Cyclostratigraphy of the Late Miocene to Pliocene sediments at IODP sites U1425 and U1430 in the Japan Sea and paleoceanographic implications

Abstract

High-resolution studies of sedimentary sequences have reconstructed paleoceanographic changes in the Atlantic and southern and equatorial Pacific Oceans during the Late Miocene and Pliocene, but comparable analyses are lacking for the North Pacific Ocean. However, continuous samples of hemipelagic sequences covering this time interval were obtained at Integrated Ocean Drilling Program sites U1425 and U1430 in the Japan Sea during expedition 346. Because the paleoceanography of the Japan Sea was sensitive to glacio-eustatic sea-level changes, changes in the sediment record are manifested as cyclic lithological changes. By using a gamma ray attenuation (GRA) density, which reflects biogenic silica content, as an indicator of sea-level changes, we developed an independent orbitally tuned chronology at each site to construct high-resolution, high-precision age models for the time span of 11.8 to 1.45 Ma. First, the 405-kyr-filtered GRA profile at each site was tuned to 405-kyr-filtered orbital eccentricity. Then, using the 405-kyr-tuned age model, the 100-kyr-filtered GRA profile was tuned to shorteccentricity cycles to adjust the 405-kyr-tuned age models. We used the resulting age models to revise the time intervals of previously published lithological units and paleoceanographic stages for the Japan Sea. Our profiles based on physical properties are a good match to the oxygen isotope record, except for 6.6-3.6 Ma, a time interval with small-amplitude fluctuations in the oxygen isotope record.

Aeolian delivery to Ulleung Basin, Korea (Japan Sea), during development of the East Asian Monsoon through the last 12 Ma

“…7). The low dust flux in the late Pliocene may be attributed to possible localized winnowing effects, or sediment remobilization during sea-level lowstands specific to this site during this time, as there is a hiatus from 4.1 to 7.3 Ma and similar hiatuses are not seen at other sites from Expedition 346 (Kurokawa et al 2019). Following the hiatus at Site U1430, Pliocene total dust flux is low (c. 0.25-0.75 g cm −2 ka −1 ), before increasing to 3.1 g cm −2 ka −1 in the Pleistocene during a time of global cooling and drying (Shen et al 2017).…”

“…We integrate several age models for Site U1430 (Kamikuri et al 2017;Matsuzaki et al 2018;Kurokawa et al 2019) that are of similar sampling resolution and cover the same age range as our study. We therefore use these models rather than, for example, a higherresolution age model for only the youngest 1 Ma (Tada et al 2018).…”

Deep‐Water Formation in the North Pacific During the Late Miocene Global Cooling

“…It has been reported that the North Pacific (20-40°N) at 1,000-3,000 m water depth was dominated by water of low dissolved oxygen content during the middle-late Miocene, the so-called oxygen minimum zone (OMZ), although with possible controversy for its existence (Tada, 1994;Woodruff & Savin, 1989); this OMZ structure could have exerted a major control on the formation of oxygen-deficient deep-water in the Japan Sea during this interval (Tada, 1994). The sulfur isotope of pyrite and redox-sensitive elements (e.g., Mn and U) at the Ocean Drilling Program (ODP) leg 127/128 sites indicated that deep-water fluctuated between suboxic to euxinic during 9-6.5 Ma in the Japan Sea (Masuzawa et al, 1992), approximately spanning the ∼11-7.4 Ma interval with the latest reestablished age model (Kurokawa et al, 2019;Matsuzaki et al, 2018;Tada et al, 2015). Likewise, the coeval occasional occurrence of parallel laminations at sites U1425 and U1430 suggests the suppression of bioturbation due to low oxygen levels (Tada et al, 2015).…”

“…This hiatus coincides in depth with a regional unconformity on seismic profiles (MB3 unconformity) extending over much of the eastern South Korea Plateau (Horozal et al, 2017). Although the cause is uncertain, it may be attributed to erosion by bottom currents or a brief episode of local tectonic uplift (Horozal et al, 2017;Kurokawa et al, 2019). Age models of the sediments from Sites U1425 and U1430 were established on the basis of magnetostratigraphy and biostratigraphy (S. I.…”

Preface for article collection “Evolution and variability of Asian Monsoon and its linkage with Cenozoic global cooling”

“…A continuous Neogene sedimentary record of the AM was also obtained from the Japan Sea by IODP Expedition 346. Kurokawa et al (2019) demonstrated that gamma-ray attenuation (GRA) density of the hemipelagic sediments of the Japan Sea reflects biogenic silica content that changed in association with glacio-eustatic sea-level changes. They established a high-resolution age model covering the last~12 Myr by tuning a 100-kyrfiltered GRA density profile to short eccentricity cycles for the sediments obtained from IODP Sites U1425 and U1430 in the central and southwestern parts of the Japan Sea.…”