Paleogene Molluscan Faunas from the Kushiro Coal Field, Eastern Hokkaido

• Main Author: Honda Yutaka
• Format: Report
• Language: English
• Published: Tohoku University 1989
• Subjects: Paleogene; molluscs; faunal provinces; paleobiogeography; Kushiro coal field; Gulf of Alaska; McCoy; Pacific; Kamchatka; Koryak; Sakhalin; Alaska
• Online Access: http://hdl.handle.net/10097/28865; https://tohoku.repo.nii.ac.jp/?action=repository_uri&item_id=12062; https://tohoku.repo.nii.ac.jp/?action=repository_action_common_download&item_id=12062&item_no=1&attribute_id=18&file_no=1

The Urahoro Group consists of sandstone and conglomerate, with intercalated coal seams, and yields nonmarine and shallow marine molluscs, including Ostrea. Chlamys, Corbicula, Nemocardium and Mya. The Ombetsu Group rests unconformably upon the Urahoro Group, and consists of siltstone, with a basal sandstone. It yields shallow (and a few deep) marine molluscs, including Yoldia, Portlandia, Acila, Cyclocardia, Turritella, Dentalium, Eocylichna, Orectospira, Clinocardium, Neverita, Conchocele, Macoma, Periploma and Profulvia. These faunas are characterized by many cold water taxa that are widespread today in the northern Pacific. The Urahoro and Ombetsu molluscs include many species in common with those of Oligocene strata of central Hokkaido, Honshu. Japan, and Sakhalin. Kamchatka, and the Koryak Upland, eastern USSR. In contrast, they include only a few species in common with those of Oligocene strata of Kyushu, southern Japan. It is notable that several genera originated during the Late Eocene or Oligocene in Japan and Sakhalin, including Neptunea, Clinocardium and Mya. These facts imply that a significant number of northwestern Pacific taxa might have migrated eastward during Paleogene time. This is also indicated by the presence of 25% Asiatic species in western Gulf of Alaska Paleogene molluscan faunas, and a decline to only 12% Asiatic species in coeval eastern Gulf of Alaska faunas (Marincovich and McCoy, 1984). Seven species of bivalves and two species of gastropods are newly described herein : Nucula (Ennucula) omagariensis, Crenella (Megacrenella) shitakaraensis, C. (Megacrenella) nuibetsuensis, Cyclocardia poronaiensis, Solen shitakaraensis, Thracia (Thracia) shitakaraensis, Cardiomya (Cardiomya) kotakai, Turritella (Hataiella) nuibetsuensis, and Neptunea ogasawarai.