The Earth Through Time, 8e

Eighth Edition
by Harold L. Levin


Chapter 11 - page 6

Late Paleozoic Events


Permian Paleogeography

During the Permian, all of the continents had collided and joined to form the supercontinent, Pangea.

Continental collision was accompanied by orogeny, and the Appalachian mountain chain reached its peak during the Alleghanian Orogeny.

Pangea was surrounded by a huge ocean called Panthalassa. The oceanic area east of Pangea, and between Africa and Europe was called the Tethys Sea. (Sediments deposited in the Tethys Sea formed the Himalaya Mountains when the Tethys closed, much later.)

Global paleogeographic setting during the Permian legend
Global paleogeographic setting during the Permian.

The Late Permian was a time of widespread regression of the seas. The global map above indicates that sea levels were low worldwide. The vast epicontinental seas that once covered North America and parts of other continents were gone.

The Gondwana part of Pangea continued to sit atop the South Pole, and glaciation continued into the Permian.

Reconstruction of Gondwana

Reconstruction of Gondwana near the beginning of the Permian Period. Glacial deposits are shown in white. The arrows indicate direction of glacial movement as determined from glacial striations on the bedrock.

The distribution of the glaciers can be determined from locations which have Permian glacial sedimentary deposits (tillites), as well as striations or scratches on the bedrock, caused by the movement of the glaciers.

Cold air (associated with the glaciation) holds less moisture than warm air, and the climate became arid during the Permian.

Distribution of Permian sedimentary rocks used as climatic indicators

Distribution of sedimentary rocks that are used as climatic indicators during the Permian Period, about 250 my ago.
Red circles are coal deposits (humid climates during interglacial periods, possibly associated with glacial meltwaters).
Blue triangles are glacial tillites.
Irregular green areas are evaporites (arid climates).

Evaporite deposits (gypsum and salt deposits) accumulated in many areas, as indicated by the green areas in the map above. In fact there are more Permian salt deposits than any other age.

Drying of climates at low latitudes led to contraction of coal swamps and extinctions among spore-bearing plants and amphibians that required moist conditions.

Orogenies probably also affected the climate. Locations of mountains can affect climate and control precipitation (rain-shadow effect). Deserts form on the downwind side of mountain ranges.

Because of the drying, gymnosperms (seed plants, including conifers) replaced many spore-bearing plants, which require moist conditions.

Paleogeography of North America during the Permian
Paleogeography of North America during the Permian Period.

The eastern two-thirds of North America consisted of lowlands, undergoing erosion. Continental red beds were deposited locally.

The Appalachian mountains are present in the east and the Ouachita mountains are in the southeast. Farther west are the "Ancestral Rockies."
The Antler Mountains have been eroded down, and are now called uplands.
Subduction and volcanism continue to be active in the far west.


Permian Sedimentary Deposits

The Absaroka sea continued its regression during the Permian. Fossiliferous limestones were deposited in the Absaroka sea, overlain in places by shales, red beds, and evaporites.

The Kaibab Limestone, which forms the cliffs along the rim of the Grand Canyon, is a Permian carbonate deposit.

Permian brachiopods
Ornate brachiopods in the Glass Mountain reef, Early Permian (275 m.y.) Gaplank Formation, Texas.
This specimen has been soaked in acid to dissolve the limestone matrix from around the delicate shells, which have been replaced by silica. Photo courtesy of Pamela Gore.

Phosphate deposits accumulated in the northwestern US. A deep marine basin in the Wyoming, Montana, and Idaho area filled with cherts, sandstones, and mudstones of the Phosphoria Formation. The formation is named for the layers of dark phosphatic sediments and phosphorites. Phosphorite is a dark gray variety of calcium phosphate that may have been produced by the upwelling of phosphorus-rich sea water from the deeper parts of the basin. Phosphate is mined for fertilizers and other products.

Carbonates and evaporites were deposited in a few marine basins in the western US, as the Permian seas withdrew, and the basins became restricted.

Extensive salt beds were deposited in Kansas.

Evaporites were also deposited in the Permian basins in west Texas and New Mexico. Several irregularly subsiding basins (such as the Delaware basin) developed between shallow submerged carbonate platforms. Reefs formed along the basin edges (Capitan Limestone). In the shallow water lagoons behind the reefs, thin limestones, evaporites, and red beds were deposited. Darker colored limestones, shales, and sandstones were deposited in the basins. The basins became restricted, and the water evaporated to form great thicknesses of gypsum (Castille Formation) and salt. The ancient reef forms the steep El Capitan promontory in the Guadalupe Mountains.

The Delaware basin
Legend
Cross-section through the Guadalupe Mountains

Left: The Delaware basin and associated other basins in west Texas and New Mexico during the Permian.
Right: Cross-section through the Guadalupe Mountains of west Texas, illustrating the relationship of the reef deposits (Capitan Limestone) to the other facies, such as the Castille Formation gypsum deposits.

El Capitan
El Capitan, south end of the Guadalupe Mountains, West Texas. Cliff forming unit at top is a Permian reef, named the Capitan Reef (Capitan Limestone), which isolated a basin, allowing hypersaline conditions to develop. Photo courtesy of Pamela Gore.

Permian Castille Formation
The Permian Castille Formation (layered white gypsum with darker laminae of calcite) formed in the hypersaline waters in the isolated basin surrounded by the Capitan Reef. Photo courtesy of Pamela Gore.


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Document created by: Pamela J. W. Gore
Georgia Perimeter College, Clarkston, GA

November 17, 2005