Papers by Anthony R Milnes
Transactions of the Royal Society of South Australia, 2024
A suite of soft-sediment deformation structures occurs within the basal sands and gravels in the ... more A suite of soft-sediment deformation structures occurs within the basal sands and gravels in the non-marine Pleistocene succession in the Noarlunga Embayment of the Cenozoic St Vincent Basin south of Adelaide, South Australia, the significance of which has hitherto gone unrecognised. The inclusion of large, isolated blocks of well-bedded sands randomly encased within fluidised, structureless clayey sands indicates that the soft-sediment deformation was intense, occurring soon after deposition by liquefaction of a still saturated sediment. Seismic activity has been, and continues to be, a regular occurrence along the adjacent Adelaide fold belt. The intensity of the deformation is comparable to the thixotropic response to earthquake activity observed during the Christchurch (New Zealand) earthquakes of 2010 and 2011, the earthquakes and aftershocks near Quorn, South Australia, in January 1887, in the southeast of South Australia in May 1899, and west of Adelaide in April 1954. This, however, is the first record of an interpreted seismite in the St Vincent Basin, although its full extent is yet to be mapped.
Sedimentologika, 2024
Syn-and post-depositional alterations are distinguished in a detailed lithological and mineralogi... more Syn-and post-depositional alterations are distinguished in a detailed lithological and mineralogical study of the largely unconsolidated Plio-Pleistocene non-marine succession in coastal cliff sections in the St Vincent Basin south of Adelaide. At its base, the sequence interfingers with Late Pliocene estuarine marine sediments in places but mostly unconformably overlies older Cenozoic marine sediments or Neproterozoic bedrock. The fluvial and alluvial siliclastics have bioturbation, blocky-prismatic macro-peds and subtle Fe-mottling indicators of hiatuses in deposition, and imprints of soil and shallow groundwater environments. A relative abundance of kaolinite, illite and randomly interstratified illitesmectite reflects both sediment source and conditions in the local depositional environment. A thick deposit of aeolian calcareous silt with associated pedogenic calcretes blankets the succession. Conspicuous bleached Fe mega-mottled intervals and zones of alunite-halloysite within the sequence record post-depositional, groundwater-related alterations in regolith environments. These formed during incision and erosion of the sedimentary fill in the basin in response to regional falls in base level. Each marks a different time and specific geomorphic environment according to the chemistry of the discharge of local groundwaters from aquifers that were intersected by incision and scarp retreat.
BSGF - Earth Sciences Bulletin, 2024
In this paper, and in previous works, quartzites within the Sable de Fontainebleau are clearly sh... more In this paper, and in previous works, quartzites within the Sable de Fontainebleau are clearly shown to occur only near outcrops in Plio-Pleistocene plateau landscapes and are related to groundwater flows. These arrangements, together with dating of encased calcites, led us to consider that silicification occurred during Plio-Pleistocene glacial stages. The precipitation of silica was most likely triggered by cooling of groundwaters as they approached cold zones in the regolith close to points of discharge. We describe the arrangement and morphologies of quartzites in Tertiary sand formations in the Paris Basin to demonstrate how cold climates could have influenced hydrologic regimes and promoted silicification. The coeval precipitation of calcite and silica in gypseous formations at the edges of plateaux-bordering valleys, along with the dissolution of gypsum, also points to interactions between silica-laden groundwater and carbonate host rocks during cold periods. In parallel, the distribution and micromorphology of silicifications in associated Tertiary limestone formations suggests that they formed during cold climates in the Quaternary. These are key pointers to the role of groundwater in regolith environments in controlling silicification processes. We detail a link to palaeosurfaces of the distinctive meulières facies in the Paris Basin. Geotropic structures and micromorphological organisations are the basis of new ideas about their origin in a combination of vadose and phreatic environments and proximity to impervious cold horizons. The active zone in a permafrost landscape is a good hydrological example. All silicifications in Tertiary formations in the Paris Basin can be linked to the hydrology of Quaternary periglacial environments in a single model. This could apply more widely to similar silicifications elsewhere and be tested using new analytical techniques that date silicifications and unravel the isotopic relationships between silicification, groundwater composition and the prevailing climate.
Communications Earth & Environment, 2024
Detrital minerals provide valuable insights into the tectonic history of continents. Uranium-lead... more Detrital minerals provide valuable insights into the tectonic history of continents. Uranium-lead dating of detrital zircon is widely used to characterize the magmatic history of continents but is generally insensitive to metamorphism accompanying the production and reworking of crust during orogenesis. Garnet is the most important mineral for recording prograde and peak orogenic metamorphism and can occur as a common detrital phase. Here, we demonstrate laser-ablation lutetium-hafnium (Lu-Hf) geochronology of detrital garnet as a provenance tool for reconstructing orogenic histories at (super) continental scales. Detrital garnet (n = 557) from modern sands and Permo-Carboniferous glacial strata in South Australia faithfully record local garnet-grade metamorphic events but also include a major population at ca. 590 million-years with no known source in South Australia. We trace the ca. 590 million-year-old detrital garnets to a largely ice-covered orogenic province in East Antarctica, uncovering the inception of convergent margin tectonism along the palaeo-Pacific margin of Gondwana.
Journal of Archaeological Science: Reports, 2024
Although more than 2000 shelters with non-figurative carvings ascribed to a Mesolithic style are ... more Although more than 2000 shelters with non-figurative carvings ascribed to a Mesolithic style are known within the quartzitic sandstone megaclast lag deposits in the southern Paris area, only three shelters with figurative representations of Late Paleolithic style have been recognized. Upright megaclasts are rare in the regional lag deposits but two upright quartzitic sandstone megaclasts occur close to two of these Late Paleolithic shelters. Detailed morphological surveys of these megaclasts allow us to suggest that they were erected by humans. The fortuitous conjunction of finding an upright megaclast close to two Late Paleolithic shelters is infinitesimally small in term of probabilistic considerations. Thus, the Late Paleolithic engraved shelterupright megaclast pairs are not likely to be independent but are probably linked by culture, and so the megaclasts are expected to date from the Late Paleolithic. We suggest that they were 'engineered landmarks' erected to mark places that had cultural significance for Late Paleolithic hunter-gatherer people. The energy dedicated to erect the megaliths is an indication that shelter-megalith pairs probably had important spiritual and symbolic significance. We suggest that both contributed to locate and anchor stories to landscape features. Indeed, these shelter-megalith pairs were in the hinterland of the large open-air camps settled on fords on game migratory routes crossing the Seine River. These specific markers could have encompassed a storyline about landscapes as the support for learning routes through them. One possibility is that they had a timed relationship with herd migration.
Coloured heavy mineral sands are a conspicuous yet somewhat ephemeral feature on the surface of m... more Coloured heavy mineral sands are a conspicuous yet somewhat ephemeral feature on the surface of many beaches around Gulf St Vincent and in Encounter Bay in South Australia. The ultimate origin of the minerals continues to be investigated, but they are known to be important constituents of an extensive suite of Carboniferous to Permian glacigene sediments deposited over most of the region. They occur in Palaeogene palaeochannel sands as well as within overlying Pleistocene alluvial sediments and soils. It is the continued erosion of these sediments that has fed the heavy minerals into modern terrestrial landscapes and concentrated them in small-scale placer sands on the beaches around Gulf St Vincent.
Transactions of the Royal Society of South Australia, 2023
The Tate Museum (The University of Adelaide) holds a large collection of (tektites) australites i... more The Tate Museum (The University of Adelaide) holds a large collection of (tektites) australites including the Pens Collection from the Florieton area in east-central South Australia. Many of these specimens are intact or near-so and have the various forms ascribed to their behaviour as they entered the Earth's atmosphere. However, a significant number, some of which may have been initially fractured and broken by erosional processes on the Earth's surface, were later reworked by Aboriginal Australians to form small tools and hence are important artefacts. Of the Florieton specimens, 6.5% have been reworked into microlithic flakes. This note points to the historical value of the Pens Collection, discusses the nature of the environment in which they were found, and speculates about the collecting and adaptation of australites by Aboriginal Australians.
Informa tion for farm busines ses and the commu nity in South Austral ia Und erst and ing min era... more Informa tion for farm busines ses and the commu nity in South Austral ia Und erst and ing min eral exp lora tion Version 1.
Geochimica et Cosmochimica Acta, 1987
The relative abundances and 2wU/238U activity ratios of tetravalent and hexavalent U in 33 phosph... more The relative abundances and 2wU/238U activity ratios of tetravalent and hexavalent U in 33 phosphorite nodules from the East Australian continental margin have been determined. U(IV) constitutes between59-96% (average 80%) of the total U in non-ferruginous Quaternary nodules, but between 1 l-86% (average 63%) in ferruginous Tertiary nodules. Quatemary phosphorite nodules on the East Australian continental margin form within well-oxygenated, low carbon-flux environments on the upper continental slope, generally at water depths between 350-450 m. Predictable relationships exist between the radiometric age and tetravalent U content (%U(IV)) of the nodules and their Pr05, FerOr, and labile organic carbon concentrations. The nodules probably initially form as patt of a more widespread phosphatic layer which contains 7-9% P20J, has Fe203/K20 ratios between 3-4, hydrogen indices (HI) >80, and is relatively uranium-rich (II/ PrOI X lo-' = 15-20). Virtually all the U is originally incorporated into the nodules as U(IV). The layer is subsequently broken up into discrete nodules which are periodically reworked and exposed at the sediment-water interface. During this exposure, the nodules preferentially gain both apatite and iron hydroxide. As a result, their Pros concentrations increase to 16-185s~ within 80 kyr of their formation, whereas the FerOr/KrO ratios increase to 8-10. Little or no U apparently accompanies this apatite, for the U/Pro5 ratios approximately halve as the Pro, concentration doubles, and the nodules have concordant 2seTh/2yU and 23'Pa/235U ages. Contemporaneously, exposure causes progressive oxidation of both the organic carbon (HI decreases to 20) and tetravalent uranium (U(IV) decreases to 60-70%) contents. The high U concentrations and high %U(IV) of the East Australian samples show that the presence of abundant organic matter is not necessary for the fixation of U in sedimentary apatite. Moreover, the %U(IV) in these phosphorites is not a direct function of the redox potential of the depositional environment, but rather an indicator of the amount of sea-tloor weathering experienced by the nodules.
Geological Society, London, Special Publications, 1990
During 1987, the Australian Bureau of Mineral Resources conducted a multidisciplinary investigati... more During 1987, the Australian Bureau of Mineral Resources conducted a multidisciplinary investigation of the modern phosphorites on the continental margin of southeastern Australia between 28 and 32~ The objectives of the work were to examine the processes controlling the cycling of organic carbon and bioactive elements, nitrogen, phosphorus, sulphur and iron in the sediments, and to investigate the roles which these processes played in the formation of the modern phosphorites. Bacterial productivities, sulphate-reduction rates, sedimentary oxygen and pore-water concentrations of nitrate, ammonia, phosphate, iron, sulphate and fluoride were measured at sea. The highest rates of microbial productivity were found in the surficial (0-20 mm) sediments of the modern phosphorite zone in 350-460 m water depth. These rates were about double those in shallower shelf (<300 m) sediments and 3-4 fold those rates in mid-slope (600-1000 m) sediments. Aerobic and anaerobic oxidation rates of organic matter, calculated from sediment oxygen profiles and sulphate-reduction rates were highest in the surface sediments in the modern phosphoritc zone. The recycling of sedimentary iron, via reductive dissolution of iron oxyhydroxides and reprecipitation at the oxic/anoxic boundary results in a near-surface sedimentary trap for iron in the phosphorite zone sediments. Phosphate released from organic matter in the interfacial sediments, and fluoride from seawater, are scavenged by iron oxyhydroxides in the top few centimetres of sediment. Phosphorus, in this way, is decoupled from organic carbon in the near-surface sediments and linked to the redox cycling of iron. Phosphate and fluoride scavenged onto iron oxyhydroxides, and concentrated in the surficial sediments, are subsequently released to pore waters in the anoxic sediments when iron oxyhydroxides are buried and dissolve. The recycling process releases phosphate and fluoride for incorporation into apatite; fluoride is depleted from pore waters at depths <18 cm, phosphorite nodules form within anoxic sediments at depths <18 cm and continue to accumulate iron and phosphorus while resident in the mixed layer. Combinations of rapid sediment mixing rates, a slow sedimentation rate and a mixed layer to about 18 cm result in an average particle residence time in the phosphorite zone sediments which is about tenfold that of the mid-slope sediments. Long residence times and rapid mixing promote the oxidation of organic carbon and release of phosphate, while the continuous recycling of iron and phosphate concentrates the phosphorus for apatite precipitation and accumulation into phosphorite nodules. Phosphorite nodules are not found in mid-slope sediments probably because of combinations of relatively rapid sedimentation rates, ineffective iron, phosphorus and fluoride recycling and trapping mechanisms, plus dilution and dissemination of any incipient apatite.
Quaternary Research, 2020
We tested the potential for sand calcites to serve as a novel paleoclimate archive by investigati... more We tested the potential for sand calcites to serve as a novel paleoclimate archive by investigating their age and formation conditions. Fontainebleau sand calcites are Pleistocene in age (based on 14 C and U-Th dating) and were primarily formed during glacial periods. δ 13 C values increase with the depth at which these sand calcites formed, consistent with open and closed CO 2 systems. Interpretation of the δ 18 O-T relationship in sand calcites points primarily to their formation at a low temperature, around 2°C in shallow ground water and at about 9°C in deeper groundwater settings. Their occurrence, characteristics, and compositions suggest crystallization from paleo-ground waters in permafrost environments. Crystallization of sand calcites was triggered by degassing of cold carbonate-containing surface waters as they infiltrated warmer subsurface groundwater environments. We consider sand calcites to be important indicators of interactions between meteoric water and ground water in Pleistocene periglacial landscapes. Their disposition may point to specific features of periglacial landscapes, and their ages could permit an assessment of landscape incision rates. Large crystals and zoned spheroliths may, in fact, encapsulate continuous high-resolution records of continental glacial and periglacial paleoenvironments.
Department of Mines & Energy SA Report Book 86/58, 2016
has taken up an exchange contract with the Geological Survey in Oman, and will not be with us on ... more has taken up an exchange contract with the Geological Survey in Oman, and will not be with us on the Workshop. Preliminary runs along the proposed route have now been completed, and final arrangements for the Workshop are in hand. The one major problem with which we cannot cope is widespread rain through the areas we will traverse. If rains do occur, we see no option but to abandon the Workshop, and you will be notified by telephone in the week preceding Saturday August 17. Participants The following is a list of registrants. A few have not yet firmed their arrangements with us, and some have not yet paid a registration fee. I ask those concerned to confirm their participation as soon as possible.
Journal of Archaeological Science: Reports, 2017
Silcretes are clearly observed and abundant as components of paleolandscapes on several continent... more Silcretes are clearly observed and abundant as components of paleolandscapes on several continents. Mechanisms for the formation of several varieties of silcrete, with specific relationships to paleolandscapes, are described. Each type of silcrete displays particular morphological features in its profile in the paleo-regolith, and these features provide pointers to its origin via mechanisms of absolute or relative accumulation of silica in specific environments relating to groundwater or soil-water hydrology. The characters of silcrete varieties that may have triggered the interest of prehistoric peoples to exploit them for manufacturing stone tools, and which control knappability, include granulometry and the specific nature of silica cements. The successions of silica precipitation and recrystallisation events are clearly evident as a complex of micromorphological features that provide clues to the hydrological environment and its geochemistry at the time or times of silicification. Examples are given of the distribution of different silcrete facies, which could have had differing values for exploitation for stone tool production, in modern-day landscapes in France and Australia.
International Conference on Environmental Radioactivity: from Measurements and Assessments to Regulation. Vienna, Australia, 23-27 April, 2007. Paper IAEA-CN-145/049, 2007
International Journal of Surface Mining, Reclamation & Environment, 2003
The AusIMM Bulletin (Journal of the Australasian Institute of Mining and Metallurgy), No. 5, September/October 2002, 2002
Tailings and Mine Waste '01, Fort Collins, Colorado, January 2001, 2001
Proceedings International Symposium on Land Reclamation 2000 (ISLR), Beijing, China, May 15-19, 2000., 2000
Ranger Mine is located about 260 kilometres east of Darwin, the capital city of the Northern Terr... more Ranger Mine is located about 260 kilometres east of Darwin, the capital city of the Northern Territory, Australia. The mine lease is surrounded by Kakadu National Park which is designated a World Heritage Area. The mining operations are heavily regulated by Government authorities and representatives of community groups. As a result, rehabilitation planning has been an important component of mine operations since they commences in the late 1970's. Long term security and effective rehabilitation of tailings is one of the principal rehabilitation goals for Ranger Mine. Since 1996, tailings have been deposited in a mined-out pit. In-pit disposal has the advantages of relocating the mine wastes to the site from which the original ore was mined, as well as secure containment due to the low possibility of structural failure of the pits. There are issues relating to the prevention of groundwater contamination from transport of tailings pore fluids during mine operations and after decommissioning and rehabilitation. In addition, post-deposition settlement of the tailings mass is likely to be large unless adequate settled densities can be achieved during the life of the mine. Strategies that are being investigated and implemented to ensure that the tailings deposits achieve high settled densities during operations to reduce the residual settlement are described. In addition, techniques for measuring and monitoring the key properties of the in-pit tailings deposits are reported.
4th International Conference on Case Histories in Geotechnical Engineering, March 1998, Missourii USA. Paper 10.01, 1998
The environmental regulation for Ranger Uranium Mine, in the Northern Territory, Australia, requi... more The environmental regulation for Ranger Uranium Mine, in the Northern Territory, Australia, requires the stored tailings (irrespective of where they are finally stored, whether in a tailings dam or in mined-out pits) be capped safely to minimise contamination, erosion and radon gas emission, and also to enable the site to be rehabilitated through revegetation. The hydraulically deposited neutralised tailings in the existing tailings dam have a 'gel-like' structure which hinders the consolidation process. Consequently. the in situ tailings have a high water content, low permeability and extremely low shear strength. The present paper describes the case history of a successful capping trial constructed on these extremely soft tailings. Environmental geotechnical issues are highlighted and investigated. Results, especially the characteristics of the tailings observed during the construction and subsequent monitoring, are also discussed.
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Papers by Anthony R Milnes