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At least 559 records · Page 31Linked to original sources
USGS1984

Regional geohydrology of the northern Louisiana salt-dome basin, part II, geohydrologic maps of the Tertiary aquifers and related confining layers

Regional geohydrologic maps show the altitude of the base and the thickness of the aquifers of Tertiary age and related confining layers in the northern Louisiana salt-dome basin. The limit of freshwater in aquifers is also shown. The basin has an area of about 3,000 square miles, and four geologic units of Tertiary age contain regional aquifers. From oldest (deepest) to youngest, the aquifers are in the Wilcox Group, Carrizo Sand, Sparta Sand, and Cockfield Formation. As the Wilcox is hydraulically interconnected with the overlying Carrizo, they are treated as one hydrologic unit, the Wilcox-Carrizo aquifer. The aquifers are separated by confining layers that retard water movement. In the northwestern part of the area, the Wilcox-Carrizo aquifer is separated from the underlying sand facies of the Nacatoch Sand (Cretaceous age) by a confining layer composed of the Midway Group (Tertiary age) and the underlying Arkadelphia Marl and an upper clay and marl facies of the Nacatoch Sand (both of Cretaceous age). In the remainder of the area, the Wilcox-Carrizo aquifer is separated from an underlying Cretaceous aquifer comprised of the Tokio Formation and Brownstown Marl by the Midway Group and several underlying Cretaceous units which in order of increasing age are the Arkadelphia Maril, Nacatoch Sand, Saratoga Chalk, Marlbrook Marl , and Annona Chalk. The Wilcox-Carrizo aquifer is separated from the Sparta aquifer by the overyling Cane River Formation. The Sparta aquifer is separated from the Cockfield aquifer by the overlying Cook Mountain Formation.

Louisiana↗
USGS1997

Chemical evolution and estimated flow velocity of water in the Trinity Aquifer, south-central Texas

Three permeable zones with varying lithology and water chemistry compose the Trinity aquifer, a principal source of water in the 5,500- square-mile study area in south-central Texas. The upper permeable zone locally yields small quantities of water to wells and was not included in this study. The middle permeable zone primarily is composed of limestone with minor amounts of dolostone. Terrigenous sand and marine limestone, with minor amounts of dolostone, are the principal lithologic units in the lower permeable zone. Dissolved solids concentrations range from 329 to 1,820 milligrams per liter in water samples from the middle permeable zone and from 518 to 3,030 milligrams per liter in water samples from the lower permeable zone. Principal hydrochemical facies in the middle permeable zone are calcium magnesium bicarbonate and calcium magnesium sulfate. Hydrochemical facies in ground-water samples from the lower permeable zone vary. Tritium concentrations as large as 5.3 tritium units in the southeastern part of the study area are indicative of relatively recent recharge. Results of a geochemical mass balance simulation along a flowpath in the middle permeable zone indicate a mass transfer of 4.25 millimoles per liter of dolomite dissolved, 5.74 millimoles per liter of gypsum dissolved, 0.46 millimole per liter of sodium chloride dissolved, 8.07 millimoles per liter of calcite precipitated, and 0.67 millimole per liter of calcium-for-sodium cation exchange between solid and aqueous phases. These results support dedolomitization as a principal chemical process in the middle permeable zone of the Trinity aquifer. Results of a simulation along a flowpath in the lower permeable zone indicate a mass transfer of 0.41 millimole per liter of dolomite dissolved, 0.001 millimole per liter of gypsum dissolved, 9.58 millimoles per liter of sodium chloride dissolved, 1.09 millimoles per liter of calcite precipitated, and 1.11 millimoles per liter of sodium-forcalcium cation exchange between solid and aqueous phases. Lower permeable zone processes indicate sodium chloride dissolution, dedolomitization, and cation exchange. Ground-water-flow velocities determined from adjusted carbon-14 ages, calculated using NETPATH, for selected flowpaths in the middle and lower permeable zones were about 1.7 feet per year and less than about 4.4 feet per year, respectively.

Texas↗
USGS2022

Geologic characterization and depositional history of the Uteland Butte member, Green River Formation, southwestern Uinta Basin, Utah

The 15- to 65-m-thick informal Uteland Butte member of the Eocene Green River Formation represents the first widespread transgression of Lake Uinta in the Uinta Basin, Utah. This study assesses the spatial and temporal variation of Uteland Butte member deposits along a 40-km transect in the southwestern margin of the Uinta Basin using detailed measured sections, organic and inorganic geochemical data, and outcrop gamma ray logs. Fourteen lithofacies are identified, which comprise seven facies associations linked to with lacustrine, palustrine, and deltaic depositional settings. Facies associations are traceable laterally across the study area, where five 4- to 12-m-thick depositional cycles are identified. Each shallowing upwards cycle is defined by a >1.5-m-thick basal package of organic-rich, argillaceous laminated mudstone, and is capped by thick packages of bedded carbonate. In the far western study area (Kyune Creek Canyon), thick deposits of organic-rich mudstone are present and represent the most distal outcrop section; time-equivalent strata in the eastern study area (Minnie Maud Creek Canyon) are relatively organic lean with higher silt and clay content, interpreted to represent proximal lake margin deposits influenced by a nearby delta. The outcrop belt is correlated to more distal cores and well logs across the western Uinta Basin. Similar lithological and petrophysical patterns across the western Uinta Basin are used to subdivide stratigraphy into nine laterally contiguous sub-units based on nomenclature from the oil-producing area of the central basin (from base to top: lower Uteland Butte, D Bench, D Shale, C Bench, C Shale, B Bench, B Shale, A Bench, and A Shale). Siliciclastic clay-rich and carbonaterich intervals are correlated across the region and indicate distinct siliciclastic- and carbonate-dominated lake phases during Uteland Butte member deposition. Climate is interpreted to be the dominant driver of these claycarbonate cycles, in which relatively humid periods resulted in increased fluvially derived siliciclastic sediment into the basin (clay-rich periods), and arid periods resulted in evaporative conditions with decreased fluvial sediment input that favor carbonate accumulation. Climatically driven depositional cycles within the Uteland Butte member reflect, to a smaller degree, the larger scale climatically driven depositional cycles observed at the member- and formation levels of Paleocene and Eocene Uinta Basin stratigraphy. Importantly, the Uteland Butte member clay-carbonate cycles showcase how relatively small-scale climate shifts can impact basin-scale lacustrine deposition.

Utah↗
USGS2022

Depositional controls on detrital zircon provenance: An example from upper Cretaceous strata, southern Patagonia

Understanding how depositional environments within a sedimentary system redistribute and sequester sediment is critical for interpreting basin-scale provenance trends. However, sedimentary source-to-sink models commonly examine temporal changes and do not consider how variation in sedimentation processes across a dispersal pathway may result in contrasting provenance signatures. In this paper, we demonstrate a down-paleoslope shift in detrital zircon provenance signatures correlated with shallow-marine lithofacies patterns from the Upper Cretaceous La Anita Formation and underlying continental slope lithofacies of the Alta Vista Formation (Magallanes-Austral Basin, southern Patagonia). New stratigraphic, sedimentologic, and lithofacies analysis results from the La Anita Formation suggest an upward shoaling succession, from a (i) storm-influenced shoreface, (ii) fluvially-dominated, wave-influenced delta, and a (iii) high-energy, gravelly foreshore. Stratigraphic sections are paired with U-Pb detrital zircon sandstone samples (N = 20; n = 5219), which provide both maximum depositional ages and provenance characteristics. While all samples contain abundant zircon derived from the Andean volcanic arc (ca. 145–75 Ma), the amount from both Jurassic distal volcanic massifs (ca. 188–162 Ma) and recycled orogenic sources exhumed during the advance of the Cretaceous fold-and-thrust belt (>200 Ma; 157–142 Ma) vary with changes in depositional environment. We argue that down-paleoslope, systematic enriching of local fold-and-thrust belt material within the La Anita Formation is reflective of progressive mixing of grains transported via shallow-marine processes, while distally enriched fluvio-deltaic transported zircons were sourced from large, regional catchments. This suggests that competition between transport processes across a shallow and marginal marine sequence of rocks affects the resulting provenance signatures recorded within a single stratigraphic succession. These data also detail the degree of sediment pathway connectivity between shallow-marine sources and deep-marine sinks. Detrital zircon results from muddy continental slope facies of the Alta Vista Formation are made up entirely locally derived material, while zircon results from deep-water, sand-rich channel facies of the Formation are indistinguishable from coeval fluvio-deltaic zircon signatures. This implies that continental shelf-to-slope connectivity in a sediment dispersal system, via submarine canyons or shelf-edge delta progradation, is necessary for detrital zircon distributions from the shallow-marine realm to propagate into the deeper marine.

Patagonia↗
USGS2023

Assessing environmental change associated with early Eocene hyperthermals in the Atlantic Coastal Plain, USA

Eocene transient global warming events (hyperthermals) can provide insight into a future warmer world. While much research has focused on the Paleocene–Eocene Thermal Maximum (PETM), hyperthermals of a smaller magnitude can be used to characterize climatic responses over different magnitudes of forcing. This study identifies two events, namely the Eocene Thermal Maximum 2 (ETM2 and H2), in shallow marine sediments of the Eocene-aged Salisbury Embayment of Maryland, based on magnetostratigraphy, calcareous nannofossil, and dinocyst biostratigraphy, as well as the recognition of negative stable carbon isotope excursions (CIEs) in biogenic calcite. We assess local environmental change in the Salisbury Embayment, utilizing clay mineralogy, marine palynology, δ 18 O of biogenic calcite, and biomarker paleothermometry (TEX 86 ). Paleotemperature proxies show broad agreement between surface water and bottom water temperature changes. However, the timing of the warming does not correspond to the CIE of the ETM2 as expected from other records, and the highest values are observed during H2, suggesting factors in addition to p CO 2 forcing have influenced temperature changes in the region. The ETM2 interval exhibits a shift in clay mineralogy from smectite-dominated facies to illite-rich facies, suggesting hydroclimatic changes but with a rather dampened weathering response relative to that of the PETM in the same region. Organic walled dinoflagellate cyst assemblages show large fluctuations throughout the studied section, none of which seem systematically related to CIE warming. These observations are contrary to the typical tight correspondence between climate change and assemblages across the PETM, regionally and globally, and ETM2 in the Arctic Ocean. The data do indicate very warm and (seasonally) stratified conditions, likely salinity-driven, across H2. The absence of evidence for strong perturbations in local hydrology and nutrient supply during ETM2 and H2, compared to the PETM, is consistent with the less extreme forcing and the warmer pre-event baseline, as well as the non-linear response in hydroclimates to greenhouse forcing.

Atlantic Coastal Plain↗
USGS1982

Cretaceous biostratigraphy in the Wyoming thrust belt.

In the Cretaceous section of the thrust belt, fossils are especially useful for dating and correlating repetitive facies of different ages in structurally complex terrain. The biostratigraphic zonation for the region is based on megafossils (chiefly ammonites) , which permit accurate dating and correlation of outcrop sections, and which have been calibrated with the radiometric time scale for the Western Interior. Molluscan and vertebrate zone fossils are difficult to obtain from the subsurface, however, and ammonites are restricted to rocks of marine origin. Palynomorphs (plant microfossils) have proven to be the most valuable fossils in the subsurface because they can be recovered from drill cuttings. Palynomorphs also are found in both marine and nonmarine rocks and can be used for correlation between facies. Stratigraphic ranges of selected Cretaceous marine and nonmarine palynomorphs in previously designated reference sections in Fossil Basin, Wyoming are correlated with the occurrence of ammonites and other zone fossils in the same sections. These correlations can be related to known isotopic ages, and they contribute to the calibration of palynomorph ranges in the Cretaceous of the Western Interior. -from Authors

Mountain Geologist↗
USGS1989

The campi flegrei (Italy) geothermal system: A fluid inclusion study of the mofete and San Vito fields

A fluid inclusion study of core from the Mofete 1, Mofete 2, Mofete 5, San Vito 1, and San Vito 3 geothermal wells (Campi Flegrei, Campania, Italy) indicates that the hydrothermal minerals were precipitated from aqueous fluids (??CO2) that were moderately saline (3-4 wt.% NaCl equiv.) to hypersaline (> 26 wt.% NaCl equiv.) and at least in part, boiling. Three types of primary fluid inclusions were found in authigenic K-feldspar, quartz, calcite, and epidote: (A) two-phase [liquid (L) + vapor (V)], liquid-rich inclusions with a range of salinity; (B) two-phase (L + V), vaporrich inclusions with low salinity; and (C) three-phase [L + V + crystals (NaCL)], liquid-rich inclusions with hypersalinity. Results of microthermometric and crushing studies are reported for twenty drill core samples taken from the lower portions of the five vertical wells. Data presented for selected core samples reveal a general decrease in porosity and increase in bulk density with increasing depth and temperature. Hydrothermal minerals commonly fill fractures and pore-spaces and define a zonation pattern, similar in all five wells studied, in response to increasing depth (pressure) and temperature. A greenschist facies assemblage, defined by albite + actinolite, gives way to an amphibolite facies, defined by plagioclase (andesine) + hornblende, in the San Vito 1 well at about 380??C. The fluid inclusion salinity values mimic the saline and hypersaline fluids found by drilling. Fluid inclusion V/L homogenization temperatures increase with depth and generally correspond to the extrapolated down-hole temperatures. However, fluid inclusion data for Mofete 5 and mineral assemblage data for San Vito 3, indicate fossil, higher-temperature regimes. A limited 87Sr/86Sr study of leachate (carbonate) and the leached cores shows that for most samples (except San Vito 3) the carbonate deposition has been from slightly 87Sr-enriched fluids and that Sr isotopic exchange has been incomplete. However, San Vito 3 cores show an approach to fluid/rock Sr equilibrium with a fluid similar to modern ocean water in 87Sr/86Sr ratio. The Campi Flegrei volcanic system has evolved undersaturated products, mostly trachyte, and defines a large (??? 12 km) caldera. The hydrothermal system developed in this location can be used as an analog for fossil systems in similar trachytic environments. The potential for ore mineralization is expressed by the recognition, from fluid inclusion and drilling data, of ore-forming environments such as boiling and brine stratification. ?? 1989.

Journal of Volcanology and Geothermal Research↗
USGS1993

Sedimentology of Permian upper part of the Minnelusa Formation, eastern Powder River Basin, Wyoming, and a comparison to the subsurface

Describes dolomite, gypsum, and sandstone units deposited in transgressive-regressive cycles. Three depositional cycles are partly exposed. The cycles observed in outcrop were informally labelled cycle 1, cycle 2, and cycle 3 in ascending stratigraphic order. West Mellott field represents a subsurface example of the facies and facies relationships observed in outcrop. The eolian-dune sandstone of the C cycle, which was partially reworked by the transgression of the B cycle, produces oil at West Mellott. The draping of dolomite and anhydrite of the B cycle on the eolian-dune sandstone of the C cycle is analogous to the draping gypsum on dune sand in cycle 2 in outcrop. -from Authors

Mountain Geologist↗
USGS1993

Holocene sedimentation and coastal wetlands response to rising sea level at the Aucilla river mouth, a low energy coast in the Big Bend area of Florida

The shallow dip of the Florida carbonate platform results in low wave energy on Florida ???Big Bend??? coasts. Therefore sedimentation is dominated by river-and tidal-hydrodynamics near the Aucilla River mouth. Where present, Holocene sediments are thin and unconformably overlie Oligocene-aged Suwannee Limestone. The oldest unlithified sediments include reworked carbonate rubble with clay and wood fragments (seven thousand years old or less, based on wood radio-carbon dating). Although this basal sequence is observed in most areas, the sediments that overlie it vary. Sediment sequences from the outer littoral to submarine environments include organic-rich sands, oyster biotherm remains, and cleaner sands with organic-filled burrows. Inner littoral (salt-marsh) sequences generally consist of sandy, fining-upwards sequences in which dry weights of fine-grained clastics and organic components increase up-sequence at similar rates. Offshore sediments preserve greatly attenuated fluvial and salt-marsh facies, if these facies are preserved at all. With sea-level rise, erosion can result from insufficient sediment supply and down-cutting by tidal currents (Dolotov, 1992; and Dalrymple et al., 1992). Dolotov (1992) attributes displacement of original coastal stratigraphy to insufficient sediments for beach profile maintenance, while Dalrymple et al. (1992) attribute erosional truncation (ravinement) or complete removal of portions of typical estuarine sequences to headward migration of tidal channels.

Conference Paper↗
USGS1996

Ramah Member of the Crevasse Canyon Formation - A new stratigraphic unit in the Zuni Basin, west-central New Mexico

Nonmarine deposition accompanying and following a regression of the Cretaceous Interior Seaway during late Turonian time left a sedimentary sequence consisting of fluvial channel sandstones, thin overbank sandstones, and paludal shales containing thin coal beds. This unit is herein designated the Ramah Member of the Crevasse Canyon Formation. The Ramah Member is locally well exposed in the Zuni Basin of west-central New Mexico where it rests on the Gallup Sandstone (marine) and is overlain by the distinctive, feldspathic Torrivio Member of the Crevasse Canyon Formation (formerly of the Gallup Sandstone) Near Ramah, New Mexico the sequence overlies the F member of the Gallup but northward it overlies progressively younger members. These younger members are discrete sand-stone units associated with minor oscillations of relative sea level during a major regional-scale regression. North and east of Puerco Gap, near Gallup. New Mexico, the Ramah Member thins appreciably, and where unmappable it may be included with the Torrivio Member Southward from Gallup in the Zuni Basin. the Ramah locally approaches 150 ft in thickness and contains minable coal beds. The interval was previously referred to as the coal-bearing member of the Gallup (Mapel and Yesberger, 1985) or the Ramah unit (Anderson and Stricker, 1904). In the northern part of the Zuni Basin a problem may exist locally in determinig the top of the Ramah Member. This is due to the presence of fluviel sandstone with coarse-grained facies that looks much the s ame as the Torrivio Member, but underlines it Two criteria may be employed to distiguish the lower sandstone from the Torrivio and properly place it in the strartigraphic succession: (1) the lower sandstone is generally not as feldspathic as the Torrivio nor do the coarse-grained facies contain pebble-size material; and (2) the lower sandstone is not nearly as widespread as the overlying Torrivio. which has a blanket geometry. The type section of the Ramah Member is in the SE1/4 NW1/4 sec. 16 T10N R16W approximately 4 mi southwest of the town of Ramah. The principal coal lies near the top of the member and was mined during the 1920s to supply coal for the Zuni Pueblo schools.

New Mexico Geology↗
USGS1997

Depositional sequence stratigraphy and architecture of the cretaceous ferron sandstone: Implications for coal and coalbed methane resources - A field excursion

This Field Excursion will visit outcrops of the fluvial-deltaic Upper Cretaceous (Turonian) Ferron Sandstone Member of the Mancos Shale, known as the Last Chance delta or Upper Ferron Sandstone. This field guide and the field stops will outline the architecture and depositional sequence stratigraphy of the Upper Ferron Sandstone clastic wedge and explore the stratigraphic positions and compositions of major coal zones. The implications of the architecture and stratigraphy of the Ferron fluvial-deltaic complex for coal and coalbed methane resources will be discussed. Early works suggested that the southwesterly derived deltaic deposits of the the upper Ferron Sandstone clastic wedge were a Type-2 third-order depositional sequence, informally called the Ferron Sequence. These works suggested that the Ferron Sequence is separated by a type-2 sequence boundary from the underlying 3rd-order Hyatti Sequence, which has its sediment source from the northwest. Within the 3rd-order depositional sequence, the deltaic events of the Ferron clastic wedge, recognized as parasequence sets, appear to be stacked into progradational, aggradational, and retrogradational patterns reflecting a generally decreasing sediment supply during an overall slow sea-level rise. The architecture of both near-marine facies and non-marine fluvial facies exhibit well defined trends in response to this decrease in available sediment. Recent studies have concluded that, unless coincident with a depositional sequence boundary, regionally extensive coal zones occur at the tops of the parasequence sets within the Ferron clastic wedge. These coal zones consist of coal seams and their laterally equivalent fissile carbonaceous shales, mudstones, and siltstones, paleosols, and flood plain mudstones. Although the compositions of coal zones vary along depositional dip, the presence of these laterally extensive stratigraphic horizons, above parasequence sets, provides a means of correlating and defining the tops of depositional parasequence sets in both near-marine and non-marine parts of fluvial-deltaic depositional sequences. Ongoing field studies, based on this concept of coal zone stratigraphy, and detailed stratigraphic mapping, have documented the existence of at least 12 parasequence sets within the Last Chance delta clastic wedge. These parasequence sets appear to form four high frequency, 4th-order depositional sequences. The dramatic erosional unconformities, associated with these 4th-order sequence boundaries, indicate that there was up to 20-30 m of erosion, signifying locally substantial base-level drops. These base-level drops were accompanied by a basin ward shift in paleo-shorelines by as much as 5-7 km. These 4th-order Upper Ferron Sequences are superimposed on the 3rd-order sea-level rise event and the 3rd-order, sediment supply/accommodation space driven, stratigraphie architecture of the Upper Ferron Sandstone. The fluvial deltaic architecture shows little response to these 4th-order sea-level events. Coal zones generally thicken landward relative to the mean position of the landward pinch-out of the underlying parasequence set, but after some distance landward, they decrease in thickness. Coal zones also generally thin seaward relative to the mean position of the landward pinch-out of the underlying parasequence set. The coal is thickest in the region between this landward pinch-out and the position of maximum zone thickness. Data indicate that the proportion of coal in the coal zone decreases progressively landward from the landward pinch-out. The effects of differential compaction and differences in original pre-peat swamp topography have the effect of adding perturbations to the general trends. These coal zone systematics have major impact on approaches to exploration and production, and the resource accessment of both coal and coalbed methane.

Brigham Young University Geology Studies↗
USGS1998

Structure, age, and tectonic setting of a multiply reactivated shear zone in the piedmont in Washington, D.C., and vicinity

The Rock Creek shear zone is the dominant tectonic feature in the Piedmont in Washington, D.C. and adjacent parts of Maryland, has an exposed length of 25 km, and a width of up to 3 km. The shear zone is characterized by a complicated composite fabric produced by the imposition of both ductile and brittle structures as well as the reactivation, transposition, and folding of older structures during subsequent antithetic displacement. At least five main types of structural elements are discernible and include: 1) relict, medium- to coarse-grained mylonitic foliation and related structures produced by sinistral shearing under at least middle amphibolite facies conditions; 2) a ductile fault zone having an apparent sinistral displacement of at least several km and an unknown, but possibly significant component of upward throw of the east wall; 3) pervasive, fine-grained ultramylonitic foliation associated with quartz ribbons and late oblique shear bands, generated by dextral shearing under thermal conditions that appear to have progressed from middle greenschist to sub-greenschist (semi-brittle); 4) a system of oblique-(west wall up) and dextralship faults localized chiefly within a tectonic me??lange at the junction of two major strands, and whose motion spanned the ductile-brittle transition; and 5) a system of post-Cretaceous thrust faults that cut Coastal Plain rocks as young as Quaternary as well as the previously deformed crystalline rocks. The first two sets of structures are of probable Ordovician age and are thus believed to coincide with the Taconic event, which produced regional middle to upper amphibolite facies metamorphism, widespread plutonism, and extensive southwest-vergent fold phases in this area. In contrast, the dextral shearing and faulting were generated during final thermal cooling and represent the latest Paleozoic penetrative deformation that affected this area. They are very likely Alleghanian because of their great similarity to other better-dated Alleghanian structural features in the Maryland and Virginia Piedmont.

Southeastern Geology↗
USGS2005

Ordovician conodonts and stratigraphy of the ST. Peter sandstone and glen wood shale, central United States

The age of the St. Peter Sandstone in the central and northern Midcontinent has long been considered equivocal because of the general absence of biostratigraphically useful fossils. Conodonts recovered from the St. Peter Sandstone in Iowa, Minnesota, Nebraska, and Kansas for this study help place some age constraints on this renowned formation in its northern and western extent. Faunas from the lower St. Peter include Phragmodus flexuosus, Cahabagnathus sp., and Leptochirognathus sp., and a late Whiterockian (Chazyan) correlation is indicated. Juvenile or immature elements of P. flexuosus from these collections show morphologies trending toward P. cognitus and P. inflexus, and paedomorphic derivation of these latter species is proposed. Diverse assemblages of hyaline forms also occur in the St. Peter strata (Erismodus spp., Erraticodon sp., Curtognathus sp., Coleodus sp., Archeognathus sp., Stereoconus sp., others) along with various albid elements (Plectodina sp., Eoplacognathus sp., others). The overlying Glenwood Shale contains abundant conodonts dominated by Phragmodus cognitus, Erismodus sp., and Chirognathus duodactylus, and the fauna is interpreted as an early Mohawkian (Blackriveran) association. Certain thin shale units in the St. Peter-Glenwood succession represent condensed intervals, in part reflected by their exceptionally high conodont abundances. Some organic-rich phosphatic shale units in the lower St. Peter of western Iowa have produced equivalent yields of tens of thousands of conodonts per kilogram, and many Glenwood Shale samples yield thousands of conodonts per kilogram. Previous depositional models have proposed that the St. Peter is primarily a succession of littoral and nearshore facies forming a broadly diachronous transgressive sheet sand. However, broad-scale diachroneity cannot be demonstrated with available biostratigraphic control. The recognition of condensed marine shale units, phosphorites, ironstones, and pyritic hardgrounds in the western facies tract of the St. Peter Sandstone has necessitated a re-evaluation of previous regional models of St. Peter deposition. The St. Peter is interpreted to be a composite stratigraphic interval deposited during a succession of transgressive-regressive sedimentary cycles. Transgressive episodes in some cycles were marked by offshore sediment condensation or starvation within a stratified seaway.

Bulletins of American Paleontology↗
USGS2006

Vertical variability in saturated zone hydrochemistry near Yucca Mountain, Nevada

The differences in the saturated zone hydrochemistry with depth at borehole NC-EWDP-22PC reflect the addition of recharge along Fortymile Wash. The differences in water chemistry with depth at borehole NC-EWDP-19PB appear to indicate that other processes are involved. Water from the lower part of NC-EWDP-19PB possesses chemical characteristics that clearly indicate that it has undergone cation exchange that resulted in the removal of calcium and magnesium and the addition of sodium. This water is very similar to water from the Western Yucca Mountain facies that has previously been thought to flow west of NC-EWDP-19PB. Water from the lower zone in NC-EWDP-19PB also could represent water from the Eastern Yucca Mountain fades that has moved through day-bearing or zeolitized aquifer material resulting in the altered chemistry. Water chemistry from the upper part of the saturated zone at NC-EWDP-19PB, both zones at NC-EWDP-22PC, and wells in the Fortymile Wash facies appears to be the result of recharge through the alluvium south of Yucca Mountain and within the Fortymile Wash channel.

Conference Paper↗
USGS1970

Biostratigraphy and dolomite porosity trends of the Lisburne Group

This preliminary study is based on measured and carefully collected sections of the Lisburne Group (fig. 1, sees. 1-29). The outcrops extend from Cape Lisburne (sec. 1) in the west to Egaksrak River (sec. 29) in northeastern Alaska and are used as the basic building blocks for the carbonate facies maps and the cross section. Lithologic and foraminifera samples were collected at 10-foot intervals and rugose corals were collected within each section where found. The rock material was cut into thin section, and petrographic and microfossil studies were made to determine environments of deposition, facies, diagenetic changes, and microfossil content. Coral collections were studied in thin section.

Alaska↗
USGS1989

Holocene sand shoals offshore of the Mississippi River delta plain

Offshore of the Mississippi River delta plain lies a series of Holocene sand shoals marking the position of ancient submerged shorelines associated with younger shelf-phase delta plains. These submerged shorelines represent positions when sea level stood lower than present. Short periods of rapid sea level rise during the Holocene transgression, in combination with subsidence, led to the submergence of these sandy shorelines, which can be recognized at the -33 ft (-10 m) and -66 ft (-20 m) isobaths on the Louisiana continental shelf The -33 ft (-10 m) shoreline trend is represented by Trinity Shoal and Ship Shoal, which are associated with the late Holocene Mississippi River delta plain. Trinity Shoal is derived from the Cypremont-Sale delta complex and is located 12 mi (20 km) offshore of Marsh Island. This shoal is 22 mi (35 km) long, 5 mi (8 km) wide, and 16 - 20 ft (5 - 6 m) thick. The facies relationships indicate that Trinity Shoal is a submerged barrier system in the initial stages of shoreface reworking. To the east is Ship Shoal which is associated with the Maringouin-Teche delta complex. This shoal is located 12 mi (20 km) offshore of the Isles Dernieres and is 31 mi (50 km) long, 5 - 6 mi (8 - 10 km) wide, and 13 - 20 ft (4 - 6 m) thick. The facies relationships indicate that Ship Shoal is a marine sand body derived from shoreface reworking of a submerged barrier island. The -66 ft (-20 m) shoreline trend is represented by the Outer Shoal and St. Bernard Shoals, which are associated with the early Mississippi River delta plain. The Outer Shoal is a low relief sand body, which lies seaward of Ship Shoal immediately west of the Mississippi Canyon. The eastern continuation of the -66 ft (-20 m) shoreline trend is the St. Bernard Shoals, which lie 16 mi (25 km) offshore of the Chandeleur Islands. In contrast to the other shoal systems, the St. Bernard Shoals form a shore-parallel zone of more than seven smaller sand shoals which, in many respects, are similar to a shore-oblique sand-ridge field. Collectively, these sand shoals represent a large potential source of aggregate for shoreline restoration and erosion control as well as possible hard mineral resources. Scientifically, these shoals provide insight into the processes which control coastal evolution and shelf sand development under the condition of relative sea level rise.

Mississippi River↗
USGS1989

Inner shelf deposits of the Louisiana-Mississippi-Alabama region, Gulf of Mexico

The late Quaternary morphology, shallow stratigraphy and sediment distribution of the Louisiana-Mississippi-Alabama inner shelf region are the product of transgressive and regressive sedimentary processes. Shelf sedimentary facies were deposited by deltaic progradation, followed by shoreface erosion and submergence. This information is based on interpretations and synthesis of more than 4,160 mi (6,700 km) of high resolution seismic profiles, 75 grab samples, and 77 vibracores. The shelf can be divided into two main depositional regions. The southwestern region, east and south of the Mississippi River plain, was formed by early Holocene delta complexes, overlying a late Wisconsinan delta. Deposits of the late Wisconsinan delta consist of well-defined coarsening-upward sequences and represent deltaic progradation during low sea level stands. The relatively recent Mississippi delta complexes have deposits which consist of fine-grained sands, silt and clay. With the late Holocene rise in sea level, asymmetrical sand ridges (16 ft, or 5 m, relief) have formed due to marine reworking of shoreline features. The northeastern region, offshore of the Mississippi-Alabama barrier islands, was formed by Pleistocene fluvial systems and Recent shoreface erosion and ravinement. Underlying the relatively thin Holocene sediment cover are relict fluvial sands which were deposited during the late Wisconsinan lowstand. Subsequent sea level rise allowed marine processes to rework and redistribute sediments forming the nearshore fine-grained facies and shelf sands sheet.

Gulf of Mexico↗
USGS1967

Devonian of the Southwestern United States

The structural framework that controlled Devonian deposition consisted of, from west to east: (1) a eugeosynclinal area in northern California and western Nevada; (2) a miogeosynclinal area in southeastern California, eastern Nevada, and western Utah; and (3) a cratonic area in Arizona, eastern Utah, Colorado, New Mexico, and western Texas, east of a northeast-trending hinge line (Wasatch line). The eugeosyncline contains a fragmentary record of Middle Devonian rocks at least 4,000 feet thick characterized by thin-bedded chert, siliceous mudstone, and some limestone and volcanic rocks. The original thickness, however, probably exceeded 6,000 feet and probably included Lower and Upper Devonian rocks. The miogeosyncline contains Lower, Middle, and Upper Devonian rocks as much as 6,000 feet thick characterized by thick units of dolomite and limestone and some local interbeds of sandstone. A transitional zone perhaps 50 miles wide separates the eugeosynclinal and miogeosynclinal facies. The craton contains mostly Upper Devonian rocks, generally less than 1,000 feet thick, characterized by dolomite and limestone and local interbeds of sandstone and mudstone. Widespread crustal movements occurred during Late Devonian time. The Antler orogeny in Nevada initiated a culm facies in the geosyncline. Eugeosynclinal and transitional rocks including those of Devonian age were uplifted to form the Antler orogenic belt, and then were thrust eastward over autochthonous miogeosynclinal rocks in latest Devonian or earliest Mississippian time. Folding and faulting, and subsequent erosion on local uplifts, produced clastic deposits of Late Devonian age in Utah and southwestern Colorado. Devonian rocks in many parts of the geosynclinal area have been moved since Devonian time by large-scale, generally eastward thrusting, oroflexural bending and strike-slip faulting. Four major subdivisions of the Devonian System and related rocks are treated separately: 1) Lower Devonian (Gedinnian, Siegenian, Emsian) and related Upper Silurian (Ludlovian) rocks. 2) Middle Devonian (Eifelian and Givetian) rocks. 3) Lower Upper Devonian (Frasnian, to I ) rocks. 4) Upper Upper Devonian (Famennian, to II-VI ) and related lowermost Mississippian (Tournaisian, cu I ) rocks.

Conference Paper↗