Palaeoecology of Ediacaran metazoan reefs

Abstract

AbstractTerminal Ediacaran metazoan reefs (c. 548–541 Ma) can be locally substantial and the skeletal metazoans Cloudina riemkeae, C. hartmannae, Namacalathus and Namapoikia produced diverse reef types with complex ecologies in association with varied microbialite support or influence. In the Nama Group, Namibia, metazoan reefs grew in three associations with differing dominant frameworks: (1) monospecific aggregations of Cloudina; (2) Cloudina–Namacalathus–thrombolite assemblages; and (3) thrombolite-dominated metazoan communities. Cloudina hartmannae formed monospecific reefs up to 7 m wide and 3 m high with no microbialite component. The synoptic relief was probably <1 m. Cloudina riemkeae formed densely aggregating assemblages associated with microbialites and thrombolites, each from 30 to 100 mm high, which successively colonized former generations. Isolated Namacalathus either intergrew with C. riemkeae or formed dense, low-relief, monospecific aggregations succeeding C. riemkeae frameworks. Thrombolite-dominated metazoan reefs reached up to 20 m in height and width, with a synoptic relief of up to several metres. Cloudina and Namacalathus grew closely associated with these framework thrombolites and Namapoikia, which was encrusting and modular, reached up to 1 m in size and occupied neptunian dykes and fissures. Cloudina and Namacalathus also grow cryptically, either as pendent aggregations from laminar crypt ceilings in microbial framework reefs, or as clusters associated with thrombolite attached to neptunian dyke walls.