Stratigraphy of the mid‐ to upper‐Cretaceous System in the Aridagawa area, Wakayama, Southwest Japan

Abstract

The litho-and biostratigraphy of the mid-to upper-Cretaceous System around the Yagumaike Pond in the Aridagawa area, Wakayama, Southwest Japan, were investigated. Many Middle to Late Albian megafossils were found in the strata of a block bounded by faults. It was also revealed that the Upper Cretaceous System of other blocks ranges from the Middle Turonian to Santonian. The Albian megafossil assemblage contains few benthic organisms, in contrast with the abundance of nektons found (e.g. cephalopods). Sedimentological observations of the mudstone profiles also indicate that scarcely or weakly bioturbated, well-laminated mudstone is dominant among the Albian deposits. These results suggest deposition of the Albian mudstone under a dysaerobic to anoxic environment. It is comparable to the extended oceanic anoxia (OAEs) in mid-Cretaceous time. Albian deposits with similar characteristics are also known to exist in Shikoku, Southwest Japan. A wide sedimentary basin that was directly affected by global environmental events, such as OAEs, seemed to be formed on the Chichibu Belt in the Albian. The Upper Cretaceous strata in the study area are extremely thin, similar to the coeval deposits on the Chichibu Belt in Shikoku. It is suggested that the sedimentation rate in the sedimentary basin on the Chichibu Belt was extremely low during early Late Cretaceous time.

Depositional age of the Himenoura Group on the Amakusa‐Kamishima area, Kyushu, southwest Japan: Using zircon U–Pb dating of the acidic tuffs

“…The Hinoshima Formation yields Santonian to lower Campanian ammonoid assemblage consisting of Texanites kawasakii , Protexanites fukazawai and Gaudryceras tenuiliratum (Kojo et al, ; Ueda, ). T. kawasakii and P. fukazawai are recognized as important age diagnostic species of the Santonian to lowermost Campanian (Misaki & Maeda, ; Okamoto, Matsunaga, & Okada, ; Toshimitsu, ; Toshimitsu & Hirano, ). The Santonian ammonoid Texanites collignoni was reported from the lower part of the Hinoshima Formation (Ueda, ).…”

Late Cretaceous uplift history of the Cretaceous volcanic arc in Southwest Japan: Provenance analysis of the Yuasa–Aridagawa basin based on U–Pb zircon ages

“…Shigeta et al (2012) found new index fossils indicating Maastrichtian from the strata which were estimated to be Santonian or Campanian in the Shimizu area (Hirayama & Tanaka, 1956b). Therefore, a geological map ( Figure 3a) was created to confirm the Hirayama & Tanaka (1956a,1956b, Kashiwagi (1999), Kurimoto et al (1998), Maejima (1986), (2009), Misaki & Maeda (2010), Shigeta et al (2012), Tanaka (1985), Yamamoto (1989), and Yao (1984). Fm., Formation with lenticular conglomerates.…”

“…These strata have yielded a large number of animal and plant fossils, and these and their associated stratigraphy have been studied in detail for a long time (e.g. Hirayama & Tanaka, , ; Matsumoto, ; Misaki, ; Misaki, Kadota, & Maeda, ; Misaki & Maeda, , ; Misaki & Ohara, ; Shigeta, Misaki, & Ohara, ; Tanaka, ). Initiation of sedimentation of the basin is Oxfordian (Kashiwagi & Yao, ).…”