沉积盆地隐性断裂带特征及其地质意义

Characteristics of hidden fault zone and its significance in geology in sedimentary basin

隐性断裂带是区域或局部应力场或基底断裂活动影响下在沉积盆地盖层中产生的断裂趋势带,由于特征不明显、隐蔽性强、识别困难常常被忽略。对国内外多个沉积盆地盖层断裂系统的特征进行研究。研究结果表明:隐性断裂带是沉积盆地盖层常见的一种构造现象并且具有多种表现形式。依据组成成分分为4种类型:疏密相间,走向一致、长短不一的小断层形成的雁列构造型隐性断裂带;多个凹陷线状排列、首尾相连、侧列式展布形成的凹陷侧列型隐性断裂带;雁列式展布的多条断裂,其间由小断层或局部构造断续相连形成的断续断层型隐性断裂带;复杂构造型隐性断裂带。盆地盖层中的这些隐性断裂带没有明显的控制性主断裂存在,但依据小型断层、褶皱、凹陷、油藏等的规律性分布可以初步识别隐性断裂带的存在,结合重磁资料、地震资料以及地质和钻井资料,就可确定和预测隐性断裂带发育区。隐性断裂带具有多方面的地质意义,可以作为调节构造带调节盆地不均匀伸展活动,并分隔凹陷、隆起等构造单元,影响盆地构造格局;可以控制盆地沉积相带发育分布,影响断陷湖盆砂体的展布范围;隐性断裂带上常常形成串珠状、带状、环状油气富集带;长期活动的隐性断裂带其交汇处既是地震易发区,也是油气等矿产最易聚集区。

Hidden fault zone refers to the zone bearing rupture tendency yield by regional, local stress field or basement rift in the cap strata of sedimentary basin. These zones are hidden and exhibit insignificant characteristics. Therefore, they are difficult to be identified and likely to be ignored. The characteristics of the rift system in the cap strata of sedimentary basin were repeatedly studied by the researchers around the world. The results show that hidden fault zone is a tectonic phenomenon commonly arising in the cap strata of sedimentary basin in multiple forms. According to composition, hidden fault zone can be classified into 4 types： en echelon tectonic type which is composed by the small faults with consistent strikes but differed lengths and densities; Depression lateral alignment type, which contains a plurality of depressions aligned linearly by end to end; Fault type, which is constituted by the en echelon aligned rifts intermittentlyconnected by small faults and local structures, complex tectonic type despite of the deficiency of apparent major controllable rift. These fault zones can be preliminarily recognized through the regular distribution of small faults, folds, depressions and reservoirs etc. Furthermore, the developed area of the hidden fault zone can be determined and predicted using magnetic data, seismic data, geological data and drilling data. Hidden fault zone is proved to be of geological significance. Firstly, it affects the tectonic pattern of basin by adjusting the inhomogeneous extension activities of fault zone in basin and separating the tectonic units including sags and uplifts etc.. Secondly, it determines the development and distribution of basin sedimentary facies and influences the distribution area of the sand in faulted basin; Thirdly, it yields bead string-like, belt-like, and ring-like oil-gas enrichment zones. The long-term active fault zones are prone to induce earthquake and gather minerals such as oil and gas on the junctions.