INSTITUTO ARGENTINO DE NIVOLOGIA, GLACIOLOGIA Y CIENCIAS AMBIENTALES
Unidad Ejecutora - UE
New palynological data from the Upper Ordovician of the Precordillera Basin, Argentina: 1 A potential key for understanding the geological history of the Precordillera terrain
DE LA PUENTE, G. SUSANA; RUBINSTEIN, CLAUDIA V.
Lugar: New York; Año: 2013 vol. 10 p. 229 - 248
Biostratigraphic data from the Precordillera Basin have traditionally been analyzed to contribute to the understanding of its biogeographic evolution as an allochthonous microcontinent accreted to the western Gondwanan margin in the Middle-Late Ordovician. The first palynological data from Late Ordovician units of the eastern Precordillera are incorporated in an attempt to better constrain the timing of the collision. The Las Vacas Formation has previously been assigned to the Sandbian (gracilis-bicornis Zones). Chitinozoans from the Las Vacas Formation are numerous, although poorly diversified. The assemblages from its upper part contain primarily Spinachitina oulebsiri, Cyathochitina sp. aff. macastyensis, and Desmochitina minor form typica. The lower-upper part of this formation also yields Ordochitina sp. cf. nevadensis. The basal Las Vacas Formation contains Lagenochitina sp. cf. baltica. Acritarchs are poorly preserved and the few recognized genera are not biostratigraphically significant. Cryptospore findings contribute to the record of evidences for land plants in the Ordovician of Argentina and suggest that the upper part of the unit was deposited proximal to the shoreline. The lower part of the Trapiche Formation contains a few poorly preserved chitinozoans, acritarchs and algae (cf. Gloeocapsomorpha sp.), probably due to reworking of the material. The basal chitinozoan assemblage could indicate that the deposition of the Las Vacas Formation started during the Darriwillian. Typical Gondwanan Katian-Hirnantian chitinozoans from the uppermost part of the Las Vacas Formation indicate that these deposits would have reached the Hirnantian. Palynological studies seem to be a useful tool to constrain the geological history of controversial microplates, such as the Precordillera terrain.