The Chachao Formation is a geological formation in the Mendoza Province in northern Patagonian Argentina. It is Valanginian in age and is predominantly marine, being deposited at a time of marine transgression in the Neuquén Basin, and predominantly consists of carbonate rocks.
| Chachao Formation | |
|---|---|
| Stratigraphic range: Valanginian ~ | |
| Type | Geological formation |
| Unit of | Mendoza Group |
| Underlies | Agrio Formation |
| Overlies | Vaca Muerta |
| Lithology | |
| Primary | Limestone |
| Other | Mudstone |
| Location | |
| Coordinates | 35°00′S 69°42′W / 35.0°S 69.7°W |
| Approximate paleocoordinates | 33°48′S 33°00′W / 33.8°S 33.0°W |
| Region | Mendoza Province |
| Country | Argentina |
| Extent | Neuquén Basin |
  Chachao Formation (Argentina) | |
The formation belongs to the Mendoza Group, sediments deposited on the Mendoza Shelf. The formation overlies the Vaca Muerta and is overlain by the Agrio Formation.
Description
editA typical feature of the Chachao Formation is the dominance of oysters, many of them quite large e.g. Aetostreon latissimun, and others small, e.g. Ceratostreon minos. Different kinds of semi-infaunal soft bottom dwellers and swimming bivalves were recognized. Additional forms are represented by gastropods, ammonites (Olcostephanus curacoensis), and ichnofossils such as Thalassinoides sp. Serpulids are represented by the colonial Sarcinella sp., and the solitary form Parsimonia sp. The highly diverse fauna of the analyzed succession, made up with numerous stenohaline elements such as echinoderm, bryozoa, ammonite as well as serpulids and typical marine pelecypods indicate a fully marine environment.[1]
Fossil content
editThe formation has provided the following fossils:[2]
References
edit- ^ a b Chachao Coquina - Taphofacies 3 at Fossilworks.org
- ^ Chachao Formation at Fossilworks.org
Bibliography
edit- Gómez Dacal, Alejandro R.; Gómez Peral, Lucía E.; Spalletti, Luis A.; Sial, Alcides N.; Siccardi, Aron; Poiré, Daniel G. (2018), "First record of the Valanginian positive carbon isotope anomaly in the Mendoza shelf, Neuquén Basin, Argentina: palaeoclimatic implications", Andean Geology, 45 (2): 111–129, doi:10.5027/andgeoV45n2-3059, hdl:11336/64562, retrieved 2019-02-22
- Palma, R. M.; Lanes, S. G. (2001), "Shell Bed Stacking Patterns in the Chachao Formation (Early Valanginian) in Malargüe Area, Mendoza Province, Neuquen Basin, Argintina", Carbonates and Evaporites, 16 (2): 168–180, Bibcode:2001CarEv..16..168P, doi:10.1007/BF03175834
- Aguirre Urreta, M. B.; Álvarez, P. P. (1999), "The Berriasian genus Groebericeras in Argentina and the problem of its age", Scripta Geologica, 3 (Special Issue): 15–29
- Palma, R. M.; Angeleri, M. P. (1992), "Early Cretaceous serpulid limestones: Chachao Formation, Neuquen basin, Argentina", Facies, 27 (1): 175–178, Bibcode:1992Faci...27..175P, doi:10.1007/BF02536810
- Aguirre Urreta, M.B (1989), "The Cretaceous decapod Crustacea of Argentina and the Antarctic Peninsula", Palaeontology, 32: 499–552