The Geste Formation () is a fossiliferous geologic formation of the Puna Plateau in the western Salta Province and northern Catamarca Province of the Argentine Northwest, northwestern Argentina.
The formation, reaching a thickness of , is the oldest unit of the Pastos Grandes Group, underlying the Pozuelos Formation and unconformably overlying various Paleozoic formations. The Geste Formation comprises red sandstones and conglomerates deposited in a fluvial to alluvial environment. The formation was initially dated to the Mustersan (Middle Eocene), but subsequent research proved the formation to date to the Late Eocene (Divisaderan in the SALMA classification, ranging approximately from 42 to 36 Ma.
The Geste Formation has provided a faunal assemblage of vertebrates unique for the Argentine Northwest, with several groups of mammals, most notably the only Paleogene interatheres of northwestern Argentina, reptiles and frogs. Only partly they correspond to other fossiliferous formations in the area; the upper part of the Lumbrera Formation and the Quebrada de los Colorados Formation.
Description The Geste Formation crops out in isolated patches on the Puna Plateau, stretching from the Salar de Arizaro in the north to the Colorado Ridge, southeast of the Salar de Antofalla in the south. covering the western part of Salta Province and the northern part of Catamarca Province. The most extensive outcrops of the formation occur between three volcanoes in the area; the Tebenquicho in the west, Cerro Ratones in the east and Hombre Muerto to the southeast.Grosse et al., 2017, p.494 The formation was defined based on a type section of the Pastos Grandes Basin by Turner in 1960, 1961 and 1964. The formation comprises mainly coarsening upward sandstones, conglomerates and subordinate shales, deposited in a fluvial and alluvial environment. The Geste Formation is the lowermost unit of the Pastos Grandes Group and unconformably overlies different Paleozoic basements; the Late Ordovician Copalayo or Coquena Formation in the Pastos Grandes Basin, Ordovician Falda Ciénaga Formation in Antofagasta de la Sierra and Cordón del Gallego, Coquena Formation in the Sierra de Calalaste, or the Permian Patquía de la Cuesta Formation in the area surrounding the Antofalla volcano.Ciancio et al., 2016, p.577
The formation, reaching a thickness of , is overlain by the evaporites and claystones of the Pozuelos Formation of the Pastos Grandes Group.Alonso & Viramonte, 1987, p.397 The small Pastos Grandes Basin was formed during the Incan orogeny in the Eocene.Koukharsky, 1988, p.31 The Geste Formation is the only fossiliferous Paleogene formation cropping out in the Argentine Northwest. In the Pastos Grandes Basin, in outcrops located on the eastern flank of the Sierra de Copalayo in Salta Province, the Geste Formation was divided by Alonso (1992) into three members: lower, middle, and upper. The middle member contains fossils of vertebrates and represents deposition by medium-to-fast-flowing rivers, laying down the fine-to-medium-grained micaceous sandstones, grading into coarser sandstones towards the top of the middle member.
The sediments of the Geste Formation were sourced by the provenance area of the Oira Eruptive Complex, which formed a paleohigh between the Puna Plateau and the Calchaquí Valley where the contemporaneous Quebrada de los Colorados Formation was deposited.Aramayo et al., 2017, p.532
The middle member of the formation has been dated at maximum 37.5 ± 0.1 and minimum 35.4 ± 1.5 Ma, corresponding to the Priabonian stage of the Eocene.
Paleoecology The paleoclimate of the time was much more humid than today, with elevated temperatures compared to the present-day climate and the area was at lower altitudes before the final phase of the Andean orogeny which did not take place before the Miocene. In this subtropical fluvial biome, a diverse fauna established, with fossils of various groups found in the formation. Several clades found in the Geste Formation have not been found elsewhere in northwestern Argentina. The fauna of the area is only partly overlapping with the upper Lumbrera Formation and that of the Quebrada de los Colorados Formation.Babot et al., 2017, p.737
Paleontological significance The Geste Formation is an important Paleogene formation, as it is the only formation that has provided interathere fossils. Two fossil localities on the Puna Plateau are known, Antofagasta de la Sierra in Catamarca at an approximate altitude of and Pozuelos in Salta Province at .Reguero et al., 2008, p.226 The faunal assemblage comprises mammals of various groups, with notoungulates and armadillos dominating, reptiles (crocodiles, turtles and snakes not assigned to specific genera) and frog fossils.
Fossil content The formation has provided the following fossils:Antofagasta de la Sierra, Catamarca at Fossilworks.orgPozuelos salt flat, Quebrada El Paso, Salar de Pastos Grandes, Salta at Fossilworks.org
Class Group Fossils Image Notes Mammals Armadillos Parastegosimpsonia cf. peruana Ciancio et al., 2016, p.580 Parutaetus punaensis Ciancio et al., 2016, p.581 Prostegotherium notostylopianum Babot et al., 2017, p.741 Pucatherium parvum Ciancio et al., 2016, p.583 Punatherium catamarcensis Ciancio et al., 2016, p.584 Astegotherium sp. Ciancio et al., 2016, p.578 Prostegotherium sp. Ciancio et al., 2016, p.579 cf. Utaetus sp. Powell et al., 2011, p.361 Notoungulates Antofagastia turneri García López, 2015, p.287 Punahyrax bondesioi Punapithecus minor López & Bond, 1995, p.90 cf. Pampahippus sp. López, 1997, p.72 Notostylopidae indet. Notoungulata indet. Marsupials Bonapartherium serrensis Babot et al., 2017, p.740 Punadolops alonsoi Reigia punae Typotheres Suniodon catamarcensis López, 1995, p.168 ?Colbertia sp. López, 1995, p.169 Oldfieldthomasiidae indet. López, 1995, p.170 Polydolopimorphia Apeirodon solanoi Babot et al., 2020 Didolodontidae Ernestokokenia cf. yirunhor Pyrotheres Propyrotherium sp. López, 1997, p.70 Sparassodonts Callistoe sp. Astrapotheres Astrapotheriidae indet. Litopterns Litopterna indet. García & Babot, 2015, p.19 Reptiles Crocodiles Sebecidae indet. López, 1997, p.67 Snakes Boidae indet. Turtles Testudines indet. Amphibians Frogs Anura indet.
See also South American land mammal ages Guabirotuba Formation, contemporaneous fossiliferous formation of the Curitiba Basin, Brazil Seca Formation, contemporaneous fossiliferous formation of Ecuador La Meseta Formation, contemporaneous fossiliferous formation of Antarctica
References
Bibliography Geology
Paleontology