The postrifting tectonic subsidence of the U.S. Atlantic continental margin appears to be due to thermal contraction following continental breakup. This subsidence is greatly increased by the effect of sediment loading. Models for the response of the lithosphere to loads show that the rigidity of the lithosphere is a strong function of temperature. Hence the flexural rigidity at the U.S. margin should vary in both space and time. The thermal structure and subsidence of the margin has been modelled using a two-dimensional extension model where the amount of extension has been allowed to vary across the margin and lateral conduction of heat has been included. The equivalent elastic thickness of the lithosphere has been approximated as the depth to an isotherm. Thermoelastic effects of the cooling lithosphere, as well as the flexural loading of the sediments, have been included. The lateral flow of heat and flexure have contrasting effects. The lateral heat flow tends to cause uplift of the coastal plain region landward of the hinge zone and to increase the subsidence rate in the regions of the transitional crust. In addition, the effects of lateral heat flow modify the thermal history of the sediments and heat flow. Flexure, on the other hand, causes subsidence of the coastal plain and decreases the sediment accumulation beneath the transition zone. The stratigraphy of the U.S. margin is seen to be the result of the complex interaction of these effects as their contributions vary through the history of the margin.

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