Gippsland Basin Research Articles

Optimising value in the mature Turrum Field: integrating modern seismic, high-resolution sequence stratigraphy and production data in a 3D geological model

The Turrum Field in the offshore Gippsland Basin has been a significant producing field since first development in 2004 and remains a keystone gas resource for the future as many of the Gippsland assets continue to deplete. The Turrum Field is a faulted anticlinal structure with multiple, stacked, Paleocene-aged fluvial to lagoonal reservoirs that stratigraphically sit below the overlying Marlin Field gas cap. This field was developed in two phases with drilling campaigns in 2004 and 2015 and includes a dedicated platform (Marlin B) for the higher pressure, higher CO2 gas. Leveraging the 2018 reprocessed Northern Margins 3D seismic survey with a modern broadband processing workflow and wider bandwidth and higher signal-to-noise ratio has led to a seismic image with greater resolution and allowed improved reservoir characterisation. The uplift in seismic data together with the colour blending capabilities in GeoTeric®, has led to the seismic identification of large-scale fluvial reservoir systems. These products have been integrated with a revised field-wide sequence stratigraphic framework, petrophysical analysis and incorporated into a full-field 3D geological model of the Turrum Field. The resultant geological model has improved our understanding of reservoir connectivity and will enable rapid integration of production and surveillance data to optimise gas deliverability. This will also provide increased confidence for future field depletion planning including the identification of potential bypassed gas opportunities prior to end of field life.

Overcoming COVID challenges in project execution – West Barracouta

The West Barracouta (BTW) field, one of the largest proven undeveloped gas fields off the south-eastern Australian coast, commenced production in April 2021. The project was developed by Esso-BHP Gippsland Basin Joint Venture (GBJV), a 50–50 JV between ExxonMobil’s subsidiary Esso Australia and BHP Petroleum. The BTW gas field is situated ~6 km south west of the existing Barracouta gas field and platform, the first GBJV platform in Bass Strait. The BTW development involved drilling two subsea production wells, installation of umbilical controls from the existing platform and installation of a ~6 km subsea flowline to connect to existing gas pipeline via a hot tap. The BTW team successfully navigated through engineering, fabrication, testing, mobilisation of an international team and installation of the facilities in a COVID environment. The paper shares insights on how to: manage fabrication impacts with closures and restricted workhours to minimise disruption to the project; complete videoconference Hazid Identification Risk Assessment workshops across different geographical locations; develop and execute methodology for distributed component integrated testing with hardware located in different geographical locations; complete remote inspections, Factory Acceptance Tests (FAT)/verification using videoconference; complete enhanced familiarisation and testing activities at shorebase, prior to offshore installation, given restrictions in overseas travel/access to FAT locations; and safely manage installation personnel to ensure continuity of activities in a COVID environment, e.g. platform, installation vessel and diver COVID requirements.

Sedimentology and seismic geomorphology of Paleocene coastal peatlands from the offshore Gippsland Basin, SE Australia

The Eocene–Miocene succession of the onshore Gippsland Basin is host to some of the world's thickest coal seams. Here, we document well-preserved Paleocene coals from the offshore Gippsland Basin. The Paleocene sediments in the basin consist of three stacked coastal units, known informally here as T8, T7 and T6, in order of decreasing age. Each unit consists of, from seaward to landward, a sediment starved marine facies, a sand-rich, wave-dominated shoreface facies, lower coastal plain tidal and peatland facies, and upper coastal plain sandy, fluvial facies. Seismic amplitude extractions reveal unprecedented details of the peatland palaeogeography. The early Paleocene T8 palaeogeography reveals a wave-dominated, sandy strandplain seaward of a >1000 km2 lower coastal plain peatland. The peats extend inland to ~35 km from the paleocoastline and are dissected by a series of meandering and anastomosing channel systems. This geometry is remarkably similar to the modern tropical peatlands of the Rajang Delta in Sarawak, where forested domed peats have formed over tidal and shoreline sediments. The Paleocene coals of the Gippsland Basin have likely formed in a very similar stratigraphic setting and provide a large-scale ancient example of lower coastal plain coal deposition.

A new perspective on Late Eocene and Oligocene vegetation and paleoclimates of South-eastern Australia

We present a composite terrestrial pollen record of latest Eocene through Oligocene (35.5–23 Ma) vegetation and climate change from the Gippsland Basin of south-eastern Australia. Climates were overwhelmingly mesothermic through this time period, with mean annual temperature (MAT) varying between 13 and 18 °C, with an average of 16 °C. We provide evidence to support a cooling trend through the Eocene–Oligocene Transition (EOT), but also identify three subsequent warming cycles through the Oligocene, leading to more seasonal climates at the termination of the Epoch. One of the warming episodes in the Early Oligocene appears to have also occurred at two other southern hemisphere sites at the Drake Passage as well as off eastern Tasmania, based on recent research. Similarities with sea surface temperature records from modern high southern latitudes which also record similar cycles of warming and cooling, are presented and discussed. Annual precipitation varied between 1200 and 1700 mm/yr, with an average of 1470 mm/yr through the sequence. Notwithstanding the extinction of Nothofagus sg. Brassospora from Australia and some now microthermic humid restricted Podocarpaceae conifer taxa, the rainforest vegetation of lowland south-eastern Australia is reconstructed to have been similar to present day Australian Evergreen Notophyll Vine Forests existing under the sub-tropical Köppen-Geiger climate class Cfa (humid subtropical) for most of the sequence. Short periods of cooler climates, such as occurred through the EOT when MAT was ~ 13 °C, may have supported vegetation similar to modern day Evergreen Microphyll Fern Forest. Of potentially greater significance, however, was a warm period in the Early to early Late Oligocene (32–26 Ma) when MAT was 17–18 °C, accompanied by small but important increases in Araucariaceae pollen. At this time, Araucarian Notophyll/Microphyll Vine Forest likely occurred regionally.

3D seismic geomorphology of Early Cenozoic incised channels, Gippsland Basin, SE Australia: Evidence for submarine origin

The Latrobe Group in the Gippsland Basin consists of well-developed, stacked shoreface and coastal plain deposits, cut by large, incised channel systems up to 500 m deep. These large channels are conspicuous on seismic intersections and have previously been interpreted as the result of fluvial incision associated with basin inversion/compressional tectonics. Here we have used 3D seismic, well log, and core to re-evaluate the origin of these channel systems. We interpret three major phases of channel incision-infilling; Tuna Channel 1, Tuna Channel 2 and the Marlin Channel. Biostratigraphic data shows that the channels range in age from the Palaeocene-Eocene transition to the Late Eocene. These ages indicate channel formation occurred prior to the onset of compressional tectonics in the Gippsland Basin, which began at the Eocene-Oligocene transition.Correlation of these channels with coeval palaeoshoreface systems reveals that the channels are located seaward of, and in close proximity to these shorelines. Well data indicates that the channel fill sediments are of marine origin, consisting of glauconite, dinoflagellates, foraminifera, and marine macro fossils. We do not observe evidence for a regional unconformity which would correlate with over 500 m of subaerial channel incision. These channels are therefore interpreted as submarine canyons, rather than channels of fluvial origin. They are interpreted as shelf-incising, with canyon heads located close to coeval palaeoshorelines where they received sediment via longshore/littoral processes. The erroneous identification of submarine canyons as incised valleys in sedimentary basins has significant implications for tectonic and eustatic histories globally.

Scoping study of the economics of CO2 transport and storage options for steel manufacturing emissions in eastern Australia

The main source of CO2 emissions in an integrated steel manufacturing plant comes from the need to use a carbon source, often coal, in the steel making process. Amongst the pathways for reducing CO2 emissions is the application of carbon capture, transport and storage (CCS) technologies. This paper presents a scoping-level economic evaluation of transport and storage location options for CO2 captured from an iron and steel plant located in Port Kembla, NSW, Australia. Pipeline (single and hub) and ship transport of CO2, and two injection locations are considered. Estimated costs are lowest for the hub transport case injecting at the Gippsland basin (∼35% lower than for single source cases) and highest for the shipping case. For the single-source cases, transport via pipeline to the Darling basin is slightly more attractive in terms of unit costs. The hub transport cases were between two-thirds and half of the cost of the shipping case. Although the shipping transport option presented the highest cost of the cases considered, there is still a case to be made for ship transport if the project duration is short.

Shoreline evolution from the Late Cretaceous to the Miocene: A record of eustasy, tectonics and palaeoceanography in the Gippsland Basin

AbstractWell‐developed clastic shoreline systems have been deposited in the Gippsland Basin over a 70 Ma period, from the latest Cretaceous to the present day. Twenty‐three stacked coastal units have been mapped and described in the Traralgon and Balook formations of the Latrobe and Seaspray groups. These units are made up of prograding and backstepping shoreface deposits, which, in plan view, display well‐developed strandline geometries at the terrestrial–marine interface. Shoreface deposits are interpreted to include prograding beach, barrier island and transgressive beach deposits. The lower coastal plain is characterised by persistent deposition of coals despite changes in shoreface type and significant palaeoclimate fluctuations. These coastal deposits display approximately 123 km of transgression from the Late Cretaceous shoreline at the base of the study interval to the mid Miocene Yallourn Formation near the top. The Late Cretaceous and Palaeocene shoreline deposits individually prograde and are separated by flooding surfaces reflecting eustatic changes. Overall they display long‐term backstepping behaviour (retrogradation) as a result of basin subsidence. Though shorelines of the Eocene–Miocene are distinctly transgressional, probably reflecting basin subsidence, in the mid‐Miocene they become individually and collectively progradational. A series of unconformities in the Oligocene, coupled with Miocene progradation, likely reflects a combination of a compressional tectonic regime and glacioeustatic fluctuations. Despite major changes in the tectonics and palaeoclimate, basin subsidence appears to be the dominant driver for changes in shoreline location.

Lithospheric evolution, thermo-tectonic history and source-rock maturation in the Gippsland Basin, Victoria, southeastern Australia

A fully integrated 3D basin model was built to study the lithospheric structural evolution and the thermal history of the offshore part of the Gippsland Basin to investigate the type, timing and magnitude of its initial opening mechanism and their effects on source rocks. The applied workflow included seismic interpretation of major faults and magmatic features, seismic reinterpretation of existing main stratigraphic boundaries and adjustment of the basement topography. Different scenarios for a McKenzie-type basal heat flow evolution were tested based on a two-step inversion approach, which translates the thickness changes of lithospheric layers into basal heat flow. Finally, a crustal layer model was assigned to the existing 3D numerical basin model and the effects on thermal maturation of petroleum source rocks were investigated. The results of the calibrated inversion model suggest intense lithospheric stretching and mantle upwelling during the Early Cretaceous caused initial breakup and subsidence of the Gippsland Basin. This syn-rift phase was accompanied by increasing basal heat flow from initially ∼50 mW/m2 to a maximum of 80–90 mW/m2. The resulting upwelled Moho with an associated crustal thickness of locally only 8 km agrees with geophysical observations. Elevated paleogeothermal gradients between 50 and 60 °C/km prevailed from ca 120 to 80 Ma. Episodes of compression, uplift, erosion, and thermal subsidence resulted in fast and continuous cooling during the early post-rift and a constant basal heat flow of 45–50 mW/m2 since the Eocene. Two main pulses of petroleum generation were identified in the Paleocene and in the Miocene–Pliocene. This novel two-step crustal layer inversion method allows a detailed reconstruction of the thermal history of rift basins and can provide useful information about the maturation of petroleum source rocks. KEY POINTS A temperature history reconstruction of the Gippsland Basin is given based on a large-scale numerical 3D model. Tectonically induced strong variability in paleoheat flows is recognised. Strong maturation and petroleum generation developed during the Paleogene and Neogene.

Scoping Study of the Economics of CO2 Transport and Storage Options for Steel Manufacturing Emissions in Eastern Australia

The main source of CO2 emissions in an integrated steel manufacturing plant comes from the need to use a carbon source, often coal, in the steel making process. Among the pathways for reducing CO2 emissions is the application of carbon capture, transport and storage (CCS) technologies. This study undertakes a scoping-level evaluation of the economic viability of transport and storage location options for CO2 captured from an iron and steel plant located in Port Kembla, NSW, situated on the eastern coast of Australia. Both pipeline and ship transport of CO2 are considered, as well as two injection locations: the Darling Basin in NSW and the Gippsland Basin in the state of Victoria, Australia. The cost of CO2 transport and storage are estimated for four specific transport and storage options in south-east Australia, including the cost of pipelines/shipping, boosters, wells, other facilities, monitoring, energy and on-costs. The cases consider either a single CO2 source (emissions from Port Kembla) to a single pipeline or shipping port, or the contribution by the CO2 source from Port Kembla to a collection of CO2 sources including other CO2 sources in NSW, into a pipeline network. The sensitivity of the results to several economic and design parameters, such as flow rate, and project lifetime, is also assessed. Scoping level cost estimates for transport and storage of the CO2 are lowest for the hub transport case injecting at the Gippsland basin and highest for the case involving shipping with injection in the Gippsland basin. For the single-source cases, transport via pipeline to the Darling basin is a slightly more attractive option in terms of unit costs. Although pipeline transport to both the Darling and Gippsland basins are very close in terms of transport and storage costs (less than 0.2% difference), the cost of transporting to the Darling basin is less sensitive to variations of the cost parameters explored in this study. The lowest transport and storage costs found in this study were for the pipeline hub transport cases, more than 35% lower on average than for the single source cases. Regardless of the sensitivity scenario, the hub transport cases were between two-thirds and half of the cost of the shipping case. This highlights the importance of economies of scale in CO2 transport, achieved by employing larger diameter pipelines. This leads to decreases in both the unit capital costs by allowing larger capacities of transport, as well as in operating expenses by decreasing pressure losses along the pipelines, thus requiring less energy for compression. Although the shipping transport option presented the highest cost of the cases considered, there is still a case to be made for ship transport if the project duration is short. As ship transport is less CAPEX intensive (35% of total cost), this mode of transport becomes competitive with pipeline transport if the project duration is decreased, or if the discount rate is increased. Further, shipping also becomes more competitive for longer transport distances. For example, if the hub transport options would take several years to implement, a case could be made for utilising ship transport for a few years while the hub pipeline is constructed, and then transporting via the hub once it is available.

Storing CO2 in buried volcanoes

Australia contains rich natural gas resources, but many of Australia’s currently producing and undeveloped gas fields contain relatively high CO2 contents; if not captured and stored, the venting of co-produced CO2 could hinder efforts to meet Australia’s emission reduction targets. The most mature technology for isolating produced CO2 from the atmosphere is by containing it in deep sedimentary formations (e.g. saline aquifers or depleted oil and gas reservoirs). The effectiveness of this approach is dependent on factors such as reservoir capacity, the presence of low-permeability seals that physically impede vertical migration of injected CO2, the chemical reactivity of both reservoir and seal minerals, the risk for leakage, and a gas-entrapping structure. An alternative and attractive mechanism for permanent storage of CO2 is geochemical or mineral trapping, which involves long-term reactions of CO2 with host rocks and the formation of stable carbonate minerals that fill the porosity of the host rock reservoir. Natural mineral carbonation is most efficient in mafic and ultramafic igneous rocks, due to their high reactivity with CO2. Here we review the outcomes from a series of recent pilot projects in Iceland and the United States that have demonstrated high potential for rapid, permanent storage of CO2 in basalt reservoirs, and explore the practicalities of geochemical trapping of CO2 in deeply buried basaltic volcanoes and lava fields, which are found in many basins along the southern (e.g. Gippsland Basin) and northwestern (e.g. Browse Basin) Australian margins, often in close proximity to natural gas fields with high CO2 content.

Geological overview of the 2021 offshore acreage release areas

In 2021, a total of 21 areas were released for offshore petroleum exploration. They are located in the Bonaparte Basin, Browse Basin, Northern Carnarvon Basin, Otway Basin, Sorell Basin and Gippsland Basin. Despite COVID-19 negatively impacting the industry, participation in the acreage release nomination process was again robust. However, as has been the case in recent years, industry interest is focussed on those areas that are close to existing discoveries and related infrastructure. In tune with the Australian government’s resource development strategy, the areas being offered for exploration are likely to supply extra volumes of natural gas, both for export to Southeast Asian markets and domestically to meet the forecasted shortage in supply to eastern Australia. According to the 2019 implementation of a modified release process, only one period for work program bidding has been scheduled. The closing date for all submissions is Thursday, 3 March 2022. Geoscience Australia continues to support industry activities by acquiring, interpreting and integrating pre-competitive datasets that are made freely available in the context of the agency’s regional petroleum geological studies. As part of a multidisciplinary study, new data, including regional seismic and petroleum systems modelling, for the Otway Basin are now available. Also, a stratigraphic/sedimentological review of the upper Permian to Early Triassic succession in the southern Bonaparte Basin has been completed, the results of which are being presented at this APPEA conference. Large seismic and well data sets, submitted under the Offshore Petroleum and Greenhouse Gas Storage Act 2006 (OPGSSA), are made available through the National Offshore Petroleum Information Management System (NOPIMS). Additional data and petroleum-related information can be accessed through Geoscience Australia’s data repository.

Using External Peer Review to Build Confidence of the Pelican Storage Site

[The CarbonNet Project is investigating the potential for a commercial scale, multi-user CCS network with geological carbon storage in the nearshore Gippsland Basin, Victoria in SE Australia. Sources of CO2 include the potential production of hydrogen from nearby Latrobe Valley coal fields by a consortium that is currently establishing a pilot project to produce and transport clean hydrogen from Victoria to Japan. CarbonNet has been investigating potential storage sites and has identified a preferred site called Pelican in the nearshore. It is a 10 km by 7 km, east-west trending structural closure with excellent injectivity and effective seals comprising laterally extensive tidal/lagoonal shales and seat earths underneath well-mapped coal beds. The process used to select the preferred site for appraisal followed international best practice, aligned to DNV GL Recommended Practice (DNV-RP-J203), and has been previously reported. CarbonNet has now acquired high quality 3D seismic data and undertaken a further range of seal and modelling studies that have confirmed the ability of the storage formation to securely and permanently store at least 125 Mt of CO2 injected at 5 Mtpa over 25 years. In order to progress to injection at the site, the Australian regulatory regime requires that it first be Declared to be an “Identified Greenhouse Gas Storage Formation”. The Regulations set out matters to be addressed including structure and faulting, reservoir, seal, geomechanics, geochemistry well integrity and plume migration. The Pelican site will represent the first site to be evaluated under Australian offshore legislation and as such, there is no precedent for the structure or degree of detail of the application although some general principles can be derived from analogous petroleum documentation. CarbonNet decided that the format of the application for a Declaration would comprise a series of technical modules each addressing a geological element of the application. A Summary Document is laid out to respond to each of the regulations in the form and sequence set out in the Regulations. The Summary Document layout suits evaluation by the regulator, while the supporting technical modules are suited to providing a coherent geological description. In order to build internal, stakeholder, and regulator confidence in the Declaration document, CarbonNet engaged a panel of international experts to review the document against regulatory requirements and international norms. Panel membership was developed with consideration of: • CO2 storage project expertise; • technical expertise (particularly seal); • research reputation; and • regulatory experience. DNV GL was engaged to additionally act as an independent chair/facilitator of the panel and to take advantage of its experience in setting standards for certification of projects. The balance of the membership, particularly their experience with existing projects, was invaluable in making an informed and credible assessment of the documentation. The panel was provided with the draft application for review with topics allocated to subject experts. Initial comments were collated by the chair/facilitator. The panel convened in Melbourne for a two-day meeting of CarbonNet presentations and panel discussion. It held a half day closed discussion to agree an assessment of the documentation. The panel’s assessment was that Pelican is a high-quality storage site compared to many other CO2 storage projects the panel had experience with. It was able to conclude that the documentation provided, and the technical work performed by the CarbonNet team, is of very high quality and, in the opinion of the panel, sufficient to meet all regulatory requirements pertaining to the Declaration for the Pelican storage formation. In particular, the seals for the site were effective to injected CO2 over relevant timescales. CarbonNet has completed a comprehensive study of the Pelican storage site over many years. CarbonNet has assessed the site to have world class reservoirs demonstrate high injectivity and nearby oil and gas fields demonstrate that the seal systems are effective. It has modelled the CO2 plume and is confident that the CO2 will remain safely and securely stored for many thousands of years. This conclusion is supported by the panel of international experts that reviewed the CarbonNet documentation. The support of the panel provides strong, independent support of CarbonNet’s position and confirms the site to compare favourably with other international CO2 storage projects. The panel report will form part of the submission to the regulator in support of its application for a Declaration of Storage at the Pelican site. It will also support the commercialisation process which commenced in late 2019.

Geochemical comparison of three oil families from the Gippsland Basin, SE Australia

The biomarker and aromatic compounds, including polycyclic aromatic hydrocarbons (PAHs), in three oil families composed of 29 crude oils from the Gippsland Basin, SE Australia were studied using gas chromatography-mass spectrometry. Environment-related parameters, such as the Pr/Ph ratio and the gammacerane index, indicate that all the oils originated from a lacustrine/fluvial-deltaic environment with fresh water. Thermal maturity-related parameters, including aliphatic and aromatic maturity indicators (e.g. C29 sterane isomerisation parameters, alkylnaphthalene indices, and methylphenanthrene index), show that all the oils from the GA1 oil family have a similar thermal maturity in the peak-late oil window. However, oils from the GA2 and GB families vary in thermal maturity and are interpreted to be mixtures of less mature and more mature crude oils. Source-related biomarkers (e.g. isopimarane, labdane and phyllocladane) and PAHs (e.g. retene and oleanane-/ursane-/lupane-derived aromatic triterpenoids) suggest that the GA1 oils were mainly derived from source rocks rich in conifer-derived organic matter. The organic matter source of the GA2 and GB oil families included both angiosperms and gymnosperms, with a relatively stronger angiosperm contribution to the organic matter in the source rock(s) of the GB oils, based on the PAH analysis. Moreover, higher plant-derived triterpenoids can be effectively used to correlate oil families across the study area, supplementing the n-alkane carbon isotope and biomarker data of the three oil families reported previously.

Late Cretaceous–Paleogene palaeoclimate reconstruction of the Gippsland Basin, SE Australia

The Cretaceous–Paleogene palaeovegetation and palaeoclimate in the Gippsland Basin was reconstructed using vascular plant-derived biomarkers, and are consistent with other proxy evidence for palaeoclimate (e.g. spore-pollen assemblages and plankton foraminifera oxygen isotopes). Variation in the higher plant-derived aliphatic and aromatic sesquiterpenoids, diterpenoids and triterpenoids resulted from vegetation succession, and is different in the T. lilliei, F. longus, L. balmei, M. diversus, P. asperopolus and N. asperus palynological biozones. Analyses of the oleanane index, the higher plant parameter, the higher plant index, the higher plant fingerprint, and various aliphatic and aromatic angiosperm/gymnosperm indices indicate the late Cretaceous–Paleogene (ca. 80–40 Ma) palaeoclimate in the Gippsland Basin was initially warm (Campanian T. lilliei Biozone), and then changed in this way: → cool (Maastrichtian upper F. longus Biozone), → warm (Paleocene L. balmei Biozone), → hot (early Eocene M. diversus and P. asperopolus Biozones), → warm and then cool (middle Eocene N. asperus Biozone). This changing climate trend is mostly consistent with global climate changes. In comparison to the analogous Taranaki Basin (western New Zealand), the Gippsland Basin is inferred to have had a less gymnosperm-dominated rainforest and a warmer climate in the late Cretaceous. During the Paleogene the palaeoclimate was similar in the two basins, as deduced from the angiosperm/gymnosperm indices of the sedimentary rocks.

Palynological-age determination of Early Cretaceous vertebrate-bearing beds along the south Victorian coast of Australia, with implications for the spore-pollen biostratigraphy of the region

Palynology is used to provide new age controls for the coastal exposures yielding Early Cretaceous vertebrate faunas in the Otway and Gippsland basins, southeast Australia. This work shows all vertebrate-bearing deposits in the Otway Basin are Albian in age. On the eastern margin of Cape Otway, vertebrate-bearing deposits are attributed to the early Albian Crybelosporites striatus Zone, except for one in the younger Coptospora paradoxa Zone. To the west of Cape Otway, the sampled deposits range from the oldest zone in the Albian, the C. striatus Zone, to the C. paradoxa and Phimopollenites pannosus zones, providing a complete section of the Albian stage. In the Gippsland Basin, the structural setting of vertebrate deposits is more complicated and large portions of the coastal exposures consist of repeated sections controlled by small-scale faults. Sites in this region lie below or above the Barremian/Aptian boundary. However, owing to the paucity of age indicator species, some sampled deposits remain undated. In this basin, the ranges of certain key palynomorph species (e.g., Pilosisporites notensis and Pilosisporites parvispinosus) differed from those outlined in some previously published biostratigraphic schemes. The discovery of the angiosperm pollen Clavatipollenites hughesii in the lowermost Aptian deposits of the Gippsland Basin is consistent with its first occurrence elsewhere in Australia and shows it is a reliable indicator for the Aptian stage. This study shows that there is currently a collection bias towards vertebrate assemblages that are latest Barremian and early Albian in age.Barbara E. Wagstaff [wagstaff@unimelb.edu.au], The School of Earth Sciences, The University of Melbourne, Victoria 3010, Australia; Stephen J. Gallagher [sjgall@unimelb.edu.au], The School of Earth Sciences, The University of Melbourne, Victoria 3010, Australia; W. Michael Hall [mike.hall@monash.edu], School of Earth, Atmosphere and Environment, Monash University, Clayton, Victoria 3800, Australia; Vera A. Korasidis [korasidisv@si.edu], Smithsonian Institution, National Museum of Natural History, Department of Paleobiology, NHB121, 10th and Constitution Avenue, NW, Washington, DC20013-7012, USA; Thomas H. Rich [trich@museum.vic.gov.au], Melbourne Museum, 11 Nicholson Street, Carlton, Victoria 3053, Australia; Doris E. Seegets-Villiers [doris.seegets-villiers@monash.edu], School of Earth, Atmosphere and Environment, Monash University, Clayton, Victoria 3800, Australia; Patricia A. Vickers-Rich [pat.rich@monash.edu], School of Earth, Atmosphere and Environment, Monash University, Clayton, Victoria 3800, Australia and Swinburne University of Technology, Department of Chemistry and Biotechnology, Faculty of Science, Hawthorn, Victoria 3122, Australia.

Geochemical evaluation of aliphatic and aromatic hydrocarbons in Palaeogene source rocks from the Latrobe Group, Gippsland Basin, Australia

Twenty-seven hydrocarbon source rocks from the Proteacidites asperopolus, Malvacipollis diversus and Lygistepollenites balmei biozones, Palaeogene Latrobe Group in the Gippsland Basin were analysed using gas chromatography-mass spectrometry. Based on the molecular geochemistry of the aliphatic and aromatic fractions, together with bulk geochemical data (including Rock-Eval pyrolysis and total organic carbon contents), the thermal maturity, palaeoenvironments, and organic matter source of these Palaeogene samples were systematically evaluated. The results provide a useful comparison with those from Upper Cretaceous source rocks in the Gippsland Basin (Jiang and George, 2018, 2019). Similar to the Upper Cretaceous rocks, the aliphatic hydrocarbons in the Paleogene samples are mainly comprised of n-alkanes, isoprenoids, terpanes, hopanes and steranes. The aromatic hydrocarbons are dominated by naphthalene, phenanthrene, anthracene, fluorene, dibenzofuran, dibenzothiophene and their alkyl homologues. Other aromatic hydrocarbons detected include land plant-derived compounds (e.g. retene, methylretenes, cadalene, simonellite, etc), and combustion-derived compounds (e.g. chrysene, pyrene, picene, benzo[b]fluoranthene, benzo[a]anthracene, etc). These 4- to 6-ring polycyclic aromatic hydrocarbons are more abundant in the Paleogene samples compared to the Upper Cretaceous rocks. Biomarker and aromatic hydrocarbon distributions indicate that the Proteacidites asperopolus and Malvacipollis diversus samples are immature or are in the early stage of the oil generation window, while the Lygistepollenites balmei samples correspond to the low maturity to mature stage. The samples were all deposited under sub-oxic to oxic conditions in fresh water with low salinity, possibly in a lacustrine depositional environment. The organic matter inputs are from plankton/algae and higher land plants, but are dominated by organic matter with a terrigenous origin.

A probability model to detect carbonate cementation in sandstones and other enigmatic wireline facies

Zones of carbonate cementation identified within lower Paaratte Formation sandstones of the eastern Otway Basin, Victoria, southeastern Australia, can be quantitatively detected by a wireline log-based probability model. Though trained on these zones, the same model appears to accurately predict carbonate cementation within Late Cretaceous-to-Eocene reservoir sandstones of the Latrobe Group supersequence of the Gippsland Basin, 100s of km to the east. Predicted carbonate cementation matches published evidence (a regional petrographic study) and provides a plausible interpretation for corresponding sections of Formation Micro-Imager data acquired more recently. These Latrobe Group sandstones are thought to have once been pervasively cemented prior to development of the secondary porosity responsible for providing reservoirs to the main petroleum system of the basin. However, model predictions imply that discrete, heavily cemented zones remain, which must have acted, and must still act, as local obstructions to reservoir fluid migration. These zones would also likely react with carbonic acid formed at plume fronts generated by dedicated CO2 storage operations of the future. The cemented zones that have been predicted are sparse, spatially sporadic and cannot be resolved by 3D seismic reflection survey data at present-day reservoir depths. These predictions therefore emphasise the difficulty in mapping the distribution of carbonate cemented zones. However, they provide calibration data for future mapping systems.Two different tests of the probability log model were undertaken. One benchmarks its predictions against those of a neural network trained using the original model development dataset from the Otway Basin. Predictive performance of the neural network model is significantly worse than that of the probability log model when making predictions using wireline data acquired at a well in the Gippsland Basin. The second test demonstrates that the general probability log modelling approach is amenable to classifying other cryptic ‘electro-facies’, for example those representing enigmatic or ambiguous rock types not easily interpreted from common wireline log data using standard theory. This test presents a case study by which the probability log modelling approach predicts the presence of both basic and evolved, felsic igneous sill intrusions within the stratigraphic succession of the Faroe-Shetland Basin of NW Europe.

Amber from the Triassic to Paleogene of Australia and New Zealand as exceptional preservation of poorly known terrestrial ecosystems

The Northern Hemisphere dominates our knowledge of Mesozoic and Cenozoic fossilized tree resin (amber) with few findings from the high southern paleolatitudes of Southern Pangea and Southern Gondwana. Here we report new Pangean and Gondwana amber occurrences dating from ~230 to 40 Ma from Australia (Late Triassic and Paleogene of Tasmania; Late Cretaceous Gippsland Basin in Victoria; Paleocene and late middle Eocene of Victoria) and New Zealand (Late Cretaceous Chatham Islands). The Paleogene, richly fossiliferous deposits contain significant and diverse inclusions of arthropods, plants and fungi. These austral discoveries open six new windows to different but crucial intervals of the Mesozoic and early Cenozoic, providing the earliest occurrence(s) of some taxa in the modern fauna and flora giving new insights into the ecology and evolution of polar and subpolar terrestrial ecosystems.

Cenozoic structural evolution of the Mount Lofty Ranges and Flinders Ranges, South Australia, constrained by analysis of deformation bands

The presence of deformation bands in Upper Cretaceous–Pleistocene sediments of the St Vincent and Lake Eyre basins, South Australia supports the occurrence of intraplate normal and reverse faulting in this region throughout the Cenozoic. Current tectonic models for the development of this region lack structural evidence and underestimate the role and influence of extensional tectonics in the Cenozoic tectonic evolution of the Mount Lofty Ranges and Flinders Ranges. This lack of understanding has resulted in poor structural and chronological constraints of the regions paleostress models. For the first time, we use detailed mapping and structural analysis of deformation bands across different chronostratigraphic units to identify variations in paleostress. Deformation bands are discrete, measurable strain features that develop readily in clastic sedimentary rocks in response to regional stress. We present a comprehensive structural analysis of five study sites across six chronostratigraphic units adjacent to the Mount Lofty Ranges and Flinders Ranges. Here, we have recorded 737 cataclastic and dilation bands and 397 fractures adjacent to reactivated Cenozoic faults, which reveal step changes in structural sets, identifying temporal constraints for our paleostress model. Our analysis supports the notion of a regional late Miocene shift in the paleostress regime from N–S extension to N–S compression, followed by a rotation of the maximum horizontal stress (σ H ) from NW–SE to E–W. This coincides with a well-documented pulse of late Miocene–Pliocene compression and uplift observed throughout southeastern Australia. Our results indicate that deformation bands are a useful resource for constraining discrete changes in local stress regimes and enhance our understanding of dynamic intraplate strain accommodation within the Mount Lofty Ranges and Flinders Ranges. These have proven useful for hydrocarbon and mineral exploration in neighbouring Otway Basin and Gippsland Basin.

Cenozoic structural history of the Gippsland Basin: Early Oligocene onset for compressional tectonics in SE Australia

Abstract The Gippsland Basin contains some of the largest hydrocarbon accumulations in Australia, and has been in production since the 1920's. These hydrocarbons are trapped by large growth anticlines offshore, in reservoirs of the Cretaceous to Eocene-aged Latrobe Group. Despite the obvious importance of these growth anticlines, the timing of their formation, and the overall Cenozoic tectonic history of the basin is not well understood. Here, we present a detailed growth strata analysis of the faults and anticlines within the Cenozoic sediments of the Gippsland Basin. This indicates two major phases of tectonism in the basin: 1. Late Cretaceous to Eocene extension, and 2. Oligocene to Holocene compression. Detailed analysis of the extensional phase indicates the development of numerous normal growth faults, which display an overall reduction in the magnitude of extension from the Late Cretaceous to the Eocene, commonly terminating at the top of the Latrobe Group. The shift to compressional tectonism occurred at approximately the Eocene-Oligocene boundary (~34 Ma). A major and widespread episode of compression then occurred, with evidence of growth on anticlines and reverse faults beginning in the early Oligocene. This previously unrecognized early Oligocene event produced significant growth (20–50% total growth) of the major anticlines which host hydrocarbon accumulations. The early Oligocene event represents the first phase of the compressional tectonic regime that continues to the present day in SE Australia. It appears likely that this Oligocene event affected other basins in SE Australia and probably contributed to uplift of the Eastern Highlands. The underlying tectonic cause for this Oligocene compressional regime is enigmatic and may be related to far field tectonic processes. A second pulse of compressional tectonism and anticline growth occurred during the mid-Miocene and is generally more significant in the onshore regions of the basin. The youngest phase of compressional tectonism beginning in the Late Miocene (~10 Ma) is also more intense in onshore regions and is marked by an unconformity that is widespread in SE Australia.