A late eocene-early Oligocene transgressive event in the Golfo San Jorge basin: Palynological results and stratigraphic implications

PAREDES JOSE; FOIX NICOLAS; GUERSTEIN RAQUEL; GULER M. VERONICA

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2015

0895-9811

A new Cenozoic dataset in the subsurface of the South Flank of the Golfo San Jorge Basin (Santa Cruz province) allowed to identify a non-previously recognized transgressive event of late Eocene to early Oligocene age. Below of a marine succession containing a dinoflagellate cyst assemblage that characterizesthe C/G palynological zone of the Chenque Formation (early Miocene), a 80e110 m thick marine succession contains a palynological assemblage integrated by Gelatia inflata, Diphyes colligerum and Reticulatosphaera actinocoronata supporting the occurrence of a marine incursion in the basin during theEoceneeOligocene transition (EOT). The new lithostratigraphic unit - here defined as El Huemul Formation e covers in sharp contact to the Sarmiento Formation, and become thinner from East to West;the unit has been identified in about 1800 well logs covering up to 3500 km2, and its subsurface distributionexceed the boundaries of the study area. The El Huemul Formation consists of a thin lag of glauconitic sandstones with fining-upward log motif, followed by a mudstone-dominated succession that coarsening-upward to sandstones, evidencing a full T-R cycle. Preservation of the El Huemul Formation in the subsurface of the South Flank has been favored by the reactivation of WNW-ESE late Cretaceous normal faults, and by the generation of NeS striking normal faults of Paleocene-Eocene age. Flexural loading associated to igneous intrusions of Paleocene?- middle Eocene age also promoted the increase of subsidence in the South Flank of the basin prior to the transgression.