Presentation - Tectonic At the same time that Gondwana was...

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Tectonic At the same time that Gondwana was being glaciated near the south pole, Laurussia was partially straddling the equator. As the  Carboniferous glaciers waxed and waned, the resulting glacioeustatic changes in sea level (150 to 200 m.), combined in some cases  with local tectonic subsidence, caused the shore to repeatedly transgress and regress over an enormous area where the Permo- Mississippian coals are now found. Each time the glaciers receded, sea level rose again, burying coastal swamps and forests of  Lycopod trees and seed ferns under shale and limestone. Each time the glaciers began to accumulate again, sea level dropped, and  the forests returned to the coastal areas.  The resultingly cyclic sedimentary deposits, known as cyclothems, are dustributed across the Laurasian landmasses, including North  America, northwest Europe, and western Russia. Each cyclothem is the record of a single transgression/regression cycle. In Illinois, up  to 60 individual cyclothems are stacked on top of each other (Condie, p. 301). In each cyclothem (as originally defined), a coal bed rests  atop a  paleosol underclay , and is covered by a transgressive sedimentary sequence of shale grading upward into marine limestone, 
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This note was uploaded on 03/27/2012 for the course GEOL 2413 taught by Professor Moody during the Spring '10 term at Texas A&M University, Corpus Christi.

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Presentation - Tectonic At the same time that Gondwana was...

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