1. North Wall of the Grand Canyon
Paleozoic
Pre-Cambrian
SLIDE 15
Here I’ve added some interpretation of the stratal layering
In the bottom half, strata are dipping down towards the right (east)
These are pre-Cambrian aged rocks
On the top of the wall, the layers are nearly horizontal
About midway down there is a change in the dip of the strata – marked by the magenta line
This is a classic angular unconformity
We can deduce the following geologic history:
The pre-Cambrian rocks were deposited horizontally near sea level
There was a tectonic event that tilted the area down to the east
When sedimentation resumed, the Paleozoic rocks were deposited horizontally near sea level
More recently, the whole area is uplifted without tilting since the nershore Paleozoic rocks are now 7000 to 8000 ft above sealevel
The angular discordance between the Pre-Cambrian rocks and the Paleozoic rocks marks an unconformity that separates
an older stratigraphic package from a younger stratigraphic package
The angular discordance between the Pre-Cambrian rocks and the Paleozoic rocks marks an unconformity that separates an older stratigraphic package from a younger stratigraphic package
Courtesy of ExxonMobil
L 11 – Stratigraphic Analysis