Satellite overview of the tortured curves of Lerderderg Gorge carved out by ice sheets.

While the Earth has seen numerous Ice Ages, only one has affected Victoria

While the Earth has seen numerous Ice Ages, only one has affected Victoria

Roughly 400-500 million years ago, the sea covered the area, allowing sand and mud to be deposited. After the sea withdrew, uplifting occurred, forming north-south running mountain ranges. This was followed by a long period of erosion. Approximately 250 million years ago, glaciers formed and as they moved over the land they exposed large granitic rocks. Rubble was deposited in the valleys and conglomerates and sandstone were deposited in the lakes and rivers that were created as the glaciers melted. These are some of the earliest glacial deposits known to exist in the world, adding to the geological significance of the Bacchus Marsh area.

During the Permian (299-251 million years ago) Victoria was located at much higher latitudes (near the South Pole), attached to a giant landmass called Gondwana (see reconstruction). Gondwana itself was one of two land masses that formed the super continent Pangaea. The early Permian was a time of glaciation, with giant ice sheets covering the southern-most parts of Gondwana, including Africa, America and Australia. While the Earth has seen numerous Ice Ages, this is the only confirmed glacial episode that affected Victoria. And two of the few places that exposes evidence of it ever having occurred are in the Lerderderg Gorge and at Lake Eppalock (100km to the north).

How did these internationally significant geological features re-emerge into the light of day after being buried for hundreds of millions of years under layer after layer of sandstone sediments?

Powerful as the glaciers were, it was the erosive force of water – not ice – that formed the Lerderderg Gorge. Around 210 million years ago, a large river flowed through the area. In 1873, the Bacchus Marsh Shire quarried a small pit at what has become Triassic Park, a site of registered geological significance. Exposed in the Council trench were extremely rare evidence of plant fossils along with a swirling pattern in the sandstone made by the river’s movement. The Triassic Park Reserve is well worth a visit to read interpretation signage about the glaciation event in Lerderderg Gorge. Actual evidence of glaciation can be seen across the road in the walls of Korkuperrimul Creek, opposite Triassic Park.

At the mouth of the Lerderderg Gorge, there’s more evidence of the glaciers’ scouring of the landscape. One million years ago, an uplift along what is known as the Rowsley fault blocked the path of the Lerderderg River, forcing it to cut down through the sandstone. Eventually, 300 metres down, the flowing water reached the scratched and polished sub-glacial pebbles and boulders that you can see embedded in the outcrops at the southern end of the gorge.

Plants and wildlife flourish in the park’s wide range of habitats. The 14,250 hectare Lerderderg State Park varies from the fern-lined river’s edge to damp forest pockets and dry rocky outcrops along high ridges. More than 320 native plant species have been recorded in the park, with 11 species regarded as either rare or threatened. Unusual associations of blue gum and manna gum flourish in the gorge.

So far as wildlife, the park plays host to 125 native bird species including rare peregrine falcons nesting in the rocky hills and powerful owls, whose distinctive ‘whoo hoo’ call can be heard at dusk. Powerful owls nest in the hollows of very large trees, often at the head of a gully. Of the 28 native mammals recorded, the bent-wing bat and the brush-tailed phascogale are considered threatened.

A small nocturnal carnivore, the brush-tailed phascogale prefers box ironbark forest and is also dependent on tree hollows for habitat. The brush-tailed phascogale (Phascogale tapoatafa), also known by its Australian native name tuan, is a rat-sized arboreal carnivorous marsupial of the family Dasyuridae, characterised by a tuft of black silky hairs on the terminal portion of its tail. Males of this species do not live past the age of one, as they die after reproducing.

Wildlife includes 21 reptiles and 16 amphibians, such as the mountain dragon lizard and freshwater blackfish.