Cenozoic Channel Deposits of the Bowen Basin, Queensland

Yu, Tianjiao1, Dube,Kudzai1, Moss, Professor Patrick1, Abylgazina, Adiya1, Cooling, Jennifer1, Esterle, Professor Joan1

1School of Earth and Environmental Sciences, The University Of Queensland, Australia

During the Late Cretaceous through Cenozoic, uplift and weathering in the northern Bowen Basin region, created a series of deep (up to 150 m) channels that filled with sediments and lava flows. The Australian Cenozoic was a time of great climatic and tectonic change. From the Late Cretaceous as Australia and Antarctica separated and the Australian plate moved northwards, the climate became warmer and drier, and the characteristic modern Australian flora developed. These paleochannels provide an important record of these changes, however their development, age of deposition and the impact of changing weathering conditions are poorly understood. Analysis of core samples confirm that the channel sediments host palynofloras identified as Late Cretaceous to Eocene, and record a change from a fire prone environment to a warm and wet high-density rainforest by the Paleogene. Aridification followed from the Neogene into the Quaternary. Lithological and mineralogical analysis of basaltic lavas from the area indicate they were deposited both as subaerial pahoehoe and sub-aqueous pillow lavas, suggesting that inland lakes covered the landscape at the same time as the volcanisms occurred. These lakes also form carbonaceous mudstones and lignite.

Some channels also floored by tens of metres of breccia that contain angular clasts of underlying Permian strata which fine upwards to conglomerates and sandstones, and also exhibit soft sediment deformation and sedimentary injection features.  These are interpreted as alluvial fans initiated by extensional faulting that may have been seismically active during deposition, and contributed to subsidence resulting in the inland lakes.  Here thick (2 to 4 m) lignites alternating with kaolinite-rich white clays and heavily altered claystones complete the sedimentary sequence that is then capped by basaltic lava flows. The kaolinite-rich clays can have a number of different origins. It may be primary, or weathering products of intrusive quartz rich rhyolite, tuff, or other sediments subjected to hydrothermal alteration beneath the basalts or stripped by humic acids from the lignites. The origins and timing of kaolinite development is being investigated.


Biography

Tianjiao is currently in Honours year in a Bachelor of Environmental Science at UQ, majoring in Earth Resources.

Dryland Coastal Deltas of Western Australia – Reservoir Analogues for Mixed-influenced Fluvial-deltaic Depositional Systems

Lang, Prof. Simon1, Paumard, Victorien1, O’Leary, Mick1, Goodwin, Ian1, Cousins, Victoria1, Lebrec, Ulysse1, Jian, Andy1, Holbrook, John2, Smith III, Pomeroy2, Hasiotis, Stephen3, Vakarelov, Boyan4 & Krapf, Carmen5

1University Of Western Australia, , Australia 2Texas Christian University, Dallas, Texas, USA 3Kansas University, Lawrence, Kansas 4Sedbase, OOD, Sophia, Bulgaria 5Geological Survey of South Australia, Department of Energy and Mining, Adelaide

Marine deltas are controlled by the dominance of fluvial outflow (F) relative to the influence of waves (W) and tides (T) that control facies distribution. However, in dryland deltaic systems, the rivers typically flow only following ephemeral or seasonal flooding events (i.e., a few weeks of the year either following cyclones or winter storms).

This study focusses on the influence of increasing tidal range and wave power on the coastal geomorphology of three coastal deltas along the arid to semi-arid coast of Western Australia (Gascoyne, Ashburton, and de Grey river deltas), and the role of distributary channel avulsion that build large distributary fluvial systems. Satellite image-derived bathymetry, dGPS transects, digital elevation models, ground penetrating radar, auger holes and outcrops are used for facies mapping of the surficial stratigraphy. Initial results show internal geometries and facies distribution of channel bar forms (dominated by coarse- and medium grained downstream and lateral accretion macroforms), alluvial and delta plain silt- and mud-prone oxidised overbank facies, sandy and silty coastal plain tidal-flats, tidal channels, well-sorted fine-grained sandy strandplain beach ridges, and fine-medium grained distributary mouth bars.

Fluvial distributary channels undergo upstream avulsion and new fluvial mouth-bars grow, and alluvial flood deposits accrete or are eroded on the upper and lower delta plain. Most of the year, the mouth-bars are reworked by waves and tides to build asymmetric, mixed-influenced deltas, and aeolian processes rework the delta/coastal plain. As the tidal range increases from micro-tidal to meso- and macro-tidal, the individual mouth-bar elements become amalgamated into a very broad sand-prone delta front, increasing sand connectivity. Tidal reworked sands are pumped up the distributary channels in the lower delta plain, especially in the dry seasons, where they are highly bioturbated, and homogenized. Laterally, waves generate highly elongate beach-ridges accreting up-drift from the mouth-bars and becoming moulded by aeolian processes. Down-drift, tidal flats pre-dominate, stabilised by mangroves that also line the mud-prone tidal creeks.

High evaporation rates lead to high salinity in the delta plain distributary channels, coastal lagoons and salinas. Calcareous ooids in foreshore deposits are preserved in some of the beach-ridges.

The 2D and 3D geometry and spatial juxtaposition of facies has implications for the range of uncertainty in subsurface reservoir/aquifer modelling of dryland fluvial-deltaic reservoirs.


Biography

Professor Simon Lang is a sedimentologist and stratigrapher with global experience including regional geological mapping, sedimentology/stratigraphy research, and petroleum exploration & development. He is Director of the Centre for Energy Geoscience, University of Western Australia, leading industry-funded research on quantitative seismic stratigraphy and reservoir analogues.

Late Holocene landscape dynamics and sediment cycling around Lake Callabonna, Central Australia

May, J.-H.1,2, Marx, S.2, Cohen, T.2, Schuster, M.3 & May, S.M.4

1School of Geography, University of Melbourne, Melbourne, Australia, 2GeoQUEST Research Centre, University of Wollongong, Wollongong, Australia; 3Institut de Physique du Globe, University of Strasbourg, France; 4Institute of Geography, University of Cologne, Cologne, Germany

Lake Callabonna is one of four large connected playa lakes northwest of the Flinders Ranges in South Australia. These lakes are now mostly dry but would have joined to form mega-lake Frome that existed until ~45 ka. Although interrupted by major highstands, lakes declined in size since then and became successively disconnected. While this would significantly alter lake hydrology over time, the pronounced variability in lake levels also must have had a profound impact on the ways in which sediment were (i) supplied to the lakes by fluvial processes, (ii) distributed and deposited in various parts of the lake basin by lacustrine and coastal processes, or (iii) re-activated to be exported from the playa lake system by aeolian processes. In this spatially and temporally highly dynamic system, source-bordering lunettes play a particularly significant role by linking these different depositional and erosional environments. Despite the important clues these landforms may therefore hold in assessing mechanisms, timescales and controls on landscape-scale sediment flux in drylands, existing models of lunette formation are still very limited and often oversimplified. To contribute new data and discussions towards a better understanding the dynamically evolving landscapes around dryland playa lakes, we therefore explore the use of ‘source-to-sink’ perspectives in unravelling the palaeoenvironmental potential of desert lunettes, and specifically discuss geomorphic, sedimentary and geochronological data from Lake Callabonna in South Australia.

Multiple lunettes were identified around Lake Callabonna and occur in various shapes, sizes and orientations reflecting significant variability in sediment source and/or aeolian transport processes over time. We here present new data from a small km-scale lunette adjacent to the Moppa-Colina delta in the northwestern corner of the lake. Lunette texture is dominantly sandy and implies depositional processes analogous to coastal foredunes. Sedimentary architecture, however, is characterized by laterally continuous and finely interbedded intercalations of well-sorted fine and loamy sands, respectively. These observations are inconsistent with foredune formation, and rather point to processes of frequent and alternating processes of extensive aeolian sand accretion (i.e. draping) across the landscape. Our topographic and new chronological constraints suggest that sustained sediment supply in a late Holocene seasonally active deltaic environment at the interface between fluvial, lacustrine, coastal and aeolian process domains may best explain the observed morpho-stratigraphic data. In contrast to its growth over more than two millennia, the lunette has been actively eroding over the last few centuries from the combined effects of wind and water. In combination, our observations and preliminary results imply that in addition to variations in wind speed and direction, or the source and supply of sandy sediment, changes in vegetation cover (e.g. pre vs post-European land use) have to be considered when discussing the depositional and post-depositional mechanisms involved in sandy lunette formation as well as their potential for recording late Quaternary palaeoenvironmental conditions and pathways of sediment transport in drylands.


Biography

Dr Jan-Hendrik May is a Physical Geographer. Following from his PhD in Bern, Switzerland, he worked on several postdoctoral and assistant positions in Australia, China and Germany, and is now senior lecturer in Melbourne. His research interests are Quaternary climate-driven sedimentary dynamics in arid Central Australia and the Central Andes.

Lacustrine littoral landforms in drylands: diversity and significance with examples from Quaternary megalakes of Africa and Australia

Schuster Mathieu1, May Jan-Hendrik2,3, Nutz Alexis4

1CNRS & University of Strasbourg, Strasbourg, France, 2School of Geography, University of Melbourne, Melbourne, Australia, 3GeoQUest, University of Wollongong, Wollongong, Australia, 4Aix-Marseille University, Aix-en-Provence, France

Due to the scarcity of water that defines dryland continental systems, the superficial processes (erosion, transport and deposition) are there dominantly controlled by wind and intermittently by water. As such, sedimentologists and geomorphologists working in drylands expect to find there a great diversity of landforms, bedforms and surfaces related to aeolian and alluvial-fluvial environments. However, it is not rare to also identify abandoned landforms which are quite exotic for drylands, such as beach ridges-and-swales, spits, cuspate forelands, barrier islands, wave-ravinement surfaces, or lobate-cuspate deltas. These typical shore-related morpho-sedimentary structures evidence past more humid events or periods that have culminated in the development of large lakes. As for their marine counterparts, these littoral landforms provide key geomarkers to restore the trajectory of the shorelines through time, and to understand the cross-shore and alongshore redistribution of clastics by waves and currents.

To illustrate the diversity of the lacustrine littoral landforms that can be preserved in drylands and to explain their significance for climate, environments and hydrodynamics, we focus here on a selected number of remarkable very large paleolakes which developed over Quaternary times in continental deserts from both hemispheres. These are Megalakes Chad, Eyre Kati-Thanda and Frome (Cohen et al. 2012; May et al. 2015; Schuster et al. 2005).

According to both the physiography of the lake basins and the importance of the associated littoral landforms marking their shorelines, these megalakes can be considered as wind-driven waterbodies (Nutz et al. 2018), a category of lakes for which sedimentation is dominated by wind-wave-related processes and basin-scale wind-induced hydrodynamics.

References cited

Cohen et al. 2012. https://doi.org/10.1016/j.palaeo.2011.06.023

May et al. 2015 https://doi.org/10.1016/j.yqres.2014.11.002

Nutz et al. 2018. https://doi.org/10.1007/s10933-016-9894-2

Schuster et al. 2005. https://doi.org/10.1016/j.quascirev.2005.02.001


Biography

I received my PhD in sedimentary geology from the University of Strasbourg in 2002. I then worked at the universities of Cologne, Brest and Poitiers, and at the French geological survey. My deals with continental paleoenvironments, with a focus on clastic littoral lacustrine systems.

Circadian rhythm of dune-field activity

Gunn, Andrew1, Lancaster, Nicholas2, Edmonds, Douglas3, Ewing, Ryan4, Jerolmack, Douglas1

1University of Pennsylvania, Philadelphia, United States, 2Desert Research Institute, Reno, United States, 3Indiana University, Bloomington, United States, 4Texas A&M University, College Station, United States

Wind-blown sand dunes are both a consequence and a driver of climate dynamics; they arise under persistently dry and windy conditions, and are sometimes a source for airborne dust. Dune fields experience extreme daily changes in temperature, yet the role of atmospheric stability in driving sand transport and dust emission has not been established. Here we report on an unprecedented multi-scale field experiment at the White Sands Dune Field (New Mexico, USA), where we demonstrate that a daily rhythm of sand and dust transport arises from non-equilibrium atmospheric boundary layer convection. A global analysis of 45 dune fields, including those in Australia, confirms the connection between surface wind speed and diurnal temperature cycles, revealing an unrecognized land-atmosphere feedback that may contribute to the growth of deserts on Earth and dune activity on Mars.


Biography

Andrew Gunn is a PhD candidate in Earth & Environmental Sciences at the University of Pennsylvania advised by Prof. Douglas Jerolmack. His dissertation is on aeolian process geomorphology. He completed his undergraduate at the University of Melbourne in Applied Mathematics, and Honours at the University of Tasmania in Physical Oceanography.

Australian Drylands Depositional Environments: Local News, Globally Relevant

Wakelin-King, Gresley A.1

1Wakelin Associates, Melbourne, Australia

Landforms and sediments of continental drylands are relevant to the rock record and to sustainable land management. Globally, many strata were deposited in dryland settings, and modern landscapes are used as analogues for conceptual models of depositional processes. In the present day, ~40% of the world’s land is drylands, and it houses >30% of the people ; Australian drylands are ~80% of the main continent and contain communities, industries and biodiversity.  Understanding how drylands work is clearly desirable. Globally, drylands have highly variable rainfall, highly to extremely variable flow regimes, and a moisture deficit: attributes which govern biota life strategies, and create characteristic sedimentary deposits.

Previously, modern analogues focussed on northern hemisphere examples, typically from coarse-clastic, tectonically vigorous, high gradient catchments with flashy hydrology. Australia‘s context is different: low-relief, low-gradient, subtly expressed neotectonism, a blanket of regolith, and ephemeral rivers capable of big floods and sustained flows. Few Australian drylands sediments have been well-documented; other similar drylands (Thar desert, India; sub-Saharan Africa) may also be under-represented in (English-language) literature, or under-utilised as modern analogues.

This presentation journeys through some Australian continental sedimentary landscapes.

Mud-Aggregate Floodplain, Massive Mudrock

Mud aggregate floodplains are the modern analogue for massive mudrock. The current modern analogues (both located in Australia) are vertic soils transported as sand/ silt-sized bedload. Cooper Creek’s floodplain has black muds deposited/reworked in braid-like bars; Fowlers Creek is a cut-and-fill floodplain with vertically-accreted red muds.

Low-Angle Alluvial Fans

In Australia downstream-diverging fluvial networks are common, usually as low-angle alluvial fans. Channel systems range from coeval multithread to ~single channels sequentially moving across a depositional surface. Fine sediments transported by low-energy flows create broad low-gradient fans. Diverse topographic and climatic contexts lead to a range of sedimentary deposits, most of which are undocumented. Two examples are the mud-dominant Lodden Fan in semi-arid grassland, and the complex aeolian and fluvial sands in the Cooper Creek Fan (Strzelecki Desert).

Floodouts: a Fluvial Process

Floodouts are unchannelised river reaches (flow path is 100% floodplain). Declining discharge during development of Cainozoic aridity means that many Australian drylands rivers are underfit, or their flows no longer extend down the length of the network. Episodic and incomplete sediment transport promotes floodout formation, typically where flow emerges from lateral constriction and loses sediment transport capacity. Floodouts occur in rangefront plains, macrochannels, and valley confluences; they are valuable in land management. Some floodout bedding sequences could be identifiable in the rock record.

Flashy Flow Events, Froude Numbers, and Flat Bedding

Sedimentary fluvial rocks from a drylands setting may include planar-bedded sands. Comparison with the standard bedform diagram may lead to an interpretation of deposition during the high-energy (F = 1) flood peak of a “typical” flashy desert flow. However, bedforms in modern drylands rivers demonstrate more complex conditions including widespread subcritical (F <1) planar bedding, and low-energy gravel imbrication. Bedforms are governed by grain size and flow velocity, but also by flow depth and sediment composition; this leads to intriguing bedform combinations in rivers with rapid flood recession.


Biography

Dr. Wakelin-King is a geological geomorphologist, specialising in drylands rivers and sediments. Her professional practice aims at normalising geomorphology within sustainable landscape management. She researches fluvial processes in the Lake Eyre Basin and western NSW, and strongly advocates for fieldwork as a necessary component of remote-area landscape studies.

About the GSA

The Geological Society of Australia was established as a non-profit organisation in 1952 to promote, advance and support Earth sciences in Australia.

As a broadly based professional society that aims to represent all Earth Science disciplines, the GSA attracts a wide diversity of members working in a similarly broad range of industries.