Benthic foraminiferal biofacies associated with middle Miocene to early Pliocene oxygen-deficient conditions in the eastern Mediterranean

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Abstract
Benthic foraminiferal faunal changes were examined across 26 Middle Miocene to Early Pliocene sapropels and sapropelic layers from DSDP [Deep Sea Drilling Project] Sites 374, 375, 376, 378 and 378A in the eastern Mediterranean. The abundant and diverse benthic foraminiferal assemblages from Sites 378 and 378A made a Q-mode principal components analysis very useful for identifying faunal trends and for comparing the ancient faunas with the Recent eastern Mediterranean benthic fauna described by Parker (1958). Principal components analysis shows that in the modern Mediterranean, a benthic fauna that is most similar to the sapropel-assemblage found at Sites 378 and 378A is associated with intermediate water depths on the margin and in the Aegean Sea. Relative abundances of 2 spp. frequently associated with the low O2 conditions, Bolivina dilatata and Uvigerina mediterranea, increase in the organic-rich layers of 378 and 378A. A periodic expansion of the O2-minimum zone in the Aegean Sea may have led to the deposition of sapropels and sapropelic layers during the Early Pliocene at Holes 378 and 378A. At Sites 374, 375 and 376, Middle Miocene to Early Pliocene benthic foraminiferal assemblages are dominated by deep water faunas. The absence of organic-rich sediments of this age from topographically elevated areas in the eastern Mediterranean suggests that an expanded O2-minimum zone is not a viable model for the deposition of sapropels and sapropelic layers studies at these sites. In addition, planktonic foraminiferal faunal and isotopic studies of these Early Pliocene organic-rich layers reveal that there was little change in surface water conditions during sapropel deposition, thus eliminating a model involving a density stratification resulting from a low salinity and/or warm surface layer. Overall warm climates and the periodic enhancement of restricted basinal communication may be responsible for sapropel deposition in the eastern Mediterranean from the Middle Miocene to Early Pliocene at Sites 374, 375 and 376.