SEDIMENTOLOGY AND PROVENANCE OF MIOCENE-PLIOCENE ALLUVIAL FAN DEPOSITS IN THE FIAMBALÁ BASIN, NW ARGENTINA

The ca. 4 km thick clastic-continental succession of Late Miocene/Pliocene foreland basin fill of the Fiambalá Basin in NW Argentina constitutes a unique spatio-temporal record related to late Tertiary deformation within the Sierras Pampeanas. We apply here facies analysis, sandstone petrography and modeling of petrographic data (SandGEM), in order to unravel the tecto-sedimentary evolution of this region.

The 2.5 km and 1.2 km thick late Miocene Tamberia and Guanchin formations, and the overlying 0.8 km thick Pliocene Punaschotter Formation reflect an overall coarsening and thickening upward succession of fluvial deposits reflecting progradation and syn-tectonic deformation. Sedimentation of the Tamberia Formation commenced at ca. 9 Ma with medium-grained sandstone intercalated with mudstones showing mudcracks; and tabular, clast-supported conglomerates. These deposits are the result of channel flows in a high-energy, ephemeral, braided fluvial system. The Guanchin Formation comprises coarse-grained lenticular sandstones with intercalations of conglomerates and mudstones. The Guanchin sandstones and conglomerates represent bedload deposits in small channels. Intercalated mudstone bodies represent pond-fill in floodplain areas. The Punaschotter Formation comprises coarse-grained conglomerates resulting from high-density stream flows in a proximal alluvial fan environment.

Paleocurrent measurements and provenance data indicate a paleo-drainage network integrating sources located to the west/northwest of the Fiambalá Basin and eastward directed paleoflow. Sandstone petrography indicates a large compositional variation along strike. The sandstone compositions are typical of recycled orogen and magmatic arc tectonic settings. These results were modeled using the Sand Generation and Evolution Model (SandGEM).

Overall the upward coarsening and thickening trend of the Mio-Pliocene sequence and sandstone compositions reconcile with deposition in an arid/semi-arid braided fluvial system. Up section changes in facies and sedimentary rock composition indicate a reorganization of drainage in the late Miocene in response to enhancement of tectonic activity, and potential eastward propagation of deformation, driving source exhumation, erosion, and sedimentation.