Carmel Formation
The Middle Jurassic marine-and-gypsum base of the San Rafael Group — the sea's return over the Navajo dunes, below the Entrada.
Also known as: Carmel
Jurassic — the golden age of dinosaurs
The world back then
Middle Jurassic, around 165 million years ago. The great Navajo desert has finally drowned — a shallow, salty sea has flooded back over the dunes, leaving warm lagoons, tidal flats, and crusts of gypsum baking at the edges. It's hot, briny, and shallow, the water coming and going with the tides. Shellfish litter the muddy bottom under a hazy sky.
You drift over that old lagoon now, the whole flood-dry-flood saga sliding by in an afternoon. The sea couldn't make up its mind for a million years; your trip is decisive and short. It's easy to take for granted, but a comfortable pass through 165 million years of someone else's weather is about as lucky as a body gets.
Recognize it in the field
- Typical color
- pale red to brick red, gray, greenish; white gypsum
- Weathers as
- Soft, banded slope-former between the Navajo slickrock and the Entrada; its harder oolitic limestones cap domes (Capitol Reef's 'Golden Throne').
- Grain
- sandy to dense limestone; silt-clay mudstone
Look for
- pale marine limestone, oolitic in part
- brick-red gypsiferous mudstone
- contorted white gypsum beds
- marine fossils in the limestones
- sits on the Navajo across the J-2 gap
How this rock was made
A Middle Jurassic sea (the Carmel/Sundance seaway) flooding back across the former Navajo sand sea (erg), with periodic terrigenous input.
The setting: shallow marine to salty coastal flat (tidal sabkha)
GeoLex: 50 ft (mouth of the Dolores River) to 650 ft (San Rafael Swell); Wikipedia gives up to ~1,000 ft.
In the rock record
Part of the San Rafael Group.
↑ Younger — rests above
↓ Older — sits beneath
Where to see it
Regions: Colorado Plateau