辽东湾地区辽西凹陷中南部古近系构造-层序地层格架与古地理分析

辽西凹陷位于辽东湾地区西部，是一箕状凹陷，辽西凹陷中南部总体勘探程度偏低。辽西凹陷中南部古近系横向上隆、坳地形分异明显，存在一个继承性发育的凹间孤岛，呈链状分布（简称“凹间链状岛”），该岛将辽西凹陷中南部分为东西两次凹，岛两侧沉积相差异明显，轴向上构造格架比横向上复杂，具有明显的构造分割。在构造格架分析的基础上，依据钻井和地震资料，在辽西凹陷中南部古近系识别出六个层序界面和五个层序，并详细阐述了每个层序界面的成因、地震特征、测井响应特征以及每个层序的体系域与沉积体系的构成特征。在构造－层序地层格架内，分析本区不同层序沉积相古地理，发现各个时期的古地理均呈有规律的分布，即凹陷西部为冲洪积相、辫状河相、三角洲平原相；向东为三角洲前缘和湖相。辽西凹陷中南部沉积相古地理演化受控于层序界面的转换、走滑构造、古地貌、古气候等因素的影响，并且四个因素对湖盆沉积作用的制约不是孤立的，是相互关联、制约的综合效应，不同演化阶段控制因素有主、次之别，其中古气候周期性变化决定湖扩与湖缩，构造是控制充填物有效可容空间的关键，沉积基准面和侵蚀基准面以及湖水面不仅决定碎屑物供给率，也是湖盆沉积速率的关键。

Structural and sequence stratigraphic frameworks and palaeogeography of the Paleogene in central-southern Liaoxi Sag, Liaodongwan Bay area

Liaoxi Sag, located in the western Liaodongwan Bay area of the Bohai Bay Basin,was a half-graben in the Paleogene. The exploration maturity of the central-southern Liaoxi Sag is relatively low in Liaodongwan Bay area. In this paper, the structural and sequence stratigraphic frameworks, sedimentary systems and palaeogeography of the Paleogene in the study area are respectively analyzed. The topography in the cross section of the central-southern Liaoxi Sag was irregular in the Paleogene.An inherited inter-sag isolated-island was developed. The distribution of the island was chain-like in shape, namely inter-sag chain-like island. The central-southern Liaoxi Sag in the Paleogene is divided into two sub-sags by the island, eastern and western sub-sags. The island controlled the distribution of the sedimentary systems of the Paleogene. The sedimentary systems on the two sides of the island are obviously different. The structural framework in the axial section is more complex than that in the cross section. According to the well and seismic data, six sequence boundaries and five sequences can be recognized in the Paleogene. The geneses of each sequence boundary are analyzed, and the seismic features, logging response features and the composing features of system tract and sedimentary systems in each sequence are also described. The palaeogeographic characteristics of different sequences are analyzed in the structural and sequence stratigraphic frameworks. The sedimentary systems distribution of the Paleogene in the study area shows regularity. In the western part of the sag, the major sedimentary systems are alluvial fan, fluvial and delta facies, while towards the eastern part, the major systems are delta and lacustrine facies. The palaeogeographic evolution of the Paleogene in the central-southern Liaoxi Sag is controlled by factors such as structural transition boundaries, strike-slip structure, palaeo-geomorphology, and paleoclimate. The four factors above controlled the sedimentation of the lacustrine basin not in an isolated way but in an interactional one. The major factor was different in each stage. The periodic paleoclimatic changes controlled the expanding and shrinking of the lacustrine basin, the tectonic activities controlled the efficient accommodation, while the base level and lake level controlled both the supplying rate of clastic sediments and the depositional rate of the basin.