MODERN STROMATOLITE GEOCHEMISTRY AS A PALAEOENVIRONMENTAL PROXY

Stromatolites in the Archaean rock record have historically been interpreted as the result of cyanobacterial activity and are considered by many to be the oldest direct record of life on Earth. Comparisons with modern locales such as Shark Bay, Australia, have also often resulted in interpretations of these structures as indicative of both warm climate and shallow, quiescent water environments. However, modern cyanobacterial activity is not restricted to such a narrow range of environmental conditions. These cyanobacteria also produce similar depositional structures as observed in ancient stromatolites, albeit typically on a smaller scale.

In this study, the trace element characteristics of modern stromatolites from a variety of environments are examined and compared with stromatolites from the Archaean. Modern marine peritidal stromatolites have been collected from both the Indian and Atlantic coastal areas of southern Africa as well as from Scotland, Eire, Singapore, and Malaysia. These represent a variety of coastal environments and ambient water temperatures. In addition, two Holocene salt pan stromatolite samples from Etosha and Sua Pans (Namibia and Botswana, respectively) have been analysed.

Preliminary results show that REE+Y data from the marine and salt pan stromatolites plot in two distinct fields. Comparison with literature data from Archaean samples shows that 3.4 Ga chert data (interpreted as marine) plot in the marine field, but 2.97 Ga stromatolite data (also interpreted as marine) plot with the Holocene salt pan data. These results suggest that this could be a useful proxy for differentiating stromatolite palaeoenvironments.