A couple of inches of gravel and/or sand over hardpack is our usual riding surface here in Western Australia. It’s called ‘pea gravel’ and can be described as like riding on ball bearings over concrete!
We don’t have much choice so we choose the best tyres for the conditions and adapt our riding style accordingly (don’t make any sudden changes of direction!)
But to answer the question, Maxxis Ignitor or Ardent front in a 2.3 width, matched to a 2.1 Crossmark on the rear is a very common choice, as its the front wheel washing out you have to worry about on gravel. The Ignitor is a bit more surefooted, but the Ardent faster. Both let go in a reasonably predictable fashion. I’ve run both tubed and tubeless, and it doesn’t make much difference, although I’m all tubeless now but that’s for pinch-flat prevention.