Modern Stromatolites from Marion Bay


Geological Time: Holocene to Pleistocene

Size: Stromatolite is 4.2 inches across widest diagonal on polished surface, and up to 1.5 inches thick

Fossil Site: Marion Lake, York Peninsula, South Australia

Modern Stromatolites from Marion BayThis is for all practical purposes, modern stromatolite from the Holocene to pleistocene, coming from the famous selenite collecting beds of Lake Marion, Australia. In fact, the specimen contains crystals of selenite. The specimen also exhibits extremely fine layering. The material is difficult to obtain, coming only from old collections, as the site is now a protected park. Coming from a lake/lagoon environment with brackish and hypersaline water, this stromatolite is an example of how modern stromatolite has retreated to less hospital habitats where competition from other forms is reduced and where the bacterial mats Living Stromatolite Colonywill not become part of the food chain. Being more modern, this domal section of stromatolite has apparently retained its form from when the colony was alive and growing. Unlike most ancient stromatolite, it has not been metamorphosized. Marion Bay is now a park with no access to collectors, making this specimen from an old collection impossible to replace.

During much of precambrian time, microbial mats built massive near-shore reef systems across a planet with a paleoenvironment hostile to modern life. These reef building prokaryotes where mostly photosynthetic (e.g., cyanobacteria). The coasts provided water shallow enough to gather visible spectrum light for energy, while affording some attenuation to the prevailing, deadly ultraviolet light. By the Cambrian, the buildup of atmospheric oxygen as by product of photosynthesis was powering an explosion of eukaryotic life, including many who would be the new reef builders from the Paleozoic to modern time If fact, the microbial mats formed by prokaryotic bacteria (slang name is blue-green algae owning to pigmentation involved in photosynthesis) became part of the food chain for the new life forms. Stromatolites as shown here from Marion Bay in Australia are modern stromatolites now only found on earth in areas where there is reduced grazing and burrowing by other organisms, and a low occurrence of macro-algae and plants. Environments where modern stromatolites are typically found are hypersaline, but also include areas of high alkalinity, low nutrients, high or low temperatures, and strong wave or current actions. The obvious pattern emerges that modern stromatolites tend to exist in areas that most other life forms consider less desirable or possibly intolerable. Thus, organisms producing modern stromatolites are generally limited to areas where organisms with which they have to compete and/or organisms that might use them for nutrients are not prevalent.

Also see: Stromatolites Across Geologic Time


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