The Southern California Public Radio news item What Cassini saw on Titan: 'Dunes of the Arabian desert' but made of water chips, not sand explains:
"Little chips of water ice come off (the mountains) and get washed downstream, and then they get pushed up onto the beaches," Ray said. "They get dried out and then they get picked up by the wind and blown into the deserts. And around the entire equator of Titan is nothing but dunes as far as the eye can see -- just like the dunes of the Arabian desert. But they're made out of little chips of water covered in hydrocarbon goo."
According to the article, Trina Ray is the Titan orbiter science co-chair at JPL.
Question: What is the evidence that the dunes of Titan are made of "water chips"?
below: Dune patterns on Titan, pia15225 from NASA JPL. Click for full size. Despite the names, these represent various imaging techniques by Cassini of dunes on Titan. There is a much longer description in the pia15225 link.