WAS THE TAGHANIC EVENT (GIVETIAN, MIDDLE DEVONIAN) ASSOCIATED WITH A SIGNIFICANT CONODONT EXTINCTION? A PYRENEAN VIEW

The Taghanic Event was a multi-episodic event that lasted up to about 800 ky spanning from the ansatus Zone through the semialternans-latifossatus Zone (Middle Givetian). It has been recognized in many places and it is believed that major extinctions in different groups (ammonoids, corals, trilobites, brachiopods, stromatoporoids) were associated with it, leading to some authors suggesting that probably the Taghanic extinction was the greatest in the mid-Paleozoic; however, others considered the Taghanic Event (or rather, Crisis) a second order global extinction.

The sedimentological change associated with a biotic turnover or extinction has not been clearly documented. The association of the Taghanic Event with a large extinction has been assumed but not documented in detail yet. We present our data from three sections in the Spanish Pyrenees. In one of them, Villech section, a thin black layer of shale and limestone represents one of the latest phases of the Taghanic Event, already in the upper half of the semialternans-latifossatusZone.

The Pyrenean conodont record shows that only a few taxa became extinct in the upper part of the ansatus Zone, mainly Polygnathus hemiansatus, P. rhenanus, P. ensensis and Icriodus difficilis. However, the former and latter extinctions seem to be local as they have longer ranges in other regions. Within the event however, the blooming and short-living of several species of Tortodus, which disappear in the upper part of the semialternans Zone, at the end of the event, is remarkable. After the event, either in the overlying hermanni or disparilis zones many taxa that started in the Lower Givetian and survived the Taghanic Event disappear. The radiation of Schmidtognathus in the hermanniZone is also remarkable.

In brief, the Pyrenean conodont record doesn’t show a clear relation between the Taghanic Event and (an even minor) mass conodont extinction. Locally, in the Villech section where the black shale and limestone Bed 29 represents the sedimentological expression of a late phase of this event, no clear extinction is demonstrated at or close to this level.