40Ar/39Ar age and oxygen isotope temperature of the Centinela Formation, southwestern Argentina: An Eocene age for crustacean-rich "Patagonian" beds.

CASADÍO, S.; FELDMANN, R.

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2000 vol. 13 p. 123 - 132

0895-9811

The presence of a prominent volcanic ash enclosed within sediments of the Centinela Formation, southwestern Argentina, permits establishment of an 40Ar/39Ar age of approximately 46 Ma for these rocks. Oxygen isotopic analysis of shell material from the oyster Crassostrea? hatcheri Ortmann, 1897, suggests seasonal ¯uctuation of temperature from about 158C to about 218C. In concordance with this, a diverse crustacean fauna, including nine families within the order Decapoda and one within Isopoda, bears strong a?nities with temperate and subtropical faunas of the Atlantic Ocean basin and documents the southernmost extension of low latitude oceanographic in¯uence on this region during the Paleogene. Establishment of an Eocene age for the rocks in the Centinela Formation provides the ®rst de®nitive documentation of rocks of that age in the region of Calafate, permits correlation of these rocks with Eocene strata southward to the vicinity of RõÂo Turbio, and suggests that these rocks, assigned to the Patagonian sequence, may be substantially older than those in eastern Argentina. 7 2000 Elsevier Science Ltd. All rights reserved.