Where: Santa Cruz, Argentina (47.6° S, 71.9° W: paleocoordinates 48.3° S, 66.4° W)
• coordinate stated in text
• outcrop-level geographic resolution
When: Santa Cruz Formation, Santacrucian (17.5 - 16.3 Ma)
• Santacrucian age.
•The age of the SCF in Lago Posadas is based on six 40Ar/39Ar dates provided by Blisniuk et al. (2005), with an age span of 22-14 Ma. Based on regional tephrochronology and sedimentation rates estimations, Perkins et al. (2012) questioned the age for the lower strata of the SCF of Lago Posadas and concluded it should be close to 18 Ma. The latter was also supported by Cuitiño et al. (2015) based on Sr-stratigraphy for the underlying marine deposits, whose younger beds are chronologically located in 18 Ma. These age estimations provide an age span of roughly 4 my, from 18 Ma to 14 Ma, for the SFC in Lago Posadas. A note of caution has to be made related to the younger age (14.24±0.78 Ma) obtained by Blisniuk et al. (2005), since the stratigraphic position of this dated level corresponds to a tuff located 3 m beneath the top of the SCF in a place located 10 km southeast of the locality studied herein. That locality, shows thicker exposures of the SCF, which means that the dated level is probably not represented in the locality studied in this work and consequently the age of the top of our section should be somewhat older than 14.24±0.78 Ma.
• formation-level stratigraphic resolution
Environment/lithology: fluvial; lithified sandstone
• Sedimentologic data suggest that the sedimentary record begins with restricted marine-estuarine deposits grading upward to fluvial floodplains and fluvial channels. Extensive floodplains, occasionally interrupted by low-sinuosity, sand-dominated channels, show dominant reddish coloration, moderate to low paleosol development, abundant crevasse splay sandstones and lack of vegetal remains, suggesting deposition in a low gradient, oxygenated setting under elevated sedimentation rates. Vertical stratigraphic trends are subtle, suggesting little paleoenvironmental changes during deposition of the whole SCF in this region. Paleocurrent directions, sandstone composition and paleogeographic reconstructions all indicate that deposition of the SCF was strongly associated to the contemporaneous uplift of the Andes.
• The study area shows exposures of the Cretaceous-Miocene infill of the Austral (or Magallanes) Basin (Giacosa and Franchi, 2001). The section of the SCF studied herein is exposed along the north margin of the Meseta Belgrano (Fig. 1), where several older stratigraphic units are also exposed. North of this margin, a wide and deep glacial valley develops, exposing the basement volcaniclastic rocks of the basin assigned to El Quemado Complex (Mid to Late Jurassic). To the west, cretaceous sedimentary units are exposed, including the marine Springhill, Río Mayer and transitional Río Belgrano formations, all mapped as “Cretaceous units” in figure 1. Above the former and outcropping at the base of the Lago Posadas-Meseta Belgrano cliffs, is the Río Tarde Formation (Aptian; Ghiglione et al., 2015) which is covered by the Eocene Posadas Basalt, which in turn is covered by the early to middle Miocene marine and continental deposits. The early Miocene marine deposits are considered as part of the Patagonian Transgression and were formally named as the El Chacay Formation (Chiesa and Camacho, 1995; Cuitiño et al., 2015), which in turn are followed by the continental deposits of the SCF. The top of the Miocene succession in this area, roughly about 1200- 1,400 m above sea level (m a.s.l.), is truncated by an erosional surface which forms a plateau slightly dipping to the east. South of the northern margin and forming the core of the Meseta Belgrano is the Belgrano Basalt (late Miocene; Gorring et al., 1997) (Fig. 1), which is located at the highest elevation within the plateau reaching up to 2000 m a.s.l.
•Very detailed geology is found in Cuitiño, et al. 2019
Size class: macrofossils
Collection methods: The specimens collected belong to the Museo Regional Provincial P.M.J. Molina (MPM; Río Gallegos, Santa Cruz Province, Argentina).
•
•The material is fragmentary and was recovered loose on the surface, except for two specimens that were found in situ (the toxodonts Homalodotherium and Nesodon). Most of them come from the lower to mid-levels of the stratigraphic column (Fig. 9).
Primary reference: J. I. Cuitiño, S. F. Vizcaíno, M. S. Bargo and I. Aramendía. 2019. Sedimentology and fossil vertebrates of the Santa Cruz formation (early Miocene) in Lago Posadas, southwestern Patagonia, Argentina. Andean Geology 46(2):383-420 [P. Mannion/M. Kouvari/M. Kouvari]more details
Purpose of describing collection: taxonomic analysis
PaleoDB collection 210154: authorized by Philip Mannion, entered by Miranta Kouvari on 22.05.2020
Creative Commons license: CC BY (attribution)
Taxonomic list
Show authors, comments, and common names
| Mammalia |
| Cingulata - Propalaehoplophoridae |
"Propalaehoplophorinae indet." = Propalaehoplophoridae Ameghino 1891 edentate
MLP 84-III-2-10, 6, MPV-PV 17454, 17472
|
| Cingulata - Chlamyphoridae |
Proeutatus sp. Ameghino 1891 edentate
MLP 84-III-2-15, 34, 33, MPV-PV 17465
|
| Megatherioidea - |
|
| Megatherioidea - Megalonychidae |
|
| Notoungulata - Interatheriidae |
|
| Notoungulata - Hegetotheriidae |
|
| Notoungulata - Toxodontidae |
|
| Notoungulata - Homalodotheriidae |
|
| Rodentia - |
|
| Rodentia - Dinomyidae |
|
| Rodentia - Neoepiblemidae |
|
| Placentalia - |
|
| Panameriungulata - Proterotheriidae |
"cf. Diadiaphorus sp." = Proterotherium Ameghino 1883 placental
MPV-PV 17468
|