Abstract
This study aims to determine the atomic ratio of O/C in an archaeological black earth (ABE) profile of the Ilha de Terra site, a region of Caxiuana in the Para State, Brazil, to determine the types of pyrogenic carbon (PyC) particles and to infer the source of biomass and burning temperature necessary to produce the PyC. The O/C ratios were monitored using scanning electron microscopy combined with energy dispersive spectroscopy (SEM/EDS). The results indicated atomic ratios for clay, silt and fine sand fractions that were between those registered for the PyC particles types: condensed combustion (CC) (0.09, 0.1, 0.13), charcoal (0.32, 0.31, 0.34) and char (0.43, 0.45, 0.52). CC is the predominant type of particle found because of the high firing temperature (> 350 °C), which is consistent with the probable biomass sources of wood, cellulose and lignin.
Highlights
Pyrogenic carbon (PyC) is the term widely used for highly condensed carbonaceous material originating from the incomplete combustion of fossil fuels and biomass,[1,2] and it includes a wide variety of fire-derived polymeric, aromatic and graphitic carbon forms, such as char, charcoal, soot and graphite.[3]
According to the O/C ratios obtained for the samples fractionated from the archaeological black earth (ABE) profile (Table 11), we suggest that the biomass sources of pyrogenic carbon (PyC) in this study were equivalent to those considered for the condensates of combustion, such as coniferous wood and charcoal, which are usually produced from the burning of lignin, cellulose and wood
Micromorphological observations and monitoring of the O/C atomic ratios in fractionated samples of archaeological black earth (ABE) profiles from the Ilha de Terra site in the Caxiuanã Region showed the presence of pyrogenic carbon (PyC) particles with the following characteristics: A significant decrease was found in the possible forms of PyC from horizons of the ABE profile, which occur in the following order: A1 > A2 > A3 > AB
Summary
Pyrogenic carbon (PyC) is the term widely used for highly condensed carbonaceous material originating from the incomplete combustion of fossil fuels and biomass,[1,2] and it includes a wide variety of fire-derived polymeric, aromatic and graphitic carbon forms, such as char, charcoal, soot and graphite.[3] Other terms used to describe PyC are black carbon, elemental carbon or carbon plant.[4] PyC is an important component of natural organic matter,[5,6] which is intimately tied to carbon and global oxygen cycles,[7] and may play a significant role in global climate change[8] because it is highly resistance to a range of chemical oxidants.[6]. There is not a dividing point between the different physical and chemical properties of the PyC or a boundary between different combustion by products. Each material has a different definition based on different areas of studies and technical recognition.[9]
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