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Thrombolites have a clotted structure without the laminae of stromatolites.Each clot within a thrombolite mound is a separate cyanobacterial colony.The clots are on the scale of millimetres to centimetres and may be interspersed with sand, mud or sparry carbonate. [1]
Thrombolites are poorly laminated or non-laminated clotted structures formed by cyanobacteria, common in the fossil record and in modern sediments. [18] There is evidence that thrombolites form in preference to stromatolites when foraminifera are part of the biological community. [33]
Oncolites are very similar to stromatolites, but, instead of forming columns, they form approximately spherical structures. [3] The oncoids often form around a central nucleus, such as a shell fragment, [ 4 ] and a calcium carbonate structure is deposited by encrusting microbes .
Ancient giant stromatolites used to be widespread in Earth’s Precambrian era, which encompasses the early time span of around 4.6 billion to 541 million years ago, but now they are sparsely ...
Stromatolites, bioherms (domes or columns similar internally to stromatolites) and biostromes (distinct sheets of sediment) are among such microbe-influenced build-ups. [3] Other types of microbial mat have created wrinkled "elephant skin" textures in marine sediments, although it was many years before these textures were recognized as trace ...
Stromatolites are alternating layers of cyanobacteria and sediments. The grain size of sediment portion of stromatolites is affected by the depositional environment. During the Proterozoic, stromatolites' compositions were dominated by micrite and thinly laminated lime mud, with thicknesses no greater than 100 microns. [3]
"Spongiostromata" is an antiquated form taxon that refers primarily to fossil cyanobacteria. "Spongiostromate" is also used to describe stromatolites and oncolites that do not preserve clear tubules or other cellular microstructure.
Stromatolites were much more abundant in Precambrian times. While older, Archean fossil remains are presumed to be colonies of cyanobacteria, younger (that is, Proterozoic) fossils may be primordial forms of the eukaryote chlorophytes (that is, green algae). One genus of stromatolite very common in the geologic record is Collenia. The earliest ...