Ryukyu Limestone" of Okinawa-Jima, South Japan : A Title Stratigraphical and Sedimentological Study
Author(s) Takayasu, Katsumi
Memoirs of the Faculty of Science, Kyoto University. Series of Citation geology and mineralogy (1978), 45(1): 133-175
Issue Date 1978-07-31
URL http://hdl.handle.net/2433/186623
Right
Type Departmental Bulletin Paper
Textversion publisher
Kyoto University MEMolRs oF THE FAcuLTy oF SclENcE, KyoTo UNIvERsny, SERIEs oF GEoL. & MINERAL., Vol. XLV, No. 1, pp, 133-175, Pls. 14--16, 1978
"Ryukyu Limestone" of Okinawa-jima, South Japan
A Stratigraphical and Sedimentological Study
By
Katsumi TAKAyAsu
(Text and Plates)
Abstract
The "Ryukyu Limestone", the host of the Quaternary geology of the Ryukyu Islands, is divided fundamenta!ly into the rnain limestones and the accessory limestones. This division is based on the differences in lithological characters, fossil assemblages, distribution and thickness ofbeds, age ofsedimen. tation, etc. The rnain limestones composing the major part of the "Ryukyu Limestone" constitute the Ryukyu Group together with the contemporaneous noncalcareous deposits, and they are the basement of the accessory limestones. The Ryukyu Group is divided stratigraphically into two formations; the Lower and the Upper¥ The Lower Formation is the sediments which accumu!ated in the basins of the tectonic origin or in the valleys of the eroded basement and is represented by various lithofaÅëies. On the other hand, the Upper Formtion is more widely distributed than the Lower Formation, and its stratigraphical sequence of the lithofacies is rather constant everywhere. The Upper Formation is subdivided into the A, B and C Members based on characteristicfossil assemblages, Within these Members, theA Memberis represented by some foraminiferal and molluscan fossils showing deeper water than a coral reef environment. Fur. thermore, the Cptcloe(ypm'-OPerculiua bed of this Member, being fairly continuous, is a good horizon marker for the correlation of the Ryukyu Group not only in Okinawa-iima but also other islands. The biolithite facies, though poor in the Ryukyu Group as a whole, is recognized in the C Member of the Upper Forma- tion and a part of the Lower Formation. In order to analyse the sedimentary environments of the Ryukyu Group, the petrography and the fossil analysis under the optical microscope were made in connection to the field observation. As a result, the sedimentary environments of the Ryukyu Group can be generally inferred to have been shifted from the land prevailing condition disqualified for coral reef formation to the favourable condition for reef building, though the process of reef forming of the latter was interrupted for a short time by the intervcn- tion of deep sea environment as represented by the A Member in the Upper Formation. As for the age of the Ryukyu Group, it is regarded to be Early and early Middle Pleistocene from the paleontological and stratigraphical aspects. The geologic stmcture of the Ryukyu Group is composed of many tilting blocks brought in by faulting after the completion of sedimentation. These tectonic movements of the maximum stage brought about the original configuration of the present islands. Since then, to the fringing areas of these emerged blocks the accessory limestones represented by the Minatogawa Limestone Formation were attached. However, it is also evident that mainly the tectonic movements affected the mode of the Ryukyu Group sedimentation such as !ocal unconformities between the Lower and the Upper Formation and accelerated the change to shallow water of the sedimentary environment. Therefore, the Ryukyu Group is the product of transgression due to tectonism, especially shown in the later stage. Contrasting with- the main limestone deposition, the accessory limestones wcre the deposits formed under the influence of the eustatic sea level changes. 134 Katsumi TAKAyAsu
Lastly, the Quaternary geohistory of the Ryukyu Islands is reviewed from the viewpoint of the "Ryukyn limestone" stratigraphy.
I. Introduction
One of the most peculiar features in the geology of the Ryukyu Islands is the wide distribution of the Quaternary limestone, collectively called the "Ryukyu Limestone". The name "Ryukyu Limestone", originally spelled Riukiu Limestone, was first proposed by YABE and HANzAwA (1930) with regard to distinctions among raised coral reefs. Thereafter, by a series ofworks, especially by the paper of 1935, HANzAwA was highly esteemed for carrying out a detailed description of the geology of the Ryukyu Islands. Owing to HANzAwA's works, many researchers first recognized the significance of the "Ryukyu Limestone" in considering the geology of the Islands. The studies on the "Ryukyu Limestone", however, together with the studies on the other geological formations, were forcibly interrupted for a long time by un- fortunate circumstances in the Ryukyus such as the years of the Second World War and the succeeding occupation. After the War, with the remarkable progress of the geological sciences, several new interpretations and methods were rapidly introduced into the studies of the "Ryukyu Limestone" with in suthcient stratigraphical and sedimentological data. During the time under occupation, the "Ryukyu Limestone" of Okinawa-jima was subdivided into three formations, that is, the Naha formation (the Naha limestone), the Yontan and the Machinato limestones ascendingly, and they were collectively called the Ryukyu Group in the reports on military geology by U.S. Army Forces and associated studies (FuNT et al., 1959; MAcNEiL, 1960). NAKAGAwA (1967; 1969a, b), who surveyed in Tokuno-shima and its neighbouring islands, Kagoshima Prefecture, applied the concept of sea level changes obtained from the studies at the Northeast Japan coast to the study of the Ryukyu Islands, and he regarded each formation of the Ryukyu Group as the terrace deposits which are correlated with each other by the altitude of their distribution. In this sense, the studies of HiRATA (1956, 1958) and YAMAzATo (1959, 1960) are similar to NAKAGAwA's work. They also divided the "Ryukyu Limestone" on the basis of the altitude of the distribution, and tried to compare the topographical and the ecological characters of the living coral reefs with those of the "fossil reefs". Further, KoNisHi and his colleagues (KoNisHi et al., 1967; KoNisHi et al,, 1970; KoNisHr et al., 1974) applied for the first time the radiometry of Th230 and Pa23i growth methods for the dating of the "Ryukyu Limestone", and they insisted in the explanation that neotectonism is a more effective gauge than eustatic sea level changes. They stated little about the stratigraphy and sedimentology of the limestones, but it seems that they subscribe to ToKuNAGA's opinion (1901), the limestones of the Ryukyu Islands are composite of raised coral reefs. It is also true that several researchers have the opinion that the sedimentary "Ryukyu Limestone" of Okinawa-jima, South Japan 135 environment of the "Ryukyu Limestone" was not always so shallow as the coral reefs environment; HANzAwA (1948) already pointed out from the viewpoint of the study on larger foraminifers that sedimentation underwent at the depth of not shallow but of moderate. Since the retrocession of"Okinawa" in 1972, manyJapanese geologists have much interest in the study of the "Ryukyu Limestone", and a lot of information has been accumulated. YAzAKr (1976) and OyAMA (1976) reported the presence of deep sea mo!luscan fossils from the "Ryukyu Limestone" of Miyako-jima, Furthermore, the OKINAwA QuATERNARy REsEARcH GRoup (1976) clarified that most of the "Ryukyu Limestone" has nothing to do with the terrace deposits, though only a few limestones younger than the Middle terrace can be the object of the topographical correlation. Putting a heavy emphasis on this point, the writer stated in his paper dealing with the Quaternary limestones ofthe Motobu Peninsula, Okinawa-jima (TAKAyAsu, 1976a), that the name of the Ryukyu Group should be used for the main part of the "Ryukyu Limestone" and the sediments of their contemporaneous facies other than younger terrace limestone. OKiMuRA (1976) summarized his work on the Quaternary geology of Yoron-jima, Kagoshima Prefecture, in the same manner as the writer's proposal. On the age of the main part of the Ryukyu Group or the "Ryukyu Limestone", there are divergences of opinion; some geologists regard it as the Middle and Late Pleistocene terrace deposits or the raised coral reefs, while others regard it as the Pliocene or the Early to Middle Pleistocene basement rocks. In such circumstances, it was requested at first to establish an accurate stratigraphy of the "Ryukyu Limestone" as far as possible and to criticize those various opinions concerning the "Ryukyu Limestone". The writer started his work as a member of the Okinawa Quaternary Research Group in 1973, and surveyed the "Ryukyu Limestone" of about twenty islands in Okinawa Prefecture. An outline of the results obtained by the Research Group and the writer has been reported in several articles (OKiNAwA 9uATERNARy REsEARcH GRoup, 1976; KizAKi and TAKAyAsu, 1976; OKrMuRA and TAKAyAsu, 1976; TAKAyAsu, 1976a, b). In this paper, the writer gives more detailed stratigraphical and sedimentological considerations on the "Ryukyu Limestone", with special reference to the Ryukyu Group of Okinawa-jima. The Q;uaternary geohistory of the Ryukyu Islands is briefly discussed from the viewpoint of the "Ryukyu Limestone".
II. GeologicOutlineofOkinawa-jima A. Topography Okinawa-jima, the largest islands of the Ryukyu Islands, is located at the middle ofthe Islands which extend from 310N lat. to 240N lat. (Fig. 1). From the viewpoint of geography, this island is divided into several units as shown in Fig. 2. 136 Katsumi TAKAyAsU
sc..11e ---- .-126'-r--IZer-"t'JS i '7vrv.e. ..l3 .',/I-li-"' lr' lt' 1 IAcri iifiS,iiSi -t 1 "-- 12r 124. Nz - 1---"e / i' x N Xf 1' ilO i'i 3ti¥ v 1 i1. i L x F icEIL,,,, KYUSI L.==..),- ' 1 z -.Li ji -l. '1 1 lo'¥ x 32' K3"bNlt- 1i/ . t.t.t tJ. ' -+.r ;rf" f il ,tl.[l/ .oo{sJm-,Al!,to iVl'"-' )'h L ;ll,3e ' 'rns"Xt'j I¥ 1 -rr- i F ) /1 7 ;,`(r.... [I.li v / t.t t il . ,g li 1;¥iii', i Ii --- 3o¥' CL!:!.1"!)!Ak.7i[!i!-, i }/ . .1.r .....4 itggttL¥1 'g" i EAST I, ii lle/ii/;e-D'--l?-,,i/1.f.i,x ,(. 1'i 9HINA SEA 1 r/i,t" '[ l 1i 2cr ft7il-'` '- r- 'r''' r lf f¥1 IL li }. l 3 gl' x/ y ,.s,e.nvlyy/:isi,oto1/1 . 1'-m----:'bmuwA' ,- v 26.--t-.. F"eWrm ..4r"- .-f' N 1 1 ] L.," 1 i l ¥'e 1 s, Daito¥stvtoi1-f ! -- l¥ Okinawa Prefecture v ! lj ?rAi, I/1 6:N5MaTAfo 1 --L.-,.....,l. ! 2" 1' e k6Yftfil-, /l sli9ilfll'tin/A:A /' ! ! / -.--.- UJ .-t-t-.".-. - . 11[ 9 U ,lo ! ! , l ww 1 / fh i sEA l i ] PHiLtPPtNE 1 l : ' L--- t 2", sx,1 cbaptel Lv! l il ge " L"T x f L , ; 1 i ,
Fig. 1. Map showing Iocation of the Ryukyu Islands. The Islands are divided geographically into three parts; the Northern Ryukyus (Osumi-shoto), the Central Ryukyus (Amami- and Okinawa-shoto) and the Southern Ryukyus (Sakishima-shoto consisting of Miyako- and Yaeyama-shoto). The numbers in the map are index for Table 4 in Chapter III; 1. 0kinawa- jima, 2. Yoron-jima, 3. Kume-jima, 4. Aguni-jima, 5. Miyako-jima, 6. Tarama-jima, 7. Ishigaki-jima, 8. Taketomi-jima, 9. Kohama-jima, 10. Iriomote-jima, 11. Hateruma-jima, 12. Yonaguni-jima. (shoto; islands,jima; island)
The topographical divisions of Okinawa-jima are summarized as shown in Table 1. Among these topographical divisions, the terraces are classified into the Higher, the Middle and the Lower in accordance with their surface altitudes. The Higher terraces are distributed in Kunigami and Motobu areas, Northern Okinawa, and usually covered by so called "Kunigami gravels". HANzAwA (1935) considered that gravels as the deposits overlying the "Ryukyu Limestone", but his "Kunigami gravels" is known as the collective name for gravel deposits of various stages (NAKAGAwA, 1969b; TAKAyAsu, 1976b). It is conspicuous that the height of the surfaces lower than of the Middle terrace of the Minatogawa Plane are rather constant without any local variation. This is characteristic of the terrace topography throughout Okinawa-jima as well as in other islands. In addition, it is unique in Okinawa-jima that the land form of the "Ryukyu "Ryukyu Limestone" of Okinawa-jima, South Japan 137
H -m;saki
le-shima Northern part of Motoby Peninsula .- t c> /rr."ine.?&.Xps¥st se.s.jSAO.
MOTOBU AREA NA t.l trgldi,Åë.."Noj
Yarna -on n 1sin-y
Kin-wan shlkawa elkoi-jima CENTRA Miyagi-jirna OKlNAW im"jimo {Nakagami OKINAWA VHcLrnahiga-jima courity) (KOZA) Gushikawa-Kats' kimi urn Nakagusuku eTsuken-jirna , N .wan SOUTHERN OKI NAWA iprKuctc ka-jima CShlncjiri County)
10Krn SOUtheef paoktt¥inanNa-jima -
Fig. 2. Index map of Okinawa-jima showing location of study areas.
Limestone" is represented by mesa and cuesta topographies in southern part (Pl, 14, Fig. 1), and butte in central part. It may due to the effect of lithologic or tectonic control otherwise. Furthermore, the limestone walls observed in everywhere along cliffs are considered to be case hardening ofexposed limestone beds (FuNT et al., 1953). B. Geology The basement rocks of the "Ryukyu Limestone" are composed of various sedi- mentary rocks and small intrusive rocks ranging from Permian to Neogene (Fig. 3). They are arranged zonally and divided structurally from inner (continental side) to outer (oceanic side), the Motobu belt (Permian and Triassic), the Kunigami belt (Jurassic?-Eocene) and the Shimajiri belt (Neogene) respectively (KoNisHi, 1965). Among them, the Shimajiri Group of the Shimajiri belt is the most important de- posit in relation to the "Ryukyu Limestone". It is more than 2,OOO rn in total thick- ness, and is composed of thick siltstone with intercalations of sandstone and tuff (FuKuTA et al., 1971). According to the studies ofplanktonic foraminifers and calcare- 138 Katsumi TAKAyAsu
Table 1. Classification oflandforms ofOkinawa-jima
Topographic division Type area Altitude Geology
Mountain land Northern Okinawa 496 m (Yonaha-dake) Pre-Neogene basement rocks (Kunigami, Motobu) 453 m (Yae-dake)
Central and Southern Hilll Less than 100m and Okinawa Shimajiri Group
Limestone landforms Central and Southern The highest point is Ryukyu Group (the main part (mesa, cuesta, butte) Okinawa 198 m of the "Ryukyu Limestone")
Northern Okinawa "Kunigami gravels" Higher (Kunigami, Motobu) 80-200 m '" 4'O'-6o ifi'' " Terrace Middle 20-30m (Minatogawa Plane) Gravels and the accessory part of the "Ryukyu Limestone" aoastal area 10-15m Lower 5-7 m Coastal landforrns Postglacial raised 6oral reef (bench, dune, reef, Less than 5 m limestone, calcareous beach mangrove swamp) deposits, alluvial clay, etc.
-ILL,-.o: ` ui g 11 - 1, es / a ¥ e-I-lil , t /. 1. fi 10 km y -
Il y s... tt / !C,T- '' pt,' m ee -. .k Y be' 7-Okinawa''t' ? OAIIuvium x iiZ /--l -u 4' inh'x.x '/''/' Ryukyu G. t Terrace deposits EllilZ sh;mdjiri G. lll ) -.lii ' v M Iii.Il Nage F. g )cayo F. ei Eiliilll Nakij,n E ' OIIrelm Motobe G,
Fig. 3. Geologic outline ofOkinawa-jima. I; Motobu belt (the Motobu Group, Permian, and the Nakijin Formation, Trias), II; Kunigami belt (the Nago and the Kayo Formations, Jurassic?- Eocene), III; Shimajiri belt (the Shimajiri Group, Neogene). The name of each belt is based on KoNisHi (1965). "Ryukyu Limestone" of Okinawa-jima, South Japan 139
Table 2. Stratigraphic sequence of the QLuaternary System of Okinawa-jima (Takayasu, 1976b) FLINT et at,"gsg) TAKAyAsu "g76b) eKww/NAWA 8tU l]M/gW6)
Udi8d= x NewSandDuneBeach¥cockj RecentCoralReet,etc. Nevv Sand Otg}fTc . x 8 Beach deposits .x--xit IV g ,RaisedCoraIReeft-2:VT i Raised Caul Reel 2 gEgE, 'LowerTerracet6J 'M' Machinato Ls. (VeneerType) Lower Terraoe : Ls,orgfqvet III (VeneerType) t-51 "Awaishi'Ls. g ? Yontan Ls. MinatogawaLs.E s '5ango'Ls. 2 (AccumutationType)t40) Yemiten Ls. Upper TerTuoe Gtvvel Kunigami Grcrvet :. ---. . ererra7Gvt --.-..-- 'li' NxNs c(Corutlinebiol+thite)rao. tllt ul s J Atternated"Ls. s It NN- ..-(9gp!-b.ea-ciNbioclasticLsl ;IV:, g z - L' BCNgalbdlL,mesto-n- w . ei"---- +"-- s s ta taa= ? k tl U N lt lt s tt s o w Nbha E N ' N nr F , ut z N g !A.wot.tu.`pe.rpE"ne."b.ni'.!L--..(Bbchs'ti' ttokazu Ls. s s. ur N hl , s wtleJ /Chinen Sand s -..Itct-c.are' .,.t' spl'rtfr'one)t-4o)Nontatc"--..-x-.-sandagraveO'-'--- l J N ,o u' ' U x ' cr a ' N Guga Grave( N o xNN (GraveO? " NakoshiSandlChinenSandno.1ls2sil
Shimoiiri F, g9o a ,GogaGravei:t7oil,ShinzatoTuft Shimajiri F. wiad ! t60.1 8u E ous nannoplanktons, the Shimajiri Group is regarded as the sediments of the Late Miocene to Early Pleistocene (NAToRi et al., 1972; NisHmA, 1973; IBARAKi and TsuaHi, 1976; NAToRi, 1976). As the result of geological re-examination (TAKAyAsu, 1976b), the Quaternary System of Okinawa-jima was summarized as in Table 2.
III. Stratigraphical Study of the "Ryukyu Limestone" A. GeneralStratigraphy 1. Fundamental division ofthe "Ryukyu Limestone" The writer proposed tentatively to divide the "Ryukyu Limestone" into the Ryukyu Group and the "terrace limestones" (TAKAyAsu, 1976a, b). Though this concept is still valid, the terminology of "terrace" seems to cause confusion in the definition. Therefore, in this paper the writer adopts the new term ofaccessor2 limestones, i.e. the accessory part of the "Ryukyu Limestone", instead of the "terraec limestones". The Minatogawa Limestone distributed in Southern Okinawa is a representative of the accessory limestones in Okinawa-jima. The limestones of the Ryukyu Group are called the main limestones, i.e. the main part of the "Ryukyu Limestone" excluding the accessory limestones. The reason why the "Ryukyu Limestone" should be divided into two parts would be understandable in Table 3. , 140 Katsumi TAKAyAsu
Table 3. Comparison between the main limestones and the accessory limestones
Main limestones Accessory limestones widely (overlapping whole area of the limited (accessory distribution at the Distribution Shimajiri Group and also moderate area circumference of each island). of the pre-Neogene basements).
Thickness about 100 m or more. less than 40 m.
bioclastic limestone for the most part biolithite rather predominant. sparry and biolithite in part. micrite matrix Lithology calcite cement rich. rich. including some fossils showing not such representatives at shallow Envir6iifiiEn-t-" Fossils shallow water as the coral reef can be similar to the littoral zone around formed. present islands. Identity of fairly continuous laterally in accordance not clear as its limited distribution. stratigraphy with the more upper horizon. Preservation of depositional extremely poor clear as the terrace topography surface faulted and tilted. more than 20e in dip scarcely disturbed by tectonic move- Structure near fault. ments.
Besides, following the definition of YABE and HANzAwA (1930), the name of "Ryukyu Limestone" is adopted for collective use to the Pleistocene limestones* excluding Postglacial raised coral reef limestone. 2. The Ryukyu Group-the main limestones and their contemporaneous sediments In consideration of the lithofacies and the fossil assemblages, the Ryukyu Group is divided stratigraphically into two formation units, the Lower and the Upper. Furthermore, the Upper Formation is subdivided by the characteristic fossil assemblages into three members ofthe A, B and C ascendingly (TAKAyAsu, 1976a, b). The Lower Formation is the sediment which accumulated in the tectonic basins or in the valleys of the eroded basements. Therefore, the thickness of the Formation varies from place to place. The lithofacies of the Lower Formation also vary from noncalcareous to calcareous facies according to the basement topography and the quantity of the terrigeneous fragments. But, in general, it becomes more calcareous towards the upper part and at the top the coralline and/or algal biolithite facies are observed distinctly. The Upper Formation overlies the Lower Formation conformably, and is distri- buted more widely than the Lower Formation. The unconformity between the basement and the Upper Formation is rather smooth as compared with the relation between the Lower Formation and the basement. From the evidence ofoverlapping, it is clear that the depositional area of the Upper Formation spreaded out successively. Therefore, the lateral facies change is not conspicuous in comparison with the Lower
* Though HANzAwA (1935) considered the age of the "Ryukyu Limestone" to be the Pliocene to Early Pleistocene, the present researchers regard it as the Pleistocene based on the relation to the Shimajiri Group. "Ryukyu Limestone" of Okinawa-jima, South Japan 141
Formation. In the lowest part of the Upper Formation, the CLycloclL7Peus-OPerculina beds in the limestone facies are fairly continuous laterally, and form a good horizon marker. The Operculina bed occupies a position slightly lower than the C2clocl)Peus bed generally, but sometimes either one is missing. Cl!clocllpeas assemblage is dominated by C. carPenteri. According to HANzAwA (1948), this larger foraminifera is usually known at the depth of about 100 m in the present sea bottom, and some other larger foraminifers accompanied with it are also in- habitants of the moderate depth. Therefore, he considered that the "Ryukyu Lime- stone" was deposited at deeper environment than the depth of coral reef formation. In addition to this, a bivalve, Plicatula mulicata, is sometimes found at a horizon immedi- ately above the Clclocl!Petts bed. This bivalve is also present in the "Ryukyu Lime- stone" of Miyako-jima. The molluscan assemblages of the Plicanta horjzon are represented by shells which are considered to be indicative of the depth between 60 and IOO m (OyAMA, 1976). From the facts mentioned above, the C)clocl7Peus bed and its associated horizons are significant to consider the sedimentary environment ofthe Ryukyu Group. The writer called the beds of OPerculina and Clclocl"Peusas the A Member. In the lower half of the A Member are often some terrigeneous fragments, and in a part of the Operculina swarm, generally about two meters in thickness, are sometimes intercalated one or two thin layers of the tenigeneous reddish brown clay. The A Member is overlain by the B Member which is cheracterized by the presence of algal limestone. The algae appears to be ball-like in many cases, but sometimes is broken into fine fragments in situ. In the B Member, the number of fossil species in- creases upward, while the content of terrigeneous fragments decreases more and more. The C Member covers the B Member, and is represented by coralline bioclastic limes- tones. In some areas it changes laterally into coralline biolithites. 3. The Minatogawa Limestone Formation-as a representative of the accessory lime- stones The Minatogawa Limestone corresponds roughly to the Machinato limestone of FuNT et al. (1959). But now, the topographical situation of type locaiity ofthe latter has been strongly changed artificially and moreover is hard to access owing to the mili- tary establishments. Therefore, the writer made the re-definition of that limestone formation in Minatogawa, Southern Okinawa, and requests to shift the type locality (TAKAyAsu, 1976b). The Minatogawa Limestone Formation fi11ed Iow relief on the erosion surface of both the Ryukyu Group and Shimajiri Group with remarkable unconformities. The Formation is divided lithologically into the Lower and the Upper Members. The Lower Member represented by coralline biolithites usually contains the huge limestone blocks of the Ryukyu Group. The Upper Member conformably overlying the Lower 142 Katsumi TAKAyAsu
Member is represented by foraminiferal calcarenite or calcirudite with many rounded intraclasts. The distribution of the Minatogawa Limestone is followed up to about 30 m above sea level continuously, and forms the Minatogawa Plane of20-30 m in height. Besides, it must be mentioned that even at some places of 55-60 m in height, other limestones which look like the Upper Member of the Minatogawa Formation distributed in a small amount near the distribution area of the Minatogawa Limestone Formation. The relation between those two limestones is not yet clarified. As for other accessory limestones, the small distributions ofcoralline biolithite andl or algal ball limestones are observed on the Lower surfaces of 10-15 m and 5-7 m in height respectively. Their thickness is generally less than 5 m. B. LocalStratigraphyoftheRyukyuGroup !. NorthernpartofMotobuPeninsula The writer already reported on the Quanterary limestones ofthis area (TAKAyAsu, 1976a), and the summary will be mentioned briefly in this article. The lithofacies ofthe Lower Formation differs with each other between the eastern area (Nakijin Village area) and the western area (Motobu Town area) (Fig. 12a, in Chapter IV). In the eastern area, it is represented by calcaroeus sand beds called the Untensandbeds. The Unten sand beds become more calcareous westwardly. The lower Formation of the western area is stratified bioclastic limestones of the Urasaki limestone beds. It should be noted that the Urasaki limestone beds reveal sometimes remarkable cross bedding or lamination (Pl. 15, Fig. 5), with many terrigeneous fragments int he lower part. The difference between the lithofacies of the eastern and the western areas may be explained as that of contemporaneous heterotopism due to the difference in sedimentary environments, but the calcareous sand of the Unten sand beds is recognized below the bioclastic facies of the Urasaki limestone beds at several localities. There fore, the sedimentation of the Unten sand beds might have preceeded that of the Urasaki limestone beds during the first stage of the deposition. The Lower Formation abuts on the basement rocks, having fragments or boulders ofbasement rocks abundantly in the basal part. On the other hand, the Lower Formation of Kouri- jima, off Unten, Nakijin Village, is represented by the stratified bioclastic limestones with poor cross bedding, different from the Urasaki limestone beds. As for the Upper Formation of this area, it is easy to distinguish among the three Members, A, B and C, especially in the eastern area. The Operculina bed ofthe A Mem- ber (Pl. 14, Fig. 4) has a good lateral continuity all over the Peninsula and also in Kouri- jima. In the western area ofthe Peninsula, the C2clocl7Peus limestone Iies directly above the Operculina swarm part. The B Member is slightly thicker in the eastern area than in the western area. Furthermore, in the western area it is often difficult to distinguish lithologically the B Member from the C Member. The C Member is represented by weakly layered bioclastic limestones (Pl. 15, Fig. 4), and the coralline biolithitic lime- -t N. -7,,: tr
t/t,.,. z, l:- i¥ ttv tt l,,., ' , '
:i¥ :ttt N 'j LEGEND f' :" .,xe .pa : `':' rS ''"' .iÅÄ: ',J:, -t-tt.- ' tt llPpt" " ' ' tt s ' .-.-. -. 'i Sl¥'. i:,' lt tt . L.l 't, ,/ J''+.s. t' ,. 1. " ,' At{uvium & beach sand , r:. ..J 'S:';' tJt ' "ii'';"'' -.tt t l /t'' .s' i'-,.¥ , .¥ :t] oTe IitFi9 1' 1"'''i'' E-i¥.¥ "1 Elliili![] ::s v AA -- Lower terrace deposits .oit .,:. ,.:.1,,. -r' ',,t1,, ; '"!iv,.... -.¥. tt-t e + o Nk e ee :t ,:lit[.l ..itr,,4 NeoNo e Middle terrace deposits e' 'z¥.,¥ t t "h eo e. ¥,-¥ iel¥'i,'i: i N oo g-B ,l." ,' -2 ¥ ¥,. ij -¥ ,iA, a .. 5 Ftyukyu Group - ":r N e ,,.p- ttt: ------.-- rF''. o e os i¥ s tt o e 4 1:terrigeneous graveLsand,and clay, t/t t ttt .- uB¥3 1. ..Åí " A " e rENGAN-GAWA t t tttt 3 and catcareous sand(Lower-¥UpperFormation) / -; .e. A IL A .tl 2:b'mstic sandy or brecciated timestone Ko a .3 z?./ : Haebanj .- v. 1 -p:' /9 ss¥ t R Nakagusuku '¥iE.e::i. -wan i. Nishi ra:==T- YaSvemu "3- ko a ¥4 -O "'t': o' 5 va " i" YAB ucH l-J IMA ". ¥g/ s ` t iveb"ma s ¥'¥ aB-2 xs 11 1km -- .4e Q Ao aB¥1 :i'¥ '`Ao t -- N b eshikiya /5 .-- WHITE BEACH ? IU,S. NAVAt BASE) a . m -t-H-.-.---i-- GuBJ3 50 ittJ- t;',z't.L¥L.i-¥¥ ;l :t-'':t'''/--'-'.-,,.-tt -tt -t --.-.r "t -t-t t- '¥.' ttt ttt -t t'' t-t--t tt t' ]''":-4't' -t- -t-t-tt'.L¥. -tt--:;,1,L,-:::,,,.:,..1 I,..,.-.',J¥,--tt -" .., t- -t tt --.-.. .,. . . /- Agena -t ; ' --.,-::-:,-..-,t,t- -o tt -.,. .-,. -.,.- t-.ttttttt -, -,. L-t. ':,-.-.4s--' --e"Ooee-Oe"ee---e-- " GuB'2 t- -' rb' '"-::o'n.:' i:e:¥ ':A':¥' 9e-:.,".io'""le¥-v t oe-- .- a b ttt ' tt t -o ..4,- ' .-e t'' "t -''t';' B .i:.:.1:,j,l tt :,,¥¥:-.¥-, tJi..i- ''tj': I' tt-t -- -t-t t'"., tit4t ¥.. ¥jl' t- .l ":-'t t-tt .2 tti tt 'rH' ' : --t ::ttt-t t-- t1-t:t:-ttlt:tt- i:, t-.t--rt :t-tt-----tt it L' tt-. tttt A j-tt t.t -tt-- ttt ' :t A A ttt ' .- ¥.- ' l: tt. tt tt tttt :''''tt Jgettt.tt:ti- tt tt -t /1km :. ¥.¥.¥tIt-t: N t:ttt )N,l 1OOm c-o D 1:.-.-==L::-.m-."500 m Fig. 4. Geologic map of Gushikawa-Katsuren area. "Ryukyu Limestone" of Okinawa-jima, South JapOn 143 stones are also distributed sporadically around the salient part of the basement (Pl. 14, Fig. 3). Hitherto, these biolithitic limestones had been once regarded as a part of the "terrace limestones" of the upper surface of the Middle terraces (TAKAyAsu, 1976a)¥ However, after detailed surveys, the writer has come to conclusion that these biolithitic limestones are correlated with the coralline biolithitic limestones of the C Member, and both are contemporaneous. At several localities in the eastern area of the Peninsula, the biolithite ofthe C Member unconformably overlies the Unten sand beds. 2. Gushikawa-Katsuren area This area is divided lithologically into three areas as foilows; the western area (the western area of Gushikawa City) where the Lower and Upper Formations are both predominated by noncalcareous facies, the central area (the eastern area of Gushikawa City and the neck ofKatsuren Peninsula) where the Lower Formation is dominant in the noncalcareous facies but the Upper Formation is characterized by the calcareous facies, and the eastern area (the largest part of Katsuren Peninsula) where both Formations are represented by calcareous facies (Fig. 4). The correlation between the three areas is not yet suMciently confirmed because a good horizon marker is absent in the noncal- careous facies. In calcareous facies, however, the C!clocllpetas bed can be fairly well traced laterally. The Lower Formation of the western area consists mainly of noncalcareous gravels or sands, and contains many molluscan shells and sometimes coralline fragments. The Upper Formation intercalatcs with the limestone pebble beds in the lower part. Though this information was obtained from a drilling core (GuB-3, in Fig. 5), it is possible to say that these limestone pebbles were derived from the limestones of the Lower Formation somewhere in the more eastern area. The calcareous parts increase upward in the Upper Formation, but most of the Upper Formation is occupied by noncalcareous sand and gravel facies. In the noncalcareous parts of the Upper Formation, the fossils are not yet reported. The calcareous parts are intercalated within the noncalcareous parts in large lenticular limestone bodies. These limestones remain as buttes which escaped erosion. The Lower Formation of the central area reveals particularly complicate facies changes. From the drilling (GuB-1, in Fig. 5) near the estuary of the Tengan-gawa, dark greyish silt beds containing organic matter were found. In the silt beds, brackish water foraminifcrs represented by Ammonia were yielded. Similar silt beds were also found in the dri11ing cores ofthe Ishikawa City area (IsB-1 and IsB-2, in Fig. 5). Well sorted and weakly cross laminated noncalcareous sand beds which look like dune sand beds are distributed in the neck of Katsuren Peninsula (CGS-Ol, in Fig. 5), where the altitude of the basement Shimajiri Group is generally higher than in other areas. To- wards the west, the sand beds change gradually into startified sand beds intercalating thin silt layers (CGS-09, in Fig. 5), and towards the east they change to sand beds con- taining sporadic calcareous parts (CYN-Ol, in Fig. 5). Another variety of the Lower 1" Katsumi TAKAyAsu lshkowa :se-? ' Xtes-m 4 , ." k -'h- . [fiS-Ol SN nhb/ " Sss t. LL '1 Tcfngan t `:' N g N)L Nt 1 ) XCGS-Ol lt 1 eGsB¥1 OKINAWA C., A9'op N eose-3 l ,,Gigi".7Kag"aN-ta"/C;"'iZ,/,":>IIIII//.. ll ' O 1 lkm n M ch,boop r AkemX(Che,s;sJ{ ' }Gvtkt,-os s ' 1 -1 -- ' L / s. 'N x Kelo 's " ' y ,,:ebi" y6oNAousuxu v. xcKTmimp--lr ,t'"ket.,deA eK"ctlhhrtTV KATsuREN 1 V. wiLmor-¥ h- r- (a) Fig. 5. Columnar sections (right) and theirlocalities in Gushikawa-Katsuren area (on legend see Fig. 6). Formation in this area is represented by well stratified bioclastic limestones. The limestones are distributed in the northern area of Tairagawa and Gushikawa, Gushi- kawa City. They overlie the noncalcareous sand beds, a part of which shows cross bedding (Pl. 15, Fig. 6). The Upper Formation of the central area is represented by stratified bioclastic limestones. Though the coralline biolithites correlative with the C Member are also distributed on the top of the ridge north ofTengan, in most of this area, it seems that only the B Member is distributed. In the neck ofKatsuren Peninsula, all ofthe Upper Formation is absent. Additionally, near the neck ofKatsuren Peninsula (CGS-09, in Fig. 5), the Upper Formation overlies the Lower Formation unconformably (Pl. 15, Fig. 3). Giving attention to these facts of distribution and local uncornformity, the writer inferred that the Ryukyu Group of this area suffered the tectonic movements during the deposition, and the sedimentary basin was separated into the east and the "Ryukyu Limestone" of Okinawa-jima, South Japan 145 lsB-1 4sB-2 GLS+1 Gue-2 GLS-3 KaB-2 KaB-3 CGS¥Ol CGS-02 ces-o3 CG5¥ec CGS-05 m gm m Lm m :em 30 4e 21 o 8 -Er,.ttl`¥¥ J.tt -!- T 4 d c)e ,' .- n U T L". L ' . e n -t-t ' eh m s -t-.-.t 4 ".... a ng -v ' le" .-' e --T- t:L) U e--- " tt/tt t" t- X/lr¥,'.'/ ==. L t-- - L. -z '= a T.--- Lt U -t-t sc i'g'-.1Oeo s .L" ()eee U eA 1' t- c) 10 -tt 10 -v t-HT , tt 'tl" e 1.ZLtt L p- a .ShrJ- rw . e" e" n't- N"LL !tt lx} eV ' .¥ ".¥ fitts " eJ )../ s L e'e .t " " ¥he e 4 D. eV tt.t v" t. -" et 1e' -. A! .Lfi.t CGS-06 CGS-07 cGs-oe CG5-09 CGS-10 1 i}' .r.Y. Om 51m 7m m m m v 'o"(-"e ,- k ea " eoe eoe o;,-.br.;i-J4.".Vn.X,,.s x--' moees.e.Je nv U D L ro 'o t-ttt "t ts g! . ;//. " L I,11lr,l,, e Ll... e be e tl. eO ..t t'Yi'VA Ll..'.A ilLl U , c)- u l;¥)S.,;,1 Vn" ".ie ia t./t Z'h'-.'7A ,i nT.i' L -.. '.a -"e .i¥lii-/L11:-tl.tTl ,,'ill'11."}1,1 ..A' S U L-.--:¥. '"Lr Sh itttljl' tt¥?ttl¥ vn'e U .e e rasi ,/rL;//. Ae '//?tc.te".KJ¥. E' b;¥1.¥/ "IR' Je ?- e. ¥. }L t.t -- .'l-,ISt¥.,: t"t Lrtt x' ,,-/i,1¥¥.1.1 /.e'= e, :o iilili';' ,.x 'p'."' -'"'' s. t//..tt-.tt./ .¥-e" ,e.. -'A'ele E¥,t:.,,,{'i,¥. '.l'.'i/ tt ttt ttttttt ¥-L'''V¥tt 't/"i/ t t tt b.' tl. oo-x' 30 '1';;/'1/'11il t/ /.t. ;` '-.rt ../A .. .Y..E. ng ¥¥' //1,tL¥l¥1¥il//¥']. p:, ,' .x L tte¥¥ii se.p. ,' s}1,¥¥ ¥{etu Sh ts,t.s:.) gee its' ig tttiL} i¥tfe.¥ iL' th /ttttt tt ttt CGS-11 CGS-12 CYN-Ol CYN-02 CYN-03 X'B'n' t. Ch t t. Sh di .7LZD!7 65m 40m 45m 36m x¥' L=. '.ul `x,r )ee -. T 'i,.s,¥ 1" F ..t'/t't./.ttL :::' v" ¥.. s, tt ' Sh ttttt 1'1'i'//'"iiii t./ 1-:t, e-.'>.¥tt d\.I,r...]. ,1,rl/it/1'11 lita tt t i4". ttrtrI t .t L tt ' tttlt L Ltt 40 tt L. l i t.t ;= .tk¥¥tZ,,l¥ill il.-QL- --- 'N¥ u r,¥, i,,,1il//.,S' .¥ '\`""li" tt U .yt' o; zLr..11;',tt 1,/,,k.i i'v' thlt.tt. L ,.. L4 ."ll:.. "t xli1 ,. ."g,¥,iii xetT' ¥."Egl,tL-,'Y-. ,.¥ tx .F L;)" -o '"'t/"/' l¥,v,}¥s;tt¥¥ 10 vt) ttt t. t4 r7 ,il¥L-1:,.¥ L Sh ye." .' t- a"-e '¥1"11i.r¥:,. t'.L¥- 1{rv,,//,i/ll'. 5h . so T/Terrace depos;t ¥ltt¥tt,/t ti' il:e.e,FFOor:.e leion.}twukyu Group Sh ,' "/X..L.. CYN-04 CKT-Ol CKT-02 CKT-03 om 49m 43m m esm y ¥1'r,",¥'' T .F.t :eeeee Ch,Chinensandstene ¥' . -,,1¥']'/¥ ;T- ShimajiriG. ':11Il./v,'.'l', -- U ,1 e Sh/ L t/t .t /tt it/t -/'"ti/- -- 'LJ l'¥llllz'1.'i¥/ttill.t.1..T 10 lttl'pt''1'i"/:/,i,r,4Ji,,.,. ,g,r/iX /1:t:.,.Jl:;1,/ ¥- ///-1""1'tl'' :"'lr"t'1'.-!¥:-,., ;;,//.[.,:iiLi 70 5 Fig. 5. (b) 146 Katsumi TAKAyAsu west by uplift of the neck ofKatsuren Peninsula (TAKAyAsu, 1976b). In the eastern area, it is known by the results of drillings (KaB-2 and KaB-4, in Fig. 5) that the thick Lower Formation is distributed under the axial part of the Penin- sula. The lithofacies changes from the calcareous sand of the west to the clastic lime- stone ofthe east, At several outcrops, the clastic limestones show remarkable stratifi- cation and cross bedding. The Upper Formation of this area is distributed mainly along the southeastern edge of the Peninsula, and it overlies directly the Shimajiri Group in general. The sequence from the OPercutina-C!ctocl2Petts limestone of the A Member to the algal ball limestone ofthe B Member can be observed at several outcrops (CKT-02, in Fig. 5), while the C Member is absent. 3. SouthernpartofOkinawa-jima In this part, the Lower and Upper Formations are both represented by calcareous facies. As shown in Fig. 7, this part is divided on the bsais ofthe difference in tectonism into the western area, west to the Minatogawa Limestone, and the eastern area of the opposite side. In the western area (mainly Itoman City area), tectonic movements were vigorous after the deposition ofthe Ryukyu Group, while in the eastern area (main- ly the area ofChinen Peninsula) the erosion was more predominated than the tectonic -¥-¥'N SNNSii IKt .v N SAS " .}'CHI S!IS¥ Shinzato shiki .1 rf hinen .t ,.t 'x ¥.. .'c' -.e...l x STM-02 XSCN-Ol Z'Z --l Sc(ii sN Ltoka2u yOyakeboru s STMDI s NN A,YN la, N-t-TAMAGUSUKU V. US(ltO V SJf Hyakuna KOCHIN v. s-oc Yoza N siT-osxtN ' X5KC-02 Tomori ss¥ lto n SKC-Ol S-05 Ozato ' e9.) ,x,,s-ibla' x5Xx,,,-,, s'N. t Micat /. l sostoX7scS'06 l t XS-GS-Ol GtshicimX IT-03 i'-¥ / :T-06 GUSH1KAM1 V. kabe '"'k, / 4 a tTOMAN C. IK )scgsS.GoS2'o3 Komesu Nxtko; bun,1"' Kyan )]i,i,, ,UXSS"07 XSIT-09 -2km (a) Fig. 6. Columnarsections (right) ancl theirlocalities in thesouthern partofOkinawa-jima. siT-O! NTD2 stT-a3 SIT.04 SlT-OS SIT-os srT-o7 slT-oe SIT¥09 S4C-Ol SKC¥02 scs¥a SGS-02 Om m S3m 25m m m ] -) t-- "to .." p, eS ;-ig] ee"--- O.O o o e c o" -ay.- 3 e s "a")J " e -- --e eA¥g oLhe oa e" n" -ee e ---t oCa e e c Åës B "- e C)ea;. za .cg- --o e-" "'"s tle n" 4"n t .e.ee ) " e est t¥ +Sp ee ) ete za " eOa e- t) -s oo yte o--' ¥e,i"e ' e c -"e+- st- . r¥i. "eA mn gg )e.Nj -p -)- ;- A t- i e- eQLS- .¥ 7b . - s" -e SEjs e ,s) A :sttt oe o' 5J e "Tt- .l -s A" L la" -- -¥ e'L- A 4a " ]s). -- - A9.A. cv tw l " A¥ A).a . " L Å}1 •- -- ie`i6 eo' B p A ' o rg B ) i -e -: &.t e} :`' oa t" /L -t- L ee6 5Sas i 'e- -¥i -.:tt - efii- e!s "9 )2 s A -LA -' fi- 2.e:.e ,N. " o]. e. e i-' eo " e) ,.e ."e-- e. eTbS Ss .o-V' . L o t4i ffr a Ua' A .- 1 g'- 4r!.,,' - 'e ¥A . h. trr¥ i OA' '.O?.: A H ro .Il )/ th' 2 .A off L : o: LEGEND g SGSor SGS-04 seS-05 scrse6 ssS07 5TM-eT 5rvM sa"ot tr.o di nm 22m Sm va5tn .5Q[!! Ntitude{abeve sea levcL) ,., .# !.,.-t! 3m : ge--- " pt M Soo ss e ag.O. Algat boll [ZZi] Tracc tossii E M ftSa De8 e 't! eu e ltto : =tpt . A.n cl e Matty atgae Ei ] sandv :16;s/ QeOo T /.;..L.] e e" L i-.- g lj¥) B eLl -po s9s% s' i EilE!1 Fera"gntttra [III erecciated Ae- Aee -" e, -. h!e,ea . v m "-'i L -e:, [iiX] coraL esElilsl catcareeus sand o M -/ i = '}it/'i r.f. !T ff -"s, tr r7- ..!.' II!llilMottusca an Terrigeneous yvvet `. c, p ¥/" gpa /p.el }¥ "1 [!Z] Bryezea =i: Beddlng sc IhSS,- -a v L '- eJ as .-¥TLI. "'t i" es Cross lamina v'`'fi - Echincid bei eL M/Minatogawa Lirnestone Formetion ,e Jo- C/C Member IUpper Fon"atbn l RYul,U Oro"P e B/B Member .e.e. A'A Metnber ro . ;.i3 L' Lower Forrnation ctiinen$andstone }Sh;maiti oroup waSittstone "N Fig. 6. (b) N 148 Katsumi TAKAyAsU control of topography. The Lower Formation of the western area is limited in the eroded depressions on the Shimajiri Group, and in some basal horizons the presence ofcalcareous sand beds is recognized (SIT-03 and SGS-04, in Fig. 6). At the top ofthe Lower Formation, coral- line or algal biolithites are sometimes recognized (SIT-03, in Fig. 6). The Upper Formation of the western area is divided into three Members lithologically. Among them, the algal ball limestone of the B Member (Pl. !4, Fig. 5) and coralline bioclastic limestone or coralline biolithite ofthe C Member are distinctive. In the eastern area, the unconformity between the Shimajiri Group and the Ryu- kyu Group has a position up to more than 100 m above sea level. The bioclastic lime- stones of thc Lower Formation are distributed in the neighborhood of Oyakebaru (STM-02, in Fig. 6), and the sequence from the Clclocl7peus limestone of the A Member (Pl. 14, Fig. 6, Pl. 16, Fig. 2) to the algal ball limestone of the B Member of the Upper Formation is observed at several outcrops around the plateau of Itokazu (SIT-Ol, in Fig. 6). The limestones correlative with the C Member are absent. The coralline limestones are observed in only a part of the top of the Lower Formation. Furthermore, the Itokazu limestone and the "Alternated limestone" of the OKi- NAwA QuATERNARy REsEARcH GRoup (1976) are correlated respectively with the Up- per Formation and with a part of the Lower Formation and the Upper Formation of the Ryukyu Group in the writer's stratigraphical definition. 4. Hedo-misaki The limestones of the Ryikyu Group are distributed in a small area at Hedo-misaki cape. In this area the limestones cover the basement of the Triassic limestone of the basement and those include numerous granules of the latter. As for the fossi!s, algae which coat the granules in ball shape ofless than 1 cm in diameter are abundant, and ClcloclyPeus is common. Hitherto, the limestones were correlated with the Machinato limestone, since the topography ofthis cape shows the flat plane of20-30 m in height (FuNT et al., 1959). From the lithological characteristics, however, those limestones may belong to the upper part of the A Member. Besides, the limestone similar to the algal ball-Cyctoct!peus limestone ofHedo-misaki is also recognized in Yoron-jima, about 20 km offthe cape. OK:MuRA (1976) correlated this limestone with the lowest horizon ofthe Middle Formation ofthe Ryukyu Group of his stratigraphical division. 5. CircumferenceofHaneji-naikai In the neck of Motobu Peninsula, loose sand beds with gravels of about 30 m in thickness, are laid horizontally on the Goga gravel beds and Nakoshi sand beds which incline towards the southeast. Sand beds with gravels intertongue with the calcareous sand beds near Nakoshi. Calcareous sand beds with numerous granules and quartz grains are also distributed in O-jima and Yagachi-jima, northern partitions ofHaneji- CHZNA¥SAKI a A"uvium.beach sand & dune .te Recent corqtreef e ) eATEN [IllllllillgS !wtny/.a....tg.!;S!y!gT JtEgupgS.bt Q!o/ o calcarenite- -rudite(Vpper Member) e9."! Fqult HARBOR 9 Aza/ma biolithite (Lower M.) - T//za" .R. -Tll. .t. wntraltmectasticlimestone¥-bio[ithite L..,i -L¥ , th7 -7 }iilil +;LS bioclasttc ts.-¥ alpat }(Upper ball ls. FQrmattan) tt ' gyL!!bgs!clyps!,Is bed .Z7Zz Shirvato s '2' 1 Sashiki ,.t7 T is;lllllLrfir bioclastic sandy ts..calcareous sand (Lower F.) /f i-.i.,l. ,..Zt//. . . hima'iri rou D ' CHINEN r`1"2.. ca careous sand silt (Chinen sandstone) / chtn En -MISAKt Sitt StOne tLrff 7z¥Zz:- zi !'Å}'•i 'Oyq*e.ba.ru h / ' zt12i3fi '' .2.;i'illt9A,k"ig.3.¥..:ii¥.''¥.il.;l¥i¥.i.ililll.il-1'rLttL74t :. . ... ,trl thlt Z "'f i¥iilt¥,,.,tf'¥s. Z.X/Zk.2.Z. /ZT' 'tbS'! " ' ';' ''': 't . 10 ¥¥.-' , .. ¥'¥ ¥¥'- ¥1 'T ' Z..!ttYi2Ji ---- T -- .-' i4'li;li¥'¥¥$kazu Hr' r' r/ t' '' r15"''' X.ck.st3,Fgt3i8i;#?-T.trx i.tLr - !.. ge fl ;.,ri¥ ;: =' .r. iL L ilfi/r; ¥s ¥.¥ .¥ .7s>- T -•- ."D :Å}r' - u- i,2 ¥¥¥¥ T -= -TL XI ,..: .!H yptune 'tt''tl].. ilr:T - -¥: ; i' ' 'rll t¥ ZE.,-,Gii 5/ Arqgus,u .U .¥ 12¥1--¥::: - ee.tntttt .'t' ]viu ;Zlll-f l?;llf ¥' -- .l] [: ¥, t-tt"it' . . .. =.S---J.' k"¥-.J'.:..t, ' ¥!!' N rrU,f;. .e`u 5 '' .t '19f TA' 1.2. 4,k, -.. . [-.g., i/'; Yoz ['L L.lnt: .¥ /t ;I¥.llliilillil 7Li¥ ;:`i illlll.Z./t¥-y -f' 1.T'VO - - I¥ llllif,..,&,,., .z/ZTZ om / 'T lti i - JLYipt' ] ! ttokg,ttt.Ii-tl•it4'•SltÅí' .¥ f . I,¥ tMinatg.awa. ptIPstzfiica'Or""'I'i-,¥-- rep- & 9/ ' O-JIM.A ;lÅ}i!ili7' '-•,/ 163-e-e Fl lriT' ¥':`", yoZA' KE yAE.'i l-DSI'i:fitl.iig;g2/e -v "hi s -J iikk -`-.-"- -: J v-.t > tt..'.t.T.S'--:iX...Yvm#t,t]f,S'`".: .-t ,g i.,l! Gus tchgn N"J- ' ¥- T..;1 .L. ? irf.tt.itlt.igglgi.llll-- lt. 1 YT T:P J" Tt'r .:i' '4.-= - t ./t,,t It / /"1'tt r {..l -. -"rl"----. -v M'ait)ltSt-tu .' -" - .r' i /J T I c/ 9t) --Tv'tl]ltTtT- T :"=-Iy l;ll.l-IEi ¥ ,¥ k' 2v y¥Z ..Zl//2 ¥t ' )s . :./rJtt .T-[ ll t , '-F /' T .v. )rj.'tt! :l;.Li-ii ,i tfll tt': I-' iiC. Iil.LllirLitlii-t. ,¥ et e t- Z/yK,/Ki.¥ .Z. .,.. ' --e i¥trR t ! tlll'l,iillilllt'mi 'I-'r-'t - ;---¥' :ILtlT E ¥.,' N II!Si..i.II- Itl¥ttLIZiJ¥ IIi t .l !I'ti , ttl) o liILE,ILt,Ii/ii,,.,¥E-'--=¥fi ee ...LT 'f '' ' , t..h' g4;-eZZ/.Zi.i ' 7- -- 'L-' r ttL!¥!5Fl:i=t-O;-lts.V t: t ",'.s'.t' /U : Makabe 't" i ' l:"'':`i-i:}iiN';./i/lii2/;7iJ/ 10!Lt=ETi-.-";n" 1,i.i'rU.nt'4:L:: ; -'r:r.rtrl)l3x-¥--- iif{[Lili.-:,u.....' te II "7 E ¥/.. -L ;t/l!EISill.I L;`/r. . J ' t' ';' ;pt' ece E I/Ltii-L- 1.L " tL','#'-'{'1'-'tt"¥;"';!'lllZTTolk?ri-ilit:liJitt7'7;;'ti,ri;7" c ..r"rL-"'t . .L E ;.;t!5Il`IEi-;il'lit:¥lll'l"Trll-IIIIi."=---T tL..,Lfi. -F. '::[;.-Ti o 1 2km cct " .:=N.lj , . ' n.;Korne5U' . =T¥ ]- . ¥ Ma tiunLi. = ' c -M' -thTiT'i =- ¥,' .' ii5.9"a, " . L' t' f uS iEEEIIIII!lltt¥ [J]I[;th=- "',xr, r'"'rL [} Å}, s` ,"-¥¥i¥¥,¥.- iili[¥`'' Ji"t".'. u--''.' 2 '¥ :il;li[ FF'T'i `- 'X.H] '1'' '1 tt : L ""J JLj fwJ Yv I '' pt"-'Jt'-' ' - k LliElli!.JSg";.i'."1x't-.: .....uJ' v v" aa-4 Cg l.L ' Eiile t-' KYAN-MtSAKt ..- T it,l-] / Eli¥Ii f s})-- ARA-SAKI 200- m YOZA¥DAKE 100- N MiNATOGAWA - KYAN B c D A 1 1km Fig. 7. Geologic map of the southern part of Okinawa-jima. "Ryukyu Limestone" of Okinawa-jima, South Japan 149 naikai. The calcareous sand beds ofthese islets are considered to be contemporaneous with the loose sand beds in the neck ofMotobu Peninsula. OPerculina swarm parts are found in these calcareous sand beds, while their lateral continuity has not been clarified. The calcareous sand beds of the western area of Yagachi-jima contain abundant re- mains of Pecten and they are lithologically similar te the Unten sand beds of the eastern area in Motobu Peninsula, which is the opposite coast with a narrow strait. Most of the sediments in this area are probably correlated with the Lower Forma- tion of the Ryukyu Group. 6. Yamada-onsen The lowest part is represented by noncalcareous sand beds with a large amount of phyllite fragments of the Nago Formation. Fossils have not yet been found in these sand beds. The noncalcareous sand facies change promptly to calcareous sand facies and upwardly to bioclastic limestone (Fig. 8). In accordance with such Iithological change, the amount offossils and also the species number seem to be increased. The amount of terrigeneous fragments increase again nearby in the middle horizon of this outcrop, and in this horizon thin noncalcareous sand beds are sometimes partly intercalated. Between this horizon and the upper horizon 7-8 m above, OPerculina and C)clo- cllpeus are found sporadically. Therefore, it seems that this part is correlated with the A Member. On the other hand, this part also shows different characteristics; the amount of foraminifers is less than that of the A Member in other areas, and Operculina is observed abundantly in the lower horizons rather than in this part. Moreover, algal fragments are found commonly and coralline debris is sometimes contained in this part. These characteristics seem to be intermediate between the A and B Members. It is necessary to establish more suMcient stratigraphical divisions and the correlation ofthis outcrop with those ofother areas should be studied more precisely in the future. 7. Tako-yama By means of the geological survey nearby, it is confirmed that noncalcareous sand beds are buried below this outcrop, the calcareous facies occupies most of this outcrop (Fig. 8). A sand bed ofO.5-1 m in thickness containing many of the basement lithoclasts is intercalated in the middle horizon of the outcrop, and between the base ofthis sand bed and the upper horizon about 6 m above, OPerculina and C!cloct"Peus are abundantly yield- ed. Therefore, the writer correlated this part with the A Member of the Upper For- mation. Both the A and B Members decrease in thickness northward (toward right in Fig. 8), while the biolithites of the C Member increase in thickness. Biolithitic lime- stones intertongue with the bioclastic limestones in the Lower Formation. The sedi- ments of the Ryukyu Group are dislocated frequently by faults in this outcrop, while a plane of about 75 m above sea level is developed which uniformly cuts these geological structures. TAK-1 TNC-2 TAK-3 TAK-4 a- clv, 75m 74.Sm 7asm 71Dm YAM-1 YAM-2 YAM-3 YAM-4 YAM-5 o eht." 32.0m ss.sm 24.Y! 25.0m eÅëh- -9 .r- om 26Sm c c e ;si-¥.L}i ------e"tl ..4 eE)- LS-e i4 ------B e e B-- 14.}¥!"-s¥¥ "t?1q.,'itotA" EAST CHINA SEA -::'=-----Sse . -- Bt- bo B :..L v-..-`"f"'X. ett B A tFt t- ygme.Zll'el9?" pi ra A ----r . -- J-- ot tTt A Llillmada ot #!¥-l o-o--t- 9g.Ll ./ i-`e A -sv w¥"¥ .e.,e .vh¥¥,:- 1¥:¥¥ tt e..t ,/ f2 A "L A ."sf A 'T ¥y.'¥i.ls, p.s/'/ f "t '.L).e' /e/./) ttt tiLht"t L ,"-L¥ ;t't Takovame L }'j ''' t" k`1"A-iirt-i L1¥H6.s Habe Center eL) '6S. ;.11.:1 t!s .tl' l.fi'l}i¥¥.1. i"'h" ':'i'tLt" .o¥ t)v' ei t)ttt V"M .?L" l' ll . L h =." tt.Yl,1g"= ..--.. Llt ':'SiZ,. L L n:Dljtttie .lc... oaj/ooom ri-./ Afii-e t., rc ,' ... to 'lt t. {¥i-1¥1¥,;¥ -21 .t-. --e"" "n -l. toL -ttt c AAIe IZ;1-¥ m"t klC) "tl -i.,l Art"A o s- dt.t" 20 g)" 1"x,rs' a-i i`i L g: ii gs L ,)oe s [l.L `JIA ii¥,7i E. '{" ? ge som- " 30 TAK-1 8 r¥'"e¥.tl,ti.tt.e,f./¥, YAM-3 3oM- YAM- ls bo "L ¥Sv -. v Sp t.tes the" 1e.s:...... 'e i'l.,r-.."-. 10- '1';'tt¥Z:¥t"-i,.[i¥./i:s/"¥ .e" ..x -.' )---- -' t- gÅë. "t :tb"ais}s";It-isir-i-=r'-s:LlL.rit,.. N pt' n -e- "i. "i ¥' 20- .AMYAM-5 s.:.;"i-.l''s/'.¥//¥.,..:..L..r.:;..-,irxgTk fii-sst iii.ili-:11i,,llS¥3¥l;,f,:it¥ii'ii';'i",¥'ii/Fi,11i'i/ili.Ii"igl,/11¥.i/l¥¥.I,,l-ll/'iill.,llli-1111'll-l'il.i,.,g,,tth;'..':':J:'.{'i.1't"1,';t/.i].t'/V:.:l:.'::li'vti"txt.'.-J O tO 20 30m .er. ts lo- Ln -2-spt-gs-.t,.o- o le 2o 3om Fig. 8. Sketches and columnar sections of the outcrops at Takoyama (TAK) and Yamada-onsen(YAM). , 'K 4ox, x i/ Va ' x, " h..,.m X'7o. 'A.' ' t¥ t/. .t ltt i/ YOMITAN. '¥.. ' ' Vi-N,,t t"t/,t.. 'ttx t'"' t. 1 1, n. 'k L-",,,, x, . pS x 'c. CoraUinebiotithite g o. tt ttt ttttt "Oe x...t .. anditsc{astics 1 ' x a' ) or.Y x rr. nile,,, 'I ca H r e.. I -" ' ,sl-i .sb 'j PA i 1 't OL,, ] 'e" el ;.. s esi -; : 2 J ¥1'1 ( Uc n: x t:. -it L l -Lfl v t O.., , .:tt t 100m itt eoO t' -- S .. ,¥f,.., 1 ts i e s"LL N t. ;- rr.o .'i "" t' BeddedclasticLs. npt N'; / .e' 'r1;l"'i's'.itii LEGEND --' N 't'." 'ttt E)} x.. 'x'x.. withbiotithitetense $ -- N N rp .- k Ceraltine bioLithite 0 o ",' r'¥. ll: ee and itsclastics Ok;nowa illLSIrpf.,2seFk . s ouar a-.¥ ¥t h. tL- "pt E eorutthe bbiithite Lertse i ' "/ "t -in N 152 Katsumi TAKAyAsu 8. Yomitan The limestone quarry ofYomitan was designated as the type locality ofthe Yontan limestone by FLiNT et al. (1959). The writer, however, regards most ofthis limestone in this quarry to the C Member of the Ryukyu Group, notwithstanding its large thickness (Fig. 9). Therefore, it may be concluded that the Yontan limestone of FLINT et al. is synonymous with the writer's C Member in this paper. At this quarry, the writer observed the conformable relation ofthe C Member with the lower beds. Therefore, it should be discarded to postulate the presence of the unconformity between the Yontan limestone and the Naha formation as pointed out by FLiNT et al. (1959). Near Zakimi Castie, the northern part ofYomitan Village, the coralline biolithite overlies unconformably the noncalcareous sand and gravel beds which are correlated with the noncalcareous sand beds ofthe outcrop ofYamada-onsen. On the other hand, the coralline biolithite seems to be corelated with the C Member. The stratigraphical relation ofthe local unconformity between the Lower Formation and the C Member of the Upper Formation is similar to that in the eastern part of Motobu Peninsula. 9. Makiminato Well stratified calcareous sand beds and bioclastic limestone with numerous quartz grains are distributed in Makiminato, Urasoe City. They are rich in mollusks, bryo- zoans, echinoderms and brachiopods, and similar lithologically to the Lower Formation of Katsuren Peninsula' and the southern part of Okinawa-jima. Besides, though it is hard to approach the good outcrops ofthe Machinato limestone ofFuNT et al. (1959) in this area, as already mentioned, a few small outcrops ofthe cross laminated calcarenite can be seen in the former foreigner's residental district nearby the shore. The limestone is similar to the Minatogawa Limestone having abundant foraminifers and intraclasts, but the grain size of the former is finer than that of the latter. C. Discussion As mentioned above, for the stratigarphy of the Ryukyu Group, the main part of the "Ryukyu Limestone", the writer's division is shown to be available everwhere in Okinawa-jima, ifsome local differences in lithology are disregarded. Thus, the writer's Ryukyu Group is considered to be approximately eqivalent to the Naha formation plus the Yontan limestone formation ofFLiNT et al. (1959). In this sense, the algal limestone beds of the horizon marker by FLiNT et al. (1959) and SHoJi (1968) seem probably to be equal to the B Member in the writer's stratigraphical division; even though, the algal limestones are also recognized in other horizons ofthe Ryukyu Group. In addition, the local differences of the mode of occurrence of fossil algae and the lithology of the B Member make it diMcult to discriminate definite horizons ofthe algal beds stratigraphi- cally. Neverthless, the C!clocl2Peus-OPerculina swarm bed is usually recognized as one definite horizon everywhere, with remarkable petrographic characteristics. Table 4. Tentative correlation of the late Pliocene and the QLuaternary formations of the southern half of the Ryukyu Islands a=e-e 0to,cC OKINAWA YORON KUMEAGUNI MlYAKOTARAMAISHIGAKI TAKETOMIKOHAMAIRIOMOTEHAT YONAGUNI (SHtNOHAHA&KezAKp pS Kunigami Motobu Nakagarni Shirnajiri cr (ro-30)'imeLsh (201"Awaislii'LIike (20-30}--Ybsiiiwata4s {15-20) (20-30) (20)'imlit. t20¥30) (20-30) oo 'OharaL.s. (20-30) "5-20} [30) B Kyodaterrece MSnetogawe ShirTx)ji-jima btomiL.s," 9 L.s.F. Ls. Ls. PanariL.s. 6 {60) (40-oo) (40-60) (40-60) (30-50) t30-50) C40-501 (50-60} C45) f40-so) C40} g mZmoobm-mAm t55-oo) (oo} : {BO) 75 .U[1, Åëinner g coratline coral"ne 1corellinebieclasticLs. coralSine L' c corattinel.s. abiolithite Ls. i,s. HiraraL.s. ut1inet,s. L' Ls. o "- )feeie$ . tr. ' co Loaa= j=Lenre,Exo- U;'inner aigalhaII meliuscan Ururo Loaa= brecclated : BA obielitNte-facies end dij¥:oEFO Upper Ls. algelI,s. l.s. eoralline L.s. algelbetl1.s. p .8E bioelastic E :T - .misS(i ---- qyokutypevs outer Amagawa Ls. pt clasticLs.f. ei: CrctoCtvpeu ewrcultna percuhne Crctec+rpeus CycteCtypaul Middle L.s. CycbeJvpt"s Opercutina sand,gravel cla ------browny B ul terrigeneous elgelbell biodestic corelline LL'pebt"e- bieelasticI.s ul "po sand. bioclastic emdfo(am coralline Ls. Le)oJ granule bioclestic rt Levver ? LÅëloJ Uoctastic --- ls bieclasti'c ealc.sand gravetI.s. LCORgl G-vei Ls. m olectasticts.f. Ls. o Tpt Bunera g eaic.sen sandysilt BoraL.s. clay g N sendysilt tr- gpo Nskeshi5and ChinenSend tL rv rv ? e:Higas vpo tio:N ke IM lm Im t'i con9la GegaGravel Sh;nzetoTuff SonaiCongle. := conglo, v q Elr-utpt ? YonaberuF. ShimajiriGroup p eea 154 Katsumi TAKAyAsU Further, the continuity of the ClcloclJpetts-OPerculina bed is verified by the writer not only in Okinawa-jima but also in other islands of the Ryukyu Islands. Therefore, it is probable that the stratigarphy ofthe "Ryukyu Limestone" established in Okinawa- jima is applicable to so-called "Ryukyu Limestone" in other islands throughout the Ryukyu Islands. In this way, the writer compiled the stratigarphy of "Rhukyu Lime- stone" in a correlation chart ofTable 4 on the basis of his data together with others. IV. Sedimentological Study of the "Ryukyu Limestone" In order to consider the sedimentary environment of the "Ryukyu Limestone", the writer made petrographical observations and fossil analysis on the samples of main outcrops and drilling cores under the optical microscope. The results will be described below briefly. A. TexturalComponents The fundamental textural components ofthe "Ryukyu Limestone", are classified as follows: matrices, framework grains (allochemical grains or allochems, by FoLK, 1959) and pores. The matrices in the writer's usage imply not only the microcrystalline calcite ooze but also sparry calcite cement. They are easily distinguished from each other under the microscope. Although diagenetic fabrics are observed in some cases and seem to ex- plain only partially the hysteresis of the limestone, the writer could not find out the pertinent facts on this point. The constituents of the framework grains are occupied by skeletal grains of fossil for the most part. Besides, the presence oflithoclasts and quartz grains ofthe terrigeneous fragments are confined to some specific horizon ofthe Ryukyu Group. On the contra- ry, it is characteristic that the Minatogawa Limestone contains well rounded intraclasts abundant and sometimes lithoclasts of the Ryukyu Group. Pellets are rarely found, and oolites have not been found yet in the "Ryukyu Limestone". As for fossils, though it is necessary to distinguish detrital skeletal grains from ske- letons in situ, it is almost impossible in practice to discriminate them in thin sections. Therefore, the writer discrirninated the clastic limestones from the biolithites on the occasion ofsampling, and made an anlysis in the laboratory only for the former in order to know the constituents ofthe skeletal grains. B. MethodofFossilAnaylsis Even though the skeletal grains which constitute most of the "Ryukyu Limestone" are supposed to be detrital, they play an important role in the inference ofthe sedimen- tary environments and also in the accurate correlation of the stratigraphical sequences. From the viewpoint stated above, the writer tried with his colleagues to establish the method for the recognition of the skeletal constituents of the "Ryukyu Limestone" more objectively and quantitatively, as far as possible. Consequently, two methods "Ryukyn Limestone" of Okinawa jima, South Japan 155 used here are condidered. Though these methods connote many problems to be solved and improvements to be made**, it seems that these methods contribute to objective and quantitative studies on the skeletal consituents of those materials. Method-A: Counting each skeletal grain as one unit, and after summing them up the composition of each taxon is shown by percentage. In order to keep the stability in the analytical value, the total nulpber of skeletal grains should be counted more than 500. Though the amount of indeterminable ske- letal grains often reachs to the value more than thirty percent, the outline of the quanti- tative distribution of main taxa can be known from the determinable skeletal grains. Method-B : Using a mechanical stage, move the thin section sideways and forwards and backwards in equal distances ofO.2 mm each, and identify constituents juSt under the cross hair. Then summing up the number of the points, the composition of each constituent is shown in percentage. In this method, all of the constituents including pores are calculated. But at this time, as the problem on the origin of the pores is still unsolved, the proportion to the value subtracted of the point numbers of pores from the total count is substituted as the approximate proportion of each constituent, By means of this method, the ratios ofthe microcrystalline calcite matrix, the sparry calcite cement and allochemical grains which are fundamental components for petro- graphicai classification oflimestone, can be represented by numerical values . There- fore, this method can be applied to the fossil analysis as well as the petrographical des- cription. For keeping the stability in the analytical value, the total count is recom- mended to be more than 1,OOO points in the case of the calculation of those three com- ponent ratios and more than 2,OOO or 2,500 points in the case of the examination of the skeletal proportion. C. Discussion The results of the analysis are summarized in Fig. 10-15. Only SHoJi (l968) has carried out a study on the microscopic petrography and sedimentology ofthe "Ryukyu Limestone". Though it was conventional SHoJi stated that some sedimentary subcycles are present in each limestone ofgravel, sand, sparite, sparmicrite and micrite succession, and there are three cycles in the Naha limestone, two cycles in the Yomitan limestone, and one in the Machinato limestone. ** In Method-A, it is impossible to denote quantitative comparison among different sel¥mples in the strict sense, because there is a certain difference in the amount ofskeletal grains in each sample. In the case of the "Ryukyu Limestone", however, this anxiety can be negated, for the s'keletal grains show high occupancy in most samples. In Method-B, there is suspicion that the large fragments show a large value of proportion, because the value of the constituent proponion obtained by this method is cal- culated as the ratio of area. Furthermore, as for both methods, all skeleta! grains are regarded as objects having equal valuation whether the grain is broken or not, because the observation is made only on one section of each skeleton. Therefore, the analitical value may also be affected by the differences in the structural intensity of the individual skeleton. - ¥ 156 Katsumi TAKAyAsu ALLOCHEM (a) GRAINS N=179 . e. . . .: :e-- , -- . --et -- e- . :e .: --. . --"t"-. ---e t"'tt"t""':" . e- e-- "1 --. . ::e re t-: . . .ee MICROCRYSTALLINE SPARRY CALCtTE CALCITE MATRIX CEMENT ALLOCHEM (b) Okinawa-jima GRAiNS N=35 o MhatoDcpNct Ls. kyukvu Group A o eMe"sber "''''--'"--""'"' VPPerE A - AMembtr -o A Lewtr Formation A ee A eo 5 A"A Oo A . A A . MtCROC V5TALLINE 5n4RRY CALCITE CALCITE MATRIX CEMENT ' ALLOCHEM (c) GRAINS Kouri-j ima Ns,6e mCMemberT eBM"mbtrtUFPePr:ation A eAMember1 aa A Lewer Formation Bn es A . A o Fig. 10. n A Triangle diagramg showing the pro- atp noAAo A portion of three fundamenta1 com- a eV eO A o ponents. (a) All analyzed samples A- . n D - a (b) Sarnples of Okinawa-jima (c) A Samples of Kouri-jima. oop MICROCRYSTALLINE SPARRY CALCITE CALCITE MATRtX CEMENT SStseigigLQLpms Fo rami nifers o 50 foo o 50 1OO M 26 16m Ub Ua 25mma Ua - r El ml L Ua -. ;-- :i-: t- .- L . tr: . 'i)" ':I); t- : .- .- ---- ¥T.: r.¥ - --tt '..r--t :f' l: T:'¥. - :.L tt tt-t t-. ' -¥ .' sre --- s=:..: ;'";!il¥, ----vt Å~ ----e---- tt- MB-3- .t tt 13.8m ------.L - I',;,f¥'ii¥¥,¥,:,tl¥'l¥ - ,. ------Ua 'N. :-- , -. :---- t-t ' -ttt t. r i,L/t¥r,l{- ---- ' t, ttl "' t'I' E .:. :- :tl:. ttt- ---- ;- 9 tt - -... Nts -tt "'¥/z:.,:.t:;.." s,. . ttt 1.' MB;gL -:¥:.:,r.s, E pto S Colcareous algae(Corallinaceoe) Eii!!i Plonktonic g Foraminifers .E opercult'na g Bryozoons E c)tcloclLvpeus :':.;.:¥'i:i,r.:¥:/i.:.:',;s. Echir)oderrns ge Amphistegina ' MoHusks g Calcarina aOthers eAcervutt'naEEEEEEII Homotrematidae EEI Massive Iirnestone "'i¥i.L:;':.: Catcareoussand l¥l'::'i:tr;,':ee't:'IS-{';"¥ Soritidoe IIil] Loose timestone :t.:.,,;.i: Terrigeneous sand,gravel Arenoceous ,. .- -J a others Fig. Il. Diagrams ofskeletal components ofsome columnar sections in Motobu Peninsula (analyzed by Method-A). -- ' N , KOURt-JIMA . Bise ..:.. . :l::.::: : :-- . .B3. ... '.... !:1.B.2.:il:: ¥ ::: '// t - - :: - -:li:--i. B4 XM26z"s./.,/,,..,,, M le ttt ''fi' t/tt } t/ ... ttt. ..t..{ ' .. t. il. •,• Åé •••• "'f'' .¥ Nakason.e li'ten XM5 : N"t Terrace deposlts IZZ!]gravel EIIIIIIItimestone i E Ryukyu Group E Upper E es 1km :. Lower F. E::] timestone E[EXIcaicareous sand B Akk#:;gbeE 2 s : o: Oe Biofacies Foraminiferal assemblage o a: -" p ------} -- .- po CF-A) kel : t -- :- E t:t:: -tt--- e . t- t- -- ] Il'::¥1:::,1¥f,','.': ',:,l¥1:1¥1'.:,:' :'.:'1::i-r¥ {ifi6b'/'i"sl'.-.i'r -':tL.t4 -po - t-ttt Y"tu"'-s- -t ---: :-i --: -: -- --: t- s.,tf.i::.' -pa=tix':n"tt:l -):h,"I.:t- 9 -s -"---- ' -- ' (Ac¥H) m CF-A) -- c------H-"- 2 nv 1 -LL -- '- H--- e L-.-' -- cis' =- ' --= -- -- ' - -- g CAm¥Ca)r.1=..-re'-tL..T.tmtTLL " :LF-B)------: ---- CF-B-E) m- -- ttt - y////x ------u. tmt -.....--tdt--.- N-tu-- tt ------ Arn'A-tphisteg,!nlg Ca CgLgpm C) CycÅ}n,ririypegs. (1 ) Sand and gruvel (2) Calcareeus sand (3)Terrigeneous F, Forwrinifers B /Bryozoans E/EChinoderms Hcnr,o:refixitidae fragrnents bearing ctastic timestone (4)Fine qained A/ Calcareous aLgae CCoraLEnaceae) Op¥ OpRcg-LIDg Ac,Acervut[na H massiye lirTvestone (5}Loosely hrecciated timestene P: Plaakton[c foraminifers Fig. 12. Geologic outline of the northern part of Mobuto Peninsula (above), and lithological and paleontological correlation among the sections shown in Fig 11, (below). - . sua 158 Katsumi TAKAyAsu e - --SZ-----!SS7-J-t-J -- llX. It lntTi' T- ---J t2-!w,'twli41il ¥Ti - ;.sMT., ':"T-- - - pt .l 'l' iL ITA-"J ¥' [-i' -TI iF f fi ,/ 1l 4"7,4 pt 1 1 1[1 i ill em ylIi " ¥, ] 1¥ I pt 11 ! IIi, hLYfi r¥ - ., il 1 lr l' il i l,,i ti r, :Ll ¥1 l i'jvI' i¥ l-!1 Il i ' il 1 tl' "1t/ 1/ } f ' -i-i' I' [ gs G--deqic octtine ' t'-tt .L-''if' o' t ic- ]Xlte: EG' --- LowerE [EE] itRt:.Tg?ts o soom MATRIX !Gl!gL!-Ebg2g-&-m!Lsgrainsh a e y]-.{V) ," IJil:g e,,e...... ,¥¥ .L :il.'1 ss ,:ii'i"' V '" /.,i/,E,iLl,g>,k :," -' ii''/' /,/ f" ./ii''' ,Xt i: '' x 'ii' ' )! t/. t .t/. t// t /tt e .- -l ll/,"It'1 t. tttlttlt// gttttt ILtis I"' /tt t/ t //. / ., ttt 1/ t/ "" x //1;", " ,/ t. i ::¥)'i' tttt/,/t t Q "i,,tt x, ¥ii,,R t ':'j K .),?-IliXi;rL'>f'. . III' ,K v " ii':' ttttt t ¥,1/., / i';" t/l:' ' ttt' 'l";Ei;I-.[Z'(' //.tLJ"/"..,,,fx .s . 't i'7 Eg- 5A ' i,x,Cgelssr63"2:,Ol) /t% ' O.pa,,rc,VS',,",,., YY"tl//1-11/it,oOill A.m,p,7J.sfg,'"a5*,O,'cHeg:;"g;7smatLdae t CO-i25-O,25) eenthonic farorninifer oCg-O,125) 1'' cornposit[on ' ' Fig. 13. Distributive patern of tteach ' component of the Ryukyu Group of Kouri-jima. (a) Matrix and shape and size ofgrains. (b) Skeletal components (analyzed by Method-B), Calcareous algae Halimeda Planktonic foraminifers Benthonic foraminifers (Corallinaceae) 7,.,l.iSl,.:ll.lliilk,,.L.itLg.k),,,,.N o -'' .,,,--.le,¥¥e¥g ¥,,-,,¥¥ ¥ -s¥ ss '' be. . tlt . t- ...... -..t. t".t.. i SX.? x pa: "" t' x.e''' P XI ,'e }1 xl t/"k,, ¥< [' 41'' '::"' g /t. ¥tt, .1. E ¥itt 1./ x. /tit tt tt¥ t"t/ :¥ 'le,,., ,C x. ,; .,.: N.. >1 '1" '1'i '' t" s I;t.) .',.)x -/¥t. ' 't. 2 7Y -9 o- g < : o. o 5 : po Corals Bryozoans Mollusks Echinodertns E v . e: ' B scIXk>r% .o iaG7 -pt r ss -- .e-'' 9¥ ,,. ¥; M s .. .tttttt )pa e ge ./ 'VS --' ',- g k tr x'1¥ -¥¥- !t ttt.tt. ,/.' c.,'., pt ,1i,1¥ eji'i'' g sx8 o tt// ttt f(,' x,J' X i ft x vpo l,i,' Q e ' ee R,iiii¥i¥i x -s p t.t.//'.1. tt e -tt ' i:- X,4N¥-fi{L ox 'tC, tt X, e e "'li illl 't"' Xe .tb' e $ t/tX ts 1 e Å~• ' t/!¥ ,"}¥ .t lt" ,' 'N X. -t i ) :' x -X ! K ' / tt lttt x. N G Fig. 13. (b) o 160 Katsumi TAKAyASU AtgCit ForBlt 3, fS.'5.: Corlt Brzlt aAtgHlt(detied) aFerPltcdotted} Mo[tt Echlt t. {: t/ 'i t.. 2 To.t ,,t ¥1 .a tt t:1:E.t. t't' :'I'¥i,.i le I¥'l¥S'./{ rl.t'.'trI"IriS.l t..t 10 ttt .. - tt H,g i l'li tt l ttt tt/ ¥ill ¥1 tt .,¥ T¥li'tt':' o t-'.l ro I Å~ /r / t t ' U;nB ' ' ' ¥il,- ¥' j t g-l¥ e t tt I x H,-,A i li / N .h l¥l{ ...ttr..'i' O1" IU rvVVI .UX O1lt Å}111yvv/e b11 tN lv) vlrX1twu e1IX lix t" )VVV" V"V lrX Ob" ldb lVvvt ml vl lxX Fig. 14. Stratigraphical distribution of the skeletal components of the Ryukyu Group in Kouri-jima. Lateral axis shows content: O; less than O.1250/., I; O.125-O.250/., II; O.25-O.50/., III; O.5-1O/o, IV; 1-20/., V;2-4%, VI; 4-8%, VIII; 8-160/,, VIII; 16-320/., IX; 32-640/., X; more than 640/o to total counts without pores (t). Longitudinal axis shows frequency. AlgC; Corallina- ce2e, AlgH; Halimeda, ForB; Benthonic foraminifers, For P; Planktonic foraminifers, Cor; Corals, Brz; Bryozoans, Mol; Mo]lusks, and Ech; Echinoderms. SHoJi considered the formation ofthose cycles as the reflection ofthe developrnental process of the coral reef controlled by sea level change or tectonic movement, and re- garded the microcrystalline limestone as product of the last stage of each cycle, that is, a stagnant shallow lagoon environment. As mentioned formerly, MAcNEiL's stratigraphical division on which SHoJi relied is different from the writer's. Therefore, it is diMcult to compare directly SHoJi's work with the results of the writer's analysis. But, on the constituent of matrices, to which SHoJi paid much attention, the following facts must be pointed out from the results of the writer's analysis. (a) In the matrices of the "Ryukyu Limestone", microcrystalline calcite is the dominant constituent in general (Fig. 10a), and the typical spartie is observed to be limited in the Minatogawa Limestone and a part of the Ryukyu Group (Fig. 1Ob, c). (b) Even in the same horizon (for example, in the B Member or in the C Member "Ryukyu Limestone" of Okjnawa-jima, South Japan 161 ofthe Upper Formation ofthe Ryukyu Group, shown in Fig. 1Ob, c), the constituents of matrices are variable in accordance with the difference ofsampling point. (c) The A Member ofthe Upper Formation ofthe Ryukyu Group is represented generally by microcrystalline limestones (Fig. 10b, c). From these facts, the writer does not agree with SHoJi's opinion that the "Ryukyu Limestone" consists of many sedimentary subcycles. According to the writer's con- sideration, the Ryukyu Group itself, the main part of the "Ryukyu Limestone", is a product ofa Iarge sedimentary cycle as a whole. But in general, in this large cycle, there are small two cycles which are regarded as corresponding to the Lower and the Upper Formations respectively. From this viewpoint, the writer gives his consideration to explain the sedimentary environment ofthe Ryukyu Group. 1) With good correlation between lithofacies and biofacies, the sedimentary facies of the Lower Formation varies from place to place. For example, in Motobu Penin- sula, as shown in Fig. 12, the biofacies change from [foraminifers-bryozoans-echino- derms] to [foraminifers-bryozoans], and [foraminifers-calcareous algae] in parallel with the change oflithofacies from abundant terrigeneous fragment situation to poor ones. 2) The correlation between lithofacies and biofacies mentioned above can be R b y.g tsbu ti Rg ts= .b GV "8- b .9oE o "sC" ts g.. O y- l g F XB D A abundant Fig. 15. General tendency of the stratigraphical distribution of skeletal components and terrigeneous fragments, on the basis of field observation and indoor anal ysis, 162 Katsumi TAKAyAsu generally ascertained in vertical change (Fig. I2) as well. It suggests that the sedi- mentary environment of the Lower Formation changed from the sea unfavorable for coral reef forming to those of favorable. Actually, this is attested by the presence of coralline biolithite at the top horizon of the Lower Formation. Uc ¥xt UB UA U-L Lu LL Fig. 16. Schema of the sedimentary process of the Ryukyu Group. LL and Lu are the stages of the lower and the upper parts of the Lower Formation respectively, and UA, UB and Uc are the stages of the A, B and C Members of the Upper Formation respectively. U-L is the interval stage between the Lower and the Upper Formations. Showing the imaginative section in Central Okinawa, E-W trend. "Ryukyu Limestone" of Okinawa-jima, SouthJapan 163 3) During the deposition of the A Member of the Upper Formation, the sedi- mentary environment turned to those of unfavorable for coral reef forming. This inference is based on the fact that confined species such as C"clocl2peus and allies of deeper environment are chief components of the biofacies of the A Member and are rich in number as shown in Fig. 1 1. As for the A Member, some other characteristics were already mentioned, and they are as follows; terrigeneous fragrnents are often contained in the lower part of the A Member, and the thin layers of terrigeneous reddish brown clay are sometimes intercalated in the OPerculina swarm part, and C2cloclJpeus are often yielded in swarm immediately above the OPerculina swarm part. These facts suggest that the coral reef environment deteriorated rapidly due to the inflow process oflithoclasts and residual clay from the land area, and the increase of the depth ofthe sea. 4) In the stage of the Upper Formation, the area ofsedimentation expanded ra- pidly more than the Lower Formation as mentioned in the former chapter. The fact that the uniform stratigraphical sequence of the Upper Formation is tracable in wider areas than those of the Lower Formation, suggests the advent ofa uniform sedi- mentary environment by transgression. Succeedingly the sea became gradually shal- lower after the A Member stage, and then in the C Member stage, the typical coral reef environment was initiated. This explanation is supported by the increase of Coral- linaceae and the decrease of bryozoans upwardly in the Upper Formation, and the rapid increase of Halimeda and corals in the C Member (Fig. 13, 14). The decrease in the number ofplanktonic formainifers towards the upper in the Upper Formation (Fig. 13, I4) also suggests the environmental change from open sea to reef. The stratigraphical distribution of the fossils in the Ryukyu Group is shown sche- matically in Fig. 15, and the environmental changes during the sedimentation of the Ryukyu Group are shown in Fig. 16. Incidentally, the Minatogawa Limestone Formation is considered to be the sedi- ments of an extreme shallow environment affected by constant wave action or a sub- aerial sand beach environment in part, because these limestones are represented by sparite and all grains are well rounded without exeption (Pl. 16, Fig. 1). V. General Discussion on the Quaternary Geohistory of the Ryukyu Islands A. Age of the Ryukyu Group There are very few reports of fossils available for determining the age of "Ryukyu Limestone". But the following discussion will be possible. YABE and HATAi (1941) reported the occurrence of AmussioPecten praesignis and Pecten naganumantts in the "Ryukyu Limestone" in Naha City. Though they described 164 Katsumi TAKAyAsu these fossil horizons with uncertainty, it is probable that they were yielded from the Lower Formation of the Ryukyu Group in the writer's division. In Honshu, A. Pra- esignds is known from the Pliocene and the Lower Pleistocene, and P. naganumanus is abundant especially in the Lower Pleistocene. Therefore, these mollusks support HANzAwA's opinion (1935) that the age ofthe "Ryukyu Limestone" is Late Pliocene or from Late Pliocene to Early Pleistocene. On the other hand, the uppermost part of the Shimajiri Group, below the Ryukyu Group, is considered Lower Pleistocene according to the latest micropaleontological works. As for the planktonic foraminifers, NAToRi et al. (1972) reported the first ap- pearance of Ctoborotaria (Gtoborotaria) truncatutinoides from the top of the Shinzato For- mation (upper Shimajiri), and IBARAKi and TsucHr (1975) reported abundant occur- rences of that species from the Chinen Sandstone (upper-most Shimajiri). On the cal- careous nannoplankton, NisH:DA (1973) recognized that Clclococotithtts macint2rei and Discoaster brouweri range up to the overlying Chinen Sandstone. He described the ap- pearence of GePh2rocaPsa oceanica from the Nakoshi Sand Beds. These reports suggest that the age ofthe Chinen Sandstone is the Early Pleistocene¥ Therefore, it is certain that the lowest horizon of the Ryukyu Group does not go back to the Pliocene. Several vertebrate fossils have been obtained from cave or fissure deposits in the "Ryukyu Limestone" (Table 5). Among them, Metacervulus astylodon is most abundant, and is regarded as an important element of the paleovertebrate fauna of the Ryukyu Islands. M. ast21odon was also reported from the Lower Formation of the Ryukyu Group of Ishigaki-jima (FosTER 1965; OTsuKA and HAsEGAwA, 1973). The "Muntiacus" that occurred in the basal part of the Ryukyu Group (SHiKAMA and OTsuKA, 1971) is con- sidered to be identified as Metacervultts astylodon, too (OTsuKA and HAsEGAwA. 1973)¥ According to ToKuNAGA and TAKAi (1939), M. ast21odon ofthe Ryukyu Islands and M. kendengensis, a member ofthe Trinil marnmalian fauna ofJava, are both the nearest desendants of M. caPreolinus which occurs in the Yushe Series (Zone II and Zone III, Villafranchian equivalent), South-Eastern Shansi, China. And they considered that M. kendengensis is a relative of living muntjacs of Southeast Asia and Taiwan, while ex- tinct M. astllodon was the insular form in Ryukyu. Based on their opinions, the lowest horizon ofthe Ryukyu Group deduced from M. astltodon may go back to Early Pleistocene. The elephantoid molar teeth discovered from the cave deposits ofMiyako-jima and from the "Ryukyu Limestone" at Kyan-misaki, Southern Okinawa, are also worthy of notice among the vertebrate fossils in the Ryukyu Islands. Hitherto, two specimens have been discovered in Miyako-jima; one was reported by ToKuNAGA (1940) as a molar of Pataeoloxodon namadicus or ElePhas trogonterii and the other was reported by OTsuKA (1941) as a molar of Palaeotoxodon?. After the re-examination of the site and "Ryukyu Limestone" of Okinawa-jima, South Japan 165 Table 5. List of fossil vertebrates of the Ryukyu Islands Mammalia Rodentia DiPlethrix te,gata (THoMAs) Miyake-jima (Amagawa and Tanabaru Caves) Okinawa-jima (Minatogawa fissure) Artiodactyla CaPreelus mi akoenst's OTsuKA Miyakorjima (Amagawa Cave) CaPreottts sp. Miyakorjima (Tanabaru and Nakabaru Caves) Metacerr,ultts astylodon (MA rsuMoTo) Miyako-jima (Amagawa Cave) Ie-jime (caves) Okinawa-jima (fissures and Ryukyu Group) Ishigaki-jima (Ryukyu Group) Proboscidea TriloPhodon sp. Miyakorjima (Shimajiri Group) Palaeoloxodon or "Archidiskodon" Miyako-jima (Tanabaru aave) Okinawa-jima (Ryukyu Group) Reptilia Chelonia Tetudo cf. emvs ScHLEGER et MuLLER Miyakojima (Amagawa Cave> Okinawa-jirna (caves) Clemm)s cft rrtutica (CArgToN) Miyako-jima (Arnagawa Cave) by the articles ; ToKuNAaA and TAKAi (1939), ToKuNAGA (19. 2K)), OlsuKA (1941), FosTER (1965), OmsuKA and HAsEaAwA (l973), HAsEGAwA et al. (1973), NoHARA and HAsEGAWA (1973) the photographs of those fossil molars, KAMEi (1970) suggested that these were "Archi- diskodon" rather than Pataeoloxodon. The fossil horizon of Kyan-misaki is the B Member of the Upper Formation in the writer's dividion. NoHARA and HAsEGAwA (1973) identified it as a fragmentary molar of Palaeoloxodon? sp., but they stated that the possibility of "Archidiskodon" still remains. If these elephants are "Archidiskodon", it is possible to correlate the Ryukyu Group with the upper part of the Osaka Group and the upper part of the Kazusa Group. The highest horizon of the Ryukyu Group, therefore, is considered to be Early and early Middle Pleistocene. Additionally, it was reported by SHiKAMA et al. (1975) that the Cho-chen fauna of Taiwan, Early and Middle Pleistocene in age, is represented by Mummuthus armeniaczes taiwanicus and ElePhas hlsudricus. The relation between the fossil elephants of Taiwan and the Ryukyu Islands is a very interesting problem. Based on the paleontological aspects mentioned above and the geological relation 166 Katsumi TAKAyAsu between the terrace formations and the Ryukyu Group, the writer considers the age of the Ryukyu Group as Early to early Middle Pleistocene. It may be possible that the Ryukyu Group is correlated with the upper part of the Osaka Group. After the general report of Th230 -Pa2Si ages of the "Ryukyu Limestone" by Ko- NisHi et al. (1974), all measured values are included in Late Pleistocene. But it seems that these values are inconsistent with paleontological evidence and the results of the geohistorical considerations of the Ryukyu Islands mentioned below. B. "UrumaCrustalMovement" Many faults caused network dislocation in the Ryukyu Group, and consequently, many tilting blocks are formed (Fig. 7). In so far as Southern Okinawa area in con- cerned, the C!clocllPeus bed is distributed in various heights from near sea level to about 155 m above sea level due to such dislocation. Covering the area from Central to Sou- thern Okinawa, a dome structure with a long axis ofNE to SW trend is confirmed (Fig. 17), which is called the Nakagusuku Dome (FLiNT et al., 1959). The fault system of these districts is supposed to be urdergone through the destruction process of the Naka- gusuku Dome (KizAKi and TAKAyAsu, 1976; TAKAyAsu, 1976b). The fault system which dislocate the Ryukyu Group are also developed in Miyako- jima and Kikai-jima, and those structures are clearly recognized from topographical features. In these areas without exception, the thick Shimajiri Group exists below the Ryukyu Group. This fact suggests that the tectonic movement such as dome forming and the fault system development is closely related with the extermination of the sedi- llllllif1((S diXs, K2,.e,,,,,i//,,//,I/i'i'¥i/1/l'l-liii/illil"i,'i,''kl'i''''' 'Xgek @ 1, ' ./PENINsuL ,.1./.,,i;.,,,/Si,/1:,.l./ .1 e " tt /it/ttttttttttt t"ttt 1 / g Fig. 17. Structural outline of Central and Southern Okinawa (TAKAyAsu, 1976 eAv b). 1; "Rynkyu Limestone", 2; Shimajiri Group, 3; Basements, 4; General structure of the Ryukyu CHINEN Group, 5; General structure of the lliiX.ii f Chinen Sandstone, 6; General struc- 4 ture of the Shimajiri Group, 7; Axis of the Nakagusuku Dome, 8; Fault. 5km 1 3.[E] 7. >< 1 8. lt E' 4.Y 5./ 6./ t "Ryukyu Limestone" of Okinawa-jima, South Japan 167 mentary basin being continued from Neogene time. It is accepted by all researchers that the relation between the Shimajiri Group and the Ryukyu Group is generally represented by an angular unconformity. This relation is clearly observed in the west coast of Okinawa-jima, where the Shimajiri Group in- clines to the east or southeast, while the Ryukyu Group has gentle structure or slightly inclines to the west in direction. In the east coast of Central and Southern Okinawa ' however, both ofthe Groups incline to east or southeast gently. So, it is possible to say that the relation between the two Groups is represented as a whole by an indistinct un- conformity or disconformity. In several places, the Ryukyu Group is successively with- out any marked break with the Chinen Sandstone, as in the cases of Chinen Peninsula and Henza-jima, off the coast ofKatsuren Peninsula, The writer, with reference to these significant relations, tried to explain the conver- sion from the "Shimajiri Sea" to the "Ryukyu Coral Sea". It was explained by means of the shifting of the upheaval center from west to east (Fig. 18; KizAKi and TAKAyAsu, 1976; TAKAyAsu, 1976b). That is, at the close of the "Shimaijri Sea" stage, the upheaval center of the area where was to the west of Okinawa-jima became to be covered widely by shallow facies, which was represented by the uppermost part ofthe Shimajiri Group (LERoy, l965; NoHARA, 1976). Succeedingly, thesedimentary center of the basins was shifted toward the east. As a result, the Shimajiri Group was characterised in having the structure with uniform inclination to the east or southeast, and thus the emerged areas came to be under erosion. Succeedingly, the "Ryukyu Coral Sea" was initiated by the next transgression. During the "Ryukyu Coral Sea" stage, the upheaval center was shifted further to the east, and the embryo of the Nakagusuku Dome became to exist. The local uncon- formity present between the Lower and Upper Formations in the Ryukyu Group, as mentioned in Chapter III, might be the result of that dome forming. Further, the development of the coral reef in the C Member of the Upper Formation may also be accompanied with the appearance of the shallow environment due to the accentuation of the Nakagusuku Dome. Later, after the collapse of that dome by faulting, the pre- sent configuration of Okinawa-jima was brought about. A series of these tectonic movements is called the "Uruma*** Crustal Movement" (OKiNAwA QuATERNARy REsEARcH GRoup, 1976; KizAKi and TAKAyAsu, 1976; TAKAyAsu, 1976b). Taking a general view of the Ryukyu Group, it is possible to say that the Plio- Pleistocene sea of this area went to extinction step by step through the course of the "Uruma Crustal Movement", and the estate of the "Ryukyu Coral Sea" of the last stage is the Ryukyu Group itself. Thought the details of the "Uruma Crustal Movement" will be discussed in ano- ther paper, it is possible to infer that similar tectonic movement had an influence throu- *** "Uruma" means coral is!and in the dialect of Ryukyu. 168 Katsumi TAKAyAsu Kume Tonaki Kerama Okinawa vY (T} : ,saAt l--)t-lst.'; -- x ',tt.q + "+ eea¥. ':. //'ltt' /'..'1/l'/. ,."/t.1 . . {R} vJvNv ,-,A -+ -- --t i`/L/////i/i.,/,/i//il/¥i/.,,-,.///i'//11/l//l///" S'-1¥r g¥/'/g"'i'' -.-S' s, L ' "i'I"" ff z(> clN[Tlu-. . -;+ Cs) v v vv A, : l¥k{¥i- AA ' '1111;/'t/li/i l'1}11: ' E b ..tll,/.l.i.i.. ,.ul¥¥leS.tse;m.tt.-J .¥' -.: Å}. ,x'v w...' IX. .'.'.{ .¥` .' ¥¥¥ ¥ ",f i,-/w¥"¥/,}'/'/l/r/:\/,¥'//l¥,f'¥¥/'ii'l¥ Fig. 18. Schema showing the process ofthe "Uruma Crustal Movement" (KizAKi and TAKAyAsv, 1976). (S) The last stage of the "Shimajiri Sea". (R) The stage of the "Rytikyu Coral Sea". (T) Post-"Ryukyu Coral Sea" stage. ghout Ryukyu Islands, , Therefore, as the Quaternary tectonic movement, the "Uruma Crustal Movement" has a significant position in the establishment of the Ryukyu arc. C. OutlineoftheQuaternaryGeohistoryoftheRyukyuIslands In the foregoing chapters, the writer has come to conclude that the Ryukyu Group, main part of the "Ryukyu Limestone", was the product of the tectonism during Early to early Middle Pleistocene, and not ofeustatic movement alone. From this viewpoint, he tries to make an outline of the Q;uaternary geohistory of the Ryukyu Islands here- inafter. For converience, it will be mentioned in following stages successively. (I) The stage prior to the Ryukyu Group sedimentation, or the last stage of the "Shimajiri Sea" (Earliest Pleistocene). (II) The "Ryukyu Coral Sea" stage (Early-early Middle PIeistocene) (II/III) The maximum stage ofthe "Uruma Crustal Movement" (middle Middle Pleistocene) (III) The Minatogawa stage (late Middle Pleistocene-Late Pleistocene) (IV) The Ryukyu Islands stage (Late Pleistocene-Holocene) (I) The last stage of the "Shimaj'in' Sea" As a result of depth decrease of the Shimajiri Sea, calcareous sands deposited and "Ryukyu Limestone" of Okinawa-jima, South Japan r69 the Chinen Sandstone was formed. Accompanied with it, vast land areas emerged and extended near and a!ong the present position of the Ryukyu Islands as the hinterland for successive sedimentation. Probably deer of Metacervulus migrated into the Ryukyu Islands area from the continental area through land bridge of East China Sea. It is probable that Honshu and its adjacent islands had been already separated from the Ryukyu Is!ands, and yet the latter might be without connection to Taiwan, because those fossil deer have not been reported from Honshu and Taiwan. (U) The "R2ukyu Coral Sea" stage It is the stgae in which transgression initiated the deposition of the Ryukyu Group and completed its accumulation. This stage is subdivided further into the early and the late substages. The early substage is represented by the sedimentation of the Lower Formation of the Ryukyu Group. At first, a large quantity of terrigeneous materials flowed into the marginal sea from the land area of hinterland which still remained widely nearby. Consequently, the resultant decreasing oftemperature, salinity, transparency, etc. ofsea water might spoil the activity of reef-building organisms. Nevertheless, following the depression ofbasin floor oceanic conditions were introduced to the Ryukyu Islands area. Thus, some parts of the sea area might promote favourable conditions for the coral reef building. But some temporary pause ofbasin depression brought about suspension or relative drop of the sea level, and thus, the sedimentation of the Lower Formation of the Ryukyu Group ceased. The late substage is the sedimentation of the Upper Formation of the Ryukyu Group. As the sea level was rising again rapidly, the sea covered the Iand area more widely and the depth deepened for a while. After that, the depth of the sea decreased gradually, and at last the coral reef building became more active than the previous time. Alongside ofthis, the tectonic movements such as the Nakagusuku Dome forming might control or influence the sedimentary facies variations. Early in this substage, archaic elephant or primitive "Mammuthus", "Archidiscodon", existed in the Ryukyu Islands area, and these elephants seem to have close relationships to the fossil elephant of the Cho-chen fauna ofTaiwan of that time. Therefore, it is probabale that the transient land connection between Taiwan and the Ryukyu permitted elephant migration. (II/III) The maximum stage ofthe "Urama Crustal Movement" It was the stage ofdestruction ofthe Nakagusuku Dome and dislocation ofthe Ryu- kyu Group. Thus, many tilting blocks were formed. Isolation of the Ryukyu Islands were completed, because continental land mammals of the Middle Pleistocene Chou- k'outien fauna and the Late Pleistocene Huangt'u fauna, which were present in Taiwan in one hand and Honshu area on the other hand, are not known from the Ryukyu Islands. (III) The Minatogawa stage Since this stage, it semes that the influence of the eustatic sea level changes surpass Table 6. Summarized chart of the geohistory during the late Neogene and the QLuaternary periods of the Ryukyu Islands Nl- o Age Stratigraphy & Lithotogy Pateontot ogy Geohi story Recent Reef limestone. sand. HOL eeachde osits gravet E I: IV :: e ti CENE Rt ised CotvtReef coraUine biotithite Mammat -o Postglaciat transgression(+2rT" ¥} e LoAtTerrace corattine biotithite. 2 vtu m dep. & 2 " di i" gravet.ctay Capreetus o vefitti s U, .vc-v 111 Um "A rchidiskoden" J oo i an op a sparry calcarenite .E te- LtuLn Lirnestone Metacervutus ¥= Mi,natogcrwa tranagression Åë tuv ForTnafon corattine bio{ithite = {+55m?,+20-30m) i F Lo p. c c ccralline biolithite (Corat-Hatimeda abundant) s Sepcrated t.1.1 E o 'v ¥+- from . op o coralline g z a E gglj.'. Taiwan = 6 andlor (Corattinaceae abundant) O "A rchidiskodon " g lnner w B atgat ubllttoral o c 9n"'.T.hEl;.e.$fmmkyate U L Mem. bioclastic Ls. : o .9 L tu L e X Pticatuta E ut ut o foraminiferou$ uter m g: o a AMem t XCyctectypeus e ut' a rnicritic L.s. X oparcblina o Sutiittor L fromTeiwan D ' l en H o ut g = c L nner c 1.s.S A ¥.-o o ubiittorat o s. " bioc[astic Ls., i - > U -Reef : L oE N i'i" v,:' = J il-.' catcareous sand, s J ? 6 r. e = r, 11il i ts Ranktonic h h a ti. -¥, //.g ge noncaLc. sand, t forarninifera t) x x= Separated w Lts J orh -'Bh,l Catcareous lniet orh from graveL. sx nannofossiLr) lMetaceryuius or K ) E¥! e/.R..,i -Estuari Continent % o silt a J Geophrrocapsa Rs. oceanica Zone Chinen RR nner il "lj Sutiittorat cdcareous sand N" SE Pseudoemilia Potten Sand taeunesa. Z. flora s) a 6 Mstecervukes = # Outer o oc s Discoaster . ubtittoral immlgrcte L ¥; "t -..'tlf. tuff, btounvi Z. U from i' tu e oU sandstone ut China w 6E2 ts sittstone h.N"le c continent ::Il¥/ ¥,¥1,/.l./¥i. g" zt.L.1 L- Disccaster Rge ¥- L I NljN ;t Ltlt-1' pentaradlatus Z, =ut l-l-t-' gg 'o U l= ;t {t-i-t- l-1-ts E o ll- t U c ' ts ¥= ' Retievtotenestrv ih e ut Upper E , J L'=o sitts{one. ath at g , a Uo 1 tettculate Z. : , sandstone 1 tc = eE;.di. , ut ' ,-"o N 1 R tt 1) Natori et al. (1972), Ibaraki and Tsuchi (G975) ; 2) Nishida (1975) ; 5) Nishida and Itokazu (1976) "Ryukyu Limestone" of Okinawa-jima, South Japan 171 that oftectonic movements in the sedimentation. The terraces and the accessory lime- stones were formed around each isolated land. The latter is represented by the Minato- gawa Limestone Formation, and the highest sea level of that time is inferred to be 20- 30 m (or maximum about 55 m) above present sea level. Most of the deposits in caves and fissurs of the "Ryukyu Limestone" might belong to this stage. (IV) TheR2uk2ulslandsstage Formation of the raised coral reefs at the height of about 2 m above present sea level. Deposition of the dune sand and other beach sediments. Formation of the pre- sent coral reefs. The sequence of the geological events metioned above is shown in Table 6. Acknowledgements In carrying out fieldwork and in completing this study, I have been aided by many persons and several organizations to whom I wish to express my sincere thanks. Es- pecially, I am grateful to Prof. T. KAMEi, Prof. K. NAKAzAwA, Associate Prof. S. IsHiDA, Associate Prof. T. SHiKi, Dr. D. SHiMrzu and Dr. T. ToKuoKA of Kyoto University for their helpfu1 suggestions and critical readings ofthe manuscript, and to Prof. lkzAKi and Associate Prof. H. FuRuKAwA of the University of the Ryukyus, Associate ProÅí Y. OKi- MuRA of Hiroshima University and Dr. T. SHiBAsAKi a consulting geologist for their continuing guidances and encouragements. I am also much indebted to the members ofthe Geologist Association of Okinawa and the Okinawa Quaternary Research Group and fellow students of the Department of Geology and Mineralogy, Kyoto University for their criticisms, insights, arguments and general commentaries and dialogues, which have added up to a large contribution to this work. Acknowledgements are likweise due to Mr. M. KuRoKAwA of Okinawa General Bureau, Dr. K. ONo and Mr. M. TANAKA ofKokusai Aerial Survey Co. Ltd. and Dr. K. TsuJi of Nippon Koei Co. Ltd. for their ready offering of the unpublished data and helpfu1 suggestions, and Mr. H. TsuTsuMr of Kyoto University for preparation ofmany rock thin sections. References Fur(T, D. E., CoRwiN, G., DiNGs, M. G., FuLLER, W. T., MAeNEiL, F. S. and SApLrs, R. A. (1953), Limest one Walls ofOkinawa. Bll. Geol. Soc. Amer., 64, pp. 1247-1260. , SApus, R. A. and CoRwiN, G. (1959), Military Geology of Okinawa-Jirna, Ryukyu-Retto. 5. Ceol. Surv. Branch, lntell. Div. Ofice Eng. Hg. U. S. Arm] Ferces, Far East, Personnel of U. S. Ceol. Surv, 88 p. FoLK, R. L. (1959), Practical Petrographic Clasbification of Limestone. Butl. Amer. Petrl. Geet., 43, pp. 1-38. FosTER, H. L. (1965), Geology of Ishigaki-shima, Ryulcyu-retto. Prof. Paper, U. S. Geol. Surv., 339-A, 172 Katsumi TAKAyAsu 119 p. FuKuTA, O. et al. (1971), Neogene of the Ryukyu Islands. S"mposium on Geological Problems in the AdJ'acent Sea Province ofKJushu, pp. 91-101. (inJapanese) HAr"zAwA, S. (1935), Topography and Geology of the Riukyu Islands. Sci. ReP. Tohoku ImP. Univ., 2nd Ser., 17, 59 p. (1948), A Comparative Study of the Fossil Foraminiferal Fauna of the Ryukyu Limestone and the Recent Fauna ofthe Ryukyu Islands. Jaztr. Geol. Soc. JaPan, 54, pp. 123-124. (inJapanese) HiRATA, K. (1956), Ecological Studies on the Recent and Raised Coral Reefs in Yoron Island. Sci. ReP. Kagoshima Univ., (5), pp. 97-118. (1958), Ecological Studies on the Recent and Raised Coral Reefs in Yoron Island II. ibid., (7), pp. 69-84. IBARAKi, M. and Tsucm, R. (1975), Planktonic Foraminifera from the Upper Part of the Neogene Shimajiri Group and Chinen Sand, the Okinawa Island. ReP. Fac. Sci. Shizuoka Univ., 10, pp. I29- 143. KAMEi, T. (1970), Horizon of the Elephant Fossil in Miyako Island. Tsttkttmo-Chigaku, (5), pp. 1-8. (in Japanese) KizAKi, K. and TAKAyAsu, K. (1976), Outline of Geohistory of the Ryukyu Arc. "Kai o Kagaku" (Marine Sct'ences), 8, pp. 50-56. (in Japanese with English abstract) KoNtsHi, K. (1965), Geotectonic Framework of the Ryukyu Islands (Nansei-shoto). Jottr. Geol. Soc. Japan, 71, pp. 437-457. (in Japanese with English abstract) , OMtJRA, A. and KiMuRA, T. (1967), Dating and Rates of Vertical Displacement of Reefy Limestones in the Marginal Facies of the Pacific Ocean. JaPan. Quart. Res., 6, pp. 207-223. (in Japanese with English abstract) ,ScHr.ANGER, S. O. and OMuRA, A. (1970), Neotectonic Rates in the Central Ryukyu Islands derived from Th2SO Coral Ages. Mar. GeeL, 9, pp. 225-240. , OMuRA, A. and NAK2iMicHt, O. (l974), Radiometric Coral Ages and Sea Level Records from the Late Quaternary Reef Complexes of the Ryukyu Islands. Proc. 2nd lnt. Coral Reef SJm. 2. (Great Barrier Reef Committee, Brisbane) pp. 595-613. LERoy, L. W. (1965), Smaller Foraminifera frorn the Late Tertiary of Southern Okinawa. Proc. PaPer, U. S. Geol. Suri,., 454-F, 58 p. MAcNEit, F.S. (1960), The Tertiary and Quaternary Gastropoda of Okinawa. Prof. Pa]ber, U. S. Geol. Surv., 339, 148 p. NAKAGAwA, H. (1967), Geology of Tokuno-shima, Okierabujima, Yronto and Kikaijima, Amami Gunto (I). Contrib. Tohoku Uni.v. Inst. Geol. Paleent., 63, pp. 1-3. (inJapanese with English abstract) (1969a), Geology of Tokuno-shima, Okierabujima, Yoron o and Kikaijirna, Amami Gunto (II). ihid., 68, pp. 1-17. (inJapanese with English abstract) (1969b), Quaternary Sea-level Changes in the Ryukyu Tslands. QLuaternar7 Svstem of JaPan (ed. Research Group on the Quaternary ofJapan), Monograph 15, The Assosiation for the Geological Col- laboration inJapan (Chidanken), pp. 429-435. (inJapanese with English abstract) NAToRi, H., FuKuTA, O. and IsHmA, M. (1972), Younger Cenozoic Foraminiferal Biostratigraphy in Okinawa and Miyazaki Prefecture,Japan (Preliminary Rep.). Jour. JaP. Asoc. Petrol. Thech., 37, pp. 416-421. (in Japanese) (1976), Planktonic Foraminiferal Biostratigraphy and Datum Planes in the Late Cenozoic sedimentary Sequence in Okinawa-jima, Japan. Progress in MicroPaleontologl (ed. TAKAyANAGr, Y. and SATTo, T.), pp. 214-243. NisHrDA, S. (1973), Preliminary Study of the Upper Cenozoic Calcareous Nannoplankton Assemblages from the Nansei Islands. Mem. Geol. Soc. JaPan. (8), pp. 65-75. (inJapanese with English abstract) and IToKAzv, Y. (1976), A Palynological Study of the Shimajiri Group, Nansei Islands. "Kai o-Kagaku" (Marine Sct'ences), 8, pp. 201-206. (inJapanese with English abstract) "Ryukyu Limestone" of Okinawa-jima, South Japan 173 NoHARA, T. and HAsEGAwA, Y. (1973), An Elephantoid Tooth from Kyan, Okinawa-jima. (Studies of the Palaeovertebrate Fauna of Ryukyn Islands,Japan. Part III). Mem. Nat. Sci. Mus., (6), pp. 59-63. (inJapanese with English abstract) (1976), The Shimajiri Group on the Basis ofOstra-coda. Geologicat Stt"lies ofthe Rpt]u Islanals (ed. Kizaki, K.), 1, pp. 71-74. (in Japanese) OKiMuRA, Y. and TAKAyAsu, K. (1976), Quaternary Geology in Limestone Area. (The Latest Studies on Quaternary Geology. 8). " Tsuchi to Ktso" (Soil andFoundations), 24, pp. 65-72. (inJapanese) (1976), The QLuaternary System of Yoron lsland, Ryulcyu Islands: as regards the Stratigraphy and Sedimentology in the "Ryukyu Limestone" Area. Geological Studies of the RLpmkLJ,tt Istands (ed. KizAKi, K.), 1, pp. 97-109. (inJapanese with Eng!ish abstract) OkiNAwA QuAiERNARy REsEARcH GRoup (1976), Quaternary System ofOkinawa and Miyako Gunto, Ryukyu Islands -Especially on the Stratigraphy of "Ryukyu Limestone". "ChikLyu Kagaku" (llarth Science), 30, pp. 145-162. OTsuKA, Y. (1941), On the Stratigraphic Horizon ofElephas from Miyako Is., Ryukyu Islands,Japan. Proc. ImP. Acad. Tok2o, 17, pp. 43-47. O:suKA, H. and HAsEGAwA, Y. (1973), Fossil Deer from Ishigaki Island. (Studies ofthe Palaeovertebrate Fauna ofRyulcyu Islands,Japan. Part II). Mem. Nat. Sci. Mus., (6), pp. 53-57. (inJapanese with English abstract) OyAMA, K. (1976), Biofacies of the Miyako-jima Limestone and the Discovery of Pleurotomariidae Fossil. GeologicalStudiesoftheR]rkluIslands (ed. KizAKi, K,), 1, pp. 125-126. (inJapanese) SHrKAMA, T. and OTsuKA, H. (l971), Land Bridge of the East China Sea. SvmPosium on Geological Pro- blems in the Adj'acent Sea Province ofjK77 ushu, pp. 131-139. (inJapanese) , and ToMiDA, Y. (1975), Fossil Probosidea from Taiwan. Sci. ReP. Yokehama IVat. Um'v., 2nd Sec., 22. pp. 13-62. SHrNoHARA, Y. and KrzAKi, K. (1976), Geology of Kohama-jima, Yaeyama-gunto. Geologieal Studies ofthe R2ttkptu Islands (ed. KizAKi, K.), 1, pp. 37"ll. (inJapanese) SHoJi, R. (1968), Sedimentological Studies on the Ryukyu Limestone of Okinawa, Ryukyu Islands. Sci. ReP. Tohoku Univ., 2nd Ser., 40, pp. 67-77. TAKAy.4su, K. (1976a), The QLuaternary Limestones in the Northern Part of the Motobu Peninsula, Okinawa Islands. Jour. Geet. Soc. Japan, 82, pp. 153-162. (inJapanese with English abstract) (1976b), Re-examination on the QLuaternary System of Okinawa-jima, Ryukyu Islands. Geologt'cal Studies of the Rlttk.yu Istands (ed. KTzAKi, K.), 1, pp. 79-96. (in Japanese) ToKuNAGA (formerly YosHiwARA), S. (1901a), Note on the Raised Coral Reefs in the Islands of the Riukiu Curve. Jour. Cell. Sci. Imp. Tok),o, 16, (1.1), pp. 1-14. (1901b), Geologic Structure of the Riukiu (Loo Choo) Curve, and its Relation to the Northern Part of Formosa. ibid., 16, (1.2), pp. 1-67. and TAKAr, F. (1939), A Study of Metacervulus astylodon (Matsumoto) from the Ryukyu Islands, Japan. Trans. Biogeo.or. Soc. JaPan, 3, pp. 221-248. (19iro), A Fossil Elephant Tooth Discovered in Miyakozima, an Island of the Ryukyu Archi- pelago,Japan. Proc. Imp. Acad. Toltvo, 16, pp. 122-124. YABE, H. and HANzAwA, S. (1930), Tertiary Foraminiferous Rocks ofTaiwan (Formosa). SctL ReP. Tohoka lmp. Univ., 2nd Ser., 14, (1), pp. 1-tK}. . and HATAi, K. M. (1941), A Sapplementary Note on the Fossil Marine Fauna from Okinawa- jima, Ryukyu Islands. Jour. Geol. Soc. JaPan, 48, pp. 78-83. YAMAzATo, K. (1959), Ecological Studies on the Coral Reefs of Kume Island. I. Disuibution of the Coral Reefs. Bull. Arts. and Sci Div. Univ. R),tcklus (Math. and IVat. Sci.), (3), pp. 53-64. . (1960), On thc Limestone ofMiyako Island. ibid., (4), pp. 88-92. YAzAKi, K. (1976), Stratigraphy and Sedimentary Process of the Miyako-jima Limestone. Geologicat Studies ofthe R"uklu Zslartds (ed. lkzAKi, K.), 1, pp. 111-121. (inJapanese) 174 Katsumi TAKAyAsu Place Narnes Chinen joft.. Goga,Guga gea Gushikawa R,=Li:.JII Haneji-naikai ntept-ua Hedo-misaki mu)!fMqu Henza-jima SIZImbes Ishikawa EIjll Itokazu "SxX Itoman "SN'ra Katsuren maif Kouri-jima ili"Iii*UU Kunlgami Mee Kyan-misaki Sesrtthrp Machinato,Makiminato t5cue Minatogawa 'rs)i] Motobu Azz Naha asee Nakagusuku rptw Nakijin A-rat Nakoshi tvE71l o-jima eqrkB Oyakebaru meeetn Shimajiri Ent Tairagawa SIZNJII Tako-yama ;iLtJ Tengan )Eiva Unten if:E Urasaki 'math Urasoe thut Yamada-onsen LIJNim'7R Yagachi-jima msRteB Yomhan,Yontan tiiiii' 2:i zakimi ptggik Explanation of PIate 14 Fig. 1. Cuestatopographyformedbytiltingblocks,westernpartofSouthernOkinawa¥ Fig¥ 2. Well stratified clastic limestone facies of the Lower Formation of the Ryukyu Group bent by faulting, near Minatogawa, central part of Southern Okinawa. Fig. 3. Coralline biolithite facies of the C Member of the Upper Formation of the Ryukyu Group, near Yamagawa, Motobu Town, western part of Motobu Peninsula. Fig. 4. 0Perculina limestones of the A Member of the Upper Formation of the Ryukyu Group, at Nakasone, Nakijin Village, eastern part of Motobu Peninsula. Fig¥ 5. Algal ball limestone of the B Member of the Upper Formation of the Ryukyu Group, near Itoman, western part of Southern Okinawa. Fig. 6. C)clecl)Peus in the A Member of the Upper Formation of the Ryukyu Group, near Itokazu, eastern part of Southern Okinawa. Explamation of Plate 15 Fig. 1. 0utcrop ofNo. M26, near Nakasone, Motobu Peninsula. Lcs; calcareous sand facies of the Lower Formation, Lcl; clastic limestone facies of the Lower Formation, UA; A Member of the Upper Formation represented by Opercttlina limestone with a dark band of terrigeneous clay layer. All this section belongs to the Ryukyu Group. Fig. 2. 0utcrop showing the relation between the Lower and the Upper Members of the Minatogawa Limestone Formation, coast of Minatogawa, central part of Southern Okinawa. C; coralline biolithite of the Lower Member, F; foraminiferal sandy limestone of the Upper Member. Fig. 3. 0utcrop showing the regional unconformity between the Lower and the Upper Formation of the Ryukyu Group, near Gushikawa, the neck part ofKatsuren Peninsula. L; noncalcareous sand and silt of the Lower Formation, U; bioclastic limestone of the Upper Formation. Fig. 4. Weakly layered coralline bioclastic limestone facies ofthe C Member of the Upper Formation of the Ryukyu Group, in Kouri-jima, off the north coast of Motobu Peninsula. Fig. 5. Cross lamination in the clastic limestone facies of the Lower Formation of the Ryukyu Group, near Urasaki, Motobu Town, Motobu Peninsula. Fig. 6. Cross bedding in theclastic limestone facies ofthe Lower Formation ofthc Ryukyu Group, near Tairagawa, Gushikawa City, Central Okinawa. "Ryukyu Limestone" of Okinawa-jima, South Japan 175 Explanation of Plate 16 Fig . 1. Foraminiferal and algal biosparudite, the Upper Member of the Minatogawa Limestone Formation. Co; coral, Al; coralline algae (Corallinaceae), Cl; Calcarina, Am; AmPhiste.gina, ic; intraclast, RG; grain of the Ryukyu Group, probably A Member as Operculina micrite. Loc., Minatogawa, central part of the Southern Okinawa. Fig . 2. C7clocl7peus biomicrudite, the A Member of the Upper Formation of the Ryukyu Group. Cy; C]clocl),PetLs, Bz; Bryozoa. Loc., STM-Ol, near Itokazu, eastern part of Southern Okinawa. Fig . 3. Forarniniferal and algal biosparmicrudite, the B Member of the Upper Formation ofthe Ryu- kyu Group. Al; coralline algae (Corallinaceae), Ha; Halimeda. Loc., MB-1, Koechi, Nakljin Village, Motobu Peninsula. Fig . 4. 0Perculina and C7clocllPeus biomicrudite, the A Member of the Upper Formation of the Ryukyu Group. Op; OPerculina, Cy; CJclocCyPeus. Loc., MB-2, Sakiyama, Nakijin Village, Motobu Peninsula. Fig . 5. Foraminiferal and algal biosparudite, the top part of the Lower Formation of the Ryukyu Group. Ec; Echinoid spine, TG; terrigeneous grain, ic; intraclast, Al; coralline algae (Coral- limaceae), Op; OPerculina. Loc., same to Fig. 3. Fig . 6, Well sorted foraminiferal and algal biosparite, the upper middle part of the Lower Formation of the Ryukyu Group. Loc., M-50, Urasaki, Motobu Town, Motobu Peninsula. Mem. Fac. Sci., Kyoto Univ., Ser. Geol. & Min., Vo]. XLV, No. 1. Pl. 14 1 l,¥g¥.,--. - ' .tt.tt tt.t..t.ttttt t. .t. . ttttt..t tt ..,,,..,.1.- ttt ttt ttth.t t .,. ttt tttt t t.ttt t, tt..t ttttt .,ll/t.t,' r t"t - , .-----: tt .- t tl..ttttt 't'tt ..g "tttttttt t'.- 2 3 "t-f.ll..iwa-tw - .ks? g.t anitza-} -'sg!qlptg: th-:detw ,,¥.¥.t,x,$-i '.Lpt1t .. Ui,tt-','fi,1.t/,1'-,,,,..lttt,,1 . .... tt. .L.'.: t.' - / 4 't.ecrt"rvt. di, ge .": thfrfifptr ¥¥ ptpa-:-"¥ ¥\in -ce¥¥ -Qgma 5 6 .N ee¥thkgt- TAKAyAsu: "Ryukyu Limestone" of Okinawa-jima Mem. Fac. Sci., Kyoto Univ., Ser. Geol. & Min., Vol. XLV, No. 1 . PL 15 1 2 ",exm-.S3ipmua in, M 4 3 www....vaanr-,',a.va,st...' lll'lll,.pt.t/tw.tl'."sm.,yk.w.'}ag.'vnigs 5 6 .di= T TAKAyAsu: "Ryukyu Limestone" of Okinawa-jima Mem. Fac. Sci., Kyoto Univ., Ser. Geol. & Min., Vol. XLV, No. !. Pl. 16 stpt N,v ¥5 oo ' -- opA X/' . tis.,ge "4.Xk k s (Photo b) Mr. Y. Okazaki) 5mm - TAKAyAsu : "Ryukyu Limestone" of Okinawa-jima