Structural geometry of the Jura-Cretaceous rift of the Middle Magdalena Valley basin, Colombia

The Middle Magdalena Valley (MMV) basin, Colombia, evolved to its actual configuration through several stages closely linked with the tectonic events of the northwest corner of South America.; Early Jurassic extensional deformation related to the break-up of Pangea, resulted in the development of rift structures in the MMV basin area. The syn-rift infill consists of fluvial and lacustrine sedimentary rocks (Jordan, Giron and Santos formations), overlain by limestones and shales (Basal Lime Group). Irregular discontinuous reflectors, rotated by normal faults and increasing thickness towards the south-east, characterize the Jurassic syn-rift section. In Early Aptian, a post-rift phase controlled by thermal subsidence started. During this phase the Simiti, La Luna and Umir formations were deposited. The seismic character of this sequence consists of continuous reflections and gradual changes in thickness. From the end of the Cretaceous through the present, the collision of oceanic terranes against the western margin of Colombia caused thrusting in the Central and Eastern Cordilleras. The MMV basin became an intermontane basin. Sedimentation during this period consisted of fluvial deposits accumulated as continental molasses.; I propose an asymmetrical half graben geometry for the Jura-Cretaceous structure of the northern part of the MMV basin. The range-bounding faults of the Eastern Cordillera: the Bucaramanga, La Salina, and Cambao-Bituima faults were originally normal faults that controlled thickness of the synrift sequence and, in general, the geometry of the structure.; The rift structures are well preserved in the study area. However, most of the preserved faults were inverted during the Tertiary orogeny. Inversion can be documented by structures such as shortcuts, thicker rift strata on the hanging wall, and by variation of fault throw.