Abstract

Core, well log and seismic data are used to investigate relationships between fan-delta facies architecture, basin margin morphology and sediment transportation into a deep-lacustrine environment of the Dongying Formation of Nanpu Sag, Bohai Bay Basin. The study interval is subdivided into two fan-delta dominant, third-order sequences of Stratasequence Paleogene Dongying Formation 1 (SQEd₁) (younger) and Stratasequence Paleogene Dongying Formation 2 (SQEd₂) (older). Fan-delta growth occurred in two stages with changing of facies architecture and morphology. During the early stage (SQEd₂), the facies architecture is characterised by smaller and thin, channelised deposits, an extended mouth bar (delta-front sandy deposits) and slump/slides/flood turbidite dominated sandy deposits in the prodelta. However, during the late stage (SQEd₁), the facies architecture is characterised by extended and thicker channelised deposit-dominated area, a local mouth bar (delta-front sandy deposits) and slump/slide-dominated sandy deposits in the prodelta. From the early to late stage, the delta morphology also changed with an upward increase in the delta-plain areal extent and delta-front gradient. Facies architecture variations indicate differences in sediment dispersal. The upward thickening and extending delta plain implies that more sediment was trapped in the proximal area owing to sufficient accommodation space generated by increasing boundary fault displacement. The upward increasing delta-front gradient resulted in differences in the type of prodelta/deep-lacustrine sandy deposits, while grainsize variations of the delta-front deposits affect the prodelta/deep-lacustrine sandy deposits. Boundary fault growth occurred with upward increasing displacement and length with the result that sediment supply outpaced accommodation-space creation and controlled the facies architecture changes.

1. KEY POINTS

2. A two-stage fan delta developed with changing facies architecture is analysed.

3. Facies architecture controlled fan-delta morphology with sediment transport into a deep-lacustrine area.

4. Faults control the facies architecture and sand-rich deposit distribution.

摘要

利用岩心、测井和地震数据研究了渤海湾盆地南堡凹陷东营组扇三角洲相结构、盆地边缘形态和沉积物向深湖环境输送的关系。研究层段细分为地层古近系东营组1 (SQE d ₁ ) (年轻) 和地层古近系东营组2 (SQE d ₂ ) (旧)两个扇三角洲主导的三级层序。扇三角洲的生长发生在两个阶段，随着相结构和形态的变化。在早期阶段（SQE d ₂)，相结构的特点是较小而薄的通道化沉积物、延伸的河口坝（三角洲前缘砂质沉积物）和前三角洲中以塌陷/滑坡/洪水浊积岩为主的砂质沉积物。然而，在后期阶段（SQE d ₁)，相结构的特点是扩大和更厚的通道化沉积为主的区域，一个局部的河口坝（三角洲前缘砂质沉积物）和前三角洲中滑塌/滑移为主的砂质沉积物。从早期到晚期，三角洲形态也随着三角洲平原面积和三角洲前缘梯度的向上增加而发生变化。相结构变化表明沉积物扩散的差异。向上增厚和延伸的三角洲平原意味着更多的沉积物被困在近端区域，因为边界断层位移增加产生了足够的容纳空间。向上增加的三角洲前缘梯度导致了前三角洲/深湖砂质沉积物类型的差异，而三角洲前缘沉积物的粒度变化影响了前三角洲/深湖相砂质沉积物。

1. 关键点

2. 分析了随着相结构变化而形成的两级扇三角洲。

3. 相结构控制扇三角洲形态，沉积物输送到深湖区。

4. 断层控制着相结构和富砂矿床分布。