Ranquil Formation

{{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.{{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}} The formation is part of the fill of Arauco Basin which is a sedimentary basin that extends south of Concepción.

Macrofossils of the formation are similar to those of Navidad (34° S) and Lacui Formations (43° S), two nearby Miocene marine formations.{{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}}

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.{{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}}

The formation was first defined in 1942 by Juan Tavera.