Lebu Group is stratigraphic unit of Arauco Basin in south-central Chile. The group consists of a sequence of four

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondary ...

s, of both marine and nonmarine origin, deposited between the Early Paleocene and Middle Eocene.

Description

The group is made up of four formations, from youngest to oldest these are: Millongue Formation, Trihueco Formation, Boca Lebu Formation and Curanilahue Formation. The Eocene Millongue Formation is composed of

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...

and

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, p ...

of both marine and continental origin. Its top is marked by an unconformity, the so-called “main unconformity” of Arauco Basin, which is thought to have formed by erosion during a period of tectonic inversion.

Notes

References

{{Geology of Chile Geologic groups of South America Geologic formations of Chile Paleocene Series of South America Eocene Series of South America Paleogene Chile Danian Stage Selandian Stage Thanetian Stage Ypresian Stage Lutetian Stage Bartonian Stage Shale formations Sandstone formations Siltstone formations Mudstone formations Coal formations Geology of Biobío Region