Paleoenvironmental reconstruction of the Middle Eocene Trieste-Pazin basin (Croatia) from benthic foraminiferal assemblages

Abstract

Foraminiferal assemblages from four stratigraphic sections of the Trieste-Pazin basin in central Istria, Croatia (southwest- ern Tethyan realm) were investigated to reconstruct paleoenvironmental conditions and to determine the age of these deposits. The fol- lowing five Middle Eocene planktonic foraminiferal zones were identified from the range and frequency of foraminiferal species: Globigerinatheka kugleri/Morozovella aragonensis Zone (E9), Acarinina topilensis Zone (E10), Morozovelloides lehneri Zone (E11), Orbulinoides beckmanni Zone (E12), and Morozovelloides crassatus Zone (E13). A data set of benthic foraminifera relative frequency has been subjected to R- and Q-mode cluster analyses to demonstrate the linkage between taxa distribution and paleoenvironmental gra- dients. Benthic foraminiferal biofacies indicate that the environment evolved from an initially mesotrophic upper bathyal slope setting towards a deeper, more oligotrophic, middle bathyal setting influenced by turbidity currents. The oligotrophy was a result of the deepen- ing processes, and a consequential decrease in organic flux. The documented short-term periods of eutrophic to mesotrophic conditions within the deeper oligotrophic regime might represent a paleoceanographic influence of water-masses from an adjacent basin to the northwest, thus recording its paleogeographic connection with the Trieste-Pazin basin during the Middle Eocene (Lutetian).