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USGS2016

Regional chloride distribution in the Northern Atlantic Coastal Plain aquifer system from Long Island, New York, to North Carolina

The aquifers of the Northern Atlantic Coastal Plain are the principal source of water supply for the region’s nearly 20 million residents. Water quality and water levels in the aquifers, and maintenance of streamflow, are of concern because of the use of this natural resource for water supply and because of the possible effects of climate change and changes in land use on groundwater. The long-term sustainability of this natural resource is a concern at the local community scale, as well as at a regional scale, across state boundaries. In 2010, the U.S. Geological Survey (USGS) began a regional assessment of the Northern Atlantic Coastal Plain aquifers. An important part of this assessment is a regional interpretation of the extent of saltwater and the proximity of saltwater to fresh-groundwater resources and includes samples and published interpretations of chloride concentrations newly available since the last regional chloride assessment in 1989. This updated assessment also includes consideration of chloride samples and refined interpretations that stem from the 1994 discovery of the buried 35 million year old Chesapeake Bay impact structure that has substantially altered the understanding of the hydrogeologic framework and saltwater distribution in eastern Virginia. In this study, the regional area of concern for the chloride samples and interpretations extends from the Fall Line in the west to the outer edge of the Continental Shelf in the east and from the eastern tip of Long Island in the north to about halfway down the North Carolina coast in the south. Discussions of chloride distribution are presented for each of the 10 regional aquifer layers of the Northern Atlantic Coastal Plain, including the offshore extents. Maps of interpreted lines of equal concentration or isochlors were manually prepared for nine of the regional aquifers; a map was not prepared for the surficial regional aquifer. The isochlor interpretations include the offshore extent of the nine regional aquifers and are presented on a 1:2,000,000 scale base map. Vertically, the chloride samples and interpretations range from deepest (oldest) to shallowest (youngest)—Potomac-Patuxent, Potomac-Patapsco, Magothy, Matawan, Monmouth-Mount Laurel, Aquia, Piney Point, Lower Chesapeake, and Upper Chesapeake regional aquifers. The approach of this study maximizes the overall density of chloride information and data by assessing relevant published interpretations, all USGS chloride samples, and all relevant offshore samples in one comprehensive interpretation. Published isochlors, where they were interpreted by regional aquifer, were used as much as possible for this regional isochlor assessment. Publication dates for the isochlors used range from 1982 to 2015, and the scales for the isochlors range from local (county or municipality) to state (sub-regional) to regional. The USGS National Water Information System database provided well sample data for the parts of aquifers that are mainly beneath the land areas and yielded 37,517 water-quality records for 1903 through 2011. Published data reports from four phases of research-related offshore coring (1976, 1993, 1997, 2009) were the main source of water-quality data for the parts of aquifers from the shoreline to the outer edge of the Continental Shelf and yielded samples from multiple depths of each of 13 cores. This study also used interpretations and offshore core data from the last regional chloride assessment (1989) which, in addition to 7 offshore cores, included water-quality data from about 500 wells, and borehole geophysics interpretations from a subset of 11 wells. All published information and data that were used in this study were considered time independent and did not assess the published interpretations or data for temporal trends. The approach used here examined only published interpretations and available chloride data, and did not directly use supplemental techniques that can provide insight into the distribution of saltwater, such as geochemical characterization, borehole geophysical information, and geochronology. Isochlor maps for this study are limited to manual interpretations of the 250-milligram per liter (mg/L) and 10,000-mg/L boundaries developed for 9 of the 10 regional aquifers that constitute the regional hydrogeologic framework of the Northern Atlantic Coastal Plain. For a given aquifer, the approach was to initially consider published isochlor interpretations, where available, then to modify the published interpretations, if necessary, to the extent indicated by the well and core samples. The final step was to interpolate isochlors to the full extent of each aquifer layer in areas with sufficient samples or cited interpretations, or to extrapolate isochlors in areas with no samples or where samples were sparse. The principal limitation of this study is that, because of its regional extent, data and information density can vary greatly, and thus confidence in interpretations can vary widely for onshore and offshore areas across the study area. In areas of sparse data, some samples of elevated chloride could be misinterpreted as being part of a regional elevated chloride trend, and in other cases, an elevated concentration could be misinterpreted as being of only local importance. The interpretive work of this study was applied to a 1:2,000,000 scale base map. Locations of isochlors, wells, cores, political boundaries, and shorelines are meant to be considered approximate. The isochlors presented in this study were manually interpreted for each aquifer unit as a conceptual representation of an equal concentration line approximately in the middle of an aquifer’s thickness. Differences in chloride concentration lines between the top and bottom of an aquifer could be substantial, especially for the thick parts of aquifers, but that information is not presented in this regional assessment. Although additional offshore chloride data are available compared to 27 years ago (1989), the offshore information remains sparse, resulting in less confidence in the offshore interpretations than in the onshore interpretations. Regionally, the 250- and 10,000-mg/L isochlors tend to map progressively eastward from the deepest to the shallowest aquifers across the Northern Atlantic Coastal Plain aquifer system but with some exceptions. The additional data, conceptual understanding, and interpretations in the vicinity of the buried Chesapeake Bay impact structure in eastern Virginia resulted in substantial refinement of isochlors in that area. Overall, the interpretations in this study are updates of the previous regional study from 1989 but do not comprise major differences in interpretation and do not indicate regional movement of the freshwater-saltwater interface since then.

Delaware, Maryland, New Jersey, New York, North Ca↗

USGS2000

Morphology and acoustic character of the Antarctic Wilkes Land turbidite systems: Ice-sheet-sourced versus river-sourced fans

The Wilkes Land continental slope contains an intricate network of submarine canyons that on the continental rise develop into a series of channel and overbank deposits of turbidite systems. We can define upper-fan, middle-fan, and lower-fan provinces. The Wilkes Land upper fans are characterized by large channels with relief up to 900 m, distances between levee crests up to 18 km, and channel-floor widths up to 6 km. Middle-fan channels also have high relief (∼300 m), and locally, interchannel areas exhibit mounded contourite-style deposits with high relief (up to 490 m). Within middle-fan sediment mounds there are acoustic facies of channel-overbank deposits from turbidity currents, and of sediment waves from contour-current sedimentation. The lower rise is characterized by small, shallow channels (50-75 m relief) and by interchannel areas of low relief, both characteristic of a lower-fan environment. The Wilkes Land turbidite systems show the following significant morphological differences compared to most river-sourced fans: (1) multiple large tributary channels across the upper and middle fan, (2) channel relief several times greater (900 m) than typical relief (100-200 m) for channels on fans less than 300 km in diameter, and (3) steep middle-fan and lower-fan gradients. We interpret the differences in channel network patterns, channel size, and middle-fan and lower-fan gradients between the Wilkes Land fans and other fans to result from the continental ice sheet feeding glacial ice streams that reached the outer continental shelf at times of glacial maxima. The Wilkes Land canyon-channel network patterns are comparable with the high-latitude Laurentian Fan and Labrador Sea channels. The Laurentian Fan also has large upper-fan channels with larger relief (800 m) than typical relief (200-300 m) expected for fans that are 600 km in diameter. Both the Labrador Sea and Laurentian Fan are fed by continental ice sheets at the shelf edge.

Journal of Sedimentary Research↗

USGS2000

Influence of inner-continental shelf geologic framework on the evolution and behavior of the barrier-island system between Fire Island Inlet and Shinnecock Inlet, Long Island, New York

High-resolution, sea-floor mapping techniques, including sidescan-sonar and subbottom profiling, were used to investigate how the geologic framework of the inner-continental shelf influenced the Holocene evolution and modern behavior of the Fire Island barrier-island system, Long Island, New York. The inner-continental shelf off Long Island is divided into two physiographic provinces by a broad outcrop of Cretaceous coastal-plain strata offshore of Watch Hill; this outcrop was part of a subaerial headland during the Holocene marine transgression. Erosion of the headland during transgression furnished sediment to the inner-continental shelf downdrift to the west. The sediment was, in turn, reworked by oceanographic processes into a series of shoreface-attached sand ridges. The oldest (~1200 yr BP) and most stable part of the barrier-island system is immediately landward of the outcropping coastal-plain strata and thickest sand ridges. East of Watch Hill, Pleistocene sediment either is exposed on the inner-continental shelf or is buried by a veneer of modern reworked sediment. Here the barrier-island system has migrated landward at a faster rate than the segment west of Watch Hill and has been breached by numerous historic inlets. Because the Pleistocene sedimentary deposit is generally of uniform thickness throughout the study area and unconformably overlies the Cretaceous coastal-plain strata, both the Holocene and historical evolution of the Fire Island barrier-island system are controlled by the physiography of this regional unconformity. In particular, the shoreface-connected sand ridges appear to be a significant source of sediment to the western portion of Fire Island. Previous attempts to develop a sediment budget for this coastal system have failed to explain volumetric discrepancies, primarily because poor assumptions were made about the nature of sediment transport in the system. A more realistic sediment budget must include a significantly larger spatial scale, including sediment input from the inner-continental shelf.

New York↗

USGS2004

A preliminary assessment of geologic framework and sediment thickness studies relevant to prospective US submission on extended continental shelf

Under the provisions of Articles 76 and 77 of the United Nations Convention on the Law of the Sea (UNCLOS), coastal States have sovereign rights over the continental shelf territory beyond 200-nautical mile (nm) from the baseline from which the territorial sea is measured if certain conditions are met regarding the geologic and physiographic character of the legal continental shelf as defined in those articles. These claims to an extended continental shelf must be supported by relevant bathymetric, geophysical and geological data according to guidelines established by the Commission on the Limits of the Continental Shelf (CLCS, 1999). In anticipation of the United States becoming party to UNCLOS, Congress in 2001 directed the Joint Hydrographic Center/Center for Coastal and Ocean Mapping at the University of New Hampshire to conduct a study to evaluate data relevant to establishing the outer limit of the juridical continental shelf beyond 200 nm and to recommend what additional data might be needed to substantiate such an outer limit (Mayer and others, 2002). The resulting report produced an impressive and sophisticated GIS database of data sources. Because of the short time allowed to complete the report, all seismic reflection data were classified together; the authors therefore recommended that USGS perform additional analysis on seismic and related data holdings. The results of this additional analysis are the substance of this report, including the status of geologic framework, sediment isopach research, and resource potential in the eight regions1 identified by Mayer and others (2002) where analysis of seismic data might be crucial for establishing an outer limit . Seismic reflection and refraction data are essential in determining sediment thickness, one of the criteria used in establishing the outer limits of the juridical continental shelf. Accordingly, the initial task has been to inventory public-domain seismic data sources, primarily those regionally extensive data held within the Department of the Interior (DOI). The numerous seismic reflection and refraction surveys collected prior to 1970 by academic and governmental institutions are generally not included in this compilation, except where they provide unique data in a region. These data sources were omitted from this report because they were deemed to be of insufficient quality (poorly navigated or low resolution) to meet the CLCS standards for a submission, or they were redundant with higher-quality, more modern data. Hence, this report attempts to identify those data sets of highest utility for establishing the outer limits of the juridical continental shelf. If there was any ambiguity or uncertainty about the relevance of a data set to a continental shelf submission, either by its quality, location, or other parameter, it was included in this compilation. This report does not summarize other geophysical data (such as marine magnetics or gravity) that might be relevant to understanding crustal provenance and geological continuity. Detailed metadata tables and maps are included to facilitate the location and utilization of these sources when a comprehensive assessment (?desktop study?) is undertaken.

Open-File Report↗

USGS1979

Structure and development of the Southeast Georgia Embayment and northern Blake Plateau: Preliminary analysis

Multichannel seismic reflection profiles from the Southeast Georgia Embayment and northern Blake Plateau show reflectors that have been correlated tentatively with horizons of known age. The top of the Cretaceous extends smoothly seaward beneath the continental shelf and Blake Plateau, unaffected at the present shelf edge. A reflector inferred to correspond approximately to the top of the Jurassic section onlaps and pinches out against rocks below. A widespread smooth reflector probably represents a volcanic layer of Early Jurassic age that underlies only the northwestern part of the research area. A major unconformity beneath the inferred volcanic layer is probably of Late Triassic or Early Jurassic age. This unconformity dips rather smoothly seaward beneath the northern Blake Plateau, but south of a geological boundary near 31°N, it has subsided much more rapidly, and reaches depths of more than 12 km. Development of the continental margin north of the boundary began with rifting and subsidence of continental basement in the Triassic. An episode of volcanism may have been due to stresses associated with a spreading center jump at about 175 million years ago. Jurassic and Cretaceous deposits form an onlapping wedge above the inferred early Jurassic volcanics and Triassic sedimentary rocks. During Cenozoic times, development of Gulf Stream flow caused a radical decrease in sedimentation rates so that a shelf that was much narrower than the Mesozoic shelf was formed by progradation against the inner edge of the stream. South of the 31°N geological boundary, the basement probably is semi-oceanic and reef growth, unlike that in the area to the north, has been very active at the outer edge of the plateau.

Blake Plateau, Southeast Georgia Embayment↗

USGS1987

Nature and distribution of potential heavy-mineral resources offshore of the Atlantic Coast of the United States.

The US is dependent on foreign imports of placer heavy minerals for a majority of its ilmenite and rutile, and virtually all of its monazite requirements. Although sand deposits in the SE US are important domestic sources of these heavy minerals (HM) and a number of other less well-known heavy-mineral species, global onshore reserves of placer minerals may fall short of demand in as few as 20 years. Insofar as they are important commodities for the future, offshore HM placers will become more important, but much research on them remains to be done. Results of recent offshore studies, based on surficial grab samples, indicate an average of about 2 weight percent HM in surficial Atlantic Continental Shelf (ACS) sediments, in strong contrast with previous estimates of an average of 0.16% HM. Although provocative, the information from these grab samples does not include the thickness of the HM deposits and thus their volume and tonnage cannot be estimated.-from Author

Marine Mining↗

USGS1987

The stable isotopic composition of a phosphorite deposit: δ13C, δ34S, and δ18O

The stable isotopes of carbon and sulfur in a major marine sedimentary phosphate deposit from the northwestern United States (the Phosphoria Formation of Permian age) characterize the chemical properties of the depositional environment. The δ 34 S and δ 13 C analyses suggest deposition under conditions of variable redox from a solution the acidity of which was controlled by reaction with carbonate rocks and exchange with seawater. The δ 18 O concentration of apetite indicates phosphatization in a shallow sea, during three glacial and intervening interglacial stages. These data tend to corroborate the interpretation of field studies by others, that the apatite formed on a continental shelf in an area of intense oceanic upwelling during several episodes of sea level change.

Deep Sea Research Part A, Oceanographic Research P↗

USGS1972

Acoustic-reflection profiles, Bay of Campeche: International Decade of Ocean Exploration, U.S. Geological Survey, Leg 1, 1971 cruise, UNITEDGEO I

Introduction As part of a cooperative marine research program designated the International Decade of Ocean Exploration (IDOE), the United States Geological Survey is participating in an investigation of the geologic framework and resource potential of continental margins and small ocean basins in the Gulf of Mexico, Caribbean Sea, and west African continental shelf areas. These studies are funded through the National Science Foundation. Acoustic-reflection profiles of Leg 1, described in this report concern mainly a 200 X 250 kilometer project area in the Bay of Campeche in the southwestern part of the Gulf of Mexico. The cruise leg began at Corpus Christi, Texas, and ended at Veracruz, Mexico. Other geophysical records collected during the cruise include magnetometry, gravimetry, and bathymetry. Visiting scientists from the Institute of Geophysics of the National University of Mexico, the Oceanographic Commission of the Mexican Navy, and the Mexican Institute of Petroleum joined the research vessel UNITEDGEO I throughout the cruise in the Bay of Campeche. The cruise offered an excellent opportunity for scientific interchange between investigators from Mexico and the United States and permitted collaboration in the instrumentation, operational techniques, and interpretation of acoustic-reflection records aboard the research vessel.

Bay Of Campeche;Gulf Of Mexico↗

USGS2014

Upwelling rebound, ephemeral secondary pycnoclines, and the creation of a near-bottom wave guide over the Monterey Bay continental shelf

Several sequential upwelling events were observed in fall 2012, using measurements from the outer half of the continental shelf in Monterey Bay, during which the infiltration of dense water onto the shelf created a secondary, near-bottom pycnocline. This deep pycnocline existed in concert with the near-surface pycnocline and enabled the propagation of near-bottom, cold, semidiurnal internal tidal bores, as well as energetic, high-frequency, nonlinear internal waves of elevation (IWOE). The IWOE occurred within 20 m of the bottom, had amplitudes of 8–24 m, periods of 6–45 min, and depth-integrated energy fluxes up to 200 W m −1 . Iribarren numbers (<0.03) indicate that these IWOE were nonbreaking in this region of the shelf. These observations further demonstrate how regional upwelling dynamics and the resulting bulk, cross-margin hydrography is a first-order control on the ability of internal waves, at tidal and higher frequencies, to propagate through continental shelf waters.

California↗

USGS1992

Remote sensing of suspended sediment discharge into the western Gulf of Maine during the April 1987 100-year flood

The suspended sediment discharge during this event was identified using NOAA-9 and NOAA-10 Advanced Very High Resolution Radiometer (AVHRR) data from March 29 to April 14. The sediment plumes showed a westward movement upon reaching the Gulf of Maine. 105 metric tons of fine-grained sediments were carried onto the continental shelf in the largest plume, that from the Kennebec-Androscoggin river system. -from Authors

Journal of Coastal Research↗

USGS2006

Hydratools manual version 1.0, documentation for a MATLAB ® -based post-processing package for the Sontek Hydra

The Sediment Transport Instrumentation Group (STG) at the U.S. Geological Survey (USGS) Woods Hole Science Center has a long-standing comitment to providing scientists with high quality oceanographic data. To meet this commitment, STG personnel are vigilant in checking data as well as hardware for signs of instrument malfunction. STG data sets are accompanied by processing histories to detail data processing procedures that may have modified the natural data signal while removing noise from the data. The history also allows the data to be reprocessed in the ligth of new insight into instrument function and moored conditions. This toolbox was compiled to meet these data quality commitments for data generated by Sontek Hydra systems using both ADV and PCADP probes. In the mid 1900's, the USGS Coastal and Marine Program began frequent deployments of Sontek Hydra systems in support of projects in estuaries, coastal, and continental shelf regions nationwide. Hydra data sets are large and complex in structure, and existing processing and editing tools consisted of fragments of MATLAB code written by USGS scientists to satisfy personal research needs. This code did not meet STG quality control criteria. This toolbox permits engineers and scientists to monitor data quality by: 1. processing data with interactive critical review; 2. preserving data quality indicators; 3. preserving minimally processed and partially processed versions of data sets. STG usually deploys ADV and PCADP probes configured as downward looking, mounted on bottom tripods, with the objective of measuring high-resolution near-bed currents. The velocity profiles are recorded with minimal internal data processing. Also recorded are parameters such as temperature, conductivity, optical backscatter, light transmission, and high frequency pressure. Sampling consists of high-frequency bursts(1–10 Hz) bursts of long duration (5–30 minutes) at regular and recurring intervals for a duration of 1 to 6 months. The result is very large data files, often 500 MB per Hydra, per deployment, in Sontek's compressed binary format. This section introduces the Hydratools toolbox and provides information about the history of the system's development. The USGS philosophy regarding data quality is discussed to provide an understating of the motivation for creating the system. General information about the following topics will also be discussed: hardware and software required for the system, basic processing steps, limitations of program usage, and features that are unique to the programs.

Open-File Report↗

USGS2011

GLORIA II sonograph mosaic of the western U.S. Exclusive Economic Zone

In 1983 the United States declared sovereign rights and jurisdiction over living and nonliving resources in an area extending 200 nautical miles (370 km) seaward from its shores. In response to the establishment of this Exclusive Economic Zone (EEZ), the U.S. Geological Survey (USGS) has implemented a program, called EEZ‐Scan, to systematically map the EEZ, using the Geological Long‐ Range Inclined ASDIC (GLORIA) II longrange side scan sonar system developed by the Institute of Oceanographic Sciences (IOS) of Great Britain [Somers et al, 1978]. The first part of the EEZ‐Scan field program was completed in the summer of 1984, when USGS and IOS scientists surveyed the EEZ off the western conterminous United States aboard the British research vessel Farnella (Figure 1). The west coast survey, requiring 96 days of ship time and four separate legs, has resulted in virtually total sonograph coverage of the sea floor from the continental shelf break to the 200‐nautical mile limit between the Mexican and Canadian borders, an area of about 850,000 km 2 . Other data collected on the cruises included two‐channel digital seismic reflection and 3.5‐kHz highresolution and 10‐kHz bathymetric profiles, as well as towed magnetometer data along approximately 20,000 km of trackline spaced nominally at 30‐km intervals.

Western U.S. Exclusive Economic Zone↗

USGS2020

Benthic infaunal communities of Baltimore and Norfolk Canyons

The imperative for finding, cataloging, and understanding continental margin diversity derives from the many key functions, goods and services provided by margin ecosystems and by an increasingly deleterious human footprint on our continental slopes (Levin and Dayton 2009). Progress in seafloor mapping technology and direct observation has revealed unexpected heterogeneity, with a mosaic of habitats and ecosystems linked to geomorphological, geochemical, and hydrographic features that are capable of influencing biotic diversity (Levin and Sibuet 2012). Submarine canyons are dramatic and widespread topographic features crossing continental and island margins in oceans, connecting shelf-margins to deep ocean basins (Harris and Whiteway 2011). Their importance as biodiversity hotspots has continued to emerge over the last two decades as research efforts have increased. Understanding the physical parameters within a canyon system is a primary factor for understanding habitat variability and ecological patterns within the confines of canyon systems (Levin et al. 2001). Margin sediments exhibit ubiquitous depth zonation (Carney et al. 2005), with a diverse suite of species that occupy restricted bathymetric ranges along any given section of the margin. Major shifts in composition among taxa are observed at the shelf-slope transition zone (canyons <500 m), along the upper slope (1,000 m), and at the lower slope transition zone (<3,000 m) (Gibson et al. 2005). In the deep sea, macrofaunal assemblages are generally limited by the availability of allochthonous organic material (Rowe et al. 1982, Billet et al. 1983, Rex et al. 2005, Smith et al. 2008) where macrofaunal densities usually decline with depth and distance from the shore (Rowe et al. 1982, Houston and Haedrich 1984, Rex et al. 2005). However, canyon fauna can experience enhanced food supply through the resuspension and deposition of organic-rich sediments, delivered by increased current velocities within the confines of the canyon (Rowe 1971, Shepard et al. 1974). As a result, canyons are often reported as sustaining enhanced abundances and biomass compared with nearby open slope habitats at similar depths (Vetter and Dayton 1998, Duineveld et al. 2001, De Leo et al. 2010) as well as enhancing regional (γ) and local (α) biodiversity (Hecker et al. 1983, Vetter and Dayton 1998, De Leo et al. 2010, Vetter et al. 2010). Furthermore, enhanced habitat heterogeneity can also be a major structuring agent of ecological assemblages, promoting beta (β) diversity (McClain and Barry 2010) in canyon environments. Canyon systems have often been described as biodiversity hotspots, especially at mid-slope depths (Levin and Sibuet 2012) where physical processes, characterized by complex patterns in hydrography, promote topographically induced upwelling, enhanced mixing via internal tides, and the focusing of tidal bores (Vetter and Dayton 1998, Cacchione et al. 2002). Additionally, sediment transport and accumulation (García et al. 2008) represent important influential ecological drivers. Factors such as substrata heterogeneity (Levin and Sibuet 2012) and concentration of organic matter (De Leo et al. 2010) have been suggested to explain higher faunal diversity, abundance, and benthic productivity found in canyon systems compared with surrounding areas. Bathymetric patterns of species diversity have been attributed to changes in sediment characteristics (Etter and Grassle 1992), productivity, currents, oxygen, disturbance, and the interplay of biotic effects with depth and latitude (Levin et al. 2001, Carney et al. 2005). Recent studies report on the uniqueness of canyon benthic communities and habitats and the view that no two canyons are alike (Cunha et al. 2011). Certain submarine canyons may maintain 436 characteristic and unique faunas, but more often canyon macrofaunal assemblages show high dominance and locally reduced biodiversity (Rowe 1971, Gage 1997, Curdia et al. 2004, Cun

Baltimore Canyon, Norfolk Canyon↗

USGS2006

Gas hydrate potential of the mid Atlantic outer continental shelf

For the last two years, the Minerals Management Service (MMS) has been studying the resource potential of gas hydrates in federal offshore lands of the Outer Continental Shelf (OCS) off the Atlantic, Gulf of Mexico, Pacific, and Alaska in collaboration with the U.S. Geological Survey (USGS), the Department of Energy (DOE), the National Oceanic and Atmospheric Administration (NOAA), the Naval Research Lab (NRL) and academia. Utilizing its extensive seismic, well, and geochemical databases, the MMS will be reporting the in-place resource numbers within the next few months. Though the methodology of the study was not prospect oriented, discrete prospects have been recognized.

Fire in the Ice: NETL Methane Hydrate Newsletter↗

USGS2012

An instrument system for long-term sediment transport studies on the continental shelf

A bottom-mounted instrument system has been designed and built to monitor processes of bottom sediment movement on the continental shelf. The system measures bottom current speed and direction, pressure, temperature, and light transmission and photographs the bottom. The system can be deployed for periods of 2–6 months to monitor intermitent processes of sediment movement such as storms and to assess seasonal variability. Deployments of the system on the U.S. east coast continental shelf show sediment resuspension and changes in bottom microtopography due to surface waves, tidal currents, and storms.

Journal of Geophysical Research: Oceans↗

USGS2012

Tectonic history of the north portion of the San Andreas fault system, California, inferred from gravity and magnetic anomalies

Geologic and geophysical data for the San Andreas fault system north of San Francisco suggest that the eastern boundary of the Pacific plate migrated eastward from its presumed original position at the base of the continental slope to its present position along the San Andreas transform fault by means of a series of eastward jumps of the Mendocino triple junction. These eastward jumps total a distance of about 150 km since 29 Ma. Correlation of right-laterally displaced gravity and magnetic anomalies that now have components at San Francisco and on the shelf north of Point Arena indicates that the presently active strand of the San Andreas fault north of the San Francisco peninsula formed recently at about 5 Ma when the triple junction jumped eastward a minimum of 100 km to its present location at the north end of the San Andreas fault. Prior to 5 Ma the triple junction was located at the north end of a proposed northwesterly extension of the Pilarcitos fault. This jump took place at what is now about latitude 38°20′N on the North American plate and may have occurred during part of the time when the relative motion between the North American and Pacific plates rotated 20° clockwise, resulting in transpression along the earlier transcurrent San Andreas fault system. The proposed 150-km eastward movement of the triple junction explains the submarine topography near Cape Mendocino where the continental shelf south of the Mendocino fault extends about 130 km farther west than does the shelf directly north of the fault.

Journal of Geophysical Research Solid Earth↗

USGS2006

usSEABED: Gulf of Mexico and Caribbean (Puerto Rico and U.S. Virgin Islands) offshore surficial sediment data release

Over the past 50 years there has been an explosion in scientific interest, research effort and information gathered on the geologic sedimentary character of the United States continental margin. Data and information from thousands of publications have greatly increased our scientific understanding of the geologic origins of the shelf surface but rarely have those data been combined and integrated. This publication is the first release of the Gulf of Mexico and Caribbean (Puerto Rico and U.S. Virgin Islands) coastal and offshore data from the usSEABED database. The report contains a compilation of published and previously unpublished sediment texture and other geologic data about the sea floor from diverse sources. usSEABED is an innovative database system developed to bring assorted data together in a unified database. The dbSEABED system is used to process the data. Examples of maps displaying attributes such as grain size and sediment color are included. This database contains information that is a scientific foundation for the USGS Marine Aggregate Resources and Processes Assessment and Benthic Habitats projects, and will be useful to the marine science community for other studies of the Gulf of Mexico and Caribbean continental margins. This publication is divided into ten sections: Home, Introduction, Content, usSEABED (data), dbSEABED (processing), Data Catalog, References, Contacts, Acknowledgments and Frequently Asked Questions. Use the navigation bar on the left to navigate to specific sections of this report. Underlined topics throughout the publication are links to more information. Links to specific and detailed information on processing and those to pages outside this report will open in a new browser window.

Caribbean Sea, Gulf of Mexico↗

USGS2001

The STRATAFORM Project: U.S. Geological Survey geotechnical studies

This report presents physical property logs of core samples from an offshore area near Eureka, CA. The cores were obtained as part of the STRATAFORM Program (Nittrouer and Kravitz, 1995, 1996), a study investigating how present sedimentation and sediment transport processes influence long-term stratigraphic sequences preserved in the geologic record. The core samples were collected during four separate research cruises to the northern California study area, and data shown in the logs of the cores were collected using a multi-sensor whole core logger. The physical properties collected are useful in identifying stratigraphic units, ground-truthing acoustic imagery and sub-bottom profiles, and in understanding mass movement processes. STRATA FOR mation on M argins was initiated in 1994 by the Office of Naval Research, Marine Geology and Geophysics Department as a coordinated multi-investigator study of continental-margin sediment transport processes and stratigraphy (Nittrouer and Kravitz, 1996). The program is investigating the stratigraphic signature of the shelf and slope parts of the continental margins, and is designed to provide a better understanding of the sedimentary record and a better prediction of strata. Specifically, the goals of the STRATAFORM Program are to (Nittrouer and Kravitz, 1995): - determine the geological relevance of short-term physical processes that erode, transport, and deposit particles and those processes that subsequently rework the seabed over time scales <10 2 years. - improve capabilities for identifying the processes that form the strata observed within the upper ~100 m of the seabed commonly representing 104-106 years of sedimentation. - synthesize this knowledge and bridge the gap between time scales of sedimentary processes and those of sequence stratigraphy. The STRATAFORM Program is divided into studies of the continental shelf and the continental slope; the geotechnical group within the U.S. Geological Survey provides support to both parts of the project.

California↗