La Irene Formation

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]

La Irene Formation
Stratigraphic range: Maastrichtian
~70–66 Ma
↓
TypeGeological formation
UnderliesChorrillo Formation
OverliesCerro Fortaleza Formation
Thickness230 m (750 ft)
Lithology
PrimarySandstone
OtherShale
Location
LocationPatagonia
Coordinates50.4°S 72.2°W / -50.4; -72.2
Approximate paleocoordinates52.3°S 62.0°W / -52.3; -62.0
RegionSanta Cruz Province
Country Argentina
ExtentAustral Basin
La Irene Formation (Argentina)

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]

References
  1. Marenssi et al., 2003, p.406
  2. La Irene Formation at Fossilworks.org
  3. Povilauskas et al., 2008

Bibliography
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