Geologic Time: a Brief Synopsis of the Cretaceous Period

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Geologic Time

A Brief Synopsis of the Cretaceous Period

Prepared by Jamie L. Martinez

The Cretaceous period is part of the Mesozoic Era, and took place approximately 65 to 144 million years ago between the Paleogene period (marking the extinction of Mesozoic mammals) and Jurassic period (age of the dinosaurs).

Common Fossils of the Cretaceous
The Cretaceous period is often noted for the formation of the first fossils of many insect groups, modern mammal and bird groups, and the first flowering plants. The end of the Cretaceous brought the end of many previously successful and diverse groups of organisms, such as non-avian dinosaurs and ammonites. Most fossils that exhibit Cretaceous remains are often found in marine, sedimentary limestone deposits.

The Origin of the Name “Cretaceous”
In 1822, Belgian geologist D'Omalius d'Halloy gave the name Terrain Cretace, for the chalk and rock outcrops of the Paris Basin, and for similar outcrops in Belgium and Holland. This term "Cretaceous" "chalk-bearing" (from Creta, the Latin word for chalk) later came to be used.

Cretaceous Strata around the World
Much of the landmasses during the Cretaceous period were covered by shallow continental oceans and inland swamps and seas. This period was also a time of lengthening and widening of the Atlantic Ocean, which spread southward as part of the break-up of world-continent Pangaea. As Pangaea began to undergo the process of “continental drift”, two individual landmasses formed known as “Laurasia” (the upper continent) and “Gondwanaland” (the southern continent).

The further fragmentation of Pangaea caused the separation of South America and Africa. Australia separated from South America, but remains connected to Antarctica. The North Atlantic Ocean continues to open along the continental ridge, a divergent plate boundary. Climate became more seasonal and cooler at the end of the...
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