The Lourinhã Formation is a fossil rich geological formation in western Portugal, named for the municipality of Lourinhã. The formation is Late Jurassic in age and is notable for containing a fauna especially similar to that of the Morrison Formation in the United States and a lesser extent to the Tendaguru Formation 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 the Sobral Unit.
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.
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 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 Kimmeridigan to earliest Tithonian.
Assenta Member
The Assenta Member is around 300 metres 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 bioclastic limestones 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. The environment of deposition is interpreted as being an upper fluvial-dominated delta to meandering fluvial systems flowing on a 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.
