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(a) Areal density of Mn (DMn) vs. areal density of Fe (DFe), (b) normalized areal densities, NMn vs. NFe, on the petroglyphs. The lines represent linear regressions; the regression parameters can be found in Table 3. Negative DFe values are a consequence of the relatively large uncertainty resulting from the subtraction of the host rock Fe contribution from the Fe signal.
