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

¹ 7136 Aberdeen Avenue, Dallas, Texas 75230-5407, USA
² U.S. Geological Survey, M.S. 977, 345 Middlefield Road, Menlo Park, California 94025-3591, USA
³ Mobil Exploration and Producing Technology Center, Mobil Place, 3033 Irving Boulevard, Dallas, Texas 75247, USA

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 southern California. A linear axis of greatest thickness for the combined upper Paleocene and lower to lower-middle Eocene clastic formations intersects the fault zone and is offset by it to give the new measure. Fragmentary evidence 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-slip and present deformational style is younger than ca. 8 Ma.

Our Paleogene isopach map extends as far west as long 117°58'W and is a foundation for companion zonal maps of predominant lithology and depositional environments. Integration of new palynological data with published biostratigraphic results and both new and published lithologic and sedimentological interpretations support the zonal maps. Reconstruction of marine-nonmarine facies and fragmented basin margins yields a model for the northeastern corner of a Paleogene coastal basin.

Palinspastic adjustment for the Neogene–Quaternary Whittier fault offset and a reasoned westerly extension of the northern edge of the basin model yield a reconstruction of Paleogene paleogeography-paleoceanography. Our reconstruction is based partly on the absence of both Paleocene and Eocene deposits beneath the unconformable base of the middle Miocene Topanga Group in a region nowhere less than 15 km wide between the Raymond–Sierra Madre–Cucamonga fault zone and the northern edge of the Paleocene basin. Thus, Paleogene strata of the Santa Monica Mountains could not have been offset from the northern extension of the Santa Ana Mountains by sinistral slip on those boundary faults. Structural rearrangements needed to accommodate the clockwise rotation of the western Transverse Ranges from the early Miocene starting position are thereby fixed.

Key Words: Los Angeles basing • Neogene structure • Paleogene • palynology • Whitter fault

This article has been cited by other articles:

				R. S. Yeats Tectonics of the San Gabriel Basin and surroundings, southern California Geological Society of America Bulletin, September 1, 2004; 116(9-10): 1158 - 1182. [Abstract] [Full Text] [PDF]