Arid zone geomorphology

Arid zone geomorphology

Sedimentary Geology, 75 (1991) 163-169 163 Elsevier Science Publishers B.V., Amsterdam Book Reviews Arid Zone Geomorphology. David S.G. Thomas (Ed...

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Sedimentary Geology, 75 (1991) 163-169

163

Elsevier Science Publishers B.V., Amsterdam

Book Reviews

Arid Zone Geomorphology. David S.G. Thomas (Editor). Halstead Press, New York, N.Y., 1989, 372 pp., £40 (hardcover).

Arid Zone Geomorphology was written mostly by geographers, and therefore concentrates on the present. This review, however, appears in Sedimentary Geology. As a former oil-company geologist with a deep interest in deserts and their sediments, 1 will attempt to indicate its usefulness for those concerned with ancient sequences and especially with the sub-surface. The book is divided into 16 chapters grouped into four sections. After an introductory chapter on " T h e Nature of Arid Environments", "Section 1, Material Influences", has three chapters. Chapter 2, "Weathering Processes", by Andrew Goudie covers the whole range of weathering processes in deserts, and stresses the importance of salt as an agent. It is useful for a better understanding of how rocks break down, and what may have taken place at and below an unconformity surface. This leads logically to Chapter 3, "Desert Crusts and Varnishes" by Andrew Watson. Rock varnish probably can never be recognised on ancient rock surfaces, but calcretes and silcretes are known from many sequences back to the Precambrian. Most geologists think in terms of palaeo-slopes and ancient pediments beneath onlapping sequences, but little thought is given to how that pediment was formed. Although some of these processes are understood, Oberlander's message in Chapter 4, "Slope and Pediment Systems", is that there is still much to learn. These chapters set the scene for many of the arid-zone fluvial and aeolian processes that follow. The five chapters of Section 2 cover " T h e Work of Water". In Chapter 5, "Run-off Generation and Sediment Mobilisation by Water", He-

len Scoging describes how sediment is removed from rock and soil by rain and flowing water, a topic of greater importance to engineering geologists trying to prevent erosion than to the subsurface specialist. In Chapter 6, "Channel Form, Flows and Sediments in Deserts", Reid and Frostick give a useful modern summary of their topic. They stress the ephemeral nature of desert streams, and the need for more documentation of water volumes and their rates of flow; for the first time, the reader is given some ancient examples and limited three-dimensional control. Chapter 7, " T h e Occurrence and Role of Arid Zone Alluvial Fans" by Adrian Harvey, is limited largely to modern alluvial fans, but the importance of tectonic influences in their formation and distribution is recognised. "Badlands and Badland Gulleys" are covered by Ian Campbell in Chapter 8, and while of interest, has little of immediate value for the sub-surface geologist, whereas "Playas, Pans and Salt Lakes" by Shaw and Thomas is of more direct application to some ancient sequences in terms of processes and evaporite chemistry. The four chapters of Section 3 cover " T h e Work of the Wind". Apart from the effects of the granulometry of sands on aeolian transport, in the chapter on "Windflow Characteristics and Aeolian Entrainment", Andrew Watson also discusses the origin of dune sands. The next chapter on "Aeolian Sand Deposits" by David Thomas has a direct application to many hydrocarbon reservoir sequences. He politely takes me to task for not following the "party line" on the origin of longitudinal dunes by bimodal winds. "Desert Dust" by Nicholas Middleton is a topic that is ignored in most studies of ancient rocks but is beginning to be recognised as the source of anomalous layers of silt in some marine sequences, as an important constituent of some

0037-0738/91/$03.50 © 1991 - Elsevier Science Publishers B.V. All rights reserved

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British terrestrial Triassic, and as a potential instigator of diagenesis in other ancient rock units. Breed et al. write on "Wind Erosion Forms". Apart from the rare association of ventifacts with ancient unconformities, wind-eroded rocks are probably never recognised by sub-surface geologists; wind-blown dust as well as sand can scour rock surfaces and must have left their mark on ancient mesas buried beneath dunes. "Extensions of the Arid Realm" are discussed in Section 4. David Thomas covers the first and last of the three chapters. Apart from reproducing some global maps of ancient desert areas, in his chapter on "Reconstructing Ancient Arid Realms", the antiquity of arid environments is confined to the Quaternary, and mostly to the last 20 ka or so, whereas his "Perspectives on Arid Zone Geomorphology" is an editorial round-up of the state of the science. Meanwhile, Wells and Zimbelman provide a lot of data on the Martian surface in "Extraterrestrial Arid Surface Processes", but little is of relevance to students of the earth-bound pre-Quaternary. For a science that depends so much on visual memory, the book is marred by poor reproduction of many of the photographs. It is also marred by far too many typographical errors (over 60). With hardly a chapter that is free of them, some obviously have many. Where not corrected by the authors, most should have been picked up by the publisher's editorial staff. Also, in some chapters, many sentences have to be re-read because of inadequate punctuation or the presence of that bane of modern scientific writing, the over-use of ugly, unhyphenated, compound adjectival nouns. If hyphens had been applied correctly, the writers surely would then have seen the need to change the word order to a more pleasing and readily understood form. In addition, there are still some sentences whose meaning is obscure even after several readings. On the positive side, the book is full of numerical data, other facts and plausible hypotheses, and I have already found many useful references in the long lists that accompany most chapters; to our own detriment, we geologists probably ignore too many journals of a geographical nature. Despite the above strictures, geologists working on the Permian Rotliegend se-

BOOK REVIEWS

quences of the southern North Sea, for example, will find plenty of food for thought in Arid Zone

Geornorphology. K.W. GLENNIE(Ballater, Grampian)

Glaciotectonic Landforms and Structures. J.S. Aber, D.G. Croot and M.M. Fenton. Kluwer Academic Publishers Group, Dordrecht, 1989, ix + 200 pp., Dfl.155.-, US$79.-, £49.-, ISBN 0-7923-0100-5 (hardcover). The book, published as the fifth volume in the series "Glaciology and Quaternary Geology", is a fairly systematic approach to a complex (sub)discipline in the earth sciences. A first chapter is devoted to the nature of glaciotectonism. It comprises not only a historical overview of glaciotectonic research, but also clear definitions of glaciotectonism and related terms (with, for instance, a most useful distinction between "glaciotectonics" and "glaciotectonism"), and general descriptions of what are glaciotectonic structures and landforms (including an account of the types of landforms dealt with in separate chapters). This introductional chapter is followed by six chapters that deal each with one specific type of glaciotectonic landform or structure, viz. hill-hole pairs, large composite ridges, small composite ridges, cupola hills, megablocks and rafts, and diapirs (with related intrusions and wedges). Each chapter starts with an introduction, which is followed by descriptions and analyses of three or four examples. These examples are taken from Canada, Iceland, Denmark, the United States, The Netherlands, Norway and Sweden. There follow chapters on applied glaciotectonics, the distribution of glaciotectonic phenomena, the dynamism of glaciotectonic deformation, and glaciotectonic analogs. A bibliography and a subject index conclude the book. There are also two enclosures. The first is a map of North America, showing the extent of the Laurentide ice sheet at various stages, and also the sites of the American case samples. The second map is an analog for Europe, but it should