1. The vast Devonian shallow seas persisted into Early Carboniferous time but retreated during the mid-Carboniferous.

2. The seaways returned again during the Late Carboniferous and deltas became sites of densely-wooded swamps that would later be buried and convert into massive coal-deposits.

3. The late Paleozoic was a time when the continents assembled to form the supercontinent of Pangea.

4. During the late Carboniferous and Permian, North America's eastern margin collided with Africa while the southern margin closed against South America.

5. The late Paleozoic sea floor was again abundant in ammonoids, crinoids, bryozoans, corals, molluscs and brachiopods.

6. Land plants continued to diversify in the late Paleozoic such that by mid-Permian times, conifers and other primitive seed plants replaced the lowlands coal forests and invaded uplands for the first time.

7. The vertebrates evolved into two main groups, (a) the synapsid lineage which would eventually give rise to the mammals and (b) the reptiles which eventually evolved into turtles, lizards, snakes, crocodiles and dinosaurs during the Mesozoic.

8. Finally, the end of the Permian was marked by the greatest mass extinction on earth which resulted in the demise of 95% of all marine species.

Figure 13.2: The early Carboniferous was a time when the great supercontinent of Gondwanaland was about to assemble with Laurentia. Subduction zones flanked much of the perimeters of the great continents. Eastern and southern North America was undergoing (or about to undergo) major collisions with Gondwanaland.

1. Figure 13.3: The early Carboniferous or Mississippian Period (362-322 Ma) was a time when the North American continent was covered by the Kaskaskia epeiric sea as evidenced by extensive marine strata preserved throughout the craton.

2. All over the world, Mississippian deposits are characterized by thick sequences of limestone.

3. In North America, the Mississippian Period was the last time that widespread carbonate deposition occurred across most of the craton.

4. These carbonate deposits included limestone rich in crinoid fragments in addition to oolite deposits, fossil fragments, cross stratification, ripple marks and scour structures indicative of warm, shallow and often agitated seaways.

5. Reef communities stretched from the southern United States to northern Alaska but they were smaller than the great barrier-reef complexes of the middle Paleozoic.

1. During Late Mississippian time, however, distinct changes were occurring in the sedimentation pattern of North America. The pure quartz sandstone characteristic of Early to Middle Paleozoic rocks gave way to more heterogeneous sandstone containing feldspars and micas in addition to quartz. The heterogeneous sandstone first appeared in the southeastern part of the craton and gradually became more widespread in subsequent periods, attesting to the growing tectonism and deformation around the margins of North America.

2. Warping within the cratonic interior intensified due to the tectonic collisions occurring around the periphery of the continent.

3. The vast Kaskaskian epeiric sea retreated during the Late Mississippian, leaving the continent exposed to extensive erosion that eventually produced a widespread, major unconformity. Similar unconformities also occur on other continents, suggesting that the Late Mississippian regression resulted from a major drop of sea level on a global scale.

4. Figure 13.8: During the Early Pennsylvanian, the North American continent experienced another transgression which led to the deposition of the Absaroka Sequence over the vast erosional surface.

5. The diverse mineralogy of the sediments deposited during this time point to heterogeneous source areas resulting from exhumation and erosion of chiefly igneous and metamorphic rocks which that had been previously been buried beneath early Paleozoic strata but were now exposed. Facies and paleocurrent directions indicate that much of the source area laid in eastern Canada, the site of two major orogenic events (Caledonian and Acadian orogenies).

6. Figure 13.7: Gradual uplift of eastern North America occurred during the Pennsylvianian Period as evidenced by the eastern limits of coarse clastic areas and coal-bearing (deltaic) strata.

7. During this same period, the western regions of North America were dumping grounds for pure quartz sediments derived largely from erosion of earlier Paleozoic sandstone located in the west-central craton of Canada.

1. Beginning in Late Mississippian time and continuing into the Early Permian, the strata being deposited in North America took on a striking repetitive pattern in which sandstone-shale-limestone sets were repeated several times vertically.

2. The sandstone and shale are thought to represent deltaic deposits formed by river systems originating from southeastern Canada and, later on, from the Appalachian region of eastern U.S.

3. Figure 13.9: The most striking repetitive patterns occur in coal-bearing sequences where at least 40-50 late Paleozoic cycles have been recognized along the southern part of the craton. These repetitive sedimentary packages are called cyclothems.

4. A typical cyclothem begins with a base of cross-stratified sandstone and conglomerate resting unconformably upon older strata and possibly deposited by rivers. The middle of the cycle contains coal and plant-bearing shale while the upper part generally contains brackish water or marine fossiliferous shale and limestone. Many cyclothems are found vertically stacked on one another and also show lateral variations within them.

5. The upper marine rocks are best developed in the central states whereas coal-bearing non-marine rock types predominate in the east.

6. Repetitive cycles along the western part of the craton were different, consisting of widespread, thin marine limestone alternating with sandstone that may have been deposited within eolian environments.

7. Figure 13.11: The alternating marine and nonmarine deposits of cyclothems point to many transgressions and regressions, possibly over 100 transgression-regression cycles over the coarse of 100 million years from Mississippian to Permian time. These rapid Late Paleozoic oscillations in sea level averaged one per million years, which were much shorter than the major early Paleozoic transgressive-regressive episodes which averaged tens of millions of years each.

1. Repetitive sedimentation patterns of cyclothems may reflect spasmodic uplifts and subsidence of the craton due to tectonic forces acting along the edges of the continent. The long-term tectonic rise of eastern North America may have been locally modified by rising arches and subsiding basins that affect the number of transgressive-regressive cycles within a particular area.

2. Cyclothems may reflect fluctuations in the amount of clastic sediment supplied to deltas in response to cyclic climatic changes that affect erosion of the uplands. Deltas advance during times of greater sediment supply but are flooded during periods of reduced sedimentation.

3. Cyclothems may reflect repeated rise and fall of sea level on a global scale due to cyclic melting and growth of continental glaciers. Glacially produced sea-level changes would explain repetitive sedimentation occurring simultaneously in both western and eastern North America and on other continents.

1. The basal sandstone and shale of the Carboniferous cyclothems are interpreted as river and delta deposits, but the coal layers indicate formation in vast coastal plain swamps containing jungle-like vegetation. Coal formed through vast accumulation of plant material, or peat, which then coverts to coal upon burial.

2. The ancient coal swamps were dominated by large, scaly-barked trees called lycopsids in addition to ferns and tree ferns. The nature of the vegetation and presence of primitive reptiles, amphibians and insects that inhabited the soggy forests suggest that the climate for these ancient coal swamps was warm and humid.

3. As trees and shrubs died, they were rapidly submerged and buried so that the debris was isolated from oxygen and subjected only to decay by anaerobic bacteria. Over time, the debris was compacted to peat by the weight of overlying material. Through increased burial and gradual escape of volatile hydrocarbon compounds, the peat was gradually transformed to carbon-rich coal.

4. Today, Pennsylvanian coal is commercially mined in the Illinois Basin, centeral Appalacian Mountains and the Maritime Provinces of Canada.

1. Much of the Pennsylvanian sandstone and shale in the central United States represent environments associated with deltas deposited near sea level. River-channel sandstone passes laterally into black shale while coals formed in swamps between river channels. As the shoreline oscillated, so did the deltas.

2. Figure 13.15: Ultimately the sea flooded the low, coastal plain swamps during transgression and deposited the marine sediments that comprise the upper portion of each cyclothem.

3. A subsequent small drop in sea level and associated regression would initiate the next cyclothem deposit resulting from the expansion (progradation) of rivers, deltas and swamp forests over the once-flooded region.

4. Figure 13.8: The Pennsylvanian cyclothems are therefore thought to have been deposited along a swampy coastal plane that was 800-1000 km wide and located between the low mountainous uplands of the Appalachian orogenic belt to the east and a persistent epeiric sea which covered the craton to the west. Repeated oscillations of the shoreline produced the cyclothems that today comprise much of the Carboniferous rock record.

1. Figure 13.17: The eastern side of North America was tilting upward during the late Paleozoic, resulting in more land area and greater average elevation than ever before during the Paleozoic Era. By early Permian time, the epeiric sea had retreated to the present area of southwestern Texas and the northern region of what would eventually become the Rocky Mountains.

2. Figure 13.16: Along the western edge of the continent, phosphate-bearing black shale accumulated as a product of upwelling, nutrient-rich cold waters along the edge of the continent.

3. Permian evaporites and red beds accumulated over vast regions of the western United States and evaporites and carbonates formed in northern Canada. The vast expanse of Permian evaporites attest to the slow drying up of epeiric seas as the land area enlarged.

4. Figure 13.20: The late Paleozoic rock and fossil record indicate that North America was in the tropics and thus in the Trade Winds belt during the Late Paleozoic. The Appalachian region may have had a monsoon-like climate during the Pennsylvanian Period characterized by markedly seasonal rainfall like that of India and southeastern Asia today. As African approached America during the late Paleozoic, however, the Appalachian climate gradually became drier as the ocean between the two continents shrank.

5. Throughout the late Paleozoic, western North America was probably mostly arid.

1. During the Late Paleozoic, the North American craton suffered more severe deformation than ever before.

2. Figure 13.21: During Pennsylvanian time, Mountains over 1,000 meters high were formed within the interior of the cration in what is now Colorado and Oklahoma, possibly due to Late Paleozoic collision of Gondwanaland with southern North America.

1. Up until the late Paleozoic, the southern margin of North America was a passive, stable shelf and continental slope.

2. Figure 13.23: Prior to the Mississippian Period, the Ouachita area of Arkansas and Oklahoma was situated in a deep-water environment where only thin layers of deep-water shale and chert were deposited. Beginning in Late Mississippian time, however, turbidity currents began bringing in large volumes of sand from the Appalachian region to the east. Volcanic ash deposits soon followed, indicating that a volcanic arc was forming somewhere to the south.

3. During the Pennsylvanian Period, the trough between the southern arc and northern shelf filled rapidly with clastic sediments. The region was eventually deformed and uplifted into the Ouachita-Marathon Mountains by Permian time due to collision of the southern margin with the South American portion of Gondwanaland.

4. Figure 13.18: In the area that is now southwestern Texas, a great Late Permian organic reef complex formed around the edge of a basin that was more than 300 meters deep. As the sea retreated further, the reef community died and the Permian Basin became filled with thick deposits of evaporite and red-beds.

5. Figure 13.25: Further northeast, intense folding and thrust faulting was also occurring in the main Appalachian region due to collision with the African portion of Gondwanaland. The intense folding and faulting associated with this Appalachian Orogeny was superimposed upon earlier Acadian and Taconian deformation.

6. Field evidence indicates that the Appalachian orogeny occurred between Late Pennsylvanian and Late Triassic times. Isotopic dating of granitic rocks indicates an average age between 250 and 260 million years.

7. Figure 13.26: Along the axis of the orogenic belt, Paleozoic and Crytozoic rocks were most intensely deformed and metamorphosed by the overprinting of several orogenies:

(a) The Ridge & Valley and Blue Ridge areas were part of the eastern North American Craton prior to collision with Gondwanaland.

(b) The Piedmont area may represent a microcontinent caught between the colliding North American and Gondwanaland continents.

(c) The rocks east of the Piedmont include portions of the Avalonia Microcontinent and a piece of Gondwanaland left behind following Early Mesozoic opening of the Atlantic Ocean.

8. Figure 13.28: Hypothetical scenario for the evolution of the southern Appalachian orogenic belt.

1. Figure 13.29: The end of the Paleozoic Era was a time of widespread mountain building culminating in the assembly of the interconnected super-supercontinent called Pangea.

2. Central Europe became the site of intense mountain building during the Hercynian orogeny resulting from collision between Europe and Northern Africa. The Hercynian orogeny began in Late Carboniferous time and was characterized by widespread metamorphism and granitic plutonism. The Hercynian orogenic belt of Europe is an extension of the Appalachian belt in North America, both being related to collision with Gondwanaland at about the same time.

3. The Siberian craton collided with Eastern Europe during Late Paleozoic assembly of Pangea to produce the Ural Mountains.