The geology of the region to the southeast of Lugo (N.W. Spain)

The area described comprises the SE plunging extension of the anticlinorium of Mondoñedo-Lugo-Sarria and several structural units to the NE of it. The stratigraphy compares with that of neighbouring areas. Certain new observations have been made regarding the west flank of the East Galician-West Asturian miogeosyncline at the end of the Precambrium and during the Early Palaeozoic. Stromatolites or algae played an important part in the formation of carbonate deposits during late Precambrian (Cándana limestone) and Lower Cambrian time (Vegadeo limestone). An imprint, possibly attributable to a specimen belonging to the Precambrian Ediacara fauna, was found in the Cándana Schist Formation. A shallow or relatively high zone existed during that time in the region around Incio. The same general area formed a high again at the end of the Ordovician, causing erosion and a marked disconformity of the Silurian. The Hercynian structures can be explained by assuming roughly WSW-ENE compression and shortening. In the NW of the area this is expressed in the first place by the recumbent folds of the Lugo-Sarria anticlinorium, and in the SE by the narrowness of the steep folds and their slightly changed direction in the general area of Seoane and El Cebrero. Normal crossfaults are related to the folding and the compression. They show locally a deviation in accordance with the direction of shear stress. Horizontal displacement along such faults in an EW direction was probably of little importance. Finally a few observations are given on the occurrence of Pb-Zn ores at the mine of Rubiales.