Onset of the Miocene Chaco foreland basin: depositional conditions, provenance and paleogeographic implications of the Tranquitas Formation (Argentina)

TINEO, D.E.; POIRÉ, D.G.; VARELA, A.N.; MOYANO PAZ, D.

INTERNATIONAL JOURNAL OF EARTH SCIENCES

SPRINGER

Lugar: Berlin; Año: 2022 vol. 111 p. 1739 - 1771

1437-3254

During the Oligocene-early Miocene, the Chaco foreland basin records the initial infill stage in a retroarc scenario. The Tranquitas Formation was deposited during this initial basin configuration within the southern sector of the basin. The aims of this contribution are: (i) to provide original data of the depositional conditions of the Tranquitas Formation deposits, (ii) to determinate the role of tectonic and climate processes on the depositional conditions and on the composition of these deposits, and (iii) propose a sequence stratigraphic evolutionary model of accumulation. The detailed analysis of these deposits resulted in the definition of six facies associations, including: Complex sandy narrow sheets channels (FA1), Sandy narrow sheets channels with lateral accretion surfaces (FA2), Sandstone ribbons channels (FA3), Tabular muddysandstone deposits (FA4), Sandstone lobes (FA5), and Fine-grained deposits (FA6). Based on the spatial distribution and the vertical stacking of these associations the Tranquitas Formation was divided into two major intervals. Interval 1 (lower section) is characterized by the braided fluvial deposits and represents low accommodation conditions with a high proportion of channel deposits. Interval 2 (upper section) reflects increase in the accommodation space characterized by the higher preservation of floodplain deposits in moderate to high sinuosity meandering fluvial systems. The integration of paleocurrent, petrography, and clay mineralogy analyses indicate that detrital components were apported from the orogenic region located to the west, in an overfilled stage of the foreland basin. Clay mineral assemblage analysis suggest a long-term climate change from drier to higher humid conditions and reflect the climate effect on the depositional paleoenvironments developed in the distal position of the basin. In addition, this study suggests that the resultant vertical and lateral stacking of sedimentary paleoenvironments of the Tranquitas Formation could be correlated with the Petaca and lower-Yecua formations located in the center and north of the basin.