Inverloch – Bunurong coastal cliffs and marine platforms

The site of the excursion was accessed from The Caves carpark. It is about 6 km. south-west of Inverloch on the scenic coast road to Cape Paterson, and within the Bunurong Marine Park.

From the top of the cliff in the carpark could be seen the entrance of Anderson’s Inlet into Bass Strait with the sand spit of Point Smythe bordering the further side of the entrance. Beyond that the broad sweep of Venus Bay arcs around to the east, terminating in Cape Liptrap, beyond which lies Wilson’s Promontory. Below this vantage point lay the coastal cliffs and marine platforms of 120 million year old Cretaceous freshwater sandstone, mudstone and conglomerate sediments, although the tide covered much of the marine platform.

From the beach the sediments in the cliff face appear to be gently dipping to the north-east and are transversed by numerous nearly vertical faults. At one prominent fault plane the bending of sedimentary layers downward indicated that the north-easterly section had moved upwards relative to the south-westerly section’s downward movement, and showed a section of greatly shattered rocks. Similar fault planes along the cliff face indicate this is an area where step faulting has occurred.

There is much evidence of fossilized wood: some resembles black coal formed as a result of heat and pressure, while other wood fragments have been infilled with calcite to give a yellowish appearance. On the marine platform were a couple of large fossilized tree stumps, presumably of conifers. Most of the cliff and marine platform exhibit faulting and joint planes (a crack in which there has been no movement). Some of these have acted as sites for calcite to crystallize, while others have allowed iron rich minerals to permeate a little way into the adjoining sediments. In one location rock boulders containing small crystals drew attention to a dyke of basalt in the base of the cliff face.

Information boards alongside the track from the carpark to the beach had already provided information on aspects of the Museum Victoria and Monash University’s joint dinosaur dig site, which although only operating during low tides mostly in February of most years, has yielded thousands of bone fragments. While to recognize bone and identify them is a highly skilled activity, many of them have been identified as being fragments of two legged carnivorous dinosaurs of the theropod group. A number of likely bone pieces did appear as being slightly more brown than the host rock.

The drive towards Cape Paterson gave a stunning overlook on a few more kilometres of coastal cliffs and marine platforms of the Bunurong Marine Park.

Graeme Rowe

Cliffs at Dinosaur Coast