DOI: 10.5061/dryad.pc866t1kk
title: Middle Holocene relative sea-level changes and vertical tectonic crustal movements on Shikoku Island near the Nankai Trough, Japan

description: The Philippine Sea plate subducts beneath the Eurasia plate at the Nankai
 Trough, northwestern Pacific, causing crustal deformation, mega-thrust
 earthquakes, and tsunami events. Shikoku Island, 150 km northwest of the
 trough, experiences both coseismic and interseismic deformation. Coastal
 sediments potentially record vertical crustal movements as relative sea
 level (RSL) changes. We studied sedimentary facies and microfossil
 ostracodes in core SKM from southwestern Shikoku Island for evidence of
 middle Holocene tsunami events and deformation. The core sediments
 included nine event layers corresponding to storm or tsunami events. Using
 modern analog techniques, we estimated RSLs from the ostracode assemblages
 of core SKM and 13 other cores from Shikoku Island and the surrounding
 region. Then, we subtracted RSL changes due to glacio-hydro isostatic
 adjustment from the estimated RSLs to estimate vertical tectonic movement
 rates in these cores between 8.6 and 4.7 ka. The inferred RSL changes
 suggest that the Sukumo site has experienced both uplift and subsidence
 since 8.6 ka. Before 6.6 ka, rates of the tectonic crustal movement were
 higher than the modern-day rate, and its spatial distribution also
 differed. After 6.6 ka, the tectonic crustal movement showed a similar
 spatial pattern and occurred at rates close to the modern-day interseismic
 rate. The spatial pattern and rates of tectonic crustal movement could be
 caused by changes in rupture areas between Eurasia and the Philippine Sea
 plates beneath Shikoku Island and in stress conditions of the
 asthenosphere.  Some of the vertical displacements can be
 explained by the movements of local active faults.
description: The modern data (i.e. the
 training data) for the modern analogous technique consist of 341 samples
 and 574 taxa (Modern_data.csv). Each sample has at least 50 ostracodes.
 The water depth of the modern data ranges from 0.3 to 50 m
 (Modern_data_WD_Coord.csv). To organize the data, we selected and complied
 ostracode census data tagged with water depth to corelate with the census
 ostracode data in 25 bays of the Japanese coasts
 (Modern_data_localities.pdf), referring to 27 studies (Bodergat and Oki,
 2020; Frydl, 1982; Ikeya and Hanai, 1982; Ikeya and Suzuki, 1992; Irizuki
 et al., 2003, 2006, 2008, 2009, 2018; Ishizaki, 1968, 1969, 1971; Itoh,
 1998; Kamiya et al., 2001; Kawano et al., 2013; Masuma and Yamada, 2014;
 Tanaka, 2008; Tanaka et al., 2019; Tsukawaki et al., 1997, 1998, 2000;
 Yamane, 1998; Yasuhara and Irizuki, 2001; Yasuhara et al., 2002, 2005;
 Yasuhara and Seto, 2006). In taxonomy of the data, we merged a species
 compared to a described species, that has “cf.” in scientific name to the
 described species and
 lumped <em>Microcythere</em>, <em>Neocytherideis</em>, <em>Paradoxostoma</em>,<em>Pseudocythere</em>, <em>Sclerochilus</em>, <em>Sulcocytherura</em>, <em>Triebelina</em>, and <em>Xiphichilus</em>species to each genus. The taxonomic names in the data files are abbreviated as Codes, that are referred to Taxon_references.csv.  References Bodergat, A.-M., Oki, K., 2020. Ostracods surface species in Kagoshima Bay and their distribution. Nature of Kagoshima 46, in press. <br>Frydl, P.M., 1982. Holocene ostracods in the southern Boso Peninsula, in: Hanai, T. (Ed.), Studies on Japanese Ostracoda, Bulletin, University Museum, University of Tokyo. University of Tokyo, Tokyo, pp. 61–140, 257–267.<br>Ikeya, N., Hanai, T., 1982. Ecology of recent ostracods in the Hamana-ko region, the Pacific coast of Japan, in: Hanai, T. (Ed.), Studies on Japanese Ostracoda, Bulletin, University Museum, University of Tokyo. pp. 15–59.<br>Ikeya, N., Suzuki, C., 1992. Distributional patterns of modern ostracodes off Shimane, southwestern Japan Sea. Rep. Fac. Sci. Shizuoka Univ. 26, 91–137.<br>Irizuki, T., Fujihira, Y., Iwatani, H., Kawano, S., 2018. Recent ostracode assemblages from Shushi Bay, Tsushima Island, southwestern Japan and their ecological and zoogeographical characteristics. Laguna 25, 39–54.<br>Irizuki, T., Gotomyo, A., Kawano, S., Yoshioka, K., Nomura, R., 2009. Relationships between Recent ostracode assemblage and environmental factors in the northern part of Harima-nada Bay off Aioi City, Hyogo Prefecture, Southwest Japan. Geosci. Rep. Shimane Univ. 28, 1–9. [in Japanese with English abstract]<br>Irizuki, T., Ito, H., Yoshioka, K., Kawano, S., Nomura, R., Tanaka, Y., Sako, M., 2010. Recent ostracode assemblages and the marine environment around Kasado Bay in northeastern Suo-nada Bay, Yamaguchi Prefecture, Southwest Japan. Geosci. Rep. Shimane Univ. 29, 11–20. [in Japanese with English abstract]<br>Irizuki, T., Nakamura, Y., Takayasu, K., Sakai, S., 2003. Faunal changes in Ostracoda (Crustacea) in Lake Nakaumi, southwest Japan, over the last 40 years. Geosci. Rep. Shimane Univ. 22, 149–160. [in Japanese with English abstract]<br>Irizuki, T., Seto, K., Nomura, R., 2008. The impact of fish farming and bank construction on Ostracoda in Uranouchi Bay on the Pacific coast of southwest Japan–––Faunal changes between 1954 and 2002/2005. Paleontol. Res. 12, 283–302.<br>Irizuki, T., Takata, H., Ishida, K., 2006. Recent Ostracoda from Urauchi Bay , Kamikoshiki-jima Island , Kagoshima Prefecture, southwestern Japan. Laguna 13, 13–28.<br>Ishizaki, K., 1971. Ostracodes from Aomori Bay, Aomori Prefecture, Northeast Honshu, Japan. Sci. Reports Tohoku Univ. Sendai, Second Ser. 43, 59–97.<br>Ishizaki, K., 1969. Ostracodes from Shinjiko and Nakanoumi, Shimane Prefecture, Western Honshu, Japan. Sci. Reports Tohoku Univ. Sendai, Second Ser. 41, 197–224.<br>Ishizaki, K., 1968. Ostracodes from Uranouchi Bay, Kochi Prefecture, Japan. Sci. reports Tohoku Univ. Second Ser. Geol. 43, 59–97.<br>Itoh, H., 1998. Ostracode assemblages from Lake Hamana, Shizuoka Prefecture, Japan in 1996. Laguna 5, 93–99. [in Japanese with English abstract]<br>Kamiya, T., Ozawa, H., Obata, M., 2001. Quaternary and Recent marine Ostracoda in Hokuriku district, the Japan Sea coast, in: Ikeya, N. (Ed.), Guidebook of Excursions, the 14th International Symposium of Ostracoda. Organising Committee of ISO, Shizuoka, pp. 73–106.<br>Kawano, S., Irizuki, T., Nomura, R., 2013. Temporal changes of recent ostracode assemblages and bay environment with relation to the opening and extension of the Manzeki-seto Strait in the Tsushima Island, southwest Japan. Earth Sci. (Chikyu Kagaku) 67, 89–99. [in Japanese with English abstract]<br>Masuma, T., Yamada, K., 2014. Recent ostracode distributions in Kumihama Bay ( brackish lake ) in the northern part of Kyoto Prefecture, central Japan. Laguna 21, 1–14. [in Japanese with English abstract]<br>Tanaka, G., 2008. Recent benthonic ostracod assemblages as indicators of the Tsushima warm current in the southwestern sea of Japan. Hydrobiologia 598, 271–284. doi:10.1007/s10750-007-9162-6<br>Tanaka, G., Henmi, Y., Masuda, T., Moriwaki, H., Komatsu, T., Zhou, B., Maekawa, T., Niiyama, S., Nguyen, P.D., Doan, H.D., Ikeya, N., 2019. Recent ostracod distribution in western Kyushu, Japan, related to the migration of Chinese continental faunal elements. Mar. Micropaleontol. 146, 1–38. doi:10.1016/j.marmicro.2018.12.002<br>Tsukawaki, S., Kamiya, T., Kato, M., Matsuzaka, T., Naraoka, H., Negishi, K., Ozawa, H., Ishiwatari, R., 1997. Preliminary results from the R.V. Tansei-maru Cruise KT95-14 Leg 2 in the southern marginal area in the Japan Sea–Part 1: Sediments, benthic foraminifers and ostracodes. Bull. Japan Sea Res. Inst. 13–43.<br>Tsukawaki, S., Kamiya, T., Ozawa, H., Kato, M., 1998. Preliminary results from the R.V. Tansei-maru Cruise KT96-17 Leg 2 in the southwestern part of the Japan Sea–Sediments, benthic foraminifers and ostracodes. Bull. Japan Sea Res. Inst. 67–89.<br>Tsukawaki, S., Ozawa, H., Domitsu, H., Kamiya, T., Kato, M., Oda, M., 2000. Preliminary results from the R.V. Tansei-maru Cruise KT98-17 in the southern marginal part of the Japan Sea–Sediments, benthic and planktonic foraminifers, and ostracodes. Bull. Japan Sea Res. Inst. 89–119.<br>Yamane, K., 1998. Recent ostracode assemblages from Hiuchi-nada Bay, Seto Inland Sea of Japan. Bull. Dep. Nat. Hist. Ehime Pref. Sci. Museum 3, 19–59. [in Japanese with English abstract]<br>Yasuhara, M., Irizuki, T., 2001. Recent Ostracda from the northeastern part of Osaka Bay, southwestern Japan. J. Geosci. Osaka City Univ. 44, 57–95.<br>Yasuhara, M., Irizuki, T., Yoshikawa, S., Nanayama, F., 2002. Change in Holocene ostracode faunas and depositional environments in the Kitan Strait, Sothwestern Japan. Paleontol. Res. 6, 85–99.<br>Yasuhara, M., Seto, K., 2006. Holocene relative sea-level change in Hiroshima Bay, Japan: a semi-quantitative reconstruction based on ostracodes. Paleontol. Res. 10, 99–116.<br>Yasuhara, M., Yoshikawa, S., Nanayama, F., 2005. Reconstruction of the Holocene seismic history of a seabed fault using relative sea-level curves reconstructed by ostracode assemblages : Case study on the Median Tectonic Line in. Palaeogeogr. Palaeoclimatol. Palaeoecol. 222, 285–312. doi:10.1016/j.palaeo.2005.03.019
description: Modern_data.csv and
 Modern_data_WD_Coord.csv are dataset to perform the modern analogue
 technique, using R and its software package
 “analgoue”.