probably younger.----less sediment would mean less time.
Layers of cross-bedded sand can be indicative of a DESERT environment wind is responsible for the formation of these sedimentary structures. Sand dunes preserved in rocks can be quite large. These structures form as a result of the migration of dunes due to the action of the wind. Dunes are not often preserved but a few can be observed in thick sandstone units.
C. Flood protection is the answer
