Introduction


Early Cretaceous


Mid-Cretaceous


Late Cretaceous


Palaeontological
Evidence


Sedimentological
Evidence


Isotope Evidence


Summary


Glossary


Further Reading


Climate Change Home Page


KT Event
Links


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Bristol Palaeontology
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Mid-Cretaceous

General

In the Mid-Cretaceous the Tethys Ocean was closing and the Alps began to form. Geological evidence points towards an unusually high rate of volcanic activity, especially at mid-oceanic ridges.

Magmas erupted at oceanic ridges created new oceanic crust forcing the continental land masses apart. Rates of continental drift (i.e. also sea-floor spreading rate) were then about three times as great as they are now. Ridge systems rose high above the old ocean depths and lifted the neighbouring deep ocean floors with them. Floors rose, forcing the sea water to rise worldwide flooding up to 40 % of the continents. Sea levels were up to 200 m higher than present day levels. This sea level rise commenced in the Aptian.

In addition, vast outpourings of lava created a succession of great undersea plateaux across the southern Pacific Ocean between 135 and 115 million years ago (Mid-Cretaceous), the time of maximum Cretaceous warmth. One of these - the Ontong Java Plateau in the southwest Pacific - has more than twice the size of Alaska and reaches a thickness of 40 km. These vast lava outpourings are proposed to be the result of super hot spots.

Climate Such a high rate of volcanic activity released massive amounts of carbon dioxide into the ocean and ultimately the atmosphere.

This quantity of carbon dioxide would have made the oceans relatively short of oxygen. The evidence for this is displayed in the geological record. The abundance of black shale and petroleum-rich formations, suggest they formed in an oxygen poor environment.

Extensive outgassing of carbon dioxide would have led to climatic warming, due to the greenhouse effect also thought to be occurring today. Therefore the global climate was one of the warmest in Earth's history.

 
 

| Intro | Early Cretaceous | Mid-Cretaceous | Late Cretaceous |

| Palaeontological Evidence | Sedimentological Evidence | Isotope Evidence |

| Summary | Glossary | Further Reading | Climate Change Home Page | KT Event Links | Back to Bristol Palaeontology Homepage |