G. Drozdzewski, 1983. "Tectonics of the Ruhr District, Illustrated by Reflection Seismic Profiles", 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 surveys were made in the context of an intensive exploration and reserve assessment of the coal mines on the northwestern margin of the Ruhr district. Combined with hundreds of 1,500 m (4,921 ft) coreholes, the seismic lines served to clarify structural details in the coal mining district. Results of the program were published in a monograph (Drozdzewski et al, 1980), which provided a detailed analysis of the structures of the area. Both Vibroseismic and explosive sources were used to obtain seismic sections and 3-D seismic sections which were produced by the Prakla-Seismos GMBH processing center in Hannover, and interpreted by teams of geophysicists, mining engineers and geologists.
The Ruhr district is part of the foredeep of the Variscan folded belt of western Europe. Mining operations in an area of 110 by 50 km (68 by 31 mi), provide access to very detailed subsurface structural information.
During the Upper Carboniferous some 6,000 m (19,685 ft) of paralic sediments were deposited. Coals seams first appear during the Namurian C and range into the Westfalian C. While sedimentation persisted in the northern Ruhr district, folding already started to the south of the area. Thus, in this process the southern Ruhr district was shortened by folding and subordinate thrust faulting to about one-half of its original width. Toward the north and west, folding intensity decreases gradually. The foldbelt is segmented by conspicuous transversal and diagonal faults.
During and after the folding regional differential uplift occurred. In the Niederrhein area up to 2,000 m (6,562 ft) of Upper Carboniferous strata were eroded prior to the deposition of the Late Permian Zechstein formation. Overlying the folded and block-faulted Variscan folded belt, a relatively thin veneer of Zechstein marls, clays, anhydrites, dolomites, and most importantly, salt was deposited. The original salt thickness in the Niederrhein area is estimated to be about 250 m (820 ft). Salt solution has modified the original thickness. The overlying Triassic Buntsandstein formation is about 500 m (1,640 ft) thick and consists of poorly consolidated sandstones, which are often acquifers, and clays with some salt toward the top.
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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.