HR: 1400h
AN: PP43C-13    [Abstracts]
TI: Palaeoenvironmental Fluctuations Identified by Diatoms, Ostracode, Geochemistry and Sedimentary Facies from a Tropical Crater Lake on Western Mexico
AU: * Caballero, M
EM: maga@geofisica.unam.mx
AF: Instituto de Geofísica, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria, Del. Coyoacán, Mexico, DF 04510, Mexico
AU: Rodriguez, A
EM: alerdz@servidor.unam.mx
AF: Posgrado en Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria, Del. Coyoacán, Mexico, DF 04510, Mexico
AU: Vazquez, G
EM: gvazquez@geofisica.unam.mx
AF: Posgrado en Ciencias de la Tierra, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria, Del. Coyoacán, Mexico, DF 04510, Mexico
AU: Ortega, B
EM: bortega@geofisica.unam.mx
AF: Instituto de Geofísica, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria, Del. Coyoacán, Mexico, DF 04510, Mexico
AU: Lozano, M
EM: mslozano@servidor.unam.mx
AF: Instituto de Geología, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria, Del. Coyoacán, Mexico, DF 04510, Mexico
AU: Vilaclara, G
EM: amatrin@servidor.unam.mx
AF: FES Iztacala, Universdiad Nacional Autónoma de México, Avenida de los Barrios, S/N, Los Reyes Iztacala, Tlalnepantla, Mex 54090, Mexico
AB: A ca. 2500 cal. yr record from Santa Maria del Oro (SMO) was studied for its diatoms, ostracodes, magnetic mineralogy, geochemestry, organic matter and carbonate content to document climatic and limnological trends over western Mexico, a site sensitive to the intensity of monsoon circulation and to any latitudinal shifts of the high pressure subtropical cells as it is currently located on a transition zone between the temperate climates of central Mexico highlands and the arid climates of northern Mexico. The sediment sequence (8.8 m) has a chronology is based on 7 AMS dates. The sequence shows an irregular sequence of four distinctive facies (laminations). Data derived from the analysis of easch facies and of modern sediments supports the interpretation that sand and peaty layers are mostly alloctonous in origin while the silty layers (ochre, brown and greenish silt) are mostly autigenic. Ochre layers represent times of anoxic bottom lake conditions favoured by a warmer environment. Long term trends are also present along the sequence. Warm and relatively humid conditions change to a drier climate by ca. AD 600, with the driest and warmest stage recorded at AD 990. This dry period is consistent with records of arid phases at other sites in Mesoamerica. From AD 990 to AD 1260 there is evidence of a sudden transition to warm-humid conditions and dilution of lake water coeval with the Medieval Warm Period. From AD 1260 to AD 1480 climatic conditions were unstable and afterwards the onset of drier climates is recorded until the present. Due to its geographical position, moisture availability fluctuations are responding to atmospheric circulation changes such as latitudinal shifts of the Intertropical Convergence Zone and Subtropical High- Pressure Cells resulting in the strengthening or weakening of the summer monsoon, which is the main moisture source for western Mexico. This sequence records environmental and climatic variability for western central Mexico and extends the geographical range of paleoclimatic records for this latitude in North America.
DE: 4942 Limnology (0458, 1845, 4239)
DE: 4944 Micropaleontology (0459, 3030)
DE: 4950 Paleoecology
DE: 4952 Palynology
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Joint Assembly