Sorry, geological evidence just doesn't accomodate one mass extinction. The fossils are deposited in multiple strata separated by hundreds of millions of years. Radiometry and sedimentation analysis of the surrounding rocks prove this. One catastrophe could not deposit huge numbers of layers of dirt, instantly condense them to rock, then deposit more layers of dirt that instantly turn into rock, etc. Not to mention that each strata in the column give radiometric dating rates that correspond to gradual accumulation. And the fact that particular fossils are only found in the appropriate strata (no method of deposition can explain that).
It sounds like you are reaching. For there to have been only one flood, many physical laws would have to be suspended. There is no way for creationists to explain the dating differences of the layers combined with the types of fossils found in the layers. The separation of fossils is not along any lines that make sense if you assume a single catastrophic event.
If you want just so stories, consider the various speculations by the so-called creation scientists. They not on make up just-so stories, they suspend just about all we know and accept of a number of physical laws including the Second Law of Thermodynamics.
Many extreme pressure tests have been conducted on radioactive materials. No significant changes to their decay rates have been found, certainly nothing that would result in errors as large as creation supposes. Have you considered the enormous heat that would result from increased decay rates? If decay rates of any of the materials used in radiometric dating were fast enough during the flood, the energy released would have boiled the oceans and every living thing on the ark. At the end, there would be no water left (the heat would break the water molecules apart and most of the hydrogen would escape) and no life left.