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Freshwater stromatolites are found in Lake Salda in southern Turkey. The waters are rich in magnesium and the stromatolite structures are made of hydromagnesite. [50] Two instances of freshwater stromatolites are found in Canada, at Pavilion Lake and Kelly Lake in British Columbia.
Most archean stromatolites older than 3.0 Ga are found in Australia or South Africa. Stratiform stromatolites from the Pilbara Craton have been identified in the 3.47 Ga Mount Ada Basalt. [59] Barberton, South Africa hosts stratiform stromatolites in the 3.46 Hooggenoeg, 3.42 Kromberg and 3.33 Ga Mendon Formations of the Onverwacht Group.
Modern stromatolites are relatively small, Hynek said, whereas ancient stromatolites used to grow to 20 feet (6 meters) tall and 16 to 22 feet (5 to 7 meters) wide, he said.
The oldest stromatolites have been dated to approximately 3.5 billion years old. [18] Stromatolites in Barberton have been dated to about 3.3 billion years. Microfossils found in chert extend the Barberton microfossil record back to 3.5 billion years. All three types of microfossil morphologies are found in cherts.
The Gunflint Iron Formation is a banded iron formation, composed predominantly of dense chert and slate layers interbedded with ankerite carbonate layers. The chert layers can be subdivided into black layers (containing organic material and pyrite), red layers (containing hematite), and green layers (containing siderite). [5]
During her PhD, she published on 3.45 billion years old stromatolites in the Pilbara formation, describing the diversity of early life on the Archean Earth. [7] In 2006 Allwood's research into micro fossils won her a position at California Institute of Technology in Pasadena, working with geologist John Grotzinger. [8]
The stromatolite fossils appear wavy and dome-shaped, are typically 1–4 cm (0.4–1.6 in) high, and were found in iron- and magnesium-rich dolomites that had recently been exposed by melting snow. [39] The surrounding rocks suggest that the stromatolites may have been deposited in a shallow marine environment. [38]
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