benthic foraminifera across the cretaceous–tertiary (k–t) boundary: a review

Benthic foraminifera across the Cretaceous^Tertiary (K^T)boundary: a review

Stephen J. Culver �

Department of Geology, East Carolina University, Cromwell Road, Greenville, NC 27858, USA

Received 3 July 2001; received in revised form 10 June 2002; accepted 10 July 2002

Abstract

The response of the Earth’s biota to global change is of fundamental interest to paleontologists, but patterns ofchange in paleontologic data are also of interest to a wider spectrum of Earth scientists in that those patterns are ofgreat significance in constraining hypotheses that attempt to explain physical changes in the Earth’s environment. TheCretaceous^Tertiary (K^T) boundary is a case in point. Some paleontologists have criticized the bolide impacthypothesis, not because they deny the impact but because the proposed effects of that impact do not always conformto the available paleontological data. Benthic foraminifera are of particular interest in this context because it has beensuggested for over 20 years that shallow-water benthic foraminifera were affected more severely than deep-waterbenthic foraminifera by events at the K^T boundary. This observation adds to the fact of planktonic foraminiferalextinction and indicates that K^T boundary environmental effects were largely restricted to shallow waters. In thispaper I review all published works on smaller benthic foraminifera at the K^T boundary and conclude the following.(1) Shallow-water benthic foraminifera were not more severely affected than deeper dwelling species. True extinction,as opposed to local extinction and/or mass mortality, is generally quite low no matter what the water depth. (2) Thedata are not sufficient in quality, quantity and geographic range to conclude that there is a latitudinal pattern ofextinction. (3) In general, biotic changes (such as they are) begin before the boundary in shallow and intermediatedepth waters and at the boundary in deep water. Disagreements about the placement of the boundary and thepresence, absence and duration of hiatuses hinder more precise conclusions. (4) There appears to be preferentialsurvivorship of epifaunal species into the early Danian with a short interval dominated by infaunal taxa in the earliestDanian. This pattern can best be explained by short-lived input of increased amounts of organic matter at theboundary followed by a sudden collapse of primary productivity and, hence, major reduction or cessation of organicflux to the seafloor. In summary, based on the current dataset, smaller benthic foraminifera, no matter whether theylived in shallow or deep waters, high or low latitudes, or infaunal or epifaunal microhabitats, survived theenvironmental events across the K^T boundary quite well. Mass extinction does not characterize this group oforganisms at this time.5 2002 Elsevier Science B.V. All rights reserved.

Keywords: foraminifera; benthic; extinction; Cretaceous^Tertiary boundary

1. Introduction

Much has been written in recent years about

0377-8398 / 02 / $ ^ see front matter 5 2002 Elsevier Science B.V. All rights reserved.PII: S 0 3 7 7 - 8 3 9 8 ( 0 2 ) 0 0 1 1 7 - 2

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Marine Micropaleontology 47 (2003) 177^226

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the events of around 65 million years ago andtheir e¡ects on the Earth’s biota. After extensivediscussion, it now seems to be generally acceptedthat a bolide collided with the Earth (Alvarez etal., 1980), probably in northern Mexico at Chic-xulub (Hildebrand et al., 1991), leaving a hugecrater and precipitating a mega-tsunami and var-ious other environmental e¡ects that would havebeen deleterious to life. From a paleontologist’sviewpoint, the interesting question is: ‘How ex-actly did the Earth’s biota respond to these sud-den environmental challenges?’ Were there sud-den catastrophic extinctions or were theextinctions instead part of a longer-term patternrelated to environmental perturbations, such assea level, oceanographic and climatic changes,that were unrelated to bolide impact? Do extinc-tions exhibit patterns related to latitudinal orbathymetric locations of the organisms in ques-tion? Were particular taxonomic groups victim-ized and, if so, why did they cease to exist whileothers continued on into the Cenozoic?Many of these questions have been addressed

for many groups of organisms in a recent reviewpaper (MacLeod et al., 1997), but it is clear fromwritten comments (e.g., Hudson, 1998; MacLeod,1998) and verbal comments at conferences andother venues that there remains considerable dis-agreement amongst paleontologists about the bi-otic response to Late and end-Cretaceous envi-ronmental change. Such disagreement is not badgiven that we are still acquiring data (e.g., Shee-han et al., 2000; Je¡ery, 2001), but new data needto be placed in the context of what is alreadyknown.In recent years I have contributed several brief

reviews on benthic foraminiferal changes acrossthe Cretaceous^Tertiary (K^T) boundary (Culver,1987, 1993; MacLeod et al., 1997; Culver andBuzas, 2000). These necessarily short contribu-tions were so brief that justice could not be giveneither to the data or to the various workers’ argu-ments.In the earliest of my reviews (Culver, 1987,

p. 206), I noted that the ‘Tnature of the benthonicforaminiferal faunal changes at the Cretaceous/Tertiary boundary is in some doubt. Although itis widely stated that there was a mass extinction

of shallow-water benthonic foraminifera at theCretaceous/Tertiary boundary, while deeper-dwelling forms were generally una¡ected (e.g.,Boersma, 1978; Lipps and Hickman, 1982), thissupposition has not been rigorously tested. Miller(1982) brie£y summarized some of the literatureon Late Cretaceous to early Tertiary benthonicsand concluded that neither shallow nor deep-dwelling foraminifera exhibit mass extinction.’ Inthe most recent review (Culver and Buzas, 2000),I repeated the essence of the above quote (stillpertinent 13 years later) but added the furtherobservation that workers independently investi-gating the same section reach con£icting conclu-sions. For example, working at El Kef, Tunisia,Keller (1988a) attributed the faunal changes sheobserved at El Kef to a series of environmentalchanges prior to, at, and after the K^T boundary.However, Speijer and Van Der Zwaan (1996) de-scribed a sudden, impact-related ecosystem col-lapse at the K^T boundary. Other brief reviewsprovided by authors in their research papers (e.g.,Keller, 1992; Coccioni et al., 1993; Speijer andVan Der Zwaan, 1996; Widmark, 1997; Peyrt etal., 2002) have repeated the general statement thatdeep-sea assemblages were less severely a¡ectedthan shallow assemblages. We would be wise,however, to recognize that consensus amongworkers does not necessarily equate to scienti¢caccuracy.In this paper I will attempt to summarize the

¢ndings of all the major works on benthic fora-miniferal changes (or lack thereof) across the K^Tboundary. I have tried to be inclusive and hopethat I have not missed any relevant major contri-butions to this question. In addition, I have notexcluded any papers because of any opinions Imight have regarding their methodologies, resultsor conclusions.Presentation of the data is followed by a dis-

cussion and attempted summary of what we knowabout the response of benthic foraminifera to re-gional and global environmental change acrossthe K^T boundary. The information gleanedfrom papers, unless speci¢cally noted, is presentedwithout any attempt at standardization of taxon-omy and biostratigraphic zonation (see Huber etal., 1994 and Keller and MacLeod, 1994 for an

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S.J. Culver /Marine Micropaleontology 47 (2003) 177^226178

example of the complexity of such issues), at cor-rection for di¡erent methodological approaches(e.g., sieve size used, number of specimenscounted, presentation of raw numbers or percen-tages, etc.) or at standardization of terminologyused. To attempt a standardization of this widevariety of variables would, undoubtedly, be be-yond the bounds of my capabilities. However, Ido point out inconsistencies where I perceivethem. Calculations of extinction/turnover arethose of the original authors, or are based ontheir data, unless otherwise noted, as is the termi-nology used to characterize biotic changes. Fig. 1shows the location of all sites discussed in thispaper.The simple purpose of this paper, then, is to see

if it can be determined, based on the publishedliterature, what happened to benthic foraminiferaat the K^T boundary. The idea is simple, but aswe shall see, the process and the outcome are not.

2. Shallow-water faunas

Twenty years ago, it was noted that there is adearth of shallow-water (de¢ned here as neritic,less than 200 m water depth) sites that straddlethe K^T boundary (E. Kau¡man quoted in Emi-liani et al., 1981). Things have not changed. Only¢ve recent papers and one unpublished thesis dealspeci¢cally with benthic foraminiferal faunalchanges across the K^T boundary in water depthsof less than 200 m (Sikora, 1984; Huber, 1988;Keller, 1992; Schmitz et al., 1992; Olsson et al.,1996; Keller et al., 1998). To these can be addedthe classic papers by Plummer (1927) on Midway(Paleocene) and Cretaceous foraminifera fromTexas, and by Olsson (1960) on the latest Creta-ceous and earliest Tertiary foraminifera from NewJersey.

Fig. 1. Paleogeographic map of 65 million years ago showing all localities discussed in the text (modi¢ed from Keller et al.,1993). Reconstruction based on Denham and Scotese (1987), Stanley (1989) and Ziegler (1980).

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S.J. Culver /Marine Micropaleontology 47 (2003) 177^226 179

2.1. Texas, USA

Plummer (1927) compared at considerablelength Navarro (Maastrichtian) and Midway(Danian) benthic foraminiferal assemblages inTexas. She characterized the Midway assemblageas ‘Tindicative of a comparatively shallow sea’(1927, p. 12) based on the paucity of pelagicforms. The benthic assemblages of both Midwayand Navarro strata are dominated by the generaBulimina, Clavulina, Gaudryina, Bolivina, Cristel-laria, Nodosaria, Vaginulina, Frondicularia, Trun-catulina, Rotalia and Anomalina. In her text,Plummer included nine species that are restrictedto the Navarro, but a perusal of the taxonomicsection of her paper, which includes notes onstratigraphic distribution, indicates a far greaternumber of species (47) crossed the K^T bound-ary. A similar number of species (51) are re-stricted to Danian and later deposits.These results, indicating a signi¢cant propor-

tion of species crossing the K^T boundary, werecon¢rmed by the study of Maastrichtian (Navar-roan) Kemp Clay faunas in north central Texas(Sikora, 1984). Sikora noted that the benthic fo-raminiferal community in what he considered tobe an outer shelf environment (100^200 m) con-tained species originally described as being re-stricted to the Tertiary. He documented an assem-blage, dominated by a group of seven species, thatwas rapidly replaced by a more characteristic‘Midway’ (i.e., Paleocene) assemblage 6 cm be-neath the disconformable K^T boundary. Sikora(1984) listed eight ‘Midway’ species in the KempClay that previously had been described onlyfrom the Tertiary.Sikora (1984, p. 10) further noted that contrary

to the notion that late Cretaceous and early Pa-leocene benthic assemblages were di¡erent fromeach other, in fact ‘Tboth are fairly similar.’ Hecame to this conclusion after considering whichCretaceous species were reworked into the basalTertiary and removing them from his comparison,although he did note (p. 60) that ‘TThe similarityof the Tertiary and Cretaceous communitiesmakes it di⁄cult to estimate the magnitude ofthis reworkingT’.

In 1992, Keller brie£y reported on the benthicforaminifera from a cored section at Brazos Riv-er, Texas. She described (1992, p. 82) ‘Ta dramaticturnover across the K^T transition’ in the middleneritic benthic foraminiferal assemblage (Fig. 2).It is unfortunate that there is a typographic trans-position in her text (p. 82), but the abstract makesit clear that Keller considered the turnover acrossthe probably disconformable boundary (Keller,1989) to be environmentally driven: ‘Tmost spe-cies decline in dominance or disappear/emigrateduring the K/T crisis only to reappear when fa-vorable conditions returnT’. Further, she statedthat ‘Tno extinctions are apparent’ (Keller, 1992,p. 77). She attributed the turnover to a latest Cre-taceous sea-level fall followed by a sea-level riseacross the K^T boundary and continuing into theDanian (Fig. 2). Her analysis of benthic forami-niferal morphotypes (see Corliss, 1985; Corlissand Chen, 1988) led her to conclude that thebenthic assemblages at Brazos (almost 100% epi-faunal) were too shallow to have been a¡ected bythe expansion of the oxygen minimum zone thatoccurred during the transgression associated withthe sea-level rise (Keller, 1992). Keller (1992) fur-ther noted that the foraminiferal turnover oc-curred below the K^T boundary in the BrazosRiver core.The timing of faunal turnover relative to the

K^T boundary, of course, depends on the phys-ical location of the boundary and recognition ofhiatuses. MacLeod and Keller (1991b), using agraphic correlation approach, concluded that con-tinuous sedimentation occurred across the K^Tboundary (placed at a thin clay layer and theiridium anomaly) and that a hiatus in the BrazosRiver core occurs in the upper part of basal Dan-ian Zone P0. Montgomery et al. (1992), however,placed the boundary lower in the section at Bra-zos River, at the disconformable base of the‘event bed.’ They also noted the absence of thelatest Cretaceous Abathomphalus mayaroensisZone at Brazos River and argued that this ab-sence was not due to conditions being too shallowfor this species (Keller, 1989) because A. mayaro-ensis had been recorded elsewhere from neriticstrata (Montgomery et al., 1992).

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Fig. 2. Relative abundance of benthic foraminifera across the K^T boundary in the Brazos River Core, Texas (modi¢ed fromKeller, 1992).

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Fig. 3. Relative abundance of benthic foraminifera across the K^T boundary at Millers Ferry, Alabama (modi¢ed from Olssonet al., 1996).

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2.2. Alabama, USA

Maastrichtian to Danian strata at MillersFerry, Alabama, deposited in water depths of30^100 m, based on the paleodepth models ofOlsson and Nyong (1984) and Olsson and Wise(1987) (Olsson et al., 1996), contain benthic fora-miniferal assemblages that show a seeminglycounter-intuitive pattern given the paleoenviron-mental interpretation of the strata in question.Maastrichtian Prairie Blu¡ Chalk is disconform-ably overlain by Danian Clayton Sands (repre-senting a brief hiatus). The Clayton Sands com-mence with a chaotic layer of large blocks ofPrairie Blu¡ Chalk and coarse sand, interpretedby Olsson et al. (1996) as a tsunami-generateddeposit, perhaps related to a bolide impact atChicxulub in Yucatan. However, Olsson et al.(1996, p. 273) pointed out that ‘A disruption ofbenthic assemblages following the K/T event mayhave occurred, but if it did, benthic assemblagesrecovered rapidly as can be observed by theirstratigraphic distribution’ (see Fig. 3). Olsson etal. (1996) noted that benthic assemblages, basedon morphotype analysis (Koutsoukos and Hart,1990), are infaunal deposit feeders in the PrairieBlu¡ Chalk and epifaunal deposit feeders in theClayton Sands, a faunal change attributed by Ols-son et al. (1996) to substrate change. They furthernoted (p. 273) that ‘Most of these species havegeologic ranges in the Cretaceous and Tertiary.’

2.3. New Jersey, USA

The work of Olsson (1960) on Maastrichtianand Paleocene neritic strata in New Jersey indi-cates a somewhat di¡erent pattern of speciesranges across the K^T boundary than in theGulf Coast. Although the Cretaceous and Paleo-cene faunas are similar at the generic level (Ols-son, 1960; Miller, 1982), Olsson’s notes on strati-graphic distribution indicate that only 13 speciesrange across the K^T boundary (disconformablein places and apparently continuous in others). Incomparison, 47 species do not cross the boundaryand 79 species are restricted to Paleocene andyounger strata. The ¢ndings of Sikora (1984) in-

crease the number of species that cross the K^Tboundary to 16 and reduce those that do not to44, but, even so, the New Jersey faunas, at thespecies level, show greater di¡erences across theK^T boundary than do the Gulf Coast faunas.

2.4. Stevns Klint, Denmark

Schmitz et al. (1992) documented the shallow-water K^T benthic foraminifera at Stevns Klint,Denmark. At this locality, nannofossil chalk andbryozoan limestone were deposited in an epicon-tinental sea at water depths of 100^250 m (Ha-kansson et al., 1974; Bromley, 1979). The benthicforaminiferal record is di⁄cult to evaluate, how-ever, because of severe dissolution above the K^Tboundary. Further, there is disagreement as to thephysical nature of the boundary. Hakansson andHansen (1979) and Perch-Nielsen et al. (1982)proposed the presence of a hiatus at the boundarywhile Schmitz et al. (1992) recognized a hiatusslightly higher in the section (Fig. 4) at or nearthe top of the Fish Clay (Zone P1a missing) andanother higher in the section (part of Zone P1cmissing).Prior to the boundary, changes in benthic fora-

miniferal assemblages were related by Schmitz etal. (1992) to sea-level change. About 2.7 m belowthe boundary the outer shelf taxa, Gyroidinoidesspp., Angulogerina cuneata and Tappanina selmen-sis, decline in abundance whereas the mid-shelftaxa, Pyramidina cimbrica, Rosalina koeneni, Spi-rillina subornata and Praebulimina cushmani, in-crease (Fig. 4), thus indicating a sea-level fallfrom about 200 to 100 m (Schmitz et al., 1992).About 50^20 cm below the K^T boundary, a sea-level rise is suggested by the reappearance of thedeeper-dwelling T. selmensis and Anomalinoideswelleri (Fig. 4).Severe carbonate dissolution beginning in the

boundary clay results in in£ated relative abundan-ces of solution-resistant taxa (Cibicidoides alleni,Cibicidoides succedens, Osangularia lens in Fig. 4).For this reason, and the presence of two hiatusesin the early Danian, Schmitz et al. (1992) con-cluded that is was not possible to evaluate extinc-tion (or lack of it) at the K^T boundary.

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2.5. Seymour Island, Antarctica

A similar dissolution problem a¡ects evaluationof benthic foraminiferal changes across the K^Tboundary on Seymour Island, Antarctic Peninsula(Huber, 1988). The boundary at this location isplaced above foraminifera-bearing silt and within

a 9.5-m glauconitic interval in the neritic (aboveshelf/slope break; Huber, 1988) Lopez de Berto-dano Formation, 50^90 m of section beneath thebase of the overlying Sobral Formation. Overly-ing the glauconitic unit are carbonate poor siltreferred to as the ‘dissolution facies’, followedby foraminifera-bearing silt at the top of the Lo-

Fig. 4. Relative abundance of common benthic foraminifera across the K^T boundary at Stevns Klint, Denmark (modi¢ed fromSchmitz et al., 1992).

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pez de Bertodano Formation and the base of theSobral Formation. The remaining section is com-posed of barren deltaic deposits (Huber, 1988).Cretaceous benthic foraminiferal assemblages

are mostly agglutinated. These were interpretedby Huber (1988) to be ‘residue assemblages’ (Sli-ter, 1975) where calcareous taxa have been dis-solved. Samples where calcareous material hasbeen preserved are dominated by more than 30calcareous species, with fewer than 10 aggluti-nated species of low to moderate abundance.The ‘dissolution facies’ just above the K^Tboundary contains only two agglutinated specieswhereas overlying Danian strata at the top of theLopez de Bertodano Formation and at the base ofthe Sobral Formation exhibit near absence of ag-glutinated species and low species equitability re-sulting from the dominance of Buliminella pro-cera, which does not occur in the Maastrichtianof Seymour Island. This assemblage, considerablydi¡erent from those of the Maastrichtian, was in-terpreted as being representative of a low-oxygen,chemically reducing environment (Huber, 1988).It yielded 32 mostly calcareous, benthic foraminif-eral species (in three fossiliferous samples) in com-parison to the last stratigraphic interval in theMaastrichtian that contained 65 species (in 22samples). Twenty-six (81%) of the 32 speciesrange through from the Cretaceous. If the dataare looked at another way, however, only 19(29%) of 65 species occurring in the uppermostCretaceous unit are recorded in the Tertiary.However, the data of Huber (1988) show thatan additional seven Cretaceous species rangeinto the Tertiary, although they do not occur inthe highest Maastrichtian unit. Therefore, perhapsthe best measure of faunal change results from acalculation based on 46 species last occurring inthe highest Cretaceous unit and 26 species rangingthrough from the Cretaceous into the Tertiary.Thus 64% of the 72 species occurring in the Creta-ceous do not cross the K^T boundary. Thus,Huber (1988) concluded that extinction of numer-ous benthic taxa had occurred. However, thelikely dissolution problem, the presence of di¡er-ent facies above and below the boundary and thedearth of fossiliferous samples above the bound-ary clearly indicate that this percent value is in-

£ated to an unknown but considerable degree andthat the Seymour Island section cannot be used toassess extinction patterns across the K^T bound-ary.

2.6. Seldja, Tunisia

Keller et al. (1998) conducted a multidiscipli-nary investigation of perhaps the shallowest K^T boundary site yet studied. The Seldja locality,about 200 km south of El Kef, is located in theGafsa Basin that, during the Maastrichtianthrough Eocene, was connected to the Saharanplatform and separated from the Tethys by theKassarine Island. Sediments were deposited in re-stricted seas in inner neritic to coastal environ-ments (Keller et al., 1998).The characteristic K^T boundary clay and red

layer (zone P0) is missing and latest Maastrichtiansilt is overlain by a 10-cm-thick sandstone with anerosional base (Fig. 5). Keller et al. (1998) tenta-tively placed the K^T boundary at this erosionalcontact. Above this sandstone is silt assigned toZone P1a but planktonic foraminifera are rela-tively rare and many samples are barren due todissolution (Keller et al., 1998). A sandy phos-phatic layer overlies the silt and is, in turn, over-lain by silt assigned to Zone P1c(2). Thus, theerosional contact at the base of the phosphaticlayer (Fig. 5) represents a hiatus spanning theupper part of Zone P1a through the lower partof Zone P1c (Keller et al., 1998).Most of the 30 species of benthic foraminifera

recovered have previously been recorded fromother shallow-water north African sections (e.g.,Aubert and Berggren, 1976; Saint-Marc andBerggren, 1988; Saint-Marc, 1992). Keller et al.(1998) recognized three groups within the com-mon species : one restricted to the late Maastricht-ian or early Danian Zone P1a, a smaller groupthat ranges through the studied interval, butshowing early Danian abundance variation, andanother small group that were restricted to ZoneP1c (Fig. 5). These assemblages were interpretedas representing inner neritic to coastal environ-ments in the latest Maastrichtian, changing to anearshore coastal environment in the early Dan-ian (Zone P1a), and deepening to an o¡shore in-

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ner neritic environment during the middle Danian(Zone P1c) (Fig. 5).Keller et al. (1998, p. 973) concluded that the

bolide impact at the K^T boundary ‘Thad a rela-tively incidental short-term e¡ectT’ on the plank-tonic and benthic foraminiferal biota at Seldja.‘Climate, sea-level, nutrient oxygen and salinity£uctuations were the primary causes for the even-tual demise of the Cretaceous fauna in the earlyDanian.’

3. Intermediate-water faunas

Several studies deal with faunas from outer ne-ritic to upper/middle bathyal depths. Althoughthere are bathymetric overlaps, it seems usefulto distinguish these from neritic and bathyal^abyssal faunas.

3.1. Kerguelen Plateau, Southern Indian Ocean(ODP Hole 738C)

The Maastrichtian^Danian interval is biostrati-graphically complete in Hole 738C (Huber, 1991,p. 459; Keller, 1993, p.1; Keller and MacLeod,1994, p. 112) although foraminiferal preservationis poor both immediately above and below the K^T boundary (Huber, 1991). Based on a compar-ison with the Californian benthic foraminiferaldata and interpretations of Berggren and Aubert(1983), Huber (1991) considered the Maastricht-ian^Danian sediments to have been deposited be-yond the shelf-slope break at depths of greaterthan 500^600 m. Huber’s paper, primarily onplanktonic foraminiferal biostratigraphy, brie£ysummarizes the benthic foraminiferal changesacross the Maastrichtian-Danian section as fol-lows. Firstly, robust and ornate morphotypeslast occur several meters below the K^T boundaryclay. Secondly, the test size of a dominant benthicspecies is reduced and taxonomic diversity is di-

Fig. 5. Relative abundance of benthic foraminifera across theK^T boundary at Oued Seldja, Tunisia (modi¢ed from Kel-ler et al., 1998).

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Fig. 6. Relative abundance of common benthic foraminifera across the K^T boundary at Kawaruppa, Hokkaido, Japan (modi-¢ed from Kaiho, 1992). Planktonic foraminiferal zonation from Smit (1982).

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Fig. 7. Relative abundance of benthic foraminifera across the K^T boundary at Agost, Spain (modi¢ed from Pardo et al., 1996).

Fig. 8. Relative abundance of common benthic foraminifera across the K^T boundary, at Caravaca, Spain (modi¢ed from Keller,1992).

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minished 0.5 m below the boundary. Thirdly,‘Tthere is no recognizable taxonomic turnoveramong the benthic foraminifers at the Creta-ceous/Tertiary boundary clay’ (Huber, 1991, p.455).

3.2. Hokkaido, Japan

Kaiho (1992) investigated the extinction rate ofintermediate-water benthic foraminifera acrossthe K^T boundary at Kawaruppu, Hokkaido, Ja-pan. Maastrichtian strata were inferred to havebeen deposited in the lower part of the upperbathyal zone (300^600 m) (based on the paleoba-thymetric scheme of Sliter and Baker (1972)),whereas Danian sediments were from shallowerdepths (150^300 m, upper part of the upper bath-yal zone). Kaiho (1992) distinguished local extinc-tion from true extinction in his calculations anddetermined that only ¢ve of 40 benthic speciesbecame extinct at or between 0.4 and 0.1 m belowthe K^T boundary. Two of these were rare taxaand so the exact level of true extinction is indoubt (Kaiho, 1992). Thus, Kaiho (1992) recog-nized an extinction rate of 13% (10% for calcare-ous benthic foraminifera) (see Fig. 6), in strongcontrast to extinction rates of about 80% forplanktonic foraminifera at El Kef, Tunisia (Kel-ler, 1988b) and similar to deeper-water benthicspecies from the Weddell Sea, Antarctica (Tho-mas, 1990a). This led Kaiho (1992) to suggestthat there was a rapid change from higher extinc-tion rate to low extinction rate at about 150 mwater depth, approximately the boundary be-tween surface and intermediate waters and theeuphotic and aphotic zones.

3.3. Tawanui section, Dannevirke, New Zealand

In de¢ning uppermost Cretaceous to Paleogenebenthic foraminiferal biostratigraphic zones inNew Zealand and Hokkaido, Japan, Kaiho(1988) brie£y commented on the faunal assem-blages from upper to middle bathyal water depthsacross the K^T boundary. As in Japan ‘Tbenthicforaminifera show little change across the K^Tboundary’ (Kaiho, 1988, p. 554).

3.4. Agost, Spain

The late Maastrichtian benthic foraminifera atAgost, Spain lived at upper bathyal water depthsbefore shallowing to outer neritic depths prior tothe K^T boundary (Pardo et al., 1996). The sealevel rose and upper bathyal depths were againattained early in the Danian (Zone P1b). Pardoet al. (1996) recognized benthic faunal turnoversassociated with sea-level changes. A strong turn-over in the latest Maastrichtian (near paleomag-netic boundary C30N^C29R) was related to a sea-level fall of about 100 m (Pardo et al., 1996). Fo-raminiferal morphotypes suggest decreased oxy-gen levels and expansion of the oxygen minimumzone. The sea level started to rise in the uppermostpart of the Plummerita hantkeninoides Zone andcontinued across the K^T boundary where a sec-ond major benthic foraminiferal turnover, a¡ect-ing 42% of the Cretaceous fauna, occurred (Fig.7). Species richness dropped as a result of tempo-rary disappearance of some taxa and local extinc-tion of others. Pardo et al. (1996, p. 164) con-cluded that ‘there appears to be no major massextinction in benthic foraminifera associated withthe K^T boundary, although a major faunal turn-over is apparent and continued into the DanianT’because ‘most speciesT reappear when favorableconditions returned in the later DanianT’. Pardoet al. (1996, p. 164) noted, however, ‘Tthat theK^T boundary event greatly accelerated ongoingenvironmental changes in benthic foraminifera’.

3.5. Caravaca, Spain

The K^T transition in benthic foraminiferafrom Caravaca, Spain has been investigated byKeller (1992), Coccioni et al. (1993) and Coccioniand Galeotti (1994). Keller (1992) interpreted pa-leowater depths of 600 m (upper bathyal) in thelatest Maastrichtian, shallowing to 200 m (outerneritic) in the early Danian. A strong faunal turn-over (Fig. 8) but no mass extinction of benthicforaminifera occurred at the K^T boundary (Kel-ler, 1992). Nineteen Cretaceous species (39%) dis-appear in the earliest Tertiary or at the K^Tboundary, 16 species ¢rst appear or become dom-

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Fig. 9. Summary of benthic foraminiferal changes across the K^T boundary at Caravaca, Spain (modi¢ed from Coccioni andGaleotti, 1994). IDF, infaunal deposit feeder; EDF, epifaunal deposit feeder; ESF, epifaunal suspension feeder.

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inant after the boundary, and 14 species ‘Trangethrough the K/T transitionT’ (Keller, 1992, p. 79).Based on foraminiferal morphotypes, Keller(1992) noted that epifaunal species preferentiallyrange across the boundary. Superimposed on thisbroad scheme is a distinct assemblage, restrictedto the 6-cm-thick boundary clay, that is dominat-ed by the low-oxygen-tolerant infaunal speciesPraebulimina venusa, Bolivina incrassata giganteaand Bulimina farafraensis (Keller, 1992).Coccioni et al. (1993) interpreted late Maas-

trichtian to early Danian environments at Cara-vaca to be middle bathyal (600^1000 m), slightlydeeper than the estimate of Keller (1992). Theirinvestigation found more than 100 species in 39samples taken from 80 cm below to 120 cm abovethe K^T boundary, an interval (based on the sed-imentation rates of Smit, 1990) representing thelast 20 000 years of the Cretaceous and the ¢rst60 000 years of the Paleocene (Coccioni et al.,1993; Coccioni and Galeotti, 1994). The data pre-sented in their papers, however, are at the genericlevel.Coccioni et al. (1993) and Coccioni and Galeot-

ti (1994) found a trend of decreasing relativeabundance of putatively infaunal genera duringthe latest Maastrichtian, suggesting to the authorsa decrease of organic £ux to the sea£oor. At theK^T boundary, diversity (number of genera)drops and only two taxa, Spiroplectammina andBolivina ‘survive’. At the same time the dissolvedoxygen index decreases, faunal density increases,as does the relative abundance of infaunal mor-photypes (Spiroplectammina and Bolivina), all at-tributed to ‘Ta sudden and exceptionally large nu-trient £ux on the sea £oor’ resulting from massmortality in surface waters (Coccioni et al., 1993,p. 16). The benthic foraminiferal ecosystem recov-ered relatively quickly, within 7000 years, as moreoxygenated bottom-water conditions and environ-mental stability returned (Fig. 9). The suddenchange in the benthic faunas, according to Coc-cioni et al. (1993, p. 7; Coccioni and Galeotti,1994, p. 782) ‘Tcan only be explained by a geo-

logically instantaneous, catastrophic event’. How-ever, it is hard to imagine that the organic £uxresulting from a pelagic instantaneous mass mor-tality event could persist for 7000 years in thebenthic environment. Kaiho et al. (1999, p. 523)noted that the low-oxygen conditions evident atCaravaca were globally developed in intermediatewater and suggested that this ‘Twas likely relatedto an increase in supply of organic matter fromterrestrial biomass and sediments to intermediatewaters following the mass mortality event’.Because the data presented (Coccioni et al.,

1993; Coccioni and Galeotti, 1994) are at the ge-neric level, it is not possible to evaluate the scaleof species extinction, if any, that occurred at theK^T boundary. Evidently, at the generic level,mass mortality, rather than mass extinction, fol-lowed by rapid recovery characterizes the benthicforaminiferal fauna at Caravaca.

3.6. Negev^Sinai, Israel

Benthic foraminiferal changes across the K^Tboundary near the Negev^Sinai border of Israelwere presented in Keller (1992). A faunal turnoveroccurs across the broader boundary interval (Fig.10), but the boundary itself is not marked by anabrupt faunal change (Keller, 1992). Nineteenspecies range across the boundary according toKeller but Fig. 10 indicates a higher number.The species present were interpreted as represen-tative of an upper bathyal depth in the latest Cre-taceous, shallowing to outer neritic depths in theearliest Danian and deepening to upper bathyalagain by Zone P1b. Thus, a sea-level fall followedby a sea-level rise in the early Tertiary was in-ferred (Keller, 1992). On the basis of foraminiferalmorphotype distributional patterns, Keller (1992,p. 82) noted ‘Ta strong survivorship preference forspecies of epifaunal habitat’.

3.7. El Kef, Tunisia

The benthic foraminifera of the upper Creta-

Fig. 10. Relative abundance of benthic foraminifera across the K^T boundary near the Negev^Sinai border, Israel (modi¢edfrom Keller, 1992).

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ceous to lower Tertiary transition at El Kef, Tu-nisia (the Global Stratotype Section and Point forthe K^T boundary) have been the subject ofindependent studies by Keller (Keller, 1988a,1992; Keller and Lindinger, 1989) and Speijerand Van Der Zwaan (1994, 1996). The El Kefsection is more complete and has a higher sedi-mentation rate than other sites (Perch-Nielsen,1981; Romein and Smit, 1981; MacLeod andKeller, 1991a,b; Keller, 1992; Olsson and Liu,1993; Keller et al., 1995; Speijer and Van DerZwaan, 1996) and so is particularly informative.According to Keller (1992), depth of deposition

at El Kef changed from upper bathyal to outerneritic in the latest Cretaceous. Further shallow-ing to middle to outer neritic depths occurred inthe earliest Danian followed by deepening to out-er neritic depths during Zone P1b. Keller (1992)recognized changes in the benthic foraminiferalfauna at El Kef below, at and above the boundary(Fig. 11). Thirty-one species (50% of the fauna)disappeared at or just (up to 30 cm) beneath theboundary, three just (5^20 cm) above the bound-ary. Eleven species appeared in the basal 50 cm ofsediment after the boundary, while 34 speciesranged across the boundary (apparently not allspecies are plotted in Fig. 11). Keller (1988a) at-tributed the disappearance of mainly bathyal toouter shelf benthic species in the latest Maas-trichtian to circulation changes and/or sea-levelfall. Whilst acknowledging the geologically instan-taneous and catastrophic event at the K^Tboundary (Keller and Lindinger, 1989), Keller(1992, p. 168) noted that ‘Tit is di⁄cult to judgewhich benthic species went extinct as a result ofthe K/T boundary event and which species extinc-tion resulted from the pre-boundary adverse eco-logical conditions’. However, Keller, using fora-miniferal morphotype comparisons (e.g., Corliss,1985) characterized the K^T boundary as beingmarked by a ‘dramatic’ (Keller, 1988a) and‘abrupt’ (Keller, 1992) faunal change from speciestypical of oxygen-rich environments to a faunacomposed of epifaunal and infaunal taxa thatwere tolerant of low-oxygen conditions. When

the sea level began to rise again in Zone P1b(Keller, 1992), low-oxygen-tolerant species werereplaced by normal oxygen condition specieswhich had last been recorded at the K^T bound-ary (Keller, 1988a). Thus, Keller (1992) suggestedthat expansion of the oxygen minimum zone as-sociated with sea-level rise might have caused thebenthic foraminiferal turnover across the K^Tboundary.In summary, Keller (1992, pp. 77^89) con-

cluded that, at El Kef, as well as at the Tethyansites of Caravaca, Negev, and the Brazos River,no species extinctions directly coincide with theK^T boundary and that there is no evidence fora sudden crisis in benthic foraminiferal faunas.Keller et al. (1995), in noting a 45% decline inbenthic foraminiferal species richness across theboundary at El Kef, again invoked the sea-levelchange/oxygen minimum zone expansion hypoth-esis and observed (p. 250) that ‘Since the strongbenthic foraminiferal turnover at El Kef is notobserved elsewhere in the Tethys or globally, itmust be largely due to local environmental con-ditions’.Speijer and Van Der Zwaan (1994, 1996)

reached strongly contrasting conclusions follow-ing their studies at El Kef. They also inferred ashallowing from upper bathyal (300^500 m) con-ditions in the latest Maastrichtian to a somewhatshallower (middle outer neritic) environment inthe earliest Danian, returning to upper bathyalconditions by the upper part of the Parvularugo-globigerina eugubina Zone. They did not recognizesea-level changes within the late Maastrichtianalthough Li et al. (1999, 2000), based on stableisotopes, lithological changes and faunal associa-tions, have recently recognized a regression at65.45^65.3 Ma. Speijer and Van Der Zwaan(1996) described three distinct assemblages in asection spanning the upper 30 m of Maastrichtiandeposits and the lowermost 10 m of Paleocenedeposits at El Kef (Fig. 12). The latest Maas-trichtian assemblage is diverse and, although rel-ative abundances of species vary, the assemblagewas considered by Speijer and Van Der Zwaan

Fig. 11. Relative abundance of benthic foraminifera across the K^T boundary at El Kef, Tunisia (modi¢ed from Keller, 1992).

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(1996, p. 354) to be ‘Trelatively stable up to theK/Pg boundary’. By a level 12.5 cm above theboundary, 67% of the taxa present in the topmostmeter of Maastrichtian section disappear (Speijerand Van Der Zwaan, 1996). Thus, this latest Cre-taceous assemblage is succeeded quite suddenly bya low-diversity earliest Paleocene fauna dominat-ed by the calcareous species Cibicidoides pseudo-acutus. In contrast, the change from this C. pseu-doacutus fauna to the overlying, increasinglydiverse, early Paleocene fauna is gradual (Speijerand Van Der Zwaan, 1996). Lazarus taxa contrib-ute to the increasing diversity. Of the 67% of taxa

that disappear close to the K^T boundary, only30% do not return.The latest Maastrichtian benthic foraminiferal

fauna is diverse but is characterized by speciesindicative of high organic carbon £ux. The highdiversity suggested to Speijer and Van Der Zwaan(1996) that a strong oxygen minimum zone didnot develop at the upper bathyal depths of ElKef during the latest Maastrichtian. The earliestPaleocene low-diversity, high-dominance, shal-lower-water fauna, however, indicates consider-able oxygen de¢ciency (as do absence of burrow-ing organisms and preservation of laminae)

Fig. 12. Relative abundance of benthic foraminifera across the K^T boundary at El Kef, Tunisia. 1^5 are groups of taxa charac-terized by similar stratigraphic distributions (modi¢ed from Speijer and Van Der Zwaan, 1996).

Fig. 13. Relative abundance of dominant and common benthic foraminifera across the K^T boundary at A|«n Settara, Tunisia(modi¢ed from Peyrt et al., 2002).

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(Speijer and Van Der Zwaan, 1996). The succeed-ing early Paleocene fauna represents the gradualreturn to normal, oxygenated upper bathyal as-semblages, complete with Lazarus taxa, but ‘Tverydi¡erent from the Maastrichtian one’ (Speijer andVan Der Zwaan, 1996, p. 363).In summary, Speijer and Van Der Zwaan

(1996) suggested that their El Kef data showed‘Ta distinct sequence of sudden ecosystem collapsefollowed by gradual recovery’ (p. 363) and that‘Ta prolonged reduction in surface fertility andfood £ux to the sea-£oor invoked worldwide(but diachronous) benthic extinctions’ (p. 343).They concluded (Speijer and Van Der Zwaan,1994, p. 19) that the end-Cretaceous environmen-tal changes leading to these extinctions ‘Tcouldhave been triggered by the impact of an extra-terrestrial object, and ampli¢ed by various posi-tive feedback mechanisms.’

3.8. A|«n Settara, Tunisia

The K^T boundary at A|«n Settara, just 50 kmsouth of El Kef, exhibits a major planktonic fo-raminiferal extinction and geochemical markersindicative of bolide impact (Arenillas et al.,2000b; Tribovillard et al., 2000). The benthic fo-raminifera at this outer shelf to upper slope sec-tion exhibit faunal turnover (Fig. 13), at the levelof plankton extinction and geochemical anoma-lies, at the base of the Guembelitria cretaceaZone (Peyrt et al., 2002). Several genera disap-peared; some of these became extinct (Bolivi-noides, Bolivinopsis, Heterostomella, Sliteria andVerneuilina) whereas other reappeared in the low-er Danian (Peyrt et al., 2002). High-diversity as-semblages with infaunal and epifaunal morpho-types were suddenly replaced by lower-diversityassemblages of epifaunal morphotypes. Lazarustaxa reappear in the lower part of the Parvularu-goglobigerina eugubina Zone and epifaunal mor-phogroups became less dominant. By the middlepart of this zone, the foraminiferal assemblageindicates a return to pre-K^T boundary condi-tions (Peyrt et al., 2002).The low-diversity assemblages that immediately

follow the K^T boundary were not caused bylow-oxygen conditions (Tribovillard et al., 2000)

or by sea-level change (cf. Keller, 1988a,b, at ElKef) but by a change in the nature and abundanceof food supply to the sea£oor. Peyrt et al. (2002)pointed out that the dominant primary producersin the late Cretaceous, calcareous nannoplankton,su¡ered a mass extinction but dino£agellates didnot and that this change of food supply to thesea£oor may have precipitated the faunal turn-over. In a broader context, Peyrt et al. (2002)attributed the benthic foraminiferal changes atA|«n Settara to asteroid impact on the Yucatanand the resulting global drop in primary produc-tivity (D’Hondt et al., 1998).

4. Deep-water faunas

Soon after Alvarez et al. (1980) argued for anextraterrestrial cause for K^T extinctions, Emilia-ni et al. (1981) brie£y reviewed the biotic changesof deep-sea faunas across the boundary. Theiranalysis of data in Deep Sea Drilling Program(DSDP) publications (e.g., Resig, 1976; Boersma,1977; Sliter, 1977; Hooper and Jones, 1977; Lut-ze, 1978; Stenestad, 1979) indicated that 75^85%of benthic foraminiferal genera survived the ter-minal Cretaceous event. The review of Douglasand Woodru¡ (1982) of data from a generallydi¡erent set of DSDP volumes (McGowren,1974; Sigal, 1974; McNulty, 1976; Sliter, 1976,1977; Beckmann, 1978) provided similar results.Maastrichtian and early Paleocene benthic assem-blages are nearly identical whereas at the specieslevel, although there is ‘Tsome change across theboundaryT many deep sea species important inthe Maastrichtian continue into the Danian’(Douglas and Woodru¡, 1982). They furthernoted that abyssal agglutinated faunas from be-low the CCD are similar across the boundary(Krashininnikov, 1973, 1974; Webb, 1973) andconcluded that environmental change at theK^T boundary was minor and had little e¡ecton benthic foraminifera.Miller (1982) concurred in his coeval review. He

observed that Cushman and Renz (1946) notedthe similarity of the lower Lizard Springs faunain Trinidad with the underlying Cretaceous faunaand that all of the Paleocene deep-water Atlantic

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species recognized by Tjalsma and Lohmann(1982) were also recorded from Cretaceous depos-its (Tjalsma and Lohmann (1982), considered Pa-leocene assemblages to be largely relicts from theLate Cretaceous). Miller (1982), referring to Mill-er et al. (1982), also described the close similaritybetween Cretaceous and Tertiary ‘£ysch-type’ ag-glutinated foraminifera but did note that Cush-man and Renz (1946) and Webb (1973) suggestedthat only V50% of deep-sea species survived theCretaceous.Also in 1982, Thierstein reviewed terminal Cre-

taceous plankton extinctions, but in mentioningbenthic foraminifera he noted (Thierstein, 1982,p. 389) that ‘The evolutionary pattern of benthicdeep water foraminifera show no evidence of en-vironmental change at the K^T boundary (Beck-mann, 1960; Dailey, in press [1983])’. This contra-dicts the abstract of Dailey (1983) which statesthat there were ‘Tmajor changes in benthic faunalcomposition at the Cretaceous/Tertiary boundarytransition’ (Dailey, 1983, p. 757).In the following review of relevant deep-sea fo-

raminiferal papers, I deal ¢rst with the highest-latitude, deep-sea foraminiferal study. The re-mainder of the published literature investigateslow- to mid-latitude foraminifera. Tethyan loca-tions are treated last.

4.1. Maud Rise, Weddell Sea, Antarctica

Ocean Drilling Program Sites 689 and 690 re-covered upper Cretaceous through lower Eocenecalcareous chalk and ooze that were deposited inlower bathyal depths of 1000^1500 m at Site 689and 1500^2000 m at Site 690 based on benthicforaminiferal faunas (Thomas, 1990a) and con-¢rmed by adjacent thermal subsidence models(Thomas, 1990a,b). The deeper site is more com-plete and so was the primary resource used todetermine faunal events (Thomas, 1990b), but agraphic correlation study of Site 690 indicatedthat most of the early Danian zones P0 and P1aare missing (MacLeod, 1995a).At Site 690, seven species (8%) last occur close

to the K^T boundary, four in the interval 0.5 mybefore the boundary, three in the interval 0.5 myafter the boundary, and none at the boundary. At

Site 689, 11 species (13%) last occur close to theboundary, three in the interval 0.5 my before theboundary, three at the boundary, and ¢ve in theinterval 0.5 my after the boundary. Not surpris-ingly, Thomas (1990b, p. 487) concluded: ‘Thispattern of faunal events at the K/T boundarydoes not conform to the pattern during a largecatastrophe.’ Further, she made it quite clearthat she was discussing local last appearancesand not necessarily true extinction (Thomas,1990b, p. 489).Using foraminiferal morphotypes (e.g., Corliss

and Chen, 1988) as an indicator of infaunal orepifaunal mode of life, Thomas (1990b) describeddominance of epifaunal species, often indicativeof high oxygen content and/or low nutrient con-centration (e.g., Sen Gupta et al., 1981; Bernhard,1986), in the Cretaceous section. Just above theK^T boundary, epifaunal species peak (Fig. 14)followed by the recovery of infaunal species. Tho-mas (1990b) believed that this is the pattern thatwould be expected from the collapse of produc-tivity in surface waters; that is, the disappearanceof several high carbon £ux, infaunal species andan increase in low-nutrient, epifaunal species justafter the K^T boundary. The lack of mass extinc-tion was attributed to the fact that deep-sea fora-

Fig. 14. Percentage of species in the assemblages that belongto epifaunal (spiral) taxa as estimated from test morphology(Corliss and Chen, 1988) at Site 690, Weddell Sea, Antarcti-ca (modi¢ed from Thomas, 1990b).

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minifera ‘Tcommonly live in an environment ofvery low food supply and are thus well suited tosurvive periods of low productivity’ (Thomas,1990b, p. 491). Thomas (1990b) also invoked thepossibility of detritus feeding as a bu¡er to extinc-tion (Sheehan and Hansen, 1986).

4.2. Lord Howe Rise, Tasman Sea

Webb (1973) calculated K^T extinction ratesfrom DSDP Site 208 of 73% for agglutinatedbenthic foraminifera, 52% for calcareous benthicforaminifera, and 54% for agglutinated and cal-careous combined. He compared them to themuch lower extinction rates in Trinidad (Beck-mann, 1960) and suggested that this might be be-cause the Trinidad sections were shallower, in-shore sites where taxa might have highertolerance to environmental changes. Alternatively,Webb (1973) suggested that Trinidad might haveexperienced little climatic £uctuation across the

K^T boundary. However, Thomas (1990b) re-es-timated extinction rates using the tables of Webb(1973) with presence^absence data to counter thee¡ect of few (6 100) benthic foraminifera pickedper sample. Her calculations resulted in an extinc-tion rate of 14% ‘Twith 40 out of 106 species toorare to be useful’ (Thomas, 1990b, p. 490).

4.3. Rio Grande Rise, Western South Atlantic

Dailey (1983) documented the Late Cretaceousto Paleocene benthic foraminifera from DSDPSite 516, Hole 516F. He found 153 species that,within the Campanian^Paleocene interval, wereliving at middle to lower bathyal depths. Dailey(1983) considered the section of nannofossil lime-stone with marly claystones to be continuousacross the K^T boundary.The benthic foraminiferal assemblages across

the K^T boundary exhibit turnover (Fig. 15)over a period of hundreds of thousands of years

Fig. 15. Maastrichtian^lower Paleocene benthic foraminiferal data at DSDP Hole 516F. Species occurring only once are omitted(modi¢ed from Dailey, 1983).

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(Dailey, 1983). However, there is an acceleratedrate of last occurrences (local species extinctions,according to Dailey, 1983), in the ¢nal 2 my ofthe Maastrichtian, with a peak of extinctions inthe ¢nal 0.5 my. Complementing these disappear-ances is a fourfold increase in ¢rst appearances inthe last 1 my of the Maastrichtian. The number oflocal extinctions continues in the lowest Paleocenewith most occurring in the ¢rst 0.5 my. Dailey(1983 p. 764) indicated that 28% of the benthicspecies present in the ¢nal 0.5 my of the Maas-trichtian ‘Tdo not survive to the end of Creta-ceous’. He pointed out, however, that a few ofthese species range into the Paleocene elsewhere.In summary, Dailey (1983) documented what hedescribed (p. 757) as ‘Tmajor changes in benthicfaunal composition at the Cretaceous/Tertiaryboundary transition. It was a time of rapid turn-over, with the extinctions of numerous species andthe introduction of many new species’.

4.4. Broken Ridge, eastern Indian Ocean

Benthic foraminiferal changes from the upperMaastrichtian to lower Eocene nannofossil chalk

at ODP Site 752 (1086 m present water depth)were described by Nomura (1991). Cretaceous toPaleogene sediments at this site accumulated atwater depths of several hundred to 1000 m ac-cording to Rea et al. (1990). Nomura subjectedhis data to Q-mode factor analysis which identi-¢ed eight assemblages. The Stensioina beccariifor-mis assemblage ranged from the upper Maas-trichtian through most of the Paleocene. Thisrelative lack of change at the K^T boundary isre£ected by the ranges of individual taxa. ‘Amongcommon taxa in the upper Maastrichtian, onlyseven species disappeared or became extinct atthe Cretaceous/Tertiary boundary at Site 752’(Nomura, 1991, p. 3). When the total fauna(187 species) was considered, only 23 species(12.3%) disappeared at the boundary. Nomura(1991, p. 13) concluded that ‘TThere was no majorextinction event of benthic foraminifera at theCretaceous/Tertiary boundaryT’ at Site 752. How-ever, Nomura (1991) did note that carbon iso-topic data from benthic foraminifera indicates nu-trient-depleted water at Site 752 immediately afterthe boundary, thus supporting the theory of sur-face productivity collapse.

Fig. 16. Changes in relative abundances of benthic foraminiferal morphotypes across the K^T boundary at DSDP Sites 465, 525and 527 (modi¢ed from Widmark and Malmgren, 1992).

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4.5. Hess Rise, North Paci¢c, Walvis Ridge,South Atlantic, and Angola Basin, South Atlantic

Widmark and Malmgren (1992) investigatedbenthic foraminiferal changes across the K^Tboundary at DSDP Sites 525, 527, and 465. Thesediments from these sites are nannofossil ooze orchalk that were deposited at paleodepths of 1500m (Site 465, Hess Rise), 1100 m (Site 525, WalvisRidge) and 2700 m (Site 527, Angola Basin). Ac-cording to MacLeod and Keller (1991a,b), 50^200kyr of basal Danian might be missing at Sites 525and 527, but D’Hondt and Herbert (1992) andOlsson and Liu (1993) disagreed. (See MacLeod,1995a for further discussion.) The speci¢c goals ofWidmark and Malmgren (1992) were to determinechanges in benthic foraminiferal assemblagesacross the K^T boundary from di¡erent oceans,paleolatitudes, and paleodepths.Taxonomic disappearances of Maastrichtian

taxa in Danian strata ranged from 40% in theshallower Atlantic Site 525 to 18% in the deeperAtlantic Site 527 when using complete faunas.When more rarely occurring species (whose ob-served stratigraphic ranges are less reliable) wereexcluded, 23% (Site 525) to 9% (Site 527) of taxadisappeared. These results suggested a paleoba-thymetric control at middle latitudes in the SouthAtlantic (Widmark and Malmgren, 1992). Thelow-latitude Paci¢c Site 465 exhibited a lower de-gree of species disappearances than the South At-lantic sites (13% all taxa; 5% minus rarely occur-ring taxa). Thus a paleolatitudinal control oftaxonomic disappearances was suggested (Wid-mark and Malmgren, 1992). Widmark (1997)laterconsidered the low number of taxonomic disap-pearances to be an artifact caused by the inclusionof samples from a 30-cm mixed zone of Maas-trichtian and Danian sediments. By excludingthese samples from his calculations, Widmark(1997) obtained a range of 22^44% disappearancefor Site 465. This result, in e¡ect, reversed theapparent latitudinal gradient of taxonomic disap-pearances.Although species disappearances occurred

across the K^T boundary, their generally low lev-el led Widmark and Malmgren (1992, p. 81) toconclude that ‘Tdeep-sea benthic foraminifera

were not severely a¡ected by the K/T transitionevent’. Using foraminiferal morphotypes to infermode of life, Widmark and Malmgren (1992)documented the disappearance or decrease in rel-ative abundance of putatively infaunal species atthe South Atlantic sites, whereas at the Paci¢c siteinfaunal species did not decrease in abundanceacross the K^T boundary (Fig. 16). This patternwas attributed to a decrease in primary produc-tivity in the South Atlantic, a more stressed andunstable deep-sea environment than the lower-lat-itude Paci¢c (Widmark and Malmgren, 1992).

4.6. Tampico^Misantia basin, Mexico

The K^T boundary in northeastern Mexico ismarked by a clastic deposit separating Maas-trichtian and Danian marly formations. The marlshave been interpreted as deep-water deposits(Berggren and Aubert, 1975; Longoria and Gam-per, 1993). The clastic unit, according to Kellerand Stinnesbeck (1996) and Keller et al. (1997)was deposited by gravity £ows or turbidity cur-rents at outer shelf to upper slope depths during alatest Maastrichtian sea-level lowstand. However,this unit has also been interpreted as resultingfrom mass wasting initiated by K^T boundaryimpact; shallower deposits were transported intothe deep basin (e.g., Bralower et al., 1998; Soriaet al., 2001).Alegret et al. (2001) examined K^T benthic fo-

raminifera in seven sections in northeastern Mex-ico, only 1000 m from the Chicxulub crater. Themarls contained benthic foraminifera that indicatemiddle to lower bathyal paleodepths for six of thesections. The clastic unit contained a mixed nerit-ic^bathyal assemblage (Fig. 17) that indicated ba-sinal redeposition following impact-initiated masswasting (Alegret et al., 2001). Benthic assemblagesin the marls exhibit temporary changes in compo-sition but no extinctions. Only two species havelast occurrences close to the K^T boundary in allsections. Alegret et al. (2001) used foraminiferalmorphotypes (Corliss, 1985) to infer microhabitatpreferences and nutrient supply (Jorissen et al.,1995). They recognized a drastic decrease infood supply just after the K^T boundary followedby a slow recovery in the Danian (Fig. 17). This

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was explained by sudden collapse (mass extinc-tion) followed by recovery of surface productivity.Algeret et al. (2001) suggested that K^T deep-seabenthic foraminifera, unlike modern deep-sea fo-raminifera (Gooday, 1993; Thomas and Gooday,1996), did not rely on benthic^pelagic couplingfor their food supply but instead used sedimenta-ry organic material. This, therefore, shelteredthem from mass extinction.

4.7. Trinidad, West Indies

The study of Beckmann (1960) is perhaps the¢rst to document faunal changes in the deep seaacross the K^T boundary. Beckmann (1960, p.68) characterized the environment of depositionto be ‘Tfairly deep sea’ in concurrence with Cush-man and Renz (1946, p. 1) who considered the

Paleocene Lizard Springs Formation (thought byCushman and Renz to be late Cretaceous in age)to have been deposited in ‘Tcomparatively deepwater.’ Berggren and Aubert (1975) later coinedthe term ‘Velasco-type’ fauna for these lowerslope to abyssal plain deep-water assemblages.Beckmann (1960) stated that 176 of 215 (82%)benthonic species (60 of 66 agglutinated, 91%)range across the K^T boundary. These numberswere revised to 190 out of 280 species surviving(68%) in 1982 (Beckmann in Beckmann et al.,1982). Beckmann (1960, p. 68) also noted that‘Tchanges in the benthonic Foraminifera at theend of the Cretaceous were not nearly as revolu-tionary as the extinction of the planktonic Fora-miniferaT’. Thomas (1990b) pointed out that theestimates of extinction of Beckmann (1960),although small, are maximum estimates because

Fig. 17. Faunal turnover of common benthic foraminifera across the K^T boundary in the Tampico^Misantia basin, Mexico.P.h., Plummerita hantkeninoides ; G.c., Guembelitria cretacea ; Pv.e., Parvularugoglobigerina eugubina ; P.ps., Parasubbotina pseudo-bulloides (modi¢ed from Alegret et al., 2001).

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they include last appearances that occurred withinthe Maastrichtian and not just at the K^T bound-ary.

4.8. Tethys: Monte Giglio, Italy

Beckmann (in Beckmann et al., 1982) describedthe late Cretaceous^Paleocene benthic foraminif-era from Monte Giglio, Italy. The Campanian^Maastrichtian assemblages obtained from softmarl of the Scaglia Formation are of quite lowdiversity (3^15 species per sample). A total of 52species were recorded of which 50% are aggluti-nated. Based on a comparison with the paleoba-thymetric scheme of Sliter and Baker (1972),Beckmann interpreted the assemblages to repre-sent the lower bathyal zone (1500^2500 m waterdepth) and possibly as deep as 3000 m.A hiatus occurs at the K^T boundary (Beck-

mann et al., 1982); part of the Maastrichtian,the lower Paleocene, and part of the middle Pa-leocene are missing. Even so, the faunas on eitherside of the boundary are quite similar. Eighteen of52 species (40%) range across the boundary andthe faunal composition in Maastrichtian and mid-dle Paleocene strata is similar, although some var-iations in relative abundances occur (Beckmann,in Beckmann et al., 1982). The fauna on bothsides of the boundary is of open marine, deep-water ‘Velasco-type.’

Beckmann (in Beckmann et al., 1982) brie£ydiscussed the quite variable (17^68%) values ofpercent survivors across the K^T boundary inpublished studies of deep-water benthic foraminif-era. In Trinidad and Mexico, where deep-water‘Velasco-type’ assemblages occur on both sidesof the boundary, the di¡erence between latestCretaceous and earliest Tertiary assemblages isless pronounced than, for example, the GulfCoast region of the USA where shallower-water‘Midway-type’ assemblages (Berggren and Au-bert, 1975) succeed deeper-water faunas (Beck-mann in Beckmann et al., 1982).

4.9. Tethys: Coldorso, Italy

Coccioni and Savelli (1983) commented on thebenthic foraminiferal assemblages of uppermostMaastrichtian (Abathomphalus mayaroensisZone) limestone and the overlying basal Paleo-cene marl of their Globigerina eugubina Zone.This pelagic^hemipelagic succession was depos-ited at water depths of 3000^4000 m. Assemblagesfrom only four samples were described, two fromthe marly interbeds about 1 m below the bound-ary and two from the boundary clay (0.5^3 cmthick), one at the base and one at the top. Theassemblages are dominated by agglutinated fora-minifera and, according to Coccioni and Savelli(1983, p. 199), ‘No signi¢cant di¡erence exists be-

Fig. 18. Relative abundance of agglutinated foraminifera across the K^T boundary in the Gubbio area (Bottaccione and Contes-sa sections) (modi¢ed from Kuhnt, 1990).

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tween the character of the assemblages of theK^T clayey/marly interbeds and those of themain underlying marly interbeds.’

4.10. Tethys: Gubbio, Italy

The late Cretaceous to early Paleocene aggluti-nated foraminifera of the Bottaccione and Con-tessa sections near Gubbio were described byKuhnt (1990). Based on the nature of the forami-niferal assemblages, Kuhnt (1990) considered theScaglia Rossa limestone to have been deposited ina deep bathyal environment between 1500 and2500 m water depth. Numbers of agglutinated fo-raminifera decrease drastically at the boundary(Fig. 18), in particular, tubular forms, whichmake up 90% of the upper Cretaceous assemblag-es. Spiroplectammina and Reophax dominate thelowest Paleocene samples. Kuhnt (1990) suggestedthat the change in assemblages may have beendue to the low capability of tubular forms, con-

sidered to be epifaunal in habit, to recolonize thesubstrate after the K^T boundary event (Kamin-ski et al., 1988).Kaminski (in MacLeod et al., 1997) summa-

rized the record of agglutinated benthic foraminif-era across the K^T boundary at Gubbio with aslightly larger data set. He recognized a shift incommunity structure and decrease in abundanceand diversity commencing in the late Maastricht-ian (Fig. 19) but, unfortunately, his ¢gure did notinclude a time scale or biostratigraphic zonation.However, just beneath the boundary, epifaunalsuspension and detritus feeders dominate whereas,just above the boundary, infaunal, probably bac-teriovore, species dominate. Kaminski suggestedthat this change may have resulted from a de-crease in organic matter reaching the sea£oor asa result of the K^T boundary event. A successionof episodes of increased organic £ux during a pe-riod of generally low productivity resulted in in-creased abundance of a succession of species at

Fig. 19. Abundance of selected deep-water agglutinated foraminifera across the K^T boundary in the Contessa section near Gub-bio, Italy. K^T boundary at 0 cm level. Abundance values (horizontal axes) are number of individuals s 125 mm per gram ofdissolved sediment. Events 1^3 are episodes of increased organic £ux (modi¢ed from Kaminski in MacLeod et al., 1997).

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events 1^3 (Fig. 19), but note the small scale ofabundance increases. Event 2 is de¢ned by an in-crease in abundance of Spiroplectammina ex. gr.dentata from about 0.5 to 1.5 specimens per gramof sediment, and event 3 is de¢ned by an increasein Spiroplectammina ex. gr. spectabilis from about0.02 to 0.125 specimens per gram of sediment.Although small, the same sequence of abundancechanges involving the same species is also recog-

nized at the Bottaccione section near Gubbio. Re-covery of communities in the early Paleocenelasted several hundred thousand years (Kuhntand Kaminski, 1993).

4.11. Tethys: Basque Basin, Northern Spain

Changes in deep-water (middle bathyal) agglu-tinated foraminiferal assemblages across the K^T

Fig. 20. Abundance of characteristic representatives of three faunal groups recognized across the K^T boundary at the Sopelanasection, Basque Basin, northern Spain. M1, uppermost Maastrichtian sample. BC-1 to BC-6, six contiguous boundary clay sam-ples (each 5 cm thick) taken from the 30-cm-thick boundary clay (modi¢ed from Kuhnt and Kaminski, 1993).

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Fig. 21. Changes in the deep-water agglutinated foraminiferal fauna across the K^T boundary at Rotwandgraben, Austria.(A) Morphotypic assemblages; (B) number of specimens per gram of sediment; (C) number of species; (D^G) relative abundan-ces of dominant genera; (H) proportion of epifaunal and infaunal morphotypes (modi¢ed from Peryt et al., 1997).

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boundary at two sections, Zumaya and Sopelana,were described by Kuhnt and Kaminski (1993).No major extinction event or taxonomic turnoverwas recognized at the K^T boundary. Of the 45species present in the uppermost Maastrichtian ofthe Sopelana section, only nine were not recordedin the overlying (Paleocene) boundary clay. Of the45 species present in the lowermost 5 cm of theboundary clay, only 10 were not observed in theuppermost Maastrichtian (Kuhnt and Kaminski,1993). However, marked changes in communitystructure across the K^T boundary, based onmorphotype studies (Jones and Charnock, 1985;Corliss and Chen, 1988) and modern recoloniza-tion studies (Kaminski et al., 1988), were de-scribed by Kuhnt and Kaminski (1993). Suspen-sion feeders and epifaunal detritivores dominatethe late Maastrichtian assemblage (Fig. 20). Theseforms disappear almost completely at the base ofthe boundary clay, a change, according to Kuhntand Kaminski (1993, p. 69), ‘Ttriggered by a dra-matic drop of productivity in surface watersT[which] Tled to a collapse of the food web forbenthic communities’. The lower part of theboundary clay (Zone P0) contains low-oxygen-tol-erant and infaunal species. Assemblages of higher-diversity infaunal taxa return in the upper part ofthe boundary clay (their Zone P1a), more than100 000 years after the boundary (Fig. 20). Kuhntand Kaminski (1993, p. 69) concluded that ‘What-ever the ultimate cause for the K/T boundaryevent was, the slow recovery of benthic foraminif-eral community structure during the early Paleo-cene does not support a scenario of a single short-term event causing faunal changes at the K/Tboundary’.

4.12. Tethys: Rotwandgraben, Austria

Peryt et al. (1997) studied the deep-water agglu-tinated foraminiferal changes across the K^Tboundary in the Rotwandgraben section in theeastern Alps. The partly turbiditic and partlyhemipelagic deposits in this section were depos-ited above the CCD at a depth of about 2000 m(Peryt et al., 1993). Peryt et al. (1997) recognizedfour assemblages based on the relative abundan-ces of epifaunal and infaunal species, as inferred

from morphotypes (Jones and Charnock, 1985;Corliss and Chen, 1988).Assemblage I, in the uppermost Abathomopha-

lus mayaroensis Zone, was composed of a mix ofepifaunal and infaunal species (53^75% epifaunal)(Fig. 21). Peryt et al. (1997, p. 297) consideredsuch an assemblage to be ‘Ttypical for deep-watermarine environments with normal primary pro-ductivity and a £ux of organic detritus and calci-um carbonate that is su⁄cient to sustain infaunalbottom-dwelling organisms’. Assemblage II, oc-curring in the lower part of the Guembelitria cre-tacea Subzone (Fig. 21), is composed of very fewspecies. Those present are epifaunal suspensionfeeders, deposit feeders and shallow infaunal de-trital/bacterial scavengers. Peryt et al. (1997) con-sidered that this assemblage re£ected the collapseof food supply to the deep-sea £oor. AssemblageIII, occurring in the upper part of the Guembeli-tria cretacea Subzone (Fig. 21), is composed of80^95% epifaunal taxa. According to Peryt et al.(1997), this indicates that very little food wasavailable to benthic communities. AssemblageIV, occurring in Zones P0b, PK and P1a (Fig.21), indicates a return to latest Cretaceous condi-tions with a diverse fauna composed of 53^68%epifaunal taxa. Within the infaunal group, spiro-plectamminids dominate (Fig. 21). Peryt et al.(1997) concluded that the community change atthe K^T boundary, including the drastic decreaseof abundance and diversity, was related to a re-duction in primary productivity. They judged thisenvironmental stress to be instantaneous and‘Tcompatible with a large bolide impact’ (Perytet al., 1997, p. 287).

5. Discussion

Much has been written about the e¡ects on theEarth’s biota of a bolide impact at the K^Tboundary, or longer-term environmental changecommencing before the boundary (e.g., Ryder etal., 1996; MacLeod et al., 1997). It is important,however, that before explanations are o¡ered, thepatterns of faunal, £oral, and microbiotic changeshould ¢rst be documented and understood. It ismy opinion that this has not been the case for

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benthic foraminifera. Thus, statements based onfew data have entered the literature and have beenperpetuated by later authors (including myself).The most glaring example is the idea that shal-low-water benthic foraminifera were a¡ectedmore severely by environmental events at theK^T boundary than their deeper-water counter-parts. No in-depth analysis or review has conclu-sively demonstrated this to be the case.There is now a considerable, primary literature

on benthic foraminiferal changes across the K^Tboundary. Some 34 papers have dealt withbenthic foraminifera from 28 geographic localitiesscattered around the world (Fig. 1), representingeight shallow-water (neritic), 10 intermediate-water (outer neritic to middle bathyal) and 15deep-water (middle bathyal to abyssal) datapoints. The pertinent summary data from thosestudies are summarized in Tables 1^3.Various terms have been used to describe the

changes that occurred in benthic foraminiferal as-semblages across the K^T boundary (‘extinction’,‘local extinction’, ‘last occurrence’, ‘disappear-ance’, ‘reduction in numbers’, ‘reduction in diver-sity’, ‘do not cross the boundary’, ‘faunal turn-over’). Further, the numbers/percentages ofspecies or genera that ‘disappear’ have been cal-culated and presented in many di¡erent ways, forexample, species level data often include entriessuch as ‘nodosariids’ or ‘Pullenia spp.’. Howmany species are truly represented by such en-tries? Yet further, the primary data have beencollected di¡erently with di¡erent sampling tech-niques, di¡erent numbers of specimens per sam-ple, and di¡erent size fractions of specimens. And,of course, there is always the problem of di¡er-ences amongst workers of taxonomic conceptsand the lingering question of how con¢dent wecan be that the last observed occurrence of a spe-cies equals its last true occurrence (e.g., MacLeod,1996). Indeed, even when an attempt is made toaddress these kinds of issues, as with blind sampletest conducted on the planktonic foraminifera ofthe El Kef section, it can still be inconclusivewhether or not a particular extinction pattern ispresent (Canudo, 1997; Ginsburg, 1997a,b; Kel-ler, 1997; Lipps, 1997; Masters, 1997; Olsson,1997; Orue-Etxebarria, 1997; Smit and Neder-

bragt, 1997; Smit et al., 1997). This great varietyof approaches seriously hinders analysis of the K^T boundary biotic changes. Nevertheless, in thefollowing sections I will attempt to ¢nd patternsin the data that are available.

5.1. Bathymetric pattern

Let us ¢rst evaluate the benthic foraminiferalchange across the K^T boundary if published es-timates/calculations of change are accepted at facevalue and without a critical appraisal of con-founding factors. Five of eight studies are avail-able for evaluation of change at or near theboundary in neritic environments (Table 1). InTexas, 16% of species do not cross the K^Tboundary (Plummer, 1927); at the Brazos River,Texas, approximately 50% disappear/emigrate (al-beit temporarily) (Keller, 1992); in New Jersey,32% do not cross the boundary (Olsson, 1960);at Seymour Island, Antarctica, 64% do not crossthe boundary (Huber, 1988); and at Seldja, Tuni-sia, 13% of ‘common’ species are restricted to thelate Maastrichtian (Keller et al., 1998).At intermediate water depths (outer neritic to

middle bathyal), six studies can be used (Table 2).At Hokkaido, Japan, 13% of latest Cretaceousspecies became extinct (Kaiho, 1992); at Danne-virke, New Zealand, 13 of 13 species cross theboundary (Kaiho, 1988); at Agost, Spain, thereis a 42% turnover (Pardo et al., 1996); at Cara-vaca, Spain, 39% of species disappear (Keller,1992); at El Kef, 50% disappear at or just beneaththe boundary (Keller, 1988a, 1992); and, also atEl Kef, more than 67% of species disappear butonly 30% disappear permanently (Speijer and VanDer Zwaan, 1994, 1996).In deep waters (middle bathyal to abyssal) (Ta-

ble 3), on Maud Rise, Antarctica (ODP Site 690),8% of species last occur close to the boundary(Thomas, 1990a,b). On the Lord Howe Rise, Tas-man Sea (DSDP Site 208), 54% become extinctaccording to Webb (1973) but only 14% accordingto Thomas (1990b). On the Rio Grande Rise,South Atlantic (DSDP Site 516), 28% disappearin the ¢nal 0.5 my of the Cretaceous (Dailey,1983). On the Walvis Ridge, South Atlantic(DSDP Site 525), 40% disappear (23% when

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Table 1Summary notes on environmental and benthic foraminiferal changes across the K^T boundary: shallow-water (neritic) studies

Author/date Location Paleodepth/paleoenvironment

Paleolatitude Taxonomic change acrossK^T boundary

Extinctions Sea-level changeacross boundary

Species diversity/richness

Epifaunal/infaunalchanges acrossboundary (based onmorphotypes)

Time of faunalchange

Disconformity/hiatus at/nearboundary

Preservation

Plummer, 1927 Texas, USA ‘comparativelyshallow sea’

ca. 30‡N 9 of 56 (16%) species donot cross boundary

Sikora, 1984 Texas, USA outer shelf100^200 m

ca. 30‡N ‘fairly similar’ faunas onboth sides of boundary

below boundary yes

Keller, 1992 Brazos R., Texas middle neritic6 100 m

ca. 30‡N about 50% of speciesdisappear/emigrate:most return later

no extinctions sea-level lowstand small and gradualdecrease, 5%lower in Danianthan Cretaceous

almost 100%epifaunal inMaastrichtian andDanian

below boundary probably; but according toMacLeod and Keller (1991b)hiatus is in upper part of P0.According to Montgomeryet al. (1992) the uppermostMaastrichtian is missing

Olsson et al.,1996

Millers Ferry,Alabama

30^100 m(30 m at boundary)

ca. 30‡N most species crossboundary

sea-level lowstand most species infaunaldeposit feeders inMaastrichtian, mostare epifaunal depositin feeders in Danian

yes, very short hiatus

Olsson, 1960 New Jersey, USA shelf ca. 40‡N 44 of 139 (32%) speciesdo not cross boundary

yes in some places, no in others

Schmitz et al.,1992

Stevns Klint,Denmark

epicontinental sea100^200 m

ca. 50‡N sea-level rise hiatus above Fish Clay(Zone P1a missing); also partof Zone P1c missing

carbonate dissolutionin lowermost Danian

Huber, 1988 Seymour Island,Antarctica

above shelf/slopebreak

ca. 65‡S 46 of 72 (64%) speciesdo not cross boundary

numerousbenthics

boundary placed within a 9.5-mglauconitic interval

carbonate dissolutionin lower Danian

Keller et al.,1998

Seldja, Tunisia inner neritic tocoastal

ca. 25‡S 3 of 23 (13%) ‘common’species restricted to lateMaastrichtian

sea-level fall inlatest Maastrichtian

decreasing in latestMaastrichtian, lowin early Danian,increasing inmiddle Danian

below, at andabove boundary

yes, K^T boundary hiatus andearly Danian hiatus

carbonate dissolutionin Zone P1a silt

Notes re£ect original authors’ opinions/data unless otherwise stated.

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Table 2Summary notes on environmental and benthic foraminiferal changes across the K^T boundary: intermediate-water (outer neritic to middle bathyal) studies


Paleolatitude Taxonomic changeacross K^T boundary



Epifaunal/infaunal changesacross boundary (based onmorphotypes)


Disconformity/hiatus at/near/boundary

Preservation

Huber, 1991 Hole 738C,Kerguelen Plateau,Indian Ocean

beyond shelf/slopebreak, s 500^600m

ca. 55‡S no recognizable faunalturnover

falls 0.5 m belowboundary

below boundary no, biostratigraphicallycontinuous

recrystallized andovergrown withcalcite

Kaiho, 1992 Hokkaido, Japan upper bathyal(300^600 m)shallowing to150^300 m

ca. 50‡N 5 of 40 (13%) speciesbecame extinct

sea-level fall below boundary no, biostratigraphicallycontinuous

Kaiho, 1988 Dannevirke, NewZealand

upper to middlebathyal

ca. 50‡S 13 of 13 Cretaceousspecies cross boundary

yes, at K^T boundary lower part of ZoneP1 is barren

Pardo et al.,1996

Agost, Spain upper bathyalshallowing toouter neritic thendeepening toupper bathyal

ca. 30‡N faunal turnover of 42%of Cretaceous faunas

no major massextinctions

sea-level rise fall at boundary increase of infaunal andlow-oxygen epifaunalspecies in latestMaastrichtian continuingthrough early Danian


yes at P0^P1a boundary andwithin uppermost zone P1a

Keller, 1992 Caravaca, Spain upper bathyal(600 m) shallowingto outer neritic(200 m)

ca. 30‡N 19 species (39%)disappear

no massextinction

sea-level fall short-lived decrease(10%) beginning atboundary

epifaunal speciespreferentially survive butlow-oxygen speciesdominate in boundary clay

at and aboveboundary

yes at P0^P1a boundary

Coccioni et al.,1993; Coccioniand Galeotti,1994

Caravaca, Spain middle bathyal,600^1000 m

ca. 30‡N number of genera dropsfrom ca. 25 to 2 at theboundary

fall at boundary decreasing abundance ofinfaunal species in latestMaastrichtian; increase inabundance of infaunalspecies in earliest Danian,infaunal and epifaunalspecies by 7 ka afterboundary

at boundary basal 2 mm ofboundary clay layerare barren offoraminifera,otherwisepresentationmoderate to good

Keller, 1992 Negev^Sinai,Israel

upper bathyalshallowing to outerneritic deepeningto upper bathyal

ca. 15‡N 23 species (42%)dominant or presentonly during latestMaastrichtian; 12species (23%) dominantor present only inDanian

no abruptfaunal change

sea-level fall decrease (12%)beginning atboundary

epifaunal speciespreferentially survive; only3 of 19 species (16%) thatrange across the boundaryare infaunal

above boundary yes, at P0^P1a and P1a^P1bboundaries. Also at K^Tboundary according toMacLeod and Keller (1991b)

Keller, 1988a,1992; Keller etal., 1995

El Kef, Tunisia upper bathyalshallowing tomiddle^outer neriticthen deepening toouter neritic

ca. 25‡N 31 species (about 50%)disappear just beneathor at boundary; 3species disappear justabove boundary

no speciesextinctionscoincide withK^T boundary

sea-level fall decrease (20%)beginning atboundary

change from normal-oxygen-condition speciesto low-oxygen-tolerantepifaunal and infaunalspecies


no, biostratigraphicallycontinuous

Speijer andVan Der Zwaan,1994, 1996

El Kef, Tunisia upper bathyal(300^500 m);somewhat shallowerin earliest Danian(middle^outerneritic)

ca. 25‡N 67% of speciesdisappear, but only30% disappear and donot return

worldwide, butdiachronous,benthicextinctions

sea-level fall andcooling

sudden diversityfall at boundary

preferential survival oftrochospiral (epifaunal)species ; opportunistic,low-oxygen-tolerantspecies dominateimmediately above thisboundary

at boundary no, biostratigraphicallycontinuous

Peyrt et al.,2002

A|«n Settara,Tunisia

outer shelf toupper slope

ca. 25‡N extinction of 5 genera.9 genera disappear butreturn in lower Danian

faunal turnoverand extinction

sudden diversity fallat boundary

extinction or temporaryemigration of mostinfaunal taxa

at boundary no, biostratigraphicallycontinuous; iridium anomalypresent


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Table 3Summary notes on environmental and benthic foraminiferal changes across the K^T boundary: deep-water (middle bathyal to abyssal) studies


Paleolatitude Taxonomic change across K^Tboundary



Epifaunal/infaunalchanges across boundary(based on morphotypes)


Disconformity/hiatusat/near boundary

Preservation

Thomas, 1990a,b Site 690, MaudRise, Weddell Sea,Antarctica

lower bathyal1500^2000 m

ca. 65‡S 7 species (8%) last occurclose to boundary

local lastappearances;not necessarilytrue extinction;no majorextinction event

epifaunal dominancepeaking just aboveboundary followed byrecovery of infaunal species

below and aboveboundary

yes, most of Zones P0and P1a are missing

calciteovergrown nearboundary

Webb, 1973 Site 208, LordHowe Rise,Tasman Sea

relatively deepwater; shallowerin Paleocene

ca. 45‡S 54% of benthic foraminiferabecome extinct at boundary(73% agglutinated species).14% extinction according toThomas (1990b)

extinction atboundary

sea-level fall sharp increase innumber ofcalcareous benthicspecies at base ofPaleocene

at boundary yes poorlypreserved,brokenspecimens inlowermostPaleocene

Dailey, 1983 Hole 516F, RioGrande Rise,western SouthAtlantic

middle to lowerbathyal

ca. 35‡S 28% of speciesdisappear in ¢nal0.5 my of Cretaceous; manynew species ¢rst appear in last1 my of Cretaceous

rapid faunalturnover withlocal extinctions

decrease of about20%

beginning belowand continuingabove boundary

no

Nomura, 1991 Site 752, BrokenRidge, easternIndian Ocean

several hundred to1000 m

ca. 55‡S 23 (12%) of 187species disappear at boundary

no majorextinction event

somewhat lowerspecies diversitynear the K^Tboundary

at boundary no, biostratigraphicallycontinuous

some chert-rich‘drillingbiscuits’ mayhave been lostin region ofboundary

Widmark andMalmgren,1992

Site 465, HessRise, North Paci¢c

lower bathyal1500 m

ca. 15‡N 13% of all species disappeared,5% when more rarely occurringtaxa are excluded^recalculatedto 44% and 22% disappearanceby Widmark (1997)


relative abundance ofinfaunal speciesunchanged acrossboundary

at boundary boundary within a30-cm mixed zone


Site 525,Walvis Ridge,South Atlantic

middle bathyal,1100 m

ca. 35‡S 40% of all species disappeared;23%when more rarely occurringtaxa are excluded


decrease in relativeabundance of infaunalspecies

at boundary no


Site 527, AngolaBasin, SouthAtlantic

abyssal, 2700 m ca. 35‡S 18% of all species disappeared;9% when more rarely occurringtaxa are excluded

no majorextinction

decrease in relativeabundance of infaunalspecies

at boundary no

Beckmann,1960

Trinidad, WestIndies

‘fairly deep sea’(lower slope toabyssal)

ca. 5‡N 39 of 215 species(18%) and 6 of 66 agglutinatedspecies(9%) do not cross the K^Tboundary

comparativelysmall changesat K^Tboundary

Beckmannet al., 1982

Monte Giglio,Italy

lower bathyal1500^2500 m

ca. 40‡N 34 of 52 species(60%) do notcross K^T boundary

yes, part of Maastrichtian,lower and part of middlePaleocene missing

Coccioni and Savel-li, 1983

Coldorso, Italy abyssal3000^4000 m

ca. 35‡N no signi¢cant change inassemblage across boundary

Kuhnt, 1990 Gubbio, Italy lower bathyal1500^2500 m

ca. 35‡N tubular agglutinated speciesdominate in uppermostCretaceous but decreasedrastically in number at K^Tboundary

epifauna dominatesuppermost Cretaceousand infauna lowermostDanian assemblages

at boundary

Kaminski et al. inMacLeod et al.,1997

Gubbio, Italy lower bathyal1500^2500 m

ca. 35‡N 80% reduction in numbers oftubular agglutinated species5 cm below K^T boundary

few speciesextinctions inlate Cretaceous

decrease in lateMaastrichtian

epifaunal suspensionfeeders dominate justbelow K^T boundary,infaunal bacteriovoresdominate just above

below boundary

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Table 3 (Continued).


Paleolatitude Taxonomic change acrossK^T boundary



Epifaunal/infaunalchanges across boundary(based on morphotypes)


Disconformity/hiatus at/nearboundary

Preservation

Kuhnt andKaminski, 1993

Sopelana, BasqueBasin, Spain

middle bathyal1000 m

ca. 35‡N 9 of 45 species (20%)do not cross boundary


epifaunal detritivores andsuspension feeders dominatejust below boundary; low-oxygen-tolerant andinfaunal species in lowerpart of boundary clay;higher-diversity infauna inupper part of boundaryclay

at boundary no, biostratigraphicallycontinuous (but most of P0except very lowermost partis missing according toMacLeod and Keller,1991b)

Peryt et al., 1997 Rotwandgraben,Austria

lower bathyal/abyssal2000 m

ca. 45‡N 15 of 46 species (33%) do notcross the boundary


decrease atboundary

mix of infaunalêpifaunalspecies in latestMaastrichtian; low-diversityinfaunalêpifaunalassemblage in lowermostDanian; mainly epifaunalspecies in upper part ofZone P0a; mix of infaunalêpifaunal species returns inZone P0b

at boundary no, biostratigraphicallycontinuous; iridiumanomaly present

Alegret et al., 2001 Tampico^Misantiabasin, Mexico

middle to lowerbathyal

ca 20‡N last occurrence of only2 species close to boundary.Mixed neritic/bathyal faunasimmediately above boundary

minorextinction

decrease in infaunal taxaat boundary

at boundary yes, boundary at base ofmass wasting unit accordingto Alegret et al., 2001.(This unit latestMaastrichtian channel ¢ll/fan according to Keller etal., 1997)


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177^226213

rarely occurring taxa are excluded) (Widmark andMalmgren, 1992). In the Angola Basin, South At-lantic (DSDP Site 527), 18% disappear (9% whenrarely occurring taxa are excluded) (Widmark andMalmgren, 1992). On Broken Ridge, eastern In-dian Ocean (ODP Site 752), 12% of species dis-appear (Nomura, 1991). On the Hess Rise, NorthPaci¢c (DSDP Site 465), 44% of species disappear(22% when rarely occurring taxa are excluded)(Widmark, 1997). In Trinidad, West Indies, 18%of species do not cross the boundary (Beckmann,1960); later revised to 32% (Beckmann et al.,1982). At Monte Giglio, Italy, 60% do not crossthe boundary (Beckmann et al., 1982). At Sope-lana, Spain, 20% of agglutinated species do notcross the boundary (Kuhnt and Kaminski, 1993).And at Rotwandgraben, Austria, 33% of aggluti-nated species do not cross the boundary (Peryt etal., 1997).Many variables a¡ect these data, including a

large hiatus at Monte Giglio (Beckmann et al.,1982), several grouped taxa at El Kef (Speijerand Van Der Zwaan, 1996), reference to only‘common’ species rather than complete assem-blages (Keller et al., 1998), di¡erent facies aboveand below the boundary (e.g., Huber, 1988), rarespecies sometimes included and sometimes not(e.g., Webb, 1973; Thomas, 1990b), Lazarustaxa sometimes identi¢ed (e.g., Speijer and VanDer Zwaan, 1996) and sometimes not. However,if the percentage data are taken at face value andaveraged for shallow, intermediate and deepwater, the results come out as follows: shallow,40% disappear; intermediate 35% (using maxi-mum ¢gures), or 29% (using minimum ¢gures)disappear; deep 32% (maximum) or 22% (mini-mum) disappear (the ¢gures for deep-water stud-ies reduce to 29% maximum and 19% minimumwhen Monte Giglio is excluded). Although thereis a weak trend of decreasing values with increas-ing depth, this pattern of approximately one thirddisappearance/extinction/turnover, no matterwhat the depth, does not strongly support theoft-stated and generally accepted idea that shal-low-water benthic foraminifera were more se-verely a¡ected by environmental events acrossthe K^T boundary than intermediate- or deep-water faunas.

Indeed, because temporary disappearances arenot re£ected in many of these percentages, onethird is probably a grossly in£ated ¢gure no mat-ter what the water depth. For example, the reviewof Kaiho (1994) concluded that only 5^14% ofcalcareous benthic foraminiferal species fromwater depths of 150^3000 m became extinct atthe K^T boundary. The most di⁄cult variableto deal with when trying to elucidate changes inbenthic foraminifera across the K^T boundary isthe descriptive terminology used by the variousauthors. The previous few paragraphs includethe terms/phrases, ‘disappear’, ‘turnover’, ‘donot cross boundary’, ‘became extinct’, ‘disappearpermanently’, ‘last occur close to the boundary’.Perhaps the best way to circumvent this problemis to examine the summary statements by variousauthors of whether or not there was a mass ex-tinction or abrupt faunal change in benthic faunasacross the K^T boundary. Only Huber (1988),Speijer and Van Der Zwaan (1994, 1996) andWebb (1973) indicate that major extinctionstook place (Tables 1^3); that is, one examplefrom shallow, one from intermediate and onefrom deep water. In the study of Huber (1988),however, although there is a 64% turnover of spe-cies across the boundary (Table 1), 26 of 32 low-ermost Tertiary species (81%) range through fromthe Cretaceous; and this is despite a shift fromneritic silts in the Maastrichtian to laminated siltrepresenting a low-oxygen environment in theDanian. In the study of Speijer and Van DerZwaan (1994, 1996), only 30% of the Cretaceoustaxa do not reappear; and the estimate of Webb(1973) of 54% extinction was reduced to 14% byThomas (1990b), who excluded rare taxa (less re-liable data) from her calculations using Webb’sdata.Aside from the Seymour Island data (Huber,

1988) which are a¡ected by facies shifts, the larg-est ¢gure for species disappearances in shallowwaters is approximately 50% for the Brazos Rivercore in Texas (Keller, 1992). Of course, Keller didnot infer a mass extinction because many speciesreappeared in the Danian when favorable condi-tions returned (Keller, 1992). Widmark (1997)suggested that the amount of disappearance inthe Brazos River core was possibly an artifact

MARMIC 899 28-1-03


resulting from a hiatus in the latest Maastrichtianand the fact that Keller placed the K^T boundaryabove the so-called tsunami beds (Keller, 1989,1992), a placement in agreement with Jiang andGartner (1986) but in con£ict with other studies(e.g., Montgomery et al., 1992; Smit et al., 1994;Rudolph et al., 1995) which place the ‘tsunami’beds just above the boundary (at least 230 000years after the boundary according to Montgom-ery et al., 1992).The largest ¢gure for disappearances in inter-

mediate depth waters is 67% (Speijer and Van DerZwaan, 1994, 1996) but we have seen above that,in fact, only 30% of taxa do not return. In deepwater, Beckmann et al. (1982) found that 60% ofspecies do not cross the K^T boundary. This ¢g-ure actually indicates surprisingly high faunal sim-ilarity between upper Cretaceous and Paleocenestrata because part of the Maastrichtian, the low-er Paleocene and part of the middle Paleocene aremissing at Monte Giglio (Beckmann et al., 1982).In summary, the published data (abstracted in

Tables 1^3), even if taken at face value, do notsupport the idea that shallow-water benthic fora-minifera were a¡ected more severely than deeperspecies at/across the K^T boundary. But thesedata should not be taken at face value becausethe amount of true extinction, as compared tolocal extinction (sometimes followed by returningLazarus taxa) and/or mass mortality, is generallyquite low (probably considerably and signi¢cantlylower than one-third, but, unfortunately, thenumbers of Lazarus taxa are not always given)no matter what the water depth in the latest Cre-taceous. This conclusion di¡ers from that drawnby Widmark (1997), who reviewed the publisheddata and concluded that a bathymetric signalcould be recognized. His opinion, however, was,in essence, guided by the results of only two stud-ies, Widmark and Malmgren (1992) and Thomas(1990b), each of which compared two deep-watersites at middle-bathyal to upper-abyssal depths.

5.2. Latitudinal pattern

It is unclear whether or not there is a latitudinalpattern of faunal change across the K^T bound-ary, again because of methodological and presen-

tational di¡erences in the data sets. First, thereare only two usable data points in low latitudes(6 20‡N or S), Trinidad and Site 465 in the Pa-ci¢c. Second, as discussed above, some of thelarger estimates of disappearances/extinctions/turnovers are signi¢cantly in£ated for various rea-sons. Third, the New Zealand data point (Kaiho,1988) almost certainly represents an incompletedata set (only 13 species were recorded in thelate Cretaceous). Fourth, there are no data fromnorthern high latitudes greater than 45‡N.When New Zealand and Monte Giglio are ex-

cluded from the data and minimum values areincorporated, the average disappearance/extinc-tion/turnover for latitudinal segments is as follows(data from all depths are incorporated because nobathymetric pattern has yet to be conclusivelydemonstrated): greater than 40‡N, 26%; 20^40‡N, 34%; 0^20‡N, 20%; 0^20‡S, no data; 20^40‡S, 20%; greater than 40‡S, 25%. Combiningthe northern and southern data results in: greaterthan 40‡N and S, 25%; 20^40‡N and S, 30%; and0^20‡N and S, 20%.Although these percentages do not reveal a

strong, distinct latitudinal pattern, they do con-tain a hint that high latitudes and low latitudeshave lower rates of disappearance/extinction/turn-over than mid-latitudes. If boundaries for calcu-lation are placed at 45‡N and S rather than at40‡N and S (and New Zealand and Monte Giglioare excluded), the following average ¢gures fordisappearance/extinction/turnover result : 0^20‡Nand S, 20%; 20^45‡N and S, 29%; greater than45‡N and S, 24%. Is this a valid latitudinal pat-tern? The inconsistencies in the data and, in par-ticular, the lack of good data on local versus trueextinction in the entire data set, but particularly inthe mid-latitudes, suggest it is not. Thus, it is pre-mature to form hypotheses explaining a latitudi-nal pattern of disappearance/extinction/turnoveruntil a data set is constructed that reliably dem-onstrates such a pattern.The review of Widmark (1997) tentatively

reached a di¡erent conclusion. He considered itdi⁄cult to assess the latitudinal pattern becausedata are from di¡erent depths. However, his anal-ysis of a small subset of the available benthic fo-raminiferal data, a comparison of the low-latitude

MARMIC 899 28-1-03


Site 465 with high-latitude Sites 689, 690 and 738revealed a 2^3 times higher extinction rate at thelow-latitude site (22^42% disappearance com-pared to 9^14% and 12% disappearance). The ¢g-ure of 22^42% disappearance at Site 465 di¡ersfrom the previously published ¢gures of 5^13%disappearance at the same site (Widmark andMalmgren, 1992). Widmark (1997), however, re-calculated the percent taxonomic disappearancebecause he believed the 5^13% ¢gures were arti¢-cially low due to his inclusion of three samplesfrom a 30-cm-thick mixed zone of Maastrichtianand Danian sediments in the basal Danian. Byexcluding these samples, a higher percent disap-pearance (22^42%) resulted, yielding values simi-lar to mid-latitude Site 525 (Widmark, 1997).Widmark (1997) suggested that the recalculateddata indicate that tropical faunas were more se-verely a¡ected by events at the K^T boundary butacknowledged that more data are needed to verifythis conclusion. It is of interest to note that Raupand Jablonski (1993) did not detect latitudinalgradients in extinction intensities of marine bi-valves at the K^T boundary but MacLeod andKeller (1994) and MacLeod (1995b) did forplanktonic foraminifera.

5.3. Temporal pattern

Much debate has centered on the temporal pat-tern of biotic change across the K^T boundary,speci¢cally on whether the disappearances/extinc-tions/turnovers were sudden or spread out over amore extended interval of time (e.g., see Smit,1982; Brinkhuis and Zachariasse, 1988; Keller,1988b, 1997; Olsson and Liu, 1993; Keller etal., 1995; D’Hondt, 1996; Huber, 1996; MacLeodand Keller, 1996; MacLeod et al., 1997; Smit andNederbragt, 1997; Hudson, 1998; Pardo et al.,1999; Arenillas et al., 2000a,b, and their includedreferences). Of course, recognition of whether ornot biotic change occurred at the boundary de-pends on the presence of a complete section. Aswith any other facet of K^T boundary study,great debate centers on the presence or absenceof gaps in the record at the boundary and whethergaps occur di¡erentially in various paleobathy-metric settings. Further, whether a hiatus occurs

at the boundary or not depends on where oneplaces the boundary.Using a graphic correlation approach, Mac-

Leod and Keller (1991a,b) and MacLeod(1995a) concluded that most deep-sea sites exhibitK^T boundary hiatuses whereas outer neritic toupper bathyal settings (El Kef, Caravaca, Agost,Brazos River) are stratigraphically more completeacross the boundary, although hiatuses occur lat-er in the Danian. MacLeod and Keller (1991a,b)suggested that apparently instantaneous mass ex-tinctions of marine plankton may be artifacts ofan incomplete stratigraphic record in the deep sea.Olsson and Liu (1993) took issue with Mac-

Leod and Keller’s conclusions and, followingtheir own review of the stratigraphic data, con-cluded that prolonged extinctions of planktonicforaminifera at El Kef, Tunisia (Keller, 1988b)and Brazos River, Texas (Keller, 1989), as wellas Brinkhuis and Zachariasse’s late Cretaceousand prolonged Paleocene extinctions of the plank-ton in Tunisia (Brinkhuis and Zachariasse, 1988),resulted from placement of the boundary basedon equivocal criteria, asynchronous placement ofthe boundary at di¡erent sections, and the treat-ment of reworked Cretaceous species occurring inthe lower Paleocene as survivor species (Olssonand Liu, 1993). Olsson and Liu (1993) did agreewith MacLeod and Keller (1991a,b) in consider-ing the K^T boundary to be represented in con-tinuous sections at El Kef and Agost. They dis-agreed, however, in considering the record at Site577 to be continuous. Further, Olsson and Liu(1993) believed that non-recognition of Zone P0at some deep-sea sites is due to very low sedimen-tation rates and the temporally short interval rep-resented by Zone P0.Despite some agreement, the uninitiated are left

with two quite convincing arguments that are al-most diametrically opposed. Remembering thatthe apparent timing of faunal change can be af-fected by completeness of the stratigraphic record,can the opinions of the many authors of benthicforaminiferal papers shed any light on these argu-ments? Tables 1^3 summarize the data and opin-ions. A pattern in these data, again with somecontradictions, is apparent. Opinions on the tim-ing of faunal changes for deep-water studies are

MARMIC 899 28-1-03


available for 12 localities (Table 3). Nine of these12 indicate that faunal changes took place at theboundary. Of these nine, two localities (Site 208and Tampica^Misantia basin) have a recognizablehiatus at the K^T boundary, one (Site 465) hasthe boundary occurring in a mixed zone and ¢ve(Site 752, Site 525, Site 527, Sopelana, and Rot-wandgraben) are considered by the original au-thors to have a continuous section. At three local-ities (Site 690, Site 516, Gubbio) faunal changesoccur below the K^T boundary. Note that Kellerand Stinnesbeck (1996) and Keller et al. (1997)place the K^T boundary in the Tampica^Misan-tia basin at a di¡erent level than Alegret et al.(2001).At intermediate water depths, seven localities

can be considered (Table 2). Of these, three, Ca-ravaca (Keller, 1992; Coccioni et al., 1993; Coc-cioni and Galeotti, 1994), El Kef (Speijer and VanDer Zwaan, 1994, 1996) and A|«n Settara, only 50km from El Kef (Peyrt et al., 2002), exhibit fora-miniferal assemblage changes commencing at theK^T boundary. At other localities (Site 738, Hok-kaido, Agost) and at El Kef, according to Keller(1988a) biotic changes commenced below the K^Tboundary. At Negev^Sinai, changes occurredabove the boundary (Keller, 1992).In shallow water, two data points in Texas (Si-

kora, 1984; Keller, 1992) and one in Tunisia (Kel-ler et al., 1998) are available. In all three studies,biotic change commences below the boundary. Ofcourse, some ‘below the boundary’ changes atBrazos River (Keller, 1992) may possibly be ‘atthe boundary’ if the placement of the boundary ofOlsson and Liu (1993) is accepted.Thus, it seems that, in general, faunal changes

begin before the K^T boundary in shallow andarguably, in intermediate-depth water. In compar-ison, in deep water, the preponderance of local-ities exhibit faunal change at the boundary andthe majority of those localities are considered bythe original authors to be stratigraphically contin-uous. However, if the model of less completedeep-sea sections of MacLeod and Keller(1991a,b) is correct (but graphic correlation anal-yses of some of the sections in question are cur-rently lacking), then these ‘at the boundary’changes could be artifactual.

Widmark (1997) reviewed the pattern and tim-ing of recovery of benthic foraminiferal commun-ities in the Danian. Again, contradictory resultsare evident. At El Kef, Keller (1992) and Speijerand Van Der Zwaan (1996) independently deter-mined that environmental conditions returned to‘normal’ by 250^300 ka after the K^T boundary.In sharp contrast, in only slightly deeper water atCaravaca, Coccioni and Galeotti (1994) con-cluded that normal conditions returned about7 ka after the boundary. Kuhnt and Kaminski(1993) found an intermediate recovery time inter-val of 50^100 ka for agglutinated foraminifera atSopelana. Widmark (1997) pointed out that com-parisons such as these are hard to evaluate be-cause of the lack of standardization of Danianbiostratigraphic zonal duration and di¡erent zo-nal designations. Other problems occur in theDSDP/ODP cores, namely quite low resolutionsampling and insu⁄cient temporal range of sam-pling in the Danian (Widmark, 1997).These recovery times are also di⁄cult to recon-

cile with carbon isotopic studies of planktic andbenthic foraminifera. D’Hondt et al. (1998) ar-gued that marine primary production may haverecovered within a few thousand years after theboundary but that a smaller proportion of thatproduction reached the deep-sea £oor in thepost-extinction ocean. The planktic to benthicN13C di¡erences recovered to pre-extinction levels¢rst in shallow waters and much later (3 millionyears into the Danian) in the deep ocean.

5.4. Ecological pattern

Until the 1960’s, all foraminifera were generallybelieved to live at the surface of the seabed (Cush-man, 1948; Myers and Cole, 1957). It was thendemonstrated, ¢rst in shallow waters (e.g.,Richter, 1961; Buzas, 1965) and later in deepwater (e.g., Corliss, 1985; Corliss and Emerson,1990), that foraminifera could live and reproducewithin the sediment. Particular foraminiferal mor-phologies were then suggested as being character-istic of epifaunal and infaunal habitats and tro-phic structure (e.g., Jones and Charnock, 1985;Corliss and Chen, 1988; Denne and Sen Gupta,1989; Koutsoukos and Hart, 1990).

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It now seems to be widely accepted that epifau-nal species are dominated by trochospiral testmorphologies and that they are less tolerantthan infaunal species to low-oxygen conditions.Infaunal species are either elongate in shape, oftencomposed of uniserially, biserially or triseriallyarranged chambers, or are planispirally coiled(Corliss, 1985, 1991; Corliss and Chen, 1988;Corliss and Emerson, 1990). Infaunal speciessupposedly £ourish in environments where foodsupply is high and oxygen is low (Jorissen,1999). The result of this wide acceptance is thatpapers routinely contain ecological inferencesbased on proportions of putatively infaunal andepifaunal species (see Tables 1^3).Is this general acceptance of the morphology^

microhabitat correlation appropriate? I wouldargue that this analytical approach should beused with considerable reserve because of variouscompounding factors. For example, several stud-ies have shown that benthic foraminifera not onlycan be surprisingly mobile (e.g., Severin and Er-skian, 1981; Kitazato, 1988; Wetmore, 1988;Bornmalm et al., 1997) but many taxa can changetheir typical microhabitat within hours. Severin etal. (1982) ran experiments where they buried liv-ing, shallow-water foraminifera (a single species)under several centimeters of sediment. The fora-minifera rapidly moved to the upper centimetersof sediment where they moved around as mem-bers of the shallow infauna. Some individualsthen migrated onto the surface and moved aroundas members of the epifauna before diving backinto the subsurface. Linke and Lutze (1993) laterobserved that some species are strictly infaunalbut many change from infaunal to epifaunal ina response to food availability or changing envi-ronmental conditions. Buzas et al. (1993, p. 311)observed that ‘Tas more observations are made, itbecomes increasingly di⁄cult to assign a speciesexclusively to a speci¢c habitat category’. Buzas etal. (1993) also believed that the term ‘epifaunal’had been applied too loosely to species that live inthe top 1 cm of sediment. They pointed out(p. 312) that ‘One centimeter of sediment for a 100Wm diameter foraminiferan is equivalent to a 2 mperson buried within 200 m of sediment!’ Buzas etal. (1993) suggested that ‘shallow infaunal’ would

be a much more appropriate term for an individ-ual living within the top 1 cm of sediment. Theirstudy also showed that assignment of taxa intoshallow infaunal and deep infaunal habitat cate-gories on the basis of their morphology had anaccuracy of only 75%.Jorissen (1999) recently reviewed the subject of

benthic foraminiferal microhabitats and their re-lation to foraminiferal morphology. He pointedout that infaunal taxa may exhibit great variationin living depth from site to site and from time totime at a single site (e.g., Corliss, 1985; Corlissand Emerson, 1990; Barmawidjaja et al., 1992;Alve and Bernhardt, 1995; Kitazato and Ohga,1995). Even more signi¢cantly, he noted severaltimes that the close relationship between test mor-phology and microhabitat is assumed and not ob-served, and is based on the distribution of porepatterns in modern foraminifera (Corliss, 1991;Jorissen, 1999). He described the separation be-tween epifaunal and infaunal taxa as drawn atan arbitrary boundary and pointed out that spe-cies such as Cibicides wuellerstor¢, which has amorphology that is classically epifaunal (Lutzeand Thiel, 1989), have been found quite oftenwith considerable infaunal populations (e.g., Jo-rissen et al., 1988; Corliss, 1991).I have devoted quite a few words to the topic of

foraminiferal morphology and microhabitats be-cause the relationship is usually accepted andquite complex paleoecological scenarios are oftenconstructed. Although the relationship for manytaxa is assumed rather than demonstrated (Joris-sen, 1999), nevertheless, it appears it may be ac-curate about 75% of the time (Buzas et al., 1993).As Jorissen (1999, pp. 175^176) concluded, allgeneralizations have signi¢cant exceptions, but‘Tit cannot be denied that there is a relationshipbetween test morphology and microhabitat’.With these cautionary words in mind, what is

the pattern of epifaunal^infaunal change acrossthe K^T boundary? At shallow water depthsthere are only two data points. At Brazos River,Texas, the faunas are almost entirely infaunal onboth sides of the boundary (Keller, 1992). AtMillers Ferry, Alabama, the fauna changes frominfaunal in the Maastrichtian to epifaunal in theDanian (Olsson et al., 1996) (Table 1).

MARMIC 899 28-1-03


At intermediate water depths, the pattern is notuniversal but there does appear to be a domi-nance (often termed ‘preferential survivorship’)of epifaunal species in the early Danian (Table2). This change sometimes commences prior tothe boundary (Coccioni and Galeotti, 1994; Par-do et al., 1996). At Caravaca, Spain, Coccioni andGaleotti (1994), however, described a short-livedincrease in abundance of infaunal species in theearliest Danian. It may well be that this event hasnot been recorded elsewhere because of less densesampling schemes.In deeper water (Table 3) this short-lived event

is recorded at Gubbio, Italy (Kuhnt, 1990; Ka-minski in MacLeod et al., 1997), Sopelana, Spain(Kuhnt and Kaminski, 1993), and Rotwandgra-ben, Austria (Peryt et al., 1997). Otherwise, thegeneral pattern of epifaunal dominance in theearly Danian again is apparent. Later in the Dan-ian, mixed infaunal^epifaunal communities return(e.g., Kuhnt and Kaminski, 1993; Peryt et al.,1997).Widmark (1997), in his review of benthic fora-

miniferal ecology and morphotypic changesacross the K^T boundary, clearly demonstratedthe danger in accepting this general pattern ofepifaunal dominance/preferential survivorship inthe early Danian. He pointed out that at theSouth Atlantic Site 525 (Widmark and Malmgren,1992) the late Cretaceous mixed epifaunal^infau-nal assemblage changes via the disappearance ofseveral abundant infaunal species at the bound-ary. However, simultaneous with their disappear-ance, other infaunal species increase in abun-dance. This pattern is also seen at Paci¢c Site465 where the Danian infaunal component ac-tually outnumbers the epifaunal component (Wid-mark and Malmgren, 1992). Widmark (1997)speculated that an excess of Caþ in the earliestTertiary Ocean, resulting from the extinction ofvarious calcareous plankton, favored heavily cal-ci¢ed infaunal species and these forms increasedin number.The general pattern of infaunal disappearance

and epifaunal dominance in the early Danian isgenerally explained by a sudden decline of pri-mary productivity at the K^T boundary, and,therefore, the cessation of organic carbon £ux to

the sea£oor (e.g., Thomas, 1990b; Widmark andMalmgren, 1992; Alegret et al., 2001; Peyrt et al.,2002). This would cause the decline in infaunaltaxa that typically are adapted to low-oxygen con-ditions/high food supply. This general pattern isinterrupted (more precisely, preceded) by theshort-term event immediately after the boundarywhere the boundary clay contains a low-diversityinfaunal assemblage that may well represent anopportunistic community responding to a largebut short-lived input of organic matter, and re-lated low-oxygen conditions, resulting from thesudden mass mortality of surface water-dwellingoceanic plankton (Kuhnt and Kaminski, 1993;Coccioni and Galeotti, 1994; Kaminski in Mac-Leod et al., 1997).At A|«n Settara, Tunisia, early Danian sediment

contains low-diversity foraminiferal assemblagesdominated by epifaunal morphogroups, indicativeof extreme oligotrophic conditions (Peyrt et al.,2002). At El Kef, just 50 km to the north, similarlow diversity and dominance were attributed tolow-oxygen conditions, an interpretation basedon the presence of laminated sediments resultingfrom the lack of burrowing macrofauna (Keller,1988a; Speijer and Van Der Zwaan, 1996). Peyrtet al. (2002) pointed out, however, that there is nogeochemical indication of low-oxygen conditions(Tribovillard et al., 2000) and that the lack ofburrowing could simply be related to the K^Tmass extinction of burrowing invertebrates. Theyargued further that the low-diversity assemblagesimmediately above the K^T boundary may havebeen caused by environmental stress resultingfrom changes in the nature of the phytoplankton£ux to the sea£oor. The late Cretaceous primaryproducers, calcareous nannofossils, su¡ered a ma-jor extinction (Romein and Smit, 1981) and soearly Danian benthic foraminifera were left witha changed food supply composed mainly of dino-£agellates, a group that did not experience massextinction (Brinkhuis et al., 1998).Food, therefore, and related oxygen conditions,

are seen as prime ecological factors in controllingbenthic foraminiferal assemblage changes acrossthe K^T boundary (Widmark, 1997). Widmark(1997) further speculated that shallow bathyalfaunas were better adapted to eutrophic condi-

MARMIC 899 28-1-03


tions than deeper, oligotrophic communities andso were harder hit when food supplies failed in theearly Danian. However, as noted above, a bathy-metric pattern is not readily apparent in the avail-able data. Widmark (1997) applied a similar argu-ment to explain lower extinction rates in the highlatitudes. But again, as we have seen above,a simple latitudinal pattern of faunal changeis not clearly demonstrated at the K^T bound-ary.

6. Summary and conclusions

Benthic foraminiferal communities changed incomposition in response to sea-level change inthe late Maastrichtian continuing into the Dan-ian. These changes were punctuated by a bolideimpact at the K^T boundary.The e¡ects of that impact on the benthic fora-

minifera are, however, unclear. Contrary to mostprevious reports, there is no demonstrable, paleo-bathymetric gradient in severity of biotic re-sponse. There are species extinctions, but theseare generally local extinctions and Lazarus speciesreturn to their former habitats at varying intervalsof time after the boundary. Even in the Gulf ofMexico, very close to K^T ‘ground-zero’, shallow-water benthic foraminiferal communities do notexhibit a mass extinction.In deeper waters, some sites preserve an appar-

ently short-lived, opportunistic, low-diversity as-semblage composed of infaunal species that mayhave increased in abundance in response to amass mortality of surface plankton that sent largeamounts of organic matter to the sea£oor anddepleted the upper layers of sediment of its dis-solved oxygen. This short-lived event is superim-posed upon the longer-term phenomenon of low-ered surface productivity and hence reducedorganic £ux to the sea£oor in the early Danian.These oligotrophic conditions would have favoredthe development of epifaunal-dominated assem-blages (cf., Corliss and Emerson, 1990). Depend-ing on location (i.e., regional environmental var-iation), faunas recovered to pre-boundaryconditions by the return of largely infaunal, Laza-

rus taxa, over varying intervals of time during the¢rst 300 kyr of the Danian.Contrary to previous reports, the published

data when considered in toto do not reveal a dis-tinct latitudinal pattern of change cross the K^Tboundary. The inconsistent nature of the micro-paleontological data at hand make it unlikely thatthese data can or should be used for any seriousbiogeographic hypothesis testing.The available stratigraphic data have also

weaknesses and inconsistencies that seriouslyhamper realistic interpretation of timing of faunalchange. Hiatuses occur at the boundary and inthe Danian, but whether or not there is a depth-related pattern, with shallow-water sections beingmore continuous across the boundary than deep-er-water sections, is the subject of vigorous de-bate. It does seem, however, that faunal changemay have commenced in the late Maastrichtian inshallow and intermediate water depths but at theboundary in deep water. This makes sense if theMaastrichtian biotic changes are a response tosea-level change or other non-impact-related pro-cesses (e.g., Je¡ery, 2001).Benthic foraminifera survived late Maastricht-

ian environmental instability and end-Cretaceousbolide impact rather well, whether they were shal-low or deep dwellers, or high-latitude or low-lat-itude forms, or dwellers in infaunal or epifaunalhabitats. Even where foraminiferal community re-sponse to the end-Cretaceous event was severe,within a few thousand to a few hundred thousandyears, Lazarus taxa returned from their refugia toreconstruct essentially late Cretaceous faunal as-semblages.

Acknowledgements

I thank Brian Huber for suggesting that I writethis paper. Brian Huber, Norm MacLeod, ScottSnyder and Marty Buzas kindly provided sub-stantive reviews before submittal. Gerta Keller,Mark Leckie and Kunio Kaiho did the same aftersubmittal. Dare Merritt, Leah Fuller, MeganMurphy and Chris Smith provided invaluabletechnical help.

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