Memoir of the Fukui Prefectural Dinosaur Museum 14: 11–18 (2015)

ARTICLE© by the Fukui Prefectural Dinosaur Museum

MIDDLE JURASSIC RADIOLARIANS FROM CALCAREOUS NODULES WITHINSILTY SANDSTONE FLOAT BOULDER DERIVED FROM THE KAIZARAFORMATION OF THE TETORI GROUP IN CENTRAL JAPANKenji KASHIWAGI1 and Satoshi HIRASAWA2
1

Graduate School of Science and Engineering for Research, University of Toyama, 3190 Gofuku, Toyama, Toyama 930-8555, Japan
2
Toyama Science Museum, 1-8-31, Nishinakano-machi, Toyama, Toyama 939-8084, Japan

ABSTRACTThis is the first report on radiolarians present in the Kaizara Formation of the Kuzuryu Subgroup, Tetori Group,
located in the Shimoyama–Kaizara area, in central Japan. Previous works based on ammonoid biostratigraphy date
the Kaizara Formation in the late Bathonian to early Callovian. The radiolarian fossils were extracted from two
calcareous nodules included in silty sandstone that was collected as a ﬂoat boulder on a river bed draining into the
Taniyama River, a tributary of the Kuzuryu River. Although its precise stratigraphic horizon is unknown, the locationof collection and characteristic features, namely the presence of calcareous nodules, make it a probable derivate of
the Kaizara Formation. Several other microfossils and bioclasts were also retrieved from the same radiolarian-bearing
nodules: benthic foraminifers, sponge spicules, prodissoconchs of pelecypods, and echinoderm fragments. According
to the Unitary Associations Zones (UAZ.) of Baumgartner et al. (1995), the presence of Dictyomitrella ? kamoensis,
Striatojaponocapsa conexa, Stichocapsa naradaniensis and Williriedellum carpathicum places the radiolarian age
between the late Bathonian and early Callovian (Middle Jurassic) of UAZ. 7. In addition, the radiolarian zonation
for Japan and the western Paciﬁc proposed by Matsuoka (1995a) suggests the age to fall in the interval ranging fromthe Callovian to Oxfordian (Middle–Late Jurassic) based on the co-occurrence of Stichocapsa naradaniensis andStriatojaponocapsa conexa. According to the UAZ. of Baumgartner et al. (1995), the radiolarian age of the Kaizara
Formation is shown to range from the late Bathonian to early Callovian, based on the consistency between theradiolarian age and the ammonoid age.
Key words : Tetori Group, Kuzuryu Subgroup, Kaizara Formation, Middle Jurassic, radiolaria, calcareous nodule
柏木健司・平澤 聡（2015）手取層群貝皿層に由来するシルト質砂岩転石中の石灰質団塊から産したジュラ
紀中世放散虫化石．福井県立恐竜博物館紀要 14：11‒18．
下山−貝皿地域に分布する手取層群九頭竜亜層群の貝皿層から，放散虫化石の産出を初めて報告する．貝皿層は，アンモナイト化石の生層序に基づき，既にBathonian後期〜Callovian前期の時代を示すことが知られている．放散虫化石は，下山−貝皿地域の九頭竜川支流の谷山川に流れ込む河床から採取したシルト質砂岩の転石中に含まれる石灰質団塊 2 試料から得られた．採取試料は，その正確な層序位置は不明であるものの，その採取地点と石灰質団塊を含む岩相的特徴から，貝皿層に由来すると判断される．また，底生有孔虫，
海綿骨針，二枚貝原殻，および棘皮動物片を含む微化石と生砕片が，同じ含放散虫化石団塊試料から得られた．放散虫化石の示す時代は，Baumgartner et al. (1995)のUnitary Association Zones（UAZ.）に基づくと，Dictyomitrella ? kamoensis，Stichocapsa naradaniensis，Striatojaponocapsa conexa，およびWilliriedellum
carpathicum の共産するUAZ. 7 のBathonian後期〜Callovian前期（ジュラ紀中世）に，Matsuoka (1995a)による日本−西太平洋の放散虫化石帯に従うとStichocapsa naradaniensis とStriatojaponocapsa conexa の共産よりジュラ紀中世Callovian〜ジュラ紀新世Oxfordianを示す．貝皿層の放散虫化石時代は，アンモナイ
ト時代と一致することが期待されることから，Baumgartner et al. (1995)のUAZ.に基づくBathonian後期〜
Callovian前期である．

Received November 4, 2014. Accepted September 17, 2015.
Corresponding author̶Kenji KASHIWAGI
E-mail: kasiwagi*sci.u-toyama.ac.jp
編集注）：「古世」「中世」「新世」は，それぞれ「前期」「中期」「後期」と同義．

(The asterisk should be replaced by @)11

12

KENJI KASHIWAGI AND SATOSHI HIRASAWA

i

dan

ama

iy
Tan

a)
hiro

Itos

Shimoyamab)

137° E＋ 37° N

＋

r
ive

R

Jinzu
RegionKaizara
Ku

zu

ry

uR

ive

r

1 km

Tetori Group
Itoshiro Subgroup
Itsuki, Obuchi, Ashidani, and Yambara formations in descending order
Kuzuryu Subgroup
Pre-Jurassic basement rocks
Yambarazaka Formation
Hida gneiss
Kaizara Formation
Tochimochiyama Formation
Oidani Formation
Shimoyama Formation

fault

HakusanRegion0 10 20km

Figure 1b■

conformity

Akaiwa and Itoshiro subgroups

unconformity
sampling localityof the radiolarian-bearing rockKuzuryu Subgroup

FIGURE 1. Geological map in the Shimoyama–Kaizara area in central Japan, featuring the sampling locality of the ﬂoat boulder used for radiolarian analyses.
Modiﬁed from Maeda (1952).

INTRODUCTION
The Tetori Group in northern central Japan predominantly
comprises non-marine deposits along with some intercalations ofmarine sediments. It also includes high diversiﬁed zoo- and phytoassemblages (e.g., Maeda, 1961b; Sato, 1962, 2008; Sato andWestermann, 1991; Fujita, 2003; Matsukawa et al., 2003a; Yabe etal., 2003; Yamada and Uemura, 2008; Sato et al., 2012; Goto andHanda, 2014; Handa et al., 2014; Sato and Yamada, 2014). The
marine strata have been divided into three intervals dated mainly
by ammonoid fossils: from the Bathonian to Oxfordian, theTithonian to Berriasian, and the Hauterivian to Barremian (Sato etal., 2003, 2008; Sato and Yamada, 2005; Goto, 2007; Matsukawa
et al., 2007; Matsukawa and Fukui, 2009). Although ammonoid
fossils have been used all over the world as an index for the
diagnosis of fossil age through the Paleozoic to Mesozoic strata,
ammonoid ages of the Tetori Group still remains to be conﬁrmed
through the use of other fossil taxa, or better preserved andmore abundant ammonoid fossils. The Mitarai Formation of theTetori Group, in the Shokawa area, for example, have originallybeen dated in the Callovian by the reason of the presence of anammonoid Lilloetia sp. described by Sato and Kanie (1963).
Its age had been widely accepted by many geologists in thefollowing four decades (e.g., Fujita, 2003). In the last over ten
years, however, the Mitarai Formation has been dated in the
Berriasian, on the basis of the abundant, well-preserved collectionof ammonoid on that location (Sato et al., 2003, 2008).
Radiolarians are generally considered as one of the mostuseful fossil indexes for dating, owing to their widespread andabundant occurrence, even on small-size piece rock samples.
From this point of view, the authors have reported radiolarians
from several marine strata of the Tetori Group, and dated them inorder to verify the age previously reported on ammonoid fossils(e.g., Hirasawa and Kashiwagi, 2008; Kashiwagi and Hirasawa,
2010; Kashiwagi et al., 2011; Kashiwagi, 2014). The present
paper serves the purpose of reporting ﬁrst on the Middle Jurassic
radiolarian assemblage from the Kaizara Formation, exposed in
the Shimoyama–Kaizara area, and to discuss its age determination
based on the two radiolarian zonations of the Middle to Late
Jurassic interval.
GEOLOGICAL OUTLINE
The Middle Jurassic to Lower Cretaceous Tetori Group issporadically distributed in the Hakusan and Jinzu regions (Fig. 1).
It has been stratigraphically divided into the Kuzuryu, Itoshiro andAkaiwa subgroups, in ascending order (e.g., Maeda, 1952, 1961b;
Maeda and Takenami, 1957; Fujita, 2003). Recently, Matsukawa
et al. (2014) revised the widely accepted stratigraphy of the Tetori
Group in the Jinzu Region, by defferentiating the Jinzu Group in
the upper horizon from the Tetori Group in the lower one. The
Jinzu Group, which is mainly composed of non-marine deposits,
includes the Ioridanitoge, Inotani, and Shiroiwagawa formations,in ascending order. Furthermore, the Group is assigned to the
Aptian–Albian based on zircon ﬁssion track dating of tuffaceous
sandstones in the Inotani Formation (Matsukawa et al., 2014).
Although Matsukawa et al. (2014) emphasized the discrepancy
between the Tetori and Jinzu Groups' depositional ages, the

Ri
ve
r

MIDDLE JURASSIC RADIOLARIANS FROM THE KAIZARA FORMATION OF THE TETORI GROUP

Ito
sh
iro

sampling locality
Shimoyama
yu
ur
uz
K

Kaizara

Ri
r
ve
1 km

FIGURE 2. Sampling locality of the silty sandstone float boulder in the
Shimoyama–Kaizara area. Based maps are 1:25,000 maps of Shimoyama
and Echizen-asahi of the Geographical Survey Institute of Japan.

lowermost and uppermost horizons of the Jinzu Group have notbeen dated so far. In this paper, we adopt the division in threesubgroups proposed by Maeda (1961b) for the lithostratigraphy of
the Tetori Group in the Jinzu Region.
The Kuzuryu Subgroup is widely distributed in the upper
reaches of the Kuzuryu River on the southern margin of the
Hakusan Region (Fig. 1). Its lithostratigraphy has been the objectof extensive research (e.g., Oishi, 1933; Maeda, 1952, 1961a;
Kawai et al., 1957; Yamada et al., 1989; Fujita, 2002; Matsukawa
et al., 2003b). In this paper, we follow the stratigraphic scheme
described by Maeda (1952, 1961b) and Fujita (2003) for the
Kuzuryu Subgroup, which consists of the Shimoyama, Oidani,
Tochimochiyama, Kaizara, and Yambarazaka formations inascending order, and they conformably pile up in turn. In the
Shimoyama–Kaizara area, where the type locality of the Kaizara
Formation is located, these formations feature NW–SE strikes
and steep N-dipping. The Yambara Formation, the lowermost
formation of the Itoshiro Subgroup, unconformably overlies the
Yambarazaka Formation.
The Kaizara Formation, the object for the present study,
mainly consists of black massive and/or laminated sandy siltstone
with some intercalations of fine- to coarse-grained sandstones.
Spherical to ellipsoidal calcareous nodules can be found at a
few specific horizons in sandy siltstone. The formation features
abundant marine invertebrate fossils: ammonoids, belemnites,
pelecypods and so on (e.g., Yokoyama, 1904; Kobayashi, 1947;
Maeda, 1952, 1961b; Hayami, 1960; Sato, 1962; Sano et al., 2010;
Handa et al., 2014), as well as fewer plant fossils (Yamada andUemura, 2008). According to the ammonoid biostratigraphy, theKaizara Formation is dated as the late Bathonian–early Callovian(Maeda, 1961b; Sato, 1962, 1992; Sato and Westermann, 1991;
Handa et al., 2014).

13

MATERIALS AND METHODS FOR EXTRACTING
RADIOLARIANS
We examined radiolarians from two calcareous nodule samples(KAI and KAN) collected from a single float boulder of a silty
sandstone on a river bed draining into the Taniyama River, atributary of the Kuzuryu River, in the Shimoyama–Kaizara area
(Fig. 2). The Kaizara Formation crops out in and around thesampling locality (Figs. 1, 2). The calcareous nodules are oneof the distinguishable lithological characteristics for the Kaizara
Formation, because they have not been observed in the underlying
Tochimochiyama and overlying Yambarazaka formations, in bothof which lithofacies are dominated by sandstone facies (Maeda,
1952; Maeda, 1977; Yamada et al., 1989). Although the precise
reconstruction of the stratigraphic horizon of the float boulder,
where radiolarian-bearing calcareous nodules occur, is difficult,above-mentioned lithological features and sampling locality
support the argument that the studied samples probably derivefrom the Kaizara Formation.
The ﬂoat of ca. 40 cm in length features silty very ﬁne-grainedsandstone with thin intercalations of ﬁne-grained sandstone beds
and spherical to ellipsoidal calcareous nodules. Two fragments ofelliptical nodules ― approximately 3 cm in minor axis (sample
KAI), and spherical nodule of 〜3 cm in diameter (sample KAN,
Fig. 3a) ― are examined. Standard rock thin sections wereprepared from the studied samples in order to investigate theirmicrofacies.
Both silty sandstone part and calcareous nodules are bioturbatedby abundant small burrows such as Phycosiphon and Planolites.
The burrows display unbranched and simple cylindrical shape (lessthan 1.5 mm wide). They are ﬁlled with a massive muddy matrix
containing sand-sized grains. Some burrows show obscure muddy
lining or back ﬁll structure. The inner part of calcareous nodules
show a matrix-supported texture as well.
The radiolarians and some other microfossils were extracted
from the calcareous nodules basically following to the method
proposed by Dumitrica (1970) and Pessagno and Newport (1972).
The rock samples were treated with a 5 % diluted hydrofluoric
acid solution for ca. 24 hours, and rinsed under running water inorder to remove radiolarians from the rock surface. The residue
was collected through 425 and 63 µm meshes and subsequently
boiled for up to a minute with diluted hydrogen peroxide, andthen dried slowly in an oven (no more than ca. 60 degrees).
Abundant microfossils were found in two samples (KAI and
KAN). Sample KAI contains abundant radiolarians with a few
benthic foraminifers. Sample KAN displays a lesser quantity ofradiolarians compared to sample KAI, as well as various othermicrofossils, including benthic foraminifers, sponge spiculesand prodissoconchs of pelecypods (Fig. 3c, d). Microfossils arepresent only in calcareous nodules, and not in the surrounding
silty sandstone matrices (Fig. 3b). Radiolarian tests and sponge
spicules are partly replaced by calcite and/or pyritized overall. A
few plates of echinoderm are only observed in rock thin section(Fig. 3c).

14

KENJI KASHIWAGI AND SATOSHI HIRASAWA

FIGURE 3. Calcareous nodule sample KAN and photographs of microfossils and bioclasts in sample KAN. a, Polished hand specimen of calcareous nodulewith its surrounding matrix. Scale bar indicates 1 cm. b, Sponge spicule in calcareous nodule. Note that the silty sandstone matrix contains no fossils at all.
c, Echinoderm fragment in calcareous nodule. d, Benthic foraminifer in calcareous nodule. Scale bars in b–d are 100 µm.

RADIOLARIAN AGE ASSIGNMENTS
Radiolarian ages of both samples KAI and KAN should nearlycoincide on the ground that they were collected from the same
float boulder. We can adopt two biostratigraphic schemes for
the Middle–Late Jurassic biostratigraphic markers: the Unitary
Association Zones (UAZ.) of Baumgartner et al. (1995) and the
Middle Jurassic to Early Cretaceous radiolarian zonation forJapan and the western Pacific proposed by Matsuoka (1995a).
Radiolarians from samples KAI and KAN are listed in Table 1,
and are illustrated with other microfossils in Fig. 4.
Among the listed species in Table 1, the UAZ. of thefollowing species are indicated according to Baumgartner et al.
(1995): Dictyomitrella ? kamoensis (UAZ. 3–7); Parvicingula
dhimenaensis s.l. (UAZ. 3–11); Parvicingula ? spinata (UAZ.
3–10); Podobursahelvetica (UAZ. 3–10); Ristola altissima (UAZ.
5–12); Stichocapsa naradaniensis (UAZ. 6–7); Striatojaponocapsa
conexa (UAZ. 4–7); and Williriedellum carpathicum (UAZ. 7–11)
for nassellarians, and Triactoma blakei (UAZ. 4–11); Triactoma
mexicana (UAZ. 5–9); and Tritrabs ewingi (UAZ. 4–22) forspumellarians. Their co-occurrence is restricted to UAZ. 7, whichcorresponds to the late Bathonian–early Callovian following the
UAZ. of Baumgartner et al. (1995) (Fig. 5).
The radiolarian zonation of Matsuoka (1995a) has beencommonly aligned to Jurassic to Early Cretaceous radiolarianassemblages reported from the Japanese Islands and East AsianContinent by many Japanese researchers. Among the listed species,
Stichocapsa naradaniensis and Striatojaponocapsa conexa are
the age indicative species for the biochronology of Matsuoka(1995a). Stichocapsa naradaniensis points out to a Middle–Late
Oxfordian age in the upper Kilinora spiralis zone (Matsuoka,
1986; Matsuoka and Yao, 1986). However, this species has been
also reported to be from the upper half of the Striatojaponocapsa
conexa zone (Ishida, 2011), as well as from the upper half of theStriatojaponocapsa conexa to Kilinora spiralis zones (Nishizono,
1996). Consequently, the age range of Stichocapsa naradaniensis
could be from the upper half of the Striatojaponocapsa conexa
zone to the Kilinora spiralis zone, corresponding to Callovian–
Oxfordian age. Striatojaponocapsa conexa, which is a taxon forage diagnosis from the Striatojaponocapsa conexa zone to theMIDDLE JURASSIC RADIOLARIANS FROM THE KAIZARA FORMATION OF THE TETORI GROUP

15

FIGURE 4. Radiolarians and other microfossils from the calcareous nodules from silty sandstone ﬂoat boulder probably derived from the Kaizara Formationof the Tetori Group. 1, Dictyomitrella ? kamoeisis, KAI; 2, Ristola altissima, KAI; 3, Pseudoeucyrtis sp., KAI; 4, Podobursa helvetica, KAI; 5, Parvicingula
dhimenaensis s.l., KAI; 6, Parvicingula ? spinata, KAN; 7a, b, Striatojaponocapsa conexa, KAI; 8a, b, Zhamoidellum sp., KAN; 9a, b, Williriedellum
carpathicum, KAN; 10, Stichocapsa naradaniensis, KAI; 11, Sethocapsa sp., KAI; 12, Triactoma blakei, KAI; 13, Triactoma mexicana, KAN; 14, Paronaellasp., KAI; 15, Tritrabs exotica, KAI; 16, Sponge spicule, KAN; 17, 18. Benthic foraminifers, KAI, KAN, respectively. Scale bars = 50 µm.

Kilinora spiralis zone, indicates an age interval ranging fromthe middle Bathonian to Oxfordian (Matsuoka, 1995a). The cooccurrence of Stichocapsa naradaniensis and Striatojaponocapsa
conexa shows that the radiolarian age of the Kaizara Formation
is Callovian–Oxfordian based on the radiolarian zonation of
Matsuoka (1995a).

Comparing age of radiolarians determined using the UAZ. of
Baumgartner et al. (1995) and the radiolarian zonation of Matsuoka(1995a), it is evident that the former is almost concordant withthe ammonoid age (late Bathonian–early Callovian) as reported
by Sato (1962) and Sato and Westermann (1991), whereas thelatter points out to a younger age than the one suggested by

16

KENJI KASHIWAGI AND SATOSHI HIRASAWA

TABLE 1. Middle Jurassic radiolarians from the calcareous nodules collected from silty sandstone ﬂoat boulder probably derived from the Kaizara Formationof the Tetori Group.

FIGURE 5. Selected radiolarians species from the Kaizara Formation relevant for the age assignment. The Unitary Association Zones (UAZ.) is based on
Baumgartner et al. (1995).

ammonoid biochronology. The age of the Kaizara Formation has
been assigned to the late Bathonian–early Callovian in the lightof precise ammonoid biochronology by Sato (1962), and further
confirmed by more recent research on ammonoids provided by
Handa et al. (2014). In consequence, the radiolarian age of the
Kaizara Formation falls more probably in the late Bathonian–early Callovian according on Baumgartner s et al. (1995) method.
Additionally, some researchers (Matsuoka, 1995b; Suzuki etal., 2004) have pointed a discrepancy in the age assignmentof Middle–Late Jurassic radiolarian assemblages reported by
Baumgartner et al. (1995) and Matsuoka (1995a). This resultshows the urgent necessity to further study the correlation between
the Middle–Late Jurassic radiolarian zonations of Baumgartner

et al. (1995) and Matsuoka (1995a), as Matsuoka (1995b) has
pointed out.
SUMMARY
This is the first report on radiolarians from the Kaizara
Formation of the Tetori Group. It has been dated as the late
Bathonian–early Callovian based on ammonoid biochronology.
The sampling locality and occurrence of calcareous nodules
suggest that the float boulder, from which radiolarian-bearing
calcareous nodules were collected, probably derive from the
Kaizara Formation. Its radiolarian age is late Bathonian–early
Callovian according to the UAZ. of Baumgartner et al. (1995),

MIDDLE JURASSIC RADIOLARIANS FROM THE KAIZARA FORMATION OF THE TETORI GROUP

and Callovian–Oxfordian based on the radiolarian zonation of
Matsuoka (1995a). Based on the already well-known age of theammonoid, we can infer that the radiolarian age of the Kaizara
Formation is likely to fall in the late Bathonian–early Callovian.
ACKNOWLEDGMENTS
We give our thanks to Dr. Shin-ichi SANO (Fukui Prefectural
Dinosaur Museum) for reading an early version of the manuscript,
for his valuable suggestions, as well as for his support andsupervision of the work performed on the SEM at the Fukui
Prefectural Dinosaur Museum. Special thanks to Dr. Shugo
OHI and Mr. Masaki TAKAYA (Dept. Geol. Mineral., Kyoto
Univ.) for discussing the petrography of the rock samples. We
also thank Prof. Atsushi MATSUOKA (Niigata Univ.) and an
anonymous reviewer for helpful comments and recommendations
for the improvement of the manuscript. The study was ﬁnancially
supported in part by a Grant-in-Aid for Scientiﬁc Research fromthe Japan Society for the Promotion of Science (Kashiwagi, K.,
No. 23540547, 2011–2013).
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: in Japanese with English abstract: in Japanese with English outline of the paper: in Japanese with German and English abstracts: in Japanese: English title translated from the original written in
Japanese