Paleogeography and Geology of the Neogene:
Continued Himalayan Orogeny (especially 20 Ma onward) lifts Himalayan Plateau:

• Modifies global air circulation
• Coincides with general drying episode and lowered amount of greenhouse gasses in atmosphere
• Obliteration of eastern Tethys
• Huge molasse deposits from the Himalaya across India and into Indian Ocean

Northward migration of Africa blocks off entrance to greatly reduced western Tethys (aka Mediterranean): Messinian salinity crisis:

• From c. 6 to 5.3 Ma, sea-level drops dramatically in Mediterranean
• Huge salt desert with hypersaline "lakes"
• 5.3 Ma: return of sea water to the Med.

Isthmus of Panama forms around 3 Ma: allows direct land-to-land connection between North and South America (see below), and blocks Atlantic-Pacific water interchange. Beginning of deep-sea Oceanic Conveyer Belt, isolating Arctic Ocean and beginning of northern polar ice.

In eastern North America, shallow water deposits including Chesapeake Group (Miocene). Erosion of Appalachian system causes pulses of isostatic uplift (at least three pulses), producing modern Appalachian Mountains out of fold-and-thrust belt.

Western North America has an extremely complex Neogene geological history:

• Pulses of isostatic rebound (and possible other causes?) raise up the current Rocky Mountains (in the Early Miocene)
• Uplift of Colorado Plateau as single, mostly undisturbed unit in Middle Miocene (beginning of the formation Grand Canyon), possibly buoyed up by some portion of the foundered Farallon Plate
• Pulses of large-scale hotspot volcanism in the Far West, including Columbia River Basalts (largest Cenozoic flood basalts, Miocene), Snake River extrusives (Pliocene), Cascade volcanism (Pliocene-Holocene);
• Basin and Range province
  • Large scale extension
  • Origin poorly understood (possibly foundering Farallon Plate?)
  • Geographic width may have increased from 50-100%, with corresponding thinning of crust
• Tilting and uplift of Sierra Nevada (Middle Miocene)
• Farallon Plate largely subducted underneath North America, Mexican & Californian coastline changes from subduction to transform boundary:
  • Beginning of San Andreas and related fault systems
  • Separation of Baja California from coast
  • Closure of Great Valley in California, etc.

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Last modified: 10 March 2011