Dinocyst biostratigraphic framework from the Maastrichtian to Danian at Southern Hemisphere mid-latitudes, Argentina

Abstract

During the Maastrichtian to Danian, an epicontinental sea covered large areas of Patagonia and the adjacent continental shelf, connecting several previously isolated basins in Argentina, including the Colorado and Neuquén basins. Our goal is to establish a regional dinocyst biostratigraphy, supported by independent calcareous microfossils age control, using multiple sedimentary successions from both basins. For this purpose, we analyzed subsurface sections from the Pedro Luro Formation in the Colorado Basin and compared them with taxonomically revised and biostratigraphically updated outcrop sections of the Jagüel Formation in the Neuquén Basin. We identified two biostratigraphical intervals: late Maastrichtian and early Danian. The late Maastrichtian interval is characterized by the lowest occurrence of Disphaerogena carposphaeropsis and the highest occurrences of Dinogymnium spp. (D. acuminatum, D. undulosum), Diconodinium lurense, Kleithriasphaeridium spp. (K. loffrense, K. sp. 1), and Manumiella spp. (M. bertodano, M. conorata, M. seelandica), associated with the nannofossil UC20 Zone. The absence of the globally index Manumiella druggii in northern Patagonia may indicate that the topmost Maastrichtian would be not represented. The early Danian interval is defined by the lowest occurrences of Danea californica and Senoniasphaera inornata, and the highest occurrences of Trithyrodinium spp. (T. evittii, T. verrucosum), along with the typical Classopollis pollen spike, correlated with the NP1-NP3 nannofossil zones. The highest occurrences of the southwestern Atlantic margin endemics D. lurense and T. verrucosum serve as reliable biostratigraphic markers, enabling high-resolution correlation of late Maastrichtian (∼67 Ma) and early Danian units, respectively.