Salamanca Formation

The Salamanca Formation is a geologic formation in the Golfo San Jorge Basin of central Patagonia that yields well-preserved, well-dated fossils from the early Paleocene. Studies of these fossils are providing new data on plant and animal diversity following the end-Cretaceous extinction event.^[1][2]

Unit ofRío Chico Group

UnderliesPeñas Coloradas Formation
(Río Chico Group)

OverliesLago Colhué Huapí Formation
(Chubut Group)

PrimarySandstone, mudstone

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Salamanca Formation
Stratigraphic range: latest Maastrichtian-Danian (Tiupampan-Riochican) ~66.0–57 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Unit of	Río Chico Group
Underlies	Peñas Coloradas Formation (Río Chico Group)
Overlies	Lago Colhué Huapí Formation (Chubut Group)
Lithology
Primary	Sandstone, mudstone
Other	Limestone
Location
Country	Argentina
Extent	Golfo San Jorge Basin
Type section
Region	Chubut and Santa Cruz Provinces
Country	Argentina
Location of the Salamanca Formation within Argentina

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The Salamanca Formation crops out in the San Jorge Basin in southern Chubut and northern Santa Cruz provinces, Argentina, overlying the Cretaceous Chubut Group and is part of the Paleocene and Eocene Río Chico Group.^[3][4][5][6] The formation yields abundant plant remains^{[7][8][9][10][11][12]} as well as fossils of invertebrates, marine macrofaunas,^[13] reptiles,^{[14][15][16][17][18]} and mammals.^{[2][19][20][21][22][23][24][4][3]} The formation consists primarily of estuarine to shallow marine deposits.^[25][26]

Palynological analysis of the Salamanca Formation shows low floral diversity after the end-Cretaceous mass extinction, followed by a rapid recovery. 50% of all pollen types are angiosperms, whereas gymnosperms accounted for only ~13% of total richness; however, Classopollis pollen, representing the extinct conifer family Cheirolepidiaceae, is the most abundant palynomorph.^[3] Wood assemblages from the Salamanca Formation are dominated by conifers, but the presence of fossil angiosperm woods indicate that they were also part of the canopy.^[8][9] The co-occurrence of palms, dicot woods with indistinct growth rings, and alligatorids,^{[15][16][17][18]} indicates temperature remained above freezing year-round. The results of leaf physiognomic analyses indicate that the climate in the San Jorge Basin during the early Paleocene was warm subtropical.^{[27][28][29][30]}