Oh yeah? Who sez?

I continue to maintain that lots of circular formations on Mars are misidentified as impact craters (primary or secondary), so even if an appropriate adjustment factor for Mars could be developed, the dating would still be significantly off.

A fair reading of the surface would suggest that large areas have recently (~100,000,000 years or so) been resurfaced -- either with lavas or with muds (which would operate similarly to lava under Martian surface conditions.) Many of the formations identified as impact craters may be the result of bubbling of volatiles on the surface. Many others may be vents from the interior (especially in Acidalia).

All of this indicates a significantly warmer and more active near-surface interior than some in the field are willing to allow for. Of course until we actually see some surface activity caused by interior forces -- and that activity is accepted for what it is -- it will be hard to change prevailing perceptions.

As for those secondaries, it is fairly obvious that enormous numbers of secondary craters sometimes result from impacts into Mars. But it doesn't alway happen, and even when the identification of a crater is positively from impact, it can still be difficult/impossible to be sure the impact was primary or secondary in some cases.

Cheers,