I would like to talk about breakfast for a minute but to do so I will have to take you across Wyoming for a while. I love the drive on St. Rt. 26 from Dubois Wyoming to Riverton Wyoming because the highway takes you by some amazing geology. The Wind River Mountains (like the Bighorns) are the result of a gigantic uplift of really old Precambrian (greater than 600 million year old) granite in the center with all the younger sediments draped on the sides steeply tilting (dipping) away into the basin. Around 10 miles south of Dubois, the massive beds of red Morrison Formation (Upper Jurassic) become quite obvious as hundreds of feet of rusty deltaic muds tower over the right of way. These beds are dipping steeply away from the mountains core as does all of the succession of geologic formations for the next 5 miles to the southeast following the road. Yes, I said 3 miles of tilted beds stacked on top of each other like pancakes. That is over 15000 feet of sediment piled on top of another additional mile of rock sequence stratigraphically below (older than) the Morrison Formation Red Beds. These beds expose on the flank of the Wind River Mountains way above the road and end at the granite core of the Wind Rivers. This makes for a 20000 foot plus thick sequence of sedimentary rocks.
I ask the simple question, was there a 20000 foot thick hole there that filled up with sediment over time? Think about that for a second. That is a really big, thick pile of sediment piled up in a non-repeating sequence of events. Was there a really big hole in Wyoming that was nearly as deep as the deepest abyss in the ocean today?
The answer is simple. No! As the sediment accumulated, the huge amount of weight above pressed down on the rocks below and they simply sank deeper to maintain their equilibrium with the plastic mantle rocks much deeper in the crust. To think of this another way…
I think of the North American Continent like a series of teeter totters. As weight is removed from one location by erosion, transported by water and deposited in another location. Something has to give as the amount of mass is just too large to ignore. This resultant subsidence and subsequent rising of the lands that were the source of heavy sediment is well understood by earth scientists.
Another excellent example of this phenomena is the Mississippi Delta region. The Mississippi River and it’s tributaries drain all of the central continent and all the sediment it carries has built up in the delta area. We now extract oil from river sediment at depths exceeding 35000 feet. Again, there was not a 35000 foot deep hole there.
Is there other evidence? (An attorney says, “never ask a question if you don’t know the answer”!)
Of course, it exists in the Great Lakes. If the part of the country that is unloading sediments is rising (to counter act the lowering of the Mississippi delta) then there should be proof of that. There is! The northern shores of all the great lakes show exposed ancient beaches and the southern shores show submerged beaches. Just as you would expect if you tip your morning bowl of milk and cereal toward you. A ring of milk appears on the side of the bowl away from you and the side of the bowl toward you is about to spill over on your lap. The great lakes are just big bowls of water that are tipping along with the continental teeter totter they are sitting on.
A geologist loves a good breakfast.
Leave A Comment