G.H. Bachmann, K. Koch, 1983. "Alpine Front and Molasse Basin, Bavaria", 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 foreland of the Bavarian Alps consists of the Tertiary Molasse and its Mesozoic substratum. So far 38 oil and gas fields have been found with reserves of 14 million bb1 (2.0 million MT of oil and 140 Bcf(4.0 B cu m) of natural gas (Figure 1). The fields are predominantly associated with antithetic normal faults. The lower part of the Molasse and its Mesozoic substratum dips to the south under the Alpine thrust units. The Bavarian Alps consist of four tectonic units: folded molasse, helveticum, flysch, and kalkalpin. Additional tectonic units occur to the south in Austria. The individual units are actually gigantic nappes, which were thrust upon each other from south to north.
The first section (Figures 2, 3) is located east of Munich and represents a typical part of the Molasse basin. The second section (Figures 4, 5) is located at the Alpine front east of the Iller river. Despite a distance of 100 km (62 mi) the two sections supplement each other.
Seismic exploration in the Alps and the Molasse basin is difficult because of the rough topography of the Alps, Quaternary sediments of differing thicknesses, a deep weathering zone, and heterogeneous seismic velocities in the thrust units and the Quaternary.
The top of the Variscan basement, which consists of gneisses and granites, is here only poorly defined. The basement is transgressively overlain by thin Dogger clastics and thick Malm limestone. Cretaceous (Hauterivian - Turonian) marls, limestones, and sandstone overlie transgressively the Malm and become thicker from north to south.
The most prominent reflection in the Molasse basin is at the base of the Tertiary Molasse. It can readily be correlated and mapped and is of great importance for petroleum exploration. The Cretaceous is transgressively overlain by the Molasse, which is late Eocene to Pliocene in age and consists of marls and sandstones, (i.e. the clastic debris of the rising Alps). The Molasse in eastern Bavaria is predominantly marine and brackish, and only the uppermost few hundred meters are limnofluviatile. The Molasse thickens from north to south and at the front of the orogene it is up to 5,000 m (16,400 ft) thick (Figure 1).
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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.