Hell Creek Formation
The Hell Creek Formation is a sequence of continental sedimentary rocks from the Late Cretaceous and the earliest Paleocene in the northwestern United States . It is named after the Hell Creek river near Jordan (Montana) and contains some significant deposits of dinosaur fossils. The formation in the badlands of eastern Montana and parts of North Dakota , South Dakota and Wyoming minded . The remains of popular dinosaur genera such as Tyrannosaurus , Triceratops , Ankylosaurus and Edmontosaurus were recovered from these outcrops . Furthermore, in its upper section it contains the iridium-enriched Cretaceous-Tertiary boundary layer , a thin layer that has also been found elsewhere on earth, the upper boundary of which separates the Mesozoic Era ( Mesozoic Era) from the subsequent Cenozoic Era (Earth Modern Era).
The Hell Creek Formation , which has been intensively studied geologically and palaeontologically, consists of claystones and sandstones , which were formed 67 to 65 million years ago, mainly during the Maastrichtian , the last stage of the Cretaceous period, from the deposits of rivers (fluvial) as well as lakes and ponds ( lakustrin). At the time of the deposition, the rivers flowed into the Western Interior Seaway , an epicontinental sea that stretched across North America, from northern Canada to the Gulf of Mexico , from northern Canada to the Gulf of Mexico during the late Cretaceous (see also → Laramidia ). Some of the easternmost deposits in the formation were therefore formed in coastal swamps. The presence of crocodiles suggests a subtropical climate without pronounced annual cold spells at the time of deposition.
Similar formations of the same age (lateral equivalents) of the Hell Creek Formation are the Lance Formation, spread further south, as well as the Frenchman Formation and the Scollard Formation in Canada. In the hanging wall of the Hell Creek Formation follows the Paleocene Tullock Formation (or Tullock subformation of the Fort Union Formation) and, in North and South Dakota, the Ludlow Formation (or Ludlow subformation of the Fort Union -Formation). The Hell Creek Formation, separated by a layer gap of around 2 million years, is underlain by the Fox Hills Formation, which falls into the oldest Maastrichtian.
Fossils
The Hell Creek Formation is home to an impressive number of invertebrates , plants , mammals , fish , reptiles, and amphibians . In 2000, the most complete hadrosaurid dinosaur skeleton ever found was discovered. In addition to dinosaurs, the fossils of some birds and pterosaurs ( pterosaurs ) have also been found. Shark and ray teeth are also occasionally found in these river deposits, suggesting that some of these taxa were more tolerant of freshwater than they are today. The bony fish are represented in the Hell Creek fauna with the sturgeon-like Paleopsephurus and Protoscaphirhynchus .
The dinosaurs found include various theropods, such as the common genera Paronychodon and Ricardoestesia , the tyrannosaurs Tyrannosaurus rex and Nanotyrannus lancensis , the ornithomimosaur Ornithomimus sp., The Caenagnathiden Chirostenotes sp. and Elmisaurus elegans , and other maniraptors such as Troodon sp., cf. Dromaeosaurus , Avisaurus archibaldi and remains of velociraptorins.
The Ornithischia (bird dinosaurs) are represented by Ankylosaurus magniventris , Edmontonia sp., Pachycephalosauriden as dracorex hogwartsia , Pachycephalosaurus wyomingensis , sphaerotholus bucholtzae and stygimoloch spinifer , Ceratopsia as cf. Leptoceratops sp., Torosaurus latus , the very frequent Triceratops horridus and Triceratops prorsus , and finally ornithopods such as Bugenasaura infernalis , Thescelosaurus neglectus and the very common Edmontosaurus ( Edmontosaurus annectens and Edmontosaurus sp.).
Some of the fossils in the Hell Creek Formation are commercially mined and marketed by companies. Usually these are bones, osteoderms and teeth from dinosaurs, crocodiles and fish. A representative collection of fossils from this formation is exhibited in the Museum of the Rockies in Bozeman, Montana.
Evidence for the formation of the Chicxulub crater
In 2019, an international team of researchers published a study of deposits in the area of the Tanis deposit in North Dakota, which the researchers said were formed less than an hour after the formation of the Chicxulub Crater , an impact crater on the Yucatán Peninsula . A tidal wave had piled numerous ammonites, fish (including sturgeon and dipper ), land animals and parts of plants on top of each other, mixed with ejecta from the impact , which was preserved in the gills of fossil fish as well as in the interior of amber .
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- Phillip Bigelow: Hell Creek life: Fossil Flora & Fauna, a Paleoecosystem. ( Memento of January 14, 2006 in the Internet Archive ) Private website
- Cretaceous “Hell Creek Faunal Facies”. ( Memento of February 6, 2006 in the Internet Archive ) Subpage of this page with an extensive list of fauna.
- Hell Creek Formation - List of localities and / or collections of fossils in the Hell Creek Formation in the Paleobiology Database
Web links
- The Day the Dinosaurs Died. About the connection between the formation and the Chicxulub crater. On: newyorker.com on March 29, 2019
Individual evidence
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^ Robert A. DePalma, Jan Smit, David A. Burnham et al .: A seismically induced onshore surge deposit at the KPg boundary, North Dakota. In: PNAS . Advance online publication of April 1, 2019, doi: 10.1073 / pnas.1817407116
Chicxulub asteroid impact: Stunning fossils record dinosaurs' demise. On: bbc.com of March 29, 2019
Astonishment, skepticism greet fossils claimed to record dinosaur-killing asteroid impact. On: sciencemag.org from April 1, 2019
Mass grave of victims of the "Dinokiller". Death from glass rain and tidal waves after asteroid impact 66 million years ago. On: scinexx.de from April 1, 2019