冀中坳陷晋县凹陷古近系震积岩的发现及地质意义

Discovery and Geological Significance of Seismites of Paleogene in Jinxian Sag,Jizhong Depression

晋县凹陷是渤海湾盆地内典型的新生代小型断陷湖盆,古近系孔一沙四段地层中发育大量的软沉积物变形构造,包括液化砂泥岩脉、泥岩株、泄水通道、重荷模与火焰状构造、球枕构造、振动液化卷曲变形构造、串珠状构造、微同沉积断层、地裂缝等,研究认为具有典型的震积岩特征,并在此基础上建立了研究区古近系震积岩垂向序列。孔一沙四段地层中发育震积岩、膏岩和凝灰岩等,研究认为深大断裂的活动诱发多期地震,形成各种类型的震积岩,同时深大断裂作为岩浆上涌的通道和沟通深部盐源的通道,为凝灰岩和膏岩的形成提供物质基础,该认识从沉积学的角度证明孔一沙四段地层沉积时期为晋县凹陷构造活动最强烈的时期。通过微裂缝等沟通原有孔隙,震积作用能够明显改善储层渗透性。

This paper mainly discussed the sedimentary characteristics,vertical sequence and geological significance of seismites of Palaeogene in Jinxian sag,Jizhong depression. In the Bohai Bay Basin,the Jinxian sag was a typical small fault basin of Cenozoic. And a lot of soft sediment deformation structures developed in the layers in the 4th Member of Shahejie Formation and the 1st Member of Kongdian Formation,including liquefied sand-mudstone veins,mud stocks,water-escape channels,load cast and flame structures,ball-and-pillow structures,vibrational liquefaction deformation structures,beads-shaped structures,micro synsedimentary faults and ground fissures. The study indicated that deformation structures above were typical characteristics of seismites. Based on the study,vertical sequence of seismites was established,including underlying unshocked layer,seismic fall layer,shattered layer,seismic corrugated layer,ball-and-pillow layer,liquefied homogeneous layer,and overlying unshocked layer. Seismites,evaporates and tuff which were all related to the activity of deep fracture,developed in the layers in the 4th Member of Shahejie Formation and the 1st Member of Kongdian Formation. The study indicated that activity of deep fracture induced multiperiod earthquakes,and lead to further the formation of seismites. At the same time,as channel of magma upwelling and deep salt sources,the deep fracture provided material basis for the formation of evaporates and tuff. It indicated that the maximum tectonic intensity of Jinxian sag happened in that period,from sedimentary perspective. Seismic deposition can improve the permeability of reservoirs through the connection of original pores by micro fissures.