Structure and Stratigraphy of the Bakersfield Arch as the Markers of Active Epeirogenic Uplift Superimposed Across a Complex Basinal Facies System
Zorka Saleeby and Jason Saleeby
Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena CA 91125
The Bakersfield Arch is an actively growing basement salient, continuous with the southern Sierra (SS) uplift/diffuse extensional zone. The presence of Miocene to upper Pliocene marine strata on the Arch indicate that much of its growth occurred in the past 2-3 m.y. Such uplift led to stripping off of eastern San Joaquin basin strata from the adjacent SS basement, and subsequent incision of the lower Kern gorge. The lower Kern River has a profile that is typical of other major SS rivers that were incised in late Pliocene-Quaternary time. Stratigraphic changes across the Arch have led to the erroneous interpretation of the Arch as an old structure. These changes represent a complex polyphase tectonic history dating back to deep exhumation of the SS batholith and adjacent forearc during the Late Cretaceous. Following this exhumation the region consisted of a west-directed basinal slope through Eocene time. Filling of the northern San Joaquin Valley (SJV) and subsidence of the proto-“Maricopa” basin in the Oligocene to Miocene turned the area of the Arch into a south-directed basinal slope. Middle and Upper Miocene strata of the Arch record bathyal water depths, consistent with the eastern basin edge lying well east of the current Sierran range front. Initial westward tilt of the Sierran microplate in the Late Miocene caused a marine invasion into the northern SJV with “Santa Margarita” deposition. Chanac, Etchegoin and Kern River Frms. of the Arch reflect transitional shallow marine, deltaic and fluvial environments, with westward migration of the shoreline across a progressively narrower fluvial plane. Accelerated subsidence of Maricopa in the early Pliocene may be related to mantle lithosphere foundering with northward migration of the foundered mass pulling Plio-Pleistocene Tulare subsidence. Recent uplift of the Arch and adjacent SS are dynamically linked to foundering as a response to underlying asthenosphere ascent.
AAPG Search and Discovery Article #90076©2008 AAPG Pacific Section, Bakersfield, California