MICROBIALITE ABUNDANCE AND DISTRIBUTION THROUGH TIME

Microbialites are potentially the oldest evidence of life on Earth, and dominate over 80% of the fossil record. Microbialite abundance began to decline in the Late Proterozoic and records have been inconsistent through the Phanerozoic. The appearance and disappearance of microbialites in the fossil record has commonly been attributed to the action of grazing metazoans, and they are often classed as a disaster taxa. However, data on microbialite abundance throughout the Phanerozoic does not support this assertion.

In addition, distribution of modern microbialites is spread over a wide range of environments, including open marine, freshwater, alkaline lake, hypersaline, and hot spring environments. Modern investigations in open marine environments justify their utility as an appropriate analog site because most fossil specimens are from open marine environments. However, data show that Phanerozoic microbialites represent a range of different environments similar to their distribution today. Also, the majority of open marine microbial reefs that dominate at two mass extinction events may have resulted from a drastic change in ocean chemistry, further calling into question the value of open marine microbialites as a preferential analog. Environmental characteristics associated with the formation of ancient microbialites should be carefully considered before referring to analogous modern sites. Modern analog work is very important for elucidating the processes that contributed to the formation of ancient microbialites, but care should be taken when associating environment with specific formation processes.