下刚果盆地白垩系盐筏物理模拟研究

Physical Modelling of Cretaceous Salt Rafts in the Lower Congo Basin

被动陆边边缘含盐盆地广泛发育的盐筏是一种重力滑脱作用下的极端薄皮伸展形成的构造样式,对于盆地后裂谷期的演化都有着重要的影响。基于物理模拟,除去考虑常规的盐层厚度、基底倾角、前构造沉积层厚度等单因素的影响之外,研究着重基底倾角与同沉积速率的组合影响,同时注重初始模型的设置与实际地质条件的吻合,使模拟结果更有意义。实验结果表明,触发下刚果盆地白垩系盐筏活动的机制为重力滑脱作用而非差异负载作用;盐筏构造最关键的控制因素为基底倾角及同沉积速率;其中基底倾角控制了盐筏形成过程中断裂的分布及筏体的滑脱速率,而同沉积速率则控制了筏体之间沉积填充的样式,两者相对速度的快慢控制了盐筏的构造样式,下刚果盆地白垩系盐筏构造是沉积速率相对较快条件控制的结果。

As an extreme structural form of thin-skined extension under gravitational gliding,salt rafts are widely developed in the salt-bearing basins on a passive margin,which exerts important impacts on the evolution of the basin after the rifting period.Based on physical modelling,the combined effects of basement angle and syn-kinematic deposition rate are studied.In this study,the initial model setting and actual geological conditions are emphasized in addition to considering the single factor effects of salt layer thickness,base angle,and thickness of pre-kinematic sedimentary layer,making the results more meaningful.The results show that the Cretaceous salt raft activity in the Congo Basin was caused by gravity gliding rather than differential loading;the most critical controlling factors of the salt raft structures are the basement angle and the syn-kinematic deposition rate;the basal angle controls the fracture distribution and rafts gliding rates;while the syn-kinematic deposition rate controls the pattern of deposition between the rafts during the formation process.The relative speed of the two controls the structural styles of the salt rafts.The Cretaceous salt rafts in the Lower Congo Basin was a result of the relatively fast depositional conditions.