Bacchus Marsh Council Trench Geological Reserve (Triassic Park)

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. In Triassic Park you'll see a piece of Victoria's only Triassic Age rocks (250 million years old). Formations from a time when dinosaurs roamed.

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 paleontologist 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 Pentland 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 Chenopod Woodland. The yellow gums and wattles are 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.

Lystrosaurus a Triassic sheep-sized plant-eating mammal-like reptile with prominent canine teeth could well have grazed at Triassic Park.

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 east corner of the reserve, views over Bacchus Marsh and the Pentland 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.

How to get there
Triassic Park is located about 2 km north of Bacchus Marsh.

From Melbourne, approach the site via the Western Freeway, then exit the freeway at the first Bacchus Marsh exit and stay on Main Road, pass through the township continuing until the freeway overpass is crossed to Condons Lane, then turn right at Tramway Lane.

From Ballarat simply exit the freeway at the first Bacchus Marsh ramp and turn left along Condons Lane, then right at Tramway Lane.

The entrance gate is about 100m along Tramway Lane from Condons Lane.

Caring for the Area
Please help us to conserve this special area.

Collection of plants or wildflowers is prohibited.

Do not remove rocks from the site. The site is used by university students for teaching purposes and it is important to protect the outcropping rocks to study in the future.

Information Boards on Site

Bacchus Marsh Council Trench Geological Reserve (Triassic Park)

How did it happen?
When glaciers covered Victoria
280 million years ago in the Permian Period, Bacchus Marsh, and the land that forms present-day Victoria, was covered by huge glaciers. These glaciers had their origins in mountains that are now part of Antarctica.

When Australia and Antarctica were joined they formed part of the super continent named Gondwana. At the end of the Permian Period (250 Ma), the Earth experienced the greatest mass extinction of life ever known, the causes of which are not certain.

Triassic river deposits
Despite this mass extinction, life continued to evolve during the Triassic Period. Dinosaurs and reptiles roamed across Gondwana at this time.

By about 210 million years ago a large river flowed through this area. The sandstones and siltstones that you see exposed in the quarry were deposited by this river system. Where you are now standing would have been in this river!

Why Triassic Park?
Plant fossils found in the Council Trench outcrop were deposited 210 million years ago. They represent plants from the Triassic Period. These plants may have been food for dinosaurs and reptiles similar to Lystrosourus, that roamed the landscape of Victoria at that time.

Palaeo-artist John Sibbick has imagined the Triassic landscape in the illustration below. As the Triassic Period progressed, dinosaurs evolved to set the stage for their predominance during the following Jurassic and Cretaceous Periods.

Bacchus Marsh Council Trench Geological Reserve (Triassic Park)

Understanding the rocks
At the top of the trench there is a mixture of rocks and pebbles called conglomerate. The layer is tilted because of faulting nearby. Beneath the conglomerate is a narrow layer of siltstone, and below that is the large yellow layer of quartz sandstone. The rocks at this site contain small fragments of fossils from the trees and plants, which dinosaurs and reptiles may have eaten.

Geologists have described the sequence of rocks present. The swirling pattern in the sandstone is due to Leisegang banding, which is the precipitation of iron oxide-rich layers during the semi-fluid stages of sandstone sediment deposition.

Plant fossils from the Council Trench
The thin siltstone layer contains plant fossils of Triassic age. These are uncommon and now highly weathered.

Detailed scientific study of the types of plants present indicates that the area was a cool freshwater environment with plants such as horsetails, liverworts and ferns. There are also species that would have grown on nearby higher ground on the edge of the swamp. These include Cycads, Ginkgo and Conifers.

The presence of fossils of the extinct seed fern (pteridosperm) species Dicroidium identifies the Triassic age for the sediments in the Council Trench.

Bacchus Marsh Council Trench Geological Reserve (Triassic Park)

Triassic Flora
Fossil records show that flora during the Triassic Period included species of fern, horsetail, liverwort, cycad, ginkgo, conifer (pine) and seed ferns. All of the plant species found as fossils are now extinct. There were no angiosperms - flowering plants - in the Triassic period.

Flora of the Council Trench Today
Communities of Plants
Remnant Rocky Chenopod (saltbush) Woodland and remnant Grassy Woodland flora communities cover the Reserve. Rocky Chenopod Woodland occurs on soils derived from Permian origin. Grassy Woodland occurs mainly on soils of volcanic origin. Grassy Woodland is classified as 'endangered' in this bioregion. The native vegetation has been modified over the years and one of the management objectives is to restore these communities.

Rocky Chenopod Woodland
In the Rocky Chenopod Woodland on the reserve Yellow Gum provides the overstory. Saltbushes, which are Chenopods, are common understorey plants. Some of the other species in this woodland include Bacchus Marsh Wattle, Golden Wattle, Lightwood Wattle, Small leaf Clematis, Sweet Bursaria, Tree Violet and Black anther Flax-lilies. Rocky Chenopod Woodland is classified as 'Vulnerable' because of reduced distribution.

Grassy Woodland
Grassy Woodland is dominated by native grasses and herbs with scattered Grey Box trees. On the Reserve the native grassland has been invaded by exotic pasture grasses. However remnant native grassland plants such as Small-leaved Clematis, Pink Bindweed, Black-anther Flax-lily, Grey Tussock, Wallaby and Kangaroo Grass are recovering.

Birds of the Reserve
Council Trench Reserve is home to birds like the Superb Fairy-wren, Yellow-rumped Thornhill, Yellow Thornbill, New Holland Honeyeater, Willie Wagtail and Zebra Finch. Some of these birds nest at the Reserve. These birds benefit from the woodland-grassland edge available at the Reserve.

Some birds are seasonal visitors to the Reserve. These include Purple-crowned Lorikeet, Spiny-cheeked Honeyeater, Flame Robin, Golden Whistler, Dusky Woodswallow and Silvereye.

Birds like Wedge-tailed Eagle, Nankeen Kestrel, Galah, Sulphur-crested Cockatoo, Eastern Rosella, Red Wattlebird, Magpie-lark, Australian Magpie and Little Raven visit the Reserve as part of a larger territory.

Some visits are fleeting as birds pass over or rest at the Reserve during migration from one area to another.

Review:

A wonderful insight into the world of geology with impressive layers of sedimentary rocks. Some areas are like beautiful polished wood knots.

You can follow the gully up to a picnic table with an information board, picnic table and views across the surrounding area. There were some kangaroos in the reserve.