Widespread biostrome? at base of Nullarbor Limestone (3500 square miles). Ubiquitous coralline algae, numerous large benthic foraminifers, more abundant mollusks, and local concentrations of zooxanthellate corals 

Age given as late early to early midde Miocene at:
http://www-odp.tamu.edu/publications/182_IR/chap_02/c2_4.htm