A. W. Bally, 1977. "Ancient and Modern Continental Margins, A Perspective for Future Research", Geology of Continental Margins, Joseph R. Curray, William R. Dickinson, Wallace G. Dow, Kenneth O. Emery, Donald R. Seely, Peter R. Vail, Hunter Yarborough
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The reconstruction of ancient mobile belts reveals the presence of old continental margins. The reconstructions are rather hazardous and uncertain, but they do permit us to compare and contrast ancient with modern continental margins. Information from folded belts derives mostly from surface and subsurface observations, whereas continental margins are generally described in geophysical terms. This contrast in the nature of information helps to focus on a number of problem areas, which are listed below:
Passive margins appear to be emplaced on a previously attenuated crust characterized by extensive rifting. Several intriguing geophysical models have been proposed to explain the attenuation process, but they remain to be documented. Sedimentation and erosion during the rifting process can be observed in a number of ancient fold belts (Alps, Caledonides). The nature of volcanism associated and immediately following the attenuation process should be studied in ancient analogs.
Reflection seismic work on passive margins reveals stratigraphic geometries which should inspire a new look at the stratigraphy of miogeosynclinal sequences.
Much has been written about marginal highs on passive margins, but equivalents in folded belts are difficult to document.
The angularity of the outline of passive margins is often due to transform faults. Pattern of mobile belts reflects former angular outlines, but the anatomy of the relation remains to be studied.
Ancient marginal seas have been postulated in many areas (S. Andes, Western Cordillera, eastern Australia). Marginal seas appear to be destined for destruction by folding process, yet there is little evidence for this in modern marginal seas.
Active margins continue on land, where “accretionary wedges” can be studied in substantial detail both in surface and subsurface.
The lithospheric and thermal regime in subduction zones has been modeled by geophysicists, but remains to be documented on the landward side of subduction zones.
Figures & Tables
Written in 1977 the publication presents interpretations of then-new data bearing on the geology and geophysics of continental margins. The book includes a discussion of plate tectonics and evolution of continental margins; presentations on the stratigraphy and structure of pull-apart and compressional margin;, prospective petroleum source rocks, their organic content, rate of burial, and distribution on slopes and rises of different margin types; prospective reservoir rock patterns in relation to depositional processes and to the sedimentary and structural histories for different types of continental margins; and seismic recognition of depositional facies on slopes and rises for different margin types with varying rates of sediment supply during eustatic sea-level changes.