EOCENE OPENING OF DRAKE PASSAGE: GEOLOGICAL AND GEOPHYSICAL EVIDENCE FROM TIERRA DEL FUEGO

MATIAS C. GHIGLIONE; YAGUPSKY, D.; GHIDELLA, M.; RAMOS V.A

Gottingen, Alemania

Simposio; LateinAmerika Kolloquium; 2009

German Science Foundation

Due to the tremendous impact of the present global warming, it has became essential to understand the causes and processes involved in past climate changes. One of the most prominent events in Earth´s climatic evolution was the transition from the global warmth of the Eocene "greenhouse" to the Oligocene "icehouse" glacial conditions, but, why did it happen? It is widely believed that the separation of South America from Antarctica and the subsequent  formation of Drake Passage have influenced Cenozoic global cooling because these events enabled the development of the Antarctic Circumpolar Current. This wind-driven current is speculated to have reduced heat transport to Antarctica, triggering the Oligocene global cooling. It has been proposed alternatively that opening of Drake Passage influenced circulation-induced productivity increase that may have sequestered atmospheric CO2, contributing to global cooling and Antarctic glaciation. While the former theory is based on the presumption that the marine connection was coeval with initiation of the Antarctic glaciation at the Eocene-Oligocene boundary, the latter requires an earlier (middle Eocene) ocean water exchange. Unfortunately, age estimates for the onset of a seaway through Drake Passage range from middle Eocene to Miocene, complicating interpretations of the relation between ocean circulation and global cooling.Studying the southeast tip of Tierra del Fuego, a region that was once attached to the Antarctic Peninsula, we discovered evidences for the opening of widespread early Eocene extensional depocenters. Here we present evidence for the presence of a Paleocene – Eocene extensional basin (i.e. lateral rift) located parallel to the actual continental-oceanic crust boundary in Tierra del Fuego. An accurately-dated post-rift unconformity indicates that extensional faulting ended in this area at ~50 Ma, in concurrence with a previously reported eightfold increase in South America – Antarctica separation rate, and the onset of oceanic basins in the incipient Drake Passage. The coincidence of these facts indicates progressive strain concentration on the zone of future crustal separation (i.e. Drake Passage) after abandonment of lateral rifts. The presented data bolster previously proposed interpretations of an early (Eocene) marine gateway by confirming the prediction of a continental extensional regime in the region during the period prior to the opening of the small Protector and Dove basins near 42 Ma. This succession of events is in accordance with recent theories supporting that the opening of a seaway through Drake Passage was early enough to contribute to global cooling through lowering levels of atmospheric CO2.