Early Devonian organic-walled phytoplankton and miospores from the Precordillera Basin of San Juan, Argentina: biostratigraphic and paleobiogeographic implications

RUBINSTEIN, CLAUDIA V.; RUSTÁN, J.J.; GARCÍA MURO, V.J.,

PALYNOLOGY

AMER ASSOC STRATIGRAPHIC PALYNOLOGISTS FOUNDATION

Año: 2017 vol. 41 p. 138 - 157

0191-6122

Thepalynological assemblages of the Talacasto Formation and the lower part of thePunta Negra Formation, located along the Argentinean Central Precordillera,were analyzed. Marine phytoplankton is dominant in both stratigraphic units. Cordobesia sp. cf. C. oriental, ?Cymatiosphaeraflorida, Evittia sommeri, Palacanthusledanoisii, Polyedryxium sp. cf. P. decorum, Riculasphaera fissa, Schizocystiapilosa, Tysanoprobolus polykionand Winwaloeusia distracta are amongthe most age significant phytoplankton species of the Talacasto Formation, atthe Cerro La Chilca section, while Amicosporitessp. cf. A. streelii, Dictyotriletes emsiensis Morphon, Dictyotriletes favosus and ?Knoxisporitesriondae prove the most biostratigraphically significant miospore species. ALochkovian to Pragian (probably late Pragian) age is interpreted based on themarine and terrestrial palynomorphs recovered. Given that the inferred age forthe Talacasto Formation based on palynomorph evidence has discrepancies withthe age based on faunas, further studies are necessary to establish a moreaccurate biostratigraphic scheme. The lower part of the Punta Negra Formation,in the Talacasto Creek section, contains phytoplankton species such as Cordobesia oriental, Cordobesia uruguayensis, Duvernaysphaera stellata, Estiastra sp. cf. E. rhytidoa, Navifusa bacilla, Polyedryxium fragosulum, Pterospermellasp.cf. P. pernambucensis as well as the miospores Acinosporites sp. cf. A. lindlarensis and Apiculatasporites microconus, which suggest an early Emsian age forthis part of the unit. This palynological age interpretation agrees with theage based on faunas. The diachronism of the boundary between both formationsthroughout the basin is supported by the palynological data. Typical Gondwanantaxa, such as Cordobesia, Schizocystia and Winwaloeusia, were recognized and the affinities of the ArgentineanDevonian palynomorphs with this paleocontinent are therefore confirmed.