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＜departmental bulletin paper＞
Occurrence and origin of rhythmites, in Lower Cretaceous lacustrine sediments in the W akino Subgroup, Kyushu
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| Abstract | The occurrence of rhythmites developed in the W akino Subgroup of the Lower Cretaceous Kanmon Group is described, and their origins are discussed. According to the thickness of laminae and their inter...al structures, the following three modes of occurrence are discriminated: types A, B and C. Type-A rhythmite consists of regularly alternated dark and light gray laminae of less than 1mm thick, which form varve-like couplets. The contact between dark and light-coloured laminae of a couplet is sharp. Individual laminae show graded or massive structure. The deposition of this type rhythmite takes place from suspension cloud. The microcycles of dark and light laminae might indicate seasonal and/or weather fluctuations. Type-B rhythmite is composed of about 1-5mm thick laminae, which have an erosive base. Individual laminae show normaly graded, convolute, and parallel to massive sublaminae upwards internally, and some laminae are rarely amalgamated. Sedimentation of the lower part of this type occurs under the low-density turbidity current, and the upper part is from suspension cloud. Type-C rhythmite consists of laminae over 5mm in thickness. Rhythmite of this type might be originated from mudflows.show more |
| Table of Contents | I. はじめに II. 地質概説 III. リズマイトの産状 IV．考察 まとめ |
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| Created Date | 2021.10.18 |
| Modified Date | 2022.06.20 |