The Eocene Hiwadatoge Formation, SW Japan: Constraints on the timing of the denudation of the Sambagawa metamorphic rocks
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- Kusuhashi Nao
- Graduate School of Science and Engineering, Ehime University
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- Ando Yuichi
- Faculty of Science, Ehime University Present address: Nippon DR System
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- Tani Kenichiro
- Department of Geology and Paleontology, National Museum of Nature and Science
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- Matsubara Takashi
- Hokkaido University of Education
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- Kurita Hiroshi
- Faculty of Science, Niigata University
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- Nara Masakazu
- Faculty of Science and Technology, Kochi University
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- Yamaji Atsushi
- Division of Earth and Planetary Sciences, Kyoto University
Bibliographic Information
- Other Title
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- 四国北西部の始新統ひわだ峠層と三波川変成岩類の露出年代の再確認
Abstract
<p>The Hiwadatoge Formation in northwestern Shikoku, Southwest Japan, represents the oldest strata overlying the Sambagawa metamorphic rocks and is, therefore, often used to constrain the timing of the denudation of the Sambagawa metamorphic rocks. Despite its significance, previous studies on the formation are limited, and even the geological relationship between the formation and the Sambagawa metamorphic rocks has yet to be described in detail. To rectify this, we conducted geological mapping and detrital zircon U-Pb dating. The Hiwadatoge Formation is >100 m thick and composed of pebble to granule conglomerate and sandstone, which have local calcareous matrices. The formation is interpreted as southward-prograding shallow marine fan delta deposits. Most of the clasts in the formation were derived from the Sambagawa metamorphic rocks, but igneous rocks of the Ryoke, San-yo, and San-in belts were probably also sources of clastic grains. In addition to foraminifers and dinoflagellate cysts from previous studies, fossil bivalves and detrital zircon U-Pb ages in our study indicate that the formation was deposited during the early Lutetian (middle Eocene). The formation nonconformably overlies the Sambagawa metamorphic rocks and is unconformably overlain by the Kuma Group (and locally by the Ishizuchi Group). Therefore, the Sambagawa metamorphic rocks had been exposed and started eroding by the earliest middle Eocene, at least in the Shikoku region.</p>
Journal
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- The Journal of the Geological Society of Japan
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The Journal of the Geological Society of Japan 128 (1), 411-426, 2022-12-29
The Geological Society of Japan
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Details 詳細情報について
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- CRID
- 1390576059521257472
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- ISSN
- 13499963
- 00167630
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- Text Lang
- ja
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- Data Source
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- JaLC
- Crossref
- KAKEN
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- Abstract License Flag
- Disallowed