Overview of the Montalbano Jonico area and section: a proposal for a boundary stratotype for the lower-middle Pleistocene, Southern Italy Foredeep

摘要

In the southernmost part of the Southern Apennine Foredeep crops out a well-exposed and continuous succession, about 500 m thick, of muds and muddy silts and several interbedded volcaniclastic layers. On the basis of nannofossil biostratigraphy it ranges from "large" Gephyrocapsa to Pseudoemiliania lacunosa Zones that indicate the upper part of the Lower Pleistocene and the lower part of the Middle Pleistocene. The vertical distribution of both invertebrate fossil assemblages and teleostean otoliths points out changes in the primary environmental parameters, particularly bathymetry, sedimentation rate and oxygen concentration. The observations allowed the reconstruction of several deepening-shallowing cycles within a general regressive framework. The Montalbano Jonico composite section is likely to represent a regressive portion of a third-order cycle in which relevant tectonic pulses should be the main reason for the general shallowing, possibly related to the beginning of the filling-up phase of the southern part of the Apennines Foredeep. The two recognized fourth-order cycles could be related to tectonoeustatic causes. The higher-frequency cyclicity, represented by several fifth-order cycles, seems to be mainly connected with astronomical relationships. The Montalbano Jonico section could be suitable for defining the Lower/Middle Pleistocene boundary stratotype: the potential GSSP could be located close to the "small" Gephyrocapsa /P. lacunosa zonal boundary, near a biohorizon rich in Delectopecten vitreus, a muddy dark-grey sapropelitic layer rich in Chondrites ichsp. and in oxygen isotopic stage 25. Another potential location of the GSSP of Middle Pleistocene could be near the volcaniclastic horizon V4, close to the isotopic stage 19 boundary.