Abstract

There are many Cenozoic (Late Oligocene(?)–Early Miocene) non-marine onshore basins in NW Spain. Among these onshore basins two NW–SE alignments of small strike–slip basins occur. These strike–slip faults, which can be related to similar faults recorded in the offshore continental margin zones, have affected the NW Galician region and have given rise to a number of small basins which evolved independently, under the influence of local tectonic structures. Tectonic events resulted in quick changes in local drainage conditions which gave rise to poorly drained depressions. Development of palustrine, marsh–swamp and lacustrine systems, which were sometimes of a very small size, was enhanced by these geomorphic conditions. Workable coal deposits resulted from this tectonic and sedimentary evolution. Understanding of the structure and stratigraphy of these basins should contribute to a better understanding of the recent evolution of the westernmost end of the Northern Iberian continental margin.

Introduction

There are many small Tertiary non-marine basins in Galicia, NW Spain (Birot and Solé Sabarís, 1954; Nonn and Medus, 1963; Virgili & Brell, 1975; Martin Serrano, 1979; 1982; Santanach et al.,1988). Some of these basins (1 to 9 in Fig. 1) occur in two NW–SE alignments, related to two strike–slip faults systems located in NW Galicia (Monge, 1987; Santanach et al., 1988).