CONCENTRATION OF IRON AND MANGANESE JUST AFTER THE PALEOPROTEROZOIC GLACIATIONS

Atmospheric oxygen level is considered to have increased during the early Paleoproterozoic (2.45-2.0 Ga). The Kalahari Manganese Field in the Transvaal Supergroup, South Africa, is the first and largest manganese deposit in the Earth history, which formed just above the low-latitude glacial sediments (at 2.22Ga). Kirschvink et al.,(2000) interpreted this as a result of a rise of oxygen in the atmosphere just after a snowball Earth event. There is, however, no evidence for these global events in the areas other than South Africa. The Huronian Supergroup in Canada consists of Paleoproterozoic sedimentary rocks, including three discrete glacial diamictite layers. We analyzed core samples of the Gowganda Formation, the uppermost glacial diamictites of the Huronian Supergroup, taken from the Cobalt area in Ontario, Canada. We found that there is a manganese anomaly preceded by iron concentration in the black laminated siltstone layer overlying the last glacial dropstone. In this study, we tried to confirm that the iron and manganese anomalies found in the Cobalt area are generally seen in the Gowganda Formation in the Elliot Lake and Espanola areas in Ontario, Canada. While we couldn't find any anomalies in the Elliot Lake area, we found iron concentration followed by small but significant manganese anomaly for the samples taken from the Espanola area. Based on observations of sedimentary structures and chemical mapping, we suppose that these elements could have precipitated directly from sea-water. We suggest that differences in the concentrations of iron and manganese are derived from different depositional depth of each sedimentary basin. We suspect that the iron manganese concentration in the Gowganda Formation could be compared with those of the Kalahari Manganese Field in South Africa in terms of ages, implying the rise of atmospheric oxygen level occurred globally just after the extreme glaciations.