MIDDLE-LATE SILURIAN AND EARLY DEVONIAN CHITINOzOANS FROM THE CHACOPARANA BASIN, SALTA PROVINCE, ARGENTINA

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 deposited in an offshore shelf environment and composed of micaceous dark-gray shales with pyrrhotite intercalated with fine-grained quartzitic sandstones. Thirty-nine core samples were processed, and 11 yielded chitinozoan specimens that allowed taxonomic classification. Seven genera and 13 species were identified; four were retained in open nomenclature, and the new species Cingulochitina chacoparanaense sp. nov. is erected. Three chitinozoan assemblages were recognized: Chitinozoan assemblage I of a middle-late Silurian age, Chitinozoan assemblage II of a late Silurian age, and Chitinozoan assemblage III of a late Lochkovian (Early Devonian) age. A new upper 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 Chacoparana Basin.