Extensive transformation of organic matter and excellent lipid preservation at the upper, superhumid Guandera páramo

The volcanic ash soils in the Guandera region in northern Ecuador exhibit a typical accumulation of organic matter. However, while accumulated, the organic matter present in the mineral soil bears hardly any resemblance with the covering vegetation and its litter. A strong degradation of the ligno–cellulose complex and a large accumulation of aliphatic components were the main characteristics. The accumulation of aliphatic moieties coincided with an excellent preservation of the solvent extractable n-alkanes and n-alcohols as evidenced by large carbon preference indexes (CPIs) and, consequently, a typical plant-derived signature. Although well-preserved, the n-alkanes underwent β-oxidation yielding n-methyl ketones in a somewhat different distribution. The differences observed between n-alkanes and n-methyl ketones were attributed to a relatively more rapid oxidation of alkanes derived from the grass Calamagrostis effusa as compared to the more woody roots of Neurolepis aristata. From top to bottom of the profile, and therefore with time, all lipid signals had rather similar compositions with limited (microbial) degradation implying their significant value as potential biomarkers.