Mineralogía magnética como indicador de sequía en los sedimentos lacustres de los últimos ca. 2,600 años de Santa María del Oro, occidente de México

Combined magnetic mineral, organic and inorganic carbon content and geochemical analysis were conducted on laminated sediments from Santa Maria del Oro, a crater lake in Nayarit (western Mexico), to build up a model of the palcoenvironmental conditions for the last 2,600years. This sequence is of particular importance as it constitutes a high resolution record of late Holocene climatic and environmental change in west-central Mexico. The analyses attainied in this study allowed to recognize abrupt changes, to identify dry periods, and to compare these variations with available records in central Mexico. Laminations are caused in general by alternations of their main components: lithogenic detritus, biogenic and authigenic carbonates, and amorphous material from biological and volcanic remains. The volcaniclastic accumulations include two tephras, one of them, the Toba Jala, produced by the Ceboruco volcano. Six facies of sill, sand and peat were recognized. Horizons characterized by high inorganic carbon content, authigenic siderite, and the dissolution of the finest ferrimagnetic mineralogy (magnetite) in reductive conditions, are upward followed by an increase in the concentrations of fine grained ferrimagnetic minerals. This sequence represents dissolution-precipitation cycles of magnetic minerals by anoxic/oxic variations in the water-sediment interface during warmer and dryer periods. These environmental conditions are especially present around 600-1140 A.D., and 1410-1830 A.D., which coincide with the archeological Classic period (300-900 A.D.) drought, the Little Ice Age (1350-1800 A.D.) and the droughts of the last 700 years. The effects of climatic variations such as the drought occurred in the archeological Classic period, the Medieval Warm, Period, the Litte Ice Age, and the droughts over the last 700 years, have been documented in sites along central Mexico.