Downloaded from http://sp.lyellcollection.org/ by guest on October 1, 2021 Introduction: the nature and significance of aeolian sedimentary systems K. PYE Postgraduate Research Institute for Sedimentology, University of Reading, Whiteknights, Reading RG6 2AB, UK The past 20 years have seen a major growth and bedforms provides a useful means of testing of interest in aeolian processes, landforms and the predictions of global circulation models for sediments, as witnessed by a growing number of different times in previous earth history (e.g. published papers in journals, conference pro- Kutzbach & Guetter 1986; Parrish & Peterson ceedings and edited volumes (e.g. see the collec- 1988). However, successful interpretation and tions in Morales 1979; McKee 1979; P6wd 1981; use of the aeolian sedimentary record in this way Brookfield & Ahlbrandt 1983; Barndorff- requires that the nature of aeolian processes, Nielsen et al. 1985; Nickling 1986; Liu 1987; and the environmental controls on them, are Eden & Furkert 1988; Kocurek 1988; Hesp & adequately understood. In simple terms, the for- Fryberger 1988; Gimingham et al. 1989; Okuda mation of aeolian sedimentary sequences has et al. 1989; Leinen & Sarnthein 1989; Nordstrom only three basic requirements: (1) a source of et al. 1990; Barndorff-Nielsen & Willetts sediment; (2) sufficient wind energy to sort and 1991a,b; Kocurek 1991; Carter et al. 1992; Pye transport the sediment; and (3) a suitable loca- & Lancaster 1993. A number of monographs tion where part or all of the sediment can dealing with sand dunes, dunefields, dust and accumulate. In practice, a wide range of loess have also been published (Greeley & environmental factors may influence the Iversen 1985; Pye 1987; Lancaster 1989; Pye distribution, morphology and sedimentological & Tsoar 1990; Coudd-Gaussen 1991). Several character of aeolian deposits. These include factors have contributed to this increased level tectonic factors, which affect weathering and of interest, including a desire to achieve a better erosion rates, influence the nature of the wind understanding of recent aeolian environments regime, and control the location, form and as analogues for ancient aeolian hydrocarbon preservation potential of the resulting deposits. reservoirs (e.g. Glennie 1972; Fryberger et al. Climate also exercises a strong control on sedi- 1983) and other planets where aeolian processes ment production rates and the potential for play an important role (e.g. Breed & Grow 1979; aeolian transport, both directly and indirectly Greeley & Iversen 1985), the requirement for through its influence on vegetation cover and the development of improved methods of groundwater levels. In near-coastal areas, sea- desertification and sand control in arid and level fluctuations may also have a strong influ- semi-arid regions (Khalaf 1989; Watson 1990), ence, either by initiating phases of transgressive particularly in view of the predicted effects of dune activity associated with shoreline changes, global climate change (Houghton et al. 1990), or by triggering widespread changes in ground- the identification of coastal dune systems as water level (Chan & Kocurek 1988). Finally, an important recreational and conservation human activities play an ever-increasing role, resource which is under threat from rising sea- being responsible under different circumstances level and human activities (ver der Meulen 1989; both for destabilization of partially vegetated Bakker et aI. 1990; van der Meulen et al. 1991), dunes and for stabilization and control of active and the recognition that aeolian sedimentary systems. sequences both on land and in the oceans poten- Against this background, the papers included tially preserve a detailed record of changes in in this volume have been grouped into five main regional climate and global atmospheric trans- sections. The first section contains four papers port during the Quaternary and earlier times dealing with aeolian grain mechanics and dune (e.g. Rea et al. 1985; Rea & Leinen 1988; Kukla morphodynamics. Although the basic physics of et al. 1988; Beget & Hawkins 1989; Ruddiman aeolian sediment transport have been relatively et al. 1989; Pye & Zhou 1989; Clemens & Prell well understood for more than 50 years, and 1990; Sirocko et al. 1991; Sirocko & Lange many of the fundamental principles elucidated 1991). in Bagnold's (1941) The Physics of Blown Sand The evidence provided by aeolian sediments and Desert Dunes remain basically valid, recent From Pye, K. (ed.), 1993, The Dynamics and Environmental Context of Aeolian Sedimentary Systems. Geological Society Special Publication No. 72, pp. 1-4. Downloaded from http://sp.lyellcollection.org/ by guest on October 1, 2021 2 K. PYE laboratory experimental and numerical model- sedimentary architecture of the Jurassic Entrada ling work has allowed the refinement of the basic Sandstone in the Utah area, USA, and discuss model, as discussed in McEwan & Willett's the evidence which suggests that large-scale paper in Section I. Difficulties remain, however, aeolian deflation and accumulation events in this in taking full account of the effects of turbulence area were controlled principally by changes in at different spatial and temporal scales. In this groundwater levels which in turn were related connection, gain function analysis promises to to movements in sea-level. Careful evaluation be a useful new approach, as described in the of sedimentary structures is also used by paper by Hardisty. An important challenge also Chakraborty & Chaudhuri as the basis for their remains to relate models of aeolian grain trans- interpretation that the Precambrian Mancheral port over flat or uniformly sloping beds to real Quartzite of northern India is principally com- field situations with complex terrain, where posed of thin aeolian sand layers which accumu- wind speed profiles may deviate markedly from lated under conditions of a high water table the theoretical logarithmic profile. The paper by within a broad river floodplain environment. Burkinshaw et M. presents data which illustrate Section III contains seven papers dealing with the variability of wind profiles over a reversing coastal dunes. The first paper in this section, by transverse dune in the Alexandra coastal Psuty, considers the relationship between recent dunefield of South Africa, while Wiggs illus- beach changes at Perdido Key, Florida and the trates the problems involved in evaluating shear development of foredune morphology. On a velocity from wind profile measurements in the related theme, the relationship between coastal context of a dynamic dune in Oman. wind regime, sediment transport and foredune Section II contains seven papers which deal development at Tentsmuir, Fife, is considered primarily with the development and sedimen- by Wal & McManns, while Carter & Wilson tary history of desert dunefields, including the provide an overview of thc location, morph- determination of sand chronostratigraphy. The ology, and historical development of coastal first paper in this section by Wintle provides an dune sand accumulations in Ireland. overview of recent advances in luminescence The complex pattern of sand transport and dating of aeolian sands. The methodologies of mixing of sediment from different sources thermoluminescence and optical luminescence around the Baix Empord~, eastern Spain, is dating are outlined, together with outstanding documented by Cros & Serra, while Pye & Neal problems and promising areas for future present the results of a stratigraphic drilling and development. The following three papers, by radiocarbon-dating investigation which have Edwards, Rendell etaL and Stokes & Breed, pro- allowed the development of a model for the vide case studies of the application of lumi- development of the late Holocene Sefton barrier nescence dating to the evolutionary history dune complex in northwest England. of dunes in the Kelso area of California, the The final two papers in this section, by northern Negev Desert, and northeastern Gardner & McLaren and McLaren, consider the Arizona, respectively. Although some pro- nature and significance of post-depositional cedural problems remain, and there are cur- cementation and diagenesis within carbonate- rently too few dates available to draw firm rich coastal dune sands from different parts of conclusions about the number, timing and the world. They demonstrate that a simple causation of dune episodes in these areas, the model of progressive diagenesis in carbonate preliminary results are encouraging. aeolianites cannot be supported, and that The paper by Livingstone & Thomas provides palaeoenvironmental interpretations based on a discussion of the environmental factors which degree of diagenetic alteration need to be made govern the morphological development and with caution. dynamics of linear dunes in southern Africa. It Section IV contains two papers relating to is pointed out that the presence of vegetation aeolian deposits in temperate and cold conti- cover does not in itself imply that these features nental environments. The first paper, by Koster are entirely relict. Some sand movement is poss- et aL, examines the genesis and sedimento- ible under conditions of partial vegetation cover, logical character of late Holocene drift sands in and episodic sand transport in response to northwest Europe which have formed by aeolian climate fluctuations on time scales of 10-100 reworking of older Pleistocene sands. The years should not be ignored. second paper, by