Pennsylvanian palynofloras from the Retamito Formation (Argentina): Their relationship with the marine transgressions in westernmost Gondwana

Abstract

The westernmost Carboniferous Gondwanan deposits in Argentina recorded the Late Paleozoic Ice Age (LPIA) and the subsequent sea level changes in different fossiliferous stratigraphic units. One of them, the Retamito Formation, located at the southern extreme of the Paganzo Basin in the San Juan Province, contains the first Carboniferous paleoflora described in the country at the end of the 19th century. A recent revision of the outcrops allowed the recognition of invertebrates in marine strata linked to the Moscovian postglacial sea level rise characterized by the Tivertonia jachalensis-Streptorhynchus inaequiornatus (TS Biozone). These deposits overlie Bashkirian coal beds bearing plant remains of the Nothorhacopteris-Botrychiopsis-Ginkgophyllum flora (NBG Biozone), and both sequences provide abundant palynological assemblages. The palynofloras reveal the presence of Subzones B and C of the Raistrickia densa-Convolutispora muriornata (DM) Biozone. Subzone B is represented in the coal beds, and diagnostic palynological species indicate the presence of Subzone C in the transgressive event bearing the invertebrate fauna and microplankton elements. Approximately two tens of meters above the marine strata were recognized seeds linked to the Ferugliocladus Superzone of early Cisuralian age. The continuous succession, bearing palynological assemblages of the two subzones, spans the Bashkirian-Moscovian interval and allows comparisons with coeval palynofloras from Argentina and Brazil.