The Mata Amarilla Formation is a
fossiliferous formation of the
Austral Basin in southern
Patagonia
Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and g ...
,
Argentina
Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...
. 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.
The Mata Amarilla Formation has provided many fossil vertebrates, among which
dinosaur
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
s, fish and turtles, as well as fossil insects, flora and molluscs.
Age
The middle section of the Mata Amarilla Formation has widely been regarded as
Maastrichtian
The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval ...
in age, but recent dating of a lava tuff layer shows that it dates back to 96.2 ± 0.7 Ma, during the
Cenomanian.
[Varela et al., 2012]
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 . 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 Formation
Tobífera Formation ( es, Formación Tobífera) is a volcano-sedimentary formation of Middle to Late Jurassic age. The formation is crops out in the Magallanes Region in southern Patagonia and Tierra del Fuego of Chile, the Santa Cruz Province ...
s.
[Santamarina et al., 2018, p.608]
Subsequently, the
thermal subsidence In geology and geophysics, thermal subsidence is a mechanism of subsidence in which conductive cooling of the mantle thickens the lithosphere and causes it to decrease in elevation. This is because of thermal contraction: as mantle material cools an ...
stage resulted in the deposition of the
transgressive quartz
Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...
ose
sandstone
Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks.
Most sandstone is composed of quartz or feldspar (both silicates ...
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
Piedra is a hair disease caused by a fungus, which causes formation of nodules on the hair shaft.Veasey JV, Avila RB, Miguel BAF, Muramatu LH. White piedra, black piedra, tinea versicolor, and tinea nigra: contribution to the diagnosis of superfic ...
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
Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks.
Most sandstone is composed of quartz or feldspar (both silicates ...
. 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
Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks.
Most sandstone is composed of quartz or feldspar (both silicates ...
and
siltstone representing meandering
fluvial channels and
crevasse splay
A crevasse splay is a sedimentary fluvial deposit which forms when a stream breaks its natural or artificial levees and deposits sediment on a floodplain. A breach that forms a crevasse splay deposits sediments in similar pattern to an alluvial f ...
deposits, intercalated with fine-grained
floodplain
A floodplain or flood plain or bottomlands is an area of land adjacent to a river which stretches from the banks of its channel to the base of the enclosing valley walls, and which experiences flooding during periods of high discharge.Goudi ...
s and subordinate
lacustrine
A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larger ...
deposits. The upper section is dominated by fine-grained deposits, related to distal fluvial channels.
Paleosol
In the geosciences, paleosol (''palaeosol'' in Great Britain and Australia) is an ancient soil that formed in the past. The precise definition of the term in geology and paleontology is slightly different from its use in soil science.
In geolo ...
features and paleosol-derived climatic proxies suggest a subtropical temperate-warm, at and humid, with /yr, climate with marked rainfall seasonality during the deposition of this unit (Varela et al. 2012b; 2018), in accordance with previous paleobotanical interpretations.
[Santamarina et al., 2018, p.609]
Fossil content
Dinosaurs
Other vertebrates
* ''
Ceratodus iheringi''
* ''
Lepidotes sp.''
*
Chelidae indet.
*
Elasmosauridae indet.
* ?
Docodonta indet.
*
Ausktribosphenidae
Ausktribosphenidae is an extinct family of australosphenidan mammals from the Early Cretaceous of Australia and mid Cretaceous of South America.
Classification and taxonomy
Ausktribosphenidae is closely related to monotremes and hence the two f ...
indet.
* ''
Amarillodon meridionalis''
* ''
Treslagosodon shehuensis''
Molluscs
* ''
Glyphea oculata''
* ''
Anagaudryceras cf. politissimum''
* ''
Baculites cf. kirki''
* ''
Polyptychoceras (Polyptychoceras) sp.''
* ''
cf. Potamides sp.''
Insects
* ''
Aonikenkissus zamunerae''
[Cerro Waring]
at Fossilworks.org
* ''
Myrcia acutifolia''
* ''
M. santacruzensis''
* ''
Zygadenia sp.''
Flora
* ''
Arcellites disciformis''
[Santamarina et al., 2018, p.610]
* ''
Bignonites chalianus''
* ''
Fitzroya tertiaria''
* ''
Laurophyllum kurtzi''
* ''
?Schinopsis dubia''
* ''
Equisetites sp.''
* ''
Phylites sp.''
References
Bibliography
*
Material was copied from this source, which is available under
Creative Commons Attribution 4.0 International License
*
*
available under
Creative Commons Attribution 4.0 International License* {{doi, 10.11646/zootaxa.2450.1.1
Further reading
* J. F. Petrulevicius, A. N. Varela, A. Iglesias, A. B. Zamuner, and D. G. Poiré. 2014. First Cenomanian record of insects in the southern Hemisphere, with Perforissidae (Fulgoroidea) and Cupedidae (Coleoptera) from southern Patagonia, Argentina. Cretaceous Research 51:174-185
* J. P. O'Gorman and A. N. Varela. 2010. The oldest lower Upper Cretaceous plesiosaurs (Reptilia, Sauropterygia) from Southern Patagonia, Argentina. Ameghiniana 47(4):447-459
* A. Iglesias, A. B. Zamuner, D. G. Poiré and F. Larriestra. 2007. Diversity, taphonomy, and palaeoecology of an angiosperm flora from the Cretaceous (Cenomanian-Coniacian) in southern Patagonia, Argentina. Palaeontology 50(2):445-466
* F. J. Goin, D. G. Poire, M. S. De Fuente, A. L. Cione, F. E. Novas, E. S. Bellosi, A. Ambrosio, O. Ferrer, N. D. Canessa, A. Carloni, J. Ferigolo, A. M. Ribeiro, M. S. Sales Viana, M. A. Reguero, M. G. Vucetich, S. Marenssi, M. F. Lima Filho and S. Agostinho. 2002. Paleontologia y geologia de los sedimentos del cretacico superior aflorantes al sur del rio shehuen (Mata Amarilla, Provincia de Santa Cruz, Argentina). Actas del XV Congreso Geologico Argentino, El Calafate, 2002 1-6
* M. B. Aguirre Urreta. 1989. The Cretaceous decapod Crustacea of Argentina and the Antarctic Peninsula. Palaeontology 32(3):499-552
* J. Frenguelli. 1953. La Flora Fósil de la región del Alto Río Chalia en Santa Cruz (Patagonia). Paleontología. Notas del museo XVI(98):239-257
* F.
Ameghino. 1899. Nota preliminar sobre el Loncasaurus argentinus un representante de la familia de los Megalosauridae en la República Argentina
reliminary note on Loncasaurus argentinus, a representative of the family Megalosauridae in the Argentine Republic Anales de la Sociedad Científica Argentina 47:61-62
Geologic formations of Argentina
Upper Cretaceous Series of South America
Cretaceous Argentina
Cenomanian Stage
Sandstone formations
Shale formations
Siltstone formations
Tuff formations
Formations
Fossiliferous stratigraphic units of South America
Paleontology in Argentina
Geology of Santa Cruz Province, Argentina
Geology of Patagonia