Strong magnetic levels in Lake Chapala sediments (western Mexico) : their mineralogy and stratigraphic significance

Autor: François Fernex, François Michaud, Pedro F. Zárate del Valle, Hermes U. Ramírez-Sánchez, G. Barci-Funel, Claude Parron
Přispěvatelé: Géoazur (GEOAZUR 6526), Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)
Rok vydání: 2006
Předmět:
Zdroj: Journal of Paleolimnology
Journal of Paleolimnology, Springer Verlag, 2006, 35 (4), pp.819-836. ⟨10.1007/s10933-005-5971-7⟩
Journal of Paleolimnology, 2006, 35 (4), pp.819-836. ⟨10.1007/s10933-005-5971-7⟩
ISSN: 0921-2728
1573-0417
DOI: 10.1007/s10933-005-5971-7⟩
Popis: Lake Chapala, located 120 km northeast of Colima Volcano, lies at the north and northeast of the Citala rift in the Trans-Mexican Volcanic Belt. It belongs to the watershed of the Lerma River, which originates from the Mexico City area, 450 km to the east. Sediment cores, 0.5-2 m long, were collected from the lake. Magnetic susceptibility of the lake sediments generally ranges from 400 to 800 x 10(-9) m(3) kg(-1); but in some layers it exceeds 1000 or 1500 x 10(-9) m(3) kg(-1). The magnetic susceptibility vertical profiles display a thin peak (2-5 cm) or a double peak with magnetic susceptibility > 2000 x 10(-9) m(3) kg(-1). Scanning electron microscope analysis shows that the main mineral responsible for the magnetic susceptibility is titano-magnetite, which is relatively abundant in the magnetic layers. In most of the cores, the layer with magnetic susceptibility > 2000 x 10(-9) m(3) kg(-1) is coarser grained than the directly under and overlying sediments, which are composed of fine silt. But not all coarser levels are magnetic nor are all magnetic levels bound to coarser layers. The high titano-magnetic concentration probably originates from volcanic ash falls. Sedimentation rates, evaluated for several sites by means of the Pb-210 and Cs-137 methods, allow a date approximation (between 1535 and 1670) for the strong magnetic layer deposition. Since important eruptions of Colima Volcano, with ash fall, were reported from 1576 to 1623, the main peak of magnetic susceptibility in the sediment profiles is assumed to be related to these events. The main magnetic layer extends to greater depth in the profiles of the eastern part of the lake plain than at the west. It can, therefore, be suggested that a relative subsidence occurs in the eastern part of the lake; the axis of the eastern plain overlaps the area displaying the maximum subsidence rate and seems therefore to correspond to the prolongation of Citala rift.
Databáze: OpenAIRE
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