MIDDLE – LATE SILURIAN AND EARLY DEVONIAN CHITINOZOANS FROM THE CHACOPARANÁ BASIN, SALTA PROVINCE, ARGENTINA

Abstract

The first chitinozoan assemblages from the middle - late Silurian and Early Devonian strata of the Copo Formation in the Rivadavia borehole, Salta province, Argentina, are described. The studied interval was considered as deposited in an offshore shelf environment and is composed of micaceous dark-gray shales with pyrrhotite intercalated with fine-grained quartzitic sandstones. Thirty-nine core samples were processed and eleven yielded chitinozoan specimens that allowed taxonomic classification. Seven genera and thirteen species were identified, four of them were retained in open nomenclature, and the new species Cingulochitina chacoparanaense sp. nov. is erected. Three chitinozoan assemblages were recognized: CAI of a middle - late Silurian age, CAII of a late Silurian age, and CAIII of late Lochkovian (Early Devonian) age. A new late Lochkovian chitinozoan concurrent range biozone of Cingulochitina striata and Ancyrochitina asterigis is proposed for northwestern Argentina. The chitinozoan assemblages support Gondwanan affinities from the middle Silurian to Early Devonian of the Chacoparaná Basin.