On the Rocks presents, When the Colorado flowed through Montana to Canada's Labrador Sea: New evidence from detrital zircon correlations

Dr. James Sears will be sharing his latest research –

The origin of Grand Canyon is still debated. Where did the Colorado flow to the sea when it first started cutting the canyon? Where was its delta? New evidence shows erosion was deeply dissecting the canyon and Colorado Plateau for 20 million years before the first grain of sand reached its modern delta in the Gulf of California. The Gulf didn’t even exist until the canyon’s Inner Gorge was incised.

I propose that the missing delta is way up north in Canada’s Labrador Sea. Luke Beranek of Memorial University and I sampled sand cuttings from a deep exploration well in a giant delta in the Labrador Sea. The sand was deposited when early Grand Canyon was eroding. We extracted zircon sand grains from the cuttings and U-Pb dated them at the University of Arizona Laserchron Lab. We found that, indeed, groups of the grains matched potential sources in the southern Colorado Plateau.

The river was the scale of the Amazon, and would have flowed south to north across Montana, either through the course of the ancestral Missouri or Yellowstone. The gigantic river was destroyed by tectonics, volcanism, and continental glaciation. But evidence remains in tiny zircon sand grains.