Paleontological Events: Stratigraphical, Ecological, and Evolutionary Implications

Reviewed by Walter Etter

Article number: 17.2.#A
1 August 1998

edited by C. E. Brett and G. C. Baird
Columbia University Press
New York, 1997, xv + 604p.
ISBN 0-231-08250-9. Hb $65.00 (US), £50.00 (UK).

One of the exciting aspects in every scientific discipline is that unexpected bursts of new developments are witnessed in areas that have formerly received little attention. In paleobiology, the last decades have seen various fast growing fields: paleontology has contributed to an expanded evolutionary theory, new methods for documenting phylogenetic and biogeographic patterns have become established, extinction phenomena became the focus of interdisciplinary research programs, and studies on evolutionary radiations, most notably the diversification of life during late Precambrian / early Cambrian, have appeared in profusion. Another area where new progress was made at a fast pace has been taphonomy. While earlier investigations concentrated on naming and describing the various modes of fossil preservation (see Müller 1979 for a summary and a review), the value of taphonomy in contributing towards a better understanding of the depositional environment was underestimated for a long time although earlier attempts date back some time (e.g., Seilacher 1973). It was not until the mid 1980's that the developments of a "new" taphonomy were brought to the attention of a broader audience. During that time period, several seminal papers appeared that concentrated on the sedimentary facies-dependencies of preservational modes, and the terms "comparative taphonomy" and "taphofacies" were coined (Brett and Baird 1986, Speyer and Brett 1988). Interest was immediate and sustained, with a flood of new papers appearing, culminating in the publication of some very important books (Allison and Briggs 1991, Donovan 1991, Einsele et al. 1991).

Now two of the proponents of this "new" taphonomy have edited a new book, bringing together 28 experts, most of them from the U.S. The title is sensational but to make it clear from the beginning, this is not a book on all aspects of paleontological events. The primary focus is on short-term events. Such events will lead to fossil beds that are recognizable in the field and can be traced on a regional scale. As such, these thin stratigraphic horizons can have a variety of physical and/or biological causes as becomes amply clear when reading through the first few chapters.

The book is organized in two sections, each with an introductory chapter and many case histories. Part One (chapters 1 through 9) addresses the genesis of single fossil beds or Lagerstätten. In Chapter 1, Brett, Baird and Speyer present an overview about the various mechanisms which can lead to fossil bed genesis. Basically, the classification proposed by Kidwell (1991) is adopted, and the stratigraphic usefulness of such event horizons are emphasized. In Chapter 2, modern Anadara shell populations are studied in order to see how they might turn into a fossil assemblage. The author's conclusion is rather pessimistic: it can be extremely difficult to recognize the sometimes subtle taphonomic overprinting of such assemblages. Even in tidal environments, short-term time-averaging and distortion through predation/shell boring can severely alter the original composition of such populations. Rather more optimistic, however, are the results of Chapter 3, in which it is suggested that meso-scale spatial variability in benthic assemblages can be discerned. This was demonstrated by investigating Ordovician brachiopod communities in a single outcrop (150 m transect). Such research has the potential for far-reaching consequences as this meso-scale provides a possible link between within-community and between-community diversity studies (alpha versus beta diversity). Unlike the previous chapters, Chapter 4 is a review dealing with the usefulness of trace fossils in stratigraphy. Most paleontologists think of trace fossils as classical facies dependent fossils, and as ecological indicators they have indeed proven their usefulness. However, they also allow paleontologists to better recognize event beds, most notably turbidites and tempestites. Each tempestite has its characteristic trace fossils composed of a stable (resident) and an unstable (pioneer) storm assemblage. When putting together all the evidence, ichnology can significantly contribute to establishment of basin-wide high-resolution stratigraphy. The remainder of the chapters in Part One are case histories dealing with the genesis of Ordovician carbonate tempestites with trepostome bryozoan colonies (Chapter 5), the paleoecology and taphonomy of Ordovician trilobite bearing shales (Chapter 6), the analysis of pentamerid horizons in the Silurian of North America, Europe, Siberia and China (Chapter 7), Silurian crinoid beds from New York and Ontario (Chapter 8), and Middle Devonian trilobite clusters from Iowa and Illinois (Chapter 9). All of these chapters are worth reading, although they do not really present anything spectacular. A common theme is that with an adequate approach (sedimentology plus taphonomy plus high-resolution stratigraphy) the mechanisms leading to event bed formation can be recognized. This in turn will help to improve our understanding of the dynamic history of sedimentary basins.

In Part Two (chapters 10 through 20), the focus is on slightly longer time units, on stratigraphic intervals that are only rarely the result of single events. Here, in their introductory Chapter 10, Brett and Baird discuss the hierarchical nature of the stratigraphic record. This chapter is very well written and personally I think it is the best chapter of the book. The link between sequence stratigraphy and paleontology is provided as paleontological events of varying temporal and spatial magnitudes are shown to be the paleontological expressions of patterns observed in sequence stratigraphy. An old term, epibole, is revived to have a descriptor for the extraordinary abundance of certain taxa that are normally uncommon in a particular sedimentary basin. In its original meaning, the term simply denoted a stratigraphic interval that was characterized by maximum abundance of a particular species. Epibole was therefore roughly synonymous with "hemera" and "acme zone" of other authors. Such anomalous abundances can have, of course, various causes. Consequently, Brett and Baird distinguish between taphonomic, ecological, and incursion (biogeographic) epiboles. At the same time, they maintain that usage of the general term epibole should be used in a non-genetic manner. For the contrasting phenomenon of absence of normally common taxa in a particular stratigraphic interval, the authors advocate the usage of a new term: outage (= antiepibole). The recognition of real outages which again can have different causes is difficult as this is based on negative evidence. Included in Chapter 10 is also a short discussion of long-term events such as evolutionary radiations and mass extinction events, although the reader is mainly referred to the literature. The references are not quite up-to-date, however, and such an eminent book as the one edited by Walliser (1996) is not cited.

Chapters 11 through 16 deal with such epiboles and provide, in ascending stratigraphic order, case studies from various regions in the U.S. Stromatolite horizons might be useful as marker beds in intrabasinal stratigraphic correlation (Chapter 11). This comes as little surprise, though I doubt that such isochronous horizons are the rule and not the exception. A novel methodologic approach for the study of sedimentary basins is presented by Holland in Chapter 12. By sacrificing some temporal resolution, sequence stratigraphy is used as the time scale whereas depositional environments defined by sedimentologic and paleontologic features provide the spatial units. This combination allows a time/environment analysis over a large area and a long chronostratigraphic interval. Certainly, such an approach is desirable as "there is a tendency to study basinwide or even global phenomena on the scale of a single outcrop" (Holland, p. 310). Further use of epiboles in refining basinwide stratigraphic correlations are illustrated in Chapters 13 (Ordovician brachiopods in the Cincinnati Arch), 14 (Silurian horizons in New York dominated by algae and dendroid graptolites), 15 (rugosan coral thickets in the Devonian of New York and Ontario) and 16 (various Upper Carboniferous event beds from the Midcontinent). As the horizons investigated in Chapter 14 also include the preservation of some soft-bodied organisms, the authors also discusses some factors controlling Konservat-Lagerstätten genesis. This section could either have been omitted as it is built on a very slim data base and does not really present anything new, or it should have been significantly expanded to include many other examples (perhaps also some non-Silurian examples).

The final four chapters deal with longer time spans. In Chapter 17, a larger bio-event recognized in the Silurian of Gotland (Sweden) is analyzed. The author (L. Jeppson) develops a model where faunal changes are linked to cycles in the atmosphere-ocean exchange patterns and these in turn are linked with Milankovitch cycles. This mid-Early Silurian event has only recently been recognized but it might have been of global effect. Biogeographic and evolutionary patterns in the Late Devonian of Eastern North America are the topic of G. R. McGhee in Chapter 18. Using statistical analyses, McGhee shows that the old scenario "European immigrants competitively replaced East American resident brachiopods" is a gross simplification of a much more complex pattern. The vanished facies of regional encrinites (defined as thick strata with a considerable areal extent, in which more than 50% of the rock volume is pelmatozoan debris) is investigated in Chapter 19 by W. I. Ausich, and Chapter 20 (B. B. Sageman, E. G. Kauffman, P. J. Harries and W. P. Elder) summarizes the author's long-time work on the Upper Cretaceous of the Western Interior Basin. The approach in the latter chapter is similar to the one chosen in Chapter 12 but with a much higher stratigraphic resolution. Within this framework, a hierarchy of paleontological events could be recognized that ranges from bedding plane surfaces (single event horizons) to changes in species composition (intervals a few meters thick) to long-term diversification/reduction trends in the benthic communities. The primary agents responsible for middle- and long-term changes were changes in bottom-water oxygen content, and this in turn was strongly influenced by changes in relative sea levels and climatic conditions.

This book certainly brings together a wealth of information and helps to elucidate the hierarchy of paleontological events. Nevertheless, I am not really enthusiastic about it. What I really missed in both sections were more review articles instead of just another case history. This makes access difficult for most readers who will not go through the entire book but select only a few chapters. For the generally interested paleontologist, an overview about the still expanding field of taphonomy and event stratigraphy is not provided. Such readers would benefit from a more rigid frame and from a more structured organization. Therefore I feel that the present book will not have the same impact as the 1991 volumes edited by Einsele et al., Allison and Briggs, and Donovan. The most serious handicap of the book is, however, that it is not up-to date. Appearing in 1997, I expected to find many references dating from 1994, 1995 and perhaps 1996. A compilation of the literature cited in Chapter 1 (but any other chapter could have been selected with similar results) reveals two patterns (see Figure 1). First, the growing interest in taphonomy and increasing production of relevant papers in the 1980's and early 1990's, culminating in the appearance of the three eminent books mentioned above in 1991, becomes evident. This pattern does not just represent the author's preferences but is a real one. Second, literature appearing after 1991 is grossly underrepresented. This even includes some of the authors' own important papers (e.g., Brett and Baird 1995). Although this deficit is probably not only in the responsibility of the editors, it greatly reduces the value of this book. As is stated in Chapter 17 by L. Jeppson (p. 485), the manuscript was submitted in late 1990. Seven years of editing, reviewing and proof-reading is much too long, especially when considering the reputation of Columbia University Press. This is indeed the best propaganda for electronic publishing!

References Cited

Allison, P. A., and Briggs, D. E. G., eds. 1991. Taphonomy: Releasing the Data Locked in the Fossil Record. Topics in Geobiology, vol. 9. Plenum Press, New York, xiv + 560p.

Brett, C. E., and Baird, G. C. 1986. Comparative taphonomy: A key to paleoenvironmental interpretation based on fossil preservation. Palaios, 1:207-227.

Brett, C. E. and Baird, G. C. 1995. Coordinated stasis and evolutionary ecology of Silurian to Middle Devonian faunas in the Appalachian Basin. In: Erwin, D. H. and Anstey, R. L., eds. 1995. New Approaches to Speciation in the Fossil Record. Columbia University Press, New York: 285-314.

Donovan, S. K., ed. 1991. The Processes of Fossilization. Belhaven Press, London, xi + 303p.

Einsele, G., Ricken, W., and Seilacher, A., eds. 1991. Cycles and Events in Stratigraphy. Springer Verlag, Berlin, xix + 955p.

Kidwell, S. M. 1991. The stratigraphy of shell concentrations. In: Allison, P. A., and Briggs, D. E. G., eds. 1991. Taphonomy: Releasing the Data Locked in the Fossil Record. Topics in Geobiology, vol. 9. Plenum Press, New York: 211-290.

Müller, A.H. 1979. Fossilization (taphonomy).In: Treatise on Invertebrate Paleontology. Part A, Introduction (Robison, R. A. and Teichert, C. eds.). Geological Society of America, Boulder, Colorado, and University of Kansas Press, Lawrence, Kansas, pp. 2-78.

Seilacher, A. 1973. Biostratinomy: The sedimentology of biologically standardized particles. In: Evolving Concepts in Sedimentology (Ginsburg, R. N. ed.). Johns Hopkins University Press, Baltimore, pp. 159-177.

Speyer, S. E., and Brett, C. E. 1988. Taphofacies models for epeiric sea environments: Middle Paleozoic examples. Palaeogeography, Palaeoclimatology, Palaeoecology, 63:225-262.

Walliser, O. H., ed. 1996. Global Events and Event Stratigraphy in the Phanerozoic. Springer Verlag, Berlin, viii + 333p.