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北部湾是一个亚热带新月形浅海盆地。其北面和西面与亚洲大陆接界,其东面是海南岛。狭小的海底平原和附近的高地表现出陆地的特征。北部湾南部是北西一南东向的深度在50—100米之间的浅海湾。深水地区被分选较差的砂和粉砂所充填,其侧面大致是粘土和粉砂。两个较大的三角洲(红河三角洲和昌江三角洲)向海湾的北部和东部提供了大量沉积物,而一些较小的三角洲向海湾西部提供了大量沉积物。随季风变化的潮流和碎屑物质的来源不同明显地影响到沉积物,其分布状况是复杂的。从浅海一侧到较深的砂质海槽,表层沉积物的凝聚力不断增大,这种力在浅海一侧也是随深度而增加的。但是,在海盆里这种凝聚力明显地减小,这主要是因为海盆底粉砂和粘土上面是砂子。在北西—南东向的海湾南面,由于充填着砂子,湿容重较大,而沿轴向的孔隙度较小。在一些岩心样品中可看到两层较古老的层位。一层是浅兰色硬粘土,所处的时代可能是更新世。另一层是更新世(?)淡红—棕色粉砂质硬粘土。没有一个岩心样品能穿透这两层较古老的层位。
North Bay is a subtropical crescent-shaped shallow sea basin. Its northern and western borders with the Asian continent, the east of Hainan Island. The narrow submarine plains and nearby highlands show the characteristics of the land. The southern part of the northern Gulf is a shallow bay with a depth of between 50 and 100 meters north-south-east. Deepwater areas are filled with poorly sorted sand and silt, with the sides roughly clay and silt. The two larger deltas (the Red River Delta and the Changjiang Delta) provide large amounts of sediments to the north and east of the Gulf, while some of the smaller ones provide large deposits to the western part of the Gulf. With the trend of monsoon changes and the source of detritus material obviously affect the sediment, the distribution is complex. From the shallow sea side to the deeper sandy trough, the cohesion of the surface sediments is continuously increasing, which also increases with depth on the shallow sea side. However, this cohesion is significantly reduced in the basins, mainly because of the sand at the bottom of the basin and above the clay. South of the North West - South East Bay, due to the filling of the sand, the wet bulk density is greater while the axial porosity is less. In some core samples, two more ancient layers can be seen. The first layer is light blue hard clay, which may be in the Pleistocene era. The other is the Pleistocene (?) Pale red-brown silty hard clay. None of the core samples penetrate the older layers of the two layers.