The Cellon Section: a Review of the Stratotype Section for the Southern Alps (1894-2009)

Among the many geological sections located in the Central and Southern Alps the Cellon Section represents one of the most important as it serves as a reference section for the Upper Ordovician and the Silurian. There is no other profile which has beed visited so often or has attracted so many Earth scientists for basic or comparative studies. In fact, the long lasting history of research started with a mapping report of the area by Geyer (1894) which served as a basis for further studies. Geyer correlated the section with the upper Silurian in the former terminology of the 19th century. After the Great War scientistsfrom both Austria and Italy worked in the area. Of particular importance is the comprehensive study carried out by von Gaertner who focused his work on the Cellon section and introduced a formal lithostratigraphic subdivision which has partly been in use until the present. In the late 1950s Otto H. Walliser studied the conodont biostratigraphy for the Upper Ordovician, Silurian and lowermost Devonian portion of the Cellon Section.Based on more than 250 samples he collected almost 35,000 conodont elements which he assigned to 11 Silurian conodont zones. This zonation (Walliser, 1964) has served for many years as a standard for global correlation of Silurian strata. An Hirnantian conodont fauna has also now been documented (Ferretti & Schönlaub, 2001). In recent times, however, some additions and amendments from other sections have provided a more detailed zonation. Other studies on chitinozoans (Priewalder, 1997) and graptolites (Jaeger, 1975: Storch pers. comm. - presence of Glyptograptus persculptus) have added further important data so the section is now fully defined biostratigraphically using three standardarized zonations. Over the last four decades a variety of systematic palaeontologicalresearch by diverse authors has been carried out in the Cellon Section, e.g. on bivalves, brachiopods, nautiloids, graptolites, agglutinated foraminifers, ostracods, acritarchs, chitinozoans, trilobites and most recently even corals. Detailed studies have been done of the microfacies and faunal taphonomy in addition to studies of the sedimentology, geochemistry and application of C and O isotope analysis methods for the whole section.More recently, bentonite-bearing horizons in the Late Ordovician, upper Llandovery and Wenlock have been correlated with coeval occurrences in other parts of Europe. The ash layers originated from a subduction-related volcanism of an active plate margin and was dominated by calcalcalic mafic lavas of a volcanic arc setting with andesitic-rhyodacitic/dacitic magmatism, data of important significance with relation to geodynamics andpalaeogeographical reconstructions of the Peri-Gondwanan terranes (Histon et al., 2007).Finally, sequence stratigraphic methods were applied to the Silurian part of the Cellon Section by a team headed by Carl Brett which highlighted eustatic changes which may be traced across four palaeocontinents (Brett et al., in press).Present and Future - A valuable multidisciplinary data set is now available with regard to the Cellon Section which may be used for subdivision, to discriminate minute timelapses and to recognize short or long-lasting events in Earth’s history which occursimultaneously in other parts of the world. A short overview of the research done to date and present/future projects regarding faunal response to eustatic changes will be presented so as to highlight the still outstanding importance of this standard section.REFERENCESBRETT C.E., FERRETTI A., HISTON K. & SCHÖNLAUB H.P. (in press). Silurian sequence stratigraphy of the Carnic Alps (Austria). Palaeogeography, Palaeoclimatology, Palaeoecology.FERRETTI A. & SCHÖNLAUB H.P. (2001). New conodont faunas from the Late Ordovician of the Central Carnic Alps, Austria. Bollettino della Società Paleontologica Italiana, 40: 3-15.HISTON K., KLEIN P., SCHÖNLAUB H.P. & HUFF W.D. (2007). Lower Paleozoic K-bentonites from the Carnic Alps, Austria. Austrian Journal of Earth Sciences, 100: 26-42.JAEGER H. (1975). Die Graptolithenführung im Silur/Devon des Cellon-Profils (Karnische Alpen). Carinthia II, 165 (85): 111-126.PRIEWALDER H. (1997). The distribution of the chitinozoans in the Cellon section (Hirnantian – lower Lochkovian)- A preliminary report. Berichte der Geologischen Bundesanstalt, 40: 74-85.WALLISER O.H. (1964). Conodonten des Silurs. Abhandlungen des Hessischen Landesamtes für Bodenforschung, 41: 1-106.