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Sample records for margin sediments santa

  1. Modern sedimentary processes in the Santa Monica, California continental margin: sediment accumulation, mixing and budget.

    PubMed

    Alexander, Clark R; Venherm, Claudia

    2003-01-01

    Sediment input to SMB appears to be associated with at least two point sources on the shelf, with Malibu Creek and the Hyperion sewage outfall being the most significant. Sediment contributions are sufficient to support apparent mass accumulation rates near these sources up to approximately 1.8 g/cm(2) year, which with distance decrease to approximately 0.5 g/cm(2) year near the shelf break (approximately 80-100 m water depth). Sequestering of material on the shelf and decreasing sediment supply to the slope is evident as rates decrease between 100 and 200 m water depths to less than 0.2 g/cm(2) year. Below 100-200 m water depth, rates are relatively slow throughout a broad region of the slope (0.07-0.14 g/cm(2) year). These slower rates are in general agreement with rates determined on the flanks of the California Borderland basins. Sediment texture fines from approximately 3.5 phi to approximately 7 phi with distance offshore. Texture does not exhibit significant changes from surficial values with depth in the seabed at any given site or between sites on the slope. This similarity in rates and downcore texture over such a broad extent suggests that hemiplegic sedimentation is the dominant mechanism of sediment delivery in water depths >200 m. Seabed distributions of radionuclides suggest that apparent accumulation rates in SMB may be twice the actual accumulation rates. A sediment budget documents that over the past century at least, SMB has served as a sink for 50-100% of the natural and anthropogenic inputs to the coastal ocean.

  2. Variations in archaeal and bacterial diversity associated with the sulfate-methane transition zone in continental margin sediments (Santa Barbara Basin, California).

    PubMed

    Harrison, Benjamin K; Zhang, Husen; Berelson, Will; Orphan, Victoria J

    2009-03-01

    The sulfate-methane transition zone (SMTZ) is a widespread feature of continental margins, representing a diffusion-controlled interface where there is enhanced microbial activity. SMTZ microbial activity is commonly associated with the anaerobic oxidation of methane (AOM), which is carried out by syntrophic associations between sulfate-reducing bacteria and methane-oxidizing archaea. While our understanding of the microorganisms catalyzing AOM has advanced, the diversity and ecological role of the greater microbial assemblage associated with the SMTZ have not been well characterized. In this study, the microbial diversity above, within, and beneath the Santa Barbara Basin SMTZ was described. ANME-1-related archaeal phylotypes appear to be the primary methane oxidizers in the Santa Barbara Basin SMTZ, which was independently supported by exclusive recovery of related methyl coenzyme M reductase genes (mcrA). Sulfate-reducing Deltaproteobacteria phylotypes affiliated with the Desulfobacterales and Desulfosarcina-Desulfococcus clades were also enriched in the SMTZ, as confirmed by analysis of dissimilatory sulfite reductase (dsr) gene diversity. Statistical methods demonstrated that there was a close relationship between the microbial assemblages recovered from the two horizons associated with the geochemically defined SMTZ, which could be distinguished from microbial diversity recovered from the sulfate-replete overlying horizons and methane-rich sediment beneath the transition zone. Comparison of the Santa Barbara Basin SMTZ microbial assemblage to microbial assemblages of methane seeps and other organic matter-rich sedimentary environments suggests that bacterial groups not typically associated with AOM, such as Planctomycetes and candidate division JS1, are additionally enriched within the SMTZ and may represent a common bacterial signature of many SMTZ environments worldwide.

  3. Geology of the continental margin beneath Santa Monica Bay, Southern California, from seismic-reflection data

    USGS Publications Warehouse

    Fisher, M.A.; Normark, W.R.; Bohannon, R.G.; Sliter, R.W.; Calvert, A.J.

    2003-01-01

    We interpret seismic-reflection data, which were collected in Santa Monica Bay using a 70-in3 generator-injector air gun, to show the geologic structure of the continental shelf and slope and of the deep-water, Santa Monica and San Pedro Basins. The goal of this research is to investigate the earthquake hazard posed to urban areas by offshore faults. These data reveal that northwest of the Palos Verdes Peninsula, the Palos Verdes Fault neither offsets the seafloor nor cuts through an undeformed sediment apron that postdates the last sea level rise. Other evidence indicates that this fault extends northwest beneath the shelf in the deep subsurface. However, other major faults in the study area, such as the Dume and San Pedro Basin Faults, were active recently, as indicated by an arched seafloor and offset shallow sediment. Rocks under the lower continental slope are deformed to differing degrees on opposite sides of Santa Monica Canyon. Northwest of this canyon, the continental slope is underlain by a little-deformed sediment apron; the main structures that deform this apron are two lower-slope anticlines that extend toward Point Dume and are cored by faults showing reverse or thrust separation. Southeast of Santa Monica Canyon, lower-slope rocks are deformed by a complex arrangement of strike-slip, normal, and reverse faults. The San Pedro Escarpment rises abruptly along the southeast side of Santa Monica Canyon. Reverse faults and folds underpinning this escarpment steepen progressively southeastward. Locally they form flower structures and cut downward into basement rocks. These faults merge downward with the San Pedro Basin fault zone, which is nearly vertical and strike slip. The escarpment and its attendant structures diverge from this strike-slip fault zone and extend for 60 km along the margin, separating the continental shelf from the deep-water basins. The deep-water Santa Monica Basin has large extent but is filled with only a thin (less than 1.5-km

  4. Continental margin sedimentation: from sediment transport to sequence stratigraphy

    USGS Publications Warehouse

    Nittrouer, Charles A.; Austin, James A.; Field, Michael E.; Kravitz, Joseph H.; Syvitski, James P.M.; Wiberg, Patricia L.; Nittrouer, Charles A.; Austin, James A.; Field, Michael E.; Kravitz, Joseph H.; Syvitski, James P. M.; Wiberg, Patricia L.

    2007-01-01

    This volume on continental margin sedimentation brings together an expert editorial and contributor team to create a state-of-the-art resource. Taking a global perspective, the book spans a range of timescales and content, ranging from how oceans transport particles, to how thick rock sequences are formed on continental margins. - Summarizes and integrates our understanding of sedimentary processes and strata associated with fluvial dispersal systems on continental shelves and slopes - Explores timescales ranging from particle transport at one extreme, to deep burial at the other - Insights are presented for margins in general, and with focus on a tectonically active margin (northern California) and a passive margin (New Jersey), enabling detailed examination of the intricate relationships between a wide suite of sedimentary processes and their preserved stratigraphy - Includes observational studies which document the processes and strata found on particular margins, in addition to numerical models and laboratory experimentation, which provide a quantitative basis for extrapolation in time and space of insights about continental-margin sedimentation - Provides a research resource for scientists studying modern and ancient margins, and an educational text for advanced students in sedimentology and stratigraphy

  5. Sedimentation in Santa Margarita Lake, San Luis Obispo County, California

    USGS Publications Warehouse

    Glysson, G. Douglas

    1977-01-01

    The 1975 storage capacity of Santa Margarita Lake in San Luis Obispo County, Calif., was 41,400 acre-feet, a decrease of 3,400 acre-feet since 1941. Usable capacity decreased from 25,800 to 23,000 acre-feet. Long-term sediment yield for the Salinas River basin upstream from the lake was estimated at 1,150 tons per square mile per year. A correlation between the annual water discharge of the Salinas River near Pozo and the annual quantity of sediment deposited in the lake was developed that can be used to stimate future sediment deposition. (Woodard-USGS)

  6. Sediment accumulation on the Southern California Bight continental margin during the twentieth century

    USGS Publications Warehouse

    Alexander, C.R.; Lee, H.J.

    2009-01-01

    Sediment discharged into the portion of the Southern California Bight extending from Santa Barbara to Dana Point enters a complex system of semi-isolated coastal cells, narrow continental shelves, submarine canyons, and offshore basins. On both the Santa Monica and San Pedro margins, 210Pb accumulation rates decrease in an offshore direction (from ??0.5 g cm-2yr-1 to 0.02 g cm-2yr -1), in concert with a fining in sediment grain size (from 4.5?? to 8.5??), suggesting that offshore transport of wave-resuspended material occurs as relatively dilute nepheloid layers and that hemiplegic sedimentation dominates the supply of sediment to the outer shelf, slope, and basins. Together, these areas are effectively sequestering up to 100% of the annual fluvial input. In contrast to the Santa Monica margin, which does not display evidence of mass wasting as an important process of sediment delivery and redistribution, the San Pedro margin does provide numerous examples of failures and mass wasting, suggesting that intraslope sediment redistribution may play a more important role there. Basin deposits in both areas exhibit evidence of turbidites tentatively associated with both major floods and earthquakes, sourced from either the Redondo Canyon (San Pedro Basin) or Dume Canyon (Santa Monica Basin). On the Palos Verdes shelf, sediment-accumulation rates decrease along and across the shelf away from the White's Point outfall, which has been a major source of contaminants to the shelf deposits. Accumulation rates prior to the construction of the outfall were ??0.2 g cm-2yr-1 and increased 1.5-3.7 times during peak discharges from the outfall in 1971. The distal rate of accumulation has decreased by ??50%, from 0.63 g cm -2yr-1 during the period 1971-1992 to 0.29 g cm -2yr-1 during the period 1992-2003. The proximal rate of accumulation, however, has only decreased ??10%, from 0.83 g cm -2yr-1 during the period 1971-1992 to 0.73 g cm -2yr-1 during the period 1992-2003. Effluent

  7. Across-shelf sediment transport since the Last Glacial Maximum, southern California margin

    USGS Publications Warehouse

    Sommerfield, C.K.; Lee, H.J.

    2004-01-01

    Correlation of continental shelf-slope stratigraphy in Santa Monica Bay (southern California) with Ocean Drilling Program records for nearby slope-basin sites has illuminated the timing and scale of terrigenous sediment dispersal on margin since the Last Glacial Maximum (LGM). Marine flooding surfaces preserved in a transgressive sequence on the Santa Monica Shelf provide a key link between base-level elevation and sediment transport across shelf. Sediment-accumulation rates at slope-basin sites were maximal ca. 15-10 ka, well after the LGM, decreased during the 12-9 ka transition from fluvial-estuarine to fully marine conditions on the shelf, and decelerated throughout the Holocene to 30%-75% of their values at the LGM. The deceleration is interpreted to manifest a landward shift in the margin depocenter with the onset of transgressive sedimentation beginning when sea level surmounted the shelf edge ca. 13 ka, as predicted by sequence-stratigraphic models. However, the records make clear that factors other than base level modulated slope-basin accumulation rates during the deglaciation. ?? 2004 Geological Society of America.

  8. Late Pleistocene to Holocene sedimentation and hydrocarbon seeps on the continental shelf of a steep, tectonically active margin, southern California, USA

    USGS Publications Warehouse

    Draut, Amy E.; Hart, Patrick E.; Lorenson, T.D.; Ryan, Holly F.; Wong, Florence L.; Sliter, Ray W.; Conrad, James E.

    2009-01-01

    Small, steep, uplifting coastal watersheds are prolific sediment producers that contribute significantly to the global marine sediment budget. This study illustrates how sedimentation evolves in one such system where the continental shelf is largely sediment-starved, with most terrestrial sediment bypassing the shelf in favor of deposition in deeper basins. The Santa Barbara-Ventura coast of southern California, USA, is considered a classic area for the study of active tectonics and of Tertiary and Quaternary climatic evolution, interpretations of which depend upon an understanding of sedimentation patterns. High-resolution seismic-reflection data over >570 km2 of this shelf show that sediment production is concentrated in a few drainage basins, with the Ventura and Santa Clara River deltas containing most of the upper Pleistocene to Holocene sediment on the shelf. Away from those deltas, the major factor controlling shelf sedimentation is the interaction of wave energy with coastline geometry. Depocenters containing sediment 5-20 m thick exist opposite broad coastal embayments, whereas relict material (bedrock below a regional unconformity) is exposed at the sea floor in areas of the shelf opposite coastal headlands. Locally, natural hydrocarbon seeps interact with sediment deposition either to produce elevated tar-and-sediment mounds or as gas plumes that hinder sediment settling. As much as 80% of fluvial sediment delivered by the Ventura and Santa Clara Rivers is transported off the shelf (some into the Santa Barbara Basin and some into the Santa Monica Basin via Hueneme Canyon), leaving a shelf with relatively little recent sediment accumulation. Understanding factors that control large-scale sediment dispersal along a rapidly uplifting coast that produces substantial quantities of sediment has implications for interpreting the ancient stratigraphic record of active and transform continental margins, and for inferring the distribution of hydrocarbon resources

  9. Eel River margin source-to-sink sediment budgets: revisited

    USGS Publications Warehouse

    Warrick, Jonathan A.

    2014-01-01

    The Eel River coastal margin has been used as a representative source-to-sink sediment dispersal system owing to its steep, high-sediment yield river and the formation of sedimentary strata on its continental shelf. One finding of previous studies is that the adjacent continental shelf retains only ~25% of the Eel River fine-grained sediment (less than 63 μm) discharged over time scales of both individual floods and the 20th century, thus suggesting that the Eel shelf trapping-efficiency is uniquely lower than other similar systems. Here I provide data and analyses showing that sediment discharge relationships in the Eel River have varied strongly with time and include substantial decreases in suspended-sediment concentrations during the latter 20th century. Including these trends in margin-wide sediment budgets, I show that previous Eel River sediment discharge rates were overestimated by a factor of two. Thus, revised sediment budgets shown here reveal that the Eel shelf retained ~50% of the discharged river fine-grained suspended sediment during intensively sampled events of 1995–97 and over the 20th century. In light of this, hypotheses about high rates of sediment export away from the primary shelf depocenter should be reevaluated.

  10. Terrestrial organic carbon contributions to sediments on the Washington margin

    NASA Astrophysics Data System (ADS)

    Prahl, F. G.; Ertel, J. R.; Goni, M. A.; Sparrow, M. A.; Eversmeyer, B.

    1994-07-01

    Elemental and stable carbon isotopic compositions and biomarker concentrations were determined in sediments from the Columbia River basin and the Washington margin in order to evaluate geochemical approaches for quantifying terrestrial organic matter in marine sediments. The biomarkers include: an homologous series of long-chain n-alkanes derived from the surface waxes of higher plants; phenolic and hydroxyalkanoic compounds produced by CuO oxidation of two major vascular plant biopolymers, lignin and cutin. All marine sediments, including samples collected from the most remote sites in Cascadia Basin, showed organic geochemical evidence for the presence of terrestrial organic carbon. Using endmember values for the various biomarkers determined empirically by two independent means, we estimate that the terrestrial contribution to the Washington margin is ~ 60% for shelf sediments, ~ 30% for slope sediments, and decreases further to ≤15% in basin sediments. Results from the same geochemical measurements made with depth in gravity core 6705-7 from Cascadia Seachannel suggest that our approach to assess terrestrial organic carbon contributions to contemporary deposits on the Washington margin can be applied to the study of sediments depositing in this region since the last glacial period.

  11. Sediment discharge in the Santa Clara River Basin, Ventura and Los Angeles Counties, California

    USGS Publications Warehouse

    Williams, Rhea P.

    1979-01-01

    Sediment data collected in the Santa Clara River in California basin, during the 1967-75 water years were analyzed to determine the particle size and quantity of sediment transported past three gaging stations. The total sediment discharge of the basin , computed from records of Santa Clara River at Montalvo for water years 1968-75, was 63.5 million tons, of which 59.5 million tons was carried in suspension and an estimated 4 million tons was transported as unsampled sediment discharge. About 17.7 million tons, or 28 percent of the total sediment discharge, was coarse sediment (particles larger than 0.062 millimeter). Most of the sediment was transported during only a few days of floodflow each year. During the 1968-75 water years, approximately 55 percent of the total sediment was transported in 2 days and 92 percent was transported in 53 days. The long-term (1928-75) average annual sediment discharge of the Santa Clara River at Montalvo is estimated at 3.67 million tons. Of that quantity, 2.58 million tons consisted of fine sediment and 1.09 million tons consisted of coarse sediment. A sediment budget for the Santa Clara River basin was estimated for sediment discharges under both natural and actual conditions. The major difference between natural and actual sediment discharges of the Santa Clara River basin is the sediment intercepted upstream from Lake Piru. The combined trap efficiency of Lake Piru and Pyramid Lake approaches 100 percent. Sediment deposited in these reservoirs resulted in about a 6-percent reduction of sediment to the Santa Clara River basin during the historical period (1928-75) and a 12-percent reduction during the period most affected by dams (1953-75). Sediment losses to the basin by gravel mining, diversion of flows, and interception of sediment in the Castaic Creek basin resulted in additional reductions of 2 percent during the period 1928-75 and 4 percent during the period 1953-75. (Kosco-USGS)

  12. Physical subdivision and description of the water-bearing sediments of the Santa Clara Valley, California

    USGS Publications Warehouse

    Wentworth, Carl M.; Jachens, Robert C.; Williams, Robert A.; Tinsley, John C.; Hanson, Randall T.

    2015-01-01

    Maps and cross sections show the elevations of cycle boundaries and the underlying bedrock surface, the varying thicknesses of the cycles and of their fine tops and coarse bottoms, and the aggregate thickness of coarse layers in those bottom intervals. Coarse sediment is more abundant toward some parts of the basin margin and in the southern part of the basin. Cycle boundary surfaces are relatively smooth, and their shapes are consistent with having been intercycle topographic surfaces. The underlying bedrock surface has a relief of more than 1,200 feet and deepens toward the center of the basin and the west edge of the fault-bounded Evergreen Basin, which is concealed beneath the east side of the Quaternary basin. The absence of consistent abrupt changes in thicknesses or boundary elevations across the basin or in cross section indicates that the interior of the basin is largely unfaulted, with the Silver Creek strand of the San Andreas system at the west edge of the Evergreen Basin being the sole exception. The east and west margins of the Santa Clara Basin, in contrast, are marked by reverse and thrust fault systems.

  13. SEDIMENT AND PLANT PHOSPHORUS IN TWO THALASSIA TESTUDINUM SEAGRASS BEDS OF SANTA ROSA SOUND, NW FLORIDA

    EPA Science Inventory

    We investigated phosphorus concentrations in the seagrass, Thalassia testudinum, and the supporting quartz sediments of two meadows in Santa Rosa Sound. One meadow was sampled during 2002, and the other during 2003. Triplicate sediment and biomass cores were obtained from beneath...

  14. Physical properties of southern Alaska margin sediments in the context of global convergent margins

    NASA Astrophysics Data System (ADS)

    Daigle, H.; Piña, O.; Screaton, E.; James, S.

    2014-12-01

    At convergent margins, the deformation response due to external forcing by sedimentation, tectonic stress, and volume changes during chemical reactions is closely interrelated with the ability of excess pore pressure to dissipate. These excess pore pressures in turn can affect plate boundary fault location and strength, rates of sediment accretion or subduction, the taper angle of material on the overriding plate, and may also play a role in the generation of earthquakes and propagation of seismic slip. Offshore southern Alaska, rapid sedimentation and glacial loading are interpreted to have influenced the location of thrust faulting by rapid transport of sediment offshore, where previously active faults were deactivated by increased normal stresses as a result of sediment loading. The response of the wedge to external forcing is linked to permeability of the wedge sediments, as well as those in the underriding plate. We determined permeability of sediments from the glacial sediment dominated accretionary wedge, sampled at Sites U1420 and U1421 on the Yakutat Block, and sediments from the Surveyor Fan that overlies the Pacific Plate and are inputs to the Aleutian Trench, sampled at Sites U1417 and U1418. We found that the Surveyor Fan sediments have porosity-permeability relationships that are comparable to sediments from other reference sites worldwide. However, the sediments in the wedge have somewhat higher permeability, much larger grain sizes, and are much less compressible compared with other wedge sediments. This suggests that the physical properties that control overpressure generation and dissipation in the input sediments to the Aleutian Trench are comparable to other subduction zones, but that the accretionary wedge on the Yakutat Block is uniquely strong and well-drained due to the predominance of glacigenic sediments.

  15. Geohistory analysis of the Santa Maria basin, California, and its relationship to tectonic evolution of the continental margin

    SciTech Connect

    McCrory, P.A.; Arends, R.G. ); Ingle, J.C. Jr. ); Isaacs, C.M.; Stanley, R.G. ); Thornton, M.L.C. )

    1991-02-01

    The Santa Maria basin of central California is a geologically complex area located along the tectonically active California continental margin. The record of Cenozoic tectonism preserved in Santa Maria strata provides an opportunity to compare the evolution of the region with plate tectonic models for Cenozoic interactions along the margin. Geohistory analysis of Neogene Santa Maria basin strata provides important constraints for hypotheses of the tectonic evolution of the central California margin during its transition from a convergent to a transform plate boundary. Preliminary analyses suggest that the tectonic evolution of the Santa Maria area was dominated by coupling between adjacent oceanic plates and the continental margin. This coupling is reflected in the timing of major hiatuses within the basin sedimentary sequence and margin subsidence and uplift which occurred during periods of tectonic plate adjustment. Stratigraphic evidence indicates that the Santa Maria basin originated on the continental shelf in early Miocene time. A component of margin subsidence is postulated to have been caused by cessation of spreading on adjacent offshore microplates approximately 19-18 ma. A sharp reduction in rate of tectonic subsidence in middle Miocene time, observed in the Santa Maria basin both onshore and offshore, was coeval with rotation of crustal blocks as major shearing shifts shoreward. Tectonic uplift of two eastern sites, offshore Point Arguello and near Point Sal, in the late Miocene may have been related to a change to transpressional motion between the Pacific and North American plates, as well as to rotation of the western Transverse Ranges in a restraining geometry.

  16. Patterns of late Quaternary shelf-margin sedimentation, southwest Louisiana

    SciTech Connect

    Suter, J.R.; Berryhill, H.L.

    1986-09-01

    Late Quaternary extension of the continental shelf in the northern Gulf of Mexico has been largely accomplished by deposition at the shelf margin during sea level lowstands. The distribution and geometry of facies suggest that delta progradation during sea level fall and lowstand is a principal process for shelf accretion. Along the shelf margin of southwest Louisiana, sets of deltaic deposits corresponding to the last two lowstands of sea level have been mapped from high-resolution seismic profiles. Individual deltas extend farther than 5000 m/sup 2/ and are more than 160 m thick. Diapirism has had a controlling effect on sedimentation patterns of the shelf-margin deltas throughout their depositional histories. Shelf-margin deltas have also been the loci for the transfer of large volumes of sediment from the shelf to the upper slope by mass transport, with buried submarine troughs formed by retrogressive shelf-edge failure in association with major streams acting as conduits for sediment movement. In southwest Louisiana, mass transport deposits follow depressions formed by salt diapirism rather than creating broad aprons on the slope.

  17. Cretaceous to Eocene passive margin sedimentation in Northeastern Venezuela

    SciTech Connect

    Erikson, J.P. )

    1993-02-01

    Twenty two palinspastic paleogeographic maps are presented for the Cretaceous to Eocene strata of the Serrania del Interior of northeastern Venezuela. The mapped lithologies, environmental conditions, and evolving depositional systems record [approximately]90 m.y. of dominantly marine sedimentation on the only observable Mesozoic passive margin in the Western Hemisphere. The depositional systems of the passive margin are heterogeneous at lateral (i.e., along-margin) length scales greater than [approximately]40 km. The primary lateral heterogeneity is caused by a major Lower Cretaceous deltaic system that emanated southwest of the Serrania del Interior. All important intervals, such as the laterally variable Aptian-Albian El Cantil platform limestone and the hydrocarbon source rocks of the Upper Cretaceous Querecual and San Antonio formations, are related to probable causal mechanisms and environmental conditions. Stratigraphic events have been interpreted as of either local or regional extent; based on a combination of outcrop sedimentologic analyses and regional depositional systems interpretation. The 3-dimensional distribution of depositional systems and systems tracts reveals 4-6 regional sequence boundaries separated by 4-20 m.y. Subsidence analyses support the facies interpretation of a passive margin by showing continuous, thermally dominated subsidence during the Cretaceous to Eocene interval. Subsidence and accumulation rates increased and facies changed significantly in the Oligocene, indicating the end of passive margin sedimentation and the initiation of foredeep subsidence and accumulation associated with overthrusting the eastward-advancing Caribbean Plate.

  18. Thickness of Santa Fe Group sediments in the Espanola Basin south of Santa Fe, New Mexico, as estimated from aeromagnetic data

    USGS Publications Warehouse

    Phillips, Jeffrey D.; Grauch, V.J.S.

    2004-01-01

    In the southern Espa?ola basin south of Santa Fe, New Mexico, weakly magnetic Santa Fe Group sediments of Oligocene to Pleistocene age, which represent the primary aquifers for the region, are locally underlain by moderately to strongly magnetic igneous and volcaniclastic rocks of Oligocene age. Where this relationship exists, the thickness of Santa Fe Group sediments, and thus the maximum thickness of the aquifers, can be estimated from quantitative analysis of high-resolution aeromagnetic data. These thickness estimates provide guidance for characterizing the ground-water resources in between scattered water wells in this area of rapid urban development and declining water supplies. This report presents one such analysis based on the two-step extended Euler method for estimating depth to magnetic sources. The results show the general form of a north-trending synclinal basin located between the Cerrillos Hills and Eldorado with northward thickening of Santa Fe Group sediments. The increase in thickness is gradual from the erosional edge on the south to a U-shaped Santa Fe embayment hinge line, north of which sediments thicken much more dramatically. Along the north-south basin axis, Santa Fe Group sediments thicken from 300 feet (91 meters) at the hinge line near latitude 35o32'30'N to 2,000 feet (610 meters) at the Cerrillos Road interchange at Interstate 25, north of latitude 35o36'N. The depth analysis indicates that, superimposed on this general synclinal form, there are many local areas where the Santa Fe Group sediments may be thickened by a few hundred feet, presumably due to erosional relief on the underlying Oligocene volcanic and volcaniclastic rocks. Some larger areas of greater apparent thickening occur where the presence of magnetic rocks directly underlying the Santa Fe Group is uncertain. Where magnetic rocks are absent beneath the Santa Fe Group, the thickness cannot be estimated from the aeromagnetic data.

  19. Radiocarbon geochronology of the sediments of the São Paulo Bight (southern Brazilian upper margin).

    PubMed

    Mahiques, Michel M; Sousa, Silvia H M; Burone, Leticia; Nagai, Renata H; Silveira, Ilson C A; Figueira, Rubens C L; Soutelino, Rafael G; Ponsoni, Leandro; Klein, Daniel A

    2011-09-01

    The aim of this work was to generate an inventory of the data on radiocarbon datings obtained from sediments of the São Paulo Bight (southern Brazilian upper margin) and to analyze the data in terms of Late Quaternary sedimentary processes and sedimentation rates. A total of 238 radiocarbon datings from materials collected using differents ampling procedures was considered for this work. The sedimentation rates varied from less than 2 to 68 cm.kyr(-1). The highest sedimentation rate values were found in a low-energy (ría type) coastal system as well as in the upwelling zones of Santa Catarina and Cabo Frio. The lowest rates were found on the outer shelf and upper slopes. Our results confirm the strong dependency of the shelf currents, with an emphasis to the terrigenous input from the Río de La Plata outflow which is transported via the Brazilian Coastal Current, as well as of the coupled Brazil Current - Intermediate Western Boundary Current (BC-IWBC) dynamics on the sedimentary processes. At least three indicators of the paleo sea level were found at 12200 yr BP (conventional radiocarbon age) (103 meters below sea level - mbsl), 8300-8800 cal yr BP (13 mbsl) and 7700-8100 cal yr BP (6 mbsl).

  20. 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.

  1. Changes in ice-margin processes and sediment routing during ice-sheet advance across a marginal moraine

    USGS Publications Warehouse

    Knight, P.G.; Jennings, C.E.; Waller, R.I.; Robinson, Z.P.

    2007-01-01

    Advance of part of the margin of the Greenland ice sheet across a proglacial moraine ridge between 1968 and 2002 caused progressive changes in moraine morphology, basal ice formation, debris release, ice-marginal sediment storage, and sediment transfer to the distal proglacial zone. When the ice margin is behind the moraine, most of the sediment released from the glacier is stored close to the ice margin. As the margin advances across the moraine the potential for ice-proximal sediment storage decreases and distal sediment flux is augmented by reactivation of moraine sediment. For six stages of advance associated with distinctive glacial and sedimentary processes we describe the ice margin, the debris-rich basal ice, debris release from the glacier, sediment routing into the proglacial zone, and geomorphic processes on the moraine. The overtopping of a moraine ridge is a significant glaciological, geomorphological and sedimentological threshold in glacier advance, likely to cause a distinctive pulse in distal sediment accumulation rates that should be taken into account when glacial sediments are interpreted to reconstruct glacier fluctuations. ?? 2007 Swedish Society for Anthropology and Geography.

  2. River sediment flux and shelf sediment accumulation rates on the Pacific Northwest margin

    NASA Astrophysics Data System (ADS)

    Wheatcroft, R. A.; Sommerfield, C. K.

    2005-02-01

    To test the generality of insight obtained from recent STRATAFORM studies of northern California's Eel margin, river sediment sources and continental shelf sinks were examined on the Pacific Northwest margin from 38° to 44.5°N. River discharge and sediment concentration data acquired by the US Geological Survey were used to update long-term annual suspended-sediment loads for 17 rivers that range in basin area from 635 to ˜22,000 km 2. Resulting annual load estimates vary over 3 orders of magnitude (0.065-18×10 9 kg/yr), with major suspended-sediment fluxes supplied by, in decreasing order, the Eel, Klamath/Trinity, Mad, Rogue, Umpqua and Russian rivers. Down-core profiles of excess 210Pb and 137Cs were used to estimate sediment accumulation rates (SARs) at prescribed depths (70 and 110 m) and distances (0-40-km north and south along-shelf) from each of the major rivers. SARs were found to vary much less than the river flux estimates, and are mostly in the range of 1.5 to 6 mm/yr. Most significantly, shelf SARs on the other Pacific Northwest margins are only slightly less than those observed on the Eel shelf, implying that much higher proportions of riverine sediment are retained on those shelves. Likely reasons that the Eel dispersal system exhibits greater off-shelf transport are (1) the narrower and steeper shelf geometry, and (2) the existence of a newly documented cross-isobath sediment transport mechanism that involves wave-modulated fluid mud flows. Testing whether the fluid mud flows are a consequence of the Eel River basin's high sediment yield, and are thus unique to the Eel, or are caused by intense wave energy during discharge events, and hence are operative on many other margins, awaits future bottom-boundary layer measurements.

  3. Towards a sediment budget for the Santa Cruz shelf

    USGS Publications Warehouse

    Eittreim, S.L.; Xu, J. P.; Noble, M.; Edwards, B.D.

    2002-01-01

    A conceptual model is presented for the northern Monterey Bay continental shelf in which coarse sediment moves southward along the coast in the littoral zone while fine sediment moves to the north by advection and diffusion along the midshelf. Data from measurements and estimates of various sediment sources and sinks show that the midshelf mudbelt is the dominant sink for fine-grained sediment introduced into Monterey Bay. The principal sources of the fine sediment are the three rivers that enter Monterey Bay: the San Lorenzo, Pajaro and Salinas rivers. Accumulation rates in the midshelf mudbelt are high relative to documented yields of rivers and cliff erosion, and also are high relative to other documented mud accumulations of the west coast continental shelves. ?? 2002 Elsevier Science B.V. All rights reserved.

  4. Magnitude and variability of Holocene sediment accumulation in Santa Monica Bay, California

    USGS Publications Warehouse

    Sommerfield, C.K.; Lee, H.J.

    2003-01-01

    The spatial variability of Holocene (past 10,000 years) sediment accumulation in Santa Monica Bay (California) was examined to identify controls sediment trapping in a bathymetrically complex coastal embayment and to provide geologic context for the post-industrial sedimentary record and associated pollution gradients. Sediment chronologies based on downcore AMS 14C dates were used to quantify long-term (millennia) accumulation rates in an effort to elucidate particle-transport pathways and sinks. Sediment accumulation rates for the full range of bayfloor environments (50-630 m water depths) range from 22 to 102 mg/cm2/year (15-88 mm/100 year), have an overall mean of 51??21 mg/cm2/year (1??, n=11), and are comparable to rates reported for adjacent borderland basins. Maximal accumulation rates on the Malibu shelf and within a reentrant to Redondo canyon are interpreted to reflect (1) proximity to sediment sources and (2) localized oceanographic and topographic conditions conducive to sediment trapping and deposition. The 14C-derived accumulation rates are 2-10 times lower than rates determined through 210Pb geochronology for the same sites in a related study, revealing that Holocene sediment accumulation has been non-steady-state. Santa Monica Bay is an important sink for suspended matter; averaged over the past several millennia a mass of sediment equivalent to 10-80% of the modern annual river supply is sequestered yearly. Net influx of suspended matter derived from the adjacent Palos Verdes shelf is evinced by a concentration gradient of p,p???-DDE in bayfloor sediments, whereas the distribution of anthropogenic silver suggests transport from Santa Monica shelf to the southeastern boundary of the bay. The results of this study provide new insight to the long-term fates of particulate matter in Los Angeles coastal waters. ?? 2003 Elsevier Science Ltd. All rights reserved.

  5. Remineralization of organic carbon in eastern Canadian continental margin sediments

    NASA Astrophysics Data System (ADS)

    Silverberg, Norman; Sundby, Bjørn; Mucci, Alfonso; Zhong, Shaojun; Arakaki, Takeshi; Hall, Per; Landén, Angela; Tengberg, Anders

    2000-04-01

    Undisturbed sediment samples were collected for chemical analyses at six sites during winter and summer cruises to the eastern Canadian continental margin. Micro-electrode oxygen profiles were obtained in freshly collected multicorer samples, and replicate cores were incubated at in situ temperature for 48 h to monitor changes in the concentrations of dissolved oxygen and nitrate. In addition, box cores were subsampled vertically for porewater chemistry, porosity, and particulate carbon. The data obtained are combined with estimates of sedimentation rate based on sediment trap measurements, 210Pb dating and historical data to evaluate the role of benthic processes in the carbon cycle on the eastern Canadian continental margin. With one exception, oxygen uptake rates determined from incubations and calculated from micro-profiles were very similar, indicating that exchange of oxygen across the sediment-water interface was dominated by molecular diffusion. On the basis of this observation, transport by diffusion is assumed for the calculation of the flux rates for other solutes from their respective porewater gradients. The fluxes of oxygen into the sediments were low, but generally comparable to other continental margins at comparable depths. They varied from 1.4 to 1.8 mmol/m 2/d in December 1993 and from 2.8 to 4.5 mmol/m 2/d in June 1994. Uptake of nitrate by the sediment occurred at all sites except for the continental slope off Nova Scotia. Both oxygen and nitrate uptake were higher in summer than in winter, indicative of a lingering response to the input of organic matter associated with the early spring bloom. At one of the sampling sites, Miscou Channel, the measured oxygen uptake rate far exceeded the flux calculated from the oxygen gradient. The difference suggests biologically enhanced exchange with the overlying waters at this site, consistent with the greater abundance of benthic organisms. The rate of organic carbon mineralization at the seafloor (1

  6. Estimating floodplain sedimentation in the Laguna de Santa Rosa, Sonoma County, CA

    USGS Publications Warehouse

    Curtis, Jennifer A.; Flint, Lorraine E.; Hupp, Cliff R.

    2013-01-01

    We present a conceptual and analytical framework for predicting the spatial distribution of floodplain sedimentation for the Laguna de Santa Rosa, Sonoma County, CA. We assess the role of the floodplain as a sink for fine-grained sediment and investigate concerns regarding the potential loss of flood storage capacity due to historic sedimentation. We characterized the spatial distribution of sedimentation during a post-flood survey and developed a spatially distributed sediment deposition potential map that highlights zones of floodplain sedimentation. The sediment deposition potential map, built using raster files that describe the spatial distribution of relevant hydrologic and landscape variables, was calibrated using 2 years of measured overbank sedimentation data and verified using longer-term rates determined using dendrochronology. The calibrated floodplain deposition potential relation was used to estimate an average annual floodplain sedimentation rate (3.6 mm/year) for the ~11 km2 floodplain. This study documents the development of a conceptual model of overbank sedimentation, describes a methodology to estimate the potential for various parts of a floodplain complex to accumulate sediment over time, and provides estimates of short and long-term overbank sedimentation rates that can be used for ecosystem management and prioritization of restoration activities.

  7. Authigenic carbonate formation at hydrocarbon seeps in continental margin sediments: A comparative study

    USGS Publications Warehouse

    Naehr, T.H.; Eichhubl, P.; Orphan, V.J.; Hovland, M.; Paull, C.K.; Ussler, W.; Lorenson, T.D.; Greene, H. Gary

    2007-01-01

    Authigenic carbonates from five continental margin locations, the Eel River Basin, Monterey Bay, Santa Barbara Basin, the Sea of Okhotsk, and the North Sea, exhibit a wide range of mineralogical and stable isotopic compositions. These precipitates include aragonite, low- and high-Mg calcite, and dolomite. The carbon isotopic composition of carbonates varies widely, ranging from -60??? to +26???, indicating complex carbon sources that include 13C-depleted microbial and thermogenic methane and residual, 13C-enriched, bicarbonate. A similarly large variability of ??18O values (-5.5??? to +8.9???) demonstrates the geochemical complexity of these sites, with some samples pointing toward an 18O-enriched oxygen source possibly related to advection of 18O-enriched formation water or to the decomposition of gas hydrate. Samples depleted in 18O are consistent with formation deeper in the sediment or mixing of pore fluids with meteoric water during carbonate precipitation. A wide range of isotopic and mineralogical variation in authigenic carbonate composition within individual study areas but common trends across multiple geographic areas suggest that these parameters alone are not indicative for certain tectonic or geochemical settings. Rather, the observed variations probably reflect local controls on the flux of carbon and other reduced ions, such as faults, fluid conduits, the presence or absence of gas hydrate in the sediment, and the temporal evolution of the local carbon reservoir. Areas with seafloor carbonates that indicate formation at greater depth below the sediment-water interface must have undergone uplift and erosion in the past or are still being uplifted. Consequently, the occurrence of carbonate slabs on the seafloor in areas of active hydrocarbon seepage is commonly an indicator of exhumation following carbonate precipitation in the shallow subsurface. Therefore, careful petrographic and geochemical analyses are critical components necessary for the

  8. Estimated post-Messinian sediment supply and sedimentation rates on the Ebro continental margin, Spain

    USGS Publications Warehouse

    Nelson, C.H.

    1990-01-01

    Because of the extensive data base of seismic profiles, radiometric ages, and stratigraphic time markers such as the subaerial Messinian surface, sedimentation rates and Ebro River sediment discharge can be estimated for different periods and environments of the Ebro continental margin. New values for sediment discharge (i.e., 6.2 versus previous estimates of 2-3.5 million t/yr) for the Holocene highstand are more reliable but remain minimum estimates because a small proportion of Ebro sediment advected to the Balearic Rise and Abyssal Plain cannot be accounted for, especially during lowstands. The general highstand conditions of the Pliocene, which were similar to those of the Holocene, resulted in a low discharge of Ebro River sediment (ca. 6.5 million t/yr) and an even thickness of sediment across the margin that deposited at rates of about 24-40 cm/ky. In contrast, sediment supply increased two-three times during the Pleistocene, the margin prograded rapidly and deposition occurred at rates of 101-165 cm/ky on the outer shelf and slope, but basin floor rates remained anomalously low (21-26 cm/ky) because sediment was drained and broadly dispersed eastward in Valencia Trough. During the late Pleistocene rise of sea level, the main depocenters progressively shifted shoreward and sedimentation rates greatly decreased from 175 cm/ky on the upper slope during the early transgression to 106 cm/ky on the outer shelf and then to 63 cm/ky on the mid-shelf during the late transgression as the river sediment discharge dropped to half by Holocene time. Maximal sedimentation rates occurred in active depocenters of sediment dispersal such as the Holocene delta (370 cm/ky) or the youngest Pleistocene Oropesa channel-levee complex (705 cm/ky) where deposition rates increased by an order of magnitude or more compared to average Ebro shelf (38 cm/ky) or base-of-slope rates in the Pleistocene (21 cm/ky). The sedimentation rates verify the importance of sea-level control on the

  9. Monitoring sediment transfer processes on the desert margin

    NASA Technical Reports Server (NTRS)

    Millington, Andrew C.; Arwyn, R. Jones; Quarmby, Neil; Townshend, John R. G.

    1987-01-01

    LANDSAT Thematic Mapper and Multispectral Scanner data have been used to construct change detection images for three playas in south-central Tunisia. Change detection images have been used to analyze changes in surface reflectance and absorption between wet and dry season (intra-annual change) and between different years (inter-annual change). Change detection imagery has been used to examine geomorphological changes on the playas. Changes in geomorphological phenomena are interpreted from changes in soil and foliar moisture levels, differences in reflectances between different salt and sediments and the spatial expression of geomorphological features. Intra-annual change phenomena that can be detected from multidate imagery are changes in surface moisture, texture and chemical composition, vegetation cover and the extent of aeolian activity. Inter-annual change phenomena are divisible into those restricted to marginal playa facies (sedimentation from sheetwash and alluvial fans, erosion from surface runoff and cliff retreat) and these are found in central playa facies which are related to the internal redistribution of water, salt and sediment.

  10. Sediment Dynamics Affecting the Threatened Santa Ana Sucker in the Highly-modified Santa Ana River and Inset Channel, Southern California, USA

    NASA Astrophysics Data System (ADS)

    Minear, J. T.; Wright, S. A.

    2015-12-01

    In this study, we investigate the sediment dynamics of the low-flow channel of the Santa Ana River that is formed by wastewater discharges and contains some of the last remaining habitat of the Santa Ana Sucker (Catostomus santaanae). The Santa Ana River is a highly-modified river draining the San Bernardino Mountains and Inland Empire metropolitan area east of Los Angeles. Home to over 4 million people, the watershed provides habitat for the federally-threatened Santa Ana Sucker, which presently reside within the mainstem Santa Ana River in a reach supported by year-round constant discharges from water treatment plants. The nearly constant low-flow wastewater discharges and infrequent runoff events create a small, approximately 8 m wide, inset channel within the approximately 300 m wide mainstem channel that is typically dry except for large flood flows. The sediment dynamics within the inset channel are characterized by constantly evolving bed substrate and sediment transport rates, and occasional channel avulsions. The sediment dynamics have large influence on the Sucker, which rely on coarse-substrate (gravel and cobble) for their food production. In WY 2013 through the present, we investigated the sediment dynamics of the inset channel using repeat bathymetric and substrate surveys, bedload sampling, and discharge measurements. We found two distinct phases of the inset channel behavior: 1. 'Reset' flows, where sediment-laden mainstem discharges from upstream runoff events result in sand deposition in the inset channel or avulse the inset channel onto previously dry riverbed; and 2. 'Winnowing' flows, whereby the sand within the inset channel is removed by clear-water low flows from the wastewater treatment plant discharges. Thus, in contrast to many regulated rivers where high flows are required to flush fine sediments from the bed (for example, downstream from dams), in the Santa Ana River the low flows from wastewater treatment plants serve as the flushing

  11. Suspended-sediment rating curve response to urbanization and wildfire, Santa Ana River, California

    USGS Publications Warehouse

    Warrick, J.A.; Rubin, D.M.

    2007-01-01

    River suspended-sediment concentrations provide insights to the erosion and transport of materials from a landscape, and changes in concentrations with time may result from landscape processes or human disturbance. Here we show that suspended-sediment concentrations in the Santa Ana River, California, decreased 20-fold with respect to discharge during a 34-year period (1968−2001). These decreases cannot be attributed to changes in sampling technique or timing, nor to event or seasonal hysteresis. Annual peak and total discharge, however, reveal sixfold increases over the 34-year record, which largely explain the decreases in sediment concentration by a nonlinear dilution process. The hydrological changes were related to the widespread urbanization of the watershed, which resulted in increases in storm water discharge without detectable alteration of sediment discharge, thus reducing suspended-sediment concentrations. Periodic upland wildfire significantly increased water discharge, sediment discharge, and suspended-sediment concentrations and thus further altered the rating curve with time. Our results suggest that previous inventories of southern California sediment flux, which assume time-constant rating curves and extend these curves beyond the sampling history, may have substantially overestimated loads during the most recent decades.

  12. Chromium geochemistry of serpentinous sediment in the Willow core, Santa Clara County, California

    USGS Publications Warehouse

    Oze, Christopher J.; LaForce, Matthew J.; Wentworth, Carl M.; Hanson, Randall T.; Bird, Dennis K.; Coleman, Robert G.

    2003-01-01

    A preliminary investigation of Cr geochemistry in serpentinous sediment completed for a multiple-aquifer ground-water monitoring well (Willow core of Santa Clara County, CA) determined sediment at depths >225 meters contains Cr concentrations ranging from 195 to 1155 mg/kg. Serpentinous sediment from this site is a potential source of non-anthropogenic Cr contamination. Chromium-bearing minerals such as Cr-spinel appear to be the main source of Cr in the sediment; however, Cr-bearing silicates and clay minerals are additional Cr sources. Aqueous Cr concentrations in the sediment are <4.6 mg/L; however, the valence of Cr was not identified in the solutions or in the sediment. Although there is no indication of Cr(VI) contamination derived from the serpentinous sediment, elevated Cr concentrations in the sediment, the observed ‘dissolution’ textures of the Cr-bearing minerals, the estimated redox environment, and water chemistry indicate the formation of Cr(VI) is potentially favorable.

  13. Modeling studies of dissolved organic matter cycling in Santa Barbara Basin (CA, USA) sediments

    NASA Astrophysics Data System (ADS)

    Burdige, David J.; Komada, Tomoko; Magen, Cédric; Chanton, Jeffrey P.

    2016-12-01

    Here we describe new reaction-transport models for the cycling of dissolved organic matter (DOM, both dissolved organic carbon [DOC] and dissolved organic nitrogen [DON]) in anoxic marine sediments, and apply these models to data from Santa Barbara Basin sediment cores (maximum depth of 4.6 m). Model results show that most organic carbon (and nitrogen) flow in the sediments occurs through reactive DOM intermediates that turn over rapidly to produce inorganic remineralization end-products. Refractory DOM is also produced, and the vast majority of this refractory DOM is not remineralized and either escapes as a benthic flux across the sediment-water interface or is buried. Except near the sediment surface, refractory DOM represents >95% of the total pore water DOM. Pore water DOM appears to be consistently depleted in nitrogen as compared to its source organic matter, which may be the result of differential production of carbon- versus nitrogen-containing refractory DOM during remineralization. Refractory DOC (DOCr) in Santa Barbara Basin sediment pore waters is largely produced from degradation of sediment particulate organic carbon (POC). In addition, there is an upward basal flux of DOCr that is strongly depleted in 14C (-810‰). The Δ14C value of DOCr varies according to its source, ranging from +60‰ (a component of surface sediment POC enriched with radiocarbon from nuclear weapons testing in the 1960's) to -810‰ (the basal DOC flux). Each contributes to the DOCr benthic flux, which has a weighted-average Δ14C value of -40‰. The model-determined DOCr benthic flux is roughly half of the total DOC benthic flux, consistent with observations in the literature that sediments are a source of both labile and refractory DOC to bottom waters. These results support previous arguments that sediment benthic fluxes represent an important source of refractory DOC to the oceans. The benthic flux of refractory DOC from these sediments may also contribute pre-aged DOC

  14. Antarctic glacial history from numerical models and continental margin sediments

    USGS Publications Warehouse

    Barker, P.F.; Barrett, P.J.; Cooper, A. K.; Huybrechts, P.

    1999-01-01

    The climate record of glacially transported sediments in prograded wedges around the Antarctic outer continental shelf, and their derivatives in continental rise drifts, may be combined to produce an Antarctic ice sheet history, using numerical models of ice sheet response to temperature and sea-level change. Examination of published models suggests several preliminary conclusions about ice sheet history. The ice sheet's present high sensitivity to sea-level change at short (orbital) periods was developed gradually as its size increased, replacing a declining sensitivity to temperature. Models suggest that the ice sheet grew abruptly to 40% (or possibly more) of its present size at the Eocene-Oligocene boundary, mainly as a result of its own temperature sensitivity. A large but more gradual middle Miocene change was externally driven, probably by development of the Antarctic Circumpolar Current (ACC) and Polar Front, provided that a few million years' delay can be explained. The Oligocene ice sheet varied considerably in size and areal extent, but the late Miocene ice sheet was more stable, though significantly warmer than today's. This difference probably relates to the confining effect of the Antarctic continental margin. Present-day numerical models of ice sheet development are sufficient to guide current sampling plans, but sea-ice formation, polar wander, basal topography and ice streaming can be identified as factors meriting additional modelling effort in the future.

  15. Sediment flux and accretion history on the Cascadia and Sumatra margins

    NASA Astrophysics Data System (ADS)

    McNeill, L. C.; Geersen, J.; Springett, J.; Trehu, A. M.; Wilson, D. J.

    2013-12-01

    The growth of accretionary prisms and continental margins, and the properties of the prism interior and plate boundary are a function of input sediment through time and the history of accretion, erosion, and sediment subduction on the margin. Input sediment volumes are affected by changing sediment sources and pathways, climate, oceanic basement topography, and erosion and reworking of material from the forearc itself. Seismic reflection data have been compiled on the Cascadia margin, imaging the oceanic plate structure and stratigraphy, and forearc structure to analyse these processes at several locations along the margin, providing more detail than earlier compilations of sediment flux. These seismic data are integrated with ocean drilling data on the oceanic plate to establish the history of deposition on the oceanic plate and in the trench. Sediment flux into the subduction zone since the late Miocene can then be estimated and compared with the volume of the currently active prism. Several specific factors are considered, including: décollement position; compaction; reaccretion of sediment eroded from the prism into the trench; prism age; reduction in sediment flux prior to Pleistocene glaciation on the margin; mixing of older prism mélange with the modern prism on the Washington margin; potential changes in convergence rate and direction with time; margin-parallel motion of forearc material. In some cases, these parameters or their temporal change generate significant uncertainty. Initial results suggest that on the southern Washington margin, input sediment since late Miocene broadly balances with prism volume, supporting predominant accretion. On the central Oregon margin (where the prism may be younger), the prism volume is similar or slightly less than the sediment input, and on the southern Oregon margin, the prism volume is significantly less than the sediment input. This supports the hypothesis that basal and surface erosion of the prism and sediment

  16. Rapid and widespread dispersal of flood sediment on the northern California margin

    USGS Publications Warehouse

    Wheatcroft, R.A.; Sommerfield, C.K.; Drake, D.E.; Borgeld, J.C.; Nittrouer, C.A.

    1997-01-01

    The dispersal of flood sediment from small river systems is a poorly studied, yet potentially important aspect of active continental-margin sedimentation. In January 1995, during a flood with a 30 yr return period, the Eel River (northern California) delivered an estimated 25 ?? 3 ?? 106 t (metric tons) of tine-grained (<62 ??m) sediment to the ocean. The flood formed a distinct layer on the sea bed that was centered on the 70 m isobath, extended for 30 km along shelf and 8 km across shelf, and was as thick as 8.5 cm, but contained only 6 ?? 106 t of sediment. Thus, 75% of the flood-derived sediment did not form a recount/able deposit, but was instead rapidly and widely dispersed over the continental margin. Stratigraphic models of, and compilations of sediment flux to, active continental margins need to take the dispersive nature of small river systems into account.

  17. Dissolved sulfide distributions in the water column and sediment pore waters of the Santa Barbara Basin

    USGS Publications Warehouse

    Kuwabara, J.S.; VanGeen, A.; McCorkle, D.C.; Bernhard, J.M.

    1999-01-01

    Dissolved sulfide concentrations in the water column and in sediment pore waters were measured by square-wave voltammetry (nanomolar detection limit) during three cruises to the Santa Barbara Basin in February 1995, November-December 1995, and April 1997. In the water column, sulfide concentrations measured outside the basin averaged 3 ?? 1 nM (n = 28) in the 0 to 600 m depth range. Inside the basin, dissolved sulfides increased to reach values of up to 15 nM at depths >400 m. A suite of box cores and multicores collected at four sites along the northeastern flank of the basin showed considerable range in surficial (400 ??M at 10 cm. Decreases in water-column nitrate below the sill depth indicate nitrate consumption (-55 to -137 ??mole m-2 h-1) similar to nearby Santa Monica Basin. Peaks in pore-water iron concentrations were generally observed between 2 and 5 cm depth with shallowest peaks at the 590 m site. These observations, including observations of the benthic microfauna, suggest that the extent to which the sulfide flux, sustained by elevated pore-water concentrations, reaches the water column may be modulated by the abundance of sulfide-oxidizing bacteria in addition to iron redox and precipitation reactions.

  18. Sediment discharge in the Upper Arroyo Grande and Santa Rita Creek basins, San Luis Obispo County, California

    USGS Publications Warehouse

    Knott, J.M.

    1976-01-01

    Sediment data collected in the upper Arroyo Grande and Santa Rita Creek basins, San Luis Obispo County, California, during the 1968-73 water years were analyzed to determine total sediment discharge at four stations in the basins. Water discharge and total sediment discharge at these stations, representative of the 1943-72 period, were estimated from long-term flow data for nearby gaging stations and water-sediment discharge relations determined for the 1968-73 water years. Most of the total annual sediment discharge at each station occurs during a few days each year. The quantity of sediment transported in a single day often accounts for more than 40 percent of the total annual sediment discharge. Estimated sediment discharge for the upper Arroyo Grande and Santa Rita Creek basins during the 1943-72 water years averaged 53,000 tons and 23,000 tons per year. Long-term sediment deposition in Lopez Reservoir, which is in the southern part of the upper Arroyo Grande basin, was estimated to be 35 acre-feet per year. (Woodard-USGS)

  19. Temporal and spatial distributions of contaminants in sediments of Santa Monica Bay, California

    USGS Publications Warehouse

    Bay, S.M.; Zeng, E.Y.; Lorenson, T.D.; Tran, K.; Alexander, Corrine

    2003-01-01

    Contaminant inputs from wastewater discharge, a major source of contamination to Santa Monica Bay (SMB), have declined drastically during the last three decades as a result of improved treatment processes and better source control. To assess the concomitant temporal changes in the SMB sediments, a study was initiated in June 1997, in which 25 box cores were collected using a stratified random sampling design. Five sediment strata corresponding to the time intervals of 1890-1920, 1932-1963, 1965-1979, 1979-1989, and 1989-1997 were identified using 210Pb dating techniques. Samples from each stratum were analyzed for metals, 1,1,1-Trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) and its metabolites (DDTs), polychlorinated biphenyls (PCBs), and total organic carbon (TOC). Samples from the 1965-1979, 1979-1989, and 1989-1997 strata were also analyzed for polycyclic aromatic hydrocarbons (PAHs) and linear alkylbenzenes (LABs). Sediment metal concentrations increased from 1890-1979 and were similar during the time intervals of 1965-1979, 1979-1989, and 1989-1997, although the mass emissions of trace metals from sewage inputs declined substantially during the same time period. Trace organic contamination in SMB was generally highest in sediments corresponding to deposition during the years of 1965-1979 or 1979-1989 and showed a decline in concentration in the 1989-1997 stratum. Temporal trends of contamination were greatest in sediments collected from areas near the Hyperion Treatment Plant (HTP) outfall system and on the slope of Redondo Canyon. The highest contaminant concentrations were present in sediments near the HTP 7-mile outfall in the 1965-1979 stratum. Elevated trace metal and organic concentrations were still present in the 1989-1997 stratum of most stations, suggesting that sediment contaminants have moved vertically in the sediment column since sludge discharges from the 7-mile outfall (a dominant source of contamination to the bay) ceased in 1987. The

  20. Particulate Organic Carbon Burial in Ocean Margin Sediments in the Oregon Upwelling Margin: Terrestrial vs. Marine Sources

    NASA Astrophysics Data System (ADS)

    Hastings, R. H.; Goni, M. A.; Wheatcroft, R. A.

    2010-12-01

    Eastern boundary currents are often sites of intense primary production fueled by coastal upwelling. Along these same margins there are often numerous small, mountainous rivers that have high sediment (and POC) yields. In some cases, for example the California Current system, there is a seasonal offset between these two sources of POC, whereby marine POC is delivered to the seabed during spring/summer, and terrestrial POC is delivered during fall/winter. Processes that determine the dispersal, transformation and ultimate burial of this material differ substantially between seasons, therefore the fate of POC on the shelf is complex and uncertain. To investigate these issues we have initiated a study of the Umpqua River dispersal system on the central Oregon margin, a region that is well known for its upwelling-fueled primary production. Elemental, stable isotopic and biomarker analyses were done on surface sediments from ~65 short cores collected on the shelf and upper slope adjacent to the Umpqua River. Multiple tracers of terrestrial organic matter indicate a well-resolved depocenter centered approximately 8 km north of the river mouth at 80-90 m water depth. The terrestrial organic matter depocenter stretches along-margin for ~40 km, is 6-8 km wide and covers an area of approximately 200 square km. Sediment accumulation rates within the depocenter (based on Pb-210 geochronology) are 3-5 times ambient shelf sediments. In addition, measurements of river suspended sediment indicate that much the organic matter carried by the Umpqua River is modern in age (i.e., is not petrogenic). Collectively, these data indicate that both modern terrestrial organic matter as well as marine organic matter are being actively buried on the Umpqua shelf.

  1. Pathways of organic carbon oxidation in three continental margin sediments

    NASA Technical Reports Server (NTRS)

    Canfield, D. E.; Jorgensen, B. B.; Fossing, H.; Glud, R.; Gundersen, J.; Ramsing, N. B.; Thamdrup, B.; Hansen, J. W.; Nielsen, L. P.; Hall, P. O.

    1993-01-01

    We have combined several different methodologies to quantify rates of organic carbon mineralization by the various electron acceptors in sediments from the coast of Denmark and Norway. Rates of NH4+ and Sigma CO2 liberation sediment incubations were used with O2 penetration depths to conclude that O2 respiration accounted for only between 3.6-17.4% of the total organic carbon oxidation. Dentrification was limited to a narrow zone just below the depth of O2 penetration, and was not a major carbon oxidation pathway. The processes of Fe reduction, Mn reduction and sulfate reduction dominated organic carbon mineralization, but their relative significance varied depending on the sediment. Where high concentrations of Mn-oxide were found (3-4 wt% Mn), only Mn reduction occurred. With lower Mn oxide concentrations more typical of coastal sediments, Fe reduction and sulfate reduction were most important and of a similar magnitude. Overall, most of the measured O2 flux into the sediment was used to oxidized reduced inorganic species and not organic carbon. We suspect that the importance of O2 respiration in many coastal sediments has been overestimated, whereas metal oxide reduction (both Fe and Mn reduction) has probably been well underestimated.

  2. 19th-20th century rainfall patterns reconstructed from sediment provenance in a Santa Barbara Basin box core

    NASA Astrophysics Data System (ADS)

    Napier, T.; Hendy, I. L.; Schimmelmann, A.

    2013-12-01

    Rainfall patterns in Southern California directly affect the availability of water resources and induce hazards in this highly populated and water stressed region. Extreme weather consists of heavy rainfall events in winter associated with atmospheric rivers, and drought conditions when winter rains do not arrive. Water availability has a significant societal impact in Southern California. Here we reconstruct 19th-20th century precipitation history of river catchments draining into Santa Barbara Basin (SBB) through a combination of high-resolution elemental and mineralogical analyses. The deep center of the SBB features suboxic bottom waters and high sedimentation rates resulting in minimal bioturbation of annual sedimentation, which enables high-resolution paleoclimate research. Scanning XRF analysis at a 200 μm resolution of box core SPR0901-04BC from SBB was used to determine annual changes in sediment composition. Samples at 1 cm resolution from the same box core were analyzed for a more extensive suite of elements by ICP-MS, while mineralogy in each sample was determined from whole rock and clay fraction (<2 μm) analysis using X-ray defraction. Elements associated with siliciclastic sediment increase in relative abundance during wet years when significant river runoff events (floods) occurred. The relative proportions of these elements differ between flood events, possibly reflecting differences in temporal and/or spatial rainfall patterns that vary the response of each river catchment draining into SBB. Watershed sediment from the Santa Ynez Mountain streams and Ventura and Santa Clara River catchments derives mostly from Cenozoic sedimentary units, except the Santa Clara River catchment, which contains metamorphic and igneous units. As river runoff is responsible for a significant portion of the terrigenous input into SBB, and is primarily the result of precipitation events, characteristic mineralogy and elemental signatures are a direct recorder of

  3. Sedimentology of subaqueous volcaniclastic sediment gravity flows in the Neogene Santa Maria Basin, California

    USGS Publications Warehouse

    Cole, Ronald B.; Stanley, Richard G.

    1994-01-01

    Subaqueous tuff deposits within the lower Miocene Lospe Formation of the Santa Maria Basin, California, are up to 20 m thick and were deposited by high density turbidity flows after large volumes of ash were supplied to the basin and remobilized. Tuff units in the Lospe Formation include a lower lithofacies assemblage of planar bedded tuff that grades upward into massive tuff, which in turn is overlain by an upper lithofacies assemblage of alternating thin bedded, coarse grained tuff beds and tuffaceous mudstone. The planar bedded tuff ranges from 0.3 to 3 m thick and contains 1-8 cm thick beds that exhibit inverse grading, and low angle and planar laminations. The overlying massive tuff ranges from 1 to 10 m thick and includes large intraclasts of pumiceous tuff and stringers of pumice grains aligned parallel to bedding. The upper lithofacies assemblage of thin bedded tuff ranges from 0.4 to 3 m thick; individual beds are 6-30 cm thick and display planar laminae and dewatering structures. Pumice is generally concentrated in the upper halves of beds in the thin bedded tuff interval.The association of sedimentary structures combined with semi-quantitative analysis for dispersive and hydraulic equivalence of bubble-wall vitric shards and pumice grains reveals that particles in the planar bedded lithofacies are in dispersive, not settling, equivalence. This suggests deposition under dispersive pressures in a tractive flow. Grains in the overlying massive tuff are more closely in settling equivalence as opposed to dispersive equivalence, which suggests rapid deposition from a suspended sediment load. The set of lithofacies that comprises the lower lithofacies assemblage of each of the Lospe Formation tuff units is analogous to those of traction carpets and subsequent suspension sedimentation deposits often attributed to high density turbidity flows. Grain distributions in the upper thin bedded lithofacies do not reveal a clear relation for dispersive or settling

  4. Sedimentation and potential venting on the rifted continental margin of Dronning Maud Land

    NASA Astrophysics Data System (ADS)

    Huang, Xiaoxia; Jokat, Wilfried

    2016-12-01

    The relief of Dronning Maud Land (DML), formed by Middle and Late Mesozoic tectonic activity, had a strong spatial control on the early fluvial and subsequent glacial erosion and deposition. The sources, processes, and products of sedimentation along the DML margin and in the Lazarev Sea in front of the DML mountains have been barely studied. The onshore mountain belt parallel to the coast of the DML margin acts as a barrier to the transport of terrigenous sediments from the east Antarctic interior to the margin and into the Lazarev Sea. Only the Jutul-Penck Graben system allows a localized ice stream controlled transport of material from the interior of DML across its old mountain belt. Offshore, we attribute repeated large-scale debris flow deposits to instability of sediments deposited locally on the steep gradient of the DML margin by high sediment flux. Two types of canyons are defined based on their axial dimensions and originated from turbidity currents and slope failures during glacial/fluvial transport. For the first time, we report pipe-like seismic structures in this region and suggest that they occurred as consequences of volcanic processes. Sedimentary processes on the DML margin were studied using seismic reflection data and we restricted the seismic interpretation to the identification of major seismic sequences and their basal unconformities.

  5. Data report: Permeabilities of eastern equatorial Pacific and Peru margin sediments

    USGS Publications Warehouse

    Gamage, K.; Bekins, B.; Screaton, E.

    2006-01-01

    Constant-flow permeability tests were conducted on core samples from Ocean Drilling Program Leg 201 from the eastern equatorial Pacific and the Peru margin. Eighteen whole-round core samples from Sites 1225, 1226, 1227, 1230, and 1231 were tested for vertical permeabilities. Sites 1225, 1226, and 1231 represent sediments of the open ocean, whereas Sites 1227 and 1230 represent sediments of the ocean margin. Measured vertical permeabilities vary from ???8 ?? 10-19 m2 to ???1 ?? 10-16 m2 for a porosity range of 450%-90%.

  6. SEISMIC AND GEOCHEMICAL EVIDENCE FOR SHALLOW GAS IN SEDIMENT ON NAVARIN CONTINENTAL MARGIN, BERING SEA.

    USGS Publications Warehouse

    Carlson, Paul R.; Golan-Bac, Margaret; Karl, Herman A.; Kvenvolden, Keith A.

    1985-01-01

    Marine sesmic studies coupled with geochemical investigations demonstrate tha hydrocarbon gases are ubiquitous in the near-surface sediment of the Navarin continental margin in the northern Bering Sea. Three types of acoustic anomalies appear to be related to the presence of gas in the sediment. These anomalies are most prevalent in the northern half of the Navarin basin. Acoustic anomalies attributed to gas hydrates and to diagenetic boundaries are present on seismic records of the lower slope between Navarinsky and Zhemchug Canyons. Hydrocarbon gases, methane through butanes, are common in the surface sediment of the Navarin continental margin. The source of methane is mainly biogenic, but the hydrocarbon gas compositions in 17 of 141 cores suggest the presence of thermogenic gas. No direct correlation could be found between acoustic anomalies and gas concentrations in the sediment. Refs.

  7. Geochemical discrimination of siliciclastic sediments from active and passive margin settings

    NASA Astrophysics Data System (ADS)

    Verma, Surendra P.; Armstrong-Altrin, John S.

    2016-03-01

    Discrimination of active and passive margins is important from both academic and economic aspects. This can only be successfully achieved, however, if there are major compositional differences among sediments derived from different continental margins. A worldwide database of active and passive margin settings was established from published major and trace element geochemical data of Neogene to Quaternary siliciclastic sediments. These data were used to evaluate the performance of existing discrimination diagrams, which were shown to work unsatisfactorily with success values of mostly between 0% and 30%. Because these diagrams were not based on a statistically coherent methodology, we proposed two new discriminant functions from linear discriminant analysis of multinormally distributed isometric log-transformed ratios of major and combined major and trace elements. These new diagrams showed very high percent success values of about 87%-97% and 84%-86% for the active and passive margins, respectively, for the original database. Excellent performance of the multidimensional diagrams and related discriminant functions was confirmed from 11 test studies involving Quaternary to Holocene siliciclastic sediments from known tectonic margins. The expected result of an active or passive margin was obtained, with most samples plotting correctly in the respective field.

  8. Physical resuspension and vertical mixing of sediments on a high energy continental margin (Sydney, Australia).

    PubMed

    Matthai, C; Birch, G F; Jenkinson, A; Heijnis, H

    2001-01-01

    Four sediment cores from the continental margin adjacent to Sydney were analyzed for 210Pb, 137Cs, trace metals (Ag, Cd, Co, Cu, Mn, Ni, Pb, Zn), iron, dry bulk density, mud and moisture content. The concentrations of trace metals in the total sediment are low at all sites, although slightly elevated concentrations of Ag, Cu, Pb and Zn are present in the fine fraction of sediment (< 62.5 microns) near a major ocean outfall. Concentrations of trace metals in the fine fraction of sediment are similar in the upper 10-15 cm, indicating strong vertical mixing of the sediments, whereas an upward coarsening grain size in the upper 1-3 cm of sediment supports physical resuspension during storms. Sediment accumulation rates on the middle shelf adjacent to Sydney were estimated from downcore profiles of 210Pb and 137Cs and range between 0.2 and 0.4 cm yr-1. Although the mass fluxes of Cu, Pb and Zn within a distance of 2 km from the outfall (up to 36.1, 30.8 and 86.2 micrograms cm-2 yr-1, respectively) are greater than 20 km north of the outfall (< 23.5 micrograms cm-2 yr-1), the low concentrations of trace metals in sediments near the outfall support an efficient dispersal of anthropogenic contaminants on this continental margin.

  9. Simulation of continental basin margin sedimentation in response to crustal movements, eustatic sea level change, and sediment accumulation rates

    SciTech Connect

    Helland-Hansen, W.; Kendall, C.G.St.C.; Lerche, I.; Nakayama, K.

    1988-10-01

    As eustasy, subsidence, and sediment accumulation vary, a 2D computer-based graphical simulation generates on-lapping and off-lapping geometries of both marine and near coastal alluvial deposits, reproducing timelines within sediment-bodies at basin margins. In the simulation, deposition is expressed by creation of new surfaces above previous ones. Thicknesses of layers are reduced by both erosion and compaction while their surfaces move vertically in response to tectonic change and loading. Simulation is divided into a series of equal time steps in which sediment is deposited as an array of en-echelon columns that mark the top of the previous depositional surface. The volume of sediment deposited in each time step is expressed as a 2D cross section and is derived from two right-angle triangles (sand and shale), whose areas are a 2D expression of the quantity of sediment deposited at that time step and whose length matches the width of the offshore sediment wedge seaward of the shoreline. Each column in the array is filled by both marine sediments up to sea level, and alluvial sediments to a surface determined by an alluvial angle that is projected landward from the shore to its intersection with the previous surface. Each time the area representing the sediment column is subtracted from the triangles, the triangle heights are reduced correspondingly. This process is repeated until the triangle heights match the position of sea level above the sediment surface, at which time the remaining area of the sediment triangle is deposited seaward as a single wedge of offshore sediments. This simulation is designed to aid interpretation of stratigraphic sequences. It can be used as a complement to seismic stratigraphy or can be used alone as an inexpensive test of stratigraphic models.

  10. Observations at convergent margins concerning sediment subduction, subduction erosion, and the growth of continental crust

    USGS Publications Warehouse

    Von Huene, R.; Scholl, D. W.

    1991-01-01

    At ocean margins where two plates converge, the oceanic plate sinks or is subducted beneath an upper one topped by a layer of terrestrial crust. This crust is constructed of continental or island arc material. The subduction process either builds juvenile masses of terrestrial crust through arc volcanism or new areas of crust through the piling up of accretionary masses (prisms) of sedimentary deposits and fragments of thicker crustal bodies scraped off the subducting lower plate. At convergent margins, terrestrial material can also bypass the accretionary prism as a result of sediment subduction, and terrestrial matter can be removed from the upper plate by processes of subduction erosion. Sediment subduction occurs where sediment remains attached to the subducting oceanic plate and underthrusts the seaward position of the upper plate's resistive buttress (backstop) of consolidated sediment and rock. Sediment subduction occurs at two types of convergent margins: type 1 margins where accretionary prisms form and type 2 margins where little net accretion takes place. At type 2 margins (???19,000 km in global length), effectively all incoming sediment is subducted beneath the massif of basement or framework rocks forming the landward trench slope. At accreting or type 1 margins, sediment subduction begins at the seaward position of an active buttress of consolidated accretionary material that accumulated in front of a starting or core buttress of framework rocks. Where small-to-mediumsized prisms have formed (???16,300 km), approximately 20% of the incoming sediment is skimmed off a detachment surface or decollement and frontally accreted to the active buttress. The remaining 80% subducts beneath the buttress and may either underplate older parts of the frontal body or bypass the prism entirely and underthrust the leading edge of the margin's rock framework. At margins bordered by large prisms (???8,200 km), roughly 70% of the incoming trench floor section is

  11. Manganese and copper fluxes from continental margin sediments

    SciTech Connect

    Heggie, D.; Klinkhammer, G.; Cullen, D.

    1987-05-01

    Total dissolvable Cu and Mn have been measured in sea water collected from the continental shelf of the eastern Bering Sea. Copper concentrations of <3 nmole kg/sup -1/ were measured over the shelf break but concentrations increased to >4 nmole kg/sup -1/ inshore of a hydrographic front over the 100 m isobath. Manganese concentrations also were low over the shelf break, <10 nmole kg/sup -1/, and increased systematically to concentrations >10 nmole kg/sup -1/ inshore of the hydrographic front. Depth distributions of Mn at all continental shelf stations showed gradients into the sediments, with concentrations typically >20 nmole kg/sup -1/ in a bottom layer extending about 30 m off the bottom. Benthic Cu and Mn fluxes are indicated by cross-shelf pore water profiles that show interfacial concentrations more than an order of magnitude greater than in bottom water. These data and the results of a model of metal transport across the shelf suggest that Cu and Mn fluxes, estimated at 2 and 18 nmole cm/sup -2/y/sup -1/, respectively, from continental shelf sediments may be one source of these metals to the deep sea.

  12. Shelfal sediment transport by undercurrents forces turbidity current activity during high sea level, Chile continental margin

    NASA Astrophysics Data System (ADS)

    Bernhardt, Anne; Hebbeln, Dierk; Regenberg, Marcus; Lückge, Andreas; Strecker, Manfred. R.

    2016-04-01

    Understanding the links between terrigenous sediment supply and marine transport and depositional processes along tectonically active margins is essential to decipher turbidite successions as potential archives of climatic and seismic forcings and to comprehend timing and quantity of marine clastic deposition. Sequence stratigraphic models predict coarse-grained terrigenous sediment delivery to deep-marine sites mainly during sea-level fall and lowstand. Marine clastic deposition during periods of transgression and highstand has been attributed to the continued geomorphic connectivity between terrestrial sediment sources and marine sinks (e.g., rivers connected to submarine canyons) often facilitated by narrow shelves, high sediment supply causing delta migration to the shelf edge, and/or abrupt increases in sediment supply due to climatic variability or catastrophic events. To decipher the controls on Holocene highstand turbidite deposition, we analyzed twelve sediment cores of spatially disparate, coeval Holocene turbidite systems along the Chile margin (29-40°S) with changing climatic and geomorphic characteristics but uniform changes of sea level. Intraslope basins in north-central Chile (29-33°S) offshore a narrow to absent shelf record a shut-off of turbidite activity during the Holocene. In contrast, core sites in south-central Chile (36-40°S) offshore a wide continental shelf have repeatedly experienced turbidite deposition during sea-level highstand conditions, even though most of the depocenters are not connected via canyons to sediment sources. The interplay of stable high sediment supply related to strong onshore precipitation in combination with a wide shelf, over which undercurrents move sediment towards the shelf edge, appears to control Holocene turbidite sedimentation and sediment export to the deep sea.

  13. Organic geochemistry of continental margin and deep ocean sediments

    SciTech Connect

    Whelan, J.K.; Hunt, J.M.; Seewald, J.M.; Eglinton, L.B.; Zawoysky, M.; Dickinson, P.; Dickneider, T.

    1992-09-01

    Objective was to study petroleum formation, migration, and accumulation in marine sediments. Collaboration in Global Basin Research Network (GBRN) showed that the hydrocarbon parameters used in oil exploration are also valuable in understanding sedimentary basin fluid flow processes, crucial to production of drinking water, metal ore deposits, and gas and oil. Two goals are : (1) to run hydrous pyrolysis experiments on immature gas-prone source rocks, in order to evaluate the potential influence of gas evolution on oil migration and subsurface pressurization, and (2) to integrate organic geochemical data from the Louisiana Gulf Coast into GBRN subsurface visualization and computer modeling. Experimental methods (petrography, EPR, thermogravimetric Fourier transform infrared spectroscopy) were also studied.

  14. Impacts of flamingos on saline lake margin and shallow lacustrine sediments in the Kenya Rift Valley

    NASA Astrophysics Data System (ADS)

    Scott, Jennifer J.; Renaut, Robin W.; Owen, R. Bernhart

    2012-11-01

    Studies of modern, Holocene, and Pleistocene sediments around saline to hypersaline, alkaline Lake Bogoria and Lake Magadi show that evidence of flamingo activity in marginal areas of these lakes is nearly ubiquitous. Flamingos produce discrete structures such as webbed footprints (~ 9 cm long, ~ 11 cm wide) and nest mounds (~ 30 cm wide, ~ 20 cm high), and they also extensively rework sediments in delta front, delta plain, and shoreline areas. Large (~ 0.5-2 cm in diameter), pinched, 'bubble pores' and ped-like mud clumps are formed by the trampling and churning of wet clay-rich sediments in these settings. Flamingo nest mounds, although superficially similar to some thrombolite mounds, are typically internally structureless, unless formed on pre-existing sediments that preserve internal structures. The flamingo mounds consist of a dense, packed oval-shaped core, a surrounding 'body' of packed sediment, and an external layer with a ped-like texture of clumped mud. The nests may contain open holes from roots or feather shafts incorporated into the nest, and (or) burrows produced once the nests are abandoned. In areas with high densities of flamingos, lake margin sediments may be preferentially compacted, particularly at breeding sites, and become resistant to subaerial erosion and the effects of transgressive ravinement on time scales ranging from seasons to tens of thousands of years. The relatively well-compacted nest mounds and associated sediments also contribute to the stability of delta distributary channels during regressive-transgressive cycles, and can lead to the minor channelization of unconfined flows where currents are diverted around nest mounds. Pleistocene exhumed surfaces of relatively well-indurated lake margin sediments at Lake Bogoria and Lake Magadi that are interpreted as combined regressive and transgressive surfaces (flooding surface/sequence boundary) preserve evidence of flamingo activities, and are overlain by younger, porous lacustrine

  15. Application of compound-specific radiocarbon dating for Antarctic margin sediments

    NASA Astrophysics Data System (ADS)

    Ohkouchi, N.; Koizumi, M.; Anderson, J. B.; Eglinton, T. I.; Miura, H.; Yokoyama, Y.

    2008-12-01

    Radiocarbon dating has been extensively applied for the development of chronologies of Antarctic margin sediments deposited during the late Quaternary. However, the problems are 1) the DIC reservoir age in the surface mixed layer is much older than that of the other oceans, 2) Antarctic margin sediments generally lack calcareous foraminifera conventionally used for radiocarbon dating and as stratigraphic tool, and 3) the sediments are subjected to significant "contamination" of relict organic matter eroded from the Antarctic continent, leading to substantially older radiocarbon ages of bulk sedimentary organic matter. Ohkouchi et al. (2003) first applied compound-specific radiocarbon dating to the surface sediments collected from Ross Sea, Antarctica for resolving the problem. They reported that the radiocarbon ages of solvent-extractable, short-chain (C14, C16, and C18) fatty acids are consistent with the modern DIC reservoir age (Pre-bomb: 14C -150, Post-bomb: 14C -100). Furthermore, the radiocarbon ages of these fatty acids at five down-core intervals progressively increase with the core depth. These results clearly show a utility of the compound- specific radiocarbon dating for developing sediment chronologies in Antarctic margin sediments. We also determined radiocarbon ages of the fatty acids from a core recovered in the NW Ross Sea to reconstruct sediment chronologies. Furthermore, we determined hydrogen isotopic compositions of sedimentary biomarkers in the core. Around 6.8, 5.7, 4.1, 2.5, and 1.5 kyr ago, the reconstructed D values of paleo- seawater were -200 or lower, suggesting a large amount of meltwater influx to the Ross Sea. Currently, we are applying the method to more sediment samples collected from wider area of Ross Sea to investigate the timing and pattern of retreat of West Antarctic Ice Sheet in the Holocene. I will present the up-dated results in my talk.

  16. Shelf-slope sedimentation during the late Quaternary on the southwestern Kuril forearc margin, northern Japan

    NASA Astrophysics Data System (ADS)

    Noda, Atsushi; TuZino, Taqumi

    2010-12-01

    We studied an active forearc margin off eastern Hokkaido, northern Japan, to identify the main influences on stratigraphic development from the last glacial to the present highstand. This paper presents new data on the environment, texture, and sedimentation rates of forearc shelf-slope sediments, based on more than 300 samples of seafloor sediments and densely gridded sub-bottom profiling records. Lowstand sedimentary wedges developed upon the shelf margins in areas with a large sediment supply and without incising canyons. The transgressive and highstand deposits formed on the shelf in extensive, low-gradient, and topographically low areas. The narrow shelf is covered by sandy sediments, where winnowed fines are likely to have escaped to the slope via gravity-driven across-shelf transport or ocean-current-induced along-shelf transport. The slope has a mid-slope mud belt at water depths of 700-1600 m. The sedimentation rates on the slope subsequent to 15 ka (the late transgressive to highstand stage) were just 10-70% of the rates prior to this period. These changes in sedimentation rates are ascribed to spatially variable topography. High sedimentation rates were maintained at topographically low and gently sloping areas even during highstand periods, due to concentrations of nepheloid layers or deposition via sediment gravity flows. On the other hand, low sedimentation rates were recognized on topographic highs of interfluves on the upper slope or on axes of anticlines, where main flows or overspills of turbidity currents decreased as sealevel rose. These results suggest that sedimentologic and stratigraphic variations are tied to variations in the physical configuration of the shelf/slope system being influenced by the local topography in addition to the climatic and oceanographic processes.

  17. Black carbon and polycyclic aromatic hydrocarbons (PAHs) in surface sediments of China's marginal seas

    NASA Astrophysics Data System (ADS)

    Kang, Yanju; Wang, Xuchen; Dai, Minhan; Feng, Huan; Li, Anchun; Song, Qian

    2009-05-01

    This study investigates the distribution of black carbon (BC) and its correlation with total polycyclic aromatic hydrocarbons (ΣPAH) in the surface sediments of China’s marginal seas. BC content ranges from <0.10 to 2.45 mg/g dw (grams dry weight) in the sediments studied, and varied among the different coastal regions. The Bohai Bay sediments had the highest BC contents (average 2.18 mg/g dw), which comprises a significant fraction (27%-41%) of the total organic carbon (TOC) preserved in the sediments. In comparison, BC in the surface sediments of the North Yellow Sea, Jiaozhou Bay, East China Sea and the South China Sea is less abundant and accounted for an average of 6%, 8%, 14% and 5%, respectively, of the sedimentary organic carbon pool. The concentration of ΣPAH in the surface sediments ranges from 41 to 3 667 ng/g dw and showed large spatial variations among the sampling sites of different costal regions. The Bohai Bay has the highest ΣPAH values, ranging from 79 to 3 667 ng/g dw. This reflects the high anthropogenically contaminated nature of the sediments in the bay. BC is positively correlated to TOC but a strong correlation is not found between BC and ΣPAH in the surface sediments studied, suggesting that BC and PAHs preserved in the sediments are derived from different sources and controlled by different biogeochemical processes. Our study suggests that the abundance of BC preserved in the sediments could represent a significant sink pool of carbon cycling in China’s marginal seas.

  18. Evidence of Active Methanogen Communities in Shallow Sediments of the Sonora Margin Cold Seeps

    PubMed Central

    L'Haridon, Stéphane; Godfroy, Anne; Roussel, Erwan G.; Cragg, Barry A.; Parkes, R. John; Toffin, Laurent

    2015-01-01

    In the Sonora Margin cold seep ecosystems (Gulf of California), sediments underlying microbial mats harbor high biogenic methane concentrations, fueling various microbial communities, such as abundant lineages of anaerobic methanotrophs (ANME). However, the biodiversity, distribution, and metabolism of the microorganisms producing this methane remain poorly understood. In this study, measurements of methanogenesis using radiolabeled dimethylamine, bicarbonate, and acetate showed that biogenic methane production in these sediments was mainly dominated by methylotrophic methanogenesis, while the proportion of autotrophic methanogenesis increased with depth. Congruently, methane production and methanogenic Archaea were detected in culture enrichments amended with trimethylamine and bicarbonate. Analyses of denaturing gradient gel electrophoresis (DGGE) fingerprinting and reverse-transcribed PCR-amplified 16S rRNA sequences retrieved from these enrichments revealed the presence of active methylotrophic Methanococcoides burtonii relatives and several new autotrophic Methanogenium lineages, confirming the cooccurrence of Methanosarcinales and Methanomicrobiales methanogens with abundant ANME populations in the sediments of the Sonora Margin cold seeps. PMID:25769831

  19. Evidence of active methanogen communities in shallow sediments of the sonora margin cold seeps.

    PubMed

    Vigneron, Adrien; L'Haridon, Stéphane; Godfroy, Anne; Roussel, Erwan G; Cragg, Barry A; Parkes, R John; Toffin, Laurent

    2015-05-15

    In the Sonora Margin cold seep ecosystems (Gulf of California), sediments underlying microbial mats harbor high biogenic methane concentrations, fueling various microbial communities, such as abundant lineages of anaerobic methanotrophs (ANME). However, the biodiversity, distribution, and metabolism of the microorganisms producing this methane remain poorly understood. In this study, measurements of methanogenesis using radiolabeled dimethylamine, bicarbonate, and acetate showed that biogenic methane production in these sediments was mainly dominated by methylotrophic methanogenesis, while the proportion of autotrophic methanogenesis increased with depth. Congruently, methane production and methanogenic Archaea were detected in culture enrichments amended with trimethylamine and bicarbonate. Analyses of denaturing gradient gel electrophoresis (DGGE) fingerprinting and reverse-transcribed PCR-amplified 16S rRNA sequences retrieved from these enrichments revealed the presence of active methylotrophic Methanococcoides burtonii relatives and several new autotrophic Methanogenium lineages, confirming the cooccurrence of Methanosarcinales and Methanomicrobiales methanogens with abundant ANME populations in the sediments of the Sonora Margin cold seeps.

  20. Manganese flux from continental margin sediments in a transect through the oxygen minimum

    SciTech Connect

    Johnson, K.S. Monterey Bay Aquarium Research Inst., Pacific Grove, CA ); Berelson, W.M.; Iams, H.D.; Kilgore, T.E. ); Coale, K.H.; Coley, T.L.; Elrod, V.A.; Fairey, W.R.; Nowicki, J.L. )

    1992-08-28

    The flux of manganese from continental margin sediments to the ocean was measured with a free-vehicle, benthic flux chamber in a transect across the continental shelf and upper slope of the California margin. The highest fluxes were observed on the shallow continental shelf. Manganese flux decreased linearly with bottom water oxygen concentration, and the lowest flux occurred in the oxygen minimum zone (at a depth of 600 to 1,000 meters). Although the flux of manganese from continental shelf sediments can account for the elevated concentrations observed in shallow, coastal waters, the flux from sediments that intersect the oxygen minimum cannot produce the subsurface concentration maximum of dissolved manganese that is observed in the Pacific Ocean.

  1. Manganese flux from continental margin sediments in a transect through the oxygen minimum.

    PubMed

    Johnson, K S; Berelson, W M; Coale, K H; Coley, T L; Elrod, V A; Fairey, W R; Iams, H D; Kilgore, T E; Nowicki, J L

    1992-08-28

    The flux of manganese from continental margin sediments to the ocean was measured with a free-vehicle, benthic flux chamber in a transect across the continental shelf and upper slope of the California margin. The highest fluxes were observed on the shallow continental shelf. Manganese flux decreased linearly with bottom water oxygen concentration, and the lowest fluxes occurred in the oxygen minimum zone (at a depth of 600 to 1000 meters). Although the flux of manganese from continental shelf sediments can account for the elevated concentrations observed in shallow, coastal waters, the flux from sediments that intersect the oxygen minimum cannot produce the subsurface concentration maximum of dissolved manganese that is observed in the Pacific Ocean.

  2. Distributions of Pu, Am and Cs in margin sediments from the western Mediterranean (Spanish coast).

    PubMed

    Gascó, C; Antón, M P; Pozuelo, M; Meral, J; González, A M; Papucci, C; Delfanti, R

    2002-01-01

    Continental margins are important areas to be considered when studying the distributions and depositions of pollutants, both conventional and radioactive. Coastal sediments accumulate most of those contaminants which can be introduced following atmospheric and/or fluvial pathways. Moreover, their residence times within the water column are usually shortened due to their affinity to associate with the downward falling particulate matter, more abundant at shallower depths. In this paper the distribution profiles and inventories of plutonium, americium and cesium are detailed, providing useful information about recent sedimentation phenomena such as sediment mixing, slumping processes and bioturbation. Unsupported 210Pb data are used as reliable indicators of enhanced/reduced deposition events. Also, the calculated inventories have enabled the estimation of the radiological contribution of the Spanish Mediterranean margin to the total radioactivity deposited onto the Mediterranean sea floor.

  3. Organic geochemistry of continental margin and deep ocean sediments

    SciTech Connect

    Whelan, J.K.; Hunt, J.M.; Eglinton, T.; Dickinson, P.; Johnson, C.; Buxton, L.; Tarafa, M.E.

    1990-08-01

    The objective of this research continues to be the understanding of the complex processes of fossil fuel formation and migration. DOE funded research to date has focused on case histories'' of down-hole well profiles of light hydrocarbons, pyrograms, pyrolysis-GC and -GCMS parameters, and biomarker data from wells in the Louisiana and Texas Gulf Coasts the Alaskan North Slope. In the case of the Alaskan North Slope, geological data and one-dimensional maturation modeling have been integrated in order to better constrain possible source rocks, timing, and migration routes for oil and gas generation and expulsion processes.This period, biomarker analyses and organic petrographic analyses were completed for the Ikpikpuk well. In the case of the Gulf Coast, we have obtained a one-dimensional maturation model of the Cost B-1 well in E. Cameron field of the Louisiana Gulf Coast. The completed E. Cameron data set adds to the enigma of the Gulf Coast oils found on the continental shelf of Louisiana. If significant quantities of the oil are coming from relatively organic lean Tertiary rocks, then non-conventional'' expulsion and migration mechanisms, such as gas dissolved in oil must be invoked to explain the Gulf Coast oils reservoired on the Louisiana continental shelf. We are designing and starting to assemble a hydrous pyrolysis apparatus to follow, the laboratory, rates of generation and expulsion of sediment gases. Initiation of some new research to examine {delta}{sup 13}C of individual compounds from pyrolysis is also described. We are beginning to examine both the laboratory and field data from the Gulf Coast in the context of a Global Basin Research Network (GBRN). The purpose is to better understand subsurface fluid flow processes over geologic time in sedimentary basins and their relation to resource accumulation (i.e., petroleum and metal ores). 58 refs.

  4. Effect of Seasonal Variation on Sediment Transport and Deposition on a Collision Margin: the Umpqua River

    NASA Astrophysics Data System (ADS)

    Moriarty, J.; Kniskern, T.; Harris, C.

    2008-12-01

    Small mountainous rivers transport over half of the global sediment flux from terrestrial to marine environments. Over 9 billion tons per year of sediment and associated nutrients and contaminants, including organic carbon, are transported from these rivers'floodplains to continental margins, primarily during flood events. The fate of such sediments is controlled by the sediment load, river discharge, waves, wind-driven currents, and larger scale currents. The study focused on the Umpqua River, OR because of its low sediment load and simple bathymetry. Seasonal variances in waves, river and sediment discharge, and wind-forced currents and their effect on sediment transport and deposition were analyzed using a version of the ECOMSED model on the continental shelf offshore of the Umpqua River, Oregon. This model is a three-dimensional hydrodynamic model with 9 vertical sigma layers and a horizontal resolution of 200 to 500 m that accounts for sediment transport, including gravity flows. Ten years of hourly data were averaged to obtain input parameters describing waves, winds, and sediment and water discharge for an average December flood (2.6x108 kg) and an average April/May flood (0.4x108 kg). Model results showed that seasonal variations in input parameters significantly affected sediment budgets. December deposits (6.9x107 kg) reached as far as 110 m depth, but April/May deposits (0.3x107 kg) occurred at depths shallower than 100 m. Additionally, the December deposit was over 20 times thicker and occupied an area 3 times larger than the size of the April/May deposit. 41.3% and 50.7% of sediment escaped the shelf during December and April/May storms, primarily to the Northwest. Differences in sediment budgets occurred because December flood events are characterized by stronger waves, larger sediment loads and stronger converging currents near the river mouth than April/May flood events. In December, these conditions initiated gravity flows, despite the small

  5. Authigenic molybdenum formation in marine sediments: A link to pore water sulfide in the Santa Barbara Basin

    USGS Publications Warehouse

    Zheng, Yen; Anderson, Robert F.; VanGeen, A.; Kuwabara, J.

    2000-01-01

    Pore water and sediment Mo concentrations were measured in a suite of multicores collected at four sites along the northeastern flank of the Santa Barbara Basin to examine the connection between authigenic Mo formation and pore water sulfide concentration. Only at the deepest site (580 m), where pore water sulfide concentrations rise to >0.1 ??M right below the sediment water interface, was there active authigenic Mo formation. At shallower sites (550,430, and 340 m), where pore water sulfide concentrations were consistently <0.05 ??M, Mo precipitation was not occuring at the time of sampling. A sulfide concentration of ???0.1 ??M appears to be a threshold for the onset of Mo-Fe-S co-precipitation. A second threshold sulfide concentration of ???100 ??M is required for Mo precipitation without Fe, possibly as Mo-S or as particle-bound Mo. Mass budgets for Mo were constructed by combining pore water and sediment results for Mo with analyses of sediment trap material from Santa Barbara Basin as well as sediment accumulation rates derived from 210Pb. The calculations show that most of the authigenic Mo in the sediment at the deepest site is supplied by diffusion from overlying bottom waters. There is, however, a non-lithogenic particulate Mo associated with sinking particles that contributes ???15% to the total authigenic Mo accumulation. Analysis of sediment trap samples and supernant brine solutions indicates the presence of non-lithogenic particulate Mo, a large fraction of which is easily remobilized and, perhaps, associated with Mn-oxides. Our observations show that even with the very high flux of organic carbon reaching the sediment of Santa Barbara Basin, active formation of sedimentary authigenic Mo requires a bottom water oxygen concentration below 3 ??M. However, small but measurable rates of authigenic Mo accumulation were observed at sites where bottom water oxygen ranged between 5 and 23 ??M, indicating that the formation of authigenic Mo occured in the

  6. Marine Coral and Sediment Records of Intermediate Water History from Decadal to Millennial Timescales on the California Margin

    NASA Astrophysics Data System (ADS)

    Hill, T. M.; Kennett, J. P.; Spero, H. J.

    2005-12-01

    Intermediate waters (300-2500m) are critically important to the earth's climate system for the transport of heat and salt around the globe, as well as influencing the carbon cycle via the oxygen minimum zone (OMZ). Results from the California margin indicate that intermediate waters are sensitive to climate change across multiple timescales. Sediment cores in Santa Barbara Basin (MD02-2503 and MD02-2504) provide high-resolution records of surface and intermediate water processes during the most recent deglaciation. Oxygen isotopic values of planktonic and benthic foraminifera indicate that surface and intermediate waters warmed synchronously,~2ka prior to Termination IA. These findings are consistent with previous studies that indicate intermediate waters responded prior to or synchronously with surface waters during major climatic transitions (Kennett et al., 2002; Hendy and Kennett, 2003). Studies from the Santa Barbara Basin also indicate dramatic changes in oxygenation during the Bolling-Allerod, associated with the combined influences of water column methane oxidation, intermediate water ventilation and surface productivity. These studies indicate that intermediate waters are highly sensitive to climate change on millennial timescales. However, it is poorly understood how intermediate waters will respond to climate change on short timescales, such as during ENSO episodes, Pacific Decadal Oscillation mode shifts, or anthropogenic forcing. Investigations of deep-sea bamboo corals collected along the California margin (250-2200m) are utilized to reconstruct the recent environmental history of intermediate waters in this region. Preliminary radiocarbon analyses of four coral specimens from south of Pt. Conception suggest that bamboo corals live for centuries with growth rates of 50-100 microns/year. Radiocarbon content of recently precipitated coral calcite reflects equilibrium with that of ambient seawater (Δ14Ccalcite = ¬ 249.7 ‰ Δ14CDIC = ¬ 242.2 ‰). A

  7. 7Be as a tracer of flood sedimentation on the northern California continental margin

    USGS Publications Warehouse

    Sommerfield, C. K.; Nittrouer, C. A.; Alexander, C. R.

    1999-01-01

    Sediment inventories of the cosmogenic radionuclide 7Be (t1/2=53 d) were measured on the Eel River shelf and slope (northern California continental margin) to investigate sedimentation processes associated with coastal river flooding. Seabed coring shortly after major riverflow events in 1995 and 1997 documented a shelf-wide flood deposit, and subsequent radionuclide studies determined 7Be to be a powerful tracer of fine-grained river sediment. In addition, distinctive signatures of 234Th and 210Pb were observed in oceanic flood deposits and provided additional information regarding depositional processes. During the 1995–1997 monitoring period, 7Be was present (2–35 dpm cm-2) in shelf and slope sediments only after periods of high rainfall and river runoff during the winter months. It is suggested that fluvial input was the primary source of 7Be in shelf sediments after the floods. 7Be sediment inventories and sediment-trap fluxes determined after the 1997 flood revealed that fine-grained fluvial sediments were rapidly (within one month) broadcast over the continental margin, to the 500 m isobath. Dispersal was apparently facilitated by energetic storm waves, which resuspended and redistributed some fraction of the suspended load residing on the shelf prior to accretion as flood deposits. These observations illustrate that floods are an important sedimentary process for modern environments of the Eel shelf and slope, and perhaps for other fluviomarine sedimentary systems of the northern California continental margin. Ratios of the 210Pb sediment-accumulation rate (100 yr average) to the 7Be deposition rate (1–2 month average) for shelf sites illustrate the episodic nature of shelf sedimentation, and suggest that a minimum of 3–30 depositional events complete the most recent stratigraphic record. This observation is consistent with the magnetude and frequency of fluvial sediment input, as Eel River floods with return periods of 3–33 yr (3% of the time of

  8. Anomalous subsidence at South China Sea rifted margin: Sediments digging their own hole

    NASA Astrophysics Data System (ADS)

    Brune, Sascha; Clift, Peter; Quinteros, Javier

    2015-04-01

    Rifted continental margins subside as a consequence of combined crustal thinning and mantle lithosphere cooling. While standard models predict a slowing of subsidence after the end of rifting, the deep basins on the northern margin of the South China Sea, notably the Baiyun Sag exhibit subsidence that accelerated several million years after the end of active extension. Additionally, backstripping analysis at the South China margin has shown that the amount of subsidence is much greater than that predicted from the degree of brittle upper crustal extension seen in seismic profiles. Here we explain these observations by linking climate change onshore and deformation of the crystalline crust offshore: Early Miocene monsoon intensification increased erosion and thus the sediment flux to offshore basins after the cessation of active extension. When the sediment load encountered the weak crust of the South China Sea margin, it induced lower crustal flow away from the basin axis so that the deep Baiyun basin was formed nearly without brittle extension. We corroborate this concept using seismic observations and backstripping techniques, as well as thermo-mechanical forward modeling. The numerical forward model is a 2D version of the finite element code SLIM3D. The code includes nonlinear temperature- and stress-dependent elasto-visco-plastic rheology and is able to reproduces a wide range of rift-related deformation processes such as flexure, lower crustal flow, and faulting. We find that two factors allow to satisfy the observational constraints: (1) Post-rift increase of sediment load: The East Asian Summer Monsoon strengthened around the start of the Miocene (~23 Ma), several million years after continental rupture. Changes in the flora of continental China date from around this time and sedimentation rates across continental margins and deltas in South and Southeast Asia increased, as might be expected under the influence of heavier precipitation driving faster erosion

  9. A comparison of Nd isotopes in seawater and authigenic sediments from the South African Margin

    NASA Astrophysics Data System (ADS)

    Jones, K. M.; Goldstein, S. L.; Hemming, S. R.; Murthy, P.; Hall, I.; Zahn, R.

    2008-12-01

    The neodymium isotopic composition of marine archives is an exciting paleocirculation tracer with the potential to provide information on changes in ocean circulation during periods of drastically different climate. An outstanding question that this tracer may help to answer is how the vertical structure of the ocean has changed through time. With this goal in mind we analyzed seawater and leachates of authigenic core-tops sediments from the South African margin, essentially creating depth profiles for seawater and modern sediments for this margin, which can be directly compared. We use this to evaluate the suitability of using leachates of authigenic sediments to recreate the water mass distribution along this margin, where NADW is exported out of the Atlantic system, through time. We report Nd isotopes in two seawater depth profiles as well as in authigenic leachates of multiple sediment core-tops collected from depths ranging between 1010m and 3706m. The core locations span nearly the entire South African margin, from near Durbin to near Cape Town, and the locations of the seawater profiles fall within this span. The seawater profiles show low ɛNd values (ɛNd ~ - 13.5) in the near surface Agulhas Current waters, then trend toward higher values (ɛNd ~ -9) at intermediate depths where waters represent mainly AAIW. The ɛNd values in deep waters show a minimum (ɛNd ~ -12) at depths of the core of NADW (depth ~2500m) then trend toward higher values, with a maximum of -10.5 in the deepest sample (~3600m), which is a NADW-AABW mixture. Some simple calculations show that these profiles are consistent with mixtures of the major end-member water masses present at this location. The Nd isotope ratios of the core-top leachates range in ɛNd from -14 to -9. Some core-top leachates do not match seawater measurements from the same depth, with a maximum deviation of nearly 4 ɛ-units at a depth of 1000m near the Tugela River cone. However, when sediment cores located near

  10. Interim report on streamflow, sediment discharge, and water quality in the Calabazas Creek Basin, Santa Clara County, California

    USGS Publications Warehouse

    Knott, J.M.; Pederson, G.L.; Middelburg, Robert F.

    1978-01-01

    Streamflow, sediment-discharge, and water-quality data are being collected in the Calabazas Creek basin, Santa Clara County, Calif., to determine annual water and sediment discharge at base-line conditions that are representative of a basin prior to urbanization. Results of the first 3 years of the study (1973-75) are given in this report. Climatic conditions during this period were representative of a very wet year (1973) and 2 years of above-average rainfall (1974 and 1975). Daily water and sediment discharge were monitored at three primary stations, and periodic measurements were made at five secondary stations during selected storms. Most of the total annual sediment discharge at each station was transported during a few days each year. Maximum daily sediment discharge in a given year ranged from 23 to 62 percent of the annual total. Daily water discharge at the gaging station Calabazas Creek at Rainbow Drive, near Cupertino, ranged from no flow to 3.31 cubic meters per second. Streamflow at this location was significantly augmented during low flow by diversion of water from the South Bay Aqueduct. Annual sediment discharge at Calabazas Creek at Rainbow Drive was 4,900 t in 1974 and 9,570 t in 1975. A large quantity of sediment was trapped in a debris basin at Comer Drive upstream from this station during both years. If this sediment had not been trapped, sediment discharge at the station would have been about 35 percent greater in 1974 and 30 percent greater in 1975. Most of the trapped sediment consists of sand and gravel that would probably have been deposited in the Calabazas Creek channel downstream from the station. (Woodard-USGS)

  11. On the preservation of laminated sediments along the western margin of North America

    USGS Publications Warehouse

    VanGeen, A.; Zheng, Yen; Bernhard, J.M.; Cannariato, K.G.; Carriquiry, J.; Dean, W.E.; Eakins, B.W.; Ortiz, J.D.; Pike, J.

    2003-01-01

    Piston, gravity, and multicores as well as hydrographic data were collected along the Pacific margin of Baja California to reconstruct past variations in the intensity of the oxygen-minimum zone (OMZ). Gravity cores collected from within the OMZ north of 24??N did not contain laminated surface sediments even though bottom water oxygen (BWO) concentrations were close to 5 ??mol/kg. However, many of the cores collected south of 24??N did contain millimeter- to centimeter-scale, brown to black laminations in Holocene and older sediments but not in sediments deposited during the Last Glacial Maximum. In addition to the dark laminations, Holocene sediments in Soledad Basin, silled at 290 m, also contain white coccolith laminae that probably represent individual blooms. Two open margin cores from 430 and 700 m depth that were selected for detailed radiocarbon dating show distinct transitions from bioturbated glacial sediment to laminated Holocene sediment occurring at 12.9 and 11.5 ka, respectively. The transition is delayed and more gradual (11.3-10.0 ka) in another dated core from Soledad Basin. The observations indicate that bottom-water oxygen concentrations dropped below a threshold for the preservation of laminations at different times or that a synchronous hydrographic change left an asynchronous sedimentary imprint due to local factors. With the caveat that laminated sections should therefore not be correlated without independent age control, the pattern of older sequences of laminations along the North American western margin reported by this and previous studies suggests that multiple patterns of regional productivity and ventilation prevailed over the past 60 kyr. Copyright 2003 by the American Geophysical Union.

  12. On the preservation of laminated sediments along the western margin of North America

    NASA Astrophysics Data System (ADS)

    van Geen, A.; Zheng, Y.; Bernhard, J. M.; Cannariato, K. G.; Carriquiry, J.; Dean, W. E.; Eakins, B. W.; Ortiz, J. D.; Pike, J.

    2003-12-01

    Piston, gravity, and multicores as well as hydrographic data were collected along the Pacific margin of Baja California to reconstruct past variations in the intensity of the oxygen-minimum zone (OMZ). Gravity cores collected from within the OMZ north of 24°N did not contain laminated surface sediments even though bottom water oxygen (BWO) concentrations were close to 5 μmol/kg. However, many of the cores collected south of 24°N did contain millimeter- to centimeter-scale, brown to black laminations in Holocene and older sediments but not in sediments deposited during the Last Glacial Maximum. In addition to the dark laminations, Holocene sediments in Soledad Basin, silled at 290 m, also contain white coccolith laminae that probably represent individual blooms. Two open margin cores from 430 and 700 m depth that were selected for detailed radiocarbon dating show distinct transitions from bioturbated glacial sediment to laminated Holocene sediment occurring at 12.9 and 11.5 ka, respectively. The transition is delayed and more gradual (11.3-10.0 ka) in another dated core from Soledad Basin. The observations indicate that bottom-water oxygen concentrations dropped below a threshold for the preservation of laminations at different times or that a synchronous hydrographic change left an asynchronous sedimentary imprint due to local factors. With the caveat that laminated sections should therefore not be correlated without independent age control, the pattern of older sequences of laminations along the North American western margin reported by this and previous studies suggests that multiple patterns of regional productivity and ventilation prevailed over the past 60 kyr.

  13. Chromium isotope composition of reducing and anoxic sediments from the Peru Margin and Cariaco Basin

    NASA Astrophysics Data System (ADS)

    Gueguen, B.; Planavsky, N.; Wang, X.; Algeo, T. J.; Peterson, L. C.; Reinhard, C. T.

    2014-12-01

    Chromium isotope systematics in marine sediments are now being used as a new redox proxy of the modern and ancient Earth's surface. Chromium is primarily delivered to the oceans by riverine inputs through weathering of Cr(III)-rich minerals present in the continental crust and oxidation of insoluble Cr(III) to soluble Cr(VI) species. Since oxidation-reduction reactions fractionate Cr isotopes whereby oxidized Cr(VI) species are preferentially enriched in heavy Cr isotopes, the Cr isotope composition of marine sediments may be useful tracers of redox conditions at the Earth's surface through geological time. Chromium is quantitatively removed in organic-rich sediments where reducing conditions prevail and promote reduction of Cr(VI) to Cr(III), and thus, these sediments should capture the ambient seawater Cr isotope composition. However, the isotopic composition of modern organic-rich sediments is poorly documented so far, and this step is essential for further modeling the global oceanic Cr isotope mass balance and assessing the effects of sedimentation and post-depositional processes on the marine Cr isotopes archive. In this study, we have characterized modern marine organic-rich sediments for their Cr isotope composition (δ53/52Cr) from two different settings, the Peru margin upwelling zone and the anoxic Cariaco Basin (Venezuela). Chromium isotopes were measured on a MC-ICP-MS (Nu Plasma) using a double-spike correction method. The authigenic fraction of shallow samples from the Peru margin sedimentary sequence with a high Total Organic Carbon (TOC) content (>10 wt%) yield an average δ53/52Crauthigenic value of +0.67 ±0.05 ‰ (2sd). However, although this value is close to the seawater value (Atlantic Ocean) and to Cariaco basin sediments (~ +0.6 ‰), reducing sediments from the Peru margin are on average isotopically slightly heavier, especially in samples having a low authigenic fraction and a low TOC content (δ53/52Crauthigenic values up to +1.30

  14. Sediment flux, east Greenland margin. Final report, 1 October 1988-1 September 1991

    SciTech Connect

    Andrews, J.T.; Williams, K.M.

    1991-09-17

    We investigated sediment flux across an ice-dominated, high latitude continental margin, using cores from the East Greenland Shelf (ca. 68 deg N). Density, weight percentages of the various sediment components, and sediment/age relations (AMS C- 14 dates) were investigated from cores collected 1988 and 1990. High-resolution DTS Huntec surveys indicated 10-20 m of acoustically transparent sediment. Maximum core length was 3 m and most of the gravity cores were between 1-2 m. The radiocarbon assays show that basal core sediments date between ca. 9,000 and 14,500 BP. The acoustic characteristics, the low dry volume densities (ca. 600 kg/m3 and the faunal and floral assemblages) suggest ice-distal conditions between ca. 14,500 and the present. Net sediment flux in the Kangerdlugssuaq Trough during the last 14,500 years has been low; this might be explained by either (1) cold-based glaciological conditions of the East Greenland ice sheet; and/or (2) efficient sediment trap(s) lying along the inner shelf/fjords of East Greenland.

  15. Ice Sheet History from Antarctic Continental Margin Sediments: The ANTOSTRAT Approach

    USGS Publications Warehouse

    Barker, P.F.; Barrett, P.J.; Camerlenghi, A.; Cooper, A. K.; Davey, F.J.; Domack, E.W.; Escutia, C.; Kristoffersen, Y.; O'Brien, P.E.

    1998-01-01

    The Antarctic Ice Sheet is today an important part of the global climate engine, and probably has been so for most of its long existence. However, the details of its history are poorly known, despite the measurement and use, over two decades, of low-latitude proxies of ice sheet volume. An additional way of determining ice sheet history is now available, based on understanding terrigenous sediment transport and deposition under a glacial regime. It requires direct sampling of the prograded wedge of glacial sediments deposited at the Antarctic continental margin (and of derived sediments on the continental rise) at a small number of key sites, and combines the resulting data using numerical models of ice sheet development. The new phase of sampling is embodied mainly in a suite of proposals to the Ocean Drilling Program, generated by separate regional proponent groups co-ordinated through ANTOSTRAT (the Antarctic Offshore Acoustic Stratigraphy initiative). The first set of margin sites has now been drilled as ODP Leg 178 to the Antarctic Peninsula margin, and a first, short season of inshore drilling at Cape Roberts, Ross Sea, has been completed. Leg 178 and Cape Roberts drilling results are described briefly here, together with an outline of key elements of the overall strategy for determining glacial history, and of the potential contributions of drilling other Antarctic margins investigated by ANTOSTRAT. ODP Leg 178 also recovered continuous ultra-high-resolution Holocene biogenic sections at two sites within a protected, glacially-overdeepened basin (Palmer Deep) on the inner continental shelf of the Antarctic Peninsula. These and similar sites from around the Antarctic margin are a valuable resource when linked with ice cores and equivalent sections at lower latitude sites for studies of decadal and millenial-scale climate variation.

  16. A study of the TEX86 paleothermometer in the water column and sediments of the Santa Barbara Basin, California

    NASA Astrophysics Data System (ADS)

    Huguet, Carme; Schimmelmann, Arndt; Thunell, Robert; Lourens, Lucas J.; Sinninghe Damsté, Jaap S.; Schouten, Stefan

    2007-09-01

    Particulate organic matter collected during a 2-year period, as part of an ongoing sediment trap study, and a high-resolution sediment record from 1850 to 1987 A.D. from the Santa Barbara Basin were analyzed for TEX86, a temperature proxy based on marine crenarchaeotal membrane lipids. Highest fluxes of crenarchaeotal lipids in the water column were found in May-June 1996 and from October 1996 to January 1997 and, in general, showed a good correlation with mass fluxes. TEX86 reconstructed temperatures from the sediment trap series ranged from 8 to 11°C and were usually substantially lower than sea surface temperatures (SST), indicating that unlike in previous studies, the TEX86 corresponds to subsurface temperatures, likely between 100 and 150 m. TEX86 temperature variations observed in trap samples were not coupled to changes in SST or deep-water temperatures and only to some degree with crenarchaeotal lipid fluxes. This suggests that a complex combination of different depth origins and seasonal growth periods of Crenarchaeota contributed to the variations in TEX86 signal during the annual cycle. TEX86 temperatures in the two sediment cores studied (8-13°C) were also substantially lower than those of instrumental SST records (14-17.5°C) confirming that TEX86 records a subsurface temperature signal in the Santa Barbara Basin. This result highlights the importance of performing calibration studies using sediment traps and core tops before applying the TEX86 temperature proxy in a given study area.

  17. Variations in sediment transport at the central Argentine continental margin during the Cenozoic

    NASA Astrophysics Data System (ADS)

    Gruetzner, Jens; Uenzelmann-Neben, Gabriele; Franke, Dieter

    2012-10-01

    The construction of the sedimentary cover at most passive continental margins includes gravitational downslope transport and along-slope contourite deposition, which are controlled by tectonics, climate and oceanography. At the eastern continental margin of Argentina the history of deposition and erosion is intimately linked to the evolution of the South Atlantic and its water masses. Here we present a detailed seismic investigation of the mixed depositional system located between 41°S and 45°S. The study provides a northward complement to prior investigations from the southern Argentine margin and together with these may be used as background information for future ocean drilling in the region. Prominent features in our seismic cross sections are submarine canyons, mass wasting deposits, contourite channels, and sediment drifts. Four major seismic units above regional reflector PLe (˜65 Ma) are separated by distinct unconformities of regional extent. Using a dense grid of reflection seismic profiles, we mapped the depocenter geometries of the seismic units and derived a chronology of the depositional processes during the Cenozoic. While the Paleocene/Eocene (˜65-34 Ma) is characterized by hemipelagic sedimentation under relatively sluggish bottom water conditions, strong Antarctic bottom water (AABW) circulation led to widespread erosion on the slope and growth of a detached sediment drift during the Oligocene and early Miocene (˜34-17 Ma). After deposition of an aggradational seismic unit interpreted to represent the Mid-Miocene climatic optimum (˜17-14 Ma), gravitational downslope sediment transport increased during the middle to late Miocene (˜14-6 Ma) possibly related to tectonic uplift in South America. The Pliocene to Holocene unit (<˜6 Ma) is very heterogeneous and formed by interactions of downslope and along-slope sediment transport processes as indicated by the evolution of canyons, slope plastered drifts and channels.

  18. The impact of ocean deoxygenation on iron release from continental margin sediments

    NASA Astrophysics Data System (ADS)

    Scholz, Florian; McManus, James; Mix, Alan C.; Hensen, Christian; Schneider, Ralph R.

    2014-06-01

    In the oceans' high-nitrate-low-chlorophyll regions, such as the Peru/Humboldt Current system and the adjacent eastern equatorial Pacific, primary productivity is limited by the micronutrient iron. Within the Peruvian upwelling area, bioavailable iron is released from the reducing continental margin sediments. The magnitude of this seafloor source could change with fluctuations in the extension or intensity of the oxygen minimum zones. Here we show that measurements of molybdenum, uranium and iron concentrations can be used as a proxy for sedimentary iron release, and use this proxy to assess iron release from the sea floor beneath the Peru upwelling system during the past 140,000 years. We observe a coupling between levels of denitrification, as indicated by nitrogen isotopes, trace metal proxies for oxygenation, and sedimentary iron concentrations. Specifically, periods with poor upper ocean oxygenation are characterized by more efficient iron retention in the sediment and a diminished iron supply to the water column. We attribute efficient iron retention under more reducing conditions to widespread sulphidic conditions in the surface sediment and concomitant precipitation of iron sulphides. We argue that iron release from continental margin sediments is most effective in a narrow redox window where neither oxygen nor sulphide is present. We therefore suggest that future deoxygenation in the Peru upwelling area would be unlikely to result in increased iron availability, whereas in weaker oxygen minimum zones partial deoxygenation may enhance the iron supply.

  19. Sediment delivery to the Gulf of Alaska: source mechanisms along a glaciated transform margin

    USGS Publications Warehouse

    Dobson, M.R.; O'Leary, D.; Veart, M.

    1998-01-01

    Sediment delivery to the Gulf of Alaska occurs via four areally extensive deep-water fans, sourced from grounded tidewater glaciers. During periods of climatic cooling, glaciers cross a narrow shelf and discharge sediment down the continental slope. Because the coastal terrain is dominated by fjords and a narrow, high-relief Pacific watershed, deposition is dominated by channellized point-source fan accumulations, the volumes of which are primarily a function of climate. The sediment distribution is modified by a long-term tectonic translation of the Pacific plate to the north along the transform margin. As a result, the deep-water fans are gradually moved away from the climatically controlled point sources. Sets of abandoned channels record the effect of translation during the Plio-Pleistocene.

  20. 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. 

  1. Distinguishing Terrestrial Organic Carbon in Marginal Sediments of East China Sea and Northern South China Sea

    NASA Astrophysics Data System (ADS)

    Kandasamy, Selvaraj; Lin, Baozhi; Wang, Huawei; Liu, Qianqian; Liu, Zhifei; Lou, Jiann-Yuh; Chen, Chen-Tung Arthur; Mayer, Lawrence M.

    2016-04-01

    Knowledge about the sources, transport pathways and behavior of terrestrial organic carbon in continental margins adjoining to large rivers has improved in recent decades, but uncertainties and complications still exist with human-influenced coastal regions in densely populated wet tropics and subtropics. In these regions, the monsoon and other episodic weather events exert strong climatic control on mineral and particulate organic matter delivery to the marginal seas. Here we investigate elemental (TOC, TN and bromine-Br) and stable carbon isotopic (δ13C) compositions of organic matter (OM) in surface sediments and short cores collected from active (SW Taiwan) and passive margin (East China Sea) settings to understand the sources of OM that buried in these settings. We used sedimentary bromine to total organic carbon (Br/TOC) ratios to apportion terrigenous from marine organic matter, and find that Br/TOC may serve as an additional, reliable proxy for sedimentary provenance in both settings. Variations in Br/TOC are consistent with other provenance indicators in responding to short-lived terrigenous inputs. Because diagenetic alteration of Br is insignificant on shorter time scales, applying Br/TOC ratios as a proxy to identify organic matter source along with carbon isotope mixing models may provide additional constraints on the quantity and transformation of terrigenous organics in continental margins. We apply this combination of approaches to land-derived organic matter in different depositional environments of East Asian marginal seas.

  2. Geochemistry of stream-sediment samples from the Santa Renia Fields and Beaver Peak quadrangles, northern Carlin Trend, Nevada

    USGS Publications Warehouse

    Theodore, Ted G.; Kotlyar, Boris B.; Berger, Vladimir I.; Moring, Barry C.; Singer, Donald A.; Edstrom, Sven A.

    1999-01-01

    A broad west-to-east increase of many metal concentrations has been found in stream sediments during a reconnaissance investigation conducted in conjunction with geologic studies in the Santa Renia Fields and Beaver Peak 7–1/2 minute quadrangles near the northern end of the Carlin trend of gold deposits in the Tuscarora Mountains. This regional increase in metal concentrations coincides with a dramatic change in landform wherein high concentrations of metals in stream sediments appear to correlate directly with areas of high elevations and steep slopes in the Beaver Peak quadrangle. Robust erosion combined with high flow rates in streams from these higher elevations are envisaged to have contributed significantly to increased metal concentrations in the stream sediments by an enhanced presence of minerals with high specific gravities and a correspondingly diminished presence of minerals with low specific gravities. Minerals with low specific gravities probably have been preferentially flushed down stream because of high transporting capacities for sediment by streams in the Beaver Peak quadrangle. In addition, the Carlin trend, a generally northwest-alignment of gold deposits in the Santa Renia Fields quadrangle, is well outlined by arsenic concentrations that include a maximum of approximately 54 parts per million. Further, a weakly developed distal-to-proximal metal zonation towards these gold deposits appears to be defined respectively in plots showing distributions of thallium, arsenic, antimony, and zinc. A broad area of high metal concentrations—including sharply elevated abundances of Ag, As, Au, Cd, Co, Cu, Mn, Ni, P, Sb, Sc, Te, V, and especially Zn—near the southeast corner of the Beaver Peak quadrangle primarily could be the result of stratiform mineralized rocks in the Ordovician Vinini Formation or Devonian Slaven Chert, or the result of a subsequent Mesozoic or Tertiary epigenetic overprint.

  3. Tectonic controls on sedimentation in Mesozoic convergent margin basin of Baja California (Mexico)

    SciTech Connect

    Busby-Spera, C.J.; Smith, D.P.; Morris, W.R. )

    1990-05-01

    Mesozoic rocks of the Baja California peninsula form one of the most extensive, best exposed, oldest (160 m.y.), and least-tectonized and metamorphosed convergent margin basin complexes in the world. Much of the fill of these basins consist of coarse-grained volcaniclastic and epiclastic sequences that directly reflect the tectonic evolution of the region. The early history of the convergent margin was dominated by sedimentation in small, steep-sided basins within oceanic island arc systems. The Triassic and Jurassic convergent margin basins probably represent proto-Pacific terranes that traveled from another area. These terranes were assembled by the Late Jurassic to Early Cretaceous, and underlie the forearc region of a medial Cretaceous oceanic island arc system. Tbis system fringed the Mesoamerican continental margin and underwent regional-scale extension during subduction of old, dense lithosphere. The latest phases of sedimentation in the convergent margin occurred in broad, relatively stable forearc basins of a mature continental arc, during the Late Cretaceous to Paleocene. Nonetheless, intrabasinal faults provided some controls on depositional systems and bathymetry. The authors speculate that these faults formed in response to oblique convergence which ultimately resulted in 10-19{degree} northward displacement of Baja California relative to the North American craton, from the latitude of Central America to northern Mexico. The fill of oceanic island arc basins in Baja California is dominated by coarse-grained marine wedges including (1) arc apron deposits, consisting of pyroclastic and/or volcanic epiclastic debris deposited in intra-arc or back-arc basins, and (2) slope apron deposits, consisting of epiclastic debris shed from local fault scarps and more distally derived arc volcaniclastics, deposited in forearc basins.

  4. Late Cretaceous - Paleogene forearc sedimentation and accretion of oceanic plateaus and seamounts along the Middle American convergent margin (Costa Rica)

    NASA Astrophysics Data System (ADS)

    Baumgartner, Peter O.; Baumgartner-Mora, Claudia; Andjic, Goran

    2016-04-01

    The Late Cretaceous-Paleogene sedimentation pattern in space and time along the Middle American convergent margin was controlled by the accretion of Pacific plateaus and seamounts. The accretion of more voluminous plateaus must have caused the temporary extinction of the arc and tectonic uplift, resulting in short lived episodes of both pelagic and neritic biogenic sedimentation. By the Late Eocene, shallow carbonate environments became widespread on a supposed mature arc edifice, that is so far only documented in arc-derived sediments. In northern Costa Rica forearc sedimentation started during the Coniacian-Santonian on the Aptian-Turonian basement of the Manzanillo Terrane. The arrival and collision of the Nicoya Terrane (a CLIP-like, 139-83 Ma Pacific plateau) and the Santa Elena Terrane caused the extinction of the arc during late Campanian- Early Maastrichtian times, indicated by the change to pelagic limestone sedimentation (Piedras Blancas Formation) in deeper areas and shallow-water rudistid - Larger Benthic Foraminfera limestone on tectonically uplifted areas of all terranes. Arc-derived turbidite sedimentation resumed in the Late Maastrichtian and was again interrupted during the Late Paleocene - Early Eocene, perhaps due to the underplating of a yet unknown large seamount. The extinction of the arc resulted in the deposition of the siliceous pelagic Buenavista Formation, as well as the principally Thanetian Barra Honda carbonate platform on a deeply eroded structural high in the Tempisque area. In southern Costa Rica the basement is thought to be the western edge of the CLIP. It is Santonian-Campanian in age and is only exposed in the southwestern corner of Herradura. Cretaceous arc-forearc sequences are unknown, except for the Maastrichtian-Paleocene Golfito Terrane in southeastern Costa Rica. The distribution and age of shallow/pelagic carbonates vs. arc-derived detrital sediments is controlled by the history of accretion of Galápagos hot spot

  5. Geomicrobial characterization of gas hydrate-bearing sediments along the mid-Chilean margin.

    PubMed

    Hamdan, Leila J; Gillevet, Patrick M; Sikaroodi, Masoumeh; Pohlman, John W; Plummer, Rebecca E; Coffin, Richard B

    2008-07-01

    Bacterial diversity in eight sediment cores from the mid-Chilean margin was studied using length heterogeneity (LH)-PCR, and described in relation to in situ geochemical conditions. DNA from the sulfate-methane transition (SMT) of three cores [one containing methane gas; two proximal to a gas hydrate mound (GHM)] was cloned and sequenced. Clones related to uncultured relatives of Desulfosarcina variabilis were found in all clone libraries and dominated one. Desulfosarcina variabilis related clones were similar to phylotypes observed at the SMT in association with anaerobic methane oxidation in the Eel River basin, Cascadia margin and the Gulf of Mexico. The LH-PCR amplicon associated with D. variabilis clones matched the amplicon that dominated most SMT samples, indicating environmental selection for D. variabilis relatives. Clones related to the Verrucomicrobia dominated the library for the methane gas-containing core. Uncultured Treponema relatives dominated the library for the core obtained on the edge of a GHM. Statistical analysis using geochemical data to describe variance in LH-PCR data revealed that stable carbon isotope ratios of dissolved inorganic carbon are the principal structuring factor on SMT communities. These data suggest that D. variabilis relatives are involved in anaerobic oxidation of methane at the SMT in Chilean margin sediments.

  6. A 250-Year Sediment Record of Anthropogenic Contaminants in the Lisbon Canyon, Portuguese Margin

    NASA Astrophysics Data System (ADS)

    de Stigter, H. C.; Richter, T. O.; Booij, K.; Boer, W.; Jesus, C. C.; van Weering, T. C.

    2008-12-01

    The Lisbon Canyon on the continental margin of Portugal is located in the immediate vicinity of a densely populated and industrialized metropolitan area, and receives terrigenous sediments from the Tagus River draining a large part of the Iberian Peninsula. Radionuclide records (210Pb, 137Cs) for piston cores retrieved from the canyon indicate rapid and almost continuous accumulation over the last 250 years, with sedimentation rates of up to 1 cm per year. The devastating 1755AD Lisbon Earthquake is represented in some cores by a sandy turbidite layer with erosive base, but subsequently disturbance of the sedimentary record by mass sedimentation events has been very limited. In one core at 1710 m water depth, Pb concentrations increased gradually over the last 250 years, and more abruptly after ~1960AD. Subsequently, anthropogenic lead contributed more than half of total lead deposition. Stable Pb isotope ratios indicate concurrent shifts in sources of Pb and increasing influence of anthropogenic pollutants. A slight reversal in both long-term trends after ~1990AD presumably reflects the phase-out of leaded gasoline. Organic contaminant analyses of a core collected from 1112 m water depth demonstrate enrichment of the canyon sediments with a variety of polychlorinated biphenyls (PCBs) and polyaromatic hydrocarbons (PAHs) over the last century. PCBs increased abruptly during the second half of the 20th century but show a slight decrease over the most recent decade. PAHs appear to have had their maximum in the late 19th century, possibly reflecting fallout of coal dust from one of the busiest shipping routes of the eastern Atlantic. The present study illustrates the potential of submarine canyon sediments as high-resolution archives of human impacts on the continental margin.

  7. Evidence and biogeochemical implications for glacially-derived sediments in an active margin cold seep

    USGS Publications Warehouse

    Pohlman, John W.; Riedel, Michael; Novosel, Ivana; Bauer, James E.; Canuel, Elizabeth A.; Paull, Charles K.; Coffin, Richard B.; Grabowski, Kenneth S.; Knies, David L.; Hyndman, Roy D.; Spence, George D.

    2011-01-01

    Delineating sediment organic matter origins and sediment accumulation rates at gas hydratebearing and hydrocarbon seeps is complicated by the microbial transfer of 13C-depleted and 14Cdepleted methane carbon into sedimentary pools. Sediment 13C and 14C measurements from four cores recovered at Bullseye vent on the northern Cascadia margin are used to identify methane carbon assimilation into different carbon pools. While the total organic carbon (TOC) is mostly unaltered and primarily terrigenous in origin, planktonic foraminifera and the bulk carbonate display evidence of methane overprinting. Mass balance models are applied to determine the extent to which methane overprinting increased the radiocarbon ages of the biogenic foraminifera. The corrected and calibrated foraminifera ages between sediment depths of 70 and 573 cm are from 14.9 to 15.9 ka BP, which coincides with the retreat of the late Quaternary Cordilleran Ice Sheet from Vancouver Island. Uniform TOC _13C values of -24.5 ± 0.5‰ from the upper 8 meters of sediment at Bullseye vent suggest all cored material is Pleistocene-derived glacimarine material deposited as the ice edge retreated landward. Bullseye vent is located within an uplifted sediment block isolated from turbidite deposition and has been a site of non-deposition since the ice sheet retreated from the shelf. Biogeochemical implications of seep sediments being dominated by aged, organic-poor (<0.4 wt% TOC) material are that methane is the primary energy source, and microbes directly and indirectly associated with the anaerobic oxidation of methane (AOM) will dominate the seep microbial community.

  8. Cenozoic ice sheet history from East Antarctic Wilkes Land continental margin sediments

    USGS Publications Warehouse

    Escutia, C.; De Santis, L.; Donda, F.; Dunbar, R.B.; Cooper, A. K.; Brancolini, Giuliano; Eittreim, S.L.

    2005-01-01

    The long-term history of glaciation along the East Antarctic Wilkes Land margin, from the time of the first arrival of the ice sheet to the margin, through the significant periods of Cenozoic climate change is inferred using an integrated geophysical and geological approach. We postulate that the first arrival of the ice sheet to the Wilkes Land margin resulted in the development of a large unconformity (WL-U3) between 33.42 and 30 Ma during the early Oligocene cooling climate trend. Above WL-U3, substantial margin progradation takes place with early glacial strata (e.g., outwash deposits) deposited as low-angle prograding foresets by temperate glaciers. The change in geometry of the prograding wedge across unconformity WL-U8 is interpreted to represent the transition, at the end of the middle Miocene "climatic optimum" (14-10 Ma), from a subpolar regime with dynamic ice sheets (i.e., ice sheets come and go) to a regime with persistent but oscillatory ice sheets. The steep foresets above WL-U8 likely consist of ice proximal sediments (i.e., water-lain till and debris flows) deposited when grounded ice-sheets extended into the shelf. On the continental rise, shelf progradation above WL-U3 results in an up-section increase in the energy of the depositional environment (i.e., seismic facies indicative of more proximal turbidite and of bottom contour current deposition from the deposition of the lower WL-S5 sequence to WL-S7). Maximum rates of sediment delivery to the rise occur during the development of sequences WL-S6 and WL-S7, which we infer to be of middle Miocene age. During deposition of the two uppermost sequences, WL-S8 and WL-S9, there is a marked decrease in the sediment supply to the lower continental rise and a shift in the depocenters to more proximal areas of the margin. We believe WL-S8 records sedimentation during the final transition from a dynamic to a persistent but oscillatory ice sheet in this margin (14-10 Ma). Sequence WL-S9 forms under a polar

  9. Diatoms and aquatic palynomorphs in surface sediments of the White Sea bays as indicators of sedimentation in marginal filters of rivers

    NASA Astrophysics Data System (ADS)

    Polyakova, Ye. I.; Novichkova, Ye. A.; Lisitzin, A. P.; Shevchenko, V. P.; Kravchishina, M. D.

    2016-03-01

    Diatom algae, aquatic palynomorphs, and the grain-size of surface sediments from bays of the White Sea were investigated in a program dedicated to the study of marginal filters (MF) in the Severnaya Dvina, Onega, and Kem rivers. Three microalgal assemblages are established in surface sediments, which replace each other successively with distance from river mouths and are characterized by a gradual decrease in a share of freshwater species of diatoms and Chlorophyceae algae, significantly varying concentrations of marine diatoms and dinocysts due to changes in water salinity, grain-size composition of sediments, quantitative distribution of suspended particulate matter (SPM), and water productivity at different marginal filter stages.

  10. Sedimentation and diagenesis along open and island-protected windward carbonate platform margins of the Cretaceous El Abra Formation, Mexico

    NASA Astrophysics Data System (ADS)

    Minero, Charles J.

    1991-05-01

    The windward margin of the mid-Cretaceous Valles-San Luis Potosi carbonate platform in northeastern Mexico included open and island-protected segments. Depositional environments and diagenesis vary markedly with margin type. Sand shoals near the windward open margin are composed of oncoid-bioclastic and cross-laminated carbonates. Increasingly restricted and finer lagoonal and tidal-flat environments occurred bankwards, recording gradually decreasing wave and current energy. Lithofacies include peloid-miliolid, cryptalgal laminite, lime mudstone, and molluscan carbonates. Islands along the windward margin are composed of rudistid-skeletal debris from adjacent reefs. Lagoonal to tidal-flat sediments were deposited bankwards. Similar lithofacies occur as in these environments along the open margin but they are muddier and contain less diverse fauna. The different energy regimes along the margin influenced the distribution and packaging of banktop sediments. The bankward transition to low-energy, restricted environments was gradual across the open margin. In contrast, muddy sediments with restricted fauna accumulated in close proximity to the island-protected margin. Non-cyclic vertical lithofacies successions characterized the open platform margin, whereas asymmetric shoaling-upward sequences characterized the island-protected margin. Early diagenesis along the open margin was minor; burial diagenesis was of major importance. Thin rinds of marine cement are widespread but meteoric diagenesis was minor. Burial promoted extensive compaction. Mg-rich connate brines expressed from Guaxcama gypsum resulted in dolomitization and lithification, thereby precluding further compaction. Pore fluids resulting from dehydration of Guaxcama gypsum to anhydrite yielded pore-filling and replacement anhydrite in the El Abra Formation. Burial and Laramide deformation (Maastrichtian-Paleocene) resulted in stylolitization and extensive fracturing. Uplift produced widespread meteoric

  11. Phosphate oxygen isotope ratio proxy for specific microbial activity in marine sediments (Peru Margin)

    NASA Astrophysics Data System (ADS)

    Liang, Y.; Blake, R. E.

    2005-12-01

    Oxygen (O) isotope ratios of biogenic apatites have been widely used as paleotemperature and environmental geochemical proxies. With improved knowledge of the phosphate O isotope effects of different P cycling pathways, the δ18O value of inorganic phosphate (δ18OP) has been proposed as a useful proxy and tracer of biological reactions and P cycling in natural environments[1,2,3,4]. Being the only way of removing P from oceanic water, sedimentary P burial is one of the most important processes during biogeochemical cycling of P. The high concentrations of organic matter and pronounced microbial activity at ODP Site 1230 along the Peru Margin result in unusually high interstitial water phosphate concentrations, which provides a unique opportunity to use δ18OP to investigate inorganic phosphate (Pi) regeneration and P cycling pathways in marine sediments. The isotopic measurements of both dissolved inorganic phosphate (DIP) and bulk sediment Pi show that DIP δ18OP values are affected by three different processes, which are all induced by specific microbial activities present in the sediments. In sediments at ~ 65 to 120 mbsf, porewater DIP is derived from dissolved organophosphorus compounds (DOP) through enzymatic degradation pathways, evidenced by both DIP δ18OP values and interstitial water chemistry. Measured porewater DIP δ18OP values also suggest that 4 to 8% of interstitial water DIP reflects regeneration of Pi from Porg by microbially-synthesized enzymes. Throughout the sediment column and especially at ~ 120 to 150 mbsf, DIP is released from the sediments by microbially-induced reductive dissolution of Fe-oxides, which contributes to the overall high DIP concentrations at Site 1230. The third and dominant process controlling measured DIP δ18OP values is microbial turnover of regenerated Pi. The presence of high microbial activities in organic-rich Site 1230 sediments promotes the remobilization of P and affects marine P cycling by potentially enhancing

  12. Controls of tectonics and sediment source locations on along-strike variations in transgressive deposits on the northern California margin

    USGS Publications Warehouse

    Spinelli, G.A.; Field, M.E.

    2003-01-01

    We identify two surfaces in the shallow subsurface on the Eel River margin offshore northern California, a lowstand erosion surface, likely formed during the last glacial maximum, and an overlying surface likely formed during the most recent transgression of the shoreline. The lowstand erosion surface, which extends from the inner shelf to near the shelfbreak and from the Eel River to Trinidad Head (???80 km), truncates underlying strata on the shelf. Above the surface, inferred transgressive coastal and estuarine sedimentary units separate it from the transgressive surface on the shelf. Early in the transgression, Eel River sediment was likely both transported down the Eel Canyon and dispersed on the slope, allowing transgressive coastal sediment from the smaller Mad River to accumulate in a recognizable deposit on the shelf. The location of coastal Mad River sediment accumulation was controlled by the location of the paleo-Mad River. Throughout the remainder of the transgression, dispersed sediment from the Eel River accumulated an average of 20 m of onlapping shelf deposits. The distribution and thickness of these transgressive marine units was strongly modified by northwest-southeast trending folds. Thick sediment packages accumulated over structural lows in the lowstand surface. The thinnest sediment accumulations (0-10 m) were deposited over structural highs along faults and uplifting anticlines. The Eel margin, an active margin with steep, high sediment-load streams, has developed a thick transgressive systems tract. On this margin sediment accumulates as rapidly as the processes of uplift and downwarp locally create and destroy accommodation space. Sequence stratigraphic models of tectonically active margins should account for variations in accommodation space along margins as well as across them. ?? 2003 Elsevier Science B.V. All rights reserved.

  13. Reconstructing Quaternary precipitation periodicities with Santa Barbara Basin sediment cores: application of the siliciclastic detrital element proxy at annual resolution

    NASA Astrophysics Data System (ADS)

    Napier, T.; Hendy, I. L.; Hinnov, L.; Brown, E. T.

    2015-12-01

    Precipitation patterns in Southern California directly affect water availability, and extreme weather exacerbates water stress and subsequent societal impacts in this highly populated and vital agricultural region. In the future, mean annual precipitation is predicted to decrease in California, although frequency of heavy precipitation events may increase. To reconstruct annual precipitation history in Southern California, including both the magnitude and recurrence intervals, we analyze sediment from two Late Holocene (past ~150 years and past ~2 ka) and five Pleistocene (~400-450 ka [MIS 11 and 12] and ~735 ka [MIS 18]) cores collected in Santa Barbara Basin using data from XRF core scans for elements associated with the terrigenous siliciclastic detrital fraction of core sediment (Al, Fe, K, Rb, Si, Ti, Zr). We develop a floating annual age model for each core through identification of the annual signal in the siliciclastic detrital fraction. Siliciclastic detrital element concentrations increase in sediment associated with precipitation events and floods, and decrease in sediment associated with droughts. Variability in the concentrations of these elements can thus be used as a precipitation and river runoff proxy. We investigate changes in annual detrital sediment input during glacial, deglacial, and interglacial climate states, and changes due to rapid climate change (centennial to millennial time scales). Power spectral analysis of our annually tuned time series reveals precipitation periodicities associated with the Pacific Decadal Oscillation (15-25, 50-70 years) and El Niño-Southern Oscillation (2-7 years) that are dissimilar to common tidal perigee and nodal periods. These results provide information on the nature and response of precipitation patterns due to past changes in climate forcing, which will improve climate predictions for this region, especially interannual and decadal variability that impact climate on human timescales (i.e. <100 years).

  14. Potential toxicity of chemical elements in beach sediments near Santa Rosalía copper mine, Baja California Peninsula, Mexico

    NASA Astrophysics Data System (ADS)

    Jonathan, M. P.; Shumilin, E.; Rodríguez-Figueroa, G. M.; Rodriguez-Espinosa, P. F.; Sujitha, S. B.

    2016-10-01

    A total of 17 beach sediment samples were analyzed for the determination of thirty-one chemical elements to generate a geochemical data set from the Santa Rosalía mining area in the State of Baja California Sur (south), Mexico. Results indicate that the beach sediments were enriched in Cu, Zn, Co, Pb, Cd (3856, 2599, 635, 236, 240 mg kg-1, respectively) and in Mn (2.01%) due to a century of mining and smelting activities. Comparison of these concentration with ecotoxicological sediment quality criteria (ERL, ERM, LEL, SEL) indicated the values of As, Cd, Co, Cr, Cu, Ni, Pb, Sr, Zn and Mn were higher than the permissible limits. Average values of the calculated geoaccumulation index (Igeo) suggest that the key elements such as Mn, Ba, Cd, Co, Mo, Pb, Sr, Zn are categorized in class 4 to 6 encompassing the strongly polluted to extremely polluted groups. The association and enrichment of the above elements are also well supported statistically (factor analysis) which points to the role of Fe-Mn oxides as the main scavengers for retaining these chemical elements.

  15. Long-distance multistep sediment transfer at convergent plate margins (Barbados, Lesser Antilles)

    NASA Astrophysics Data System (ADS)

    Limonta, Mara; Garzanti, Eduardo; Resentini, Alberto; Andò, Sergio; Boni, Maria; Bechstädt, Thilo

    2015-04-01

    analysis is a basic tool in paleogeographic reconstructions when multicyclic sediment dispersal along and across convergent plate margins occur. Such analysis provides the link between faraway factories of detritus and depositional sinks, as well as clues on subduction geometry and the nature of associated growing orogenic belts, and even information on climate, atmospheric circulation and weathering intensity in source regions. REFERENCES Garzanti, E., Limonta, M., Resentini, A., Bandopadhyay, P.C., Najman, Y., Andò, S., Vezzoli, G., 2013. Sediment recycling at convergent plate margins (Indo-Burman Ranges and Andaman-Nicobar Ridge). Earth Sci. Rev., 123, 113-132. Speed, C. and Sedlock, R. 2012. Geology and geomorphology of Barbados. Geol. Soc. Am. Spec. Pap., 491, 63 p.

  16. Joint Electrical and Seismic Interpretation of Gas Hydrate Bearing Sediments From the Cascadia Margin

    NASA Astrophysics Data System (ADS)

    Ellis, M.; Minshull, T.; Sinha, M.; Best, A.

    2008-12-01

    Gas hydrates are found in continental margin sediments worldwide. Their global importance as future energy reserves and their potential impact on slope stability and abrupt climate change all require better knowledge of where they occur and how much hydrate is present. However, current estimates of the distribution and volume of gas hydrate beneath the seabed range widely. Improved geophysical methods could provide much better constraints on hydrate concentrations. Geophysical measurements of seismic velocity and electrical resistivity using seabed or borehole techniques are often used to determine the hydrate saturation of sediments. Gas hydrates are well known to affect these physical properties; hydrate increases sediment p-wave velocity and electrical resistivity by replacing the conductive pore fluids, by cementing grains together and by blocking pores. A range of effective medium theoretical models have been developed to interpret these measurements in terms of hydrate content, but uncertainties about the pore-scale distribution of hydrate can lead to large uncertainties in the results. This study developed effective medium models to determine the seismic and electrical properties of hydrate bearing sediments in terms of their porosity, micro-structure and hydrate saturation. The seismic approach combines a Self Consistent Approximation (SCA) and Differential Effective Medium (DEM), which can model a bi-connected effective medium and allows the shape and alignment of the grains to be taken into account. The electrical effective medium method was developed to complement the seismic models and is based on the application of a geometric correction to the Hashin-Shrikman conductive bound. The electrical and seismic models are non-unique and hence it was necessary to develop a joint electrical and seismic interpretation method to investigate hydrate bearing sediments. The joint method allows two variables (taken from porosity, aspect ratio or hydrate saturation

  17. Preglacial to glacial sediment thickness grids for the Southern Pacific Margin of West Antarctica

    NASA Astrophysics Data System (ADS)

    Lindeque, Ansa; Gohl, Karsten; Wobbe, Florian; Uenzelmann-Neben, Gabriele

    2016-10-01

    Circum-Antarctic sediment thickness grids provide constraints for basin evolution and paleotopographic reconstructions, which are important for paleo-ice sheet formation histories. By compiling old and new seismic data, we identify sequences representing preglacial, transitional, and full glacial deposition processes along the Pacific margin of West Antarctica. The preglacial sediment grid depicts 1.3-4.0 km thick depocenters, relatively evenly distributed along the margin. The depocenters change markedly in the transitional phase at, or after, the Eocene/Oligocene boundary when the first major ice sheets reached the shelf. Full glacial sequences, starting in the middle Miocene, indicate new depocenter formation North of the Amundsen Sea Embayment and localized eastward shifts in the Bellingshausen Sea and Antarctic Peninsula basins. Using present-day drainage paths and source areas on the continent, our calculations indicate that an estimated observed total sedimentary volume of ˜10 × 106 km3 was eroded from West Antarctica since the separation of New Zealand in the Late Cretaceous. Of this, 4.9 × 106 km3 predates the onset of glaciation and need to be considered for a 34 Ma paleotopography reconstruction. Whereas 5.1 × 106 km3 postdates the onset of glaciation, of which 2.5 × 106 km3 were deposited in post mid-Miocene full glacial conditions.

  18. Organic carbon accumulation and preservation in surface sediments on the Peru margin

    USGS Publications Warehouse

    Arthur, M.A.; Dean, W.E.; Laarkamp, K.

    1998-01-01

    Concentrations and characteristics of organic matter in surface sediments deposited under an intense oxygen-minimum zone on the Peru margin were studied in samples from deck-deployed box cores and push cores acquired by submersible on two transects spanning depths of 75 to 1000 m at 12??and 13.5??S. The source of organic matter to the seafloor in these areas is almost entirely marine material as confirmed by the narrow range of ??13C of organic carbon obtained in the present study (-20.3 to -21.6???; PDB) and the lack of any relationship between pyrolysis hydrogen index and carbon isotope composition. Organic carbon contents are highest (up to 16%) on the slope at depths between 75 and 350 m in sediments deposited under intermediate water masses with low dissolved oxygen concentrations (< 5 ??mol/kg). Even at these low concentrations of dissolved oxygen, however, the surface sediments that were recovered from these depths are dominantly unlaminated. Strong currents (up to 30 cm/s) associated with the poleward-flowing Peru Undercurrent were measured at depths between 160 and 300 m on both transects. The seafloor in this range of water depths is characterized by bedforms stabilized by bacterial mats, extensive authigenic mineral crusts, and (or) thick organic flocs. Constant advection of dissolved oxygen, although in low concentrations, active resuspension of surficial organic matter, activity of organisms, and transport of fine-grained sediment to and from more oxygenated zones all contribute to greater degradation and poorer initial preservation of organic matter than might be expected under oxygen-deficient conditions. Dissolved-oxygen concentrations ultimately may be the dominant affect on organic matter characteristics, but reworking of fine-grained sediment and organic matter by strong bottom currents and redeposition on the seafloor in areas of lower energy also exert important controls on organic carbon concentration and degree of oxidation in this region.

  19. Distribution and sources of organic matter in surface marine sediments across the North American Arctic margin

    NASA Astrophysics Data System (ADS)

    Goñi, Miguel A.; O'Connor, Alison E.; Kuzyk, Zou Zou; Yunker, Mark B.; Gobeil, Charles; Macdonald, Robie W.

    2013-09-01

    As part of the International Polar Year research program, we conducted a survey of surface marine sediments from box cores along a section extending from the Bering Sea to Davis Strait via the Canadian Archipelago. We used bulk elemental and isotopic compositions, together with biomarkers and principal components analysis, to elucidate the distribution of marine and terrestrial organic matter in different regions of the North American Arctic margin. Marked regional contrasts were observed in organic carbon loadings, with the highest values (≥1 mg C m-2 sediment) found in sites along Barrow Canyon and the Chukchi and Bering shelves, all of which were characterized by sediments with low oxygen exposure, as inferred from thin layers (<2 cm) of Mn oxihydroxides. We found strong regional differences in inorganic carbon concentrations, with sites from the Canadian Archipelago and Lancaster Sound displaying elevated values (2-7 wt %) and highly depleted 14C compositions consistent with inputs from bedrock carbonates. Organic carbon:nitrogen ratios, stable carbon isotopes, and terrigenous organic biomarkers (lignin phenols and cutin acids) all indicate marked regional differences in the proportions of marine and terrigenous organic matter present in surface sediments. Regions such as Barrow Canyon and the Mackenzie River shelf were characterized by the highest contributions of land-derived organic matter, with compositional characteristics that suggested distinct sources and provenance. In contrast, sediments from the Canadian Archipelago and Davis Strait had the smallest contributions of terrigenous organic matter and the lowest organic carbon loadings indicative of a high degree of post-depositional oxidation.

  20. GLORIA imagery links sedimentation in Aleutian Trench to Yakutat margin via surveyor channel

    SciTech Connect

    Carlson, P.R.; Bruns, T.R.; Mann, D.M.; Stevenson, A.J. ); Huggett, Q.J. )

    1990-06-01

    GLORIA side-scan sonar imagery shows that the continental slope developing along the active margin of the Gulf of Alaska is devoid of large submarine canyons, in spite of the presence of large glacially formed sea valleys that cross the continental shelf. In the western and northern Gulf, discontinuous, actively growing deformation structures disrupt or divert the downslope transport of sediment into the Aleutian Trench. To the east of Middleton Island, the slope is intensively gullied and incised only by relatively small canyons. At the base of the gullied slope between Pamplona Spur and Alsek Valley, numerous small slope gullies coalesce into three turbidity current channels that merge to form the Surveyor deep-sea channel. About 350 km from the margin, the channel crosses the structural barrier formed by the Kodiak-Bowie Seamount chain and heads south for another 150 km where it bends northerly, perhaps influenced by the oceanic basement relief of the Patton Seamounts. The channel, now up to 5 km wide and deeply entrenched to 450 m, continues northerly for 200 km where it intercepts the Aleutian Trench, some 700 km from the Yakutat margin. South of Surveyor Channel, GLORIA imagery revealed evidence of another older channel. The older channel meanders through a gap in the seamount chain and eventually bends northwesterly. This now inactive, largely buried channel may have carried turbidity currents to the Aleutian Trench concurrent with the active Surveyor Channel.

  1. Radiocarbon calibration-comparison records based on marine sediments from the Pakistan and Iberian Margins

    NASA Astrophysics Data System (ADS)

    Bard, E.; Ménot, G.; Licari, L.

    2009-04-01

    We present new results on the radiocarbon records based on planktonic foraminifera of core MD042876 from the Pakistan Margin and updated results for core MD952042 from the Iberian Margin (Bard et al. 2004, Science 303, 178; 2004, Quat. Res. 61, 204; 2004, Radiocarbon 46, 1189; Shackleton et al. 2004, QSR 23, 1513). Both cores exhibit high sedimentation rates on the order of 50 and 40 cm/kyr for the Pakistan and Iberian cores, respectively. For a calendar age scale, we matched climate records of both cores to the oxygen isotopic profile of the Hulu Cave stalagmites that have been accurately dated by U-Th (Wang et al. 2001, Science 294, 2345). Our new comparison data can be compared with the IntCal04 record (Reimer et al. 2004, Radiocarbon 46, 1029) and with individual records based on other archives: corals from Barbados (Fairbanks et al. 2005, QSR 24, 1781), marine sediments of the Cariaco Basin (Hughen et al. 2004, Science 303, 202; 2006, QSR 25, 3216), varves of Lake Suigetsu (Kitagawa & van der Plicht 1998, Science 279, 1187; 2000, Radiocarbon 42, 369), and speleothems from the Bahamas (Beck et al. 2001, Science 292, 2453). Up to 26,000 cal-yr-BP, the Pakistan and Iberian data can be used to validate the precision and accuracy of the marine sediment approach. In the interval between 26,000 and 50,000 cal-yr-B.P., the Pakistan and Iberian records agree closely with each other and with the Cariaco and Barbados data. This agreement clearly shows the feasibility of extending the IntCal04 14C calibration curve.

  2. Phylogenetic diversity of sediment bacteria from the southern Cretan margin, Eastern Mediterranean Sea.

    PubMed

    Polymenakou, Paraskevi N; Lampadariou, Nikolaos; Mandalakis, Manolis; Tselepides, Anastasios

    2009-02-01

    This study is the first culture-independent report on the regional variability of bacterial diversity in oxic sediments from the unexplored southern Cretan margin (SCM). Three main deep basins (water column depths: 2670-3603m), located at the mouth of two submarine canyons (Samaria Gorge and Paximades Channel) and an adjacent slope system, as well as two shallow upper-slope stations (water column depths: 215 and 520m), were sampled. A total of 454 clones were sequenced and the bacterial richness, estimated through five clone libraries using rarefaction analysis, ranged from 71 to 296 unique phylotypes. The average sequence identity of the retrieved Cretan margin sequences compared to the >1,000,000 known rRNA sequences was only 93.5%. A diverse range of prokaryotes was found in the sediments, which were represented by 15 different taxonomic groups at the phylum level. The phylogenetic analysis revealed that these new sequences grouped with the phyla Acidobacteria, Planctomycetes, Actinobacteria, Gamma-, Alpha- and Delta-proteobacteria. Only a few bacterial clones were affiliated with Chloroflexi, Bacteroidetes, Firmicutes, Gemmatimonadetes, Verrucomicrobia, Nitrospirae, Beta-proteobacteria, Lentisphaerae and Dictyoglomi. A large fraction of the retrieved sequences (12%) did not fall into any taxonomic division previously characterized by molecular criteria, whereas four novel division-level lineages, termed candidate division SCMs, were identified. Bacterial community composition demonstrated significant differences in comparison to previous phylogenetic studies. This divergence was mainly triggered by the dominance of Acidobacteria and Actinobacteria and reflected a bacterial community different from that currently known for oxic and pristine marine sediments.

  3. Early diagenesis and trace element accumulation in North American Arctic margin sediments

    NASA Astrophysics Data System (ADS)

    Kuzyk, Zou Zou A.; Gobeil, Charles; Goñi, Miguel A.; Macdonald, Robie W.

    2017-04-01

    Concentrations of redox-sensitive elements (S, Mn, Mo, U, Cd, Re) were analyzed in a set of 27 sediment cores collected along the North American Arctic margin (NAAM) from the North Bering Sea to Davis Strait via the Canadian Archipelago. Sedimentary distributions and accumulation rates of the elements were used to evaluate early diagenesis in sediments along this section and to estimate the importance of this margin as a sink for key elements in the polar and global oceans. Distributions of Mn, total S and reduced inorganic S demonstrated that diagenetic conditions and thus sedimentary carbon turnover in the NAAM is organized regionally: undetectable or very thin layers (<0.5 cm) of surface Mn enrichment occurred in the Bering-Chukchi shelves; thin layers (1-5 cm) of surface Mn enrichment occurred in Barrow Canyon and Lancaster Sound; and thick layers (5-20 cm) of surface Mn enrichment occurred in the Beaufort Shelf, Canadian Archipelago, and Davis Strait. Inventories of authigenic S below the Mn-rich layer decreased about fivefold from Bering-Chukchi shelf and Barrow Canyon to Lancaster Sound and more than ten-fold from Bering-Chukchi shelf to Beaufort Shelf, Canadian Archipelago and Davis Strait. The Mn, total S and reduced inorganic S distributions imply strong organic carbon (OC) flux and metabolism in the Bering-Chukchi shelves, lower aerobic OC metabolism in Barrow Canyon and Lancaster Sound, and deep O2 penetration and much lower OC metabolism in the Beaufort Shelf, Canadian Archipelago, and Davis Strait. Accumulation rates of authigenic S, Mo, Cd, Re, and U displayed marked spatial variability along the NAAM reflecting the range in sedimentary redox conditions. Strong relationships between the accumulation rates and vertical carbon flux, estimated from regional primary production values and water depth at the coring sites, indicate that the primary driver in the regional patterns is the supply of labile carbon to the seabed. Thus, high primary production

  4. Mercury profiles in sediment from the marginal high of Arabian Sea: an indicator of increasing anthropogenic Hg input.

    PubMed

    Chakraborty, Parthasarathi; Vudamala, Krushna; Chennuri, Kartheek; Armoury, Kazip; Linsy, P; Ramteke, Darwin; Sebastian, Tyson; Jayachandran, Saranya; Naik, Chandan; Naik, Richita; Nath, B Nagender

    2016-05-01

    Total Hg distributions and its speciation were determined in two sediment cores collected from the western continental marginal high of India. Total Hg content in the sediment was found to gradually increase (by approximately two times) towards the surface in both the cores. It was found that Hg was preferentially bound to sulfide under anoxic condition. However, redox-mediated reactions in the upper part of the core influenced the total Hg content in the sediment cores. This study suggests that probable increase in authigenic and allogenic Hg deposition attributed to the increasing Hg concentration in the surface sediment in the study area.

  5. Stability studies of surficial sediments in the Wilmington-Lindenkohl Canyons area, eastern U.S. margin

    USGS Publications Warehouse

    Almagor, G.; Bennett, R.H.; Mc Gregor, B.A.; Shephard, L.E.

    1982-01-01

    Stability analysis, based on infinite slope analysis and geotechnical data from a suite of 34 cores collected from the continental slope between Wilmington and Lindenkohl Canyons, indicates that the Quaternary surficial silty clay sediments on gentle slopes are stable; that sediment stability on steeper slopes (14??-19??) is marginal; and that on precipitous slopes (>50??) only a thin veneer of unconsolidated sediments can exist. Small earthquake-induced accelerations or the effects of internal waves can result in slope sediment instabilities. ?? 1982 A. M. Dowden, Inc.

  6. Geochemistry, faunal composition and trophic structure in reducing sediments on the southwest South Georgia margin

    PubMed Central

    Aquilina, Alfred; Woulds, Clare; Glover, Adrian G.; Little, Crispin T. S.; Hepburn, Laura E.; Newton, Jason; Mills, Rachel A.

    2016-01-01

    Despite a number of studies in areas of focused methane seepage, the extent of transitional sediments of more diffuse methane seepage, and their influence upon biological communities is poorly understood. We investigated an area of reducing sediments with elevated levels of methane on the South Georgia margin around 250 m depth and report data from a series of geochemical and biological analyses. Here, the geochemical signatures were consistent with weak methane seepage and the role of sub-surface methane consumption was clearly very important, preventing gas emissions into bottom waters. As a result, the contribution of methane-derived carbon to the microbial and metazoan food webs was very limited, although sulfur isotopic signatures indicated a wider range of dietary contributions than was apparent from carbon isotope ratios. Macrofaunal assemblages had high dominance and were indicative of reducing sediments, with many taxa common to other similar environments and no seep-endemic fauna, indicating transitional assemblages. Also similar to other cold seep areas, there were samples of authigenic carbonate, but rather than occurring as pavements or sedimentary concretions, these carbonates were restricted to patches on the shells of Axinulus antarcticus (Bivalvia, Thyasiridae), which is suggestive of microbe–metazoan interactions. PMID:27703692

  7. Geochemistry, faunal composition and trophic structure in reducing sediments on the southwest South Georgia margin

    NASA Astrophysics Data System (ADS)

    Bell, James B.; Aquilina, Alfred; Woulds, Clare; Glover, Adrian G.; Little, Crispin T. S.; Reid, William D. K.; Hepburn, Laura E.; Newton, Jason; Mills, Rachel A.

    2016-09-01

    Despite a number of studies in areas of focused methane seepage, the extent of transitional sediments of more diffuse methane seepage, and their influence upon biological communities is poorly understood. We investigated an area of reducing sediments with elevated levels of methane on the South Georgia margin around 250 m depth and report data from a series of geochemical and biological analyses. Here, the geochemical signatures were consistent with weak methane seepage and the role of sub-surface methane consumption was clearly very important, preventing gas emissions into bottom waters. As a result, the contribution of methane-derived carbon to the microbial and metazoan food webs was very limited, although sulfur isotopic signatures indicated a wider range of dietary contributions than was apparent from carbon isotope ratios. Macrofaunal assemblages had high dominance and were indicative of reducing sediments, with many taxa common to other similar environments and no seep-endemic fauna, indicating transitional assemblages. Also similar to other cold seep areas, there were samples of authigenic carbonate, but rather than occurring as pavements or sedimentary concretions, these carbonates were restricted to patches on the shells of Axinulus antarcticus (Bivalvia, Thyasiridae), which is suggestive of microbe-metazoan interactions.

  8. Geochemistry, faunal composition and trophic structure in reducing sediments on the southwest South Georgia margin.

    PubMed

    Bell, James B; Aquilina, Alfred; Woulds, Clare; Glover, Adrian G; Little, Crispin T S; Reid, William D K; Hepburn, Laura E; Newton, Jason; Mills, Rachel A

    2016-09-01

    Despite a number of studies in areas of focused methane seepage, the extent of transitional sediments of more diffuse methane seepage, and their influence upon biological communities is poorly understood. We investigated an area of reducing sediments with elevated levels of methane on the South Georgia margin around 250 m depth and report data from a series of geochemical and biological analyses. Here, the geochemical signatures were consistent with weak methane seepage and the role of sub-surface methane consumption was clearly very important, preventing gas emissions into bottom waters. As a result, the contribution of methane-derived carbon to the microbial and metazoan food webs was very limited, although sulfur isotopic signatures indicated a wider range of dietary contributions than was apparent from carbon isotope ratios. Macrofaunal assemblages had high dominance and were indicative of reducing sediments, with many taxa common to other similar environments and no seep-endemic fauna, indicating transitional assemblages. Also similar to other cold seep areas, there were samples of authigenic carbonate, but rather than occurring as pavements or sedimentary concretions, these carbonates were restricted to patches on the shells of Axinulus antarcticus (Bivalvia, Thyasiridae), which is suggestive of microbe-metazoan interactions.

  9. Carbonate sedimentation in an extensional active margin: Cretaceous history of the Haymana region, Pontides

    NASA Astrophysics Data System (ADS)

    Okay, Aral I.; Altiner, Demir

    2016-10-01

    The Haymana region in Central Anatolia is located in the southern part of the Pontides close to the İzmir-Ankara suture. During the Cretaceous, the region formed part of the south-facing active margin of the Eurasia. The area preserves a nearly complete record of the Cretaceous system. Shallow marine carbonates of earliest Cretaceous age are overlain by a 700-m-thick Cretaceous sequence, dominated by deep marine limestones. Three unconformity-bounded pelagic carbonate sequences of Berriasian, Albian-Cenomanian and Turonian-Santonian ages are recognized: Each depositional sequence is preceded by a period of tilting and submarine erosion during the Berriasian, early Albian and late Cenomanian, which corresponds to phases of local extension in the active continental margin. Carbonate breccias mark the base of the sequences and each carbonate sequence steps down on older units. The deep marine carbonate deposition ended in the late Santonian followed by tilting, erosion and folding during the Campanian. Deposition of thick siliciclastic turbidites started in the late Campanian and continued into the Tertiary. Unlike most forearc basins, the Haymana region was a site of deep marine carbonate deposition until the Campanian. This was because the Pontide arc was extensional and the volcanic detritus was trapped in the intra-arc basins and did not reach the forearc or the trench. The extensional nature of the arc is also shown by the opening of the Black Sea as a backarc basin in the Turonian-Santonian. The carbonate sedimentation in an active margin is characterized by synsedimentary vertical displacements, which results in submarine erosion, carbonate breccias and in the lateral discontinuity of the sequences, and differs from blanket like carbonate deposition in the passive margins.

  10. Pathways of carbon oxidation in continental margin sediments off central Chile.

    PubMed

    Thamdrup, B; Canfield, D E

    1996-12-01

    Rates and oxidative pathways of organic carbon mineralization were determined in sediments at six stations on the shelf and slope off Concepcion Bay at 36.5 degrees S. The depth distribution of C oxidation rates was determined to 10 cm from accumulation of dissolved inorganic C in 1-5-d incubations. Pathways of C oxidation were inferred from the depth distributions of the potential oxidants (O2, NO3-, and oxides of Mn and Fe) and from directly determined rates of SO4(2-) reduction. The study area is characterized by intense seasonal upwelling, and during sampling in late summer the bottom water over the shelf was rich in NO3- and depleted of O2. Sediments at the four shelf stations were covered by mats of filamentous bacteria of the genera Thioploca and Beggiatoa. Carbon oxidation rates at these sites were extremely high near the sediment surface (>3 micromol cm-3 d-1) and decreased exponentially with depth. The process was entirely coupled to SO4(2-) reduction. At the two slope stations where bottom-water O2 was > 100 microM, C oxidation rates were 10-fold lower and varied less with depth; C oxidation coupled to the reduction of O2, NO3-, and Mn oxides combined to yield an estimated 15% of the total C oxidation between 0 and 10 cm. Carbon oxidation through Fe reduction contributed a further 12-29% of the depth-integrated rate, while the remainder of C oxidation was through SO4(2-) reduction. The depth distribution of Fe reduction agreed well with the distribution of poorly crystalline Fe oxides, and as this pool decreased with depth, the importance of SO4(2-) reduction increased. The results point to a general importance of Fe reduction in C oxidation in continental margin sediments. At the shelf stations, Fe reduction was mainly coupled to oxidation of reduced S. These sediments were generally H2S-free despite high SO4(2-) reduction rates, and precipitation of Fe sulfides dominated H2S scavenging during the incubations. A large NO3- pool was associated with the

  11. Measurement of sediment and crustal thickness corrected RDA for 2D profiles at rifted continental margins: Applications to the Iberian, Gulf of Aden and S Angolan margins

    NASA Astrophysics Data System (ADS)

    Cowie, Leanne; Kusznir, Nick

    2014-05-01

    Subsidence analysis of sedimentary basins and rifted continental margins requires a correction for the anomalous uplift or subsidence arising from mantle dynamic topography. Whilst different global model predictions of mantle dynamic topography may give a broadly similar pattern at long wavelengths, they differ substantially in the predicted amplitude and at shorter wavelengths. As a consequence the accuracy of predicted mantle dynamic topography is not sufficiently good to provide corrections for subsidence analysis. Measurements of present day anomalous subsidence, which we attribute to mantle dynamic topography, have been made for three rifted continental margins; offshore Iberia, the Gulf of Aden and southern Angola. We determine residual depth anomaly (RDA), corrected for sediment loading and crustal thickness variation for 2D profiles running from unequivocal oceanic crust across the continental ocean boundary onto thinned continental crust. Residual depth anomalies (RDA), corrected for sediment loading using flexural backstripping and decompaction, have been calculated by comparing observed and age predicted oceanic bathymetries at these margins. Age predicted bathymetric anomalies have been calculated using the thermal plate model predictions from Crosby & McKenzie (2009). Non-zero sediment corrected RDAs may result from anomalous oceanic crustal thickness with respect to the global average or from anomalous uplift or subsidence. Gravity anomaly inversion incorporating a lithosphere thermal gravity anomaly correction and sediment thickness from 2D seismic reflection data has been used to determine Moho depth, calibrated using seismic refraction, and oceanic crustal basement thickness. Crustal basement thicknesses derived from gravity inversion together with Airy isostasy have been used to correct for variations of crustal thickness from a standard oceanic thickness of 7km. The 2D profiles of RDA corrected for both sediment loading and non-standard crustal

  12. The Peru Margin as an Authigenic Mineral Factory, Evidence From Surface Sediments and Oceanography

    NASA Astrophysics Data System (ADS)

    Dean, W. E.; Arthur, M. A.

    2004-12-01

    Characteristics of sediments deposited within an intense oxygen-minimum zone (OMZ) on the Peru continental margin were mapped by submersible, and studied in samples collected in deck-deployed box cores and submersible push cores on two east-west transects over water depths of 75 to 1000 m at 12 degrees and 13.5 degrees S. On the basis of sampling of the top 1-2 cm of available cores, three main belts of sediments were identified in each transect with increasing depth: 1) organic-carbon (OC)-rich muds; 2) authigenic phosphatic mineral crusts; and 3) glaucony facies. These facies patterns are primarily controlled by redox conditions and strength of bottom currents. OC-rich sediments on the 12-degree transect were mainly located on the outer shelf and upper slope (150-350 m), but they occurred in much shallower water (ca. 100 m) on the 13.5-degree transect. The organic matter is almost entirely marine, resulting from very high primary productivity. The OC concentrations are highest (up to 18%) in sediments where intermediate water masses with low dissolved oxygen concentrations (less than 5 micromoles/kg) impinge on the slope at water depths between 75 and 450 m. The region between 175 and 350 m depth is characterized by bedforms stabilized by bacterial mats, extensive authigenic mineral crusts, and (or) thick organic flocs. Currents as high as 30 cm/sec were measured over that depth interval. Current-resuspension of surficial organic matter, activity of organisms, and transport to and from more oxygenated zones contribute to greater oxidation and poorer preservation of organic matter than occur under oxygen-deficient conditions. Phosphate-rich sediments occurred at depths of about 300 to 550 m on both transects. Nodular crusts cemented by carbonate-fluorapatite (CFA; phosphorite) or dolomite form within the OMZ. The crusts start by cementation of sediment near the sediment-water interface forming stiff but friable phosphatizes claystone "protocrusts". The protocrusts

  13. Interactions of Thalassia testudinum and sediment biogeochemsistry in Santa Rosa Sound, NW Florida

    EPA Science Inventory

    Northern Gulf of Mexico Thalassia testudinum biomass, leaf measurements, and shoot growth rates were determined during three surveys each from a different meadow over consecutive years, and correlated with sediment biogeochemical measurements by correlation analyses and multiple ...

  14. Budgeting postglacial sedimentation history on the Santa Cruz, California mid-continental shelf

    USGS Publications Warehouse

    Grossman, E.E.; Eittreim, S.L.; Hanes, D.M.; Field, M.E.; Edwards, B.D.; Fallon, S.J.; Anima, R.J.

    2003-01-01

    High-resolution seismic reflection profiling and surface texture mapping of the central California continental shelf, reveal a prominent subsurface reflector interpreted as a low stand erosion surface and an overlying mudbelt that covers 421 km2 of the mid-shelf in depths of 40-90 m. Radiometric and sedimentologic analyses of samples from vibracores taken along the seaward edge of the mudbelt show that initial deposition above the pre-Holocene erosion surface began ca. 14.5 ka. These data and model results of sea-level history, tectonics, and the Monterey Bay littoral sediment budget support the notion that the entire midshelf deposit was formed during the postglacial transgression. An alternative explanation, that <30% of the deposit is Holocene, requires that (1) sediment input is overestimated and/or loss is greatly underestimated, and (2) preservation on the shelf was significant despite deep and active wave scour observed in the form of rapid cliff and bedrock cutting early and late in the transgression. The difference between a basal age of ???14.5 ka and residence time of midshelf sediment (3,273 years), derived from dividing mudbelt volume by modern accumulation rate, implies: (1) significant sediment loss occurred since the mudbelt formed and/or (2) sediment accumulation has varied greatly over time. Although modern sediment budgets are relatively well constrained, it remains uncertain how well we can apply them to the past. An evolving model of sedimentation history explores the likelihood of changes in sediment supply, accumulation patterns, and depositional patterns owing to postglacial sea-level history and human land-use activities while providing important boundary conditions for modeling shoreface evolution.

  15. Analysis of methods to determine storage capacity of, and sedimentation in, Loch Lomond Reservoir, Santa Cruz County, California, 2009

    USGS Publications Warehouse

    McPherson, Kelly R.; Freeman, Lawrence A.; Flint, Lorraine E.

    2011-01-01

    In 2009, the U.S. Geological Survey, in cooperation with the City of Santa Cruz, conducted bathymetric and topographic surveys to determine the water storage capacity of, and the loss of capacity owing to sedimentation in, Loch Lomond Reservoir in Santa Cruz County, California. The topographic survey was done as a supplement to the bathymetric survey to obtain information about temporal changes in the upper reach of the reservoir where the water is shallow or the reservoir may be dry, as well as to obtain information about shoreline changes throughout the reservoir. Results of a combined bathymetric and topographic survey using a new, state-of-the-art method with advanced instrument technology indicate that the maximum storage capacity of the reservoir at the spillway altitude of 577.5 feet (National Geodetic Vertical Datum of 1929) was 8,646 ±85 acre-feet in March 2009, with a confidence level of 99 percent. This new method is a combination of bathymetric scanning using multibeam-sidescan sonar, and topographic surveying using laser scanning (LiDAR), which produced a 1.64-foot-resolution grid with altitudes to 0.3-foot resolution and an estimate of total water storage capacity at a 99-percent confidence level. Because the volume of sedimentation in a reservoir is considered equal to the decrease in water-storage capacity, sedimentation in Loch Lomond Reservoir was determined by estimating the change in storage capacity by comparing the reservoir bed surface defined in the March 2009 survey with a revision of the reservoir bed surface determined in a previous investigation in November 1998. This revised reservoir-bed surface was defined by combining altitude data from the 1998 survey with new data collected during the current (2009) investigation to fill gaps in the 1998 data. Limitations that determine the accuracy of estimates of changes in the volume of sedimentation from that estimated in each of the four previous investigations (1960, 1971, 1982, and 1998

  16. Planktonic and sediment-associated aerobic methanotrophs in two seep systems along the North American margin.

    PubMed

    Tavormina, Patricia L; Ussler, William; Orphan, Victoria J

    2008-07-01

    Methane vents are of significant geochemical and ecological importance. Notable progress has been made toward understanding anaerobic methane oxidation in marine sediments; however, the diversity and distribution of aerobic methanotrophs in the water column are poorly characterized. Both environments play an essential role in regulating methane release from the oceans to the atmosphere. In this study, the diversity of particulate methane monooxygenase (pmoA) and 16S rRNA genes from two methane vent environments along the California continental margin was characterized. The pmoA phylotypes recovered from methane-rich sediments and the overlying water column differed. Sediments harbored the greatest number of unique pmoA phylotypes broadly affiliated with the Methylococcaceae family, whereas planktonic pmoA phylotypes formed three clades that were distinct from the sediment-hosted methanotrophs and distantly related to established methanotrophic clades. Water column-associated phylotypes were highly similar between field sites, suggesting that planktonic methanotroph diversity is controlled primarily by environmental factors rather than geographical proximity. Analysis of 16S rRNA genes from methane-rich waters did not readily recover known methanotrophic lineages, with only a few phylotypes demonstrating distant relatedness to Methylococcus. The development of new pmo primers increased the recovery of monooxygenase genes from the water column and led to the discovery of a highly diverged monooxygenase sequence which is phylogenetically intermediate to Amo and pMMO. This sequence potentiates insight into the amo/pmo superfamily. Together, these findings lend perspective into the diversity and segregation of aerobic methanotrophs within different methane-rich habitats in the marine environment.

  17. Estimating suspended sediment concentrations in turbid coastal waters of the Santa Barbara Channel with SeaWiFS

    USGS Publications Warehouse

    Warrick, J.A.; Mertes, L.A.K.; Siegel, D.A.; Mackenzie, C.

    2004-01-01

    A technique is presented for estimating suspended sediment concentrations of turbid coastal waters with remotely sensed multi-spectral data. The method improves upon many standard techniques, since it incorporates analyses of multiple wavelength bands (four for Sea-viewing Wide Field of view Sensor (SeaWiFS)) and a nonlinear calibration, which produce highly accurate results (expected errors are approximately ±10%). Further, potential errors produced by erroneous atmospheric calibration in excessively turbid waters and influences of dissolved organic materials, chlorophyll pigments and atmospheric aerosols are limited by a dark pixel subtraction and removal of the violet to blue wavelength bands. Results are presented for the Santa Barbara Channel, California where suspended sediment concentrations ranged from 0–200+ mg l−1 (±20 mg l−1) immediately after large river runoff events. The largest plumes were observed 10–30 km off the coast and occurred immediately following large El Niño winter floods.

  18. Late Pleistocene valley fills source sediment flux of Tibetan Plateau margin rivers, Zanskar, India

    NASA Astrophysics Data System (ADS)

    Blöthe, J. H.; Munack, H.; Korup, O.; Fulop, R. H.; Codilean, A.; Fink, D.

    2015-12-01

    The Indus and its tributaries, one of Asia's largest river systems, drain the NW Himalaya and the Transhimalayan ranges that border the western Tibetan Plateau margin. From the internally drained low-relief areas of the Tibetan Plateau, local relief increases towards the Western Himalayan Syntaxis, where it exceeds 7 km. Simultaneously, average denudation rates rise from as little as 10 mm ka-1 at the Tibetan Plateau margin to rates of >1000 mm ka-1 close to the western Himalayan Syntaxis. In this rugged bedrock landscape, river valleys frequently alternate between deeply incised gorges and broad alluviated reaches. Vast fill terrace staircases of up to 400 m height above current river levels, and intercalated lake sediments point to repeated phases of incision and aggradation within the region. Despite a broad interest in a better understanding of mechanisms that modulate plateau erosion, age constraints on the generation of these impressive features remain sparse, though indicate mainly Pleistocene formation ages. Here we present new data from the More Plains section, a vast sedimentary fill, located in the headwaters of the Zanskar River, the largest tributary to the upper Indus. The vast sedimentary successions of the More Plains originally belonged to a former endorheic basin that has been tapped by the Zanskar River, today revealing a sedimentary exposures of >250 m thickness. We combine morphometric analysis and field based observations with 10Be surface exposure dating and basin-wide denudation rates to constrain the late Quaternary history of this setting. Analysis of a 10Be depth profile on top of the More Plains section indicate a surface exposure age of ~125 +/- 15 ka, which is supported by ages from nearby amalgamated surface samples. Grounding on a morphometric approach, we estimate that ~1.65-1.95 km3 were removed from this section by fluvial erosion since aggradation ceased, requiring a specific sediment yield of 85-100 t km-2 yr-1 averaged over the

  19. Diverse origins and pre-depositional histories of organic matter in contemporary Chinese marginal sea sediments

    NASA Astrophysics Data System (ADS)

    Tao, Shuqin; Eglinton, Timothy I.; Montluçon, Daniel B.; McIntyre, Cameron; Zhao, Meixun

    2016-10-01

    Marginal seas are estimated to account for up to 90% of organic carbon (OC) burial in marine sediments, and thus play an important role in global carbon cycle. However, comprehensive assessments of carbon budgets for marginal sea systems are challenging due to their inherent complexity, with spatial and temporal variability in carbon inputs and dispersal processes. We examine the Bohai Sea and Yellow Sea (BS-YS) in order to further our understanding of sedimentary OC delivery, translocation and accumulation in a shallow marginal sea system. Bulk properties and the content and isotopic compositions (Δ14C, δ13C) of source-specific plant wax n-alkyl lipid biomarkers were determined for a suite of surficial sediment samples. Variable δ13C values (-25.1‰ to -28.5‰) and contemporary radiocarbon ages of short-chain n-fatty acids (FAs; C16, C18) reflect modern autochthonous marine and/or fresh terrestrial plant input. In contrast, extremely depleted Δ14C values (-932‰ to -979‰) of short-chain n-alkanes (C16, C18) suggest a predominant input from sedimentary rocks (petrogenic OC) or petroleum. Abundance-weighted average δ13C and Δ14C values of long-chain leaf wax lipids (C26+28+30n-FAs, C24+26+28n-alkanols, C27+29+31n-alkanes) are -29.1 ± 1.1‰ to -30.2 ± 0.3‰, and -286 ± 150‰ to -442 ± 119‰, respectively, illustrating that terrestrial OC delivery is dominated by pre-aged (∼3000-5000 14C yrs) C3 vegetation sources. A coupled carbon-isotopic mixing model, based on the bulk and compound-specific biomarker δ13C and Δ14C values, is used to partition the BS-YS sedimentary OC into three components that reflect both origins and transport processes. For all sampling sites, 31-64% is modern/contemporary OC, 24-49% is pre-aged terrestrial OC, and 7-26% is fossil OC, the latter likely derived from both physical erosion of ancient sedimentary rocks and fossil fuel sources. Pre-aged soil OC is most prominent in front of the modern and old Huanghe (Yellow

  20. Trace metals and organochlorines in sediments near a major ocean outfall on a high energy continental margin (Sydney, Australia).

    PubMed

    Matthai, C; Birch, G F

    2000-12-01

    Sewage effluent from a large ocean outfall south of Sydney, southeastern Australia, is efficiently dispersed on this high energy continental margin. An enrichment of Ag, Cu, Pb and Zn is only detectable in the fine fraction (<62.5 microm) of sediment. Ag, Co, Cu, Ni, Pb and Zn in the bulk sample correlate strongly with the mud content of surficial sediment, making an identification of the anthropogenic trace metal source difficult using total sediment analyses. The concentrations of HCB and DDE in the total sediment are also slightly elevated near the outfall. In the vicinity of the outfall, the estimated sewage component in the fine fraction of sediment, using Ag, Cu and Zn in a conservative, two-endmember physical mixing model, is <5% and is <0.25% of the total sediment. A greater anthropogenic Pb component in the fine fraction (mean: 24.8%) of surficial sediment compared to Ag, Cu and Zn may suggest a source other than sewage to Sydney continental margin sediments.

  1. Organic Matter Sequestration in Oregon Margin Sediments: Tectonic, Climatic and Oceanographic Controls

    NASA Astrophysics Data System (ADS)

    Coccoli, C. A.; Goni, M. A.; Alleau, Y.; Smith, L.

    2014-12-01

    A combination of box, gravity and piston cores from a site on the upper slope off the Umpqua River in the central Oregon margin were used to create a high-resolution record of organic matter burial over the past ~13,000 years. Our objective is to understand how variations in precipitation intensity and frequency, tectonic uplift rates, and topographic relief affect the magnitude and composition of organic matter deposited along this margin. To examine the possible tectonic and climatic factors influencing the land-ocean relationship of Cascadia during the late Holocene, we measured the organic carbon content, carbon-nitrogen ratio, stable isotopic compositions of organic carbon, yields of lignin-derived and lipid-derived constituents, and mineral surface area of collected sediments from box, kasten and piston cores. Decreases in several organic constituents revealed a potential preferential degradation of marine organic matter over time. Lignin phenol abundances oscillated downcore, pointing towards changes in the provenance of terrigenous organic matter transported to this site. Primary component analysis (PCA) illustrated distinct marine and terrestrial organic matter-dominated segments of the record, which will be correlated to eustatic, tectonic and climatic forcings over the late Holocene.

  2. Single cell genomic study of Dehalococcoidetes species from deep-sea sediments of the Peruvian Margin.

    PubMed

    Kaster, Anne-Kristin; Mayer-Blackwell, Koshlan; Pasarelli, Ben; Spormann, Alfred M

    2014-09-01

    The phylum Chloroflexi is one of the most frequently detected phyla in the subseafloor of the Pacific Ocean margins. Dehalogenating Chloroflexi (Dehalococcoidetes) was originally discovered as the key microorganisms mediating reductive dehalogenation via their key enzymes reductive dehalogenases (Rdh) as sole mode of energy conservation in terrestrial environments. The frequent detection of Dehalococcoidetes-related 16S rRNA and rdh genes in the marine subsurface implies a role for dissimilatory dehalorespiration in this environment; however, the two genes have never been linked to each other. To provide fundamental insights into the metabolism, genomic population structure and evolution of marine subsurface Dehalococcoidetes sp., we analyzed a non-contaminated deep-sea sediment core sample from the Peruvian Margin Ocean Drilling Program (ODP) site 1230, collected 7.3 m below the seafloor by a single cell genomic approach. We present for the first time single cell genomic data on three deep-sea Chloroflexi (Dsc) single cells from a marine subsurface environment. Two of the single cells were considered to be part of a local Dehalococcoidetes population and assembled together into a 1.38-Mb genome, which appears to be at least 85% complete. Despite a high degree of sequence-level similarity between the shared proteins in the Dsc and terrestrial Dehalococcoidetes, no evidence for catabolic reductive dehalogenation was found in Dsc. The genome content is however consistent with a strictly anaerobic organotrophic or lithotrophic lifestyle.

  3. Single cell genomic study of Dehalococcoidetes species from deep-sea sediments of the Peruvian Margin

    PubMed Central

    Kaster, Anne-Kristin; Mayer-Blackwell, Koshlan; Pasarelli, Ben; Spormann, Alfred M

    2014-01-01

    The phylum Chloroflexi is one of the most frequently detected phyla in the subseafloor of the Pacific Ocean margins. Dehalogenating Chloroflexi (Dehalococcoidetes) was originally discovered as the key microorganisms mediating reductive dehalogenation via their key enzymes reductive dehalogenases (Rdh) as sole mode of energy conservation in terrestrial environments. The frequent detection of Dehalococcoidetes-related 16S rRNA and rdh genes in the marine subsurface implies a role for dissimilatory dehalorespiration in this environment; however, the two genes have never been linked to each other. To provide fundamental insights into the metabolism, genomic population structure and evolution of marine subsurface Dehalococcoidetes sp., we analyzed a non-contaminated deep-sea sediment core sample from the Peruvian Margin Ocean Drilling Program (ODP) site 1230, collected 7.3 m below the seafloor by a single cell genomic approach. We present for the first time single cell genomic data on three deep-sea Chloroflexi (Dsc) single cells from a marine subsurface environment. Two of the single cells were considered to be part of a local Dehalococcoidetes population and assembled together into a 1.38-Mb genome, which appears to be at least 85% complete. Despite a high degree of sequence-level similarity between the shared proteins in the Dsc and terrestrial Dehalococcoidetes, no evidence for catabolic reductive dehalogenation was found in Dsc. The genome content is however consistent with a strictly anaerobic organotrophic or lithotrophic lifestyle. PMID:24599070

  4. Seismo-turbidite Sedimentology: Implications for Active Tectonic Margin Stratigraphy and Sediment Facies Patterns

    NASA Astrophysics Data System (ADS)

    Nelson, C. H.; Goldfinger, C.; Gutierrez Pastor, J.; Polonia, A.; Van Daele, M. E.

    2014-12-01

    Earthquakes generate mass transport deposits (MTDs); megaturbidites (MTD overlain by coeval turbidite); multi-pulsed, stacked, and mud homogenite seismo-turbidites; tsunamites; and seiche deposits. The strongest (Mw 9) earthquake shaking signatures appear to create multi-pulsed individual turbidites, where the number and character of multiple coarse-grained pulses for correlative turbidites generally remain constant both upstream and downstream in different channel systems. Multiple turbidite pulses, that correlate with multiple ruptures shown in seismograms of historic earthquakes (e.g. Chile 1960, Sumatra 2004 and Japan 2011), support this hypothesis. The weaker (Mw = or < 8) (e.g. northern California San Andreas) earthquakes generate dominantly upstream simple fining-up (uni-pulsed) turbidites in single tributary canyons and channels; however, downstream stacked turbidites result from synchronously triggered multiple turbidity currents that deposit in channels below confluences of the tributaries. Proven tsunamites, which result from tsunami waves sweeping onshore and shallow water debris into deeper water, are a fine-grained turbidite cap over other seismo-turbidites. In contrast, MTDs and seismo-turbidites result from slope failures. Multiple great earthquakes cause seismic strengthening of slope sediment, which results in minor MTDs in basin floor turbidite system deposits (e.g. maximum run-out distances of MTDs across basin floors along active margins are up to an order of magnitude less than on passive margins). In contrast, the MTDs and turbidites are equally intermixed in turbidite systems of passive margins (e.g. Gulf of Mexico). In confined basin settings, earthquake triggering results in a common facies pattern of coeval megaturbidites in proximal settings, thick stacked turbidites downstream, and ponded muddy homogenite turbidites in basin or sub-basin centers, sometimes with a cap of seiche deposits showing bi-directional flow patterns.

  5. Increased continental-margin slumping frequency during sea-level lowstands above gas hydrate-bearing sediments

    SciTech Connect

    Paull, C.K.; Buelow, W.J.; Ussler, W. III; Borowski, W.S.

    1996-02-01

    We present {sup 14}C data on sediment samples from cores of the upper 7 m of the sediment column overlying a major continental-rise gas hydrate field on the southern Carolina Rise and inner Blake Ridge offshore the southeastern United States. The data show that glacial-age sediments are underrepresented in the cores. The observation is consistent with a previously predicted association between sea-level lowstands and increased frequency of sea-floor slumping on continental margins containing gas hydrates. 26 refs., 3 figs.

  6. Nd isotope calibration of core top sediments along the South African Margin

    NASA Astrophysics Data System (ADS)

    Jones, K. M.; Goldstein, S. L.; Hemming, S. R.; Hall, I.; Zahn, R.

    2006-12-01

    Nd isotope ratios in the authigenic ferromanganese fraction of deep-sea sediments show great promise as tracers of ocean circulation. Its designation as a focus tracer for the new GEOTRACES program requires a better understanding of the processes that affect seawater Nd isotope ratios and their transfer to sediments. In this context, the southern tip of Africa is an important location for inter-ocean exchange. There, the North Atlantic Deep Water (NADW) leaves the Atlantic system and flows northeastward, sandwiched by Antarctic Intermediate Water (AAIW) above and Antarctic Bottom Water (AABW) below. It is an ideal place to calibrate coretop samples against these water masses in the hopes of using the successful cores to constrain changes in paleocirculation. Water column samples and cores at various depths were collected during Cruise 154 of the RRS Charles Darwin during Dec.-Jan. 2003-2004 along the eastern margin of South Africa. We report the first results of Holocene coretop ferromanganese leachates from sediment cores at water depths ranging between 1010 and 3706 m, where ambient water masses range from AAIW through NADW-AABW mixtures. Thus, we expected the Nd isotope ratios to be high at AAIW and AABW depths and low at NADW depths, at values that compare favorably with published water column data from the south Atlantic and western Indian Oceans. A few samples showed Nd isotope ratios clearly different from seawater; these are from the submarine fan of the Tugela River and a region with documented slump deposits near East London. Filtering these out, the remaining samples display a distinct U-shape in a plot of ɛNd vs depth, with those samples from the NADW cores yielding the lowest Nd isotope ratios (ɛNd ~ -11.5 to -12.5) and those reflecting mixtures showing appropriately higher values. This was true despite slightly elevated Sr isotope ratios in all but one core. We calculated a synthetic seawater Nd depth profile from 1500m to 4000m depth with three end

  7. Magnetic fabric (AMS, AAR) of the Santa Marta batholith (northern Colombia) and the shear deformation along the Caribbean Plate margin

    NASA Astrophysics Data System (ADS)

    Salazar, Carlos A.; Bustamante, Camilo; Archanjo, Carlos J.

    2016-10-01

    Anisotropy of low-field magnetic susceptibility (AMS) and anhysteretic remanence (AAR) were measured in the Santa Marta Batholith formed by subduction of the Caribbean Plate beneath the northern South America. The batholith, elongated in the N-S direction, records multiple pulses of quartzdiorite to tonalite and granodiorite magmas between 58 and 49 Ma. The high mean magnetic susceptibility (4 × 10-3 SI) combined with thermomagnetic and partial magnetic remanence measurements indicate that the magnetic susceptibility depends on Ti-poor magnetite. AMS is defined by ellipsoids that are dominantly oblate. The foliation was used to distinguish a narrow band of E-trending magnetic structures that separate the batholith in two lobes. The southern lobe is characterized by foliations that are broadly parallel to the contact with the wall rocks, while the northern lobe by foliations oblique to the batholith elongation. Late tonalitic magmas dated at c. 50 Ma record, in turn, a fabric apparently controlled by E-trending tectonic events. Partial AAR indicates that the subfabrics of magnetite with different grain sizes are nearly parallel to AMS, therefore discarding the possibility of superposed fabrics with different orientations. The magnetic fabric pattern is consistent with a magma emplaced in an arc setting deformed by a dextral shear. Synthetic extensional shear bands localize the magmatic deformation along East-trending corridors that probably were exploited to emplace the late magmatic pulses. Accretion of the Eocene batholith and the Late Cretaceous metasedimentary host-rocks to the South American continent defines a major strike-slip shear suture that resulted from the oblique convergence of the Caribbean Plate.

  8. Modeling of depth to base of Last Glacial Maximum and seafloor sediment thickness for the California State Waters Map Series, eastern Santa Barbara Channel, California

    USGS Publications Warehouse

    Wong, Florence L.; Phillips, Eleyne L.; Johnson, Samuel Y.; Sliter, Ray W.

    2012-01-01

    Models of the depth to the base of Last Glacial Maximum and sediment thickness over the base of Last Glacial Maximum for the eastern Santa Barbara Channel are a key part of the maps of shallow subsurface geology and structure for offshore Refugio to Hueneme Canyon, California, in the California State Waters Map Series. A satisfactory interpolation of the two datasets that accounted for regional geologic structure was developed using geographic information systems modeling and graphics software tools. Regional sediment volumes were determined from the model. Source data files suitable for geographic information systems mapping applications are provided.

  9. Deformation from the 1989 Loma Prieta earthquake near the southwest margin of the Santa Clara Valley, California

    USGS Publications Warehouse

    Schmidt, Kevin M.; Ellen, Stephen D.; Peterson, David M.

    2014-01-01

    To gain additional measurement of any permanent ground deformation that accompanied this damage, we compiled and conducted post-earthquake surveys along two 5-km lines of horizontal control and a 15-km level line. Measurements of horizontal distortion indicate approximately 0.1 m shortening in a NE-SW direction across the valley margin, similar to the amount measured in the channel lining. Evaluation of precise leveling by the National Geodetic Survey showed a downwarp, with an amplitude of >0.1 m over a span of >12 km, that resembled regional geodetic models of coseismic deformation. Although the leveling indicates broad, regional warping, abrupt discontinuities characteristic of faulting characterize both the broad-scale distribution of damage and the local deformation of the channel lining. Reverse movement largely along preexisting faults and probably enhanced significantly by warping combined with enhanced ground shaking, produced the documented coseismic ground deformation.

  10. Methane Production In Forearc Sediments At The Costa Rican Convergent Margin

    NASA Astrophysics Data System (ADS)

    Cardace, D.; Morris, J. D.; Peacock, A.; White, D. C.

    2004-12-01

    Plate tectonics creates suitable habitats for deep biosphere organisms, affecting the distribution of biological communities on Earth. Subduction zones, where crustal materials return to the planetary interior through plate convergence, expose active microbial communities in subducting seafloor sediments to a fresh chemical inventory as diagenesis, metamorphic reactions, and tectonically-induced fluid flow alter sediments and surrounding porewaters. The plate interface (the decollement) experiences persistent geochemical flux of light hydrocarbon- and metal-bearing fluids from depth. This project (1) examines the habitability of the decollement zone at the Costa Rican convergent margin from a geochemical perspective, (2) uses lipid biomarkers to describe biomass distribution in sediment samples adjacent to and within the decollement, and (3) cites methanogenesis as a likely metabolic strategy employed by the resident microbial community. Sterile plugs of sediment were recovered from cores taken during Leg 205 of the Ocean Drilling Program, in the Middle America Trench off Costa Rica. Samples are from the incoming carbonate section of Site 1253 at 370-437 meters below seafloor (mbsf), in the forearc sedimentary wedge at Site 1255 at 134-145 mbsf, and around an upper fault (153-220 mbsf) and in the decollement zone (305-366 mbsf) at Site 1254. Drilling mud and fluid were sampled to monitor potential microbial contamination. Samples were immediately frozen at -80ºC. Prior to analysis, samples were freeze-dried in preparation for serial extraction of DNA and lipids. DNA was identified by fluorometry in 13 of 26 samples tested. The DNA was screened for methanogens by real time polymerase chain reaction (PCR), employing ME1 and ME2 primers that amplify a 0.75-kb region of the alpha-subunit gene for methyl coenzyme M reductase (MCR). Methanogen-specific genes were detected in DNA extracted from one Site 1253 sample (at 436.9 mbsf in the basal carbonates) and four Site

  11. Microbial methanogenesis in the sulfate-reducing zone of surface sediments traversing the Peruvian margin

    NASA Astrophysics Data System (ADS)

    Maltby, J.; Sommer, S.; Dale, A. W.; Treude, T.

    2015-09-01

    We studied the concurrence of methanogenesis and sulfate reduction in surface sediments (0-25 cm below sea floor, cmbsf) at six stations (70, 145, 253, 407, 770 and 1024 m) along the Peruvian margin (12° S). This oceanographic region is characterized by high carbon export to the seafloor, creating an extensive oxygen minimum zone (OMZ) on the shelf, both factors that could favor surface methanogenesis. Sediments sampled along the depth transect traversed areas of anoxic and oxic conditions in the bottom-near water. Net methane production (batch incubations) and sulfate reduction (35S-sulfate radiotracer incubation) were determined in the upper 0-25 cmbsf of multicorer cores from all stations, while deep hydrogenotrophic methanogenesis (> 30 cmbsf, 14C-bicarbonate radiotracer incubation) was determined in two gravity cores at selected sites (78 and 407 m). Furthermore, stimulation (methanol addition) and inhibition (molybdate addition) experiments were carried out to investigate the relationship between sulfate reduction and methanogenesis. Highest rates of methanogenesis and sulfate reduction in the surface sediments, integrated over 0-25 cmbsf, were observed on the shelf (70-253 m, 0.06-0.1 and 0.5-4.7 mmol m-2 d-1, respectively), while lowest rates were discovered at the deepest site (1024 m, 0.03 and 0.2 mmol m-2 d-1, respectively). The addition of methanol resulted in significantly higher surface methanogenesis activity, suggesting that the process was mostly based on non-competitive substrates, i.e., substrates not used by sulfate reducers. In the deeper sediment horizons, where competition was probably relieved due to the decline of sulfate, the usage of competitive substrates was confirmed by the detection of hydrogenotrophic activity in the sulfate-depleted zone at the shallow shelf station (70 m). Surface methanogenesis appeared to be correlated to the availability of labile organic matter (C / N ratio) and organic carbon degradation (DIC production

  12. Microbial methanogenesis in the sulfate-reducing zone of surface sediments traversing the Peruvian margin

    NASA Astrophysics Data System (ADS)

    Maltby, J.; Sommer, S.; Dale, A. W.; Treude, T.

    2016-01-01

    We studied the concurrence of methanogenesis and sulfate reduction in surface sediments (0-25 cm below sea floor) at six stations (70, 145, 253, 407, 990 and 1024 m) along the Peruvian margin (12° S). This oceanographic region is characterized by high carbon export to the seafloor creating an extensive oxygen minimum zone (OMZ) on the shelf, both factors that could favor surface methanogenesis. Sediments sampled along the depth transect traversed areas of anoxic and oxic conditions in the bottom-near water. Net methane production (batch incubations) and sulfate reduction (35S-sulfate radiotracer incubation) were determined in the upper 0-25 cm b.s.f. of multiple cores from all stations, while deep hydrogenotrophic methanogenesis (> 30 cm b.s.f., 14C-bicarbonate radiotracer incubation) was determined in two gravity cores at selected sites (78 and 407 m). Furthermore, stimulation (methanol addition) and inhibition (molybdate addition) experiments were carried out to investigate the relationship between sulfate reduction and methanogenesis.

    Highest rates of methanogenesis and sulfate reduction in the surface sediments, integrated over 0-25 cm b.s.f., were observed on the shelf (70-253 m, 0.06-0.1 and 0.5-4.7 mmol m-2 d-1, respectively), while lowest rates were discovered at the deepest site (1024 m, 0.03 and 0.2 mmol m-2 d-1, respectively). The addition of methanol resulted in significantly higher surface methanogenesis activity, suggesting that the process was mostly based on non-competitive substrates - i.e., substrates not used by sulfate reducers. In the deeper sediment horizons, where competition was probably relieved due to the decrease of sulfate, the usage of competitive substrates was confirmed by the detection of hydrogenotrophic activity in the sulfate-depleted zone at the shallow shelf station (70 m).

    Surface methanogenesis appeared to be correlated to the availability of labile organic matter (C / N ratio) and organic carbon

  13. Coarse-grained sediment delivery and distribution in the Holocene Santa Monica Basin, California: Implications for evaluating source-to-sink flux at millennial time scales

    USGS Publications Warehouse

    Romans, B.W.; Normark, W.R.; McGann, M.M.; Covault, J.A.; Graham, S.A.

    2009-01-01

    Utilizing accumulations of coarse-grained terrigenous sediment from deep-marine basins to evaluate the relative contributions of and history of controls on sediment flux through a source-to-sink system has been difficult as a result of limited knowledge of event timing. In this study, six new radiocarbon (14C) dates are integrated with five previously published dates that have been recalibrated from a 12.5-m-thick turbidite section from Ocean Drilling Program (ODP) Site 1015 in Santa Monica Basin, offshore California. This borehole is tied to high-resolution seismic-reflection profiles that cover an 1100 km2 area of the middle and lower Hueneme submarine fan and most of the basin plain. The resulting stratigraphic framework provides the highest temporal resolution for a thick-bedded Holocene turbidite succession to date, permitting an evaluation of source-to-sink controls at millennial (1000 yr) scales. The depositional history from 7 ka to present indicates that the recurrence interval for large turbidity-current events is relatively constant (300-360 yr), but the volume of sediment deposited on the fan and in the basin plain has increased by a factor of 2 over this period. Moreover, the amount of sand per event on the basin plain during the same interval has increased by a factor of 7. Maps of sediment distribution derived from correlation of seismic-reflection profiles indicate that this trend cannot be attributed exclusively to autogenic processes (e.g., progradation of depocenters). The observed variability in sediment accumulation rates is thus largely controlled by allogenic factors, including: (1) increased discharge of Santa Clara River as a result of increased magnitude and frequency of El Ni??o-Southern Oscillation (ENSO) events from ca. 2 ka to present, (2) an apparent change in routing of coarse-grained sediment within the staging area at ca. 3 ka (i.e., from direct river input to indirect, littoral cell input into Hueneme submarine canyon), and (3

  14. 14C and 13C characteristics of higher plant biomarkers in Washington margin surface sediments

    NASA Astrophysics Data System (ADS)

    Feng, Xiaojuan; Benitez-Nelson, Bryan C.; Montluçon, Daniel B.; Prahl, Fredrick G.; McNichol, Ann P.; Xu, Li; Repeta, Daniel J.; Eglinton, Timothy I.

    2013-03-01

    Plant wax lipids and lignin phenols are the two most common classes of molecular markers that are used to trace vascular plant-derived OM in the marine environment. However, their 13C and 14C compositions have not been directly compared, which can be used to constrain the flux and attenuation of terrestrial carbon in marine environment. In this study, we describe a revised method of isolating individual lignin phenols from complex sedimentary matrices for 14C analysis using high pressure liquid chromatography (HPLC) and compare this approach to a method utilizing preparative capillary gas chromatography (PCGC). We then examine in detail the 13C and 14C compositions of plant wax lipids and lignin phenols in sediments from the inner and mid shelf of the Washington margin that are influenced by discharge of the Columbia River. Plant wax lipids (including n-alkanes, n-alkanoic (fatty) acids, n-alkanols, and n-aldehydes) displayed significant variability in both δ13C (-28.3‰ to -37.5‰) and Δ14C values (-204‰ to +2‰), suggesting varied inputs and/or continental storage and transport histories. In contrast, lignin phenols exhibited similar δ13C values (between -30‰ and -34‰) and a relatively narrow range of Δ14C values (-45‰ to -150‰; HPLC-based measurement) that were similar to, or younger than, bulk OM (-195‰ to -137‰). Moreover, lignin phenol 14C age correlated with the degradation characteristics of this terrestrial biopolymer in that vanillyl phenols were on average ˜500 years older than syringyl and cinnamyl phenols that degrade faster in soils and sediments. The isotopic characteristics, abundance, and distribution of lignin phenols in sediments suggest that they serve as promising tracers of recently biosynthesized terrestrial OM during supply to, and dispersal within the marine environment. Lignin phenol 14C measurements may also provide useful constraints on the vascular plant end member in isotopic mixing models for carbon source

  15. Survival Of Magnetic Paleoclimatic Signals From Shallow To Deep Water Marine Redoxomorphic Sediments Across The Northwest Iberian Continental Margin

    NASA Astrophysics Data System (ADS)

    Mohamed Falcon, K. J.; Rey, D.; Rubio, B.

    2013-05-01

    The magnetic properties of marine sediments on the North Atlantic Iberian continental Margin are strongly dependent on the organic matter input to the sediments and the onset of reductive diagenesis. An onshore-offshore gradient in the intensity of early diagenesis was recently described for the Ría de Vigo, matched by similar patterns in the adjacent rias of Pontevedra and Muros. In the ria environments of NW Iberia, early diagenetic dissolution of magnetic minerals can lead to magnetite half-lives of a few decades, and virtually obliterates any paleoenvironmental signal carried by magnetic minerals, rendering magnetic properties especially useful for the study of early diagenesis dynamics. Early diagenesis has also been identified in sediments of the adjacent continental shelf and deeper environments of the Galician Bank and Iberian Abyssal Plain. However, in these settings, slower dissolution of magnetic minerals allows the preservation of paleoclimatic signatures on different temporal scales. For instance, magnetic properties of continental shelf sediments reveal periods of enhanced rainfall and continental sediment input to the shelf, coincident with the Roman Warm Period and Medieval Climatic Optimum. On the contrary, cold periods are associated with less detrital input. Furthermore, levels of intensified diagenesis are also recorded during cold periods, which have been interpreted as periods of intensified coastal upwelling probably related to long-term North Atlantic Oscillation positive state. At the Galician Bank and Iberian Abyssal Plain sediments early diagenesis is also pervasive, although a paleoceanographic record of changes in the concentration of magnetic minerals transported by water masses flowing from the Portuguese Margin can still be identified. In addition to the progressive dissolution of magnetic minerals with depth, bulk magnetic properties in these deep marine settings show strong dependence on the pelagic carbonate sedimentation and low

  16. Phylogenetic and functional diversity of microbial communities associated with subsurface sediments of the Sonora Margin, Guaymas Basin.

    PubMed

    Vigneron, Adrien; Cruaud, Perrine; Roussel, Erwan G; Pignet, Patricia; Caprais, Jean-Claude; Callac, Nolwenn; Ciobanu, Maria-Cristina; Godfroy, Anne; Cragg, Barry A; Parkes, John R; Van Nostrand, Joy D; He, Zhili; Zhou, Jizhong; Toffin, Laurent

    2014-01-01

    Subsurface sediments of the Sonora Margin (Guaymas Basin), located in proximity of active cold seep sites were explored. The taxonomic and functional diversity of bacterial and archaeal communities were investigated from 1 to 10 meters below the seafloor. Microbial community structure and abundance and distribution of dominant populations were assessed using complementary molecular approaches (Ribosomal Intergenic Spacer Analysis, 16S rRNA libraries and quantitative PCR with an extensive primers set) and correlated to comprehensive geochemical data. Moreover the metabolic potentials and functional traits of the microbial community were also identified using the GeoChip functional gene microarray and metabolic rates. The active microbial community structure in the Sonora Margin sediments was related to deep subsurface ecosystems (Marine Benthic Groups B and D, Miscellaneous Crenarchaeotal Group, Chloroflexi and Candidate divisions) and remained relatively similar throughout the sediment section, despite defined biogeochemical gradients. However, relative abundances of bacterial and archaeal dominant lineages were significantly correlated with organic carbon quantity and origin. Consistently, metabolic pathways for the degradation and assimilation of this organic carbon as well as genetic potentials for the transformation of detrital organic matters, hydrocarbons and recalcitrant substrates were detected, suggesting that chemoorganotrophic microorganisms may dominate the microbial community of the Sonora Margin subsurface sediments.

  17. Phylogenetic and Functional Diversity of Microbial Communities Associated with Subsurface Sediments of the Sonora Margin, Guaymas Basin

    PubMed Central

    Vigneron, Adrien; Cruaud, Perrine; Roussel, Erwan G.; Pignet, Patricia; Caprais, Jean-Claude; Callac, Nolwenn; Ciobanu, Maria-Cristina; Godfroy, Anne; Cragg, Barry A.; Parkes, John R.; Van Nostrand, Joy D.; He, Zhili; Zhou, Jizhong; Toffin, Laurent

    2014-01-01

    Subsurface sediments of the Sonora Margin (Guaymas Basin), located in proximity of active cold seep sites were explored. The taxonomic and functional diversity of bacterial and archaeal communities were investigated from 1 to 10 meters below the seafloor. Microbial community structure and abundance and distribution of dominant populations were assessed using complementary molecular approaches (Ribosomal Intergenic Spacer Analysis, 16S rRNA libraries and quantitative PCR with an extensive primers set) and correlated to comprehensive geochemical data. Moreover the metabolic potentials and functional traits of the microbial community were also identified using the GeoChip functional gene microarray and metabolic rates. The active microbial community structure in the Sonora Margin sediments was related to deep subsurface ecosystems (Marine Benthic Groups B and D, Miscellaneous Crenarchaeotal Group, Chloroflexi and Candidate divisions) and remained relatively similar throughout the sediment section, despite defined biogeochemical gradients. However, relative abundances of bacterial and archaeal dominant lineages were significantly correlated with organic carbon quantity and origin. Consistently, metabolic pathways for the degradation and assimilation of this organic carbon as well as genetic potentials for the transformation of detrital organic matters, hydrocarbons and recalcitrant substrates were detected, suggesting that chemoorganotrophic microorganisms may dominate the microbial community of the Sonora Margin subsurface sediments. PMID:25099369

  18. Continental-Margin Processes Recorded in Shelf and Canyon Sediments. Sediment Deposition, Erosion and Accumulation on a Tidal Flat Adjacent to a River Mouth

    DTIC Science & Technology

    2007-01-01

    Sequence Stratigraphy , IAS Spec. Pub. 37, Blackwell Publishing, Oxford, 549 pp. (2007). C.A. Nittrouer, J.A. Austin, M.E. Field, J.H. Kravitz, J.P.M...Continental Margin Sedimentation: From Sediment Transport to Sequence Stratigraphy , IAS Spec. Pub. 37, Blackwell Publishing, Oxford, 1-48 (2007... Stratigraphy , IAS Spec. Pub. 37, Blackwell Publishing, Oxford, 157-212 (2007). L.F. Pratson, C.A. Nittrouer, P.L.Wiberg, M.S. Steckler, J.B. Swenson

  19. Potential for generation of natural gas in sediments of the convergent margin of the Aleutian Trench Area

    SciTech Connect

    Kvenvolden, K.A.; von Huene, R.

    1983-01-01

    Sediment being subducted in the eastern part of the convergent margin of the Aleutian Trench has a potential to generate large volumes of natural gas, perhaps as much as 2.8 x 10/sup 6/ m/sup 3/ of methane per km/sup 3/ of sediment, even though the content of organic carbon in the sediment is very low, averaging about 0.4%. This high potential for gas generation results primarily from the enormous volume of sediment undergoing subduction. Along the eastern Aleutian Arc-Trench system a 3-km thick sheet of sediment is being subducted at a rate of about 60 km per million years. We estimate, based on considerations of the stability requirements for gas hydrates observed as anomalous reflectors in some of our seismic records, and on one measurement in a deep well, that the geothermal gradient in this region is about 30/sup 0/C/km. Such a gradient suggests a temperature regime in which the maximum gas generation in the subducting sediment occurs beneath the upper slope. Thus the sediment of the upper slope, as opposed to that of the shelf and lower slope, could be the most prospective for gas accumulation if suitable reservoirs are present. 40 refs., 11 figs., 3 tabs.

  20. Morphology, seismic characteristics and development of the sediment dispersal system along the Taiwan-Luzon convergent margin

    NASA Astrophysics Data System (ADS)

    Hsiung, Kan-Hsi; Su, Chih-Chieh; Yu, Ho-Shing; Chang, Jih-Hsin

    2015-12-01

    The sediment dispersal system along the convergent margin between Taiwan and Luzon links the terrestrial and shallow marine sediments from the source areas nearby Taiwan orogen to the ultimate sink in the northern Manila Trench. Using seismic reflection profiles and bathymetry mapping we determine three distinct morpho-tectonic features of the Penghu Submarine Canyon, deep-sea Penghu Channel and oceanic Manila Trench which are linearly interconnected to form a longitudinal sediment route. Seismic profiles show characteristic features of truncated strata along canyon walls and cut-and-fills in canyon bottom. Deformed and uplifted bathymetric ridges and troughs and volcanic intrusions with unstratified and chaotic seismic facies are associated with the Penghu Channel. The seismic facies of the trench wedge are characterized by sub-horizontal and conformable layers of sediment stacking upwards to the trench floor. The sediment wedge adjacent to the inner lower slope is deformed to blind folds and thrust faults as precursors of the accretionary prism. The most prominent seismic characteristics is wide-spread undulating reflectors on the seafloor along the west edge of the sediment dispersal system and the toe of the South China Sea Basin floor, suggesting a large sediment wave field with a turbidity currents origin. The location, orientation and geometry of this sediment routing system are mainly controlled by underlying tectonics in progressive changes from arc-continental collision in transition to subduction. The deep-sea Penghu Channel is formed by compression in transitional zone of the North Luzon Ridge region, neither subduction nor channel erosion. The sediments in northern Manila Trench are mainly transported by turbidity currents via the upslope deep-sea Penghu Channel and Penghu Canyon and trench axis is filled up to a flat-floor trench wedge without sediment ponding. A four-stage development of sediment dispersal system in Taiwan-Luzon convergent margin

  1. Geological and Sediment Thickness Data Sources From the U.S. Continental Margins

    NASA Astrophysics Data System (ADS)

    Hutchinson, D. R.; Childs, J. R.; Edgar, N. T.; Barth, G.; Hammar-Klose, E.; Dadisman, S. V.; Rowland, R.

    2005-12-01

    Although the United States has not yet ratified the United Nations Convention on the Law of the Sea (UNCLOS), work has begun to assess the geophysical and geological data sources that might be applied to an extended continental shelf submission under Article 76 of the UNCLOS. The U.S. Geological Survey, as a follow-up to the Congressional Report published by the University of New Hampshire on data relevant to a potential U.S. submission (Mayer and others, 2002), has identified existing seismic reflection, seismic refraction, and drill-hole data on the U.S. margins for the areas where an extended continental shelf submission could be considered. This work complements ongoing NOAA efforts to map the foot-of-the-slope. The USGS compilation includes more than 80,000 km of multichannel seismic data, 70,000 km of single-channel seismic reflection data, 25 refraction experiments, and 12 drill holes that penetrate to basement. Data quality varies according to year collected and acquisition system used. Data coverage is generally excellent within the 200-nm EEZ boundary, but new data will be required to adequately assess sediment thickness in the area beyond 200-nm in some of the poorly surveyed regions (e.g., the Arctic). Velocity and drill-hole control for deeper sedimentary units is generally poor; this deficiency will also need to be addressed in new data gathering efforts. Subsea mineral resources that might exist in the region of an extended continental shelf vary by region and include conventional hydrocarbons, gas hydrate, ferro-manganese crusts and nodules, and possibly phosphorite deposits. On-going efforts are directed at interpreting these data with reference to UNCLOS criteria and guidelines, as well as evaluating how recent submissions to the United Nations by other States might affect a possible U.S. submission.

  2. Fresh and Salt Water Distribution in Passive Margin Sediments: Insights from Iodp Expedition 313 ON the New Jersey Margin

    NASA Astrophysics Data System (ADS)

    Lofi, J.; Inwood, J.; Proust, J.; Monteverde, D.; Loggia, D.; Basile, C.; Hayashi, T.; Stadler, S.; Fehr, A.; Pezard, P.

    2012-12-01

    For the first time in the history of international scientific drillings, the Integrated Ocean Drilling Program (IODP) mission-specific platform (MSP) Expedition 313 drilled three 631-755 m-deep boreholes on the middle shelf of a clastic passive margin. This expedition gathered a full set of geophysical data tied to drillcores with 80% of recovery. It offers a unique opportunity to access the internal structure of a siliciclastic system, at scales ranging from the matrix to the margin, and to correlate the geological skeleton with the spatial distribution and salinity of saturating fluids. In addition to the discovery of very low salinity pore water (<3g/l) at depths exceeding 400 m below the middle shelf, this expedition provides evidence for a multi-layered reservoir, with fresh/brackish water intervals alternating vertically with salty intervals. Our observations suggest that the processes controlling salinity distribution are strongly influenced by lithology, porosity and permeability. Saltier pore waters are recovered in less porous, more permeable, intervals whereas fresher pore waters are recovered in more porous, less permeable, intervals. Pore water concentrations are inversely correlated to the Thorium content, with high salinities in low Th intervals (i.e. sandy formations). The transition from fresher to saltier intervals is often marked by cemented horizons acting as permeability barrier. In the lower part of some holes, the salinity varies independently of lithology, suggesting different mechanisms and/or sources of salinity. We have developed a 2D model of permeability distribution along a dip transect of the margin, extrapolated from combined clinoform geometries observed on seismic data and sedimentary facies described on cores. This model clearly illustrates the importance of taking into account the spatial heterogeneity of geological system at several scales. Lithology reflects permeability at a small scale whereas seismic facies and system tracts

  3. Geoacoustic characteristics at the DH-2 long-core sediments in the Korean continental margin of the East Sea

    NASA Astrophysics Data System (ADS)

    Ryang, Woo Hun; Kim, Seong Pil; Hahn, Jooyoung

    2015-04-01

    A long core of 27.2 m was acquired at the DH-2 site (37°34.355'N and 129°19.516'E) in the Korean continental margin of the western East Sea. The core site is located near the Donghae City and the water depth is 316.6 m deep. The long-core sediment was recovered using the Portable Remotely Operated Drill (PROD), a fully contained drilling system, remotely operated at the seafloor. The recovered core sediments were analyzed for physical, sedimentological, and geoacoustic properties mostly at 10~30 cm intervals. Based on the long-core data with subbottom and air-gun profiles at the DH-2 core site, geoacoustic characteristics of the deeper sedimentary successions were firstly investigated in the Korean continental margin of the western East Sea. The geoacoustic measurements comprise 86 P-wave velocities and 76 attenuation values. These geoacoustic characteristics of the DH-2 long core probably contribute for reconstruction of geoacoustic models reflecting vertical and lateral variability of acoustic properties in the Korean continental margin of the western East Sea. Keywords: long core, geoacoustic, East Sea, continental margin, P-wave speed Acknowledgements: This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2010-0025733) and by the Agency of Defense Development (UD140003DD).

  4. Tectonically active sediment dispersal system in SW Taiwan margin with emphasis on the Gaoping (Kaoping) Submarine Canyon

    NASA Astrophysics Data System (ADS)

    Yu, Ho-Shing; Chiang, Cheng-Shing; Shen, Su-Min

    2009-03-01

    The sediment dispersal system in southwestern Taiwan margin consists of two main parts: the subaerial drainage basin and the offshore receiving marine basin. In plan view, this sediment dispersal system can be further divided into five geomorphic units: (1) the Gaoping (formerly spelled Kaoping) River drainage basin, (2) the Gaoping (Kaoping) Shelf, (3) the Gaoping (Kaoping) Slope, (4) the Gaoping (Kaoping) Submarine Canyon and (5) the Manila Trench in the northernmost South China Sea. The Gaoping River drainage basin is a small (3250 km 2), tectonically active and overfilled foreland basin, receiving sediments derived from the uprising Central Range of Taiwan with a maximum elevation of 3952 m. The Gaoping Submarine Canyon begins at the mouth of the Gaoping River, crosses the narrow Gaoping Shelf (~ 10 km) and the Gaoping Slope, and finally merges into the northern termination of the Manila Trench over a distance of ~ 260 km. The SW Taiwan margin dispersal system is characterized by a direct river-canyon connection with a narrow shelf and frequent episodic sediment discharge events in the canyon head. In a regional source to sink scheme, the Gaoping River drainage basin is the primary source area, the Gaoping Shelf being the sediment bypass zone and the Gaoping Slope being the temporary sink and the Manila Trench being the ultimate sink of the sediment from the Taiwan orogen. It is inferred from seismic data that the outer shelf and upper slope region can be considered as a line source for mass wasting deposits delivered to the lower Gaoping Slope where small depressions between diapiric ridges are partially filled with sediment or are empty. At present, recurrent hyperpycnal flows during the flood seasons are temporarily depositing sediments mainly derived from the Gaoping River in the head of the Gaoping Submarine Canyon. On the decadal and century timescales, sediments temporarily stored in the upper reach are removed over longer timescales probably by

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

    NASA Astrophysics Data System (ADS)

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

    2007-05-01

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

  6. Strong Acid Mixture and Sequential Geochemical Arsenic Extractions in Surface Sediments from the Santa Maria La Reforma Coastal Lagoon, Mexico: A Bioavailability Assessment.

    PubMed

    Rivera-Hernández, José R; Green-Ruiz, Carlos

    2016-02-01

    Thirty-three sediment samples were collected from the Santa Maria La Reforma coastal lagoon and digested by way of a strong acid mixture and sequential arsenic (As)-extraction method to determine the arsenic (As) content and bioavailability. The As content was determined by atomic fluorescence spectrometry. In addition, grain-size analyses were performed, and organic carbon, carbonate, and iron (Fe) and manganese (Mn) concentrations were determined. Fe and Mn determination was performed by atomic absorption spectroscopy. A Pearson correlation matrix and As enrichment factors were calculated. Sediment concentrations from Santa Maria La Reforma ranged from 3.6 to 25 µg As g(-1) with an average of 13.4 ± 7.6 µg As g(-1). The highest values were observed in the northern (Playa Colorada), north-central (Mocorito River discharge zone), and southern zones ("El Tule" agricultural drain). Most samples were classified as exhibiting no or minor As enrichment and were lower than the threshold effect level (TEL; 7.24 µg g(-1)) for biota (MacDonald et al. in Ecotoxicology 5:253-278, 1996). Low bioavailable As values (<3 %) were measured in the majority of the sediment. The highest As percentages were associated with the oxyhydroxide fraction (F5). The results indicate that As bioavailability is negligible.

  7. Spatial and temporal variability in sediment deposition and seabed character on the Waipaoa River margin, New Zealand

    NASA Astrophysics Data System (ADS)

    Walsh, J. P.; Corbett, D. R.; Kiker, J. M.; Orpin, A. R.; Hale, R. P.; Ogston, A. S.

    2014-09-01

    The stratigraphic record is the manifestation of a wide range of processes, interactions and responses to environmental drivers. Understanding the functioning of river sediment dispersal systems is necessary to determine the fate of sediment and associated material in the marine environment and differentiate key influences in the development of the stratigraphic record. To that end, this study uses sediment cores collected on four successive cruises (January, May and September 2010 and February 2011) on the Waipaoa River margin, New Zealand, to provide insight into spatial and temporal variability in sediment deposition and seabed character. The Waipaoa River discharges a large sediment load into an energetic coast that has a complex margin morphology. Several flood and wave events occurred during the study, and sedimentation varied spatially and temporally. X-radiographs and short-lived radioisotopes indicate emplacement of new event layers prior to all cruises. Notable variation in surficial seabed character (grain-size composition, loss-on-ignition percentage) was apparent on the inner shelf (water depths <40 m), but mid-shelf areas and seaward had more homogeneous sediment properties. 7Be inventories indicate variable patterns of deposition related to fluvial and oceanographic conditions prior to cruises. Ephemeral sediment storage occurs on the inner-shelf of Poverty Bay, into which the Waipaoa River discharges directly, and subsequent export and dispersal patterns are linked to the relative timing and size of flood and wave events. Surficial deposits with characteristics of fluid muds and wave-enhanced sediment gravity flows were noted at some (<25 sites total) mid-shelf and shallower sites from all cruises. During the last cruise considerable inter- and intra-site seabed variability occurred in the interbedded river-proximal inner-shelf deposits over spatial scales of less than a few kilometers. Evidence from earlier sidescan data infer that this could be

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    In 2010 the MD179 project was undertaken by the Marion Dufresne aiming at recovery of deep seated gas and gas hydrate, methane induced carbonate, and deep sediments in order to develop the geologic model of gas hydrate accumulation and evaluate the possible environmental impact of gas hydrate for the last glacial-interglacial cycles. Sediment samples below the seafloor were obtained in the Umitaka Spur, Joetsu Channel, Toyama Trough, Japan Basin, Nishi Tsugaru and Okushiri Ridge areas by the cruise. Small amounts of sandy sediment have been retrieved as thin intercalations in Pleistocene and Holocene silty layers, where trace fossils and strong bioturbations are commonly observed. Those sandy sediments consist of very fine- to fine-grained sand grains, and are sometimes tuffaceous. Pore-size distribution measurements and thin-section observations of these arenite sands were carried out, which indicates that porosities of silty sediments are around 50 % but those of arenites range from 42 to 52 %, of which mean pore sizes and permeabilities are larger than those of silty sediments. These coarser sediments might have been transported approximately around 3 to 30 ka according to the tephra ages, where supplying sediments might have not been abundant due to sea level fluctuation during the Pleistocene ice age. While the presence of gas hydrate in intergranular pores of arenite sands has not been confirmed, the soupy occurrence in recovered sediments may strongly indicate the presence of gas hydrate filling the intergranular pore system of arenite sands that is called pore-space hydrates. They have been recognized till now in the Mallik as well as in the Nankai Trough areas, which are considered to be common even in the subsurface sandy sediments at the eastern margin of Japan Sea. Time of deposition of coarse-grained sediments can be recognized by the thermoluminescence (TL) dating method. The TL dating works on the principle that materials containing naturally

  9. Using ammonium pore water profiles to assess stoichiometry of deep remineralization processes in methanogenic continental margin sediments

    NASA Astrophysics Data System (ADS)

    Burdige, David J.; Komada, Tomoko

    2013-05-01

    many continental margin sediments, a deep reaction zone exists which is separated from remineralization processes near the sediment surface. Here, methane diffuses upward to a depth where it is oxidized by downwardly diffusing sulfate. However, the methane sources that drive this anaerobic oxidation of methane (AOM) in the sulfate-methane transition zone (SMT) may vary among sites. In particular, these sources can be thought of as either (i) "internal" sources from in situ methanogenesis (regardless of where it occurs in the sediment column) that are ultimately coupled to organic matter deposition and burial, or (ii) "external" sources such as hydrocarbon reservoirs derived from ancient source rocks, or deeply buried gas hydrates, both of which are decoupled from contemporaneous organic carbon deposition at the sediment surface. Using a modeling approach, we examine the relationship between different methane sources and pore water sulfate, methane, dissolved inorganic carbon (DIC), and ammonium profiles. We show that pore water ammonium profiles through the SMT represent an independent "tracer" of remineralization processes occurring in deep sediments that complement information obtained from profiles of solutes directly associated with AOM and carbonate precipitation, i.e., DIC, methane, and sulfate. Pore water DIC profiles also show an inflection point in the SMT based on the type of deep methane source and the presence/absence of accompanying upward DIC fluxes. With these results, we present a conceptual framework which illustrates how shallow pore water profiles from continental margin settings can be used to obtain important information about remineralization processes and methane sources in deep sediments.

  10. The Response of Sediments and Dissolved Organic Matter to Rapid Rainfall in the Santa Maria da Vitoria Watershed, Espírito Santo, BR

    NASA Astrophysics Data System (ADS)

    Ward, N. D.; Firme de Almeida, L.; Dias, G.; Gould, R.; Tan, A.; Bianchi, T. S.; Krusche, A. V.; Keil, R. G.; Richey, J. E.

    2015-12-01

    The Santa Maria da Vitória River supplies over 30% of the water for the greater Vitória, Espírito Santo, BR metropolitan area, which has a population of roughly 1.6 million people. The availability of clean freshwater is severely limited during periods of heavy rainfall because water sanitation facilities are "clogged" by high sediment discharge. The headwaters of the Santa Maria da Vitória River are characterized by relatively pristine forested environments, transitioning into primarily agricultural and rural land uses, and finally reaching the large urban center of Vitória near its marine receiving waters. The discharge of suspended sediments and dissolved organic matter (DOM) was examined at a 3 hour frequency during heavy storm flows from October 2013 to May 2015 in the Santa Maria da Vitória River main channel and a small tributary, the Mangaraí River. Bulk isotopic analyses were used to determine potential sediment sources and whether specific landscape/land use features were functionalized during periods of high runoff. Likewise, time of flight mass spectrometry (GC-ToF-MS) was used to identify a broad suite of DOM compounds that responded positively with river discharge in an effort to determine the influence of land use on the delivery of dissolved components to the river. For example, the abundance of compounds related to specific agricultural settings increased during storm flow along with anthropogenic DOM sources such as plasticizer and pesticide-derived compounds. Suspended sediment concentrations increased by as much as 70 times during peak river discharge relative to base flow several days earlier with similar increases in particulate organic carbon and nitrogen observed. Results from this study and previous field measurements were integrated into a coupled hydrology-sediment transport model, DHSVM, as part of a dynamic information framework with the goal of predicting water/sediment discharge to inform management and policy sectors of the

  11. Effects of urbanization and long-term rainfall on the occurrence of organic compounds and trace elements in reservoir sediment cores, streambed sediment, and fish tissue from the Santa Ana River basin, California, 1998

    USGS Publications Warehouse

    Burton, Carmen A.

    2002-01-01

    Organcochlorine compounds, semivolatile-organic compounds (SVOC), and trace elements were analyzed in reservoir sediment cores, streambed sediment, and fish tissue in the Santa Ana River Basin as part of the U.S. Geological Survey's National Water-Quality Assessment Program. Three reservoirs were sampled in areas that have different degrees of urbanization. Streambed sediment and fish tissue collected at 12 sites were divided into two groups, urban and nonurban. More organochlorine compounds were detected in reservoir sediment cores, streambed sediment and fish tissue, and at higher concentrations at urban sites than at nonurban sites. At all sites, except West Street Basin, concentrations of organochlorine compounds were lower than the probable-effect concentration (PEC). At the highly urbanized West Street Basin, chlordane and p,p'-DDE exceeded the PEC throughout the historical record. The less stringent threshold-effect concentration (TEC) was exceeded for six compounds at eight sites. Most of the organochlorine compounds detected in streambed sediment and fish tissue were at urban sites on the Santa Ana River as opposed to its tributaries, suggesting accumulation and persistence in the river. More SVOCs were detected in reservoir sediment cores and streambed sediment, and at higher concentrations, at urban sites than at nonurban sites. At all the sites, except West Street Basin, concentrations of SVOCs were lower than the PEC. At West Street Basin, chrysene, pyrene, and total polycyclic-aromatic hydrocarbons exceeded the PEC throughout the historical record. The TEC was exceeded for 10 compounds at 3 sites. Most of the SVOCs were detected in streambed sediment at urban sites on tributaries to the Santa Ana River rather than the mainstem itself. The less frequent occurrence and lower concentrations in the Santa Ana River suggest that SVOCs are less persistent than organochlorine compounds, possibly as a result of volatization, gradation, or dilution. Most trace

  12. Lipid Biomarkers and Carbon Isotopic Composition from Authigenic Carbonates and Seep Sediments from the US Mid-Atlantic Margin

    NASA Astrophysics Data System (ADS)

    Campbell, P.; Prouty, N.; Demopoulos, A. W.; Roark, B.; Coykendall, K.

    2015-12-01

    Anaerobic oxidation of methane (AOM), mediated by Archaea and sulfate-reducing bacteria, is common in continental margin sediment and can result in authigenic carbonate precipitation. A lipid biomarker study was undertaken in Mid-Atlantic submarine canyons, focusing specifically on Baltimore and Norfolk canyons, to determine biomarker variability of carbonate rock and the associated sediment in cold seep communities dominated by chemosynthetic mussels, Bathymodiolus childressi. Preliminary 16S metagenomic results confirm the presence of free-living sulfur-reducing bacteria and methantrophic endosymbiotic bacteria in the mussels. Depleted d13C values in both the mussel tissue (-63 ‰) and authigenic carbonates (-48 ‰) support methanotrophy as the dominant nutritional pathway and AOM as the main driver of carbonate precipitation. In addition, paired 14C and 230Th dates are highly discordant, reflecting dilution of the 14C pool with fossil hydrocarbon derived carbon. Seep and canyon sediment, as well as authigenic carbonates, were collected and analyzed for a suite of biomarkers, including sterols, alcohols, alkanes and fatty acids, as well as δ13C values of select biomarkers, to elucidate pathways of organic matter cycling. A comparison of terrestrial biomarker signatures (e.g., n-alkane carbon preference index and C23 / (C23 + C29) values, HMW n-alkanes and C29 sterols) suggests that terrestrial inputs dominate the submarine canyon surface sediment, whereas seep sediment is predominantly marine autochthonous (i.e., cholesterol and 5α-cholestanol). Lipid biomarker profiles (e.g., n-alkanes in the C15 to C33 range) from authigenic carbonates mirror those found in the seep sediment, suggesting that the organisms mediating carbonate precipitation on the seafloor are characteristic of the assemblages present in the sediment at these sites. With widespread methane leakage recently discovered along the Atlantic Margin, the presence of AOM-mediated carbonate

  13. Community Proteogenomics of a Cold-methane Seep Sediment at Nyegga, Mid-Norwegian Margin

    NASA Astrophysics Data System (ADS)

    Stokke, R.; Roalkvam, I.; Lanzen, A.; Chen, Y.; Haflidason, H.; Steen, I.

    2010-12-01

    Anaerobic oxidation of methane (AOM) is limited to anoxic environments and differs in its rates from a few pmol cm-3day-1 in subsurface SMTZ (sulfate-methane transition zone) of deep margins, to a few μmol cm-3 day-1 in surface sediments above gas hydrates [1]. This process is catalyzed by consortia of anaerobic methane oxidizing archaea (ANME) in association with sulfate-reducing bacteria. The Nyegga area is located on the Mid-Norwegian continental slope at the northern flank of the Storegga Slide at 700-800 mbsl. Hundreds of pockmarks are widespread on the seabed in Nyegga and sub-zero temperatures (-0.7 °C), and pingo-structures within the pockmarks are indicators of active fluid flow locations. Preliminary microbial and geochemical profiling of a 22 cm push-core within the G11 pockmark gave strong indications of an ANME-1 dominated community at 14-16 cmbsf. In light of these findings we submitted extracted DNA to 454-pyrosequencing. Sequencing data (829,527 reads) was assembled using the Newbler v2.3, resulting in 13,151 contigs (357,530 reads) over 500 bp with the longest contig being 24,521 bp. MEGAN taxonomic analysis supported the high abundance of Euryarchaea (70%) with 66% of the assembled metagenome belonging to ANME-1. In order to obtain functional information of the ANME-1 community, protein extraction protocols from sediment samples was established. Extracted proteins was separated on a large (18cm) 1D-SDS-PAGE and subsequently cut in 30 gel slices. Peptides extracted after In-gel tryptic digest was injected into an Ultimate 3000 nanoLC system connected to a linear quadropole ion trap-orbitrap (LTQ-Orbitrap XL) mass spectrometer equipped with a nanoelectrospray ion source. A custom database of open reading frames (ORFs) from the metagenome including known contaminants such as trypsin and human keratin was search against using Mascot 2.2. IRMa tool box [2] was used in peptide validation and peptides whose score >= 25.0 (i.e avg identity, p<0.05) and

  14. Breaks in Pavement and Pipes as Indicators of Range-Front Faulting Resulting from the 1989 Loma Prieta Earthquake near the Southwest Margin of the Santa Clara Valley, California

    USGS Publications Warehouse

    Schmidt, Kevin M.; Ellen, Stephen D.; Haugerud, Ralph A.; Peterson, David M.; Phelps, Geoffery A.

    1995-01-01

    Damage to pavement and near-surface utility pipes, caused by the October 17, 1989, Loma Prieta earthquake, provide indicators for ground deformation in a 663 km2 area near the southwest margin of the Santa Clara Valley, California. The spatial distribution of 1284 sites of such damage documents the extent and distribution of detectable ground deformation. Damage was concentrated in four zones, three of which are near previously mapped faults. The zone through Los Gatos showed the highest concentration of damage, as well as evidence for pre- and post-earthquake deformation. Damage along the foot of the Santa Cruz Mountains reflected shortening that is consistent with movement along reverse faults in the region and with the hypothesis that tectonic strain is distributed widely across numerous faults in the California Coast Ranges.

  15. Rheological implications of sediment transport for continental rifting and its impact in margin geometry and major unconformities

    NASA Astrophysics Data System (ADS)

    Andres-Martinez, Miguel; Perez-Gussinye, Marta; Armitage, John; Morgan, Jason

    2016-04-01

    The inner dynamics of the Earth such as mantle convection, geochemical reactions and isostasy have been typically interpreted as the main engine of plate tectonics and crustal deformation. However, nowadays it is well established that processes transporting material along the surface of the Earth influence the inner dynamics. Surface processes play a key role particularly during rifting, where great subsidence rates occur at synrift basins while shoulder uplift provides rock to be eroded for later infilling of these basins. Erosion implies unloading of the crust which favours uplift, and sedimentation at basins results in loading which favours subsidence. Consequently, erosion and sedimentation amplify stresses and the flexural response of the lithosphere in situations with extensive faulting. These changes to the stress field may be large enough to result in changes in the evolution of rifting and its modes of extension. Additionally, higher subsidence rates and thermal blanketing due to sediments may result in higher geotherms and consequently, a weaker/more-viscous behaviour of the crustal rocks. This would also have a large impact on the deformation style during extension. Here, we explore the interactions between surface processes and tectonics using numerical modelling. Experiments are run with the absence of sediment transport and with different sediment transport regimes for 35 and 40 km crustal thicknesses. Tests with higher transport coefficient show more effective localization of deformation into upper crustal faults which results in effective crustal thinning, larger blocks and longer-lived faults. Our experiments also prove that more effective surface processes reduce the length of margins generated by sequential faulting. For our end member situations, high sedimentation rates lead to pure shear extension of the crust induced by high temperatures, which finally results in broad extension and symmetric margins. Furthermore, our model allows for the

  16. Sedimentation on continental margins: An integrated program for innovative studies during the 1990s

    NASA Astrophysics Data System (ADS)

    Nittrourer, Charles A.; Coleman, James M.; Rouge, Baton; Flood, Roger D.; Ginsburg, Robert N.; Gorsline, Donn S.; Hine, Albert C.; Sternberg, Richard W.; Swift, Donald J. P.; Wright, L. Donelson

    Continental margins are of great scientific interest, and they represent the focus of human interaction with the ocean. Their deep structure forms the transition from continental to oceanic crust, and their surface expression extends from coastal environments of estuaries and shorelines across the continental shelf and slope to either the base of a continental rise or a marginal trough. Modern continental margins represent natural laboratories for investigation of complex relationships between physical, chemical, and biological phenomena, which are sensitive to environmental conditions both on the land and in the ocean. The history of these conditions is preserved within the sedimentary deposits of continental margins. The deposits form repositories for much of the particulate material transported off the world's land masses and produced from dissolved components in the world ocean. Past deposits of continental margins have been uplifted to form many mountain ranges and sedimentary terrains of the world, which record details of Earth history and contain valuable natural resources, such as petroleum and natural gas. Modern deposits of continental margins record the more recent events that have influenced Earth and also contain natural resources (for instance, minerals, sand, and gravel), as well as anthropogenic pollutants (for example, heavy metals and pesticides). The fates of many materials beneficial and deleterious to humans are dependent on the pathways followed by sedimentary particles on continental margins.

  17. The Mid Pleistocene Climate Transition Recorded in a Hemipelagic Sediment Drift (ODP Leg 194): Implications for the Understanding of Continental Margin Sediment Sources and Sinks

    NASA Astrophysics Data System (ADS)

    Obrochta, S. P.; Hine, A. C.; Flower, B. P.; Locker, S. D.; Brooks, G. R.

    2002-12-01

    The Marion Plateau (NE Australia margin) provides an ideal setting to study continental margin paleoceanographic history. It is not significantly current scoured and is located at upper continental slope depths, freeing it from the influence of large sediment gravity flows. Atop the plateau, a hemipelagic sediment drift is perched and was drilled on Ocean Drilling Program Leg 194 (site 1198). The lithologic record and other shipboard-acquired data sets (physical properties, downhole logging), as well as the site-survey seismic data all suggest that cyclicity dominates this sedimentary section, which encompasses the Mid Pleistocene climate transition (0.9 to 0.92 Ma). This period contains the transition from a 41 k.y. cycle (ice volume and temperature) to 100 k.y. (ice volume and temperature) cycle dominated world. Preliminary results indicate that the basic stratigraphic units of this drift record terrestrial climate, continental margin, and pelagic processes. Mass accumulation rates of the siliciclastic, neritic carbonate, and pelagic carbonate components represent orbitally-forced cycles that form a predictable sedimentary architecture, and grain size variations are a proxy for fluctuations in bottom current strength. The terrigenous flux varies as a function of both aridity/humidity variation on the adjacent continent and sea-level fluctuations, while the carbonate flux varies as a function of paleoproductivity of the overlying water column plus lateral input from the developing Great Barrier Reef. Examination of the changing sedimentary architecture of this drift during the Mid Pleistocene climate transition will further the understanding of sedimentary sources and sinks along continental margins, including their sensitivity to sea level, climate, and circulation changes.

  18. Early Neogene unroofing of the Sierra Nevada de Santa Marta along the Bucaramanga -Santa Marta Fault

    NASA Astrophysics Data System (ADS)

    Piraquive Bermúdez, Alejandro; Pinzón, Edna; Bernet, Matthias; Kammer, Andreas; Von Quadt, Albrecht; Sarmiento, Gustavo

    2016-04-01

    Plate interaction between Caribbean and Nazca plates with Southamerica gave rise to an intricate pattern of tectonic blocks in the Northandean realm. Among these microblocks the Sierra Nevada de Santa Marta (SNSM) represents a fault-bounded triangular massif composed of a representative crustal section of the Northandean margin, in which a Precambrian to Late Paleozoic metamorphic belt is overlain by a Triassic to Jurassic magmatic arc and collateral volcanic suites. Its western border fault belongs to the composite Bucaramanga - Santa Marta fault with a combined left lateral-normal displacement. SE of Santa Marta it exposes remnants of an Oligocene marginal basin, which attests to a first Cenoizoic activation of this crustal-scale lineament. The basin fill consists of a sequence of coarse-grained cobble-pebble conglomerates > 1000 m thick that unconformably overlay the Triassic-Jurassic magmatic arc. Its lower sequence is composed of interbedded siltstones; topwards the sequence becomes dominated by coarser fractions. These sedimentary sequences yields valuable information about exhumation and coeval sedimentation processes that affected the massif's western border since the Upper Eocene. In order to analyse uplifting processes associated with tectonics during early Neogene we performed detrital zircon U-Pb geochronology, detrital thermochronology of zircon and apatites coupled with the description of a stratigraphic section and its facies composition. We compared samples from the Aracataca basin with analog sequences found at an equivalent basin at the Oca Fault at the northern margin of the SNSM. Our results show that sediments of both basins were sourced from Precambrian gneisses, along with Mesozoic acid to intermediate plutons; sedimentation started in the Upper Eocene-Oligocene according to palynomorphs, subsequently in the Upper Oligocene a completion of Jurassic to Cretaceous sources was followed by an increase of Precambrian input that became the dominant

  19. Zambezi continental margin: compartmentalized sediment transfer routes to the abyssal Mozambique Channel

    NASA Astrophysics Data System (ADS)

    Wiles, E.; Green, A. N.; Watkeys, M. K.; Jokat, W.

    2017-03-01

    Sediment delivery to the abyssal regions of the oceans is an integral process in the source to sink cycle of material derived from adjacent continents and islands. The Zambezi River, the largest in southern Africa, delivers vast amounts of material to the inner continental shelf of central Mozambique. The aim of this contribution is to better constrain sediment transport pathways to the abyssal plains using the latest, regional, high-resolution multibeam bathymetry data available, taking into account the effects of bottom water circulation, antecedent basin morphology and sea-level change. Results show that sediment transport and delivery to the abyssal plains is partitioned into three distinct domains; southern, central and northern. Sediment partitioning is primarily controlled by changes in continental shelf and shelf-break morphology under the influence of a clockwise rotating shelf circulation system. However, changes in sea-level have an overarching control on sediment delivery to particular domains. During highstand conditions, such as today, limited sediment delivery to the submarine Zambezi Valley and Channel is proposed, with increased sediment delivery to the deepwater basin being envisaged during regression and lowstand conditions. However, there is a pronounced along-strike variation in sediment transport during the sea-level cycle due to changes in the width, depth and orientation of the shelf. This combination of features outlines a sequence stratigraphic concept not generally considered in the strike-aligned shelf-slope-abyssal continuum.

  20. Estimates of Biogenic Methane Production Rates in Deep Marine Sediments at Hydrate Ridge, Cascadia Margin

    SciTech Connect

    F. S. Colwell; S. Boyd; M. E. Delwiche; D. W. Reed; T. J. Phelps; D. T. Newby

    2008-06-01

    Methane hydrate found in marine sediments is thought to contain gigaton quantities of methane and is considered an important potential fuel source and climate-forcing agent. Much of the methane in hydrates is biogenic, so models that predict the presence and distribution of hydrates require accurate rates of in situ methanogenesis. We estimated the in situ methanogenesis rates in Hydrate Ridge (HR) sediments by coupling experimentally derived minimal rates of methanogenesis to methanogen biomass determinations for discrete locations in the sediment column. When starved in a biomass recycle reactor Methanoculleus submarinus produced ca. 0.017 fmol methane/cell/day. Quantitative polymerase chain reaction (QPCR) directed at the methyl coenzyme M reductase subunit A (mcrA) gene indicated that 75% of the HR sediments analyzed contained <1000 methanogens/g. The highest methanogen numbers were mostly from sediments <10 meters below seafloor. By combining methanogenesis rates for starved methanogens (adjusted to account for in situ temperatures) and the numbers of methanogens at selected depths we derived an upper estimate of <4.25 fmol methane produced/g sediment/day for the samples with fewer methanogens than the QPCR method could detect. The actual rates could vary depending on the real number of methanogens and various seafloor parameters that influence microbial activity. However, our calculated rate is lower than rates previously reported from such sediments and close to the rate derived using geochemical modeling of the sediments. These data will help to improve models that predict microbial gas generation in marine sediments and determine the potential influence of this source of methane on the global carbon cycle.

  1. Estimates of biogenic methane production rates in deep marine sediments at Hydrate Ridge, Cascadia margin.

    PubMed

    Colwell, F S; Boyd, S; Delwiche, M E; Reed, D W; Phelps, T J; Newby, D T

    2008-06-01

    Methane hydrate found in marine sediments is thought to contain gigaton quantities of methane and is considered an important potential fuel source and climate-forcing agent. Much of the methane in hydrates is biogenic, so models that predict the presence and distribution of hydrates require accurate rates of in situ methanogenesis. We estimated the in situ methanogenesis rates in Hydrate Ridge (HR) sediments by coupling experimentally derived minimal rates of methanogenesis to methanogen biomass determinations for discrete locations in the sediment column. When starved in a biomass recycle reactor, Methanoculleus submarinus produced ca. 0.017 fmol methane/cell/day. Quantitative PCR (QPCR) directed at the methyl coenzyme M reductase subunit A gene (mcrA) indicated that 75% of the HR sediments analyzed contained <1,000 methanogens/g. The highest numbers of methanogens were found mostly from sediments <10 m below seafloor. By considering methanogenesis rates for starved methanogens (adjusted to account for in situ temperatures) and the numbers of methanogens at selected depths, we derived an upper estimate of <4.25 fmol methane produced/g sediment/day for the samples with fewer methanogens than the QPCR method could detect. The actual rates could vary depending on the real number of methanogens and various seafloor parameters that influence microbial activity. However, our calculated rate is lower than rates previously reported for such sediments and close to the rate derived using geochemical modeling of the sediments. These data will help to improve models that predict microbial gas generation in marine sediments and determine the potential influence of this source of methane on the global carbon cycle.

  2. Distribution and preservation of black carbon in the East China Sea sediments: Perspectives on carbon cycling at continental margins

    NASA Astrophysics Data System (ADS)

    Huang, Liang; Zhang, Jing; Wu, Ying; Wang, Jinlong

    2016-02-01

    We determined the concentrations and radiocarbon (14C) compositions of black carbon (BC) in the sediments of the East China Sea (ECS). The BC concentrations, which were in the range of 0.30-1.52 mg/g, accounted for 12-65% of the total organic carbon (TOC). The distribution of BC in ECS sediments was controlled by factors such as grain size, distance from the coast, and deposition rate. Radiocarbon measurements of BC yielded ages of 6350-10,440 years before present (BP), suggesting that the percentage of BC derived from biomass combustion was in the range of 29-48%. The BC burial flux in sediments of the ECS was estimated to be ∼1.39×106 t/yr, which was similar to burial fluxes reported for shelf sediments in other areas. However, the magnitude of the total BC sink was far greater than that of any other shelf regions studied to date, indicating the global importance of BC accumulation in the ECS, and the magnitude of BC input from large rivers (e.g., the Changjiang). The riverine delivery of BC to the ECS (73%) was far greater than that of atmospheric flux (27%). Further study of the BC cycle and the interactions of BC with other organic compounds in marginal seas was required to better understand the role of BC in the global carbon cycle.

  3. Temporal and spatial patterns of sediment routing across the southeast margin of the Tibetan Plateau: Insights from detrital zircon

    NASA Astrophysics Data System (ADS)

    Wissink, Gregory K.; Hoke, Gregory D.; Garzione, Carmala N.; Liu-Zeng, Jing

    2016-11-01

    The Cenozoic deposits of the Tibetan Plateau's southeastern margin are often cited as part of a continental-scale river system connecting the Paleo-Yangtze River with the Paleo-Red River. Confirming the purported connection and any subsequent drainage reorganization has garnered significant attention and varied proposed ages for reorganization. This study presents detrital zircon U-Pb ages and paleocurrents in Eocene to Pleistocene sedimentary basin deposits distributed over a broad area of the southeast Tibetan Plateau margin within the area of proposed paleoriver connectivity. When combined with previously published studies, our U-Pb ages allow examination of the temporal and spatial distributions of provenance throughout the Cenozoic. We identify six key age components of the detrital U-Pb age distributions and use these to examine the patterns of sediment provenance for different Cenozoic epochs. Detailed analysis of these components shows that provenance for both onshore and offshore deposits is best described by local bedrock sources and provides little to no evidence of regional changes in provenance. This suggests that a stable fluvial system similar to the modern drainage network has existed since the Eocene with no evidence for major provenance-altering river capture. Paleoflow measurements taken throughout the SE margin further corroborate the results of detrital zircon provenance. The combination of U-Pb age components and paleocurrent directions does not support a Cenozoic connection between the Paleo-Yangtze and Paleo-Red Rivers.

  4. Coupled onshore erosion and offshore sediment loading as causes of lower crust flow on the margins of South China Sea

    NASA Astrophysics Data System (ADS)

    Clift, Peter D.

    2015-12-01

    Hot, thick continental crust is susceptible to ductile flow within the middle and lower crust where quartz controls mechanical behavior. Reconstruction of subsidence in several sedimentary basins around the South China Sea, most notably the Baiyun Sag, suggests that accelerated phases of basement subsidence are associated with phases of fast erosion onshore and deposition of thick sediments offshore. Working together these two processes induce pressure gradients that drive flow of the ductile crust from offshore towards the continental interior after the end of active extension, partly reversing the flow that occurs during continental breakup. This has the effect of thinning the continental crust under super-deep basins along these continental margins after active extension has finished. This is a newly recognized form of climate-tectonic coupling, similar to that recognized in orogenic belts, especially the Himalaya. Climatically modulated surface processes, especially involving the monsoon in Southeast Asia, affects the crustal structure offshore passive margins, resulting in these "load-flow basins". This further suggests that reorganization of continental drainage systems may also have a role in governing margin structure. If some crustal thinning occurs after the end of active extension this has implications for the thermal history of hydrocarbon-bearing basins throughout the area where application of classical models results in over predictions of heatflow based on observed accommodation space.

  5. Towards Biogeochemical Modeling of Anaerobic Oxidation of Methane: Characterization of Microbial Communities in Methane-bearing North American Continental Margin Sediments

    NASA Astrophysics Data System (ADS)

    Graw, M. F.; Solomon, E. A.; Chrisler, W.; Krause, S.; Treude, T.; Ruppel, C. D.; Pohlman, J.; Colwell, F. S.

    2015-12-01

    Methane advecting through continental margin sediments may enter the water column and potentially contribute to ocean acidification and increase atmospheric methane concentrations. Anaerobic oxidation of methane (AOM), mediated by syntrophic consortia of anaerobic methanotrophic archaea and sulfate-reducing bacteria (ANME-SRB), consumes nearly all dissolved methane in methane-bearing sediments before it reaches the sediment-water interface. Despite the significant role ANME-SRB play in carbon cycling, our knowledge of these organisms and their surrounding microbial communities is limited. Our objective is to develop a metabolic model of ANME-SRB within methane-bearing sediments and to couple this to a geochemical reaction-transport model for these margins. As a first step towards this goal, we undertook fluorescent microscopic imaging, 16S rRNA gene deep-sequencing, and shotgun metagenomic sequencing of sediments from the US Pacific (Washington) and northern Atlantic margins where ANME-SRB are present. A successful Illumina MiSeq sequencing run yielded 106,257 bacterial and 857,834 archaeal 16S rRNA gene sequences from 12 communities from the Washington Margin using both universal prokaryotic and archaeal-specific primer sets. Fluorescent microscopy confirmed the presence of cells of the ANME-2c lineage in the sequenced communities. Microbial community characterization was coupled with measurements of sediment physical and geochemical properties and, for samples from the US Atlantic margin, 14C-based measurements of AOM rates and 35S-based measurements of sulfate reduction rates. These findings have the potential to increase understanding of ANME-SRB, their surrounding microbial communities, and their role in carbon cycling within continental margins. In addition, they pave the way for future efforts at developing a metabolic model of ANME-SRB and coupling it to geochemical models of the US Washington and Atlantic margins.

  6. Basement - Cover decoupling and progressive exhumation of metamorphic sediments at hot rifted margin. Insights from the Northeastern Pyrenean analog

    NASA Astrophysics Data System (ADS)

    Clerc, Camille; Lagabrielle, Yves; Labaume, Pierre; Ringenbach, Jean-Claude; Vauchez, Alain; Nalpas, Thierry; Bousquet, Romain; Ballard, Jean-François; Lahfid, Abdeltif; Fourcade, Serge

    2016-08-01

    We compile field data collected along the eastern part of the North Pyrenean Zone (NPZ) to point to a tectonic evolution under peculiar thermal conditions applying to the basin sediments in relation with the opening of the Cretaceous Pyrenean rift. Based on this compilation, we show that when thinning of the continental crust increased, isotherms moved closer to the surface with the result that the brittle-ductile transition propagated upward and reached sediments deposited at the early stage of the basin opening. During the continental breakup, the pre-rift Mesozoic cover was efficiently decoupled from the Paleozoic basement along the Triassic evaporite level and underwent drastic ductile thinning and boudinage. We suggest that the upper Albian and upper Cretaceous flysches acted as a blanket allowing temperature increase in the mobile pre-rift cover. Finally, we show that continuous spreading of the basin floor triggered the exhumation of the metamorphic, ductily sheared pre-rift cover, thus contributing to the progressive thinning of the sedimentary pile. In a second step, we investigate the detailed geological records of such a hot regime evolution along a reference-section of the eastern NPZ. We propose a balanced restoration from the Mouthoumet basement massif (north) to the Boucheville Albian basin (south). This section shows a north to south increase in the HT Pyrenean imprint from almost no metamorphic recrystallization to more than 600 °C in the pre- and syn-rift sediments. From this reconstruction, we propose a scenario of tectonic thinning involving the exhumation of the pre-rift cover by the activation of various detachment surfaces at different levels in the sedimentary pile. In a third step, examination of the architecture of current distal passive margin domains provides confident comparison between the Pyrenean case and modern analogs. Finally, we propose a general evolutionary model for the pre-rift sequence of the Northeastern Pyrenean rifted

  7. Radiocarbon Evidence for Active Turnover of Pore-Water Dissolved Organic Carbon in the Methanogenic and Sulfate-Methane-Transition Zones of Santa Barbara Basin Sediments

    NASA Astrophysics Data System (ADS)

    Komada, T.; Li, H. L.; Cada, A. K.; Burdige, D.; Magen, C.; Chanton, J.; Grose, A. M.

    2014-12-01

    Diverse metabolic activities have been documented in the deep biosphere. However, how these activities affect carbon cycling in the subsurface, and how they in turn affect the marine and global cycles of carbon are still unclear. Here we present natural-abundance 14C and 13C data from the uppermost 4.5 m of the sediments of the Santa Barbara Basin, California Borderland, showing active turnover of dissolved organic carbon (DOC) within, and immediately below, the sulfate-methane transition zone (SMTZ; ~1.25 m). DOC concentrations increased with depth throughout the core, indicating net production within the sediment column. Enhanced DOC production was observed near the sediment-water interface, and also at ~30 cm below the SMTZ (~1.55 m). ∆14C values of DOC increased across the sediment-water interface, then decreased with depth, consistent with net production of modern DOC near the sediment-water interface, and input of 14C-depleted DOC from deeper horizons. An isotope mixing plot constructed with these data shows that the DOC diffusing upward at the base of the core is devoid of 14C, yet the DOC diffusing into and out of the SMTZ is relatively enriched (-460‰ and -300‰, respectively). This difference in 14C content of the DOC flux can only be reconciled if the following two are occurring within, and immediately below, the SMTZ: (1) >90% of the 14C-dead basal DOC flux is removed from the pore water (by, e.g., oxidation, fermentation, methanogenesis, precipitation), and (2) this DOC is replaced by material produced in this region at a rate that exceeds the upward basal flux. The 14C and 13C signatures suggest sedimentary organic matter to be the dominant source of DOC in process (2). Our data provide a unique insight into the active transformation of DOC and sedimentary organic matter in the subsurface.

  8. Temporal evolution of lead isotope ratios in sediments of the Central Portuguese Margin: a fingerprint of human activities.

    PubMed

    Mil-Homens, Mário; Caetano, Miguel; Costa, Ana M; Lebreiro, Susana; Richter, Thomas; de Stigter, Henko; Trancoso, Maria A; Brito, Pedro

    2013-09-15

    Stable Pb isotope ratios ((206)Pb/(207)Pb, (208)Pb/(206)Pb), (210)Pb, Pb, Al, Ca, Fe, Mn and Si concentrations were measured in 7 sediment cores from the west coast of the Iberian Peninsula to assess the Pb contamination throughout the last 200 years. Independently of their locations, all cores are characterized by increasing Pb/Al rends not related to grain-size changes. Conversely, decreasing trends of (206)Pb/(207)Pb were found towards the present. This tendency suggest a change in Pb sources reflecting an increased proportion derived from anthropogenic activities. The highest anthropogenic Pb inventories for sediments younger than 1950s were found in the two shallowest cores of Cascais and Lisboa submarine canyons, reflecting the proximity of the Tagus estuary. Lead isotope signatures also help demonstrate that sediments contaminated with Pb are not constrained to estuarine-coastal areas and upper parts of submarine canyons, but are also to transferred to a lesser extent to deeper parts of the Portuguese Margin.

  9. Lack of enhanced preservation of organic matter in sediments under the oxygen minimum on the Oman Margin

    SciTech Connect

    Pedersen, T.F. ); Shimmield, G.B.; Price, N.B. )

    1992-01-01

    The impingement of oxygen minima on continental margins is widely thought to promote the accumulation of sedimentary facies enriched in well-preserved organic matter. It is shown here, however, that such a relationship does not clearly apply to the productive Oman Margin in the Arabian Sea, which hosts one of the most severe oxygen minima in the oceans. Measurements made on the 0-1 cm depth interval from fourteen box cores collected from the outer shelf-upper continental slope area off Oman show that (1) deposited organic matter is overwhelmingly of marine origin, (2) there is no significant correlation between the abundance of sedimentary organic carbon (C{sub org}) and the bottom-water O{sub 2} concentration, (3) there is no relation between the sedimentary C{sub org}:N ratio and bottom-water O{sub 2}, and (4) there is no correlation between the hydrogen index (HI) of the organic matter and bottom water oxygen. There are, however, significant correlations between the C{sub org}:N ratio and the I:C{sub org}, Cr:Al, and Zr:Al ratios, as well as between the C{sub org}:N ratio and the hydrogen index. Overall, these data suggest that the bottom water oxygen concentration has little effect in governing either the distribution of the degree of preservation of organic matter on this margin. Thus, the generally high but spatially variable C{sub org} content of the sediments on the Oman Margin may not reflect the occurrence of an oxygen minimum but instead be the result of a high settling flux of organic matter, supported by monsoon-driven upwelling, and post-depositional redistribution of the organic material by hydrodynamic influences.

  10. 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

  11. Benthic remineralisation rates in shelf and slope sediments of the northern Benguela upwelling margin

    NASA Astrophysics Data System (ADS)

    Neumann, Andreas; Lahajnar, Niko; Emeis, Kay-Christian

    2016-02-01

    The Benguela Upwelling System off Namibia is a region of intensive plankton production. Remineralisation of this biomass frequently causes the formation of an oxygen minimum zone. A part of the organic matter is further deposited on the broad shelf in form of an extensive mudbelt with high TOC concentrations. During February 2011 we retrieved sediment samples from shelf and slope sediment along the Namibian coast to establish fluxes of nutrients, oxygen, and N2 on the basis of pore water concentrations. In mudbelt sediment, fluxes were estimated as high as 8 mmol NH4+ m-2 d-1 and 0.9 mmol PO43 - m-2 d-1, which is probably attributable to the activity of large sulphur bacteria. Especially phosphate is mobilised from sediment overlain by oxygen deficient bottom water when and where bottom water oxygen concentrations fall below 50 μmol l-1. In comparison to nutrient transport by Southern Atlantic Central Water flowing onto the Namibian shelf, benthic nutrient fluxes of the mudbelt contribute less than 5% to the nutrient budget of the shelf.

  12. Surface current patterns suggested by suspended sediment distribution over the outer continental margin, Bering Sea

    USGS Publications Warehouse

    Karl, Herman A.; Carlson, P.R.

    1987-01-01

    Samples of total suspended matter (TSM) were collected at the surface over the northern outer continental margin of the Bering Sea during the summers of 1980 and 1981. Volume concentrations of surface TSM averaged 0.6 and 1.1 mg l-1 for 1980 and 1981, respectively. Organic matter, largely plankton, made up about 65% of the near-surface TSM for both years. Distributions of TSM suggested that shelf circulation patterns were characterized either by meso- and large- scale eddies or by cross-shelf components of flow superimposed on a general northwesterly net drift. These patterns may be caused by large submarine canyons which dominate the physiography of this part of the Bering Sea continental margin. ?? 1987.

  13. Diversity, Community Composition and Abundance of Anammox Bacteria in Sediments of the North Marginal Seas of China

    PubMed Central

    Shehzad, Ahmed; Liu, Jiwen; Yu, Min; Qismat, Shakeela; Liu, Jingli; Zhang, Xiao-Hua

    2016-01-01

    Over the past few decades, anammox bacteria have been recognized as key players that contribute significantly to the release of large amounts of nitrogen in the global marine nitrogen cycle. In the present study, the diversity, community composition, and abundance of anammox bacteria from the sediments of four diverse regions in the north marginal seas in China were determined via clone library construction and a quantitative PCR analysis. The clone libraries retrieved by the 16S rRNA gene and Hzo gene markers indicated that “Candidatus Scalindua” was the predominant group throughout the sites examined. The 16S rRNA gene clone libraries revealed exceptional diversity by identifying two potential novel anammox clades, as evidenced by the high sequence similarities between these two clades and known anammox genera, and their unique phylogenetic positions with high bootstrap values. However, their potential roles in the anammox reaction need to be validated. Six novel members of Planctomycetes, divergent from the known genera of anammox bacteria, were also detected. A phylogenetic analysis by Hzo protein sequences revealed the existence of two known genera, i.e., “Candidatus Jettenia” and “Candidatus Anammoxoglobus”, which are rarely captured from marine sediments. Among all ecological parameters investigated, the distribution patterns and composition of anammox bacteria were found to be influenced by salinity, total organic matter, and temperature. The abundance of the anammox bacterial 16S rRNA gene from the sites examined ranged between 3.95×105 and 9.21×105 copies g−1 wet sediment and positively correlated with the median size of the sediment sample. PMID:27180640

  14. Linking Short and Long Term Sediment Delivery to Morphology and Seascape Evolution of Continental Margins

    DTIC Science & Technology

    1999-09-30

    history. OBJECTIVES 1) Is the variability in a river’s sediment load, observed over the last 100 years or less, adequate to provide a proxy for longer-term...experiments, small basins are able to capture in terms of textural proxies , both the natural variability associated with precipitation and temperature...as well as realistic scenarios of abrupt climate change. Open ocean basins, like the Eel River, are less likely to record the proxy record of ambient

  15. Stratigraphy of two conjugate margins (Gulf of Lion and West Sardinia): modeling of vertical movements and sediment budgets

    NASA Astrophysics Data System (ADS)

    Leroux, Estelle; Gorini, Christian; Aslanian, Daniel; Rabineau, Marina; Blanpied, Christian; Rubino, Jean-Loup; Robin, Cécile; Granjeon, Didier; Taillepierre, Rachel

    2016-04-01

    The post-rift (~20-0 Ma) vertical movements of the Provence Basin (West Mediterranean) are quantified on its both conjugate (the Gulf of Lion and the West Sardinia) margins. This work is based on the stratigraphic study of sedimentary markers using a large 3D grid of seismic data, correlations with existing drillings and refraction data. The post-rift subsidence is measured by the direct use of sedimentary geometries analysed in 3D [Gorini et al., 2015; Rabineau et al., 2014] and validated by numerical stratigraphic modelling. Three domains were found: on the platform (1) and slope (2), the subsidence takes the form of a seaward tilting with different amplitudes, whereas the deep basin (3) subsides purely vertically [Leroux et al., 2015a]. These domains correspond to the deeper crustal domains respectively highlighted by wide angle seismic data. The continental crust (1) and the thinned continental crust (2) are tilted, whereas the intermediate crust, identified as lower continental exhumed crust [Moulin et al., 2015, Afhilado et al., 2015] (3) sagged. The post-break-up subsidence re-uses the initial hinge lines of the rifting phase. This striking correlation between surface geologic processes and deep earth dynamic processes emphasizes that the sedimentary record and sedimentary markers is a window into deep geodynamic processes and dynamic topography. Pliocene-Pleistocene seismic markers enabled high resolution quantification of sediment budgets over the past 6 Myr [Leroux et al., in press]. Sediment budget history is here completed on the Miocene interval. Thus, the controlling factors (climate, tectonics and eustasy) are discussed. Afilhado, A., Moulin, M., Aslanian, D., Schnürle, P., Klingelhoefer, F., Nouzé, H., Rabineau, M., Leroux, E. & Beslier, M.-O. (2015). Deep crustal structure across a young 1 passive margin from wide-angle and reflection seismic data (The SARDINIA Experiment) - II. Sardinia's margin. Bull. Soc. géol. France, 186, ILP Spec. issue, 4

  16. Paleoenvironmental records from newly recovered sediment cores at the southeast margin of the Salar de Atacama, Chile

    NASA Astrophysics Data System (ADS)

    Boutt, D. F.; Munk, L. A.; Hynek, S. A.; Corenthal, L.; Huff, H. A.

    2014-12-01

    A suite of new cores recovered from recent boreholes in the southeastern margin of the Salar de Atacama, Chile span a modern environmental gradient from distal alluvial fans, groundwater discharge marshes, sulfate-rich playas, saline lagoons, and the halite nucleus of the salar. These same environments are preserved as stratigraphic records of environmental change in the cores. Cores from the salar nucleus are dominated by halite, and similarly alluvial cores provide a poor paleoenvironmental record. However, the cores from the transition zone between the salar margin and the halite nucleus document alluvial, lagoonal, and evaporite environments. Cores near the halite nucleus record inter-bedded carbonate, gypsum, and halite. Finely laminated carbonates inter-bedded with cm-thick halite beds are a target for U-series geochronology. Cores near modern lagoons contain 2-6 m thick diatomites in addition to microbially-mediated carbonate, organic-rich mud, and minor alluvium. The uppermost 20 cm of diatomite deposits are commonly rooted with vascular plant material which is being processed for 14C geochronology. Ignimbrite and tephra deposits are also encountered and will provide important chronological control. The presence and absence of the 3.5-4.0 Ma Tucucaro ignimbrite in various cores documents a complex pattern of subsidence near the salar margin, some areas have accumulated little sediment since its deposition while in other areas the cores likely record only late Pleistocene deposition. Preliminary interpretations of the stratigraphic records within a paleohydrologic context are tenable. The specific control on this paleohydrologic record is likely to be a combination of increased inflow due to wetter climates and migration of the freshwater/brine interface which underlies the margins of the Salar de Atacama. Stratigraphic variations in the lithium content of evaporite minerals is being explored as a potential indicator of water balance. Lithium concentrations

  17. Gas content and composition of gas hydrate from sediments of the southeastern North American continental margin

    USGS Publications Warehouse

    Lorenson, T.D.; Collett, T.S.

    2000-01-01

    Gas hydrate samples were recovered from four sites (Sites 994, 995, 996, and 997) along the crest of the Blake Ridge during Ocean Drilling Program (ODP) Leg 164. At Site 996, an area of active gas venting, pockmarks, and chemosynthetic communities, vein-like gas hydrate was recovered from less than 1 meter below seafloor (mbsf) and intermittently through the maximum cored depth of 63 mbsf. In contrast, massive gas hydrate, probably fault filling and/or stratigraphically controlled, was recovered from depths of 260 mbsf at Site 994, and from 331 mbsf at Site 997. Downhole-logging data, along with geochemical and core temperature profiles, indicate that gas hydrate at Sites 994, 995, and 997 occurs from about 180 to 450 mbsf and is dispersed in sediment as 5- to 30-m-thick zones of up to about 15% bulk volume gas hydrate. Selected gas hydrate samples were placed in a sealed chamber and allowed to dissociate. Evolved gas to water volumetric ratios measured on seven samples from Site 996 ranged from 20 to 143 mL gas/mL water to 154 mL gas/mL water in one sample from Site 994, and to 139 mL gas/mL water in one sample from Site 997, which can be compared to the theoretical maximum gas to water ratio of 216. These ratios are minimum gas/water ratios for gas hydrate because of partial dissociation during core recovery and potential contamination with pore waters. Nonetheless, the maximum measured volumetric ratio indicates that at least 71% of the cages in this gas hydrate were filled with gas molecules. When corrections for pore-water contamination are made, these volumetric ratios range from 29 to 204, suggesting that cages in some natural gas hydrate are nearly filled. Methane comprises the bulk of the evolved gas from all sites (98.4%-99.9% methane and 0%-1.5% CO2). Site 996 hydrate contained little CO2 (0%-0.56%). Ethane concentrations differed significantly from Site 996, where they ranged from 720 to 1010 parts per million by volume (ppmv), to Sites 994 and 997

  18. Sediment recycling at convergent plate margins (Indo-Burman Ranges and Andaman-Nicobar Ridge)

    NASA Astrophysics Data System (ADS)

    Garzanti, Eduardo; Limonta, Mara; Resentini, Alberto; Bandopadhyay, Pinaki C.; Najman, Yani; Andò, Sergio; Vezzoli, Giovanni

    2013-08-01

    Subduction complexes large enough to be exposed subaerially and become significant sources of terrigenous detritus are formed by tectonic accretion above trenches choked with thick sections of remnant-ocean turbidites. They thus need to be connected along strike to a major collision zone, where huge volumes of orogenic detritus are produced and conveyed via a major fluvio-deltaic system to the deep sea. In this article we investigate sediment generation and recycling in the archetype of such settings, the eastern prolongation of the Himalayan collisional system. We illustrate the petrographic and heavy-mineral suites of modern sands produced all along the Indo-Burman-Andaman-Nicobar subduction complex, which includes accreted abyssal-plain sediments overthrust by ophiolites and unconformably overlain by volcaniclastic forearc strata. "Subduction Complex Provenance" is thus composite, and overwhelmingly consists of detritus recycled from largely turbiditic parent rocks (Recycled Clastic Provenance), with local supply from obducted ultramafic and mafic rocks of forearc lithosphere (Ophiolite Provenance) or recycled paleovolcanic to neovolcanic sources (Volcanic Arc Provenance). In order to specifically investigate the effect of recycling, we characterize the diverse detrital signatures of Cenozoic sandstones originally deposited during subsequent stages of "soft" and "hard" Himalayan collision and presently exposed from Bangladesh to the Andaman Islands, and discuss the reasons for compositional discrepancies between parent sandstones and their recycled daughter sands. Long-distance, multistep and multicyclic sediment transfer along and across convergent plate boundaries follows complex trajectories in space and time, which must be resolved whenever we want to obtain a reasonably faithful paleogeographic reconstruction for the recent and less recent geological past.

  19. Erosion processes, fluvial sediment transport, and reservoir sedimentation in a part of the Newell and Zayante Creek basins, Santa Cruz County, California

    USGS Publications Warehouse

    Brown, W. M.

    1973-01-01

    The drainage basins upstream from Loch Lomond, a water-supply reservoir on Newell Creek, and a proposed reservoir site on Zayante Creek were investigated for their characteristics with respect to the erosion, transportation, and deposition of sediment. The study area is underlain predominantly by sandstone, siltstone, and shale of Tertiary age that decompose readily into moderately deep soils, friable colluvium, and easily transported sediment particles. The Rices Mudstone and Twobar, Shale Members of the San Lorenzo Formation of Brabb (1964) underlie steep dip slopes in the study area, and probably are the most highly erodible of the several geologic units present there. However, nearly all of the geologic units have shown a propensity for accelerated erosion accompanying the disturbance of the land surface by the roadbuilding practices that predominate over other types of sediment-producing land-use activities in the study area. Sediment transport in the study area was estimated from (1) a reservoir survey of Loch Lomond in 1971 that was compared with a preconstruction survey of 1960, and (2) sampling of sediment transported in suspension by Zayante Creek during the 1970 and 1971 water years. At least 46 acre-feet of sediment accumulated in Loch Lomond in a 10-year period, and an unmeasured quantity of very fine sediment in the form of a thin layer over much of the reservoir bottom was observed. The measured quantity of deposited sediment in a 10-year period represented a sediment yield of about 1,100 tons annually per square mile of drainage basin upstream from the reservoir arms where the major deposition occurred. This sediment occupied less than i percent of the original capacity of Loch Lomond, but the volume of measured sediment deposition is probably conservative in view of the unmeasured deposits observed and a reservoir trap efficiency of about 95 percent. Sediment sampling on Zayante Creek indicated suspended-sediment yields of about 4,570 and 570 tons

  20. Mixed carbonate-siliciclastic sedimentation on a tectonically active margin: Example from the Pliocene of Baja California Sur, Mexico

    NASA Astrophysics Data System (ADS)

    Dorsey, Rebecca J.; Kidwell, Susan M.

    1999-10-01

    Bioclast-rich, coarse-grained deposits in the Pliocene Loreto basin provide a record of mixed carbonate and siliciclastic sedimentation at the steep hanging-wall margin of this small, fault-controlled basin. Sedimentary facies consist of sand- to gravel-sized carbonate debris mixed with volcaniclastic sand and gravel in a proximal to distal facies tract that includes matrix-rich and matrix-poor shelly conglomerate, impure calcirudite and calcarenite, mixed-composition turbidites, and bioturbated calcarenitic sandstone. Carbonate material was produced by mollusks and other benthic organisms on a narrow, high-energy shelf and mixed with volcaniclastic sand and gravel in cross-shelf channels. These mixtures were transported down a steep subaqueous slope by debris flows, grain flows, and turbidity currents, forming foresets and bottomsets of marine Gilbert-type deltas. This style of mixed carbonate-siliciclastic sedimentation has not been documented in detail elsewhere but should be locally abundant in the stratigraphic record of fault-bounded basins, particularly those with cool or nutrient-rich waters that support relatively few binding and framework-building faunas. Recognition of similar facies in other settings can provide useful insights into ancient conditions of carbonate production, oceanography, climate, and tectonics.

  1. Ostracoda and Foraminifera associated with macrofauna of marginal marine origin in continental sabkha sediments of Tayma (NW Saudi Arabia)

    NASA Astrophysics Data System (ADS)

    Pint, Anna; Frenzel, Peter; Engel, Max; Plessen, Birgit; Melzer, Sandra; Brückner, Helmut

    2016-04-01

    The oasis Tayma in northwestern Saudi Arabia (27°38'N, 38°33'E) is well known for its rich archaeological heritage and also hosts a key sedimentary record of Holocene environmental change.The palaeontologically investigated material comes from two 5.5 m long sediment cores taken in the northeastern and central part of the sabkha and two outcrops of shoreline deposits at the northeastern and southwestern margin of a large lake. Microfossil-rich layers have an age of about 9.2-ca. 8 ka BP. The sandy and carbonate-dominated sediments contain autochthonous balanids, the gastropods Melanoides tuberculatus and hydrobiids as well as the foraminifers Ammonia tepida (Cushman, 1926), Quinqueloculina seminula (Linnaeus, 1758), and Flintionoides labiosa (d'Orbigny, 1839). This brackish water association is completed by partially mass-occurrence of Cyprideis torosa (JONES, 1850), an euryhaline and generally widely tolerant ostracod species. Only the smooth shelled morphotype littoralis occurs. The association indicates a large brackish water lake with temporary freshwater inflows. All species documented originate in the marginal marine environment of the Red or Mediterranean Sea within the intertidal zone and hence they are adapted for strong environmental changes. We assume negative water balance under arid climatic conditions as cause for the high salinity of this athalassic lake. Sieve-pore analyses and shell chemistry suppose a trend of increasing salinity towards the top of the studied microfossil-bearing sections. This pattern is confirmed by increasing test malformation ratios of foraminifers. The marine origin of the fauna is surprising in this area 250 km away from the sea in an altitude of about 800 m a.s.l. We assume an avian-mediated transport of eggs, larvae or even adult animals to this site. The brackish water character of the lake enabled a permanent settling of marginal marine foraminifers, ostracods and even macrofauna as gastropods and balanids. The studied

  2. Structure and Development Processes of the Sediment Ridges on the Continental Rise off the Prydz Bay Margin, East Antarctica

    NASA Astrophysics Data System (ADS)

    Shen, Z.; Yang, C.; Gao, J.; Ji, F.

    2015-12-01

    Several sediment ridges (SRs) are located on the continental slope and rise off the Prydz Bay margin, East Antarctica. These SRs contain the history of the regional glacial movements and bottom current activities. Multichannel seismic reflection data and bathymetric data in this region have been interpreted to know the planar distribution, cross-section structures along strike, and the formation and development processes of the SRs. Based on the above work, two different groups of the SRs have been identified. The first one includes two SRs which were asymmetric levees on both sides of the Wild Canyon in the western part of the study area. The second one includes SRs in the eastern part of the study area whose formation and development are closely related to the local, diachronous hiatuses generated by the turbidity flow. The onset time of the turbidity activities in different canyons are not concurrent. For Wild Canyon in the west, the onset time is P1, which is the base of the glaciomarine deposit on the continental rise, while for Wilkins and Murray Canyon in the east, it is a later time P3 (~26.1 Ma), which represents an expansion of the glaciers in Prydz Bay area. All the canyons and the turbidity currents within them both extend seaward with time and so does the consequent SRs. In the areas north of the seaward edge of the SRs, large deep-sea sediment waves consisting of fine-grain sediments supplied mainly by down-slope turbidity currents were generated under westward-flowing bottom currents.

  3. Environmental Conditions Outweigh Geographical Contiguity in Determining the Similarity of nifH-Harboring Microbial Communities in Sediments of Two Disconnected Marginal Seas

    PubMed Central

    Zhou, Haixia; Dang, Hongyue; Klotz, Martin G.

    2016-01-01

    Ecological evidence suggests that heterotrophic diazotrophs fueled by organic carbon respiration in sediments play an important role in marine nitrogen fixation. However, fundamental knowledge about the identities, abundance, diversity, biogeography, and controlling environmental factors of nitrogen-fixing communities in open ocean sediments is still elusive. Surprisingly, little is known also about nitrogen-fixing communities in sediments of the more research-accessible marginal seas. Here we report on an investigation of the environmental geochemistry and putative diazotrophic microbiota in the sediments of Bohai Sea, an eutrophic marginal sea of the western Pacific Ocean. Diverse and abundant nifH gene sequences were identified and sulfate-reducing bacteria (SRB) were found to be the dominant putative nitrogen-fixing microbes. Community statistical analyses suggested bottom water temperature, bottom water chlorophyll a content (or the covarying turbidity) and sediment porewater Eh (or the covarying pH) as the most significant environmental factors controlling the structure and spatial distribution of the putative diazotrophic communities, while sediment Hg content, sulfide content, and porewater SiO32−-Si content were identified as the key environmental factors correlated positively with the nifH gene abundance in Bohai Sea sediments. Comparative analyses between the Bohai Sea and the northern South China Sea (nSCS) identified a significant composition difference of the putative diazotrophic communities in sediments between the shallow-water (estuarine and nearshore) and deep-water (offshore and deep-sea) environments, and sediment porewater dissolved oxygen content, water depth and in situ temperature as the key environmental factors tentatively controlling the species composition, community structure, and spatial distribution of the marginal sea sediment nifH-harboring microbiota. This confirms the ecophysiological specialization and niche differentiation

  4. A phylogenetic analysis of microbial communities associated with methane hydrate containing marine fluids and sediments in the Cascadia margin (ODP site 892B).

    PubMed

    Bidle, K A; Kastner, M; Bartlett, D H

    1999-08-01

    Methane hydrates represent an enormous carbon and energy source in many low temperature deep marine sediments. However, little information is available concerning the nature of the microbial communities associated with these structures. Here, we describe a phylogenetic analysis based on ribosomal DNA (rDNA) sequences obtained from sediment and fluid samples present in a region of gas hydrate formation in shallow sediments within the Cascadia margin in and around Ocean Drilling Program (ODP) Site 892B. Our studies detected diverse sulfur-utilizing microbes, methanogens, methanotrophs, and non-thermophilic members of the kingdom Crenarchaeota. This is the first culture-independent phylogenetic analysis of a gas hydrate habitat.

  5. Radiolarian indicators of El Nino and anti-El Nino events in Holocene sediments of Santa Barbara basin

    SciTech Connect

    Weinheimer, A.L.

    1986-04-01

    Radiolarian distributions and physical oceanographic data from the Santa Barbara basin indicate the following. Strong anti-El Nino periods can be characterized by (1) intermediate radiolarian density, (2) high percentage of transition-central radiolarian fauna, and (3) low percentage and number of warm-water radiolarian fauna. This distribution pattern is attributed to strong wind-driven upwelling and reduced northward transport by the California Countercurrent during anti-El Nino periods. Strong El Nino periods are typically (1) high in radiolarian density, and (2) low in percentage but high in number of warm-water fauna. This distribution is attributed to reduced wind-driven upwelling, enhanced northward countercurrent transport, and geostrophic doming of the cold-water masses in the shear zone between the California Current and California Countercurrent.

  6. Submarine fan sedimentation at a convergent margin: the cretaceous mangapokia formation, New Zealand

    NASA Astrophysics Data System (ADS)

    Barnes, Philip M.

    1988-10-01

    The middle Cretaceous Mangapokia Formation (Pahaoa Group) near Te Awaiti, southeast North Island, New Zealand, consists of indurated, poorly fossiliferous, alternating sandstone and argillite, minor conglomerate, grit, pebbly-sandstone, and pebbly-mudstone (terrigenous sedimentary assemblage), and minor basalt, coloured argillite, chert, and micritic limestone (ocean-floor assemblage). Seven lithofacies are distinguished in the sedimentary assemblage on the basis of lithology, bed thickness and geometry, sand/mud ratio, grain size and internal sedimentary features. Facies 1 (10-15% of total exposure), which includes all sediments coarser than sand grade, comprises seven subfacies as follows: lenticular and erosive beds of coarse-grained (Subfacies 1Ai), medium-grained (Subfacies 1Aii) and fine-grained (Subfacies 1Aiii) predominantly clast-supported conglomerate, grit (Subfacies 1Aiv) and pebbly-sandstone (Subfacies 1Av) displaying numerous types of graded bedding and sedimentary structures, were all deposited predominantly from high-concentration turbidity currents or bed-load inertia flows. Minor chaotic sand or mud matrix-supported conglomerate lenses (Subfacies 1Bi), and beds which show clear evidence of post-depositional remobilisation (Subfacies 1Bii), represent debris flow deposits. Thick lenses of sandstone and minor argillite interbeds (Facies 2) were deposited from large-volume inertia flows, possibly grainflows. Facies 3, the most common lithofacies, consists of laterally more extensive, medium thickness, graded beds of alternating sandstone and argillite with rare Bouma sequences. These deposits are proximal turbidites which accumulated in environments more distal than Facies 1 and 2. Thin-bedded (Facies 4) and very thin-bedded (Facies 5) alternating sandstone and argillite, and argillite-dominated sequences with minor interbedded sandstone (Facies 6) were deposited in interchannel depressions, on channel levees, or in areas distant from high

  7. Sources of terrestrially-derived organic carbon in lower Mississippi River and Louisiana shelf sediments: Implications for differential sedimentation and transport at the coastal margin

    USGS Publications Warehouse

    Bianchi, T.S.; Mitra, Siddhartha; McKee, B.A.

    2002-01-01

    In this study, we examined the temporal and spatial variability of terrestrial organic carbon sources in lower Mississippi River and Louisiana shelf sediments (during 11 cruises over a 22-month period) to further understand the sorting dynamics and selective transport of vascular plant materials within the primary dispersal system of the river. Bulk ??13C values in lower river sediments ranged from -21.90??? to -24.64??? (mean=-23.20??1.09???), these values were generally more depleted than those found in shelf sediments (-22.5??? to -21.2???). The ??8 (??8 = sum of vanillyl, syringyl and cinnamyl phenols produced from the oxidation of 100 mg of organic carbon) values in the lower river ranged from 0.71 to 3.74 (mean = 1.78??0.23). While there was no significant relationship between ??8 and river discharge (p>0.05), the highest value occurred during peak discharge in April 1999-which corresponded to the highest observed C/N value of 17.41. The ??8 values on the shelf ranged from 0.68 to 1.36 (mean = 0.54??0.30) and were significantly lower (p <0.05) than the average value for lower river sediments. The range of S/V (syringyl/vanillyl) and C/V (cinnamyl/vanillyl) ratios on the shelf, 0.11 to 0.95 and 0.01 to 0.08, respectively, were similar to that found in the lower river. These low C/V ratios are indicative a mixture of woody and non-woody carbon sources. Recent work by Goni et al. [Nature 389 (1997) 275; Geochim. Cosmochim. Acta 62 (1998) 3055], which did not include sampling transects within the primary dispersal system of the Mississippi River, showed a non-woody vascular plant signature on the Louisiana shelf. This suggests that riverine-derived woody tissues preferentially settle out of the water column, in the lower river and inner shelf, prior to the selective dispersal of C3 versus C4 non-woody materials in other regions the shelf and slope. This works further demonstrates the importance of differential settlement of particles, sampling location within the

  8. Sedimentation in the Southern Okinawa Trough: enhanced particle scavenging and teleconnection between the Equatorial Pacific and western Pacific margins

    NASA Astrophysics Data System (ADS)

    Lee, Shih-Yu; Huh, Chih-An; Su, Chih-Chieh; You, Chen-Feng

    2004-11-01

    Owing to its location, geomorphology and hydrodynamic conditions, the southernmost part of the Southern Okinawa Trough (SOT) acts like an efficient receptacle for sediments from Taiwan and the East China Sea shelf. The high sediment flux coupled with the passage, bifurcation, upwelling, swirling and detour of Kuroshio in the SOT area result in intense particle scavenging, with sedimentary inventories of 210Pb and 239, 240Pu far greater than expected from local atmospheric input and in situ water column production. The unusually high inventories, as well as the deposition history of Pu isotopes must be explained by advective transport of Pu westward from the Marshall Islands, the largest source of Pu in the Pacific, by the North Equatorial Current (NEC) followed by northward transport of Kuroshio to the SOT area. The high sedimentation rate in the SOT area enabled us to differentiate the subsurface peak of 239, 240Pu resulting from the global fallout maximum in AD 1963 and the subsurface maximum of 240Pu/239Pu caused by close-in fallout from neutron-rich thermonuclear tests conducted by the US during AD 1952-1954 at the Enewetak and Bikini Atolls. The vertical offset between the subsurface peaks of 239, 240Pu and 240Pu/239Pu in sediments suggests that deposition of the 240Pu/239Pu maximum preceded that of the 239, 240Pu maximum by 3-5 yr and that the transit time of the 240Pu-enriched Pu from its source (at ∼12°N, 162°E) to the SOT area is ∼6 yr. The mean velocity of NEC thus calculated is ∼0.022 m s-1. The present is the key to the past. This study reveals teleconnection between the Equatorial Pacific and the western Pacific margins and suggests that ODP and IMAGES cores recently collected from the SOT area holds great promise for the reconstruction of high-resolution paleoceanographic records along the trajectories of NEC and Kuroshio.

  9. Methane and other hydrocarbon gases in sediment from the southeastern North American continental margin

    USGS Publications Warehouse

    Kvenvolden, K.A.; Lorenson, T.D.

    2000-01-01

    Residual concentrations and distributions of hydrocarbon gases from methane to n-heptane were measured in sediments at seven sites on Ocean Drilling Program (ODP) Leg 164. Three sites were drilled at the Cape Fear Diapir of the Carolina Rise, and one site was drilled on the Blake Ridge Diapir. Methane concentrations at these sites result from microbial generation which is influenced by the amount of pore-water sulfate and possible methane oxidation. Methane hydrate was found at the Blake Ridge Diapir site. The other hydrocarbon gases at these sites are likely the produce of early microbial processes. Three sites were drilled on a transect of holes across the crest of the Blake Ridge. The base of the zone of gas-hydrate occurrence was penetrated at all three sites. Trends in hydrocarbon gas distributions suggest that methane is microbial in origin and that the hydrocarbon gas mixture is affected by diagenesis, outgassing, and, near the surface, by microbial oxidation. Methane hydrate was recovered at two of these three sites, although gas hydrate is likely present at all three sites. The method used here for determining amounts of residual hydrocarbon gases has its limitations and provides poor assessment of gas distributions, particularly in the stratigraphic interval below about ~ 100 mbsf. One advantage of the method, however, is that it yields sufficient quantities of gas for other studies such as isotopic determinations.

  10. A time-transgressive Holocene onset from Globorotalia menardii records on Brazilian continental margin sediments

    NASA Astrophysics Data System (ADS)

    Iwai, F. S.; Costa, K. B.; Toledo, F. A. D. L.; Santarosa, A. C. A.; Chiessi, C. M.; Camillo, E., Jr.; Quadros, J. P.

    2014-12-01

    The planktic foraminifer Globorotalia menardii presents a cyclic behavior within Pleistocene glacial cycles on Atlantic; it disappears during glacial periods and returns to this ocean after deglaciations. Therefore, G. menardii has been used to identify limits between those cycles and the last limit is recognized as the Holocene onset. The Holocene onset has been reported before as being more than 4 kyrs later than expected at the equatorial Atlantic Ocean based on a G. menardii record (Broecker & Pena, 2014). In this study, we explore the time-transgressive Holocene onset of G. menardii in the Atlantic from 21 piston cores collected along the Brazilian continental margin, between 7 ˚N and 33 ˚S. Radiocarbon dating was conducted on Globigerinoides ruber on samples prior to and after G. menardii reappearance in the cores. Reservoir-age corrected 14C dates vary between 17 and 6.5 cal kyrs; the older ages are found at ~14 ˚S and younger ages at 6 ˚N and 33 ˚S. From these ages and latitudes, we hypothesize that G. menardii's population has spread at higher rates southward. From the scenario observed on Brazilian coast it is possible to conclude that although ocean circulation has an important role on dispersion of planktonic foraminifera, it may be superimposed by ecological constraints of the species. G. menardii absence during glacials is linked to the Agulhas Leakage activity, which is prevented from getting to the Atlantic due the northern position of the Subtropical Convergence Zone during glacials. On interglacials, warm and saline waters carrying G. menardii are transported into the Subtropical Gyre currents, achieving Brazil's coast through the South Equatorial Current and spreading south and northward through Brazil Current and North Brazil Current, respectively. Nonetheless, from velocity and volume registered for this currents, we would expect a higher G. menardii dispersion rate northward. A faster southward dispersal during the deglaciation suggests

  11. 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.

  12. The biogeochemistry of carbon in continental slope sediments: The North Carolina margin

    SciTech Connect

    Blair, N.; Levin, L.; DeMaster, D.; Plaia, G.; Martin, C.; Fornes, W.; Thomas, C.; Pope, R.

    1999-12-01

    The responses of the continental slope benthos to organic detritus deposition were studied with a multiple trace approach. Study sites were offshore of Cape Fear (I) and Cape Hatteras (III), N.C. (both 850 m water depth) and were characterized by different organic C deposition rates, macrofaunal densities (III>I in both cases) and taxa. Natural abundances of {sup 13}C and {sup 12}C in particulate organic carbon (POC), dissolved inorganic carbon (DIC) and macrofauna indicate that the reactive organic detritus is marine in origin. Natural abundance levels of {sup 14}C and uptake of {sup 13}C-labeled diatoms by benthic animals indicate that they incorporate a relatively young component of carbon into their biomass. {sup 13}C-labeled diatoms (Thalassiorsira pseudonana) tagged with {sup 210}Pb, slope sediment tagged with {sup 113}Sn and {sup 228}Th-labeled glass beads were emplaced in plots on the seafloor at both locations and the plots were sampled after 30 min., 1-1.5 d and 14 mo. At Site I, tracer diatom was intercepted at the surface primarily by protozoans and surface-feeding annelids. Little of the diatom C penetrated below 2 cm even after 14 months. Oxidation of organic carbon appeared to be largely aerobic. At Site III, annelids were primarily responsible for the initial uptake of tracer. On the time scale of days, diatom C was transported to a depth of 12 cm and was found in animals collected between 5-10 cm. The hoeing of tracer from the surface by the maldanid Praxillela sp. may have been responsible for some of the rapid nonlocal transport. Oxidation of the diatom organic carbon was evident to at least 10 cm depth. Anaerobic breakdown of organic matter is more important at Site III. Horizontal transport, which was probably biologically mediated, was an order of magnitude more rapid than vertical displacement over a year time scale. If the horizontal transport was associated with biochemical transformations of the organic matter, it may represent an

  13. Late Holocene Sediment Study From Santa María del Oro Crater Lake, Nayarit, México, Using Environmental Magnetism

    NASA Astrophysics Data System (ADS)

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

    2007-05-01

    The lake is located near the Pacific coast of Mexico, at the western end of the Trans Mexican Volcanic Belt. It is a deep lake (ca. 65 m) with steep sides and only a small bay (Agua Caliente) has shallower water (ca. 12 m). Four parallel cores between 4 and 9 m long were recovered in March 2002 from this shallower area. Sediments are characterized by alternated laminations (few millimeters to 2 cm) of sand, brown silt, green silt, reddish silt, ochre silt, and peat. The 14-C dated sequence spans the last ca. 2,600 yrs. Given this age, it is possible that each set of laminations represent annual sedimentation cycles. The record is a potential high- resolution archive of environmental and climatic variability for western Mexico for late Holocene. Magnetic measurements of susceptibility along the cores show a high variability in the concentration of magnetic mineralogy. Different magnetic and non-magnetic properties show two sets of facies in relation to its magnetic mineralogy; one group composed by sand, brown silt, green silt and peat has the magnetite and Ti-magnetite as the principal magnetic phase; the second group, composed by reddish and ochre silt, has a low Ti magnetite component and siderite, as the principal paramagnetic component. The effects of climatic variations such as the drought occurred in the archeological Classic period (100 - 900 dC), the Medieval Warm Period (950 - 1350 dC), the Little Ice Age (1400 - 1800 dC), and the droughts over the last 700 years, documented in sites along central Mexico, are recognized in the magnetic mineralogy of Santa Maria del Oro.

  14. Spatial and temporal distribution of contaminated, effluent-affected sediment on the Palos Verdes margin, southern California

    USGS Publications Warehouse

    Lee, H.J.; Sherwood, C.R.; Drake, D.E.; Edwards, B.D.; Wong, F.; Hamer, M.

    2002-01-01

    A sedimentary deposit on the continental margin near the Palos Verdes Peninsula, California is comprised of sewage effluent and geologic materials and is contaminated with metals, pesticides (including DDT and associated compounds), and PCBs. The deposit was mapped with subbottom acoustic profilers, and sediment cores were analyzed for geochemical and physical properties to determine the volume of the deposit and the distribution and mass of contaminants. Mapping showed that the deposit ranges up to 60-cm thick, has a total volume exceeding 9 million m3, and covers over 40 km2. Virtually the entire effluent-affected deposit is contaminated with DDT and PCBs. Nearly half of the area of the deposit lies on the continental slope, but 70-75% of the volume of the deposit and total mass of DDT reside on the continental shelf. Analysis of data collected biennially since 1981 by the Sanitation Districts of Los Angeles County show that the mass of DDT has apparently decreased at some stations but has remained essentially constant at others. Temporal changes m mass per unit area of DDT are not statistically significant (at the 90% confidence level) at the most contaminated locations over a 16-yr period. The results of this mapping effort were used as a basis for modeling efforts described elsewhere in this issue. ?? 2002 Elsevier Science Ltd. All rights reserved.

  15. Organic matter pools, C turnover and meiofaunal biodiversity in the sediments of the western Spitsbergen deep continental margin, Svalbard Archipelago

    NASA Astrophysics Data System (ADS)

    Pusceddu, A.; Carugati, L.; Gambi, C.; Mienert, J.; Petani, B.; Sanchez-Vidal, A.; Canals, M.; Heussner, S.; Danovaro, R.

    2016-01-01

    We investigated organic matter (OM) quantity, nutritional quality and degradation rates, as well as abundance and biodiversity of meiofauna and nematodes along the deep continental margin off Spitsbergen, in the Svalbard Archipelago. Sediment samples were collected in July 2010 and 2011 along a bathymetric gradient between 600 m and 2000 m depth, and total mass flux measured at the same depths from July 2010 to July 2011. In both sampling periods sedimentary OM contents and C degradation rates increased significantly with water depth, whereas OM nutritional quality was generally higher at shallower depths, with the unique exception at 600 m depth in 2010. Meiofaunal abundance and biomass (largely dominated by nematodes) showed the highest values at intermediate depths (ca 1500 m) in both sampling periods. The richness of meiofaunal higher taxa and nematode species richness did not vary significantly with water depth in both sampling periods. We suggest here that patterns in OM quantity, C degradation rates, and meiofauna community composition in 2011 were likely influenced by the intensification of the warm West Spitsbergen Current (WSC). We hypothesize that the intensity of the WSC inflow to the Arctic Ocean could have an important role on benthic biodiversity and functioning of deep-sea Arctic ecosystems.

  16. Variations in Organic Matter Burial and Composition in Sediments from the Indian Ocean Continental Margin Off SW Indonesia (Sumatra - Java - Flores) Since the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Jennerjahn, T. C.; Gesierich, K.; Schefuß, E.; Mohtadi, M.

    2014-12-01

    Global climate change is a mosaic of regional changes to a large extent determined by region-specific feedbacks between climate and ecosystems. At present the ocean is forming a major sink in the global carbon cycle. Organic matter (OM) storage in sediments displays large regional variations and varied over time during the Quaternary. Upwelling regions are sites of high primary productivity and major depocenters of organic carbon (OC), the least understood of which is the Indian Ocean upwelling off Indonesia. In order to reconstruct the burial and composition of OM during the Late Quaternary, we analyzed five sediment cores from the Indian Ocean continental margin off the Indonesian islands Sumatra to Flores spanning the last 20,000 years (20 kyr). Sediments were analyzed for bulk composition, stable carbon and nitrogen isotopes of OM, amino acids and hexosamines and terrestrial plant wax n-alkanes and their stable carbon isotope composition. Sedimentation rates hardly varied over time in the western part of the transect. They were slightly lower in the East during the Last Glacial Maximum (LGM) and deglaciation, but increased strongly during the Holocene. The amount and composition of OM was similar along the transect with maximum values during the deglaciation and the late Holocene. High biogenic opal covarying with OM content indicates upwelling-induced primary productivity dominated by diatoms to be a major control of OM burial in sediments in the East during the past 20 kyr. The content of labile OM was low throughout the transect during the LGM and increased during the late Holocene. The increase was stronger and the OM less degraded in the East than in the West indicating that continental margin sediments off Java and Flores were the major depocenter of OC burial along the Indian Ocean margin off SW Indonesia. Temporal variations probably resulted from changes in upwelling intensity and terrestrial inputs driven by variations in monsoon strength.

  17. Liquid chromatography-atmospheric pressure photoionization-Orbitrap analysis of fullerene aggregates on surface soils and river sediments from Santa Catarina (Brazil).

    PubMed

    Sanchís, Josep; Oliveira, Luis Felipe Silva; de Leão, Felipe Baptista; Farré, Marinella; Barceló, Damià

    2015-02-01

    In the present work, a new analytical approach is proposed for the analysis of seven fullerenes (C₆₀, C₇₀, N-methylfulleropyrrolidine, [6,6]-phenyl C₆₁ butyric acid methyl ester, [6,6]-thienyl C61 butyric acid methyl ester, C60 pyrrolidine tris-acid ethyl ester and [6,6]-phenyl C₇₁ butyric acid methyl ester fullerenes) in soils and sediments. This procedure combines an ultrasound-assisted solvent extraction (UAE) with toluene followed by liquid chromatography (LC), using a pyrenylpropyl group bonded silica based column, coupled to a high-resolution mass spectrometer (HRMS) using atmospheric pressure photoionisation (APPI) in negative ion mode. The analytical performance for fullerene separation of the pyrenylpropyl group bonded silica column was compared to the C18 column. For the ultra-trace analysis of fullerenes in complex environmental samples, the use of the APPI source and the use of the electrospray ionisation (ESI) source were compared. Using this approach for the analysis of fullerenes in complex matrices, a series of advantages, in terms of sensitivity and specificity, have been demonstrated. The method limits of detection (MLOD) and the method limits of quantification (MLOQ) in soils and sediments ranged from 0.022 to 0.39 pg/g and from 0.072 to 1.3 pg/g, respectively. Recoveries were between 68 and 106%. The analytical method was applied in order to assess the occurrence of selected fullerenes in 45 soils of Sul Catarinense (Santa Catalina State, Brazil) and 15 sediments from the Tubarão River, presenting different pressures of contamination: a coal-combustion power plant, car exhaust, coal mining industry and wastewater effluents. C₆₀ and C₇₀ fullerenes have been detected at concentrations ranging from the MLOD to 0.150 ng/g. None of the functionalised fullerenes were detected in any of the samples. Combustion processes, in particular car exhaust, were identified as the main source of fullerenes. However, the potential

  18. The importance of fine-grained channel margin (FGCM) deposits in assessing the multiple residence times of suspended sediment and contaminants in gravel-bed rivers

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

    We have found that fine-grained channel margin (FGCM) deposits conditioned by large woody debris (LWD) are a significant component of sediment budgets in agricultural watersheds. By volume, the deposits store about 28 percent of the annual suspended sediment load. Radiocarbon, Pb-210, and Cs-137 analyses indicate a range of sediment ages (1 year to several decades). Reservoir theory analysis indicates an average turnover time of 1.5 years and an annual mass flux equivalent to 5 percent of the annual sediment load. The power function that best fits the transit time distribution suggests that there are multiple transit times and that most sediment in the deposits is reworked on short timescales, but a portion remains in place for several decades or more. The presence of a long tail in the distribution suggests anomalous transport, which indicates a well-developed framework for subsurface contaminant transport, continuous time random walks (CTRW), could be utilized for suspended sediment transport and contaminants associated with suspended sediment. South River has a history of mercury (Hg) contamination from an industrial release that occurred 1930-1950. The distribution of ages and Hg concentrations suggest that approximately 10 percent of the sediment and 75 percent of the Hg in the deposits dates from the release period. If the sediment in FGCM deposits has been transported primarily in suspension then we can reconstruct the loading history of Hg from the plant and predict that centuries will be required to remove this material. Our approach can be generalized to assess storage of sediments and contaminants in other gravel-bed rivers.

  19. Sediment dispersal system in the Taiwan-South China Sea collision zone along a convergent margin in the perspective of source to sink

    NASA Astrophysics Data System (ADS)

    Hsiung, K.; Yu, H.

    2011-12-01

    Through a large-scale examination of the morpho-sedimentary features on seafloor in the Taiwan-Luzon convergent margin, we determined the main sediment dispersal system which stretches from 23°N to 20°N and displays as an aligned linear sediment pathway, consisting of the Penghu Canyon, the deep-sea Penghu Channel and northern Manila Trench. The seafloor of South China Sea (SCS) north of 21°N are underlain by a triangle-shaped collision basin, resulting from oblique collision between the Luzon Arc and Chinese margin, and is mainly occupied by two juxtaposed slopes, the SCS and Kaoping slopes. The Penghu Canyon is located along the tilting basin axis where is the physiographic boundary separating the SCS and Kaoping slopes. Progressive subsidence of the basin floor from this nearby uplifted Taiwan orogen results in the linear basin axis deepening and tilting towards the open SCS, serving as a longitudinal sediment conduit. Two major tributary canyons of the Formosa and Kaoping and small channels and gullies on both slopes join into the axial Penghu Canyon and form a dendritic canyon drainage system in this collision basin. The canyon drainage system is characteristic of lateral sediment supply from flank slopes and axial sediment transport down-canyon following the tilting basin axis. The significance of the collision basin in term of source to sink is that terrestrial and shallow marine sediments derived from nearby Taiwan orogen, Chinese margin and the Taiwan Strait are transported to and accumulated in the collision basin, serving as a temporary sediment sink and the major marine transport route along the basin axis. The multi-sourced sediments in the collision basin are then delivered down-dip via the Penghu Canyon to the deep-sea Penghu Channel and ultimately to the final destination of the Manila Trench, representing a regional longitudinal sediment dispersal route along the convergent margin between Taiwan and Luzon. A comparison with other examples is a

  20. A quantitative assessment of methane cycling in Hikurangi Margin sediments (New Zealand) using geophysical imaging and biogeochemical modeling

    NASA Astrophysics Data System (ADS)

    Luo, Min; Dale, Andrew W.; Haffert, Laura; Haeckel, Matthias; Koch, Stephanie; Crutchley, Gareth; De Stigter, Henko; Chen, Duofu; Greinert, Jens

    2016-12-01

    Takahe seep, located on the Opouawe Bank, Hikurangi Margin, is characterized by a well-defined subsurface seismic chimney structure ˜80,500 m2 in area. Subseafloor geophysical data based on acoustic anomaly layers indicated the presence of gas hydrate and free gas layers within the chimney structure. Reaction-transport modeling was applied to porewater data from 11 gravity cores to constrain methane turnover rates and benthic methane fluxes in the upper 10 m. Model results show that methane dynamics were highly variable due to transport and dissolution of ascending gas. The dissolution of gas (up to 3761 mmol m-2 yr-1) dwarfed the rate of methanogenesis within the simulated sediment column (2.6 mmol m-2 yr-1). Dissolved methane is mainly consumed by anaerobic oxidation of methane (AOM) at the base of the sulfate reduction zone and trapped by methane hydrate formation below it, with maximum rates in the central part of the chimney (946 and 2420 mmol m-2 yr-1, respectively). A seep-wide methane budget was constrained by combining the biogeochemical model results with geophysical data and led to estimates of AOM rates, gas hydrate formation, and benthic dissolved methane fluxes of 3.68 × 104 mol yr-1, 73.85 × 104 mol yr-1, and 1.19 × 104 mol yr-1, respectively. A much larger flux of methane probably escapes in gaseous form through focused bubble vents. The approach of linking geochemical model results with spatial geophysical data put forward here can be applied elsewhere to improve benthic methane turnover rates from limited single spot measurements to larger spatial scales.

  1. Glaciomarine sedimentation and bottom current activity on the north-western and northern continental margins of Svalbard during the late Quaternary

    NASA Astrophysics Data System (ADS)

    Chauhan, Teena; Noormets, Riko; Rasmussen, Tine L.

    2016-04-01

    Palaeo-bottom current strength of the West Spitsbergen Current (WSC) and the influence of the Svalbard-Barents Sea Ice Sheet (SBIS) on the depositional environment along the northern Svalbard margins are poorly known. Two gravity cores from the southern Yermak Plateau and the upper slope north of Nordaustlandet, covering marine isotope stage (MIS) 1 to MIS 5, are investigated. Five lithofacies, based on grain size distribution, silt/clay ratio, content and mean of sortable silt (SS), are distinguished to characterise the contourite-dominated sedimentary environments. In addition, depositional environments are described using total organic carbon (TOC), total sulphur (TS) and calcium carbonate (CaCO3) contents of sediments. Facies A, containing coarse SS, suggests strong bottom current activity and good bottom water ventilation conditions as inferred from low TOC content. This facies was deposited during the glacial periods MIS 4, MIS 2 and during the late Holocene. Facies B is dominated by fine SS indicating weak bottom current and poor ventilation (cf. high TOC content of 1.2-1.6%), and correlates with the MIS 4/3 and MIS 2/1 transition periods. With an equal amount of clay and sand, fine SS and high content of TOC, facies C indicates reduced bottom current strength for intervals with sediment supply from proximal sources such as icebergs, sea ice or meltwater discharge. This facies was deposited during the last glacial maximum. Facies D represents mass-flow deposits on the northern Svalbard margin attributed to the SBIS advance at or near the shelf edge. Facies E sediments indicating moderate bottom current strength were deposited during MIS 5 and MIS 3, and during parts of MIS 2. This first late Quaternary proxy record of the WSC flow and sedimentation history from the northern Svalbard margin suggests that the oceanographic conditions and ice sheet processes have exerted first-order control on sediment properties.

  2. Decadal changes in carbon fluxes at the East Siberian continental margin: interactions of ice cover, ocean productivity, particle sedimentation and benthic life

    NASA Astrophysics Data System (ADS)

    Boetius, A.; Bienhold, C.; Felden, J.; Fernandez Mendez, M.; Gusky, M.; Rossel, P. E.; Vedenin, A.; Wenzhoefer, F.

    2015-12-01

    The observed and predicted Climate-Carbon-Cryosphere interactions in the Arctic Ocean are likely to alter productivity and carbon fluxes of the Siberian continental margin and adjacent basins. Here, we compare field observations and samples obtained in the nineties, and recently in 2012 during the sea ice minimum, to assess decadal changes in the productivity, export and recycling of organic matter at the outer East Siberian margin. In the 90s, the Laptev Sea margin was still largely ice-covered throughout the year, and the samples and measurements obtained represent an ecological baseline against which current and future ecosystem shifts can be assessed. The POLARSTERN expedition IceArc (ARK-XXVII/3) returned in September 2012 to resample the same transects between 60 and 3400 m water depth as well as stations in the adjacent deep basins. Our results suggest that environmental changes in the past two decades, foremost sea ice thinning and retreat, have led to a substantial increase in phytodetritus sedimentation to the seafloor, especially at the lower margin and adjacent basins. This is reflected in increased benthic microbial activities, leading to higher carbon remineralization rates, especially deeper than 3000 m. Besides a relative increase in typical particle degrading bacterial types in surface sediments, bacterial community composition showed little variation between the two years, suggesting that local microbial communities can cope with changing food input. First assessments of faunal abundances suggest an increase in polychaetes,holothurians and bivalves at depth, which fits the prediction of higher productivity and particle deposition rates upon sea ice retreat. The presentation also discusses the controversial issue whether there is evidence for an Arctic-wide increase in carbon flux, or whether we are looking at a spatial shift of the productive marginal ice zone as the main factor to enhance carbon flux to the deep Siberian margin.

  3. Sediments overlying exhumed continental mantle: a proxy for the morphotectonic evolution of the Ocean Continent Transition in magma-poor rifted margins

    NASA Astrophysics Data System (ADS)

    Karpoff, A. M.; Manatschal, G.; Bernoulli, D.; Lagabrielle, Y.

    2003-04-01

    Observations from ancient and present-day magma-poor rifted margins in the Alps and Iberia provide compelling evidence that within the ocean-continent transition (OCT) crustal and sub-continental mantle rocks were exhumed along downward-concave faults which were active during final rifting and accommodated high amounts of extension. The faults are overlain by stranded allochthons of continental origin, pillow basalts, and pelagic sediments, i.e. radiolarites and/or pelagic limestones, and hemipelagic shales. Associated with the faults are tectono-sedimentary breccias and various types of clastic sediments, ranging from debris flow deposits to laminated sandstone, and quartz-rich silt- and claystones. Mineralogical studies of the shales, red jaspers, and red cherts overlying mantle rocks in the Alps of eastern Switzerland are typically quartz-rich and contain variable amounts of phyllosilicates (chlorite and/or mica), feldspars, ± calcite, oxides, pyrite, and epidote. Their main geochemical characteristic is the high silica and low iron and manganese content, which contrasts with that of "metalliferous" Fe-Mn-Si-rich sediments overlying oceanic basalts. High Fe, Ba, REE, U/Th values measured in black shales overlying mantle rocks in the proximal OCT point to a strong hydrothermal activity associated with mantle exhumation. The clastic sediments in the OCT show a wide range of compositions related to mantle, continental crust, and/or pelagic contributions. In particular, the fact that these sediments contain abundant material derived from continental basement rocks seems at odds with their occurrence on top of tectonized mantle rocks. However, drilling in the Iberia margin, where tectonized mantle rocks are overlain by sedimentary breccias (e.g. ODP Sites 1068, 1070), shed new light on the observations in the Alps. Based on drill-hole and seismic data, the tectono-sedimentary breccias drilled in the OCT off Iberia may be interpreted to result from a conveyor

  4. Organic geochemistry of sediments from the continental margin off southern New England, U.S.A.--Part I. Amino acids, carbohydrates and lignin

    NASA Technical Reports Server (NTRS)

    Steinberg, S. M.; Venkatesan, M. I.; Kaplan, I. R.

    1987-01-01

    Total organic carbon (TOC), lignin, amino acids, sugars and amino sugars were measured in recent sediments for the continental margin off southern New England. The various organic carbon fractions decreased in concentration with increasing distance from shore. The fraction of the TOC that was accounted for by these major components also decreased with increasing distance from shore. The concentration of lignin indicated that only about 3-5% of the organic carbon in the nearshore sediment was of terrestrial origin. The various fractions were highly correlated, which was consistent with a simple linear mixing model of shelf organic matter with material form the slope and rise and indicated a significant transport of sediment from the continental shelf to the continental slope and rise.

  5. Organic geochemistry of sediments from the continental margin off southern New England, U.S.A.--Part I. Amino acids, carbohydrates and lignin.

    PubMed

    Steinberg, S M; Venkatesan, M I; Kaplan, I R

    1987-01-01

    Total organic carbon (TOC), lignin, amino acids, sugars and amino sugars were measured in recent sediments for the continental margin off southern New England. The various organic carbon fractions decreased in concentration with increasing distance from shore. The fraction of the TOC that was accounted for by these major components also decreased with increasing distance from shore. The concentration of lignin indicated that only about 3-5% of the organic carbon in the nearshore sediment was of terrestrial origin. The various fractions were highly correlated, which was consistent with a simple linear mixing model of shelf organic matter with material form the slope and rise and indicated a significant transport of sediment from the continental shelf to the continental slope and rise.

  6. Influence of the Portuguese Bend landslide on the character of the effluent-affected sediment deposit, Palos Verdes margin, southern California

    USGS Publications Warehouse

    Kayen, R.E.; Lee, H.J.; Hein, J.R.

    2002-01-01

    Historic accretion of sediment on the Palos Verdes margin off Los Angeles County, CA, is dominated by two sources, effluent from Whites Point outfall and sediment eroded from the toe of Portuguese Bend landslide. In this paper, we document the recent history of sedimentation from these non-marine sources from 1937 until the late 1990s, and attempt to estimate the amount of material preserved on the shelf. Toward that end, we characterized offshore sediment by physical and geotechnical testing, using non-destructive gamma-ray whole-core logging techniques and conventional geotechnical strength tests, and X-ray diffraction. Results are reported within a geographic information system framework that allows for: (1) the evaluation of the spatial variability of the measured properties, and (2) assessment of the influence of these properties on processes affecting the effluent-affected Sediment layer. In the inner shelf, material eroded by wave action from the toe of the Portuguese Bend landslide since 1956 has contributed 5.7-9.4 million metric tons (Mmt) of sediment, from a total eroded mass of 12.1 Mmt. A lesser fraction (???2.7Mmt) of sediment is incorporated into the mid- and outer-shelf effluent-affected sediment layer. Evidence from X-ray diffractograms clearly indicates that landslide material has mixed with the mid- and outer-shelf effluent. From 1937-1987, it is estimated that 3.8 Mmt of solid anthropogenic effluent was discharged into the water column and onto the Palos Verdes Shelf.

  7. Quantification of microbial communities in near-surface and deeply buried marine sediments on the Peru continental margin using real-time PCR.

    PubMed

    Schippers, Axel; Neretin, Lev N

    2006-07-01

    Deeply buried marine sediments harbour a large fraction of all prokaryotes on Earth but it is still unknown which phylogenetic and physiological microbial groups dominate the deep biosphere. In this study real-time PCR allowed a comparative quantitative microbial community analysis in near-surface and deeply buried marine sediments from the Peru continental margin. The 16S rRNA gene copy numbers of prokaryotes and Bacteria were almost identical with a maximum of 10(8)-10(10) copies cm(-3) in the near-surface sediments. Archaea exhibited one to three orders of magnitude lower 16S rRNA gene copy numbers. The 18S rRNA gene of Eukarya was always at least three orders of magnitude less abundant than the 16S rRNA gene of prokaryotes. The 16S rRNA gene of the Fe(III)- and Mn(IV)-reducing bacterial family Geobacteraceae and the dissimilatory (bi)sulfite reductase gene (dsrA) of sulfate-reducing prokaryotes were abundant with 10(6)-10(8) copies cm(-3) in near-surface sediments but showed lower numbers and an irregular distribution in the deep sediments. The copy numbers of all genes decreased with sediment depth exponentially. The depth gradients were steeper for the gene copy numbers than for numbers of total prokaryotes (acridine orange direct counts), which reflects the ongoing degradation of the high-molecular-weight DNA with sediment age and depth. The occurrence of eukaryotic DNA also suggests DNA preservation in the deeply buried sediments.

  8. Modeling sulfate reduction in methane hydrate-bearing continental margin sediments: Does a sulfate-methane transition require anaerobic oxidation of methane?

    USGS Publications Warehouse

    Malinverno, A.; Pohlman, J.W.

    2011-01-01

    The sulfate-methane transition (SMT), a biogeochemical zone where sulfate and methane are metabolized, is commonly observed at shallow depths (1-30 mbsf) in methane-bearing marine sediments. Two processes consume sulfate at and above the SMT, anaerobic oxidation of methane (AOM) and organoclastic sulfate reduction (OSR). Differentiating the relative contribution of each process is critical to estimate methane flux into the SMT, which, in turn, is necessary to predict deeper occurrences of gas hydrates in continental margin sediments. To evaluate the relative importance of these two sulfate reduction pathways, we developed a diagenetic model to compute the pore water concentrations of sulfate, methane, and dissolved inorganic carbon (DIC). By separately tracking DIC containing 12C and 13C, the model also computes ??13C-DIC values. The model reproduces common observations from methane-rich sediments: a well-defined SMT with no methane above and no sulfate below and a ??13C-DIC minimum at the SMT. The model also highlights the role of upward diffusing 13C-enriched DIC in contributing to the carbon isotope mass balance of DIC. A combination of OSR and AOM, each consuming similar amounts of sulfate, matches observations from Site U1325 (Integrated Ocean Drilling Program Expedition 311, northern Cascadia margin). Without AOM, methane diffuses above the SMT, which contradicts existing field data. The modeling results are generalized with a dimensional analysis to the range of SMT depths and sedimentation rates typical of continental margins. The modeling shows that AOM must be active to establish an SMT wherein methane is quantitatively consumed and the ??13C-DIC minimum occurs. The presence of an SMT generally requires active AOM. Copyright 2011 by the American Geophysical Union.

  9. Late Quaternary slip on the Santa Cruz Island fault, California

    USGS Publications Warehouse

    Pinter, N.; Lueddecke, S.B.; Keller, E.A.; Simmons, K.R.

    1998-01-01

    The style, timing, and pattern of slip on the Santa Cruz Island fault were investigated by trenching the fault and by analysis of offset late Quaternary landforms. A trench excavated across the fault at Christi Beach, on the western coast of the island, exposed deformation of latest Pleistocene to Holocene sediments and pre-Quaternary rocks, recording repeated large-magnitude rupture events. The most recent earthquake at this site occurred ca. 5 ka. Coastal terraces preserved on western Santa Cruz Island have been dated using the uranium-series technique and by extrapolation using terrace elevations and the eustatic record. Offset of terraces and other landforms indicates that the Santa Cruz Island fault is predominantly left lateral, having a horizontal slip rate of not more than 1.1 mm/yr and probably about 0.8 mm/yr. The fault also has a smaller reverse component, slipping at a rate of between 0.1 and 0.2 mm/yr. Combined with measurements of slip per event, this information suggests a long-term average recurrence interval of at least 2.7 k.y. and probably 4-5 k.y., and average earthquake magnitudes of Mw 7.2-7.5. Sense of slip, recurrence interval, and earthquake magnitudes calculated here for the Santa Cruz Island fault are very similar to recent results for other faults along the southern margin of the western Transverse Range, including the Malibu Coast fault, the Santa Monica fault, the Hollywood fault, and the Raymond fault, supporting the contention that these faults constitute a continuous and linked fault system, which is characterized by large but relatively infrequent earthquakes.

  10. Differences in meiofauna communities with sediment depth are greater than habitat effects on the New Zealand continental margin: implications for vulnerability to anthropogenic disturbance

    PubMed Central

    Leduc, Daniel; Rowden, Ashley A.; Clark, Malcolm R.; Probert, P. Keith; Berkenbusch, Katrin; Neira, Carlos

    2016-01-01

    Studies of deep-sea benthic communities have largely focused on particular (macro) habitats in isolation, with few studies considering multiple habitats simultaneously in a comparable manner. Compared to mega-epifauna and macrofauna, much less is known about habitat-related variation in meiofaunal community attributes (abundance, diversity and community structure). Here, we investigated meiofaunal community attributes in slope, canyon, seamount, and seep habitats in two regions on the continental slope of New Zealand (Hikurangi Margin and Bay of Plenty) at four water depths (700, 1,000, 1,200 and 1,500 m). We found that patterns were not the same for each community attribute. Significant differences in abundance were consistent across regions, habitats, water and sediment depths, while diversity and community structure only differed between sediment depths. Abundance was higher in canyon and seep habitats compared with other habitats, while between sediment layer, abundance and diversity were higher at the sediment surface. Our findings suggest that meiofaunal community attributes are affected by environmental factors that operate on micro- (cm) to meso- (0.1–10 km), and regional scales (> 100 km). We also found a weak, but significant, correlation between trawling intensity and surface sediment diversity. Overall, our results indicate that variability in meiofaunal communities was greater at small scale than at habitat or regional scale. These findings provide new insights into the factors controlling meiofauna in these deep-sea habitats and their potential vulnerability to anthropogenic activities. PMID:27441114

  11. Distribution of aliphatic hydrocarbons, polycyclic aromatic hydrocarbons and organochlorinated pollutants in deep-sea sediments of the Southern Cretan margin, Eastern Mediterranean Sea: a baseline assessment.

    PubMed

    Mandalakis, Manolis; Polymenakou, Paraskevi N; Tselepides, Anastasios; Lampadariou, Nikolaos

    2014-07-01

    Deep sediments from the southern Cretan margin were analyzed to establish baseline levels for various types of organic pollutants before the anticipated intensification of anthropogenic activities. The total concentration of aliphatic hydrocarbons (ΣAH:326-3758ngg(-1), dry weight) was similar to those reported for deep sediments of the western Mediterranean Sea, while considerably lower levels were measured for polycyclic aromatic hydrocarbons (ΣPAH:9-60ngg(-1)). Source-diagnostic ratios suggested that the aliphatic hydrocarbons in sediments were mainly of terrestrial biogenic origin, while polycyclic aromatic hydrocarbons stemmed from the deposition of long-range transported combustion aerosols. Among the organochlorinated compounds analyzed, β-hexachlorocyclohexane (β-HCH:222-7052pgg(-1)), 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (p,p'-DDT:37-2236pgg(-1)) and polychlorinated biphenyls (ΣPCB:38-1182pgg(-1)) showed the highest abundance in sediments. The presence of HCHs and PCBs was attributed to historical inputs that have undergone extensive weathering, whereas an ongoing fresh input was suggested for p,p'-DDT. Multiple linear regression analysis revealed that the levels of the various pollutants in sediments were controlled by different factors, but with organic carbon content playing a prominent role in most cases.

  12. Differences in meiofauna communities with sediment depth are greater than habitat effects on the New Zealand continental margin: implications for vulnerability to anthropogenic disturbance.

    PubMed

    Rosli, Norliana; Leduc, Daniel; Rowden, Ashley A; Clark, Malcolm R; Probert, P Keith; Berkenbusch, Katrin; Neira, Carlos

    2016-01-01

    Studies of deep-sea benthic communities have largely focused on particular (macro) habitats in isolation, with few studies considering multiple habitats simultaneously in a comparable manner. Compared to mega-epifauna and macrofauna, much less is known about habitat-related variation in meiofaunal community attributes (abundance, diversity and community structure). Here, we investigated meiofaunal community attributes in slope, canyon, seamount, and seep habitats in two regions on the continental slope of New Zealand (Hikurangi Margin and Bay of Plenty) at four water depths (700, 1,000, 1,200 and 1,500 m). We found that patterns were not the same for each community attribute. Significant differences in abundance were consistent across regions, habitats, water and sediment depths, while diversity and community structure only differed between sediment depths. Abundance was higher in canyon and seep habitats compared with other habitats, while between sediment layer, abundance and diversity were higher at the sediment surface. Our findings suggest that meiofaunal community attributes are affected by environmental factors that operate on micro- (cm) to meso- (0.1-10 km), and regional scales (> 100 km). We also found a weak, but significant, correlation between trawling intensity and surface sediment diversity. Overall, our results indicate that variability in meiofaunal communities was greater at small scale than at habitat or regional scale. These findings provide new insights into the factors controlling meiofauna in these deep-sea habitats and their potential vulnerability to anthropogenic activities.

  13. Sediment movement and dispersal patterns on the Grand Banks continental shelf and slope were tied to the dynamics of the Laurentide ice-sheet margin

    NASA Astrophysics Data System (ADS)

    Rashid, H.; MacKillop, K.; Piper, D.; Vermooten, M.; Higgins, J.; Marche, B.; Langer, K.; Brockway, B.; Spicer, H. E.; Webb, M. D.; Fournier, E.

    2015-12-01

    The expansion and contraction of the late Pleistocene Laurentide ice-sheet (LIS) was the crucial determining factor for the geomorphic features and shelf and slope sediment mobility on the eastern Canadian continental margin, with abundant mass-transport deposits (MTDs) seaward of ice margins on the upper slope. Here, we report for the first time sediment failure and mass-transport deposits from the central Grand Banks slope in the Salar and Carson petroleum basins. High-resolution seismic profiles and multibeam bathymetry show numerous sediment failure scarps in 500-1600 m water depth. There is no evidence for an ice margin on the upper slope younger than MIS 6. Centimeter-scale X-ray fluorescence analysis (XRF), grain size, and oxygen isotope data from piston cores constrain sediment processes over the past 46 ka. Geotechnical measurements including Atterberg limit tests, vane shear measurements and triaxial and multi-stage isotropic consolidation tests allowed us to assess the instability on the continental margin. Cores with continuous undisturbed stratigraphy in contourite silty muds show normal downcore increase in bulk density and undrained peak shear strength. Heinrich (H) layers are identifiable by a marked increase in the bulk density, high Ca (ppm), increase in iceberg-rafted debris and lighter δ18O in the polar planktonic foram Neogloboquadrina pachyderma (sinistral): with a few C-14 dates they provide a robust chronology. There is no evidence for significant supply of sediment from the Grand Banks at the last-glacial maximum. Mass-transport deposits (MTD) are marked by variability in the bulk density, undrained shear strength and little variation in bulk density or Ca (ppm) values. The MTD are older than 46 ka on the central Grand Banks slope, whereas younger MTDs are present in southern Flemish Pass. Factor of safety calculations suggest the slope is statically stable up to gradients of 10°, but more intervals of silty mud may fail during earthquake

  14. Conditions and mechanism for the formation of iron-rich Montmorillonite in deep sea sediments (Costa Rica margin): Coupling high resolution mineralogical characterization and geochemical modeling

    NASA Astrophysics Data System (ADS)

    Charpentier, D.; Buatier, M. D.; Jacquot, E.; Gaudin, A.; Wheat, C. G.

    2011-03-01

    Iron-rich smectite is commonly described in the diagenetic fraction of deep-sea sediment, as millimeter to centimeter aggregates dispersed in the sediment, or as a coating on sedimentary particles or nodules. This study examines several factors to elucidate formation mechanisms of a particular iron-rich smectite and its potential transformation to glauconite. The study combines a detailed mineralogical investigation on natural samples and a chemical modeling approach to assess mineralogical reactions and pathways. Transmission electron microscopy (TEM) observations and analytical electron microscopy (TEM-AEM) analyses were conducted on microtomed samples of millimeter- to centimeter-long green grains. These grains are widespread in pelagic calcareous sediment from the Costa Rica margin. They are composed of pyrites that are partially dissolved and are surrounded by amorphous or very poorly crystallized iron-rich particles. Iron-rich montmorillonite grows from an amorphous precursor and its formation requires the input of Si, O, Mg, K, Na and Ca; our results suggest that these inputs are supported by the dissolution of sedimentary phases such as volcanic glasses, siliceous fossils and silicates. Thermodynamic modeling of fluid-sediment interactions was conducted with the geochemical computer code PhreeqC, using mineralogical and pore fluid compositions from sediment samples and calculated estimates for thermodynamic constants of smectites that are not maintained by the computer code. Simulations confirm the possibility that the green grains are the product of pyrite alteration by seawater under oxidizing conditions. The extent of smectite production is controlled by the kinetics of pyrite dissolution and fluid migration. The absence of aluminum in the Costa Rica margin system explains the formation of an iron-rich montmorillonite instead of glauconite, whereas the presence of calcite that buffers the system explains the formation of an iron-rich montmorillonite

  15. Factors governing abundance of hydrolyzable amino acids in the sediments from the N.W. European Continental Margin (47 50°N)

    NASA Astrophysics Data System (ADS)

    Boski, T.; Pessoa, J.; Pedro, P.; Thorez, J.; Dias, J. M. A.; Hall, I. R.

    1998-12-01

    Fifty-six samples representing 6 sediment cores taken along the N.W. European Continental Margin from the shelf, slope and abyssal plain of the Goban Spur and Meriadzek Terrace were quantitatively analysed for total hydrolyzable amino acids (THAA) and clay minerals. In descending order, the five most abundant amino acids making up more than 70% of the total were: aspartic acid, glycine, serine, alanine and glutamic acid. Clay mineral proportions were typical for the N.E. Atlantic, in order of descending abundance: illite, kaolinite, chlorite, smectite and mixed layers. The Meriadzek Terrace area is characterised by fine grain suspension sedimentation with a low pelagic carbonate input and the lowest content of THAA. In contrast, the Goban Spur transect is characterised by much higher carbonate inputs and more vigorous hydrodynamics as judged from granulometry and the high abundance of minerals of shelf and continental origin and a generally higher THAA content. The pelagic portion of THAA deposited at the sea floor is more readily mineralised during early diagenesis than the more `refractory', clay mineral-associated continental portion. Along this margin the average mineralization of THAA down to 25 cm in the sediment is about 54%. There is a significant affinity between chlorites and amino acids which we suggest may involve the formation of ionic bonds between the octahedral layers of the clay and the amino acids.

  16. Evolution of post-rift sediment transport on a young rifted margin : Insights from the eastern part of the Gulf of Aden

    NASA Astrophysics Data System (ADS)

    Baurion, C.; Gorini, C.; Leroy, S.; Lucazeau, F.; Migeon, S.

    2012-04-01

    The formation of gravity-driven sedimentary systems on continental rifted margins results from the interaction between climate, ocean currents and tectonic activity. During the early stages of margin evolution, the tectonic processes are probably as important as climate for the sedimentary architecture. Therefore, the young margins (ca. 35 Ma) of the Gulf of Aden provide the opportunity to evaluate the respective roles of monsoon and tectonic uplift in the formation and evolution through the post-rift period of gravity-driven deposits (Mass Transport Complexes (MTCs) and deep-sea systems) on the continental slopes and in the oceanic basin respectively. Here we present a combined geomorphologic and stratigraphic study of the northern margin (Oman and Yemen) and the southern margin (Socotra island), in which we classified and interpreted the gravity-driven processes, their formation and their evolution during the post-rift period. The interpretation of seismic lines reveals the presence of bottom currents since the drift phase, suggesting that the Gulf of Aden was connected to the world oceans at that time. An abrupt depositional change affected the eastern basin of the Gulf of Aden around 10 Ma or thereafter (Chron 5), characterised by the first occurrence of deep sea fans and an increase in the number of MTCs. The first occurrence of MTCs may be explained by the combined 2nd-3rd order fall of the relative sea-level (Serravalian/Tortonian transition). This variation of relative sea level combined with a climatic switch (Asian monsoon onset around 15 Ma and its intensification around 7-8 Ma) control the sediment flux. The youngest unit of the post-rift supersequence is characterised by a second important MTC occurrence that is restricted to the eastern part of the deep basin. This is caused by a late uplift of the northern and southern margins witnessed onshore by the presence of young stepped marine terraces.

  17. Suspended sediment and phosphorus in proglacial rivers: bioavailability and potential impacts upon the P status of ice-marginal receiving waters

    NASA Astrophysics Data System (ADS)

    Hodson, Andy; Mumford, Paul; Lister, Debbie

    2004-09-01

    This paper adopts standard tests developed in temperate catchment research to determine the total phosphorus (TP) and the algal available (base-extractable) phosphorus (NaOH-P) content of a wide range of glaciofluvial sediments from the Northern Hemisphere. We find that the TP content of these sediments is broadly similar to the P content of major rock types in Earth's crust (230-670 μgP/g) and so the TP yields of glacier basins may be high owing to the efficacy of suspended sediment evacuation by glacial meltwaters. We show that this is best achieved where subglacial drainage systems are present. The NaOH-P pool of the sediments is found to be low (1-23 μgP/g) relative to the TP pool and also to the NaOH-P pool of suspended sediments in temperate, non-glacierized catchments. This most probably reflects the restricted duration of intimate contact between dilute meltwaters and glacial suspended sediments during the ablation season. Thus, despite the high surface-area:volume ratio of glacial suspended sediments, the potential for P adsorption to mineral surfaces following release by dissolution is also low. Further, sorption experiments and sequential extraction tests conducted using glacial suspended sediments from two Svalbard catchments indicate that the generation of reactive secondary minerals (e.g. Fe- and other hydroxides) with a strong capacity to scavenge P from solution (and thereby promote the continued dissolution of P) may also be limited by the short residence times. Most P is therefore associated with poorly weathered, calcite/apatite-rich mineral phases. However, we use examples from the Svalbard glacier basins (Austre Brøggerbreen and Midre Lovénbreen) to show that the high sediment yields of glaciers may result in appreciable NaOH-P loading of ice-marginal receiving waters. Again, the importance of subglacial drainage is highlighted, as it produces a major, episodic release of NaOH-P at Midre Lovénbreen that results in a yield (8.2 kg Na

  18. An Assessment of Global Organic Carbon Flux Along Continental Margins

    NASA Technical Reports Server (NTRS)

    Thunell, Robert

    2004-01-01

    This project was designed to use real-time and historical SeaWiFS and AVHRR data, and real-time MODIS data in order to estimate the global vertical carbon flux along continental margins. This required construction of an empirical model relating surface ocean color and physical variables like temperature and wind to vertical settling flux at sites co-located with sediment trap observations (Santa Barbara Basin, Cariaco Basin, Gulf of California, Hawaii, and Bermuda, etc), and application of the model to imagery in order to obtain spatially-weighted estimates.

  19. Sediment transport processes at the head of Halibut Canyon, Eastern Canada margin: An interplay between internal tides and dense shelf water cascading.

    NASA Astrophysics Data System (ADS)

    Puig, Pere; Greenan, Blair J. W.; Li, Michael Z.; Prescott, Robert H.; Piper, David J. W.

    2013-04-01

    To investigate the processes by which sediment is transported through a submarine canyon incised in a glaciated margin, the bottom boundary layer quadrapod RALPH was deployed at 276-m depth in the West Halibut Canyon (off Newfoundland) during winter 2008-2009. Two main sediment transport processes were identified throughout the deployment. Firstly, periodic increases of near-bottom suspended-sediment concentrations (SSC) were recorded associated with the up-canyon propagation of the semidiurnal internal tidal bore along the canyon axis, carrying fine sediment particles resuspended from deeper canyon regions. The recorded SSC peaks, lasting less than one hour, were observed sporadically and were linked to bottom intensified up-canyon flows concomitant with sharp drops in temperature. Secondly, sediment transport was also observed during events of intensified down-canyon current velocities that occurred during periods of sustained heat loss from surface waters, but were not associated with large storms. High-resolution velocity profiles throughout the water column during these events revealed that the highest current speeds (~1 m s-1) were centered several meters above the sea floor and corresponded to the region of maximum velocities of a gravity flow. Such flows had associated low SSC and cold water temperatures and have been interpreted as dense shelf water cascading events channelized along the canyon axis. Sediment transport during these events was largely restricted to bedload and saltation, producing winnowing of sands and fine sediments around larger gravel particles. Analysis of historical hydrographic data suggests that the origin of such gravity flows is not related to the formation of coastal dense waters advected towards the canyon head. Rather, the dense shelf waters appear to be generated around the outer shelf, where convection during winter is able to reach the sea floor and generate a pool of near-bottom dense water that cascades into the canyon

  20. Vertical distribution of nitrite reductase genes (nir S) in continental margin sediments of the Gulf of Mexico.

    PubMed

    Tiquia, Sonia M; Masson, Steven A; Devol, Allan

    2006-12-01

    Marine sediments account for up to 66% of the loss of nitrogen load to coastal areas. Sedimentary denitrification is the main sink for fixed nitrogen in the global nitrogen budget, and thus it is important to understand the structure and composition of denitrifying communities. To understand the structure and composition of denitrifying communities, the diversity of nitrite reductase (nirS) genes from sediments along the Gulf of Mexico was examined using a PCR-based cloning approach. Sediments were collected at three different depths (0-0.5, 4-5 and 19-21 cm). Geochemical analysis revealed decreasing nitrate and oxygen concentrations with increasing sediment depth. This trend coincided with the decrease in diversity of denitrifying bacteria. LIBSHUFF analysis indicated that the clone library in the shallowest sediment (depth, 0-0.5 cm) was significantly different from that in the deepest sediment (depth, 19-21 cm), and that the deeper sediments (depths of 4-5 and 19-21 cm) were significantly similar. Community structural shifts were evident between the shallowest (oxic zone) and deepest (anoxic zone) sediments. Community changes within the deepest sediments were more subtle, with the presence of different nirS clone sequences gradually becoming dominant or, alternatively, decreasing with depth. The changes in community structure at this depth are possibly driven by nutrient availability, with lower quality sources of carbon and energy leading to the disappearance of nirS sequences common in the top layer. The majority of recovered nirS sequences were phylogenetically divergent relative to known denitrifying bacteria in the database.

  1. Landscape response to late Pleistocene climate change along the Puna Plateau margin: Sediment flux and cosmogenic landslide signatures modulated by basin geometry

    NASA Astrophysics Data System (ADS)

    Schildgen, T. F.; Robinson, R. A. J.; Savi, S.; Phillips, W. M.; Spencer, J. Q. G.; Bookhagen, B.; Scherler, D.; Tofelde, S.; Alonso, R. N.; Kubik, P.; Binnie, S. A.; Strecker, M. R.

    2015-12-01

    Along the steep flanks of the southern Central Andes (eastern margin of the Puna Plateau), fluvial fill terraces preserve archives of landscape response to climate change over millennial timescales. These archives record information about past erosion and aggradation rates, erosion processes, and even paleoclimate. In the Humahuaca Basin of NW Argentina, our 29 new optically stimulated luminescence ages of late Pleistocene fill terrace sediments demonstrate that past river aggradation occurred over different intervals on the west and east sides of the valley. On the west side, aggradation coincided with periods of increasing intensity of the South American Monsoon System and the South Atlantic Convergence Zone (increasing precipitation), while on the east side, aggradation coincided with periods of decreasing intensities of both systems (decreasing precipitation) or with more variable conditions. Denudation rates and grain-size dependencies from 70 new cosmogenic 10Be analyses reveal that landslides were more important during periods of increasing precipitation compared to today. On the west side of the valley, a sudden pulse of sediment led to aggradation near the intersection with the trunk stream. In contrast, on the east side, the pulse of sediment likely blocked the narrow bedrock gorges that characterize those catchments, leading to temporary sediment storage in upstream perched basins; sediment evacuation into the main valley occurred preferentially during periods of decreasing precipitation and fewer landslides. Different levels of fluvial connectivity to the trunk stream for the western and eastern catchments within the Humahuaca Basin produces heterogeneity in the locus of aggradation and the timing of sediment movement through the system. Hence, for larger basins that integrate sub-basins with differing geometries or degrees of connectivity, sedimentary responses to climate forcing are likely to be attenuated.

  2. Geomorphology, acoustic backscatter, and processes in Santa Monica Bay from multibeam mapping.

    PubMed

    Gardner, James V; Dartnell, Peter; Mayer, Larry A; Hughes Clarke, John E

    2003-01-01

    Santa Monica Bay was mapped in 1996 using a high-resolution multibeam system, providing the first substantial update of the submarine geomorphology since the initial compilation by Shepard and Emery [(1941) Geol. Soc. Amer. Spec. Paper 31]. The multibeam mapping generated not only high-resolution bathymetry, but also coregistered, calibrated acoustic backscatter at 95 kHz. The geomorphology has been subdivided into six provinces; shelf, marginal plateau, submarine canyon, basin slope, apron, and basin. The dimensions, gradients, and backscatter characteristics of each province is described and related to a combination of tectonics, climate, sea level, and sediment supply. Fluctuations of eustatic sea level have had a profound effect on the area; by periodically eroding the surface of Santa Monica plateau, extending the mouth of the Los Angeles River to various locations along the shelf break, and by connecting submarine canyons to rivers. A wetter glacial climate undoubtedly generated more sediment to the rivers that then transported the increased sediment load to the low-stand coastline and canyon heads. The trends of Santa Monica Canyon and several bathymetric highs suggest a complex tectonic stress field that has controlled the various segments. There is no geomorphic evidence to suggest Redondo Canyon is fault controlled. The San Pedro fault can be extended more than 30 km to the northwest by the alignment of a series of bathymetric highs and abrupt changes in direction of channel thalwegs.

  3. Chemistry and mineralogy of pyrite-enriched sediments at a passive margin sulfide brine seep: abyssal Gulf of Mexico

    USGS Publications Warehouse

    Commeau, R.F.; Paull, C.K.; Commeau, J.A.; Poppe, L.J.

    1987-01-01

    Pyrite is rapidly accumulating at the contact between the Cretaceous limestones of the Florida Platform and the hemipelagic sediments of the abyssal Gulf of Mexico. Sediments sampled with the submersible "Alvin" in 3266 m of water are associated with a dense community of organisms that depend on chemosynthetic primary production as a food source. Analysis of the chemistry, mineralogy, and textural composition of these sediments indicate that iron sulfide mineralization is occurring at the seafloor within an anoxic micro-habitat sustained by the advection of hydrogen sulfide-charged saline brines from the adjacent platform. The chemosynthetic bacteria that directly overlie the sediments oxidize hydrogen sulfide for energy and provide elemental sulfur that reacts with iron monosulfide to form some of the pyrite. The sediments are mixtures of pyrite (??? 30 wt.%), BaSr sulfates (??? 4 wt.%), clays, and locally derived biogenic carbonates and are progressively being cemented by iron sulfides. Oxidation of hydrogen sulfide produces locally acidic conditions that corrode the adjacent limestones. Potential sources of S, H2S, Fe, Ba, and Sr are discussed. ?? 1987.

  4. Continental-Margin Processes Recorded in Shelf and Canyon Sediments Documenting Fine-Sediment Import and Export for Two Contrasting Mesotidal Flats

    DTIC Science & Technology

    2008-01-01

    are the foundation for understanding and interpreting sedimentary processes and seabed stratigraphy . To investigate the relationship between... Sedimentological Congress, Fukuoka (2006). T.M. Drexler, C.A. Nittrouer, A.S. Ogston, P. Puig, Sediment record on the Rhone prodelta and processes controlling

  5. Isopach map showing Quaternary deposits in the Gulf of Santa Catalina area, California

    USGS Publications Warehouse

    McCrory, Patricia A.

    1993-01-01

    The Gulf of Santa Catalina is part of the California Continental Borderand, an active transform margin characterized by narrow shelves, steep slopes, and deep closed basin separated by shallow banks and islands. The Gulf of Santa Catalina extend from Point Fermin south to San Diego. It is bounded on the west by prominent bedrock ridges, 30 to 45 km offshore, compromising Santa Catalina Island and Thirtymile Bank. The predominant structural grain within the Gulf of Santa Catalina trends northwesterly. Two major fault zones bound a relatively undeformed structural block, the Catalina block (Clarke and others, 1983). The Newport-Inglewood-Rose Canyon Fault Zone forms the northeast boundary of the Catalina block, and the Palos Verdes Hills-Coronafo Bank Fault Zone forms the southwest boundary (Figure 1). Both of these fault zones are characterized by discontinuous, right-stepping en echelon faults and associated folds. Major structural and physiographic features within and bounding the Catalina block are compatible with wrench-style tectonism (Harding, 1973; Wilcox and others, 1973; Nardin and Henyey, 1978). The distribution of seismicity, along with geophysical evidence showing local displacement of sea floor and Holocene deposits, indicate that Newport-Inglewood, Palos Verdes Hills, and subsidiary faults are active (Clarke and others, 1983). The distribution of Quaternary sediments (Pleistocene and Holocene) off the coast of southern California provides insight into recent sedimentation patterns and recency of faulting and tectonic deformation. This report focuses on the distribution of Quaternary sediments, particularly in the shelf and upper slop areas, the sources of detrial sediment, and depositional environments of Holocene as well as relict deposits.

  6. Methanogen and bacterial diversity and distribution in deep gas hydrate sediments from the Cascadia Margin as revealed by 16S rRNA molecular analysis.

    PubMed

    Marchesi; Weightman; Cragg; Parkes; Fry

    2001-01-01

    The microbial community of a deep (to 234 m below the sea floor) sediment gas hydrate deposit (Cascadia Margin Ocean Drilling Program Site 889/890, Leg 146) was analysed for the first time by molecular genetic techniques. Both bacterial and methanogen diversity were determined by phylogenetic analysis of ribosomal DNA sequences. High molecular mass DNA, indicative of active bacteria, was present in all of the samples. Ribosomal RNA genes were amplified from extracted DNA extracted from sediment using bacteria, and methanogen specific PCR primers, the latter designed in this study. Phylogenetic analysis of approximately 400 bacterial clones demonstrated that 96% were members of the Proteobacteria. These clones were affiliated with the alpha, beta and gamma subdivisions, with Caulobacter (Zymomonas group), Ralstonia and Pseudomonas phylotypes predominating. The methanogen clones were of low diversity and clustered in three sub-groups. Two of these sub-groups (contained 96% of the 400 clones) were closely related to Methanosarcina mazeii, while the third sub-group clustered in the Methanobacteriales. This analysis of a deep sediment gas hydrate environment shows a bacteria and methanogen community of limited diversity and confirms that the gas hydrate zone is biogeochemically active. These results are consistent with the presence of bacterial populations capable of methanogenesis throughout the core, and suggest that the methane hydrate at this site is at least partially biogenic in origin.

  7. Quantification of the effects of eustasy, subsidence, and sediment supply on Miocene sequences, mid-Atlantic margin of the United States

    USGS Publications Warehouse

    Browning, J.V.; Miller, K.G.; McLaughlin, P.P.; Kominz, M.A.; Sugarman, P.J.; Monteverde, D.; Feigenson, M.D.; Hernandez, J.C.

    2006-01-01

    We use backstripping to quantify the roles of variations in global sea level (eustasy), subsidence, and sediment supply on the development of the Miocene stratigraphic record of the mid-Atlantic continental margin of the United States (New Jersey, Delaware, and Maryland). Eustasy is a primary influence on sequence patterns, determining the global template of sequences (i.e., times when sequences can be preserved) and explaining similarities in Miocene sequence architecture on margins throughout the world. Sequences can be correlated throughout the mid-Atlantic region with Sr-isotopic chronology (??0.6 m.y. to ??1.2 m.y.). Eight Miocene sequences correlate regionally and can be correlated to global ??18O increases, indicating glacioeustatic control. This margin is dominated by passive subsidence with little evidence for active tectonic overprints, except possibly in Maryland during the early Miocene. However, early Miocene sequences in New Jersey and Delaware display a patchwork distribution that is attributable to minor (tens of meters) intervals of excess subsidence. Backstripping quantifies that excess subsidence began in Delaware at ca. 21 Ma and continued until 12 Ma, with maximum rates from ca. 21-16 Ma. We attribute this enhanced subsidence to local flexural response to the progradation of thick sequences offshore and adjacent to this area. Removing this excess subsidence in Delaware yields a record that is remarkably similar to New Jersey eustatic estimates. We conclude that sea-level rise and fall is a first-order control on accommodation providing similar timing on all margins to the sequence record. Tectonic changes due to movement of the crust can overprint the record, resulting in large gaps in the stratigraphic record. Smaller differences in sequences can be attributed to local flexural loading effects, particularly in regions experiencing large-scale progradation. ?? 2006 Geological Society of America.

  8. Potential Feedbacks Between Tectonics, Climate, and Sediment Accumulation in a Neogene-Quaternary Intermontane Basin on the Margin of the Puna Plateau, Quebrada de Humahuaca, NW Argentina

    NASA Astrophysics Data System (ADS)

    Streit, R. L.; Burbank, D. W.; Strecker, M. R.; Alonso, R. N.

    2014-12-01

    Feedbacks between tectonics, climate, and sediment storage or removal in intermontane basins have the potential to modulate plateau growth. Previous studies suggest that the lithostatic load of thick sedimentary basin fills promotes the propagation of deformation into the foreland, whereas the removal of large volumes of sediment results in thrusting stepping back into the hinterland. To investigate these feedbacks, we reconstruct the Neogene-Quaternary deformational and sedimentary history of the northern Humahuaca basin, an intermontane basin on margin of the Puna Plateau. The timing of faulting, folding, sediment accumulation, and unconformities is constrained by U-Pb zircon dating of volcanic ashes interbedded with the sedimentary fill. As in the southern Humahuaca basin, the transition from westerly-derived sandstone and conglomeratic foreland basin deposits (Maimará Fm.) to predominately conglomeratic intermontane basin fills with variable provenance occurred at 4.3 Ma and is interpreted to result from uplift of the eastern basin-bounding ranges. In the northern Humahuaca basin, however, this transition is punctuated by two unconformities between 5 - 3.8 Ma. Between 4.3 - 2.5 Ma, the basin fill was dominated by rounded pebble-cobble conglomerates. Around 2.5 Ma, these conglomerates gave way to the fine-grained deposits of the Uquía Fm. and sediment-accumulation rates increased from 200-400 m/Myr to >500 m/Myr. This interval of fine-grained deposition and high sediment-accumulation rates may reflect a period of basin isolation and severed fluvial connectivity with the foreland related to increased aridity as a result of uplift of the eastern ranges. The transition back to conglomerates occurs at 2.2 Ma in the southern part of the northern Humahuaca basin and sometime between 2.1 and 1.3 Ma in the north. An unconformity exists between 2 Ma and 1 Ma strata. Thrust faults on the west side of the basin were active from >4.3 Ma to <3 Ma. Thrusts in the center of

  9. Organic geochemistry of sediments from the continental margin off southern New England, U.S.A.--Part II. Lipids

    NASA Technical Reports Server (NTRS)

    Venkatesan, M. I.; Ruth, E.; Steinberg, S.; Kaplan, I. R.

    1987-01-01

    Organic geochemical measurements of the lipid fraction, comparing saturated and aromatic hydrocarbons, fatty acids, alcohols and sterols, have been carried out on six sediments cores collected from the Atlantic shelf, slope and the rise areas to evaluate the cross-shelf transport of the organic carbon. The concentration of most of the organic compound classes studied is correlated with the total organic carbon, which decreases from the shelf through slope to the rise. Terrigenous carbon is recognizable even in the slope and rise sediments, but terrestrial influx decreases relative to marine generated lipids in the slope and rise organic matter. We estimate that approximately 50% of the shelf organic matter is exported to the slope. Data of sediment trap material collected at 1200 m from 1250 m water depth are discussed and compared with that of surface sediment from 1280 m water depth (slope). Fluxes for specific organic compound classes have been computed. The fluxes are of the same magnitude as for equatorial North Atlantic trap particulates at comparable water depth, studied by other investigations.

  10. Fan sedimentation on continental margins: A comparison of Miocene Gulf Coast systems with the Middle Eocene Cozy Dell Formation of southern California

    SciTech Connect

    Riese, W.C.R. ); Clark, M.S. )

    1990-05-01

    Recent seismic and subsurface stratigraphic studies of the Miocene System, offshore Texas resulted in the development of a depositional model that documents and explains the deposition of sand-prone fans on the outer shelf during times when these areas were still covered by several hundred feet of water. This model suggests that sediment transport was by turbid flow and that sedimentation resulted in the development of leveed channel systems. The geometries and scales of these fan systems have been documented by three-dimensional seismic analysis and field-wide well penetrations in the Matagorda 668 field. It further advances the hypothesis that global eustatic levels were generally higher and basin water budgets greater during the Miocene than during later times in at least the Gulf Coast area. Translation of this model to outcrop areas is hampered in the Gulf Coast, and detail verification and refinement of the model has been restricted to subsurface work alone. This has also hampered the authors attempt to carry this model to non-Miocene-age systems. Work on the middle Eocene Cozy Dell Formation exposures in the Topatopa and Santa Ynez Mountains of southern California has revealed that this formation has a depositional history which may not be different than that interpreted for the Gulf Coast Miocene. This formation was deposited by turbidity currents in what has been interpreted to be an upper slope setting. The fans deposited by these currents have well-developed channel-levee complexes and display scales of geometry similar to those seen in the Gulf Coast Miocene. This formation displays seismic-sequence scale stratal geometries that suggest that it was deposited during lowstands of sea level.

  11. Seismic modelling of gas hydrate and free gas in sediments, from ocean-bottom seismometer data along the continental margin of Western Svalbard

    NASA Astrophysics Data System (ADS)

    Chabert, A.; Minshull, T. A.; Westbrook, G. K.; Berndt, C.

    2009-12-01

    Over the next decades, the shallow parts of continental margins in the Arctic are likely to experience warming of bottom-water. It is, therefore, important to evaluate how methane hydrate beneath the seabed in these margins will react to future increases in bottom-water temperature and whether release of methane from hydrate will have an impact on climate. As part of the International Polar Year initiative, a multidisciplinary marine expedition was carried out in August-September 2008 along the continental margin west of Svalbard in the Arctic Ocean. One of its objectives was to determine the extent of the gas hydrate stability zone (GHSZ) along the continental slope and to quantify the amount of methane present as hydrate or gas beneath the seabed, using seismic techniques. Thirteen ocean-bottom seismometers (OBS) were deployed at 5 representative sites along and across the continental margin. High frequency airguns (GI guns) were fired at 5-s intervals and the data were recorded at a high sampling rate (1 kHz) in the OBS. The records show clear P-wave reflections at short offsets, as well as refracted arrivals at larger offsets, from depths up to 2 km below the seabed. The sub-seabed variation of P-wave velocity was modelled for three sites located above and below the upper limit of GHSZ, using ray-traced forward modelling. The velocity model for the deepest site (~1250 m deep) below the upper limit of the GHSZ shows a zone about 120 metres below the seabed with a greater velocity (1.8 km/s) than expected for terrigenous sediment. This high velocity zone lies above a lower velocity zone (1.55 km/s) and the acoustic contrast between the two zones forms a bottom simulator reflector (BSR) at approximately 170 m below the seabed. The BSR marks the boundary between sediments containing gas hydrate above and free gas below. The velocity model from the shallow site (~480 m deep), below the upper limit of the GHSZ, indicates the presence of a low velocity zone (1.60 km

  12. Remnants of Miocene fluvial sediments in the Negev Desert, Israel, and the Jordanian Plateau: Evidence for an extensive subsiding basin in the northwestern margins of the Arabian plate

    NASA Astrophysics Data System (ADS)

    Zilberman, Ezra; Calvo, Ran

    2013-06-01

    Relics of a thick, widely spread, fluvial sequence of Early Miocene age are scattered throughout southern Israel, eastern Sinai, the Dead Sea Rift Valley and the western margins of the Jordanian Plateau. These relics are mainly preserved in structural lows, karstic systems, and abandoned stream valleys. The paleogeography of this fluvial system was reconstructed based on the relations between the sequence remnants and the main structural and morphological features of the southeastern Levant region. Three sedimentary associations were identified in the Miocene sequence: a lower part dominated by locally derived clastic sediments; a thicker middle part, composed mostly of far-field allochthonous clastic sediments; and an upper part composed of local as well as allochthonous sediments. The two lower parts are regionally distributed whereas the upper part is syn-tectonic and confined to the Dead Sea basin and the Karkom graben in the central Negev. The composition of the far-field allochthonous sediments points to a provenance of Precambrian crystalline rocks of the Arabo-Nubian massif that were exposed along the uplifted shoulders of the Red Sea Rift as the upper drainage basin of the fluvial system. The diverse mammal remains found in this fluvial sequence suggest a complex of savanna, forests and fluvial habitats similar to those of present East Africa, with monsoon-type rains, which were the dominant water source of the rivers. The thickness of the Miocene sequence in the central Negev is at least 1700 m, similar to that of the subsurface sequence encountered in the Dead Sea basin. This similarity suggests that both were parts of an extensive subsiding sedimentary basin that developed between the Neo-Tethys and the uplifted margins of the Red Sea. The relations between the reconstructed pre-depositional landscape of southern Israel during the Early Miocene and the overlying fluvial sequence indicate that the entire area was buried under several hundred meters of

  13. The relationships between soft-sediment deformation structures and synsedimentary extensional tectonics in Upper Triassic deep-water carbonate succession (Southern Tethyan rifted continental margin - Central Sicily)

    NASA Astrophysics Data System (ADS)

    Basilone, Luca; Sulli, Attilio; Gasparo Morticelli, Maurizio

    2016-10-01

    We describe soft-sediment deformation structures into the Upper Triassic cherty limestone outcropping in the Pizzo Lupo section (Central Sicily, Italy), pertaining to the deep-water palaeodomain of the Southern Tethyan margin. In the study section, mainly consisting of thin-bedded mudstone/marl alternations with bedded chert intercalations, some lithofacies have been separated on the basis of the abundance of the calcium carbonate/clay content and the overall textural features. The deformational structures, displaying different deformational styles as folded and faulted beds, disturbed layers, clastic dikes, and slumps occur mainly in the deformed horizons that involve marl-dominated lithofacies. Small-scale water-escape structures involve beds with nodular fabric. Synsedimentary faults affect the mud-limestone dominated lithofacies, which are characterized by fault-rotating blocks producing lateral thinning. These bodies appear to have moved coherently along an overall planar surface. We relate these soft-sediment deformations to slump sheets, associated with down-slope sliding of sedimentary masses. The deformation mechanism and driving force for these soft-sediment deformations are due essentially to gravitational instability and dewatering. Detailing, rotational (slump) and translational (glide) slides and water-escape are the main processes causing the distinguished deformational styles. The synsedimentary extensional tectonics that affected the Upper Triassic pelagic deposits was the triggering process responsible for the instability of the seafloor inducing loss of coherence of the unconsolidated sediments on the sea bottom, developing a large number of gravity-driven slides. The analysis of both of these SSDSs and their relationships with the structural scenario allow us to hypothesise that they are seismically-induced.

  14. Chronic Polyaromatic Hydrocarbon (PAH) Contamination Is a Marginal Driver for Community Diversity and Prokaryotic Predicted Functioning in Coastal Sediments

    PubMed Central

    Jeanbille, Mathilde; Gury, Jérôme; Duran, Robert; Tronczynski, Jacek; Ghiglione, Jean-François; Agogué, Hélène; Saïd, Olfa Ben; Taïb, Najwa; Debroas, Didier; Garnier, Cédric; Auguet, Jean-Christophe

    2016-01-01

    Benthic microorganisms are key players in the recycling of organic matter and recalcitrant compounds such as polyaromatic hydrocarbons (PAHs) in coastal sediments. Despite their ecological importance, the response of microbial communities to chronic PAH pollution, one of the major threats to coastal ecosystems, has received very little attention. In one of the largest surveys performed so far on coastal sediments, the diversity and composition of microbial communities inhabiting both chronically contaminated and non-contaminated coastal sediments were investigated using high-throughput sequencing on the 18S and 16S rRNA genes. Prokaryotic alpha-diversity showed significant association with salinity, temperature, and organic carbon content. The effect of particle size distribution was strong on eukaryotic diversity. Similarly to alpha-diversity, beta-diversity patterns were strongly influenced by the environmental filter, while PAHs had no influence on the prokaryotic community structure and a weak impact on the eukaryotic community structure at the continental scale. However, at the regional scale, PAHs became the main driver shaping the structure of bacterial and eukaryotic communities. These patterns were not found for PICRUSt predicted prokaryotic functions, thus indicating some degree of functional redundancy. Eukaryotes presented a greater potential for their use as PAH contamination biomarkers, owing to their stronger response at both regional and continental scales. PMID:27594854

  15. Chronic Polyaromatic Hydrocarbon (PAH) Contamination Is a Marginal Driver for Community Diversity and Prokaryotic Predicted Functioning in Coastal Sediments.

    PubMed

    Jeanbille, Mathilde; Gury, Jérôme; Duran, Robert; Tronczynski, Jacek; Ghiglione, Jean-François; Agogué, Hélène; Saïd, Olfa Ben; Taïb, Najwa; Debroas, Didier; Garnier, Cédric; Auguet, Jean-Christophe

    2016-01-01

    Benthic microorganisms are key players in the recycling of organic matter and recalcitrant compounds such as polyaromatic hydrocarbons (PAHs) in coastal sediments. Despite their ecological importance, the response of microbial communities to chronic PAH pollution, one of the major threats to coastal ecosystems, has received very little attention. In one of the largest surveys performed so far on coastal sediments, the diversity and composition of microbial communities inhabiting both chronically contaminated and non-contaminated coastal sediments were investigated using high-throughput sequencing on the 18S and 16S rRNA genes. Prokaryotic alpha-diversity showed significant association with salinity, temperature, and organic carbon content. The effect of particle size distribution was strong on eukaryotic diversity. Similarly to alpha-diversity, beta-diversity patterns were strongly influenced by the environmental filter, while PAHs had no influence on the prokaryotic community structure and a weak impact on the eukaryotic community structure at the continental scale. However, at the regional scale, PAHs became the main driver shaping the structure of bacterial and eukaryotic communities. These patterns were not found for PICRUSt predicted prokaryotic functions, thus indicating some degree of functional redundancy. Eukaryotes presented a greater potential for their use as PAH contamination biomarkers, owing to their stronger response at both regional and continental scales.

  16. The stable carbon isotope biogeochemistry of acetate and other dissolved carbon species in deep subseafloor sediments at the northern Cascadia Margin

    USGS Publications Warehouse

    Heuer, V.B.; Pohlman, J.W.; Torres, M.E.; Elvert, M.; Hinrichs, K.-U.

    2009-01-01

    Ocean drilling has revealed the existence of vast microbial populations in the deep subseafloor, but to date little is known about their metabolic activities. To better understand the biogeochemical processes in the deep biosphere, we investigate the stable carbon isotope chemistry of acetate and other carbon-bearing metabolites in sediment pore-waters. Acetate is a key metabolite in the cycling of carbon in anoxic sediments. Its stable carbon isotopic composition provides information on the metabolic processes dominating acetate turnover in situ. This study reports our findings for a methane-rich site at the northern Cascadia Margin (NE Pacific) where Expedition 311 of the Integrated Ocean Drilling Program (IODP) sampled the upper 190 m of sediment. At Site U1329, ??13C values of acetate span a wide range from -46.0??? to -11.0??? vs. VPDB and change systematically with sediment depth. In contrast, ??13C values of both the bulk dissolved organic carbon (DOC) (-21.6 ?? 1.3??? vs. VPDB) and the low-molecular-weight compound lactate (-20.9 ?? 1.8??? vs. VPDB) show little variability. These species are interpreted to represent the carbon isotopic composition of fermentation products. Relative to DOC, acetate is up to 23.1??? depleted and up to 9.1??? enriched in 13C. Broadly, 13C-depletions of acetate relative to DOC indicate flux of carbon from acetogenesis into the acetate pool while 13C-enrichments of pore-water acetate relative to DOC suggest consumption of acetate by acetoclastic methanogenesis. Isotopic relationships between acetate and lactate or DOC provide new information on the carbon flow and the presence and activity of specific functional microbial communities in distinct biogeochemical horizons of the sediment. In particular, they suggest that acetogenic CO2-reduction can coexist with methanogenic CO2-reduction, a notion contrary to the hypothesis that hydrogen levels are controlled by the thermodynamically most favorable electron-accepting process

  17. Fluid flow, methane fluxes, carbonate precipitation and biogeochemical turnover in gas hydrate-bearing sediments at Hydrate Ridge, Cascadia Margin: numerical modeling and mass balances

    NASA Astrophysics Data System (ADS)

    Luff, Roger; Wallmann, Klaus

    2003-09-01

    A numerical model was applied to investigate and to quantify biogeochemical processes and methane turnover in gas hydrate-bearing surface sediments from a cold vent site situated at Hydrate Ridge, an accretionary structure located in the Cascadia Margin subduction zone. Steady state simulations were carried out to obtain a comprehensive overview on the activity in these sediments which are covered with bacterial mats and are affected by strong fluid flow from below. The model results underline the dominance of advective fluid flow that forces a large inflow of methane from below (869 μmol cm -2 a -1) inducing high oxidation rates in the surface layers. Anaerobic methane oxidation is the major process, proceeding at a depth-integrated rate of 870 μmol cm -2 a -1. A significant fraction (14%) of bicarbonate produced by anaerobic methane oxidation is removed from the fluids by precipitation of authigenic aragonite and calcite. The total rate of carbonate precipitation (120 μmol cm -2 a -1) allows for the build-up of a massive carbonate layer with a thickness of 1 m over a period of 20,000 years. Aragonite is the major carbonate mineral formed by anaerobic methane oxidation if the flow velocity of methane-charge fluids is high enough (≥10 cm a -1) to maintain super-saturation with respect to this highly soluble carbonate phase. It precipitates much faster within the studied surface sediments than previously observed in abiotic laboratory experiments, suggesting microbial catalysis. The investigated station is characterized by high carbon and oxygen turnover rates (≈1000 μmol cm -2 a -1) that are well beyond the rates observed at other continental slope sites not affected by fluid venting. This underlines the strong impact of fluid venting on the benthic system, even though the flow velocity of 10 cm a -1 derived by the model is relative low compared to fluid flow rates found at other cold vent sites. Non-steady state simulations using measured fluid flow

  18. High-resolution seismic-reflection interpretations of some sediment deposits, Antarctic continental margin: Focus on the western Ross Sea

    USGS Publications Warehouse

    Karl, Herman A.

    1989-01-01

    High-resolution seismic-reflection data have been used to a varying degree by geoscientists to interpret the history of marine sediment accumulations around Antarctica. Reconnaissance analysis of 1-, 3.5-, and 12-kHz data collected by the U.S. Geological Survey in the western Ross Sea has led to the identification of eight echo-character facies and six microtopographic facies in the sediment deposits that overlie the Ross Sea unconformity. Three depositional facies regions, each characterized by a particular assemblage of echo-character type and microtopographic facies, have been identified on the continental shelf. These suites of acoustic facies are the result of specific depositional processes that control type and accumulation of sediment in a region. Evidence of glacial processes and products is uncommon in regions 1 and 2, but is abundant in region 3. McMurdo Sound, region 1, is characterized by a monospecific set of acoustic facies. This unique assemblage probably represents turbidity current deposition in the western part of the basin. Most of the seafloor in region 2, from about latitude 77??S to 75??S, is deeper than 600 m below sealevel. The microtopographic facies and echo-character facies observed on the lower slopes and basin floor there reflect the thin deposits of pelagic sediments that have accumulated in the low-energy conditions that are typical of deep-water environments. In shallower water near the boundary with region 3, the signature of the acoustic facies is different from that in deeper water and probably indicates higher energy conditions or, perhaps, ice-related processes. Thick deposits of tills emplaced by lodgement during the most recent advance of the West Antarctic Ice Sheet are common from latitude 75??S to the northern boundary of the study area just south of Coulman Island (region 3). The signature of microtopographic facies in this region reflects the relief of the base of the grounded ice sheet prior to decoupling from the

  19. Tracking Monsoon Related Provenance Changes in Continental Margin Sediments of the East China Sea: Preliminary Results from IODP Expedition 346.

    NASA Astrophysics Data System (ADS)

    Anderson, C. H.; Dunlea, A. G.; Murray, R. W.; Kinsley, C. W.; McGee, D.; Giosan, L.; Zheng, H.; Tada, R.; Alvarez Zarikian, C. A.

    2014-12-01

    Sedimentation in the East China Sea (ECS) is driven largely by fluvial and eolian fluxes that are likely influenced by the East Asian Monsoon (EAM). Terrigenous matter from the Yangtze River is transported into the ECS and is also carried by winds of the Westerly Jet. Seasonal and long term shifts in the atmospheric and precipitation regimes over Asia are recorded in the inorganic chemistry of the sediment of the ECS and other Asian coastal seas. For example, changes in intensity and timing of the EAM over short and long term time scales likely impact the relative proportion of fluvial and eolian inputs to the region, and perhaps their individual sources. Bulk sediment was recovered from IODP Sites U1428 and U1429 in the ECS during Expedition 346. T these sites are separated by 7.4 km, located in the northernmost portion of the ECS in the Danjo Basin, and are generally characterized by two sedimentary units. Unit A is largely nannofossil-rich calcareous ooze and calcareous-rich clays, punctuated with smaller tephra layers throughout. Unit B is composed of fine- to medium-grained, rounded sands. Here we present major, trace and rare earth element (REE) data for 54 bulk sediment samples analyzed via ICP-ES and ICP-MS. We trace downhole fluctuations in the geochemical data in order to investigate the provenance of terrigenous material during the Pleistocene. Preliminary major element concentration data indicate the presence of distinct continental sediment and carbonates at both sites. Average downhole major element ratios exhibit limited variation at both sites. For example, Ti/Al (g/g) is tightly constrained with values of 0.05 /- 0.003, Fe/Al 0.5 /- 0.05, and Si/Al 3.3 /- 0.3. In addition to standard geochemical techniques to assess provenance, we are using multivariate statistics (e.g., Q-Mode Factor Analyses, Multiple Linear Regressions) to examine this large dataset. We focus on a smaller suite of elements that are exclusively associated with the terrigenous

  20. Mineralogical, geochemical and isotopic characterization of authigenic carbonates from the methane-bearing sediments of the Bering Sea continental margin (IODP Expedition 323, Sites U1343-U1345)

    NASA Astrophysics Data System (ADS)

    Pierre, C.; Blanc-Valleron, M.-M.; Caquineau, S.; März, C.; Ravelo, A. C.; Takahashi, K.; Alvarez Zarikian, C.

    2016-03-01

    During Expedition 323 of the Integrated Ocean Drilling Program to the Bering Sea (July 5-September 4, 2009), three sites were drilled along the Bering Sea northeastern continental margin [U1343 down to 745 meters below sea floor (mbsf), U1344 (745 mbsf), U1345 (150 mbsf)]. Diagenetic carbonates are present at all sites within the clayey, diatom-rich oozes of the Bering Sea, where pore waters are also characterized by extremely high methane concentrations. We here present mineralogical, elemental and isotopic data obtained from the authigenic carbonate-rich intercalations within the clay-rich Pleistocene sediments deposited along the Bering Sea continental margin. The mineralogy of the authigenic carbonates is generally represented by composite mixtures of very small crystals of magnesian calcite, dolomite, and iron-rich carbonates, with the latter phases occurring below 260 mbsf at Site U1343, below 200 mbsf at Site U1344, and below 130 mbsf at Site U1345. Element geochemistry shows that Ca, Mg, Fe, Ba, Mn, Sr and U are enriched in the carbonate-rich intercalations relative to the background sediments due to their incorporation into the carbonates and into other authigenic phases (e.g., barite and pyrite). The oxygen and carbon isotopic compositions of the authigenic carbonate minerals show that they were sequentially precipitated from pore waters at different temperatures (i.e., different burial depths) and with different isotopic compositions of dissolved inorganic carbon (DIC). The authigenic Mg-calcite precipitated early during diagenesis and shallow burial from a 13C-depleted DIC pool, whereas dolomite and Fe-rich carbonates formed during later diagenesis and deeper burial from a 13C-enriched DIC pool. These authigenic carbonate occurrences are interpreted as resulting from microbial sulfate reduction combined with anaerobic oxidation of methane, and methanogenesis that was intimately linked to the alteration of silicates, especially iron-rich clay minerals.

  1. DEPSCoR FY 99: Use of Stochastic Modeling of Stratigraphic Relationships in High Resolution Seismic Reflection Data for Prediction of the Distribution of Acoustic and Geotechnical Property Variability in Near Surface Sediments on the East China Sea Continental Margin

    DTIC Science & Technology

    2016-06-13

    Distribution of Acoustic and Geotechnical Property Variability in Near Surface Sediments on the East China Sea Continental Margin Louis R. Bartek Department of...of vertical and horizontal distribution of seismic facies (and therefore geotechnical and acoustic properties) • Determine the minimum data required...Resolution Seismic Reflection Data for Prediction of the Distribution of Acoustic and Geotechnical Property Variability in Near Surface Sediments on the

  2. Zircon from Mesoproterozoic sediments sheds light on the subduction-collision history at the eastern active continental margin of the Archaean Kalahari-Grunehogna Craton

    NASA Astrophysics Data System (ADS)

    Marschall, H.; Hawkesworth, C. J.; Leat, P. T.; Dhuime, B.; Storey, C.

    2013-12-01

    The Grunehogna Craton (East Antarctica) was a part of the Archean Kalahari Craton of southern Africa prior to Gondwana breakup. Granite from the basement of the craton has been dated by U-Pb zircon dating to 3,067 Ma with inherited grains showing ages of up to 3,433 Ma [1]. At the eastern margin of the craton, the Ahlmannryggen nunataks comprise an ~2000 m thick pile of clastic and volcanic sediments of the Ritscherflya Supergroup. These were sourced from eroding a proximal active continental arc as demonstrated through the age distribution and internal zoning of detrital zircon [2]. Detrital zircon grains from the Ritscherflya Supergroup show an age distribution with a dominant age peak at ~1,130 Ma, i.e., close to the sedimentation age. Older age peaks include those at 1370 Ma, 1725 Ma, 1880 Ma, 2050 Ma, and 2700 Ma. Palaeo- and Mesoarchaean zircon grains (2800-3445 Ma) were also discovered, corresponding to the age of the Kalahari-Grunehogna Craton basement. Most significantly we found a number of inherited Archaean cores in ~1130 Ma zircons. They demonstrate that the volcanic arc was indeed located on Archaean continental crust, rather than in Mesoproterozoic, intra-oceanic island arcs. The age spectrum of the zircons bears strong evidence for (i) derivation of the entire Ritscherflya sediment sequence from an active continental convergent margin; (ii) a cratonic provenance of part of the sediments from population peaks coinciding with major tectono-thermal events in the Kalahari Craton; (iii) at least some of the active volcanism being located on cratonic basement rather than a juvenile island arc. Detrital zircons in the ~1130 Ma age group show several distinct populations in their Hf isotopic compositions. The dominant group shows negative ɛHf values of -11.5 corresponding to a model age (TDM) of ~2700 Ma (average crustal 176Lu/177Hf = 0.015). A smaller group shows ɛHf values of +2 to +6, which may represent mantle-derived subduction-zone volcanism at

  3. Impact of water depth on the distribution of iGDGTs in the surface sediments from the northern South China Sea: applicability of TEX86 in marginal seas

    NASA Astrophysics Data System (ADS)

    Chen, Jiali; Hu, Pengju; Li, Xing; Yang, Yang; Song, Jinming; Li, Xuegang; Yuan, Huamao; Li, Ning; Lü, Xiaoxia

    2017-01-01

    The TEX{86/H} paleothermometer on the base of isoprenoid glycerol dialkyl glycerol tetraethers (iGDGTs) has been widely applied to various marine settings to reconstruct past sea surface temperatures (SSTs). However, it remains uncertain how well this proxy reconstructs SSTs in marginal seas. In this study, we analyze the environmental factors governing distribution of iGDGTs in surface sediments to assess the applicability of TEX{86/H} paleothermometer in the South China Sea (SCS). Individual iGDGT concentrations increase gradually eastwards. Redundancy analysis based on the relative abundance of an individual iGDGT compound and environmental parameters suggests that water depth is the most influential factor to the distribution of iGDGTs, because thaumarchaeota communities are water-depth dependent. Interestingly, the SST difference (ΔT) between TEX{86/H} derived temperature and remote-sensing SST is less than 1°C in sediments with water depth>200 m, indicating that TEX{86/H} was the robust proxy to trace the paleo-SST in the region if water depth is greater than 200 m.

  4. Mass-physical properties of surficial sediments on the Rhoˆne continental margin: implications for the nepheloid benthic layer

    NASA Astrophysics Data System (ADS)

    Chassefiere, Bernard

    1990-09-01

    Mass-physical properties of the surficial (upper 5 m) sediments on the Gulf of Lions continental margin were analysed, from more than 100 short (1 m) and longer (5 m) cores obtained during several cruises. Data include water content, unit weight, Atterberg limits (liquid limit, plastic limit, plasticity index), shear strength and compression index, and are used to determine: first, the mass property distribution, according to the main parameters influencing mass-physical properties; the relationships between these properties and the nepheloid layer on the shelf. The shoreline (lagoons) and inner shelf are characterized by low density and shear strength and high water content deposits, due to electrochemical flocculation of the sediment. The outer shelf is blanketed by higher density and shear strength and lower water content deposits generated by normal settling of suspended particles. On the inner shelf, during river peak discharges, a short-term thin bottom layer of "yogurt-like" [ FASS (1985) Geomarine Letters, 4, 147-152; FASS (1986) Continental Shelf Research, 6, 189-208] fluid-mud (unit weight lower than 1.3 mg m -3) is supplied, by a bottom nepheloid layer. During stormy periods, this "yogurt-like" layer (about 10 cm thick) partly disappears by resuspension of suspended particulate matter; this is advected, in the bottom nepheloid layer, over the shelf and the canyons within the upper slope.

  5. Neural network interpretation of LWD data (ODP Leg 170) confirms complete sediment subduction at the Costa Rica convergent margin

    NASA Astrophysics Data System (ADS)

    Moritz, Erik; Bornholdt, Stefan; Westphal, Hildegard; Meschede, Martin

    2000-01-01

    The internal structure of a convergent plate boundary was the focus of ODP Leg 170 in 1996 at the subduction zone off Costa Rica. Although the structure of the subduction zone is rather well known from seismic surveys, prior to drilling of ODP Leg 170 it was a matter of discussion whether it is accretionary or non-accretionary. With a neural network approach, we confirm the evidence gained during drilling of Leg 170, that at least presently no lower-plate sediments are transferred to the upper plate by accretion. To supplement lithological information, Logging-While-Drilling geophysical data have been included in this study and were interpreted in terms of lithology using a genetically trained artificial neural network.

  6. Organic geochemistry of continental margin and deep ocean sediments. Progress report, 1 March 1991--28 February 1993

    SciTech Connect

    Whelan, J.K.; Hunt, J.M.; Seewald, J.M.; Eglinton, L.B.; Zawoysky, M.; Dickinson, P.; Dickneider, T.

    1992-09-01

    Objective was to study petroleum formation, migration, and accumulation in marine sediments. Collaboration in Global Basin Research Network (GBRN) showed that the hydrocarbon parameters used in oil exploration are also valuable in understanding sedimentary basin fluid flow processes, crucial to production of drinking water, metal ore deposits, and gas and oil. Two goals are : (1) to run hydrous pyrolysis experiments on immature gas-prone source rocks, in order to evaluate the potential influence of gas evolution on oil migration and subsurface pressurization, and (2) to integrate organic geochemical data from the Louisiana Gulf Coast into GBRN subsurface visualization and computer modeling. Experimental methods (petrography, EPR, thermogravimetric Fourier transform infrared spectroscopy) were also studied.

  7. Regional implications of an extensive linear sediment-dispersal system along western margin of Cretaceous interior seaway

    SciTech Connect

    Vondra, C.F.; Khandaker, N.I.

    1988-01-01

    The Second Wall Creek sand in the Powder River basin in Johnson and Natrona Counties is similar in clast lithology, primary sedimentary structures, and facies association to the Torchlight Sandstone at the top of the Frontier Formation in the northern Big Horn basin. The Second Wall Creek sand is predominantly composed of medium to coarse-grained, moderately sorted massive to cross-bedded quartz-lithic wacke with a minor amount of carbonaceous shale and siltstone. The unit is conglomeraic at the top and contains abundant granule to cobble-size clasts of andesite, quartzite, chert, granite, and sandstone. The largest clasts are concentrated in the Kaycee-Mayworth area in Johnson County and progressively decrease in size southward toward Arminto in Natrona Country, Paloeocurrent directions obtained from the cross-bedded unit indicate a general south-southeast trend. The Second Wall Creek sand is thickest in the Kaycee-Mayworth area and thins southward towards Arminto. The presence of a unique petrologic suite places a constraint on provenance and sediment-dispersal patterns in a tectonically active rapidly evolving foreland basin. Of particular interest is the peculiar lensoid distribution of andesite clasts, which follows a general northwest-southeast trend for more than 150 mi from Cody to the Kaycee-Mayworth area, Wyoming. Noticeable absence of andesite clasts on either side of this observed trend suggests a strong dependence of the ultimate sediment-dispersal system on several physical constraints, including local morphotectonic setting, paleohydraulics, and provenance. A large high-energy distributary complex is invoked for the deposition of this linear conglomeratic facies. This dispersal system extended east-southeastward from the orogenic fold-and-thrust-belt into the adjoining foreland basin.

  8. Sediment geochemical records of productivity and oxygen depletion along the margin of western North America during the past 60,000 years: teleconnections with Greenland Ice and the Cariaco Basin

    USGS Publications Warehouse

    Dean, W.E.

    2007-01-01

    Many sediment records from the margins of the Californias (Alta and Baja) collected in water depths between 60 and 1200 m contain anoxic intervals (laminated sediments) that can be correlated with interstadial intervals as defined by the oxygen-isotope composition of Greenland ice (Dansgaard-Oeschger, D-O, cycles). These intervals include all or parts of Oxygen Isotope Stage 3 (OIS3; 60-24 cal ka), the Bo??lling/Allero??d warm interval (B/A; 15-13 cal ka), and the Holocene. This study uses organic carbon (Corg) and trace-element proxies for anoxia and productivity, namely elevated concentrations and accumulation rates of molybdenum and cadmium, in these laminated sediments to suggest that productivity may be more important than ventilation in producing changes in bottom-water oxygen (BWO) conditions on open, highly productive continental margins. The main conclusion from these proxies is that during the last glacial interval (LGI; 24-15 cal ka) and the Younger Dryas cold interval (YD; 13-11.6 cal ka) productivity was lower and BWO levels were higher than during OIS3, the B/A, and the Holocene on all margins of the Californias. The Corg and trace-element profiles in the LGI-B/A-Holocene transition in the Cariaco Basin on the margin of northern Venezuela are remarkably similar to those in the transition on the northern California margin. Correlation between D-O cycles in Greenland ice with gray-scale measurements in varved sediments in the Cariaco Basin also is well established. Synchronous climate-driven changes as recorded in the sediments on the margins of the Californias, sediments from the Cariaco Basin, and in the GISP-2 Greenland ice core support the hypothesis that changes in atmospheric dynamics played a major role in abrupt climate change during the last 60 ka. Millennial-scale cycles in productivity and oxygen depletion on the margins of the Californias demonstrate that the California Current System was poised at a threshold whereby perturbations of

  9. Tracking Sediment Sources to Pacific Northwest Margin Sites through Radiometric Ages of Clays: Ocean-Land Response to Millenial Scale Climate Change

    NASA Astrophysics Data System (ADS)

    Duncan, R. A.; Pisias, N. G.; Hostetler, S. W.

    2001-12-01

    The terrigenous fraction of marine sediments carries the memory of its source through its mineralogy, composition and age. This signal may also carry important information about tectonic and climatic conditions on the continents and about the mechanisms by which material is transported to the depositional site. Sediments recovered from long piston cores at sites along the Pacific Northwest margin of North America contain highly correlated records of oceanographic and terrestrial vegetation changes over the last full glacial cycle. We speculate that these records reflect principally climate-induced changes in terrestrial vegetation rather than changes in ocean circulation and sediment transport. To test this, we have begun to identify specific sources of terrigenous sediment through 40Ar-39Ar radiometric dating of clays from Pacific NW rivers. Age spectra from 15-20 step heating experiments reveal well-resolved clay formation ages from two size fractions (2-20 and 20-63 micron), and evidence of post-formation Ar-loss from low temperature steps. From these we make several important conclusions: First, the individual river clay ages are distinct from one another, and reflect the age of terranes from which they derive. Thus clay ages fingerprint discharge from specific rivers. Second, plateau (formation) ages for the two size fractions are the same. This is a different observation from that seen in previous K-Ar results, probably because the smaller size fraction has experienced more Ar-loss and K-addition during transport, and thus produces generally younger ages. However, the 40Ar-39Ar experiments reveal the same plateau (formation) ages. Thus the additional information gained from incremental heating is important in better defining the source identity. Third, we can directly measure the composition of phases carrying the age information. Two isotopes (37Ar and 39Ar) determine the Ca and K content of the phase(s) contributing to each step. The K/Ca is not strictly

  10. Sediment dispersal system in the Taiwan-South China Sea collision zone along a convergent margin: A comparison with the Papua New Guinea collision zone of the western Solomon Sea

    NASA Astrophysics Data System (ADS)

    Hsiung, Kan-Hsi; Yu, Ho-Shing

    2013-01-01

    Through a large-scale examination of the morpho-sedimentary features on sea floors in the Taiwan-Luzon convergent margin, we determined the main sediment dispersal system which stretches from 23°N to 20°N and displays as an aligned linear sediment pathway, consisting of the Penghu Canyon, the deep-sea Penghu Channel and northern Manila Trench. The seafloor of South China Sea north of 21°N are underlain by a triangle-shaped collision marine basin, resulting from oblique collision between the Luzon Arc and Chinese margin, and are mainly occupied by two juxtaposed slopes, the South China Sea and Kaoping Slopes, and a southward tilting basin axis located along the Penghu Canyon. Two major tributary canyons of the Formosa and Kaoping and small channels and gullies on both slopes join into the axial Penghu Canyon and form a dendritic canyon drainage system in this collision marine basin. The canyon drainage system is characteristic of lateral sediment supply from flank slopes and axial sediment transport down-canyon following the tilting basin axis. The significance of the collision marine basin in term of source to sink is that sediments derived from nearby orogen and continental margins are transported to and accumulated in the collision basin, serving as a temporary sediment sink and major marine transport route along the basin axis. The comparison of the Taiwan-South China Sea collision zone with the Papua New Guinea collision zone of the western Solomon Sea reveals remarkable similarities in tectonic settings and sedimentary processes that have resulted in similar sediment dispersal systems consisting of (1) a canyon drainage network mainly in the collision basin and (2) a longitudinal sediment transport system comprising a linear connection of submarine canyon, deep-sea channel and oceanic trench beyond the collision marine basin.

  11. 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

  12. A high-resolution record of Holocene millennial-scale oscillations of surface water, foraminiferal paleoecology and sediment redox chemistry in the SE Brazilian margin

    NASA Astrophysics Data System (ADS)

    Dias, B. B.; Barbosa, C. F.; Albuquerque, A. L.; Piotrowski, A. M.

    2014-12-01

    Holocene millennial-scale oscillations and Bond Events (Bond et al. 1997) are well reported in the North Atlantic as consequence of fresh water input and weaking of the Atlantic Meridional Overturning Circulation (AMOC). It has been hypothesized that the effect of weaking of AMOC would lead to warming in the South Atlantic due to "heat piracy", causing surface waters to warm and a reorganization of surface circulation. There are few reconstructions of AMOC strength in the South Atlantic, and none with a high resolution Holocene record of changes of productivity and the biological pump. We reconstruct past changes in the surface water mass hydrography, productivity, and sediment redox changes in high-resolution in the core KCF10-01B, located 128 mbsl water depth off Cabo Frio, Brazil, a location where upwelling is strongly linked to surface ocean hydrography. We use Benthic Foraminiferal Accumulation Rate (BFAR) to reconstruct productivity, which reveals a 1.3kyr cyclicity during the mid- and late-Holocene. The geochemistry of trace and rare earth elements on foraminiferal Fe-Mn oxide coatings show changes in redox-sensitive elements indicating that during periods of high productivity there were more reducing conditions in sediment porewaters, producing a Ce anomaly and reduction and re-precipitation of Mn oxides. Bond events 1-7 were identified by a productivity increase along with reducing sediment conditions which was likely caused by Brazil Current displacement offshore allowing upwelling of the nutritive bottom water South Atlantic Central Waters (SACW) to the euphotic zone and a stronger local biological pump. In a global context, correlation with other records show that this occurred during weakened AMOC and southward displacement of the ITCZ. We conclude that Bond climatic events and millennial-scale variability of AMOC caused sea surface hydrographic changes off the Brazilian Margin leading to biological and geochemical changes recorded in coastal records

  13. Late quaternary deposition in the inner basins of the California continental borderland - Part A. Santa Monica Basin

    USGS Publications Warehouse

    Normark, William R.; McGann, Mary

    2004-01-01

    Radiocarbon dating of sediment core samples from Santa Monica Basin document Holocene (younger than approximately 11 ka) landslides and fault offsets along the basin margin. The new dates include 17 from six piston cores on the continental slope and 11 from Ocean Drilling Program Site 1015 on the basin floor. The dates, which are based on data from pelagic and benthic foraminifera in addition to several dates from mollusk shells, are used to provide chronostratigraphic control for a previously determined basin-wide seismic stratigraphy. The geologic setting at the core sites and a sediment log for each core are shown. In addition, each sediment log is accompanied by a color core photograph as well as P-wave velocity and gamma-ray density profiles. The primary purpose of the report is to make the radiocarbon dates available for other studies in the Santa Monica Basin. A comparison of sediment accumulation rates between the late Pleistocene and Holocene provides insight to the effects of sea-level change on sediment input to the basin. In addition, the results can be used to evaluate the effectiveness of wire-line piston coring in providing age control for earthquake hazard and sedimentologic studies.

  14. Sedimentary response to Milankovitch-type climatic oscillations and formation of sediment undulations: evidence from a shallow-shelf setting at Gela Basin on the Sicilian continental margin

    NASA Astrophysics Data System (ADS)

    Kuhlmann, Jannis; Asioli, Alessandra; Trincardi, Fabio; Klügel, Andreas; Huhn, Katrin

    2015-01-01

    A multi-proxy chronological framework along with sequence-stratigraphic interpretations unveils composite Milankovitch cyclicity in the sedimentary records of the Last Glacial-Interglacial cycle at NE Gela Basin on the Sicilian continental margin. Chronostratigraphic data (including foraminifera-based eco-biostratigraphy and δ18O records, tephrochronological markers and 14C AMS radiometric datings) was derived from the shallow-shelf drill sites GeoB14403 (54.6 m recovery) and GeoB14414 (27.5 m), collected with both gravity and drilled MeBo cores in 193 m and 146 m water depth, respectively. The recovered intervals record Marine Isotope Stages and Substages (MIS) from MIS 5 to MIS 1, thus comprising major stratigraphic parts of the progradational deposits that form the last 100-ka depositional sequence. Calibration of shelf sedimentary units with borehole stratigraphies indicates the impact of higher-frequency (20-ka) sea level cycles punctuating this 100-ka cycle. This becomes most evident in the alternation of thick interstadial highstand (HST) wedges and thinner glacial forced-regression (FSST) units mirroring seaward shifts in coastal progradation. Albeit their relatively short-lived depositional phase, these subordinate HST units form the bulk of the 100-ka depositional sequence. Two mechanisms are proposed that likely account for enhanced sediment accumulation ratios (SAR) of up to 200 cm/ka during these intervals: (1) intensified activity of deep and intermediate Levantine Intermediate Water (LIW) associated to the drowning of Mediterranean shelves, and (2) amplified sediment flux along the flooded shelf in response to hyperpycnal plumes that generate through extreme precipitation events during overall arid conditions. Equally, the latter mechanism is thought to be at the origin of undulated features resolved in the acoustic records of MIS 5 Interstadials, which bear a striking resemblance to modern equivalents forming on late-Holocene prodeltas of other

  15. Fluxes of uranium and thorium series isotopes in the Santa Barbara Basin

    NASA Astrophysics Data System (ADS)

    Moore, Willard S.; Bruland, Kenneth W.; Michel, Jacqueline

    1981-05-01

    Samples from the MANOP Santa Barbara Basin sediment trap intercomparison were analyzed for the isotopes of uranium, thorium, radium, lead, and polonium. All of the traps showed approximately the same compositions and isotopic ratios, indicating that they trapped similar materials. The 234Th flux via falling particles was very close to the flux predicted from the production and scavenging rates of 234Th from the water column. The 210Pb content of the trapped particles and the surface sediments were the same, however, the measured flux of 210Pb was seven times greater than the predicted flux. Predicted and measured fluxes of 228Th and 210Po were similarly out of balance. To explain this apparent inconsistency, we suggest (as others have done) that the Santa Barbara Basin is an area where scavenging from the water column is intensified and where sediments deposited initially on the margins may be physically remobilized on a short time scale. These two effects increase the apparent area from which the basin derives the longer-lived isotopes but does not increase significantly the supply of the short-lived 234Th.

  16. Holocene late Pleistocene non-tropical carbonate sediments and tectonic history of the western rift basin margin of the southern Gulf of California

    NASA Astrophysics Data System (ADS)

    Halfar, Jochen; Godinez-Orta, Lucio; Goodfriend, Glenn A.; Mucciarone, David A.; Ingle, James C.; Holden, Peter

    2001-10-01

    Using high-resolution seismic reflection profiling and dating of (1) shallow marine vibracores and (2) sediments collected from uplifted marine terraces we reconstruct the tectonic history and sediment accumulation patterns of Holocene to late Pleistocene warm-temperate to subtropical carbonates in the southern Gulf of California, Mexico. The study was conducted in the vicinity of La Paz where carbonates form along the fault bounded narrow western shelf of the tectonically active Gulf of California rift basin. The non-tropical nature of the setting is responsible for (1) poor cementation of the bioclastic carbonates, and (2) a composition which is dominated by rhodoliths (coralline red algae), corals and mollusks. Unrimmed carbonate flats forming in small pocket bays and a rhodolith bioherm, which has a surface area of more than 20 km 2 and is up to 16 m thick, constitute the major carbonate factories. Holocene carbonate accumulation rates were deduced from seismic and core data and are highest on the rhodolith bioherm (260 cm/ka) and in subtidal zones of pocket bays (210 cm/ka), and lowest on the inner and middle shelf (100 cm/ka). Taken together, rates of carbonate accumulation are intermediate in magnitude between higher rates recorded in fully tropical carbonate settings and lower rates typical of cool-water carbonates. Seismic reflection profiles demonstrate that Isla Espiritu Santo in the center of the study area is a west dipping fault block, which is tectonically influenced by two distinct faults, the La Paz and Espiritu Santo faults. The latter fault accommodates at least 700 m of east-side down normal offset, and forms a steep eastern escarpment leading into the La Paz slope basin. Some of the sediments produced in the shallow carbonate factories of the narrow La Paz shelf are transported across this escarpment and are redeposited in the slope basin at a water depth of 750 m. Uranium-series dates of marine terraces exposed on Isla Espiritu Santo indicate

  17. Microbioirrigation of marine sediments in dysoxic environments: Implications for early sediment fabric formation and diagenetic processes

    NASA Astrophysics Data System (ADS)

    Pike, Jennifer; Bernhard, Joan M.; Moreton, Steven G.; Butler, Ian B.

    2001-10-01

    It is manifest in the study of dysoxic sediments from the geological record that infaunal burrowing is considered so severely limited by the lack of dissolved oxygen as to be nonexistent. Although the effects of megafauna and macrofauna on sedimentary and geochemical processes are well known, the effects of meiofauna are largely ignored. Here we document abundant meiofauna in the recent severely dysoxic, laminated sediments from the Santa Barbara basin, California margin, and also microcavities and microtunnels in laminated deglacial sediments from Palmer Deep, west Antarctic Peninsula, that we interpret to be open, relict nematode burrows. Santa Barbara basin box-core subcores were sieved to quantify metazoan abundance, and others were embedded with resin for examination of meiofaunal life positions using confocal microscopy. Metazoan densities in the surface centimeters of sediment range from 80.7 to 117.9 cm-3, and nematode populations, together with their abundant burrows, remain quite high to at least 3 cm. Scanning electron microscope analysis of fractured surfaces in Palmer Deep sediments revealed that the rigid diatom ooze framework aids the preservation of ˜50 μm diameter open nematode burrows. These structures were observed to at least 40 m below the seafloor surface. This is the first description of a nematode-produced open burrow network preserved in the geological record. Optical microscopy of resin-embedded thin sections revealed widespread sediment redistribution without significant lamina disruption. The implications of abundant nematode burrows in surface sediments, and their preservation in the geological record, are wide ranging for both modern and ancient dysoxic marine environments, including for determining early sediment fabric production, geochemical processes, and diagenetic reactions in the oxic and suboxic zones.

  18. Configuration of Miocene Basins Along the Santa Cruz-Catalina Ridge, California Continental Borderland

    NASA Astrophysics Data System (ADS)

    Stoller, A. R.; Legg, M.; Malone, D. H.

    2015-12-01

    Miocene basins associated with the oblique rifting of the Inner Continental Borderland offshore Southern California are preserved along the flanks of the transpressional Santa Cruz-Catalina Ridge. Using 184 lines of two-dimensional seismic data including high resolution records from Oregon State University and deep penetration data from Western Geco archived in USGS/NAMSS, we were able to map the configuration of the Miocene basin along the flanks of the northern core complex on the Santa Cruz-Catalina Ridge. There are distinct early and middle Miocene basins along the flanks of the ridge, which we are using to try to define the initial configuration of the Inner Borderland Rift. Along the hinge, between the uplifted ridge and the sub-horizontal basement in the Santa Monica Basin, lies the thickest part of the sequence. Pliocene to Recent sediments lap on to the tilted and uplifted Miocene basin sequences and constrain timing of uplift when transpression commenced. Segmentation and other distinctive character of the basin along the ridge flank may be correlated with similar features in the Miocene basin on the conjugate margin of the rift. Our working model for oblique rifting in the Borderland resembles of the Gulf of California, where right-stepping echelon transform faults link left-stepping extensional basins. The objective of our project is to reconstruct the configuration of the middle Miocene rift and to further our quest to understand the rifting process and tectonic evolution of the Pacific-North American plate boundary.

  19. Hyperextension along the pre-Caledonian margin of the Iapetus? Age and origin of discontinuous gneiss sheets associated with deep-marine sediments, Alpine metaperidotites and detrital serpentinites

    NASA Astrophysics Data System (ADS)

    Jakob, Johannes; Alsaif, Manar; Corfu, Fernando; Andersen, Torgeir B.

    2016-04-01

    A mélange zone is positioned structurally below some large Proterozoic crystalline nappe complexes (NC), including the Upper Bergsdalen, Jotun and Lindås NCs in the South Norwegian Caledonides. The mélange is characterized by a lithological association of originally deep marine sediments intercalated with some coarser grained siliciclastic metasediments including meta-sandstone and conglomerates, thin slivers of gneisses, as well as detrital serpentinites and 'Alpine-type' metaperidotites. The formation of the mélange and particularly the origin of the detrital serpentinites are disputed. Several models have been suggested including formation as a) an ophiolitic mélange during ophiolite obduction, b) an unconformable post-obduction transgressive sequence or c) a mélange formed during hyperextension along the pre-Caledonian margin of Baltica. Here we present new ID-TIMS U-Pb geochronology of zircon and titanite separated from some of the laterally discontinuous gneiss slivers of variably granitic to gabbroic composition. These gneisses are intercalated with the metasediments as sheets with a maximum strike length of up to 40 km, in the case of the Haukenes gneiss in the Bergen area. Two main groups of gneisses can be distinguished; a) rocks formed at ca. 1495 Ma, 1212 Ma, and 1094 Ma, respectively and b) felsic to mafic meta-intrusives formed in the Early Ordovician between 486 and 474 Ma. In the Samnanger Complex the mélange was truncated by little deformed minor granitoid intrusives at 420 Ma. We propose a Baltican origin for the Mesoproterozoic gneisses. This also implies that the mélange has an affinity with Baltica as is also suggested by its tectonostratigraphic position below the Jotun, Lindås and Upper Bergsdalen Nappe complexes.

  20. Is these a link between eustatic variations, platform drowning, oceanic anoxic events, and ammonite faunal turnovers ? Case study of the Aptian sediments along the northern Tethyan margin

    NASA Astrophysics Data System (ADS)

    Pictet, Antoine; Föllmi, Karl; Spangenberg, Jorge

    2014-05-01

    The early Aptian witnessed an important episode of paleoenvironmental change, which has been linked to major marine volcanic activity related to the formation of the Ontong-Java large igneous province (e.g., Larson and Erba, 1999). This phase culminated in the formation of hemipelagic and pelagic organic-rich sediments, whereas profound changes are also observed in shallow-water settings, with the step-by-step disappearance of the northern Tethyan platform. Results show that the northern Tethyan platform has passed through three major crises in its evolution during the early Aptian. A first one started with an emersion phase, marked by a subaerial karstified discontinuity reported from the middle early Aptian (Deshayesites forbesi or early D. deshayesi zone). This is directly followed by the drowning of the Urgonian platform along the northern Tethyan margin, preceding the Selli Episode. The period following this drowning phase coincides with the negative and the following positive excursions in the δ13C records and went along with the deposition of the so-called Lower Grünten Member, which is the result of heterozoan carbonate production and characterized by increased detrital input. Ammonite fauna witnessed an important diversification of hemipelagic forms, especially inside the heteromorph Ancyloceratacea. This radiation is probably linked to the expansion of hemipelagic facies, one of the main habitats of ammonites. A second phase, reported from the late early Aptian (late D. deshayesi zone), started with a small drowning event, marked by a firmground and by a phosphatic enrichment. This stratigraphical layer also corresponds to the establishment of the anoxic Apparein level. Above, the Upper Grünten Member continues with heterozoan carbonate production or with glauconitic condensed sediments. The corresponding δ13C record is a the onset of a long-term decrease. The ammonite fauna is marked by a first turnover with the disappearance of Deshayesites, and the

  1. Real-Time PCR Quantification and Diversity Analysis of the Functional Genes aprA and dsrA of Sulfate-Reducing Prokaryotes in Marine Sediments of the Peru Continental Margin and the Black Sea.

    PubMed

    Blazejak, Anna; Schippers, Axel

    2011-01-01

    Sulfate-reducing prokaryotes (SRP) are ubiquitous and quantitatively important members in many ecosystems, especially in marine sediments. However their abundance and diversity in subsurface marine sediments is poorly understood. In this study, the abundance and diversity of the functional genes for the enzymes adenosine 5'-phosphosulfate reductase (aprA) and dissimilatory sulfite reductase (dsrA) of SRP in marine sediments of the Peru continental margin and the Black Sea were analyzed, including samples from the deep biosphere (ODP site 1227). For aprA quantification a Q-PCR assay was designed and evaluated. Depth profiles of the aprA and dsrA copy numbers were almost equal for all sites. Gene copy numbers decreased concomitantly with depth from around 10(8)/g sediment close to the sediment surface to less than 10(5)/g sediment at 5 mbsf. The 16S rRNA gene copy numbers of total bacteria were much higher than those of the functional genes at all sediment depths and used to calculate the proportion of SRP to the total Bacteria. The aprA and dsrA copy numbers comprised in average 0.5-1% of the 16S rRNA gene copy numbers of total bacteria in the sediments up to a depth of ca. 40 mbsf. In the zone without detectable sulfate in the pore water from about 40-121 mbsf (Peru margin ODP site 1227), only dsrA (but not aprA) was detected with copy numbers of less than 10(4)/g sediment, comprising ca. 14% of the 16S rRNA gene copy numbers of total bacteria. In this zone, sulfate might be provided for SRP by anaerobic sulfide oxidation. Clone libraries of aprA showed that all isolated sequences originate from SRP showing a close relationship to aprA of characterized species or form a new cluster with only distant relation to aprA of isolated SRP. For dsrA a high diversity was detected, even up to 121 m sediment depth in the deep biosphere.

  2. Sediment yields from small, steep coastal watersheds of California

    USGS Publications Warehouse

    Warrick, Jonathan A.; Melack, John M.; Goodridge, Blair M.

    2015-01-01

    Global inventories of sediment discharge to the ocean highlight the importance of small, steep watersheds (i.e., those having drainage areas less than 100,000 km2 and over 1000 m of relief) that collectively provide a dominant flux of sediment. The smallest of these coastal watersheds (e.g., those that have drainage areas less than 1000 km2) can represent a large portion of the drainage areas of active margin coasts, such as California’s coast, but remain almost universally unmonitored. Here we report on the suspended-sediment discharge of several small coastal watersheds (10-56 km2) of the Santa Ynez Mountains, California, that were found to have ephemeral discharge and suspended-sediment concentrations ranging between 1 and over 200,000 mgL-1. Sediment concentrations were weakly correlated with discharge (r2 = 0.10–0.25), and all types of hysteresis patterns were observed during high flows (clockwise, counterclockwise, no hysteresis, and complex). Sediment discharge varied strongly with time and was measurably elevated in one watershed following a wildfire. Although sediment yields varied by over 100-fold across the watersheds (e.g., 15 – 2100 tkm-2 yr -1during the relatively wet 2005 water year), the majority of sediment discharge (65-80%) occurred during only 1% of the time for all watersheds. Furthermore, sampling of dozens of high flow events provides evidence that sediment yields were generally related to peak discharge yields, although these relationships were not consistent across the watersheds. These results suggest that small watersheds of active margins can provide large fluxes of sediment to the coast, but that the rates and timing of this sediment discharge is more irregular in time – and thus more difficult to characterize – than the better monitored and studied watersheds that are 1000-100,000 km2.

  3. Rapid formation of hyperpycnal sediment gravity currents offshore of a semi-arid California river

    USGS Publications Warehouse

    Warrick, J.A.; Xu, Jie; Noble, M.A.; Lee, H.J.

    2008-01-01

    Observations of sediment dispersal from the Santa Clara River of southern California during two moderately sized river discharge events suggest that river sediment rapidly formed a negatively buoyant (hyperpycnal) bottom plume along the seabed within hours of peak discharge. An array of acoustic and optical sensors were placed at three stations 1 km from the Santa Clara River mouth in 10-m water depth during January-February 2004. These combined observations suggest that fluid mud concentrations of suspended sediment (>10 g/l) and across-shore gravity currents (???5 cm/s) were observed in the lower 20-40 cm of the water column 4-6 h after discharge events. Gravity currents were wave dominated, rather than auto-suspending, and appeared to consist of silt-to-clay sized sediment from the river. Sediment mass balances suggest that 25-50% of the discharged river sediment was transported by these hyperpycnal currents. Sediment settling purely by flocs (???1 mm/s) cannot explain the formation of the observed hyperpycnal plumes, therefore we suggest that some enhanced sediment settling from mixing, convective instabilities, or diverging plumes occurred that would explain the formation of the gravity currents. These combined results provide field evidence that high suspended-sediment concentrations from rivers (>1 g/l) may rapidly form hyperpycnal sediment gravity currents immediately offshore of river mouths, and these pathways can explain a significant portion of the river-margin sediment budget. The fate of this sediment will be strongly influenced by bathymetry, whereas the fate of the remaining sediment will be much more influenced by ocean currents.

  4. Sediment transport and deposition processes near ocean outfalls in Southern California

    USGS Publications Warehouse

    Lee, H.J.; Noble, M.A.; Xu, Jie; ,

    2003-01-01

    An urbanized coastal ocean that has complex topography and large-scale atmospheric and oceanographic forcing can contain a variety of sediment and pollutant distribution patterns. For example, the central southern California Bight has two large embayments, Santa Monica and San Pedro Bays, that are connected by a short, very narrow shelf off the Palos Verdes peninsula. The complex topography causes quite different oceanographic and sediment distribution patterns in this fairly small region of the coastal ocean. In addition, three sewage outfalls discharge material over the outer shelf. A large suite of sediment cores was obtained and analyzed for contaminants, physical properties, accumulation rates, and grain sizes. Arrays of instrumented moorings that monitor currents, waves, water clarity, water density and collect resuspended materials were deployed. The data and models developed for the Palos Verdes margin suggest that a large reservoir of DDT and its byproducts exists in the coastal ocean sediment and will continue to be exhumed and transported along the shelf for a long time. On the Santa Monica shelf, very large internal waves, or bores, are generated at the shelf break. The near-bottom currents associated with these waves sweep sediment and the associated contaminants from the shelf onto the continental slope. On the San Pedro margin an initial examination of recent data collected in the coastal ocean does not suggest that bacterial contamination on local beaches is primarily caused by transport of material from the adjacent ocean outfall.

  5. Sea level reconstructions and non-marine sedimentation at the Triassic-Jurassic boundary: southwestern margin of the Neotethys in the Salt Range, Pakistan

    NASA Astrophysics Data System (ADS)

    Iqbal, Shahid; Wagreich, Michael

    2016-04-01

    The environmental changes during the Triassic-Jurassic boundary interval and the associated mass extinction event are still strongly debated. Sea-level reconstruction records during this interval reveal an end-Triassic global regression event. Erosion and karstification at the top of Triassic sediments, and Lower Jurassic fluvial channels with reworked Triassic clasts indicate widespread regression in the European basins. Laterite at the top of the Triassic, and quartzose conglomerates/sandstones at the base of the Jurassic indicate a fluvial/terrestrial onset in Iran and Afghanistan. Abrupt emergence, erosion and facies dislocation, from the Triassic dolomites (Kingriali Formation) to Lower Jurassic fluvial/continental quartzose conglomerates/pebbly sandstones (Datta Formation) occur in the Tethyan Salt Range of Pakistan. Sedimentological analyses indicate marine regression and emergence under tropical-subtropical conditions (Greenhouse conditions) and negates the possibility of glacial influence in this region. Field evidences indicate the presence of an undulatory surface at the base of the Jurassic and a high (Sargodha High) is present south of the Salt Range Thrust, the southern boundary of the basin. Furthermore, geophysical data (mostly seismic sections) in different parts of the basin display normal faults in the basement. These features are interpreted as horst and graben structures at the Triassic-Jurassic boundary in the Kohat-Potwar Plateau. The Lower Jurassic Datta Formation appears to have been deposited in an overall graben fill settings. Similar normal faults and graben fill geometries are observed on seismic sections in Tanzania, Mozambique, Madagascar and other regions of the southeastern margin of the African Plate and are related to the Karoo rift system. To summarize, the basement normal faults and the graben fill features at the Triassic-Jurassic boundary in the Kohat-Potwar Plateau can be correlated to similar features common in the Karoo

  6. Record of a Mid-Pleistocene depositional anomaly in West Antarctic continental margin sediments: an indicator for ice-sheet collapse?

    NASA Astrophysics Data System (ADS)

    Hillenbrand, C.-D.; Kuhn, G.; Frederichs, T.

    2009-06-01

    Modern global warming is likely to cause future melting of Earth's polar ice sheets that may result in dramatic sea-level rise. A possible collapse of the West Antarctic Ice Sheet (WAIS) alone, which is considered highly vulnerable as it is mainly based below sea level, may raise global sea level by up to 5-6 m. Despite the importance of the WAIS for changes in global sea level, its response to the glacial-interglacial cycles of the Quaternary is poorly constrained. Moreover, the geological evidence for the disintegration of the WAIS at some time within the last ca. 750 kyr, possibly during Marine Isotope Stage (MIS) 11 (424-374 ka), is ambiguous. Here we present physical properties, palaeomagnetic, geochemical and clay mineralogical data from a glaciomarine sedimentary sequence that was recovered from the West Antarctic continental margin in the Amundsen Sea and spans more than the last 1 Myr. Within the sedimentary sequence, proxies for biological productivity (such as biogenic opal and the barium/aluminum ratio) and the supply of lithogenic detritus from the West Antarctic hinterland (such as ice-rafted debris and clay minerals) exhibit cyclic fluctuations in accordance with the glacial-interglacial cycles of the Quaternary. A prominent depositional anomaly spans MIS 15-MIS 13 (621-478 ka). The proxies for biological productivity and lithogenic sediment supply indicate that this interval has the characteristics of a single, prolonged interglacial period. Even though no proxy suggests environmental conditions much different from today, we conclude that, if the WAIS collapsed during the last 800 kyr, then MIS 15-MIS 13 was the most likely time period. Apparently, the duration rather than the strength of interglacial conditions was the crucial factor for the WAIS drawdown. A comparison with various marine and terrestrial climate archives from around the world corroborates that unusual environmental conditions prevailed throughout MIS 15-MIS 13. Some of these

  7. Earthquake site response in Santa Cruz, California

    USGS Publications Warehouse

    Carver, D.; Hartzell, S.H.

    1996-01-01

    Aftershocks of the 1989 Loma Prieta, California, earthquake are used to estimate site response in a 12-km2 area centered on downtown Santa Cruz. A total of 258 S-wave records from 36 aftershocks recorded at 33 sites are used in a linear inversion for site-response spectra. The inversion scheme takes advantage of the redundancy of the large data set for which several aftershocks are recorded at each site. The scheme decomposes the observed spectra into source, path, and site terms. The path term is specified before the inversion. The undetermined degree of freedom in the decomposition into source and site spectra is removed by specifying the site-response factor to be approximately 1.0 at two sites on crystalline bedrock. The S-wave site responses correlate well with the surficial geology and observed damage pattern of the mainshock. The site-response spectra of the floodplain sites, which include the heavily damaged downtown area, exhibit significant peaks. The largest peaks are between 1 and 4 Hz. Five floodplain sites have amplification factors of 10 or greater. Most of the floodplain site-response spectra also have a smaller secondary peak between 6 and 8 Hz. Residential areas built on marine terraces above the flood-plain experienced much less severe damage. Site-response spectra for these areas also have their largest peaks between 1 and 4 Hz, but the amplification is generally below 6. Several of these sites also have a secondary peak between 6 and 8 Hz. The response peaks seen at nearly all sites between 1 and 4 Hz are probably caused by the natural resonance of the sedimentary rock column. The higher amplifications at floodplain sites may be caused by surface waves generated at the basin margins. The secondary peak between 6 and 8 Hz at many sites may be a harmonic of the 1- to 4-Hz peaks. We used waveforms from a seven-station approximately linear array located on the floodplain to calculate the apparent velocity and azimuth of propagation of coherent

  8. C sub 1 -C sub 8 hydrocarbons in sediments from Guaymas Basin, Gulf of California: Comparison to Peru margin, Japan Trench and California borderlands

    SciTech Connect

    Whelan, J.K.; Tarafa, M.E. ); Simoneit, B.R.T. )

    1988-01-01

    Surface sea floor sediments, hydrothermal vent samples, and Deep Sea Drilling Project sediments (Hole 481 A) from the Guaymas Basin were examined for C{sub 1}-C{sub 8} hydrocarbons. The proportions of various classes of compounds were examined and compared to those from other geographic areas (Peru upwelling region and Japan Trench) to gain insight into the relative importance of thermal generation, migration and biodegradation. Concentrations of C{sub 2}-C{sub 7} hydrocarbons were about 10-10,000 times higher in geothermally warm Guaymas Basin sediments in comparison to the low concentrations (0.1-10 ppb per compound) typical of geothermally cold sea floor and DSDP diatomaceous sediments. Alkene/alkane ratios of 0.1 or greater were typical of both geothermally cold sediments and also of very hydrocarbon-rich Alvin samples recovered from the sea floor. Because little or no alkene was generally detected in buried sediments exposed to geothermal temperatures greater than 30C, it is suggested that the alkenes are produced by biogenic processes. Normal alkanes predominated over cyclic and branched structures in geothermally cooler (<20{degree}C) sediments, with the proportion of cyclic and branched compounds increasing in hotter sediments. Similarities in compositions of branched and cyclic compounds were observed in some pairs of bitumen-rich Guaymas sea floor samples recovered from different areas, suggesting common mechanisms of light hydrocarbon generation and/or migration. 76 refs.

  9. Quaternary sedimentation and active faulting along the Ecuadorian shelf: preliminary results of the ATACAMES Cruise (2012)

    NASA Astrophysics Data System (ADS)

    Michaud, F.; Proust, J. N.; Collot, J. Y.; Lebrun, J. F.; Witt, C.; Ratzov, G.; Pouderoux, H.; Martillo, C.; Hernández, M. J.; Loayza, G.; Penafiel, L.; Schenini, L.; Dano, A.; Gonzalez, M.; Barba, D.; De Min, L.; Ponce, G.; Urresta, A.; Calderon, M.

    2015-03-01

    Selected high-resolution seismic-reflection profiles and multibeam bathymetry acquired along the convergent Ecuador margin during the ATACAMES cruise on onboard the R/V L'Atalante (Jan.15-Feb.18, 2012) allow a preliminary evaluation of the neotectonic development and stratigraphic evolution of the margin based on the sismo-stratigraphic analysis of Quaternary sediment preserved on the margin shelf and upper slope. We present three major preliminary results. (1) The evolution of the Esmeraldas, Guayaquil and Santa Elena canyons. The head of the Esmeraldas canyon is the location of a continuous significant sediment transport. The Guayaquil canyon shows several episodes of deposition and incision. Aggrading sedimentation pattern in the canyon records several changes in relative sea-level. The subsidence of the Gulf of Guayaquil probably contributes to the good preservation of the canyon filling stages. The Santa Elena canyon is controlled by a SW-NE trending normal fault. (2) Variations of sediment accumulation and relative vertical motions are shown along-strike the shelf edge. Offshore the uplifted Manta peninsula, a pronounced subsidence of the shelf edge is documented by sedimentary clinoforms that have deposited in a morphological reentrant, and have migrated upslope testifying of a local subsidence meanwhile the adjacent La Plata Island area underwent uplift. In the Esmeraldas canyon area, a local uplift of the shelf is documented. (3) Two neotectonic fault systems with a possible transcurrent component are imaged across the shelf edge and upper margin slope offshore Jama, and Cape Galera. This possible transcurrent motion could be related to the reactivation of ancient faults of the upper plate by the subduction. These preliminary results indicate that the ATACAMES data set has a strong potential to evaluate the spatial and temporal contribution of tectonic and climate changes on the structural development and stratigraphic evolution of the Ecuador continental

  10. Effects of bottom water dissolved oxygen variability on copper and lead fractionation in the sediments across the oxygen minimum zone, western continental margin of India.

    PubMed

    Chakraborty, Parthasarathi; Chakraborty, Sucharita; Jayachandran, Saranya; Madan, Ritu; Sarkar, Arindam; Linsy, P; Nath, B Nagender

    2016-10-01

    This study describes the effect of varying bottom-water oxygen concentration on geochemical fractionation (operational speciation) of Cu and Pb in the underneath sediments across the oxygen minimum zone (Arabian Sea) in the west coast of India. Both, Cu and Pb were redistributed among the different binding phases of the sediments with changing dissolved oxygen level (from oxic to hypoxic and close to suboxic) in the bottom water. The average lability of Cu-sediment complexes gradually decreased (i.e., stability increased) with the decreasing dissolved oxygen concentrations of the bottom water. Decreasing bottom-water oxygen concentration increased Cu association with sedimentary organic matter. However, Pb association with Fe/Mn-oxyhydroxide phases in the sediments gradually decreased with the decreasing dissolved oxygen concentration of the overlying bottom water (due to dissolution of Fe/Mn oxyhydroxide phase). The lability of Pb-sediment complexes increased with the decreasing bottom-water oxygen concentration. This study suggests that bottom-water oxygen concentration is one of the key factors governing stability and lability of Cu and Pb complexes in the underneath sediment. Sedimentary organic matter and Fe/Mn oxyhydroxide binding phases were the major hosting phases for Cu and Pb respectively in the study area. Increasing lability of Pb-complexes in bottom sediments may lead to positive benthic fluxes of Pb at low oxygen environment.

  11. Santa Cruz River Options

    EPA Science Inventory

    This presentation summarizes qualitative research insights gained during development of a nonmarket valuation survey for changes to the Santa Cruz River in Southern Arizona. Qualitative research provides an important avenue for understanding how the public interprets valuation s...

  12. Reconstructing 2000 years of hydrological variation derived from laminated proglacial sediments of Lago del Desierto at the eastern margin of the South Patagonian Ice Field, Argentina

    NASA Astrophysics Data System (ADS)

    Kastner, Stephanie; Enters, Dirk; Ohlendorf, Christian; Haberzettl, Torsten; Kuhn, Gerhard; Lücke, Andreas; Mayr, Christoph; Reyss, Jean-Louis; Wastegård, Stefan; Zolitschka, Bernd

    2010-06-01

    Lago del Desierto (49°02'S, 72°51'W) is situated in the climatically sensitive area of Southern Patagonia close to the Hielo Patagonico Sur (HPS or South Patagonian Ice Field, Argentina). Next to marine records and Antarctic ice cores, this continental area is important to reveal hemispheric and global climate trends. As instrumental climate records from this region are generally short and scarce, environmental archives are the only source of long-term records of climate variations. In this study, the potential of laminated proglacial sediments from Lago del Desierto as a palaeoclimate archive is evaluated. Two parallel gravity cores (max. length 283 cm) were analysed using a multi-proxy approach. Radiometric dating ( 14C, 210Pb and 137Cs) and tephrochronology document that the sediment cover the last 2000 years. Especially in the middle part of the record, numerous turbidites make climate variations difficult to decipher. However, after exclusion of event layers changes in sedimentological, mineralogical, and geochemical parameters reveal a long-term trend of runoff variations and sediment accessibility controlled by changes in temperature and precipitation. An abrupt transition in sediment composition occurred around AD 850 and is interpreted as a change in sediment availability related to the initial exposure of formerly glaciated areas in the catchment. This striking change mirrors the onset of warmer climate conditions during the Medieval Climate Anomaly. Moreover, the Little Ice Age cooling and the subsequent 20th century warming can be traced in the sediment record corresponding to an overall trend observed for southern South America. The proglacial lacustrine sediment record of Lago del Desierto thus constitutes a link between glacier studies of the HPS and other terrestrial climate archives in a region were long, and continuous climate records are still rare.

  13. Holocene ice-rafting and sediment transport from the glaciated margin of East Greenland (67-70°N) to the N Iceland shelves: detecting and modelling changing sediment sources

    NASA Astrophysics Data System (ADS)

    Andrews, John T.; Bigg, Grant R.; Wilton, David J.

    2014-05-01

    We examine variations in the ice-rafted sources for sediments in the Iceland/East Greenland offshore marine archives by utilizing a sediment unmixing model and link the results to a coupled iceberg-ocean model. Surface samples from around Iceland and along the E/NE Greenland shelf are used to define potential sediment sources, and these are examined within the context of the down-core variations in mineralogy in the <2 mm sediment fraction from a transect of cores across Denmark Strait. A sediment unmixing model is used to estimate the fraction of sediment <2 mm off NW and N Iceland exported across Denmark Strait; this averaged between 10 and 20%. Both the sediment unmixing model and the coupled iceberg-ocean model are consistent in finding that the fraction of “far-travelled” sediments in the Denmark Strait environs is overwhelmingly of local, mid-East Greenland, provenance, and therefore with a significant cross-channel component to their travel. The Holocene record of ice-rafted sediments denotes a three-part division of the Holocene in terms of iceberg sediment transport with a notable increase in the process starting ca 4000 cal yr BP. This latter increase may represent the re-advance during the Neoglacial period of land-terminating glaciers on the Geikie Plateau to become marine-terminating. The contrast in spectral signals between these cores and the 1500-yr cycle at VM28-14, just south of the Denmark Strait, combined with the coupled iceberg-model results, leads us to speculate that the signal at VM28-14 reflects pulses in overflow waters, rather than an ice-rafted signal.

  14. Provenance of Holocene sediment on the Chukchi-Alaskan margin based on combined diffuse spectral reflectance and quantitative X-Ray Diffraction analysis

    USGS Publications Warehouse

    Ortiz, J.D.; Polyak, L.; Grebmeier, J.M.; Darby, D.; Eberl, D.D.; Naidu, S.; Nof, D.

    2009-01-01

    Sediment clay and silt mineral assemblages provide an excellent means of assessing the provenance of fine-grained Arctic sediment especially when a unique mineral assemblage can be tied to specific source areas. The diffuse spectral reflectance (DSR) first derivative measurements and quantitative X-Ray Diffraction (qXRD) on a high-resolution sediment core from the continental slope north of Alaska constrain the sediment mineralogy. DSR results are augmented by measurements on several adjacent cores and compared to surface sediment samples from the northern Alaskan shelf and slope. Using Principal Component Analysis (PCA), we infer that the three leading DSR modes relate to mixtures of smectite + dolomite, illite + goethite, and chlorite + muscovite. This interpretation is consistent with the down core qXRD results. While the smectite + dolomite, and illite + goethite factors show increased variability down core, the chlorite + muscovite factor had highest positive loadings in the middle Holocene, between ca. 6.0 and 3.6??ka. Because the most likely source of the chlorite + muscovite suite in this vicinity lies in the North Pacific, we argue that the oscillations in chlorite + muscovite values likely reflect an increase in the inflow of Pacific water to the Arctic through the Bering Strait. The time interval of this event is associated in other parts of the globe with a non-linear response of the climate system to the decrease in insolation, which may be related to changes in water exchange between the Pacific and Arctic Ocean. ?? 2009 Elsevier B.V.

  15. Principles of Geological Mapping of Marine Sediments (with Special Reference to the African Continental Margin). Unesco Reports in Marine Science No. 37.

    ERIC Educational Resources Information Center

    Lisitzin, Alexandre P.

    Designed to serve as a complement to the Unesco Technical Papers in Marine Science, this report concentrates on theoretical and practical problems of geological mapping of the sea floor. An introduction is given to geological mapping procedures at continental margins as well as some practical recommendations taking as an example the African region…

  16. The zircon evidence of temporally changing sediment transport—the NW Gondwana margin during Cambrian to Devonian time (Aoucert and Smara areas, Moroccan Sahara)

    NASA Astrophysics Data System (ADS)

    Gärtner, Andreas; Youbi, Nasrrddine; Villeneuve, Michel; Sagawe, Anja; Hofmann, Mandy; Mahmoudi, Abdelkader; Boumehdi, Moulay Ahmed; Linnemann, Ulf

    2017-03-01

    Detrital zircon provenance studies are an established tool to develop palaeogeographic models, mostly based on zircon of siliciclastic rocks and isotope data. But zircon is more than just istopes and features well definable morphological characteristics. The latter may indicate single grain transport histories independent of the individual grade of concordance. This additional tool for palaeogeoraphic reconstructions was tested on zircon from siliciclastic and carbonate sedimentary rocks of Palaeozoic age from the Aoucert and Smara areas of the Souttoufides, while findings of zircon in limestone generally open new archives for sedimentary provenance analysis. The morphologies—length, width, roundness, grain surfaces—of 834 detrital zircons from sediments of allochthonous Cambrian, and (par-)autochthonous Ordovician, and Devonian units were studied, while 772 of them were analysed for their U-Th-Pb isotopes by LA-ICP-MS. Mesoproterozoic zircon contents of more than 10% in the Cambrian sediments exclude the West African Craton (WAC) as exclusive source area. Thus, at least one additional external source is suggested. This is likely the western Adrar Souttouf Massif with its significant Mesoproterozoic zircon inheritance, or comparable, yet unknown sources. Decreasing Mesoproterozoic zircon age populations in Ordovician sediments are thought to be linked to the rifting of the terranes in the course of the Rheic Ocean opening and a predominant supply of WAC detritus. The Devonian sediments likely contain reworked material from the Cambrian siliciclastics, which is shown by the zircon age distribution pattern and the zircon morphologies. Therefore, multiple shifts in the direction of sedimentary transport are indicated.

  17. Biotic and a-biotic Mn and Fe cycling in deep sediments across a gradient of sulfate reduction rates along the California margin

    NASA Astrophysics Data System (ADS)

    Schneider-Mor, A.; Steefel, C.; Maher, K.

    2011-12-01

    The coupling between the biological and a-biotic processes controlling trace metals in deep marine sediments are not well understood, although the fluxes of elements and trace metals across the sediment-water interface can be a major contribution to ocean water. Four marine sediment profiles (ODP leg 167 sites 1011, 1017, 1018 and 1020)were examined to evaluate and quantify the biotic and abiotic reaction networks and fluxes that occur in deep marine sediments. We compared biogeochemical processes across a gradient of sulfate reduction (SR) rates with the objective of studying the processes that control these rates and how they affect major elements as well as trace metal redistribution. The rates of sulfate reduction, methanogenesis and anaerobic methane oxidation (AMO) were constrained using a multicomponent reactive transport model (CrunchFlow). Constraints for the model include: sediment and pore water concentrations, as well as %CaCO3, %biogenic silica, wt% carbon and δ13C of total organic carbon (TOC), particulate organic matter (POC) and mineral associated carbon (MAC). The sites are distinguished by the depth of AMO: a shallow zone is observed at sites 1018 (9 to 19 meters composite depth (mcd)) and 1017 (19 to 30 mcd), while deeper zones occur at sites 1011 (56 to 76 mcd) and 1020 (101 to 116 mcd). Sulfate reduction rates at the shallow AMO sites are on the order 1x10-16 mol/L/yr, much faster than rates in the deeper zone sulfate reduction (1-3x10-17 mol/L/yr), as expected. The dissolved metal ion concentrations varied between the sites, with Fe (0.01-7 μM) and Mn (0.01-57 μM) concentrations highest at Site 1020 and lowest at site 1017. The highest Fe and Mn concentrations occurred at various depths, and were not directly correlated with the rates of sulfate reduction and the maximum alkalinity values. The main processes that control cycling of Fe are the production of sulfide from sulfate reduction and the distribution of Fe-oxides. The Mn distribution

  18. Hydrothermal versus active margin sediment supply to the eastern equatorial Pacific over the past 23 million years traced by radiogenic Pb isotopes: Paleoceanographic and paleoclimatic implications

    NASA Astrophysics Data System (ADS)

    Höfig, Tobias W.; Hoernle, Kaj; Hauff, Folkmar; Frank, Martin

    2016-10-01

    We investigated the evolution of the Pb isotopic composition of bulk sediments on the Cocos Plate in sedimentary successions of Deep Sea Drilling Project (DSDP) Site 495 and Ocean Drilling Program/Integrated Ocean Drilling Program (ODP/IODP) Site 1256 over the past 23 million years of depositional history. Our study addresses the relationship of the sediment Pb isotope record to plate tectonics, weathering inputs, and paleoceanography. It is the first effort to characterize the Pb isotopic evolution of eastern equatorial Pacific sedimentation covering the entire tectonic pathway of the Cocos Plate from its formation at the East Pacific Rise to its arrival at the Central American subduction zone. The Sites 495 and 1256 bulk sediment Pb isotope records are fully consistent over time despite distinct differences between the type of sediment deposited at both locations. A systematic and continuous trend from ∼23 to ∼6-4 Ma toward more radiogenic Pb isotopic compositions, e.g., 206Pb/204Pb ratios increase from 18.29 to 18.81, reflects a decrease in the contribution of hydrothermal particles from the East Pacific Rise and an increase in the predominantly eolian contribution of mixed weathering products from the continental arcs of the Northern and south Central Andes as well as from southern Mexico. Surprisingly, both the Pb isotopic composition of the detrital fraction and that of past seawater indicate that inputs from nearby Central America and the Galápagos Archipelago did not significantly contribute to the sediments of our core locations but were overwhelmed by other sediment sources. A systematic change to less radiogenic Pb isotope ratios in sediments younger than ∼4-3 Ma, reaching present-day 206Pb/204Pb values near 18.70, reflects a reduction of the continental input from the South Central Volcanic Zone of the Andean Arc and increased contributions from southern Mexican igneous complexes. This isotopic trend reversal took place as a consequence of

  19. Tracking Soil Organic Carbon Transport to Continental Margin Sediments Using Soil-Specific Hopanoid Biomarkers: a Case Study From the Congo Fan (ODP Site 1075)

    NASA Astrophysics Data System (ADS)

    Cooke, M. P.; Talbot, H. M.; Eniola, O.; Zabel, M.; Wagner, T.

    2007-12-01

    The transport and subsequent deposition of terrestrially derived organic matter into the ocean is an important but poorly constrained aspect of the modern global carbon cycle. In regions associated with large river systems it is likely that the terrestrial input of organic carbon is much more complex than commonly considered and very difficult to trace based on established geochemical proxies. It is therefore important to develop proxies that target the movement and fate of this terrestrial organic material. The identification of bacteriohopanepolyol (BHP) biomarkers unique to soil derived organic carbon (SOC) has enabled the transport of SOC into aquatic sediments to be traced. The extreme recalcitrance of BHPs enables these source specific compounds to be used on recent and ancient sediments to identify periods of high and low SOC input into sediments. BHPs are bacterial membrane compounds with a high degree of structural variability. They are analogous to steroids in eukaryotes and have been identified in over half of all bacteria studied for their presence. BHPs have a wide range of over 40 functional groups on the side chain, with up to 6 functional groups in each structure, and with methylation and unsaturation over 100 total structures have been identified1. During the BHP analysis of a wide range of soils from around the world we consistently measure high levels adenosylhopane, known to originate from purple non-sulphur, nitrogen fixing and ammonia oxidising bacteria and 2-methyl adenosyl hopane (m/z 802)2, from nitrogen fixing bacteria. Only 3 lacustrine sediments with large SOC supply from their catchments areas have been found to contain these markers in a survey of over 40 different non-marine settings. Recent studies on Late Quaternary sediments from the Congo deep sea fan (OPD site 1075, approximately 2 km water depth) provide a strong case to expect markers for SOC3. An initial analysis of the core samples confirms the presence of soil specific BHP

  20. Biological nitrate transport in sediments on the Peruvian margin mitigates benthic sulfide emissions and drives pelagic N loss during stagnation events

    NASA Astrophysics Data System (ADS)

    Dale, A. W.; Sommer, S.; Lomnitz, U.; Bourbonnais, A.; Wallmann, K.

    2016-06-01

    Benthic N cycling in the Peruvian oxygen minimum zone (OMZ) was investigated at ten stations along 12 °S from the middle shelf (74 m) to the upper slope (1024 m) using in situ flux measurements, sediment biogeochemistry and modeling. Middle shelf sediments were covered by mats of the filamentous bacteria Thioploca spp. and contained a large 'hidden' pool of nitrate that was not detectable in the porewater. This was attributed to a biological nitrate reservoir stored within the bacteria to oxidize sulfide during 'dissimilatory nitrate reduction to ammonium' (DNRA). The extremely high rates of DNRA on the shelf (15.6 mmol m-2 d-1 of N), determined using an empirical steady-state model, could easily supply all the ammonium requirements for anammox in the water column. The model further showed that denitrification by foraminifera may account for 90% of N2 production at the lower edge of the OMZ. At the time of sampling, dissolved oxygen was below detection limit down to 400 m and the water body overlying the shelf had stagnated, resulting in complete depletion of nitrate and nitrite. A decrease in the biological nitrate pool was observed on the shelf during fieldwork concomitant with a rise in porewater sulfide levels in surface sediments to 2 mM. Using a non-steady state model to simulate this natural anoxia experiment, these observations were shown to be consistent with Thioploca surviving on a dwindling intracellular nitrate reservoir to survive the stagnation period. The model shows that sediments hosting Thioploca are able to maintain high ammonium fluxes for many weeks following stagnation, potentially sustaining pelagic N loss by anammox. In contrast, sulfide emissions remain low, reducing the economic risk to the Peruvian fishery by toxic sulfide plume development.

  1. The Santa Dilemma.

    ERIC Educational Resources Information Center

    Imber, Michael

    2003-01-01

    Discusses legal issues related to the celebration of Christmas in public schools. Concludes that schools can display secular symbols of Christmas such as reindeer, elves, and Santa Clause, but not religious ones, such as wise men, angels, and nativity scenes. (PKP)

  2. The Santa Ana Partnership

    ERIC Educational Resources Information Center

    Cournoyer, David, Ed.

    2004-01-01

    One of the priority interests of the W.K. Kellogg Foundation is to connect the knowledge and resources of institutions with communities in order to improve the quality of life in community. Partnerships achieve uncommon results. In Santa Ana, California, an unusual partnership of public schools, community college, universities, community…

  3. Marginal Matter

    NASA Astrophysics Data System (ADS)

    van Hecke, Martin

    2013-03-01

    All around us, things are falling apart. The foam on our cappuccinos appears solid, but gentle stirring irreversibly changes its shape. Skin, a biological fiber network, is firm when you pinch it, but soft under light touch. Sand mimics a solid when we walk on the beach but a liquid when we pour it out of our shoes. Crucially, a marginal point separates the rigid or jammed state from the mechanical vacuum (freely flowing) state - at their marginal points, soft materials are neither solid nor liquid. Here I will show how the marginal point gives birth to a third sector of soft matter physics: intrinsically nonlinear mechanics. I will illustrate this with shock waves in weakly compressed granular media, the nonlinear rheology of foams, and the nonlinear mechanics of weakly connected elastic networks.

  4. Physical Properties Record of Current Flow From Magnetic Analysis of Deep-sea Sediments at the Antarctic Peninsula Pacific Margin (OPP Sites 1095, 1101)

    NASA Astrophysics Data System (ADS)

    Pares, J. M.; Hassold, N. J.; Rea, D. K.; van der Pluijm, B. A.

    2005-12-01

    The physical properties of bottom-current flow recorded by deep-sea sediments provide valuable information about the history of oceanic currents, their strength and direction. Specifically, details on the Antarctic Circumpolar Current (ACC) would significantly increase our understanding of late Cenozoic paleoceanography, as it is thought to isolate Antarctica from the warmer waters to the north. The Anisotropy of Magnetic Susceptibility (AMS) provides a powerful gauge for sediment fabric, as it senses preferred grain orientation in sediments and sedimentary rocks. We have determined both relative speed and azimuth of bottom-current flow in drift deposit sediments recovered at ODP Sites 1095 and 1101, Antarctic Peninsula. A total of 35 cores have been measured for AMS, providing new clues on the physical record of the ACC in the Plio-Pleistocene. Because ODP holes are drilled and recovered in successive 9 meters-long cores, which usually do not have relative orientation, we have based our analysis on samples grouped by cores. Our results indicate that the degree of anisotropy provides a proxy for current strength: The higher the latter, the higher is the anisotropy of the magnetic ellipsoid. Further, grouping of the principal axes of maximum susceptibility is interpreted in terms of preferred grain orientation, providing a proxy for the azimuth of the paleocurrent flow. As revealed by experimental studies, AMS maximum axes are grouped in the azimuth of flow and inclined at a few degrees to the sediment surface dipping downward into the direction of the flow's origin. In the studied samples, when imbrication is observed, we have been able to determine the orientation and sense of the paleocurent. Declination and inclination of the paleomagnetic vector of each core segment was used for reorientation of AMS principal axes to the geographic coordinates to obtain the absolute orientation of the directional data. Once the cores have been reoriented using the measured

  5. The influence of El Niño-Southern Oscillation (ENSO) cycles on wave-driven sea-floor sediment mobility along the central California continental margin

    USGS Publications Warehouse

    Storlazzi, Curt D.; Reid, Jane A.

    2010-01-01

    Ocean surface waves are the dominant temporally and spatially variable process influencing sea floor sediment resuspension along most continental shelves. Wave-induced sediment mobility on the continental shelf and upper continental slope off central California for different phases of El Niño-Southern Oscillation (ENSO) events was modeled using monthly statistics derived from more than 14 years of concurrent hourly oceanographic and meteorologic data as boundary input for the Delft SWAN wave model, gridded sea floor grain-size data from the usSEABED database, and regional bathymetry. Differences as small as 0.5 m in wave height, 1 s in wave period, and 10° in wave direction, in conjunction with the spatially heterogeneous unconsolidated sea-floor sedimentary cover, result in significant changes in the predicted mobility of continental shelf surficial sediment in the study area. El Niño events result in more frequent mobilization on the inner shelf in the summer and winter than during La Niña events and on the outer shelf and upper slope in the winter months, while La Niña events result in more frequent mobilization on the mid-shelf during spring and summer months than during El Niño events. The timing and patterns of seabed mobility are addressed in context of geologic and biologic processes. By understanding the spatial and temporal variability in the disturbance of the sea floor, scientists can better interpret sedimentary patterns and ecosystem structure, while providing managers and planners an understanding of natural impacts when considering the permitting of offshore activities that disturb the sea floor such as trawling, dredging, and the emplacement of sea-floor engineering structures.

  6. Marginality principle

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Soil is a fragile resource supplying many goods and services. Given the diversity of soil across the world and within a landscape, there are many different capacities among soils to provide the basic soil functions. Marginality of soils is a difficult process to define because the metrics to define ...

  7. Seismic vis-a-vis sonic attenuation in gas hydrate bearing sediments of Krishna-Godavari basin, Eastern Margin of India

    NASA Astrophysics Data System (ADS)

    Nittala, Satyavani; Sain, Kalachand; Nara, Damodara

    2017-03-01

    Seismic velocities in the sediments containing gas hydrates show a marked increase compared to the background, intuitively implying that there would be a reduction in the seismic attenuation (Q-1) of such sediments. However, the attenuation measurements carried out in the sonic frequency range from various gas hydrate provinces show that there is a notable increase in seismic attenuation within the gas hydrate layers and the results obtained are counter-intuitive. In the present work we try to compare the attenuation derived by applying frequency shift method to the multi-channel seismic (MCS) and sonic datasets at the same location in the Krishna-Godavari (KG) basin. The role of complex geology in attenuating the seismic signal is also studied by generating synthetic seismic data for different geologic models and by computing the corresponding attenuation. It has been found that the Q-1 obtained from the field seismic data compares well with the Q-1 computed for a simple layered geological model. The results indicate that the Q-1 (0.0029) from field seismic data is ∼4.3 times lower than Q-1 (0.0123-0.0125) obtained from the sonic data, implying that the thickness of the gas hydrate layer in the KG basin is not sufficient enough to average the bulk properties. Our results also indicate that there could be substantial contribution of the pore scale interaction to the observed attenuation.

  8. Atlantic marginal basins of Africa

    SciTech Connect

    Moore, G.T.

    1988-02-01

    The over 10,000-km long Atlantic margin of Africa is divisible into thirty basins or segments of the margin that collectively contain over 18.6 x 10/sup 6/ km/sup 3/ of syn-breakup and post-breakup sediments. Twenty of these basins contain a sufficiently thick volume of sediments to be considered prospects. These basins lie, at least partially, within the 200 m isobath. The distribution of source rocks is broad enough to give potential to each of these basins. The sedimentation patterns, tectonics, and timing of events differ from basin to basin and are related directly to the margin's complex history. Two spreading modes exist: rift and transform. Rifting dates from Late Triassic-Early Jurassic in the northwest to Early Cretaceous south of the Niger Delta. A complex transform fault system separated these two margins. Deep-water communication between the two basins became established in the middle Cretaceous. This Mesozoic-Cenozoic cycle of rifting and seafloor spreading has segmented the margin and where observable, basins tend to be bounded by these segments.

  9. Detrital zircon U-Pb geochronology and whole-rock Nd-isotope constraints on sediment provenance in the Neoproterozoic Sergipano orogen, Brazil: From early passive margins to late foreland basins

    NASA Astrophysics Data System (ADS)

    Oliveira, E. P.; McNaughton, N. J.; Windley, B. F.; Carvalho, M. J.; Nascimento, R. S.

    2015-11-01

    SHRIMP U-Pb detrital zircon geochronology and depleted-mantle Nd-model ages of clastic rocks were combined to understand the sediment provenance in the Neoproterozoic Sergipano Belt. The Sergipano is the main orogenic belt between the Borborema province and the São Francisco Craton, eastern South America; it is divisible into several lithostratigraphic domains from North to South: Canindé, Poço Redondo-Marancó, Macururé, Vaza Barris, and Estância. Nd model ages (TDM) and detrital zircon U-Pb SHRIMP geochronology indicate that the protoliths of clastic metasedimentary rocks from the Marancó and Macururé domains were mostly derived from eroded late Mesoproterozoic to early Neoproterozoic rocks (1000-900 Ma), whereas detritus of similar rocks from the Canindé domain came from a younger source (ca. 700 Ma and 1000 Ma). Samples from the Vaza Barris domain show the greatest scatter of both TDM and zircon ages amongst all domains, but with important contributions from Proterozoic sources (690-1050 Ma and ca. 2100 Ma) and less from Archaean sources. The Estância domain samples have zircon population peaks at 570 Ma, 600 Ma, and 920-980 Ma, with a few older grains; one diamictite contains only ca. 2150 Ma zircon grains. Our preliminary results support a model in which sediments of the Marancó and Macururé domains were deposited on a continental margin of the ancient Borborema plate before its collision with the São Francisco Craton; the Canindé domain is likely to be an aborted Neoproterozoic rift assemblage within the southern part of the Borborema plate (Pernambuco-Alagoas massif). The basal units of the Vaza Barris and Estância domains have clast sources from the São Francisco Craton and are best interpreted as passive margin sediments. However, the uppermost units of the Estância and Vaza Barris domains come from foreland basins formed during collision of Borborema plate with the São Francisco Craton.

  10. Flow dynamics and sedimentation of lateral accretion packages in sinuous deep-water channels: A 3D seismic case study from the northwestern South China Sea margin

    NASA Astrophysics Data System (ADS)

    Li, Shengli; Gong, Chenglin

    2016-07-01

    The current study uses 3D seismic data to document architectural styles and flow dynamics of lateral accretion packages (LAPs) associated with sinuous deep-water channels, contributing to a better understanding of flow processes and sedimentation associated with LAPs. The documented LAPs underwent three main stages of architectural evolution, including the early incision stages characterized by intense downcutting, active migration stages characterized by active migration and avulsion of the individual channels, and late abandonment stages characterized by the termination of sediment gravity-flows and LAP growth. These three stages of LAP growth repeated through time, yielding a fining-upward pattern from sandy channel-fill turbidites, into sand-mud couplets, all capped by muddy turbidites. A river-reversed helical flow circulation was created by an imbalance, through the flow depth, of inwardly directed pressure gradient forces near the bed and outwardly directed centrifugal forces near the surface. It consists of low-velocity cores near the outer banks and low-velocity cores along the inner banks. Such river-reversed helical flow pattern is evidenced by volumetrically extensive LAPs and toplap and downlap terminations along the gentle banks and by aerially restricted, seismically unresolvable levees and truncation terminations near the steep banks. This river-reversed helical flow circulation favors asymmetric intra-channel deposition characterized by inner bank deposition versus outer bank erosion, and which, in turn, forced individual channels to consistently migrate towards outer banks, resulting in significant asymmetric cross-channel profiles with aerially extensive LAPs along inner banks.

  11. Climatically related millennial-scale fluctuations in strength of California margin oxygen-minimum zone during the past 60 k.y.

    SciTech Connect

    Cannariato, K.G.; Kennett, J.P.

    1999-11-01

    A strong oxygen-minimum zone (OMZ) currently exists along the California margin because of a combination of high surface-water productivity and poor intermediate-water ventilation. However, the strength of this OMZ may have been sensitive to late Quaternary ocean-circulation and productivity changes along the margin. Although sediment-lamination strength has been used to trace ocean-oxygenation changes in the past, oxygen levels on the open margin are not sufficiently low for laminations to form. In these regions, benthic foraminifera are highly sensitive monitors of OMZ strength, and their fossil assemblages can be used to reconstruct past fluctuations. Benthic foraminiferal assemblages from Ocean Drilling Program Site 1017, off Point Conception, exhibit major and rapid faunal oscillations in response to late Quaternary millennial-scale climate change (Dansgaard-Oeschger cycles) on the open central California margin. These faunal oscillations can be correlated to and are apparently synchronous with those reported from Santa Barbara Basin. Together they represent major fluctuations in the strength of the OMZ which were intimately associated with global climate change--weakening, perhaps disappearing, during cool periods and strengthening during warm periods. These rapid, major OMZ strength fluctuations were apparently widespread on the Northeast Pacific margin and must have influenced the evolution of margin biota and altered biogeochemical cycles with potential feedbacks to global climate change.

  12. Effects of Wildfire on Fluvial Sediment Regime through Perturbations in Dry-Ravel

    NASA Astrophysics Data System (ADS)

    Florsheim, J. L.; Chin, A.; Kinoshita, A. M.; Nourbakhshbeidokhti, S.; Storesund, R.; Keller, E. A.

    2015-12-01

    In steep chaparral ecosystems with Mediterranean climate, dry ravel is a natural process resulting from wildfire disturbance that supplies sediment to fluvial systems. When dense chaparral vegetation burns, sediment accumulated on steep hillslopes is released for dry-season transport (dry ravel) down steep hillslopes during or soon after the wildfire. Results of a field study in southern California's Transverse Ranges illustrate the effect of wildfire on fluvial sediment regime in an unregulated chaparral system. Big Sycamore Canyon in the steep Santa Monica Mountains burned during the May 2013 Springs Fire and experienced one small sediment-transporting stormflow during the following winter. We conducted pre- and post-storm field campaigns during the fall and winter following the fire to quantify the effect of wildfire on the fluvial sediment regime. We utilized a sediment mass balance approach in which: 1) sediment supply, consisting primarily of dry ravel-derived deposits composed of relatively fine grained-sediment, was measured in the upstream basin and in the hillslope-channel margin adjacent to the study reach; 2) changes in storage in the study reach were quantified by analyzing the difference between pre- and post-storm channel topography derived from Terrestrial LiDAR Scanning (TLS) and field surveys; and 3) transport from the study reach was estimated as the difference between supply and change in storage where uncertainty is estimated using calculated sediment transport as a comparison. Results demonstrate channel deposition caused by changes in the short-term post-wildfire sediment regime. The increased sediment supply and storage are associated with significant changes in morphology, channel bed-material characteristics, and ecology. These results suggest that dry-ravel processes are an important factor to consider in post-wildfire sediment management.

  13. Molecular diversity of denitrifying genes in continental margin sediments within the oxygen-deficient zone off the Pacific coast of Mexico.

    PubMed

    Liu, Xueduan; Tiquia, Sonia M; Holguin, Gina; Wu, Liyou; Nold, Stephen C; Devol, Allan H; Luo, Kuan; Palumbo, Anthony V; Tiedje, James M; Zhou, Jizhong

    2003-06-01

    To understand the composition and structure of denitrifying communities in the oxygen-deficient zone off the Pacific coast of Mexico, the molecular diversity of nir genes from sediments obtained at four stations was examined by using a PCR-based cloning approach. A total of 50 operational taxonomic units (OTUs) for nirK and 82 OTUs for nirS were obtained from all samples. Forty-four of the nirS clones and 31 of the nirK clones were sequenced; the levels of similarity of the nirS clones were 52 to 92%, and the levels of similarity of the nirS clones were 50 to 99%. The percentages of overlapping OTUs between stations were 18 to 30% for nirS and 5 to 8% for nirK. Sequence analysis revealed that 26% of the nirS clones were related to the nirS genes of Alcaligenes faecalis (80 to 94% similar) and Pseudomonas stutzeri (80 to 99%), whereas 3 to 31% of the nirK clones were closely related to the nirK genes of Pseudomonas sp. strain G-179 (98 to 99%), Bradyrhizobium japonicum (91%), Blastobacter denitrificans (83%), and Alcaligenes xylosoxidans (96%). The rest of the clones, however, were less than 80% similar to nirS and nirK sequences available in sequence databases. The results of a principal-component analysis (PCA) based on the percentage of OTUs and biogeochemical data indicated that the nitrate concentration and oxygen have an effect on the denitrifying communities. The communities at the stations in oxygen-deficient zones were more similar than the communities at the stations in the oxygenated zone. The denitrifying communities were more similar at the stations that were closer together and had similar nitrate levels. Also, the results of PCA based on biogeochemical properties suggest that geographic location and biogeochemical conditions, especially the nitrate and oxygen levels, appear to be the key factors that control the structure of denitrifying communities.

  14. Latest Cretaceous sedimentation on Peninsular Ranges block

    SciTech Connect

    Abbott, P.L.

    1986-04-01

    The Peninsular Ranges block is dominated by a Late Jurassic-middle Cretaceous batholithic belt that extends from the Santa Ana Mountains in southern California southward through the state of Baja California. From paleomagnetic evidence, the block appears to have moved north about 11/sup 0/ with respect to the North American craton since the Late Cretaceous. The Campanian-Maestrichtian sedimentary record along the western side of the block shows that sedimentation occurred contemporaneously with faulting. Dominantly coarse sediments were stripped off the batholithic complex, carried westward relatively short distances, and deposited in alluvial-fan, fluvial, fan-delta, and shelf environments as well as in submarine fans built into local, fault-created basins. The Peninsular Ranges block apparently moved northward in response to oblique subduction of the Farallon plate; it seemingly rode along on a reasonably even keel as transcurrent faulting wrenched pieces off its western side. The steady keel allowed the sedimentary record to reflect eustatic changes. Along the west side of the Peninsular Ranges block, the Campanian column typically has a retrogradational sequence lower in the section that is overlain by a progradational sequence. This pattern holds for the Santa Ana Mountains, San Diego, California, and Descanso, Salsipuedes, and El Rosario, Baja California. Eustatic sea level changes left a dominant imprint on the entire stratigraphic column, although local facies may be distinctly different because basins were created by contemporaneous faulting. The fault basins may have had a borderland-style topography, judging from their relatively small size, discontinuous and sporadic development, and apparently linear margins.

  15. Evidence for enhanced phosphorus regeneration from marine sediments overlain by oxygen depleted waters

    SciTech Connect

    Ingall, E.; Jahnki, R.

    1994-06-01

    Phosphorus regeneration and burial fluxes determined from in situ benthic flux chamber and solid phase measurements at sites on the Californian continental margin, Peruvian continental slope, North Carolina continental slope, and from the Santa Monica basin, California are reported. Comparison of these sites indicates that O{sub 2}-depleted bottomwaters enhance P regeneration from sediments, diminishing overall phosphorus burial efficiency. Based on these observations, a positive feedback, linking ocean anoxia, enhanced benthic phosphorus regeneration, and marine productivity is proposed. On shorter timescales, these results also suggest that O{sub 2} depletion in coastal regions caused by eutrophication may enhance P regeneration from sediments, thereby providing additional P necessary for increased biological productivity. 42 refs., 2 figs., 2 tabs.

  16. Subsurface and petroleum geology of the southwestern Santa Clara Valley ("Silicon Valley"), California

    USGS Publications Warehouse

    Stanley, Richard G.; Jachens, Robert C.; Lillis, Paul G.; McLaughlin, Robert J.; Kvenvolden, Keith A.; Hostettler, Frances D.; McDougall, Kristin A.; Magoon, Leslie B.

    2002-01-01

    Gravity anomalies, historical records of exploratory oil wells and oil seeps, new organic-geochemical results, and new stratigraphic and structural data indicate the presence of a concealed, oil-bearing sedimentary basin beneath a highly urbanized part of the Santa Clara Valley, Calif. A conspicuous isostatic-gravity low that extends about 35 km from Palo Alto southeastward to near Los Gatos reflects an asymmetric, northwest-trending sedimentary basin comprising low-density strata, principally of Miocene age, that rest on higher-density rocks of Mesozoic and Paleogene(?) age. Both gravity and well data show that the low-density rocks thin gradually to the northeast over a distance of about 10 km. The thickest (approx 4 km thick) accumulation of low-density material occurs along the basin's steep southwestern margin, which may be controlled by buried, northeast-dipping normal faults that were active during the Miocene. Movement along these hypothetical normal faults may been contemporaneous (approx 17–14 Ma) with sedimentation and local dacitic and basaltic volcanism, possibly in response to crustal extension related to passage of the northwestward-migrating Mendocino triple junction. During the Pliocene and Quaternary, the normal faults and Miocene strata were overridden by Mesozoic rocks, including the Franciscan Complex, along northeastward-vergent reverse and thrust faults of the Berrocal, Shannon, and Monte Vista Fault zones. Movement along these fault zones was accompanied by folding and tilting of strata as young as Quaternary and by uplift of the modern Santa Cruz Mountains; the fault zones remain seismically active. We attribute the Pliocene and Quaternary reverse and thrust faulting, folding, and uplift to compression caused by local San Andreas Fault tectonics and regional transpression along the Pacific-North American Plate boundary. Near the southwestern margin of the Santa Clara Valley, as many as 20 exploratory oil wells were drilled between 1891

  17. Effect of Wildfire on Sediment Sorting in a Steep Channel

    NASA Astrophysics Data System (ADS)

    Florsheim, J. L.; Chin, A.; O'Hirok, L.; Storesund, R.

    2014-12-01

    Wildfire is an external forcing factor in the landscape. In chaparral environments, wildfire initiates transport of well-sorted fine sediment through dry-ravel processes on hillslopes and facilitates delivery of sediment to stream channels. In turn, this periodic post-fire sediment influx governs sorting of channel-bed material during subsequent floods that mobilize and transport the sediment downstream. We investigated the effects of the May 2013 Springs Wildfire in the Santa Monica Mountains in semi-arid southern California with field measurements and terrestrial LiDAR scanning. Before the fire, sediment sorting within the heterogeneous bed material present in Big Sycamore Creek was controlled by organized step-pool bedforms. Boulders formed steps with relatively finer cobbles, gravel, and sand filling the pools. Before the fire, the grain size distribution present in the substrate between boulder steps was relatively coarse (D84 = 250 mm), in contrast to that in the influx of sediment contributed by post-fire dry-ravel processes deposited at channel margins (D84 = 8 mm). Flow shear stress during one small flood in 2014 (post-fire) was adequate to mobilize fine dry ravel- related sediment. Transport capacity was sufficient to mobilize and transport this sediment within a study reach; however, it was not adequate to flush the fine material downstream. Shear stress required to mobilize sediment contributed by dry ravel was substantially less than that required to transport the substrate material present before the wildfire. The small flood deposited fine sediment (D84 = 16 mm) as flow lost capacity. Resulting deposition buried bedforms, changing the step-pool profile to a plane bed. The relatively poorly sorted, coarse, rough bed changed to a well sorted, fine, smooth, bed. These changes have implications for sediment transport dynamics and aquatic ecology. In steep, semi-arid, chaparral fluvial systems, sediment derived from dry-ravel processes influences the

  18. Magnitude and composition of sinking particulate phosphorus fluxes in Santa Barbara Basin, California

    NASA Astrophysics Data System (ADS)

    Sekula-Wood, Emily; Benitez-Nelson, Claudia R.; Bennett, Melissa A.; Thunell, Robert

    2012-06-01

    The composition and bioavailability of particulate P influence marine biological community production on both modern and geologic time-scales, and continental margins play a critical role in the supply, modification, and storage of particulate P. This study examined particulate P cycling in the Santa Barbara Basin (SBB) off the coast of southern California using a ˜520 m deep-moored sediment trap deployed from 1993-2006 and a sediment core collected in 2005 directly beneath the sediment trap at 590 m. Total particulate P (TPP), particulate inorganic P (PIP), and particulate organic P (POP) were quantified using a 5-step sequential extraction method (SEDEX) that chemically separates PIP into loosely bound, oxide-bound, authigenic, and detrital P phases. POP fluxes, while similar in magnitude to other coastal regions (22 ± 10 μmol m-2 d-1) were a small component of the TPP pool (15%). Seasonal trends revealed significant increases in POP fluxes during upwelling due to increased biological production in surface waters by organisms that increased mineral ballast. High particulate organic carbon (POC) to POP ratios (337 ± 18) further indicated rapid and efficient remineralization of POP relative to POC as particles sank through the oxic water column; however, further reduction of POP ceased in the deeper anoxic waters. Loosely bound, oxide-bound, and authigenic P, dominated the TPP pool, with PIP fluxes substantially higher than those measured in other coastal settings. Strong correlations between oxide-associated, authigenic, and detrital P fluxes with lithogenic material indicated a terrestrial source associated with riverine discharge. Furthermore, more than 30% of the loosely bound and oxide-bound P was remineralized prior to burial, with the magnitude of dissolution far exceeding that of POP. These results highlight the dynamic nature of the particulate P pool in coastal ecosystems and how changes in P source can alter the composition and lability of P that

  19. The occupational health of Santa Claus.

    PubMed

    Straube, Sebastian; Fan, Xiangning

    2015-01-01

    Previous publications in the field of Santa studies have not focused on health and safety issues arising from Santa's workplace activities. However, it should be acknowledged that unique occupational hazards exist for Santa Claus. Major occupational health issues affecting Santa are discussed, along with suggestions for future research directions.

  20. California State Waters Map Series: offshore of Santa Barbara, California

    USGS Publications Warehouse

    Johnson, Samuel Y.; Dartnell, Peter; Cochrane, Guy R.; Golden, Nadine E.; Phillips, Eleyne L.; Ritchie, Andrew C.; Greene, H. Gary; Krigsman, Lisa M.; Kvitek, Rikk G.; Dieter, Bryan E.; Endris, Charles A.; Seitz, Gordon G.; Sliter, Ray W.; Erdey, Mercedes D.; Gutierrez, Carlos I.; Wong, Florence L.; Yoklavich, Mary M.; Draut, Amy E.; Hart, Patrick E.; Conrad, James E.; Cochran, Susan A.; Johnson, Samuel Y.; Cochran, Susan A.

    2013-01-01

    In 2007, the California Ocean Protection Council initiated the California Seafloor Mapping Program (CSMP), designed to create a comprehensive seafloor map of high-resolution bathymetry, marine benthic habitats, and geology within the 3-nautical-mile limit of California’s State Waters. The CSMP approach is to create highly detailed seafloor maps through collection, integration, interpretation, and visualization of swath sonar data, acoustic backscatter, seafloor video, seafloor photography, high-resolution seismic-reflection profiles, and bottom-sediment sampling data. The map products display seafloor morphology and character, identify potential marine benthic habitats, and illustrate both the surficial seafloor geology and shallow (to about 100 m) subsurface geology. The Offshore of Santa Barbara map area lies within the central Santa Barbara Channel region of the Southern California Bight. This geologically complex region forms a major biogeographic transition zone, separating the cold-temperate Oregonian province north of Point Conception from the warm-temperate California province to the south. The map area is in the southern part of the Western Transverse Ranges geologic province, which is north of the California Continental Borderland. Significant clockwise rotation—at least 90°—since the early Miocene has been proposed for the Western Transverse Ranges province, and geodetic studies indicate that the region is presently undergoing north-south shortening. Uplift rates (as much as 2.2 mm/yr) that are based on studies of onland marine terraces provide further evidence of significant shortening. The city of Santa Barbara, the main coastal population center in the map area, is part of a contiguous urban area that extends from Carpinteria to Goleta. This urban area was developed on the coalescing alluvial surfaces, uplifted marine terraces, and low hills that lie south of the east-west-trending Santa Ynez Mountains. Several beaches line the actively

  1. Volcanism and sedimentation along the western margin of the Rio Grande rift between caldera-forming eruptions of the Jemez Mountains volcanic field, north-central New Mexico, USA

    NASA Astrophysics Data System (ADS)

    Jacobs, Elaine P.; WoldeGabriel, Giday; Kelley, Shari A.; Broxton, David; Ridley, John

    2016-11-01

    The Cerro Toledo Formation (CTF), a series of intracaldera rhyolitic dome complexes and their associated extracaldera tephras and epiclastic sedimentary deposits, records the dynamic interplay between volcanic, tectonic, and geomorphic processes that were occurring along the western margin of the Rio Grande rift between major caldera-forming eruptions of the Bandelier Tuff 1.65-1.26 Ma. The Alamo Canyon and Pueblo Canyon Members differ significantly despite deposition within a few kilometers of each other on the Pajarito Plateau. These differences highlight spatial distinctions in vent sources, eruptive styles, and depositional environments along the eastern side of the Jemez Mountains volcanic field during this ca. 400,000 year interval. Intercalated pyroclastic fall deposits and sandstones of the Pueblo Canyon Member reflect deposition with a basin. Thick Alamo Canyon Member deposits of block-and-ash-flow tuff and pyroclastic fall deposits fill a paleovalley carved into coarse grained sedimentary units reflecting deposition along the mountain front. Chemistry and ages of glass from fall deposits together with clast lithologies of sedimentary units, allow correlation of outcrops, subsurface units, and sources. Dates on pyroclastic fall deposits from Alamo Canyon record deep incision into the underlying Otowi Member in the southern part of the Pajarito Plateau within 100 k.y. of the Toledo caldera-forming eruption. Reconstruction of the CTF surface shows that this period of rapid incision was followed by aggradation where sediments largely filled pre-existing paleocanyons. Complex sequences within the upper portion of the Otowi Member in outcrop and in the subsurface record changes in the style of eruptive activity during the waning stages of the Toledo caldera-forming eruption.

  2. Transport of clays in the eastern part of santa barbara channel, California

    USGS Publications Warehouse

    Kolpack, R.L.; Drake, D.E.

    1984-01-01

    A record discharge of about 54 ?? 106 metric tons of predominantly fine-grained detrital sediment was introduced during 1969 into the eastern part of Santa Barbara Channel from the Santa Clara and Ventura Rivers. The clay-size fraction from bottom samples collected during a time-series of about 18 months revealed movement across the shelf and into the adjacent basin in a repetitive sequential pattern. Light transmission profiles show resuspension and transport of sediments at depths of up to 225 m. This transport and distribution history is attributed to seasonal variations in the vertical and lateral position of a poleward-flowing current. ?? 1985 Springer-Verlag New York Inc.

  3. Sea level controls on the textural characteristics and depositional architecture of the Hueneme and associated submarine fan systems, Santa Monica Basin, California

    USGS Publications Warehouse

    Normark, W.R.; Piper, D.J.W.; Hiscott, R.N.

    1998-01-01

    Hueneme and Dume submarine fans in Santa Monica Basin consist of sandy channel and muddy levee facies on the upper fan. lenticular sand sheets on the middle fan. and thinly bedded turbidite and hemipelagic facies elsewhere. Fifteen widely correlatable key seismic reflections in high-resolution airgun and deep-towed boomer profiles subdivide the fan and basin deposits into time-slices that show different thickness and seismic-facies distributions, inferred to result from changes in Quaternary sea level and sediment supply. At times of low sea level, highly efficient turbidity currents generated by hyperpycnal flows or sediment failures at river deltas carry sand well out onto the middle-fan area. Thick, muddy flows formed rapidly prograding high levees mainly on the western (right-hand) side of three valleys that fed Hueneme fan at different times: the most recently active of the lowstand fan valleys. Hueneme fan valley, now heads in Hueneme Canyon. At times of high sea level, fans receive sand from submarine canyons that intercept littoral-drift cells and mixed sediment from earthquake-triggered slumps. Turbidity currents are confined to 'underfit' talweg channels in fan valleys and to steep, small, basin-margin fans like Dume fan. Mud is effectively separated from sand at high sea level and moves basinward across the shelf in plumes and in storm-generated lutite flows, contributing to a basin-floor blanket that is locally thicker than contemporary fan deposits and that onlaps older fans at the basin margin. The infilling of Santa Monica Basin has involved both fan and basin-floor aggradation accompanied by landward and basinward facies shifts. Progradation was restricted to the downslope growth of high muddy levees and the periodic basinward advance of the toe of the steeper and sandier Dume fan. Although the region is tectonically active, major sedimentation changes can be related to eustatic sea-level changes. The primary controls on facies shifts and fan growth

  4. Santa Maria Volcano, Guatemala

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The eruption of Santa Maria volcano in 1902 was one of the largest eruptions of the 20th century, forming a large crater on the mountain's southwest flank. Since 1922, a lava-dome complex, Santiaguito, has been forming in the 1902 crater. Growth of the dome has produced pyroclastic flows as recently as the 2001-they can be identified in this image. The city of Quezaltenango (approximately 90,000 people in 1989) sits below the 3772 m summit. The volcano is considered dangerous because of the possibility of a dome collapse such as one that occurred in 1929, which killed about 5000 people. A second hazard results from the flow of volcanic debris into rivers south of Santiaguito, which can lead to catastrophic flooding and mud flows. More information on this volcano can be found at web sites maintained by the Smithsonian Institution, Volcano World, and Michigan Tech University. ISS004-ESC-7999 was taken 17 February 2002 from the International Space Station using a digital camera. The image is provided by the Earth Sciences and Image Analysis Laboratory at Johnson Space Center. Searching and viewing of additional images taken by astronauts and cosmonauts is available at the NASA-JSC Gateway to

  5. Off-shore to near-shore transects of ferromanganese crusts adjacent to the California margin Tracey A. Conrad1, James R. Hein2, Adina Paytan1 1University of California Santa Cruz, CA, 95064 (tconrad@ucsc.edu) 2USGS, Menlo Park, CA, 94025, USA (jhein@usgs.gov)

    NASA Astrophysics Data System (ADS)

    Conrad, T. A.; Hein, J. R.; Paytan, A.

    2012-12-01

    Marine ferromanganese (Fe-Mn) crusts growing on seamounts along the California Margin (CM) are influenced by terrestrial and biogenic input. These continental margin crusts have higher concentrations of Si, K, Fe, Na, Ag, Cr, B, and Ba than Fe-Mn crusts from the global open-ocean. Al is also higher but only relative to Pacific open-ocean crusts. These relative enrichments may reflect the high primary productivity near the CM caused by seasonal upwelling and high sediment transport to the region from river/eolian input and cliff erosion. Two transects with samples from five seamounts each are used to compare seaward changes. Transect A includes analyses of 66 bulk samples from Flint, Ben, and Little Joe seamounts, Patton Escarpment, and Northeast Bank. It spans ~400 km of seafloor heading ~58N and coming within ~220 km of the shoreline with samples collected at water depths ranging from 570-2925 m. Transect B includes analyses of 136 bulk samples from Adam, Hoss, San Marcos, San Juan, and Rodriguez seamounts at water depths ranging from 692-3880 m. This transect spans ~240 km heading ~10N and comes within ~75 km of the shoreline near the base of the continental slope. For both transects, mean water depth increases with mean longitude, and latitude is fairly constant varying by approximately 2 degree latitude for transect A and 1degree for B. Both transects show statistically significant trends at the 99% confidence level for element concentrations versus water depth. Concentrations of Fe, Ca, P, Co, and Pb increase as water depth decreases. For transect (A), Mn and Mg also follow this trend, as do Mo and Al for transect (B); Mn also shows this trend for transect (B) but at the 95% confidence level. For both transects, Cu and Zn show the opposite trend, with concentrations increasing in crusts with increasing water depth. For Transect (B), Ni and Al also show this trend. Si and K show no statistically significant trends for either transect. In open-ocean samples

  6. Santa Ana Forecasting and Classification

    NASA Astrophysics Data System (ADS)

    Rolinski, T.; Eichhorn, D.; D'Agostino, B. J.; Vanderburg, S.; Means, J. D.

    2011-12-01

    Southern California experiences wildfires every year, but under certain circumstances these fires grow into extremely large and destructive fires, such as the Cedar Fire of 2003 and the Witch Fire of 2007. The Cedar Fire burned over 1100 km2 , destroyed more than 2200 homes and killed 15 people; the Witch fire burned more than 800 km2, destroyed more than 1000 homes and killed 2 people. Fires can quickly become too large and dangerous to fight if they are accompanied by a very strong "Santa Ana" condition, which is a foehn-like wind that may bring strong winds and very low humidities. However there is an entire range of specific weather conditions that fall into the broad category of Santa Anas, from cold and blustery to hot with very little wind. All types are characterized by clear skies and low humidity. Since the potential for destructive fire is dependent on the characteristics of Santa Anas, as well as the level of fuel moisture, there exists a need for further classification, such as is done with tropical cyclones and after-the-fact with tornadoes. We use surface data and fuel moisture combined with reanalysis to diagnose those conditions that result in Santa Anas with the greatest potential for destructive fires. We use this data to produce a new classification system for Santa Anas. This classification system should be useful for informing the relevant agencies for mitigation and response planning. In the future this same classification may be made available to the general public.

  7. 5. PASEO DELICIAS, CORNER OF VIA DE SANTA FE, SERVICE ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    5. PASEO DELICIAS, CORNER OF VIA DE SANTA FE, SERVICE STATION ON LEFT, SANTA FE LAND IMPROVEMENT COMPANY OFFICE BLOCK ON RIGHT, CA. 1925-26 - Rancho Santa Fe Civic Center, Rancho Santa Fe, San Diego County, CA

  8. Nutrient contributions to the Santa Barbara Channel, California, from the ephemeral Santa Clara River

    USGS Publications Warehouse

    Warrick, J.A.; Washburn, L.; Brzezinski, Mark A.; Siegel, D.A.

    2005-01-01

    The Santa Clara River delivers nutrient rich runoff to the eastern Santa Barbara Channel during brief (???1-3 day) episodic events. Using both river and oceanographic measurements, we evaluate river loading and dispersal of dissolved macronutrients (silicate, inorganic N and P) and comment on the biological implications of these nutrient contributions. Both river and ocean observations suggest that river nutrient concentrations are inversely related to river flow rates. Land use is suggested to influence these concentrations, since runoff from a subwatershed with substantial agriculture and urban areas had much higher nitrate than runoff from a wooded subwatershed. During runoff events, river nutrients were observed to conservatively mix into the buoyant, surface plume immediately seaward of the Santa Clara River mouth. Dispersal of these river nutrients extended 10s of km into the channel. Growth of phytoplankton and nutrient uptake was low during our observations (1-3 days following runoff), presumably due to the very low light levels resulting from high turbidity. However, nutrient quality of runoff (Si:N:P = 16:5:1) was found to be significantly different than upwelling inputs (13:10:1), which may influence different algal responses once sediments settle. Evaluation of total river nitrate loads suggests that most of the annual river nutrient fluxes to the ocean occur during the brief winter flooding events. Wet winters (such as El Nin??o) contribute nutrients at rates approximately an order-of-magnitude greater than "average" winters. Although total river nitrate delivery is considerably less than that supplied by upwelling, the timing and location of these types of events are very different, with river discharge (upwelling) occurring predominantly in the winter (summer) and in the eastern (western) channel. ?? 2004 Elsevier Ltd. All rights reserved.

  9. Santa Clara Demonstration Status

    SciTech Connect

    Leo, Anthony J.; Skok, Andrew J.; O'Shea, Thomas P.

    1996-08-01

    Fuel Cell Engineering Corporation (FCE) is in the fourth year of a DOE Cooperative Agreement Program (private-sector cost-shared) aimed at the demonstration of ERC's direct carbonate fuel cell (DFC) technology at full scale. FCE is a wholly owned subsidiary of Energy Research Corporation (ERC), which has been pursuing the development of the DFC for commercialization near the end of this decade. The DFC produces power directly from hydrocarbon fuels electrochemically, without the need for external reforming or intermediate mechanical conversion steps. As a result, the DFC has the potential to achieve very high efficiency with very low levels of environmental emissions. Modular DFC power plants, which can be shop-fabricated and sited near the user, are ideally suited for distributed generation, cogeneration, industrial, and defense applications. This project is an integral part of the ERC effort to commercialize the technology to serve these applications. Potential users of the commercial DFC power plant under development at ERC will require that the technology be demonstrated at or near the full scale of the commercial products. The objective of the Santa Clara Demonstration Project (SCDP) is to provide the first such demonstration of the technology. The approach ERC has taken in the commercialization of the DFC is described in detail elsewhere [1]. Briefly, an aggressive core technology development program is in place which is focused by ongoing contact with customers and vendors to optimize the design of the commercial power plant. ERC has selected a 2.85 MW power plant unit for initial market entry. Two ERC subsidiaries are supporting the commercialization effort: The Fuel Cell Manufacturing Corporation (FCMC) and the Fuel Cell Engineering Corporation (FCE). FCMC manufactures carbonate stacks and multi-stack modules, currently from its manufacturing facility in Torrington, CT. FCE is responsible for power plant design, integration of all subsystems, sales

  10. Myth 14: Waiting for Santa Claus

    ERIC Educational Resources Information Center

    Adams, Cheryll M.

    2009-01-01

    Just as in 1982, when the myth of waiting for Santa Claus was first addressed in "Gifted Child Quarterly," many districts all over the country are still waiting for Santa Claus to arrive with a sleigh full of presents. Unfortunately, Santa and his presents in the form of mandates to identify and serve, funding, teachers licensed in…

  11. Holocene variations in mineral and grain-size composition along the East Greenland glaciated margin (ca 67°–70°N): local versus long-distance sediment transport

    USGS Publications Warehouse

    Andrews, John T.; Jennings, Anne E.; Coleman, George C.; Eberl, Dennis D.

    2010-01-01

    Quantitative X-Ray Diffraction (qXRD) analysis of the <2 mm sediment fraction from surface (sea floor) samples, and marine sediment cores that span the last 10-12 cal ka BP, are used to describe spatial and temporal variations in non-clay mineral compositions for an area between Kangerlussuaq Trough and Scoresby Sund (???67??-70??N), East Greenland. Bedrock consists primarily of an early Tertiary alkaline complex with high weight% of pyroxene and plagioclase. Farther inland and to the north, the bedrock is dominantly felsic with a high fraction of quartz and potassium feldspars. Principal Component (PC) analysis of the non-clay sediment compositions indicates the importance of quartz and pyroxene as compositional end members, with an abrupt shift from quartz and k-feldspar dominated sediments north of Scoresby Sund to sediments rich in pyroxene and plagioclase feldspars offshore from the early Tertiary basaltic outcrop. Coarse (<2 mm or <1 mm) ice-rafted sediments are largely absent from the trough sediments between ???8 and 5 cal ka BP, but then increase in the last 4 cal ka BP. Compositional unmixing of the sediments in Grivel Basin and Kangerlussuaq Trough indicate the dominance of local over long distance sediment sources, with pulses of sediment from tidewater glaciers in Kangerlussuaq and Nansen fjords reaching the inner shelf during the Neoglaciation. The change in IRD is more dramatic in the sediment grain-size proxies than in the quartz wt%. Forty to seventy percent of the variance in the quartz records from either side of Denmark Strait is explained by low frequency trends, but the data from the Grivel Basin, East Greenland, are distinctly different, with an approximate 2500 yr periodicity. ?? 2010 Elsevier Ltd.

  12. Seismic images of modern convergent margin tectonic structure

    SciTech Connect

    Von Huene, R.; Miller, J.

    1986-07-01

    An atlas of 14 seismic sections shows major tectonic features across various convergent margins. All sections are at the same scale and have been processed to a research level. Such processing produces clear images of sediment accretion from below. Most margins show sediment subduction. The results of tectonic erosion are seen in midslope areas as buttresses against which the accretion complex is stacked. The images of structures indicating tectonic erosion are about as common as the images of structure indicating accretion.

  13. The PDO and Infaunal Foraminfera Isotopic Values: Multi-Decadal Variations in Santa Monica and Santa Barbara Basins

    NASA Astrophysics Data System (ADS)

    Berelson, W.; Stott, L.

    2002-12-01

    Laminated sediments within Santa Monica, Santa Barbara and Soledad (Mexico) Basins provide an opportunity to study carbon export at sites dominated by coastal upwelling. Multi-cores were collected in 2001 and sampled with mm scale resolution for both solid phase and pore water investigations. The infaunal foram, B. tenuata was analyzed for its del13C value; this down-core record indicates systematic changes in pore water del13C, reflecting differences in the amount of organic carbon oxidation occurring on the sea floor. Two cores collected from Santa Monica Basin, one in the 1980's and the second in 2001 show identical trends and structure in B. tenuata del13C values between 1700 AD and the present. Because B. tenuata is recording pore water del13CO2, it becomes a sensitive proxy for the benthic organic carbon oxidation rate, which in-turn relates to the amount of organic carbon delivered to the sea floor. In Santa Monica Basin we see a trend from 1700 AD to the present toward greater carbon oxidation. This trend is consistent with the observation that the extent of laminated sediments has expanded within this basin over the past 300 years. Within this general trend there are some very well defined patterns and reversals, most notably is the trend toward lower rates of carbon oxidation between 1980 and the present; the documented PDO phase-shift that occurs around 1980 shows up clearly in this analyses. Other similar shifts in `carbon production' have occurred since 1700 AD, notably one occurred in the late 1800's and another around 1800. These both mark periods when there was a reversal from increasing inputs of organic carbon to decreasing inputs. The increase in organic carbon delivery to the sea floor of Santa Monica Basin since 1700 has been quantified by deriving estimates of carbon oxidation rates and combining them with measurements of carbon burial rates. The range in carbon oxidized has fluctuated from about 1 to 3 mmolC m-2 day-1 and the overall carbon

  14. Coastal Processes Study of Santa Barbara and Ventura Counties, California

    USGS Publications Warehouse

    Barnard, Patrick L.; Revell, David L.; Hoover, Dan; Warrick, Jon; Brocatus, John; Draut, Amy E.; Dartnell, Pete; Elias, Edwin; Mustain, Neomi; Hart, Pat E.; Ryan, Holly F.

    2009-01-01

    The Santa Barbara littoral cell (SBLC) is a complex coastal system with significant management challenges. The coastline ranges broadly in exposure to wave energy, fluvial inputs, hard structures, and urbanization. Geologic influence (structural control) on coastline orientation exerts an important control on local beach behavior, with anthropogenic alterations and the episodic nature of sediment supply and transport also playing important roles. Short- and long-term temporal analyses of shoreline change, beach width, and volume change show no obvious trends in regional beach behavior. Extensive armoring along the SBLC has accreted the back beach, narrowing beach widths and in some cases increasing sediment transport. Unarmored beaches have exhibited mild erosion while maintaining similar widths. Harbor constructions have had notable impacts on downdrift beaches, but once the coastal system has equilibrated the signal becomes strongly dampened and littoral-drift gradients driven by natural shoreline orientation again become dominant. Sediment inputs from the Santa Clara River dominate sediment processes on beaches to the south. The SBLC is dominated by episodic flood and storm-wave events. Exceptionally large accretion signals along this stretch of coastline are closely tied to major flood events when large amounts of sediment are deposited in deltas. These deltas decay over time, supplying downdrift beaches with sediment. Storm-wave impacts and gradients in alongshore transport can lead to beach rotations and migrating erosion hotspots when geological controls are weak. Annual and seasonal rates of cross-shore and alongshore transport are at least 2-3 times higher for the more west- and southwest-facing beaches south of the Ventura River as compared to the more sheltered beaches to the west/north. Gross littoral transports are good approximations of net littoral transports for beaches west/north of Ventura as transport is almost purely unidirectional. However

  15. The diffuse seismicity of the Sierra Nevada of Santa Marta, the Perijá Range, and south of the La Guajira peninsula, Colombia and Venezuela: Result of the convergence between Caribbean plate and the South American margin during the Late Neogene?

    NASA Astrophysics Data System (ADS)

    Chicangana, G.; Pedraza, P.; Mora-paez, H.; Ordonez Aristizabal, C. O.; Vargas-Jimenez, C. A.; Kammer, A.

    2012-12-01

    A diffuse low deep microseismicity located overall between the Guajira peninsula and the Sierra Nevada de Santa Marta (SNSM) was registered with the recent installation (2008 to Present) of three seismological stations in northeastern Colombia by the Colombian Seismological Network (RSNC), but mainly with the Uribia station in (the) central region of La Guajira peninsula, The microseismicity is characterized by a great population of events with 1.2 < Ml < 3.0. and few events of 3.0 < Ml < 4.0 that sporadically occur. The poor number of seismological stations in this region of Colombia impedes to locate the origin of the local seismicity; however, this seismic activity is associated to the tectonic activity of the Oca fault because with the GPS displacement analysis, neotectonics evidence found in faults traces associated to the Oca fault and the historical earthquake that affected the Colombian city of Santa Marta in 1834, lead us to conclude this. This is a big cortical fault that sets the limit between La Guajira peninsula and the SNSM. Its cortical characteristics were verified from geological data together with gravimetric and seismic exploration. The SNSM limits toward the southeast with the Cesar - Ranchería basin, and this basin in turn limits with the Perijá Range that is localized in the Colombia - Venezuela border. The SNSM, Cesar - Ranchería basin and Perijá Range limit toward the southwest with the Bucaramanga - Santa Marta fault (BSMF), the Oca fault toward the north, and Perijá - El Tigre fault toward the southeast defining a pyramidal orogenic complex. Using remote sensing images data with geological and regional geophysical information, we proposed that this orogenic complex was originated as a result of the Panama arc with the northwestern South America accretion. The final adjustment of the Caribbean plate (CP) between North America and South America during the Late Neogene produced the big cortical faults systems activation like Oca - Moron

  16. Northern and eastern margins of the Siberian continent in Triassic

    SciTech Connect

    Egorov, A.Yu. )

    1993-09-01

    Siliciclastic sedimentation has been predominant on the northern and eastern margins of the Siberian continent since the Triassic period. Seven transgression-regression cycles can be recognized in the Triassic succession: Griesbachien-Dienerian, Smithian-Low Spathian, Upper Spathian, Anissian (with subcycles), Ladian, Carnian, and Norlan (with subcycles). All zonal units were distinguished within transgressive portions of the cycles. Regressive portions of the cycles formed practically instantaneously. Very high sedimentation rate (300-3000 mm/1000 yr), specific structures of sedimentary rocks, and distribution of unconformities led to the conclusion that active avalanche sedimentation at the basin margins was of major significance. six facies regions are recognized in the sedimentation area: Taimyr, Kotuy-Anabar, Leno-Anabar, Bur-Olenek, Verkhoyansk, and Novosibirsk (New Siberian Islands). The main source areas were located at the Patoma Mountains for the eastern margin and at the Anabar anticline and Olenek uplift for the northern margin. Most sediments were transported to the eastern margin by a large river with a huge delta which was similar in size to the modern Lena's delta. Sediments were further distributed by contour streams. Local synsedimentary structures controlled the paleogeography of the entire area. The paleogeographical evolution of the eastern margin is the history of this delta development. The rifting activities with the trappean magmatism were the main events at the northern margin, especially in the Talmyr area. The pelagic sedimentation has been predominant in the New Siberian Islands area and most of the Laptev Sea aquatoria. The organic-rich sediments have been distinguished in Low Olenekian (Smithian), Low Anissian, Low Ladinian, and Low Carnian substages. Most of them could be hydrocarbon source rocks. Triassic oil and gas seeps have been discovered at the northern portion of the Vilyui syncline, near the Lena's delta and the Nordvic Bay.

  17. Carbon and Nitrogen Stable Isotopes of Sedimentary Organic Matter From the Santa Monica Basin

    NASA Astrophysics Data System (ADS)

    Luo, J. Y.; Erohina, T.; Paytan, A.

    2005-12-01

    The California Continental Borderland is a tectonically active area, characterized by 23 basins located at different distances from sources of terrigenous sediment, local intermittent rivers and coastal upwelling zones and thus displaying different sedimentation sources and processes. The Santa Monica Basin (938m depth), a Southern California Inner Borderland basin, is a closed basin and fed by the Santa Barbara littoral cell. During sea level lowstands, the littoral cell is inactive and the canyon was fed directly by the Santa Clara River, which is presently not dammed and is known to be capable of generating hyperpycnal flows during ENSO related floods. Ocean Drilling Program (ODP) Site 1015 was drilled in the basin plain area and penetrated through a 150-meter late Quaternary sedimentary section. The sediments recovered at Site 1015 are grouped into a single lithostratigraphic unit consisting of three alternating sedimentary units: medium- to fine-grained sand, silty clay, and nanofossil clay. Samples of the drill core from the top 60 meters of sediment was obtained and analyzed at ~50cm intervals to obtain a high-resolution record of organic matter distribution and isotope record within the different intervals. The δ13C values of total organic carbon (TOC) and δ15N values, as well as the C/N ratio were obtained and used to differentiate between marine and terrestrial sediment inputs to the basin. Additionally, the TOC data may indicate if highstand and lowstand deposits show significant compositional differences.

  18. Heavy mineral provinces of the Palos Verdes margin, southern California

    USGS Publications Warehouse

    Wong, F.L.

    2002-01-01

    Natural sources of sediment for the Palos Verdes margin, southern California, have been augmented by effluent discharged from Los Angeles County Sanitation District's sewage-treatment facility and by the reactivation of the Portuguese Bend landslide. Heavy minerals in very fine and fine sand (63-250 ??m) from beach and shelf sites off the Palos Verdes Peninsula distinguish effluent-affected sediment from unaffected deposits, and track the sediment contributed by the Portuguese Bend landslide. Heavy minerals also identify heterogeneous sediment sources for the nearshore zone and relate outer-shelf sediment to depositional cells north and south of the area.

  19. On the Evolution of Glaciated Continental Margins

    NASA Astrophysics Data System (ADS)

    Sverre Laberg, Jan; Rydningen, Tom Arne; Safronova, Polina A.; Forwick, Matthias

    2016-04-01

    Glaciated continental margins, continental margins where a grounded ice sheet repeatedly has been at or near the shelf break, are found at both northern and southern high-latitudes. Their evolution are in several aspects different from their low-latitude counterparts where eustatic sea-level variations possess a fundamental control on their evolution and where fluvial systems provide the main sediment input. From studies of the Norwegian - Barents Sea - Svalbard and NE Greenland continental margins we propose the following factors as the main control on the evolution of glaciated continental margins: 1) Pre-glacial relief controlling the accommodation space, 2) Ice sheet glaciology including the location of fast-flowing ice streams where source area morphology exerts a fundamental control, 3) Composition of the glacigenic sediments where the clay content in previous studies have been found to be important, and 4) Sea-level controlled both by eustacy and isostacy. From three case studies, 1) the western Barents Sea, 2) part of the North Norwegian (Troms), and 3) the Mid-Norwegian margin, the influence on these factors for the sea-floor morphology, sedimentary processes of the continental slope - deep sea and continental margin architecture are discussed. The pre-glacial relief of the mid-Norwegian and Troms margins relates to the onset of rifting and plate break-up from the early Cenozoic while for the SW Barents Sea, plate shear was followed by rifting. A wide zone of extended continental crust occurs offshore mid-Norway while this zone is much narrower offshore Troms leading to a more pronounced pre-glacial relief. Regarding sediment delivery and ice sheet glaciology the western Barents Sea exemplifies very high sediment input corresponding to an estimated average erosion of the source area of ~0.4 mm/yr (SW Barents Sea), much of which is related to subglacial erosion of Mesozoic - Cenozoic sedimentary rocks from large paleo-ice streams. The mid-Norwegian margin

  20. A 150 year record of inter-annual climate variability and organic carbon burial in Santa Monica and Santa Barbara Basins

    SciTech Connect

    Hagadorn, J.W.; Stott, L.D.; Sinha, A.; Rincon, M. . Dept. of Geological Sciences); Schimmelmann, A. . Scripps Inst. of Oceanography)

    1992-01-01

    Stable isotopic measurements were conducted on total organic carbon (TOC) and fossil planktonic foraminifera in laminated sediments collected from Santa Monica and Santa Barbara Basins, California Borderland, in order to investigate relationships between climatic variability and organic carbon burial. These data currently provide biannual sample resolution back to 1750 AD. During the past 150 years, there has been a positive covariance between the carbon isotopic composition of fossil planktonic foraminifera and of TOC. Periods of increased delta C-13 of TOC and foraminifera correspond to higher organic carbon burial in Santa Monica and Santa Barbara Basins. When combined, these patterns are interpreted as variation in productivity within the basins. Isotopic variability in TOC and planktonic foraminifera is significantly higher prior to 1900 AD. Although spring sea surface temperatures were also significantly more variable during this period, the authors do not recognize a systematic relationship between temperature and organic carbon burial. Spectral analysis of isotopic compositions of fossil foraminifera calcite, TOC, organic carbon burial and lamination frequency in the sediments reveal distinct spectral peaks at 5 and 7.7 years, corresponding to ENSO/El Nino frequencies. Additional spectral peaks occur at 19 and 20 years. Previous time series analyses of tree ring width records indicate similar decadal-scale frequencies and suggest a possible link to solar and/or lunar nodal tidal cycles. While these initial results suggest a relationship between climate-cyclicity, primary productivity and organic carbon burial, the phase relationship cannot be deciphered from this preliminary data set.

  1. Two opposed subduction modes at the southern Caribbean plate margin of Colombia

    NASA Astrophysics Data System (ADS)

    Kammer, Andreas; Piraquive, Alejandro

    2014-05-01

    Cretaceous to Paleogene convergence at the southern Caribbean plate margin is still little deciphered and a generalized interpretation is hindered by the absence of regionally correlatable tectonic elements, like magmatic arcs, time constraints and an intense crustal fragmentation brought about by Neogene strike-slip tectonics. In order to illustrate the diversity of these subduction settings and discuss possible tectonic controls on their subsequent collisional evolution, we outline the structural evolution along a thickened and a thinned continental segment. The first case is exemplified by the Sierra Nevada de Santa Marta, a triangular block that exposes an imbricated lower crustal section capped by nested plutons and a volcanic sequence of a Jurassic to Early Cretaceous arc. This exceptionally thick crustal section forms the upper plate of a continent-ward dipping main suture that is underlain by strongly sheared platform sediments and transitional basement rocks of a lower plate. Penetrative deformation developed under medium-grade conditions with a uniform top-to-the NE shear attests to a stable subduction interval of a still unknown duration. Onset of a collisional phase is marked by a crustal imbrication further inboard of the main suture, leading to a further crustal thickening, and links in the Paleogene to the emplacement of the dome-like Santa Marta batholith within the lower plate. It is likely that the juxtaposition of thickened continental Southamerican and thinner oceanic Caribbean crust triggered a crustal channel flow that fed the magmatic dome in the transitional part of these crustal realms, leading thus to some gravitational collapse of the continental crust. The opposite case of the juxtaposition of a continental platform, previously thinned by Jurassic to Early Cretaceous rifting and a relatively thick Caribbean crust is documented in the northwestern Guajira Peninsula. Here platform sequences and their corresponding basement were subducted

  2. 2009 Santa Fe Bone symposium.

    PubMed

    Lewiecki, E Michael; Bilezikian, John P; Laster, Andrew J; Miller, Paul D; Recker, Robert R; Russell, R Graham G; Whyte, Michael P

    2010-01-01

    Osteoporosis is a common skeletal disease with serious clinical consequences because of fractures. Despite the availability of clinical tools to diagnose osteoporosis and assess fracture risk, and drugs proven to reduce fracture risk, it remains a disease that is underdiagnosed and undertreated. When treatment is started, it is commonly not taken correctly or long enough to be effective. Recent advances in understanding of the regulators and mediators of bone remodeling have led to new therapeutic targets and the development of drugs that may offer advantages over current agents in reducing the burden of osteoporotic fractures. Many genetic factors that play a role in the pathogenesis of osteoporosis and metabolic bone disease have now been identified. At the 2009 Santa Fe Bone Symposium, held in Santa Fe, New Mexico, USA, the links between advances in genetics, basic bone science, recent clinical trials, and new and emerging therapeutic agents were presented and explored. Socioeconomic challenges and opportunities in the care of osteoporosis were discussed. This is a collection of medical essays based on key presentations at the 2009 Santa Fe Bone Symposium.

  3. Sea-level and tectonic control of middle to late Pleistocene turbidite systems in Santa Monica Basin, offshore California

    USGS Publications Warehouse

    Normark, W.R.; Piper, D.J.W.; Sliter, R.

    2006-01-01

    Small turbidite systems offshore from southern California provide an opportunity to track sediment from river source through the turbidity-current initiation process to ultimate deposition, and to evaluate the impact of changing sea level and tectonics. The Santa Monica Basin is almost a closed system for terrigenous sediment input, and is supplied principally from the Santa Clara River. The Hueneme fan is supplied directly by the river, whereas the smaller Mugu and Dume fans are nourished by southward longshore drift. This study of the Late Quaternary turbidite fill of the Santa Monica Basin uses a dense grid of high-resolution seismic-reflection profiles tied to new radiocarbon ages for Ocean Drilling Program (ODP) Site 1015 back to 32 ka. Over the last glacial cycle, sedimentation rates in the distal part of Santa Monica Basin averaged 2-3 mm yr-1, with increases at times of extreme relative sea-level lowstand. Coarser-grained mid-fan lobes prograded into the basin from the Hueneme, Mugu and Dume fans at times of rapid sea-level fall. These pulses of coarse-grained sediment resulted from river channel incision and delta cannibalization. During the extreme lowstand of the last glacial maximum, sediment delivery was concentrated on the Hueneme Fan, with mean depositional rates of up to 13 mm yr-1 on the mid- and upper fan. During the marine isotope stage (MIS) 2 transgression, enhanced rates of sedimentation of > 4 mm yr-1 occurred on the Mugu and Dume fans, as a result of distributary switching and southward littoral drift providing nourishment to these fan systems. Longer-term sediment delivery to Santa Monica Basin was controlled by tectonics. Prior to MIS 10, the Anacapa ridge blocked the southward discharge of the Santa Clara River into the Santa Monica Basin. The pattern and distribution of turbidite sedimentation was strongly controlled by sea level through the rate of supply of coarse sediment and the style of initiation of turbidity currents. These two

  4. Particle Size, Bed Properties, and Transport of Sediment on European Epicontinental Shelves

    DTIC Science & Technology

    2004-09-30

    Survey Pacific Science Center, UC Santa Cruz 1156 High Street, Santa Cruz , CA 95064 U. S. A. 1 831 459 5430; 1 831 427 4748 fax; drubin@usgs.gov...and Ancona , and near Chienti are artifacts from the unrealistic uniform initial sediment distribution. The depositional regions off the Po delta and

  5. Depositional environments of the Santa Margarita Formation in the Miocene Santa Maria basin, Huasna syncline

    SciTech Connect

    Phillips, R.L. )

    1991-02-01

    Preliminary investigation of the depositional environments of the middle sandstone member of the late middle Miocene Santa Margarita Formation in the Huasna syncline suggests a current-dominated shallow shelf environment. Progradation of coarse-grained clastic and bioclastic-rich sediment over siltstone documents the initial stage of deposition of this sand body. Overlying the basal intensely bioturbated bioclastic sediments are large-scale tabular cross-beds, up to 16 m thick, interbedded with tabular lag deposits of barnacles, oysters, and echinoids. The tabular fossil-rich beds, which form sequences up to 6 m thick between the large-scale cross-beds, represent either deposition of bottom set beds of the large-scale cross-beds or current swept lag deposits. Increasing energy conditions are recorded vertically by a decrease in the amount of bioturbation and by an increase in large-scale cross-bed sets and cosets. however, in the northern outcrop area subtidal channels are incised into the upper bioclastic sediments suggesting local shoaling conditions. Paleocurrent data record a unidirectional southwest-directed current trend normal to the basin axis and the East Huasna fault. The coarse clastic deposition terminates with deposition of siltstone as energy conditions decreased and water depth again increased. A current-swept shallow shelf containing extensive sandwaves comprises the major depositional environments. The paleocurrent data and large-scale cross-beds suggest that the shallow shelf extended to the east of the Huasna syncline and that the currents were most likely tidal in origin.

  6. EFFECTS OF SEDIMENT TYPE ON BENTHIC MACROINFAUNAL COLONIZATION OF LABORATORY MICROCOSMS

    EPA Science Inventory

    We tested the effects of four different sediment types on macroinfaunal colonization and community development in our laboratory flow-thru microcosm system (all microcosms were 20 cm side-1 and sediment depth was 5 cm) over a period of 41 days. Sediments included Santa Rosa Islan...

  7. [Marginalization and health. Introduction].

    PubMed

    Yunes, J

    1992-06-01

    The relationship between marginalization and health is clear. In Mexico, for example, life expectancy is 53 years for the poorest population sectors and 20 years more for the wealthiest. Infant mortality in poor Colombian families is twice that of wealthier families, and one-third of developing countries the rural population is only half as likely as the urban to have access to health services. Women in the Southern hemisphere are 12 times likelier than those in the Northern to die of maternal causes. The most important step in arriving at a solution to the inequity may be to analyze in depth the relationship between marginality and health. Marginality may be defined as the lack of participation of individuals or groups in certain key phases of societal life, such as production, consumption, or political decision making. Marginality came to be viewed as a social problem only with recognition of the rights of all individuals to participate in available social goods. Marginality is always relative, and marginal groups exist because central groups determine the criteria for inclusion in the marginal and central groups. Marginality thus always refers to a concrete society at a specific historical moment. Marginal groups may be of various types. At present, marginal groups include women, rural populations, people with AIDS or mental illness or certain other health conditions, refugees, ethnic or religious groups, homosexuals, and the poor, who are the largest group of marginal persons in the world. Even in developed countries, 100-200 million persons live below the poverty line. Latin America is struggling to emerge from its marginal status in the world. The economic crisis of the 1980s increased poverty in the region, and 40% are not considered impoverished. Latin America is a clear example of the relationship between marginality and health. Its epidemiologic profile is intimately related to nutrition, availability of potable water, housing, and environmental

  8. Stratigraphy and structure along the Pensacola Arch/Conecuh Embayment margin in northwest Florida

    SciTech Connect

    Duncan, J.G. . Geology Dept. Florida Geological Survey, Tallahassee, FL )

    1993-03-01

    Stratigraphic and structural analysis of deep borehole data along the Pensacola Arch/Conecuh Embayment margin in eastern Santa Rosa County, Florida reveals a northeast-trending basement normal fault that is downthrown to the northwest. The fault functioned as a border fault of a half-graben (or graben ) that developed during continental rifting of Pangea in the Late Triassic and Early Jurassic. The upthrown or horst block was a paleotopographic high that formed the southeastern boundary of the Middle to Late Jurassic Conecuh Embayment. A second, younger basement fault trends approximately perpendicular to the half-graben border fault. Late Triassic synrift continental sediments, deposited on the downthrown block of the half-graben, pinch-out abruptly to the southeast pre-Mesozoic Suwannee Basin basement. The border fault is located approximately where the Triassic sedimentary wedge pinches out. Middle to Upper Jurassic drift-stage strata of the Conecuh embayment progressively onlap the post-rift unconformity toward the southeast. Upper Jurassic Smackover Formation carbonates and evaporites apparently overstep Triassic deposits and rest directly on Suwannee Basin quartzitic sandstone near their depositional limit at the Pensacola Arch. The Smackover Formation thins significantly toward the southeast in association with the Triassic pinch-out and half-graben border fault. The pinch-out trend of the Smackover Formation suggests a northeast-southwest orientation for the Triassic border fault and supports a horst-block origin for the Pensacola Arch.

  9. The Antarctic continental margin: Geology and geophysics of offshore Wilkes land

    SciTech Connect

    Eittreim, S.L.; Hampton, M.A.

    1987-01-01

    This book contains 14 chapters. Some of the chapter titles are: An Interpretation of the Multichannel Seismic Reflection Profiles across the Continental Margin of the Dumont D'Urville Sea, off Wilkes Land, East Antarctica; Hydrocarbon Geochemistry of Sediments Offshore from Antarctica: Wilkes Land Continental margin; and the Conjugate Continental margins of Antarctica and Australia.

  10. Focused fluid flow in passive continental margins.

    PubMed

    Berndt, Christian

    2005-12-15

    Passive continental margins such as the Atlantic seaboard of Europe are important for society as they contain large energy resources, and they sustain ecosystems that are the basis for the commercial fish stock. The margin sediments are very dynamic environments. Fluids are expelled from compacting sediments, bottom water temperature changes cause gas hydrate systems to change their locations and occasionally large magmatic intrusions boil the pore water within the sedimentary basins, which is then expelled to the surface. The fluids that seep through the seabed at the tops of focused fluid flow systems have a crucial role for seabed ecology, and study of such fluid flow systems can also help in predicting the distribution of hydrocarbons in the subsurface and deciphering the climate record. Therefore, the study of focused fluid flow will become one of the most important fields in marine geology in the future.

  11. The basins on the Argentine continental margin

    SciTech Connect

    Urien, C.M.

    1996-08-01

    After the stabilization of the central Gondwana Craton, orogenic belts were accreted, as a result of convergence events and an extensive passive margin developed in southwestern Gondwana. Thermal subsidence in Parana, Karoo-Ventania basins and the Late Paleozoic-Early Mesozoic rifts, were modified by the Gondwana breakup and the South Atlantic opening. Early Paleozoic marine transgressions deposited the Table Mountain Group in Ventania. In southwestern Patagonia foreland clastics were deposited. Magmatic arcs and marine units indicate a tectonic trough was formed, alternating with continental sequences, over Late Paleozoic metamorphics and intrusives, resulting from plastered terrains along the Gondwana margin. In Patagonia, Permo-Carboniferous continental and glacio marine clastics infill the basins, while in Ventania, paralic sequences, grade from neritic to continental to the northeast, extending beneath the continental margin. The Triassic-Jurassic rift basins progressed onto regional widespread acid lavas and were infilled by lagoonal organic-rich sequences. Early drift phase built basins transverse to the margin, with fluvio-lacustrine sequences: Salado, Colorado, Valdes-Rawson, San Julian and North Malvinas intracratonic basins, which underwent transtensional faulting. Post-Oxfordian to Neocomian brackish sequences, onlapped the conjugate basins during the margin`s drift, with petroleum systems, as in Austral and Malvinas. In the Valanginian, basic extrusions commenced to form on the continental border, heralding the oceanic phase. Due to thermal subsidence, offlaping sediments prograded onto the remaining half-grabens. Several petroleum systems, proven and hypothetical, are identified in this region.

  12. Modeling Sedimentary Deposits on the Continental Margin

    DTIC Science & Technology

    2001-09-30

    sedimentation processes. P. 151-164, in Numerical Experiments in Stratigraphy : Recent Advances in stratigraphic and sedimentologic Computer Simulations. Soc...Niedoroda, A.W., 1996, Modeling the sedimentology and stratigraphy of continental margins, Oceanography, v. 9, p183-188 Swift, D. J. P. B. S. Parsons...hypothesis that on muddy shelves such as the northern California shelf, Holocene event stratigraphy consists of the deposits of high-concentration

  13. Gas hydrates of outer continental margins

    SciTech Connect

    Kvenvolden, K.A. )

    1990-05-01

    Gas hydrates are crystalline substances in which a rigid framework of water molecules traps molecules of gas, mainly methane. Gas-hydrate deposits are common in continental margin sediment in all major oceans at water depths greater than about 300 m. Thirty-three localities with evidence for gas-hydrate occurrence have been described worldwide. The presence of these gas hydrates has been inferred mainly from anomalous lacoustic reflectors seen on marine seismic records. Naturally occurring marine gas hydrates have been sampled and analyzed at about tensites in several regions including continental slope and rise sediment of the eastern Pacific Ocean and the Gulf of Mexico. Except for some Gulf of Mexico gas hydrate occurrences, the analyzed gas hydrates are composed almost exclusively of microbial methane. Evidence for the microbial origin of methane in gas hydrates includes (1) the inverse relation between methane occurence and sulfate concentration in the sediment, (2) the subparallel depth trends in carbon isotopic compositions of methane and bicarbonate in the interstitial water, and (3) the general range of {sup 13}C depletion ({delta}{sub PDB}{sup 13}C = {minus}90 to {minus}60 {per thousand}) in the methane. Analyses of gas hydrates from the Peruvian outer continental margin in particular illustrate this evidence for microbially generated methane. The total amount of methane in gas hydrates of continental margins is not known, but estimates of about 10{sup 16} m{sup 3} seem reasonable. Although this amount of methane is large, it is not yet clear whether methane hydrates of outer continental margins will ever be a significant energy resource; however, these gas hydrates will probably constitute a drilling hazard when outer continental margins are explored in the future.

  14. Hyperpycnal plume-derived fans in the Santa Barbara Channel, California

    USGS Publications Warehouse

    Warrick, Jonathan A.; Simms, Alexander R.; Ritchie, Andy; Steel, Elisabeth; Dartnell, Pete; Conrad, James E.; Finlayson, David P.

    2013-01-01

    Hyperpycnal gravity currents rapidly transport sediment across shore from rivers to the continental shelf and deep sea. Although these geophysical processes are important sediment dispersal mechanisms, few distinct geomorphic features on the continental shelf can be attributed to hyperpycnal flows. Here we provide evidence of large depositional features derived from hyperpycnal plumes on the continental shelf of the northern Santa Barbara Channel, California, from the combination of new sonar, lidar, and seismic reflection data. These data reveal lobate fans directly offshore of the mouths of several watersheds known to produce hyperpycnal concentrations of suspended sediment. The fans occur on an upwardly concave section of the shelf where slopes decrease from 0.04 to 0.01, and the location of these fans is consistent with wave- and auto-suspending sediment gravity current theories. Thus, we provide the first documentation that the morphology of sediment deposits on the continental shelf can be dictated by river-generated hyperpycnal flows.

  15. Holocene paleoecology of an estuary on Santa Rosa Island, California

    USGS Publications Warehouse

    Cole, K.L.; Liu, Gaisheng

    1994-01-01

    The middle to late Holocene history and early Anglo-European settlement impacts on Santa Rosa Island, California, were studied through the analysis of sediments in a small estuarine marsh. A 5.4-m-long sediment core produced a stratigraphic and pollen record spanning the last 5200 yr. Three major zones are distinguishable in the core. The lowermost zone (5200 to 3250 yr B.P.) represents a time of arid climate with predominantly marine sediment input and high Chenopodiaceae and Ambrosia pollen values. The intermediate zone (3250 yr B.P. to 1800 A.D.) is characterized by greater fresh water input and high values for Asteraceae and Cyperaceae pollen and charcoal particles. The uppermost zone (1800 A.D. to present) documents the unprecedented erosion, sedimentation, and vegetation change that resulted from the introduction of large exotic herbivores and exotic plants to the island during Anglo-European settlement. The identification of pollen grains of Torrey Pine (Pinus torreyana) documents the persistence of this endemic species on the island throughout the middle to late Holocene.

  16. You're a "What"? Santa Claus

    ERIC Educational Resources Information Center

    Royster, Sara

    2013-01-01

    Professional Santas entertain children and adults during the holiday season at all types of events. They work at shopping malls or stores; entertain crowds at parades and tree lightings; and make appearances at holiday parties, charity events, and people's homes. Most Santas work during the Christmas holiday season, which usually lasts from late…

  17. Origin and dynamics of depositionary subduction margins

    NASA Astrophysics Data System (ADS)

    Vannucchi, Paola; Morgan, Jason P.; Silver, Eli A.; Kluesner, Jared W.

    2016-06-01

    Here we propose a new framework for forearc evolution that focuses on the potential feedbacks between subduction tectonics, sedimentation, and geomorphology that take place during an extreme event of subduction erosion. These feedbacks can lead to the creation of a "depositionary forearc," a forearc structure that extends the traditional division of forearcs into accretionary or erosive subduction margins by demonstrating a mode of rapid basin accretion during an erosive event at a subduction margin. A depositionary mode of forearc evolution occurs when terrigenous sediments are deposited directly on the forearc while it is being removed from below by subduction erosion. In the most extreme case, an entire forearc can be removed by a single subduction erosion event followed by depositionary replacement without involving transfer of sediments from the incoming plate. We need to further recognize that subduction forearcs are often shaped by interactions between slow, long-term processes, and sudden extreme events reflecting the sudden influences of large-scale morphological variations in the incoming plate. Both types of processes contribute to the large-scale architecture of the forearc, with extreme events associated with a replacive depositionary mode that rapidly creates sections of a typical forearc margin. The persistent upward diversion of the megathrust is likely to affect its geometry, frictional nature, and hydrogeology. Therefore, the stresses along the fault and individual earthquake rupture characteristics are also expected to be more variable in these erosive systems than in systems with long-lived megathrust surfaces.

  18. Origin and dynamics of depositionary subduction margins

    USGS Publications Warehouse

    Vannucchi, Paola; Morgan, Jason P.; Silver, Eli; Kluesner, Jared

    2016-01-01

    Here we propose a new framework for forearc evolution that focuses on the potential feedbacks between subduction tectonics, sedimentation, and geomorphology that take place during an extreme event of subduction erosion. These feedbacks can lead to the creation of a “depositionary forearc,” a forearc structure that extends the traditional division of forearcs into accretionary or erosive subduction margins by demonstrating a mode of rapid basin accretion during an erosive event at a subduction margin. A depositionary mode of forearc evolution occurs when terrigenous sediments are deposited directly on the forearc while it is being removed from below by subduction erosion. In the most extreme case, an entire forearc can be removed by a single subduction erosion event followed by depositionary replacement without involving transfer of sediments from the incoming plate. We need to further recognize that subduction forearcs are often shaped by interactions between slow, long-term processes, and sudden extreme events reflecting the sudden influences of large-scale morphological variations in the incoming plate. Both types of processes contribute to the large-scale architecture of the forearc, with extreme events associated with a replacive depositionary mode that rapidly creates sections of a typical forearc margin. The persistent upward diversion of the megathrust is likely to affect its geometry, frictional nature, and hydrogeology. Therefore, the stresses along the fault and individual earthquake rupture characteristics are also expected to be more variable in these erosive systems than in systems with long-lived megathrust surfaces.

  19. Santa Claus, Ga./Ind.

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The towns of Santa Claus, Ga., (top) and Santa Claus, Ind. (bottom), are shown in these two images from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument on NASA's Terra satellite. They are the only two Santa Claus towns in the United States with post offices and zip codes, although there are 11 towns with this name in the United States. Santa Claus, Ga. is located in Toombs County, and has a population of 237. Santa Claus, Ind. is located in Spencer County, and has a population of 2,041. Its name was accepted by the United States Postal Service in 1856. The images were acquired on July 3, 2000 (top) and June 16, 2001 (bottom), respectively.

    With its 14 spectral bands from the visible to the thermal infrared wavelength region, and its high spatial resolution of 15 to 90 meters (about 50 to 300 feet), ASTER images Earth to map and monitor the changing surface of our planet.

    ASTER is one of five Earth-observing instruments launched December 18, 1999, on NASA's Terra satellite. The instrument was built by Japan's Ministry of Economy, Trade and Industry. A joint U.S./Japan science team is responsible for validation and calibration of the instrument and the data products.

    The broad spectral coverage and high spectral resolution of ASTER will provide scientists in numerous disciplines with critical information for surface mapping, and monitoring of dynamic conditions and temporal change. Example applications are: monitoring glacial advances and retreats; monitoring potentially active volcanoes; identifying crop stress; determining cloud morphology and physical properties; wetlands evaluation; thermal pollution monitoring; coral reef degradation; surface temperature mapping of soils and geology; and measuring surface heat balance.

    Dr. Anne Kahle at NASA's Jet Propulsion Laboratory, Pasadena, Calif., is the U.S. science team leader; Bjorn Eng of JPL is the project manager. The Terra mission is part of NASA's Earth Science

  20. Temporal and spatial patterns of Cenozoic and Late Mesozoic erosion and deposition along the western margin of southern Africa

    SciTech Connect

    Brown, R.W.; Gleadow, A.J.W. ); Rust, D.J.; Summerfield, M.A. )

    1990-05-01

    Compared with subsidence history and eustatic sea level change, sediment supply has been a neglected component of studies of passive margin stratigraphy. The spatial and temporal pattern of sediment supply to continental margin, however, is a critical factor in determining the architecture of offshore sedimentary sequences. Sediment routing across passive margins is controlled primarily by their tectonic development and the consequent morphological evolution of the subaerial part of the margin. By combining offshore sediment volume and sedimentation rate data based on isopach maps and borehole records with apatite fission-track analysis and denudational modeling onland, the depositional history of the western margin of southern Africa has been related to its geomorphic response to continental rifting. The sediment volume data indicate a declining rate of sedimentation after rifting in the Early Cretaceous despite a probable enlargement of the sediment source area through time. Similarly, apatite fission-track ages and confined track length distributions indicate an Early Cretaceous episode of relatively high erosion rates which affected areas both inland and oceanward of the major topographic discontinuity along the margin represented by the Great Escarpment. Late Cenozoic rates of erosion and sediment supply have been low, although much of the sediment source area is still at a significant elevation. Although aridity may have contributed to this reduction in sediment supply, the morphological response to the tectonic evolution of the margin has also been crucial.

  1. Dynamics of the continental margins

    SciTech Connect

    Not Available

    1990-11-01

    On 18--20 June 1990, over 70 oceanographers conducting research in the ocean margins of North America attended a workshop in Virginia Beach, Virginia. The purpose of the workshop was to provide the Department of Energy with recommendations for future research on the exchange of energy-related materials between the coastal and interior ocean and the relationship between the ocean margins and global change. The workshop was designed to optimize the interaction of scientists from specific research disciplines (biology, chemistry, physics and geology) as they developed hypotheses, research questions and topics and implementation plans. The participants were given few restraints on the research they proposed other than realistic time and monetary limits. The interdisciplinary structure of the meeting promoted lively discussion and creative research plans. The meeting was divided into four working groups based on lateral, vertical, air/sea and sediment/water processes. Working papers were prepared and distributed before the meeting. During the meeting the groups revised the papers and added recommendations that appear in this report, which was reviewed by an Executive Committee.

  2. Seasonal Patterns of Flood, Wind, and Wave Coherence Along the US West Coast: Implications for Sediment Dispersal and Deposition.

    NASA Astrophysics Data System (ADS)

    Kniskern, T. A.; Warrick, J. A.; Farnsworth, K. L.

    2008-12-01

    Small rivers with mountainous catchments account for over half of the terrigenous material delivered to the coastal ocean. Dispersal, deposition, and cycling of sediments and associated nutrients ultimately influence shelf carbon budgets. Recent work on collision margins revealed that these small rivers flood during energetic ocean conditions, creating conditions conducive to dispersal of sediments via multiple sediment transport mechanisms. Furthermore, the relative timing of the peak flood and peak wave conditions influences dispersal and depositional patterns. Our study sought to identify patterns of fluvial and oceanic coherence along the US west coast by analyzing 10 years (1996-2006) of NOAA buoy, Climate Prediction Center storm track, and USGS gauge data. Discharge, buoy data, and storm tracks for the Umpqua, Eel, Salinas, and Santa Clara rivers and their adjacent shelves revealed temporal and spatial coherence patterns of wave event and flood magnitude, frequency, and timing. The seasonal period of energetic waves for each river-shelf system began 1-2 months earlier than the flood season (November) and extended 1 month beyond the end of flood season (May). There was also a seasonal disconnect in the timing of peak wave energy (December) and peak floods (January to February). Peak flood activity occurred in January on the Umpqua and Eel Rivers, and in February for the Salinas and Santa Clara Rivers. Flooding and wave events were more frequent and greater in magnitude on the Eel and Umpqua river shelves. The Salinas and Santa Clara rivers displayed lower fluvial inputs, but Salinas River shelf wave events were greater in magnitude. The magnitude and timing of peak waves and peak discharges during floods varied characteristically for each river-shelf system. Peak discharge and peak wave magnitude during floods generally decreased from December to May, indicating that dispersal and depositional patterns vary over the season. Additionally, the timing between

  3. Ocean margins workshop

    SciTech Connect

    1990-12-31

    The Department of Energy (DOE) is announcing the refocusing of its marine research program to emphasize the study of ocean margins and their role in modulating, controlling, and driving Global Change phenomena. This is a proposal to conduct a workshop that will establish priorities and an implementation plan for a new research initiative by the Department of Energy on the ocean margins. The workshop will be attended by about 70 scientists who specialize in ocean margin research. The workshop will be held in the Norfolk, Virginia area in late June 1990.

  4. Extensive management of field margins enhances their potential for off-site soil erosion mitigation.

    PubMed

    Ali, Hamada E; Reineking, Björn

    2016-03-15

    Soil erosion is a widespread problem in agricultural landscapes, particularly in regions with strong rainfall events. Vegetated field margins can mitigate negative impacts of soil erosion off-site by trapping eroded material. Here we analyse how local management affects the trapping capacity of field margins in a monsoon region of South Korea, contrasting intensively and extensively managed field margins on both steep and shallow slopes. Prior to the beginning of monsoon season, we equipped a total of 12 sites representing three replicates for each of four different types of field margins ("intensive managed flat", "intensive managed steep", "extensive managed flat" and "extensive managed steep") with Astroturf mats. The mats (n = 15/site) were placed before, within and after the field margin. Sediment was collected after each rain event until the end of the monsoon season. The effect of management and slope on sediment trapping was analysed using linear mixed effects models, using as response variable either the sediment collected within the field margin or the difference in sediment collected after and before the field margin. There was no difference in the amount of sediment reaching the different field margin types. In contrast, extensively managed field margins showed a large reduction in collected sediment before and after the field margins. This effect was pronounced in steep field margins, and increased with the size of rainfall events. We conclude that a field margin management promoting a dense vegetation cover is a key to mitigating negative off-site effects of soil erosion in monsoon regions, particularly in field margins with steep slopes.

  5. Santa Barbara Final Technical Report

    SciTech Connect

    Hacker, Angela; Hansen, Sherman; Watkins, Ashley

    2013-11-30

    This report serves as the Final Report for Santa Barbara County’s Energy Efficiency and Conservation Block Grant (EECBG) BetterBuildings Neighborhood Program (BBNP) award from the U.S. Department of Energy (DOE). This report explains how DOE BBNP funding was invested to develop robust program infrastructure designed to help property owners complete energy improvements, thereby generating substantial outcomes for the local environment and economy. It provides an overview of program development and design within the grant period, program accomplishments and challenges to date, and a plan for the future sustainability of emPower, the County’s innovative clean energy and building efficiency program. During the grant period, Santa Barbara County’s emPower program primarily targeted 32,000 owner occupied, single family, detached residential homes over 25 years old within the County. In order to help these homeowners and their contractors overcome market barriers to completing residential energy improvements, the program developed and promoted six voluntary, market-based service areas: 1) low cost residential financing (loan loss reserve with two local credit unions), 2) residential rebates, 3) local customer service, 4) expert energy advising, 5) workforce development and training, and 6) marketing, education and outreach. The main goals of the program were to lower building energy use, create jobs and develop a lasting regional building performance market. These services have generated important early outcomes and lessons after the program’s first two years in service. The DOE BBNP funding was extended through October 2014 to enable Santa Barbara County to generate continued outcomes. In fact, funding related to residential financing remains wholly available for the foreseeable future to continue offering Home Upgrade Loans to approximately 1,300 homeowners. The County’s investment of DOE BBNP funding was used to build a lasting, effective, and innovative

  6. Partial melting of fertile peridotite fluxed by hydrous rhyolitic melt at 2-3 GPa: implications for mantle wedge hybridization by sediment melt and generation of ultrapotassic magmas in convergent margins

    NASA Astrophysics Data System (ADS)

    Mallik, Ananya; Nelson, Jared; Dasgupta, Rajdeep

    2015-05-01

    We investigated the melting behavior of peridotite fluxed with 25 wt% of H2O-bearing rhyolitic sediment melt (1.8 wt% bulk H2O), by performing experiments from 1100 to 1300 °C at 2 GPa and 1050-1350 °C at 3 GPa. The apparent solidus of our bulk composition lies between 1100 and 1150 °C at both pressures, which is at a higher temperature than the vapor-saturated solidus and close to the pargasite dehydration solidus of peridotite. With increasing temperature, reacted melt fraction increases from 20 to 36 wt% from 1200 to 1300 °C at 2 GPa and 7 to 24 wt% from 1225 to 1350 °C at 3 GPa. Orthopyroxene is present as a residual phase in all the experiments, while olivine is present as a residual phase in all the experiments at 2 GPa only. Amphibole is absent above 1100 °C at both pressures, clinopyroxene disappears above 1200 and 1300 °C at 2 and 3 GPa, respectively, and garnet (only present at 3 GPa) melts out above 1300 °C. Upon reaction with the mantle wedge and subsequent melting of the hybrid rock, subducted sediment-derived rhyolites evolve in composition to a nepheline-normative ultrapotassic leucitite, similar in major element composition to ultrapotassic lavas from active arcs such as Sunda and inactive arcs such as in the Roman Magmatic Province. Fluxing peridotite with H2O versus H2O-bearing sediment melt at similar pressures does not appear to have an effect on isobaric melt productivity, but does have significant effect on melting reactions and resultant melt composition, with influx of sediment melt adding K2O to the system, thereby stabilizing phlogopite, which in turn buffers the reacted melt to ultrapotassic compositions. Previous experimental studies, along with this study, find that phlogopite can be stable near the hotter core of the mantle wedge and, hence, is likely to be subducted to deeper mantle, thereby influencing deeper cycling of volatiles and large ion lithophile elements. Also, because D {Rb/phl/melt} ≫ D {Sr/phl/melt} and D {Nd

  7. 33 CFR 80.1126 - Santa Barbara Harbor, CA.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 33 Navigation and Navigable Waters 1 2010-07-01 2010-07-01 false Santa Barbara Harbor, CA. 80.1126... NAVIGATION RULES COLREGS DEMARCATION LINES Pacific Coast § 80.1126 Santa Barbara Harbor, CA. A line drawn from Santa Barbara Harbor Light 4 to Santa Barbara Harbor Breakwater Light....

  8. 33 CFR 80.1138 - Santa Cruz Harbor, CA.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 33 Navigation and Navigable Waters 1 2010-07-01 2010-07-01 false Santa Cruz Harbor, CA. 80.1138... NAVIGATION RULES COLREGS DEMARCATION LINES Pacific Coast § 80.1138 Santa Cruz Harbor, CA. A line drawn from the seaward extremity of the Santa Cruz Harbor East Breakwater to Santa Cruz Harbor West...

  9. Estimating crustal thickness using SsPmp in regions covered by low-velocity sediments: Imaging the Moho beneath the Southeastern Suture of the Appalachian Margin Experiment (SESAME) array, SE Atlantic Coastal Plain

    NASA Astrophysics Data System (ADS)

    Parker, E. Horry, Jr.; Hawman, Robert B.; Fischer, Karen M.; Wagner, Lara S.

    2016-09-01

    Deconvolved waveforms for two earthquakes (Mw: 6.0 and 5.8) show clear postcritical SsPmp arrivals for broadband stations deployed across the coastal plain of Georgia, allowing mapping of crustal thickness in spite of strong reverberations generated by low-velocity sediments. Precritical SsPmp arrivals are also identified. For a basement in which velocity increases linearly with depth, a bootstrapped grid search suggests an average basement velocity of 6.5 ± 0.1 km/s and basement thickness of 29.8 ± 2.0 km. Corresponding normal-incidence Moho two-way times (including sediments) are 10.6 ± 0.6 s, consistent with times for events interpreted as Moho reflections on coincident active-source reflection profiles. Modeling of an underplated mafic layer (Vp = 7.2-7.4 km/s) using travel time constraints from SsPmp data and vertical-incidence Moho reflection times yields a total basement thickness of 30-35 km and average basement velocity of 6.35-6.65 km/s for an underplate thickness of 0-15 km.

  10. Discovery and Description of Extinct Asphalt Volcanoes Along the Southern California Margin

    NASA Astrophysics Data System (ADS)

    Valentine, D. L.; Reddy, C.; Ventura, G. T.; Nelson, R. K.

    2007-12-01

    Asphalt volcanism is increasingly being recognized as an important process at cold seeps, linking ancient subsurface carbon reservoirs with more rapid biogeochemical processes at the surface. Here we describe two extinct asphalt volcanoes discovered off the coast of Santa Barbara, CA, using the DSV Alvin during the July 2007 SEEPS (Studies on the Ecology and Evolution of Petroleum Seeps) cruise. These structures are located approximately 10 kilometers offshore and 2 kilometers apart from each other, at a water depth of 150 to 200 meters. The volcanoes occur as asphalt mounds closely associated with sediment-laden depressions, suggesting extrusion of liquid petroleum coupled with localized subsidence or gas blowout. The volcanoes range from 10 to 30 meters in height off the sea floor and may extend below the present level of sediment cover. No active seepage was observed during approximately 10 hours of visual and video surveys from the DSV Alvin, but the volcanoes appear to serve as an oasis for benthic life when compared to the surrounding sediment. Four asphalt samples were collected throughout each site during these surveys and all show remarkable similarity in their structure and chemical composition. Organic carbon comprises 50 percent of the mass for each sample, with sulfur, hydrogen and nitrogen comprising another 10 percent in aggregate. Inclusions of fine-grained sediment and microfossils comprise much of the residual mass and are being used in an attempt to determine the timing of the eruptive events. Each sample was analyzed for the stable isotope composition of carbon, nitrogen and sulfur, and results are consistent with a petroleum source from the Miocene-age Monterey Formation. Analysis of biomarkers using comprehensive two-dimensional gas chromatography yields a suite of hopanes and steranes also consistent with petroleum from the Monterey Formation, but with anomalously high concentrations of bisnorhopane. To our knowledge, this is the first report

  11. Chapter 34: Geology and petroleum potential of the rifted margins of the Canada Basin

    USGS Publications Warehouse

    Houseknecht, D.W.; Bird, K.J.

    2011-01-01

    Three sides of the Canada Basin are bordered by high-standing, conjugate rift shoulders of the Chukchi Borderland, Alaska and Canada. The Alaska and Canada margins are mantled with thick, growth-faulted sediment prisms, and the Chukchi Borderland contains only a thin veneer of sediment. The rift-margin strata of Alaska and Canada reflect the tectonics and sediment dispersal systems of adjacent continental regions whereas the Chukchi Borderland was tectonically isolated from these sediment dispersal systems. Along the eastern Alaska-southern Canada margin, termed herein the 'Canning-Mackenzie deformed margin', the rifted margin is deformed by ongoing Brooks Range tectonism. Additional contractional structures occur in a gravity fold belt that may be present along the entire Alaska and Canada margins of the Canada Basin. Source-rock data inboard of the rift shoulders and regional palaeogeographic reconstructions suggest three potential source-rock intervals: Lower Cretaceous (Hauterivian-Albian), Upper Cretaceous (mostly Turonian) and Lower Palaeogene. Burial history modelling indicates favourable timing for generation from all three intervals beneath the Alaska and Canada passive margins, and an active petroleum system has been documented in the Canning-Mackenzie deformed margin. Assessment of undiscovered petroleum resources indicates the greatest potential in the Canning-Mackenzie deformed margin and significant potential in the Canada and Alaska passive margins. ?? 2011 The Geological Society of London.

  12. Reconnaissance of alluvial fans as potential sources of gravel aggregate, Santa Cruz River valley, Southeast Arizona

    USGS Publications Warehouse

    Lindsey, David A.; Melick, Roger

    2002-01-01

    This investigation was conducted to provide information on the aggregate potential of alluvial fan sediments in the Santa Cruz River valley. Pebble lithology, roundness, and particle size were determined in the field, and structures and textures of alluvial fan sediments were photographed and described. Additional measurements of particle size on digital photographs were made on a computer screen. Digital elevation models were acquired and compiled for viewing the areal extent of selected fans. Alluvial fan gravel in the Santa Cruz River valley reflects the lithology of its source. Gravel derived from granitic and gneissic terrane of the Tortolita, Santa Catalina, and Rincon Mountains weathers to grus and is generally inferior for use as aggregate. Gravel derived from the Tucson, Sierrita, and Tumacacori Mountains is composed mostly of angular particles of volcanic rock, much of it felsic in composition. This angular volcanic gravel should be suitable for use in asphalt but may require treatment for alkali-silica reaction prior to use in concrete. Gravel derived from the Santa Rita Mountains is of mixed plutonic (mostly granitic rocks), volcanic (mostly felsic rocks), and sedimentary (sandstone and carbonate rock) composition. The sedimentary component tends to make gravel derived from the Santa Rita Mountains slightly more rounded than other fan gravel. The coarsest (pebble, cobble, and boulder) gravel is found near the heads (proximal part) of alluvial fans. At the foot (distal part) of alluvial fans, most gravel is pebble-sized and interbedded with sand and silt. Some of the coarsest gravel was observed near the head of the Madera Canyon, Montosa Canyon, and Esperanza Wash fans. The large Cienega Creek fan, located immediately south and southeast of Tucson, consists entirely of distal-fan pebble gravel, sand, and silt.

  13. The geodynamics of the Levant margin

    NASA Astrophysics Data System (ADS)

    Ben-Avraham, Z.

    2006-12-01

    The Levant continental margin, offshore Israel, Lebanon and Syria, is usually defined as a passive margin that was formed through rifting processes. During the formation two major continental fragments are assumed to separate from the northern edge of the Afro-Arabian plate to form the Levant basin: the Tauride and Eratosthenes blocks. Today an oceanic crust and, in places, a very thin continental crust are present between the Levant margin and Eratosthenes seamount. The margin can be divided into two distinct provinces that are separated by the Carmel Structure, which extends from seawards to the northwest across the continental shelf and slope. The preservation of segmentation, both in the shallow and in the deep structure, insinuates that the two segments were formed through different continental breakup processes, which continue to dictate the style of sediment accumulation. The nature and development of the continental margin offshore Israel were the subject of numerous studies, which suggest that the southern Levant segment (south of the Carmel Structure) was formed through continental rifting processes. In contrast, the northern segment, from the Carmel structure northwards and offshore southern Lebanon, was hardly studied before. Recent studies however indicate that the northern segment shows a strong similarity to classical transform margins in the world. In view of the new classification of the northern Levant margin a modified scenario is suggested for: (a) the initial stages in which the Levant margin was formed; and (b) the present day structural differences between the two segments of the margin. At present, the northern Levant continental margin is being reactivated by transpressional faulting of the marine continuation of the Carmel fault which bends northward at the base of the continental slope due to the rheological discontinuity in this region. This fault system coincides with the sharp continental-oceanic crustal transition, and acts as an

  14. Santa Ynez Chumash Community Energy Project

    EPA Pesticide Factsheets

    The Santa Ynez Band of Chumash Indians is an EPA Climate Showcase Community. EPA’s CSC Program helps local governments and tribal nations pilot innovative, cost-effective and replicable community-based greenhouse gas reduction projects.

  15. ChE at UC Santa Barbara.

    ERIC Educational Resources Information Center

    Seborg, Dale E.

    1981-01-01

    Describes the chemical engineering program at the University of California, Santa Barbara, including history of the department, faculty research interests and professional activities, graduate and undergraduate programs, and research in nuclear engineering. (SK)

  16. Structural and Seismic Stratigrapic study in the Center of the Magdalena Shelf in the Western Margin of Baja California Based on Seismic Reflection Data

    NASA Astrophysics Data System (ADS)

    González-Escobar, Mario; Salazar-Cárdenas, Rosa M.; Munguía, Luis; Martín, Arturo; Suárez-Vidal, Francisco

    2016-10-01

    The Magdalena Shelf is a shallow, low-relief surface located along the Baja California Pacific margin. As part of a forearc basin, the shelf was a convergent margin setting before the oblique divergent plate boundary formed in the Gulf of California at 12 Ma. It is thought that since 12-8 Ma, this basin has been a transtensional or strike-slip basin. To constrain the geometry, structural characteristics and some stratigraphic relationships, an active-source, seismic-reflection study was carried out in the central part of the shelf. As a result, the analyzed data show faults, basins and unconformities. Two out of four observed basins are clearly controlled by the Santa Margarita and San Lázaro faults that dip ~40° NE; a third basin is controlled by the Tosco-Abreojos fault. These three basins are part of the deformation zone that is associated with the Tosco-Abreojos fault system. The Iray-Margarita basin, on the other hand, is a fourth basin located at the northeast sector of the study area. An additional feature observed is a stepover lying between the overlapping ends of the Santa Margarita and San Lázaro faults. Small faults oriented sub-parallel to the above major faults are present, mainly throughout the western sector of the study area. Some of those minor faults cut through the seafloor indicating recent tectonic activity. Santa Margarita, San Lázaro and Tosco-Abreojos are also the names given to half-grabens controlled by the active faults that have the same names. The first two basins are affected by many more small faults in comparison with what we see in the third basin. Tectonically, this means that those two basins are the more active in the area of study. In all four basins, the upper seismic sequence consists of sediments controlled by faults of Neogene age. We found that the Iray-Santa Margarita basin is the deepest of all four basins (beyond the resolution of the data, >5 km), and lack of minor faults there indicates that the basin is not

  17. On the formation of ultra-thick sedimentary basins on rifted margins: a comparison of the Scotian and Labrador margins

    NASA Astrophysics Data System (ADS)

    Louden, K.; Funck, T.

    2003-12-01

    Sedimentary basins that form on rifted continental margins exhibit a great variety of shapes and sizes. In particular, the total sediment thickness can vary significantly and in certain sub-basins can approach 15-20 km. The deeper structure of these ultra-thick basins is typically not well resolved by seismic reflection profiles due to poor penetration within the thickest parts of the basin. Wide-angle seismic reflection/refraction profiles can help resolve these deeper features. We compare two such sub-basins that occur on the eastern Canadian margins, where reflection and refraction profiles are able to define the complete sedimentary and crustal structures: the Sable sub-basin on the northeast Nova Scotian margin and the Hopedale sub-basin on the central Labrador margin. We compare the development of these basins by converting the sediment refraction velocities to density and back-stripping assuming local isostasy. Although these basins formed during completely different episodes of rifting on different types of continental crust, we find a surprising similarity in the characteristics of crustal thinning across each margin, especially for the lower crust. Initial thinning of the crust by 50-60% occurs within 50 km followed by more gradual thinning over the subsequent 100 km. This leaves a tongue of lower continental crust extending 150 km seaward of the unstretched continental crust. This outer region becomes the location of the thickest initial sediment deposition, followed by up-building and out-building of the shelf. The local form of this deposition differs between the two margins: with much larger syn- and immediately post-rift sediments on the Scotian margin and thicker recent deposition on the Labrador margin, probably controlled by the local availability of sediment fill. Comparison with previous models of rifting based on borehole observations for the Scotia margin compare well with the overall width of the rifting (150 km), but our results suggest more

  18. Submarine Landslides at Santa Catalina Island, California

    NASA Astrophysics Data System (ADS)

    Legg, M. R.; Francis, R. D.

    2011-12-01

    Santa Catalina Island is an active tectonic block of volcanic and metamorphic rocks originally exposed during middle Miocene transtension along the evolving Pacific-North America transform plate boundary. Post-Miocene transpression created the existing large pop-up structure along the major strike-slip restraining bend of the Catalina fault that forms the southwest flank of the uplift. Prominent submerged marine terraces apparent in high-resolution bathymetric maps interrupt the steep submarine slopes in the upper ~400 meters subsea depths. Steep subaerial slopes of the island are covered by Quaternary landslides, especially at the sea cliffs and in the blueschist metamorphic rocks. The submarine slopes also show numerous landslides that range in area from a few hectares to more than three sq-km (300 hectares). Three or more landslides of recent origin exist between the nearshore and first submerged terrace along the north-facing shelf of the island's West End. One of these slides occurred during September 2005 when divers observed a remarkable change in the seafloor configuration after previous dives in the area. Near a sunken yacht at about 45-ft depth where the bottom had sloped gently into deeper water, a "sinkhole" had formed that dropped steeply to 100-ft or greater depths. Some bubbling sand was observed in the shallow water areas that may be related to the landslide process. High-resolution multibeam bathymetry acquired in 2008 by CSU Monterey Bay show this "fresh" slide and at least two other slides of varying age along the West End. The slides are each roughly 2 hectares in area and their debris aprons are spread across the first terrace at about 85-m water depth that is likely associated with the Last Glacial Maximum sealevel lowstand. Larger submarine slides exist along the steep Catalina and Catalina Ridge escarpments along the southwest flank of the island platform. A prominent slide block, exceeding 3 sq-km in area, appears to have slipped more than

  19. Jurassic through Oligocene pre-basin stratigraphy in the Santa Maria basin area, California

    SciTech Connect

    Fritsche, A.E. ); Yamashiro, D.A. )

    1991-02-01

    Compilation from published records of 30 pre-Miocene stratigraphic columns in the Santa Maria basin area of California (west of the Sur-Nacimiento fault and north of the Santa Ynez fault) reveals two basement units and 22 overlying sedimentary units. This article displays the stratigraphic columns and includes descriptions and environmental interpretations of the 24 rock units. The basement rocks include an Upper Jurassic ophiolite sequence and the Lower Jurassic through Upper Cretaceous Franciscan Complex. Most of the 22 sedimentary units were deposited along a subduction-type margin prior to development of the late Tertiary Santa Maria basin. Overlying and generally in fault contact with the basement rocks are four Upper Jurassic through Lower Cretaceous units that were deposited in basin plain and out continental margin environments. Unconformably overlying these units are eight Upper Cretaceous units that were deposited in a wide range of environments that ranged from trench, slope, and submarine fan up through shelf and nonmarine fluvial environments. Lower Tertiary units onlap unconformably onto the Cretaceous rocks and were deposited only in the southernmost part of the area. These rocks include lower Eocene basin plain and outer submarine fan deposits; middle Eocene mid-fan and slope deposits; upper Eocene inner fan, shelf, shoreface, and foreshore deposits; and Oligocene shoreface, foreshore, and nonmarine fluvial deposits.

  20. Hydrocarbon source potential in Brazilian margin basins

    SciTech Connect

    Mello, M.R.; Estrella, G.D.O.; Gaglianone, P.C.

    1984-04-01

    Twenty thousand samples from the Brazilian continental shelf basins were analyzed to characterize and evaluate the hydrocarbon source potential of the areas. The geochemical evaluation of the rock and oil samples was performed by organic carbon determinations, Rock-Eval pyrolysis, vitrinite reflectance, thermal alteration index, liquid and gas chromatographies, gas chromatography-mass spectrometry, and carbon isotope analyses. Three source rock systems have been identified: lower Neocomian shales deposited in a continental environment, upper Neocomian shales grading from continental to lagoonal environment, and Aptian shales related to evaporitic and lacustrine sequences. Upper Cretaceous and Tertiary open marine slope sediments are not considered as source rocks. Locally, these sediments present high organic carbon content but show an extremely poor hydrocarbon yield. Anoxic depositional conditions, nevertheless, can be traced locally along some levels of the Santonian to Cenomanian shales and marls. These sediments are generally immature in the Brazilian margin basins and no oil was generated from this section. Three oil families were distinguished through oil-to-oil and oil-to-source rock correlations: the lower Neocomian continental type, the upper Neocomian continental to lagoonal type, and the Aptian evaporitic to lacustrine related sequences. The geochemical studies, together with geologic and geophysical data, provided the basis to display some models for the migration pathways and habitat of oils in the Brazilian margin basins.

  1. Coastal sedimentation

    NASA Technical Reports Server (NTRS)

    Schubel, J. R.

    1980-01-01

    Several important coastal sedimentation problems are identified. Application of existing or anticipated remote sensing techniques to examine these problems is considered. Specifically, coastal fine particle sediment systems, floods and hy hurricanes and sedimentation f of coastal systems, routes and rates of sediment transport on continental shelves, and dredging and dredged material disposal are discussed.

  2. Types of convergent margins and structural and metamorphic patterns of accretionary prisms

    SciTech Connect

    Cloos, M.; Shreve, R.L.

    1985-01-01

    Theoretical modeling of the subduction channel (shear zone) at convergent plate margins quantifies the processes of sediment subduction, offscraping, underplating and formation of subduction melange by upwelling. Although bedding anisotropy and variations in lithology and pore-fluid pressure control the details of the deformation near the inlet to the subduction channel, the theory shows there are only five basic kinematic patterns which can result in the development of a distinctive type of margin (Types A-E). All incoming sediment is subducted and subduction erosion can occur at Type A margins. All sediment is subducted but a thick, narrow accretionary prism grows by underplating of subducted sediment at Type B margins. Offscraping leads to the development of a broad, tapering prism at Type C, D, and E margins. Incoming sediment is offscraped and subducted sediment is underplated at Type C margins. Melange upwells from depth and is offscraped and underplated at Type D and E margins. Incoming sediment is also offscraped at Type D margins. The structural and metamorphic histories of the fundamental tectonostratigraphic units within the accretionary prism are distinct during steady-state subduction. The bedded slope cover is not metamorphosed and not intensely tectonized upslope from the inlet. During final dewatering and accretion, offscraped materials undergo a subhorizontally-directed compression whereas underplated materials undergo a simple-shear-style of deformation. The metamorphic changes in subducted sediment or upwelled melange depend upon the depth of maximum burial and the thermal structure of the margin. Various episodic factors, such as seamount or ridge subduction, can modify the structural and metamorphic contrasts.

  3. 77 FR 36955 - Security Zone; Cruise Ships, Santa Barbara Harbor, Santa Barbara, CA

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-06-20

    ... Barbara, California. This proposed regulation is needed for national security reasons to protect cruise... Barbara, California. This security zone helps the Coast Guard to prevent vessels or persons from engaging... and under cruise ships which visit Santa Barbara Harbor, Santa Barbara, California. This proposed...

  4. Geology of the Santa Elena Peninsula, Costa Rica and its implications for the tectonic evolution of the Central America-Caribbean region

    SciTech Connect

    Lew, L.R.

    1985-01-01

    The Santa Elena Peninsula of Costa Rice represents an Aptian to Middle Eocene intraoceanic volcanic arc formed on a basement of serpentinized periodotite. This peridotite was probably part of the oceanic lithosphere formed at a spreading ridge which began to separate South America from North America in pre-Jurassic time. The arc resulted from northward subduction of oceanic crust along one ENE-trending trench about 70 km south of Santa Elena. The first phase of tectonism, arc volcanism, and sedimentation occurred in the area from Aptian to Campanian time. Carbonate bank limestone were deposited on the peridotite, which had been tilted and uplifted along E-W-trending high angle faults. A second volcanic arc developed above the limestone and was active until the Middle Eocene. From the Campanian to the Middle Eocene a forearc basin evolved south of the arc and a backarc basin north of it. A major Middle Eocene tectonic episode was associated with termination of activity of the Santa Elena subduction zone. This involved both thin-skinned deformation and reactivation of the steep basement faults to juxtapose peridotite and Campanian to Middle Eocene sediments. Existing models of the early plate tectonic evolution of the region, postulating initiation of spreading in the Jurassic, and development of a major transform in the Santa Elena area in the Cretaceous, are incompatible with the geology of the Santa Elena area. New models have been formulated genetically relating the structures in the Santa Elena tectonic province to northward subduction.

  5. Marginal Zone Lymphoma

    MedlinePlus

    ... zone lymphomas are a group of indolent (slow-growing) NHL B-cell lymphomas, which account for approximately 12 percent of all B-cell lymphomas. The median age for diagnosis is 65 years old. There are three types of marginal zone lymphoma: ...

  6. Splenic marginal zone lymphoma.

    PubMed

    Piris, Miguel A; Onaindía, Arantza; Mollejo, Manuela

    Splenic marginal zone lymphoma (SMZL) is an indolent small B-cell lymphoma involving the spleen and bone marrow characterized by a micronodular tumoral infiltration that replaces the preexisting lymphoid follicles and shows marginal zone differentiation as a distinctive finding. SMZL cases are characterized by prominent splenomegaly and bone marrow and peripheral blood infiltration. Cells in peripheral blood show a villous cytology. Bone marrow and peripheral blood characteristic features usually allow a diagnosis of SMZL to be performed. Mutational spectrum of SMZL identifies specific findings, such as 7q loss and NOTCH2 and KLF2 mutations, both genes related with marginal zone differentiation. There is a striking clinical variability in SMZL cases, dependent of the tumoral load and performance status. Specific molecular markers such as 7q loss, p53 loss/mutation, NOTCH2 and KLF2 mutations have been found to be associated with the clinical variability. Distinction from Monoclonal B-cell lymphocytosis with marginal zone phenotype is still an open issue that requires identification of precise and specific thresholds with clinical meaning.

  7. Predicting service life margins

    NASA Technical Reports Server (NTRS)

    Egan, G. F.

    1971-01-01

    Margins are developed for equipment susceptible to malfunction due to excessive time or operation cycles, and for identifying limited life equipment so monitoring and replacing is accomplished before hardware failure. Method applies to hardware where design service is established and where reasonable expected usage prediction is made.

  8. Maintaining plant safety margins

    SciTech Connect

    Bergeron, P.A.

    1989-01-01

    The Final Safety Analysis Report Forms the basis of demonstrating that the plant can operate safely and meet all applicable acceptance criteria. In order to assure that this continues through each operating cycle, the safety analysis is reexamined for each reload core. Operating limits are set for each reload core to assure that safety limits and applicable acceptance criteria are not exceeded for postulated events within the design basis. These operating limits form the basis for plant operation, providing barriers on various measurable parameters. The barriers are refereed to as limiting conditions for operation (LCO). The operating limits, being influenced by many factors, can change significantly from cycle to cycle. In order to be successful in demonstrating safe operation for each reload core (with adequate operating margin), it is necessary to continue to focus on ways to maintain/improve existing safety margins. Existing safety margins are a function of the plant type (boiling water reactor/pressurized water reactor (BWR/PWR)), nuclear system supply (NSSS) vendor, operating license date, core design features, plant design features, licensing history, and analytical methods used in the safety analysis. This paper summarizes the experience at Yankee Atomic Electric Company (YAEC) in its efforts to provide adequate operating margin for the plants that it supports.

  9. Aggregate Settling Velocities in San Francisco Estuary Margins

    NASA Astrophysics Data System (ADS)

    Allen, R. M.; Stacey, M. T.; Variano, E. A.

    2015-12-01

    One way that humans impact aquatic ecosystems is by adding nutrients and contaminants, which can propagate up the food web and cause blooms and die-offs, respectively. Often, these chemicals are attached to fine sediments, and thus where sediments go, so do these anthropogenic influences. Vertical motion of sediments is important for sinking and burial, and also for indirect effects on horizontal transport. The dynamics of sinking sediment (often in aggregates) are complex, thus we need field data to test and validate existing models. San Francisco Bay is well studied and is often used as a test case for new measurement and model techniques (Barnard et al. 2013). Settling velocities for aggregates vary between 4*10-5 to 1.6*10-2 m/s along the estuary backbone (Manning and Schoellhamer 2013). Model results from South San Francisco Bay shoals suggest two populations of settling particles, one fast (ws of 9 to 5.8*10-4 m/s) and one slow (ws of < 1*10-7 to 1.4*10-5 m/s) (Brand et al. 2015). While the open waters of San Francisco Bay and other estuaries are well studied and modeled, sediment and contaminants often originate from the margin regions, and the margins remain poorly characterized. We conducted a 24 hour field experiment in a channel slough of South San Francisco Bay, and measured settling velocity, turbulence and flow, and suspended sediment concentration. At this margin location, we found average settling velocities of 4-5*10-5 m/s, and saw settling velocities decrease with decreasing suspended sediment concentration. These results are consistent with, though at the low end of, those seen along the estuary center, and they suggest that the two population model that has been successful along the shoals may also apply in the margins.

  10. Population size of island loggerhead shrikes on Santa Rosa and Santa Cruz Islands

    USGS Publications Warehouse

    Stanley, Thomas R.; Teel, Susan; Hall, Linnea S.; Dye, Linda C.; Laughrin, Lyndal L.

    2012-01-01

    Island loggerhead shrikes (Lanius ludovicianus anthonyi) are an endemic, genetically distinct subspecies of loggerhead shrike on California's Santa Rosa, Santa Cruz, and Santa Catalina Islands (USA). This subspecies is listed as a Species of Special Concern by the California Department of Fish and Game and has been petitioned for federal listing under the Endangered Species Act. The combination of suspected low numbers and the possibility of federal listing, prompted us to undertake a study to rigorously estimate the number of remaining individuals on Santa Rosa and Santa Cruz Islands. During the 2009 and 2010 breeding seasons, we surveyed sample units on Santa Rosa and Santa Cruz Islands using a double-observer method with independent observers to estimate joint detection probabilities (p), where we selected units under a stratified random sampling design. We estimated shrike abundance to be 169 in 2009 (p = 0.476) and 240 in 2010 (p = 0.825) for Santa Rosa Island, and 35 in 2009 (p = 0.816) and 42 in 2010 (p = 0.710) for Santa Cruz Island. These numbers, especially for Santa Rosa Island, are higher than previously reported but nevertheless are still low. Rapid vegetation change on both islands due to recent removal of nonnative herbivores may threaten the habitat and status of this subspecies and, therefore, we suggest that intensive demographic and habitat use research be initiated immediately to obtain additional information vital for the management of this subspecies. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.

  11. Littoral transport rates in the Santa Barbara Littoral Cell: a process-based model analysis

    USGS Publications Warehouse

    Elias, E. P. L.; Barnard, Patrick L.; Brocatus, John

    2009-01-01

    Identification of the sediment transport patterns and pathways is essential for sustainable coastal zone management of the heavily modified coastline of Santa Barbara and Ventura County (California, USA). A process-based model application, based on Delft3D Online Morphology, is used to investigate the littoral transport potential along the Santa Barbara Littoral Cell (between Point Conception and Mugu Canyon). An advanced optimalization procedure is applied to enable annual sediment transport computations by reducing the ocean wave climate in 10 wave height - direction classes. Modeled littoral transport rates compare well with observed dredging volumes, and erosion or sedimentation hotspots coincide with the modeled divergence and convergence of the transport gradients. Sediment transport rates are strongly dependent on the alongshore variation in wave height due to wave sheltering, diffraction and focusing by the Northern Channel Islands, and the local orientation of the geologically-controlled coastline. Local transport gradients exceed the net eastward littoral transport, and are considered a primary driver for hot-spot erosion.

  12. Environmental evaluations for deepening of Richmond Harbor and Santa Fe Channels

    SciTech Connect

    Brown, B.; Kohn, N.P.; Crecelius, E.A.; Ward, J.A.; Bjornstad, B.N. )

    1990-09-01

    Richland, California is an important commercial port in San Francisco Bay. The San Francisco District of the US Army Corps of Engineers (USACE) plans to increase the depth of Richmond Harbor and Santa Fe Channels to -38 feet Mean Lower Low Water (MLLW) to accommodate deep-draft commercial vessels. The total volume of dredged material is expected to be approximately 1.4 million cubic yards. The options for disposal of the dredged material are aquatic disposal and upland disposal. The purpose of this study was to develop a database on chemical compounds in the dredged material to assist with determination of disposal methods and the need for additional testing. This purpose was accomplished through an extensive field sampling program followed by chemical analysis of samples. Field sampling involved collection of core samples from Sante Fe and Richmond Harbor Channels. Cores were shipped to Battelle/Marine Sciences Laboratory, where they were subsampled for chemical analysis and/or archived by freezing. All sediment and water samples were analyzed for priority pollutants, including metals, organotins, base/neutral semivolatile organic compounds, chlorinated pesticides and PCBs, herbicide acids, and acidic phenols. Sediment samples were also analyzed for oil and grease and total organic carbon. Organophosphorus pesticides and dioxins and furans were measured in selected sediment samples from Richland Harbor Channel and from both sediment and water samples from Santa Fe Channel. 21 refs., 10 figs., 60 tabs.

  13. Recent acoustic studies of western Canadian continental margin

    SciTech Connect

    Bornhold, B.D.; Brandon, M.T.; Clowes, R.M.; Currie, R.G.; Davis, E.E.; Hussong, D.M.; Hyndman, R.D.; Riddihough, R.P.; Rogers, G.C.; Yorath, C.J.

    1986-07-01

    A regional survey of the western Canadian continental margin from the central Queen Charlotte Island, 52/sup 0/40'N, to the Strait of Juan de Fuca, 47/sup 0/40'N, has been completed with the acoustic imaging system SeaMARC II. These data, combined with single-channel and multichannel seismic reflection data, reveal many new insights concerning the deep structure of the subduction margin off Vancouver Island. Clearly evident in the imagery are the deformation of sediments at the base of the slope, the surface expression of seismically active faults, the mass wasting of sediment frequently observed at the base of the slope, and the erosional canyons and sediment transport channels on the slope and adjacent abyssal plain. The variability in the surficial and deep structures along the length of the margin is great and corresponds well with the postulated variations in the local ocean/continent motion vectors: motion along the southern Queen Charlotte Islands margin is primarily transform (about 55 mm/year) with a small component of convergence (about 10 mm/year); motion south of the triple junction at the Wilson Knolls is convergent but at a very slow rate (about 10 mm/year); and motion along the central and southern Vancouver Island margin is nearly orthogonal to the coast and more rapid (about 40 mm/year).

  14. Extracting a redox signal from Scanning XRF results in Santa Barbara Basin to reconstruct annual shifts in bottom water oxygen concentration

    NASA Astrophysics Data System (ADS)

    Hendy, I. L.; Napier, T.

    2013-12-01

    Santa Barbara Basin (SBB) is well known for producing high quality paleoclimate reconstructions due to high lithogenic and biogenic sediment input and low bottom water oxygen concentrations which preserve annual scale laminations in basin sediments. An subannually resolved reconstruction of elemental composition of Santa Barbara Basin (SBB) sediments has been produced for the last 150 years based on scanning XRF elemental composition of bulk sediments. The first Principle Component (PC1) of the elemental data contains high loadings of Ti, K, Al, Si, Rb and Fe, and explains 40% of the variance in SPR0901-04BC. We associate PC1 with siliciclastic sediment delivered to SBB by river runoff. The second Principle Component (PC1) of the elemental data contains high loadings of Br/Cl and Sr and we associate with biogenic sediment input. Further variance is explained by S/Cl and Fe/Ti, which we associate with iron sulphide minerals. Here we compare the annually resolved Fe-sulphide record for the last 150 years with ICP-MS derived redox sensitive trace metal results (Mo, Re, Ag, Cd, U) to validate the use of this novel redox proxy in Santa Barbara Basin at an unprecedented resolution. We explore the utility of ultra-high resolution sediment redox chemistry in modern climate reconstruction as the magnitude of anthropogenic environmental impacts increase.

  15. Carbonate comparison of west Florida continental margin with margins of eastern United States

    SciTech Connect

    Doyle, L.J.

    1986-05-01

    Temperate carbonate margins may have as many similarities to clastic margins as to other carbonate systems. An example is the west Florida continental margin north of Florida Bay, a vast area of more than 150,000 km/sup 2/. The facies of this area differ from those of other Holocene carbonates, such as the Bahama Banks, the Great Barrier Reef, and the Caribbean and Pacific bioherms. The west Florida margin is analogous to the predominantly clastic southeastern US in both physiology and sedimentary processes. The shelf facies is a veneer of carbonate sand, primarily molluscan shell fragments, with low sedimentation rates. It is similar to the southeastern US sand veneer with the clastic component removed. Like the US system, the west Florida shelf has a ridge and swale topography replete with sedimentary structures, such as sand waves, with a series of drainage systems incised into its surface at lower stands of sea level. On the outer edge, it is commonly bounded by outcrops with considerable positive relief. The upper slope of the west Florida margin is a calcilutite, a Holocene chalk deposit accumulating at rates of tens of centimeters/1000 years, comparable to the clastic lutite depositional rates of the eastern US continental slope, and two orders of magnitude higher than deep-sea oozes of similar composition. These relatively high rates are probably caused by fines pumped from and across the coarser shelf-sand sheets in both systems.

  16. The Cadiz margin study off Spain: An introduction

    USGS Publications Warehouse

    Nelson, C.H.; Maldonado, A.

    1999-01-01

    The Cadiz continental margin of the northeastern Gulf of Cadiz off Spain was selected for a multidisciplinary project because of the interplay of complex tectonic history between the Iberian and African plates, sediment supply from multiple sources, and unique Mediterranean Gateway inflow and outflow currents. The nature of this complex margin, particularly during the last 5 million years, was investigated with emphasis on tectonic history, stratigraphic sequences, marine circulation, contourite depositional facies, geotechnical properties, geologic hazards, and human influences such as dispersal of river contaminants. This study provides an integrated view of the tectonic, sediment supply and oceanographic factors that control depositional processes and growth patterns of the Cadiz and similar modem and ancient continental margins.

  17. Biostratigraphy of the Santa Rosita Formation (Furongian-Tremadocian) in its type area, Eastern Cordillera, NW Argentina

    NASA Astrophysics Data System (ADS)

    Voldman, G. G.; Albanesi, G. L.; Ortega, G.; Monaldi, C. R.; Zeballo, F. J.; Giuliano, M. E.

    2012-04-01

    The Cambrian - Lower Ordovician stratigraphic units from the Eastern Cordillera were originally defined in the Santa Victoria Range, Salta Province, NW Argentina. At the southern margin of the Santa Victoria River, near the homonymous locality, the Santa Rosita Formation is conformably overlain by the Acoite Formation. These stratigraphic units are dated by means of conodont, graptolite and trilobite biostratigraphy in the type sections. The upper interval (ca. 700 m) of the Santa Rosita Formation consists of sandstones interbedded with purplish to grayish shales and occasional coquinas, which were sampled for microfossils. 15 carbonate samples (35 kg) were processed following standard laboratory techniques for conodont recovery. A number of species from the genera Acanthodus, Acodus, Decoriconus, Drepanodus, Drepanoistodus, Iapetognathus, Kallidontus, Paltodus, Utahconus, Teridontus and the protoconodont Phakelodus were recovered from 5 productive samples. The conodont elements exhibit a CAI 3 and correspond to the Paltodus deltifer deltifer Subzone of the P. deltifer Zone (middle Tremadocian, Tr2). Pelites of the Acoite Formation, at 300 m from its base, bear Araneograptus murrayi and Thysanopyge sp., whose ranges span the Tremadocian - Floian boundary. Conodonts and graptolites were also yielded by outcrops of the Santa Rosita Formation at the Nazareno area, 30 km to the south of the Santa Victoria type locality. The conodont associations were recorded from calcareous levels of the Alfarcito and Rupasca members, including Drepanodus arcuatus, Drepanoistodus chucaleznensis, Teridontus gallicus, Utahconus humahuacensis, Acanthodus sp. and Utahconus sp. They also integrate the eponymous subspecies from the Paltodus deltifer pristinus and P. d. deltifer subzones of the P. deltifer Zone (middle Tremadocian, Tr2). The Santa Rosita Formation correlates with a thick heterolithic succession at the Zenta Range, 120 km to the southwest of the Santa Victoria type area. This

  18. Some faulting patterns in the eastern Santa Monica Mountains

    SciTech Connect

    Aguilar, A.A. ); Denison, F.E.

    1993-04-01

    New 1:24,000 scale mapping of the eastern Santa Monica Mountains (SMM) indicates additional braiding, branching and sub parallel faults to the main trace of the 21 km-long northeast-trending Benedict Canyon fault (BCF), which displays over 2.5 km of left lateral strike slip separation. Some of the 1931 USGS Professional Paper 165-C geologic cross sections for the eastern portion of SMM have also been revised using the 1991 Dibble Geological Foundation Maps ([number sign]DF-30 and 31) along with additional data from individual study areas and some unpublished reports. The geometry of folding on both sides of the BCF is very similar and it indicates some mapped north-dipping faulting which are not related to the BCF occurred during folding of the Cretaceous to Middle Miocene sediments by either flexural-slip or by thrust faulting along one or more northwest-trending synclinoria prior to the upper Miocene. An unconformable contact separates the more folded Cretaceous to Middle Miocene rocks from the upper Miocene marine sediments. The entire eastern SMM has undergone later regional uplift along the east west anticlinorium which was later faulted by the BCF. The BCF zone is a significant ground water barrier in this mountainous urban region. To date several major surface and underground engineering projects are now planned to be located on or to be excavated through the Benedict Canyon fault.

  19. U-Pb geochronology of the Santa Cruz Formation (early Miocene) at the Río Bote and Río Santa Cruz (southernmost Patagonia, Argentina): Implications for the correlation of fossil vertebrate localities

    NASA Astrophysics Data System (ADS)

    Cuitiño, José I.; Fernicola, Juan Carlos; Kohn, Matthew J.; Trayler, Robin; Naipauer, Maximiliano; Bargo, M. Susana; Kay, Richard F.; Vizcaíno, Sergio F.

    2016-10-01

    The early Miocene Santa Cruz Formation (SCF) in southern Patagonia hosts the Santacrucian South American Land Mammal Age (SALMA), whose age is known mainly from exposures along the Atlantic coast. Zircon U-Pb ages were obtained from intercalated tuffs from four inland sections of the SCF: 17.36 ± 0.63 Ma for the westernmost Río Bote locality, and 17.04 ± 0.55 Ma-16.32 ± 0.62 Ma for central Río Santa Cruz localities. All ages agree with the bounding age of underlying marine units and with equivalent strata in coastal exposures. New ages and available sedimentation rates imply time spans for each section of ∼18.2 to 17.36 Ma for Río Bote and 17.45-15.63 Ma for central Río Santa Cruz (Burdigalian). These estimates support the view that deposition of the SCF began at western localities ∼1 Ma earlier than at eastern localities, and that the central Río Santa Cruz localities expose the youngest SCF in southern Santa Cruz Province. Associated vertebrate faunas are consistent with our geochronologic synthesis, showing older (Notohippidian) taxa in western localities and younger (Santacrucian) taxa in central localities. The Notohippidian fauna (19.0-18.0 Ma) of the western localities is synchronous with Pinturan faunas (19.0-18.0 Ma), but older than Santacrucian faunas of the Río Santa Cruz (17.2-15.6 Ma) and coastal localities (18.0-16.2 Ma). The Santacrucian faunas of the central Río Santa Cruz localities temporally overlap Colloncuran (15.7 Ma), Friasian (16.5 Ma), and eastern Santacrucian faunas.

  20. Actively stressed marginal networks.

    PubMed

    Sheinman, M; Broedersz, C P; MacKintosh, F C

    2012-12-07

    We study the effects of motor-generated stresses in disordered three-dimensional fiber networks using a combination of a mean-field theory, scaling analysis, and a computational model. We find that motor activity controls the elasticity in an anomalous fashion close to the point of marginal stability by coupling to critical network fluctuations. We also show that motor stresses can stabilize initially floppy networks, extending the range of critical behavior to a broad regime of network connectivities below the marginal point. Away from this regime, or at high stress, motors give rise to a linear increase in stiffness with stress. Finally, we demonstrate that our results are captured by a simple, constitutive scaling relation highlighting the important role of nonaffine strain fluctuations as a susceptibility to motor stress.

  1. Estimating the population size of island loggerhead shrikes on Santa Rosa and Santa Cruz Islands, USA

    USGS Publications Warehouse

    Stanley, Thomas R.; Teel, Susan; Hall, Linnea S.; Dye, Linda C.; Laughrin, Lyndal L.

    2012-01-01

    Island loggerhead shrikes (Lanius ludovicianus anthonyi) are an endemic, genetically distinct subspecies of loggerhead shrike on California’s Santa Rosa and Santa Cruz Islands. This subspecies is listed as a Species of Special Concern by the California Department of Fish and Game and has been petitioned for federal listing under the Endangered Species Act. Because of suspected low numbers and the possibility of federal listing, there was an urgent need to rigorously estimate the number of remaining individuals on the Islands. In 2009 and 2010, biologists from the U.S. Geological Survey and the National Park Service surveyed sample units on Santa Rosa and Santa Cruz Islands using a double-observer method with independent observers, where units were selected under a stratified random sampling design. Shrike abundance was estimated to be 169 in 2009 and 240 in 2010 for Santa Rosa Island, and 35 in 2009 and 42 in 2010 for Santa Cruz Island. These numbers, especially for Santa Rosa Island, are higher than previously reported but nevertheless are still low. Rapid vegetation change on both islands due to recent removal of non-native herbivores may threaten the habitat and status of this subspecies. In view of this circumstance and the still-low numbers of shrikes, additional intensive demographic and habitat-use studies are critical for obtaining information vital for the perpetuation of this subspecies.

  2. Core drilling provides information about Santa Fe Group aquifer system beneath Albuquerque's West Mesa

    USGS Publications Warehouse

    Allen, B.D.; Connell, S.D.; Hawley, J.W.; Stone, B.D.

    1998-01-01

    Core samples from the upper ???1500 ft of the Santa Fe Group in the Albuquerque West Mesa area provide a first-hand look at the sediments and at subsurface stratigraphic relationships in this important part of the basin-fill aquifer system. Two major hydrostratigraphic subunits consisting of a lower coarse-grained, sandy interval and an overlying fine-grained, interbedded silty sand and clay interval lie beneath the water table at the 98th St core hole. Borehole electrical conductivity measurements reproduce major textural changes observed in the recovered cores and support subsurface correlations of hydrostratigraphic units in the Santa Fe Group aquifer system based on geophysical logs. Comparison of electrical logs from the core hole and from nearby city wells reveals laterally consistent lithostratigraphic patterns over much of the metropolitan area west of the Rio Grande that may be used to delineate structural and related stratigraphic features that have a direct bearing on the availability of ground water.

  3. Contaminated Sediment

    EPA Pesticide Factsheets

    Contaminated sediments are a significant problem in the Great Lakes basin. Persistent high concentrations of contaminants in the bottom sediments of rivers and harbors pose risks to aquatic organisms, wildlife, and humans.

  4. 53. NEW BCB AND LIGHTNING ARRESTER ARRANGEMENT, SANTA ANA RIVER ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    53. NEW BCB AND LIGHTNING ARRESTER ARRANGEMENT, SANTA ANA RIVER NO. 2, JAN. 24, 1977. SCE drawing no. 455670-0. - Santa Ana River Hydroelectric System, SAR-2 Powerhouse, Redlands, San Bernardino County, CA

  5. 3. View of Santa Elena, looking from water level (Note: ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    3. View of Santa Elena, looking from water level (Note: The lighthouse of Del Morro is just visible in the background) - Murallas del Viejo San Juan, Baluarte de Santa Elena, San Juan, San Juan Municipio, PR

  6. 4. INTERIOR OF ABANDONED SANTA ANA CANAL TUNNEL, SHOWING CEMENT ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    4. INTERIOR OF ABANDONED SANTA ANA CANAL TUNNEL, SHOWING CEMENT TROUGH FLOOR AND UNFINISHED GRANITE ROOF. VIEW TO SOUTHWEST. - Santa Ana River Hydroelectric System, Abandoned Tunnel, Redlands, San Bernardino County, CA

  7. 53. SIPHON NO. 1, SANTA ANA RIVER NO. 2 PROJECT, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    53. SIPHON NO. 1, SANTA ANA RIVER NO. 2 PROJECT, EXHIBIT L, PROJECT 1933, MAY 1973. SCE drawing no. 5110869 (sheet no. 11; for filing with Federal Power Commission). - Santa Ana River Hydroelectric System, Redlands, San Bernardino County, CA

  8. 34. ELEVATION OF RELAY AND CONTROL SWITCHBOARD, SANTA ANA RIVER ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    34. ELEVATION OF RELAY AND CONTROL SWITCHBOARD, SANTA ANA RIVER P.H. #3, JUNE 23, 1943. SCE drawing no. 413187-1. - Santa Ana River Hydroelectric System, SAR-3 Powerhouse, San Bernardino National Forest, Redlands, San Bernardino County, CA

  9. Tectonostratigraphy and Paleotectonics of the Santa Monica Mountains and Vicinity, Southern California

    NASA Astrophysics Data System (ADS)

    Ingersoll, R. V.

    2001-12-01

    Southern California has experienced the following stages of development, which are recorded in corresponding tectono-stratigraphic sequences in the Santa Monica Mountains: Late Jurassic remnant ocean (Santa Monica Slate); Cretaceous continental-margin dissected arc (quartz diorite of Hollywood Hills); Cretaceous-Eocene forearc (Tuna Canyon/Chatsworth-Santa Susana Fms.); Oligocene-Early Miocene forearc and triple-junction transition (Sespe-Vaqueros Fms.); 18-12 Ma Transrotation (Topanga Fm.); 12-6 Ma Transtension (Modelo Fm.); and 6-0 Ma Transpression (Fernando Fm.). Transrotation of the Western Transverse Ranges (WTR) occurred as they were transferred to the Pacific plate during capture of the Monterey and Arguello mircoplates. Extension along low-angle detachment faults exhumed mid- and lower-crustal rocks (accretionary prism) in the continental borderland. The magnitude of extension decreased toward the northeastern pivot point; thus, the Middle Miocene Topanga basin deepened to the south and west as the WTR rotated. The Santa Ynez Canyon transfer zone (SYCTZ) separated the highly extended western Santa Monica Mountains (WSMM) from the slightly extended eastern Santa Monica Mountains (ESMM). The breakaway zone, along which the rotating Western Transverse Ranges separated from the northern Peninsular Ranges, formed along the south side of the ESMM and the north side of the WSMM, with the SYCTZ connecting the two segments of the breakaway. As a result, all of the Sespe-Vaqueros Fms. and much of the Santa Susana Fm. were eroded from the ESMM due to footwall uplift prior to deposition of the Topanga Fm., in contrast to the WSMM. North of the WSMM, the Cretaceous-Paleogene sequence was uplifted in the footwall of the breakaway to form the Chatsworth Hills, in contrast to north of the ESMM, where this forearc sequence remains buried below the San Fernando Valley. Another right-stepping transfer zone probably truncates the western end of the Chatsworth Hills. Some of

  10. Monitoring Domoic Acid production by Solid Phase Adsorption Toxin Tracking off the Santa Cruz Municipal Warf, Santa Cruz, California

    NASA Astrophysics Data System (ADS)

    Nolan, M.; Ziccarelli, L.; Kudela, R. M.

    2013-12-01

    Certain species of the diatom genus Pseudo-nitzschia are producers of the neurotoxin, domoic acid (DA). DA is known to cause amnesic shellfish poisoning also known as domoic acid poisoning, which can lead to permanent brain damage in humans and marine mammals. DA accumulates at higher trophic levels, generally due to consumption of toxic cells or through trophic transfer, and can potentially cause death of both humans and marine wildlife. The Santa Cruz Municipal Warf experiences periodic rises in DA concentrations, which can reach toxic levels in shellfish, fish, and other marine organisms. While these increases in toxicity often occur during Pseudo-nitzschia blooms, several periods of elevated DA have occurred when diatom abundance is restricted and/or dominated by non-toxic species, and there is increasing evidence that DA dissolved in seawater may be prevalent. One theory suggests that senescent or dead Pseudo-nitzschia cells sink to the benthos while retaining their toxin and are buried in sediment following the death of a bloom. Therefore, DA may accumulate in the benthos, where it is eventually released during storms or wave and tide conditions that disturb the sediment. We sampled DA in situ using Solid Phase Adsorption Toxin Tracking (SPATT) bags SPATT uses a synthetic resin to capture dissolved DA, allowing for the determination of integrated DA concentrations at known time intervals. The alternative method is mussel biotoxin monitoring, but it is less accurate due to uncertainties in the time of DA accumulation within the mussel, and the lack of uptake of dissolved DA by the mussel. We deployed and collected SPATT off the Santa Cruz Municipal Wharf at multiple depths beginning in February 2013. We expect to see increasing DA following the death of a harmful algal bloom. Under pre-bloom conditions, little to no DA has been detected in mussels or surface SPATT, but DA from SPATT is frequently observed at depth, suggesting that the sediment is exposed to

  11. Aquatic Sediments.

    ERIC Educational Resources Information Center

    Sanville, W. D.; And Others

    1978-01-01

    Presents a literature review of aquatic sediments and its effect upon water quality, covering publications of 1976-77. This review includes: (1) sediment water interchange; (2) chemical and physical characterization; and (3) heavy water in sediments. A list of 129 references is also presented. (HM)

  12. Hydrogeologic framework of the Santa Clara Valley, California

    USGS Publications Warehouse

    Hanson, Randall T.

    2015-01-01

    The hydrologic framework of the Santa Clara Valley in northern California was redefined on the basis of new data and a new hydrologic model. The regional groundwater flow systems can be subdivided into upper-aquifer and lower-aquifer systems that form a convergent flow system within a basin bounded by mountains and hills on three sides and discharge to pumping wells and the southern San Francisco Bay. Faults also control the flow of groundwater within the Santa Clara Valley and subdivide the aquifer system into three subregions.After decades of development and groundwater depletion that resulted in substantial land subsidence, Santa Clara Valley Water District (SCVWD) and the local water purveyors have refilled the basin through conservation and importation of water for direct use and artificial recharge. The natural flow system has been altered by extensive development with flow paths toward major well fields. Climate has not only affected the cycles of sedimentation during the glacial periods over the past million years, but interannual to interdecadal climate cycles also have affected the supply and demand components of the natural and anthropogenic inflows and outflows of water in the valley. Streamflow has been affected by development of the aquifer system and regulated flow from reservoirs, as well as conjunctive use of groundwater and surface water. Interaquifer flow through water-supply wells screened across multiple aquifers is an important component to the flow of groundwater and recapture of artificial recharge in the Santa Clara Valley. Wellbore flow and depth-dependent chemical and isotopic data indicate that flow into wells from multiple aquifers, as well as capture of artificial recharge by pumping of water-supply wells, predominantly is occurring in the upper 500 ft (152 m) of the aquifer system. Artificial recharge represents about one-half of the inflow of water into the valley for the period 1970–1999. Most subsidence is occurring below 250 ft

  13. Dispersal of river sediment in the Southern California Bight

    USGS Publications Warehouse

    Warrick, J.A.; Farnsworth, K.L.

    2009-01-01

    The rivers of Southern California deliver episodic pulses of water, sediment, nutrients, and pollutants to the region's coastal waters. Although river-sediment dispersal is observed in positively buoyant (hypopycnal) turbid plumes extending tens of kilometers from river mouths, very little of the river sediment is found in these plumes. Rather, river sediment settles quickly from hypopycnal plumes to the seabed, where transport is controlled by bottom-boundary layer processes, presumably including fluid-mud (hyperpycnal) gravity currents. Here we investigate the geographical patterns of river-sediment dispersal processes by examining suspended-sediment concentrations and loads and the continental shelf morphology offshore river mouths. Throughout Southern California, river sediment is discharged at concentrations adequately high to induce enhanced sediment settling, including negative buoyancy. The rivers draining the Western Transverse Range produce suspended-sediment concentrations that are orders of magnitude greater than those in the urbanized region and Peninsular Range to the south, largely due to differences in sediment yield. The majority of sediment discharge from the Santa Clara River and Calleguas Creek occurs above the theoretical negative buoyancy concentration (>40 g/l). These rivers also produce event sediment loading as great as the Eel River, where fluid-mud gravity currents are observed. The continental shelf of Southern California has variable morphology, which influences the ability to transport via gravity currents. Over half of the rivers examined are adjacent to shelf slopes greater than 0.01, which are adequately steep to sustain auto-suspending gravity currents across the shelf, and have little (<10 m) Holocene sediment accumulation. Shelf settings of the Ventura, Santa Clara, and Tijuana Rivers are very broad and low sloped (less than 0.004), which suggests that fluid-mud gravity currents could transport across these shelves, albeit slowly

  14. 2. 'SANTA ANA RIVER AT CHINO CREEK, RIVERSIDE COUNTY.' This ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    2. 'SANTA ANA RIVER AT CHINO CREEK, RIVERSIDE COUNTY.' This is an oblique aerial view to the north, looking over the flooded fields between Chino Creek and the Santa Ana River, just upstream of the Prado Dam site. File number written on negative: R & H 80 024. - Prado Dam, Santa Ana River near junction of State Highways 71 & 91, Corona, Riverside County, CA

  15. 27 CFR 9.54 - Santa Ynez Valley.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... (photoinspected 1974); (8) “Santa Rosa Hills, Cal.”, 7.5 minute series, edition of 1959; (9) “Santa Ynez, Cal.”, 7... straight line for approximately 3.2 miles to the point where Santa Rosa Road intersects Salsipuedes...

  16. 51. INTAKE AND POWER HOUSE AREAS, SANTA ANA NO. 1; ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    51. INTAKE AND POWER HOUSE AREAS, SANTA ANA NO. 1; DETAIL MAP OF SANTA ANA NO. 1 AND NO. 2 HYDROELECTRIC PROJECT, EXHIBIT K, APR. 30, 1945. SCE drawing no. 523690 (sheet no. 5; for filing with the Federal Power Commission). - Santa Ana River Hydroelectric System, Redlands, San Bernardino County, CA

  17. 33 CFR 80.1102 - Santa Catalina Island, CA.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 33 Navigation and Navigable Waters 1 2010-07-01 2010-07-01 false Santa Catalina Island, CA. 80... INTERNATIONAL NAVIGATION RULES COLREGS DEMARCATION LINES Pacific Coast § 80.1102 Santa Catalina Island, CA. The 72 COLREGS shall apply to the harbors on Santa Catalina Island....

  18. 33 CFR 80.1102 - Santa Catalina Island, CA.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 33 Navigation and Navigable Waters 1 2011-07-01 2011-07-01 false Santa Catalina Island, CA. 80... INTERNATIONAL NAVIGATION RULES COLREGS DEMARCATION LINES Pacific Coast § 80.1102 Santa Catalina Island, CA. The 72 COLREGS shall apply to the harbors on Santa Catalina Island....

  19. 33 CFR 80.1102 - Santa Catalina Island, CA.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 33 Navigation and Navigable Waters 1 2012-07-01 2012-07-01 false Santa Catalina Island, CA. 80... INTERNATIONAL NAVIGATION RULES COLREGS DEMARCATION LINES Pacific Coast § 80.1102 Santa Catalina Island, CA. The 72 COLREGS shall apply to the harbors on Santa Catalina Island....

  20. 33 CFR 80.1102 - Santa Catalina Island, CA.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 33 Navigation and Navigable Waters 1 2013-07-01 2013-07-01 false Santa Catalina Island, CA. 80... INTERNATIONAL NAVIGATION RULES COLREGS DEMARCATION LINES Pacific Coast § 80.1102 Santa Catalina Island, CA. The 72 COLREGS shall apply to the harbors on Santa Catalina Island....

  1. 33 CFR 80.1102 - Santa Catalina Island, CA.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 33 Navigation and Navigable Waters 1 2014-07-01 2014-07-01 false Santa Catalina Island, CA. 80... INTERNATIONAL NAVIGATION RULES COLREGS DEMARCATION LINES Pacific Coast § 80.1102 Santa Catalina Island, CA. The 72 COLREGS shall apply to the harbors on Santa Catalina Island....

  2. 33 CFR 110.115 - Santa Barbara Harbor, Calif.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 33 Navigation and Navigable Waters 1 2010-07-01 2010-07-01 false Santa Barbara Harbor, Calif. 110... ANCHORAGES ANCHORAGE REGULATIONS Special Anchorage Areas § 110.115 Santa Barbara Harbor, Calif. North of the Santa Barbara breakwater; seaward of the line of mean high water; and southwest of a line bearing...

  3. 75 FR 53371 - Environmental Impact Statement; Santa Rosa County, FL

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-08-31

    ... Federal Highway Administration Environmental Impact Statement; Santa Rosa County, FL AGENCY: Federal... project in Santa Rosa County, Florida. FOR FURTHER INFORMATION CONTACT: Ms. Cathy Kendall, AICP... Department of Transportation will prepare an EIS for a proposal to improve SR 87 in Santa Rosa...

  4. 27 CFR 9.28 - Santa Maria Valley.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2010-04-01 2010-04-01 false Santa Maria Valley. 9.28... OF THE TREASURY LIQUORS AMERICAN VITICULTURAL AREAS Approved American Viticultural Areas § 9.28 Santa Maria Valley. (a) Name. The name of the viticultural area described in this section is “Santa...

  5. 77 FR 39726 - Land Acquisitions: Pueblo of Santa Clara

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-07-05

    ... of Santa Clara AGENCY: Bureau of Indian Affairs, Interior. ACTION: Notice of final agency... determination to acquire approximately 1,219.24 acres of land into trust for the Pueblo of Santa Clara on... Interior, Bureau of Land Management, New Mexico State Office, in Santa Fe, New Mexico. Together With T....

  6. 27 CFR 9.54 - Santa Ynez Valley.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2010-04-01 2010-04-01 false Santa Ynez Valley. 9.54... OF THE TREASURY LIQUORS AMERICAN VITICULTURAL AREAS Approved American Viticultural Areas § 9.54 Santa Ynez Valley. (a) Name. The name of the viticultural area described in this section is “Santa...

  7. 27 CFR 9.217 - Happy Canyon of Santa Barbara.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2010-04-01 2010-04-01 false Happy Canyon of Santa... Areas § 9.217 Happy Canyon of Santa Barbara. (a) Name. The name of the viticultural area described in this section is “Happy Canyon of Santa Barbara”. For purposes of part 4 of this chapter, “Happy...

  8. 78 FR 66982 - Santa Clara Pueblo Disaster #NM-00039

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-11-07

    ... ADMINISTRATION Santa Clara Pueblo Disaster NM-00039 AGENCY: U.S. Small Business Administration. ACTION: Notice... for the Santa Clara Pueblo (FEMA- 4151-DR), dated 10/29/2013. Incident: Severe Storms and Flooding... disaster: Primary Areas: Santa Clara Pueblo. The Interest Rates are: Percent For Physical Damage:...

  9. 52. POWER HOUSE AREA, SANTA ANA NO. 2; DETAIL MAP ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    52. POWER HOUSE AREA, SANTA ANA NO. 2; DETAIL MAP OF SANTA ANA NO. 1 AND NO. 2 HYDROELECTRIC PROJECT, EXHIBIT K, APR. 30, 1945. SCE drawing no. 523691 (sheet no. 6; for filing with the Federal Power Commission). - Santa Ana River Hydroelectric System, Redlands, San Bernardino County, CA

  10. Instability and Tsunamigenic Potential at Convergent Margins

    NASA Astrophysics Data System (ADS)

    von Huene, R.; Ranero, C. R.; Watts, P.

    2001-12-01

    Along many convergent margins multibeam echosounding navigated with GPS has revealed large slope failures that were probably tsunamigenic. Bathymetric data combined with seismic reflection imaging indicate multiple causes. The 55-km wide Nicoya Slump resulted from the steepening slope above an underthrusting seamount on the subducting oceanic plate. This slump may have generated a 27-m high wave. Several 5-7 km wide mid-slope slides off central Nicaragua probably resulted from steepening of the continental slope by tectonic erosion. They may have generated waves 6-7 m high. A 30 km wide mid-slope slump off northern Peru may have generated a 5 m high wave. Its cause will not be understood without better seismic reflection imaging but considerable fluid venting was observed across its headwall. In the Gulf of Alaska a large slide appears to have resulted from rapid sedimentation. Tsunamigenic slope failure along convergent margins is only beginning to be resolved and the causes vary. Subducted ocean floor relief, tectonically steepened slopes, and sites of rapid sedimentation can help target potential failure and possible future tsunami hazards.

  11. Marginality of Transfer Commuter Students.

    ERIC Educational Resources Information Center

    Kodama, Corinne Maekawa

    2002-01-01

    Examines marginality issues facing transfer commuter students attending a mid-Atlantic university and what student characteristics relate to their sense of marginality. Results showed that transfer students have few sources of on-campus support, which may lead to their feelings of marginality. Results were particularly true for woman and Asian…

  12. Amphetamine margin in sports

    SciTech Connect

    Laties, V.G.; Weiss, B.

    1981-10-01

    The amphetamines can enhance athletic performance. That much seem clear from the literature, some of which is reviewed here. Increases in endurance have been demonstrated in both humans and rats. Smith and Beecher, 20 years ago, showed improvement of running, swimming, and weight throwing in highly trained athletes. Laboratory analogs of such performances have also been used and similar enhancement demonstrated. The amount of change induced by the amphetamines is usually small, of the order of a few percent. Nevertheless, since a fraction of a percent improvement can make the difference between fame and oblivion, the margin conferred by these drugs can be quite important.

  13. East Africa continental margins

    SciTech Connect

    Bosellini, A.

    1986-01-01

    New well data from Somalia, together with the history of sea-floor spreading in the Indian Ocean derived from magnetic anomalies, show that the East African margins from latitude 15/sup 0/S into the Gulf of Aden comprise four distinct segments that formed successively by the southward drift of Madagascar from Somalia during the Middle to Late Jurassic and Early Cretaceous, by the northeastward drift of India along the Owen Transform during the Late Cretaceous and Paleocene, and by the opening of the Gulf of Aden during the Neogene.

  14. Pellucid marginal corneal degeneration.

    PubMed

    Krachmer, J H

    1978-07-01

    Pellucid marginal degeneration of the cornea is a bilateral, clear, inferior, peripheral corneal-thinning disorder. Protrusion of the cornea occurs above a band of thinning, which is located 1 to 2 mm from the limbus and measures 1 to 2 mm in width. American ophthalmologists are generally not familiar with the condition because most of the literature concerning pellucid degeneration is European. Four cases are described. This condition is differentiated from other noninflammatory cornel-thinning disorders such as keratoconus, keratoglobus, keratotorus, and posterior keratoconus. It is also differentiated from peripheral corneal disorders associated with inflammation such as Terrien's peripheral corneal degeneration, Mooren's ulcers, and ulcers from connective tissue disease.

  15. New sensitive marginal oscillator

    NASA Astrophysics Data System (ADS)

    Rahf, L.

    1981-09-01

    A new type of a sensitive marginal oscillator has been developed for the determination of high magnetic inductions by means of nuclear magnetic resonance. Obtaining a high sensitivity with this measuring principle demands a soft behavior of the oscillator which is a particular feature of the circuit presented. It is shown that this behavior is due to the fact that a very weak positive feedback is established by the inner capacitances of the single field effect transistor used in the circuit. Optimal values for the operation parameters are calculated.

  16. Ecotourism: The Santa Elena Rainforest Project.

    ERIC Educational Resources Information Center

    Wearing, Stephen

    1993-01-01

    Describes an ecotourism project in which the community of Santa Elena, Costa Rica, are developing a rainforest reserve on government land leased permanently to the local high school. Discusses the impact of the project on the community's economy and environment. (Contains 30 references.) (MDH)

  17. USEPA Santa Cruz River Public Survey Research

    EPA Science Inventory

    The USEPA Office of Research and Development, Western Ecology Division is investigating how urban households value different possibilities for the Santa Cruz River in southern Arizona. A random sample of households in the Phoenix and Tucson areas are being asked to provide their ...

  18. Santa Claus and the Conservation of Energy

    ERIC Educational Resources Information Center

    Hassani, Sadri

    2005-01-01

    This article examines an amusing application of the concept of kinetic energy. Using some rudimentary physical notions, we have analysed the energetics of the motion of Santa Claus. The results, which are quite surprising, can be of interest to high school and early college physics educators when they teach kinetic energy, and energy conservation…

  19. Santa Fe Junior College, Gainesville, Florida.

    ERIC Educational Resources Information Center

    Caudill, Rowlett and Scott, Architects, Houston, TX.

    The design of Santa Fe Junior College is examined, beginning with the development of an educational philosophy. Subsequent design decisions are based largely upon this philosophy which emphasizes the development of the individual student and the fulfillment of his needs. Further, the need for flexibility is recognized and is an important aspect of…

  20. SOUTH SANTA CLARA COUNTY MIGRANT TREATMENT CLINIC.

    ERIC Educational Resources Information Center

    SKILLICORN, STANLEY A.

    IN THE SUMMER OF 1965, A MIGRANT HEALTH CLINIC WAS STARTED IN THE SOUTHERN PART OF SANTA CLARA COUNTY, CALIFORNIA. THE CLINIC DIFFERS FROM THE PUBLIC HEALTH DEPARTMENT'S CLINICS BY OFFERING TREATMENT AND MEDICATION, INSTEAD OF ONLY PREVENTIVE SERVICES. THE ENTIRE STAFF, FROM DOCTORS TO BABY-SITTERS, VOLUNTEERS ITS TIME, AND THE CLINIC IS NOW OPEN…

  1. Santa Rosa, California: Solar in Action (Brochure)

    SciTech Connect

    Not Available

    2011-10-01

    This brochure provides an overview of the challenges and successes of Santa Rosa, CA, a 2008 Solar America City awardee, on the path toward becoming a solar-powered community. Accomplishments, case studies, key lessons learned, and local resource information are given.

  2. Ocean Margins Programs, Phase I research summaries

    SciTech Connect

    Verity, P.

    1994-08-01

    During FY 1992, the DOE restructured its regional coastal-ocean programs into a new Ocean Margins Program (OMP), to: Quantify the ecological and biogeochemical processes and mechanisms that affect the cycling, flux, and storage of carbon and other biogenic elements at the land/ocean interface; Define ocean-margin sources and sinks in global biogeochemical cycles, and; Determine whether continental shelves are quantitatively significant in removing carbon dioxide from the atmosphere and isolating it via burial in sediments or export to the interior ocean. Currently, the DOE Ocean Margins Program supports more than 70 principal and co-principal investigators, spanning more than 30 academic institutions. Research funded by the OMP amounted to about $6.9M in FY 1994. This document is a collection of abstracts summarizing the component projects of Phase I of the OMP. This phase included both research and technology development, and comprised projects of both two and three years duration. The attached abstracts describe the goals, methods, measurement scales, strengths and limitations, and status of each project, and level of support. Keywords are provided to index the various projects. The names, addresses, affiliations, and major areas of expertise of the investigators are provided in appendices.

  3. Sedimentary loading, lithospheric flexure and subduction initiation at passive margins

    SciTech Connect

    Erickson, S.G. . Dept. of Earth Sciences)

    1992-01-01

    Recent theoretical models have demonstrated the difficulty of subduction initiation at passive margins, whether subduction is assumed to initiate by overcoming the shear resistance on a thrust fault through the lithosphere or by failure of the entire lithosphere in bending due to sedimentary loading. A mechanism for subduction initiation at passive margins that overcomes these difficulties incorporates the increased subsidence of a marginal basin during decoupling of a previously locked margin. A passive margin may decouple by reactivation of rift-related faults in a local extensional or strike-slip setting. Flexure of marginal basins by sedimentary loading is modeled here by the bending of infinite and semi-infinite elastic plates under a triangular load. The geometry of a mature marginal basin fits the deflection produced by loading of an infinite plate in which the flexural rigidity of continental lithosphere is larger than that of oceanic lithosphere. Decoupling of such a locked passive margin by fault reactivation may cause the lithospheric bending behavior of the margin to change from that of an infinite plate to that of a semi-infinite plate, with a resultant increase in deflection of the marginal basin. The increase in deflection depends on the flexural rigidities of continental and oceanic lithosphere. For flexural rigidities of 10[sup 30]-10[sup 31] dyn-cm (elastic lithosphere thicknesses 24--51 km), the difference in deflections between infinite and semi-infinite plates is 15--17 km, so that decoupling sinks the top of the oceanic lithosphere to depths of ca 35 km. Additional sedimentation within the basin and phase changes within the oceanic crust may further increase this deflection. Subduction may initiate if the top of the oceanic lithosphere sinks to the base of the adjacent elastic lithosphere.

  4. Marginal erg facies: A trial approach toward a descriptive classification

    SciTech Connect

    Caputo, M.V. ); Langford, R.P. )

    1991-03-01

    During the late 1970s and early 1980s, sedimentologists began recognizing the margins of eolian sand seas as separate, components which differed from interior sand seas in geometry, extent, and facies. Stratigraphers have now observed these differences in eolian rocks. Erg margins may be grouped in five ways: (1) by associations with extradunal environments-coastal plain, lacustrine, periglacial, marine (tidal flat, coastal sabkha, beach, and lagoon), and arid alluvial (alluvial fan, fluvial, playa, inland sabkha); (2) by allocyclic controls-eustasy, plate tectonism, and climate; (3) by autocyclic controls-local tectonism, topography, vegetation, hydrology, structure, sediment source and supply, and wind regime; (4) by geographic position-upwind, downwind, and along-wind margins; and (5) by sedimentary facies-texture and architecture. In contrast with erg interiors, erg margins are characterized by smaller, less complex dune-forms related to thinner sand accumulation; elementary dune architecture; more vegetation and bioturbation; high occurrence of sand sheet, zibar, and serir facies; expansive, low-relief interdunes with widely distributed dunes; and a greater proportion of interbedded extradunal deposits. Some of the published studies on ancient eolian systems have identified erg margin facies that have been influences by marine and arid alluvial processes. Few reports have described lacustrine-eolian and periglacial-eolian interactions. This study is an attempt to organize known features of modern and ancient erg margins into a scheme based on erg margin controls.

  5. Remagne California margin

    USGS Publications Warehouse

    Hagstrum, J.T.; Sedlock, R.L.

    1998-01-01

    Paleomagnetic data for two sections of Cretaceous forearc strata with different structural attitudes on Santa Margarita and Magdalena Islands in Baja California Sur, Mexico, indicate that these rocks have been remagnetized, probably during the late Cenozoic. The in situ paleomagnetic directions, however, are similar to data from other Cretaceous rocks on peninsular California with unexpectedly shallow inclinations and easterly declinations. These data have been interpreted as indicating either northward tectonic transport (10??15?? of latitude) and clockwise rotation (>20??) or compaction shallowing of magnetic inclinations in sedimentary rocks combined with southwestward tilting of plutonic rocks. The available paleomagnetic data for Cretaceous forearc strata in southern and Baja California can be divided into three groups: (1) sections with normal-polarity magnetizations that fail fold tests and are remagnetized, (2) sections with normal-polarity magnetizations with no or inconclusive fold tests that may or may not be remagnetized, and (3) sections with both normaland reversed-polarity intervals where pervasive remagnetization has not occurred. Other rocks of the Mesozoic Great Valley Group, Coast Range ophiolite, and Franciscan Complex in California also have secondary magnetizations with directions similar to younger geomagnetic field directions. Although these widespread remagnetizations could have variable local causes, we propose regional burial and uplift, related to changes in subduction parameters, as a possible explanation. Two episodes of remagnetization are apparent: one in the Late Cretaceous and a second in the late Cenozoic. On the other hand, the unremagnetized and apparently reliable data from sedimentary and plutonic rocks on the Baja Peninsula consistently indicate northward translation (14???? 3??) and clockwise rotation (29???? 8??) with respect to North America since the Late Cretaceous. Copyright 1998 by the American Geophysical Union.

  6. Iberian Atlantic Margins Group investigates deep structure of ocean margins

    NASA Astrophysics Data System (ADS)

    The Iberian Atlantic Margins Group; Banda, Enric; Torne, Montserrat

    With recent seismic reflection data in hand, investigators for the Iberian Atlantic Margins project are preparing images of the deep continental and oceanic margins of Iberia. In 1993, the IAM group collected near vertical incidence seismic reflection data over a total distance of 3500 km along the North and Western Iberian Margins, Gorringe Bank Region and Gulf of Cadiz (Figure 1). When combined with data on the conjugate margin off Canada, details of the Iberian margin's deep structure should aid in distinguishing rift models and improve understanding of the processes governing the formation of margins.The North Iberian passive continental margin was formed during a Permian to Triassic phase of extension and matured during the early Cretaceous by rotation of the Iberian Peninsula with respect to Eurasia. From the late Cretaceous to the early Oligocene period, Iberia rotated in a counterclockwise direction around an axis located west of Lisbon. The plate boundary between Iberia and Eurasia, which lies along the Pyrenees, follows the north Spanish marginal trough, trends obliquely in the direction of the fossil Bay of Biscay triple junction, and continues along the Azores-Biscay Rise [Sibuet et al., 1994]. Following the NE-SW convergence of Iberia and Eurasia, the reactivation of the North Iberian continental margin resulted in the formation of a marginal trough and accretionary prism [Boillot et al., 1971].

  7. Preliminary geologic map of the Santa Barbara coastal plain area, Santa Barbara County, California

    USGS Publications Warehouse

    Minor, Scott A.; Kellogg, Karl S.; Stanley, Richard G.; Stone, Paul; Powell, Charles L.; Gurrola, Larry D.; Selting, Amy J.; Brandt, Theodore R.

    2002-01-01

    This report presents a new geologic digital map of the Santa Barbara coastal plain area at a compilation scale of 1:24,000 (one inch on the map = 2,000 feet on the ground) and with a horizontal positional accuracy of at least 20 m. This preliminary map depicts the distribution of bedrock units and surficial deposits and associated deformation underlying and adjacent to the coastal plain within the contiguous Santa Barbara and Goleta 7.5' quadrangles. A planned second version will extend the mapping westward into the adjoining Dos Pueblos Canyon quadrangle and eastward into the Carpinteria quadrangle. The mapping presented here results from the collaborative efforts of geologists with the U.S. Geological Survey Southern California Areal Mapping Project (SCAMP) (Minor, Kellogg, Stanley, Stone, and Powell) and the tectonic geomorphology research group at the University of California at Santa Barbara (Gurrola and Selting). C.L. Powell, II, performed all new fossil identifications and interpretations reported herein. T.R. Brandt designed and edited the GIS database,performed GIS database integration and created the digital cartography for the map layout. The Santa Barbara coastal plain is located in the western Transverse Ranges physiographic province along a west-trending segment of the southern California coastline about 100 km (62 mi) northwest of Los Angeles. The coastal plain region, which extends from the Santa Ynez Mountains on the north to the Santa Barbara Channel on the south, is underlain by numerous active and potentially active folds and partly buried thrust faults of the Santa Barbara fold and fault belt. Strong earthquakes that occurred in the region in 1925 (6.8 magnitude) and 1978 (5.1 magnitude) are evidence that such structures pose a significant earthquake hazard to the approximately 200,000 people living within the major coastal population centers of Santa Barbara and Goleta. Also, young landslide deposits along the steep lower flank of the Santa

  8. Silica burial enhanced by iron limitation in oceanic upwelling margins

    NASA Astrophysics Data System (ADS)

    Pichevin, L. E.; Ganeshram, R. S.; Geibert, W.; Thunell, R.; Hinton, R.

    2014-07-01

    In large swaths of the ocean, primary production by diatoms may be limited by the availability of silica, which in turn limits the biological uptake of carbon dioxide. The burial of biogenic silica in the form of opal is the main sink of marine silicon. Opal burial occurs in equal parts in iron-limited open-ocean provinces and upwelling margins, especially the eastern Pacific upwelling zone. However, it is unclear why opal burial is so efficient in this margin. Here we measure fluxes of biogenic material, concentrations of diatom-bound iron and silicon isotope ratios using sediment traps and a sediment core from the Gulf of California upwelling margin. In the sediment trap material, we find that periods of intense upwelling are associated with transient iron limitation that results in a high export of silica relative to organic carbon. A similar correlation between enhanced silica burial and iron limitation is evident in the sediment core, which spans the past 26,000 years. A global compilation also indicates that hotspots of silicon burial in the ocean are all characterized by high silica to organic carbon export ratios, a diagnostic trait for diatoms growing under iron stress. We therefore propose that prevailing conditions of silica limitation in the ocean are largely caused by iron deficiency imposing an indirect constraint on oceanic carbon uptake.

  9. Synthetic passive margin stratigraphy

    SciTech Connect

    Turcotte, D.L.; Kenyon, P.M.

    1984-06-01

    Synthetic stratigraphic cross sections are derived mathematically for a variety of simple conditions. The variables considered in the mathematical model include variations in sea level, rate of tectonic subsidence, rate of sedimentation, and rate of erosion. Derived stratigraphic relationships include unconformities, correlative conformities and disconformities, coastal onlap, coastal toplap, erosional truncation, pinch-out, and sigmoidal progradational clinoforms. An important conclusion is that the rate of erosion is a dominant variable in determining the type of stratigraphic section observed. The proposed approach may provide the basis for either a forward or inverse modeling of seismic stratigraphic sections.

  10. Metabolic activity of subsurface life in deep-sea sediments.

    PubMed

    D'Hondt, Steven; Rutherford, Scott; Spivack, Arthur J

    2002-03-15

    Global maps of sulfate and methane in marine sediments reveal two provinces of subsurface metabolic activity: a sulfate-rich open-ocean province, and an ocean-margin province where sulfate is limited to shallow sediments. Methane is produced in both regions but is abundant only in sulfate-depleted sediments. Metabolic activity is greatest in narrow zones of sulfate-reducing methane oxidation along ocean margins. The metabolic rates of subseafloor life are orders of magnitude lower than those of life on Earth's surface. Most microorganisms in subseafloor sediments are either inactive or adapted for extraordinarily low metabolic activity.

  11. Marginally Stable Nuclear Burning

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod E.; Altamirano, D.

    2012-01-01

    Thermonuclear X-ray bursts result from unstable nuclear burning of the material accreted on neutron stars in some l