Annual Meeting - SCEC.org

Poster Abstracts
thus erosion rates and exposure ages, vary with grain size and suggest sediment transport pathways and sources of sediment
outside the catchment should be considered in any cosmogenic 10Be study.
QUATERNARY CONGLOMERATE DEPOSITION AND IMPLICATIONS ON FAULT EVOLUTION IN THE
OJAI AND UPPER OJAI VALLEYS, WESTERN TRANSVERSE RANGES, CA (A-128)
H.L. McKay and R.V. Heermance
Ojai and Upper Ojai Valleys are intermontane basins in the western Transverse Ranges filled with Quaternary conglomerate
(Ojai Conglomerate) that records a rare record of fault slip, uplift of surrounding ranges, evolution of the drainage system,
and landscape development since mid Quaternary time. Here we combine mapping and stratigraphy of exhumed strata in the
hanging walls of the Arroyo Parida-Santa Ana and La Vista faults and in the footwall of the Devil’s Gulch/Lion fault with
subsurface well data to document late-Quaternary provenance changes, depositional settings, and geometry of the basin fill.
New measured sections, clast counts, paleocurrent measurements, and mapping suggest that an E-W paleodrainage system
was present and sourced from the Topatopa Mountains to the north. Assymetrical depocenters 240 and 550 m deep in Ojai
and Upper Ojai Valleys, respectively, are preserved beneath the valleys implying complex paleotopography was present
during conglomerate deposition. At least 300 and 220 m of displacement must have occurred on the Lion and Santa Ana
Faults, respectively, based on offset of the base of the conglomerate unit. Lion Creek flows through incised meanders in Lion
Canyon that expose the basal contact of the basin fill and provide evidence for a much wider and flatter E-W paleovalley in
the past between the Lion and Santa-Ana Faults. Age constraints on the conglomerate are limited. As evidenced by the cross
cutting relationship between the deformed conglomerate and terrace surfaces, the fill must be older than the oldest terrace
surface (~92,000 y.b.p). Although previously interpreted as correlative with mid-Quaternary Saugus Formation (200,000-
800,000 y.b.p.), the local deposition, E-W directed paleocurrents, and buttress unconformity between the Quaternary
conglomerate and Neogene basement suggests that the basin fill in Ojai and Upper Ojai valleys are a separate entity from the
rest of the Ventura Basin stratigraphy. We therefore consider the onset of deposition of Ojai Conglomerate to be middle-late
Pleistocene, prior to or contemporaneous with uplift of Sulphur Mountain. Further constraining the age of the Ojai
Conglomerate, are overlying lacustrine deposits in Upper Ojai Valley with ages of >46,000 to