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Triassic Park

Bacchus Marsh Council Trench Reserve

Tramway Lane,
Bacchus Marsh, VIC 3340
Location in Google Maps

The following external links provide some more information.
• Geological Society of Australia - Heritage Case Study
• Geological Society of Australia - Victorian Geologist March 2006
• Geological Society of Australia - Geological Significance

Visitor Guide

This small reserve located to the north of Bacchus Marsh holds an important key to understanding the past. In a small quarry, unusual sedimentary rocks are exposed providing a window into Victoria's distant geological history.

A brief history

Once a small test quarry, this site is now known to contain the only Triassic age (about 205 to 250 million years ago) sedimentary rocks in Victoria.

Rare plant fossils from the site were identified as Triassic in age by eminent palaeontologist Frederick McCoy in 1892. He determined that the sediments were deposited about 210 million years ago in an ancient river bed. Later investigations have confirmed this early work.

During the Triassic period dinosaurs and early mammals evolved. The climate was warmer than today, after a long cold period in the Permian when ice sheets and glaciers covered much of Australia. The remains of the Permian glaciers can be seen throughout the Bacchus Marsh area as vast deposits of grey or white glacial rocks. including those at Werribee and Lerderderg gorges and nearby at Bald Hill, but little is known of the Triassic landscape.

The derivation of the name Council Trench is uncertain. The site was referred to as the trench in the Council Paddock in 1927. The term Council Trench first appeared in studies of the site in 1937.

Set aside as a quarry in 1873, the land is now reserved for its natural values including the Triassic sedimentary rocks and as a rare small refuge for native plants and animals.

Plants and animals

The eucalypt and wattle woodland is an important remnant of native vegetation in the largely cleared landscape of the Pcntland Hills.

Conservation of natural values including indigenous vegetation is an important management objective for the committee that maintains the reserve. This also includes the range of native grasses found within the southern part of the site, and on the rock exposures.

Flora

The reserve is host to an important vegetation community that is rare throughout the Midlands region known as a Rocky Chcnopod Woodland. The yellow gums and wattles arc characteristic of the overstorey of this type of vegetation which grows on infertile soils and may appear stunted from a lack of nutrients.

The ground level plants consist of saltbush, flax lily and native grass such as wallaby and kangaroo grass.

The south-east portion of the reserve contains remnants of Grassy Woodland with exotic grasses.

Things to do and see

Take in the view of Bacchus Marsh and the Pentland Hills from the highest point or trace the Triassic sandstones and conglomerates along the trench or cut, and into the side of the hill.

Watch birds of prey soar on thermals over the Korkuperrimul Creek valley and Pentland Hills where once pterosaurs may have flown. Explore the woodlands where superb fairy wrens forage, but millions of years ago strange reptiles like the Lystrosaurus came to eat and drink.

From the highest point at the north cast comer of the reserve, views over Bacchus Marsh and the Pcntland Hills can be obtained. The incision of Korkuperrimul Creek can be traced to the west with cliffs exposing light coloured Permian glacial sandstones, brown-yellow Tertiary iron-strained sandstones and conglomerates and dark coloured Tertiary Older Volcanics basalts.

Geological Timeline

The origin of the earth is estimated to be at about 4500 million years ago or Ma (that's 4,500,000,000 years!). For a long period there is no evidence of life on the earth The first organic remains are found in rocks of about 3500 Ma. At some stage in the early Pre Cambrian, all of the landmasses merged to form the supercontineni Rodinia. Later in the Proterozoic, Rodinia broke up into segments including a large segment now known as Gondwana. During the middle and Late Proterozoic Era, other continents joined Gondwana and formed Pangea. By the start of the Cambrian period, tectonic movements had again separated the landmass into two major sections: Pangea and Gondwana.

During the Triassic, Australia was part of a supercontinent called Gondwana. Soon after this time the huge land mass began to break up into smaller parts forming the continents we know today. Triassic sedimentary rocks are known from other areas of Australia (Sydney Basin, Queensland, Tasmania and north Western Australia). From these rocks we can establish a picture of the climate and life forms of that period. The near-absence of Triassic age sedimentary rocks in Victoria may indicate that this area was eroding during that time, perhaps supplying sediments to the Sydney Basin or Tasmania.

Australia remained attached to Antarctica, Africa and South America for millions of years but finally began to separate at about 150 Ma. The final break up between Australia and Antarctica started at about 140 million years but did not break to form the Southern Ocean until almost 50 million years ago - very recent in geological terms!

Gondwana

The distribution of fossil plant and land animal species from the Permian, Triassic and Jurassic periods has been used to indicate that several now separate continents were once Joined in an enormous landmass known as Gondwana (modified after Rich and Rich 1993 Wildlife of Gondwana}. This ancient landmass consisted of the present continents of Australia. Antarctica, India, South America and Africa.