Definition | Chalk | Planet Futura

The Cretaceous period corresponds to the last period mesozoicmesozoic (or minor era). It extends from -145.5 to -65.5 million years ago. The end of the Cretaceous period was marked by a biological crisis that led to the extinction of the dinosaurs.

subdivision

The Cretaceous period is usually divided into two series: the Lower Cretaceous (from -145.5 to -99.6 Ma) and the Upper Cretaceous (from -99.6 to -65.5 Ma). These two series are themselves divided into several stages: Berriasian, Valanginian, Hauterivian, Barremian, Aptian and Albian for the Lower Cretaceous; then Cenomanian, Turonian, Cognac, Santonian, Campanian and Maastrichtian for the Upper Cretaceous.

The term “Cretaceous” refers to large deposits of chalk characteristic of this period, which can be observed, in particular, in France and Great Britain.

Geodynamic context

The Cretaceous period was marked by the end of the fragmentation of the supercontinent Pangea and, in particular, the breakup gondwanagondwana, a step that will give rise to the current continents. However, the configuration of the continental blocks is still very different from today.

Thus, Gondwana is divided into different continents:AntarcticAntarctic, South America, Africa, Australia and India. The South Atlantic Ocean begins to open 120 million years ago, after which the Indian Ocean opens. Conversely, the ocean TethysTethys continues to close. Therefore, tectonic and magmatic activity during this period is intense. Thus, several large oceanic plateaus date from the Cretaceous, such as the Caribbean Plateau or the Otong Java Plateau.

In a continental context, the end of the Cretaceous is marked by an eruption Deccan TrapsDeccan Traps, west of present-day India. This major volcanic episode produced a gigantic amount lavalava which formed a huge plateau more than 2 km thick. Volcanic activity could last more durationduration tens of thousands of years, releasing large amounts of greenhouse gasgreenhouse gas (especially CO2) to L’atmosphereatmosphere Earth, which led to global climate change. Deccan trap activity is thought to have contributed to the biological crisis that marks the end of the Cretaceous.

Magmatic activity at the news level ocean ridgesocean ridgeswho produce oceanic crustoceanic crust young oceans in the process of discovery, and then provides, for its part, an important contribution in terms of calciumcalcium in sea water, an element that will contribute to the productionseaweedseaweed planktonic with a calcareous skeleton. This explains the abundance of Cretaceous limestone formations.

Paleoenvironment

The Cretaceous period begins with a rather cold climate, which warms up rapidly under the influence of rising CO levels.2 in the atmosphere, due to the intense volcanic activity that the planet experienced during the entire period. Continental blocks do not have the same configuration as they do today, and ocean and atmospheric currents are also very different. Temperature difference betweenequatorequator and therefore the poles are less important than at present. The waters of the oceans are less agitated and therefore less oxygenated. Then the period has several episodes of events. anoxicanoxicthat affect ocean life.

Therefore, the global climate is quite warm and conditions are favorable for the development of terrestrial flora. During the Cretaceous period, there is a variety of flowering plants and the appearance of deciduous trees. This diversity is due, in particular, to the appearance of bees, which will help in the distribution pollenpollen. This is also an important period for the diversity of insects: butterflies, grasshoppersgrasshoppers, antsantstermites appear. wildlifewildlife on earth is dominated by dinosaursdinosaurs. However, mammals also performed well. coexist in the oceans FishFishsharks, ammonites and reptilesreptiles sailors are like ichthyosaurs.

Cretaceous-Tertiary Biological Crisis

This is important biodiversitybiodiversity however, it will begin to decline during the Maastrichtian, undoubtedly under the influence of volcanismvolcanism Dean traps. The biological crisis reached its peak at the end of the Cretaceous, after the fall of the Chicxulub meteorite, which dramatically changed environmental conditions. Due to the large amount of suspended particles in the atmosphere, the amountenergyenergy sunlight reaching the earth is greatly reduced and organisms depend on photosynthesisphotosynthesis drop rapidly causingcollapsecollapse Total food chainfood chain. Terrestrial and marine fauna are affected and some varietyvariety eventually disappear completely like ammonitesammonites and dinosaurs.

Thereafter mass extinctionmass extinctionit will take a long time for biodiversity to restore the wealth of the Cretaceous period.

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