Palynological record and associated faunas of Serpukhovian-Bashkirian sequences (El Paso and Majaditas formations) from the Barreal área, San Juan province, Argentina

MARÍA DEL MILAGRO VERGEL; GABRIELA A. CISTERNA; ANDREA F. STERREN

Salvador

Congreso; XIV International Palynological Congress X Internationanl Organisation of Palaeobotany Conference; 2016

The Gondwanic glaciations of the Late Paleozoic were one of the most important paleoclimatic events in the earth history. As a consequence of the glacial conditions, with glacial and interglacial periods, the sedimentation of the Gondwanic basins was affected with the deposition of different sedimentary facies. The Argentine Precordillera can be considered a classical study área where the glaciation was clearly recorded with different facies in particular paleoenvironments. At the Barreal área, San Juan province, the typical glacial deposits appear discontinued in an irregular pattern along western margin of the Tontal Hill. Their Carboniferous stratigraphic units, interpreted as product of advancing and retreating of the ice masses in dominant glaciomarine scenery, have been mainly dated through of their marine faunas.However, there are still some difficulties regarding the precise age of some stratigraphic units, such as the El Paso Formation and correlatives as the Majaditas Formation. This controversial interpretation isdue to the determination at sequences of the El Paso Formation of different brachiopod assemblages: the Rugosochonetes-Bulahdelia biozone assigned to Late Visean-Early Namurian, placed below the base of the Levipustula levis Biozone (Serpukhovian-Bashkirian), and the Aseptella-Tuberculatella and Rhipidomella-Micraphelia associations that indicated a younger Carboniferous age. In this context, the recently known palynological content from the El Paso Formation, with the significant register of monosaccate pollengrains and diagnostic spores, allowed to propose a late Serpukhovian-Bashkirian age to the El Paso Formation, and a correlation with the Subzone A of the Raistrickia densa-Convolutispora muriornata (DM) Biozone from Western Argentina. This biozone have been assigned to the Serpukhovian-early Bashkirian(confirmed by radiometric age), concordant with the age of the Levipustula fauna that characterizes the glacial interval of marine facies of the Hoyada Verde Formation (also from the Barreal área and equivalent to El Paso Formation). Likewise, the palynological record of the middle part of the Majaditas Formationwith the following taxa: Granulatisporites parvus, Dibolisporites disfacies, Reticulatisporites passaspectus, Verrucosisporites chiqueritensis, Convolutispora muriornata, Raistrickia densa, R. rotunda, Apiculatisporitesvariornatus, Ahrensisporites cristatus, Cristatisporites rolleri, C. stellatus,Indotriradites volkheimeri,Psomospora detecta, Circumplicatipollis plicatus, Cannanoropolis janakii, Plicatipollenites sp., Crucisaccites monoletus, Potonieisporites sp., among others, also allows to suggest a correlation with the Subzone A of the DM Biozone. In both assemblages is recorded microplancton. The differences between the microflores are the better preservation and diversification in the Majaditas assemblage that could be due to a different depositional environment, or a paleoclimatic improvement of a slightly younger microflore.