Ranquil Formation
Miocene and Pliocene sedimentary formation in south-central Chile From Wikipedia, the free encyclopedia
The Ranquil Formation (Spanish: 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.[1] The formation is part of the fill of Arauco Basin which is a sedimentary basin that extends south of Concepción.[2]
| Ranquil Formation | |
|---|---|
| Stratigraphic range: Miocene–Pliocene | |
| Type | Geological formation |
| Underlies | Tubul Formation |
| Overlies | Lebu Group |
| Lithology | |
| Primary | Conglomerate with clay and silt matrix, breccia, sandstone, siltstone, mudstone |
| Other | Conglomerate with sand matrix |
| Location | |
| Coordinates | 37.6°S 73.7°W |
| Approximate paleocoordinates | 37.9°S 71.4°W |
| Region | Bío Bío Region |
| Country | Chile |
| Type section | |
| Named for | Caleta Ranquil |
| Named by | Juan Tavera |
| Year defined | 1942 |
 Ranquil Formation (Chile) | |
Macrofossils of the formation are similar to those of Navidad (34° S) and Lacui Formations (43° S), two nearby Miocene marine formations.[3]
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.[4]
The formation was first defined in 1942 by Juan Tavera.[1]
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.[2] The sediments of Huenteguapi sandstone evidences that a megatsunami struck the coast of south–central Chile in the Pliocene,[2] 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.[5]
See also
- Arauco Peninsula – Peninsula in Chile
References
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