Reconstruction of the pre-Merida glaciation, northwestern Venezuelan Andes

Abstract

Valley glaciers have been well studied in the northwestern Venezuelan Andes over the last 20-year period but most reconstructions have been limited to the Last Glacial Maximum (LGM). Analyses have been confined to the mapping of moraine positions and the detailed analysis of pedostratigraphic sequences reaching back through the Middle to the Early Wisconsinan (Weichselian) Glaciation. Using bedding macrofeatures, fabric analysis (magnetic azimuths) with mirror images, clast inclination and microtextural evidence much has been learned about the lithology, source of ice, growth of an ice cap in the eastern cordillera and weathered state of surface paleosols. Analysis of two sections of pre-Mérida age, the only two such sections known in the Sierra de Santa Domingo (eastern cordillera), provides new information on lithology, source of the ice and weathered state of sediment of pre-Mérida age. The fabric in these sections is used to deduce the build-up of valley ice in the lower El Caballo Valley from an ice cap similar to one that developed later in Early Mérida time (~ 90 ka to ~ 65 ka). The presence of weathered tills in both sections suggests two glaciations perhaps correlative with the Illinoian and Kansan glaciations of North America. The weathered state of tills and outwash in both sections is assessed on the basis of geochemical (INAA) and mineral composition (XRD) and microtextural evidence determined by SEM/EDS.