Petrofacieson Sandy Upper Pleistocene Depositsof Makinohara
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The AssociationfortheAssociation for the Geological Collaboration in JapanJapan{AGCJ) (AGCJ) 1-kptl,P:,',s4ts. (2ooolr-} EarLh Sdence23---32(Chikyu Kaguku) vel. 5・1, 23 32, 2C)OO 23 Petrofacies on sandy deposits of an ineised-valley fill: Upper Pleistocene in the Makinohara Upland, Shizuoka, Japan ', "and '** Yasuhiro Takashimizu Fujio Masuda Masaaki Tateishi Abstract The Makinohara Upland, cenrral west Shizuoka Prefecture, central Japan, faces the Suruga Trough, which is formed by the subduction of' the Philippine Sea Plate beneath the Eurasia Plate. The Upper Pleistocene of the Makinohara Upltind consists of incised va[ley which comprises a fi11s, depositionalsequence, Cempositional trends of the sands from the Upland area Makinohara (Makinoharasands) are p]ottedin the Lt-rich field, w'ithin the lithic recycled-transitiona] field Dickinson of and Seel)'(1979)and Dickinson et al. (1983).The sands of the Makinohara ttnd area show mineralogically Upland area Kanto immature trend than those ot' the U,S,A, (continental area), The Makinohara sands are deposited in fluvial environments during lo-'stand and highstand periods, and regpectivel}, has,e dfl'erent plots on Qm-Fl-Lt and Ma (grain-size) versus Qml(Qm+Lt) diagrams, The sands ot' the LST mostly have high Qmf(Qm-+- Lt) ratios (",ell niatured), and those of the HST have Iow ratio matured) The tsunami Qm,/'(Qm+Lt) (poorly , sands of deposits,which sN'ere deposited in a barriersand body and a drowned valley environment of Makinohara Upper Pleistocene. are plotted in differentfields on the diagrams ofMa versus Qml(Qm +Lt) . Those deposited in the drowned vatley contain more monocrystalline quartz ; those deposited in the barrier sand body contain more lithic fragments, The drowned- valley tsunamiite is plotted in a similar fietd to the drowned valle}・ deposits. The tsunamiite in the barriet sand body is plotted En a similar field to the barr{cr sands and beach-shoreface sands. Relationships of grain-size characteristics and Qml' (Qm+Lt)plot do not show un>・ clear correlation. KqJ words: detrital mode, incised-valley fill, Makinohara Upland, mineralogical maturity, petrofacies, tsunami depesits souree area and tectonic setting of the Upper Pleistocene Introduction in Lhe Makinohara Upland, Shizuoka, Japan. Character- is located in an activ・e inargin. istics Japan plate Man}' of the mineral composition and its relationship studies of mineral and chernical compositions of sands with grain-size in the Upper Pleistocene sands of Ma- and sandstones hav・e been done to e]ucidate provenance kinohara IJpland, which are c()nsidered te have been terranes (Kiminami et al. {eds) 1992), The relationships deposited in N,arious sedimentar}' environments, are de- between depesitional environments and sand composi- scribed in this paper. This study aims at explaining the tions, has also been studied by many researchers (e.g,, sand characteristics on mineral compesition of incised- I)aviesand Ethridge 1975; Ito and DLilasuda 1987, 1989; va]Iey fi]Is that these do net clarify how petrofacies et al. 1991; Murakoshi Sakuraiet al. 1994; Critelliet al. changes, and the difference on petrofacies between lew- 1997). These studies has,e clarified how differentde- stand and highstund period. Moreov・er, the petrofacies of positional environments influence spatial ancl temporal two tsunamiites that were discovered from clrowned variation in sand conipositioris. valley and barrier deposits were clarified, Sand compositions were studied to elucidate the Received July 1,1, l999. Aecepted Deceinber 16, 1999. *Graduate School of' Seience and Technology, Niigutu Univcrsity, Niigata 950'2181, Japan, * ± Department of Earth and Planetary S¢ iences, Graduate Schoo[ of Scicnce,Kyoto Universily,Kyoto 606-8502,Jupun, "'Department of' Geology, Facult), of Seience, Niiguta University, Niigata 950-2・ l81. Japan. (23) NII-Electronic Library Service The AssociationforAssociation for the Geological Collaboration in JapanJapan{AGCJ) (AGCJ) 24 Yasuhiro Takashimizu, Fujio rv'[asudaand DvTasaaki Tateishi Geological framework and stratigraphy DEIii$iiliiN]uvialMeistoeenesediments N The Makinohara Upland, in central to western Sbizu- oka Prefecture, central Japan has a length of 20 kilo- TerdarySystems N+G'1・-.tttt'b:.・・,./,.' meters frQm north to sQuth and a width of 10 kilometers ''・o・'.o'.1ny''.qrb'o・・-d,"O,b.'P,-,..q...1/..tt6....;.t.../,,. ShimantoBelt Nie.'tt6・?,'f'i" from east to w・est. It faces the west coast of Suruga Bay EE]E][Il]N :.tttt/t //.,;1.・1・ (Figs. 1, 2),a marinc trough formed by the active sub- ChichibuBelt duction of the Philippine Sea Plate beneath the Eurasia Sanbagawa-MikabuBelt nt, k-o..e..,'s-dv/."tt-o,'・p・tt/d.D・・9,m/d,'P,g・・Q・o',.q''.・b'・P.1・6I,,,'e'P,gn''j'tt''.q・.q/.・・tt.o.'p,o.',・.o.'Q'P.'o'.ool-d"''/o'/lq'1.,.9'-b,.c,'1.e.1,bp',・,o・b.'p.・'・Pp'1ttg・geptut'ittttt/.tt/t''/1'/:"'/''tt''/t:ttt1tny.ttttltt.-t-・1,・,・1・:1・・tittttttve""pttt/ttttti"-''1・l,・!.o,//,rJ.'''"'."m':"'・tt.r':,・・・-tt11:1i:lii'/111'!/.,, Plate (e.g., Sugimura 196e), s+.,e..nb,.6Pii,,・,o/,b.,'q'','9b・,.c'.P'''p,'..・'lq'''.o'・'a'・"F・lb・[・9'・・,b・l The the I'leis- stratigraphy and paleontology of Upper tocene of the Makjnohara IJ'pland have been well 'se,e-"s・.eeS"'/O,'/ documented (e.g., Makiyama 196], 1963; Tsuchi 1958, ttttlottt.?・'glb'ottt l960; Osada 1980, 1998; Ikeya and Horie 1982; Sugiyama et al. I988; Nirei and "Jatanabe 1990). The basements of ,N..s ,s.'q''・ this Upper Pleistocene eonsist of the Neogene Sagara tes.o'P ts-.si・--. Group and Kakegawa Group fonning fore-arc basin fi]1. nub"'/o'/ This is the place where the Philippine Sea plate goes 35dN..'E"ti.lobttttt.tio・ttloP...'6''''' down under the Eurasia plate, and keeps upheavjng at .,.g. tt'o.''.,,・619'?.・ts/o/tttt'o'ttt.t''SumgABa or Q・'・'.O.・b'9,p',o'.el・o・''',o' present, too. IIinterlancl of the )'Iakinohara Upland is composecl mainly by Shimanto Super Group .p.・/tt'tttttttt ('`Shimanto z..--"-.l/ig<..,,,/1.,di. Belt" in Fig. O. tttt/tt//tttttttttttt/t/ttt,,/,.Qoiruver The facies consists of the Upper Pleis- succession /t't/ttt''li'/1'.,/.'ssMakinoh tocene deposits, which unconformabl.v overlie a Mio- Pliocene forearc basin fill, consist of incised valley fill m"oO '' and shallow marine ancl fluvial deposits formed during a Upland n- single transgressive-and-regressive cycle (Sugiyama et aL et al. are 1988,Takashimizu 1996).These deposits Fig. 1, Index map of the study area, Makinohara Upland, classified into three formations, in ascending order] Shizuoka Prefecture, central Japan. Furuya Mud (Tsuchi 1960; Ikeya and Horie 1982), Kyomatsubara Sand (Osada 1980; the equivalent of the Methods lower part of the Makinohara Gravel of Ikey・ a and I'Iorie 1982) and Makjnohara Gravel (Watanabe 1928; Takashimizu et al. (1999) clarified grain-size charac- Sugiyama et al. 1988) . The Kyomatsubara Sand is absent teristics of sandy deposits from the same Upper Pleis- in the northern part of the upland. The Ochii Gravel tocene of the Makinohara Upland. In the present study, samples referred result of (Sugiyamaet al. 1988), a correlative of the Makinohara we used the same sand and its Gravel, is restricted in the southern area (Sugiyama et grain-size analysis. A total of 160 samples were collected al. 1988; Takashimizu et al. 1996), The Upper I'leis- from sandy beds on all of the studied outcrops except for tocenedeposits in-fi]1 two paleo-valleys (Tsuchi 1960; the locality E, where sand beds poorly crop out. Sarnple Osada 1980; lkeya and Horie 1982). Takashirnizu et al. locations are shown in Fig. 2, and sample horizons are (1996) studied the depositional facies (major lithology indicated on the left side of the measured sections in Fig. and inferred dep6sitional environments are summarized 3. The samples are from the sandy beds of the following in Table 1) ancl sequence stratigraphy of the Upper facies; lo"'er shoreface (25 samples), upper shoreface Pleistocene and identified four depositional systems. (24 samples), beach (7 samples), fluvial (7 samples), These are drewned valley, estuary, beach-shoreface and estuary mouth bars (10 samples), drowned valley (6 alluvial s},stems (Table 2). Moreover, two tsunami samples), bay floor (5 samples), barrier (re]ict barrier deposits were discovered from the drownecl valley fill and tidal inlet): (16 samples), bay-head delta (18 sam- and barrier sand body (Takashimizu et al. 1996; Taka- ples),alluvial facies (11 samples) and tsunarni facies (31 shimizu and Masuda 2000, in print) , samples) , (24) NII-Electronic Library Service The Association for thetheGeological Geological Collaboration in JapanJapan{AGCJ) (AGCJ) Petrofacies on sandy deposits of an incised-valley fill' Upper Pleistocene in the Makinohara Upland, Shizuoka,Japan 25 7 North 1 g"ean 'M : / l380 00' E 100km il1' L ・-1 Iiil Holoeene ' Kasana & Omaezaki ewtttterrace deposits Malcinoharagravel lli IIIOohii gravel ew Kyoumatsubara sand - Furuya mud i' Basements Location ef iO/ Outcrop Fig. 2. Geological map of the study area, Makinohara Shizuoka Prefecture, central Japan, A to J are lucations of outcrops described in Figure 3,Upland, Samples were treated with epoxy resin and made into Results and discussions thin sections, and 20e-point counts w・ere made for each section using the traditional method and Gazzi・Dickinson Qm-FI-Lt diagram method (Gazzi 1966; Dickinson 1970; Ingersoll et a!. 1984). The traditional method only describes the rela- Qm-Fl-Lt diagrams for each depositional facies of the tionship between the grain-size and the mjneral composi- Upper Pleistocene sands in Makinohara