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Trilobite systematics, biostratigraphy and palaeoecology of the lower ordovician komstad limestone and huk formations, southern Scandinavia
als and biogenic grains from bacteria. As a result. a variety of magnetic acquisition and demagnetisation methods coupled with analytical techniques such as XRD and SEM must be used to identify the magnetic carriers. Such techniques are of interest to all students of sedimentary rock magnetism as well as the petroleum industry. The time of magnetic acquisition is further controlled by the subsequent burial history and the creation and transport of hydrocarbons. This complicates the interpretation of the resulting signal, but can also reveal the diagenetic history. Five papers focus on one of the more classical applications of paleomagnetism: magnetostratigraphy. The examples are again mainly from the North Sea and cover sediments of Triassic to latest Cenozoic in age. The success in correlation is varied. depending on the continuity of sampling interval and degree of magnetic overprinting which results from drilling procedures as well as diagenesis. Identification and elimination of these secondary magnetisations are crucial in establishing a magnetostratigraphy, as shown by Hounslow et al. The potential for inter-core correlation is great. although correlation to the geomagnetic time scale is more tenuous. depending on reliable and independent biostratigraphic markers. The uses of susceptibility and geotechnical applications are presented in the last six papers. Sections of cores can be re-aligned by using the present-day viscous magnetic overprint as outlined by Rolph et al., or by the conventional paleomagnetic method (Hailwood and Ding). This allows the reconstruction of fracture patterns, and of paleotlow directions. Lovlie and van Veen show that magnetic susceptibility logging is becoming an increasingly useful parameter in lithological studies of cores. Measurement of the anisotropy of magnetic susceptibility can be used as a proxy for sediment imbrication and thus an indicator of paleoflow directions. Subsequent migration of fluids through these sediment channels may superimpose a measurable secondary fabric, giving insight into their pathways (Tarling and Shi). A possible remedy for drilling-induced remanence is suggested by Shi and Tarling who have determined that most of the overprinting comes from the magnetic field concentrated just behind the drill bit. The final section contains one paper by Stewart and
Jackson who have developed a fold test to determine the geometry of periclinal folds, hence the volume of closure may be estimated. For a few papers, the definition or significance of rock formations or group names and their geographic distribution would have been helpful to the non-local reader. In particular, Perroud et al. omitted a locality map. Generally, the reproduction of figures and photographs are excellent, however some of the figures in the magnetostratigraphic papers have suffered a loss of resolution due to their great reduction in size. This publication represents a broad and detailed coverage of paleomagnetism with respect to petroleum exploration. In many papers, the importance of paleomagnetism is briefly introduced and then an advanced treatment of paleoeomagnetic or rock magnetic studies is presented. This limits the book’s use for the exploration geologist, who may have little or no background in paleomagnetism. In this respect. the publication is better suited for paleomagnetists who require an up-to-date summary of techniques and applications for the petroleum industry.
T. Black. Auckland,
New Zealand
Trilobites Arne Thorshej Nielsen. Trilobite Systenzutics, Bio.vtnrtigruph~ and Palaenecology of the Low,er Ordolsicinn Komstud Limestone and Huk Formations, Southern Scandinaz~iu. Fossils & Strata, 38, 374 pp. Scandinavian University Press. ISBN 8200-37658-3. In this monograph, Arne Nielsen presents a revi4on of part of the Lower Ordovician trilobite faunas of southern Scandinavia, based on restudy of classic localities in Denmark. Sweden and Norway. The work focuses on the Komstad Limestone (ArenigLlanvirn) on the Danish island of Bomholm and in the Scania region of southern Sweden. but also includes the correlative Huk Formation of the Oslo region, Norway. The meticulous detail of the field work is admirable: Nielsen sampled the formations on a bed-by-bed basis and collected 8000 trilobites. Many older exposures were excavated to provide
Book Reviews
complete stratigraphic sections, one flooded quarry was drained and the subtidal portion of a coastal exposure in Scania was investigated by scuba-diving! The impressive 374 page tome is primarily systematic in content but also includes discussion of the lithostratigraphy, a comprehensive revision of the zonal biostratigraphy, as well as a bold attempt to establish an ecostratigraphic framework from a bathymetric interpretation of trilobite biofacies. It is, however, only a first installment in which about 40% of the material (mostly asaphine, illaenid, styginid and raphiophorid trilobites) are described. The remaining taxa, including agnostids, ptychopygines and cyclopygids, will presumably be the subject of a sequel. The author concentrates primarily on the species level and, here, the systematic work is uniformly excellent. All species are described in detail and are illustrated beautifully. In many cases, biometrical data for a variety of skeletal dimensions are also presented. However, treatment of supraspecific taxa is relatively superficial and readers may be surprised to find that most genera and suprageneric taxa are not even diagnosed. Nielsen presents a detailed discussion of stratigraphic variation in abundances of the trilobite genera, which he uses to define a series of intergrading biofacies that are interpreted as being depth-related. He then infers fluctuations in sea level from sequences of biofacies replacements in his stratigraphic sections. Unfortunately, this work is undermined by the small sample size of most of his collections. For example, 72 collections are shown for the Killerijd section (Fig. 46). However, 45 of the collections contain less than 20 specimens and, of these, 30 have less than 10 specimens. With such small numbers, we can expect variation in generic abundances simply because of random sampling effects. The problem of small sample size is compounded by expressing abundances as percentages, which exaggerates the apparent significance of fluctuations. For example, when discussing the Skelbro section (p. 53 and Fig. 451, the author suggests that: “the latter Symphysurus biofacies is abruptly replaced by a Megistuspis biofacies in bed - 17, suggesting a significant and, possibly, fast drowning”. Fig. 45 certainly shows the disappearance of Symphysurus and a sharp increase in percent abundance of Megistaspis. How-
131
ever, it also shows that bed - 17 yielded a very small sample (less than 5 specimens), so that the changes in abundance and distribution of Symphysurus and Megistuspis can be interpreted simply as random variation introduced by small sample size. Certainly, there is no concrete evidence for a rapid sea level change. Similar problems plague the attempts to infer environmental distributions of trilobite species: shifts in the stratigraphic distributions and abundances of six species of Nileus are documented in Figs. 55 and 56, but more than half of the collections contain less than 10 specimens. There is little doubt that the ecostratigraphic approach taken by Nielsen is potentially fruitful, but he will have to expand his data base greatly if his conclusions are to be accepted widely. Aside from the treatment of trilobite abundance data, there is little to complain about in this monograph. It is clear that Arne Nielson has produced a monumental work that will become a classic of the modern trilobite literature. Hopefully, a second volume dealing with the remaining taxa will be completed soon. All trilobite specialists will need this monograph and no self-respecting institutional library should be without a copy. S.R. Westrop, St. Catharines,
Ont.
Fossil footprints Martin Lockley and Adrian P. Hunt. Dinosaur Trucks and other Fossil Footprints of the Western United States. Columbia
hardcover,
University Press, xx + 388 pp., Price $ 29.95. ISBN o-231-07926-5.
The world’s first two books on dinosaur tracks published over half a century apart - were regional studies, both of the same region in New England. Hitchcock’s 1858 study created a methodology for the study of tracks and described the tracks of what the author reasonably thought were birds, while Lull’s 1915 (revised 1953) investigation of the same region placed the original and extensive additional material in the context of more recent dinosaur studies. The flurry of recent interest in fossil tracks has produced many limited studies and some general books (including several written or edited by the authors of
Jackson who have developed a fold test to determine the geometry of periclinal folds, hence the volume of closure may be estimated. For a few papers, the definition or significance of rock formations or group names and their geographic distribution would have been helpful to the non-local reader. In particular, Perroud et al. omitted a locality map. Generally, the reproduction of figures and photographs are excellent, however some of the figures in the magnetostratigraphic papers have suffered a loss of resolution due to their great reduction in size. This publication represents a broad and detailed coverage of paleomagnetism with respect to petroleum exploration. In many papers, the importance of paleomagnetism is briefly introduced and then an advanced treatment of paleoeomagnetic or rock magnetic studies is presented. This limits the book’s use for the exploration geologist, who may have little or no background in paleomagnetism. In this respect. the publication is better suited for paleomagnetists who require an up-to-date summary of techniques and applications for the petroleum industry.
T. Black. Auckland,
New Zealand
Trilobites Arne Thorshej Nielsen. Trilobite Systenzutics, Bio.vtnrtigruph~ and Palaenecology of the Low,er Ordolsicinn Komstud Limestone and Huk Formations, Southern Scandinaz~iu. Fossils & Strata, 38, 374 pp. Scandinavian University Press. ISBN 8200-37658-3. In this monograph, Arne Nielsen presents a revi4on of part of the Lower Ordovician trilobite faunas of southern Scandinavia, based on restudy of classic localities in Denmark. Sweden and Norway. The work focuses on the Komstad Limestone (ArenigLlanvirn) on the Danish island of Bomholm and in the Scania region of southern Sweden. but also includes the correlative Huk Formation of the Oslo region, Norway. The meticulous detail of the field work is admirable: Nielsen sampled the formations on a bed-by-bed basis and collected 8000 trilobites. Many older exposures were excavated to provide
Book Reviews
complete stratigraphic sections, one flooded quarry was drained and the subtidal portion of a coastal exposure in Scania was investigated by scuba-diving! The impressive 374 page tome is primarily systematic in content but also includes discussion of the lithostratigraphy, a comprehensive revision of the zonal biostratigraphy, as well as a bold attempt to establish an ecostratigraphic framework from a bathymetric interpretation of trilobite biofacies. It is, however, only a first installment in which about 40% of the material (mostly asaphine, illaenid, styginid and raphiophorid trilobites) are described. The remaining taxa, including agnostids, ptychopygines and cyclopygids, will presumably be the subject of a sequel. The author concentrates primarily on the species level and, here, the systematic work is uniformly excellent. All species are described in detail and are illustrated beautifully. In many cases, biometrical data for a variety of skeletal dimensions are also presented. However, treatment of supraspecific taxa is relatively superficial and readers may be surprised to find that most genera and suprageneric taxa are not even diagnosed. Nielsen presents a detailed discussion of stratigraphic variation in abundances of the trilobite genera, which he uses to define a series of intergrading biofacies that are interpreted as being depth-related. He then infers fluctuations in sea level from sequences of biofacies replacements in his stratigraphic sections. Unfortunately, this work is undermined by the small sample size of most of his collections. For example, 72 collections are shown for the Killerijd section (Fig. 46). However, 45 of the collections contain less than 20 specimens and, of these, 30 have less than 10 specimens. With such small numbers, we can expect variation in generic abundances simply because of random sampling effects. The problem of small sample size is compounded by expressing abundances as percentages, which exaggerates the apparent significance of fluctuations. For example, when discussing the Skelbro section (p. 53 and Fig. 451, the author suggests that: “the latter Symphysurus biofacies is abruptly replaced by a Megistuspis biofacies in bed - 17, suggesting a significant and, possibly, fast drowning”. Fig. 45 certainly shows the disappearance of Symphysurus and a sharp increase in percent abundance of Megistaspis. How-
131
ever, it also shows that bed - 17 yielded a very small sample (less than 5 specimens), so that the changes in abundance and distribution of Symphysurus and Megistuspis can be interpreted simply as random variation introduced by small sample size. Certainly, there is no concrete evidence for a rapid sea level change. Similar problems plague the attempts to infer environmental distributions of trilobite species: shifts in the stratigraphic distributions and abundances of six species of Nileus are documented in Figs. 55 and 56, but more than half of the collections contain less than 10 specimens. There is little doubt that the ecostratigraphic approach taken by Nielsen is potentially fruitful, but he will have to expand his data base greatly if his conclusions are to be accepted widely. Aside from the treatment of trilobite abundance data, there is little to complain about in this monograph. It is clear that Arne Nielson has produced a monumental work that will become a classic of the modern trilobite literature. Hopefully, a second volume dealing with the remaining taxa will be completed soon. All trilobite specialists will need this monograph and no self-respecting institutional library should be without a copy. S.R. Westrop, St. Catharines,
Ont.
Fossil footprints Martin Lockley and Adrian P. Hunt. Dinosaur Trucks and other Fossil Footprints of the Western United States. Columbia
hardcover,
University Press, xx + 388 pp., Price $ 29.95. ISBN o-231-07926-5.
The world’s first two books on dinosaur tracks published over half a century apart - were regional studies, both of the same region in New England. Hitchcock’s 1858 study created a methodology for the study of tracks and described the tracks of what the author reasonably thought were birds, while Lull’s 1915 (revised 1953) investigation of the same region placed the original and extensive additional material in the context of more recent dinosaur studies. The flurry of recent interest in fossil tracks has produced many limited studies and some general books (including several written or edited by the authors of