P.J. Laroche, 1983. "Appalachians of Southern Quebec Seen Through Seismic Line No. 2001", 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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In the fall of 1978, the Societe Quebecoise d'Initiatives Petrolieres (SOQUIP), using a Geosource vibrator crew, recorded for the Government of Quebec a 150 km (93 mi) long seismic line across the St. Lawrence Lowlands in order to promote interest in the area.
This seismic line was shot from a point on the St. Lawrence River 50 km (31 mi) southwest of Quebec City southeastward to the USA border.
The profile crosses Cambro-Ordovician rocks of the Taconian orogen subdivided in three northeast-to-southwest-trending lithostructural domains: the autochthonous domain of the foreland thrust belt, the allochthonous domain of the Humber zone and the Dunnage zone, and overlying rocks of the Connecticut Valley-Gaspe synclinorium. For more geological information about the general tectonic and stratigraphic context of the area, the reader is referred to a list of selected papers.
The geophysical interpretation of this relatively fair-to-poor quality seismic data (Figure 1) is based on correlations from many deep wells, other seismic lines, and surface geology. Thrusted sheets can be recognized on the seismic profile and numerous fault planes can be interpreted of which a few are marked on Figure 2.
Depth conversions (Figure 3) were done by extracting average velocity information from available sonic logs and applying it to the different rock units or their lateral equivalent throughout the seismic profile.
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.