Palaeobiogeographic context in the development of shallow-water late Viséan-early Bashkirian benthic foraminifers and calcareous algae in the Cantabrian Mountains (Spain)

Abstract

The late Viséan to early Bashkirian shallow-water carbonate Valdediezma Platform in the Picos de Europa Province of the Cantabrian Zone, has been subdivided into eight microbiotic intervals by means of similarity clusters (using the Morisita coefficient). The most complete Viséan-Bashkirian interval is represented in the Valdediezma Valley – Jitu l'Escarandi –road to Tresviso, where only the Steshevian to lower part of the Protvian (middle Serpukhovian) is missing. This interval is better represented in the Pompedrei Bridge to La Hermida composite section, and also in the deeper water section at Vegas de Sotres. These intervals contain a succession from the Mikhailovian (upper Viséan) up to the Krasnopolyanian (lower Bashkirian).

The assemblages of the Valdediezma Limestone show, comparatively, low similarity indices with the neighbouring basins in the collisional front in the western extremity of the Palaeotethys during the progression of the Variscan Orogeny. In this mobile belt, two domains are recognized; a western domain composed of outcrops in south-western Spain and in the Moroccan Meseta, and an eastern domain comprising basins located in southern France. Some basins, such as the Betic Cordillera, initially had more influence from the western domain, but later, during the late Serpukhovian, it is considered as being part of the eastern domain. The Valdediezma Platform foraminiferal and algal content is coincident with its location as an isolated platform, surrounded by deep-water seas, and with higher similarities with the eastern domain.

Regional tectonic events are recognized from the late Viséan onward, and they are mostly masked by the overprint of latest Pennsylvanian events. Facies changes are commonly observed, particularly at the base of the intervals, suggesting that facies control is the most important factor controlling the assemblages. It is considered that eustatic sea-level changes exerted a certain control on the assemblages.