Maastrichtian to Pliocene dinocyst biostratigraphy of the Lobo X-1 well, Punta del Este Basin, Uruguay

A palynological characterization was conducted on marine sediments from the Lobo X-1 well, drilled by Chevron at the Punta del Este Basin. This basin, situated along the Uruguayan continental margin (UCM)—a passive volcanic margin formed during the breakup of Gondwana—has been the focus of detailed stratigraphic and palynological studies aimed at refining its geological framework. A total of 54 cutting samples collected from depths of 369 to 1869 m yielded moderate to well preserved palynomorphs were analyzed. The samples correspond the following stratigraphic units, from oldest to youngest: Migues, Mercedes, Gaviotín, Fray Bentos, and Camacho formations. The palynological analysis focused primarily on dinoflagellate cyst bioevents allowed to recognize seven stratigraphic intervals. These intervals are: Pliocene; middle to late Miocene; early Miocene; late Eocene; early to middle Eocene; late Maastrichtian to early Danian (tentatively); and early Maastrichtian. The position of the K-Pg transition is also suggested. Some samples were selected to perform calcareous nannofossil analyses and integrate their data with dinoflagellate cyst bioevents to enhance stratigraphic resolution, supporting age interpretations and refining previous stratigraphic frameworks. This multidisciplinary approach, which combines geological and geophysical data—including spontaneous potential (SP) and gamma-ray (GR) logs—with palynological and micropaleontological evidence, strengthens regional correlations within the South Atlantic basins. Moreover, this study presents the first record of calcareous nannofossils in Uruguayan deposits.