Stratigraphic control and chronology of peat bog deposition in the Serra do Espinhaco Meridional, Brazil

Peat bogs consist of a heterogeneous substrate whose physical characteristics vary in accordance with botanical composition, inorganic sediment content and the degree of organic matter (OM) decomposition. Although rare in the tropical zone of South America, they can form in places where temperature and drainage favor the accumulation of OM. Due to the anoxic character of the environment, OM remains preserved, providing a valuable record of the climate during its genesis. In the Serra do Espinhaco, bogs can be found buried under sand deposits and given the difficulty of mapping such deposits by conventional methods, Ground Penetrating Radar (GPR) was used in their location and the study of the relationship between peat bog genesis and bedrock setting. GPR data revealed blocks of quartzite located perpendicular to the drainage pattern; which are assumed to partially restrict the water flow and maintain wet conditions upstream, favoring the development of hygrophilous vegetation and the accumulation of OM. Radiocarbon dating showed that buried bogs are contemporary to the deeper parts of non-buried peats and that there is a strong correlation between their stratigraphy and climatic conditions. Between 30,250 and 12,400 years before present (BP), the conditions were favorable for the accumulation of OM; between 12,400 and 7900 years BP, erosive processes caused sand deposition in the depression. Favorable conditions for deposition of OM resumed around 7900 years BP and lasted until about 3300 years BP. Over the past 2600 years the climate has been similar to the present, with three brief periods favorable to OM deposition. (C) 2016 Elsevier B.V. All rights reserved. (AU)