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At least 37 records · Page 2Linked to original sources

USGS2014

Geologic assessment of undiscovered oil and gas resources in Aptian carbonates, onshore northern Gulf of Mexico Basin, United States

Carbonate lithofacies of the Lower Cretaceous Sligo Formation and James Limestone were regionally evaluated using established U.S. Geological Survey (USGS) assessment methodology for undiscovered conventional hydrocarbon resources. The assessed area is within the Upper Jurassic–Cretaceous–Tertiary Composite total petroleum system, which was defined for the assessment. Hydrocarbons reservoired in carbonate platform Sligo-James oil and gas accumulations are interpreted to originate primarily from the Jurassic Smackover Formation. Emplacement of hydrocarbons occurred via vertical migration along fault systems; long-range lateral migration also may have occurred in some locations. Primary reservoir facies include porous patch reefs developed over paleostructural salt highs, carbonate shoals, and stacked linear reefs at the carbonate shelf margin. Hydrocarbon traps dominantly are combination structural-stratigraphic. Sealing lithologies include micrite, calcareous shale, and argillaceous lime mudstone. A geologic model, supported by discovery history analysis of petroleum geology data, was used to define a single regional assessment unit (AU) for conventional reservoirs in carbonate facies of the Sligo Formation and James Limestone. The AU is formally entitled Sligo-James Carbonate Platform Oil and Gas (50490121). A fully risked mean undiscovered technically recoverable resource in the AU of 50 million barrels of oil (MMBO), 791 billion cubic feet of natural gas (BCFG), and 26 million barrels of natural gas liquids was estimated. Substantial new development through horizontal drilling has occurred since the time of this assessment (2010), resulting in cumulative production of >200 BCFG and >1 MMBO.

Cretaceous Research↗

USGS2016

Upper Maastrichtian ammonite biostratigraphy of the Gulf Coastal Plain (Mississippi Embayment, southern USA)

The Cretaceous outcrop belt of the Mississippi Embayment in the Gulf Coastal Plain (GCP) spans the Cretaceous/Paleogene (K/Pg) boundary. A detailed reconstruction of this time interval is critical for understanding the nature of biotic and environmental changes preceding the end-Cretaceous Mass Extinction event and for deciphering the likely extinction mechanism (i.e., bolide impact versus volcanism). Eight sections encompassing the K/Pg succession across the Mississippi Embayment were analyzed using biostratigraphic sampling of ammonites, dinoflagellates, and nannofossils. An upper Maastrichtian ammonite zonation is proposed as follows, from oldest to youngest: Discoscaphites conradi Zone, D. minardi Zone, and D. iris Zone. Our study documents that the ammonite zonation established in the Atlantic Coastal Plain (ACP) extends to the GCP. This zonation is integrated with nannofossil and dinoflagellate biostratigraphy to provide a framework to more accurately determine the age relationships in this region. We demonstrate that ammonites and dinoflagellates are more reliable stratigraphic indicators in this area than nannofossils because age-diagnostic nannofossils are not consistently present within the upper Maastrichtian in the GCP. This biostratigraphic framework has the potential to become a useful tool for correlation of strata both within the GCP and between the GCP, Western Interior, and ACP. The presence of the uppermost Maastrichtian ammonite D. iris , calcareous nannofossil Micula prinsii , and dinoflagellates Palynodinium grallator and Disphaerogena carposphaeropsis suggests that the K/Pg succession in the GCP is nearly complete. Consequently, the GCP is an excellent setting for investigating fine scale temporal changes across the K/Pg boundary and ultimately elucidating the mechanisms causing extinction.

Alabama, Arkansas, Missouri, Mississippi↗

USGS2018

A fossiliferous spherule-rich bed at the Cretaceous–Paleogene (K–Pg) boundary in Mississippi, USA: Implications for the K–Pg mass extinction event in the Mississippi Embayment and Eastern Gulf Coastal Plain

We describe an outcrop of the Cretaceous–Paleogene (K–Pg) boundary exposed due to construction near New Albany, Union County, Mississippi. It consists of the Owl Creek Formation and overlying Clayton Formation. The Owl Creek Formation is rich in the ammonites Discoscaphites iris and Eubaculites carinatus, which, along with biostratigraphically important dinoflagellate cysts and calcareous nannofossils, indicate deposition occurred within the last 1 million years, most likely last 500 kyrs, of the Cretaceous. The base of the overlying Clayton Formation marks the K–Pg boundary, and consists of a 15-30 cm thick muddy, poorly sorted quartz sand containing abundant spherules representing ejecta derived from the Chicxulub impact event. Impact spherules range in size from 0.5 mm to 1 mm in diameter and are hollow and well preserved, with details such as smaller vesicular spherules enclosed within. The spherules are altered to clay minerals such as smectite and are typical of those found at K–Pg boundary sites in the Gulf of Mexico and beyond. Spherules are scattered throughout the bed, and surface counts suggest an average of 4 spherules per cm2. Macrofossils within the spherule bed represent a rich fauna of ammonites, benthic molluscs (bivalves and gastropods), echinoids, as well as crabs and sharks. Macrofossil preservation ranges from whole to fragmentary, with most fossils preserved as internal moulds. The infill of the fossils is lithologically identical to the matrix of the spherule bed, including impact ejecta preserved within phagmocones and body chambers of ammonites, and differs from the underlying Owl Creek Formation. This suggests that the animals were either alive or loosely scattered on the sea floor at the time of deposition. Grain size changes indicate multiple events were responsible for deposition, and together with taphonomic evidence are consistent with dynamic high energy post-impact processes. Later sea level change during the Paleocene is responsible for a sharp contact at the top of the spherule bed. Geochemical evidence from the Owl Creek and Clayton Formations at this locality indicate numerous local palaeoenvironmental changes affected the Mississippi Embayment at the time of the K–Pg boundary and mass extinction event.

Mississippi↗

USGS2022

Calcareous plankton biostratigraphic fidelity and species richness during the last 10 m.y. of the Cretaceous at Blake Plateau, subtropical North Atlantic

Species distributions of well-preserved and diverse assemblages of planktonic foraminifera and calcareous nannofossils spanning the last 10 m.y. of the Cretaceous (middle Campanian through Maastrichtian) are analyzed from samples taken across a 1400 m depth transect at Blake Nose in the western subtropical North Atlantic (Ocean Drilling Program Sites 1049, 1050 and 1052). Age models constructed by integrating foraminiferal, calcareous nannofossil, and magnetic polarity datum events provide a reliable framework for temporal correlation of the sites. This framework enables comparisons of species richness and abundance among sites and evaluation of the reliability of first and last appearance datums for regional and global correlation. Among the standard primary zonal marker datums, six of nine planktonic foraminifer and six of seven calcareous nannofossil events are considered reliable for constraining the age-depth models. Secondary datum ages calculated for 17 planktonic foraminiferal events suggest correlation offsets among the three sites of <0.1 m.y. for four species (including Pseudoguembelina praehariaensis Tur and Huber n. sp.), 0.1–0.5 m.y. for six events, and 0.6–1.0 m.y. for eight species. Secondary calcareous nannofossil datum ages calculated for six species show less reliability, with offsets of <0.1 m.y. for one species, 0.7 m.y. for one species, and 1.0–1.5 m.y. for the remaining four species. The distinctly identifiable new species Trinitella suturis Tur and Huber has lowest occurrences that are diachronous by as much as 1.73 m.y. among the Blake Nose sites. Occurrence rarity is the most likely explanation for the age offsets of this and other diachronous species. Planktonic foraminiferal assemblages show no significant differences in species composition and relative abundance among the three sites, suggesting the sites were all located below a single oligotrophic surface water mass. Species richness counts pooled in 200 kyr bins for the Blake Nose sites reveals high species origination rates from the late Campanian through early Maastrichtian and highest species richness (51–63 species) during the Maastrichtian. The only significant extinction pulse during the mid-Campanian through Maastrichtian occurs between 66.2 and 66.4 Ma with loss of five species representing ∼9% of the assemblage. These extinctions occur at the same time as a globally recognized warming event correlated with a pulse of eruptions at the Deccan Traps in India. Calcareous nannofossil assemblages show no significant change in relative abundance among the three sites. Two significant extinction events are documented: one from 75.20 to 75.40 Ma with a loss of six species representing ∼6% of the assemblage and one from 66.2 to 66.4 Ma with a loss of nine species representing ∼9% of the assemblage. The former event is associated with a hiatus at the base of Zone CC24, and the latter corresponds to Deccan Trap warming. Hiatuses are identified at all three Blake Nose sites near the base of the Maastrichtian (∼71.5 Ma; lowermost Pseudoguembelina palpebra /CC24 Zone) and only at the deeper Sites 1049 and 1050 in the mid-Maastrichtian (∼67.2 Ma; Pseudoguembelina hariaensis /CC26b Zone) and the mid-Campanian (∼75.9 Ma; base of Radotruncana calcarata /CC22 Zone). Slumping from across the shelf and slope could have caused the early Maastrichtian hiatus while changes in the pattern and strength of deep-water circulation may have been responsible for the mid-Maastrichtian and mid-Campanian hiatuses.

Cretaceous Research↗

USGS2003

Aggradation of gravels in tidally influenced fluvial systems: Upper Albian (Lower Cretaceous) on the cratonic margin of the North American Western Interior foreland basin

Alluvial conglomerates were widely distributed around the margin of the Early Cretaceous North American Cretaceous Western Interior Seaway (KWIS). Conglomerates, sandstones, and lesser amounts of mudstones of the upper Albian Nishnabotna Member of the Dakota Formation were deposited as fill-in valleys that were incised up to 80 m into upper Paleozoic strata. These paleovalleys extended southwestward across present-day northwestern Iowa into eastern Nebraska. Conglomerate samples from four localities in western Iowa and eastern Nebraska consist mostly of polycrystalline quartz with lesser amounts of microcrystalline (mostly chert), and monocrystalline quartz. Previous studies discovered that some chert pebbles contain Ordovician-Pennsylvanian invertebrate fossils. The chert clasts analyzed in this study were consistent with these findings. In addition, we found that non-chert clasts consist of metaquartzite, strained monocrystalline quartz and 'vein' quartz from probable Proterozic sources, indicating that parts of the fluvial system's sediment load must have travelled distances of 400-1200 km. The relative tectonic stability of this subcontinent dictated that stream gradients were relatively low with estimates ranging from 0.3 to 0.6 m/km. Considering the complex sedimentologic relationships that must have been involved, the ability of low-gradient easterly-sourced rivers to entrain gravel clasts was primarily a function of paleodischarge rather than a function of steep gradients. Oxygen isotopic evidence from Albian sphaerosiderite-bearing paleosols in the Dakota Formation and correlative units from Kansas to Alaska suggest that mid-latitude continental rainfall in the Albian was perhaps twice that of the modern climate system. Hydrologic fluxes may have been related to wet-dry climatic cycles on decade or longer scales that could account for the required water supply flux. Regardless of temporal scale, gravels were transported during 'high-energy' pulses, under humid climatic conditions in large catchment areas. An overall rising sea level during the late Albian created accommodation space for the gravelly lithofacies equivalent to the Kiowa-Skull Creek rocks. As Western Interior sea level rose, regional stream gradients were reduced, resulting in regional fluvial aggradation. The conglomeratic lower parts of the Nishnabotna Member of the Dakota Formation formed the transgressive systems tract within an upper Albian sequence that is defined by two unconformities that can be traced from marine Kiowa strata in western Kansas northeastward into western Iowa (Brenner et al., 2000). Mud-draped cross-bedded sandstone bodies, laminated mudstone intervals, and vertical burrows in the lower strata of the Nishnabotna Member indicate that estuarine conditions existed at the mouths of the river system, and tidal effects were transmitted at least 200 km inland from the interpreted late Albian coast. These observations suggest that estuarine conditions stepped up the incised valleys as fluvial sediments aggraded in response to regional transgression that continued through the Late Albian. ?? 2003 Elsevier Ltd. All rights reserved.

Cretaceous Research↗

USGS2003

Depositional environments and processes in Upper Cretaceous nonmarine and marine sediments, Ocean Point dinosaur locality, North Slope, Alaska

A 178-m-thick stratigraphic section exposed along the lower Colville River in northern Alaska, near Ocean Point, represents the uppermost part of a 1500 m Upper Cretaceous stratigraphic section. Strata exposed at Ocean Point are assigned to the Prince Creek and Schrader Bluff formations. Three major depositional environments are identified consisting, in ascending order, of floodplain, interdistributary-bay, and shallow-marine shelf. Nonmarine strata, comprising the lower 140 m of this section, consist of fluvial distributaries, overbank sediments, tephra beds, organic-rich beds, and vertebrate remains. Tephras yield isotopic ages between 68 and 72.9 Ma, generally consistent with paleontologic ages of late Campanian-Maastrichtian determined from dinosaur remains, pollen, foraminifers, and ostracodes. Meandering low-energy rivers on a low-gradient, low-relief floodplain carried a suspended-sediment load. The rivers formed multistoried channel deposits (channels to 10 m deep) as well as solitary channel deposits (channels 2-5 m deep). Extensive overbank deposits resulting from episodic flooding formed fining-upward strata on the floodplain. The fining-upward strata are interbedded with tephra and beds of organic-rich sediment. Vertical-accretion deposits containing abundant roots indicate a sheet flood origin for many beds. Vertebrate and nonmarine invertebrate fossils along with plant debris were locally concentrated in the floodplain sediment. Deciduous conifers as well as abundant wetland plants, such as ferns, horsetails, and mosses, covered the coastal plain. Dinosaur skeletal remains have been found concentrated in floodplain sediments in organic-rich bone beds and as isolated bones in fluvial channel deposits in at least nine separate horizons within a 100-m-thick interval. Arenaceous foraminifers in some organic-rich beds and shallow fluvial distributaries indicate a lower coastal plain environment with marginal marine (bay) influence. Marginal marine strata representing interdistributary bay deposits overlie the nonmarine beds and comprise about 15 m of section. Extensive vegetated sand flats, shoals, and shallow channels overlain by shallow bay deposits (less than 7 m deep), containing storm-generated strata characterize the marginal marine beds. Abundant bioturbation and roots characterize the stratigraphic lowest bay deposits; bioturbated sediment, pelecypods, barnacles, and benthic microfossils are found in the overlying bay storm deposits. The sediments abruptly change upward from hummocky cross-stratified bay deposits to a muddy marsh deposit containing shallow organic-rich channels to prograding nonmarine to marginal marine beds. Transgressive, abundantly fossiliferous shallow-marine strata more than 13 m thick comprise the uppermost exposures at Ocean Point. The marine beds overlie nonmarine and bay strata and represent an environment dominated episodically by storms. The age of the marginal marine and marine beds is late Maastrichtian based on pollen. ?? 2003 Elsevier Ltd. All rights reserved.

Cretaceous Research↗

USGS2021

Multimineral petrophysics of thermally immature Eagle Ford Group and Cretaceous mudstones, U.S. Geological Survey Gulf Coast 1 research wellbore in central Texas

Traditional petrophysical methods to evaluate organic richness and mineralogy using gamma-ray and resistivity log responses are not diagnostic in source rocks. We have developed a deterministic, nonproprietary method to quantify formation variability in total organic carbon (TOC) and three key mudrock mineralogical components of nonhydrocarbon-bearing source rock strata of the Eagle Ford Group by developing a set of log-derived multimineral models calibrated with Fourier transform infrared spectroscopy core data from the research borehole U.S. Geological Survey Gulf Coast 1 West Woodway. We determined that bulk density response is a reliable indicator of organic content in these thermally immature, water-bearing source rocks. Multimineral findings indicate that a high degree of laminae-scale mineralogical heterogeneity exists due to thinly interbedded carbonate cements amid clay-rich mudstone layers. The lower part of the Eagle Ford Group contains the highest average TOC content (4.7 wt%) and the highest average carbonate volume (64.1 vol%), making it the optimal target in thermally mature areas for source-rock potential and hydraulic-fracture placement. In contrast, the uppermost portion of the Eagle Ford Group contains the highest average volume of clay minerals (42.6 vol%), which increases the potential for wellbore stability issues. Petrophysical characterization reveals that porosity is approximately 30% in this relatively uncompacted formation. In this thermally immature source rock, water saturation is nearly 100% and no free hydrocarbons were observed on the resistivity logs. No evidence of borehole ellipticity was observed on the three-arm caliper log, and horizontal stresses are presumed to be directionally uniform in the vicinity of this near-surface wellbore. This shallow wellbore has a temperature gradient of 1.87°F/100 ft (16.3°C/km) and is likely influenced by earth surface heating.

Texas↗

USGS1977

Exchangeable cations in Cretaceous bentonites from Wyoming and Montana

The research described herein was designed to determine the relationship between physical and chemical properties of bentonite and to evaluate the feasibility of using chemical properties of bentonites to predict their suitability for various industrial uses. Samples were chosen from both Wyoming and Montana from as broad an areal and stratigraphic distribution as possible. They may or may not be typical of mine-grade bentonite or of "average" bentonite. Samples described as containing volcanic ash or as being otherwise contaminated were omitted from this study.

Montana, Wyoming↗

USGS2014

U.S. Geological Survey unconventional petroleum systems research in south Mississippi: Observations on burial history and thermal maturity in the Cretaceous

Shale hydrocarbon ‘resource’ plays have revolutionized the United States energy mix over the last 5 years. These plays are diverse in lithology and age but share the common feature of occurring in ‘tight’ formations which require hydraulic (hydro-) fracturing for economic flow rates. In general, economic success requires an organic-rich reservoir with a quartz- or carbonate-rich mineralogy that responds to artificial stimulation by fracturing. The U.S. Geological Survey (USGS) is tasked with estimating the quantity and quality of undiscovered hydrocarbons reservoired in shales. In support of that mission, we began an investigation of unconventional petroleum systems in the southern part of the Mississippi Salt Basin in 2012, building on earlier reconnaissance work that identified this area as potentially prospective for ‘shale’ gas (Enomoto et al., 2012). While our recent studies (Valentine et al., 2014a; Hackley et al., 2014) have suggested poor ‘shale’ gas prospectivity (due to low organic content, low porosity, high clay content, and significant depth), at least for the Aptian section, they also have generated a wealth of new information about thermal maturity in the Cretaceous of south Mississippi. In addition, our work to-date has set the stage for future USGS evaluation of unconventional hydrocarbons reservoired in the Upper Cretaceous Tuscaloosa Marine Shale (TMS). Here, we summarize recent USGS thermal maturity studies in the south Mississippi Salt Basin.

Mississippi↗

USGS2002

Vitrinite reflectance data for the Greater Green River basin, southwestern Wyoming, northwestern Colorado, and northeastern Utah

The Greater Green River Basin is a large Laramide (Late Cretaceous through Eocene) structural and sedimentary basin that encompasses about 25,000 square miles in southwestern Wyoming, northwestern Colorado, and northeastern Utah (fig. 1). Important conventional oil and gas resources have been discovered and produced from reservoirs ranging in age from Cambrian through Tertiary (Law, 1996). In addition, an extensive overpressured basin - centered gas accumulation has also been identified in Cretaceous and Tertiary reservoirs by numerous researchers including Law (1984a, 1996), Law and others (1980, 1989), McPeek (1981), and Spencer (1987). The purpose of this report is to present new vitrinite reflectance data to be used in support of the U.S Geological Survey assessment of undiscovered oil and gas resources of the Greater Green River Basin. One hundred eighty-six samples were collected from Cretaceous and Tertiary coalbearing strata (figs. 1 and 2) in an effort to better understand and characterize the thermal maturation and burial history of potential source rocks. Two samples were from core, one from outcrop, and the remainder from well cuttings. These data were collected to supplement previously published data by Law (1984b), Pawlewicz and others (1986), Merewether and others (1987), and Garcia-Gonzalez and Surdam (1995) and are presented in table 1.

Colorado, Utah, Wyoming↗

USGS2012

Megaporosity and permeability of Thalassinoides-dominated ichnofabrics in the Cretaceous karst-carbonate Edwards-Trinity aquifer system, Texas

Current research has demonstrated that trace fossils and their related ichnofabrics can have a critical impact on the fluid-flow properties of hydrocarbon reservoirs and groundwater aquifers. Most petroleum-associated research has used ichnofabrics to support the definition of depositional environments and reservoir quality, and has concentrated on siliciclastic reservoir characterization and, to a lesser degree, carbonate reservoir characterization (for example, Gerard and Bromley, 2008; Knaust, 2009). The use of ichnology in aquifer characterization has almost entirely been overlooked by the hydrologic community because the dynamic reservoir-characterization approach has not caught on with hydrologists and so hydrology is lagging behind reservoir engineering in this area (de Marsily and others, 2005). The objective of this research is to show that (1) ichnofabric analysis can offer a productive methodology for purposes of carbonate aquifer characterization, and (2) a clear relation can exist between ichnofabrics and groundwater flow in carbonate aquifers.

Texas↗

USGS2003

Biodiversity changes in Cretaceous palynofloras of eastern Asia and western North America

Palynology has great potential for providing comparative data and interpretations about changes in biodiversity during the Cretaceous Period. This is especially true for both eastern Asia and western North America because of strong floristic similarities that existed between these regions during Cretaceous time. Also, because palynomorphs of terrestrial origin can be deposited in offshore as well as terrestrial environments, significant potential exists for marine-to-continental palynostratigraphic correlations in both regions. Palynological biostratigraphy can improve the geologic dating of changes in biodiversity. During the Early Cretaceous, eastern Asia and western North America lay within the Cerebropollenites palynofloral province, a circumpolar phytogeographic zone characterized by distinctive palynological assemblages. During most of the Late Cretaceous, these regions lay within the palynofloristically unique Aquilapollenites Province, which was more restricted geographically than the Cerebropollenites Province. The most important development during Cretaceous time that is reflected in palynological assemblages was the rise of the angiosperms as the numerically and ecologically dominant forms of vegetation. The most striking short-term palynofloral event in the two regions was the sudden disappearance of species of Aquilapollenites and associated genera at the Cretaceous-Tertiary (K/T) boundary. Both of these occurrences produced major changes in biodiversity in the terrestrial realm. Geologic research in International Geological Correlation Program Project 434 can benefit from applications of palynostratigraphy. Palynologic research within Project 434 could include development of a comprehensive palynostratigraphic zonation for the Cretaceous, the definition of regional palynostratigraphic datums, and investigation of the record of floral change at the K/T boundary. ?? 2002 Elsevier Science Ltd. All rights reserved.

Journal of Asian Earth Sciences↗

USGS1994

Cyclostratigraphic calibration of cretaceous magnetic polarity events (Cismon, Southern Alps, Italy)

In an introductory section the problems of constructing a geologic time scale and the role of magnetic reversals and Milankovitch cycles in geochronology are outlined. Results of a detailed cyclostratigraphic and magnetostratigraphic study of the Valanginian/Hauterivian part of the pelagic limestone section at Cismon in the Southern Alps are presented and used in conjunction to estimate the duration of magnetic subchrons between CM10N and CM8. The new estimates are shorter than in most published time scales by a factor of two to three. More research along these lines may make a revision of the Early Cretaceous time scale necessary. ?? 1994 International Association for Mathematical Geology.

Mathematical Geology↗

USGS1989

Search for clues to Mesozoic graben on Long Island

The position of Long Island between the Hartford Basin of Connecticut and graben structures reported from seismic reflection studies offshore to the south of the island suggests the possibility that other grabens associated with the early Mesozoic rifting might be buried beneath central Long Island. The hypothesis that post-rift tectonic activity would be related to the rift grabens and that such activity would be expressed in the post-rift sedimentary deposits led to a study of the Cretaceous and Pleistocene section to seek clues for buried grabens on Long Island. The Pleistocene glacial deposits in central and eastern Long Island have been mapped and a pollen zonation in the Upper Cretaceous section in the central part established. This work, combined with literature research, suggests the following: 1. (1) In central Long Island, the spacing of wells which reach basement enables a NE- striking zone free of basement samples to be defined where a buried graben could occur. This zone is referred to as the “permissible zone” because within it the data permit the existence of a hidden graben. 2. (2) The abrupt changes in the thickness of some pollen zones in the Upper Cretaceous deposits of central Long Island may be related to Cretaceous faulting. 3. (3) Buried preglacial valleys, the confluence of glacial lobes and major glacial outwash channels seem concentrated in west central and central Long Island. The loci of these drainage features may reflect structural control by a basement depression. 4. (4) The “permissible zone” is aligned with the zone of structures in an offshore zone south of central Long Island and with the Hartford Basin in Connecticut. Geophysical anomalies also fit into this pattern. 5. (5) A definitive answer to the question of a buried graben on Long Island will require a seismic line across the “permissible zone”, or further drilling.

Marine Geology↗

USGS2005

Huminite reflectance measurements of Paleocene and Upper Cretaceous coals from borehole cuttings, Zavala and Dimmit counties, South Texas

The reflectance of huminite in 19 cuttings samples was determined in support of ongoing investigations into the coal bed methane potential of subsurface Paleocene and Upper Cretaceous coals of South Texas. Coal cuttings were obtained from the Core Research Center of the Bureau of Economic Geology, The University of Texas at Austin. Geophysical logs, mud-gas logs, driller's logs, completion cards, and scout tickets were used to select potentially coal-bearing sample suites and to identify specific sample depths. Reflectance measurements indicate coals of subbituminous rank are present in a wider area in South Texas than previously recognized.

Open-File Report↗

USGS1987

Maps showing distribution of the Middle Cretaceous unconformity in the eastern Gulf of Mexico

Several theories on the origin of the Gulf of Mexico basin have been introduced by various researchers (Beloussov, 1970; Freeland and Dietz, 1971; Malfait and Dinkelman, 1972; Wood and Walper, 1974; Pilger, 1978; Buffler and others, 1980; Dickinson and Coney, 1980; Gose and others, 1980; Schmidt-Effing, 1980; Walper, 1980; Schlager and others, 1984). Although no final agreement has been reached, one prominent geologic feature is generally recognized. The early evolution of the basin ended with a major middle Cretaceous event resulting in a Gulf-wide unconformity referred to as the middle Cretaceous unconformity (MCU). This event represents a major shift from Early Cretaceous shallow-water bank sedimentation to Late Cretaceous deeper water carbonates (Worzel and others, 1973; Mitchum, 1978). Seismic data collected by the U.S. Geological Survey and the University of Texas Marine Science Institute, Galveston Geophysics Laboratory (UTMSI-GGL) were used to map the MCU and its relationship to the deep stratigraphy and structure of the eastern Gulf basin east of long 90° W. In addition, data from the Deep Sea Drilling Project (DSDP) in the southeastern Gulf and along the Campeche Escarpment and dredge samples collected by Schlager and others (1984) from the Florida Escarpment provide an age for the MCU (Cenomanian, 97 m. y. ) and a detailed lithological record. This report emphasizes the salt diapirs, pillows, and ridges in the northeastern Gulf of Mexico because of the profound effect these geologic structures have on the MCU. Salt locations are shown on the isopach of post-MCU sediments (fig. 1). A second map shows pre-middle Cretaceous outcrops terminated by the MCU along the Florida Escarpment, the southeastern Gulf, and the Campeche Escarpment (fig. 2).

Miscellaneous Field Studies Map↗

USGS1953

Correlation of the Cretaceous formations of Greenland and Alaska

This is Number 10d of a series of correlation charts prepared for the Committee on Stratigraphy of the National Research Council. It has been sponsored by the U.S. Geological Survey and has required about seven months' time of both authors gathering and compiling data and evaluating fossil evidence. As the two regions dealt with in the chart are widely separated, the lists of references are also given separately. The annotations dealing with Greenland are based entirely on published information. The annotations dealing with Alaska are based on a re-examination of nearly all the Cretaceous fossils from Alaska are based on a re-examination of nearly all the Cretaceous fossils from Alaska in the collections of the Geological Survey. This has resulted in many concepts not hitherto published and in some concepts that are completely at variance with those that have been published. Naturally for large areas undergoing active exploration, such as Alaska, a correlation chart is out of date in many particulars as soon as published. Nevertheless it is valuable to the field man whose activities are confined to small areas but who must interpret much of his data in terms of surrounding areas that he has not seen. It is valuable to the student and to the general geologist because it organizes scattered information in a manner that can be applied in their field problems, makes quite unnecessary the memorization of stratigraphic correlations are based on observation and reasoning and not on a vast memory. It is probably of greatest value to the specialist who makes the chart because he discovers what areas and problems are most in need of research and can thereby direct his efforts and those of his associates in a manner that will yield the greatest results.

Alaska↗

USGS2004

Upper Cretaceous sequences and sea-level history, New Jersey Coastal Plain

We developed a Late Cretaceous sealevel estimate from Upper Cretaceous sequences at Bass River and Ancora, New Jersey (ODP [Ocean Drilling Program] Leg 174AX). We dated 11-14 sequences by integrating Sr isotope and biostratigraphy (age resolution ??0.5 m.y.) and then estimated paleoenvironmental changes within the sequences from lithofacies and biofacies analyses. Sequences generally shallow upsection from middle-neritic to inner-neritic paleodepths, as shown by the transition from thin basal glauconite shelf sands (transgressive systems tracts [TST]), to medial-prodelta silty clays (highstand systems tracts [HST]), and finally to upper-delta-front quartz sands (HST). Sea-level estimates obtained by backstripping (accounting for paleodepth variations, sediment loading, compaction, and basin subsidence) indicate that large (>25 m) and rapid (???1 m.y.) sea-level variations occurred during the Late Cretaceous greenhouse world. The fact that the timing of Upper Cretaceous sequence boundaries in New Jersey is similar to the sea-level lowering records of Exxon Production Research Company (EPR), northwest European sections, and Russian platform outcrops points to a global cause. Because backstripping, seismicity, seismic stratigraphic data, and sediment-distribution patterns all indicate minimal tectonic effects on the New Jersey Coastal Plain, we interpret that we have isolated a eustatic signature. The only known mechanism that can explain such global changes-glacio-eustasy-is consistent with foraminiferal ??18O data. Either continental ice sheets paced sea-level changes during the Late Cretaceous, or our understanding of causal mechanisms for global sea-level change is fundamentally flawed. Comparison of our eustatic history with published ice-sheet models and Milankovitch predictions suggests that small (5-10 ?? 106 km3), ephemeral, and areally restricted Antarctic ice sheets paced the Late Cretaceous global sea-level change. New Jersey and Russian eustatic estimates are typically one-half of the EPR amplitudes, though this difference varies through time, yielding markedly different eustatic curves. We conclude that New Jersey provides the best available estimate for Late Cretaceous sea-level variations. ?? 2004 Geological Society America.

Geological Society of America Bulletin↗