Intraplate Stresses, Nonthermal Subsidence, and Fluid Regimes in Rifted Basins

Abstract

Short-term fluctuations of the level of intraplate stresses modulate the shape of rifted basins and therefore affect the stratigraphic record. We investigated the effect of such stress variations on fluid flow and sedimentation patterns in sedimentary basins using a dynamic numerical model which combines the stretching mechanism for rifted-basin formation with the lithospheric necking concept. The results show that increases in the level of compressive intraplate stresses strongly influence the hydrodynamic regime during the postrift phase of sedimentary basins by causing an increase of meteoric water influx and compactional driven flow. These short-term perturbations in fluid-flow patterns occur simultaneously with subsidence rates far in excess of those predicted by thermal models. The results of the modeling enable us to discriminate the effect of tectonically induced distortions of the basin shape (and associated differential vertical motions in rifted basins) on the fluid-flow regime from perturbations induced by changes in eustatic sea level. We discuss implications of the modeling predictions for maturation and migration of hydrocarbons and diagenesis. Episodic diagenetic and expulsion events can be explained by short-term changes in the magnitude of nonthermal subsidence.