Oligocene benthic foraminifers from North Altantic Sites: benthic foraminifers as water-mass indexes in the North and South Atlantic.

Abstract

Examination of faunas across the Eocene/Oligocene boundary and through the Oligocene from 12 North and South Atlantic locations has indicated that the distribution of Nuttallides umbonifera can be used to trace the pathways and depth-migration of newly-derived deep-water masses through the Atlantic. After the Eocene/Oligocene boundary event, the variations in the geographic occurrences of N. umbonifera from several deep-water and bottom-water depth sites parallel the stable isotopic records of bottom-water characteristics, thus reflecting the incursion of cooled bottom waters, which aged from the south to north. At one South Atlantic site (1000 m paleodepth), the brief but significant appearance of N. umbonifera is interpreted to reflect the influx of a new intermediate-water mass that entered the Atlantic during Zone-P20 time (about 32-33 Ma ago), coincident with the establishment of a circum-Antarctic surface circulation. Faunas at all sites markedly changed their generic and intrageneric contents between the early and late Oligocene. The first appearences of several characteristic Neogene species through the upper Oligocene Zones P21-P22 are hypothesized to reflect the diachronous evolution of essentially 'Neogene' water-mass stratification in the North and South Atlantic.-from Author