The first recorded decline of the Malvinokaffric Devonian fauna in the Paraná Basin (southern Brazil) and its cause; taphonomic and fossil evidences

Abstract

Abstract The first recorded decline of the Malvinokaffric Devonian fauna in the Parana Basin, south Brazil, occurred between early and early late Emsian. The event is recognized on biostratigraphic implications, and it coincides with a regional hiatus resulting from tectonic activity during a Precordilleran epeirogeny. The Emsian beds, dated with palynomorphs, indicate a late Pragian - early Emsian (PoW Su spore Zone) age below, and an early late Emsian (upper FD – lower AP spore Zones) age above the hiatus. The extinctions that occurred between the late Pragian – early Emsian regression, and the initial transgression in the early late Emsian, were extensive and more dramatic than elsewhere on the globe. In the Parana Basin invertebrates 4 classes, 25 families, 41 genera, and 54 species become extinct. The Emsian sedimentation in the Parana Basin was realized under constant oscillation of sea level punctuated by storm events, probably due to Milankovitch orbital cycles. It is known that the eccentricity cycles are the most striking in regions at higher latitudes, which was the case of the ParanaBasin during the Emsian. This was, however, not a factor of major importance for the large decline of the fauna. The decline of the shelly fauna was an effect of the late Pragian – early Emsian regression, and the early late Emsian transgression introduced a reduced and less provincial shelly fauna.