Structure and sedimentology of the upper carboniferous of the upper Pisuerga Valleys, Cantabrian Mountains, Spain

The results of an investigation of the structure and sedimentology of Upper Westphalian and Lower Stephanian strata in the eastern end of the Cantabrian palaeozoic core (NW Spain), are presented. The sediments, shales, sandstones, limestones and coal seams occur in three main associations: the orthoquartzite-carbonate, the turbidite and paralic associations. Two facies are dstinguished: a western, without turbidites, with relatively many coal seams and an eastern, with turbidites and a few coal seams. Some evidence for a zone of less subsidence is present. This zone separates the two facies. The western and eastern facies are represented by the rocks in the Sierra Corisa and Redondo synclines respectively. Between the two synclines occurs a zone of long stretched narrow folds, often upthrusted to the west. Fold axes generally plunge SSE. Some of the structural features are explained by disharmonic folding and extrusion tectonics. In the eastern facies a formation occurs, which consists of graded sandstones alternating with mudstones. Thickness measurements of the individual sandstone and mudstone beds are analysed with non-parametric statistical methods. Several regularities in the succession of lithological types or thicknesses are revealed. Correlations between thickness or position of variates (i. e. sandstone, mudstone, sideritic concretion) are tentatively explained in the light of the turbidity current hypothesis. Especially the successive sandstone thicknesses show an interdependence expressed in “fluctuations”. Sandstone-mudstone thickness-correlation leads to the assumption of a very high mud content of the turbidity current in these cases, and considerable erosion by successive currents. Sedimentary structures, especially those of the turbidite association, are described in detail. A short annotated bibliography on sole markings is given. The palaeocurrent directions measured from sole markings and cross-bedding are discussed. The sequence of sole-marking-directions on successive turbidite layers indicates interdependence of these dirctions, which could also mean the interdependence of the depositing currents. A litho-stratigraphic map, three structural sections and twelve stratigraphic sections are given.