Mata Amarilla Formation

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Mata Amarilla Formation
Stratigraphic range: Mid Cenomanian
96.94–95.52  Ma
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Austral Basin - Geologic Map - Mata Amarilla, La Anita & Piedra Clavada Formations, Argentina.jpg
Map of Mata Amarilla and surrounding formations
Type Geological Formation
Sub-unitsUpper, Middle and Lower members
Underlies Alta Vista Formation
Overlies Piedra Clavada Formation
Lithology
Primary Siltstone, claystone
Other Sandstone, tuff, paleosols
Location
Coordinates 49°30′S71°30′W / 49.5°S 71.5°W / -49.5; -71.5
Approximate paleocoordinates 56°30′S48°48′W / 56.5°S 48.8°W / -56.5; -48.8
Region Santa Cruz Province
CountryArgentina
Extent Austral Basin
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Mata Amarilla Formation (Argentina)
Stratigraphic column Mata Amarilla Formation - stratigraphic column.jpg
Stratigraphic column

The Mata Amarilla Formation is a fossiliferous formation of the Austral Basin in southern Patagonia, Argentina. The formation consists of sediments deposited during the Middle Cenomanian, dated to 96.94 to 95.52 Ma. The middle section of the formation was previously considered to be the Pari Aike Formation.

Contents

The Mata Amarilla Formation has provided many fossil vertebrates, among which dinosaurs, fish and turtles, as well as fossil insects, flora and molluscs.

Age

Paleogeography of the Late Cretaceous (90 Ma) with known distribution of Arcellites disciformis indicated 90 Ma - Late Cretaceous paleogeography with known distribution of Arcellites disciformis indicated.jpg
Paleogeography of the Late Cretaceous (90 Ma) with known distribution of Arcellites disciformis indicated

The middle section of the Mata Amarilla Formation has widely been regarded as Maastrichtian in age, but recent dating of a lava tuff layer shows that it dates back to 96.2 ± 0.7 Ma, during the Cenomanian. [1]

Description

The Austral (or Magallanes) Basin, is located on the southwestern end of the South American Plate and it is bordered to the south by the Scotia Plate covering an area of approximately 230.000 square kilometres (88.803 sq mi). In the studied area, the Austral Basin underwent three main tectonic stages: (i) a rift stage; (ii) a thermal subsidence stage; and (iii) a foreland stage.

The rifting stage is related to the break-up of Gondwana, grabens and half-grabens were formed and filled with volcaniclastic and volcanic rocks intercalated with epiclastic sediments of the El Quemado and Tobífera Formations. [2]

Subsequently, the thermal subsidence stage resulted in the deposition of the transgressive quartzose sandstone of the Springhill Formation, and the black mudstone and marl of the Río Mayer Formation. Towards the end of this stage, the Piedra Clavada Formation was deposited, representing a large passive-margin delta system.

The foreland stage, in response to the regional change from extensive to compressive regime, resulted in the deposition of the continental Mata Amarilla Formation. This unit is mainly composed of grey and blackish siltstone and claystone, alternating with whitish and yellowish-grey fine to medium grained sandstone. Varela (2014) recognized three informal sections (lower, middle, and upper) on the bases of sedimentological and sequence stratigraphic analysis. The lower section consists of fine-grained intervals with paleosols interbedded with laminated shale and coquina, representing coastal plain and lagoon paleoenvironments.

The middle section comprises sandstone and siltstone representing meandering fluvial channels and crevasse splay deposits, intercalated with fine-grained floodplains and subordinate lacustrine deposits. The upper section is dominated by fine-grained deposits, related to distal fluvial channels.

Paleosol features and paleosol-derived climatic proxies suggest a subtropical temperate-warm, at 12 ± 2.1 °C (53.6 ± 3.8 °F) and humid, with 1,404 ± 108 millimetres (55.3 ± 4.3 in)/yr, climate with marked rainfall seasonality during the deposition of this unit (Varela et al. 2012b; 2018), in accordance with previous paleobotanical interpretations. [3]

Fossil content

Dinosaurs

Dinosaurs
GenusSpeciesLocationStratigraphic positionMaterialNotesImages
Clasmodosaurus C. spatulaMiddle Section
Loncosaurus L. argentinusMiddle Section

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References

  1. Varela et al., 2012
  2. Santamarina et al., 2018, p.608
  3. Santamarina et al., 2018, p.609
  4. 1 2 3 4 Martin, T.; Goin, F. J.; Schultz, J. A.; Gelfo, J. N. (2021). "Early Late Cretaceous mammals from southern Patagonia (Santa Cruz province, Argentina)". Cretaceous Research. 133: 105127. doi:10.1016/j.cretres.2021.105127. S2CID   245549530.
  5. Cerro Waring at Fossilworks.org
  6. Santamarina et al., 2018, p.610

Bibliography

Further reading