A.W. Erxleben, G. Carnahan, 1983. "Slick Ranch Area, Starr County, Texas", Seismic Expression of Structural Styles: A Picture and Work Atlas. Volume 1–The Layered Earth, Volume 2–Tectonics Of Extensional Provinces, & Volume 3–Tectonics Of Compressional Provinces, A. W. Bally
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The Slick Ranch area is interpreted to be a gravity slide (slump structure) developed contemporaneously with rapid Early Oligocene clastic sedimentation. Seismic data illustrates a classic rollover anticline onto an east-dipping regional glide plane. Slick Ranch is located along the east central boundary of Starr County, Texas, approximately 40 km (25 mi) northeast of Rio Grande City.
In 1978, Tenneco drilled the Slick Ranch No. 66 discovery which encountered multiple objectives in Frio (Upper Oligocene) and Vicksburg (Lower Oligocene) sandstones. The Slick Ranch structure is one of several similar features developed basinward of the Vicksburg Flexure system as thick accumulations of Oligocene age sediments were deposited downdip from the Jackson (Late Eocene) shelf edge.
The Vicksburg Formation (Lower Oligocene) of south Texas consists of laterally stacked wedges of regressive coarse terrigenous clastics separated locally by intervening transgressive marine shales. The area in eastern Starr, western Hidalgo, and southern Brooks counties (see index map) was a sub-basin or a localized clastic depocenter of the larger Rio Grande Embayment during Early Oligocene time. in this area, numerous down-to-the-coast syndepositional (growth) faults formed in conjunction with rapid sedimentation (see cross section). Development of these syndepositional faults was aided by the formation of an extensive "glide plane" or detachment surface coincident with the surface of older Jackson and Yegua formation (Eocene) shales.
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Seismic Expression of Structural Styles: A Picture and Work Atlas. Volume 1–The Layered Earth, Volume 2–Tectonics Of Extensional Provinces, & Volume 3–Tectonics Of Compressional Provinces
Until a few decades ago, structural and regional geology were traditionally the preserve of field geologists. They usually mapped areas of outcropping deformed rocks and supplemented their work by laboratory studies of rock deformation and by theoretical work. Structural geology became tied to the geology of uplifts, folded belts, and underground mines, all of which were accessible to direct observation. Since World War II we have witnessed a tremendous development of geophysics in oceanography and in petroleum geology. Academic geophysicists in oceanography led their geological colleagues into modern plate tectonics and industry geophysicists developed reflection seismology into a superb structural mapping tool that penetrated the subsurface.
Today we are facing a situation where instruction and textbooks in structural geology are almost entirely dedicated to rock deformation, analytical techniques in detailed field geology and summaries of plate tectonics. Illustrations based on reflection seismic profiles are virtually absent in textbooks of structural geology. These texts illustrate only the parts of the proverbial elephant, together with some conjecture, but without ever offering a glimpse of the whole elephant.
Some of the reason cited for the relative scarcity of published reflection profiles are: 1) the confidentiality of exploration data; 2) difficulties in the photographic reduction and reproduction of seismic profiles for a book format; 3) the two-dimensional nature of vertical reflection profiles; and 4) the obvious distortions in reflection profiles that are typically recorded in time.
The AAPG leadership felt that it was time to attempt to correct the situation and to produce this picture and work atlas. The first volumes, of what may become a series of volumes, are addressing an audience that includes: petroleum geologists concerned with structural interpretations; exploration companies that provide in-house training; the AAPG continuing education program; and academic colleagues interested in updating their curricula in structural geology by inclusion of reflection profiles from the “real world” in their teaching.
The atlas is not meant to be a textbook in reflection seismology (instead we listed some at the end of this introduction) nor a text in structural and/or regional geology. Our intent is simply to provide a teaching tool.