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).
I would dare say you have NO IDEA what a "one catastrophe" could or could not do, one castatrophy, could have many different compositions weather,deluges,respites,deluges, earthquakes,tremors,earthquakes,eruptions,steamvents,respites, repeat. not to mention how this would effect radiometric decay(unknowable pressures,temperatures,leaching,etc..).multiple strata doesn't demand long ages.
fossil fish scream out rapid burial and preservation/hardening, the are preserved with no sign of decay.