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Oarai Formation
- Type locality: Oarai seashore, Oarai city, Higashiibaraki county, Ibaraki prefecture
- Coherent formation
- Cretaceous - Paleogene
- Sedimentary facies: Fluvial, Marsh
- Lithofacies: Conglomerate
- Lithofacies (Minor): Sandstone, Siltstone, Coal
- Sedimentary structures (Minor): Cross stratification
- Distribution: Oarai seashore, Oarai city, Higashiibaraki county, Ibaraki pref.; Nakaminato, Hitachinaka city, Ibaraki pref.
- Fossils (Oarai flora): Adiantites? oaraiensis, Adiantites sewardi?, Andromeda cfr. scripta, Aporosa nanacarpa, Aralia disectifolia, Aralia cfr. taurinensis, Asplenites sp., Betula cfr. maximowicziana, Brachyphyllum japonicum, Broussonetia praestans, Calyptrocalyx spicalus, Castaliites flabelliformis, Celastrophyllum sp., Cercidiphyllum cfr. eojaponica, Cinnamomum linifolium, Coniopteris burejensis, Corylus? cfr. heterophylla, Credneria kashimaensis, Diospyros cfr. anceps, Doryanthites cretacea, Equisetum cfr. arcticum, Equisetum oregonensis, Ficus? cfr. alaskana, Ficus antiquorum, Fraxinus denticulata, Glyptostrobus cfr. pencilis, Hedera primordialis, Hovenia cfr. dulcis, Ilex? sp., Juglans? cfr. orientalis, MacClintokia sp., Magnolia pseudoacuminata?, Otozamites cfr. sewardi, Paliurus cfr. upatoiensis, Paulownia sp., Platanus cfr. septentrionalis, Populus cfr. arctica?, Populus aff. rotundifolia, Populus speciofolia, Quercus sp., Sabalites oaraiensis, Sagus filaris, Sequoia cfr. jeholensis, Sphenopteris cfr. yokoyamai, Sterculia? sp., Taxodium cfr. dubium, Thallites yabei, Tilia maximowiczianoides, Tilia cfr. protojaponica, Ulmus sp., Viburnum? cfr. simile, Zamiophyllum cfr. buchianum, Zamites megaphyllus, Zelkova sp., Zizyphus cfr. fibrillosus, Zizyphus pentaxus, Zizyphus cfr. pseudomeeki
- Fossils (Spores): Cicatricosisporites sp., Lygodium spp., Triplanosporites sp., Verrucatosporites sp.
- Fossils (Pollen): Abies? sp., Aquifoliaceae, Betula sp., Carpinus sp., Castanea sp., Chenopodium sp., Corylus sp., Ephedra? sp., Fagus sp., Monocolpopollenites spp., Picea sp., Pinus spp., Podocarpus sp., Quercus sp., Tricolpopollenites sp., Tsuga? sp.
- Sakamoto (1975) Geology of the Isohama District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 55p. (in Japanese with English abstract 4p.)
- Sakamoto et al. (1972) Geology of the Nakaminato District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 94p. (in Japanese with English abstract 5p.)