Chichinales Formation

The Chichinales Formation is a geological formation in Río Negro Province, Argentina which dates from the Late Oligocene to the Early Miocene, around 23 to 17.5 million years ago. It predominantly consists of pyroclastic deposits, which were deposited in a semi-arid environment. It is divided up into a number of members. The diverse fauna of the Chichinales Formation, including a variety of turtles and birds, also includes many mammals such as South American native ungulates (notoungulates and litopterns) as well as armadillos, and caviomorph rodents.^[1][2]

Chichinales Formation
Stratigraphic range: Chattian-Burdigalian (Deseadan-Colhuehuapian) ~23–17.5 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Underlies	El Palo Formation
Overlies	Roca Formation
Thickness	90 m (300 ft)
Lithology
Primary	Sandstone, mudstone
Other	Limestone
Location
Coordinates	39.1°S 67.8°W / -39.1; -67.8
Approximate paleocoordinates	39.8°S 62.2°W / -39.8; -62.2
Region	Río Negro Province
Country	Argentina
Extent	Neuquén Basin
Type section
Named for	Chichinales

It is named after the type locality and extends over a large part of the province of Río Negro. It outcrops in the valle de Río Negro, in the towns of General Roca, Río Negro and Villa Regina, bordering the southern bank of the Río Negro. Part of the most important outcrops are located within the Paso Córdova Natural Protected Area.^[2]

The Chichinales Formation, broadly speaking, is made up of grayish sandstones, whitish tuffs, siltstones and greenish claystones with paleo soil levels. It is divided into 3 members: lower, middle and upper. The lower one is composed of grayish brown sandstones with low-angle cross bedding, alternating with light brown tuffs, tuffaceous sandstones, sandstones with carbonate cement and shales. In this member, the presence of "opalized" fossil logs is common. The middle member is formed by paleosols and sequences of siltstones, shales and fine sands that in some sectors form lenses in the form of fluvial channels. Finally, the upper member is represented by more homogeneous levels of tuffs, whitish gray tuffites, siltstones, green claystones and tuffaceous sandstones This member, in some sectors, is laterally interdigitated with marginal marine levels of the Gran Bajo del Gualicho Formation, which dates from the Late Oligocene to the Early Pliocene.^[3][4] The Chichinales Formation is correlated with the contemporaneous fluvial and lacustrine tuffaceous Collón Curá Formation of the central Neuquén Basin.^[5]

The sedimentological and paleontological evidence provided by the Chichinales Formation suggests the existence of open environments with low relief, restricted wooded areas with temporary water bodies and warm temperate climate, in agreement with other Colhuehuapian localities of Chubut Province. In this context, it is possible to interpret, at least tentatively, that the differences between the set of taxa represented in the Cerro Bandera Formation and those of the Chichinales Formation are due to contrasts between the local environmental conditions of each unit rather than to differences in temporal range. It is likely that such differences are the result of the particular conditions that prevailed in the Neuquén region during the Early Miocene, which would be a consequence of its proximity to the Andean zone rather than its latitudinal location.^[6]

Paleoflora

Name	Species	Member/Locality	Material	Notes	Image
Nothofagus[7]	N. menendezii

Paleofauna

Reptiles

Lepidosaurs

Name	Species	Member	Material	Notes	Image
Callopistes[8]	C. rionegrensis

Crocodylomorphs

Name	Species	Member	Material	Notes	Image
Crocodyliformes indet.[9]	Currently undescribed		Isolated fragment of the posterior region of the skull roof.

Testudines

Name	Species	Member	Material	Notes	Image
Chelonoidis[10]	C. cf. gringorum
Geochelone	G. sp.

Birds

Name	Species	Member	Material	Notes	Image
Charadriiformes indet.[11]	Currently undescribed
Opisthodactylus[11]	O. horacioperezi
Patagorhacos[11]	P. terrificus
Phorusrhacidae indet.[1]	Currently undescribed		Distal extremity of tibiotarsus

Mammals

Meridiungulates

Name	Species	Material	Notes	Image
Cochilius[11]	C. volvens		An interatheriid
Colpodon[1]	C. sp.	Several maxillary remains
Cramauchenia[1]	C. sp.		A macraucheniid
Hegetotheriopsis[12]	H. sulcatus		A hegetotheriid
Hegetotherium[12][1]	H. sp.
Interatheriidae indet.	Currently undescribed	Mandibular and maxillary fragment
Mesotheriidae indet.[13]	Currently undescribed
Proterotheriidae indet.[1]	Currently undescribed	Maxillary and mandibular fragment
Protypotherium[1]	P. sp.		An interatheriid
Toxodontidae indet.[1]	Currently undescribed	Left and right mandibular fragments with incomplete series of teeth

Xenarthrans

Name	Species	Member	Material	Notes	Image
Glyptodontinae indet.	Currently undescribed
Proeutatus[1]	P. sp.
Stenotatus[1]	cf. S. sp.

Rodents

Name	Species	Member	Material	Notes	Image
Australoprocta[14]	A. fleaglei
Caviocricetus[14]	C. lucasi
Echimyidae indet.[1]	Currently undescribed
Eoviscaccia[14]	E. australis
Octodontoidea indet.[14]	Currently undescribed
Willidewu[14][15]	W. esteparius

Metatherians

Name	Species	Member	Material	Notes	Image
Cladosictis[1]	C. cf. patagonica		Complete right maxillary fragment

References

1. Barrio, Claudio; Carlini, Alfredo A.; Goin, Francisco J. (1989). "Litogénesis y antigüedad de la Formación Chichinales de Paso Córdoba (Río Negro, Argentina)". Actas, IV Congreso Argentino de Paleontología y Bioestratigrafía, Mendoza. 4: 149–156.
2. Vincenty, Lorena (2020-08-30). "Por qué en la Formación Chichinales se rastrea el origen de la Patagonia". Diario Río Negro | Periodismo en la Patagonia (in Spanish). Retrieved 2022-09-04.
3. Hugo, Carlos A.; Leanza, Héctor A. (2001). "Hoja Geológica 3966-III - Villa Regina" (PDF). Boletín Nº 309 Instituto de Geología y Recursos Minerales - Servicio Geológico Minero Argentino. ISSN 0328-2333.
4. Huyghe, Damien; Bonnel, Cédric; Nivière, Bertrand; Fasentieux, Bertrand; Hervouët, Yves (2015-09-02). "Neogene tectonostratigraphic history of the southern Neuquén basin (39°–40°30′S, Argentina): implications for foreland basin evolution". Basin Research. 27 (5): 613–635. doi:10.1111/bre.12091. ISSN 1365-2117. S2CID 128632229.
5. Rodríguez, María F.; Leanza, Héctor A.; Salvarredy Aranguren, Matías (2007). "Hoja Geológica 3969-II, NEUQUÉN, provincias del Neuquén, Río Negro y La Pampa 1:250,000". Instituto de Geología y Recursos Minerales: 1–165. Retrieved 2019-02-23. {{cite journal}}: Cite journal requires |journal= (help)
6. Kramarz, Alejandro; Garrido, Alberto; Forasiepi, Analía; Bond, Mariano; Tambussi, Claudia (2005). "Stratigraphy and vertebrates (Aves and Mammalia) from the Cerro Bandera Formation, Early Miocene of Neuquén Province, Argentina". Revista Geológica de Chile. 32 (2). doi:10.4067/S0716-02082005000200006. Material was copied from this source, which is available under a Creative Commons Attribution 3.0 International License
7. Ragonese, Ana María (1977). "Nothofagoxylon menendezii, leño petrificado del Terciaro de General Roca, Río Negro, Argentina". Ameghiniana (in Spanish). 14 (1–4): 59–74. ISSN 1851-8044.
8. Quadros, Ana B.; Chafrat, Pablo; Zaher, Hussam (2018-07-04). "A new teiid lizard of the genus Callopistes Gravenhorst, 1838 (Squamata, Teiidae), from the Lower Miocene of Argentina". Journal of Vertebrate Paleontology. 38 (4): (1)–(18). doi:10.1080/02724634.2018.1484754. ISSN 0272-4634. S2CID 91195492.
9. Lio, Gabriel; Agnolin, Federico; Chimento, Nicolás Roberto; Chafrat, Pablo Anselmo (2019). "The youngest crocodyliform record from Patagonia (Chichinales Formation, Early Miocene)". Brazilian Geographical Journal: Geosciences and Humanities Research Medium. 8 (2): 136–143. ISSN 2179-2321.
10. De Broin, F; De la Fuente, M. (1993). "Les tortues fossiles d'Argentine:synthèse". Les tortues fossiles d'Argentine: Synthèse. 79 (3): 169–232. ISSN 0753-3969.
11. Federico L. Agnolin and Pablo Chafrat (2015). "New fossil bird remains from the Chichinales Formation (Early Miocene) of northern Patagonia, Argentina". Annales de Paléontologie. 101 (2): 87–94. Bibcode:2015AnPal.101...87A. doi:10.1016/j.annpal.2015.02.001.
12. Kramarz, Alejandro Gustavo; Paz, Ernesto Rodrigo (2013). "Un Hegetotheriidae (Mammalia, Notoungulata) basal del Mioceno temprano de Patagonia". Revista Mexicana de Ciencias Geológicas (in Spanish). 30 (1): 186–195. ISSN 1026-8774.
13. Paz, E. Rodrigo; Kramarz, Alejandro; Bond, Mariano (2011). "Mesotheriid (Mammalia, Notoungulata) Remains from the Colhuehuapian Beds (Early Miocene) of Chichinales Formation, Río Negro Province, Argentina". Ameghiniana. 48 (2): 264–269. doi:10.5710/AMGH.v48i2(242). hdl:11336/135387. ISSN 0002-7014. S2CID 131568947.
14. Madden, Richard H.; Carlini, Alfredo A.; Vucetich, Maria Guiomar; Kay, Richard F. (2010-06-17). "Colhuehuapian rodents from Gran Barranca and other Patagonian localities: the state of the art.". The Paleontology of Gran Barranca: Evolution and Environmental Change Through the Middle Cenozoic of Patagonia. Cambridge University Press. ISBN 978-0-521-87241-6.
15. Vucetich, María Guiomar; Verzi, Diego H. (1991). "Un nuevo Echimyidae (Rodentia, Hystricognathi) de la edad Colhuehuapense de Patagonia y consideraciones Sobre la sistemática de la familia". Ameghiniana (in Spanish). 28 (1–2): 67–74. ISSN 1851-8044.