Cretaceous

Continental Breakup

By the beginning of the Cretaceous, the old supercontinent Pangea divided into two large continents: the northern Laurasia (including present-day North America, Europe, and Asia), and the southern Gondwana (including present-day South America, Africa, Antarctica, Australia, and India-Madagascar). They were separated by an east-west equatorial seaway known as the Tethys Ocean. During the Cretaceous, there was a second phase of continental breakup. In Laurasia, the drifting of the continents caused the separation between North America and Europe and the birth of the North Atlantic Ocean. Moreover, Gondwana began to break into four large pieces: South America, Antarctica-Australia, Africa, and India-Madagascar. The progressive drifting of these continents opened the South Atlantic and Indian oceans. These plate tectonic movements during the Cretaceous were concurrent with a period of unusual seafloor spreading. For example, the volume of mid-oceanic crust produced in the Aptian-Campanian interval was almost three times greater than in the Jurassic or Paleocene periods. The high oceanic volcanic activity caused flooding of the continents, especially around the Cenomanian-Turonian when the sea level was about 200 meters higher than at present, and one third of present-day Earth's land area was submerged. During that time, Europe was an archipelago.

Climate Change

The abundant emission of volcanic greenhouse gases (mainly carbon dioxide) into the atmosphere-ocean system caused a global warming during the middle part of the Cretaceous, about 120 to 80 million years ago. This interval is considered an example of ice-free greenhouse climate conditions. Fossil [Page 244]records suggest a gentler latitudinal temperature gradient becoming the high-latitude climate that was one of the warmest in the earth's history. For example, Upper Cretaceous dinosaurs and palm trees were present in the Arctic Polar Circle, in Antarctica, and in southern Australia; Cenomanian breadfruits flourished in Greenland; and crocodiles and turtles inhabited the Turonian-Coniacian Canadian Arctic. Although there is evidence of some cooler episodes in the Lower Cretaceous, geological and geochemical data support that the global annual mean temperature during the Cretaceous was 6°C to 14°C higher than at present.

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