{{Short description|Miocene and Pliocene sedimentary formation in south-central Chile}} {{Infobox rockunit | name = Ranquil Formation | image = | caption = | type = Geological formation | period = Pliocene | age = Miocene–Pliocene | prilithology = Conglomerate with clay and silt matrix, breccia, sandstone, siltstone, mudstone | otherlithology = Conglomerate with sand matrix | namedfor = Caleta Ranquil | namedby = Juan Tavera | year_ts = 1942 | region = Bío Bío Region | country = Chile | coordinates = {{coord|37.6|S|73.7|W|display=inline,title}} | paleocoordinates = {{coord|37.9|S|71.4|W|display=inline}} | unitof = | subunits = | underlies = Tubul Formation | overlies = Lebu Group | thickness = | extent = | area = | map = {{Location map+ | Chile | relief = 1 | width = 150 | float = center | places = {{Location map~ | Chile | lat_deg = -37.6 | lon_deg = -73.7 | mark = Yellow ffff00 pog.svg | marksize = 12 }} }} | map_caption = }} The '''Ranquil Formation''' ({{langx|es|Formación Ranquil}}) is a Miocene and Pliocene sedimentary formation located in Arauco Province in south–central Chile, including outcrops in Mocha Island. The formation has its greatest thicknesses in the south-west, where its sediments were largely deposited in marine conditions. It overlies unconformably sedimentary formations of the Paleocene-Eocene Lebu Group.<ref name=Garcia1968>{{cite book |last=García A. |first=Floreal |date=1968 |title=El Terciario de Chile Zona Central |editor-last=Ceccioni |editor-first=Giovanni |location=Santiago de Chile |publisher=Editorial Andrés Bello |pages=25–57 |language=es}}</ref> The formation is part of the fill of Arauco Basin which is a sedimentary basin that extends south of Concepción.<ref name=LeRouxetal2008/>
Macrofossils of the formation are similar to those of Navidad (34° S) and Lacui Formations (43° S), two nearby Miocene marine formations.<ref>{{cite journal |last1=Finger |first1=Kenneth L. |last2=Nielsen |first2=Sven N. |last3=Devries |first3=Thomas J. |last4=Encinas |first4=Alfonso |last5=Peterson |first5=Dwan E. |date=2007 |title=Paleontologic evidence for sedimentary displacement in Neogene forearc basins of Central Chile |url=http://www.ucmp.berkeley.edu/people/klf/KLF_files/Palaios.pdf |journal=PALAIOS |volume=22 |issue=1 |pages=3–16 |doi= 10.2110/palo.2005.p05-081r|bibcode=2007Palai..22....3F |s2cid=59383760 |access-date=28 July 2016}}</ref>
The base of the Ranquil Formation is the so-called "main unconformity", which is thought to have been formed by erosion during a period of tectonic inversion.<ref name=Becerraetal2013>{{cite journal|last1=Becerra|first1=Juan|last2=Contreras-Reyes |first2=Eduardo |last3=Arriagada |first3=César |title=Seismic structure and tectonics of the southern Arauco Basin, south-central Chile (~ 38°S) |journal=Tectonophysics|date=2013|volume=592|pages=53–66 |doi=10.1016/j.tecto.2013.02.012|bibcode=2013Tectp.592...53B|hdl=10533/238054|hdl-access=free}}</ref>
The formation was first defined in 1942 by Juan Tavera.<ref name=Garcia1968/>
== Units == The formation has been subdivided into five units, with the lowermost being made up of sandstone and shale, and the second lowest one being made up of a conglomerate. The middle unit is made up of mudrock and massive sandstone. At some places the middle unit is overlain by a unit made up of sandstone with thin layers of conglomerate and sandstone that has been bioturbated. The uppermost unit include a breccia and the so-called ''Huenteguapi sandstone''.<ref name=LeRouxetal2008>{{cite journal |last1=Le Roux |first1=J.P. |last2=Nielsen |first2= Sven N. |last3=Kemnitz |first3=Helga |last4=Henriquez |first4=Álvaro |date=2008 |title=A Pliocene mega-tsunami deposit and associated features in the Ranquil Formation, southern Chile |url=http://repositorio.uchile.cl/bitstream/handle/2250/125260/Le%20Roux_J_P.pdf?sequence=1 |journal=Sedimentary Geology |volume=203 |issue=1 |pages=164–180 |doi= 10.1016/j.sedgeo.2007.12.002|bibcode=2008SedG..203..164L |access-date=11 April 2016}}</ref> The sediments of Huenteguapi sandstone evidences that a megatsunami struck the coast of south–central Chile in the Pliocene,<ref name=LeRouxetal2008/> which has been linked to the hypothetical Eltanin impact.
== Fossil content == The Ranquil Formation contains the following trace fossils: ''Zoophycos'', ''Chondrites'', ''Phycosiphon'', ''Nereites missouriensis'', ''Lockeiasiliquaria'', ''Parataenidium'', ''Ophiomorpha'', ''Rhizocorallium'' and possibly also ''Psammichnites''.<ref>{{cite journal |last1=Le Roux |first1=Jacobus P. |last2=Nielsen |first2=Sven N. |last3=Henríquez |first3=Álvaro |date=2008 |title=Depositional environment of Stelloglyphus llicoensis isp. nov.: a new radial trace fossil from the Neogene Ranquil Formation, south-central Chile |url=http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0716-02082008000200006 |journal=Revista Geológica de Chile |volume=35 |issue=2 |pages=307–319 |doi= 10.5027/andgeov35n2-a06|access-date=29 July 2016|doi-access=free }}</ref>
== See also == * {{annotated link|Arauco Peninsula}}
== References == {{reflist}}
{{Sedimentary formations and groups in Chile}}
Category:Geologic formations of Chile Category:Miocene Series of South America Category:Pliocene Series of South America Category:Neogene Chile Category:Conglomerate formations of Chile Category:Geology of Biobío Region Category:Coasts of Biobío Region