Global paleogeography during the Devonian.
As the Late Paleozoic began, the continents were fairly fragmented and separate, particularly in the Northern Hemisphere.
There is an extensive sedimentary record for the Devonian Period. Note that North America sat on the equator, with warm, tropical climatic conditions.
A large continental landmass named Gondwana (composed of South America, Africa, India, Antarctica, and Australia) was present in the southern hemisphere, on or near the South Pole.
Laurentia and Baltica collided to form Laurasia in the Caledonian orogeny affecting northeastern Canada, Greenland, and Europe).
A volcanic island arc or exotic terrane, called the Avalon terrane (or Carolina terrane), collided with Eastern North America in the Acadian orogeny.
The effects of the Acadian orogeny are seen in a belt extending from Newfoundland to West Virginia, where thick sequences of sedimentary rocks are interbedded with rhyolitic volcanic rocks and granitic intrusions.
Paleogeography of North America during the Devonian Period.
The Acadian highlands in eastern North America (orange), form a continuous belt with the Caledonian Mountains adjacent to Greenland and Europe.
Erosion of these mountains resulted in the deposition of the Catskill Red beds in the Appalachian area, and the Old Red Sandstone in Europe.
Sea levels were fairly high worldwide during the Devonian (indicating that there were no glaciers). Much of the North American continent was flooded by shallow seas.
The seas regressed from the continents at the end of the Early Paleozoic as a result of the Ordovician-Silurian glaciation.
Gradual flooding of the North American craton occurred in the Late Paleozoic, reaching its maximum extent during the Mississippian Period. This new inland sea was called the Kaskaskia sea.
In eastern North America, the initial deposits of the transgressing Kaskaskia sea were clean quartz sands, such as those of the Devonian Oriskany Sandstone, which is used for glass making because of its purity.
As the sea continued to transgress, shales, and then limestones with reef-forming coral were deposited over the sands. In areas where water circulation was more restricted, evaporites were deposited.
Reefs and carbonates indicate a warm climate, and evaporites suggest dry conditions.
After the Acadian orogeny in the Appalachian region, carbonate sedimentation was followed by the deposition of clastic sediments. The clastic sediments are thicker and coarser to the east, nearer their source area in the Acadian highlands. They are primarily continental red beds (stream deposits), and they form a wedge-shaped deposit called the Catskill clastic wedge or Catskill delta (although these are not deltaic deposits). The reddish brown sandstones of the Catskill are used in building the "brownstone" buildings in cities in the eastern US.
Similar red beds of Devonian age are also present in Europe, such as the Old Red Sandstone. The red color of the sandstone indicates deposition under oxidizing conditions in continental or non-marine environments.
Interpretive diagram for the depositional setting of the Catskill clastic wedge.
East-west cross-section across the Devonian Catskill clastic wedge in New York.
Isopach (sediment thickness) and lithofacies map of the Upper Devonian in the eastern US. The Catskill clastic wedge sediments are thicker and coarser in the east. The sediments become finer-grained westward, away from the Acadian highland source area.
Farther west, black shales were deposited in a relatively thin unit (less than about 10-20 m thick) over a wide area (Chattanooga Shale) in the Late Devonian and Early Mississippian. It is the offshore equivalent of the 3000 m thick Catskill clastic wedge. The Chattanooga Shale is an important marker bed for regional correlation. It has a high organic carbon content, along with finely disseminated pyrite, and uranium. The Chattanooga Shale was deposited in stagnant, oxygen-deficient water.
In the Williston Basin area (South Dakota, Montana, and adjacent Canada), extensive reefs formed. Restricted circulation within the reef-encircled basin led to the deposition of thick evaporite deposits. The reefs of the Williston Basin provided permeable structures into which petroleum migrated, forming rich oil fields.
November 13-15, 2005