Abstract

Marine terraces along active continental margins reflect the interplay between sea-level oscillations and rock uplift. Well-dated marine terraces record the timing of sea-level highstands and delimit both uplift and geomorphic rates. Cosmogenic radionuclides provide a new tool for dating previously undatable terraces. Because the five marine terraces north of Santa Cruz, California, are capped by well-developed soils formed in regressive marine sands, both predepositional cosmogenic radionuclide inheritance and bioturbation of the profile must be accounted for. We present a new cosmogenic radionuclide inventory method that uses the depth-integrated cosmogenic radionuclide concentration to determine the terrace age. This method yields terrace ages that correlate well with sea-level highstands of marine oxygen isotope stages 3, 5a, 5c, 5e, and 7. The implied uplift rate is steady at 1.1 mm/yr, and is two to three times higher than rates suggested by earlier studies.

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