Taxonomy and biostratigraphy of Cretaceous megaspores from Patagonia, Argentina

Megaspores from the Kachaike and Piedra Clavada formations of Albian and ?Cenomanian age in Santa Cruz Province, Argentina, are described and illustrated by scanning electron micrographs. These include six new species: Arcellites humilis, A. pentagonalis, A. sp. A, Erlansonisporites verrucatus, Minerisporites aequatus and Striatriletes areolatus. Striatriletes reticulatus (Zerndt) Sweet and Trileites cf. T. murrayi (Harris) Marcinkiewicz are recorded for the first time from Argentina. Another eight species that were previously recorded in Patagonia are also described based on specimens found in new localities. Comparison with similar megaspore taxa from other palaeofloristic regions suggests that the megaspores in these formations are of Albian age (perhaps extending into the Cenomanian), confirming previous data obtained from other studies of marine and terrestrial fossils from these formations. The botanical affinities of the megaspores with heterosporous lycopsids (Isoetaceae and Selaginellaceae) and water ferns (Marsileaceae and Salviniaceae) suggest that a warm, humid climate and abundant water bodies prevailed during the Albian in Patagonia. The stratigraphic distribution of all known Early Cretaceous Patagonian megaspores allows recognition of three separate assemblages, M1-M3, each characterized by several exclusive taxa. M1 spans the Berriasian-Barremian, M2 is Aptian, and M3 is Albian-?Cenomanian.