Rock-magnetic study of Late Pleistocene-Holocene sediments from the Babícora lacustrine basin, Chihuahua, northern Mexico

Abstract

Rock-magnetic and sedimentological studies of the Quaternary sequence of lake Babícora (29.4oN, 107.7oW; 2,100 m a.s.l.) from Late Wisconsin to Holoccne are reportcd. Two vertical profiles have been studied. Magnetic susceptibilities and natural remanence (NRM) and isotherrnal remanence (IRM) intensities correlate with sand, silt and clay contents in the sedimcnts, suggesting that magnetic minerals are allogenic. IRM acquisition curves and altcrnating field coercivity spectra document the occurrence of Ti-poor titanomagnetites, hematites and iron-hydroxides. The fluctuations in the input of sedi- ment correlate with changes in erosiona! processcs, climate and tectonics in the catchment basin. Five radiocarbon dates ranging from 4,346 to 16,343 yr B.P. wcre obtained. The southern profile covers a longer time span than the western pro- file, which spans from 11,000 to 6,000 yr B.P., when the lake extended overa larger area. Two major periods of increased rainfall and high lake levels in Late Pleistocene and Early Holocene are recognized. The Late Wisconsin wet period was fol- lowed by gradual drying up to around 6,000 yr B.P. Between 11,000 and 8,000 yr B.P. there was another wet period, related to increased summer rainfall. The dry period between 3,000 and 2,000 yr B.P. was followed by widespread erosion.