[F] Bajo Barreal Formation - Part of the Castillo Formation - Argentina
The presumed Cenomanian age of the Bajo Barreal has been based largely on the phylogenetic relationships of the dinosaurs to other Cenomanian taxa however the dinosaurian record shows great similarities with other South American formations from Campanian and Maastrichtian age
a. Lower Bajo Barreal Formation (110 meters).
For some authors this unit belongs to the high part of the \\\\\\\"Serie de Castillo\\\\\\\" (Ferello, 1950; Ferello and Tealdi, 1950).
This unit consists of alternating gray and greenish tuffs. Gradually it incorporates sandstone banks, each time more frequent toward the top, showing an inverse megasequence and a composition each time more epiclastic in that direction. The presence of pumice clasts and scarce small bombs indicate the proximity of the explosive centers, which would have contributed the great quantity of pyroclastic material present in this unit.
A gradual lithologic variation exists from the base to the top, passing progressively from:
i. The base, constituted by massive tuffaceous mudstones and gray tuffs, deposited on a gentle slope; it could correspond to a continental floodplain environment.
ii. In the central area, dominantly pyroclastic, clear brown tuffs prevail, with characteristic soil-forming zeolite-rich green tuffs and other green, laminated tuffs, suggestive of lacustrine environments. In the middle of this section small well preserved bones of a dinosaur were exhumed (J. Rodríguez, pers. comm.)2, coming from a greenish brown tuff, of kidneyshaped to almost spherical fracture, bioturbated (by roots?), directly under a conspicuous bank of green tuff, 1.5 meters thick, laminate, wavy, tabular, of lacustrine aspect and that has regionality. This last is not the only stratum with these characteristics since other interbedded strata appear, under and on the same. Intercalated among these sediments, ephemeral sandstone beds appear, of pure and erosive base, fining-upward and of reduced lateral extension; disappearing to appear in other levels, alternating and with similar characteristics, that is to say, with little fluidity in the detritic movement, maybe as debris flows of high density and viscosity. These ephemeral fluvial courses would contribute sediment to the floodplains and the small lakes mentioned above.
iii. The upper section is characterized by the presence of greenish sandstones and conglomerates that are arranged in tabular form inside greenish gray and gray tuffaceous mudstones and fine tuffs. Although they have a clear and erosive base, their tops are highly planar, similar to the G4 and G5 facies of Hechem et al. (1989). These sandstones have, in general, an important lateral extension, compared with those of the lower level, their internal structure suggesting an origin mediated by intermittent, rapid dense currents of short duration, where the source area would be in the vicinity or in nearby areas. Although they usually grade to fine sandstones and mudstones, with evidence of paleosols in the upper levels (covered, possibly by rains of volcanic ash of a few centimeters of thickness), in many cases the interruption of flow was quite rapid since there are frequent thick and clear ends. Internally they present variable transported structures in the vertical, although diffuse, from massive in the base, parallel stratification of high flow régime above and stratification intertwined in the top. These fining-upward cycles are superimposed several times and suggest a poorly defined drainage network defined on an apparently planar relief, where lagoons and lakes of little depth were located.Included in these sandstones that are not exclusive of the section, since they continue to appear in the upper member of the Bajo Barreal Formation, is where fossil remains of dinosaurs and other vertebrates have been found. This sector of the Bajo Barreal Formation, that comprises the top of the lower member and a great part of the upper member, is taphonomically controlled by rapid burial and also, it was more favorable for the development of these vertebrates, since the climate would have been more humid than that of the underlying sediments, according to what is indicated by the textural and structural characteristics of the sandstones, the low pyroclastic participation, low oxidation, and larger proportion of tuffaceous rocks altered to bentonitic clays (expansibles).
b. Upper Bajo Barreal Formation (70 meters).
It corresponds that denominated “Barreal Gris\\\\\\\" of the internal reports of the investigators of Yacimientos Petroliferos Fiscales S. A. Usually appears semicovered by a scab of clayey weathering (regional characteristic). This is constituted by a repetition of cycles of 2 to 5 meters of thickness, between sandstones and gray and graygreen mudstone-tuff material. The lower sandstones have characteristics equal to those of the top of the member mentioned before (here, too, dinosaur remains are found).
Source: A new fossiliferous outcrop from the Bajo Barreal Fm. (Late Cretceous) and its sauropod fauna. Juan C. Sciutto and Rubén D. Martínez Universidad Nacional de la Patagonia San Juan Bosco, Facultad de Ciencias Naturales, Cuidad Universitaria Km 4, (9000) Comodoro Rivadavia, Province of Chubut Translated by Matthew C. Lamanna June-November 2001 Polyglot Paleontologist
Aeolosaurus colhuehuapensis - Provincia de Chubut - Sauropoda Titanosauria - Cretaceous Late
Anikosaurus darwini - Provincia de Chubut - Coelurosauria Nomen Nudem - Cretaceous Late Cenomanian
Aniksosaurus darwini - Central Patagonia - Tetanurae Coelurosauria - Cretaceous Late
Antarctosaurus wichmannianus - Provincia de Chubut - Sauropoda Titanosauria - Cretaceous Late Campanian Maastrichtian
Argyrosaurus superbus - Provincia de Chubut - Sauropoda Titanosauria - Cretaceous Late Campanian Maastrichtian
Campylodon ameghinoi - Provincia de Chubut - Sauropoda Incerate Sedis - Cretaceous Late Campanian Maastrichtian
Campylodoniscus ameghinoi - Provincia de Chubut - Sauropoda Incerate Sedis - Cretaceous Late Campanian Maastrichtian
Drusilasaura deseadensis - Santa Cruz Province, Patagonia - Titanosauria Lognkosauria - Cretaceous Late Cenomanian Turonian
Elaltitan lilloi - Provincia de Chubut - Sauropoda Titanosauria - Cretaceous Late Cenomanian
Epachthosaurus sciuttoi - Provincia de Chubut - Sauropoda Titanosauria - Cretaceous Late Campanian Maastrichtian
Laplatasaurus araukanicus - Provincia de Chubut - Sauropoda Titanosauria - Cretaceous Late Campanian Maastrichtian
Notohypsilophodon comodorensis - Provincia de Chubut - Ornithopoda Hypsilophodontidae - Cretaceous Late Campanian Maastrichtian
Secernosaurus koerneri - Provincia de Rio Negro - Ornithopoda Hadrosauridae - Cretaceous Late Maastrichtian
Xenotarsosaurus bonapartei - Provincia de Chubut - Carnosauria Allosauridae - Cretaceous Late Campanian Maastrichtian
Laplatasaurus sp. - Provincia de Chubut - Sauropoda Titanosauria - Cretaceous Late Campanian Maastrichtian
Theropoda indet. - Provincia de Chubut - Theropoda - Cretaceous Late Campanian Maastrichtian
Titanosaurid indet. - Provincia de Chubut - Sauropoda Titanosauria - Cretaceous Late Campanian Maastrichtian
Undescribed titanosaurid (Powell, 1986) - Provincia de Chubut - Sauropoda Titanosauria - Cretaceous Late Campanian Maastrichtian
?Abelisaurid indet. - Provincia de Chubut - Theropoda - Cretaceous Late Campanian Maastrichtian
Rebbachisaurid indet - Provincia de Chubut - Sauropoda: Diplodocoidea - Cretaceous Late Campanian Maastrichtian
Lucio M. Ibiricu, Gabriel A. Casal, Matthew C. Lamanna, Rubén D. Martínez,Jerald D. Harris, Kenneth J. Lacovara (2011) The southernmost records of Rebbachisauridae (Sauropoda: Diplodocoidea), from early Late Cretaceous deposits in central Patagonia. Cretaceous Research (advance online publication) doi:10.1016/j.cretres.2011.11.003