Quaternary calcareous benthic foraminifers, Leg 80.

Abstract

Calcareous benthic foraminifers were recovered from Quaternary sediments from 3 sites in the NE Atlantic, more specifically on the slope of the Goban Spur and the neighboring abyssal plain (Leg 80, Holes 548, 549A and 550. Hole 548, at a water depth of 1256m, presents a complete Quaternary series 110m thick from which 138 samples were studied. The autochthonous benthic foraminifers belong to 2 biologic units. One is at the upper part of the Quaternary and has a usually poor microfauna; the other, at the lower part of the Quaternary, is characterized by a richer and more homogeneous microfauna. Quaternary paleohydrologic variations were observed. Displaced fauna from the neighboring continental shelf appear to be quite abundant throughout the Quaterary. Coastal displaced faunas were found at points corresponding to periods of deglaciation-the transitions. The occurrence of these faunas suggests the existence of two episodes of low sea levels on the neighboring continental shelf. The degree of glaciation determined benthic foraminiferal abundance. The benthic foraminifers in the upper part of the sequence where there were numerous fossil-poor levels corresponding to glacial maxima, vary widely in number, whereas the benthic foraminifers in the lower part of the sequence do not. As shown by Holocene benthic microfauna, the site is overlain today by the well oxygenated North Atlantic Water. Almost the same type of watermass characterized this site during the Quaternary, when Planulina wuellerstorfi and Hoeglundina elegans prevailed. Indications of less oxygenated waters were, however, observed in bioclimatic Stages XIII to XII and VI to V; where a spectacular development of Uvigerina peregrina (90% of faunal assemblage) was noted, often in assocation with pyrite. The oxygenation decrease could have been the result of the influx of organic matter. -from Author