渤海湾曹妃甸深槽海区地形地貌特征及控制因素

Characteristic geomorphology and controlling factors of Caofeidian Channel in the Bohai Bay

通过研究浅层地震剖面、侧扫声纳和水深地形等数据资料,得出,曹妃甸沙岛的岬角地貌引起深槽海域局部潮流流速增大,甸头前沿深槽区以冲刷为主,最大水深达42 m,刷新了渤海湾最大水深记录,深槽部位的侵蚀量最大,深槽南坡冲刷幅度大于北坡,工程建设后期深槽区侵蚀冲刷程度有变小变缓趋势。早期深槽的形成是由于浅部断层受深部构造影响发生阶梯状错断沉陷,海底地层形成古凹槽,但深槽海底地层沉陷速率略大于沉积速率,使得深槽海域长期保持了渤海湾最大的水深环境。初步得出在历史时期曹妃甸深槽经过2万a以上长期存在,深槽的走向经历了南北向-北东向-北西向的转化过程。认为地质构造、古滦河三角洲演变、海洋水动力作用和人类活动等内外营力作用共同控制了曹妃甸海区地貌体系的发育与演化。达到了研究渤海湾曹妃甸深槽海区地形地貌控制因素和深槽的地质演化的目的,为曹妃甸港的规划、运营期维护和未来发展提供科学依据具有重要意义。

In this study, using the shallow seismic detection, side-scan sonar, and bathymetric survey data of multiple historical periods, we outline geomorphic features and characteristics of the bottom sediments of the Caofeidian Channel. Results indicate that unique terrain conditions cause the local enhancement of the tidal current. The channel at the front end is dominated by erosion, and the maximum water depth reaches 42 m, which sets the highest record for water depth in the Bohai Bay. The greatest amount of erosion is at the channel, and the scouring magnitude on the south slope is greater than that on the north slope. The scouring degree of seabed erosion was smaller in the project construction period. We can preliminarily conclude that the formation of the early channel occurred because of shallow step-fault subsidence due to the influence of the deep structure. However, the subsidence rate of the deep structure is slightly less than the deposition rate of the upper strata, and thus, the channel sea area maintains the maximum depth of the Bohai Bay. The Caofeidian Channel has existed for more than 20 000 years. The directional trending of the channel has experienced a transition from NS to NE and then to NW. We conclude that endogenic and exogenic processes, such as those of the geological structure, the evolution of the ancient Luanhe River Delta, marine hydrodynamics, and human activity have jointly controlled the development and evolution of the geographic system in the Caofeidian sea area. Studies on the controlling factors of the sea topography and the geological evolution of the deep grooves of the Bohai Bay and Caofeidian deep trench are significant to establish a scientific basis for the planning, operation, port maintenance, and future development of Caofeidian.