Latest Ordovician-earliest Silurian chitinozoans from the Puna region, north-western Argentina (Western Gondwana)

Abstract

Late Ordovician–early Silurian chitinozoans from the Upper Member of the Salar del Rincón Formation of northwestern Argentina are described. The study area belongs to the Central Andean Basin situated on the western Gondwana margin during the Early Palaeozoic. Chitinozoan assemblages correlate with those from Northern Gondwana, where the effects of the glacial and postglacial events that occurred around the Ordovician–Silurian boundary, are quite well-documented. The recovered chitinozoan associations from the upper part of the Salar del Rincón Formation record the uppermost Ordovician–lowest Silurian deposits representing the postglacial stage of the late Hirnantian glaciation. Similar strata are usually absent in other parts of the Central Andean Basin. Tasmanites tzadiaensis is recovered for the first time outside of the northeast of Africa, supporting the northern Gondwana affinities. Associated land-derived components indicate a nearshore environment with terrestrial input. The other associated palynomorphs support the latest Hirnantian–earliest Rhuddanian postglacial stage correlation, as well. The ranges of several Late Ordovician– early Silurian Spinachitina and Cyathochitina species are discussed in terms of the Ordovician–Silurian boundary. Five new species are formally described: Spinachitina titae sp. nov., Cyathochitina brussai sp. nov., Cyathochitina lariensis sp. nov., Cyathochitina punaensis sp. nov. and Ramochitina deynouxi sp. nov.