W.J. Jankowsky, G. Schlapak, 1983. "Guyana Offshore", 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 sections presented are located on the continental shelf off the northeastern coast of South America. The strata under discussion belong to the sedimentary fill of the Guyana coastal basin which, together with the Eastern Venezuela/Trinidad basin further to the north, frames the cratonic Guyana shield (Figure 1). Primary sedimentary features which can be seen in the sections are shelf edges, foreset bedding, disconformities, fractured and folded allochthonous masses, and reefal bodies.
The Guyana coastal basin lies adjacent to the Western Atlantic passive margin. The tectonics are predominantly controlled by a gradual subsidence of the Guyana shield toward the spreading zone of the oceanic floor of the Western Atlantic. Spreading seems to have started in Late Jurassic time. The oldest known deposits are Upper Jurassic carbonaceous sandstones which initiate a series of mainly transgressive cycles commencing with a deposition of predominantly coarser clastics, and gradually changing into carbonates.
This cyclic sedimentation continues from Lower Cretaceous until middle Tertiary time when, finally, a large carbonate platform was formed. During Oligocene time a major regression took place which resulted in substantial erosion and destruction of parts of the carbonate platform and, there after, in a progradational fill of the seaward basin with mainly unconsolidated clastics in front of the remnants of the coastal platform (Figures 1, 5, and 8).
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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.