Classification of Microbial Carbonates

Abstract

The main groups of organisms participating in the formation of benthic microbial carbonates are bacteria, cyanobacteria and algae. Three main processes are involved in the formation of microbial carbonates: (1) trapping of sedimentary particles; (2) biomineralization of organic tissue; (3) surficial precipitation of minerals on organisms and sediments. Of these, biomineralization preserves the most information concerning the organisms involved, and trapping preserves the least. Surface mineralization is intermediate, in that it preserves information concerning the exterior size and shape of the organisms. The principal categories of benthic microbial carbonate deposits are: stromatolite, laminated microbial deposit: agglutinated stromatolite fine-grained, well-laminated coarse-grained, crudely laminated tufa stromatolite skeletal stromatolite subaerial stromatolite dendrolite, dendritic microbial deposit thrombolite, clotted microbial deposit travertine, layered microbial deposit with a dendritic macrofabric cryptic microbial carbonates: microbial deposits with micritic, clotted, peloidal or sparitic microfabrics, but lacking distinctive macrofabrics. Only agglutinated stromatolites are dominated by trapping. Skeletal stromatolites, dendrolites, and thrombolites are dominated by biomineralization. Tufa stromatolites, subaerial stromatolites and travertine are dominated by surficial mineralization. Tufa stromatolites, subaerial stromatolites, and travertine are essentially non-marine, whereas skeletal stromatolites, dendrolites, and thrombolites are essentially marine and restricted to the Palaeozoic and Mesozoic. Agglutinated stromatolites occur in both marine and non-marine environments. Travertine, and especially tidal flat and subaerial stromatolites, are strongly influenced by desiccation.