The northern Gulf of Mexico and the Niger Delta are both dominated by large deltaic depocenters situated on passive continental margins. Both areas are characterized by widespread growth faulting, a substratum of over-pressured shale and deep-water contractional folded belts. The main difference is that the Gulf of Mexico is additionally characterized by extensive and complex salt tectonics. Figure I summarizes the structural styles of both the northern Gulf of Mexico and the Gulf of Guinea.
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.
A detailed structural and stratigraphic study of a deep water (>200 m) sub-basin in the East Java Sea utilized 2-D seismic and well log data in the vicinity of four Amoco wildcats drilled in the early 1980`s. A pelitic basement was deformed in an accretionary prism during the Cretaceous and uplifted and peneplained during the early Tertiary. Extensional half-grabens trending ENE with respect to present geography formed in the Sunda back-arc during the middle Eocene to early Oligocene. The basin- bounding faults are highly listric and are inferred to sole into a sub-horizontal detachment at a depth of less than 10 km. The location and orientation of the extensional structures was strongly controlled by pre-existing thrusts and shaly bedding planes within basement. Isochron maps show Eocene rifting to be localized in a few deep basins, and Oligocene rifting to be more broadly distributed in shallower basins. Inversion began during the early Miocene as listric basin-bounding faults were reactivated in a compressional mode and graben-filling sediments were displaced towards adjacent horst blocks. Most inversions trend ENE with respect to present geography and have grown in bathyal water depths by differential subsidence due to tectonic loading of paleo-horst blocks. Inversion progressed throughoutmore » the Miocene and culminated in the development of a regional basement-involved inversion high (eastern extension of Kangean high) which was uplifted and truncated in the latest Miocene. Despite regional compression which continues today at a deep structural level, small-displacement domino-style normal faults are ubiquitous at a shallow structural level and apparently form on the flanks of the growing inversions by a gravity sliding mechanism.« less
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