The fossil record from Pizzo Mondello (Sicani Mountains, Sicily) Norian GSSP candidate

Pizzo Mondello (Sicani Mountains, western Sicily, Italy) is one of the best localities in the world for the definition of the Carnian/Norian (C/N) boundary. This boundary is recorded within a succession of about 400 m thick Late Carnian-Late Norian “Calcari con selce”, well known for the good primary magnetostratigraphic record and stable carbon isotope variations (Muttoni et al, 2001, 2004). This succession has become de facto the standard Tethyan marine reference for the Newark astrochronological polarity time scale (Kent et al., 1999; Muttoni et al., 2004) but it is also extremely interesting for the rich fossil record, consisting of ammonoids, conodonts, pelagic bivalves and radiolarians (Balini et al., 2008). Ammonoids are rather sparse but they provided accurate age constraints for the conodont and pelagic bivalve bioevents, that have been identified through very detailed bedby- bed samplings. Some radiolarian bearing levels also provide additional information for correlations. The collected ammonoid faunas are very similar to the rich faunas described from western Sicily by Gemmellaro in his famous monograph (1904), but the new collection is bed-by-bed sampled. The most important ammonoid taxa so far identified document very well the Upper Carnian Discotropites plinii Zone and the Lower Norian Guembelites jandianus Zone, while in between the faunas are dominated by the group of Anatomites sensu Gemmellaro and by Gonionotites. Conodont populations are very rich. The large number of specimens recovered in each sample allows statistical analyses of absolute abundances, the analysis of the different morphologies and the study of the relationships among genera and species, that are described in detail in separate contributions (Mazza et al., 2009; Rigo et al. 2009 in the present abstract volume). Currently 29 established conodont species, 5 new species and several transitional forms have been recognized. The classified species belong to 8 genera, among which the five most widespread Upper Carnian/Lower Norian genera have been recognized: Paragondolella, Carnepigondolella, Metapolygnathus, Epigondolella and Norigondolella. Conodonts are the most abundant and promising fossil group, then possibly the selection of the Norian GSSP marker event will be chosen within this taxon. Two possible bioevents for the definition of the Carnian/Norian boundary have been identified: the FAD of Epigondolella quadrata Orchard and the FAD of Metapolygnathus communisti Hayashi. The halobiids are undoubtedly the most common megafossil group recorded in the “Calcari con selce”. Some 1100 specimens coming from about 230 beds were collected. Nine halobiid species and two sub-species have been recognized, grouped in seven assemblages spanning from the Upper Carnian to the Lower Norian. Of special interest is the occurrence in the C/N boundary interval of the sequence of species Halobia areata, H. superba and H. styriaca, which is typical of the Lower Norian in the North American (Stikinoceras kerri Zone; McRoberts, pers. comm., Krystyn et al., 2002) and Thetyan successions (lower to upper G. jandianus Zone; Krystyn and Gallet, 2002). The abundance of halobiids and the great similarity of the faunas from Sicily with the faunas from North America suggest the possible selection of secondary C/N marker events within this group. An additional tool for global correlations is represented by radiolarians, which were found in some samples with high diversity assemblages. In the 30 m-thick boundary interval there is an overlap between species previously considered Late Carnian with species usually regarded as Early Norian. The first Early Norian radiolarian assemblage occurs above the FAD of E. quadrata. This fauna consists of Braginastrum curvatus Tekin, Capnuchosphaera deweveri Kozur and Mostler, Capnuchosphaera tricornis De Wever, Kahlerosphaera norica Kozur and Mock, Mostlericyrtium sitepesiforme Tekin, Podobursa akayi Tekin and Xiphothecaella longa (Kozur and Mock).