Continental Margins from Viewpoint of the Petroleum Geologist

Abstract

Major features of earth's surface are its continents and its ocean basins--which in turn reflect fundamental differences between its continental crust and its oceanic crust. The broad zone of contact between continental and oceanic domains has been called continental margin. Geomorphically, margin is expressed by continental slope, but also includes seaward part of submerged continental shelf and landward part of continental rise. Geologically, margin includes zone of lateral change in lithosphere marking oceanward limits of characteristic continental crust. Many of most exciting events in history of our planet have taken place at this contact zone, between continental and oceanic crust, and between continents and oceans; continental margin represents stage where, throughout earth history, this drama has been played. Important elements of continental margin are outer shelf, borderland, marginal plateau, slope, base of slope, rise, and marginal trench. The nature and origin of these features and their sediments are of vital importance to petroleum geology. Of particular interest to petroleum geologist are sediment-rich, semi-enclosed basins or seas associated worldwide with continental margin; structural barriers and reefs commonly developed near rim of continental slope; numerous manifestations of gravity tectonics and diapirism on slope; and growing evidence for impressive vertical movements associated with continental margins. Great advances in our understanding of processes active at continental margins have come from subsea geologic and geophysical studies of last decades, and rapid additional progress may be expected from stimulus of the new global tectonics; but current hypotheses are still largely in a developmental stage. Factual data are still woefully inadequate, and need for additional continuous refraction seismic profiles across margin is critical. Moreover, continuing studies are needed, not only to better know margins of present, but also to better identify margins of past. Of special interest are extent and age of transmarginal features. For petroleum geologist, it is significant that through ages continental margin has been great mixing bowl in which has been brewed most of world's petroleum and from which most of its petroleum production to date has been derived. The continental margin should be fruitful meeting ground of petroleum geologist, geologist of oceans, and student of earth history.