The Colorado Basin (Spanish: Cuenca del Colorado) is a sedimentary basin located in northeastern Patagonia. The basin stretches across an area of approximately 180,000 square kilometres (69,000 sq mi), of which 37,000 square kilometres (14,000 sq mi) onshore in the southern Buenos Aires Province and the easternmost Río Negro Province extending offshore in the South Atlantic Ocean.
The basin comprises a sedimentary succession dating from the Permian (pre-rift stage) and Early Cretaceous (rift stage) to the Quaternary, representing the passive margin tectonic phase of the basin history. The Mesozoic rifting in the basin resulted from the break-up of Pangea and the formation of the South Atlantic. Long hiatuses exist in the succession.
Contrasting with the South Atlantic passive margin basins to the north (Santos Basin in southern Brazil) and south; Golfo San Jorge and Austral Basins, the Colorado Basin does not produce hydrocarbons. Exploration for petroleum started in the 1940 with the drilling of two onshore wells and several onshore and offshore wells have been drilled in the 1960s, 1970s and 1990s. The main source rocks are found in the Permian succession, with reservoir rocks the Colorado Formation. Seals are provided by the Early PaleocenePedro Luro Formation.
Description
View of Viedma and Carmen de Patagones, separated by the Río Negro
The Colorado Basin stretches across an approximate area of 180,000 square kilometres (69,000 sq mi) with about 37,000 square kilometres (14,000 sq mi) onshore, underlying the southernmost Buenos Aires Province and the southeasternmost Río Negro Province. Cities inside the basin are Bahía Blanca and Carmen de Patagones in Buenos Aires Province and Viedma in Río Negro Province, the earliest founded city in Patagonia. The onshore part of the basin is crossed by the eponymous Colorado and Río Negro rivers. Surrounding the Río Negro, many salt lakes are present in the basin.[1]
Some authors group the basin together with the Claromecó Basin to the north.[2] The offshore part of the Colorado Basin laterally correlates with and gradually ranges into the sub-parallel Salado Basin and the deeper offshore Argentina Basin.[3][4] The offshore extension of the basin into neighboring basins led to different definitions of its area, some authors use a surface area of 125,000 square kilometres (48,000 sq mi).[5]
Pangea in the Permian (~250 Ma). The Colorado Basin experiences glaciations and a marine transgressive phase in the south polar region.Sketch of the paleogeographic situation of South America during the Late Cretaceous and Early Paleogene, roughly 85 to 63 Ma. The Colorado Basin, located north of the North Patagonian Massif in the South Gondwanan Province (grey), is exposed and eroded during the Maastrichtian.
Contrary to other Southern Atlantic marginal basins, as the Golfo San Jorge and Austral Basins to the south, and Santos Basin of Brazil to the north, the Colorado Basin is not producing hydrocarbons. The first wells in the northern onshore part of the basin were drilled in 1946 (Pedro Luro-1) and 1948 (Ombucta-1) by YPF. Another phase of onshore exploration happened in the 1960s, with seven wells drilled by Shell.[36] Offshore drilling started in 1970 by Hunt Oil and after seismic acquisition in the 1970s by YPF,[37] some wells were drilled in 1977 by the same company. Renewed exploration started in the mid-1990s with several wells drilled by Union Texas and Shell.[38] The offshore Cruz del Sur x-1 well provided oil shows of 39° API.[39]
Balarino, M. Lucía (2009), Palinoestratigrafía del Paleozoico Superior de la Cuenca Colorado, República Argentina, y su correlación con áreas relacionadas (PhD thesis), Universidad Nacional de La Plata, pp. 1–566