Cañadón Asfalto Formation
The Cañadón Asfalto Formation is a lithostratigraphic formation in Argentina . Outcrops can be found along the Río Chubut in the Chubut Province . This series of continental sedimentary rocks is dated to the Jurassic and is known for its rich fossil fauna, which includes the fossils of dinosaurs.
Definition and geological framework
The Cañadón-Calcáreo Formation is part of the Cañadón-Asfalto Basin, a sedimentary basin belonging to the Somuncura Massif . The range of the formation is controversial, whereby two competing research opinions exist: According to the first opinion, this formation consists of two sub- formations , the Las Chacritas member , which consists of lacustrine (deposited in lakes) sediments of the Central Jurassic , and the Puesto- Almada member , which consists of mainly fluvial (deposited by rivers) sediments of the Upper Jurassic . The second research opinion classifies the younger Puesto Almada member as a separate formation known as the Cañadón-Calcáreo formation . The following text only deals with the Central Jurassic section of the formation (Cañadón-Asfalto-Formation sensu stricto ), for the Upper Jurassic section see the article Cañadón-Calcáreo-Formation .
The Cañadón-Asfalto Basin opened up as a result of the beginning breakup of South America and Africa through extension movements, the structure is known as the hemi rift . The Cañadón-Asfalto Formation sensu stricto was deposited during the Syn-Rift stage, i.e. at the same time as the tectonic activity of the Hemi Rift . In contrast to the Cañadón-Calcáreo formation in the hanging wall, this formation is tectonically folded.
Below the formation lies the Lonco Trapail Group , which consists of the Cañadón Puelman Formation and the Cerro Carnerero Formation .
Age
The middle Jurassic Cañadón Asfalto Formation has often been in the past on the Callovian dated, based on comparing the fossil flora with other formations. More recent studies based on radiometric dating and pollen analysis indicate, however, that the formation is significantly older and was probably deposited between the Upper Toarcian and the Lower Bathonian .
Lithology
The Central Jurassic formation consists mainly of lacustrine sediments, especially thin-layered, marly pelites and limestones, which are occasionally interposed with basaltic lava and clastic sediments ( conglomerates and breccias ).
Fossils
The most famous area of discovery for fossils is around the village of Cerro Cóndor . Most of the dinosaur finds in the formation, which were recovered between 1976 and 1985 under the direction of paleontologist José Bonaparte, come from this area . Fossils of the formation include invertebrates, plants, and vertebrates. The most common invertebrates of the formation are mussel shells (Conchostraca) and clams (Bivalvia). The vertebrate fauna consists of fish, frogs , turtles , scaled lizards , crocodiles , pterosaurs , dinosaurs and mammals . Dinosaurs in the formation include the theropods Piatnitzkysaurus , Condorraptor and Eoabelisaurus , the heterodontosaurid Manidens, and the original sauropods Volkheimeria and Patagosaurus .
Individual evidence
- ^ A b c d e Fernando E. Novas: The age of dinosaurs in South America . Indiana University Press, Bloomington 2009, ISBN 978-0-253-35289-7 , pp. 95-96 .
- ↑ a b c d Diego Pol, Oliver WM Rauhut: A Middle Jurassic Abelisaurid from Patagonia and the Early Diversification of Theropod Dinosaurs . In: Proceedings of the Royal Society B: Biological Sciences . April 23, 2012, doi : 10.1098 / rspb.2012.0660 . Supplementary Information, Section: Cañadón Asfalto Formation .
- ↑ a b Oliver WM Rauhut: A brachiosaurid sauropod from the Late Jurassic Cañadón Calcáreo Formation of Chubut, Argentina . In: Fossil Record . tape 9 , no. 2 , 2006, p. 226–237 , doi : 10.1002 / mmng.200600010 . Section: Geological and palaeontological context , p. 228.