Palynostratigraphical characterization of the OAE1b and OAE1c in the Umbria-Marche Basin (Northern Apennines, Italy)

The Early Cretaceous of Umbria-Marche Basin is marked by 3 Oceanic Anoxic Events (OAEs) belonging to the Marne a Fucoidi Formation (early Aptian-late Albian). This formation consists of multicolor marlstones and marly limestones, interbedded by organic-rich black shale levels. Anoxic events are associated with the widespread deposition of dark-colored, laminated, organic-carbon-rich shales due to the development of dysoxic to anoxic condition at the sea bottom. These events may be on a global scale such as the early Aptian OAE1a, or on a regional scale such as the late Aptian-early Albian OAE1b and the late Albian OAE1c. In the present study was analyzed the microfloristic content, from Fiume Bosso, Roccaccia and Bottaccione sections, for the first time and from Poggio le Guaine section. The Bottaccione section became worldwide famous for the detected presence of Cretaceous-Paleogene boundary and the GSSP for the base of the Campanian stage. After undergoing standard palynological treatment, it has been mounted a total number of 175 slides from 39 samples. The OAE1b palynological assemblage is characterized by the occurrence of sporomorphs, such as Cyathidites spp. and Afropollis spp., and dinocysts, such as Florentinia mantellii and Spiniferites spp. The overlaying OAE1c consists of sporomorphs, such as Cicatricosisporites spp. and Callialasporites trilobatus and dinocysts, such as Litosphaeridium conispinum and L. siphoniphorum. These assemblages show close similarities with other areas of the Tethyan domain such as France and northern Egypt. The key species L. conispinum was recorded in all studied sections. Its first occurrence marks the late Albian in the Tethyan domain and allows to refer the black shale levels in which it was recorded to the OAE1c. The occurrence of Elaterosporites klaszii and Elaterosporites verrucatus, which are typical of the Albian to Cenomanian Elaterates Province, was also recorded in this study, in association with L. conispinum and L. siphoniphorum in the Fiume Bosso section, and just below the first occurrence of L. conispinum in the Bottaccione section.