Biostratigraphic studies of 17 piston cores from the continental slope off the coast of Washington indicate that the change in the foraminiferan-radiolarian ratio at the glacial-postglacial boundary separates geologic-climate units and is time-transgressive in the northeast Pacific. This change from foraminiferan-rich to radiolarian-rich sediment begins at 13,000 yrs B.P. west of the continental slope in Cascadia Basin, between 11,500 and 9,500 yrs B.P. on the lower continental slope, and at 8,000 yrs B.P. on the upper continental slope. The ratio, therefore, cannot be used to define the Pleistocene-Holocene time-stratigraphic boundary and should be used cautiously as an isochronous biostratigraphic indicator, especially where large depth variations exist.

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