Abstract The Kwanza Basin is located at the passive margin of West Africa in the Central Segment of the South Atlantic, and is an important area for oil and gas exploration. The distribution and deformation characteristics of thick Lower Cretaceous (Aptian) salt deposits in the basin have significant impacts on hydrocarbon accumulation. However, reports on their 3D interpretation, together with an understanding of the genesis and evolution of salt tectonics in this area, are scarce in the literature. In this paper, 3D analogue experiments and 3D Discrete-Element numerical simulations are carried out to analyze the zonal characteristics (extension-translation-contraction), the main control factors, and to develop a kinematic model of salt tectonics in the basin. According to our modeling, we make the following conclusions. (1) The zonal characteristics of salt tectonics formed in the basin reflect the superposition of gravity gliding and gravity spreading. The main control factor of basin-scale salt deformation is basement structural activity, which can be summarized into three points: early post-salt basement extension, initial presence of local variation of base of salt gradient and more recent differential subsidence between landward side and seaward side. (2) Salt deformation is episodic, having experienced one stage of regional deformation (Late Aptian to Albian) and two stages of inherited developmental deformation (Campanian, and Eocene to Miocene), mainly resulting in forward expansion towards the ocean. (3) During the early stage of salt deformation, faults developed in suprasalt layers in the extensional and translational zones of the basin, resulting in local high-velocity areas and a large vertical upward velocity component in the salt layer. Later, due to blocking by the outer high region and increasing overburden, salt in contact with the outer high developed a vertical upward velocity component, gradually forming thrust structures. (4) 3D analysis highlights the pervasive lateral deformation of the salt. The main factors governing it are the distribution of accommodation in the salt basin and the initial morphology of the salt layer. In the early stages, salt layer had a velocity component to the salt-scarce side (from north to south), whereas in the later stages, it developed a velocity component to the wide side of the basin (from south to north), leading to the gradual accumulation of salt in the north of the basin. We have shown that 3D simulations can complete the analysis of salt deformation both parallel and perpendicular to the slope in a passive-margin basin. This may provide guidance for the exploration of oil and gas reservoirs in the context of salt tectonics, especially in asymmetrical basins where seismic imaging is poor and has to be supplemented by strong geological concepts including understanding 3D movement of salt.

中文翻译：

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宽扎盆地盐构造的 3D 模拟：来自模拟和离散元数值建模的见解

摘要 宽扎盆地位于南大西洋中段西非被动边缘，是油气勘探的重要区域。盆地下白垩统(Aptian)厚盐矿床的分布和变形特征对油气成藏具有显着影响。然而，关于他们的 3D 解释的报告，以及对该地区盐构造的起源和演化的理解，在文献中很少见。本文通过3D模拟实验和3D离散元数值模拟，分析了盆地的带状特征（伸展-平移-收缩）、主要控制因素，建立了盆地盐构造运动学模型。根据我们的建模，我们得出以下结论。(1)盆地内形成的盐构造带特征反映了重力滑移和重力扩散的叠加。盆地尺度盐层变形的主要控制因素是基底构造活动，可归纳为三点：盐后基底早期伸展、盐基梯度基底局部变化的初始存在以及最近的陆侧和海侧差异沉降边。(2) 盐分变形是间歇性的，经历了一个区域变形阶段（阿普世晚期至阿尔比阶）和两个继承性发育变形阶段（坎帕阶、始新世至中新世），主要是向前向海洋扩张。(3) 盐体变形初期，盆地伸展带和平移带的盐上层发育断层，导致局部高速区和盐层中较大的垂直向上速度分量。之后，由于外高压区的阻塞和上覆层的增加，与外高压接触的盐分发展出垂直向上的速度分量，逐渐形成逆冲构造。(4) 3D 分析突出了盐的普遍横向变形。控制它的主要因素是盐盆内的可容性分布和盐层的初始形态。早期盐层具有向盐少侧（从北向南）的速度分量，而在后期向盆地宽侧（由南向北）发展出速度分量，导致到盆地北部的盐分逐渐积累。我们已经表明，3D 模拟可以完成对被动边缘盆地中平行和垂直于斜坡的盐变形的分析。这可以为盐构造背景下的油气藏勘探提供指导，特别是在地震成像较差且必须辅以强大的地质概念（包括了解盐的 3D 运动）的不对称盆地。