Paleogene Depositional Systems, Western Transverse Ranges, Southern California: ABSTRACT

Abstract

Paleogene strata of the western Transverse Ranges include varied clastic facies that prograded southwestward from arkosic sediment sources in granitic and metamorphic terranes of the Salinian and Mojave blocks. Deposition occurred within a complex fore-arc basin whose bathymetry was modified by pronounced uplift of a structural high along the trench slope break, and by internal deformation associated with oblique subduction during shallow plate descent beneath the Laramide cordillera. Integrated depositional systems produced intertonguing deep-marine, shallow-marine, marginal-marine, and nonmarine deposits. Exposed transitions between basinal turbidite successions, deltaic strandline complexes, and alluvial-plain sequences are common at several horizons. Mappable formatio s and local members are distinguished chiefly by their shaly, sandy and conglomeratic, or mixed lithologic character. Each such stratigraphic unit typically includes several facies associations. Shale-rich facies were deposited on terrestrial flood plains, prodelta and basin-flank slopes, overbank surfaces of subsea fans, and distal basin plains. Sand-rich intervals include thickening-upward cycles of sheet-flow depositional lobes on subsea fans, thinning-upward cycles of turbidite channels on subsea fans, coarsening-upward cycles of prograding shelf breaks, fining-upward cycles of migratory shelf and shoal-water bars, coarsening-upward cycles of distributary-mouth bars, and fining-upward cycles of fluviodeltaic End_Page 698------------------------------ channels. Conglomeratic strata occur both as piedmont-fan deposits and within proximal turbidite channel complexes. Sparse nonclastic facies include local algal carbonate platforms built on isolated submarine banks formed by tectonic uplift, and minor lagoonal beds of algal carbonate rocks and gypsiferous evaporites associated with delta platforms. End_of_Article - Last_Page 699------------