David J Och

The Port Macquarie district is situated about 400 km north of Sydney in the Mid- North
Coast region of New South Wales (Fig. 1). Geologically it is notable for the presence of
high pressure metamorphic rocks, serpentinite mélange, broken formation, and a wide
variety of mafic igneous intrusive rocks, very well exposed in the coastal tract between
Port Macquarie township and Tacking Point, some 5 km to the south. This field guide
provides a description of two critical areas in this tract as well as outlining the overall
geology of the coastal zone and the general geology of the surrounding area (the Port
Macquarie Block).

Port Macquarie lies a few kms east of the Pacific Highway from which it is accessed by way of a well signed slip road and a short section of the Oxley Highway. It is a tourist town with abundant and varied accommodation which should be booked ahead in busy times.  All services are available.

The Port Macquarie - Tacking Point coastal tract consists of a series of headlands
separated by sandy beaches with most beaches readily accessed by car. Cliff-top walks and short scrambles provide access to most headlands and some can be traversed at sea level at low tide, the best time to for a visit. Rough seas render the headlands and associated shore platforms dangerous, especially after a southerly change. Caution needs to be exercised at all times but especially when the seas are heavy.

Please do not collect any samples from Rocky Beach. The high-pressure eclogite,
omphacitite and blueschist phacoids here provide the only readily accessible
occurrence of this association in NSW and should be preserved for teaching future
generations of geologists. Sampling for research purposes requires prior approval
from Hastings Shire Council or the NSW National Parks and Wildlife Service.

The Rocky Beach Metamorphic Melange contains metre-scale phacoids of high-P low-T metamorphic rocks embedded in chlorite-actinolite schist. The phacoids include eclogite, glaucophane schist and omphacitite and provide evidence for four episodes of metamorphism with mineral assemblages: M1 = actinolite-glaucophane-titanite-apaite, M2 = almandine-omphacite-lawsonite ±quartz, M3 = phengite- glaucophane-K-feldspar-quartz, and M4 = chlorite-actinolite-calcite-quartz-titanite-white mica ± albite ± talc. M1-M3 occurred at a Neoproterozoic-Early Palaeozoic convergent plate boundary close to the eastern margin of Gondwana. Peak metamorphic conditions were attained during the static phase M2, with temperatures of ~560°C and pressures in excess of 1.8 GPa, equivalent to a depth of burial of at least 54 km.

Small outcrops of blueschist and eclogite occur at Rocky Beach, Port Macquarie, on the NSW mid north coast. These are geologically significant as they represent a unique insitu exposure of a rare high-pressure - low-temperature metamorphic sequence not seen elsewhere in Australia. They are also of great educational value to universities, school groups and the general public as they illustrate the effects and consequences of subduction zone processes at depth, now exposed on the surface. Being relatively easily accessible, the site is in danger of destruction by removal of samples and hence should be protected by being listed as a national geoheritage site or included within the nearby Sea Acres National Park.

One of the greatest project challenges and risks for the eastern (Minmi to Buchanan) section of the Hunter Expressway was the management and design for the proportionally large amounts of poor quality materials derived from the Newcastle Coal Measures formation. The near balanced earthworks design, coupled with the very strict clearing restrictions and challenging terrain, compelled designers to incorporate expansive and carbonaceous materials, which would otherwise be spoiled because of their poor engineering properties, into the road formation. This paper presents the geological setting, characterisation of the earth materials, development of the encapsulation design approach used and implementation to date. In conclusion opportunities for further design development are discussed

Abstract: Two assemblages of rugose and tabulate corals, with accessory stromatoporoids and chaetetids, are described from the Touchwood and Mile Road Formations of the Wauchope - Port Macquarie district of northeastern New South Wales. Both assemblages are derived ...

Conodonts of Middle to Late Ordovician age, obtained from cherts of the Watonga Formation exposed in the Port Macquarie Block of the Mid North Coast region of New South Wales, establish this unit as the oldest biostratigraphically-dated part of the southern New England Fold Belt subduction-accretion complex. Correlation of the Watonga Formation with the Woolomin Formation, faunas from which are no older than Pridoli, cannot be sustained. This revised age provides evidence of possible early Palaeozoic subduction-accretion in this region at the same time as arc magmatism, volcaniclastic sedimentation and exhumation of high-pressure metamorphic rocks were proceeding further west.

A collaborative data-sharing approach and extensive desktop study as part of the Sydney Metro City & Southwest project, which includes 15.5 km of twin tube tunnels, enabled the use of ground data from more than 50 selected historical projects. This data was used by an integrated team managing the ground investigation and undertaking the design, to mitigate or reduce tunnel construction risks at an early stage, and target the site investigation to maximise value. The compilation of all available ground data in single spatial (GIS) and geotechnical (gINT) databases enabled a robust geotechnical model to be built and created a valuable legacy for future projects. This paper presents the value and limitations of this historical ground data, and recommendations to improve the "useful lifespan", storage and sharing of available and future site investigation data.

There is a rapid and unprecedented scale of infrastructure planning and development across the Sydney region. A SMART approach that captures historical ground investigation and regional geological data is required to support early transport planning by Government. This will allow the refinement of geological and geotechnical knowledge gaps that will be augmented with additional investigation once these corridors are further assessed as the design develops. To allow a SMART approach in infrastructure planning and development, Government Departments and potentially the private sector could integrate their internal geological and geotechnical data as part of a centralised statewide data collection centre. This will require Government to legislate a registry system for factual geotechnical data for all Departments and Authorities. Consideration would also need to be given to how to release this information from the private sector many of whom would claim this was their intellectual property despite typically being derived (and paid services for) from Government projects. Consideration should be given to a two-stage process so as not to derail the implementation due to potential delays with the private sector: (i) Combine and integrate geological and geotechnical data from historical Government projects including those delivered under corporatised government entities. (ii) Integration of factual data obtained from the private sector. Any data compiled under both (i) and (ii) will need to be relied upon without any impact or recourse to the originators. This has been key to the success of similar data sharing mechanisms in the United Kingdom (British Geological Survey) and the Netherlands (Dutch Geological Survey). A way of making this work successfully in New South Wales, following successful international models such the UK and Netherlands, is to have government allow contracts or documentation to have historic data relied upon. The State will achieve better value for money by way of having significantly more geological and geotechnical data as part of Environmental Impacts Statements to inform approvals and stakeholders as well as for its Request for Proposals (RFP). In all cases with more reliable information a better outcome will be achieved by way of increased certainty and avoiding approval delays, possible injunctions, as well as more informed Request for Tenders (RFTs).

Lawsonite eclogite and garnet blueschist occur as metre-scale blocks within serpentinite mélange in the southern New England Orogen (SNEO) in eastern Australia. These high-P fragments are the products of early Palaeozoic subduction of the palaeo-Pacific plate beneath East Gondwana. Lu–Hf, Sm–Nd, and U–Pb geochronological data from Port Macquarie show that eclogite mineral assemblages formed between c. 500 and 470 Ma ago and became mixed together within a serpentinite-filled subduction channel. Age data and P–T modelling indicate lawsonite eclogite formed at ~2.7 GPa and 590°C at c. 490 Ma, whereas peak garnet in blueschist formed at ~2.0 GPa and 550°C at c. 470 Ma. The post-peak evolution of lawsonite eclogite was associated with the preservation of pristine lawsonite-bearing assemblages and the formation of glaucophane. By contrast, the garnet blueschist was derived from a precursor garnet–omphacite assemblage. The geochronological data from these different aged high-P assemblages indicate the high-P rocks were formed during subduction on the margin of cratonic Australia during the Cambro-Ordovician. The rocks however now reside in the Devonian–Carboniferous southern SNEO, which forms the youngest and most outboard of the eastern Gondwanan Australian orogenic belts. Geodynamic modelling suggests that over the time-scales that subduction products accumulated, the high-P rocks migrated large distances (~>1,000 km) during slab retreat. Consequently, high-P rocks that are trapped in subduction channels may also migrate large distances prior to exhumation, potentially becoming incorporated into younger orogenic belts whose evolution is not directly related to the formation of the exhumed high-P rocks.

Translating burial and exhumation histories from the petrological and geochronological record of high-pressure assemblages in subduction channels is key to understanding subduction channel processes. Convective return flow, either serpentinite or sediment hosted, has been suggested as a potential mechanism to retrieve rocks from significant depths and exhume them. Numerical modelling predicts that during convective flow, subducted material can be cycled within a serpentinite-filled subduction channel. Geochronological and petrological evidences for such cycling during subduction are preserved in lawsonite eclogite from serpentinite melange in the Southern New England Orogen, eastern Australia. Ar–Ar, Rb–Sr phengite and U–Pb titanite geochronology, supported by phase equilibrium forward modelling and mineral zoning, suggest Cambro–Ordovician eclogite underwent two stages of burial separated by a stage of partial exhumation. The initial subduction of the eclogite at ca. 490 Ma formed porphyroblastic prograde-zoned garnet and lawsonite at approximate P–T conditions of at least 2.9 GPa and 600 °C. Partial exhumation to at least 2.0 GPa and 500 °C is recorded by garnet dissolution. Reburial of the eclogite resulted in growth of new Mg-rich garnet rims, growth of new prograde-zoned phengite and recrystallization of titanite at P–T conditions of approximately 2.7 GPa and 590 °C. U–Pb titanite, and Ar–Ar and Rb–Sr phengite ages constrain the timing of reburial to ca. 450 Ma. This was followed by a second exhumation event at approximately 1.9 GPa and 520 °C. These conditions fall along a cold approximate geotherm of 230 °C/GPa. The inferred changes in pressure suggest the lawsonite eclogite underwent depth cycling within the subduction channel. Geochronological data indicate that partial exhumation and reburial occurred over ca. 50 M y., providing some estimation on the timescales of material convective cycling in the subduction channel.

Sydney Metro is Australia's biggest public transport project.

Stage 2 of the project will extend metro rail from the city's northwest under Sydney Harbour, through new stations in the CBD and southwest to Bankstown.
Sydney Metro has two core components:
- Sydney Metro Northwest -now under construction and to open in the first half of 2019
- Sydney Metro City and Southwest a new twin 12.5-km tunnel linking with Sydney Metro Northwest at Chatswood
- then under Sydney Harbour, through the CBD to Sydenham and continuing 13. 4 km along the existing line to
Bankstown due for completion in 2024.
A joint venture between Parsons Brinckerhoff and AECOM (PB-AECOM JV) was appointed as the consultant for the Sydney Metro Technical Services project, which commenced in September 2014. The team will prepare a preliminary evaluation, scoping design, definition design and ultimately reference designs for the Sydney Metro Stage 2.
In November 2014 the marine geophysics contract was awarded to Earth Technology Solutions Pty Ltd and the intrusive investigation followed in April 2015 by the Golders-Douglas Partners joint venture.
As Sydney Harbour is a key element of Sydney Metro, early planning and design work included essential geotechnical investigations. Sydney Harbour is a busy waterway, so the investigation works began, after extensive consultation with all relevant harbour authorities, with standard marine geophysical surveys (reflection, 1 refraction, 1 magnetics and sonar) west of the Sydney Harbour Bridge.
Land-based investigation began in April 2015 following extensive community consultation and services searches. The firstnole (BH015) began at Blues Point with a commissioning ceremony by the NSW Premier Mike Baird. This was the start of 27 boreholes that extend from Chatswood to Sydenham. These boreholes have been planned to target and intersect the Ashfield Shale, Mittagong Formation and Hawkesbury Sandstone to assess the rocks geomechanical properties.

The Sydney Harbour crossing is a key element of Sydney Metro City & Southwest, which includes 15.5 km of twin tube running tunnels extending from Chatswood at the north through to Sydenham, south of the Central Buisness District (CBD). One of the key features is the 1 % length of the alignment that passes under Sydney Harbour. The rest of the alignment is through rock, but the harbour crossing is designed to pass through harbour sediments and mixed face conditions undersea. An in depth study and analysis was required to confirm the feasibility of the safe construction of this short length of the tunnel in sub-aqueous, soft ground conditions. It was necessary to carry out detailed, targeted investigation of the ground to enable the selection of an appropriate tunnelling technique for constructing the tunnels.

The Rocky Beach Metamorphic Melange contains metre-scale phacoids of high-P low-T metamorphic rocks embedded in chlorite-actinolite schist. The phacoids include eclogite, glaucophane schist and omphacitite and provide evidence for four episodes of metamorphism with mineral assemblages: M1 = actinolite-glaucophane-titanite-apaite, M2 = almandine-omphacite-lawsonite ±quartz, M3 = phengite- glaucophane-K-feldspar-quartz, and M4 = chlorite-actinolite-calcite-quartz-titanite-white mica ± albite ± talc. M1-M3 occurred at a Neoproterozoic-Early Palaeozoic convergent plate boundary close to the eastern margin of Gondwana. Peak metamorphic conditions were attained during the static phase M2, with temperatures of ~560°C and pressures in excess of 1.8 GPa, equivalent to a depth of burial of at least 54 km.

The Hunter Expressway will provide a 40 km long four-lane divided carriageway motorway between the F3 Interchange at Newcastle and the New England Highway at Branxton, New South Wales Australia. The project is due to be opened by the end of 2013. The Hunter Expressway Alliance (HEA), comprising Roads and Maritime Services (RMS), Thiess Pty Ltd, Parsons Brinckerhoff and Hyder Consulting, is responsible for the design and construction of the 13 km eastern section of new freeway and local road adjustments. There are 28 bridges and major culvert structures and 29 Reinforced Soil Walls (RSWs). This paper discusses the design challenges faced by the RSW designers and the innovative engineering solution developed for RW17, a 120 m long RSW up to 10m in height on sloping ground with foundations containing bands of low strength tuffaceous claystone. To achieve the minimum design factor of safety (FOS) of 1.35 for the overall slope stability of the RSW as stipulated in RMS Specification R57, three rows of 450 mm/750 mm diameter and one row of 1500 mm diameter bored piles were designed and adopted at various selected sections along the 120 m long slope. Both the limit equilibrium program Slope/W and the finite element program Plaxis were used to assess the FOS for the global stability of the RSW, ground movements during and after RSW construction and forces in the piles. Two inclinometers were installed to monitor the field lateral ground movements during and after construction to verify the design assumptions. This paper describes the challenging ground conditions, the development of the stabilising pile design, the analytical models used and the results of the construction phase monitoring of the completed RSW.

The Hunter Expressway is a  new government funded dual carriageway  motorway built  to relieve congestion between Newcastle  and  Thornton,  Maitland  and  Rutherford.  The  expressway  is  continuous  over  40 km  between  the  F3  at Seahampton  and  Branxton.  The  easternmost  13 km  between  the  F3  and  Kurri  Kurri  is  being  built  by  the  Hunter Expressway Alliance (HEA), comprising constructors Thiess and designers Parsons Brinckerhoff and Hyder Consulting partnering  with  NSW  Roads  and  Maritime  Services  (RMS).  A  solution  was  required  to  manage  the  risk  of  mine subsidence under the viaduct and bridge foundations. The solution used was to fill the mine voids out to a distance of half the seam depth. 
The  extent  and  depth  of  the  mine  voids  and  related subsidence  fractures  was  required  before  treating  the  voids. First assessment  was  to  complete  a  detailed  geological  long  section  of  key  existing  boreholes.  Following  this,  further
boreholes with video camera footage were made to assess the mine workings. The footage, with GIS, was used to map and correlate pillar and roadway networks with existing mining surveys, to accurately determine the volume of mining space to grout. After grouting, 140 validation holes were made to assess if the mine voids had been filled successfully. 
The assessment of video footage also helped the geological and geotechnical assessment of abutment structures on the viaducts  as  there  were  numerous  joints  and  fractures.  With  mapping,  and  from  assessing  the  videos,  the  team  could decide  whether  these  fractures  were  formed  by  earlier  tectonic  events,  stress  relief  due  to  valley  formation,  or  mine subsidence.
The fractures are differentiated by their source — stress relief fractures related to valley formation, fractures caused by pillar collapse, and fractures related to tectonic joint/fault systems. The valley-forming fractures were found in an upper sandstone  layer  (Figure  3).  These  fractures  are  consistent  in  the  three  viaducts  where  bridge  abutments  have  been exposed. The fractures caused by pillar collapse were found in a sandstone layer about 40 m above the mined horizon, between two coal bearing layers. 
There  were  several  outcomes  from  the  work  done.  It  has  been  demonstrated  video  camera  monitoring  can  play  a significant role in mining and geotechnical applications, and have a positive impact on time and budget-related issues.

"Below Sydney’s central business district (CBD) lies a complex network of transport and service tunnels competing for space  with  building  basements  and  confined  by  changes  in  topography.  Although  the  geological  setting  is  well understood and documented, potentially millions of dollars are spent each year on new ground investigations. Why? 
Over the last 50  years, NSW Government departments have spent  millions of dollars on substantial engineering and geotechnical site investigations within the Sydney CBD and are estimated to have drilled thousands of boreholes. 
The  majority  of  existing  geotechnical  information  was  collected  by  government  departments  and  geotechnical consultancies and stored in libraries or archived. Over time this data may become misplaced or in many cases disposed of.  There  are  many  government  departments  and  consultancies that  preserve  data  in  systematic  electronic  GIS  type databases. Indeed, if the basic information was attributed (e.g. grid coordinates, borehole No., Department, and Project No.  etc.)  the  stored  data  could  be  assessed  quickly  to  determine if  any  data  is  located  within  a  project  area  by
interrogating a central GIS database (or GIS web service) and therefore retrieved from the relevant storage achieve or geotechnical  consultant  at  minimal  cost.  The  NSW  Government  is  planning  on  making  it  mandatory  to  apply  for permits  to  drill,  but  also  to  record  information  from  any  borehole  that  encounters  groundwater  or  potentially  water bearing rocks. Permits and recording of boreholes is also the case within mining and mineral exploration in NSW. It is
therefore  envisaged  that  much  of  the  geotechnical  investigation  data  produced  across  the  Sydney  CBD  could  be centrally stored in a GIS database. A data model based on the British Geological Survey – National Geoscience Data
Centre model is proposed to more efficiently store large amounts of geotechnical data. Access to this information could then be provided through a secure, GIS-based Internet web portal. In many cases, planning for new projects could rely heavily on accessing existing data through this single point-of-truth database and over time, new geotechnical models
could be added to further develop an evolving 3-D geological model of the Sydney CBD and other key locations. "

One of the greatest project challenges and risks for the eastern (Minmi to Buchanan) section of the Hunter Expressway was the management and design for the proportionally large amounts of poor quality materials derived from the Newcastle Coal Measures formation. The near balanced earthworks design, coupled with the very strict clearing restrictions and challenging terrain, compelled designers to incorporate expansive and carbonaceous materials, which would otherwise be spoiled because of their poor engineering properties, into the road formation. This paper presents the geological setting, characterisation of the earth materials, development of the encapsulation design approach used and implementation to date. In conclusion opportunities for further design development are discussed

Small outcrops of blueschist and eclogite occur at Rocky Beach, Port Macquarie, on the NSW mid north coast. These are geologically signifi cant as they represent a unique insitu exposure of a rare high-pressure - low-temperature metamorphic sequence not seen elsewhere in Australia. They are also of great educational value to universities, school groups and the general public as they illustrate the effects and consequences of subduction zone processes at depth, now exposed on the surface. Being relatively easily accessible, the site is in danger of destruction by removal of samples and hence should be protected by being listed as a national geoheritage site or included within the nearby Sea Acres National Park.

Nine units, six formally defined here, have been identified along the coastal tract between Port Macquarie and Tacking Point in the NSW Mid-North Coast part of the New England Fold Belt. All show the imprint of convergent margin tectonics. The oldest rocks are the (?)650 Ma MORB protolith of eclogite phacoids embedded in the chlorite-actinolite schist matrix of the Rocky Beach Metamorphic Mélange that occurs as a slab within the Port Macquarie Serpentinite Mélange. The last is a product of alteration of cumulate rocks of a c.530 Ma fore-arc ophiolite. The Watonga Formation comprises broken formation that includes Late Ordovician pelagic rocks, the MORB substrate on which these were deposited, younger basalt and olistostromes of ocean island origin, and tuff, siltstone and sandstone inferred to be trench fill. These were off-scrapped in the Late Ordovician-Carboniferous interval and form part of the Palaeozoic New England accretionary subduction complex. In the Permian the Tacking Point Gabbro and the Town Beach Diorite, calc-alkaline plutons geochemically allied with the Clarence River Supersuite of the New England Batholith, mark the establishment of a magmatic arc. Dykes of Karikeree Metadolerite and Nobbys Beach Lamprophyre, geochemically allied to the plutons, comprise later products of arc activity. Uncommon felsic dykes are considered minor components of the Late Triassic leucoadamellite suite of the New England Batholith. Little-altered Shelly Beach Dolerite dykes characterised by high Ti and Fe were subsequently emplaced in the coastal tract. Their geochemistry suggests a source influenced by subduction-derived fluids and they were probably emplaced in a backarc setting following eastward relocation of the magmatic arc
Several deformational and metamorphic episodes have been identified. Eclogite shows syn-deformational prograde (De1, Me1) and retrograde (De2, Me3) (469 Ma) blueschist facies metamorphism separated by static eclogite recrystallisation (Me2) (c.570 Ma), and a later greenschist overprint (De4, Me4). Accretion of the Watonga Formation was accompanied by deformations D1 and D2 that led to stratal disruption and local folding and foliation development and low-grade metamorphism. Subsequently expansion-related deformation and protrusion of the Port Macquarie Serpentinite led to its multiply deformed mélange character (Ds1, Ds2) that is also shown by the matrix of the related Rocky Beach Metamorphic Mélange (Dr1, Dr2). Serpentinisation occurred under conditions such that chrysotile and lizardite were stable and the altering ultramafic protolith, early mafic dykes, and eclogite were boudinaged during expansion, producing mélange. Blocks of the Watonga Formation were incorporated into the mélange during its emplacement as a series of lenses probably in the late Carboniferous.
Emplacement of Permian-Triassic magmatic arc rocks was accompanied by shearing, faulting and large-scale open folding (D3, D4). Elevated temperatures were maintained and the intrusive rocks and the Watonga Formation were affected by low-grade regional alteration and local thermal metamorphism. Mylonite zones formed in the cooling plutons during D3.
The Tacking Point coastal tract contains a history, albeit fragmentary, of convergent margin activity extending over at least 370 Ma (c.570 Ma–c.200 Ma). Over this interval it was successively the site of forearc underplating, subduction accretion, arc magmatism and backarc magmatism.

The Point Macquarie–Tacking Point coastline provides excellent exposures of the accretionary subduction complex and younger magmatic arc rocks that make up much of the New England Fold Belt (also known as the New England Orogen) in north-eastern New South Wales. Nine geological units, including six formally defined here (Port Macquarie Serpentinite, Rocky Beach Metamorphic Mélange, Tacking Point Gabbro, Town Beach Diorite, Nobbys Beach Lamprophyre and Sea Acres Dolerite), have been identified along this coastal tract. The Karikeree Metadolerite has been redefined. The oldest rocks are prograde lawsonite eclogite and retrograde blueschist blocks embedded in the chlorite–actinolite schist matrix of the Rocky Beach Metamorphic Mélange that occurs as a slab within the Port Macquarie Serpentinite. The Port Macquarie Serpentinite is a product of alteration of cumulate ultramafic rocks of a c.530 Ma forearc ophiolite. The Watonga Formation is a mostly broken formation that consists of Middle–Late Ordovician pelagic rocks, the mafic oceanic substrate on which these were deposited; younger basalt and olistostromes of probable ocean island origin; and tuff, siltstone and sandstone inferred to be trench fill accreted in the Late Ordovician–Carboniferous interval. Later intrusive rocks of probable Permian age are the geochemically similar Tacking Point Gabbro, Town Beach Diorite, Karikeree Metadolerite and Nobbys Beach Lamprophyre that are possibly related to the Clarence River Supersuite of the New England Batholith. Uncommon felsic dykes are considered minor components of the Middle Triassic leucoadamellite suite of the New England Batholith. Little altered dykes of Sea Acres Dolerite, characterised by high Ti, Fe and Zr, are Late Triassic or younger.

Two assemblages of rugose and tabulate corals, with accessory stromatoporoids and chaetetids, are described from the Touchwood and Mile Road Formations of the Wauchope – Port Macquarie district of northeastern New South Wales. Both assemblages are derived from allochthonous limestone clasts, except that the Mile Road fauna is accompanied at the same level by branching tabulate corals occurring in the matrix, indicating probable contemporaneity. The fauna from the Touchwood Formation indicates an Early Devonian (Emsian) age. Macrofossils from the Mile Road Formation indicate a broad Middle Devonian, probably Givetian age; conodonts accompanying the coral assemblage yield a precise age in the upper part of the early Givetian varcus Zone. Geographic affinities of the assemblages are typically eastern Australian, so that if terranes are represented in the block, these were not remote. Stratigraphic and structural relationships of the units are discussed. The name Mile Road Formation is formally defined.

Areas of rocks which contain naturally occurring asbestos (NOA) occur within every state of the Australian continent, in a variety of geologic environments. Any activity (including road and urban construction, farming, forestry and landscaping) which causes NOA-bearing soils and rocks to be disturbed can potentially result in releasing asbestos fibres into the air. Unintentional, environmental  and non-occupational exposure to asbestos dust is recognized as a significant geological hazard in California and a number of other countries. Specialised geological maps and investigation guidelines have been developed by geoscientists in California to help deal with the issue. Geologists in Australia will need to play a significant role in preparing similar material for Australia.

The Rocky Beach Metamorphic Melange contains metre-scale phacoids of high-pressure low-temperature metamorphic rocks embedded in chlorite-actinolite schist. The phacoids include eclogite, glaucophane schist and omphacitite and provide evidence for 4 episodes of metamorphism with mineral assemblages: M1 = actinolite - glaucophane - titanite - apatite, M2 = almandine - omphacite - lawsonite ± quartz, M3 = phengite - glaucophane - K feldspar - quartz, and M4 = chlorite - actinolite - calcite - quartz - titanite - white mica ± albite ± talc. M1 - M3 occurred at a Neoproterozoic - Early Palaeozoic convergent plate boundary close to the eastern margin of Gondwana. Peak metamorphic conditions were attained during the static phase M2, with temperatures of about 560oC and pressures in excess of 1.8 GPa, equivalent to a depth of burial of at least 54 km.

Conodonts of Middle to Late Ordovician age, obtained from cherts of the Watonga Formation exposed in the Port Macquarie Block of the Mid North Coast region of New South Wales, establish this unit as the oldest biostratigraphically-dated part of the southern New England Fold Belt subduction-accretion complex. Correlation of the Watonga Formation with the Woolomin Formation, faunas from which are no older than Pridoli, cannot be sustained. This revised age provides evidence of possible early Palaeozoic subduction-accretion in this region at the same time as arc magmatism, volcaniclastic sedimentation and exhumation of high-pressure metamorphic rocks were proceeding further west.

Sydney Metro is Australia’s biggest public transport project. In 2024, this new standalone railway will deliver 31 metro stations and more than 66 km of new metro rail, evolutionising the way Australia’s biggest city travels. Sydney Metro is being delivered in four phases. Sydney’s Metro Northwest line has been in service since May 2019. Sydney Metro City & Southwest is a 30 km extension of metro rail from the end of Sydney Metro Northwest at Chatswood under Sydney Harbour, through new CBD stations and southwest to Bankstown. Sydney Metro West will extend metro rail to Western Sydney, linking the Sydney city centre with Greater Parramatta via almost 50 km of underground tunnels. The Sydney Metro – Western Sydney Airport project will become the transport spine for Greater Western Sydney, connecting communities with the growing region and the new Western Sydney International (Nancy-Bird Walton) Airport. Sydney Metro recognises the important issue of preventing work related illness and diseases in the thousands of workers who contribute to the successful delivery of this world-class infrastructure. As such Sydney Metro established an occupational health and hygiene program which set performance requirements to provide governance and an understanding of occupational health risks through our supply chain. This included a specific focus on Respirable Crystalline Silica (RCS). This industry-leading program has enabled the collection of data to highlight areas of excellence and to inform areas that would benefit from future intervention and engineering solutions. This paper provides a case study of Sydney Metro’s program approach to managing health risks through the supply chain. It includes an overview of best practices observed across Sydney Metro’s projects that have relevance to tunnel construction and the wider infrastructure sector.

Sydney Metro is Australia’s largest public transport project, and historical and recent ground data is being collected and used at an unprecedented scale to create robust rock models for the proposed tunnel alignments. Geotechnical investigations target the Triassic Wianamatta Group, Mittagong Formation and Hawkesbury Sandstone of the Sydney Basin. Despite these geological units being well documented, the new knowledge gained during the Sydney Metro projects is enabling a better definition of the Wianamatta Group. In particular, the Rouse Hill Siltstone Member is typically described as a homogenous siltstone unit at the base of the Wianamatta Group. However, this unit often includes a thin “tuff” layer, which is typically ignored in geological models. Data from 70+ historical and recent boreholes across Sydney indicates that, where present, this layer is remarkably uniform across the central Sydney Region and sits horizontally at 3 m above the base of the Rouse Hill Siltstone Member. This marker horizon assisted in identifying vertical offsets in the strata caused by faulting. The characterisation and identification of this layer will greatly improve our understanding of the geology across Sydney and allow efficient targeting of geological structure for future tunnelling projects in these units.