear stress field displayed substantial variability and controlled the bed load transport rates and direction in which sediment moved. The divergence in bed shear stress caused by the hemispheres promoted size-selective bed load deposition, which formed patches of coarse sediment upstream of the hemisphere. Sediment deposition caused a decrease in local bed shear stress, which combined with the coarser grain size, enhanced the stability of this patch. The region downstream of the hemispheres was largely controlled by a recirculation zone and had little to no change in grain size, bed elevation, and bed shear stress. The formation, development, and stability of sediment patches in mountain streams is controlled by the bed shear stress divergence and magnitude and direction of the local bed shear stress field.

Comparative research on soil magnetic susceptibility and Chroma and grain of grassland soil and farmland soil in alpine region

NASA Astrophysics Data System (ADS)

Jie, Yuan; Guangchao, Cao; Chongyi, E.; Gang, Jiang; Youjing, Yuan; Cheng, Xiang

2017-03-01

This thesis aims at researching unchanged perennial farmland and grassland soil on the northern of Qinghai Lake basin and differences between soil magnetic susceptibility, chroma and soil particle size composition of grassland and farmland in lengthways profile(0-60cm). The result shows that the distinction of Xlf between grassland and farmland is smaller above 15cm, and farmland Xlf is finer than grassland below 15cm. The Xfd of grassland is finer than farmland above 30cm, which has a little difference below 30cm. Farmland chroma value is finer than the grassland generally. The lightness of grassland has increased trend and farmland has the decrease trend above 30cm, the lightness of grassland and farmland has no other changes below 30cm, the change of redness and yellowness in lengthways profile has a decrease trend from 0 to 60cm; the clay and silt content of grassland are finer than farmland except sand content; the sand maximum content of farmland in 0-10cm segment; 20 to 35 cm segment sand content decrease and began to increase from 35-60cm segment; the soil particle size composition has a big difference, in particular, when it is above 30cm, it has a little difference below 30cm.

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.

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.

Mixed sediment beach processes: Kachemak Bay, Alaska

USGS Publications Warehouse

Ruggiero, P.; Adams, P.N.; Warrick, J.A.

2007-01-01

Mixed sediment beaches are morphologically distinct from and more complex than either sand or gravel only beaches. Three digital imaging techniques are employed to quantify surficial grain size and bedload sediment transport rates along the mixed sediment beaches of Kachemak Bay, Alaska. Applying digital imaging procedures originally developed for quickly and efficiently quantifying grain sizes of sand to coarse sediment classes gives promising results. Hundreds of grain size estimates lead to a quantitative characterization of the region's sediment at a significant reduction in cost and time as compared to traditional techniques. Both the sand and coarse fractions on this megatidal beach mobilize into self-organized bedforms that migrate alongshore with a seasonally reflecting the temporal pattern of the alongshore component of wave power. In contrast, the gravel bedforms also migrate in the cross-shore without significant seasonally suggesting that swash asymmetry is sufficient to mobilize the gravel even during low energy summer conditions. ?? 2007 ASCE.

Environmental effects of dredging on sediment nutrients, carbon and granulometry in a tropical estuary.

PubMed

Nayar, S; Miller, D J; Hunt, A; Goh, B P L; Chou, L M

2007-04-01

This monitoring study encompassed a period prior to dredging, during dredging and post dredging between July 1999 to June 2000 in Ponggol estuary located along the northeastern coast of Singapore. Mean concentrations of sediment nutrients in mg x Kg(-1) (+/- standard error of means) prior to dredging, during dredging and post dredging were 9.75 +/- 4.24, 8.18 +/- 4.29 and 11.46 +/- 4.74 for ammonium, 0.08 +/- 0.05, 0.06 +/- 0.02 and 0.09 +/- 0.01 for nitrite, 0.04 +/- 0.04, 0.11 +/- 0.17 and 0.25 +/- 0.30 for nitrate, 4.83 +/- 3.48, 0.77 +/- 0.48 and 8.33 +/- 9.73 for phosphate respectively. Pre dredge, dredge and post dredge levels of total carbon (TC) were 18.5 +/- 3.7, 20.2 +/- 3.5 and 34.6 +/- 12.0, of total organic carbon (TOC) were 10.5 +/- 2.9, 19.5 +/- 3.6 and 34.6 +/- 12.0 and of total inorganic carbon (TIC) were 7.9 +/- 1.0, 0.7 +/- 0.4 and non detectable in the sediments, respectively. Both, sediment nutrients and carbon registered lower concentrations with onset of dredging, with the exception of nitrate and TOC. A shift in sedimentary carbon from inorganic carbon to organic carbon was also observed with the onset of the dredging activities when the organically enriched historically contaminated layer was exposed. Sediment granulometry showed that the sediments in the estuary were predominantly silt and clay prior to dredging, which changed to sand with onset of dredging. Silt load in the sediments was highest post-dredge. Sediment nutrients and sediment organic carbon were observed to associate with the finer fractions (silt and clay) of sediments. Finer fractions of sediments get resuspended during a dredging event and are dispersed spatially as the result of tides and water movements. Prior to this study, the potential for nutrient release and sediment granulometry due to dredging have been suggested, but there have been few studies of it, especially in the tropics. The baseline information gathered from this study could be used to work out effective management strategies to protect similar tropical ecosystems elsewhere, should there be no other alternative to dredging.

The Physical Accessibility of Public Libraries to Users: A GIS Study

ERIC Educational Resources Information Center

Park, Sung Jae

2011-01-01

The purpose of this study is to gain a finer-grained picture and better understanding of the travel patterns of library users, and the activities, demographics, and other factors that affect library access. Previous studies of physical accessibility of public libraries, which have focused on library users' single-destination trips and their travel…

Early Prediction of Student Dropout and Performance in MOOCSs Using Higher Granularity Temporal Information

ERIC Educational Resources Information Center

Ye, Cheng; Biswas, Gautam

2014-01-01

Our project is motivated by the early dropout and low completion rate problem in MOOCs. We have extended traditional features for MOOC analysis with richer and higher granularity information to make more accurate predictions of dropout and performance. The results show that finer-grained temporal information increases the predictive power in the…

Understanding Teachers: The Potential and Possibility of Discourse Analysis

ERIC Educational Resources Information Center

Barker, Dean M.; Rossi, Anthony

2011-01-01

Understanding the ways in which teachers make sense of what they do and why is critical to a broader understanding of pedagogy. Historically, teachers have been understood through the thematic and content analysis of their beliefs or philosophies. In this paper, we argue that discourse analysis (DA) involves a much finer-grained analysis of the…

Salton Sea 1/sup 0/ x 2/sup 0/ NTMS area California and Arizona: data report (abbreviated)

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

Heffner, J.D.

1980-09-01

Surface sediment samples were collected at 997 sites. Ground water samples were collected at 76 sites. Neutron activation analysis results are given for uranium and 16 other elements in sediments, and for uranium and 9 other elements in ground water. Mass spectrometry results are given for helium in ground water. Data from ground water sites include (1) water chemistry measurements (pH, conductivity, and alkalinity) (2) physical measurements (water temperature, well description where applicable, and scintillometer reading) and (3) elemental analyses (U, Al, Br, Cl, Dy, F, He, Mg, Mn, Na and V). Data from sediment sites include (1) stream watermore » chemistry measurements from sites where water was available and (2) elemental analyses (U, Th, Hf, Al, Ce, Dy, Eu, Fe, La, Lu, Mn, Sc, Sm, Na, Ti, V, and Yb). Sample site descriptors are given. Areal distribution maps, histograms, and cumulative frequency plots for the elements listed above; U/Th and U/Hf ratios; and scintillometer readings at sediment sample sites are included. Analyses of the sediment fraction finer than 149..mu..m show high uranium values clustered in the Eagle and Chuckwalla Mountains. High uranium values in the 420 ..mu..m to 1000 ..mu..m fraction are clustered in the McCoy Mountains. Both fractions show groups of high values in the Chocolate Mountains at the Southeastern edge of the Chocolate Mountains Aerial Gunnery Range. Aerial distribution of analytical values shows that high values of many elements in both size fractions are grouped around the Eagle Mountains and the Chuckwalla Mountains. Fe, Mn, Ti, V, Sc, Hf, and the rare earth elements, all of which typically occur in high-density minerals, have higher average (log mean) concentrations in the finer fraction than in the coarser fraction.« less

A Novel Field-Based Approach for Analysing Bar Reworking: Trialled in the Tongariro River, New Zealand

NASA Astrophysics Data System (ADS)

Reid, H. E.; Williams, R. D.; Coleman, S.; Brierley, G. J.

2012-04-01

Bars are key morphological units within river systems, fashioning the sediment regime and bedload transport processes within a reach. Reworking of these features underpins channel adjustment at larger scales, thereby acting as a key determinant of channel stability. Yet, despite their fundamental importance to channel evolution, few investigations have acquired spatially continuous data on bar morphology and sediment particle size to facilitate detailed investigations on bar reworking. To this end, four bars along a 10 km reach of wandering gravel bed river were surveyed, capturing downstream changes in slope, bed material size and channel planform. High resolution surveys of bar topography and grain-size roughness were acquired using Terrestrial Laser Scanning (TLS). The resulting point clouds were then filtered to a quasi-uniform point spacing of 0.05 m and statistical attributes were extracted at a 1 m resolution. The detrended standard deviations from the TLS data were then correlated to the underlying median grain size (D50), which was measured using the Wolman transect method. The resulting linear regression model had a strong relationship (R2 = 0.92) and was used to map median sediment size across each bar. Representative cross-sections were used to interpolate water surfaces across each bar, for flood events with recurrence intervals (RI) of 2.33, 10, 20, 50 and 100 years, enabling flow depth to be calculated. The ratio of dimensionless shear stress (from the depth raster and slope) over critical shear stress (from the D50 raster) was used to map entrainment across each bar at 1 m resolution for each flood event. This is referred to as 'relative erodibility'. The two downstream bars, which are characterised by low slope and smaller bed material, underwent greater entrainment during the more frequent 2.33 RI flood than the higher energy upstream bars which required floods with a RI of 10 or greater. Reworking was also assessed for within-bar geomorphic units. This work demonstrated that floods with a 2.33 year RI flush material on the bar tail, while 10 year RI floods rework the supra-platform and back channel deposits and only the largest flows (RI of > = 50) are able to entrain the bar head materials. Interestingly, despite dramatic differences between slope, grain-size and planform, all bar heads were found to undergo minimal entrainment (between 10 - 20 %) during the frequent 2.33 RI flood. This indicates that resistance at the bar head during frequent floods promotes the deposition of finer-grained, more transient units in their lee. This process-based appraisal explains channel adjustment at the reach-scale, whereby the proportion of the bar made out of more frequently entrained units (tail, backchannel, supra-platform) relative to more static units at the bar head exerts a direct influence upon the extent of adjustment of the bar and the reach as a whole.

Local variation of inundation, sedimentary characteristics, and mineral assemblages of the 2011 Tohoku-oki tsunami on the Misawa coast, Aomori, Japan

NASA Astrophysics Data System (ADS)

Nakamura, Yugo; Nishimura, Yuichi; Putra, Purna Sulastya

2012-12-01

The 2011 Tohoku-oki tsunami caused severe damage to the coastal regions of eastern Japan and left a sediment veneer over affected areas. We discuss differences in depositional characteristics of the 2011 Tohoku-oki tsunami from the viewpoint of the sediment source, coastal topography and flow height. The study area on the Misawa coast, northern Tohoku, includes a 20 km long coastline with sandy beaches, coastal dunes and a gently sloping lowland. This landscape assemblage provides an opportunity to examine the effects of topography on the characteristics of the tsunami deposit. During field surveys conducted from April 10 to May 2, 2011, we described the thickness, facies, and structure of the tsunami deposit. We also collected sand samples at approximately 20 m intervals along 13 shore-perpendicular transects extending up to 550 m inland, for grain size and mineral assemblage analysis. The tsunami flow height was estimated by measuring the elevation of debris found in trees, broken tree limbs, or water marks on buildings. The nature of the coastal lowland affected the flow height and inundation distance. In the southern part of the study area, where there is a narrow, 100 m wide low-lying coastal strip, the run-up height reached 10 m on the landward terrace slopes. To the north, the maximum inundation reached 550 m with a run-up height of 3.2 m on the wider, low-lying coastal topography. The average flow height was 4-5 m. The tsunami eroded coastal dunes and formed small scarps along the coast. Immediately landward of the coastal dunes the tsunami deposit was more than 20 cm thick, but thinned markedly inland from this point. Close to the dunes the deposit was composed largely of medium sand (1-2 Φ) with planar and parallel bedding, but with no apparent upward fining or coarsening. The grain size was similar to that of the coastal dune and we infer that the dunes were the local source material for the tsunami deposit at this point. The mineral assemblage of the tsunami deposit was dominated by orthopyroxene and clinopyroxene and was also similar to the dune and beach sand. At sites more than half the inundation distance inland, the thinner tsunami deposit consisted mainly of fine sand (2.375 Φ) with some upward fining. The difference in grain size and sedimentary characteristics was probably caused by differences in sediment transportation and depositional processes. We infer that the well-sorted, finer sediments were deposited out of suspension, whereas the relatively coarse sands were laid down from traction flows. The depositional characteristics of the 2011 Tohoku-oki tsunami deposit appeared to have been affected mainly by the coastal topography and the extent of erosion at any one point, as opposed to flow height.

Quantitative characterisation of sedimentary grains

NASA Astrophysics Data System (ADS)

Tunwal, Mohit; Mulchrone, Kieran F.; Meere, Patrick A.

2016-04-01

Analysis of sedimentary texture helps in determining the formation, transportation and deposition processes of sedimentary rocks. Grain size analysis is traditionally quantitative, whereas grain shape analysis is largely qualitative. A semi-automated approach to quantitatively analyse shape and size of sand sized sedimentary grains is presented. Grain boundaries are manually traced from thin section microphotographs in the case of lithified samples and are automatically identified in the case of loose sediments. Shape and size paramters can then be estimated using a software package written on the Mathematica platform. While automated methodology already exists for loose sediment analysis, the available techniques for the case of lithified samples are limited to cases of high definition thin section microphotographs showing clear contrast between framework grains and matrix. Along with the size of grain, shape parameters such as roundness, angularity, circularity, irregularity and fractal dimension are measured. A new grain shape parameter developed using Fourier descriptors has also been developed. To test this new approach theoretical examples were analysed and produce high quality results supporting the accuracy of the algorithm. Furthermore sandstone samples from known aeolian and fluvial environments from the Dingle Basin, County Kerry, Ireland were collected and analysed. Modern loose sediments from glacial till from County Cork, Ireland and aeolian sediments from Rajasthan, India have also been collected and analysed. A graphical summary of the data is presented and allows for quantitative distinction between samples extracted from different sedimentary environments.

Asia from Space: New Ideas for Exploration

NASA Technical Reports Server (NTRS)

Wilkinson, M. Justin

2011-01-01

Megafans, also known (incorrectly) as inland deltas, are partial cones of fluvial sediment with radii >100 km. Each is generated by a formative river avulsing across a lowland. The alluvial tract (channel, levee, overbank, etc.) is the building block for megafans. Planform and sectional analyses, based on SRTM data, reveal their conical, low-angle morphology. Megafans are not geologically rare as often assumed but a normal feature in the hierarchy of fluvial features that is slowly beginning to be understood. Our global survey contains a total of >150 examples worldwide, in all tectonic basin types, with a majority of smaller, more easily distinguished megafans occupying classic foreland basins (54%) which may explain the general view that megafans only form in Himalaya-like foreland basins, especially since the Kosi Megafan in the Indogangetic Plain is one of the best known in the geological literature. Recent research has shown that all actively alluviating basins are occupied by fanlike sediment masses, from the well known smaller and steeper alluvial fan (level 8 in Miall s hierarchy of fluvial forms), to the much larger megafan feature (level 9). A close relationship exists between upland basin size and fan size and slope. Larger upland drainage basins give rise to low-slope megafan sedimentation, which can cover very large areas where the receptacle basin exists individual megafan areas are 10(sup 3-5) square kilometers, and collectively cover 1.2 million square kilometers in South America, for example. The habitat of megafans is now sufficiently well understood that prediction of some modern cryptic megafan locations has been successfully achieved. Underground prediction therefore seems possible, where sufficient data exists. It seems necessary to distinguish megafans from (i) steep, coarse-grained mountain-front alluvial fans which are overwhelmingly coarse-grained, (ii) deltas, since megafans lack distal shoreline processes), and (iii) confined floodplains which lack radial drainage. Numerous other differences can be identified. As a normal component of the modern fluvial environment, megafans must exist in the subsurface. Megafan size, predictable channel patterns of the formative river, and the gradation from coarser to finer sediments from apex to toe of megafans are characteristics that ought to assist in understanding subsurface patterns of hydrocarbon host rocks, and possibly source rocks as well. We show examples from various producing basins. A roughness map of Asia, based on an algorithm developed for Mars, shows megafan landscapes to be dominated by short baseline roughness and low slopes, consistent with megafan-dominated plains worldwide. Interestingly, this a unique signature for a larger continental landform.

Flow regulation in the Swiss Alps: a river network modelling approach to investigate the impacts on bed load and grain size distribution

NASA Astrophysics Data System (ADS)

Costa, A.; Molnar, P.; Schmitt, R. J. P.

2017-12-01

The grain size distribution (GSD) of river bed sediment results from the long term balance between transport capacity and sediment supply. Changes in climate and human activities may alter the spatial distribution of transport capacity and sediment supply along channels and hence impact local bedload transport and GSD. The effects of changed flow are not easily inferable due the non-linear, threshold-based nature of the relation between discharge and sediment mobilization, and the network-scale control on local sediment supply. We present a network-scale model for fractional sediment transport to quantify the impact of hydropower (HP) operations on river network GSD. We represent the river network as a series of connected links for which we extract the geometric characteristics from satellite images and a digital elevation model. We assign surface roughness based on the channel bed GSD. Bed shear stress is estimated at link-scale under the assumptions of rectangular prismatic cross sections and normal flow. The mass balance between sediment supply and transport capacity, computed with the Wilcock and Crowe model, determines transport rates of multiple grain size classes and the resulting GSD. We apply the model to the upper Rhone basin, a large Alpine basin in Switzerland. Since 1960s, changed flow conditions due to HP operations and sediment storage behind dams have potentially altered the sediment transport of the basin. However, little is known on the magnitude and spatial distribution of these changes. We force the model with time series of daily discharge derived with a spatially distributed hydrological model for pre and post HP scenarios. We initialize GSD under the assumption that coarse grains (d90) are mobilized only during mean annual maximum flows, and on the basis of ratios between d90 and characteristic diameters estimated from field measurements. Results show that effects of flow regulation vary significantly in space and in time and are grain size dependent. HP operations led to an overall reduction of sediment transport at network scale, especially in summer and for coarser grains, leading to a general coarsening of the river bed sediments at the upstream reaches. The model allows investigating the impact of modified HP operations and climate change projections on sediment dynamics at the network scale.

Spatial variations in geochemical characteristics of the modern Mackenzie Delta sedimentary system

NASA Astrophysics Data System (ADS)

Vonk, Jorien E.; Giosan, Liviu; Blusztajn, Jerzy; Montlucon, Daniel; Graf Pannatier, Elisabeth; McIntyre, Cameron; Wacker, Lukas; Macdonald, Robie W.; Yunker, Mark B.; Eglinton, Timothy I.

2015-12-01

The Mackenzie River in Canada is by far the largest riverine source of sediment and organic carbon (OC) to the Arctic Ocean. Therefore the transport, degradation and burial of OC along the land-to-ocean continuum for this riverine system is important to study both regionally and as a dominant representative of Arctic rivers. Here, we apply sedimentological (grain size, mineral surface area), and organic and inorganic geochemical techniques (%OC, δ13C-OC and Δ14C-OC, 143Nd/144Nd, δ2H and δ18O, major and trace elements) on particulate, bank, channel and lake surface sediments from the Mackenzie Delta, as well as on surface sediments from the Mackenzie shelf in the Beaufort Sea. Our data show a hydrodynamic sorting effect resulting in the accumulation of finer-grained sediments in lake and shelf deposits. A general decrease in organic carbon (OC) to mineral surface area ratios from river-to-sea furthermore suggests a loss of mineral-bound terrestrial OC during transport through the delta and deposition on the shelf. The net isotopic value of the terrestrial OC that is lost en route, derived from relationships between δ13C, OC and surface area, is -28.5‰ for δ13C and -417‰ for Δ14C. We calculated that OC burial efficiencies are around 55%, which are higher (∼20%) than other large river systems such as the Amazon. Old sedimentary OC ages, up to 12 14C-ky, suggest the delivery of both a petrogenic OC source (with an estimated contribution of 19 ± 9%) as well as a pre-aged terrestrial OC source. We calculated the 14C-age of this pre-aged, biogenic, component to be about 6100 yrs, or -501‰, which illustrates that terrestrial OC in the watershed can reside for millennia in soils before being released into the river. Surface sediments in lakes across the delta (n = 20) showed large variability in %OC (0.92-5.7%) and δ13C (-30.7‰ to -23.5‰). High-closure lakes, flooding only at exceptionally high water levels, hold high sedimentary OC contents (>2.5%) and young biogenic OC with a terrestrial or an autochthonous source whereas no-closure lakes, permanently connected to a river channel, hold sediments with pre-aged, terrestrial OC. The intermediate low-closure lakes, flooding every year during peak discharge, display the largest variability in OC content, age and source, likely reflecting variability in for example the length of river-lake connections, the distance to sediment source and the number of intermediate settling basins. Bank, channel and suspended sediment show variable 143Nd/144Nd values, yet there is a gradual but distinct spatial transition in 143Nd/144Nd (nearly three ε units; from -11.4 to -13.9) in the detrital fraction of lake surface sediments from the western to the eastern delta. This reflects the input of younger Peel River catchment material in the west and input of older geological source material in the east, and suggests that lake sediments can be used to assess variability in source watershed patterns across the delta.

Autonomous bed-sediment imaging-systems for revealing temporal variability of grain size

USGS Publications Warehouse

Buscombe, Daniel; Rubin, David M.; Lacy, Jessica R.; Storlazzi, Curt D.; Hatcher, Gerald; Chezar, Henry; Wyland, Robert; Sherwood, Christopher R.

2014-01-01

We describe a remotely operated video microscope system, designed to provide high-resolution images of seabed sediments. Two versions were developed, which differ in how they raise the camera from the seabed. The first used hydraulics and the second used the energy associated with wave orbital motion. Images were analyzed using automated frequency-domain methods, which following a rigorous partially supervised quality control procedure, yielded estimates to within 20% of the true size as determined by on-screen manual measurements of grains. Long-term grain-size variability at a sandy inner shelf site offshore of Santa Cruz, California, USA, was investigated using the hydraulic system. Eighteen months of high frequency (min to h), high-resolution (μm) images were collected, and grain size distributions compiled. The data constitutes the longest known high-frequency record of seabed-grain size at this sample frequency, at any location. Short-term grain-size variability of sand in an energetic surf zone at Praa Sands, Cornwall, UK was investigated using the ‘wave-powered’ system. The data are the first high-frequency record of grain size at a single location of a highly mobile and evolving bed in a natural surf zone. Using this technology, it is now possible to measure bed-sediment-grain size at a time-scale comparable with flow conditions. Results suggest models of sediment transport at sandy, wave-dominated, nearshore locations should allow for substantial changes in grain-size distribution over time-scales as short as a few hours.

Delineation of Areas Contributing Water to the Dry Brook Public-Supply Well, South Hadley, Massachusetts

USGS Publications Warehouse

Garabedian, Stephen P.; Stone, Janet Radway

2004-01-01

Areas contributing water to the Dry Brook public-supply well in South Hadley, Massachusetts, were delineated with a numerical ground-water-flow model that is based on geologic and hydrologic information for the confined sand and gravel aquifer pumped by the supply well. The study area is along the Connecticut River in central Massachusetts, about 12 miles north of Springfield, Massachusetts. Geologic units in the study area consist of Mesozoic-aged sedimentary and igneous bedrock, late-Pleistocene glaciolacustrine sediments, and recent alluvial deposits of the Connecticut River flood plain. Dry Brook Hill, immediately south of the supply well, is a large subaqueous lacustrine fan and delta formed during the last glacial retreat by sediment deposition into glacial Lake Hitchcock from a meltwater tunnel that was likely near where the Connecticut River cuts through the Holyoke Range. The sediments that compose the aquifer grade from very coarse sand and gravel along the northern flank of the hill, to medium sands in the body of the hill, and to finer-grained sediments along the southern flank of the hill. The interbedded and overlapping fine-grained lacustrine sediments associated with Dry Brook Hill include varved silt and clay deposits. These fine-grained sediments form a confining bed above the coarse-grained aquifer at the supply well and partially extend under the Connecticut River adjacent to the supply well. Ground-water flow in the aquifer supplying water to Dry Brook well was simulated with the U.S. Geological Survey ground-water-flow modeling code MODFLOW. The Dry Brook aquifer model was calibrated to drawdown data collected from 8 observation wells during an aquifer test conducted by pumping the supply well for 10 days at a rate of 122.2 cubic feet per minute (ft3/min; 914 gallons per minute) and to water levels collected from observation wells across the study area. Generally, the largest hydraulic conductivity values used in the model were in the sand and gravel aquifer near the Dry Brook well, which is consistent with the geologic information. Results of aquifer-test simulation indicated that spatially variable aquifer hydraulic properties and boundary conditions affected heads and ground-water flow near the well. A comparison and analysis of water-level fluctuations in study area wells to fluctuations in the Connecticut River indicated a hydraulic connection of the aquifer with the river, which is also consistent with geologic information. Simulated ground-water levels indicated that most ground water in the study area flowed toward and discharged to the Connecticut River and the Dry Brook well. Small amounts of ground water also discharged to smaller streams (Dry Brook and Bachelor Brook) in the study area. Areas contributing water to the well were delineated with the MODPATH particle-tracking routine. Results of the contributing-area analysis indicated that the greatest sources of water to the well were recharge in the Dry Brook Hill area and infiltration of Connecticut River water in an area beyond the extent of the confining bed where the aquifer is in hydraulic connection with the river. The amount of water entering the Dry Brook well from recharge dominated at a lower pumping rate (40.0 ft3/min); about 90 percent of the pumped water originated from recharge and boundary flow, and infiltration from the Connecticut River supplied the remaining 10 percent. At a high pumping rate (122.2 ft3/min), however, about half of the water pumped from the Dry Brook well originated from recharge and boundary flow (49 percent), and half originated from infiltration of water from the Connecticut River (51 percent). Results of a sensitivity analysis of the extent of areas contributing water to the Dry Brook well when pumped at 122.2 ft3/min indicated that the size of these areas did not substantially change when aquifer properties were varied. In contrast, however, the size of these areas changed most when the recharge

Effects of Annular Electromagnetic Stirring Coupled with Intercooling on Grain Refinement and Homogeneity During Direct Chill Casting of Large-Sized 7005 Alloy Billet

NASA Astrophysics Data System (ADS)

Luo, Yajun; Zhang, Zhifeng; Li, Bao; Gao, Mingwei; Qiu, Yang; He, Min

2017-12-01

To obtain a large-sized, high-quality aluminum alloy billet, an advanced uniform direct chill (UDC) casting method was developed by combining annular electromagnetic stirring (A-EMS) with intercooling in the sump. The 7005 alloy was chosen to investigate the effect of UDC on grain refinement and homogeneity during normal direct chill (NDC) casting. It was concluded that the microstructure consisting of both primary α-Al phase and secondary phases becomes finer and more homogeneous for the billets prepared with UDC casting compared to those prepared with NDC casting, and the forced cooling from both the inner and outer melt under A-EMS has a measurable effect on grain refinement and homogeneity.

Mineralogical characterization of rendering mortars from decorative details of a baroque building in Kozuchow (SW Poland)

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

Bartz, W., E-mail: wojciech.bartz@ing.uni.wroc.pl; Filar, T.

Optical microscopic observations, scanning electron microscopy and microprobe with energy dispersive X-ray analysis, X-ray diffraction and differential thermal/thermogravimetric analysis allowed detailed characterization of rendering mortars from decorative details (figures of Saints) of a baroque building in Kozuchow (Lubuskie Voivodship, Western Poland). Two separate coats of rendering mortars have been distinguished, differing in composition of their filler. The under coat mortar has filler composed of coarse-grained siliceous sand, whereas the finishing one has much finer grained filler, dominated by a mixture of charcoal and Fe-smelting slag, with minor amounts of quartz grains. Both mortars have air-hardening binder composed of gypsum andmore » micritic calcite, exhibiting microcrystalline structure.« less

Grain-Size Based Additivity Models for Scaling Multi-rate Uranyl Surface Complexation in Subsurface Sediments

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

Zhang, Xiaoying; Liu, Chongxuan; Hu, Bill X.

This study statistically analyzed a grain-size based additivity model that has been proposed to scale reaction rates and parameters from laboratory to field. The additivity model assumed that reaction properties in a sediment including surface area, reactive site concentration, reaction rate, and extent can be predicted from field-scale grain size distribution by linearly adding reaction properties for individual grain size fractions. This study focused on the statistical analysis of the additivity model with respect to reaction rate constants using multi-rate uranyl (U(VI)) surface complexation reactions in a contaminated sediment as an example. Experimental data of rate-limited U(VI) desorption in amore » stirred flow-cell reactor were used to estimate the statistical properties of multi-rate parameters for individual grain size fractions. The statistical properties of the rate constants for the individual grain size fractions were then used to analyze the statistical properties of the additivity model to predict rate-limited U(VI) desorption in the composite sediment, and to evaluate the relative importance of individual grain size fractions to the overall U(VI) desorption. The result indicated that the additivity model provided a good prediction of the U(VI) desorption in the composite sediment. However, the rate constants were not directly scalable using the additivity model, and U(VI) desorption in individual grain size fractions have to be simulated in order to apply the additivity model. An approximate additivity model for directly scaling rate constants was subsequently proposed and evaluated. The result found that the approximate model provided a good prediction of the experimental results within statistical uncertainty. This study also found that a gravel size fraction (2-8mm), which is often ignored in modeling U(VI) sorption and desorption, is statistically significant to the U(VI) desorption in the sediment.« less

A combined model for Sediment TRansport In Coastal Hazard Events (GeoClaw-STRICHE): Theoretical formulation and validation

NASA Astrophysics Data System (ADS)

Tang, H.; Weiss, R.

2016-12-01

GeoClaw-STRICHE is designed for simulating the physical impacts of tsunami as it relates to erosion, transport and deposition. GeoClaw-STRICHE comprises GeoClaw for the hydrodynamics and the sediment transport model we refer to as STRICHE, which includes an advection diffusion equation as well as bed-updating. Multiple grain sizes and sediment layers are added into GeoClaw-STRICHE to simulate grain-size distribution and add the capability to develop grain-size trends from bottom to the top of a simulated deposit as well as along the inundation. Unlike previous models based on empirical equations or sediment concentration gradient, the standard Van Leer method is applied to calculate sediment flux. We tested and verified GeoClaw-STRICHE with flume experiment by Johnson et al. (2016) and data from the 2004 Indian Ocean tsunami in Kuala Meurisi as published in Apotsos et al. (2011). The comparison with experimental data shows GeoClaw-STRICHE's capability to simulate sediment thickness and grain-size distribution in experimental conditions, which builds confidence that sediment transport is correctly predicted by this model. The comparison with the data from the 2004 Indian Ocean tsunami reveals that the pattern of sediment thickness is well predicted and is of similar quality, if not better than the established computational models such as Delft3D.

Aeolian Grain Evolution on Mars: Implications for Regolith Origins

NASA Astrophysics Data System (ADS)

Sullivan, R. J.; Cabrol, N. A.; Golombek, M.; Herkenhoff, K. E.; Landis, G.; Mer Athena Science Team

2010-12-01

Early wind tunnel experiments and the Viking Lander experience led to concepts of grain evolution and regolith development on Mars. Wind tunnel experiments showed that 100-150 μm grains are easiest to entrain on Mars, but at 10 times higher wind speeds than on Earth. Even if trajectory speeds of martian saltating grains achieve smaller fractions of entraining wind speeds than on Earth, kinetic energies of these grains would be much higher, with greater potential for damage to the grains during return collisions with the particle bed. On this basis Sagan et al. [1977] JGR 82, 28, 4430 proposed that aeolian grain evolution on Mars followed a “kamikaze” pattern in which an initially coarse grain, entrained only relatively rarely by the strongest winds, would be abraded by high kinetic energy impacts and migrate through successively smaller size-frequencies at an ever-increasing rate (as entrainment became easier and thus more likely) until the grain was essentially turned to dust. On this basis it was proposed that sand-sized grains might be relatively short-lived and perhaps rare on Mars. MER observations motivate adjustments to these concepts, with implications for origins of martian regolith reworked by wind. Along both MER traverses, on opposite sides of the planet, regolith is volumetrically dominated by very fine sand mixed with unresolved finer grains. Sorting probably is poor, based on weakly cohesive remolding by rover wheel cleats. The size-frequency of this material, even if not precisely known, is consistent with grains that have evolved by attrition to sizes smaller than the most easily-moved 100-150 μm interval, to where entrainment becomes more difficult due to the increasing relative importance of inter-particle surface forces. At these smaller sizes also, kinetic energies have been reduced proportionally by the cube of the particle radius, so grain-to-grain attrition is less effective for further evolution to even smaller grain sizes. Characteristics of the most ubiquitous, volumetrically dominant regolith component at both MER sites are consistent with a residuum of grains developed by aeolian grain-to-grain collisions. At both MER sites also: (1) there is a paucity of grains between 300 and 850 μm; and (2) grains >850 μm have participated in creep movements (driven by saltation of finer grains) during past migrations of coarse-grained ripples. These and other observations suggest aeolian grain evolution in which (1) the coarsest grains initially would be driven in creep only, where attrition efficiency might be limited; (2) probability of saltation increases when grain size evolves somewhere below ~900 μm, accelerating further grain evolution to smaller sizes until slowed by decreasing susceptibility to entrainment and (more importantly) decreased collisional effectiveness at grain sizes of <100 μm. We speculate that on a planet where aeolian working of surface materials is common, this grain evolution scenario could have widespread applicability and that regolith grain size-frequency characteristics encountered at both MER sites might be common in many regolith units across the martian surface that have been processed by wind.

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.

Heavy metal anomalies in the Tinto and Odiel River and estuary system, Spain

USGS Publications Warehouse

Nelson, C.H.; Lamothe, P.J.

1993-01-01

The Tinto and Odiel rivers drain 100 km from the Rio Tinto sulphide mining district, and join at a 20-km long estuary entering the Atlantic Ocean. A reconnaissance study of heavy metal anomalies in channel sand and overbank mud of the river and estuary by semi-quantitative emission dc-arc spectrographic analysis shows the following upstream to downstream ranges in ppm (??g g-1): As 3,000 to <200, Cd 30 to <0.1, Cu 1,500 to 10, Pb 2,000 to <10, Sb 3000 to <150, and Zn 3,000 to <200. Organic-rich (1.3-2.6% total organic carbon, TOC), sandysilty overbank clay has been analyzed to represent suspended load materials. The high content of heavy metals in the overbank clay throughout the river and estuary systems indicates the importance of suspended sediment transport for dispersing heavy metals from natural erosion and anthropogenic mining activities of the sulfide deposit. The organic-poor (0.21-0.37% TOC) river bed sand has been analyzed to represent bedload transport of naturally-occurring sulfide minerals. The sand has high concentrations of metals upstream but these decrease an order of magnitude in the lower estuary. Although heavy metal contamination of estuary mouth beach sand has been diluted to background levels estuary mud exhibits increased contamination apparently related to finer grain size, higher organic carbon content, precipitation of river-borne dissolved solids, and input of anthropogenic heavy metals from industrial sources. The contaminated estuary mud disperses to the inner shelf mud belt and offshore suspended sediment, which exhibit metal anomalies from natural erosion and mining of upstream Rio Tinto sulphide lode sources (Pb, Cu, Zn) and industrial activities within the estuary (Fe, Cr, Ti). Because heavy metal contamination of Tinto-Odiel river sediment reaches or exceeds the highest levels encountered in other river sediments of Spain and Europe, a detailed analysis of metals in water and suspended sediment throughout the system, and epidemiological analysis of heavy metal effects in humans is appropriate. ?? 1993 Estuarine Research Federation.

The Problem of Alluvial Fan Slopes

NASA Astrophysics Data System (ADS)

Stock, J. D.; Schmidt, K.

2005-12-01

Water and debris flows exiting confined valleys have a tendency to deposit sediment on steep fans. On alluvial fans, where water transport predominates, channel slopes tend to decrease downfan from ~0.08 to ~0.01 across wide ranges of climate and tectonism. Some have argued that this pattern reflects downfan grainsize fining so that higher slopes are required just to entrain coarser particles in the waters of the upper fan, while entrainment of finer grains downfan requires lower slopes (threshold hypothesis). An older hypothesis is that slope is adjusted to transport the supplied sediment load, which decreases downfan as deposition occurs (transport hypothesis). We have begun to test these hypotheses using detailed field measurements of hydraulic and sediment variables in sediment transport models. On some fans in the western U.S. we find that alluvial fan channel bankfull depths are largely 0.5-1.5 m at fan heads, decreasing to 0.1-0.2 m at distal margins. Contrary to many previous studies, we find that median gravel diameter does not change systematically along the upper 60- 80% of active fan channels. So downstream gravel fining cannot explain most of the observed channel slope reduction. However, as slope declines, surface sand cover increases systematically downfan from values of <20% above fan heads to distal fan values in excess of 70%. As a result, the threshold for sediment motion might decrease systematically downfan, leading to lower slopes. However, current models of this effect alone tend to underpredict downfan slope changes. This is likely due to off- channel gravel deposition. Calculations that match observed fan long-profiles require an exponential decline in gravel transport rate, so that on some fans approximately half of the load must be deposited off-channel every ~0.25-1.25 km downfan. This leads us to hypothesize that alluvial fan long- profiles are largely statements about the rate of deposition downfan. If so, there may be climatic and tectonic information in the long-profile, but a mechanistic theory for downfan deposition rate will be needed.

Morphology, spatial pattern and sediment of Nitraria tangutorum nebkhas in barchans interdune areas at the southeast margin of the Badain Jaran Desert, China

NASA Astrophysics Data System (ADS)

Yang, YanYan; Liu, LianYou; Shi, PeiJun; Zhang, GuoMing; Qu, ZhiQiang; Tang, Yan; Lei, Jie; Wen, HaiMing; Xiong, YiYing; Wang, JingPu; Shen, LingLing

2015-03-01

To understand the characteristics of the nebkhas in barchan interdune areas, isolated barchan dunes at the southeast margin of the Badain Jaran Desert in China and Nitraria tangutorun nebkhas in the interdune areas were selected, and the morphometric parameters, spatial patterns, and granulometric characteristics of the nebkhas in various interdune zones were compared. According to the locations relative to barchan dunes, the interdune areas were divided into three zones: the windward interdune zone (Zw), the leeward interdune zone (Zl), and the horn interdune zone (Zh). The zone that is proximal to barchan dunes and has never been disturbed by barchan dunes was also selected (Zi). The morphometric parameters were measured through a satellite image and field investigation. The population density and spatial patterns were analyzed using the satellite image, and surface sediment samples of the nebkhas and barchan dunes were collected for grain size analysis. The morphometric parameters of Nitraria tangutorun nebkhas in the interdune zones differ significantly. The nebkhas in Zh are larger than those observed in the other zones, and the nebkhas are the smallest in Zl. In all of the zones, the long-axis orientation of the nebkhas is perpendicular to the prevailing wind direction. The population density of the nebkhas in Zw is relatively higher, whereas the density in Zh and Zl becomes obviously lower. The spatial distribution of nebkhas in all of the zones can be categorized as a dispersed pattern. The sediments of the nebkhas are coarsest in Zh and finest in Zl. In addition, the sediments of the nebkhas in all of the zones are finer than those of barchan dunes. The amount of sand captured by the nebkhas in the interdune areas is approximately 20% of the volume of barchan dunes. The variations of the nebkhas' sizes, spatial pattern and sediment are subjected to migration, flow field and sand transport of barchan dunes and sand accumulation with plant growth in the interdune areas, which suggest complex mutual interactions between barchan dunes and the nebkhas in the interdune areas.

Stepwise morphological evolution of the active Yellow River (Huanghe) delta lobe (1976-2013): Dominant roles of riverine discharge and sediment grain size

NASA Astrophysics Data System (ADS)

Wu, Xiao; Bi, Naishuang; Xu, Jingping; Nittrouer, Jeffrey A.; Yang, Zuosheng; Saito, Yoshiki; Wang, Houjie

2017-09-01

The presently active Yellow River (Huanghe) delta lobe has been formed since 1976 when the river was artificially diverted. The process and driving forces of morphological evolution of the present delta lobe still remain unclear. Here we examined the stepwise morphological evolution of the active Yellow River delta lobe including both the subaerial and the subaqueous components, and illustrated the critical roles of riverine discharge and sediment grain size in dominating the deltaic evolution. The critical sediment loads for maintaining the delta stability were also calculated from water discharge and sediment load measured at station Lijin, the last gauging station approximately 100 km upstream from the river mouth. The results indicated that the development of active delta lobe including both subaerial and subaqueous components has experienced four sequential stages. During the first stage (1976-1981) after the channel migration, the unchannelized river flow enhanced deposition within the channel and floodplain between Lijin station and the river mouth. Therefore, the critical sediment supply calculated by the river inputs obtained from station Lijin was the highest. However, the actual sediment load at this stage (0.84 Gt/yr) was more than twice of the critical sediment load ( 0.35 Gt/yr) for sustaining the active subaerial area, which favored a rapid seaward progradation of the Yellow River subaerial delta. During the second stage (1981-1996), the engineering-facilitated channelized river flow and the increase in median grain size of suspended sediment delivered to the sea resulted in the critical sediment load for keeping the delta stability deceasing to 0.29 Gt/yr. The active delta lobe still gradually prograded seaward at an accretion rate of 11.9 km2/yr at this stage as the annual sediment load at Lijin station was 0.55 Gt/yr. From 1996 to 2002, the critical sediment load further decreased to 0.15 Gt/yr with the sediment grain size increased to 22.5 μm; however, the delta suffered net erosion because of the insufficient sediment supply (0.11 Gt/yr). In the most recent stage (2002 - 2013), the intensive scouring of the lower river channel induced by the dam regulation provided relatively coarser sediment, which effectively reduced the critical sediment load to 0.06 Gt/yr, much lower than the corresponding sediment load at Lijin station ( 0.16 Gt/yr). Consequently, the subaerial Yellow River delta transitioned to a slight accretion phase. Overall, the evolution of the active Yellow River delta is highly correlated to riverine water and sediment discharge. The sediment supply for keeping the subaerial delta stability is inconstant and varying with the river channel morphology and sediment grain size. We conclude that the human-impacted riverine sediment discharge and grain-size composition play dominant roles in the stepwise morphological evolution of the active delta lobe.

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.

Physically based method for measuring suspended-sediment concentration and grain size using multi-frequency arrays of acoustic-doppler profilers

USGS Publications Warehouse

Topping, David J.; Wright, Scott A.; Griffiths, Ronald; Dean, David

2014-01-01

As the result of a 12-year program of sediment-transport research and field testing on the Colorado River (6 stations in UT and AZ), Yampa River (2 stations in CO), Little Snake River (1 station in CO), Green River (1 station in CO and 2 stations in UT), and Rio Grande (2 stations in TX), we have developed a physically based method for measuring suspended-sediment concentration and grain size at 15-minute intervals using multifrequency arrays of acoustic-Doppler profilers. This multi-frequency method is able to achieve much higher accuracies than single-frequency acoustic methods because it allows removal of the influence of changes in grain size on acoustic backscatter. The method proceeds as follows. (1) Acoustic attenuation at each frequency is related to the concentration of silt and clay with a known grain-size distribution in a river cross section using physical samples and theory. (2) The combination of acoustic backscatter and attenuation at each frequency is uniquely related to the concentration of sand (with a known reference grain-size distribution) and the concentration of silt and clay (with a known reference grain-size distribution) in a river cross section using physical samples and theory. (3) Comparison of the suspended-sand concentrations measured at each frequency using this approach then allows theory-based calculation of the median grain size of the suspended sand and final correction of the suspended-sand concentration to compensate for the influence of changing grain size on backscatter. Although this method of measuring suspended-sediment concentration is somewhat less accurate than using conventional samplers in either the EDI or EWI methods, it is much more accurate than estimating suspended-sediment concentrations using calibrated pump measurements or single-frequency acoustics. Though the EDI and EWI methods provide the most accurate measurements of suspended-sediment concentration, these measurements are labor-intensive, expensive, and may be impossible to collect at time intervals less than discharge-independent changes in suspended-sediment concentration can occur (< hours). Therefore, our physically based multi-frequency acoustic method shows promise as a cost-effective, valid approach for calculating suspended-sediment loads in river at a level of accuracy sufficient for many scientific and management purposes.

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.

3D granulometry: grain-scale shape and size distribution from point cloud dataset of river environments

NASA Astrophysics Data System (ADS)

Steer, Philippe; Lague, Dimitri; Gourdon, Aurélie; Croissant, Thomas; Crave, Alain

2016-04-01

The grain-scale morphology of river sediments and their size distribution are important factors controlling the efficiency of fluvial erosion and transport. In turn, constraining the spatial evolution of these two metrics offer deep insights on the dynamics of river erosion and sediment transport from hillslopes to the sea. However, the size distribution of river sediments is generally assessed using statistically-biased field measurements and determining the grain-scale shape of river sediments remains a real challenge in geomorphology. Here we determine, with new methodological approaches based on the segmentation and geomorphological fitting of 3D point cloud dataset, the size distribution and grain-scale shape of sediments located in river environments. Point cloud segmentation is performed using either machine-learning algorithms or geometrical criterion, such as local plan fitting or curvature analysis. Once the grains are individualized into several sub-clouds, each grain-scale morphology is determined using a 3D geometrical fitting algorithm applied on the sub-cloud. If different geometrical models can be conceived and tested, only ellipsoidal models were used in this study. A phase of results checking is then performed to remove grains showing a best-fitting model with a low level of confidence. The main benefits of this automatic method are that it provides 1) an un-biased estimate of grain-size distribution on a large range of scales, from centimeter to tens of meters; 2) access to a very large number of data, only limited by the number of grains in the point-cloud dataset; 3) access to the 3D morphology of grains, in turn allowing to develop new metrics characterizing the size and shape of grains. The main limit of this method is that it is only able to detect grains with a characteristic size greater than the resolution of the point cloud. This new 3D granulometric method is then applied to river terraces both in the Poerua catchment in New-Zealand and along the Laonong river in Taiwan, which point clouds were obtained using both terrestrial lidar scanning and structure from motion photogrammetry.

The effects of lithology and landsliding on hillslope sediment supply: case study from southern Italy

NASA Astrophysics Data System (ADS)

Roda-Boluda, Duna; D'Arcy, Mitch; Whittaker, Alex; McDonald, Jordan

2017-04-01

Sediment supply from hillslopes -including volumes, rates and grain size distributions- controls the sediment fluxes from upland areas and modulates how landscapes respond to tectonics. Here, we present new field data from tectonically-active areas in southern Italy that quantifies how lithology and rock-mass strength control the delivery processes and grain size distributions of sediment supplied from hillslopes. We evaluate the influence of landslides on sediment supply along 8 normal faults with excellent tectonic constraints. Frequency-area analysis of the landslide inventory, and a new field-calibrated area-volume scaling relationship, reveal that landsliding in the area is not dominated by large landslides (β ˜2), with 83% of landslides being < 0.1 km2 and shallower than 3 m. Based on volumetric estimates and published erosion rates, we infer that our inventory likely represents the integrated record of landsliding over 1-3 kyrs, implying minimum sediment fluxes between 6.90 x 102 and 2.07 x 103 m3/yr. We demonstrate that outcrop-scale rock-mass strength controls both landslide occurrence and the grain sizes supplied by bedrock weathering, for different lithologies. Comparisons of particle size distributions from bedrock weathering with those measured on landslide deposits demonstrates that landslides supply systematically coarser material, with lithology influencing the degree of coarsening. Finally, we evaluate the effect of landslide supply on fluvial sediment export, and show that D84 grain size increases by ˜ 6 mm for each 100-m increment in incision depth, due to the combination of enhanced landsliding and transport capacity in more incised catchments. Our results reveal a dual control of lithology and rock-mass strength on both the sediment volumes and grain sizes supplied to the fluvial system, which we demonstrate has a significant impact on sediment export from upland areas. This study provides a uniquely detailed field data set for studying how tectonics and lithology control hillslope erosion and sediment characteristics.

Strain localization in the lower crust: brittle precursors versus lithological heterogeneities (Musgrave Ranges, Central Australia)

NASA Astrophysics Data System (ADS)

Hawemann, Friedrich; Mancktelow, Neil; Wex, Sebastian; Pennacchioni, Giorgio; Camacho, Alfredo

2016-04-01

The Davenport shear zone in Central Australia is a strike-slip ductile shear zone developed during the Petermann Orogeny (~ 550 Ma). The conditions of shearing are estimated to be amphibolite-eclogite facies (650 °C, 1.2 GPa). The up to seven kilometre thick mylonite zone encloses several large low strain domains with excellent exposure, thus allowing a thorough study of the initiation of shear zones. Quartzo-feldspathic gneisses and granitoids inherit a suite of lithological heterogeneities such as quartz-rich pegmatites, mafic layers and dykes. When in a favourable orientation to the shortening direction, these rheologically different pre-existing layers might be expected to localize deformation. However, with the singular exception of long, continuous and fine-grained dolerite dykes, this is not observed. Quartz-rich pegmatites are mostly unsheared, even if in a favourable orientation, and sometimes boudinaged or folded. There are instead many shear zones only a few mm to cm in width, extending up to tens of metres, which are in fact oriented at a very high angle to the shortening direction. Parallel to these, a network of little to moderately overprinted brittle fractures are observed, commonly marked by pseudotachylyte (pst) and sometimes new biotite. Shear reactivation of these precursor fractures is generally limited to the length of the initial fracture and typically re-uses and shears the pst. The recrystallized mineral assemblage in the sheared pst consists of Cpx+Grt+Fsp±Ky and is the same to that in the adjacent sheared gneiss, with the same PT estimates (650 °C, 1.2 GPa). In some cases, multiple generations of cross-cutting and sheared pst demonstrate alternating fracture and flow during progressive shear zone development and a clear tendency for subsequent pst formation to also localize in the existing shear zone. The latest pst may be both unsheared and unrecrystallized (no grt) and is probably related to a late stage, still localized within the same shear zone. The observation that pst is preferentially sheared indicates that it is weaker than the host rock, although their bulk compositions are about the same, suggesting that the governing factors for localization are the finer grain size and the elongate, nearly planar geometry of the original pst generation zone. The same may be true of the sheared dolerite dykes, which are long, narrow and generally finer grained than the surrounding gneiss or granite. Although quartz-rich pegmatites are not preferred sites of localization, quartzo-feldspathic mylonites are fully recrystallized with a relatively coarse grain size (typically > 50 microns) typical of rather low long-term flow stress. We therefore propose that localization in the lower crust only occurs on long planar layers with a finer grain size that can promote weakening by grain-size sensitive creep. Coarser-grained lithological layers and boundaries are not exploited during the initiation of a shear zone and, in particular, quartz-rich layers are not preferentially sheared.

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.

Are mangroves as tough as a seawall? Flow-vegetation interaction in a living shoreline restoration

NASA Astrophysics Data System (ADS)

Kibler, K. M.; Kitsikoudis, V.; Spiering, D. W.

2017-12-01

This study aims to assess the impact of an established living shoreline restoration on near-shore hydraulics, shoreline slope, and sediment texture and organic matter content. We collected data from three 100 m shoreline sites within an estuarine lagoon in Canaveral National Seashore: one restored; one that had been stabilized by a seawall; and one in a reference condition stabilized by mature mangrove vegetation. The living shoreline site was restored five years prior with a breakwater of oyster shell bags, emergent marsh grasses (Spartina alterniflora), and mangroves (Rhizophora mangle and Avicennia germinans). We sampled water depth and incoming velocity profiles of the full water column at 2 Hz using a 2 MHz Acoustic Doppler Current Profiler (ADCP, Nortek), stationed down-looking, approximately 10 m offshore. A 2 - 3 cm velocity profile above the bed was sampled on the shoreline at 100 Hz, using a Nortek Vectrino profiler. In restored and reference sites, the onshore probe was placed within vegetation. We surveyed vegetation upstream of the probe for species and diameter at water level. Windspeed and direction were collected 2 m above the water surface. Shorelines were surveyed in transects using GPS survey equipment. Five sediment cores were collected to 20 cm depth from both onshore and offshore of each site. Individual cores were processed for loss on ignition before being pooled by site for analysis of grain size distribution. While incoming velocity profiles were similar between sites, hydraulic conditions onshore within the vegetated sites deviated from the seawall site, which was devoid of vegetation. Offshore to onshore gradients in shear stress, mean velocity, and turbulent kinetic energy differed widely between sites, despite similar wind and tidal conditions. Sediment grain sizes were finer and contained more organic matter in the restored and reference sites than in the seawall site. Profiles of the restored and seawall sites were similar, though the reference site had a more complex bathymetry. Variable hydraulic patterns observed at restored and reference sites may attribute to differences in dominant vegetation-water interactions. Interactions at the reference site were characterized by flow between mangrove prop roots while the restored site consisted mainly of Spartina leaves.

Particle size reduction in debris flows: Laboratory experiments compared with field data from Inyo Creek, California

NASA Astrophysics Data System (ADS)

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

2014-12-01

Rock particles in debris flows are reduced in size through abrasion and fracture. Wear of coarse sediments results in production of finer particles, which alter the bulk material rheology and influence flow dynamics and runout distance. Particle wear also affects the size distribution of coarse particles, transforming the initial sediment size distribution produced on hillslopes into that delivered to the fluvial channel network. A better understanding of the controls on particle wear in debris flows would aid in the inferring flow conditions from debris flow deposits, in estimating the initial size of sediments entrained in the flow, and in modeling debris flow dynamics and mapping hazards. The rate of particle size reduction with distance traveled should depend on the intensity of particle interactions with other particles and the flow boundary, and on rock resistance to wear. We seek a geomorphic transport law to predict rate of particle wear with debris flow travel distance as a function of particle size distribution, flow depth, channel slope, fluid composition and rock strength. Here we use four rotating drums to create laboratory debris flows across a range of scales. Drum diameters range from 0.2 to 4.0 m, with the largest drum able to accommodate up to 2 Mg of material, including boulders. Each drum has vanes along the boundary to prevent sliding. Initial experiments use angular clasts of durable granodiorite; later experiments will use less resistant rock types. Shear rate is varied by changing drum rotational velocity. We begin experiments with well-sorted coarse particle size distributions, which are allowed to evolve through particle wear. The fluid is initially clear water, which rapidly acquires fine-grained wear products. After each travel increment all coarse particles (mass > 0.4 g) are weighed individually. We quantify particle wear rates using statistics of size and mass distributions, and by fitting various comminution functions to the data. Laboratory data are compared with longitudinal evolution of grain size and angularity of particles deposited by debris flows along Inyo Creek, Sierra Nevada, California. Preliminary results suggest wear rates can be scaled across drum sizes and to field conditions using non-dimensional metrics of flow dynamics including Savage, Bagnold, and Froude numbers.

How well do basic models describe the turbidity currents coming down Monterey and Congo Canyon?

NASA Astrophysics Data System (ADS)

Cartigny, M.; Simmons, S.; Heerema, C.; Xu, J. P.; Azpiroz, M.; Clare, M. A.; Cooper, C.; Gales, J. A.; Maier, K. L.; Parsons, D. R.; Paull, C. K.; Sumner, E. J.; Talling, P.

2017-12-01

Turbidity currents rival rivers in their global capacity to transport sediment and organic carbon. Furthermore, turbidity currents break submarine cables that now transport >95% of our global data traffic. Accurate turbidity current models are thus needed to quantify their transport capacity and to predict the forces exerted on seafloor structures. Despite this need, existing numerical models are typically only calibrated with scaled-down laboratory measurements due to the paucity of direct measurements of field-scale turbidity currents. This lack of calibration thus leaves much uncertainty in the validity of existing models. Here we use the most detailed observations of turbidity currents yet acquired to validate one of the most fundamental models proposed for turbidity currents, the modified Chézy model. Direct measurements on which the validation is based come from two sites that feature distinctly different flow modes and grain sizes. The first are from the multi-institution Coordinated Canyon Experiment (CCE) in Monterey Canyon, California. An array of six moorings along the canyon axis captured at least 15 flow events that lasted up to hours. The second is the deep-sea Congo Canyon, where 10 finer grained flows were measured by a single mooring, each lasting several days. Moorings captured depth-resolved velocity and suspended sediment concentration at high resolution (<30 second) for each of the 25 events. We use both datasets to test the most basic model available for turbidity currents; the modified Chézy model. This basic model has been very useful for river studies over the past 200 years, as it provides a rapid estimate of how flow velocity varies with changes in river level and energy slope. Chézy-type models assume that the gravitational force of the flow equals the friction of the river-bed. Modified Chézy models have been proposed for turbidity currents. However, the absence of detailed measurements of friction and sediment concentration within full-scale turbidity currents has forced modellers to make rough assumptions for these parameters. Here we use mooring data to deduce observation-based relations that can replace the previous assumptions. This improvement will significantly enhance the model predictions and allow us to better constrain the behaviour of turbidity currents.

Sediment transport by runoff on debris-mantled dryland hillslopes

NASA Astrophysics Data System (ADS)

Michaelides, Katerina; Martin, Gareth J.

2012-09-01

Hillslopes supply sediment to river channels, and therefore impact drainage basin functioning and evolution. The relationship between hillslope attributes and sediment flux forms the basis of geomorphic transport laws used to model the long-term topographic evolution of drainage basins, but their specific interactions during individual storm events are not well understood. Runoff-driven erosion of coarse particles, prevalent in dryland environments, presents a particular set of conditions for sediment transport that is poorly resolved in current models. In order to address this gap, we developed a particle-based, force-balance model for sheetwash sediment transport on coarse, debris-mantled hillslopes within a rainfall-runoff model. We use the model to examine how the interplay between hillslope attributes (gradient, length and grain size distribution) and runoff characteristics affects sediment transport, grain-size changes on the hillslope, and sediment supply to the slope base. The relationship between sediment flux and hillslope gradient was found to transition from linear above a threshold to sigmoidal depending on hillslope length, initial grain sizes, and runoff characteristics. Grain sizes supplied to the slope base vary in a complex manner with hillslope attributes but an overall coarsening of the hillslopes is found to occur with increasing gradient, corroborating previous findings from field measurements. Intense, short duration storms result in within-hillslope sediment redistribution and equifinality in sediment supply for different hillslope characteristics, which explain the lack of field evidence for any systematic relationships. Our model findings provide insights into hillslope responses to climatic forcing and have theoretical implications for modeling hillslope evolution in dry lands.

Size stratification in a Gilbert delta due to a varying base level: flume experiments.

NASA Astrophysics Data System (ADS)

Chavarrias, Victor; Orru, Clara; Viparelli, Enrica; Vide, Juan Pedro Martin; Blom, Astrid

2014-05-01

A foreset-dominated Gilbert delta is a delta that is dominated by sediment avalanches (i.e., discontinuous grain flows) over its front. It forms when a river flows into a basin or sea characterized by a flow depth that is much larger than the one in the fluvial reach, and the conditions are such that the transported sediment passing the brinkpoint forms a wedge at the topmost part of the foreset, which results in avalanches down the foreset and a fining upward pattern within the foreset deposit. A Gilbert delta is typically described in terms of a low-slope topset (resulting from deposition over the fluvial reach), a steep-slope foreset (resulting from sediment avalanches over the lee face), and a bottomset (resulting from deposition of fine sediment passing the brinkpoint as suspended load). The objective of the present study is to gain insight into the mechanisms taking part in Gilbert delta formation and progradation under variable base level conditions. In order to do so, three flume experiments were conducted in which the water discharge and sediment feed rate were maintained constant but the base level varied between the experiments: (I) constant base level, (II) a gradually rising base level, and (III) a slowly varying base level. The stratigraphy within the delta deposit was measured using image analysis combined with particle coloring. A steady base level resulted in aggradation over the fluvial reach in order to maintain a slope required to transport the supplied sediment downstream. Sea level rise enhanced the amount of aggradation over the fluvial reach due to the presence of an M1 backwater curve. The aggrading flux to the substrate was slightly coarser than the fed sediment. The sediment at the base of the foreset deposit appeared to become coarser in streamwise direction. Eventually, a fall of the base level induced an M2 backwater curve over the fluvial reach that caused degradation of the fluvial reach. Base level fall first induced erosion of the mobile armor that covered the fluvial reach. This led to an initial coarsening of the brinkpoint load (and foreset deposit). Once the mobile armour was eroded, base level fall led to degradation of the finer substrate, which resulted in a fining of the brinkpoint load and foreset deposit. The relation between the sediment size stratification and the base level change may be used for the reconstruction of the paleo sea level from the stratigraphy of ancient Gilbert deltas.

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.

Sediment suspension and the dynamic mechanism during storms in the Yellow River Delta.

PubMed

Bian, Shuhua; Hu, Zjian; Liu, Jianqiang; Zhu, Zichen

2016-12-01

The suspension and hydrodynamic characteristics of the Yellow River Delta during storms were analyzed based on suspended samples obtained using automatic samplers during a storm event in the Yellow River Delta. Synchronous data for winds, waves, and tides were also collected from a nearby station. The results show that under wind speeds of 5-15 m/s and wave heights of 50-150 cm, the suspended content reached 5.7-49.6 kg/m 3 , which is 10-100 times higher than that under normal weather conditions. The medium diameter of suspended particles was 1.2-2.1 μm (8.9-9.7 Φ), which was approximately 1-2 Φ finer than that under normal weather conditions. During the early stages of the measurements, the sea level had risen by 50 cm owing to the storm, which was in addition to the tidal sea level change. We suggest that during the storms, the waves strengthened and the storm-induced sea level change, which was combined with tidal currents moving in the same direction, produced high-speed currents. This overcame the cohesive forces among the fine sediment particles and suspended a large amount of sediment. As a result, the suspended content increased markedly and the suspended particle size became finer. This explains the intense siltation and erosion of the Yellow River Delta during storms.

Liquid impact and fracture of free-standing CVD diamond

NASA Astrophysics Data System (ADS)

Kennedy, Claire F.; Telling, Robert H.; Field, John E.

1999-07-01

The Cavendish Laboratory has developed extensive facilities for studies of liquid and solid particle erosion. This paper describes the high-speed liquid impact erosion of thin CVD diamond discs and the variation with grain sizes of the absolute damage threshold velocity (ADTV), viz., the threshold below which the specimen shows no damage. All specimens fail by rear surface cracking and there is shown to be a shallow dependence of rear surface ADTV on grain size. Fracture propagation in CVD diamond has also been monitored using a specially-designed double-torsion apparatus and data for K1C are presented. Tentatively, the results suggest that finer-grained CVD diamond exhibits a higher fracture toughness, although the differences are slight even over a fourfold variation in the mean grain size. No preference for intergranular fracture was observed and one may conclude from this that the grain boundaries themselves do not seriously weaken the material. The large pre-existing flaws, both within and between grains, whose size varies the grain size are believed to be the dominant source of weakness.

Evaluation of suspended sediment concentrations in a hydropower reservoir by using a Laser In-Situ Scattering and Transmissometry instrument

NASA Astrophysics Data System (ADS)

Lizano, Laura; Haun, Stefan

2014-05-01

Sediment transported by rivers start to settle when they enter a reservoir due to reduced flow velocities and turbulences. Reservoir sedimentation is a common problem today and eliminates about 1% of the worldwide existing storage capacity annually. However, depending on the climate conditions and the geology in the catchment area this value can increase up to 5% and higher. Among the results of reservoir deposition is the loss of the storage capacity, a loss of flood control benefits or even blockage of intakes due to sediment accumulation in front of the structure. As a consequence, management tasks have to be planned and conducted to guarantee a safe and economical reservoir operation. A major part of the sediment particles entering the reservoir is transported as suspended sediment load. Hence, accurate knowledge of the transport processes of these particles in the reservoir is advantageous for planning and predicting a sustainable reservoir operation. Of special interest is the spatial distribution of the grain sizes in the reservoir, for example, which grain sizes can be expected to enter the waterway and have a major contribution in turbine abrasion. The suspended sediment concentrations and the grain size distribution along the Sandillal reservoir in Costa Rica were measured in this study by using a Laser In-Situ Scattering and Transmissometry instrument (LISST-SL). The instrument measures sediment concentrations as well as the grain size distributions instantaneously (32 grain sizes in the range between 2.1 and 350 μm) with a frequency of 0.5 Hertz. The measurements were applied at different pre-specified transects along the reservoir, in order to assess the spatial distribution of the suspended sediment concentrations. The measurements were performed in vertical lines, at different depths and for a period of 60 seconds. Additionally, the mean grain size distribution was calculated from the data for each measured point. The measurements showed that the suspended sediment concentrations were low during the field campaign. However, they gave insight of the spatial distribution of the suspended sediments along the reservoir and at different depths. The measurements in front of the intake were especially interesting, since the concentration and the sizes of the particles, which will furthermore enter the intake, could be evaluated.

Riparian soil development linked to forest succession above and below dams along the Elwha River, Washington, USA

USGS Publications Warehouse

Perry, Laura G; Shafroth, Patrick B.; Perakis, Steven

2017-01-01

Riparian forest soils can be highly dynamic, due to frequent fluvial disturbance, erosion, and sediment deposition, but effects of dams on riparian soils are poorly understood. We examined soils along toposequences within three river segments located upstream, between, and downstream of two dams on the Elwha River to evaluate relationships between riparian soil development and forest age, succession, and channel proximity, explore dam effects on riparian soils, and provide a baseline for the largest dam removal in history. We found that older, later-successional forests and geomorphic surfaces contained soils with finer texture and greater depth to cobble, supporting greater forest floor mass, mineral soil nutrient levels, and cation exchange. Forest stand age was a better predictor than channel proximity for many soil characteristics, though elevation and distance from the channel were often also important, highlighting how complex interactions between fluvial disturbance, sediment deposition, and biotic retention regulate soil development in this ecosystem. Soils between the dams, and to a lesser extent below the lower dam, had finer textures and higher mineral soil carbon, nitrogen, and cation exchange than above the dams. These results suggested that decreased fluvial disturbance below the dams, due to reduced sediment supply and channel stabilization, accelerated soil development. In addition, reduced sediment supply below the dams may have decreased soil phosphorus. Soil δ15N suggested that salmon exclusion by the dams had no discernable effect on nitrogen inputs to upstream soils. Recent dam removal may alter riparian soils further, with ongoing implications for riparian ecosystems.

The effect of grain size and surface area on organic matter, lignin and carbohydrate concentration, and molecular compositions in Peru Margin sediments

USGS Publications Warehouse

Bergamaschi, B.A.; Tsamakis, E.; Keil, R.G.; Eglinton, T.I.; Montlucon, D.B.; Hedges, J.I.

1997-01-01

A C-rich sediment sample from the Peru Margin was sorted into nine hydrodynamically-determined grain size fractions to explore the effect of grain size distribution and sediment surface area on organic matter content and composition. The neutral monomeric carbohydrate composition, lignin oxidation product yields, total organic carbon, and total nitrogen contents were determined independently for each size fraction, in addition to sediment surface area and abundance of biogenic opal. The percent organic carbon and percent total nitrogen were strongly related to surface area in these sediments. In turn, the distribution of surface area closely followed mass distribution among the textural size classes, suggesting hydrodynamic controls on grain size also control organic carbon content. Nevertheless, organic compositional distinctions were observed between textural size classes. Total neutral carbohydrate yields in the Peru Margin sediments were found to closely parallel trends in total organic carbon, increasing in abundance among grain size fractions in proportion to sediment surface area. Coincident with the increases in absolute abundance, rhamnose and mannose increased as a fraction of the total carbohydrate yield in concert with surface area, indicating these monomers were preferentially represented in carbohydrates associated with surfaces. Lignin oxidation product yields varied with surface area when normalized to organic carbon, suggesting that the terrestrially-derived component may be diluted by sorption of marine derived material. Lignin-based parameters suggest a separate source for terrestrially derived material associated with sand-size material as opposed to that associated with silts and clays. Copyright ?? 1997 Elsevier Science Ltd.

The effect of grain size and surface area on organic matter, lignin and carbohydrate concentration, and molecular compositions in Peru Margin sediments

NASA Astrophysics Data System (ADS)

Bergamaschi, Brian A.; Tsamakis, Elizabeth; Keil, Richard G.; Eglinton, Timothy I.; Montluçon, Daniel B.; Hedges, John I.

1997-03-01

A C-rich sediment sample from the Peru Margin was sorted into nine hydrodynamically-determined grain size fractions to explore the effect of grain size distribution and sediment surface area on organic matter content and composition. The neutral monomeric carbohydrate composition, lignin oxidation product yields, total organic carbon, and total nitrogen contents were determined independently for each size fraction, in addition to sediment surface area and abundance of biogenic opal. The percent organic carbon and percent total nitrogen were strongly related to surface area in these sediments. In turn, the distribution of surface area closely followed mass distribution among the textural size classes, suggesting hydrodynamic controls on grain size also control organic carbon content. Nevertheless, organic compositional distinctions were observed between textural size classes. Total neutral carbohydrate yields in the Peru Margin sediments were found to closely parallel trends in total organic carbon, increasing in abundance among grain size fractions in proportion to sediment surface area. Coincident with the increases in absolute abundance, rhamnose and mannose increased as a fraction of the total carbohydrate yield in concert with surface area, indicating these monomers were preferentially represented in carbohydrates associated with surfaces. Lignin oxidation product yields varied with surface area when normalized to organic carbon, suggesting that the terrestrially-derived component may be diluted by sorption of marine derived material. Lignin-based parameters suggest a separate source for terrestrially derived material associated with sand-size material as opposed to that associated with silts and clays.

Sedimentology of the upper Karoo fluvial strata in the Tuli Basin, South Africa

NASA Astrophysics Data System (ADS)

Bordy, Emese M.; Catuneanu, Octavian

2001-08-01

The sedimentary rocks of the Karoo Supergroup in the Tuli Basin (South Africa) may be grouped in four stratigraphic units: the basal, middle and upper units, and the Clarens Formation. This paper presents the findings of the sedimentological investigation of the fluvial terrigenous clastic and chemical deposits of the upper unit. Evidence provided by primary sedimentary structures, palaeontological record, borehole data, palaeo-flow measurements and stratigraphic relations resulted in the palaeo-environmental reconstruction of the upper unit. The dominant facies assemblages are represented by sandstones and finer-grained sediments, which both can be interbedded with subordinate intraformational coarser facies. The facies assemblages of the upper unit are interpreted as deposits of a low-sinuosity, ephemeral stream system with calcretes and silcretes in the dinosaur-inhabited overbank area. During the deposition of the upper unit, the climate was semi-arid with sparse precipitation resulting in high-magnitude, low-frequency devastating flash floods. The current indicators of the palaeo-drainage system suggest flow direction from northwest to southeast, in a dominantly extensional tectonic setting. Based on sedimentologic and biostratigraphic evidence, the upper unit of the Tuli Basin correlates to the Elliot Formation in the main Karoo Basin to the south.

Erosion of ejecta at Meteor Crater, Arizona

NASA Technical Reports Server (NTRS)

Grant, John A.; Schultz, Peter H.

1993-01-01

New methods for estimating erosion at Meteor Crater, Arizona, indicate that continuous ejecta deposits beyond 1/4-1/2 crater radii from the rim have been lowered less than 1 m on the average. This conclusion is based on the results of two approaches: coarsening of unweathered ejecta into surface lag deposits and calculation of the sediment budget within a drainage basin on the ejecta. Preserved ejecta morphologies beneath thin alluvium revealed by ground-penetrating radar provide qualitative support for the derived estimates. Although slightly greater erosion of less resistant ejecta locally has occurred, such deposits were limited in extent, particularly beyond 0.25R-0.5R from the present rim. Subtle but preserved primary ejecta features further support our estimate of minimal erosion of ejecta since the crater formed about 50,000 years ago. Unconsolidated deposits formed during other sudden extreme events exhibit similarly low erosion over the same time frame; the common factor is the presence of large fragments or large fragments in a matrix of finer debris. At Meteor Crater, fluvial and eolian processes remove surrounding fines leaving behind a surface lag of coarse-grained ejecta fragments that armor surfaces and slow vertical lowering.

Quantifying grain shape with MorpheoLV: A case study using Holocene glacial marine sediments

NASA Astrophysics Data System (ADS)

Charpentier, Isabelle; Staszyc, Alicia B.; Wellner, Julia S.; Alejandro, Vanessa

2017-06-01

As demonstrated in earlier works, quantitative grain shape analysis has revealed to be a strong proxy for determining sediment transport history and depositional environments. MorpheoLV, devoted to the calculation of roughness coefficients from pictures of unique clastic sediment grains using Fourier analysis, drives computations for a collection of samples of grain images. This process may be applied to sedimentary deposits assuming core/interval/image archives for the storage of samples collected along depth. This study uses a 25.8 m jumbo piston core, NBP1203 JPC36, taken from a 100 m thick sedimentary drift deposit from Perseverance Drift on the northern Antarctic Peninsula continental shelf. Changes in ocean and ice conditions throughout the Holocene recorded in this sedimentary archive can be assessed by studying grain shape, grain texture, and other proxies. Ninety six intervals were sampled and a total of 2319 individual particle images were used. Microtextures of individual grains observed by SEM show a very high abundance of authigenically precipitated silica that obscures the original grain shape. Grain roughness, computed along depth with MorpheoLV, only shows small variation confirming the qualitative observation deduced from the SEM. Despite this, trends can be seen confirming the reliability of MorpheoLV as a tool for quantitative grain shape analysis.

Seafloor Mapping and Benthic Habitats off Assateague Island National Seashore: can we Resolve any Effects of Superstorm Sandy?

NASA Astrophysics Data System (ADS)

Miller, D.; Trembanis, A. C.; Kennedy, E.; Rusch, H.; Rothermel, E.

2016-02-01

The National Park Service has partnered with faculty and students at the University of Delaware to map the length of Assateague Island and sample benthic communities there for two purposes: (1) to provide a complete inventory of benthic habitats and their biota, and (2) to determine if any changes from a pre-storm survey can be ascribed to Superstorm Sandy in 2012. During the 2014 and 2015 field seasons over 75 km2 of high-resolution ( 50 cm/pixel) side-scan sonar and collocated bathymetry were collected with a surface vessel mounted bathy side-scan sonar (EdgeTech 6205), spanning the shore from depths of less than 2 m out to a distance of approximately 1 nautical mile and depths of 10-12 m. Furthermore, we have resampled using standard methodology (modified Young grab and 0.5-mm sieve) a subset of the previously sampled benthic stations that represent all sediment classes identified in prior studies. Additionally, we have obtained novel data with our ROV and AUV assets, including finer scale bottom video and multibeam bathymetry, at specifically chosen locations in order to enhance understanding of the benthic habitat and bottom type changes. In addition to providing a habitat and faunal inventory for resource management purposes, we will compare our side scan and benthic survey data to the pre-storm 2011 data products with comparable coverage. To date we have found that ArcGIS and ENVI sediment classifications agree well with those from the 2011 study, but spatially we note more areas of finer sediments and less of gravel. As was expected, 2014 benthic assemblages differ significantly among sediment classes (PRIMER ANOSIM), and sediment class is the best predictor of the benthic community (PERMANOVA+ distance-based RDA). Our goal here is to use consistent analytical approaches to characterize changes that occur over season and inter-annual time scales. This is a critical step toward attributing sediment, habitat and biological changes to Superstorm Sandy.

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.

JPRS Report, Science & Technology, Japan

DTIC Science & Technology

1991-01-31

final test. Keywords: Spherical Pressure Hull, Titanium Alloy , Three-Dimensional Machining, Electron Beam Welding . 1. Introduction In bodies like... processed (the heat treatment involving high-temperature heating and rapid quenching in order to obtain finer grains of the titanium alloy ) and...given m Table 3. The test results were all satisfactory. Forged material of titanium alloy , manufactured by forging, beta processing , and billet

Integrating Colon Cancer Microarray Data: Associating Locus-Specific Methylation Groups to Gene Expression-Based Classifications.

PubMed

Barat, Ana; Ruskin, Heather J; Byrne, Annette T; Prehn, Jochen H M

2015-11-23

Recently, considerable attention has been paid to gene expression-based classifications of colorectal cancers (CRC) and their association with patient prognosis. In addition to changes in gene expression, abnormal DNA-methylation is known to play an important role in cancer onset and development, and colon cancer is no exception to this rule. Large-scale technologies, such as methylation microarray assays and specific sequencing of methylated DNA, have been used to determine whole genome profiles of CpG island methylation in tissue samples. In this article, publicly available microarray-based gene expression and methylation data sets are used to characterize expression subtypes with respect to locus-specific methylation. A major objective was to determine whether integration of these data types improves previously characterized subtypes, or provides evidence for additional subtypes. We used unsupervised clustering techniques to determine methylation-based subgroups, which are subsequently annotated with three published expression-based classifications, comprising from three to six subtypes. Our results showed that, while methylation profiles provide a further basis for segregation of certain (Inflammatory and Goblet-like) finer-grained expression-based subtypes, they also suggest that other finer-grained subtypes are not distinctive and can be considered as a single subtype.

Integrating Colon Cancer Microarray Data: Associating Locus-Specific Methylation Groups to Gene Expression-Based Classifications

PubMed Central

Barat, Ana; Ruskin, Heather J.; Byrne, Annette T.; Prehn, Jochen H. M.

2015-01-01

Recently, considerable attention has been paid to gene expression-based classifications of colorectal cancers (CRC) and their association with patient prognosis. In addition to changes in gene expression, abnormal DNA-methylation is known to play an important role in cancer onset and development, and colon cancer is no exception to this rule. Large-scale technologies, such as methylation microarray assays and specific sequencing of methylated DNA, have been used to determine whole genome profiles of CpG island methylation in tissue samples. In this article, publicly available microarray-based gene expression and methylation data sets are used to characterize expression subtypes with respect to locus-specific methylation. A major objective was to determine whether integration of these data types improves previously characterized subtypes, or provides evidence for additional subtypes. We used unsupervised clustering techniques to determine methylation-based subgroups, which are subsequently annotated with three published expression-based classifications, comprising from three to six subtypes. Our results showed that, while methylation profiles provide a further basis for segregation of certain (Inflammatory and Goblet-like) finer-grained expression-based subtypes, they also suggest that other finer-grained subtypes are not distinctive and can be considered as a single subtype. PMID:27600244

Alpine lakes preserve mineral dust signatures: Implications for long-range mineral dust transport and Last Glacial Maximum (LGM) tornado frequency in the United States

NASA Astrophysics Data System (ADS)

Bhattacharya, A.; Lora, J. M.; Pollen, A.; Vollmer, T.; Thomas, M.; Leithold, E. L.; Mitchell, J.; Tripati, A.

2016-12-01

The net amount of mineral dust accumulation in arid and semi-arid regions might not be entirely sourced locally or even regionally; in fact, new evidence suggests that there could be significant contributions from distal sources. The contribution from the distal sources needs to be identified, and accounted for, in order to accurately understand the meteorological and climatologic factors, both regional and global, that control mineral dust accumulation in arid and semi-arid regions. Most importantly, if identified, the two components of mineral dust accumulation- fine fraction (typically <4 microns) and coarse fraction (typically >25 microns)- could provide critical information about regional as well as global climate. There are large-scale climatological controls on the finer fraction of mineral dust, while the coarser fraction is related to intense invents (i.e., the occurrence of cyclones). However, studies attempting to separate these two size fractions in terrestrial archives have been limited. Here we separate the two size fractions using grain size analysis, and use trace element analysis in each size fraction to identify contributing source regions. We apply this technique to well-dated cores collected from three lakes that are distributed across the western, southwestern and Great Plains in the United States: Pear Lake in the Sierra Nevada Mountains (CA), Senator Beck Lake in the San Juan Mountains (CO), and North Lake (WY). These lakes are uniquely situated to monitor dust fluxes; previous studies have demonstrated that sedimentation in these lakes are dominated by mineral dust accumulation; there is also evidence of remotely and locally sourced dust in these lakes, and of textural differences between the two types of dust fractions. We compare our results with previously published data on dust from loess deposits in the United States, and isotopic modeling (LMDZ). We find evidence that the finer-grain size fraction in alpine lake cores could be of remote origin; work is underway to quantify this contribution. Most importantly, we find that during the Last Glacial Maximum (LGM) the Great Plains may not have witnessed an increase in the incidence of tornado frequency. Acknowledgements: James Sigman, Jacob Ashford, Jason Neff and Amato Evan

Grain size analysis and depositional environment of shallow marine to basin floor, Kelantan River Delta

NASA Astrophysics Data System (ADS)

Afifah, M. R. Nurul; Aziz, A. Che; Roslan, M. Kamal

2015-09-01

Sediment samples were collected from the shallow marine from Kuala Besar, Kelantan outwards to the basin floor of South China Sea which consisted of quaternary bottom sediments. Sixty five samples were analysed for their grain size distribution and statistical relationships. Basic statistical analysis like mean, standard deviation, skewness and kurtosis were calculated and used to differentiate the depositional environment of the sediments and to derive the uniformity of depositional environment either from the beach or river environment. The sediments of all areas were varied in their sorting ranging from very well sorted to poorly sorted, strongly negative skewed to strongly positive skewed, and extremely leptokurtic to very platykurtic in nature. Bivariate plots between the grain-size parameters were then interpreted and the Coarsest-Median (CM) pattern showed the trend suggesting relationships between sediments influenced by three ongoing hydrodynamic factors namely turbidity current, littoral drift and waves dynamic, which functioned to control the sediments distribution pattern in various ways.

Anaerobic production of magnetite by a dissimilatory iron-reducing microorganism

USGS Publications Warehouse

Lovley, D.R.; Stolz, J.F.; Nord, G.L.; Phillips, E.J.P.

1987-01-01

The potential contribution of microbial metabolism to the magnetization of sediments has only recently been recognized. In the presence of oxygen, magnetotactic bacteria can form intracellular chains of magnetite while using oxygen or nitrate as the terminal electron acceptor for metabolism1. The production of ultrafine-grained magnetite by magnetotactic bacteria in surficial aerobic sediments may contribute significantly to the natural remanent magnetism of sediments2-4. However, recent studies on iron reduction in anaerobic sediments suggested that bacteria can also generate magnetite in the absence of oxygen5. We report here on a sediment organism, designated GS-15, which produces copious quantities of ultrafine-grained magnetite under anaerobic conditions. GS-15 is not magnetotactic, but reduces amorphic ferric oxide to extracellular magnetite during the reduction of ferric iron as the terminal electron acceptor for organic matter oxidation. This novel metabolism may be the mechanism for the formation of ultrafine-grained magnetite in anaerobic sediments, and couldaccount for the accumulation of magnetite in ancient iron formations and hydrocarbon deposits. ?? 1987 Nature Publishing Group.

Evaluation of a small beach nourishment project to enhance habitat suitability for horseshoe crabs

USGS Publications Warehouse

Jackson, N.L.; Smith, D.R.; Tiyarattanachai, R.; Nordstrom, K.F.

2007-01-01

This field study evaluates the effect of nourishing an estuarine beach with gravel to enhance spawning rates by horseshoe crabs. A total of 564??m3 of coarse sand and gravel were emplaced in two 90??m-long treatment segments at Bowers Beach, Delaware, USA from 9 to 11 April 2002. Field data were gathered between 6 April and 24 May 2002 to characterize the two fill segments and the un-nourished segments between them as well as two control segments at the adjacent Ted Harvey Beach. Sediment samples were taken from the foreshore surface and at depth before and after the nourishment. Bay water levels, wave heights, and beach ground water characteristics were monitored over a 12-hour tidal cycle at one of the nourished (15 May 2002) and the unnourished segment (16 May 2002) at Bowers Beach and at one of the control segments at Ted Harvey Beach (21 May 2002) using piezometers and pressure transducers inserted in wells. The beaches were cored to estimate the density of horseshoe crab eggs deposited during the spawning season. Horseshoe crab eggs were buried in pouches at 0.15 to 0.20??m depth for 30 to 40??days to evaluate their survival in developing into embryo or larval stage. Bulk sediment samples were taken to evaluate moisture characteristics near locations where egg pouches were buried. Density of spawning females at Bowers Beach was 1.04??m- 2 in 2001 and 1.20??m- 2 in 2002. These rates are lower than at Ted Harvey Beach but reveal an increase in spawning while Ted Harvey Beach underwent a considerable decrease (2.63??m- 2 to 1.35??m- 2). Sediments low on the foreshore remained nearly saturated throughout the tidal cycle at both beaches. The average hydraulic conductivity on the upper foreshore at the non-treatment section at Bowers Beach (0.19??cm s- 1) was less than at Ted Harvey Beach (0.27??cm s- 1), and the finer, better sorted sediments at depth at Bowers Beach resulted in a higher porosity, creating greater moisture retention potential. Egg development was greatest at mid foreshore at all sites. Eggs at the lower foreshore elevation remained viable, but did not develop to the embryo stage. Between-beach differences were limited to high elevations where higher mortality occurred at Ted Harvey Beach due to desiccation. Adding small amounts of gravel to a sand beach may change the appearance of the surface but may not appreciably increase mean grain size and sorting at depth or the hydraulic conductivity over the spawning season. The pebble fraction may be important for site selection, but finer sizes may be more important for egg survival because of moisture retention. ?? 2006 Elsevier B.V. All rights reserved.

The effect of grain size on aluminum anodes for Al-air batteries in alkaline electrolytes

NASA Astrophysics Data System (ADS)

Fan, Liang; Lu, Huimin

2015-06-01

Aluminum is an ideal material for metallic fuel cells. In this research, different grain sizes of aluminum anodes are prepared by equal channel angular pressing (ECAP) at room temperature. Microstructure of the anodes is examined by electron backscatter diffraction (EBSD) in scanning electron microscope (SEM). Hydrogen corrosion rates of the Al anodes in 4 mol L-1 NaOH are determined by hydrogen collection method. The electrochemical properties of the aluminum anodes are investigated in the same electrolyte using electrochemical impedance spectroscopy (EIS) and polarization curves. Battery performance is also tested by constant current discharge at different current densities. Results confirm that the electrochemical properties of the aluminum anodes are related to grain size. Finer grain size anode restrains hydrogen evolution, improves electrochemical activity and increases anodic utilization rate. The proposed method is shown to effectively improve the performance of Al-air batteries.

Tensile creep behavior of polycrystalline alumina fibers

NASA Technical Reports Server (NTRS)

Yun, H. M.; Goldsby, J. C.

1993-01-01

Tensile creep studies were conducted on polycrystalline Nextel 610 and Fiber FP alumina fibers with grain sizes of 100 and 300 nm, respectively. Test conditions were temperatures from 800 to 1050 C and stresses from 60 to 1000 MPa. For both fibers, only a small primary creep portion occurred followed by steady-state creep. The stress exponents for steady-state creep of Nextel 610 and Fiber FP were found to be about 3 and 1, respectively. At lower temperatures, below 1000 C, the finer grained Nextel 610 had a much higher 0.2 percent creep strength for 100 hr than the Fiber FP; while at higher temperatures, Nextel 610 had a comparable creep strength to the Fiber FP. The stress and grain size dependencies suggest Nextel 610 and Fiber FP creep rates are due to grain boundary sliding controlled by interface reaction and Nabarro-Herring mechanisms, respectively.

Field test comparison of an autocorrelation technique for determining grain size using a digital 'beachball' camera versus traditional methods

USGS Publications Warehouse

Barnard, P.L.; Rubin, D.M.; Harney, J.; Mustain, N.

2007-01-01

This extensive field test of an autocorrelation technique for determining grain size from digital images was conducted using a digital bed-sediment camera, or 'beachball' camera. Using 205 sediment samples and >1200 images from a variety of beaches on the west coast of the US, grain size ranging from sand to granules was measured from field samples using both the autocorrelation technique developed by Rubin [Rubin, D.M., 2004. A simple autocorrelation algorithm for determining grain size from digital images of sediment. Journal of Sedimentary Research, 74(1): 160-165.] and traditional methods (i.e. settling tube analysis, sieving, and point counts). To test the accuracy of the digital-image grain size algorithm, we compared results with manual point counts of an extensive image data set in the Santa Barbara littoral cell. Grain sizes calculated using the autocorrelation algorithm were highly correlated with the point counts of the same images (r2 = 0.93; n = 79) and had an error of only 1%. Comparisons of calculated grain sizes and grain sizes measured from grab samples demonstrated that the autocorrelation technique works well on high-energy dissipative beaches with well-sorted sediment such as in the Pacific Northwest (r2 ??? 0.92; n = 115). On less dissipative, more poorly sorted beaches such as Ocean Beach in San Francisco, results were not as good (r2 ??? 0.70; n = 67; within 3% accuracy). Because the algorithm works well compared with point counts of the same image, the poorer correlation with grab samples must be a result of actual spatial and vertical variability of sediment in the field; closer agreement between grain size in the images and grain size of grab samples can be achieved by increasing the sampling volume of the images (taking more images, distributed over a volume comparable to that of a grab sample). In all field tests the autocorrelation method was able to predict the mean and median grain size with ???96% accuracy, which is more than adequate for the majority of sedimentological applications, especially considering that the autocorrelation technique is estimated to be at least 100 times faster than traditional methods.

Cobble cam: Grain-size measurements of sand to boulder from digital photographs and autocorrelation analyses

USGS Publications Warehouse

Warrick, J.A.; Rubin, D.M.; Ruggiero, P.; Harney, J.N.; Draut, A.E.; Buscombe, D.

2009-01-01

A new application of the autocorrelation grain size analysis technique for mixed to coarse sediment settings has been investigated. Photographs of sand- to boulder-sized sediment along the Elwha River delta beach were taken from approximately 1??2 m above the ground surface, and detailed grain size measurements were made from 32 of these sites for calibration and validation. Digital photographs were found to provide accurate estimates of the long and intermediate axes of the surface sediment (r2 > 0??98), but poor estimates of the short axes (r2 = 0??68), suggesting that these short axes were naturally oriented in the vertical dimension. The autocorrelation method was successfully applied resulting in total irreducible error of 14% over a range of mean grain sizes of 1 to 200 mm. Compared with reported edge and object-detection results, it is noted that the autocorrelation method presented here has lower error and can be applied to a much broader range of mean grain sizes without altering the physical set-up of the camera (~200-fold versus ~6-fold). The approach is considerably less sensitive to lighting conditions than object-detection methods, although autocorrelation estimates do improve when measures are taken to shade sediments from direct sunlight. The effects of wet and dry conditions are also evaluated and discussed. The technique provides an estimate of grain size sorting from the easily calculated autocorrelation standard error, which is correlated with the graphical standard deviation at an r2 of 0??69. The technique is transferable to other sites when calibrated with linear corrections based on photo-based measurements, as shown by excellent grain-size analysis results (r2 = 0??97, irreducible error = 16%) from samples from the mixed grain size beaches of Kachemak Bay, Alaska. Thus, a method has been developed to measure mean grain size and sorting properties of coarse sediments. ?? 2009 John Wiley & Sons, Ltd.

Sediment Burial Intolerance of Marine Macroinvertebrates.

PubMed

Hendrick, Vicki J; Hutchison, Zoë L; Last, Kim S

2016-01-01

The marine environment contains suspended particulate matter which originates from natural and anthropogenic sources. Settlement of this material can leave benthic organisms susceptible to smothering, especially if burial is sudden i.e. following storms or activities such as dredging. Their survival will depend on their tolerance to, and their ability to escape from burial. Here we present data from a multi-factorial experiment measuring burial responses incorporating duration, sediment fraction and depth. Six macroinvertebrates commonly found in sediment rich environments were selected for their commercial and/or conservation importance. Assessments revealed that the brittle star (Ophiura ophiura), the queen scallop (Aequipecten opercularis) and the sea squirt (Ciona intestinalis) were all highly intolerant to burial whilst the green urchin (Psammichinus miliaris) and the anemone (Sagartiogeton laceratus), showed intermediate and low intolerance respectively, to burial. The least intolerant, with very high survival was the Ross worm (Sabellaria spinulosa). With the exception of C. intestinalis, increasing duration and depth of burial with finer sediment fractions resulted in increased mortality for all species assessed. For C. intestinalis depth of burial and sediment fraction were found to be inconsequential since there was complete mortality of all specimens buried for more than one day. When burial emergence was assessed O. ophiura emerged most frequently, followed by P. miliaris. The former emerged most frequently from the medium and fine sediments whereas P. miliaris emerged more frequently from coarse sediment. Both A. opercularis and S. laceratus showed similar emergence responses over time, with A. opercularis emerging more frequently under coarse sediments. The frequency of emergence of S. laceratus increased with progressively finer sediment and C. intestinalis did not emerge from burial irrespective of sediment fraction or depth. Finally, and perhaps unsurprisingly, the greatest ability to emerge from burial in all other species was from shallow (2 cm) burial. Although survival was consistently highly dependent on duration and depth of burial as expected, emergence behaviour was not as easily predictable thereby confounding predictions. We conclude that responses to burial are highly species specific and therefore tolerance generalisations are likely to be oversimplifications. These data may be used to inform environmental impact models that allow forecasting of the cumulative impacts of seabed disturbance and may provide mitigation measures for the sustainable use of the seabed.

The Effects of Grain Size and Texture on Dynamic Abnormal Grain Growth in Mo

NASA Astrophysics Data System (ADS)

Noell, Philip J.; Taleff, Eric M.

2016-10-01

This is the first report of abnormal grain morphologies specific to a Mo sheet material produced from a commercial-purity arc-melted ingot. Abnormal grains initiated and grew during plastic deformation of this material at temperatures of 1793 K and 1813 K (1520 °C and 1540 °C). This abnormal grain growth during high-temperature plastic deformation is termed dynamic abnormal grain growth, DAGG. DAGG in this material readily consumes nearly all grains near the sheet center while leaving many grains near the sheet surface unconsumed. Crystallographic texture, grain size, and other microstructural features are characterized. After recrystallization, a significant through-thickness variation in crystallographic texture exists in this material but does not appear to directly influence DAGG propagation. Instead, dynamic normal grain growth, which may be influenced by texture, preferentially occurs near the sheet surface prior to DAGG. The large grains thus produced near the sheet surface inhibit the subsequent growth of the abnormal grains produced by DAGG, which preferentially consume the finer grains near the sheet center. This produces abnormal grains that span the sheet center but leave unconsumed polycrystalline microstructure near the sheet surface. Abnormal grains are preferentially oriented with the < 110rangle approximately along the tensile axis. These results provide additional new evidence that boundary curvature is the primary driving force for DAGG in Mo.

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.

Interstratified arkosic and volcanic rocks of the Miocene Spanish Canyon Formation, Alvord Mountain area, California: descriptions and interpretations

USGS Publications Warehouse

Buesch, David C.

2014-01-01

The Spanish Canyon Foundation in the Alvord Mountain area, California, varies from about 50 to 120 m thick and records the interstratification of arkosic sandstone and conglomerate with tuffaceous deposits and lava flows. In the lower third of the formation, arkosic sandstone and conglomerate are interstratified with tuffaceous deposits. Some tuffs might have been deposited as primary, nonwelded to partially welded ignimbrites or fallout tephra. Many of the tuffaceous deposits represent redeposited material that formed tuffaceous sandstone, and many of these deposits contain arkosic grains that represent mixing of different source matieral. Arkosic sandstone, and especially conglomerate (some with maximum clast lengths up to 1 m), represent intermittent incursions of coarser plutoniclastic fan deposits into other finer grained and mostly volcaniclastic basin deposits. After deposition of the 18.78 Ma Peach Spring Tuff, the amount of tuffaceous material decreased. The upper two-thirds of the formation has arkosic sandstone and conglomerate interstratified with two olivine basalt lave flows. locally, conglomerate clasts in this part of the section have maximum lengths up to 1 m. Many tuffaceous and arkosic sandstone beds of the Spanish Canyon Formation have tabular to broad (low-relief) lenticular geometry, and locally, some arkosic conglomerate fills channels as much as 1.5 m deep. These bedforms are consistent with deposition in medial to distal alluvial-fan or fluvial environments; some finer-grained deposits might have formed in lacustrine environments.

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.

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.

Anthropogenic effects on sedimentary facies in Lake Baldeney, West Germany

NASA Astrophysics Data System (ADS)

Neumann-Mahlkau, Peter; Niehaus, Heinz Theo

1983-12-01

Analysis of well logs of Lake Baldeney, a reservoir of the Ruhr River, yields four facies factors that reflect the effect of anthropogenic processes on the sediment. First, the sedimentation rate is directly related to the subsidence caused by mining. The extent of the subsidence was such that the sediment load of the river could not compensate for the sinking of the lake bottom. Discharged sediment filled about one-fifth of the basin within 40 years. In certain areas of the basin the sedimentation rate reached up to 10 cm per year. Second, the grain-size distribution of the sediment was influenced by long-term and short-term events. During the subsidence, grain-size distribution remained relatively constant. The destruction of the Möhne River dam during World War II resulted in the presence of an extremely large grain size as evidenced by the so-called Möhnelage. The filling of the lake after 1961 was accompanied by a continual increase in medium grain size. Third, until 1975, the mode of the lake sediment reflects the effect of mining in the vicinity of the lake. High coal content can be traced to its origin. The introduction of modern production processes, modernization of coal dressing, and hydraulic hauling is documented in the sediment. Finally, the heavy metal content of the sediment corresponds to the industrial development in the drainage area the Ruhr River. The accumulation of Cd reached an extreme concentration, exceeding the natural content by a thousand times. Variation in concentration reflects an increase in industrial production, as well as measures undertaken to restore water quality.

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.

Effects of sediment-associated extractable metals, degree of sediment grain sorting, and dissolved organic carbon upon Cryptosporidium parvum removal and transport within riverbank filtration sediments, Sonoma County, California.

PubMed

Metge, David W; Harvey, Ronald W; Aiken, George R; Anders, Robert; Lincoln, George; Jasperse, Jay; Hill, Mary C

2011-07-01

Oocysts of the protozoan pathogen Cryptosporidium parvum are of particular concern for riverbank filtration (RBF) operations because of their persistence, ubiquity, and resistance to chlorine disinfection. At the Russian River RBF site (Sonoma County, CA), transport of C. parvum oocysts and oocyst-sized (3 μm) carboxylate-modified microspheres through poorly sorted (sorting indices, σ(1), up to 3.0) and geochemically heterogeneous sediments collected between 2 and 25 m below land surface (bls) were assessed. Removal was highly sensitive to variations in both the quantity of extractable metals (mainly Fe and Al) and degree of grain sorting. In flow-through columns, there was a log-linear relationship (r(2) = 0.82 at p < 0.002) between collision efficiency (α, the probability that colloidal collisions with grain surfaces would result in attachment) and extractable metals, and a linear relationship (r(2) = 0.99 at p < 0.002) between α and σ(1). Collectively, variability in extractable metals and grain sorting accounted for ∼83% of the variability in α (at p < 0.0002) along the depth profiles. Amendments of 2.2 mg L(-1) of Russian River dissolved organic carbon (DOC) reduced α for oocysts by 4-5 fold. The highly reactive hydrophobic organic acid (HPOA) fraction was particularly effective in re-entraining sediment-attached microspheres. However, the transport-enhancing effects of the riverine DOC did not appear to penetrate very deeply into the underlying sediments, judging from high α values (∼1.0) observed for oocysts being advected through unamended sediments collected at ∼2 m bls. This study suggests that in evaluating the efficacy of RBF operations to remove oocysts, it may be necessary to consider not only the geochemical nature and size distribution of the sediment grains, but also the degrees of sediment sorting and the concentration, reactivity, and penetration of the source water DOC.

Bright x-rays reveal shifting deformation states and effects of the microstructure on the plastic deformation of crystalline materials

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

Beaudoin, A. J.; Shade, P. A.; Schuren, J. C.

The plastic deformation of crystalline materials is usually modeled as smoothly progressing in space and time, yet modern studies show intermittency in the deformation dynamics of single-crystals arising from avalanche behavior of dislocation ensembles under uniform applied loads. However, once the prism of the microstructure in polycrystalline materials disperses and redistributes the load on a grain-by-grain basis, additional length and time scales are involved. Thus, the question is open as to how deformation intermittency manifests for the nonuniform grain-scale internal driving forces interacting with the finer-scale dislocation ensemble behavior. In this work we track the evolution of elastic strain withinmore » individual grains of a creep-loaded titanium alloy, revealing widely varying internal strains that fluctuate over time. Here, the findings provide direct evidence of how flow intermittency proceeds for an aggregate of ~700 grains while showing the influences of multiscale ensemble interactions and opening new avenues for advancing plasticity modeling.« less

Bright x-rays reveal shifting deformation states and effects of the microstructure on the plastic deformation of crystalline materials

DOE PAGES

Beaudoin, A. J.; Shade, P. A.; Schuren, J. C.; ...

2017-11-30

The plastic deformation of crystalline materials is usually modeled as smoothly progressing in space and time, yet modern studies show intermittency in the deformation dynamics of single-crystals arising from avalanche behavior of dislocation ensembles under uniform applied loads. However, once the prism of the microstructure in polycrystalline materials disperses and redistributes the load on a grain-by-grain basis, additional length and time scales are involved. Thus, the question is open as to how deformation intermittency manifests for the nonuniform grain-scale internal driving forces interacting with the finer-scale dislocation ensemble behavior. In this work we track the evolution of elastic strain withinmore » individual grains of a creep-loaded titanium alloy, revealing widely varying internal strains that fluctuate over time. Here, the findings provide direct evidence of how flow intermittency proceeds for an aggregate of ~700 grains while showing the influences of multiscale ensemble interactions and opening new avenues for advancing plasticity modeling.« less

Ubiquity of microplastics in coastal seafloor sediments.

PubMed

Ling, S D; Sinclair, M; Levi, C J; Reeves, S E; Edgar, G J

2017-08-15

Microplastic pollutants occur in marine environments globally, however estimates of seafloor concentrations are rare. Here we apply a novel method to quantify size-graded (0.038-4.0mm diam.) concentrations of plastics in marine sediments from 42 coastal and estuarine sites spanning pollution gradients across south-eastern Australia. Acid digestion/density separation revealed 9552 individual microplastics from 2.84l of sediment across all samples; equating to a regional average of 3.4 microplastics·ml -1 sediment. Microplastics occurred as filaments (84% of total) and particle forms (16% of total). Positive correlations between microplastic filaments and wave exposure, and microplastic particles with finer sediments, indicate hydrological/sediment-matrix properties are important for deposition/retention. Contrary to expectations, positive relationships were not evident between microplastics and other pollutants (heavy metals/sewage), nor were negative relationships with neighbouring reef biota detected. Rather, microplastics were ubiquitous across sampling sites. Positive associations with some faunal-elements (i.e. invertebrate species richness) nevertheless suggest high potential for microplastic ingestion. Copyright © 2017 Elsevier Ltd. All rights reserved.

An automated and universal method for measuring mean grain size from a digital image of sediment

USGS Publications Warehouse

Buscombe, Daniel D.; Rubin, David M.; Warrick, Jonathan A.

2010-01-01

Existing methods for estimating mean grain size of sediment in an image require either complicated sequences of image processing (filtering, edge detection, segmentation, etc.) or statistical procedures involving calibration. We present a new approach which uses Fourier methods to calculate grain size directly from the image without requiring calibration. Based on analysis of over 450 images, we found the accuracy to be within approximately 16% across the full range from silt to pebbles. Accuracy is comparable to, or better than, existing digital methods. The new method, in conjunction with recent advances in technology for taking appropriate images of sediment in a range of natural environments, promises to revolutionize the logistics and speed at which grain-size data may be obtained from the field.

Estimating suspended sediment using acoustics in a fine-grained riverine system, Kickapoo Creek at Bloomington, Illinois

USGS Publications Warehouse

Manaster, Amanda D.; Domanski, Marian M.; Straub, Timothy D.; Boldt, Justin A.

2016-08-18

Acoustic technologies have the potential to be used as a surrogate for measuring suspended-sediment concentration (SSC). This potential was examined in a fine-grained (97-100 percent fines) riverine system in central Illinois by way of installation of an acoustic instrument. Acoustic data were collected continuously over the span of 5.5 years. Acoustic parameters were regressed against SSC data to determine the accuracy of using acoustic technology as a surrogate for measuring SSC in a fine-grained riverine system. The resulting regressions for SSC and sediment acoustic parameters had coefficients of determination ranging from 0.75 to 0.97 for various events and configurations. The overall Nash-Sutcliffe model-fit efficiency was 0.95 for the 132 observed and predicted SSC values determined using the sediment acoustic parameter regressions. The study of using acoustic technologies as a surrogate for measuring SSC in fine-grained riverine systems is ongoing. The results at this site are promising in the realm of surrogate technology.

Grain size and shape analysis of the AD 1226 tephra layer, Reykjanes volcanic system

NASA Astrophysics Data System (ADS)

Ösp Magnúsdóttir, Agnes; Höskuldsson, Ármann; Larsen, Guðrún; Tumi Guðmunsson, Magnús; Sigurgeirsson, Magnús Á.

2014-05-01

Recent explosive eruptions in Iceland have drawn attention to long range tephra transport in the atmosphere. In Iceland tephra forming explosion eruptions are frequent, due to abundance of water. However, the volcanism on the island is principally basaltic. Volcanism along the Reykjanes Peninsula is divided into five distinct volcanic systems. Volcano-tectonic activity within these systems is periodic, with recurrence intervals in the range of 1 ka. Last volcano-tectonic sequence began around AD 940, shortly after settlement of Iceland, and lasted through AD 1340. During this period activity was characterized by basaltic fissure eruptions. Furthermore, this activity period on the Reykjanes peninsula began within the eastern most volcanic system and gradually moved towards the west across the peninsula. The 1226 eruption was a basaltic fissure eruption with in the Reykjanes volcanic system. The eruption began on land and gradually progressed towards the SW until the volcanic fissure extended into the sea. Water-magma interaction changed the eruption from effusive into explosive forming the largest tephra layer on the peninsula. Due to its close proximity to the Keflavik international airport and that of the capital of Iceland it is important to get an insight into, the characteristics, generation and distribution of such tephra deposits. In this eruption the tephra produced had an approximate volume of 0.1 km3 and covered an area of some 3500 km2 within the 0.5 cm isopach. Total grain size distribution of this tephra layer will be presented along with analysis of principal grain shapes of the finer portion of the tephra layer as a function of distance from the source. The tephra grain size is dominated by particles finer than 1 millimeter with an almost complete absence of large grains independent of distance from the source. Comprehensive understanding of the characteristics of tephra generated in this eruption can help us to understand hazards posed by future eruptions of similar nature in the area.

Detecting rare, abnormally large grains by x-ray diffraction

DOE PAGES

Boyce, Brad L.; Furnish, Timothy Allen; Padilla, H. A.; ...

2015-07-16

Bimodal grain structures are common in many alloys, arising from a number of different causes including incomplete recrystallization and abnormal grain growth. These bimodal grain structures have important technological implications, such as the well-known Goss texture which is now a cornerstone for electrical steels. Yet our ability to detect bimodal grain distributions is largely confined to brute force cross-sectional metallography. The present study presents a new method for rapid detection of unusually large grains embedded in a sea of much finer grains. Traditional X-ray diffraction-based grain size measurement techniques such as Scherrer, Williamson–Hall, or Warren–Averbach rely on peak breadth andmore » shape to extract information regarding the average crystallite size. However, these line broadening techniques are not well suited to identify a very small fraction of abnormally large grains. The present method utilizes statistically anomalous intensity spikes in the Bragg peak to identify regions where abnormally large grains are contributing to diffraction. This needle-in-a-haystack technique is demonstrated on a nanocrystalline Ni–Fe alloy which has undergone fatigue-induced abnormal grain growth. In this demonstration, the technique readily identifies a few large grains that occupy <0.00001 % of the interrogation volume. Finally, while the technique is demonstrated in the current study on nanocrystalline metal, it would likely apply to any bimodal polycrystal including ultrafine grained and fine microcrystalline materials with sufficiently distinct bimodal grain statistics.« less

Magnetic signature of the 22 June 1932 tsunami deposits (Jalisco, Mexican Pacific coast)

NASA Astrophysics Data System (ADS)

Bógalo, M. F.; Ramírez-Herrera, M.-T.; Goguitchaichvili, A.; Rey, D.; Mohamed, K. J.; Calvo-Rathert, M.; Corona, N.

2017-06-01

Recent studies have demonstrated that rock-magnetic analysis may provide additional information to distinguish and characterize extreme marine inundation events such as tsunamis. Rock-magnetic proxies reinforce and improve the environmental evidences supplied by other methods, adding some decisive clues for the interpretation of the origin and genesis of the sedimentary deposits. Here we report rock-magnetic, XRD, and SEM microscopy results obtained in the Palo Verde estuary (Colima Pacific coast, Mexico) in order to enhance the tools for identification and reconstruction of two tsunami-induced deposits. The sedimentary sequence includes two sand units, a tsunami deposit (PV1) associated with the 22 June 1932 tsunami and a deeper sandy layer (PV2) related to a possible paleotsunami that occurred around 1300 C.E. Both sandy units are topped by finer grained units. Magnetic properties exhibit a significant correlation with the stratigraphy. High susceptibility (χ) and high saturation isothermal remanence (SIRM) values typical of high concentrations of (titano)magnetite are a distinctive feature of the most recent sandy tsunamigenic unit PV1 and the overlaying soil. The lower sandy tsunamigenic unit PV2 shows significantly lower χ and SIRM values, indicating lower concentration of (titano)magnetite in this unit and the overlaying clayey-silt unit. The latter also shows a higher coercivity component associated with (titano)hematite. Magnetic grain-size differences are also observed between PV1 and PV2 suggesting differences in hydraulic conditions at the time of deposition. The bulk mineralogical composition and sediment texture of these units also support the hypothesis of different provenances for each tsunamigenic unit as inferred from magnetic properties.

Interaction between riverbed condition and characteristics of debris flow in Ichino-sawa subwatershed of Ohya-kuzure landslide, Japan

NASA Astrophysics Data System (ADS)

Tsunetaka, Haruka; Hotta, Norifumi; Imaizumi, Fumitoshi; Hayakawa, Yuichi S.; Yumen, Noriki

2015-04-01

Large-scale sediment movements, such as a deep-seated landslide, not only induce immediate sediment disasters but also produce a large amount of unstable sediment upstream. Most of the unstable sediment residing in the upstream area is discharged as debris flow. Hence, after the occurrence of large-scale sediment movement, debris flows have a long-term effect on the watershed regime. However, the characteristics of debris flow in upstream areas are not well understood, due to the topographic and grain-size conditions that are more complicated than the downstream area. This study was performed to reveal the relationship between such a riverbed condition and the characteristics of debris flow by field observations. The study site was Ichinosawa-subwatershed in the Ohya-kuzure basin, Shizuoka Prefecture, Japan. The basin experienced a deep-seated landslide about 300 years ago and is currently actively yielding sediment with a clear annual cycle. During the winter season, sediment is deposited on the valley bottom by freeze-thaw and weathering. In the summer season, the deposited sediment is discharged incrementally by debris flows related to storm events. Topographical survey and grain-size analysis were performed several times between November 2011 and November 2014. High-resolution digital elevation models (10 cm) were created from the results of a topographical survey using a terrestrial laser scanner. A grain-size analysis was conducted in the upper, middle, and lower parts of the study site. Debris flow occurrences were also monitored in the same period by a sensor-triggered video camera and interval camera. Rainfall was observed during the summer season for comparison with debris flow occurrence. Several debris flows of different magnitudes were observed during the study period. Although heavy rainfall events altered the bed inclination, the thickness of deposited sediment, and the grain-size distribution, more significant changes were detected after the debris flow. While the initial grain-size distribution in early spring was roughly identical across the study site, the subsequent changes in the grain-size distribution differed according to location. The source, transport and deposition areas of the debris flows differed among rainfall events, resulting in different transitions in topographic conditions at different locations. Furthermore, surges of debris flow not only induced erosion-deposited sediment but also suspended and deposited sediment in the same area during one typhoon event. A comparison of the results indicated that, in addition to the conditions of the triggering rainfall, topographic and grain-size conditions affected the debris flow occurrence and magnitude. These interactions also showed that the magnitude and form of the succeeding debris flow could be dominant, depending on changing riverbed condition by past debris flows in upstream areas.

Effects of low-level dams on the distribution of sediment, trace metals, and organic substances in the lower Schuylkill River basin, Pennsylvania

USGS Publications Warehouse

Yorke, Thomas H.; Stamer, John K.; Pederson, Gary L.

1985-01-01

Heavy use of the Schuylkill River for municipal water supplies and a history of accidental spills and discharges of trace metals and organic substances have been a concern of State and local officials for many years. The U.S. Geological Survey, as part of their River Quality Assessment Program, developed a study to assess the occurrence and distribution of trace substances that pose a threat to human health and aquatic life. This report presents the results of the part of the study that evaluates the effects of low-level dams in the lower basin on the distribution and transport of sediment and trace substances. A combination of historical and current data were used in the assessment. Suspended-sediment data collected at several mainstem and tributary sites from 1954 to 1979 and sedimentation surveys of the six pools in the lower basin were used to define the sediment-transport characteristics of the river. These data provided a base for assessing the transport of trace substances, which are associated closely with riverbed sediments and suspended particles. Water and riverbed samples were collected for analyses of trace substances at numerous sites in the lower basin from 1978 to 1980. The six dams on the river between Pottstown and Philadelphia have had a significant effect on the transport of sediment and trace substances. Between 1954 and 1970, more than 4.7 million cubic yards of sediment accumulated in the pools formed by the dams. The quantity of sediment deposited in the pools ranged from 150,000 cubic yards in Plymouth Pool to 1.6 million cubic yards in Fairmount Pool. The rate of accumulation in the pools was a function of pool size and geometry and the frequency of storms. About 35 percent of the total sediment discharged by the river was stored in the six pools from 1954 to 1970. Since 1970, the net change in sediment accumulation has been minimal. More than 24 percent of the sediment in Fairmount Pool in 1970 was scoured from the pool during Hurricane Agnes in 1972; however, total sediment accumulation returned to the 1970 level within 2 years. Analyses of water samples showed that some trace substances are associated closely with particulate material transported by the river. The concentration of suspended and total cadmium, chromium, copper, lead, nickel, and zinc correlated well with the concentration of suspended sediment and suspended organic carbon. The average annual discharge of metals in suspension as a percentage of total average annual discharge ranged from 46 percent for nickel to 94 percent for lead for the Schuylkill River at Manayunk. The average annual discharge of each metal remained about the same or decreased between Pottstown and Philadelphia. Synoptic sampling of the inflow and outflow of several pools during storm runoff showed that the pools limit the transport of trace metals. More than 50 percent of the suspended copper transported by the river at Pottstown was deposited in Vincent Pool during the storm of May 12-15, 1980. Similar reductions were observed between Port Kennedy and Manayunk as the storm runoff passed through Norristown, Plymouth, and Flat Rock Pools. Analyses of riverbed sediments showed that concentrations of trace substances were higher in sediments that included all particles finer than 0.062 millimeter than in sediments that included only particles finer than 0.016 millimeter. This suggests that medium and coarse silt particles or conglomerates of finer particles sorb as much or more trace constituents as the individual fine silts and clay particles. Concentrations of trace metals were as much as 90 percent higher in the sediments that included coarse silt. Concentrations of trace organic substances were several times higher in the sediments that included coarse silt than in sediments consisting of only fine silt or clay. Surficial and core samples of riverbed sediments were used to define the present and historical distribution of trace substances in

Estimating the settling velocity of bioclastic sediment using common grain-size analysis techniques

USGS Publications Warehouse

Cuttler, Michael V. W.; Lowe, Ryan J.; Falter, James L.; Buscombe, Daniel D.

2017-01-01

Most techniques for estimating settling velocities of natural particles have been developed for siliciclastic sediments. Therefore, to understand how these techniques apply to bioclastic environments, measured settling velocities of bioclastic sedimentary deposits sampled from a nearshore fringing reef in Western Australia were compared with settling velocities calculated using results from several common grain-size analysis techniques (sieve, laser diffraction and image analysis) and established models. The effects of sediment density and shape were also examined using a range of density values and three different models of settling velocity. Sediment density was found to have a significant effect on calculated settling velocity, causing a range in normalized root-mean-square error of up to 28%, depending upon settling velocity model and grain-size method. Accounting for particle shape reduced errors in predicted settling velocity by 3% to 6% and removed any velocity-dependent bias, which is particularly important for the fastest settling fractions. When shape was accounted for and measured density was used, normalized root-mean-square errors were 4%, 10% and 18% for laser diffraction, sieve and image analysis, respectively. The results of this study show that established models of settling velocity that account for particle shape can be used to estimate settling velocity of irregularly shaped, sand-sized bioclastic sediments from sieve, laser diffraction, or image analysis-derived measures of grain size with a limited amount of error. Collectively, these findings will allow for grain-size data measured with different methods to be accurately converted to settling velocity for comparison. This will facilitate greater understanding of the hydraulic properties of bioclastic sediment which can help to increase our general knowledge of sediment dynamics in these environments.

A Field Exercise in Fluvial Sediment Transport.

ERIC Educational Resources Information Center

Tharp, Thomas M.

1983-01-01

Describes an investigation which introduces the mathematical principles of stream hydraulics and fluvial sediment in a practical context. The investigation has four stages: defining hydrology of the stream; defining channel hydraulics in a study reach; measuring grain size; and calculating transportable grain size and comparing measure stream-bed…

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.

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.

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.

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.

Effect of initial grain size on inhomogeneous plastic deformation and twinning behavior in high manganese austenitic steel with a polycrystalline microstructure

NASA Astrophysics Data System (ADS)

Ueji, R.; Tsuchida, N.; Harada, K.; Takaki, K.; Fujii, H.

2015-08-01

The grain size effect on the deformation twinning in a high manganese austenitic steel which is so-called TWIP (twining induced plastic deformation) steel was studied in order to understand how to control deformation twinning. The 31wt%Mn-3%Al-3% Si steel was cold rolled and annealed at various temperatures to obtain fully recrystallized structures with different mean grain sizes. These annealed sheets were examined by room temperature tensile tests at a strain rate of 10-4/s. The coarse grained sample (grain size: 49.6μm) showed many deformation twins and the deformation twinning was preferentially found in the grains in which the tensile axis is parallel near to [111]. On the other hand, the sample with finer grains (1.8 μm) had few grains with twinning even after the tensile deformation. The electron back scattering diffraction (EB SD) measurements clarified the relationship between the anisotropy of deformation twinning and that of inhomogeneous plastic deformation. Based on the EBSD analysis, the mechanism of the suppression of deformation twinning by grain refinement was discussed with the concept of the slip pattern competition between the slip system governed by a grain boundary and that activated by the macroscopic load.

Apollo 16 exploration of Descartes - A geologic summary.

NASA Technical Reports Server (NTRS)

1973-01-01

The Cayley Plains at the Apollo 16 landing site consist of crudely stratified breccias to a depth of at least 200 meters, overlain by a regolith 10 to 15 meters thick. Samples, photographs, and observations by the astronauts indicate that most of the rocks are impact breccias derived from an anorthosite-gabbro complex. The least brecciated members of the suite include coarse-grained anorthosite and finer-grained, more mafic rocks, some with igneous and some with metamorphic textures. Much of the transverse area is covered by ejecta from North Ray and South Ray craters, but the abundance of rock fragments increases to the south toward the younger South Ray crater.

A novel route for processing cobalt–chromium–molybdenum orthopaedic alloys

PubMed Central

Patel, Bhairav; Inam, Fawad; Reece, Mike; Edirisinghe, Mohan; Bonfield, William; Huang, Jie; Angadji, Arash

2010-01-01

Spark plasma sintering has been used for the first time to prepare the ASTM F75 cobalt–chromium–molybdenum (Co–Cr–Mo) orthopaedic alloy composition using nanopowders. In the preliminary work presented in this report, the effect of processing variables on the structural features of the alloy (phases present, grain size and microstructure) has been investigated. Specimens of greater than 99.5 per cent theoretical density were obtained. Carbide phases were not detected in the microstructure but oxides were present. However, harder materials with finer grains were produced, compared with the commonly used cast/wrought processing methods, probably because of the presence of oxides in the microstructure. PMID:20200035

Microstructure and Mechanical Properties of Highly Alloyed FeCrMoVC Steel Fabricated by Spark Plasma Sintering

NASA Astrophysics Data System (ADS)

Oh, Seung-Jin; Jun, Joong-Hwan; Lee, Min-Ha; Shon, In-Jin; Lee, Seok-Jae

2018-05-01

In this study, we successfully fabricated highly alloyed FeCrMoVC specimens within 2 min by using the spark plasma sintering (SPS) method. The densities of the sintered specimens were almost identical to their theoretical values. Fine (Mo, V)-rich carbides with lamellar structure were precipitated along the grain boundaries of the as-sintered specimen, whereas relatively large carbides were formed additionally in the transgranular region during the tempering treatment. Compared with the specimen produced by a conventional casting method, the FeCrMoVC specimens from SPS showed smaller grain size with finer carbides and higher hardness values.

Effects of Grain Size on the Fatigue Properties in Cold-Expanded Austenitic HNSs

NASA Astrophysics Data System (ADS)

Shin, Jong-Ho; Kim, Young-Deak; Lee, Jong-Wook

2018-05-01

Cold-expanded austenitic high nitrogen steel (HNS) was subjected to investigate the effects of grain size on the stress-controlled high cycle fatigue (HCF) as well as the strain-controlled low cycle fatigue (LCF) properties. The austenitic HNSs with two different grain sizes (160 and 292 μm) were fabricated by the different hot forging strain. The fine-grained (FG) specimen exhibited longer LCF life and higher HCF limit than those of the coarse-grained (CG) specimen. Fatigue crack growth testing showed that crack propagation rate in the FG specimen was the same as that in the CG specimen, implying that crack propagation rate did not affect the discrepancy of LCF life and HCF limit between two cold-expanded HNSs. Therefore, it was estimated that superior LCF and HCF properties in the FG specimen resulted from the retardation of the fatigue crack initiation as compared with the CG specimen. Transmission electron microscopy showed that the effective grain size including twin boundaries are much finer in the FG specimen than that in the CG specimen, which can give favorable contributions to strengthening.

The Lithological Constraint To Gas Hydrate Formation: Evidence OF Grain Size Of Sediments From IODP 311 On CASCADIA Margin

NASA Astrophysics Data System (ADS)

Wang, J.

2006-12-01

A total of 614 sediment samples at intervals of about 1.5 m from all 5 sites of the Integrated Ocean Drilling Program (IODP) Expedition 311 on Cascadia Margin were analyzed using a Beckman Coulter LS-230 Particle Analyzer. The grain-size data were then plotted in depth and compared with other proxies of gas hydrate- occurrence such as soupy/mousse-like structures in sediments, gas hydrate concentration (Sh) derived from LWD data using Archie's relation, IR core images (infrared image) and the recovered samples of gas hydrate¨Cbearing sediments. A good relationship between the distribution of coarse grains in size of 31-63¦Ìm and 63-125¦Ìm sediments and the potential occurrence of gas hydrate was found across the entire gas hydrate stability zone. The depth distribution of grain size from the Site U1326 shows clear excursions at depths of 5-8, 21-26, 50- 123, 132-140, 167-180, 195-206 and 220-240 mbsf, which coincide with the potential occurrence of gas hydrate suggested by soupy/mousse-like structures, logging-derived gas hydrate concentrations (Sh) and the recovered samples of the gas hydrate¨Cbearing sand layers. The lithology of sediments significantly affects the formation of gas hydrate. Gas hydrate forms preferentially within relatively coarse grain-size sediments above 31 ¦Ìm. Key words: grain size of sediments, constraint, occurrence of gas hydrate, IODP 311 IODP Expedition 311 Scientists: Michael Riedel (Co-chief Scientist), Timothy S. Collett (Co-chief Scientist), Mitchell Malone (Expedition Project Manager/Staff Scientist), Gilles Gu¨¨rin, Fumio Akiba, Marie-Madeleine Blanc-Valleron, Michelle Ellis, Yoshitaka Hashimoto, Verena Heuer, Yosuke Higashi, Melanie Holland, Peter D. Jackson, Masanori Kaneko, Miriam Kastner, Ji-Hoon Kim, Hiroko Kitajima, Philip E. Long, Alberto Malinverno, Greg Myers, Leena D. Palekar, John Pohlman, Peter Schultheiss, Barbara Teichert, Marta E. Torres, Anne M. Tr¨¦hu, Jiasheng Wang, Ulrich G. Wortmann, Hideyoshi Yoshioka. Acknowledgement: This study was supported by the IODP/JOI Alliance, IODP-China 863 Project (grant 2004AA615030) and NSFC Project (grant 40472063).

A Froude-scaled model of a bedrock-alluvial channel reach: 2. Sediment cover

NASA Astrophysics Data System (ADS)

Hodge, Rebecca A.; Hoey, Trevor B.

2016-09-01

Previous research into sediment cover in bedrock-alluvial channels has focussed on total sediment cover, rather than the spatial distribution of cover within the channel. The latter is important because it determines the bedrock areas that are protected from erosion and the start and end of sediment transport pathways. We use a 1:10 Froude-scaled model of an 18 by 9 m reach of a bedrock-alluvial channel to study the production and erosion of sediment patches and hence the spatial relationships between flow, bed topography, and sediment dynamics. The hydraulic data from this bed are presented in the companion paper. In these experiments specified volumes of sediment were supplied at the upstream edge of the model reach as single inputs, at each of a range of discharges. This sediment formed patches, and once these stabilized, flow was steadily increased to erode the patches. In summary: (1) patches tend to initiate in the lowest areas of the bed, but areas of topographically induced high flow velocity can inhibit patch development; (2) at low sediment inputs the extent of sediment patches is determined by the bed topography and can be insensitive to the exact volume of sediment supplied; and (3) at higher sediment inputs more extensive patches are produced, stabilized by grain-grain and grain-flow interactions and less influenced by the bed topography. Bedrock topography can therefore be an important constraint on sediment patch dynamics, and topographic metrics are required that incorporate its within-reach variability. The magnitude and timing of sediment input events controls reach-scale sediment cover.

Results of Copper-Silver Rail Materials Tests

DTIC Science & Technology

2006-05-01

dislocation-dense grain structure. An annealing, recrystallization , and re-straining model is proposed to predict the bandwidth within which the...darker phase is the copper-rich solid solution, while the lighter regions are the eutectic structure consisting of both copper-rich and silver-rich solid...solutions. The eutectic phase ribbons consist of finer copper and silver filaments [1], [5]. The two phases are inhomogeneously deformed during the

Glacial-marine sediments record ice-shelf retreat during the late Holocene in Beascochea Bay on the western margin of the Antarctic Peninsula

NASA Astrophysics Data System (ADS)

Hardin, L. A.; Wellner, J. S.

2010-12-01

Beascochea Bay has an overall rapid rate of sedimentation due to retreating fast-flowing ice, and thus contains high-resolution records of Antarctica’s glacial and climate history. Beascochea Bay is a 16 km long by 8 km wide bay located on the western margin of the Antarctica Peninsula, centered between Anvers Island and Renaud Island, but open to the Bellingshausen Sea. Currently, three tidewater glaciers draining the Bruce Plateau of Graham Land enter into the fjords of Beascochea Bay, releasing terrigenous sediments which have left a record of the fluctuations of the Antarctic Peninsula Ice Cap since the grounded ice decoupled from the seafloor after the last glacial maximum. These three glaciers have played a significant role in providing sediment to the main basin, allowing a detailed sediment facies analysis to be conducted from eight sediment cores which were collected during the austral summer of 2007. Pebbly silty clay sediment cores, along with 3.5 kHz seismic data and multibeam swath bathymetry data, are integrated to reconstruct a glacial retreat timeline for the middle to late Holocene, which can be compared to the recent retreat rates over the last century. Paleoenvironment of deposition is determined by mapping lateral facies changes from the side fjords (proximal) to the outer basin (distal), as each region records the transition from glacial-marine sediments to open-marine sediments. As the ice retreated from the outer basin to the inner basin, and most recently leaving the side fjords, each facies deposited can be age-constrained by radiocarbon, 210Pb, and 137Cs dating methods. A distinct 137Cs signal is readily seen in two kasten cores from a side fjord and the inner basin of Beascochea Bay. This dating method revealed an average sedimentation rate of 2.7 mm per year for approximately the last century, which is comparable to 210Pb rates obtained in other studies. Lithology variations in each sediment core record indications of ice-shelf influence in Beascochea Bay throughout the Holocene deglaciation. The distinctively laminated sub-ice shelf facies can be clearly seen in the x-rays of these cores, and can be easily distinguished from the poorly sorted glacial-marine facies and the greenish finer-grained facies deposited in open-marine conditions. A 14 m long sediment core taken from the outer basin of Beascochea Bay recovered the greatest length of sediment and dates back to the middle Holocene. X-rays of this core show a possible mid-Holocene retreat of the ice shelf followed by intermittent advance and retreat that precedes the most recent retreat. The inner basin of Beascochea Bay has been without an ice shelf for the last 200 years, based on the sedimentation rates of the last century projected downcore.

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.

Modeling of Grain Size Distribution of Tsunami Sand Deposits in V-shaped Valley of Numanohama During the 2011 Tohoku Tsunami

NASA Astrophysics Data System (ADS)

Gusman, A. R.; Satake, K.; Goto, T.; Takahashi, T.

2016-12-01

Estimating tsunami amplitude from tsunami sand deposit has been a challenge. The grain size distribution of tsunami sand deposit may have correlation with tsunami inundation process, and further with its source characteristics. In order to test this hypothesis, we need a tsunami sediment transport model that can accurately estimate grain size distribution of tsunami deposit. Here, we built and validate a tsunami sediment transport model that can simulate grain size distribution. Our numerical model has three layers which are suspended load layer, active bed layer, and parent bed layer. The two bed layers contain information about the grain size distribution. This numerical model can handle a wide range of grain sizes from 0.063 (4 ϕ) to 5.657 mm (-2.5 ϕ). We apply the numerical model to simulate the sedimentation process during the 2011 Tohoku earthquake in Numanohama, Iwate prefecture, Japan. The grain size distributions at 15 sample points along a 900 m transect from the beach are used to validate the tsunami sediment transport model. The tsunami deposits are dominated by coarse sand with diameter of 0.5 - 1 mm and their thickness are up to 25 cm. Our tsunami model can well reproduce the observed tsunami run-ups that are ranged from 16 to 34 m along the steep valley in Numanohama. The shapes of the simulated grain size distributions at many sample points located within 300 m from the shoreline are similar to the observations. The differences between observed and simulated peak of grain size distributions are less than 1 ϕ. Our result also shows that the simulated sand thickness distribution along the transect is consistent with the observation.

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.

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.

Minimum and Maximum Times Required to Obtain Representative Suspended Sediment Samples

NASA Astrophysics Data System (ADS)

Gitto, A.; Venditti, J. G.; Kostaschuk, R.; Church, M. A.

2014-12-01

Bottle sampling is a convenient method of obtaining suspended sediment measurements for the development of sediment budgets. While these methods are generally considered to be reliable, recent analysis of depth-integrated sampling has identified considerable uncertainty in measurements of grain-size concentration between grain-size classes of multiple samples. Point-integrated bottle sampling is assumed to represent the mean concentration of suspended sediment but the uncertainty surrounding this method is not well understood. Here we examine at-a-point variability in velocity, suspended sediment concentration, grain-size distribution, and grain-size moments to determine if traditional point-integrated methods provide a representative sample of suspended sediment. We present continuous hour-long observations of suspended sediment from the sand-bedded portion of the Fraser River at Mission, British Columbia, Canada, using a LISST laser-diffraction instrument. Spectral analysis suggests that there are no statistically significant peak in energy density, suggesting the absence of periodic fluctuations in flow and suspended sediment. However, a slope break in the spectra at 0.003 Hz corresponds to a period of 5.5 minutes. This coincides with the threshold between large-scale turbulent eddies that scale with channel width/mean velocity and hydraulic phenomena related to channel dynamics. This suggests that suspended sediment samples taken over a period longer than 5.5 minutes incorporate variability that is larger scale than turbulent phenomena in this channel. Examination of 5.5-minute periods of our time series indicate that ~20% of the time a stable mean value of volumetric concentration is reached within 30 seconds, a typical bottle sample duration. In ~12% of measurements a stable mean was not reached over the 5.5 minute sample duration. The remaining measurements achieve a stable mean in an even distribution over the intervening interval.

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.

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.

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.

Impact of tsunami on texture and mineralogy of a major placer deposit in southwest coast of India

NASA Astrophysics Data System (ADS)

Babu, N.; Babu, D. S. Suresh; Das, P. N. Mohan

2007-03-01

The great Indonesian earth quake (26 December 2004) triggered a tsunami wave across the Bay of Bengal and Indian Ocean basins and has brought a major havoc in several countries including India. The coastal segment between Thotapalli and Valiazhikal in Kerala state of southwest India, where considerably rich beach placer deposit with ilmenite percentage of more than 70% is concentrated, has been investigated to understand the impact of tsunami on coastal sediments. The grain size analysis flashes out the significant differences between the pre- and post-tsunami littoral environments. While the mineral grains collected during pre-tsunami period show well-sorted nature, the post-tsunami samples represent moderately to poorly sorted nature. Similarly, unimodal and bimodal distributions of the sediments have been recorded for pre- and post-tsunami sediments, respectively. Further, mineral assemblages corresponding to before and after this major wave activity clearly indicate the large-scale redistribution of sediments. The post-tsunami sediments register increasing trends of garnet, sillimanite and rutile. The total heavy mineral percentage of the post-tsunami sediment also shows an improved concentration, perhaps due to the large-scale transport of lighter fraction. Magnetite percentage of post-tsunami samples reflects higher concentration compared to the pre-tsunami samples, indicating the intensity of reworking process. X-ray diffraction patterns of ilmenite grains have confirmed the increased presence of pseduorutile, and pseudobrookite in post-tsunami samples, which could be due to the mixing of more altered grains. SEM examination of grains also confirms the significant alteration patterns on the ubiquitous mineral of placer body, the ilmenite. The reason for these textural, mineralogical and micromorphological changes in heavy minerals particularly in ilmenite, could be due to the churning action on the deeper sediments of onshore region or on the sediments entrapped in the near shelf region of the area, by the ˜ 6 m high tsunami waves.

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.

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.

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

Instant Grainification: Real-Time Grain-Size Analysis from Digital Images in the Field

NASA Astrophysics Data System (ADS)

Rubin, D. M.; Chezar, H.

2007-12-01

Over the past few years, digital cameras and underwater microscopes have been developed to collect in-situ images of sand-sized bed sediment, and software has been developed to measure grain size from those digital images (Chezar and Rubin, 2004; Rubin, 2004; Rubin et al., 2006). Until now, all image processing and grain- size analysis was done back in the office where images were uploaded from cameras and processed on desktop computers. Computer hardware has become small and rugged enough to process images in the field, which for the first time allows real-time grain-size analysis of sand-sized bed sediment. We present such a system consisting of weatherproof tablet computer, open source image-processing software (autocorrelation code of Rubin, 2004, running under Octave and Cygwin), and digital camera with macro lens. Chezar, H., and Rubin, D., 2004, Underwater microscope system: U.S. Patent and Trademark Office, patent number 6,680,795, January 20, 2004. Rubin, D.M., 2004, A simple autocorrelation algorithm for determining grain size from digital images of sediment: Journal of Sedimentary Research, v. 74, p. 160-165. Rubin, D.M., Chezar, H., Harney, J.N., Topping, D.J., Melis, T.S., and Sherwood, C.R., 2006, Underwater microscope for measuring spatial and temporal changes in bed-sediment grain size: USGS Open-File Report 2006-1360.

Continental-scale transport of sediments by the Baltic Ice Stream elucidated by coupled grain size and Nd provenance analyses

NASA Astrophysics Data System (ADS)

Boswell, Steven M.; Toucanne, Samuel; Creyts, Timothy T.; Hemming, Sidney R.

2018-05-01

We introduce a methodology for determining the transport distance of subglacially comminuted and entrained sediments. We pilot this method on sediments from the terminal margin of the Baltic Ice Stream, the largest ice stream of the Fennoscandian Ice Sheet during the Last Glacial Maximum. A strong correlation (R2 = 0.83) between the εNd and latitudes of circum-Baltic river sediments enables us to use εNd as a calibrated measure of distance. The proportion of subglacially transported sediments in a sample is estimated from grain size ratios in the silt fraction (<63 μm). Coupled εNd and grain size analyses reveal a common erosion source for the Baltic Ice Stream sediments located near the Åland sill, more than 850 km upstream from the terminal moraines. This result is in agreement with both numerical modeling and geomorphological investigations of Fennoscandinavian erosion, and is consistent with rapid ice flow into the Baltic basins prior to the Last Glacial Maximum. The methodology introduced here could be used to infer the distances of glacigenic sediment transport from Late Pleistocene and earlier glaciations.

Experimental Rock-on-Rock Abrasive Wear Under Aqueous Conditions: its Role in Subglacial Abrasion

NASA Astrophysics Data System (ADS)

Rutter, E. H.; Lee, A. G.

2003-12-01

We have determined experimentally the rate of abrasive wear of rock on rock for a range of rock types as a function of normal stress and shear displacement. Unlike abrasive wear in fault zones, where wear products accumulate as a thickening gouge zone, in our experiments wear particles were removed by flowing water. The experiments are thus directly pertinent to one of the most important processes in subglacial erosion, and to some extent in river incision. Wear was produced between rotating discs machined from rock samples and measured from the progressive approach of the disc axes towards each other under various levels of normal load. Shear displacements of several km were produced. Optical and scanning electron microscopy were used to study the worn rock surfaces, and particle size distributions in wear products were characterized using a laser particle size analyzer. Rock types studied were sandstones of various porosities and cement characteristics, schists and a granite. In all cases abrasion rate decreased logarithmically with displacement by up to 2 orders of magnitude until a steady state was approached, but only after at least 1 km displacement. The more porous, less-well cemented rocks wore fastest. Amount of abrasion could be characterized quantitatively using an exponentially decaying plus a steady-state term. Wear rate increased non-linearly with normal contact stress, apparently to an asymptote defined by the unconfined compressive strength. Microstructural study showed that the well-cemented and/or lowest porosity rocks wore by progressive abrasion of grains without plucking, whereas whole grains were plucked out of weakly-cemented and/or more porous rocks. This difference in behavior was reflected in wear-product particle size distributions. Where whole-grain plucking was possible, wear products were dominated by particles of the original grain size rather than finer rock flour. Comparison of our results to glacier basal abrasive wear estimated from suspended sediment load (Findeln Glacier, Switzerland) showed the steady-state experimental data seriously to underestimate the natural wear rate. This suggests continuous resetting of the subglacial surface occurs, so that wear is continuously in the 'running-in' stage.

Sedimentology of the lower Karoo Supergroup fluvial strata in the Tuli Basin, South Africa

NASA Astrophysics Data System (ADS)

Bordy, Emese M.; Catuneanu, Octavian

2002-11-01

The Karoo Supergroup in the Tuli Basin (South Africa) consists of a sedimentary sequence (˜450-500 m) composed of four stratigraphic units, namely the informal Basal, Middle and Upper Units, and the formal Clarens Formation. The units were deposited in continental settings from approximately Late Carboniferous to Middle Jurassic. This paper focuses on the ˜60-m-thick Basal Unit, which was examined in terms of sedimentary facies and palaeo-environments based on evidence provided by primary sedimentary structures, palaeo-flow measurements, palaeontological findings, borehole data (59 core descriptions) and stratigraphic relations. Three main facies associations have been identified: (i) gravelstone (breccias and conglomerate-breccias), (ii) sandstone and (iii) fine-grained sedimentary rocks. The coarser facies are interpreted as colluvial fan deposits, possibly associated with glaciogenic diamictites. The sandstone facies association is mainly attributed to channel fills of low sinuosity, braided fluvial systems. The coal-bearing finer-grained facies are interpreted as overbank and thaw-lake deposits, and represent the lower energy correlatives of the sandy channel fills. Sediment aggradation in this fluvio-lacustrine system took place under cold climatic conditions, with floating lake ice likely associated with lacustrine environments. Palaeo-current indicators suggest that the highly weathered, quartz-vein-rich metamorphic rock source of the Basal Unit was situated east-northeast of the study area. The accumulation of the Basal Unit took place within the back-bulge depozone of the Karoo foreland system. In addition to flexural subsidence, the amount of accommodation in this tectonic setting was also possibly modified by extensional tectonism in the later stages of the basin development. Based on sedimentological and biostratigraphic evidence, the coal-bearing fine-grained facies association displays strong similarities with the Vryheid Formation of the main Karoo Basin to the south. The lowermost non-fossiliferous breccias have been correlated before with the Dwyka Group in the main Karoo, and hence the Basal Unit may be regarded as the distal equivalent of the Dwyka and Ecca groups to the south.

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.

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.

Grain-Size Based Additivity Models for Scaling Multi-rate Uranyl Surface Complexation in Subsurface Sediments

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

Zhang, Xiaoying; Liu, Chongxuan; Hu, Bill X.

The additivity model assumed that field-scale reaction properties in a sediment including surface area, reactive site concentration, and reaction rate can be predicted from field-scale grain-size distribution by linearly adding reaction properties estimated in laboratory for individual grain-size fractions. This study evaluated the additivity model in scaling mass transfer-limited, multi-rate uranyl (U(VI)) surface complexation reactions in a contaminated sediment. Experimental data of rate-limited U(VI) desorption in a stirred flow-cell reactor were used to estimate the statistical properties of the rate constants for individual grain-size fractions, which were then used to predict rate-limited U(VI) desorption in the composite sediment. The resultmore » indicated that the additivity model with respect to the rate of U(VI) desorption provided a good prediction of U(VI) desorption in the composite sediment. However, the rate constants were not directly scalable using the additivity model. An approximate additivity model for directly scaling rate constants was subsequently proposed and evaluated. The result found that the approximate model provided a good prediction of the experimental results within statistical uncertainty. This study also found that a gravel-size fraction (2 to 8 mm), which is often ignored in modeling U(VI) sorption and desorption, is statistically significant to the U(VI) desorption in the sediment.« less

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.

Regional Jurassic Submarine Arc-Apron Complex in the Northern Sierra Nevada, California

NASA Astrophysics Data System (ADS)

Templeton, J. H.; Hanson, R. E.; Hargrove, U. S.; Ruff, K. L.

2005-05-01

The Tuttle Lake Formation (TLF), a distinctive unit forming part of the wall rocks to the Mesozoic Sierra Nevada batholith in northern California, is interpreted to have developed within a major island arc fringing the western margin of North America during the Jurassic. It extends for 75 km along strike, from mountainous terrain NW of Truckee to the Mt. Tallac pendant SW of Lake Tahoe. Superb glaciated exposures at various locations along strike provide a window into the proximal parts of a submarine Jurassic arc-apron complex. The TLF is >4 km thick and consists mainly of massively bedded, matrix-supported, polymict volcanic breccias containing poorly vesicular, subangular to angular basaltic to andesitic clasts up to 2 m in length. Characteristics of the polymict breccias indicate deposition from submarine debris flows derived from slumping of near-vent accumulations of lithic debris or sector collapse of parts of the volcanic edifice. Interbeds of finer grained andesitic and silicic turbidites and ash-fall tuffs occur sparsely within the debris-flow sequence, as do volumetrically minor pillow-hyaloclastite breccias, recording local extrusion of lavas on the seafloor. Coarse-grained TLF debris-flow deposits abruptly overlie the Early to Middle Jurassic Sailor Canyon Formation, which consists dominantly of andesitic volcanic sandstones and mudstones deposited from distal turbidity currents in a long-lived, deep marine basin. This marked lithologic change records rapid influx of coarse-grained volcanogenic detritus into the Sailor Canyon basin, related to a major shift in position of volcanic centers. Available data show that the TLF accumulated in a narrow time frame in the Middle Jurassic, just prior to regional tilting and batholith emplacement at ~165 Ma. Coeval basaltic to andesitic hypabyssal intrusions typically compose >15% of the exposed area of the TLF. They have identical major- and trace-element compositions and REE patterns to clasts within the host debris-flow sequence, and all analyses plot as a tight group in calc-alkaline, volcanic-arc fields on standard discrimination diagrams. The intrusions range from 3 km in length down to smaller pods and intrusive pillows a few meters across, many of which appear to be tubular feeder conduits in 3D. Marginal peperites indicate that intrusion occurred while the host sediments were still wet and unconsolidated. Abundant, isolated pockets of globular and blocky peperite are inferred to have been supplied by conduits extending from larger intrusions. Magma/sediment interaction was generally non-explosive, but steam explosions locally played a role in generating dispersed peperite. The overall characteristics of the TLF support a model in which coarse-grained volcaniclastic deposits accumulated rapidly in a proximal submarine setting around a major vent complex within the Middle Jurassic arc. Magma/wet-sediment interaction occurred over large areas within proximal parts of the arc apron, where uprising batches of magma were unable to penetrate the thick volcaniclastic sequence to undergo extrusion. Instead, an extensive network of hypabyssal intrusions and peperite formed at shallow levels beneath the sea floor. Complex hypabyssal networks of this type are probably common in submarine arc sequences, but detailed mapping is required to document their full extent and significance.

Temporally Dynamic, Spatially Static, Cobble Bedforms In Reversing Subtidal Currents

NASA Astrophysics Data System (ADS)

Abdulkade, Akirat; Carling, Paul; Zong, Quanli; Leyland, Julian; Thompson, Charlie

2016-04-01

Cobble bedforms, transverse to the reversing tidal currents, are exposed at extreme low-water Spring tides on an inter-tidal bedrock shelf in the macro-tidal Severn Estuary, UK. Near-bed flow velocities during Spring tides can exceed 1.5m/s, with water depths varying from zero to in excess of 10m. During neap tides the bedforms are not exposed, and sediment is expected to be of limited mobility. When exposed, the bedform geometry tends to be asymmetric; orientated down estuary with the ebb current. During Spring tides, vigorous bedload transport of gravel (including large cobbles) occurs during both flood and ebb over the crests and yet, despite this temporal dynamism, the bedforms remain spatially static over long time periods or show weak down-estuary migration. Stasis implies that the tidal bedload transport vectors are essentially in balance. Near-bed shear stress and bed roughness values vary systematically with the Spring-tide current speeds and the predicted grain-size of the bed load using the Shields criterion is in accord with observed coarser grain-sizes in transport. These hydrodynamic data, delimited by estimates of the threshold of motion, and integrated over either flood or ebb tides are being used to explain the apparent stability of the bedforms. The bulk hydraulic data are supplemented by particle tracer studies and laser-scanning of bed configurations between tides. The high-energy environment results in two forms of armouring. Pronounced steep imbrication of platy-cobbles visible on the exposed up-estuary side of dunes is probably disrupted during flood tides leading to rapid reworking of the toe deposits facing up-estuary. In contrast, some crest and leeside locations have been stable for prolonged periods such that closely-fitted fabrics result; these portions of the bedforms are static and effectively are 'armour-plated'. Ebb-tide deposits of finer, ephemeral sandy-units occur on the down estuary side of the bedforms. Sandy-units (although not observed at low tide) presumably also are deposited on the up estuary side during flooding tides but these deposits are destroyed by ebb flows. The implication of these sediment transport processes on the stratification of the bedforms is considered.

Physical abrasion of mafic minerals and basalt grains: application to Martian aeolian deposits

USGS Publications Warehouse

Cornwall, Carin; Bandfield, Joshua L.; Titus, Timothy N.; Schreiber, B. C.; Montgomery, D.R.

2015-01-01

Sediment maturity, or the mineralogical and physical characterization of sediment deposits, has been used to locate sediment source, transport medium and distance, weathering processes, and paleoenvironments on Earth. Mature terrestrial sands are dominated by quartz, which is abundant in source lithologies on Earth and is physically and chemically stable under a wide range of conditions. Immature sands, such as those rich in feldspars or mafic minerals, are composed of grains that are easily physically weathered and highly susceptible to chemical weathering. On Mars, which is predominately mafic in composition, terrestrial standards of sediment maturity are not applicable. In addition, the martian climate today is cold, dry and sediments are likely to be heavily influenced by physical weathering rather than chemical weathering. Due to these large differences in weathering processes and composition, martian sediments require an alternate maturity index. Abrason tests have been conducted on a variety of mafic materials and results suggest that mature martian sediments may be composed of well sorted, well rounded, spherical basalt grains. In addition, any volcanic glass present is likely to persist in a mechanical weathering environment while chemically altered products are likely to be winnowed away. A modified sediment maturity index is proposed that can be used in future studies to constrain sediment source, paleoclimate, mechanisms for sediment production, and surface evolution. This maturity index may also provide details about erosional and sediment transport systems and preservation processes of layered deposits.

The Role of Grain Dynamics in the Onset of Sediment Transport

NASA Astrophysics Data System (ADS)

Clark, A., IV; Shattuck, M. D.; Ouellette, N. T.; O'Hern, C.

2016-12-01

Despite decades of research, the grain-scale mechanisms that control the onset of sediment transport are still not well understood. A large collection of data, known as the Shields curve, shows that Θ c, which is the minimum dimensionless shear stress at the bed for grains to move, is primarily a function of the shear Reynolds number Re*. To understand this collapse, it is typically assumed that the onset of grain motion is determined by the conditions at which fluid forces violate static equilibrium for surface grains. Re* compares the grain size to the size of the viscous sublayer in the fluid flow, so the relevant fluid lift and drag forces vary with Re*. A complimentary approach, which remains relatively unexplored, is to ask instead when mobilized grains can stop. In this case, Re* is the ratio of two important time scales related to grain motion: (1) the time for a grain to equilibrate to the fluid flow and (2) the time for the shear stress to accelerate a grain over the characteristic bed roughness. Thus, Re* controls whether grains are accelerated significantly between collisions with the bed. To test how this effect relates to the Shields curve, we perform simulations of granular beds sheared by a model fluid flow, where Re* is varied only through the fluid-grain coupling, which alters the grain dynamics. We find good qualitative agreement with the Shields curve, and the quantitative discrepancies are consistent with lift forces calculations at varying Re*. Our results suggest that the onset of sediment transport may be better described as when mobile grains are able to stop, which varies significantly with Re*, and theoretical descriptions that account for this effect may be more successful than those that consider only static equilibrium.

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.

Erosion and sediment transport in the Owens River near Bishop, California

USGS Publications Warehouse

Williams, Rhea P.

1975-01-01

Closure of Pleasant Valley Dam in 1954 has almost eliminated the supply of gravel to the 16-mile (25.7-kilometre) study reach of the Owens River. Because of armoring of the channel, scour has been limited to approximately 1 foot (0.3 metre) in the upper 2.3 miles (3.7 kilometres).This report presents information useful in determining long-term erosion effects below Pleasant Valley Dam, in assessing the feasibility of a proposed bypass channel versus retention of the main channel in its present state, and in determining man's influence on river morphology.Bedload transport is dependent on the hydraulics of a section and the availability of material. Ninety-eight percent by weight of the sampled bedload transported between sites 1 and 6 in the study reach was finer than 8 millimetres, although only 6 to 12 percent of the material in the bed available for transport was finer than 8 millimetres. Bank material, a prime source of new material for transport, is predominantly finer than 16 millimetres.Bank erosion is accelerated by wide ranges in flow release. The bank-erosion rates interpreted from aerial photographs indicate average annual erosion rates of 750 tons (680 tonnes) from 1947 to 1967, 1,970 tons (1,790 tonnes) from 1967 to 1968, and 2,020 tons (1,830 tonnes) from 1968 to 1971. These rates are compatible with the water discharge-sediment discharge relation developed from field data collected during 1972-73.Hydraulic geometry of the six sites indicates a shift in the river system regime since 1954. These changes have progressed downstream from the dam to a point between sites 4 and 5. Farther downstream channel changes will occur until the channel stabilizes.

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.

Experimental testing of flexible barriers for containment of debris flows

USGS Publications Warehouse

DeNatale, Jay S.; Iverson, Richard M.; Major, Jon J.; LaHusen, Richard G.; Fliegel, Gregg L.; Duffy, John D.

1999-01-01

In June 1996, six experiments conducted at the U.S. Geological Survey Debris Flow Flume demonstrated that flexible, vertical barriers constructed of wire rope netting can stop small debris flows. All experimental debris flows consisted of water-saturated gravelly sand with less than two percent finer sediment by weight. All debris flows had volumes of about 10 cubic meters, masses of about 20 metre tons, and impact velocities of 5 to 9 meters per second. In four experiments, the debris flow impacted pristine, unreformed barriers of varying design; in the other two experiments, the debris flow impacted barriers already loaded with sediment from a previous flow. Differences in barrier design led to differences in barrier performance. Experiments were conducted with barriers constructed of square-mesh wire-rope netting with 30centimeter, 20centimeter, and 15 centimeter mesh openings as well as 30centimeter diameter interlocking steel rings. In all cases, sediment cascading downslope at the leading edge of the debris flows tended to spray through the nets. Nets fitted with finer-mesh chain link or chicken wire liners contained more sediment than did unlined nets, and a ring net fitted with a synthetic silt screen liner contained nearly 100 percent of the sediment. Irreversible net displacements of up to 2 meters and friction brake engagement on the support and anchor cables dissipated some of the impact energy. However, substantial forces developed in the steel support columns and the lateral and tie-back anchor cables attached to these columns. As predicted by elementary mechanics, the anchor cables experienced larger tensile forces when the support columns were hinged at the base rather than bolted rigidly to the foundation. Measured loads in the lateral anchor cables exceeded those in the tie-back anchor cables and the load cell capacity of 45 kilo-Newtons. Measurements also indicated that the peak loads in the tie- back anchors were highly transient and occurred at the points of maximum momentum impulse to the net.

Surficial deposits in the Bear Lake Basin

USGS Publications Warehouse

Reheis, Marith C.; Laabs, Benjamin J.C.; Forester, Richard M.; McGeehin, John P.; Kaufman, Darrell S.; Bright, Jordon

2005-01-01

Mapping and dating of surficial deposits in the Bear Lake drainage basin were undertaken to provide a geologic context for interpretation of cores taken from deposits beneath Bear Lake, which sometimes receives water and sediment from the glaciated Bear River and sometimes only from the small drainage basin of Bear Lake itself. Analyses of core sediments by others are directed at (1) constructing a high-resolution climate record for the Bear Lake area during the late Pleistocene and Holocene, and (2) investigating the sources and weathering history of sediments in the drainage basin. Surficial deposits in the upper Bear River and Bear Lake drainage basins are different in their overall compositions, although they do overlap. In the upper Bear River drainage, Quaternary deposits derived from glaciation of the Uinta Range contain abundant detritus weathered from Precambrian quartzite, whereas unglaciated tributaries downstream mainly contribute finer sediment weathered from much younger, more friable sedimentary rocks. In contrast, carbonate rocks capped by a carapace of Tertiary sediments dominate the Bear Lake drainage basin.

PROCEDURE FOR DETERMINATION OF SEDIMENT PARTICLE SIZE (GRAIN SIZE)

EPA Science Inventory

Sediment quality and sediment remediation projects have become a high priority for USEPA. Sediment particle size determinations are used in environmental assessments for habitat characterization, chemical normalization, and partitioning potential of chemicals. The accepted met...

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 influence of sediment transport rate on the development of structure in gravel bed rivers

NASA Astrophysics Data System (ADS)

Ockelford, Annie; Rice, Steve; Powell, Mark; Reid, Ian; Nguyen, Thao; Tate, Nick; Wood, Jo

2013-04-01

Although adjustments of surface grain size are known to be strongly influenced by sediment transport rate little work has systematically explored how different transport rates can affect the development of surface structure in gravel bed rivers. Specifically, it has been well established that the transport of mixed sized sediments leads to the development of a coarser surface or armour layer which occurs over larger areas of the gravel bed. Armour layer development is known to moderate overall sediment transport rate as well as being extremely sensitive to changes in applied shear stress. However, during this armouring process a bed is created where, smaller gain scale changes, to the bed surface are also apparent such as the development of pebble clusters and imbricate structures. Although these smaller scale changes affect the overall surface grain size distribution very little their presence has the ability to significantly increase the surface stability and hence alter overall sediment transport rates. Consequently, the interplay between the moderation of transport rate as a function of surface coarsening at a larger scale and moderation of transport rate as a function of the development of structure on the bed surface at the smaller scale is complicated and warrants further investigation. During experiments a unimodal grain size distribution (σg = 1.30, D50 = 8.8mm) was exposed to 3 different levels of constant discharge that produced sediment transport conditions ranging from marginal transport to conditions approaching full mobility of all size fractions. Sediment was re-circulated during the experiments surface grain size distribution bed load and fractional transport rates were measured at a high temporal resolution such that the time evolution of the beds could be fully described. Discussion concentrates on analysing the effects of the evolving bed condition sediment transport rate (capacity) and transported grain size (competence). The outcome of this research is pertinent to developing new methods of linking the development of bed surface organisation with near bed flow characteristics and bed load transport in gravel bed rivers. Keywords: Graded, Sediment, Structure

Effects of sediment-associated extractable metals, degree of sediment grain sorting, and dissolved organic carbon upon Cryptosporidium parvum removal and transport within riverbank filtration sediments, Sonoma County, California

USGS Publications Warehouse

Metge, D.W.; Harvey, R.W.; Aiken, G.R.; Anders, R.; Lincoln, G.; Jasperse, James; Hill, M.C.

2011-01-01

Oocysts of the protozoan pathogen Cryptosporidium parvum are of particular concern for riverbank filtration (RBF) operations because of their persistence, ubiquity, and resistance to chlorine disinfection. At the Russian River RBF site (Sonoma County, CA), transport of C. parvumoocysts and oocyst-sized (3 μm) carboxylate-modified microspheres through poorly sorted (sorting indices, σ1, up to 3.0) and geochemically heterogeneous sediments collected between 2 and 25 m below land surface (bls) were assessed. Removal was highly sensitive to variations in both the quantity of extractable metals (mainly Fe and Al) and degree of grain sorting. In flow-through columns, there was a log–linear relationship (r2 = 0.82 at p < 0.002) between collision efficiency (α, the probability that colloidal collisions with grain surfaces would result in attachment) and extractable metals, and a linear relationship (r2 = 0.99 at p < 0.002) between α and σ1. Collectively, variability in extractable metals and grain sorting accounted for ∼83% of the variability in α (at p < 0.0002) along the depth profiles. Amendments of 2.2 mg L–1 of Russian River dissolved organic carbon (DOC) reduced α for oocysts by 4–5 fold. The highly reactive hydrophobic organic acid (HPOA) fraction was particularly effective in re-entraining sediment-attached microspheres. However, the transport-enhancing effects of the riverine DOC did not appear to penetrate very deeply into the underlying sediments, judging from high α values (∼1.0) observed for oocysts being advected through unamended sediments collected at ∼2 m bls. This study suggests that in evaluating the efficacy of RBF operations to remove oocysts, it may be necessary to consider not only the geochemical nature and size distribution of the sediment grains, but also the degrees of sediment sorting and the concentration, reactivity, and penetration of the source water DOC.

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.

Effect of Zn addition on bulk microstructure of lead-free solder SN100C

NASA Astrophysics Data System (ADS)

Nur Nadirah M., K.; Nurulakmal M., S.

2017-12-01

This paper reports the effect of adding Zn (0.5 wt% Zn, 1.0 wt% Zn) to the bulk microstructure and intermetallic compound (IMC) formation of commercial SN100C (Sn-0.7Cu-0.05Ni+Ge) lead-free solder alloy. Solder alloys were prepared by melting SN100C ingot and Zn shots, and subsequently casted into steel mold. Samples were ground and polished for XRF, and polished samples were then etched for microstructure analysis. Microstructure of bulk solder and the IMC were observed using SEM equipped with EDX. SEM result showed the addition of 0.5 wt% Zn resulted in increased grain size of β-Sn matrix but further addition of Zn (1 wt%) reduced the size of β-Sn dendrites in the bulk solder. Several intermetallic compounds (IMCs) were observed distributed in the Sn matrix; Cu-Zn, Ni-Zn and Cu-Zn-Ni IMC but in relatively small percentage compared to Cu-Zn and Ni-Zn. These particles could be considered as effective nucleating agent that led to finer β-Sn grains. It is expected that the finer β-Sn will contribute towards higher solder strength and the various IMCs present could act as suppressant for Sn diffusion which will then tend to reduce the IMC growth during thermal aging.

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.

Relation between gas hydrate and physical properties at the Mallik 2L-38 research well in the Mackenzie delta

USGS Publications Warehouse

Winters, W.J.; Dallimore, S.R.; Collett, T.S.; Jenner, K.A.; Katsube, J.T.; Cranston, R.E.; Wright, J.F.; Nixon, F.M.; Uchida, T.

2000-01-01

As part of an interdisciplinary field program, a 1150-m deep well was drilled in the Canadian Arctic to determine, among other goals, the location, characteristics, and properties of gas hydrate. Numerous physical properties of the host sediment were measured in the laboratory and are presented in relation to the lithology and quantity of in situ gas hydrate. Profiles of measured and derived properties presented from that investigation include: sediment wet bulk density, water content, porosity, grain density, salinity, gas hydrate content (percent occupancy of non-sediment grain void space), grain size, porosity, and post-recovery core temperature. The greatest concentration of gas hydrate is located within sand and gravel deposits between 897 and 922 m. Silty sediment between 926 and 952 m contained substantially less, or no, gas hydrate perhaps because of smaller pore size.

Sedimentology and geochemistry of mud volcanoes in the Anaximander Mountain Region from the Eastern Mediterranean Sea.

PubMed

Talas, Ezgi; Duman, Muhammet; Küçüksezgin, Filiz; Brennan, Michael L; Raineault, Nicole A

2015-06-15

Investigations carried out on surface sediments collected from the Anaximander mud volcanoes in the Eastern Mediterranean Sea to determine sedimentary and geochemical properties. The sediment grain size distribution and geochemical contents were determined by grain size analysis, organic carbon, carbonate contents and element analysis. The results of element contents were compared to background levels of Earth's crust. The factors that affect element distribution in sediments were calculated by the nine push core samples taken from the surface of mud volcanoes by the E/V Nautilus. The grain size of the samples varies from sand to sandy silt. Enrichment and Contamination factor analysis showed that these analyses can also be used to evaluate of deep sea environmental and source parameters. It is concluded that the biological and cold seep effects are the main drivers of surface sediment characteristics from the Anaximander mud volcanoes. Copyright © 2015 Elsevier Ltd. All rights reserved.

Effects of Sediment Patches on Sediment Transport Predictions in Steep Mountain Channels

NASA Astrophysics Data System (ADS)

Monsalve Sepulveda, A.; Yager, E.

2013-12-01

Bed surface patches occur in most gravel-bedded rivers and in steep streams can be divided between relatively immobile boulders and more mobile patches of cobbles and gravel. This spatial variability in grain size, roughness and sorting impact bed load transport by altering the relative local mobility of different grain sizes and creating complex local flow fields. Large boulders also bear a significant part of the total shear stress and we hypothesize that the remaining shear stress on a given mobile patch is a distribution of values that depend on the local topography, patch type and location relative to the large roughness elements and thalweg. Current sediment transport equations do not account for the variation in roughness, local flow and grain size distributions on and between patches and often use an area-weighted approach to obtain a representative grain size distribution and reach-averaged shear stress. Such equations also do not distinguish between active (patches where at least one grain size is in motion) and inactive patches or include the difference in mobility between patch classes as result of spatial shear stress distributions. To understand the effects of sediment patches on sediment transport in steep channels, we calculated the shear stress distributions over a range of patch classes in a 10% gradient step-pool stream. We surveyed the bed with a high density resolution (every 5 cm in horizontal and vertical directions over a 40 m long reach) using a total station and terrestrial LiDAR, mapped and classified patches by their grain size distributions, and measured water surface elevations and mean velocities for low to moderate flow events. Using these data we calibrated a quasi-three dimensional model (FaSTMECH) to obtain shear stress distributions over each patch for a range of flow discharges. We modified Parker's (1990) equations to use the calculated shear stress distribution, measured grain sizes, and a specific hiding function for each patch class, and then added the bedload fluxes for each patch to calculate the reach-averaged sediment transport rate. Sediment mobility in patches was highly dependent on the patch's class and location relative to the thalweg and large roughness elements. Compared to deterministic formulations, the use of distributions of shear stress improved predictions of bedload transport in steep mountain channels.

Sedimentary and structural patterns on the northern Santa Rosa-Cortes Ridge, southern California

USGS Publications Warehouse

Field, M.E.; Richmond, W.C.

1980-01-01

The Santa Rosa-Cortes Ridge is an 1800 m high, 180 km long feature lying approximately 90 km off the coast of southern California and directly south of the northern group of Channel Islands. Geophysical profiling and sampling cruises to the northern part of the ridge, an area of recent and future lease sales for petroleum development, provide a strong data base for interpretation of structural and sedimentary patterns and their relation to potential geologic hazards. The northern part of the ridge is a complexly folded and faulted northwest-trending anticlinorium composed mostly of lower and middle Miocene shale and mudstone. Erosional remnants of upper Miocene and Pliocene rocks unconformably overlie highly folded pre-upper Miocene strata. The major structure of the ridge developed almost continuously from Oligocene or early Miocene time to the end of the Tertiary; many small folds formed between post-late Miocene and pre-late Pleistocene time. Numerous small faults cut the rocks on the ridge top. Faults cut basement rocks on the west side of the ridge along the Ferrelo fault zone. Published data on historical epicenters and evidence of offsets on the seafloor from seismic reflection and side-scan profiles, including limited evidence of possible strike-slip movement along fault traces, indicate that the northern Santa Rosa-Cortes Ridge is tectonically active. The crest of the ridge was truncated as the result of repeated sea-level fluctuations in the Quaternary. A thin veneer of unconsolidated medium to fine sand, less than 3 m thick, mantles most of the ridge; locally in topographically low areas and on the upper flanks of the ridge, thickness exceeds 20 m. The meager sediment cover, coupled with available evidence of relatively strong currents flowing across the ridge top, indicate that the ridge is an area of nondeposition or winnowing of fine sediments. Modern sediments become thicker and finer-grained from the ridge top to the ridge flanks, suggesting active accretion in those areas. Slumps are present at various depths on the flanks, and it seems probable that the thicker deposits (> 20 m) of modern sediments on the upper flanks will be sites of future slumping. ?? 1980.

Tectonic setting of Cretaceous basins on the NE Tibetan Plateau: Insights from the Jungong basin

USGS Publications Warehouse

Craddock, W.H.; Kirby, E.; Dewen, Z.; Jianhui, L.

2012-01-01

Quantifying the Cenozoic growth of high topography in the Indo-Asian collision zone remains challenging, due in part to significant shortening that occurred within Eurasia before collision. A growing body of evidence suggests that regions far removed from the suture zone experienced deformation before and during the early phases of Himalayan orogenesis. In the present-day north-eastern Tibetan Plateau, widespread deposits of Cretaceous sediment attest to significant basin formation; however, the tectonic setting of these basins remains enigmatic. We present a study of a regionally extensive network of sedimentary basins that are spatially associated with a system of SE-vergent thrust faults and are now exposed in the high ranges of the north-eastern corner of the Tibetan Plateau. We focus on a particularly well-exposed basin, located ~20km north of the Kunlun fault in the Anyemaqen Shan. The basin is filled by ~900m of alluvial sediments that become finer-grained away from the basin-bounding fault. Additionally, beds in the proximal footwall of the basin-bounding fault exhibit progressive, up-section shallowing and several intraformational unconformities which can be traced into correlative conformities in the distal part of the basin. The observations show sediment accumulated in the basin during fault motion. Regional constraints on the timing of sediment deposition are provided by both fossil assemblages from the Early Cretaceous, and by K-Ar dating of volcanic rocks that floor and cross-cut sedimentary fill. We argue that during the Cretaceous, the interior NE Tibetan Plateau experienced NW-SE contractional deformation similar to that documented throughout the Qinling-Dabie orogen to the east. The Songpan-Ganzi terrane apparently marked the southern limit of this deformation, such that it may have been a relatively rigid block in the Tibetan lithosphere, separating regions experiencing deformation north of the convergent Tethyan margin from regions deforming inboard of the east Asian margin. ?? 2011 The Authors. Basin Research ?? 2011 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists.

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.

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.

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.

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.

[Effects of the grain size and thickness of dust deposits on soil water and salt movement in the hinterland of the Taklimakan Desert].

PubMed

Sun, Yan-Wei; Li, Sheng-Yu; Xu, Xin-Wen; Zhang, Jian-Guo; Li, Ying

2009-08-01

By using mcirolysimeter, a laboratory simulation experiment was conducted to study the effects of the grain size and thickness of dust deposits on the soil water evaporation and salt movement in the hinterland of the Taklimakan Desert. Under the same initial soil water content and deposition thickness condition, finer-textured (<0.063 mm) deposits promoted soil water evaporation, deeper soil desiccation, and surface soil salt accumulation, while coarse-textured (0.063-2 mm) deposits inhibited soil water evaporation and decreased deeper soil water loss and surface soil salt accumulation. The inhibition effect of the grain size of dust deposits on soil water evaporation had an inflection point at the grain size 0.20 mm, i. e., increased with increasing grain size when the grain size was 0.063-0.20 mm but decreased with increasing grain size when the grain size was > 0.20 mm. With the increasing thickness of dust deposits, its inhibition effect on soil water evaporation increased, and there existed a logarithmic relationship between the dust deposits thickness and water evaporation. Surface soil salt accumulation had a negative correlation with dust deposits thickness. In sum, the dust deposits in study area could affect the stability of arid desert ecosystem.

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.

A universal approximation to grain size from images of non-cohesive sediment

USGS Publications Warehouse

Buscombe, D.; Rubin, D.M.; Warrick, J.A.

2010-01-01

The two-dimensional spectral decomposition of an image of sediment provides a direct statistical estimate, grid-by-number style, of the mean of all intermediate axes of all single particles within the image. We develop and test this new method which, unlike existing techniques, requires neither image processing algorithms for detection and measurement of individual grains, nor calibration. The only information required of the operator is the spatial resolution of the image. The method is tested with images of bed sediment from nine different sedimentary environments (five beaches, three rivers, and one continental shelf), across the range 0.1 mm to 150 mm, taken in air and underwater. Each population was photographed using a different camera and lighting conditions. We term it a “universal approximation” because it has produced accurate estimates for all populations we have tested it with, without calibration. We use three approaches (theory, computational experiments, and physical experiments) to both understand and explore the sensitivities and limits of this new method. Based on 443 samples, the root-mean-squared (RMS) error between size estimates from the new method and known mean grain size (obtained from point counts on the image) was found to be ±≈16%, with a 95% probability of estimates within ±31% of the true mean grain size (measured in a linear scale). The RMS error reduces to ≈11%, with a 95% probability of estimates within ±20% of the true mean grain size if point counts from a few images are used to correct bias for a specific population of sediment images. It thus appears it is transferable between sedimentary populations with different grain size, but factors such as particle shape and packing may introduce bias which may need to be calibrated for. For the first time, an attempt has been made to mathematically relate the spatial distribution of pixel intensity within the image of sediment to the grain size.

A universal approximation of grain size from images of noncohesive sediment

NASA Astrophysics Data System (ADS)

Buscombe, D.; Rubin, D. M.; Warrick, J. A.

2010-06-01

The two-dimensional spectral decomposition of an image of sediment provides a direct statistical estimate, grid-by-number style, of the mean of all intermediate axes of all single particles within the image. We develop and test this new method which, unlike existing techniques, requires neither image processing algorithms for detection and measurement of individual grains, nor calibration. The only information required of the operator is the spatial resolution of the image. The method is tested with images of bed sediment from nine different sedimentary environments (five beaches, three rivers, and one continental shelf), across the range 0.1 mm to 150 mm, taken in air and underwater. Each population was photographed using a different camera and lighting conditions. We term it a "universal approximation" because it has produced accurate estimates for all populations we have tested it with, without calibration. We use three approaches (theory, computational experiments, and physical experiments) to both understand and explore the sensitivities and limits of this new method. Based on 443 samples, the root-mean-squared (RMS) error between size estimates from the new method and known mean grain size (obtained from point counts on the image) was found to be ±≈16%, with a 95% probability of estimates within ±31% of the true mean grain size (measured in a linear scale). The RMS error reduces to ≈11%, with a 95% probability of estimates within ±20% of the true mean grain size if point counts from a few images are used to correct bias for a specific population of sediment images. It thus appears it is transferable between sedimentary populations with different grain size, but factors such as particle shape and packing may introduce bias which may need to be calibrated for. For the first time, an attempt has been made to mathematically relate the spatial distribution of pixel intensity within the image of sediment to the grain size.

Influence of the Atlantic inflow and Mediterranean outflow currents on late Quaternary sedimentary facies of the Gulf of Cadiz continental margin

USGS Publications Warehouse

Nelson, C.H.; Baraza, J.; Maldonado, A.; Rodero, J.; Escutia, C.; Barber, J.H.

1999-01-01

The late Quaternary pattern of sedimentary facies on the Spanish Gulf of Cadiz continental shelf results from an interaction between a number of controlling factors that are dominated by the Atlantic inflow currents flowing southeastward across the Cadiz shelf toward the Strait of Gibraltar. An inner shelf shoreface sand facies formed by shoaling waves is modified by the inflow currents to form a belt of sand dunes at 10-20 m that extends deeper and obliquely down paleo-valleys as a result of southward down-valley flow. A mid-shelf Holocene mud facies progrades offshore from river mouth sources, but Atlantic inflow currents cause extensive progradation along shelf toward the southeast. Increased inflow current speeds near the Strait of Gibraltar and the strong Mediterranean outflow currents there result in lack of mud deposition and development of a reworked transgressive sand dune facies across the entire southernmost shelf. At the outer shelf edge and underlying the mid-shelf mud and inner shelf sand facies is a late Pleistocene to Holocene transgressive sand sheet formed by the eustatic shoreline advance. The late Quaternary pattern of contourite deposits on the Spanish Gulf of Cadiz continental slope results from an interaction between linear diapiric ridges that are oblique to slope contours and the Mediterranean outflow current flowing northwestward parallel to the slope contours and down valleys between the ridges. Coincident with the northwestward decrease in outflow current speeds from the Strait there is the following northwestward gradation of contourite sediment facies: (1) upper slope sand to silt bed facies, (2) sand dune facies on the upstream mid-slope terrace, (3) large mud wave facies on the lower slope, (4) sediment drift facies banked against the diapiric ridges, and (5) valley facies between the ridges. The southeastern sediment drift facies closest to Gibraltar contains medium-fine sand beds interbedded with mud. The adjacent valley floor facies is composed of gravelly, shelly coarse to medium sand lags and large sand dunes on the valley margins. By comparison, the northwestern drift contains coarse silt interbeds and the adjacent valley floors exhibit small to medium sand dunes of fine sand. Because of the complex pattern of contour-parallel and valley-perpendicular flow paths of the Mediterranean outflow current, the larger-scale bedforms and coarser-grained sediment of valley facies trend perpendicular to the smaller-scale bedforms and finer-grained contourite deposits of adjacent sediment drift facies. Radiocarbon ages verify that the inner shelf shoreface sand facies (sedimentation rate 7.1 cm/kyr), mid-shelf mud facies (maximum rate 234 cm/kyr) and surface sandy contourite layer of 0.2-1.2 m thickness on the Cadiz slope (1-12 cm/kyr) have deposited during Holocene time when high sea level results in maximum water depth over the Gibraltar sill and full development of the Atlantic inflow and Mediterranean outflow currents. The transgressive sand sheet of the shelf, and the mud layer underlying the surface contourite sand sheet of the slope, correlate, respectively, with the late Pleistocene sea level lowstand and apparent weak Mediterranean outflow current.

Role of grain-size in phyllonitisation: Insights from mineralogy, microstructures, strain analyses and numerical modeling

NASA Astrophysics Data System (ADS)

Bose, Narayan; Dutta, Dripta; Mukherjee, Soumyajit

2018-07-01

Brittle Y- and P-planes exist in an exposure of greywacke in the Garhwal Lesser Himalaya, India. Although, Y-planes are well developed throughout, the P-planes are prominent only in some parts (domain-A), and not elsewhere (domain-B). To investigate why the P-planes developed selectively, the following studies were undertaken: 1. Clay-separated XRD analyses: clinochlore and illite are present in both the domains. 2. Strain analyses by Rf-φ method: it deduces strain magnitudes of ∼1.8 for the ductile deformed quartz grains from both the domains A and B. 3. Grain size analyses of quartz clasts: domain-A is mostly composed of finer grains (area up to 40,000 μm2), whereas domain-B consists of a population of coarser grains (area >45,000 μm2). A 2D finite element modeling of linear elastic material was performed using COMSOL software to investigate the control of grain-size variation on the generation brittle shear planes. The results of numerical modeling corroborate the known fact that an increase in grain-size reduces the elastic strain energy density. A broader grain-size distribution increases the effects of diffusion creep and resists the onset of dislocation creep. Thus, rocks with coarser grain population (domain B) tend to resist the generation of shear fractures, unlike their fine-grained counterpart (domain A).

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.

Ductility Improvement of an AZ61 Magnesium Alloy through Two-Pass Submerged Friction Stir Processing

PubMed Central

Luo, Xicai; Cao, Genghua; Zhang, Wen; Qiu, Cheng; Zhang, Datong

2017-01-01

Friction stir processing (FSP) has been considered as a novel technique to refine the grain size and homogenize the microstructure of metallic materials. In this study, two-pass FSP was conducted under water to enhance the cooling rate during processing, and an AZ61 magnesium alloy with fine-grained and homogeneous microstructure was prepared through this method. Compared to the as-cast material, one-pass FSP resulted in grain refinement and the β-Mg17Al12 phase was broken into small particles. Using a smaller stirring tool and an overlapping ratio of 100%, a finer and more uniform microstructure with an average grain size of 4.6 μm was obtained through two-pass FSP. The two-pass FSP resulted in a significant improvement in elongation of 37.2% ± 4.3%, but a slight decrease in strength compared with one-pass FSP alloy. Besides the microstructure refinement, the texture evolution in the stir zone is also considered responsible for the ductility improvement. PMID:28772614

Fabric and texture at Siple Dome, Antarctica

USGS Publications Warehouse

Diprinzio, C.L.; Wilen, Lawrence A.; Alley, R.B.; Fitzpatrick, J.J.; Spencer, M.K.; Gow, A.J.

2005-01-01

Preferred c-axis orientations are present in the firn at Siple Dome, West Antarctica, and recrystallization begins as shallow as 200 m depth in ice below -20??C, based on digital analysis of c-axis fabrics, grain-sizes and other characteristics of 52 vertical thin sections prepared in the field from the kilometer-long Siple Dome ice core. The shallowest section analyzed, from 22 m, shows clustering of c axes toward the vertical. By 200 m depth, girdle fabric and other features of recrystallized ice are evident in layers (or regions), separated by layers (regions) of typically finer-grained ice lacking evidence of recrystallization. Ice from about 700-780 m depth, which was deposited during the last ice age, is especially fine-grained, with strongly vertical c axes, but deeper ice shows much larger crystals and strong evidence of recrystallization. Azimuthal asymmetry of some c-axis fabrics, trends in grain-size, and other indicators reveal additional information on processes and history of ice flow at Siple Dome.

The microstructural evolution, crystallography, and thermal processing of ultrahigh carbon Fe-1.85 pct C melt-spun ribbon

NASA Technical Reports Server (NTRS)

Spanos, G.; Ayers, J. D.; Vold, C. L.; Locci, I. E.

1993-01-01

A study is presented to determine if fine microstructures could be achieved using rapid solidification to produce a fine-grained fully austenitic starting structure and then using thermal processing cycles to produce an even finer ferrite-cementite structure. The evolution, mechanisms of grain refinement, and crystallography of the resultant microstructures were examined by TEM. A thermal processing cycle consisted of quenching the ribbon in liquid nitrogen, tempering at 600 C for 10 sec, 'upquenching' to 750 C for 10 sec, and subsequently quenching again in liquid nitrogen. The heat-treatment resulted in martensite grains with sizes of about 1 micron or less in both length and thickness and cementite particles of 0.4 micron or less. It is concluded that these microstructures could be used for producing fine-grained ultrahigh carbon steels of very high strength without the brittleness associated with the formation of coarse carbide particles of the loss of strength due to graphite formation.

Wire Arc Additive Manufacturing of AZ31 Magnesium Alloy: Grain Refinement by Adjusting Pulse Frequency.

PubMed

Guo, Jing; Zhou, Yong; Liu, Changmeng; Wu, Qianru; Chen, Xianping; Lu, Jiping

2016-10-09

Wire arc additive manufacturing (WAAM) offers a potential approach to fabricate large-scale magnesium alloy components with low cost and high efficiency, although this topic is yet to be reported in literature. In this study, WAAM is preliminarily applied to fabricate AZ31 magnesium. Fully dense AZ31 magnesium alloy components are successfully obtained. Meanwhile, to refine grains and obtain good mechanical properties, the effects of pulse frequency (1, 2, 5, 10, 100, and 500 Hz) on the macrostructure, microstructure and tensile properties are investigated. The results indicate that pulse frequency can result in the change of weld pool oscillations and cooling rate. This further leads to the change of the grain size, grain shape, as well as the tensile properties. Meanwhile, due to the resonance of the weld pool at 5 Hz and 10 Hz, the samples have poor geometry accuracy but contain finer equiaxed grains (21 μm) and exhibit higher ultimate tensile strength (260 MPa) and yield strength (102 MPa), which are similar to those of the forged AZ31 alloy. Moreover, the elongation of all samples is above 23%.

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

Laboratory measurements of grain-bedrock interactions using inertial sensors.

NASA Astrophysics Data System (ADS)

Maniatis, Georgios; Hoey, Trevor; Hodge, Rebecca; Valyrakis, Manousos; Drysdale, Tim

2016-04-01

Sediment transport in steep mountain streams is characterized by the movement of coarse particles (diameter c.100 mm) over beds that are not fully sediment-covered. Under such conditions, individual grain dynamics become important for the prediction of sediment movement and subsequently for understanding grain-bedrock interaction. Technological advances in micro-mechanical-electrical systems now provide opportunities to measure individual grain dynamics and impact forces from inside the sediments (grain inertial frame of reference) instead of trying to infer them indirectly from water flow dynamics. We previously presented a new prototype sensor specifically developed for monitoring sediment transport [Maniatis et al. EGU 2014], and have shown how the definition of the physics of the grain using the inertial frame and subsequent derived measurements which have the potential to enhance the prediction of sediment entrainment [Maniatis et al. 2015]. Here we present the latest version of this sensor and we focus on beginning of the cessation of grain motion: the initial interaction with the bed after the translation phase. The sensor is housed in a spherical case, diameter 80mm, and is constructed using solid aluminum (density = 2.7 kg.m-3) after detailed 3D-CAD modelling. A complete Inertial Measurement Unit (a combination of micro- accelerometer, gyroscope and compass) was placed at the center of the mass of the assembly, with measurement ranges of 400g for acceleration, and 1200 rads/sec for angular velocity. In a 0.9m wide laboratory flume, bed slope = 0.02, the entrainment threshold of the sensor was measured, and the water flow was then set to this value. The sensor was then rolled freely from a static cylindrical bar positioned exactly on the surface of the flowing water. As the sensor enters the flow we record a very short period of transport (1-1.5 sec) followed by the impact on the channel bed. The measured Total Kinetic Energy (Joules) includes the translational energy component of transport (defined as a function of 3-dimensional translational velocity) as well as the rotational component (a function of the 3-axis angular velocity measurements from the gyroscope) which is neglected in the majority of contemporary saltation models. The results suggest that, for this grain scale, the magnitude of the impact of mobile grains on the bed is primarily controlled by their inertia. References Maniatis et al. 2014 EGU General assembly http://meetingorganizer.copernicus.org/EGU2014/EGU2014-12829.pdf Maniatis et. al 2015: "CALCULATION OF EXPLICIT PROBABILITY OF ENTRAINMENT BASED ON INERTIAL ACCELERATION MEASUREMENTS" J. Hydraulic Engineering, Under review.

Palaeoecological implications of the preservation potential of soft-bodied organisms in sediment-density flows: testing turbulent waters

NASA Astrophysics Data System (ADS)

Bath Enright, Orla G.; Minter, Nicholas J.; Sumner, Esther J.

2017-06-01

Interpreting how far organisms within fossil assemblages may have been transported and if they all originated from the same location is fundamental to understanding whether they represent true palaeocommunities. In a three-factorial experimental design, we used an annular flume to generate actualistic sandy sediment-density flows that were fast (2 ms-1) and fully turbulent in order to test the effects of flow duration, sediment concentration, and grain angularity on the states of bodily damage experienced by the freshly euthanized polychaete Alitta virens. Results identified statistically significant effects of flow duration and grain angularity. Increasing sediment concentration had a statistically significant effect with angular sediment but not with rounded sediment. Our experiments demonstrate that if soft-bodied organisms such as polychaetes were alive and then killed by a flow then they would have been capable of enduring prolonged transport in fast and turbulent flows with little damage. Dependent upon sediment concentration and grain angularity, specimens were capable of remaining intact over flow durations of between 5 and 180 min, equating to transport distances up to 21.6 km. This result has significant palaeoecological implications for fossil lagerstätten preserved in deposits of sediment-density flows because the organisms present may have been transported over substantial distances and therefore may not represent true palaeocommunities.

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.

Spatial niche partitioning in dinosaurs from the latest cretaceous (Maastrichtian) of North America.

PubMed

Lyson, Tyler R; Longrich, Nicholas R

2011-04-22

We examine patterns of occurrence of associated dinosaur specimens (n = 343) from the North American Upper Cretaceous Hell Creek Formation and equivalent beds, by comparing their relative abundance in sandstone and mudstone. Ceratopsians preferentially occur in mudstone, whereas hadrosaurs and the small ornithopod Thescelosaurus show a strong association with sandstone. By contrast, the giant carnivore Tyrannosaurus rex shows no preferred association with either lithology. These lithologies are used as an indicator of environment of deposition, with sandstone generally representing river environments, and finer grained sediments typically representing floodplain environments. Given these patterns of occurrence, we argue that spatial niche partitioning helped reduce competition for resources between the herbivorous dinosaurs. Within coastal lowlands ceratopsians preferred habitats farther away from rivers, whereas hadrosaurs and Thescelosaurus preferred habitats in close proximity to rivers, and T. rex, the ecosystem's sole large carnivore, inhabited both palaeoenvironments. Spatial partitioning of the environment helps explain how several species of large herbivorous dinosaurs coexisted. This study emphasizes that different lithologies can preserve dramatically dissimilar vertebrate assemblages, even when deposited in close proximity and within a narrow window of time. The lithology in which fossils are preserved should be recorded as these data can provide unique insights into the palaeoecology of the animals they preserve.

Spatial niche partitioning in dinosaurs from the latest cretaceous (Maastrichtian) of North America

PubMed Central

Lyson, Tyler R.; Longrich, Nicholas R.

2011-01-01

We examine patterns of occurrence of associated dinosaur specimens (n = 343) from the North American Upper Cretaceous Hell Creek Formation and equivalent beds, by comparing their relative abundance in sandstone and mudstone. Ceratopsians preferentially occur in mudstone, whereas hadrosaurs and the small ornithopod Thescelosaurus show a strong association with sandstone. By contrast, the giant carnivore Tyrannosaurus rex shows no preferred association with either lithology. These lithologies are used as an indicator of environment of deposition, with sandstone generally representing river environments, and finer grained sediments typically representing floodplain environments. Given these patterns of occurrence, we argue that spatial niche partitioning helped reduce competition for resources between the herbivorous dinosaurs. Within coastal lowlands ceratopsians preferred habitats farther away from rivers, whereas hadrosaurs and Thescelosaurus preferred habitats in close proximity to rivers, and T. rex, the ecosystem's sole large carnivore, inhabited both palaeoenvironments. Spatial partitioning of the environment helps explain how several species of large herbivorous dinosaurs coexisted. This study emphasizes that different lithologies can preserve dramatically dissimilar vertebrate assemblages, even when deposited in close proximity and within a narrow window of time. The lithology in which fossils are preserved should be recorded as these data can provide unique insights into the palaeoecology of the animals they preserve. PMID:20943689

Late Glacial and Early Holocene Climatic Changes Based on a Multiproxy Lacustrine Sediment Record from Northeast Siberia

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

Kokorowski, H D; Anderson, P M; Sletten, R S

Palynological (species assemblage, pollen accumulation rate), geochemical (carbon to nitrogen ratios, organic carbon and biogenic silica content), and sedimentological (particle size, magnetic susceptibility) data combined with improved chronology and greater sampling resolution from a new core from Elikchan 4 Lake provide a stronger basis for defining paleoenvironmental changes than was previously possible. Persistence of herb-dominated tundra, slow expansion of Betula and Alnus shrubs, and low percentages of organic carbon and biogenic silica suggest that the Late-Glacial transition (ca. 16,000-11,000 cal. yr BP) was a period of gradual rather than abrupt vegetation and climatic change. Consistency of all Late-Glacial data indicatesmore » no Younger Dryas climatic oscillation. A dramatic peak in pollen accumulation rates (ca. 11,000-9800 cal. yr BP) suggests a possible summer temperature optimum, but finer grain-sizes, low magnetic susceptibility, and greater organic carbon and biogenic silica, while showing significant warming at ca. 11,000 cal. yr BP, offer no evidence of a Holocene thermal maximum. When compared to trends in other paleo-records, the new Elikchan data underscore the apparent spatial complexity of climatic responses in Northeast Siberia to global forcings between ca. 16,000-9000 cal. yr BP.« less

Anatomy of biocalcarenitic units in the Plio-Pleistocene record of the Northern Apennines (Italy)

NASA Astrophysics Data System (ADS)

Cau, Simone; Roveri, Marco; Taviani, Marco

2017-04-01

The Castell'Arquato Basin (CAB) in the foothills of the thrust-belt Northern Apennines is a foreland basin infilled by Plio-Quaternary sediments and a reference area for Plio-Pleistocene biostratigraphy. The CAB exposes plurimetric biodetrital carbonate units at discrete temporal intervals. Such shell-rich units are at places lithified, turning into conspicuous biodetritral carbonate rocks (biocalcarenites) that display a cyclical stacking motif highlighted by the regular alternation with finer-grained marine deposits. The cyclical nature of thick biocalcarenites has been hypothesized to be orbitally-controlled by obliquity and/or precession cyclicity. Furthermore, biocalcarenite-mudstone couplets form distinct clusters governed by 100-400 ka eccentricity maxima starting from 3.1 Ma at the inception of the Northern Hemisphere glaciation. They correlate with sapropels cycles formed at times of maximum insolation (precession minima). The CAB calcarenites are poorly known with respect to their environmental genetic context what motivated a detailed paleoecological analysis to unravel at best their formative context. Five distinct biofacies arranged in stacking patterns are identified through two-way cluster analysis based on the macrofossil content. Our quantitative and qualitative results suggest that these polytaxic shell concentrations and their bracketing marine mudstones developed in middle shelf settings being sensitive to climatically-driven changes.

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.

Petrology of the Indian Eucrite Piplia Kalan

NASA Technical Reports Server (NTRS)

Buchanan, Paul C.; Mittlefehldt, D. W.; Hutchinson, R.; Koeberl, C.; Lindstrom, D. J.; Pandit, M. K.

1999-01-01

Piplia Kalan is an equilibrated eucrite consisting of 60-80 vol.% lithic clasts in a subordinate brecciated matrix. Ophitic/subophitic lithic clasts fall into two groups: finer-grained lithology A and coarser-grained lithology B. Very fine-grained clasts (lithology C) also occur and originally were hypocrystalline in texture. The variety of materials represented in Piplia Kalan suggests cooling histories ranging from quenching or fast crystallization to slower crystallization. Despite textural differences, clasts and matrix have similar mineral and bulk compositions. Thus. Piplia Kalan is probably best classified as a genomict breccia that could represent fragments of a single lava flow or shallow intrusive body, including fine-grained or glassy outer margin and more slowly cooled coarser-grained interior. Piplia Kalan displays evidence of an early shock event, including brecciated matrix and areas of lithic clasts that contain fine-grained, equigranular pyroxene between deformed feldspar laths. The meteorite also displays evidence of at least one episode of thermal metamorphism: hypocrystalline materials are recrystallized to hornfelsic textures and the matrix has a nonporous texture similar to those of eucrites that were affected by post-brecciation heating. Veins of brown glass transect both lithic clasts and brecciated matrix and indicate a second, post-metamorphism shock event.

Effect of non-metallic precipitates and grain size on core loss of non-oriented electrical silicon steels

NASA Astrophysics Data System (ADS)

Wang, Jiayi; Ren, Qiang; Luo, Yan; Zhang, Lifeng

2018-04-01

In the current study, the number density and size of non-metallic precipitates and the size of grains on the core loss of the 50W800 non-oriented electrical silicon steel sheets were investigated. The number density and size of precipitates and grains were statistically analyzed using an automatic scanning electron microscope (ASPEX) and an optical microscope. Hypothesis models were established to reveal the physical feature for the function of grain size and precipitates on the core loss of the steel. Most precipitates in the steel were AlN particles smaller than 1 μm so that were detrimental to the core loss of the steel. These finer AlN particles distributed on the surface of the steel sheet. The relationship between the number density of precipitates (x in number/mm2 steel area) and the core loss (P1.5/50 in W/kg) was regressed as P1.5/50 = 4.150 + 0.002 x. The average grain size was approximately 25-35 μm. The relationship between the core loss and grain size (d in μm) was P1.5/50 = 3.851 + 20.001 d-1 + 60.000 d-2.

Conductivity dependence of seismoelectric wave phenomena in fluid-saturated sediments

NASA Astrophysics Data System (ADS)

Block, Gareth I.; Harris, John G.

2006-01-01

Seismoelectric phenomena in sediments arise from acoustic wave-induced fluid motion in the pore space, which perturbs the electrostatic equilibrium of the electric double layer on the grain surfaces. Experimental techniques and the apparatus built to study the conductivity dependence of the electrokinetic (EK) effect are described, and outcomes for studies in loose glass microspheres and medium-grain sand are presented. By varying the NaCl concentration in the pore fluid, we measured the conductivity dependence of two kinds of EK behavior: (1) the electric fields generated within the samples by the passage of transmitted acoustic waves and (2) the electromagnetic waves produced at the fluid-sediment interface by the incident acoustic wave. Both phenomena are caused by relative fluid motion in the sediment pores; this feature is characteristic of poroelastic (Biot) media but is not predicted by either viscoelastic fluid or solid models. A model of plane wave reflection from a fluid-sediment interface using EK-Biot theory leads to theoretical predictions that compare well to the experimental data for both loose glass microspheres and medium-grain sand.

Grain-resolving simulations of settling cohesive sediment

NASA Astrophysics Data System (ADS)

Vowinckel, Bernhard; Whithers, Jade; Meiburg, Eckart; Luzzatto-Fegiz, Paolo

2017-11-01

Cohesive sediment is ubiquitous in natural environments such as rivers, lakes and coastal ecosystems. For this type of sediment, we can no longer ignore the short-range attractive forces that result in flocculation of aggregates much larger than the individual grain size. Hence, understanding the complex dynamics of the interplay between flocculated sediment and the ambient fluid is of prime interest for managing aquatic environments, although a comprehensive understanding of these phenomena is still lacking. In the present study, we address this issue by carrying out grain-resolved simulations of cohesive particles settling under gravity using the Immersed Boundary Method. We present a computational model formulation to accurately resolve the process of flocculation. The cohesive model is then applied to a complex test case. A randomly distributed ensemble of 1261 polydisperse particles is released in a tank of quiescent fluid. Subsequently, particles start to settle, thereby replacing fluid at the bottom of the tank, which induces a counter flow opposing the settling direction. This mechanism will be compared to experimental studies from the literature, as well as to the non-cohesive counterpart to assessthe impact of flocculation on sedimentation.

Paleovalley fills: Trunk vs. tributary

USGS Publications Warehouse

Kvale, E.P.; Archer, A.W.

2007-01-01

A late Mississippian-early Pennsylvanian eustatic sea level drop resulted in a complex lowstand drainage network being eroded across the Illinois Basin in the eastern United States. This drainage system was filled during the early part of the Pennsylvanian. Distinct differences can be recognized between the trunk and tributary paleovalley fills. Fills preserved within the trunk systems tend to be fluvially dominated and consist of bed-load deposits of coarse- to medium-grained sandstone and conglomerate. Conversely, the incised valleys of tributary systems tend to be filled with dark mudstone, thinly interbedded sandstones, and mudstones and siltstones. These finer grained facies exhibit marine influences manifested by tidal rhythmites, certain traces fossils, and macro- and microfauna. Examples of tributary and trunk systems, separated by no more than 7 km (4.3 mi) along strike, exhibit these styles of highly contrasting fills. Useful analogs for understanding this Pennsylvanian system include the Quaternary glacial sluiceways present in the lower Ohio, White, and Wabash river valleys of Indiana (United States) and the modern Amazon River (Brazil). Both the Amazon River and the Quaternary rivers of Indiana have (or had) trunk rivers that are (were) dominated by large quantities of bed load relative to their tributaries. The trunk valley systems of these analogs aggraded much more rapidly than their tributary valleys, which evolved into lakes because depositional rates along the trunk are (were) so high that the mouths of the tributaries have been dammed by bed-load deposits. These Holocene systems illustrate that sediment yields can significantly influence the nature of fill successions within incised valleys independent of rates of sea level changes or proximity to highstand coastlines. Copyright ?? 2007. The American Association of Petroleum Geologists. All rights reserved.

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.

Textural analysis of marine sediments at the USGS Woods Hole Science Center; methodology and data on DVD

USGS Publications Warehouse

Poppe, Lawrence J.; Williams, S. Jeffress; Paskevich, Valerie F.

2006-01-01

Marine sediments off the eastern United States vary markedly in texture (i.e., the size, shape, composition, and arrangement of their grains) due to a complex geologic history. For descriptive purposes, however, it is typically most useful to classify these sediments according to their grain-size distributions. In 1962, the U.S. Geological Survey began a program to study the marine geology of the continental margin off the Atlantic coast of the United States. As part of this program and numerous subsequent projects, thousands of sediment grab samples and cores were collected and analyzed for grain size at the Woods Hole Science Center. USGS Open-File Report 2005-1001 (Poppe et al., 2005), available on DVD and online, describes the field methods used to collect marine sediment samples as well as the laboratory methods used to determine and characterize grain-size distributions, and presents these data in several formats that can be readily employed by interested parties. The report is divided into three sections. The first section discusses procedures and contains pictures of the equipment, analytical flow diagrams, video clips with voice commentary, classification schemes, useful forms and compiled and uncompiled versions of the data-acquisition and data-processing software with documentation. The second section contains the grain-size data for more than 23,000 analyses in two “flat-file” formats, a data dictionary, and color-coded browse maps. The third section provides a GIS data catalog of the available point, interpretive, and baseline data layers, with FGDC-compliant metadata to help users visualize the textural information in a geographic context.

The Impact of Fire on Mercury Cycling in Watershed Systems

NASA Astrophysics Data System (ADS)

Lopez, S.; Mendez, C.; Hogue, T.; Jay, J.

2006-12-01

Mercury methylation is a process by which the less-toxic inorganic mercury is transformed into methylmercury (MeHg). MeHg is a potent neurotoxin with a strong tendency to biomagnify within the food chain. Limited studies suggest that wildfires change the soil characteristics and contribute to Hg transport and possibly methylation in downstream ecosystems. We propose that post-fire Hg cycling can be related to various soil properties and burn characteristics. In order to better understand the effects of wildfires on Hg cycling, studies were undertaken within a burned watershed and a neighboring unburned site, Malibu Creek and Cold Creek, respectively. Soil sampling of the burned and control (unburned) regions were composed of 25 square foot grids with nine equidistant sampling points. Sediment samples for soil sieve analysis were collected at all grid points to determine the particle size distribution of the fine and coarse grain aggregates. Total Hg sediments were collected from the three middle points of the grid at two soil horizons to provide a vertical profile. Total Hg concentrations of the sediment samples were measured using the Direct Mercury Analyzer (DMA80). Initial analysis of the soil profiles reveals a decrease in Hg concentration at the soil surface (89 percent loss). Preliminary results indicate sites with the lowest concentration of Hg are characterized by a higher percentage of finer grain aggregates. Runoff from the first post-fire storm was extremely turbid and dark gray in color due to high levels of suspended solids (3980 mg/L). Total Hg concentrations in unfiltered and filtered samples (0.2 micron) were 196 and 4.7 ng/L, respectively, compared to the control which had unfiltered and filtered Hg levels of 6.1 and 2.3 ng/L, respectively, and 450 mg/L total suspended solids. The concentration of Hg on the particles was six times higher than the Hg content of suspended particles at the control site. Results also show much stronger partitioning (three-fold higher Kd's) to the solid phase in the fire- impacted site. On-going work includes: 1) analysis of Hg and ancillary geochemical parameters overlying water and porewater from samples collected in the streambed downstream of the fire, 2) analysis of Hg concentrations in various particle size fractions of soil; and 3) preliminary characterization of recovery through analysis of soil properties and Hg levels at the burned and control sites, one-year post-fire.