Lithofacies characterization of fluvial sandstones from outcropudgamma-ray logs (Loranca Basin, Spain): the influence of provenance

摘要

Natural gamma spectral (NGS) log motifs and cluster analysis wereudused to characterize outcropping sandstone bodies formed in braided and highsinuosityudstreams of the Tertiary Tórtola fluvial system of the Loranca Basin (Spain).udFive coarse-grained lithofacies comprise these deposits and determine distinct NGSudlog motif. Cross-plots and cluster analysis of NGS log data of the lithofacies suggestudthree distinct clusters. These clusters reflect distinct values for sandstones with smalludsets of ripple lamination, cross-stratification, and conglomerates and pebbles.udRipple-laminated sandstones show the most variability in NGS signature, whereasudconglomeratic sandstones show the most uniform signature. Such cluster analysisudmay be used to assign NGS log data points of unknown origin to a specific fluvialudlithofacies under conditions of equal rock provenance and diagenetic history. Audsedimentaclastic (i.e. sedimentary parent rock) origin of sediments appears to be theudmain control on detrital composition that, in turn, varies with grain size.