Tectonic stability, which characterized earlier periods in this area, came to a dramatic halt during the Pennsylvanian Period as continental fragments began moving together to form the supercontinent of Pangaea.ĭuring the early stages of tectonic activity, shallow seas invaded the region from the southeast, depositing marine sediments in the basins between the mountain uplifts. Some 300 million years ago the Rocky Mountain region of southern Wyoming, Colorado, and northern New Mexico was the site of intense tectonic activity, which culminated in the uplift of an ancient mountain chain that reached as much as 10,000 feet (3,050 m) of relief in some areas (Benedict 1991). Learn more about events in the Pennsylvanian Period Millipedes, scorpions, and spiders also became significant inhabitants of the lush forests. Some of these insects grew to very large sizes for example, some dragonflies had wingspans of up to 2.5 feet (0.8 m), and some cockroaches were a foot long. For example, insects with non-folding wings appeared. Also characteristic of Pennsylvanian time was the diversification of amphibians and insects. The vast amount of plant material provided by extensive forests resulted in the later formation of coal, which characterizes the Pennsylvanian Period. In both cases, these adaptations severed the ties to water, allowing for life-long terrestrial habitation. In the case of animals, it was the amniotic egg-a key feature in the origin of reptiles. In the case of plants, the adaptation was the further evolution of the seed, which first appeared in the Devonian Period. Therefore, Pennsylvanian strata contain more sandstone and shale (terrestrial) layers than Mississippian strata.ĭuring the Pennsylvanian Period, adaptations occurred in animals and plants that allowed for reproduction on dry land. Swamp forests and terrestrial habitats became more common and widespread. The uplift of the continent, which resulted in the Ancestral Rocky Mountains, caused transition to a more extensive terrestrial environment during the Pennsylvanian Period. As a result, most of the rocks found from Mississippian time are marine limestone. In North America, seas covered parts of the continent during the Mississippian subperiod. In general, the rocks of the Pennsylvanian subperiod can be distinguished from those of the older Mississippian by their terrestrial nature. In North America, the Mississippian and Pennsylvanian periods are used instead of the Carboniferous Period, which covers that same time frame in other parts of the world. These rocks serve as a counterpart to the previous geologic period-the Mississippian. In 1891 Henry Shaler Williams coined the name for the younger strata of the Carboniferous Period that are well exposed in Pennsylvania. The Pennsylvanian subperiod is named for the state of Pennsylvania. Pennsylvanian age fossil tracks, Grand Canyon National Park, Arizona.
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