Use of a new Be-10 and Al-26 inventory method to date marine terraces, Santa Cruz, California, USA

Marine terraces along active continental margins reflect the interplay betw een sea-level oscillations and rock uplift. Well-dated marine terraces reco rd the timing of sea-level highstands and delimit both uplift and geomorphi c rates. Cosmogenic radionuclides provide a new tool for dating previously undatable terraces. Because the five marine terraces north of Santa Cruz, C alifornia, are capped by well-developed soils formed in regressive marine s ands, both predepositional cosmogenic radionuclide inheritance and bioturba tion of the profile must be accounted for. We present a new cosmogenic radi onuclide inventory method that uses the depth-integrated cosmogenic radionu clide concentration to determine the terrace age. This method yields terrac e ages that correlate well with sea-level highstands of marine oxygen isoto pe 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 studi es.