Rock magnetism for the last 45,000 yr in Chalco lacustrine sediments, central Mexico

The Chalco lake is part of the basin of Mexico, a high altitude tropical site that had an extensive lake system, sensitive to climatic fluctuations during the past times. Rock magnetism analyses were performed in the lacustrine sequence recovered in two cores up to 26 m depth in Chalco sub-basin (19°15' N, 98°59' W, 2,250 m asl). This lacustrine sequence spans the last ca. 40,500 yr, according to >20 14C dates and tephrachronology. Rock magnetism analyses will allow understanding the link between detrital input, biogenic productivity and diagenesis; and in turn these will allow us to establish the link between magnetic mineralogy and paleoclimate, and to validate the paleomagnetic variations recorded in Chalco sediments. Rock magnetism parameters characterize the magnetic components in terms of mineralogy, grain size distribution and concentration. The analyses include identification of magnetic mineral phases by Curie temperatures and FORC analyses, and measurement of magnetic susceptibility, NRM, ARM, IRM, hysteresis parameters Ms, Mr, Hc, Hcr; and the ratios S300 and HIRM300. In the active volcanic geological setting of Chalco sediments, most of primary magnetic minerals are Ti-magnetites/maghemites of detrital origin, with subordinate (Ti)-hematite. The preliminary results show a correspondence between rock magnetism parameters with the sedimentary facies.