柴达木盆地北缘欧龙布鲁克微地块早古生代岩相古地理

The early Paleozoic lithofacie-palaeogeography of Olongbluk micro-massif on the northern margin of Qaidam Basin

通过对柴达木盆地北缘欧龙布鲁克微地块的野外地质调查及精细观察,根据剖面中发育的岩石组合关系、沉积构造特征以及地层接触关系,对该区早古生代寒武纪—早奥陶世沉积及岩相古地理特征进行了详细研究。认为早古生代欧龙布鲁克微地块处于火山岛弧弧后区域,柴北缘洋俯冲及陆陆碰撞控制了该时期的盆山格局与沉积充填演化。欧龙布鲁克微地块下古生界主要发育一套海相碳酸盐岩建造,仅在寒武系底部以及下奥陶统存在陆源碎屑沉积。从岩石组合来看,沉积相类型大致可划分为蒸发潮坪相、局限台地相、开阔台地相、台地边缘相和复理石盆地沉积5大类及相应的亚类。研究区早古生代整体处于海侵状态,欧龙布鲁克微地块早寒武世经历蒸发潮坪沉积,中、晚寒武世海侵范围逐步扩大,研究区接受了一套以浅海碳酸盐岩建造为特点的局限台地—开阔台地沉积。早奥陶世基本继承了寒武纪海侵范围,欧龙布鲁克微地块沉积环境向台地边缘浅滩—前缘斜坡转变,直至早奥陶世晚期台地相向中南方向迁移而形成于高海平面下的台缘斜坡—欠补偿深水陆棚沉积环境。

Through field geological investigation and elaborate observation of Olongbluk micro- massif on the north margin ofQaidam Basin in combination with the rock, sedimentary structural characteristics and contact relationship of strata in the profiles,the authors studied features of the Early Paleozoic Cambrian to early Ordovician sedimentary and lithofacies palaeogeography in thestudy area. Olongbluk micro- massif is located in a volcanic island arc back- arc area, and ocean subduction and collision ofcontinental plates control basin-orogen pattern and evolution of sedimentary fillings in North Qaidam. The lower Paleozoic periodof Olongbluk micro-massif mainly developed a set of marine carbonatite, with some terrigenous detrital rock in Cambrian bottomand early Ordovician strata. According to lithological association, there are five kinds of sedimentary facies, i.e., evaporated tidal flatfacies, restricted platform facies, open platform facies, platform edge facies and flysch sediment. The study area mainly experiencedtransgression impact in that epoch. In Early Cambrian period, the study area received evaporation tidal flat sediments. In middle andLate Cambrian period, the study area accepted a set of shallow sea carbonatite formation, and the transgression range was enlarged,thus belonging to an area of restricted platform-open platform sediments. In Early Ordovician period, the sedimentary environmentshifted into shoal of platform margin facies-foreslope. In the late of Early Ordovician period, the platform migrated southward, andbecame platform margin or slope under the compensated deep shelf sedimentary environment.