Australian Rocks and the Search for Life on Mars

David Flannery1

1Queensland University of Technology, Brisbane, Australia

Recent orbiter and rover missions to Mars have culminated in a new appreciation of the vastly difference surface conditions that prevailed in Mars’ distant past. During the Noachian (roughly corresponding to the Hadean and early Archean), Mars appears to have supported a much denser atmosphere, abundant standing bodies of liquid water, significant volcanism and a stronger magnetic field. The next few years will see the arrival of several geology-focused, multi-billion-dollar, lander and rover missions supported by the USA, the European Union, and China.

Astrobiologists interested in the possibility of a Martian biosphere are focusing their attention on rocks dating from the Noachian, which, compared to the Earth, appear to be well-preserved and exposed in relatively extensive outcrop. NASA has chosen an extensive package of sedimentary rocks dating from this time period for it’s next flagship mission: the Perseverance Rover. Perseverance will study clay-rich deltaic units and chemical sedimentary rocks deposited at the margin of a paleolake in Jezero Crater, hoping that they will yield informative evidence for past environmental conditions, and evidence for life itself. Fluvial and lacustrine rocks in Earth’s geological record are driving the exploration of these exciting Martian deposits. Well-preserved Archean river and lake systems in Western Australia are providing a valuable depositional analogue for a closed basin that may also have developed on a microbially-dominated planet, several billion years ago.

Along with modern and other ancient analogues, Australian fluvio-lacustrine systems preserved in the Neoarchean Fortescue Group have been used to develop an exploration model for microbial biosignatures sought by upcoming Mars missions. In the Fortescue Group, the greatest abundance and diversity of macroscopic biosignatures is found at the upper contacts of regressive lithostratigraphic cycles and at lake peripheries. Macroscopic biosignatures such as stromatolites can in turn be used to target fine-scale lithochemistry instruments, for example those carried on the robotic arm of Perseverance, and the drilling/caching of samples that will be returned to Earth for study in laboratories.


Biography

David is an astrobiologist focused on palaeoenvironments of the early Earth and Mars. He completed a postdoc at Caltech before joining NASA’s Jet Propulsion Laboratory in 2015. He’s a Long Term Planner for NASA’s upcoming Perseverance Rover mission, and a Co-Investigator for an instrument on the rover’s robotic arm.

A Pb Isotope Regolith Map of Australia

Desem, Candan1, Maas,Dr Roland1, Woodhead, Professor Jon1, Carr,Dr Graham2, de Caritat, Dr Patrice3

1The University Of Melbourne, Parkville, Australia, 2CSIRO, North Ryde, Australia, 3Geoscience Australia, Canberra, Australia

The lead (Pb) isotopic composition of the regolith reflects contributions from bedrock geology, mineralisation, wind-blown dust and anthropogenic contamination (industry, transport, agriculture,
residential, waste handling). Evaluating the relative roles of each contribution is critical to many studies ranging from attempts to capture the history and extent of Pb pollution through to mineral
resource exploration programs. To this end we have produced the first Pb isotope map of Australia’s regolith at a continental scale. Catchment outlet (~ floodplain sediment) samples collected for
Geoscience Australia’s National Geochemical Survey of Australia (NGSA) program, with an average sampling density of 1 site/5200 km2 and covering ca. 81% of the Australian continent, were utilised here. The coarse grain-size fractions (<2 mm) of the top outlet sediment (0-10 depth) samples were selected.

A number of acid leaching protocols have been devised to separate loosely bound Pb (e.g. aerosol from anthropogenic contamination) from Pb structurally bound in minerals (from the underlying
geology, mineralisation, or their weathering products). We utilised a sequential leach protocol with ammonium acetate followed by aqua regia (HNO3-HCl), originally developed by Mike Korsch and Graham Carr at CSIRO. Ammonium acetate is expected to extract loosely bound Pb sourced from windblown dust (including anthropogenic contributions) or from shallow groundwater interaction. Pb extracted using the more aggressive aqua regia step represents the underlying geological signature. Pb isotope compositions were acquired using a sector-field ICP-MS, which provided ‘fit for purpose’ levels of precision/accuracy and the high throughput required in order to process large sample sets – more than 1500 samples in this case.

Our research program aims to (i) compare the Pb isotope signatures released by the two leach protocols, (ii) examine if soil Pb isotope mapping can identify underlying geology and metallogenic
provinces, and (iii) investigate anthropogenic signals across the continent. Preliminary analysis of the data obtained for the aqua regia leachates shows clear and distinct trends reflecting the underlying bedrock geology. For example, the Archaean rocks of the Yilgarn and Pilbara Cratons are marked by regolith with more radiogenic Pb isotope compositions, while regolith samples from younger geological provinces (e.g. Tasmanides of eastern Australia) have less radiogenic Pb isotope signatures. Other geological elements (e.g. Gawler Craton, Curnamona Province) are also clearly distinguished. Preliminary Pb isotope maps of the continent will be presented.


Biography

Candan is a PhD candidate at the University of Melbourne, School of Earth Sciences. In a collaboration with Geoscience Australia, Candan’s PhD investigates the use of Pb isotopes in the regolith as tracers for environmental contamination and mineral exploration. Candan has developed the first Pb isotope regolith map of Australia.

Reviewing stratigraphic units defined in the ACT

Marais-van Vuuren, Christo1 , Brown, Catherine1, Jarrett, Amber1

1Geoscience Australia / GSA ACT and External Territories Stratigraphy Subcommission, Canberra, Australia

The usual role for Australian Stratigraphy Commission members in most of Australia is to assist geologists writing up unit definitions or redefinitions, in areas of recent study http://www.ga.gov.au/data-pubs/datastandards/stratigraphic-units/unit-definition-form . The situation in the ACT is a bit different. Although there has been recent mapping work in surrounding areas of NSW, and recent geochronology done on 9 units in the ACT, there has been no new mapping or revision of geological units in the ACT since Bob Abell’s (1991) Geology of the Canberra 1:100 000 sheet area, which only covers the northeastern part of the ACT. Geological mapping over the rest of the ACT (Brindabella, Tantangara and Michelago sheets) is even older. Many of the original unit descriptions and definitions were done by Armin Opik in 1958. Some of these have never been revised.

Prior to self-government in the Australian Capital Territory (ACT), the Bureau of Mineral Resources had an engineering geology and mapping role in the Territory, but that role has not been maintained at either local or federal level. So, given the urban development and other landscape modifications in the ACT, the ACT Stratigraphy Subcommission has decided it would be useful to review the type section locations of units defined in the ACT. The initial aim is to make it easier to find most of them, but we will also need to consider replacement type sections/type areas, in cases where the original is no longer accessible, and possibly some additional reference sections too.

There are 78 current stratigraphic units identified in the ACT, many of them also extending into NSW. At least 22 of those units have been defined/redefined in the ACT. All of the type sections or type areas need locations revised to a modern, known co-ordinate system (GDA 2020). It is already clear that locating some of the type sections will involve some historical research and comparison of old maps with modern ones. We have also identified that some of the original locations are no longer accessible due to road realignments, modification or ‘treatments’ of road cuttings, flooding (creation of artificial lakes) etc. Where type or reference sections have been nominated in drill core, we need to ascertain whether or not the core is still accessible, as well as the location of the hole.

The project is in the early stages, and has started with a review of the information available through the Australian Stratigraphic Units Database http://www.ga.gov.au/data-pubs/datastandards/stratigraphic-units  and information in other Geoscience Australia and ANU databases. We expect the review will lead to some local field trips and hope that our work may encourage further review of ACT geology generally, to improve edge-matching with more recent geological work by the Geological Survey of New South Wales, in particular.

Ultimately this work will represent a major update to type section understanding and definitions of stratigraphic units in the ACT, which is decades overdue. If it also encourages some other old definition reviews, that would be a bonus.


Biography

Christo graduated from Macquarie University in 2014 with a BSc majoring in geology and geophysics. He then worked for industry as a geophysicist prior to joining GA in 2016 in the stratigraphy section where he works on maintaining the Australian Stratigraphic Units Database. Recently he has joined the Stratigraphy Commission.

Quantifying lateral and distal variability within hybrid beds, case studies from Central and Northern Italy

Brooks, Dr Hannah1, Steel,Dr Elisabeth2

1 School of Earth Sciences, 253-283 Elgin St, University of Melbourne, Carlton Victoria, Australia, 2 Department of geological sciences and geological engineering, Bruce Wing/Miller Hall, 36 Union Street, Queen’s University, Kingston, Ontario, Canada.

Hybrid beds or linked debrites are deposits that form under bi- or tri-partite flow conditions, involving both turbulent and laminar flow conditions. Often, hybrid beds occur with distal or lateral flow transformation following significant entrainment of a muddy substrate and/or declining turbulent energy. Hybrid beds have been noted to make up significant proportions of deposits within basin floor setting worldwide, most commonly within the distal fringes of lobe systems. The study examines dip and lateral variations in facies and architecture in hybrid beds using detailed facies analysis of selected sections within the Castagnola, Marnoso-Arenacea, and Gottero Formations, deposited within three different basins within central and northern Italy. Sections within these systems were selected where hybrid beds could be traced out laterally or down-dip for several metres to several kilometres. In total 407 samples were taken for laser-diffraction grain-size analysis. Samples were selected through beds at 20 cm intervals and across/ down-dip at 10’s of metre to several kilometre intervals. Layers within beds were classified into facies divisions which were ran through ‘EMMA’ End Member Modelling Analysis, this splits beds into an optimum number of end members that when combined create the trends found within the dataset. This method is utilized to establish patterns of changes within beds laterally and down-dip which are otherwise difficult or too complex to be quantified from field data alone.

This detailed study of facies, architectural and grain-size changes within the targeted deposits will help to establish how flow processes varied as flows spread laterally and moved downstream. Through quantifying the amount of mud within the matrix and clasts at any one time within the flow it is possible to interpret how and when turbidites and hybrid beds erode and incorporate sediment from underlying substrate. Initial results from EMMA indicate that using three end members for each formation is an optimum number for observing basinal trends within beds. These end members constitute a sand-rich unimodal end member, a silt-rich unimodal end member, and a bimodal poorly sorted end member, interpreted to represent a high-density turbidite, a low-density turbidite and a debrite respectively. Recognised trends within the data include a decrease laterally in the sand-rich unimodal end member within the Marnoso-Arenacea section, interpreted as an increased distance from the flow input or the presence of a lateral basin slope. Through application of this methodology in basins with well-established bed correlation it is possible to provide novel understanding that will significantly augment traditional field techniques. It is evident that laser diffraction grain-size analysis and EMMA are vital tools in furthering our understand of process sedimentology and should be applied more widely.


Biography

PhD in Sedimentology, University of Leeds, UK, studying Permian deepwater sediments in the Karoo Basin, South Africa. Undertook postdoc in Chiba University, Japan studying Pliocene deepwater outcrops, and Queens University studying hybrid beds in central and northern Italy. Now, postdoc at University of Melbourne studying Neoproterozoic rocks in Flinders Ranges.

Correlation of stratigraphic sequences to evaluate downstream transitions within the Wonoka canyon at Umberatana syncline, South Australia

Giles, Sarah M.1, Christie-Blick, Nicholas 1

1Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964, USA

Mid-Ediacaran (~580 Ma) paleocanyons as much as 1 km deep in the Wonoka Formation of South Australia are associated with the largest carbon-isotope excursion in Earth history, the Shuram anomaly. Widely interpreted as submarine, the canyons are thought by many to be comparable to those found at modern continental margins. New data from the northern Flinders Ranges reinforce an alternative hypothesis: that the Wonoka canyons were subaerially incised as a result of evaporative drawdown in a temporarily isolated marine embayment at the onset of the Gaskiers glaciation. Critical supporting evidence has emerged in the canyon-fill at Umberatana syncline, where four oblique cross-sections interpreted as a single sinuous canyon are being independently analyzed. The three incisions studied so far are characterized at the base by ~ 30-m-thick conglomerate-based cycles that are bounded by laterally persistent erosion surfaces and fine upwards into sandstone, siltstone, and minor carbonate (canyon-marginal tongues). Nine such cycles are confidently correlated between the first two incisions (Fortress Hill and Mt. Curtis), and at least plausibly related to seven cycles identified in the third incision (Muccabaloona south) on the basis of 168 measured sections and high-resolution physical stratigraphic mapping. Our correlation of cycles is based on similarities in facies stacking and stratigraphic position. Greater variability in cycle thickness at Muccabaloona south is attributed to facies changes within some cycles in the direction of sediment transport from channelized boulder conglomerate to pervasively rippled sheet-like sandstone and siltstone event layers, as well as a northward increase in structural complexity. The local erosional relief at cycle boundaries is comparable across the three outcrops: 3-6 m at Fortress Hill, 5-10 m at Mt. Curtis, and 3-7 m at Muccabaloona south. The observed stratigraphic organization and details of the facies lead us to interpret the diffusely stratified, channelized conglomerates as fluvial, and the prevalently rippled and laminated tabular sandstones/siltstones as deltaic. The lack of dish structures and nested channels in the sandstone facies, as well as the apparent absence of classical turbidites interstratified with hemipelagic mudstone further supports our fluvial-deltaic interpretation rather than a deep marine interpretation. An upward transition to primarily siltstone event layers interstratified with cm-scale carbonate couplets and monolithologic breccias is interpreted to represent canyon drowning. New field work is planned at the fourth incision (Muccabaloona north) to further test our model. We expect fewer conglomerate-based cycles, and additional fining overall. The correlation of stratigraphic cycles across all four incisions will allow us to evaluate the length scale of downstream facies transitions, which we expect to be much more abrupt in the subaerial incision model than the deep marine canyon interpretation.


Biography

Sarah Giles is a Ph.D. student at Columbia University in New York City, USA. Sarah’s Ph.D. research integrates geologic mapping, sedimentology, stratigraphy, isotope geochemistry, and geochronology to evaluate the origins, timing, and stratigraphic context of the mid-Ediacaran Shuram carbon isotope excursion in South Australia and eastern California.

Preservation of ancient eolian landscapes beneath flood basalt: an example from the Officer Basin, Western Australia

Haines, Peter1

1Geological Survey of Western Australia, Perth, Australia

Eolian landscapes should be common on planets with an atmosphere, and were presumably more widespread on Earth before the evolution of land plants. However, preservation of intact ancient eolian landscapes from this time period are rare. The Ediacaran to middle Cambrian succession of the Western Australian (WA) Officer Basin is dominated by eolian sandstone with interbedded alluvial fan, fluvial and playa deposits. Outcrops of this succession near the western end of the basin (McFadden Formation) include eolian foresets on a massive scale, possibly exceeding 60 m in height. Farther east, the broadly equivalent concealed Lungkarta Formation displays steeply-dipping single foresets up the 30 m in thickness in drillcore, and other sedimentary features confirming an eolian mode of deposition. In the central Officer Basin in eastern WA this eolian sandstone succession is overlain by the basaltic Table Hill Volcanics (THV), a component of the widespread c. 511 Ma (middle Cambrian) Kalkarindji Large Igneous Province of flood basalts and associated intrusions. Although rarely exposed, the distribution of the flat-lying THV can be mapped from drillhole intersections and aeromagnetic datasets. In one area the aeromagnetic patterns indicate that the basalt flowed over and entombed an active dune field. Near the southern margin of the flood basalt the flows thinned to be thinner than the height of the dune crests, allowing the dunes (relatively non-magnetic) to be clearly distinguished from the interdune corridors (filled with magnetic basalt). The resulting aeromagnetic patterns, enhanced by viewing the first vertical derivative of the total field data, indicate south-southwest trending compound linear dune ridges, each separated by parallel interdune corridors. The parallel basalt flows terminate southward along an irregular north-northwest trending boundary that was likely controlled by an inflection in the paleoslope. Details of dune morphologies indicate east-northeast directed prevailing winds, somewhat oblique to the east-southeast migration direction the overall composite linear dune crests. Modern analogues can be found in extremely arid vegetation-free dune areas such as the Rub’ Al-Khali sand sea of southern Saudi Arabia. A particularly good match is found in the east of this extensive sand sea (near 21ºN, 54ºE). This area likewise shows compound linear dune ridges moving obliquely to the prevailing wind direction indicated by the orientation of smaller scale dune components, although the interdune corridors are broader than the Officer Basin example. Coincidently, the ancient Officer Basin dune crest spacing (1 – 1.5 km) is similar to that of the modern vegetation-stabilised longitudinal dunes of the Great Victoria Desert in the same area today, although dune type is different and inferred crest heights are significantly greater in the ancient deposit. Apart from revealing the morphology of an ancient eolian landscape, the relationship with the dated basalt can now be used to infer a precise date for the top of this previously poorly-dated succession, as the dunes were apparently active at the time of entombment in the middle Cambrian. Similar burial of eolian and fluvial landscapes are suggested by aeromagnetic patterns elsewhere in the Kalkarindji Large Igneous Province.


Biography

Peter Haines has Honours and PhD degrees from the University of Adelaide. He has worked for the Northern Territory Geological Survey and Universities of South Australia and Tasmania. He is currently with the Geological Survey of Western Australia where he works on Neoproterozoic and Paleozoic basins throughout the state.

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