As you move up the strata, organisms become increasingly more complicated. However some creationists don't understand the nature of fossils. They claim that fossils should reflect all of evolution. But fossils are only a small fraction of animals and plants that existed. Also the record is biased.
Some species are more likely to be fossilized than others.
Mollusks are more likely than birds or insects. Fossil order presents a problem for creationists because they hold that everything was created at once. They propose that the fossil record is a result of the Flood. The details of how this worked and how humans survived with the animals for the 371 days of the flood are vague. To explain the order creationists say that animals living at the lowest level are found buried there.