23. DAY 5 U1 0 w STW’3: MountYork(hwrry (Middle Triassic, Mount York Claystone) The most accessible exposure of the Mount York Claystone, which has previously been seen only in cliff faces, occurs here. The red-brown colouration is typical of these redbeds along the western margin of the basin. The underlying Triassic formations have thinned, and this unit lies less than 60 m above the Late Permian Illawarra Coal Measures. Mount York Quarry to Victoria Pass Peturn to the Great Western Highway and, if time permits, drive down and back up Victoria Pass to briefly examine the coal measure section. To reach Victoria Pass turn right (west) and follow the highway to the foot of the pass, which is approximately the base of the Illawarra Coal Measures (Charbon Sub—Group). STOP 4: VictorkiPass (Late Permian to Early Triassic) The Illawarra Coal Measures have thinned to approximately 110 m. The Marrangaroo Conglomerate, at the base of the Charbon Sub—Group, can be seen outcropping in the fields at the foot of the pass to the north of the road. Coal is a minor lithology in the section here, but the 5 m thick Middle River seam and the siliceous Burragorang Claystone can be distinguished. The uppermost Katoomba seam, once mined at Katoomba, has here deteriorated to a thin carbonaceous band. Interbedded sandstone and Claystone of the Caley Formation occur above the coal measures, overlain again by the massive sand- stone of the Burra-Moko Head Sandstone. Near the top of the pass the red-brown Mount York Claystone crops out prominently. Mount Victoria to Garie Beach Proceed eastwards from Victoria Pass along the Great Western Highway via Mount Victoria. Turn left (north) at Mount Victoria for Bell, Bilpin, Mount Tomah, and Kurrajong Heights via Bells Line of Road. A brief stop could be made on the Lapstone Monocline at Kurrajong Heights overlooking the Cumberland Basin (figure 1.2). Photo 23.16. View from,Govetts Leap Lookout down Govetts Leap Creek to the Grose RiveerIthe distant valley. Details of the Permo-Triassic sequence are shown on the photograph. Hawkesbury Sandstone and Lshfield Shale are preserved under a capping of Tertiary basalt on Mount Hay, the flat-topped mountain on the right of the photograph. Day 5, stop 2. (Photo: G. Hicks) Photo 23.17. Bridal Veil Falls from Govetts Leap Lookout. The Banks Wall Sandstone forms the topmost part of the cliff. It is separated from the Burra- Moko Head Sandstone, comprising the lower part of the cliff, by the Mount York Claystone, which weathers to yield the vegetated ledge about half-way down the ' '“ ' ' ' \\||\\\|\I\\||\)||\\\|\|\|1|)\||\\\|||\|\\\|\|\\\\\|\\||\ 0004277591 504 EXCURSION GUIDE On the journey between Mount Victoria and Bell some interesting views may be had of the Grose Valley (to the right), with Mount Banks and Mount Hay prominent in the middle distance. These mountains are capped by Hawkesbury Sandstone and Miocene basalt. The journey between Mount Victoria and Mount Tomah is mostly over the Banks Wall Sandstone. Approximately 1 km past the Hartley Vale railway station surface installations of the Hartley Main No. 4 Colliery may be seen on the right. This is the only colliery operating at the head of the Grose Canyon, extracting the Katoomba Goal by fully mechanized methods. Dark—grey Wianamatta Group shale overlying thin Hawkesbury Sandstone may be seen in the road cutting when climbing up Mount Tomah. This shale is, in turn, overlain by prismatically jointed Miocene olivine basalt. Fertile soil is produced on the basalt and supports a luxuriant tree fern stand which can be seen to the left (north) as the road ascends Mount Tomah. The country from Mount Tomah to Bilpin has a thin covering of Wianamatta Group shale supporting numerous fruit orchards (mainly apple). The Kurrajong Fault (downthrown to the west) is crossed at the foot of the climb up the western side of the Lapstone Monocline. Drag folding of the sandstone beds can be seen here. An extensive view of the Hawkesbury-Nepean River flood plain can be had from the lookout at Kurrajong Heights before proceeding down the eastern slope of the Lapstone Monocline. Upon reaching Richmond turn right (south) along the Penrith-—Castlereagh road. At Penrith turn left (east) on to the Great Western Highway and immediately turn right (south) along the Mulgoa road to Wallacia. From Richmond to Penrith the route passes over a Tertiary alluvial terrace (highest terrace) and over a lower Pleistocene alluvial terrace. Large gravel quarries in the Pleistocene terrace will eventually be rehabilitated as large recreational lakes. South of Penrith the Wianamatta Group is traversed. Note one of the best natural exposures of Ashfield Shale, capped by Tertiary gravel, exposed in a cliff to the left (east) of the Mulgoa road about 2 km south of Regentville. The route continues to pass overrolling countryside formed by the non- outcropping Wianamatta Group. Characteristic indigenous vegetation of the dry schlerophyl type comprises the eucalyptus Grey Box (Eucalyptus moZuccana) and Forest Red Gum (E. tereticomis). This eucalypt assemblage, together with the Blackthorn bush (&amaria sphwsah has been used to indicate the presence of the Wianamatta Group with considerable accuracy. Turn left at Wallacia towards Luddenham for nearly 5 km and turn left at a "T" intersection. After a little more than 1 km turn right to Liverpool via Elizabeth Drive. At Liverpool cross the Georges River bridge and immediately turn right down the Heathcote road. Turn right (south) at a "T" intersection with the Princes Highway past Heathcote to Waterfall. South of Heathcote the Princes Highway passes over the northerly sloping Woronora Plateau (Nepean Ramp). Outcrops of Hawkesbury Sandstone can be seen in road cuttings and cliff sections. Higher parts of the plateau are capped by Tertiary laterite, much of which has been quarried for use as road base. 23. DAY 5 505 From Waterfall turn left (east) from the highway and descend to the Port Hacking River. The topmost units of the Narrabeen Group are exposed here, beneath the Hawkesbury Sandstone (figure 11.1). The Newport and Garie Formations and the Bald Hill Claystone can be seen in cuttings and roadside quarries. The upper facies of the Bulgo Sandstone crops out nearest the river (shaly facies, Ward article 11). East of the river the road rises again to the level of the Hawkesbury Sandstone, and then descends through the same sequence to the coast at Garie (signposted). The Narrabeen Group in the south coast district contrasts strongly with the same unit in the western part of the basin. Lithic arenites, some of which represent reworked volcanic detritus, make up most of the sequence, and the only quartzose sediment.occurs in the relatively thin Newport Formation at the top. This lateral facies change is due mainly to provenance factors and to the mineral dispersal pattern (Ward 1972a). The overall depositional environment in the two areas is fairly similar. STOP 5: GarfiaBeach (Early and Middle Triassic, Narrabeen Group) A well—exposed sequence comprising the Bulgo Sandstone, Bald Hill Claystone, Garie Formation, and the overlying Newport Formation can be observed at Garie Beach (figure 23.13). All formations are of Early and Middle Triassic age and constitute the upper part of the Narrabeen Group. The Bulgo Sandstone is the thickest of the seven formations recognized by Hanlon (1956) in the Narrabeen Group of the Illawarra district. It is 120 m thick at Clifton, forming over half of the total Narrabeen succession (see Ward article 11). (a) Northern Headland At the northern headland (photo 23.18), the top of the "volcanic facies" of the Bulgo Sandstone can be seen, overlain by the "shaly facies". By climbing part way up the coastal cliffs, where accessible, the red brown coloured Bald Hill Claystone can be inspected. It is overlain by the clay pellet Garie Formation. Note the carbonaceous sediments and soil profiles which are developed just above the Bald Hill Claystone. The Bald Hill Claystone at Long Reef, north of Sydney has been interpreted as a sequence of superimposed soil profiles (Retallack 1977a, b). (b) Southern Headland (Thelma Head) Only the middle portion of the Bulgo Sandstone, the "volcanic facies", can be examined on Thelma Head, south of Garie. These distinctive green—coloured sediments consist mainly of altered volcanic rock fragments, replaced by chlorite, mixed- layer clays and iron oxide minerals. In thin section the original