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Ice-Marginal and Periglacial Processes and Sediments: an Introduction

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Ice-Marginal and Periglacial Processes and Sediments: an Introduction Downloaded from http://sp.lyellcollection.org/ by guest on September 29, 2021 Ice-marginal and periglacial processes and sediments: an introduction I. PETER MARTINI1*, HUGH M. FRENCH2 & AUGUSTO PE´ REZ ALBERTI3 1School of Environmental Sciences, University of Guelph, Guelph, Ontario N1 G 2W, Canada 2Departments of Geography and Earth Sciences, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada 3Departamento de Xeografı´a, Universidade de Santiago de Compostela, Santjago de Compostela, Spain *Corresponding author (e-mail: [email protected]) Abstract: The volume focuses on the analysis of glacial clastic sedimentary deposits, both ancient and recent. The papers range from reviews of glacial systems and cold-climate weathering products and processes to conceptual and field studies of specific ice-marginal and cold-climate sediments. Papers are included that deal with tidewater glaciers, mountain settings on Earth, permafrost areas on both Earth and Mars and detailed regional analyses of cold-climate sediments of Late Pleistocene and Holocene age. The identification of sedimentary facies allows an accurate reconstruction of many of the developmental processes that are involved in ice-marginal and periglacial environments. Lithostratigraphic characteristics of clastic deposits also constitute circumstantial evidence for the previous existence of ancient, and certainly pre-Quaternary, cold-climate systems. This is demonstrated by a study on putative Palaeozoic glacial deposits in Saudi Arabia. This volume presents a number of papers that relate these Pleistocene-age ice sheets still exist today, to both current and ancient ice-marginal and cold- the largest being in Antarctica and Greenland. climate environments. Studies of their sediments, These ice bodies and the many other smaller gla- weathering and transportation processes contribute ciers, together with their immediate pro-glacial or to an understanding of the cryosphere. The cryo- ice-marginal surroundings, constitute the glacial sphere includes Earth’s surface areas that experi- environments of today. Equally extensive, both ence one or more of the following: snow cover, sea now and in the past, are vast ice-free areas that ice, glaciers, perennial and seasonal frost (Fig. 1). have either experienced or currently experience Here, we are concerned with the sediments and cold-climate conditions. These may have lasted for weathering processes that occur in the environments thousands, and in some cases millions, of years. that are immediately adjacent to glaciers as well as These areas constitute the so-called periglacial the frost-dominated environments that characterize environments. Collectively, these two environments cold-climate settings in general. We include contri- extend over approximately one-third of the Earth’s butions that involve not only present-day cases but land surface; they undoubtedly occupied much also those that occurred in the Pleistocene and, in more during the cold periods of the Pleistocene minor measure, the more ancient geological past. and even earlier during the cold events in ancient In addition, and in anticipation of the future, we geological time. include a paper that summarizes recent progress in The extraordinarily high erosive and transpor- planetary (Martian) observations. tational power of glaciers has been well known for over 150 years. Prior to that, during the first half of the 1800s, the full potential of glaciers was not Glacial and periglacial environments recognized although icebergs and the biblical flood were considered suitable agents for moving Vast continental areas of Earth have been large erratic boulders and heterogeneous sedi- sculpted by glaciers and many regions are now ments over considerable distances. The early devel- covered by glaciogenic sediments. Remnants of opment of the glacial hypothesis encountered From:Martini, I. P., French,H.M.&Pe´rez Alberti, A. (eds) Ice-Marginal and Periglacial Processes and Sediments. Geological Society, London, Special Publications, 354, 1–13. DOI: 10.1144/SP354.1 0305-8719/11/$15.00 # The Geological Society of London 2011. Downloaded from http://sp.lyellcollection.org/ by guest on September 29, 2021 2 I. P. MARTINI ET AL. Fig. 1. (a, b) A schematic diagram that illustrates how geography and geomorphology interact with the related physical science disciplines and (c) the major constituents of the cryosphere. Studies of the sediments associated with either ice-marginal or periglacial environments lie within either the shaded or cross-hatched areas in (c) (from French 2007). opposition but the ever-increasing evidence gradu- Today, Łozinski’s definition is regarded as ally converted the leading earth scientists of the unnecessarily restricting; few, if any, modern time such as William Buckland and Charles Lyell analogues exist (French 2000). There are two main (Chorley et al. 1964). A somewhat refined glacial reasons. First, frost action phenomena are known hypothesis was developed by Louis Agassiz in to occur at great distances from both present-day 1840 but the first real scientific glacial study was and Pleistocene ice margins. In fact, frost-action published by Archibald Geikie in 1863 for Scotland phenomena can be completely unrelated to ice- (followed by several other publications that in- marginal conditions. Second, the term has been cluded the first edition of The Great Ice Age; increasingly understood to refer to a complex of Geikie 1874). By the turn of the century, the cold-dominated geomorphic processes. These theory of Pleistocene ice ages was well established include not only unique frost-action and perma- both in Europe and North America (Wright 1890; frost-related processes but also a range of azonal Geikie 1897; Daly 1934; North 1943). processes, such as those associated with snow, The periglacial concept is more recent in origin. running water and wind, which demand neither a The term was first used by a Polish geologist, peripheral ice-marginal location nor excessive Walery von Łozinski, in the context of the mechan- cold. Instead, these processes assume distinctive ical disintegration of sandstones in the Gorgany or extreme characteristics under cold, non-glacial Range of the southern Carpathian Mountains (a conditions. region now part of central Romania). He described Studies of the ice-marginal and periglacial the angular rock-rubble surfaces that charac- environments do not differ tactically from those of terize the mountain summits as ‘periglacial facies’ other Earth surface systems except for one impor- formed by the previous action of intense frost tant fact: one is dealing with environments in (Łozinski 1909). Subsequently, the concept of a which an unusual mineral (ice, H2O) is very close ‘periglacial zone’ was introduced (Łozinski 1912) to its melting point. It also experiences sublimation. to refer to the climatic and geomorphic conditions As a result, the presence of snow and ice generates of areas peripheral to Pleistocene ice sheets and conditions and landscapes that are unusual and glaciers. Theoretically, this was a tundra zone that highly variable over both short and long time extended as far south as the treeline. In the moun- spans (night and day, seasonal and multi-annual, tains, it was a zone between the timberline and century, millennia). A number of texts cover the snowline. broad fields of ice, glaciology and glacial Downloaded from http://sp.lyellcollection.org/ by guest on September 29, 2021 INTRODUCTION 3 geomorphology (Souchez & Lorrain 1991; Paterson 1994; Benn & Evans 1998; Liestol 2000; Martini et al. 2001). Ancient environments and geological contexts In the study of Earth systems, we are trained to learn from the present in order to interpret the past. However, we must be mindful of the very different settings that are involved and that some events are so rare they may not be observed directly during a life- time and need to be inferred from the sediment/rock record they leave. Moreover, the geo(morpho)logic system is complex; a full understanding requires contributions from a myriad of sciences that have become increasingly complex in the last two to three decades. For example, the basic sciences such as physics, chemistry and biology must be applied to understand the main component of both the ter- restrial glacial and periglacial systems and Martian geology, namely ice. The rheological behaviour of glaciers and the landscape, both erosive and deposi- tional, that glaciers leave behind are also central concerns while an understanding of the freezing process, be it seasonal or perennial, is an essential but not defining aspect of periglacial geomorphol- ogy. There is also overlap with other subdisciplines; for example, in both glacial and periglacial environ- ments, azonal processes such as running water, wind and gravity-induced displacements often assume critical importance. The same combination of pro- cesses must also be considered when inferring the nature of wind-related processes on the Martian surface. Since early times, Earth’s climate has experien- ced variations from cool long-lasting (‘Ice-house’) periods to warm (‘Greenhouse’) periods (Fig. 2). Humans have evolved and still live in the last Ice- house period, the Quaternary, a period punctuated by relatively short warmer stages when glaciers retreated (interglacial) and longer colder stages (glacial) during which glaciers advanced and snow and ice covered large expanses of the Earth’s surface. Within each glacial stage, smaller tem- Fig. 2. A graph showing estimated changes
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