The formation comprises several lithologies, from sandstone, conglomerates and shales to marls, siltstones, limestones and lignite and gypsum beds and ranges between 250 and 800 metres (820 and 2,620 ft) in thickness.

The Tremp Basin evolved into a sedimentary depression with the break-up of Pangea and the spreading of the North American and Eurasian plates in the Early Jurassic.

A first phase of tectonic compression commenced in the Cenomanian, lasting until the late Santonian, around 85 Ma, when Iberia started to rotate counterclockwise towards Europe, producing a series of piggyback basins in the southern Pre-Pyrenees.

The main phase of movement of another major thrust fault, the Montsec to the south of the Tremp Basin, happened not before the Early Eocene.

A rich and diverse assemblage of fossils has been reported from the formation, among which more than 1000 dinosaur bones, tracks dating up to just 300,000 years before the Cretaceous-Paleogene boundary, and many well-preserved eggs and nesting sites in situ, spread out over an area of 6,000 square metres (65,000 sq ft).

Multiple specimens and newly described genera and species of crocodylians, mammals, turtles, lizards, amphibians and fish complete the rich vertebrate faunal assemblage of the Tremp Formation.

Additionally, fresh-to-brackish water clams as Corbicula laletana, bivalves of Hippurites castroi, gastropods, plant remains and cyanobacteria as Girvanella were found in the Tremp Formation.

The abundant paleontological finds are displayed in the local natural science museums of Tremp and Isona, where educational programs have been established explaining the geology and paleobiology of the area.

[8][9] The Tremp Formation is a marginally marine to fluvial to lacustrine and continental sedimentary unit with a thickness varying between 250 and 800 metres (820 and 2,620 ft).

The formation comprises several different lithologies, as sandstones, shales, limestones, marls, lignites, gypsum beds, conglomerates and siltstones have been registered.

[36] During this period, evaporites were deposited in the rift basins,[37] later in the tectonic history becoming important décollement surfaces for the compressional movements.

[44] This period is characterized by a local unconformity in the Tremp Basin,[45] while this is not registered farther to the west of the Pre-Pyrenean minibasins near Pont de Suert.

Global examples of halokinesis in compressional inverted tectonic regimes include the south Viking Graben, and Central Graben in the North Sea,[62] offshore Tunisia,[63] the Zagros Mountains of Iraq and Iran,[64][65] northern Carpathians in Poland,[66] western,[67] and eastern Colombian, along the Eastern Frontal Fault System of the Eastern Ranges of the Andes,[68] the Al Hajar Mountains of Oman,[69] Dnieper-Donets Basin in Ukraine,[70] the Sivas Basin in Turkey,[71] the Kohat-Potwar fold and thrust belt of Pakistan,[72] the Flinders Ranges in South Australia,[73] during the Eurekan orogeny in the Sverdrup Basin of northeastern Canada and western Greenland,[74] and many more.

[75] In the western Cotiella Basin, salt inflation and withdrawal played a major role in the differential sedimentary thicknesses, facies changes and tectonic movements.

[79] The depositional environment of the Tremp Formation varies between continental, lacustrine, fluvial, and marginally marine (estuarine to deltaic and coastal).

[18] The biochemical data, based on C and O isotope analysis could indicate a rise in temperature, an increase in evaporation and a higher production of plant material at the transition of Maastrichtian and Paleocene.

In the Tremp Basin, the boundary is registered at Coll de Nargó, Isona and Fontllonga and established on the basis of paleomagnetism and a strong decrease of ∂13C and ∂18O isotopes.

[85] The typical iridium layer, found in other sites where the Cretaceous-Paleogene boundary has been noted, as Gubbio in Italy and Caravaca in Spain,[86] has not been registered in the Tremp Formation.

[90] The Tremp and underlying Arén Formations are the richest sites for dinosaur fossils in the Pyrenees,[19] with only at Basturs more than 1000 bone fragments found.

[81] The holes found on the dip slope at Ermita La Posa were initially interpreted as tracks produced by sauropod dinosaurs.

[91] The Reptile Sandstone, when identified as a separate unit, was called as such because of the great abundance of fossil chelonid turtles,[97] Bothremydidae, crocodile teeth, theropod limbs,[98] and hadrosaur femurs.

The rocks, in a 36 metres (118 ft) thick interval,[100] are interpreted as sedimentary deposits of a fluvial environment located some distance away from an active stream channel.

[101] Most eggs exposed at the Pinyes locality were incompletely preserved because of recent erosion; however, excavation occasionally revealed relatively intact specimens in the subsurface.

The description was done on the basis of egg size, shape, eggshell microstructure, tuberculate ornamentation, and the presence of transversal canals in a tubocanaliculate pore system, an unequivocal feature of this oospecies.

The distinct clutch geometry reported at Pinyes and other megaloolithid localities worldwide, strongly suggests a common reproductive behavior that resulted from the use of the hind foot for scratch-digging during nest excavation.

[108] The egg spatial distribution, in small clusters linearly to compactly grouped, but contained in round shaped areas of up to 2.3 metres (7.5 ft) would either support burrow- or mound-nesting at Pinyes.

[178] On April 17, 2018, UNESCO accepted the proposal and designated the site as Conca de Tremp-Montsec Global Geopark, stating:[5] "This area is internationally recognized as a natural laboratory for sedimentology, tectonics, external geodynamics, palaeontology, ore deposits and pedology.