Ainoshima Island (facies 5): Rupelian, Japan

List of taxa
Where & when
Geology
Taphonomy & methods
Metadata & references
Taxonomic list
Chondrichthyes - Hexanchiformes - Hexanchidae
Hexanchus sp. Rafinesque 1810
Chondrichthyes - Squaliformes - Squalidae
Chondrichthyes - Myliobatiformes - Myliobatidae
Myliobatis sp. Cuvier 1816
Chondrichthyes - Carcharhiniformes - Carcharhinidae
Negaprion sp. Whitley 1940
Chondrichthyes - Lamniformes - Lamnidae
Isurus sp. Rafinesque 1810
Chondrichthyes - Lamniformes - Carchariidae
Carcharias sp. Rafinesque 1810
see common names

Geography
Country:Japan
Coordinates: 34.0° North, 130.8° East (view map)
Paleocoordinates:36.5° North, 127.6° East (Wright 2013)
Basis of coordinate:based on nearby landmark
Geographic resolution:local area
Time
Period: Paleogene Epoch: Oligocene
Stage: Rupelian 10 m.y. bin: Cenozoic 4
Key time interval: Rupelian
Age range of interval: 33.9 - 27.3 m.y. ago
Stratigraphy
Geological group:Ashiya Formation:Yamaga
Stratigraphic resolution:group of beds
Stratigraphy comments: The age of the Yamaga Formation in the Ashiya area was placed at 31.7±2.3 Ma (upper Lower Oligocene) based on fission track dating (Ozaki and Hamasaki, 1991). This was supported by further fission track dating and biostratigraphic studies conducted in the upper and lower formations (Tsuchi et al., 1987; Ozaki
and Hamasaki, 1991; Okada, 1992).
Lithology and environment
Primary lithology:hummocky CS,fine sandstone
Lithology description: his facies is composed of amalgamated hummocky cross-stratified fine sandstones, and often includes thick lags of shells and pebbles. HCS lags are present and maybe well developed to more than 10 cm thick and 1 m wide.
Environment:transition zone/lower shoreface
Geology comments: Amalgamated hummocky cross-stratification and rare bioturbation allow this facies to be interpreted as representing a lower shoreface setting (e.g., Saito, 1989). In contrast to Facies 4, bioturbated layers are poorly developed, the wavelength of hummocky cross-stratification is short, and HCS beds contain abundant thick lags. These characteristics suggest that the sedimentary environment of Facies 5 was shallower and more storm-dominant than that of Facies 4.
Taphonomy
Modes of preservation:body
Size of fossils:macrofossils
Collection methods and comments
Reason for describing collection:paleoecologic analysis
Collection method comments: Repository: University Museum, The University of Tokyo (UMUT)
Metadata
Database number:277777
Authorizer:M. Clapham Enterer:M. Clapham
Research group:vertebrate
Created:2026-02-11 21:50:00 Last modified:2026-02-11 21:50:00
Access level:the public Released:0000-00-00 00:00:00
Creative Commons license:
Reference information

Primary reference:
94182. T. Tomita and T. Oji. 2010. Habitat reconstruction of Oligocene elasmobranchs from Yamaga Formation, Ashiya Group, western Japan. Paleontological Research 14:69-80 [M. Clapham/M. Clapham]