珠江口盆地开平凹陷构造—地层层序与盆地演化

开平凹陷位于珠江口盆地珠Ⅱ坳陷的西部，处于洋陆过渡带的特殊位置，大部分区域位于陆坡深水区。研究开平凹陷的构造—地层层序和盆地演化，对认识盆地结构和油气勘探具有重要意义，对南海北部洋陆过渡带的结构特征和成因机制的研究也有一定的帮助。本文基于井震结合的思路，利用最新的钻井和高精度地震资料，并结合区域地质背景，建立了开平凹陷的地层系统；依据区域性不整合面的发育特征，对开平凹陷构造—地层层序进行了划分；利用平衡剖面技术，重点分析了开平凹陷始新世以来的构造演化。研究发现开平凹陷发育始新统文昌组底部、渐新统珠海组底部和上中新统粤海组底部3个区域性不整合面，由此将开平凹陷在纵向上划分为4个构造层：基底构造层、断陷期构造层、拗陷期构造层和加速沉降期构造层。开平凹陷的形成演化经历了基底形成、始新世断陷、渐新世—中中新世拗陷及晚中新世—第四纪加速沉降4个阶段。凹陷内的断陷活动主要受拆离断层差异性活动的控制。

Tectono-stratigraphic sequence and basin evolution of Kaiping Sag in the Pearl River Mouth Basin

The Kaiping Sag is located in the western Zhu?Ⅱ depression in the Pearl River Mouth Basin and is situated in the continental?ocean transition zone, most of which is in the sloped deepwater area. The study of tectono-stratigraphic sequence and basin evolution in Kaiping Sag is of great significance to the understanding of the basin structure and the petroleum exploration and also helps to the understanding of structural characteristics and genetic mechanisms of the continental-ocean transition of the northern South China Sea. This paper documents the stratigraphic framework of the Kaiping Sag using the latest seismic profiles in addition to drilling data integrated with the regional geological background. The tectono-stratigraphic sequence is constrained based on the regional unconformities. The tectonic evolution of Kaiping Sag since the Eocene is mainly discussed according to the balanced cross-section technique. Three regional unconformities including the bottom of the Eocene Wenchang Formation, the bottom of the Oligocene Zhuhai Formation and the bottom of the Upper Miocene Yuehai Formation, according to which four tectonic layers are recognized basement tectonic layer, rift tectonic layer, depression tectonic layer and accelerate subsidence tectonic layer. This study demonstrates that tectonic evolution of the Kaiping Sag can be divided into four stages: basement formation stage, Eocene rifting stage, Oligocene-Middle Miocene depression stage and Late Miocene-Quaternary accelerated subsidence stage. Rifting in the Kaiping Sag is mainly controlled by the differential activity of the extensional detachment fault.