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At least 487 records · Page 27Linked to original sources
USGS2007

Sedimentary properties of shallow marine cores collected in June and September 2006, Hanalei Bay, Kaua'i, Hawai'i

Sedimentary facies, short-lived isotopes 7 Be, 137 Cs, and 210 Pb, and magnetic properties of sediment cores in Hanalei Bay, Kaua‘i, Hawai‘i, were used to assess sediment sources and patterns of deposition associated with seasonal flooding of the Hanalei River. Sediment cores were collected from the seafloor in June and September of 2006 to supplement similar data collected during the summer of 2005. The youngest and thickest terrigenous sediment was observed on the east side of the bay: near the Hanalei River mouth and in a bathymetric depression, known locally as the Black Hole, that acts as a temporary sediment sink. Deposits from floods that occurred between February and April 2006 left flood deposits in the eastern bay that, by June of 2006, were on the order of 10 cm thick. A flood occurred on August 7, 2006, that was smaller than floods that occurred the previous winter but was a substantial discharge event for the summer season. Deposits from the winter 2006 floods continued to dominate the sedimentary record in the eastern bay through early fall, even after the addition of newer sediment during the August 7 flood; this is consistent with the much higher sediment input of the winter floods compared with the August 7 flood. Broad variations in magnetic grain size and relative magnetite-hematite abundance in several sediment cores indicate many sources of upland terrigenous sediment. As a group, recent flood deposits show much less variation in these properties compared with older deposits, implying either that the 2006 winter–spring flood sediment originated from one or more distinct upland settings, or that substantial mixing of sediment from multiple sources occurred during transport. Sediment is most readily remobilized and advected out of the bay during winter, when oceanic conditions are energetic. In summer, wave and current measurements made concurrently with this study showed weak currents and little wave energy, indicating that sediment delivered during summer floods most likely remains in the bay until winter storms can remove it. Increased turbidity and sedimentation on corals resulting from floods of the Hanalei River could affect the sustainability of coral reefs and their many associated species. This possibility is of particular concern during summer months when wave energy is low and sediment is not readily remobilized and transported out of the bay. The timing (seasonality) and magnitude of sediment input to the coastal ocean relative to seasonal variations in wave and current energy could have significant ecological consequences for coral-reef communities in the Hawaiian Islands.

Hawai'i↗
USGS2003

Cascadia Tsunami Deposit Database

The Cascadia Tsunami Deposit Database contains data on the location and sedimentological properties of tsunami deposits found along the Cascadia margin. Data have been compiled from 52 studies, documenting 59 sites from northern California to Vancouver Island, British Columbia that contain known or potential tsunami deposits. Bibliographical references are provided for all sites included in the database. Cascadia tsunami deposits are usually seen as anomalous sand layers in coastal marsh or lake sediments. The studies cited in the database use numerous criteria based on sedimentary characteristics to distinguish tsunami deposits from sand layers deposited by other processes, such as river flooding and storm surges. Several studies cited in the database contain evidence for more than one tsunami at a site. Data categories include age, thickness, layering, grainsize, and other sedimentological characteristics of Cascadia tsunami deposits. The database documents the variability observed in tsunami deposits found along the Cascadia margin.

British Columbia;California;Oregon;Washington↗
USGS2007

Geologic framework studies of South Carolina's Long Bay from Little River Inlet to Winyah Bay, 1999-2003: Geospatial data release

The northern South Carolina coast is a heavily developed region that supports a thriving tourism industry, large local populations and extensive infrastructure (Figure 1). The economic stability of the region is closely tied to the health of its beaches: primarily in providing support for local tourism and protection from storm events. Despite relatively low long-term shoreline erosion rates, and the implied stability of the beaches, the economic impact of storm events to coastal communities has been costly. For example, Hurricane Hugo made landfall on the central South Carolina coast in 1989. High winds and storm surge inflicted roughly $6 billion in property loss and damages, and Hugo remains the costliest storm event in South Carolina history. Localized erosion, commonly occurring around tidal inlets and erosion "hot spots", has also proved costly. Construction and maintenance of hard structures and beach nourishment, designed to mitigate the effects of erosion, have become annual or multi-annual expenditures. Providing a better understanding of the physical processes controlling coastal erosion and shoreline change will allow for more effective management of coastal resources. In 1999, the U.S. Geological Survey (USGS), in partnership with the South Carolina Sea Grant Consortium (SCSGC), began a study to investigate inner continental shelf and shoreface processes. The objectives of the USGS/SCSGC cooperative program are: 1) to provide a regional synthesis of the shallow geologic framework underlying the shoreface and inner continental shelf, and to define its role in coastal evolution and modern beach behavior; 2) to identify and model the physical processes affecting coastal ocean circulation and sediment transport, and to define their role in shaping the modern shoreline; and 3) to identify sediment sources and transport pathways in order to develop a regional sediment budget. This report contains the geospatial data used to define the geologic framework offshore of the northern South Carolina coast. The digital data presented herein accompany USGS Open-File Reports OFR 2004-1013 and OFR 2005-1345, describing the stratigraphic framework and modern sediment distribution within Long Bay, respectively. Direct on-line links to these publications are available within 'References' on the navigation bar to the left. Additional links to other publications and web sites are also available.

South Carolina↗
USGS2020

Sediments and the sea floor of the continental shelves and coastal waters of the United States—About the usSEABED integrated sea-floor-characterization database, built with the dbSEABED processing system

Since the second half of the 20th century, there has been an increase in scientific interest, research effort, and information gathered on the geologic sedimentary character of the continental margins of the United States. Data and information from thousands of sources have increased our scientific understanding of the character of the margin surface, but rarely have those data been combined and integrated. Initially, the U.S. Geological Survey (USGS), in cooperation with the Institute of Arctic and Alpine Research at the University of Colorado Boulder, created the usSEABED database to provide surficial sea-floor-characterization data for USGS assessments of marine-based aggregates and for studies of sea-floor habitat. Since then, the USGS has continued to build up the database as a nationwide resource for many uses and applications. Previously published data derived from the usSEABED database have been released as three USGS data series publications containing data covering the U.S. Atlantic margin, the Gulf of Mexico and Caribbean regions, and the Pacific coast. An updated USGS data release unifies the three publications, incorporates additional data and sources including data from Alaska, Hawaii, and U.S. overseas territories, and provides revised output files that fix known errors and add known or inferred sampling dates. This report accompanies the data release and contains information on the methodology and products of the usSEABED database.

Open-File Report↗
USGS2007

Summary of Optical-Backscatter and Suspended-Sediment Data, Tomales Bay Watershed, California, Water Years 2004, 2005, and 2006

The U.S. Geological Survey, in cooperation with Point Reyes National Seashore, is studying suspended-sediment transport dynamics in the two primary tributaries to Tomales Bay, Lagunitas Creek and Walker Creek. Suspended-sediment samples and continuous optical backscatter (turbidity) data were collected at three locations during water years 2004?06 (October 1, 2003?September 30, 2006): at two sites in the Lagunitas Creek watershed and at one site in the Walker Creek watershed. Sediment samples were analyzed for suspended-sediment concentration, grain size, and turbidity. Data were used to estimate mean daily and annual seasonal suspended-sediment discharge, which were published in U.S. Geological Survey Annual Water-Data Reports. Data were utilized further in this report to develop field-based optical-backscatter calibration equations, which then were used to derive a continuous time series (15-minute interval) of suspended-sediment concentrations. Sensor fouling and aggradation of the channel bed occurred periodically throughout the project period, resulting in data loss. Although periods of data loss occurred, collection of optical sensor data improved our understanding of suspended-sediment dynamics in the Lagunitas Creek and Walker Creek watersheds by providing continuous time-series storm event data that were analyzed to determine durations of elevated sediment concentrations (periods of time when suspended-sediment concentration was greater than 100 mg/L). Data derived from this project contributed baseline suspended-sediment transport information that will be used to develop and implement sediment total maximum daily loads for Tomales Bay and its tributary watersheds, and provides supporting information for additional total maximum daily loads (pathogens, nutrients, and mercury) and restoration efforts for four federally listed aquatic species that are affected directly by sediment loading in the Tomales Bay watershed. In addition, this project provided an opportunity to evaluate the suitability of using optical data as a surrogate for more traditional labor-intensive methods of measuring suspended-sediment transport in steep coastal watersheds.

Scientific Investigations Report↗
USGS2021

Simulation of groundwater flow in the aquifer system of the Anacostia River and surrounding watersheds, Washington, D.C., Maryland, and Virginia

The U.S. Geological Survey, in cooperation with the District Department of Energy & Environment, Water Quality Division, is investigating the hydrogeology of the tidal Anacostia River watershed within Washington, D.C., with the goal of improving understanding of the groundwater-flow system and the interaction of groundwater and surface water in the watershed. To help meet this goal, a three-dimensional steady-state groundwater-flow model for the Anacostia River and surrounding watersheds in Washington, D.C., Maryland, and Virginia was constructed. The goal of the modeling study was to quantify the rate and pattern of groundwater flow to the tidal Anacostia River. The model domain includes weathered and unweathered rocks of the Piedmont Physiographic Province and the southeast-dipping sediments of the Atlantic Coastal Plain Physiographic Province. The model includes processes of recharge, evapotranspiration, withdrawals from wells, and base flow to streams, rivers, and tidal waters. Final model calibration was achieved by using the objective parameter estimation and sensitivity analysis capabilities of UCODE_2005. Simulated gradients in the surficial aquifer in the vicinity of the tidal Anacostia River indicate that flow is predominantly toward the river, with changes in the magnitude and direction of the gradients from the northeast, where the Anacostia River enters Washington, D.C., to the southwest, toward the confluence with the tidal Potomac River. Flow paths to the tidal Anacostia River from the north are largely horizontal through the surficial aquifer and Patuxent aquifer. From the south, the flow paths toward the river originate in the elevated topographic areas southeast of the river and pass through the surficial aquifer and Patapsco confining unit, lower Patapsco aquifer/Arundel Clay, and to some extent, the Patuxent aquifer. Groundwater-flow rates to and from the tidal rivers (Potomac and Anacostia) are generally greatest near the land-water boundary, where the gradient in the water table is greatest, and diminish toward the middle of the tidal river channels. The tidal rivers are predominantly areas of groundwater discharge, although there are areas where tidal waters are recharging the subsurface, typically where small variations or depressions in the topography produce small locally reversed gradients in the water table. Substantial recharge of tidal waters to the groundwater system is observed for the tidal Potomac where the upper Patapsco aquifer subcrops south of Washington, D.C. Water budget calculations indicate that inflows to the groundwater system beneath the tidal Anacostia River are predominantly from the land area of Washington, D.C., followed by tidal surface water and flows from lower layers. Outflows are largely to the tidal Anacostia River, with a smaller part going to the land area underlying Washington, D.C.

Delaware, Maryland, Washington D.C.↗
USGS1989

Hydrogeology of the Canal Creek area, Aberdeen Proving Ground, Maryland

Geologic and borehole geophysical logs made at 77 sites show that the hydrogeologic framework of the study area consists of a sequence of unconsolidated sediments typical of the Coastal Plain of Maryland. Three aquifers and two confining units were delineated within the study area. From the surface down, they are: (1) the surficial aquifer; (2) the upper confining unit; (3) the Canal Creek aquifer; (4) the lower confining unit; and (5) the lower confined aquifer. The aquifer materials range from fine sand to coarse sand and gravel. Clay lenses were commonly found interfingered with the sand, isolating parts of the aquifers. All the units are continuous throughout the study area except for the upper confining unit, which crops out within the study area but is absent in updip outcrops. The unit also is absent within a Pleistocene paleochannel, where it has been eroded. The surficial and Canal Creek aquifers are hydraulically connected where the upper confining unit is absent, and a substantial amount of groundwater may flow between the two aquifers. Currently, no pumping stresses are known to affect the aquifers within the study area. Under current conditions, downward vertical hydraulic gradients prevail at topographic highs, and upward gradients typically prevail near surface-water bodies. Regionally, the direction of groundwater flow in the confined aquifers is to the east and southeast. Significant water level fluctuations correspond with seasonal variations in rainfall, and minor daily fluctuations reflect tidal cycles. (USGS)

Water-Resources Investigations Report↗
USGS2000

Hydrogeology and simulation of ground-water flow at Dover Air Force Base, Delaware

Dover Air Force Base in Kent County, Delaware, has many contaminated sites that are in active remediation. To assist in this remediation, a steady-state model of ground-water flow was developed to aid in understanding the hydrology of the system, and for use as a ground-watermanagement tool. This report describes the hydrology on which the model is based, a description of the model itself, and some applications of the model.Dover Air Force Base is underlain by unconsolidated sediments of the Atlantic Coastal Plain. The primary units that were investigated include the upper Calvert Formation and the overlying Columbia Formation. The uppermost sand unit in the Calvert Formation at Dover Air Force Base is the Frederica aquifer, which is the deepest unit investigated in this report. A confining unit of clayey silt in the upper Calvert Formation separates the Frederica aquifer from the lower surficial aquifer, which is the basal Columbia Formation. North and northwest of Dover Air Force Base, the Frederica aquifer subcrops beneath the Columbia Formation and the upper Calvert Formation confining unit is absent. The Calvert Formation dips to the southeast. The Columbia Formation consists predominately of sands, silts, and gravels, although in places there are clay layers that separate the surficial aquifer into an upper and lower surficial aquifer. The areal extent of these clay layers has been mapped by use of gamma logs. Long-term hydrographs reveal substantial changes in both seasonal and annual ground-water recharge. These variations in recharge are related to temporal changes in evaporation, transpiration, and precipitation. The hydrographs show areas where extensive silts and clays are present in the surficial aquifer. In these areas, the vertical gradient between water levels in wells screened above and below the clays can be as large as several feet, and local ground-water highs typically form during normal recharge conditions. When drought conditions persist, water drains off these highs and the vertical gradients decrease. At the south end of Dover Air Force Base, hydrographs of water levels in the Frederica aquifer show that off-Base pumping can cause the water levels to decline below sea level during part of the year.A 4-layer, steady-state numerical model of ground-water flow was developed for Dover Air Force Base and the surrounding area. The upper two layers represent the upper and lower surficial aquifers, which are in the Columbia Formation. In some areas of the model, a semi-confining unit is used to represent an intermittent clay layer between the upper and lower surficial aquifer. This semi-confining unit causes the local groundwater highs in the surficial aquifer. The third model layer represents the upper part of the Calvert Formation, a confining unit. The fourth model layer represents the Frederica aquifer. The model was calibrated to hydraulic heads and to ground-water discharge in Pipe Elm Branch, both of which were measured in September 1997. For the calibrated model, the root-mean-squared errors for the hydraulic heads and the ground-water discharge in the Pipe Elm Branch were 9 percent of the range of head and 3 percent of discharge, respectively. Heads simulated by use of the model were consistent with a map showing average water levels in the region. The U.S. Geological Survey?s MODPATH program was used to simulate ground-water-flow directions for several areas on the Base. This analysis showed the effects of the local groundwater highs. In these areas, ground water can flow from the highs and then dramatically change flow direction as it enters the lower surficial aquifer. The steady-state model has several limitations. The entire ground-water system is under transient hydraulic conditions, due mainly to seasonal and yearly changes in recharge and to withdrawal from irrigation wells. Yet this steady-state model is still considered to be an effective tool for understanding the ground-water-flow system u

Water-Resources Investigations Report↗
USGS2007

Organic geochemistry of sediments in nearshore areas of the Mississippi and Atchafalaya Rivers: I. General organic characterization

This report presents results on the general organic characteristics of sediment cores collected from the coastal zone of the Mississippi River system, including distributions of the important nutrient elements (C, N, P, and S). This was part of a larger study conducted from 2001-2005 to examine the delivery of sediment-associated contaminants to the Gulf of Mexico by the Mississippi River system, funded by the USGS Coastal and Marine Geology Program. Companion reports emphasize organic contaminants (Rosenbauer and others, 2006), and metals (Swarzenski and others, 2006). The level of contamination within the deltaic system of the Mississippi River system was determined through the collection of sediment cores from interdistributary bays, and offshore in the Gulf of Mexico, including the zone of hypoxia. Results provide the basis for reconstructing contaminant inventories from which to develop historic perspectives on nutrient loading and hypoxia, and to better understand how sediment-hosted contaminants either directly or indirectly move through biota and ultimately affect ecosystem health. Concentrations of C, N, P, and S in sediments varied by a factor of 10 between sites, and in down core profiles. Nearshore cores collected in 2001 proved to have erratic downcore C, N, P, and S profiles and sediment deposition rates, suggesting a high energy regime controlled more by variability in river flow rather than by geochemical processes and reactions within the system. These results focused further coring activities further offshore. Atomic C/N ratios suggest that organic matter deposited at all sites is a mix of microbial (algal) and terrestrial (vascular plant) remains, but with algal material dominant. Concentrations of total sulfur in sediments from cores in the zone of hypoxia were often higher than those in nearby zones with oxic water columns. Corresponding atomic C/S ratios were typically lower in sediments from sites in the zone of hypoxia compared to nearby sites with oxic water columns, and thus atomic C/S values may be useful as a proxy for identifying sites impacted by hypoxic conditions in the water column and for examining historical trends in hypoxia. At one site examined in this study, maximum hypoxic conditions were observed in the mid 1960's. The organic elemental composition (C, N, P, and S) of sediments was also used to guide sample selection for contaminant analysis, and to normalize the contaminant data to organic C content of the sediments. Dissolved hydrocarbon gases in sediments showed a dominance of methane, but identifiable concentrations of ethane and hexane, and trace concentrations of propane, butane, and pentane were also detected. All dissolved gases except hexane were dominated by 'bound' gas, gas released only after agitation of the sediment in a blender. Hexane, in contrast was observed mostly as free gas, determined by headspace analysis.

Louisiana↗
USGS2023

Reconstructing the geomorphic evolution and sediment budget history of a dynamic barrier island: Anclote Key, Florida

Decadal to centennial variations in sediment availability are a primary driver of coastal change within barrier systems. Models help explore how barrier morphology relates to past changes in magnitude of sediment availability, but this requires insights and validation from field efforts. In this study, we investigate the progradation of Anclote Key via its morphostratigraphy, a presently dynamic barrier on the Central Florida Gulf Coast. The results of our field efforts, including vibracores, ground-penetrating radar scans, and optically stimulated luminescence dating of sediments, reveal that Anclote Key has gone through at least two phases of sustained island-scale progradation, with an intervening episode of transgression followed by relative stability. We show that these shifts were likely driven by relatively small changes in shoreface sediment availability owing to the island’s limited accommodation and suggest that Anclote Key may have been relatively isolated from the alongshore sediment supply of nearby barriers prior to the late 20 th century.

Florida↗
USGS2026

Net widening of Southern California beaches

Human impacts from dams reduce river sediment fluxes and are primary causes of coastal erosion worldwide. Here we provide new satellite-derived shoreline observation techniques to examine beach area trends across the diverse coastal settings of California. Contrary to global trends, these data reveal that the most heavily urbanized and dammed region of southern California experienced net beach growth of over 2 million m 2 during 1984-2024. While several beaches experienced severe erosion, overall widening is explained by sufficient sediment supply and concentrated widening from longshore transport captured at coastal structures and in littoral convergence zones. These results indicate that adequate sediment sources exist in this human-modified landscape to mitigate coastal erosion, but that this sediment is not effectively distributed to vulnerable beaches. This highlights the critical role that longshore sediment transport plays in long-term beach trends and illuminates management opportunities for coastal sustainability at the regional scale.

California↗
USGS1991

Regressive coastal deposits on Quaternary continental shelves: Preservation and legacy

Regressive coastal deposits containing internal downlapping surfaces are common on continental shelves of the world. Through theoretical considerations and evaluation of examples from the literature and our own studies in California and Italy, we have examined the conditions that lead both to the formation and preservation of these deposits. Coastal downlapping deposits form by progradation of coastal and deltaic lithosomes during stable and falling sea level. in addition to the rate and direction of sea-level change, the major controls governing the development of downlapping deposits are sediment availability and shelf morphology (gradient, surface irregularity, and depth of shelf break). Continental margins receiving a large, continuous supply of sediment commonly have vertical stacks of thick, laterally extensive deposits; those fed by relatively small coastal streams may have well-developed shelf-margin deposits if accommodation space was available. in the absence of feeder streams, shelf-margin downlapping deposits can form from locally derived sediment. Regressive coastal deposits are preserved in a variety of settings, but they are least likely to be preserved on broad, low-gradient (coastal plain) shelves, where small drops in relative sea level were accompanied by large seaward shifts of the shoreline. Even on high-gradient tectonic margins, downlapping deposits commonly are not preserved on the midshelf. The process of shoreface erosion during a transgression is efficient at planing off deposits from previous depositional cycles. Where the deposits are thin, the deposit is partially or wholly reworked; where they are thick, the basal part may be preserved. Regressive deposits are most likely to be preserved along the shelf margin, where relatively thick sequences form at or below the position of the lowstand sea level. On many continental shelves, the coarse sandy texture of outer-shelf sediment largely reflects original deposition in a regressive coastal environment during a fall and lowstand of relative sea level.

California↗
USGS2024

Vortex trapping of suspended sand grains over ripples

Coastal hydrodynamics and morphodynamics integrate the effects of small-scale fluid-sediment interactions; yet, these small-scale processes are not well understood. To investigate sediment trapping by turbulent coherent structures or vortices, the transport of coarse sand over ripples was analyzed in a small-oscillatory flow tunnel with phase-separated Particle Image and Tracking Velocimetry. Results from one of the first direct measurements of vortex-trapped sand grains under oscillatory flows are presented. The vortices mobilized sand grains along the ripple slopes just prior to flow reversal and transported the suspended sediment grains. During several flow cycles, some sand grains were temporarily trapped in the vortex, prescribing semi-circular trajectories off-center from the vortex core in quadrants of the vortex that were closest to the ripple slope, as illustrated by Nielsen (1992, https://doi.org/10.1142/1269 ). Comparisons of the horizontal sediment grain velocity with the horizontal fluid velocity yielded a linear relationship with a slope of 0.87. The vertical grain velocities also varied linearly with the vertical fluid velocity with a slope of approximately 1 and an offset of −0.08 m s −1 . The offset is close to the still water settling velocity for coarse sand grains, as hypothesized during vortex trapping. Additionally, estimates of the off-center distance, between the centers of the semi-circular sediment paths and vortex cores, compared well with the ratio of the settling velocity to the radian frequency of the vortex yielding a linear regression slope of 0.99. Improved understanding of vortex trapping effects on sediment dynamics may decrease uncertainty in model predictions of large-scale coastal hydrodynamics and sediment transport.

Journal of Geophysical Research: Earth Surface↗
USGS1991

The last interglaciation in Alaska: Stratigraphy and paleoecology of potential sites

At least 20 localities in Alaska contain deposits that may provide information on the last interglaciation (Oxygen-Isotope Substage 5e). These widely dispersed localities include river bluffs, coastal bluffs and terraces, elevated marine shorelines, lake basins, and artificial excavations. Most of the inferred interglacial deposits contain macrofossils or pollen that are older than the range of radiocarbon dating and commonly indicate climate as warm as or warmer than the present. At a few localities, evidence for deep thaw of permafrost also indicates a warm paleoclimate. At eight localities, the Old Crow tephra occurs at or below organic deposits that may represent Substage 5e. The tephra occurs beneath conspicuous organic deposits at Fairbanks, the Yukon Palisades, and Holitna lowland, and directly above a peat bed at Hogatza Mine. At Birch Creek, Halfway House, Ky-11, and Imuruk Lake, the tephra occurs within a paleosol or organic deposit, but other organic horizons that more likely indicate interglacial conditions occur at higher stratigraphic levels. The varied stratigraphic relations of the Old Crow tephra suggest that it may have been deposited close to the boundary between Isotope Substages 6 and 5, which is dated at about 130 ka in the marine record and between 132 and 140 ka on land. These age relations suggests that the tephra may have been deposited about 135 ?? 5 ka, validating the recent fission-track age determination of 140 ?? 10 ka for this deposit. Six coastal localities contain deposits of probable interglacial age, and these commonly are associated with evidence for eustatic sea levels higher than those of the present. Beach and sublittoral sediments of the Pelukian transgression occur up to 12 m asl along the northwest coast of Alaska, and are correlative with barrier island and lagoonal sediments on the Alaskan Arctic Coastal Plain. Both sets of deposits commonly contain extralimital mollusks and microfauna that indicate marine water slightly warmer than present and suggest that seasonal sea ice did not extend south of Bering Strait during the last interglacial as it does today. Farther south, elevated marine-terrace deposits on Amchitka Island contain marine invertebrates that indicate a climate warmer than at present. Peat horizons in coastal exposure at Goose Bay and coastal terraces at Lituya Bay contain pollen spectra that suggest forests like those of the present day, and spruce macrofossils exposed on Baldwin Peninsula indicate boreal forest more extensive than at present. Sediments from several lakes in northwestern Alaska may contain continuous records of the last interglaciation. A major warm interval, possibly Isotope Substage 5e, has been identified in a core from Squirrel Lake by a peak in Picea pollen that indicates forest extension beyond present limits. Similar pollen records are potentially available from two maars which formed in the Cape Espenberg area more than 125 ka. Terrestrial organic deposits thought to record the last interglaciation occur interstratified with marine and glaciogenic sediments in the Nushagak Lowland of southwest Alaska and on Baldwin Peninsula in Kotzebue Sound. Extensive exposures along the Copper and Nenana Rivers may also contain organic deposits that record the last interglaciation. ?? 1992.

Quaternary International↗
USGS2015

Mineral potential for sediment-hosted copper deposits in the Islamic Republic of Mauritania (phase V, deliverable 75)

The presence of Neoproterozoic through Cambrian, continental, siliciclastic sedimentary rocks interbedded with dolomitic carbonates, shales, and glacial tillites similar to the Katanga Supergroup host rocks of the Central African Copperbelt and other sediment-hosted copper-bearing Proterozoic sequences worldwide, is first order criteria for consideration of the Neoproterozoic units of the Taoudeni Basin in Mauritania as prospective for sediment-hosted copper deposits. Review of the National Mineral Occurrences Database (Marsh and Anderson, 2015) and previous literature suggest that only a handful of small sediment-hosted copper occurrences have been found to date in Mauritania and that the resource potential for this deposit type is low. In the northern Taoudeni Basin, the most important occurrence is at Taradent. This occurrence consists of three mineralized horizons in the lower Neoproterozoic Char Group in three outcrop areas separated by alluvium over a strike length of 12 kilometers (km). The most extensively mineralized horizon consists of malachite and disseminated copper sulfides, and is concentrated at the base of a dolomitic interval, consistent with a reduced faciestype sediment-hosted copper deposit model. Additional and poorly described copper occurrences in the Taoudeni Basin margin sedimentary rocks in northeastern Mauritania, such as Chegga Guettatira and Sidi Bara, may be sediment-hosted copper occurrences and extend the potential throughout this portion of the Basin. Additional potential for sediment-hosted copper deposits is indicated in reports by the British Geological Survey (BGS; Gunn and others, 2004) and BRGM (Salpeteur, 2005) in the Neoproterozoic-Cambrian sedimentary rocks (Teniagouri Group) of the central and southern Taoudeni Basin at a number of occurrences in the vicinity of Fouges, Weringuel, and Gig Zig. These occurrences exhibit characteristics consistent with a reduced-facies-type sediment-hosted copper deposit model and based on correlation of similar host rocks extend the potential throughout the entire Taoudeni Basin margin. Very poorly described copper occurrences in the northeastern and southeastern part of the Basin at Kreb en Naga, Kreb en Naga SW, Berbere, Dhar Nema, Dhar Nema 2, Saile, and Nejam-Medroume all are described as occurring in sedimentary rocks and are hosted by or are in close proximity to voluminous outcrops of Jurassic microgabbros (also referred to as dolerite or diabase). Uncertainty exists as to whether they are sediment-hosted copper occurrences. They are likely more closely analogous to copper occurrences associated with mafic igneous activity. The determination of whether reported copper occurrences and associated sedimentary rocks at Kreb en Naga and Kreb en Naga SW in the northeastern Taoudeni Basin and the Dhar Nema occurrences in the southeastern Taoudeni are permissive of sediment-hosted copper mineralization was inconclusive due to the absence of copper showings. While sedimentary host rocks at these locations must be broadly considered permissive, the absence of other favorable geologic features in these areas indicates that the potential for mineral deposits of this type is low. The widespread presence of mafic sills and dikes of Jurassic age throughout these areas and descriptions of associated minor copper mineralization suggests that many of the copper occurrences in these areas are not of the sediment-hosted copper type. Highly speculative potential exists in the Coastal Basin for Revett-type copper deposits in unexposed Jurassic-Cretaceous sandstones that may contain structural traps with gas accumulations. Eocene continental red bed sandstones of the Gorgol Formation, where overlain by the shallow marine sedimentary rocks of the Rinndiao Formation, represent an additional low potential rock sequence within the southeastern portion of the Coastal Basin that is permissive of sediment-hosted copper deposits. Field examinations of outcrop areas in the vicinity of many of the known occurrences were performed in late 2007 to provide additional criteria for evaluating the potential for this type of mineralization in Mauritania. In general, the geographic coordinates of occurrences are imprecise and many of the occurrences could not be located. Examination of outcrops of the Char Group in the Taradent area confirms the permissive nature of these rocks for reduced-facies-type sediment-hosted copper deposits. Inspection of weak copper mineralization hosted by black shales at several occurrences in the Gadel-Maylime area confirms that these occurrences are also of the reduced-faciestype and that the black and green shales of the Bouly and Ould Yenje Formations are permissive. Reported copper analyses up to 0.75 percent copper at Taradent and a single analysis of mineralized shale in the Gadel-Maylime area containing 0.55 percent copper indicate that low grade ore material exists at these locations. However indications that such copper grades are continuous over significant intervals and present in large tonnages are lacking. Although mineral occurrence data and descriptive geological information are adequate to delineate areas favorable for sediment-hosted copper deposits, this review indicates that potential for this type of deposit in Mauritania is low.

Open-File Report↗
USGS2013

Inundation, sedimentation, and subsidence creates goose habitat along the Arctic coast of Alaska

The Arctic Coastal Plain of Alaska is characterized by thermokarst lakes and drained lake basins, and the rate of coastal erosion has increased during the last half-century. Portions of the coast are <1 m above sea level for kilometers inland, and are underlain by ice-rich permafrost. Increased storm surges or terrestrial subsidence would therefore expand the area subject to marine inundation. Since 1976, the distribution of molting Black Brant (Branta bernicla nigricans) on the Arctic Coastal Plain has shifted from inland freshwater lakes to coastal marshes, such as those occupying the Smith River and Garry Creek estuaries. We hypothesized that the movement of geese from inland lakes was caused by an expansion of high quality goose forage in coastal areas. We examined the recent history of vegetation and geomorphological changes in coastal goose habitat by combining analysis of time series imagery between 1948 and 2010 with soil stratigraphy dated using bomb-curve radiocarbon. Time series of vertical imagery and in situ verification showed permafrost thaw and subsidence of polygonal tundra. Soil stratigraphy and dating within coastal estuaries showed that non-saline vegetation communities were buried by multiple sedimentation episodes between 1948 and 1995, accompanying a shift toward salt-tolerant vegetation. This sedimentation allowed high quality goose forage plants to expand, thus facilitating the shift in goose distribution. Declining sea ice and the increasing rate of terrestrial inundation, sedimentation, and subsidence in coastal estuaries of Alaska may portend a 'tipping point' whereby inland areas would be transformed into salt marshes.

Alaska↗
USGS2019

Impacts of suspended sediment on nearshore benthic light availability following dam removal in a small mountainous river:In situ observations and statistical modeling

The 2011–2014 removal of two dams from the Elwha River, WA, delivered ~ 19 Mt of sediment to the marine environment, creating an opportunity to study the sensitivity of a coastal ecosystem to large-scale sediment input. Macroalgae, the primary habitat-forming species in the nearshore, disappeared from the region. It was hypothesized that this mortality event was caused by a reduction in benthic light availability due to increased turbidity. To investigate this connection, nearshore processes and benthic light availability were monitored at 7 locations along the 10-m isobath in 2016 and 2017. The primary driver of light attenuation was suspended sediment, with measured chlorophyll-a and CDOM concentrations contributing < 15% to observed attenuation values. A Bootstrap-aggregated Regression Tree was trained to predict attenuation from the in situ data. Light attenuation was impacted by both sediment transport in the river plume, represented in the model by fluvial suspended sediment load and tidal current direction, and subsurface resuspension, represented by wave height and bed shear velocity. The models were used to hindcast light availability during the dam removal. Total daily benthic light availability was below the 1–2 mol photons/m2/day threshold for macroalgae growth consistently in 2013 and seasonally in 2012 and 2014, supporting the hypothesis that reduced light availability caused the mortality event. Light availability increased in 2016–2017 as the annual sediment load decreased, and macroalgae were concurrently observed in the region. Predicting benthic light availability over event, tidal, and seasonal timescales by accounting for both near-surface and subsurface attenuation will improve management strategies designed to limit ecosystem damage during sediment delivery events.

Washington↗
USGS2020

Dynamics of marsh-derived sediments in lagoon-type estuaries

Salt marshes are valuable ecosystems that must trap sediments and accrete in order to counteract the deleterious effect of sea‐level rise. Previous studies have shown that the capacity of marshes to build up vertically depends on both autogenous and exogenous processes including eco‐geomorphic feedbacks and sediment supply from in‐land and coastal ocean. There have been numerous efforts to quantify the role played by the sediments coming from marsh edge erosion on the resistance of salt marshes to sea‐level rise. However, the majority of existing studies investigating the interplay between lateral and vertical dynamics use simplified modelling approaches and they do not consider that marsh retreat can affect the regional scale hydrodynamics and sediment retention in back‐barrier basins. In this study, we evaluated the fate of the sediments originating from marsh lateral loss by using high‐resolution numerical model simulations of Jamaica Bay, a small lagoonal estuary located in New York City. Our findings show that up to 42% of the sediments released during marsh edge erosion deposits on the shallow areas of the basin and over the vegetated marsh platforms, contributing positively to the sediment budget of the remaining salt marshes. Furthermore, we demonstrate that with the present‐day sediment supply from the ocean the system cannot keep pace with sea‐level rise even accounting for the sediment liberated in the bay through marsh degradation. Our study highlights the relevance of multiple sediment sources for the maintenance of the marsh complex.

New York↗