Story ark is refering to 1 story of a larger spectrum. So there will be more halo games but taking place at different time lines with totally different conflicts. Example: Star wars movies is one story ark and Star Wars knights of the old republic is a different story ark of the same universe.
Also just so you know flood = sins , halo = biblical flood Ark = noahs ark , Halo 1-3 = End of days , Truth = false prophet , Gravemind = beast of the end of days , cortana = prostiute of the end of days.
Noahs ark uses the forerunner crystals . One was on reach and later fell in the hands of truth and a second was found on coral. The crystals have special powers. The one found on reach could bend time. Using one small shard of the crystal after it was smashed allowed master chief to be leaving to earth 2 days before he left halo. He left halo and then 3 days later left for earth. So for a while master chief was in two places, one on reach and one in space time heading for earth. Eventually the past master chief used the crystal as well and he was only in 1 place again.