Relationships of Bexar shale, Hensel sandstone, and Hensel dolomite (basal upper Trinity, Comanchean Cretaceous) in south-central Texas

Conference · Sun Apr 01 04:00:00 EST 1984 · Am. Assoc. Pet. Geol., Bull.; (United States)

OSTI ID:6609379

Amsbury, D L

The Bexar Shale has been considered the offshore equivalent of the Cow Creek Limestone, the overlying Hensel sandstone, or of the disconformity between them in outcropping sections. Cores and outcrops in Comal, Kendall, and northern Bexar Counties preserve calcitic and dolomitic caliche in the top of the Cow Creek Limestone. Above the caliche is 8-16 m(25-50 ft) of laminated or bioturbated, dolomitic siltstone and silty dolomite (Hensel dolomite). Dolomite is euhedral and silt-sized. The lower part contains collophane grains and oyster shells replaced partly by chalcedony. Carbonate grains within the upper part include angular and well-rounded mollusk and echinoid fragments; many are pyritic and coated by glauconite. Terrigenous grains in Hensel dolomite grade upward from silt to coarse subarkose sand from central Texas. In southern Bexar County, about 35 m (115 ft) of silt-, clay-, and calcite-mudstone referable to the Bexar Shale sharply overlie shallow marine Cow Creek Limestone, and grade abruptly upward into about 7 m (23 ft) of Hensel dolomite. Dolomite is overlain by calcarenite of the Glen Rose Formation containing subarkose sand grains. Similar distinctive sand grains occur in well cuttings of basal Glen Rose beds northeastward through Travis County. The Bexar represents a flood of clay-sized sediment from a distant source, spread across the San Marcos arch during a rapid transgression. Slightly younger sand, silt, and local clay of the Hensel sandstone were eroded from central Texas by a few flash floods during a major period of caliche formation in the area.

• OSTI ID: 6609379
• Report Number(s): CONF-8405216-
• Conference Information: Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Journal Volume: 68:4
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020200* -- Petroleum-- Reserves
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& Exploration
03 NATURAL GAS
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ALKALINE EARTH METAL COMPOUNDS
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CARBON COMPOUNDS
CARBONATE MINERALS
CARBONATES
DOLOMITE
FEDERAL REGION VI
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MAGNESIUM CARBONATES
MAGNESIUM COMPOUNDS
MINERALS
NORTH AMERICA
OXYGEN COMPOUNDS
ROCKS
SANDSTONES
SEDIMENTARY ROCKS
SEDIMENTATION
SHALES
STRATIGRAPHY
TEXAS
USA