Evolution from early diagenesis to metamorphism ofpedogenetic nodules of the Urbion group (Early Cretaceous). Cameros basin. La Rioja. Northern Spain

Pedogenetic carbonate nodules are a common feature in most of the depositional sequences of the Late Jurassic-Early Cretaceous Cameros Basin. This study deals with postsedimentary history (from early diagenesis to metamorphism) of nodules that appear in the Early Cretaceous (Barremian) host grey lutites of Urbion Croup at Valdeperillo where a pyrite hydrothermal mineralization was developed. Some of them are micritic nodules which are microseptarized. Inside this septaria is possible to recognize calcite cements from early to burial diagenesis. Inside the micritic matrix of these nodules, and replacing it, phyllosilicates as chlorites and muscovites are also recognized. These phyllosilicates would have precipitated during hydrothermal metamorphism that affected the area. The other type correspond to replaced nodules which do not conserve their original texture. In these nodules phyllosilicates (chlorites and muscovites) precipitated during the hydrothermal metamorphism. Afterwards a series of calcite cements precipitate also during and after the hydrothermal episod