沾化凹陷断层活动性及其对层序发育的控制作用

FAULT ACTIVITIES AND THEIR CONTROLS ON THE DEVELOPMENT OF LITHOLOGIC SEQUENCES IN ZHANHUA SAG

济阳坳陷早第三纪属于裂陷盆地 ,发育了众多的断层 ,绝大多数断层属于生长断层。这些断层具有幕式活动的特点 ,即在沙河街三段 (Es3 )早期构造活动强烈 ,沙河街三段中期、沙河街三段晚期—沙河街二段早期构造活动变弱 ,至沙河街二段晚期—沙河街一段早期构造活动又变强 ,东营早期和晚期又变弱。主要断层活动控制着层序地层的发育 ,具体表现在 :(1)对二级层序发育的控制 ,断层的总落差在二级层序开始时最大 ,以后逐渐减缓 ;(2 )对准层序叠加样式的控制 ,即在构造拉张期 ,以发育退积式准层序为主 ,在构造挤压期 ,以发育进积式准层序组为主。同时 ,断层的活动也控制了三级层序 (层序Ⅰ ,Ⅱ ,Ⅲ ,Ⅳ ,Ⅴ和Ⅵ )的厚度和展布形态 。

Zhanhua sag is located in northeastern Jiyang depression. The development of Zhanhua sag was controlled by the NE and NEE extensional and tenso-shear faults,which constituted tectonic framework characterized by alternation of sag and arch. Complex half graben is the characteristics of Zhanhua sag was controlled mainly by the first- and second-order faults with the strike of NE and NEE.The third- and the fourth-order faults are associated faults or antithetic adjustment faults. In Zhanhua sag,many boundary faults lack of footwalls, so, falls of the faults have been used to indicate the intensity of fault activities. Fall of fault refers to the amplitude of relatively fluctuation of the two walls. The larger the fall is, the more intensive the fault activity would be. In the early Es 3 period, Gubei fault had the largest fall; in the middle Es 3 period, Chengdong fault had the largest fall; during the late Es 3 to the early Es 2 period, Gubei fault had the largest fall; during the late Es 2 to Es 1 period, Yidong fault had the largest fall; in the early Ed period, Chengdong fault had the largest fall; and in the late Ed period, Gubei fault had the largest fall. In Zhanhua sag, the most tectonic intensive activity occurred during the deposition of upper Es 2 to Es 1; the next is that developed during the deposition of upper Es 3, and then are those developed during the middle Es 3, late Es 3 to early Es 2 and early Ed periods; and the weakest tectonic activities was in late Ed. Obviously,the tectonic activities were characterized by episodes, i.e.tectonic activity was intensive in early Es 3 period,became weak in middle Es 3,late Es 3 to early Es 2; in late Es 2 to Es 1 period,tectonic activities became intensive again,and weak again in early and late Ed period.In Zhanhua sag, the Paleogene Es 3 to Ed sediments can be divided into two second-order sequences and six third-order sequences.Total fall of faults is used to indicate the intensity of fault activity here. The largest fall amplitude of fault corresponds to the beginning of the second-order sequence, i.e. the total fall of faults had been the largest at the beginning of each second-order sequence,and then gradually became smaller, which indicates that faults have controlled the development of second-order sequences.In Jiyang depression,there are six third-order tectonic cycles from Es 3 to Ed. They are characterized by strong extensional movement in the early period of each cycle,extensional movement in the middle and late periods of each cycle, and compressional movements in the final period of each cycle. Their activity periods correspond to the development periods of the six third-order sequences in Zhanhua sag. The responses of high-resolution sequence stratigraphy logging rhythms of Fu-111 and other eight wells to tectonic activities show that tectonic activities have controlled the overlapping mode of parasequences, i.e. they are characterized by intensive extension and retrograding parasequence set in the early period of each third-order cycle,and by intensive compression and progradational parasequence set in the final period of each cycle.Fault activities controlled the thicknesses and distributions of third-order sequences,as well as the migration of depocenter .As a starting point,the depocenter had been in the area near to Wuhaozhuang-Changdi fault zone during the development period of sequence I,and then migrated successively in clockwise direction to the southern part of Bonan sub-sag and the eastern side of Gubei fault during the development period of sequence II,to the northern side of the western sector of Gubei fault during the development period of sequence III,to the the southern part of Bonan sub-sag during the development period of sequence IV,to the area near the Chengdong fault during the development period of sequence V,and to the western part of Wuhaozhuang sub-sag during the development period of sequence VI .