Examinando por Autor "Velez, Maria I."

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    Palynofacies analysis of the late Holocene San Nicolás terrace of the Cauca paleolake and paleohydrology of northern South America
    (ELSEVIER SCIENCE BV, 2011-01-01) Garcia, Yuri C.; Ignacio Martinez, J.; Velez, Maria I.; Yokoyama, Yusuke; Battarbee, Richard W.; Suter, Fiore D.; Universidad EAFIT. Departamento de Geología; Ciencias del Mar
    The detailed palynofacies analysis of the late Holocene laminated succession of the San Nicolás terrace in the middle Cauca Valley, northern Colombia, is interpreted as the product of sedimentation in a lacustrine to fluvial dominated setting. Radiocarbon analyses reveal that the succession was deposited between ~. 3500 and a few hundreds of years with sedimentary rates in excess of ~. 600. cm/ka. The milimetric laminae and the high frequency fluctuations in the content of the palynodebris of terrestrial origin, i.e., the high altered ligno-cellulosic debris/amorphous organic matter ratio, together with diatoms typical of fluvial conditions, such as Aulacoseira granulata do suggest an intermittent and continuous hydrological and biological connectivity with the Cauca River, akin to a varzea lacustrine environment. Drier to wetter conditions appear to occur, moving upward in the succession. This might reflect regional precipitation conditions all along the Cauca Valley and the southern migration of the intertropical convergence zone. © 2010 Elsevier B.V.
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    The San Nicolás succession of the Cauca paleolake: A late Holocene laminated ria lake record from the Neotropics
    (SPRINGER, 2013-02-01) Ignacio Martinez, J.; Mayr, Christoph; Yokoyama, Yusuke; Velez, Maria I.; Battarbee, Richard W.; Universidad EAFIT. Departamento de Geología; Ciencias del Mar
    The stratigraphic, geochemical, and organic matter study of the late Holocene San Nicolás succession of the Cauca paleolake (Santa Fé-Sopetrán pull-apart basin) in the middle Cauca Valley, northern Colombia, suggests that it was deposited in a ria lake environment, at sedimentary accumulation rates in excess of 600 cm ky-1 between ~3500 and ~500 yr BP. Laminated deposition occurred, first under igapo (black-water), and then under varzea (white-water) conditions. The transition occurred ca. 3000 yr BP, a time of major change in El Niño/Southern Oscillation (ENSO) behavior in the Cariaco Basin, thus reflecting the southern migration of the intertropical convergence zone and intensified rain upstream the Cauca Valley. A second, but less conspicuous change occurred ca. 2000 yr BP, which apparently corresponds to the intensified and/or more frequent ENSO activity in the Galapagos Islands. Our contribution describes, for the first time, a ria lake sedimentary succession from the northern Andes and demonstrates the high potential of these hitherto undervalued deposits for the reconstruction of the paleohydrological history of the northern Andes. © 2012 Springer Science+Business Media Dordrecht.