2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 82-10
Presentation Time: 10:55 AM


LEIGH, David S.1, GRAGSON, Theodore L.2 and COUGHLAN, Michael R.2, (1)Department of Geography, The University of Georgia, Geog.-Geol. Building, 210 Field St., Room 204, Athens, GA 30602, (2)Department of Anthropology, The University of Georgia, Athens, GA 30602, dleigh@uga.edu

Little is known of erosional impacts on mountain soils resulting from late Neolithic to Bronze Age pastoral landscape transformation in the Pyrenees. A general chronology of pastoral activity is known from paleoenvironmental proxies in wetland bogs and archaeological sites (e.g. charcoal, pastoral pollen, fungal spores of sheep dung), but the magnitude and spatial dimensions of erosion and sediment yield remain vague. To address these knowledge gaps, we identified several toeslopes beneath ancient pastures containing stratigraphic records of slopewash continuously spanning the entire Holocene. Two to five meter auger holes were sampled in contiguous 5-10 cm intervals beneath zero-order hollows draining several hectares in the commune of Larrau, Pyrénées Atlantiques, France. Samples were processed for charcoal content, magnetic susceptibility, particle size, organic matter, and radiocarbon dating. Results indicate that intentional burning and clearing were initiated by the Late Neolithic (ca. 5000-6000 cal. BP), but more intense burning, extensive forest clearance, and pronounced erosion occurred later during the Bronze Age and Iron Age. Charcoal concentrations and low frequency magnetic susceptibility provide evidence of initial burning and subsequent intensification of fire use. Radiocarbon chronologies exhibit late Holocene order-of-magnitude spikes in sedimentation rates (1-10 mm/yr) that are asynchronous between some sites, which favors anthropic versus climatic drivers. Sedimentation rates, and presumably erosion rates, returned to very near pre-pastoral background levels (<1mm/yr) during the post-Roman era during the last 1500 years. Soil properties in present-day pastures indicate sustainable, and in many ways improved, soils that commonly exhibit better qualities than comparable hillslopes with very mature forests. Thus, a pristine-degraded-recovery cycle is revealed, illustrating not all pastures persist with stereotypical degraded soils.