Benthic foraminiferal bioevents through the Italian geological sheet N. 377 "Trasacco" (CARG Project)

Geological mapping represents a valuable tool to understand the past settings and future evolution of the Earth system. Through the several activities involved for the final release of an official geological survey, biostratigraphy may have a pivotal role. This is true in particular when fossil-rich rock succession crops out into the studied area, and even more when shallow-water carbonate units have to be characterized and mapped in detail. The lithostratigraphy of the Mesozoic and Cenozoic units of carbonate platform is, usually, intimately related with the fossil content, benthic foraminifera among others, and to the relative stratigraphic extension for each taxon or assemblages. We present an example coming from the succession cropping out into the Apennines (Central Italy), included into the geological sheet n. 377 "Trasacco" (CARG Project), that has been characterized by applying a micropaleontological analysis based on benthic foraminifera and algae. Even not completely calibrated against the chronostratigraphic scale, the shallow-water zones here used help to define the relative position of taxa through time, supporting the characterization of the lithostratigraphic units and the recognition of stratigraphic gaps. The observation of foraminifera by hand lens has first permitted to establish some unit boundaries in the field, whereas refined biostratigraphy by using thin sections helped to solve problems at the mesoscale. The shallow-water succession encompasses great part of the Jurassic and Cretaceous with 'Bahamian-type' facies, overlain by Lower Miocene succession made of heterozoan carbonates. This has helped to broadly resume the bioevents recorded through the platform, especially during the Mesozoic. Through the Lower Jurassic only oligotypic foraminiferal associations developed, constrained by the environmental conditions of supratidal and near-emersion settings. The Middle to Upper Jurassic succession records a recovery of larger foraminiferal species included into the family Pfenderinidae, among others. Through the Lower Cretaceous some larger agglutinated and porcelaneous foraminifera typify the benthic association, among representative of the genera Akcaya, Mesorbitolina, Praechrysalidina, Cribellopsis and Archaeoalveolina, associated with green algae and the bivalve Chondrodonta. The Cenomanian records high diversity with Cisalveolina, Sellialveolina, Rotorbinella, several soritids and nezzazatids, among others, which underwent mostly extinguished soon after at the Cenomanian-Turonian boundary (related to the Oceanic Anoxic Event 2). The following Upper Cretaceous succession records a post OAE2 diversification of several groups of larger benthic foraminifera such as the lamellar perforated rotaloideans whose evolution started by small representatives that likely survived to the Cenomanian-Turonian boundary extinction. The Lower Miocene benthic coenosis was inhabited by the foraminiferal genera Neorotalia,