Pliocene cryptic subsidence followed by rapid Quaternary uplift in relation to mantle lithosphere removal, Kern Arch, eastern San Joaquin Basin (SJB), California

Abstract

The Kern Arch (arch) is an actively growing promontory that extends westwards from the western Sierra Nevada into the eastern SJB where marine strata as young as upper Pliocene are undergoing erosion. Active uplift of the arch is controlled by west-side-up normal faulting along the Kern Canyon-Breckenridge system and northeast-side-up normal faulting along the Kern range front. Quaternary uplift and erosion have resulted in the loss of much of the arch's Pliocene subsidence history. This cryptic subsidence is reconstructed from low-grade metamorphic assemblages and compaction granulation textures in cores, and truncated down-hole thermal gradients from deep wells. These constraints indicate >1400m of cryptic Pliocene subsidence in the crest area of the arch, and a comparable additional minimum Quaternary uplift component to that which is expressed by topography and erosion. Pliocene-Quaternary facies relations are lost across the crest area of the arch, although depositional environments represented by the upper Miocene-Pliocene Kern River, Etchegoin and San Joaquin formations, as preserved off the flanks of the arch, suggest that a fluvial plain-deltaic environment faced northwest across the southern arch and graded northwestwards into a Pliocene marine embayment that developed across the former northern shelf edge of the SJB. How far to the east this facies system once lapped across recently exhumed western Sierra basement is poorly constrained. As the arch began its uplift in the latest Pliocene the marine embayment persisted in the eastern Tulare sub-basin. Lingering late Quaternary subsidence in the eastern Tulare sub-basin is marked by fluvial plain burial of mountainous western Sierra topography. Use of the upper Miocene shallow marine Santa Margarita Fm. as a strand line datum constrained by the resolved cryptic subsidence-uplift signals produces subsidence and uplift rolling hinges that resemble vertical transients that arise in numerical models of epeirogenic deformation resulting from the progressive peeling away of mantle lithosphere during delamination. We posit that such transients along the eastern SJB resulted when the southern Sierra Nevada mantle lithosphere drip progressively detached in Pliocene-Quaternary time.

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