Dinoflagellate cysts of the La Meseta Formation (middle to late Eocene), Antarctic Peninsula: implications for biostratigraphy, palaeoceanography and palaeoenvironment

MONTES, MANUEL; AMENÁBAR, CECILIA R.; SANTILLANA, SERGIO; NOZAL, FRANCISCO

GEOLOGICAL MAGAZINE

CAMBRIDGE UNIV PRESS

Año: 2019 p. 1 - 16

0016-7568

Dinoflagellate cyst assemblages recovered from the La Meseta Formation cropping out inSeymour Island, Antarctic Peninsula, are studied herein and their distribution is compared withthe biostratigraphic scheme available for the Palaeogene of the Southern Ocean and other highlatituderegions. In this way, the La Meseta Formation is dated as middle Lutetian to Priabonian(46.2?36 Ma), which differs from the age provided by other fossils, isotopes and also with themagnetostratigraphic scheme recently performed for the unit. The dinoflagellate cyst data supportthe proposal of ocean circulation patterns on the South American Shelf prior to the openingof Drake Passage. Assemblages from the La Meseta Formation contain Antarctic-endemictaxa which are also dominant in several circum-Antarctic sites, located south of 45° S. Theirdistribution reflects an ocean-circulation scheme with wide clockwise gyres surroundingAntarctica that were disrupted as a consequence of the deepening and definitive aperturesof the Tasmanian Gateway and Drake Passage towards the Eocene/Oligocene transition.The palaeoenvironmental inference based on the S/D ratio (sporomorphs versus dinoflagellatecysts) and the P/G ratio (peridinioid versus gonyaulacoid dinoflagellate cysts) suggests an overalltrend through the section from marine-dominated assemblages with poorly productivewaters in the lower part of the section to more terrestrially dominated assemblages with increasingproductivity in the upper part of the unit, reflecting a shallowing trend to the top.