Benthic foraminifera of surface samples and sediment cores off Senegal and Gambia, West Africa

Water depth zonation of fifty nine benthonic foraminiferal species in marine sediment surfaces has been described. Some species are combined to groups which mark particular depth zones: an upper and lower shelf-fauna, an upper and lower slope fauna, and a shelf-slope fauna. Dependence on latitude could be ascertained for Textularia panamensis, and submergence effects for Hyalinea balthica.

Pliocene-Pleistocene distribution of benthic foraminifers from ODP Hole 110-672A (Table 2)

Site 672 is located on the Atlantic abyssal plain to the east of the Lesser Antilles forearc region. It serves as a stratigraphic reference section for sediments entering the Barbados accretionary prism. A relatively complete Pliocene through lower Pleistocene section was recovered from Site 672 that contains a moderately well-preserved population of benthic foraminifers. Q-mode factor analysis of the benthic population data identified three Pliocene-Pleistocene assemblages that inhabited this site. The Factor 1 fauna, characterized by Nuttallides umboniferus, is commonly associated with the presence of Antarctic Bottom Water (AABW). The Factor 2 assemblage is characterized by Globocassidulina subglobosa, Epistominella exigua, and a combined category of unilocular species. The Factor 3 assemblage is characterized by Epistominella exigua, and Planulina wuellerstorfi. The Factor 2 and 3 faunas are associated with bottom water significantly warmer than that preferred by the Factor 1 assemblage. The distribution of these assemblages has been used to distinguish three climatic intervals in the abyssal environment during the Pliocene-Pleistocene. An early Pliocene warm interval occurred from the Ceratolithus rugosus Subzone to the middle of the Discoaster tamalis Subzone. The upper Pliocene is characterized by oscillations between the Factor 1 and Factor 2 assemblages, which suggests climatic deterioration and increased pulses of AABW flow. The persistence of an essentially modern (Factor 1) fauna throughout the early Pleistocene suggests full glacial development at both poles and a substantial volume of AABW production.

Late Oligocene to Recent benthic foraminifers from the northeastern North Atlantic

Deep-sea benthic foraminiferal faunas were studied from Sites 608 (depth 3534 m, 42°50'N, 23°05'W) and 610 (depth 2427 m, 53°13'N, 18°53'W). The sampling interval corresponded to 0.1 to 0.5 m.y. at Site 608 and in the sections of Site 610 from which core recovery was continuous. First and last appearances of benthic foraminiferal taxa are generally not coeval at the two sites, although the faunal patterns are similar and many species occur at both sites. Major periods of changes in the benthic faunas, as indicated by the numbers of first and last appearances and changes in relative abundances, occurred in the early Miocene (19.2-17 Ma), the middle Miocene (15.5-13.5 Ma), the late Miocene (7-5.5 Ma), and the Pliocene-Pleistocene (3.5-0.7 Ma). A period of minor changes in the middle to late Miocene (10-9 Ma) was recognized at Site 608 only. These periods of faunal changes can be correlated with periods of paleoceanographic changes: there was a period of sluggish circulation in the northeastern North Atlantic from 19.2 to 17 Ma, and the deep waters of the oceans probably cooled between 15.5 and 13.5 Ma, as indicated by an increase in delta18O values in benthic foraminiferal tests. The period between 10 and 9 Ma was probably characterized by relatively vigorous bottom-water circulation in the northeastern Atlantic, as indicated by the presence of a widespread reflector. The faunal change at 7 to 5.5 Ma corresponds in time with a worldwide change in delta13C values, and with the Messinian closing of the Mediterranean. The last and largest faunal changes correspond in time with the onset and intensification of Northern Hemisphere glaciation.