Estudio diagenético y sedimentológico preliminar de biohermos de algas filoides y esponjas (?) en la Caliza de la Cervatina (Pensilvaniense, sector PiedrafitaLillo, Cuenca Carbonífera Central, Zona Cantábrica, NO de España

Résumé

The aim of this work is to study the depositional and diagenetic history of some small (a few meters high and several meters wide) phylloid algal and sponge (?) bioherms, developed in a Pennsylvanian carbonate ramp (the Cervatina Limestone, Cantabrian Zone, NW Spain). The mound cores are composed of micritic boundstones with abundant early diagenetic isopachous crusts of bladed cements and of radiaxial-fibrous calcite (up to 60%), which were mostly developed in shelter porosities. Other porosities that also occur are biomoldic, interparticle and vug. On the basis of their depositional geometry and textural relationships, it is inferred that the bioherms developed a rigid framework with topographic relief above the sea floor. The Cervatina Limestone shows a complex sedimentary and diagenetic history. Cathodoluminescence microscopy has revealed several different cementation stages of the primary and secondary porosity and the following general sequence has been identified: dull bright dull non-luminescent dull. The main stages of secondary porosity development and of formation of isopachous crusts occurred during early diagenesis, whereas during subsequent diagenesis precipitation of coarse blocky spar cements took place filling the central parts of the voids.