ABSTRACT
The Ordovician sequence in the Melbourne region consists of a sequence of marine, quartz-rich, turbiditic sediments deposited in deep, quiet water of the Melbourne Trough. Lower to Upper Ordovician sediments occur in the Melbourne region at Darraweit Guim, and on the Mornington Peninsula. In general, the Ordovician sequences are quartz rich in comparison to the Silurian sequences, and the Ordovician is notable for the occurrence of black shales. Shales commonly occur in the Ordovician and are rarer in the Silurian. The Board of Works Frankston Tunnel at Baxter, excavated as part of the South East Effluent Outfall , intersected the Ordovician sequence. The Ordovician sequence in the Melbourne region is folded, faulted and intruded by sills and dykes. Igneous intrusive rocks, mostly as sills, and to a lesser extent dykes, were frequently intersected by the tunnel. The sills range in thickness from 1 m to 24 m.
