The formation was first defined by Fossa Mancini in 1937 as the Formación Continental de Paso Flores. Later, Frenguelli called the formation Estratos de Paso Flores and Galli described it as Serie de Paso Flores. Finally, the formation was described as Paso Flores Formation. based on a type section exposed along the Limay River in the southern Neuquén Basin. The Paso Flores Formation comprises conglomerates, sandstones and shales.
Extent
The formation crops out in its largest extent around the Limay River and the Ranquel-Huao hill and north of EstanciaCorral de Piedra. Other outcrops are found northeast of Estancia Collón Curá y on the right banks of the Collón Curá River and in the cañadones of Pancho and El Pedregoso. The type section is found in the eponymous Paso Flores, on the left banks of the Limay River and around Cerro Mariana. The national roads 40 and 237 cross-cut the formation.
González Díaz assigned a Late Triassic age to the formation, based on a paleofloristic analysis of the Paso Flores Formation executed west of the Collón Curá River. Ganuza et al. realized a paleobotanical study at Cañadón de Pancho and reached the same conclusion of a Late Triassic age. Zavattieri observed that the macro- and microflora indicated a Rhaetian age. Several taxa known from the Jurassic are present as well as typical Triassic taxa as Telemachus elongatus and Pagiophyllum. The formation is the only fossiliferous latest Triassic formation. The Paso Flores Formation is correlated with the Garamilla, Los Menucos and Sierra Colorada Formations elsewhere in Argentina. Dictyophyllum tenuifolium, whose type locality is the Paso Flores Formation, is also found in the LadinianCortaderita Formation of San Juan Province.
Lithology
The Paso Flores Formation is a terrestrial unit with a high fossil content, composed of conglomerates, conglomeratic sandstones and lightbrown sandstones and shales with iron staining. The thickness of the formation varies from in the Ranquel Huao hills, in the Cañadón de Pancho and according to Frenguelli and Spalletti et al., in Estancia Paso Flores and Cerro Mariana. The well-consolidated conglomerates comprise rounded polymictgranitic and volcanic clasts of up to in a sandy matrix. Intercalated in the conglomerates are lenses of fine-to-medium grained sandstones and shales preserving fossil leaves and fossilized treetrunks.
Fossil content
The Paso Flores has provided a variety of flora fossils, reported from three outcrops: In 2003, more specific descriptions were carried out of Cladophlebis grahami, C. denticulata, Dictyophyllum chihuiuensis, D. tenuiserratum and D. rothi, Rhexoxylon brunoi, Dicroidium crassum, D. odontopteroides, D. lancifolium, Xylopteris argentina and X. elongata. Abundant other flora are Scleropteris grandis, Linguifolium arctum, L. lilleanum, L. tenisonwoodsii and L. steinmannii, Cycadocarpidium and Heidiphyllum, Telemachus and Protocircoporoxylon marianaensis. In 2017, several flora were described; Lutanthus ornatus, Rissikistrobus plenus, Rissikistrobus reductus, Rissikia media, Umkomasia sp., Sphenobaiera argentinae, Pseudoctenis spatulata, Taeniopteris crassinervis and Yabeiella brackebuschiana. Additionally, Baiera triassica, in replacement of the homonymous species previously identified in Argentina as Baiera taeniata, Ginkgo taeniata and Sphenobaiera taeniata, were described as well as new species previously described from other locations than the analyzed Quemquemtreu area of the Cañadón Pancho locality. These species are: Asterotheca rigbyana, Marattiopsis muensteri, Cladophlebis kurtzii, C. indica, Dictyophyllum tenuifolium, Goeppertella stipanicicii, Dicroidium incisum, D. odontopteroides, D. lancifolium, Pachydermophyllum praecordillerae, Heidiphyllum elongatum, Baiera furcata, Sphenobaiera robusta, Pseudoctenis carteriana and P. falconeriana.
