The Lourinhã Formation (Portuguese pronunciation:[loɾiˈɲɐ̃]ⓘ) is a fossil-rich geological formation in western Portugal, named for the municipality of Lourinhã. The formation is mostly Late Jurassic in age (Kimmeridgian/Tithonian). It is notable for containing a fauna especially similar to that of the Morrison Formation in the United States and to a lesser extent to the Tendaguru Formation in Tanzania. There are also similarities to the nearby Villar del Arzobispo Formation and Alcobaça Formation. Besides the fossil bones, Lourinhã Formation is also 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, Praia Azul Member, the Santa Rita Member, and the Assenta Member. The stratigraphy of the formation is complex and controversial, with the constituent member beds belonging to the formation varying between different authors.
Lithology and depositional history
Depositional history
Location of the Lusitanian basin within the Iberian Peninsula
The Lourinhã Formation is located within the Lusitanian Basin, a mostly onshore North South orientated rift basin within western Portugal, formed during the Opening of the North Atlantic Ocean, with sediment deposition beginning during the Late Triassic-Early Jurassic. It primarily consists of syn-rift near-coastal continental siliciclastic sediments, with several marine intercalations. The primary flow direction was North to South, originating from Galicia and flowing between the Iberian landmass to the east and the now largely submerged Berlengashorst, a north–south oriented ridge, to the west. The Lourinha Formation is regarded as being coeval with the younger parts of the Morrison Formation.
The Lourinha Formation is interpreted as being an island, separated from North America and the rest of Europe by marine barriers. The paleoclimate is interpreted as being semi arid, with less than 50cm (20in) of annual precipitation and an average annual temperature of 16–19°C. It is interpreted as having a variety of different habitats, including deltas, coastal plains and open woodlands.
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, from oldest to youngest: the Praia da Amoreira-Porto Novo Member, Praia Azul Member, and the Assenta Member.
The age of the Lourinha formation has been regarded as Kimmeridgian to Tithonian. The age of the overlying Alcobaca Formation has been determined to be 152.5 mya at the point of contact with Lourinha. The overlying and intefingering Freixial Formation has been dated through magnetostratigraphy to 150.8 to 146.5 mya. Therefore, the age of the Lourinha formation is between 152.5 and 146.5 mya. The Alcobaça Formation has been regarded as Pro parte with the Lourinha Formation, meaning they are partially time equivalent.
Praia da Amoreira-Porto Novo Member
The Praia da Amoreira-Porto Novo Member is composed of the Praia de Amoreira Member, which consists of massive mudrock-sand with metre-thick sandstone lenses, with massive mudrock with calcrete. The overlying Porto Novo Mb. consists of massive bodies of sandstone, often cross bedded. The environment of deposition is interpreted as a meandering 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. The continental facies of the Porto Novo Member intersperse into the Praia Azul Member and transition vertically and laterally into each other. At Vale Pombas at least 2 tongues of the Porto Novo Member are interspersed with 2 tongues of the Praia Azul Member. At Porto Dinheiro, the continental fluvial environment at the top of Porto Novo Member shows tidal influence, possible evidence of interaction with the coastal ecosystem of the Praia Azul Member. In the region from Paimogo to Areia Branca the overlaying deposits of the Praia Azul Member correspond to the upper Porto Novo Member in that section, implying they intercalate. These details indicate the Praia Azul and Porto Novo members represent laterally equivalent environments deposited simultaneously in adjacent, shifting, and laterally migrating sedimentary environments.
Praia Azul Member
The Praia Azul Member, formerly known as the Sobral unit/member, is 80–130m (260–430ft) thick and consists of tabular marls and mudstones, with rare sandstone bodies. There are three distinct laterally extensive (>20km (12mi)) thin shelly carbonate horizons within this member, indicating brief marine transgressions. 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.
Santa Rita and Assenta members
The Santa Rita Member in the Consolação sub-basin and its lateral equivalent in the Turcifal Basin, the Assenta Member, is around 300m (980ft) thick and predominantly consists of mudstones with frequent layers of caliche. Near the top of the member, several layers of tens of metres thick nodular and marly bioclasticlimestones are present, containing marine benthic forams. The nodularity is derived from intense Thalassinoides burrowing. It was originally interpreted as being Tithonian in age, but reinterpretation of the magnetostraitgraphic data now places it in the Upper Kimmeridgian to Lower Tithonian. The environment of deposition is interpreted as being an upper fluvial-dominated delta to meandering fluvial systems flowing on a paralic plain. The Assenta Member is thought to represent the upper delta-plain and fluvial domain of the Praia Azul Member.
Fauna
Dinosaurs
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.
Giant track of an ornithopod suggestive of an animal with a hip height of 2.8–3 metres (9.2–9.8ft).No known Jurassic ornithopod reaches this size. Found alongside the Deltapodus print.
A specimen consists of a collection of skeletal remains consisting of a nearly complete dorsal vertebra, three dorsal vertebral centra, nine dorsal neural arch fragments, an incomplete sacrum that preserves only four sacral vertebrae, two sacral ribs, fragments of the dorsal sacral plate, the anterior process of the right pubis, and numerous fragmentary remains belonging to the dermal armor, in addition to several indeterminate fragments.
A stegosaurid; material referred to Miragaia may belong to this taxon. Fossils from Lourinha come from a particularly large animal. Maidment et al. regard the material of Dacentrurus from Lourinha as diagnostic to the genus level.
The tracks can be separated into three different morphologies. However, all fall within the range of the ornithopod association of the pes and manus tracks to the same taxon, cannot be directly supported. Preserve various well-preserved skin impressions. The largest prints are larger than those from the type horizon. The tracks are individually represented and do not form any sort of trackway, though one print is associated with a giant ornithopod track, potentially representing that the creatures were traveling together or were otherwise going to a similar location. Another is similarly associated with theropod and sauropod prints.
It was discovered in the Casal Novo locality which was originally interpreted as coming from the Alcobaça Formation, but recent studies reassign the locality to the Lourinha Formation. Specimen is regarded as referable to Stegosaurus, with characters particularly relating it to S. ungulatus, notably the posterior edge of the neural arch sloping posteriorly on the anterior cervical vertebrae and bifurcated apices of the anterior caudal neural arches.
Represented by 2 partial skeletons,SHN 177 and 178. Remains long considered to be from an animal closely related to Diplodocus and recently suggested to be a potential representative of this genus. SHN 178 comes from the Freixial Formation.
Teeth from an indeterminate flagellicaudatan, possibly a diplodocid. The tooth from the Praia Azul Member has a dental morphology similar to that reported from juvenile diplodocines.
Potentially a synonym of the type species, C. nasicornis. Sometimes referred to as C. sp., giving indication of possible distinctiveness or of being intermediate. Remains also known from the Praia Azul Member. Remains come from Porto das Barcas, considered part of the Sobral Fm/Praia Azul Member.
Three individuals, one largely complete; over 100 eggs with significant amount of skeletal material.
Has come out in various places in the tree, erroneously said to be a megalosaur, mostly accepted to be a carnosaur, probably allosauroid, or basal coelurosaur. Currently unstable on the tree.
Only definite record of this taxon is from the Late Cretaceous of North America, despite erroneous and referrals from other sites in Portugal. Probably a close relative of Richardoestesia and not an actual representation of the taxon.
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