西北大学学报(自然科学版)

目的查明鄂尔多斯晚三叠世延长期沉积体系、岩相古地理特征及演化规律。方法根据大量钻井、露头及岩芯资料,采用野外观察与室内研究相结合的方法。结果研究区在延长期发育的沉积体系有河流、辫状河三角洲、曲流河三角洲、湖泊及深湖浊积岩。在古地理演化过程中,长10期内陆湖盆开始形成,东西两岸两大三角洲裙初步形成;长9期湖盆快速下沉,湖区迅速扩大,三角洲多为破坏性的;长8期三角洲进一步发育;长7期湖岸线大幅度向外推移,西部浊积岩发育,东部三角洲面积明显减小;长6期湖盆面貌发生了显著的变化,深湖-半深湖面积大大减少,三角洲沉积体系极为发育;长4+5期继承了长6的沉积格局,三角洲建设进程减慢,三角洲大面积沼泽化;从长3期湖盆开始逐步淤浅、萎缩、消亡,河道逐渐发育;长2期分流河道发育;长1期由于差异沉降,在东部子长一带形成沉降中心,沉积了湖相浊积岩。结论在继续重视三角洲砂体的同时,也要加强深湖区浊积岩的勘探。

Aim To ascertain the depositional systems,paleogeographic characteristics and evolution of the late Triassic Yanchang Stage in Ordos Basin.Methods Based on large quantities of drilling,outcrop and core data,combined research methods of field exploration and indoor analysis are adopted.Results River,braided delta,delta,lake and deep lake turbidite are developed.During the paleo-geography evolution,inland lacustrine basin began to form,and the two delta skirt in east and west lakeshore are primary formed in Chang 10,lacustrine basin subsidized quickly,lake district enlarged rapidly and destructive delta are developed in Chang 9,delta are more developed in Chang 8,lakeshore line move outward at large range,turbidite developed well near west lakeshore,delta range is decreased in east lakeshore in Chang 7,features of lacustrine basin are changed remarkably,deep lake and half deep lake area is decreased greatly,while delta sedimentary system is developed at its most in Chang 6,framewok is inherited better,but delta′s construction is slowed and is swamping at large scale in Chang 4+5,lacustrine basin began to be silting,shrinking and dying out,and riverway gradually developed well since Chang 3,distributary riverway developed best in Chang 2,because of imbalance subsidence,subsidence center is formed in east Zichang area and in which lacustrine turbidite is sedimented.Conclusion Delta sand body is still the target of exploration and exploitation in the near future,meanwhile the exploration of turbidite in deep lake should be increased.