陆相坳陷盆地边缘沉积区古地貌恢复:以准噶尔盆地玛湖地区三叠系百口泉组为例

Ancient landform restoration of marginal sedimentary area in the continental depression basin: A case study of the Triassic Baikouquan Formation in Mahu area of Junggar Basin

常用的古地貌恢复方法侧重于利用地层厚度反映古地貌形态,而忽略沉积前由于盆地差异沉降导致地层厚度反映古地貌的不准确性。笔者以准噶尔盆地玛湖地区三叠系百口泉组沉积前古地貌恢复为例,提出一种沉积趋势校正的新方法。百口泉组沉积前为一种陆缘剥蚀区-过渡区-沉积区背景下的冲积扇-扇三角洲陆-湖相逐渐过渡的沉积体系,以地层厚度反映的古地貌形态能较好地刻画湖盆水下部分,较难合理地刻画陆上的古地貌特征。结合研究区资料情况,优选残余厚度法和地震层拉平法开展古地貌恢复工作。首先获取三叠系百口泉组地层真厚度,经过压实、古水深校正之后,对陆上部分的古地貌进行沉积趋势校正。校正后的古地貌较前人研究结果更加合理,对准噶尔陆相坳陷盆地的复杂源-汇沉积体系分析的指导更加准确。

The main techniques of ancient landform restoration focus on formation thickness,ignoring the inaccuracy caused by differential subsidence before deposition. Take the study of ancient landform restoration before deposition of the Triassic Baikouquan Formation in Mahu area of Junggar Basin for example,the authors put forward a new technology of deposition trend correction. The depositional system before the Baikouquan Formation is alluvial fan-fan delta in the background of continental margin denudation zone-transition zone-sedimentary zone,the stratigraphic thickness method can reasonably describe the underwater part of the lake basin,but can not reasonably describe its ancient landform features of the continental part. Based on the geological data from the research area,the authors selected residual thickness method and seismic flattening method to restore the ancient landform. The authors get the true thickness of the Triassic Baikouquan Formation firstly,after compaction and paleobathymetric correction,we correct the deposition trend of the continental part finally. The result shows that,the ancient landform after correction is more reasonable than before,and it is more accurate to guide the analysis of the complex sourcesink depositional system.