what materials are needed for a imprint fossil to form?

Answer 1

A fine grained, soft sediment like clay (sand will also do it but you get a much poorer imprint).

Something to cement the sediment together.

The organisms remains.

Answer 2

Water deposited sediment. Which means it is buried rapidly because only rapidly moving water can carry sediment. Then there has to be a hyatus or a pause in the sediment deposition producing a fine grained flat layer. Then animals walk over this. In Germany where the famous fossil bird Archaeopteryx was found they used it for carving for printing plates called lithography. To produce fossil tracks you need fing grained sediment mixed with volcanic minerals and lime to harden rapidly into rock. Then you need softer sediment to shower down on it like volcanic ash, and/or be carried by slower moving water. Then all these layers become lithafied (harden into stone).