Vertical Tectonic Motion at the Intersection of the Santa Cruz-Catalina Ridge and Northern Channel Island Platform, California Continental Borderland, Derived from Submerged Paleoshoreline

J. D. Chaytor¹, C. Goldfinger², M. A. Meiner³, G. J. Huftile⁴, M. R. Legg⁵, and C. G. Romsos^2
1Woods Hole Oceanographic Inst., Woods Hole, MA, [email protected]
²Oregon State University, Corvallis, OR, ([email protected]), ([email protected])
³University of Hawaii at Hilo, Hilo, HI, [email protected]
⁴Queensland University of Technology, Brisbane, QLD, Australia, [email protected]
⁵Legg Geophysical, Huntington Beach, CA, [email protected]

Using submerged paleoshorelines as strain markers, we investigated Holocene and late Pleistocene vertical tectonic movement at the intersection of the offshore Santa Cruz-Catalina Ridge with the southern boundary of the western Transverse Ranges, within the California Continental Borderland. Submerged shoreline positions were identified via the integration and analysis of high-resolution multibeam bathymetry, side-scan sonar, submersible observations, and the presence of intertidal and subtidal invertebrate fossils. Accelerator mass spectrometry ¹⁴C ages of shells from these paleoshorelines were found to be between ca. 27,000 radiocarbon years and 11,500 years before present, indicative of shoreline colonization during and following the Last Glacial Maximum (LGM). These ages establish these paleoshorelines as a useable datum for measuring vertical change since this time. Removal of the non-tectonic component of vertical change using a post-25 ka ice-volume equivalent eustatic sea level compilation indicates between 20 m and 45 m of uplift of the eastern portion of the Northern Channel Islands block over the last ca. 23 ka. Using these values as the minimum and maximum amounts of uplift of the Northern Channel Islands block, respectively, results in a post-LGM uplift rate of 1.50 ± 0.59 mm/yr. This rate closely matches uplift predicted by published slip-rates for the Channel Islands thrust that underlies the Northern Channel Islands platform. Results from post-LGM shoreline features on Pilgrim Banks are somewhat more ambiguous likely resulting from the combination of tectonic and biologic mechanisms. Submarine paleoshoreline uplift together with the extensive upper-crustal fold-thrust style deformation, illustrates the transpressional interaction of the Borderland and Western Transverse Ranges blocks where the Santa Cruz-Catalina Ridge and northern Channel Islands intersect.

AAPG Search and Discovery Article #90088©2009 Pacific Section Meeting, Ventura, California, May 3-5, 2009