Resumen de Reactivación Neógena de estructuras de rift del Cretácico Temprano asociadas con la Falla de Chámeza, Pajarito, Boyacá (Colombia): evidencias tectónicas y bioestratigráficas
Alejandro Piraquive Bermúdez, Juan Sebastián Díaz Cañas, Tomás Cuellar Aldana, Germán Pardo Torres, Andreas Kammer
The early evolution of the Cretaceous Colombian Basin represents an illustrative case of extensional tectonics in a back-arc environment. Syn-rift type marine deposits show an abundant bivalve an ammonite fauna widely spread along different stratigraphic levels, documented mainly at the axial zone of the Eastern Cordillera. Varied paleogeography in rift basins is a key factor which controls the lateral lithofacies change and the development of organism communities and their environmental associations.
22 ammonite fossils were collected in the Lutitas de Macanal Formation and 30 bivalves at the Lutitas de Macanal and Fómeque Formations respectively, which defines an age range from the Early Berriasian to the Early Hauterivian on the hanging wall of the Chámeza Fault (Lutitas de Macanal Fm.) and an age range from the Early Barremian to Early Albian (Fómeque Fm.) in the Chámeza Fault footwall.
A peculiarity within the structural frame refers to the reactivation of the former normal faults as thrust faults and the consequent basin inversion during a Neogene contractional event, evidencing a noticeable deformation as documented by deformed molds of ammonites. By means of graphic retrodeformation to their initial spiral shapes, we obtained elipticity values for the deformed fossils collected en el hanging wall of the Chámeza Fault. The long axes of these strain ellipses match the strike of a regional cleavage, which nearby of the Chámeza Fault turns to an almost E-W direction, becoming sub-parallel to this transversal accident. With these strain we document that the Chámeza Fault is related, at least in its current exposure level, to a ductile folding. We speculate that this ductile deformation zone developed as a consequence of an obliquity between tectonic transport and an inherited fault from the Neocomian Rift event, which prefigured the current Chámeza Fault.
