A mess that begins in the Jurassic
In both the work of 1898 and 1902, Vidal tentatively gives it a Jurassic age (Vidal, 1898), and then specifies its ascription to the Kimmeridgian stage (between 155 and 152 million years ago) once he had carried out the first scientific studies on the flora, fauna and lithology (Vidal, 1902). For Vidal, among the fossils and lithic composition of La Pedrera there were great similarities with the Jurassic sites of Cerin (France) and Solnhofen (Germany), although the latter were considered slightly more modern, of Tithonian age (between 152 and 145 million years ago).
This proposal of the Jurassic age for the site of La Pedrera was maintained until the 30s of the twentieth century. Dalloni (1930), Chevalier (1932) and Broili (1932) date these lithographs to the Upper Jurassic. Chevalier mentions a discovery by Faure i Sans, a plant identified as Onychiopsis mantelli, a plant recovered from sites from the Lower Cretaceous, but does not take this into account when reviewing the original dating. Broili, who had visited the fossil collection of La Pedrera at the Museum of Geology of Barcelona, during the XIV International Congress of Geology in 1926, carried out a study of the lithographic sites of Cerin, Solnhofen and Rúbies and confirmed a Tithonian age for the Catalan site, mainly for sedimentological and stratigraphic considerations.
Micropaleontological studies change age
The first change in relation to the age of the site is made by Krusat (1966). In his work he mentions the micropalentologic study with ostracods and foraminifera that allows him to say that we are in an age between the Upper Tithonian to the Barremian (from 132 to 124 million years ago), but he does not dare to advance further in the precision of the age. As for the formation of the site, Krusat proposes that they were formed in lagoons very close to the coast. For him, the plants that appear in it were washed away by the floods and the lake itself was the biotope for reptile fish, crustaceans and foraminifera. Possibly, according to Krusat, the entire area of sediment deposit was separated from the open sea, to the north, by a thin barrier that could be permeable to migrations of marine fauna.
At the beginning of the 70s there are still doubts about the age of the locality and Delmas et al. (1971) and Via (1971) only report the ages already proposed that range between the Kimmeridgian and Barremian (between 155 and 124 million years ago).
A detailed study of the tiny crustaceans (ostracods) preserved in the lithographic slabs allows Peybernès and Oertli (1972) to date the transit between the Berriasian and the Valanginian (about 140 million years ago). Another study of ostracods refines the dating in the Upper Berriatian-Lower Valanginian (Brenner et al., 1974). This dating, already fully accepted by Barale (1984), allows him to propose that this site is pioneering for the appearance of the first known angiosperms. Another clue that pointed to a similar age was the identification of the plant genus Frenelopsis (Barale 1973), of Cretaceous age, which reinforced the previous proposal.
Finally, two works in the decade of the 90s, propose a new dating. Ansorge (1993), based on the study of insects in fossilized faeces (coprolites) and Martín-Closas and López-Morón (1995), based on the study of charophytic algae, propose a Barremian age (130-125 ma), which is currently the most widely accepted.