Mata Amarilla Formation - stratigraphic column

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 ...

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, t ...

. 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

90 Ma - Late Cretaceous paleogeography with known distribution of Arcellites disciformis indicated

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 interv ...

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 Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final st ...

graben In geology, a graben () is a depressed block of the crust of a planet or moon, bordered by parallel normal faults. Etymology ''Graben'' is a loan word from German, meaning 'ditch' or 'trench'. The word was first used in the geologic contex ...

s and

half-graben A half-graben is a geological structure bounded by a fault along one side of its boundaries, unlike a full graben where a depressed block of land is bordered by parallel faults. Rift and fault structure A rift is a region where the lithosphe ...

s were formed and filled with volcaniclastic and volcanic rocks intercalated with epiclastic sediments of the El Quemado and Tobífera Formations.Santamarina et al., 2018, p.608 Subsequently, the thermal subsidence 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 Rio or Río is the Portuguese, Spanish, Italian, and Maltese word for "river". When spoken on its own, the word often means Rio de Janeiro, a major city in Brazil. Rio or Río may also refer to: Geography Brazil * Rio de Janeiro * Rio do Sul, a ...

. 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 Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, ...

and

claystone Mudrocks are a class of fine-grained siliciclastic sedimentary rocks. The varying types of mudrocks include siltstone, claystone, mudstone, slate, and shale. Most of the particles of which the stone is composed are less than and are too sm ...

, alternating with whitish and yellowish-grey fine to medium grained

. 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

and

representing meandering

fluvial channel In physical geography, a channel is a type of landform consisting of the outline of a path of relatively shallow and narrow body of water or of other fluids (e.g., lava), most commonly the confine of a river, river delta or strait. The word is ...

s 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 geol ...

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 Docodonta is an order of extinct mammaliaforms that lived during the Mesozoic, from the Middle Jurassic to Early Cretaceous. They are distinguished from other early mammaliaforms by their relatively complex molar teeth, from which the order gets ...

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 ''Glyphea'' is a genus of fossil Glypheoidea, glypheoid crustaceans that lived from the Jurassic to the Eocene. It includes the following species: *''Glyphea alexandri'' Taylor, 1979 *''Glyphea arborinsularis'' Etheridge Jr., 1917 *''Glyphea a ...

'' * '' Anagaudryceras cf. politissimum'' * '' Baculites cf. kirki'' * '' Polyptychoceras (Polyptychoceras) sp.'' * '' cf. Potamides sp.''

Insects

* '' Aonikenkissus zamunerae''Cerro Waring
at

Fossilworks Fossilworks is a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database, a large relational database assembled by hundreds of paleontologists from around the world. History Fossilworks was cre ...

.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

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available under
Creative Commons Attribution 4.0 International License
* {{doi, 10.11646/zootaxa.2450.1.1

Age