M. Pieri, 1983. "Three Seismic Profiles Through the Po Plain", 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:
The alluvial Po Plain extends over about 5,000 sq km (1,931 sq mi) in Northern Italy, between the Southern Alpine and the Northern Appenninic borders. Its subsurface structure has been revealed by the petroleum exploration carried out since 1940 by Agip (the Italian State Oil Company) with extensive and detailed seismic reflection surveys, and the drilling of more than 700 exploratory wells.
The known sedimentary sequence consists of a Mesozoic carbonate section overlain by Tertiary and Quaternary clastics, with a total thickness that exceeds 12 km (7.5 mi) in the structurally lowest areas.
In the southern part of the Po Plain, the subsurface structures correspond to the external elements of the Northern Apennines thrusted and folded belt. From west to east, three main folded arcs can be identified: the Monferrato arc (partly outcropping in the western Po Plain and bordered to the South by the South-Piedmont episutural basin), the Emilia arc, and the Ferrara-Romagna arc.North of the folded arc the foreland area includes the Pedealpine Homocline and the Veneto Plain. These are two structural units separated by the Berici-Euganei Hills axis, which corresponds to a transcurrent fault system accompanied by Tertiary volcanic centers.
The subsurface structure of the Po Plain is the result of late Miocene, Pliocene, and Quaternary tectonics associated with the subduction and/or the shortening of basement and involving the compression of the sequence deposited on the northern part of the Apulo-Adriatic block (a sunken continental margin of the Mesozoic Tethys). The southwestern border of the Alps, folded in late Miocene is relatively unaffected by later tectonic phases. Therefore, the southern external alpine folds are buried under the foredeep sediments of the Pedealpine Homocline. The less competent Tertiary clastic section, where shaly layers are common, is frequently detached from the lower carbonate sequence, and disharmonic folding results.
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.