The Triassic timescale edited by Spencer G. Lucas. Geological Society Special Publication, 334, 2010. No. of pages: 514. ISBN 978-1-86239-296-0 (hardback).
THE TRIASSIC TIMESCALE edited by Spencer G. Lucas. Geological Society Special Publication, 334, 2010. No. of pages: 514. Price: £120.00. ISBN 978-1-86239-296-0 (hardback).
Michael J. Simms*, * National Museums Northern Ireland, Cultra, Holywood, Northern Ireland BT18 0EU.
With such a bold title it would be unwise for anyone working on the Triassic System to ignore this volume. With more than 500 pages this is certainly a substantial tome, but with such an alarmingly hefty price tag most will be immediately discouraged from buying it.
Following the introduction, the first five chapters are reviews of broad stratigraphic themes and, as such, provide invaluable summaries of the current state of the subject. This is the most broadly useful part of the book and should be of interest to anyone working on the Triassic. In his introduction Lucas outlines the various branches of stratigraphy before elaborating on some of the fossil groups used in biostratigraphy (although sadly omitting crinoids). He follows this with a well-written review of the history of the Triassic timescale, effectively cutting through the morass of sometimes conflicting, and frequently synonymous, names to establish a solid chronostratigraphic scheme for the Triassic System in the 21st Century. Despite this, more than one contributor appears not to have entirely adopted it, the Cordevolian sometimes sneaking back in as the lowest division of the Carnian Stage. Oops!
Mundil and his colleagues undertake a thorough review and reassessment of published radiometric dates for the Triassic, along with some new data. Their resultant radiometric chronology is a significant advance on the 2004 timescale compilation (Gradstein et al., 2004) and differs from it at every single stage boundary.
Hounslow and Muttoni present an extremely useful and thorough review of the current state of knowledge of Triassic palaeomagnetic timescales, constructing a series of Geomagnetic Polarity Timescales (GPTS) for the Triassic from a wealth of published logs. Clearly a useful tool for establishing a chronology in red-bed sequences, nonetheless they exemplify its limitations by presenting three different options for correlating the Newark Supergroup with their standard Triassic GPTS.
Tanner concedes that isotope stratigraphy has its limitations, being not so much a stratigraphic tool as a measure of environmental change, and so this chapter may be of greater interest to palaeobiologists than to stratigraphers. The tendency to focus isotopic analyses on narrow stratigraphic intervals associated with major biotic events limits what can be said about the broader picture. Tanner follows this with a similarly critical examination of the cyclostratigraphic record. Triassic sequences were the focus of some of the great pioneering work in this field, such as the Van Houten cycles of the Newark Basin and the Lofer cycles of the Alps, and many more have been documented since. Tanner concludes that many authors have not been entirely objective when interpreting supposedly cyclic successions and it is debatable whether much progress has been made in tying any of these cyclic sequences into an anchored stratigraphy.
The remaining nine contributions address various biostratigraphic topics, mostly in the form of review papers. Two contributions provide relatively brief reviews. Balini and his co-authors present a broad overview of ammonite biostratigraphy. This is a topic with a longer history than any other branch of biostratigraphic research. With so much historical ‘baggage’ to contend with they provide a useful discussion on some of the issues surrounding modern ammonite biostratigraphy. Orchard's account of conodont stratigraphy is almost too brief—little more than a when and where of conodont taxa through the Triassic—and ends rather abruptly without even a mention of the demise of the group in the basal Jurassic.
Three other chapters provide a rather skewed picture. Two deal with palynology, but unfortunately they neither duplicate nor complement each other. The first (Kürschner and Herngreen) covers the entire Triassic, but only for part of Europe, while the second (Cirilli) deals with just the Upper Triassic, but across the entire globe. There is a laudable amount of detail in both accounts, but, with palynology being so crucial to correlating non-marine sequences, a more inclusive account would have been more appropriate. McRoberts contribution on bivalves has a rather misleading title, implying that all Triassic bivalves will be dealt with whereas it deals largely with just a handful of stratigraphically useful genera of the so-called ‘flat clams’. Perhaps this should not be a criticism since so many other bivalves make such lousy zone fossils.
O'Dogherty and co-authors provide perhaps the clearest and most useful of the biostratigraphic reviews, looking at radiolaria through the Triassic and the difficulties of tying in their stratigraphy to the existing chronostratigraphy. Their inclusion of thumbnail images of each radiolarian genus (and there are far more than I imagined!) in their range charts is a particularly useful addition to the normally rather dry roll-call of taxonomic names in these kinds of figures.
Conchostracans are a neglected group that deserve greater attention, offering perhaps the best prospects for correlation between marine and non-marine successions. Kozur and Weems establish a conchostracan zonation scheme which is of comparable resolution to ammonites and conodonts. Their chapter is easily the longest (102 pages) in the book although half of this centres on discussion of particular successions which will be of only limited interested to most readers.
Tetrapods are the subject of two contributions. Klein and Lucas conclude that tetrapod footprint biostratigraphy has significant limitations, but may offer clues when body fossils are lacking. Lucas provides a review of LVFs (Land Vertebrate Faunochrons, though this acronym has a rather different meaning here in Northern Ireland!) to which he has contributed such a great deal over the last two decades. It seems remarkable that the resolution achieved from non-marine tetrapods is comparable with that for palynomorphs despite their vastly disparate abundances. Or perhaps it is not so surprising in light of the much greater abundance of fossil vertebrate specialists compared with experts on palynomorphs or, for that matter, ammonites (Gaston 1992).
For the most part this book does provide some useful reviews and a wealth of references at the end of each chapter (which, despite Google, is still the best way of tracking down related literature), but it would require another volume or two to really be as comprehensive as its title implies! For those with broad, or even quite specific, interests in the Triassic System in particular or Phanerozoic stratigraphy in general, this book is a must. Some of the first few contributions also may be of more general interest and are certainly accessible to higher level students or postgraduates. As with all Geological Society Special Publications it is nicely bound with a glossy hard cover but, as with most of them, it is ‘nice book, shame about the price’.