The Lourinhã Formation () is a fossil rich

geological formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics (lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock expo ...

in western Portugal, named for the municipality of

Lourinhã Lourinhã () is a municipality in the District of Lisbon, in the Oeste Subregion of Portugal. The population in 2011 was 25,735, in an area of 147.17 km². The seat of the municipality is the town of Lourinhã, with a population of 8,800 inhab ...

. The formation is mostly

Late Jurassic The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987. In European lithostratigraphy, the ...

in age (Kimmeridgian/Tithonian), with the top of the formation extending into the earliest Cretaceous (Berriasian). It is notable for containing a fauna especially similar to that of the

Morrison Formation The Morrison Formation is a distinctive sequence of Upper Jurassic sedimentary rock found in the western United States which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandstone, siltstone, ...

in the United States and a lesser extent to the

Tendaguru Formation The Tendaguru Formation, or Tendaguru Beds are a highly fossiliferous formation and Lagerstätte located in the Lindi Region of southeastern Tanzania. The formation represents the oldest sedimentary unit of the Mandawa Basin, overlying Neoprote ...

in Tanzania. There are also similarities to the nearby Villar del Arzobispo Formation. The stratigraphy of the formation and the basin in general is complex and controversial, with the constituent member beds belonging to the formation varying between different authors. Besides the fossil bones, Lourinhã Formation is well known for the fossil tracks and fossilized dinosaur eggs. The Lourinhã Formation includes several lithostratigraphic units, such as Praia da Amoreira-Porto Novo Members and Praia Azul Member and the Assenta Member.

Lithology and depositional history

Depositional history

The Lourinhã Formation is located within the Lusitanian Basin, a mostly onshore North South orientated

rift basin In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-grabe ...

within western Portugal, formed during the Opening of the North Atlantic Ocean, with sediment deposition beginning during the

Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch ...

Early Jurassic The Early Jurassic Epoch (in chronostratigraphy corresponding to the Lower Jurassic Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic-Jurassic extinction event, 201.3 Ma ...

. It primarily consists of syn-rift near-coastal continental

siliciclastic Siliciclastic (or ''siliclastic'') rocks are clastic noncarbonate sedimentary rocks that are composed primarily of silicate minerals, such as quartz or clay minerals. Siliciclasic rock types include mudrock, sandstone, and conglomerate Conglome ...

sediments, with several marine intercalations. The primary flow direction was North to South, originating from

Galicia Galicia may refer to: Geographic regions * Galicia (Spain), a region and autonomous community of northwestern Spain ** Gallaecia, a Roman province ** The post-Roman Kingdom of the Suebi, also called the Kingdom of Gallaecia ** The medieval King ...

and flowing between the Iberian landmass to the east and the now largely submerged

Berlengas The Berlengas are a Portuguese archipelago consisting of small Atlantic islands off the coast of Peniche, Portugal, in the Oeste region. These islands were traditionally known to British mariners as "the Burlings". The only inhabited island is ...

horst, a north–south oriented

ridge A ridge or a mountain ridge is a geographical feature consisting of a chain of mountains or hills that form a continuous elevated crest for an extended distance. The sides of the ridge slope away from the narrow top on either side. The line ...

, to the west.

Stratigraphy

The unit was first formally proposed by Hill in 1988. The stratigraphy of the Lourinhã Formation is complex and varies between sub-basins with several competing stratigraphic proposals and there is currently no consensus on the matter, one of the most recent stratigraphies, divides the formation into three members which are from oldest to youngest the Praia da Amoreira-Porto Novo Member, Praia Azul Member, and the Assenta Member.

Praia da Amoreira-Porto Novo Member

The Praia da Amoreira-Porto Novo Member is composed of the Priaia de Amoreira Member, which consists of massive

mudrock 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 sma ...

-sand with metre thick sandstone

lenses A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements ...

, with massive mudrock with

calcrete Caliche () is a sedimentary rock, a hardened natural cement of calcium carbonate that binds other materials—such as gravel, sand, clay, and silt. It occurs worldwide, in aridisol and mollisol soil orders—generally in arid or semiarid region ...

. The overlying Poto Novo Mb. consists of massive bodies of sandstone, often cross bedded. The environment of deposition is interpreted as a

meander A meander is one of a series of regular sinuous curves in the channel of a river or other watercourse. It is produced as a watercourse erodes the sediments of an outer, concave bank ( cut bank) and deposits sediments on an inner, convex ban ...

ing fluvial system, while the Porto Novo Mb is interpreted as a deltaic deposit. It is interpreted to be latest Kimmeridgian in age, and overlies the Consolacao Unit at the top of the '' Aulacostephanus eudoxus'' ammonite zone.

Praia Azul Member

The Praia Azul Member, formerly known as the Sobral unit/member is 80 to 130 metres thick and consists of tabular marls and mudstones, with rare sandstones bodies. There are three distinct laterally extensive (>20 km) thin shelly

carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonat ...

horizons within this member, indicating brief

marine transgression A marine transgression is a geologic event during which sea level rises relative to the land and the shoreline moves toward higher ground, which results in flooding. Transgressions can be caused by the land sinking or by the ocean basins filling ...

s. South of Santa Cruz primarily consists of sandstone with rare conglomerate. The age is considered to be latest Kimmeridgian to earliest Tithonian, correlated to the ammonite zones of '' Hybonoticeras beckeri'' and '' Hybonoticeras hybonotum''.

Assenta Member

The Assenta Member is around 300 metres thick and predominantly consists of mudstones with frequent layers of

caliche Caliche () is a sedimentary rock, a hardened natural cement of calcium carbonate that binds other materials—such as gravel, sand, clay, and silt. It occurs worldwide, in aridisol and mollisol soil orders—generally in arid or semiarid regio ...

. Near the top of the member several layers of tens of metres thick nodular and marly

bioclast Bioclasts are skeletal fossil fragments of once living marine or land organisms that are found in sedimentary rocks laid down in a marine environment—especially limestone varieties around the globe. some of which take on distinct textures and col ...

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms wh ...

s are present, containing marine benthic forams, the nodularity is derived from intense '' Thalassinoides'' burrowing. It is predominately late Tithonian in age, with the last few metres probably being earliest

Berriasian In the geological timescale, the Berriasian is an age/ stage of the Early/Lower Cretaceous. It is the oldest subdivision in the entire Cretaceous. It has been taken to span the time between 145.0 ± 4.0 Ma and 139.8 ± 3.0 Ma (million years a ...

, with the top of the formation roughly correlative with the base of the magnetochron M18n. (~144.7 Ma) The environment of deposition is interpreted as being an upper fluvial-dominated delta to meandering fluvial systems flowing on a paralic plain.

Dinosaurs of the Lourinhã Formation

In a 2003 study, an analysis of all Portuguese dinosaurs was published. The study created a cladogram showing the possible relations of all Portuguese dinosaurs, including those at the time known from the Lourinhã Formation.

Saurischia

Theropods

Sauropods

Ornithischia

Thyreophorans

Ornithopods

additionally remains belonging to a dryosaurid and ankylopollexian unreferrable to either eousdryosaurus or draconyx have been found, the ankylopollexian possessed a 44cm scapula.
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Synapsids of the Lourinhã Formation

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 ...

Dryolestoidea

Flora

Correlation

References

Bibliography

* Antunes, M.T. and Mateus, O. (2003). ''Dinosaurs of Portugal.'' C. R. Palevol, 2:77–95 * Mateus, O. (2006). "Late Jurassic dinosaurs from the Morrison Formation, the Lourinhã and Alcobaça Formations (Portugal), and the Tendaguru Beds (Tanzania): a comparison," in Foster, J.R. and Lucas, S. G. R.M., eds., 2006, "Paleontology and Geology of the Upper Jurassic Morrison Formation." ''New Mexico Museum of Natural History and Science Bulletin'' 36 *

External links

Antunes & Mateus (2003)

Mateus (2006)
{{DEFAULTSORT:Lourinha Formation Geologic formations of Portugal Jurassic System of Europe Sandstone formations Mudstone formations Conglomerate formations