Zipper in the Sky

Please, help: What did I photograph in this photo...??
I took this image a few days ago at the time of sunrise. The skies were just coming alive with colors, somewhat separated by the layers of high clouds. When I looked through the zoom lens, I noticed the strange, band of clouds stretching all the way across the top of the image, resembling half a zipper.
I have been photographing clouds for quite a few years by now (FYI: I even published a book about my favorite subject - "Clouds" at blurb.com"), but I cannot recall having ever encountered such a pattern before... Does anyone know what this is...??
Thank You!

Nikon D 850 w/70-300mm lens and Polarizing Fliter

Minor adjustments in LIGHTROOM