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The geology of the East Atlantic continental margin
Deep-Sea Research, 1972, Vol. 19, pp. 275 to 276. Pergamon Press Printed in Great Britain.
BOOK
REVIEW
The geology of the East Atlantic continental margin, F. M. DFLANY(Ed.) 1970, 1971. 4 vols., price f340. Inst. Geol. Sci. Reports 70/13,70/14,70/15, 70/16. Published by H.M.S.O. THEFOUR volumes which make up The geology of the East Atlantic continental margin wntain all but six of the papers presented at the symposium of the same name sponsored by the ICSU/SCOR Working Party 31 and held in Cambridge, Enghmd during March, 1970. The tirst volume contains papers of general and economic interest while the second and third vohnnes deal with the European wntinental margin and the last volm with the African wntinental margin. ‘l’be.papers are mostly written in English with summar~‘es in English, French and German as well. The average length of the articles is about 11 pages. The contributions to the first volume contain the substance of ten invited lectures given at the symposium. The subject matter of these papers sets a pattern for the following volumes. Emery and Guilcher cover the Quatemary and Tertiary history of various continental margins and shelves. In an interesting paper Lacombe illustrates the importance of a good understanding of both surface and deep oceanic currents when studying sedimentation processes on continental margins. Pastemak simiily indicates the relation of plankton and benthos to sedimentation processes, showing how a bottom fauna which feeds on detritus is found in areas of sediit precipitation while fllter feeders occur where sediient is held in suspension. Another group of papers written by Dunham, Baturin. Fothergill and Murray et al. deals more or less thoroughly with various economic deposits treating hydrocarbons, metalliferous deposits, sand, gravel, evaporites, phosphates and diamonds. Fothergill presents a useful summary of petroleum fields and prospects from the North Sea to Capetown. Murray et al. give a rather detailed account of the occurrence of diamond deposits off the coast of South West Africa. Dietz and Sproll cover some well-trodden ground in discussing the least squares
fit of the continental margins of North America and Africa but also attempt to explain in detail areas of overlap (Cap Blanc, Bahamas) or gaps (Ifni) in their fit. Schneider and Johnson step warily while discussing deep ocean diapirs. Unfortunately only in rare instamm, as in the Gulf of Mexico, have so-called salt diapirs been proven by the drill and it is perhaps dangerous to identify deep ocean salt diapirs on the main basis that salt is found on the adjacent continent when irregularity of the oceanic basement can commonly produce diapir-like structures on seismic reflection records. The remaining 33 papers, 19 of which are invited regional lectures, although the reader is not told which these are, cover similar ground to that outlined in the first volume but in greater detail. It is not feasible here to enumerate either all the authors or all the subjects covered in the remaining three volumes. I shall only report on the general impression left by these papers and mention a few articles of particular interest. In spite of the climate the northern and western continental margins of Scandinavia are being looked at in some detail, especially by the Norwegians as indicated by Holtedahl and Sellevoll who mention results obtained by standard geophysical techniques as well as by some sediint sampling. The continental margin and shelves of the British Isles have of course been intensely investigated and a large number of papers deal with this subject. Bott and Watts and Eden et al. produce especially complete and complementary summaries of the deep and shallow structure, respectively, of the wntinental margin adjacent to the British Isles. There are also two papers dealing with the semi-isolated continental fragments Rockall Plateau and Porcupine Bank. Another group of papers discusses work
in the North Sea but the discussion is necessarily restricted to subjects of only marginal interest to petroleum exploration companies (surficial sediments, a model accounting for the subsidence of the North Sea basin). In contrast the reconnaissance work of a consortium of French oil interests in the Bay of Biscay is presented by Montadert et al. This is one of the few papers in the Symposium to consider the continental margin in its fullest meaning, i.e. as extending from the foot of the continental rise to the dry land and contains some fine reflection protiles across the submarine part of the margin. The majority of papers which cover the African continental margin discuss the sediments of the shelves and in many cases geophysical data are lacking. It is also noticeable that unfortunately the areas covered in many papers seem to be limited by political rather than geological boundaries. Several papers deal with areas north of latitude 4 degrees north which can be specifically compared with complementary parts of the eastern continental margin of North America on the basis of continental drift. Templeton, in a paper discussing the geology from Dakar to Cape Pahnas, makes a plea for closer w-operation between workers on offshore and onshore areas since he asserts that incomplete understanding of the onshore geology is beginning to hamper the correct interpretation of offshore 275
276
Book Review
regional areas. It seems to me that the choice of the 'correct' interpretation may, like many geological solutions, be subjective. A fascinating literally in depth description of the evolution and extent of the Niger Delta is given by Hospers. South of the Niger there are still 34 degrees of latitude of Atlantic continental margin. This region is covered in five papers. Simpson reviews the geology of the southern 21 degrees and Bryan and Simpson present a structural profile 600 km long parallel to the coast north of Cap, town which neatly suggests an uplift of the southern part of the profile by 400 metres in presumably late Cretaceous times. The preface states that the principal aims of the symposium were (i) to review present knowledge and plans for investigation of the East Atlantic continental margin (ii) to identify gaps in knowledge that could be filled by co-ordinated national or international marine research prograrnmes. The published volumes certainly seem to be a comprehensive review of present knowledge and on the basis of these data the way is now open for comparisons with the continental margin of the West Atlantic. Plans for future work were e x c ~ informally as well as being summarised in a talk by Dr. G. Gierrnann at the Cambridge meeting. Besides the geographical gaps in knowledge, which are sometimes extensive south of the Bayof Biscay, there has also been a failure in the past to embrace both the continental slope and rise and the dry land where appropriate within the confines of the continental margin. Several authors have diagrams illustrating data which do not extend beyond the 100-fathom line or the adjacent coast. It is also questionable whether the southern North Sea or English Channel can be described as continental margins; certainly the fact that they are covered by the sea is no qualification and perhaps these areas, although well studied, are irrelevant to the subject matter of the symposium. Other gaps in knowledge discussed by Seibold and Emery in the introduction include the genesis and sedimentation processes of the continental margins, as well as the part which oil companies can play by releasing information when it no longer need he treated as confidential. The Institute of Geological Sciences and the editor, Miss Delany, have produced the proceedings of the symposium with commendable speed and scarcity of errors. It is a pity that the binding of the four volumes, which on my copy was showing wear after just the first reading, should be so weak. It was also confusing to read from top left to top right and then from bottom left to bottom right when a figure interrupted the columns in mid-page. However these are petty criticisms when judged against the usefulness of this comprehensive account of present knowledge of the East Atlantic continental margin. Perhaps even the built-in self-destructing binding is an advantage since it would perhaps be exceptional, remembering the last decade in earth sciences, if within the next decade these four volumes were not quite out of date. R. B. WHITMARSH
National Institute of Oceanography, Wormley, Godalming, Surrey, U.K.
BOOK
REVIEW
The geology of the East Atlantic continental margin, F. M. DFLANY(Ed.) 1970, 1971. 4 vols., price f340. Inst. Geol. Sci. Reports 70/13,70/14,70/15, 70/16. Published by H.M.S.O. THEFOUR volumes which make up The geology of the East Atlantic continental margin wntain all but six of the papers presented at the symposium of the same name sponsored by the ICSU/SCOR Working Party 31 and held in Cambridge, Enghmd during March, 1970. The tirst volume contains papers of general and economic interest while the second and third vohnnes deal with the European wntinental margin and the last volm with the African wntinental margin. ‘l’be.papers are mostly written in English with summar~‘es in English, French and German as well. The average length of the articles is about 11 pages. The contributions to the first volume contain the substance of ten invited lectures given at the symposium. The subject matter of these papers sets a pattern for the following volumes. Emery and Guilcher cover the Quatemary and Tertiary history of various continental margins and shelves. In an interesting paper Lacombe illustrates the importance of a good understanding of both surface and deep oceanic currents when studying sedimentation processes on continental margins. Pastemak simiily indicates the relation of plankton and benthos to sedimentation processes, showing how a bottom fauna which feeds on detritus is found in areas of sediit precipitation while fllter feeders occur where sediient is held in suspension. Another group of papers written by Dunham, Baturin. Fothergill and Murray et al. deals more or less thoroughly with various economic deposits treating hydrocarbons, metalliferous deposits, sand, gravel, evaporites, phosphates and diamonds. Fothergill presents a useful summary of petroleum fields and prospects from the North Sea to Capetown. Murray et al. give a rather detailed account of the occurrence of diamond deposits off the coast of South West Africa. Dietz and Sproll cover some well-trodden ground in discussing the least squares
fit of the continental margins of North America and Africa but also attempt to explain in detail areas of overlap (Cap Blanc, Bahamas) or gaps (Ifni) in their fit. Schneider and Johnson step warily while discussing deep ocean diapirs. Unfortunately only in rare instamm, as in the Gulf of Mexico, have so-called salt diapirs been proven by the drill and it is perhaps dangerous to identify deep ocean salt diapirs on the main basis that salt is found on the adjacent continent when irregularity of the oceanic basement can commonly produce diapir-like structures on seismic reflection records. The remaining 33 papers, 19 of which are invited regional lectures, although the reader is not told which these are, cover similar ground to that outlined in the first volume but in greater detail. It is not feasible here to enumerate either all the authors or all the subjects covered in the remaining three volumes. I shall only report on the general impression left by these papers and mention a few articles of particular interest. In spite of the climate the northern and western continental margins of Scandinavia are being looked at in some detail, especially by the Norwegians as indicated by Holtedahl and Sellevoll who mention results obtained by standard geophysical techniques as well as by some sediint sampling. The continental margin and shelves of the British Isles have of course been intensely investigated and a large number of papers deal with this subject. Bott and Watts and Eden et al. produce especially complete and complementary summaries of the deep and shallow structure, respectively, of the wntinental margin adjacent to the British Isles. There are also two papers dealing with the semi-isolated continental fragments Rockall Plateau and Porcupine Bank. Another group of papers discusses work
in the North Sea but the discussion is necessarily restricted to subjects of only marginal interest to petroleum exploration companies (surficial sediments, a model accounting for the subsidence of the North Sea basin). In contrast the reconnaissance work of a consortium of French oil interests in the Bay of Biscay is presented by Montadert et al. This is one of the few papers in the Symposium to consider the continental margin in its fullest meaning, i.e. as extending from the foot of the continental rise to the dry land and contains some fine reflection protiles across the submarine part of the margin. The majority of papers which cover the African continental margin discuss the sediments of the shelves and in many cases geophysical data are lacking. It is also noticeable that unfortunately the areas covered in many papers seem to be limited by political rather than geological boundaries. Several papers deal with areas north of latitude 4 degrees north which can be specifically compared with complementary parts of the eastern continental margin of North America on the basis of continental drift. Templeton, in a paper discussing the geology from Dakar to Cape Pahnas, makes a plea for closer w-operation between workers on offshore and onshore areas since he asserts that incomplete understanding of the onshore geology is beginning to hamper the correct interpretation of offshore 275
276
Book Review
regional areas. It seems to me that the choice of the 'correct' interpretation may, like many geological solutions, be subjective. A fascinating literally in depth description of the evolution and extent of the Niger Delta is given by Hospers. South of the Niger there are still 34 degrees of latitude of Atlantic continental margin. This region is covered in five papers. Simpson reviews the geology of the southern 21 degrees and Bryan and Simpson present a structural profile 600 km long parallel to the coast north of Cap, town which neatly suggests an uplift of the southern part of the profile by 400 metres in presumably late Cretaceous times. The preface states that the principal aims of the symposium were (i) to review present knowledge and plans for investigation of the East Atlantic continental margin (ii) to identify gaps in knowledge that could be filled by co-ordinated national or international marine research prograrnmes. The published volumes certainly seem to be a comprehensive review of present knowledge and on the basis of these data the way is now open for comparisons with the continental margin of the West Atlantic. Plans for future work were e x c ~ informally as well as being summarised in a talk by Dr. G. Gierrnann at the Cambridge meeting. Besides the geographical gaps in knowledge, which are sometimes extensive south of the Bayof Biscay, there has also been a failure in the past to embrace both the continental slope and rise and the dry land where appropriate within the confines of the continental margin. Several authors have diagrams illustrating data which do not extend beyond the 100-fathom line or the adjacent coast. It is also questionable whether the southern North Sea or English Channel can be described as continental margins; certainly the fact that they are covered by the sea is no qualification and perhaps these areas, although well studied, are irrelevant to the subject matter of the symposium. Other gaps in knowledge discussed by Seibold and Emery in the introduction include the genesis and sedimentation processes of the continental margins, as well as the part which oil companies can play by releasing information when it no longer need he treated as confidential. The Institute of Geological Sciences and the editor, Miss Delany, have produced the proceedings of the symposium with commendable speed and scarcity of errors. It is a pity that the binding of the four volumes, which on my copy was showing wear after just the first reading, should be so weak. It was also confusing to read from top left to top right and then from bottom left to bottom right when a figure interrupted the columns in mid-page. However these are petty criticisms when judged against the usefulness of this comprehensive account of present knowledge of the East Atlantic continental margin. Perhaps even the built-in self-destructing binding is an advantage since it would perhaps be exceptional, remembering the last decade in earth sciences, if within the next decade these four volumes were not quite out of date. R. B. WHITMARSH
National Institute of Oceanography, Wormley, Godalming, Surrey, U.K.