A.W. Bally, 1983. "The Layered Earth—Introductory Comments", 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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Seismic sections almost always display significant examples of primary structures, that is structures that are primarily the product of sediment deposition or have an igneous origin, and that were not affected by later structural deformation. We, therefore, solicited a number of examples illustrating structurally undisturbed stratigraphic features, igneous structures, and the layering of the lower crust.
Section 112 of this atlas complements the many publications which have recently appeared on the subject of seismic stratigraphy. The reader should particularly refer to AAPG Memoir 26, edited by C.E. Payton, 1977. This classic volume will serve for some time as the foremost introductory text on the matter. In particular, we refer to the series of articles published by Gil et al (1977) on seismic stratigraphy and global changes of sea level. Additional material that highlights some of the geophysical aspects is offered by Anstey (1980), Neidell (1980), and Sheriff (1980).
Section 121 contains some high frequency profiles that offer a high resolution of stratigraphic and structural details. The reader is advised to initially focus on the paper by Bouma et al, because that paper provides an overview of the differences obtained by applying different high frequency techniques.
Section 122, on unconformities, 123 on illustrating sequences, 124 on carbonates, and 125 on clastics offer perhaps a somewhat artificial subdivision of various aspects of seismic stratigraphy.
Note that a number of profiles occurring in other sections of this atlas also contain very fine examples of seismic stratigraphy. This applies particularly to a number of papers in section 222 on rifts, 223 on passive margins, 224 on cratonic basins (atlas Volume 2), and some of the foredeep profiles included in section 341 on decollement tectonics (atlas Volume 3).
We obtained a number of profiles across various igneous structures (section 13) and would like to point out that there is an additional profile across a volcanic seamount in the paper by Lehner et al on the Tonga Trench (section 342, atlas plume 3).
Section 14 contains a profile across a presumed impact structure. We would like to obtain more examples of similar features, because of their importance for the evaluation of the current hypothesis on mass extinction (for a summary see McLaren, 1983, and Silver, 1982).
Section 15 includes a number of crustal profiles that were not easily included under some of the other subdivisions. But it should be noted that additional crustal profiles are presented in section 221 (atlas Volume 2), crustal profiles across extensional provinces, and section 321 (atlas Volume 3), crustal profiles across compressional provinces.
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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.