Arroyo Cochicó / Mina Zitro (Lower Section) (Miocene of Argentina)

Where: Mendoza, Argentina (35.0° S, 68.5° W: paleocoordinates 35.7° S, 63.2° W)

• coordinate estimated from map

When: Aisol Formation, Colhuehuapian (21.0 - 17.5 Ma)

• Garrido, et al. 2014: It's Aisol Fm in the literature (Gonzalez Díaz, 1972; Sepulveda et al., 2000) but needs verification.

•Btw they re-defined the Aisol FM and it's Early Miocene for their area of study

•Forasiepi et al 2015: This contribution presents a new radiometric dating of a 19.480 ± 0.025 Ma tuff bed, which constrains the absolute age of the mammalian assemblage at these latitudes to the Early Miocene.

•In preliminary studies, the Aisol Formation was con- sidered early Miocene (probably Santacrucian SALMA; e.g., Groeber 1951; Dessanti 1954, 1956; González Díaz 1972; Núñez 1976) based upon few fossil findings and stratigraphic correlations. Nonetheless, it is also worth mentioning that in one of those preliminary studies, Groeber (1952) suggested that the unit (informally called «Estratos Calchaquíes» by then) was late Miocene, and was included among the «Arauco-Entrerriano» levels. Later studies did not further the debate. Pascual and Odreman-Rivas (1973; see also Pascual and De la Fuente 1993) placed the Aisol Formation in the Miocene, in the temporal interval between the Santacrucian and Friasian SALMAs. It was after the analysis of new fossil findings that Soria (1983) specifically allocated the Aisol Formation to the Friasian s.l. (including Colloncuran, Friasian s.s., and Mayoan, following Bondesio et al. 1980), because of the occurrence of post-Santacrucian and pre- Chasicoan mammals. This hypothesis was also followed by later authors (Sepúlveda et al. 2001, 2007). The analysis of the new fossil material and the strati- graphic control of the findings led to recognize two dif- ferent fosiliferous sections in the profile, with faunal as- semblages of different ages. The LS is probably middle Miocene, as Soria suggested (1983), perhaps Friasian s.s. (older than 15 Ma; Marshall and Salinas 1990) or Collon- curan (15.5-14 Ma; Marshall et al. 1977; Marshall and Salinas 1990), following the Patagonian scheme. Unfor- tunately, there is no consensus about the time span cov- ered by some of the SALMAs, including the Friasian one. Specific studies on age and taxonomic composi- tion are needed before making any comparisons with more distantly located stratigraphic units.

•Three different sections are recognized within the Aisol Formation, with fossil vertebrates in the lower (LS) and middle (MS) sections. According to preliminary results of Forasiepi et al., 2011: Lower Section: Friasian s.s (not used anymore). or Colloncuran and Middle Section: Huayquerian.

• member-level stratigraphic resolution

Environment/lithology: terrestrial; sandstone

• The lower section (LS) of the profile is composed mainly of medium to fine-grained sandstones predominantly grey, reddish, yellow, and less frequently pale green; the entire bed is roughly sub-horizontal. The sandstones are calcite-cemented and the entire bed has strong cross- stratification (Fig. 2), with higher angles towards the middle and upper parts of the section. Between the sandstones, levels of reddish to brownish, fine siltstones are interbedded. The thickness of the siltstone levels is larger towards the lower part of the section. In contrast, towards the upper part, reddish to greenish siltstones intraclasts are frequently found within the sandstones (Fig. 2). The intraclasts are variable in size and their surfaces are mostly rounded. Fossil wood and vertebrate remains are common in different parts of the LS. With the exception of the bones found in the siltstone, other material is highly eroded, showing signals of transportation and corrosion of biological organisms. In the area of the profile, the LS is approximately 15 m thick. The base, however, was not observed; it is covered by recent deposits.

Size class: macrofossils

Collection methods: Museo de Historia Natural de San Rafael, Mendoza, Argentina

Primary reference: A. M. Forasiepi, A. G. Martinelli, M. S. Fuente, S. Dieguez, and M. Bond. 2011. Paleontology and stratigraphy of the Aisol Formation (Neogene), San Rafael, Mendoza. Cenozoic Geology of the Central Andes of Argentina 135-154 [E. Vlachos/E. Vlachos]more details

Purpose of describing collection: taxonomic analysis

PaleoDB collection 189522: authorized by Evangelos Vlachos, entered by Evangelos Vlachos on 25.10.2017, edited by Miranta Kouvari

Creative Commons license: CC BY (attribution)

Taxonomic list

Mammalia
  - Mylodontidae
Mylodontinae indet. Gill 1872 edentate
MACN-PV18605, right astragalus
Reptilia
 Testudines - Testudinidae
Chelonoidis sp. Fitzinger 1835 turtle
MHNSR- PV1024, partial shell, large size
Aves
 Gruiformes - Phorusrhacidae
Phorusrhacidae indet. Ameghino 1889 terror bird
MACN-PV18602, right tarsometatarsus
 Rheiformes - Rheidae
Pterocnemia cf. mesopotamica Agnolín and Noriega 2012 rhea
see also Agnolin y Noriega, 2012