Aptian–Albian benthic foraminifera from DSDP Site 364 (offshore Angola): A paleoenvironmental and paleobiogeographic appraisal

Abstract

This work presents a paleoenvironmental and paleobiogeographical appraisal of the benthic foraminiferal assemblages recovered from the Aptian–Albian carbonate-dominated succession of Deep Sea Drilling Project (DSDP) Site 364, located in the Kwanza Basin (offshore Angola). Forty-two species were identified within the studied interval, and their stratigraphic distributions enabled the recognition of two events of diversification, the first within the latest Aptian and the second within the late Albian. Q-mode and R-mode cluster analyses of the benthic foraminifera allowed to recognize three associations (Bathysiphon sp., Gyroidinoides infracretaceus and Kadriayina gradata), which seem to have been mainly controlled by paleobathymetry. The studied fauna is characteristic of neritic to upper bathyal depths. At and/or close to black shale levels low values of benthic foraminiferal abundance and species richness could be indicative of low-oxygen (dysoxic) bottom water conditions. The black shales deposition in Site 364, cores 42 to 39 (likely related to an Aptian dysoxic-anoxic event), occurred at shallow to middle neritic water depths. Some typical tropical/subtropical planktic biostratigraphic markers are missing from specific stratigraphic intervals of Site 364, in which shallow (neritic) water depths were inferred. Their absence from the northern South Atlantic Ocean (north to the Walvis Ridge–Rio Grande Rise) may be rather a result of their deeper-dwelling habitat preferences, than to the influx of colder-water masses from the southern South Atlantic Ocean, as previously reported. Paleobiogeographically, the studied Aptian–Albian benthic foraminifera present a predominant Austral/Transitional affinity, in contrast to the evidence of the planktic foraminifera, which indicate the influence of tropical/subtropical conditions in surface waters.