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HISTORICAL GEOLOGY LECTURE 9. EARLY PALEOZOIC GEOLOGY II.

HISTORICAL GEOLOGY LECTURE 9. EARLY PALEOZOIC GEOLOGY II. . ORDOVICIAN (488-443 MYBP) 1. Paleogeography

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HISTORICAL GEOLOGY LECTURE 9. EARLY PALEOZOIC GEOLOGY II.

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  1. HISTORICAL GEOLOGY LECTURE 9. EARLY PALEOZOIC GEOLOGY II. ORDOVICIAN (488-443 MYBP) 1. Paleogeography The major difference in geography between the Cambrian and Ordovician is that the craton margins became ZONES OF CONVERGENCE during the Ordovician; fragmented Rodinia was just beginning to reassemble. Harry Williams, Historical Geology

  2. Harry Williams, Historical Geology

  3. The result of this was the formation of subduction zones on the craton margins: -> TACONIC HIGHLANDS of east coast -> highlands bordering Franklin Seaway -> volcanic island arc along the margin of the Cordilleran seaway. Rocks deposited adjacent to these areas are characteristic of subduction zones: - erosion of rugged rapidly growing uplands -> graywackes, conglomerates, shales. - volcanic activity -> volcanic rocks - no carbonates (in areas adjacent to subduction). Harry Williams, Historical Geology

  4. 2. Transgressions and Regressions The beginning of the Ordovician is marked by the SAUK REGRESSION, which left a major EROSIONAL UNCONFORMITY, used to identify the boundary between the SAUK and the TIPPECANOE strata sequences. The rest of the Ordovician, like the Cambrian, is characterized by a marine transgression - THE TIPPECANOE TRANSGRESSION. Typical transgressive sequences were deposited in the advancing epeiric seas. Harry Williams, Historical Geology

  5. Harry Williams, Historical Geology

  6. 3. Orogenies The major orogenic episode occurred during the middle-late Ordovician - THE TACONIC OROGENY This was associated with the subduction zone that had formed down the east coast of the craton. The development of a convergent margin caused the formation of the TACONIC HIGHLANDS, down the N.E. coast (remnants of which form the Taconic Mountains of New York State). These uplands consisted of folded/metamorphosed sedimentary rocks + accreted and intruded volcanics; and probably reached over 13000 feet in height. Harry Williams, Historical Geology

  7. Harry Williams, Historical Geology

  8. Harry Williams, Historical Geology

  9. Harry Williams, Historical Geology

  10. Later, intense erosion of the Taconic highlands resulted in the QUEENSTON CLASTIC WEDGE This is a great wedge of non-marine clastic sediments which spread westward from the growing highlands (contains 600,000 km3 of eroded rock). PROXIMAL = CONGLOMERATES SANDSTONES DISTAL = SHALES Harry Williams, Historical Geology

  11. Harry Williams, Historical Geology

  12. Harry Williams, Historical Geology

  13. The other noticeable event of this period was the beginning of thick sedimentation in the OUACHITA TROUGH - the deep marine S.W. extension of the Appalachian Seaway. Harry Williams, Historical Geology

  14. Silurian (443-416 mybp). 1. Paleogeography The east coast from Newfoundland to Florida was now continuous highlands due to the continuing growth of the Taconic orogeny. Harry Williams, Historical Geology

  15. 2. Transgressions/Regressions Most of Silurian time was characterized by the Tippecanoe regression. The major effect of the regression was the formation of landlocked, reef-fringed marine basins in the region now occupied by the Great Lakes. Evaporation from these inland seas created vast EVAPORITE DEPOSITS (salts) up to 500 m thick - these are presently mined. Harry Williams, Historical Geology

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  17. Harry Williams, Historical Geology

  18. Harry Williams, Historical Geology

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  20. Harry Williams, Historical Geology

  21. 3. Orogenies The closure of the Proto-Atlantic (Iapetus) Ocean continued during Silurian time, culminating in a continent-continent collision between Laurentia (N. America) and Baltica (Europe) in late Silurian/early Devonian time. This resulted in the Caledonian Orogeny and LAURUSSIA. Harry Williams, Historical Geology

  22. The most intense effects of the Caledonian Orogeny were in Scandinavia and Northern Europe (Norway, Scotland). On the North American craton the effects were less severe, but helped to create the mountainous terrain of the Northern Appalachian Mountains. This mountain-building episode continued into Devonian time as the ACADIAN OROGENY (more on this later). Harry Williams, Historical Geology

  23. A major result of the Caledonian Orogeny in Northern Europe was the building of mountains (CALEDONIDES) which underwent intense erosion and formed a wedge of non-marine clastics over much of what is now Northern Europe. This was the "Old Red Continent" - composed mainly of rusty-colored sandstones (old red sandstones) - similar to the Queenston Clastic Wedge of North America. Harry Williams, Historical Geology

  24. Part of the Caledonian orogenic belt, Scotland. Harry Williams, Historical Geology

  25. The other notable event of late Silurian time was that Siberia begun to converge on Laurussia - forming subduction zones at their margins and beginning the closure of the Uralian Seaway. Harry Williams, Historical Geology

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