DISTRIBUTION AND COMPARISON OF STERANES FROM BLUE-GREEN-ALGAE UNDER DIFFERENT SIMULATED CONDITIONS

Two remarkably opposite distribution patterns of sterane series are revealed from living blue-green alga (or cyanobacterium) under different simulated conditions. The organic matter derived from hydrous-pressure pyrolysis of the blue-green alga is characterised by the predominance Of C27 sterane over C29 sterane; this is coincident with traditional thought. On the contrary, the organic matter derived from artificially silicified microfossils of the blue-green alga is characterised by the predominance of C29 sterane over C27 sterane; this appears to be an unusual distribution pattern. Such kind of unusual sterane distribution also has been found in the samples of Precambrian cherts with abundant well-preserved microfossil algae. All these imply that the special source of organisms and the medium, procedure or conditions of simulated pyrolysis may result in the different distribution patterns of sterane biomarkers.