Abstract:
We investigate Pliocene to Late Quaternary deformation of the eastern Santa Barbara Channel and western Ventura basin using the technique of 3D map restoration. We have correlated approximately 110 ka and -200 ka horizons through the central Channel, modified a 1 Ma horizon map by Yeats, and mapped a approximately 1.7 Ma (top Venturian faunal stage) horizon. This approximately 1.7 Ma horizon has been mapped using paleontology, e-log correlations and a grid of multi-channel seismic reflection data in the eastern Channel. Post-160 ka horizons are dated at ODP corehole 893A, and we date the approximately 200 ka reflection by extrapolation. The 1 Ma horizon has been digitized and the surface unfolded and restored to horizontal using the software UNFOLD. Displacements are calculated by comparing the restored surface to the present state with respect to a fixed line. South of Santa Barbara, the increase in amplitude of a fold above a S-dipping Oak Ridge fault has been 2 mm/yr since 200 ka, the same rate as the vertical motions due to fault slip and folding since 1 Ma. Vertical motions due to Oak Ridge slip and hanging-wall folding reach a minimum offshore south of Ventura, 1 km for the 1 Ma horizon and 1.4 km for the approximately 1.7 Ma horizon. Post-1 Ma vertical separation due mainly to faulting is 4-5 km near Santa Paula. There, the map restoration documents space problems that require the post 1 Ma left-lateral slip to be less than half the 3.5 km proposed by Yeats and Taylor, or else that left-lateral shear is transferred across the footwall (north) block. Shortening and vertical motion across the onshore E-W Oak Ridge fault are related to left-lateral motion on the ENE coastal section, which is transformed into shortening and vertical motions on the WNW segment south of Santa Barbara. NE-striking cross faults are suggested by the sharp bends in both the fault and fold limbs.