鄂尔多斯盆地东南部本溪组障壁迁移样式及控制因素

Migration patterns and controlling factors of barrier of the Benxi Formation in southeastern Ordos Basin

鄂尔多斯盆地上古生界本溪组历经多次海侵,发育广阔陆表海沉积,其东南部地区碎屑障壁体系的展布特征和控制因素尚不明确。基于现场岩心、电测井等资料,研究建立障壁体系的沉积序列,恢复宏观古地貌特征,并刻画障壁砂体的平面展布,明确本溪组障壁体系的迁移样式和控制因素。研究识别出障壁海岸沉积体系中的障壁岛—冲溢扇、潮汐水道—三角洲、潮坪—潟湖和沼泽4类沉积序列,刻画本1段底部台阶式陡坡地形和本2段底部连续性缓坡地形2类古地貌特征。障壁沿多期平行岸线方向展布,沿岸线方向砂体连续性高,垂直岸线方向呈现多期迁移特征。障壁体系表现出2类平面迁移模式,本1段以滚动连续式迁移为主,垂向叠置程度低,横向连续性较强;本2段以跳跃间隔式迁移为主,叠置程度高,横向连续性较弱。海侵过程促进了障壁体系的保存,但其展布和迁移主要受古地貌控制,其中岸线轨迹控制障壁的优势长轴展布方向,陡缓坡分别主导障壁的迁移样式差异。研究同时强调海平面上升、古地形在建立古代障壁体系演化模式中的重要性。

The Upper Paleozoic Benxi Formation in the Ordos Basin experienced multiple transgressions and developed extensive epicontinental sea deposits.The distribution characteristics and control factors of the clastic barrier system in the southeastern of the basin are still not clear.Based on the field core,electric logging,and other data,this paper studied and established the sedimentary sequence of barrier system,restored the macro palaeogeomorphic features,depicted the plane distribution of barrier sand body,and clarify the migration style and control factors of the barrier system in Benxi Formation.Four types of sedimentary sequences,barrier island,tidal channel delta,tidal flat lagoon and swamp,were iden tified in the barrier coastal sedimentary system;moreover,two types of palaeogeomorphic features,namely,the stepped steep slope at the bottom of the Member 1 of Benxi Formation and the continuous gentle slope at the bottom of the Member 2 of Benxi Formation,were characterized.The barrier is distributed along the multi-stage parallel shoreline.the sand body continuity along the shoreline is high,and the vertical shoreline presents multi-stage migration characteristics.The barrier system shows two types of migration modes in map view.The Member 1 of Benxi Formation is dominated by rolling continuous migration,with low vertical overlap and strong horizontal continuity.The Member 2 of Benxi Formation is dominated by jump interval migration,with high overlap and weak horizontal continuity.The transgression process promoted the preservation of barrier system,but its distribution and migration were mainly controlled by palaeogeomorphology.The coastline trajectory controlled the distribution direction of the dominant long axis of barrier,and the steep and gentle slopes caused the differences in migration patterns of barriers.This study also emphasizes the importance of sea level rise and palaeogeomorphic slope in establishing the evolution model of ancient barrier systems.