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Constraining paleo-latitude of a biogeographic boundary in mid-Panthalassa:Fusuline province shift on the Late Guadalupian (Permian) migrating seamount

Akihisa Kasuya a, Yukio Isozaki a,⁎, Hisayoshi Igo b

a Department of Earth Science and Astronomy, The University of Tokyo, Komaba, Meguro, Tokyo 153-8902, Japanb Institute of Natural History, Takada, Toshima, Tokyo 171-0033, Japan

a b s t r a c ta r t i c l e i n f o

Article history:Received 24 June 2010Received in revised form 4 June 2011Accepted 6 June 2011Available online 12 June 2011

Handling Editor: M. Santosh

Keywords:PanthalassaSeamountFusulineProvincialismPaleo-latitudePermianExtinction

The Guadalupian paleo-atoll limestone (Iwato Formation) in SW Japan was primarily formed in low-latitudemid-Panthalassa and was later tectonically accreted to South China (Japan) margin during the Jurassic. Thepresent biostratigraphic study clarified that the Iwato Formation consists of 5 biostratigraphical intervals; i.e.four fusuline assemblage zones (Assemblage zones 1 to 4) and a barren interval on the top. Assemblage zones1 to 4 correspond to the Neoschwagerina craticulifera Zone, N. margaritae Zone, Yabeina globosa Zone, andLepidolina multiseptata Zone of the conventional Tethyan fusuline stratigraphy, respectively. The presentstudy newly clarified the following significant aspects of paleobiogeography of the Permian fusulines as to theextinction of large-tested taxa in the latest Guadalupian. 1) The long unknown stratigraphic relationship wasdocumented for the first time between the Yabeina-dominant interval and the overlying Lepidolina-dominantone within a single limestone unit. 2) The occurrence of Lepidolina cf. kumaensis Kanmera, the unique lastrunner of large-tested fusuine, was detected for the first time in mid-oceanic paleo-atoll limestones. 3) Withrespect to the northbound migration history of the paleo-seamount capped by the Iwato Formation, thedevelopment of the two coeval fusuline biogeographic territories in the low-latitude Panthalassa, i.e., theYabeina territory on the south and the Lepidolina territory on the north, was confirmed. 4) The paleo-latitudeof the biogeographic boundary between the Yabeina and Lepidolina territories is constrained around 12° in thesouthern hemisphere on the basis of the latest geomagnetic data from the same limestone. This new approachutilizing biostratigraphy on ancient migrating seamounts coupled with geomagnetic paleo-latitude data isapplicable to other cases in different time-space co-ordinates and of other fossil groups for constrainingposition of ancient biogeographic boundaries within lost oceanic domains of deep past.

© 2011 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

1. Introduction

Fusuline (foraminifera) represents one of the major Late Paleozoicmarine fossil groups that has been conventionally utilized in bio-stratigraphic zonation and international correlation of the UpperCarboniferous and Permian rocks. The overall evolutionary history offusulines recorded a clear trend of size increase and sophistication ofwall structures throughout the Late Carboniferous and Permian (e.g.,Loeblich and Tappan, 1964; Ross, 1967; Ozawa, 1970; Rozovskaya,1975; Kanmera et al., 1976; Sheng, 1990; Rauser-Chernousova et al.,1996). Like modern foraminifera, fusulines belong to protists, i.e.unicellular eukaryotes. Nonetheless some of the Middle Permian taxabecome extremely large up to the centimeter-scale, e.g., Eopolydiex-odina up to 16 cm in length (Vachard and Bouyx, 2002). Judging fromthe similarity to the modern large foraminifers (e.g. Hallock, 1999),the Permian large-tested fusulines are likewise regarded to have

hosted symbiont photosynthetic algae to reach that size (Ross, 1972;Wilde, 2002; Vachard et al., 2004; Yang et al., 2004; Ota and Isozaki,2006).

This long-term trend of fusuline gigantism, however, was punctu-ated abruptly at the end of Middle Permian (Guadalupian), or moreprecisely in the late Capitanian (Late Guadalupian) around 260 Ma.The thorough extinction of large-tested fusulines (i.e. Schwagerinidaeand Verbeekinidae) left solely smaller and simpler-formed dwarf taxa(Schubertidae, Ozawainellidae, and Staffellidae) in the Lopingian (LatePermian) considerably before the final extinction of all fusulines at theend of the Permian ca. 252 Ma (Wilde, 2002; Yang et al., 2004; Ota andIsozaki, 2006). The selective termination of the large-tested fusulinesat the end-Guadalupian is particularly noteworthy because this faunalre-organization was the biggest bioevent in the nearly 100 million-year fusuline history besides their final extinction at the end-Permian.

Another interesting aspect of the Permian fusulines is the remark-able development of provincialism, as up to six realms were hithertodistinguished; e.g. western Tethys, eastern Tethys, Panthalassa, NE Asia,northern Gondwana, and western America (e.g., Ross, 1967, 1995; Ishiiet al., 1985; Ozawa, 1987; Kobayashi, 1997). Nevertheless the above-

Gondwana Research 21 (2012) 611–623

⁎ Corresponding author. Tel.: +81 3 5454 6608; fax: +81 3 5465 8244.E-mail address: [email protected] (Y. Isozaki).

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mentioned screening of large-tested fusulines occurred at the end-Guadalupian regardless of such clear provincialism, confirming that theextinction-relevant environmental change at the end-Guadalupian wasglobal in context. The selective extinction of warm-water adaptedfaunas suggests the appearanceof a cool climate; however, thedirect killmechanism of marine animals, including fusulines, has not been fullyclarified yet. In this regard, the extinction pattern of temperature-sensitive photosymbiotic organisms, such as large-tested Capitanianfusulines, holds a key significance in the studies of the end-Guadalupianextinction and relevant global environmental changes.

Among the Capitanian large-tested fusulines, two representativegenera,Yabeinaand Lepidolina, are of profound interestnot only becauseboth represent the pre-extinction last runners of the above-mentionedgigantic fusulines but also because these two rarely co-occurred evenwithin the same oceanic domains. The significance of this remarkabledichotomyof the Capitanian fusulineswasfirst pointed out by Toriyama(1967) who tried to explain the phenomenon in terms of sedimentaryfacies-control of fusulines by proposing two contrasting lithofacies inJapan; i.e., the limestone-dominated Kinshozan facies with Yabeinaversus the terrigenous clastics-dominated Kuma facies with Lepidolina.It was still not clear-cut, however, if this dichotomy simply reflectedsedimentary facies control because Lepidolina in fact occurs also fromnon-terrigenous limestones as in South China, Indochina, BritishColumbia (e.g., Ishii et al., 1969; Goto et al., 1986). By analyzing fusulinewall structure, Ozawa (1970) clarified two independent lineages for theGuadalupian verbeekinids; i.e. the Neoschwagerina craticulifera–N. margaritae–Yabeina lineage and the Cancellina–Colania–Lepidolinalineage, bothbranchedoff from late Cisuralian (Early Permian)Misselinaand evolved into the forms with larger test and complicated internalwall structures. Later in the 1980s, two coeval but contrasting fusuline(biogeographic) territories within the Tethys–Panthalassa realms wereproposed; i.e., the Neoschwagerina–Yabeina territory and Colania–Lepidolina territory (Ishii et al., 1985; Ishii, 1990; Hada et al., 2001).The strictly separated occurrence of Yabeina and Lepidolina, however,has been themain obstacle to examine these hypotheses and to identifythe mutual province/territory boundary.

We recently found out a stratigraphic relationship between theYabeina Zone and the Lepidolina Zone for the first time within a singlestratigraphic sequence of a paleo-atoll limestone in Japan. This articlereports our new finding that provides the first direct clue to solve thelong-lasting conundrum of the Capitanian dichotomy of large-testedfusulines. In addition, we discuss some geological implications of thepresent results with particular emphasis on constraining paleo-latitudeof ancient biogeographic boundary within lost oceanic domains, byutilizing the biostratigraphical data from ancient migrating seamountsand their paleo-geomagnetism data from the same limestone unit.

2. Geological Setting

The Permian and Triassic limestones in the Kamura area in centralKyushu (Takachiho town, Miyazaki prefecture) form a part of anancient mid-oceanic atoll complex that primarily developed on amid-Panthalassan paleo-seamount (Fig. 1; Sano and Nakashima, 1997;Isozaki and Ota, 2001; Ota and Isozaki, 2006). After a long journeyacross the superocean, the limestone was secondarily incorporated asallochthonous (exotic) blocks into the Middle–Upper Jurassic accre-tionary complex in SW Japan (Isozaki, 1997b) together with deep-seacherts and other rock types (e.g., Nakagawa et al., 2009). Within theaccreted limestone blocks in the Kamura area, the primary stratigra-phy of mid-oceanic shallow marine carbonates is preserved; thelimestone ranges in age from the Guadalupian to Norian (LateTriassic) with several sedimentary breaks in the Triassic part (Saitoet al., 1958; Kanmera and Nakazawa, 1973; Watanabe et al., 1979;Koike, 1996; Ota and Isozaki, 2006).

The Permo-Triassic limestone in the Kamura area occurs as an over2 km long and 100–150 mwide body, forming an allochthonous block

surrounded by the Jurassic sandstone and mudstone (Fig. 2). As theTriassic part is highly limited in volume, the limestone is mostlycomposed of the Permian strata. The Permian limestone generallystrikes in ENE–WSW with almost vertical bedding planes, facingconsistently to the north. Later tectonic disturbance often dissectedthe limestone by N–S running minor faults, but the internal stra-tigraphy was kept coherent, thus is laterally traceable from section tosection within the studied limestone block.

The Permian limestone is composed of the Guadalupian IwatoFormation (ca. 100 m thick) and the overlying Lopingian MitaiFormation (ca. 30 m thick) (Fig. 2). These formations consist of darkto light gray, pure bioclastic limestone without coarse-grainedterrigenous clastics, and yield typical Tethyan shallow marine faunasthat include various fusulines, smaller foraminifera, calcareous algae,bivalves, gastropods, brachiopods, bryozoans, ostracods, crinoids, andrugose corals (Ota and Isozaki, 2006; Isozaki et al., 2007b; Kani et al.,2008). The base of the Iwato Formationwas not exposed in this area, butjudging from the geology of neighboring areas, its basement is likelycomposed of basaltic lava of oceanic island basalt affinity. The IwatoFormation is composed mainly of massive, dark gray wackestone withminor amount of packstone and lime mudstone. The dominantoccurrence of large-tested fusulines (Neoschwagerina, Yabeina, Lepido-lina) and calcareous algae (Mizzia, Permocalculus, Gymnocodium),together with rugose corals (Waagenophyllidae) and also with large-shelled bivalves (Alatoconchidae) in part, indicates tropical–subtropicalwarm-water environments for the primary depositional site (Isozaki,2006; Isozaki and Aljinovic, 2009). In accordance, the latest paleomag-neticmeasurement for the upper part of the Iwato Formation confirmedthat the Capitanian limestone was deposited at ca. 12° in the southernhemisphere (Kirschvink and Isozaki, 2007).

Previous studies provided fragmentary fusuline data; i.e. thesporadic occurrence of Middle Permian Neoschwagerina, Yabeina andLepidolina from the Iwato Formation, and that of Late PermianCodonofusiella, Reichelina, Palaeofusulina from the Mitai Formation(Saito et al., 1958; Kambe, 1963; Kanmera and Nakazawa, 1973;Isozaki and Ota, 2001; Murata et al., 2003). These preliminary datasuggest that the Iwato Formation ranges by and large in the later half ofthe Guadalupian, and the Mitai Formation in the Lopingian (Wuchia-pingian+Changhsingian), respectively. Ota and Isozaki (2006) iden-tified the top of the Iwato Formation, i.e. the boundary between theGuadalupian Iwato Formation and the Lopingian Mitai Formation;however, neither detailed fusuline zonation within the entire IwatoFormation nor the precise age of its base has been clarified yet. Thepresent study analyzed fusuline stratigraphy of the Guadalupian IwatoFormation at 12 stratigraphic sections (Sections 1–12 from east towest; Fig. 2) in the Kamura area; all are in the main limestone bodyexcept Section 10 in an isolated block. As all the efforts to extractconodonts from this formation to date ended in vain likely owing tothe strong facies control, fusulines provide a basis for subdivision of theIwato Formation. Although the relatively poor exposures with thickvegetation and strong deformation/recrystallization hampered thehigh-resolution biostratigraphy, the general fusuline stratigraphy wasclarified as described below.

3. Fusuline stratigraphy

Nine stratigraphic sections (Sections 2–5 and7–11)out of 12yieldedinformative fusulines for biostratigraphy of the Iwato Formation. Thestratigraphic columns of the studied sections are illustrated in Figs. 3and 4. Abundance of fusulines varies drastically from section to sectionand/or from sample to sample. We conducted microscopic observationfor over 400 thin sections for fusuline analysis. The preservation offusuline tests is generally poor due to severe deformation, frequentcalcite veining, and secondary recrystallization. Owing to the limitednumber of available axial sections of fusuline individuals, their iden-tification were mostly difficult on species level; however, identified

612 A. Kasuya et al. / Gondwana Research 21 (2012) 611–623


genus names with some species names from the studied sections arelisted in Table 1 and partly illustrated in Fig. 5. A brief description ofidentified fusulines is given in the caption to Fig. 5.

The listed fusuline faunas are categorized roughly into the following4 assemblages; i.e. Assemblages 1 to 4. Assemblage 1 is dominated byNeoschwagerina cf. craticulifera (Schwager), a primitiveNeoschwagerinawith relatively simple septula. Assemblage 2 is composed mainly ofNeoschwagerina cf. margaritae Deprat, an advanced Neoschwagerina.Assemblage 3 is dominated by Yabeina and advanced Neoschwagerina,and Assemblage 4 by Lepidolina andGifuella, respectively. Defining strictbiozonation in terms of taxon range zone appears difficult for the Iwato

Formation because we cannot identify precise horizons of the first andlast occurrences of diagnostic taxa owing to the scarcity of well-preserved specimens. Under the circumstances, hereweuse assemblagezones for subdivision of the Iwato Formation.

As to the fusuline-bearing 9 stratigraphic sections, the following setsof assemblage zones are recognized; Section 2with Assemblage zones 1and 3, Section 3 with Assemblage zones 1 and 3, Section 4 with As-semblage zones 1, 2, and 3; Section 5with Assemblage zones 1, 2, 3 and4; Section 7with Assemblage zone 3, Section 8with Assemblage zone 4;Section 9 with Assemblage zone 3; Section 10with Assemblage zones 3and 4; Section 11 with Assemblage zones 3 and 4. Sections 3–5, 8, 10,

Pan

gea

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Chichibu belt

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300 km

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oceanic plate

Fig. 1. Indexmap of the Kamura area in central Kyushu, Japan (A), a simplified cartoon showing a ridge-arc transect with amid-oceanic seamount (B), and the paleogeography of thePermian world with the primary location of the Kamura seamount (filled circle) (C).

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Fig. 2. Geologic sketch map of the Kamura area, showing the distribution of the Permo-Triassic allochthonous paleo-atoll limestone within the Jurassic accretionary complex and thelocations of analyzed sections (topographic map: 1/5000 basic forest map prepared by Miyazaki prefecture). The extensive blank areas represent the Middle Jurassicmudstone/sandstone that surrounds exotic limestone block.

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and 11 provide critical pieces of information for fusuline stratigraphy ofthe Iwato Formation. In particular, Section 5 demonstrates the suc-cessive occurrence of 4 distinct assemblage zones, plus the probablebarren interval on top, in a single stratigraphic sequence (Fig. 4). Theresults from the rest sections support the sequence of Section 5withoutany discrepancy. Section 10 solely recorded the co-occurrence ofYabeina and Lepidolina (Table 1; Fig. 3), suggesting that a tran-sitional interval develops between Assemblage zones 3 and 4. Inaddition, Section 8 displays a direct contact between the Assemblagezone 4 and the overlying barren interval, and also that between thebarren interval and the overlying Wuchiapingian Codonofusiella–Reich-elina Zone (Fig. 3; Ota and Isozaki, 2006).

On the basis of these data, it is confirmed for the first time that theIwato Formation in the Kamura area comprises 4 distinct fusulineassemblage zones; i.e. Assemblage zones 1–4 in ascending order. Whenthe barren interval over the Assemblage zone 4 is added, it makes 5fusuline intervals in total (Fig. 6). It is noteworthy that Assemblage zone4 replete with Lepidolina represents the topmost fusuline-bearinginterval in the Iwato Formation and that the top of this zone marks theend-Guadalupian extinction horizon of the large-tested fusulines (e.g.,Stanley and Yang, 1994; Yang et al., 2004; Ota and Isozaki, 2006). Inaddition, another interestingpoint to note is theoccurrence of Lepidolinacf. kumaensis Kanmera from Section 5 because L. kumaensis has neverbeen reported from mid-oceanic paleo-seamount limestone.

According to the composite stratigraphic column based on the 9sections, thickness of each assemblage zone is estimated as follows;Assemblage zone 1: over 20 m; Assemblage zone 2: ca. 25 m; Assem-blage zone 3: ca. 20 m; Assemblage zone 4: ca. 10 m; and the barreninterval: 15 m (Fig. 6). Although the base of the Iwato Formation wasnot identified, the total accumulated thickness of the Guadalupianpaleo-atoll carbonate buildup is estimated to bemore than 100 m. Theeastern half of the limestone body is dominated by the lower half ofthe Iwato Formation, whereas the western half by the upper half(Figs. 2 and 3).

4. Correlation

It is noteworthy that 4 fusuline assemblage zones and 1 barreninterval are recognized in sequencewithin a single limestone body inthe Kamura area (Fig. 6) because previous studies randomlyreported sporadic occurrences of various fusulines. According tothe conventional Middle Permian fusuline studies in Japan, theabove-described 4 fusuline assemblage zones roughly correspond tothe following 4 Tethyan fusuline zones; i.e. N. craticulifera Zone,N. margaritae Zone, Yabeina Zone, and Lepidolina Zone, respectively.The N. craticulifera Zone and N. margaritae Zone are correlated withthe Murgabian to lower Midian in Transcaucasia, and the latter twozones with the middle–upper Midian in Transcaucasia (Leven, 1996;Ueno, 1996; Kobayashi et al., 2007). The former two zones arecorrelated also with the Wordian (Middle Guadalupian) at GSSP(Global Stratotype Point and Section) in Texas, while the YabeinaZone and Lepidolina Zone are correlated with the Capitanian (UpperGuadalupian) at GSSP in Texas (Wilde et al., 1999). As the Lopingianfusuline fauna appeared from the base of the overlying MitaiFormation, the barren interval is assigned to the upper Capitanian(Ota and Isozaki, 2006). Thus the Iwato Formation ranges in theWordian to Capitanian.

The Iwato Formation is by and large similar to the Akasakalimestone in central Japan (Fig. 1A) in terms of lithofacies and faunalcontent; however, a higher-resolution zoning of fusulines wasperformed for the same interval in the Akasaka limestone (ZawWin, 1999). The present dataset from the Kamura area is not yetsufficient enough to correlate in the same resolution. These twolimestones are separated from each other for ca. 500 km at present,they were likely derived from independent paleo-seamounts;nonetheless their mutual similarity probably comes from thephysiographical proximity in origin. Other Permian paleo-atolllimestone blocks in the Jurassic accretionary complex in SW Japanalso have similar faunal composition to these two; e.g., the Tsukumi

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(2007b)

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Sec. 9

Sec. 8Ota & Isozaki (2006)Isozaki et al. (2007a)

Sec. 7

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Fig. 3. Stratigraphic column of the Permian and Triassic limestones at 12 analyzed sections in the Kamura area. Note Sections 2, 8, and 10 correspond to the previously studied ones byMurata et al. (2003), Ota and Isozaki (2006) and Isozaki et al. (2007a, 2007b). Note the close association of giant bivalve (Alatoconchiadae) and large fusulines (see text in detail).



limestone in eastern Kyushu, Torigatayama limestone in centralShikoku, Shirasaki limestone in western Kii Peninsula, and Kuzuulimestone in northern Kanto. These paleo-atoll complexes likelydeveloped on neighboring but different seamounts within the sameseamount chain or swarm (= hotspot track) developed in low-latitude Panthalassa (Fig. 1C).

5. Discussion

5.1. The Lepidolina Zone above the Yabeina Zone

The most significant result obtained in this study is the documen-tation of the stratigraphic relationship between the Lepidolina-domi-

nant assemblage and Yabeina-dominated assemblage for the first timewithin a single limestone mass derived from a paleo-atoll complex inmid-Panthalassa. Sections 2, 5 and 9 display that the Neoschwagerina-dominated Assemblage zones 1 and/or 2 are directly overlain by theAssemblage zone 3 replete with Yabeina without any in-betweenoccurrence of Lepidolina (Fig. 6). In particular, Section 5 demonstratesthat the Assemblage zone 4 occurs at ca. 7 m above the horizon ofAssemblage zone 3 (with a 2 m-thick gap on the exposure betweenthem) (Fig. 4).

On the other hand, Section 8 proves that the Assemblage zone 4with Lepidolina is directly overlain by the Lopingian Mitai Formationvia the barren interval without any in-between occurrence of Yabeina(Ota and Isozaki, 2006). After all, at least within the Kamura area, the

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Gifuella sp. Gifuella gifuensis? Lepidolina sp., L. cf. kumaensis, Gifuella gifuensis

Yabeina sp. (advanced form)

Neoschwagerina cf. margaritae

Neoschwagerina margaritae

Neoschwagerina cf. craticulifera

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light gray dolomite

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fusuline

Alatoconchidae (bivalve)

Fig. 4. Stratigraphic column of the Iwato Formation at Section 5. Note that this section has 4 assemblage zones and a barren interval in sequence.



Table 1Occurrence of Middle Permian fusulines from the Iwato Formation in central Kyushu, Japan (data mostly from the present study and partly fromMurata et al., 2003; Ota and Isozaki,2006; Isozaki et al., 2007a, 2007b). Refer to Figs. 3 and 4.

Fusuline name Section number (stratigraphic level in each section in meter)

2 3 4 5 7 8 9 10 11

Neoschwagerina cf. craticulifera 24 0 18.5–20.5 37.5Neoschwagerina margaritae Deprat 39.5N. cf. margaritae Deprat 25.5 49–53 22–28N. larga Morikawa & Suzuki 5–5.5N. cf. colaniae Ozawa 5–5.5N. minoensis Deprat 5–5.5Neoschwagerina sp. 40 41.5–43 43.5Verbeekina sp. 28Gifuella gifuensis Honjo 58 6Gifuella sp. 39.5 59 12.5–17 33.5 6Yabeina cf. globosa (Yabe) 5–5.5Y. cf. katoi (Ozawa) 5–5.5Yabeina sp. 55 53.1 50 10–20 28–38 2–4Lepidolina cf. shiraiwensis (Ozawa) 1–6L. cf. kumaensis Kanmera 58Lepidolina sp. 58 0–6 5–5.5 13.3Colania sp. 3 5–5.5Parareichelina sp. 5Kahlerina sp. 6

Fig. 5. Photomicrographs of large-tested fusulines from the Guadalupian Iwato Formation in the Kamura area (A–F: entire views of test; G–K: enlarged views of wall structure).A: Neoschwagerina cf. craticulifera (Schwager) from Sample D17 at Section 5, B, G: N. cf.margaritae Deprat from C5 at Section 4, C, H: Yabeina sp. from E1 at Section 7, D, I: Gifuella sp.from D10 at Section 5, E, J: Lepidolina sp. from D11 at Section 5, F, K: L. cf. kumaensis Kanmera from D11 at Section 5. Scale bar (upper left for A–F, lower right for G–K) is 1 mm for allspecimens. Note the clear difference in preserved wall structures that are critical in identification for 4 genera discussed in this article despite of the severe secondary deformation,vein development, and recrystallization of calcite tests. G: N. cf. margaritae, wall rather thick; primary transverse septula short and broad, connecting with top of parachomata. H:Yabeina sp., thickness of wall moderate to thin; primary transverse septula elongate and triangular in shape; secondary transverse septula short and thin, well developed in outervolutions. I: Gifuella sp., wall thin; primary transverse septula slender, connecting with top of parachomata; secondary transverse septula almost lacking but one or two septulasporadically occur in outer volutions. J: Lepidolina sp., wall very thin; primary transverse septula thin and short; secondary transverse septula first appear in inner 3rd to 5th volution.K: Lepidolina cf. kumaensis, fragmented outer elongate volutions with very thin wall and many thin parachomata; primary transverse septula short and thin; secondary transverseseptula well developed and pendant shape with parachomata-like deposits.



Yabeina-dominated interval occurs always below the Lepidolina-dominant part and not vice versa, suggesting the primary superiorityof the Lepidolina-interval in stratigraphy. In addition, Section 10 has ahorizon that yields Yabeina cf. globosa together with Colania sp. andLepidolina sp. (Murata et al., 2003). This short section likely preservesa transitional interval that spans across the two assemblage zones(Fig. 6).

As mentioned before, the stratigraphic relationship between theYabeina Zone (often defined as the Yabeina globosa Zone in Japan) andthe Lepidolina Zone (the Lepidolina multiseptata Zone) has been anissue of long-lasting uncertainty because these two zones hardly co-occur from any Permian limestone section in Japan. Also in otherTethyan domains, their mutual stratigraphic relationship was notclearly documented. Kanmera (1953, 1954) assigned the LepidolinaZone above the Yabeina Zone, whereas Hanzawa and Murata (1963)proposed the opposite relation (Fig. 7). Ever since the compromisingassignment by treating these two zones as being coeval by Yabe(1966), both the Yabeina Zone and Lepidolina Zone were tentativelyregarded as facies-dependent variations for the same time interval(Toriyama, 1967), and both were correlated all together to theCapitanian in Texas and the Midian in Transcaucasia (e.g., Ishii, 1990;Leven, 1996). Consequently, the present results proved that theinterpretation by Kanmera (1953, 1954) was correct at least for themid-Panthalassan paleo-atoll carbonates within the Jurassic accre-tionary complexes in Japan. The stratigraphical superiority of theLepidolina Zone over the Yabeina Zone was confirmed to date solely inthe Kamura area. Although no positive evidence for reversed super-position has been hitherto reported, we definitely need to check themutual relationship in other sections in Japan and also in the rest ofthe world. In this regard, what is concerned is the extremely rareoccurrence of Lepidolina from the Yabeina-dominant limestone (ZawWin and Sakagami, 1996).

5.2. Lepidolina kumaensis from mid-oceanic paleo-atoll carbonate

Another noteworthy aspect on fusuline biostratigraphy found inthis study is the occurrence of Lepidolina cf. kumaensis Kanmera from

Section 5 (Figs. 3–5) because this is the first record from mid-oceanicpaleoatoll-type limestone. Kanmera (1953, 1954) originally describedL. kumaensis from the Kuma Formation that consists mainly of coarse-grained terrigenous clastics (conglomerate, sandstone, mudstone)with minor amount of fusuline-bearing impure (terrigenous grain-rich) limestone. As this unit likely represents fore-arc shelf/slopesediments covering older accretionary complexes (Isozaki, 1987)along the South China margin, its sedimentary facies is remarkablydifferent from the mid-oceanic paleoatoll pure carbonates like theIwato Formation.

The age of the Kuma Formation is no doubt sometime in the later halfof the Permian but was not sufficiently constrained in detail owing to itsuniqueness in faunal composition and to the absence of stratigraphicrelationshipwith other datedunits. L. kumaensis, aswell as accompanyingL. toriyamai Kanmera as a synonym, represents one of themost advancedforms of verbeekinidae fusulines. This species rarely occurs from theordinary Lepidolina Zone dominated by L. multiseptata (Deprat) orL. multiseptata shiraiwensis (Ozawa). Within a possible range from theCapitanian to the Wuchiapingian, nonetheless, the age of the KumaFormation and that of the L. kumaensis Zone per se remainedunconstrained (e.g., Toriyama, 1967; Kanmera et al., 1976) despite theadded radiolarian information (Ishiga and Miyamoto, 1986).

The sporadic occurrences of L. kumaensis were reported addition-ally from the sub-Lopingian strata in East Asia; i.e., the SouthKiatakamibelt in NE Japan (Choi, 1970), the Primorye region of Far East Russia(e.g., Sosnia, 1960; Kotlyar et al., 2007), and South China (Rui,1983). The restricted occurrences in East Asia also suggest the facies-controlled endemic nature of the L. kumaensis fauna (Toriyama, 1967).Under such uncertainty in age, the L. kumaensis-bearing interval wasseparated from the L. multiseptata Zone (or L. shiraiwensis Zone) as theL. kumaensis Zone that was tentatively placed stratigraphically abovethe L. multiseptata Zone (e.g., Yabe, 1966; Kanmera et al., 1976; Ishii,1990). Leven (1996) summarized all these data and concluded that theL. kumaensis Zone is properly correlated with the Capitanian in Texasor with the Midian in Transcaucasia.

The present find of L. cf. kumaensis from the upper part of theIwato Formation accords with Leven's interpretation because the L. cf.

0 m

100

50

Assemblage Zone 1(Neoschwagerina craticulifera Z.)

Assemblage Zone 2(Neoschwagerina margaritae Z.)

Assemblage Zone 3(Yabeina Z.)

Assemblage Zone 4(Lepidolina Z.)

barren interval

Codonofusiella-Reichelina Zone

Cap

itani

anW

uchi

apin

g.W

ordi

an

?

transitional interval between Zone 3 and Zone 4

Nc

NmNm

N+G

Y

Nc

L

LL

Y+LY

L

G

YY+GGGY+N

Nc

YY+Nm

Nm

Nm

Nm

G

YYGY+G+N

L+G

Y

Nm

N

Nc

NmY

NN

Y

Nc

Nm Neoschwagerina cf. margaritae

Nc Neoschwagerina cf. craticulifera

Y : Yabeina sp.

G : Gifuella sp.L : Lepidolina sp.

Iwat

o F

mM

itai F

m fusulineAlatoconchidae

Sec. 2

Sec. 11

Sec. 10

Sec. 8

Sec. 7Sec. 5

Sec. 4

Sec. 3

Fusulines

Sec. 9

N : Neoschwagerina sp.

Fig. 6. Fusuline zones of the Iwato Formation in the Kamura area. Five biostratigraphic intervals are recognized; i.e. Assemblage zones 1 to 4 and the barren interval in ascendingorder. Assemblage zones 1–4 correspond to the Tethyan standard fusuline zones, i.e. Neoschwagerina craticulifera Zone, N. margaritae Zone, Yabeina globosa Zone, and Lepidolinamultiseptata Zone, respectively. The former two zones are correlated with the Wordian, whereas the latter two and the barren interval with the Capitanian.



kumaensis-bearing horizon is ca. 15 m lower than the stratigraphiccontact between the Iwato Formation and the Wuchiapingian MitaiFormation at Section 5 (Figs. 3 and 4). Thus it appears likely that theL. kumaensis fauna never made its way into the Lopingian but becameterminated by the end of the Capitanian (Fig. 7), and that theL. kumaensis Zone belongs to Capitanian.

In addition, it is also noteworthy to detect L. cf. kumaensis frommid-oceanic paleo-atoll buildups for the first time in the viewpoint ofbiogeography. The Kuma Formation was located at the fore-arc of theactive margin of Permian South China, whereas the Iwato Formationwas migrating in somewhere within the low-latitude domain of mid-Panthalassa, ca. 3000 km away from South China. This suggeststhat L. kumaensis likely had a wider distribution than previouslybelieved, i.e., not only in the peripheries of East Asia but also in themiddle of the superocean. In other words, the former interpretationof facies-dependent endemism of the L. kumaensis fauna appearshighly unrealistic. Nevertheless we need to explain any possible reasonfor the rare occurrence of L. kumaensis from mid-oceanic paleo-atolllimestones.

5.3. Two modes in extinction of large-tested fusulines

The disappearance of large-tested fusulines and the followingdevelopment of the barren interval essentially suggest the onset of asevere environmental stress that prohibited the survival of large-tested fusulines into the Lopingian (e.g., Jin et al., 1994; Stanley andYang, 1994; Wilde, 2002; Yang et al., 2004; Ota and Isozaki, 2006).Neither themain cause nor the precise timing of the extinction has yetbeen identified; however, the common lines of evidence throughoutthe Tethyan (e.g., Leven, 1996; Yang et al., 2004) and circum-Pacificregions (e.g., Ross, 1995; Zaw Win, 1999; Wilde, 2002; Ota andIsozaki, 2006) suggest the appearance of a global-scale environ-mental stress during the Capitanian. Various possible kill mech-anisms of fusulines, in particular, that of the large-tested ones havebeen proposed, e.g., drop of seawater temperature, change in salinity,eutrophication etc. (e.g., Brasier, 1995; Wilde, 2002; Yang et al., 2004)through comparison with ecology of modern large foraminifers.Recent facies analysis, C-isotope chemostratigraphy and magnetos-tratigraphy of fusuline-bearing Guadalupian sequences suggest thatthe cooling in the tropics in Tethys and Panthalassa may have been

effective in terminating large-tested fusulines (Isozaki et al., 2007a,2007b; Isozaki, 2009a, 2009b). In particular, the drop in sea-surfacetemperature coupled with the ocean circulation-driven eutrophica-tion may have been critical for the photosymbiotic organismsadapted to the pre-existing oligotrophic conditions, such as large-tested fusulines, rugose corals, and aberrant bivalves (Isozaki, 2006;Aljinovic et al., 2008; Isozaki and Aljinovic, 2009; Isozaki et al., inpress). The Phanerozoic sea-level minimum appeared around the endof the Capitanian (Haq and Schutter, 2008) and the coeval migrationof mid-latitude fauna into tropical regions (Shen and Shi, 2002)support the onset of cooling in the Capitanian. Although further prooffor the kill mechanism is still needed, it is emphasized that theextinction of the Permian large-tested fusulines occurred extensivelythroughout Tethys–Panthalassa regardless of paleobiogeographicprovincialism.

Most of the Permian limestones in Japan occur as allochthonousblocks embedded within younger matrices, which were primarilyderived frompaleo-atoll complexes inmid-Panthalassa (e.g., Kanmeraand Nishi, 1983; Kanmera et al., 1990; Sano and Kanmera, 1991;Isozaki, 1997a). Among them, the occurrences of Lepidolina arerestricted to the Permian accretionary complexes (of the Akiyoshi,Maizuru, and Kuroseagwa belts in Southwest Japan), whereas those ofYabeina to the Jurassic accretionary complexes (of theMino-Tanba andChichibu belts) (Ishii et al., 1985; Ishii, 1990). The former group of thelimestone with Lepidolina, including the well-known Akiyoshi lime-stone (Fig. 1), was accreted to the Japanmarginmostly during the LatePermian, whereas the latter group (including the Akasaka limestone)with Yabeinaduring theMiddle–Late Jurassic, nearly 100 Ma later thanthe former (Maruyama et al., 1997; Isozaki et al., 2010; Fig. 8). Thesetwo contrasting groups of the Guadalupian limestones recorded asimilar scenario for the large-tested fusuline extinction but in sharpcontrast in major genera.

The Iwato Formation witnessed this extinction of large-testedGuadalupian fusulines (Lepidolina, Yabeina) in the low-latitude mid-Panthalassa (Kirschvink and Isozaki, 2007). A similar extinction patternof the Yabeina-dominant fauna and the following development of abarren interval were observed also in the Akasaka limestone (ZawWin,1999; Ota and Isozaki, 2006) and in other Permian allochthonouslimestones in the Jurassic accretionary complex in Japan. In contrast, thehighest fusuline zone in the Akiyoshi limestone is represented by the

Capitanian

Wuchiapingian

(Lopingian)

Wordian

This study Kanmera (1953, 1954) Hanzawa & Murata (1963) Yabe (1966) Ishii (1990)G

uada

lupi

an

Yabeina Yabeina

Yabeina

Yabeina Yabeina

Lepidolina Lepidolina

Lepidolina

Lepidolina

Lepidolina

L. kumaensis

Codonofusiella-Reichelina





Neoschwagerina Neoschwagerina Neoschwagerina Neoschwagerina Neoschwagerina

Age

globosa

Lepidolina

kumaensis

globosa

multiseptata

globosa

multiseptataglobosa

multiseptata

barren interval

+ kumaensisglobosa

multiseptata+ kumaensis) (multiseptata

(kumaensis)

Yabeina-Lepidolina

Fig. 7. Comparison of fusuline zoning scheme for the Middle Permian accreted paleo-atoll carbonates in Japan (compiled from Kanmera, 1953, 1954; Hanzawa and Murata, 1963;Yabe, 1966; Ishii, 1990; this study). For convenience's sake, some taxonomic names are modified from the original descriptions into the currently accepted synonymous names; e.g.L. toriyami Kanmera=L. kumaensis Kanmera, Y. shiraiwensis (Ozawa)=L. multiseptata (Deprat).

Fig. 8. Paleogeographic maps of the Late Guadalupian (A, B: based on Ziegler et al., 1997 and modified according to Maruyama et al., 1997; Muttoni et al., 2009) and of the Mid-Jurassic (C: modified from Rees et al., 2000). A: the relative positions of the two groups (the Akiyoshi-type and Akasaka-type) of Permian seamounts within the superoceanPanthalassa; B: theMiddle Permian fusuline territories (compiled fromHada et al., 2001, Ueno, 2003, and the present study). Note the boundary between the Lepidolina territory andthe Yabeina territory in mid-Panthalassa is marked by the paleo-seamount with the Iwato Formation (Akasaka-type paleo-atoll limestone) at 12° S and 3000 km to the east of SouthChina. C: the relative position of the paleo-seamount immediately before accretion to the South China margin, together with the migration trajectory of the seamount and that ofSouth China per se during the Late Permian, Triassic, and Early–Middle Jurassic times.



Mid-Jurassic

S.China

60N

60S

30S

30N

equator

Iwato Fm

accretion

on a paleo-seamount

Pan

gea

Panthalassa

Neo-Tethys

Shelf (-200–0 m)Deep Ocean (< -200 m)

Late Guadalupian(260 Ma)

Land (> 0 m)

A

B

C

equator

Pan

gea

Panthalassa

Panthalassa

Paleo-TethysS.China

Indochina Akasaka-grouppaleo-seamount

Akiyoshi-grouppaleo-seamount

30N

60N

30S

60S

N.China

Bureya

Sibumasu

equator

30N

60N

30S

60S

Lepidolina territory

Yabeina territory

?

?

Yabeina territory

Lepidolina Yabeina Eopolydiexodina



LepidolinaZone (Toriyama, 1967;Ueno, 1996). The fusuline stratigraphyof the topmost Akiyoshi limestone is still not clear because this part iscomposed of limestone conglomerate with abundant L. multiseptatawithout any trace of the L. kumaensis fauna. A fairly short time interval isestimated between the final deposition of limestone and the subduc-tion–accretion at an ancient trench along the South China marginduring the latest Guadalupian and early Lopingian; i.e. the wholelimestone complex was tectonically destructed, partly accreted and/orsubducted at the active trench, immediately after the deposition (SanoandKanmera, 1991). Thus a full record of the extinction history of large-tested fusulines for the Lepidolina-dominant groupwas not preserved indetail in the Akiyoshi limestone and its equivalents contained in thePermian accretionary complex in Japan. Nonetheless it is noteworthythat theAkiyoshi-type limestonewas completely free from Yabeina, andthat the end-Guadalupian extinction of large-tested fusulines in theAkiyoshi-type limestone group wasmarked by the die-off of Lepidolina.The development of the two contrasting faunas of large-tested fusulinesin Panthalassa and their coeval extinction provide an interesting aspectof the Middle Permian fusuline biogeography.

5.4. Migrating seamounts and fusuline territories in Panthalassa

Between the two groups of Permian paleo-seamount limestones inJapan, there was a large time lag of ca. 100 Ma in accretion timing; i.e.the Lepidolina-bearing Akiyoshi-type group accreted around 260–255 Ma (Late Permian), whereas the Yabeina-bearing Akasaka-typegroup around 165–160 Ma (mid-Jurassic) (Isozaki et al., 2010).During the Middle Permian immediately before their final subduc-tion–accretion, the Akiyoshi-type paleo-seamounts were locatedadjacent to the South China margin (Fig. 8A) that stayed in the trop-ical domain across the equator (e.g., Maruyama et al., 1989; Ziegleret al., 1997). This is in accordance with the fact that Lepidolina occurscommonly from the shelf limestones both in South China (e.g., Sheng,1990; his Yabeina corresponds to Lepidolina) and in Indochina (e.g.,Deprat, 1912; Ishii et al., 1969; Fig. 8B).

On the other hand, the Akasaka-type paleo-seamounts werelocated far away from South China in the Middle–Late Permianwhen the Akiyoshi-type seamounts were under accretion along theSouth China margin. Given a conservative plate consumption rate attrench around 3 cm/year, the minimum distance between the SouthChina margin and the mid-oceanic Akasaka-type paleo-seamounts isestimated ca. 3000 km. The paleo-latitude of the depositional site ofthe Capitanian Iwato Formation was recently determined at 12° S bythe geomagnetic measurement (Kirschvink and Isozaki, 2007). Thusthe Akasaka-type seamount chain (or swarm) was probably locatedin the low-latitude mid-superocean in the southern hemisphere,and was separated for more than 3000 km (ca. 40° in equatoriallongitude) to the east from South China (Fig. 8). Thus the two groupsof accreted Permian limestones in Japan represent two distinct oceandomains within Panthalassa characterized by distinct fusuline faunafor each (e.g., Ozawa, 1987; Ishii, 1990; Kobayashi, 1999; Hada et al.,2001).

From the paleo-biogeographical viewpoint, therefore, it is significantthat the Iwato Formation solely recorded the co-occurrence of Yabeinaand Lepidolina in an intimate stratigraphic relationship. The IwatoFormation basically belongs to the Yabeina-bearing Akasaka-typelimestones that accreted to South China (Japan) margin during theJurassic; however, its top part exceptionally yields Lepidolina. Thisstratigraphic change in faunal composition from the Yabeina-dominantto Lepidolina-dominant nature within a continuous sequence likelyreflects the northboundmigration history of the paleo-seamount acrossthe fusuline biogeographical territory/province boundary withinPanthalassa (Fig. 8B). The lower half of the Iwato Formation wasdeposited within the Yabeina territory (sensu Ishii et al., 1985) in mid-Panthalassa of the southern hemisphere (in low latitude domains with

latitudes higher than 12° S), whereas its upper part was formed withinthe Lepidolina territory on the north of the border.

As to the paleo-seamount that accommodated the Iwato Forma-tion, the entire travel history from its departure in mid-superocean toits arrival at subduction zone is summarized as follows; 1) originatedat somewhere in the mid-Panthalassa in the southern hemispherewhere Neoschwagerina (ancestor of Yabeina) dominated, 2) tres-passed northward through the Yabeina-dominant territory up to 12° Sand migrated into the domain replete with Lepidolina during theCapitanian (Fig. 8B), 3) experienced the end-Guadalupian extinctionnear the equator, 4) kept moving northwestward during theLopingian, Triassic, and Early Jurassic in the northern hemisphere,and 5) finally docked to the South China margin at mid-latitude in thelate Middle–early Late Jurassic (Fig. 8C; Maruyama et al., 1997; Otaand Isozaki, 2006).

The remarkable dichotomy in coeval fusuline assemblages sug-gests the relatively sharp differentiation of the Yabeina and Lepidolinaterritories within Panthalassa, and also the relatively northerly and/orwesterly development of the Lepidolina territory, as suggested before(e.g., Ozawa, 1987; Kobayashi, 1999; Hada et al., 2001). Althoughmerely a few examples were listed, Hada et al. (2001) in a preliminarydiscussion proposed the chronological order of accretion of thePermian seamounts in Canadian Cordillera and in New Zealand.Without practical paleo-latitudinal constraints, however, the actualdistribution pattern of the two territories in mid-Panthalassa hasremained nomore than imaginary. In this regard, the Iwato Formationis a sole recorder of such across-latitude migration of the Permianseamounts with practical paleo-latitude data for the border. A similaracross-latitude migration scenario was discussed for the Shan–Thai(Sibumasu) block in Thailand (Hada et al., 2001) and the EkonayTerrane in Koryak–Kamtchatka belt in NE Russia (Shi, 2006);however, these cases lack quantitative constraints for paleo-latitudeof any province boundary. Furthermore, continental blocks are ofteninvolved in local rifting, collision, rotation, and/or strike-slip dis-placement, thus some complexities are added to paleo-biogeograph-ical discussion. In addition, often in cases of poorly defined “terranes”,basement-covering autochthonous strata and accreted allochthonousones are not clearly separated, therefore, loosely defined identity offusuline-bearing limestone may lead erroneous biogeographicalinterpretation. In this respect, paleogeographical analysis focusingsolely on paleo-seamount appears more straightforward, as discussedabove.

The present confirmation of the gradual transition from theYabeina Zone to the Lepidolina Zone in the paleo-atoll limestone(Fig. 6) demonstrated the first reference point for the actual locationof the territory border within the superocean Panthalassa (Fig. 8B). Inorder to reconstruct the overall framework of the Middle Permianfusuline paleogeography in Panthalassa, we need more referencepoints for confining positions of multiple territory/province bound-aries. By performing similar analyses to other circum-Pacific orogensthat potentially preserve numerous remnants of far-traveled mid-Panthalassan seamounts, more precise image of the provincialismwillbe available in much higher resolution.

As to the global fusuline biogeography, the province/territorysubdivision appears not simple. For example, the Sibumasu block ofthe so-called “Cimmerian” affinity, originated from high-latitudeGondwanaland further to the south (Fig. 8B), is characterized by aunique fauna with Eopolydiexodina (anti-tropical taxon) but withoutYabeina and Lepidolina (Ueno, 2003). In the middle latitude of thenorthern hemisphere, on the other hand, the southeastern side of theBureya block in Primorye (Far East Russia) is characterized by anotherdistinct fauna dominated by Monodiexodina (anti-tropical taxon) andLepidolina (e.g., Kotlyar et al., 2007). The middle-latitude domainsboth in the southern and northern hemispheres during the Permianlikely formed anti-tropical distinct fusuline provinces/territories,suggesting the latitude-controlled provincialism of Middle Permian



biota (e.g., Shi, 2006). Nonetheless, along the eastern Panthalassanmargin in the tropical domain, the extension of the Yabeina territorywas recognized in West Texas (Skinner and Wilde, 1953). Further-more, the Middle Permian fusuline provincialism within Paleo-Tethysappears more complicated than in Panthalassa (e.g., Ueno, 2003).These indicate that the development of fusuline provincialism wasdependent not only on paleo-latitude but also on other factors, such asocean current, nutrient availability etc.

5.5. Paleolatitude of biogeographic province boundary

The end-Guadalupian extinction horizon in mid-Panthalassa wasmarked either at the top of the Yabeina Zone in the Yabeina territory(e.g., Akasaka limestone) or at the top of Lepidolina Zone in theLepidolina territory (e.g., Akiyoshi limestone). Both Yabeina andLepidolina were derived from the same lineage of late Early Permianverbeekinidae, and radiated/adapted separately into different terri-tories during the Guadalupian. When the end-Guadalupian extinctionoccurred globally, involving both the Yabeina and Lepidolina terri-tories, the paleo-position of each Capitanian seamount decided thepre-extinction last runner of the large-tested fusulines according to itsrelative position with respect to the territory border at 12° S (Fig. 8B).Even in the same seamount chain or swarm, therefore, the coevalextinction was recorded in different faunas. For instance, except forthe Iwato Formation, most of the Akasaka-type limestones witnessedthe end-Guadalupian fusuline extinction solely in the Yabeina Zone.The paleo-seamount with the Iwato Formation likely represented anorthernmost segment of the seamount chain that alone crossed theterritory border before the extinction, whereas the rest still remainedon the south of the border within the Yabeina territory (Fig. 9). As tothe Akiyoshi-type limestones, on the other hand, the entire paleo-seamount chain/swarm was already positioned in the middle of theLepidolina territory adjacent to South China margin during the

Guadalupian, and the extinction horizon was recorded ubiquitouslyin the Lepidolina Zone. Likewise, the accreted Permian limestones inthe western North America yield both Yabeina and Lepidolina(Thompson et al., 1950; Skinner and Wilde, 1966; Goto et al., 1986;Ross, 1995; Stevens et al., 1997), suggesting the occurrence of thesimilar examples to the Japanese ones mentioned above. In particular,the possible co-occurrence of Yabeina and Lepidolina in MarbleCanyon in British Columbia (Skinner and Wilde, 1966; Goto et al.,1986; Kobayashi et al., 2007) appears interesting for further checking.

Thus those records from migrating paleo-seamounts provide in-teresting data that can document the relationship between the fusulineterritories and extinction.We can test this hypothesis by checking otherexamples of Permianpaleoatoll limestones in accretionary complexes inthe Cordilleran orogen in western North America on the other side ofPanthalassa, and also in the circum-Pacific subduction-related orogensin the southern hemisphere because southbound paleo-seamountsmight record an overturned stratigraphy with the Yabeina Zone abovethe Lepidolina Zone owing to the opposite direction of seamountmigration (Fig. 9). This approach utilizing biostratigraphy on migratingpaleo-seamounts is applicable to other cases to constrain paleo-latitudes of biogeographical province boundaries, thus paleo-biogeo-graphic frameworks, even though ancient seamounts and/or seafloorsalready disappeared from the Earth's surface by the non-stop oceanicsubduction processes.

6. Conclusions

The present fusuline biostartigraphic study distinguished 5 biostrat-igraphic intervals in sequence within a Guadalupian paleo-atoll lime-stone (Iwato Formation) in the Kamura area, SW Japan, which wasprimarily formed in the low-latitude mid-Panthalassa and was latertectonically accreted to South China (Japan) margin during the Jurassic.The Iwato Formation is composed of four assemblage zones (1 to 4 in

N

S

equator

Yabeina territory Lepidolina territory

crossing territory boundary (~12o S)

Age

Wuc

h.

Lop.

Gua

dalu

pian

Cap

itani

an

G-LB

northbound

barren interval

seam

ount

posi

tion

no knownexampleseamount

Akasaka Kamuraseamount seamount

Akiyoshi

staying withinstaying within

extinction

Lepidolina territory

Yabeina territory

territory boundary

at 12o S

relative migration trajectory of mid-oceanic seamount with repsect to the terriotry boundary

southbound

Lepi

dolin

a

Lepi

dolin

a

Lepi

dolin

a

Yab

eina

Yab

eina

Yab

eina

Fig. 9. Relative trajectories of paleo-seamount drifting within the mid-superocean (arrows) with respect to the biogeographic boundary between the Lepidolina territory and theYabeina territory (sensu Hada et al., 2001) (above), and the resultant superposition of the Late Guadalupian fusuline assemblages recorded in paleo-atoll limestone; i.e., 4 possiblealternatives with 3 confirmed examples (Akasaka, Kamura, and Akiyoshi seamounts in Japan) (below). Note the Kamura paleo-seamount with the Iwato Formation recorded thetrespassing episode across the boundary between southerly Yabeina territory and the northerly Lepidolina territory. In contrast, the Akasaka paleo-seamount recorded its long stableresidence within the Yabeina territory, and so did the Akiyoshi paleo-seamount within the Lepidolina territory. An imaginary southbound seamount might record the oppositesuperposition between the Lepidolina Zone and overlying Yabeina Zone.



ascendingorder) andabarren interval on the top.Assemblage zones 1 to4 correspond to the N. craticulifera Zone, N. margaritae Zone, Y. globosaZone, and L.multiseptata Zone of the conventional Guadalupian Tethyanfusuline stratigraphy, respectively. The former two are correlated withtheWordian in Texas, whereas the latter two and the barren interval tothe Capitanian in Texas. As to the extinction of large-tested fusulinesat the end of the Guadalupian, the following significant aspects inbiostratigraphy and paleobiogeography of the Permian fusulines werenewly clarified.

1. The stratigraphic relationship of the Lepidolina-dominant intervalabove the Yabeina-dominant one was confirmed for the first timeafter the long-time controversy owing to the absence of their co-occurrence.

2. The occurrence of L. cf. kumaensis was detected for the first time inmid-oceanic paleo-atoll pure limestone. This species was hithertoknown to occur solely from continental shelf facies sequencesenriched with terrigenous clastics. The age of the L. cf. kumaensis-bearing horizon was also constrained to the Capitanian.

3. With respect to the northboundmigration history of a mid-oceanicseamount, the development of the two coeval fusuline biogeo-graphic territories in the low-latitudemid-Panthalassa domain, i.e.,the Yabeina territory on the south and the Lepidolina territory onthe north, was confirmed. The boundary between these twoterritories lay around 12° in the southern hemisphere.

4. The extinction of large-tested fusulines occurred throughout thetropical–subtropical domains of Permian Panthalassa, regardless ofthe biogeographic provincialism. The extinction horizon wasrecorded at the top of the Yabeina Zone or of the Lepidolina Zone,according to the relative position of the paleo-seamounts withrespect to the biogeographic border within Panthalassa.

Acknowledgments

This article is dedicated to late Professor Kametoshi Kanmera(1923–2008) who made outstanding contributions to the studies onfusuline paleontology and on tectonics of Japan. C.A. Ross, G.R. Shi, andan anonymous reviewer gave many constructive comments to theoriginal manuscript. D. Vachard helped in reference search. M. Saitoh,T. Sato and S. Ogata provided great help in fieldwork, and K. Aoki indrafting some figures. This study was supported by Grant-in-Aid fromJapan Society of Promoting Science (no. 20224012 to Y. I.).

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