Stromatolites (Bindstone) are becoming widespread: finely laminated sedimentary structures belonging to the group of non-particulate, bioconstructed limestones, resulting from the activity of benthic photosynthetic microorganisms such as prokaryotes (e.g., cyanobacteria) and even microscopic eukaryotic algae. They form through periodic entrapment of very fine particulate sediment, primarily composed of carbonate mud, in mucilage produced by blue-green algae and/or bacteria. After the first algal mat has fixed sediment particles onto its gelatinous surface until it is completely covered, algal filaments develop above, forming another mat. This creates a succession of alternating organic-rich layers. Due to diagenetic processes, microalgal remains are rarely preserved, and lamination is the only evidence of their activity. A current site of stromatolite formation is Shark Bay in Western Australia. Among the best known are those found in the Gunflint Iron Formation in Canada, dating back to around 2 billion years ago.
