Abstract

This study deals with the evolution of the Rioja area in structural and stratigraphic terms. This area is located at the western end of the Ebro basin. Field data, particularliy subsurface data from hydrocarbon exploration activity, allow a new integrated approach. The Rioja area has experienced a particular evolution at least since the Mesozoic, and can be differentiated from neighbouring Ebro basin domains. Major thrusting along the northern (Cantabrian Chain) and southern (Iberian Chain) margins of the Rioja basin lead to a reduction in the extent of the original basin of approximately 70%. Syntectonic subsidence, coeval with the major thrusting on both margins, took place during Tertiary times. On the northern thrusted domain, piggy-back basins developed. Diapirism is also a significant feature of the Cantabrian region.

Geological setting

The geology of the Rioja area is dominated by a grabenlike basin filled with continental sediments of Tertiary age (including the continental Garumnian facies). Thrust sheets form the northern and southern boundaries of the basin (see Riba and Jurado, 1993; and older papers, for example, Joly, 1922a, 1922b; Schriel, 1930; Saenz, 1942; Riba, 1955; Lotze, 1958; Colchen, 1966). The northern margin corresponds to the Montes Obarenes-Sierra de Cantabria range, a southwards-directed thrust unit which forms part of the westernmost Pyrenean thrust belt. The southern margin is bounded by the Demanda–Cameros ranges, with northwardsdirected thrusts at the western limit of the Iberian Chain.