Conodont biostratigraphy of the middle Darriwilian (Ordovician) in the eastern flank of the Villicum Range (Eastern Precordillera, Argentina)
DOI:
https://doi.org/10.21701/bolgeomin.125.1.004Keywords:
biostratigraphy, conodonts, Darriwilian, Ordovician, PrecordilleraAbstract
A transitional contact between the San Juan and Los Azules formations is present in the eastern flank of the Villicum Range. The very top of the San Juan is characterized by dark greenish grey to black burrowed bioclastic wackestone and tabular dark grey to black bioclastic packstone-grainstone. The Los Azules Formation is composed of black shale with levels and nodules of mudstone. A detailed study of the conodont fauna and biostratigraphy of the uppermost metre of the San Juan Formation and the lower levels of the Los Azules formation from three sections suggesting the Yangtzeplacognathus crassus Zone for these levels. The correlation between these studied sections of the Eastern Precordillera with those of the Central Precordillera allows us to suggest that the contact between San Juan Formation and the Los Azules and Las Aguaditas formations was diachronic during the Darriwilian, from the Y. crassus to the Eoplacognaths pseudoplanus zones, and we conclude that the younger tops are found in the western-central part of the Central Precordillera.
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