頁籤選單縮合
題 名 | Late Pleistocene Volcanic Ash Layers in Core MD972142, Offshore from Northwestern Palawan, South China Sea: A Preliminary Report=南海東部帕拉望島西北外海MD972142岩心晚第四紀火山灰層初探 |
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作 者 | 魏國彥; 李德貴; IMAGES第三航次登船科學研究群; | 書刊名 | Terrestrial, Atmospheric and Oceanic Sciences |
卷 期 | 9:1 1998.03[民87.03] |
頁 次 | 頁143-152 |
分類號 | 354.1 |
關鍵詞 | 南海東部; 帕拉望島; 西北外海; MD972142岩心; 晚第四紀火山灰層; South china sea; Pleistocene; Volcanic ash; Tephrochronology; |
語 文 | 英文(English) |
英文摘要 | More than 18 distinct, well-defined ash-rich layers were recognized from the piston core MD972142 raised offshore from northwestern Palawan during the IMAGES III - IPHIS - Leg II Cruise in the South China Sea. The thickness of these macroscopically recognizable ash layers varies from 0.5 cm to 10 cm with a mode of 4 cm. Microscopic examination of the ashes reveals that these ash layers consist of vitric, microlite-bearing and crystalline components. Strong reflection signals in the 3.5 kHz acoustic stratigraphy were found to be caused by various tephra layers down to 18 m in the upper section of the core. On-board measurement of bulk density confirms that the ash layers are more dense than the hemipelagic sediments. In addition, these layers also show much stronger magnetic susceptibilities than the intervening sediments. It indicates that the ash layers contain more abundant magnetic minerals than the microfossil-bearing hemipelagic sediments. The last appearance datum of pink Globigerinoides ruber (planktic foraminifera) at 9.72 m and the absence of Pseudoemiliania lacunosa (calcareous nannofossil) in the core provide good age constraints for a preliminary correlation. The tephra layers in the top 7 meters can be correlated to the Upper, Middle and Lower Units of volcanic layers previously recognized in the northern South China Sea. Our preliminary correlation suggests that these ash-rich layers were deposited at 10 ka, 26-42 ka, 64-79 ka, and probably 110-290 ka, and 390-430 ka during the last 430 kyrs. |
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