Petrobras, 1983. "Potiguar Basin, 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
Download citation file:
This seismic section is located in the central graben of the Potiguar basin, with a northwest to southeast direction. in its central part, there is a structural high called Alto de Quixaba (Quixaba High), originated during Lower Cretaceous time by an intense tensional tectonism. The Central Graben is filled with Neocomian lacustrine sediments, cut by a Cenomanian angular unconformity. The sedimentary sequence deposited from Cenomanian to Coniacian/Santonian, grades from fluvial clastics to shallow platform limestones.
The seismic data was recorded with DDS-888 48-channel equipment, using vibroseis as source (16 sweeps per point of vibration, weighted array; 64 sweeps in 100 m, or 328 ft), and 36 geophones per station (180 m, or 591 ft, long array, 36 geophones per station). Coverage was 24fold and maximum offset was 1,350 m (4,420 ft).
This chapter depicts a northeast to southwest seismic line located in the central part of submerged Potiguar basin. Horizon 3 (interpreted time section, offshore) represents the top of a "rift" sequence (Aptian) which is affected by normal faults. Horizon 2 indicates the top of a carbonate transgressive sequence (Turonian to late Campanian) interbedded with shales and sandstones. Horizon 1 shows the base of Tertiary regressive platform sequence. The interval between reflectors (1) and (2) constitutes the shale, sandstone, and turbidite slope sequence.
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.