Paleogene depositional framework of western Transverse ranges

In the western Transverse Ranges, widespread Paleogene sequences (mid-Paleocene to mid-Oligocene) accumulated to thicknesses locally in excess of 5000 m. The Paleogene basin occupied a complex forearc setting located near the offshore Franciscan trench, but distant from the inland Laramide orogenic system, where magmatism was quiescent during the interval of most rapid sedimentation. The pre-Tertiary substratum, largely masked by its Paleogene cover, was probably disrupted by transpressional and/or transtensional tectonics associated with separate episodes of mid-Cretaceous sinistral and Late Cretaceous (to Paleocene.) dextral dislocation of the continental margin. Paleogene strata include diachronous facies of intertonguing deep-marine, shallow-marine, marginal-marine, and nonmarine clastic strata representing varied depositional systems. Turbidite assemblages include both progradational and retrogradational phases of canyon-fed submarine fans and delta-fed submarine ramps. Exposed shelf-break successions were deposited offshore from strandline complexes fringing delta margins and broad coastal plains. Sparse but diagnostic nonclastic facies include local algal carbonate edifices built on isolated submarine banks, and minor lagoonal beds of algal carbonates and gypsiferous evaporites associated with emergent delta platforms. The complex Paleogene forearc basin was flanked on the northeast by Salinian basement rocks and on the southwest by a tectonic ridge of subduction complex uplifted along the Paleogene trench-slope break. Themore » present geographic distribution of Paleogene facies tracts is fully compatible with proposed Neogene tectonic rotations of panel-like basin segments, bounded by antithetic sinistral faults within the dextral San Andreas system, as detected by recent paleomagetic investigations.« less