document08

The Cretaceous^Tertiary (K^T) mass extinction in plankticforaminifera at Elles I and El Melah, Tunisia

Narjess Karoui-Yaakoub a;*, Dalila Zaghbib-Turki a, Gerta Keller b

a Faculte des Sciences de Tunis, De¤partement de Ge¤ologie Campus Universitaire, 1060 Tunis, Tunisiab Geosciences, Princeton University, Princeton, NJ 08544, USA

Received 1 July 1999; accepted 9 August 2001

Abstract

Planktic foraminiferal faunas across the K^T transition at Elles and El Melah in northwestern and northeasternTunisia, respectively, reveal patterns of species extinctions and species survivorship similar to those found at the El Kefstratotype and the Ain Settara sections. Slightly more than 2/3 of the species disappeared at or before the K^Tboundary event and slightly less than 1/3 survived into the Danian where most disappeared sequentially within zone P1a(Parvularugoglobigerina eugubina). Relative species abundance patterns reveal that the 13^16 K^T survivors dominated(80%) the assemblages in the latest Maastrichtian, whereas the K^T extinct species were rare and totaled less than 20%of the total assemblages.

The K^T survivors are generally small with little surface ornamentation and geographically widespread from low tohigh latitudes. In contrast, K^T extinct species are large, highly ornamented and geographically restricted to lowlatitudes. This indicates that the K^T mass extinction was selective, rather than random, and predominantly affectedthe less robust tropical species. With the exception of the opportunistic Guembelitria species which dominate the earlyDanian, most K^T survivor species suffered severely as is evident by the decreased species populations after the K^Tevent. Their eventual demise appears to have been related to post-K^T environmental changes and competition fromevolving Tertiary species. These results reveal a complex mass extinction pattern that in addition to the K^T impactevent is keyed to long-term environmental changes preceding and following this event. ß 2002 Elsevier Science B.V.All rights reserved.

Keywords: K^T boundary; mass extinction; Tunisia

1. Introduction

The Cretaceous^Tertiary (K^T) boundary massextinction in planktic foraminifera is well knownfrom the El Kef stratotype (e.g. Smit, 1982;Brinkhuis and Zachariasse, 1988; Keller, 1988,

1995; Keller et al., 1995; Ben Abdelkader, 1995;Ben Abdelkader et al., 1997) which for the mostpart has de¢ned the extent of the biotic catastro-phe in low latitudes. This is largely because the ElKef section has remained the most expanded andcontinuous sediment record of this boundaryevent known to date worldwide (Keller, 1996).In recent years, continued research in Tunisiahas uncovered several new K^T boundary transi-tions, including the deeper water El Melah section

0031-0182 / 02 / $ ^ see front matter ß 2002 Elsevier Science B.V. All rights reserved.PII: S 0 0 3 1 - 0 1 8 2 ( 0 1 ) 0 0 3 9 8 - 4

* Corresponding author. Fax: +216-1-871-666.E-mail address: [email protected] (G. Keller).

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in the northeast, the Elles and Ain Settara sec-tions to the northwest and north of the KasserineIsland which were deposited at middle to outerneritic depths, and the inner neritic Oued Seljasection south of the Kasserine Island and at theedge of the Sahara platform (e.g. Karoui et al.,1995; 1996; Keller et al., 1998; Molina et al.,1998; Dupuis et al., 1998; 2002; Karoui-Yaa-koub, 1999; Zaghbib-Turki et al., 2000; 2001)(Fig. 1).

We report here on the planktic foraminiferalturnovers of two of these sections: Elles and ElMelah. El Melah is unique in that it represents adeeper more open ocean environment than any ofthe other sections and Elles appears to have anexpanded K^T transition equal to the El Kef stra-totype. The propitious discovery and analysis ofthese new K^T transitions (by N.K.-Y.) comes ata time when the El Kef stratotype is itself endan-gered by oversampling and agricultural encroach-ment. Alternative and equally continuous K^Tboundary transitions, like Elles, are therefore anecessary and welcome addition to El Kef.

The Elles sequence is located 75 km southeastof El Kef in a valley near the hamlet of Elles(Fig. 1) where sediments spanning from Campa-nian to lower Eocene are continuously exposed.The K^T transition outcrops in numerous placesand can be traced over hundreds of meters alongthe slopes of the valley. Therefore, oversamplingis not a concern, unlike at El Kef, nor is there anydanger of obliteration due to agricultural en-croachment because of the steep valley slopes.For biostratigraphers interested in the K^T massextinction as well as environmental changes be-fore and after this event, the Elles section o¡ersthe necessary continuous outcrops that are largelymissing at the El Kef and other Tunisian sections.

The late Cretaceous to early Tertiary sequenceat Elles was ¢rst reported by Pervinquiere (1903)who noted the expanded Cretaceous^Tertiarysedimentary record, which was later con¢rmedby Said (1978) who documented the biostratigra-phy based on ostracods and planktic and benthicforaminifera. Said’s study was done at about 1 mintervals and consequently did not specify the K^T boundary transition. Karoui-Yaakoub (1999)and this study re-examined this section and lo-

cated the K^T transition based on the same litho-logical changes and planktic foraminiferal extinc-tions and evolutions as at the El Kef stratotype(see also Karoui and Zaghbib-Turki, 1998),whereas Robin et al. (1998) identi¢ed the K^Tspinel horizon and Rocchia (Zaghbib-Turki etal., 2000) identi¢ed the Ir anomaly. In addition,ostracods of the Elles section have been re-exam-ined in a recent study by Said-Benzarti (1998).

This study details the planktic foraminiferalbiostratigraphy, mass extinction and faunal turn-over across the K^T transition at Elles from twodi¡erent sample sets of the same outcrop which ishere labelled Elles I. The ¢rst sample set detailsthe species ranges from the latest Maastrichtianthrough the Danian. The second sample set wassubsequently taken for direct comparison with El

Fig. 1. Paleogeography of Tunisia during the late Maastricht-ian and early Tertiary with paleolocations of the K^Tboundary sections (modi¢ed after Burollet, 1967).

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Kef for the interval from 0.5 m below to 0.8 mabove the K^T boundary. This study shows thesimilarities between El Kef and Elles in speciesextinctions, survivorship and relative abundancechanges and generally con¢rms the pattern previ-ously revealed at El Kef (e.g. Keller et al., 1995)and also con¢rmed at Ain Settara (see Luciani,2002). In addition, we present the biostratigraphyand species ranges at El Melah.

2. Location and lithology

2.1. Elles section

The Elles section, located about 75 km south-east of the town of El Kef and near the hamlet ofElles, can be reached by the road from Maktar toSers. About 26 km along this road is a turno¡ toan unpaved road leading to the village of Elles.About 7 km along this road and prior to reachingthe village, there is a house on top of Campanianlimestones and behind it, the begin of a wide val-ley cut by the Karma river (usually dry). TheKarma valley is about 4 km long. Coming upthrough the valley (about 3 km), one passesthrough thick light gray late Campanian to earlyMaastrichtian limestones of the Abiod Formationwhich are rich in inoceramids, stegasters and ich-nofossils. This interval is followed by gray marlsinterspersed with about seven to eight 20 cm thickresistant marly limestone layers with fewer macro-fossils (e.g. Stegaster, Micraster and Holectypoids,see Li and Keller, 1998a; Zaghbib-Turki et al.,2000). Above this interval, gray marls of the ElHaria Formation continue for about 200 m wherethe valley forks. The right side fork has steepsides of gray marly shales with a few thin marlylimestone layers. The Elles I outcrop (Karoui-Yaakoub, 1999) is located in this valley about200 m past the fork on the left side wall. Addi-tional K^T outcrops, including Elles II (see Kelleret al., 2002) are located on the right side of theleft valley fork.

The K^T transition at Elles I is exposed on theleft side slope (of the right valley fork) about 12^14 m up from the valley £oor and marked by darkgray shales and clays. Near the base the slope is

covered by debris and only about 7^8 m are ex-posed below the K^T boundary. These latestMaastrichtian sediments consist of gray shales,marly shales and several thin resistant marly lime-stone layers between 4 and 7 m below the K^Tboundary. Although these resistant limestonelayers can be traced through both valley forks,the meter distance to the K^T boundary mayvary as a result of local erosion or topography.

The K^T transition is well marked by a 5^7 cmthick bioclastic packstone at Elles I. But the thick-ness of this bioclastic layer is laterally variableand may reach 25^30 cm in some outcrops, espe-cially in the valley to the left of the fork (e.g. EllesII, Keller et al., 2002). Above this bioclastic layeris a 0.5^1.0 cm thick clay layer followed by a 3^4mm thick rusty red layer associated with two thingypsum layers. This red layer marks the K^Tboundary event and contains altered spherules,spinels (enriched in Cr and Ni) and anomalousconcentrations of iridium (Robin et al., 1998;Zaghbib-Turki et al., 2000). Above this interval,the basal Danian consists of a 50^60 cm thickdark gray to black clay layer followed by 6 mof gradually lighter colored clayey shales andshales. Upsection, between 7.5 and 12 m grayshales are interbedded with several thin resistantmarly limestone layers followed by another 8 m ofmarly shales which grade into rhythmically inter-bedded limestone and marl layers.

2.2. El Melah section

The El Melah section is located in northeasternTunisia about 36 km west from the town of Ma-teur and 3 km southeast of the village of El Aoua-na. The section can be reached by taking the roadleading from Mateur to Sejnene. About 16 kmbefore Sejnene at a locality marked by the cross-ing of the Oued El Maleh river is a chalk quarry.From here onwards, the K^T section is reachedon foot by following the wide valley cut by theOued El Maleh river (rarely dry) through Campa-nian to early Maastrichtian light gray limestonesrich in megafossils followed by alternating graymarls and marly limestone layers (Abiod Forma-tion) similar to the Karma valley at Elles. Con-tinuing along the valley one traverses the gray

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marls of the El Haria Formation and after about2 km reaches the darker gray shales of the K^Tboundary transition. The K^T boundary horizonis marked by a thin rusty red layer similar to Ellesand El Kef. A dark organic-rich clay layer ofDanian age overlies the red layer. The 20 cmabove and below the K^T red layer are stronglybioturbated as evident by Thalassinoides burrows.Upsection, gray shales and marls alternate andthe ¢rst marly limestone is present at 1.80 mabove the rusty red layer that marks the K^Tboundary.

3. Methods

The Elles section was sampled at two di¡er-ent times. The ¢rst sample set (by N.K.-Y. andD.Z.-T.) shown here spans from 6 m below to 8 mabove the K^T boundary. Samples were taken atabout 25^30 cm intervals, except for the K^Ttransition from 1 m below to 2 m above theboundary where samples were taken at closer in-tervals of 5^10 cm and at 1^2 cm spacing acrossthe rusty red layer. The second sample set (G.K.)was taken during a subsequent visit when the sec-tion was trenched and resampled at 5 cm intervalsbetween 0.5 m below to 0.8 m above the K^Tboundary rusty red layer in order to obtain acomparable sample set to the El Kef stratotype(see Keller et al., 1995). The results of both Ellesstudies are described herein. The El Melah sectionwas generally sampled at 5^10 cm intervals ex-cept across the rusty red layer and organic-richclay where samples were taken at 2^5 cm inter-vals.

Laboratory procedures di¡ered somewhat forthe two sample sets. For the ¢rst study, sampleswere soaked in water and dilute hydrogen perox-ide and then washed through a 63 Wm screen. Thesame procedure was followed for the subsequentmore detailed K^T intervals at Elles and El Mel-ah, except that these samples were washedthrough a 38 Wm screen. The smaller size fractionwas used because previous studies have shownthat the earliest Danian species are often smallerthan 63 Wm (e.g. Keller, 1993; Keller et al., 1995).As a result, Danian species ranges, and conse-

quently the biozonations may di¡er dependingon the size fraction used.

For the ¢rst study the s 63 Wm size fraction ofeach sample was analyzed, a species census takenfor biostratigraphic analysis, determination ofspecies ranges and evaluation of the mass extinc-tion. The same method was followed for the ElMelah section. For the detailed K^T study at El-les and comparison with the El Kef stratotype,the s 38 Wm size fraction was quantitatively an-alyzed and relative abundances determined fromrepresentative sample splits of about 250^350specimens (Table 1).

Fig. 2. Planktic foraminiferal zonation of Keller et al. (1995)with some modi¢cations by N.K.-Y. and D.Z.-T. and com-parison with Berggren et al. (1995).

PALAEO 2757 1-5-02


Tab

le1

Rel

ativ

epe

rcen

tab

unda

nce

data

ofpl

ankt

icfo

ram

inif

era

acro

ssth

eK

^Tbo

unda

ryat

Elle

sI,

Tun

isia

(G.K

.da

tase

t)

Rel

ativ

epe

rcen

tab

unda

nces

ofpl

ankt

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ram

inif

era

acro

ssth

eK

^Tbo

unda

ryat

Elle

sI,

Tun

isia

(s63

Wm

)

cmbe

low

K^T

boun

dary

cmab

ove

base

ofK

^Tbo

unda

rycl

ay

Bio

zone

sP

lum

mer

ita

hant

keni

noid

es(C

FI)

P0

(s63

Wm

)P

1a

Dep

th(c

m)

45^

5040

^45

35^

4030

^35

25^

3020

^25

15^

2010

^15

5^ 100^

50^

11^

33^

66^ 10

10^

1515

^20

20^

2525

^30

30^

3535

^40

40^

4545

^50

50^

5555

^60

60^

6565

^70

70^

75

Eog

lobi

geri

naed

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UU

2U

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bige

rina

frin

gaU

11

UU

UU

11

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sim

plic

issi

ma

UU

UU

UU

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Par

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long

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3129

3613

2820

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1930

2727

2116

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814

17

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310

99

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62

2123

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11

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87

63

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66

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312

103

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PALAEO 2757 1-5-02


Tab

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(con

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ed)

Rel

ativ

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tab

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Elle

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low

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dary

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ove

base

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zone

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ita

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1a

Dep

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m)

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5040

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4030

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15^

2010

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11^

33^

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10^

1515

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20^

2525

^30

30^

3535

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40^

4545

^50

50^

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^60

60^

6565

^70

70^

75

G.

stua

rti

UU

UU

UU

UU

UU

UG

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UU

UU

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unca

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peta

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PALAEO 2757 1-5-02


Tab

le1

(con

tinu

ed)

Rel

ativ

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rcen

tab

unda

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ankt

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low

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dary

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base

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zone

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(s63

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1a

Dep

th(c

m)

45^

5040

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35^

4030

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3020

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15^

2010

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5^ 100^

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11^

33^

66^ 10

10^

1515

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20^

2525

^30

30^

3535

^40

40^

4545

^50

50^

5555

^60

60^

6565

^70

70^

75

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udot

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form

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inte

rmed

iaU

UU

UU

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pow

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nasp

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euvi

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Tot

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mbe

rco

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d35

633

338

834

740

839

133

741

042

937

437

056

346

139

334

013

578

202

333

412

376

369

414

296

263

324

275

63W

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eP

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terv

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cmab

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the

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dary

)w

here

few

non-

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situ

spec

imen

sar

epr

esen

tan

dm

ost

ofth

efa

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Not

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the

split

used

for

the

faun

alco

unt.

PALAEO 2757 1-5-02


PALAEO 2757 1-5-02


4. Biostratigraphy

The biozonation of Keller et al. (1995) is usedin this study with some modi¢cations by N.K.-Y.and D.Z.-T. (e.g. combining zones P1b and P1c asParasubbotina pseudobulloides (P1b) zone and us-ing the Abathomphalus mayaroensis zone to markthe latest Maastrichtian, Fig. 2). The alternativebiozonation of Berggren et al. (1995) is shown forcomparison. Stratigraphically important speciesare illustrated in Plates I and II.

A new classi¢cation of Paleocene planktic fora-minifera was recently published based on wall tex-ture (Olsson et al., 1999). This study generallyfollows this new classi¢cation scheme and newgeneric assignments with exceptions as noted be-low.

We retain the species name Eoglobigerina fringafor the small four-chambered early Danian mor-photype which Olsson et al. (1999) now consideras part of a very widely varying Eoglobigerinaedita population. We also retain the name Parvu-

larugoglobigerina longiapertura for the very com-pressed ¢ve- to eight-chambered forms with longslit-like apertures which Olsson et al. (1999) in-clude within the Parvularugoglobigerina eugubinapopulation. In addition, Olsson et al. also consid-er all triserial species as variants of a very hetero-geneous population of Guembelitria cretacea. Weretain the species name Guembelitria irregularisfor morphotypes with irregularly stacked cham-bers, Guembelitria danica for morphotypes withhighly regularly arranged chambers and elongatespires and Guembelitria trifolia for the very shortspired forms. These morphologies are easily dis-tinguished from G. cretacea and their relativeabundance distributions suggest di¡erent ecologica⁄nities (see Keller et al., 2002, for further dis-cussion).

4.1. Plummerita hantkeninoides zone

This zone spans the range of P. hantkeninoidesand was originally de¢ned by Masters (1984,1993) and subsequently by Pardo et al. (1996).At Elles I the range of P. hantkeninoides spansthe last 7 m of the Maastrichtian and 10 m atElles II (located in the left fork of the valley) ascompared with 6 m at El Kef (Li and Keller,1998a). The range of this excellent latest Maas-trichtian marker species spans the last 300^400kyr of the Maastrichtian, or most of chron 29rbelow the K^T boundary, as estimated from thepaleomagnetic record at Agost (see Pardo et al.,1996; Groot et al., 1989). This species is easilyidenti¢ed by its long apical spines and is commonin Tunisian sections where its stratigraphic range(generally s 6 m) provides a good estimate of the

Plate I. All specimens from Elles I, Tunisia.

1^3 Abathomphalus mayaroensis (BOLLI)4 Rugoglobigerina reicheli (BROº NNIMANN)5 Plummerita hantkeninoides (BROº NNIMANN)6^7 Guembelitria cretacea (CUCHMAN)8 Guembelitria danica (HOFKER)9 Geumbelitria trifolia (MOROZOVA)10 Eoglobigerina moskvini (SHUTSKAY)11 Eoglobigerina fringa (MOROZOVA)12^14 Globoconusa conusa (CHALILOV)15 Eoglobigerina pentagona (MOROZOVA)

Previous taxonomy Revised taxonomy (Olssonet al., 1999)

Subbotina pseudobulloides Parasubbotinapseudobulloides

Subbotina varianta Parasubbotina variantaEoglobigerina trivialis Subbotina trivialisGloboconusa conusa Parvularugoglobigerina

extensaChiloguembelina waiparaensis Zeauvigerina waiparaensisPlanorotalites compressa Globanomalina compressaGlobigerina taurica Praemurica tauricaMorozovella inconstans Praemurica inconstansMorozovella trinidadensis jun.Synonym of

Praemurica inconstans

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completeness of the latest Maastrichtian interval.The P. hantkeninoides zone replaces the Abathom-phalus mayaroensis zone for the top part of theMaastrichtian.

4.2. Abathomphalus mayaroensis zone

The total range of A. mayaroensis has long beenused to de¢ne the late Maastrichtian. However, inrecent years there has been a shift towards replac-ing the top of this zone by the Plummerita hant-keninoides zone (Plate I). There are two majorreasons for this zonal change. Firstly, the rangeof A. mayaroensis is rather long (about 2 myr)and therefore the zone provides poor biostrati-graphic resolution to determine how complete,or incomplete, the late Maastrichtian is. For ex-ample, although intrazonal hiatuses may bepresent within the 2 myr interval of the range ofthe zonal index, this could not be determinedfrom the presence of the A. mayaroensis zone.But by identifying the short-ranging P. hantkeni-noides, it can be determined whether the top ofthe Maastrichtian is present. Secondly, it is wellknown that A. mayaroensis is generally morecommon in high latitudes and in deeper wateropen ocean environments, and rare or sporadi-cally present in low latitudes and shelf regions.For this reason, the ¢rst and last appearances ofA. mayaroensis are often diachronous and henceunreliable for global correlations (e.g. Masters,1984, 1993; Keller, 1988; Olsson and Liu, 1993;Pardo et al., 1996).

Nevertheless, in this study N.K.-Y. and D.Z.-T.prefer to use the last appearance of Abathompha-lus mayaroensis to mark the latest Maastrichtian,

rather than the Plummerita hantkeninoides zone,because they did not ¢nd P. hantkeninoides inthe last 10 cm below the red layer in their sampleset of Elles I, whereas A. mayaroensis was present(Fig. 3). However, P. hantkeninoides is present inthis interval in the second more closely spacedsample set of the same outcrop (Fig. 4), as wellas in the nearby Elles II outcrop. Besides the con-sistent and common occurrence of A. mayaroensisreported by N.K.-Y. and D.Z.-T. is very atypicaland possibly due to particular and intensivesearch of the species in the below K-T boundarysamples. In our sample set of the same outcrop,this species is only observed at 40^45 cm belowthe K^T boundary (Table 1). A similarly rare andsporadic occurrence of A. mayaroensis is observedin the nearby Elles II outcrop (see Keller et al.,2002), as well as at El Kef and Ain Settara. AtAin Settara, isolated occurrences of A. mayaroen-sis are reported at 14 m below the K^T boundaryand just below the K^T boundary (Dupuis et al.,1998; Molina et al., 1998; Luciani, 2002). At ElKef, this species is only reported as isolated oc-currence at 20 m below the K^T boundary (Liand Keller, 1998a,b,c).

4.3. K^T boundary and mass extinction

This boundary is de¢ned by the coincidence ofseveral characteristic lithological and geochemicalcriteria: a lithological change from marls or shalesto dark gray or black clay; a 2^4 mm thin rustyred layer at the base of the clay; the presence ofspherules, spinels and anomalous concentrationsof iridium and other plantinum group elementsin the rusty red layer. Paleontological criteria in-

Plate II. All specimens from Elles I, Tunisia.

1^4 Parvularugoglobigerina eugubina (LUTTERBACHER and PREMOLI SILVA)5 Chiloguembelina midwayensis (CUCHMAN)6 Chiloguembelina taurica (MOROZOVA)7^8 Praemurica inconstans (SUBBOTINA)9 Parasubbotina pseudobulloides (PLUMMER)10^11 Praemurica trinidadensis (BOLLI)12, 16 Subbotina triloculinoides (PLUMMER)13 Praemurica taurica (MOROZOVA)14^15 Globoconusa daubjergensis (BROº NNIMANN)

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clude the extinction of all ornate large tropicaland subtropical species, including all globotrunca-nids, racemiguembelinids and rugoglobigerinidsbelow the red layer and organic-rich clay layer.This extinction horizon is followed by the ¢rstappearance of Danian species at or near thebase of the organic-rich clay (e.g. Globoconusaconusa, Eoglobigerina fringa, Eoglobigerina edita,Eoglobigerina eobulloides, Woodringina horner-stownensis, Plates I and II; Keller et al., 1995).The survivors are Cretaceous ecological general-ists, characterized by small size, little or no testornamentation and wide geographic ranges. TheK^T boundary is marked by these criteria in boththe Elles I and El Melah sections, as also observedat El Kef and Ain Settara (Keller, 1988; Keller etal., 1995; Molina et al., 1998; Luciani, 2002).

4.4. P0 zone

This zone spans the part of the basal Danianorganic-rich black clay layer from the extinctionof the tropical^subtropical species group (at therusty red layer) to the ¢rst appearance of Parvu-larugoglobigerina eugubina and/or Parvularugoglo-bigerina longiapertura (Plate II). In many earlierstudies zone P0 was considered to span the organ-ic-rich clay layer (e.g. Smit, 1982; Keller, 1988;Olsson and Liu, 1993; Molina et al., 1998). How-ever, new studies based on the smaller 38^63 sizefraction suggest that P0 may be restricted to thelower part of this black clay layer. At El Melah,zone P0 is condensed, about 10 cm thick, andspans the dark clay interval. At Elles I, zone P0spans the clay layer (66 cm) in N.K.-Y.’s sampleset, but is restricted to the lower part of this in-terval (20^25 cm) in G.K.’s sample set due to thepresence of tiny P. eugubina and P. longiaperturain the smaller size fraction as discussed below.Zone P0 is characterized by abundant triserialspecies (Guembelitria cretacea, Guembelitria trifo-lia, Guembelitria danica, Plate I).

4.5. P1a zone

This range zone spans from the ¢rst appearanceof Parvularugoglobigerina eugubina and/or longia-pertura to the extinction of these taxa. At El Mel-ah, the ¢rst P. eugubina (lumped with P. longia-pertura) were observed 10 cm above the K^Tboundary red layer and zone P1a spans 140 cm(Fig. 3, Plate II). At Elles I, the P1a zone is 5.6 mthick and comparable to the 4.5 m observed at ElKef (Keller, 1988, Fig. 6). Zone P1a can be sub-divided into P1a(1) and P1a(2) based on the ¢rstappearance (FA) of Subbotina pseudobulloides(Fig. 2).

The ¢rst appearances of Parvularugoglobigerinaeugubina and/or Parvularugoglobigerina longiaper-tura di¡er in the two di¡erent sample sets anddi¡erent size fractions analyzed at Elles I. In the¢rst sample set (long section, Fig. 4), based onthe s 63 Wm size fraction, P. eugubina (lumpedwith P. longiapertura) ¢rst appears at 66 cm abovethe K^T boundary near the top of the organic-rich clay. But in the second sample set based onthe 38^63 Wm size fraction (Fig. 5), the ¢rst P.longiapertura and P. eugubina appear at 20^25cm and 40^45 cm, respectively, above the redlayer and K^T boundary. This suggests that inthe early evolutionary range P. longiaperturaand P. eugubina remained morphologically smallspecies (6 63 Wm), but generally increased in sizeabove the organic-rich clay layer. It further sug-gests that the origination of P. longiapertura mor-photype may precede that of P. eugubina, thoughthis was not observed at El Kef by Keller et al.(1995).

4.6. P1b zone

This zone marks the interval from the last ap-pearance of Parvularugoglobigerina eugubina tothe ¢rst appearance of Parasubbotina varianta(Keller et al., 1995). At El Melah, P. varianta is¢rst observed at 250^300 cm above the K^Tboundary and zone P1b spans 100 cm (Fig. 3).At Elles I, the ¢rst appearance of P. varianta isnearly coincident with the disappearance of P.eugubina which is marked by a major faunal turn-over just below a limestone layer (Figs. 3, 6). A

Fig. 3. Planktic foraminiferal species ranges across the K^Ttransition at El Melah based on the s 63 Wm size fraction.

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Fig.

4.P

lankticforam

iniferalspecies

rangesacross

theK

^Ttransition

atE

llesI

basedon

thes

63Wm

sizefraction

analyzedby

N.K

.-Y.

Note

thedi¡

erencesbe-

tween

thespecies

censusdata

ofthe

two

separatesam

plesets

inF

ig.6A

andB

.

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Fig.

5.P

lankticforam

iniferalspecies

rangesacross

theK

^Ttransition

atE

llesI

basedon

thes

38Wm

sizefraction

anda

di¡erent

sample

setand

analyzedby

G.K

.N

otethe

di¡erences

between

speciesranges

andspecies

censusdata

arepartly

attributableto

di¡erences

insam

plingprocedures,

laboratoryand

analyticaltechniques

(e.g.size

fractionanalyzed),

reworking

andbioturbation

(possiblesam

plingof

burrows),

andtaxonom

icview

s(e.g.

identi¢cationas

well

aslum

pingor

splittingof

species).See

textfor

discussion.

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Fig.

6.(A

)R

elativespecies

abundancesof

theindigenous

Cretaceous

plankticforam

iniferalacross

theK

^Tboundary

atE

llesI

inthe

s63

Wmsize

fraction.N

otethat

allof

thesespecies,

which

areconsidered

extinctat

ornear

theK

^Tboundary,

aretropical

tosubtropical

andrare

tofew

oronly

sporadicallypresent

nearthe

endof

theM

aastrichtian.T

heircom

binedtotal

abundanceis

lessthan

20%of

theC

retaceousassem

blage.T

hus,the

K^T

boundarym

assextinction

selectivelyelim

inatedthese

subtropicalto

tropicalecological

specialists.(B

)R

elativespecies

abundancesof

Cretaceous

survivorsand

evolvingearly

Tertiary

plankticforam

ini-fera

inlatest

Maastrichtian

andearly

Danian

sediments

atE

llesI.

Faunal

countsare

basedon

thes

63Wm

sizefraction,

exceptfor

theP

0interval

where

most

ofthe

speciesare

dwarfed

andpresent

onlyin

thesm

aller38^63

Wmsize

fraction.N

otethe

unusuallyhigh

abundanceof

biserialspecies

inthe

earlyD

anianis

consid-ered

reworked.

PALAEO 2757 1-5-02


Fig.

6.(continued).

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similar faunal turnover is observed at Ain Settarawhere Molina et al. (1998) also note the FA of P.varianta near the extinction of P. eugubina andnearly coincident with the simultaneous appear-ance of seven new species and disappearance ofsix. At El Kef, a major faunal turnover also co-incides with the extinction of P. eugubina, in ad-dition to an abrupt increase in the size of Danianspecies (Keller, 1988). This suggests that zone P1bis condensed or missing in these sections.

Though earlier studies of El Kef and Ain Set-tara considered the early Danian interval to becomplete, the abrupt faunal turnover marked byseveral species extinctions (e.g. Parvularugoglobi-gerina eugubina, Parvularugoglobigerina longiaper-tura, Globoconusa conusa) and originations (e.g.Globanomalina planocompressa, Parasubbotinavarianta, Subbotina trivialis, S. triloculinoides, Glo-boconusa daubjergensis, Praemurica inconstans,Plates I and II), the abrupt decline in species pop-ulations, and the abrupt change to large morpho-types (s 150 Wm, see ¢g. 6 in Keller, 1988) allsuggest the presence of a hiatus. Hiatuses arecommon in Danian sections at the P1a/P1b inter-val as noted in sections worldwide (MacLeod andKeller, 1991). In Tunisian sections, this hiatus isapparently also present, though the stratigraphicextent may vary depending on paleodepth, topog-raphy and currents. For example, the shallow Sa-hara platform section at Oued Selja has a hiatusthat spans from P1c(1) to near the top of P1a(Keller et al., 1998). This errosive event may ex-press itself as a short hiatus or condensed intervalat the Ain Settara, Elles and El Kef localities tothe north.

4.7. P1c zone

This zone spans the interval from the ¢rst ap-pearance of Parasubbotina varianta to the ¢rst ap-pearance of Praemurica trinidadensis. At Elles thisinterval spans about 10 m (Fig. 6), whereas at ElMelah zone P1c spans 5 m (Figs. 3, 4). Zone P1ccan be subdivided based on the ¢rst occurrence ofPraemurica inconstans which at Elles and AinSettara nearly coincides with the extinction of Par-vularugoglobigerina eugubina. As noted above themajor faunal turnover at this interval suggests a

hiatus with P1b and the lower part of P1c(1) miss-ing.

Alternative zone P1b: N.K.-Y. and D.Z.-T.prefer to use a Parasubbotina pseudobulloides(P1b) zone to mark the interval from the extinc-tion of Parvularugoglobigerina eugubina to the¢rst appearance of Praemurica trinidadensis ; thiszone is equivalent to zones P1b and P1c of Kelleret al. (1995) (Fig. 2).

5. Analytical reproducibility

Can faunal and biostratigraphic analyses of oneworker be reproduced reliably by another work-er? Perhaps most of the controversies surroundingthe K^T boundary mass extinction in plankticforaminifera, or indeed in all fossil groups, maybe resolved if uniform species concepts and thesame analytical methods could be employed byall workers. Unfortunately, this is still an unreal-ized dream among paleontologists. As a result,the data set of one worker is generally di⁄cultto reproduce by another worker. Nevertheless,there is signi¢cant progress with very similar re-sults obtained when the same analytical tech-niques and species concepts are employed (e.g.compare Keller et al., 1995, 2002, with Luciani,1997, 2002).

The El Kef foraminiferal blind test was de-signed to test the reproducibility of planktic for-aminiferal species census data and thereby resolvethe continuing controversy regarding the mass ex-tinction pattern. This test failed. It was initiatedduring the Snowbird II Conference (1988) to re-solve a disagreement between Smit and Keller re-garding the mass extinction pattern at El Kef inparticular. Smit (1982, 1990) argued that plankticforaminifera exhibit a pattern of abrupt and si-multaneous disappearance for all but one species(Guembelitria cretacea) at the K^T boundary withno reductions of species or species abundancesbelow the boundary. He interpreted this extinc-tion pattern as indicative of a geologically instan-taneous mass kill e¡ect as a result of a bolideimpact. Keller (1988) and Keller et al. (1995) re-ported local disappearances of about 10% of theCretaceous species within the last 50 cm below the

PALAEO 2757 1-5-02


K^T boundary and about 30% of the Cretaceousspecies surviving into the Danian. She interpretedthis progressive mass extinction pattern as the re-sult of late Maastrichtian environmental changeswith accelerated extinctions of tropical species atthe K^T boundary possibly due to a bolide im-pact and the survivorship of ecological generalistsinto the Danian. Many recent publications havesupported the Keller scenario of survivorship,though the percentage of species extinctions be-fore the K^T boundary remains a controversialissue (e.g. Luciani, 1997; Apellaniz et al., 1997;Molina et al., 1998). The blind test failed to gen-erate closely comparable results of replicate sam-ples and hence failed to resolve the controversy(see Canudo, 1997; Masters, 1997; Olsson, 1997;Smit and Nederbragt, 1997; Keller, 1997; Mac-Leod, 1996a,b; 1998).

MacLeod (1998) (p. 43) noted that although theblind test failed to resolve the controversy, it high-lighted the need for studies that address the issueof paleontological data reproducibility at both theempirical and theoretical levels. He noted thatpaleontologists must either improve the reproduc-ibility of systematic results, or develop methods toincorporate relatively high levels of uncertainty inboth qualitative and quantitative analyses. Weagree with this assessment, but note that the ma-jor problems may well be due to systematics andthe di¡erent conceptual approaches betweenlumpers and splitters. This report o¡ers anotherexample of this problem.

In this study, N.K.-Y. with D.Z.-T. and G.K.independently analyzed two di¡erent sample setsof the same Elles I section for a narrow intervalspanning the K^T boundary (Figs. 4, 5). Themethods employed di¡er (species census vs. quan-titative analyses of assemblages) and species con-cepts also di¡er for a number of species. There-fore, the results vary in detail, but are comparablein general. For example, N.K.-Y. identi¢ed 56Cretaceous species at Elles I (Fig. 4). 76% (43species) of these are in common with G.K.’s spe-cies list of the same section, but from a di¡erentsample set (Fig. 5). The species which are notrepresented in G.K.’s study are generally includedin closely related species morphologies and can beattributed to the lumper-splitter e¡ect (e.g. Clavi-

hedbergella^Shackoina, R. milamensis^R. rotunda-ta^R. penny^R. robusta, G. orientalis^G. arca,G. acuta^G. robusta, Globigerinella volutus^Globi-gerinelloides aspera, P. nuttali^Pseudotextulariadeformis^P. riograndensis^Planoglobulina brazoen-sis, P. excolata^Pseudoguembelina costulata,G. havanensis^G. petaloidea), and four were notobserved (P. glabrata, P. cornuta, P. acervuli-noides, G. mariei).

G.K. identi¢ed 61 Cretaceous species for thesame section (di¡erent sample set). 66% (41 spe-cies) of these are also present in N.K.-Y.’s study.Of the 20 species which are not present inN.K.-Y.’s study, all but one species (Zeuvigerina),are probably lumped with other species and hencecan be attributed to the lumper-splitter e¡ect (e.g.Globigerinelloides volutus^G. yaucoensis^Globige-rinelloides aspera, G. subcarinatus^G. petaloidea,Heterohelix dentata^H. globulosa^H. moremani,G. stuartiformis^G. falsostuarti^G. stuarti, Plano-globulina brazoensis^P. riograndensis, H. gla-brans^H. pulchra^Heterohelix complanata, G.arca^G. orientalis^G. esnehensis, Pseudotextulariadeformis^P. nuttali, Shackoina^Clavihedbergella).

Because of the lumper-splitter dichotomy, ahigh degree of reproducibility between workersis only possible if they share the same taxonomicconcepts. Since this is frequently not the case,analytical reproducibility even in the same sectionhas very high variability as seen in the example ofthe Elles I section. Therefore, one would assumethat the reproducibility would be better, even be-tween di¡erent sections and regardless of the spe-ci¢c worker, as long as the same taxonomic con-cepts are used. For example, a study by Luciani(1997, 2002) of the Erto section in Italy and AinSettara section in Tunisia shows very similar re-sults to those earlier obtained from the El Kefand Elles sections by Keller et al. (1995, 2002).This suggests that these workers have indepen-dently used the same species concepts based solelyon comparisons of published illustrations.

Many factors in£uence the reproducibility ofspecies range data, including ¢eld sampling tech-niques (e.g. sample spacing, size of samples, sam-ple contamination at outcrops), methods of sam-ple processing (e.g. mechanical breakage, acidtreatment causing dissolution, sieve size used),

PALAEO 2757 1-5-02


sample analysis (size fraction analyzed, time spentsearching for rare species, qualitative vs. quanti-tative analysis, problems in recognizing reworkedspecies), systematics (species concepts of outlierspecies) and ecological variations in species distri-butions. Given all these variables, it is perhapsmore surprising that the mass extinction patternis so consistent, than that there are still some ar-guments over the ¢ner points of the mass extinc-tion pattern.

6. K^T faunal turnover

The K^T mass extinction pattern in plankticforaminifera at Elles I analyzed for the two sam-ple sets di¡ers in some details. For example, theN.K.-Y. sample set (Fig. 4) shows an unusualpresence of many large tropical species abovethe K^T boundary (zones P0 and P1a(1)), whichare known to be extinct at or near the boundary(P. multicamerata, P. palpebra, Rugoglobigerinahexacamerata, R. scotti, P. riograndoensis, P. ele-gans, P. nutalli, G. aygyptiaca, Racemiguembelinafructicosa, R. rugosa, P. kempensis). Their pres-ence is likely a result of reworking and bioturba-tion as suggested by discolored, abraided and bro-ken tests, as well as the common presence ofThalassinoides burrows above and below the redlayer. In the second sample set where burrowswere carefully avoided wherever possible (Fig. 5),only a few of these tropical species are present atthe base of P0 and are attributed to reworking.Though P. kempensis and Pseudoguembelina cos-tulata are consistently present in the early Danianat Elles I as well as the nearby Elles II and AinSettara sections (Keller et al., 2002; Luciani,2002). Thus these species may also have survivedthe K^T event.

The overall extinction patterns of both Elles Istudies are similar to those observed in other Tu-nisian sections. Some species (V16%) are veryrare or sporadically present and not observed torange up to the K^T boundary. Their true extinc-tion level can not be determined. This is especiallyevident in that the species with early disappearan-ces di¡er between the two sample sets analyzed(Figs. 4, 5). For many species, single isolated oc-

currences are reported within the last 10 cm belowthe K^T boundary, an interval that consists of aforaminiferal packstone. At Elles II, where thisforaminiferal packstone is about 25^30 cm thick,cross-bedding is apparent and indicates a trans-ported and probably reworked older assemblage.For this reason, no conclusions can be drawn re-garding the extinction level of species that areonly sporadically present below this foraminiferalpackstone.

Nevertheless, the overall mass extinction pat-tern at Elles I is similar to that observed at ElKef (Keller et al., 1995), Ain Settara (Luciani,2002), Mexico (Keller et al., 1994; Lopez-Olivaand Keller, 1996; Keller, 1996), Italy (Luciani,1997) and other localities with tropical to sub-tropical planktic foraminiferal assemblages.Nearly 2/3 of the species disappeared at or nearthe K^T boundary and about 1/3 of the speciessurvived into the early Danian. The K^T extinctspecies group (which here includes species whichare rare and appear to disappear earlier) consistsof ecological specialists which includes all tropicaland subtropical species. These ecological special-ists are generally characterized by highly orna-mented, large multiserial or keeled morphologies.Their combined relative abundance is less than20% of the total planktic foraminiferal assemblag-es (Fig. 6A,B). In contrast, the K^T survivorgroup consists of ecological generalists. They arecharacterized by small biserial, triserial, trochospi-ral or planispiral morphologies with little surfaceornamentation. Ecological generalists dominatethe latest Maastrichtian oceans and their com-bined relative abundance may exceed 80%(Fig. 6B).

Above the K^T boundary, triserial species(Guembelitria) dominate (V80^90%) in the small38^63 Wm size fraction, but are relatively few(6 10%) in the larger s 63 Wm size fraction.This is likely a result of the high stress post-K^T boundary environment (MacLeod, 1993; Mac-Leod and Keller, 1994; MacLeod et al., 2000).Curiously, Cretaceous survivor species are rathercommon in zone P1a above the K^T boundary,especially the relative abundance of Heterohelixnavarroensis which appears to increase. In fact, apeak of the latter species reaches 60% at the P0/

PALAEO 2757 1-5-02


P1a boundary (Fig. 6B). This is very unusual. Ingeneral, survivor species strongly decrease in theearly Danian zones P0 and P1a in all Tunisiansections, including at Elles II which was collectedonly 200 m distant from Elles I (see Keller et al.,2002). The anomalous abundance of small Creta-ceous survivors at Elles I can therefore not beattributed to di¡erential local ecological condi-tions, but is likely due to locally abundant re-worked sediments as also suggested by the com-mon presence of obviously reworked largetropical species (Fig. 4).

7. Discussion and conclusions

The progressive extinction pattern at Elles I isoverall similar to that observed previously for thesame interval at outcrops at El Kef and Ain Set-tara (Keller, 1988, 1996; Keller et al., 1995; Mo-lina et al., 1998; Luciani, 2002), as well as insections in Israel, Spain, Italy, Lattengebirge,Mexico and Brazil (Canudo et al., 1991; Kellerand Benjamini, 1991; Peryt et al., 1993; Kelleret al., 1993, 1994; Lopez-Oliva and Keller,1996; Abramovich et al., 1998; Luciani, 1997;Apellaniz et al., 1997). Although in each of theselocalities the overall extinction pattern of special-ists and survivorship of generalists is similar, thereare enough di¡erences to fuel a continuing con-troversy about the nature of the K^T mass extinc-tion, whether progressive or instantaneous. Onepart of the controversy centers over whether thereare pre-K^T extinctions that foreshadow stressfulenvironmental changes during the latest Maas-trichtian, or whether a bolide impact at the K^Tboundary was solely responsible for the mass ex-tinction. The other part centers over the natureand number of Cretaceous species survivorship.

These arguments are unlikely to be solvedbased on a narrow interval spanning the K^Tboundary. Most K^T studies have concentratedon an interval of 50^100 cm below and abovethe boundary, or included at most the topmostfew meters of the Maastrichtian, and few haveexamined environmental and faunal changes dur-ing the entire late Maastrichtian. However, stableisotope studies demonstrate profound climatic

changes during the last 500 kyr of the Maastricht-ian (Stott and Kennett, 1990; Barrera and Keller,1990, 1994; Barrera, 1994; Li and Keller,1998a,b). High resolution studies are needed todetermine the nature of the progressive biotic ef-fects associated with climatic and environmentalchanges before the K^T boundary event.

Acknowledgements

We gratefully acknowledge Dr. N. Ben Haj Ali,Director of the Geological Survey of Tunisia,Tunis, and Dr. H. Ben Salem, for their tremendouslogistical and transportation support for the fieldexcursion and Workshop of May 1998 on TunisianK^T boundary sections. Fieldwork for the Ellesand El Melah sections was a joint effort withThierry Adatte and Wolfgang Stinnesbeck and wegratefully acknowledge their collaboration. Wethank H.P. Luterbacher and one anonymousreviewer for their comments and suggestions. Thisstudy was supported by NSF-INT 95-04309.

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