塔里木盆地良里塔格地区奥陶系生物礁的沉积特征和成礁模式*
Sedimentary characteristics and reef-forming models of the Ordovician reefs in Lianglitage area,Tarim Basin

塔里木盆地奥陶系生物礁储集层受到广泛关注。笔者优选塔里木盆地良里塔格地区奥陶系鹰山组顶部生物礁体(NYG-1)和一间房组底部生物礁体(NYG-2)为研究对象,通过详细的野外观察、实测和薄片鉴定,对生物礁的生物类型、岩性特征和沉积相单元进行分析。结果表明:塔里木盆地良里塔格地区鹰山组和一间房组的造礁生物主要由瓶筐石组成,与生物礁相关的岩性有障积礁灰岩、粘结礁灰岩、生屑粒泥灰岩、生屑泥粒灰岩、内碎屑泥粒灰岩、生屑颗粒灰岩、内碎屑颗粒灰岩和球粒颗粒灰岩。NYG-1礁体发育礁基、礁核、礁顶、礁翼和礁盖5个沉积相单元;NYG-2发育礁基、礁核与礁盖3个沉积相单元。从生物类型来看,鹰山组的礁为托盘—障积礁,为近似圆形的台内点礁,展布无明显的方向性;一间房组的礁为托盘障积—粘结礁,属台缘礁,常呈现出礁体迁移的特征。鹰山组和一间房组成礁模式的共同点是都经历了礁基的形成、礁体的发育和礁体的衰亡3个阶段,而差异主要表现在生物礁体的灭亡阶段: 对鹰山组生物礁而言,海平面的快速下降和高能水动力条件导致了瓶筐石的灭亡和内碎屑灰岩的产生;对一间房组生物礁而言,海平面的上升和浮游藻类生物大量发育造成造礁生物甁筐石的灭亡。以上研究对于建立符合塔里木盆地地区条件的礁体沉积模式和探索露头与井下生物礁对比研究有重要意义。
The Ordovician reef reservoirs in the Tarim Basin have been receiving more and more attention. The present research describes the reefs in Lianglitage area, Tarim Basin: NYG-1 reef (at the top of Yingshan Formation) and NYG-2 reef (at the bottom of Yijianfang Formation). Biotypes, lithologies, and sedimentary facies units of these two reefs were detailed documented, using detailed field observations, measurements, and thin section identifications. The results suggest that reef-building organisms are mainly composed of calathiums and that lithology associated with reefs is bafflestones, boundstones, bioclastic wackestones, bioclastic packstones, intraclastic packstones, bioclastic grainstones, intraclastic grainstones, and peloidal grainstones. Facies units in the NYG-1 reef mainly contain reef base, reef core, reef top, reef flank and reef cap. However, the NYG-2 reef consist only of reef base, reef core and reef cap. The Yingshan Formation is rich in calathium-baffle reefs, while Yijianfang Formation is dominated by calathium baffle-binding reefs. Reefs in Yingshan Formation are in the shape of circle-like and intra-platform patches, without obvious directional anisotropies. Reefs in Yijianfang Formation, in contrast, contain platform margin reefs that extensively show the vertical migration characteristics. Both formations have experienced three phases of evolutions, namely colonization, vertical aggradation, and capping. The difference lies mainly in the capping phase. More specifically, during the deposition of Yingshan Formation, the rapid decrease of sea levels and the high water energy led to the perish of calathium and the formation of grainstones, whereas the rise of sea levels and the development of considerable planktonic algae organisms caused the suffocation of