High resolution 40Ar/39Ar geochronology in continental margin settings – the Aegean plate margin as a natural laboratory for subduction processes.

Wijbrans, Jan1, Uunk, Bertrum1, de Paz Alvarez,Manuel1, Huybens, Rosanne1, Brouwer, Fraukje1

1Department of Earth Sciences, Vrije Universiteit Amsterdam, the Netherlands

Time scales of tectonic and metamorphic processes in the greenschist-blueschist domain are essential to better understand the dynamics of accretionary wedges. However, such time scales are difficult to obtain because the number of geochronometers available to us is limited. For these geochronometers only partial setting, or resetting, of the isotopic clocks can be expected at temperatures reached in the blueschist and greenschist facies, whilst shear zone deformation may not cause full recrystallization. New, or more refined geochronological approaches, can thus shed additional light on the processes in accretionary wedges.

The Aegean subduction complex has emerged over the years as a key natural laboratory to study subduction processes. Our focus in recent years has been on the subduction related processes as experienced by the rocks of Syros and Sifnos islands. Here, we report (1) our efforts to further refine dating approaches:  40Ar/39Ar by dating of suites of single phengite crystals on an outcrop to section scale, and (2) our work exploring new approaches of dating of minerals free of lattice-bound potassium such as garnet, amphiboles and epidotes by dating the signal derived from the fluid inclusions by stepwise crushing.

Dating complete 100+ m sections by single grain phengite dating has the added benefit that all available lithologies in the section contribute to a histogram or PD- plot. Where previously a multigrain average from a single rock specimen was obtained, now is revealed that different units record an age range often as much as 10 Myrs wide, the oldest ages recording crystallization and the younger resetting following crystallization. Dating fluid inclusions by stepwise crushing allows the identification of multiple fluid reservoirs that contribute to the obtained signal sequentially. Typically, the first crushing steps reveal a reservoir that contains large amounts of excess 40Ar, whereas following exhaustion of this reservoir other distinctly different sources of argon are revealed. Age signals thus obtained are interpreted as documenting periods of increased fluid mobility during and following mineral crystallisation.

Combination of these two approaches provides new insights into the tectonic processes during deep subduction and subsequent exhumation to shallower depths.


Biography

Jan Wijbrans is currently professor of Argon Geochronometry at the Vrije Universiteit Amsterdam. Jan was an ANU postgraduate research scholar at the Research School of Earth Sciences, ANU from 1981 until 1985, when he worked under the guidance of prof. Ian McDougall on timescales of metamorphic processes using the 40Ar/39Ar method.

40Ar/39Ar geochronology of syn-kinematic phengite reveals the tectonic history of underthrusted European crust (W Alps): a synthesis

Rolland, Yann1

1EDYTEM, Université de Savoie Mont Blanc, La Bourget du Lac, France

The major problem of 40Ar/39Ar geochronology applied to deformation is often to find sufficiently large crystals that grew in a clear relationship to the deformation context, and that have been preserved in the following tectonic history.

The dating of white mica syn-kinematic fibres (phengite) in complement to their PT conditions (obtained by combined mineralogical mapping for instance) allows the dating of deformation stages at a depth constrained by PT calculations and along certain geothermal conditions. Kinematics of related shear zones provide the polarity of tectonic motions. The integration of such data into the tectonic framework of a geodynamic zone allow deciphering along-belt variations, which relate to strain propagation and changes in the stress field through time and space.

The External Crystalline Massifs (ECM) of the Alps provide a nice case example of a crustal domain in which this technique was successfully applied to the dating of brittle-ductile motions at mid-crustal levels (10-15 km). The Western Alps are a curved mountain belt that accommodated tectonic motions related to subduction dynamics in the Mediterranean domain after a brief period of continent-continent collision of the Apulian microblock with Eurasia. Subsequently, the timing and the along-belt variations of deformations has been progressive through time.

In this presentation, I propose a synthesis of analyses conducted at the External Alps scale to investigate the timing of shear zone deformation since the onset of Eocene-Oligocene collision. The data include 40Ar/39Ar stepwise dating of synkinematic phengites, the associated shear zone kinematics and thermobarometric constraints on the depth and temperature of deformation. The advent of new dating approaches, based on U-Pb dating of syn-kinematic allanite, of hydrothermal vein monazite, and more recently, of calcite from veins and fault gouges, do confirm the timing of deformation suggested by the obtained 40Ar/39Ar ages on micas.

These dating constraints are used to discuss the timing of deformation of underthrusted European crust related to changes in tectonic modes during the Alps’ tectonic history. These changes are related, at the larger scale, to the evolution of the Mediterranean domain, i.e., to the rapid underthrusting of the external part of European plate, dated in the ECM at 35-32 Ma, followed by the onset a mainly dextral strike-slip context. This strike-slip context is controlled by the anticlockwise rotation of Apulia, notably driven by the Apulian roll-back.


Biography

Yann has worked on many orogen examples, starting from his PhD work on the Himalaya-Karakoram, to the Alps, Caucasus, Tien Shan… He develops approaches coupling geochronology and geodynamics. He has used the Ar/Ar chronometer applied to dating shear zone activity since his post-doc at the ANU in 2001.

Bitterroot and Anaconda Core Complexes: Cretaceous Ductile Flow and Eocene Detachment Faulting in the Northern U.S. Rocky Mountains Defined by Ar/Ar Thermochronology

Foster, David1

1Department of Geological Sciences, University of Florida, Gainesville, United States

The Bitterroot and Anaconda metamorphic core complexes of western Montana and central Idaho, U.S.A. were exhumed by Eocene extensional detachment faulting between about 53 and 38 Ma.  The rocks in the lower plates of these core complexes include highly sheared Proterozoic to Palaeozoic metasediments, Cretaceous granitoids, and Eocene felsic plutonic rocks. Early exhumation of the core rocks occurred after crust of in the Montana hinterland was dramatically thickened (forming the “Montanaplano”) between about 130 and 80 Ma. By Late Cretaceous time the middle crust of the orogenic pile was plastically deforming, resulting in large-scale nappes and shear zones. Voluminous intermediate to felsic igneous rocks intruded the shear zones and formed sheet-like plutons at thrust ramps.  Plastic flow led to ductile thinning of the middle crust coincident with out-wedging in the Montana fold and thrust belt. Rocks exposed in these two core complexes experienced about 5-10 km of exhumation in the Late Cretaceous on the basis of metamorphic assemblages, reconstruction of sections, and thermochronology of upper plate rocks. Eocene extension began in the Northern Rockies about 53 Ma and resulted in linked extensional detachments and magmatism in both core complexes. The Bitterroot complex underwent as much as 15 km of additional exhumation along a ductile to brittle detachment system that initiated with amphibolite facies mylonite. The Anaconda complex underwent about 10-12 km in the deepest part and records green-schist facies mylonite overprinted by transitional brittle-ductile fabrics, and brittle deformation.  Ar/Ar mica cooling ages from both detachments decrease from west to east and constrain the rates of fault slip and unroofing. Exhumation of the middle crustal rocks was at least a two-stage process with significant Cretaceous-Paleogene thinning by ductile flow, followed by unroofing beneath the east-rooted detachment systems. Thermochronology data indicate that both detachment systems developed as composite structures with shallower crustal levels and less exhumation in the west rooting to about 10-km deeper to the east. The hanging wall of the Anaconda complex includes the less-deformed Cretaceous Boulder batholith and related volcanic rocks, while hanging wall rocks of the Bitterroot complex, in the Sapphire Range, record Cretaceous exhumation and more limited Eocene unroofing.


Biography

Professor David A. Foster is Chair of the Department of Geological Sciences at the University of Florida.  His research is focussed on applications of geochronology and thermochronology to Precambrian to Recent tectonics.

The Role of Isostasy in the Evolution and Structural Styles of Fold and Thrust Belts

Ibrahim, Youseph1, Rey, A/ Prof. Patrice1

1University Of Sydney, Sydney, Australia

Fold and thrust belts (FTB) are highly deformed regions that form as the crust accommodates shortening. The evolution of FTB’s records the dynamic interplay between crustal and surface
processes, in conjunction with the rocks’ intrinsic properties. The stacking of thrust sheets and mass transfer of sediment during orogenesis imposes a load on the lower crust and the mantle underneath, inducing isostatic adjustment and a flexural response, which may also contribute to the overall architecture of FTB’s. The tempo at which a fold and thrust belt forms is a consequence of plate kinematics. The tempo of the isostatic response, however, is reliant on the rheology of the mantle and the elastic thickness of the crust. Here, we focus on the role isostasy plays in controlling structural style in FTB’s. We run two-dimensional, coupled thermal and mechanical, numerical experiments using the Underworld framework to explore the interplay between the rate of compression and the rate of isostasy on the structural evolution of FTB’s.

The numerical model runs in a cartesian domain by solving the conservation of energy, mass, and momentum equations. The numerical domain is 42 km wide and 16 km tall, with a grid resolution of 80 m. From top to bottom, the model consists of ‘sticky air’, 4 km of sediment that alternates in competence at 500 m intervals, a 3 km thick basement, and a virtual basal layer, which allows us to implement a local ‘psuedo-isostasy’ boundary condition. Models are run with varying compressional velocities and isostatic rates.

Our suite of models demonstrates the relationship between tectonic and isostatic rates. When the tectonic rate is greater than the isostatic rate, subsidence or flexure is post-tectonic mainly, and
therefore isostasy is unlikely to play a role in the development of the FTB, however, it may modify its architecture post-loading. Alternatively, when the tectonic rate is slower than or equal to the isostatic rate, subsidence will keep pace with tectonic loading. In this scenario, isostasy plays an important role in the development of FTB’s, influencing the topographic elevation generated, the outward extent of the FTB, and thrust fault angles.


Biography

Youseph is a first year Ph.D. student at the University of Sydney studying the evolution and structural styles of fold and thrust belts in Central Australia and Papua New Guinea.

Assessment of quartz in Sydney’s rock formations associated with recent engineering infrastructure projects; implications for workplace health and safety

Och, David J.1&2 and Cole, Kate3

1Adj. Assoc. Professor, University of New South Wales, Kensington, NSW.d.och@unsw.edu.au, 2Senior Principal Engineering Geoscientist, WSP Australia Pty Ltd, Sydney, NSW. David.och@wsp.com, 3A/Director Health & Occupational Hygiene, Sydney Metro, Sydney NSW 2000. kate.cole@transport.nsw.gov.au

Sydney Metro is Australia’s largest public transport project. This new standalone railway will deliver 31 metro stations and more than 66 kilometres of new metro rail, revolutionising the way Australia’s biggest city travels. As part of the development of Sydney Metro, both historical and current ground data is being collected and compiled to better understand the proportion of quartz that will be encountered along the proposed tunnel alignments.

Tunnelling and excavation work being undertaken in quartz-containing rock creates a dust comprising of a very fine shard particulate due to the impact and grinding reduction of the tunnelling and excavation equipment (i.e. road header, rock breaker and Tunnel Boring Machine (TBM)). As the dominant hard-mineral component is quartz, at the point of excavation, fine particulates of respirable crystalline silica dust can be released which can be suspended into the atmosphere. These fine particulates can be suspended in the air column and may create an occupational health risk resulting in illness and disease such as silicosis and lung cancer.

Geotechnical investigations across Sydney Metro have targeted the Triassic Wianamatta Group, Mittagong Formation and Hawkesbury Sandstone of the Sydney Basin. Quartz was found to make up to 90% (avg. 72%) of the grains in Hawkesbury Sandstone with the other components being siderite and clays. The hard-mineral component in Hawkesbury Sandstone is dominantly quartz detritus with other mineral components being moderate to weak in strength and less susceptible to micro-fracturing due to the mineral’s crystal framework.

This paper will provide an overview of the predicted proportion of quartz along the Triassic Wianamatta Group, Mittagong Formation and Hawkesbury Sandstone formations in the Sydney Basin.


Biography

Assoc. Prof David Och is a Fellow of the Geological Society of Australia and a 2019 Winston Churchill Fellow working as a Senior Principal Engineering Geoscientist with WSP Australia.  David’s expertise is demonstrated by performing key roles on large infrastructure projects including Sydney Metro City & Southwest, Sydney Metro West.

Rock Stress in Tasmania

Hills, Peter1

1Pitt & Sherry Operations Pty Ltd, Hobart, Australia

Rock stress can have a profound impact on underground excavations in mining and civil space. Rock stress measurement was first undertaken in Tasmania to inform the design of excavations for the Poatina Power Station in 1960 and led to an innovative trapezoidal section to the crown of station cavern in near horizontal Permian sediments. Since that time stress measurements have been undertaken at 15 sites across western and northern Tasmania and this has provided a database, which in addition to assisting in the management of individual assets, has allowed a number of more general observations to be made[1].

Rock stress is the result of tectonic forces and overburden pressures. The former creates a background stress condition that is widely evident within a given geological terrane. All Tasmania’s stress measurements have been undertaken in the Western Tasmanian Terrane and indicate a major principal stress (σ1) orientation striking WSW-ENE which is an anticlockwise rotation from that observed in Victoria where measurements have largely been undertaken in rocks of the Lachlan Fold Belt. This is thought to reflect upon the key location of Tasmania during the accretion of Gondwanaland and the eventual separation from Antarctica. The latter typically reflects depth below surface with the magnitude of the stress generally increasing with depth. In most cases in Australia, and it is the case in Tasmania, that the orientation of the minor principal stress (σ3) steep and consequently the intermediate principal stress (σ2) is relatively flat. The general stress condition in Tasmania can be described in terms of orientation and magnitude as follows:

  • σ1; 23°/261°         (0.039 x depth) + 10.7 MPa
  • σ2; 15°/164°         035 x depth MPa
  • σ3; 62°/043°         023 x depth MPa

Local geological and geomorphological setting can significantly impact the stress locally. At Cethana Power Station the stress measured in the crown of the station prior to excavation of the cavern was found to be four times the expected magnitude. However it is readily explained by its location in the steep sided Forth River Gorge which was rapidly cut through the Fossey Mountains during relatively recent glaciation. At Hellyer Mine the magnitude of the measured stress is more-or-less consistent with the depth of the measurements beneath the Waratah Plateau, but the orientation of the shallower measurements is strongly influenced by the orientation of the nearby Southwell River Gorge. Renison Mine provides a further example where the orientation of the stress field is strongly influenced by the orientation of the Federal-Bassett Fault and the associated Pine Hill Horst.

Stress measurement in Tasmania has been undertaken for direct engineering construction as in the case of the John Butters Tunnel where is was specifically directed at determination of the length of tunnel lining required. It has also been used extensively to understand the orientation and magnitude of the stress condition in deep mines at Mount Lyell, Renison, Rosebery and Beaconsfield and assist with excavation, and particularly, stope design. Stress change due to extraction has also been monitored at those mines as well as Dolphin and Cleveland.

[1] Hills, P B, 2020. Tasmanian rock stress, Australian Geomechanics, 55(1), 77-111.


Biography

Originally graduating as a geologist at UTAS in the early 1980’s, Peter undertook further studies in rock mechanics and Commenced transitioning to mining geomechanics over the following 10-15 years. He now consults in the field geomechanics after a 30 year career in underground mines in Tasmania and Papua New Guinea.

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.

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About the GSA

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