Memoir of the Fukui Prefectural Dinosaur Museum 10 : 103−112 (2011)

ARTICLE! by the Fukui Prefectural Dinosaur Museum

AN EXOTIC BODY OF THE MIDDLE JURASSIC TORINOSU-TYPE LIMESTONE
IN THE HIKAWA FORMATION, SOUTHEASTERN KANTO MOUNTAINS, JAPANNaoto ISHIDA
Faculty of Science, Niigata University, Niigata, 950−2181, Japan

ABSTRACTAn exotic body of the Middle Jurassic Torinosu-type limestone was found in the Upper Jurassic Hikawa
Formation, southeastern Kanto Mountains, Japan. A radiolarian assemblage containing Kilinora tecta (Matsuoka),
Striatojaponocapsa conexa (Matsuoka), Sj. plicarum (Yao) sensu Hatakeda et al. (2007), Japonocapsa fusiformis(Yao), Stichocapsa japonica Yao, Stc. naradaniensis Matsuoka, Zhamoidellum ovum Dumitrica, Praewilliriedellum
spinosum Kozur, Tethysetta dhimenaensis (Baumgartner), and Dictyomitrella (?) kamoensis Mizutani and Kido wasrecovered from the limestone body and is equivalent to that from the upper part of the Sj. conexa Zone (Bathonian tomiddle Callovian). The limestone body occurred in an Upper Jurassic (Kimmeridgian to lower Tithonian) gravelly
mudstone of the lower member of the Hikawa Formation as a boulder-sized clast.
An exotic body of the Middle Jurassic Torinosu-type limestone has also been reported from the Upper Jurassic
Ebirase Formation, western Kyushu. The Hikawa and Ebirase formations are two of the Upper Jurassic trench-slope
basin deposits formed simultaneously in the Southern Chichibu Belt. The occurrences of the exotic Middle Jurassic
limestone bodies in these Upper Jurassic formations indicate that Middle Jurassic shallow-marine strata containing
carbonate sediments were eroded on the accretionary complexes in widespread areas of the Southern Chichibu Beltand rock debris originating from these strata was transported into trench-slope basins during the Late Jurassic.
Key words: Torinosu-type limestone, radiolaria, Jurassic, Hikawa Formation, Southern Chichibu Belt, Kanto
Mountains

石田直人（２０１１）関東山地南東部，上部ジュラ系氷川層に産する異地性岩体としてのジュラ紀中世鳥巣式
石灰岩. 福井県立恐竜博物館紀要 10 : 103−112.
関東山地南東部の秩父累帯南帯に分布する上部ジュラ系氷川層において, 異地性の産状を示すジュラ紀
中世鳥巣式石灰岩体が確認された. この石灰岩体から産する放散虫化石群集は Striatojaponocapsa conexa
帯上部から産するものに一致し, ジュラ紀中世後期（Bathonian期〜Callovian期中期）を示す. この岩体は, 上部ジュラ系 Kimmeridgian 階とTithonian階の境界付近の層準の含礫泥岩に礫として含まれており,周囲の砕屑岩との年代差に加え, 堆積環境の相違からも異地性岩体と結論できる. 異地性のジュラ紀中世
鳥巣式石灰岩は, 九州西部に分布する上部ジュラ系箙瀬層にも知られている. 氷川層と箙瀬層は共に, 同時に形成された海溝斜面海盆堆積物とされる. 両層に産する異地性の鳥巣式石灰岩は, 付加体上にあるジ
ュラ紀中世の炭酸塩岩を含む浅海成層がジュラ紀新世に浸食され, その岩屑が海溝斜面海盆へと流入した現象が広域に生じたことを示唆する.

INTRODUCTION――――――――――――――――――――――――――The distribution of upper Mesozoic strata containing theTorinosu-type limestone in the Japanese Islands is well known(e.g., Tamura, 1960). “Torinosu-type limestone” is a genericname for Japanese Jurassic and Lower Cretaceous shallowmarine limestone that commonly contains ooids and reef
components along with terrigenous siliciclastic grains andReceived March 20, 2011. Accepted October 12, 2011.
Present: Venture Business Laboratory, Niigata University, Niigata, 9502181, Japan
E-mail: nao.ishida21*mbn.nifty.com（The asterisk should be replaced by ＠.）
編集注）「中世」「新世」は、それぞれ「中期」「後期」と同義.
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NAOTO ISHIDAFIGURE 1. Distribution of the Southern Chichibu and Northern Shimanto belts in the Outer Zone of Southwest Japan (referenced from the Geological
Survey of Japan, 1992). Median Tectonic Line, Usuki–Yatsushro Tectonic Line, and Butsuzo Tectonic Line are indicated by heavy lines. Locations of the
microfossil age-ascertained Torinosu-type limestone bodies (diamonds), the southeastern Kanto Mountains (black frame), and study area (black square) arealso shown.

organic matter.
Occurrences of the shallow-marine Torinosu-type limestonebodies are known from the Southern Chichibu and Northern
Shimanto belts of the Outer Zone of Southwest Japan. However,deep-marine siliciclastic sediments of Jurassic to Cretaceous
accretionary complexes are widely distributed in these belts.
Ages of the Torinosu-type limestone and limestone-bearing
strata in these belts have been determined over the last two
decades using microfossils (Fig. 1). In addition, studies ofsedimentary facies (Kano, 1988; Kano and Jiju, 1995), strontium
isotopic ages (Shiraishi et al., 2005), carbon isotope stratigraphyof this type of limestone (Kakizaki and Kano, 2009), and rudist
bivalve fauna (Sano et al., 2007; Sano and Skelton, 2010) havealso been performed. Nevertheless, the reason so many Torinosutype limestone bodies are found in and around the deep-marine
siliciclastics of the accretionary complexes remains unexplained.
A previous study of an exotic body of the Middle Jurassic
Torinosu-type limestone found in the Upper Jurassic Ebirase
Formation in the Southern Chichibu Belt, western Kyushu,
elucidated the formative and redepositional processes relevant tothe sedimentary and tectonic evolution of accretionary
complexes (Ishida, 2006). A Middle Jurassic radiolarian age was
newly obtained from a Torinosu-type limestone body in theUpper Jurassic Hikawa Formation in the Southern Chichibu Beltin the southeastern Kanto Mountains (Fig. 1) and it turned outthat the limestone body is an exotic clast contained in deepmarine siliciclastics. This paper describes faunal composition of
the radiolarian assemblage and mode of occurrence of thelimestone body, and provides insight into the tectonosedimentary implication of the limestone body in the context of
the Late Jurassic evolution of the accretionary complexes in theSouthern Chichibu Belt.

HIKAWA FORMATIONThe Hikawa Formation, established by Fujimoto (1939), is an
Upper Jurassic siliciclastic formation in the Southern Chichibu
Belt in the southeastern Kanto Mountains (e.g., Yasuda, 1989;
Ishida, 2004). The formation conformably overlies the lower to
middle Upper Jurassic Mitsugo Formation (Ishida, 2004). These
Upper Jurassic formations are distributed among accretionary
complexes and are in fault contact with the Middle to early Late
Jurassic thrust pile of the Unazawa Formation in the northeast
and with the Early Cretaceous limestone−mafic volcanic rockcomplexes (Kanoto and Gozenyama formations) in thesouthwest (Takaoka, 1954; Takashima and Koike, 1984; Sakai,
1987; Yasuda, 1989; Takahashi, 2000; Ishida, 2004) (Fig. 2A).
The approximately 700 m thick Mitsugo Formation is mainlycomposed of muddy turbidites with massive sandstone beds andexotic bodies of chert (Ishida, 2004). The Hikawa Formation,
approximately 1,100 m in thickness, is subdivided into lower
and upper members (Yasuda, 1989). The lower member consistsof thick coarse-grained turbiditic sandstone in conjunction withmuddy turbidites and gravelly mudstone beds. The upper
member is mainly composed of muddy turbidites, gravelly
mudstone, and turbiditic sandstone. Torinosu-type limestonebodies mainly occur in four stratigraphic horizons of the Hikawa
Formation: one is in the lower member and the others are in theupper member (Ishida, 2004). In ascending order, the Upper
Jurassic radiolarian zones of the Hikawa Formation (Ishida,2004) are the Hsuum maxwelli Zone, Loopus primitivus Zone,
and the Pseudodictyomitra carpatica Zone of Matsuoka (1995).
Hexacorals and other reefal biota have been reported from theTorinosu-type limestone bodies in the Hikawa Formation (e.g.,
Fujimoto, 1939). Additionally, fossil corals were recovered from

MIDDLE JURASSIC TORINOSU-TYPE LIMESTONE

105

FIGURE 2. A, Map showing the location of studied route. The simplified geologic map is after Ishida (2004). The map is based on the 1:25,000“Okutamako” topographic sheet (Geographical Survey Institute of Japan). B, Route map along the Akaizawa River. A black frame indicates the location ofstudied outcrop shown in Fig. 3. Stars show the locations of radiolarians by Ishida (2004). The World Geodetic System was used to designate thelongitudes and latitudes. C, Stratigraphic column of the lower member of the Hikawa Formation exposed in the study route..

a limestone body in the lower member during this study (Fig. 2
A).
Radiolarian fossils have also been recovered from twolimestone bodies (Sashida et al., 1989): one is certainly from thelower member, whereas the stratigraphic horizon of the other is
unknown. The presence of radiolarians such as Tricolocapsa
plicarum Yao, T. conexa Matsuoka, Protunuma turbo Matsuoka,
and Eucyrtidiellum unumaense (Yao) indicates an age around thelate Middle Jurassic. Two species referred to as the genus
Tricolocapsa in this study were reassigned to the genus
Striatojaponocapsa by Hull (1997).
Recently, foraminifers have been reported from four limestonebodies in the formation (Kobayashi and Vuks, 2006) and havebeen identified to species level in one body in the lower part of

the upper member. The foraminiferal assemblage, containing
Nautiloculina oolithica Mohler, Haplophragmium lutzei Hanzlikova,
Melathrokerion spiralis Gorbachik, and Everticyclammina cf.
virguliana (Koechlin), is considered to be Tithonian in age.
Thus, Middle Jurassic ages have been reported for the
limestone bodies in the lower member, whereas, the Tithonian
limestone body occurred in the upper member. This study
focused on Middle Jurassic limestone in the lower member andreassessed the age because scanning electron microscope (SEM)
images of radiolarians and the mode of occurrence of thelimestone bodies were not included in the previous study. A
Middle Jurassic radiolarian age was newly obtained for anotherlimestone body in the lower member during this study,
confirming the results of Sashida et al. (1989).

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NAOTO ISHIDAFIGURE 3. Mode of occurrence of the Torinosu-type limestone bodies in the Hikawa Formation on the right bank of the Akaizawa River. Boulders of
Torinosu-type limestone, mudstone, acidic tuff, and alternating beds of sandstone and mudstone occur in a mudstone matrix. The radiolarian location isindicated by a star.

EXAMINED TORINOSU-TYPE LIMESTONE BODY
The examined Torinosu-type limestone body crops out on theright bank of the Akaizawa River in Hinohara Village, westernTokyo Metropolis (Fig. 2A). A 160 m thick succession of the
middle part of the lower member of the Hikawa Formation is
exposed in the studied route along the river, with a WNW−ESE
strike and a 68°–83° northward dip (Fig. 2B). This succession ismainly dominated by coarse-grained sandstone, with a 35 m
thick muddy intercalation in the middle part (Fig. 2C). A ~3.2 m
thick gravelly mudstone bed containing clasts of the Torinosutype limestone is found in the lowermost part of thisintercalation.
The gravelly mudstone bed has a matrix-supported frameworkand is overlain by a contorted bed. The examined limestone bodyoccurs in the gravelly mudstone bed with cobble- to bouldersized clasts of felsic tuff, alternating beds of mudstone andsandstone, and mudstone (Fig. 3). The apparent major axis of thelimestone boulder is ~1.5 m in length. This limestone is grayishblack and no internal structure was visible during fieldobservation.
A radiolarian assemblage equivalent to that in the H. maxwelli
Zone has been recovered from the horizon of 26 m below thegravelly mudstone bed (HKW-7 in Ishida, 2004), whereas thehorizon 25 m above the bed (HKW-8 in Ishida, 2004) yieldedradiolarians equivalent to those in the L. primitivus Zone (Fig. 2
B). The gravelly mudstone bed horizon is biostratigraphically inthe transition between the H. maxwelli Zone and L. primitivus
Zone, which is equivalent to the middle to upper Upper Jurassic(Kimmeridgian to lower Tithonian).

Petrographic examination under a polarizing microscope
revealed that the examined body is an arenaceous limestone (Fig.
4A) composed of poorly-sorted fine to very fine sand-sized
quartz, organic matter, indeterminate carbonate grains, andopaque minerals in a clayey matrix with calcite cement (Fig. 4
B). A small amount of altered mica and altered plagioclase
grains are also present. Radiolarian tests are contained rarely(Fig. 4B). Other fossils such as those of cnidarians, bivalves, andforaminifers, were not recognized in this limestone.
Although the typical fossils of Torinosu-type limestone are notpresent in this radiolarian-bearing limestone, fossil corals wererecovered from another limestone body in the same gravelly
mudstone bed, exposed 450 m southeast of the radiolarianbearing limestone (Fig. 5A). This limestone body, with anapparent major axis is ~5 m in length, is an arenaceous limestone
having a very similar lithofacies to the radiolarian-bearing
limestone. Bioclastic layers are sometimes observed in thislimestone (Fig. 5B).
RADIOLARIANS
A rock sample, approximately 800 g in weight, was collectedfrom the limestone (Fig. 3). The sample was crushed into pieces
1–2 cm in diameter and soaked in a dilute hydrochloric acid(10%) for several hours. After soaking, the pieces were washedthrough a 63 micron mesh sieve. To remove calcite andextraneous matters from radiolarians, sieved residue was rinsed
by a concentrated hydrochloric acid for several minutes andboiled by a hydrogen peroxide solution. Radiolarian tests were
picked from the dried residue under an optical stereomicroscopeand photographed under a SEM.

MIDDLE JURASSIC TORINOSU-TYPE LIMESTONEFIGURE 4. Thin-section photomicrographs of the studied Torinosutype limestone (plane polarized light). A, Overview of the limestone. A
white frame indicates the area of photo B. B, Close-up view of thecentral part of photo A. Grains of fine to very fine sand-sized quartz(Qtz), organic matter (Ogm), and opaque minerals (Opq) can be seen.
A radiolarian test (R) is present.

Radiolarian fossils were rare in this sample. Although all of
the radiolarians were recrystallized, the surface ornamentation ofsome tests was moderately to well preserved. From 259
radiolarian specimens examined under the SEM, 18 genera and13 species were identified (Fig. 6). The assemblage was mainlycomposed of nassellarians such as Kilinora tecta (Matsuoka),
Striatojaponocapsa conexa (Matsuoka), Sj. plicarum (Yao)sensu Hatakeda et al. (2007), Japonocapsa fusiformis (Yao),
Stichocapsa japonica Yao, Stc. naradaniensis Matsuoka,
Williriedellum
cf.
dierschei
Suzukiand
Gawlick,
Praewilliriedellum spinosum Kozur, Zhamoidellum ovum
Dumitrica, Protunuma cf. ochiensis Matsuoka, Eucyrtidiellum
nodosum Wakita, Hsuum cf. maxwelli Pessagno, H. cf.
brevicostatum( Ozvoldova ) ,Tethysetta
dhimenaensis

107

FIGURE 5. Fossil corals (A) and indeterminate bioclasts (B) foundfrom a limestone body in the gravelly mudstone.

(Baumgartner), and Dictyomitrella (?) kamoensis Mizutani and
Kido.
The assemblage contained several age-diagnostic species. The
stratigraphic range of Sj. conexa extends from the base of the Sj.
conexa Zone to the top of the Kilinora spiralis Zone (Matsuoka,
1995). The first appearance of K. tecta is located in the upper
part of the Sj. conexa Zone (Matsuoka, 1983; Aita, 1987;
Nishizono, 1996). Although the genus Kilinora is abundant in
the lower part of the K. spiralis Zone (Matsuoka, 1983; Aita,
1987; Nishizono, 1996), the assemblage did not contain speciesof the genus Kilinora with the exception of K. tecta. The
occurrence of J. fusiformis in the Sj. plicarum and Sj. conexa
zones is generally common (e.g., Matsuoka, 1983; Yao, 1997),
even though it has not been reported from the K. spiralis Zone.
The specific co-occurrence in the assemblage is correlative withthat in the upper part of the Sj. conexa Zone, which Matsuoka(1995) considered late Middle Jurassic (Bathonian to middle
Callovian) in age.

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NAOTO ISHIDAFIGURE 6. Scanning electron micrographs of radiolarians from the Torinosu-type limestone body in the Hikawa Formation. 1, Kilinora tecta(Matsuoka); 2, Striatojaponocapsa conexa (Matsuoka); 3, Striatojaponocapsa plicarum (Yao) sensu Hatakeda et al. (2007); 4, Japonocapsa
fusiformis (Yao); 5, Japonocapsa aff. fusiformis (Yao); 6, Williriedellum cf. dierschei Suzuiki and Gawlick; 7, Praewilliriedellum spinosum
Kozur; 8, Zhamoidellum ovum Dumitrica; 9, Zhamoidellum (?) sp.; 10, Stichocapsa japonica Yao; 11, Stichocapsa naradaniensis Matsuoka;
12, Stichocapsa sp. E sensu Baumgartner et al. (1995); 13, Stichocapsa (?) sp.; 14, Protunuma cf. ochiensis Matsuoka; 15, Protunuma sp. E sensu
Yao (1997); 16, Archaeodictyomitra sp. 1; 17, Archaeodictyomitra sp. 2; 18, Dictyomitrella (?) kamoensis Mizutani and Kido; 19, Tethysetta
dhimenaensis (Baumgartner); 20, Parvicingula sp.; 21, Stichomitra annibille Kocher sensu Suzuki and Gawlick (2003); 22, Spongocapsula sp.;23, Spongocapsula cf. krahsteinensis Suzuki and Gawlick; 24, Quarticella hunzikeri O’Dogherty, Gorican and Dumitrica; 25, Eucyrtidiellum
nodosum Wakita; 26, Eucyrtidiellum sp.; 27, Hsuum cf. brevicostatum (Ozvoldova); 28, Hsuum cf. maxwelli Pessagno; 29, Hsuum sp.; 30,
Orbiculiforma sp.

DISCUSSION
Torinosu-type limestone as exotic bodies
The gravelly mudstone characterized by a matrix-supported
framework with the contorted bed can be compared with adebrite. The Torinosu-type limestone and various kinds of clasts
in the gravelly mudstone were obviously transported from theirinitial site of deposition.
Cnidarian fossils have been recovered from limestone bodies
in the Hikawa Formation (e.g., Fujimoto, 1939). In addition,
fossil corals and other bioclasts were discovered from alimestone body in the gravelly mudstone (Fig. 5). The limestonebodies in the Hikawa Formation, notably the limestone clasts in
the gravelly mudstone, seem to have initially been deposited in ashallow-marine environment. In contrast, the facies associationof the Hikawa Formation, dominated by turbiditic siliciclastics
with gravelly mudstone beds, represents a deep-marine
depositional environment (e.g., Walker, 1992).
The stratigraphic horizon of the gravelly mudstone bed isapproximately correlative with the boundary between the
Kimmeridgian and Tithonian (Fig. 2C), whereas the examinedradiolarian-bearing Torinosu-type limestone body is of late
Middle Jurassic age. An age difference between the limestone
body and the surrounding siliciclastic sediments is present.
Considering the age difference, the mode of occurrence of theMIDDLE JURASSIC TORINOSU-TYPE LIMESTONE109

TABLE 1. Microfossil age-ascertained Torinosu-type limestone bodies in and around the accretionary complexes in the Southern Chichibu and Northern
Shimanto belts. Location of each body is shown in Fig. 1. The ages of siliciclastics of the Hikawa Formation were revised according to Ishida (2004).

limestone body, and the differing sedimentary environment, it isevident that the examined limestone constitutes an exotic block.
Therefore, the Middle Jurassic limestone bodies examined by
Sashida et al. (1989) seems to be also exotic. On the other hand,as the lower part of the upper member has been correlated withthe lower Tithonian (Ishida, 2004), the Tithonian body
(Kobayashi and Vuks, 2006) was probably transported to thedeeper basin immediately after the deposition.
A similar occurrence of an exotic Torinosu-type limestone
body was reported from the Upper Jurassic Ebirase Formation(Oxfordian to Tithonian) in the Southern Chichibu Belt, western
Kyushu (Ishida, 2006), approximately 900 km west of the Kanto
Mountains. In this case, a radiolarian-dated Middle Jurassic
Torinosu-type limestone boulder is contained in the lower

Tithonian (Loopus primitivus Zone) turbiditic siliciclastics. In
addition, Matsuoka (1992) suggested a possible exotic origin of
the limestone bodies in the Upper Jurassic Naradani Formation(Oxfordian to Tithonian) in the Southern Chichibu Belt, Sakawa,
Shikoku, approximately 640 km west of the Kanto Mountains.
Because the Hikawa, Ebirase, and Naradani formations are
considered to be parts of the Upper Jurassic trench-slope basin
deposits that were contemporaneously formed on theaccretionary complexes in the Southern Chichibu Belt (Ishida,2009), the exotic limestone bodies were probably transported
from shallow-marine sources into the trench-slope basins.

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NAOTO ISHIDA

Implications for Middle to Late Jurassic tectono-sedimentaryevolutioneroded and their only remnants are exotic clasts in younger
strata, such as the limestone boulder in the Hikawa Formation.

The Yatsuji Formation of the Torinosu Group in Sakawa,
Shikoku, contains characteristic Torinosu-type limestone. The
age of the Torinosu Group ranges from Late Jurassic (Tithonian)
to the Early Cretaceous (Matsuoka and Yao, 1985; Aita andOkada, 1986). The limestone bodies and adjacent sediments inthis formation are considered contemporaneous (Aita and Okada,
1986; Siraishi et al., 2005). Furthermore, transitional lithofacies
between the limestone and surrounding siliciclastics have beenrecognized (Kano, 1988; Kano and Jiju, 1995).
In contrast, the examined limestone in the Hikawa Formation
is an exotic body that was transported to the deep-marine
environment. Furthermore, the radiolarian-dated limestone bodyin the lower member of the Hikawa Formation is older than thelimestone bodies in the Yatsuji Formation. The ages of Torinosutype limestone bodies and the surrounding siliciclastics in theSouthern Chichibu and Northern Shimanto belts have been
determined using microfossils over the last two decades (Aitaand Okada, 1986; Sashida et al., 1989; Ishida, 1994; Sashida andUematsu, 1996; Uematsu and Sashida, 1996; Ishida, 2003, 2006;
Kobayashi and Vuks, 2006) and are summarized in Table 1: eightof the limestone bodies formed around the late Middle Jurassic.
Considering that these Middle Jurassic bodies are scatteredacross the Kanto Mountains, eastern Shikoku, and western
Kyushu, Middle Jurassic shallow-marine strata containing
carbonate bodies must have been deposited in widespread areasof the Southern Chichibu Belt.
The original depositional setting of the shallw-marine strata
has been inferred from the stratigraphy and sedimentary featuresof the Torinosu Group (Ishida, 2006, 2009). Matsuoka (1992)
has presented a schematic model of the deposition of theTorinosu Group on the accretionary complexes in the Southern
Chichibu Belt in a shallow-marine environment. During the
Middle Jurassic, the accretionary complexes grew upward
rapidly (Matsuoka, 1992). Topographic peaks of the accretionary
complexes, i.e., trench-slope breaks, reached close to or above
sea level, and strata containing carbonate bodies appear to haveformed under these shallow-marine conditions (Ishida, 2006, 2009).
During the Late Jurassic, the Middle Jurassic sedimentary
bodies on the accretionary complexes were probably incised bysubmarine canyons and eroded subaerially. Fragmented shallowmarine rock bodies were transported into deeper depositional
environments, such as trench-slope basins, by gravity flows andsubmarine slides. The widespread distribution of the Middle
Jurassic Torinosu-type limestone bodies and the exotic bodies inthe Hikawa and Ebirase formations suggest that the erosion andreworking of the shallow-marine bodies occurred over a large
area of the Southern Chichibu Belt.
No Middle Jurassic formation bearing in situ Torinosu-typelimestone bodies has been found (Table 1). It would appear that
the Middle Jurassic shallow-marine strata have been completely

ACKNOWLEDGMENTS
I gratefully acknowledge Prof. Atsushi Matsuoka of Niigata
University for his helpful discussion and useful comments on
this subject. I am indebted to Professor Emeritus Kenji Konishiof Kanazawa University, Mr. Shin-ichi Sano, and Dr. Hiroto
Ichishima of the Fukui Prefectural Dinosaur Museum for theircareful reviews and advice that improved this manuscript. This
study was partly funded by Grants-in-Aid from the Fukada
Geological Institute and by Sasakawa Scientific Research Grant
from the Japan Science Society.
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Akaizawa …………………… 赤井沢
Ebirase Formation …………… 箙瀬層
Gozenyama Formation …… 御前山層
Hikawa Formation…………… 氷川層
Hinodani Formation ……… 日野谷層
Hinohara Village …………… 檜原村

Japan 95: 463−478. ** : in Japanese with English abstract**: in Japanese＜ 地名・地層名 ＞
Imaura Group …………… 今浦層群
Kanoto Formation …………… 神戸層
Kosode Formation…………… 小袖層
Kurasawa Fault …………… 倉沢断層
Mitsugo Formation ……… 三都合層
Okutamako ……………… 奥多摩湖

Oonari Formation …………… 大成層
Sakawa ………………………… 佐川
Tochidani Formation ………… 栩谷層
Torinosu Group …………… 鳥巣層群
Unazawa Formation ………… 海沢層
Yatsuji Formation …………… 谷地層