Ediacaran microbial mats and microbially induced sedimentary structures in lacustrine deposits, Arabo-Nubian Shield, Egypt

Abstract

Photoautotrophic microbial mats flourished on the substrates of the Precambrian marine environments but are barely reported from non-marine settings. Extraordinarily preserved microbial mats and microbially induced sedimentary structures (MISS) have been reported from the Ediacaran lacustrine deposits of the Hammamat Group in the Arabian Nubian Shield, Egypt. Biogenicity of microbial mats is affirmed by sporadically preserved filamentous cyanobacteria, copious remains of extracellular polymeric substances (EPS) and considerable organic‑carbon content. Locally abundant and diversified assemblages of 11 types of MISS signify optimal paleoecological conditions for proliferous photoautotrophic microbenthic growth, biostabilization and binding activities in oligotrophic fresh-water lakes. Microbial mats and MISS are so far the only terrestrial example in fresh-water lakes during the Ediacaran, specifically between Marinoan and Gaskiers glaciations, and possibly the most diversified assemblages in non-marine realms. Extreme paleoecological stresses throughout the Precambrian and repeatedly during the Phanerozoic reveal that microbial mats were the safe haven—and a primary source of food and oxygen—for early aquatic multicellular organisms. Accordingly, biosignatures of microbial mats and MISS in the Ediacaran lakes prove that the Precambrian non-marine aquatic environments were as important as marine settings in the evolution of ancient life on Earth and possibly on other planets such as Mars.