In the Furlo section the CTBI lies within the Scaglia Bianca Formation, which includes abundant biosiliceous limestone. The Livello Bonarelli is a 1 m thick condensed interval of millimetre-laminated black shale and brown radiolarian sand that represents the sedimentary expression of part of OAE 2 (Arthur and Premoli Silva, 1982). Up to 20 m beneath the Bonarelli level there are numerous centimetre scale organic-rich shale layers (Jenkyns et al., 2007). The δ13Corg record has a narrow variation in background values prior to OAE 2, ∼−25.9 to −26.5‰. The characteristic positive excursion in δ13Corg is a 4‰ shift, −27.2 to −23.1‰, occurring within <0.5 m (Fig. 2; Supplementary Material, Table 1e).
Livello Bonarelli
thick
1 m
m
numerous centimetre scale organic-rich shale layers
beneath the Bonarelli
Up to 20 m
m
δ13Corg record
narrow variation in background values prior to OAE 2
∼−25.9 to −26.5‰.
‰
characteristic positive excursion in δ13Corg
shift
4‰
‰
characteristic positive excursion in δ13Corg
shift
−27.2 to −23.1‰
‰
characteristic positive excursion in δ13Corg
shift
within <0.5 m
m