Pre-Middle Cretaceous Geologic History of the Deep Southeastern Gulf of Mexico
R.L. Phair, R.T. Buffler, 1983. "Pre-Middle Cretaceous Geologic History of the Deep Southeastern Gulf of Mexico", 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 University of Texas Institute for Geophysics (UTIG) has been conducting studies in the Gulf of Mexico for many years utilizing mainly multifold seismic data. One of the major areas now being studied is the deep southeastern Gulf of Mexico, where UTIG has collected an extensive grid of multifold seismic data (Figure 1). The study area lies north of Cuba between the Campeche and Florida Escarpments. The sea floor is shallower than the deep Gulf to the north and is characterized by erosional channels and large knolls.
Using the seismic data, a Deep Sea Drilling Project leg (DSDP Leg 77) was planned and carried out in December-January, 1980-81. The locations of the holes are shown on the map (Figure 1). Two sets of holes were drilled. Shallow basement was the objective of the three western sites (536, 537, and 538A), and penetration of a thick Mesozoic section was the objective of the eastern sites (535 and 540) (Schlager et al, in press).
Seismic and drilling results are being used to map the regional pre-middle Cretaceous structural and stratigraphic features and to interpret the geologic history of the area. This area is well suited for this type of study because the entire older sequence of rocks lies, in part, at shallow depths or is exposed by erosion at the sea floor. Because there is very little overburden of younger rocks, these older sedimentary sequences can easily be "seen" by the seismic data and reached by the D/VGlomar Challenger.
The purpose of this text is to describe briefly the gross structural and stratigraphic setting of the area (i.e., transitional crust overlain by a thick Jurassic to Lower Cretaceous sequence) and to show examples of seismic data that illustrate these aspects (Figures 2 through 5). Various line information for the seismic examples is included in the Appendix.
Figures & Tables
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.