Estudio preliminar de la diagénesis temprana en secuencias de alta frecuenciaejemplo de las Calizas de Piedrasluengas (Pensilvaniense, Zona Cantábrica, NW España)

Resumo

The aim of this preliminary study is to analyse the diagenetic model of high-frequency sequences (4th/5th order of likely glacio-eustatic origin) deposited in a Pennsylvanian carbonate ramp in a foreland basin (Piedrasluengas Limestones, Cantabrian Zone, NW Spain). Sequence boundaries are karstic surfaces, whereas the maximum flooding interval is composed of organic-rich black mudrocks with elevated contents of U (up to 8,96 ppm), suggesting rapid burial rates and anoxic conditions during the early diagenetic stages. During the transgression and most of the regression, the sediments were in the marine-phreatic diagenetic environment and pervasive marine cementation took place (non-luminescent fibrous, bladed and botryoidal cements), followed by burial non-luminescent scalenohedral calcites and dull spar. During sea-level falls, the top of the regressive system tract was subaerially exposed and marine pore waters were replaced by meteoric fluids in the complete cycle thickness. Dissolution, leaching, neomorphism of unstable phases, and cementation of dogtooth, drusy, sparry nonferroan calcite (non-luminescentbanded non-luminescent and brightdull) and ferroan calcite took place.