Geomorphic constraints on the incision history of the lower Kern River, southern Sierra Nevada, California

摘要

Stream profile analysis of the lower Kern River and its tributaries help to constrain the landscape response to late Cenozoic tectonics in the southern Sierra Nevada of California. In this study, we identify two relict landscapes that have been offset from the Kern Plateau by periodic displacement along the southern Sierra Nevada fault system starting ca. 20 Ma. These remnants provide context from which to evaluate existing models of rock uplift and exhumation in the region. Reconstructed channel profiles on the relict landscapes indicate a slow incision rate of ～0.07 mm/yr throughout most of the Miocene. An increase in incision ca. 6 Ma resulted in the formation of the Kern Canyon. This increase in incision likely occurred in response to east-west delamination of a lithospheric root beneath the southern Sierra Nevada and is reflected in a pulse of vertical incision (～0.11 mm/yr) that has propagated upstream at a rate of ～7.3 mm/yr to its current position near Isabella Lake. Another two pulses of rapid incision were likely generated by increased rock uplift associated with the northward migration of the delamination hinge after 1 Ma. Incision rates of 0.58–1.2 mm/yr have propagated up the lower Kern River resulting in formation of the Kern River gorge. These new constraints on the incision history of the lower Kern River provide further corroborating evidence for existing models of late Cenozoic mantle delamination and associated epeirogenic processes that have helped shape the landscape of the southern Sierra Nevada.