TECTONIC STAGE IDENTIFICATION VIA GEOPHYSICAL AND GEOLOGICAL SURVEY, SOUTHERN PART OF THE MIOCENE-PLIOCENE EL BOLEO BASIN, BAJA CALIFORNIA SUR

Within the Baja California Central Domain [BCCD] hardly any structural and sedimentological characteristics are known from the El Boleo basin. This basin keeps a record that brings in elements that broaden the accepted evolution model for the BCCD. With the purpose of defining the geometry and the structural limits of the southern part of the basin, aeromagnetic data acquired by the Consejo de Recursos Minerales were analyzed, in conjunction with an aeromagnetic and magnetometric support profile on land. The profile was performed along an East-West direction, perpendicular to the scarp of the master fault for the basin. Several filtered and modeled bi-dimensional charts were used as part of the geophysical analysis. The results from the geophysical survey, supported with geology and well data, indicate a maximum calculated sediment thickness of ~300 meters for the western side of the asymmetrical basin, interpreted as a half graben. The stratigraphic column represents an alluvial fan deposit associated to a listric fault, with a NNW-SSE strike. Laterally to the east, the sedimentary units graduate to alluvial plain deposits, and Pliocene marine units. The alluvial fan deposits characterize the syn-extensional tectonic phase, associated mainly to the Proto-Gulf stage, and the marine units to the post-extensional phase within the basin. The presence of strata that reflects a post-extensional stage constitutes an element not previously considered in the general tectonic evolution model for the BCCD.