TheTenneru Formation (天寧層,Tenneru-sō), sometimes in older literature the Tenneru Conglomerate Member of the Chorobetsu Formation,[1]: 260 is ageological formation in southeastHokkaidō, Japan, in the area ofKushiro.[2]: 152 Depositedbetween the Harutori Formation and Yūbetsu Formation in the Urahoro Group thatunconformably overlies the Nemuro Group in theNemuro Belt, the Tenneru Formationcorrelates with the Rushin Formation at its western end.[3] The Formation, laid down in theLate Eocene,[2]: 160 consists mainly of reddish and reddish brownconglomerate, with somesandstone andmudstone; there are severalintercalatedcoal seams.[2]: 152 [4] New species of faunadescribed from the Tenneru Formation include the "Kushiro tapir"[ja] (Plesiocolopirus kushiroensis;protonym:Colodon kushiroensis),[2] and of flora,Actinidia harutoriensis,Alnus ezoensis,Aralia ezoana,Cordia japonica,Cupania japonica,Idesia kushiroensis,Lastrea kushiroensis, andMaesa nipponica.[5]: 432–4
The Tenneru Flora as described by Tanai Toshimasa in 1970 from the areas where the Tenneru Formation is exposed, with a thickness of some 300 m (980 ft), along the upper stretches of the Tokomuro River (常室川) in the westernKushiro coal field [ja], comprises sixteen families and twenty genera, including twoPteridophytes, oneEquisetum, and twoconifers, the remaining species beingdicotyledons:[5]: 432–4