John A. Breyer

Hydrocarbon potential of the Barnett Shale (Mississippian), Delaware Basin, west Texas and southeastern New Mexico

The Barnett Shale (Mississippian) in the Delaware Basin has the potential to be a prolific gas producer. The shale is organic rich and thermally mature over large parts of the basin. Depths to the Barnett range from 7000 ft (2133 m) along the western edge of the basin to more than 18,000 ft (5486 m) along the basin axis. The Barnett Shale began generating petroleum about 250 Ma and reached its maximum temperature about 260 Ma. Present-day thermal maturity is indicative of maximum burial and temperature. Wells in northern Reeves County are in the gas window based on measured vitrinite reflectance values and kerogen transformation ratios. The shale can be divided into an upper clastic unit and a lower limy unit by changes in resistivity. The lower unit can be subdivided into five subunits by distinctive well-log markers. Preliminary analyses suggest that intervals in the lower Barnett marked by high resistivity and high neutron porosity readings on well logs have high gas contents. Areas in which to focus the future exploration in the lower Barnett can be delineated by mapping a net resistivity greater than 50 ohm m. The Barnett Shale contains significant gas resources in the Delaware Basin. Realizing the potential of these resources depends on the current efforts to optimize drilling and completion techniques for this shale-gas play.

Possible new evidence for the origin of metazoans prior to 1 Ga: Sediment-filled tubes from the Mesoproterozoic Allamoore Formation, Trans-Pecos Texas

Possible new evidence for the origin of metazoans prior to 1 Ga comes from sediment-filled tubes preserved on a bedding-plane parting in a chert in the Allamoore Formation (Mesoproterozoic) in a talc quarry in the Millican Hills, near Van Horn, Trans-Pecos Texas. Available data for the Van Horn region indicate that the age of the Allamoore Formation is ∼1250 Ma. The sediment-filled tubes are most likely the feeding traces of animals grazing on algal mats in shallow subtidal or intertidal environments.

Sequence stratigraphy of Gulf Coast lignite, Wilcox Group (Paleogene), South Texas

ABSTRACT Initial sequence-stratigraphic analysis indicates that widespread lignite deposits in the Paleogene strata of the Gulf Coast of the United States are found only in highstand systems tracts. However, not all highstand systems tracts contain widespread lignite. Bluffs rising above the Nueces River in Zavala County, Texas, contain parts of two depositional sequences. The lower sequence contains lignite and includes sediment of both the Midway and Wilcox Groups (Paleogene). All of the lignite in the lower sequence is in the highstand systems tract. The upper sequence lacks lignite and consists entirely of sandstone and shale of the Carrizo Formation (Wilcox Group). High rates of siliciclastic sedimentation probably precluded formation of peat during deposition of the highstand systems tra t of the upper sequence. Direction and rate of relative change in sea level and other extrabasinal factors seem to have exerted a more fundamental control on the abundance and distribution of lignite in the Paleogene strata of the Gulf Coast region than did factors related to depositional setting of the peat precursor.

Evidence for Late Cretaceous Volcanism in Trans‐Pecos Texas

Cretaceous basaltic pyroclastic strata have been discovered in a fault block on the southern edge of the Rosillos Mountains laccolith in the Big Bend area of Trans‐Pecos Texas. The sequence comprises base‐surge and pyroclastic‐fall deposits inferred to have accumulated on the flanks of a small phreatomagmatic volcano. A diverse assemblage of freshwater turtles (including Aspideretes), crocodile teeth, and dinosaur bones have been recovered from the uppermost part of the sequence. The fauna indicate a Late Cretaceous, probably Campanian age. An outward‐dipping normal fault bounding the pyroclastic strata on the southeast juxtaposes sediments of the Upper Cretaceous Javelina Formation in the hanging wall with pyroclastic rocks in the footwall, indicating the pyroclastic strata must be Maastrichtian or older. U‐Pb SHRIMP‐RG analyses of zircons separated from a basaltic block thrown out of the volcano yield an inferred igneous crystallization age of \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Sedimentary facies and depositional history of the Swan Islands, Honduras

72.6\pm 1.5

Shale facies and mine roof stability: A case study from the Illinois basin

\end{document} Ma, consistent with the biostratigraphic and structural evidence. The pyroclastic strata in the fault block provide the first evidence for Late Cretaceous volcanism in the Trans‐Pecos region. Previously, the onset of igneous activity in the area was thought to be no older than 64 Ma. We speculate that the basaltic pyroclastic rocks represent an extension of the Upper Cretaceous Balcones magmatic province into Trans‐Pecos Texas.

A High-Resolution Local Sea Level Curve from Detailed Mapping of the Wales Sand Interval (Wilcox Group, Paleogene), Lasalle and McMullen Counties, South Texas

The margins of the Pedregosa basin can be defined in outcrops of Pennsylvanian and Permian strata in southwestern New Mexico and southeastern Arizona. Siliciclastic basinal rocks crop out along the eastern flank of the Sierra del Cuervo, near Villa Aldama, Chihuahua, Mexico. The late Paleozoic rocks exposed near Villa Aldama have experienced four phases of deformation. Two sedimentary assemblages are recognized within the deformed late Paleozoic section. The upper sedimentary assemblage is a thin-bedded turbidite sequence. Sandstones near the stratigraphic top of the upper assemblage contain Wolfcampian fusulinids. The sandstones and siltstones in the late Paleozoic sequence are quartz-rich rocks with sub-equal amounts of feldspar and lithic fragments. The sediments are of continental block provenance, recycled from quartz-rich, shallow-marine sandstones exposed above rising basement blocks. Granitic debris denoting unroofing of Precambrian granites on the rising basement blocks is found only in a sandstone near the stratigraphic top of the late Paleozic sequence. The rocks exposed near Villa Aldama indicate the existence of a Pennsylvanian-Permian deep-water basin. The mineralogy of the basin-fill sandstones corroborates previous interpretations of the geology of the margins and adjoining shelf and source areas of the Pedregosa Basin.

Coarsening-Upward Tidal Sequences in Wilcox Group in East Texas: ABSTRACT

Abstract Swan Island is a Honduran possession in the western Caribbean, located on the southeastern side of the Cayman Trench. Two sedimentary assemblages are found on the island: an older bedded sequence of mid-Tertiary age (Aquitanian or Burdigalian) and a younger sedimentary sequence of Late Pleistocene age. The older sequence is composed of a series of calcarenites, calcilutites, and siliciclastic mudstones; capping these are cliff-forming reefal carbonates of the younger sequence. The rocks of the older bedded sequence accumulated in deep water. Sedimentation consisted of a constant rain of pyroclastic debris interrupted by the episodic introduction of upslope carbonate material by turbidity currents. Uplift and deformation of this sequence was initiated sometime after the Early Miocene. By the Late Pleistocene, uplift had brought the rocks into water depths conducive to coral growth. Pleistocene sedimentation on the island was controlled by the interaction between tectonic uplift and eustatic sea-level changes. The primary controlling force on the tectonic history of the island is its proximity to the boundary between the North American and Caribbean plates.