If you return to the image of the large crater that Robert Clark posted, you'll see lots of phreatic cones all along the flow ridges that go round both sides of the large feature.

The main crater is obviously different in size and scale from these and predates the "floods" rather than being syn- or immediately post "flood"

It's a bit big to be a phreatic feature, but could conceivably be a Maar, except the geometry looks more impact-like, IMHO.

The flat floor is due to fill, of course, but fill by what, and when? One could argue all sorts of scenarios.

The best thing to do (as I have done) is to download all the local images and look at the full range of features. Interestingly, there is a "sister" feature to this one with almost identical appearance, including the two breaches in the upstream crater wall at about 2 o'clock and 10 o'clock wrt the incoming flood at 12 o'clock.