Paleogene strata of the eastern Los Angeles basin, California: Paleogeography and constraints on Neogene structural evolution

Post-Paleogene dextral slip of 8-9 km is demonstrated for the southeastern part of the Whittier fault zone in the eastern Los Angeles basin area of so uthern California. A linear axis of greatest thickness for the combined upp er Paleocene and lower to lower-middle Eocene elastic formations intersects the fault zone and is offset by it to give the new measure. Fragmentary ev idence hints that the Whittier structural zone may have exerted control on bathymetric-topographic relief and sedimentation even in latest Paleocene ( ca. 54 Ma). A clear topographic influence was exerted by 20-17 Ma. Strike-s lip and present deformational style is younger than ca. 8 Ma. Our Paleogene isopach map extends as far west as long 117 degrees 58'W and is a foundation for companion zonal maps of predominant lithology and depos itional environments. Integration of new palynological data with published biostratigraphic results and both new and published lithologic and sediment ological interpretations support the zonal maps. Reconstruction of marine-n onmarine facies and fragmented basin margins yields a model for the northea stern corner of a Paleogene coastal basin. Palinspastic adjustment for the Neogene-Quaternary Whittler fault offset an d a reasoned westerly ex-tension of the northern edge of the basin model yi eld a reconstruction of Paleogene paleogeography-paleoceanography. Our reco nstruction is based partly on the absence of both Paleocene and Eocene depo sits beneath the unconformable base of the middle Miocene Topanga Group in a region nowhere less than 15 km wide between the Raymond-Sierra Madre-Cuca monga fault zone and the northern edge of the Paleocene basin. Thus, Paleog ene strata of the Santa Monica Mountains could not have been offset from th e northern extension of the Santa Ana Mountains by sinistral slip on those boundary faults. Structural rearrangements needed to accommodate the clockw ise rotation of the western Transverse Ranges from the early Miocene starti ng position are thereby fixed.