Oriki area, Hirono town: Late Turonian - Early Coniacian, Japan

List of taxa
Where & when
Geology
Taphonomy & methods
Metadata & references
Taxonomic list
Chondrichthyes - Hexanchiformes - Hexanchidae
Hexanchus sp. Rafinesque 1810
Chondrichthyes - Lamniformes
Chondrichthyes - Lamniformes - Pseudoscapanorhynchidae
Chondrichthyes - Lamniformes - Cretoxyrhinidae
Chondrichthyes - Lamniformes - Otodontidae
Chondrichthyes - Lamniformes - Mitsukurinidae
see common names

Geography
Country:Japan
Coordinates: 37.2° North, 140.9° East (view map)
Paleocoordinates:45.1° North, 142.7° East (Wright 2013)
Basis of coordinate:based on nearby landmark
Geographic resolution:outcrop
Time
Period: Cretaceous Epoch: Late Cretaceous
Stage: Turonian - Coniacian 10 m.y. bin: Cretaceous 6
Key time interval: Late Turonian - Early Coniacian
Age range of interval: 93.9 - 85.7 m.y. ago
Stratigraphy
Geological group:Futaba Formation:Ashizawa Member:Obisagawa
Stratigraphic resolution:bed
Stratigraphy comments: Lowermost part of the Obisagawa Formation, which is the uppermost part of the Ashizawa Formation, the lowest formation of the Futaba Group. According to Muramiya et al. 2025: "The Obisagawa Member of the Ashizawa Formation has been correlated to the lower to middle (?) Coniacian on the basis of ammonoids, such as Forresteria alluaudi, Yabeiceras orientale, and Baculites yokoyamai (Tokunaga and Shimizu, 1926), and the bivalves of Inoceramus uwajimensis and Didymotis akamatsui (Yehara, 1924). However, Inose et al. (2024a) described several upper Turonian inoceramids from the basal to middle part of this member, such as Mytiloides incertus Jimbo, 1894, and “Cremnoceramus rotundatus” sensu (Matsumoto and Noda, 1985). Among them, the occurrence of Cremnoceramus waltersdorfensis waltersdorfensis (Andert, 1911) is confined to a relatively narrow biostratigraphic interval spanning the uppermost Turonian to the lowermost Coniacian in Europe and North America (Walaszczyk and Cobban, 1998, 2000; Walaszczyk and Wood, 1998, 2018). On the other hand, associated ammonoids from the Obisagawa Member generally suggest the lower to middle (?) Coniacian (Matsumoto et al., 1982; Ando et al., 1995; Futakami et al., 2016). Yezoceras miotuberculatum and Yezoc. elegans described here also indicate a Coniacian age (Matsumoto, 1977; Aiba et al., 2021). Although the strict horizons of these index taxa have not been completely confirmed (Figure 2), there remains a biostratigraphic inconsistency between some ammonoids and inoceramids. From current knowledge, the basal to middle part of the Obisagawa Member of the Ashizawa Formation can be provisionally correlated to the uppermost Turonian to the lowermost Coniacian interval."
Lithology and environment
Primary lithology: calcareous conglomerate
Lithology description: calcareous conglomerate with medium-sized pebbles
Environment:shoreface
Geology comments: This conglomerate layer is thought to be discontinuous and lenticular (Kubo et al., 2002), and sedimentary facies analysis suggests that it is a deposit from a beach to upper shoreface environment (Ando et al., 1995).
Taphonomy
Modes of preservation:body
Size of fossils:macrofossils
Collection methods and comments
Collection methods:field collection
Reason for describing collection:general faunal/floral analysis
Collection method comments: Repository: Fukushima Prefectural Museum
Metadata
Database number:277046
Authorizer:M. Clapham Enterer:M. Clapham
Research group:vertebrate
Created:2026-01-19 22:31:45 Last modified:2026-01-19 22:31:45
Access level:the public Released:0000-00-00 00:00:00
Creative Commons license:
Reference information

Primary reference:
93940. Y. Takakuwa, Y. Hasegawa, N. Watanabe and N. Nemoto. 2018. Elasmobranch remains from the Upper Cretaceous Ashizawa Formation (Coniacian), Futaba Group, in Hirono Town, Fukushima Prefecture, Japan. Bulletin of Gunma Museum of Natural History 22:59-66 [M. Clapham/M. Clapham]