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At least 721 records · Page 40Linked to original sources
USGS2004

Integrating digital information for coastal and marine sciences

A pilot distributed geolibrary, the Marine Realms Information Bank (MRIB), was developed by the U.S. Geological Survey Coastal and Marine Geology Program and the Woods Hole Oceanographic Institution, to classify, integrate, and facilitate access to scientific information about oceans, coasts, and lakes. The MRIB is composed of a categorization scheme, a metadata database, and a specialized software backend, capable of drawing together information from remote sources without modifying their original format or content. Twelve facets are used to classify information: location, geologic time, feature type, biota, discipline, research method, hot topics, project, agency, author, content type, and file type. The MRIB approach allows easy and flexible organization of large or growing document collections for which centralized repositories would be impractical. Geographic searching based on the gazetteer and map interface is the centerpiece of the MRIB distributed geolibrary. The MRIB is one of a very few digital libraries that employ georeferencing -- a fundamentally different way to structure information from the traditional author/title/subject/keyword approach employed by most digital libraries. Lessons learned in developing the MRIB will be useful as other digital libraries confront the challenges of georeferencing.

Journal of Digital Information Management↗
USGS2000

Protection of fish spawning habitat for the conservation of warm-temperature reef-fish fisheries of shelf-edge reefs of Florida

We mapped and briefly describe the surficial geology of selected examples of shelf-edge reefs (50–120 m deep) of the southeastern United States, which are apparently derived from ancient Pleistocene shorelines and are intermittently distributed throughout the region. These reefs are ecologically significant because they support a diverse array of fish and invertebrate species, and they are the only aggregation spawning sites of gag ( Mycteroperca microlepis ), scamp ( M. phenax ), and other economically important reef fish. Our studies on the east Florida shelf in the Experimental Oculina Research Reserve show that extensive damage to the habitat-structuring coral Oculina varicosa has occurred in the past, apparently from trawling and dredging activities of the 1970s and later. On damaged or destroyed Oculina habitat, reef-fish abundance and diversity are low, whereas on intact habitat, reef-fish diversity is relatively high compared to historical diversity on the same site. The abundance and biomass of the economically important reef fish was much higher in the past than it is now, and spawning aggregations of gag and scamp have been lost or greatly reduced in size. On the west Florida shelf, fishers have concentrated on shelf-edge habitats for over 100 yrs, but fishing intensity increased dramatically in the 1980s. Those reefs are characterized by low abundance of economically important species. The degree and extent of habitat damage there is unknown. We recommend marine fishery reserves to protect habitat and for use in experimentally examining the potential production of unfished communities.

Florida↗
USGS2000

Protection of fish spawning habitat for the conservation of warm temperate reef fish fisheries of shelf-edge reefs of Florida

We mapped and briefly describe the surficial geology of selected examples of shelf-edge reefs (50–120 m deep) of the southeastern United States, which are apparently derived from ancient Pleistocene shorelines and are intermittently distributed throughout the region. These reefs are ecologically significant because they support a diverse array of fish and invertebrate species, and they are the only aggregation spawning sites of gag ( Mycteroperca microlepis ), scamp ( M. phenax ), and other economically important reef fish. Our studies on the east Florida shelf in the Experimental Oculina Research Reserve show that extensive damage to the habitat-structuring coral Oculina varicosa has occurred in the past, apparently from trawling and dredging activities of the 1970s and later. On damaged or destroyed Oculina habitat, reef-fish abundance and diversity are low, whereas on intact habitat, reef-fish diversity is relatively high compared to historical diversity on the same site. The abundance and biomass of the economically important reef fish was much higher in the past than it is now, and spawning aggregations of gag and scamp have been lost or greatly reduced in size. On the west Florida shelf, fishers have concentrated on shelf-edge habitats for over 100 yrs, but fishing intensity increased dramatically in the 1980s. Those reefs are characterized by low abundance of economically important species. The degree and extent of habitat damage there is unknown. We recommend marine fishery reserves to protect habitat and for use in experimentally examining the potential production of unfished communities.

Florida↗
USGS2009

Investigation into the Origin and Character of Surficial Sedimentary Deposits at the Midshore Regional Solid Waste Facility near Easton, Maryland

A temporary exposure at the Midshore Regional Solid Waste Facility near Easton, MD, provided an opportunity to document the characteristics of the complex assemblage of surficial facies in that area. This unusually large cross section allowed interpretation of the changing processes that shaped the landscape in response to climate change through the late Pleistocene. Eight stratigraphic units were recognized: (1) gray, fossiliferous, muddy silt of the marine Miocene Choptank Formation; (2) coarse, crossbedded conglomerate of the late Miocene to Pliocene fluvial Pensauken Formation; (3) bioturbated muddy conglomerate interpreted as deposits of small colluvial fans; (4) pebbly, quartzose sand overlying a planar erosional surface reflecting a marine transgression; (5) irregular pods and lenses of sand and gravel deformed into bowl-shaped folds and faulted, which are interpreted as wind deposits over a semipermanent snow cover (niveo-aeolian deposits); (6) crossbedded sand and conglomerate with abundant mud partings indicating tidal influences on sinuous stream channels; (7) heavily bioturbated silt and sand with abundant root casts and flattened vesicles interpreted as aeolian loess deposits in marshy fens; and (8) pebbly sand and mud with scattered boulders and cobbles that reflect modern infill of the excavation by the operators. Soils formed on units 3, 4, and 7. Superimposed on units 4, 5, and 7 is evidence of deep freezing and permafrost development and subsequent thermokarst development after thawing, which includes large, complexly filled wedge-shaped cracks, deformed bedding and faults, fluid-injection structures, and spherical blobs of sand and mud. Each of the stratigraphic units has irregular distributions and lateral changes. The results of this study provide a unique insight into the geometry of surficial deposits that will help facilitate mapping of units, interpretation of cored intervals, and understanding of ground-penetrating radar profiles. The study also documents the widespread effects of permafrost during the last glacial episode well south of the maximum advance of ice sheets.

Open-File Report↗
USGS2013

Impact of Late Holocene climate variability and anthropogenic activities on Biscayne Bay (Florida, U.S.A.): Evidence from diatoms

Shallow marine ecosystems are experiencing significant environmental alterations as a result of changing climate and increasing human activities along coasts. Intensive urbanization of the southeast Florida coast and intensification of climate change over the last few centuries changed the character of coastal ecosystems in the semi-enclosed Biscayne Bay, Florida. In order to develop management policies for the Bay, it is vital to obtain reliable scientific evidence of past ecological conditions. The long-term records of subfossil diatoms obtained from No Name Bank and Featherbed Bank in the Central Biscayne Bay, and from the Card Sound Bank in the neighboring Card Sound, were used to study the magnitude of the environmental change caused by climate variability and water management over the last ~ 600 yr. Analyses of these records revealed that the major shifts in the diatom assemblage structures at No Name Bank occurred in 1956, at Featherbed Bank in 1966, and at Card Sound Bank in 1957. Smaller magnitude shifts were also recorded at Featherbed Bank in 1893, 1942, 1974 and 1983. Most of these changes coincided with severe drought periods that developed during the cold phases of El Niño Southern Oscillation (ENSO), Atlantic Multidecadal Oscillation (AMO) and Pacific Decadal Oscillation (PDO), or when AMO was in warm phase and PDO was in the cold phase. Only the 1983 change coincided with an unusually wet period that developed during the warm phases of ENSO and PDO. Quantitative reconstructions of salinity using the weighted averaging partial least squares (WA-PLS) diatom-based salinity model revealed a gradual increase in salinity at the three coring locations over the last ~ 600 yr, which was primarily caused by continuously rising sea level and in the last several decades also by the reduction of the amount of freshwater inflow from the mainland. Concentration of sediment total nitrogen (TN), total phosphorus (TP) and total organic carbon (TOC) increased in the second half of the 20th century, which coincided with the construction of canals, landfills, marinas and water treatment plants along the western margin of Biscayne Bay. Increased magnitude and rate of the diatom assemblage restructuring in the mid- and late-1900s, suggest that large environmental changes are occurring more rapidly now than in the past.

Florida↗
USGS2010

EAARL coastal topography-Cape Hatteras National Seashore, North Carolina, post-Nor'Ida, 2009: first surface

These remotely sensed, geographically referenced elevation measurements of lidar-derived first-surface (FS) topography datasets were produced collaboratively by the U.S. Geological Survey (USGS), St. Petersburg Coastal and Marine Science Center, St. Petersburg, FL, and the National Park Service (NPS), Northeast Coastal and Barrier Network, Kingston, RI. This project provides highly detailed and accurate datasets of a portion of the National Park Service Southeast Coast Network's Cape Hatteras National Seashore in North Carolina, acquired post-Nor'Ida (November 2009 nor'easter) on November 27 and 29 and December 1, 2009. The datasets are made available for use as a management tool to research scientists and natural-resource managers. An innovative airborne lidar instrument originally developed at the NASA Wallops Flight Facility, and known as the Experimental Advanced Airborne Research Lidar (EAARL), was used during data acquisition. The EAARL system is a raster-scanning, waveform-resolving, green-wavelength (532-nanometer) lidar designed to map near-shore bathymetry, topography, and vegetation structure simultaneously. The EAARL sensor suite includes the raster-scanning, water-penetrating full-waveform adaptive lidar, a down-looking red-green-blue (RGB) digital camera, a high-resolution multispectral color-infrared (CIR) camera, two precision dual-frequency kinematic carrier-phase GPS receivers, and an integrated miniature digital inertial measurement unit, which provide for sub-meter georeferencing of each laser sample. The nominal EAARL platform is a twin-engine aircraft, but the instrument was deployed on a Pilatus PC-6. A single pilot, a lidar operator, and a data analyst constitute the crew for most survey operations. This sensor has the potential to make significant contributions in measuring sub-aerial and submarine coastal topography within cross-environmental surveys. Elevation measurements were collected over the survey area using the EAARL system, and the resulting data were then processed using the Airborne Lidar Processing System (ALPS), a custom-built processing system developed in a NASA-USGS collaboration. ALPS supports the exploration and processing of lidar data in an interactive or batch mode. Modules for presurvey flight-line definition, flight-path plotting, lidar raster and waveform investigation, and digital camera image playback have been developed. Processing algorithms have been developed to extract the range to the first and last significant return within each waveform. ALPS is used routinely to create maps that represent submerged or sub-aerial topography. Specialized filtering algorithms have been implemented to determine the 'bare earth' under vegetation from a point cloud of last return elevations. For more information about similar projects, please visit the Decision Support for Coastal Science and Management website.

Data Series↗
USGS2011

EAARL Coastal Topography-Cape Hatteras National Seashore, North Carolina, Post-Nor'Ida, 2009: Bare Earth

These remotely sensed, geographically referenced elevation measurements of lidar-derived bare-earth (BE) topography datasets were produced collaboratively by the U.S. Geological Survey (USGS), St. Petersburg Coastal and Marine Science Center, St. Petersburg, FL, and the National Park Service (NPS), Northeast Coastal and Barrier Network, Kingston, RI. This project provides highly detailed and accurate datasets of a portion of the National Park Service Southeast Coast Network's Cape Hatteras National Seashore in North Carolina, acquired post-Nor'Ida (November 2009 nor'easter) on November 27 and 29 and December 1, 2009. The datasets are made available for use as a management tool to research scientists and natural-resource managers. An innovative airborne lidar instrument originally developed at the NASA Wallops Flight Facility, and known as the Experimental Advanced Airborne Research Lidar (EAARL), was used during data acquisition. The EAARL system is a raster-scanning, waveform-resolving, green-wavelength (532-nanometer) lidar designed to map near-shore bathymetry, topography, and vegetation structure simultaneously. The EAARL sensor suite includes the raster-scanning, water-penetrating full-waveform adaptive lidar, a down-looking red-green-blue (RGB) digital camera, a high-resolution multispectral color-infrared (CIR) camera, two precision dual-frequency kinematic carrier-phase GPS receivers, and an integrated miniature digital inertial measurement unit, which provide for sub-meter georeferencing of each laser sample. The nominal EAARL platform is a twin-engine aircraft, but the instrument was deployed on a Pilatus PC-6. A single pilot, a lidar operator, and a data analyst constitute the crew for most survey operations. This sensor has the potential to make significant contributions in measuring sub-aerial and submarine coastal topography within cross-environmental surveys. Elevation measurements were collected over the survey area using the EAARL system, and the resulting data were then processed using the Airborne Lidar Processing System (ALPS), a custom-built processing system developed in a NASA-USGS collaboration. ALPS supports the exploration and processing of lidar data in an interactive or batch mode. Modules for presurvey flight-line definition, flight-path plotting, lidar raster and waveform investigation, and digital camera image playback have been developed. Processing algorithms have been developed to extract the range to the first and last significant return within each waveform. ALPS is used routinely to create maps that represent submerged or sub-aerial topography. Specialized filtering algorithms have been implemented to determine the 'bare earth' under vegetation from a point cloud of last return elevations.

Data Series↗
USGS2019

Structure contour and overburden maps of the Niobrara interval of the Upper Cretaceous Cody Shale in the Wind River Basin, Wyoming

The Wind River Basin in central Wyoming is one of many structural and sedimentary basins that formed in the Rocky Mountain foreland during the Laramide orogeny. The basin is bounded by the Washakie, Owl Creek, and southern Bighorn uplifts on the north, the Casper arch on the east, the Granite Mountains uplift on the south, and Wind River uplift on the west. The first commercial oil well in Wyoming was drilled at Dallas dome near an oil seep along the southwestern edge of the Wind River Basin in 1884. Since then, many important conventional oil and gas fields, that produce from reservoirs ranging in age from Mississippian through Tertiary, have been discovered in this basin. In addition, an extensive unconventional (continuous) overpressured basin-centered gas accumulation has been identified in Cretaceous and Tertiary strata in the deeper parts of the basin. It has been suggested that various Upper Cretaceous marine shales, including the Cody Shale, are the principal hydrocarbon source rocks for many of these accumulations. With recent advances in horizontal drilling and multistage fracture stimulation, there has been an increase in exploration and completion of wells in equivalent marine shales in other Rocky Mountain Laramide basins that were traditionally thought of only as hydrocarbon source rocks. The maps presented in this report were constructed as part of a project carried out by the U.S. Geological Survey to characterize the geologic framework of potential undiscovered continuous (unconventional) oil and gas resources of the Niobrara interval of the Upper Cretaceous Cody Shale in the Wind River Basin in central Wyoming.

Wyoming↗
USGS1984

Ferromanganese micronodules from the surficial sediments of Georges Bank

Ferromanganese micronodules have been found on Georges Bank, off the U.S. northeast coast, distributed throughout the surficial sediments within an area about 125 km long and at least 12 km wide. These coarse, sand-sized concretions have precipitated from metal-rich interstitial waters and contain many of the textural and structural features common to other neritic nodules. Most of the nodules have accreted around detrital grains, and X-ray powder diffraction analyses indicate the presence of geothite and vernadite (  -MnO 2 ) in the ferromanganese layers. Chemical analyses of the micronodules, when compared with similar data on deep-sea manganese nodules, reveal lower Mn/Fe ratios, significantly higher concentrations of V and As, comparable values of Mo, and an order of magnitude less of Co, Ni, Ce and most other metals.

Georges Bank↗
USGS2010

Three-dimensional geologic modeling of the Santa Rosa Plain, California

New three-dimensional (3D) lithologic and stratigraphic models of the Santa Rosa Plain (California, USA) delineate the thickness, extent, and distribution of subsurface geologic units and allow integration of diverse data sets to produce a lithologic, stratigraphic, and structural architecture for the region. This framework can be used to predict pathways of groundwater flow beneath the Santa Rosa Plain and potential areas of enhanced or focused seismic shaking. Lithologic descriptions from 2683 wells were simplified to 19 internally consistent lithologic classes. These distinctive lithologic classes were used to construct a 3D model of lithologic variations within the basin by extrapolating data away from drill holes using a nearest-neighbor approach. Subsurface stratigraphy was defined through the identification of distinctive lithologic packages tied, where possible, to high-quality well control and to surface exposures. The 3D stratigraphic model consists of three bounding components: fault surfaces, stratigraphic surfaces, and a surface representing the top of pre-Cenozoic basement, derived from inversion of regional gravity data. The 3D lithologic model displays a west to east transition from dominantly marine sands to heterogeneous continental sediments. In contrast to previous stratigraphic studies, the new models emphasize the prevalence of the clay-rich Petaluma Formation and its heterogeneous nature. Isopach maps of the Glen Ellen Formation and the 3D stratigraphic model show the influence of the Trenton Ridge, a concealed basement ridge that bisects the plain, on sedimentation; the thickest deposits of the Glen Ellen Formation are confined to north of the Trenton Ridge.

California↗
USGS2016

Shallower structure and geomorphology of the southern Puerto Rico offshore margin

Oblique convergence between the North American and Caribbean plates along the eastern Greater Antilles island arc has yielded the compressive Muertos margin in the backarc region. The Muertos margin is characterized by an asymmetric thrust belt with overall opposite vergence to the subduction system in the forearc region. Offshore south of Puerto Rico, this thrust belt disappears and is replaced by a succession of NE─SW- and E─W-trending deep basins and steep ridges that characterize the western Anegada passage, resulting in a complex deformation pattern. Using new high-resolution multibeam bathymetry and a dense data set of mostly new seismic reflection profiles, we studied the along- and across-strike variations of the geomorphology and shallower structure of the southern Puerto Rico offshore margin. We have identified four morphotectonic provinces: the Puerto Rican sub-basin and Muertos trough, the Muertos margin, the insular shelf and the western Anegada passage. The Muertos margin province shows two distinct slope sub-provinces: the active Muertos thrust belt formed by N─S-compression between the island arc and the Caribbean plate’s interior ─which includes lower and upper thrust belts with distinct deformational styles and lateral continuity─ and the shelf slope covered by a thick package of layered sediments highly-incised by a dense canyon network. This network is disrupted by the Investigator fault zone consisting of a 130 km-long E─W-trending band of active extensional deformation. The Investigator fault zone shows differential surface expression caused by along-strike changes in the magnitude and distribution of the deformation, though this deformation is driven by a N─S-oriented extension, and if there is any amount of strike-slip it is insignificant. In the western Anegada passage province, the Whiting basin and Whiting and Grappler ridges are formed by large dipslip normal faults driven by a NW─SE-oriented extensional regime. The western St. Croix rise shows a complex structure as attested by the existence of NE─SW- and E─W-oriented normal faults. The NE─SW-trending NW-dipping normal faults observed at the summit of the rise predate the E─W-bounding faults that could accommodate the extensional deformation at the Present. This study provides detailed observations on the active tectonic and sedimentary processes to help future studies assessing the natural resources and the seismic and tsunamigenic hazard in the Puerto Rico region.

Marine and Petroleum Geology↗
USGS2016

Seasonal sediment dynamics shape temperate bedrock reef communities

Mobilized seafloor sediment can impact benthic reef communities through burial, scour, and turbidity. These processes are ubiquitous in coastal oceans and, through their influence on the survival, fitness, and interactions of species, can alter the structure and function of benthic communities. In northern Monterey Bay, California, USA, as much as 30% of the seafloor is buried or exposed seasonally, making this an ideal location to test how subtidal temperate rocky reef communities vary in the presence and absence of chronic sediment-based disturbances. Designated dynamic plots were naturally inundated by sediment in summer (50 to 100% cover) and swept clean in winter, whereas designated stable plots remained free of sediment during our study. Multivariate analyses indicated significant differences in the structure of sessile and mobile communities between dynamic and stable reef habitats. For sessile species, community structure in disturbed plots was less variable in space and time than in stable plots due to the maintenance of an early successional state. In contrast, community structure of mobile species varied more in disturbed plots than in stable plots, reflecting how mobile species distribute in response to sediment dynamics. Some species were found only in these disturbed areas, suggesting that the spatial mosaic of disturbance could increase regional diversity. We discuss how the relative ability of species to tolerate disturbance at different life history stages and their ability to colonize habitat translate into community-level differences among habitats, and how this response varies between mobile and sessile communities.

California↗
USGS1999

Recent advances in life history of Gulf of Mexico sturgeon, Acipenser oxyrinchus desotoi, in the Suwannee River, Florida, USA: A synopsis

Gulf sturgeon spawn on portions of three sites in the upper Suwannee River, which may appropriately be described as spawning reefs. The same areas are utilized from year to year. Habitat factors important in spawning site determination include gravel/cobble substrate, the presence of eddy fields, a neutral to slightly alkaline pH, and an empirically observed range in calcium ion content (6-18 mg/L Ca++, corresponding to a conductivity range of 40-110??S). Eggs are deposited contagiously within a small area (< 10,000 m2) with very little scatter, suggesting little if any current drift. They are not found from samplers on immediately adjacent sand substrate. The broadcast spawner model does not seem to fit the Gulf sturgeon. Spawning begins 4-7 days after the March new moon, with water temperature above 17.0 oC, and extends for 9-23 days as discrete events involving individual females. Spawning may continue, if water temperature remains below 21-22oC. The total annual pool of spawning females in the Suwannee population is estimated at 80 individuals. Young of the year utilize open sand habitat away from shoreline and vegetated habitat. They disperse widely, and occur over freshwater reaches from rkm 10-237; no particular affinity with spring water habitat is evident. Larger Gulf sturgeon tend to congregate in deep holes serving as summer-fall holding areas. They fast and lose weight while remaining in freshwater, but more than compensate this loss during winter feeding in marine waters. The major downriver migration to the estuary takes place in October-November. After a period of river mouth staging, subadults and adults migrate into Gulf of Mexico nearshore mesohaline waters. They move further out and into deeper water (> 3 m) when water temperatures drop in mid-December, but final destinations in mid-winter remain unknown. Age-2 through 6 juveniles remain in the river mouth estuary over winter. In late January through early February YOY migrate downriver for the first time, joining larger juveniles to overwinter and feed. Tag and recapture data yield a Suwannee River population of Gulf sturgeon estimated at 7,650 individuals, with an annual turnover rate of 16%. Based on stability in cumulative recapture rates from 1991-1998, population size is stable with an effective balance between recruitment and mortality. However, population structure is dynamic, controlled by the juxtaposition, conjunction, and summation of successive strong and weak year classes. Length/age frequency distributions for 1995 and 1998 populations censuses are very different. The 1995 distribution is bimodal with a dominant mode of 9-14 year old subadults/adults, and a sub-dominant of mode of 2-4 year old juveniles. The 1998 distribution is trimodal, but overwhelmingly dominated by 6-9 year old subadults. Erosion by 1998 of the major subadult/adult mode from the 1995 census illustrates that large adults encounter the same high mortality as smaller fish. Ultimate adult size in the population has remained constant at 2.2 cm TL over 13 years, indicating a maximum life expectancy of 25 years for Suwannee River Gulf sturgeon.

Conference Paper↗
USGS2015

Age, growth rates, and paleoclimate studies of deep sea corals

Deep-water corals are some of the slowest growing, longest-lived skeletal accreting marine organisms. These habitat-forming species support diverse faunal assemblages that include commercially and ecologically important organisms. Therefore, effective management and conservation strategies for deep-sea corals can be informed by precise and accurate age, growth rate, and lifespan characteristics for proper assessment of vulnerability and recovery from perturbations. This is especially true for the small number of commercially valuable, and potentially endangered, species that are part of the black and precious coral fisheries (Tsounis et al. 2010). In addition to evaluating time scales of recovery from disturbance or exploitation, accurate age and growth estimates are essential for understanding the life history and ecology of these habitat-forming corals. Given that longevity is a key factor for population maintenance and fishery sustainability, partly due to limited and complex genetic flow among coral populations separated by great distances, accurate age structure for these deep-sea coral communities is essential for proper, long-term resource management.

Report↗
USGS1980

Structural framework, stratigraphy, and petroleum geology of the area of oil and gas lease Sale No. 49 on the U.S. Atlantic continental shelf and slope

On September 23, 1977, the U.S. Department of the Interior announced the tentative selection of 136 tracts for Sale No. 49 of oil and gas leases in the Baltimore Canyon Trough on the U.S. Atlantic Continental Shelf and Slope. This report summarizes the geology and petroleum potential of the area. The Baltimore Canyon Trough is an elongate, seaward-opening sedimentary basin filled by as much as 14 km of Mesozoic and Cenozoic sedimentary rocks. The basin first formed under the New Jersey shelf and gradually spread west and south as the area subsided after the rifting that formed the Atlantic basin. Rocks of the Triassic and Jurassic Systems together are more than 8 km thick in a depocenter areally restricted to the northern part of the trough. Basal Jurassic rocks are apparently nonmarine sedimentary rocks bedded with evaporite deposits. Direct evidence that some salt is in the basal Jurassic section comes from the Houston Oil and Minerals 676-1 well, which penetrated salt at a depth of about 3.8 km. During the Middle and Late Jurassic, more open marine conditions prevailed than in the Early Jurassic, and carbonate banks and reefs formed discontinuously along the seaward side of the shelf. Sand flats likely occupied the central part of the shelf, and these probably graded shoreward into nonmarine red beds that accumulated in a bordering coastal plain. Thick nonmarine sands and silty shales of Late Jurassic age were deposited in what is now the nearshore and midshelf area. These sedimentary rocks probably grade into thick marine carbonate rocks near the present shelf edge. During the Cretaceous, less sediment accumulated (about 4 km) than during the Jurassic, and most was deposited during Early Cretaceous time. The Cretaceous units show two main trends through time-a diminishing rate of sediment accumulation and an increase in marine character of sediments. During the Middle and Late Cretaceous, calcareous sand and mud filled the basin, buried the shelf-edge reefs and later spilled across the reefs into the oceanic basin as worldwide sea level reached a maximum. Cenozoic deposits are spread over the present shelf and adjacent Coastal Plain in overlapping sheets of marine and nonmarine sediment. The maximum thickness (1.5 km) is along the outer part of the present shelf. Major tectonic deformation in the Baltimore Canyon Trough area appears to have terminated near the end of the Early Cretaceous, when at least one large mafic intrusion (Great Stone dome) was emplaced. Upper Cretaceous sedimentary rocks are arched above older uplifted fault blocks near the shelf edge; this arching may be the result of draping due to differential compaction or, perhaps, minor movement of the fault blocks during Late Cretaceous time. The dominance of terrestrial over marine-derived organic matter in sediment samples from the COST No. B-2 well indicates that economic amounts of liquid petroleum hydrocarbons were probably not generated in the area but suggests a high potential for generation of wet or dry gas. Supporting evidence for the presence of natural-gas deposits on the slope comes from AMCOR 6021, the upper 305 m of which penetrated sediments that contained methane, ethane, and propane. Texaco, Inc., has announced that its 598-1 well yielded nearly 479,000 m s of natural gas per day from two zones during early testing. Further indication of possible gas deposits comes from analyzing the amplitude (bright spots) of seismic data. Geochemical studies of the COST No. B-2 well have shown that the shelf area of the Baltimore Canyon Trough has a relatively low geothermal gradient today and that it apparently has had a gradient as low or even lower throughout the Cretaceous to Holocene. A controversy exists concerning the maturity of the basal sediments penetrated by the COST No. B-2 well. Although significant amounts of gaseous hydrocarbons may have been generated, large amounts of liquid petroleum hydrocarbons probably hav

Circular↗
USGS2024

Testing food web theory in a large lake: The role of body size in habitat coupling in Lake Michigan

The landscape theory of food web architecture (LTFWA) describes relationships among body size, trophic position, mobility, and energy channels that serve to couple heterogenous habitats, which in turn promotes long-term system stability. However, empirical tests of the LTFWA are rare and support differs among terrestrial, freshwater, and marine systems. Further, it is unclear whether the theory applies in highly altered ecosystems dominated by introduced species such as the Laurentian Great Lakes. Here, we provide an empirical test of the LTFWA by relating body size, trophic position, and the coupling of different energy channels using stable isotope data from species throughout the Lake Michigan food web. We found that body size was positively related to trophic position, but for a given trophic position, organisms predominately supported by pelagic energy had smaller body sizes than organisms predominately supported by nearshore benthic energy. We also found a hump-shaped trophic relationship in the food web where there is a gradual increase in the coupling of pelagic and nearshore energy channels with larger body sizes as well as higher trophic positions. This highlights the important role of body size and connectivity among habitats in structuring food webs. However, important deviations from expectations are suggestive of how species introductions and other anthropogenic impacts can affect food web structure in large lakes. First, native top predators appear to be flexible couplers that may provide food web resilience, whereas introduced top predators may confer less stability when they specialize on a single energy pathway. Second, some smaller bodied prey fish and invertebrates, in addition to mobile predators, coupled energy from pelagic and nearshore energy channels, which suggests that some prey species may also be important integrators of energy pathways in the system. We conclude that patterns predicted by the LTFWA are present in the face of species introductions and other anthropogenic stressors to a degree, but time-series evaluations are needed to fully understand the mechanisms that promote stability.

Lake Michigan↗
USGS1969

Geologic structure between the Murray fracture zone and the Transverse Ranges

The Murray fracture has been thought to extend ashore into the Transverse Ranges of California, but a geophysical study shows no evidence of structural continuity between these features. Instead, basement morphology typical of the Murray fracture zone ends where its known magnetic and bathymetric expression dies out. Similarly, east-west Transverse Range structures change direction so that they are parallel to the northwest trend of the coast rather than crossing the continental shelf and slope. The lack of continuity suggests an independent development of the Transverse Ranges since at least mid-Tertiary time along an older structural trend continuous with the Murray fracture zone. Possibly a fundamental lineament in the crust, an extension of the Murray, inactive since at least the mid-Tertiary, provided a convenient trend for development of the Transverse Ranges in response to deformation along the San Andreas fault system. The Murray fracture zone is thought by some authors to be a transform-fault. The transform-fault hypothesis alleviates some difficulties that arise in explaining the origin of the zone by transcurrent faulting but equivalent uncertainties seem to accompany the newer explanation.

Marine Geology↗
USGS1990

Faults of the central part of the Lewis and Clark line and fragmentation of the Late Cretaceous foreland basin in west-central Montana

The Lewis and Clark line is a prominent zone of strike-slip, dip-slip, and oblique-slip faults that extends from near Wallace, Idaho, to east of Helena, Montana. Faults of this zone have been intermittently active from Middle Proterozoic to Holocene time, and because of numerous tectonic overprints, controversy continues about displacement directions and times of displacement along specific faults. Geologic mapping shows evidence that many principal faults of the Lewis and Clark line, such as the St. Marys-Helena Valley, Bald Butte, Ninemile, and Osburn faults, had right separation or slip that ranged between 28 and 11 km, and this displacement probably occurred during Late Cretaceous time. Other faults, such as the Elevation Mountain, Placer Creek, and Ranch Creek faults, have Late Cretaceous right separations that range between 8 and 3.2 km, and the Mount Sentinel fault zone has between 6.5 and 3 km of right separation of probable Late Cretaceous age. Subsidiary structures of the Lewis and Clark line postdate Paleozoic and Lower Cretaceous rocks and predate Late Cretaceous stocks at some places; subsidiary faults and folds that have age constraints have slip directions compatible with right slip along adjacent, principal faults. Sedimentation patterns of Lower and Upper Cretaceous rocks indicate that faults of the Lewis and Clark line fragmented the foredeep region of the foreland basin into separate northern and southern basins in Late Cretaceous time. The Lower and Upper Cretaceous Blackleaf Formation (Albian and lower Cenomanian) was deposited in a continuous foredeep basin that extended across the Lewis and Clark line from north of the Canadian border to southwestern Montana, a distance of about 450 km. North of the Lewis and Clark line, middle and upper Cenomanian rocks are absent, and a thin sequence of uppermost Cenomanian to Campanian rocks was deposited in a marine environment that changed to a strand-line and continental environment in early Campanian time. South of the Lewis and Clark line, middle and upper Cenomanian deposits are also absent, but a thick sequence of Turonian-to-Campanian rocks was deposited in brackish water and strand-line environments, and during later Campanian time, in a continental environment. In the region between the St. Marys-Helena Valley and Bald Butte faults, a barrier may have formed that served as a local sediment source between foredeep regions in the northern and southern foreland basin during the period 91 to 75 Ma. South of the Bald Butte fault, an extensional tectonic regime contributed to a higher sediment-accumulation rate in the foredeep region along the north border of the southern basin (30 cm/1,000 yr), as compared to lower sediment-accumulation rates (6.9 and 7.8 cm/ 1,000 yr) in the foredeep region of the south part of the northern basin.

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