Sedimentología de las calizas de Piedrasluengas (carbonífero medio de la región del pisuerga-carrión, zona cantábrica)

Resumo

The Piedrasluengas Limestone is a carbonate unit, Kashirian-late Vereian in age (substage belong to stage Moscovian; serie Middle Carboniferous; subsystem Pennsylvanian; system Carboniferous) (Menning et al., 2006), which crops out in the NE limb of the Casavegas syncline of the Pisuerga Area (Pisuerga- Carrión Province, Cantabrian Zone). This work presents a stratigraphic and sedimentological study of the Piedrasluengas Limestone in the vicinity of its type area, between the localities of Camasobres and Piedrasluengas. In this area, the unit, which ranges from 200 to 300 m in thickness, gradationally overlies the marine siliciclastics of the Potes Group whereas its top is truncated by a major discontinuity, namely, the Palentian unconformity. In the study area, 15 lithofacies have been distinguished in the Piedrasluengas Limestone, which fits a carbonate-platform ramp model. In this model, inner ramp deposits comprise mainly ooidal, peloidal and skeletal grainstones, whereas wacke- and packstones with abundant beresellid algae and Chaetetes sponges account for the mid ramp and, finally, wacke- to packstones with abundant siliceous sponge spicules and micrite buildups represent the outer ramp. Facies vertical stacking patterns permit to individualize up to 12 transgressiveregressive cycles in the Piedrasluengas Limestone, which range between 5 and 50 m in thickness and are bound by subaerial exposure surfaces developed on subtidal facies. These sequences are interpreted as the record of high amplitude and high frequency (4th-5th order) cycles controlled by glacioeustatic sea-level changes, which were characteristic of the Carboniferous glacial periods (icehouse cycles).