Intermontane basins and hydrocarbon potential at the Central to Northern Andes

In the Central to Northern Andes transition zone (Ecuador and Northern Peru), several Tertiary intermontane basins have been preserved (e.g. Bagua Basin in Peru, Zumba, Nabon, Loja, Malacatos- Vilcabamba, Giron and Cuenca basins in Ecuador). The analysis of these intermontane basins showed similarities in their sedimentological evolution and ages of infilling; however structurally, three groups can be separated: the Cuenca and Giron-Santa Isabel basins related to dextral movement of allochtonous terranes sutures (Raspas- Peltetec; Calacali-Pallatanga-Palenque). The Loja and Vilcabamba-Malacatos basins are associated to N-S sutures activation (Las Aradas- Zamora). The third group includes the Bagua Basin and others small piggyback basins purely related to the eastward migration of the main fold and thrust deformation front of the Central Andes during the Upper Miocene. Exploration point of view, the Miocene intermontane basins often contain a thick sequence of lacustrine and/or shallow marine deposits that could host potential source rocks. Indeed, coal layers are described and were traditionally exploited for domestic use. Nevertheless, the Miocene basin fill could at depth have triggered the activation of Mesozoic and older petroleum systems. In the area of the Bagua Basin exists two potential petroleum systems. The Jurassic (Aramachay Fm) and Cretaceous (Goyllarisquizga Gp and Inca Fm) sequences have an excellent source rock potential. One oil seep sample hosted in the Upper Cretaceous reservoirs was collected in the Bagua Basin. According to its geochemical characterization it is from a marine source rock, kerogene type II and a Pre-Cretaceous age has been postulated.