Integrated biostratigraphy of the Agrio Formation in its type locality, Early Cretaceous of the Neuquén Basin

The Lower Cretaceous of the Neuquén Basin represents one of the most complete series in the Andes of South America. Highly fossiliferous exposures make correlation easy among different localities and allow to perform detailed studies of the fossil content. This paper presents, for the first time, an integrated biostratigraphic zonation for the Agrio Formation in its type section, based on ammonoids, bivalves, nannofossils and palynomorphs. A detailed section from base to top of the Agrio Formation was measured in the Bajada del Agrio region near the junction of Salado and Agrio Rivers in Central Neuquén. Our focus centred on the two marine members. In the field 39 ammonoid levels were identified and 74 samples of black and grey shales were collected to search calcareous nannofossils and palynomorphs. In addition, 41 Steinmanella Crickmay bearing levels and four levels containing Neocomiceramus curacoensis (Weaver) were identified. Four ammonoids zones, eight ammonoids subzones and two bivalve zones were recognized in the Pilmatué Member encompassing the late Valanginian to the early Hauterivian. Four ammonoids zones and two bivalve zones were recognized in the Agua de la Mula Member encompassing the late Hauterivian and reaching the basal Barremian. Another bivalve zone was identified in the Spitidiscus riccardii Zone, but left undefined due to unsolved taxonomy. The analyzed fossil groups have mainly tethyan affinities. Correlations to the European standard zonations are possible due to the presence of some index ammonoids, but also due to some nannofossil bioevents. Palynomorphs resulted not very useful in biostratigraphy. Continental palynomorphs have affinities to Gondwana while marine palynomorphs have clear tethyan affinities. Bivalves have proved locally useful in biostratigraphy, but index species are endemic to the basin and thus difficult to correlate to other regions or continents.Fil:Lazo, D.G. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Concheyro, G.A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Ottone, E.G. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Aguirre-Urreta, B. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Nuevos registros palinológicos en los depósitos glacimarinos de la formación el paso (Serpukhoviano tardío-Bashkiriano), Precordillera Argentina: implicancias bioestratigráficas.

Se presenta nueva información palinológica para la Formación El Paso. Esta unidad aflora en el sector austral de la Sierra de Barreal, provincia de San Juan, Argentina (Cuenca Calingasta-Uspallata), y las asociaciones palinológicas se recuperaron de la parte media a superior de la sección. Contiene abundantes esporas trilete (75–907%) e hilate (1–57%), asignadas a Cyclogranisporites rinconadensis, Apiculatisporis variornatus, Raistrickia rotunda, Tricidarisporites gutii, Ahrensisporites sp. cf. A. cristatus, Cristatisporites stellatus, Indotriradites volkheimeri, Vallatisporites ciliaris y Psomospora detecta, entre otros. También, granos de polen subordinados (1,5–20%): Circumplicatipollis plicatus, Costatascyclus crenatus, Plicatipollenites sp. cf. P. malabarensis, Potonieisporites spp., Divarisaccus sp. cf. D. stringoplicatus. Acritarcos retrabajados y autóctonos (e.g., Cymatyogalea sp., Gorgonisphaeridium sp., Verhyachium sp.) y algas Zygnematalean (Tetraporina sp., Brazilea scisa) estan presentes con menos de 2,57%. Se propone una edad serpukhoviana tardía-bashkiriana y la correlación con la Subzona A de la Biozona Raistrickia densa-Convolutlspora muriornata (DM) para las asociaciones de la Formación El Paso.New palynological information from the El Paso Formation cropping out at the southern Sierra de Barreal (Calingasta-Uspallata Basin), San Juan Province, Argentina is presented. The palynologic assemblages were recovered from the middle to upper part of the section. Abundant trilete (75–90%) and hilate (1–57%) spore species are recognized: Cyclogranisporites rinconadensis, Apiculatisporis variornatus, Raistrickia rotunda, Tricidarisporites gutii, Ahrensisporites sp. cf. A. cristatus, Cristatisporites stellatus, Indotriradites volkheimeri, Vallatisporites ciliaris and Psomospora detecta, among others. Also, subordinate pollen grains (1.5–207%): Circumplicatipollis plicatus, Costatascyclus crenatus, Plicatipollenites sp. cf. P. malabarensis, Potonieisporites spp. and Divarisaccus sp. cf. D. stringoplicatus. Recycled and autochthonous acritarchs (e.g., Cymatiogalea sp., Gorgonisphaeridium sp., Verhyachium sp.) and Zygnematalean algae (Tetraporina sp., Brazilea scisa) with less of 2.57% are also present. We propose a late Serpukhovian-Bashkirian age, and a correlation with the Subzone A of the Raistrickia densa-Convolutispora muriornata (DM) Biozone to the El Paso assemblages.Fil: Vergel, Maria del Milagro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Correlación Geológica. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Departamento de Geología. Cátedra Geología Estructural. Instituto Superior de Correlación Geológica; ArgentinaFil: Cisterna, Gabriela Adriana. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de La Rioja; ArgentinaFil: Sterren, Andrea Fabiana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones Paleobiológicas; Argentin