Holocene aridification, vegetation change, sedimentation regime and limits of carbon isotope data as indicated by the alluvial pollen sites of Arroyo Grande and El Molino in North-Central Mexico

Abstract

A multi-proxy record of palynological, sedimentological, archaeological and carbon isotopic data of alluvial sites in the Upper Nazas basin (Arroyo Grande, Durango, 1855 m amsl) and the Parras basin (El Molino, Coahuila, 1245 m amsl) is introduced, describing environmental changes across a short grassland-desert ecotone from the eastern margins of the Sierra Madre Occidental (SMO). These sites reconstruct Holocene vegetation history in semi-arid North-Central Mexico and integrate fluvial geomorphology and palynology data. In particular, pollen data links a rise of xeric flora with higher-energy deposition and increased erosion in upland basins of the eastern SMO. According to archaeological finds at examined sites, human occupation is linked to mesic or afforested conditions. However, limitations of carbon isotope data for environmental historical reconstruction are indicated by somewhat stable values at Arroyo Grande, Durango especially, while pollen sites show a replacement of short-grasses and park woodlands by a more xeric flora at higher elevations, with a development of Chihuahuan Desert flora at low elevations (El Molino, Coahuila). Vegetation reconstructions are supported by pollen analog data collected from the Cuatro Cienegas region in Coahuila, Mexico.