Ainoshima Island (facies 2): Rupelian, Japan

List of taxa
Where & when
Geology
Taphonomy & methods
Metadata & references
Taxonomic list
Chondrichthyes - Carcharhiniformes - Triakidae
Galeorhinus sp. de Blainville and Prévost 1816
Chondrichthyes - Carcharhiniformes - Carcharhinidae
Negaprion sp. Whitley 1940
Chondrichthyes - Lamniformes - Cetorhinidae
Cetorhinus sp. de Blainville 1816
Chondrichthyes - Lamniformes - Lamnidae
Isurus sp. Rafinesque 1810
Chondrichthyes - Lamniformes - Carchariidae
Carcharias sp. Rafinesque 1810
Chondrichthyes - Squatiniformes - Squatinidae
Squatina sp. Dumeril 1806
Chondrichthyes - Squaliformes - Squalidae
Chondrichthyes - Hexanchiformes - Hexanchidae
Hexanchus sp. Rafinesque 1810
Chondrichthyes - Heterodontiformes - Heterodontidae
Heterodontus sp. de Blainville 1816
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:planar lamination,bioturbation,very fine,concretionary sandstone
Lithology description: This facies is characterized by very fine-grained to fine-grained laminated sandstones. Laminae are often disturbed or completely destroyed by bioturbation. Sorting is relatively poor when compared to the sandstones of Facies 3 and 4. Gray calcareous nodules, 10 to 30 cm in diameter often occur in this facies with abundant burrows obscuring original sedimentary structures.
Environment:offshore
Geology comments: Mud layers and mud-filled burrows indicate that the environment was low-energetic. Extensive bioturbation has destroyed much of the original sedimentary structure, but the original lithology is thought to have been laminated very fine- to fine-grained sandstones, intercalated with thin mud layers. This facies is interpreted as having been accumulated in an outer shelf environment.
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:277775
Authorizer:M. Clapham Enterer:M. Clapham
Modifier:M. Clapham Research group:vertebrate
Created:2026-02-11 21:43:34 Last modified:2026-03-24 19:54:09
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]