Testing Mechanisms of Paleo-Environmental Change during the Latest Pleistocene, Northern Channel Islands, California

This investigation tests multiple hypotheses to explain dramatic paleo-environmental change on the Northern Channel Islands (NCI) of California near the end of the Pleistocene.  Elements of this change include: (1) a vegetation shift from widespread coniferous forest to grassland and chaparral, (2) deposition of charcoal and burnt wood, (3) large-scale landsliding and (4) initiation of island-wide hillslope transport and fluvial aggradation.

Detailed descriptions of the sedimentology and stratigraphy, as well as high-resolution ¹⁴C and OSL age dating, are being applied to sections on Santa Cruz and Santa Rosa Islands.  Extraterrestrial signatures described as microspherules have been proposed as indicators of an impact event at ~12.9 ka on these islands and elsewhere.  To investigate this hypothesis on the NCI, magnetic microspherules have been extracted from bulk sediment samples collected from thick fluvial deposits that date back to the latest Pleistocene to mid-Holocene.  Magnetic grains and microspherules are present in multiple strata both above and below the 12.9 ka time horizon.  Microspherules from these bulk samples do not appear to be indicative of a single event, but instead are interpreted as micrometeorite ablation debris accumulating on the surface as microspherular dust.  Alternating light and dark strata within these fluvial sequences indicate changes in depositional environments, and new ¹⁴C dates from disseminated charcoal and burnt wood within these sequences reveal fire activity on the NCI back to ~16.5 ka, well before the proposed 12.9 ka impact. 

On-going research is focusing on the nature and cause(s) of fire linked to the landscape changes across the NCI during the latest Pleistocene.  The preliminary age control precedes impact ignition at ~13 ka, but climate change and pre-Clovis human influence remain strong hypotheses that will be further tested.