Floian chitinozoans (Lower Ordovician) from the Santa Victoria area, Cordillera Oriental, north-western Argentina. Part 2. Biostratigraphic, paleobiogeographic and paleoenvironmental implications. This is the first study of the Floian chitinozoans in the Acoite Formation exposed at Quebrada La Huerta and Quebrada Grande, Santa Victoria area, northeastern end of the Argentinian Cordillera Oriental (Salta Province). Biostratigraphic analysis of this group is calibrated with the graptolite zones Tetragraptus akzharensis, “Baltograptus deflexus” and Didymograptellus bifidus, previously established in the area and ranging from the latest early Floian to the late Floian. Chitinozoans are also calibrated with acritarchs that include some species of the messaoudensis-trifidum assemblage, among others. According to the most recent studies on chitinozoans conducted in Northwestern Argentina two biostratigraphically meaningful chitinozoan assemblages are proposed for the Santa Victoria area, i.e., Lagenochitina sp. A (early middle Floian) and Eremochitina baculata brevis? (late Floian). The latest early Floian-latest middle Floian chitinozoan assemblages reveal affinities with North Gondwana and South China whereas the late Floian chitinozoan assemblages are cosmopolitan. Distribution of the studied Early Ordovician chitinozoan assemblages suggests that the development of the active thermohaline oceanic circulation for this portion of the Western Gondwana margin—globally recorded in the Middle Ordovician—occurred earlier than in other regions. Chitinozoans also reveal paleoenvironmental differeces between the eastern and central outcrop belts in the Central Andean Basin, Northwestern Argentina.
Vol. 47 • No. 3
Vol. 47 • No. 3