Evidence from lithology, foraminiferal assemblages, and high-resolution X-ray fluorescence scanning data of core SFK-1 indicates tidally influenced paleo-fluvial sedimentation during the last glacial maximum (LGM) on the outer shelf of the East China Sea. The paleo-fluvial deposits consist of river channel facies and estuarine incised-valley-filling facies. Different reflections on the seismic profile across core SFK-1 suggest that the river channels shifted and overlapped. River channel deposition formed early in the LGM when sea level fell and the estuary extended to the outer shelf. Channel sediments are yellowish- brown in color and rich in foraminifera and shell fragments owing to the strong tidal influence. Following the LGM, the paleo-river mouth retreated and regressive deposition of estuarine and incised-valley-filling facies with an erosion base occurred. The river channel facies and estuarine incised-valley-filling facies have clearly different sedimentary characteristics and provenances. The depositional environment of the paleo-river system on the wide shelf was reconstructed from the foraminiferal assemblages, CaCO3 content and Ca/Ti ratio. The main results of this study provide further substantial constraints on the recognition of late Quaternary stratigraphy and land-sea interactions on the ECS shelf.
伊平屋北部热液区(Iheya North hydrothermal field)位于冲绳海槽中部地区。综合大洋钻探计划(IODP)331航次于2010年9月1日至10月4日在该区钻探了5个站位(C0013～C0017):C0016站位位于North Big Chimney(NBC)地区活跃的热液烟囱和硫化物—硫酸盐丘状体上;在C0013、C0014、C0015、C0016站位发现了异常高热流值;在热液补给区C0017站位,实现最大钻探深度达到海底下151 m。在活跃的丘状热液喷口处的C0016站位,尽管取芯率只有4.7%,但首次在现代海底获得黑矿型(Kuroko-type)、富闪锌矿的黑色矿石样品。其他4个站位岩芯主要为具有不同热液蚀变和矿化程度(沸石相到绿片岩相)的互层状半深海和火山碎屑沉积物,及火山角砾和浮岩砾屑。钻孔中不规则的地温梯度剖面变化揭示出地下流体的横向运移趋势。现场数据表明,岩芯孔隙水和气体组成在垂向和横向上变化较大。海底作用主要包括通过相态分离而形成高盐水和富气体的流体,矿物蚀变释放Ca而吸附Mg和Na,高温下K释放而低温吸收,硬石膏形成,有机质的微生物氧化和甲烷利用硫酸盐的厌氧氧化,微生物作用下甲烷形成等。船上研究未证实研究区存在活跃的深部生物圈,细胞丰度明显低于以前的ODP/IODP在陆架边缘的钻探站位。
Chemical weathering of continental silicates significantly influences global climate change,earth surface processes,material cy-cling and oceanic chemical composition.How to quantitatively reconstruct chemical weathering history has become an important issue in global change research.Chemical index of alteration(CIA) has been widely used as a quantitative indicator for estimating the degree of silicate weathering.However,its method of calculation and the limitations of its application are not well understood.In this study,we calculated CIA values from suspended particulate matter collected from the mainstream and major tributaries of the Changjiang River.The values yielded considerable variations at different temporal and spatial scales.The average CIA values increased from the upper to middle-lower reaches,and were lower in the suspended samples taken during the flood than in the dry season.The spatial variation in the CIA is predominantly controlled by basinal monsoon climate.In contrast,the temporal varia-tion in the Changjiang River basin is controlled mainly by the changing provenance of suspended samples in relation to the shift of the precipitation zone.The CIA probably indicates the integrated weathering history in the river basin,and thus,cannot be used as a reliable proxy of instantaneous chemical weathering.Furthermore,the calculation method and hydrodynamic sorting also influence the CIA values.Therefore,caution should be taken when using the CIA as a proxy for studying chemical weathering from different regions.
