The Chichinales Formation is a geological formation in Río Negro Province, Argentina which dates from the Late Oligocene to the Early Miocene, around 23 to 17.5 million years ago. It predominantly consists of pyroclastic deposits, which were deposited in a semi-arid environment. It is divided up into a number of members. The diverse fauna of the Chichinales Formation, including a variety of turtles and birds, also includes many mammals such as South American native ungulates (notoungulates and litopterns) as well as armadillos, and caviomorph rodents.
It is named after the type locality and extends over a large part of the province of Río Negro. It outcrops in the valle de Río Negro, in the towns of General Roca, Río Negro and Villa Regina, bordering the southern bank of the Río Negro. Part of the most important outcrops are located within the Paso Córdova Natural Protected Area.
The Chichinales Formation, broadly speaking, is made up of grayish sandstones, whitish tuffs, siltstones and greenish claystones with paleo soil levels. It is divided into 3 members: lower, middle and upper. The lower one is composed of grayish brown sandstones with low-angle cross bedding, alternating with light brown tuffs, tuffaceous sandstones, sandstones with carbonate cement and shales. In this member, the presence of "opalized" fossil logs is common. The middle member is formed by paleosols and sequences of siltstones, shales and fine sands that in some sectors form lenses in the form of fluvial channels. Finally, the upper member is represented by more homogeneous levels of tuffs, whitish gray tuffites, siltstones, green claystones and tuffaceous sandstones This member, in some sectors, is laterally interdigitated with marginal marine levels of the Gran Bajo del Gualicho Formation, which dates from the Late Oligocene to the Early Pliocene. The Chichinales Formation is correlated with the contemporaneous fluvial and lacustrine tuffaceous Collón Curá Formation of the central Neuquén Basin.
The sedimentological and paleontological evidence provided by the Chichinales Formation suggests the existence of open environments with low relief, restricted wooded areas with temporary water bodies and warm temperate climate, in agreement with other Colhuehuapian localities of Chubut Province. In this context, it is possible to interpret, at least tentatively, that the differences between the set of taxa represented in the Cerro Bandera Formation and those of the Chichinales Formation are due to contrasts between the local environmental conditions of each unit rather than to differences in temporal range. It is likely that such differences are the result of the particular conditions that prevailed in the Neuquén region during the Early Miocene, which would be a consequence of its proximity to the Andean zone rather than its latitudinal location. Material was copied from this source, which is available under a Creative Commons Attribution 3.0 International License
Paleoflora Name Species Member/Locality Material Notes ImageNothofagusN. menendezii
Paleofauna Reptiles Lepidosaurs Name Species Member Material Notes ImageCallopistesC. rionegrensis
Crocodylomorphs Name Species Member Material Notes ImageCrocodyliformes indet.Currently undescribedIsolated fragment of the posterior region of the skull roof.
Testudines Name Species Member Material Notes ImageChelonoidisC. cf. gringorumGeocheloneG. sp.
Birds Name Species Member Material Notes ImageCharadriiformes indet.Currently undescribedOpisthodactylusO. horaciopereziPatagorhacosP. terrificusPhorusrhacidae indet.Currently undescribedDistal extremity of tibiotarsus
Mammals Meridiungulates Name Species Material Notes ImageCochiliusC. volvensAn interatheriidColpodonC. sp.Several maxillary remainsCramaucheniaC. sp.A macraucheniidHegetotheriopsisH. sulcatusA hegetotheriidHegetotheriumH. sp.Interatheriidae indet.Currently undescribedMandibular and maxillary fragmentMesotheriidae indet.Currently undescribedProterotheriidae indet.Currently undescribedMaxillary and mandibular fragmentProtypotheriumP. sp.An interatheriidToxodontidae indet.Currently undescribedLeft and right mandibular fragments with incomplete series of teeth
Xenarthrans Name Species Member Material Notes ImageGlyptodontinae indet.Currently undescribedProeutatusP. sp.Stenotatuscf. S. sp.
Rodents Name Species Member Material Notes ImageAustraloproctaA. fleagleiCaviocricetusC. lucasiEchimyidae indet.Currently undescribedEoviscacciaE. australisOctodontoidea indet.Currently undescribedWillidewuW. esteparius
Metatherians Name Species Member Material Notes ImageCladosictisC. cf. patagonicaComplete right maxillary fragment
References