52 000 years of environmental history in Zacapu basin, Michoacan, Mexico: the magnetic record

Mineral magnetic and total organic carbon (TOC) measurements were performed on a 10.9 m long core from Zacapu basin, central Mexico. The sequence, dated by AMS C-14, spans the last ca. 52 kyr. Curie temperature measurements, low-temperature susceptibility and low-temperature remanence indicate that the magnetic fraction is characterized by oxidized titanomagnetites with variable Ti content. Low S-300 ratios reflect the existence of high-coercivity iron oxide phases. These characteristics are considered to reflect the presence of goethite rather than hematite, formed in relatively wet, organic conditions, where soil-forming processes were intense. Comparison between magnetic and TOC results suggests that the sediments record relatively humid conditions before 35 kyr BP, and a later trend towards drier conditions. A probable hiatus is recorded before 25 kyr, and relatively dry conditions after this time that persisted throughout the Late Glacial Maximum and Mid Holocene, at 4.8 kyr. These results contrast with previous observations of deep lake phases in the neighboring Lake Patzcuaro, considered to be result of increased precipitation between 34 and 21 kyr BP. (C) 2002 Elsevier Science B.V. All rights reserved.