The striped light gray rocks in the foreground originated from the deep red-colored cliff in the background. How's that possible?
Fallen rocks from the background cliff of Redwall limestone, Grand Canyon. Photo: © Donald J. Rommes. Click on the photo to go to it on the website.
Redwall Limestone is a prominent cliff-forming, cave-making, fossil-containing rock layer in the Grand Canyon. It was formed 340 million years ago from the compaction of countless calcium-rich shells of sea creatures when this part of Arizona was an inland ocean. Typically light gray, iron leaching from rock layers above the Redwall limestone has stained its surface a deep red.
The lower part of Saddle Canyon, at river mile 47, cuts through the Redwall limestone, and large blocks have fallen to the canyon floor here and there. The stripes in the unstained rock indicate regularly fluctuating sea levels when mud deposition in shallower seas alternated with shell deposition when ocean depths were greater.
This photo shows blocks of Redwall limestone lying at the base of a towering, vertical, red-stained cliff from which they fell. The rocks' relationship to each other is essential to the composition and hints at a more extensive geologic backstory.
Comentarios