Also, the Bible says that the rain and water from underground continued for 40 days and nights. Now imagine sediments continually being added to the water for 40 days and nights.
1) You have the sediments continually making layers for this time period.
2) And you have hydrologic sorting of the animals when they died.
In case you are not sure what hydrologic sorting is. Ponder this question. If you drop a mouse and a elephant in the ocean, which would reach the bottom first? You would normally think the elephant would because of it's weight, right? But there are several factors that determine the out come.
3) Size. More water has to move around a big animal, which would slow up the process of getting to the bottom.
4) If said animal floats, how long until it starts to sink after death?
The other factor to hydrolic sorting, and how the sediments worked for the flood. Is that bottom dwellers would end up covered first along with any life that happened to be down there when this happened. And because they would not have been dead yet. A lot of the fossil record would have shown this.