Palynology from the Cenomanian Puesto El Moro Formation (Santa Cruz Province, Argentina)

During the Late Cretaceous and the Paleocene, terrestrial floras witnessed the so-called “Angiosperm Terrestrial Revolution”, when several modern clades of angiosperms originated and diversified. This process is scarcely studied in the Southern Hemisphere. Also, during the Cretaceous several carbon cycle alterations were registered, producing climatic modifications, and affecting both continental and marine biota. We present the palynological composition of the Puesto El Moro Formation, from the Cenomanian of Santa Cruz Province, Argentina. The sequence shows a progressive continentalization from coastal to fluvial sediments, representing an opportunity to understand how terrestrial floras evolved during this period in the Southern Hemisphere and how global climatic events affected them. Fifteen fertile palynological samples were studied. 142 species were recovered, with 23 bryophytes and lycophytes, 64 ferns, 34 gymnosperms, and 13 angiosperms. Dinoflagellate cysts are moderately abundant in the basal levels, but have poor preservation. The age of the unit was previously established as Cenomanian based on stratigraphic relations, and the palynostratigraphy supports this conclusion. Counts show that almost all the assemblages are dominated by gymnosperms (primarily Classopollis), followed by ferns (primarily Cyathidites). Bryophytes, lycophytes and angiosperms represent a minor proportion. Richness analysis shows that, on average, it tends to increase, with a great rise in the uppermost levels, pointing out the possible location of the Mid-Cenomanian Event. The Puesto El Moro palynoflora is closely related with the ones from the Classopollis-Cyclusphaera palynological sub-province. The analysis shows a latitudinal arrangement of the palynofloras, differentiated between them by their most abundant gymnosperm pollen grain.