Search USGS⌕ Search

SEARCH · Search USGS

Results for “Coastal Sediments”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 811 records · Page 45Linked to original sources
USGS2013

Tracking and forecasting the Nation’s water quality - Priorities and strategies for 2013-2023

Water-quality issues facing the Nation are growing in number and complexity, and solutions are becoming more challenging and costly. Key factors that affect the quality of our drinking water supplies and ecosystem health include contaminants of human and natural origin in streams and groundwater; excess nutrients and sediment; alteration of natural streamflow; eutrophication of lakes, reservoirs, and coastal estuaries; and changes in surface and groundwater quality associated with changes in climate, land and water use, and management practices. Tracking and forecasting the Nation's water quality in the face of these and other pressing water-quality issues are important goals for 2013-2023, the third decade of the U.S. Geological Survey's National Water-Quality Assessment (NAWQA) program. In consultation with stakeholders and the National Research Council, a new strategic Science Plan has been developed that describes a strategy for building upon and enhancing assessment of the Nation's freshwater quality and aquatic ecosystems. The plan continues strategies that have been central to the NAWQA program's long-term success, but it also makes adjustments to the monitoring and modeling approaches NAWQA will use to address critical data and science information needs identified by stakeholders. This fact sheet describes surface-water and groundwater monitoring and modeling activities that will start in fiscal year 2013. It also provides examples of the types of data and information products planned for the next decade, including (1) restored monitoring for reliable and timely status and trend assessments, (2) maps and models that show the distribution of selected contaminants (such as atrazine, nitrate, and arsenic) in streams and aquifers, and (3) Web-based modeling tools that allow managers to evaluate how water quality may change in response to different scenarios of population growth, climate change, or land-use management.

Fact Sheet↗
USGS2012

Shipboard surveys track magnetic sources in marine sediments--geophysical studies of the Stono and North Edisto Inlets near Charleston, South Carolina

Magnetic field data are traditionally used to analyze igneous and metamorphic rocks, but recent efforts have shown that magnetic sources within sediments may be detectable, suggesting new applications for high-resolution magnetic field surveys. Candidates for sedimentary sources include heavy mineral sand concentrations rich in magnetite or hematite, alteration-induced glauconite, or biogenic magnetite. Magnetic field surveys can be used to map the distributions of such sources with much denser and more widespread coverage than possible by sampling. These data can then provide constraints on the composition history of local sediments. Mapping such sediments requires the sensor to be relatively close to the source, and filtering approaches may be needed to distinguish signals from both system noise and deeper basement features. Marine geophysical surveys conducted in July, 2010, over the Stono and North Edisto River inlets and their riverine inputs south of Charleston, South Carolina, showed 10- to 40-m-wide, 1- to 6-nT magnetic anomalies associated with shallow, sand-covered seabed. These anomalies are distinct from system noise but are too narrow to represent basement features. The anomalies are present mostly in shallow areas where river sediments originating from upland areas enter the inlets. Surface grab samples from the North Edisto River contain trace amounts of heavy mineral sediments including hematite, maghemite, ilmenite, and magnetite, as well as garnet, epidote, zircon, and rutile. Previous stream sediment analyses show enhanced titanium over much of the Atlantic Coastal Plain. The combined data suggest that the anomalies are generated by titanium- and iron-rich heavy mineral sands ultimately originating from the Piedmont and Blue Ridge provinces, which are then reworked and concentrated by tidal currents.

South Carolina↗
USGS1975

Tectonic framework of petroliferous rocks in Alaska

Alaska, comprising 3.6 X 10 6 sq km (about 28 percent) of the land, shelf, and upper continental slope of the United States, has been estimated by the U.S. Geological Survey (1974) to contain about 25 percent of the Nation's petroleum resources. Some 11 billion barrels of petroleum liquids and 31 trillion cubic feet of natural gas have been announced as discovered to date. In northern Alaska, Paleozoic and Mesozoic shelf and slope deposits of the Brooks Range orogen were thrust relatively northward over the depressed south margin of the Paleozoic and Mesozoic Arctic platform, upon which a foredeep (the Colville geosyncline) developed in earliest Cretaceous time. Detritus from the Brooks Range filled the foredeep and pro-graded northwest and northeast to fill the Cretaceous and Tertiary North Chukchi and Umiat-Camden basins and form the Beaufort shelf. In southern Alaska, a series of arc-trench systems developed on oceanic rocks during the Jurassic and Cretaceous. Between the arcs and the metamorphic (continental) terranes of east-central and northern Alaska, large back-arc and arc-trench gap basins received thick volcanic and detrital deposits. These deposits were extensively deformed and disrupted by mid-Jurassic to Tertiary plutonism, Laramide oroclinal bending, wrench faulting, and arc-related compression. The Laramide events 'continentalized' the late Mesozoic back-arc basin deposits and welded them to the older continental terranes to the north and east. Subsequent sedimentation was localized and nonmarine except in onshore and offshore coastal basins, where thick mixed marine and nonmarine sections were deposited. The Aleutian arc and associated Queen Charlotte transform fault system have dominated structural and depositional patterns in southern Alaska since the early Cenozoic. The largest petroleum reserves in Alaska (the Prudhoe Bay and associated fields) and the best prospects for additional large discoveries are in northern Alaska, where an extensive terrane is underlain by Upper Paleozoic to Tertiary carbonate and shelf, slope and delta clastic deposits. The pre-Tertiary back-arc and arc-trench gap basins in southern and interior Alaska are too intensely deformed or too low in porosity (because of diagenetic mobilization of labile constituents) to offer more than modest local prospects. The Tertiary coastal basins do, however, offer large tracts of thick marine and nonmarine clastic rocks and in some areas many large folds to exploration. Such basins are known to be petroliferous on Bristol Bay and the Gulf of Alaska and to contain major accumulations of oil and gas at Cook Inlet, but they are relatively little explored.

Alaska↗
USGS2006

Geohydrology of the lower Apalachicola-Chattahoochee-Flint River basin, southwestern Georgia, northwestern Florida, and southeastern Alabama

The lower Apalachicola-Chattahoochee-Flint (ACF) River Basin contains about 4,600 square miles of karstic and fluvial plains and nearly 100,000 cubic miles of predominantly karst limestone connected hydraulically to the principal rivers and lakes in the Coastal Plain of southwestern Georgia, northwestern Florida, and southwestern Alabama. Sediments of late-middle Eocene to Holocene in hydraulic connection with lakes, streams, and land surface comprise the surficial aquifer system, upper semiconfining unit, Upper Floridan aquifer, and lower semiconfining unit and contribute to the exchange of ground water and surface water in the stream-lake-aquifer flow system. Karst processes, hydraulic properties, and stratigraphic relations limit ground-water and surface-water interaction to the following hydrologic units of the stream-lake-aquifer flow system: the surficial aquifer system, upper semiconfining unit, Upper Floridan aquifer, and lower confining unit. Geologic units corresponding to these hydrologic units are, in ascending order: Lisbon Formation; Clinchfield Sand; Ocala, Marianna, Suwannee, and Tampa Limestones; Hawthorn Group; undifferentiated overburden (residuum); and terrace and undifferentiated (surficial) deposits. Similarities in hydraulic properties and direct or indirect interaction with surface water allow grouping sediments within these geologic units into the aforementioned hydrologic units, which transcend time-stratigraphic classifications and define the geohydrologic framework for the lower ACF River Basin. The low water-transmitting properties of the lower confining unit, principally the Lisbon Formation, allow it to act as a nearly impermeable base to the stream-lake-aquifer flow system. Hydraulic connection of the surficial aquifer system with surface water and the Upper Floridan aquifer is direct where sandy deposits overlie the limestone, or indirect where fluvial deposits overlie clayey limestone residuum. The water level in perched zones within the surficial aquifer system fluctuates independently of water-level changes in the underlying aquifer, adjacent streams, or lakes. Where the surficial aquifer system is connected with surface water and the Upper Floridan aquifer, water-table fluctuations parallel those in adjacent streams or the underlying aquifer. More...

Alabama, Florida, Georgia↗
USGS2009

Latitudinal trends in Spartina alterniflora productivity and the response of coastal marshes to global change

Marshes worldwide are actively degrading in response to increased sea level rise rates and reduced sediment delivery, though the growth rate of vegetation plays a critical role in determining their stability. We have compiled 56 measurements of above-ground annual productivity for Spartina alterniflora, the dominant macrophyte in North American coastal wetlands. Our compilation indicates a significant latitudinal gradient in productivity, which we interpret to be determined primarily by temperature and/or the length of growing season. Simple linear regression yields a 27 g m-2 yr -1 increase in productivity with an increase of mean annual temperature by one degree C. If temperatures warm 2?4 C over the next century, then marsh productivity may increase by 10?40%, though physiological research suggests that increases in the north could potentially be offset by some decreases in the south. This increase in productivity is roughly equivalent to estimates of marsh lost due to future sea level change. If a warming-induced stimulation of vegetation growth will enhance vertical accretion and limit erosion, then the combined effects of global change may be to increase the total productivity and ecosystem services of tidal wetlands, at least in Northern latitudes.

Global Change Biology↗
USGS2014

Evaluating the effects of land use on headwater wetland amphibian assemblages in coastal Alabama

Anthropogenic land use is known to impact aquatic ecosystems in several ways, including increased frequency and intensity of floods, stream channel incision, sedimentation, and loss of microtopography. Amphibians are susceptible to changes in wetland and surrounding habitats. This study evaluated amphibian assemblages of fifteen headwater slope wetlands in coastal Alabama across a gradient of land uses. Amphibians were surveyed on a seasonal basis and land use was delineated within wetland watersheds and within a 200-m buffer surrounding each wetland. Amphibian presence/absence and land use data were used to develop species occupancy models. Both urban and agricultural land use were shown to influence amphibian occurrence. Species richness ranged from five to ten species across sites; however, five species only occurred in wetlands surrounded by forested lands. Many species were detected more frequently on these wetlands compared to wetlands surrounded by urban or mixed land uses. Occupancy models showed Acris gryllus was negatively associated with the amount of agriculture within a buffer around the wetland. Hyla squirella , Lithobates clamitans , and L. sphenocephalus were positively associated with agricultural land within a watershed. Anaxyrus terrestris and the non-native Eleutherodactylus planirostris were positively associated with the amount of impervious surface area within the wetland buffer.

Alabama↗
USGS2020

Degradation of RDX (Hexahydro-1,3,5-trinitro-1,3,5-triazine) in contrasting coastal marine habitats: Subtidal non-vegetated (sand), subtidal vegetated (silt/eel grass), and intertidal marsh

Hundreds of explosive-contaminated marine sites exist globally, many of which contain the common munitions constituent hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). Quantitative information about RDX transformation in coastal ecosystems is essential for management of many of these sites. Isotopically labelled RDX containing 15 N in all 3 nitro groups was used to track the fate of RDX in three coastal ecosystem types. Flow-through mesocosms representing subtidal vegetated (silt/eel grass), subtidal non-vegetated (sand) and intertidal marsh ecosystems were continuously loaded with isotopically labelled RDX for 16–17 days. Sediment, pore-water and overlying surface water were analyzed to determine the distribution of RDX, nitroso-triazine transformation products (NXs) and nitrogen containing complete mineralization products, including ammonium, nitrate+nitrite, nitrous oxide and nitrogen gas. The marsh, silt, and sand ecotypes transformed 94%, 90% and 76% of supplied RDX, respectively. Total dissolved NXs accounted for 2%–4% of the transformed 15 N-RDX. The majority of RDX transformation in the water column was by mineralization to inorganic N (dissolved and evaded; 64%–78% of transformed 15 N-RDX). RDX was mineralized primarily to N 2 O (62–74% of transformed 15 N-RDX) and secondarily to N 2 (1–2% of transformed 15 N-RDX) which exchanged with the atmosphere. Transformation of RDX was favored in carbon-rich lower redox potential sediments of the silt and marsh mesocosms where anaerobic processes of iron and sulfate reduction were most prevalent. RDX was most persistent in the carbon-poor sand mesocosm. Partitioning of 15 N derived from RDX onto sediment and suspended particulates was negligible in the overall mass balance of RDX transformation (2%–3% of transformed 15 N-RDX). The fraction of 15 N derived from RDX that was sorbed or assimilated in sediment was largest in the marsh mesocosm (most organic carbon), and smallest in the sand mesocosm (largest grain size and least organic carbon). Sediment redox conditions and available organic carbon stores affect the fate of RDX in different coastal marine habitats.

Connecticut, New York↗
USGS2014

Sediment data collected in 2010 from Cat Island, Mississippi

Scientists from the U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center, in collaboration with the U.S. Army Corps of Engineers, conducted geophysical and sedimentological surveys in 2010 around Cat Island, Mississippi, which is the westernmost island in the Mississippi-Alabama barrier island chain. The objective of the study was to understand the geologic evolution of Cat Island relative to other barrier islands in the northern Gulf of Mexico by identifying relationships between the geologic history, present day morphology, and sediment distribution. This data series serves as an archive of terrestrial and marine sediment vibracores collected August 4-6 and October 20-22, 2010, respectively. Geographic information system data products include marine and terrestrial core locations and 2007 shoreline data. Additional files include marine and terrestrial core description logs, core photos, results of sediment grain-size analyses, optically stimulated luminescence dating and carbon-14 dating locations and results, Field Activity Collection System logs, and formal Federal Geographic Data Committee metadata.

Mississippi↗
USGS2018

A Holocene record of ocean productivity and upwelling from the northern California continental slope

The Holocene upwelling history of the northern California continental slope is examined using the high-resolution record of TN062-O550 (40.9°N, 124.6°W, 550 m water depth). This 7-m-long marine sediment core spans the last ∼7500 years, and we use it to test the hypothesis that marine productivity in the California Current System (CCS) driven by coastal upwelling has co-varied with Holocene millennial-scale warm intervals. A combination of biogenic sediment concentrations (opal, total organic C, and total N), stable isotopes (organic matter δ 13 C and bulk sedimentary δ 15 N), and key microfossil indicators of upwelling were used to test this hypothesis. The record of biogenic accumulation in TN062-O550 shows considerable Holocene variability despite being located within 50 km of the mouth of the Eel River, which is one of the largest sources of terrigenous sediment to the Northeast Pacific Ocean margin. A key time interval beginning at ∼2900 calibrated years before present (cal yr BP) indicates the onset of modern upwelling in the CCS, and this period also corresponds to the most intense period of upwelling in the last 7500 years. When these results are placed into a regional CCS context during the Holocene, it was found that the timing of upwelling intensification at TN062-O550 corresponds closely to that seen at nearby ODP Site 1019, as well as in the Santa Barbara Basin of southern California. Other CCS records with less refined age control show similar results, which suggest late Holocene upwelling intensification may be synchronous throughout the CCS. Based on the strong correspondence between the alkenone sea surface temperature record at ODP Site 1019 and the onset of late Holocene upwelling in northern California, we suggest that CCS warming may be conducive to upwelling intensification, though future changes are unclear as the mechanisms forcing SST variability may differ.

California↗
USGS2001

Tectonic erosion and consequent collapse of the Pacific margin of Costa Rica: Combined implications from ODP leg 170, seismic offshore data, and regional geology of the Nicoya Peninsula

The convergent margin off the Pacific coast of the Nicoya Peninsula of Costa Rica exhibits evidence for subduction erosion caused by the underthrusting Cocos plate. Critical evidence for efficacy of this process was recovered at the Ocean Drilling Program (ODP) drilling Site 1042 (Leg 170), positioned ???7 km landward of the Middle America trench axis off the Nicoya Peninsula. The primary drilling objective at this site was to identify the age and origin of a regionally extensive and prominent seismic discontinuity, the so-called base-of-slope sediment (BOSS) horizon or surface. The BOSS horizon, which can be traced landward from near the trench to the Nicoya coastal area and parallel to it for hundreds of kilometers, separates a low-velocity (??? 2.0-2.5 km s-1) sequence of slope sediment, from an underlying sequence of much higher-velocity (> 4-4.5 km s-1) rock. Site 1042 reached the acoustically defined BOSS horizon at a below sea level depth of ??? 3900 m and yielded a carbonate-cemented calcarenitic breccia of early-middle Miocene age. Sedimentological, geochemical, paleontological, and cement paragenesis data document that the breccia accumulated in a shallow water depositional environment. On the basis of coastal exposures, the BOSS horizon, as a margin-wide geologic interface, can be temporally and lithostratigraphically correlated to a regional angular unconformity. This unconformity, known as the Mal Pais unconformity, separates Neogene and younger shelf-to-littoral beds from the underlying mafic units of the Mesozoic Nicoya Complex and Cretaceous and early Tertiary sedimentary sequences. At Site 1042 it is inferred that tectonism caused the vertical subsidence of the early Neogene breccia from a shallow to a deep water setting. The Mal Pais unconformity of the BOSS horizon thus connects the rock fabric of the outermost part of margin to that of coastal Nicoya and implies that in the early Neogene the Nicoya shelf extended seaward to near the present trench axis. This circumstance requires that the early Neogene trench axis was at least 50 km seaward of where it is now located. The long-term effects of subduction erosion, similar to those described for the scientifically drilled Japan, Tonga, and Peru margins, best account for offshore and onshore evidence for a post-Paleogene history of crustal thinning and landward trench migration of Costa Rica's Pacific margin. During the past 16-17 Myr the calculated mass removal and landward migration rates are 34-36 km3 Myr-1 km-1 of margin, and 3 km Myr-1, respectively. These values are similar to those found for other Pacific margins dominated by nonaccretionary subduction zone processes.

Tectonics↗
USGS2011

Benthic habitat classification in Lignumvitae Key Basin, Florida Bay, using the U.S. Geological Survey Along-Track Reef Imaging System (ATRIS)

The Comprehensive Everglades Restoration Plan (CERP) funded in partnership between the U.S. Army Corps of Engineers, South Florida Water Management District, and other Federal, local and Tribal members has in its mandate a guideline to protect and restore freshwater flows to coastal environments to pre-1940s conditions (CERP, 1999). Historic salinity data are sparse for Florida Bay, so it is difficult for water managers to decide what the correct quantity, quality, timing, and distribution of freshwater are to maintain a healthy and productive estuarine ecosystem. Proxy records of seasurface temperature (SST) and salinity have proven useful in south Florida. Trace-element chemistry on foraminifera and molluscan shells preserved in shallow-water sediments has provided some information on historical salinity and temperature variability in coastal settings, but little information is available for areas within the main part of Florida Bay (Brewster-Wingard and others, 1996). Geochemistry of coral skeletons can be used to develop subannually resolved proxy records for SST and salinity. Previous studies suggest corals, specifically Solenastrea bournoni, present in the lower section of Florida Bay near Lignumvitae Key, may be suitable for developing records of SST and salinity for the past century, but the distribution and species composition of the bay coral community have not been well documented (Hudson and others, 1989; Swart and others, 1999). Oddly, S. bournoni thrives in the study area because it can grow on a sandy substratum and can tolerate highly turbid water. Solenastrea bournoni coral heads in this area should be ideally located to provide a record (~100-150 years) of past temperature and salinity variations in Florida Bay. The goal of this study was to utilize the U.S. Geological Survey's (USGS) Along-Track Reef Imaging System (ATRIS) capability to further our understanding of the abundance, distribution, and size of corals in the Lignumvitae Key Basin. The study area was subdivided into four areas whereby corals and other benthic habitats were classified based on ATRIS imagery.

Florida↗
USGS2008

Coast salish and U.S. Geological Survey: Tribal journey water quality project

The ancestral waters of the Coast Salish People, the Salish Sea, comprise a large inland sea contained within both United States (Puget Sound) and Canadian (Georgia Strait) territory. The Salish Sea is home to more than 220 species of fish, 29 species of marine mammals, more than 40 species of commercial and recreationally harvested invertebrates, and numerous resident and migratory bird species (Washington Sea Grant Program, 2000). Unfortunately, at least 60 of these marine based species are listed as threatened, endangered or of concern (Fraser and others, 2006), many of which sustained Coast Salish for millennia and are of essential cultural importance. The cumulative impacts of human activities and climate change are deteriorating coastal ecosystems and accelerating the loss of ecologically and culturally important marine resources. Watershed modifications, coastal development and industrial activities are altering river and tidal flow, sediment transport, and nutrient delivery all across the region, leading to the break down of ecosystem functions and decreasing biodiversity, thus changing the face of the Salish Sea. A cooperative trans-boundary partnership between the U.S. Environmental Protection Agency (USEPA) and the Government of Canada has identified Salish Sea indicators of health. Several of these indicators have been noted as having degrading quality including urbanization and forest change, river, stream, and lake quality, marine species at risk, toxics in harbor seals, and marine water quality conditions (USEPA, 2008). The functioning of the Salish Sea ecosystem is increasingly threatened by ever more frequent observations and expanding zones of anoxia. The complexities of monitoring, protecting, and restoring such a large and diverse geographical area are exacerbated by a political border. The Coast Salish Peoples and U.S. Geological Survey (USGS) have commenced on a partnership to examine water quality throughout the Georgia Straits and Puget Sound, blending tradition and science, in response to this deterioration of coastal environments and loss of essential habitats and marine resources of cultural and ecological importance throughout the ancestral waters of the Salish Sea. This report describes the Coast Salish Tribal Journey Water Quality Project, its inception, the results of the 2008 Tribal Journey project, lessons learned, and recommendations for future directions.

Report↗
USGS2016

Seismic evidence of glacial-age river incision into the Tahaa barrier reef, French Polynesia

Rivers have long been recognized for their ability to shape reef-bound volcanic islands. On the time-scale of glacial–interglacial sea-level cycles, fluvial incision of exposed barrier reef lagoons may compete with constructional coral growth to shape the coastal geomorphology of ocean islands. However, overprinting of Pleistocene landscapes by Holocene erosion or sedimentation has largely obscured the role lowstand river incision may have played in developing the deep lagoons typical of modern barrier reefs. Here we use high-resolution seismic imagery and core stratigraphy to examine how erosion and/or deposition by upland drainage networks has shaped coastal morphology on Tahaa, a barrier reef-bound island located along the Society Islands hotspot chain in French Polynesia. At Tahaa, we find that many channels, incised into the lagoon floor during Pleistocene sea-level lowstands, are located near the mouths of upstream terrestrial drainages. Steeper antecedent topography appears to have enhanced lowstand fluvial erosion along Tahaa's southwestern coast and maintained a deep pass. During highstands, upland drainages appear to contribute little sediment to refilling accommodation space in the lagoon. Rather, the flushing of fine carbonate sediment out of incised fluvial channels by storms and currents appears to have limited lagoonal infilling and further reinforced development of deep barrier reef lagoons during periods of highstand submersion.

Tahaa barrier reef↗
USGS2023

The concept of land bridge marshes in the Mississippi River Delta and implications for coastal restoration

Louisiana has high coastal wetland loss rates due to natural processes such as subsidence and anthropogenic activities such as construction of river levees and dams, pervasive alteration of surface hydrology by local industries such as oil and gas, and navigation. With the exception of the Atchafalaya River discharge area, most of Louisiana's marsh coastline is retreating and coastal marshes are degrading. In the inactive degrading delta regions, there exists a previously uncharacterized landform referred to colloquially as coastal ‘land bridge’ marshes. Land bridge marshes are saline or brackish marshes fronting large estuarine bays or lakes with sufficient fetch and wave energy to supply high levels of resuspended sediments to the marsh surface. They are generally linear features that are oriented parallel to the coast and the shoreline front retreats landward due to erosion from wave energy. These marshes persist over time vertically due to input of resuspended sediments but are experiencing rapid edge erosion due to wave attack. Comparison of data from Louisiana's Coastal Reference Monitoring System (CRMS) sites show that land bridge marshes have a greater frequency of higher soil surface elevation and higher soil bulk density than non-land bridge marshes. Because land bridges are vertically stable relative to other coastal wetlands, identification of measures to sustain these landscape features is important. Simulations using MarshMorpho2D, a process-based reduced-complexity morphology model, suggest that protection barriers installed on the seaward side of land bridge marshes will attenuate wave energy and, thus, edge erosion. Shoreline protection that can reduce wave energy but still allow sediment input to marshes include living shorelines, rock barriers, and/or breakwaters. Periodic thin layer nourishment of the marsh surface may be necessary to help sustain vertical growth. Further, marsh creation projects directly landward of land bridge marshes may benefit from their protection from waves and as a source of sediment. Consideration of land bridge marshes as distinct marsh types in the State Master Plan and integrated modeling could help to identify measures to sustain these landscape features.

Louisiana↗
USGS2009

Rates and trends of coastal change in california and the regional behavior of the beach and cliff system

The U.S. Geological Survey (USGS) recently completed an analysis of shoreline change and cliff retreat along the California coast. This is the first regional, systematic measurement of coastal change conducted for the West Coast. Long-term (-120 y) and short-term (-25 y) shoreline change rates were calculated for more than 750 km of coastline, and 70 year cliff-retreat rates were generated for 350 km of coast. Results show that 40% of California's beaches were eroding in the long term. This number increased to 66% in the short term, indicating that many beaches have shifted toward a state of chronic erosion. The statewide average net shoreline change rates for the long and short term were 0.2 m/y and -0.2 m/y, respectively. The long-term accretional signal is likely related to large coastal engineering projects in some parts of the state and to large fluxes of sediment from rivers in other areas. The cliff-retreat assessment yielded a statewide average of -0.3 m/y. It was found that Northern California has the highest overall retreat rates, which are influenced by erosion hot spots associated with large coastal landslides and slumps. The databases established as part of the shoreline change and cliff-retreat analyses were further investigated to examine the dynamics of the beach/cliff system. A correlation analysis identified a strong relationship between the geomorphology of the coast and the behavior of the beach/cliff system. Areas of high-relief coast show negative correlations, indicating that higher rates of cliff retreat correlate with lower rates of shoreline erosion. In contrast, low- to moderate-relief coasts show strong positive correlations, wherein areas of high shoreline change correspond to areas of high cliff retreat.

Journal of Coastal Research↗
USGS1984

Rippled scour depressions on the inner continental shelf off central California

Side-scan sonar records taken during the recent Coastal Ocean Dynamics Experiment (CODE) show elongate, shore-normal rippled depressions of low relief on the inner continental shelf off central California between Bodega Bay and Point Arena. These features extend up to 2 km from the coast into water depths of up to 65 m. The proposed mechanism for their generation is storm-generated bottom currents associated with coastal downwelling during the late fall and winter which scour the surficial fine-sand sediment and expose the coarser-sand substrate in the depressions. The zones of most intense erosion and the irregular spacing of the features may be controlled by submerged rock ledges and other prominent coastal features. The large straight-crested ripples within the depressions (heights to 40 cm; wavelengths to 1.7 m) are probably formed by large-amplitude, long-period surface waves generated by winter storms.

California↗
USGS2004

Upper Cretaceous sequences and sea-level history, New Jersey Coastal Plain

We developed a Late Cretaceous sealevel estimate from Upper Cretaceous sequences at Bass River and Ancora, New Jersey (ODP [Ocean Drilling Program] Leg 174AX). We dated 11-14 sequences by integrating Sr isotope and biostratigraphy (age resolution ??0.5 m.y.) and then estimated paleoenvironmental changes within the sequences from lithofacies and biofacies analyses. Sequences generally shallow upsection from middle-neritic to inner-neritic paleodepths, as shown by the transition from thin basal glauconite shelf sands (transgressive systems tracts [TST]), to medial-prodelta silty clays (highstand systems tracts [HST]), and finally to upper-delta-front quartz sands (HST). Sea-level estimates obtained by backstripping (accounting for paleodepth variations, sediment loading, compaction, and basin subsidence) indicate that large (>25 m) and rapid (???1 m.y.) sea-level variations occurred during the Late Cretaceous greenhouse world. The fact that the timing of Upper Cretaceous sequence boundaries in New Jersey is similar to the sea-level lowering records of Exxon Production Research Company (EPR), northwest European sections, and Russian platform outcrops points to a global cause. Because backstripping, seismicity, seismic stratigraphic data, and sediment-distribution patterns all indicate minimal tectonic effects on the New Jersey Coastal Plain, we interpret that we have isolated a eustatic signature. The only known mechanism that can explain such global changes-glacio-eustasy-is consistent with foraminiferal ??18O data. Either continental ice sheets paced sea-level changes during the Late Cretaceous, or our understanding of causal mechanisms for global sea-level change is fundamentally flawed. Comparison of our eustatic history with published ice-sheet models and Milankovitch predictions suggests that small (5-10 ?? 106 km3), ephemeral, and areally restricted Antarctic ice sheets paced the Late Cretaceous global sea-level change. New Jersey and Russian eustatic estimates are typically one-half of the EPR amplitudes, though this difference varies through time, yielding markedly different eustatic curves. We conclude that New Jersey provides the best available estimate for Late Cretaceous sea-level variations. ?? 2004 Geological Society America.

Geological Society of America Bulletin↗
USGS2017

Revised Ages for Laminated Sediment and a Holocene-Marker Diatom from the Northern California Continental Slope

Conventional and accelerator mass spectrometry 14C ages indicate that laminated sediment in three cores from the northern California continental slope near 38??N and 39??N were deposited between 42,000 and 25,000 yr B.P. This revises and refines our previous estimates that laminated sediment accumulated during the late Pleistocene to early Holocene (J. V. Gardner and E. Hemphill-Haley, 1986, Geology 14, 691-694). Preservation of laminated sediment on the upper slope in this area suggests a period of intense coastal upwelling, high primary productivity, and resultant depletion of oxygen in bottomwaters preceding the onset of global glacial conditions. The transition from Pleistocene to Holocene conditions, and the establishment of a modern climatic regime driven by the California Current, included the incursion of the subtropical diatom, Pseudoeunotia doliola. P. doliola is common in sediment younger than about 10,000 yr and thus is a reliable marker species for identifying Holocene deposits off northern California.

Quaternary Research↗