The up to 380 metres (1,250 ft) thick stratigraphic unit comprises mudstones, sandstones, siltstones and conglomerates, sourced from the North Patagonian Massif and deposited in a deltaic to shallow marine environment with a strong tidal influence.

Insect predation on fossil leaves shows a considerably more rapid recovery from the extinction in event in Patagonia (about 4 Ma) than in the Western Interior of North America, estimated at 9 million years.

The Danian part of the succession contains fossil flora of Lactoridaceae, presently a monotypic family restricted to the subtropical forests of the Juan Fernández Archipelago in the South Pacific Ocean, offshore Chile.

[6] At the fossil site of Cocatherium, the formation is 200 metres (660 ft) thick and comprises a Maastrichtian succession of massive mudstones with intercalating parallel and cross-bedded sandstone beds and coquinas that preserve a molluscan fauna.

[7] Phosphatic levels occur in both the Maastrichtian and Danian parts of the formation,[8] and the sandstones contain grains of biotite, zircon, kyanite, amphibole and pyroxene, all typical of an igneous and metamorphic provenance.

[11] The lower part of the formation was mainly deposited in a shallow marine shoreface environment with strong tidal influence and beds rich in phosphatic concretions.

[7] The environment evolved to a tide to wave-dominated deltaic system in the middle part of the sequence,[12] with a maximum flooding surface representing the transgression and deepening of the basin at the start of the Paleocene.

[26] The fossils of Retrophyllum superstes is associated with numerous dark, circular marks of about 0.1 to 0.2 millimetres (0.0039 to 0.0079 in) in diameter, that most likely represent piercing-and sucking damage of hemipteran insects.

The abundant monocots, primarily Liliaceae and some Sparganiaceae, Chloranthaceae and the diverse ferns may have grown in the understory, associated with ponds, small streams or rivers, just landward of the shoreline.

Earliest Danian assemblages were characterized by the striking abundance of Classopollis, a pollen type linked to Casuarinaceae (Haloragacidites harrisii), the consistent presence of Beauprea (Peninsulapollis gillii), and ferns of Gleicheniaceae, among others.

Other elements included Nothofagus, diverse eudicots of uncertain affinity, and new species of Proteaceae and Ericaceae, indicating that several typical components of extant austral forests were in place by the Danian.

Several Cretaceous taxa return again in this part of the sequence; including Liliaceae and temperate to warmer climate families: Aquifoliaceae, Malvaceae (Bombacoideae) and Arecaceae (Nypa type).

The presence of Lactoridaceae, a monotypic family today restricted to subtropical forests of the Juan Fernández Archipelago, offshore Chile in the South Pacific Ocean, is particularly striking.