LEFT = Global paleogeography during the Late Neoproterozoic, about 750 my
RIGHT = Global paleogeography during the Cambrian Period, about 520 my
Compare the Cambrian paleogeography with that of the Neoproterozoic.
Note that by the Cambrian, the continents have moved off the South Pole, and some are
sitting on the equator.
(We don't expect glaciations in the Cambrian.)
Because the glaciers are melting (or have melted), sea levels are rising, and shallow epicontinental seas flood the continents.
Global temperatures were probably warm, because tropical waters could not flow far before running into a continent, and being deflected N or S, and spreading warm waters toward the poles.
Note that some of the continents are separating. Laurentia and Baltica have moved away from South America.
The Iapetus Ocean (or Proto-Atlantic Ocean) formed as Laurentia drifted away from South America.
Note the Ouachita trough segment (green on the map above), which separates off as a microcontinent.
Another map of the global distribution of continents during the Cambrian.
This map shows water depths and presence of evaporite deposits (E), which indicate arid (dry) paleoclimates during the Cambrian.
Shallow seas cover many of the continents. The evaporite deposits are clustered within about 30 degrees north and south of the equator. This is the latitude at which the great deserts of the world occur today.
The paleogeographic and tectonic map of North America in the Cambrian shows the distribution of seas and sediment types.
North America during the Cambrian Period. Note: The outlines of the continents and Great Lakes are shown for reference only. They did not exist at the time.
Laurentia (North America) is nearly covered by shallow epicontinental seas.
Because North America is sitting on the equator (see it running north or south through the center of the map), we expect the waters to be warm.
The deposition of carbonate sediments in the central US during the Cambrian is exactly what would be expected. The presence of stromatolites and mudcracks in these carbonate rocks indicate deposition in shallow water.
The water deepens toward the edges of the continent, where deep water shale is deposited (blue-green). Sand is deposited along the edge of the exposed land mass (yellow).
November 11, 2005