Insights into the biostratigraphy of the Silurian–Devonian transition in Southwestern Gondwana, based on a new graptolite record from Argentina

Abstract

The Silurian–Devonian transition witnessed not a single mass faunal turnover but minor extinctions and recovery intervals. Planktonic graptolites experienced a reduction in diversity before their extinction in the Early Devonian. Due to the scarce fossil record from high-latitude cold waters, these interpretations have been primarily based upon the best known low-latitude faunas. The graptolite herein presented is the first record of latest Silurian to possibly Devonian age from high southern paleolatitudes of Gondwana. A new fossil locality of the Argentine Precordillera yielded Slovinograptus? microdon curvatus, previously found only in the Canadian Arctic. This is the youngest Silurian graptolite record in south-western Gondwana, constituting a useful global biostratigraphic marker. The fossil-bearing strata can, at least partially, be correlated with the latest Silurian Uncinatograptus birchensis Zone, and can be referred to the latest Pridolian in accordance with evidence from the co-occurring brachiopod assemblage, as well as from conodont data from equivalent stratigraphic sections. Furthermore, the brachiopod faunal turnover recorded in the studied stratigraphic section potentially correlates with the Transgrediens Extinction Event, a biotic crisis not older than latest Pridolian. Evidence suggests that the brachiopod (and probably the trilobite) turnover and the concomitant biogeographic reconfiguration of provincialism of Gondwanan benthic faunas around the Silurian–Devonian boundary might be related to the aftermath of the Transgrediens Event.