Coarse sand‐sized (0.5–1.0 mm) grains of vein quartz were subjected to frost‐induced stress under controlled laboratory conditions. A total of 1,000 freeze–thaw (FT) cycles, simulated under different ...(low, high) water mineralization conditions in the temperature range from −5°C up to +10°C, were used to test effects on collected samples. Scanning electron microscopic (SEM) microtextural analysis of grain surfaces was performed at 0 (start) and after 50, 100, 300, 700, and 1,000 FT cycles. The results indicate that variable frost‐induced microtextural imprints encountered on quartz grain surfaces prior to and following analysis depend largely on the mineralization (dissolved solute content) of water involved in the weathering process. The higher the water mineralization, the greater the intensity of mechanical weathering. Two predominant outcomes in the course of these micro‐scale frost weathering tests have been identified: a physical (mechanical) aspect manifested by the occurrence of conchoidal fractures and breakage block microtextures dominating up to 300 FT cycles, and a chemical aspect resulting in the occurrence of precipitation crusts and obliteration of grain microrelief. Moreover, three additional stages of microtexture development may be distinguished with the evolution of frost‐induced microrelief on the surface of quartz grains: (i) initial cracks of large‐sized conchoidal fractures, (ii) increasing frost cycles yielding additional small‐sized conchoidal fractures, and (iii) advanced breakage blocks. Frost‐induced exposure of fresh, unweathered grain surfaces leads to refreshing of the grain surface.
Aeolian‐originated quartz grains of coarse‐sand size (0.5–1 mm) were subjected to experimental frost weathering. A total of 1,000 freeze–thaw cycles with temperature ranges from −5 to +10°C were ...simulated under full water availability conditions. Scanning electron microscope microtextural analysis of grain surfaces conducted after 0, 50, 100, 300, 700, and 1,000 freeze–thaw cycles resulted in different‐sized conchoidal fractures and breakage blocks as frost‐induced microtextures. The vast majority of these microtextures were encountered on the most convex parts of aeolian grains and their number increased with ongoing freeze–thaw cycles. However, the number of recorded frost‐originated microtextures remained relatively small up to 700 freeze–thaw cycles and increased after 1,000 freeze–thaw cycles. Transmission electron microscope microstructural analysis of grains after 0, 100, and 1,000 freeze–thaw cycles showed both primary (e.g., inclusions, grain boundaries) and secondary (e.g., cracks) defects in quartz crystals. The frequency of the latter remained unexpectedly low. The susceptibility of aeolian‐originated sand‐sized quartz grains to frost‐induced modifications is interpreted here to depend mainly on their internal characteristics. These include aeolian‐driven development of a subsurface impact zone that determines the depth to which frost‐originated microtextures develop. The outer impact zone consists of a thin layer of surficial crust and a series of more or less parallel ridges arranged into mechanically upturned plates. The inner impact zone consists of intact or cracked quartz crystals. The susceptibility of aeolian‐originated quartz grains to frost‐induced modifications depends therefore on a combination of internal (i.e., original crystallography of quartz grains) and external (i.e., aeolian and frost processes acting upon the grains) factors.
Sand-sized quartz grains selected from sediments of a Pleistocene inland dune (eastern Poland) were subjected to a series of laboratory analyses, including grain-size distribution, morphoscopy ...analysis, microtextural analysis using scanning electron microscope (SEM) and nanostructural analysis using transmission electron microscope (TEM). The results indicate the presence of a crust on the surface of all of the studied quartz grains and a surprisingly low number of aeolian-induced mechanical microtextures. The TEM examination identifies illite-smectite assemblages as the main component of the crust, accompanied by amorphous silica, local accumulation of Fe, K, Ca, Mg oxides, and mineral particles (quartz, K-feldspar, chlorite). The thickness of the crust reaches approx. 0.1–0.2 μm and varies from the minimum on micro-protrusions up to the maximum in micro-cavities. Here, we present a new theory on the origin of the crust observed on the surface of cold-climate aeolian quartz grains. We postulate that the crust is formed within a near-surface saltation layer during active aeolian transport of sand-sized grains and clay-sized particles operating under cold-climate conditions. The development of abrasion features and the formation of the crust are interpreted here to occur simultaneously and continuously during the aeolian transport. The formation of the crust results from specific properties of aeolian transport (i.e. self-induced electrification and electrification mechanisms of quartz grains) and the quartz grains themselves (i.e. grain shape and surface microtopography).
•Micro- and nano-scale microscopic analyses of cold-climate aeolian quartz grains•The formation of the crust during aeolian transport under cold-climate conditions•The formation of the crust within a near-surface saltation layer•The influence of self-induced aeolian electrification on the formation of the crust•The influence of grain shape and microtopography on the formation of the crust
Microtextures imprinted on the surface of quartz grains provide in-depth information on the environmental conditions and sedimentary processes that affected the study sediments. Microtextural ...analyses are therefore widely used in the provenance studies of sediments. In order to minimize the subjectivity of microtextural recognition, we propose a new software, called DeepGrain (source codes are available at https://github.com/deepgrains/deepgrain), for the automatic identification of microtextures on the surface of quartz grains using the DeepLabV3 model with applied improving techniques. The approach provides an accuracy of 99 % of the area of the tested grains and 63 % of the mechanical features on the surfaces of the tested grains. The inference of a single SEM image of quartz grain took an average of 3.10 sec, leading to a significant reduction in the analysis time of a single grain.
•Artificial intelligence limits inter-operator variation on microtextural analysis of quartz grains.•DeepGrain software as a tool for quick (∼3 sec) recognition of mechanical microtextures on the surface of quartz grains.•Limitation in the automatic recognition of chemical microtextures on the surface of quartz grains.•Mechanical microtextural marks were correctly recognized on approx. 2/3 of grain’s surfaces analyzed.
•Impact of water content and water mineralization on the course of the micro-scale frost weathering.•Frost-induced production of coarse-grained sand fraction.•Small production of silt-sized grain ...fraction.•Lack of correlation of micro-scale frost weathering intensity and moisture content.•Preparation/inherited and primary defects as frost-driven factors.
The experimental simulation of a micro-scale frost weathering of sand-sized (0.5–1.0 mm) quartz grains has been conducted to investigate the frost-induced changes in the grain-size distributions and factors that affect the weathering process. For the first time we present the results concerning the relationship between the course of frost weathering and the characteristics of water (content and mineralization) involved in the process. The simulation involved two types of vein quartz crushed to fresh, angular grains and arranged into dry, moistened and wet samples. Grain samples were subjected to fixed temperature oscillations (from −5 °C to +10 °C) under controlled laboratory conditions. Grain-size analysis were conducted after 50, 100, and 300 freeze–thaw cycles. Differences in the distributions, resulting from the production of the frost debris, were observed at each stage of the weathering process. Statistical analyses (Kolmogorov-Smirnov test, PCA, cluster analysis) demonstrated that both types of quartz grains react differently to the ongoing weathering process regardless of the moisture conditions. The production of very coarse (1.0–2.0 mm) and coarse sand (0.5–1.0 mm) fractions, resulting from the frost-induced destruction, was observed. This issue has never been addressed or expounded before. The production of fine (0.125–0.25 mm) and very fine (0.063–0.125 mm) sands was notable while the silt-sized grains (0.002–0.063 mm) constituted only a minor product of the frost weathering. Nevertheless, the combined increase in the content of these fractions may have a significant impact on the properties of the frost-affected sediments/soils. The sample preparation (resulting in preparation defects) and the internal structure of quartz grains (resulting in primary defects) had a great influence on the initial course and manner of the frost weathering process. Other factors, such as content or mineralization of water, exerted much less influence on the frost-driven destruction during the studied weathering period.
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