PHYSIOGRAPHIC PROVINCES OF THE UNITED STATES

Although the physiographic provinces of the United States are based largely on topography, they are a product of their geologic history. Tectonics, structure, lithology, erosion and sedimentation each play an important role in shaping each province. This site provides a brief introduction to each province and provides links to relavant sites obtained from the USGS, NASA, Academic Institutions, State Surveys, the National Parks Service and comerical and private web sites.The heading format: Geomorphology; Geology; Resources; Important Geologic Feature, was adapted from Pirkle and Yoho, 1982. Natural Landscapes of the United States: Kendall/Hunt/Dubuque, Iowa, pp 399.

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Visit these sites for a good introduction to landforms: 

• Introduction to Regional Landforms (NASA GFS)
• Tectonic Landforms (NASA GFS) 

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Conventions:

• Red links go directly to State Geological Survey homepage. Pertinent survey sites are listed below the link or are initialed in black (e.g. FGS=Florida Geological Survey).
  • An * marks a site with abundant online information. Most survey sites allow you to order paper copies of maps and publication. However, a few allow you to access and download material online.
• Sources:
  • EFS: Nasa Earth from Space An Astronauts view of the home Planet; NASA Space Shuttle photography database containing images with brief descriptions. You can search for features and landforms of interest, but don't go here if you want a detailed veiw or description.
  • NASA GFS: Nasa's Geomorphology from Space: A global overview of Regional Landforms: Edited by Nicholas Short and Rover Blair. The geology and geomorphology of select features is discussed and illustrated with maps and satellite images.
  • NPS: National Park Service
  • LAUS maps: Shaded relief maps from the USGS Landforms Atlas of the United States. These maps are excellent for visualizing the topography of each state.
  • USGS: United State Geological Survey

 

 

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A Brief Introduction to

Second Order Features and the Orogenic History of North America

I. The North American continent consists of the following features:

 

A. The interior stable craton. The core of the continent, underlain by Precambrian crystalline rocks generally greater than 1 ba.

• Shields are regions of the craton where Precambrian rock is exposed (Nasa Image)
  
• Around the exposed shield areas the craton is draped with Paleozoic marine platform sedimentary rocks, generally shallow-water carbonates and sandstones (e.g. Central Lowlands), and sedimentary plateaus, clastic wedges (e.g. Appalachian Plateau, Ozark Plateau, and Great Plains) that thicken toward the mobile belts.

 

B. Exterior mobile belts. Regions of folded and intruded Phanerozoic rocks deformed by orogenic events.

 

• Eastern Appalachians (inactive): The result of three orogenic events:
  1. Middle Ordovician Taconic Orogeny (collision between Proto-NA and a volcanic arc/micro-continent, which now forms the basement of much of the New England Province and the Piedmont Province)--Appears to have affected the entire Appalachian belt.
     
  2. Lower-Middle Devonian Acadian Orogeny (collision between NA and Avalon)--Felt along the entire Appalachian front. Responsible for most of the post-Taconic deformation in the northern Appalachians.
     
  3. Late Carboniferous-Permian Alleghenian Orogeny (Proto-Africa and South America collides with Proto-NA). Resulted in the final westward emplacement of the Blue Ridge, and the folding and faulting of the Valley and Ridge province of the southern Appalachians. Collision with South America was responsible for Ouachitas.

 

 

 

• Western Cordilleran (active)

   

  • From the end of the Paleozoic to the late Cenozoic the western margin has been subjected to a number or orogenic events caused by the collision of island arcs, rifted continental fragments, or some other oceanic debris (seamounts, plateaus, etc) with the continental margin. Each event resulted in accretion, and the continental margin built westward to its present position. These events are recorded by unconformities, clastic wedges and the emplacement of thrust sheets. Cordilleran Accretionary Terranes (NASA GFS)
  • The animated Cordillera: Tectonic movements from 220-60 Ma (James Sears)

   

  1. Late Devonian and Early Carboniferous Antler Orogeny (best exposed in Nevada): evidenced by a clastic wedge and emplacement of the Roberts Mountain Allocthon (thrust sheet composed of continental rise and slope sediments). Its effects are strongly overprinted by later events. Probably the result of an arc-continent collision.
     
  2. Late Carboniferous and Permian formation of the Ancestral Rocky Mountains (Colorado): Block faulting of Precambrian basement. Deformation can be traced to the Ouachita orogenic belt. Faulting is attributed to failure of the interior craton in response to collision of SA and Africa with NA.
     
  3. Late Permian and Early Triassic Sonoma Orogeny: Collision which resulted in the emplacement of the Golconda allochthon (easterly thrust slope and rise sediments). Theories on the causes of the orogeny range from
     • Closure of a back-arc basin
     • volcanic-arc/continent collision
       
  4. Early Mesozoic truncation event: NNE-to-SSW structures, formed during the Antler and Sonoma orogenies, were truncated and existing NW-SE structural trend established. Truncation appears to have occurred along a major sinistral (left lateral) fault. The displaced terrane migrated SE during the rifting of Pangea and is now part of mainland Mexico.
  5. 
     175 my--Middle Jurassic; beginning of west-coast subduction: West coast became the site of a continental-margin subduction zone characterized by extensive magmatism.
     
  6. Early Cretaceous Nevadan Orogeny (160-125 my)-Collision of Sierran arc block (Smartville block)
     
  7. Mid-late Cretaceous Sevier Orogeny (105-75 my)-Back arc thrusting behind the Nevadan arc resulted in extensive foreland basin deformation to the east.
     
  8. Late Cretaceous-Tertiary Laramide Orogeny (50-75 my)-Franciscan subduction and formation of Sierran Magmatic arc which was superimposed on earlier accreted terrane. Related Laramide deformation took place 1500 miles cratonward from the active plate boundary (uplift of basement-cored blocks along high-angle faults in the Middle-Southern Rockies --Teton, Gros Ventre, Wind River, Unita, San Rafael, Front Range, etc.)This anomalous deformation pattern has been attributed to a decrease in the angle of subduction related to subduction of an aseismic ridge.
     
  9. When subduction was shallow (Oligocene) arc volcanism jumped eastward into Colorado and then migrated westward as the subduction zone resteepened.
     
  10. Neogene(24 my)-present strike slip motion along the San Andreas fault, block faulting in the Basin and Range, rejuvenation of Laramide uplifts (Rocky Mountains--e.g. Grand Tetons, and Colorado Plateau), and uplift of the present Sierra Nevadas.
      

 

• After each orogenic event, erosion and westward transport of sediment into the foreland basins produced the clastic wedges which now underlie the Appalachian Plateau and Great Plains.

 

 

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