Fig. 3

Biostratigraphy and chemostratigraphy of the bedded cherts in the Sakahogi section (Onoue et al. 2016a; Sato et al. 2016). a Stratigraphic profiles of organic carbon isotopes, mass accumulation rates of biogenic silica, and radiolarian biostratigraphy. The mass accumulation rate of biogenic silica was estimated by assuming a constant sedimentation rate of 1.1–1.6 mm kyr⁻¹ in the middle–upper Norian chert succession (Onoue et al. 2016a), which is an alternative to a previous model assuming different sedimentation rates between chert and claystone (Hori et al. 1993). b Stratigraphic profiles of PGE concentrations in the claystones of the studied section. NH52-R2 indicates the lower sublayer of claystone (ejecta layer) with microspherules and Ni-rich magnetite