Darriwilian (Middle Ordovician) conodont biofacies from the Central Precordillera of Argentina

• Published in: Marine micropaleontology Vol. 130; pp. 15 - 28
• Main Authors: Serra, Fernanda, Feltes, Nicolás A., Henderson, Miles A., Albanesi, Guillermo L.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.01.2017
• Subjects: Argentina; Conodont paleoecology; Middle Ordovician; Precordillera; Middle Ordovician; Argentina; Conodont paleoecology; Precordillera
• ISSN: 0377-8398; 1872-6186
• DOI: 10.1016/j.marmicro.2016.12.002

Conodont biofacies structure was recognized throughout detailed stratigraphic sampling at three localities from the Central Precordillera of Argentina; from north to south: Las Aguaditas Creek, Las Chacritas River and Cerro La Chilca sections. A total of 50 carbonate samples yielded over 9900 identified specimens, including a new conodont species, Fahraeusodus jachalensis, which is described due to its paleoecological connotations. The Yangtzeplacognathus crassus – Eoplacognathus pseudoplanus and Periodon macrodentatus zones are dominated by the ubiquitous species Periodon macrodentatus and Paroistodus horridus at the three study areas. This enables the recognition of the Periodon–Paroistodus biofacies in the Central Precordillera. Numerical cluster methodology allowed the identification of conodont sub-biofacies: the Protopanderodus–Semiacontiodus sub-biofacies in the Las Aguaditas Creek, the Protopanderodus–Parapaltodus sub-biofacies in the Las Chacritas River, the Parapaltodus sub-biofacies at the Cerro La Chilca and the Fahraeusodus–Ansella sub-biofacies in all of the study sections. These sub-biofacies present distinctive attributes, which are correlative with changes in the depositional environment. The diverse Protopanderodus–Parapaltodus sub-biofacies developed with a shallowing of the basin while the Fahraeusodus–Ansella sub-biofacies is characteristic of deep environments. Shallower water settings resulted in higher species richness, diversity, and evenness of conodont communities, the eustatic change that led to the drowning of the carbonate platform produced a shift to deeper, anoxic benthic conditions that in turn induced a change in the taxonomic composition of the fauna, and affected the diversity of the conodont communities. •The Periodon-Paroistodus biofacies is recognized spanning the Yangtzeplacognathus crassus–Eoplacognathus pseudoplanus zones in the Central Precordillera.•Modifications in the biofacies structure accompany changes in the lithofacies and depositional environments.•Fluctuations in sea level to shallower water settings lead to higher species richness, diversity, and evenness of conodonts.•Darriwilian conodont faunas were compared among diverse localities at a global scale.•A new conodont species Fahraeusodus jachalensis n. sp. Feltes and Albanesi, is defined and described.