湘西北保靖地区志留系小河坝组震积岩的发现及意义

湘西北保靖地区志留系小河坝组主要发育一套砂、泥质沉积。探井岩心观察发现,小河坝组部分层位具有震积岩的典型特征——阶梯状微断层、串珠状构造、球-枕状构造、重荷模和火焰状构造、液化粉砂岩脉、液化卷曲变形构造、震裂缝和角砾状构造等。通过对区内保参1井、保参2井和保参3井纵向震积岩特征的统计,共识别出74层古地震层,根据地震幕的概念,总结出小河坝组地震幕。从3口探井间的横向对比可以看出,大部分地震幕主要集中在小河坝组的2段地层中,从而划分出小河坝期2次地震活跃期和3次平静期。分析了震积岩特征与地震强度和震中距离的关系,结合大地构造背景综合研究发现,该区震积岩的发育受保靖—慈利断裂带构造演化所控制。研究结果对恢复研究区构造背景、地层对比与储层预测具有重要意义。

Discovery and significance on the seismite of Silurian Xiaoheba Formation in Baojing area of Northwestern Hunan

A set of sand-mud deposit was mainly developed in the Silurian Xiaoheba Formation in Baojing area of northwest Hunan Province. There are many typical seismite characteristics in some layers of Xiaoheba Formation, such as step micro-fault, pinch and swell structure, ball and pillow structure, load casts and flamy structure, liquefaction sandy dyke, liquefied fold, seismic fissure bed and autoclastic brecciated structure. Based on the vertical statistics of the seismite characteristics in well Baocan 1, Baocan 2 and Baocan 3, the authors identified 74 ancient seismic strata. According to the concept of seismic episode, the authors summarized the seismic episodes in Xiaoheba Formation. By transverse comparison of the seismic episodes in the wells, the authors found that the seismic episodes are mainly distributed in two members of Xiaoheba Formation. And then two active seismic periods and three seismic quiet periods during the Xiaoheba period have were identified. Through the relationship analysis of seismite characteristics, earthquake intensity and distance, combining with the tectonic setting of the study area, the authors found that the development of the seismites was controlled by the tectonic evolution of Baojing-Cili fault zone. The research results have important significance for the palaeostructure recovery, stratigraphic correlation and reservoir prediction.