| Resumo: |
In the southern flank of the Cantabrian Mountains, northwestern Spain, a sequence of Upper Carboniferous sediments is exposed in a synclinal structure, probably coinciding with the original basin, near the villages of Prioro and Tejerina. By means of palaeontological dating with several fossil groups (e.g. fusulinids, brachiopods, calcareous algae and land plants) the lower sequence of these sediments could be dated as Westphalian B/C to lower or middle Westphalian D (Yuso Group). After a relatively short time interval follows a sequence with an uppermost Westphalian D to lower Cantabrian age (Cea Group). These two groups are separated by an angular unconformity. These sediments together represent a regressive sequence, starting with a turbidite facies and gradually passing into a shallow marine facies at the top of the Yuso Group. The Cea Group is possibly fully continental, except for a few metres of shallow marine sediments in the middle part. Facies interpretations were made by investigation of the fossil content and the sedimentary structures. Rapid lateral facies changes could be traced from 15 stratigraphic sections through the best exposed parts. Six of these sections were sampled in detail to enable a petrographic investigation to be made. This resulted in the possibility of drawing conclusions on the lateral and vertical facies changes by means of grain-size distribution, micro-fossil content and, especially, the modal distribution of matrix-sized (<25 microns) material. From these data, together with field observations, the palaeogeography could be reconstructed: a deltaic complex, emerging from the northern border and supplying much material from the N, prograded into an E-W trending basin. In the deeper parts this material was transported to the E along the basinal axis. The prograding of the delta caused a gradual shallowing of the basin, which, finally, resulted in fluvial sedimentation with coal layers.
|
