Landscape paleodynamics in siliciclastic domains with the use of phytoliths, sponge spicules and carbon isotopes: The case of southern Espinhaço Mountain Range, Minas Gerais, Brazil

Abstract

Mountain ranges formed mainly of siliciclastic rocks in humid tropical regions, such as that of Espinhaço, Brazil, present particular landscape features related to processes not yet fully understood. These processes are mainly controlled by the response of the rocks to climate and vegetation characteristics occurring through time. The present study investigates the geomorphological dynamics leading to the formation of recurrent, relatively flat slopes, developed near quartzite outcrops, through the inference of climatic variations and insights into dominant relief processes. These analyses are based on a geomorphological approach with the support of data from phytoliths, sponge spicules and carbon isotopes. Results of field and laboratory analyses of twelve soil profiles sampled in three distinct areas (Guinda, Morrinhos and Chapadinha) show no major overall changes in the vegetation type over 14C dated time, though there are variations along the slope profiles. In Guinda and Morrinhos, phytolith stocks do not follow the pattern of decreasing with depth, varying instead according to the granulometry. In Chapadinha, the stocks decreased with depth, D/P (tree density) ratios were always low (0.06–0.29) and Bi (water stress) indices were very high (48–94%). In Guinda and Chapadinha, the phytoliths present a high degree of alteration, indicating intense erosive processes, while in Morrinhos the presence of well preserved phytoliths indicates greater geomorphological stability of the slopes. δ13C results show dominance of C4 grasses. The presence of woody species varies with slope stability but decreases with depth were observed in all areas enabling the inference that a less humid environment occurred at ca. 6000 yr cal BP and also that cerrado vegetation has predominated since then. Results showed that the applied analyses have a great potential for temporal reconstruction therefore helping the interpretation of geomorphological processes operating during paleoclimates.