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

STERREN, A.F.; CISTERNA, G.A.; VERGEL, M.M.

Bahia

Congreso; XIV International Palynological Congress (IPC) and the X International Organisation of Palaeobotany Conference (IOPC); 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 area where the glaciation was clearly recorded with different facies in particular paleoenvironments. At the Barreal area, 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 is due to the determination at sequences of the El Paso Formation ofdifferent brachiopod assemblages: the Rugosochonetes-Bulahdelia biozone assigned to LateVisean-Early Namurian, placed below the base of the Levipustula levis Biozone (Serpukhovian?Bashkirian), and the Aseptella-Tuberculatella and Rhipidomella-Micraphelia associations thatindicated a younger Carboniferous age. In this context, the recently known palynologicalcontent from the El Paso Formation, with the significant register of monosaccate pollen grainsand diagnostic spores, allowed to propose a late Serpukhovian?Bashkirian age to the El PasoFormation, and a correlation with the Subzone A of the Raistrickia densa-Convolutisporamuriornata (DM) Biozone from Western Argentina. This biozone have been assigned to theSerpukhovian?early Bashkirian (confirmed by radiometric age), concordant with the age of theLevipustula fauna that characterizes the glacial interval of marine facies of the Hoyada VerdeFormation (also from the Barreal area and equivalent to El Paso Formation). Likewise, thepalynological record of the middle part of the Majaditas Formation with the following taxa:Granulatisporites parvus, Dibolisporites disfacies, Reticulatisporites passaspectus, Verrucosisporites chiqueritensis, Convolutispora muriornata, Raistrickia densa, R. rotunda,Apiculatisporites variornatus, Ahrensisporites cristatus, Cristatisporites rolleri, C. stellatus, Indotriradites volkheimeri, Psomospora detecta, Circumplicatipollis plicatus, Cannanoropolisjanakii, Plicatipollenites sp., Crucisaccites monoletus, Potonieisporites sp., among others, alsoallows to suggest a correlation with the Subzone A of the DM Biozone. In both assemblages isrecorded microplancton. The differences between the microflores are the better preservation anddiversification in the Majaditas assemblage that could be due to a different depositionalenvironment, or a paleoclimatic improvement of a slightly younger microflore.