Late Quaternary Accumulation Rates of Opal, Quartz, Organic Carbon, and Calcium Carbonate in the Cascadia Basin Area, Northeast Pacific
G. Ross Heath, Ted C. Moore, Jr., J. Paul Dauphin, 1976. "Late Quaternary Accumulation Rates of Opal, Quartz, Organic Carbon, and Calcium Carbonate in the Cascadia Basin Area, Northeast Pacific", Investigation of Late Quaternary Paleoceanography and Paleoclimatology, R. M. Cune, J. D. Hays
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Accumulation rates of terrigenous (quartz, organic carbon) and biogenic (calcium carbonate, opaline silica) components of two cores from southern Cascadia Basin are highly correlated with total-sediment accumulation rate and each other throughout late Pleistocene and Holocene time. In contrast, the correlations of the biogenic and terrigenous rates in a core on the east flank of Gorda Ridge are much lower (nonsignificant in the case of carbonate). In Cascadia Basin, sedimentation during late Pleistocene time was controlled by turbidite deposition. Apparently, the turbidity currents entrained biogenic debris produced by intense upwelling close to shore; this has resulted in the high correlations between the accumulation rates of the two sediment types. The only climatic signals evident in the Cascadia Basin cores are (1) pulses of accelerated deposition that correspond to glacial advances and catastrophic Columbia River floods at 32,000 and 18,000 B.P. and (2) marked reductions in sedimentation rates due to the sea-level rise at the end of the Wisconsin glaciation.
Accumulation rates of terrigenous components on the east flank of Gorda Ridge decreased fairly uniformly from 35,000 B.P. to the present. In contrast, the rate of carbonate accumulation was markedly lower prior to 32,000 B.P., from 29,000 to27,000 B.P., and since, 15,000 B.P., apparently because of increased corrosiveness of bottom waters. The marked increase in carbonate dissolution in all cores in the area during Holocene time points to a regional increase in corrosiveness of bottom waters at the end of Pleistocene time.
Our study suggests that the increased resolution of late Quaternary oceanographic changes, which is theoretically possible in rapidly deposited hemipelagic sediments, is readily degraded by turbidite deposition, even where classic coarse-grained turbidites are absent. Cores from hemipelagic areas free of sediments carried in autosuspension are most likely to preserve detailed climatic and oceanographic records of late Quaternary time.