Cañadón-Calcáreo Formation
The Cañadón-Calcáreo Formation is a lithostratigraphic formation in the Argentine province of Chubut , known for its dinosaur and fish fossils. It is a series of continental sedimentary rocks, which were mainly deposited fluviatil (by rivers) and which can be dated to the Upper Jurassic . Status as an independent formation is controversial - so assume different geologists that it is in this rock unit is a subunit ( Subformation of) Cañadón Asfalto Formation is. This subformation is referred to as the Puesto Almada member .
Geological framework and definition
The Cañadón-Calcáreo Formation is part of the Cañadón-Asfalto Basin, a sedimentary basin belonging to the Somuncura Massif . This sedimentary basin is a hemi trench , a stretch structure that has formed as a result of the beginning of South America and Africa to break apart. This formation was created in the post-rift phase of the basin, i.e. after the rift was completed .
The formation lies above a central Jurassic sediment sequence, which is referred to as either the Cañadón-Asfalto formation sensu stricto or the Las Chacritas member . The Cañadón-Calcáreo Formation is discordantly separated from this sediment sequence . Various geologists see the Cañadón-Calcáreo Formation as the youngest layer member of the Cañadón-Asfalto Formation and refer to them as Puesto-Almada-Member.
Lithology
The sediments of the formation represent the progressive filling of the hemi trench after the latter became tectonically inactive. At the base of the formation there are lacustrine (deposited in lakes) slates, above that lie fluvial (deposited by rivers) sandstones . Overall, the sediments are significantly less tectonically overprinted than the older sediment sequences of the Cañadón-Asfalto formation sensu stricto .
Age
In the past, this series of rocks was dated to the Upper Cretaceous or the Lower and Middle Jurassic. Today it is assumed that it is a succession of the Upper Jurassic - a more recent radiometric dating comes to the conclusion that these sediments come from the Tithonian .
Fossils
The formation is known for its abundant and well-preserved fish fossils, as well as for its dinosaur fossils. The fish come from the lower, lacustrine section of the formation and include at least two representatives of the real bony fish (Teleostei) and one representative of the ray fins (Actinopterygii) as well as various as yet undescribed taxa. Apart from fragments of turtle shells, dinosaurs are the only surviving land vertebrates . Sauropods are represented with the titanosauriforms Tehuelchesaurus as well as with the dicraeosaurids Brachytrachelopan as well as with an undescribed brachiosaurid . Theropods are covered with a fragmentary skeleton of a tetanurae and teeth. Ornithic remains are missing.
Individual evidence
- ^ Diego Pol, Oliver WM Rauhut: A Middle Jurassic Abelisaurid from Patagonia and the Early Diversification of Theropod Dinosaurs. Supplementary Information, Cañadón Safalto Formation section . In: Proceedings of the Royal Society B: Biological Sciences . April 23, 2012, doi : 10.1098 / rspb.2012.0660 .
- ↑ 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 e Oliver WM Rauhut: A brachiosaurid sauropod from the Late Jurassic Cañadón Calcáreo Formation of Chubut, Argentina . In: Fossil Record . tape 9 , no. 2 , 2006, section: Geological and palaeontological context , p. 228 , doi : 10.1002 / mmng.200600010 .