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The Appalachian and Pangea connection: How are their fates intertwined?
The Appalachian Mountains have a long geological history. As early as 1.2 billion years ago in the Mesoproterozoic, the collision of two continental blocks formed the supercontinent Rodinia. This event occurred 500 million years ago, during the formation of Pangea. Rock outcrops in the present-day Appalachians show extended folds and squeezed layers of marine sediments, volcanic rocks, and ancient ocean floor rocks, showing that these rocks were deformed during the plate collision. Following the birth of this mountain range, several different orogenies followed, eventually leading to the formation of the Pangea, and the Appalachians joined with the Anti-Atlas Mountains in Morocco, which at the time were probably at an altitude comparable to today's Alps and Rockies, but which continued to lose height due to weathering and erosion.
Overview of Geological History
The Appalachian Mountains have undergone more than 1.2 billion years of mountain building, mainly in the following periods:
- Grenville Orogeny: Started 1250 million years ago and lasted 270 million years.
- Taconic Orogeny: Started 450 million years ago and lasted 10 million years.
- Acadian Orogeny: Started 375 million years ago and lasted 50 million years.
- Alleghan Orogeny: Started 325 million years ago and lasted 65 million years.
Mesoproterozoic and the Grenville Orogeny
The Appalachian Mountains were formed during the Grenville Orogeny, one of the earliest continental collision events, during the formation of the supercontinent Rodinia. This event caused the North American craton to collide with other continental plates such as the Amazon, creating part of today's Appalachian Mountains, especially the Blue Ridge Mountains and the Adirondack Mountains. The rocks in this area began to show characteristics of folding and compression.
Rodinia's Split
After the Grenville orogeny, Rodinia began to split as plate movement changed. This process led to the erosion of ancient mountains and the flattening of the land surface. The eroded sediments provided material for the formation of sedimentary basins, such as the Ocoee Basin in the present-day southern United States. As ocean water entered these basins, sediments began to accumulate on the ground, forming rich layers of sedimentary rock. Likewise, over time, new geological evidence has been discovered pointing to the presence of volcanic activity that left its mark on the peaks of the Blue Ridge Mountains.
Paleozoic orogeny
As the Paleozoic Era began, the North American continent was located near the equator, an area that was once a relatively static plate edge and was occasionally flooded by shallow seas. As the years passed, the appearance of new oceanic crust created new areas of subsidence, marking the beginning of the Taconic Orogeny. This movement promoted volcanic activity and the formation of early Appalachia, and caused early sedimentary rocks to be uplifted and deformed. Over time, the resulting erosion hastened the breakup of the mountains.
The formation and subsequent changes of Pangea
230 million years ago, the Pangea began to break apart, easing the formation of the Appalachian Mountains and related mountain ranges and initiating the process of weathering and erosion. By the end of the Paleozoic Era, these mountains had been eroded to a nearly flat state. Entering the Cenozoic Era, the area was uplifted again, leading to the evolution of new terrain, forming today's distinct landforms and promoting the development of rivers and environmental changes.
Appalachian Basin
The Appalachian Basin is a foreland basin associated with Paleozoic sedimentary rocks, containing sediments from the Early Cambrian to the Early Permian. The region is rich in coal and has become one of the largest coal producing areas in the United States and even the world. Additionally, the discovery of oil and gas marked the beginning of the petroleum industry in the Appalachian Basin, particularly around the Drake Well in Pennsylvania.
The formation and changes of the Appalachian Mountains are not only important indicators of geological history, but also demonstrate the amazing power of geodynamics.
In the long geological evolution, the Appalachian Mountains are closely related to the formation of Pangea, and their fates are intertwined. Throughout history, how have the changes of these natural wonders affected today's ecosystems and human life?
