Oral Presentation Sub22 Conference

Organic production rates in the Proterozoic has long been a subject of debate. Most studies focused on understanding the dynamics of primary productivity in Precambrian sediments conclude that as the atmospheric oxygen concentration was lower than today, the oxygen content in the oceans and organic primary productivity were also lower. However, recent work on this topic has identified areas of high primary productivity in the Mesoproterozoic Artic Bay Formation in northern Canada. Is this formation an anomaly, or should it be the new norm?

This work presents observations from the organic-rich Mesoproterozoic Velkerri Formation demonstrating that the Artic Bay Formation is one of several high primary productivity areas during the Precambrian. Based on a detailed study of the stratigraphic architecture of the Velkerri Formation, we built a stratigraphic forward model to simulate the evolution of the Beetaloo Sub-basin fill during the deposition of the Velkerri Formation. By running a sensitivity analysis on the three sets of parameters that affect organic matter accumulation we demonstrate that the controls on organic matter accumulations varies spatially and temporally across the basin. This finding challenges traditional hypotheses that organic richness in black shales is controlled by either the production, dilution, or preservation of organic particles. Furthermore, stratigraphic modelling suggest that to reach the level of organic richness measured in the Amungee member of the Velkerri formation, primary productivity in the Proterozoic must have been similar to that measured in present day oceans. This second finding further supports that primary productivity in the Precambrian was not as low as previously reported.