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1970年10月和11月间,南朝鲜地球物理人员乘《大洋118》号船,在黄海北部进行了船上声波和磁力调查。根据调查所揭示的海底地质构造,可将测区以东经125°30′为界划为两部份:内带和外带。内带在东经126°00′以东,地质似乎类似于毗邻的陆区;而外带在东经125°30′以西,其地质则明显不同。东经126°00′以东的近岸区域,磁场强度变化很强烈,且不规则;但东经125°30′以西就变得比较平滑,这表明不是磁性基底埋藏很深,就是弱磁性基底。声波剖面揭示出海底地形和松散及固结沉积物的厚度。沉积物可能属近代沉积。松散沉积物的平均厚度在整个调查区约为20米;在近岸区域,它们直接上覆于基底之上。东经126°00′以西,近代松散沉积之下可能属新第三纪的固结沉积物和一个最大厚度约100米的浅沉积盆地,继续向西存在于125°30′左右。在内带,沉积物下面的反射层似乎是基底,延伸的极大深度约150米;但外带的基底面似乎深得多,由于太深以致所采用的最大穿透能力为300米的能源也不能达到。在外带,近代沉积物下面的某些反射层似乎是新第三纪沉积层内的声速层,其中一层也许代表了老第三纪和新第三纪沉积之间的界线。蔚岛以南发现一个1800伽玛的大的磁异常。这可能是由含大量磁铁矿的岩脉造成的。此次调查的成果暗示,将来在此区域勘探重砂矿时,应限于东经126°00′以东的近岸区。
During October and November 1970, South Korean geophysical personnel carried out a survey of ship’s sonic and magnetic forces on the “Oceanic 118” vessel in the northern Yellow Sea. According to the geological structure of the seabed revealed by the survey, the test area can be divided into two parts by the boundary of 125 ° 30 ’east of the test area: inner zone and outer zone. The inner zone is east of 126 ° 00’E with geology similar to that of adjacent land areas. The outcrops are distinctly different to the west of 125 ° 30’E. The intensity of the magnetic field changes strongly and irregularly in the nearshore area east of 126 ° 00’E. However, the west of 125 ° 30’E becomes smoother, indicating that the magnetic substrate is not buried deeply and is a weakly magnetic substrate. The sonic profile reveals the thickness of the seabed topography and loose and consolidated sediments. Sediments may belong to modern deposition. The average thickness of loose sediments is about 20 meters throughout the survey area; in the nearshore area, they are directly overlying the substrate. East of 126 ° 00’E, the Neogene of the sediments under the loose modern sediments and a shallow sedimentary basin with a maximum thickness of about 100 meters continue to exist westward at about 125 ° 30 ’. In the inner zone, the reflective layer beneath the sediment appears to be the base, extending to an extremely deep depth of about 150 m; however, the abaxially basal plane appears to be much deeper, so deep that the adopted energy source with a maximum penetration of 300 m Can not be achieved. In the outer zone, some of the reflective layers beneath modern sediments appear to be sound velocities in the Neogene sediments, one of which may represent the boundary between the Neogene and Neogene sediments. A large magnetic anomaly 1800 Gamma is found south of Island Island. This may be caused by dikes containing a large amount of magnetite. The results of this survey suggest that in the future heavy sand mining in this area should be limited to the coastal areas east of 126 ° 00’E.