During the Cretaceous period, chalk formations, derived from deposits of foraminifers, predominated and gave the epoch its name. These deposits, which also include greensand marl, shale, sandstone, and small amounts of limestone, reached thicknesses of 200 to 10,000 feet in regions such as the foothills of the Rocky Mountains and Europe. These porous layers store water, making them crucial for supplying arid regions today. Additionally, tectonic movements and associated volcanic activity contributed to significant crustal deformations, impacting Pacific coastal areas and mountain regions like the Andes. [1]
The Cretaceous period marked the end of major marine invasions, especially in North America, where 24 extensive inundations had shaped the land. Chalk formations from this time, derived from marine deposits, remain prominent today. These include limestone now uplifted to 10,000 feet in the Alps, 16,000 feet in the Himalayas, and 20,000 feet in Tibet. Chalk deposits are also found along the coasts of Africa and Australia, the west coast of South America, and around the West Indies. [2]