Conodont biostratigraphy and correlation of the San Juan Formation at the Cerro La Silla section, middle Tremadocian-lower Dapingian, Central Precordillera, Argentina.

ALBANESI G. L.; MANGO M. J.

ANDEAN GEOLOGY

SERVICIO NACIONAL GEOLOGIA MINERVA

Lugar: Santiago de Chile; Año: 2020 vol. 47 p. 577 - 598

0718-7092

This study deals with the conodont biostratigraphy from the uppermost part of La Silla Formation (9.6 m)and the overlying San Juan Formation (264.7 m), at the Cerro La Silla section, Central Precordillera of San Juan,Argentina. The 41 samples of carbonate rocks that were digested for microfossils yielded 11,388 conodont elementscorresponding to 78 species. The Paltodus deltifer deltifer Subzone of the Paltodus deltifer Zone from the Balticbiostratigraphic scheme is represented at the top stratum of the La Silla Formation and the basal part of the San JuanFormation (28.4 m), which correlates with the Macerodus dianae Zone (middle Tremadocian) of the Precordilleran andNorth American schemes. Following upwards, the Paroistodus proteus, Prioniodus elegans, Oepikodus evae, Oepikodusintermedius and Baltoniodus triangularis-Tripodus laevis zones (middle Tremadocian-lower Dapingian) are recordedin the San Juan Formation. The Baltoniodus triangularis-Tripodus laevis Zone is recognized from the second reeflevel (177.3 m from the base of the San Juan Formation) up to the top stratum in the section, in contrast to previousinterpretations that assigned the referred interval to the Baltoniodus navis, Paroistodus originalis and Microzarkodinaparva zones of the Baltic biostratigraphic scheme. The division of the Oepikodus evae Zone in subzones, according toits original definition for the Precordillera, is not applicable at the Cerro La Silla section due to the particular speciesdistribution. The conodont elements show a brown alteration color (CAI 2-2.5), which indicates a burial paleotemperatureof 60-155°C for the bearer strata.