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At least 469 records · Page 26Linked to original sources
USGS1976

Geologic appraisal of the petroleum potential of offshore southern California; the borderland compared to onshore coastal basins

Offshore southern California is part of a much larger Pacific continental margin, and the two areas have a similar geologic history at least as far back as middle Tertiary time. Assessment of the petroleum potential of the offshore Southern California borderland is accomplished by examining the adjacent highly explored productive coastal basins in the tectonically unstable area west of the San Andreas fault. Known oil and gas accumulations in this region can be characterized as follows: 88 percent comes from the Los Angeles and Ventura basins; 87 percent has been found in late Miocene and younger strata and only 0.2 percent has been found in Eocene strata; 80 percent has been found in thick deposits of deep-water turbidite reservoirs; and 5 percent has been found in fractured Miocene siliceous shale reservoirs. The percentage of siliceous shale reservoirs will increase as a result of recent discoveries in this rock type in the Santa Barbara Channel. Of the 212 known fields only 5 are giants (greater than 500 million barrels), and these fields account for 52 percent of all past production from the region. Most fields are faulted anticlines, and the largest fields have the highest oil recoveries per acre. Geologic knowledge of the offshore is limited by the availability of data. Data have been obtained from geophysical surveys, analyses of bedrock samples from the sea floor, and extrapolations of data from the mainland and offshore islands. Several factors have a negative effect on the assessment of the petroleum potential of the southern California borderland. They are: 1. The Neogene section is relatively thin, and the Paleogene section is thin and has a limited distribution. 2. Over large areas, Miocene sediments apparently rest directly on basement. 3. Along much of the Santa Rosa-Cortes Ridge, sediments are uplifted and truncated, exposing Paleogene rocks. 4. Organic content in Paleogene sediments is believed too low to generate large amounts of petroleum. 5. Source rocks are immature, even in sediments as old as Eocene. 6. Burial and thermal history are insufficient for the generaton of hydrocarbons over much of the borderland area. 7. Documented oil and gas seeps are unknown seaward of the Channel Islands. 8. Limited exploratory drilling nearshore, the best prospective area, has not been favorable. 9. Adequate or thick reservoirs of deep-water turbidire origin are not evident. These negative factors are partly offset by the following positive factors: 1. Miocene sediments are excellent potential source rocks. 2. Asphaltic oil in rocks of Monterey-type lithology may be generated at lower than normal temperatures. 3. Shallow-water sands of reservoir quality possibly are present in the uppermost Paleogene and lowermost Neogene section. 4. Potential structural traps may be analogous to major structural producing trends onshore. 5. Fractured shale reservoirs may be present along flanks of major banks and ridges. 6. Buried and unsampled Paleogene and Late Cretaceous sediments may be better source rocks than those sampled and measured. The southern California borderland, although a part of a locally rich petroliferous region, has no known basins with geologic histories or characteristics similar to the Los Angeles and Ventura basins. Some offshore basins are similar to less endowed basins in terms of petroleum potential such as the Santa Maria and Salinas basins. Areas with the best petroleum potential may be in deep water (greater than 500 m). Some of the past high estimates of the petroleum potential may have been overstated; the existing geologic data tend to substantiate low estimates of 0.6 to 5.8 billion barrels of oil and 0.6 to 5.8 trillion ft3 of gas for the southern California borderland at the 5 and 95 percent probability level.

Circular↗
USGS1979

Initial report of the Petrophysics Laboratory

Current national requirements for energy and mineral resources, and for protection of the quality of the environment, have focused attention on the need to develop new methods and interpretation techniques to be used in understanding geologic systems. Geophysical surveys play a significant role in acquiring this information, particularly by providing data in the third dimension--at depth beneath the surface.

Circular↗
USGS1986

The Conterminous United States Mineral Assessment Program; background information to accompany folio of geologic, geophysical, geochemical, mineral-occurrence, mineral-resource potential, and mineral-production maps of the Charlotte 1 degree x 2 degrees Quadrangle, North Carolina and South Carolina

This Circular and the folio of separately published maps described herein are part of a series of reports compiled under the Conterminous United States Mineral Assessment Program ICUSMAP). The folio on the Charlotte 1 degree ? 2 degree quadrangle, North Carolina and South Carolina, includes (1) a geologic map; (2) four geophysical maps; (3) geochemical maps for metamorphic heavy minerals, copper, lead and artifacts, zinc, gold, tin, beryllium, niobium, tungsten, molybdenum, titanium, cobalt, lithium, barium, antimony-arsenic-bismuth-cadmium, thorium-cerium-monazite, and limonite; (4) mineral-occurrence maps for kyanite-sillimanite-lithium-mica-feldspar-copper-lead-zinc, gold-quartz-barite-fluorite, iron-thorium-tin-niobium, and construction materials-gemstones; (5) mineral-resource potential maps for copper-lead-zinc-combined base metals, gold, tin-tungsten, beryllium-molybdenum-niobium, lithium-kyanite- sillimanitebarite, thorium (monazite)-uranium, and construction materials; and (6) mineral-production maps. The Charlotte quadrangle is mainly within the Piedmont physiographic province and extends from near the Coastal Plain on the southeast into the Blue Ridge province on the northwest for a short distance. Parts of six lithotectonic belts are present--the Blue Ridge, the Inner Piedmont, the Kings Mountain belt, the Charlotte belt, the Carolina slate belt, and the Wadesboro basin. Igneous, metamorphic, and sedimentary rocks are present and range in age from Proterozoic to Mesozoic; alluvial sediments of Quaternary age occur along rivers and larger streams. Rocks of the Blue Ridge include Middle Proterozoic granitoid gneiss intruded by Late Proterozoic granite; Late Proterozoic paragneiss, schist, and other metasedimentary and metavolcaniclastic rocks (Ashe and Grandfather Mountain Formations); Late Proterozoic and Early Cambrian metasedimentary rocks (Chilhowee Group); and Early Cambrian sedimentary rocks (Shady Dolomite). Paleozoic granites intrude the Proterozoic rocks. The Inner Piedmont contains noncarbonate metasedimentary rocks and amphibolite of medium to high metamorphic grades. These rocks are intruded by the Toluca Granite and Henderson Gneiss of Cambrian and Ordovician(?) age. The Charlotte belt consists largely of Late Proterozoic to Late Paleozoic granitic and gabbroic plutonic rocks and intervening enclaves of metasedimentary and metavolcanic rocks. The narrow Kings Mountain belt is located between the Charlotte and the Inner Piedmont belts and contains mainly Late Proterozoic metasedimentary rocks and plutonic rocks similar to those of the Charlotte belt. The Carolina slate belt, flanking the Charlotte belt on the east, contains weakly metamorphosed volcanic and sedimentary rocks. East of this belt, at the southeast corner of the quadrangle, is the Wadesboro basin, which has continental sedimentary rocks of Triassic age. Layered rocks westward from and in the Charlotte belt are complexly folded, are steeply dipping, and in the Blue Ridge and Inner Piedmont are contained within major thrust slices. Rocks of the Carolina slate belt are gently folded. Rocks of the Wadesboro basin occur in downfaulted blocks. The geophysical surveys of the Charlotte quadrangle consisted of Bouguer gravity, aeromagnetic, and aeroradioactivity surveys and used both newly obtained data and information from prior work. The gravity survey disclosed a distinct northeast-trending, northwest-decreasing gradient, which is part of the major gravity gradient that extends the length of the Appalachian Mountains. Granitic plutons of the Charlotte belt, in particular, are marked by gravity lows, and gabbro plutons, by highs. Several of the geologic belts display distinct magnetic character. The aeroradioactivity surveys showed a swath of consistently high gamma-ray intensities along the central part of the Inner Piedmont belt; these high intensities correspond to the so-called monazite belt. Oval patterns of high gamma-ray readi

Circular↗
USGS2008

Continuous Temperature and Water-Level Data Collected for a Heat Tracer Study on a Selected Reach of Tri-State Canal, Western Nebraska, 2007

The water supply in parts of the North Platte River Basin in the Nebraska Panhandle has been designated as fully appropriated or over appropriated by the Nebraska Department of Natural Resources. Recent legislation (LB 962) requires the North Platte Natural Resources District and the Nebraska Department of Natural Resources to develop an Integrated Management Plan to balance ground- and surface-water supply and demand within the North Platte Natural Resources District. For a ground-water-flow model to accurately simulate existing or future ground-water and surface-water conditions, accurate estimates of specific input variables such as streambed conductance or canal-seepage rates are required. As of 2008, the values input into ground-water models were estimated on the basis of interpreted lithology from test holes and geophysical surveys. Often, contrasts of several orders of magnitude exist for streambed conductance among the various sediment textures present locally, and thin, near-surface layers of fine sediment can clog the streambed, substantially reducing conductance. To accurately quantify the rates of leakage from irrigation canals and estimate ground-water recharge, the U.S. Geological Survey, in cooperation with the North Platte Natural Resources District, collected continuous temperature and water-level data to use heat as a tracer for a selected reach of Tri-State Canal west of Scottsbluff, Nebraska. Continuous records of subsurface temperature, ground-water level, canal stage, and water temperature, and sediment core data are presented in this report. Subsurface temperature was monitored at four vertical sensor arrays of thermocouples installed at various depths beneath the canal bed from March through September 2007. Canal stage and water temperature were measured from June to September 2007. Ground-water level was recorded continuously in an observation well drilled near the subsurface temperature monitoring site. These data sets were collected for use as inputs for a computer model to estimate the vertical hydraulic conductivity. Before the initiation of flow, diurnal variations in subsurface temperature occurred because of daytime heating and nighttime cooling of bed sediment. Flow in Tri-State Canal was first detected on June 16 at the monitoring site as a disruption in the temperature signal in the shallowest thermocouple in all four vertical sensor arrays. This disruption in the temperature pattern occurred in deeper thermocouples at slightly later times during the rapid infiltration of canal water. The ground-water level began to rise approximately 23 hours after flow was first detected at the monitoring site. Canal stage rose for 7 days until the maximum flow capacity of the canal was approached on June 23, 2007. Measured water temperatures ranged from 18 to 25 degrees Celsius (C) while the canal was flowing near maximum capacity. Small diurnal variations of 1.0 to 1.5 degrees C in water temperature were recorded during this time. Measured ground-water levels rose constantly during the entire irrigation season until levels peaked on September 3, 2007, 3 days after diversions to Tri-State Canal ceased.

Data Series↗
USGS2015

Seismic data collection from water gun and industrial background sources in the Chicago Sanitary and Ship Canal area, Illinois, 2011

The water gun is a tool adapted from deep marine geophysical surveys that is being evaluated for use as an acoustic fish deterrent to control the movement of invasive marine species. The water gun creates a seismic signal by using a compressed air discharge to move a piston rapidly within the water, resulting in an implosion. This energy pulse may be able to modify fish behavior or destroy marine life, such as the Asian carp, at some distance. The effects of this energy pulse on structures in the Chicago Sanitary and Ship Canal (CSSC), such as canal walls, shore lines, and lock structures, are not known. The potential effects of the use of a water gun on structures was identified as a concern in the CSSC and was assessed relative to existing background sources during this study. During September 2011, two water guns with piston sizes of 80 and 343 cubic inches, respectively, were tested in the CSSC at varying pressures and distances from a canal wall consisting of dolomite and dolomite setblock. Seismic data were collected during these water gun firings using geophones on land, in boreholes, and at the canal wall interface. Data were collected at varying depths in the canal water using hydrophones. Seismic data were also collected during the occurrences of barge traffic, railroad traffic located near the electric fish barrier in Lemont, and coal-loading operations at a coal power plant near the electric fish barrier. In general, energy produced by barge and railroad sources was less than energy created by the water gun. Energy levels produced by coal-loading operations at least 200 feet from geophones were approximately four times lower than energy levels measured during water gun operations.

Illinois↗
USGS1996

Airborne hunt for faults in the Portland-Vancouver area

Geologic hazards in the Portland-Vancouver area include faults entirely hidden by river sediments, vegetation, and urban development. A recent aerial geophysical survey revealed patterns in the Earth's magnetic field that confirm the existence of a previously suspected fault running through Portland. It also indicated that this fault may pose a significant seismic threat. This discovery has enabled the residents of the populous area to better prepare for future earthquakes.

Fact Sheet↗
USGS1997

On the watch for geomagnetic storms

Geomagnetic storms, induced by solar activity, pose significant hazards to satellites, electrical power distribution systems, radio communications, navigation, and geophysical surveys. Strong storms can expose astronauts and crews of high-flying aircraft to dangerous levels of radiation. Economic losses from recent geomagnetic storms have run into hundreds of millions of dollars. With the U.S. Geological Survey (USGS) as the lead agency, an international network of geomagnetic observatories monitors the onset of solar-induced storms and gives warnings that help diminish losses to military and commercial operations and facilities.

Fact Sheet↗
USGS2007

Geohydrologic Framework of the Edwards and Trinity Aquifers, South-Central Texas

This five-year USGS project, funded by the National Cooperative Geologic Mapping Program, is using multidisciplinary approaches to reveal the surface and subsurface geologic architecture of two important Texas aquifers: (1) the Edwards aquifer that extends from south of Austin to west of San Antonio and (2) the southern part of the Trinity aquifer in the Texas Hill Country west and south of Austin. The project's principal areas of research include: Geologic Mapping, Geophysical Surveys, Geochronology, Three-dimensional Modeling, and Noble Gas Geochemistry. The Edwards aquifer is one of the most productive carbonate aquifers in the United States. It also has been designated a sole source aquifer by the U.S. Environmental Protection Agency and is the primary source of water for San Antonio, America's eighth largest city. The Trinity aquifer forms the catchment area for the Edwards aquifer and it intercepts some surface flow above the Edwards recharge zone. The Trinity may also contribute to the Edwards water budget by subsurface flow across formation boundaries at considerable depths. Dissolution, karst development, and faulting and fracturing in both aquifers directly control aquifer geometry by compartmentalizing the aquifer and creating unique ground-water flow paths.

Fact Sheet↗
USGS2015

Chesapeake Bay impact structure: A blast from the past

About 35 million years ago, a 2-mile-wide meteorite smashed into Earth in what is now the lower Chesapeake Bay in Virginia. The oceanic impact vaporized, melted, fractured, and displaced rocks and sediments and sent billions of tons of water, sediments, and rocks into the air. Glassy particles of solidified melt rock rained down as far away as Texas and the Caribbean. Large tsunamis affected most of the North Atlantic basin. The resulting impact structure is more than 53 miles wide and has a 23-mile-wide, filled central crater surrounded by collapsed sediments. Now buried by hundreds of feet of younger sediments, the Chesapeake Bay impact structure is among the 20 largest known impact structures on Earth. Since its discovery in the early 1990s, scientists have conducted deep drilling and geophysical surveys of the impact structure to find out more about its size, composition, structure, age, and biological effects and to understand its lingering influences on the regional groundwater system. These efforts culminated in the drilling of a 1-mile-deep, continuously sampled corehole in 2005 by an international group of scientists and agencies.

Chesapeake Bay↗
USGS1988

Heavy-Mineral Placer Potential Map of the U.S. Continental Shelf, Western and Northern Gulf of Mexico

The establishment of the Exclusive Economic Zone (EEZ) in 1983 by Presidential Proclamation opened for natural resource exploration a vast offshore frontier area contiguous to the United States and its territories. The EEZ extends from the seaward limit of state waters (3 nautical mi from shore) to 200 nautical mi offshore, and it includes the continental shelves. Within the context of the EEZ natural resource assessment effort, the purpose of this study is to delineate, on a regional basis, the potential for heavy-mineral placers on the U.S. Continental Shelf in the western and northern Gulf of Mexico from the United States-Mexico border to the Alabama-Florida state line. This map is intended to serve as a general guide for placer exploration. It shows favorable sea-floor areas for placer occurrence in water depths ranging from 0 to 100 fathoms (600 ft). The map can be used as a guide for focusing costly exploratory efforts, such as coring operations and geophysical surveys. The potential economic value of heavy-mineral placer concentrations on the U.S. Continental Shelf is a function of both geologic and economic variables. Geologic variables include the composition and concentration of the heavy-mineral assemblages and their environment of deposition. Economic variables include the current world market price of extracted metals, as well as the cost of mining, processing, and marketing the metals. These economic factors, in turn, are tempered by the nation1s socio-political climate, which determines its need for specific mineral resources at any given time.

Miscellaneous Field Studies Map↗
USGS2007

Airborne geophysics as a tool for geoscientific research in Antarctica: some recent examples

The polar regions play an important role in Earth's geodynamic and climatic systems. Modern airborne geophysical surveys combine radio-echo sounding, aeromagnetic and aerogravity methods to explore the geology of these regions. This paper reviews some recent aerogeophysical investigations undertaken by the British Antarctic Survey to: 1) Image subglacial rifts of Jurassic age in western Dronning Maud Land, which were associated with early Gondwana break-up; 2) Investigate crustal growth over the Antarctic Peninsula by Cretaceous arc magmatism and terrane accretion along the paleo-Pacific margin of Gondwana; 3) Analyse geological boundary conditions for presentday ice dynamics over Coats Land.

Open-File Report↗
USGS2007

Technical-information products for a National Volcano Early Warning System

Technical outreach — distinct from general-interest and K-12 educational outreach — for volcanic hazards is aimed at providing usable scientific information about potential or ongoing volcanic activity to public officials, businesses, and individuals in support of their response, preparedness, and mitigation efforts. Within the context of a National Volcano Early Warning System (NVEWS) (Ewert et al., 2005), technical outreach is a critical process, transferring the benefits of enhanced monitoring and hazards research to key constituents who have to initiate actions or make policy decisions to lessen the hazardous impact of volcanic activity. This report discusses recommendations of the Technical-Information Products Working Group convened in 2006 as part of the NVEWS planning process. The basic charge to the Working Group was to identify a web-based, volcanological "product line" for NVEWS to meet the specific hazard-information needs of technical users. Members of the Working Group were: Marianne Guffanti (Chair), USGS, Reston VA Steve Brantley, USGS, Hawaiian Volcano Observatory HI Peter Cervelli, USGS, Alaska Volcano Observatory, Anchorage AK Chris Nye, Division of Geological and Geophysical Surveys and Alaska Volcano Observatory, Fairbanks AK George Serafino, National Oceanic and Atmospheric Administration, Camp Springs MD Lee Siebert, Smithsonian Institution, Washington DC Dina Venezky, USGS, Volcano Hazards Team, Menlo Park CA Lisa Wald, USGS, Earthquake Hazards Program, Golden CO

Open-File Report↗
USGS2014

Continuous resistivity profiling and seismic-reflection data collected in April 2010 from Indian River Bay, Delaware

A geophysical survey to delineate the fresh-saline groundwater interface and associated sub-bottom sedimentary structures beneath Indian River Bay, Delaware, was carried out in April 2010. This included surveying at higher spatial resolution in the vicinity of a study site at Holts Landing, where intensive onshore and offshore studies were subsequently completed. The total length of continuous resistivity profiling (CRP) survey lines was 145 kilometers (km), with 36 km of chirp seismic lines surveyed around the perimeter of the bay. Medium-resolution CRP surveying was performed using a 50-meter streamer in a baywide grid. Results of the surveying and data inversion showed the presence of many buried paleochannels beneath Indian River Bay that generally extended perpendicular from the shoreline in areas of modern tributaries, tidal creeks, and marshes. An especially wide and deep paleochannel system was imaged in the southeastern part of the bay near White Creek. Many paleochannels also had high-resistivity anomalies corresponding to low-salinity groundwater plumes associated with them, likely due to the presence of fine-grained estuarine mud and peats in the channel fills that act as submarine confining units. Where present, these units allow plumes of low-salinity groundwater that was recharged onshore to move beyond the shoreline, creating a complex fresh-saline groundwater interface in the subsurface. The properties of this interface are important considerations in construction of accurate coastal groundwater flow models. These models are required to help predict how nutrient-rich groundwater, recharged in agricultural watersheds such as this one, makes its way into coastal bays and impacts surface-water quality and estuarine ecosystems.

Delaware↗
USGS2013

Methods and spatial extent of geophysical Investigations, Mono Lake, California, 2009 to 2011

This report summarizes the methods and spatial extent of geophysical surveys conducted on Mono Lake and Paoha Island by U.S. Geological Survey during 2009 and 2011. The surveys include acquisition of new high resolution seismic reflection data, shipborne high resolution magnetic data, and ground magnetic and gravity data on Paoha Island. Several trials to acquire swath bathymetry and side scan sonar were conducted, but were largely unsuccessful likely due to physical properties of the water column and (or) physical properites of the highly organic bottom sediment.

California↗
USGS2014

Chirp seismic-reflection data from the Baltimore, Washington, and Norfolk Canyons, U.S. mid-Atlantic margin

A large number of high-resolution geophysical surveys between Cape Hatteras and Georges Bank have been conducted by federal, state, and academic institutions since the turn of the century. A major goal of these surveys is providing a continuous view of bathymetry and shallow stratigraphy at the shelf edge in order to assess levels of geological activity during the current sea level highstand. In 2012, chirp seismic-reflection data was collected by the U.S. Geologial Survey aboard the motor vessel Tiki XIV near three United States mid-Atlantic margin submarine canyons. These data can be used to further our understanding of passive continental margin processes during the Holocene, as well as providing valuable information regarding potential submarine geohazards.

Mid-atlantic Margin↗
USGS2016

GIS-based identification of areas that have resource potential for critical minerals in six selected groups of deposit types in Alaska

Alaska has considerable potential for undiscovered mineral resources. This report evaluates potential for undiscovered critical minerals in Alaska. Critical minerals are those for which the United States imports more than half of its total supply and which are largely derived from nations that cannot be considered reliable trading partners. In this report, estimated resource potential and certainty for the state of Alaska are analyzed and mapped for the following six selected mineral deposit groups that may contain one or more critical minerals: (1) rare earth elements-thorium-yttrium-niobium(-uranium-zirconium) [REE-Th-Y-Nb(-U-Zr)] deposits associated with peralkaline to carbonatitic igneous intrusive rocks; (2) placer and paleoplacer gold (Au) deposits that in some places might also produce platinum group elements (PGE), chromium (Cr), tin (Sn), tungsten (W), silver (Ag), or titanium (Ti); (3) platinum group elements(-cobalt-chromium-nickel-titanium-vanadium) [PGE(-Co-Cr-Ni-Ti-V)] deposits associated with mafic to ultramafic intrusive rocks; (4) carbonate-hosted copper(-cobalt-silver-germanium-gallium) [Cu(-Co-Ag-Ge-Ga)] deposits; (5) sandstone-hosted uranium(-vanadium-copper) [U(-V-Cu)] deposits; and (6) tin-tungsten-molybdenum(-tantalum-indium-fluorspar) [Sn-W-Mo(-Ta-In-fluorspar)] deposits associated with specialized granites. This study used a data-driven, geographic information system (GIS)-implemented method to identify areas that have mineral resource potential in Alaska. This method systematically and simultaneously analyzes geoscience data from multiple geospatially referenced datasets and uses individual subwatersheds (12-digit hydrologic units) as the spatial unit of classification. The final map output uses a red, yellow, green, and gray color scheme to portray estimated relative potential (High, Medium, Low, Unknown) for each of the six groups of mineral deposit types, and it indicates the relative certainty (High, Medium, Low) of that estimate for each 12-digit hydrologic unit through color shading. Accompanying tables describe the data layers employed to score favorability for the presence of each mineral deposit group, the values assigned for specific analysis parameters, and the relative weighting of each data layer that contributes to estimated measures of potential and certainty . Core datasets used include the Alaska Geochemical Database, Version 2.0 (AGDB2); the Alaska Division of Geological & Geophysical Surveys (ADGGS) web-based geochemical database; the digital “Geologic Map of Alaska;” the Alaska Resource Data File (ARDF); and aerial gamma-ray surveys flown as part of the National Uranium Resource Evaluation (NURE) Program by the U.S. Department of Energy. Maps accompanying this report illustrate the scores for estimated mineral resource potential for the six deposit groups for the state of Alaska. Areas that have known potential, as well as new areas that were not previously known to have potential, for the targeted minerals and deposit groups are identified and described. Numerous areas in Alaska, some of them large, have high potential for one or more of the selected groups of deposit types within Alaska. Contributors Matthew Granitto, Timothy S. Hayes, James V. Jones, III, Susan M. Karl, Keith A. Labay, Jeffrey L. Mauk, Jeanine M. Schmidt, Nora B. Shew, Erin Todd, Bronwen Wang, Melanie B. Werdon, and Douglas B. Yager

Alaska↗
USGS2017

Nearshore sediment thickness, Fire Island, New York

Investigations of coastal change at Fire Island, New York (N.Y.), sought to characterize sediment budgets and determine geologic framework controls on coastal processes. Nearshore sediment thickness is critical for assessing coastal system sediment availability, but it is largely unquantified due to the difficulty of conducting geological or geophysical surveys across the nearshore. This study used an amphibious vessel to acquire chirp subbottom profiles. These profiles were used to characterize nearshore geology and provide an assessment of nearshore sediment volume. Two resulting sediment-thickness maps are provided: total Holocene sediment thickness and the thickness of the active shoreface. The Holocene sediment section represents deposition above the maximum flooding surface that is related to the most recent marine transgression. The active shoreface section is the uppermost Holocene sediment, which is interpreted to represent the portion of the shoreface thought to contribute to present and future coastal behavior. The sediment distribution patterns correspond to previously defined zones of erosion, accretion, and stability along the island, demonstrating the importance of sediment availability in the coastal response to storms and seasonal variability. The eastern zone has a thin nearshore sediment thickness, except for an ebb-tidal deposit at the wilderness breach caused by Hurricane Sandy. Thicker sediment is found along a central zone that includes shoreface-attached sand ridges, which is consistent with a stable or accretional coastline in this area. The thickest overall Holocene section is found in the western zone of the study, where a thicker lower section of Holocene sediment appears related to the westward migration of Fire Island Inlet over several hundred years.

New York↗