THE GEOLOGIC RECORD OF QUATERNARY INTERGLACIAL-GLACIAL CYCLES IN CHANNEL ISLANDS NATIONAL PARK, CALIFORNIA

Quaternary interglacial-glacial climate changes are important in understanding the range of natural climate variability. Channel Islands National Park, California and the southern Channel Islands (outside the park proper) contain a rich record of these paleoclimate changes. Interglacial-glacial cycles produced dramatic sea level fluctuations that generated distinctive coastal landforms and deposits. Interglacial high-sea stands are recorded as emergent marine terraces, exposed as a result of ongoing tectonic uplift. Corals in these terraces are dated by U-series methods to correlate with major high stands of sea recorded worldwide. Fossil marine mollusks in terrace deposits yield detailed paleotemperature information, including evidence for a much-warmer last interglacial period at ~120 ka that may be a future warm-climate analog.

Glacial-period low-sea stands exposed broad insular shelves off the Channel Islands that today are rich in skeletal carbonate sands. Exposure of calcareous sands to strong northwesterly winds during glacial low-sea stands generated extensive carbonate dunes that are partially cemented into eolianite. Paleosols that formed after dune stabilization bracket each period of dune building. Radiocarbon ages of carbonate rhizoliths in the paleosols indicate that the last major period of dune building in the Channel Islands occurred from ~35-25 ka (cal yr BP) to ~16-10 ka (cal yr BP), in good agreement with the timing of the last glacial period. The records of global Quaternary climate change and sea level fluctuations, preserved on islands of limited geographic extent, showcase the unusual geologic nature of Channel Islands National Park.