北部湾盆地涠西南凹陷南部复杂断块区成因地层分析

Genetic Analysis of Strata of Complex Fault Block in Southern Weixinan Depression, Beibuwan Basin

李倩 万丽芬 侯林秀

Li Qian Wan Lifen Hou Linxiu

中国石油化工股份有限公司上海海洋油气分公司研究院, 上海 200120

Institute of SINOPEC Shanghai Offshore Oil&Gas Company, Shanghai 200120, China

北部湾盆地涠西南凹陷断裂活动频繁，地层分割严重，层序地层分析难度很大。为了解决构造破碎小区块之间的砂体对比问题，通过涠西南低凸起前缘三口井流沙港组、涠洲组钻井层序地层对比分析，揭示了不同时期断陷结构内层序地层格架及体系域发育特点，确认了流沙港组、渐新世涠洲组各为一个三级层序，层序四分，但由于断层切割存在部分地层缺失，而涠洲组顶面强烈剥蚀遭致部分地层缺失。而基准面变动机制下的岩相成因、层序特征及演化则取决于构造活动、湖平面变动以及碎屑供给，气候变化系基准面旋回的主控因素，碎屑供给能力决定了垂向层序的变化特征。文章认为：涠洲组高碎屑含量来自于渐新世涠西南低凸起构造抬升再遭剥蚀所提供物源。

The fault activities were frequent and the stratum was divided severely in Weixinan Depression of Beibuwan Basin, which makes sequential stratigraphic analysis much more difficult. In order to solve the problem of comparative study of sandbodies in tectonic fractured blocks, We found the development characteristics of the sequential stratigraphic framework and the system tracts from the different periods of fault depression in our target area by the comparison and analysis of Liushagang Formation and Weizhou Formation according to the 3 wells in the front of lower uplift in Weixinan Depression. Besides, it is confirmed that both Liushagang Formation and Weizhou Formation are third-order sequences which can be divided into four sub-sequences. However, some strata are missing due to fault cutting, meanwhile the layer loss on the top of Weizhou Formation was caused by strong denudation. The petrographic formation mechanism, sequence characteristic and development under the background of different datum depend on the tectonics, lake level changes and clastic sediment supply. The paleoclimatic changes determined the base level cycle, while the clastic supply capacity has a great effect on vertical sequence characteristics. Writers believe that large amount of debris in Weizhou Formation came from the provenance which was derived from the denudation of lower uplift of Weixinan Depression during Oligocene period.

https://doi.org/10.3969/j.issn.1008-2336.2019.04.012