Kaibab Limestone
The cherty gray Permian limestone that caps the Grand Canyon's rims — the youngest Paleozoic layer, laid down in a warm shallow sea.
Also known as: Kaibab, Kaibab Formation
Permian — vast deserts, ending in the worst extinction ever
The world back then
Permian, about 278 million years ago. A warm, shallow sea — the Kaibab Sea — spreads across the region, its floor a soft lime ooze full of shells, sponges, and swimming things. Clear, tropical, and calm out west; briny and restricted to the east. The last big sea before the whole place turns to red desert.
That old sea floor is the rock you stand on at the canyon rim — and down here you're gliding along beneath the whole thing. The sea packed up and left; the river stayed behind and cut you a seat with a view. Being the animal at the pleasant end of that story is a quiet, enormous stroke of luck.
Recognize it in the field
- Typical color
- cream to gray-white
- Weathers as
- Cliff- and ledge-former — the canyon rim rock; cherty beds weather into recesses along the cliff face.
- Grain
- fine- to medium-grained
Look for
- cherty (chert from siliceous sponges)
- carbonate-rich westward, sandy/dolomitic eastward
- two members (Fossil Mountain, Harrisburg)
- forms the flat, forested rim benchland
How this rock was made
A warm Permian sea (open-marine west, restricted east); the upper Harrisburg Member records the sea's retreat.
The setting: warm, shallow just below the tideline (subtidal)-to-shallow-marine sea (the Kaibab Sea)
300–400 ft at the Grand Canyon.
In the rock record
↑ Younger — rests above
↓ Older — sits beneath
Where to see it
Regions: Grand Canyon / Colorado Plateau
- both Grand Canyon rims
- the Kaibab Plateau
- widely across the Colorado Plateau surface
Float past it: Grand Canyon