Abstract
A recent field-intensive program in Shark Bay, Western Australia provides new multi-scale perspectives on the world’s most extensive modern stromatolite system. Mapping revealed a unique geographic distribution of morphologically distinct stromatolite structures, many of them previously undocumented. These distinctive structures combined with characteristic shelf physiography define eight ‘Stromatolite Provinces’. Morphological and molecular studies of microbial mat composition resulted in a revised growth model where coccoid cyanobacteria predominate in mat communities forming lithified discrete stromatolite buildups. This contradicts traditional views that stromatolites with the best lamination in Hamelin Pool are formed by filamentous cyanobacterial mats. Finally, analysis of internal fabrics of stromatolites revealed pervasive precipitation of microcrystalline carbonate (i.e. micrite) in microbial mats forming framework and cement that may be analogous to the micritic microstructures typical of Precambrian stromatolites. These discoveries represent fundamental advances in our knowledge of the Shark Bay microbial system, laying a foundation for detailed studies of stromatolite morphogenesis that will advance our understanding of benthic ecosystems on the early Earth.
Highlights
Dominating the fossil record for 80% of Earth history, microbial reefs known as stromatolites are among the most widespread and recognized components of Precambrian carbonate platforms[1]
Depth soundings were combined with satellite imagery to produce a detailed bathymetry map of Hamelin Pool (Fig. 1; see methods)
Despite major similarities within the cyanobacterial populations of the three stromatolite-building mats, 16 S rRNA gene analysis revealed that, collectively, each mat type is a distinctive microbial community correlating to its water depth and geographic location
Summary
Dominating the fossil record for 80% of Earth history, microbial reefs known as stromatolites are among the most widespread and recognized components of Precambrian carbonate platforms[1]. As part of our multi-scale approach to studying stromatolite growth in Hamelin Pool, a two-pronged approach, including microscopy and molecular techniques, was used to document and characterize microbial mat communities. Progressing seaward, mats in the lower intertidal to subtidal zones with pustular, smooth and colloform surface textures lithify to form cemented fabrics that build discrete stromatolites (Fig. 3).
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