One sees a landscape which was under water. It requires imagination.....yet it was..under water : )
This is not the easiest concept to grasp. The Lone Ranger and his trusty steed are standing upon, and looking out at, highly eroded sedimentary rock. Monument Valley, Utah, for example is described thus :
The elevation of the valley floor ranges from 5,000 to 6,000 feet (1,500 to 1,800 m) above sea level. The floor is largely siltstone of the Cutler Group, or sand derived from it, deposited by the meandering rivers that carved the valley.
The valley's vivid red color comes from iron oxide exposed in the weathered siltstone. The darker, blue-gray rocks in the valley get their color from manganese oxide.
The buttes are clearly stratified, with three principal layers. The lowest layer is the Organ Rock Shale, the middle is de Chelly Sandstone, and the top layer is the Moenkopi Formation capped by Shinarump Conglomerate
Therefore, at some time this sedimentation occurred under water - fresh or sea. The altitude of up to 6000 ft precludes this sedimentation occurring in the "400 ft sea level rise" era. So, what actually happened?
Possibilities include :
1) The water was 6000 ft high. But how did the sedimentation occur which caused the eroded peaks?
2) The water was always much the same as now (+400 ft or so). Again, how could these peaks have occurred?
3) There has been upthrusts which pushed the sedimentary rock up to 6000 ft. Again, difficult to conceive the dynamics involved in the sedimentary phase with precipitation on dry land causing run-off of silts, sand etc and resulting in what would have been virtually an underwater landscape similar to what we now see minus wind erosion.
4) Other explanations.
Hi, Ho Silver. Away!
Edited 1 time(s). Last edit at 29-Oct-15 21:53 by loveritas.