Here is where we look for Fossils on Mars

[_Mercury]

One study, published in the July 17 issue of Nature, shows that vast regions of the ancient highlands of Mars—which cover about half the planet—contain clay minerals, which can form only in the presence of water. Volcanic lavas buried the clay-rich regions during subsequent, drier periods of the planet's history, but impact craters later exposed them at thousands of locations across the planet.

http://www.scienceblog.com/cms/diverse-wet-environments-ancient-mars-16908.html

A. I am not a scientist of any kind. I am a former technocrat and fanboy of Geology, that's all.
B. I like Science fiction. There, I said it.
C. Science is a fun speculative hobby. It beats the hell out of Eschatology any day.

Those given, I can now proceed:

Why there? those thousands of possible areas are, if we are lucky Chalk (HAHA!) full of fossils.

Goodbye North Downs (cliffs of Dover), hello Martian "Geologic series 1', Post fossil discovery.