OMOTO  Kunio

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OMOTO, Kunio

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Geomorphology of Narugo and its Vicinities,North Japan - Chronological View Based onRadiocarbon著者 OMOTO  Kunio雑誌名 The science reports of the Tohoku University.7th series, Geography巻 25号 1ページ 151-157発行年 1975-06URL http://hdl.handle.net/10097/45006      Geomorphology of Narugo and its Vicinities,                     North Japan  -- Chronological View Based on Radiocarbon Dates —  Kunio OMOTO  1 Introduction     The present author reported on geomorphic development of  Onikae, Narugo Nakayamadaira nd  Mukaimachi Basins crossing the Ohu backbone range (Omoto 1964, 1966, 1967 and 1968), in which he described and clarified geomorphological characteristics related with Pleistocene lake deposits in the tectonic basins of  OnikObe, Narugo, Nakayamadaira nd Mukaimachi. But the absolute chronology on geomorphic surfaces and lake deposits remained unsolved.     Recently the author dated the samples taken from the above basins by means of radiocarbon measurements (Nishimura et  al. 1972, Omoto et  al. 1974). The absolute ages of other Pleistocene lake deposits at Kutchan, Togatta and Shiobara were reported (Omoto 1971, Imaizumi 1974, and Kobayashi  et  al. 1971). It is interesting  for the author as to their situations and origins that the absolute ages of the lake deposits are all included in  Wiirm Ice Age. In addition, the above mentioned basins have volcanoes and volcanic deposits (some are welded tuff and pyroclastics) in and surrounding.     In this paper, the author correlated the geomorphic surfaces of Narugo Basin and its vicinities based on the radiocarbon dates, and discussed the synchroniza-tion of Pleistocene lake deposits in the northern Japan. 2 Outline of Geomorphology and Geology    The Mukaimachi, Nakayamadaira, Narugo and  Onikabe Basins are continuous in a transverse valley across the  Ohu backbone range. The margins of basins are clearly defined by steep mountain flanks, except west and east margins of Nakayamadaira Basin. The Oguni River flows westward (the Sea of Japan drainage) and the Eai River eastward (the Pacific Ocean drainage). The water divide between both drainages forms a divide in valley near Sakaida Railway Station, at about 340 m  a.s.I., the lowest divide in the  Ohu backbone range. Along these rivers develop several levels of river terraces. At the foot of mountain flanks, there are hill-lands with the elevation of 560 m to 280 m, not so much dis-sected, still keeping original flat surfaces. The mountains north of each basin rise152 K. OMOTO about 1000 m to 1350 m  a.s.l., while the mountains outh 700 m to 900 m a.s.l.    Based on Ikeda (1946), Kato and Shimada (1953), Shimada (1955), Nakamura and Maeda (1959), Oide and Onuma (1960), Taguchi (1961), Osawa (1964), and the present author (1964, 1966, 1967 and 1968), the geology is outlined as following: The surrounding mountains consist of granite, diorite, green  tuff and Tertiary volcanic rocks. The hill-lands consist of Yamaya formation and Mitsusawa dacite overlaid with Akakura formation in Mukaimachi, green  tuff and dacitic  tuff in Nakayamadaira, Miyazawa formation, Uwahara dacite and  Onik6be formation in  Onikabe, green  tuff, Onoda formation, and Uwahara dacite in Narugo. The fanglomerate and terrace deposits are younger deposits than above mentioned.    In these basins, there develop well laminated siltstone beds including plant          vi,6"         Crn  1  2    3  x             1=1- 4MM°  MUKAIMACHI HANAYAMAFig. "X  NAKAYAMA-  DA1  RA 0  5  10  15  20km     •  . 1 Index Map  of the Surveyed Area and  Distribution Map Deposits in Narugo Basin and its  Adjacent Area. 1: Pleistocene Lake Deposits 2: Sampling site of the Lake Deposits for  14C-Age dating 3: Sampling site of the Terrace Deposits (or Fan) for  "C-A 4: Pleistocene Pyroclastic Deposits 5:  Dacite Lava and Pumice  Tuff of Takahinata  and Nampa ,f  I  n ap of the Pleistocene ating r  -Age dating  1 aruzo VolcanoesLake                Geomorphology of Narugo and its Vicinities 153 fossils, drift woods, and sometimes vivianite (Shimada et  al. 1974). The facies change ascendingly from siltstone into sand or sand and gravel gradually. These sediments are Pleistocene lake deposits (Kato and Shimada 1953, Shimada 1955, Oide and Onuma 1960, Nakamura and Maeda 1959, Nakamura 1962, Omoto 1964, 1966, 1967 and 1968), whose distribution is shown in Figure 1. 3 Previous Correlations of Geomorphic surfaces     In the former studies (Omoto 1964, 1966,1967 and 1968), the author correlated geomorphic surfaces based on the geomorphic and geologic evidences. Interdrainage correlation was done by the continuity of Makinohara surface in Mukaimachi Basin to Shokubutsuen surface in Nakayamadaira Basin. The author suggested on the possible correlation of Sugenodai surface and Nishihara surface, both of which include drift woods and peaty clay beds, by radiocarbon dates.     Between Nakayamadaira Basin and Narugo Basin, the geomorphic surfaces were correlated based on tephrochronological method and surface geology. The east part of Nakayamadaira Basin and whole Narugo Basin are covered with four layers of aeolian volcanic ash from Narugo Volcano, which cover the terrace deposits higher than Nishihara surface and  Daigakuni5j6 surface. It is obvious that the terrace surfaces covered with aeolian volcanic ash layers were formed before the volcanic activity of Narugo Volcano.    Between Narugo Basin and  Onik5be Basin, the geomorphic surfaces are dis-continuous at the east of Mt. Hanabuchi, and they were correlated with the relative height above the present river floor, dissection and sedimentary environment. 4 Absolute Correlations by Radiocarbon Dates    Radiocarbon data quoted in this paper are listed in Table 1. The author infers the age of formation of geomorphic surfaces in Narugo and its vicinities as follows; 1) Sugenodai surface a. 23,0057_1218°5°yrs.B.P.(TH-015), 2) Nishihara surface  ca. 18,595+705 yrs. B.P. (TH-033), 3) Daigakunojo surface before 11,950+ 285 yrs. B.P.  (TH-007), 4) Makinohara surface  ca.  15,925+445 yrs. B.P. (TH-005), and presents the correlations based on radiocarbon dates, together with continuity of geomorphic surfaces and surface geology in Table 2.    Direct correlation of geomorphic surfaces far away is possible only by radio-carbon dates. For example, IVb surface near Sakunami Railway Station, upstream of the Hirose River, is correlative with Nakamachi Terrace (Tayama 1933) in Sendai (Ouchi 1973). The date of wood sample from the IVb surface was 19,215+760 yrs. B.P. (TH-031). The sample was taken from organic clay bed overlaid by terrace gravels, about 4 m in thickness, near Sakunami Railway154Table               K.  1 RadiocarbonOMOTO Dates quoted in this PaperSample Onikabe Lake Deposits (Wood) Narugo Lake Deposits (Wood) Hanayama Lake Deposits (Wood) Shiobara Lake Deposits (Wood)  Za.6 Lake Deposits (Peat) Kutchan (1) (Peat)Narugo (2) (Peat) Narugo (3) (Wood)  Mukaimachi (1) (Wood) Nakayamadaira (1) (Wood)CodeTH-032  TH-034 Gak-314 TK-66 Gak-4853 N-927 TH-005  TH-007 TH-015 TH-033yrs. B.P.     —1745  27,100  +2270  28, 495—2035  +2785 27,  900+1700  33,  40011200  34,  400+1000  37,  300+220015,  925±445  11, 950+285      —1100 23, 005+1285 18,  595±705Table 2 Correlations of Geomorphic SurfacesMukaimachi Basin Nakayamadaira Basin Narugo Basin  14C-AgeSugenodai surface* -  Makinohara  surface* Akakura surface — Mukaimachi surface—Higashizawa surface  —   Nishihara  surface*  —Shokubutsuen  surface  — —Nakayamadaira surface  Hebinoyu surface —Yakeishihata surface  — Sanja surface  Daigakunaja surface  MyOsade surface Takehara surface Kamigawara surface*23, 005 *18, 595  *15,  925Station by Tamura and Okubo in 1967. Hence, Nishihara surface is correlative with the IVb surface in Sendai. Some humic soil layers of Tachikawa surface in  Kanto were dated by Kigoshi et  al.  (1969). The first layer, 150 to 180 cm in  depth was dated  17,000±400 yrs. B.P.  (Gak-1129) with total organic carbon in soil,  16,000±300 yrs. B.P. (Gak-1014) with humic acid separated, and 19,800+500 yrs. B.P. (Gak-1015) with humin sample separated. The second layer, 200 to 290 cm in depth was dated  24,900+900  yrs. B.P.  (Gak-1130) with total organic carbon, 22,300+900 yrs. B.P. (Gak-1016) with humic acid separated, and 21,400+600 yrs. B.P. (Gak-1017) with humin sample separated. These dates suggest that the Tachikawa surface (terrace) was formed at 24,900+900 yrs.  B.P., and is correlative with Sugenodai surface in Mukaimachi Basin. 5  Paleo-lakes during  Wiirm Ice Age, in north Japan    It is clarified from the above mentioned radiocarbon dates that there were several ate Pleistocene paleo-lake basins in north Japan, although whole of late Pleistocene lake deposits are not listed in Table 1. The author would like to                   Geomorphology f Narugo and its Vicinities 155 emphasize that it should be noteworthy that late Pleistocene lake deposits were aged within the Main  Wurm Ice Age. Most of these paleo-lake basins were tectonic in origin under the influence of uplifting backbone range since Miocene. Each lake deposit does not have the same level in altitude, which means that each seems to have kept isolated level.    Eustatic sea-level fall in the Ice Age brought active downcutting along the coast, but it could not reach so fast inland. The above inland basins could maintain the isolated levels till the downcutting arrived. Climatic changes related to the Ice Age brought a lot of lake sediments. Abundant plant fossils in the lake sediments and pollen diagrams indicate cool and moist climate. The author confirmed the close relationships between paleo-lake basins and lacustrine sediments derived of volcanic activity, and between geomorphic situations fixed by geotectonic structure and geomorphic developments of paleo-lake basin regions. But more accurate discussion eeds more data both of radiocarbon dates on late Pleistocene lacustrine deposits and of geomorphic developments on late Pleis-tocene paleo-lake basins.    The terrace surface was eroded deeply between Nakayamadaira nd Narugo Basins, showing ravine topography. The author supposed that the ravine had been formed after the sea-level fall in the last glaciation (Omoto 1968), which was proved by the radiocarbon age of  18,595±705 yrs. B.P. (TH-033). Judging from the erosion depth of Narugo-kyo (ravine), or the lowering of the Daiya River floor since Nishihara surface, the  downcutting has continued at least 70 meters since 18,595 yrs. B.P. at the eastern margin of the Ohu Mountains. Strictly speaking, the upheaval amount of the region should be reduced, but it should be noticed that the downcutting caused by the sea-level fall in the Ice Age arrived inland with such a time lag as shown by radiocarbon age. Another ravine, where the Narugo Dam is situated, might be cut at the same age with the Narugo-kyo (ravine).    The  Onik8be lake deposits eem to be aged younger than the author expected. If the age is correct, the lake deposits of Narugo,  OnikObe, and Hanayama are correlative in age and those of  Nakayamadaira nd Mukaimachi seem to be aged contemporaneously. The river terraces and fans in the basin are expected younger than the lake deposits. The above geomorphic development is not definite because of the lack of radiocarbon dates. 6 Conclusions    Followings are main results of the present study.    1) Geomorphic surfaces of Narugo and its vicinities were correlated with radiocarbon dates as Table 2.156 K.  OMOTO   2) The lake deposits of he surreyed area re aged between 27,100-4_2172g yrs. B.P. (TH-032) and 28,495722°455yrs.B.P.(TH-034). Other late Pleistocene lake deposits in north Japan are expected to be aged between  37,300+2200 yrs. B.P. (N-927) and  33,400+1200 yrs. B.P. (TK-66).    3) Narugo-kyo (ravine) was cut afterthe sea-level lowering of the  Wiirm Ice Age.    4) Downcutting caused by the sea-level lowering of last glaciation arrived at the eastern margin of Ohu Mountains in retard of several thousands years, and eroded the terrace surface more than 70 meters deep.    5) The river terraces and fans in  Onikobe Basin were formed during or after the  Wiirrn Ice Age. More radiocarbon dates are necessary to compile the geomorphic development in the  Onikobe Basin in detail.      The author would like to dedicatethis paper to Professor Toshio Noh, Tohoku  University, with hearty thanks for his useful suggestions and encouragement, for the  commemoration of his retirement. The author wishes to express his appreciations to  Professor Kasuke Nishimura, Tohoku University, for his critical reading of the manuscript  and many suggestions on this study. Miss  Yoko Koseki helped kindly the author to  carry out the carbon datings.                            References (*in Japanese)  Ikeda, T.  (1946): Geology and Topography of Narugo, Nakayamadaira and Mukaimachi*.          Grad. Thesis. Geol., Tohoku Univ. 1-43  Imaizumi,  R.  (1974)  :  "C-Age of Peat Bed of Zao Lake Deposits, Togatta Hotspring Area,         Miyagi  Prefecture  —  "C-Age of the Quaternary Deposits in Japan (103)—*.        Earth  Sci.  (Chikyu Kagaku) 28 199-201  KatO, I. and  Shimada,  I. (1953): Onthe green  tuff geology of the southwestern foot of  Kurikoma volcano and the origin of the Sanzugawa, Onikobe Uppermost Miocene          basins*. Jour.  Jap. Assoc.  Min. Petr. Econ. Geol. 37 178-190  Kigoshi, K., Aizawa, H. and Suzuki, N.  (1969): Gakushuin Natural Radiocarbon          Measurements  VII. Radiocarbon. 11 295-326  Kobayashi, H.,  Matsui, Y. and Suzuki,H. (1971): University of Tokyo Radiocarbon         Measurements IV. ibid. 13 97-102  Nakamura, H. and Maeda, K.  (1959):  Geology and thermal water of Narugo, Kawatabi          and Nakayamadaira geothermal reas, Miyagi  Prefecture* Bull. Geol.Sure.  Jap. 10 227-236  Nakamura, H.  (1962): Report on the Geological Studies of Hotsprings in Japan*. Rep.         Geol. Sure.  Jap. 192  6-21  Nishimura, K., Omoto, K. and Koseki, Y.  (1972): Tohoku University Radiocarbon         Measurements I.  Sci. Rep. Tohoku Univ. 7th Ser. (Geogr.) 22 271-274  Oide, K. and Onuma, K.  (1960): Igneous activity of the "Green  Tuff Region" in northeast         Honshu, Japan*. Earth  Sci. (Chikyu Kagaku). Nos. 50-51  36-55  Oide, K.  (1964): On the  Wiirmian Lake Deposits at HanayamaVillage, Miyagi Prefecture  —"C-Age of the Quaternary Deposits in Japan XXVII  —*. ibid. 71 38  Omoto, K.  (1964): Geomorphic development of the  Onik8be basin, Miyagi prefecture*.          Ann.  Tohoku Geogr. Assoc. 16 61-70   (1966): Geomorphological development of he Narugo basin, Miyagi prefecture,Geomorphology of Narugo and its Vicinities 157 northeast  Japan*.  Geogr. Rev.  jap. 39 521-537    (1967)  : Geomorphology of the Nakayamadaira Basin, Miyagi  Prefecture.  Sci.  Rep. Tohoku Univ. 7th Ser. (Geogr.). 16 19-39    (1968): Geomorphological Development of the Mukaimachi Basin, Yamagata        Prefecture. ibid. 17 31-52   (1971): Age of the Rusuttu Formation and Disappearance of Kutchan Lake        Basin, Southwest of  Hokkaido*. Ann. Tohoku Geogr.  Assoc. 23 165   , Makita, H. and Koseki, Y.  (1974): Tohoku University Radiocarbon        Measurements II. Sci. Rep. Tohoku Univ. 7th Ser. (Geogr.) 24 205-209 Osawa, K.  (1964):  Ge  ological Map of  Shinjo*. Geol. Sur.  jap. Ouchi, S. (1973):  River Terraces and their Displacement  along the Hirose River, Miyagi  Prefecture*. Ann. Tohoku Geogr. Assoc. 25 84-90  Shimada, I.  (1955)  : Sedimentological Studies on Paleo Lake Basins (1st Report) — On        the Sedimentation of the Lake Deposit in the  OnikObe Basin, Miyagi Prefecture, Japan  —*. Geol. Mag. 61 218-226   and Konno, H.  (1971): Earthly Vivianite from the Pleistocene Lacustrine        Sediments in the  OnikObe Basin, Miyagi Prefecture, Japan. Sci. Rep. Tohoku        Univ. 3rd Ser.  (Min. Petr. Econ. Geol.) 11  143-157 Taguchi, K.  (1960): Stratigraphical Studies of the Neogene Tertiary in the Southern        Part of the Oguni River, Mogami-gun, Yamagata Prefecture (GeologicalStudies        of the  "Dewa Geosyncline", Northern  Honshu-IV)*. Geol. Mag. 67 157-170Tayama, R.  (1933): Geomorphic Study of Kitakami Mountains (Part 1. River terraces). (A)        — River Terraces of Sendai and its  vicinities*. Saito-hdonkai Mus. Res. Bull. 17 83

Geomorphology of Narugo and its Vicinities, North Japan - Chronological View Based on Radiocarbon

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Geomorphology of Narugo and its Vicinities, North Japan - Chronological View Based on Radiocarbon

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