tectonics & quarries
We've been in multiple quarries, farms, and roadcuts, looking at the results of having a carbonate bank shoved up and west by plate tectonics. This place is almost a munged up as California is. It just happened longer ago, and was by thrusting instead of by grinding.
The quarry geologists seem happy to let us in. They seem to learn as much from our faculty as we all learn from the quarry, so I guess that's a win/win situation. It is certainly easier to visualize what's going on when you have a nice clean slice through it. But I do have a bit of a problem with the fact that we are benefiting from these huge open pit mines.
I enjoy the fact that our faculty (from all our local colleges) are so willing to ask each other questions about things outside their geological specialty. (It's a nice model for the students.) And I love the fact that our faculty are so eager to understand and so eager to help others understand.
So: There was a big old carbonate bank off the east coast of North America, and it deposited lots of limestone and dolomite. (Many people think that limestone turns to dolomite well after deposition, but the rocks here make a pretty good case that if it's "after" it must be a very soon after.) It was a passive continental margin, but then something started moving toward the coast. This "something" was probably kinda like Madagascar off the coast of Africa, and I've been trying to figure out what relationship it might have with Avalonian Terrane (which Mark has been correlating up and down the east coast), but the faculty member I asked did not know.
This collision caused the carbonates to be deformed like crazy and shoved up on top of the older existing rocks, creating some spectacular folds, and lots of metamorphic rocks that get certain members of the group really excited.
For me the best outcrop was alongside a school, where we saw a slope on the carbonate bank that had undergone a landslide, and we could follow the sequence from top to bottom. The other best was a spot where one face of the vertical outcrop looked like a bunch of flat boulders in layers, and then we walked around the corner and saw that all these supposedly disk-like boulders were an illusion. They actually due to directional weaknesses in the rock caused by deformation (cleavage) that actually sliced across the pre-deformaiton bedding planes.
We'll get more of the story tomorrow.
The quarry geologists seem happy to let us in. They seem to learn as much from our faculty as we all learn from the quarry, so I guess that's a win/win situation. It is certainly easier to visualize what's going on when you have a nice clean slice through it. But I do have a bit of a problem with the fact that we are benefiting from these huge open pit mines.
I enjoy the fact that our faculty (from all our local colleges) are so willing to ask each other questions about things outside their geological specialty. (It's a nice model for the students.) And I love the fact that our faculty are so eager to understand and so eager to help others understand.
So: There was a big old carbonate bank off the east coast of North America, and it deposited lots of limestone and dolomite. (Many people think that limestone turns to dolomite well after deposition, but the rocks here make a pretty good case that if it's "after" it must be a very soon after.) It was a passive continental margin, but then something started moving toward the coast. This "something" was probably kinda like Madagascar off the coast of Africa, and I've been trying to figure out what relationship it might have with Avalonian Terrane (which Mark has been correlating up and down the east coast), but the faculty member I asked did not know.
This collision caused the carbonates to be deformed like crazy and shoved up on top of the older existing rocks, creating some spectacular folds, and lots of metamorphic rocks that get certain members of the group really excited.
For me the best outcrop was alongside a school, where we saw a slope on the carbonate bank that had undergone a landslide, and we could follow the sequence from top to bottom. The other best was a spot where one face of the vertical outcrop looked like a bunch of flat boulders in layers, and then we walked around the corner and saw that all these supposedly disk-like boulders were an illusion. They actually due to directional weaknesses in the rock caused by deformation (cleavage) that actually sliced across the pre-deformaiton bedding planes.
We'll get more of the story tomorrow.