1981 Theses Doctoral

The thermal and mechanical evolution of Atlantic-type continental margins

Steckler, Michael S.

Atlantic-type continental margins are the sites of large (>12 km) sediment accumulations. Most of these sediments were deposited in shallow-water environments, implying contemporaneous subsidence. The sediment accumulations provide the best record of this subsidence and its causes. The sediment accumulations, however, are a distorted record of the subsidence. A technique called backstripping is developed which corrects for the effects of sediment loading, sediment compaction, paleo-water depth, and sea level changes in order to isolate the tectonic part of the subsidence.

Backstripping of borehole data off eastern North America reveals that the tectonic subsidence is exponential at times greater than approximately 20 m.y. after rifting and is considerably smoother than the observed sediment accumulation. Based on this observation, it is possible to isolate the effect of sea level changes from the tectonic subsidence. This yields a sea level curve similar in shape to those based on mid-ocean ridge volumes, but smaller by a factor of 2-3, in accord with estimates based on continental flooding.

The exponential nature of the tectonic subsidence and its linearity versus √time for ages 10-80 m.y. rifting suggest that the post-rifting subsidence is thermal in origin. The most likely cause for the tectonic subsidence is thermal contraction of the lithosphere following heating and crustal thinning during rifting. The variation in the tectonic subsidence across the margins of eastern North America and the Gulf of Lion indicates that the hinge zone is the major