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Abstract

The Eocene La Meseta Formation is an unconformity-bounded unit that records the geological evolution of the James Ross Basin, NE Antarctic Peninsula, during a period of decreasing tectonism and a lull in volcanic activity. This unit represents a composite incised valley, filled with deltaic, estuarine and shallow-marine deposits showing a landwards facies shift that indicates deposition during an overall sea-level rise. The six unconformity-based internal units (Valle de las Focas, Acantilados, Campamento, Cucullaea I, Cucullaea II and Submeseta allomembers) are interpreted to represent minor-scale regressive-transgressive events. Geological, palaeontological and new strontium isotopic ages allow the correlation of base-level changes with second- and third-order eustatic sea-level fluctuations. The base of the La Meseta Formation is correlated with a global 56 Ma lowstand in sea level followed by a main episode of flooding between 54.3 and 52.4 Ma. The base of the Cucullaea I Allomember is correlated with the well-known late Ypresian (49 Ma) lowstand, and the base of the Submeseta Allomember with the 36 Ma lowstand. Correlation of Eocene sea-level fluctuations in the northern Antarctic Peninsula with the global sea-level curve strengthens the concept of global syncroneity of the eustatic sea-level curve.

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