Stromatolites occurred in Archean, and reached their peak during the Mesoproterozoic (from 1600 to 1000 Ma). After that peak they continued to decline. Subsequently, stromatolites experienced a resurgence during the Cambrian and Early Ordovician, after early Ordovician which they decreased again and never recovered.
However, the abundant stromatolites can be found in middle Ordovician strata of Ordos basin, China. During Ordovician time, the evaporitic basins are very rare, but huge evaporites including halite can be find in Ordos basin during Ordovician. The abundant stromatolites can be found in these evaporitic surroundings. Metazoan grazing and burrowing can account for the stromatolite decline after early Ordovician, but the high salinity in evaporitic surroundings of Ordos basin can help the resurgence of stromatolites in middle Ordovician evaporitic surroundings.
Dr. MENG Fanwei from Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences and other experts found these resurgence of stromatolites in middle Ordovician evaporitic surroundings. The shallow water sedimentary evidences from bottom grown gypsum and chevron halite. Carbon isotope curve from carbonates coincides with the Middle Darriwilian excursion of the Middle Ordovician and sulfur isotope data from anhydrite imply that these strata belong to middle Ordovician. The anhydrite sulfur isotopes (δ34S) from Majiagou Formation, Ordos basin, China range from +27.1 to +28.0‰ (lower than sulfur isotopes Cambrian data, but higher than late Ordovician data) imply that these evaporites were deposited in middle Ordovician.
Stromatolite structures in drill cores from the Majiagou Formation (shallow brine)
Cumulate and Chevon halite with carbonates in Majiagou Formation, Ordos basin
Bottom grown Anhydrite growth structure in Majiagou Formation, Ordos basin (shallow brine)
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