Northern Arizona Stratigraphy
The Grand Canyon is perhaps the best place to get oriented.
It is critical to point out that some layers have significant
lateral variation (facies change) or may vanish entirely.
Others are incredibly uniform and widespread. You have been warned.
Here is a quick run through of the layers (with my own commentary) from
top to bottom:
- Claron formation -- pinnacles at Bryce
- Wahweap / Kaiparowits formation
- Straight Cliffs formation
- Tropic Shale
- Morrison formation fits in here somewhere ...
- Dakota formation
- Entrada sandstone
- - above here found in the Grand Staircase area.
- Carmel formation - found in Zion NP.
- Navajo sandstone - massive cliff former, cross bedded sandstones.
This and the two formations below form the vermillion cliffs,
and is prominent in the Zion area, forms rainbow bridge.
- Kayenta formation
- Moenave formation
- Wingate sandstone fits in here somewhere....
- Chinle formation
- Moenkopi formation - forms odd colored outcrops, not prominent
in the grand canyon area.
- - above here not found in the Grand Canyon proper.
- Kaibab limestone - the top of the Grand Canyon on the south rim.
- Toroweap formation - easy to miss below the kaibab
- Coconino sandstone - forms beautiful white and cream colored
cliffs of cross bedded sandstone near the top of the canyon.
(also present in the Sedona area, but with the Schnebly Hill formation
underlying it in that area)
- Hermit shale - another bench former atop the supai.
- Supai group - actually 4 formations are now recognized,
but few will subdivide this red sandstone layer.
- Redwall limestone - the equivalent of the Escabrosa limestone
in southern Arizona. Forms massive cliffs, stained red from
iron oxides from the Supai above.
- Temple Butte formation - tucked away under the redwall.
- Muav limestone - easy to miss.
- Bright Angel shale - this weak layer forms the wide bench far
down inside the grand canyon.
- Tapeats sandstone - the lowest of the "true layers". This thin
Cambrian sandstone lies unconformably on the vishnu shist in most
places, unconformably atop the grand canyon group where the latter
- Grand Canyon group - much like the apache group in southern arizona,
these are precambrian sediments lying unconformably atop the vishnu schist.
- Vishnu schist - this is the crystalline basement, the nasty dark rocks
that form the inner gorge wherein runs the Colorado river.
Drop me a line!
Tom's Geology Info / firstname.lastname@example.org