Synsedimentary ash rains and paleoenvironmental conditions during the deposition of the Chachil Formation (Pliensbachian) at its type locality, Neuquén Basin, Argentina

LEANZA HÉCTOR A.; ARMELLA, CLAUDIA; FERNANDO CORFU

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2016 vol. 71 p. 82 - 95

0895-9811

A detailed sedimentological analysis of the so called "ChachilLimestones" at its type locality around the Mirador del Chachil area,southwestern Neuquén province, Argentina, is presented in this paper forthe first time. It is based on a macro/microfacial analysis and theirenvironmental interpretation by means on texture, fabric, bioclasts,intrabasinal and extrabasinal grain amounts, sedimentary structures,bioturbations and hydro-dynamism. Because of the recognition of differentfacies associations, but no pure limestones, it is more suitable to referthese sediments as the Chachil Formation. The depositional environment ofthis unit is interpreted to correspond to an internal platform dominatedby tides, with carbonate sedimentation disturbed by repeated explosivevolcanic episodes, which reduced the sedimentation space, causingretrogradation of the sedimentary system and coastal onlap. In addition,a new recalibration of the U-Pb zircon dating used for thegeochronological analysis reveals a small change with regard to previousinformation that has been used to recalculate the data, is presented inthis paper.