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OLIVE 香川大学学術情報リポジトリ OLIVE 香川大学学術情報リポジトリ OLIVE 香川大学学術情報リポジトリ The Geology of Kagawa and Northern Ehime Prefectures, Shikoku, Japan Minoru SAITO List of Contents Page Abstract 1 Introduction 2 Acknowledgements 3 I Historical Review of the Works on the Geology and Paleontology of the Setouchi Area 3 IT. Geology of the Inner Zone of Shikoku 12 A -Sambagawa Metamorphics 12 B -Yamaguchi Group 14 C -Ryoke Metamorphics 14 D -GI anite 15 E -1zumi Group 17 F -Kuma Group 19 G -Tonosh0 Group 20 H-Sanuki Group 21 I -1shizuchi Group 23 J -The Lacustrine Deposits 24 K-Yakeotoge Gravels 36 L -Ter r ace and Fan Deposits 37 a. Igneous Activity 38 IV. Geological Structures 40 A-Unconf or mities 40 B -Faults 42 C -Median Line 44 D -Folding 45 E-Basin Structure 46 V . Sedimentary Structures 46 VI. Geological Ages of the Formations 5 1 W Boundary between the Pliocene and Pleistocene Deposits in Kagawa and Ehime Prefectures 56 m. Correlation 58 M Geological History 61 Bibliography 67 Explanation to Plates Abstract More than ten years field and laboratory work on the geology and paleontology of the deposits ranging from Cretaceous to Pleistocene distributed in Kagawa and northern Ehime Prefectures has resulted in the distinction of lacustrine deposits of Pliocene age, the establishments of stratigraphic units, recognition of geological structures hitherto left unnoticed, concrete evidence for the number of activities of the Median Line and others The previously considered Quaternary deposits are shown to belong to the Pliocene and to represent lacustrine deposits. These lacustrine deposits have extensive distribution throughout Ehime and Kagawa Prefectures and continue farther eastwards to Nara, Mie and Aichi Prefectures and are characterized everywhere by the yield of Metasequoia-Stegodon assemblage. Throughout northern Shikoku deposits of Miocene marine sediments are missing except in small patches in the island of ShBdo-shima, whereas those of the Paleogene are represented by the Kuma group of Eocene age This shows that the period of denudation was a long and varied one, ranging from Oligocene throughout the Miocene in northern Shikoku aside from ShBdo-shima OLIVE 香川大学学術情報リポジトリ 2 M. Saito Similary the restricted distribution of marine Pleistocene deposits in the Setouchi area also shows that the conditions were varied during the late Pliocene to Pleistocene ages It is shown that the marine Pleistocene invasion into the Setouchi area was contemporaneous with the intense crustal movement during the post-Pliocene pre-Pleistocene break The long debated problem of number of time of activity of the Median Line is now proved by field evidence have taken place at least three time, namely, during the post-Cretaceous pre-Kuma, post- Kuma pre-Ishizuchi, and post - lacustr ine deposits and pre-Yakeotoge gravels Although it may be problem that other ages of the movements may be discovered, at least in northe~nShikoku, it is deemed that the stated three movements are well established. From sedimentary structure preserved in the Cretaceous Izumi group and in the Pliocene lacustrine deposits, it is shown that deposition was rapid in the rapidly downsinking through of the Izumi sea in which turbidities are well developed and have dist~ibution,showing there many interesting structures However, in the lacustrine deposits where sedimentary structure also well preserved, the inferred conditions are quite different from that of the Izumi group because deposition was in a linear basin, shallow, now preserved only in the depressed areas, in that major structure are not developed Another characteristics of the lacustrine sedimentary structures is the development of local features However, it is noticeable that the local structures reflect the sedimentary environment of the different part of the extensive paleo-Setouchi Lake Aside from the geological structure which is given in detail considerable details are given to the correlation of the Pliocene and Pleistocene deposits in the Setouchi area as well as also with adjacent areas From this correlation table it is evident that the climatic conditions were varied from cold to moderate or warm and it is well reflected in the flora, fauna and also in the kinds of sediments distributed in the different parts of the Pleistocene deposits Introduction The present work which commenced more than ten years ago concentrates on the geo- logy of the rocks ranging pre-Cretaceous, Cretaceous up to and through the Pleistocene distributed in the northern part of Ehime Prefecture and Kagawa Prefecture. This par- ticular area was selected for several reasons, such as, the hitherto accepted deposits ex- tensively distributed in the two Prefectures actually comprise sediments of the Pliocene and of the Pleistocene, the number of time of activity of the Median Line had been interpreted variously and the field evidence had been obscure in many cases, and the sequence of the different deposits (volcanic and sedimentary) had been clear. Also the geological structures of the deposits ranging from Cretaceous to Pleistocene had been left almost untouched. For such reasons as well as for others, the writer studied the area in detail and for the purpose several provinces were distinguished for the sake of brevity. Since rocks of pre-Cretaceous age are not well distributed in the studied area and because they are better developed in other areas, details concerning them have not been included into the present work. The chief purpose of the present study is to clarify the sedimentary environment of the lacustrine deposits of Pliocene age, to settle the boundary between the Pliocene and Pleistocene deposits to find their relationship within the Setouchi areas as well as in the adjacent ones. For the study mechanical analysis of many samples from different stratigraphic levels and geographic positions were undertaken, detail stratigraphic columns were whereas possible, sedimentary structures were recorded in detail and their occurrences plotted, data from drilled wells as well as those dug for irrigation purposes were also included into the study, and paleontological evidence was incoporated. By field and laboratory works just outlined, this work was brought to its present condition and although it is felt that more evidence is necessary it also is considered that our knowledge to date should be into a published to advance our knowledge on the geology of Shikoku and also of Japan OLIVE 香川大学学術情報リポジトリ The Geolog,y gf' Kagawa and Nortlzern Ehime Prefectures 3 Acknowledgements The writer wishes to express his thanks to Professor Kotora HATAI of the Institute of Geology and Paleontology, Tohoku University, for his kind guidance in the field and in the laboratory . The writer, who wzs first introduced to the study of geology by Dr. Shbshiro HANZAWA, Professor Emeritus of the Tohoku University, takes this opportunity to express his deep gratitude to him for his continued encouragement. Sincere thanks are expressed to Prfessors Enzb KONNOand Kiyoshi ASANO,both of the Institute of Geology and Paleontology, Faculty of Science, Tohoku University for their encouragements. He deeply appreciates the kindness of Professor Tadao MAEKAWA,Dean of the Faculty of Agriculture of the Kagawa University who made possible the writer's research during 1960 to 1961 in the Institute of Geology and Paleontology, Tohoku University. During the course of the present work the writer has received valuable support from the following persons to whom he tskes this opportunity to express his deep gratitude, Dr. Hisakatsu YABE, Professor E~neritusof the Tohoku University and P~ofessorMotoki EGUCHIof the Faculty of Technology of the Tohoku University for their encouragements in various way; Dr. Shigeru MIKI, Professor of the Bsaka City University and Dr. Keiji SUZUKIof the Fukushima University for their valuable suggestions concerning the plant fossils; Professor Koz6 NAGAI of the Ehime University for his permission to study his data and Dr. Kankichi SOHMAof the Tohoku University for his pollen analysis of peaty matter and Dr. Taiji KUROKAMIfor his encouragement in various way. Acknowledgements are also due to the following persons for their help in many ways; Dr. Tamio KOTAKA,Dr. Shozb HAYASAKA,Dr. Koichiro MASUDA,Dr. Shin KITAMURA, Dr. Masafumi MURATA, and the members of the Institute of Geology and Paleontology, Tohoku University; Professor Wataru ISHIJIMAof the Rikkyo University; Dr. Rikii SHOJI of the Tohoku University; Dr. Yoshio ARAKI and Mr. Jun YAMADA, both of the Mie University; Dr Jiro KATTO and Dr. Jun NAKAMURA,both of the Kochi University; Dr. Jun AKUTSUof the Utsunomiya University; Mr. Shigeichi YAGI of the Matsuyama Museum; Mr. Katsuaki HIYAMAof the Bo~rdof Education of Ehime Prefecture; Mr. Kazu TAKAHASHIof the Mizukue Middle School, Ehime Prefecture; Mr Shoichi KONDO of the Kaneko Primary School, Niihama City; Mr. Yuji BANDOof the Faculty of Liberal Arts and Education of the Kagawa University ; Dr Masaki UEHARA,DI . Hachiro KIRA, Mr Hiroo INOUE,Mr. Kazuyoshi NAKAYAMA,Mr. Yutaka UMEDA,Mr. Takeshi WAKIYA, and the members of the Faculty of Agriculture, Kagawa University. For Photographic work of Mr. Kimiji KUMAGAIof the Tohoku University, the writer's thanks are also expressed. Thanks are also due to the Ministry of Education, for financial support from the Sci- ence Expeditur e Fund, I . Historical Review of the Works on the Geology and Paleontology of the Setouchi Area In 1894, K. WAKABAYASHIwrote on the discovery of mammalian fossils from the vicinity of Shaganohana in Sh6do-shima, but gave neither generic or specific names. U. OGAMI (1895) reported that Mt. Iyatani in the Sanuki district consists of conglo- merate, but made no mention as to its age. T. SUZUKI(1896) in his explanatory text to the geological map of Tokushima in the scale of 1:200,000; wrote that the pyroclastic group bearing sanukite (including the coal OLIVE 香川大学学術情報リポジトリ 4 M. Saito bearing strata) belong to Pliocene in age. E. SAKAWA(1898) reported that Mt. Iino in Sanuki province is independent of the older volcano.