A new record of the messaoudensis-trifidum acritarch assemblage (Late Tremadocian-Floian) in the Cordillera Oriental, Central Andean Basin, northwestern Argentina

RUBINSTEIN, CLAUDIA V.; SOLANO RODRÍGUEZ, CRISTIAN C.; DE LA PUENTE, G. SUSANA

Salvador

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

Asociación Latinoamericana de Paleobotánica y Palinología

Lower and Upper Ordovician sedimentary rocks crop out in the Caspaláarea, Sierra de Zenta (Jujuy Province), on the eastern margin of the CordilleraOriental. Even though the Lower Ordovician stratigraphic units have not beenwell defined in the area so far, they are considered as equivalent to the SantaVictoria Group. This group comprises the Santa Rosita and Acoite formations of lateCambrian-Tremadocian and Floian ages, respectively. The group reaches more than3000 m of thickness in the Sierra de Zenta and is composed of alternating sandyand shaly packages indicating prograding coastal system successions. The LowerOrdovician marine deposits are interpreted as wave-dominated delta lobes withintervals of subaerial exposure. The overlying glacial deposits of the CaspaláFormation (Katian?-Hirnantian) present an erosive contact with the LowerOrdovician Acoite Formation. Eighteen samples from a section that spans theTremadocian - Floian boundary, in the Caspalá area, were taken forpalynological analysis and fourteen of them proved productive. The studiedsamples yield organic-walled phytoplankton and chitinozoans. The organic-walledphytoplankton assemblages are low in diversity and abundance and moderately tobadly preserved. Levels of the Santa Rosita Formation in this area areconsidered as late Tremadocian. They contain Stelliferidium trifidum, Eisenackidiumorientalis, Polygonium spp. and Michrystridium spp. and correspond tothe Euconochitina paschaensis chitinozoanassemblage recorded in the Sierra de Zenta. In spite of the scarcity and lowpreservation of the phytoplankton, the identification of Stelliferidium trifidum,which is one of the index species of the messaoudensis-trifidumacritarch assemblage, favors the recognition of this typical peri-Gondwananassemblage in the studied area. The overlying Floian Acoite Formation yields a morediverse acritarch assemblage that corresponds to the Lagenochitina sp. A chitinozoan assemblage. It is composed of Acanthodiacrodium costatum, Arbusculidium filamentosum, Coryphidium bohemicum, Coryphidiumsp., Cymatiogalea cuvillieri, Cymatiogalea velifera, Dactylofusa velifera brevis, Eisenackidium orientalis, Stellechinatum cf. brachyscolum, Striatothecaspp., Veryhachium lairdii group, Leiofusa sp., Michrystridium spp. and Polygoniumspp. Most of these taxa were previously recorded, in different localities, fromthe messaoudensis-trifidum assemblagesand with first occurrences in the late Tremadocian.  A.filamentosum, a recognized marker of the beginning of the Floian of the messaoudensis-trifidum assemblage, first appears inthe same level of Eremochitina brevis,which is typically associated with Lagenochitinasp. A, and is the index species of the late middle Floian in North Gondwana. Thesenew data contribute to the better knowledge of the biostratigraphicallyrelevant messaoudensis-trifidumassemblage in western Gondwana.