珠江三角洲及河网形成演变的数值模拟和地貌动力学分析:距今6000~2500a

珠江三角洲是我国一个极其复杂的大尺度河口系统,具有独特的河网体系和河口湾.为了探讨距今6 000 a以来珠江三角洲和河网的形成演变,提出一个长周期动力形态模型(PRD-LTMM)并讨论长周期模拟方法的建模和验证思想,重建了距今6 000 a海进盛期的古珠江河口湾的水下地形作为模型的初始边界.在模型中考虑的驱动力和控制因素包括代表潮、河流流量、泥沙输入、海平面变化、沉积物压实率及新构造运动等.分析和计算了三角洲总沉积量、有效堆积空间和沉积速率,用于模型控制和校验.应用必要的模型约减技术,实际模拟了长周期模型.34个14C测年钻孔资料初步验证了模型的正确性,一些古文化遗迹证据可以印证模拟结果.地貌动力学分析进一步论证了计算结果的合理性,阐述了模型输出的地学意义.现阶段的研究揭示出海进盛期以来珠江三角洲的时空演进过程具有一些与已有研究成果大不相同的新的特征.提出距今6 000 a以来珠江三角洲等沉积时间线和若干沉积模式.珠江三角洲发育演变及其特征在很大程度上源自其继承性的地质地貌构造所造成的独特的古海湾构造形态及其对河流和海洋动力分布的重塑.珠江河口的“门”及其双向射流动力体系对珠江三角洲和河网主干,特别对口门的形成演变起了控制性的作用,模拟结果还表明,古珠江河口湾中散落的众多基岩岛丘边沿沉积是影响珠江三角洲长期演变的重要因素.

A numerical simulation and mophodynamic analysis on the evolution of the Zhujiang River Delta in China: 6 000～2 500 a BP

The Zhujiang River Delta is one of the most complicated large-scale estuarine systems in China.It consists of a reticulated network system and several estuary bays.A long-term morphdynamic model(PRD-LTMM) is developed to simulate the evolution of the Zhujiang River Delta and its estuarine system.Long-term simulation method and concept of model verification are discussed.The underwater topography of the estuarine bay in the last transgression maximum about 6 000 a BP is reconstructed and serves as an initial condition of this model.The driving forces and control factors considered in the long-term delta evolution model include presentative tides,river discharge,and sediment supply from the Zhujiang River system,sea-level variation,sediment compaction and neotectonic movement. Deposition rates and total deposition volume are investigated and determined and then used to calibrate the model.More than 34 bore hole data with ~(14)C dating are carefully analyzed to verify the model-simulated deposition.The local archaeological evidence is compared with the model output as circumstantial verification.New findings of the Holocene delta evolution indicate that the chronological and spatial progress of the delta is different from previous studies in many aspects.More details are provided to the delta and network development originated from the effects of the morphodynamic sturctures "gate" and associated bi-directional jets.The model confirms that the morphological constraint,e.g.,the rocky islands in the shallow estuarine bays is one of the most important control factors affecting the long-term delta evolution of the Zhujiang River Delta.