EARLY PALEOGENE CLIMATIC CONDITIONS AT MID LATITUDE SOUTHERN HEMISPHERE: MINERALOGICAL AND PALEOBOTANICAL PROXIES FROM CONTINENTAL SEQUENCES IN GOLFO SAN JORGE BASIN (PATAGONIA, ARGENTINA)

RAIGEMBORN, M, BREA, M, ZUCOL, A AND MATHEOS, S.D

GEOLOGICA ACTA

UNIV BARCELONA

Lugar: Barcelona; Año: 2009 vol. 7 p. 125 - 145

1695-6133

ABSTRACT: The Paleocene-Eocene boundary was a period of transient and intense global warming that had a deep effect on plant groups in high latitudes. Nevertheless, few paleoclimatic reconstructions of early Paleogene age from South American continental sequences are known. In this contribution, we present the use of proxy indicators, like clay mineral and paleobotanical analyses (fossil woods and phytoliths) from the lower and middle section of the Río Chico Group, in the Golfo San Jorge basin, Patagonia, Argentina. These data can be a useful tool to understand the change in climatic conditions that happened coeval with deposition of the units, during part of the Paleocene-Eocene boundary. In this context, three clay minerals assemblages were identified: S1 assemblage (smectite) dominates the Peñas Coloradas Formation, S2 assemblage (smectite>kaolinite) is present towards the Las Flores Formation and S3 assemblage (kaolinite>smectite) dominates the Las Flores Formation. These fluctuations in detrital clay mineral composition identified can be mainly related to source area lithology and paleoclimatic conditions, which changes from a seasonal warm temperate to a tropical climate. The paleobotanical data suggests that vegetation in the Golfo San Jorge basin during the Early Paleogene was variable with significant changes in composition and diversity through time, from mixed temperate to subtropical forest to mixed subtropical to tropical and humid forests. In combination, the clay mineral composition and palaeovegetation assemblages suggest that during the Paleocene-Eocene boundary in central Argentinean Patagonia a change of temperate-warm and humid conditions, with highly seasonal precipitation were replaced by subtropical-tropical conditions with more year-round rainfall.