| Summary: | Paleogene abyssal environments in the eastern South Atlantic were analyzed with respect to stable isotopes, population dynamics, and patterns of dissolution. Combined results of these studies indicate three times of change in the abyssal environment: the Paleocene-Eocene boundary, the middle-late Eocene boundary, and the Eocene-Oligocene boundary. An extinction event occurred at the end of the Paleocene which removed many species from the benthic foraminiferal population. This event was cosmopolitan and may have been the result of altered circulation patterns due to the separation of Australia and Antarctica or the initiation of subsequent climate cooling. In the middle Eocene the benthic fauna oscillated between opportunist taxa typical of the early Paleogene and generalist species which were dominant in the late Eocene. The middle Eocene shifts in assemblage components appear to be due to pulses of cold, dense bottom water from polar regions. A decisive shift from opportunist taxa toward a generalist assemblage occurs in the late Eocene. Species originations are high in the late Eocene which results in high species diversity prior to the Eocene-Oligocene boundary. In the early late Eocene a 5(DEGREES)C drop in bottom water temperature is interpreted from a (delta)('18)O shift of 1.2('o)/oo. This temperature decline may have been the result of the continuous flow of polar bottom water. An additional shift in ('18)O values occurred at the Eocene-Oligocene boundary indicating a temperature drop of 4(DEGREES)C. This may be a result of the full development of a psychrospheric ocean and initiation of intensification of AABW flow. The extinction rate rose sharply at the Eocene-Oligocene boundary causing lowered diversity values in the earliest Oligocene. All significant originations or migrations into the Angola Basin abyssal environment cease at the end of the Eocene; this condition, which persists until the end of the Oligocene, indicates unfavorable conditions in the deep sea during this time. ...
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