4:45 PM - 5:00 PM
[MIS15-06] Radiolarian faunas around the Jurassic-Cretaceous boundary in the Bosso Valley section, central Italy
Keywords:Jurassic–Cretaceous boundary , GSSP, Radiolaria
Radiolarians are good candidates for defining the JKB because they are wide spread and can be found both shallow and deep sedimentary facies. Pelagic sequences across the JKB have been reported in ODP/IODP sites in the western Pacific and land sections in Japan, the Philippines, southern Tibet, Iran and others. Evolutionary lineages of several radiolarian taxa across the JKB are reviewed and suitable bioevents, which are approximate to the JKB, are presented. The Loopus–Pseudodictyomitra lineage can be the most important phylogeny for defining the JKB.
The Bosso Valley section in Umbria–Marche, central Italy, is one of potential candidates for GSSP of the JKB. The Maiolica Formation, which crosses the JKB, is characterized by whitish, beige to gray colored, well-bedded micritic limestones with abundant black to gray chert layers and nodules. Calpionellid stratigraphy and magnetostratigraphy have been studied sufficiently in the section. The base of the Calpionella alpina Subzone, i.e. the JKB, is placed between Beds 77 and 78. We carried out detailed field observations and careful sample collections in a 4-m interval across the JKB. Acid-etched examination of rock samples revealed that well-preserved radiolarians are recognized inside the lime part near the chert layers or nodules. Several samples of micritic limestone below and above the JKB yield well-preserved radiolarians. The result of radiolarian faunal analysis in the Bosso Valley section is presented.