Editing Geology of the Appalachians (section)

=== Paleozoic era ===
[[File:Eastern North American Paleogeography Middle Devonian.gif|thumb|[[Palaeogeography|Paleogeographic]] reconstruction showing the Appalachian Basin area during the [[Middle Devonian]] period.<ref name="url">{{cite web |url=http://jan.ucc.nau.edu/rcb7/nam.html |title=Paleogeography and Geologic Evolution of North America |first=Ron |last=Blakey |publisher=Northern Arizona University |work=Global Plate Tectonics and Paleogeography |access-date=July 4, 2008 |archive-url=https://web.archive.org/web/20080621201253/http://jan.ucc.nau.edu/rcb7/nam.html |archive-date=June 21, 2008 |url-status=dead }}</ref>]]

[[File:Appalachian Pennsylvania salient satfoto.jpg|thumb|The "Pennsylvania Salient" in the Appalachians appears to have been formed by a large, dense block of [[mafic]] volcanic rocks that became a barrier and forced the mountains to push up around it. 2012 image from NASA's [[Aqua (satellite)|Aqua satellite]].]]
[[File:Catskill section.gif|upright=1.3|thumb|Generalized east-to-west cross section through the central Hudson Valley region. [[United States Geological Survey|USGS]] image.]]During the earliest part of the [[Paleozoic]], the continent that would later become [[North America]] straddled the [[equator]]. The Appalachian region was a [[Passive margin|passive plate margin]], not unlike today's [[Atlantic Plain|Atlantic Coastal Plain]] province. During this interval, the region was periodically submerged beneath shallow seas. Thick layers of sediment and [[carbonate rock]] were deposited on the shallow sea bottom when the region was submerged. When seas receded, terrestrial sedimentary deposits and erosion dominated.<ref name="usgs">{{USGS|url=http://geomaps.wr.usgs.gov/parks/province/appalach.html|title=Geologic Provinces of the United States: Appalachian Highlands Province|access-date=September 2, 2007|archive-url=https://web.archive.org/web/20080114232613/http://geomaps.wr.usgs.gov/parks/province/appalach.html|archive-date=January 14, 2008|url-status=dead}}</ref>

During the middle [[Ordovician]] (about 458-470 million years ago), a change in plate motions set the stage for the first Paleozoic mountain building event ([[Taconic orogeny]]) in North America. The once quiet Appalachian passive margin changed to a very active plate boundary when a neighboring [[oceanic crust]], the Iapetus, collided with and began sinking beneath the North American craton. With the creation of this new [[subduction]] zone, the early Appalachians were born.<ref name="usgs" />

[[Volcano]]es grew along the [[continental margin]], coincident with the initiation of subduction. Thrust faulting uplifted and warped older sedimentary rock laid down on the passive margin. As mountains rose, erosion began to wear them down. Streams carried rock debris downslope to be deposited in nearby lowlands.<ref name="usgs" />

Mountain building continued periodically throughout the next 250 million years (the [[Caledonian orogeny|Caledonian]], [[Acadian orogeny|Acadian]], [[Ouachita orogeny|Ouachita]], [[Variscan orogeny|Hercynian]], and [[Alleghanian orogeny|Alleghanian]] orogenies). Continent after continent was thrust and [[Suture (geology)|sutured]] onto the North American craton as Pangea began to take shape. [[Terrane|Microplates]], smaller bits of crust too small to be called continents, were swept in one by one to be welded to the growing mass.<ref name="usgs" />

By about 300 million years ago (the [[Pennsylvanian (geology)|Pennsylvanian]] period), [[Africa]] was approaching the North American craton. The collisional belt spread into the [[Ozarks|Ozark]]-[[Ouachita Mountains|Ouachita]] region and through the [[Marathon Uplift|Marathon Mountains]] area of Texas. Continental collisions raised the Appalachian-Ouachita chain to a lofty mountain range on the scale of the present-day [[Himalayas]]. The massive bulk of Pangea was completed near the end of the Paleozoic era (the [[Permian]] period) when Africa ([[Gondwana]]) plowed into the continental agglomeration, with the Appalachian-Ouachita mountains near the middle.<ref name="usgs" />