![using flac3d for modeling sediments prograding wedge using flac3d for modeling sediments prograding wedge](http://sepmstrata.org/CMS_Images/Stokes1968.gif)
Metamorphism and folding also affected the piedmont during the orogeny.īut as with all orogenies, once the collision is done the only thing remaining is for the mountain to erode and the foreland basin to fill with sediment. the Petersburg granite piedmont belt map, or dark green on the geologic map). There is evidence a large volcano existed in the Richmond area, and a large number of igneous plutons intruded into the eastern piedmont with the Acadian orogeny (e.g. But, eastern Virginia also shows the effects. It produced a small foreland subsidence and a moderate volume of sediment spreading west and north from the collision ( map).Īs with the Taconic orogeny in the Mid-Atlantic, we are most aware of the Acadian from the sedimentary record, and the thick accumulation of clastic sediments that are spread throughout the western Valley and Ridge and eastern Allegheny plateau ( province map). The third and last, Pocono impact, (called the Price in the south) was smaller and took place in southern Virginia. The Catskill clastic wedge in east-central Pennsylvania is many thousands feet thick, but we can see the diminishing effects of the collision as the sediments thin steadily westward, and southwestward through western Virginia and eastern West Virginia toward Tennessee. The second, Catskill, impact in New Jersey, southeastern New York and eastern Pennsylvania produced the large, deep Catskill foreland basin ( catskill cross section). The northern collision in the maritime provinces of Canada is recognized primarily by the severely deformed igneous and metamorphic rocks of Nova Scotia, with sediments spreading southward. The result is a ragged, "hit and run" type of mountain building that began in the north and migrated south through time. The North American coast, although not as irregular as during the Taconic orogeny ( Stage H) still had projecting irregularities that Avalon struck hardest. We will use the term Avalon from this point on even though until the Triassic it is technically still Armorica.Īvalon did not hit North America head on but slid in obliquely from the southeast, something like a baseball runner sliding into home plate. and out to the edge of the continental shelf ( province map). Avalon added to the Mid-Atlantic all the land lying under the coastal plain province, east of Richmond and Washington, D.C. Armorica originally included portions of Great Britain and southern Europe, but during the Triassic rifting that opened the Atlantic it was torn in two the portion remaining with North America is Avalon. The Acadian orogeny occurred when the Armorica terrane, traveling along an east dipping subduction zone (modern direction), collided with North America. (Greenland, although now separated, was a part of North America until the Triassic when the Pangaea breakup/Atlantic rifting separated it Stage L.) The Caledonian orogeny began before the Acadian and resulted from a collision between Baltica (western Europe, parts of Great Britain, Scandinavia, and Siberia) and the Greenland region of North America ( "Old Red" map). Eventually it lapped onto the inland margins of the Acadian mountains in the east and the Antler mountains in the west (Nevada). In time practically every continent will be affected.Īt the same time sea level was rising and the Kaskaskia sea, entering from the Gulf of Mexico, spread north across North America placing most of it under water. The Acadian orogeny occurred near the beginning of a major period of mountain building in earth history lasting for the next 150 million years. The Caledonian and Acadian orogenies created the supercontinent Laurussia, also known as the "Old Red Sandstone" continent ( "Old Red" map). At its peak it formed a continuous chain of mountains along the east coast from southern Virginia north to Newfoundland, where it connected with another chain of mountains, the Caledonides, that continued on for thousands of miles more between Greenland and the Scandinavian countries. The Acadian orogeny was first recognized in the 19th century in the severely deformed and metamorphosed rocks around the Bay of Fundy, Nova Scotia, Canada.