Agrio Formation
{{Short description|Geologic formation in Argentina}}
{{distinguish|Bajada del Agrio Group}}
{{Infobox rockunit
| name = Agrio Formation
| image = Formación Agrio (Cretácico inferior) en su localidad tipo.jpg
| caption = Agrio Formation at its type section
| type = Geological formation
| period = Barremian
| age = Late Valanginian-earliest Aptian
~{{fossil range|130|120}}
| prilithology = Shale, sandstone
| otherlithology = Limestone, conglomerate
| namedfor = Agrio River
| namedby = Weaver
| year_ts = 1931
| region = Mendoza & Neuquén Provinces
| country = Argentina
| coordinates = {{coord|38.0|S|70.0|W|display=inline,title}}
| paleocoordinates = {{coord|38.2|S|33.7|W|display=inline}}
| unitof = Mendoza Group
| subunits = Pilmatué, Avilé & Agua de la Mula Members
| underlies = Huitrín & La Amarga Formations
| overlies = Mulichinco & Bajada Colorada Formations
| thickness = Up to {{convert|1500|m|ft|abbr=on}}
| extent = Neuquén Basin
| area = {{convert|220|x|50|km|mi|abbr=on}}
| map = {{Location map+ | Argentina
| relief = 1
| width = 250
| float = center
| places =
{{Location map~ | Argentina
| lat_deg = -38.0
| lon_deg = -70.0
| mark = Green pog.svg
| marksize = 12
}}
}}
| map_caption =
}}
The Agrio Formation is an Early Cretaceous geologic formation that is up to {{convert|1500|m|ft}} thick and is located in the southern Mendoza Province and northern-central Neuquén Province, in the Neuquén Basin of northwestern Patagonia, Argentina.Weaver, C. E. (1931). Paleontology of the Jurassic and cretaceous of west central Argentina. In Memoires of the University of Washington (Vol. 1, pp. 1–599). This formation is the youngest one of the Mendoza Group, overlying the Mulichinco and Bajada Colorada Formations and overlain by the Huitrín and La Amarga Formations. It is dated to the Late Valanginian to Early Hauterivian,Voglino, 2017, p.39 Late Valanginian to Early Barremian,Voglino, 2017, p.49 or Hauterivian to earliest Aptian.Gómez Dacal et al., 2018, p.113
The Agrio Formation is considered the third most important source rock in the hydrocarbon-rich Neuquén Basin, after the Vaca Muerta Formation and Los Molles Formation. Similarly to these older units, it is potentially a source of shale gas.
This formation has provided fossils of ichthyosaurs, ammonites, gastropods, bivalves, decapods, echinoderm, corals and fish. The newly described species of fish, Tranawuen agrioensis, the ammonite Holcoptychites agrioensis, and the bivalve Pholadomya agrioensis have been named after the formation.
Description
File:Formación Agrio en Aguada de la Mula. Panorámica 2.jpg
The Agrio Formation was first described by Weaver in 1931 and its three members, from bottom to top: Pilmatué, Avilé and Agua de la Mula Members, were defined by Leanza and Hugo in 2001.Archuby, F. M. (2009). Taphonomy and palaeoecology of benthic macroinvertebrates from the Agua de la Mula Member of the Agrio Formation, Neuquén Basin (Neuquén province, Argentina): sequence stratigraphic significance [Würzburg University]. http://www.opus-bayern.de/uni-wuerzburg/volltexte/2009/3717/index.html The formation crops out in an approximately {{convert|50|km|mi}} wide band from north to south along 70° longitude west, from 37° to 39° south in the northern-central part of the Neuquén Basin.Voglino, 2017, p.50 The southern termination of the formation is the Huincul High, formed by the Huincul Fault. Towards the east in the basin, the formation grades into the Centenario Formation.
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= Stratigraphy =
File:Mapa afloramientos de la Formación Agrio. De Spalletti et al 2011..png
The Agrio Formation is included in the Mendoza Group, representing its youngest formation. In the east of the Neuquén Basin, the formation rests upon continental clastic deposits of the Mulichinco Formation, with the contact between the two formations characterized by a regional transgressive surface. Towards the west, the formation unconformably overlies the Bajada Colorada Formation.Leanza, H. A., Hugo, C. A., & Repol, D. (2001). Hoja Geológica 3969-I, Zapala. Provincia del Neuquén. In Referencia bibliográfica LEANZA, H.A., C. A. HUGO y D. REPOL, 2001. Hoja Geológica 3969-I, Zapala. Provincia del Neuquén. Instituto de Geología y Recursos Minerales, Servicio Geoló- gico Minero Argentino. Boletín (Vol. 275).Olivo et al., 2016, p.218Gallina et al., 2014, p.2 In its eastern part, the Agrio Formation is overlain by the clastic, carbonaceous and evaporitic deposits of the Huitrín Formation and in the western area by the La Amarga Formation. The total thickness of the Agrio Formation reaches up to {{convert|1500|m|ft}}, with the Pilmatué Member having a thickness of {{convert|718|m|ft}} and the Agua de la Mula Member reaching {{convert|501|m|ft}}.Voglino, 2017, p.51
= Lithologies =
File:Formación Agrio (Cretácico inferior) cerca de Pilmatué.jpg
The Agrio Formation is primarily composed of pelitic rocks with intercalations of limestones, sandstones and rare fine conglomerates. The Pilmatué and Agua de la Mula Members are characterized by thick successions of black shales with intercalating limestones and sandstones. The Avilé Member comprises sandstones and claystones with conglomerates.Archuby, F. M., & Fürsich, F. T. (2010). Facies analysis of a {{sic|?|higly}} cyclic sedimentary unit: the Late Hauterivian to Early Barremian Agua de la Mula Member of the Agrio Formation, Neuquén Basin, Argentina. Beringeria, 41, 53–106. https://doi.org/https://doi.org/10.15517/rbt.v56i3.27147
= Depositional environment =
The Agrio Formation was deposited in a post-rift setting of the Neuquén Basin, probably representing a tectonic regime of thermal subsidence. The sediments of the lower and upper members of the formation are marine in character, interpreted as the combination of thermal subsidence and a eustatic sea level rise.Archuby, F. M., Wilmsen, M., & Leanza, H. A. (2011). Integrated stratigraphy of the Upper Hauterivian to Lower Barremian Agua de la Mula Member of the Agrio Formation, Neuquén Basin, Argentina. Acta Geologica Polonica, 61(1), 1–26.Archuby, F. M., & Fürsich, F. T. (2010). Facies analysis of a higly cyclic sedimentary unit: the Late Hauterivian to Early Barremian Agua de la Mula Member of the Agrio Formation, Neuquén Basin, Argentina. Beringeria, 41, 53–106. https://doi.org/https://doi.org/10.15517/rbt.v56i3.27147 The middle Avilé member was deposited in a fluvial environment. Within the marine Pilmatué Member, a succession of approximately {{convert|130|m|ft}} thick, described as "San Eduardo Beds", is recognized as deposited in a wave-dominated deltaic setting with hyperdense currents. This sequence is overlain by about {{convert|40|m|ft}} thick limestones deposits in a reefal environment. The presence of the newly described gastropod Eunerinea mendozana led researchers to estimate tropical conditions for the Agrio Formation.Cataldo, 2012
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Fossil content
The formation has provided many fossils of ammonites,Aguirre Urreta, 1998 gastropods, bivalves, corals, decapods, echinoids, crinoids and nano and microfossils (calcareous nannofossils, ostracods, foraminifers).Kauffman & Leanza, 2004[https://paleobiodb.org/classic/displayCollResults?collection_no=47202 Agrio Formation] at Fossilworks.orgBallent, S., Concheyro, A., Náñez, C., Pujana, I., Lescano, M., Carignano, A. P., Caramés, A., Angelozzi, G., & Ronchi, D. (2011). Microfósiles Mesozoicos Y Cenozoicos. Relatorio Del XVIII Congreso Geológico Argentino, September 2017, 489–528.{{Cite journal|last1=Ballent|first1=Sara|last2=Concheyro|first2=Andrea|last3=Sagasti|first3=Guillermina|date=January 2006|title=Bioestratigrafía y paleoambiente de la Formación Agrio (Cretácico Inferior), en la Provincia de Mendoza, Cuenca Neuquina, Argentina|url=https://scielo.conicyt.cl/scielo.php?script=sci_abstract&pid=S0716-02082006000100003&lng=en&nrm=iso&tlng=en|journal=Revista Geológica de Chile|volume=33|issue=1|pages=47–79|doi=10.4067/S0716-02082006000100003|issn=0716-0208|doi-access=free|hdl=11336/93727|hdl-access=free}}{{Cite journal|last1=Caratelli|first1=Martina|last2=Archuby|first2=Fernando M.|last3=Fürsich|first3=Franz|last4=Pignatti|first4=Johannes|date=2021-07-01|title=Macroids from mixed siliciclastic-carbonate high-frequency sequences of the Agrio Formation (Lower Cretaceous), Neuquén Basin: Palaeoecological and palaeoenvironmental constraints|url=http://rid.unrn.edu.ar/bitstream/20.500.12049/9510/3/Caratelli.pdf|journal=Cretaceous Research|language=en|volume=123|pages=104778|doi=10.1016/j.cretres.2021.104778|bibcode=2021CrRes.12304778C |s2cid=233951814 |issn=0195-6671}}
In 2018, ichthyosaur remains not determined to the genus level were described from the Agrio Formation, suggesting the possibility of viviparity of these marine reptiles in the epeiric sea of the Neuquén Basin. The finds were notable as well because of a relative lack of abundance of ichthyosaur fossils from the Valanginian to Hauterivian worldwide.Lazo et al., 2018 Fossil fish of Gyrodus huiliches, and Tranawuen agrioensis were described from the formation in 2019.Gouiric Cavalli et al., 2019
The decapod Palaeohomarus pacificus,Aguirre Urreta et al., 2012 and ammonites Curacoites rotundus and Sabaudiella riverorum were described from the formation in 2012,Aguirre Urreta & Rawson, 2012 the gastropods Ampullina pichinka and Mesalia? kushea in 2016,Cataldo & Lazo, 2016 and the ammonite Comahueites aequalicostatus in 2018.Aguirre Urreta & Rawson, 2018
Newly described species of fish, Tranawuen agrioensis, ammonite, Holcoptychites agrioensis,Lazo, 2003 and the bivalve Pholadomya agrioensis were named after the formation.
The first known brittle stars in the Southern Hemisphere and Cretaceous age have been identified in Agrio Formation.Fernández et al., 2019 However, fossils are not complete enough to define species.
Petroleum geology
The Agrio Formation is considered the third-most important source rock of the hydrocarbon-rich Neuquén Basin, after the older Vaca Muerta and Los Molles Formations.Geologic Map, 2007, p.142 Two levels of organic-rich sediments exist in the formation, related to the marine transgressions of the late Valanginian and the late Hauterivian, in the Pilmatué and Agua de la Mula Members respectively. The marly shales of the Pilmatué Member reach up to {{convert|400|m|ft}} thickness in the western Neuquén Basin, while the same facies in the Agua de la Piedra Member is less than {{convert|100|m|ft}} thick. The organic properties of the formation are similar to the Vaca Muerta, with a TOC value averaging 2.5%, with some levels up to 5%. The kerogen types are II to II/III.Voglino, 2017, p.39
Gallery
Fragmento de amonoide (Formación Agrio, Cretácico inferior, cerro Marucho).jpg|Ammonite from the Agrio Formation
Bivalvo (Formación Agrio, Cretácico inferior, cerro Santa Elena).jpg|Bivalve from the formation
Fosíl de Ptychomya koeneni.jpg|Bivalve (Ptychomya koeneni)
See also
- List of dinosaur-bearing rock formations
- Caiuá Formation, contemporaneous fossiliferous formation of the Paraná Basin
- Cerro Barcino Formation, contemporaneous fossiliferous formation of the Cañadón Asfalto Basin
- Zapata and Río Belgrano Formations, contemporaneous fossiliferous formations of the Magallanes or Austral Basin
References
{{reflist|20em}}
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{{commons category}}
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;Geologic map
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Category:Geologic formations of Argentina
Category:Lower Cretaceous Series of South America
Category:Conglomerate formations
Category:Shallow marine deposits
Category:Source rock formations
Category:Geology of Mendoza Province