黔北—川东南志留系层序格架下的沉积体系演化特征及有利区带预测

Depositional System Evolution Characteristics in the Framework of Sequences of Silurian and Prediction of Favorable Zones in the Northern Guizhou-Southeastern Sichuan

黔北—川东南志留系受加里东运动抬升剥蚀仅残留中、下统地层,通过大量钻井及野外露头资料的沉积学研究,应用层序地层学方法,划分出8个三级层序,其中下志留统龙马溪组2个(SSQ1～SSQ2),石牛栏组或小河坝组2个(SSQ3～SSQ4),中下志留统韩家店组4个(SSQ5～SSQ8),识别出三角洲、陆棚、碳酸盐台地3类沉积体系,在等时地层格架中探讨了各沉积体系特征及其平面展布。通过层序地层划分对比及有利沉积相带研究,指出了两类有利储集层:一类为台地浅滩相和台地前缘斜坡相礁滩型生物灰岩、颗粒灰岩储层,主要发育于石牛栏期三级层序SSQ3和SSQ4的高位体系域,纵向上分布于石牛栏组中、上部,横向上分布于研究区南部叙永—习水—观音桥一带;另一类为浅水陆棚碎屑岩储层,主要发育于小河坝期三级层序SSQ4高水位体系域,横向上分布于南川—石柱—利川等地。

Because of uplifting by Caledonian movement,most of the Silurian had been denuded and only its middle and lower series remained in the Northern Guizhou-Southeastern Sichuan.On the basis of the comprehensive study cores and log wells and outcrops,8 sequences and 2 system tracts were divided by use of sequence stratigraphic method,there are two sequences（SSQ1~SSQ2）in Longmaxi Formation of the Lower Silurian,one sequence（SSQ3~SSQ4） in Xiaoheba Formation,four sequences（SSQ5~SSQ8） in middle-lower Silurian Hanjiadian Formation.3 depositional systems of delta,coastal and shelf were developed to explore the characteristics of the depositional systems and their planar distribution in isochronous stratigraphic framework.One is reef flat biolithite and granule limestone developed in the platform shallow facies and platform foreslope facies,mainly in highstand systematic tract of the third sequence SSQ3 and SSQ4 in the Shiniulan Age.The vertical distribution is in the middle and upper of the Shiniulan formation,and horizontal distribution in Xuyong-Xishui-Guanyinqiao in the southern of the study area.The other is shallow continental shelf clasolite reservoir,mainly developed in highstand systems tract of the third sequence SSQ4 in the Xiaoheba Age,laterally distributed in Nanchuan-Shizhu-Lichuan and other places.