Japan Geoscience Union Meeting 2018

Presentation information

[JJ] Oral

B (Biogeosciences) » B-PT Paleontology

[B-PT06] Biotic History

Sun. May 20, 2018 9:00 AM - 10:30 AM 101 (1F International Conference Hall, Makuhari Messe)

convener:Isao Motoyama(Department of Earth and Environmental Sciences, Yamagata University), Takao Ubukata(Division of Geology & Mineralogy, Department of Earth & Planetary Sciences, Kyoto University), Kazuyoshi Moriya(早稲田大学 教育・総合科学学術院 地球科学専修), Chairperson:Motoyama Isao, Ubukata Takao, Moriya Kazuyoshi

10:00 AM - 10:15 AM

[BPT06-05] Estimating the degree of compactional thinning of fine-grained clastic rock based on ichnological observation

*Kentaro Izumi1, Ryota Suzuki2, Mutsuko Inui3 (1.Faculty & Graduate School of Education, Chiba University, 2.Arima Junior High School, 3.School of Science and Engineering, Kokushikan University)

Keywords:Fine-grained clastic rocks, Compaction, Trace fossils

This study proposed the empirical relationship between the degree of compactional thinning and geochemical composition for fully consolidated fine-grained clastic rocks. New data were provided by sedimentological, ichnological, and geochemical analyses of the mudrock samples from the Eocene Naharigawa Formation, Muroto-Hanto Group, Kochi Prefecture, Japan. Based on these analyses, the degree of compaction of the Naharigawa mudstones as a percentage of shortening (Cms) was calculated as 83.01 %. To quantitatively estimate the empirical relationship, the Cms values for various fine-grained clastic rocks, whose geochemical compositions are available by previous studies, were further calculated and compiled. As a result of the compilation, a significant and strong negative correlation between the Cms values and CaO abundances (r = −0.75; p < 0.05) was recognized. Furthermore, the Cms values show negative correlation between Ca concentrations normalized to terrigenous material (CaO/Al2O3, CaO/TiO2) that are considered as proxies for relative contribution of non-terrigenous (i.e. biogenic) carbonates, although the recognized correlations are not statistically significant. These lines of evidence strongly suggest that the degree of physical compaction of fine-grained clastic sediments is affected by carbonate contents. Although the obtained relationship may hold only for fully consolidated fine-grained clastic rocks of the Paleogene or older ages, it is very helpful for quantitatively estimating the degree of compactional thinning for any fine-grained clastic rock-dominated succession, as long as the major element composition of the sediments is determined.
Furthermore, a geological example of application of the proposed empirical relationship to consolidated mudstone-dominated succession is also discussed.