Stratotype for the Mérida Glaciation at Pueblo Llano in the northern Venezuelan Andes |
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| Authors: | W C Mahaney M W Milner J Voros V Kalm G Hütt M Bezada R G V Hancock S Aufreiter |
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| Institution: | a Geomorphology and Pedology Laboratory, Atkinson College, York University, 4700 Keele St., North York, Toronto, Ont., Canada M3J 1P3;b Institute of Geology, Tartu University, Estonia;c Institute of Geology, Tallinn Technical University, Tallinn, Estonia;d Department of Earth Sciences, Universidad Pedagogica Experimental Libertador, Caracas, Venezuela;e Department of Chemistry and Chemical Engineering, Royal Military College, Kingston, Ont., Canada, K7K 7B4;f Department of Chemical Engineering, University of Toronto, Toronto, Ont., Canada |
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| Abstract: | The Mérida Glaciation (cf. Wisconsinan, Weichselian) as proposed by Schubert (1974b) culminated at about 18 ka during the last glacial maximum (LGM) and ended at about 13 ka as indicated by 14C dating and correlation with the Cordillera Oriental of Colombia. Moraines of an early stade of Mérida Glaciation reached to 2800 m a.s.l. and were largely overrun or eradicated by the maximum Wisconsinan advance (LGM); where they outcrop, the older moraines are characterized by eroded, weathered glacial diamictons and outwash fans.At Pueblo Llano in the central Mérida Andes (Cordillera de Trujillo), older to younger beds of contorted glacitectonized diamict, overlying beds of bouldery till and indurated outwash, all belong to the early Mérida stade. Overlying the early Mérida stade, deposits of rhythmically bedded glaciolacustrine sediments are in turn overlain with contorted sand and silt beds capped with outwash. Above the outwash terrace a loop moraine of LGM age completely encircles the margins of the basin. A stream cut exposed by catastrophic (tectonic or surge?) release of meltwater displays a lithostratigraphic succession that is bereft of organic material for radiocarbon dating. Five optically-stimulated luminescence (OSL) dates place the maximum age of the lowest till at 81 ka.Particle size distributions allow clear distinctions between major lithic units. Heavy mineral analysis of the middle and lower coarse units in the section provide information on sediment sourcing and on major lithostratigraphic divisions. Trace element concentrations provide information on the relative homogeneity of the deposits. The HREE (heavy rare earth element) concentrations allow discrimination of the lower till from the rest of the section; the LREE (light rare earth element) concentrations highlight differences between the lower till, LGM till, and the rest of the section. |
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| Keywords: | Mé rida Glaciation Last Glacial Maximum Till inclusion Mineral microtextures Ree geochemistry Heavy minerals OSL dates |
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