The Early Pennsylvanian transgressions in western Gondwana, the Pituil Formation as a reference in the Calingasta–Uspallata Basin

Abstract

During the Carboniferous, western Gondwana was affected by numerous transgressions resulting from fluctuations in the ice sheet throughout the Late Paleozoic Ice Age. These sea level rises are well documented in western Argentina basins: Paganzo, Río Blanco, San Rafael, and Calingasta–Uspallata. Three transgressive events are recognized: The first corresponds to the post-glacial transgression of early Bashkirian age, which flooded the basins of western Argentina. The second transgression, the Pennsylvanian Transgression 1, is limited to the San Rafael, Río Blanco, western Paganzo, and Calingasta–Uspallata basins. This transgression facilitated the deposition of carbonaceous shales and thin coal beds in transitional estuarine-type environments. This stratigraphic interval is accompanied by megaflora of Nothorhacopteris–Botrychiopsis–Ginkgophyllum, microflora of Raistrickia densa–Convolutispora muriornata Subzone b, and an association of marine invertebrates that constitute the Marginovatia–Maemia Fauna. Finally, Pennsylvanian Transgression 2 or “Stephanian” transgression is more extensive and is associated with a Moscovian age invertebrate fauna. This contribution focuses on a sedimentological and paleontological analysis of the Pituil Formation. This unit comprises five facies associations: I, offshore; II, shoreface; III, deltaic systems; IV, barrier islands; and V, coastal lagoon. These sedimentological data and the fossil content of the Pituil Formation allow us to characterize the Pennsylvanian Transgression 1 in the Calingasta–Uspallata Basin and correlate it with other basins in western Gondwana.