Three time lines through the neritic stratigraphic record distributed around the northern margin of the Australo-Antarctic Gulf (AAG) mark three fundamental shifts in global environments collectively comprising the Auversian facies shift. The three lines are: (1) the beginning: the Khirthar transgression and the onset of neritic carbonate accumulation in the Bartonian Age (preceding onset of the Middle Eocene climatic optimum [MECO]); (2) the midlife change (Bartonian-Priabonian transition): the shift from carbonate-rich to carbonate-poor, higher-nutrient environments under estuarine circulation, causing widespread dysaerobia culminating in opaline silicas; and (3) the Eocene-Oligocene = Priabonian-Rupelian boundary and glaciation during oxygen isotope event Oi-1, with return of improved ventilation in neritic environments and resumption of carbonate accumulation. Meanwhile, it was warm and very wet at ~60°S. In developing a scenario for the death of the AAG, the birth of the Southern Ocean, and the transition from Paleogene greenhouse Earth to Neogene icehouse Earth, the neritic record of the northern margin is more in accord with the “Dinocyst biogeographic hypothesis” than with the “Tasman gateway hypothesis.”