表題番号:2017A-016 日付:2018/02/28
研究課題白亜紀における亜熱帯高圧帯の緯度方向シフト:地球温暖化に伴うハドレー循環の拡大と縮小
研究者所属(当時) 資格 氏名
(代表者) 教育・総合科学学術院 教育学部 教授 太田 亨
(連携研究者) Waseda Univ. student Higuchi taro
(連携研究者) Curtin Univ. Professor Mazmuder Rajat
研究成果概要

The present study investigated the geochemistry and clay mineralogy of mudstones collected from the lower to middle Cretaceous strata distributed in Vietnam and Borneo island, in order to assess the paleoclimate.

We found that mineralogical and geochemical differences that the present sample bear are due the differences in the degree of hinterland weathering. During early Cretaceous, Vietnam was exposed to a severe weathering environment, while hinterland weathering almost halted in middle Cretaceous. As for Borneo, early Cretaceous was a time of severe weathering, which slightly calmed in middle Cretaceous. The reason for the decrease can be attributed to the aridification.

Two new findings can be proposed by the present result. First, the area that undergone middle Cretaceous aridification was more extensive than previously thought, reaching to Vietnam, and probably prevailed further to the equatorial region (Borneo). Secondly, note that Sichuan, Simao and Korat basins are located in the continental interior, while the studied Vietnam and Borneo region are located in the coastline of southeast Asia. Therefore, this suggests that the aridification is not due to the simple enhancement of the inland dry climate, but more likely related to a major turnover in the climate system in mid-Cretaceous.