Sr-stratigraphy and sedimentary evolution of early Miocene marine foreland deposits in the northern Austral (Magallanes) Basin, Argentina

CUITIÑO, J.I.; VENTURA SANTOS, R.,; ALONSO MURUAGA, P.J.; SCASSO, R.A.

ANDEAN GEOLOGY

SERVICIO NACIONAL GEOLOGIA MINERVA

Lugar: Santiago de Chile; Año: 2015 vol. 42 p. 364 - 385

0718-7092

Early Miocene shallow marine deposits in the region of Lago Posadas-Meseta Belgrano (Argentina) represent part of the ?Patagoniense? transgression, an Atlantic marine incursion that flooded large part of Patagonia, including the Austral (foreland) Basin (southern Patagonia). These deposits, referred as El Chacay (Argentina) or Guadal (Chile) formations, and the transition to the overlying Santa Cruz Formation were divided into six facies: subtidal sandbars, shallow marine sandy deposits, muddy shelf deposits, estuarine complex deposits, fluvial channels and fluvialfloodplains. These are arranged in a general transgressive-regressive cycle, subdivided into two stratigraphic sequences, separated by a major erosional surface. 87Sr/86Sr ages from shell carbonate in eight oysters yielded an age range of 20.3 to 18.1 Ma for these ?Patagoniense? deposits. Correlation with other dated ?Patagoniense? sections in southern Patagonia,like those at Lago Argentino or Comodoro Rivadavia, indicates that they belong to a single transgression that flooded several Patagonian basins approximately at the same time. Eustasy, flexural subsidence created by tectonic loading in the adjacent fold-and-thrust belt, and basin floor paleo-topography controlled the duration of the depositional event and the sedimentation style of these shallow marine deposits.