This paper describes two brachiopod species, Cyrtospirifer cf. procumbens Simorin and Tylothyris sp., from the Upper Devonian Naidaijin Formation of the Chunoboridake area in the Kurosegawa Belt of Kyushu, southwestern Japan. The age of the small brachiopod fauna is assigned to the Late Devonian (probably Famennian). In terms of palaeobiogeography, the Chunoboridake fauna has a certain affinity with the Famennian brachiopod fauna of northwestern China (Xinjiang). Proto-Japan was probably located north of the North China Block during the Late Devonian.
Introduction
In Japan, Devonian rocks are restricted to three belts: the Hida Gaien Belt, the South Kitakami Belt and the Kurosegawa Belt (Figure 1A). Devonian geography and palaeobiogeography are important in understanding the geotectonic history of the Japanese Islands. Brachiopods, as well as trilobites and ostracods, are the most useful groups for the Devonian palaeobiogeographical study (Williams et al., 2014; Tazawa, 2018a). Many authors considered that Proto-Japan, including the Hida Gaien, South Kitakami and Kurosegawa belts, was located near the South China Block during the Devonian based on Devonian coral palaeobiogeography and U–Pb detrital zircon ages (e.g. Ehiro, 2001; Isozaki et al., 2011; Okawa et al., 2013; Wakita et al., 2021). In contrast, Tazawa (2000, 2002, 2004, 2018a) maintained that Proto-Japan was probably located near the North China Block during the Devonian, based mainly on Devonian brachiopod palaeobiogeography.
This study describes two brachiopod species, Cyrtospirifer cf. procumbens Simorin and Tylothyris sp., from the Upper Devonian Naidaijin Formation of the Chunoboridake area in the Kurosegawa Belt of Kyushu, southwestern Japan. This occurrence is the first record (with systematic description) of Cyrtospirifer and Tylothyris in the Kurosegawa Belt. The small brachiopod fauna of Chunoboridake has a certain affinity with the Famennian brachiopod fauna of Junggar, Xinjiang, northwestern China. Thus, Proto-Japan was probably located north of the North China Block during the Late Devonian.
Stratigraphy and collections
The Chunoboridake area (around Mt. Chunoboridake), Gokase-cho, Miyazaki Prefecture in the Kurosegawa Belt of Kyushu, southwestern Japan, is located approximately 5 km NE of Mt. Gionyama, a well-known fossil locality for Silurian halysitids (Hamada, 1958, 1959; Figure 1B, C). In this area, Kido et al. (2007) recognized Upper Devonian and lower Carboniferous rocks on the basis of the lycopod Leptophloeum rhombicum and two rugose coral species, Siphonodendron pseudomartini and Diphyphyllum aff. delicatum. Kido et al. (2007) regarded the Upper Devonian rocks as the eastern extension of the Naidaijin Formation (Miyamoto and Tanimoto, 1993) in the Kamoshishigawa area, Kumamoto Prefecture and the lower Carboniferous rocks as the eastern extension of the Yuzuruha Formation (Kambe, 1957) in the Yuzuruha area, Kumamoto Prefecture.
According to Kido et al. (2007), the Upper Devonian Naidaijin Formation in the Chunoboridake area consists of approximately 40 m thickness of sandstone and mud-stone interbedded with conglomerate (Figure 2). There is a faulted contact between the Naidaijin Formation and the lower Carboniferous (upper Visean) Yuzuruha Formation. The brachiopods described herein were collected by two of the present authors (T. Y. and T. S.) from a greenish-grey to grey tuffaceous siltstone bed (= mud-stone of Kido et al., 2007) that also contains numerous crinoid stem moulds. The bed is 1 m below the top of the Naidaijin Formation and 8 m above the Leptophloeum horizon in the Naidaijin Formation at locality CND1 (32°39′49″N, 131°13′43″E) on the southern slope of Mt. Chunoboridake. The brachiopod specimens are registered (prefix GF.D, numbers 24001–24003) and housed in the Department of Earth System Science, Faculty of Science, Fukuoka University in Fukuoka, Japan.
Figure 1.
Location and geology of the Chunoboridake area. A, Geotectonic map of the Japanese Islands (modified from Tazawa, 2000), showing the Hida Gaien, South Kitakami and Kurosegawa belts in black. MTL: Median Tectonic Line, TTL: Tanakura Tectonic Line; B, geotectonic map of Kyushu (modified from Saito et al., 2005) showing the Palaeozoic rocks of the Kurosegawa Belt in black between the Usuki–Yatsushiro Tectonic Line (MTL: Median Tectonic Line) and the Butsuzo Tectonic Line; C, topographic map of the Chunoboridake area showing the fossil locality CND1 (using a digital topographic map of the Geospatial Information Authority of Japan).
Stratigraphical and geographical distributions of Cyrtospirifer and Tylothyris
Cyrtospirifer is cosmopolitan in the Upper Devonian (Ma and Day, 2003; Johnson, 2006). In Japan, more than ten species of Cyrtospirifer have been described or figured from the Upper Devonian strata of the Hida Gaien Belt in central Japan (Tazawa et al., 2000), the South Kitakami Belt in northeastern Japan (Yabe and Noda, 1933; Tachibana, 1953; Hayasaka and Minato, 1954; Noda and Tachibana, 1959; Yanai et al., 1988; Tazawa et al., 2006, 2017; Tazawa, 2017, 2018b), and the Kurosegawa Belt in southwestern Japan (this study).
Johnson and Hou (2006) summarized the stratigraphical and geographical distributions of Tylothyris as cosmopolitan in the Middle Devonian (upper Givetian) to Carboniferous (Visean). In fact, Tylothyris has been recorded from Upper Devonian (Frasnian and Famennian) rocks of Montana, Arizona and New Mexico in the USA (Cooper, 1944; Stainbrook, 1947; Cooper and Dutro, 1982), Ireland (North, 1920), Xinjiang in northwestern China (Zong and Ma, 2012, 2018), the South Kitakami Belt in northeastern Japan (Tazawa, 2018b) and the Kurosegawa Belt in southwestern Japan (this study). It is noteworthy that Tylothyris is known from Upper Devonian of northwestern China (Xinjiang), but there is no record of the genus from Upper Devonian successions of southern China.
Figure 3.
Palaeogeographic map for Devonian time, showing the palaeoposition of Proto-Japan (Asterisk) (after Tazawa, 2018a; base map from Scotese, 2004). AU: Australia, E: Europe, KA: Kazakhstan, MO: Mongolia, NA: North America, NC: North China, S: Siberia, SC: South China.
Discussion and conclusion
The age of the Chunoboridake fauna, consisting of two brachiopod species, Cyrtospirifer cf. procumbens Simorin and Tylothyris sp., is identified as Late Devonian, probably Famennian. These two species resemble Cyrtospirifer procumbens Simorin and Tylothyris cf. novamexicana Stainbrook, respectively, both of which were described by Zong and Ma (2018) from Famennian strata of Junggar, Xinjiang, northwestern China. In terms of palaeobiogeography, it is important that Upper Devonian occurrences of Tylothyris have been recorded from North America, Ireland, northwestern China and Japan, but not from southern China. Moreover, the two species in the Chunoboridake fauna resemble the Famennian species of Junggar, Xinjiang, northwestern China. Given the occurrences noted above, we conclude that the Chunoboridake fauna has a certain affinity with the Late Devonian (Famennian) brachiopod fauna of northwestern China (Xinjiang). Proto-Japan was probably located north of the North China Block during the Late Devonian (Figure 3).
Systematic descriptions
(by J. Tazawa)
Order Spiriferida Waagen, 1883
Suborder Spiriferidina Waagen, 1883
Superfamily Cyrtospiriferoidea Termier and Termier,
1949
Family Cyrtospiriferidae Termier and Termier,
1949
Subfamily Cyrtospiriferinae Termier and Termier,
1949
Genus Cyrtospirifer Nalivkin in Fredericks, 1924
Type species.―Spirifer verneuili Murchison, 1840.
Figure 4.
Brachiopods from the Naidaijin Formation in the Chunobidake area. A, Cyrtospirifer cf. procumbens Simorin, external latex cast (A1) and internal mould (A2, A3) showing a pair of long dental plates of ventral valve, GF.D24002; B, C, Tylothyris sp.; B, external latex cast (B1, B2) and enlarged external mould (B3) showing imbricate growth lamellae of ventral valve, GF.D24002; C, external latex cast (C1, C2) and internal mould (C3) showing a low median ridge of dorsal valve, GF.D24003. Scale bars except for that in B3 are 1 cm.
Cyrtospirifer cf. procumbens Simorin in Litvinovich
et al., 1963
Figure 4A
cf. Cyrtospirifer procumbens Simorin in Litvinovich et al., 1963, p. 288, pl. 60, figs. 1–4; Zong and Ma, 2018, p. 79, figs. 5.1, 12.1–10, 13, 14, 18.1.
Material.—One specimen, external and internal moulds of ventral valve, GF.D24001.
Description.— Shell small in size for genus, wider than long, trapezoidal in outline, greatest width at hinge; length 15 mm; width more than 16 mm. Ventral valve slightly convex in both lateral and anterior profiles; sulcus shallow, with flat bottom and distinct boundaries. External surface of ventral valve ornamented with numerous simple, often bifurcated costae, numbering 22 per flank and 6–7 on sulcus. Micro-ornament not well preserved and obscure. Interior of ventral valve with a pair of well-developed long dental plates, which slightly diverge anteriorly.
Remarks.—The single ventral valve specimen from Chunoboridake is safely assigned to the genus Cyrtospirifer Nalivkin in Fredericks, 1924 in having a pair of long dental plates in the ventral valve. The Chunoboridake species resembles Cyrtospirifer procumbens Simorin in Litvinovich et al., 1963, redescribed by Zong and Ma (2018, p. 79, figs. 5.1, 12.1–12.10, 13, 14, 18.1) from the Hongguleleng Formation (Famennian) of western Junggar, Xinjiang, northwestern China, in its small, transverse ventral valve and in having a shallow sulcus with flat bottom and distinct boundaries, but accurate comparison is difficult for the poorly preserved specimen. Cyrtospirifer procumbens has been known from the Famennian of Kazakhstan and northwestern China (Litvinovich et al., 1963; Zong and Ma, 2018). Cyrtospirifer sp. B Tazawa et al. (2000, p. 731, figs. 5.5–5.8) from the Rosse Formation in the Moribu area, Hida Gaien Belt, central Japan, also has a ventral sulcus with flat bottom and distinct boundaries, but differs from the present species in its less transverse outline. The type species, Cyrtospirifer verneuili (Murchison, 1840), redescribed by Ma and Day (2003, p. 274, figs. 3, 4, 5.1, 5.2, 6.1–6.14, 6.17, 6.18, 8.3), from the lower Frasnian of Ferques, Pas de Calais, France, is readily distinguished from the Chunoboridake species by its larger size and more transverse outline.
Suborder Delthyridina Ivanova, 1972
Superfamily Delthyridoidea Phillips, 1841
Family Mucrospiriferidae Boucot, 1959
Subfamily Tylothyridinae Carter, 1972
Genus Tylothyris North, 1920
Type species.—Cyrtia laminosa M'Coy, 1844.
Tylothyris sp.
Figure 4B, C
Material.—Two specimens: (1) external and internal moulds of ventral valve, GF.D24002; and (2) external and internal moulds of dorsal valve, GF.D24003.
Description.—Shell medium in size for genus, transversely trapezoidal in outline, with greatest width at hinge; cardinal extremities and interarea of both valves broken; length about 9 mm, width more than 21 mm in the ventral valve specimen (GF.D24002); length about 14 mm, width more than 25 mm in the dorsal valve specimen (GF.D24003). Ventral valve strongly and unevenly convex in lateral profile, most convex in umbonal region; sulcus narrow and deep, bearing a single low median ridge. Dorsal valve less convex than ventral valve, moderately convex in umbonal region, flattened anteriorly; fold narrow and moderately high, widening anteriorly, with flat crest bearing a median groove. External surface of both valves ornamented with numerous costae and distinct imbricate growth lamellae; costae simple and rounded, numbering 12 on each lateral flank of both valves, but completely lacking on ventral sulcus and dorsal fold; strong imbricate growth lamellae over the entire surface of both valves, numbering 5 per mm in the ventral valve specimen. Interior of dorsal valve with a low, moderately long median ridge. Other internal structures of both ventral and dorsal valves not well preserved.
Remarks.—These specimens can be assigned to the genus Tylothyris North, 1920 by the external ornament of both valves consisting of numerous simple rounded costae and distinct imbricate growth lamellae, and in having a low median ridge in the dorsal valve. The Chunoboridake species most resembles Tylothyris cf. novamexicana Stainbrook, described by Zong and Ma (2018, p. 87, figs. 16.15–16.25, 18.6) from the Hongguleleng Formation (Famennian) of western Junggar, Xinjiang, northwestern China in its transverse outline and in having numerous costae on both valves, but the Chinese species differs from the present species in its smaller size and in having fewer costae on lateral flanks of the both valves. Tylothyris novamexicana Stainbrook (1947, p. 323, pl. 47, figs. 31–33), from the Percha Formation (Famennian) of New Mexico, differs from the Chunoboridake species in its less transverse outline and much smaller size. Tylothyris multicostatus Maxwell (1964, p. 30, pl. 5, figs. 25–32), from the Baywulla Formation (lower Visean) of the Yarrol Basin, eastern Australia, is distinguished from the present species in having more numerous costae on lateral flanks. Tylothyris rockportensis Rogers and Pitrat (1987, p. 502, figs. 4–10, 11.7–11.11), from the Rockport Quarry Limestone (Givetian) of Michigan, resembles the Chunoboridake species in size, outline and number of costae on lateral flanks, but differs from the latter in having ventral sulcus lacking a median ridge and dorsal fold lacking a median groove. The type species, Tylothyris laminosa (M'Coy, 1844), redescribed by North (1920, p. 197, pl. 13, figs. 1, 2, 12, 13, 16; text-figs. 1m, 4a, 4b) from the Tournaisian of Ireland, differs from the present species in its less transverse outline, slightly larger size, and in having fewer costae on lateral flanks of both valves. The Chunoboridake species may be a new species of Tylothyris, but the poor material precludes that determination.
Acknowledgements
We sincerely thank three anonymous reviewers for their constructive comments and suggestions on the manuscript; Erika Kido (University of Graz, Austria) and Koichi Nagai (former University of the Ryukyus, Naha) for providing information about the stratigraphy of the Silurian–Carboniferous rocks in the Chunoboridake area; Ronald R. West (Professor Emeritus of Kansas University, Manhattan) for reviewing the manuscript; and Yousuke Ibaraki (Fossa Magna Museum, Itoigawa) for his help in drawing figures.
© by the Palaeontological Society of Japan
