Introduction

The Nabeyama Formation in the Kuzu area, Tochigi Prefecture, is designated as the standard chronostratigraphic unit of the lower Middle Permian of Japan (Nabeyaman) on account of the abundant occurrence of well preserved fusulinoideans (Toriyama, 1967). Several species of Parafusulina were described from the lower part of the formation (Hanzawa, 1942; Morikawa and Takaoka, 1961; Igo, 1964; Chisaka and Fuse, 1973) and the underlying Izuru Formation (Morikawa and Horiguchi, 1956). However, the stratigraphic distribution of these parafusulinids and other fusulinoideans in these two formations has remained uncertain.

This paper shows the stratigraphic distribution of fusulinoideans in the formations, and discusses the faunal composition in the established three zones from lower to upper: Parafusulina nakamigawai, P. yabei, and P. tochigiensis zones. Nine species of schwagerinid, neoschwagerinid, and verbeekinid fusulinoideans, including two new species of Parafusulina, P. shimotsukensis and P. tochigiensis, are described. Many photographs of parafusulinids are illustrated so as to understand their wide morphologic variation. Schubertellid and ozawainellid fusulinoideans and non-fusulinoidean foraminifers of the Izuru and Nabeyama Formations will be described and discussed in future.

All limestone thin sections used in this study are registered and stored in the collection of the Museum of Nature and Human Activities, Hyogo (Fumio Kobayashi Collection).

Stratigraphy

Jurassic accretionary complexes in the Ashio Mountains consist of tectonically repeated stratigraphic sequences of Triassic to Jurassic chert and Jurassic terrigenous clastic rocks, and contain huge blocks of Upper Paleozoic limestone and basaltic rocks in the Kuzu area in the southern part of the mountains (e.g., Kamata, 1996; 1997). These rocks had been thought to be Permian by the end of 1960's, and were originally classified from lower to upper into the Aisawa, Nabeyama, Adoyama, Maki, and Mikagura formations in the Kuzu area (Yoshida, 1956; 1957). Fujimoto (1961) redefined the Nabeyama Formation by establishing the Izuru Formation and subdivided the newly defined Nabeyama Formation into three members, the lower Yamasuge Limestone, middle Hanezuru Dolostone, and upper Karasawa Limestone. The Izuru and Nabeyama formations are laterally traceable for more than 20 km, showing a horseshoe-shaped outline (Figure 1).

Figure 1.

Index map showing the surveyed area and distribution of Nabeyama and Izuru Formations in the Kuzu area.

The Izuru Formation is about 400 m in its maximum thickness and is in thrust contact with the Jurassic siliciclastic rocks assiganble to the Aisawa Formation (Koike et al., 1971). It consists mostly of basaltic pyroclastic rocks and lava. Lenticular limestones are intercalated within pyroclastic rocks in the upper part. They are dark gray, bedded, tuffaceous, and partly dolomitized. Many fossils such as crinoids, foraminifers, marine algae, sponges, brachiopods, and bryozoans are abundant in them. Some of these fossils also occur in pyroclastic rocks.

The Nabeyama Formation consists of limestone, dolomitic limestone, and dolostone of about 300 m thickness measured at Yamasuge (Figure 2), Karasawa (Figure 3), Nagaami (Figure 4), and Ohgama (Figure 5). Lenticular pyroclastic rocks are intercalated in its lower part. Although the formation is not lithostratigraphically subdivided, it is correlated on the basis of the stratigraphic boundary between the Izuru and Nabeyama Formations as done by Kobayashi (1979) (Figure 6).

Figure 2.

Geological map and sample localities in Yamasuge.

Figure 3.

Geological map and sample localities in Karasawa. Legend of lithology is the same as in Figure 2.

Figure 4.

Geological map and sample localities in Nagaami. Legend of lithology is the same as in Figure 2.

Figure 5.

Geological map and sample localities in Ohgama. Legend of lithology is the same as in Figure 2.

Figure 6.

Stratigraphic columns (after Kobayashi, 1979), stratigraphic distribution of fusulinoideans, and biostratigraphic zonation in the Izuru and Nabeyama Formations. The locations of stratigraphic columns A-A′ and B-B′ in Yamasuge, and those of A-A′ and B-B′-B″ in Karasawa are shown in Figure 2 and 3, respectively.

Limestones of the lower part of the formation are mostly dark gray and bedded. They are partly laminated, interbedded with thin tuffaceous and calcareous argillaceous rocks, and contain nodular chert. These limestones consist of dominant pack-stone, wackestone, and lime-mudstone, and subordinate oncoidal boundstone/framestone and grainstone. Some of them are secondarily dolomitized, and the post-depositional dolomitization becomes conspicuous stratigraphically upwards (Kobayashi, 1979). The middle part of the Nabeyama Formation consists mostly of dolostone (Figure 6). The upper part of the Nabeyama Formation is composed mainly of light gray to dark gray massive limestones. They consist of dominant fusulinoidean packstone and accessary wackestone, lime-mudstone, grainstone, oncoidal boundstone/framestone, and cerioid coral boundstone.

Fossils are diversified and abundant in limestones of the Nabeyama Formation, such as foraminifers, especially large-sized fusulinoideans, marine algae, crinoids, sponges, hydrozoans, rugose corals, bryozoans, brachiopods, bivalves, gastropods, and ostracods. They are dolomitized variously in the lower part of the formation (Kobayashi, 1979). Fusulinoideans, crinoids, brachiopods, and other indeterminable fossils are nearly completely replaced by mosaic dolomite in the middle part of the formation.

The limestone conglomerate unconformably overlying the Nabeyama Formation consists of ill-sorted granules to boulders of limestone, dolomitic limestone, dolostone, and chert, which are packed within laminated, arenaceous to argillaceous limestone. Most of these lithic clasts were derived from the Nabeyama Formation. Pebbles to boulders of Middle to Late Permian limestone are also discriminated in this limestone conglomerate (Igo and Igo, 1977; Kobayashi, 1979). The laminated limestone originated from the karst deposits fills up the crevices of dolostone and limestone in the middle and upper parts of the formation, showing several millimeter- to centimeter-order depositional sequences with upward-fining successions (Kobayashi, 1979). A mixed fauna of late Olenekian to early Norian conodonts is reported from these laminated limestones (Koike et al., 1974).

Biostratigraphy

Three fusulinoidean zones are distinguished from lower to upper: the Parafusulina nakamigawai, Parafusulina yabei, and Parafusulina tochigiensis zones, based on their stratigraphical distribution in the Izuru and Nabeyama Formations (Figure 6). Biostratigraphic subdivision by other foraminifers is inferior to these parafusulinids.

Parafusulina nakamigawai Morikawa and Horiguchi, 1956 is found only in impure limestone and pale green basaltic tuff at Loc. 4 in Nagaami (Figure 4) in association with Parafusulina sp., which occurs in two levels of the Izuru Formation in Yamasuge. The Parafusulina nakamigawai Zone is assigned to the Izuru Formation except for its uppermost part where Parafusulina yabei Hanzawa, 1942 first occurs. Other fusulinoideans such as Dunbarula? sp. and Rauserella? sp. are exceedingly rare in this zone.

The base of the Parafusulina yabei Zone is defined at Yamasuge by the first occurrence of Parafusulina yabei in the uppermost part of the Izuru Formation. The top of this zone corresponds to the level of the first occurrence of Parafusulina tochigiensis in Ohgama (Figure 6). This zone represents the bedded limestone of the lower part of the Nabeyama Formation. Parafusulina yabei is very characteristic and abundant in this zone along with Parafusulina kuzuensis Chisaka and Fuse, 1973. In addition to these two species of Parafusulina, Rauserella ellipsoidalis Sosnina, 1968, R. sp. A, Dunbarula schubertellaeformis Sheng, 1958, D. sp. A, Codonofusiella sp. B, C. sp. C and Neofusulinella sp. are discriminated in this zone. The occurrence of the latter two species is restricted to this zone. The former five species also occur in the Parafusulina tochigiensis Zone. Neither verbeekinid nor neoschwagerinid fusulinoideans are detected from this zone.

The Parafusulina tochigiensis Zone corresponds to the middle and upper parts of the Nabeyama Formation. The zonal species first occurs in the level beneath thick dolostone of the middle part of the formation in Ohgama (Figure 6). Although specific identification of Parafusulina is impossible due to remarkable replacement by dolomite in the middle part of the formation, Parafusulina yabei and Parafusulina kuzuensis seem not to extend to this zone. Parafusulina tochigiensis co-exists with Parafusulina shimotsukensis in the middle and upper parts of this zone. Parafusulina japonica (Gümbel, 1874) occurs in more than twenty stratigraphic levels and its biostratigraphic range extends to the uppermost part of the Nabeyama Formation. Gifuella amicula Honjo, 1959, Gifuella sp., Neoschwagerina spp., and Pseudodoliolina ozawai Yabe and Hanzawa, 1932 are restricted to this zone, and occur in association with dominant Parafusulina japonica. Other fusulinoideans including Chusenella sp., Yangchienia compressa (Ozawa, 1927), and Paradoxiella sp. also exclusively occur in this zone.

Fusulinoidean fauna and its correlation

Taxonomic diversity of the Parafusulina nakamigawai Zone is very low. Dunbarula? sp., Rauserella? sp., and a palaeotextulariid of unknown affinity are rarely discriminated in addition to the zonal species and Parafusulina sp. (Figure 6). Parafusulina nakamigawai was described from the limestone intercalated within tuff, exposed in Nagaami, which was erroneously referred to the Adoyama Formation by Morikawa and Horiguchi (1956). This species is restricted to the basal part of the Akasaka Limestone and does not extend to the Cancellina nipponica Zone in the limestone (Ozawa and Nishiwaki, 1992) and the limestone immediately above the Misellina claudiae Zone of the Kozaki Formation of west Kyushu (Kanmera, 1963). The Parafusulina nakamigawai Zone of the Izuru Formation is correlated to the P. nakamigawai Zone of the Akasaka Limestone. This zone is thought to be probably equivalent to Kubergandian in age in the Tethyan standard scale based on the stratigraphic distribution of Misellina and Cancellina in Southeast Pamir (Leven, 1967) and Afghanistan (Leven, 1997), and the comparison of verbeekinid and neoschwagerinid faunas between Japan and outside Japan (Kobayashi, 1997a; 1997b). Low specific diversity of foraminifers in the Parafusulina nakamigawai Zone in Kuzu is common in the biostratigraphic range of the species in Akasaka and Kozaki.

Parafusulina yabei and Parafusulina kuzuensis are abundant in and restricted to the Parafusulina yabei Zone. This zone is surely younger than the Kubergandian Parafusulina nakamigawai Zone, and other fusulinoideans in this zone such as Rauserella ellipsoidalis and two unnamed species of Codonofusiella, C. sp. B and C. sp. C, suggest a Middle Permian age. More detailed age determination of the zone is, however, difficult due to complete absence of neoschwagerinids and verbeekinids in the Kuzu area.

Parafusulina yabei and its allied forms were reported from the Mino Terrane (Morikawa, 1958; Igo, 1959; Morikawa and Isomi, 1961) and Kozaki (Kanmera, 1963). Biostratigraphic and paleontologic data, however, are insufficient in them to discuss closely the age and correlation of the Parafusulina yabei fauna. On the other hand, as well as Parafusulina nakamigawai, complete absence of Parafusulina yabei in the Permian terranes of Japan is very significant paleobiogeographically and tectonically with respect to westward drifting of the Panthalassan seamount (Kobayashi, 1997b, 1999, 2004).

Species composition of foraminifers is more diversified in the Parafusulina tochigiensis Zone than in the Parafusulina yabei Zone, though it is unclear in the dolomitized lower part. More than twenty species of fusulinoideans are discriminated, and about half of them exclusively occur in this zone (Figure 6). Non-fusulinoidean foraminifers are also prolific and diversified. Among them, Neodiscus padangensis (Lange, 1925), Climacammina valvulinoides Lange, 1925, Pachyphloia schwageri Sellier de Civrieux and Dessauvagie, 1965, and Tetrataxis spp. are prevailing. However, detailed discussion on biostratigraphic correlation and age determination is not easy in this zone, because the zonal species and Parafusulina shimotsukensis are newly proposed herein, and a reliable biostratigraphic range for Parafusulina japonica, the most dominant species in this zone, cannot be determined exactly from the many previously published references (e.g., M. Kobayashi, 1957; Morikawa, 1958; Ozawa and Nishiwaki, 1992; F. Kobayashi, 1997b; 2005b).

The occurrence of Gifuella amicula is restricted to the upper part of the Neoschwagerina craticulifera Zone to the lower part of the Neoschwagerina margaritae Zone of the Akasaka Limestone (Honjo, 1959; Ozawa and Nishiwaki, 1992; Zaw Win, 1999). Pseudodoliolina ozawai is dominant in the Pseudodoliolina ozawai Zone between the lower Cancellina nipponica Zone and the upper Neoschwagerina craticulifera Zone in the Akasaka Limestone (Ozawa and Nishiwaki, 1992; Zaw Win, 1999), and ranges upward into the Neoschwagerina craticulifera Zone (Ozawa and Nishiwaki, 1992).

Biostratigraphic correlation between the Nabeyama Formation and the Akasaka Limestone shows that the middle part of the Parafusulina tochigiensis Zone with Gifuella amicula is probably correlative to the upper part of the Neoschwagerina craticulifera Zone to the lower part of the Neoschwagerina margaritae Zone. The Murgabian age of the Neoschwagerina craticulifera Zone is widely accepted among fusulinoidean paleontologists. On the other hand, there are unresolved problems concerning the age assignment of the Neoschwagerina margaritae Zone in relation to the species identification of “Neoschwagerina margaritae Deprat, 1913” by authors and the taxonomic validity of Yabeina ozawai Honjo, 1959 (Honjo, 1959; Leven, 1996), and the first appearance of Yabeina in the Tethyan regions especially in the Akasaka Limestone, based on which the Murgabian-Midian boundary is defined (Leven, 1993Leven, 1996). Faunal correlation of the Middle Permian fusulinoideans in the Tethyan (Kobayashi, 1997a) and Circum-Pacific regions (Kobayashi, 1997b) suggests that the middle part of the Parafusulina tochigiensis Zone corresponds to the Murgabian or Wordian in age. The Parafusulina tochigiensis Zone does not exactly correspond to the stratigraphic range of Pseudodoliolina ozawai in the Nabeyama Formation. Other fusulinoideans exclusively found in this zone are also less useful and reliable for correlation.

The difficulty of correlation of the Nabeyama Formation by fusulinoidean biostratigraphy is obviously caused by and related to the absence of such marker species as Cancellina nipponica Ozawa, 1927, Neoschwagerina simplex Ozawa, 1927, Neoschwagerina craticulifera (Schwager, 1883), and Neoschwagerina margaritae, which have been used widely for the regional biostratigraphic correlation of the Japanese Middle Permian since Y. Ozawa (1927). More precise correlation and age determination of three fusulinoidean zones proposed herein are possible when bio-stratigraphic zonation by schwagerinids is made clear in relation to the stratigraphic range of neoschwageri-nids in Middle Permian limestones of the Jurassic terrane of Japan.

Systematic paleontology

Superfamily Fusulinoidea von Möller, 1878

Family Schwagerinidae Dunbar and Henbest, 1930

Genus Parafusulina Dunbar and Skinner, 1931

Type species.—Parafusulina wordensis Dunbar and Skinner, 1931, p. 261–263, pl. 2, figs. 1–4.

Discussion.—Although typical species assigned to Parafusulina (Skinnerella) by Coogan (1960) are easily distinguished from those of Parafusulina (Parafusulina) by many test characters, there are some species uneasily determinable in their generic affinity to either Parafusulina (Parafusulina) or Parafusulina (Skinnerella) with respect to the form of outer and inner whorls, development of cuniculi and axial filling, and septal folds, as pointed out by Kanmera (1963) and Skinner (1971). On the other hand, the much larger test size of microspheric forms of Parafusulina (Parafusulina) than those of Parafusulina (Skinnerella) is very characteristic (Skinner, 1971). This difference in test size is thought to be closely related to the evolution of advanced forms of schwagerinids, in comparison with the marked difference of test size between megalospheric and microspheric forms of neoschwa-gerinids assignable to Neoschwagerininae Dunbar and Condra, 1927 and Lepidolininae A.D. Miklukho-Maklay, 1958.

Parafusulina yabei and P. japonica, characteristic in the Nabeyama Formation, were assigned to Parafusulina (Skinnerella) by Coogan (1960). Other species of Parafusulina from the formation have also some morphologic characters closer to Parafusulina (Skinnerella) than Parafusulina (Parafusulina). Certain authors such as Leven (1997), Kobayashi and Ishii (2003), and Leven and Mohaddam (2004) recognized the taxonomic validity of Skinnerella from characteristic features of septal fluting in their Afghan and Iranian materials. However, no microspheric forms of Skinnerella or Parafusulina were shown by them. Although Leven and Mohaddam (2004) suggested the gradual morphologic change of test characters from Chalaroschwagerina to Skinnerella, any differences between Skinnerella and Parafusulina were not pointed out by them.

In this paper, Parafusulina is not treated as a sub-generic rank, and species described below are all assigned to Parafusulina until taxonomic discussion on the basis of the ontogenetic and phylogenetic relationships or other paleontologic analysis of Middle Permian schwagerinids is possible.

Material examined.—Illustrated twenty-five and other specimens.

Discussion.—According to T. Kobayashi (1980), Gümbel introduced “Fusulina japonica” in 1874 for a form having a shorter cylindrical test, and a greater number of and larger height of whorls in comparison with those of Fusulina cylindrica Fischer de Waldheim, 1829. Later, Schwager (1883) illustrated “Fusulina japonica” based on the original materials by Gümbel probably collected in the Akasaka Limestone.

The present materials are closely similar to the original ones from the Akasaka Limestone by Gümbel in Schwager (1883). Distinction of this species from immature specimens or fusiform forms of Parafusulina tochigiensis is not easy. Specific identification of either P. japonica or P. tochigiensis requires many well oriented mature specimens. The former has a larger proloculus, smaller form ratio of test and of corresponding whorls, and more arched periphery than the latter. Parafusulina japonica differs from Parafusulina sp. from the Izuru Formation in having a larger test, larger proloculus, and more strongly folded septa.

Figure 7.

Schwagerinids of the lower part of the Nabeyama Formation (1). 1–20. Parafusulina yabei Hanzawa. All from Yamasuge (Figure 2). 1, 4 and 7: ×10; others: & times;5. 1: D2-006421, Loc. Ya-30; 2: D2-006439, Loc. Ya-30; 3: D2-006560, Loc. Ya-32; 4: D2-006448, Loc. Ya-30; 5: D2-006532, Loc. Ya-32; 6: D2-006502, Loc. Ya-30; 7: D2-006541, Loc. Ya-32; 8: D2-006454a, Loc. Ya-30; 9: D2-006572, Loc. Ya-32; 10: D2-006445, Loc. Ya-30; 11: D2-006531, Loc. Ya-32; 12: D2-006320, Loc. Ya-22; 13: D2-006437, Loc. Ya-30; 14: D2-006236, Loc. Ya-14; 15: D2-006623a, Loc. Ya-32; 16: D2-006497, Loc. Ya-30; 17: D2-006472, Loc. Ya-30; 18: D2-006441, Loc. Ya-30; 19: D2-006556, Loc. Ya-32; 20: D2-006374, Loc. Ya-27.

Figure 8.

Schwagerinids of the lower part of the Nabeyama Formation (2). 1–18. Parafusulina kuzuensis Chisaka and Fuse. 1–12, 15, 17, 18: from Yamasuge (Figure 2); others: from Ohgama (Figure 6). 1, 2, 4 and 5: ×10; others: ×5. 1: D2-006568, Loc. Ya-32; 2: D2-006479, Loc. Ya-30; 3: D2-006594, Loc. Ya-32; 4: D2-006370, Loc. Ya-27; 5: D2-006499, Loc. Ya-30; 6: D2-006494, Loc. Ya-30; 7: D2-006474, Loc. Ya-30; 8: D2-006581, Loc. Ya-32; 9: D2-006482, Loc. Ya-30; 10: D2-006550, Loc. Ya-32; 11: D2-006570, Loc. Ya-32; 12: D2-006548, Loc. Ya-32; 13: D2-008596, Loc. Og-12; 14: D2-008532, Loc. Og-2; 15: D2-006571, Loc. Ya-32; 16: D2-008575, Loc. Og-9; 17: D2-006473, Loc. Ya-30; 18: D2-006545, Loc. Ya-32.

Material examined.—Illustrated eighteen and other specimens.

Discussion.—Present specimens are variable in many characters such as size, form, and expansion of test, septal folds in tunnel and polar regions, and development of axial filling. All these differences from specimen to specimen are considered to merely represent the intraspecific variation of Parafusulina kuzuensis originally described from the lower part of the Nabeyama Formation by Chisaka and Fuse (1973). Smaller forms illustrated are thought to represent the immature stage or specimens whose outer whorls were abraded. Ten specimens named Parafusulina kaerimizensis in association with Parafusulina yabei by Igo (1964) from the lower part of the Nabeyama Formation may be referable to Parafusulina kuzuensis on account of the wide morphologic variation of this species.

The holotype of this species of Chisaka and Fuse (1973) attains an axial length of about 25 mm, which is the longest length recorded among Parafusulina described from Japan. The holotypes of Parafusulina tomeganensis from the Akasaka Limestone (Morikawa, 1958) and Parafusulina iisakai from the Funafuseyama Limestone (Igo and Ogawa, 1958) also have large and elongate tests. These three species may be conspecific. However, close comparison of the three species is difficult and is postponed until more specimens from the Akasaka and Funafuseyama limestones are accumulated.

Figure 9.

Schwagerinids of the upper part of the Nabeyama Formation (1). 1–8. Parafusulina shimotsukensis, n. sp. All from Karasawa (Figure 3). 1, 4 and 7: ×10; others: ×5. 1: D2-007817, Loc. Ka-70; 2: D2-007789, Loc. Ka-70; 3: D2-007960, Loc. Ka-71; 4: D2-007774, Loc. Ka-70; 5: D2-007819, Loc. Ka-70; 6: D2-007775, Loc. Ka-70; 7: D2-007746, Loc. Ka-70; 8: D2-007796, Loc. Ka-70.

Figure 10.

Schwagerinids of the upper part of the Nabeyama Formation (2). 1–13. Parafusulina shimotsukensis, n. sp. All from Karasawa (Figure 3). 1, 4 and 13: ×10; others: ×5. 1: D2-008353, Loc. Ka-86; 2: D2-008344a, Loc. Ka-86; 3: D2-007440, Loc. Ka-47; 4: D2-007777, Loc. Ka-70; 5: D2-008179, Loc. Ka-73; 6: D2-007437, Loc. Ka-47; 7: D2-007453, Loc. Ka-47; 8: D2-007751, Loc. Ka-70; 9: D2-007577, Loc. Ka-57; 10: D2-007761, Loc. Ka-70; 11: D2-007809, Loc. Ka-70; 12: D2-007787, Loc. Ka-70; 13: D2-008186, Loc. Ka-73.

Figure 11.

Schwagerinids of the upper part of the Nabeyama Formation (3). 1–20. Parafusulina tochigiensis, n. sp. All from Karasawa (Figure 3) except for 18 and 19 from Ohgama (Figure 6). 1, 2 and 8: ×10; others: ×5. 1: D2-007864, Loc. Ka-70; 2: D2-007443, Loc. Ka-47; 3: D2-007449, Loc. Ka-47; 4: D2-007450, Loc. Ka-47; 5: D2-007852b, Loc. Ka-70; 6: D2-007447, Loc. Ka-47; 7: D2-007853, Loc. Ka-70; 8: D2-007849, Loc. Ka-70; 9: D2-007855, Loc. Ka-70; 10: D2-007828, Loc. Ka-70; 11: D2-008209, Loc. Ka-73; 12: D2-007441, Loc. Ka-47; 13: D2-007827, Loc. Ka-70. 14: D2-007442, Loc. Ka-47; 15: D2-007860, Loc. Ka-70; 16: D2-007824, Loc. Ka-70; 17: D2-007863, Loc. Ka-70; 18: D2-008561, Loc. Og-4; 19: D2-008554, Loc. Og-4; 20: D2-007902, Loc. Ka-70.

Figure 12.

Schwagerinids of the upper part of the Nabeyama Formation (4). 1–25. Parafusulina japonica (Gümbel). All from Karasawa (Figure 3). 1, 6, 9: ×10; 21b: ×20; others: ×5. 1: D2-006765, Loc. Ka-2; 2: D2-008128, Loc. Ka-72; 3: D2-007119, Loc. Ka-28; 4: D2-007204, Loc. Ka-33; 5: D2-008273, Loc. Ka-85; 6: D2-007140, Loc. Ka-28; 7: D2-007269, Loc. Ka-36; 8: D2-008357, Loc. Ka-87; 9: D2-007561, Loc. Ka-56; 10: D2-006767, Loc. Ka-2; 11: D2-007156, Loc. Ka-28; 12: D2-007120, Loc. Ka-28; 13: D2-007118, Loc. Ka-28. 14: D2-007283, Loc. Ka-36; 15: D2-007565, Loc. Ka-56; 16: D2-007267, Loc. Ka-36; 17: D2-007153, Loc. Ka-28; 18: D2-007114, Loc. Ka-28; 19: D2-007130, Loc. Ka-28; 20: D2-007117, Loc. Ka-28. 21: D2-008214, Loc. Ka-78; 22: D2-007546, Loc. Ka-54; 23: D2-007385, Loc. Ka-42; 24: D2-007202, Loc. Ka-33; 25: D2-006763, Loc. Ka-2.

Figure 13.

Schwagerinids of the Izuru Formation, and schwagerinids, neoschwagerinids, and verbeekinids of the upper part of the Nabeyama Formation. 1, 8–12. Parafusulina nakamigawai Morikawa and Horiguchi. All from Loc. Na-4 in Nagaami (Figure 4). 1: ×10; others: ×5. 1: D2-008462, 8: D2-008468, 9: D2-008464, 10: D2-008465, 11: D2-008474, 12: D2-008463. 2–7. Parafusulina sp. Fig. 2 from Loc. Na-4 in Nagaami, and others from Loc. Ya-25 in Yamasuge (Figure 2). 3: ×10, and others: ×5. 2: D2-008473, 3: D2-006342. 4: D2-006340, 5: D2-006341, 6: D2-006345, 7: D2-006358. 13–15. Chusenella sp. All from Karasawa (Figure 3), ×10. 13: D2-006883, Loc. Ka-14; 14: D2-007347, Loc. Ka-40; 15: D2-006880, Loc. Ka-14. 16–18. Gifuella amicula Honjo. All from Loc. Ka-40 in Karasawa, ×10. 16: D2-007360, 17: D2-007343, 18: D2-007344a. 19. Gifuella sp., D2-007344b, Loc. Ka-40 in Karasawa, ×10. 20–29. Pseudodoliolina ozawai Yabe and Hanzawa. All from Karasawa, ×10. 20: D2-007419, Loc. Ka-47. 21: D2-007325, Loc. Ka-40; 22: D2-008242, Loc. Ka-84; 23: D2-008232, Loc. Ka-81; 24: D2-007320, Loc. Ka-40; 25: D2-008355, Loc. Ka-87; 26: D2-007324, Loc. Ka-40; 27: D2-007323, Loc. Ka-40; 28: D2-008228, Loc. Ka-81; 29: D2-008246, Loc. Ka-84.

Lectotype.—Specimen illustrated by Morikawa and Horiguchi (1956, pl. 35, fig. 1) designated by Kanmera (1963), kept in the Department of Earth Sciences, Saitama University (register number not indicated), probably from a small limestone intercalated in the Izuru Formation exposed at Nagaami, Kuzu Town, Sano City, Tochigi Prefecture.

Material examined.—Illustrated six and other specimens.

Discussion.—This species has a characteristic subcylindrical test with slightly concave periphery, slightly curved axis of coiling, and bluntly to broadly rounded poles. Present materials are safely identical to the original ones of Morikawa and Horiguchi (1956).

Two specimens described by Igo (1964) as Parafusulina nakamigawai from the lower part of the Nabeyama Formation are associated with Parafusulina yabei. They appear to be more similar to P. nakamigawai than to the original specimens of P. yabei of Hanzawa (1942), as discussed later. However, my examination of more than one hundred free specimens which came from the same locality as Igo's, about 300 m west of Kuzu Railway Station, shows that the two specimens of Igo (1964) represent intraspecific variation in P. yabei and are referable to Parafusulina yabei rather than to Parafusulina nakamigawai.

Parafusulina shimotsukensis n. sp. Figures 9.1–9.8, Figures 10.1–10.13

Derivation of name.—Ancient geographic name, Shimotsuke, for the present Tochigi Prefecture.

Type specimens.—Holotype D2-007817 (axial section, Fig. 9.1). Paratypes D2-007789 (sagittal section, Fig. 9.2), D2-007960 (sagittal section, Fig. 9.3), D2-007774 (axial section, Fig. 9.4), D2-007819 (axial section, Fig. 9.5), D2-007775 (axial section, Fig. 9.6), D2-007746 (axial section, Fig. 9.7), D2-007796 (sagittal section, Fig. 9.8), D2-008353 (axial section, Fig. 10.1), D2-008344a (sagittal section, Fig. 10.2), D2-007440 (sagittal section, Fig. 10.3), D2-007777 (axial section, Fig. 10.4), D2-008179 (axial section, Fig. 10.5), D2-007437 (axial section, Fig. 10.6), D2-007453 (axial section, Fig. 10.7), D2-007751 (tangential section, Fig. 10.8), D2-007577 (axial section, Fig. 10.9), D2-007761 (axial section, Fig. 10.10), D2-007809 (sagittal section, Fig. 10.11), D2-007787 (sagittal section, Fig. 10.12), D2-008186 (sagittal section, Fig. 10.13).

Type locality.—Karasawa, Kuzu Town, Sano City, Tochigi Prefecture.

Diagnosis.—Large-sized Parafusulina, showing very wide morphologic variation in many characters, represented by strongly and rather irregularly fluted septa throughout test so as to produce indistinct cuniculi, and numerous chamberlets on and above chamber floor.

Description.—Test inflated to elongate fusiform with broadly arched periphery, straight to slightly convex lateral slopes, rounded to bluntly pointed poles, and straight axis of coiling. Mature test with eight to ten whorls, more than 15 mm in length, about 6 to 7 mm in width, and about 1.9 to 3.2 in form ratio. Proloculus nearly spherical, 0.36–0.61 mm in outer diameter. Test gradually increasing in length and height, but last whorl of fully mature specimens less high than preceeding whorl.

Septa thin for large test, strongly fluted throughout test. Septal folds commonly more than half as high as chambers, and commonly reach the top of chambers. Combination of strongly folded adjacent septa results in numerous, various-sized, various-shaped chamberlets on and above the chamber floor, especially in polar regions. Rather irregular folds of adjacent septa, however, not producing distinct cuniculi except for the median part of test in outer whorls. Phrenotheca developed in middle to outer part of test in most specimens. Septal counts 11–13, 17–22, 24–29, 32–38, 34–40, 39–47, 43–50, 47–53, and 59 (?) in the first to the ninth whorl in the illustrated eight paratypes. Wall thin in comparison with test size, 0.072–0.106 mm in the last whorl, consisting of tectum and fine alveolar keriotheca. Rudimentary chomata present only on the proloculus. Tunnel low, not well defined due to strongly fluted septa even in median part of test. Axial filling developed in axial region and both sides of tunnel of inner whorls, but obscure in specimens.

Material examined.—Twenty-one types and other specimens.

Discussion.—This new species is of particular interest because it apparently represents a highly specialized group and the largest known form of inflated Parafusulina. Its test is larger in volume and shorter in axial length than elongate forms of Parafusulina commonly over 2 cm reported from North America including Coahuila, Mexico (Dunbar et al., 1935), west Texas (Dunbar and Skinner, 1937), northern California (Coogan, 1960; Skinner and Wilde, 1965), and Washington (Mills and Davis, 1962; Skinner and Wilde, 1966). Except for having large tests in common, no similar or related test characters can be recognized between Parafusulina shimotsukensis and these North American Parafusulina. They are thought to be quite different phylogenetically.

As to septal folds, development of phrenotheca, and indistinct cuniculi, this new species is more similar to forms assignable to Parafusulina (Skinnerella) proposed by Coogan (1960) and emended by Skinner (1971). Parafusulina shimotsukensis is not like any described species outside Japan. It is closest to Parafusulina yabei in strongly and rather irregularly fluted septa, development of indistinct cuniculi and axial filling, and numerous chamberlets on and above the chamber floor. Parafusulina shimotsukensis, however, has a larger test, larger proloculus, and larger height and width in the corresponding whorls than Parafusulina yabei. This new species is considered to be the direct descendant of Parafusulina yabei based on those test characters that are intimately related phylogenetically, and its occurrence higher than P. yabei in the Nabeyama Formation.

Parafusulina tochigiensis n. sp. Figures 11.1–11.20

Derivation of name.—Prefectural name Tochigi.

Type specimens.—Holotype D2-007864 (axial section, Fig. 11.1). Paratypes D2-007443 (axial section, Fig. 11.2), D2-007449 (sagittal section, Fig. 11.3), D2-007450 (sagittal section, Fig. 11.4), D2-007852b (sagittal section, Fig. 11.5), D2-007447 (sagittal section, Fig. 11.6), D2-007853 (sagittal section, Fig. 11.7), D2-007849 (sagittal section, Fig. 11.8), D2-007855 (sagittal section, Fig. 11.9), D2-007828 (axial section, Fig. 11.10), D2-008209 (sagittal section, Fig. 11.11), D2-007441 (axial section, Fig. 11.12), D2-007827 (axial section, Fig. 11.13), D2-007442 (axial section, Fig. 11.14), D2-007860 (axial section, Fig. 11.15), D2-007824 (axial section, Fig. 11.16), D2-007863 (axial section, Fig. 11.17), D2-008561 (tangential section, Fig. 11.18), D2-008554 (axial section, Fig. 11.19), D2-007902 (sagittal section, Fig. 11.20).

Type locality.—Ohgama (two paratypes, D2-008561 and D2-008554) and Karasawa (holotype and other seventeen paratypes), Kuzu Town, Sano City, Tochigi Prefecture.

Diagnosis.—Large, elongate fusiform to subcylindrical Parafusulina, having small proloculus for large test and for the genus, strongly folded septa, and not so well developed cuniculi for the genus, and thought to belong to the P. japonica species group.

Description.—Test elongate fusiform to subcylindrical with nearly straight to broadly arched periphery, straight to slightly convex lateral slopes and bluntly pointed poles. Axis of coiling nearly straight, slightly oscillating in specimens. Mature test with eight to nine whorls, 14 to 19 mm in length, about 4.5 to 6 mm in width, and about 2.7 to 3.9 in form ratio. Length reaches more than 20 mm in the holotype. Proloculus nearly spherical to subspherical, 0.28–0.52 mm in longer outer diameter. Test tightly coiled in inner one to two whorls, then gradually increasing in length and height in the succeeding two to four whorls, with the rate of increase finally becoming nearly steady or slightly decreasing.

Septa strongly fluted throughout test, especially in polar regions. Septal folds generally high, some reaching the top of the chamber. Combination of strongly folded adjacent septa forms numerous chamberlets on and above the chamber floor. Cuniculi, low, narrow, and not so well developed as in typical Parafusulina. Weak phrenotheca present in outer whorls of some specimens. Septal counts 8–13, 18–23, 22–28, 24–32, 27–36, 31–41, 34–45, and 43 (?)–44 in the first to the eighth whorl in the illustrated eight paratypes. Wall thin in comparison with test size, 0.031–0.074 mm in the last whorl, consisting of tectum and fine alveolar keriotheca. Rudimentary chomata present only on the proloculus. Tunnel low, rather narrow, and indistinct in its path. Axial filling developed in the axial region, but not in outer few whorls.

Material examined.—Twenty types and other specimens.

Discussion.—This new species closely resembles and appears to be conspecific with Parafusulina kuzuensis due to their many similarities, such as large and elongate fusiform to subcylindrical test, proloculus size, mode of septal folds, and development of axial filling and indistinct cuniculi. These test characters are highly variable in specimens. On the other hand, careful examination of a few hundred axial and sagittal sections of these two forms reveals that the former has more septa and a greater width in the corresponding whorl, and a larger test volume than the latter. These differences suggest the taxonomic independence of these two forms, and P. tochigiensis is thought to be the direct descendant of P. kuzuensis based on more advanced test characters of the former and their stratigraphic distribution in the Nabeyama Formation.

Parafusulina tochigiensis is, moreover, similar to many other species of Parafusulina described from the Middle Permian limestones of Japan, such as Parafusulina japonica (Gümbel), P. gigantojaponica Kobayashi, 1957, P. japonica kinshoensis Morikawa, 1958, and P. kawaii Morikawa, 1958. All of them are thought to belong to a species group around Parafusulina japonica, and it is difficult to strictly separate them from P. japonica. However, Parafusulina tochigiensis seems to be distinguished from others in the P. japonica species group by its larger and slenderer test in the mature stage, more whorls, and relatively smaller proloculus in comparison with a large test.

Lectotype.—Here designated as the specimen illustrated by Hanzawa (1942, pl. 14, fig. 1), I.G.P.S.J. Coll. No. 22321, from the lower part of the Nabeyama Formation exposed at Tomuro, a few km SW of Yamasuge, Tanuma Town, Sano City, Tochigi Prefecture.

Material examined.—Illustrated twenty and other specimens.

Discussion.—Original description by Hanzawa (1942) is based on free specimens with short subcylindrical to short fusiform test and axial filling in inner whorls. Species or subspecies names of nabeyamensis, tomuroensis, and hanzawae were given by later authors for forms with a more inflated test, more elongate test and weaker axial filling, and larger test than P. yabei sensu stricto. All the material of Hanzawa (1942), Morikawa and Takaoka (1961), and Igo (1964) are from the lower part of the Nabeyama Formation. These morphologic differences in thin sections can be ascribed to intraspecific variation in Parafusulina yabei, because my close examination of more than one hundred axial sections from the same limestone sample reveals that the differences are gradual from specimen to specimen. The same morphologic variation as in this sample is recognized in other samples from lower and higher stratigraphic levels in the lower part of the Nabeyama Formation.

Also thought only to represent intraspecific variation of this species are two specimens named Parafusulina nakamigawai by Igo (1964), which were described from the same locality as were the four subspecies of Parafusulina yabei by Igo (1964). Schwagerina kinosakii proposed by Morikawa (1958) from the Akasaka Limestone may be synonymous with Parafusulina yabei, as Igo (1964) indicated. Also possibly identical with this species are some specimens named Parafusulina iwasensis Morikawa and Isomi, 1961 from a limestone block east of Lake Biwa. However, detailed comparison between P. iwasensis and P. yabei is impossible, because no axial section of P. iwasensis was shown by Morikawa and Isomi (1961). Although not pointed out by Kanmera (1963), Parafusulina (Skinnerella) figueroai described from the Kozaki Formation is more closely similar to this species in many points of test morphology than to Schwagerina figueroai Thompson and Miller, 1944 from the La Vainilla Limestone (Wolfcampian to Leonardian) of southern Chiapas, southernmost Mexico.

This species was thought to be one of the typical examples assignable to Skinnerella proposed as a subgenus of Parafusulina by Coogan (1960). Skinner (1971) emended Coogan's original definition and insisted on its subgeneric validity on the basis of diagnostic characters such as well developed phrenotheca, low and narrow cuniculi that present invariably in the outer whorls of the middle part of the test, septal folds showing a mushroomshape in axial sections, and other features. These characters are well represented by Parafusulina yabei, but are lacking or not common in typical Parafusulina. However, this species, as well as Parafusulina shimotsukensis, P. tochigiensis, and others, is tentatively assigned to Parafusulina until further discussion is possible on the basis of stratigraphic distribution and phylogenetic relationships of Middle Permian schwagerinids.

Parafusulina sp. Figures 13.2–13.7

Material examined.—Illustrated six and other specimens.

Discussion.—Schwagerinids found in the Izuru Formation are more or less deformed and their outer whorls are mostly abraded or destroyed. Although this unnamed species of Parafusulina is found in association with Parafusulina nakamigawai in Nagaami, they are quite different morphologically. Parafusulina sp. is probably distinguished from P. kuzuensis restricted to the lower part of the Nabeyama Formation by its smaller test. Detailed comparison with Parafusulina japonica is difficult because of insufficient preservation and small number of well oriented specimens of this unnamed species.

Material examined.—Illustrated ten and other specimens.

Discussion.—This species was proposed by Yabe and Hanzawa (1932) for the specimens named Doliolina lepida Schwager, 1883 by Deprat (1914) and Ozawa (1927) from the Akasaka Limestone, based on a difference of wall structure. Thompson and Foster (1937) made clear the taxonomic validity of Pseudodoliolina and Pseudodoliolina ozawai through their historical review and examination of topotype materials. Pseudodoliolina ozawai first occurs above the Cancellina nipponica Zone and ranges up to the Neoschwagerina craticulifera Zone in the Akasaka Limestone, and shows gradual morphologic changes with increasing test size and number of whorls from lower to upper in the limestone.

The Kuzu specimens were obtained from several stratigraphic levels in the upper part of the Parafusulina tochigiensis Zone. They are larger and more advanced morphologically than Pseudodoliolina ozawai that are crowded in a few horizons above the Cancellina nipponica Zone in the Akasaka Limestone. The present specimens are, on the other hand, similar to topotype specimens shown by Thompson and Foster (1937) except for more parachomata in the corresponding whorls, and different from Pseudodoliolina pseudolepida (Deprat, 1912), a direct descendent species of P. ozawai, in their subcylindrical and smaller test, smaller proloculus, and fewer whorls. The Kuzu materials are confidently identifiable as Pseudodoliolina ozawai based on these morphological features.

Material examined.—Illustrated three specimens.

Discussion.—Gifuella, proposed by Honjo (1959) from the lower part of the Neoschwagerina margaritae Zone in the Akasaka Limestone, has been regarded as a junior synonym of Neoschwagerina (Morikawa and Suzuki, 1961; Zaw Win, 1999) or Colania (Ozawa, 1970; Ozawa and Nishiwaki, 1992).

The most diagnostic character of Gifuella is the nearly complete lack of secondary transverse septula even in large specimens of the type species more than 1 cm in axial length (Kobayashi, 2005a). Gifuella is easily distinguished from Neoschwagerina by its larger proloculus and slenderer septula, and from Colania by its smaller proloculus, not clearly defined secondary transverse septula, and easily distinguishable micro-spheric forms of Colania. By these characters, Gifuella is considered to be taxonomically independent from Neoschwagerina and Colania, as discussed by Kobayashi (2005a). Gifuella amicula, Gifuella gifuensis Honjo, 1959, and allied species such as Gifuella larga (Morikawa and Suzuki, 1961) occur from the upper part of the Neoschwagerina craticulifera Zone to the lower part of the Yabeina globosa Zone in the Akasaka Limestone (Morikawa and Suzuki, 1961; Ozawa and Nishiwaki, 1992; Zaw Win, 1999).

Specific identification of most neoschwagerinids in the Nabeyama Formation is difficult because of exceedingly rare occurrence and insufficient preservation. The three specimens illustrated here, however, are most reasonably identified as Gifuella amicula by having a larger proloculus and less distinct axial septula than contemporaneous Neoschwagerina, and by having a smaller proloculus and test than Colania. They are considerably different from Gifuella sp. in this paper by their stouter transverse septula and more massive parachomata.