Understanding the geology of the U.S. Atlantic margin is based on a sparse set of drilling and dredge data integrated with a much larger base of geophysical data. Geophysical data provide the primary basis for interpreting structural features and extrapolating from the sparse geological control. The purpose of this chapter is to present the scope of geophysical data coverage of the Atlantic continental margin in a general review format. The discussion will touch on the kinds of data produced by different technologies, the historical reasons for the use of various methods, and the improvement of methods.
There are two basic classes of geophysical data used in margin studies: seismic data and potential field data. Seismic techniques utilize acoustic energy sources and receivers to examine seismic-wave propagation characteristics of the subsurface rocks. This information includes variation in acoustic reflectivity and velocity within the rock. Near-vertical incidence reflection profiling is used to map structures on a regional basis. Wide-angle seismic-reflection and seismic-refraction profiling are used to examine seismic-velocity structures. Magnetic and gravity potential field anomaly data sets complement the seismic information, providing a means for extrapolating it over broad regions. The comparatively low cost of magnetic and gravity surveying has resulted in the acquisition of fairly dense regional data sets (2 to 10 km line spacing) compared with more coarse regional seismic grids (20 to 30 km line spacing).
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The Atlantic Continental Margin
This synthesis covers stratigraphy, depositional processes, and geophysical interpretation of the major onshore and offshore marginal basins from Maine to the Bahamas, and includes an up-to-date review of thinking on regional tectonic history. Additional chapters discuss the theoretical aspects of thermal evolution, subsidence, and seismic stratigraphy as applied to this region. Geological resources including petroleum, water, sand and gravel, hard minerals, and heat flow are reviewed, and environmental hazards such as seismicity, coastal erosion, waste disposal and submarine instability as it relates to site of drilling platforms and mining are evaluated. A summary chapter reviews areas of controversy and suggests key topics for research.