The Devonian System in northwestern Gondwana: Focus on Colombia

Abstract

The Devonian Period experienced the proliferation of vascular plants and had the highest levels of carbonate production, reef-building, and marine faunal diversity in the Paleozoic Era, which led to a diverse biostratigraphic record. While the presence of extensive reef systems is a characteristic feature of many Devonian deposits worldwide, this aspect is relatively subdued in northwestern South America. Instead, the Devonian stratigraphy of Colombia and Venezuela is characterized by marine faunas and flora which altogether point to a connection between Laurussia and Gondwana.Despite these biostratigraphic pieces of evidence, paleogeographic reconstructions of northwestern Gondwana are challenging. For these reasons in this contribution, we summarize the current knowledge of metamorphic, plutonic, and sedimentary Devonian rocks from northwestern Brazil to Venezuela along with our new results to propose paleogeographic evolution during Early, Middle, and Late Devonian time.Devonian sedimentation in northwestern Gondwana took place under an extensional tectonic regime widely documented at the current Eastern Cordillera and Llanos basin in Colombia delineating a Devonian back-arc basin, shaped by normal and dextral strike-slip en echelon faults. Paleontological data discloses to ages ranging from Pragian to Frasnian for the Devonian sedimentary rocks in northwestern Gondwana deposited during a transgression along a north-south trending epicontinental basin, on top of a Proterozoic-Early Paleozoic metamorphic basement. During Eifelian-Givetian times, the build-up of a carbonate platform indicates the maximum flooding surface of the basin. Finally, during the Frasnian-Fammenian, a regressive cycle characterized by coastal facies indicates a period of uplift possibly linked with the first stages of western Pangaea amalgamation and the Rheic Ocean closure.Recently, published UPb detrital zircon geochronology from Devonian sediments of Colombia basins suggests a protracted active margin during Paleozoic times, with near-zero lag times between zircon crystallization and sedimentation. These provenance constraints appear to contradict Devonian magmatic quiescence in northwestern Gondwana. In contrast, south of the Macarena Range in the structural domain of the Guiana Shield, Devonian sedimentary rocks exclusively yield Proterozoic zircon inheritance.Observed changes in detrital zircon provenance suggest, 1) A Devonian magmatic arc in the Oaxaquia, Mixteca, or Maya blocks, was likely the source of detritus to Devonian basins in northern Colombia and Venezuela, and 2) A paleogeographic control must have prevented the interconnection of northern Devonian sediment routing systems with their southern counterparts in the Guiana Shield. In this scenario, basement highs within the Guiana Shield vicinity likely acted as paleogeographic barriers compartmentalizing Devonian sedimentary basins in northwestern Gondwana.