One the top chart it should include both lines and also be the cause of the ice in the south melting. The Traps spilled out a known amount of magma and the temp can be estimated and the heat released into the air can be calculated but not gas change unless Greenland or the Antarctic ice cores go that far back
Since the last global ice age 650M the south has had ice when the north was ice free it is possible that the crust was warmer without lava breaking through to the surface and the heat radiated by the traps took about 100M years to cool down and the temp seems to have balanced out so north and south experience the same changes at the same time. The oceanic crust dates back 200M years and the spreading in the north created more area than in the south. With just a quick look at the rock formations in BC and the east side of the Mississippi the formations are in the same direction as the Atlantic Rift and the Pacific Rift.
The AB/BC border should be where the rift broke through the surface, prior to that it could have moved all the way from the Great Lakes is the land formations allow that. The C. Shield could have been a Siberian traps type of event only much earlier. The Great Lakes and Hudson Bay would have been the up-flows (same with the Gulf of Mexico) and when that stopped and the cooling took place the holes were created. If the Yellowstone caldera was by the Great Lakes way back then it was on its way to becoming the next lake in a chain.
Since I have my doubts about ice carving the holes for a few reasons those lakes would have been up flows and cooled and shrank. Same with all the lakes in Canada’s north.
A retreating glacier would leave gravel bars like there is in AB. When ice is 1 mile tall and moving to the ocean the ice would break where the beach is and only the ice higher would move until the sheet melted. The peaks would be cut off and
The theory behind that would also have to be the answer to the ‘cart ruts’ found in a few locations in/near Germany. If the surface bock was magma flowing up of the ground cracks that match the ruts then when the flow stopped and the cooling started the magma in the cracks would shrink more than the rock that was fractured rather than melted.
In the 2nd chart 250MYA would be the dip in ice, if all that heat was needed to change it that much what changed it 125MYA as 2x as much sea-ice was gone. Another Siberian traps event only the surface rocks only got warmer without breaking apart. The pressure being spread out under a larger surface only has 40,000 miles of oceanic rifts spreading a 1”/yr, or take a few more.
If they ever stop and the earth wants to contract it will be the crust above where the magma already descends, it will dip more and eventually break and the crust will end up being vertical rather than horizontal like it is today
The ‘snowball’ part should have been when we gained all the ice that is now the water we have. It came in so thick that it could not be melted in real time, 2x rather than 1 if that is the whole history.
I will probably want to add to this.