You are surrounded by evidence of geologic change taking place over millions of years. Can you stop the evidence for an ancient sea, a large cave, tropical climate and continental drift?
Madison Limestone and Kibbey Shale
The steep limestone cliffs rising up form Belt Creek in front of you are composed of seashell deposited about 330 million years ago when this area was below sea level and covered by a vast sea. Slow uplift caused the area to rise. 325 million years ago, it was above sea level. At that time this area was close to the equator when red tropical soil washed into fresh lakes on a large coastal plain.
Look at the bright red Kibbey Shale in the roadcut behind you – evidence of a much warmer climate than today. Continental drift and plate tectonics moved Montana to its present location, and caused the area to be uplifted above sea level and subside below sea level many times since the red Kibbey Shale was deposited.
Each time that Madison Limestone was uplifted above sea level, ground water percolated through the cracks and dissolved out a large network of tunnels and caves. When the land subsided, many of these caves collapsed. The limestone beds or strata beneath you are strongly tilted because there is a large collapsed cave underneath.
The calcium carbonate deposited in those seas accumulated to as much as 2,000 feet thick in parts of Montana. Limestone is easily soluble in rainwater, which is normally slightly acidic because of the reaction between water and carbon dioxide in the atmosphere, which makes carbonic acid. Even in arid country like Montana, caves can develop.Lewis and Clark Caverns, Montana, (You can see the earthcache @ GC3T80G) is an example of a cave developed in the Madison. The rocks were deposited in a generally shallow marine setting, indicated by the richly fossiliferous rocks of the Madison. In the Williston Basin, water was shallow enough for oolite shoals to develop; they later became reservoirs for oil. The gray cliffs along the Missouri River in the Gates of the Mountains, Montana are formed by Madison Limestone.
The Madison Limestone is the largest artesian aquifer in the US. Most of the groundwater that enters this formation in the Little Belt Mountains comes out at Giant Springs State Park, 30 miles NW as the crow flies. (You can see the earthcache Giant Springs of Great Falls @ GC5AE8G)
To log this Earthcache please e-mail the answers to the following questions. (Please do not post answers in your log.)
1. How do you think the cave was form in this location?
2. What do you think caused the cave to collapse?
Optional: Post a picture of you with belt creek in the background, preferably from the overlook.