Throughout geological history, organic-rich shales show systematic enrichment in uranium compared to other crustal rocks. Uranium concentrations vary significantly ( 500ppm) among these shales in both time and space, as a result of global changes in the chemistry of the atmosphere and oceans through geological time, as well as local physical and chemical conditions of sedimentation and diagenetic processes. This experiment will be the first to use high resolution XANES spectroscopy to characterize U speciation in marine sediments. The aim of the study is to check the hypothesis that sorption rather than simple reduction might control the primary correlation between organic carbon content and U in shales.