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Vertebrates, less severely affected by the extinction than invertebrates, diversified progressively throughout the Triassic.The Triassic terrestrial environment was dominated by the therapsids, sometimes referred to as “mammal-like reptiles,” and the thecodonts, ancestors of dinosaurs and crocodiles, both of which appeared during the Late Triassic.Marine transgression was so extensive that in North America, for example, a seaway spread all the way from the Arctic to the Gulf of Mexico in the Cretaceous Period.Widespread deposition of chalk, clay, black shales, and marl occurred.For example, the northwesterly movement of North America resulted in a collision of the western edge of the North American continental plate with a complex of island arcs during the Late Jurassic.
The timing of these volcanic events appears to overlap the Triassic-Jurassic and Cretaceous-Tertiary, or Cretaceous-Paleogene, mass extinctions, and they may have played a role in them.
The Central Atlantic Magmatic Province, a huge volume of basalt, was created at the end of the Triassic during the initial rifting of Pangea.
The surface area of this igneous province originally covered more than 7 million square km (about 3 million square miles), and its rocks can be found today from Brazil to France.
In parts of North America, lake and river sediments rich in dinosaur fossils were deposited alongside marine sediments. The orogenies of the Jurassic and Cretaceous periods involved volcanism and plutonic intrusion such as occurred during the emplacement of granites and andesites in the Andes of South America during the Late Jurassic.
Two of the largest volcanic events in Earth’s history occurred during the Mesozoic.