塔中地区晚奥陶世碳酸盐台缘与台内沉积差异——定性和定量的碳酸盐岩微相综合分析

The Depositional Diversity between Platform Margin and Platform Interior on the Late Ordovician Carbonate Rimmed-platform of Tazhong Area: A case study of qualitative and quantitative integrated microfacies analysis

为揭示塔中地区东部的晚奥陶世镶边型碳酸盐台地边缘与台地内部的沉积差异,利用钻井岩芯及薄片资料,对良里塔格组开展了定性的和定量的碳酸盐岩微相分析研究。研究表明,台缘—台内沉积区发育9种微相类型(MF1~MF9),不同颗粒岩类微相所代表的几种颗粒滩具有典型差别的粒度累积频率曲线样式。台地边缘主要发育各种高能颗粒滩的微相组合(MF1~MF4),与台缘生物礁构成礁滩复合体;台地内部主要发育代表中—低能的潮坪—潟湖沉积的微相组合(MF5~MF9)。结合定量的粒度分析分析认为生屑砂屑颗粒灰岩微相(MF1)、生屑砾屑灰岩微相(MF2)和鲕粒颗粒灰岩微相(MF3)是冲流带(前滨)环境的产物,分别代表着台地边缘生屑滩、鲕粒滩和礁前砾屑滩沉积;球粒颗粒灰岩微相(MF5)为位于受障壁的台地内部、中等能量波浪控制的球粒滩;棘屑泥粒灰岩—漂浮岩微相(MF4)发育于台缘礁后的中—高能生屑滩。

In order to reveal the deposition diversity between platform margin and platform interior on the Late Ordovician carbonate rimmed platform of Tazhong area,we made an integrated microfacies analysis from both qualitative and quantitative aspects by using core and thin section data of the Lianglitage Formation. The result show that nine types of microfacies（ MF1 ~ MF9） can be recognized,and each type of the grainstones which represents different type of carbonate sand shoals has distinct shape of grain-size accumulation curves. The platform margin is composed of several types of microfacies（ MF1 ~ MF4） indicating high-energy sand shoals that form reef-shoal complex together with platform margin reefs. The platform interior is composed of these types of microfacies（ MF5 ~ MF9） that representing medium-to low-energy lagoon and tidal flat deposits. Combining with the quantitative grain-size analysis results,these microfacies including bioclast intraclast grainstone（ MF1）,bioclast rudstone（ MF2） and ooid grainstone（ MF3） were deposited in foreshore environment,respectively indicating platform margin bioclast sand shoals,ooid sand shoals,and reef-front gravel shoals. The peloid grainstone（ MF5） was deposited in the barrier platform interior that was dominated by moderate wave energy. The enchinoid packstone and floatstone（ MF4） was deposited just at the back of platform reef forming bioclast sand shoal.