饶阳凹陷古近系沙河街组古地震记录及地质意义

Ancient earthquake records of Palaeogene Shahejie Formation in Raoyang Sag and their geological significance

综合区域构造背景和岩心观察,对饶阳凹陷东部陡坡带、中央隆起带及北部任丘潜山上覆的古近系沙河街组地震成因的软沉积物变形构造类型、沉积特征、成因机制及地质意义展开研究。结果表明:研究区发育多种原地形成的拉伸—挤压作用及液化作用成因的软沉积物变形构造;由下至上依次为同沉积断裂层段、地震角砾岩层段、液化砂岩脉层段、软沉积变形层段和液化均一层段;沙三段沉积时期是控盆边界断层以及控制潜山活动的控山断层活动强烈时期,频繁引发震级高于5级的地震,且越靠近凹陷东部断裂带,地震构造发育的类型越多;微断层、微裂缝等的形成能极大地改善储层渗透率,使之成为潜在的油气储层或油气运移通道。

In Raoyang Sag,a large number of soft-sediment deformation structures caused by earthquakes were observed in Palaeogene Shahejie Formation along its east steep slope,the central uplift belt and the northern Renqiu paleoburial hill zone.These soft-sediment deformation structures were mainly autochthonously caused by liquefaction and stretch-extrusion effects.A vertical sequence of seismits could be established and classified into five intervals from bottom to top,which were syn-sedimentary fault interval,seismic breccia interval,liquefied sandstones dyke interval,soft-sediment deformation intervals and liquefies homogeneous interval,respectively.Our research shows that seismites were mostly developed in the third member of Shahejie Formation,indicating that basin-controlling and buried-hill-controlling faults were strongly active in the period and frequently triggered earthquakes of magnitude higher than 5.The closer to the eastern fault zone of the sag,the more types and bigger sizes of the seismitic structures were developed,whereas no ancient earthquake records have been found in the western gentle slope.Our results may help to recover tectonic activities and buried hill uplift features of Raoyang Sag in terms of sedimentology.Moreover,the research also has found that microfaults and microfissures developed in seismites are able to improve the reservoir permeability greatly,forming potential oil and gas reservoirs or migration channels.