The Agua de la Piedra is geologically part of the Neuquén Basin, Argentina's most prolific onshore petroleum producing basin of northwestern Patagonia, and crops out in the geographical feature of the Andean orogeny; the Argentinian Precordillera of the higher Andes in the hinterland. The Malargüe Group, of which the Agua de la Piedra Formation is the uppermost unit, hosts among the most spectacular dinosaur fossils and nesting sites in the Allen Formation, the lowermost stratigraphic unit of the group.
The Neuquén Basin started forming in the latest Jurassic as one of the rift basins resulting from the break-up of Pangea. While the earlier formations in the basin are mostly distal terrestrial in nature, the Agua de la Piedra Formation is a unique combination of purely terrestrial influence (paleosols) with the early Andean volcanism in the form of tuffs.
Oligocene South America differed quite substantially from the Eocene period preceding it. Isolated from Gondwana for 70 million years, the continent had developed widespread lush forests with their own specific faunas. The climate drastically cooled at the Eocene-Oligocene boundary with global cooling as a result of the formation of the Antarctic Ocean current. The South American landscape became more arid than in the Eocene with ongoing volcanism related to the Andean orogeny affecting the local climates.
Oligocene fauna
The Oligocene of South America is characterized by the arrival of the first monkeys, possibly rafting from Africa, which in the Oligocene was significantly removed from South America. The first rodents had arrived to the island continent in the Late Eocene before,[6] perhaps using similar methods of transoceanic transport. The rodents of South America diversified in the Oligocene. Cabeza Blanca, where the Sarmiento Formation outcrops, has provided the richest and most diverse Oligocene fauna of South America.[7]
The cooler Oligocene climate led to the widespread extension of savanna and other grasslandbiomes. In the Early Oligocene, these rodents inhabited open and arid landscapes with wind-blown dust and grasslands environments.[8]
The rodents had arrived in the Late Eocene and diversified greatly during the Deseadan following the appearance of Andemys with species A. frassinettii and A. termasi in the Tinguirirican (Abanico Formation; Tinguiririca fauna). Caviomorphs arrived in Patagonia during the latest Eocene or early Oligocene, and
by the Late Oligocene they were highly diversified, with representatives of the four main lineages. A great morphological disparity, at least in tooth morphology, was then acquired mainly by the development of hypsodonty in several lineages. The early evolution of each of the major clades was complex, especially for chinchilloids and octodontoids. The first stages of the evolution of cavioids are more obscure because they are recognized through the relatively derived Deseadan species of Cavioidea.[10]
The Oligocene (Tinguirirican and Deseadan SALMAs plus La Cantera fauna) has a rich record of caviomorphs showing a greater morphological disparity than older faunas. Representatives of the four superfamilies, with the archetypal dental features that characterize species of the subsequent SALMAs, can be clearly recognized, at least since the Deseadan SALMA. Although a few genera (e.g., Andemys, Branisamys) cannot be assigned with certainty to any supra generic taxa. The Acaremyidae were likely a group of austral differentiation. The first representatives, the Deseadan Platypittamys brachyodon, Galileomys baios and Changquin woodi,[11] attest to its differentiation into several lineages.[12]
Oligocene volcanism
Early Andean volcanism in the Southern Cone of South America dating to the Oligocene has been found in:
The formation comprises the "Rodados Lustrosos" level, formed by clastic heterogeneous conglomerates in a silty matrix, considered as the stratigraphic evidence of the Pehuenche orogenic phase of the Andean orogeny, followed by uniform sequences, variable in thickness, of whitish-ocher tuffaceouspaleosols with concretions and whitish-gray tuffs with intercalations of pyroclastic deposits.[19]
The upper part of the Agua de la Piedra Formation consists of 37 metres (121 ft) of white-grayish tuffs and tobaceous paleosols, with laminated or massive parallel stratification constitute the fossiliferous level of Quebrada Fiera.[20] The formation overlies the Pircala-Coihueco Formation.[21]
Depositional environment
The studied profiles of the Agua de la Piedra Formation show large lateral lithological varieties, typical of alluvial fan depositional setings. The climate during deposition has been estimated to be semi-arid and the differential thicknesses of facies associations within the Agua de la Piedra Formation may represent the infill of minibasins in the forming foreland of the Andes. Sedimentary loading can enhance the effect of tectonic forces in foreland basins. The variety in volcanic fragments and composition indicates local ash fall caused by contemporaneous volcanism in the area of deposition.[22]
2017 research on the Deseadan fauna (late Oligocene) from Quebrada Fiera, south of Mendoza Province, Argentina, evidences a rich mammal assemblage that shows the existence of common elements with Deseadan faunal associations of Patagonia and those of lower latitudes such as Salla, Bolivia, as well as endemic taxa of different groups.[23]
Endemism refers to Notohippidae (Mendozahippus fierensis), Leontiniidae (Gualta cuyana), Homalodotheriidae (Asmodeus petrasnerus) and Metatheria
(Fieratherium sorex); to these mammals a new terrestrial snail has been added in 2016.[24]
Faunal data published in 2019 confirm the Deseadan age, but as per 2020, absolute dating is lacking for Quebrada Fiera.[19]
The geological characterization and the preliminary faunal list were published by Gorroño et al. (1979). The faunal assemblage was then assigned to the Late Oligocene (Deseadan SALMA) based on the presence of two typical representatives of the Deseadean fauna of Patagonia; PyrotheriumAmeghino 1888 and Proborhyaena giganteaAmeghino 1897,[19] both also found in the Puesto Almendra member of the Sarmiento Formation.[27]
Balgord, Elizabeth A (2017), "Triassic to Neogene evolution of the south-central Andean arc determined by detrital zircon U-Pb and Hf analysis of Neuquén Basin strata, central Argentina (34°S–40°S)", Lithosphere, 9 (3): 453–462, Bibcode:2017Lsphe...9..453B, doi:10.1130/L546.1
Mella, M.; Quiroz, D. (2010), Geología del Área Temuco-Nueva Imperial escala 1:100.000, Región de La Araucanía. Servicio Nacional de Geología y Minería, Carta Geológica de Chile, Serie Geología Básica, vol. 122, pp. 1–46
Elgueta, Sara; Le Roux, Jacobus; Duhart, Paul; McDonough, Michael; Urqueta, Esteban (2000), Estratigrafía y sedimentología de la cuencas terciarias de la Región de Los Lagos (39-41°30'S), Servicio Nacional de Geología y Minería, p. 15, ISSN0020-3939
Alfaro, G.; Gantz, E.; Magna, O. (1990), El yacimiento de carbón Catamutún (La Unión), Segundo Simposio sobre el Terciario de Chile, Departamento de Geociencias, Facultad de Ciencias, Universidad de Concepción, pp. 11–28
Cerdeño, Esperanza; Reguero, M.; Vera, B. (2010), "Deseadan Archaeohyracidae (Notoungulata) from Quebrada Fiera (Mendoza, Argentina) in the Paleobiogeographic Context of the South American Late Oligocene", Journal of Paleontology, 84 (6): 1177–1187, doi:10.1666/10-024.1
Carlini, A.A.; Ciancio, M.R.; Flynn, J. J.; Scillato Yané, G. J.; Wyss, A. R. (2009), "The phylogenetic and biostratigraphic significance of new armadillos (Mammalia, Xenarthra, Dasypodidae, Euphractinae) from the Tinguirirican (early Oligocene) of Chile", Journal of Systematic Palaeontology, 7 (4): 489–503, Bibcode:2009JSPal...7..489C, doi:10.1017/S1477201908002708
Patterson, Bryan; Marshall, Larry G. (1978), "The Deseadan, Early Oligocene, Marsupialia South America", Fieldiana: Geology, 41 (2): 37–100
Vassallo, Aldo I.; Antenucci, Daniel (2015), Biology of Caviomorph Rodents: Diversity and Evolution, SAREM, pp. 1–330, ISBN9789879849736
Vassallo, Aldo I.; Antenucci, Daniel (2015), "Caviomorph rodents: an introduction", SAREM Series A, Prologue: 2–10
Vucetich, María G.; Arnal, Michelle; Deschamps, Cecilia M.; Pérez, Maria E.; Vieytes, Emma C. (2015), "A brief history of caviomorph rodents as told by the fossil record", SAREM Series A, Chapter 1: 11–63
Ojeda, Ricardo A.; Novillo, Agustina; Ojeda, Agustina A. (2015), "Large-scale richness patterns, biogeography and ecological diversification in caviomorph rodents", SAREM Series A, Chapter 3: 121–138
Pérez, María Encarnación; Krause, Marcelo; Vucetich, María Guiomar (2012), "A new species of Chubutomys (Rodentia, Hystricognathi) from the late Oligocene of Patagonia and its implications on the early evolutionary history of Cavioidea sensu stricto", Geobios, 45 (6): 573–580, Bibcode:2012Geobi..45..573P, doi:10.1016/j.geobios.2012.06.001
Acosta, Jorge E.; Guatame, Rafael; Caicedo A., Juan Carlos; Cárdenas, Jorge Ignacio (2002), Mapa Geológico de Colombia - Plancha 245 - Girardot - 1:100,000 - Memoria Explicativa, INGEOMINAS, pp. 1–92
Acosta, Jorge E.; Ulloa, Carlos E. (2001), Mapa Geológico de Colombia - Plancha 246 - Fusagasugá - 1:100,000 - Memoria Explicativa, INGEOMINAS, pp. 1–77
Tremembé Formation
Do Couto Ribeiro, Graziella (2010), Avaliação morfológica, taxonômica e cronológica dos mamíferos fósseis da Formação Tremembé (Bacia de Taubaté), Estado de São Paulo, Brasil, Universidade de São Paulo, pp. 1–112