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At least 649 records · Page 36Linked to original sources

USGS2012

Near-surface, marine seismic-reflection data defines potential hydrogeologic confinement bypass in a tertiary carbonate aquifer, southeastern Florida

Approximately 210 km of near-surface, high-frequency, marine seismic-reflection data were acquired on the southeastern part of the Florida Platform between 2007 and 2011. Many high-resolution, seismic-reflection profiles, interpretable to a depth of about 730 m, were collected on the shallow-marine shelf of southeastern Florida in water as shallow as 1 m. Landward of the present-day shelf-margin slope, these data image middle Eocene to Pleistocene strata and Paleocene to Pleistocene strata on the Miami Terrace. This high-resolution data set provides an opportunity to evaluate geologic structures that cut across confining units of the Paleocene to Oligocene-age carbonate rocks that form the Floridan aquifer system.Seismic profiles image two structural systems, tectonic faults and karst collapse structures, which breach confining beds in the Floridan aquifer system. Both structural systems may serve as pathways for vertical groundwater flow across relatively low-permeability carbonate strata that separate zones of regionally extensive high-permeability rocks in the Floridan aquifer system. The tectonic faults occur as normal and reverse faults, and collapse-related faults have normal throw. The most common fault occurrence delineated on the reflection profiles is associated with karst collapse structures. These high-frequency seismic data are providing high quality structural analogs to unprecedented depths on the southeastern Florida Platform. The analogs can be used for assessment of confinement of other carbonate aquifers and the sealing potential of deeper carbonate rocks associated with reservoirs around the world.

Florida↗

USGS2003

Interplay of late Cenozoic siliciclastic supply and carbonate response on the southeast Florida platform

High-resolution seismic-reflection data collected along the length of the Caloosahatchee River in southwestern Florida have been correlated to nannofossil biostratigraphy and strontium-isotope chemostratigraphy at six continuously cored boreholes. These data are interpreted to show a major Late Miocene(?) to Early Pliocene fluvial-deltaic depositional system that prograded southward across the carbonate Florida Platform , interrupting nearly continuous carbonate deposition since early in the Cretaceous. Connection of the platform top to a continental source of siliciclastics and significant paleotopography combined to focus accumulation of an immense supply of siliciclastics on the southeastern part of the Florida Platform . The remarkably thick (> 100 m), sand-rich depositional system, which is characterized by clinoformal progradation, filled in deep accommodation, while antecedent paleotopography directed deltaic progradation southward within the middle of the present-day Florida Peninsula. The deltaic depositional system may have prograded about 200 km southward to the middle and upper Florida Keys, where Late Miocene to Pliocene siliciclastic form the foundation of the Quaternary carbonate shelf and shelf margin of the Florida Keys. These far-traveled siliciclastic deposits filled accommodation on the southeastern part of the Florida Platform so that paleobathymetry was sufficiently shallow to allow Quaternary recovery of carbonate sedimentation in the area of southern peninsular Florida and the Florida Keys.

Florida↗

USGS2012

Sequential development of platform to off-platform facies of the great American carbonate bank in the central Appalachians

In the central Appalachians, carbonate deposition of the great American carbonate bank began during the Early Cambrian with the creation of initial ramp facies of the Vintage Formation and lower members of the Tomstown Formation. Vertical stacking of bioturbated subtidal ramp deposits (Bolivar Heights Member) and dolomitized microbial boundtsone (Fort Duncan Member) preceded the initiation of platform sedimentation and creation of sand shoal facies (Benevola Member) that was followed by the development of peritidal cyclicity (Daragan Member). Initiation of peritidal deposition coincided with the development of a rimmed platform that would persist throughout much of the Cambrian and Early Odrovician. At the end of deposition of the Waynesboro Formation, the platform became subaerially exposed because of the Hawke Bay regression, bringing the Sauk I supersequence to and end. In the Conestoga Valley of eastern Pennsylvania, Early Cambrian ramp deposition was succeeded by deposition of platform-margin and periplatfrom facies of the Kinzers Formation. The basal Sauk II transgression during the early Middle Cambrian submerged the platform and reinitiated the pertidal cyclicity that had characterized the pre-Hawke Bay deposition, This thick stack of meter-scale cycles is preserved as the Pleasant Hill and Warrior Formations of the Nittany arch, the Elbrook Formation of the Great Valley, and the Zooks Corner Formations of the Conestoga Valley. Deposition of peritidal cycles was interrupted during deposition of the Glossopleura and Bathuriscus-Elrathina Biozones by third-order deepening episodes that submerged the platform with subtidal facies. Regressive facies of the Sauk II supersequence produced platform-wide restrictions and the deposition of the lower sandy member of the Gatesburg Formation, the Big Spring Station Member of the Conococheague Formation, and the Snitz Creek Formation. Submergence of the platform was initiated during the late Steptoean ( Elvinia Zone) with the epansion of extensive subtidal thrombotic boundstone facies. Vertical stacking of no fewer than four of these thrombolite-dominated intervals records third-order deepening episodes separated by intervening shallowing episodes that produced peritidal ribbony and laminated mudcracked dolostone. The maximum deepening of the Sauk III transgression produced the Stonehenge Formation in two separate and distinct third-order submergences. Circulation restriction during the Sauk III regression produced a thick stack of meter-scale cycles of the Rockdale Run Formation, and the lower Bellefonte Dolomite of the Nittany arch (central Pennsylvania). This regressive phase was interrupted by a third-order deepening event that produced the oolitic member of the lower Rockdale Run and the Woodsboro Member of the Grove Formation in the Frederick Valley. Restricted circulation continued into the Whiterockian, with deposition of the upper Rockdale Run and the Pinesberg Station Dolomite in the Great Valley and the missile and upper parts of the Bellefonte Dolomore and the Nittany Arch region. This deposition was continuous from the Ibexian into the Whiterockian; the succession lacks significant unconformities and there are no missing biozones through this interval, the top of which marks the end of the Sauk megasequence. During deposition of the Tippecanoe megasequence, the peritidal shelf cycles were reestablished during deposition of the St. Paul Group. The vertical stacking of lithologies in the Row Park and New Market Limestones represents transgressive and regressice facies of a third-order deepening event. This submergence reached its maximum deepening within the lower Row Park Limestone and extended with the Nittany arch region with deposition of equivalent Loysburg Formation.. Shallow tidal-flat deposits were bordered to the south and east by deep-water ramp deposits of the Lincolnshire Formation. The St. Paul Group is succeeded upsection by ramp facies of the Chamersberg and the Edinburg Formations in the Great Valley, whereas shallow-shelf sedimentation continued in the Nittany-arch area with the depostion of the Hatter Limestoen and the Snyder and Linden Hall Formations. Carbonate deposition on the great American carbonate bank was brought to an end when it was buried beneath clastic flysch deposits of the Martinsberg Formation. Foundering of the bamk was diachronus, and the flysch seidments prograded from east to west.

Maryland, Pennsylvania, Virginia, West Virginia↗

USGS1984

Empirical relation between carbonate porosity and thermal maturity: An approach to regional porosity prediction

Data indicate that porosity loss in subsurface carbonate rocks can be empirically represented by the power function, ^Thgr = a (TTI) b , where ^Thgr is regional porosity, TTI is Lopatin's time-temperature index of thermal maturity, the exponent, b, equals approximately -0.372, and the multiplier, a, is constant for a given data population but varies by an order of magnitude overall. Implications include the following. 1. The decrease of carbonate porosity by burial diagenesis is a maturation process depending exponentially on temperature and linearly on time. 2. The exponent, b, is essentially independent of the rock matrix, and may reflect rate-limiting processes of diffusive transport. 3. The multiplying coefficient, a, incorporates the net effect on porosity of all depositional and diagenetic parameters. Within constraints, carbonate-porosity prediction appears possible on a regional measurement scale as a function of thermal maturity. Estimation of carbonate porosity at the time of hydrocarbon generation, migration, or trapping also appears possible.

American Association of Petroleum Geologists Bulle↗

USGS2022

A comprehensive assessment of mangrove species and carbon stock on Pohnpei, Micronesia

Mangrove forests are the most important ecosystems on Pohnpei Island, Federated States of Micronesia, as the island communities of the central Pacific rely on the forests for many essential services including protection from sea-level rise that is occurring at a greater pace than the global average. As part of a multi-component assessment to evaluate vulnerabilities of mangrove forests on Pohnpei, mangrove forests were mapped at two points in time: 1983 and 2018. In 2018, the island had 6,426 ha of mangrove forest. Change analysis indicated a slight (0.76%) increase of mangrove area between 1983 and 2018, contrasting with global mangrove area declines. Forest structure and aboveground carbon (AGC) stocks were inventoried using a systematic sampling of field survey plots and extrapolated to the island using k-nearest neighbor and random forest species models. A gridded or wall to wall approach is suggested when possible for defining carbon stocks of a large area due to high variability seen in our data. The k-nearest neighbor model performed better than random forest models to map species dominance in these forests. Mean AGC was 167 ± 11 MgC ha -1 , which is greater than the global average of mangroves (115 ± 7 MgC ha -1 ) but within their global range (37–255 MgC ha -1 ) Kauffman et al. (2020). In 2018, Pohnpei mangroves contained over 1.07 million MgC in AGC pools. By assigning the mean AGC stock per species per area to the map, carbon stock distributions were visualized spatially, allowing future conservation efforts to be directed to carbon dense stands.

Pohnpei Island↗

USGS2003

Potential effects of organic carbon production on ecosystems and drinking water quality

Restoration of tidal wetlands in the Sacramento-San Joaquin Delta (Delta) is an important component of the Ecosystem Restoration Program of the CALFED Bay-Delta Program (CALFED). CALFED is a collaborative effort among state and federal agencies to restore the ecological health and improve water management of the Delta and San Francisco Bay (Bay). Tidal wetland restoration is intended to provide valuable habitat for organisms and to improve ecosystem productivity through export of various forms of organic carbon, including both algae and plant detritus. However, the Delta also provides all or part of the drinking water for over 22 million Californians. In this context, increasing sources of organic carbon may be a problem because of the potential increase in the production of trihalomethanes and other disinfection by-products created during the process of water disinfection. This paper reviews the existing information about the roles of organic carbon in ecosystem function and drinking water quality in the Bay-Delta system, evaluates the potential for interaction, and considers major uncertainties and potential actions to reduce uncertainty. In the last 10 years, substantial progress has been made on the role of various forms of organic carbon in both ecosystem function and drinking water quality; however, interactions between the two have not been directly addressed. Several ongoing studies are beginning to address these interactions, and the results from these studies should reduce uncertainty and provide focus for further research.

California↗

USGS2002

Spatial scales of carbon flow in a river food web

Spatial extents of food webs that support stream and river consumers are largely unknown, but such information is essential for basic understanding and management of lotic ecosystems. We used predictable variation in algal δ 13 C with water velocity, and measurements of consumer δ 13 C and δ 15 N to examine carbon flow and trophic structure in food webs of the South Fork Eel River in Northern California. Analyses of δ 13 C showed that the most abundant macroinvertebrate groups (collector-gatherers and scrapers) relied on algae from local sources within their riffle or shallow pool habitats. In contrast, filter-feeding invertebrates in riffles relied in part on algal production derived from upstream shallow pools. Riffle invertebrate predators also relied in part on consumers of pool-derived algal carbon. One abundant taxon drifting from shallow pools and riffles (baetid mayflies) relied on algal production derived from the habitats from which they dispersed. The trophic linkage from pool algae to riffle invertebrate predators was thus mediated through either predation on pool herbivores dispersing into riffles, or on filter feeders. Algal production in shallow pool habitats dominated the resource base of vertebrate predators in all habitats at the end of the summer. We could not distinguish between the trophic roles of riffle algae and terrestrial detritus, but both carbon sources appeared to play minor roles for vertebrate consumers. In shallow pools, small vertebrates, including three-spined stickleback ( Gasterosteus aculeatus ), roach ( Hesperoleucas symmetricus ), and rough-skinned newts ( Taricha granulosa ), relied on invertebrate prey derived from local pool habitats. During the most productive summer period, growth of all size classes of steelhead and resident rainbow trout ( Oncorhynchus mykiss ) in all habitats (shallow pools, riffles, and deep unproductive pools) was largely derived from algal production in shallow pools. Preliminary data suggest that the strong role of shallow pool algae in riffle steelhead growth during summer periods was due to drift of pool invertebrates to riffles, rather than movement of riffle trout. Data for δ 15 N showed that resident rainbow trout (25-33 cm standard length) in deep pools preyed upon small size classes of juvenile steelhead that were most often found in riffles or shallow pools. While many invertebrate consumers relied primarily on algal production derived from local habitats, our study shows that growth of top predators in the river is strongly linked to food webs in adjacent habitats. These results suggest a key role for emigration of aquatic prey in determining carbon flow to top predators.

California↗

USGS1998

Quantitative controls on location and architecture of carbonate depositional sequences: upper miocene, cabo de gata region, se Spain

Sequence stratigraphy, pinning-point relative sea-level curves, and magnetostratigraphy provide the quantitative data necessary to understand how rates of sea-level change and different substrate paleoslopes are dominant controls on accumulation rate, carbonate depositional sequence location, and internal architecture. Five third-order (1-10 my) and fourth-order (0.1-1.0 my) upper Miocene carbonate depositional sequences (DS1A, DS1B, DS2, DS3, TCC) formed with superimposed higher-frequency sea-level cycles in an archipelago setting in SE Spain. Overall, our study indicates when areas of high substrate slope (>15 degrees ) are in shallow water, independent of climate, the location and internal architecture of carbonate deposits are not directly linked to sea-level position but, instead, are controlled by location of gently sloping substrates and processes of bypass. In contrast, if carbonate sediments are generated where substrates of low slope (<15 degrees in our area) are in shallow water, then architecture and location of deposits may be more directly controlled by the relative position of sea level. For these systems, the rates of relative sea-level change are important for determining which systems tracts develop. DS1A-DS1B, cooler-water ramps, result from sediment bypass across steep paleoslopes to toes of slopes. Accumulation rates decreased from >15.6 cm/ky to approximately 2 cm/ky and overall relative sea level rose at rates of 17-21.4 cm/ky. Higher frequency sea-level rates were about 111 to more than 260 cm/ky, producing onlapping, fining- (deepening-) upward cycles. Decreasing accumulation rates resulted from decreasing surface area for shallow-water sediment production, drowning of shallow-water substrates, and complex sediment dispersal related to the archipelago setting. Typical systems tract and parasequence development should not be expected in "bypass ramp" settings; facies of onlapping strata do not track base level and are likely to be significantly different compared to onlapping strata associated with coastal onlap. Basal and upper DS2 reef megabreccias (indicating the transition from cool to warmer climatic conditions) were eroded from steep upslope positions and redeposited downslope onto areas of gentle substrate during rapid sea-level falls (>22.7 cm/ky) of short duration. Such rapid sea-level falls and presence of steep slopes are not conducive to formation of forced regressive systems tracts composed of down-stepping reef clinoforms. The DS3 reefal platform formed where shallow water coincided with gently sloping substrates created by earlier deposition. Slow progradation (0.39-1.45 km/my) is best explained by the lack of an extensive bank top, progressively falling sea level, and low productivity resulting from siliciclastic debris and excess nutrients shed from nearby volcanic islands. Although DS3 strata were deposited during a third-order relative sea-level cycle, a typical transgressive systems tract is not recognizable, indicating that the initial relative rise in sea level was too rapid (>>19 cm/ky). Downstepping reefs, forming a forced regressive systems tract, were deposited during the relative sea-level fall at the end of DS3, indicating that relatively slow rates of fall (10 cm/ky or less) over favorable paleoslope conditions are conducive to generation of forced regressive systems tracts consisting of downstepping reef clinoforms. The TCC sequence consists of four shallow-water sedimentary cycles that were deposited during a 400 ky to 100 ky time span. Such shallow-water cycles, typical of many platforms, form only where shallow water intersects gently sloping substrates. The relative thicknesses of cycles (<2 m to 15 m thick), magnitudes of relative sea-level fluctuations associated with each cycle (25-30 m), high rates of relative sea-level fluctuations (minimum of 25-120 cm/ky), and the widespread distribution of similar TCC cycles in the Mediterranean and elsewhere are supportive of a glacio-eustatic influence. With rates of sea-level change so high, typical systems tracts do not form.

Journal of Sedimentary Research↗

USGS2012

Sulfur, carbon, hydrogen, and oxygen isotope geochemistry of the Idaho cobalt belt

Cobalt-copper ± gold deposits of the Idaho cobalt belt, including the deposits of the Blackbird district, have been analyzed for their sulfur, carbon, hydrogen, and oxygen isotope compositions to improve the understanding of ore formation. Previous genetic hypotheses have ranged widely, linking the ores to the sedimentary or diagenetic history of the host Mesoproterozoic sedimentary rocks, to Mesoproterozoic or Cretaceous magmatism, or to metamorphic shearing. The δ 34 S values are nearly uniform throughout the Blackbird dis- trict, with a mean value for cobaltite (CoAsS, the main cobalt mineral) of 8.0 ± 0.4‰ ( n = 19). The data suggest that (1) sulfur was derived at least partly from sedimentary sources, (2) redox reactions involving sulfur were probably unimportant for ore deposition, and (3) the sulfur was probably transported to sites of ore for- mation as H 2 S. Hydrogen and oxygen isotope compositions of the ore-forming fluid, which are calculated from analyses of biotite-rich wall rocks and tourmaline, do not uniquely identify the source of the fluid; plausible sources include formation waters, metamorphic waters, and mixtures of magmatic and isotopically heavy meteoric waters. The calculated compositions are a poor match for the modified seawaters that form vol- canogenic massive sulfide (VMS) deposits. Carbon and oxygen isotope compositions of siderite, a mineral that is widespread, although sparse, at Blackbird, suggest formation from mixtures of sedimentary organic carbon and magmatic-metamorphic carbon. The isotopic compositions of calcite in alkaline dike rocks of uncertain age are consistent with a magmatic origin. Several lines of evidence suggest that siderite postdated the emplacement of cobalt and copper, so its significance for the ore-forming event is uncertain. From the stable isotope perspective, the mineral deposits of the Idaho cobalt belt contrast with typical VMS and sedimentary exhalative deposits. They show characteristics of deposit types that form in deeper environments and could be related to metamorphic processes or magmatic processes, although the isotopic evidence for magmatic components is relatively weak.

Idaho↗

USGS1979

Environment of ore deposition in the Creede mining district, San Juan Mountains, Colorado; Part IV, source of fluids, from oxygen, hydrogen, and carbon isotope studies

The hydrogen isotopic composition of fluids responsible for formation of the near-surface silver-base metal vein deposits at Creede was measured by direct analysis of inclusion fluids in sphalerite, quartz, and rhodochrosite and was estimated from analyses of illite and chlorite. The oxygen isotopic composition was determined directly on inclusion fluids in sphalerite and was estimated from analyses of quartz, illite, rhodochrosite, siderite, and adularia. The carbon isotopic composition was estimated from analyses of rhodochrosite and siderite. The ranges in isotopic composition for water and CO 2 in the fluids associated with the formation of each of the minerals is given below (number of determinations given in parentheses):Mineral delta D (sub H 2 ) O ppm delta 18 O (sub H 2 ) O ppm delta 13 C (sub CO 2 ) ppmSphalerite -81 to -54 (4) -10.1 to -4.5 (4)Quartz -97 to -86 (4) -5.9 to 1.8 (18)Illite -62 to -50 (8) -1.6 to 1.2(7)Chlorite -64 to -55 (10) -2.2 to 0.8 (10)Adularia 4.2 (1)Rhodochrosite -82 to -78 (2) 4.2 to 9.4 (9) -5.7 to -4.2 (9)Siderite 4.9 to 9.9 (6) -6.9 to -2.7 (6)The delta D (sub H 2 ) O and delta 18 O (sub H 2 ) O values of fluids associated with the formation of sphalerite, quartz, illite/chlorite, and carbonate minerals differ substantially from one another, and these differences appear to have been maintained throughout the depositional history, regardless of the positions of the minerals in the paragenetic sequence.The data suggest that waters from three coexisting reservoirs fed the vein system alternately and episodically during vein formation, and apparently there was little mixing of the fluids from the different reservoirs. The hydrogen, oxygen, and carbon isotope data suggest that the carbonate waters were deep seated, probably dominantly magmatic, in origin. The sphalerite and illite/chlorite waters must have been dominantly meteoric in origin and substantially oxygen shifted by exchange with the volcanic country rocks. The quartz waters were also oxygen shifted meteoric waters but were some 40 per mil lower in deuterium content than the sphalerite and illite/chlorite waters.We propose that the quartz fluids entered the vein system from reservoirs beneath the mountainous areas to the north in the vicinity of the present Continental Divide, but that the sphalerite and illite/chlorite fluids entered the vein system from a topographically low area to the south along the structural moat of the Creede caldera. The difference in delta D between the two meteoric waters may reflect differences in altitude of the recharge areas for the two reservoirs or may be clue to isotopic evolution of the closed-basin lake and interstitial waters in the moat surrounding the Creede caldera.

Colorado↗

USGS2025

U.S. Geological Survey research and assessments supporting carbon dioxide removal

Both carbon capture and storage (CCS) and carbon dioxide removal (CDR) are methods to limit future global temperature rise and ocean acidification. CCS sequesters (stores) carbon dioxide (CO2) captured from industrial sources thereby preventing the CO2 from reaching the atmosphere. The captured CO2 is injected into underground geologic reservoirs or is converted into stable industrial products. CDR enhances natural processes or uses technical approaches to remove excess CO2 from the atmosphere. Carbon dioxide is sequestered in natural sinks such as vegetation and soil, or injected into underground reservoirs or converted into durable products. The U.S. Geological Survey (USGS) conducts research and resource assessments that support biologic and geologic CDR approaches. This report will review some of the ongoing USGS CDR research and assessment efforts.

Conference Paper↗

USGS1986

Late Neogene and Quaternary coarse-fraction and carbonate stratigraphies for Site 586 on Ontong-Java Plateau and Site 591 on Lord Howe Rise

Carbonate oozes recovered by hydraulic piston coring at DSDP Site 586 on Ontong-Java Plateau and Site 591 on Lord Howe Rise have carbonate contents that are consistently higher than 90% with only minor variations. Consequently, paleoceanographic signals were not recorded in detail in the carbonate contents. However, mass accumulation rates of carbonate increased in the late Miocene to mid-Pliocene, reflecting an increase in productivity, then abruptly decreased from mid-Pliocene to the present. Variations in relative abundances of coarse material (foraminifers) and fine material (mostly calcareous nannofossils) do reflect histories of current winnowing and biogenic productivity at the two sites. The late Miocene from 10.5 to 6.5 m.y. ago was a time of relatively constant, quiet, pelagic sedimentation with typical southwest Pacific sedimentation rates of 20-25 m/m.y. The average coarse-fraction abundances are always higher at Site 586 than at Site 591, which reflects winnowing at Site 586. These conditions were interrupted between 6.5 to 4.0 m.y. ago when increased upwelling at the Subtropical Divergence and the Equatorial Divergence produced greater productivity of calcareous planktonic organisms. The increased productivity is suggested by large increases in both fineand coarse-fraction material and constant ratios of foraminifers to nannofossils. The maximum of productivity was about 4.0 m.y. ago. This period of increased upwelling is coincident with the inferred development of the West Antarctic ice sheet. The high productivity was followed by an abrupt increase in winnowing about 2.5 m.y. ago at Site 591, but not until about 2.0 m.y. ago at Site 586. By 2.0 m.y. ago in the late Pliocene, quiet, pelagic sedimentation conditions prevailed, similar to those of the late Miocene. The last 0.7 m.y. has been a period of relatively intense winnowing on Lord Howe Rise but not on Ontong-Java Plateau. The coarse-fraction data have both long- and short-period fluctuations. Long-period fluctuations at Site 591 average about 850 × 103 yr./cycle and those at Site 586 average 430 × 103 yr./cycle. The highest amplitudes are found in the Pliocene and Quaternary sections. The short-period fluctuations range from 100 to 48 × 103 yr./cycle at Site 586 and from 250 to 33 × 103 yr./cycle at Site 591. The effects of local fluctuations of productivity and winnowing have modified the primary orbital forcing signals at these two sites to yield complex paleoceanographic records

Initial Reports of the D.S.D.P.↗

USGS2007

Strontium Isotopic Composition of Paleozoic Carbonate Rocks in the Nevada Test Site Vicinity, Clark, Lincoln, and Nye Counties, Nevada, and Inyo County, California

Ground water moving through permeable Paleozoic carbonate rocks represents the most likely pathway for migration of radioactive contaminants from nuclear weapons testing at the Nevada Test Site, Nye County, Nevada. The strontium isotopic composition (87Sr/86Sr) of ground water offers a useful means of testing hydrochemical models of regional flow involving advection and reaction. However, reaction models require knowledge of 87Sr/86Sr data for carbonate rock in the Nevada Test Site vicinity, which is scarce. To fill this data gap, samples of core or cuttings were selected from 22 boreholes at depth intervals from which water samples had been obtained previously around the Nevada Test Site at Yucca Flat, Frenchman Flat, Rainier Mesa, and Mercury Valley. Dilute acid leachates of these samples were analyzed for a suite of major- and trace-element concentrations (MgO, CaO, SiO2, Al2O3, MnO, Rb, Sr, Th, and U) as well as for 87Sr/86Sr. Also presented are unpublished analyses of 114 Paleozoic carbonate samples from outcrops, road cuts, or underground sites in the Funeral Mountains, Bare Mountain, Striped Hills, Specter Range, Spring Mountains, and ranges east of the Nevada Test Site measured in the early 1990's. These data originally were collected to evaluate the potential for economic mineral deposition at the potential high-level radioactive waste repository site at Yucca Mountain and adjacent areas (Peterman and others, 1994). Samples were analyzed for a suite of trace elements (Rb, Sr, Zr, Ba, La, and Ce) in bulk-rock powders, and 87Sr/86Sr in partial digestions of carbonate rock using dilute acid or total digestions of silicate-rich rocks. Pre-Tertiary core samples from two boreholes in the central or western part of the Nevada Test Site also were analyzed. Data are presented in tables and summarized in graphs; however, no attempt is made to interpret results with respect to ground-water flow paths in this report. Present-day 87Sr/86Sr values are compared to values for Paleozoic seawater present at the time of deposition. Many of the samples have 87Sr/86Sr compositions that remain relatively unmodified from expected seawater values. However, rocks underlying the northern Nevada Test Site as well as rocks exposed at Bare Mountain commonly have elevated 87Sr/86Sr values derived from post-depositional addition of radiogenic Sr most likely from fluids circulating through rubidium-rich Paleozoic strata or Precambrian basement rocks.

Data Series↗

USGS1997

Can the global carbon budget be balanced?

The Mississippi Basin Carbon Project of the U.S. Geological Survey (USGS) is an effort to examine interactions between the global carbon cycle and human-induced changes to the land surface, such as farming and urbanization. Investigations in the Mississippi River basin will provide the data needed for calculating the global significance of land-use changes on land-based carbon cycling. These data are essential for predicting and mitigating the effects of global environmental change. The Mississippi Basin Carbon Project is focused on the third largest river system in the world. The Mississippi River and its tributaries drain more than 40% of the conterminous United States. The basin includes areas that typify vast regions of the Earth's surface that have undergone human development.

Fact Sheet↗

USGS2004

Latitudinal variation in carbon storage can help predict changes in swamps affected by global warming

Plants may offer our best hope of removing greenhouse gases (gases that contribute to global warming) emitted to the atmosphere from the burning of fossil fuels. At the same time, global warming could change environments so that natural plant communities will either need to shift into cooler climate zones, or become extirpated (Prasad and Iverson, 1999; Crumpacker and others, 2001; Davis and Shaw, 2001). It is impossible to know the future, but studies combining field observation of production and modeling can help us make predictions about what may happen to these wetland communities in the future. Widespread wetland types such as baldcypress (Taxodium distichum) swamps in the southeastern portion of the United States could be especially good at carbon sequestration (amount of CO2 stored by forests) from the atmosphere. They have high levels of production and sometimes store undecomposed dead plant material in wet conditions with low oxygen, thus keeping gases stored that would otherwise be released into the atmosphere (fig. 1). To study the ability of baldcypress swamps to store carbon, our project has taken two approaches. The first analysis looked at published data to develop an idea (hypothesis) of how production levels change across a temperature gradient in the baldcypress region (published data study). The second study tested this idea by comparing production levels across a latitudinal range by using swamps in similar field conditions (ongoing carbon storage study). These studies will help us make predictions about the future ability of baldcypress swamps to store carbon in soil and plant biomass, as well as the ability of these forests to shift northward with global warming.

Fact Sheet↗

USGS2004

Dissolved pesticide and organic carbon concentrations detected in surface waters, northern Central Valley, California, 2001-2002

Field and laboratory studies were conducted to determine the effects of pesticide mixtures on Chinook salmon under various environmental conditions in surface waters of the northern Central Valley of California. This project was a collaborative effort between the U.S. Geological Survey (USGS) and the University of California. The project focused on understanding the environmental factors that influence the toxicity of pesticides to juvenile salmon and their prey. During the periods January through March 2001 and January through May 2002, water samples were collected at eight surface water sites in the northern Central Valley of California and analyzed by the USGS for dissolved pesticide and dissolved organic carbon concentrations. Water samples were also collected by the USGS at the same sites for aquatic toxicity testing by the Aquatic Toxicity Laboratory at the University of California Davis; however, presentation of the results of these toxicity tests is beyond the scope of this report. Samples were collected to characterize dissolved pesticide and dissolved organic carbon concentrations, and aquatic toxicity, associated with winter storm runoff concurrent with winter run Chinook salmon out-migration. Sites were selected that represented the primary habitat of juvenile Chinook salmon and included major tributaries within the Sacramento and San Joaquin River Basins and the Sacramento?San Joaquin Delta. Water samples were collected daily for a period of seven days during two winter storm events in each year. Additional samples were collected weekly during January through April or May in both years. Concentrations of 31 currently used pesticides were measured in filtered water samples using solid-phase extraction and gas chromatography-mass spectrometry at the U.S. Geological Survey's organic chemistry laboratory in Sacramento, California. Dissolved organic carbon concentrations were analyzed in filtered water samples using a Shimadzu TOC-5000A total organic carbon analyzer.

California↗

USGS2006

delta 15N and non-carbonate delta 13C values for two petroleum source rock reference materials and a marine sediment reference material

Samples of United States Geological Survey (USGS) Certified Reference Materials USGS Devonian Ohio Shale (SDO-1), and USGS Eocene Green River Shale (SGR-1), and National Research Council Canada (NRCC) Certified Marine Sediment Reference Material (PACS-2), were sent for analysis to four separate analytical laboratories as blind controls for organic rich sedimentary rock samples being analyzed from the Red Dog mine area in Alaska. The samples were analyzed for stable isotopes of carbon (delta13Cncc) and nitrogen (delta15N), percent non-carbonate carbon (Wt % Cncc) and percent nitrogen (Wt % N). SDO-1, collected from the Huron Member of the Ohio Shale, near Morehead, Kentucky, and SGR-1, collected from the Mahogany zone of the Green River Formation are petroleum source rocks used as reference materials for chemical analyses of sedimentary rocks. PACS-2 is modern marine sediment collected from the Esquimalt, British Columbia harbor. The results presented in this study are, with the exceptions noted below, the first published for these reference materials. There are published information values for the elemental concentrations of 'organic' carbon (Wt % Corg measured range is 8.98 - 10.4) and nitrogen (Wt % Ntot 0.347 with SD 0.043) only for SDO-1. The suggested values presented here should be considered 'information values' as defined by the NRCC Institute for National Measurement Reference Materials and should be useful for the analysis of 13C, 15N, C and N in organic material in sedimentary rocks.

Open-File Report↗

USGS1976

Progress report on geology of the Edwards aquifer, San Antonio area, Texas, and preliminary interpretation of borehole geophysical and laboratory data on carbonate rocks

This report describes the geology and porosity of the rocks of the Edwards aquifer, with particular attention to the eastern half of the San Antonio area. The data were obtained from geologic and geophysical studies of nine cored test holes, from laboratory analyses of samples of the aquifer materials, and from recent stratigraphic studies by other investigators. The Georgetown Formation and the Edwards Group or their equivalent stratigraphic units are extensively exposed in central Texas and they occur in the subsurface throughout southern Texas. They consist of a complex sequence of carbonate rocks deposited during Early Cretaceous time under different depositional conditions. Within the study area, the thickness of the carbonate rocks ranges from less than 400 feet (122 m) in the eastern part of the area to more than 600 feet (183 m) in the southwestern part. The depositional environments significantly affected the texture and the composition of the sediments. The Maverick Basin in the southwestern part of the study area was a euxinic basin surrounded by a barrier rudistid reef. Fine-grained carbonates and some associated evaporites occur within this basin. The San Marcos Platform in the eastern part of the study area was intermittently submerged by a transgressing continental sea. Much of the sediments are extensively reworked and burrowed by marine organisms. Several thick sequences of dolomites, evaporites, and associated collapsed deposits occur on the San Marcos Platform. The carbonates of the San Marcos Platform are extensively dissolved within the fresh-water zone. Much of the dissolution is selective of beds containing evaporites or porous dolomites. The dominant structural feature of the study area is a broad homocline that extends from nearly flat-lying beds on the Edwards Plateau to steeply dipping beds of the deep subsurface of the Gulf Coastal Plain. The homocline is interrupted by the Balcones Fault Zone, which is a zone of normal faults that extend across the study area. The intensity and complexity of faulting increases eastward as part of a progression from gentle flexures in the southwestern part of the study area to a complex pattern of tilted fault blocks on the San Marcos Platform.

Texas↗