I think you may be misunderstanding some things about Noah's Flood. Go back to Genesis 2:5-6. You will find that water was coming up from the ground to water the earth. Water does not go UP unless it is under pressure. That means there was pressure under the surface of the earth. Pressure means heat.
We know that the original earth (whatever its age) did not have radioactive materials on the surface. They are heavy elements and were concentrated in the mantle and below. In addition, at the beginning, both short and long half life elements were decaying. The heat was building in the interior of the earth and was enormous. It was driving the water out of the serpentine (13% water) and pooling it, leaving olivine (serpentine with the water driven out by heat, which is a major mineral in the mantle today). If you look at Genesis 7:11, you will notice that the first thing that happened was a bursting forth of ALL the fountains at the same time. This means that the heat/pressure had reaching a critical point beneath the crust and that the explosions of water upwards were violent in the extreme. To compare them to a tsunami of today is like comparing a stone skipped in a pond with a tsunami.
These waters exploded upwards and a number of ancient legends tell us that the waters were scalding hot, burning everything they touched. The exploding waters would have torn up and pulverized great amounts of crustal materials. The materials and the water would have gone much higher than our volcanoes of today, cooled, condensed, and come down as a rain of water and debris unlike anything we have ever even imagined.
The evidence for this lies beneath the Cambrian strata. There we have, two major strata from the Flood. The lower is a cobbled layer of rocks, boulders and all sorts of sizes of stuff in a cement-like matrix. These are called diamictites, or tillite. This was the first effect of the Flood. Then, on top of this, over two miles thick in places, is a carbon-rich sedimentary layer. This is the muds and debris from a destroyed world. No fossils.
Fossilization occurred later.
And, contrary to your assertion, the actual replacement of biologic material with minerals cannot be seen to happen today. I have a friend who is a microbiologist who has been involved in experiments for at least ten years now trying to create conditions which would cause fossilization. Neither he nor anyone else can do it.
It is easy to make imprint fossils. I can do that with jello! And we do see mineral encrustation happen fairly quickly. But these are not what we have tried to accomplish. The actual replacement of living, or post-living, matter with minerals is something that required extremely specialized conditions which we have not yet been able to imitate.
The trees at Mt. St. Helens have not yet petrified. However we have seen rapid coalification take place on the bottom of Spirit Lake where the trees are.
http://www.grisda.org/origins/10009.htm
http://www.cnt.ru/users/chas/sthelens.htm
Those links are both excellent articles on what happened at Mt. St. Helens