Approximately 90% of known reserves of oil and gas has accumulated within the past 250 million years, concurrent with formation of the present ocean basins, island ridges, and linear mountain chains of Andean and Alpine types. Concepts of crustal rifting, sea-floor

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spreading, and plate tectonics help explain these tectonic features of the earth and may help locate additional reserves of petroleum, particularly along the present continental margins.

Differential extension of the lithosphere may result in high temperatures in the upper continental crust concurrent with local accumulations of shallow-water sands, carbonate rocks, euxinic muds, evaporites, and volcanic rocks. Where the lithosphere rifts apart, seawater encroaches and the asthenosphere wells up in the formation of oceanic crust. During continued divergence of the continents, this new crust subsides as it cools and moves away from the rifts, downwarping with it the thinned edges of rifted continental crust. Remnants of tear faults on the rifted continental blocks, and the presence of volcanic rocks and salt diapirs may be clues to petroleum provinces buried beneath the detrital continental rises and/or carbonate platforms that characterize such divergent margins.

Convergence of crustal plate margins (marked by oceanic trenches, linear trends of deep focus earthquakes, volcanic island ridges, and linear mountain chains) results in dominance of detrital over carbonate sedimentation, abrupt facies changes, locally rapid burial of deep water pelagic sediment with thick turbidites, shale diapirs, and layered sediment structures related to drape over differentially uplifted basement blocks, all on the trench side of volcanic island ridges and linear mountains. High temperature may accelerate the generation of petroleum on the continent side of such island ridges and mountains. Strike-slip displacements between adjacent crustal plates, combined with rifting or convergence, may explain other patterns of sedimentation, structure, and geothermal trends elated to accumulations of oil and gas.

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