High resolution stratigraphy

Book Reviews with anecdotal reminiscences of work carried out with Wright. The second, by Jan Mangerud, is entitled 'The last interglacial/glacial cycle in northern Europe' and is a treatise on Late Pleistocene stratigraphy in this area, of which more below. In Chapter 3, Richard Clymo provides an admirable examination of the subject of peat growth, written with a clarity that makes it especially suitable for the unitiated. The fourth chapter, much shorter than the others, is a review of plant palaeoecology by James Ritchie. Richard Battarbee is the author of Chapter 5, on palaeolimnology, with particular attention to diatom-based environmental reconstruction. In this thorough review the value of studying lacustrine deposits as a means of assessing contemporary environmental problems is stressed. Finally, John E. Kutzbach and Thompson Webb III examine late Quaternary climatic and vegetational changes in eastern North America, with emphasis on palaeloclimatic modelling and, in particular, the C O H M A P (Cooperative Holocene Mapping Project) enterprise, in which they collaborated with H.E. Wright. It might be expected with such a varied content that the volume will have something to attract most of those interested in the Quaternary; conversely, any particular reader is likely to be really interested in only one or two of the chapters. Thus the present reviewer was drawn to the contribution by Mangerud (on the last interglacial/glacial cycle) as the one on which he is best qualified to comment. In keeping with the general style of the volume, Mangerud assumes a minimal knowledge of the subject and starts by explaining what is meant by the terms interglacial and glacial. In only a few pages he skilfully raises the tempo, to discuss the burning issues of the day - - such as whether the Eemian was the last interglacial in Europe. He provides a balanced discussion and yet puts his own view across strongly. His arguments are forceful in their simplicity. He points out that areas glaciated in the Weichselian are marked by a profusion of Holocene lake infills, whereas areas glaciated in the Saalian but not the Weichselian have numerous lake basins filled with Eemian sediments and capped by Weichselian solifluction deposits. The significance of this is that these basins were completely infilled during this single climatic cycle, mainly because of the rapid sedimentation rate during the cold period; none contain Hoiocene sediments. Thus in glaciated areas there is, to quote Mangerud, 'a limited potential for recording more than one interglacial in a lacustrine basin, even if glaciers do not overrun the basin during the intervening glaciation'. It seems to this reader that this simple statement of observed fact has great significance for the British Quaternary. Here we have a number of excellent sequences through the interglacial that succeeded the Anglian, many of which are believed to be in kettle-hole lake infills. We have no complete sequences from any later interglacials; these are pieced together mainly from fragmentary evidence in fluviatile sediments. Perhaps this fact is telling us something. If there had been a post-Anglian/pre-Devensian glaciation

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in Britain that extended beyond the Devensian limit, we should, according to Mangerud's observations, have glacial-lake infilis dating from the interglacial that immediately followed that glaciation. The same type of reasoning might provide an explanation for the relative profusion of Middle Pleistocene Gortian sites in Ireland, where later interglacial sediments are extremely rare. The above digressions show the extent to which Mangerud's chapter set this reviewer thinking. It shows the value of 'going back to basics' and 'stating the obvious' in a clear and reasoned argument; it could be given to undergraduates as an excellent initiation into literature on glacial/interglacial stratigraphy. Others who have seen Quaternary Landscapes have found other chapters equally stimulating and have suggested similar uses. The question remains, however, as to the appeal of a volume like this, even to libraries. It would be a pity if this excellent selection of top quality reviews were to sink into obscurity. Much will depend on the extent to which the papers are cited elsewhere. Most potential readers will probably be content to obtain offprints of the chapter(s) that interest(s) them most. D.R. Bridgland

Earth Science Cor~ultancy, 41 Geneva Rd, Darlington, County Durham, DL1 4NE, U.K. High Resolution Stratigraphy, E.A. Haiiwood and R.B. Kidd, Geological Society Special Publication No. 70, The Geological Society, London, 1993. ISBN0-903317-86-9, £58.00, 323 pp. Stratigraphy is the foundation of geology. At least that is what I was taught as a student. This fact alone therefore makes the recent trend towards abandoning the teaching of stratigraphy and historical geology in Earth Science courses a disturbing development. It suggests that most geologists are of the opinion that the sequence of events in most areas is generally known and therefore to teach stratigraphy in the traditional way by presenting the evolution of an area is deemed to no longer provide sufficient challenge to students. I am certain that sedimentary sequences in many parts of the world are not well understood and it is certainly not true that Quaternary sequences hold no surprises, even in intensively studied regions like NW Europe. Indeed, I need hardly emphasise that in our subject no one would suggest that the sequence was 'known' apart from perhaps that in the deep sea or the last glacialinterglacial cycle on land. Indeed it seems that each new technique or each new section hold some new detail of climatic events or oscillations of ever decreasing scale that further illuminate our understanding of the remarkably short period of Quaternary time. Even within the small island of Britain there is healthy discussion on the nature of the Quaternary sequence

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Book Reviews

and correlation with that on the Continent remains incomplete at its best. Inter-continental correlation seems to be a distant goal that may be achieved, but is still unreliable beyond the Last Interglacial. What then is 'High resolution stratigraphy'? All things to all people, it would seem if the editors of this book are to be believed! In their interesting introductory chapter they say 'it depends on where you are in the geological timescale [and is] dependant on the particular application'. For the Quaternary they suggest <1-3 ka, hut note that this is changing rapidly because of the rapid developments, in the Early Cenozoic they suggest 10 ka-1 Ma and for the Triassic they propose 225 ka-2 Ma. Clearly in the Holocene we could reduce this further perhaps to a few hundred years. What becomes clear very quickly when reading this book is that almost all these authors have not appreciated that terrestrial high resolution stratigraphy has been practised in the Quaternary for over 40 years, particularly since the advent of radiocarbon dating. It is the deep sea record that has prompted pre-Quaternary workers to examine their sequences to attempt to identify oscillations at scales that might reflect global variations driven by, at least in part, extra-terrestrial changes e.g. Milankovitch cycles, solar flickering etc. All credit for this must go to students of deep sea sediments because it is their work that has inspired the geological stratigraphical community to look again at their records. Suddenly we see a whole spectrum of cyclic or rhythmic sequences being ascribed to the type of changes that have been established in the Quaternary for some time, albeit modified in some cases by cyclic tectonics, sequence stratigraphical concepts etc. At any rate this is a valuable and welcome development and serves to illustrate the great advantage of short sequences like the Quaternary as a test bed for refining stratigraphical techniques in order to resolve shorter and shorter term cycles. The nature of such cycles and their correlation across regions, continents and even between continents and oceans and

finally hemispheres all require stretching stratigraphical techniques to their maximum. We as a Quaternary community have much to congratulate ourselves for and have much still to offer those whose stratigraphical resolution is still measured in the order of millions rather than hundreds of thousands of years. Our challenge is to constantly refine our approach to finer and better correlation to clarify our own time period but also to provide the pre-Quaternary community with tools to unravel their longer, less easily resolved sequences. The book is a first-rate compilation of valuable reviews and articles. It begins with three papers on correlation techniques, then progresses through the column from the Quaternary and Tertiary on which there are nine contributions; next comes the Mesozoic with five papers and finally there are four papers on the Palaeozoic ending at the Cambrian. Do not look here for an appreciation or an understanding of terrestrial Quaternary, but marine and deep sea sediments are reviewed and the impressive influence they have had on almost all the remaining papers is readily apparent. One only needs to look at Schwarzacher's paper on Milankovitch cycles in the pre-Pieistocene record to confirm this view. There is no doubt that this approach will help stimulate stratigraphical studies in student courses and renew interest in pure stratigraphy for research investigations. This is a worthy, well-edited, stimulating volume that I enjoyed reading for its diverse topics. It is also very reassuring, in that at last we see the Quaternary has so much to offer fundamental geology, as many have been saying for years. P.L. Gibbard

Sub-Department of Quaternary Research, University of Cambridge, Downing Street, Cambridge, CB2 3EA, U.K.