Geochemical record of chemical weathering and monsoon climate change since the early Miocene in the South China Sea
Geochemical record of chemical weathering and monsoon climate change since the early Miocene in the South China Sea
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DOI：
10.1029/2006pa001300
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发表时间：
2006-12
期刊：
影响因子：
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通讯作者：
G. Wei;Xian‐Hua Li;Y. Liu;L. Shao;Xi-rong Liang
中科院分区：
文献类型：
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作者：
G. Wei;Xian‐Hua Li;Y. Liu;L. Shao;Xi-rong Liang
通过对南海北方大洋钻探1148站碎屑沉积物化学蚀变指数（CIA）和对化学风化敏感的元素比值（Ca/Ti、Na/Ti、Al/Ti、Al/Na、Al/K和La/Sm）的分析，揭示了南海北部早中新世源区的化学风化信息。沉积物在23 Ma时具有较高的CIA值（80 ~ 1000），Al/Ti和Al/Na值较高，Na/Ti和Ca/Ti值较低，表明北部源区化学风化强度较高，华南随后逐渐降低Al/Ti，Al/Na，La/Sm和Al/K比，以及CIA值，并增加Ca/Ti和Na/Ti比。这些记录与其它古气候代用指标如黑碳δ 13 C、底栖有孔虫δ 18 O等一起，为华南地区气候变化提供了可靠的信息。结果表明，根据化学风化记录，中新世早期（1.23 Ma）中国南方气候温暖湿润。早中新世至今华南地区的湿度呈下降趋势，并在15.7Ma、8.4Ma和2.5Ma左右出现多次波动，与中中新世以来的全球变冷相一致。这些气候变化表明，中新世早期东亚夏季风对华南地区的影响是显著的，而此后夏季风对华南地区的影响不断减弱，可能是由于冬季风的加强。东亚季风的这种演变不同于印度季风。
The chemical index of alteration (CIA) and elemental ratios that are sensitive to chemical weathering, such as Ca/Ti, Na/Ti, Al/Ti, Al/Na, Al/K, and La/Sm, were analyzed for detrital sediments at Ocean Drilling Program Site 1148 from the northern South China Sea to reveal information of chemical weathering in the source regions during the early Miocene. High CIA values of ∼80, coupled with high Al/Ti and Al/Na and low Na/Ti and Ca/Ti, are observed for the sediments at ∼23 Ma, indicating a high chemical weathering intensity in the north source region, i.e., south China. This was followed by gradual decreases in Al/Ti, Al/Na, La/Sm, and Al/K ratios, as well as the CIA values, and increases in Ca/Ti and Na/Ti ratios. These records together with other paleoclimate proxies, such as black carbonδ13C and benthic foraminiferδ18O, give reliable information on the climate changes in south China. Our results show that the climate in south China was warm and humid in the early Miocene (∼23 Ma) according to the chemical weathering records. The humidity in south China decreased from the early Miocene to Present with several fluctuations centering at approximately 15.7 Ma, 8.4 Ma, and 2.5 Ma, coincident with the global cooling since the middle Miocene. These climate changes implied that the summer east Asian monsoon has dramatically affected south China in the early Miocene, whereas the influence of the summer monsoon on this region has decreased continuously since that time, probably because of the intensification of the winter monsoon. Such an evolution for the east Asian monsoon is different from that for the Indian monsoon.