Age of the SKP-I and SKP-II tephras from the southern East Sea/Japan Sea: Implications for interstadial events recorded in sediment from marine isotope stages 3 and 4

초록

The ages of two newly identified tephras in marine oxygen isotope stages (MIS) 3 and 4 from the southern East Sea/Japan Sea (ES/JS) have been determined. Analysis of chemical composition, grain-size distribution, sediment texture, and pumice micromorphology of material from 24 marine sediment cores was combined with a high-resolution age model established for core MD01-2407. The marine sedimentary record of the ES/JS is characterized by a drastic, millennium-scale variation in paleoceanographic conditions that is closely linked to Dansgaard-Oeschger (D-O) events. The chemical composition of the two tephras, which are stratigraphically located between previously dated AT (29.24 ka) and Aso-4 (88 ka) tephras, varies from phonolitic to trachytic (57.11-62.87 wt% SiO2 with 5.03-6.81 wt % K2O and 6.32-9.87 wt% Na2O). They exhibit a conspicuously bimodal grain-size distribution, and have randomly oriented vesicles with thick walls. The dispersal patterns of these tephras differ markedly from that of the U-Oki tephra, which is originated from a subaerial eruption on Ulleung Island. The two newly identified tephras, named SKP-I and SKP-II, reach their maximum thickness and grain-size at a location near the South Korea Plateau (SKP). An age model for a core from the Oki Ridge (MD01-2407) yields eruptive ages of about 40-41 ka for the SKP-I tephra and about 60-61 ka for the SKP-II tephra. A comparison of sediment lightness (L*) with GISP2 oxygen isotope data suggests that the SKP-1 tephra is stratigraphically between D-O Interstadial (IS) 9 and 10, and the SKP-II tephra is between D-O IS 17 and 18. The SKP-1 and SKP-II tephras are equivalent to the U-Ym tephra described by Arai et al. [Arai, F., Oba, T., Kitazato, H., Horibe, Y., Machida, H., 1981. Late Quaternary tephrochronology and paleo-oceanography of the sediments of the Japan Sea. Quat. Res. (Daiyonki-kenkyu) 20, 209-230 (in Japanese, with English Abstr.)] and that described by Ikehara et al. [lkehara, K., Kikkawa, K., Chun, J.-H., 2004. Origin and correlation of three tephras that erupted during oxygen isotope stage 3 found in cores from the Yamato Basin, central Japan Sea. Quat. Res. (Daiyonki-kenkyu) 43, 201-212 (in Japanese, with English Abstr.)], respectively. They not only provide marker horizons within the stratigraphic interval corresponding to MIS 3 and 4 but also can be useful to identify D-O events for marine cores from the southern part of the ES/JS. (C) 2007 Elsevier B.V All rights reserved.

키워드