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Two Books Reviewed

 

TGEOSAThe Geologic Evolution of Saudi Arabia: A voyage through space and time


David Grainger
Published by: Saudi Geological Survey
Publication date: 2007
ISBN: 978-1-905755-073
264pp plus nine booklets

www.sgs.org.sa

 

This handsome boxed set of book plus six Geologic Field Excursion booklets and three on Geonotes aims to explain the geology and geological evolution of Saudi Arabia for the non-specialist. All the parts are extremely well produced and lavishly illustrated with excellent photographs of Saudi geological features, explanatory maps and diagrams.

The first one third of the book is taken up with explanations of standard geological concepts and features, written for the layperson and illustrated with Saudi examples. It is unfortunate that in order to simplify concepts some explanations border on being incorrect; e.g. it is stated that continents are moved around and torn apart by convection cells in the mantle and that mantle plasticity is provided by radiogenic heat. This general part of the book is followed by a chapter on the Geologic Framework of Saudi Arabia which gives a short plate tectonic account of the Arabian Plate’s movements and uses clear, simple diagrams to set the scene for the rest of the book in which there are chapters on: the Arabian Shield, Arabian Platform, Fossils, Red Sea Rift Basin, Harrats Volcanic Fields, Quaternary Geology and Mineral Wealth.

TGEOSA2The chapter on the Arabian Shield has an explanation of subduction magmatism so simplified as to be incorrect in describing the production of andesites and granites. The concept of terranes and their accretion is also introduced here, which will be of interest to the geologist reader, but the explanation will leave others confused. The Arabian Platform chapter provides a description of the post-Precambrian stratigraphy with a good stratigraphic column diagram and a description of the various units and the sedimentary environments in which they were deposited. The Hercynian and Alpine orogenies produced major unconformities in this succession but these are not described or illustrated with photographs. Mixed in here also are various aspects of hydrogeology and karstic weathering, both of which would be better placed in later chapters. The development of the Red Sea Rift Basin and the Cenozoic Harrats Volcanics are each given a separate chapter. The two are inextricably linked and yet the major concept and example of continental rifting is given less space than the Harrats, possibly because the volcanoes lend themselves to more spectacular photographic images. Quaternary Geology provides an interesting description of climate change in Arabia’s history, the development of the sand deserts, recent meteorite impact structures and human settlement. The final chapter on the Kingdom’s Mineral Wealth is disappointing. There is a simplified description of oil and gas formation and accumulation, but the opportunity to give a general account of the oilfields, trap types etc is missed. The other aspects of mineral wealth are given scant treatment and the reader is left with no understanding of the various mineral deposits and their origins. Groundwater, which is mentioned many times in earlier parts of the book, is also given little space and surely deserves more.

Overall this is a very attractive book for the coffee table but I believe that it has tried to do too much. For the layman it is a pretty picture book into which one might dip for information, but it is likely to cause some confusion. I am particularly disappointed that more is not made of the excellent photographs. For the geologist the book is an enjoyable read giving a flavour of the Kingdom’s geology, but it is lacking in detail and its reading list is both restricted and dated.

Possibly of greater interest to the geologist will be the accompanying booklets on Geological Excursions and Geonotes, which cover many of the Kingdom’s geological features. The six well-selected excursions are based on trips around Jeddah and along the road to Riyadh, with one off to the North to the Harrats. They all have good field safety and fieldwork code advice, high quality photographic illustration and give excellent information on exact positions of localities, distances for travel and lengths of time needed. They are however general and totally descriptive in their approach requiring the visitor to provide their own interpretations. The thee Geonotes booklets give details of individual features at some 16 localities. The first nine are in the Jeddah area and demonstrate features of the Red Sea Rift Basin and the Arabian Shield, and include a fossil vertebrate locality and the ancient tombs carved into the Cambro-Ordovician Saq Sandstone. The next five localities show the stratigraphy of the Arabian Platform, desert environments, an oilfield structure, groundwater and sabkhas. The final two include a Tertiary sharks’ teeth locality and a spectacular white volcano (comendite) crater in the Harrats.

All in all these booklets make the whole package very attractive and whet the appetite for a visit to see the spectacular geology of Saudi Arabia. The Geological Society of London has recently accredited the degrees at King Abdulaziz University in Jeddah. If the students there benefit from studying in the field the wealth of geology outlined in these booklets then they will not go far wrong.

J W Gaskarth

 

SP296Landscape Evolution: Denudation, climate and tectonics over different time and space scales
Geological Society Special Publication No. 296

K Gallagher, S J Jones & J Wainwright (eds)
Published by: The Geological Society of London
Publication date: 2008
ISBN: 978-1-86239-250-2 (hbk)
List price: £80.00; GSL Member price: £40.00
198 pp


www.geolsoc.org.uk/bookshop

The landscape provides perhaps the most accessible manifestation of the impact of geological processes. But are these continuous or catastrophic in character, and over what kind of timescale, and have they yet reached equilibrium? The editors of this volume have brought together a dozen papers which address these questions, arising from the 2004 William Smith meeting of the Society in London. Three themes have been pursued: (1) how the geological record preserves the nature and variability of erosion processes; (2) how can this record be interpreted using observation and laboratory analysis; (3) how can physical models be integrated with these data to facilitate understanding of the interactions between surface processes, climate and tectonics?

The opening paper presents an overview of the timescales that need to be considered, in particular response times to perturbations in the conditions coupling tectonics with climate and extant topography. The succeeding papers provide a series of examples exploring these concepts, from fluvial systems, through mass movement on slopes to karstic development. The later papers focus on regional considerations of landscape development. A wide variety of evidence is invoked - stratigraphy, geometrical relationships, palaeontology - yet the variety of possible interpretations remains large.

General lessons are drawn, such as avoiding oversimplification of the nature of erosion surfaces, in particular assuming peneplanation reaches sea-level; indeed, peneplanation may instead reflect upland processes related to continental convergence as a result of raised foreland base levels. The inability to resolve short timescale phenomena within long timescale records remains an obstacle to removing ambiguities when examining the evidence of the geological record. Current models remain empirical in nature and thus unable to provide accurate forecasting on a human timescale.

The editors conclude that the future lies in landscape-evolution models able to describe past processes over geological timescales. These will need to balance a wide range of processes that exhibit variable degrees of mutual dependence, such as tectonics, isostasy, weathering and sediment erosion, transport and deposition, recognising that response times may well be different for each.

Mike Rosenbaum
Ludlow