Most thermo-mechanical models for the development of sedimentary basins and continental margins assume that the rifting responsible for the formation of the basin occurred instantaneously and that the post-rift development of the basin has been examined. We have examined the effects of a finite rifting time on the development of sedimentary basins using an analytic technique which allows an arbitrary rifting history in both time and space and which considers the effects of both horizontal and

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... rtical heat transfer. We are able to calculate the thermal structure of the lithosphere throughout the rifting event and thus trace the history of the surface heat flow and uplift/subsidence over the developing basin. Lateral heat flow, which was not included in previous studies of the effects of finite rifting times, has a very significant effect on the subsidence history, distribution of sediments, and temperature history. In particular, for a rifting event as short as 10 m.y., the post-rift subsidence is increased by as much as 20%. This will significantly decrease the subsidence rates in the post-rift stage and implies that inferences concerning the structure, development, and thermal history of the basin derived from simply fitting "|3-curves" to the backstripped subsidence can be grossly in error. In addition, the lateral heat flow will effect the stratigraphy along the margin of the basin. The timing and extent of onlap sequences around the edges of the basin due to flexure are greatly influenced by the length of the rifting event, as is the width of the coastal plain along a rifted continental margin.