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Book Chapter

Contrasting Styles of Late Neogene Deep-Water Sandstone Deposition, Offshore Texas

By
Robert A. Morton
Robert A. Morton
Bureau of Economic Geology The University of Texas at Austin Austin, Texas 78713
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Published:
January 01, 1991

Abstract

Middle Miocene and middle Pliocene deep-water sandstone reservoirs of the western Gulf Coast Basin are associated with failed shelf margins and subregional unconformities referred to as submarine pediments. The submarine pediments formed broad, convex-landward arcs along nondeltaic slopes and on the southwestern flanks of subjacent delta systems. They were created by retrogressive failure and were later enlarged by erosion during periods of lowered sea level. At times of lowered sea level, the deep embayments that carved into the continental platform funneled nearshore sands downslope to basin-floor fans.

The pediments were first backfilled by deep-water mudstones deposited by mass-transport processes. These slump blocks and high-energy turbidites exhibit mounded to chaotic seismic reflections that dip landward. Later, sand-rich channel-levee complexes were deposited above the basal mudstones and near the seismic-facies transition from chaotic reflections to overlying horizontal or wavy reflections. The pre-entrenchment morphology of the shelf margin was finally restored by coalescence of small, prograding deltas that are recorded as clinoform reflections.

Unconfined lower-slope and basin-floor fans associated with the submarine pediments are generally sand poor. The sand-rich lowstand-fan deposits are restricted to highly elongate, dip-oriented leveed channels that mark the principal pathways of sediment transport.

Sandstones confined to leveed channels of the upper-fan and pediment fill are the most prolific hydrocarbon reservoirs within each stratigraphic sequence. These channel sandstones exhibit high vertical continuity but low lateral continuity because interbedded turbidite mudstones increase away from the channel axes. Thin sandstones of the lower fan may exhibit high lateral continuity, but they typically have poor-reservoir properties because of high concentrations of original muddy matrix.

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Contents

Concepts in Sedimentology and Paleontology

The Three-Dimensional Facies Architecture of Terrigenous Clastic Sediments and its Implications for Hydrocarbon Discovery and Recovery

Andrew D. Miall
Andrew D. Miall
Geology Department, University of Toronto, Toronto, Ontario M5S 3B1, Canada
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Noel Tyler
Noel Tyler
Bureau of Economic Geology, The University of Texas at Austin, Austin, Texas 78713-7508 U.S.A.
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SEPM Society for Sedimentary Geology
Volume
3
ISBN electronic:
9781565762268
Publication date:
January 01, 1991

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