The Upper Carboniferous postglacial transgression in the Paganzo and Río Blanco basins (northwestern Argentina): Facies and stratigraphic significance

Abstract

During the early Late Carboniferous (Namurian-early Westphalian), an important postglacial transgression took place in the basins of western Argentina. The regional distribution, lithological characteristics, facies arrangement, and age of the transgression are analyzed herein. The postglacial transgressive event was studied in the Río Blanco and Paganzo basins. Seven regionally extensive facies were recognized. Laminated mudstones were deposited during the maximum flooding stage, including some thin marls and black limestone beds interpreted as condensed levels. Laminated mudstones with dropstones facies, due to iceberg melting, point out to deglaciation processes. Bouldery and pebbly diamictites mainly represent gravity flow deposits, which, in some cases, are associated with interbedded sandstones and mudstones sequences interpreted as turbidites. Sandstones with large-scale cross-bedding represent high constructive Gilbert-type deltas. Finally, coarsening and thickening upward sequences result from the progradation of mouth bars deposited in delta-front environments. On the basis of the facies arrangement, three major postglacial facies associations were recognized: open marine, transitional, and continental-dominated. Palynological assemblages suggest a Namurian to early Westphalian age for the postglacial transgression.