Final answer:
The Great Unconformity is the geological feature that separates flat-lying Paleozoic strata from the older rocks of the Grand Canyon Supergroup in the Grand Canyon.The correct option is a.
Step-by-step explanation:
The Great Unconformity separates flat-lying Paleozoic strata of the Grand Canyon from the underlying Grand Canyon Supergroup. An unconformity represents a significant geological break or gap in the geologic record, where rock layers are missing due to erosion or lack of deposition, and the Great Unconformity is a famous example of this phenomenon. It represents a vast span of geological time where deposition ceased, erosion removed previously deposited layers, and then deposition resumed to create the stratification we observe today.
The Grand Canyon has an extensive geological history that is recorded in the layers of rocks exposed in its cliffs and walls, ranging from the Vishnu Schist at the bottom to the Kaibab Formation at the top. The Paleozoic sedimentary units, including formations such as limestone, shale, and sandstone, lie above the Great Unconformity and display a more recent history compared to the older Proterozoic-era rocks in the Grand Canyon Supergroup. This stark contrast between the ages of these rocks makes the Great Unconformity a significant feature of the Grand Canyon's geology.