Environmental change during the Late Famennian and Early Tournaisian (Late Devonian–Early Carboniferous): implications from stable isotopes and conodont biofacies in southern Europe

Abstract

A biostratigraphic correlation of the Devonian/Carboniferous (D/C) boundary sections from the Carnic Alps, the Graz Palaeozoic, the Montagne Noire and the Pyrenees resulted in a high-resolution record of the carbon isotopic composition of micrites (d 13 C carb ), of sedimentary organic matter (d 13 C org ) and of oxygen isotope ratios of conodont apatite (d 18 O phosph ). The studies focused on the interval between the Upper postera Zone (Late Famennian) and the sandbergi Zone (Lower Tournaisian). For the first time, weak but significant positive carbon isotope excursions in micrites and in the sedimentary organic matter is reported from the Middle and Upper expansa zones of the Carnic Alps. They coincide with a decrease in the oxygen isotope values of conodont apatite. The excursions indicate changes in the global carbon cycle during an episode of high seawater temperatures, and correlate with sedimentary change and a stepwise eustatic rise in the Rhenish Massif. High carbon isotope values were also measured in limestones from the Graz Palaeozoic in the Upper praesulcata Zone, which were previously reported from the Rhenish Massif, Carnic Alps, Montagne Noire and the North America continent. The change from a palmatolepid-polygnathid conodont biofacies to a palmatolepid-bispathodid-branmehlid biofacies in the expansa Zone in the Carnic Alps is obviously influenced by anoxic conditions and repeated transgressive phases. The protognathodids and the polygnathids start to radiate in the Upper praesulcata Zone, after the main end-Famennian extinction episode. This is connected with the disappearance of the palmatolepids, and environmental stress created by worldwide anoxic conditions, climate change and sea-level changes, stimulated the radiation of both protognathodids and the polygnathids. The regional correlation of the geochemical records as well as interpretations of these records on a global scale indicate that changes in conodont biofacies of Late Famennian-Early Tournaisian limestones were caused by a complex pattern of environmental changes.

The Devonian/Carboniferous boundary in the Holy Cross Mountains (Poland)

“…Apart from sim i lar lithologies, the dis ap pear ance and ap pear ance of var i ous fau nal groups took place in the same Other ex pla na tions as in Fig ure 2 time in ter vals in both ar eas, the lat ter usu ally in sim i lar lithological ho ri zons. Rel a tively rapid lithological changes in the De vo nian/Car bon if er ous bound ary beds as well as per tur bations in the biota from this time have been doc u mented in many re gions of the world and at trib uted to eustatic sea level changes linked with a re gres sion and trans gres sion (House, 1983(House, , 2002John son et al, 1985;Becker, 1993;Racki, 1997;Kai ser et al, 2006Kai ser et al, , 2008Devleeschouwer et al, 2013). Bi otic transfor ma tions at the De vo nian/Car bon if er ous bound ary, re flected by the ex tinc tion of many or gan isms, have been de ter mined as the Hangenberg Event (Walliser, 1984(Walliser, , 1985(Walliser, , 1996 or Hangenberg Cri sis , which marks the last ap pear ance of the goniatite Wocklumeria sphaeroides and ranges till the first ap pear ance of the spe cies Gattendorfia subinvoluta (Becker, 1993(Becker, , 1996Walliser, 1996).…”

“…The De vo nian-Car bon if er ous bound ary clearly falls in the time of new mi nor post-gla cial trans gres sion, and car bon ate sed i men ta tion in pe lagic con di tions, with ap pear ance of new fau nal as sem blages among cepha lo pods, trilobites, cono donts and entomozoacean ostracodes (Flajs and Feist, 1988;Bless et al, 1993;Becker, 1996;Kai ser et al, 2006Kai ser et al, , 2008Kai ser et al, , 2009. The youn ger, ma jor transgressive ep i sode is ac com panied by the Mid dle Tournaisian de po si tion of the Lower Alum Shale Event in the Rhenish Slate Moun tains (Becker, 1993(Becker, , 1996Walliser, 1996) and Zarêby Beds in the Holy Cross Moun tains (Fig.…”

“…Fluc tu a tions re lated to transgressive and re gres sive ep isodes in the Late De vo nian and Early Car bon if er ous, which are re flected in the cono dont biofacies pat tern (e.g., Dreesen, 1992;Walliser, 1996;Kai ser et al, 2008;Kalvoda et al, 2013), are also marked in the Kowala pro file. In this place within Middle-Up per expansa zones, cono dont as sem blages are predom i nated by the palmatolepid-bispathodus biofacies, which are linked to the basinal area and the lower part of its slope (e.g., Sandberg and Dreesen, 1984;Dreesen et al, 1986;Dreesen, 1992).…”

“…3). In other ar eas, the bispathodus and palmatolepid biofacies pre dom i nated up to the Mid dle praesulcata Zone (e.g., Clausen at al., 1989;Kai ser et al, 2008). Only in di vid ual spe cies of the ge nus Bispathodus passed into the Up per praesulcata, sulcata and duplicata zones (Luppold et al, 1984;Perret, 1988;Over, 1992;Nemirovskaya et al, 1993;Kai ser, 2005;Kalvoda et al, 2013).…”

“…3). In this pro file cono donts of the ge nus Prothognathodus oc cur in the Up per praesulcata Zone within limestones of the com plex C. The pres ence of these cono donts is con nected with the Late De vo nian trans gres sion, dur ing which adaptative ra di a tion took place (Becker, 1996;Kai ser et al, 2008). The protognathodid biofacies is as cribed to the outer shelf en vi ron ment and the basinal slope (Kalvoda et al, 1999) or to the shal lower sea en vi ron ment (Dreesen, 1992).…”