19 June 2015
Friday fold: subglacial drag fold (Pleistocene) in Cretaceous sediments, Alberta
Posted by Callan Bentley
Howard Allen, a retired petroleum geologist from Calgary, and longtime reader of this blog, contributed this week’s Friday fold:
Subglacial drag fold (Pleistocene) in Upper Cretaceous Horseshoe Canyon Fm. bedrock (sandstone, shale).
The locality is SE of Drumheller, AB at UTM 12U 394247 5692469 (WGS84).
Glacial drag fold in bedrock, Hwy 573, east of Willow Creek Hoodoos, SE of Rosedale, Alberta
Did you hear that right? Yes, you did: This is Cretaceous aged sedimentary rock, folded by a Pleistocene glacier, tens of millions of years after it was deposited. And a massive tongue of ice did it!
Here’s another perspective on the same fold, looking roughly along (regional) strike to north, the direction from which the Laurentide ice sheet moved:
Glacial drag fold in bedrock, Hwy 573, east of Willow Creek Hoodoos, SE of Rosedale, Alberta
A very happy Friday to you!
Callan Bentley is Associate Professor of Geology at Piedmont Virginia Community College in Charlottesville, Virginia. He is a Fellow of the Geological Society of America. For his work on this blog, the National Association of Geoscience Teachers recognized him with the James Shea Award. He has also won the Outstanding Faculty Award from the State Council on Higher Education in Virginia, and the Biggs Award for Excellence in Geoscience Teaching from the Geoscience Education Division of the Geological Society of America. In previous years, Callan served as a contributing editor at EARTH magazine, President of the Geological Society of Washington and President the Geo2YC division of NAGT.
Beautiful images there!
It seems that the rock was under the simple shearing when forming. That is, passive folding might be the major fold mechanism here.
In this case, it could belong to Class 2 folds (Similar folds).
(brief ideas from the photos)