L. Morgan, W. Dowdall, 1983. "The Atlantic Continental Margin", 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 Atlantic continental margin is often referred to as a passive margin because today it is located near the center of the North American plate and displays little seismic or volcanic activity. It is also considered to be a divergent margin because the lithospheric plates moved away or diverged from the mid-Atlantic ridge, which developed at the boundaries between the North American and the European and African plates.
The Atlantic continental margin developed during an extensional phase of crustal deformation that began in the latter part of the Triassic. Its evolution took place in three main stages (Bally, 1981): (1) a rifting phase which involved stretching of the lithosphere and thermal uplift of the mantle (this phase was characterized by complex horst and graben tectonics); (2) the onset of drifting which involved the separation of continental lithosphere (oceanic crust was emplaced for the first time and accretion by sea-floor spreading across mid-ocean ridges began in the gaps between attenuated continental blocks); and (3) a main drifting phase which was dominated by massive subsidence with rates of subsidence that decreased exponentially from the date of the onset of drifting.
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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.