Well-preserved fossil reef/mound-building communities and shallow microfacies have been recovered from Changhsingian platform−margin sponge reef at the Panlongdong Section and intraplatform sponge skeletal mound at the Yanggudong Section in NE Sichuan Basin, South China. The present contribution focuses on the palaeoenvironmental implication of the differentiated development processes on the platform−margin reef and intraplatform skeletal mound based on the palaeontology and sedimentology. Precise field assessments and macroscopic/microscopic qualitative observations led to the identification of five reef/mound-building community and 14 reef/mound-related microfacies in the 2 sections of Changxing Formation. In the Panlongdong platform−margin sponge reef, reef-building communities are recognized into Amblysiphonella Community, Preperonidella−Amblysiphonella Community, and Preperonidella–Sollasia Community in ascending order. The reef-related microfacies are mainly classified into calcisphere−pelletoid wackestone to packstone, crinoidal wackestone to packstone of shallow water bank environment, hypercalcified sponge bafflestone, calcareous algae−hypercalcified sponge binding framestone, hypercalcifed sponge−calcareous algae bindstone, and calcareous algae−hypercalcifed sponge rudstone of reef environment, and benthic foraminifera−calcareous algae wackestone to packstone of shallower water lagoon environment. Two mound-building communities can only be found in the Yanggudong intraplatform skeletal mound, including Preperonidella−Intrasporeocoelia Community of lower part and Preperonidella−Sollasia Community of upper part. The mound-related microfacies include calcisphere−calcareous algae wackestone to packstone, crinoidal wackestone to packstone and crinoidal packstone to grainstone of shallow water bank environment, hypercalcified sponge bafflestone and cyanobacteria−hypercalcified sponge binding bafflestone of skeletal mound environment, benthic foraminifera−calcareous algae packstone grainstone of shallower water bank environment and benthic foraminifera−calcareous algae wackestone to packstone of shallower water lagoon environment. These palaeontological and sedimentological analysis results have facilitated the classification of sponge reef and skeletal mound sections corresponding to a solitary shallow benthic zone into multiple microfacies attributed to variable environmental depositional conditions. The differentiated evolutional process of multiple reef/mound-building stages at the Panlongdong and Yanggudong sections clearly demonstrate a general shallowing-upward trend from an inner shelf setting to a supratidal and low energy lagoon environment.

中文翻译：

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四川盆地东北部长兴(晚二叠世)台地-边缘海绵礁和台内骨丘古生物和沉积学特征及其古环境意义

四川盆地东北部盘龙洞剖面长兴系台地-边缘海绵礁和阳谷东剖面台内海绵骨丘均发现保存完好的化石礁/丘构筑群落和浅层微相。目前的贡献集中在基于古生物学和沉积学的台缘礁和台内骨丘差异发育过程的古环境意义。精确的野外评估和宏观/微观定性观察导致在长兴组 2 个剖面中确定了 5 个礁/丘构建群落和 14 个礁/丘相关微相。在盘龙洞台地-边缘海绵礁，造礁群落被确认为Amblysiphonella群落，Preperonidella-Amblysiphonella 群落和 Preperonidella-Sollasia 群落按升序排列。与礁体有关的微相主要分为钙质球-球粒状泥灰岩至泥灰岩、海百合泥灰岩至浅水岸环境泥灰岩、高钙化海绵挡板、钙质藻-高钙化海绵结合骨架岩、高钙化海绵-钙质藻结合岩、钙质藻-高钙化珊瑚礁环境的海绵砂岩，底栖有孔虫-钙质藻类砂岩至浅水泻湖环境的砂岩。仅在阳谷洞台内骨丘内发现有两个造丘群落，即下部的Preperonidella-Intrasporeocoelia群落和上部的Preperonidella-Sollasia群落。与土丘相关的微相包括浅水岸环境的钙球-钙质藻泥石到泥石、海百合泥石到泥石、海百合泥石到颗粒石、骨丘环境的高钙化海绵挡板和蓝藻-高钙化海绵粘结挡板、底栖有孔藻粉石-钙石浅水岸环境的颗粒岩和底栖有孔虫-钙质藻类泥岩到浅水泻湖环境的泥岩。这些古生物学和沉积学分析结果促进了将对应于孤立浅底栖带的海绵礁和骨骼丘截面分类为归因于可变环境沉积条件的多个微相。