Temporal Changes in Depositional Facies in Great Valley Forearc Basin of California--Influence of Basin Evolution and Tectonics: ABSTRACT

Abstract

The Great Valley forearc basin began in the Late Jurassic as a residual forearc basin on top of oceanic crust, and evolved into a composite forearc basin on top of both oceanic and continental crust in the Late Cretaceous and Paleogene. The depositional basin widened through time owing to the westward and upward growth of the subduction complex and the eastward migration of the coeval magmatic arc. Depositional facies reflect changes in shape, size, tectonic activity, and inherited characteristics of the basin. Late Jurassic depositional environments primarily consisted of slope with locally incised channels. The basin was relatively narrow and a steep slope allowed sediment movement from the shoreline on the east directly into the trench to the west. By the Early Cretaceous, a bathymetric barrier was formed by the upward- and outward-building subduction complex, thus trapping arc-derived sediment within the forearc basin. Basin-plain environments dominated in this terraced forearc. The subduction complex continued to grow, and the magmatic arc migrated eastward during the Late Cretaceous, resulting in a wider, composite basin. Complex interbedded submarine fan, slope, and basin-plain facies formed in this setting. Submarine fan systems became larger owing to the concentration of sediment gr vity flows within submarine canyons incised into the widening shelf on the east side of the basin. The basin evolved into a broad ridged forearc and, eventually, into a broad shelved forearc during the Paleogene as the subduction complex emerged above sea level and the forearc basin filled. As a result, Upper Cretaceous submarine fan complexes are overlain by slope facies, which are overlain by shelf facies. Nonmarine environments have persisted following filling of the basin and sequential termination of subduction by the northward migration of the Mendocino triple junction during the Neogene. End_of_Article - Last_Page 727------------