Some crystallochemical and petrographic criteria for determining source rocks and sedimentary processes. The example of Neogene deposits of the Alpujarran Corridor (Betic Cordillera, SE Spain)

Abstract

AbstractThe aim of this study was to determine the influence of the various source areas on the Neogene sediments of the Alpujarran Corridor, to ascertain the type and intensity of the sedimentary processes involved, and to establish some generally applicable criteria. At the bottom of the sections the detrital pebbles are derived from the highest nappes of the Alpujárride Complex, whereas those at the top are from the deepest unit of the Nevado-Filábride Complex (the Veleta nappe); between these the entire range of materials from the lower-Alpujárride Complex and the upper-Navado-Filábride Unit (the Mulhacén nappe) is represented. Comparison of the micas and chlorites in the pebbles with those in the conglomerate matrix reveals the effect of the sedimentary processes on every aspect of the crystallochemistry. The d001 of the chlorites and the b0 of the micas are scarcely affected and can be used to determine the source area. The crystallinity, the Fe content of the chlorites and the basal spacing and angular difference (Δ2θ M-P) of the white micas, on the other hand, are all modified, especially in the clay fraction, according to the degree and nature of the alteration of the sediments, and consequently can be used as a guide to the extent of this process.