Abstract

The Upper Cretaceous part of the Great Valley Sequence of California provides a unique opportunity to study deep-marine sedimentation, petrologic evolution, and tectonic evolution of a forearc basin. Actualistic models of submarine fan sedimentation and arc-trench evolution provide the basis for unraveling the complex depositional history of the bathyal to abyssal sediment deposited between the Sierra Nevada volcano-plutonic arc to the east and the Franciscan subduction complex to the west. Submarine fan components are lenticular stratigraphic units which can be correlated along strike on the basis of both paleontologic and petrologic data. The following depositional components are present: basin plain, outer fan, midfan, inner fan, slope, and shelf. Vertical successions of fan facies associations constitute retrograding and pro-grading suites that correspond, respectively, to onlapping and offlapping relations in the basin. Sedimentation rates are similar to those of other tectonically active flysch basins. Paleocurrents are predominantly southerly and westerly in the Sacramento Valley, and predominantly westerly in the San Joaquin Valley. Microfossil evidence and the lack of carbonate material suggest deposition below the Late Cretaceous calcite compensation depth.

Dimensions and geometries of tectono-stratigraphic components of the Late Cretaceous arc-trench system are similar to those of modern arc-trench systems. The Late Cretaceous arc-trench gap widened by the prograde accretion of the Franciscan Assemblage (subduction complex) and the retrograde migration of the Sierra Nevada volcanic front (arc). Sediment dispersal systems expanded as the basin widened. The Java arc-trench system provides a modern analogue for the Late Cretaceous forearc basin, with sediment fed laterally from the arc and dispersed longitudinally along the basin axis.

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