Fig. 1: Caldeirão’s soil compositional data compared with published data of Solimões River sediments and anthropic materials.
From: Evidence confirms an anthropic origin of Amazonian Dark Earths
Data is in Supplementary Table 1; the wood ash and bone/dung fields in (C, D) are offset to compensate for soil (Ulti) background concentrations. ADE = Amazonian Dark Earth, Ulti = Ultisol soil profile. A Geogenic elements Al and Fe are similar in ADE and Ultisols, but different from Solimoes sediments. B, C Anthropogenic elements K, Ca, and P fall in the range of anthropogenic materials. Solimões sediments have much lower Ca/K ratios and far higher K concentrations. Black continuous and broken lines give the 1:2 and 1:2.13 Ca:P ratios quoted by Silva et al.5 for human faeces and freshwater fish, respectively, corrected for 500 mg/kg soil (Ulti) background. D Ca and Sr show strong correlations in ADE. The Ca/Sr ratio in ADE is close to that of wood ash, suggesting an anthropogenic origin for Sr, while Solimões sediments have overall much higher values.
