Abstract
In this contribution, we describe latest Cretaceous aquatic plant communities from the La Colonia Formation, Patagonia, Argentina, based on their taxonomic components and paleoecological attributes. The La Colonia Formation is a geological unit deposited during a Maastrichtian-Danian transgressive episode of the South Atlantic Ocean. This event resulted in the deposition of a series of fine-grained sediments associated with lagoon systems occurring along irregular coastal plains in northern Patagonia. These deposits preserved a diverse biota, including aquatic and terrestrial plants and animals. The aquatic macrophytes can be broadly divided into two groups: free-floating and rooted, the latter with emergent or floating leaves. Free-floating macrophytes include ferns in Salviniaceae (Azolla and Paleoazolla) and a monocot (Araceae). Floating microphytes include green algae (Botryoccocus, Pediastrum and Zygnemataceae). Among the rooted components, marsileaceous water ferns (including Regnellidium and an extinct form) and the eudicot angiosperm Nelumbo (Nelumbonaceae) are the dominant groups. Terrestrial plants occurring in the vegetation surrounding the lagoons include monocots (palms and Typhaceae), ferns with affinities to Dicksoniaceae, conifers, and dicots. A reconstruction of the aquatic plant paleocommuniy is provided based on the distribution of the fossils along a freshwater horizon within the La Colonia Formation. This contribution constitutes the first reconstruction of a Cretaceous aquatic habitat for southern South America.
Highlights
There are currently about 2,600 species of vascular aquatic macrophytes distributed among 87 families and 407 genera [1]; these plants inhabit all types of wetland environments and are found throughout the world [2], they are most diverse in the tropics, a pattern that is pronounced for aquatic angiosperms [3]
Macrofossils and palynological samples were collected from several localities of the La Colonia Formation, which outcrops in the central part of northern Chubut Province in Patagonia, Argentina (Fig. 1)
The frost intolerance of the modern analogues of some plants found in the La Colonia Formation sediments—such as Salviniaceae, Marsiliaceae, Araceae, and palms— indicates a tropical to subtropical climate
Summary
There are currently about 2,600 species of vascular aquatic macrophytes distributed among 87 families and 407 genera [1]; these plants inhabit all types of wetland environments and are found throughout the world [2], they are most diverse in the tropics, a pattern that is pronounced for aquatic angiosperms [3]. In Mongolia [22], several Maastrichtian localities of the Nemegt Formation bear aquatic plants that comprise three distinct assemblages: 1- a pondweed assemblage dominated by Potamogeton-like plants associated with an isoetalean component; 2- a nymphaealean assemblage; and 3- an assemblage dominated by duckweeds (Araceae subfamily Lemnoideae). These three assemblages occurred in oxbow lake deposits associated with fluvial systems under a temperature regime that was probably subtropical with a monsoonal dry season. Cretaceous and Paleocene aquatic plant communities from western North America and northeastern Asia [23,24–25,26–27] resemble modern communities, and include common elements such as Nelumbites (Proteales), Quereuxia (an angiosperm of unknown affinities), Cobbania and Limnobiophyllum (monocots in Araceae), along with extinct aquatic ferns (Hydropteris in Salviniales) [5]
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