Factores que controlan la evolución de los parámetros cristaloquímicos y asociaciones minerales en las rocas sedimentarias del Grupo Enciso (Cretácico inferior). Cuenca de Cameros, La Rioja (norte de España)

Résumé

Sedimentary rocks from Enciso Group belong to the Depositional Sequence 5 (upper Barrernian - lower Aptian) of the Cameros Basin. The basin has a thick sedimentary pile of continental materials (up to 9000 m) and the eastern sector of the Basin was affected by a hydrothermal metamorphic event. These materials were deposited in a low energy and low gradient lacustrine depositional system, and are mainly made up by an alternance of lutites, marlstones, limestones and sandstones. The bulk mineralogy of the pelitic sediments is formed by phyllosilicates, carbonates (calcite and dolomite), quartz and feldspar. The clay mineralogy is mainly formed by illite and chlorite in all the range of studied conditions. Occasionally small amounts of kaolinte, smectite, pyrophyllite and different types of mixed layered minerals are found. A decrease in the metamorphic conditions from the depocentral to the marginal areas of the basin is observed, although for a given profile, no vertical trend in the crystalchemical parameters used to estimate the metamorphic conditions is observed. This is due to factors such as bulk chemical composition and permeability, which limit the fluid flow during metamorphism, and exert an important control in the metamorphism. Therefore, the effect of the hydrothermal metamorphism would be superimposed to the deep burial diagenesis that affected these sediments.