Actually this looks like a harder layer (upper surface) displaced during the impact. I'm positionally challenged but assuming from Hortonheardawho's comment that this is near Concepcion this would be displaced ejecta. The layer could well have parted during the displacement event, the effects of shock are really complex and the most unexpected results can occur. Or as $.02 worth says, the underlying layers could have been reduced to dust - possibly having been badly fractured during the disruption.
And can't we now lose the inference that models for Meridiani are somehow wrong due to the amount of erosion over a few thousand years. Even JPL no longer espouse their initial shoot from the hip statement of a thousand year old crater.