鄂尔多斯盆地直罗组—安定组沉积期原始边界恢复

Restoration of the Original Sedimentary Boundary of the Middle Jurassic Zhiluo Formation-Anding Formation in the Ordos Basin

有关中生代鄂尔多斯盆地各时期原始沉积面貌的探讨,长期以来深受关注但认识和研究程度不一,其中对于直罗组—安定组沉积期的研究尤为薄弱。本文针对鄂尔多斯克拉通内大型坳陷型盆地的属性及其演化-改造特点,从今盆地及邻区残存沉积建造、现今构造格局两方面出发,在大量野外露头观测、钻井与测井资料分析及实验测试基础上,通过系统的地层划分与对比、沉积相分析、物源综合分析和对周邻构造单元形成演化史的分析,认为直罗组—安定组沉积期盆地的原始沉积边界大致为:东在今太行山脉以西;北在今河套盆地一带;西北部边界在狼山—巴彦浩特盆地—科学山一带;西南部边界在今六盘山西缘;南部边界在今渭河盆地一带。自盆地周缘向湖盆中心有大致7个方向的物源供给,沉积中心位于原始盆地中心偏南。该期盆地的演化记录了华北克拉通西部由印支期的南北分异向燕山期东西分异的转变过程与时限。该研究对于构建完整的中生代鄂尔多斯盆地演化时空坐标和铀矿、石油等能源矿产勘探评价具有理论和实际意义。

The sedimentary periods and features of the primary Mesozoic Ordos basin have long been paid more attention,but research degrees are very different.Among them,the study on that of Zhiluo Formation-Anding Formation is especially weaker.With an emphasis on the natures and evolution-reformation of the large depression basin in the Ordos craton,this study,starting from with residual sedimentation and current tectonic framework for the basin and its adjacent areas,and based on the a large amount of field observation,drilling and logging data,and labassays,conducted comprehensive analyses on aspects such as classification and contrast of sequences,sedimentary facies,material source,and evolution of tectonic units and surrounding areas.The research suggests that the original sedimentary boundary of the basin during deposition period of the Zhiluo Formation-Anding Formation can be summarized as follows：The eastern borderline is to the west of Taihang Mts;the northern is in the Cenozoic Hetao basin;the northwestern borderline in the Langshan-Bayanhaote basin-Kexueshan;the northeastern in the west of the Liupan Mts;the southern to present Weihe Cenozoic basin.There were about 7 material sources from the rim of the basin toward the center of the basin,with depocenter locating roughly in the centre of primary basin.The evolution of the basin at this stage records the transition process and time limit of the North China Craton＇s differentiation from north-south in Indo-Chinese epoch to west-east differentiation in Yanshan Epoch.This study is of great importance to constituting intact temporo-spatial coordinates for the evolution of Mesozoic basin,and to assessing the resources of energy minerals such as uranium deposit and petroleum.