Abstract

The modern Sacramento Valley intermontane basin is the successor to a deformed Mesozoic-Tertiary fore-arc basin. Based on analysis of seismic reflection profiles, drill hole data, and surface mapping, we propose a model for progressive arcward contraction of the fore-arc basin in the Rumsey Hills region, southwestern Sacramento Valley, beginning in Cretaceous and continuing episodically through Cenozoic time. We present our interpretation in the form of a kinematically restorable forward model. The major tectonic and depositional events include (1) mid-Cretaceous or older shortening of fore-arc basin strata along imbricate, west-dipping thrust faults; (2) erosion of the deformed fore-arc strata; (3) onlap of Cenomanian and younger fore-arc strata onto deformed older strata and crystalline Sierran basement; (4) renewed shortening in latest Cretaceous to early Tertiary, accommodated by delamination of Upper Cretaceous strata from the mid-Cretaceous angular unconformity, tectonic wedging, and west-directed backthrusting; (5) erosion of the deformed Upper Cretaceous strata and deposition of the Eocene Capay Formation; (6) uplift and east-directed shortening from Eocene to late Neogene, with local erosion of the Capay Formation over the ancestral Rumsey Hills; (7) uplift of the northern Coast Ranges beginning ca. 3.4 Ma, and deposition of the Pliocene-Pleistocene Tehama Formation in the western Sacramento Valley as a syntectonic molasse; and (8) fault-propagation folding of the Tehama Formation beginning ca. 0.5–1.0 Ma. With the exception of Quaternary shortening, progressive arcward contraction of the western basin margin occurred during east-dipping subduction and plate convergence beneath western California. The deformation of the ancestral Sacramento Valley fore-arc basin is analogous to arcward contraction of the Tobago Trough in the Lesser Antilles arc-trench system, and suggests that tectonic wedging may be a relatively common process in the evolution of fore-arc regions. Late Quaternary shortening has occurred in a transpressional setting and suggests a continuity in structural style despite a change in plate boundary kinematics from convergence to transpression during the past 3–5 m.y.

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