Inversión tectónica y efecto contrafuerte de fallas extensionales cretácicas en el Urgoniano de la ensenada de Tejilla (Región Vasco-cantábrica: Castro Urdíales, Cantabria)

Abstract

In the Basque-Cantabrian Region extensional and compresional structures exist related to the opening and closure of the Biscay Bay. In the Tejilla cove a marly-calcareous succession of Lower Creatceous age crop out. This succession is deformed by typical inversion tectonic structures, and shows extensional and compresive structures from the analysis of a cross-section in the cliff of the cove. The results of this analysis has shown the existence of four extensional faults that display a different degree of inversion, depending on the inclination of the faults in its extensional stage. From a simple restoration of the alpine deformation in the studied section. I propose a extensional model that consists in a set of planar faults which reduce their dip from East to West. During the inversion stage, the most vertical fault acts as a buffer. It exerts the main control in the deformation, which increases in a progressive way towards this fault (butress effect). This gradient revealed because folds generated in this stage show greater shortening, with development of cleavage, towards the proximities of the fault.This increasement of deformation towards the fault causes folding of the upper part of the fault. Therefore, at present time this sector dips in an opposite way than the original one