Integrated Pliocene-Pleistocene magnetostratigraphy and tephrostratigraphy of deep-sea sediments at IODP Site U1424 (Yamato Basin, Japan Sea)

Yasufumi Satoguchi,Saiko Sugisaki,Yoshitaka Nagahashi,Chuang Xuan,Yuxi Jin

doi:10.1186/s40645-020-00373-9

Abstract

Sediments from the semi-enclosed Japan Sea are sensitive to paleoclimatic perturbations and they offer great opportunities for many regional and global paleoceanographic and paleoclimatic studies. These studies often require a robust chronology. However, due to rare preservation of calcareous microfossils and drastic changes in surface water salinity during glacial lowstands, the construction of a traditional oxygen isotope stratigraphy for Japan Sea sediments is often difficult. Here, we use sediments recovered at Integrated Ocean Drilling Program (IODP) Expedition 346 Site U1424 to build an integrated Pliocene-Pleistocene reference magnetostratigraphy and tephrostratigraphy for sedimentary sequences from the region. Rock magnetic experiments indicate that magnetic remanence of Site U1424 sediments are carried primarily by (titano)magnetite with small contributions from high coercivity minerals (e.g., hematite) and possibly iron sulphides (pyrrhotite and/or greigite). Dark-colored sediments appear to contain less (titano)magnetite probably due to reductive diagenesis under euxinic conditions. Natural remanent magnetization (NRM) of u-channel samples covering a continuous ~ 167.6 m sediment sequence at Site U1424 was repeatedly measured at 1 cm intervals before and after stepwise demagnetization. Despite lower NRM intensity in dark-colored sediments, NRM directional data from both dark- and light-colored sediments are considered suitable for the construction of magnetostratigraphy. Site U1424 sediments clearly recorded the majority of the polarity chrons and subchrons within the last ~ 4.89 Myr, with the Cobb Mountain subchron, the end of Kaena subchron, and the onset of Nunivak subchron less well preserved. Sixteen tephra layers from the site were sampled for chemical composition analyses and the results were correlated to reference tephrostratigraphy of the region. Ages of the identified tephras are consistent with and can be well integrated with the magnetostratigraphy. The resulting age model suggests that sedimentation rates at Site U1424 range between ~ 1.7 and 7.6 cm/kyr with an average of ~ 3.3 cm/kyr. The acquired magnetostratigraphy and tephrostratigraphy at Site U1424 provide a reference chronology that can be correlated with and transferred to other sediment sequences in the region to study paleoceanographic and paleoclimatic changes of the region as well as their links to other regional and global changes.Graphical abstract

Highlights

The Japan Sea is a semi-enclosed marginal sea located on the eastern end of the Asian continent with an average depth of ~ 1350 m and it covers an area of about one million square kilometers
We report high-resolution magnetostratigraphy for Site U1424 sediments based on shore-based measurement of u-channel samples with complete sequence of stepwise demagnetization
Results from the samples fall into the “pseudo-single domain” (PSD) category in the area associated with magnetite particles with sizes of about a few microns to few tens of microns (Dunlop 2002), many issues including magnetic mineralogy and magnetic particle mixtures could potentially complicate the interpretation of domain state based on a Day et al plot

Summary

Introduction

The Japan Sea is a semi-enclosed marginal sea located on the eastern end of the Asian continent with an average depth of ~ 1350 m and it covers an area of about one million square kilometers. Site U1424 drilled during IODP Expedition 346 was used as a chronology reference record by Tada et al (2018) to build a “paleo-observatory network”, which comprises sediment archives from six sites drilled in the Japan Sea during IODP Expedition 346 These sites cover wide ranges of latitudes, longitudes, and water depths and allow the reconstruction of temporal-spatial changes in material fluxes in the Japan Sea. Detailed correlation of dark layers in the sediments guided by magnetostratigraphy and tephrostratigraphy was used by the authors to project the Site U1424 chronology to five other sites. We compare and discuss results from the paleomagnetism and tephra studies conducted to form an integrated magnetostratigraphy and tephrostratigraphy for the sediment sequence cored at IODP Site U1424

Samples and methods

Results and discussion

Conclusions