The formation is unique in preserving fossil flora both from the Late Cretaceous, before the
Cretaceous–Paleogene extinction event and from the Danian, after the mass extinction. The K/Pg boundary impact layer is not preserved in the formation, apparently due to
bioturbation. The Maastrichtian part of the succession shows a diverse assemblage comprising
angiosperms, including aquatic
Nelumbo leaves and fruits, and
conifers. The upper part of the formation is represented by an extremely diverse collection of angiosperms (about 70 species), as well as
monocots, conifers, and
ferns. Many of the species that disappear at the boundary, return higher in the sequence, indicating their survival in refugial areas. The overall extinction rate is difficult to estimate without more exhaustive studies, but it probably does not exceed 10% of the species. This pattern of recovery is comparable to that observed in New Zealand, where an abrupt disturbance of the vegetation across the K/Pg boundary occurred, but with a low overall extinction rate. The occurrence of the same taxa in the Maastrichtian and Danian successions, suggests that the Cretaceous-Paleogene extinction event did not affect aquatic plant communities, which retained approximately similar structure and composition during the transition between the latest Maastrichtian and the earliest Paleocene. The presence of the bivalve fauna strongly suggests the basin was connected via a seaway with the
Austral Basin and possibly with the
Pacific Ocean. The fossils of
Retrophyllum superstes is associated with numerous dark, circular marks of about in diameter, that most likely represent piercing-and sucking damage of
hemipteran insects. Comparison of the insect damage on the plant leaves between
Western Interior North America (WINA) and Patagonia, on flora recovered from the Lefipán Formation, as well as the
Salamanca and
Peñas Coloradas Formations of the
Golfo San Jorge Basin to the south, show that recovery from the Cretaceous-Paleogene mass extinction was considerably faster in Patagonia than in North America. Recovery to pre-extinction levels of insect damage diversity in the southern hemisphere flora occurred in approximately 4 Ma, whereas this recovery took about 9 Ma in North America, supporting the hypothesis of a large-scale geographic heterogeneity in extinction and recovery from the end-Cretaceous extinction event.
Maastrichtian The presence of
Spinizonocolpites, related to the tropical mangrove palm
Nypa in the Maastrichtian part of the formation indicates specialized shore-line
mangrove assemblages.
Proteaceae, related to
Beauprea and
Telopea, together with
Aquifoliaceae, may have formed a lower stratum of forests or woodlands. 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 The earliest Danian vegetation is characterized by a low diversity and was quite different in species composition and abundance from both the latest Maastrichtian and the subsequent Danian assemblages. The marked reduction in diversity affected all groups of plants, and ferns and monocots in particular, most Proteaceae species except
Beauprea-like forms, and nearly all
gymnosperms. The presence of marginal, shallow marine, somewhat stressed paleoenvironmental conditions on both sides of the K/Pg boundary indicates that changing depositional factors were unlikely to have had significant importance in driving the observed compositional changes in the palynological assemblages. 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.
Danian Later Danian vegetation was dominated by gymnosperms, including diverse Podocarpaceae related to
Podocarpus,
Microcachrys,
Dacrydium,
Lagarostrobos and
Dacrycarpus.
Classopollis remained abundant, but it shows a general reduction towards younger samples. Palms and tree ferns of
Dicksoniaceae were also important components of the Danian vegetation. 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. These assemblages are fairly diverse, although no Danian sample reaches the diversity recorded in the latest Maastrichtian.
Fossil content Fossils recovered from the formation include: == See also ==