Cretaceous Period - Geological Changes

GEOLOGICAL CHANGES

During the Cretaceous period the massive continents of Gondwanaland and Laurasia continued to separate. South America and Africa had separated, with the consequent widening of the South Atlantic. The North Atlantic continued to expand, although it appears that Europe, Greenland, and North America were still connected moving northwestward. Madagascar had separated from Africa, while India was still drifting northward toward Asia. The Tethys Sea was disappearing as Africa moved north toward Eurasia. Antarctica and Australia had yet to separate.

At the beginning of the Cretaceous in North America, the Mexican Sea of the late Jurassic period spread over Texas, Oklahoma, New Mexico, and parts of Arizona, Kansas, and Colorado. During later Cretaceous period the Colorado Sea became the greatest of the North American Mesozoic seas and extended all the way from Mexico up into the Arctic, covering most of central North America. Near the end of the Cretaceous the conditions in the west were similar to those of the Carboniferous period with swamps and bogs forming which would later become valuable deposits of coal.

During the close of the Cretaceous period, the Rockies and the East Andes mountains became elevated and there were extensive flows of lava. The Appalachians, which had been reduced almost to a base level by erosion, were rejuvenated, and the seas retreated from all parts of the continent.

The mountains in North Carolina continued to experience erosion. During the last half of the period, eastern areas sank slowly below sea level and the ocean invaded the Coastal Plain. Rocks in the Blue Ridge and Piedmont rose slightly. Warm climate in North Carolina.

There are great chalk deposits from small carbonate-bearing marine algae and calcareous fauna, now exposed in the cliffs of the English Channel (“white cliffs of Dover”). In India during the late Cretaceous there was an overflow of lava in the Deccan plateau.

The climate of the Cretaceous was apparently fairly mild and uniform, but it is possible that toward the end of the period some variant zones of climate had appeared, making the overall climate cooler. Such changes, along with changes in both the Earth’s surface and its flora and fauna, brought the Mesozoic to a close.

BIOLOGICAL CHANGES

The Cretaceous is characterized by a revolution in the plant life, with the sudden appearance of the first flower-bearing plants (angiosperms) including the early ancestors of the beech, fig, magnolia, and sassafras. Birch, elm, grape, laurel, maple, oak, sumac, and willow also appeared, along with grass and the great California sequoias. One variety of tree that grew in the swamps including fern-like trees called Tempskya (which grew to heights of 3-5 m (10-17 ft). This type of tree formed from a bundle of a large number of individual stems bound together by a matrix of roots.

With the increase in the number of angiosperms came an increase in the variety of insects, including a form of the dragonfly.

The marine invertebrates included nautiluses, barnacles, lobsters, crabs, sea urchins, ammonites, and foraminifers. There were numerous marine fish and turtles; and Ghost Sharks which grew to a length of about 4 m (13 ft). There were a smaller number of galeoid and hybodant sharks. Sawfish and rhinopterid rays found.

Reptiles reached their zenith, including such dinosaurs