Conodont stratigraphy and biodiversity of the Middle Devonian Kačàk Episode in the Pic de Bissous (Montagne Noire, S-France)

Abstract

Pic de Bissous belongs to classic sections of the latest Eifelian Kačàk Episode (KE) interval, uniquely developed in hemipelagic carbonate facies. The present conodont study is based on dense sampling of the section, yielding rich and diverse assemblages dominated by Polygnathus. The position of the lower and upper KE boundaries is here documented within the late Eifelian kockelianus Zone and at the base of the lowermost Givetian hemiansatus Zone, respectively. Both boundaries are marked by an increase of P1 elements diversity, the phenomenon reported also from other palaeogeographic setting, and accompanied by an appearance of several new taxa. This suggests a global two-step conodont biodiversity rise around the KE interval, presumably caused by the eustatic If and earliest Givetian sealevel rise, respectively. These events were accompanied by increased juvenile conodont mortality probably due to some local/regional adverse conditions of either abiotic or biotic nature.