Abstract

The facies history of the Great Valley sequence is closely linked to structural events in an arc-trench system. Upper Jurassic-Lower Cretaceous marine rocks, as much as 8,500 m thick along the western margin of the Sacramento Valley, northern California, were deposited on slopes and submarine fans that extended over an unstable basement floored by ophiolitic rocks. Paleocurrent and paleoslope analyses indicate that eastward subduction, initiated as early as Kimmeridgian, created an outer-arc ridge which bounded the west side of the basin. Debris was shed dominantly from the north and east, but significant contributions were ridge-derived. Sediment fabrics, structures, and bedding styles indicate that earliest deposition on basin plains and on eastward facing slopes was followed, at least until the Valanginian, by a stable sedimentological framework of prograding and avulsing submarine fans characterized by broad, shallow midfan channels, depositional lobes, and abundant, thick deposits of interchannel mud. The Great Valley rocks are transected by northwest-trending faults that produced strike separation of the east-dipping strata. Smooth facies transitions, but with abrupt thickness variations across faults, suggest that faulting with some normal component of motion was contemporaneous with deposition during latest Jurassic and earliest Cretaceous. Later movement, either strike-slip or reverse, brought coarse, inner-fan facies that were deposited on Klamath basement into fault contact with basin-plain facies that were deposited on ophiolitic basement.

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