塔中I号坡折带上奥陶统台缘礁滩复合体建造模式

塔中Ⅰ号坡折带的台缘高能区发育上奥陶统良里塔格组礁滩体,主要包括生物礁丘、灰泥丘、粒屑滩、滩间海等沉积类型,纵向上表现为粒屑滩、灰泥丘、礁丘的多旋回组合。单个礁滩复合体下部发育粒屑滩,上部为灰泥丘和(或)礁丘,之上为下一旋回的粒屑滩亚相所覆盖。横穿宽3～10km的区域,特别是台地边缘向陡坡转折的高地为礁生长相对集中区,而向内侧则更多出现滩相。不同沉积期礁滩单元分布范围不同,从良三段到良一段沉积期间内呈现逐步向塔中Ⅰ号坡折带迁移的缩减趋势。经后期多次成岩作用和构造破裂的改造,形成沿台缘分布且具有非均质性变化的礁滩型储层。

Reef-bank complex pattern of the Lianglitag Formation (Upper Ordovician) along the Tazhong Slopebreak I, Tarim Block, NW China

The Lianglitag Formation (Upper Ordovician) reef-bank complexes were formed in the high-energy belt of the platform margin along Tazhong Slopebreak I. Sedimentary units mainly include reef mound, carbonate mudmound, bioclastic bank and granule shoal. These units show as multiple re-occurrences throughout vertical assemblage. Single complex origins from basal bioclastic bank, successes as carbonate mudmound or reef mound in the upper part. Bioclastic bank overlaps the mound or reef marking a new cycle of the reef-bank complex building. Reefs are mainly distributed along the high part of the slopebreak with width from three to ten kilometers. Meanwhile, banks are more common in the inner side of the slopebreak. The magnitudes of the reefs are changeable temporally and spatially. Reef dwindles migrated gradually towards the slopebreak I from the Member 3 to the Member 1 of the Lianglitag Formation. Affected by multiple phases of diagenesis and structural fracturing, the reef-bank complexes along the platform margin are significant of reservoirs characterized by their variation in heterogeneity.