四川盆地东部中二叠统茅口组台内藻礁沉积特征

Sedimentary Characteristics of Middle Permian Maokou Algal Framework Reef Rock in the East of Sichuan Basin

四川盆地东部月005-H1井发现了中二叠统茅口组三段中发育的小型台内藻礁。岩心分析表明,该生物礁以藻格架灰岩为主,造礁生物以叶状藻为主、见少量苔藓虫,含虫筳类、非虫筳有孔虫、腕足类、双壳类、海百合、棘皮类等附礁生物,藻片之间沉积有灰泥和少量生物碎屑。礁体纵向上发育两个较为完整的旋回,每个旋回发育四个成礁阶段,单个旋回厚度约1.5 m,每个旋回发育四个礁阶段,并可划分出礁基、礁核、礁盖(基)等亚相类型。认为该生物礁的形成与峨眉地裂运动引起的基底正断活动有关,形成于"堑—垒"构造格局的浅水型碳酸盐岩断隆之上。推测该类藻礁灰岩可能与茅口组古风化壳岩溶型储层关系密切。

A small scale of intraplatform biological reef rock was discovered in the Middle Permian Maokou Member-3 at Well Yue-005-Hl in the east of Sichuan Basin. Based on observation of drilled cores from this well, it is shown that the reef rock is mainly composed of algal framework reef limestone. Reef-building organisms mostly are phylloid algal and seldom bryozoan with a few epipbyllous organism and a plenty of marl and biodetritus are deposited among the algae sheets. Two complete sedimentary cycles, in which any a single cycle is about 1.Sm thick, can be recognized in vertical in reef rock and every cycle can include four development phases. Some subfacies, such as reef base, reef core and reef cap（flat） facies, can be classified in reefs. It is inferred that this kind of algal reef limestone that formed on the shallow water carbonate faulted-uplift is likely to be relative with middle Permian Maokou karst weathering-crust reservoirs.