Man, tough crowd !
Why wouldn't it be possible that there were spherules at these landing sites? Do these sites correlate to zones of known hematite distribution now mapped from orbit? The third image posted by Chris below, while lacking enough resolution, is at least suggestive of particles or spheres with a narrow size distribution (the fine material). I too wonder about the extent of these tiny but indicative spheres and their associated sediments. Being so round, they may have redistributed widely in times of higher atmospheric pressure and wind.