The effects of meteoric diagenesis on the geochemical composition and microstructure of Pliocene fossil Terebratalia coreanica and Laqueus rubellus brachiopod shells from northeastern Japan
Abstract Stable carbon (δ13C) and oxygen isotope (δ18O) compositions of fossil brachiopod shells can be used to interpret paleoclimatic and paleoceanographic conditions. However, the initial isotopic composition of the living shells might be modified by diagenetic alteration. To assess the degree of...
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| Format: | Article |
| Language: | English |
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SpringerOpen
2019-06-01
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| Series: | Progress in Earth and Planetary Science |
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| Online Access: | http://link.springer.com/article/10.1186/s40645-019-0289-7 |
| _version_ | 1811313892169613312 |
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| author | Hiroshi Fujioka Hideko Takayanagi Koshi Yamamoto Yasufumi Iryu |
| author_facet | Hiroshi Fujioka Hideko Takayanagi Koshi Yamamoto Yasufumi Iryu |
| author_sort | Hiroshi Fujioka |
| collection | DOAJ |
| description | Abstract Stable carbon (δ13C) and oxygen isotope (δ18O) compositions of fossil brachiopod shells can be used to interpret paleoclimatic and paleoceanographic conditions. However, the initial isotopic composition of the living shells might be modified by diagenetic alteration. To assess the degree of this modification, we analyzed δ13C and δ18O and three common indicators of alteration in shells: minor element (manganese (Mn), iron (Fe), and strontium (Sr)) concentrations; cathodoluminescence (CL)/non-luminescence; and the shell microstructure of fossil Terebratalia coreanica and Laqueus rubellus (rhynchonellate brachiopod) shells from an exposure of conglomerates of the Tentokuji Formation (Pliocene, 3.85–2.75 Ma) in northeastern Japan. Two indices were used to quantify the preservation state of shell microstructure: the altered fiber ratio (AFR) and the altered fiber and puncta-filling cement ratio (AF-PCR). We qualified the degree of luminescence by measuring the mean cathodoluminescence index (MCLI), defined as the mean R values in a particular area of a CL image with RGB colors. The δ13C and δ18O values were negatively correlated with AFR or AF-PCR and MCLI. The sampling spots with high Mn and Fe concentrations also exhibited relatively low δ13C and δ18O. The δ13C and δ18O were more strongly correlated with Mn concentration than with Fe concentration. Therefore, of the three minor elements examined in this study, Mn concentration is the most reliable indicator of meteoric diagenesis in the studied shells. Unlike Mn and Fe concentrations, Sr concentrations in the modern and fossil brachiopod shells were similar, with overlapping ranges. This indicates that Sr concentration is not likely to be a good indicator of diagenetic alteration in the studied shells. Our study provides further evidence that multiple criteria should be applied and cross-checked when assessing diagenetic alteration of brachiopod shells. |
| first_indexed | 2024-04-13T11:02:40Z |
| format | Article |
| id | doaj.art-d0dd8855a2d84500bb94500737426965 |
| institution | Directory Open Access Journal |
| issn | 2197-4284 |
| language | English |
| last_indexed | 2024-04-13T11:02:40Z |
| publishDate | 2019-06-01 |
| publisher | SpringerOpen |
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| series | Progress in Earth and Planetary Science |
| spelling | doaj.art-d0dd8855a2d84500bb945007374269652022-12-22T02:49:21ZengSpringerOpenProgress in Earth and Planetary Science2197-42842019-06-016112310.1186/s40645-019-0289-7The effects of meteoric diagenesis on the geochemical composition and microstructure of Pliocene fossil Terebratalia coreanica and Laqueus rubellus brachiopod shells from northeastern JapanHiroshi Fujioka0Hideko Takayanagi1Koshi Yamamoto2Yasufumi Iryu3Department of Earth Science, Graduate School of Science, Tohoku UniversityDepartment of Earth Science, Graduate School of Science, Tohoku UniversityDepartment of Earth and Environmental Sciences, Nagoya UniversityDepartment of Earth Science, Graduate School of Science, Tohoku UniversityAbstract Stable carbon (δ13C) and oxygen isotope (δ18O) compositions of fossil brachiopod shells can be used to interpret paleoclimatic and paleoceanographic conditions. However, the initial isotopic composition of the living shells might be modified by diagenetic alteration. To assess the degree of this modification, we analyzed δ13C and δ18O and three common indicators of alteration in shells: minor element (manganese (Mn), iron (Fe), and strontium (Sr)) concentrations; cathodoluminescence (CL)/non-luminescence; and the shell microstructure of fossil Terebratalia coreanica and Laqueus rubellus (rhynchonellate brachiopod) shells from an exposure of conglomerates of the Tentokuji Formation (Pliocene, 3.85–2.75 Ma) in northeastern Japan. Two indices were used to quantify the preservation state of shell microstructure: the altered fiber ratio (AFR) and the altered fiber and puncta-filling cement ratio (AF-PCR). We qualified the degree of luminescence by measuring the mean cathodoluminescence index (MCLI), defined as the mean R values in a particular area of a CL image with RGB colors. The δ13C and δ18O values were negatively correlated with AFR or AF-PCR and MCLI. The sampling spots with high Mn and Fe concentrations also exhibited relatively low δ13C and δ18O. The δ13C and δ18O were more strongly correlated with Mn concentration than with Fe concentration. Therefore, of the three minor elements examined in this study, Mn concentration is the most reliable indicator of meteoric diagenesis in the studied shells. Unlike Mn and Fe concentrations, Sr concentrations in the modern and fossil brachiopod shells were similar, with overlapping ranges. This indicates that Sr concentration is not likely to be a good indicator of diagenetic alteration in the studied shells. Our study provides further evidence that multiple criteria should be applied and cross-checked when assessing diagenetic alteration of brachiopod shells.http://link.springer.com/article/10.1186/s40645-019-0289-7BrachiopodCarbon isotopesOxygen isotopesMinor element concentrationCathodoluminescenceMeteoric diagenesis |
| spellingShingle | Hiroshi Fujioka Hideko Takayanagi Koshi Yamamoto Yasufumi Iryu The effects of meteoric diagenesis on the geochemical composition and microstructure of Pliocene fossil Terebratalia coreanica and Laqueus rubellus brachiopod shells from northeastern Japan Progress in Earth and Planetary Science Brachiopod Carbon isotopes Oxygen isotopes Minor element concentration Cathodoluminescence Meteoric diagenesis |
| title | The effects of meteoric diagenesis on the geochemical composition and microstructure of Pliocene fossil Terebratalia coreanica and Laqueus rubellus brachiopod shells from northeastern Japan |
| title_full | The effects of meteoric diagenesis on the geochemical composition and microstructure of Pliocene fossil Terebratalia coreanica and Laqueus rubellus brachiopod shells from northeastern Japan |
| title_fullStr | The effects of meteoric diagenesis on the geochemical composition and microstructure of Pliocene fossil Terebratalia coreanica and Laqueus rubellus brachiopod shells from northeastern Japan |
| title_full_unstemmed | The effects of meteoric diagenesis on the geochemical composition and microstructure of Pliocene fossil Terebratalia coreanica and Laqueus rubellus brachiopod shells from northeastern Japan |
| title_short | The effects of meteoric diagenesis on the geochemical composition and microstructure of Pliocene fossil Terebratalia coreanica and Laqueus rubellus brachiopod shells from northeastern Japan |
| title_sort | effects of meteoric diagenesis on the geochemical composition and microstructure of pliocene fossil terebratalia coreanica and laqueus rubellus brachiopod shells from northeastern japan |
| topic | Brachiopod Carbon isotopes Oxygen isotopes Minor element concentration Cathodoluminescence Meteoric diagenesis |
| url | http://link.springer.com/article/10.1186/s40645-019-0289-7 |
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