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Chapter 8. Glacioaeolian Processes, Sediments, and Landforms

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Chapter 8. Glacioaeolian Processes, Sediments, and Landforms CHAPTER GLACIOAEOLIAN PROCESSES, SEDIMENTS, AND LANDFORMS 8 E. Derbyshire1 and L.A. Owen2 1Royal Holloway, University of London, Surrey, United Kingdom, 2University of Cincinnati, Cincinnati, OH, United States 8.1 INTRODUCTION The frequently strong association of aeolian processes with present and former glaciation has been recognized for over 80 years from field observations (Hogbom, 1923). Bullard and Austin (2011) point out that the interaction between glacial dynamics, glaciofluvial, and aeolian transport in proglacial landscapes plays an important role, not only in local environmental systems, but also in the global context by affecting the amount of dust generated and transported. Moreover, glacial outwash plains have been cited as a significant source of dust in the Southern Hemisphere (Sugden et al., 2009) and must also have been important dust sources in the northern hemisphere (Bullard and Austin, 2011). Cold climate aeolian processes and landforms have been widely acknowledged in proglacial and paraglacial geomorphology (e.g., Ballantyne, 2002; Seppa¨la¨, 2004). However, relatively little work has been undertaken on glacioaeolian processes, sediments, and landforms compared to other glacial systems. The ISI Web of Science does not even provide one reference to the term ‘glacioaeolian’ and Google Scholar provides a mere 61 references. Variations on the spell- ing of glacioaeolian, including glacioeolian, glacio-aeolian, glacio aeolian, and glacio-eolian yield less than 40 citations. Even the international journal Aeolian Research provides only one reference to the term glacioaeolian. A search of glacial aeolian yields 924 and 35,300 citations in the ISI Web of Science and Google Scholar, respectively. However, this includes reference to aeolian sedi- ments that are not of glacial origin, but were deposited during a glacial event. The classic textbook on glaciers, Glaciers and Glaciation,byBenn and Evans (2010) does not even list glacioaeolian in its index. Despite this, the glacioaeolian sediments and landforms are omnipresent in glacial and proglacial evironments, and many of the great loess belts owe their origin to glacioaeolian pro- cesses and the silt that is produced in the glacioaeolian environment. The importance of glacioaeolian sediments and landforms for palaeoenvironmental reconstruc- tions has a long history. The distribution of coversands, sand dunes, and loess mantles in Western Europe and North America, e.g., was used to develop the hypothesis of a glacial anticyclone associ- ated with the European ice sheet (Hobbs, 1942, 1943a,b). This became a framework used by a num- ber of authors to characterize the extraglacial environment of the last glacial maximum in North America and Europe (e.g., Schultz and Frye, 1968; Dylik 1969; Demeck and Kukla, 1969; Galon, 1959; Velichko and Morozova, 1969; Tricart, 1970; Maarleveld, 1960; Dylikowa, 1969; Krajewski, Past Glacial Environments. DOI: http://dx.doi.org/10.1016/B978-0-08-100524-8.00008-7 © 2018 Elsevier Ltd. All rights reserved. 273 274 CHAPTER 8 GLACIOAEOLIAN PROCESSES, SEDIMENTS, AND LANDFORMS 1977; Poser, 1932, 1948, 1950; Reiter, 1961; Lill and Smalley, 1978; Williams, 1975, Arbogast et al., 2015; Sebe et al., 2015). Since glacioaeolian silt can be transported vast distances it has become an important proxy for climate change ice cores and lake records (Lambert et al., 2008; Sudarchikova et al., 2015; Dorfman et al., 2015). For over a century, glaciers have been regarded as the greatest single source of aeolian silt, and the nature and distribution of much of the world’s loess (wind-deposited silts predominantly in the grain size range 0.01À0.05 mm, unstratified, relatively porous, dry, and yellow buff to brown yellow in colour—Lill and Smalley, 1978) have been explained in terms of the former presence of large ice sheets on the northern continents at various times during the Quaternary (Smalley, 1966a,b; Vita-Finzi and Smalley, 1970; Boulton, 1978; Smalley and Derbyshire, 1990). A number of authors have regarded the glacial grinding of rock as the main Earth-surface process capable of producing the huge volumes of silt making up the world’s loess lands (Smalley et al., 2014, and references therein). It is fair to say that the prevailing view still favours an origin in cold-climate conditions with increased aridity in which periglacial and montane environments are added to the strictly glacial. However, much work has recently emphasized the complex sources and pathways of the sediment that comprises the great loess deposits and other associated aeolian deposits (e.g., Nie et al., 2015; Nottebaum et al., 2015; Vanneste et al., 2015). On a more local scale, the links between glacial deposition and aeolian reworking of sediments has been illustrated from a number of glacial forelands, an early example being the observations in Greenland by Poser (1932) and, more recently, by Bullard and Austin (2011). Information on sediment generation and sources, the operation of the aeolian processes, facies discrimination, and palaeoenvironmental reconstruction is, not surprisingly, widely scattered through the literature on sedimentology, glacial and periglacial geomorphology, and Quaternary stratigraphy. In order to help to address the need to highlight the importance of glacioaeolian processes, landforms, and sediments in the study of glacial geology and geomorphology, we build on our chapter on glacioaeolian processes, sediments, and landforms that was published in the first edition of Past Glacial Environments: Sediments, Forms and Techniques (Derbyshire and Owen, 1996; Menzies, 1996). In particular, we draw on a selection of literature that emphasizes the relation between glaciers and aeolian sediments and landforms. 8.2 SEDIMENT PRODUCTION AND SOURCES Comminution of rock to produce fragments with a particle size susceptible to movement by aeolian suspension, saltation, and traction is effected on a large scale by several mechanisms including glacial grinding, weathering (notably by crystal growth), and fluvial and aeolian abrasion of particles in transport (Smalley et al., 2014; Woronko and Pisarska-Jamrozy, 2015; Fig. 8.1). More localized and less well documented processes include hydration effects, chemical and biological weathering, and mass slope failure in rock and soil including those associated with earthquake shock (Hewitt, 1988; Goudie, 2005; Graly et al., 2014; Hindshaw et al., 2016; Fig. 8.2). Most of the quartz in sedimentary rocks is derived initially from igneous and metamorphic types and is predominantly of sand size. Most of the sand-size particles in the world’s sedimentary system consist of quartz derived from massive plutonic rocks and gneiss with a mean grain size of 720 μm, 8.2 SEDIMENT PRODUCTION AND SOURCES 275 FIGURE 8.1 Views of supraglacial debris on the Khumbu glacier in Nepal. Note the abundant fine sediments generated by rock fall processes that supply the debris, and abrasion and crushing of the debris as it is transported down glacier. FIGURE 8.2 Rock avalanche debris on snow cones in the Himalaya of northern India illustrating the potential of such processes to generate abundant fine sediment that may be transported by aeolian processes into the glacioaeolian system. and sources such as schist with a mean quartz grain size of 440 μm, bringing the initial average particle size down to about 600 μm(Blatt, 1987; Livingstone and Warren, 1996). The ancient granitic rocks such as those of the heavily glaciated Laurentian and Baltic shields contain quartz in a stressed state, which facilitates comminution (Smalley, 1966a,b; Smalley et al., 2014). In contrast, the quartz in the Quaternary sands and silts of High Asia derives less from highly stressed granite and more from thick, recycled sedimentary units in the KarakoramÀHimalayanÀTibetan zone of crustal thickening. Break up and release of quartz particles results from the considerable energy 276 CHAPTER 8 GLACIOAEOLIAN PROCESSES, SEDIMENTS, AND LANDFORMS derived from tectonic and crystal-growth processes in this rapidly rising, cold, and rather dry region. The observation by Blatt (1987) that the δ18O values of quartz from plutonic igneous rocks are consistently lower than those found in quartz from many sedimentary and metamorphic sources is used by Smalley (1990) as a further distinction between loess derived from the Pleistocene ice sheet glaciations (glacial loess) and that produced in High Asia by tectonic and weathering processes (mountain loess). The production of large amounts of silt requires comminution of sand-grade material, as shown by considerable discussion of the relative importance of the glacial and nonglacial processes involved. Attrition in blowing and saltating sand grains produces some silt-size material, but the experimental results of Kuenen (1960) suggested that the volume is small; this led Smalley and Vita-Finzi (1968) to reject this origin for the great loess sheets. Instead, production of silt by the grinding action at the bed of glaciers and ice sheets has led some writers to express the view that this is the only mechanism capable of producing such large volumes of silt (e.g., Smalley and Cabrera, 1970; Boulton, 1978; Collinson, 1979). Other evidence, notably particle shape and surface texture, and the mineralogy of the clay grade (,2 μm) has been invoked to strengthen this view. Smalley and Cabrera (1970) interpreted the predominantly angular shape of loess grains as consis- tent with glacial breakage, and fracture surfaces were attributed to glacial
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