鹿児島大学リポジトリ

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TRACE FOSSILS FROM THE EOCENE KAYO FORMATION

IN OKINAWA-SHIMA, RYUKYU ISLANDS, JAPAN

著者

FUKUDA Yasuhide, HAYASAKA Shozo

journal or

publication title

鹿児島大学理学部紀要. 地学・生物学

volume

11 page range

13-25

別言語のタイトル

琉球列島沖縄島の嘉陽層の生痕化石

URL

http://hdl.handle.net/10232/5896

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TRACE FOSSILS FROM THE EOCENE KAYO FORMATION

IN OKINAWA-SHIMA, RYUKYU ISLANDS, JAPAN

著者

FUKUDA Yasuhide, HAYASAKA Shozo

journal or

publication title

鹿児島大学理学部紀要. 地学・生物学

volume

11 page range

13-25

別言語のタイトル

琉球列島沖縄島の嘉陽層の生痕化石

URL

http://hdl.handle.net/10232/00009959

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Rep. Fac. SciりKagoshima Univ. (Earth Sci. & Biol.),

No. II, p. 13-25, 3 tables, 7 figs., 2 pis., 1978

TRACE FOSSILS FROM THE EOCENE KAYO

FORMATION IN OKINAWA-SHIMA,

RYUKYU ISLANDS, JAPAN

By

Yasuhide Fukuda* and Shozo Hayasaka*

(Received Sept. 30, 1978)

Introduction and Acknowled皇ements

During the past decade, trace fossils have come to be known to occur from rather

●

poorly fossiliferous basement rocks in South Kyushu and the Ryukyu Islands. Un-fortunately, however, only a few paleontological studies on them have been published

●

to date (Konishi, 1963; Hayasaka et al., 1975).

As a part of the writers'serial study, the trace fossils from the Kayo Formation are described in the present article, with some remarks on the geologic setting and the

●

mode of occurrence of them.

Here the writers express their hearty thanks to Pr0-1essor Hakuyu Okada of the Shizuoka University for his advices on classi丘cation of sandstone, and to Drs. Akira Iwamatsu and Hiroyuki Otsuka both of the Kagoshima University for their suggestions on the geology of this area.

ノヽ

Thanks are also due to Mr. Akihiko Kaihori of the Oyo

Chishitsu Coリfor his help in the丘eld.

● Fig. 1. Indexmap.

Geolo皇ic Settin皇of the Kayo Formation

The Kayo Formation, originally named by Flint et al. (1959) as the Permian for一

maion conformably overlying the Nago Formation, is considered at present to be Eocene m age (Konishi et al., 1973) based on the common occurrence of Nummuhtes sp.

there from,早nd is regarded to represent the Shimajiri Zone (Southeasternmost zone of

the Shimanto Terrain). The distribution of the Kayo Formation has been known m the east-central part (type area) and the east coast area of the northern part of Okinawa-shima (Hashimoto et al., 1976; Osozawa et al., 1977).

Through the study on the Kayo Formation (Fukuda et at., 1978) developed in this type area, the followir唱several points have been made clear. (1) The Kayo Forma-tion is judged to contact with the underlying Nago FormaForma-tion by an overthrust dipping

●

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14 Y. Fukuda and S. Hayasaka

towards NNW. (2) The Kayo formation, of which total thickness attains to 850 m, is

composed of the alternation of quartz-rich, fine- to medium-grained sandstone and shale and subordinate intraformational conglomerates. (3) On the lower surface of sandstone beds are observed small-scale且ute casts and various kinds of trace fossils, of which two species have been described by Konishi (1963). (4) In the Kayo Formation developed in the present area,丘ve successive units were discriminated (Fig. 3, Table 1) based on the litho-facies type such as the sandstone with the intraformational conglomerates and three types of sandstone-shale alternation - predominantly sandy, uniform and regular, or predominantly shaly. (5) Through the study on the composition of sandstone forming more than 10 cm thick bed in the Kayo Formation, thrity-six among the

●

fourty一点ve examined samples were identi丘ed after Okada (1971) as the feldspathic arenite, two quartz arenite and seven feldsapathic wacke. In average, the volume

ratio of quartz is 63.6%, feldspar 26.3% and rock fragment 10.1%, respectively.

Feldspars are represented mainly by orthoclase with subordinate microeline. Rock fragments are represented by a large amount of argillaceous sedimentary rock fragments with a small amount of volcanics. Biotite, sericite and calcite crystals are also recog-nized to occur. Average grain size in each slide of thin section ranges from 0.1 to 0.3 mm,

and in general, grains are well-rounded and welLsorted.

In the present article, trace fossils from the Kayo Formation are described and discussed.

Fig. 2. Geologic map of the east-central part of Okmawa-shima, the type area of the Kayo Formation. (Numerals indicate the localites of trace fossils)

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15 hp叫qi rao03-1)SP9CL9PdS S 9 0 B I j n S J 9 M O T J T 9 q ^ . U O s T I S S O 叫 Q O B j q . U I T A ¥ . A I O X B I . ' l O O d s B T T 3 J 9 T I 8 S I I I S D J ' B M d n S u T U U T U ^ . f s s 9 U 3 T D T U q . U T U I O Q C l t o o l o * u ! β : j / e X p x e j f p a u r e j ｣ -9 s i 望 o 0 1 -a i i 唱 : ( s p i t f t i n o Q Q -Q Z ) s p o q o u o ^ . s p u ' B S

Trace Fossils from the Eocene Kayo Formation

' ( 8 Z . 6 I f ' l v P i q s i u o ^ r ) s q ^ j o u i o t S u o o 1 0 X T J 3 . T 2 日 9 ¥ n . m a n p u n o 叫 U 9 ^ I O 9 X B S T T S S O 叫 9 q . i p u i r a n j ^ ; -( p a p u n o j ) Q i i z q . x e n b ･ o q q -j o p i r e ( p 9 p u n o i q n s ) Q i i o ^ s a u i i j ' ( j r e x n S i r e q n s ) : j . J 9 i p ' ( p a p u n o i q n s ) o ^ B q s s n o 9 o i ￨ i s ^ o ' B T q ' ( x e m 2 w e ) a ^ e i i s ' ( p a p u n o i ) o u o q . s p u ' B S j o S 9 ] ; q q 8 d o q q . o p n p u i ､ S u x p ' B j S s q . u a s 8 j d 9 i a i n ^ o n j ^ s i b u i o ^ u i q o i q j w 叫 o ' s a ^ B j a u i o i S u o o r e u o r v e m i o j e j ^ u i ' I l l C Q i n o q ' B S T -B I O ^ . S G I B I Q U I O t S u O o I O S S 9 U 3 T O T U T ' ( p 9 q t T O B a I O s s a i n p i t n . u i u i o O O I -1 0 9 ) u o i : y e u r a r e T T 9 T T e V C L T R X A I O U O q -S p U -B S p 9 U I ' B j S -9 S J 宮 0 0 1 - r a n x p a r a o ^ u t u i 亀 B S O M I T E d o p i r e ( u i o Q S 9 o q . O S I H i o j j s a S i r e j s s Q i n p i T R . ) q ^ b j q u i ･ o t B u o o 叫 O U O i q . ' B T e j a q . 1 1 1 1 0 1 a q u i n u u x s a s ^ a j o u x A i r e n p ' e i S ( r a o Q 0 3 -^ 0 0 1 t n o i i

soSirej p9q uoBa 10 ssouiroiu^.) uoiq. 'eui己bt pTrexed juxja papiAcud aiioispires

p o u r e j S -8 S j 召 0 0 3 . -r a n i p a u i : ( j a p i o S u i p u a o s a p i n ) s m o i p j s ' B s o S u ^ q o s o t o b 叫 O T # コ S T T S S O 叫 G O B j q . p t r e s 月 x e u i 8 T d d u : ' s q -S -e o p ^ o t ､ S ^ s B O O ^ t i g a T B O S -T T B i n Q ● f a o i t n . x n o n S I a u o q . s p u ' e s p Q i i r e i S -u i n i p Q u i O q . -9 U 唱 0 } u o r p e u i u r e i ; i Q -f l v x e d T O M f a o ! 1 ! ! m o O S I -O O l ) s u o q . s p u ' e s p o u i ' B j S I a S 畠 o o o S -u i n i p a 己 T H O J I S 9 T O 虐 o q q . i x i n q S i t b 月｡話 j r i x t e i l a q q / e j S i w o q s i p i q M 叫 O q O B Q ､(ssQinpiqiui己OS-103)sapXoAxe^uouiiyosjbiqaqs叫OS^SISUOO︰^xedjaddnoqx s n s s o i Q ^ x x n u i i n n u S u i x e a q s p a q s y e x o u a o i B u o o a p i r e j S u t q q . q ^ j A ¥ p u -e ● s o j n i o m i s d r a m s 8 T B O S -T r e r a s t j : j . i a s . A i o i ' B 肖 a ^ B u i r a o p o j d u o i q / e u i u r e t ¥ 9 ¥ f e x e d m j M f a o r a } r a o O s r o O l ) s p a q 8 u o : } . s p i r e s p a t i i u i S -o s x e o o 0 3 . ･ u i m p a u i : ^ . j a j 9 a u > i o q x ･ S T I S S O 叫 Q ^ i p i n r a n u q q . T A ¥ . p i r e s q . u 9 i n 穿 j j G j B q s j B p S i r e j o u o p 召 t u q T O T O 畠 d q ^ i A v f a o i q i x n o O O I -O S ) S P 9 C L s u o ^ s p u 寧 p a u i ' e . i S 9 S J 召 o A n ' B u o T S ' e o o o ︰faonn.uio c-g)spaq8re月S u o x ^ 0 9 J i p } t i 9 x i n o ^ v v s Q m S u i M o q s s p a q o u o ^ s p u -B S 叫 0 2 2 月 j n s j a d d n a -. u o s i t j -b u i Q ¥ d d i i ^ u a j j n o q . q S i ' B j q . s l s p a q Q u o ^ s p u B S 叫 o s o j o s a q ^ . u o u o i r p a n p ● H ｣ T S u m o q s s ^ s ' b o ^ n y . 8 q . n u x u i 召 n i r e j o i d d i i 3 . 1 1 0 x l l l O P U B u o p / e u n i r e j 1 ; t ^ I T f■ ● ･CJa-mpapiAOjd!p9urejS-raniparaoq. -ou唱︰(spitftrao09-08)SP9CLouoispires ( ^ o i q q . u i o O I -S ) s p o q a r e 月 S s p a q Q ^ q s u x q ^ T A v p i r e s p a q a u o ^ s p i r e s j o Q O B p n s j a M o j a q ^ . u o p u n o j 9 X B S T I S S O I 9 0 だ ^ r u o i q . o a j i p ^ . u a j i r i o a s a Q V & S u i M o q s s p 8 q Q u o ^ s p u -B S 叫 O Q O B J j n S x o d d n 9 t n . u o s ^ j b u i Q j d d 叫 j ^ . u o j j n o ^ q S v e i ^ s q q . m p i r e ､召 r a r e j o j d d i j y u o i m o p i r e s u O I ^ . 召 i i i r e j ¥ o ¥ x e i a v q i / a . p o p i A O j d ! p a u x だ 2 -9 U q ︰ f a o i q i u i o O l -8 ) s p o q Q u o ^ s p u ^ c S Q I O B J -O t f t r i u o i q . n q u q . s i Q s ^ . x u n Q A i s s Q O o n s s a t ^

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Table 2. Trace fossils from the Kayo formation. (Numerals correspond to those in the figs. 2 and 3) (◎○ : Ill-preserved and undistmguishable specimens.)

ー 2 3 4 5 6 7 ■8 9 ●1 0 l l 1 2 1 3 1年 1 5 1 6 ー7 ー8 1 9 2 0 2 1● 2 2 2 3 2 4 2 5

SPIRORHAPHE SPi

SPIRORHAPHE SP一(A)

SPIRORHAPHE SP一(B)

◎

○

○ SpiRODESMOS SP.

Spirodesmos sp.CA)

SPIRODESMOS SP一

(B)

○ ㊨

㊨

○

○ ○○

○ Helm川TH0IDA SP一

(C)

Helm川THOIDA SP.(A)

HELMINTHOIDA SP. (B)

≡

三

%

@

○ ○○

○○○

○ ○○○

○

○ ○○○

○○

Helminthopsis sp,

き

○ ○

○

○ C0SMORHAPHE SP.I

*

○○ o ○

Belorhaphe sp.

α

○

○ Paleomeandron

sp. r3

○ Paleodictyon sp.

鶴

○

○ Feeding burrow

謬r

○ ○ ○

Miscellaneous

○

Distribution of Trace Fossils (Table 2)

The distribution of trace fossils in each locality is shown in the table 2, in which

● ●

all the丘gures, except for the feeding burrow, were sketched from the lower surface of sandstone beds.

Description of Trace Fossils Ichnogenus Spirorhaphe Fuchs, 1895

Spirovhaphe sp. a PI. 1,丘g. 12; table 2.

A set of parallel strings dextrally coiled; coil nearly circular in outline ; the largest diameter of coil measures about 14 cm and the shortest one about 9 cm. Only a single specimen is in the collection.

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Trace Fossils from the Eocene Kayo Formation 17

Sptrorhafthe sp. b

A set of parallel strings sinistrally coiled; coil nearly circular in outline; strings 0.8-1.8 mm thick; diameter of spiral ranges from 1.1 (shortest) × 1.5 cm (longest) to 12× 17 cm. In general, the thicker the string, the bigger the spiral.

Remarks : - This species closely resembles Spirorhaphe sp. illustrated by HÅNTZSCHEL (1975, fig. 65, la, lb). Spirorhaphe concentrica Katto described by Katto (1964) from

● ●

the Eocene Naharigawa Formation in Shikoku differs from the present species in having smaller diameter of spiral and thicker string. Five specimens are in the collection.

Ichnogenus Spirodesmos Andree, 1920 Spirodesmos sp. a

Strir唱sinistrally coiled from the center outwards; coils rather regular in shape; stnr唱0.8-1.5 mm thick; diameter of sprial rather variable, ranges from 1.6×2.4 cm to 6.6×8.9 cm.

Remarks: - This is closely similar to Spirodesmos sp. illustrated by HÅNTZSCHEL

1975,五g. 64, 6b) in having regularly coiled outline. Five specimens are in the collec-tion.

Spirodesmos sp. b PL 1,五g. ll; table 2.

St血唱dextrally coiled from the center outwards; string 0.5-0.9 mm thick; diameter

of spnal ranges from 2.2×2.4 cm to 2.8×3.4 cm. Four specimens are in the collection.

Ichnogenus Helminthoida SchafhÅuTL, 1851 Helrninthoida sp. a

PI. 1,五g. 13; table 2.

String 1.75｢2.80 mm thick, closely meandering with interspace of l12 mm; mean-●

dering string nearly straight and parallel; the width of meanders 6-ll cm.

●

Remarks : - This type closely resembles Helminthoida sp. illustrated by HANTZSCHEL

1975,五g. 44, 1c) in general appearance. Six specimens are in the collection.

Helrnmthoida sp. b PI. 2,丘gs. 1 and 2.; table 2.

String 1.98-2.84 mm thick, closely meandering with interspace of 4-6 mm;

● ●

meandering string concentric or U-shaped and parallel; width of meandering lト12 cm. Remarks: -Two specimens are in the collection. One of them has a close alliance to Tosahelminthes curvata Katto (1960) described from the Eocene Naharigawa Formation in Shikoku. Another specimen is somewhat similar to the Recent deep-sea trails described by Bourne et al., (1965).

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･18 Y. Fukuda and S. Hayasaka

Helminthoida sp. c PL 1,五g. 5.; table 2.

String 0.8-1.2 mm thick; not so closely meandering; interspace about 1 cm; width

●

of meanders 1-3 cm.

Remarks: - This is the most common type of trace fossil in the Kayo Formation.

Ichnogenus Helminthopsis Heer emend. Sacco, 1888 Helminthoftsts sp.

PI. 1,丘gs. 9 and 10; table 2. ● ●

String 0.7｢2.5 mm in thickness; simply curving in S-shape; size of specimen rather variable. ･

Remarks: - Relatively large specimens with the string of 2.0-3.0 mm resemble Helrninwopsis sp. illustrated by HAntzschel (1975, fig. 44, 2b). The specimens of this

species are often found in a crowded occurrence.

Ichnogenus Cosmorhaphe Fuchs, 1895 Cosmorhaphe sp.

PL 1,丘gs. 1 and2; table 2.

Smaller type: string 0.65-1.2 mm in thickness; wave length of S-shaped crave of

●

the primary level about 5 mm.

Larger type: string 2.5-3.5 mm in thickness; wave leng比of S-shaped curve of the

primary level 1.5-2.5 cm; that of the secondary level 3-6 cm; depressed S-shape in

●

outline.

Remarks: - The specimens of which string is rather thin resemble Cosmorhaphe sinuosa (Azpeitia) described and illustrated by Ksiazkiewicz (1970, fig. 2a), while the specimens with rather thick string resemble Cosmorhaphe helmintopsida (Sacco) also illustrated by Ksiazkiewicz (1970,丘g. 2c.

Ichnogenus Belorhaphe Fuchs, 1895 Belorhaphe sp.

PI. 1,五g. 6; table 2.

String 1.0 to 1.5 mm in thickness; zigzag-shaped with node-like projection at the

● ●

obtuse angle formed by regular alternating of straight lines of 3 and 4 mm length. Remarks: -Two specimens are in the collection. The present specimens are similar in shape to Belorhaphe sp. illustrated by HÅntzschel (1975, fig. 44, 2b) and to Belorhaphe zickzack (Heer), but the latter two species represent more regular zigzag forming acute angles.

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Arume-Teniyazaki Teniyazak i East coast-Ten iya Teniya- Banzak i ∼ Q.-n一二◎訂

⑦ョ e

Kayo

㊨唱虹24雪爵

血鴨 shale

∈ヨ alt srnation of sandstone & shale E∃ sandstone

Eヨ coarse sandstone wi地shale fragment声匡≡ヨ shale braccia

[蔓笥 conglomerate 匡司 slump bed

-1--v ripple mark

′ ripple marks, deformea by load casting -<o flute cast8

1

- groove oastB

あ Nummulite s

Fig. 3. Relation of the occurrence of trace fossils and the paleo-currents to the vertical change of lithofacies of the Kayo Formation. (◎○ : IlLpreserved and undistinguishable specimens.)

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Trace Fossils from the Eocene Kayo Formation K

Ichnogenus Paleomeandron Peruzzi, 1888 Paleomeandron sp.

PI. 1,丘gs. 7 and 8; table 2.

String 0.75 mm in thickness, irregular S-shaped meanders of straight fractions of about two millimeters length.

Remarks: -Only a single specimen is m the collection. The present specimen closely resembles Paleomeandron elegans Peruzzi illustrated by Ksiazkiewicz (1970, 五g. 3d) in having regular, smalLscale meandering.

Ichnogenus Paleodictyon Meneghini, 1850 Paleodtctyon sp.

PI. 1,丘gs. 3 and4; table 2.

Honey-comb-like network structure, pentagonal or hexagonal meshes.

Remarks:-Five specimens are in the collection, in which three types are discriminated by difference in size.

Type a (pi. 1五g- 3 : Thickness of wall of network 0.9-1.1 mm: size of mesh 6×8 mm, mesh且attened m shape; partly destroyed by stirring at the time of deposition.

●

Konishi (1963) compared this type with Paleodictyon majus Meneghini, but it may be better to compare it with Paleodictyon carpathicum Matyasovszky (Ksiazkiewicz,

1970, pi. 4n-g.

Type b (pi. 1丘g. 4): Wall thickness 0.8 mm, size of mesh 1.1×1.8 mm; slightly flattened, small-scale network. This type is closely similar to Paleodictyon intermedium Ksiazkiewicz (1970, pi. 4g) in having rather thick wall compared with mesh zise.

Type c: Wall thickness 0.5 mm, size of mesh 2.6x3.2 mm. This type resembles Paleodictyon strozzi Meneghini (Ksiazkiewicz, 1970, pi. 4h) in having rather thin wall compared with mesh size.

Mode of Occurrence of Trace Fossils

The relations of the kinds of trace fossils to thickness and internal structure of sandstone beds and to the directions of source of materials and of bottom current at the time of their deposition were examined.

The sandstone beds of the Kayo Formation are classi鮎d into the following four

●

types (after Bouma, 1962).

1) The medium- to coarse-grained sandstone beds starting with the "a" part. These are characterized by the development of very thick Hb" part and lacking in the

●

V part. In the granule conglomerates or the intraformational conglomerates,

how-ever, the "a" part is usually thicker than the "b" part.

2) The fine- to medium-grained sandstone starting with and characterized by the "b" part. As shown in the五g. 4, the sandstone beds of this type range from several centimeters to 150 cm in thickness, and are characterized by the development of

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20 _{Y. Fukuda and S. Hayasaka}

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numerous parallel laminations. On the lower surfaces of sandstone beds,且ute casts and groove casts are often observed.

3) The血e sandstone beds less than 20 cm in thickness. This type of sandstone

bed is identi鮎d as the HToe" of the Bouma's model and usually provided with current

● ●

ripple laminations and ripple marks.

4) The sandstone beds starting with the Hd" part. This type of sandstone bed is rather poor in development in the Kayo Formation. The beds showing the =Td-e' of the Bouma's model are rarely found.

∽ 望§ l lB< ●望●∈ _c ●一め .=_⊂ ⊃ 30 Tb- e 15 To- e 35 Tb- e 12 Tc- e 10 TC ーe 10 TC ーe 12 Tc - e 30 T b ーe 4 5 T bーe 12 T d ーe 10 Te 45 Tb- e 25 T b- e 25 Tb - e 15 T b- e m L*^ m ¥ / _{4 5} _{T b- e} 10 T b - e 10 T b - e ^ HH " " '" '1'* 7 T b ーe ∫ 4 3 T b - e 10 T c - e 2 3 T b - e 10 T b - e 10 0 T b ーe 1 5 T b _ e 10 T c _ e ∫ ∫ 10 T C ⊥ e

t=

′ 30 T b - c ∫ 7 T c - e 1 8 T b - e 7 0 T b - e 10 T b - e

了++.

_{70 Tb一}

_〇

7 T b - e ∫ 1 0 T b - e 8 0 T b 一〇 T b - e 7 T b - e 5 T b - e 2 0 T b - e 1 5 T b - e 8 5 T a - b / ₆₀ _{T b- e} 1 0 T b - e 1 0 T b ーe ′ ′ ′ 2 d T b - e ∫ 1 5 T c - e

/

14 5 T b - ￠ LS-LS-D LS-C LS-B

EG

a

乙＼ノ′-BC◎

( LS: Lebensspuren ]

'して

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The features of sandstone beds bearing trace fossils are summarized as follows:

●

Trace fossils Features of sandstone beds bearing trace fossils

From the above table, it can be reasonably say that the most of trace fossils from the Kayo Formation occur on the lower surface of sandstone beds being less than 30 cm in thickness and representing the Tb-e or the Toe types of Bouma's model. Even in the case of sandstone beds thinner than 30 cm, trace fossils are usually absent when

鮎w marks, such as flute casts, are markedly developed.

Td-e

Tb-e

Td-e

Tc-e

{ LS * Lebensspuren 1

Fig. 5. Mode of occurrence of trace fossils at the locality no. 25. Dual spiral: Spirorhaphe Circle: Spirodesmos

Meandering line : Helminthoida or Helminthopsts Branching dual line: feeding burrows

-LS

LS

-._LS

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The rather small-scale trace fossils having rather thin strir唱are restricted in ●

occurrence to且ne-grained sandstone, while rather large-scale ones having rather thick

●

string (1.5-3.0 mm thick) occur not only on the丘ne一grained but also on the

medium-grained sandstone beds.

To scrutinize the relation of source of supply of turbidite and the direction of bottom current to trace fossils, even the minute indications of paleo-currents were observed on the outcrops (figs. 5, 6 and 7). In the fig. 6, the specimens of Cosmorhaphe sp. seem to have no de丘nite relations to pale0-current direction. However, the specimens of

Helminthopsis sp. and Belorhaphe sp. seem to be made by the movement of animals

oblique to current direction. On the other hand, the五g. 7 shows that the directon of current ripple marks almost corresponds to that of the crowded occurrence of specimens of Helminthopsis sp. It was rather di氏cult, however, to find the clear mutual relation

between the mode of occurrence of trace fossils and the paleo-current directions through the observations at many other outcrops.

%&済廻

蝣h-r <?コ Turbldity currents </ 0 1 ≡竺聖竺至聖亡ヨHIT

Fig. 6. Direction of turbidite supply and trace fossils (Helminthopsis, Cosmorhaphe and Belorhdゆhe).

Turbidity currents

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On the pre-depositional formation of trace fossils, Seilacher (1961) pointed out that the thicker the sandstone bed, the smaller the number of trace fossil species, and he attributed it to the degree of erosive action of turbidity current, and of consolidation of the underlying mudstone bed. This seems to be an important feature also of the Kayo Formation. As judged from the foregoing Bouma's model and the thickness of sandstone bed bearing trace fossils, traces could hardly be preserved in the proximal

●

site due to strong erosive action of turbidity current, while in the distal site with rather weak erosive action they could easily be preserved as fossils. This can also be recognized

● as the change with the lapse of time through the successive facies change of the Kayo Formation (fig. 3). Looking into the four units (KrK4) of the Kayo Formation represent-● represent-● represent-●

1Ⅰ唱the丘ning-upward cycles of sedimentation, the following points are recognized. 1) The unit Kx has no trace fossils.

2) In the units K2 and K3, variability of trace fossils increases from the lower to the upper horizons.

3) In the unit K4, trace fossils attain to the largest number of individuals although 比ey are rather restricted in number of species.

Therefore, it is concluded that the sandstone bed formed under the condition available for the preservation of trace fossils increases in number from the lower to the upper horizons through the Kayo Formation.

Concludin皇 Remarks

Trace fossil assemblage of the Kayo Formation, comprising Spirorhaphe, Spirodesmos, Helminthoida, Helminthopsis, Cosmorhaphe, Paleomeandron, Belorhaphe, Paleodictyon and a few kinds of feeding burrows, are considered to represent the Nereites facies of the Seilacher's assemblage concept (Seilacher, 1967). Mode of

occurrence of trace fossils seems to be in harmony with the丘ning-upwards cycles of turbidite sedimentation of the Kayo Formation. Trace fossils increase in their variability and number of individuals from the lower to the upper horizons. Judging from the thicknesses and the internal structures of the overlying sandstone layer, it is concluded that the mode of preservation of pre-depositional sole trails is controlled primarily by

●

the biological environmental condition and secondly by the sedimentological

condi-● condi-●

tion. Through the comparison with the traces recorded from modern ocean and geological formations, the ichnofossils described in the present article are judged to

●

represent the lower bathyal to abyssal zone (roughly ranging from 3500 to 5500 meters m depth) as the depth range of their formation.

Reference s

Bouma, A.H., 1962, Sedimentology of Some Flysch Deposits. Elseviev Book Co., Amsterdam, 168 p･

Bourne, D.W. and Heezen, B.C., 1965. A wandering Enteropneust from the abyssal Pacific, and

the distribution of Hspiral" tracks on the sea且oor. Science, 150 : 60-63.

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Ryukyu-retto. 5, Geol., 88, U.S. Army Pacific Off. Eng., IntelL Div., with Personnel of U.S. Geol. Surv.

Frey, R.W. Ed., 1975, The Study of Trace Fossils. Springer-Verlag, Berlin, 562p.

●

Fukuda, Y., A. Kaihori, H. Otsuka and S. Hayasaka, 1978, A Note on the Sedimentological

●

Features of the Kayo Formation in Okinawa-shima, Ryukyu Islands. Geological Study on the Ryukyu Islands, 3 39-52. (in Japanese with English Abstract)

Hanzawa, S. 1935, Topography and Geology of the Riukiu Islands. Sci. Rep. Tohoku Imp. Unw., Ser. 2, GeoL, 17, 1-59.

HAntzschel, W., 1975, Trace Fossils and Problematica in Treatise on Invertebrate Paleont0-logy, Pt W. (Sec. Ed.)

Hashimoto, S., K. Yoshida, K. Minoura and H. Nakagawa, 1976, Geology of the Northern Part of Okinawa-Honto. Geol. Study on the Ryukyu Islands, X, 9-20. (in Japanese) Harada, T., T. Shiki, and T. Tokuoka, 1969, Sedimentary Structures in the Sandy Flysch

Developed at the Coast of Kirimezaki, Wakayama Prefecture - Part 1, Internal Sedimentary Structures and the Bouma's Model. Sci. Rep. Fac. Edit. Wakayama Univ., 19, 31-36. (m Japanese),

Hayasaka, S. and H. Aoyama, 1975, Discovery of Trails and Problematica from the Nichman Group (Oligocene) of Miyazaki Prefecture, Kyushu, Japan. Rep. Fac. Sci. Kagoshima Untv., {Earth Sci. and Biol.), 8, 27-32.

Horikoshi, M. 1971, Biological Notes on the Bottom Photography. Preliminary Rep. Hakuhd Maru Cruise KH-69-2. Ocean Res. Inst. Univ. Tokyo.

Ishida, S., 1969, Wano Formation (Eocene) in Amami-Oshima, Ryukyu Island, Japan. Jour. Geol. Soc. Japan, 75, 14ト156.

Kaihori, A., 1977, Geology of the Area East of Nago City, Okinawa Prefecture. Graduation Thesis of Kagoshima Univ. (m Japanese with English Abstract)

Katto, J., 1960, Some Problematica from the So-called Unknown Mesozoic Strata of the Southern Part of Shikoku, Japan. Set. Rep. Tohoku Univ., 2nd Ser. (GeoL), Spec. Vol. No. 4, 323-334.

1964, Some Sedimentary Structure and Problematica from the Shimanto Terrain of Kochi Prefecture, Japan. Res. Rep., Kochi Univ., 13, 6.

Kinoshita, Y., 1976, The Face of the Deep-Sea Bottom As It is. Chishitsu News, 268, 40-48. (m Japanese)

Konishi, K., 1963, Pre-Miocene Basement Complex of Okinawa, and the Tectonic Belts of Ryukyu Islands. Sci. Rep. Kanazawa Univ., 8, 569-602.

, T. Ishibashi and K. Tsuruyama, 1973, Find of Nummulites and Orthoquartzite Pebbles from the Eocene Turbidites in Shimajri Belt, Okinawa. Sci. Rep. Kanazawa Univ., 18(1), 43-53.

Ksiazkiewicz, M., 1970, Observations on the Ichnofauna of the Polish Carpathians. In. T.P. Crimes and J.C. Harper (Ed.), Trace Fossils, Geol. Jour., Spec. Issue, 3, 283-322. Okada, H., 1971, Again on Classification and Nomenclature of Sandstones. Jour. Geol. Soc. Japan,

77 (6), 395-396. (in Japanese)

1977, Preliminary Study of Sandstone of the Shimanto Supergroup in Kyushu, with●

Special Reference to "Petrographic Zone". Sci. Rep. Fac. Sci. Kyushu Univ., Geology, 12 (3), 203-214. (in Japanese with English Abstract)

Osozawa, S., S. Hashimoto, K. Yoshida, K. Minoura and H. Nakagawa, 1977, Geology of the Northern Part of Okinawa Honto, Part 2, Geol. Study on the Ryukyu Islands, 2, 35-40. (in Japanese)

Seilacher, A., 1961, Paleontological Studies on Turbidite Sedimentation and Erosion. Jour. GeoL, 70, 227-234.

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C 0 . . . . 0 3 C O b o b o b o -b o b o b o b o b o b o b o ･ l ● l ･ l ･ l ● l ･ l ･ l ● l ｡ l ･ l f e C L i t X t f e p H f e -f e f e f e P t H c O ^ I O < X > HU Explanation of Plate 1

(All figures are in natural size unless otherwise stated) and 2. Cosmorhdゆhe sp., Loc. no. 21. × lI2

Paleodictyon sp. a. Loc. no. 4. Plaster model (mold). Paleodictyon sp. b. Loc. no. 8.

Helminthoida sp. c. Loc. no. 21. Belorhaphe sp. Xoc.no. 2.

7 and 8. Paleomeandron sp. Loc. no. 21.

9 and 10. Helminthoクsis sp. Loc. no. 25. Plaster model (mold.) ll. Spirodesmos sp. Loc. no. 25. Plaster model (mold).

HU HU

2. Spirorhaphe sp. Loc. no. 21. Plaster model (mold). ×1/2

3

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Explanation of Plate 2 (All figures are in a ha一t size)

Figs. 1 and 2. Helminthoida sp. b. Loc. no. 19.

Fig. 3. Feeding burrow. Loc. no. 25. Plaster model (mold).

Fig. 4. Bilobed trail with a groove on the ridge. Loc. no. 25. Plaster model (mold). Fig. 5. Helminthoタsis sp. Loc. no. 23.

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