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

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

Salvador

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

International Federation of Palynological Societies, International Organisation of Palaeobotany, Asociación Latinoamericana de Palaeobotánica y Palinología

Lower and Upper Ordovician sedimentary rocks crop out inthe Caspalá area, Sierra de Zenta (Jujuy Province), on the eastern margin ofthe Cordillera Oriental. Even though the Lower Ordovician stratigraphic unitshave not been well defined in the area so far, they are considered asequivalent to the Santa Victoria Group. This group comprises the Santa Rositaand Acoite formations of late Cambrian-Tremadocian and Floian ages,respectively. The group reaches more than 3000 m of thickness in the Sierra deZenta and is composed of alternating sandy and shaly packages indicating progradingcoastal system successions. The Lower Ordovician marine deposits areinterpreted as wave-dominated delta lobes with intervals of subaerial exposure.The overlying glacial deposits of the Caspalá Formation (Katian?-Hirnantian) presentan erosive contact with the Lower Ordovician Acoite Formation. Eighteen samplesfrom a section that spans the Tremadocian - Floian boundary, in the Caspaláarea, were taken for palynological analysis and fourteen of them proved productive.The studied samples yield organic-walled phytoplankton and chitinozoans. Theorganic-walled phytoplankton assemblages are low in diversity and abundance andmoderately to badly preserved. Levels of the Santa Rosita Formation in thisarea are considered 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 in the same level of Eremochitinabrevis, which is typically associated with Lagenochitina sp. A, and is the index species of the late middleFloian in North Gondwana. These new data contribute to the better knowledge ofthe biostratigraphically relevant messaoudensis-trifidumassemblage in western Gondwana.