Organic geochemical evidence of postglacial paleoenvironmental evolution of the Comeya peatland (Asturias, N Spain)

摘要

Comeya peatland is located in Picos de Europa National Park (N. Spain) at 851 m above sea level, representing the continuous postglacial infill of a hollow (growth rate = 0.4 mm/yr) during the last 15,000 cal. yr BP. Three intervals can be distinguished in the profile: the bottom one, with ash content close to 90, which is previous to the peatland installation in the area and is followed by an interval with oscillating ash content (30-60) probably related to alluvial fan sedimentation. The uppermost one corresponds to the peat deposit with ash content generally close to 10. The present day vegetation consists of Sphagnum species with herbaceous plants and heathers. The study comprises the analysis of some biomarkers with potential as palaeoenvironmental proxies quantified by gas chromatography/mass spectrometry, supported by bulk delta C-13 and delta N-15 isotopic. The biomarker assemblage is dominated by the n-alkanes and methyl-ketones with medium-to-high molecular weight and odd number of carbons. The biomarker ratios indicate an enrichment in Sphagnum characteristic compounds at 120-250 cm (3150-6350 cal. yr BP) reflecting more humid conditions. This episode coincides with higher C/N atomic ratio, higher values of delta C-13 and lower of delta N-15. The wetter conditions of this interval are also shown by the depleted 8D values of the n-alkane, particularly those related with mosses as (n-C-23 and n-C-25) and the enriched delta C-13 values of both n-alkanes and methyl-ketones.