New data on the biostratigraphy of the Tuscan Cherts at Monte Cetona (Southern Tuscany, Italy)

Abstract

This note presents datings of radiolarian faunas from the Tuscan Cherts, outcropping on the southeastern slope of Monte Cetona, with a thickness (tectonically disturbed) of 24 m. The sequence is overturned and the Tuscan Cherts lie geometrically below the older “Marne a Posidonia” and above the younger “Scisti Policromi”. The stratigraphically lowest samples yielding well-preserved radiolaria were taken 920 and 1220 cm above the bottom of the formation, the highest 220 cm below its top. The lowermost sample (920 cm above the bottom, 1400 cm below the top) has a Lower Callovian to Lower Kimmeridgian age and the successive one (1220 cm above the bottom) is Upper Callovian-lower Middle Oxfordian. The age of this median part of the formation is thus comprised between Lower Callovian and Middle Oxfordian. The age of the uppermost sample is Middle Kimmeridgian-Lower Tithonian.