塔西南坳陷早、中寒武世岩相古地理格局分析

Analysis on the palaeogeographic framework of the early-middle Cambrian in southwest depression of Tarim basin

塔西南坳陷早、中寒武世岩相古地理格局是该区中、下寒武统烃源岩和白云岩规模储集层发育的重要因素。以露头、钻井及地震资料为基础,根据寒武系沉积前古构造,中、下寒武世地层结构,以及地震相特征,分析塔西南坳陷早、中寒武世古地理格局,研究寒武系生储盖特征及油气勘探意义。结果表明:研究区寒武系沉积前昆仑山前叶城—皮山—和田一带发育南华—震旦系裂谷体系,呈楔状向巴楚隆起剥蚀尖灭。受继承性沉降作用的影响,早、中寒武世巴楚隆起为克拉通内坳陷台地相碳酸盐岩沉积,山前凹陷为克拉通边缘盆地相沉积,从巴楚隆起向南到昆仑山前表现为被动大陆边缘背景下的"台地—斜坡—盆地"的古地理格局。在麦盖提斜坡南部到山前凹陷北部发育北西向展布的台地边缘相,其中下寒武统为缓坡型台缘;中寒武统在坳陷西段为缓坡型台缘,坳陷的中、东段为弱镶边型台缘。山前盆地相烃源灶、斜坡区台缘礁滩相高能颗粒白云岩及膏泥岩盖层等生储盖条件,决定塔西南坳陷中、下寒武统台缘带具有较大的勘探潜力。

The palaeogeographic framework of the early-middle Cambrian is the key for understanding the characteristics of source rock and reservoir stratum in southwest depression of Tarim basin.Based on the drilling and seismic data in southwest depression of Tarim basin,the palaeogeographic framework of the early-middle Cambrian was analyzed,through the characteristics of palaeotectonics pattern in preCambrian,stratal configuration and seismic facies in early Cambrian.It's considered that in the earlymiddle Cambrian Kunlun mountain front was deep water basin facies area,from Bachu uplift to Kunlun mountain front the palaeogeographic framework was 'platform-gentle slope-deep water basin',which is obviously characterized by gentle slope at platform margins,and slope lack of topographic break.These are the primary evidence:First,Bachu uplift and its peripheral areas were destructional landforms and in the Yecheng-Pishan-Hetian area of Kunlun mountain front,which developed cryogenian and sinian rift,were low-lying areas;second,from Bachu uplift to Kunlun mountain front the seismic facies can be divided into three second-stage unit which are parallel seismic reflection configuration at 200~250ms time depth of layers,shingled progradation configuration,parallel seismic reflection configuration at 100~150ms time depth of layers,the three second-stage unit seismic facies have a good corresponding relation to platform,platform margins,deep water basin;third,the platform and upper slope of platform margins were widely developed seismic reflecting anomaly of grain beach facies in early Cambrian.