The Jurassic-Cretaceous Boundary and the Radiolarian Biostratigraphic Research on the Bosso Valley Section, Northern Apennines (central Italy)

The Italian sections Torre de’Busi and Bosso Valley are the best GSSP candidates in the Alpine Tethys. The Maiolica Formation, which crosses the Jurassic–Cretaceous boundary (JKB), is characterized by whitish, beige to gray colored, well-bedded micritic limestones with abundant black to gray chert layers and nodules. Integrated calcareous nannofossil, calpionellid, magnetostratigraphic, and cyclostratigraphic investigations provide a reliable stratigraphic framework for the Torre de’Busi section. Calpionellid biostratigaraphic and magnetostratigraphic study was conducted in the Bosso Valley section. The Berriasian Working Group recommends to shift down the JKB to the interval between the M20n1r and the base of M19r with the primary marker being under discussion. Radiolarians are good candidates for defining the JKB because they are wide spread and can be found in both shallow and deep sedimentary facies worldwide. Totally, 49 samples in the Torre de’Busi section and 47 samples in the Bosso Valley section have been collected for radiolarian biostratigraphic study across the JKB. In the Torre de’Busi section only horizons corresponding to the lower part of M20 contain moderately preserved radiolarians. In the Bosso Valley section several horizons corresponding to the interval between the M20n1r and the base of M19r yielded moderate to well preserved radiolarians. In order to establish radiolarian biostratigraphy across the JKB, detailed study was conducted to elucidate the relationship between lithology and preservation of radiolarians in the Bosso Valley section. Well-preserved radiolarians are located inside the lime part near the chert bands or nodules. The JKB lies around the base of the Unitary Association Zone 13 and within the Pseudodictyomitra carpatica Zone. Primary results of radiolarian biostratigraphic study near the JKB are proposed. Radiolarian-bearing deep-water sequences across the JKB have been reported at ODP/IODP sites in the western Pacific and land sections in Japan, Philippines, southern Tibet, Iran, Oman and others.