准噶尔盆地腹部侏罗系顶部红层成岩作用过程中蕴藏的车莫古隆起演化信息

Evolution of the Chepaizi-Mosuowan Paleo-Uplift,Junggar Basin,China:Evidence from Diagenesis of Late Jurassic Red Beds

准噶尔盆地腹部车莫古隆起演化过程研究直接关系到油气勘探部署,最新通过对K/J不整合界面之下红层的研究发现成岩作用可以为车莫古隆起演化历史提供一些可靠信息.研究认为红层系赤铁矿化所致,非同沉积期的产物,其形成机理类似于砂岩型铀矿形成过程中的潜水氧化和层间氧化作用模式.研究区的红层曾经历了初始压实作用、淋滤作用(赤铁矿化,或称褐色蚀变,导致红层形成)、白云石化钙质胶结作用、硅质胶结作用、方解石化钙质胶结作用、再次压实作用(压裂)和绿泥石化胶结作用的演化过程.成岩作用的有序演化记录了车莫古隆起的演化历史,初始压实作用预示着侏罗系连续沉积并一度被深埋,车莫古隆起隆升速率小于盆地沉降速率;随之而来的褐色蚀变预示着车莫古隆起大幅度抬升,侏罗系被剥蚀出露地表并遭受了全面的潜水氧化和层间氧化作用;再次压实作用和大规模胶结作用预示着侏罗系被再次深埋,这是准噶尔盆地白垩系和新生界充填的结果.由此可见,成岩作用蕴藏了丰富的盆地构造演化历史信息,成岩作用是盆地构造作用的响应.

Exploration of oil and gas in the central part of Junggar basin has shed light on the evolution of the Chepaizi-Mosuowan paleo-uplift, and the study of red beds beneath the unconformity between Jurassic and Cretaceous indicates that the processes of diagenesis provides information about the evolutionary history of the uplift. It is found that the red beds did not form by syn-sedimentary rubifaction but by diagenetic hematitization which can be explained by models of phreatic oxidation and interlayer oxidation occurring during the development of sandstone hosted uranium deposits. They underwent processes of initial compaction, eluviation （hematitization or brown alteration forming red beds）, cementation by dolomite, calcite and/or silica, secondary compaction and deep diagenetic cementation by chlorite. The order of diagenetic events documents the evolutionary history of the Chepaizi-Mosuowan paleo-uplift. Initial compaction indicates that there was continuous deposition in the Jurassic, because the burial was deep and the uplift velocity of the uplift was less than the subsidence velocity of the Junggar Basin. Later eluviation indicates that uplift rates exceeded those of subsidence and Jurassic beds were exposed at the surface where they underwent general phreatic oxidation and interlayer oxidation. Subsequent secondary compaction accompanied by massive cementation indicates that the Jurassic red beds were once again deeply buried as the result of Cretaceous and Cenozoic basin filling. This sequence of diagenetic events thus documents the history of tectonism in the central part of the Junggar basin structure.