The application of quartz grain morphology measurements to studying iron-rich duricrusts
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Regolith
Morphology
Results of evaluation of natural aggregates which can be classified as slow/late expanding alkali-silica reactive rocks are presented. One common feature in these rocks was the presence of strained quartz; on the other hand, metastable silica minerals like opal or chalcedony etc, were not detected. Taking into account past service records, results of mortar-bar tests at 38 and 60 degrees C and rapid chemical tests up to 7 days, revised criteria for assessment of such aggregates are proposed. (A) For the covering abstract see IRRD 871351.
Chalcedony
Metastability
Bar (unit)
Feature (linguistics)
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Abstract The porosity of the upper layers of regolith is key to the interaction of an airless planetary body with precipitating radiation, but it remains difficult to characterize. One of the effects that is governed by regolith properties is Energetic Neutral Atom (ENA) emission in the form of reflected and neutralized solar wind protons. We simulate this process for the surface of the Moon by implementing a regolith grain stacking in the ion‐solid‐interaction software SDTrimSP‐3D, finding that proton reflection significantly depends on the regolith porosity. Via comparison with ENA measurements by Chandrayaan‐1, we derive a globally averaged porosity of the uppermost regolith layers of . These results indicate a highly porous, fairy‐castle‐like nature of the upper lunar regolith, as well as its importance for the interaction with impacting ions. Our simulations further outline the possibility of future regolith studies with ENA measurements, for example, by the BepiColombo mission to Mercury.
Regolith
Lunar soil
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Optically stimulated luminescence
Thermoluminescence dating
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Glacial settings are considered to be the most challenging context for the application of luminescence dating. The optically stimulated luminescence (OSL) signal of quartz is often preferred for luminescence dating in partially-bleached settings as it resets (or bleaches) more rapidly in response to sunlight than the post-IR IRSL (pIRIR) signal of K-feldspar, and can therefore better characterise the well-bleached part of the partially-bleached De distribution. However, the relative bleaching extents of single grains of quartz and K-feldspar have not yet been compared for sedimentary samples from the natural environment. Here we compare the De distributions and accuracy and precision of ages determined using single grains of quartz and K-feldspar from sedimentary samples deposited in a proglacial setting with independent age control. We found that the extent of bleaching of the OSL signal of quartz and pIRIR225 signal of K-feldspar was similar (with similar over-dispersion), and therefore the pIRIR225 signal bleached to similarly low levels as the OSL signal of quartz in this partially-bleached setting. We also observed a consistent offset in over-dispersion between quartz and K-feldspar of ∼10% that can be linked to scatter arising from internal dose-rates of K-feldspar and should be included when applying age models. The results here demonstrate that the accuracy and precision of ages determined using the pIRIR225 signal of single grains of K-feldspar were similar to the OSL signal of quartz. However, K-feldspars were 5–18 times more efficient than quartz at determining the population of interest for age calculation as a larger proportion of K-feldspar grains emitted a detectable luminescence signal in comparison to quartz. These findings contradict our current understanding of the bleaching of K-feldspar and quartz grains in the natural environment, and are likely applicable to other partially-bleached settings (e.g. fluvial, alluvial).
Optically stimulated luminescence
Thermoluminescence dating
SIGNAL (programming language)
Optical dating
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Abstract The production, distribution, and evolution of lunar regolith are critical in deciphering the lunar bombardment history and comprehending the transport of materials across the lunar surface, which are still not well understood. In this study, we conducted a comprehensive investigation of factors influencing the production and distribution of lunar regolith by individual simple craters. Combining our results for the impact‐generated regolith volume with a lunar production function, we developed an analytical model to describe the regolith growth process. We found that the strength of bedrock significantly affects the crater size and hence the volume of regolith produced especially for subdecameter impactors. The regolith volume produced by an individual impact crater is quantitatively characterized as a function of crater diameter and preimpact regolith thickness. This regolith production is primarily determined by how much bedrock is shattered, followed by the impact‐induced volume change of target material and lastly by the regolith volume created by secondary cratering processes. When a single crater forms, preimpact regolith thickness greatly affects the regolith distribution pattern; a larger fraction of the regolith will be distributed outside the crater rim for a deeper preimpact regolith layer. Our regolith evolution model can serve as a good first‐order estimation of the regolith growth process that provides better constraints on the regolith buffering trend than previous studies. This model also suggests that, when ignoring the contribution from large, distant impacts, the regolith growth process is dominated by impact craters at scales from a meter to a few hectometers.
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Bedrock
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