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	50°24′S 72°12′W / 50.4°S 72.2°W / -50.4; -72.2
Approximate paleocoordinates	52°18′S 62°00′W / 52.3°S 62.0°W / -52.3; -62.0
Region	Santa Cruz Province
Country	Argentina
Extent	Austral Basin
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]

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]

The formation has provided many fossil pollen of:^[3]

• Podocarpaceae
• Monocotyledoneae
• Liliidae
• Cycadopsida
• Pteridopsida
• Polypodiopsida
• Schizaeaceae
• Gleicheniaceae
• Selaginellaceae
• Lycopodiaceae
• Magnoliopsida
• Dinophyceae

• Povilauskas, L.; Barreda, V.; Marenssi, S. (2008), "Polen y esporas de la Formación La Irene (Maastrichtiano), sudoeste de la provincia de Santa Cruz, Argentina: primeros resultados", Geobios, 41 (6): 819–831, Bibcode:2008Geobi..41..819P, doi:10.1016/j.geobios.2008.07.002, hdl:11336/114579
• Marenssi, Sergio A.; Casadío, Silvio; Santillana, Sergio N. (2003), "Estratigrafía y sedimentología de las unidades del Cretácico superior-Paleógeno aflorantes en la margen sureste del lago Viedma, provincia de Santa Cruz, Argentina" (PDF), Revista de la Asociación Geológica Argentina, 58: 403–416, retrieved 2018-08-30