Campanian?Eocene dinoflagellate cyst biostratigraphy in the Southern Andean foreland basin: Implications for Drake Passage throughflow

PETER K. BIJL; RAQUEL GUERSTEIN; EDGAR A. SANMIGUEL JAIMES; APPY SLUIJS; SILVIO CASADIO; VÍCTOR VALENCIA; CECILIA AMENÁBAR ; ALFONSO ENCINAS

ANDEAN GEOLOGY

SERVICIO NACIONAL GEOLOGIA MINERVA

Lugar: Santiago de Chile; Año: 2021 vol. 48 p. 185 - 218

0718-7092

The tectonic opening of the Tasmanian Gateway and Drake Passage represented crucial geographic requirementsfor the Cenozoic development of the Antarctic Circumpolar Current (ACC). Particularly the tectonic complexity of DrakePassage has hampered the exact dating of the opening and deepening phases, and the consequential onset of throughflowof the ACC. One of the obstacles is putting key regional tectonic events, recorded in southern Patagonian sediments,in absolute time. For that purpose, we have collected Campanian-Eocene sediment samples from the Chilean sectorof Southern Patagonia. Using U-Pb radiometric dating on zircons and dinoflagellate cyst biostratigraphy, we updatedage constraints for the sedimentary formations, and the hiatuses in between. Thick sedimentary packages of shallowmarineand continental sediments were deposited in the foreland basin during the early Campanian, mid-Paleocene, thePaleocene-Eocene boundary interval and the middle Eocene, which represent phases of increased foreland subsidence.We interpret regional sedimentary hiatuses spanning the late Campanian, early-to mid-Paleocene, mid-Eocene andlatest Eocene-early Oligocene to indicate times of reduced foreland subsidence, relative to sediment supply. We relatethese changes to varying subduction rates and Andean orogeny. Dinoflagellate cyst assemblages suggest that the regionwas under the influence of the Antarctic-derived waters through the western boundary current of the Subpolar Gyre,developed in the southwest Atlantic Ocean and thus argues for limited throughflow through the Drake Passage until atleast the latest Eocene. However, the proliferation of dinoflagellate endemism we record in the southwest Atlantic iscoeval with that in the southwest Pacific, and on a species level, dinoflagellate cyst assemblages are the same in thesetwo regions. This suggests that both regions were oceanographically connected throughout the early Paleogene, likelythrough a shallow opening of a restricted Drake Passage. This implies a continuous surface-water connection betweenthe south Pacific and the South Atlantic throughout the late Cretaceous-early Paleogene.