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At least 451 records · Page 25Linked to original sources

USGS1997

Water-quality trends for streams and reservoirs in the Research Triangle area of North Carolina, 1983-95

Water-quality and streamflow monitoring data, collected from 1983 to 1995, were analyzed for 34 stream and reservoir sites in a seven-county region within the upper Neuse and upper Cape Fear River Basins. Early data (1983-88) were compiled from U.S. Geological Survey water-quality studies and from the ambient water-quality monitoring network of the North Carolina Department of Environment, Health, and Natural Resources. Analyses of major ions, nutrients, metals, trace elements, and synthetic organic compounds were compiled from samples collected by the U.S. Geological Survey from 1988 to 1995 as part of a continuing project to monitor the water quality of surface-water supplies in the Research Triangle area of North Carolina, and from the North Carolina Department of Environment, Health, and Natural Resources ambient water-quality monitoring network. This report presents the results of analysis of consistently increasing or decreasing trends in concentrations of nitrogen and phosphorus species, suspended sediment, suspended solids, sodium, chloride, iron, manganese, zinc, and chlorophyll a from seasonal Kendall trend analysis on flow-adjusted concentrations for streams and concentrations in lakes. Total phosphorus concentrations also were tested for a step decrease in concentration (step trend) associated with the North Carolina phosphate-detergent ban of 1988. For some other constituents, insufficient data or values below laboratory detection limits precluded trend analysis. A regionwide decrease in total phosphorus, ranging from 25 to 81 percent, was observed that coincided with increased phosphorus removal efforts at municipal wastewater-treatment facilities in the region and the statewide phosphate-detergent ban. Most sites had stable or decreasing trends in nitrogen concentrations; however, increasing trends occurred in the Neuse River near Clayton and at Smithfield, both of which are downstream from the developing Raleigh-Durham area. Chlorophyll a concentrations have increased by 17 to 52 percent per year at monitored reservoirs, except at Cane Creek Reservoir and Lake Michie where there was no trend. No significant trends in suspended-sediment concentrations were observed. Long-term sodium concentrations were available for only a few sites. Of these, decreasing concentrations were observed in the Neuse River at Smithfield and Cane Creek near Orange Grove, and an increasing concentration was observed in University Lake. At most sites, concentrations of manganese, iron, and zinc were stable. Decreasing iron trends were observed in Little River and Cane Creek Reservoirs and Lake Michie. Cane Creek Reservoir also had a decreasing manganese trend. Seven sites, all downstream from wastewater-treatment facilities, were analyzed for zinc trends. A decreasing trend was observed in two of these--Knap of Reeds Creek and Little Lick Creek.

North Carolina↗

USGS2008

Water-chemistry data for selected springs, geysers, and streams in Yellowstone National Park, Wyoming, 2003-2005

Water analyses are reported for 157 samples collected from numerous hot springs, their overflow drainages, and Lemonade Creek in Yellowstone National Park (YNP) during 2003–2005. Water samples were collected and analyzed for major and trace constituents from ten areas of YNP including Terrace and Beryl Springs in the Gibbon Canyon area, Norris Geyser Basin, the West Nymph Creek thermal area, the area near Nymph Lake, Hazle Lake, and Frying Pan Spring, Lower Geyser Basin, Washburn Hot Springs, Mammoth Hot Springs, Potts Hot Spring Basin, the Sulphur Caldron area, and Lemonade Creek near the Solfatara Trail. These water samples were collected and analyzed as part of research investigations in YNP on arsenic, antimony, and sulfur redox distribution in hot springs and overflow drainages, and the occurrence and distribution of dissolved mercury. Most samples were analyzed for major cations and anions, trace metals, redox species of antimony, arsenic, iron, nitrogen, and sulfur, and isotopes of hydrogen and oxygen. Analyses were performed at the sampling site, in an on-site mobile laboratory vehicle, or later in a U.S. Geological Survey laboratory, depending on stability of the constituent and whether it could be preserved effectively. Water samples were filtered and preserved onsite. Water temperature, specific conductance, pH, Eh (redox potential relative to the Standard Hydrogen Electrode), and dissolved hydrogen sulfide were measured onsite at the time of sampling. Acidity was determined by titration, usually within a few days of sample collection. Alkalinity was determined by titration within 1 to 2 weeks of sample collection. Concentrations of thiosulfate and polythionate were determined as soon as possible (generally minutes to hours after sample collection) by ion chromatography in an on-site mobile laboratory vehicle. Total dissolved-iron and ferrous-iron concentrations often were measured onsite in the mobile laboratory vehicle. Concentrations of dissolved aluminum, arsenic, boron, barium, beryllium, calcium, cadmium, cobalt, chromium, copper, iron, potassium, lithium, magnesium, manganese, molybdenum, sodium, nickel, lead, selenium, silica, strontium, vanadium, and zinc were determined by inductively-coupled plasma-optical emission spectrometry. Trace concentrations of dissolved antimony, cadmium, cobalt, chromium, copper, lead, and selenium were determined by Zeeman-corrected graphite-furnace atomic-absorption spectrometry. Dissolved concentrations of total arsenic, arsenite, total antimony, and antimonite were determined by hydride-generation atomic-absorption spectrometry using a flow-injection analysis system. Dissolved concentrations of total mercury and methyl mercury were determined by cold-vapor atomic-fluorescence spectrometry. Concentrations of dissolved chloride, fluoride, nitrate, bromide, and sulfate were determined by ion chromatography. Concentrations of dissolved ferrous and total iron were determined by the FerroZine colorimetric method. Concentrations of dissolved nitrite were determined by colorimetry or chemiluminescence. Concentrations of dissolved ammonium were determined by ion chromatography, with reanalysis by colorimetry when separation of sodium and ammonia peaks was poor. Dissolved organic carbon concentrations were determined by the wet persulfate oxidation method. Hydrogen and oxygen isotope ratios were determined using the hydrogen and CO 2 equilibration techniques, respectively.

Wyoming↗

USGS1963

Dissolved-mineral inflow to Great Salt Lake and chemical characteristics of the salt lake brine. Part I: Selected hydrologic data

This report presents the data collected for a study of the dissolved-mineral load contributed by surficial sources to Great Salt Lake, Utah. The study was conducted by the U.S. Geological Survey in cooperation with the University of Utah during the period from July 1959 through June 1962, and is part of an overall investigation of the Great Salt Lake basin by the University. Financial support for the study was provided by the U.S. Geological Survey and by the University of Utah Research Fund and Uniform School Fund. Some of the data presented in this report were obtained as part of cooperative programs between the Geological Survey and other agencies.

Utah↗

USGS2016

Estimated use of water in the Delaware River Basin in Delaware, New Jersey, New York, and Pennsylvania, 2010

The Delaware River Basin (DRB) was selected as a Focus Area Study in 2011 by the U.S. Geological Survey (USGS) as part of the USGS National Water Census. The National Water Census is a USGS research program that focuses on national water availability and use and then develops new water accounting tools and assesses water availability at both the regional and national scales. One of the water management needs that the DRB study addressed, and that was identified by stakeholder groups from the DRB, was to improve the integration of state water use and water-supply data and to provide the compiled water use information to basin users. This water use information was also used in the hydrologic modeling and ecological components of the study. Instream and offstream water use was calculated for 2010 for the DRB based on information received from Delaware, New Jersey, New York, and Pennsylvania. Water withdrawal, interbasin transfers, return flow, and hydroelectric power generation release data were compiled for 11 categories by hydrologic subregion, basin, subbasin, and subwatershed. Data availability varied by state. Site-specific data were used whenever possible to calculate public supply, irrigation (golf courses, nurseries, sod farms, and crops), aquaculture, self-supplied industrial, commercial, mining, thermoelectric, and hydroelectric power withdrawals. Where site-specific data were not available, primarily for crop irrigation, livestock, and domestic use, various techniques were used to estimate water withdrawals. Total water withdrawals in the Delaware River Basin were calculated to be about 7,130 million gallons per day (Mgal/d) in 2010. Calculations of withdrawals by source indicate that freshwater withdrawals were about 4,130 Mgal/d (58 percent of the total) and the remaining 3,000 Mgal/d (42 percent) were from saline water. Total surface-water withdrawals were calculated to be 6,590 Mgal/d, or 92 percent of the total; about 54 percent (3,590 Mgal/d) of surface water withdrawn was freshwater. Total groundwater withdrawals were calculated to be 545 Mgal/d (8 percent of the total), all of which was freshwater. During 2010, calculated withdrawals by category, in decreasing order, were: thermoelectric power, 4,910 Mgal/d; public supply, 1,490 Mgal/d; self-supplied industrial, 350 Mgal/d; irrigation, 175 Mgal/d; self-supplied domestic, 117 Mgal/d; mining, 41.3 Mgal/d; aquaculture, 19.3 Mgal/d; livestock, 6.72 Mgal/d, and commercial, 5.89 Mgal/d. The amount of instream use for hydroelectric power generation purposes in 2010 was reported to be 273 Mgal/d for the Wallenpaupack Plant and 127 Mgal/d for the Mongaup River system. Total return flows in the DRB were 2,960 Mgal/d in 2010. Although municipal wastewater-treatment plants accounted for 539 (97 percent) of the return-flow sites, they accounted for about 70 percent of the total return flows in the DRB. There was limited information on return flows from thermoelectric power.

Delaware, New Jersey, New York, Pennsylvania↗

USGS2018

Effects of feral horse herds on plant communities across a precipitation gradient

Feral horses are widespread in the western United States, with the majority of feral horse herds found in the Great Basin. There is a federal mandate to manage these herds in order to maintain “ecological balance”; however, understanding of the specific effects of feral horse grazing on rangeland plant communities in this region is incomplete. To address this research gap, we utilized long-term grazing exclosures and fenceline contrasts to evaluate the impacts of feral horses on several plant community variables (diversity, richness, dominance, and biomass) and species composition. Because the effects of grazing can vary with site precipitation and productivity, we selected 5 sites from 4 different rangeland types (Great Basin Desert, Colorado Plateau, Rocky Mountain grassland, and mixed grass prairie) that spanned a mean annual precipitation gradient of 229 to 413 mm. Our results did not reveal a significant effect of feral horse grazing on plant community composition, species richness, diversity, evenness, or dominance. In contrast, total aboveground herbaceous biomass and grass biomass were significantly reduced with feral horse grazing, but these effects did not vary with mean annual precipitation. Our results suggest that, at least at the sites we studied, feral horses have affected the plant community by reducing herbaceous biomass but have not caused plant community shifts. Additional multisite studies, preferably with standardized exclosures and larger sample sizes, would increase our understanding of feral horse grazing effects and inform management of feral horse herds in the western United States.

Colorado, Montana, Nevada, North Dakota, Utah↗

USGS2006

Shrinking ponds in subarctic Alaska based on 1950-2002 remotely sensed images

Over the past 50 years, Alaska has experienced a warming climate with longer growing seasons, increased potential evapotranspiration, and permafrost warming. Research from the Seward Peninsula and Kenai Peninsula has demonstrated a substantial landscape-level trend in the reduction of surface water and number of closed-basin ponds. We investigated whether this drying trend occurred at nine other regions throughout Alaska. One study region was from the Arctic Coastal Plain where depp permafrost occurs continuously across the landscape. The other eight study regions were from the boreal forest regions where discontinuous permafrost occurs. Mean annual precipitation across the study regions ranged from 100 to over 700 min yr-1. We used remotely sensed imagery from the 1950s to 2002 to inventory over 10,000 closed-basin ponds from at least three periods from this time span. We found a reduction in the area and number of shallow, closed-basin ponds for all boreal regions. In contrast, the Arctic Coastal Plain region had negligible change in the area of closed-basin ponds. Since the 1950s, surface water area of closed-basin ponds included in this analysis decreased by 31 to 4 percent, and the total number of closed-basin ponds surveyed within each study region decreased from 54 to 5 percent. There was a significant increasing trend in annual mean temperature and potential evapotranspiration since the 1950s for all study regions. There was no significant trend in annual precipitation during the same period. The regional trend of shrinking ponds may be due to increased drainage as permafrost warms, or increased evapotranspiration during a warmer and extended growing season. Copyright 2006 by the American Geophysical Union.

Journal of Geophysical Research G: Biogeosciences↗

USGS2017

Paleoclimatic reconstruction using the correlation in δ 18 O of hackberry carbonate and environmental water, North America

Celtis sp. (commonly known as “hackberry”) fruits were collected from 101 North American sites located in 13 states and one Canadian province between the years of 1979–1994. The biomineralized carbonate endocarp of the hackberry, which is a common botanical fossil found throughout the Quaternary sediments of the Great Plains, was analyzed for its δ 18 O value and plotted against the δ 18 O value of site environmental water to demonstrate the potential of the hackberry as a paleoclimate indicator. This correlation was reinforced by intensive studies on extracted tissue-water δ 18 O value and hackberry endocarp carbonate δ 18 O value from three trees in Sterling, Colorado. The observed correlation in the large data set between hackberry endocarp carbonate δ 18 O value and environmental water is [endocarp δ 18 O=38.56+0.69×environmental water δ 18 O] ( R =0.88; R 2 =0.78; p value<0.0001). The relation of the hackberry carbonate to temperature in the Great Plains was the following: (average daily-maximum growing season temperature [°C])=6.33+0.67 (δ 18 O of endocarp carbonate) ( R =0.73; R 2 =0.54; p value=0.0133). The δ 18 O value of early Holocene fossil hackberry carbonate in the Pintwater Cave, southern Nevada, suggested precipitation δ 18 O values more positive than today (&sim;−4&permil; early Holocene vs &sim;−9 to −10&permil; today). This shift, combined with paleobotanical data, suggests an influx of summer monsoonal moisture to this region in the early Holocene. Alternatively, the more positive δ 18 O values could be viewed as suggestive of warmer temperatures, although the direct use of Great Plains hackberry/temperature relationships to the Great Basin is of debatable value.

Quaternary Research↗

USGS2005

Old groundwater influence on stream hydrochemistry and catchment response times in a small Sierra Nevada catchment: Sagehen Creek, California

The relationship between the chemical and isotopic composition of groundwater and residence times was used to understand the temporal variability in stream hydrochemistry in Sagehen basin, California. On the basis of the relationship between groundwater age and [Ca 2+ ], the mean residence time of groundwater feeding Sagehen Creek during base flow is approximately 28 years. [Cl − ]:[Ca 2+ ] ratios in Sagehen Creek can be used to distinguish between two important processes: changes in the apparent age of groundwater discharging into the creek and dilution with snowmelt. The mean residence time of groundwater discharging into the creek is approximately 15 years during snowmelt periods. The results from this study have implications for hydrograph separation studies as groundwater is not a single, well‐mixed chemical component but rather is a variable parameter that predictably depends on groundwater residence time. Most current models of catchment hydrochemistry do not account for chemical and isotopic variability found within the groundwater reservoir. In addition, this study provides valuable insight into the long‐term hydrochemical response of a catchment to perturbations as catchment‐flushing times are related to the mean residence time of water in a basin.

California↗

USGS2011

Thorium abundances of basalt ponds in South Pole-Aitken basin: Insights into the composition and evolution of the far side lunar mantle

Imbrian-aged basalt ponds, located on the floor of South Pole-Aitken (SPA) basin, are used to provide constraints on the composition and evolution of the far side lunar mantle. We use forward modeling of the Lunar Prospector Gamma Ray Spectrometer thorium data, to suggest that at least five different and distinct portions of the far side lunar mantle contain little or no thorium as of the Imbrian Period. We also use spatial correlations between local thorium enhancements and nonmare material on top of the basalt ponds to support previous assertions that lower crustal materials exposed in SPA basin have elevated thorium abundances, consistent with noritic to gabbronoritic lithologies. We suggest that the lower crust on the far side of the Moon experienced multiple intrusions of thorium-rich basaltic magmas, prior to the formation of SPA basin. The fact that many of the ponds on the lunar far side have elevated titanium abundances indicates that the far side of the Moon experienced extensive fractional crystallization that likely led to the formation of a KREEP-like component. However, because the Imbrian-aged basalts contain no signs of elevated thorium, we propose that the SPA impact event triggered the transport of a KREEP-like component from the lunar far side and concentrated it on the nearside of the Moon. Because of the correlation between basaltic ponds and basins within SPA, we suggest that Imbrian-aged basaltic volcanism on the far side of the Moon was driven by basin-induced decompressional melting.

Journal of Geophysical Research E: Planets↗

USGS2019

Source-dependent amplification of earthquake ground motions in deep sedimentary basins

Deep sedimentary basins amplify long-period shaking from seismic waves, increasing the seismic hazard for cities within such basins. We perform 3-D simulations of point source earthquakes distributed around the Seattle and Tacoma basins in Washington State, to examine the dependence of basin amplification on source azimuth, depth, and earthquake type. For periods between 1-10 s, the pattern of amplification is spatially heterogeneous and differs considerably with the source-to-site azimuth. For close-in earthquakes, the greatest basin amplification occurs towards the far side of the basin and ground motions from crustal earthquakes experience greater amplification than those from more vertically-incident, deeper intraplate earthquakes. Love and Rayleigh waves form similar spatial patterns for a given source location, although the magnitude of amplification varies. The source dependence of basin amplification is an important factor for seismic hazard assessment, both in the Seattle and Tacoma basins, and by extension for deep sedimentary basins worldwide.

Washington↗

USGS2020

Shallow basin structure and attenuation are key to predicting long shaking duration in Los Angeles Basin

Ground motions in the Los Angeles Basin during large earthquakes are modulated by earthquake ruptures, path effects into the basin, basin effects, and local site response. We analyzed the direct effect of shallow basin structures on shaking duration at a period of 2–10 s in the Los Angeles region through modeling small magnitude, shallow, and deep earthquake pairs. The source depth modulates the basin response, particularly the shaking duration, and these features are a function of path effect and not site condition. Three-dimensional simulations using the CVM-S4.26.M01 velocity model show good fitting to the initial portion of the waveforms at periods of 5 s and longer but fail to predict the long shaking duration during shallow events, especially at periods less than 5 s. Simulations using CVM-H do not match the timing of the initial arrivals as well as CVM-S4.26.M01, and the strong late arrivals in the CVM-H simulation travel with an apparent velocity slower than observed. A higher-quality factor than traditionally assumed may produce synthetics with longer durations but is unable to accurately match the amplitude and phase. Beamforming analysis using dense array data further reveals the long duration surface waves have the same back azimuth as the direct arrivals and are generated at the basin edges, while the later coda waves are scattered from off-azimuth directions, potentially due to strong, sharp boundaries offshore. Improving the description of these shallow basin structures and attenuation model will enhance our capability to predict long-period ground motions in basins.

California↗

USGS2025

Evidence for fluid pressurization of fault zones and persistent sensitivity to injection rate beneath the Raton Basin

Subsurface wastewater injection has increased the seismicity rate within the Raton Basin over more than two decades, with the basin-wide injection rate peaked between 2009-2015. To understand the evolution of injection-induced earthquakes, we systematically analyzed 2016-2024 broadband recordings with a machine-learning-based phase picker and constructed a catalog with 95,993 earthquakes (-1≤ M L ≤4.3). We then inverted for full centroid moment tensors (CMT) for 90 M L ≥ 2 events, with a special interest in constraining the non-double-couple components via probabilistic metrics. Both relocations and CMT solutions support basement-rooted normal faults, including graben and half-graben structures. Furthermore, we observe the non-double-couple components that imply elevated pore pressure in the fault zones. An earthquake cluster emerged in the north-central basin in 2023, preceded by ~1-yr of increased injection volume from wells within 15km. Despite a basin-wide decrease in the injection volume, we highlights the persistence of seismicity that remains to sensitive to injection rates within the Raton Basin.

Colorado, New Mexico↗

USGS2010

Transport and accumulation of radionuclides and stable elements in a Missouri River Reservoir

Several long sediment cores from the Cheyenne River Embayment of Lake Oahe, a 250-km-long Missouri River reservoir in South Dakota, have been analyzed for radionuclides and stable elements. The combination of fine-scale sampling and rapid sedimentation produces radionuclide distributions that can be used to estimate the detailed chronology of particle transport processes in the Oahe reservoir system. A self-consistent and quantitative treatment of the 137 Cs data suggests processes to which characteristic times may be associated. Times that characterize system-wide processes include (1) an integration time of several years reflecting retention of the sediment-bound tracer in regions within or external to the reservoir, (2) a relaxation time of approximately 15 years reflecting a decreasing rate of sediment accumulation ascribed to shoreline stabilization, (3) a time of a few months characterizing the breadth of riverine signatures in cores due to integration effects in the Cheyenne River system and deltaic deposits, and (4) times of a few years associated with propagation of riverine load signatures along the embayment. The distribution of total sedimentary arsenic confirms the validity of the variable sedimentation model. In 1977, a tailings retention facility was built at the Homestake Mine site, and the unrestricted input of As ceased. As a result of this remedial action, the concentration of sedimentary As decreased dramatically. In the upper section of the core, above the depth represented by the year 1976, the concentration of As decreases tenfold. In this same core the distribution of lithologically discriminating chemical elements, calcium and vanadium, relate to major flow events in the Cheyenne River basin. Because there is minimal diagenesis of chemical constituents in these rapidly accumulating sediments, stable element signatures, in addition to radiotracers, may be used to reconstruct hydrologic events in drainage basins that contribute sediment to lakes and reservoirs.

South Dakota↗

USGS1998

Erosional valleys in the Thaumasia region of Mars: Hydrothermal and seismic origins

Analysis of erosional valleys, geologic materials and features, and topography through time in the Thaumasia region of Mars using co-registered digital spatial data sets reveals significant associations that relate to valley origin. Valleys tend to originate (1) on Noachian to Early Hesperian (stages 1 and 2) large volcanoes, (2) within 50–100 km of stages 1 and 2 rift systems, and (3) within 100 km of Noachian (stage 1) impact craters >50 km in diameter. These geologic preferences explain observations of higher valley-source densities (VSDs) in areas of higher elevations and regional slopes (>1°) because the volcanoes, rifts, and craters form high, steep topography or occur in terrain of high relief. Other stage 1 and stage 2 high, steep terrains, however, do not show high VSDs. The tendency for valleys to concentrate near geologic features and the overall low drainage densities in Thaumasia compared to terrestrial surfaces rule out widespread precipitation as a major factor in valley formation (as is proposed in wann, wet climate scenarios) except perhaps during the Early Noachian, for which much of the geologic record has been obliterated. Instead, volcanoes and rifts may indicate the presence of shallow crustal intrusions that could lead to local hydrothermal circulation, melting of ground ice and snow, and groundwater sapping. However, impact-crater melt would provide a heat source at the surface that might drive away water, fonning valleys in the process. Post-stage 1 craters mostly have low nearby VSDs, which, for valleys incised in older rocks, suggests burial by ejecta and, for younger valleys, may indicate desiccation of near-surface water and deepening of the cryosphere. Later Hesperian and Amazonian (stages 3 and 4) valleys originate within 100–200 km of three young, large impact craters and near rifts systems at Warrego Valles and the southern part of Coprates rise. These valleys likely developed when the cryosphere was a couple kilometers or more thick, inhibiting valley development by hydrothermal circulation. However, eruption of groundwater may have occurred from impact-induced fracturing and lateral and perhaps minor upward transport of water due to seismic pumping. The two smaller craters formed along the plateau margin where the highest potential hydraulic head would occur in aquifers beneath the plateau. In the case of the larger crater (Lowell, 200 km in diameter), potential aquifers would likely be at depths of kilometers below the cryosphere. Seismic energy generated by the Lowell impactor would have been much greater, pumping both groundwater and perhaps fluidized slurry to the surface from beneath the cryosphere to form the young valleys and flow deposit. Along the margin of Thaumasia, tectonic pressurization of groundwater also may have contributed to valley formation. Dissection of rim materials of the Argyre impact may relate to tectonic activity and the unconsolidated state of basin ejecta.

Journal of Geophysical Research E: Planets↗

USGS2012

The growth of geological structures by repeated earthquakes: 2, Field examples of continental dip-slip faults

A strong test of our understanding of the earthquake cycle is the ability to reproduce extant fault-bounded geological structures, such as basins and ranges, which are built by repeated cycles of deformation. Along strike-slip faults, the coseismic and interseismic deformation can be nearly equal in magnitude and opposite in sign, resulting in little permanent deformation except for the fault offset. For dip-slip faults, portions of the crust are lifted and dropped, and so buoyancy forces are exerted. The seismic and interseismic deformations do not balance, and structures grow and become subject to erosion and deposition. We consider three examples for which the structure and fault geometry are well known: the White Wolf reverse fault in California, site of the 1952 Kern County M=7.3 earthquake, the Lost River normal fault in Idaho, site of the 1983 Borah Peak M=7.0 earthquake, and the Cricket Mountain normal fault in Utah, site of Quaternary slip events. Basin stratigraphy and seismic reflection records are used to profile the structure, and coseismic deformation measured by leveling surveys is used to estimate the fault geometry. To reproduce these structures, we add the deformation associated with the earthquake cycle (the coseismic slip and postseismic relaxation) to the flexure caused by the observed sediment load, treating the crust as a thin elastic plate overlying a fluid substrate. The cumulative deformation is principally dependent on the elastic plate thickness, modestly sensitive to the sediment-substrate density difference, and insensitive to the fluid viscosity for the 4- to 8-Ma structures. We deduce a longterm flexural rigidity of 2–15 × 10 19 Nm; this is equivalent to an elastic plate thickness of 2–4 km for a Young's modulus of 2.5 × 10 10 Nm −2 . This value is found where independent estimates of the elastic thickness from the coherence between surface topography and gravity yield values of about 4 km, but where coseismic fault slip extends to a depth of 10–15 km. Thus much of the seismogenic crust must weaken substantially during the life of active faults, causing the fault-bounded basins to narrow over time.

Journal of Geophysical Research Solid Earth↗

USGS1976

Revision of Mississippian stratigraphy, eastern Idaho and northeastern Utah

New paleontologic evidence requires a revision of previous interpretations of the stratigraphy of Mississippian sequences in the Cordilleran miogeosyncline of eastern Idaho and northeastern Utah. A postulated unconformity between rocks of early Osagean age and rocks of middle Meramecian age is no longer tenable in the light of new data. The new evidence supports continuous deposition from the Lodgepole Limestone (Kinderhookian and early Osagean age) into the Little Flat Formation (early Osagean to middle Meramecian age) and its equivalents, and the interpretation of a phosphatic siltstone and shale interval in the lower part of the Little Flat Formation as a starved-basin facies.

Idaho, Utah↗

USGS2017

Variation and plasticity and their interaction with urbanization in Guadalupe Bass populations on and off the Edwards Plateau

The Colorado River Basin in Texas has experienced major alterations to its hydrologic regime due to changing land and water use patterns. These anthropogenic influences on hydrologic variability have had major implications for riparian and aquatic ecosystems and the species dependent upon them. However, impacts are often assessed at a limited temporal and spatial scale, tending to focus on relatively short and discrete periods or portions of a river basin. It is not clear how basin-wide alterations occurring over decades affect species. Guadalupe Bass Micropterus treculii are endemic to central Texas and are typically associated with shallow runs and riffles in small streams. However, Guadalupe Bass are found throughout the Colorado River Basin, including the mainstem portion of the lower river downstream of the city of Austin where they support a popular fishery. Because Guadalupe Bass exist across a wide range of stream orders within the basin, it is unclear whether populations respond similarly to anthropogenic disturbances or to conservation and restoration activities. Therefore, our objectives were to: Assess the effects of urbanization and hydrology on the population structure and dynamics of Guadalupe Bass. Evaluate the effects of environmental gradients on ecomorphological variation in Guadalupe Bass populations across multiple spatial scales. Describe the life history, habitat use, and behavior of the Guadalupe Bass population in the lower Colorado River and compare it to populations in more “typical” habitats. Results contribute to an understanding of the response of Guadalupe Bass to anthropogenic disturbances, including increased urbanization in central Texas and further assist in the conservation of the species. The ability of the population to not only persist, but flourish downstream of a heavily populated urban area presented a unique opportunity to investigate a native species response to anthropogenic disturbance. This research revealed differences in Guadalupe Bass habitat associations and movements, contrasts in age and growth, and morphological variation across a gradient of disturbance throughout the Colorado River Basin. Results of this work provide information on the potential effects of human population growth and increased water withdrawals on Guadalupe Bass populations. Additionally, this work adds to an understanding of the unique Guadalupe Bass population found in the lower Colorado River and how it differs from upstream tributary populations. Gathering additional population-level information facilitates conservation actions critical to preserving preferred habitat and promoting growth rates for Guadalupe Bass in streams of different sizes and flow conditions while highlighting interpopulation differences that may warrant consideration for stocking programs and other management strategies. Key findings of this study were: The similarity in response of growth rates to streamflow throughout the Colorado Basin suggests phenotypic plasticity in this trait rather than population-specific adaptations. Reductions in streamflows in the Colorado River Basin, whether due to increased frequency of drought or increased anthropogenic water withdrawal, will likely result in lower Guadalupe Bass growth rates with the potential to impact the structure of populations. Growth and recruitment showed a positive correlation with increased baseflows and mean monthly flows; however, continued assessment is necessary to determine a true relationship. We documented morphological divergence among Guadalupe Bass populations in response to spatial and temporal environmental variation. These ecomorphological differences among populations provide insight into the ability of Guadalupe Bass to respond to the differing in-stream habitat and flow conditions between small ‘typical’ tributary systems and the mainstem Colorado River. Morphological variation may be a population-level adaptation that potentially needs to be taken into consideration when choosing broodstock to maximize stocking success within a system. Understanding the morphological differences between Guadalupe Bass populations in response to local conditions could improve the success of restoration and supplemental stocking programs, especially in the ever-changing landscape of central Texas. We established a baseline for understanding the morphological response of Guadalupe Bass to increased population growth and the threats posed by increased water withdrawals and impervious surface. The mainstem population of Guadalupe Bass was generally more mobile, and more responsive to changes in streamflow, than tributary populations. The observed differences could influence the response of Guadalupe Bass populations to conservation and management actions, such as habitat restoration efforts. Continued monitoring of recruitment and angler exploitation may be beneficial to identify any changes that could negatively impact the population. Conservation initiatives solely focused on physical instream or riparian habitat are unlikely to be as beneficial to Guadalupe Bass as those focused on restoring or maintaining adequate streamflow

Cooperator Science Series↗

USGS2024

Novel insights about petroleum systems from source and reservoir rock characterization, Cretaceous Deposits, Babouri-Figuil Basin, Northern Cameroon

The Babouri-Figuil Basin (BFB) is a frontier basin for petroleum in Cameroon. It belongs to the series of Cretaceous rift basins of the West and Central Rift System (WCARS), the origin of which is related to the opening of the South Atlantic. Within the same rift system, commercial hydrocarbon accumulations have been discovered in Chad, Sudan, Niger and, more recently, in Nigeria (Gongola Basin). The study of the geology of the BFB just recently received considerable attention, mainly because of its presumed hydrocarbon potential. In the pursuit of researching possible petroleum systems in the BFB, the current study provides a first look into the characterization of source and reservoir rock and its integration into a 2D lithostratigraphic model. The study was solely based on outcrop samples. Black shale and massive claystone are good to excellent hydrocarbon source rocks [e.g., up to 38 wt% total organic carbon (TOC), up to 943 mg/g hydrogen index, up to 85 m thickness, up to 20–30 km lateral extension], with moderate to high values of extractable organic matter (e.g., >10,000 ppm). Calcareous claystone, on the other hand, are poor source rocks [e.g., <0.20 wt% TOC]. The samples are thermally immature, except for those located close to volcanic intrusion at Golombe that have reached the threshold for oil generation (Tmax >435 °C, production index >0.1). The petrographic analysis of sandstone revealed that they are fine-grained to coarse-grained, poorly to moderately sorted, texturally and compositionally immature to submature, subarkosic to arkosic arenites. The main diagenetic processes that affected sandstones are as follows: moderate to intense compaction characterized by the development of long, concavo-convex, and sutured contacts between grains; cementation through calcite, iron oxide, and quartz cements; alteration of mica and feldspar grains; partial to complete dissolution of feldspar, mica, amphibole grains, and calcite cement; and the replacement of feldspar and mica grains by clay minerals. Alteration and dissolution increase the porosity of sandstone through the creation of secondary pores. However, mechanical compaction through the development of a pseudomatrix and cementation as pore-filling materials have significantly reduced the quality of sandstone beds as conventional petroleum reservoirs. Hence, the best reservoir-quality sandstones in the basin are generally located in the upper portion of the basin in terms of its lithostratigraphic model. They are the cleanest sandstones with the smallest amount of cement and the lowest ductile grain content (pseudomatrix), with a thickness that varies from 3 m to 120 m and a lateral extension of 20 km. The lithostratigraphic model of the basin is characterized by an extensive lacustrine environment that provided a thick sequence of organic-rich formations; sand deposited as extensive reservoirs sandwiched between shale/claystone beds; the development of stratigraphic traps through lateral facies change; and the widespread deposition of lacustrine and floodplain claystone that provide regional seals. The similarities between the Babouri-Figuil Basin and proven petroleum systems in other WCARS rift basins suggest that the basin may host at least one petroleum system where actively generating source rocks are present.

Babouri-Figuil Basin↗