PALYNOLOGICAL EVIDENCE FOR A LATE EOCENE AGE OF THE SUBMESETAFORMATION FROM MARAMBIO ISLAND, ANTARCTICPENINSULA - ENVIRONMENTAL CHANGE PRIOR TO THE ONSETOF MAJOR ANTARCTIC GLACIATION

Abstract

This study presents the first detailed analysis of the organic-walled dinoflagellate cyst assemblages of the Submeseta Formation outcropping on Marambio (=Seymour) Island, northeast of the Antarctic Peninsula. Based on dinoflagellate cyst events the age of the study unit is determined to be between 36.7 and 34.1 My (Priabonian, late Eocene), which is in agreement with the ⁸⁷Sr/⁸⁶Sr ages published by other authors and recalculated in this paper. These results confirm that the Submeseta Formation does not extend into the Oligocene, as previously proposed. Paleoenvironmental inferences were based on the sporomorphs versus dinoflagellate cysts and acritarchs (S/D) and peridinioids versus gonyaulacoid dinoflagellate cysts index (P/G), indicating the existence of productive surface waters in shallow nearshore marine environments. An increase in Antarctic peridinioid taxa with cold water affinities is observed in the analyzed unit compared to the underlying La Meseta Formation, where Antarctic gonyaulacoid taxa tolerant of relatively warmer conditions dominate the assemblages. This compositional change was also observed in other Priabonian assemblages from sites located in the Austral-Magellan Basin, the Malvinas Plateau, and the northwestern Weddell Sea. This reversal in the dinoflagellate fossil record may be attributed to paleoceanographic changes resulting from the relative deepening of the Drake Passage to approximately 1,000 meters during the late Eocene.