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USGS2025

Revised marine bird collision and displacement vulnerability index for U.S. Pacific Outer Continental Shelf offshore wind energy development

The installation of offshore wind energy infrastructure (OWEI) at sea may affect marine birds by increasing the risk of mortality from collision with OWEI (Collision Vulnerability) and causing disturbance and displacement from important habitats (Displacement Vulnerability). In 2017, we published the first comprehensive database quantifying marine bird Collision Vulnerability and Displacement Vulnerability to potential OWEI in the region of the U.S. Pacific Outer Continental Shelf (POCS; waters within the Exclusive Economic Zone of California, Oregon, and Washington). We have updated this Vulnerability Index with new research and data, additional species present in the POCS, and an evolved understanding of the application and utility of the Index. Of the species assessed, phalaropes and Red-billed Tropicbird have the highest Collision Vulnerability, and gulls, terns, jaegers, skuas, and pelicans have moderately high Collision Vulnerability. Boobies, sea ducks, and pelicans have the greatest Displacement Vulnerability. The overall trends in ranked Vulnerability among marine birds in the POCS were consistent between Version 1 and Version 2 although new data and revised calculations updated the outcomes. Alcids, loons, storm-petrels, Brant, and phalaropes ranked higher for Collision Vulnerability in Version 2 compared to Version 1; sea ducks, cormorants, skua, and jaegers ranked lower for Collision Vulnerability in Version 2 compared to Version 1. Displacement Vulnerability ranks were higher in Version 2 for gulls, pelicans, sea ducks, and alcids and lower for albatrosses, terns, and loons. Vulnerability Index Version 2 is an up-to-date, representative, and transparent assessment of marine bird vulnerability to potential offshore wind energy development. This updated Vulnerability Index can assist resource managers and others in understanding and addressing potential interactions between OWEI and marine bird species that inhabit the POCS.

Data Report↗

USGS2013

Archive of digital boomer subbottom data collected during USGS cruises 99FGS01 and 99FGS02 offshore southeast and southwest Florida, July and November, 1999

In July (19 - 26) and November (17 - 18) of 1999, the USGS, in cooperation with the Florida Geological Survey (FGS), conducted two geophysical surveys in: (1) the Atlantic Ocean offshore of Florida's east coast from Orchid to Jupiter, FL, and (2) the Gulf of Mexico offshore of Venice, FL. This report serves as an archive of unprocessed digital boomer subbottom data, trackline maps, navigation files, GIS files, Field Activity Collection System (FACS) logs, and formal Federal Geographic Data Committee (FGDC) metadata. Filtered and gained (showing a relative increase in signal amplitude) digital images of the subbottom profiles are also provided. The USGS St. Petersburg Coastal and Marine Science Center (SPCMSC) assigns a unique identifier to each cruise or field activity. For example, identifiers 99FGS01 and 99FGS02 refer to field data collected in 1999 for cooperative work with the FGS. The numbers 01 and 02 indicate the data were collected during the first and second field activities for that project in that calendar year. Refer to http://walrus.wr.usgs.gov/infobank/programs/html/definition/activity.html for a detailed description of the method used to assign the field activity identification (ID).

Florida↗

USGS2015

Archive of sediment data from vibracores collected in 2010 offshore of the Mississippi barrier islands

In 2010, scientists from the U.S. Geological Survey St. Petersburg Coastal and Marine Science Center collected sediment cores from coastal waters offshore of the Mississippi barrier islands. With funding support from the Northern Gulf of Mexico (NGOM) Ecosystem Change and Hazard Susceptibility project, 65 subaqueous sediment cores were collected over an area of 480 square kilometers (km 2 ), from Ship Island to Petit Bois Island Pass, Mississippi, within the boundary of Gulf Islands National Seashore. This represents only a fraction of the total area encompassed by the NGOM project, which extends from Sabine Lake, Louisiana, to Perdido Bay, Alabama. The primary objectives of the NGOM project are to understand the evolution of coastal ecosystems on the northern gulf coast, the impact of human activities on these ecosystems, and the vulnerability of ecosystems and human communities to more frequent and intense hurricanes in the future. Selection of the core site locations was based on geophysical surveys conducted around the islands from 2008 to 2010. The surveys, using acoustic systems to image and interpret the nearsurface stratigraphy, were conducted to investigate the geologic controls on island evolution. This data series serves as an archive of sediment data collected from August to September 2010, offshore of the Mississippi barrier islands. Data products, including descriptive core logs, core photographs, results of sediment grain-size analyses, sample location maps, and geographic information system (GIS) data files with accompanying formal Federal Geographic Data Committee (FDGC) metadata can be downloaded from the data products and downloads page.

Mississippi↗

USGS2015

Archive of Sidescan Sonar and Swath Bathymetry Data Collected During USGS Cruise 13CCT04 Offshore of Petit Bois Island, Gulf Islands National Seashore, Mississippi, August 2013

In August of 2013, the U.S. Geological Survey conducted a geophysical survey offshore of Petit Bois Island, Mississippi. This effort was part of the U.S. Geological Survey Gulf of Mexico Science Coordination partnership with the U.S. Army Corps of Engineers to assist the Mississippi Coastal Improvements Program and the Northern Gulf of Mexico Ecosystem Change and Hazards Susceptibility Project, by mapping the shallow geologic stratigraphic framework of the Mississippi Barrier Island Complex. This geophysical survey will provide additional data necessary for scientists to define, interpret, and provide baseline bathymetry and seafloor habitat for this area, and to aid scientists in predicting future geomorphological changes of the islands with respect to climate change, storm impact, and sea-level rise. Furthermore, these data will provide information for barrier island restoration, particularly in Camille Cut, and protection for the historical Fort Massachusetts on Ship Island, Mississippi. The geophysical data were collected during one cruise ( USGS Field Activity Numbers 13CCT04 ) aboard the Research Vessel Tommy Munro offshore along the gulf side of Petit Bois Island, Gulf Islands National Seashore, Mississippi. Data were acquired with the following equipment: a Systems Engineering and Assessment, Ltd., SWATH plus interferometric sonar (468 kilohertz (kHz)), an EdgeTech 424 (4-24 kHz), an EdgeTech 525i chirp subbottom profiling system, and a Klein 3900 sidescan sonar system. This report serves as an archive of the processed interferometric swath bathymetry and sidescan sonar data. Geographic information system data products include an interpolated digital elevation model, an acoustic backscatter mosaic, trackline maps, and point data files. Additional files include error analysis maps, Field Activity Collection System logs, and formal Federal Geographic Data Committee metadata. NOTE: These data are scientific in nature and are not to be used for navigation. Any use of trade names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Mississippi↗

USGS1987

Map showing locations and statistical parameters of beach and offshore sand samples, Tutuila Island, American Samoa

In April 1985, sand samples were collected from many of the beaches on Tutuila Island, American Samoa, and in July 1985, three bays were surveyed using side-scan sonar and shallow seismic profiling. During that second trip, scuba divers collected sand samples from the surveyed areas. Dingler and others (1986) describes the study; this report presents the grain-size and composition data for the onshore and offshore sand samples. Locations of the onshore samples are plotted on the map of the island, which is reproduced from Normark and others (1985); locations of most of the offshore samples and side-scan sonar interpretations made during the study are plotted on enlargements (A and B, respectively) of Fagaitua and Nua-seetaga Bays. Lam Yuen (1981), U.S. Army Corps of Engineers (1980), and Sea Engineering Services Inc. (1980) provide additional information pertaining to the island's beaches.

Tutuila Island↗

USGS2003

Sandstone and shale compaction curves derived from sonic and gamma ray logs in offshore wells, North Slope, Alaska– Parameters for basin modeling

Representative compaction curves for the principle lithologies are essential input for reliable models of basin history. Compaction curves influence estimates of maximum burial and erosion. Different compaction curves may produce significantly different thermal histories. Default compaction curves provided by basin modeling packages may or may not be a good proxy for the compaction properties in a given area. Compaction curves in the published literature span a wide range, even within one lithology, e.g., sandstone (see Panel 3). An abundance of geophysical well data for the North Slope, from both government and private sources, provides us with an unusually good opportunity to develop compaction curves for the Cretaceous-Tertiary Brookian sandstones, siltstones, and shales. We examined the sonic and gamma ray logs from 19 offshore wells (see map), where significant erosion is least likely to have occurred. Our data are primarily from the Cretaceous-Tertiary Brookian sequence and are less complete for older sequences. For each well, the fraction of shale (Vsh) at a given depth was estimated from the gamma ray log, and porosity was computed from sonic travel time. By compositing porosities for the near-pure sand (Vsh<1%) and shale (Vsh>99%)from many individual wells we obtained data over sufficient depth intervals to define sandstone and shale 'master' compaction curves. A siltstone curve was defined using the sonic-derived porosities for Vsh values of 50%. These compaction curves generally match most of the sonic porosities with an error of 5% or less. Onshore, the curves are used to estimate the depth of maximum burial at the end of Brookian sedimentation. The depth of sonic-derived porosity profiles is adjusted to give the best match with the 'master' compaction curves. The amount of the depth adjustment is the erosion estimate. Using our compaction curves, erosion estimates on the North Slope range from zero in much of the offshore, to as much as 1500 ft along the coast, and to more than 10,000 ft in the foothills (Panel 3). Compaction curves provide an alternative to vitrinite reflectance for estimating erosion. Vitrinite reflectance data are often very sparse in contrast to well log data and are subject to inconsistencies when measurements are made by different labs. The phenomenon of 'recycling' can also make the reflectance values of dispersed vitrinite problematic for quantifying erosion. Recycling is suspected in dispersed vitrinite in North Slope rocks, particularly in the younger, Cretaceous-Tertiary section. The compaction curves defined here are being integrated into our burial history and thermal models to determine the timing of source rock maturation. An example on Panel 3 shows the results of calculating the maturity of the Shublik Fm. at the Tulaga well using two different sets of shale and siltstone compaction curves. Finally, accurate compaction curves improve a model's ability to realistically simulate the pressure regime during burial, including overpressures.

Alaska↗

USGS2010

Surficial geology of the sea floor in Long Island Sound offshore of Plum Island, New York

The U.S. Geological Survey (USGS), the Connecticut Department of Environmental Protection, and the National Oceanic and Atmospheric Administration (NOAA) have been working cooperatively to interpret surficial sea-floor geology along the coast of the Northeastern United States. NOAA survey H11445 in eastern Long Island Sound, offshore of Plum Island, New York, covers an area of about 12 square kilometers. Multibeam bathymetry and sidescan-sonar imagery from the survey, as well as sediment and photographic data from 13 stations occupied during a USGS verification cruise are used to delineate sea-floor features and characterize the environment. Bathymetry gradually deepens offshore to over 100 meters in a depression in the northwest part of the study area and reaches 60 meters in Plum Gut, a channel between Plum Island and Orient Point. Sand waves are present on a shoal north of Plum Island and in several smaller areas around the basin. Sand-wave asymmetry indicates that counter-clockwise net sediment transport maintains the shoal. Sand is prevalent where there is low backscatter in the sidescan-sonar imagery. Gravel and boulder areas are submerged lag deposits produced from the Harbor Hill-Orient Point-Fishers Island moraine segment and are found adjacent to the shorelines and just north of Plum Island, where high backscatter is present in the sidescan-sonar imagery.

Open-File Report↗

USGS2010

Sea-floor geology and character offshore of Rocky Point, New York

Open-File Report↗

USGS2011

The shallow stratigraphy and sand resources offshore of the Mississippi Barrier Islands

Coastal Mississippi is protected by a series of barrier islands ranging in length from 10-25 kilometers that are less than 2 kilometers wide. The majority of these islands comprise the Gulf Islands National Seashore (GUIS), an ecologically diverse shoreline that provides habitat for wildlife including migratory birds and endangered animals. The majority of GUIS is submerged, and aquatic environments include dynamic tidal inlets, ebb-tide deltas, and seagrass beds. The islands are in a state of decline, with land areas severely reduced during the past century by storms, sea-level rise, and human alteration. Morton (2008) estimates that since the mid-1800s up to 64 percent of island surface area has been lost. Heavy damage was inflicted in 2005 by Hurricane Katrina, which passed by as a Category 3 storm and battered the islands with winds of more than 160 kilometers per hour and a storm surge up to 9 meters. Since 2007, the U.S. Geological Survey (USGS), in collaboration with the National Park Service, has been mapping the seafloor and substrate around the islands as part of the USGS Northern Gulf of Mexico Ecosystem Change and Hazard Susceptibility project. The purpose of these investigations is to characterize the near-surface stratigraphy and identify the influence it may have on island evolution and fate. In 2009, this effort provided the basis for a collaborative effort with the U.S. Army Corps of Engineers (USACE) to expand the investigation outside of GUIS boundaries as part of the Mississippi Coastal Improvement Project (MsCIP). The MsCIP program consists of structural, nonstructural, and environmental project elements to restore portions of coastal Mississippi and GUIS affected by storm impact. The project includes the placement of sand along the islands, both on the present beaches and within the littoral zone, to mitigate shoreline erosion and breaching. This action requires the location and assessment of offshore sand or sediment deposits that can provide suitable material for shoreline renourishment. The geophysical and sample information collected by the USGS during geologic investigations provides this information. As part of the MsCIP program, in March 2010 the USGS mapped approximately 300 square kilometers of seafloor around GUIS. Interferometric swath bathymetry, sidescan sonar, and Chirp sub-bottom profiling were used to characterize seafloor elevations, texture, and the underlying stratigraphy. On the basis of this information, potential sediment resources were identified. The most promising offshore deposits for beach restoration include shoals, lowstand valley fill, tidal delta deposits, abandoned barrier deposits, and dredge spoil. Of these, lowstand valley fill deposits and dredge spoil are less desirable; lowstand deposits are buried under a 2- to 4-meter blanket of mud, and dredge spoil volume is small. A relict tidal delta and submerged shoals are the most desirable deposits; the tidal delta contains a large volume of material still exposed on the seafloor, and parts of submerged shoals have modest volume and thin mud cover.

Mississippi↗

USGS2012

Sea-floor geology and sedimentary processes in the vicinity of Cross Rip Channel, Nantucket Sound, offshore southeastern Massachusetts

Gridded multibeam bathymetry covers approximately 10.4 square kilometers of sea floor in the vicinity of Cross Rip Channel in Nantucket Sound, offshore southeastern Massachusetts. Although originally collected for charting purposes during National Oceanic and Atmospheric Administration hydrographic survey H12007, these acoustic data, and the sea-floor sediment sampling and bottom photography stations subsequently occupied to verify them, show the composition and terrain of the seabed and provide information on sediment transport and benthic habitat. This report is part of an expanding series of cooperative studies by the U.S. Geological Survey, National Oceanic and Atmospheric Administration, and Massachusetts Office of Coastal Zone Management that provide a fundamental framework for research and resource-management activities (for example, windfarms, pipelines, and dredging) along the inner continental shelf offshore of Massachusetts.

Massachusetts↗

USGS2016

Assessing the impact of Hurricanes Irene and Sandy on the morphology and modern sediment thickness on the inner continental shelf offshore of Fire Island, New York

This report documents the changes in seabed morphology and modern sediment thickness detected on the inner continental shelf offshore of Fire Island, New York, before and after Hurricanes Irene and Sandy made landfall. Comparison of acoustic backscatter imagery, seismic-reflection profiles, and bathymetry collected in 2011 and in 2014 show that sedimentary structures and depositional patterns moved alongshore to the southwest in water depths up to 30 meters during the 3-year period. The measured lateral offset distances range between about 1 and 450 meters with a mean of 20 meters. The mean distances computed indicate that change tended to decrease with increasing water depth. Comparison of isopach maps of modern sediment thickness show that a series of shoreface-attached sand ridges, which are the dominant sedimentary structures offshore of Fire Island, migrated toward the southwest because of erosion of the ridge crests and northeast-facing flanks as well as deposition on the southwest-facing flanks and in troughs between individual ridges. Statistics computed suggest that the modern sediment volume across the about 81 square kilometers of common sea floor mapped in both surveys decreased by 2.8 million cubic meters, which is a mean change of –0.03 meters, which is smaller than the resolution limit of the mapping systems used.

New York↗

USGS2021

Shoreface and Holocene sediment thickness offshore of Rockaway Peninsula, New York

During September and October 2019, the U.S. Geological Survey mapped the shoreface and inner continental shelf offshore of the Rockaway Peninsula in New York using high-resolution chirp seismic reflection and single-beam bathymetry geophysical techniques. The results from this study are important for assessing the Quaternary evolution of the Rockaway Peninsula and determining coastal sediment availability, which is crucial for establishing sediment budgets, understanding sediment dispersal, and managing coastlines. This report presents preliminary interpretations of seismic profiles and maps of shoreface and Holocene sediment thickness from the shoreline to about 2 kilometers offshore. The results indicate that shoreface and Holocene sediment thickness demonstrates zonal variability because of underlying geology and sediment availability. Based on geomorphic features and underlying stratigraphy, the study area is separated into west, west-central, east-central, and east zones. Holocene sediment, which includes the shoreface and seafloor features with positive morphology (for example, nearshore bars, ebb-tide deltas, and sorted bedforms), thickens to the west and may be related to accommodation and westward dip of the regional unconformity. Shoreface units, which are thought to represent the active volume of littoral sediment, are thickest in the west-central peninsula where the geologic base of the shoreface is deeper. Shoreface units with moderate thickness are in the western and eastern peninsula where there are positive morphological features (for example, deposits accumulating updrift from the jetty, ebb-tide deltas, and so on). The thinnest shorefaces are in the east-central Rockaway Peninsula because of less accommodation caused by the shoaling regional unconformity.

New York↗

USGS2022

California Deepwater Investigations and Groundtruthing (Cal DIG) I, volume 3 — Benthic habitat characterization offshore Morro Bay, California

Coastal and Marine Ecological Classification Standard (CMECS) geoform, substrate, and biotic component geographic information system (GIS) products were developed for the U.S. Exclusive Economic Zone (U.S. EEZ) of south-central California in the region of Santa Lucia Bank motivated by interest in development of offshore wind-energy capacity and infrastructure. The Bureau of Ocean Energy Management (BOEM), in coordination with the State of California and many other members of the California Task Force, issued calls for information in 2018 for the study area offshore of Morro Bay, California. The study area is in depths of 500 to 1,200 meters (m) and adjacent to a decommissioned nuclear power plant with a developed electric grid connection, and in an area of high wind resource. BOEM is the lead agency responsible for planning and leasing in the U.S. EEZ and funded this project to assess baseline conditions of, and the potential effects on, the seafloor environment. This project, carried out by the U.S. Geological Survey (USGS), resulted in three reports: one on biological analysis of seafloor video data, one on analysis of the geologic framework and hazards, and this report on seafloor habitat. The study area consists of 8,424 square kilometers (km 2 ) of multibeam echo sounder (MBES) data acquired during five surveys from 2016 to 2019. Remotely operated vehicle (ROV) video was acquired in 2019 to supervise the classification of the MBES data into habitats. Derivatives of the MBES data were classified into 16 unique biotopes, 6 substrate types, 28 modifier groups, and 22 geoforms. The study area substrate is predominantly soft sediment (mud and fine sand) covering 7,804 km 2 (92.7 percent) of the area. Mixed substrate areas on rocky banks, channel scarps, and the shelf break comprise 404 km 2 (4.8 percent) of the study area. Hard substrate areas are found predominantly on the tops and flanks of banks and on bank ridges that separate canyons incising the banks. Hard substrates comprise 211 km 2 of the study area (2.5 percent). After the bathymetry and backscatter raster images (rasters) were classified, manual editing was also done to remove noise artifacts. This effort was not completely successful and there are numerous erroneous small areas in the rasters that have been passed on to the CMECS polygon product. Nearly 120,000 annotations of organisms and their habitat were made from 25 video transects selected from 185 hours of ROV video. In total, 2,714 km 2 of seafloor were successfully assigned to biotopes. Some biotopes were assigned to separate areas spatially distant from the transects that define the biotope. Expected relations between physical habitat and biota such as the number of species and the substrate induration and rugosity were verified. Slope is typically a predictive variable and was used in the classification of habitat, but the ground truth used for biotic component analysis included very little steeply sloping area. Ground-truth ROV operations were reduced by the sea state; additional ground truth could improve the biotic results and increase confidence in the spatial distribution of classifications reported here.

California↗

USGS1980

Summary of hydrologic testing in Tertiary limestone aquifer, Tenneco offshore exploratory well-Atlantic OCS, lease block 427 (Jacksonville NH-17-5)

A summary of hydrologic testing in an offshore oil-test well drilled for Tenneco, Inc. 55 miles east of Fernandina Beach, Florida, is presented. The interval tested (1,050 to 1,070 feet below sea level) is in a calcarenite that is equivalent to the Ocala Limestone (late Eocene) of onshore Florida and South Georgia. At this site the Ocala forms the highly productive Tertiary limestone aquifer system of the southeastern United States. Pressure-head measurements indicate an equivalent freshwater head of 24 to 29 feet above sea level. These pressure-head measurements and an earlier one made in the nearby JOIDES J-1 hole are the only hydraulic head determinations to date in the offshore extensions of any of the aquifers underlying the Atlantic coastal plain. A drill-stem test recovered water samples containing about 7,000 milligrams per liter chloride. However, seawater used in the drilling process apparently contaminated the samples and the formation water is considered slightly fresher. The head and salinity data from the Tenneco well suggest that the sampled interval lies in the transition zone between fresh and seawater in the limestone aquifer. These data, when viewed with similar data from JOIDES J-1, show the transition zone to slope very slightly landward. Heads at both wells are compatible with the onshore flow system as it existed prior to development.

Florida↗

USGS1994

Habitat impacts of offshore drilling, eastern Gulf of Mexico

In this survey six offshore exploratory drill sites in a variety of environments and water depths were examined using a small research submersible. Sites varied from locations off northwest Florida to as far west as offshore Alabama. Water depths ranged from 21 m (70 ft) to 149 m (489 ft), and bottom sediments ranged from carbonate mud to Shelly quartz sand and silt to hard limestone. The age of the sites (the time between cessation of drilling activities and our observations) ranged from 15 months to 17 years . In a previous MMS-funded study, Shinn et al. (1989) and Dustan et al . (1991) examined eight sites off South Florida, where the age of the sites ranged from 2 to 29 years. The study documented repeatedly variability of impact from site to site . In the present study, we note a similar wide divergence of impacts . Using the concentration of barium (the major component of drill mud), cuttings, and trace metals as a basis, we found that time is the single most important factor determining the nature of habitat recovery. Older sites, particularly the 17-year-old site, were relatively pristine. At a 7-year-old site, two hurricanes did far more damage than drilling . At other sites, we documented a significant amount of discarded debris, and at two 5-year-old sites, large concentrations of barium and cuttings. Impacts, such as the extent of debris and cuttings, affected the bottom ranging in area from almost negligible (17-year-old site) to as much as 3 acres (4-year-old site) . As suspected, those sites with the most debris and/or open boreholes attracted the most abundant and diverse fish fauna.

Open-File Report↗

USGS1996

Offshore gas hydrate sample database with an overview and preliminary analysis

Synopsis -- A database of offshore gas hydrate samples was constructed from published observations and measurements. More than 90 samples from 15 distinct regions are represented in 13 data categories. This database has permitted preliminary description of gas hydrate (chiefly methane hydrate) tendencies and associations with respect to their geological environment. Gas hydrates have been recovered from offshore sediment worldwide and from total depths (water depth plus subseabed depth) ranging from 500 m to nearly 6,000 m. Samples have come from subbottom depths ranging from 0 to 400 m. Various physiographic provinces are represented in the data set including second order landforms such as continental margins and deep-sea trenches, and third order forms such as submarine canyons, continental slopes, continental margin ridges and intraslope basins. There is a clear association between fault zones and other manifestations of local, tectonic-related processes, and hydrate-bearing sediment. Samples of gas hydrate frequently consist of individual grains or particles. These types of hydrates are often further described as inclusions or disseminated in the sediment. Moreover, hydrates occur as a cement, as nodules, or as layers (mostly laminae) or in veins. The preponderance of hydrates that could be characterized as 2- dimensional (planar) were associated with fine sediment, either as intercalated layers or in fractures. Hydrate cements were commonly associated with coarser sediment. Hydrates have been found in association with grain sizes ranging from clay through gravel. More hydrates are associated with the more abundant finer-grained sediment than with coarser sediment, and many were discovered in the presence of both fine (silt and clay) and coarse sediment. The thickness of hydrate zones (i. e., sections of hydrate-bearing sediment) varies from a few centimeters to as much as 30 m. In contrast, the thickness of layers of pure hydrate or the dimensions of individual hydrate grains were most often characterized in terms of millimeters or centimeters, although a pure hydrate layer discovered in the Middle America Trench off Guatemala was as much as 3-4-m-thick. The data suggest that grains, or thin veins or laminae of pure gas hydrate may be ubiquitous in many hydrate zones but that typically they may only comprise a minor component of the thicker zones. In more than 80 percent of the hydrate samples the methane was of biogenic origin. The methane in the remainder was either classified as (or may be at least part) thermogenic. Each site where thermogenic gas was identified is characterized by faults or other manifestions of a dynamic geological environment (e.g., diapirs, mud volcanoes, gas seeps). Every sample in the database came from within the zone of theoretical methane hydrate stability, as determined on the basis of assumed regional pressure and temperature gradients. Most show that they were situated --- expressed in terms of depth --- well above the phase boundary and about 70% of the samples were located more than 100 m above the assumed regional position of that boundary. The calculated subseabed positions of the phase boundaries and the BSRs (bottom simulating reflector) are essentially identical. This may be taken as general corroboration of the regional phase boundary calculations and the concept of the BSR. Three provocative aspects of marine gas hydrates have been disclosed by the database: gas hydrates are frequently situated at much shallower subseabed depths than the assumed contemporary position of the regional phase boundary hydrates are often found in areas typified by faults or other indicators of a dynamic geological environment zones of gas hydrate-bearing sediment tend to be tens of centimeters to tens of meters thick but the hydrate within the thicker zones tends to be only a minor constituent. Whether existing as dispersed particles, cements, or pure layers or vein

Open-File Report↗

USGS2015

Offshore geology and geomorphology from Point Piedras Blancas to Pismo Beach, San Luis Obispo County, California

Marine geology and geomorphology were mapped along the continental shelf and upper slope between Point Piedras Blancas and Pismo Beach, California. The map area is divided into the following three (smaller) map areas, listed from north to south: San Simeon, Morro Bay, and Point San Luis. Each smaller map area consists of a geologic map and the corresponding geophysical data that support the geologic mapping. Each geophysical data sheet includes shaded-relief multibeam bathymetry, seismic-reflection-survey tracklines, and residual magnetic anomalies, as well as a smaller version of the geologic map for reference. Offshore geologic units were delineated on the basis of integrated analysis of adjacent onshore geology, seafloor-sediment and rock samples, multibeam bathymetry and backscatter imagery, magnetic data, and high-resolution seismic-reflection profiles. Although the geologic maps are presented here at 1:35,000 scale, map interpretation was conducted at scales of between 1:6,000 and 1:12,000. Sea level was approximately 120 to 130 m lower during the Last Glacial Maximum (about 21 ka). This approximate depth corresponds to the modern shelf break, a lateral change from the gently dipping (0.8° to 1.0°) outer shelf to the slightly more steeply dipping (about 1.5° to 2.5°) upper slope in the central and northern parts of the map area. South of Point San Luis in San Luis Bay, deltaic deposits offshore of the mouth of the Santa Maria River (11 km south of the map area) have prograded across the shelf break and now form a continuous low-angle (about 0.8°) ramp that extends to water depths of more than 160 m. The shelf break defines the landward boundary of slope deposits. North of Estero Bay, the shelf break is characterized by a distinctly sharp slope break that is mapped as a landslide headscarp above landslide deposits. Multibeam imagery and seismic-reflection profiles across this part of the shelf break show evidence of slope failure, such as slumping, sliding, and soft-sediment deformation, along the entire length of the scarp. Notably, this shelf-break scarp corresponds to a west splay of the Hosgri Fault that dies out just north of the scarp, suggesting that faulting is controlling the location (and instability) of the shelf break in this area.

California↗

USGS2017

Surficial geologic map of Berrien County, Michigan, and the adjacent offshore area of Lake Michigan

The surficial geologic map of Berrien County, southwestern Michigan (sheet 1), shows the distribution of glacial and postglacial deposits at the land surface and in the adjacent offshore area of Lake Michigan. The geologic map differentiates surficial materials of Quaternary age on the basis of their lithologic characteristics, stratigraphic relationships, and age. Drill-hole information correlated in cross sections provides details of typical stratigraphic sequences that compose one or more penetrated geologic map units. A new bedrock geologic map (on sheet 2) includes contours of the altitude of the eroded top of bedrock and shows the distribution of middle Paleozoic shale and carbonate units in the subcrop. A sediment thickness map (also on sheet 2) portrays the extent of as much as 150 meters of surficial materials that overlie the bedrock surface. The major physical features of the county are related principally to deposits of the last Laurentide ice sheet that advanced and then retreated back through the region from about 19,000 to 14,000 radiocarbon years before present. Glacial and postglacial deposits underlie the entire county; shale bedrock crops out only in the adjacent offshore area on the bottom of Lake Michigan. All glacial deposits and glacial meltwater deposits in Berrien County are related to the late Wisconsinan glacial advances of the Lake Michigan ice lobe and its three regional recessional moraines, which cross the county as three north-northeast-trending belts. From east to west (oldest to youngest), the three moraine belts are known as the Kalamazoo, Valparaiso, and Lake Border morainic systems. The till-ridge morainic systems (Lake Border and local Valparaiso morainic systems) consist of multiple, elongate moraine ridges separated by till plains and lake-bottom plains. Tills in ground and end moraines in Berrien County are distinguished as informal units, and are correlated with three proposed regional till units in southwestern Michigan, characterized as clayey till, loamy till, or sandy loamy till that are based in part on correlation of silty tills and clay mineralogy. The stratified morainic systems (local Valparaiso and Kalamazoo morainic systems) are composed of multiple ice-marginal glacial-lake deltas and glaciolacustrine fans that form a contiguous array of deposits, welded together at their onlapping contacts, further related by the accordant altitudes of their delta topset plains. Their bounding ice-contact slopes repeatedly are aligned parallel to the regional trend of the receding ice margin. Ice-marginal (ice-contact) deltas were deposited in glacial lakes that expanded northward as the ice sheet retreated. Glaciofluvial topset beds, which overlie deltaic foreset and bottomset facies, fine away from the ice margin. Stratified deposits associated with the Valparaiso moraine were deposited in glacial Lakes Madron and Dowagiac. Subsequent deposits of glacial Lake Baroda preceded basin-wide deposits associated with various levels of Lake Michigan. Sheet 2 includes a series of 10 map figures that show cut-away three-dimensional time slices of the stratigraphic succession, from basal tills on bedrock, to ice-marginal deltas in the three large proglacial lakes, to stacked till/lake-bottom deposits related to the Lake Border ice margin readvances, to young deposits of glacial Lake Chicago and younger phases of other glacial lakes and the Chippewa lake lowstand. The pamphlet contains a discussion of the stratigraphic framework, descriptions of each depositional unit, and graphic logs of U.S. Geological Survey stratigraphic drill holes. The pamphlet also relates the geologic history of Berrien County, beginning with bedrock Paleozoic marine deposits, continuing through erosional effects of multiple glaciations and the detailed steps of late Wisconsinan ice-margin recession as recorded in the moraines, and the rise and fall of postglacial lake levels in the Lake Michigan basin.

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