Abstract

Analysis of the Upper Cretaceous-Tertiary fill of the Great Valley forearc basin of California reveals a complicated history of subsidence partitioned in time and space. Western, oceanward parts of the basin record subsidence, then uplift, in apparent response to the angle and rate of descent of the underlying subducting plate. Specifically, uplift in the forearc basin corresponds to the onset of the Laramide orogeny and inferred low angles of subduction. In contrast, eastern, arcward parts of the basin display subsidence histories suggestive of thermal contraction and compatible with continentward migration of Sierran arc magmatism in the Late Cretaceous. These results imply that subsidence histories of forearc basins are likely to be much more complicated and less predictable than those of rifted continental margins and foreland basins, where single subsidence mechanisms predominate and time-varying subduction is not an underlying controlling factor.