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29 Late Kungurian conodonts of the pelagic Panthalassa from seamount-capping 30 limestone in Ogama, Kuzuu, Tochigi Prefecture, Japan
31
32 SHUN MUTO
33 The Geological Survey of Japan, National Institute of Advanced Science and
34 Technology (e-mail: [email protected]) (present affiliation)
35 Department of Earth and Planetary Science, Graduate School of Science, the University
36 of Tokyo (previous affiliation)
37
38 YOHOKO OKUMURA
39 Kuzuu Fossil Museum, 1-11-15, Kuzuuhigashi, Sano, Tochigi 327-0501, Japan (e-mail:
41
42 TAKESHI MIZUHARA
43 Sugaya 629-1, Ranzan-machi, Hiki-gun, Saitama 355-0221, Japan (e-mail:
45
46 Abstract
47 48 AcceptedBiostratigraphy of conodonts is widely used Manuscript for age assignment of Permian strata. In 49 this paper, we report conodonts that occurred from the limestone of the Nabeyama
50 Formation deposited on a pelagic seamount in the Panthalassa, which is an oceanic
51 realm where Permian conodont data are scarce compared to other oceanic realms. 52 Samples collected from the lower part of the Nabeyama Formation yielded
53 Mesogondolella idahoensis (Youngquist, Hawley and Miller) and Sweetognathus
54 hanzhongensis (Wang), which indicate a late Kungurian age. Previous studies and
55 fusulinids obtained in this study indicate the studied samples belong to the Parafusulina
56 yabei biozone. Therefore, the Parafusulina yabei Zone includes the uppermost
57 Kungurian. Mesogondolella idahoensis and Sweetognathus hanzhongensis are
58 respectively regarded as cool and warm water species. Hence, the distribution of cool
59 and warm water conodont species may have overlapped in the pelagic Panthalassa
60 during the late Kungurian.
61
62 Key words: conodont, fusulinid, Nabeyama Formation, Panthalassa, Permian
63
64 Introduction
65
66 The study of Permian conodonts began in the western North America as early as the
67 1930s (Branson, 1932). In the following decades, the Great Basin region was the centre
68 of Permian conodont research (Youngquist et al., 1951; Clark and Ethington, 1962;
69 Wardlaw and Collinson, 1979). Studies in the Great Basin lead to the establishment of 70 theAccepted rough framework of conodont biozones forManuscript the Permian (Clark and Behnken, 1971; 71 Clark et al., 1979). The pioneer work in western North America were followed by
72 studies in Europe (Bender and Stoppel, 1965), southern Urals (Chernykh and
73 Reshetkova, 1987), South China (Ching, 1960; Wang, 1978; Wang and Wang, 1981), 74 the Arctic region (Bender and Stoppel, 1965; Szaniawski and Malkowski, 1979;
75 Sobolev and Nakrem, 1996), Iran (Teichert et al., 1973), Japan (Igo and Koike, 1966,
76 Igo, 1981) and elsewhere. Based on the global-scale data of conodont biostratigraphy,
77 correlation of regional biozones were attempted, resulting in the proposal of biozones
78 that are traceable across the globe (Kozur, 1995). At present, conodonts are recognised
79 as one of the most useful taxa for biostratigraphic division of the Permian System, so
80 much so that all the Stage and substage boundaries of the Permian ratified to date are
81 based on conodonts (Henderson et al., 2012; Henderson, 2016).
82 While the accumulation of knowledge on Permian conodonts has led to refinements
83 in taxonomy and improvements in the resolution of biozones in the well-studied regions,
84 some regions have been left behind from the progress. One such region is Japan, where
85 Permian strata occur most typically as allochtonous rocks within accretionary
86 complexes (e.g., Isozaki et al., 1990, 2010). Such strata potentially provide precious
87 biostratigraphic and biogeographic records of the pelagic Panthalassa that occupied a
88 large part of the surface of the Earth (Figure 1.1).
89 In Japan, Permian conodonts have been reported from seamount-capping limestones
90 (Hayashi, 1971; Sobajima, 1972; Makino, 1976; Ishida, 1977, 1985; Matsuda, 1980; Igo,
91 1981, 1989; Igo and Hisada, 1986; Shen et al., 2012) and deep-sea bedded chert 92 (ToyoAcceptedhara, 1976, 1977; Ishida, 1977, 1979, 1985Manuscript; Kitao, 1996; Nishikane et al., 2011) 93 within the Jurassic accretionary complexes. In particular, the seamount-capping
94 limestones yield abundant specimens of conodonts, based on which a biostratigraphic
95 framework for the Permian was built (Igo, 1981). However, the taxonomy of Permian 96 conodonts has gone under significant revision since this framework was constructed.
97 For example, platform conodonts previously assigned to the genus Gondolella (as in
98 Clark and Mosher, 1966), were split into Mesogondolella, Jinogondolella and Clarkina
99 (Kozur, 1989; Mei and Wardlaw, 1994). Unfortunately, only a limited number of
100 specimens were illustrated by previous studies on Permian conodonts in Japan.
101 Therefore, it is important that new conodont specimens are obtained and described from
102 Panthalassic seamount-capping carbonates.
103 Investigation of conodont biostratigraphy in pelagic seamount-capping limestone
104 deposited in central Panthalassa can also aid the establishment of an integrated
105 conodont-fusulinid biostratigraphy. Fusulinid biostratigraphy has traditionally been used
106 for biostratigraphic division of Panthalassic seamount-capping limestones of Japan (e.g.,
107 Toriyama, 1967). However, fusulinid biozones are not readily correlated with the
108 international standard Geological Time Scale (Leven, 2003). Recently, correlation of
109 fusulinid biozones with conodont and radiolarian biozones and magnetic polarity
110 reversals were established for the Permian in South China (Shen et al., 2018). Igo
111 (1981) presented parallel biozonation of conodonts and fusulinids in the Panthalassic
112 seamount-capping limestone in Japan, but the conodont biostratigraphic framework
113 needs to be brushed up, as mentioned earlier. 114 AcceptedThis study reports conodonts obtained frManuscriptom the Panthalassic seamount-capping 115 limestone of the Nabeyama Formation in Ogama, Sano City, Tochigi Prefecture, Japan.
116 The Nabeyama Formation in the Kuzuu area has been a target of many biostratigraphic
117 and tectonostratigraphic studies (see also Geological setting). The age of the Nabeyama 118 Formation was previously studied based on conodonts and fusulinids. Fujimoto (1961)
119 dated the Nabeyama Formation as middle Permian based on fusulinids. Hayashi (1971)
120 reported the occurrence of Carboniferous conodonts from this formation, but Hisayoshi
121 Igo (1972) and Hisaharu Igo (1981) insisted that the “Carboniferous” species in Hayashi
122 (1971) were Permian species. Subsequently, Igo (1981) assigned the Nabeyama
123 Formation to the middle Permian based on conodonts, and Kobayashi (2006) also
124 implied a middle Permian age based on fusulinids. Herein, we reassess the age of the
125 Nabeyama Formation based on our new conodont specimens. The biogeographic
126 significance of the conodonts is also discussed.
127
128 Geological setting
129
130 The samples treated in this study are limestone samples obtained in a valley east of
131 Ogama in the northern part of Sano City, Tochigi Prefecture, Kanto District, Japan
132 (36°29’18”N 139°33’54”E). The studied limestone belongs to the Nabeyama Formation
133 (defined by Yoshida, 1956), which is a part of the Kuzuu Complex (Kuzu Complex
134 sensu Kamata, 1996, 1997) of the Tamba–Mino–Ashio Belt (also known as the
135 Mino–Tamb–Ashio Belt). The Tamba–Mino–Ashio Belt is mostly composed of Jurassic 136 accretionaryAccepted complexes (Yamakita and Otoh, 2Manuscript000; Isozaki et al., 2010; Kojima et al., 137 2016) (Figure 1.2). The Jurassic accretionary complexes of the Tamba–Mino–Ashio
138 Belt mainly comprise Carboniferous to Middle Jurassic oceanic rocks (ocean floor
139 basalt, deep-sea chert, hemipelagic siliceous mudstone, seamount basalt and 140 seamount-capping carbonate), and Jurassic to lowermost Cretaceous trench-fill
141 terrigenous clastic rocks (mudstone and sandstone). The Carboniferous to Middle
142 Jurassic oceanic rocks were deposited in the pelagic Panthalassa several thousand
143 kilometres from the nearest continent (Figure 1.1), after which they traveled to a
144 subduction zone along the palaeo-continent and formed a part of the accretionary
145 complexes by the tectonic movement of the oceanic plates (Matsuda and Isozaki, 1991;
146 Wakita and Metcalfe, 2005; Isozaki et al., 2010).
147 The Kuzuu Complex is the southernmost part of the Tamba–Mino–Ashio Belt in the
148 Kanto District of east Japan (Figure 2). Our studied samples belong to the limestone of
149 the Nabeyama Formation (Yoshida, 1956; Fujimoto, 1961). The Nabeyama Formation
150 conformably overlies the Izuru Formation that is composed mainly of basaltic volcanic
151 and volcaniclastic rocks (Yoshida, 1956; Fujimoto, 1961; Kamata, 1996). The
152 Nabeyama and Izuru formations together form a thrust sheet (Yanagimoto, 1973), which
153 is named as tectonostratigraphic “Unit 2” of the Kuzuu Complex (Kamata, 1996, 1997).
154 The Izuru and Nabeyama formations are considered to be derived from a seamount in
155 the pelagic Panthalassa (Kamata, 1996).
156 The limestone of the Nabeyama Formation is divided into three parts: the lower,
157 middle and upper parts (Yoshida, 1956; Fujimoto, 1961; Kobayashi, 1979). Fujimoto 158 (1961)Accepted and Yanagimoto (1973) classified these Manuscriptthree parts as members of the Nabeyama 159 Formation, but Kobayashi (1979) noted that this stratigraphic division is not valid,
160 because the dolomitisation of the middle part is secondary, and is also recognisable in
161 the lower and upper parts. We will follow Kobayashi (1979) and refrain from using the 162 members defined by Fujimoto (1961) and Yanagimoto (1973). The lower part of the
163 Nabeyama Formation is mainly composed of black, dark grey or grey well-bedded
164 limestone that is frequently dolomitised and includes chert nodules (Figure 3; Fujimoto,
165 1961; Kobayashi, 1979). The middle part is dominated by light grey, grey or dark grey
166 massive dolostone (Figure 3; Fujimoto, 1961; Kobayashi, 1979). The upper part is
167 mainly composed of light grey, grey, dark grey or black massive limestone that is
168 frequently dolomitised and includes chert nodules (Figure 3; Fujimoto, 1961;
169 Kobayashi, 1979).
170 The Izuru Formation has been dated as middle Permian by fusulinids (Kobayashi,
171 2006). The Nabeyama Formation has been dated as middle Permian by conodonts (Igo,
172 1981; Koike et al., 1974), fusulinids (Fujimoto, 1961; Igo, 1964; Kobayashi, 1979,
173 2006) and brachiopods (Tazawa et al., 2016). Fusulinids are the most thoroughly
174 studied index fossils in the Izuru and Nabeyama formations, and three biozones of the
175 middle Permian have been established: the Parafusulina nakamigawai, Parafusulina
176 yabei and Parafusulina tochigiensis zones in ascending order (Kobayashi, 2006). The
177 Nabeyama Formation is overlain unconformably by a limestone conglomerate that
178 yields conodonts of middle Permian to late Triassic age (Conodont Research Group,
179 1972, 1974; Yanagimoto, 1973; Koike et al., 1974) and middle to late Permian 180 fusulinidsAccepted (Figure 3; Igo and Igo, 1977; Kobayashi, Manuscript 1979). This conglomerate is thought 181 to be correlative with cave deposits that occur within the Nabeyama Formation
182 (Kobayashi, 1979).
183 In Ogama, the lower to middle part of the Nabeyama Formation is exposed (OG in 184 Figure 3; Kobayashi, 1979). Here, the Parafusulina yabei and Parafusulina tochigiensis
185 fusulinid biozones have been recognised (Figure 3; Kobayahsi, 2006). The locality we
186 studied is exactly the same as that studied by Tazawa et al. (2016) (note that the locality
187 is mislocated in their paper), and is apparently a lateral extension of the strata within the
188 Parafusulina yabei Zone of Kobayashi (2006) (Figures 3 and 4). This is further
189 supported by the finding of Parafusulina yabei Hanzawa from this locality by Tazawa et
190 al. (2016).
191
192 Methods 193
194 We conducted a field survey at the Ogama locality and collected limestone samples
195 for extraction of conodonts. We also observed the lithology of the limestone for
196 comparison with the lithostratigraphic section drawn by Kobayashi (1979). The
197 collected limestone samples were treated by 4.8 wt% formic acid. Conodonts were
198 picked up from the residue and photographed with a scanning electron microscope
199 (SEM: Keyence-VF8800) and an optical stereoscopic microscope at the University of
200 Tokyo. For observation of fusulinids, we made thin sections of the limestone and
201 observed them under a microscope through transmitted light.
202 203 AcceptedResults Manuscript 204
205 In the studied locality in Ogama, outcrops of limestone occur structurally above
206 outcrops of sandstone (Figure 4). The distribution of these two lithofacies is consistent 207 with the geological map by Kobayashi (1979, 2006) (Figure 4). Two lithostratigraphic
208 sections were observed in the limestone outcrops: Section 1 and Section 2 in
209 structurally ascending order (Figure 4). The top of Section 1 corresponds approximately
210 with the base of Section 2 according to the orientation of the bedding plane. Both
211 sections are composed of well-bedded or weakly bedded dark grey fossiliferous
212 limestone (Figures 5 and 6.1). Black chert nodules are present in the middle to upper
213 part of Section 1 and the upper part of Section 2.
214 We obtained two limestone samples from the middle part of Section 2 (2013-12 and
215 2014-236; Figure 5). We also obtained two samples from limestone floats that lay in
216 front of the outcrop of the base of Section 2 (2014-188 and 2014-215; Figure 4).
217 Treatment of these samples with formic acid yielded conodonts along with brachiopods,
218 icthyoliths, foraminifera, bryozoans, ostracods, trilobite fragments and placoid scales,
219 some of which were silicified. A total of 41 conodont elements were obtained by
220 dissolving 97 kg of limestone. A large part of the extracted conodont specimens was
221 broken, but some were valid for taxonomic investigation (Figures 7 and 8). The
222 conodonts were uniformly of black colour corresponding to conodont alteration index
223 (CAI) 5 of Epstein et al. (1977) (Figure 9). The surface of the conodont skeletons is
224 generally well-preserved, exemplified by the preservation of honeycomb structures on 225 theAccepted platform of segminiplanate elements (Figu resManuscript 7 and 8). Obvious evidence indicating 226 reworking such as abrasion was not found. Both the outcrop samples and the float
227 samples yielded Mesogondolella idahoensis (Youngquist, Hawley and Miller),
228 Mesogondolella sp. and Sweethognathus hanzhongensis (Wang) (Figures 7 and 8). Thus, 229 the conodont assemblages from the middle part of Section 2 and the floats are identical.
230 It is noteworthy that some of our specimens retain the basal bodies of conodont
231 elements, which are relatively fragile tissues that occupy the basal part of the element
232 (Donoghue, 1998). Basal bodies of conodonts are fragile due to having less densely
233 mineralised structures and are also easily broken off from the rest of the element: the
234 more resistant crown (Donoghue, 1998; Souquet and Goudemand, 2019). Therefore, the
235 basal bodies of conodonts are rarely preserved and poorly described. In our samples,
236 some specimens of Mesogondolella retain the basal bodies as white to transparent
237 tissues (Figure 9). It is rather surprising that the fragile basal bodies were found in
238 conodonts from sedimentary rocks that have experienced considerable thermal
239 maturation and tectonic deformation during subduction-accretion.
240 We also observed fusulinids from the sample obtained from Section 2. Observation
241 of thin sections confirmed the presence of Parafusulina yabei Hanzawa (Figure 6.2).
242 Since the range of Parafusulina yabei defines the Parafusulina yabei Zone of
243 Kobayashi (2006), our finding assures that the sampled horizon is within this fusulinid
244 biozone (Figures 3). This is consistent with the results of Tazawa et al. (2016) as well as
245 the position and lithofacies of the studied section (Figures 3, 4 and 5).
246 247 AcceptedDiscussion Manuscript 248
249 Age
250 Here, we will discuss the age of our samples based on the specimens obtained in this 251 study.
252 Mesogondolella idahoensis (Youngquist, Hawley and Miller) is a widely distributed
253 species found from western USA (Youngquist et al., 1951; Mytton et al., 1983;
254 Behnken et al., 1986; Wardlaw and Collinson, 1986; Lambert et al., 2007), Svalbard
255 (Szaniawski and Malkowski, 1979; Nakrem, 1991), central Tibet (Yuan et al., 2016),
256 South China (Wang, 1994; Zhang et al., 2010; Sun et al., 2017) and Japan (Igo, 1981).
257 Based on a global compilation of conodont occurrences, the range of M. idahoensis falls
258 within the late Kungurian (latest Cisuralian; latest early Permian) (Henderson, 2016).
259 Sweetognathus hanzhongensis (Wang) has been reported from Shaanxi (Wang, 1978),
260 Guangxi (Mei et al., 2002; Sun et al., 2017) and Guizhou (Mei et al., 1999) of South
261 China, Oman (Kozur and Wardlaw, 2010) and Tunisia (Angiolini et al., 2008). Based on
262 a compilation of these data, the range of S. hanzhongensis is from the
263 Kungurian–Roadian (Cisuralian–Guadalupian) boundary to the late Capitanian (latest
264 Guadalupian; latest middle Permian) (Henderson, 2016). According to high-resolution
265 investigations in Guangxi (Sun et al., 2017) and Guizhou (Mei et al., 1999), S.
266 hanzhongensis begins to occur below the first occurrence (FO) of Jinogondolella
267 nankingensis (Ching), which is a marker for the Cisuralian–Guadalupian boundary (i.e.,
268 the Kungurian–Roadian boundary) (Henderson et al., 2012). Thus, the range of S. 269 hanzhongensAcceptedis is from the latest Kungurian to Manuscriptlate Capitanian. The co-occurrence of M. 270 idahoensis and S. hanzhongensis narrows the age of our samples to the latest Kungurian
271 (latest early Permian). Our age assignment is consistent with the brachiopod-based age
272 by Tazawa et al. (2016). Comparison with fusulinid-based age assignment is a little 273 more complicated, as noted below.
274 When first established in the Izuru and Nabeyama formations, the Parafusulina
275 nakamigawai Zone and the middle part of the Parafusulina tochigiensis Zone were
276 respectively correlated to the early middle Permian (Kubergandian in the Tethyan Scale)
277 and the middle middle Permian (Murgabian in the Tethyan Scale) (Kobayashi, 2006).
278 This means that the Parafusulina yabei Zone, which lies between the Parafusulina
279 nakamigawai and Parafusulina tochigiensis zones, is within the middle Permian.
280 However, correlation with the global standard Geological Time Scale (Henderson et al.,
281 2012) was not determined, which can now be attempted based on conodonts from our
282 samples and previous studies (Igo, 1981).
283 The co-occurrence of M. idahoensis and S. hanzhongensis in our samples indicate
284 that the age of the Parafusulina yabei Zone includes the latest Kungurian. Previously, M.
285 idahoensis has been found to occur with Diplognathodus lanceolatus Igo from the
286 lower part of the Nabeyama Formation in Yamasuge in Kuzuu (Igo, 1981; see Figure 2
287 for location). The latter species is identical to S. hanzhongensis (see Plate 9 Figures 1–5,
288 7, 8, 13 of Igo, 1981), and is here considered as a junior synonym of S. hanzhongensis.
289 This is concordant with the fact that the stratigraphic range of both “D. lanceolatus” and
290 S. hanzhongensis overlap in their lower part with the range of M. idahoensis (in the 291 uppermostAccepted Kungurian). Because the horizons Manuscript in Yamasuge span a large part of the 292 Parafusulina yabei Zone of Kobayashi (2006) (compare Text-fig. 4 of Igo, 1981 and
293 “YS” in Figure 3 of this paper), much of the Parafusulina yebei Zone is probably of
294 latest Kungurian age. The upper part of the Nabeyama Formation in Nagaami, which is 295 assigned to the Parafusulina tochigiensis Zone of Kobayashi (2006), yields “D.
296 lanceolatus” but lacks M. idahoensis (Igo, 1981). Therefore, the Parafusulina
297 tochigiensis Zone may be of Guadalupian age (Henderson, 2016).
298
299 Biogeography
300 Our samples are characterised by the co-occurrence of M. idahoensis and S.
301 hanzhongensis. As mentioned above, the co-occurrence of the two species in the lower
302 part of the Nabeyama Formation can also be observed in the illustrations of Igo (1981)
303 (respectively treated as Neogondolella idahoensis and Diplognathodus lanceolatus in
304 his paper). According to Igo (1981), some horizons from the Yamasuge area in Kuzuu,
305 which are roughly correlative with the studied section in Ogama (Figure 2), yield
306 abundant specimens of both “D. lanceolatus” and M. idahoensis. Although the
307 specimens obtained in our study are not numerous, they seem to represent major
308 constituents of a typical latest Kungurian conodont fauna recorded in the Nabeyama
309 Formation.
310 Outside Japan, the co-occurrence of M. idahoensis and S. hanzhongensis has been
311 reported from South China (Sun et al., 2017), but not from other geographic areas.
312 Apart from Japan and South China, almost all of the localities of M. idahoensis are in 313 SvalbardAccepted that was located in northern high latitudes Manuscript (Szaniawski and Malkowski, 1979; 314 Nakrem, 1991) and the northwestern Pangaean margin, where the northern gyre of the
315 Panthalassa would have brought cold waters from the north (Youngquist et al., 1951;
316 Mytton et al., 1983; Behnken et al., 1986; Wardlaw and Collinson, 1986; Lambert et al., 317 2007). An exception is central Tibet that was positioned in southern mid latitudes (Yuan
318 et al., 2016). Hence, this species is regarded to represent cool water province of the
319 north Panthalassa and Boreal Ocean (Mei and Henderson, 2001; Henderson and Mei,
320 2007), while it also inhabited parts of cool waters of the southern hemisphere. In
321 contrast, Kungurian species of Sweetognathus are abundant only in equatorial regions,
322 and therefore are regarded as warm water taxa (Mei and Henderson, 2001; Mei et al.,
323 2002). In particular, S. hanzhongensis are limited to South China, Oman and Tunisia,
324 which were all positioned in low latitudes (Wang, 1978; Mei et al., 2002; Angiolini et
325 al., 2008; Kozur and Wardlaw, 2010; Sun et al., 2017). Thus, a fauna that includes M.
326 idahoensis and S. hanzhongensis as main constituents, such as that suggested for the
327 Nabeyama Formation and perhaps South China, is irregular in terms of conodont
328 provincialism. It is possible that the pelagic Panthalassa and South China was a
329 biogeographic province where cool water taxa and warm water taxa coexisted during
330 the latest Kungurian, and further research on faunal compositions will shed light on the
331 significance of these provinces.
332
333 Conclusions
334 335 AcceptedWe obtained well-preserved specimens of MesogondolellaManuscript idahoensis (Youngquist, 336 Hawley and Miller) and Sweetognathus hanzhongensis (Wang) from limestones of the
337 Parafusulina yabei Zone of the Nabeyama Formation in Ogama, Kuzuu area, Tochigi
338 Prefecture, Japan. The conodonts indicate a latest Kungurian age, which is consistent 339 with brachiopods reported from the same locality. The conodont data indicate that the
340 Parafusulina yabei fusulinid biozone includes, and is probably mostly correlated to the
341 latest Kungurian. Biogeographically, our data suggests that the conodont fauna of the
342 Nabeyama Formation may have been characterised by mixed cool water and warm
343 water taxa in the latest Kungurian.
344
345 Systematic palaeontology
346
347 Multielement taxonomy of Permian conodonts is still debated at the genus level
348 (Henderson and Mei, 2003). Therefore, only the synonym list for the P1 element is
349 presented. All specimens are deposited in the Kuzuu Fossil Museum.
350 Class Conodonta Eichenberg, 1930
351 Subclass Conodonti Sweet and Donoghue, 2001
352 Order Ozarkodinida Dzik, 1976
353 Superfamily Gondolellacea Lindström, 1970
354 Family Gondolellidae Lindström, 1970
355 Genus Mesogondolella Kozur
356 Type species.—Gondolella bisseli Clark and Behnken 357 AcceptedRemarks.—Mesogondolella was defined forManuscript segminiplanate P1 elements with the 358 following features: a platform that is not reduced; no sculptures on the platform or only
359 weak serration on the anterior part of the platform; no free blade; a lower surface with
360 shallow V-shaped keel; a terminal basal cavity. Species with serrations on the anterior 361 part of the platform were separated to the genus Jinogondolella (Mei and Wardlaw,
362 1994). Consequently, Mesogondolella is restricted to species with an unornamented
363 platform (Lambert et al., 2007). Multielement apparatus of species of Mesogondolella
364 was proposed by Lambert et al. (2007).
365
366 Mesogondolella idahoensis (Youngquist, Hawley and Miller)
367 Figure 7
368 Gondolella idahoensis Youngquist, Hawley and Miller, 1951, p. 361, pl. 54, figs. 1–3,
369 14, 15; Clark and Mosher, 1966, p. 388, pl. 47, figs. 9–12.
370 Neogondolella idahoensis (Youngquist, Hawley and Miller). Clark et al., 1979, pl. 1,
371 fig. 10; Szaniawski and Malkowski, 1979, p. 246–247, pl. 4, figs. 1–4, 6 (only), pl. 5,
372 fig. 5?; Wang and Wang, 1981, p. 230, pl. 2, figs. 15, 23; Behnken et al., 1986, p.
373 179–181, figs. 4.12–16, 4.18; Wardlaw and Collinson, 1986, figs. 17.11, 12; Wang,
374 1994, p. 211, pl. 3, figs. 3–6 (only); Kozur, 1995, pl. 3, fig. 18.
375 Mesogondolella idahoensis (Youngquist, Hawley and Miller). Wardlaw, 2000, p.44,
376 pl. 3-10, figs. 1–3; Lambert et al., 2007, pp. 215–216, figs. 4e, 6j.
377 Mesogondolella idahoensis idahoensis (Youngquist, Hawley and Miller). Henderson
378 and Mei, 2003, pl. 2, fig. 15; Zhang et al., 2010, p. 152, figs. 3H, 3Q–3R. 379 AcceptedMesogondolella? cf. idahoensis (Youngquist Manuscript et al.). Sun et al., 2017, pl. 5, fig. 4. 380 Material.—One specimen each from two samples from the outcrop (KFM-1999 from
381 2014-12 and KFM-2008 from 2014-236), and five specimens from float samples
382 (KFM-2000, 2001 from 2014-188 and KFM-2002–2004 from 2014-215). 383 Description.—The specimens obtained in our study are segminiplanate elements
384 characterised by a markedly high and thick terminal cusp. the cusp is around 3 times
385 higher than the posterior denticles. The cusp is weakly reclined to the posterior. The
386 denticles are low and discrete in the posterior, and becomes higher and fused towards
387 the anterior. The low posterior denticles are circular in cross section, while the higher
388 anterior denticles are laterally compressed. The platform that runs the full length the
389 element and is widest around mid-length. The platform tapers anteriorly, while its lateral
390 margins are sub-parallel in the posterior half. The posterior end of the platform is a
391 rounded square shape in upper and basal views. The keel has a wide v-shaped groove
392 ending around a terminally located basal pit surrounded by a wide loop.
393 Remarks.—The features of our specimens agree well with those of Mesogondolella
394 idahoensis (Youngquist et al.). Although the anterior denticles of M. idahoensis were
395 originally described to be low and widely spaced (Henderson and Mei, 2003, Plate 2
396 Figure 15; holotype), forms with high, closely spaced and fused anterior denticles have
397 been reported to occur alongside such forms (Behnken et al., 1986, Lambert et al., 2007,
398 Figures 4d, e; Figures 4.14, 16; Wardlaw and Collinson, 1986, Figure 17.11). Hence, we
399 regard that our specimens belong to M. idahoensis.
400 Mesogondolella idahoensis is similar to Mesogondolella lamberti Mei and 401 HendersonAccepted in denticulation and platform morphology. Manuscript M. lamberti was split from M. 402 idahoensis as a new subspecies by Mei and Henderson (2002), then elevated to species
403 status by Lambert et al. (2007). M. idahoensis can be separated from M. lamberti by
404 having a larger cusp. 405 Mesogondolella siciliensis (Kozur) has a similar denticulation to M. idahoensis, but
406 differs in that the cusp of the former is at most only slightly larger than the posterior
407 denticles. Furthermore, the platform of the former is widest at the middle and tapers
408 posteriorly, while that of the latter has sub-parallel lateral margins from the middle to
409 the posterior.
410
411 Mesogondolella spp.
412 Figures 8.1, 8.2
413 Material.—Two specimens (KFM-2005, 2006) from a float sample (2014-215).
414 Remarks.—These specimens differ from M. idahoensis in having very high and fused
415 anterior denticles. The specimen illustrated in Figure 8.1 has a thick cusp, has a square
416 posterior end in upper and basal views, and is strongly arched in lateral view. The
417 specimen illustrated in Figure 8.2 has a similar cusp, but has a more rounded posterior
418 end in upper and basal views, and is less arched in lateral view. Therefore, these two
419 specimens may belong to different species, although the preservation is too poor to
420 make a conclusion.
421
422 Genus Sweetognathus Clark 423 AcceptedType species.—Spathognathodus Manuscript whitei Rhodes 424 Remarks.—Sweetognathus is represented by carminiscaphate P1 elements with
425 pustulose ornamentation on a flat-topped carina that passes gradually into the anterior
426 blade (Mei et al., 2002). 427
428 Sweetognathus hanzhongensis (Wang)
429 Figures 8.3–8.5
430 Gnathodus hanzhongensis Wang, 1978, p. 217, pl. 1, figs. 33–35, 40, 41.
431 Diplognathodus lanceolatus Igo, 1981, p. 30–31, pl. 9, figs. 1–5, 7, 8, 13.
432 Sweetognathus iranicus hanzhongensis (Wang). Mei et al., 2002, p. 85, fig.
433 10.6–10.12; Angiolini et al., 2008, fig. 7.
434 Sweetognathus hanzhongensis (Wang). Sun et al., 2017, p. 60, pl. 3, fig. 15–18, pl. 7,
435 figs. 9–10.
436 Material.—Two specimens (KFM-2009, 2010) from a sample from the outcrop
437 (2014-236) and one specimen (KFM-2007) from a float sample (2014-217).
438 Description.—The specimens are carminiscaphate elements with an anterior blade of
439 fused denticles and a posterior process that is formed above an expanded basal cavity. In
440 lateral view, the anterior blade is the highest part of the element, and the upper margin
441 decreases height gradually to the posterior end where it meets the basal margin. The
442 carina on the posterior process is composed of a low and narrow row of pustulose nodes
443 that continues to the posterior end. The anterior blade is composed of laterally
444 compressed denticles that are fused to around 90% of its height. The anterior three 445 denticlesAccepted of the blade are subequal in height. TheManuscript anterior blade and carina is connected 446 by a narrow carinal ridge, which is positioned at the mid-length of the unit and above
447 the anteriormost part of the basal cavity. In lateral view the length of this ridge is around
448 three times the width of the carinal nodes. The basal cavity occupies around 60% of the 449 basal margin in lateral view. In upper and basal views, the basal cavity tapers both
450 anteriorly and posteriorly. The upper surface of the basal cavity is unornamented.
451 Remarks—The characteristics of our specimens agree well with those of
452 Sweetognathus hanzhongensis (Wang). The carinal ridge that connects the anterior
453 blade with the posterior nodes is the key feature that differentiates this species from
454 others. Note that Mei et al. (2002) regarded this species to be a geographical subspecies
455 of Sweetognathus iranicus, and treated it as S. iranicus hanzhongensis.
456 Sweetognathus iranicus (Kozur) is similar, but differs from S. hanzhongensis in
457 having discrete nodes instead of a ridge where the anterior blade connects with the
458 posterior part of the carina. In addition, S. iranicus typically has laterally broader nodes
459 on the carina.
460 Diplognathodus lanceolatus Igo from Panthalassic seamount capping limestones in
461 Kuzuu and Mt. Ibuki in Japan has all the features of S. hanzhongensis, including a
462 carinal ridge that connects the anterior blade with the posterior nodes. The stratigraphic
463 distribution of D. lanceolatus is in the middle Permian, consistent with that of S.
464 hanzhongensis. Therefore, we regard that D. lanceolatus is a junior synonym of S.
465 hanzhongensis.
466 467 AcknowledgementsAccepted Manuscript 468 We are deeply grateful for Ichiro Morishita (Senba, Sano City, Tochigi Prefecture)
469 for allowing our field survey in his property. We would like to express our sincere
470 gratitude to Yukio Miyake for his assistance in the field and fossil extraction. We are 471 also grateful to Toshihiro Tada of the University of Tokyo for his assistance in the field.
472
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741
742 Figure captions
743 Figure 1. 1, palaeogeographic map of the early Permian (Laya et al., 2013) and the
744 depositional site of pelagic Panthalassic sediments in Japan. 2, distribution of
745 the Jurassic accretionary complex of Japan, modified after Isozaki et al.,
746 (2010).
747
748 Figure 2. Geologic maps showing the geology of the Kuzuu area (Kamata, 1997). 1,
749 surface distribution of the Tamba–Mino–Ashio Belt. 2, geologic map of the
750 Ashio Mountains. 3, geologic map of the Kuzuu area and the location of the
751 areas studied by Kobayashi (1979, 2006). OG: Ogama; TJ: Takajikko; NA:
752 Nagaami; KS: Karasawa; YS: Yamasuge. 753 Accepted Manuscript 754 Figure 3. Lithostratigraphy and biostratigraphy of the Izuru and Nabeyama Formations.
755 Lithostratigraphy after Kobayashi (1979). Fusilinid biostratigraphy is after
756 Kobayashi (2006) and conodont biostratigraphy is after Igo (1981). See caption 757 for Figure 2 for abbreviation of the names of study areas.
758
759 Figure 4. Map showing the outcrops confirmed in this study (discrete outcrops in the
760 northern part), the location of the studied sections, the location of the sampling
761 point of the float samples (2014-188, 2014-215), and the geological map by
762 Kobayashi (1979, 2006).
763
764 Figure 5. Stratigraphic columns of the studied sections. The samples from the outcrop
765 (2014-12, 2014-236) were obtained from the horizon with the fossil occurrence
766 mark.
767 Figure 6. 1, Outcrop photograph of the horizon from which samples 2014-12 and
768 2014-236 were obtained. The sample for observation of fusulinids was
769 obtained from the point of the arrow. 2, photo micrograph of Parafusulina
770 yabei Hanzawa from Section 2 observed in thin section through transmitted
771 light.
772
773 Figure 7. SEM photographs of conodonts obtained in this study. 1–7, Mesogondolella
774 idahoensis (Youngquist et al.). 1, KFM-1999 from 2014-12, Section 2; 2, 775 AcceptedKFM-2002 from 2014-215, float; 3,Manuscript KFM-2003 from 2014-215, float; 4, 776 KFM-2004 from 2014-215, float; 5, KFM-2008 from 2014-236, Section 2, 6,
777 KFM-2000 from 2014-215, float; 7, KFM-2001 from 2014-215, float. a, upper
778 view; b, lateral view; c, basal view. 779
780 Figure 8. SEM photographs of conodonts obtained in this study. 1, 2, Mesogondolella
781 sp. 1, KFM-2005 from 2014-215, float; 2, KFM-2006 from 2014-215, float.
782 3–5, Sweetognathus hanzhongensis (Wang). 3, KFM-2009 from 2014-236,
783 Section 2, 4, KFM-2010 from 2014-236, Section 2, 5, KFM-2007 from
784 2014-215, float. a, upper view; b, lateral view; c, basal view.
785
786 Figure 9. Photographs of conodonts obtained in this study. 1–3, conodonts with basal
787 bodies. Mesogondolella idahoensis (Youngquist et al.). a, lateral view; b, basal
788 view. 1,. KFM-1999; 2, KFM-2000; 3, KFM-2001 from 2014-215; 4, 5,
789 conodonts without basal bodies. 4, Mesogondolella idahoensis (Youngquist et
790 al.) KFM-2008, basal view; 5, Sweetognathus hanzhongensis (Wang).
791 KFM-2009.
Accepted Manuscript Paleontological Research
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 1, palaeogeographic map of the early Permian (Laya et al., 2013) and the depositional site of pelagic 46 Panthalassic sediments in Japan. 2, distribution of the Jurassic accretionary complex of Japan, modified after 47 Isozaki et al., (2010). 48 81x140mm (300 x 300 DPI) 49 50 Accepted Manuscript 51 52 53 54 55 56 57 58 59 60 Paleontological Society of Japan Paleontological Research
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 Geologic maps showing the geology of the Kuzuu area (Kamata, 1997). 1, surface distribution of the Mino- 29 Tamba-Ashio Belt. 2, geologic map of the Ashio Mountains. 3, geologic map of the Kuzuu area and the location of the areas studied by Kobayashi (1979, 2006). OG: Ogama; TJ: Takajikko; NA: Nagaami; KS: 30 Karasawa; YS: Yamasuge. 31 32 221x144mm (300 x 300 DPI) 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 Accepted Manuscript 51 52 53 54 55 56 57 58 59 60 Paleontological Society of Japan Paleontological Research
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 Lithostratigraphy and biostratigraphy of the Izuru and Nabeyama Formations. Lithostratigraphy after 46 Kobayashi (1979). Biostratigraphy after Kobayashi (2006). See caption for Figure 2 for abbreviation of the 47 names of study areas. 48 170x234mm (300 x 300 DPI) 49 50 Accepted Manuscript 51 52 53 54 55 56 57 58 59 60 Paleontological Society of Japan Paleontological Research
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 Map showing the outcrops confirmed in this study (discrete outcrops in the northern part), the location of 34 the studied sections, the location of the sampling point of the float samples (2014-188, 2014-215), and the geological map by Kobayashi (1979, 2006). 35 36 714x578mm (72 x 72 DPI) 37 38 39 40 41 42 43 44 45 46 47 48 49 50 Accepted Manuscript 51 52 53 54 55 56 57 58 59 60 Paleontological Society of Japan Paleontological Research
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 Stratigraphic columns of the studied sections. The samples from the outcrop (2014-12, 2014-236) were 46 obtained from the horizon with the fossil occurrence mark. 47 77x113mm (300 x 300 DPI) 48 49 50 Accepted Manuscript 51 52 53 54 55 56 57 58 59 60 Paleontological Society of Japan Paleontological Research
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 1, Outcrop photograph of the horizon from which samples 2014-12 and 2014-236 were obtained. The 43 sample for observation of fusulinids was obtained from the point of the arrow. 2, photo micrograph of Parafusulina yabei Hanzawa from Section 2 observed in thin section through transmitted light. 44 45 712x782mm (72 x 72 DPI) 46 47 48 49 50 Accepted Manuscript 51 52 53 54 55 56 57 58 59 60 Paleontological Society of Japan Paleontological Research
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 SEM photographs of conodonts obtained in this study. 1–7, Mesogondolella idahoensis (Youngquist et al.). 1, 46 KFM-1999 from 2014-12, Section 2; 2, KFM-2002 from 2014-215, float; 3, KFM-2003 from 2014-215, float; 47 4, KFM-2004 from 2014-215, float; 5, KFM-2008 from 2014-236, Section 2, 6, KFM-2000 from 2014-215, float; 7, KFM-2001 from 2014-215, float. a, upper view; b, lateral view; c, basal view. 48 49 175x224mm (300 x 300 DPI) 50 Accepted Manuscript 51 52 53 54 55 56 57 58 59 60 Paleontological Society of Japan Paleontological Research
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 SEM photographs of conodonts obtained in this study. 1, 2, Mesogondolella sp. 1, KFM-2005 from 2014-215, 43 float; 2, KFM-2006 from 2014-215, float. 3–5, Sweetognathus hanzhongensis (Wang). 3, KFM-2009 from 44 2014-236, Section 2, 4, KFM-2010 from 2014-236, Section 2, 5, KFM-2007 from 2014-215, float. a, upper view; b, lateral view; c, basal view. 45 46 175x193mm (300 x 300 DPI) 47 48 49 50 Accepted Manuscript 51 52 53 54 55 56 57 58 59 60 Paleontological Society of Japan Paleontological Research
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Photographs of conodonts obtained in this study. 1–3, conodonts with basal bodies. Mesogondolella idahoensis (Youngquist et al.). a, lateral view; b, basal view. 1,. KFM-1999; 2, KFM-2000; 3, KFM-2001 from 20 2014-215; 4, 5, conodonts without basal bodies. 4, Mesogondolella idahoensis (Youngquist et al.) KFM- 21 2008, basal view; 5, Sweetognathus hanzhongensis (Wang). KFM-2009. 22 23 166x59mm (300 x 300 DPI) 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 Accepted Manuscript 51 52 53 54 55 56 57 58 59 60 Paleontological Society of Japan