Combining phytoliths and δ13C matter in Holocene palaeoenvironmental studies of tropical soils: An example of an Oxisol in Brazil

Many plants deposit the soluble silica absorbed from the soil as monosilicic acid (H4SiO4) in and between their cells, generating bodies of opal silica (SiO2·nH2O) called phytoliths. Although phytoliths are susceptible to dissolution under extreme pH conditions, they generally do remain in the soil for long periods of time and can help in the reconstruction of past vegetation and climates. In the present study, phytolith analysis was used to reconstruct the palaeoenvironmental conditions that contributed to the pedogenetic processes, the deposition of organic matter and its stabilization in a very thick (>1 m) umbric epipedon of a Humic Hapludox profile from Minas Gerais State (Brazil). The results from the phytolith assemblages were also compared to the fractions and isotopic data of soil carbon of the same profile. The result from studying these two palaeoenvironmental proxies together has shown that the environment under which the umbric epipedon was formed was a mixture of vegetation with predominance of C3 plants in mesothermic conditions and with little variation in humidity since Middle Holocene.