Maastrichtian–Danian palynomorphs from the Pedro Luro Formation, Ombucta 1 Borehole, Colorado Basin, Argentina

Abstract

In this contribution, the palynomorphs of the Pedro Luro Formation, Ombucta 1 Borehole, Colorado Basin, Argentina, were recorded to perform palinostratigraphic analysis, evaluate dinoflagellate cyst provincialism, recognise trends in sea surface temperature (SST) and estimate palaeobiogeographic affinities. Sixty eight species of palynomorphs were identified and three informal biostratigraphic intervals were recognised. The first, determined by Hafniasphaera australis associated with Alterbidinium acutulum, implies that deposits below 984 mbrf would not be younger than late Maastrichtian (calcareous nannofossil biozone CC26). The second interval between 982 and 954 mbrf is assigned to the upper Maastrichtian–Danian. It is difficult to give more accuracy to the age of this interval due to the absence of species with LADs (last appearance datum) in the latest Maastrichtian and the lack of early Danian taxa. This together with the recognition of CC26 (Maastrichtian) followed by NP2-NP3 (Danian) could suggest that the K/Pg boundary is not represented. The third interval includes Senoniasphaera inornata (LAD: 62.6 Ma), suggesting an age no younger than Danian for deposits between 952 and 946 mbrf (NP2-NP3). The typical taxa of the Tropical-subtropical Province predominate (Phelodinium magnificum, Lejeunecysta spp. and Senegalinium leavigatum) followed by genera from the Warm-temperate Province (Alterbidinium acutulum, Spinidinium macmurdoense, Spinidinium styloniferum and Diconodinium lurense), suggesting changes in SST trends, from tropical-subtropical to warm-temperate conditions. The coincidences of dinoflagellate cyst species recorded between the Colorado Basin and basins of equatorial South America, the African counterpart, Brazil and Uruguay, would suggest the exchange of dinoflagellates, reflecting palaeobiogeographic affinities.