Temporary repopulation by low-oxygen tolerant benthic foraminifera within an Upper Pliocene sapropel: Evidence for the role of oxygen depletion in the formation of sapropels

Abstract

Foraminiferal study of a continuous set of samples across the Upper Pliocene C2 sapropel (Singa section, southern Italy) revealed an interval containing substantial numbers of benthic foraminifera, bound by sediments in which benthic foraminifera are absent. The absence of benthic foraminifera is indicative of anoxic conditions. The interval with benthic foraminifera contains an association that is strongly dominated by the species Bulimina marginata, which is tolerant to low oxygen concentrations. The bottom water oxygenation did not improve sufficiently to allow development of a more diverse benthic foraminiferal fauna, or the return of intensively burrowing organisms. Variations in the planktic foraminiferal fauna and in the stable isotope records suggest that a surface water cooling preceded the benthic repopulation. A warming seems to have coincided with the return to bottom anoxia. The planktic productivity markers Globigerina bulloides and Neogloboquadrina show minor variations across the repopulated interval. The benthic repopulation, which reflects improved bottom water oxygenation, was probably favored by enhanced dense water formation in response to general cooling of the surface waters.