re: Let's say it's not limestone
but a martian analog.
What could that be? And could it be partially the product of biology?
What kind of martian biology might be responsible?
Since we don't have any acknowledged martian biota at all, speculation might run rampant, but the signs you're recognizing as possibly due to biology shouldn't be dismissed out of hand. In fact, now might be the best time for rampant speculation.
But there is no reason to expect that Mars life would necessarily resemble anything that's ever been found on Earth.
Cheers, BRFelix