The Sierra Barrosa Formation is a geologic formation of the Neuquén Basin in the northern Patagonian provinces of Mendoza and Neuquén. The formation dates to the Late Cretaceous, middle to late Coniacian, and belongs to the Río Neuquén Subgroup of the Neuquén Group. The formation overlies the Los Bastos Formation and is overlain by the Plottier Formation. As the underlying Los Bastos Formation, the Sierra Barrosa Formation comprises mudstones and sandstones deposited in a fluvial environment.

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Sierra Barrosa Formation
Stratigraphic range: Mid-late Coniacian ~88–86 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Type	Geological formation
Unit of	Neuquén Group  Río Neuquén Subgroup
Underlies	Plottier Formation
Overlies	Los Bastos Formation
Thickness	Up to 62 m (203 ft)
Lithology
Primary	Mudstone
Other	Sandstone
Location
Coordinates	38°52′10″S 68°51′20″W
Approximate paleocoordinates	42.8°S 48.4°W / -42.8; -48.4
Region	Mendoza & Neuquén Provinces
Country	Argentina
Extent	Neuquén Basin
Type section
Named for	Sierra Barrosa
Named by	2010
Year defined	Garrido
Sierra Barrosa Formation (Argentina)

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The formation was named by Garrido in 2010 as sandy unit conformably and transitionally overlying the Los Bastos Formation, which in turns overlies the Portezuelo Formation within which both units were formerly included. The formation in the same manner underlies the Plottier Formation, all belonging to the Río Neuquén Subgroup of the Neuquén Group in the Neuquén Basin. The unit now known as Sierra Barrosa Formation was included in the original definition by Herrero Ducloux (1938, 1939) as "Portezuelo Superior", as part of the "Portezuelo Beds" he described.^[1]

The type locality of the formation is located at the southern edge of the eponymous Sierra Barrosa, to the east of Cerro Challacó. The formation at its type section reaches a thickness of 62 metres (203 ft). The formation comprises fine-to-medium grained sandstones intercalated by thin levels of mudstones. The formation has similar lithological characteristics as the Portezuelo Formation and was deposited in a fluvial environment characterized by highly sinuous channels. Based on the stratigraphic relations with the overlying and underlying units, the age has been estimated to be middle to late Coniacian.^[1]

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