塔里木盆地早古生代古地貌——坡折带特征及对地层岩性圈闭的控制

Early Paleozoic palaeogeomorphology—characteristics of slope break zones and their control on stratigraphic-lithologic traps in Tarim Basin

塔里木盆地早古生代坡折很发育。中寒武世—中晚奥陶世发育典型的陆架坡折,志留纪的坡折带是一种具有地形差异的古地貌,有别于陆架坡折。在晚寒武—早奥陶世、满加尔坡折是台地边缘相和深海盆地相的分界线;中晚奥陶世时期,满加尔-塔东坡折带是盆地相和混积陆棚相的分界,塔中坡折带之上发育了典型的孤立台地相、坡折带之下则以盆地相发育为主要特征;志留纪时期,塔中南部坡折明显控制了潮坪和滨岸沉积,北部坡折是滨岸体系中远滨和前滨-临滨很好的分界带。沿着斜坡带-坡脚一带是寻找岩性圈闭的有利地区、如中上奥陶统的塔中坡折带上下和满加尔-塔东坡折的塔东段以及志留系的塔中缓坡-潮坪带柯坪塔格组上段构造及岩性圈闭发育区、阿瓦提-满加尔南坡折-滨岸带柯坪塔格组下段地层超覆及岩性圈闭发育区和阿瓦提-满加尔北坡折-滨岸带柯坪塔格组下段地层超覆及不整合面圈闭发育区。

Early Paleozoic slope breaks are well developed in Tarim basin.Typical shelf break was developed in Mid- die Cambrian-Middle-Late Ordovician.The Silurian slope break was a kind of palaeogeomorphology with landform dif- ference,which was different from the shelf break.In Late Cambiran-Early Ordovician,the Manjiaer slope break acted as the boundary of platform edge facies and deep-sea basin facies.In Middle-Late Ordovician,the Manjiaer-Tadong slope break was the boundary of basin facies and diamictic shelf facies;while typical isolated platform facies and basin facies were developed above and below the Tazhong slope break,respectively.In Silurian,the southem Tazhong slope break evidently controlled the tidal flat and coastal deposits,while the northern Tazhong slope break was a good demarcation line between offshore and foreshore-shoreface in coastal system.Along the slope belt-lower footslope would be the favorable area for discovering lithologic traps,e.g.structural and lithologic traps are well de- veloped in the Middle-Upper Ordovician above and below the Tazhong slope break and in the Tazhong segment of Manjiaer-Tadong slope break,and in the Silurian upper Kalpintag Fm Tazhong gentle slope-tidal flat belt;strati- graphic overlap and lithologic traps are well developed in the lower Kalpintag Fm in Awat-Southem Manjiaer slope break-coastal belt;and stratigraphic overlap and unconformity traps are well developed in lower Kalpintag Formation in Awat-Northern Manjiaer slope break-coastal belt.