Los Llanos Formation | |
---|---|
Stratigraphic range: Campanian ~ | |
Type | Geological formation |
Underlies | exposed to surface |
Overlies | Unconformity with Early Permian Los Sauces & Patquía Formations or Ordovician granitic basement |
Thickness | Up to ~150 m (490 ft) |
Lithology | |
Primary | Sandstone, conglomerate |
Other | Paleosols |
Location | |
Coordinates | 30°36′S66°36′W / 30.6°S 66.6°W |
Approximate paleocoordinates | 33°48′S39°30′W / 33.8°S 39.5°W |
Region | La Rioja Province |
Country | Argentina |
Extent | Sanagasta geological park , Sierra de Los Llanos, Sierra de Chepes, Sierra Ulapes, Sierra de Velasco & Sierra Brava |
Type section | |
Named for | Sierra de Los Llanos |
Named by | Bodenbender |
Year defined | 1911 |
Los Llanos Formation is a geological formation in the La Rioja Province, northwestern Argentina whose strata date back to the Campanian stage of the Late Cretaceous.
Los Llanos Formation over the years has been controversially described as ranging from Late Cretaceous to Miocene, but the Miocene succession was assigned to Las Mulitas Formation in 2019. The formation rests on top of the Early Permian Los Sauces and Patquía Formations and in parts on Ordovician crystalline basement. The maximum thickness is estimated at 150 metres (490 ft).
The sandstones and conglomerates of the formation were deposited ij a fluvial environment. The formation crops out in the Sanagasta geological park , where more than 90 titanosaurid nesting sites were discovered in Los Llanos Formation. The sites were encountered on top of areas characterized by hydrothermal activity as geysers and other vents, suggesting a preferred location for the incubation of the dinosaur eggs. Apart from fossil eggs, the formation has provided fossil flora and ostracods. The crocodyliform Llanosuchus , described in 2016 from the formation, was named after Los Llanos Formation.
The Los Llanos Formation was first formally described by Bodenbender in 1911. [1] The formation crops out in very localized patches in the south of La Rioja Province. [2] Los Llanos Formation is found on the western and eastern slopes of the eponymous Sierra de Los Llanos, in the Sierra de Chepes, Sierra Ulapes, Sierra de Velasco and Sierra Brava. [3]
Between the original definition of "Los Estratos de Los Llanos" (Los Llanos Beds) by Bodenbender and later analysis during the twentieth century, a number of controversies arose. Rusconi (1936), Bordas (1941), Pascual (1954), Guiñazú (1962) and Zuzek (1978) assigned a Miocene age to the formation, based on mammal fossils found in the strata. [4] This unit is presently known as the Las Mulitas Formation. [5] The occurrence of typical Cretaceous charophytes confirms the assigned age for Los Llanos Formation. [6]
Los Llanos Formation unconformably overlies the Permian Los Sauces Formation in the Sierra de Velasco and the Permian Patquía Formation or Ordovician granitic basement in other places. The maximum recorded thickness in the Sanagasta Geologic Park is 4 metres (13 ft), [7] while in the region of Tama the formation reaches an estimated thickness of 150 metres (490 ft). [8]
It comprises lightgrey and orange sandstones with basal conglomerate beds, [8] deposited in a fluvial environment, which in the Sanagasta park is associated with hydrothermal activity. [9] The more than 90 sauropod nests were found in direct association with these hydrothermal vents, suggesting a preferred incubation location of the mother dinosaurs. [10]
The formation has provided fossilized nesting sites attributed to a titanosaurid dinosaur. Research conducted in 2015 by Hechenleitner et al. include a comparison with the Cretaceous Sanpetru Formation of Hațeg paleo-island in Romania, the Tremp Formation of the Spanish Pre-Pyrenees and the Boseong Formation of the Gyeongsang Basin in South Korea. [11]
The following fossils were reported from the formation: [12]
Aeolosaurus is a genus of titanosaurian sauropod dinosaur from the Late Cretaceous Period of what is now South America. Like most sauropods, it would have been a quadrupedal herbivore with a long neck and tail. Aeolosaurus is well known for a titanosaur, as it is represented by the remains of several individuals belonging to at least two species. However, like most titanosaurs, no remains of the skull are known. The holotype of Aeolosaurus rionegrinus consists of a series of seven tail vertebrae, as well as parts of both forelimbs and the right hindlimb. It was discovered in the Angostura Colorada Formation in Argentina, which dates from the Campanian stage of the Late Cretaceous, about 83 to 74 million years ago. The species A. maximus was transferred over to the new genus Arrudatitan in 2021.
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Rocasaurus is a genus of titanosaurian sauropod that lived in South America. Rocasaurus was discovered in Argentina in 2000, within the Allen Formation which is dated to be middle Campanian to early Maastrichtian in age. This genus grew up to 8 metres (26 ft) long, making it one of the smaller sauropods. It seems to be closely related to saltasaurid dinosaurs, like Saltasaurus and Neuquensaurus.
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The Bajo Barreal Formation is a geological formation in the Golfo San Jorge Basin of Chubut and Santa Cruz, Argentina whose strata date back to the Middle Cenomanian to Late Turonian. The formation was first described by Teruggi & Rossetto in 1963. The sandstones, claystones, mudstones, conglomerates and tuff were deposited in a fluvial environment. The upper part of formation is laterally equivalent to the Yacimiento El Trébol and Meseta Espinosa Formation and the lower part to the Laguna Palacios, Cañadón Seco and Comodoro Rivadavia Formations. The Bajo Barreal Formation is a reservoir rock in the Golfo San Jorge Basin.
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The Uberaba Formation is a Campanian geologic formation belonging to the Bauru Group of the Bauru Sub-basin, Paraná Basin located in Minas Gerais state of southeastern Brazil. The Uberaba Formation, intercalating the fossiliferous older Adamantina and younger Marília Formation, comprises limestones, sandstones, and conglomerates, often cemented by calcite with volcaniclastic sediments. The formation interfingers with the Adamantina Formation.
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Sphaerovum is an oogenus of dinosaur egg that has only been discovered in South America.
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