Laguna del Hunco Formation
{{Short description|Geological formation in Argentina}}
{{Infobox rockunit
| name = Laguna del Hunco Formation
| period = Lutetian
| age = Ypresian
(Itaboraian)
~{{fossil range|52.44|52}}
| image =
| imagesize =
| caption =
| type = Geological formation
| prilithology = Tuff, mudstone, sandstone
| otherlithology =
| unitof = Middle Chubut River Volcanic Pyroclastic Complex
| subunits =
| underlies = Sarmiento Group
| overlies = Barda Colorada Ignimbrite
| thickness = {{convert|170|m|ft|abbr=on}}
| area =
| map = {{Location map+ | Argentina
| relief = 1
| width = 250
| float = center
| places =
{{Location map~ | Argentina
| lat_deg = -42.3
| lon_deg = -70.0
| mark = Orange pog.svg
| marksize = 12
}}
}}
| map_caption =
| location =
| coordinates = {{coord|42.3|S|70.0|W|display=inline,title}}
| paleocoordinates = {{coord|44.8|S|60.0|W|display=inline}}
| region = Chubut Province
| country = Argentina
| extent = Cañadón Asfalto Basin
| namedfor = Laguna del Hunco
| namedby = Aragón & Mazzoni
| year_ts = 1997
| location_ts = Languiñeo Department
| coordinates_ts = {{coord|42.3|S|70.0|W|display=inline}}
| paleocoordinates_ts = {{coord|44.8|N|60.0|W|display=inline}}
| region_ts = Chubut Province
| country_ts = Argentina
| thickness_ts = {{convert|170|m|ft|abbr=on}}
}}
The Laguna del Hunco Formation or Laguna del Hunco Tuff ({{langx|es|Formación Laguna del Hunco, Tufolitas Laguna del Hunco}}) is a localized Early Eocene (Itaboraian in the SALMA classification) fossiliferous geological formation of the Cañadón Asfalto Basin in central Patagonia, Argentina. The {{convert|170|m|ft}} thick formation comprises tuffaceous mudstones and sandstones deposited in a crater lake environment and crops out at Laguna del Hunco in the northwestern Chubut Province.
The formation has been precisely dated to 52.22 ± 0.22 Ma on the basis of sanidine crystals in the tuffs of the formation. The Laguna del Hunco formation overlies the Barda Colorada Ignimbrite and is covered by the Sarmiento Group. The unit is renowned for the preservation of an extraordinarily rich fossil flora assemblage of mixed South American families and presently uniquely Australasian flora, among which the oldest Eucalyptus fossils found worldwide. The formation also has provided many fossil insects, including insect eggs, fossil fish of Bachmannia chubutensis and the frog Shelania pascuali. Periodic bursts of gas in the volcanic crater lake are thought to have produced the sudden death and preservation of the floral and faunal assemblage.
Description
The Laguna del Hunco Formation, named after Laguna del Hunco ("Lake of Reeds"), a desert pond in Chubut Province,Wilf et al., 2005, p.635Wilf et al., 2005, p.636 is a localized sedimentary unit comprising tuffaceous sandstones and mudstones with primary and reworked ashfall layers. The formation was deposited in a crater lake environment. The approximately {{convert|170|m|ft}} thick formation forms part of the Middle Chubut River Volcanic Pyroclastic Complex of the western Cañadón Asfalto Basin.Figari et al., 2015, p.154 This complex comprises a variety of volcaniclastic, intrusive, pyroclastic, and extrusive rocks, deposited over several million years. The complex is characterized by a great variety of volcanogenic bodies, such as ignimbrites, domes, lava flows, necks, intrusives, tuffs, and volcaniclastic deposits (of predominantly lacustrine origin), all of them frequently interbedded.Tejedor et al., 2009, p.5
The Laguna del Hunco Formation was formerly included in the Huitrera Formation,Zamaloa et al., 2006, p.1280 overlies the Barda Colorada Ignimbrite,Figari et al., 2015, p.153 and is overlain by the Sarmiento Group.Figari et al., 2015, p.155 The formation has been dated using 40Ar/39Ar analysis on sanidine crystals of the ash beds to 52.22 ± 0.22 Ma, placing the deposits in the Early Eocene, or Itaboraian in the SALMA classification.Carvalho et al., 2013, p.1834
Paleontological significance
File:Climate sensitivity sea level and atmospheric carbon dioxide. Hansen et al 2013.png
The paleoflora of the formation is considered one of the most biodiverse Cenozoic fossil deposits worldwide.Gandolfo et al., 2011, p.1 The biota is composed of extraordinarily rich assemblages of ferns, conifers, and flowering plants, many of which have not yet been formally described.[http://bhort.bh.cornell.edu/histology/localLH.html Laguna del Hunco] - Cornell University The flora of the formation, studied since the 1920s, was formerly thought to be Miocene in age.
Three described species in the genus Gymnostoma of the family Casuarinaceae,Zamaloa et al., 2006, p.1288 and the species Ceratopetalum edgardoromeroi of the family Cunoniaceae are the only members of these families found outside of Australasia.Gandolfo & Hermsen, 2017, p.9 The floral assemblage is thought to represent a lakeshore vegetation, deposited during the Early Eocene Climatic Optimum (EECO),Sarzetti et al., 2009, p.432 with estimated average yearly temperatures of {{convert|17.2|±|2.3|C|F}} and annual rainfall of {{convert|1673|±|426|mm|in}}.Dibán Karmy, 2018, p.26 Periodic gas bursts in the crater lake of Laguna del Hunco probably led to the sudden deaths of the flora and fauna found in the formation.
= Paleobiota =
The following fossil plants and animals have been described from the formation:
References
{{reflist|20em}}
= Bibliography =
- {{citation |last1=Degrange |first1=F. J. |last2=Pol |first2=D. |last3=Puerta |first3=P. |last4=Wilf |first4=P. |year=2021 |title=Unexpected larger distribution of Paleogene stem-rollers (Aves, Coracii): new evidence from the Eocene of Patagonia, Argentina |journal=Scientific Reports |volume=11 |issue=1 |pages=Article number 1363 |doi=10.1038/s41598-020-80479-8|pmid=33446824 |pmc=7809110 |bibcode=2021NatSR..11.1363D }} 50px Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].
- {{cite thesis |last=Dibán Karmy |first=María José |year=2018 |title=Evolución del nicho climático del género Escallonia Mutis ex L.F. (Escalloniaceae) en Sudamérica |url=https://repositorio.uchile.cl/handle/2250/146618 |hdl=2250/146618 |publisher=Universidad de Chile |pages=1–73 |accessdate=2019-03-02 }}
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Category:Geologic formations of Argentina
Category:Eocene Series of South America
Category:Tuff formations of Argentina
Category:Mudstone formations of Argentina
Category:Ooliferous formations
Category:Fossiliferous stratigraphic units of South America
Category:Paleontology in Argentina