. Bulletin of the Natural Histort Museum. Geology series. PALYNOLOGICAL ZONATION OF MID-PALAEOZOIC, NW SPAIN. Pnull'. and ThruM ^^^ Oiictrop ol ihc San Pnlro R)raiiiln ^^^^^1 Mcso/nic / Tcnair^- Fig. 1 Simplified geology of the Cantabrian Region, NW Spain (based on Rodriguez, 1983). San Pedro Formation This formation was described in two main areas: a. the 'Ferruginous Sandstones of Furada' (Barrois, 1882) on the northern flank of the Cantabrian Mountains, and b, the San Pedro Formation (Comte, 1937) in the south. These two names refer to the Upper Silurian Formations of the 'Folds and Nappes
. Bulletin of the Natural Histort Museum. Geology series. PALYNOLOGICAL ZONATION OF MID-PALAEOZOIC, NW SPAIN. Pnull'. and ThruM ^^^ Oiictrop ol ihc San Pnlro R)raiiiln ^^^^^1 Mcso/nic / Tcnair^- Fig. 1 Simplified geology of the Cantabrian Region, NW Spain (based on Rodriguez, 1983). San Pedro Formation This formation was described in two main areas: a. the 'Ferruginous Sandstones of Furada' (Barrois, 1882) on the northern flank of the Cantabrian Mountains, and b, the San Pedro Formation (Comte, 1937) in the south. These two names refer to the Upper Silurian Formations of the 'Folds and Nappes Unit' of the Cantabrian Zone. Three of our sections were originally designated as the San Pedro Formation (Geras de Gordon, La Vid de Gordon and Argovejo). The fourth section was included in the Furada Formation (La Peral). As both formations constitute a single lithostratigraphic unit they are all referred to in the text as San Pedro Formation. The San Pedro Formation is predominantly sandy and overlies the Formigoso Formation; the latter is Silurian in age. The Formigoso Formation is composed of black shales, with alternating shales and quartzites in the upper part. The San Pedro Formation appears to be in stratigraphical continuity with the underlying Formigoso Forma- tion in the sections near the Precambrian of the 'Narcea Anticlinorium', but the contact is sharp and erosive in the sections situated farther east. Informally three members can be distinguished in this formation. The Lower Member consists mainly of red ferruginous, coarse- grained sandstones, sometimes with oolites, having cross-trough stratification. At some localities there are conglomeratic beds, with phosphatic, sideritic and silty clasts and intraclasts; some of these clasts have a volcanic origin (Van den Bosch 1969; Suarez deCenti. 1988). The Middle Member is composed of medium to fine grained sandstones with current and wave ripples, and grey to green intensively bioturbated mudstones and siltstones. T
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