Widmark, J. G. V., 1997, Fossils & Strata, 43, 94pp Oslo; $29.00; ISBN 82-00-37667-2 ISSN 0300-9491.
This monograph presents the results of a taxonomical study of deep-sea benthic foraminifera from Deep-Sea Drilling Project (DSDP) cores 525 (Walvis Ridge) and 527 (Angola Basin) across the Cretaceous-Paleogene (better known as the Cretaceous-Tertiary or K-T) boundary. The stated rationale for the investigation is to compare patterns of benthic foraminiferal response to latest Masstrichtian-earliest Danian environmental events from localities representing the same biogeographical province, but different depths. Unfortunately, the bulk of the material presented represents a simple taxonomic overview of the 132 genera and species recovered from a total of 36 samples in both cores. No new species are described; no generic descriptions are included; the detail with which species are described varies considerably; occurrence information is restricted to the two cores actually studied; no detailed biostratigraphical data are provided; described species are illustrated by only a single SEM photomicrograph, often of a poorly-preserved specimen. Moreover, no attempt is made to analyze the data collected from these two cores, to conduct any real comparison between the data collected for this study and the results of other studies, or to use these data to test any independently-established hypothesis concerning patterns of faunal turnover. Widmark does provide an introductory section in which he reviews several previous K-T benthic foraminiferal studies, but his review is highly idiosyncratic and fails to come to any conclusion regarding the observed patterns of K-T deep-sea benthic foraminiferal turnover or the of environmental factors responsible for these patterns. Most seriously though, his discussions of the individual studies often misrepresent their authors’ arguments by failing to mention important observations, cite relevant papers, or provide adequate descriptions of alternative interpretations.
For example, in reviewing alternative interpretations of K-T faunal turnover patterns at Brazos River, Texas, Widmark argues that Keller’s (1989a, 1992) data “are somewhat difficult to evaluate since [she] placed the [K-T] boundary considerably higher than in other studies on the general stratigraphy of the Gulf Coastal Plain” (Widmark 1997, p. 10) In fact, Keller’s data are very well documented (see Keller 1989a,b, tables 1-7, figures 4-9) and allow anyone to evaluate the pattern of faunal turnover that would obtain under alternative K-T boundary placements. Keller (1989a,b) followed Jiang and Gartner’s (1986) placement of the Brazos River K-T boundary at the horizon that contains the K-T iridium anomaly and the first occurrence of Tertiary microfossils (planktonic foraminifera and calcareous nannoplankton) in those sections. Widmark correctly states, other authors place the Brazos River K-T boundary at the base of the so-called “tsunami bed” (Bourgeois et al. 1988) but neglects to mention that the interpretation of these units as representing tsunami deposits has been questioned by many (e.g., Montgomery et al. 1992, Savarda 1993, Beeson et al. 1994, Yancey 1995). Ultimately, the question boils down to one of the stratigraphic criteria one accepts in correlating the Brazos K-T boundary to that of the El Kef boundary stratotype. At El Kef the K-T boundary is marked by the iridium anomaly and the first appearance of Tertiary microfossils. This is consistent with Jiang & Gartner’s (1986) and Keller’s (1989a,b) placement. Smit et al. (1994), Smit et al. (1995), Pospichal (1995) and a few others prefer to place the Brazos K-T boundary at the base of the (questionable) “tsunami” deposit and argue that both the “tsunami” bed and the iridium anomaly form part of a “boundary complex” that was deposited over hours to days and so, for the purposes of correlation, should be considered coeval with the El Kef iridium anomaly en toto. Montgomery et al. (1992), on the other hand, argue that Danian planktonic foraminifer assignable to Zone P1a are present within the “tsunami” bed, suggesting that this unit was actually deposited some 200,000 years after the K-T impact and is not of tsunami origin. [Note: the occurrence of Danian microfossils in the “tsunami” unit has not been confirmed by any other investigator.].
Widmark’s review of this controversy fails to mention any of these relevant factors, but seems to imply that Keller’s placement of the Brazos K-T boundary is in some way linked to Keller’s (1992) interpretation that “only two species (17%) of Cretaceous [benthic foraminiferal] species ranged across the [K-T] boundary at Brazos River (Keller 1992)” (Widmark 1997, p. 10). Referring back to Keller (1992, p. 82) we find the following statement. “Only 2 species (17%) (Lenticulina muensteri and Anomalinoides newmanae) are common throughout the K-T transition and these species significantly increase near the boundary and dominate the early post-K-T environment” (italics mine). The difference between identifying two common Cretaceous benthic foraminiferal species that survived the K-T boundary and do not exhibit excursions in relative abundance that might indicate the existence of an environmental perturbation at the Brazos River iridium anomally, and being reported to have said that these were the only two benthic species to have survived the K-T event, is rather an extreme mis-statement on the part of the reviewer. In point of fact Keller’s (1992) data show a progressive transition in the benthic foraminiferal fauna across the K-T boundary at Brazos River with only two very rare species locally disappearing coincident with the K-T iridium anomaly (Fig. 1). If the alternative K-T boundary placement is used the turnover pattern remains the same and no species extinctions coincide with this putative K-T boundary, despite the fact that the alternative placement coincides with a universally-acknowledged hiatus of unmeasured duration within the local section.
The idea that hiatuses are related to perceived extinction patterns is the cause of another error in Widmark’s review. A bit further on in his discussion Widmark argues that the low numbers (22%) of benthic species extinctions coinciding with the K-T boundary at a deep-sea locality represented by DSDP Site 465 provide evidence that this section deep-sea cores is complete across the K-T boundary. These data are also used to imply that most deep-water marine cores contain a continuous record of K-T biotas and environmental events. In any section or core in which 22% of the biota disappear at a single horizon, that horizon must be considered a potential hiatus surface, especially if the global last occurrence datums for these taxa are known to be separated in time in other sections/cores. At the very least independent evidence should be examined to determine if other biostratigraphic patterns indicate continuous sediment accumulation or the presence of a hiatus. In this instance Widmark fails to mention that the first planktonic foraminifera found in the sediments above the Site 465 K-T boundary belong to Zone P1a, suggesting that the lowermost Danian biozone (Zone P0) is indeed missing in this core and supporting the interpretation of a deep-sea K-T boundary hiatus (see MacLeod & Keller 1991 and references cited therein).
Such blatant examples of mis-statement and selective citation do not inspire confidence in Widmark’s ability to review relevant aspects of the of K-T benthic foraminiferal turnover record in a comprehensive and scholarly manner. Moreover, Widmark exhibits a disturbing tendency to uncritically transplant outmoded and oversimplified ecological concepts to the interpretation of his paleontological data [Note: compare Widmark’s statements concerning K-selection and r-selection patterns in benthic foraminifera to standard ecological discussions (e.g., Krebs 1978, Ricklefs 1979, Boyce 1984, Andrewartha & Birch 1984), of how these concepts have been rendered virtually meaningless due to similar types of oversimplification in the present instance to the point of caricature and misuse.]
In sum, there is very little to recommend this monograph as an adequate contribution to the systematics of Cretaceous and Paleogene benthic foraminiferal systematic studies or to the various K-T boundary controversies. Those who consult this monograph should be aware that they will need to recheck virtually all of the author’s statements to make sure he has not left important aspects of previous authors’ statements undiscussed and/or unreferenced. Considering the very small amount of new data and interpretation included in this work, it would be better to proceed directly to the original systematic and data analytic literature on these topics topic and/or consult alternative reviews (e.g., Hallam & Wignall 1997). More is the pity, because a high-quality, comprehensive review of K-T benthic foraminiferal studies by an experienced foraminiferal researcher, as well as a rigorous systematic and paleobiological analysis of the author’s data would have been useful.
Norman MacLeod, Department of Palaeontology, Natural History Museum, South Kensington, London SW7 5BD.
References
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Bourgeois, J., Hansen, T. A., Wiberg, P. L., and Kauffman, E. G., 1988, A tsunami deposit at the Cretaceous-Tertiary boundary in Texas: Science, v. 241, p. 557-570.
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