THE DEVONIAN SYSTEM IN NORTHWESTERN GONDWANA: FOCUS IN COLOMBIA

Almost 8.3% of generated world oil belongs to Devonian rocks. These rocks are well studied as source intervals in oil producing basins of United States, Peru and Bolivia. The latter two basins are connected to Colombia and Venezuela. In this contribution, we discuss the two main tectonic models prior and during the development of the Devonian sea in northwestern South America: a subduction-dominated model and the along-marginal migration of blocks model. Also, we summarize knowledge of metamorphic, plutonic and sedimentary Devonian rocks from northern Ecuador to Venezuela. Paleontological data show that the Devonian rock units range from Pragian to Frasnian, and that the marine faunas belong to the Eastern Americas Realm which connected eastern North America and northern South America. Based on data recompilation and our research, we observed that sedimentation was controlled mainly by the Yari-Iquitos arch; the Vaupes-Chiribiquete arch; the Soapaga - Río Servita – Mutiscua – Las Mercedes Fault System, as a regional inverted structure that currently constitutes the eastern border of the Floresta and Santander massifs; the northern Bucaramanga, Chitagá and El Tigre faults; the Chusma, Algeciras, and Altamira faults toward the south of Colombia; and the Servita – paleo Guicáramo fault system along the eastern piedmont of the current Eastern Cordillera. During Pragian-Emsian, sediments were deposited in a transgressive cycle along a north-south epicontinental basin, lying unconformably on metamorphosed Ordovician-Silurian rocks associated to the Famatinian Orogenesis. During Eifelian-Givetian times, the maximum flooding was recorded with deposition of black shales and several intervals important as hydrocarbon source rocks. Finally, during Frasnian-Fammenian the tectonic activity related to the beginning of Pangea amalgamation closed the basin, registering the deposition of a regressive cycle. There is a strong decrease in magmatic activity during the Devonian, with no radiometrically dated plutonic and volcanic rocks in Colombia or Venezuela. However, newly published U/Pb detrital geochronology data suggests a protracted active margin from Cambrian through Devonian time and implies the exhumation of basement uplifts as the Garzon, Santander or Floresta massifs. Our results highlight the importance of develop an updated tectono-sedimentary framework for Devonian deposits, useful for hydrocarbon exploration in the subsurface of the Llanos and Putumayo basins.