Tectonic evolution of the Jurassic-Cretaceous Great Valley forearc, California: Implications for the Franciscan thrust-wedge hypothesis

摘要

Interpretation of seismic reflection data and restoration of depositional geometries of Cretaceous forearc basin strata in the northwest Great Valley of California provide important controls on structural reconstructions of the western margin of the Sacramento Valley and northern Coast Ranges. Monoclinal eastward dips of Great Valley Group strata and fault systems striking northwest-southeast, which are features proposed as evidence for a west-dipping blind Great Valley–Franciscan sole thrust and related backthrusts, instead are expressions of bedding geometry that resulted from folding of the Paskenta and related synsedimentary normal faults, depositional onlap, and a major structural-stratigraphic discontinuity. The discontinuity separates east-dipping Aptian and younger Great Valley Group strata from beds of lower Great Valley Group and Coast Range ophiolite that were deformed and erosionally or structurally truncated by mid-Cretaceous time. Dip divergence imaged between the supracrop and subcrop of the discontinuity is not unique to the ancient Great Valley forearc, but is also observed in modern forearc basins.