11. What is the nature of the boundary between the Redwall Limestone and the Sup
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11. What is the nature of the boundary between the Redwall Limestone and the Supai Group? PARD One of the best-kept secrets of the US Park Ser vice is Grand Canyon National Mionument Locatec downstream from Granc Canyon National Park, the monument area displays a dramatic close-up view of the Grand Canyon/ sev 12. What was happening geologically in the Grand eral episodes of faulting, and a spectacular display of recent as well as ancient volcanic activity includ- ing a lava cascade that spilled into the Grand Can yon adjacent to Vulcan's Throme and is preserved Canyon during the Ordovician Period? now as a frozen lava fall At this location, it is possible to apply the rules of relative dating to reconstruct the local geologic history with great clarity. Superposition and cross cutting relations are clearly illustrated by the geo- logic relationships that can be observed in the rocks of the monument area. AaExplanation / Answer
Introduction:- The Redwall Limestone and the Supai Group belongs to the Grand Canyon range of rocks that age back from Proterozoic to Permian.
Stratigraphy:- There are 14 major unconformities in the stratigraphic section exposed in the Grand Canyon.
Here we discuss the boundary ( Disconformity) between the two stratigraphic divisions of Grand Canyon namely Redwall Limestone and Supai Group which age back to Mississippian and Pennsylvanian respectively.
Redwall Limestone comprises of sedimentary strata that include rock units like thick-bedded, gray limestone and dolomite with white chert lenses forming a cliff onformably overlain by Supai Group of rock divisions Pale red sandstone, siltstone and red shales forming ledges or cliffs.
The unconformities within the Paleozoic section, such as the one between the Mississippian Redwall Limestone and the Pennsylvanian Supai Group, are disconformities. This boundary is significant for the occurrence of Paleosols (ancient soil horizons). Disconformities form in response to the lowering of sea level.
Tectonics:- Tectonically these formations are the reult of Marine Transgression and Regression of the North Amercian Craton. Numerous normal faults dissect the Grand Canyon region. These faults formed in response to extensional tectonics associated with formation of the Basin and Range.
Geologic History:- Deposition of the Redwall Limestone, a marine unit, during the Mississippian marks a rise in sea level. A drop in sea level at the end of the Mississippian resulted in subaerial exposure of the Redwall Limestone and the development of an ancient karst landscape. The Pennsylvanian through Permian Supai Group was deposited in a delta to near shore beach environment.
Conclusion:- The boundary between The Redwall Limestone and Supai Group is a Disconformity- the unconformity formed in response to the lowering of sea level. The boundary with conglomeratic units that derived by the marine transgressions and regressions during the late paleozoic period pass through Supai Group which was deposited in a deltaic environment.
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