It is sure that we do not see any fluviatile layers in the delta scarp, and certainly not sandstones. This are layers of ash and were not formed in the delta itself. The pri,ary stratification documents periodic volcanic ash rains. Such rains of differently sized ash particles have consequently also produced differently structured deposits.They occur in huge blocks in the delta -- which is actually the moraine of a former dry ice glacier -- and were transported to this location from outside the Jezero crater. The cracks and gaps in the blocks or tilted slabs are a good indication of such transports.
Two interesting details:
..It is probably a primary depression
in the lower ash layers. A conglomerate-like volcanic boulder has knock through
the lower pack and filled in the resulting cavity.Today only a remnant has
been preserved in the cavity. This cavern with the filling in it must have
been created before the overlying layers of ash were deposited.
It will be continued