Late Maastrichtian dinoflagellate cysts from Cerro Butaló section, Southern Mendoza Province, Argentina

PRÁMPARO, MERCEDES B.; PAPÚ, OSCAR H.

Londres

Simposio; Thirty Fifth Annual Meeting of the American Association of Stratigraphic Palynologist; 2002

AASP, BMS, NAMS

ABSTRACT for AASP-BMS-NAMS Meeting (September 2002) Late Maastrichtian dinoflagellate cysts from Cerro Butaló Section, Southern Mendoza Province, Argentina. Prámparo, M.B. (1) and Papú, O.H. (1) (1) Unidad de Paleopalinología. Instituto Argentino de Nivologia, Glaciologia y Ciencias ambientales (IANIGLA)- CRICYT. C.C.131. (5500) Mendoza, Argentina The late Cretaceous Atlantic trangression is recorded in western Argentina in the sediments of the upper part of the Malargüe Group. The Cerro Butalo section crops out at 35º 50´ S and 69º 40´ W, southern Mendoza Province, Argentina and is constituted by sediments of the Jagüel Formation and Roca Formation, both belonging to the Malargüe Group. The Jagüel Formation at the study area is 25m thick and is characterized by grey mudstones and sandstones. The Roca Formation overlies the preceeding unit and comprises a basal white limestone (30m thick) with abundant bivalves and gastropod fragments, followed by pelitic sandstones (20 m thick). These two units correspond to the third depositional sequence  (DSIII) in the sense of Parras et. al.(1998), deposited in a subtidal to intertidal environment, and are overlain by the terrestrial Pircala Formation.  A well preserved palynological association was recovered from this section. Dinoflagellate cysts are dominating in the lower part of the profil (Jagüel Formation). Representatives of the Spiniferites/Achomosphaera group dominate the association. Biotratigraphically useful species are Areoligera medusettiformis, Areoligera coronata, Deflandrea galeata, Glaphyrocysta retiintexta, Hystrichosphaeridium tubiferum, Phelodinium magnifica, Palaeocystodinium lidiae, Paleocystodinium golzowense, Piercites pentagona. Several species of the genera Cordosphaeridium, Florentinia and Tityrosphaeridium are also common in this interval. Terrestrial palynomorphs are scarse in all the samples but become more abundant at the top of the section (Roca Formation). Spores and massulae of aquatic ferns (Azolla cretacea, Azolla (Rhizosperma) sp., Azollopsis (Spiralopsis) pusilla, Grapnelispora loncochensis) reflect the vegetation of the littoral environment and are stratigraphically  useful. Gymnosperm pollen like Classopollis, Callialasporites, Cyclusphaera, Podocarpidites are present, associated with angiosperm pollen assigned to Psilatricolporites patagonicus, Peninsulapollis gillii and the zygnematacean algae Catinipollis.             Deflandrea galeata has a first occurrence in the middle Late Maastrichtian of the Danish part of the North Sea. Disphaerogena carposphaeropsis has its first appearance (FAD) in the Late Maastrichtian (67.0 m.a.). Based on the occurrence of these two species, the Jagüel Formation at the Cerro Butalo section is considered to be of Late Maastrichtian age. Within the uppermost 10m of Roca Formation dinoflagellate cysts become scarse; only specimens belonging to Operculodinium centrocarpum are present, indicating a nearshore depositional environment. The KPB at this section is considered to be (paleontological evidence and radiometric dating) located in the continental deposits of Pircala Formation (DSIV). This is the first report of a Late Cretaceous dinoflagellate cysts association of the Mendoza Province, western Argentina.