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Abstract

AAPG Bulletin, V. 88, No. 11 (November 2004), P. 1501-1522.

Copyright copy2004. The American Association of Petroleum Geologists. All rights reserved.

Understanding growth-faulted, intraslope subbasins by applying sequence-stratigraphic principles: Examples from the south Texas Oligocene Frio Formation

L. Frank Brown Jr.,1 Robert G. Loucks,2 Ramoacuten H. Trevintildeo,3 Ursula Hammes4

1Bureau of Economic Geology, John A. and Katherine G. Jackson School of Geosciences, University of Texas at Austin, University Station Box X, Austin, Texas 78713-8924; [email protected]
2Bureau of Economic Geology, John A. and Katherine G. Jackson School of Geosciences, University of Texas at Austin, University Station Box X, Austin, Texas 78713-8924; [email protected]
3Bureau of Economic Geology, John A. and Katherine G. Jackson School of Geosciences, University of Texas at Austin, University Station Box X, Austin, Texas 78713-8924; [email protected]
4Bureau of Economic Geology, John A. and Katherine G. Jackson School of Geosciences, University of Texas at Austin, University Station Box X, Austin, Texas 78713-8924; [email protected]

AUTHORS

Frank Brown received his B.S. degree in geology and chemistry from Baylor University in 1951 and his M.S. degree and his Ph.D. from the University of Wisconsin, Madison, in 1953 and 1955, respectively. Frank worked for Standard Oil of Texas (Chevron) in 1955–1957, the Bureau of Economic Geology (BEG) in 1957–1960 and 1966–1989, and as an international consultant in 1989–1999. From 1960 to 1966, he was associate professor at Baylor University. He was professor of geological sciences at the University of Texas at Austin in 1971–1989 and emeritus professor in 1989–1999. Since 1999, he has been a research professor at BEG, where he continues his studies of the sequence stratigraphy of the Gulf Coast of Texas and Mexico.

Robert Loucks is a senior research scientist at the Bureau of Economic Geology, working on siliciclastic and carbonate reservoir characterization. He was the recipient of the 1999 AAPG Wallace E. Pratt Memorial Award for Best Paper, the 1982 SEPM Excellence of Presentation Award, and the 1991 SEPM Excellence of Poster Presentation Award. Bob served as the Mideast AAPG Dean A. McGee International Distinguished Lecturer in 1999.

Ramon Trevintildeo received his B.S. degree in geology (Texas AampI University, 1983) and his M.S. degree in geology (University of Texas at Arlington, 1988). He worked for Mobil from 1988 to 1992 and received an M.B.A. degree from the University of Oklahoma in 1994. Since 1995, he has worked on sequence-stratigraphic reservoir characterization at the Bureau of Economic Geology.

Ursula Hammes obtained her diploma in geology from the University of Erlangen, Germany, in 1987, and her Ph.D. from the University of Colorado at Boulder in 1992. She spent 10 years in industry and joined the Bureau of Economic Geology in 2002 as a research associate. Her main research focus is in clastic and carbonate sequence stratigraphy, depositional systems, and image analysis.

ACKNOWLEDGMENTS

The State of Texas Advanced Resource Recovery Program supported this research. Patricia Montoya and Randy Remington, geophysical associates at the Bureau of Economic Geology, contributed to the work on this project. Mike Pawelek of IBC Petroleum, Inc., Gary Biesiedecki and Gary Miller of SABCO Oil and Gas Corporation, and Matt Hammer of Royal Exploration Company, Inc., provided industrial support. We especially extend our gratitude to WesternGeco for use of seismic data. We thank David Jennette, Susann Doenges, and David Stephens, respectively, for critical reviews, technical editing, and graphics support during manuscript preparation.

Major credit for ideas expressed in this paper are due to Robert M. Mitchum Jr., John Sangree, and John C. Van Wagoner and their former Exxon associates, including Peter R. Vail and Henry W. Posamentier, for their original pioneering research in the field of siliciclastic sequence stratigraphy. These workers all contributed significantly not only to the entire field, but also to the valid, original static sequence model.

In addition, although conceptual differences exist be tween our sequence ideas and inferred processes proposed earlier by William E. Galloway and his associates and students, we are deeply indebted to them for providing a regional perspective of the character and distribution of Frio depositional systems. Our differing views are based on data and concepts unavailable to them and other prior workers who concentrated on the Tertiary systems of the Texas Gulf Coast Basin. To all of the numerous earlier contributors to this vital petroleum region, we extend our professional gratitude for their research efforts. For example, early work by both Merle C. Israelsky beginning in 1935 and S. W. Loman in 1949 contributed documentation of the cyclicity and deltaic facies characterizing the Tertiary rocks of the Gulf of Mexico Basin. These two geologists, among many others, such as pioneer micropaleontologists Helen Jean Plummer (Bureau of Economic Geology), Julia A. Gardner, Alva C. Ellisor, and Ester R. Applin (former University of Texas students of J. A. Udden, director, Bureau of Economic Geology, 1915–1932), who first established most benthic foraminiferal zones, are true giants in Gulf Coast Tertiary stratigraphy and micropaleontology and therefore deserve to be credited even long after their contributions. Likewise, William L. Fisher and J. H. McGowen contributed original concepts of siliciclastic depositional systems analysis applied to the Paleocene and Eocene Wilcox Group.

We thank the Geology Foundation of the John A. and Katherine G. Jackson School of Geosciences at the University of Texas at Austin for funding the color figures and the partial page charges.

ABSTRACT

A detailed analysis of Oligocene Frio Formation intraslope, growth-faulted subbasins in the Corpus Christi, Texas, area indicates that deposition during relative lowstands of sea level was the main initiator, or trigger, of growth faulting. Lowstand depocenters on the low-gradient, upper continental slope comprising basin-floor fan facies, slope-fan systems, and prograding lowstand delta systems exerted sufficient gravity stress to trigger major sections of outer shelf and upper slope strata to fail and move basinward. The faults sole out deep in the basin, and rotation of hanging-wall blocks mobilized deep-water muds and forced the mud basinward and upward to form mud (shale) ridges that constitute the basinward flank of intraslope subbasins overlying footwall fault blocks.

Sedimentation associated with third-order relative falls of sea level produced load stress that triggered a major regional syndepositional growth-fault system. Subbasins on the downthrown side of each arcuate fault segment that constitute a regional fault system are filled during the lowstands of sea level. Consequently, genetically similar but noncontemporaneous lowstand depositional systems filled each successive growth-faulted subbasin trend. The subbasin stratigraphy becomes younger basinward because the subbasin development and fill process extended the Frio shelf edge stepwise into the Oligocene Gulf of Mexico Basin, coinciding with relative third-order sea level cycles.

The subbasins have been prolific petroleum targets for decades and are now the focus of prospecting for deep gas. Lowstand sandstones are principal reservoirs, and synsedimentary tectonics produced anticlinal and fault traps and associated stratigraphic pinch-out traps on the flanks of the structures. Understanding the origin of the faulted subbasins and their chronostratigraphic relationships and depositional processes provides a perspective that can improve deep gas exploration.

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