MIDDLE JURASSIC CALCAREOUS NANNOFOSSILS FROM A NEW LOCALITY IN THE LOS MOLLES FORMATION, NEUQUÉN BASIN

CHAUMEIL RODRÍGUEZ, MICAELA; PÉREZ PANERA, JUAN PABLO; MATTIOLI, EMAUELA; ANGELOZZI, GLADYS N.

Puerto Madryn

Congreso; Reunión de Comunicaciones de la Asociación Paleontológica Argentina; 2018

Most of Middle Jurassic calcareous nannofossil studies are based upon Tethyan sections and only sporadically coccolith record has been documented from the Neuquén Basin (Pacific realm). We present the first detailed report on calcareous nannofossils from this region. The Matuasto III section (Los Molles Formation) crops out near the left margin of Arroyo Picún Leufú, 45 km south from the city of Zapala, Neuquén Province. It corresponds to 23 m of massive mudstones with few and thin intercalated fine sandstones; bivalves, ammonites, coal and leaf fragments were recovered. Calcareous nannofossil assemblages had good to moderate preservation and some samples presented high diversity and abundance. Preliminary results indicate that this section records the Aalenian/Bajocian boundary and yields one of the best calcareous nannofossil assemblages for this time-interval for the basin. The base of the section is characterized by Similiscutum novum, Biscutum intermedium, Bussonius prinsii, Discorhabdus striatus, D. criotus, Lotharingius sigillatus and Schizosphaerella punctulata. The presence of Podorhabdus grassei and Watznaueria contracta indicates an age not older than middle Aalenian (NJ8b biozone). Assemblages of the middle and upper part of the section are characterized by Biscutum depravatus, Similiscutum novum, Lotharingius hauffii and L. sigillatus. First occurrence of Watznaueria britannica and the presence of Carinolithus superbus constraints these levels to the Early Bajocian (NJ9 biozone). The preliminary data presented here show the high potential of calcareous nannofossil for biostratigraphic reconstructions in the Neuquén Basin. Furthermore, relative abundances of some species strongly vary across the section and might be related to environmental factors.