QUATERNARY SEA-LEVEL HISTORY AND THE ORIGIN OF CEMENTED CARBONATE DUNE DEPOSITS (EOLIANITE) ON SAN MIGUEL ISLAND, CHANNEL ISLANDS NATIONAL PARK, CALIFORNIA

Along coastal California, sand dunes are dominantly silicate-rich. On the Channel Islands, however, dunes are carbonate-rich, due to high productivity offshore and a lack of dilution by silicates. San Miguel Island, the westernmost island, contains well-preserved records of late Quaternary eolian sand deposition. Detailed stratigraphic studies, including thirty-eight new radiocarbon ages, provide a chronology of dune deposition that is linked to sea level history. The oldest eolian sands on San Miguel are thin (2-7 m), overlie last-interglacial-complex (~120-80 ka) marine terraces, and are >50,000 cal yr BP. A prominent, reddish-brown, clay-rich paleosol (“Simonton Soil”) developed in the upper part of these sands. After ~25,000 cal yr BP, eolian sand deposition resumed, leaving as much as ~15 m of carbonate-rich, cross-bedded eolianite. Eolian sand deposition ceased by ~18,000-15,000 cal yr BP and another soil (“Midden Soil”) developed in these deposits, at least until ~12,000 cal yr BP. Reworking of Pleistocene sands buried this soil during the early Holocene. The chronology indicates that the main period of dune building, between the Simonton and Midden soils, occurred during the last glacial maximum, when sea level was low. During this period, what is now the broad (10-15 km) insular shelf would have been emergent to the north and west of San Miguel Island, providing a carbonate-rich sediment source for dune building. Thus, while carbonate eolianites in other environments (e.g., the Bahamas and Bermuda) date to interglacial high stands of sea, eolianites on San Miguel Island correlate to the last-glacial low stand of sea.