扬子浅滩MIS6阶段沉积物流体包裹体特征及物源分析

Fluid inclusion characteristics and provenance analysis of the MIS6 stage sediments in the Yangtze shoal

为探究东海扬子浅滩晚更新世沉积物的来源,对该区域的YZ05钻孔MIS6阶段沉积物中的石英流体包裹体进行了岩相学分析,并与长江干流表层沉积物中的流体包裹体进行对比研究。结果显示,YZ05钻孔晚更新世沉积物中单位体积(0.001 mm3)石英颗粒的包裹体数量在17~47个之间,个体大小多为2~5μm,以孤立分布为主。其中次生包裹体数量较多,约占包裹体总数的88%~96%,原生包裹体以椭圆或四边形居多,室温下多为富液相,气液比大多为10%~30%。研究区及现代长江干流表层沉积物中的流体包裹体形态较为一致。此外,研究还发现了颈缩形态的包裹体及气液比大于80%的富气相原生包裹体,此类包裹体在长江上游石鼓地区较为常见。因此,可以推测晚更新世时(至少在47 ka BP),长江上游物质已经到达扬子浅滩西南海域。

In order to explore the source of Late Pleistocene sediments in the Yangtze Shoal in the East China Sea,the quartz-hosted fluid inclusions in the MIS6 stage sediments from cores of Hole YZ05 in the area were analyzed by petrog-raphy and compared with the fluid inclusions in the surface fluvial sediments of the Yangtze River.The results show that numbers and sizes of fluid inclusions,which are mostly isolated,in the per unit volume(0.001 mm')quartz grains of the late Pleistocene sediments of Hole YZ05 vary mainly from 17 to 47 and from 2μm to 5μm,respectively.Especially,the numbers of secondary fluid inclusions are accounted for 88%~96%of the total numbers of all fluid inclusions.The prima-ry fluid inclusions are mostly elliptical or quadrilateral liquid-rich aqueous fluid inclusions at room temperature with gas phase accounting for 10%~30%.The morphologies of fluid inclusions in quartz grains of sediments in the study area are relatively consistent with those of fluid inclusions in quartz grains of the surface sediments in the modern mainstream of the Yangtze River.In addition,necking fluid inclusions and vapor-rich aqueous primary fluid inclusions with more than 80%gas phase were found commonly in quartz grains of samples in the Shigu area which is located in the upstream of Yangtze River.Therefore,it can be inferred that materials from the upstream of Yangtze River had already been transported to the southwestern Yangtze Shoal in the late Pleistocene(at least 47 ka BP).