Mechanisms of Basin Subsidence: ABSTRACT

Abstract

The accumulation of sediments in interior and continental-margin basins constitutes a load on the lithosphere which sags because of the sediment weight. Studies of the geometry of deformation suggest the lithosphere responds to these loads either by local compensation of an Airy-type crust or regional flexure of a strong rigid crust. Sediment-loading models of either type cannot, however, explain the substantial thicknesses of shallow-water sediments observed in deep boreholes in these basins. Other factors, such as thermal cooling of the lithosphere, crustal stretching or necking, or deep crustal metamorphism, must therefore contribute to the subsidence. By quantitatively accounting for the subsidence due to surface loads, the subsidence caused by these other factors c n be isolated. We have used biostratigraphic data from commercial boreholes in the Mississippi embayment, the North Sea, and the Atlantic-type continental margin off the East Coast of the United States to examine the origin of the subsidence of these basins. From these data we determined the depths to stratigraphic horizons during basin development. Using the sediment-loading models the sediment layers at each basin were progressively backstripped and the depth at which the basement would have been in the absence of sediment laods was calculated. Corrections for the effects of compaction, water depth, and eustatic changes of sea level were included. The backstripped basement depths indicate there is a recognizable component of the subsidence of these basins which is caused by processes other than adjustments to the weight of the sediments. End_of_Article - Last_Page 702------------