Raman counting: a new method to determine provenance of silt

Andó, Sergio; Vignola, Pietro; Garzanti, Eduardo

doi:10.1007/s12210-011-0142-4

Cited by 23 publications

(19 citation statements)

References 38 publications

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“…On grain mounts, 200 to 250 transparent heavy‐mineral grains were point‐counted at suitable regular spacing under the petrographic microscope to obtain real volume percentages (Galehouse, ). On offshore samples, heavy‐mineral analyses were carried out by Raman point‐counting (Andò et al ., ) on the >5 μ m (silty‐clay samples) or >15 μ m fraction (sandy‐silt to silty‐sand samples) obtained by wet‐sieving. Three beach‐placer deposits were analysed by grain‐counting, point‐counting and Raman point‐counting of bulk‐sample slides.…”

Section: Sampling and Analytical Methodsmentioning

confidence: 99%

Sedimentary processes controlling ultralong cells of littoral transport: Placer formation and termination of the Orange sand highway in southern Angola

et al. 2017

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This study focuses on the causes, modalities and obstacles of sediment transfer in the longest cell of littoral sand drift documented on Earth so far. Sand derived from the Orange River is dragged by swell waves and persistent southerly winds to accumulate in four successive dunefields in coastal Namibia to Angola. All four dunefields are terminated by river valleys, where aeolian sand is flushed back to the ocean; and yet sediment transport continues at sea, tracing an 1800 km long submarine sand highway. Sand drift would extend northward to beyond the Congo if the shelf did not become progressively narrower in southern Angola, where drifting sand is funnelled towards oceanic depths via canyon heads connected to river mouths. Garnet–magnetite placers are widespread along this coastal stretch, indicating systematic loss of the low‐density feldspatho‐quartzose fraction to the deep ocean. More than half of Moçamedes Desert sand is derived from the Orange River, and the rest in similar proportions from the Cunene River and from the Swakop and other rivers draining the Damara Orogen in Namibia. The Orange fingerprint, characterized by basaltic rock fragments, clinopyroxene grains and bimodal zircon‐age spectra with peaks at ca 0·5 Ga and ca 1·0 Ga, is lost abruptly at Namibe, and beach sands further north have abundant feldspar, amphibole‐epidote suites and unimodal zircon‐age spectra with a peak at ca 2·0 Ga, documenting local provenance from Palaeoproterozoic basement. Along with this oblique‐rifted continental margin, beach placers are dominated by Fe–Ti–Cr oxides with more monazite than garnet and thus have a geochemical signature sharply different from beach placers found all the way along the Orange littoral cell. High‐resolution mineralogical studies allow us to trace sediment dispersal over distances of thousands of kilometres, providing essential information for the correct reconstruction of ‘source to sink’ relationships in hydrocarbon exploration and to predict the long‐term impact of man‐made infrastructures on coastal sediment budgets.

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Section: Sampling and Analytical Methodsmentioning

confidence: 99%

Sedimentary processes controlling ultralong cells of littoral transport: Placer formation and termination of the Orange sand highway in southern Angola

et al. 2017

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“…Raman spectroscopy is particularly useful for such investigations as it can identify each individual mineral phase at the microscopic scale. However, to dissociate the individual spectra of each component, the grains must be larger than the analysed volume …”

Section: Introductionmentioning

confidence: 99%

“…However, to dissociate the individual spectra of each component, the grains must be larger than the analysed volume. [12,13] Of specific interest for Martian missions is the search for life and the presence of organic matter in the rocks and soils of the red planet. Whether or not life emerged on Mars, organic molecules should be detected because carbonaceous meteorites and micrometeorites containing abiotic organic material reach the planet surface, even at the present day.…”

Section: Introductionmentioning

confidence: 99%

Effect of grain size distribution on Raman analyses and the consequences for in situ planetary missions

Foucher

López‐Reyes

Bost

et al. 2013

J Raman Spectroscopy

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Raman spectroscopy can be used for analysing both mineral and organic phases, thus allowing characterisation of the microbial‐scale geological context as well as the search for possible traces of life. This method is therefore very useful for in situ planetary exploration missions. Compared with the myriad of sample preparation techniques available in terrestrial laboratories, the possibilities for sample preparation during in situ missions on other planetary bodies are extremely limited and are generally restricted to abrasion of rock surfaces or crushing of the target samples. Whereas certain techniques need samples to be prepared in powder form, such as X‐ray diffraction, this kind of preparation is not particularly suitable for optical microscopy and/or Raman spectroscopy. In this contribution, we examine the effects of powdering rock and mineral samples on optical observations and Raman analyses. We used a commercial Raman spectrometer, as well as a Raman laser spectrometer that simulates the instrument being developed for the future ExoMars 2018 mission. The commercial Raman spectrometer documents significant modifications to the spectra of the powdered samples, including broadening of the peaks and shifts in their position, as well as the appearance of new peaks. These effects are caused by localised heating of the sample under the laser beam and amplification of nominal surface effects due to the increase in surface area in finer grain sizes. However, most changes observed in the Raman spectra using the Raman laser spectrometer system are negligible because the relatively large (50 µm diameter) laser spot size produces lower irradiance. Furthermore, minor phases were more easily detectable in the powdered samples. Most importantly, however, this sample preparation method results in the loss of the textural features and context, making identification of potential fossilized microbial remains more problematic. Copyright © 2013 John Wiley & Sons, Ltd.

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“…Steel sieves, which can be cleaned in ultrasonic bath, are commercially available in the market down to 32 (or 20) µm. Since in sediments deposited by tractive currents the finest tail of the size distribution is markedly enriched in ultra-dense minerals (e.g., monazite, magnetite, and zircon; [16]), in very-coarse silt to very-fine sand samples, it is crucial to consider the finest size classes of the sample as well in order not to obtain a biased heavy-mineral suite [17,18]. This holds true also for poorly sorted sediments and especially for cohesive muds and mudrocks, for which including even classes as fine as 5-15 µm is compulsory.…”

Section: Preparation Of Nylon Sieves With 5 µM and 15 µM Meshmentioning

confidence: 99%

Gravimetric Separation of Heavy Minerals in Sediments and Rocks

Andó

2020

Minerals

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The potential of heavy minerals studies in provenance analysis can be enhanced conspicuously by using a state-of-the-art protocol for sample preparation in the laboratory, which represents the first fundamental step of any geological research. The classical method of gravimetric separation is based on the properties of detrital minerals, principally their grain size and density, and its efficiency depends on the procedure followed and on the technical skills of the operator. Heavy-mineral studies in the past have been traditionally focused on the sand fraction, generally choosing a narrow grain-size window for analysis, an approach that is bound to introduce a serious bias by neglecting a large, and sometimes very large, part of the heavy-mineral spectrum present in the sample. In order to minimize bias, not only the largest possible size range in each sample should be considered, but also, the same quantitative analytical methods should be applied to the largest possible grain-size range occurring in the sediment system down to 5 µm or less, thus including suspended load in rivers, loess deposits, and shallow to deep-marine muds. Wherever the bulk sample cannot be used for practical reasons, we need to routinely analyze the medium silt to medium sand range (15-500 µm) for sand and the fine silt to sand range (5-63 or > 63 µm) for silt. This article is conceived as a practical handbook dedicated specifically to Master and PhD students at the beginning of their heavy-mineral apprenticeship, as to more expert operators from the industry and academy to help improving the quality of heavy-mineral separation for any possible field of application.Minerals 2020, 10, 273 2 of 15 (e.g., aggregates of iron or titanium oxides); and anthropogenic origin (e.g., barite in core samples and moissanite) are thus neglected. Phyllosilicates are neglected as well. Transparent heavy minerals identified under the microscope are considered separately from opaque and altered heavy minerals.The study of heavy minerals, which was quite popular in the past-for a historical overview, the reader is referred to Carver, 1971 [4] and to the monumental book edited by Mange and Wright, 2007 [5])-has recently seen a renovated and increasing interest also in source-to-sink studies aimed at the search for hydrocarbon reservoirs (e.g., Morton and McGill, 2018 [6]). Laboratory practice for sample treatment and heavy-mineral separation was thoroughly investigated and illustrated a half century ago (e.g., [7][8][9][10]), but, later on, the methodology has seen a sort of standardization, and not only for the best, and the stimulus for the betterment of laboratory procedures has seen little progress since then. An updated recent publication in which the state-of-the art techniques for heavy-mineral separation are thoroughly explained through the entire process, from sampling to mineralogical analysis, thus does not exist to the best of my knowledge. The purpose of this article is to fill this gap, especially as the study of recent unconsolidated silts a...

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Raman counting: a new method to determine provenance of silt

Cited by 23 publications

References 38 publications

Sedimentary processes controlling ultralong cells of littoral transport: Placer formation and termination of the Orange sand highway in southern Angola

Sedimentary processes controlling ultralong cells of littoral transport: Placer formation and termination of the Orange sand highway in southern Angola

Effect of grain size distribution on Raman analyses and the consequences for in situ planetary missions

Gravimetric Separation of Heavy Minerals in Sediments and Rocks

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