ALGUNOS ADELANTOS EN LA MICROBIOESTRATIGRAFIA DEL JURASICO EN LA ARGENTINA Y COMPARACION CON OTRAS REGIONES DEL HEMISFERIO AUSTRAL

Abstract

Composition and stratigraphic significance of 15 jurassic microfloras from Argentina are reported. Four Lower jurassic and ten Middle jurassic assemblages are from the Neuquén Basin; one Upper Jurassic assemblage from Extraandean Patagonia (Chubut Province). In the Lower Jurassic microfloras Classopollis is prevailing, and in one of them Nevesisporites vallatus de Jersey & Paten is an important marker. The incoming of Callialasporites dampieri (Balme ) Dev., Callialasporites segmentatus (Balme ) Srivastava and Inaperturopollenites turbatus is in the beds with Phymatoceras copiapense (Möricke) (lower Upper Toarcian, Zone of Grammoceras thouarsense); the Upper Toarcian and Middle and Upper jurassic rnicrofloras are characterized by the presence of Callialasporites dampieri and various sub-units can be distinguished within the dampieri-bearing assemblages: a) an Aalenian one with 60-70 % Classopollis and the presence of Inaperturopollenites turbatus; Microcachryidites is lacking; b) a Bajocian one with ± 40 % Classopollis and the presence of Inaperturopollenites indicus and Microcachryidites; e) a Lower Callovian one with less than 10 % Classopollis and prevailing of Podocarpidites, Microcachryidites, Callialasporites and Inaperturopollenites ; d) an Upper Jurassic one with prevailing Classopollis (67 and more %). The first typical specimens of Callialasporites trilobatus appear in this Upper jurassic assemblage which, on the other hand, is lacking Inaperturopolienites limbatus and Cicatricosisporites, forms which appear with great frequency near the Jurassic-Cretaceous boundary. The age of most of the Lower and Middle Jurassic microfloras is well documented by ammonites associated. This fact permits dating of comparable microfloras from non-rnarine beds, studied by Paten (1967), Reiser & Williams (1969) and de Jersey (1971) from the Surat Basin and Moreton Basin in Queensland (Australia). Mícrofloral similarities indicate close gondwanic relations between Australia and South America.