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Wasp Head Formation

Erosion along a fault line in the Wasp Head Formation
Box work weathering where harder minerals have filled joints in the rock and have remained when surrounding softer rocks have weathered out
Drop stone in Wasp Head Formation deposited when glacial ice carrying it melted
Spectacular bedding in Wasp Head Formation
Honeycomb and box work weathering
North Eastern end of fault shown it top photo

Murramarang National Park

Especially Wasp Head, evidence of a transition from a glacial to a non-glacial period and the unconformity between Sydney Basin and Wagonga rocks.

Latitude -35.671713, Longitude 150.304309

Located in the Eurobodalla Region on the South Coast of NSW, nearest town Batemans Bay



Source: Simplified from The Lower Permian Wasp Head Formation, Sydney Basin: High-latitude, shallow marine sedimentation following the late Asselian to early Sakmarian glacial event in eastern Australia Authors: Rygel, Michael C.; Fielding, Christopher R.; Bann, Kerrie L.; Frank, Tracy D.; Birgenheier, Lauren; and Tye, Stuart C.

Link to Detailed Map

Murramarang National Park encompasses two major geological provinces - the Permian Sydney Basin and the much older Ordovician beds of the Lachlan Fold Belt. The geological features of the park are of considerable scientific importance.

The coastline between Myrtle Beach south of Durras and Snapper Point near Pretty Beach at the northern end of the park presents a relatively complete, although discontinuous, series of exposures through the oldest Permian deposits of the southern Sydney Basin. The base of the Sydney Basin is exposed as a spectacular angular unconformity in cliffs at the northern end of Myrtle Beach and at beach level at Dark Beach.

The Permian Sydney Basin rocks overlaying the much older Ordovician beds of the Lachlan Fold Belt. Note the change in angle between the two deposits.

How to get to Myrtle Beach

Myrtle Beach is about 9km from the Princes Highway. Take the South Durras turn-off just 9.6km north of Batemans Bay and follow it until you reach the Murramarang Resort. Keep on the road and it will take you through the Murramarang Resort car parking area, keep travelling south along the Old South Coast Road for just over 1km until you get to the Dark Beach/Myrtle Beach turn off where you turn left, then drive along this road for 450 metres to the main car park to access both these beaches.

The walk from the car park to Myrtle Beach is approximately 400 metres. The start of the track is facing you as you enter the car park. This track heads part of the way east and is signposted - walk for 200 metres, take the first turn right - which is not signposted - walk a further 200 metres, descend the last part via the staircase. The closest public toilet is near Cookies Beach, next to the Murramarang Resort.

Outcrops near Wasp Head and Pebbly Beach are the type sections of the Wasp Head and Pebbly Beach Formations respectively; the basal units of the Sydney Basin (Percival, 1985).

Other significant geological features include:

1. sedimentary breccia (Wasp Head Formation) between Myrtle Beach and Wasp Head containing blocks of granitic origin which appear to have been dropped by melting ice flows.

2. Fossil logs in the Wasp Head Formation and at Pebbly Beach.

3. Ironstone boxwork at Wasp Head.

4. Fine examples of differential erosion in a varied assemblage of geological structures at Point Upright north of Durras North.

Most of the park and the islands north of Myrtle Beach consist of horizontally bedded Permian sedimentary rocks of finely interbedded siltstone, fine sandstone and conglomerate. These do not weather into the massive structures of the Triassic and Permian sandstone exhibited in most other parks in the Sydney Basin. The coastline in this area features regular cliffs and headlands, smooth intertidal platforms, caves, tombolos, islands, sandy beaches and an interesting occurrence of shingle beaches near Pebbly Beach. Fossil beds and ironstone boxwork in the Permian formations are fragile and very vulnerable to damage.

The Permian beds lie over tightly folded phyllites and cherts of the early Ordovician Wagonga Beds outcropping south of Myrtle Beach and in the Tollgate Islands. The Wagonga Beds have resulted in irregular headlands, jagged intertidal platforms, shingle beaches and stacks. In more western areas of the park, conglomerate, sandstone and siltstones of the Shoalhaven Series are exposed.

The dominant landform feature is Durras Mountain which rises to 285m above sea level. The summit of Durras Mountain is capped by Tertiary basalt with small limestone outcrops. An essexite (a type of igneous rock) intrusion occurs at the base of the mountain near the Dawson Islands and there are several small dykes nearby.

Wasp Head, evidence of a transition from a glacial to a non-glacial period

Wasp Head is located in the Murramarang National Park, north of Batemans Bay and south of South Durras. The approach to the Wasp Head area is via Durras Road which leads off the Princess Highway north of Batemans Bay. Follow the road into South Durras and past Murramurang Resort. Wasp Head lies just to the south of the township. Keep left at the fork just past the resort then take the right at the next fork. The tracks at Wasp Head lead to the interesting sandstone formations discussed below. Nearby a little further north, is Mill Point where a timber mill was situated, the only evidence remaining is a rusty old boiler on the grass. Be careful when descending to the shoreline in this area as some of the tracks are very steep and rough and large waves can wash across the rock platforms.

The Lower Permian Wasp Head Formation is a roughly 95 metre thick unit that was deposited during the transition to a non-glacial period following an earlier glacial event in eastern Australia. A facies is a distinctive rock unit that forms under certain conditions of sedimentation, reflecting a particular process or environment. This shallow marine, sandstone-dominated unit can be subdivided into six facies associations or zones. Look at the rock walls in the area and see if you can identify any of the following characteristics. The zones describe areas starting from shore side and each going deeper and further off-shore.

The shallow marine, sandstone-dominated unit can be subdivided into six facies associations or zones

Zone 1: The marine sediment gravity flow facies association consists of breccias and conglomerates deposited in close to shore water depths.

Zone 2: Upper shoreface deposits consist of cross-stratified, conglomeratic sandstones.

Zone 3: Middle shoreface deposits consist of hummocky cross-stratified sandstones and show evidence of dwelling burrows made by suspension-feeding animals. Hummocky crossstratification is a type of sedimentary structure in which the original depositional layering is tilted. Cross bedding forms during deposition on the inclined surfaces of bedforms such as ripples, and indicates that the depositional environment contained a flowing fluid and usually formed by the action of large storms. It takes the form of a series of "smile"-like shapes, crosscutting each other. It is only formed at a depth of water below fair-weather wave base and above stormweather wave base.

Zone 4: Lower shoreface deposits are similar to middle shoreface deposits, but contain more bioturbation (all encompasing displacement and mixing of sediment particles).

Zone 5: Delta-influenced, lower shoreface-offshore transition deposits are distinguished by sparsely bioturbated carbonaceous mudstone drapes within a variety of shoreface and offshore deposits.

Zone 6: The offshore transition-offshore facies association consists of mudstone and admixed sandstone and mudstone with pervasive bioturbation. The progressive decrease in ice-rafted debris upwards through the succession records the release from glacial conditions to broadly non-glacial conditions.

As well as these interesting sequences there are some amazing examples of wind and rain weathering of the sandstone including honeycomb weathering and differential weathering where harder 'ironstone' layers and bands create box work and sills.

Getting There

Murramarang National Park, is located north east of Batemans Bay on the South Coast of New South Wales. It is accessed via the Princes Highway and features interesting rock formations, heath lands, sandy beaches punctuated by rocky headlands and plenty of walking tracks.

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