四国東部の南部黒瀬川帯上部三畳系寒谷層と坂州不整合 : 層序、堆積相、フォーナ

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  • シコク トウブ ノ ナンブ クロセガワタイ ジョウブ 3ジョウケイ サブダニソウ ト サカシュウ フセイゴウ ソウジョ タイセキソウ フォーナ
  • Upper Triassic Sabudani Formation and Sakashu Unconformity of the South Kurosegawa Terrane, East Shikoku : stratigraphy, sedimentary facies and faunas
  • 南部黒瀬川帯寒谷層と坂州不整合

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The Sakashu Unconformity, a representative unconformity between Late Permian accretionary comprex and Late Triassic shallow-marine sediments in the South Kurosegawa Terrane, has investigated in stratigraphy, sedimentary facies, allochthonous and autochthonous faunas with the view point of post-accretional environmental changes. The accretion mélange of the Hisone Group, basement of the unconformity, yields Late Permian radiolarians. The lower member of the Upper Triassic Sabudani Formation is associated with two types of debris flows. One contains blocks of pelagic chert, carbonates, and greestones. The other is composed of mylonitized granitic breccias and fragments. The latter probably derived from the Mitaki Granites (400+ Ma) of the Kurosegawa Tectonic Zone that form the substratum of the Silurian limestone. The basal middle member of the Sabudani Formation contains huge blocks of weathered limestone/chert that yields late Early Permian conodont fauna (M. bisseli - S. whitei Zone). The hummocky cross-stratification in the middle member of the Sabudani Formation indicates a lower off-shore facies. Existence of the Permian conodont-bearing huge eroded limestone/chert blocks, and early Late Permian radiolarians in chert pebbles of the hummocky cross-stratified lag sediments suggests probable derivation of the conglomerates from the blocks in the Permian accretionary complexes. The Triassic mollusk fauna of the middle and upper members of the Sabudani Formation is correlative with the Carnian (-Norian) Kochigatani bivalve-fauna in the clastic facies of the Kurosegawa Terrane (Outer Zone of SW Japan) as well as with the Mine and Nabae groups, Primorye, Zabaikal and NE Siberia. From a paleobiogeographic point of view, the bivalve-fauna of the clastic sand- and marlstone Kochigatani facies is regarded to differ from that of the carbonate Tethyan facies in the South Chichibu Jurassic Accretionary Terrane.

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