Factors influencing the development of microtextures on cold‐climate aeolian quartz grains revealed by experimental frost action

Abstract

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.

Nano-scale analysis of polymineralic surface coatings on aeolian quartz grains with palaeoenvironmental implications

“…This is there fore not uni form and iso tro pic, and may di rectly in flu ence the ac cu racy and pre ci sion of the es ti mated age as mea sured by OSL meth ods (e.g., Porêba et al, 2022). It can be also as sumed that the in ter nal struc ture, es pe cially primary and sec ond ary de fects in quartz polycrystals, con trols the sus cep ti bil ity to HF acid etch ing (the acid, in stead of di gest ing the par ti cle on the sur face, can po ten tially pen e trate along cracks), sim i larly to the sus cep ti bil ity to frost-in duced mod i fi cations (es pe cially cracks or even frag men ta tion) found for quartz sand grains (Górska et al, 2023). In ad di tion, if the strongly adhe sive Type B polymineralic coat ing is not com pletely re moved (the qual ity of coat ing re moval is never con firmed -it is assumed that quartz grains are sin gle crys tals; Bell and Zimmer -man, 1978;Moska et al, 2021) in the ini tial phase of the prep ara tion (by HCl and perhydrol), as a re sult of the re ac tion of HF with el e ments such as Mo, Fe and Cr, the sur face of the etched grain may be cov ered by a pas sive film which hin ders fur ther cor ro sion (Dai et al, 2021).…”

“…TEM lamella) prep a ra tion and high-res o lu tion trans mis sion elec tron mi cros copy (Jeong and Nousiainen, 2014) de spite the prom ise of this ap proach. For ex am ple, a re cent FIB-TEM analy sis (Górska et al, 2023) re vealed that the de vel op ment of surficial marks on a quartz grain can be pro foundly in flu enced by both pri mary (e.g., in clu sions, grain bound aries) and second ary (e.g. frost-in duced cracks) crys tal de fects.…”

“…SEM is also com monly used to de scribe the coat ings or rims on such quartz grains (e.g., Weibel et al, 2010;Engelbrecht et al, 2016) or to in ter pret the microtextural features on the sur face of in di vid ual quartz grains (e.g., Górska et al, 2023), but in ves ti ga tions of the in ter nal struc tures of sin gle dust par ti cles are scarce (Jeong and Nousiainen, 2014). This is due to the lim ited pos si bil i ties to im age di rectly the cross-section of a dust par ti cle by con ven tional SEM and the need to use scan ning/trans mis sion elec tron mi cros copy (S/TEM) to study sub-sur face lay ers a few nm thick.…”

“…In ad di tion, a 'sin gle' par ti cle is rarely a sin gle crys tal or mineral, but com monly it is a polycrystalline or polymineralic form (Falkovich et al, 2001;Jeong, 2008;; an exam ple may be mo saic in ter nal struc ture of quartz (Frederickson 1955;Górska et al, 2023). Inter growths and the com pos ite min eral clus ters are also com mon (Engelbrecht et al, 2016), and so the microphysical data ob tained from a 'sin gle' par ti cle are of ten the re sult of the in ter ac tion of nu mer ous min eral grains, com posed of dif fer ent min eral types (Jeong and Nousiainen, 2014).…”

“…soil-form ing pro cesses (Biernacka and Issmer, 1996), es pe cially in the im me di ate vicin ity of aquatic en vi ron ments, have of ten been em pha sized (e.g., Lee et al, 2013;Wooldridge et al, 2019 and ref er ences therein). Of course, alu mi no sili cate coat ings are usu ally removed (or the au thors as sume they have re moved them; Bell and Zimmerman, 1978) be fore microtextural anal y sis (e.g., Górska et al, 2023) or Op ti cally Stim u lated Lu mi nes cence (OSL) dat ing (e.g., Moska et al, 2021) but lit tle is known about their in ter nal struc ture.…”