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GEOREF RECORD

Edwards Formation, North-central Texas; stratigraphy, depositional geometry, and diagenesis

D. L. Amsbury
Edwards Formation, North-central Texas; stratigraphy, depositional geometry, and diagenesis
AAPG Bulletin (March 1979) 63 (3): 409-410

Abstract

Oolitic and skeletal carbonate grainstone (Moffat Mound) is present as a nearly straight, WNW-ESE-trending belt within the upper Fredericksburg (Cretaceous Comanche) of north-central Texas. The grainstone body with its associated rudist reefs is 2 to 4 mi (3 to 6 km) wide, up to 120 ft (36 m) thick, and at least 50 mi (80 km) long. It separates normal-marine carbonate wackestone and marlstone on the north from tidal-flat dolomite on the south. Detailed tracing of key beds and hardground surfaces through closely spaced, measured sections permitted separation of the body and its finer grained equivalents into several approximate time-stratigraphic subunits. The belt began as a series of discontinuous, relatively thin rudist reefs on a broad shoal, developed into the narrow, linear, carbonate-sand buildup, and then merged with widespread rudist patch reefs to end local Fredericksburg deposition. Early multiple aragonite(?) and calcite cements filled nearly all intergranular pores and most early leached-grain pores in grainstones; most muddy marine rocks interbedded with tidal-flat dolomites were dolomitized. Both the grainstones and dolomites are very porous (up to 35 and 42%, respectively) and permeable (up to 160 and 1,430 md, respectively) because of widespread leaching of cements. The grainstone-dolomite complex forms a large, tabular body of rock which now is continuously permeable to water and which is enclosed above, below, and along one side by impermeable rocks. The linear carbonate-sand body and associated reefs controlled the distribution of original porosity, and it now marks the northeastern boundary of permeable rocks.


ISSN: 0149-1423
EISSN: 1558-9153
Coden: AAPGBS
Serial Title: AAPG Bulletin
Serial Volume: 63
Serial Issue: 3
Title: Edwards Formation, North-central Texas; stratigraphy, depositional geometry, and diagenesis
Author(s): Amsbury, D. L.
Pages: 409-410
Published: 197903
Text Language: English
Publisher: American Association of Petroleum Geologists, Tulsa, OK, United States
Meeting name: AAPG-SEPM annual meeting
Meeting location: Houston, Tex., USA, United States
Meeting date: 19790401April 1-4, 1979
Summary: Y
Accession Number: 1979-023898
Categories: Sedimentary petrology
Document Type: Serial Conference document
Bibliographic Level: Analytic
N30°00'00" - N36°00'00", W102°00'00" - W96°00'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute.
Update Code: 1979
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