kimerajamm
Joined: 28 Nov 2010
Posts: 785
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 Posted: Fri Feb 25, 2011 4:30 pm Post subject: Devonian and Carboniferous |
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Although the rock formations exposed in Colton Point State Park and the Pine Creek Gorge are at least 300 million years old, the gorge itself formed about 20,000 years ago, in the last ice age. Pine Creek had flowed northeasterly until then, but was dammed by rocks, soil, ice, and other debris deposited by the receding Laurentide Continental Glacier. The dammed creek formed a lake near what would later be the village of Ansonia, and the lake's glacial meltwater overflowed the debris dam, reversing the flow of Pine Creek. The creek flooded to the south and quickly carved a deep channel on its way to the West Branch Susquehanna River.[39][46]
Looking north to Barbour Rock (left) and other rock outcrops in the Pine Creek Gorge
The park is at an elevation of 1,637 feet (499 m) on the Allegheny Plateau,[1] which formed in the Alleghenian orogeny some 300 million years ago, when Gondwana (specifically what became Africa) and what became North America collided, forming Pangaea.[47][48] Although the gorge and its surroundings seem to be mountainous, the area is a dissected plateau. Years of erosion have cut away the soft rocks, forming the valleys, and left the hardest of the ancient rocks relatively untouched on the top of sharp ridges, giving them the appearance of "mountains".[46]
The land on which Colton Point State Park sits was once part of the coastline of a shallow sea that covered a great portion of what is now North America. The high mountains to the east of the sea gradually eroded, causing a buildup of sediment made up primarily of clay, sand and gravel. Tremendous pressure on the sediment caused the formation of the rocks that are found today in the Pine Creek drainage basin: sandstone, shale, conglomerates, limestone, and coal.[46][49]
Five major rock formations present in Colton Point State Park are from the Devonian and Carboniferous periods. The youngest of these, which forms the highest points in the park and along the gorge, is the early Pennsylvanian Pottsville Formation, a gray conglomerate that may contain sandstone, siltstone, and shale, as well as anthracite coal. Low-sulfur coal was once mined at three locations within the Pine Creek watershed. Below this is the late Mississippian Mauch Chunk Formation, which is formed with grayish-red shale, siltstone, sandstone, and conglomerate. Millstones were once carved from the exposed sections of this conglomerate. Together the Pottsville and Mauch Chunk formations are some 300 feet (91 m) thick.leather vest
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