A (CYANO-)BACTERIAL ECOSYSTEM IN THE ARCHEAN 3.49 GA DRESSER FORMATION, PILBARA, WESTERN AUSTRALIA
In the shallow subtidal zone, microbial mats developed simple stromatolites. The famous wrinkle mats grew in an evaporate-rich tidal sabkha environment. Some of the stromatolite-like upheavals in this area are here reinterpreted as petees. Polygonal oscillation cracks and gas domes, typical for tidal sabhkas, occur as well.
In the tidal flats, microbial mats produced ooids and oncoids. Fenestrate laminae record gas accumulation between coherent, EPS-rich microbial mats, which sometimes form up to a meter thick biolaminites. In clastic areas of the tidal flats, erosional remnants and pockets were formed. Here, microbial mat chips are scattered at random on the tidal surface. Sometimes they are accumulated to small piles. The chips may be deposited top-up or top-down. Some are rolled-up. Non-transparent wrinkle structures occur. In situ preserved microbial mats in tidal pools may show tufts on their surfaces. In the subtidal area, ripple marks are lined by sinoidal structures.
A lagoon was overgrown by significant biolaminites of up to 3m thicknesses. Mat chips are frequent here as well. The black-white laminae may record biovarvites. The biovarvites may reflect seasonal variations of the microbial populations.
In conclusion, stromatolites, wrinkle mats, and the various MISS in the Dresser succession show the same facies associations like the equivalent structures in the Archean, the Neoproterozoic, the Phanerozoic, and the present. This correlation points to a high diversity of mat-forming bacteria already in the antique world of the Dresser Formation. The presence of simple cyanobacteria is likely.