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Quartz Weathering in Freezethaw Cycles

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Quartz Weathering in Freezethaw Cycles QUARTZ WEATHERING IN FREEZE–THAW CYCLES: EXPERIMENT AND APPLICATION TO THE EL’GYGYTGYN CRATER LAKE RECORD FOR TRACING SIBERIAN PERMAFROST HISTORY GEORG SCHWAMBORN1, LUTZ SCHIRRMEISTER1, FRANZISKA FRÜTSCH2 and BERNHARD DIEKMANN1 1Alfred Wegener Institute for Polar and Marine Research, Potsdam, Germany 2Institut für Geologische Wissenschaften, Freie Universität Berlin, Berlin, Germany Schwamborn, G., Schirrmeister, L., Frütsch, F. and Diek- permafrost. Permafrost is usually associated with mann, B. 2012. Quartz weathering in freeze–thaw cycles: and documented in proximity to glaciated (or for- experiment and application to the El’gygytgyn Crater Lake merly glaciated) areas in the periglacial realm (e.g. record for tracing Siberian permafrost history. Geografiska Annaler: Series A, Physical Geography, 94, ••–••. doi: Harris 1994; Murton 2005). Yet, little is known 10.1111/j.1468-0459.2012.00472.x about the age and continuity of permafrost condi- tions, since permafrost is a thermal and not a ABSTRACT. The object of this study is to test the assumption stratigraphical phenomenon. Drawing an inference that cryogenic weathering (here understood as in-situ disin- about permafrost history mostly relies on studying tegration of rock under cold-climate conditions including ice as a weathering agent) preferentially breaks up quartz grains. local sections that provide insights into restricted We apply the results of laboratory tests to a Quaternary time windows, mostly of the Quaternary (Schirr- sediment record. The combination of silt production, relative meister et al. 2002; Froese et al. 2008; Wetterich quartz enrichment in the silt fraction, and quartz grain micro- et al. 2008; Lacelle et al. 2009; Meyer et al. 2010; morphology is traced in a multi-100-kyr lake sediment Reyes et al. 2010; Kanevskiy et al. 2011). More archive as indicator data for cryogenic weathering. Constant cryogenic weathering conditions are inferred for at least the limits on studying permafrost history arise from last 220 000 years from a lake sediment core of El’gygytgyn imprecise age determinations of permafrost due to Crater, northeast Russia. This is the longest continuous ter- reworked or out-of-range radiocarbon material, restrial archive currently known for the continental Arctic. insufficient bleaching of optical stimulated lumi- Quartz enrichment in the fines evolves from seasonal nescence (OSL) material, or the uncertainty of post- freeze–thaw weathering as demonstrated in laboratory testing where over 100 freeze and thaw cycles crack quartz depositional permafrost formation (Krbetschek grains preferentially over feldspar. Microscopic grain fea- et al. 2000; Schwamborn et al. 2002; Bateman, tures demonstrate that freeze–thaw cycling probably 2008; Schirrmeister et al. 2008;Arnold and Roberts disrupts quartz grains along mineral impurities such as 2011). bubble trails, gas–liquid inclusions, or mineralogical sub- The study of permafrost history also suffers grain boundaries. Single-grain micromorphology (e.g. angular outlines, sharp edges, microcracks, brittle surfaces) from a lack of suitable proxy data. Process obser- illustrates how quartz becomes fragmented due to cryogenic vation of frost shattering has a long tradition cracking of the grains. The single-grain features stemming (Grawe 1936; Tricart 1956) and combines both from the weathering dynamics are preserved even after a field studies and accompanying laboratory experi- grain is transported off site (i.e. in mobile slope material, in ments. However, this method has stimulated seasonal river run-off, into a lake basin) and may serve as first-order proxy data for permafrost conditions in Quater- ongoing debates about the main drivers of rock and nary records. grain break-up (e.g. Wiman 1963; Hall and Thorn 2011). The phase change from water to ice and Key words: quartz micromorphology, weathering, terrestrial the induced 9% volume increase as elucidated in Arctic Bridgman’s (1912) pioneering statement is recog- nized as one prominent driving factor in cracking Introduction rock; freezing can shatter rock material by expand- There is a lack of continuous sediment archives ing fissures and cracks (McGreevy and Whalley that can be used to study the history of Arctic 1985). Temperature and moisture variations can © The authors 2012 Geografiska Annaler: Series A, Physical Geography © 2012 Swedish Society for Anthropology and Geography 1 DOI:10.1111/j.1468-0459.2012.00472.x GEORG SCHWAMBORN ET AL. Fig. 1. A qualitative scheme of changes in the distribution of mineralogical parameters with grain size. (a) The distribution of basic mineral components of sedimentary rocks under mid latitude conditions, and (b) under cryogenic conditions (from Konishchev 1982). Note the absence of coarser sand under cryogenic conditions and quartz enrichment in the finer silt sizes. also cause material dilation (Thomachot et al. accumulates in the 10–50 mm silt fraction (Kon- 2005). Volumetric expansion of pore water during ishchev and Rogov 1993) (Fig. 1). This is unusual freezing adds to material cracking (Walder and and in contrast to quartz behaviour at low lati- Hallet 1986), and ice segregation at sub-zero tem- tudes (Nesbitt et al. 1997). Konishchev (1982) peratures is another productive power in cracking introduced the cryogenic weathering index (CWI) rocks as shown by Hallet et al. (1991) and that expresses relative quartz grain enrichment in Murton et al. (2006). Furthermore, thermal stress the 10–50 mm fine fraction rather than in the alone can drive rock and grain disintegration in 50–100 mm coarser fraction of the same sample. the course of high-amplitude daily or seasonal Quartz proves to be less resistant than feldspar, temperature change (Hall and André 2003). which occurs as ubiquitously as quartz and is Reviews on recent advances in frost weathering used as a reference mineral: studies understood in a more wide-ranging way are given by Matsuoka and Murton (2008) and CWI= ( Q11 F) ( Q 2 F 2) (1) Hall and Thorn (2011). First insights that cryo- genic weathering is mineralogically selective at where Q1 = quartz in the 10–50 mm fraction, the grain-scale are from Konishchev (1973). It F1 = feldspar in the 10–50 mm fraction, was found that under freeze–thaw cycles quartz Q2 = quartz in the 50–100 mm fraction and preferentially disintegrates in sandy samples and F2 = feldspar in the 50–100 mm fraction. Deposits © The authors 2012 2 Geografiska Annaler: Series A, Physical Geography © 2012 Swedish Society for Anthropology and Geography QUARTZ WEATHERING IN FREEZE–THAW CYCLES that have been created under permafrost condi- El’gygytgyn geographical setting tions have values greater than 1, indicating that cryogenic weathering was intensive (Konishchev The lake sediment archive is taken from 1999; Demitroff et al. 2007). Here, permafrost El’gygytgyn Crater Lake in northeast Russia. This denotes for ice-bearing permafrost, where the site has various advantages: (1) The basin was not underlying permafrost can block the drainage of glaciated during the Quaternary (Glushkova 2001; the active layer provoking wet active layer condi- Niessen et al. 2007), which excludes glacial grind- tions. The cryogenic break-up of grains is ing as a main driver for breaking grains. (2) It supported, because seasonal ice is available in the currently has the longest terrestrial archive available soil as an amplifying factor. Under those circum- for the Arctic and provides a unique opportunity to stances the CWI can potentially be applied to trace the late Cenozoic evolution of Arctic climate identify permafrost when studying palaeoenviron- and the associated permafrost history (Nowaczyk ments. In fact, the CWI has been used in a et al. 2002; Brigham-Grette et al. 2007; Juschus few studies to identify permafrost episodes in a et al. 2007; Melles et al. 2007). (3) The bedrock terrestrial Quaternary record (Konishchev 1999; geology around El’gygytgyn Crater is fairly homo- Demitroff et al. 2007; French et al. 2009) or to geneous. It is dominated by rhyolites that provide a support thermal modelling of permafrost environ- stable background signature of eroded rocks and ments (Romanovskii and Hubberten 2001). their mineralogical contents. In order to reinforce the geological significance El’gygytgyn is a meteorite crater, roughly of quartz weathering as a potential tracer of cryo- 18 km in diameter, which was formed 3.58 Ϯ genic conditions, we repeat a simple freeze–thaw 0.04 Ma ago (Layer 2000) on the Chukchi Penin- experiment that includes samples of Arctic and sula (Fig. 2). The crater rim is between 600 and non-Arctic origin to complement former studies 930 m a.s.l. in elevation, while the surface of the that relied only on samples of permafrost origin lake lies at 492 m. The lake basin is bowl shaped, (Konishchev 1982). We address the following with a diameter of about 12 km and a maximum questions: (1) Can quartz grain enrichment be water depth of 177 m. The area has continuous confirmed in the silt fraction following numerous permafrost 500 m thick (Yershov 1998). Most of freeze–thaw cycles for samples from other (non- the bedrock (c. 75%) is composed of Cretaceous permafrost) areas (i.e. non pre-cracked grains)? rhyolites (ignimbrites and tuffs) and some of the Quartz grain shape and surface features are bedrock is andesitic basalts (Stone et al. 2009). imaged using scanning electron microscope Ignimbrites are porphyric containing mainly (SEM) micrographs. Single quartz grain visualiza- macro crystals of quartz and feldspar next to tion
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