Composition and Microfacies of Archean Microbial Mats (Moodies Group, ca. 3.22 Ga, South Africa)
DOI | 10.2110/sepmsp.101.065 |
---|---|
Year | 2012 |
Book | Microbial Mats in Siliciclastic Depositional Systems Through Time |
Publisher | SEPM (Society for Sedimentary Geology) |
Publisher place | Tulsa |
Journal | SEPM Special Publication |
Belongs to | Noffke & Chafetz, 2012 |
Volume | 101 |
Pages | 65-74 |
Type | article in book |
Language | English |
Id | 45855 |
Abstract
The Middle Archean Moodies Group (ca. 3.22 Ga), Barberton Greenstone Belt, South Africa, exposes one of the world’s oldest ecosystems. It includes kerogen-rich laminae and thin chert bands interbedded with coarse-grained and gravelly sandstones. The strata record a medium-energy, tidal coastal environment. Analyses of the microscopic structure and chemical composition of the chert bands through petrographic microscopy, Raman microspectroscopy, laser-induced breakdown spectroscopy (LIBS) analyses, C isotopes, and scanning electron microscope (SEM) photography of macerated material, supported by textural observations of hand samples, suggest that these laminae represent variably compressed and early-silicified microbial mats. Internal wavy laminations, amorphous carbon composition, and negative d13C values strongly imply a biogenic origin. Complete HF maceration of chert bands revealed polygonal cell structures in a formerly extracellular polymeric substance matrix. The tuft- and dome-micromorphology of the laminations resembles that of recent photosynthetic filament-dominated microbial mats. Facies interpretations indicate that microbial mats extensively colonized subtidal to intertidal Archean siliciclastic coastlines