Gotlandian and Devonian Volcanic Activities in the Kitakami Mountains

Ambiguous biogeographical patterns mask a more complete understanding of the Ordovician to Devonian evolution of Japan

“…The Tobigamori Formation comprises some 2000 m of mudrocks, sandstones and conglomerates and probably overlies the Nakazato Formation unconformably (Suzuki & Minato 1958). It yields brachiopod assemblages documented by Tachibana (1952Tachibana ( , 1981b, who reported species from 11 genera, together with gastropods and bivalves.…”

“…The 'Kawauchi Formation' (sometimes referred to as 'Kawauchi Series') in the Hikoroichi region, Iwate Prefecture, is up to 300 m thick (Suzuki & Minato 1958), and is composed of limestone and mudstone. Recognition of the base of the formation is questionable, and hence our use of inverted commas to designate this uncertainty: Murata et al 1974Murata et al , 1975 and Tachibana (1976) considered it to unconformably overlie the Hikami granites, whereas other workers have considered this to be an intrusive relationship that obscures the base of the sedimentary unit (Shibata 1974 and references therein): recent dates obtained from the Hikami granite provide an age of ca 412 Ma (Shimojo et al 2010).…”

“…Recognition of the base of the formation is questionable, and hence our use of inverted commas to designate this uncertainty: Murata et al 1974Murata et al , 1975 and Tachibana (1976) considered it to unconformably overlie the Hikami granites, whereas other workers have considered this to be an intrusive relationship that obscures the base of the sedimentary unit (Shibata 1974 and references therein): recent dates obtained from the Hikami granite provide an age of ca 412 Ma (Shimojo et al 2010). The 'Kawauchi Formation' is overlain -possibly unconformably (see Tachibana 1976Tachibana , 1981a) by radiolarian mudstone not greater than 60 m thick that has been referred to as the Takainari Formation (or 'Series', Suzuki & Minato 1958;Tachibana 1976). In his estimation of the thickness of these two units, Kobayashi (1988a) Kato et al 1980;Kobayashi 1988a) and has been divided into five units (by Sugiyama 1940), in ascending order these being the: 1.…”

“…cit.) and on the basis of his descriptions, Suzuki and Minato (1958) listed a fauna with endemic species of Halysites, Tryplasma and Clathrodictyon, but with species of Heliolites that are known to have a more cosmopolitan distribution in East Asia, Europe and North America (e.g. H. decipiens, H. bohemicus, H. barrandei;see Mu et al 1986;Sakagami & Nakornsri 1987;Lee et al 1990).…”

Gotlandian Stratigraphy of the Outer Zone of Southwest Japan

“…According to Suzuki [44] and Minato and others [26], the Lower Devonian Ohno and Nakazato series are characterized by markedly keratophyric acidic volcanics, whereas the underlying Takainari and Kawauchi series and the Upper Devonian Tobigamori formation contain less acidic rocks. Minato and others [27] further considered the younger beds and mentioned that the Carboniferous system is marked with porphyritic and diabasic volcanics.…”