La Irene Formation
| La Irene Formation | |
|---|---|
| Stratigraphic range: Maastrichtian ~70–66 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓ | |
| Type | Geological formation |
| Underlies | Chorrillo Formation |
| Overlies | Cerro Fortaleza Formation |
| Thickness | 230 m (750 ft) |
| Lithology | |
| Primary | Sandstone |
| Other | Shale |
| Location | |
| Location | Patagonia |
| Coordinates |   La Irene Formation (Argentina) |
La Irene Formation is a Maastrichtian geologic formation in southern Patagonia, Argentina. The formation is 230 metres (750 ft) thick and underlies the Chorrillo Formation and rests on top of the Cerro Fortaleza Formation.[1]
Description
The formation comprises lithified, sandy sandstones and lithified, argillaceous, sandy shales deposited in a fluvial deltaic environment.
At the base of Cerro Calafate a column of about 230 metres (750 ft) in thickness was measured along the road. The 110 m below represent a succession of sandy banks clear yellowish brown color to white and dark pelitic packages fining upwards cycles are stacked to form a sequence with a clear trend growing grain and stratum. Sandy banks (coarse to fine sand) show increasing thickness from 2 m at the base to more than 9 m, whereas intercalated mudstones show an opposite trend with thickness ranging from 15 m at the base to 1 m. At the top of lower shaly packets (the thickest) are preserved carbonaceous shale intervals, thinly laminated. 120 m above correspond to a succession of amalgamated conglomeratic sandy banks where preservation is extremely rare shaly intervals.[2]
Fossil content
The formation has provided many fossil pollen of:[3]
- Podocarpaceae
- Monocotyledoneae
- Liliidae
- Cycadopsida
- Pteridopsida
- Polypodiopsida
- Schizaeaceae
- Gleicheniaceae
- Selaginellaceae
- Lycopodiaceae
- Magnoliopsida
- Dinophyceae
References
- ^ Marenssi et al., 2003, p.406
- ^ La Irene Formation at Fossilworks.org
- ^ Povilauskas et al., 2008
Bibliography
- Povilauskas, L.; V. Barreda, and S. Marenssi. 2008. Polen y esporas de la Formación La Irene (Maastrichtiano), sudoeste de la provincia de Santa Cruz, Argentina: primeros resultados. Geobios 41. 819-831. .
- Marenssi, Sergio A.; Silvio Casadío, and Sergio N. Santillana. 2003. Estratigrafía y sedimentología de las unidades del Cretácico superior-Paleógeno aflorantes en la margen sureste del lago Viedma, provincia de Santa Cruz, Argentina. Revista de la Asociación Geológica Argentina 58. 403–416. Accessed 2018-08-30.
