SEARCH · Geology Reports

Results for “Interpretation”

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

SourceResearch connectionFrom yearThrough year

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

At least 1,135 records · Page 63Linked to original sources

USGS1999

Historical trends in salinity and substrate in central and northern Florida Bay: A Paleoecological Reconstruction using modern analogue data

Understanding the natural spatial and temporal variability that exists within an ecosystem is a critical component of efforts to restore systems to their natural state. Analysis of benthic foraminifers and molluscs from modern monitoring sites within Florida Bay allows us to determine what environmental parameters control spatial and temporal variability of their assemblages. Faunal assemblages associated with specific environmental parameters, including salinity and substrate, serve as proxies for an interpretation of paleoecologic data. The faunal record preserved in two shallow (<2 m) cores in central Florida Bay (Russell Bank and Bob Allen Bank) provides a record of historical trends in environmental parameters for those sites. Analysis of these two cores has revealed two distinct patterns of salinity change at these sites: 1) a long-term trend of slightly increasing average salinity; and 2) a relatively rapid change to salinity fluctuations of greater frequency and amplitude, beginning around the turn of the century and becoming most pronounced after 1940. The degree of variability in substrate types at each locality limits interpretations of substrate trends to specific sites. A common sequence of change is present in the Russell Bank and Bob Allen Bank cores: from mixed grass and bare-sediment indicators at the bottom of the cores, to bare-sediment dwellers in the center, to a dominance of vegetative-cover indicators at the top of the cores. Changes in interpreted salinity patterns around the turn of the century are consistent with the timing of the construction of the Flagler Railroad from 1905 to 1912, and the Tamiami Trail and the canal and levee systems between 1915 and 1928. Beginning around 1940, the changes in the frequency and amplitude of salinity fluctuations may be related to changes in water management practices, meteorologic events (frequent hurricanes coupled with severe droughts in 1943 and 1944), or a combination of factors. The correspondence of these changes in Florida Bay with changes in the terrestrial Everglades suggests factors affecting the entire ecosystem are responsible for the salinity and substrate patterns seen in Florida Bay.

Florida↗

USGS1984

Proper expression of metabolizable energy in avian energetics

We review metabolizable energy (ME) concepts and present evidence suggesting that the form of ME used for analyses of avian energetics can affect interpretation of results. Apparent ME (AME) is the most widely used measure of food energy available to birds. True ME(TME) differs from AME in recognizing fecal and urinary energy of nonfood origin as metabolized energy. Only AME values obtained from test birds fed at maintenance levels should be used for energy analyses. A practical assay for TME has shown that TME estimates are less sensitive than AME to variation in food intake. The TME assay may be particularly useful in studies of natural foods that are difficult to obtain in quantities large enough to supply test birds with maintenance requirements. Energy budgets calculated from existence metabolism should be expressed as kJ of AME and converted to food requirements with estimates of metabolizability given in kJ AME/g.

Condor↗

USGS1969

Isotopic composition of lead in volcanic rocks from central Honshu — with regard to basalt genesis

The isotopic composition of lead and concentrations of lead, uranium, and thorium were determined in tholeiitic and high-alumina basalts, and their calc-alkali rock series, from central Japan. The isotopic composition of lead of high alumina basalts is similar to that of tholeiites from adjacent areas, whereas their silicic differentiates (calc-alkali rock series) are rich in 207 Pb and 208 Pb. This is interpreted as a result of crustal contamination. The isotopic composition of lead in the primary basalts gradually decreases in radiogenic character from the Pacific Ocean side to the Japan Sea side, whereas the observed 238 U/ 204 Pb and 232 Th/ 238 U ratios in the basalts increase in the same direction. This inverse correlation can be interpreted as resulting from differentiation of the upper mantle about 3.6b.y. ago, with tholeiite (Pacific side) generated from a shallower zone than the alkali basalt (Japan Sea side). The magma generation is associated with a process which extracts Pb preferentially to U and Th at shallower depth and U and Th preferentially to Pb at deeper depth in the past (multi differentiation for the source region) or at the magma generation stage. An alternative interpretation of this inverse correlation is that the ocean floor is being thrust under the Japanese Island arcs and the isotopic difference is produced by the degree of mixing of mantle material under the arcs with thrust material.

Honshu↗

USGS1999

Distinguishing Grenvillian basement from pre-Taconian cover rocks in the Northern Appalachians

Distinguishing Grenvillian basement rocks from pre-Taconian cover sequences in the Appalachians is a first-order problem essential for accurate structural interpretations. The Cavendish Formation in southeastern Vermont presents a classic example of this problem. Doll and others (1961) showed the Cavendish Formation as younger than the Middle Proterozoic Mount Holly Complex but older than the lithologically similar Cambrian Tyson and Hoosac Formations. More recently, the name Cavendish Formation has been informally abandoned, and its metasedimentary units have been mapped as the Tyson and Hoosac Formations of Late Proterozoic to Cambrian age. In a radical departure from these interpretations, Ratcliffe and others (1997) reassigned metasedimentary rocks of the Cavendish Formation to the Mount Holly Complex based on an inferred intrusive relationship between them and a 1.42 Ga tonalite. This new age assignment, if correct, requires a completely new structural interpretation of the region. SHRIMP and Pb evaporation ages of detrital zircons extracted from a quartzite layer from Cavendish Gorge near the proposed intrusive contact with the tonalite constrain the time of deposition of the Cavendish Formation. Grain shapes of the zircons vary from euhedral to nearly spherical. Virtually all the grains have pitted surfaces and show at least some rounding of edges and terminations; grains exhibit oscillatory zoning typical of zircons that crystallized from a magma. Single-grain Pb evaporation analyses of ten zircons and SHRIMP analyses of 15 zircons all yield ages less than 1.42 Ga. Seven of the grains are consistent with derivation from the Bull Hill Gneiss that postdates the Grenville orogenic cycle and predates deposition of the Cavendish Formation. Thus, the metasedimentary units of the Cavendish Formation should not be assigned to the Mount Holly Complex.

northern Appalachians↗

USGS2025

3D Converted wave reverse time migration imaging

We describe a newly developed method for recovering high-resolution images of seismic discontinuities, such as subducting slabs, in 3D. Our method makes use of converted S → P or P → S waves observed by dense arrays of seismometers to infer the locations and relative strengths of seismic discontinuities at depth in a target region. Observed direct and converted waves are backpropagated to their times of origin. The time-reversed wavefield is then separated into its constituent P and S components via the Helmholtz decomposition, and those separated wavefields are used to compute imaging functions that characterize the locations and relative strengths of seismic discontinuities. Imaging functions may be designed to use either S → P or P → S waves, so that users can target those arrivals expected to be most dominant in a given dataset. We have previously demonstrated the efficacy of our method in two dimensions, and we now present a 3D implementation of our technique which addresses the significant computational challenges posed by the size of volumetric wavefield data in three dimensions. Through a series of synthetic examples, we demonstrate that our method is capable of recovering the fine scale structure of a subducting slab given realistic station coverage and earthquake sources. We investigate optimal seismic station geometries for our technique and explore image interpretability in regions with poor data coverage. We find that linear station geometries yield more optimal, interpretable imaging functions than collections of small arrays can. We also show that our method can successfully recover bothS → P or P → S images when realistic shear earthquake sources are used, and we explore the additional computational challenges presented by the high frequency content of S waves. Our results demonstrate the potential for our technique to recover high-resolution information about subducting slabs in real-world regions, given that relatively sparse seismic arrays with only approximately 100 stations are capable of recovering interpretable imaging functions from just a few realistic earthquake sources for multiple discontinuities at significant depth in an area of approximately 400~sq~km.

Seismica↗

USGS2010

Multi-stage origin of the Coast Range ophiolite, California: Implications for the life cycle of supra-subduction zone ophiolites

The Coast Range ophiolite of California is one of the most extensive ophiolite terranes in North America, extending over 700 km from the northernmost Sacramento Valley to the southern Transverse Ranges in central California. This ophiolite, and other ophiolite remnants with similar mid-Jurassic ages, represent a major but short-lived episode of oceanic crust formation that affected much of western North America. The history of this ophiolite is important for models of the tectonic evolution of western North America during the Mesozoic, and a range of conflicting interpretations have arisen. Current petrologic, geochemical, stratigraphic, and radiometric age data all favor the interpretation that the Coast Range ophiolite formed to a large extent by rapid extension in the forearc region of a nascent subduction zone. Closer inspection of these data, however, along with detailed studies of field relationships at several locales, show that formation of the ophiolite was more complex, and requires several stages of formation. Our work shows that exposures of the Coast Range ophiolite preserve evidence for four stages of magmatic development. The first three stages represent formation of the ophiolite above a nascent subduction zone. Rocks associated with the first stage include ophiolite layered gabbros, a sheeted complex, and volcanic rocks vith arc tholeiitic or (roore rarely) low-K calc-alkaline affinities. The second stage is characterized by intrusive wehrlite-clinopyroxenite complexes, intrusive gabbros, Cr-rich diorites, and volcanic rocks with high-Ca boninitic or tholeiitic ankaramite affinities. The third stage includes diorite and quartz diorite plutons, felsic dike and sill complexes, and calc-alkaline volcanic rocks. The first three stages of ophiolite formation were terminated by the intrusion of mid-ocean ridge basalt dikes, and the eruption of mid-ocean ridge basalt or ocean-island basalt volcanic suites. We interpret this final magmatic event (MORB dikes) to represent the collision of an active spreading ridge. Subsequent reorganization of relative plate motions led to sinistral transpression, along with renewed subduction and accretion of the Franciscan Complex. The latter event resulted in uplift and exhumation of the ophiolite by the process of accretionary uplift.

California↗

USGS1963

Seismic-refraction measurements of crustal structure between Santa Monica Bay and Lake Mead

A reversed seismic-refraction profile was recorded between Santa Monica Bay, California, and Lake Mead, Nevada, during November 1961. Depth to the Mohorovicic discontinuity was determined to be approximately 29 km at Santa Monica Bay, 36 km under the Transverse Ranges, 26 km under the Mojave Desert, and 30 km at Lake Mead. Prominent events on the seismograms in the distance range 30 to 150 km are interpreted as reflections from the Mohorovicic discontinuity and from a crustal layer of intermediate velocity. These reflected events are used to make a detailed interpretation of crustal structure. The velocity of compressional waves in the mantle immediately below the Mohorovicic discontinuity was determined to be 7.8 km/sec. The velocity of compressional waves in the intermediate layer is near 7.0 km/sec. The apparent velocity of the direct arrival in the crustal rocks near the surface is 6.l km/sec north-east of Santa Monica Bay, and 6.1 km/sec southwest of Lake Mead. The higher apparent velocity for the direct arrival from Santa Monica Bay seems to be the result of thinning toward the east of low-velocity rocks near the surface. These low-velocity near-surface rocks are Cenozoic sedimentary rocks and fractured and weathered granitic and metamorphic rocks. The velocity of Sg was determined to be 3.4. km/sec near Lake Mead. A prominent phase with apparent velocity of 6.3 to 6.4 km/sec was recorded at distances beyond 200 km. This phase is identified as P and is interpreted as a reflection from the intermediate layer. Amplitude measurements support the conclusion that the P phase is a reflected arrival.

California;Nevada↗

USGS1997

Clastic rocks associated with the Midcontinent rift system in Iowa

The Middle Proterozoic Midcontinent Rift System (MRS) of North America is a failed rift that formed in response to region-wide stresses about 1,100 Ma. In Iowa, the MRS is buried beneath 2,200?3,500 ft of Paleozoic and Mesozoic sedimentary rocks and Quaternary glaciogenic deposits. An extremely large volume of sediments was deposited within basins associated with the rift at several stages during its development. Although the uplift of a rift-axial horst resulted in the erosional removal of most of these clastic rocks from the central region of the MRS in Iowa, thick sequences are preserved in a series of horst-bounding basins. Recent studies incorporating petrographic analysis, geophysical modeling, and other analytical procedures have led to the establishment of a preliminary stratigraphy for these clastic rocks and interpretations of basin geometries. This information has allowed the refinement of existing theories and history of MRS formation in Iowa. Additionally, drill samples previously interpreted as indicating the existence of early Paleozoic basins overlying the Proterozoic MRS basins were re-examined. Samples previously interpreted as deep-lying Paleozoic rocks are now known to have caved from upper levels of the drillhole and were out of stratigraphic position. No deep Paleozoic basins exist in this area. These investigations led to the development of petrographic parameters useful in differentiating the Proterozoic MRS Red clastics from Paleozoic clastic rocks having similar lithologies.

Bulletin↗

USGS2001

Potential for deep basin-centered gas accumulation in Hanna Basin, Wyoming

The potential for a continuous-type basin-centered gas accumulation in the Hanna Basin in Carbon County, Wyoming, is evaluated using geologic and production data including mud-weight, hydrocarbon-show, formation-test, bottom-hole-temperature, and vitrinite reflectance data from 29 exploratory wells. This limited data set supports the presence of a hypothetical basin-centered gas play in the Hanna Basin. Two generalized structural cross sections illustrate our interpretations of possible abnormally pressured compartments. Data indicate that a gas-charged, overpressured interval may occur within the Cretaceous Mowry, Frontier, and Niobrara Formations at depths below 10,000 ft along the southern and western margins of the basin. Overpressuring may also occur near the basin center within the Steele Shale and lower Mesaverde Group section at depths below 18,000 to 20,000 ft. However, the deepest wells drilled to date (12,000 to 15,300 ft) have not encountered over-pressure in the basin center. This overpressured zone is likely to be relatively small (probably 20 to 25 miles in diameter) and is probably depleted of gas near major basement reverse faults and outcrops where gas may have escaped. Water may have invaded reservoirs through outcrops and fracture zones along the basin margins, creating an extensive normally pressured zone. A zone of subnormal pressure also may exist below the water-saturated, normal-pressure zone and above the central zone of overpressure. Subnormal pressures have been interpreted in the center of the Hanna Basin at depths ranging from 10,000 to 25,000 ft based on indirect evidence including lost-circulation zones. Three wells on the south side of the basin, where the top of the subnormally pressured zone is interpreted to cut across stratigraphic boundaries, tested the Niobrara Formation and recovered gas and oil shows with very low shut-in pressures.

Bulletin↗

USGS2007

Geologic map of Nevada

The purpose of the Geologic Map of Nevada is to provide an integrated set of digital geologic information that can be used for regional geologic and rigorous spatial analysis. Two components of this map represent new information that has not been published in this form before. The new geology layer was created by merging into a single file individual digital Nevada county geologic maps (Hess and Johnson, 1997), published at a scale of 1:250,000. A new regional interpretation was created to unify all of the different county rock units, and then appropriate edits and modifications were made to the file to reflect additional geologic information and more current geologic interpretations. All possible sources of information were not utilized in the scope of this project, but rather the goal was to create a consistent Statewide 1:250,000-scale map that would facilitate regional geologic interpretation and be a foundation for future spatial analyses of digital data. Secondly, a new database of conodont biostratigraphic data compiled and analyzed by Anita Harris is also incorporated into the map. Information about many, but not all, of these conodont samples have been published separately elsewhere over the years, but they have not been presented together in a single digital database. Other previously published data layers are used in this map to enhance the usefulness of the geologic information. These layers include mineral deposit locations, oil well locations, and cartographic layers such as county boundaries, roads, towns, cities, rivers, water bodies, township, range and section grids, quadrangle grids, and topography. A summary of these components is given below, and complete descriptions of each layer are provided in the digital metadata.

Nevada↗

USGS2003

Geologic map of the Buckeystown quadrangle, Frederick and Montgomery Counties, Maryland, and Loudoun County, Virginia

The Buckeystown quadrangle is underlain mostly by rocks of the western Piedmont province and a portion of the eastern Blue Ridge province. The western Piedmont province is underlain by Late Proterozoic(?) and Lower Cambrian(?) metasedimentary rocks of the Westminster terrane, Lower and Middle Cambrian metasedimentary rocks and Upper Cambrian to Lower Ordovician carbonate rocks of the Frederick Valley synclinorium, Upper Triassic sedimentary rocks of the Mesozoic Culpeper basin, and Early Jurassic dikes; Lower Cambrian metasedimentary rocks underlie the Blue Ridge province. Within the western Piedmont, Lower Cambrian(?) metasedimentary rocks of the Sugarloaf Mountain anticlinorium are interpreted to be exposed in a tectonic window (A.A. Drake, Jr., U.S. Geological Survey, oral commun., 1989; Horton and others, 1989; Rankin and others, 1989) through the complexly deformed allochthonous rocks of the Westminster terrane (Muller and others, 1989). The undated rocks of the Westminster terrane are interpreted to be rise-slope deep-water deposits of the Iapetus Ocean that were transported westward onto the Laurentian margin (ancestral North America) along the Martic thrust fault during the Ordovician Taconic orogeny (Horton and others, 1989). Continental margin strata, which underlie the Sugarloaf Mountain anticlinorium and continental margin-slope strata which underlie the Frederick Valley synclinorium, are here correlated with the Lower Cambrian Chilhowee Group and overlying carbonate rocks on the limbs of the Blue Ridge-South Mountain anticlinorium to the west. The relation of the Sugarloaf Mountain Quartzite (Jonas and Stose, 1938b) to surrounding rocks is controversial (Scotford, 1951; Stose and Stose, 1951; Thomas, 1952). The Martic thrust fault (Jonas, 1924, 1927; Knopf and Jonas, 1929) and the interpretation that the Sugarloaf Mountain anticlinorium (Scotford, 1951; Thomas, 1952) is a tectonic window through the Martic thrust sheet (A.A. Drake, Jr., U.S. Geological Survey, oral commun., 1989) further complicate the stratigraphic correlation of these rocks. Upper Triassic sedimentary rocks of the Culpeper basin consist of westward-dipping conglomerate, sandstone, and siltstone. These rocks, as well as intrusive Early Jurassic diabase dikes, accumulated during an early Mesozoic rifting event that resulted in the opening of the Atlantic Ocean. Contractional faults of Paleozoic orogenesis and extensional faults related to Mesozoic rifting indicate a complex tectonic history for this region. Cenozoic deposits, which overlie the bedrock, include high- and low-level alluvial terraces, residual gravel, colluvium, and alluvium. Terrace deposits of the ancestral Potomac River and the Monocacy River are as much as 183 ft and 140 ft, respectively, above the present river levels. Isolated residual gravel deposits that form in place from the weathering of the Upper Cambrian Frederick Formation superficially resemble terrace deposits. Colluvium of quartzite boulders is concentrated in hillslope depressions on Sugarloaf Mountain, and fanlike aprons of colluvial quartz pebbles cover the Triassic rocks on the west side of the Culpeper basin. Alluvium was mapped along the Potomac and Monocacy Rivers and all their tributaries. Altitude ranges from 200 ft along the Potomac River to 1,282 ft on the crest of Sugarloaf Mountain. The map area includes the Chesapeake and Ohio Canal National Historical Park, and the Monocacy Natural Resources Area. Sugarloaf Mountain is a registered natural landmark. Parts of the Buckeystown quadrangle were mapped by Jonas and Stose (1938a, scale 1:62,500), Scotford (1951, scale 1:12,500), Thomas (1952, scale 1:25,000), Cloos and Cook (1953, 1:62,500), Reinhardt (1974, scale 1:62,500), Froelich 1975, scale 1:62,500), and Lee (1979, scale 1:24,000). The map area is subdivided into five domains. Allochthonous rocks of the Westminster terrane are thrust onto rocks of the Frederick Valley synclinorium. Within the Westminster terrane of Muller and others (1989), the Sugarloaf Mountain Quartzite and Urbana Formation underlie the parautochthonous Sugarloaf Mountain anticlinorium. The Lower and Middle Cambrian Araby Formation and Upper Cambrian Frederick Formation crop out on the east limb of the Frederick Valley synclinorium. The Frederick Formation and Upper Cambrian and Lower Ordovician Grove Formation lie in the trough of the Frederick Valley synclinorium. Lower Cambrian Harpers, Antietam, and Tomstown Formations crop out on the east limb of the Blue Ridge-South Mountain anticlinorium in the extreme northwest corner of the map. The Blue Ridge-South Mountain anticlinorium is separated from the Frederick Valley synclinorium by Upper Triassic sedimentary rocks in the Culpeper basin half graben.

Maryland, Virginia↗

USGS2001

Geologic Map of the Hellas Region of Mars

INTRODUCTION This geologic map of the Hellas region focuses on the stratigraphic, structural, and erosional histories associated with the largest well-preserved impact basin on Mars. Along with the uplifted rim and huge, partly infilled inner basin (Hellas Planitia) of the Hellas basin impact structure, the map region includes areas of ancient highland terrain, broad volcanic edifices and deposits, and extensive channels. Geologic activity recorded in the region spans all major epochs of martian chronology, from the early formation of the impact basin to ongoing resurfacing caused by eolian activity. The Hellas region, whose name refers to the classical term for Greece, has been known from telescopic observations as a prominent bright feature on the surface of Mars for more than a century (see Blunck, 1982). More recently, spacecraft imaging has greatly improved our visual perception of Mars and made possible its geologic interpretation. Here, our mapping at 1:5,000,000 scale is based on images obtained by the Viking Orbiters, which produced higher quality images than their predecessor, Mariner 9. Previous geologic maps of the region include those of the 1:5,000,000-scale global series based on Mariner 9 images (Potter, 1976; Peterson, 1977; King, 1978); the 1:15,000,000-scale global series based on Viking images (Greeley and Guest, 1987; Tanaka and Scott, 1987); and detailed 1:500,000-scale maps of Tyrrhena Patera (Gregg and others, 1998), Dao, Harmakhis, and Reull Valles (Price, 1998; Mest and Crown, in press), Hadriaca Patera (D.A. Crown and R. Greeley, map in preparation), and western Hellas Planitia (J.M. Moore and D.E. Wilhelms, map in preparation). We incorporated some of the previous work, but our map differs markedly in the identification and organization of map units. For example, we divide the Hellas assemblage of Greeley and Guest (1987) into the Hellas Planitia and Hellas rim assemblages and change the way units within these groupings are identified and mapped (table 1). The new classification scheme includes broad, geographically related categories and local, geologically and geomorphically related subgroups. Because of our mapping at larger scale, many of our map units were incorporated within larger units of the global-scale mapping (see table 1). Available Viking images of the Hellas region vary greatly in several aspects, which has complicated the task of producing a consistent photogeologic map. Best available image resolution ranges from about 30 to 300 m/pixel from place to place. Many images contain haze caused by dust clouds, and contrast and shading vary among images because of dramatic seasonal changes in surface albedo, opposing sun azimuths, and solar inclination. Enhancement of selected images on a computer-display system has greatly improved our ability to observe key geologic relations in several areas. Determination of the geologic history of the region includes reconstruction of the origin and sequence of formation, deformation, and modification of geologic units constituting (1) the impact-basin rim and surrounding highlands, (2) volcanic and channel assemblages on the northeast and south sides of the basin, (3) interior basin deposits, and (4) slope and surficial materials throughout the map area. Various surface modifications are attributed to volcanic, fluvial, eolian, mass-wasting, and possibly glacial and periglacial processes. Structures include basin faults (mostly inferred), wrinkle ridges occurring mainly in volcanic terrains and interior plains, volcanic collapse craters, and impact craters. Our interpretations in some cases rely on previous work, but in many significant cases we have offered new interpretations that we believe are more consistent with the observations documented by our mapping. Our primary intent for this mapping has been to elucidate the history of emplacement and modification of Hellas Planitia materials, which form the basis for analysis of their r

IMAP↗

USGS1983

Biostratigraphic correlation chart of some Upper Cretaceous rocks from the Lost Soldier area, Wyoming to west of Craig, Colorado

This chart depicts the time-stratigraphic relations of some Upper Cretaceous rocks along the eastern and southeastern margins of the Greater Green River Basin, south-central Wyoming and northwestern Colorado. The purpose of this report is to release a preferred set of correlations based upon marine mollusk biostratigraphy. The senior author, with the help of B. E. Law, has acquired, synthesized, compiled, and interpreted data from various sources. These include selected published documents (see "References Cited") and unpublished reports of fossil identifications by W. A. Cobban who examined collections made by the late J. R. Gill. Numerous measured sections of Gill's were also utilized. It must be emphasized that all interpretations on this chart are based on information obtained from these sources and the senior author has yet to substantiate these correlations in the field. Not all data from the area of this study is included herein because it is either repetitive in nature or its reliability is uncertain. This uncertainty is due to the ambiguity inherent in both fossil identification and stratigraphic interpretation. Questionable unpublished material has been omitted while published data which is inconsistent with the senior author's correlations may be found in the footnotes portion of this report. The rock units are assigned to a range of ammonites that have been related to an absolute time scale. The ammonite zonation and age boundaries are adapted from Obradovich and Cobban (1975). "D" numbers are provided for each geographic locality where fossils were collected and described by personnel of the U.S. Geological Survey. These fossils may be accessed at the offices of the Survey in Lakewood, Colorado.

Colorado, Wyoming↗

USGS1990

Map showing drill-hole depths, lithologic intercepts, and partial isopachs of basin fill in the Winnemucca 1 degree by 2 degrees quadrangle, Nevada

The purpose of this map is to aid in the mineral-resource assessment and exploration of covered host rocks by displaying and interpreting data that can be used to estimate the depth of basin fill in the Winnemucca 1° by 2° quadrangle, Nevada. Publicly available information used in making this map includes water, petroleum, and geothermal well data, gravity data and models, seismic profiles, and geologic and geomorphic reports. Wells logs used for this map of the Winnemucca quadrangle are from the following sources: (1) logs of more than 1,000 water wells reported to the State of Nevada Division of Water Resources, which are on file with them in Reno and at the with U.S. Geological Survey in Carson City, (2) 44 petroleum wells collected by the Nevada Bureau of Mines (Lintz, 1957; Schilling and Garside, 1968; Garside and Schilling, 1977, Garside and others, 1977; 1988), and (3) Two geothermal wells reported in Zoback (1979) and Flynn and others (1982). Data from isostatic residual and Bouguer gravity maps by Wagini (1985) contributed to the interpretation of basin configuration. Gravity models of Dixie Valley (Schaefer, 1982, and Speed, 1976) and Grass Valley (Grannell and Noble, 1977) and seismic profiles of Grass and Pine Valleys (Potter and others, 1987) helped refine basis interpretations in those areas. The geologic base map of Paleozoic and Mesozoic igneous and sedimentary rocks, Tertiary volcanic and sedimentary rocks, and Cenozoic structures was simplified from Stewart and Carlson (1976b).

Nevada↗

USGS1992

Bathymetry at the head of the Cape Fear Slide, offshore North Carolina

The Cape Fear Slide is the largest mass-movement that has been observed on the U.S. Atlantic Margin. It is located off the Carolinas on the continental rise in approximately 1,200-5,500 m water depth and extends downslope for over 300 km (Popenoe, 1982). These maps show the bathymetry at the head of the Cape Fear Slide as interpreted from single-channel 3.5 kHz seismic-reflection profiles and mid-range Sea Marc I sidescan sonar imagery (Popenoe, 1985; Popenoe and others, 1991; Schmuck, 1991). The 3.5 kHz data consist of over 1000 km of profiles that were collected in 1988 for the University of North Carolina, Department of Geology. The UNC 3.5 kHz data were used as the main data set in interpreting the bathymetry. The sidescan sonar data were collected in 1980 by the U.S. Geological Survey in cooperation with the Lamont-Doherty Geological Observatory for the U.S. Bureau of Land Management Environmental Studies Program. Only 28 km (5 km swath width) of the sidescan data were used in the interpretation to identify the morphology of the main slump scarp and visible secondary scarps.

North Carolina↗

USGS2002

Geologic map of the Storm King Mountain quadrangle, Garfield County, Colorado

New 1:24,000-scale geologic mapping in the Storm King Mountain 7.5' quadrangle, in support of the USGS Western Colorado I-70 Corridor Cooperative Geologic Mapping Project, provides new data on the structure on the south margin of the White River uplift and the Grand Hogback and on the nature, history, and distribution of surficial geologic units. Rocks ranging from Holocene to Proterozoic in age are shown on the map. The Canyon Creek Conglomerate, a unit presently known to only occur in this quadrangle, is interpreted to have been deposited in a very steep sided local basin formed by dissolution of Pennsylvanian evaporite late in Tertiary time. At the top of the Late Cretaceous Williams Fork Formation is a unit of sandstone, siltstone, and claystone from which Late Cretaceous palynomorphs were obtained in one locality. This interval has been mapped previously as Ohio Creek Conglomerate, but it does not fit the current interpretation of the origin of the Ohio Creek. Rocks previously mapped as Frontier Sandstone and Mowry Shale are here mapped as the lower member of the Mancos Shale and contain beds equivalent to the Juana Lopez Member of the Mancos Shale in northwestern New Mexico. The Pennsylvanian Eagle Valley Formation in this quadrangle grades into Eagle Valley Evaporite as mapped by Kirkham and others (1997) in the Glenwood Springs area. The Storm King Mountain quadrangle spans the south margin of the White River uplift and crosses the Grand Hogback monocline into the Piceance basin. Nearly flat lying Mississippian through Cambrian sedimentary rocks capping the White River uplift are bent into gentle south dips and broken by faults at the edge of the uplift. South of these faults the beds dip moderately to steeply to the south and are locally overturned. These dips are interrupted by a structural terrace on which are superposed numerous gentle minor folds and faults. This terrace has an east-west extent similar to that of the Canyon Creek Conglomerate to the north. We interpret that the terrace formed by movement of Eagle Evaporite from below in response to dissolution and diapirism in the area underlain by the conglomerate. A low-angle normal fault dipping gently north near the north margin of the quadrangle may have formed also in response to diapirism and dissolution in the area of the Canyon Creek Conglomerate. Along the east edge of the quadrangle Miocene basalt flows are offset by faults along bedding planes in underlying south-dipping Cretaceous rocks, probably because of diapiric movement of evaporite into the Cattle Creek anticline (Kirkham and Widmann, 1997). Steep topography and weak rocks combine to produce a variety of geologic hazards in the quadrangle.

Miscellaneous Field Studies Map↗

USGS2000

Regional seismic lines reprocessed using post-stack processing techniques: National Petroleum Reserve, Alaska

This CD-ROM contains stacked, migrated, 2-Dimensional seismic reflection data and associated support information for 22 regional seismic lines (3,470 line-miles) recorded in the National Petroleum Reserve – Alaska (NPRA) from 1974 through 1981. Together, these lines constitute about one-quarter of the seismic data collected as part of the Federal Government’s program to evaluate the petroleum potential of the Reserve. The regional lines, which form a grid covering the entire NPRA, were created by combining various individual lines recorded in different years using different recording parameters. These data were reprocessed by the USGS using modern, post-stack processing techniques, to create a data set suitable for interpretation on interactive seismic interpretation computer workstations. Reprocessing was done in support of ongoing petroleum resource studies by the USGS Energy Program. The CD-ROM contains the following files: 1) 22 files containing the digital seismic data in standard, SEG-Y format; 2) 1 file containing navigation data for the 22 lines in standard SEG-P1 format; 3) 22 small scale graphic images of each seismic line in Adobe Acrobat ® PDF format; 4) a graphic image of the location map, generated from the navigation file, with hyperlinks to the graphic images of the seismic lines; 5) an ASCII text file with cross-reference information for relating the sequential trace numbers on each regional line to the line number and shotpoint number of the original component lines; and 6) an explanation of the processing used to create the final seismic sections (this document). The SEG-Y format seismic files and SEG-P1 format navigation file contain all the information necessary for loading the data onto a seismic interpretation workstation.

Alaska↗

USGS2001

The Cretaceous-Tertiary boundary interval in Badlands National Park, South Dakota

A marine K-T boundary interval has been identified throughout the Badlands National Park region of South Dakota. Data from marine sediments suggest that deposits from two asteroid impacts (one close, one far away) may be preserved in the Badlands. These impact-generated deposits may represent late Maestrichtian events or possibly the terminal K-T event. Interpretation is supported by paleontological correlation, sequence stratigraphy, magnetostratigraphy, and strontium isotope geochronology. This research is founded on nearly a decade of NPS approved field work in Badlands National Park and a foundation of previously published data and interpretations. The K-T boundary occurs within or near the base of a stratigraphic interval referred to as the "Interior Zone." We interpret the stratigraphy of the Interior Zone as a series of distinct, recognizable lithologic members and units from oldest to youngest, an upper weathered interval of the Elk Butte Member of the Pierre Shale (early late Maestrichtian), a complete (albeit condensed) interval of Fox Hill Formation, a pedogenically altered K-T Boundary "Disturbed Zone," and a generally unresolved sequence of marine to marginal marine units ranging in age from possibly latest Maestrichtian to late Paleocene (the "Yellow Mounds"), that underlie a basal red clay unit (the late Eocene overbank channel facies of the Chamberlain Pass Formation at the base of the White River Group). Within this sequence is a series of unconformities that all display some degree of subaerial weathering and erosion. The dating of marine fossils above and below these unconformities are in line with generally accepted global sea-level changes recognized for the late Campanian through early Eocene. Within the greater framework of regional geology, these findings support that the Western Interior Seaway and subsequent Cannonball Seaway were dependently linked to the changing base-level controlled by sea-level of the global ocean through the Gulf of Mexico and possibly the Arctic Ocean. The variation of facies preserved in Late Cretaceous strata in the Badlands National Park area were in part controlled by local or regional tectonic blocks that were either rising or sinking contemporaneous with deposition.

South Dakota↗