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View from the top of Lansdowne Escarpment

Two of the older volcanic intrusions, North Brother Mountain, centre, with South Brother Mountain in the background on the left
Looking west towards Hannam Vale and Big Nellie
Looking down the Lansdowne Escarpment

Lorne Basin, Lansdowne Escarpment and Big Nellie

Flat Rock Lookout - Latitude -31.686879, Longitude 152.507111

Big Nellie Latitude -31.700299, Longitude 152.523097

Located in the Manning Valley Region (Mid North Coast) of NSW, nearest town Hannam Vale



Link to Detailed Map

Lorne Basin

Located on the mid-north coast of New South Wales, between the towns of Coopernook and Wauchope, the Lorne Basin is a nearly circular bowl-shaped formation 35 kilometres in diameter, with Triassic sedimentary rocks (in excess of 200 metres thick) of similar age to those of the much larger Sydney Basin.

The basin floor is composed of Palaeozoic rocks (250 to 550 million years ago) of New England Orogen overlain by Triassic terrestrial sedimentary rocks (from 210 to 240 million years ago). These sedimentary rocks have been intruded by Late Triassic to Early Jurassic (around 200 million years ago) igneous rocks and later by Tertiary igneous rocks (2 to 65 million years ago). Faulting has disturbed the Palaeozoic and Mesozoic sedimentary sequence and the basin floor now has an overall dip of about 4° to the east.

The Lorne Basin is unusual in that it has two circular uplifts. Circular uplifts centred within a circular basin are suggestive of the central uplift zone of a large impact crater. A possible impact origin for the Lorne Basin was first suggested, on the basis of other criteria, by Tonkin (1998). The structure may have been created by a meteor impact some 250 million years ago in the Triassic period. As well as its circular morphology, the presence of glass containing metallic iron and nickel, and Granitoid intrusions is all evidence for the Lorne Basin being the site of impact origin. Meteor impact sites are uncommon; approximately 180 terrestrial impact sites have been confirmed globally. These sites provide us with information about the creation and shaping of our planet and the solar system. Research into the role of impact events in mass extinctions (such as that of the dinosaurs) is on-going, although much of the available literature suggests a strong correlation between the two. The Lorne Basin meteor impact structure (if confirmed) would be the only known impact site in NSW with a degree of surface expression and in this regard would be of state significance. Investigations continue.

The Triassic sediments of the Lorne Basin were deposited by processes associated with rivers and streams. During the Triassic Period, structural movement caused the basement to be uplifted into the Early Triassic rocks to form the circular Black Creek Uplifts and Holey Flat Uplift (the circular uplifts mentioned above). These structures influenced the emplacement of Late Triassic to Early Jurassic igneous intrusions.

Weathering has removed the Triassic cover over the remainder of the Black Creek Uplift but its location is marked by two concentric lineaments about 300m to 400m apart. Their specific location is usually indicated topographically by gullies or saddles in the ridges. Both of these structures predate emplacement of the Brothers intrusions. Late Triassic - Early Jurassic igneous rocks of the South Brother Mountain overlie the eastern rim of the Holey Flat Uplift. To see a map showing these uplifts, download quaternary notes at the following link and view pages 18 and 19.

Around Lorne and Milligans Road (just south of Wauchope) there are the deposits of the Milligans Road Formation, composed of sandstone, airfall tuff (consolidated volcanic ash) and minor carbonaceous mudstone. While no identifiable fossil plants have been recovered to confirm age, the airfall tuffs are believed to be associated with the emplacement of Late Triassic to Early Jurassic felsic igneous rocks in the immediate vicinity i.e. North, Middle and South Brother Mountains.

Four faults splay from the Waitui Fault south of Stewarts River and appear to provide conduits for the Big Nellie, Small Nellie and Flat Nellie volcanic plugs which were formed in the Tertiary period after the Brother's intrusions.

The cliffs at Flat Rock Lookout on the Lansdowne Escarpment consist of Coorabakh Conglomerate
Summit of Big Nellie volcanic plug
Looking west over Lansdowne Valley and Comboyne Plateau from Big Nellie Road
Newbys Creek and cave

Coorabakh National Park

Situated on the Lansdowne escarpment, Coorabakh National Park lies in the western section of the Lorne Basin approximately 22 kilometres north of Taree. The area was traditionally used by the local Ngaamba (pronounced Namba) tribe and by surrounding clans as a major transport route between the coast and the Great Dividing Range. It is likely that the cliff lines and rugged topography of the park were used for cultural practises such as ceremonies and social gatherings. Today the park is visited by the local Biripi people for educational and spiritual purposes. It also contains remnants of the old Langley Vale tramway built in the 1930s. The tramway is considered to be one of the earliest logging tramways in eastern Australia.

The landscape of the area mainly consists of a steeply dissected sedimentary escarpment interspersed with numerous volcanic plugs and associated trachyte flows. The upper escarpment is fringed by a fertile basalt plateau, whilst lower down, plunging ridgelines and low rounded hills dissipate into a subdued landscape of alluvial terraces (Pain & Ollier, 1986).

Current investigations (June 2010) show that Early Triassic rocks of the Camden Haven Group (conglomerate, sandstone and claystone) form most of the Lansdowne Escarpment (located in the western part of the Lorne Basin). A subset of this group, the Coorabakh Conglomerate Member, a unit of pebble conglomerate and interbedded sandstone, is present in part of the Lansdowne Escarpment near Flat Rock Lookout (See photo). This also forms the north-facing cliffs to the south of Stewarts River and the capping of the Broken Bago Range in the north of the Lorne Basin. Fossils have not been recovered from the Coorabakh Conglomerate. However, geologists extrapolate from equivalent associated conglomerate evidence that the Coorabakh Conglomerate is of late Early Triassic age (Helby 1970, 1971, 1972).

Three prominent volcanic intrusions known as Big Nellie, Flat Nellie and Little Nellie composed of tertiary rhyolite, dominate the park. The summit of Big Nellie, which is marginally the highest plug, rises to 560 metres above sea level, Little Nellie has an elevation of 555m, and Flat Nellie 485m. The Nellies are pyroxene-rich trachyte plugs that are the remains of a Tertiary volcanic event where Triassic sediments including conglomerates and sandstones were subject to intrusion by hot, viscous, silica-rich lava.

The Lansdowne Volcanics are associated with the Comboyne Shield Volcano, a past catastrophic event that would appear to be a consequence of the passage of the Australian continent over a "hot spot" within the earth's mantle (see explanation elsewhere on this site). The residual volcanic structures are of considerable geological significance because they provide an exceptional insight into the evolution of the Great Escarpment in NSW. The Comboyne Plateau and the adjacent Bulga Plateau are now outlying residuals of the Great Escarpment which, as a result of scarp retreat, has migrated further to the west.

According to Pain and Ollier, "the Comboyne basalts and related volcanic plugs enable a chronology to be derived, and in the immediate area of the plateaus, scarp retreat has brought their escarpments to their present position within the past sixteen million years". This age has been confirmed by dating of Tertiary volcanic rocks from the trachyte plugs and flows on and adjacent to the Comboyne Plateau.

Eighteen forest ecosystems have been recorded in the Coorabakh National Park. It is important at a regional level because it contains a number of rare, threatened and significant plant species. It also supports a diverse array of fauna, including the endangered bush stone curlew and threatened species such as the spotted-tailed quoll, powerful owl and stuttering frog. Tall open eucalypt forest gives way to low stunted shrubland on the exposed summits and the Lansdowne escarpment. In the sheltered gullies, warm temperate and subtropical rainforest thrives.

At Newbys Caves, there are large overhanging conglomerate rock formations. At Flat Rock and Newbys lookouts there are constructed platforms that offer impressive views over the escarpment to the Manning Valley and the Bulga and Comboyne Plateaus. At Starrs Creek day use area there is a wheelchair accessible circular boardwalk through the rainforest. Picnic facilities are located at Newbys Lookout, Big Nellie and Starrs Creek.

Getting There

To see features such as the Lansdowne Escarpment, Flat Rock and Newbys lookouts, Big Nellie, Starrs Creek and Newbys Caves, visitors can drive through the Coorabakh National Park along Coopernook Forest Way accessed off Bangalow Road as it leads north from Coopernook village. Coopernook Forest Way is on the left (west) immediately after crossing the North Coast Railway line and Newbys Creek Road is a ring road which leads off Coopernook Forest Way approximately 13km from the Bangalow Road turn off.

If you want to take a picturesque round trip after Flat Rock Lookout follow Big Nellie Road until it becomes Waitui Road and it will lead you back to Hannam Vale..

The surrounding State Forests have a number of recreational facilities that are often used by visitors to the park. There is a camping area at the Coopernook State Forest Headquarters off Forest Road (in Lansdowne State Forest) which is accessible by two wheel drive vehicles. In the Comboyne State Forest there is a swimming hole at Waitui Falls.

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