Abstract:
An analysis of the amounts of calcium carbonate, organic carbon,
quartz, and the rates of sediment accumulation in hemipelagic sediments
off Oregon has revealed that the accumulation rates of the total
sediment, organic carbon, and quartz were at least twice as high in
the late Pleistocene as they were during the Holocene. The accumulation rate of calcium carbonate was at least 8 times as high. There
may have been a short transition period at the end of the last glacial
stage from about 14,000 to 12,500 years B.P. when the sedimentation
rate was very high up to 75 cm/l000 years.
There is evidence that the amount of organic carbon in deep-sea
sediments is a function of terrigenous influx, of preservation, and
possibly of depth of burial in the sediment. Turbidite sequences in
the deep-sea environment off Oregon contain much higher amounts of
organic carbon in the upper fine-grained portion of the sequence than in the coarser basal sediment of the sequence, indicating that organic
carbon is concentrated in the finer and slower settling parts of the
flow. In lower continental slope sediments, the greatest amounts of
organic carbon are found in the <4 micron size fraction.
