Chapter 11 Late Paleozoic Events REPLACE FIGURE (Chapter opening art)

Paleozoic overview REPLACE FIGURE (Fig. 10-1)

Paleozoic Era Paleozoic can be divided into:
Early Paleozoic = Cambrian, Ordovician and Silurian Late Paleozoic = Devonian, Mississippian, Pennsylvanian, and Permian

Carboniferous Mississippian and Pennsylvanian Periods are also referred to with one name - Carboniferous Period. Large plants (including spore-bearing trees and seed ferns) colonized the land during Late Paleozoic. Accumulation of plant remains in swamps produced the vast coal deposits for which Carboniferous was named.

Late Paleozoic plate geography
REPLACE FIGURE (Fig. 11-1) The supercontinent Pangea assembled as the continents collided during Late Paleozoic. Larger continents grew by addition of island arcs and microcontinents around their edges.

Late Paleozoic Orogenies of eastern North America
Continental collisions caused several orogenies or mountain-building events in eastern North America. Acadian orogeny and Caledonian orogeny Alleghanian orogeny in eastern North America and Hercynian orogeny in central Europe

Late Paleozoic Orogenies of eastern North America
Acadian orogeny and Caledonian orogeny Middle Silurian to Middle Devonian. Laurentia (North America) and Baltica (Europe) collide to form Laurasia. A volcanic island arc (Avalon terrane or Carolina terrane) collides with eastern North America.

Late Paleozoic Orogenies in eastern North America
Alleghanian orogeny in eastern North America and Hercynian orogeny in central Europe Late Carboniferous Gondwana (the southern continents, Africa, South America, India, Australia, Antarctica) and Laurasia collide. Southern Appalachian mountains form as Laurasia collides with northwestern Africa (part of Gondwana).

Late Paleozoic Orogenies in eastern North America
The Acadian and Alleghanian orogenies were the result of the closure of the Iapetus Ocean and continental collisions which resulted in the formation of the supercontinent Pangea.

Physiographic provinces of the Appalachian region in eastern North America.
REPLACE FIGURE (Fig a)

The Alleghanian orogeny
The Alleghanian orogeny produced folds in the Appalachian Valley and Ridge province, and large thrust faults in the southern Appalachians. Many folds are asymmetrically overturned to the northwest, and surfaces of thrust faults dip to the southeast. REPLACE FIGURE (Fig b)

The Alleghanian orogeny
REPLACE FIGURE (Fig b) Blue Ridge and Piedmont metamorphic and igneous rocks form a sheet ranging from 6-15 km thick, overlying relatively flat-lying lower Paleozoic sedimentary rocks. This type of tectonic deformation is called "thin-skinned tectonics."

Late Paleozoic Orogenies of western North America
In the western part of North America, the Antler orogeny began during Devonian with the subduction of oceanic lithosphere beneath the western margin of the continent. The Antler Orogeny continued into Mississippian and Pennsylvanian.

Late Paleozoic Orogenies of western North America
A volcanic island arc collided with the western margin of North America, crushing sediments and causing thrust faulting (Roberts Mountains Thrust Fault of Nevada). Continental rise and slope deposits were thrust as much as 80 km over shallow water sediments of the former continental shelf.

Late Paleozoic Sedimentary Sequences
Shallow epicontinental seas transgressed and regressed across Laurasia (North America) during Late Paleozoic as the glaciers melted and enlarged. These sequences are bounded by (or separated by) unconformities.

Late Paleozoic Sedimentary Sequences
Two major transgressions occurred in North America during Late Paleozoic: Kaskaskia (Devonian-Mississippian) Absaroka (Pennsylvanian-Permian) During regressions, such as the one between Mississippian and Pennsylvanian, the former seafloor was exposed to erosion, creating one of the most widespread regional unconformities in the world.

North American cratonic sequences
REPLACE FIGURE (Table 10-1) North American cratonic sequences Green = sedimentary deposits Yellow = missing strata associated with unconformities

Devonian Paleogeography
REPLACE FIGURE (Upper figure in Fig. 11-1) As Late Paleozoic began, the continents were fairly fragmented and separate, particularly in the Northern Hemisphere.

REPLACE FIGURE (Upper figure in Fig. 11-1) There is an extensive sedimentary record for Devonian. Note that North America sat on the equator, with warm, tropical climatic conditions.

REPLACE FIGURE (Upper figure in Fig. 11-1) 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.

REPLACE FIGURE (Upper figure in Fig. 11-1) Laurentia and Baltica collided to form Laurasia in the Caledonian orogeny affecting northeastern Canada, Greenland, and Europe).

REPLACE FIGURE (Upper figure in Fig. 11-1) A volcanic island arc or exotic terrane, called the Avalon terrane (or Carolina terrane), collided with Eastern North America in the Acadian orogeny.

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.

REPLACE FIGURE (Fig. 11-4) 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.

REPLACE FIGURE (Fig. 11-4) Sea levels were high worldwide during Devonian (indicating that there were no glaciers). Much of the North American continent was flooded by shallow seas.

Devonian Sedimentary Deposits
The seas regressed from the continents at the end of Early Paleozoic as a result of the Ordovician-Silurian glaciation. Gradual flooding of the North American craton occurred during Late Paleozoic, reaching its maximum extent during Mississippian Period. This new inland sea was called the Kaskaskia sea.

In eastern North America, initial deposits of the Kaskaskia sea were clean quartz sands, such as the Devonian Oriskany Sandstone, 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. Evaporites suggest dry conditions.

After the Acadian orogeny, carbonate sedimentation was followed by deposition of clastic sediments. Clastic sediments are thicker and coarser to the east, nearer their source area in the Acadian highlands. Primarily continental red beds (stream deposits). Wedge-shaped deposit called the Catskill clastic wedge or Catskill delta (although these are not deltaic deposits).

Similar Devonian red beds 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.

Catskill clastic wedge deposits
REPLACE FIGURE (Fig )

Catskill clastic wedge deposits
REPLACE FIGURE (Fig b) East-west cross-section across the Devonian Catskill clastic wedge in New York.

REPLACE FIGURE (Fig a) Isopach (sediment thickness) and lithofacies map of Upper Devonian in the eastern U.S. 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.

Chattanooga Shale Farther west, black shales were deposited in a thin unit (less than about m thick) over a wide area (Chattanooga Shale) during Late Devonian and Early Mississippian. Offshore equivalent of the 3000 m thick Catskill clastic wedge. An important marker bed for regional correlation. High organic carbon content, along with finely disseminated pyrite, and uranium. Chattanooga Shale was deposited in stagnant, oxygen-deficient water.

Williston Basin 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.

Carboniferous In North America, Carboniferous consists of two periods: Mississippian and Pennsylvanian. Mississippian is Early Carboniferous. Pennsylvanian is Late Carboniferous.

Mississippian The name "Mississippian" is derived from exposures of rock in the valley region of the Mississippi River. Mississippian sedimentary deposits contain abundant limestone with fossils of crinoids, blastoids, bryozoans, and fusulinid foraminifera.

Pennsylvanian Pennsylvanian rocks are dominated by coal-rich sediments that were deposited in swamps and deltas. Coal deposits are particularly well developed in Pennsylvania.

Mississippian Paleogeography
REPLACE FIGURE (Fig. 11-8) Landmass in eastern North America and Europe (yellow), formed as the mountains (orange) eroded after Caledonian and Acadian orogenies.

REPLACE FIGURE (Fig. 11-8) Although a large mountain range was present in the Appalachian area, another orogeny was soon to occur, as indicated by the arrows and the words "Africa approaching" along the right side of the map.

Much of North America was covered by a shallow epicontinental sea.
North America sat on the equator, so temperatures were warm. Note the Antler highlands in the western U.S. REPLACE FIGURE (Fig. 11-8)

Mississippian Sedimentary Deposits
By Mississippian, the Acadian highlands were reduced in size by erosion, and were no longer releasing large quantities of sediment. In the east, near the remaining highlands, non-marine shales, sandstones, and conglomerates were deposited. These sediments belong to the Pocono Group.

As muddy sediment from the eroding highlands decreased, carbonate deposition became widespread in the warm, shallow Kaskaskia sea. Mississippian limestones contain abundant crinoids, blastoids, bryozoans, and fusulinid foraminifera. The widespread blanket of carbonate rocks deposited during this time is called the great Mississippian lime bank. In places, Mississippian limestones are more than 700 m thick.

Crinoids REPLACE FIGURE (Fig. 11-6b) REPLACE FIGURE (Fig. 11-6a)

Sands, clays, and thin layers of carbonates were deposited during Late Mississippian time as the Kaskaskia sea regressed. These rocks are a source of petroleum in Illinois. They appear to have been deposited in stream valleys developed on the former seafloor.

Farther west, extensive reefs developed around the Williston basin (South Dakota, Montana, and part of Canada). Arid climatic conditions and restricted circulation resulted in the deposition of thick units of gypsum and salt. Petroleum migrated into the permeable reef deposits, forming rich oil fields.

In the Gulf Coast area, slow deposition continued from Early Devonian to Late Mississippian. Carbonates predominated in the more northerly shelf zone. Cherty rocks called novaculites were deposited in deeper waters to the south. Novaculites are composed of microcrystalline quartz, which has been subjected to heat and pressure. Arkansas novaculite is used as a whetstone to sharpen steel knives and tools.

Graywackes and shales spread into the depositional basin near the end of Mississippian, forming a clastic wedge more than 8000 m thick, that thickened and coarsened to the south, where a new mountain range had formed and was eroding. The remnants of this mountain range are the Ouachita Mountains of Arkansas and Oklahoma, and the Marathon Mountains of southwestern Texas.

The Kaskaskia sea retreated from the craton at the end of Mississippian. This event is marked by one of the most widespread unconformities in the world. This unconformity separates Mississippian from Pennsylvanian. The overlying Pennsylvanian rocks were deposited under very different conditions.

Alleghanian orogeny REPLACE FIGURE (Middle figure of Fig. 11-1) During Late Paleozoic, northwestern Africa collided with southeastern North America, causing the Alleghanian orogeny, and building the Appalachian mountains. The orogeny began during Mississippian and continued through Pennsylvanian and Permian.

Alleghanian orogeny REPLACE FIGURE (Middle figure of Fig. 11-1) South America collided with the Gulf Coast region of North America, forming the Ouachita Mountains, a southwestern continuation of the Alleghanian orogenic belt.

Plate tectonics model for the continental collisions during Late Paleozoic
REPLACE FIGURE (Fig – rearranged)

Pangea REPLACE FIGURE (Middle figure of Fig. 11-1) By Late Carboniferous, a large continental landmass called Pangea, had formed by the collision of Laurasia (North America plus Europe) with Gondwana (the southern continents of Africa, South America, Australia, Antarctica, and India).

Pangea on the South Pole
REPLACE FIGURE (Middle figure of Fig. 11-1) The supercontinent, Pangea, sat over the South Pole. When a continent is over a pole, conditions are right for a glaciation, if the climate is cold and if sufficient moisture is present.

Iapetus Ocean closed REPLACE FIGURE (Middle figure of Fig. 11-1) The Iapetus Ocean (or Proto-Atlantic), completely closed by Late Carboniferous. Closure of the Iapetus Ocean disrupted global ocean circulation and caused currents to be diverted from the tropics to more polar areas, contributing to glaciation.

Late Paleozoic Evaporites
REPLACE FIGURE (Middle figure of Fig. 11-1) The presence of evaporites (E) indicates that the climate was at least locally dry. This was probably due in part to changes in global oceanic and atmospheric circulation induced by the closure of the Iapetus, as well as by orogeny.

Late Paleozoic Glacial Deposits
REPLACE FIGURE (Middle figure of Fig. 11-1) Glacial deposits are present in the southern hemisphere, indicating that a glaciation occurred during Carboniferous and Permian.

Pennsylvanian Paleogeography
REPLACE FIGURE (Fig ) Large landmass in the east, with extensive lowlands (yellow). Appalachian Mountains (orange) have formed as a result of the Alleghanian orogeny.

Sediment eroding from the Appalachian Mountains was transported to the west into the epicontinental sea that covered much of North America during Mississippian. These sedimentary deposits have built a broad plain to the west, with alternating non-marine and marine deposits, as the sea transgressed and regressed.

REPLACE FIGURE (Fig ) Coal swamps formed along the western edge of the Appalachian Mountains, in what was basically a tropical rainforest setting.

REPLACE FIGURE (Fig ) Uplifts in the southern and southwestern North America (Uncompahgre mountains or ancestral Rockies, and others), and the Antler Mountains in the western U.S.

Pennsylvanian Sedimentary Deposits
The erosion of the Antler Mountains provided detrital sediment that was transported into adjacent basins. Thick sequences of Pennsylvanian and Permian shelf sediments accumulated in the area now occupied by the Wasatch and Oquirrh Mountains in Utah.

Pennsylvanian Sedimentary Deposits
The Absaroka sea began to transgress upon the North American craton near the beginning of Middle Pennsylvanian. The rocks in the eastern half of the U.S. are predominantly interbedded marine and nonmarine sediments, indicating the advance and retreat of the sea. Each nonmarine-marine sequence is called a cyclothem.

Pennsylvanian cyclothem
A typical Pennsylvanian cyclothem contains 10 units. The lower half consist of nonmarine sediments, topped by a coal deposit. The coal is overlain by marine deposits, indicating the advance of the sea into the swampy, vegetated area. REPLACE FIGURE (Fig a)

Marine and Non-marine deposits
The repetitious interbedding of non-marine and marine sedimentary deposits indicates either: Episodic regional subsidence and uplift OR Eustatic (worldwide) sea level changes related to Carboniferous-Permian glaciation in Gondwana.

Coal and Plant Fossils Pennsylvanian coal deposits are mined extensively in the Appalachian area, the Illinois basin, and in Europe. They are commonly associated with rocks containing plant fossils. REPLACE FIGURES (Fig a, b)

Southwestern North America
SW part of the North American craton experienced mountain building during Pennsylvanian. The highlands are called the Uncompahgre Mountains (or ancestral Rockies) in southwestern Colorado, and the Oklahoma Mountains of western Oklahoma. These mountains and related uplifts resulted from movement along large, nearly vertical faults.

Colorado Front Range The Colorado Front Range-Pedernal uplifts extending north-south through central Colorado formed at this time. Precambrian igneous and metamorphic rocks are now exposed in the cores of these eroded mountain ranges.

Pennsylvanian and Permian sandstone deposits
Erosion produced great wedge-shaped deposits of red arkosic sandstone during Pennsylvanian and Permian, some of which is exposed in Colorado as: The "flatirons" near Boulder The rocks at Red Rocks Amphitheatre near Morrison, west of Denver The Garden of the Gods, near Colorado Springs

REPLACE FIGURE (Fig ) Deposition of Pennsylvanian clastic sediments in eastern Colorado and New Mexico. Note the accumulation of coarse arkosic sandstones east of the Uncompahgre Mountains.

REPLACE FIGURE (Fig ) The Flatirons, near Boulder, Colorado. Steeply dipping red arkosic sandstones, conglomerates, and mudstones of Upper Pennsylvanian and Lower Permian Fountain Formation. Sediments were derived from the erosion of the ancestral Rocky Mountains to the west. The beds were tilted during the orogeny that produced the modern Rocky Mountains.

Other Uplifts Other uplifts also formed, including the Zuni-Fort Defiance uplift, the Amarillo mountains, and the Oklahoma mountains (represented today by the Arbuckle and Wichita mountains). The origin of these mountains may be related to the collision of Gondwana along the southern edge of the North American craton in the Ouachita orogenic belt.

Other Uplifts Crustal adjustments to relieve stress may have resulted in the deformation that produced the highlands and associated basins (such as the Early Pennsylvanian Paradox basin, which contains evaporites and petroleum deposits).

Paradox Basin REPLACE FIGURE (Fig ) The Paradox basin lies southwest of the Uncompahgre mountains. Clastic sediments from the mountains were deposited along the northeastern side of the basin.

Paradox Basin REPLACE FIGURE (Fig ) The Paradox basin was flooded by the Absaroka sea during Early Pennsylvanian. Shales were deposited over Mississippian limestone. The basin became restricted and thick beds of evaporites (salt, gypsum and anhydrite) were deposited.

Paradox Basin REPLACE FIGURE (Fig ) Reef-like algal mounds, associated with fossiliferous and oolitic limestones, developed along the western rim of the basin. The reefs serve as petroleum reservoirs. Near the end of Pennsylvanian, the basin filled with arkosic sediments eroded from the Uncompahgre highlands.

Regression of the Absaroka sea
The Absaroka sea, which began its transgression at the beginning of Pennsylvanian, began a slow and irregular regression before the end of Pennsylvanian, which continued into Permian.

Permian Paleogeography
REPLACE FIGURE (Lower figure in Fig. 11-1) During Permian, the continents collided and joined to form the supercontinent, Pangea. 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.

REPLACE FIGURE (Lower figure in Fig. 11-1) Continental collision was accompanied by orogeny, and the Appalachian mountain chain reached its peak during the Alleghanian orogeny.

REPLACE FIGURE (Lower figure in Fig. 11-1) 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.

REPLACE FIGURE (Lower figure in Fig. 11-1) The Gondwana part of Pangea continued to sit atop the South Pole, and glaciation continued into Permian.

Permian Paleoclimatic Indicators
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). REPLACE FIGURE (Fig. 11-2)

Permian Glaciation REPLACE FIGURE (Fig. 11-2) Distribution of glaciers can be determined from Permian glacial tillites, or striations on bedrock, caused by the movement of the glaciers. Glacial deposits are white. Arrows indicate direction of glacial movement as determined from glacial striations on the bedrock. REPLACE FIGURE (Fig. 7-28)

Permian Evaporites REPLACE FIGURE (Fig. 11-2) Cold air holds less moisture than warm air, and the climate became arid during Permian. Evaporite deposits (gypsum and salt) accumulated in the green areas on the map. There are more Permian salt deposits than any other age.

End of the Coal Swamps Drying of climates at low latitudes led to contraction of coal swamps and extinctions among spore-bearing plants and amphibians that required moist conditions. Because of the drying, gymnosperms (seed plants, including conifers) replaced many spore-bearing plants, which require moist conditions.

Orogeny and climate 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.

REPLACE FIGURE (Fig ) The eastern 2/3 of North America consisted of lowlands, undergoing erosion. Continental red beds were deposited locally.

REPLACE FIGURE (Fig ) Appalachian mountains in the east. Ouachita mountains in the southeast. Farther west are the "Ancestral Rockies." Antler Mountains have been eroded, and are called uplands. Subduction and volcanism continue in the far west.

Permian Sedimentary Deposits
The Absaroka sea continued its regression during 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.

Phosphate Deposits in NW U.S.
Deep marine basin in the Wyoming, Montana, and Idaho area filled with cherts, sandstones, and mudstones of the Phosphoria Formation. Formation named for layers of dark phosphatic sediments and phosphorites. Phosphorite = dark gray variety of calcium phosphate. May have formed by upwelling of phosphorus-rich sea water from deeper parts of basin. Phosphate is mined for fertilizers and other products.

Note phosphate deposits
Carbonates and evaporites were deposited in marine basins in the western U.S., as Permian seas withdrew, and basins became restricted. Extensive salt beds were deposited in Kansas. REPLACE FIGURE (Fig )

Permian basins in west Texas and New Mexico
Several irregularly subsiding basins (such as the Delaware basin) developed between shallow submerged carbonate platforms. REPLACE FIGURE (Fig a + legend)

REPLACE FIGURE (Fig ) Reefs formed along the basin edges (Capitan Limestone). The ancient reef forms the steep El Capitan promontory in the Guadalupe Mountains.

In the shallow water lagoons behind the reefs, thin limestones, evaporites, and red beds were deposited. REPLACE FIGURE (Fig a + legend)

Paleozoic review REPLACE FIGURE (Fig. 10-1)

Chapter 11 Late Paleozoic Events REPLACE FIGURE (Chapter opening art)

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Chapter 11 Late Paleozoic Events REPLACE FIGURE (Chapter opening art)

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