| Summary: | The GSSP (Global Boundary Stratotype Section and Point) of the Cambrian-Ordovician boundary was formally defined in 2000 in the Green Point section, western Newfoundland, Canada (Cooper, 2001) at a level coinciding with the FAD (First Appearance Datum) of Iapetognathus fluctivagus, below the appearance of planktic graptolites. Attempts to correlate the GSSP section with other areas proved to be problematic. These problems arise not only from the fact that Iapetognathus is rare in many regions, but they are mostly related to taxonomic bias, not only of the above mentioned genus, but also of other taxa spanning the Cambrian-Ordovician boundary. Main problem: taxonomy of Iapetognathus at generic and specific level. Other taxa that are, or have been used for recognition of the Cambrian-Ordovician boundary are species of the genus Cordylodus. Cordylodus is perhaps the most common and characteristic genus this interval. Cordylodus is the first euconodont genus that exhibits a complex apparatus with ramiform elements. It was very successful and its rapid diversification produced a relevant number of species that have recovered in abundance in most continents. For the taxonomy of the species of Cordylodus one of the main feature is the depth and shape of basal cavity. Among these, a species that might be helpfull to recognize the Cambrian-Ordovician boundary is Cordylodus lindstromi. Unfortunately the taxonomy of this species needs some refinements. Nicoll (XXX) provided a revision of species of Cordylodus, including C. lindstromi, and later Nicoll (XXX) introduced C. prolindstromi. Nevertheless is common to see in several papers C. lindstromi sensu lato and C. lindstromi sensu stricto. Graptolites Dayangcha has excellent potential to clarify and improve correlations, owing to its rich content in conodonts. In Dayangcha also trilobites and acritarchs are present, and in particular the first planktic graptolites currently under study by Maletz. Chemostratigraphy can also be an important tool, with a geochemical anomaly ...
|
|---|