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At least 37 records · Page 2Linked to original sources
USGS2005

Seismic architecture and lithofacies of turbidites in Lake Mead (Arizona and Nevada, U.S.A.), an analogue for topographically complex basins

Turbidites, which have accumulated in Lake Mead since completion of the Hoover Dam in 1935, have been mapped using high-resolution seismic and coring techniques. This lake is an exceptional natural laboratory for studying fine-grained turbidite systems in complex topographic settings. The lake comprises four relatively broad basins separated by narrow canyons, and turbidity currents run the full length of the lake. The mean grain size of turbidites is mostly coarse silt, and the sand content decreases from 11-30% in beds in the easternmost basin nearest the source to 3-14% in the central basins to 1-2% in the most distal basin. Regionally, the seismic amplitude mimics the core results and decreases away from the source. The facies and morphology of the sediment surface varies between basins and suggests a regional progression from higher-energy and possibly channelized flows in the easternmost basin to unchannelized flows in the central two basins to unchannelized flows that are ponded by the Hoover Dam in the westernmost basin. At the local scale, turbidites are nearly flat-lying in the central two basins, but here the morphology of the basin walls strongly affects the distribution of facies. One of the two basins is relatively narrow, and in sinuous sections reflection amplitude increases toward the outsides of meanders. Where a narrow canyon debouches into a broad basin, reflection amplitude decreases radially away from the canyon mouth and forms a fan-like deposit. The fine-grained nature of the turbidites in the most distal basin and the fact that reflections drape the underlying pre-impoundment surface suggest ponding here. The progression from ponding in the most distal basin to possibly channelized flows in the most proximal basin shows in plan view a progression similar to the stratigraphic progression documented in several minibasins in the Gulf of Mexico. Copyright ?? 2005, SEPM (Society for Sedimentary Geology).

Arizona, Nevada↗
USGS2006

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

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

Caribbean Sea, Gulf of Mexico↗
USGS2006

usSEABED: Pacific Coast (California, Oregon, Washington) Offshore Surficial-Sediment Data Release, version 1

Over the past 50 years there has been an explosion in scientific interest, research effort, and information gathered on the geologic sedimentary character of the continental margin of the United States. Data and information from thousands of publications have greatly increased our scientific understanding of the geologic origins of the margin surface but rarely have those data been combined and integrated. This publication is the first release of the Pacific coast data from the usSEABED database. The report contains a compilation of published and unpublished sediment texture and other geologic data about the sea floor from diverse sources. usSEABED is an innovative database system developed to unify assorted data, with the data processed by the dbSEABED system. Examples of maps displaying attributes such as grain size and sediment color are included. This database contains information that is a scientific foundation for the U.S. Geological Survey (USGS) Sea floor Mapping and Benthic Habitats project and the Marine Aggregate Resources and Processes assessment project, and will be useful to the marine science community for other studies of the Pacific coast continental margin. The publication is divided into 10 sections: Home, Introduction, Content, usSEABED (data), dbSEABED (processing), Data Catalog, References, Contacts, Acknowledgments, and Frequently Asked Questions. Use the navigation bar on the left to navigate to specific sections of this report. Underlined topics throughout the publication are links to more information. Links to specific and detailed information on processing and to those to pages outside this report will open in a new browser window.

California, Oregon, Washington↗
USGS2009

Sulfate-rich eolian and wet interdune deposits, erebus crater, meridiani Planum, Mars

This study investigates three bedrock exposures at Erebus crater, an ?? 300 m diameter crater approximately 4 km south of Endurance crater on Mars. These outcrops, called Olympia, Payson, and Yavapai, provide additional evidence in support of the dune-interdune model proposed for the formation of the deposits at the Opportunity landing site in Meridiani Planum. There is evidence for greater involvement of liquid water in the Olympia outcrop exposures than was observed in Eagle or Endurance craters. The Olympia outcrop likely formed in a wet interdune and sand sheet environment. The facies observed within the Payson outcrop, which is likely stratigraphically above the Olympia outcrop, indicate that it was deposited in a damp-wet interdune, sand sheet, and eolian dune environment. The Yavapai outcrop, which likely stratigraphically overlies the Payson outcrop, indicates that it was deposited in primarily a sand sheet environment and also potentially in an eolian dune environment. These three outcrop exposures may indicate an overall drying-upward trend spanning the stratigraphic section from its base at the Olympia outcrop to its top at the Yavapai outcrop. This contrasts with the wetting-upward trend seen in Endurance and Eagle craters. Thus, the series of outcrops seen at Meridiani by Opportunity may constitute a full climatic cycle, evolving from dry to wet to dry conditions. ?? 2009, SEPM (Society for Sedimentary Geology).

Journal of Sedimentary Research↗
USGS2005

Reconstructing a mid-Cretaceous landscape from paleosols in western Canada

The Albian Stage of the mid-Cretaceous was a time of equable climate conditions with high sea levels and broad shallow epeiric seas that may have had a moderating affect on continental climates. A Late Albian landscape surface that developed during a regression and subsequent sea-level rise in the Western Canada Foreland Basin is reconstructed on the basis of correlation of paleosols penetrated by cores through the Paddy Member of the Peace River Formation. Reconstruction of this landscape refines chronostratigraphic relationships and will benefit future paleoclimatological studies milizing continental sphaerosiderite proxy records. The paleosols developed in estuarine sandstones and mudstones, and they exhibit evidence of a polygenetic history. Upon initial exposure and pedogenesis, the Paddy Member developed deeply weathered, well-drained cumulative soil profiles. Later stages of pedogenesis were characterized by hydromorphic soil conditions. The stages of soil development interpreted for the Paddy Member correlate with inferred stages of pedogenic development in time-equivalent formations located both basinward and downslope (upper Viking Formation), and landward and upslope (Boulder Creek Formation). On the basis of the genetic similarity among paleosols in these three correlative formations, the paleosols are interpreted as having formed along a single, continuous landscape surface. Results of this study indicate that the catena concept of pedogenesis along sloping landscapes is applicable to ancient successions. Sphaerosiderites in the Paddy Mem ber paleosols are used to provide proxy values for meteoric ??18O values at 52?? N paleolatitude in the Cretaceous Western Interior Basin. The meteoric ??18O values are used to refine existing interpretations about the mid-Cretaceous paleolatitudinal gradient in meteoric ?? 18O values, and the mid-Cretaceous hydrologic cycle. Copyright ?? 2005, SEPM (Society for Sedimentary Geology).

Journal of Sedimentary Research↗
USGS2004

The Late Cambrian SPICE (δ13C) event and the Sauk II-Sauk III regression: new evidence from Laurentian basins in Utah, Iowa, and Newfoundland

Carbon isotope data from Upper Cambrian sections in three Laurentian basins in northern Utah, central Iowa, and western Newfoundland record a large positive ??13C excursion (SPICE event) of up to + 5???. Peak ??13C ratios are well dated by trilobite collections to the middle of the Steptoean Stage (Dunderbergia Zone) and occur during maximum regression associated with formation of the Sauk II-Sauk III subsequence boundary on the North American craton. Maximum regression was marked by an influx of quartz sand into carbonate-platform settings in all three widely separated basins. In northern Utah, this quartz sand formed a thick sequence known as the Worm Creek Quartzite, which marks a conspicuous interruption of carbonate deposition during the Middle to Late Cambrian in the region. In western Newfoundland, the thickness of the quartz sand unit is much reduced but still marks a brief shutdown of the carbonate factory that is unique to the Cambrian shelf succession of the area. In the central Iowa area of the cratonic interior, an upward-shallowing carbonate succession culminates in cross-stratified trilobite grainstones at the peak of the SPICE in Dunderbergia Zone time, and the lowest point on the relative-sea-level curve is associated with the occurrence of coarse quartz sand derived from the encroaching shoreface. Although it is difficult to determine precisely the departure from baseline ??13C that marks the beginning of the SPICE excursion in the stratigraphic successions analyzed, our results are consistent with a rise and subsequent fall in ??13C tracking a major regressive-transgressive event recorded across northern Laurentia. The correlation of a major ??13C excursion with regression is similar to that described for the Late Ordovician, for which the pattern has been attributed to either increased carbonate relative to terrigenous weathering rates as ice sheets covered up organic-matter-containing silicates at high latitudes or high productivity and organic-carbon burial driven by oceanic overturn. The lack of known Steptoean-age ice sheets that could have affected the ratio of carbonate to silicate weathering rates suggests that organic-carbon burial was the likely cause of the SPICE event. We suggest that increased weathering and erosion rates during relative sea-level fall (Sauk II-III) increased the burial fraction of organic carbon in an expanded region of fine-grained siliciclastic deposits in shelf and upper slope environments during the Steptoean. ?? 2004, SEPM (Society for Sedimentary Geology).

Journal of Sedimentary Research↗
USGS2010

Micromorphology and stable-isotope geochemistry of historical pedogenic siderite formed in PAH-contaminated alluvial clay soils, Tennessee, U.S.A

Alluvial clay soil samples from six boreholes advanced to depths of 400-450 cm (top of limestone bedrock) from the Chattanooga Coke Plant (CCP) site were examined micromorphologically and geochemically in order to determine if pedogenic siderite (FeCO3) was present and whether siderite occurrence was related to organic contaminant distribution. Samples from shallow depths were generally more heavily contaminated with polycyclic aromatic hydrocarbons (PAHs) than those at greater depth. The upper 1 m in most boreholes consisted of mixtures of anthropogenically remolded clay soil fill containing coal clinker, cinder grains, and limestone gravel; most layers of coarse fill were impregnated with creosote and coal tar. Most undisturbed soil (below 1 m depth) consisted of highly structured clays exhibiting fine subangular blocky ped structures, as well as redox-related features. Pedogenic siderite was abundant in the upper 2 m of most cores and in demonstrably historical (< 100 years old) soil matrices. Two morphologies were identified: (1) sphaerosiderite crystal spherulites ranging from 10 to 200 um in diameter, and (2) coccoid siderite comprising grape-like "clusters" of crystals 5-20 ??n in diameter. The siderite, formed in both macropores and within fine-grained clay matrices, indicates development of localized anaerobic, low-Eh conditions, possibly due to microbial degradation of organic contaminants. Stable-isotope compositions of the siderite have ??13C values spanning over 25%o (+7 to - 18%o VPDB) indicating fractionation of DIC by multiple microbial metabolic pathways, but with relatively constant ??18O values from (-4.8 ?? 0.66%o VPDB) defining a meteoric sphaerosiderite line (MSL). Calculated isotope equilibrium water ??18O values from pedogenic siderites at the CCP site are from 1 to 5 per mil lighter than the groundwater ??18O values that we estimate for the site. If confirmed by field studies in progress, this observation might call for a reevaluation of low-temperature siderite-water 18O fractionations. Investigations at the CCP site thus provide valuable information on the geochemical conditions under which siderite can form in modern soils, and thus insight on controls on siderite formation in ancient soils. Copyright ?? 2010, SEPM (Society for Sedimentary Geology).

Journal of Sedimentary Research↗
USGS2010

Correlation of aptian-albian carbon isotope excursions in continental strata of the cretaceous Foreland Basin, Eastern Utah, U.S.A.

Nodular carbonates ("calcretes") in continental foreland-basin strata of the Early Cretaceous Cedar Mountain Formation (CMF) in eastern Utah yield ??13C and ??O records of changes in the exogenic carbon cycle related to oceanic anoxic events (OAEs), and terrestrial paleoclimate. Chemostratigraphic profiles of both forebulge and foredeep sections show two prominent positive ??13C excursions, each with a peak value of -3% VPDB, and having background ??13C values of about -6% VPDB. These excursions correlate with the global early Aptian (Ap7) and late Aptian-early Albian (Apl2-All) carbon isotope excursions. Aptian-Albian positive ??13C excursions in the CMF also correspond to 3-4 per mil increases in carbonate ??18O. These phenomena record local aridification events. The chemostratigraphic profile on the thinner forebulge section of the CMF is calibrated, for the first time, by a radiogenic U-Pb date of 119.4 ?? 2.6 Ma on a carbonate bed, and by detrital zircon U-Pb dates on two bounding sandstone units (maximum depositional ages of 146 Ma and 112 Ma). P??trographie observations and diagenetic analyses of micritic to microsparitic carbonates from nodules indicate palustrine origins and demonstrate that they crystallized in shallow early meteoric phreatic environments. Meteoric calcite lines derived from CMF carbonates have ??18O values ranging between -8.1 to -7.5%o VPDB, supporting an estimate of zonal mean groundwater ??18O of -6% VSMOW for an Aptian-Albian paleolatitude of 34?? N. Furthermore, our two chemostratigraphic profiles exhibit a generally proportionate thinning of correlative strata from the foredeep on to the forebulge, suggesting that there were consistently lower rates of accumulation on the forebulge during the Aptian-Albian. Identification of the global Aptian-Albian ??13C excursions in purely continental strata, as demonstrated in this paper, opens a new avenue of research by identifying specific stratigraphie intervals that record the terrestrial paleoclimatic impacts of perturbations of the global carbon cycle. Copyright ?? 2010, SEPM (Society for Sedimentary Geology).

Journal of Sedimentary Research↗
USGS2020

Sediments and the sea floor of the continental shelves and coastal waters of the United States—About the usSEABED integrated sea-floor-characterization database, built with the dbSEABED processing system

Since the second half of the 20th century, there has been an increase in scientific interest, research effort, and information gathered on the geologic sedimentary character of the continental margins of the United States. Data and information from thousands of sources have increased our scientific understanding of the character of the margin surface, but rarely have those data been combined and integrated. Initially, the U.S. Geological Survey (USGS), in cooperation with the Institute of Arctic and Alpine Research at the University of Colorado Boulder, created the usSEABED database to provide surficial sea-floor-characterization data for USGS assessments of marine-based aggregates and for studies of sea-floor habitat. Since then, the USGS has continued to build up the database as a nationwide resource for many uses and applications. Previously published data derived from the usSEABED database have been released as three USGS data series publications containing data covering the U.S. Atlantic margin, the Gulf of Mexico and Caribbean regions, and the Pacific coast. An updated USGS data release unifies the three publications, incorporates additional data and sources including data from Alaska, Hawaii, and U.S. overseas territories, and provides revised output files that fix known errors and add known or inferred sampling dates. This report accompanies the data release and contains information on the methodology and products of the usSEABED database.

Open-File Report↗
USGS2020

Geologic map of the Paeroa Fault block and surrounding area, Taupo Volcanic Zone, New Zealand

The Taupo Volcanic Zone (TVZ), New Zealand, is the most productive area of explosive silicic volcanism in the world. Faulted early and middle Pleistocene volcanic products are generally concealed beneath voluminous, generally unfaulted, younger volcanic products. An exception is the southeast margin of the TVZ where the two parallel, northeast-trending Paeroa and Te Weta Fault blocks expose Quaternary volcanic products consisting predominantly of caldera-related, rhyolitic ignimbrites and lacustrine sediments. The Taupo-Reporoa Basin is situated along the eastern part of the map area, and its northernmost part underwent collapse to form Reporoa Caldera. The Paeroa Fault block is the largest exposed fault block within the TVZ, and it encompasses early and middle Pleistocene ignimbrites and sedimentary deposits that are buried throughout the Taupo-Reporoa Basin to the east. This map displays the volcanic and sedimentary geology of ~430 km 2 of the Paeroa Fault block and the adjacent Te Weta Fault block at a scale of 1:50,000. Volcanic and sedimentary rocks are divided into the Reporoa Group, Whakamaru Group, and Huka Group (from oldest to youngest), which are overlain by relatively unfaulted late Pleistocene and Holocene surficial volcanic and sedimentary deposits.

Open-File Report↗
USGS2006

Fish-assemblage variation between geologically defined regions and across a longitudinal gradient in the Monkey River Basin, Belize

Linkages between geology and fish assemblages have been inferred in many regions throughout the world, but no studies have yet investigated whether fish assemblages differ across geologies in Mesoamerica. The goals of our study were to: 1) compare physicochemical conditions and fish-assemblage structure across 2 geologic types in headwaters of the Monkey River Basin, Belize, and 2) describe basin-scale patterns in fish community composition and structure for the benefit of conservation efforts. We censused headwater-pool fishes by direct observation, and assessed habitat size, structure, and water chemistry to compare habitat and fish richness, diversity, evenness, and density between streams in the variably metamorphosed sedimentary geologic type typical of 80% of Belize’s Maya Mountains (the Santa Rosa Group), and an anomalous extrusive geologic formation in the same area (the Bladen Volcanic Member). We also collected species-presence data from 20 sites throughout the basin for analyses of compositional patterns from the headwaters to the top of the estuary. Thirty-nine fish species in 21 families were observed. Poeciliids were numerically dominant, making up 39% of individuals captured, followed by characins (25%), and cichlids (20%). Cichlidae was the most species-rich family (7 spp.), followed by Poeciliidae (6 spp.). Habitat size and water chemistry differed strongly between geologic types, but habitat diversity did not. Major fish-assemblage differences also were not obvious between geologies, despite a marked difference in the presence of the aquatic macrophyte, Marathrum oxycarpum (Podostemaceae), which covered 37% of the stream bottom in high-nutrient streams draining the Santa Rosa Group, and did not occur in the low-P streams draining the Bladen Volcanic Member. Correlation analyses suggested that distance from the sea and amount of cover within pools are important to fish-assemblage structure, but that differing abiotic factors may influence assemblage structure within each geologic type. The fauna showed weak compositional zonation into 3 groups (headwaters, coastal plain, and nearshore). Nearly 20% of the fish species collected have migratory life cycles (including Joturus pichardi , Agonostomus monticola , and Gobiomorus dormitor ) that use freshwater and marine habitats. Some of these species probably rely on a natural flow regime and longitudinal connectivity for reproduction and dispersal of young, and natural flow regime and longitudinal connectivity are important factors for maintenance of functional linkages between the uplands and the coast in the ridge-to-reef corridor where the Monkey River is located. Therefore, we suggest that the viability of migratory fish populations may be a good biological indicator of upland-to-estuary connectivity important both to fishes and coastal ecosystem function. We recommend follow-up studies to substantiate the relative strengths of relationships between community structure and abiotic factors in contrasting geologies and to examine potential bottom−up responses of stream biota to the higher nutrient levels that were observed in stream waters draining the Santa Rosa Group geologic type.

Journal of the North American Benthological Societ↗
USGS2006

Mapping ground water in three dimensions: An analysis of airborne geophysical surveys of the Upper San Pedro River Basin, Cochise County, southeastern Arizona

This report summarizes the results of two airborne geophysical surveys conducted in the upper San Pedro Valley of southeastern Arizona in 1997 and 1999. The combined surveys cover about 1,000 square kilometers and extend from the Huachuca Mountains on the west to the Mule Mountains and Tombstone Hills on the east and from north of the Babocomari River to near the Mexican border on the south. The surveys included the acquisition of high-resolution magnetic data, which were used to map depth to the crystalline basement rocks underlying the sediments filling the basin. The magnetic inversion results show a complex basement morphology, with sediment thickness in the center of the valley ranging from ~237 meters beneath the city of Sierra Vista to ~1,500 meters beneath Huachuca City and the Palominas area near the Mexican border. The surveys also included acquisition of 60-channel time-domain electromagnetic (EM) data. Extensive quality analyses of these data, including inversion to conductivity vs. depth (conductivity-depth-transform or CDT) profiles and comparisons with electrical well logs, show that the electrical conductor mapped represents the subsurface water-bearing sediments throughout most of the basin. In a few places (notably the mouth of Huachuca Canyon), the reported water table lies above where the electrical conductor places it. These exceptions appear to be due to a combination of outdated water-table information, significant horizontal displacement between the wells and the CDT profiles, and a subtle calibration issue with the CDT algorithm apparent only in areas of highly resistive (very dry) overburden. These occasional disparities appear in less than 5 percent of the surveyed area. Observations show, however, that wells drilled in the thick unsaturated zone along the Huachuca Mountain front eventually intersect water, at which point the water rapidly rises high into the unsaturated zone within the wellbore. This rising of water in a wellbore implies some sort of confinement below the thick unsaturated zone, a confinement that is not identified in the available literature. Occasional disparities notwithstanding, maps of the electrical conductor derived from the airborne EM system provide a synoptic view of the presence of water underlying the upper San Pedro Valley, including its three-dimensional distribution. The EM data even show faults previously only inferred from geologic mapping. The magnetic and electromagnetic data together appear to show the thickness of the sediments, the water in the saturated sediments down to a maximum of about 400 meters depth, and even places where the main ground-water body is not in direct contact with the San Pedro River. However, the geophysical data cannot reveal anything directly about hydraulic conductivity or ground-water flow. Estimating these characteristics requires new hydraulic modeling based in part on this report. One concern to reviewers of this report is the effect that clays may have on the electrical conductor mapped with the airborne geophysical system. Although the water in the basin is unusually conductive, averaging 338 microsiemens per centimeter, reasoning cited below suggests that the contribution of clays to the overall conductivity would be relatively small. Basic principles of sedimentary geology suggest that silts and clays should dominate the center of the basin, while sands and gravels would tend to dominate the margins. Although clay content may increase the amplitude of the observed electrical conductors somewhat, it will not affect the depths to the conductor derived from depth inversions. Further, fine-grained sediments generally have higher porosity and tend to lie toward a basin center, a fact in general agreement with the observed geophysical data.

Arizona↗
USGS2008

Evidence of Late Pliocene-Early Pleistocene marine environments in the deep subsurface of the Lihue Basin, Kauai, Hawaii

Cuttings recovered from two deep exploratory wells in the Lihue Basin, Kauai, Hawaii, include fossiliferous marine deposits that offer an uncommon opportunity to study paleoenvironments from the deep subsurface in Hawaii and interpret the paleogeography and geologic history of Kauai. These deposits indicate that two marine incursions gave rise to protected shallow-water, low-energy embayments in the southern part of the Lihue Basin in the late Pliocene-early Pleistocene. During the first marine incursion, the embayment was initially zoned, with a variable-salinity environment nearshore and a normal-marine reef environment offshore. The offshore reef environment eventually evolved to a nearshore, variable-salinity environment as the outer part of the embayment shallowed. During the second marine incursion, the embayment had normal-marine to hypersaline conditions, which constitute a significant departure from the variable-salinity environment present during the first marine incursion. Large streams draining the southern Lihue Basin are a likely source of the freshwater that caused the salinity fluctuations evident in the fossils from the first marine incursion. Subsequent volcanic eruptions produced lava flows that buried the embayment and probably diverted much of the stream flow in the southern Lihue Basin northward, to its present point of discharge north of Kalepa Ridge. As a result, the embayment that formed during the second marine incursion received less freshwater, and a normal-marine to hypersaline environment developed. The shallow-water marine deposits, currently buried between 86 m and 185 m below present sea level, have implications for regional tectonics and global eustasy. Copyright ?? 2008, SEPM (Society for Sedimentary Geology).

Palaios↗
USGS2001

Gore Creek watershed, Colorado — Assessment of historical and current water quantity, water quality, and aquatic ecology, 1968–98

The historical and current (1998) water-quantity, water-quality, and aquatic-ecology conditions in the Gore Creek watershed are described as part of a study by the U.S. Geological Survey, done in cooperation with the Town of Vail, the Eagle River Water and Sanitation District, and the Upper Eagle Regional Water Authority. Interpretation of the available water-quantity, water-quality, and aquatic-ecology data collected by various agencies since 1968 showed that background geology and land use in the watershed influence the water quality and stream biota. Surface-water nutrient concentrations generally increased as water moved downstream through the Town of Vail, but concentrations at the mouth of Gore Creek were typical when compared with national data for urban/undeveloped sites. Nitrate concentrations in Gore Creek were highest just downstream from a wastewater-treatment plant discharge, but concentrations decreased at sites farther downstream because of dilution and nitrogen uptake by algae. Recent total phosphorus concentrations were somewhat elevated when compared to the U.S. Environmental Protection Agency recommended level of 0.10 milligram per liter for control of eutrophication in flowing water. However, total phosphorus concentrations at the mouth of Gore Creek were relatively low when compared to a national study of phosphorus in urban land-use areas. Historically, suspended sediment associated with construction of Interstate 70 in the early 1970's has been of primary concern; however, recent data indicate that streambed aggradation of sediment originating from Interstate 70 traction sanding currently is a greater concern. About 4,000 tons of coarse sand and fine gravel is washed into Black Gore Creek each year following application of traction materials to Interstate 70 during adverse winter driving conditions. Suspended-sediment concentrations were low in Black Gore Creek; however, bedload-transport rates of as much as 4 tons per day have been measured. Water samples were collected during spring and fall of 1997 from five alluvial monitoring wells located throughout the Town of Vail. Nutrient concentrations generally were low in the alluvial monitoring wells. Specific-conductance values ranged from 265 to 557 microsiemens per centimeter at 25 degrees Celsius. Concentrations of radon in monitoring-well samples exceeded the 300-picocuries-per-liter U.S. Environmental Protection Agency proposed maximum contaminant level (which has been suspended pending further review). Low levels of bacteria and methylene blue active substances indicate there is little or no wastewater contamination of shallow ground water in the vicinity of the monitoring wells and one of the municipal water-supply wells. Ground-water ages in the alluvial aquifer ranged from about 2 to about 50 years old. These ages indicate that changes in land-management practices may not have an effect on ground-water quality for many years. Differences in macroinvertebrate-community structure were found among sites in Gore Creek by evaluating changes in relative abundance, total abundance, and dominant functional feeding groups of the major macroinvertebrate groups. Ephemeroptera (mayflies), Plecoptera (stoneflies), Trichoptera (caddisflies), and Coleoptera (beetles) exhibited relatively low tolerance to water-quality degradation when compared with Diptera (midges) and non-insects (sludge worms). More than 80 percent of the macroinvertebrate community at sites located farthest upstream was composed of mayflies, stoneflies, and caddisflies, indicating favorable water-quality and habitat conditions. The relative percentages of midges and sludge worms greatly increased in the downstream reaches of Gore Creek, which drain relatively larger areas of urban and recreation land uses, indicating the occurrence of nutrient and organic enrichment in Gore Creek. The macroinvertebrate community in Black Gore Creek indicated adverse effects from sediment deposition. Macroinvertebrate abundance was considerably reduced at the two sites where streambed sediment was more prevalent; however, differences in abundance also may have been related to differences in habitat and availability of food resources. The lower 4 miles of Gore Creek, downstream from Red Sandstone Creek, have been designated a Gold Medal fishery in recognition of the high recreational value of the abundant brown trout community. Gore Creek contained twice as many trout as a reference site with similar habitat characteristics in Rocky Mountain National Park. Moderate increases in nutrient concentrations above background conditions have increased the growth and abundance potential for aquatic life in Gore Creek, while at the same time, esthetic and water-quality conditions have remained favorable. The spatial distribution of nitrate concentrations was consistent with the observed spatial distribution of algal biomass and macroinvertebrate-community characteristics. Algal biomass was limited by available resources (sunlight and nutrients) in the upstream reaches of Gore Creek and limited by macroinvertebrate grazing and water-quality conditions in the downstream reaches. The fish community has benefited from enhanced biological production in the downstream reach of Gore Creek. Increases in algal biomass and macroinvertebrate abundance, in response to higher nutrient concentrations, provide ample food resources necessary to support the abundant fish community. Trace-element data for surface water, ground water, streambed sediment, fish tissue, and macroinvertebrate tissue indicate that concentrations are generally low in the Gore Creek watershed. In streambed-sediment samples, cadmium, copper, and zinc concentrations were below background levels reported for the Upper Colorado River Basin in Colorado. Concentrations of cadmium, copper, iron, and silver in surface water have occasionally exceeded stream standards in the past, but recent surface-water data indicate these trace elements currently are not of concern. Manganese concentrations commonly exceeded the 50-microgram-per-liter stream standard in Black Gore Creek. Elevated manganese concentrations were primarily attributable to the sedimentary geology of the area. Concentrations of organic constituents are low in the Gore Creek watershed. Pesticides were detected infrequently and at low concentrations in surface-water, ground-water, bed-sediment, and whole-body fish-tissue samples. Volatile organic compounds also were detected at low concentrations in surface- and ground-water samples.

Colorado↗
USGS1989

Application of the Graphic Correlation method to Pliocene marine sequences

Biostratigraphy — the use of paleontological evidence to establish relative chronologies, forms the cornerstone of many sedimentary geological investigations. Several different approaches to biochronology are available. Traditional interval zones, defined on lowest and/or highest occurrences of selected taxa, are used to place bodies of rock in a relative chronological framework. Fossil datum levels, which are more numerous than zones, are often used as chronohorizons for correlation purposs. The Graphic Correlation method, like interval zonations, synthesizes information from a number of different taxa but does not assume synchrony of any one taxon. A magnetobiostratigraphic model for deep-sea Pliocene sequences has been constructed by graphic correlation of Deep Sea Drilling project cores from the North Atlantic (606), Caribbean Sea (502), South Atlantic (516), Tasman Sea (590), Equatorial Pacific (573) and North Pacific (577). All cores are hydraulic piston cores which contain abundant planktonic foraminifers, calcareous nannofossils and which record many of the magnetic reversals expected in the Pliocene. The model is based on internally consistent paleontologic data gathered by the author. This study demonstrates the advantages of graphic correlation over conventional biostratigraphic procedures. Accurate inter-regional correlations can be made between core sites without resorting to multiple microfossil zonations and without invoking synchrony of fossil events. Important results of this study are: (1) many Pliocene planktonic foraminifer and calcareous nannofossil events are diachronous by more than 0.20 m.y., (2) Globorotalia truncatulinoides first occurs in the Southwest Pacific Ocean, approximately 0.50 m.y. earlier than previously reported, (3) a previously undetected hiatus of short duration (0.38 m.y.) exists just above the Cochiti subchron at DSDP 577A.

Marine Micropaleontology↗
USGS2002

History of the recognition of organic geochemistry in geoscience

The discipline of organic geochemistry is an outgrowth of the application of the principles and methods of organic chemistry to sedimentary geology. Its origin goes back to the last part of the nineteenth century and the first part of the twentieth century concurrent with the evolution of the applied discipline of petroleum geochemistry. In fact, organic geochemistry was strongly influenced by developments in petroleum geochemistry. Now, however, organic geochemistry is considered an umbrella geoscience discipline of which petroleum geochemistry is an important component.

Organic Geochemistry↗
USGS2007

Sedimentology, stratigraphy, and depositional environment of the Crystal Geyser Dinosaur Quarry, east-central Utah

The Crystal Geyser Dinosaur Quarry, near Green River, Utah, is located at the base of the Lower Cretaceous (Barremian) Yellow Cat Member of the Cedar Mountain Formation. The quarry preserves a nearly monospecific accumulation of a new basal therizinosauroid, Falcarius utahensis. We used field descriptions and petrographic analysis to determine the depositional environment and development of the quarry strata. Results of these analyses suggest that the quarry represents multiple episodes of bone accumulation buried by spring and overbank flood deposits. Evidence for these previously undescribed spring deposits includes calcite macroscopic structures within the quarry strata - such as pisolites and travertine fragments - and calcite micromorphologies - including radial-fibrous, feather, and scandulitic dendrite morphologies and tufa clasts. At least two episodes of bone incorporation are preserved in the quarry based on their stratigraphic position and lithologic associations. The unique depositional setting in and around the Crystal Geyser Dinosaur Quarry appears to have been favorable for the preservation of vertebrate fossils and provides insight into early Cretaceous environments in North America. Copyright ?? 2007, SEPM (Society for Sedimentary Geology).

Palaios↗
USGS2006

Is extinction age dependent?

Age-dependent extinction is an observation with important biological implications. Van Valen's Red Queen hypothesis triggered three decades of research testing its primary implication: that age is independent of extinction. In contrast to this, later studies with species-level data have indicated the possible presence of age dependence. Since the formulation of the Red Queen hypothesis, more powerful tests of survivorship models have been developed. This is the first report of the application of the Cox Proportional Hazards model to paleontological data. Planktonic foraminiferal morphospecies allow the taxonomic and precise stratigraphic resolution necessary for the Cox model. As a whole, planktonic foraminiferal morphospecies clearly show age-dependent extinction. In particular, the effect is attributable to the presence of shorter-ranged species (range < 4 myr) following extinction events. These shorter-ranged species also possess tests with unique morphological architecture. The morphological differences are probably epiphenomena of underlying developmental and heterochronic processes of shorter-ranged species that survived various extinction events. Extinction survivors carry developmental and morphological characteristics into postextinction recovery times, and this sets them apart from species populations established independently of extinction events. Copyright ?? 2006, SEPM (Society for Sedimentary Geology).

Palaios↗