Palaeoecological preferences and geographical distribution of Late Maastrichtian deep-sea ostracods in the South Atlantic

The distributional patterns of deep-sea ostracods in the terminal Cretaceous South Atlantic were examined from seven DSDP/ODP holes (356, 525A, 527, 528, 529, 698A and 689B). Many of the genera recorded in this study are previously known from Campanian-Maastrichtian deep-sea sediments. However, the recovery of Aversovalva, Hemiparacytheridea, Profundobythere, Mayburya and Legitimocythere reveals considerable similarities with the Tertiary deep-sea ostracod fauna of the Pacific and the North Atlantic. The underlying causes controlling the variation in faunal density among the various sites are likely to be related to variation in food supply and, to a lesser extent, to variation in oxygen levels, since all sites quantitatively assessed are regarded to represent oligotrophic, well-oxygenated conditions. A Q -mode principal component analysis with varimax rotation yielded a first component largely dominated by Bythocypris and significantly correlated with palaeotemperature; there is an increasing abundance of Bythocypris towards higher latitudes with a maximum abundance at Site 689 where the palaeotemperature was around 9°C. A species of the thermophilic genus Cytherelloidea occurs also at this site, probably as a result of a slow adjustment to colder conditions in the absence of a thermocline at that time. The second component is largely dominated by Krithe and significantly correlated with palaeotemperature and palaeodepth. Among the sites studied, Krithe is most common at Site 356, where the palaeotemperature was around 15°C; today, most representatives of this genus are psychrospheric and adapted to temperatures below 10°C.