[BBG02-05] Heterogeneity in nitrogen source for microbial activity recorded in 2.0 Ga Zaonega Formation, NW Russia
Keywords:stepwise combustion method, nitrogen isotope, Paleoproterozoic are
The origin of ammonium-nitrogen, hosted by the clay minerals, is unknown. Although maturation of organic matter would release ammonium ion that can substitute for potassium and be trapped in clay minerals, it is unlikely that the δ15N of 0‰ could produce from the +12‰ nitrogen in the organic matter. Thus, regardless the nitrogen source of component 1, it was distinctly different from that of component 2.
Our result suggests that the shallow oxic ecosystem was existed during accumulation of the 2.0 Ga ZF, while it is possible that other type of ecosystem, which may have utilized a different nutrient source, was presented near the sediment/water interface. Both ecosystems co-existed in the same sedimentary basin, which is consistent with those of predicted by the previous study in the same core sample. This study further suggests that not only carbon but also nitrogen cycle was more complicated that thought in previous studies for the Paleoproterozoic era.