Geomorphology and geochronology of the San Juan Creek terraces: Implications for Quaternary uplift of the Santa Ana Mountain foothills, Orange County, California.

摘要

Quaternary uplift of the Santa Ana Mountain foothills, Orange County, CA, is examined using geochronologic and geomorphic analyses of fluvial terraces adjacent to San Juan Creek. Specifically, detailed geologic mapping, reconstructed paleo-longitudinal profiles, and geochronology are used to infer the style, magnitude, and rate of uplift. Two potential terrace chronologies are introduced based on new OSL age data and correlations with previously dated marine terraces. Reconstructed paleo-longitudinal profiles are essentially parallel, indicating that uplift within the San Juan Creek watershed is uniform and absent of tilting or warping. Geomorphic analyses based on the new OSL chronology indicate that the San Juan Creek terraces document up to 125 m of surface uplift at a rate of 0.4-0.6 mm/yr over the past 335 ka. Alternatively, geomorphic analyses resulting from the marine terrace-based chronology indicate up to 140 m of surface uplift at a rate of 0.3--0.4 mm/yr over the past 540 ka.