Complex structure in the apical part of the western Gibraltar Arc (Tesorillo permit, Cádiz)

Resumen

Tarba energía, which is a spanish Company founded in 2008 for gas exploration, currently works on the Tesorillo Project. To better understand the exploration potential of this area, a new structural interpretation has been undertaken. We therefore present a new structural map of the “Tesorillo” pemit, Cádiz province. In this area, the rocks that crop out are: (1) Santonian clays (Almarchal U.) and Palaeogene clays (Aljibe U.) that act as detachment levels and (2) Aquitanian-Burdigalian quart- zitic sandstones (Aljibe U.). To the S of the permit, there are two NNW-SSE mountain ranges, composed of the Alijbe U. The eastern mountain range constitutes a sheet that dips smoothly to the W, under the Almarchal unit. The western Aljibe U. mountain range forms another sheet that thrusts onto the Almarchal Unit. Thus, a ENE vergent sandwiched structure characterizes this zone. Both mountain ranges are also internally deformed into ENE-vergent imbricate systems. To the N of the permit, the tectonic grain drastically changes, Aljibe U. mountain range thrust over the Almarchal U. with a SSW vergence. This thrust is locally inverted. Almar- chal U. is also deformed by en-echelon, kilometric-scale folds. These folds are WNW-ESE, thus they are counter clockwise rotated respect to the main thrust of the Aljibe unit over the Almarchal unit. These folds also affect Pliocene sediments. This complex tectonic setting, probably aided by superposition of shortening episodes, is typical of apical parts of curved orogenic systems as it is predicted by analogue models. Thus, this work constitutes a significant contribution to the knowledge of this plate margin in the S Europe yet never studied in detail, and can have critical importance in gas prospect development.