Cerro Lisandro Formation
Encyclopedia
The Lisandro Formation, alternatively known as the Cerro Lisandro Formation, is a geologic formation
with outcrop
s in the Neuquén
province of Argentina
. It is the youngest formation within the Río Limay Subgroup, the lowest section of the Neuquén Group
. Formerly that subgroup was treated as a formation, and the Lisandro Formation was known as the (Cerro) Lisandro Member.
The type locality of the Lisandro Formation is the hill known as Cerro Lisandro in Neuquén province. This formation conformably
overlies the Huincul Formation
, and it is in turn overlain by the Portezuelo Formation
, which is a part of the Río Neuquén Subgroup.
The Lisandro Formation varies between 35 and 75 meters thick, the smallest of the three formations in its subgroup. It is made up of siltstone
s and claystone
s, red in color, which have been interpreted as a swamp
y environment. Usually, the red Lisando Formation rocks are easy to distinguish from the greenish or yellowish deposits of the Huincul Formation.
Period: Late Cretaceous
Faunal stage
: late Cenomanian
– early Turonian
Absolute Age
: ~94 to ~91 mya
s are represented in the Lisandro Formation; other types of animal
s are frequently found. Fossils documented from this formation are:
The swampy terrain may have limited the numbers of larger dinosaurs such as sauropods and carcharodontosaurids, which are found in earlier formations in the region but have not yet been found in the Cerro Lisandro.
Geologic formation
A formation or geological formation is the fundamental unit of lithostratigraphy. A formation consists of a certain number of rock strata that have a comparable lithology, facies or other similar properties...
with outcrop
Outcrop
An outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth. -Features:Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficial deposits are covered by a mantle of soil and vegetation and cannot be...
s in the Neuquén
Neuquén Province
Neuquén is a province of Argentina, located in the west of the country, at the northern end of Patagonia. It borders Mendoza Province to the north, Rio Negro Province to the southeast, and Chile to the west...
province of Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
. It is the youngest formation within the Río Limay Subgroup, the lowest section of the Neuquén Group
Neuquén Group
The Neuquén Group is a group of geologic formations found in Argentina. Rocks in the Neuquén Group fall within the Cenomanian to early Campanian stages of the Late Cretaceous Period, about 100 million to 80 million years in age...
. Formerly that subgroup was treated as a formation, and the Lisandro Formation was known as the (Cerro) Lisandro Member.
The type locality of the Lisandro Formation is the hill known as Cerro Lisandro in Neuquén province. This formation conformably
Unconformity
An unconformity is a buried erosion surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval of time before deposition of the younger, but the term is used to describe...
overlies the Huincul Formation
Huincul Formation
The Huincul Formation is a geologic formation that outcrops in Río Negro and Neuquén provinces of Argentina. It is the second formation in the Río Limay Subgroup, the oldest subgroup within the Neuquén Group...
, and it is in turn overlain by the Portezuelo Formation
Portezuelo Formation
The Portezuelo Formation is a geologic formation outcropping in the Mendoza, Río Negro and Neuquén provinces of Argentina. It is the fourth-oldest formation in the Neuquén Group and the older of the two formations in the Río Neuquén Subgroup...
, which is a part of the Río Neuquén Subgroup.
The Lisandro Formation varies between 35 and 75 meters thick, the smallest of the three formations in its subgroup. It is made up of siltstone
Siltstone
Siltstone is a sedimentary rock which has a grain size in the silt range, finer than sandstone and coarser than claystones.- Description :As its name implies, it is primarily composed of silt sized particles, defined as grains 1/16 - 1/256 mm or 4 to 8 on the Krumbein phi scale...
s and claystone
Claystone
Claystone is a geological term used to describe a clastic sedimentary rock that is composed primarily of clay-sized particles ....
s, red in color, which have been interpreted as a swamp
Swamp
A swamp is a wetland with some flooding of large areas of land by shallow bodies of water. A swamp generally has a large number of hammocks, or dry-land protrusions, covered by aquatic vegetation, or vegetation that tolerates periodical inundation. The two main types of swamp are "true" or swamp...
y environment. Usually, the red Lisando Formation rocks are easy to distinguish from the greenish or yellowish deposits of the Huincul Formation.
Age
Era: MesozoicMesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
Period: Late Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
Faunal stage
Faunal stage
In chronostratigraphy, a stage is a succession of rock strata laid down in a single age on the geologic timescale, which usually represents millions of years of deposition. A given stage of rock and the corresponding age of time will by convention have the same name, and the same boundaries.Rock...
: late Cenomanian
Cenomanian
The Cenomanian is, in the ICS' geological timescale the oldest or earliest age of the Late Cretaceous epoch or the lowest stage of the Upper Cretaceous series. An age is a unit of geochronology: it is a unit of time; the stage is a unit in the stratigraphic column deposited during the corresponding...
– early Turonian
Turonian
The Turonian is, in the ICS' geologic timescale, the second age in the Late Cretaceous epoch, or a stage in the Upper Cretaceous series. It spans the time between 93.5 ± 0.8 Ma and 89.3 ± 1 Ma...
Absolute Age
Geochronology
Geochronology is the science of determining the age of rocks, fossils, and sediments, within a certain degree of uncertainty inherent to the method used. A variety of dating methods are used by geologists to achieve this, and schemes of classification and terminology have been proposed...
: ~94 to ~91 mya
Paleontology
Not many dinosaurDinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
s are represented in the Lisandro Formation; other types of animal
Animal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...
s are frequently found. Fossils documented from this formation are:
- freshwater bivalve molluscs
- fishFishFish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
- turtleTurtleTurtles are reptiles of the order Testudines , characterised by a special bony or cartilaginous shell developed from their ribs that acts as a shield...
s - crocodiliaCrocodiliaCrocodilia is an order of large reptiles that appeared about 84 million years ago in the late Cretaceous Period . They are the closest living relatives of birds, as the two groups are the only known survivors of the Archosauria...
ns - an abelisauroid theropod
- at least one birdBirdBirds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
- ornithopodOrnithopodOrnithopods or members of the clade Ornithopoda are a group of ornithischian dinosaurs that started out as small, bipedal running grazers, and grew in size and numbers until they became one of the most successful groups of herbivores in the Cretaceous world, and dominated the North American...
s (including AnabisetiaAnabisetiaAnabisetia is a genus of ornithopod dinosaur from the Late Cretaceous Period of Patagonia, South America. It was a small bipedal herbivore, almost seven feet long....
)
The swampy terrain may have limited the numbers of larger dinosaurs such as sauropods and carcharodontosaurids, which are found in earlier formations in the region but have not yet been found in the Cerro Lisandro.