ABSTRACT
Several studies have shown that the rare earth elements undergo significant fractionation during weathering the parent rock (Nesbitt 1979; Duddy 1980; HalTis 1985). Since Inost studies ofprovenance of sedimentary rocks rely on the assumption that the cOlnposition of these rocks reflect the average COlnposition oftheir source Inaterial, (Taylor & McLennan 1985; McLennan 1989) fractionation during weathering may affect the chemistry of sedimentary material and may lead to erroneous provenance interpretations. There has been some controversy regarding the chemical changes that take place in black shales during early diagenesis. For example, Chaudhuri & Cullers (1979), working on sediment cores from the Gulf coast of the US, suggested that no significant changes in the relative abundance of REEs occurred that could be ascribed to early diagenetic reactions. Hannigan & Basu (1998) suggested that significant fractionation/redistribution of the REE, especially the light REE (LREE; La - Nd) does take place during dissolution and precipitation of diagenetic Ininerals. Processes such as incorporation ofREE into diagenetic minerals or migration within pore fluids have been proposed as processes that fractionate the REE in black shales (Nesbitt 1979; Lev et al. 1999).
1.2 Geologic setting
