Usuario:Coahj/Taller

The Agrio Formation

The Agrio Formation is a lithostratographic unit of marine origin, with extensive and higly fossiliferous outcrops spread across the Argentine provinces of Neuquén, Mendoza, Río Negro and La Pampa​.

The Agrio Formation is widely exposed along the Fold and Thrust Agrio Belt in the Andean sector of the Neuquén Basin. It extends from the vicinity of La Mala Dormida in southern Mendoza southwards to Catán Lil, a few kilometers to the south of Cerro Marucho in southern Neuquén. To the west, the boundary of present-day outcrops coincides with the foothills of the Andes. Towards the eastern and southern margins of the basin, the marine rocks of the Agrio Formation interfinger with the Centenario Formation. The formation overlies marine deposits of the Mulichinco Formation and is covered discordantly by siliciclastic, carbonate, and evaporitic rocks of the Huitrín Formation.

The unit was first named by Weaver (1931) for a thick succession of marine shales overlying the Mulichinco Formation. Weaver divided the Agrio Formation into lower and upper divisions separated by a thin but laterally persistent unit, the Avilé Sandstone. The three lithostratigraphic elements are considered members. The Pilmatué (lower) Member (Leanza et al. 2001) is composed of up to 600 m of marine shales and mudstones associated with thin sandstone beds and carbonates (wackestones and packstones) (Aguirre Urreta and Rawson 1997). The middle unit, the Avilé Member, consists of up to 100 m thick sandstones with fine conglomerates and subordinated mudrocks interpreted as aeolian and arid fluvial deposits. It represents a major drop in sea level across the basin (Veiga et al. 2002). The Agua de la Mula (upper) Member (AMMb) is a marine succession, up to 1000 m thick, composed of shales, mudstones, sandstones and bioclastic carbonates (Spalletti et al. 2001b). Leanza (2003) placed the Chorreado Member, previously considered as a Hutrinian unit, in the Agrio Formation.

The unit was defined by Weaver (1931) for a thick succession of marine shales overlying the Mulichinco Formation. Weaver divided the Agrio Formation into lower and upper divisions separated by a thin but laterally persistent unit, the Avilé sandstone. the three lithostratigraphic elements are considered as members. the Pilmatué (lower) Member (Leanza et al. 2001) is composed of up to 600 m of marine shales and mudstones associated with thin sandstone beds and carbonates (wackestones and packstones; Aguirre Urreta and rawson 1997). the middle unit, the Avilé Member, consists of up to 100 m thick sandstones with fine conglomerates and subordinate mudrocks interpreted as aeolian and arid fluvial deposits. It represents a major drop in sea level across the basin (Veiga et al. 2002). the Agua de la Mula (upper) Member (AMMb) is a marine succession, up to 1000 m thick, composed of shales, mudstones, sandstones and bioclastic carbonates (spalletti et al. 2001b). Leanza (2003) placed the chorreado Member, previously considered as a Hutrinian unit, in the Agrio Formation. the Agua de la Mula Member is thus sandwiched between two continental lithostratigraphic units that represent important regressive packages: the Avilé Member below and the Huitrín Formation above