Grand Canyon Supergroup
The tilted Precambrian strata preserved in fault blocks beneath the Grand Canyon's Paleozoic — the reason the Great Unconformity is locally an angular one.
Also known as: Grand Canyon Supergroup
Proterozoic — long before animals, a world of microbes and bare rock
The world back then
Deep in the Proterozoic, somewhere between 1.2 billion and 700 million years ago. There is no complex life to see — just shallow seas and basins opening and closing as the supercontinent Rodinia assembles and tears apart, laying down red and purple and green muds, limes, and black lava. The land is bare rock. The sea is where everything is happening, and it isn't much.
More than a billion years later, here you are — warm, breathing air, glancing at those tilted old layers between rapids. The planet ran for a billion years with nobody around to appreciate a thing. You showed up at the exact moment it's possible to lie back and be impressed. So be impressed.
Recognize it in the field
- Typical color
- varied — red, purple, gray, green; black basalt (Cardenas)
- Weathers as
- Slanting, colorful wedges beneath the flat-lying Paleozoic cliffs; quartzites form ledges, shales form slopes.
Look for
- tilted 10–15° and eroded nearly flat
- preserved only in down-dropped fault blocks
- includes interbedded basalt (the Cardenas Basalt)
- stromatolites in the Unkar and Chuar carbonates
How this rock was made
Seas and basins during the assembly and breakup of the supercontinent Rodinia, ~1.25 Ga to ~0.7 Ga.
The setting: marine and basinal (Rodinia assembly and breakup)
~11,500–13,100 ft where fully preserved (Unkar + Nankoweap + Chuar + Sixtymile).
In the rock record
↑ Younger — rests above
↓ Older — sits beneath
Where to see it
Regions: Grand Canyon
- eastern Grand Canyon fault blocks (Unkar, Nankoweap, Chuar areas)
Float past it: Grand Canyon