Bio-chronostratigraphic calibration of the Upper Carnian-Lower Norian magnetostratigraphic scale at Pizzo Mondello (Sicani Mountains, Sicily).

Pizzo Mondello section is known since 15 years because of the continuous Late Triassic pelagic record of great significance for the establishment of an integrated chronostratigraphy of the Late Triassic (Gullo et al. 1996; Muttoni et al. 2001, 2004). During the last 4 years, Pizzo Mondello section has been studied in detail to provide a new and high resolution integrated bio-chronostratigraphy for the calibration of the magnetostratigraphy and chemostratigraphy proposed by Muttoni et al. (2001, 2004), and now it is one of the GSSP candidates for the definition of the base of the Norian. The lowest 143 m of the Cherty Limestone, straddling the C/N boundary have been studied in detail. The preliminary data of the ongoing research have been presented in all the meetings of the STS from Albuquerque 2007 and here we summarize the final results. The key correlation to the standard marine Triassic Scale is provided by the ammonoids. They are relatively rare, however the available collections document the Upper Carnian Discotropites plinii and Gonionotites italicus Subzones, from meter 15 to meter 80 from the base of the section. The following 15 meters are poor in ammonoids, while higher up the lower part of the Lower Norian Guembelites jandianus Zone is documented by Dimorphites cf. n. sp.1 of Krystyn, 1980. Conodonts are very abundant and have a great potential as practical tool for global correlations. The abundance of specimens at Pizzo Mondello gave the opportunity to point out clear relationships among the five most widespread Upper Camian/Lower Norian conodont genera (Paragondolella, Carnepigondolella, Metapolygnathus, Epigondolella and Norigondolella) and to identify trends of the generic turnovers (Mazza et al. 2010). The two biomarkers so far proposed as possible marker events for the GSSP were the FAD of E. quadrata (sample FNP88A) and the FAD of M. communisti (sample NA35). However, the FAD of E. quadrata occurs within the Gonionotites italicus Subzone, while the FAD of M. communisti is on its top. Halobiids are extremely common in the Cherty Limestone and they have also a great potential for large scale correlations. Nine species of Halobia have been recognized: Halobia carnica, H. lenticularis, H. simplex, H. superba, H. cf. rugosa, H. radiata, H. austriaca, H. styriaca and H. mediterranea. The best possible marker for the base of the Norian is the first occurrence of Halobia austriaca, that is recorded in the middle of the interval between the record of the Gonionotites italicus Subzone and the Guembelites jandianus Zone. Radiolarians were found in few samples but with high diversity assemblages. In the upper Gonionotites italicus Subzone to the Guembelites jandianus Zone there is an overlap of species previously considered Late Carnian with species usually regarded as Early Norian. About 4 m above the FAD of E. quadrata, in the Gonionotites italicus Subzone, the first assemblage with Capnuchosphaera deweveri Kozur & Mostler, Capnuchosphaera tricornis De Wever, Kahlerosphaera norica Kozur & Mock and Xiphothecaella longa Kozur & Mock, usually referred to Early Norian, occurs. These integrated bio-chronostratigraphic studies lead to identify some possible GSSP marker events especially on conodonts and halobiids, which occur in the upper part of magnetozone PM 4n, within PM 4r and in the lower part of PM 5n. Possibly the most suitable magnetostratigraphic event to recognize the basal Norian is the base of magnetozone PM 5n, as already suggested by Krystyn et al. 2002 and Muttoni et al. 2004

Evaluation of bulk carbonate delta C-13 data from Triassic hemipelagites and the initial composition of carbonate mud

Bulk carbonate samples of hemipelagic limestone\u2013marl alternations from the Middle and Upper Triassic of Italy are analysed for their isotopic compositions. Middle Triassic samples are representative of the Livinallongo Formation of the Dolomites, while Upper Triassic hemipelagites were sampled in the Pignola 2 section, within the Calcari con Selce Formation of the Southern Apennines in Southern Italy. Triassic hemipelagites occur either as nodular limestones with chert nodules or as plane-bedded limestone\u2013marl alternations which are locally silicified. In the Middle Triassic Livinallongo Formation, diagenetic alteration primarily affected the stable isotopic composition of sediment surrounding carbonate nodules, whereas the latter show almost pristine compositions. Diagenesis lowered the carbon and oxygen isotope values of bulk carbonate and introduced a strong correlation between d13C and d18O values. In the Middle Triassic successions of the Dolomites, bulk carbonate of nodular limestone facies is most commonly unaltered, whereas carbonate of the plane-bedded facies is uniformly affected by diagenetic alteration. In contrast to carbonate nodules, plane-bedded facies often show compaction features. Although both types of pelagic carbonate rocks show very similar petrographic characteristics, scanning electron microscopy studies reveal that nodular limestone consists of micrite (< 5 lm in diameter), whereas samples of the plane-bedded facies are composed of calcite crystals ca 10 lm in size showing pitted, polished surfaces. These observations suggest that nodular and plane-bedded facies underwent different diagenetic pathways determined by the prevailing mineralogy of the precursor sediment, i.e. probably high-Mg calcite in the nodular facies and aragonite in the case of the plane-bedded facies. Similar to Middle Triassic nodular facies, Upper Triassic nodular limestones of the Lagonegro Basin are also characterized by uncorrelated d13C and d18O values and exhibit small, less than 5 lm size, crystals. The alternation of calcitic and aragonitic precursors in the Middle Triassic of the Dolomites is thought to mirror rapid changes in the type of carbonate production of adjacent platforms. Bioturbation and dissolution of metastable carbonate grains played a key role during early lithification of nodular limestone beds, whereby early stabilization recorded the carbon isotopic composition of sea water. The bulk carbonate d13C values of Middle and Upper Triassic hemipelagites from Italy agree with those of Tethyan low-Mg calcite shells of articulate brachiopods, confirming that Triassic hemipelagites retained the primary carbon isotopic composition of the bottom sea water. A trend of increasing d13C from the Late Anisian to the Early Carnian, partly seen in the data set presented here, is also recognized in successions from tropical palaeolatitudes elsewhere. The carbon isotopic composition of Middle and Upper Triassic nodular hemipelagic limestones can thus be used for chemostratigraphic correlation and palaeoenvironmental studies

The Carnian/Norian boundary interval at Pizzo Mondello (Sicani Mountains, Sicily) and its bearing for the definition of the GSSP of the Norian Stage

We present the magnetostratigraphy and stable isotope stratigraphy from an expanded (~430-m-thick) Upper Triassic marine limestone section at Pizzo Mondello, Sicily, and review published biostratigraphic information that can be used to de\ufb01 ne the location of the conodont Carnian-Norian and Norian-Rhaetian boundaries in this section. Pizzo Mondello offers good potential for magneto-stratigraphic correlation of marine biostrati-graphic and chemostratigraphic data with the continental Newark astrochronological polarity time scale (APTS) for development of an integrated Late Triassic time scale. The relatively stable average values of \u3b418O centered on 0\u2030 are a strong indication that the Cherty Limestone at Pizzo Mondello suffered very little diagenetic overprinting. The conodont Carnian-Norian boundary is located 12.5 m above a positive shift of \u3b413C. A statistical approach was applied to evaluate various Pizzo Mondello to Newark magnetostratigraphic correlations. Two correlation options have the highest correlation coef\ufb01cients. In option #1, the base of Pizzo Mondello correlates with the middle part of the Newark APTS, whereas in option #2, the base of Pizzo Mondello starts toward the early part of the Newark APTS. We prefer option #2 in which the Carnian-Norian boundary based on conodonts, as well as its closely associated positive \u3b413C shift, correspond to Newark magnetozone E7 at ca. 228\u2013227 Ma (adopting Newark astrochronology), implying a long Norian with a duration of ~20 m.y., and a Rhaetian of ~6 m.y. duration. These ages are in fact not inconsistent with the few high-quality radiometric dates that are available for Late Triassic time scale calibration. Based on its good exposure, accessibility, stratigraphic thickness and continuity, and multiple chronostratigraphic correlation possibilities, we propose Pizzo Mondello as global stratigraphic section and point for the base of the Norian

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 \u201cCalcari con selce\u201d, 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 \u201cCalcari con selce\u201d. 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)