黔中-黔东南地区下志留统沉积相

下志留统由下向上分为龙马溪阶、大中坝阶和紫阳阶。黔北地区3个阶有连续的沉积物,而黔中-黔东南地区缺失早志留世龙马溪期和大中坝期早期的沉积。海平面的下降导致黔中隆起上的中下奥陶统成为暴露喀斯特地貌。以余庆-黄平地区为界分成了南、北2个区。南区只有紫阳阶的翁项组(或高寨田组)由南向北超覆在中下奥陶统岩溶暴露面上,在凯里至都匀一带为海湾-澙湖相的钙质砂泥岩沉积,向西至贵阳一带为开阔性的滨浅海沉积。早志留世的海侵改造了下伏岩溶喀斯特和古风化壳,沉积了波浪改造型的砾屑灰岩和海侵充填型的含灰岩砾块碎屑岩,两者均非"底砾岩"。

Sedimentary facies of the Lower Silurian in central and southeastern Guizhou Province

The Lower Silurian is divided into the Longmaxi, Dazhongba and Ziyang Stages. The sedimentation is continuous within these stages in northern Guizhou Province. The central and southeastern Guizhou Province, however, was uplifted and became a land during the Longmaxi Age and early Dazhongba Age in Early Silurian, which resulted in a stratigraphic gap. The fall of sea level made the Lower Middle Ordovician experienced exposure and a karst landform was formed. With the line from Yuqing to Huangping, the uplifting area is divided into two parts: northern area and southern area. In the southern area, the Wengxiang Formation(or the Gaozhaitian Formation)of the Ziyang Stage unconformably overlaps on the exposed surface from south to north. Bay and lagoon calcareous sand mudstone deposits were dominant in the Kaili Duyun region, while in the Guiyang region open shore shallow marine deposits were developed. During this transgression in the Early Silurian, the underlying karst and weathered crust were reworked. The wave reworked calcirudite and transgression filled limestone bearing gravely clastics were deposited, neither of which belonged to the basal conglomerate.