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The Late Cretaceous San Juan thrust system
Book reviews the Indian and South Atlantic Oceans. The book is divided into six sections containing papers loosely grouped according to theme and geographical area. The first section, entitled 'Volcanic and tectonic framework" contains three review papers. White (Cambridge, UK) presents new refraction data from the west margin of Rockall Plateau to document crustal underplating and to argue, albeit loosely, for a hot-spot origin for early Tertiary volcanism. His model, although in broad agreement with the interpretation of the refraction data, differs from the convection partial inching model developed by Mutter and Zehnder m the next section of the book. Bott (Durham, UK), from geoidal and topographic considerations also proposes a hot-spot model. In the third paper, Dewey and Windley (Oxford and Leicester, UK) present a short review of Palacogene ()ligocene tectonics in NW Europe. The second section collates 11 papers under the heading "Dipping reflectors and NE ,.kflantic Evolution'. Four papers deal with the volcanic sequences on the Vormg Plateau, three discuss seismic reflection and refraction interpretation and the fourth examines the igneous petrology/geochemistry of the sequences. ()ther papers present seismic interpretations of dipping reflector sequences off East Greenland, the Faeroes and the Jan Mayen Ridge. In an importarlt paper, Merriman el al. (BGS/Oxford, UK) show that the dipping reflectors are not oceanic in origin and widen the debate as to the position of the continent-ocean boundary and the nature of "sub-aerial sea-floor spreading'. The paper by Kristjannson and ttelgasson (Iceland) provides needed caution against over interpretation of well and seismic data when viewed in the context of outcrop data of onshore Iceland. The third section, entitled 'East Greenland and the Faeroe Islands', includes six papers that mainly present geochemical and geochronological data from these areas. The excellent paper by Waagstem (1)cnmark-Faeroes), offers an excellent overview of Facroesc geology showing two major phases of volcanism best correlated with Scotland and East Greenland. The three papers on East Greenland present a useful synthesis and new ideas on the geochemical evolution of the (;reenland lava pile. The two other papers review the chronolog} of lava eruption in East Greenland using geochronological (Noble e t a / . , UK) and palaeomagnetic (Tarling et al., UK) data. Both the latter papers emphasis the importance of precisely constraining the age of the Palacocenc-Eocene boundary. Volcanism in the basins to the north and west of the British
Isles is the subject of the fourth section. Five papers present evidence for the age and geochemistry of basalts, tufts and sills cored in shallow and commercial wells on the shelf and slope northwest of the British Isles. An important paper by Stoker et al. (BGS UK) examines the Early Tertiary volcanic rocks in partly released deepwater well 163/6-1A in the Rockall Trough. Their evidence of contamination of the basalts is of especial interest in light of new evidence for the presence of continental crust beneath the Rockall Trough. Two other papers, by Wood et al. (Glasgow, UK) and Tare and Dobson (Aberystwyth, UK) deal with evidence for Mesozoic and Early Tertiary w~lcanic activity in the Porcupine Seabight and Rockall Trough, respectively. The fifth section in the book. on the "British Tertiary Igneous Province" contains six papers, all highly focussed towards the geochemistry and geochronology of this classic area. A particularly useful overview of geochronological data and problems is provided by Musset el. a/. (Liverpool, UK) who note the problems caused by conflicting time scales. The sixth and final section contains three papers that examine the North Sea sedimentary record. As might be anticipated, the Early Tertiary North Sea sediments contain a full record of Early Tertiary w~lcanicity. Nielsen and ttelmann (Denmark) document the history established in onshore Denmark. Knox and Morton (BGS, UK) offer a very good attempt at reconciling the North Sea geological record with that observed m Greenland and elsewhere in the region. However, here again, the limitations of the biostratigraphic record constrains their interpretation. The final section contains a single review paper (Upton, Edinburgh, UK) on the history of Tertiary igneous activity in the North Atlantic borderlands. As a comprehensive overview of previous geochemical and geochronological studies, the review is useful but it makes only passing reference to the equally relevant offshore research. As a whole, the book brings together several diverse lines of study that provide new and important constraints on the evolution of this volcanic province. Where is it to lead? I believe that the book points to a clear need for future multidisciplinary studies of dipping reflector sequences onshore and offshore focussed on the North Atlantic as a natural laboratory. Unfortunately, this is a highly specialised topic. At a price of £80 (US $170), I suspect there will be few buyers.
D. G. Roberts BP, Houston, TX, USA
The Late Cretaceous San Juan Thrust System M. T. Brandon, D. S. Cowan and J. A. Vance Geological Society of America Special Paper 221' 1988; ISBN 0 8137 2221 7. Price $19.00 post paid. This Geological Society of America Special Paper is a well written compilation of the late Mesozoic geological history of the San Juan Island group of western Washington. These rocks are particularly important to the Mesozoic history of the North American Cordillera because they constitute one of the best exposed segments of the tectonic contact between Wrangellia, underlying Vancouver Island to the west, and rocks of the North American borderland. The paper focuses on the regional stratigraphic framework of Palaeozoic and Mesozoic rocks involved in fold and thrust belt deformation and post-orogenic units of Tertiary age. A brief overview of the metamorphic history associated with the Late Cretaceous tectonism outlines several unsolved problems. The structural interpretation is based primarily on regional map relations supported by a few detailed studies and adequately outlines broad, first-order relationships. Numerous intriguing structural relations are depicted on the accompanying map
but are not addressed in the text. It is clear that many important problems have yet to be solved. The paper closes with speculations on the significance of the San Juan Island thrust belt during terrane accretion along the North American Cordillera. This work will be an important and welcome addition to the library of Cordilleran geologists. One of the most significant contributions is the exhaustive compilation of fossil and isotopic age data and geochemistry tabuhited in the 31 pages of appendices. Much of the data is drawn from rather obscure references and having it compiled in one place will probably result in better informed attempts to relate these rocks to coeval units in Oregon and California.
J. S. Oldow Rice University, Houston, TX, USA
Marine and Petroleum Geology, 1990, Vol 7, February
91
Isles is the subject of the fourth section. Five papers present evidence for the age and geochemistry of basalts, tufts and sills cored in shallow and commercial wells on the shelf and slope northwest of the British Isles. An important paper by Stoker et al. (BGS UK) examines the Early Tertiary volcanic rocks in partly released deepwater well 163/6-1A in the Rockall Trough. Their evidence of contamination of the basalts is of especial interest in light of new evidence for the presence of continental crust beneath the Rockall Trough. Two other papers, by Wood et al. (Glasgow, UK) and Tare and Dobson (Aberystwyth, UK) deal with evidence for Mesozoic and Early Tertiary w~lcanic activity in the Porcupine Seabight and Rockall Trough, respectively. The fifth section in the book. on the "British Tertiary Igneous Province" contains six papers, all highly focussed towards the geochemistry and geochronology of this classic area. A particularly useful overview of geochronological data and problems is provided by Musset el. a/. (Liverpool, UK) who note the problems caused by conflicting time scales. The sixth and final section contains three papers that examine the North Sea sedimentary record. As might be anticipated, the Early Tertiary North Sea sediments contain a full record of Early Tertiary w~lcanicity. Nielsen and ttelmann (Denmark) document the history established in onshore Denmark. Knox and Morton (BGS, UK) offer a very good attempt at reconciling the North Sea geological record with that observed m Greenland and elsewhere in the region. However, here again, the limitations of the biostratigraphic record constrains their interpretation. The final section contains a single review paper (Upton, Edinburgh, UK) on the history of Tertiary igneous activity in the North Atlantic borderlands. As a comprehensive overview of previous geochemical and geochronological studies, the review is useful but it makes only passing reference to the equally relevant offshore research. As a whole, the book brings together several diverse lines of study that provide new and important constraints on the evolution of this volcanic province. Where is it to lead? I believe that the book points to a clear need for future multidisciplinary studies of dipping reflector sequences onshore and offshore focussed on the North Atlantic as a natural laboratory. Unfortunately, this is a highly specialised topic. At a price of £80 (US $170), I suspect there will be few buyers.
D. G. Roberts BP, Houston, TX, USA
The Late Cretaceous San Juan Thrust System M. T. Brandon, D. S. Cowan and J. A. Vance Geological Society of America Special Paper 221' 1988; ISBN 0 8137 2221 7. Price $19.00 post paid. This Geological Society of America Special Paper is a well written compilation of the late Mesozoic geological history of the San Juan Island group of western Washington. These rocks are particularly important to the Mesozoic history of the North American Cordillera because they constitute one of the best exposed segments of the tectonic contact between Wrangellia, underlying Vancouver Island to the west, and rocks of the North American borderland. The paper focuses on the regional stratigraphic framework of Palaeozoic and Mesozoic rocks involved in fold and thrust belt deformation and post-orogenic units of Tertiary age. A brief overview of the metamorphic history associated with the Late Cretaceous tectonism outlines several unsolved problems. The structural interpretation is based primarily on regional map relations supported by a few detailed studies and adequately outlines broad, first-order relationships. Numerous intriguing structural relations are depicted on the accompanying map
but are not addressed in the text. It is clear that many important problems have yet to be solved. The paper closes with speculations on the significance of the San Juan Island thrust belt during terrane accretion along the North American Cordillera. This work will be an important and welcome addition to the library of Cordilleran geologists. One of the most significant contributions is the exhaustive compilation of fossil and isotopic age data and geochemistry tabuhited in the 31 pages of appendices. Much of the data is drawn from rather obscure references and having it compiled in one place will probably result in better informed attempts to relate these rocks to coeval units in Oregon and California.
J. S. Oldow Rice University, Houston, TX, USA
Marine and Petroleum Geology, 1990, Vol 7, February
91