The Monte del Casino section (Northern Apennines, Italy): a potential Tortonian/Messinian boundary stratotype?

Abstract

Results are presented from a high-resolution integrated stratigraphic study of the Monte del Casino section, which is considered as a candidate boundary stratotype section for the Tortonian/Messinian (T/M) boundary. The section yields a good to excellent cyclostratigraphy. tephrastratigraphy and planktonic foraminiferal and nannofossil biostratigraphy. It can be correlated in detail to other Mediterranean sections using cyclostratigraphic patterns in combination with the planktonic foraminiferal biostratigraphy. These correlations indicate that the succession of the Monte del Casino composite section is continuous in the T/M boundary interval and that all sedimentary cycles, volcanic ash layers and bio-events can be accurately dated by tuning the sedimentary cycles to astronomical target curves. The quality of the paleomagnetic signal varies considerably throughout the section. A reliable magnetostratigraphy cannot be established for the T/M boundary interval because of a secondary magnetisation carried by iron sulphides. Cyclostratigraphic correlations indicate that discrepancies exist between the position of the reversals recorded here and those found in earlier magnetostratigraphic studies. Comparison of 40Ar/39Ar ages of ash layers with their astronomical ages, show that biotite ages give a good approximation of the age of the section, but are not suitable for high-resolution chronology. Despite these short-comings the Monte del Casino section remains a candidate to define the T/M boundary, but its qualities should be critically weighted against those of other sections.