USING BIOMARKERS TO ANALYZE BIOGEOCHEMICAL CHANGES ACROSS THE PRECAMBRIAN-CAMBRIAN BOUNDARY

Many theories have been proposed to explain the Cambrian explosion, however, there is not enough detailed paleontological and biogeochemical data available to precisely identify the procession of events that transpired. The main focus of this project is to elucidate the changing environmental conditions across the Precambrian-Cambrian boundary by using the presence and ratios of biomarkers and to further this knowledge with isotopic studies.

Three outcrop samples were obtained from near St. Petersburg in Russia. They are from the Ediacaran “Laminarite” Fm. of the lower Kotlin Horizon. The “Laminarite” Fm. is also called the Kotlin Fm. which is also called the Lyubim Fm., and that has been renamed the Mezen Fm. The samples were found to be uncontaminated and the biomarkers were studied. The results suggest the presence of a stratified water column. Sponge biomarkers are not apparent in any of the samples. The samples do contain 2,3,6-methylaryl isoprenoids, which suggests the presence of green sulfur bacteria (Chlorobiaceae) and thus a euxinic photic zone. They also contain Ni(II) porphyrins, which is suggestive of an oxic zone, though supporting evidence from other biomarkers is necessary. Current support includes the pristine/phytane ratio that is near one, the presence of large Ediacaran fauna, and the presence of steranes, which are degradation products of steroids that require oxygen for synthesis. A stratified water column is thus evidenced by the presence of both an oxygenated upper water column through Ediacaran body fossils, steroid biomarkers and Ni(II) porphyrins, and an anoxic lower layer via 2,3,6-methylaryl isoprenoids.