zircon geochronology resulted in ages of 192.4 ± 2.2 Ma in a basaltic andesite, 184.9 ± 2.0 Ma in an andesitic lava and 175.9 ± 1.1 Ma in a rhyolitic lava, indicating the occurrence of volcanic events in this section of the Noreán Formation from the Lower to the earliest Middle Jurassic. Zircon inheritance suggests that the volcanic arc was emplaced in a Meso- to Neoproterozoic basement. The Noreán Formation represents continental arc magmatism, which occurred during a phase of extensional tectonics along the continental margin of northwestern South America from approximately 195 to 168 Ma. Stratigraphy To the northwest of the Santander Massif, the formation overlies the Bocas Formation and is unconformably overlain by the Tablazo Formation. In some locations in this area, the formation is found in faulted contact with the Bucaramanga Gneiss, La Virgen Formation and the Tablazo and La Luna Formations. In the Serranía de San Lucas, the Noreán Formation conformably overlies the Morrocoyal Formation and in this area is overlain by the Tablazo Formation and the Arenal Conglomeratic Unit. Across the San Lucas mountains, the formation is in faulted and discordant contact with the Norosí Batholith, the San Lucas Gneiss and the Sudán Formation. The formation is offset by the megaregional Bucaramanga-Santa Marta Fault. Subdivision On the western flanks of the Eastern Cordillera, the formation is subdivided into six units and in the Serranía de San Lucas into four (1, 3, 5 and 6 of the six named below), from young to old: Hypobyssal Andesitic Unit (Jnha) - Effusive Rhyolitic Unit (Jner) - Dacitic Effusive Unit (Jned) - Pyroclastic and Effusive Dacitic Unit (Jnpd) - Effusive Spherulitic Unit (Jnee) - Pyroclastic-epiclastic Unit (Jnpe) - Age The age of the Noreán Formation has been established using potassium-argon (K-Ar), rubidium-strontium (Rb-Sr), and uranium-lead dating (U-Pb). The first method gave an age range of 194 ± 6 Ma, the Rb-Sr dating method provided a range of 161 ± 27 Ma and U-Pb dating of zircons resulted in ages of 201.6 ± 3.6 and 196.1 ± 4.4. Refined dating of the formation performed in 2019 by Correa Martínez et al. concluded an age range between 192.4 ± 2.2 and 175.9 ± 1.1 Ma, spanning most of the Early Jurassic, from Sinemurian to Toarcian. The Noreán Formation was intruded by the San Lucas Granitoid in the Middle Jurassic, dated at 166.9 ± 6 Ma. A 2020 thermochronological study concluded that