HR: 0800h
AN: GP21B-01    [Abstracts]
TI: Late Holocene Sediment Study From Santa María del Oro Crater Lake, Nayarit, México, Using Environmental Magnetism
AU: * Vazquez, G
EM: gvazquez@geofisica.unam.mx
AF: Universidad Nacional Autonoma de Mexico, Posgrado en Ciencias de la Tierra. Cd. Universitaria, Mexico, D.F 04510, Mexico
AU: Ortega, B
EM: bortega@geofisica.unam.mx
AF: Universidad Nacional Autonoma de Mexico, Instituto de Geofisica. Cd. Universitaria, Mexico, D.F 04510, Mexico
AU: Rodriguez, A
EM: alerdz@geofisica.unam.mx
AF: Universidad Nacional Autonoma de Mexico, Posgrado en Ciencias del Mar y L. Cd. Universitaria, Mexico, D.F 04510, Mexico
AB: The lake is located near the Pacific coast of Mexico, at the western end of the Trans Mexican Volcanic Belt. It is a deep lake (ca. 65 m) with steep sides and only a small bay (Agua Caliente) has shallower water (ca. 12 m). Four parallel cores between 4 and 9 m long were recovered in March 2002 from this shallower area. Sediments are characterized by alternated laminations (few millimeters to 2 cm) of sand, brown silt, green silt, reddish silt, ochre silt, and peat. The 14-C dated sequence spans the last ca. 2,600 yrs. Given this age, it is possible that each set of laminations represent annual sedimentation cycles. The record is a potential high- resolution archive of environmental and climatic variability for western Mexico for late Holocene. Magnetic measurements of susceptibility along the cores show a high variability in the concentration of magnetic mineralogy. Different magnetic and non-magnetic properties show two sets of facies in relation to its magnetic mineralogy; one group composed by sand, brown silt, green silt and peat has the magnetite and Ti-magnetite as the principal magnetic phase; the second group, composed by reddish and ochre silt, has a low Ti magnetite component and siderite, as the principal paramagnetic component. The effects of climatic variations such as the drought occurred in the archeological Classic period (100 - 900 dC), the Medieval Warm Period (950 - 1350 dC), the Little Ice Age (1400 - 1800 dC), and the droughts over the last 700 years, documented in sites along central Mexico, are recognized in the magnetic mineralogy of Santa Maria del Oro.
DE: 1512 Environmental magnetism
DE: 3344 Paleoclimatology (0473, 4900)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Joint Assembly