Title Sedimentological Study of the Paleogene Basin of Kushiro in Hokkaido, Japan
Author(s) Matsui, Masaru
Citation Journal of the Faculty of Science, Hokkaido University. Series 4, Geology and mineralogy, 11(3), 431-480
Issue Date 1962-03
Doc URL http://hdl.handle.net/2115/35929
Type bulletin (article)
File Information 11(3)_431-480.pdf
Instructions for use
Hokkaido University Collection of Scholarly and Academic Papers : HUSCAP SEDIMENTOLOGICAL STUDY OF THE PALEOGENE BASIN OF KUSHIRO IN HOKKAIDO, JAPAN
By
Masaru MATSUI + Contrib ; Department of Geology and Mineralogy, Faculty of Science, Holckaido University, Japan. No. 862
Contents Abstract...... ･･･.---ny･････ ------431 g 1. Introduction ...... ------t--- 432 g 2. Acl gl. Introduction Since 1951, the writer, aiming at a complete geo!ogical study of the Kushiro coal field in Hokkaido, has been carrying on these ten years' studies and investi- gation regarding the various portions of that field in cooporation with Messrs. Tsutomu FuJiE, Yasukuni FuRuHATA, Jiro IsHii, and Katsutoshi MiTANi under the very kind and most careful guidance of Dr. Masao MiNATo, Professer of Hokkaido University. What the writer intends to present briefly in this paper is nothing but a clarification of the features of the sedimentation in relation to the geological structure of the Kushiro coal-field sedimentary basin, simultaneously' with developing a theory on the relations between the various characters of sedimen- Seclimentological study of the Paleogene basin of Kushiro in Hokkaido, Japan 433 tation and the formation of the sedimentary basin of which Dr. Shoji IJiRi (l958) and Prof, Masao MiNATo (1953) have already written. Based on the facts proved so far by many previous writers and the observations of the present writer and others, the writer of this paper should like to clarify the charaeters and the changes of the thickness of lithologic-faci.es and fossil-biofacies of the various formations beionging to the Urahoro group and Onbetsu group of Paleogene which are developed in the Kushiro coad-field, and to refer to the different problems which arise in connection with the sedimentation and sub- sidence movements of this sedimentary basin*). Moreover the writer wishes to discuss how the characters of these movements changed and"deveioped through the ages. He proposes then to refer to these movements ana the formation of pyroclastic dykes, intraformational foldings and planeless fqults, and lastly to consider the general relations, which are recognizable among the characters of structural movement such as folding or faulting which developed on a iarge scale in the later stages**). Here the writer humbly awaits the criticisms of the honorable readers. gZ. Acknowledgments The writer is sincerely indebted to Prof. Masao MiNATo in the Geological and Mineralogical Institute, Hokkaido University for his kind instructions through the whole course of studies and for kind revisibn of this thesis. At the same time he fully appreciates the kindness of Messrs. Tsutomu FuJiE, Yasukuni FuRuHATA, Jiro IsHii and Katsutoshi MiTANi who were willing to cooperate with the writer in both field investigations and,laboratory studies. The writer also gratefully acknowledges the receipt of valuable materials from these people, also from Dr. Satoru UozuMi and Dr. Toshimasa TANAi to whom most hearty thanks are expressed. g3. Pre.Tertiary topography and geology of the Kushiro sedimentary basin The Kushiro Paleogene sedimentary basin extends from the outer zone of eastern Hokkaido westward to the inner zone. It covers the Nemuro group P･ The geology and stratigraphy concerning the Kushiro coal field have hitherto been studied by AsANo, K. (1952, 1954, 1955), FUJIE, T. et al. (1957), HAsHIMOTO, W. (1958), HAyAsHI, I. (1955, 1957), HAyAsAKA, I. & UozuMI, S. (1954), FUJ.IoKA, K, (1941), IIJIMA, A. (1959) IMAI, H. (1920, 1924, 1925), IsHII, J. (1957), KAwAI, M. (1958), KIzAKI, K. (1959), MATsul, ML (1950, 1951a, 1951b, 1953, 1957, 1958, 1959, 1960), MINATO, M. (1950, 1952, 1957a, 1957b), MITANI, K. (l954, 1948, 1959, 1960), MIzUNo, A. (1960), MURATA, S.. (1930) ODA,.Y,. et NEMoTo, T. (1959), OGAsAwARA, K. (1955), OTATsuME, K. (1943, 1950), SAITo, R.. (1953, 1955, 1956, 1958), SAKAI , ,'s.:",,.'.1･'ies "'` t ,,･,r.va,. k :･･'` l,(s) ,, ,tz't A .･ ! 'ag'"i'' i , o t t - liil･l.i,ii.,l:･･/A,-,../ ,,i lt /t .' ･.,tt i ･ rl･r.;',1･i;lit,., @ - l:i , ., li･,,- liii-g･:(･ E)･ ii･i･:ii.),･･'i'illl.i.i,I.iop,.,'..,.l ','.l'i ,i. i'L･･// l.l･ :･･(1', t Fig. 1. Index map of Paleogene Kushiro Basin. Pal: Onbetsu& Urahoro groups 3) Toyokoro-Kitami Tectionic Zone. Nm: Nemuro (Cretaceous) GrQups 4) Oikamanai zone 1) inner zone of Kurile Arc. 5) Hidaka zone 2) outer zone of Kurile Arc. 6) Kushiro coal field ' ' ' as its direct basis and spreads to the pre･Cretaceous area in an overiapping way. It extends at the present time to the coast of Akkeshi bay, Senposhi peninsula in the east, and to the areas of the Ashoro, Honbetsu and Nisei rivers in the west; on the north it stretches to the southern side of the Akan volcanoes and to the southernmost points of the Pacific coast in the south. Through the Rikubetsu valley to the middle course of the Honbetsu river, the Urahoro fault extends having a north-south strike as a boundary of the Cre- taceous and pre-Cretaceous areas. The pre-Cretaceous group, composed chiefiy of schalestein, red chert and green chert including pillow lava in some parts, which have a general strike N 300E, is exposed as the basis on the western side of the Urahoro fault . ., In the inner zone of the Kurile Arc, which is geologically an extension to the north-east of eastern Hokkaido, there is found in various places the same basic, granitic rock, for example in Kunashiri and Etorofu islands. The distri- bution of pre-Cretaceous deposits which are seen on the extension of the line connecting the Rikubetsu and Honbetsu rivers clearly runs obliquely to the main trend of the Hidaka orogenic zone. It is clear that the pre-Cretaceous deposits provide the composition of the Oikamanai zone which extends to the inner zone of eastern Hokkaido, the Kurile Islands and Kamchatka. As above mentioned, the basis formed of pre-Cretaceous deposits does not Sedimentological study of the Paleogene basin of Kushiro in Hokkaido, Japan 435 appear at all in the outer zone of eastern Hokkaido, east of the Urahoro fault, whiie in the chief parts of the Kushiro sedimentary basin, the Nemuro group of the Urakawa transgression, is widely exposed as the direct basis of Paleogene groups. The formation of the Cretaceous sedimentary basin in south-eastern Hok- kaido was later than that of middle Hokkaido due to the fact that the formation of the Paleogene sedimentary basin was slow in its beginning and the formation of the Miocene sedimentary basin was slow, too. This phenomenon is evidenced by the imperfectness of growth which the Oikamanai zone had from the be- ginning, and by the poverty of its geological history and sedimentation because not only is it situated in the hinterland of the Hidaka orogenic movement which is characterized by overthrusting upheaval to the west, but also at the north-west edge of "Paleo-Nemuro land" area which existed through these ages. TABLE 1. Geohistorical Development of Central and South- eastern Hokkaido in Mesozoic and Cenozoic Era. Geologic Age Central Hokkaido South-east Hokkaido Pleistocene : ･.. .: :", ..,,. ,":r,.;t. -",. ":U::,:::.i:.:･.:':'.･:,･:T:.::.t･::,.:r, - t -1 i- -- -J -4 i: -l ---- Pliocene :: : lt ti : itt:-+:- -s : 1t lt --:------; - .1 -- :- : - -i tdi- 1- -- S! --t -- - 4000 m d t -- -i : ti-4-t- tt -- -: --:+:::' :- .: ･･1 2000 m 'trfT-":-r-v-T--r--rtyt i-- "J -- : ------: -- -+ti- :r;: ti':,: 'i':, /lt:'l ,i:'tl' i･:'1,;･:'i',;ii'.g'ooo m /1: :.. l'li'i'･in",i/i'i･i::･:,:',li',i･1':,:1';.i21o'oomiJ--t------dJ Miocene. tS::ttii;-i L÷, g/leellgilSi;E";.,eo/.",.t/ges//.e,,,;,t/i,tl,?/L,t.2.,,,;".ilp,,,. ma.".".AA."a94Shsitj----tt--J----- st L`,:4.'.Alg:'; A' . 4'A･ i: :--- .. --V-, b -; 1i,I'i'1:`,'iti'i;'f,･ll･llt,;'r･;',1:･il,'i･'g･i,. -i ----- , Oligocene 1,:.･,:r i-tljti-i ,2500 m i----e j -, - ----}--- -.t. I -- -- -tt-i-t' ---4t -- -- t-t tj t-- :'t-tt- 'iv Eocene t-t------t ------J- i- t --v--4 ., ,:, .･. ::, '.･. :･2000 m FEt;7iar]{"1,s･q4.4A-a<･g.t'i tit- it'- l,･e.:'.<,,-ts:,4,it;,l-r4,fJta,-.:･,. :v:･t':1;/t'.:::･r::1･:･:.l;iaso Cretaceous -- -t-- --- t--l------l -- :- rl':-- -- :+ )-･'+l ---- '1+:' :H-'l : ------' -- t-i -- +--} -L - ::' ･1:.F:,i.l-t-::1'-!=:::,: ,- .･ -t- ･- ･1::':'::.:':IT -j --- -- '･1: - : `: '6ooo m - ---i --. Jllrassic r--b--"===--=.-.aooo.- --+ - [n1TMT[1I1 pm 1 ES]2 [E:g3 ･:･:[･:4 EggNs M[M6 AfteLM, Minato e't al l956) 1. Igneous activity of the final stage. 4. Depositional stage. 2. Igneous activity of the orogenlc stage, 5. Sed{mentation of molasse type. 3, Igneous activity of the initial stage. 6. Erosional stage. 436 M. MATsUI TABLE 2. Correlation Table of the Nemuro Group (upper Cretaceous) in Southeast Hokkai do ' -- Tokomuro I :.Vt.&fin3 Konbumori sthidstone Ochiishi Augite andesite, andesite, lava 400m 360m 1 sandstone NNN sandstone& finesand- conglome!ate 600m stone,sllt- sand&silt N NN alternatien ' stone,medium o Shloml N ' -coarse H ･H 870m pt pt =op t nnpt sandstone& Eox 500m {Basalt conglomeTate ¢M t " o M< t rd'dM F Choboshi 't -"-greysand- 800m sandstone stone&silt 'ti¢ darkgre.y l11lSenposhl xxx slltstone stone. Luff&sandstone silts'tone 1400m ecOsandstone.t 200m xIX 600m Monshizu trd gabblj alternation !1' 200m 770m P intrusion 't'' 'r txt oM basaltdyke 350m darkgrey pt 1 mal siltstone llolt ,-iH ' ･H di･ri 1/'t vNF- =co dk sandstone, M= itpt si]t.g-t.nne& 600m tt ' tt fi Apt whitetuff Iil 1io Jco 11 itM-) NemuTo I 1IZ ' tl tu'ffaceous 800m-- l･ t! sandstone aloom lt &siltstone t 1 lt (Dolerite) lt t1ttMt. cakotan ' llli volcanics ltll1 ' ltlt'lt 1900rn 1i1t' ttt'i Notsukumappu 1 'l agglo- 1 merate, l 11'pillowlava tt' t OUTLINE OF THE 'SEDIMENTOLOGY OF THE NEMURO GROUP Studies of the Cretaceous gyoups of the Nemuro and Kushiro areas have been carried out by many authors. It is still unknown on what foundation the Nemuro group developed; but from the fact that a zone of unusually high gravitational anormar}y is found in the Nemuro area, it is thought that the distribution of the basaltic layer is very shallow. When the Nemuro group is viewed from the sedimentological point of view it is seen to be composed of thick formations of alternating dark gray mudstone, siltstone and sandstone with very few fossils; that is, its noteworthy Sedimentological study of the Paleogene basin of Kushiro in Hokkaido, Japan 437 ' characters are that it is predominantly composed of geosynclinal deposits, which are occasionally of coarse grains in the uppermost part; thick formations are developed, and developments of intraformational foldings and sandstone dykes exist in the uppermost formation of this group in the Nemuro and Konbumori areas. The considerably thick formations in the lower Nemuro and Senposhi groups are found along the line connecting Nemuro and Habomai, and it is recognized that the position of the thick formation in the upper Shiomi, Tokoro and Kawarufu formations moves more to the north-west than does that of the lower formations. The geosynclinal thick deposits of Cretaceous are foided in NEE-SWW strike direction, and include a large quantity of andesitic or basaitic lavas, pillow lavas, dykes and agglomerates. It can be safely said,' that the Cretaceous sediments have been deposited in geosynclinal environments, that were newly produced in the upper Cretaceous. The structurai zone which consists of pre-Cretaceous Schalsteine as the basis, and is the boundary of the pre-Cretaceous area and the area of the Cretaceous Nemuro group, is called the Toyokoro-Kitami tectonic zone. In the west of the Kushiro sedimentary basin, this structural zone which has NEN-SWS strike like the Honbetsu, Rawan and Urahoro faults, has a deep significance in its construction, too. It is evident that this tectonic zone was in activity even before the deposition of the Paleogene group of this coal-field and it has been continuing its actiyity off and on till Miocene, Neogene Tertiary. S4. Stratigraphy of the Paleogene Groups in the Kushiro basin When one considers the general geology of the Paleogene Kushiro sedi- mentary basin, he finds that the Urahoro group, including coal-bearing formations in the lower part, covers the Cretaceous Nemuro group unconformably. The Urahoro group, through the whole area of the Kushiro coal field, shows principally fresh or brackish water facies with one or two formations bearing shallow sea facies in their several horizons. From the viewpoint of litho!ogic- facies, the Paleogene deposits are divided into six formations as listed in Table 3. The Onbetsu group, marine water facies whice covers the Urahoro group is widely distributed in the western part of this sedimentary basin and extends farther to the west. Outside the distribution area of the Uraharo group, it lies unconformably on the pre-Cretaceous group. Among the formations of the Urahoro group, coal bearing formations are characterized by alternation of sandstone and siltstone, but in the Beppo forma'tion and Tenneru formations is developed a spectacularly characterized conglomerate which bears thin layers of sandstone. Shital TABLE 3, General Stratigraphy of the Paleogene Groups in the Kushiro Basin Formation Colm Facies T. Lithology MainFossils Volc. (m) =.hLi"=`'t--t---- Darkgraytuffaceous ';'"v":----- s-1p,"tt--:-:1:t-t------=Z.-.-L-'"". sandstone,contain- Yoldialauda- oumg'>:ptose･xve'pH--iett･utath`th->2.e."em. Nuibetsu Kei'otuHpaa-x,mrr'"".H...,'ingpyroclastic bilisYok. o=crmat=QHocw v･:.:･'s:'j---4-:t grains,intercalat- rvlaltetia /'h.:a"':.:."ttt4b--s=- edthipagglomerate poronaica(Yok) , inmiddle&upper, !':,i:::.:,;'li:,-J--i--t-----m--- 300 Neptunea onbetsuensisMat. otrptnyogoH･tr Darkgraysiltstone Ancistrolepis orpoHoH}qBiLt='tt-ge:----fs,------.------::---=::------=-=-.T=.:.r:.=. interca'latedmarly J'aponicus(Tak.) layers&nodules, Catlianassa calcareousbands, murataiNag. 30- thinwhitetuff. 400 magar7 :' r:::':,tt'i'iqi------O-120Greensandstone, ",-,1' l:.t'':'::::' ;'bt:'Lit',' --- Graysiltstone, Corbicula tt-tL--t-l- sandstone,thincon- tokudai(Yok.) Shaku- -L----m --::-----4-- -t Batissasitaka- --- -tt---J--i.::...;-.:P----'-- glomerateatbasal -t --- -- betsu -=h"'="'-''- part;upperparts' t･!:'W,':!k,:t': rensis(SuzJ 280- becomesfinegrained Ostreasp, --- .,:::l::.1 ty`'"`"tw-b :.'r' j::.,..Darkgraysiltstone Nemocardium Shitakara platygreenishgrey yohoyamaiTak. cnypaveHeQno=v' 130- sandstonewithgrey Neptuneashita- :t';'''t--i----"tLs'-tt--t't:;---.-ti.:---t---ttI-:ri,,o,H'H.-ojm--tt230 thinconglomerate. karensisMat. j- Grayishsandstone, Batbssasitaha-'' i'')-- darkgraysiltstone rensis(Suz.) =E-=h:･･m,--t--tttttu''=''"-,: =-,"-･ j;- reddishconglomer-' Cerbicula`tokt.ep'dai'.(Yok:>L, Yubetsu ,tt ate,intercalatingicoalseams, :i -'"':'''-.---=･-:･=. .:t--t's-:'.-- Ostrea,praegra- :Ii--.';. vitesta..Tak. ------'300- --t------.,H.sd-.-"-. Reddisheoriglomer- Mtlagreavinghi itpt-- atewithgraysand- Mak,Nemocar-- Tenneru .vj-t-:s;,L----,.1.-tti1.--t---it+-t--t)Itj-iJ"-t---ii'-i-l:-t---t'it -t--"::-J-t---t-t stonepatchesand diumyokoya.mai "g"pte-{ thincoalseams, Tak. :-T..=.=T."o"e"t 120- -t--- Harutori --= -"-in----tr::'.::.r:.----- 120 :::tttt ttt-t- sand--siltstone. -r.' Beppo 50 Blackconglomerate. formations is not distinct. Generally every formation considerably increases in its coarse-grained part towards the west, and in the area of Rushin in the western portion of this sedimentary basin, the whole formations become considerably conglomeratic through the whol'e Urahoro group. The Urahoro group, as indicated in Table 3, starts with the Beppo conglomerate formation and Harutori coal-bearing formation of fresh water facies, and extends to the Tenneru conglomerate formation. In this formation, in the Senposhi peninsula area, the eastern end of this coal-field shows evidence of the intergression of sea water. The characters of facies in the formations of the Urahoro group, which change periodically and spaciously as illustrated in Table 3, will be discussed in a later chapter. The Onbetsu group is of marine sediments throughout with the exception of brackish fossils included in the lowest part; it commoniy produces marine molluscan and foraminiferal fossils, excepting the Omagari member which is Sedimentological study of the Paleogene basth of Kushiro in Hokkaido, Japan 4g9 found at the base of this group, and predominates in sandstone and contains pebbles, the Charo formation predominantly exhibits dark gray siltstone. The Nuibetsu formation, upper half of the Onbetsu group, consists of dark gray or black sandstone, andesitic agglomerates and tuff layers, No volcanic rock is found in the Urahoro group, but between the coal layers or in the coal layer itself are found white and fine grained tuff or tuffaceous clay layers. Especially in the Shakubetsu formation there are contained white liparitic pebbles in a large quality, the conglomerate of this material is called "Hatokuso". In the areas of Tokomuro and Rushin, the Onbetsu group bears andesitic sheet or agglomerate between the Omagari and Charo members. It has been already mentioned by previous studies, that the Nuibetsu formation contains a large quantity of basaltic or basic andesitic tuff, agglomerate and coarse-medium grained tuffaceous sandstone in the whole area of this basin. Molluscan fossils and the minor foraminiferal fossils found in the Shitakara formation and Onbetsu group include the species which are contained in the "Poronal fossil fauna" ; the Shitakara formation and the Onbetsu group can be safely correlated with the Poronai formation of the Ishikari coal-field. The brackish or marine water facies in a part of the Tenneru formation of the Urahoro group, produces molluscan fossils which are commonly found in the Shitakara formation. The stratigraphical relation between the marine formations of the Urahoro group and Akahira and Hiragishi formations which inciude brackish or marine water facies, presents a problem, but as the paleontological study of these formations advances a close relationship will probably clarified. When the age of the Onbetsu-Urahoro groups is considered in the correlation of the Poronai formation and the upper part of the Ishikari group, their age will probably be found to be from lower to upper Oligocene. This can be fully understood by a comparative study of the Yakataga formation of Alaska and the formations of Blakeley, Lincoln and Keasey from the Pacific coast of North America, by means of materials for paleontological study, such as mollusca or minor foraminifera. The geological structure of the Kushiro coal field generally consists of four anticlinal zones running NE-SW, and three synclinal zones occupying the space between two anticlinal zones. There are (from NW to SE) 1 ) Ukotal te T-CKo:fioKu ors tt " -XL, tJ il Ei tt' i' ii' D )t F,., E,?.'Xilii -t(' ･ e ANTIcuNe .Kf' , NAr .(el-:-:'J';, sTNcL]NE ls 7KNx y. ' l ld Ykg･i tttG 'v N. r ,t / tiv / FAVLT ii ' v A1･ /1' '･ rsErs 'DoN ' s ,, '･ ･ oNeETs" eftovp /lt l H s ' ' Nlp ' ' ! - uHAHoRo GRDvp 1. Ak?",(/'o.qSl.,/""` cfett.1･-K4 "t" t' )" 'to･Js llt-iki,f .v,' t'"';1':';,er"Dxt/E=-m-"/1AAHOtea-t1,,/t,' ii'.,,.･//ll'le":,,,.,.'l"ry:Rii'1･･/f"tt[.tv"v''.,'ittel 1{.' tl ..' " JlH 3 {ny Si : tcPs'SHL.:Sny.L;DOHe,OME.-yXv ',ttpt""',,stcr/.s"""' 4) ,tg'.ti,"/fi" ttx Ill tr-`1.gh-lt.1.JEL:a･h!rgrs,=to.x/t,ogte"'ttIR' sc % g-/:, v Q k 'k VX '.,,sqf'tsHLklgr.'""ttRXt;/1 ,,, tts,?tl l･ l"TsuPcrEtttt tt tt e t･･(,rtt } odi==z.le.Uua m li 'AISv..HvArpoMS.t ':I Fig. 2. Structural map of Kushiro Basin. I): Ukotakinupuri-Rushin anticlinal zone, II): Kamicharo-Tokomuro sync!inal zone, III): Yubetsu- Shakubetsu anticlinal zone, IV) : Karnishoro-Onbetsu synclinal zone, V) : Akan-Shoro anticlinal zone, VI) : Otanoshike synclinal zone, VII) : Senposhi-Harutori dome zone. A: Rawan fault, B: Honbetsugawa fault, C: Urahoro fault, D: Chikupenninai fault, E: Kami- charo fault, F: Hokuyo fault, G: Teshibetsugawa fault, H: Nagasakisawa-Irobetsu fault, I: Toko- muro fault, J: Nupukibetsu fault, K: Onbetsugawa fault, L: Yubetsu fault, M: Omagari fau!t, O: Fuppushinai fault, P: Shl,beshizawa fault, 9: Osappe fault. Sedimentological study of the Paleogene basin of Kushiro in Hokkaido, Japan 441 towards the south-east from the north-west, that is all the way from zones 1) to 7). To the north-west, the direction of the extension of each structural unit draws nearer to NS ; in the south-east area, the direction becomes more unclear, The general dip of the foldings in each anticlinal structural zone decreases toward the east from the west; the general dip of each zone is 800-600, 400- 300, 200, and 100 in zones 1), 3), 5), 7) respectively. As to the faults, in zones 1) and 2) there are several large scale vertical faults which are the same or nearly same in direction as that of the structural units. In zones 3) and 4), there are conspicuous cross faults perpendicular to the axis, besides the same faults as in zones 1) and 2) above mentioned. In zones 5)-7) the differences between two kinds faults disappear gradually, especially in zone 7) there are gonspicuous block faults which cross the lower dipped dome structure. g5. Changing of lithologic-facies, bio-facies and thickness of the Urahoro group through the ages The subdivisions of the lithologic-facies of the Urahoro and Onbetsu groups are shown in Table 1, but when these formations are considered from the viewpoint of the history of the growth and development of the Kushiro coal- field, they are grouped into the following four divisions, (1) The lower part of the Urahoro group: including the Beppo, Harutori and Tenneru formations. (2) The upper part of the Urahoro group : including the Yubetsu, Shita- kara and Shakubetsu formations. (3) The lower part of the Onbetsu group: Charo formation (including the Omagari member in its basal part). (4) The upper part of the Onbetsu group: Nuibetsu formation. In this chapter are to be discussed the characters of the Iithologic-facies, bio-facies and thickness of every formation of the Urahoro group and the changes in them through the ages. The areas examined are shown in Table 4 and Figure 3. The locality nurnbers in Table 4 are correlated with those of Figure 3. (I) The lower part of the Urahoro group 1) Beppo formation The Beppo formation is the basal conglomerate bf the Paleogene Kushiro coai-field and covers the Cretaceous Nemuro group by an unconformity plane which has a very irregular surface, but when the latter is of conglomerate, it is not always easy to discover the boundary. Structurally they are in a relation of clino-unconformity and when the relation is broadly viewed, one finds that this formation borders with every horizon of the Nemuro group. The general lithology of this formation is conglomerate with predominant medium-coarse 442' M. MATsul gravels of black s}ate, black sandstone, basic andesite, various 1 TABLE 4. The thickness of Paleogene formations in the Kushiro Basin (thickness in meters) LocalityXFormation Nb Ch Om Sb Sk Yb Tn Ht Bp remarks 1Koibokushokotsu 150' 2eo 80 176 t90 143 75 28 leo aitotMS} 2I ' AltanL e om ?･ oo s s 2o' G. IB. S = 1 f i g n..1 p"e & 3219xe" @'$.ee a e 9T'dr pt- as -es" ' pts-' e- L" e.5`;..?4. c eA 's fdols, 6 g e ' ? ruHsrsu :- 21 "tt o. Va lo 6 o ous "' N--t Eur:ktAKI i- pt-v thn"" / pm 2B "o"v o 29 o HNemSV asso eq 7nrw 3B :o ShutnlR,31 @AKAH o T224..32o. -hqlt -' nlpeb cr l3 {jeMAamot.-ssNvrs sv pa 43 9. 9' stS' .su co : @ oStse. @itfiHtoBoRe l510 Ch-tbet!q e-eAe `e4 h g e. ts . e. NSe e.@SHOno @eB?ro x 1... 41 a t" +･ Ll6 a.e"-e. AuxerlMr Er. =l,, KUS:Ho Tsmtposr 8 '-la @ ua Pe- ng s;nvta 49 .-･ ll HOHamRZ .4 S]mw-: s / : L" es s e"ptvs=rsv .ny 9AX Sfbi jt tt eseersu "" re･ se` ste . oQ p･ " e fie" 3 .; s N gpt msu"Ar v mp N: -# pt pl Fig. 3. Localities of the examined areas. ec (The numbers of the localities are correlated with those of Table 4.) pt pt pt !: 2p NK/Nx(((ilpa,/[email protected](op×/ 1$ptge/x x [Z] Bspee loNttrlos mmPS .ct s ex x Eliil] :se?A:H L:Nss eF SSerc nma1on Id x - 4n 50 x iee" -' - x e N ･ 100 t/i-'- PAntzctE sr:: OP ?reELE N IL soe .gl£s" x x N eee " - ptA-Erlnjo.ao.Leat So x x x o x ' × x K x k' xN r s. x .E K e N l N s,o > Av se G H 2} x(, s cm x .k "e n H s--ss (!5 -" -.to e Te -･.-.- - .-. e --- -= e es be , o 1 S'-er 'e -.- 't L..L=UL=Sku fo' e Fig. 4. Isopach map of the Beppo formation (Number in circle is thickness of the formation in each locality.) Sedimentological stucly of the Paleogene basin of Kushiro in Hol In field observations, this conglomcrate is called popularly "Kurodama" on acount of its conspicuous numerous black pebbles and rather few white pebbles of }iparite. It is generally of medium grained conglomerate with abundant sub-rounded or rounded pebbles and cobbles, which are cemented with granules of dark gray coarse sand. The whole formation is almost massive and the bedding of the conglomerate is not obvious ; sometimes it bears light gray coarse sandstone of lense type; no fossils have ever been found in this formation. The lithologic-facies of the Beppo formation, the grain size of pebbles and changes of thickness are shown in Figure 4. -Discttssion- The following points are what should be noticeable as regards the changes of lithologic-facies and thickness of the Beppo formation. A) The development of this formation is limited to the north or the east part of the Kushiro sedimentary basin, and characteristic feateres of this formation are not recognized in the Urahoro and Rushin areas. B) The isopach lines run from NWW to SEE. C) As for the size of pebbles, it decreases from north to south. D) The changes of thickness in the sections from Yubetsu to Kuomanai, and from Chikupenninai to Senposhi are shown in figure 7. These facts enable the wor! ti HARUTSRI FOe-ArroH otrTcRoPS coAL * Se muFF CowatoblRATE t mmTaYE Fn:Sas sltrstaNs emNoSTONeEACIEs rtns sANmmNE ceAnss srums:e"E snvnscvNE t slLrsron; enates le OMenv;testenara 10' - ii'ii i'/t'tt" /t=ii'i---ll- / '-== t::- " 1 Teo e N to g [ii'" l "o K s × / -IF'=== > 4s (( G -Ta e- qm Tm .1fi x :.1 io. H eo n ve e "NG 't ･: ･ta. o 5 E= == i= .=.l...,.,I...=.S nh- Fig. S. Isopach and lithologic facies rnap of the Harutori formation (Number in circle is the thickness of the formation in each localityJ Sedimentological study of the Paleogepe basin of Kushiro in Held the development of a tolerably thick coal bearing sandstone member is found in the Tenneru formation. The changes of facies and thickness of the Harutori formation in various areas are illustrated in Figure 5. -Discttssion- The characters of the changes of facies and thickness of the Harutori formation can be summarized as follows. A) In the area of Shiranuka and Harutori as the center, it is a thick formation principaliy composed of fine grained sediments, and at the same time seen developments of good coal layers. B) As one goes off to the west from the above areas lithologic-facies become suddenly coarse-grained, the thickness decreases, the coai layers become worse and decrease in number, too. In the areas of Takinoue or Kuomanai, the formation is composed of considerably many pebbles and conglomerate layers, which are characteristic of the formation. ' C) Likewise towards the east from the areas of Shiranuka and Harutori, there is a considerable decrease in the thickness of the formation, and the develop- ment of coal layers become worse, but this formation show no tendency of so much grain-coarseness. D) The difference, which is characteristic of the changes in facies and thickness of the Harutori formation, from every upper formation is that there can not be recognized a clear NEN-SWS directiofi o'f' extension which is seen in every formation(*) in the present area. This fact is clearly understood when com- panion is made between Figure 7, and Figure 12, below. 3) Tenneru formation This formation, throughout the upper and lower parts, is composed of conglomerate, with sometimes sandstone, siltstone and a!ternatson parts. It sometimes includes coal seams, too. Pebbles are dominantly composed of chert, red or reddish brown in color;chert pebbles may attain some 30 to 50% of the entire riumber of pebbles. This formation abounds in gray chert next to red chert, but is composed of comparatisvely less igneous rook material. It contains, as other kinds of pebbles : black slate, meta-sandstone, basalt, andesite, schlesteine, diorite, quartz porphyry, hornfels, porphyrite, dorelite and diabase. ' The characters of the facies and thickness of this formation in the vasious region are shown in Figure 6. -Discussion- What is to be noted, about the changes of facies and thickness of the Tenneru formation is the following. Gi) The character of such a vagueness of direction of extension can be considered to cor- respond to the fact that no clear direction of extension can be seen in the changes of either the thiclmess or the quantity of the coal layers, main coal or lower coal in the Harutori area, pt pt Ri Co. te' -ua 1' I `ltX x x, *ii Q l k i( s iXs eq SN b .P N / t x Ns Z rza-anV FORHsTloN euTcnops ss 1,,X rs ISoPAcH LINES oF TENHEntt FaHMATIept N to oo ･ ;ua e Tm' t.'-'- k" .PAttTlcLE.S[ze eF pEseLE e so e l"xx Se 1 v Fig. 6. Isopach map of the Tenneru formation (Number in circle is the thickness of the formation). Sedimentological study of the Paleogen'e basin of Kushiro in Hokl A) The characteristics of the facies of this formation being distinct from those of the Beppo formation, are that it is a thick formation in the southwest or in the south with decreasing thickness towards the north or northeast; the thickness suddenly decreases in the north or northeast of the areas between Chikupenninai (upper stream of the Charo river)--lower part of the Shinku- shitakara river-Shoro-Beppo. B) The change in grain size of the formation quite agrees with the changes in the thickness. In the areas of Rushin and Urahoro, the formation shows remarkable coarse lithologic-facies, and becomes gradually fine-grained towards the north and east. The grain size suddenly decreases in the parts to the east and northeast of the above mentioned Chikupenninai-Shoro-Beppo line. C) The data from Konbumori and the Senposhi peninsula are not always numerous, but the tendency is seen that the southern portions are coarse grained and the north, fine grained. ' D) Generalizing on the basis of the above mentioned points, one comes to the conclusion that the erosional area which supplied the ciastic meterials, which chiefly consist of red chert pebbles, to this basin must have been located to the west and the south of this sedimentary basin. E) It must be noted that facies of brackish or marine water fauna appear at the eastern edge of the Kushiro sedimentary basin for first time in the upper part of the Tenneru formation. And at the same time, one will be led to the thought that in almost all areas of this coal field this formation was formed as alluvial deposits in terrestriai environment. Thus far has been a report on investigations about the chahges of charac- teristics of the lithologic-facies and thickness of three formations of the lower part of the Urahoro group. A characteristic cornmon to the Beppo, Harutori and Tenneru formations is seen also in the evidences that the fundamental character of the Kushiro coal field, namely the NEN-SWS direction in the change of the thickness and lithologic-facies has not yet appeared. As already described, the two formations, Beppo and Tenneru, have been supplied with compounding materials from quite different areas to the north and west or south, and they show the opposite thickness and facies changes but the direction of extension of isopach lines is coincidentally NW-SE. It can be guessed that both formations were deposited as fan deposits or alluvial deposits constituted of the supply of coarse grain crustal material from the upheaving area which was not very far from this basin. These two formations intercalate the Harutori formation between them and they show clear difference in lithologic-facies, which indicates that when the upheaving movement in the north area was nearly ended, a more active rising started in the western and southern mountainous areas. pt oa [i. t""'f"-"""" @d..t"" """. ifv JJt""u"""::J.'.'-1"J" t" tr '""""""""'"-i-""'""..".""""f'.- Q if" -"""""."..".f.:."..e"'' """vv""""""v /s """"""'f'""." t" "" .t""""" """"" "v" yy...." "x/"xxv.s"""""./" '"if"t"""if"vi"fif""t"if" "" "vif"tt"if" '/""""" '" ".""tJif"""".x"s"'"" ."" ""-X""":"""M"X""/ """ e K fi "" /S" Slrll.tt.lilli..,.Sig'ti$.'fis.2ifi･.l'iil.o.･".il;.i.:".･.".･:,di J" =-=-;' -f-"(t")..." "" "" x N" " " "--: :" p":- @ -==-=;L:=L" ""L-L"di:. n -. c"rt:..; -:f - .c.' " "" sc.:.. .. .4x"" -""" "". "" . if"" ., K > e :.q: mf-l: k-RurePl FaRntTlets ::. --t aappo m t:NNteb teptTte- FeA-rTap o 5 le t xa C EZI - Fig. 7. Geological section of the lower Urahoro Group (A-A', B-B'-B'! sections m (Figs 4, 5 & 6) illustrating the change of thickness of Beppo, Haruton & Tenneru formation). Sedimentological study of the Paleogene basin of Kushiro in Hokkaido, Japan 451' (II) The upper part of the Urahoro group The upper part of the Urahoro group is divided into the Yubetsu, Shita- kara, and Shakubetsu formations. The characterirtics of the upper part of the Urahoro group will be grasped as the "2nd stage" of the Kushiro Paleogene sedimentary basin, which clarified its fundamental characters, and prepared for the conspicuous subsidence of this sedimentary basin in the Onbetsu stage. 4) Yubetsu formation In the neighbourhood of the Yubetsu coal mine, which is the type locality of this forrnation, its main part is a fresh water facies composed chiefly of sandstone with siltstone and sometimes conglomerate subordinately. It contains 10 coal }ayers. The uppermost part of this formation exhibits brackish water facies. It consists of aR alternation of sandstone and siltstone (thickness about 40 meters) and contains several seams of coal. Fossils are found of Cbrbicula tofeztdui, Batissa sitafea7"aensis and Ostrea sp. in large quantity. The lateral change of lithologic-facies and thickness is rather conspicuous, especially as one approaches the western part of the Kushiro coal field, namely in the upper course of the Charo river, Urahoro and Rushin areas, the lithologic-facies become remarkably coarse grained. In these areas it is diflicult to distinguish this formation from the Tenneru formation except that the former contains coal layers. The changes in thickness and lithologic-facies of the Yubetsu formation are indicated in Figure 8. -Discussion- Different from the lower part of the Urahoro group, in the Yubetsu stage, the clearly distinguishable features have clearly appeared. A detailed con- sideration of these characteristics will be presented in a later chapter. Only their main characters can be enumerated here as foliows : A) In the changes of the thickness and iithologic-facles, there appears a distinct NNE-SSW direction of extension. .B) A remarkable thick and rather coarse grained formation had been deposited in the Yubetsu-Kamicharo areas, there ascensional movement took place that expanded to the Yubetsu dome. C) Towards the west from the thick deposited area, the thickness comparatively decreases, and in the west of Rushin to the south-west this formation thins out. Changes in the lithologic-facies are seen parallel with the changes in thickness. The changes of lithologic-facies are clearly recognized in area from east to west, namely the area which consists principally of siltstone, the area of sandstone principally, and the area containing conglomerate. D) In the area south-east of the thick area in Yubetsu and Kamishoro is seen a remarkably thin formation having the NEN-SWS direction of extension which is parallel to the above-mentioned thick part. The changes in the thickness from the thick formation of Yubetsu-Takinoue to the thin formation area are " Nor 20' K yvesTsu nvTtef OurcROPS t- =-;=u- 14 -----t- [Z] ,,,tt=i'i"i-1/I･C-/E-,!-･(i4,.,;-,.-lli'l+'i`,filj2-･iLii =: 30E =--::= ceNaunnm = sANosTouE E4eT'ES ' SANDSTatiE FACIeS.' -i･ ;･. 300 .:ii ::i-=' .-:-I-:-' :u=t=-"i-: i=ll-:I :23 Elll:i SrwbSTDntE t Sl L:STvNe fiAC:ES . 1DO :V6- . I-Z-1--:--"i Jt---t-::'- ' - -..= - - t . -' =: -t :T- --. ."- +-- -==-=. .- -.", : T':::--=.'N- ..J-::=:::' = ;ir -=-IS :==:= 11 :-- :: --.----.::' - 1.! i:-"' iE' ,lo' ";' Ei-i-: de '7-ii.1.i,ig"r' --ist 3ao -- '--itttJi-t.ir la .: :,i-t/.i･ ' -' l-:';-Uf'E-l Ell3E"-tttt･ -..;.". :: ':- ii i='-"" -:.lifm....,t..t 11 =-.-. :t=-.:L l,r-,m-i",,- t..., 1 .-:i-i,.'-=.t=.:-iZFeL g 111 :- .iiilillaEliilllil --tt t +:.:=- :M-i;i+:.lpK=+ ':te":::::::n;H------=:;' ----L ------lt i' ' K 14e > 6 m -s- n - l=. r. 11 .JTso- c `p ･1 ltl :- ' ' tt: k ue I[}ii i2"-i'-- '= 4o B5 '' . ' ' .. tt 1ir# [- 'as - ' g Eg･. N ' =LptrTi[iT" v.:==:=-m 4e===- .: .: tsa e EF r- r:J-.r -' ' j ieo S po .p; .np- Io' l Se e i ,# / Fig. 8. Isopach and lithologic facies map of the Yubetsu formation. (Number in circle is the thickness of the formation in each locality). Sedimentological study of the Paleogene basin of Kushiro in Hokl VKeTAmli'vPU.:].R#S:N ANT[CL:NAL ZoNtt TVSETStt-SHAtcVVETSV A-T]CLINAL :OptE AtAN sAeRe 2eNt 42 L.S 37 3Pi 3"l 4FJ -1 " 1 2 ) e 7 ]1 T2 13 IA 16 17 IP 20 al 23 2e 27 2e se 31 3a 3b l'-::-; e. x. xpt LtJL･) -: xpt tv, / 1 /tt ;'tl I･3 gff tt-T fust" pt /, t""" .g 't ./ ' 1 / E:･･ ' x, e, £v: .. /. .ntu t;'i' R ny f " ///t -s.rt: ,[ "･ ･1, ilt .t /)t: t k". l et 6, -be 'i]': e" g. iT.' x I･i as ' s. 'i ,g- { t dix 1i !.rt', 'i' -za ff-" ITa' 'i'"'t tlg.i NX t o -rj f ' g RS..t ,' in- T /t= I f ij."'n", ys ;,a' t/}. IEhl's.{ yi, tt- el g..s- ' te. q .M 'e' ･l, '6･ er: T u- l ' p,!- / st s e' ee ee x ¥ '..c. x .-I gf ' / ,e ee sc e x tt "ei {t/N' vpt･ t"' s-: /d .' *. { l'e"L m I ,., g si' l.li･ s J #, -s .x i,' as ee... i"' lti･ ge- l ' ti/･, x t/. t. f x l,,, ,' / :'it t x ?t;･ gek Y. IS * / #tk-*t-; t n' in- s' -1 "mett X itt., f g. ag x ; pt- t.//t J:y 'r' ee･ t t{ ! tt 1 l, r x " ?")'t' ,)Sx $- " / × e x x. x ' x. s 'tE-- / ttt -'ti' x t/. " / sc $.b T k × × x ge 1 ' k x g ･W ･x s tF-- sc ' ,in: 1, ' x x .e, # su X Tts x x'X.- -sc xes w . n. TJ rlOc- i ix .' - > iif k s L-e ' x gg m :ttL " ;/tlt ¢ )/t SItTtTt-t M x-st ett[S--b:TOTt 1an l:i :eA-Stsi-o:TeHT .x ,.c cex-Lettl-Tt 1"･ lif. 1･,, ' SA--HFI o stlle lsl 'L * -e e----fldS 100VLt T se :-peltelt-tPVIt su e va tex-lttLs × tt'p × OSTIt- e t--IMt SeL;tSt- pt e Fig. 9. Columnar sections of the Shhakara formation. (Locality numbers are correlated with those of Table 4 and Figure 3). l an' is･g;:.i..,.. i?'?' .t/.:'/.11t/./l'i't.i.1t. tum -pt-. -itie'"' x .ig6., e tttt .tt t:tt tt o ' i-'/･1,,. 22fi ' ttttt t SITAKARA FDneTION DUrcRO TS '.X: 11S : .,:1.GS ' .E- : ':' ;=-･:･-･･- 1/-:I-:':-1-:-.' -o :'r Ii:iTa='･:- ':':' CoueumTE FAelES ""-i':i':'t'' o- I oo Esgg] Sn"msTvme FAcTes -- oe o l':-i'I,i'i'i-".lig'`"Seai pt SI LTSrONe FAtlES - rm lo' ,1,i･,i-l,1-/1,i-i-1･... I.-- '･- 1' 3ti IA.O . N Y e" - 1.t/1/ t:i 1fiD Nh" ' o- ll5 ve" ll@'''''15e ･=d 110- o s" =t --' wan '-'=- leo 3 'o o ..;:.:.:"l`:･:･: .:.:.i42 l'. ::-:-ii-i･f.','/J'Il' .x. 1 sc E o :-:-L:.;.:. -: i-:':::-M141 .::-::':'-:･:-:-::-i',:,'II! F : ee tu 43' ww. ":.`. ltl':::.'.'.' .=v.:::' '.;.:.;.;;:.: tr 3SP .:v. : T･4 1 ;-:･:-:･:-:･ i-:･:･:･ :.r :･::'..:.' 2 1ti t E- --o------.L 15 -:: :;: :.- :::' 3eo :-.=:::: le . .:--H' l -ab ] ig ,-:,tii`,:':L±'j,4D.,':.:",i,･,1.2.g, m.- ,x +-:' : lse ::::' il,:･,li.,,'S",,k:,-,t･i:: s ,t･` =-t--;--:-::: " b. T. ;: 's 8 i' ::=.:::...==..=:..:" 2se rt' s p' e MKI ':'i-'::-:':'/1･;{':.l'ii･:･:s:I-ll(}i' lee : o g so gi" tr. "Q' 'r' NO Fig. 10. Isopach and lithologic facies map of the Shitakara formation. ptg vm (Number in circle is the thic kness of the formation D in each locality). pt ena pt a 2od 1 pt KT-Nt N' ･ ' .1 1 1 ･･"･ -･ 1 g Ni g ., " l.ltl.:t t tt g Na･ t tttt le: ･T- ' 3 1" n N3-N4 -1 3 4 .1T- . 2" 3･ '1 2." 2.S g / , r-1 . x +3' y > 3 s l. a, Cm te 3" H ,,,T :. :.T-'5,..,, ;tt - -: tt tt :Iil: ･1 . tt t "g ,,,I ,. k t' sc oss min tt. Fig. 11. Biofacies map of the midd!e part of the Shitakara formation. NT: Tidal zone, N1: Euneritic zone, N2: Mesoneritic zone, N3: Subneritic zone, N4: Bathyneritic zone. Table．5． The Fossil Fauna of． the Shitakara ．F．or㎞ation ． Locality．Numbers correspond w三th those of the．Ta’ble 4。 ア ■ ・Occu工encg r 幽 10 11 1 2 3’． 6 7 17 19 23 26 28 31 32 34 36 38 ，rpecエeS 2122 3941 42 4344 輩．1＝ ． 「 Ac．11β （Acila）vigilエa （Schenck）． ． R R R C Dムc1」．a 8P． （ 66ugii type ） R 層 ． R ・． R R pcula胆BP、 G R ．Yoldia 〔Yoldia ） 、’1audabili8 Yokoyama ． G G A C C C C σ G C Yoldia （Tepldoleda ） 80brina 曽akgda C G G R R C G Poエtユandia（Portla且dla）田ata8ei（Kanehara） ． ．．R R C C ． C 麗alletia poτoロaica （ Y．bkoya皿a ） R R G R R R R 08trea pτaeg工avi七e8ta 甲akeda A A XA A．A 今 A A A A A ．A A A A、 A A A A A A A A Glycy団eτi3 8P， R R R ．Hytilus．mabuchi1．Oya皿a et Mizuno． R ， A R ProP臼a皿u8iu皿 k肛8iroen81s Ta≧eda R R R』 亀Clinocardium asagai．：en8i．8 Makiya皿a x G C R R 聾e由oca■α童um ezoense Ta｝【ed阜 ． ． R A X A A A A A A ．A A A A A A A A G G A R 聾θ田ocardiuH｝ yokoyamai Takeda X C G G G C G G G G ．G G C ．G Gorb工cula tokudal Yokoyama A X A A A A A A A A A A A A A A A A A Bati畠8a．8hitak母士aeRSls （Suzuki ） A A C A G G C G C． G C C G A A R Diplo〔10nta sp． R R R Go口choce18 bi8θcta （ Gonrad ） R R G C C 7’． ． kuc1且a 8P， R R Periploma be88月目ensis （Yokoya田旦＝．一）．．．．． ’ G ． C G G G A C A c Venericardia expansa Takeda X G C c C G A G G ．G G Venericardia tokudai Takeda ・ x G A G G 1 G C ． C Venerlcardia a｝【agii Kanehara X ．C G R ． ．G C ．9 MaCOma ．8ejUgata （ YOkOyalna l C C G A A A G A ．C A A A Macoma a8agaieIls18 Makiyama G c A ．G A G G A 戸ita■sorachien8i8． Oyama et Mi別no R R G R R R 一Spisula 80■ach‡en臼i8 Uozumi R R R R R Chlamy8 ku8iroen8is Tak8da ．q R R R ． A R G R Solen sp． ． C C R R G R R R R Mya grewingki Makiyama A X A A A G G A A A G．G G G G G A． A G 諏． Turritθ］Lla poronaiensis Takeda C C ． A ．C G C C R G G C．F．．奨’ Trochoceτ1thiu司匹wadanum （Yokoya皿a ） R X層 R R R R Neptunea Shitaka■ensis MatSu1 「 G C G G G ．G G G G C． Neptnn8a shoroensis Matsu1． 畠 ． R R R R R qG． R・ ．正可eptunea hu工hhatai Matsui R C R R R Neptunea modθstoidea．Takeda ． R Neptunea．ezoalla Tak6da R ．R Ancistro1βP．is sp． ． G R R 」墲盾撃盾垂盾垂?ｏｎ８ kusiroon8is Takeda G G G R R R C C R R R ．．R C G 7 ． ．一 ． ． ．．一 ．． ．． ． ． ．．撃浮撃狽撃唐博miata （ Takeda ）．． ．． rcaph註五a6r． R C． R Epiton1廷醗 （ Gir80tr．eola ） ezOen3i8 騒at台u1 R R R ． R ．R ’ EPitonium （ Boreoscala ）層yama010toi 匿atsu1 R 一 R R Eplton加皿sp． ． X R R R． R TUrriCUIa 8hitakarenSIS 蘭atSUi R R A田pulina a8agalensi8 Makiya囮a ． G X C R R A G C R C C．、 Tectonatlca 8P． ． G ’ ．R R R R ．C Dentalium nunomae Takeda C G ．G G G ．G A c C G A Llntnエa ye880θn818 理11na1｝0 R R R OPhiuroldθa sp， ：・ R R R R しaよ⊥lana8Ba 田urata1 餌agao ． R RD Sedimentological study of the Paleogene basin of Kushiro in Hokkaido, Japan 457 C) Towards the west from the area just above mentioned, the thickness decreases, and at the same time through the west from the east the whole formation becomes coarser and the subdivision by lithologic-facies becomes ambiguous. D) In the Kamishoro and Nuibetsu area, which is adjacent to the south-east of the above mentioned area of thick formation, is'see'n'a remarkable thin formation. This change is rather sudden and discoritinuous. In the south- eastern part of this basin, namely in the Shiranuka, Kushiro and Konbumori areas, this formation principally consists of fine-grained sediments, which make arather thick formation. '' -Paleoecological summary of the Shitakara fauna- The kinds- of molluscan fossils produced in various places' in this formation can be listed as in Table 5. The molluscan fauna of the Shitakara formation exhibits a gradual change of brackish-->marine->brackish from the lowest part' to the top, and if an examination is made of the whole area of this sedimentary basin, one finds remarkably distinct characteristics of each area. In the area of the Yubetsu dome district, and the eastem part of this basin there is'developed brackish facies represented by coarse sandstone bearing some layers of Osti-ea beds in th'e" lower part. This part are changes gradually to the'middle part of marine facies made of fine sandstone or siltstone containing many kinds of molluscan fossills as A]laptunea, Adya, Vlanericarclia, Ybldia, Acila'and 'so on. In the upper part, the formation changes to brackish facies producing a large quantity of Ostrea, and then this formation changes into the'Shakubetsu formation composed of fresh water facies. When the molluscan fossils are included in fine sandstone or siltstone of marine facies at the middle of this formation, it may be safely said they present strong locai characteristics. Further, as shown in Figure 9 the three facies, brackish->marine->brackish, are considerably different in their development according to the areas. In the west, almost all the formation is made of coarse-grained facies, and the thickness of the marine facies is considerably restricted. On the other hand in the west or the east there exists considerable coordination between the thickness of the marine facies member and the total thickness. In short it is known that the ratio between the marine facies in the for- mation and the brackish facies above and below, gradually increases from the west to east. It is recognized that the kinds and quality ratio of the molluscan fossils in marine facies show considerable difference according to the areas and horizons; The manner of these changes is shown in Table 6. The marine facies of the Shitakara formation is subdivided into the following five types, according to the characteristic assemb}ages of molluscan fossils which are contained in each 458 M. MArrsul TABLE 6. Bathynetrical analysis of the Shitakara and Onbetsu Faunas Bateymetrical Range Species H. Nt Nl N2 N3 N4 Nb Coi'bi]cttla tokt,tdai･.･･.･-.ny･.･ Bat-issa sitaka7uensis ･.････ Ostl'ea ' Praagrawitesta ,.･･.･ Tectonati]ca sp. ･,･･.･･,･･.･･.･ A'niLPulabza asagat'ensis･.･･.･ M),a gj'ezvt]ngki-.･･.･･.･･.･･.･ Linthia yessoensis･.･･.･･.･･.･ Oliwella ezoana･.･･..4.･･.ny･.･ Molopophorus spp. ･････････ Scmphandei' spp. ･.･･.･-.･-.･ Macoma sojt{gata-.･･.･d.･･.･ Macoma asagaienst]s ･.･･.･ Ebe)itonitti]t spp.･.`...,..,,.... AlePtunea spp. ･.･･.･-.-･.･J.･ Nlimocai'dium spp. ･.i･.･･.･ Venei'ica7'dia spp.･.･-.･i.,-.･ Tttfv't]tella po7'onaiens･is ･.･ Yoldia spp. ････.････････-････ Pbf'tlandia spp.･.･･.･･.･･.',,.･ M{cttlana spp. ･.･･.･･.･-.･･.･ Mallett]a poi'onaica i.･-.-･.･ Pk7i'iploma besshoensis ･.･･,･ IVbopsaphaea antiquioi- ･,･ Acila (Acila) wiigv]lia-････････ Anct]sti"olapis j'mponicu.s ..･ Cdlli]anassa mtt7utatl･.･･.･･.･ ,SPI]IAOtl"opiS (Anti]Planes) rugosa ･.･･.･ Tui"cicula sakhaliliiensis ･.･ Solei2ilya tokttnagai ･.･･.･･.- R'opea･inttsitein ...... ,.. kttshi;i'oensis H : Braekish zone, Nt : Tidal zone, N l : Eunerltie zone (O-20, 30 m), N 2 : Mesoneritic zone (20, 30-50, 60 m), N3 : Subneritic zone (50-100, 200 m), N4 : Bathyneritie zone (100- 200 m), Nb : Hemibathial zone (200-300 m). horizon and area. 1 ) 'Fossil assemblages of Ostrea paleagravitesta and Corbicz{la sitakai'a- ensis : (H). 2 ) Fossil assemblages of Nemoca7dium ezoana, Mova kusiroensis, Ostrea Sedimentological study of the Paleogene basin of Kushiro in Hold{aido, Japan 459 2baleagravitesta:(Nt). . .. . 3) Fossil assemblages of Chlanays kusiroensis, Macoma spp., ATk7ptunea spp., Molopophorus kz{siioensis, and A47mocardium e2oana: (Nl). 4) Fossil assemblages of Zipitonit{m spp., IVleptztnea spp., IVI7moca7"dium spp., and Venerica7zlia spp. : (N2). 5 ) Fossil assemblages of Ybldia spp., .l]brtlandia spp., R7riplonza bessho- ensis, 7le{rritella poronaica and Scaphader spp. : (N3). 6) Fossil assemblages of Acila sp., Malletia poronaica, Cbnchocele bisecta, and Nuculana sp. : (N3-N4). A careful consideration of the assemblages wili be included in the discussion below of molluscan fossils in the Onbetsu group. Here are given obvious conclusions. The change of these fossil assemblages 1) to 6) can be regarded as indicating the increasing of the depth of the esea, uneritic zone-mesoneritic zone- subneritic zone. The extension of each zone in the rniddle part of the Shitakara formation in various areas can be depicted as in Figure 11. The extent of the distribution of every zone is in close accordance with the characteristics of the lithologic-facies map. At the same time it should be considered that the characteristics of these assemblages not only reflect changes in depth but also the effect of the differences in the sea bottom sediments. As has been noticed above, the characteristics of the subsiding movements of this basin when the Shitakara formation was formed, and the changes in depth to the bottom of the sea do not always coincide. That is, that the depth of water in the sedimentary basin in respect to time and space niake rather remarkable changes, can be seen as characteristics of the basin. At the same time, it must be noticed that the subsiding movements of this area had no relations with the change of the sea depth, which evidences itself as the facies changes, and the subsiding was a higher dimensional and longer dontinued movement than the later. 6) Shakubetsu formation The area of the Shakubetsu coal mine, which is the type locality of this coal bearing formation, is composed of alternations of gray medium arkose. sandstone chiefly and dark gray siltstone subordinately; several thin conglomerate layers are seen in the lower and uppermost part. Observed in this formation are 20+cyclothems of sedimentation. In the western part of the field, the `CHato- kuso conglomerate." which is characterized by white pebbles of liparite or liparitic tuff, is developed broadly. The lower part of the formation consists of sandstone of brackish facies containing crowded Ostrea 2baleqg?"a2vitesta, Cbi"bicztla tokuclai, and Batissa sitafearaensis; the middle main part, sandstone, siltstone and numerous coal layers, is fresh water facies; in the upper part is again developed the brackish facies. Further, marine facies are seen in some parts of the eastern ares. 460 M. MATsUI The number of coal layers exceeds 10+ in each area, but their number, thickness and quality changes follow the distinct variation of the facies and thickness of this formation in each area. The changes of facies and thickness of the Shakubetsu formation in various areas are illustrated in Figure 12. ie' ii':t,trl,t-l-i./Li=' .,. .i{ T5e }i':;'='-= -=-=-=-- ---K-i' '":lee e -2bti iilT '-l[11S,/i=i =Uo-...... =' ' :'::'t :=Z-'tsl:]:-..ffx----T '21aL?-es SHSKUEEISU fOnHAtlO" ouICHOPS t2.[li.t/'.ti :=.z=ts: 21e [z] --==:==-="- , 2 I=vfiL - "o :.z.- .le.t--:l- -,isO- "o eestGtoKERkTE U SA"OSteNE EACIeS .+lg-ii[lo.'tt:IHE.;.gg.i.='.. =- .- Yrm-', -l3 - ]o' ue' 1- sAspsTaHE sAc;ss ."-- 6e =" 2ee.t. m --- 'zyi,-,-,-.-i'E.'I':i'-':i -t us t"':;="[-"':": Tl5 SrvvnsreHE t sl:Tstrona sAc:ts NtaO Z =::. ':-:J: ISePACH L!NES oF HAToKuSo sc"alO"ERATE s e ' l:: '.r::･:･ ,. 1- [z] ,,'i':ISO-e"c=eT e 25e lee-' llEili"!'i-ix:-:"t='i"-- :"- o: 43 lli,l !Ee･ =:: 3B t;:lf ,: 11' 25e fie '"'i K-[--+'2'::-:-:-:-:iit.:. '.Z e nerm -::::::i.::'-:EII/:.:. .: a e = tso ii:-lli.. :-I:'i:l--i=:il nv 25e op Iee =i i- Pe 4t I s` ,T.li l,i":'i t;:'÷/iTl'tt'.il.lffi. e no ･-. aoe -.r:Nr' s3'i,ii':ti/T' tE't.:,.i.//Tl :'n. .. te .ri"-xzx/i.'t-,i-l,i-E-,i-,. F; -:: / t tt- ee :l=-' -- --- i {gltArk l-li t･.,'i t-"14e:.:.:t- fi so .i' y. 3e Et]:-E;:.:.: -::V.:1 g -.=: a--.- -:- i-1-:-1- ,i ･I-:-:-:-. X:- l-1 =Zii.}`'t'::.:'t-l:`i-r-.':-.tLitLz･/i,"i'ioe 5n' S41:t:.-;･-.:.-'.･l-.:.:.-.. lse "' ---...... '-----t'-t-----..-.-..:.: -'".,r-.tL-,tpt-.,-, so ' . e --L"-!: ' -s Fig. 12. Isopach and lithologic facies map of the Shakubetsu formation. (Number in circle is the thickness of the formation in each Iocality). Discttssion- The characters of the changes of facies and thickness of the Shakubetsu formation show the same tendency as those of the Yubetsu and Shitakara formations. A) The changes of the thickness and facies are recognized to take the distinct direction of NEN-SWS. B) Along the line connecting Okuyubetsu-Takinoue-Kamicharo area found remarkable thick developments of the Shakubetsu formation. C) Towards the west from the area just mentioned, the thickness decreases and there seems to be a thinning out at the western areas such as at Rushin, Nisho river and the uppermost course of the Charo river areas, but as the base of the Onbetsu group covers this farmation unconformably in these areas, the usual obvious characteristics of thinning out can not be observed, Sedimentological study of the Paleogene basin of Kushiro in Hokl D) In the areas of the lower course of Shinku-shitakara, Kamishoro and Nuibetsu, which are connected with the south-east of the above mentioned area of thick formation, the thickness of this formation decreases rather suddenly and discontinuously. In the south-east of this area, the thickness is gradually increased. It attains to about 270-280 meters in Shoro-Nakashoro. The direction of the thick part is aJso NEN-SWS. ･ E) The changes Qf Iithologic-facies are remqrkable in this formation, too. The subdivision of iithologic-facies-conglomerate ' facies, sandstone-siltstone facies- can be made as illustrated in Figure 12. F) The good development of "Hatokuso conglomerate" is seen in Tokomuro and Urahoro areas; decreases in thickness and grain size are seen to the north or east. The conglomerate is traceable in the area of the upper course Qf the Charo and Shoro rivers, with branchings off of several thin layers in these areas, but in the eastern wing of the Yubetsu dome, the Hatokuso conglomerate suddenly decreases, and gradually thins out. G) Towards the east from the line connecting the Yubetsu dome area and the Shakubetsu-Kamiatsunai districts, the uppermost part of the Shakubetsu formation bears beds qrowded with Ostrea and Cbrbicula remains, 10+ meters thick. Towards the west from the above mentioned line, on the contrary, these facies are not seen; the base of the Onbetsu group unconformably covers the Shakubetsu formation. In these areas, the eroded surface of the latter is observed. In the more western area･-the upper course of the Chikupenninai -the Omagari member covers the Shitakara formation and Yubetsu formation, and at the uppermost course of this river, it unconformably covers the Tenneru formation. The same relation of the Onbetsu and Urahoro groups is seen in Tokomuro area, too. H) In Yubetsu, Kamicharo and Shoro areas the uppermost part of this formation contains numerous remains of Ostrea sp., Cbibicztla spp., Adytilz{s sp., and a few Macoma sp. This fact affords evidence that the marine water influenced this horizon near this area. This tendency is supported by the discovery of Osti"ea sp, from almost all horizons of these formations in the area of the course of the Kamishoro. I) From the above evidences, it can be conjectured that the gradual change of facies, from th･a- lower to the upper part of the Shakubetsu formation, brackish--.fresh-->brackish (a part marine), increases from the eastern to the western part of this coal field. -Summary discussion of the characteristics of facies and thickness of the upper part of the Urahoro group- The writer considers the Yubetsu, Shitakara and Shakubetsu formations as the upper part of the Urahoro group. As already described, the gradual facies change of this part is as fo!lows : fresh water-->brackish water-->marine water-> brackish water-->fresh water->brackish water (a part marine) in decending order, pl ctN -SS-.it'-"-g-g'tt'"i･'///{'///-i./rl,'.i-,/;--･/{,.,tt..z-=,,/ttti-.-.,.///.-".g-,/g',tl//3;/t.i-ii-,l//t,-2i%i/ttE-i-i-'"s-i';--;' if s-- v"t o ' ts 2o-" 2 3 -'-tt---=t"i SJLTSToNE t smosTe-e FMtEs U SAH"rra-e tae;rs e.':. oOe' co"cLontR-TE FAcTas l:ftOciSpeEeeLeeLf noom -- @ Mkkts XEs? "p " "w. S' .... g' .,. .ttl'r':,sgi.xl{･tw.,x` .･tlibel: yevav-.- --･vc-- -- "-" 'S'dith "eimH e.,;fp v"x t""" ' ig.Stas @ "di gl. x:"e, ' } .;. llli ;s X.n .ee.. ' wf. diijpp" -;v " """"/- "{ii,E "nt. ."-. ""ENr･ " . .;･ W "i$l;ny.tT･dii5 v"T-'.ti-.-ILVIL.;.'3?ElllE-S-.='ma "F"L K v def..di;x". l ajlystva "'"SL- tr ' "'( . ;". Z}lrIX,gv'; tva-;;te va" "vH E tt "tt"tJ ee K (!i)) > H ee'""ivdiJ.',")･:i"i.,"tJ"ll.,ve..::'3's et llg:"' .e::si';sts" as' ¢ an'" nv- t"pt gW S. L･"-.esk,.Zva..Xv:sibtsrvas .EsS' W-a"s 'tw. H."'1.S:t".L/,;."es-te) J'geL-" - "- m "" ".s.:i"vas H stin' @ V JA-" i"pm±"ts"ta"';"za.:epn;il'ldi' aEv, ts" ePl. vtcr '/ v" as .t2,:.."MauaL ve .mkfus-Egeta･ pt fa }lsY:ge. -. .SS.e:..t). ifis?llehaeere mpmptf @ S ")V h" s"thpt-tES, lj 3't'gkS}.' WkSggivaillSii,wallmabe"maewmawhtz sS -O-S t-k "n "t L o llgelikewl.. imiglfisil/esx ekt "V""s .sE"" $X-. ". NX" S Fig. 13. Geological section of Urahoro group (B-BX section m Fig. 4, 5, 6, 8, 10 & 12) @ Beppo formainon (li) Haruton formation @ Tenneru formataon @ Yubetsu formation @ Shitakara formation @ Shakubetsu formation Sedimentological study of the Paleogene basin of Kushiro in Hokkaido, Japan 463 Each formation or member is composed of coarse grained crastic facies in the western area, and changes gradually to finer grained facies to the east. On the other hand, characteristics of areal changes in thickness of these for- mations are almost imutable as shown by isopach lines of the above mentioned Figures. The characters which attact attention are that, in spite of the fact of repeated facies changes-marine facies->brackish facies->fresh water facies, the subsiding shown in the horizontal continuity of the faeies and the changes of tchoi tk nC innue itSyOifsesahCohwnfOI.:ia"iiOgnu'regids,ngOtanddisrlulp.tthesesamecharacteristics. This The writer wishes to characterize this 2nd stage as having the fundamental characteristics of elongated directions of the subsiding movement and sedi- mentation. This stage continued into a general subsidence as shown in the Onbetsu group. The geoiogieal section of the Urahoro group is illustrated as in Figure 13. g6. Changing of lithologic.facies, bio"facies and thickness ' of the Onbetsu group through the ages. The Onbetsu group is composed of marine deposits, consisting almost entirely of siltstone and sandstone; it overlies the Urahoro group, with a slight unconformity in the western part of this basin, or almost conformably in central part of it. The group is well developed in the central and western parts of the Kushiro sedimentary basin, but in the eastern part of the basin it is eroded Qut unconformably with the Neogene Tertiary or Quaternary deposits. On the other hand, in the western margin of this coal field, as may be observed in the middle or upper tributaries of the Horibetsu river, the Onbetsu group is developing farther to the west than the occurrence of the Urahoro group. The group is divided into two formations as follows: Alternation of dark gray tuffaceous sandstone and light gray siltstone, containing pyroclastic grains, and Nuibetsu formation : sometimes intercalated with thin and thicl< tuff-breccia or agglomerate in the middle and upper parts. Charo formation : Onbetsu group (e£:iLfy,,gimaiY,:rZ,1i:,X,,`z,:,fi:,lti:e,g?aLztf,g,.-.ite Charo member: Greenish gray sandstone, intercalated with thin conglomerates at the basal Omagari member: part, upper part gradualiy becomes fine grained and transforms to the Charo member. The ieading characteristic of the Onbetsu group will be grasped as an indication of the conspicuous subsidence of the Kushiro coal field: that is to say, this group represents a developmentai stage of the sedimentary basin. I) Charo formation A) Omagari member: This member, is the basal part of the Charo formation, composed chiefiy of greenish gray fine to medium' sandstone and includes partially interbedded thin, fine conglomerate. ･ , The upper part of the member is made up of fine sandstone, silty sandstone or platy alternation of them. The conglomerate of this member has gommonly "Hatokuso" character, but its liparitic pebbies are remarkably fewer and smaller than those of the Shakubetsu formation. In the central part of this coal field, the Omagari member consists commoniy of greenish gray platy sandstone con- taining numerous marine molluscan fossils, many marly nodules in which marine molluscs are included, sand pipes, `CGenno-ishi", coal patches, fine pebbles and glauconite grains. ut~ ,.ri7I'l"l'ii:IlilT × ･':'.,z=.'.- ...=,.:1------･･ ("'x,i,... e te `el 5 ".-;J･/ti::.:J' .:i..,-. l. E/ ."/:.1: ..,,.- ., DX ...::1-I･ ..lliil･ii･i Tl.l., q' ;-:･ .. Se "- ' :'lfl'il"1'11'"'' -× d M osAaARt HEvEER eu;cRops ex ::'1' 'i " i' ' 111/1// ,-1･-li.':,''' '' '''I- 1s Ie' .r.:l."'l:=': sAt;usToHE k coHGLemsRATE ',ea::'::1:::"tt'/;'1::: i ie -× . 45 ' ' ttt . ',..//. "!'r ... SM'osroHe "' lii- l-1i {-i/i･ -･-･ .tt. . ttttt ...,... ' 1/ 'l i' '"il';'Ifi'11 E siLTsTeHE R '' b' . × /-/.･.･./ se . /- 'x, ...1 ..-t. "' "r/'l..' e /../ .. t .. {Iflltf･,/: Nx tt... tt /tt.. x t. t. .. /. t''''s'1' . ,if Rx HH.H e: "' 'l{ii t.t..lt .t - " o 2e ..=t.. /.. - -st ttitttttLt tl:tttt/t/t e)fp .,.i!6i,i-l.:･.li.,';l.l･il"l' r, :.'J:i 5E /' `)'X-. ,@'.' sei- ee."'･ 'l2 '": I' i'ti'' -ttt.ltiiil'i?' .3e (. } s /i /s l"' ttt,l'-: tt t ff.lil. ..- ･.=. t o Fig. 14. Isopach and lithologic facies inap of the Ornagari member. (Number in circle is the thickness of the formation in each locality). Sedimentological study of the Paleogene basin of Kushiro in Hokkaido, Japan 465 The latetal changes in the lithologic-facies and thickness are rather conspicu- ous in the western part of the field where the whoie member becomes coarse grained, but it is generally known that marine mollusca are included through the whole area. '' The changes of facies and thickness of the Omagari member in various area can be illustrated as in Figure 14. The main B)part of the Charo Charo formation member:consists ' of dark gray siltstone. of marine facies in which are found a considerably iarge quantity of calcareous nodules, "Genno-ishi", sand-pipes, sandstone dykes, marine mo}luscs and foraminiferal fossils. It contains in certain parts fine-grained sandstone and thin tuff layers. In the lower part of the Yubetsu and Kdlnishoro area, is developed a grayish white tuff layer several meters thick. In the western marginal districts of this sedimentary basin-the Tokomuro & Honbetsu river areas-, this formation consists of sandy facies and is very much akin to the Omagari member. But, they can be distinguished from one d2d "-. .r e rm' ien ast]-:L 12e [IZ] auRe HeceEn e rc -rm x ･･ ee 155 [z] avbESTIE DISIMBurteH lb'o'" D -so･* IIe.M [Z] owA"Ht MtHtsER .. .1 ..:[-.v :le ･.･.'./x,.{--K: ×- ,x S]LTSTaNE FACISS mur' so -- ×･.i-kl{.tt---,.' id j iJ .ttt'/,'g"''z`'IIilllleo s4LTsTeH[ s4r:DsTOIIV rActEs to' -t.' /O./tna.' -ve ./'.'E :r-' ' 3e '.' /'1'･'?1'1' 150El'... ' l 1fiO /<--tw ------SANbSTONE FACJES 'i rm.Le'- 111;,e.-ilsl.,,-.,,.ti,･:1ille.}i.･ -o-A･ .･- -- 2ee I -- 4Aa aAA AcaLoliEmTe -/. So 2SO e ･-- - -a-･-･"e. .1 ..---. .. :n' --A･ 1.e .'' lee' vV VvV AHDEs]Te ,-2･b." a':1':--a -- i' }} .../:g',,X lso v .ilii'llgf "'"'=,',:･.so llllii'Uii.;.'T-M tt :-:-if[l!IIE] caN"LoHEHAIe ...tt .t :-ttTJilgif?/-zl t tt '-4.:.i=,.'ii.i'.:.-1-1-/･.'i･1"a'ept- "uak . t.. "oo sNIDyetiE Dvttc ossTRmuTso" JO ;'.t' :.'A. T n=.t'=.1･ kliniziysa 4eO l ilL I .I 'At'.T.=. l 3.ii-.tT'= D -----1 ------.-r ..'ttlili' 1.. ne v･., ------l .･ milgiliki-il-tL,:-r e -v---QT;.-.,- H- ui ''v.' /fi /vlt/.t... 1,,, N Y iYf,1-, -' i ･･ - ln7s ll (x '': sea I ･,., $' II¥,ig- i tr G':- -t. sl o s lo ls ;o"n t--/ So -r - .r'/':'/-/ ': ;'e igs nt . i '.- X e Fig. 15. Isopach and lithologic map of the Charo formation. (Number in circle is the thiclcness of the formation in each locality). another by the following characters. andesitic lava layer, tuff breccia bedis and agglomeratic conglomerate severa! tens of meters thick, developed at the basa} part of the Charo member, the conglomerates under these pyroclastic layers, contain 1ipante pebbles, that is they have "Hatokuso" character, whilst on the other hand, the upper part has no such character In the eastern districts-Akan and Shoro zones-the formation consists of sandy siltstone and intercalates many 1ight gray fine to medium sandstone layers, thin and thick, at the same time the formation contains only rather few molluscan fossils Such fossils obtained from various area in this formation are listed in Table 7 The changes of the thickness and 1ithologic-facies of the Charo formation are illustrated m Figures 15 & 16 @ @ Se;2iiinteelllg$giil.lsliiillig.:{eilliSlil,;)itCS}SEili$l@ @4xkNiihee,.:,,tT.llis/.iliSS,Slllltlii,Illl:.,..t,tk.S.lll.,sti.kSl"Svi"}-i;i'il･ll.,[t.iil'/･itliiililll@ "i"J"- ,@ BewsmeZsfS XSk""Ilil;tllili･Iiil".iiil'`i;"iiiiijiiLl.'.;,"= " @ @ "ss{sll.,sl,fi,-ms,,Ns}iix""?'!ewgll.iiilgiliSill･iit", ll'lilli･iiS t@ @{agg,･,-ew,.#ill¥lii.ll,.tk.,.$iii..g,.xl$ ::e-r:'1ua s=XM " @-Til.llilgll:liill¥ISI"]il:;llt-llliiifiillii/Iili;gggl,ii , l ,.s , "i.{}ti",.-X'@ 'J･ :.i]/S.t/;';' ,r, ::. ` -lo-iefik Fig. 16. Geological sections of the Charo foimation, il!ustiating the changes m thickness (Each section corresponds with sections mdicated m Figuie 15) II) Nuibetsu forrnation: This formation is the most widely distributed among the Paleogene sediments of the Kushiro coal field It consists of an alternation of black tuffaceous Sedimentological study of the Paleogene basin of Kushiro in Hokkaido, Japan 467 sandstone and light gray rather hard tuffaceous siltstone. The si}tstone contains partially siliceous hard shale, marly nodules, marly lenses or !ayers. The sand- stone consists of quartz, feldspars and idiomorphic mafic minerals such as augite, hornblende and others of volcanic origin, This pyroclastic sandstone layer gradually or discordantly changes to tuff-breccia horizontally and perpendicularly. The distinguishable development of tuff-breccia can be traced from the upper tributary area of the Akubetsu river, at the northeast edge of this field, to the Omagari area of the middle course of the Charo river via Yubetsu, Kamishoro, Nuibetsu areas, forming an arcute zone. The regional characteristics of the alternation of siltstone, sandstone and tuff breccia are conspicuous in the area deve}oping the tuff breccia. The sandstone/siltstone ratio is very high and from the northwest or south-east refinds that the siltstone facies becornes more predominant as illustrated in Figure 17. v.1'r ad t+t t.t tt..t ti/`¢ ' ･--･･/･ .t/ 1. .tt ･･ ,f,,;Jl,-･･b･;,.tfib.t .si -･ tt IL ' -Ti t:''t : lt'tit.Jt.t.' J . . tt ""f' .t EIIIIIIIS t/ stLlgToha,ssmasTeutFscJES "' .,t･httt.t. tt ..t:tt ' .4 :t"ttltt.ttltttr-t;tttlt: ',/･l･L･'iC,lili,,., L. sNtosTo"ErAtites 're /tt.- -.,.:/l.,//:"L.gtSl･'/.,Ll',,,L':'S.'ll,f:'.T･,, ll;･g,:::'""-:[ZZZZ].t. .fA,t･I,l.ttti;i 1woCuaT; -tt/ttttttt .tt .:; olsTmeuTtoltstmosTnueovkES -.･ ,sl.tt･. ./:･sttt.tttt."-ttt'.l.,'t;tt/l:.-f 't' .,..`"･ e., .･ .t･. t.t. JV-. .::t 4S ' ttt. tttt..tt:. t e /t l/tttt.t le .ttt/t-ttt ･" F') ' e -. 1 T ' ' k'StetslehSt sd .,' x. ･..-- :･- ' Ht'tT. .l' ･tt vIn Fig. 17. Lithologic facies map of the Nuibetsu formation. In the part of alternated siltstone and sandstone, intraformational foldings, large or small in scale, are developed. In the western districts of the Kamicharo- Tokomuro synclinal zone, numerous sandstone dykes frequent}y are intruded into both the Charo and Nuibetsu formations. The sandstone making up these dykes is quite similar to the black pyroclastic sandstone composing the Nuibetsu formation itself. The molluscan fossil contents of the formation, as shown in Table 7, vary with lecality within the formation. III) Paleoecological analysis of the Onbetsu fauna: In the Onbetsu group, molluscan fossils are found scattered throughout almost every horizon. The majority of the species, as Ybldia, Ilortlandia, "Vl7nericarclia, 71t{rritella, 7}-ochocei"ithium, 1]k77"iploma, and so on are not restricted to any one locality or particular horizon; however, some species such as Albptt{nea, Macoma, 772?ctonatica, A7mpztlina, A]lamocai'dium, Acila, An- cist7olepis, Turcicula, ATeopsophaea, I2i"opeamusium, Sblenaya and so on are found only in restricted localities and positions within the formation. So far as the collected materials as concerned, it is evident that the Onbetsu fauna has no typical brackish water genera, that is, no genera which lived in the supertidal zone, except the lower part of the Omagari member. Also it should be stated that specimens are always with intact valves in upright position, and in thier natural living position; those occurring as isolated examples and those occurring only as fragments are restricted to the basai coarse sandstone and conglomerate part of this group. The nature of the sediments entombing the fossils is in harmony with the state of fossil-occurrences. From the above mentioned facts, it is inferrible that physical phenomena such as currents sufliciently strong for long distance transportation of the sheils did not exist. The paleoecological distribution of the molluscan fossils is particularly obscure, and consequently the data available for deducing for ecology of Oligocene species are almost non-existent. However, it is fortunate that knowledge concerning the geographical distribution, bathymetrical range, thermai gradient and local ecological features is gradually accumulating. The principal contributions to such problems have been made mainly by OyAMA (1952), TAKEDA (1953), MINATo (1953), KANNo (1960), HIRAyAMA (1955), OMoRI (1955), MINATo & UozuMI (1957) GEKKEL, P. H. (1957) and others. Although knowledge is not compiete, according to data presented in these previous worl ．盟翻。 騙 ． ． ”罵 一・一一罰一一．一一一 一‘価匿～一 鵬醐 formation o閣船翻1 齢田ETS購 Sp臼cie8 0cc隷■ence 8 量垂 1 2 ＄ 4 5 6 ．7 17 1～1 22 23 24 33 34 36 37 8 9 賛 1 2 3 5 17 韮8 書9 20 21 24 25 25 25 26 27 28 畠｛〕 33 34 36 37 38139．41 P1 2 5 6 7 1ア 18 2 6 24 26 27 28 30 33 34 36 37 3雰 一｝ SOle康ya tokunagai Yokoya皿a R R R R@ 一 R G R R `cila （Acila ） vigilia （Sche且cll l @ R @ R G R R C A A A C R R f G G G G A A R C G `cila sp （ osugii type ） @R R R G f R @R R R G R muculana sp （ p8eudo8cissurata type ） q R q R R R 一 @ R muculana sp q C R R C R R @ C R 8 R R rYoldia （Yoldia ） 1audabi118 Yo｝【oyama A G C C C C A A C C G C G G R G G C C G R G C C C C．G G G R C C C C A R C G C C C G G R R RG G G G R R C G R R R xOldia （ Tepidoleda ） sQbエ1ロa Takeda @G C b C G C R C C G G R C R R oortlandia （Portla塾dia ） wataSei （Kanehara ） b G G R A f G C G C G C G C G G C C C @G G C G C G A G G R oo■tlaRdia （Megayoldia ＞ Qvata （Takeda ） b π @ C R C G G G G C R @ C G G G R R lalletia po■onaica （Yokoya皿a ） b R R R C R A G G C G G C G A q G G G G G G G G C G A R Lima sp R R nstrea praegravite8ta Takeda． ．@ G 『 R R R C R lytilus sp @ ， R @ R R o■opeam1真slum ku81roe且8弓 Takeda @ R R R C A C R R R C R R q G R G R R@ R blinocardiu田 asagaien8is 湖akiya出a b R C G R C C R C b C R A R R @ R R Ne皿oca■dium ezoen8e 「Pakeda’ Ne田ocardium yokoyamai Takeda G C C C R C 四等 ` G ．R G R G C @C G R R G borbicula tokuαai Yokoyama 『． @ R G A C A A @ R aatis8a 8hitakaraen3i8 （Suzuki） @ R R b。nchocele biSecta（Gq11■ad） @C R G C A R ・R C q R R C G R A R@ R b C G R C G R 恥G加a8P． 隅⑳一P R 、 9@ R R R DPe■iploma bes8110en8is （Yokoyama ） f R R R G b R C 、 C A G G C G R G G C C G @R C C G G R C R R ‘ uenericardia ezoenSe 田akeda @G C G G R A G G C C G C．G G R G C R @ G A G C G C G uene■icardia expaI1日a Takeda @R C R ， A C R R @G C R G R G G C C C R G R A R G C G q C A C C G C G G R C G uenericardia e111pt‡ca Takeda b G G C G C R C R @ R C C C C G C ．G R b G C G R C R 一 一 ． ． ． ．ヒ 一 ＿ r 一 」 ． 一uθnericardia tokudai Takeda b R C R R 一@ G R C R σ R ． C C R C G R uθnerica■dia akagii Kanehara @ C f A ．R R R R C G G G R G C R R R lacoma sejugata （Yokoyama ） q G C A A A G C A G G @A R R C C G C G R R 且 @ R R R R lagO囮a aBagaieR8i8 Makiyama @G A A A G C A、 G C @ R R gubert8chenckia ezoe夏sls Ta｝【eda @R ．G ` R 一rpi8ula sp R R R R rolen 3P qC C A A G A R R lya ku8iroen8土8 Maklyama cUrritella porOnaienSis Takeda R R Cf C G C R R G C C C G C A G C G C C R GR R R C C R R R C A G G R C G C R R f R G C G C G R ．A G G C 鼠 G G R 鼠 srochocerlthium wadanum （ Yokoyama ｝ @ R G R R G G R meptunea 8hitakaren白i8 Matsui @ C R ． G ．R R m8ptunea mode8toidea Ta1【eda @C G G c @ R G C G R G R C u 鼠 鼠 鼠 R． meptunea e属oa皿a Ta｝【eda @ G R C G C G G C R R G meptunea 8ubcarinata Mat8ui @ R C G 蛋～ R @ R R G R R @ R 駅 G meptunea onbetsuen8is Mat8u工 q R G． C R q R G C G R・R A C R C G G R R @ R G 鼠 貯 NeptURea dispa工 Takeda auccinum sp， R R R R R R R @ R ， qG R G R G 鼠 R R `ncistrolepis japOIlicus Takeda q C R R、R R R R G R lolopopho工u8 ku8iroeR8iS Takeda @ G R R lolopopho工u8 Bhltakaエen8is Matsui @ R R rcaph皐且der mul七1striata （Takeda， 一 ｝ L uC R R C R R R R R R q R R R R R R rcaphander ezoana Matsui R ． ． dpitoniU皿 （Gyro8cala ） poronaienBis 賊atヨしi ， @ R R R R R R q G R R G R q @ R R R R R．R G C R G O11vella ezoana 踊atsul @ Cq R． R meoP8ephaea aRtiqロiOr Takeda @ R G R R R R R R R R R R R TUrCiCUIa 8akhalinen6iS Takeda @ R R R ﾑuτ■icula shゴ．taka■ensls Matsui R R sudicula japonica Takeda q R sudlcula i8hli Mat8ui @ R R R @ R q R R rpiτot■opi8 （A且tiplanes）yubθts琶en8エs Mat8ui q R @ 鼠 Spiro七ropi8 （Antiplane日．＞ rugosa 『Pakeda 一 ． `皿pUlina a8agaienSIS Makiya阻a R R R R q R R R C R R R R @ R C R R G R G G q R R R R sectonatlca臼P． ■ @ G @ R R R R R R R R R R @R C C G R R G R R centaliロ皿 nURomae Takeda @ C C b G C R G C G C A G R R 一 @ 壽 SlmPl酵coral 腿 kiRthia ye8串oen8is Minato R R R nphuioτoidea BP． @ C R @ R @ R fal↓ianassa murata1 Nagao b f G C G R R R C G R A b G C R @一 罰 Sedimentological study of the Paleogene basin of Kushiro in Hokkaido, Japan 469 ) ot . x..-g 4s .£. 41fi""': ." 3:Cas;.n....; 3- l' e .:: 3" "' t"･.･ ` ?zali'･.x,-.d 't ･/l.2 ･"- 3- l g Nl-N3 3-4 '-' TS - N3-N4 te -.. .4.-S 34' 2' 3d -3' : "- ma N4-NB z 4 ' t ' ttt 3- 1 2 ee I tv 3' 3-4 4 ,.tt:' 4s 3a .. 1"' 4 i.g. tx. I.1." - ..･ 3- il3 ve -.ww '.lr3 4S' ",. 4" ':'i' 3- tpt t. sct't"'t/'i:":' 't'" 'tl ,.I t ttt:'itttit l' .,,....1-3 ...,:.･.-.. J.i /i" l l.//.'t;･Ia,/: l/±i`t. 'u", wttzt'tt ' v' ' ."IS . :.･ ' 4- 2 4-g tL {.l･ g...==g=.=..g.==.g..=..i2e"m So -mrv... " 4-B l'j 3. ,- Fig. 18. Biofacies map of the Charo formationi N2: Mesoneritic zone. N3: Subneritic zone. N4: Bathyneritic zone. Nb: Hemibathial zone. (IV) Fossil assemblage of Acila, Ancistrolapis, C2zllianassa, sSZ)i7vti'opis, and Turcicz{la. (N3-N4). (V) Fossil assemblage of sS?birotrQPis, Tu7'cicula, LSblemcra and R"opeanzztsium. (N4-N5). On the basis of the above given bathymetrical analysis, the Onbetsu fauna presents a mixture of both rather cool (shallow and inland sea type), and cold (deep and open sea type) water habitants.* That is to say the Onbetsu sea was probably not very deep ; its depth changed regionally and periodicaily, and the sedimentary environments changed gradually from conditions favorable for inner bay to those for open sea habitants, for the duration of the deposition of the Onbetsu group, as illustrated in Figures 18, 19, 20a, 20b, 20c and 20d. The characteristics of the lithologic-facies, bio-facies and thickness of the Onbetsu group may be summarized as follows : A) This group spreads to the western pre-Cretaceous area in an overlapping way. At the same time the deepest part of the Onbetsu sea and the thickest deposited area moved to northwest from southeast. ie In the Onbetsu sea, the warm thermal condition, which prevailed at the time of the middle and lower Shitakara stage, did not exert infiuence. 470 M. MATsul ro･ . ,/i,li,/･,fi'-/l･'';-3 .. . ' r:::l:;',.. . t,;;A""i':" ..,.i.i,,g./.lif" ÷::"t': l" ･' [lllllll Ni Bt 4... -Nl ' e-4 -NS l -tl.i･si:l{:i:･ 1-3 .'' "i'Ifi' gNi 41!":' .i=.:'.:';':' "t : i'Ilii .･:-s- ;-' ･ -N4 +'S/ '- = N3 2-3 [ll;llZl] N4 .÷.q - e .,. l llliS:I--,:-f･ g' -Nn ip .{=. F''.,,. 'll･i,i･,iliiili,iilllii･･::" 2L3,,. l'lt･.V･･;',/i･lj ･' f':i{･,l':' 2-3 l. i･ 'l'/E':･:.,. .,.1,..i.t/;.I･i･, ,i.f.f,,･･"' ...,,,.:':::' 3;i:! t.l i.3 - =.t.1 . 1 u･ tt)t i 1' ,.,.;..,{ i/t'.3 .,t.1,Fi:Iii ,{,E;,t.' t i ,:i.I. "tt' i:/tz' x･ ,t,･,'S.'1 .2 lii:,. l - -tl,g,;.II"/! 1'3 r･.･='÷'//i 't'i"/t:/:')"//i:'f" 4V 'l'I//ll;･ - t･･:!/l',I･･,il[,l,l'･ll:II.111i.l ': ,4 ', :-. .4-='.:';f'C")..i;･ K -" "'{"tSt/.:-f･F.i･:: ' ahl -/s,} e * 2･3 'k i.. ･l" .::) o s IO i5 7eKn EO' ---" 's,/i,,;･t/,i .. -! 'e ' Fig. 19. Biofacies map of the Nuibetsu formation. Nl: Euneritic zone. N2: Mesoneritic zone. N3: Subneritic qone. N4:･ Bathyneritic zone. Nb: Hemibathial zone. B) Just to the west of the line connecting Okuyubetsu with Omagari on the Charo river (axis of the Yubetsu-Shakubetsu anticlinal zone) is the Omagari member developed. The change in thickness and lithologic-facies takes the direction of NEN-SWS. C) The Omagari member contains "Hatokuso" conglomerate and by this feature is distinguished from the lower part of the Charo member in the western marglnalarea. The lower half of the Charo formation consists of andesitic tuff breccia ' or agglomerate in the southwestern part of the basin. D) The main part of the Charo formation (Charo member) consists chiefiy of dark gray siltstone in the who!e area, but is intercalated with rather numerous sandstone layers in the eastern area (Akan-Shoro zone), pyroclastic sandstone or conglomerate facies in western, Honbetsu and Rushin areas. The regional changes of lithologic facies are in harmony with bio-facies analysis as illustrated !n Figures 13 and 15. E) The Charo formation has the same distinct direction as that of the upper part of the Urahoro group. Along the Okuyubetsu-Omagari line are found remarkable th ick developments, Towards the west from this area, the Sedimentological study of the Paleogerre basin' of Kushiro in Hokkaido, Japan 471 2 2.i t- SaLOttEitATE '. t- t- 7-r--,==. e..n./t'.--u s]LrsTeHe t.=.1 /.y-,.t. htT-r ltlt-?; .tt-Lt t･ ,INE]ANDSfOHe "･'-r-=-i'-be'!L'---=r:-,･E-.ttA･-P'- ' :･-- ttttt.t. leARsESAHbsTOHf 1 - -4-- ;onauaSLanAT£ NaouL: /t･･t'f OQ : it"GSAt4osTetleDVHE ff-3l4' '-T-., 'a-IHOL51,' r･]--i-･,--v----- =･--- t.t 1 MoLLuscANeessLL i ･/1/･/,gl,i i, t-.-, -"- : tT' "t' - : -m-m- : ---:- --m. t- ,t./ttv nt /T,.'i/,'// : .m-r.{=-fin -n=":1==-=..tt･1.-' 25･ 26 '- --uu - =t -..-.-.==-t- itt'tt' ' -- =i=- .r l/./･.;/-.' ' .;----- ' -=. "i'"':''･a,'･1-!t-.-･ == . t'"" t" :-:-- -s l -- J t. ;.-ttt-;- z-=-'. 'i'/i't'lt :.T-. I'u /.,.t/'/･l'･. t't ･;.,m-.t "/t"tl /･,,,/-･･ 1--,-'--l- --.-t x A it'k'= -i7] "･-:.- tL'tt. i-=-- :me-ruL=J==:.==-zT. @ --':' rJ;･i.,!.,.-t-t -- ..ex;a.s 'tt=rri "'x =tv- t-..-n..7 vi-- L-tttttt rt '-il ]=- ' ..;='E t. 't'='i'' rms77 -- st=, - :ltis=II'; ',=.-= iA'=` .- ert.];Tt .r.E ''..t =--=- Ttnu --rm-=. t ---- ;-"i=1/if"t/i'i'i'ig."'4'..I'i(f./･liilll.,a/-,･.x,,'t1:,')t･1･-l:.1:.,.:t-' -J---. =t't; L LUx,uu s.:'' tt"'itti""iEISIi ' -u x',,' ../../,,//.i = - .'-- ..rr, ;-!B'i!. 'tL---e:v- T- 1"".tt'･: tt .tt.t > -Iijit l Z.-T --'-t -.".x}- "d"i -==n-='s"- :+:L:.:.1,.k･:A:L'iaUe' l-j-J E" =.=.: JJ -tTir-T4MvJuL- r.=. e"Lds 'm'=' [-] , jtJ''zt I-T :' 1 if.a.trJfiFM-.r.･' -lg-.=tt-'"tiN-TrJ"J ' eN t- =.1.u=tt .t- t'' t=u'-']el t-T-t i=' -Ytt'='.fiJtJIJfl -:===.tttt =-u- n[-i-]mta"r:i.:n:=tift.t/--t;!/ 'tttttt -..;lr=- l'i''asNr--Fil' tm-r-T t' ' r-Z ' :ft'tt''k'E-･2･li,t '' k-=.Z-"J'---'''''ttt ll ÷tt!.-:.- '. t- 'umNl-･N2ttt:aNl--NS loe :-- 1111'i,E.i,g',1:' '' :, gN:-Nl aO s ToKM ua N4-NP Fig. 20 aNd. Colmnar sections of the Onbetsu group, showing vertical succession of biotopes. 1) Locality numbers are correlated with those of Table 4 and Figure 3. 2) Each section coresponds with section in figure 15. These A-A!BB!C-C'D-D' lines mean the base of Nuibetsu formation. thickness decreases; on the other hand in the area Kamishoro-Nuibetsu which is connected with the part to the south-east of the above mentioned line, is seen a remarkable thin formation; this change of thickness is rather sudden. In the south-eastern part of this basin, namaly in the Akan-Shoro area, this formation consists of sandy siltstone alternating with sandstone layers. F) The characteristics of regional and periodical changes of iithologic-facies and bio-facies show that the most deep area (N4-Nb) occurs in the west wing of the Yubetsu-Shakubetsu anticlinal zone, and to the north-west or south-east from this area, the bathymetrical depth reaches only N2-N3. This is illustrated in Figures l8 & 20 a-d. G) In the Yubetsu-Omagari anticlinai zone, namely the area where the thickest formation was deposited, or where the most rapid sinking occurred, there develop sandstone dykes, intraformationai foldings, minor and planeless faults. The evidence afforded by lithologic and bio-facies and thickness of the 472 M, MATsUI 2e :- i- 1 : ?7 /i fiy :-: l',it,z'-"･ t.A i- 't ': : i'i'::' ii ee h '3 'm-"J 4 ･lei･ illitL/･･･1 lt'/'i/'ttl tl･-1//} IS. I･l'[:;',//'1 211 ges, IS'･,i//IIill･ i.l.i - l,,,.,-, , , B ffm B .lof...... l?iF'. N ' iE-. t ela. -e Vl E- illb. -x V gT-tte ,va -- {tsE =:-=:-- p.i .tre･ ttL-. rvrL- 1 IS.! va 'ge IL tl tJ lliV t'r, I, .rr-7 : -Ll m." tL-7 i [-=-:I/,-L ' 1 =u". .r- x' :iM3iMm 1.eCF./;=IL. l -i-r. ･..1, , # :t t=---- ,II .. /IL, :-t .i.if-- Jl vett- 'l e.Q tL, =IL--l: `: 1/.L :i t .le... it 2ODtl -T: 2ki ,IE;. i" ei.st =ar= rm ft ii /'ix ta'.- -T- 1'i･,t,. --. x =e " : .F IE.I. loe .G ti'! .. r n'' J ･-･ 'G･/1 tttJ . "" 'f rtlt "" ･'tl e o s tOKl:t Fig. 20 b. lower part of the Onhetsu group (Charo formation) shows that the actualities which are indicated in the areai difference of basemental sinking and deposition, were continued in this stage, too. Further, such items of evidence as sandstone dykes, intraformational foldings and faultings indigqte that this basin was sub- jected to stages of rapid subsidence in the who,lg ,area, partial small scaled rising and sinking, irregular deposition, folding and faulting during the sedi- mentation, after the quiet subsiding upper Urahoro stage. H) The lithologic-facies of the upper part of the Onbetsu group-Nuibetsu formation-has the characteristic, as illustrated in Figure 17, of the tuff breccia facies which develops in the Akubetsu-Kamishoro-Nuibetsu-Omagari arcuate Sedimentological study of the Paleogene basin of Kushiro in Hokkaido, Japan 473 7 6 t･e: 1 s. 'i, l,-.-'l--L.-X retL- p L il'i !t'i t' ' -ve:a. '1.: f,I-- :/,if･ ･r --- ! A 1 ve t-- itt･E･-.',----:-=l!t l-rv.-tS.Nt:l.:.i--[ 3]tt r･z･ :-:-- ""u'iJ..:. l='- =IZ I-:-' ･?4..-- im[==- ' tll-.= gt･'i/t=.E. '' ;'F'//t' .t.t ..= r. =..L =1-.- .. fi .tu t'=/"' ]-･/･･- tt t･-t- it--=･ -I-.--. /t .7./. ::t- .. 1:.t. -=-- :tti-IE==r=ttt i''!'==.--t.. tt-;... /tt-ij･ .tt- =, 1./-÷''-.. :-=- -t･ ' .--. 30 t.t..7 tt I,'.: ;-t---; r-t-..x'･ ' ;..7.7.'tt'1T.' /--- 1"S:': tt;/tt/.:.ttt. ttL==L--r..J ; ' ull. .--- i"'-1-'.- =u-r .Tt. .t-L=.t..J･/ f s r･.rr- .iL-i-....t. " E=tt' r- 30 i-]- t-r-[ =-I-i /' 'i'-r' /t'nci=-- '- ' lltttt = li I-Ir4.'----ur '' =-:- -" '' / .--:=-- '' -. .t---- ' =-=- s'v'--- .,.t-=. Edt=.･ tI":n. ;-/!---l- -a-- v=-rr. -. [t 'L..t -z-=- =ttL' ;tttt .m =.= ='[z.llm.=-==m------=--.=i='=-:-=-r-:==--ll.1,/G'u.tL- r-l:. =-T. r=]'"s tt.tE-!-:- --. 7..- t = tt' .t --- =--･---: .t.t･ ttt'! 1,"s'fi'M' -" ''.･ts..'! tlV,-.tt.tt""- -･ T-n.. .J'tt. i.'G;b'i7o'"/"ur L !-i-= [.- nLr' =t"-.･,=r.t. ttJ- ..t.ttt tt ' L d== =.]..r t- ' -.== el x "1;i't'i' 'ttE'' I=.F, =. =･ult ,r,･.. ;kei: ---tt tll t' ! x=･･'-:-'t 'T･r t.t .t. =1-ULifr-=-:i'"=':'.a'i'･tT.It.:..r;.':-z=.'c t... ;=t--. --･ c '-' =k-t''' =-. ,I-I-[.,. '''''''ttt' r.=r.-1. 't' !!i va- ,T.t.ttttt.ttt l--'i 'tt7･ ';"- -y=-u" .. .7T...J. a.t ' t f4Jrv.w'.'.-.-.ll"rJ.--J-=-i=.-Jfi.t:t=.L "rrJt=7 '"e[' t..l- itt+ rT=-- '1xttx.-::t -n-#I-=-r-T' t"- : . r.=..7I== 4"v ' lt7-o'L i't.t-t' a::-.ull J 'xt.'t-1' -- t:' ULt't.･,-] t .., el''.t tldi=･-t. .-7". /. +t,: J",･W:''=f'tt' -, .. /tT t .t : -' .-..-. # tttt .t. e-s-.... lll! l>.t.-, :'tt' :-I:--!L''L'"-ll r-==di---fi -･ --- u 'x :-=-- ;-=- t'--:'tt =- 6' =--- 'Sit-[.lr･･i'u'''l=-.;ll...d:-=-:=--EtiTli-"-.n.-.n-.tm"r".I=--r"-=--"-ut1･--.l･..-..u--tmts-J..;.tu;-=,t.t=.t'nlI- ' tt pe- =t"- -.ll.;=i=-=-:=..---:- fieUtc :r ' '}L''''':' 1---.,=tt=nt "-i tttutt tr...===.''iL..., .t i-e=.･tt N･tt';ttt:ttt = t. tl ob'' 1-.,=･ ---,.,-t-- tt r=,'t I'I'ttt tt '--i' yt , 'li t{-=-ny,. tt v tt ".t ti tt 'tt/:ttttt./.'' 7.--- :st.ttll 1･ t --fi 'ttt-:.-.tt.tttttttt:t'tt -"t,'iGi' t=-"-tti:'i:lttttt' =- 7.t... t'': ...... n .=-:T:':t==-=--=.-J=Iir =Jtl. ･. e' 't i= ･-G --- !SJ tt r' ;･,/1･ rM.-' " G tt l iits.ur.. l-=-= t.ttxZ"t/tv,:4/-:tte･.,,,: rm- ` l-:-:'l-G.1-....=-- ':ttV----. .t- ,tt 'itit:tt4tt.et-ttJttt-t't1/:.-tttiti::.Jt,//s-tlt: 7oeH eo "' .:/･ tt .t tt tl.t;T/ t tt ttt"-.:-.'!"s'Er-=-'E-T-' tx..t ':"i 'x"t' .m a:'iN''---=- ,L1.,.E:t '- =n=.tt ],NtFi1=-=.rl' ,--- ttt t. lee =''-J :,:' =-=-:･ T:=;･.:m:- L'-,:=r-.''erl' 'i: -1,,:t:tt ;=-t =-=-. l･i,t-1, Tl'I,:tt ･x:5Hu:-:----=-:- - oV-= ･N,,li'Yx-N'･･M' --- =:{{.-L+L!U:D:ue"i'"'b',/-i,tt"..･-iL'`it'14t' , ' , - Fig. 20 c. 474' M. MATsUI 31 ken -? ･ = 17 -- 37' ltt-:･ tt t--' -L=-. x=.. -ys/ ./ - 9 =-..tt u･ il-l/,,1-l'il･ ;tt-.･a.･ li[... D D i-G}i .---L T. 7-;:-i'･a'=･-=-t-. ." -=- gl-'e-l '''' nv- tLi" h- f' imtttt' h -z' '' l-= 'N---1 .s--- L------tct- .7-'{lluai'. 's l-.-= -1-.- h .a.-'t't L 1''.' ttitr'.#-n. l'x,1 l, tT.. ;. ;- ,.,.e-l ,.a, :,t [-F. i･-l{･ iOOM ･1 i ]-==- .r.er,t /. r.t.L m, "' .t-7m Fl'xIL tv 4 Jtt !3.:;.. It .1 't---o-"..tNttti....･-tlt; 'x'.-=-ai-.qL- t ;'a,-i , .'e,,･, tt.-..]t7=t. =aLi--=I-L"= ,h 74 loe rt-tt t/ t'-D'/ :gi, 'N tt. .1 xxl.t-t {=4 'x tt'="' be--.'.-L.'''-tt''' s.- .t -.=tttr-tt･'--].'-mE-=G=--=.t.ttt.･G i"': "trtt. i". id, 'x"----.u..L.J:...... r.･,10K"lg''"tL" ..."-lt-. o E 05 ･v･ Fig. 20 d. zone. To the north-west or south-east from this zone, the sandstonelsiltstone ratio decreases gradually. I) The bio-facies section of the Charo Nuibetsu formations show the deepest area was transported gradually to the Ukotakinupuri-Rushin zone from the Yubetsu-Shakubetsu zone, namaly from east to west. This change of facies of the Nuibetsu formation is illustrated in Figures 18, 19 and 20a-d. The position and direction of this tuff breccia erupted zone coincides with the main direction in which the most thick formation was deposited, during the deposition of the Yubetsu-Charo formations as already discussed and illustrated. J) Aa for the occurrence of sandstone dykes, intraformational foldings and fauitings, transport to the west wing of the Kamicharo-Tokomuro synclinal zone from the Yubetsu-Shakubetsu anticlinal zone during the Charo and Nui- betsu ages, these diastrophic movements were accompanied with rapid sinking movements. K) In the age of the Nuibetsu formation, the basin spreaded widely to the north- west and the deepest sinking area shifted to the west ; this Paleogene sedimentary basin attained to the maximum of sinking-developmental stage, and was about to upheave and undergo orogenic movements. Sedimentological study of the Paleogene basin of Kushiro in Hol g7. Relation between tectonic and sedimentary facies, and the thickness of formations in the Kushiro sedimentary basin As stated above, the development of intraformational folding, planeless faulting and sandstone dyl g8. Conclusion In this paper, there have been described the changing of lithologic-facies, bio-facies and thickness of the Paleogene groups in the Kushiro sedimentary basin, and also the relation between tectonic and sedimentary features of these groups. ' At the beginning of the movements of the sedimentary basin, it can be safely said that there were contradictions causing self-movements of the sedi- mentary basin, as the internal cause which means lithologic-facies and thickness of the formation, and the horizontai change in them. Next, the process of formation of strata is governed by the upheaving movement of the area; this movement is reflected by the distribution of facies and thickness of formations. Accordingly, the study of the process of the development of strata, the formation of the geological structures, can only be conducted in conjunction with a study of the continuity and discontinuity of facies and their thickness. References AsANo, K (1952): Paleogene Foraminifera from the Ishikari and Kushiro coal-fields, Hokkaido. Short Pmpei's, JGRS, No. 4, pp. 23-46. (1954): Foraminiferal sequence in the Paleo-Ishil Hokkaido ULtti'v,, Ser, II, Vol. 9, No.. 4, pp. 415-470. ' ''･ ' ' FuJITA, Y. (1953): On the "Shogi-daoshi"'structure. (in Japanese) Research on Cainoxoic .. Era, No.18. pp. 4-10. ･ ･'".･- ･ - GEKKEL, P. H. (1957) : Primer to Paleoecology, HASEGAWA, K. and & FuJwARA, T. (1959) : On the Alkali Basalt in the igneous Rocks of Nemuro Peninsula, Holckaido. (in Japanese) ' HAsHIMOTo, W. (1958) : Considerations on the geological history of the Yezo-Saghaiin' geosynclinal Area. ,hebilee Jlttblilcation i]n Cotnmemoiutiin of' ll,'ofl LL Eeofi- ' moto's 60th Bt]rthday, pp. 101-112. ' ' HAY!iSHi'sTc'iet(iic9e?5ili:o. 2G4?OBOpg.iga7iL4e2".idences reiated to thixotropy- (in Japanese) Earte (1957): The sandstone dykes in the Miocene Series in Chita PeninsLila (in Japanese). Rop. Aichi Gakttgei Uni'v. Vol. 6, pp. 69-76. HAyASAI OMoRI, M. (1955) : On some fossil new species of the Genus Propeamusium from Japan. Sci. Rep. Todyo Kyoikt` Daigaktt, Ser. C, No. 27, pp. 7-22. OTATSUME, K. (1943) : A brief note on fossil Corbiculides from the Kusiro coai field in Hokl