Palaeobiology and Organic Geochemistry of Archean Helen Iron formation, Michipicoten Area

Diamond Drill Core (D. D. H. U-2-647) samples of approximately 2.75 b.y. old Helen Iron Formation of Michipicoten area in the Superior Province of the Canadian Shield have been examined for morphological and molecular fossils. Evidence shows two types of bioforms - simple micron-sized filamentous microstructures resembling present day iron bacteria and laminated structures designated as cryptalgal mats.

Organic geochemical studies have shown that a variety of organic compounds is present. These include n alkanes, isoprenoid hydrocarbons pristane and phytane and fatty acids. The exact syngenetic nature of these compounds will be evaluated in the future by appropriate control experiments such as permeability measurements, diffusion studies, etc.

Presence of pristane and phytane is indicative of high photosynthetic activity. Predominance of n-C16 (palmitic) acid is significant in view of it being the major constituent of the cell membrane of an organism.

The morphological and molecular evidence and previously reported carbon and sulphur isotope data further substantiate the existence of autotrophic organisms and reducing bacteria in Archean times and they were operative during accumulation of these ancient Precambrian chemical sediments.