Sierra Baguales (Miocene of Chile)

Where: Magallanes, Chile (50.6° S, 72.5° W: paleocoordinates 51.4° S, 66.5° W)

• coordinate estimated from map

• outcrop-level geographic resolution

When: Santa Cruz Formation, Burdigalian (20.4 - 16.0 Ma)

• The lithological correlation is also confirmed by detrital zircon ages (maximum age of 18.23±0.26 Ma) and a rich assemblage of terrestrial vertebrate fossils, biostratigraphically equivalent to a post- Colhuehuapian, pre-Santacrucian South American Land Mammal Age (SALMA) fauna, suggesting a range of 19 to 17.8 Ma

•Santa Cruz Formation (first refered by Ameghino (1889) as the ‘Piso Santacruceño’ (Marshall, 1976; Vizcaíno et al., 2012a) and later formalized by Zambrano and Urien (1970)), but Keidel and Hemmer in 1931 refered to this formation in Chile as Palomares.

•The Santa Cruz Formation is exposed along the southern flank of Cerro Cono (Fig. 2), where it overlies the Estancia 25 de Mayo Formation with a conformable, gradational contact

• group of beds-level stratigraphic resolution

Environment/lithology: fluvial; mudstone and sandstone

• Santa Cruz Formation in this area was deposited in a continental, fluvial environment, as indicated by the abundance of terrestrial vertebrate fragments, Scoyenia including probable hymenopterid traces, multi-coloured (often reddish), blocky-weathering mudstones (Fig. 4) with occasional mud-cracks, and sandstones showing sedimentary structures such as trough, epsilon and high-angle planar cross-lamination (Fig. 5), with a more or less consistent paleocurrent direction towards the east-northeast
• The descriptions are very long, this is a sum up:

•Unit 1 has a total thickness of 32.7 m. Overlying an erosional contact at the base is a 0.7 m thick, reddish brown, trough cross-laminated, medium- to coarse-grained sandstone, in which the troughs are up to about 1 m wide.

•Unit 2 has an erosional basal contact overlain by a 0.5 m thick, dark brown, medium-grained sandstone showing high-angle planar cross-lamination and mi- nor trough cross-lamination indicating northwest- to east-flowing currents.

•Unit 3, with a total thickness of 13.3 m, has a 1.0 m thick conglomerate at the base with small (up to 1 cm), multi-coloured chert and quartz clasts, grading towards the east into sandy conglomerate.

•Unit 4 starts with a 1.9 m thick, whitish, medium- grained sandstone at the base, which is low-angle planar cross-laminated.

•Unit 5 is 8.6 m thick and commences with a 4.6 m thick, yellowish, clay-rich, fine- to medium-grained sandstone with upper flow regime horizontal lami- nation, rare trough cross-lamination and high-angle cross-lamination

•Unit 6 has an erosional basal contact and a total thickness of 4.6 m, which can be subdivided into 5 fining-upward sub-units (6a-e) separated by sharp to erosional contacts.

•Fossils come from units 1-7

Size classes: macrofossils, mesofossils

Preservation: trace

Primary reference: J. E. Bostelmann, J. P. Le Roux, A. Vásquez, N. M. Gutiérrez, J. L. Oyarzún, C. Carreño, T. Torres, R. Otero, A. Llanos, C. M. Fanning, and F. Hervé. 2013. Burdigalian deposits of the Santa Cruz Formation in the Sierra Baguales, Austral (Magallanes) Basin: Age, depositional environment and vertebrate fossils. Andean Geology 40(3):458-489 [P. Mannion/M. Kouvari]more details

Purpose of describing collection: general faunal/floral analysis

PaleoDB collection 204203: authorized by Philip Mannion, entered by Miranta Kouvari on 03.09.2019

Creative Commons license: CC BY (attribution)

Taxonomic list

Mammalia
 Notoungulata - Toxodontidae
Nesodon sp. Owen 1846 notoungulate
Adinotherium sp. Ameghino 1887 notoungulate
 Notoungulata - Notohippidae
 Rodentia - Neoepiblemidae
Perimys incavatus Ameghino 1902 caviomorph
 Rodentia -
Cavioidea indet. Fischer de Waldheim 1817 caviomorph
Adelphomys candidus Ameghino 1887 caviomorph
 Cingulata - Dasypodidae
Proeutatus "sp. nov." Ameghino 1891 armadillo
Proeutatus sp. Ameghino 1891 armadillo
 Xenarthra - Megalonychidae
Megalonychidae indet. Gervais 1855 edentate
 Tardigrada -
"Tardigrada indet." = Folivora
"Tardigrada indet." = Folivora Delsuc et al. 2001 edentate
 Xenarthra - Glyptodontidae
Propalaehoplophorinae indet. Ameghino 1891 glyptodon
 Ungulata - Proterotheriidae
Proterotheriinae indet. Ameghino 1885 eutherian
Paramacrauchenia scamnata Ameghino 1902 eutherian
 Ungulata - Astrapotheriidae
Astrapotheriinae indet. Soria and Alvarenga 1989 eutherian
Pinopsida
 Pinales - Podocarpaceae
Podocarpaceae indet. Endlicher 1847
Monocots
 Poales - Poaceae
Poaceae indet. Barnhart 1895
Pteridopsida
 Cyatheales - Cyatheaceae
Magnoliopsida
 Myrtales - Myrtaceae
Myrtaceae indet. de Jussieu 1789
 Myrtales - Onagraceae
Onagraceae indet. de Jussieu 1789
 Caryophyllales - Chenopodiaceae
 Proteales - Proteaceae
Proteaceae indet. de Jussieu 1789
 Asterales - Asteraceae
Asteraceae indet. von Berchtold and Presl 1820
 Fagales - Nothofagaceae
Nothofagaceae indet. Kuprian 1962
 Ichnofossils -
Skolithos sp. Haldemann 1840