The Danian Sea: Dinoflagellate cysts assemblages from Neuquén Basin, Roca Formation (Argentina) and its comparison with other southern South America localities

Abstract

The study section at the Casa de Piedra locality (Neuquén Basin) is located near the Colorado River, southwestern sector of La Pampa province, Argentina. The section is assigned to the Roca Formation, which records a shallow marine environment linked with Atlantic transgressions. It includes a new record of dinoflagellate cysts of the Danian Sea, in northern Patagonia. Most of the recognized taxa have a Late Cretaceous – Danian stratigraphic range in the Southern Hemisphere. The great similarity with the dinoflagellate cysts recorded in the uppermost Pedro Luro Formation, Colorado Basin allowed inferring a Late Danian age for the Roca Formation in the Casa de Piedra section. This age is also supported by the presence of Vozzhennikovia apertura (FAD: 65.10 Ma) and Cerodinium diebelli (LAD: 61.05 Ma) and by other micofossils data including foraminifers and nannofosils. The sedimentary facies and the dinoflagellate cysts identified suggest a neritic environment ranging from marginal-marine with scarce fluvial influence to outer neritic conditions. Taking into account the sporomorphs content, the paleoenvironment conditions would be similar to those of the North-west and Colorado Basins for the Danian, with a forest of Ulmaceae (Verrustephanoporites simplex) and montane forest (Podocarpaceae, Rutaceae). The sporomorph assemblages indicate warm paleotemperatures (subtropical-tropical). The high similarity of dinoflagellate cyst records between Roca and Pedro Luro Formations would suggest a probable link between Neuquén and Colorado basins during Danian times. This connection has been postulated by several authors and could be related to the Neuquén embayment through the Huincul fault.