Petrobras, 1983. "Campos and Espirito Santo Basins, Offshore Brazil", 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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Normal faults as shown in this seismic section display typical geometry. The fault geometry is characterized by the verticality at upper part (Upper Miocene), and by the concavity at the basal part, where the fault trace becomes asymptotic to the Aptian reflectors. These faults occur quite often in the Campos basin; the main faulting direction is northeast to southwest, which is in accordance to the present coast line, and to the hypothetic axis of the basin tilting.
The genesis of these faults is related to the tilting of the sedimentary basin and resulting movement of the Albian carbonatic sediments over the Aptian evaporites. in the Albian and Upper Cretaceous sequence, the reflectors clearly show the growth character of faults. Some of them were reactivated up to the Upper Miocene, generating compensating faults showing dip in opposite direction.
This seismic section shows various tectonic styles developed during the tecto-sedimentary evolution of the Espirito Santo basin.
First in the Neocomian, during the "rift valley phase," basement (horizon 1) was cut by normal faults in a general down-to-basin pattern, that formed horsts and grabens filled by syntectonic continental clastics.
This rift valley phase evolved, in the Aptian, to a "restricted sea phase" that progressively gave rise to a narrow sea, in the Albian/Cenomanian.
In the Aptian, evaporites (anhydride and halite; horizon 2) were deposited, while in Albian/Cenomanian time, fan deltas and alluvial fans interbedded limestones in a broad carbonate shelf. Close to the end of the Albian, there was significant oceanward tilting of this shelf, triggering gravity slide features (horizon 3) over the evaporitic surface, concomitantly with sedimentation.
The top of this section (horizon 4) is a well recognized limestone. Reactivated basement normal faults, as well as gravity faults, intersected part of the Albian/Cenomanian section.
During the third phase (Late Cretaceous/Early Tertiary) with increasing seaward tilting, the environment changed to open marine. Late Cretaceous slope shales were deposited and were covered, at the east side, by volcanic flows (horizon 5).
In Early Tertiary, a sandstone/shale sequence prograded over the onlapping slope sediments (horizon 6). A shallow water clastic/carbonatic shelf was then developed from Late Tertiary to Present. Horizon 7 represents a single carbonate layer comprised in this section.
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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.