<国立科博専報>日高累層群石灰岩の岩相と生相概報

概要

論文の詳細を見る
The Hidaka mountains, the backbone range of Hokkaido comprises the fossiliferous Cretaceous Yezo Group (Aptian-Maastrichtian), and the underlying Sorachi (roughly refered to the Upper Jurassic to Neocomian) and Hidaka (unknown ages) Group of eugeosynclinal lithologic assemblage. The latter two groups are scanty of fossils and any informationconcerning their sedimentary features has not so far been presented. This report gives a result of a preliminary study on litho- and bio-facies of limestones of the two groups. Limestones of the Hidaka Group (localities and lithologic features of samples are shown in Table 1) are characterized by dark grey, very fine-grained micritic limestone. The following lithologic types are recognized : a) homogeneous micrite, almost devoid of biogenic fragments visible under microscope; b) micrite containing a small amount (mostly less than 1%, rarely up to 3%) of bioclasts, which are crinoid osicles in most cases and rarely foraminifera; c) micrite containing almost exclusively radiolarian remains less than 20%. The above mentioned micrites are composed of subhedral calcite mosaics of 5-20 microns. The radiolarian micrite always contains nodular chert of various shape and size, and the contained radiolaria are entirely replaced and infilled with spary calcite. In short the limestones of the Hidaka Group suggest the deposition in off-shore, deep, quiet sea environment. Besides the above, oosparite and arenaceous intramicrudite or microbreccia were found at two localities in the tributary of the Horobetsu. The oosparite bed consists of coarsegrained ooids with subordinate crinoid osicles and algal remains, and grades downwards into arenaceous intramicrudite and is covered by micrite. These beds are intercalated in the sequence consisting of black slate and micritic limestone mentioned above. Their occurrence and lithologic features suggest allochthonous slump masses derived from a very shallow, wave-agitating environment where they were deposited. Limestones of the Sorachi Group (see Table 2) are similarly composed of a) micrite almost devoid of bioclasts, b) micrite containing a small amount of crinoid osicles or foraminifera, and c) radiolarian biomicrite. Thus, micritic limestone is predominat in the Sorachi Group, but in some samples (d) fragmentary calcareous algae and/or spongiomorphids are met with. Since limestones of the group are the deposits on submarine volcanic mounds, fairly variable lithologic features are expected. Some remarks should be given here regarding the Orbitolina limestone of the Lower Yezo Group, which shows a marked contrast to those of the Hidaka and Sorachi. Limestones of the Lower Yezo occur as small lentils in shale or alternating sandstone and shale at a horizon 50-200 m above the Sorachi Group, and contain, besides orbitolinids, abundant hermatypic massive corals, rudistid bivalves, a gigantic Nerinea, and solenoporacean and coralline algae. Although their occurrence have not been studied, their assemblage suggests a reefal or biohermal aspect of a very shallow sedimentary environment.
国立科学博物館の論文
1972-11-30

<国立科博専報>日高累層群石灰岩の岩相と生相概報

スポンサーリンク

概要

著者

関連論文

スポンサーリンク