东海陆架两期沙脊的时空对比

基于高分辨率的单道地震和多波束测深数据,识别并对比了东海陆架中部同一海区相距20余万年的层U₁₄和层U₂两期沙脊群,其中层U₁₄期沙脊属于埋藏沙脊,位于东海海底以下90m深处,推测属于距今320~200ka的海侵体系域(TST),沙脊顶界面是该期海侵的最大洪泛面(MFS);层U₂期沙脊位于东海陆架,属于衰退沙脊,系末次盛冰期(LGM)以来的TST,顶界面是LGM以来的MFS。尽管两期沙脊形成年代相距20余万年,地层层位相距近90m,但是沙脊群总体走向一致,表明距今2×105/a以来东海陆架潮波基本格局稳定。从层U₂期可识别出4个亚期沙脊,通过多波束海底地形图可识别出4组走向的沙脊,多亚期、多走向沙脊是LGM以来海平面阶梯状波动在海底地形演变过程中的响应证据。

Space-time contrast of two stages sand ridges on the East China Sea shelf

On the basis of the high resolution single channel sparker seismic profiles and MBES (multi beam echo sounding), the LSRs (linear sand ridges) on Stratum U2 and Stratum U14 on the ECS (East China Sea) shelf are identified and contrasted each other, their form ages are different, more than 200 ka. The sand ridges on Stratum U14 which is bellow seafloor 90 m are buried sand ridges, and belong to TST (transgressive systems tract) of 320~200 ka BP,and the upper bounding surfaces of the sand ridge units are therefore considered as the MFS (maximum flooding surface) of this transgressive. The sand ridges on Stratum U2 are recessive sand ridges, which have belonged to the TST since the LGM (last glacial maximum),and their upper bounding surfaces are the MFS of the LGM. Although the form ages of two sand ridge units are different, more than 200 ka, and their stratigraphy positions are different, more than 90 m, the general strikes of sand ridges are similar. It is suggested that the palaeo tidal components of the ECS have been steady since 200 ka. Four substages sand ridges are identified from the stratigraphy of Stratum U2, and four trends of sand ridges are distinguished from the topographic map of the MBES too. These multistages and multitrend sand ridges are the evidences that the evolution of submarine topography of the ECS has met the response of sea level stepped changes since the LGM.