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GCAGS Transactions

Abstract


Gulf Coast Association of Geological Societies Transactions Vol. 58 (2008), Pages 3-23

Seismic Geomorphology Applied to Lower Glen Rose Patch Reefs in the Maverick Basin, Southwest Texas

Enzo S. Aconcha1, Charles Kerans2, and Hongliu Zeng3

1Chevron Energy Technology Company, 1500 Louisiana St., Houston, Texas 77002

2Department of Geological Sciences, University of Texas at Austin, 1 University Station C1100, Austin, Texas 78712

3Bureau of Economic Geology, University of Texas at Austin, University Station, P.O. Box X, Austin, Texas 78713-8924

ABSTRACT

A seismic geomorphometric analysis performed over more than 30 Lower Glen Rose patch reefs in the Maverick Basin, southwest Texas, have determined that the dome-shaped buildups developed elongating in a consistent NNW-SSE direction with steeper southwest flanks. The asymmetry shown by the shoaling-reefal buildups seems to be a result of northwest-directed far-field paleo-currents and NNE-directed winddriven paleo-waves as this type of energy interaction is observed controlling the shape of more than 600 Holocene patch reefs from the Great Barrier Reef in Australia and Belize shelf in Central America. Independently of the size scale, the elongation axis of the ancient and modern buildups is 1.5-2.5 times larger than its perpendicular direction. These results imply best reservoir facies in the southwest side of the patch reefs. The buildups are preceded by biodetrital mud mounds, which are recognized by high and variable gamma-ray values correlated with anomalous high positive seismic amplitudes resembling the shape of the shoal-reefs. These features are not a seismic artifact because they extend vertically for more than the shoaling-reefal buildup equivalent wavelength. Correlating the response of the gamma ray with the seismic amplitudes has limited potential to differentiate internal facies within the shoaling-reefal buildups. In this regards high negative seismic amplitudes represent the buildups with low gamma-ray values. The rest of the seismic amplitude spectrum characterizes the off-reef deposition with high gamma-ray values.

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