| Abstract: | The accumulation of sediments at an Atlantic-type continental margin constitutes a load on the lithosphere which simply sags due to its weight. Studies of the geometry of deformation suggests the lithosphere will respond to these loads either by local loading of an Airy-type crust or flexural loading of a strong rigid crust. Sediment loading models of either type cannot, however, explain the substantial thicknesses of shallow-water sediments observed in commercial boreholes from Atlantic-type margins. Other factors such as thermal contraction, gravitational outflow of crustal material or deep crustal metamorphism may contribute to the subsidence. We have used biostratigraphic data from commercial boreholes from the Gulf of Lion and the East Coast U.S.A. to quantitatively determine the contribution of sediment loading to the subsidence. From these data we determined sea-floor and basement depths for sequential time intervals during margin development. Using the sediment loading models the sediment layers at each margin were progressively “backstripped” and the depth basement would have been without the sediment load calculated. The computed basement depths indicate there is a recognizable component of the subsidence of these margins which is caused by processes other than adjustments to the weight of the sediment. The nature of this subsidence is discussed and comparisons are made with that which would be expected from thermal-contraction models. |
