PENNSYLVANIAN - PERMIAN. 1. Paleogeography

1. HISTORICAL GEOLOGY LECTURE 11. LATE PALEOZOIC GEOLOGY II. PENNSYLVANIAN - PERMIAN. 1. Paleogeography The Pennsylvanian opened with the Kaskaskia Regression, which left a widespread erosional unconformity - the basis for the division of the CARBONIFEROUS into the MISSISSIPPIAN and PENNSYLVANIAN in North America. The regression, combined with continuing orogenic uplift in the east, and the continuing deposition of clastics, resulted in a large land area forming down the eastern half of the North American Craton. Africa was now joined to the north east of the North American Craton, the SUTURE ZONE marked by a vast mountain chain (the Appalachians). Harry Williams, Historical Geology

2. The Craton continued its counterclockwise rotation and was now moving towards the north pole - bringing the Equator into a WSW - ENE alignment across the Craton. The climate was still, however, Tropical. The Antler Mountains were continuing to grow in the west and some other small upland areas resulting from plate convergence were developing further north along the west coast. Harry Williams, Historical Geology

3. Harry Williams, Historical Geology

4. 2. Transgressions and Regressions The KASKASKIA REGRESSION continued until mid-Pennsylvanian time; the rest of the Pennsylvanian is characterized by a marine transgression - THE ABSAROKA TRANSGRESSION. An important part of Pennsylvanian deposits were the COAL BEDS that formed in low-lying areas to the west of the eastern mountains. These deposits probably originated as thickly vegetated swampy areas near the coast. Frequent marine inundation would have killed off the vegetation and ensured rapid burial under swampland muds. This would have prevented decomposition of the organic material by OXIDATION; resulting in the formation of carbon-rich peat-like deposits. Continuing burial and compaction, eventually transformed this to COAL. Harry Williams, Historical Geology

5. Features often associated with the coal beds are CYCLOTHERMS, which record frequent and rapid sea-level changes in the form of a cycle of land and sea deposits. Typically, the cyclotherm consists of a basal layer of terrestrial swampy sands, shales and clays, usually capped by coal; aburptly overlain by shallow marine shales and limestones, which gradually graded up into terrestrial deposits once again. Each cyclotherm is typically about 30 - 50 feet thick; in Missouri and Kansas, stacked cyclotherms are up to about 2500 feet in thickness. The cause of the repeated sea-level fluctuations isn't certain, but it may have been periodic regional uplift or subsidence related to the continuing orogeny in the east; or eustatic (global) sea-level changes related, perhaps, to glaciations in Gondwanaland. Harry Williams, Historical Geology

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8. By the Early Permian the sea was regressing, resulting in restricted shallow inland seas and, conequently, the development of evaporite deposits; especially notable are the large Permian salt beds in Kansas. Harry Williams, Historical Geology

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10. The Permian Basin of Texas and the Guadalupe Mountains - a Permian reef. Harry Williams, Historical Geology

11. El Capitan - part of the Permian reef. Harry Williams, Historical Geology

12. Harry Williams, Historical Geology

13. 3. Orogenies The major orogenic episode occurred during Early Pennsylvanian time - THE ALLEGHENY OROGENY. This was essentially the continuation of the (slightly) earlier HERCYNIAN OROGENY in Europe. Northwest Africa collided with eastern North America, producing mountain building, mainly in the Southern Appalachians. It was this compression that caused widespread thrust-faulting throughout the Appalachians, resulting in the "valley and ridge" province. Harry Williams, Historical Geology

14. Satellite image of severe folding recording the Allegheny Orogeny. Harry Williams, Historical Geology

15. At about the same time, South America collided with North America crumpling up the Ouachita Trough and forming a great mountain chain along the southern margin of North America - THE OUACHITA OROGENY. Harry Williams, Historical Geology

16. View of balcones escarpment. Harry Williams, Historical Geology

17. Erosion has since removed much of these mountains leaving only the Ouachita Mountains of Oklahoma/Arkansas, the Arbuckles of Oklahoma and the Marathon Mountains of Texas. This collision between Gondwanaland and Luarussia not only threw up mountain belts around the edge of the Craton, but also transmitted stress into the interior of the Craton, resulting in INTRACRATONIC OROGENESIS - the results were the COLORADO MOUNTAINS (the Ancestral Rockies). Harry Williams, Historical Geology

18. Arbuckles pix Harry Williams, Historical Geology

19. Turner Falls Harry Williams, Historical Geology

20. In the west, the ANTLER OROGENY continued into the Pennsylvanian. Subduction also continued, building an island arc down the entire west coast. These uplands provided large amounts of clastic and volcanic deposits to this region. Many of these volcanic uplands continued moving eastward, pushing up onto the North American Craton and becoming part of it in the late Permian SONOMA OROGENY. The mountainous CORDILLERA region was clearly beginning to take form. Harry Williams, Historical Geology

21. Permian sand dunes in Arizona Harry Williams, Historical Geology

22. Pennsylvanian in north Texas: variety of coastal environments – black shelf muds, patch reefs, deltas, limestones (we see these, and more, on the field trip) Harry Williams, Historical Geology

23. PANGAEA With the suturing of Baltica and Laurentia by the Caledonians " Laurussia and Gondwana " Hercynians, Appalachians, Ouachitas" Laurussia and Siberia " Urals..... Pangaea was now assembled. Of course, it promptly breaks up again… Harry Williams, Historical Geology