Preliminary chitiozoans results from the Silurian and Devonian of the Chacoparaná Basin, Salta Province, Argentina

CAMINA, SONIA CLARA; RUBINSTEIN, CLAUDIA VIVIANA; LOVECCHIO, JUAN PABLO

Buenos Aires

Exposición; XII Congreso de la Asociación Paleontológica Argentina; 2021

Asociación Paleontológica Argentina

The first chitinozoan study results from core samples of the Rivadavia well, drilled in the Chacoparaná Basin, Salta Province, are herein presented (Repository: IANIGLA, CCT CONICET Mendoza). The recorded microfauna comes from the lowermost and the upper part of the upper Wenlockian–upper Lochkovian Copo Formation. This interval is composed of micaceous dark-gray shales with pyrrhotite intercalated with fine-grained quartzitic sandstones, probably corresponding to an offshore platform environment. Two well-preserved chitinozoan assemblages were recognized at 3176 and 3408 m of measured depth. The deepest one, located just above the top of the Hirnantian Zapla Formation, yielded genera such as Angochitina, Cingulochitina, Conochitina and Desmochitina, from which Cingulochitina has not been recorded in strata older than Silurian. Therefore, this assemblage points to a maximum Silurian age for the bearing strata. These strata of the Copo Formation represent the postglacial transgression, as do the Lipeón Formation from the Sierras Subandinas and the Cordillera Oriental, in Argentina, and the Kirusillas Formation from the southern Subandean zone of Bolivia. The upper assemblage additionally includes the genera Ancyrochitina and Fungochitina. The recognition of the species Cingulochitina striata and Ancyrochitina asterigis in the upper part of the Copo Formation, undoubtedly indicates a Lochkovian age. The chitinozoan assemblages of the Copo Formation, in the Rivadavia well, allows us to confirm the age interpreted for the unit. The finding of chitinozoans close to the boundary between the Zapla and Copo formations could locally extend the age of the latter, nowadays considered as upper Wenlock, to the Llandovery.