Cura-Mallín Group () is a heterogeneous group of volcano-sedimentary formations of

Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

age,

Colhuehuapian The Colhuehuapian age is a period of geologic time (21.0–17.5 Ma) within the Early Miocene epoch of the Neogene, used more specifically within the SALMA classification in South America. It follows the Deseadan and precedes the Santacrucian ag ...

Laventan The Laventan () age is a period of geologic time (13.8 to 11.8 Ma) within the Middle Miocene epoch of the Neogene, used more specifically within the SALMA classification in South America. It follows the Colloncuran and precedes the Mayoan age. ...

in the SALMA classification, in south-central

Chile Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...

and nearby parts of

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

.Pedroza et al., 2017 The sediments belonging to the group were deposited in a

lacustrine A lake is often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from t ...

environment and alongside rivers in an intra-arc basin.Suárez & Emparan, 1995 Southeast of Laguna del Laja Cura-Mallín Group has a thickness of more than . The sediments making up the group deposited in an interval between 22 and 8 million years ago. The outcrops of Cura-Mallín Group are found along a north–south elongate area. The group is considered an equivalent of

Abanico Formation Abanico Formation () is a thick sedimentary formation exposed in the Andes of Central Chile. The formation has been deposited in a timespan from the Eocene to the Miocene. Abanico Formation's contact with the overlying Miocene Farellones Forma ...

, either as a southern extension or as a lateral equivalent of that formation.Flynn et al., 2008

Stratigraphy and members

Various subdivision schemes have been proposed for the Cura-Mallín unit since the 1980s. In 1983, Niemeyer and Muñoz identified two members; the Río Queuco Member, overlain by the Malla Malla Member. In two publications published in 1995 and 1997, Suárez and Emperan divided Cura-Mallín Formation in two

diachronous In geology, a diachronism ( Greek ''dia'', "through" + ''chronos'', "time" + ''-ism''), or diachronous deposit, is a sedimentary rock formation in which the material, although of a similar nature, varies in age with the place where it was deposite ...

members: Guapitrío and Río Pedregoso. Utgé ''et al.'' (2009) proposed instead a subdivision into an upper Arroyo Pincheira Member and a lower Lumabia Member.Utgé et al., 2009 In a 2017 revision the Cura-Mallín, formerly a formation, was redefined as a group given its great variety of lithologies. The Guapitrío, Río Pedregoso members of Suárez and Emperan became formations according to this scheme. In addition the new scheme include the Mitrauquén Formation that overlies both the Guapitrío and Río Pedregoso Formations as a third formation in the group.

Cura-Mallín Basin

A number of geologists consider Cura-Mallín Basin, the

sedimentary basin Sedimentary basins are region-scale depressions of the Earth's crust where subsidence has occurred and a thick sequence of sediments have accumulated to form a large three-dimensional body of sedimentary rock They form when long-term subsidence ...

where the formation deposited, an extensional basin that developed on the western fringes of the much larger

Neuquén Basin Neuquén Basin () is a sedimentary basin covering most of Neuquén Province in Argentina. The basin originated in the Jurassic and developed through alternating continental and marine conditions well into the Tertiary. The basin bounds to the wes ...

, while others consider it a

back-arc basin A back-arc basin is a type of geologic Structural basin, basin, found at some convergent boundary, convergent plate boundaries. Presently all back-arc basins are submarine features associated with island arcs and subduction zones, with many found ...

. In the Upper Miocene the sedimentary basin was inverted.Radic, 2010 Relative to other nearby sedimentary basins of Miocene and

age Cura-Mallín Basin has been more researched.Franzese et al., 2011

Fossil content

The group contains abundant mammal fossils including

bony fishes Osteichthyes ( ; ), also known as osteichthyans or commonly referred to as the bony fish, is a diverse clade of vertebrate animals that have endoskeletons primarily composed of bone tissue. They can be contrasted with the Chondrichthyes (cartila ...

, birds and mammals such as

rodent Rodents (from Latin , 'to gnaw') are mammals of the Order (biology), order Rodentia ( ), which are characterized by a single pair of continuously growing incisors in each of the upper and Mandible, lower jaws. About 40% of all mammal specie ...

marsupial Marsupials are a diverse group of mammals belonging to the infraclass Marsupialia. They are natively found in Australasia, Wallacea, and the Americas. One of marsupials' unique features is their reproductive strategy: the young are born in a r ...

Mylodontidae Mylodontidae is a family of extinct South American and North American ground sloths within the suborder Folivora of order Pilosa, living from around 23 million years ago (Mya) to 11,000 years ago. This family is most closely related to another fa ...

s and

Notoungulata Notoungulata is an extinct order of ungulates that inhabited South America from the early Paleocene to the end of the Pleistocene, living from approximately 61 million to 11,000 years ago. Notoungulates were morphologically diverse, with forms re ...

Economic geology

The proximity of the Cura-Mallín Group to the

stratovolcano A stratovolcano, also known as a composite volcano, is a typically conical volcano built up by many alternating layers (strata) of hardened lava and tephra. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with ...

es of Tolhuaca and Lonquimay has made it a reservoir of

geothermal energy Geothermal energy is thermal energy extracted from the crust (geology), crust. It combines energy from the formation of the planet and from radioactive decay. Geothermal energy has been exploited as a source of heat and/or electric power for m ...

of interest. Of all units the Rucañanco Member of Guapitrio Formation has been judged to have the most promising reservoir potential.

References

Bibliography

* * * * * * * {{DEFAULTSORT:Cura-Mallin Formation Geologic groups of South America Geologic formations of Chile Geologic formations of Argentina Miocene Series of South America Oligocene Series of South America Laventan Colloncuran Friasian Santacrucian Colhuehuapian Neogene Chile Paleontology in Chile Geology of Araucanía Region Geology of Biobío Region Geology of Maule Region Geology of Neuquén Province