Radiometric dating
The Margaret Formation comprises sandstones, sandy siltstones, clay-rich sandstones, coal seams and clay-rich coal seams and volcanic ash beds. The thickness of the formation, which overlies the Mount Moore Formation, reaches about . Radiometric dating of the formation provided ages of 52.6 ± 1.9 Ma (2010) and 53.7 ± 0.6 Ma (2017).