Concept

Pennsylvanien

Résumé

The Pennsylvanian (ˌpɛnsəlˈveɪni.ən , also known as Upper Carboniferous or Late Carboniferous) is, in the ICS geologic timescale, the younger of two subperiods (or upper of two subsystems) of the Carboniferous Period. It lasted from roughly . As with most other geochronologic units, the rock beds that define the Pennsylvanian are well identified, but the exact date of the start and end are uncertain by a few hundred thousand years. The Pennsylvanian is named after the U.S. state of Pennsylvania, where the coal-producing beds of this age are widespread. The division between Pennsylvanian and Mississippian comes from North American stratigraphy. In North America, where the early Carboniferous beds are primarily marine limestones, the Pennsylvanian was in the past treated as a full-fledged geologic period between the Mississippian and the Permian. In parts of Europe, the Mississippian and Pennsylvanian are one more-or-less continuous sequence of lowland continental deposits and are grouped together as the Carboniferous Period. The current internationally used geologic timescale of the ICS gives the Mississippian and Pennsylvanian the rank of subperiods, subdivisions of the Carboniferous Period. All modern classes of fungi have been found in rocks of Pennsylvanian age. The major forms of life at this time were the arthropods. Due in part to the high levels of oxygen, arthropods were far larger than modern ones. Arthropleura, a giant millipede relative, was a common sight and the giant dragonfly Meganeura "flew the skies". Amphibians were diverse and common; some were several meters long as adults. The collapse of the rainforest ecology in the mid-Pennsylvanian (between the Moscovian and the Kasimovian) removed many amphibian species that did not survive as well in the cooler, drier conditions. Amniotes, however, prospered due to specific key adaptations. One of the greatest evolutionary innovations of the Carboniferous was the amniote egg, which allowed for the further exploitation of the land by certain tetrapods.

Source officielle

https://fr.wikipedia.org/wiki/Pennsylvanien

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