Faunal composition and correlation of the late Carboniferous and Permian fusulines contained in exotic limestone blocks of the Sakamototoge area, Gifu Prefecture, Japan were reconsidered. Main alterations of the previous results are summarized as: (1) Moscovian fusulines are confined to the Myachkovian; (2) many species collectively included in Triticites are attributed to Protriticites, Montiparus, Rauserites, Triticites, or Schwagerina; (3) “Triticites” faunas designated as the Carboniferous–Permian are reorganized into three faunas: Protriticites subschwagerinoides (early Kasimovian), Montiparus mesopachus-Protriticites kiyomiensis (middle Kasimovian), and Rauserites arcticus-Carbonoschwagerina nakazawai-Quasifusulina longissimi (late Kasimovian to possibly early Gzhelian); and (4) the species assigned to Pseudoschwagerina is now attributed to late Gzhelian Carbonoschwagerina, implying the probable absence of the Asselian in the area. In addition, the Capitanian Yabeina fauna heterogeneous to the coeval neoschwagerinid faunas in the Permian terranes of Japan is ascertained.
Introduction
It had long been accepted that the C-P (Carboniferous-Permian) boundary is drawn at the stratigraphic level of the first appearance of Pseudoschwagerina or Pseudoschwagerina morikawai Igo, 1957 and its allies by almost all workers in Japan (e.g. Toriyama, 1967). This concept was based on fusuline biostratigraphy mainly of the Yayamadake Limestone (Kanmera, 1952, 1955, 1958), Ichinotani Formation (Igo, 1957), Akiyoshi Limestone Group (Toriyama, 1958), Oppara and Okumyogata formations (Kanuma, 1958a, b), and Sakamotozawa Formation (Kanmera and Mikami, 1965).
On the other hand, there were many taxonomic problems concerning the definition of Pseudoschwagerina and its international correlation. The problems had been left unresolved until the taxonomic and chronostratigraphic refinements of the fusuline faunas of the C-P boundary strata in Japan and their international correlation done by Ozawa and Kobayashi (1990), Watanabe (1991), and Ozawa et al. (1992). These authors revealed that the base of the Permian is defined by the first appearance of Sphaeroschwagerina fusiformis (Krotow, 1888) in Japan, almost the same as in the stratotype region of European Russia and the Tethyan region. Ozawa et al. (1992) proposed the genus Carbonoschwagerina so that the distinct group of the genus Pseudoschwagerina sensu Japanese workers in those days is distinguishable morphologically and phylogenetically from Sphaeroschwagerina and other Asselian inflated schwagerinids of the Tethyan region and also from the typical forms of Pseudoschwagerina of North America.
We have reconsidered the faunal composition and correlation mainly of the C-P boundary fusulines from the Oppara and Okumyogata formations in the Sakamototoge (Sakamoto Pass) area, northern part of Gifu Prefecture. Fusulines previously described by Kanuma (1953, 1958b, 1959) were faunistically reexamined in comparison with our materials of limestone blocks and float samples derived from the formations and on the basis of current taxonomic frameworks. We have also reexamined fusuline faunas from other formations in the area left unstudied since Kanuma (1958a, 1959, 1960).
Many photomicrographs of fusulines, including those not well oriented and/or incomplete specimens, are illustrated and considered for future studies of fusulines in the area. All the limestone thin sections used in this paper are stored in the Museum of Nature and Human Activities, Hyogo, Japan (Fumio Kobayashi Collection, MNHAH).
Geologic setting
The Sakamototoge area is located at the boundary between Gujyo and Takayama cities, Gifu Prefecture. The area is situated in the northern part of the Mino Belt (Terrane) consisting of Jurassic to Lower Cretaceous accretionary complex covered or intruded by post-Mesozoic rocks (Figure 1). The Sakamototoge Formation was newly introduced for the Jurassic accretionary complex developed in the Sakamototoge area by Kawada et al. (1988). The formation is the sedimentary complex previously subdivided into the upper Carboniferous Akiyama and Oppara formations, and the Permian Okumyogata and Okuzumi formations by Kanuma (1958a) based on fusuline biostratigraphy. Along with cherts and weakly altered volcaniclastic rocks contained in these formations, fusuline limestones had been presumed to be interbedded with sandstones and mudstones by the 1970s. Chaotic occurrence of these non-siliciclastic rocks within siliciclastic rocks and the new find of Jurassic radiolarians from the muddy rocks revealed that the sedimentary complex formerly assigned to the Upper Paleozoic should be referred to the Jurassic accretionary complex (Sakamototoge Formation) without any stratigraphic subdivisions (Kawada et al., 1988).
A more widespread distribution of fossiliferous limestone blocks and fragments than those shown in Kanuma (1958a) was demonstrated by Kawada et al. (1988), who reconfirmed the similar biostratigraphic distribution of limestones in the Sakamototoge area to that studied by Kanuma (1953, 1958a, b, 1959, 1960). Isomi (1988) summarized his conclusions about exotic limestones having fusulines in the area as follows: (1) biostratigraphically, limestones range from the Moscovian (Fusulinella-Fusulina Zone) to the “lower upper Permian” (Yabeina Zone); (2) lower Permian limestones are widespread, whereas middle Permian ones corresponding to the Parafusulina Zone are absent; and (3) fusulines are partly destroyed dynamically and are insufficiently preserved in general. However, a detailed comparison is impossible on account of there being neither descriptions nor illustrations of fusulines in Isomi's work, and his taxonomy of schwagerinids is far from the current framework.
Material
Among many limestone blocks in the Sakamototoge area, C-P boundary fusuline limestones are supposed to be typically developed along three streams (Irasubora, Oirasubora, and Koirasubora) south of Oppara, Takayama City, and near Akiyama, Gujyo City, as suggested by Kanuma (1958a, p. 14, 15) based on his scheme of fusuline biostratigraphy. In the present study, relatively small-sized fusulines were found with difficulty in limestone exposures on account of more or less recrystallization, deformation, and fragmentation of limestones penetrated by many veinlets. In order to obtain better preserved fusulines, we also collected many limestone float samples, regardless of the recognition of fusulines in the field. Total number of samples collected in the area amounts to 66 (Figure 2) and of limestone thin sections amounts to 459. Samples from the limestone exposure are confined to 21 (Is-1–6, 13, 15–17; Kb-1–8, 11–13). Others are assumed to be derived from a limestone block or fragment exposed at a topographic high near the sample locality.
Foraminifers are contained in about a half of the samples collected. Among them, those from 22 samples are listed (Figure 3). Species listed in Figure 3 are confined, in general, to those illustrated in Figures 4–7. Some fusulines are insufficiently preserved for detailed observation of microstructure of the test and for the reconstruction of original features of the test characters. Species of nonfusuline foraminifers listed and illustrated are restricted to those relatively well preserved (Figures 4.1–4.12).
Stratigraphic relationship of these samples was not closely described on account of their derivation mostly from limestone floats and separated limestone blocks, and similarly a detailed faunal composition of most of our material is not possible because of insufficient fossil preservation. As described and discussed in the following, however, our material is divided into eight groups of different age based on the comparison of fusulines distinguished in the following 17 samples with those of previous works in and outside Japan: (1) Is-1 of early Kasimovian; (2) Kb-1 and Kb-5 of middle Kasimovian; (3) Is-18 of late Kasimovian to possibly early Gzhelian; (4) Kb-7 possibly late Gzhelian; (5) Is-8, Is-10, Ay-1, and Ay-13 of Artinskian; (6) Ob-5b, Ob-7, and Ay-12 of possibly middle Wordian; (7) Ob-8 of late Wordian; and (8) Is-19, Ob-4, Ob-5a, and Ay-15 of Capitanian.
Taxonomic remarks
Diagnostic test characters and spatiotemporal distribution of some fusulines in the Sakamototoge area and their comparison with previous works are reviewed. Some fusulines that are less common, not well oriented, and/or not well preserved are also commented on and illustrated on account of the comparison with those of previous works and future studies in the area.
Protriticites subschwagerinoides
Rozovskaya, 1950
Figures 4.33–4.44
The illustrated specimens were obtained from one sample (Is-1) among six (Is-1–6) assigned to the Akiyama Formation in Irasubora (Fusulinella-Fusulina Zone in Kanuma, 1958a). They resemble specimens identified with Fusulinella bocki von Möller, 1878 and F. biconica (Hayasaka, 1924) by Kanuma (1953) from Irasubora. Wall of the middle and outer whorls in the present and possibly in Kanuma's specimens is composed of a tectum and a thicker translucent layer comparable to the protheca (Figure 4.44). The translucent layer is light-colored and finely perforated. It is different from the true diaphanotheca typically recognized in the wall of the genus Fusulinella. Wall structure and other test characters such as shape and size of the test, mode of septal folding, and development of chomata in the Irasubora specimens suggest their assignment to Protriticites subschwagerinoides, originally described from the lower Kasimovian of the Moscow Basin (Rozovskaya, 1950). Most specimens identified with other species of Fusulinella by Kanuma (1953) are reassigned to Protriticites due to the absence of a true diaphanotheca in their wall structure.
Protriticites kiyomiensis
(Kanuma, 1958b)
Figures 5.10–5.18
Many specimens referable to this species were recognized from Kb-5 in association with Montiparus mesopachus Rozovskaya, 1950. This species, originally assigned to Triticites by Kanuma (1958b), is somewhat similar to M. matsumotoi (Kanmera, 1955). However, the former has a smaller test and weaker chomata restricted to the tunnel sides and not extending poleward. A translucent layer with finely porous structure, though mostly obscured due to weak recrystallization of the wall, is preserved in the outer whorls (Figure 5.17). Variably deformed forms of this species appear to be an elongate form of Protriticites or a primitive form of Montiparus. This species is preferably referable to Protriticites rather than Montiparus because of its less developed chomata.
Triticites opparensis Kanuma, 1958b, T. opparensis var. longiformis Kanuma, 1958b, T. irasensis Kanuma, 1958b, and T. nakatsugawaensis Morikawa, 1953 described by Kanuma (1958b) are presumed to be conspecific with this species, since most of them seem to be represented by incomplete specimens of Protritcites kiyomiensis. They are uneasily distinguished from each other by slight differences of some test characters, as indicated by Kanuma (1958b). In addition to these five forms referable to Protriticites, Kanuma (1958b) described T. kawanoboriensis Huzimoto, 1937 from the Okumyogata Formation exposed at Irasubora. It is different from the types from Furendo (Furen Limestone Cave), Oita Prefecture (Huzimoto, 1937) in its more distinct chomata and thinner wall. “T. kawanoboriensis” from Irasubora is assumed to be reassignable to Rauserites exculptus (Igo, 1957) originally proposed from the Ichinotani Formation. R. exculptus is not recognized in our samples.
Montiparus mesopachus
Rozovskaya, 1950
Figures 5.1–5.9
Five specimens described as Schellwienia subnathorsti Lee, 1927 by Kanuma (1958b) from Irasubora are not identifiable with the original specimens of Lee (1927) from the Upper Carboniferous of North China. Types of this species have a tapering test with concave lateral sides and more protruding poles, and much more strongly folded septa. Kanuma's (1958b) specimens seem to be referable to Montiparus mesopachus, originally described as a subspecies of Triticites (Montiparus) paramontiparus from the middle Kasimovian of European Russia (Rozovskaya, 1950). Montiparus mesopachus recognized in Kb-1 and Kb-5 is distinguished from Protriticites kiyomiensis in its chambers being higher than for the corresponding whorls of the latter and a thicker wall in the outer whorls (Figure 5.7). It is different from Schwagerina satoi originally described from the Akiyoshi Limestone Group by Ozawa (1925) in its thinner wall in the outer whorls, almost planar septa in the median part of the test, more loosely coiled inner whorls, and larger proloculus. Two specimens of Triticites from Irasubora that were compared to T. plummeri Dunbar and Condra, 1928 by Kanuma (1958b) probably correspond to incomplete specimens of Schwagerina satoi.
Figure 3.
Foraminifers recognized in 22 limestone samples in the Sakamototoge area. Sample numbers correspond to those in Figure 2.
Rauserites arcticus
(Schellwien, 1908)
Figures 5.29–5.31, 6.1–6.8
Many elongate fusiform specimens contained in Is-18 are identified with Rauserites arcticus, taking broad intraspecific variations of the topotype specimens from the upper Carboniferous of Spitzbergen (Forbes, 1960) and many specimens from the upper Kasimovian of the Akiyoshi Limestone Group (Kobayashi, 2017) into account. This species is widespread in the upper Kasimovian to lower Gzhelian from the Tethyan to Arctic regions through Pechora and Timan. Triticites paraarcticus Rauzer-Chernousova, 1938 and T. pseudoarcticus Rauzer-Chernousova, 1938, both which were later reassigned to Triticites (Rauserites) by Rozovskaya (1950), are inferred to be synonymous with Rauserites arcticus as was done by Kobayashi (2017).
Triticites onoensis proposed by Kanuma (1958b) from Irasubora and Oirasubora is presumed to be a junior synonym of Rauserites arcticus. Its appearance of weaker septal folding than that of R. arcticus and of almost planar septa in the median part of the test is due to the secondary mineralization of the outer part of the test.
Figure 4.
Foraminifers from the Sakamototoge area (1). 1, 2, Pachyphloia schwageri Sellier de Civrieux and Dessauvagie, 1965, Ob-8; 1, D2-066864; 2, D2-066857; 3, Globivalvulina sp., D2-066863, Ob-8; 4, 10, Baisalina sp., both D2-066864, Ob-8; 5, 11, Baisalina ovata Han, 1982, ob-8; 5, D2-066865; 11, D2-066857; 6, 12, Hemigordiopsis minoensis Kobayashi, 2012, Is-19; 6, D2-066794; 12, D2-066789; 7, Agathammina pusilla (Geinitz, 1876), D2-066788, Is-19; 8, 9, Agathammina sp., Ob-8; 8, D2-0066859; 9, D2-0066858; 13, Nankinella sp. A, D2-066738, Is-18; 14, Nankinella sp. B, D2-066833, Ob-5b; 15–17, Kahlerina sp.; 15, D2-066912, Ob-19; 16, D2-066864, Ob-8; 17, D2-066837, Ob-5b; 18, Rauserella sp., D2-066857, Ob-8; 19, 21, Schubertella donetzica Putrya, 1940, Kb-1; 19, D2-066945; 21, D2-066931; 20, Biwaella sp., D2-067082, Ay-13; 22–27, Pamirina leveni Kobayashi, 1977, Is-8; 22, D2-0666881; 23, D2-066689; 24, 27, D2-066685; 25, D2-066692; 26, D2-066690; 28–32, Mesoschubertella thompsoni Sakagami in Kanuma and Sakagami, 1957, Ay-1; 28, 29, 31, D2-067021; 30, 32, D2-067026; 33–44, Protriticites subschwagerinoides Rozovskaya, 1950, Is-1; 33, 42, D2-066651; 34, D2-066648; 35, D-066655; 36, 38, D2-066657; 37, D2-066656; 39, D2-066645; 40, D2-066654; 41, D2-066650; 43, D2-066654; 44, enlarged part of 40. Scale bar of 1 mm is shown at the right end.
Figure 5.
Foraminifers from the Sakamototoge area (2). 1–9, Montiparus mesopachus Rozovskaya, 1950, Kb-1; 1, D2-066940; 2, D2-066930; 3, D2-066932; 4, D2-066923; 5, D2-066926; 6, D2-066933; 7, enlarged part of 2; 8, D2-066935; 9, D2-066936; 10–18, Protriticites kiyomiensis (Kanuma, 1958b), Is-18; 10, D2-066967; 11, D2-066972; 12, D2-066969; 13, D2-066965; 14, 15, D2-066964; 16, 17 (enlarged part of 16), D2-066965; 18, D2-066979; 19–23, Quasifusulina longissima (von Möller, 1878), Is-18; 19, D2-066745; 20, D2-066731; 21, D2-066754; 22, D2-066763; 23, D2-066766; 24–28, Carbonoschwagerina nakazawai (Nogami, 1961), Is-18; 24, D2-066738; 25, D2-066771; 26, D2-066773; 27, D2-066776; 28, D2-066770; 29–31, Rauserites arcticus (Schellwien, 1908), Is-18; 29, D2-066741; 30, D2-066737; 31, D2-066750. Scale bar of 1 mm is shown at the right end.
Quasifusulina longissima
(von Möller, 1878)
Figures 5.19–5.23
This species distinguished in Is-18 coexists with Rauserites arcticus and Carbonoschwagerina nakazawai. Quasifusulina longissima is widespread in the upper Carboniferous of the Tethyan regions and shows broad intraspecific variation especially in the size of the proloculus. Smaller forms among the five illustrated herein and others are only incomplete specimens of this species. This species was reported from the lower part of the Oppara Formation at Irasubora (Kanuma, 1958a), though it was neither described nor illustrated in Kanuma's later papers.
Carbonoschwagerina nakazawai
(Nogami, 1961)
Figures 5.24–5.28
Specimens illustrated are similar to the types of Carbonoschwagerina nakazawai from the Atetsu Limestone (Nogami, 1961) and to many specimens described by Kobayashi (2017) from the upper Kasimovian to middle Gzhelian of the Akiyoshi Limestone Group. Seventeen such specimens from Atetsu and Akiyoshi are illustrated in Figure 8 for comparison. In spite of the few mature and few well preserved specimens in Is-18, they are considered to be identical with a primitive form of this species based on size and shape of the test and mode of septal folding. This species is distinguished from C. morikawai by its smaller and not so inflated test with larger proloculus, and not so rapidly expanding outer whorls. It is different from C. nipponica Kobayashi, 2017, a transitional form from Montiparus to Carbonoschwagerina, in its larger test and larger length and width in corresponding whorls.
Mesoschubertella thompsoni
Sakagami in Kanuma and
Sakagami, 1957
Figures 4.28–4.32
Mesoschubertella sp. from Irasubora by Kanuma (1960) is quite identical with the present specimens from Akiyama (Ay-1, 13). It has a shorter fusiform test than M. shimadaniensis proposed by Kanuma in Kanuma and Sakagami (1957) from the Hachiman area about 25 km SSW of Sakamototoge. Mesoschubertella thompsoni is characteristic and almost confined to the Artinskian (Kobayashi, 2005).
Pamirina leveni
Kobayashi, 1977
Figures 4.22–4.27
Six specimens illustrated from Is-8 and Is-10 well resemble Staffella sp. described by Kanuma (1960) from Irasubora and the Hachiman area. They are identified with the types of Pamirina leveni from the Kanto Mountains (Kobayashi, 1977) in their many similarities of size and shape of the test and ontogenetic change of wall structure from a single layer in the inner few whorls to a tectum and thin translucent layer in the succeeding whorls.
Chusenella japonica
(Ishii and Takahashi, 1960)
Figures 6.19, 6.21–6.23
Elongate fusiform Chusenella with tightly coiled inner few whorls, sharply pointed poles, and corrugated wall was distinguished in Ob-5b and Ob-7. It is identified with Chusenella japonica based on similarities of these morphologic characters. This species, originally assigned to Schwagerina, was first described by Ishii and Takahashi (1960) in association with unnamed species of Neoschwagerina from limestone pebbles of the conglomerate of the Ogamata Formation in the Kanto Mountains. Chusenella sp. (Figures 6.9, 6.10) from Ob-4 and Ob-7 is distinguished from C. japonica in its less corrugated wall and more loosely coiled inner whorls.
“
Leeina” kraffti
(Schellwien and Dyhyrenfurth, 1909)
Figures 6.12, 6.16
Two specimens illustrated from Is-8 and Ay-1 are presumed to be identified with the type material of Schellwienia kraffti by Schellwien and Dyhrenfurth (1909) and subsequent specimens by many authors who reassigned this species to Pseudofusulina. Pseudofusulina kraffti is designated as the zonal species of the upper Artinskian of the Akiyoshi Limestone Group (Ozawa and Kobayashi, 1990). These materials referred to P. kraffti are considerably different from the type species of Pseudofusulina, and might be further reassigned to another genus, e.g. Leeina Galloway, 1933 as did Leven (2009). Although the taxonomic independency of Leeina is questionable as doubted by Thompson (1964), this species is provisionally assigned to “Leeina” herein.
Figure 6.
Foraminifers from the Sakamototoge area (3). 1–8, Rauserites arcticus (Schellwien, 1908), Is-18; 1, D2-066753; 2, D2-066754; 3, D2-066769; 4, D2-066728; 5, D2-066748; 6, D2-066773; 7, D2-066752; 8, D2-066774; 9, 10, Chusenella sp.; 9, D2-066815, Ob-4; 10, D2-066847, Ob-7; 11, Pseudofusulina? sp. A, D2-066710, Is-12; 12, 16, “ Leeina” kraffti (Schellwien and Dyhrenfurth, 1909); 12, D2-066687, Is-8; 16, D2-067026, Ay-1; 13, Schwagerinidae gen. et sp. indet. C, D2-066879, Ob-12; 14, Verbeekina sp., D2-067079, Ay-12; 15, Pseudofusulina? sp. B, D2-066683, Is-8; 17, Schwagerinidae gen. et sp. indet. A, D2-067022, Ay-1; 18, Schwagerinidae gen. et sp. indet. B, D2-066994, Kb-7; 19, 21–23, Chusenella otakiensis (Ishii and Takahashi, 1960); 19, D2-066835, Ob-5b; 21, D2-066851, Ob-7; 22, D2-066853, Ob-7; 23, D2-066846, Ob-7; 20, Schwagerinidae gen. et sp. indet. D, D2-067049, Ay-6; 24, Neoschwagerina minoensis Deprat, 1914. D2-066825, Ob-5a. Scale bar of 2 mm is for all.
Schwagerinidae gen. et sp. indet. B
Figure 6.18
Fusulines contained in Kb-7 (crinoidal packstone) are more or less deformed and recrystallized, and fragmented. Those having a relatively large test named Schwagerinidae gen. et sp. indet. B herein are questionably attributed to either Darvasoschwagerina or Carbonoschwagerina from their not elongate test, slender and numerous septa, and tightly coiled inner whorls, though exactly indeterminable due to unfavorable preservation in most specimens. Other fusulines accompaying them in Kb-7 are confined to smaller and fragmental schwagerinids questionably assigned to either Daixina or Jigulites. A Late Gzhelian age is provisionally assigned to this taxon.
Verbeekina
sp.
Figure 6.14
A few incomplete, almost spherical fusulines with thin wall and thin septa are contained in weakly recrystallized limestone of Ay-12 in association with many fragmented and crushed specimens of Neoschwagerina. They are probably assigned to Verbeekina, as parachomata that escaped recrystallization are sporadically retained in a few oblique sections.
Neoschwagerina minoensis
Deprat, 1914
Figures 6.24, 8.2, 8.10
Neoschwagerinids contained in three samples (Is-19; Ob-4, 5a) resemble the topotypes of Neoschwagerina minoensis described by Kobayashi (2011) from the Akasaka Limestone. This species is distinguished from other species of Neoschwagerina by its more narrowly rounded periphery, more or less concave lateral sides, and bluntly pointed poles in the outer whorls. Development of secondary transverse septula is not conspicuous in comparison with its large test with numerous whorls. Morphologic features of the inner whorls of this species resemble those of N. craticulifera (Schwager, 1883) and N. colaniae Ozawa, 1927 emend. Kobayashi, 2011. Precise identification of this species needs axial sections in a mature stage of the test.
Neoschwagerina margaritae
Deprat, 1913
Figure 7.3
Neoschwagerinid specimens distinguished in Ob-8 are identical with the types of Neoschwagerina margaritae described from North Vietnam by Deprat (1913). They are differentiated from Yabeina katoi (Ozawa, 1927) in their thicker wall and thicker primary transverse septula, and poorer development of secondary transverse septula, and from Y. globosa (Yabe, 1906) in their secondary transverse septula first appearing in a later ontogenetic stage.
Yabeina globosa
(Yabe, 1906)
Figures 7.4–7.7, 7.9
Specimens illustrated from three samples (Ob-4, 5a; Ay-15) are undoubtedly referable to Yabeina globosa based on the comparison with many topotype specimens from the Akasaka Limestone described by Kobayashi (2011).
Yabeina katoi
(Ozawa, 1927)
Figures 7.1, 7.11, 7.12
This species was originally assigned to Neoschwagerina by Ozawa (1927) based on the secondary transverse septula absent in inner whorls and poorly developed in outer whorls in comparison with those of Yabeina. Kobayashi (2011) made clear the morphologic variation of this species and its undoubted assignment to Yabeina based on topotype specimens from Akasaka. This species is distinguished from Yabeina globosa by its less developed secondary transverse septula, thinner wall, and slenderer septula.
Faunal analysis
The oldest fusuline fauna of the Sakamototoge area is represented by Kanmeraia hidaensis (Kanuma, 1953). This species, originally assigned to Wedekindellina?, is similar to K. pulchra (Rauzer-Chernousova and Belyaev in Rauzer-Chernousova et al., 1936) except for its larger test with more concave lateral sides. Three specimens of Fusulina quasicylindrica (Lee, 1927) identified by Kanuma (1953) from the Akiyama Formation are different from the types from the upper Moscovian of North China (Lee, 1927) in their larger and shorter subcylindrical test and greater number of whorls. These two species reported from Irasubora by Kanuma (1953), though not found in our samples, are supposed to be Myachkovian in age. This follows from the former being morphologically allied to K. pulchra, characteristic in the Myachkovian in the stratotypes of Russia (Figure 9), while similar forms to the latter are reported from the Myachkovian of the Moscow Basin (e.g. Fusulina mjachkovensis Rauzer-Chernousova in Rauzer-Chernousova et al., 1951; F. mosquensis Rauzer-Chernousova in Rauzer-Chernousova et al., 1951; F. consobrina Safonova in Rauzer-Chernousova et al., 1951).
Illustrated specimens identified with Fusulinella bocki and F. biconica from Irasubora by Kanuma (1953) are different from the type specimens of those species and are probably referable to Protriticites subschwagerinoides, as indicated above. Most specimens identified with other species of Fusulinella by Kanuma (1953) are presumably also reassignable to Protriticites. Along with Obsoletes obsoletus (Schellwien, 1908), P. subschwagerinoides is the zonal species of the lower Kasimovian in the Akiyoshi Limestone Group (Ozawa and Kobayashi, 1990; Kobayashi, 2017). Kanmeraia itoi (Ozawa, 1925) and F. biconica are designated as the zonal species of the Podolskian and Kashirian of the Akiyoshi Limestone Group (Kobayashi, 2017), respectively. “Staffella pseudosphaeroidea” Dutkevich, 1934 (= Parastaffelloides kanmerai Kobayashi, 2017) is very characteristic in the Podolskian of the Akiyoshi and Yayamadake limestones (Kobayashi, 2017; Kanmera, 1954). These three species have not been reported from the Sakamototoge area. Accordingly, the limestone blocks contained in the Akiyama Formation are considered to belong to the Myachkovian and the lower Kasimovian, and do not extend downward to the Podolskian (Figure 9).
Figure 7.
Foraminifers from the Sakamototoge area (4). 1, 11, 12, Yabeina katoi (Ozawa, 1927); 1, D2-0668115, Ob-4; 11, D2-066792, Is-19; 12, D2-066814, Ob-4; 2, 10, Neoschwagerina minoensis Deprat, 1914; 2, D2-066781, Is-19; 10, D2-066816, Ob-4; 3, Neoschwagerina margaritae Deprat, 1913. D2-066866, Ob-8; 4–7, 9, Yabeina globosa (Yabe, 1906); 4, D2-066818, Ob-4; 5, D2-067096, Ay-15; 6, D2-066828, Ob-5a; 7, D2-066813, Ob-4; 9, D-066811, Ob-4; 8, Neoschwagerina? sp., D2-066903, Ob-18. Scale bar of 2 mm is for all.
Figure 8.
Carbonoschwagerina nakazawai (Nogami, 1961). 1–3, type specimens from the Atetsu Limestone, after Nogami (1961); 1, axial section of the holotype; 2, axial section of the paratype; 3, tangential section of the paratype; 4–17, specimens from the Akiyoshi Limestone, after Kobayashi (2017); 4–11, 14–16, axial sections; 12, 13, 17, sagittal sections. Scale bar of 2 mm is for all.
Figure 9.
Fusuline biostratigraphic correlation of the Moscovian to Asselian in Akiyoshi, Yayamadake, and Sakamototoge.
Many forms with relatively small tests belonging to primitive Triticites sensu Kanuma from the Oppara Formation (Kanuma, 1958a, b) are reassigned mostly to Protriticites. More advanced forms of Triticites sensu Kanuma from the lower part of the Okumyogata Formation are attributed to Rauserites, Montiparus, Triticites, or Schwagerina. In the Akiyoshi Limestone Group, the Kasimovian is definitely divided into three zones (Figure 9; Kobayashi, 2017), previously subdivided into six by Ozawa and Kobayashi (1990). Three faunas are discriminated in the Kasimovian part of the Yayamadake Limestone, (1) Obsoletes gracilis (Kanmera, 1954), (2) M. matsumotoi (Kanmera, 1954) and Quasifusulinoides ohtanii (Kanmera, 1954), and (3) T. yayamadakensis Kanmera, 1955. They are correlative to those of the three zones of the Kasimovian in the Akiyoshi Limestone Group (Figure 9; Kobayashi, 2017). The “Triticites” faunas of the Oppara Formation and the lower part of the Okumyogata Formation by Kanuma (1958b) are reorganized and subdivided into three faunas of different ages, and compared to (1) P. subschwagerinoides, (2) M. mesopachus-P. kiyomiensis, and (3) Rauserites arcticus-Carbonoschwagerina nakazawai-Q. longissima based on our faunal and taxonomic reconsiderations, as discussed above.
Moreover, three species of Triticites having a relatively thick wall described from the lower part of the Okumyogata Formation by Kanuma (1958b) were not recognized in our material. They were identified by Kanuma (1958b) with T. cullomensis Dunbar and Condra, 1928, T. subventricosus Dunbar and Skinner, 1937, and T. uddeni Dunbar and Skinner, 1937. The first species was originally described from the Upper Pennsylvanian of Nebraska, and the second and third species from the lower Permian of Texas. These three species by Kanuma (1958b) are regarded as misidentified and should be revised to a few other species attributed to Triticites or Rauserites. They possibly range up to the early Gzhelian.
On the other hand, Triticites simplex (Schellwien, 1908) and Rauserites stuckenbergi (Rauzer-Chernousova, 1938), common in the lower Gzhelian of European Russia and the Akiyoshi Limestone Group (Kobayashi, 2017), have not been reported from the Sakamototoge area. Furthermore, R. major Rozovskaya, 1958, Jigulites magnus Rozovskaya, 1950, J. horridus (Kanmera, 1958), Daixina sokensis (Rauzer-Chernousova, 1938), and Pseudofusulina kumasoana Kanmera, 1958 have also not been reported from the area. These schwagerinid species having larger tests and more complicated test characters than those of the late Kasimovian and early Gzhelian are very common in the middle and upper Gzhelian of the Akiyoshi Limestone Group. Some of them are also characteristic in the coeval strata of the Yayamadake Limestone (Kobayashi, 2017). They are often accompanied by Carbonoschwagerina morikawai, C. minatoi, and Darvasoschwagerina shimodakensis (Kanmera, 1958) in Akiyoshi and Yayamadake (Kanmera, 1958; Kobayashi, 2017). These inflated schwagerinid species of the middle to late Gzhelian have also not been reported from the Sakamototoge area. However, Schwagerinidae gen. et sp. indet. B from Kb-7 is questionably assigned to Darvasoschwagerina or Carbonoschwagerina, as noted above. Two specimens of a relatively large and inflated schwagerinid were identified with Pseudoschwagerina orientale Huzimoto, 1937 by Kanuma (1959) from the limestone intercalated in the lower part of the Okumyogata Formation near Akiyama. This species, originally described by Huzimoto (1937), was once presumed to be one of the index species of the lowest Permian of Japan. However, the Akiyama specimens should be eliminated from Pseudoschwagerina and reassigned to an evolved form of Carbonoschwagerina similar to C. minatoi of the late Gzhelian by their large test with tightly coiled inner whorls with distinct chomata. Based on these lines of evidence, Schwagerinidae gen. et sp. indet. B contained in the limestone block at Kb-7 and “Pseudoschwagerina orientale” by Kanuma (1959) from Akiyama are supposed to be roughly coeval and probably late Gzhelian age (Figure 9).
Four specimens identified with the types of Pseudofusulinella utahensis Thompson and Bissel in Thompson (1954) were described by Kanuma (1958b) from the lower part of the Okumyogata Formation. Associated fusulines with this species are not shown and its exact age is uncertain. Kanuma's specimens should be separated from the types of North America and better reassigned to Kanmeraia japonica Ozawa, 1967. Although types of K. japonica are not accompanied by any age-diagnostic species in an exotic limestone block of the Raidenyama Formation, Ozawa (1967) designated its age as Early Permian. In this paper, “Pseudofusulinella utahensis” by Kanuma (1958b) is tentatively designated as late Gzhelian, because the “early Permian” in 1960s Japanese usage corresponds to the Gzhelian since the 1990s.
Asselian fusulines might be absent in the Sakamototoge area, since the species previously assigned to Pseudoschwagerina are attributed to Carbonoschwagerina that never extends up to the Asselian (Ozawa et al., 1992; Kobayashi, 2017). Moreover, in addition to lack of Sphaeroschwagerina, any species of Pseudoschwagerina widespread in the Asselian of Japan and the Tethyan regions (e.g. Pseudoschwagerina muongthensis Deprat, 1915) are unknown from the area. Fusulines certainly indexing the Sakmarian have also not been reported from the area. On the other hand, Kanuma (1959) described schwagerinids comparable to P. uddeni (Beede and Kniker, 1924) and Acervoschwagerina fujimotoi Kanuma, 1959 from the Hachiman area. The occurrence of these two species suggesting the presence of the lower Cisuralian, however, has not been reported from the Sakamototoge area.
Occurrences of Pamirina leveni, Mesochubertella thompsoni, and “Leeina” kraffti are highly indicative of the presence of the Artinskian in the Sakamototoge area. These species are confined to the Artinskian limestone blocks and fragments in the Kanto Mountains (Kobayashi, 1977, 2005). The first and third species are widespread in the upper Artinskian of Japan and Tethyan regions (e.g. Leven, 2009).
The presence of the Roadian and lower Wordian limestones in the Sakamototoge area is not exactly confirmed because there are no reports of Misellina or of primitive verbeekinids and neoschwagerinids. However, Verbeekina sp. and Neoschwagerina sp. from Ay-12 are supposed to be middle Wordian in age, as mentioned above. The presence of upper Wordian and Capitanian limestones was ascertained in this study. Neoschwagerina margaritae found in Ob-8 is confined to the upper Wordian of the Akasaka and other limestones in Japan. The Capitanian neoschwagerinid faunas consisting of N. minoensis, Yabeina globosa, and Y. katoi in the Sakamtotoge area closely resemble and are nearly the same as those of the Akasaka and many other limestones contained in the Jurassic terranes of Japan (e.g. Kobayashi, 1997, 2011). They are heterogeneous to the coeval neoschwagerinid faunas in the Permian terranes of Japan (Kobayashi, 1997; Kobayashi et al., 2010).
Thus, the previous results were reviewed on the basis of Kanuma's original and our additional materials, and current taxonomic and chronostratigraphic frameworks in this study. Conspicuous alterations to the previous results are summarized into: (1) Moscovian fusulines are confined to the Myachkovian, not descending into the Podolskian; (2) two species previously assigned to Fusulinella (F. biconica and F. bocki) and most specimens identified with other species of Fusulinella should be reassigned to Protriticites; (3) many species previously included collectively in Triticites are attributed to Protriticites, Montiparus, Rauserites, Triticites, or Schwagerina; (4) “Triticites” faunas previously designated as Carboniferous-Permian are reorganized and subdivided into three, P. subschwagerinoides (early Kasimovian), M. mesopachus-P. kiyomiensis (middle Kasimovian), and R. arcticus-Carbonoschwagerina nakazawai-Quasifusulina longissima (late Kasimovian to possibly early Gzhelian); and (5) the species attributed to Pseudoschwagerina is reassigned to a species of late Gzhelian Carbonoschwagerina, from which can be inferred the probable absence of the Asselian in the area. In addition, Capitanian neoschwagerinids characteristic in the Jurassic terranes of Japan and heterogeneous to the coeval neoschwagerinid faunas in the Permian terranes are ascertained in the area.
Acknowledgements
We are deeply grateful to Charles A. Ross and Atsushi Takemura who examined the early version of the manuscript and gave us constructive comments. Thanks are also due to two anonymous reviewers for their helpful comments. This study was financially supported by a Grant-in Aid for Scientific Research (C) of the Japan Society of the Promotion of Science in 2015 (Project No. 25400501).
