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The end-Cretaceous event is the only mass extinction definitively known to be associated with an impact, and other large extraterrestrial impacts, such as the Manicouagan Reservoir impact, do not coincide with any noticeable extinction events. [248]
The end of the Cretaceous is defined by the abrupt Cretaceous–Paleogene boundary (K–Pg boundary), a geologic signature associated with the mass extinction that lies between the Mesozoic and Cenozoic Eras.
The Cretaceous–Paleogene extinction event (formerly known as the Cretaceous–Tertiary extinction event) [a] occurred at the end of this age. [3] In this mass extinction, many commonly recognized groups such as non-avian dinosaurs, plesiosaurs and mosasaurs, as well as many other lesser-known groups, died out.
The impact at the end of the Cretaceous Period gouged the Chicxulub (pronounced CHIK-shu-loob) crater, 112 miles (180 km) wide and 12 miles (20 km) deep. The clay layer is rich in metals including ...
Artist's depiction of the end-Cretaceous impact eventSince the 19th century, a significant amount of research has been conducted on the Cretaceous–Paleogene extinction event, the mass extinction that ended the dinosaur-dominated Mesozoic Era and set the stage for the Age of Mammals, or Cenozoic Era.
The K–Pg boundary marks the end of the Cretaceous Period, the last period of the Mesozoic Era, and marks the beginning of the Paleogene Period, the first period of the Cenozoic Era. Its age is usually estimated at 66 million years, [2] with radiometric dating yielding a more precise age of 66.043 ± 0.043 Ma. [3]
The End Cretaceous extinction, or the K–Pg extinction (formerly K–T extinction) occurred at the Cretaceous (Maastrichtian) – Paleogene transition. [19] The event was formerly called the Cretaceous-Tertiary or K–T extinction or K–T boundary; it is now officially named the Cretaceous–Paleogene (or K–Pg) extinction event.
The Hell Creek Formation in Montana overlies the Fox Hills Formation and underlies the Fort Union Formation, and the boundary with the latter occurs near the Cretaceous–Paleogene boundary (K–Pg), which defines the end of the Cretaceous period and has been dated to 66 ± 0.07 Ma old. [6]