Abstract: Stratigraphy and Structure of Pull-Apart Margins

K. O. Emery

Seafloor spreading produces three kinds of continental margin: divergent, convergent, and translation. Oil and gas production occurs on the continental shelves of all three kinds of margins because of growth of deltas that largely are unaffected by the plate movements. However, potential future deep-ocean fields appear to owe their origins more closely to the nature of plate movements, and probably most of them are associated with plate divergence (or pull-apart). After the original separation of plates most Atlantic continental margins received thick layers of evaporites followed by much thicker prisms of detrital sediments that built continental rises. Organic matter from the many mass movements down the adjacent continental slopes and from the commonly anoxic Upper Cre aceous deep-sea sediments may have been converted to oil and gas that becomes concentrated within stratigraphic traps, folds, faults, and salt diapirs. The high heat conductivity of the salt may speed maturation of the oil. A secondary form of divergence associated with convergence is responsible for many small marginal basins that have received thick organic-rich sediments along the westernmost Pacific Ocean; these basins also have much promise for deep-ocean oil of the future. In spite of the evident need to verify the presence of oil and gas in sediments of the deep-ocean floor, test drilling has not occurred and the speculations about the resources remain untested.

AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC