A Geomorphic Investigation of the Tectonic Transition between the Santa Barbara and Ventura Fold Belts near Rincon Point, California

Abstract:

The Santa Barbara and Ventura Fold Belts have very different uplift rates: ~1-2 m/ky and ~6-8 m/ky, respectively. Differences are probably related to the position of the two belts relative to the big bend of the San Andreas fault. The onshore transition between these fold belts occurs at Rincon Creek, near Carpinteria. We use a combination of geomorphology and geochronology to describe patterns and rates of crustal deformation near Rincon Creek and test whether the known change in uplift rate is spatially discrete or distributed across the transition zone.

Five sediment samples from the first emergent marine terrace between Carpinteria and Rincon Creek are being processed for optically stimulated luminescence (OSL) dating. We expect the age of this terrace to be either MIS 3 or MIS 5. An age of MIS 3 will suggest that the terrace is continuous with the Punta Gorda terrace across Rincon Creek. An age of MIS 5 will suggest that a geologic discontinuity exists across Rincon Creek, supporting the existence of a cross-fault at Rincon Creek. Terrace chronology will also help constrain the growth rate of the Rincon Creek anticline and the slip rates of several faults that vertically displace the marine terrace.

Uplift patterns may be inferred from stream profile analysis via digital topography. Preliminary analysis of normalized stream steepness indices and stream concavities from Carpinteria to La Conchita indicate a gradational change in uplift rate rather than a sharp transition at Rincon Creek. Chi analysis and knickpoint identification are in progress and will also help delineate patterns of uplift.