Using Late and Middle Pleistocene tephrostratigraphy and cryptotephrostratigraphy to refine age models of Holes ODP1150A and ODP1151C, NW Pacific Ocean: A cross-check between tephrostratigraphy

摘要

We investigated the deep-sea sedimentary sequences of Holes ODP1150A and ODP1151C and refined the Late and Middle Pleistocene tephrostratigraphy and cryptotephrostratigraphy in the NW Pacific Ocean. Further, we correlated tephras in these sequences with marine isotope stage (MIS)-correlated tephras of Hole Chikyu C9001C and created robust age models for the ODP holes. We first counted glass shards and heavy mineral grains in marine sediment samples from the ODP holes and analyzed the major-element chemistry of glass shards and of cummingtonite grains associated with shard spikes. Then, using these major-element compositions, we correlated some glass shard spikes of Hole ODP1150A with known dated tephras for the first time: G5 with Towada-Ofudo (late MIS 3); G8 with Numazawa-Kanayama (MIS 3-4); G12.3 with Naruko-Nisaka (MIS 5b-c); G12.4 with Dokusawa (MIS 5b-c); G12.5 with C9001C G3.1 (MIS 5b-c); G13.1 with Sambe-Kisuki (MIS 5c); G13.2 with Toya (MIS 5d); G16 with C9001C G7 and G8 (MIS 7a-b); either G16.2 or G17 with C9001C G10 (MIS 7b-c); G19.5 with Shiobara-Otawara (mid MIS 8); and G21.1 with Naruohama-IV (MIS 10d). We also confirmed previously reported tephra correlations: G1 with Towada-Hachinohe (MIS 1/2 boundary); G6 with Shikotsu-1 (MIS 3); and G12 with Aso-4 (MIS 5b). Similarly, we correlated some spikes of Hole ODP1151C with known dated tephras for the first time: G0.2 with C9001C G10 (MIS 7c); G1 with ODP1150A G18; G2 with ODP1150A G19.3; G3 with Shiobara-Otawara (mid MIS 8); G3.4 with ODP1150A G20; G4.4 with C9001C G19.3 (MIS 13 or 13/14 boundary); G9 with Kaisho-Kamitakara (MIS 15-16); and G10.8 with C9001C G25.2, 25.3, 25.4, or 25.6 (MIS 18). The tephrostratigraphy results indicate that sediments corresponding to 400-770 ka (from slightly older than the Naruohama-IV tephra to the base of the Brunhes chron) are not preserved in the sediments of Hole ODP1150A. We suggest that our tephra-based age models for Holes ODP1150A and ODP1151C are more reliable tha