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Distribution of foraminifera in cores from Juan de Fuca Ridge, North East Pacific Malott, Mary Lou


Benthic and planktic Foraminifera from the Juan de Fuca Ridge, North East Pacific, were identified and counted in 55 samples from 6 cores. There is a rich foraminiferan diversity of 193 taxa, one third of which are new or undescribed species. Planktic specimens are most abundant with sinistrally coiled Globoquadrina pachyderma the most common species. The majority of the 184 benthic species come from the superfamilies Buliminacea, Orbitoidacea and Cassidulinacea. The most abundant benthic species are displaced downslope and outnumber the indigenous lower bathyal fauna. An algal 'cyst' identified as Pachysphaera sp. may prove to be a biostratigraphic marker near the Pleistocene-Holocene boundary. It occurs from the surface to between 40 and 60 cm. below a decrease in the planktic foraminiferan-radiolarian ratio, which indicates the glacial-postglacial climatic shift. This change of ratio was the only means of correlating between cores as neither the benthic nor planktic foraminiferan assemblages were useful for establishing time zones in the late Pleistocene-Holocene interval cored. Much of the sediment represented in the cores is hemipelagic and originated from upper to lower bathyal depths as indicated by the entrained benthic foraminifera. In the Pleistocene section of one core, detrital quartz grains and mica flakes in addition to shelf foraminifera indicate turbidite movement west and southward from the shelf.

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