Early Triassic Conodonts from the Tahogawa Member of the Taho Formation, Ehime Prefecture, Southwest Japan

Spathian to Aegean (upper Lower Triassic to lower Middle Triassic) carbon isotope stratigraphy constrained by the conodont biostratigraphy of carbonates on top of a mid‐oceanic seamount formed in the Panthalassic Ocean

“…The allochthonous, irregularly shaped limestone blocks (2-100 m in diameter) of the Taho Formation are scattered over a distance of 500 m along Ehime Prefectural Road 35 near Taho, Shirokawa Town, Seiyo City (Figure 1). The Taho Formation is divided into the Sakuragatouge and Tahogawa members (Maekawa et al, 2018).…”

“…According to Maekawa et al (2018), the Tahogawa Member consists mainly of partly dolomitized and bedded limestones, which contain abundant Early to Middle Triassic conodonts, ammonoids, gastropods, bivalves, brachiopods, and fish remains (Figure 2). The Sakuragatouge Member is dominated by lenticular conglomeratic limestone and massive limestone, and contains Middle to Late Triassic conodonts, gastropods, bivalves, echinoids, and fish remains.…”

“…Our study section C02 is located in a 54 m-thick fossiliferous carbonate block in the central stratotype area of the Taho Formation (Figures 1 and 4a) and corresponds to the upper part of this formation. This block consists mainly of bedded, light to dark gray, bioclastic limestone, massive white limestone, and minor conglomeratic limestone, which belong to the Tahogawa Member (Maekawa et al, 2018) (Figure 4b). This block extends to 23 m below the ground surface, where it conformably overlies dolomitized limestone of the Shirokawa Formation, which contains Changhsingian (upper Permian) fusulinids and conodonts (Koike, 1996).…”

“…These blocks are an important archive of the biotic assemblages and sedimentary evolution of oceanic sediments from the Panthalassic Ocean, and include deep-sea bedded cherts (Matsuda & Isozaki, 1991) and shallow-water carbonates (Wakita, 2019). Blocks found in Tahokamigumi, Seiyo City, western Shikoku Island, are known as the Taho Limestone (Koike, 1994) or Taho Formation (Koike, 1996;Maekawa et al, 2018Maekawa et al, , 2021, and were derived from an atoll/carbonate buildup or an isolated carbonate platform developed on top of a mid-oceanic seamount during the Triassic (Hirsch & Ishida, 2002;Maekawa et al, 2018Maekawa et al, , 2021Musashi et al, 2001) (Figures 1 and 2). These limestone blocks contain abundant, well-preserved marine fossils, such as ammonoids (Bando, 1961(Bando, , 1964Shimizu & Jimbo, 1933;Yehara, 1925), bivalves (Yehara, 1923), gastropods (Nakazawa, 1971), fish remains (Goto et al, 2010;Yamagishi, 2004), and conodonts (Koike, 1981(Koike, , 1988(Koike, , 1992(Koike, , 1994(Koike, , 1996(Koike, , 2004Maekawa et al, 2018Maekawa et al, , 2021.…”

“…Blocks found in Tahokamigumi, Seiyo City, western Shikoku Island, are known as the Taho Limestone (Koike, 1994) or Taho Formation (Koike, 1996;Maekawa et al, 2018Maekawa et al, , 2021, and were derived from an atoll/carbonate buildup or an isolated carbonate platform developed on top of a mid-oceanic seamount during the Triassic (Hirsch & Ishida, 2002;Maekawa et al, 2018Maekawa et al, , 2021Musashi et al, 2001) (Figures 1 and 2). These limestone blocks contain abundant, well-preserved marine fossils, such as ammonoids (Bando, 1961(Bando, , 1964Shimizu & Jimbo, 1933;Yehara, 1925), bivalves (Yehara, 1923), gastropods (Nakazawa, 1971), fish remains (Goto et al, 2010;Yamagishi, 2004), and conodonts (Koike, 1981(Koike, , 1988(Koike, , 1992(Koike, , 1994(Koike, , 1996(Koike, , 2004Maekawa et al, 2018Maekawa et al, , 2021. In contrast to the numerous paleontological studies, there has only been one chemostratigraphic investigation of the Taho Formation (Musashi et al, 2001), which focused on a short negative spike at the Permian-Triassic boundary.…”