Reef-dwelling brachiopods record paleoecological and paleoenvironmental changes within the Changhsingian (late Permian) platform-margin sponge reef in eastern Sichuan Basin, China.

Abstract

The eastern Sichuan Basin area (China) is the representative locality for studies of the Late Permian Changhsingian platform to basin transition. However, details of the paleoecology and paleoenvironment of rich brachiopod fauna in this area are still unclear, especially regarding the reef-dwelling brachiopods. The reef-dwelling brachiopod specimens from the Panlongdong platform-margin reefal environment are first described herein. A detailed comparison is presented with the paleoecological features and sedimentological characteristics of the reef-dwelling brachiopods and brachiopods of the reported Zhongliang Hill and Huayingshan intraplatform nonreefal environments in the transitional zone. The reef-dwelling brachiopods are dominated by the spiriferids, such as Martinia and Permophricodothyris, which are mainly found in hypercalcified sponge-calcareous algae binding framestone from the second reef-building process of the Panlongdong reef. The brachiopods in the first and third reef-building processes of the Panlongdong reef often show clear indications of transportation. The comparison of paleoecological and sedimentological evidence indicates that the reef-dwelling brachiopod specimens, which have strong pedicle-attached convex shells and supporting body spines, are commonly preserved in live positions and form a hard-bottom fauna, showing low evenness, and high dominance in both taxonomical and lifestyle diversity. The association among reef-dwelling brachiopod individuals also represents potential biological interactions to prevent the shells from being swept away by constant currents and waves, forming extremely dense concentrations on the sea floor as reef ecosystem engineers. This case study of reef-dwelling brachiopods preserved within the platform-margin reefal environment was critical for filling various gaps in our knowledge of the complexity of the Changhsingian reef-related ecosystem.