Regional Seismic Lines in the National Petroleum Reserve in Alaska
C.E. Kirschner, G. Gryc, C. Molenaar, 1983. "Regional Seismic Lines in the National Petroleum Reserve in Alaska", 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 National Petroleum Reserve in Alaska (NPRA, formerly Naval Petroleum Reserve No. 4) covers an area of about 36,000 sq mi (93,000 sq km) in northwest Arctic Alaska (Figure 1). The Reserve extends from the coastline of the Beaufort and Chukchi seas south across the Arctic coastal plain and foothills and is bounded on the southwest by the Brooks Range divide and on the southeast and east by the Colville River. To the west, the Reserve is bounded by a line from Icy Cape due south to the crest of the Brooks Range, approximately 1620W longitude.
During exploration aimed at assessing the petroleum potential of NPRA by government agencies (U.S. Navy 1944-1953 and 1974-1977, and U.S. Geological Survey 1977-1981) about 16,800 line mi (26,800 line km) of reflection seismic data were shot over the length and width of the Reserve. A selected number of the regional seismic lines were reformated by trace-dropping to reduce the horizontal scale and enable the interpreter to see regional structural and stratigraphic characteristics in a smaller desk-top format. Three of these lines have been selected for illustration in this volume; one north-to-south line, one east-to-west line, and one line trending southeast along the northeast coast of the Reserve. These lines are approximately 200, 250, and 100 mi (320, 400, and 160 km) long, respectively. Consequently, reduction to fit the format of this volume is great and only major geological features can be shown. For additional or follow-up studies, all of the seismic lines, reformated by trace-dropping, can be obtained from the National Oceanic and Atmospheric Administration, EDIS/NODC D62, 325 Broadway, Boulder, Colorado 80303. The title box and processing procedure for the three regional compressed sections used in this report are shown in Figures 5, 6, and 7.
A generalized stratigraphic section for NPRA is shown in Figures 3 and 4. For convenience in discussion, subdivision of the section into three sequences follows Grantz, Eittreim, and Dinter's (1979) adaption of Lerand's (1973) terminology defining the Franklinian, Ellesmerian, and Brookian sequences. The Franklinian sequence consists mainly of low-grade metamorphosed clastic sedimentary rocks with local granitic intrusive rocks. This sequence is considered basement for petroleum exploration. The Ellesmerian sequence includes the clastic and bioclastic sedimentary rocks derived from the northerly provenance terrane of Barrovia (Thilleur, 1973; Grantz and May, 1983) and deposited on the Arctic platform. The Brookian sequence includes the sedimentary rocks derived from a southerly provenance terrane near the site of the present Brooks Range and areas to the southwest. The base of the Ellesmerian sequence is clearly defined in the coastal plain and northern foothills areas, but in the axis of the Colville trough, the Ellesmerian and Brookian sequences probably intertongue in Jurassic to Neocomian time.
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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.