Late Paleozoic Earth – Chapter 11 • Outline the major orogenies along the easter
ID: 289570 • Letter: L
Question
Late Paleozoic Earth – Chapter 11
• Outline the major orogenies along the eastern margin of Laurentia/Laurasia during the
Late Paleozoic and how they relate to the formation of Pangea
• Outline the evidence for the major transgressive and regressive sequences in
Laurentia/Laurasia during the Late Paleozoic
• Define cyclothems and how they relate to deposition of coal during the deposition of
the Absaroka sequence
• Discuss the significance of the Old Red Sandstone and Catskill delta rocks to the Acadian
orogeny
Explanation / Answer
ANSWER-
1.)During the course of palaeozoic era,Laurentia evolved into laurasia and eventually become the western part of Pangaea.The Appalachian orogeny during the late palaezoic (Pennsylvanian and permian) resulted from the collision of Africa and North America,as part of the collision of Laurasia and Gondwana which resulted in the formation of Pangaea .In eastern N.America the orogeny resulted in the emplacement of massive thrust sheets and folds widespreaded around.This was the final phase of compressional deformation in the Appalachian orogeny.
2) Cyclothems are one of the most important evidence for major transgression and regression sequences in Laurantia during late Palaeozoic especially for Pennsylvanian period.
3) Cyclothems are alterating sequences of marine and non-marine sediments interbedded with coal seams.
The Absaroka sequence comprises of rocks deposited during pennsylvanian during the jurassic.Since cyclothems are characteristic of pennsylvanian rocks so they are evident in apsaroka sequence(illinois basin).Coalbeds containing cyclothems gave an interpretation of the interplay between non marine delta and shallow marine interdeltaic + shelf environment with the marine cycle ending with an erosional surface.Coal beds were formed during the apsaroka transgression in intermarine deltaic (transitional) environment
d)The catskill delta rocks and old red sandstones are clastic wedges formed as a result of acadian orogeny (L.SILURIAN to DEVONIAN) that affected the Appalachian mobile belt .They were formed by sediments shed from the Acadian-Caledonian Mountians into kaskaskia and Baltic seas. Catskill delta is formed by erosion of the acadian highlands with ist red beds inheriting its color from hematite mineral.Old red sandstone is its counterpart found in British Isles.
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