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Author Question: Describe the geologic history of the Ancestral Rockies. What will be an ideal ... (Read 34 times)

Shelles

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on: Jul 15, 2018
Describe the geologic history of the Ancestral Rockies. What will be an ideal response?

Question 2

How does the Absaroka sequence differ from the Kaskaskia sequence? What do these differences
  mean for the environment of the time? What will be an ideal response?



heyhey123

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Reply #1 on: Jul 15, 2018
Answer to Question 1

During the Pennsylvanian, the southwest part of the North American craton experienced deformation
as a series of fault-bounded uplifted blocks. These blocks formed the Ancestral Rockies, which were
not all elevated at the same time. Uplift of some mountains was more than 2 km along near-vertical
faults, so the overlying Paleozoic sediments were eroded and the igneous and metamorphic
Precambrian basement rocks were exposed. Tremendous quantities of eroded red sediments were
deposed in the surrounding basins.



Answer to Question 2

The Absaroka sequence, from Late Mississippian to Early Jurassic, overlies the Kaskaskia sequence
from Middle Devonian to Middle Mississippian. The sequences are the result of different tectonic
regimes. The Pennsylvanian rocks have cyclothems, indicating that sea level rose and fell repeatedly.
Ice sheets on Gondwana grew and melted, causing sea level to fall and rise.



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