[10] The Agrio Formation is primarily composed of pelitic rocks with intercalations of limestones, sandstones and rare fine conglomerates.

The Pilmatué and Agua de la Mula Members are characterized by thick successions of black shales with intercalating limestones and sandstones.

[11][10] The Agrio Formation was deposited in a post-rift setting of the Neuquén Basin, probably representing a tectonic regime of thermal subsidence.

The sediments of the lower and upper members of the formation are marine in character, interpreted as the combination of thermal subsidence and a eustatic sea level rise.

Within the marine Pilmatué Member, a succession of approximately 130 metres (430 ft) thick, described as "San Eduardo Beds", is recognized as deposited in a wave-dominated deltaic setting with hyperdense currents.

[14] The formation has provided many fossils of ammonites,[15] gastropods, bivalves, corals, decapods, echinoids, crinoids and nano and microfossils (calcareous nannofossils, ostracods, foraminifers).

[5][16][17][18][19][20] In 2018, ichthyosaur remains not determined to the genus level were described from the Agrio Formation, suggesting the possibility of viviparity of these marine reptiles in the epeiric sea of the Neuquén Basin.

[22] The decapod Palaeohomarus pacificus,[23] and ammonites Curacoites rotundus and Sabaudiella riverorum were described from the formation in 2012,[24] the gastropods Ampullina pichinka and Mesalia?