Using the average Flinders Ranges bedrock (234U/238U) ratio instead of an assumed (234U/238U) activity ratio of unity for the source would significantly reduce calculated residence times. the timeframe for 234U and 238U to reach secular equilibrium in a closed system.
Regardless of how the disequilibrium formed, over time the U-series isotopes will tend to return to a state of secular equilibrium so long as the material remains in a state that does not allow chemical exchanges in or out of it, remaining a “closed system”.
The time frame of this process, which is exploited to determine a U-series disequilibrium date, is governed by the shorter of the two half-lifes in any U-series isotope “parent-daughter” pair.
The largest radioactive disequilibria are always found in the youngest materials.
Over time, this signature goes away, eventually relaxing to a condition wherein the disequilibria are no longer detectable.
This result warrants concern for future studies using the comminution approach for which a secular equilibrium source (234U/238U) activity ratio is assumed.