Phase 1:
- Water started to erupt from "the fountains of great deep". Similarly as what we can now see for example in Iceland.
- Massive, not impossible, amount of water vapor was released, causing the heavy rain for long time period.
- Water flooding from the fault line (presumably mainly in the area of Mid Atlantic ridge) went to different directions and transferred all loose stuff on the ground. Bible tells there was dust covering earth in the beginning. Probably that dust was moved at the same time with the flood and it was formed to many sedimentary formations that can now be seen in opposite directions from the Mid Atlantic ridge.
- Heavy and long rain was one part of the flood event. It also flushed stuff on the ground, causing and mixing up own different layers.
- The broken original continent begun to sink. This cause compression on the edges of the continent and changes to the sediment layers that were formed by the flooding water.
Phase 2:
- rain and clouds cooled the planet and result was the ice age. Water begun to be collected to glaciers, causing the water level go down and exposing the dry land. Descending water level also caused changes to the fresh sediment layers.
- all sunken stuff were compressed by water, causing the water level to go further down. -> more changes to sediments through erosion. Many flood results would have been eroded from higher areas.
Phase 3:
- Melting glaciers, more smaller flood events to mix up the sediments and cause more changes to the surface of earth.
- Normal rain erosion further cleaning traces of the flood from upper areas, and burying them in lower areas. Fortunately there still are marine fossils on high mountain areas to show that the water indeed covered them at one point.
In Biblical point of view:
1) Everything was good at the beginning.
2) God was rejected and degeneration begun.
3) In earlier time there was not as much mutations, gene pool was "perfect", without errors.
4) At the flood time situation was still relatively good, much better than now.
5) After the flood, DNA are has continued to get weaker, more and more errors in copying. And more other changes also, for example from one bear couple, all modern bears.
That is why you can't see any bottleneck. There simply is no good reason why there should really be one.