Considerations for U-series dating of sediments: insights from the Flinders Ranges, South Australia

Uranium isotope ratios have been determined for the fine-grained detrital fraction of Pleistocene Wilkawillina valley-fill sediments, four local Proterozoic bedrock samples and fine-grained aeolian material from a sand dune deposit of the Flinders Ranges, South Australia. The aim was to quantify the comminution age, i.e. the time elapsed since physical weathering of the bedrock, and residence time of the valley-fill sediments and to place tighter constraints on input parameters for the comminution age calculation. Despite using two independent approaches for determination of the recoil lost fraction of 234U from the sediment (weighted geometric and surface area estimates), samples fail to produce realistic comminution ages and hence, residence times. The issues involved in the ability to determine sediment comminution ages are discussed. The (234U/238U) activity ratio of the local bedrock is not in secular equilibrium, despite the bedrock being much older than 1Ma, i.e. the timeframe for 234U and 238U to reach secular equilibrium in a closed system. Using the average Flinders Ranges bedrock (234U/238U) ratio instead of an assumed (234U/238U) activity ratio of unity for the source would significantly reduce calculated residence times. This result warrants concern for future studies using the comminution approach for which a secular equilibrium source (234U/238U) activity ratio is assumed. Significant input of aeolian material may modify the measured (234U/238U) activity ratios. Such input may be more tightly constrained in future studies using rare earth element and radiogenic isotopic data. Future comminution studies would benefit from further consideration of the importance of 1) leaching lost 234U from source rock and bulk sediment samples, 2) wind deposition of fine-grained material and 3) the appropriateness and robustness of sample pre-treatment procedures

Integrated mineralogical analysis (QEMSCAN and DRX) of transgressive black shales: Tithonian basal deposits of the Vaca Muerta Formation (Neuquén Basin, Argentina)

Se estudia la composición por difracción de rayos X y QEMSCAN (19 muestras)de fangolitas y margas de la Formación Vaca Muerta, acumuladas durante latransgresión tithoniana de la Cuenca Neuquina. Se definen importantes variaciones composicionales entre tipos litológicos y facies sedimentarias. Las rocas del sector marginal de la cuenca muestran fuerte influencia de los aportes terrígenos (cuarzo, feldespatos, illita e illita/esmectita). En las sedimentitas del sector depocentral facies de pelitas grises oscuras) son importantes los indicadores de productividad orgánica (carbonatos y cuarzo biogénico), de condiciones anóxicas (pirita, siderita) y de un lento ritmo de acumulación sedimentaria. Los depósitos depocentrales de la transgresión tithoniana corresponden a la cocina de hidrocarburos de la Formación Vaca Muerta. Sus amplias variaciones mineralógicas ejercen fuerte impacto en la conversión de materia orgánica y en la liberación de gas y petróleo, así como en las propiedades petrofísicas y la fragilidad de rocas que constituyen la fuente principal para la explotación no convencional de hidrocarburos en la Cuenca Neuquina.Recent studies have demonstrated that the mineralogical composition of shales plays an important role in unconventional hydrocarbon production (Chen et al., 2014). Mineralogy may influence the nature of the pore structure, the fracktability of these fine-grained deposits and pyrolysis reactions, all of them essential in the stimulation and extraction processes of low-permeability reservoirs (Karabakan and Yürüm, 2000; Jarvie et al., 2007; Ross and Bustin, 2009). This contribution describes and analyzes the mineralogical composition of the Tithonian basal deposits of the Vaca Muerta Formation, which resulted from two independent methodologies, QEMSCAN and DRX. The datasets comprises 19 samples distributed from the austral to the central sectors of the Neuquén Basin (Fig. 1a). The sampled sediments were deposited during the marine transgression of the early Tithonian (Fig. 1b) and accumulated under bottom conditions that favored the preservation of organic matter. The studied interval is the most important source rock of the basin. Previous geochemical studies (Spalletti et al., 2014) showed that the basal interval comprises fine-grained sediments with a very variable composition (Fig. 3), ranging from pure siliciclastic to mixed (carbonate/ siliciclastic) mudstones. Despite this compositional variability, macroscopically in the field only three main facies were recognized: greenish mudstones, yellowish mudstones and dark grey mudstones. The first two facies are commonly distributed in the marginal areas of the basin, whereas the latter is more characteristic of basinal regions (Fig. 2, Table 1). The samples were analyzed with conventional optical methods and by X-ray diffractometry (whole rock and <2 μm fraction), as well as by a combination of SEM (Scanning Electron Microscopy) and EDS (Energy Dispersive Spectrometry). This technique is known as QEMSCAN, which stands for Quantitative Evaluation of Minerals by SCANning electron microscopy. The integration of analytical methods revealed significant compositional variations between different lithologic types and lithofacies (Figs. 4-6, Table 2). Hybrid mudstones (especially marls and calcareous marls) show high calcite contents, whereas more siliciclastic deposits are dominated by quartz and feldspar, with clay minerals as illite and interstratified I/S dominant in the mudstones, together with minor contents of kaolinite and analcime. The mineralogical composition of identified lithofacies also shows changes, even among samples of the same lithofacies (Fig. 6). Greenish mudstones are characterized by illite, smectite and quartz, with subordinated contribution of kaolinite and interstratified I/S. For yellowish mudstones there are no clear trends, with a wide spectrum of quartz/calcite relationships (Fig. 6) and variable content of Illite, interstratified I/S and analcime. In turn, dark grey mudstones, which are typical of the depocentral sectors, have minerals which are indicative of low oxygenation (pyrite, siderite), but a broad compositional range in terms of calcite, quartz and clay minerals. This study has allowed establishing a significant equivalence between the information presented here (QEMSCAN and DRX), and the one gathered by means of inorganic geochemical analysis (Spalletti et al., 2014). The mineralogical composition of the sediments located toward marginal settings during the Tithonian transgression reflects a strong influence of terrigenous supply from hinterland (Fig. 7). In contrast, the sediments that accumulated in more basinal locations of the marine setting were heavily influenced by biogenic productivity (intrabasinal concentration of carbonate- and silicarich biota), anoxic conditions, and more likely, lower sedimentation rates (Fig. 7). These basinal, basal deposits (dark grey facies) of the Vaca Muerta Formation correspond to the highest total organic concentration across the basin (kitchen) and this interval was responsible for the expulsion of large quantities of hydrocarbons during different geological times (Villar et al., 1993, 2006). The mudstone mineralogy exerts a strong control in several processes such as organic matter conversion (pyrolysis-related reactions), expulsion of hydrocarbons, petrophysical properties and geomechanical attributes, that in turn influences the reservoir properties and extraction processes (cf. Patterson and Henstridge, 1990; Patterson et al., 1990). Therefore, the wide range of compositional variability that is inherent in the dark grey mudstones of the Vaca Muerta Formation (so-called "black shales") is key in order to maximize its exploration and exploitation as an unconventional resource.Centro de Investigaciones GeológicasConsejo Nacional de Investigaciones Científicas y Técnica

Integrated mineralogical analysis (QEMSCAN and DRX) of transgressive black shales: Tithonian basal deposits of the Vaca Muerta Formation (Neuquén Basin, Argentina)

Se estudia la composición por difracción de rayos X y QEMSCAN (19 muestras)de fangolitas y margas de la Formación Vaca Muerta, acumuladas durante latransgresión tithoniana de la Cuenca Neuquina. Se definen importantes variaciones composicionales entre tipos litológicos y facies sedimentarias. Las rocas del sector marginal de la cuenca muestran fuerte influencia de los aportes terrígenos (cuarzo, feldespatos, illita e illita/esmectita). En las sedimentitas del sector depocentral facies de pelitas grises oscuras) son importantes los indicadores de productividad orgánica (carbonatos y cuarzo biogénico), de condiciones anóxicas (pirita, siderita) y de un lento ritmo de acumulación sedimentaria. Los depósitos depocentrales de la transgresión tithoniana corresponden a la cocina de hidrocarburos de la Formación Vaca Muerta. Sus amplias variaciones mineralógicas ejercen fuerte impacto en la conversión de materia orgánica y en la liberación de gas y petróleo, así como en las propiedades petrofísicas y la fragilidad de rocas que constituyen la fuente principal para la explotación no convencional de hidrocarburos en la Cuenca Neuquina.Recent studies have demonstrated that the mineralogical composition of shales plays an important role in unconventional hydrocarbon production (Chen et al., 2014). Mineralogy may influence the nature of the pore structure, the fracktability of these fine-grained deposits and pyrolysis reactions, all of them essential in the stimulation and extraction processes of low-permeability reservoirs (Karabakan and Yürüm, 2000; Jarvie et al., 2007; Ross and Bustin, 2009). This contribution describes and analyzes the mineralogical composition of the Tithonian basal deposits of the Vaca Muerta Formation, which resulted from two independent methodologies, QEMSCAN and DRX. The datasets comprises 19 samples distributed from the austral to the central sectors of the Neuquén Basin (Fig. 1a). The sampled sediments were deposited during the marine transgression of the early Tithonian (Fig. 1b) and accumulated under bottom conditions that favored the preservation of organic matter. The studied interval is the most important source rock of the basin. Previous geochemical studies (Spalletti et al., 2014) showed that the basal interval comprises fine-grained sediments with a very variable composition (Fig. 3), ranging from pure siliciclastic to mixed (carbonate/ siliciclastic) mudstones. Despite this compositional variability, macroscopically in the field only three main facies were recognized: greenish mudstones, yellowish mudstones and dark grey mudstones. The first two facies are commonly distributed in the marginal areas of the basin, whereas the latter is more characteristic of basinal regions (Fig. 2, Table 1). The samples were analyzed with conventional optical methods and by X-ray diffractometry (whole rock and <2 μm fraction), as well as by a combination of SEM (Scanning Electron Microscopy) and EDS (Energy Dispersive Spectrometry). This technique is known as QEMSCAN, which stands for Quantitative Evaluation of Minerals by SCANning electron microscopy. The integration of analytical methods revealed significant compositional variations between different lithologic types and lithofacies (Figs. 4-6, Table 2). Hybrid mudstones (especially marls and calcareous marls) show high calcite contents, whereas more siliciclastic deposits are dominated by quartz and feldspar, with clay minerals as illite and interstratified I/S dominant in the mudstones, together with minor contents of kaolinite and analcime. The mineralogical composition of identified lithofacies also shows changes, even among samples of the same lithofacies (Fig. 6). Greenish mudstones are characterized by illite, smectite and quartz, with subordinated contribution of kaolinite and interstratified I/S. For yellowish mudstones there are no clear trends, with a wide spectrum of quartz/calcite relationships (Fig. 6) and variable content of Illite, interstratified I/S and analcime. In turn, dark grey mudstones, which are typical of the depocentral sectors, have minerals which are indicative of low oxygenation (pyrite, siderite), but a broad compositional range in terms of calcite, quartz and clay minerals. This study has allowed establishing a significant equivalence between the information presented here (QEMSCAN and DRX), and the one gathered by means of inorganic geochemical analysis (Spalletti et al., 2014). The mineralogical composition of the sediments located toward marginal settings during the Tithonian transgression reflects a strong influence of terrigenous supply from hinterland (Fig. 7). In contrast, the sediments that accumulated in more basinal locations of the marine setting were heavily influenced by biogenic productivity (intrabasinal concentration of carbonate- and silicarich biota), anoxic conditions, and more likely, lower sedimentation rates (Fig. 7). These basinal, basal deposits (dark grey facies) of the Vaca Muerta Formation correspond to the highest total organic concentration across the basin (kitchen) and this interval was responsible for the expulsion of large quantities of hydrocarbons during different geological times (Villar et al., 1993, 2006). The mudstone mineralogy exerts a strong control in several processes such as organic matter conversion (pyrolysis-related reactions), expulsion of hydrocarbons, petrophysical properties and geomechanical attributes, that in turn influences the reservoir properties and extraction processes (cf. Patterson and Henstridge, 1990; Patterson et al., 1990). Therefore, the wide range of compositional variability that is inherent in the dark grey mudstones of the Vaca Muerta Formation (so-called "black shales") is key in order to maximize its exploration and exploitation as an unconventional resource.Centro de Investigaciones GeológicasConsejo Nacional de Investigaciones Científicas y Técnica

A call for Australian loess

© Royal Geographical Society (with The Institute of British Geographers) 2007The definitive version is available at www.blackwell-synergy.comDavid Haberla

Loess and floods: late Pleistocene fine-grained valley-fill deposits in the Flinders Ranges, South Australia.

Terrace remnants of late Pleistocene fine-grained valley-fills, at present eroded by ephemeral traction-load streams, are reported from many semi-arid and arid parts of the world. While they present promising palaeo-environmental archives for recent geological times such as the Last Glacial Maximum (LGM) for which few other terrestrial depositional records exist, their poorly understood nature has limited their significance. This study examines the fine-grained valley-fill deposits from the Flinders Ranges in South Australia, here called Flinders Silts. It establishes the timing, mode and environmental controls of deposition as opposed to their advancing erosion under the current climate. A regional chronostratigraphy based on 124 numerical dates is discussed, of which 43 radiocarbon and 22 luminescence ages were obtained from 12 sections across three major catchments within the scope of this thesis. Regionally significant intervals of rapid aggradation, relative surface stability and erosion are established. Regional climatic controls are differentiated from intrinsic catchment- and site-specific effects on the system. Further, individual age proxies and age models are critically assessed in how far they reflect depositional events. The final aggradational interval bracketing the extended LGM is discussed in detail on a continuous layered to laminated stratigraphic sequence. The provenance question of the fine-grained sediments and the depositional environment of the Flinders Silts are further addressed by high-resolution particle-size analysis. In order to study the subtle variations within the fine-grained partially-aggregated material, an original parametric sediment-sizing approach is employed. Finally, a range of traditional and emerging analytical techniques are applied to improve our understanding of palaeo-environments promoting aggradation. In conclusion, arid intervals throughout the last glacial cycle resulted in significant quantities of proximal dust being deposited as loess mantles within the catchments of the Flinders Ranges, acting as a near-longitudinal dust trap in the centre of the late Pleistocene “dust bowl”. The fine-grained aeolian accessions were repeatedly eroded by low-frequency high-magnitude precipitation events and redistributed as loess-derived alluvium, congesting narrow gorges and raising the base level for tributaries. Locally, backflooding resulted in the aggradation of layered to laminated slackwater deposits, the most continuous recording at least 12 large and numerous smaller flood events between 24 ka and 18 ka. The synchronous termination of the Flinders Silts coincides with early Deglacial climatic amelioration. The re-establishment of a perennial plant cover stabilising both dune fields and slope mantes is discussed as a potential scenario that would have discontinued dust supply to the fluvial system, in turn promoting incision and erosion. The studied aeolian-fluvial interplay of loess and floods has large implications for our understanding of landscape evolution in semi-arid Australia.Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 200

Quantifying particle aggregation in sediments

Sediments often occur as non-normal size distributions composed of discrete, partially aggregated particle populations. These populations reflect provenance, dispersal pathways and their depositional environments. Recent experimental laboratory studies describing mud flocculation in turbulent marine systems prompted this investigation of the potential of aggregates to record size-sensitive transport dynamics in a terrestrial fluvial system. Here, sediment-size distributions in their natural condition of particle–aggregate mixtures are analysed by parametric statistics. A practical and freely available decompositional approach is outlined and field tested, which allows sediment to be viewed in both its conventional particulate form and as its naturally occurring mixture of transport-stable aggregates and elementary particles. From a sequence of upward-fining slack water couplets in the Flinders Ranges, South Australia, it is demonstrated that the characteristics, provenance and depositional history of fine-grained sediments consisting of particle-aggregate mixtures can best be understood fully by quantifying aggregation.David Haberlah and Grant H. McTains

Quantifying respirable crystalline silica in the ambient air of the Hunter Valley, NSW - sorting the silica from the silicon

Crystalline forms of silica are known to cause lung damage for which there is no effective treatment. Silicon is abundant in crustal material and silicates are the single largest mineral grouping, with silica (SiO₂) being the most abundant crustal compound. Media reports of high levels of silicon in particles in the air in the vicinity of Hunter Valley open-cut coal mines have caused community anxiety and concerns about potential health impacts on local populations. An extensive sampling campaign using continuous air quality monitoring and targeted collection of particles has been carried out in an area close to mining operations. It was determined that silicon as silica was present in the ambient air, although the concentrations of crystalline silica measured suggest that it should not should cause health problems even for sensitive individuals within the general population. The results of the research should inform more rigorous discussions of air quality management plans for fine particles in the Hunter Valley and aid discussions of community concerns over the potential health impacts of coal mining.6 page(s

'Of droughts and flooding rains': an alluvial loess record from central South Australia spanning the last glacial cycle

Deposits of proximal dust-derived alluvium (alluvial loess) within the catchments of the now semi-arid Flinders Ranges in South Australia record regionally synchronous intervals of fluvial entrainment, aggradation and down-cutting spanning the last glacial cycle. Today, these floodplain remnants are deeply entrenched and laterally eroded by ephemeral traction load streams. The north–south aligned ranges are strategically situated within the present-day transitional zone, receiving both topographically enhanced winter rainfall from the SW and convectional downpours from summer monsoonal incursions from the north. We develop a regional chronostratigraphy of depositional and erosional events emphasizing the Last Glacial Maximum (LGM). Based on 124 ages (94 accelerator mass spectrometry radiocarbon and 30 optically stimulated luminescence) from the most significant terrace remnants on both sides of the Ranges, we conclude that the last glacial cycle including the LGM was characterized by major environmental changes. Two pronounced periods of pedogenesis between c. 36 and 30 ka were followed by widespread erosion and reworking. A short-lived interval of climatic stability before c. 24 ka was followed by conditions in which large amounts of proximal dust (loess) were deposited across the catchments. These loess mantles were rapidly redistributed and episodically transported downstream by floods. The termination of this regime c. 18–16 ka was marked by rapid incision.David Haberlah, Peter Glasby, Martin A. J. Williams, Steven M. Hill, Frances Williams, Edward J. Rhodes, Victor Gostin, Anthony O'Flaherty and Geraldine E. Jacobse

Considerations for U-series dating of sediments: Insights from the Flinders Ranges, South Australia

Heather K. Handley, Simon P. Turner, Anthony Dosseto, David Haberlah, Juan C. Afons