Linear morphometry and sclerochronology as paleoclimatic tools through Middle Devonian Kačák Event (Paraná Basin, Brazil)

Abstract

The Devonian was a geological period marked by many climatic, geological and biological changes on a global scale. The Kačák Event is one of them, and it was the result of anoxia generated by a major marine transgression that began in the late Eifelian and lasted through the Givetian. In the Paraná Basin, this event had already been recognized, based on the Lilliput Effect, but without any morphometric or statistical data to infer this. Thus, we applied morphometric analysis (height and width) of brachiopods from different localities in the Paraná Basin. It was possible to verify a reduction of 67,93% (height) and 70,30% (width) in the dorsal valves, 74,59% (height) and 73,96% (width) in the ventral valves of Orbiculoidea baini. In Orbiculoidea excentrica the reduction is about 62,10% (height) and 61,57% (width) in dorsal valves, and 87,80% (height) and 87,70% (width) in the ventral valves. However, relictual benthic invertebrates that surpassed the Eifelian-Givetian transition inhabited alterated paleoenvironmental conditions after the biotic crisis. The brachiopods found in the north of the basin had a growth pattern distinct from those in the south. This may be related to the stressed conditions at the edge of the basin associated with the entry of warm waters from the Parnaíba Basin.