GeologicalSocietyof America
SpecialPaper247
1990
Late Cretaceous-earlyEocenemass extinctions in the deepsoa
Ellen Thomas
Departmmtof Eanh andEnvironmentalSciences,WesleyanUniversity,MiddletownConnecticut06457,and TlnmesScience
Center,NewLondon,Connecticut06320
ABSTRACT
Upper Maashichtian through lowermost Eocene deep-seabenthic foraminiferal
recordsfrom Maud Rise(Weddell Sea,Antarctica) demonstratethat there was no mass
extinction of theseorganismsat the endof the Cretaceous.Ihere is no significantdrop in
diversity acrossthe Cretaceous/Tertiaryboundary, butjust abovethis boundary there
is a peak in relative abundanceof speciesthat may indicate low-nutrient conditions,
probably reflecting the decreasein food supply to the ocean floor resulting from the
large-scaleextinction of surface-dwellingprimary producers.In contrast, there was a
global extinction of bathyal to abyssalbenthic foraminiferaat the end of the Paleocene,
occurring in fewer than 25,000yr at Maud Rise.Many benthicforaminiferal speciesthat
had originated during the Cretaceousbecameextinct, although there was no coeval
mass extinction (of comparableimportance) of terrestrial organismsand planktonic
marine organisms.After this extinction the diversity of benthic faunason Maud Rise
was low for about 260,000yr, and during the period of low diversity, the assemblages
were dominatedby speciesthat may indicate the presenceof abundantorganic carbon,
and possiblylow concentrationsof dissolvedoxygen. The dominancezuggeststhat the
Paleocene/Eocenedeep-seabenthic foraminiferal mass extinction was causedby a
decreasein oxygen content of the waters bathing the lower bathyal reachesof the sea
floor. Such a changecould have beencausedby a changein the circulation patternsof
deep waters: thesewaters would becomedepletedin dissolvedoxygen if there was a
change from predominant formation of deep waters at high latitudes (cooling and
sinking) to initiation of, or a strong increaseof, formation at low latitudes(evaporation
and sinking). Thus, one of the largest Phanerozoicextinctionsat the Earth's zurtaceis
not reflectedby the deep-waterforaminifera, and the largestCenozoicextinction event
in the bathyal-abyssalrealm of the oceansis of little importanceto surfacebiota: even
someof the largestextinction eventsthat we know do not reachall environmentsof the
Earth.
INTRODUCTION
"buffer to extinction"(Sheehan
and Hansen,1986;Arthur and
others,1987),althoughsomeauthorssuggest
that bunowing orAt the end of tle Cretaceous,
landdwellers and surface- ganismsunderwenta massextinction(Wright lt Hsti andothers,
dwelling organismsin the oceansunderwentone of the largest 1984,p. 335).Deepwaterostracodes
havebeenreportedto have
extinctioneventsof the Phanerozoic(e.g.,Thierstein,1982;Cle- had a "faunal crash"at the end of the Cretaceous
(Bensonand
mens,1982;Russell,1982),but extinctionratesin deep-sea
ben- othen, 1984),but few data areavailablefor faunasliving just
thic organismsare not well known (Culver, 1987; Thientein, afterthat "crash,"somass-mortality
pattemsfor that grouphave
1982;Hsii, 1986).Benthicorganisms
in the deepoceanshave not been well established(Steineck,personalcommunication,
beensaidto showlittle or no changeacrossthe Cretaceous,/Ter- 1989;Bensonandotlers,1985,Fig. l).
tiary boundaryQlsii, 1986);detritusfeedinghasbeenseenas a
Benthicforaminifera,which supplythe mostabundantfosThomas, E., 1990, l,ate Cretaceous-early Eocene massextinctions in the deep se4 lz Sharpton, V. L., and Ward p. D.,
eds.,Global catastrophesin Earth history;
An interdisciplinary conference on impacts, volcanism, and mass mortality: ceological Societybf America Special yapr j.+7.
481
482
E. Thomas
(65"9.629'5,Io12.296'E,presentwater depth2p14 m) were
drilled on Leg ll3 (January-March1987)on Maud Rise,an
aseismicridge at the eastemend of the Weddell Sea(Barker
andothers,1988;Fig. l). Site689 is on thenortheastern
sideof
the ridge near its crest,Site 690 is on the southwesternflank,
I 16 km to the southwestof Site 689. LowermostMaastrichtian
through Pleistocene
biogenicsedimentswere recoveredat both
sites(Fig.2).T\e UpperCretaceous
throughlower Eoceneconsists of calcareouschalks and oozes;fine-grainedterrigenous
materialis presentin partsof the sectionat Site690 (Barkerand
others,1988,p. 190-l9l).
Paleodepths
of the sitescouldnot be estimatedusingsimple
thermal subsidencemodelsbecauseMaud Rise is an aseismic
ridge; benthic foraminiferalfaunasindicate latest CretaceousPaleocene
depthsof 1,000to 1,500m for Site689,and 1,500to
2,000 m for Site 690 (Thomasin Barkerand others,1988;
Thomas,1990).For severalsitesdrilledon ODP Leg 114(Sites
698-702; seeFig. I for locations),paleodepthscould be estimated using simple thermal subsidencemodels;overall, these
deptls showedgoodagreement
with depthsderivedfrom faunal
data (Katz and Miller, 1990). Comparisonof the Maud Rise
faunasand the Leg 114 faunasconfirmsthe depth estimateof
1,000to 2,000m for Sites689and690duringthelateMaastrichtian-early Eocene.In this studythe following bathymetricdivisionswere recognized,in agreementwith Berggrenand Miller
(1989):neritic-<2OOm; upperbathyal-2O0to 600m; middle
bathyal-600 to 1,000m; lower bathyal-1,000 to 2,000 m;
upper abyssal-2,000 to 3,0fi) m; lower abyssal) 3,000 m.
Therefore,both sitescanbe placedin the lower bathyalinterval
for the tine periodstudied.
The biostratigraphicinformation was obtainedfrom calcareonsnannofossils(Pospichaland Wise, 1990a,b, c); only a
few datum levelsof planktonic foraminiferawere reliableage
indicaton at thesehigh latitudes (Stott and Kennett, 1990a;
Huber, 1990). In addition, data on the paleomagneticrecord
wereprovidedby Hamilton(1990) for the Mesozoic,and Spiess
(1990) for the Cenozoic.The stratigraphicinformationsupplied
by all theseauthorsis compiledin Figure2.
In this chapter,dztaue presentedfor the intervalbetween
140and 260 metenbelow seafloor (mbsf) at Site690 and 200
to 260 mbsf at Site 689, correspondingto upperMaastrichtian
(Nephrolithusfrequens Zone; Pospichal and Wise, 1990a)
throughlowermostEocene(CP9;Pospichaland Wise, 1990c).
Absoluteageswerederivedfrom crossconelationof the paleomagneticand calcareousnannofossildata with the geomagnetic
polaritytime scaleof Berggrenand others(1985).At Site689
there are unconformitiesat the K/T boundary (Zone CPla,
severalhundredthousandsof yean), in the middle Paleocene
(Zones CP4 through CP5), and in the topmost Paleocene
MATERIAL AI\D METHODS
throughlower Eocene(at leastZonesCP9throughCPI I about
6.6m.y.;Fig.2). Thereis no Ir anomalyat thestratigraphic
K/T
Sites and Stratigraphy
boundaryin Hole 6898, confirmingthe presenceof an unconOcean Drilling Program (ODP) Sites 689 (64o31.009'5, formity (Michel and others, 1990). The upper Maastrichtian03"05.996'E, present water depth 2,080 m) and 690 lowermost Eocene record at Site 690 does not contain
sils of deep-waterorganisms,were reportedly little affectedby the
mass extinction at the end of the Cretaceous (Douglas and
Woodruff, l98l; Thientein,1982; Culver, 1987),but this observation is based on few quantitative data sets. Many earlier
worken on benthic foraminifera describedthe great similarity of
Maastrichtian and Danian (lower Paleocene)faunas (e.g., Cushman, 1946). More recently, differences have been recognized,
although estimatesof extinction rates vary widely (18 to 67 percent species extinction; Beckmann, 1960; Webb, 1973; Beckmann and others, 1982; Dailey, 1983; Widmark and Malmgren,
1988; Keller, 1988b).Severalof the estimates(Beckmann,1960;
Webb, 1973; Beckmannand others, 1982) must be seenas maximum estimates,simply becausethey were derived from comparisons of faunal lists for the Maastrichtian and Danian. Therefore,
theseestimatesinclude last appearancesthat occurred a considerable time before the boundary.
Environmental conditions at the end of the Paleocenecontrast with those at the end of the Cretaceous.At the end of the
Paleocenethere were no extinctions among shallow-water and
surface dwellen comparable in size to the extinctions at the end
of the Cretaceous: it was a period of below-average extinction
rates (Raup and Sepkoski, 1986). The diversity of marine planktonic microorganisms such as dinoflagellates, calcareousnannoplankton, and foraminifera was increasing after the middle
Paleocene(e.g.,Oberhaensliand Hsii, 1986). At the sametime,
however, deep-seabenthic foraminifera underwent their largest
known extinction of the Cenozoic (e.g., Beckmann, 1960; Braga
and others,1975;Schnitker,l9T9; Douglasand Woodruff, 1981;
1-alsmaand Inhmann , 1984; Culver, 1987), and this extinction
has remained unexplained. Some authors suggestthat primary
productivity decreasedat the end of the Paleocene(Shackleton
and others, 1985), and this could have causedthe extinction of
deepwater dwellen; the suggestionhas not been widely accepted,
however (Miller and others, 1987b; Katz and Miller, 1989).
One purpose of this study was to contribute to the knowledgeofthe *fabriC'ofthe extinction at the end ofthe Cretaceous
by collecting a quantitative data set on ranges and abundance
patterns of deep-seabenthic foraminifera from Maud Rise (Weddell Sea, Antarctica). Another purpose was to compare the
changesin faunal composition of deep-seabenthic foraminifera at
the CretaceouslTertiary (K/T) boundary (a time of collapse of
the primary productivity; Arthur and others, 1987) with faunal
changesat the end ofthe Paleoceneat the samelocation, to asses
whether the pattems of faunal changewere similar. This information should be important in evaluating whether massextinctions
reach all environments from the surface to the lower bathyal
areasof the ooeans,or whether thesetwo environments (and thus
their inhabitants) are largely decoupled.
-''
Late Cretnceous-earlyEocene mrBSextinctions in the deepsea
/183
Figure l. LocationofSites 689 and 690,and othersitesat high southernlatitudesdrilled by the Deep
Sea_DrillingProjectandtheOceanDrilling hogram (ODP). Sites698 through70+weredrilleCOuring
ODP kg 114.
unconformitiesdetectableat the presentlevel of biostratigraphic Berggrenand others, 1985, but late Paleocenein Aubry and
precision,and an [r anomalywasdetectedat the locationof the others,1988).At Site690 thebenthicfaunaleventsoccurredat
calcareousnannofossilboundary(Michel and others,1990;pos- the boundarybetweenAntarctic foraminiferalZonesAP4 and
pichal and Wise, 1990b). The interval just above the K/T AP5, thoughtto be equivalentto the P6a/P6bboundary(Stott
boundary was recognizedby the presenoeof the lowermost and Kennett, 1990a).The benthic extinctionalso occurredin
Paleocene
nannofossil
zoneCPla (with the rndexformBiscutum paleomagnetic
Chron C24R and in calcareous
nannofossilZone
sparsum;PospichalandWise,1990b)andby an intervalcontain- CP8,almostexactlyin themiddleof theintervalbetweenthefirst
ing the lowermostPaleocene
index speciesEoglobigeinafinga appearance
of Discoastermultiradiatus,the lower boundaryof
andE. eobullordes
combinedwith smallheterohelicids
(Stottand that zone,and the fint appearance
of Tribrachiatusbramtettei
Kennett,1990a).Sedimentation
rateswereestimatedat Site690 thelowerboundaryofthe subsequent
zoneCPga(Pospichal
and
usingpaleomagneticdata, resultingin a sedimentationof 14.4 Wise, 1990a).This placesthe age of the benthic extinctionat
m/m.y. for the uppermostPaleocene
(Chron 24R). Sedimenta- about57.5Ma, in the late Paleocene
(in the time scaleof Aubry
tion rates for the uppermostCretaceousare more dfficult to andothers,1988),andat the Paleocene/Eocene
boundaryin the
derive,but Hamilton(1990)hassuggested
a sedimentation
rateof zonalschemeof Berggrenand otlen (1935).
about7.5m/m.y.at Site690,andnot muchdifferentfor Site689
' At theMaudRisesitesthebenthicfaunaleventoccursat the
(belowthe unconformityat the K/T boundary).
samelocationin tle sectionasa major changein dl3c valuesin
The location of the Paleocene/Eocene
boundarywith re- bulk carbonate(Stottandothers,1990)andin benthicforaminifgardto biostratigraphiczonationsis difiicult and oftendiscussed era(KennettandStotq1990).Thisisotopiceventhadbeencorre(Berggren
andothers,1985;Aubry andothers,1988).Theben- lated with the Paleocene/Eocene
boundary(Miller and others,
thic extinctionhad beenreportedto occur at the boundaryof l987a,b; Shackleton,
1986),and at Site690 it occurredat the
planktonicforaminiferalzonesP5 andP6a(i.e.,in thelatepaleo- Paleocene,/Eocene
boundaryin the zonal schene of Berggren
cene,accordingto Berggrenand others,1985)by 1-alsma
and and others (1985), but clearly before the Paleocene/Eocene
Lohmann(1983),but Boersma(1984) and Miller and othen boundaryas definedin Aubry and othen (1938);i.e., within
(1987b)placedthe eventcloserto theboundary,betweenzones Zone CP8, and preciselyat the planktonicforaminiferalzonal
P6a and P6b (the Paleocene/Eocene
boundarv as defined in boundarybetweenZonesAP4 andAP5 (equivalentto thebound-
E. Thomas
484
690B 690C Paleomagnetic
tr tr IE data
tr IJJ
IJJ
z
z
140
IJJ
o UJ o .= o
E o tr o g
o IJJ o IJJ o .c
o tr o IE o- o
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=
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Planktonic
Foraminifera
o
a
o
?
210
IJJ
AP5
a. FADA'
australiformis
AP4
23
cP8
a\FAD A. prae
pentacamerata
cP8
a
FAD
A. mckannai
"P". imitatus
11
12
?
A'
IA.FAD orae
A P3 lpentacameratacP5
15
16
lo.,oo
"P'. initatus
o
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c
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Ih-CP 2-3'
FAD
ds. inconstant
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FAD S. Dseudoa
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(t
250 27
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co
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at)
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australitomis
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E
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lr
Planktonic
Calcareous
Foraminifera Nannotossil
16
17
Paleomagnetic
tr
data
uI
6898
28
260
N
c"
at Sites689 and 690. The core
Figure 2. Core recovery,biostratigraphy,and magnetostratigraphy
for theCenozoicare
recoverydataareafterBarkerandothers(1988);dataon the magnetostratigraphy
is
after Spiess(1990),andfor the MesozoicareafterHamilton(1990).The nannofosilbiostratigraphy
after Pospichaland Wise (1990a,1990b,1990c),the planktonicforaminiferalbiostratigraphyfor the
Cenozoicis afterStottandKennett(1990a),andfor the Mesozoicis afterHuber(1990).For planktonic
foraminifera,Cenozoicdatum levelsare given in the figure,becausethe proposedzonesare not yet
widely known or accepted.
ary between Zones P6a and Pb6). It is difficult to judge whether
sections across the Paleccene/Eocene boundary are complete,
becauseso many sectionscontain unconformities in this interval
and there is thus no obvious "standard complete section." The
section at Site 690 appean to be the most complete section
available from all Deep Sea Drilling Project (DSDP) and ODP
sites, if judged on the distance between the boundary between
nannofossil Zones CP8 and CP9, and the planktonic foraminiferal boundary between AP4 and AP5 (equivalent to
P6a/P6b). Theseboundarieswere thought to be coeval (Berggren
and others, 1985), but later it was realized that there is an offset
between the two in more complete sections (Aubry and others,
1988). This offset is almost 20 n at Site 690, more than at any
other site. In addition, the thickness of Chron 24R is $eater at
Site 690 than at any other DSDP or ODP site, and comparison
of the isotope records for Site 690 with those of the southern
Atlantic sites (Shackleton, 1986) also suggeststhat the Site 690
record is the thickest section acrossthis interval. In addition, the
recovery was very good at that site (Fig. 2), and core disturbance
was minimal, with the exception of the interval of overlap between Holes 6908 and 690C (Barker and others, 1988). The
record at Site 689 is of much lower quality, because of the
presenceof several hiatuses (Fig. 2) and poor re@very in some
intervals.
Late Cretaceous-earlyEocene massextinctions in the deepsea
Samplcpreparation and data collcctian
485
difficult to quantify.The faunasaregenerallyvery divene (commonly >60 speciesper 300 specimens),
with many rare species
(<5 percenton the total fauna).The mostcommonspecieshave
very long ranges,and the shorter-ranged
speciesare rare; thus,
rangesof manyspecies
that mightbe stratigraphicallyusefulcannot be determinedpreciselyin a statisticallyvalid way, and precisetiming of many first and last appearances
is difiicult if not
impossible.In addition,a first or a lastappearance
of a speciesat
a specificsitemay not representoriginationor extinction:deepseabenthicspeciesmigrateboth geographicallyand bathymetrically (Woodrutr, 1985; Kurihara and Kennett, 1988). In
addition, the literaturecan not be easilyinterpretedbecauseof
major taxonomicconfrrsionin many taxa. Therefore,a simple
statementabout how many percentof all speciesof deep-sea
benthicforaminiferabecameextinctat a specifictime is equivocal: "extinction" ratesare ratesof local last appearances,
not
necessarily
of extinctions(which areglobalby definition).In this
chapterI disregarded
all speciesthat occurin one sampleonly,
and thencountedfint and lastappearances
in all samples.All of
thesefirst andlastappearances
(alsoof rarespecies)areincluded
in TablesI and,2.
Samples(15 cm3) weretakenat intervalsof 1.5 m; additional samplesat distancesof 0.35 m weretakenin intervalsin
which major changesoccurred.Sampleswere dried tt 75 "C,
soakedin Calgon,and washedthrougha sievewith openingsof
63 pm;residuesweredried at7soc.The sizefractionlargerthan
63 pm was usedto obtaingood representation
of small species
(Thomas,1985;fthroeder andothen, 1987).Thepreservation
of
benthicforaminiferais goodto excellentoverthestudiedinterval;
thereis no dissolutionasobservedfrom fragmentationand fluctuationsin planktonic/benthicratios,and the isotopicvaluesdo
not indicate recrystallization(seealso discussionin Stott and
othen,1990andKennettandStott,1990).
At the startof the study,rarefactioncurvesweredrawn for
somesamples(plotsof numberof speciesvenusnumberof specimens)to determinethesamplesizeneededto recovermostof tle
speciespresent.The curvesbecameparallelto the specimenaxis
at about 270 specimens
in the morediversesamples,about200
specimens
in the lessdiversesamples;about300 specimens
were
pickedfrom all samples.Partof eachsamplewasspreadin a tray
to estimatehow much materialwould be neededto collect300
specimens,
and thena split wasmadeof the estimatedsize.The DISCTJSSIONOF RESIJLTS
taxonomywasdiscussed
andall raw data(counts)werepresented
togetherwith rangechartsin Thomas(1990). The most used
The recordof late MaastrichtianthroughEocenedeep-sea
taxonomicreferencesfor the Cenozoicwere Plummer(1926), benthicfaunaleventsfrom Site690is morecompletethanthat at
Berggren
andAubert(1975),andMorkhovenandothen(1986); Site 689, so the recordat the former sitewasusedto determine
for the Mesozoic,referenceswere Cushman(1946), Dailey thesequence
offaunalevents.Thefragmented
recordofSite 689
(1983),andNyongandOlson (1984).
waslatercorrelatedto the morecompleteSite690 record.FaunCalcareousbenthicforaminiferadominatedin all samples, al events(lastappearances
andfirst appearances)
clearlywerenot
and calcareoustaxa were placedin morphologicalgroups.The spreadout evenlyovertime,but wereconcentrateAatafewtimes
three groupsdistinguishedare: (1) the spiral group (including (Fig. 3). The extinctionat the end of the Paleocene
is the most
mosttrochospiraland someplanispiralspecies);(2) thebiserial- significanteventfor benthicforaminiferain the periodfrom late
triserial group, includingspeciesthat belongin the superfamily Maastrichtianthrough early Eocene,in contrastto planktonic
Buliminacea(to whichtherecentlow-oxygen/high-nutrient
indi- taxa,wherethe extinctionat the end of the Cretaceous
is by far
catorssuchasbolivinidsanduvigerinidsalsobelong);and(3) the the most important (e.g.,Smit, 1982;Thientein, 1982;Keller,
cylindrical group (uniserialspecieswith a cylindrical shape). 1988a).At Site690,very few species
(8.3 percent)lastappear
Thesemorphologicalgroupswerethencomparedwith theclassi- closeto the K/T boundary(Table 1), whereasat the shallower
fication of morphologicalgroupsas describedby Corlis and Site689,thepercentage
oflast appearances
is higher,but still not
Chen(1988).The spiralgroup agreescloselywith the group of indicativeof a major catastrophe
(12.7 percnnt;Table l). Of the
epifaunalspecieslistedby tlese authors,and tle triserial-biserial sevenspecieswith a last appearance
nearthe K/T boundaryat
group with the infaunalspecies.
Therearefew dataon the envi- Site 690, only threehavea coevallast appearance
at Site 689:
ronmentalpreferenceof the morphologicalgroup of cylindrical Coryphostomaincrassata,Praebaliminareussi, and Spiroplecspecies,consistingof Stilostomelhspp.,Pleurostomelhspp.,and tamminaafr.spectnbilis.Coryphostoma
incrassatabwme extinct
uniseriallagenids(Thomas,1985),because
thesespeciesarerare worldwideat the endof the Cretaceous
(Morkhovenand othen,
in therecentoceans.Thereforethesespecimens
werenot included 1986);P. reussihadits lastappearance
closeto theK/T boundary
in the countsof epifaunaor infauna"but wereplottedby them- at lowerbathyalSite516(WalvisRidge,SouthAtlantic;Dailey,
selves(seebelow). Thesecylindricalspeciesmight be placedin 1983) but survivedthe boundaryat the upper bathyal El Kef
the group of infaunalspeciesin the future(Corlis, written com- section(Keller, 1988b).The UpperCretaceous
guidefossilBolimunication,1989) if this placementis supportedby additional vinoidesdracodracobecameextinctat the K/T boundary(Hildata.Thereis a significantconelation(p >97.5) betweentherela- termannandKoch,1960;Morkhovenandothers,1986),but this
tive abundances
of the infaunaland the cylindricalgroup in the is largelya neriticto upperbathyalspecies.
The speciesoccursin
Maud Risesamples.
just below the K/T boundaryat Site 689, but
a few samples
Faunaleventsin deep-sea
benthicforaminiferalfaunasare thereis only onespecimen
in onesampleat Site690.Only one
486
E. Thomas
TABLE1. FIRSTAPPEARANCES
(FAs)ANDLASTAPPEARANCE
(LAs)ACROSSTHE CRETACEOUS/TE
RTTARY
BOUNDARY
AT SITES689AND690'
lnterval at 689
FAs LAs
0.5 m.y.after
AcrossIVT
0.5m.y.before
Total
2
2
6
5
3
3
10
11
Interval at 690
0.5m.y.after
Across1(T
0.5m.y.before
FAs
6
5
2
LAs
Interval at 689
3
0
4
After
Acrossevent
Before
(o
o
-tr
(n
1 4 0 rn
u
z
u
U
o
o
o 'l80m
o
o
3
o
o
200ni
21Om
cP8
f,zzom
o
o
f zsoCL
f
3i.
o l x)t
I
II \
E
2
u
o
-CP
2-3'
cP 1b w
3
o
J
o
UH5
?20m
1z
24Om
u
z
U
2 4 Om
cP 1b
250m
-l
',
1
T
I
o
o
N
o
z
s
9
.c
ul
a <l
_vr J_
d
s
tI
E
F
o
E
J
C. daniae
Zone
F
o
=
site6eo
(o
o
-tr
(,
uo
2L
4
o
I
!
a
1
28
Numberof faunal events
cP 6-7
=
o
cP 6-7
cP4
106
o12
010
lc
IU
o
-9
. . ^O
2
0.5 m.y.after
Acrossevent
0.5 m.y.before
' li \
L
o
2.64m
cP 12
x+
r tr.
I
s ^l U^ ^U t n
CL
o
(,
t\
*+
cP8
?
18
FAs LAs
10
Calcareous
{annotossils
CN
h
fr
tt
{+
l+
cP9
?
0
?
lnterval at 690
-At Site 689 the length of a 1 m.y. interval across the boundary could
not be estimated because of the presenceof unconformities.
Total faunal events at Site 689: ?
Totallast appearancesover 1 m.y.aroundthe event:>18 (35.2
percent).
Total faunal events at Site 690: 38 (50.1 percent).
Total last appearances over 1 m.y. around the e\€nt: 28 (37.3
percent).
Numberof faunalevents
Calcareous
FAs LAs
Total
13
*Notethatthereis a short
unconformity
acrossthe boundaryat Site
689.
Totalfaunaleventsat Site689:22 (27.8percent).
Totallastappearan@s
over1 m.y.aroundthel(T boundary:
1j (19.9
percent).
Totaffaunaleventsat Site690:20 (23.8percent).
Totallastappearances
over1 m.y.aroundthe l(T boundary:7 (8.S
percent).
:oum
TABLE2. FIRSTAPPEARANCES
(FAs)ANDLAST
APPEARANCES
(LAs)AcRoSSTHELATEPALEOCENE
EXTINCTION
INTERVAL'
\
260m
Site 689
l
t
Figure3. Numberof faunaleventsplottedcumulativelyversussub-bottomdepthfor Sites690 (left) and
689 (right). The horizontal lines mark the position of the Cretaceous/Tertiary(K/T) and Paleocene/Eocene(P/E) boundariesasestablished
by calcareous
nannofossilbiostratigraphy(Pospichaland
Wise,1990a,1990b,1990c)andplanktonicforaminiferal
biostratigraphy
(StottandKennett,1990a).
Notethatthesectionof Site689is plottedat a differentdepthscale.Theleft curve(x) givesthenumber
of last eventsper sample,plottedcumulativelyfrom the first samplestudiedin this chapter;x marksa
sampleposition.The right curue(+) givesthe someof first and lastapp€arances.
c}|
(Jl
Late Cretaceous-earlyEocene massextinctiow in the deepsea
487
species(Buliminnsimplex)had its first appearance
at the K/T from the least bioturbated intervals, and were taken several lens
boundaryat both sites.
of centimeters away from the boundary itself, above and below
This patternoffaunal eventsat the K/T boundarydoesnot the samples
with high Ir contents (Michel and others, 1990). In
conformto the patternduringa largecatastrophe
(Table l, Figs. addition, there was little or no reworking of planktonic
forami_
3 and4);onewouldexpectto seea recordof a largenumberof nifera (which
are much more common than benthics and easyto
lastappearances,
followedby a periodoflow diversity,andclus_ recoglize as either Cretaceous
or Tertiary) acrossthe boundary.
teringoffint appearances
duringa periodofrecovery.Thereis a
In contrast to the eventsat the K/T boundary, the pattems
11311dron in diversityacrossthe K/T boundaryat both sites of faunal eventsand of diversity of deep-seabenthic foraminifera
(Fig. 4), but this drop is not significantlylargerthan the normal in the
latest Paleocenecorrespond closely to the pattern expected
fluctuationsin diversity.Thereis no concentrationoflast appear_ for a major
catastrophe:a precipitous drop in diversity followed
angssat the boundary,nor of first appearances
just aboveit: by a period of unusually low diversity (Fig.
a); many last appear_
rather,a few first and last appearances
occurjust below,across, ances at and just below the faunal boundary, followed
by a
andabovetheboundary(Tablel). Althoughthereis an increase period
of many first appearances
(Fig. 3,Tabti2y.Many species
in the sumoffirSt andlastappearances
in theintervalcloseto the (including Gavelinella beccaiiformis, Gavelinella hWhalu.s,
Neo_
K/T boundary(especiallyat Site 6g9; Fig. 3), this period of
flabellina semireticuhta, Neoflabellinajarvisi Bolivinoides delicaincreasedfaunaltumoverstartedseveraltrunAre* of thousands tulus,
ffiramidina rudita, putknin coryelti, Aragonin velnscoensis,
of yearsbeforethe boundary,similarto what hasbeendescribed Titaxia paleocenica,
Tritaxia havanensis,Gyroidinoidesquadra_
for planktonicforaminiferalextinctions(Keller, l9g9). The lack tw Dorothia
trochoifus, Neoeponideshiilebrandti and Neoepo_
of an interval with extinctionsat the boundary,and of first ap_ nides lunata) have
a coeval last appearanceat both sites,but also
just aboveit, might be a resultof strongbioturbation at
pearances
many other locations over a wide range of paleodepths in the
acrossthe boundary(Barkerand others,lgSg). This is improba_ Atlantic Ocean (Tjalsma
and Lohmann, l9g3; Boersma,l9g4),
ble,however,because
thesamplesusedin thisstudywereselected the equatorial Pacific (Miller and
others, l9g7b), and in the
Numberof species
Calcareous
1 4 An
O.J
Ul
-:
O)
('|
200ni
cP9
L
o
-9 "!8 0 m
cP 12
*'-,,-,r'-ft '"-'r
-'"
o
o
':,]f;'
'-'-f
o
o
=
-9
o
* r'-*
o
o
cP 6-7
lt
,c 2OOm
t::
r,- - -----'a--'
q
l
CL
o
o
7
cP5
rj
cP 8
u
z
U
o
cP4
-cP_3cP2
I..
u
230m
cP 1b
o
o
,--
'r
z +u m
o
o
o
"*
J
\
N
s
*!.---t'
'?.t
af : 91t
C. daniae
Zone
.Ct
t
a.
22Om
G
2 4 Om
cP 1b
(g
'1.
220m
ZOUM
u
o
o
u
cP8
(E
=
-9
o
O)
(,
2L
z
u
o
u
ztum
(!
up
U
I O Um
Numberof species
Calcareous
,lannolossils
@
250m
o
F
F
@
r-
E
*- { t
E
F
o
5
site6eo
*
'=i
site68e
\
>
26Om
IigT.t +. Diversity(expresedas.numberof speciesper3fi) Tecimens)plottedvenussub.bottomdepth
for Sites689 and 690. The horizontallinesmark tie positionor tm ct trc**7r".tl"ry
(K/T) and
Paleoce.nelEocene
(P/E) boudaries_asptlbtislredby iulor**
nunnofosilbiostratigraphy
(pospichal
a-ndWise,1990a,1990b,1990c)andplanktonicforaminiferalUiosuatlgraphy
1990;Stott and
-of
fffou"r,
Kennetl 1990a);notethat the section Site6g9is plottedat u oire.en"iJepil'scare.
@
(,
488
E. Thomas
Biserial/Triserialspecies,o/o
o( ' o (,
.'{
Calcareous
Nannolossil!
14 0 m
a
N)
N
cP9
u
z
U
o
U
16 0 m
o
-9
o
cP8
o
cP5
I
z
c
u
-cP_3cP2
C. daniae
Zone
cP 12
c
rl
2l
u
o
U
t\)
cn
!
){
;s
}s
('lOCN
)s
\-----._
-?
cP 8
J
,t
cP 6-7
(E
-(:P r-?,'
u
$ 2a0m
cP 1b
!
o
N
o
5
A-
22Qm
o
-9
Il
t
CL
E
cP4
. ^nO l
21Om
3230m
-9
o
{_
220m
cP 1b
200ni
o
o
":::L
!
5 !zu u m
o
Calcareous
{annotossils
o
;{
1
cP 6-7
zovm
;={
.i*
=
o
240m
}C
Biserial/Triserial species, o/o
--'--*P-a
E rao.
Il
L't
.-l
€
250m
(t
s*e6eo
Site 689
260m
that belongto infaunalspecies,
asestimatedfrom
Figure5. Percentage
of specimens
in the assemblage
testmorphology(Corlis and Chen,1988).The horizontallinesmark the positionof the Cretaceous/
(P/E) boundariesas establishedby calcareousnannofossil
Tertiary (K/T) and Paleocene/Eocene
biostratigraphy(Pospichaland Wise, 1990a,1990b,1990c)and planktonicforaminiferalbiostratigraphy(Huber,1990;StottandKennett,1990a);notethat thesectionat Site689 is plottedat a different
depthscale.
southernoceans(Katz and Miller, 1988).The sameis true for
severalof the earliestEocenefint appearances,
suchas tlose of
Abyssaminapoagi, Pulleniabulloides,Globocassidulina
sabglobosa,andAnomalinaspissiformis.At Site 690, most of the last
appearances
occunedwithin an interval of lessthan 25,000yr
(usingthe time scaleof Aubry andothers,1988,andpaleomagneticdataon thelocationof ChronC24fromSpiess,in combinanannofossildatafrom Pospichaland Wise,
tion with calcareous
1990c).This is an unusuallyshort period for faunal eventsin
deep-sea
benthicforaminifera,which areconservative
organisms
living in a (usually)conservativeenvironment(Thomas,1985,
1986;Thomasand Vincent,1987;Miller andKatz,1987;Boltovskoy,1987).
Major differences
betweenthe developments
in the bathyal
environmentat Maud Riseat theK/T boundaryandin thelatest
Paleocene
areobviousnotjust in thefrequencies
offaunal events,
but also in the characterof the dominantspeciesin the assem(Figs.5,6,7).
blages,especially
ofinfaunalandepifaunalspecies
Epifaunalspeciesare dominantat locationswhere the oxygen
contentof deepwatersis highandlor thereis a low concentration
of nutrients;infaunalspeciesdominatein the presenceof high
concentrations
of organiccarbon(e.g.,Corlissand Chen,1988;
SenGuptaandothers,l98l; Caralp,1984;LutzeandCoulbourn,
1984;Bernard,1988).[t is not easyto distinguishbetweeneffects
tlere
oflow oxygenandhighnutrientsor organiccarbonbecause
commonlyis a correlationbetweenthesetwo factors.According
to CorlissandChen(1988),thereis a strongconelationbetween
percentageof Holoceneinfaunalspeciesalonga depth transect
from a few hundredsof metersto 4,000m depthin the Norwegian Seaand the flux oforganic carbonto the seafloor; infaunal
dominatewherethe flux of organiccarbonis morethan3
species
to 6 g'm-2'y1-1.
At Site 690 there are no changesin preservationof the
faunasin thesamplesacrossthePaleocene/Eocene
boundaryand
the K/T boundary,suggesting
that the faunal changesare not
artifactsof preservation.
Thereareno dataindicatingthat Maud
Rise underwentstrongvertical motions (exceptgradualsubsidence);thus,changesin the epifaunal/infaunalratio cannotbe
explainedby depth fluctuationsof the sites.Epifaunalspecies
part of thesections,althoughfluctuadominatein the Cretaceous
tions in relative abundanceof infaunal speciesoccur, and are
strongerat theshallowerSite689.JustabovetheK/T boundary
Late Cretarcous-emly Eocene mnssextinctions in the deepsea
Spiral species,To
Calcareous
1 4 O m\
RH H $'
Spiral species,g6
O
Calcareous
tlannofossils
u
zq
200rri
cP 12
o
d'S
cP9
o
-9
5180m
(t,
=
o
o
o
21Om
cP 8
?
L
(I
--J
d.{
}t
il
=-*_
u
c
o
o
o
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cP 6-7
o
B
o
4
=zJU m
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r
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naua
cP 1b
!
E.
o
€
UFC
cl
zz9m
24Om
cP4
o
c
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o
.*
-cP 3cP2
,5
240m
250m
cP 1b
C. daniae
Zone
z
tr
v( :P
o
o
E
o
f 20Om
260m
(no(,
N
cP8
cP 6-7
o
IQ
4
u
z
U
o
o
U
160m
m
z
F
.E
E
o
o
F
=
=--{
E
m
E
F*
site6eo
260m
Figure6.
of specimens
in theassemblage
that belongto epifaunalspecies,
asestimatedfrom
-Pelcentaqe
testmorphology
(Corlissand Chen,1988).The horizontallinesmaik the positionof the Cretaceous/
Tertiary (K/T) and Paleocene,/Eocene
(P/E) boundariesas establisheriby .a*r**
nannofossil
biostratigraphy(Pospichaland Wise, 1990a,1990b,1990c)and planttonic foraminiferalbiostratigraphy(Huber,1990;StottandKennett,1990a);notethatthesectionat Site689is plotted
at a difrer;t
depthscale.
there is a pronouncedpeak in relativeabundanceof epifaunal
speciesat both sitesanda concomitantdecrease
in relativeabun_
danceof infaunalspecies.The peak is lessobviousat Site 6g9,
possiblyasa resultof theunconformityacrosstheK/T boundary.
The relative abundanceof infaunal speciesthen recovers,and
increases
againslightlyabovetheupper/lowerpaleocene
bound_
ary (Fig. 4,215 mbsfat Site690;pospichalandWise,1990).A
largeincreasein therelativeabundance
ofthe infaunalspecies
(to
about 85 percent)occursat the level of the latest paleocene
extinctions:during the period of very low diversity(Fig. 4) the
faunais dominatedby infaunalspeciesof the Supirfamily Buli_
minacea(mainlythesmallspeciesTappaninaselmensis,
Bulimina
simplex,Siphogenerinoides
brevispinosa,andin a few samples
Aragoniaaragonenis;Fig. 5).
Suchextremedominanceby buliminid speciesshortlyafter
the benthic foraminiferal extinction has not been described
before,but 'l;-alsma(1976)and Tjalsmaand Lohmann(19g3,
Fig. 46) documenteda much lessextremeincreasein relative
abundanceof buliminidsat that time at Site 329 (paleodepth
1750 m, FalklandPlateau),and Boersma(1994) describeda
decrease
in specirnensizejust afterthe extinction.other authors
(Tjalsrnaand Lohmann,1983;Miller and others,l9g7b; Katz
andMiller, 1988)described
highrelativeabundances
of the epi_
faunalspeciesNuttallidestruempyijwt after the extinctions.At
Site690 the intervalof extremelyhighrelativeabundances
of infaunal speciesis very short (about 260,000yr), and thus this
interval might not have been sampledin sectionswith much
lower sedimentationrates,or it might not be represented
in the
sediments
in sectionswith unconformitiesor low recovery.
The relativeabundanceof infaunalspeciesdecreases
higher
in thesectionat theMaudRisesites,but remainsat higherlevels
than in the lower part of the sectionthroughout the studied
interval(uppermostPaleocene-lowermost
Eocene).Thediversity
did not fully regainthe high valuesof the late Maastrichtianani
earlyPaleocene,
andreachedits peakfor theCenozoicduringthe
earlymiddleEocene(Thomas,1990).
Thelast-appearance
ratesat theK/T boundaryat Sites6g9
and690 (rememberthat theseareratesof local lastappearances,
and not necessarily
extinctions)resembleratespublishedfor Trinidad(18 percentextinction;Beckmann,1960)andpreliminary
valuesfor centralPacific Site 465 and Walvis Ridge Sites525
and527(WidmarkandMalmgren,1988;extinctionrateof l0 to
.----<-
490
E. Thomas
25 percent).In general,however,data on extinction ratesof
benthicforaminiferaarewidely divergent,rangingfrom
deep-sea
(Webb,1973;Beckmann
about17to 82 percentsurvivorspecies
and others, 1982). This divergenceis probably partly due to
rates,as
in methodsof estimatinglast-appearance
inconsistencies
well as to differencesin taxonomicconcepts.For example,for
DSDP Site 208 (Lord Howe Rise, off New Zealand),Webb
(1973) estimatedan extinctionrate of 54 percentof the species,
per sample-benthic and plankbut he counted3@ specimens
In the Maastrichtian,about75 to 80 percentof
tonic specimens.
the faunaconsistsof planktonicforaminifera,so that fewerthan
werecounted.If the diversityat Site208
100benthicspecimens
are
resembles
that at Sites689 and 690, at least270 specimens
neededto obtainan estimateof the truediversityandrepresentation of the majorityof species(seeMETHODS). A reestimateof
the extinctionrates,usingWebb's(1973) tableswith presenoeabsencedata,resultsin an extinctionrateof 14 percent,with 40
out of 106speciCItoo rareto be useful.
On the other hand, part of the wide divergencein lastappearancerates is probably real-a result of different lastratesat difrerentdepths,with higherratesoccurringat
appearance
ratesfor the upperbathyalEl
shallowerdepttrs.Lastappearance
Kefsectionareabout50 percent(Keller,1988b),andthusconsiderablyhigher than for Sites689 and 690; extinctionat the
shallowerSite 689 appearsto be greaterthan at the deeperSite
690 (Table l). This differencein last-appearancntlteaccording
with Beckmannand others'(1982)
to depth is in agreement
observationthat there is more severeextinction in "Midwaytype" (shelfto upperslope)faunasthanin "Velasco-type"(lower
slopeandabyssalplain) faunasat the endof the Cretaceous.
The large extinction of planktonic speciesat the K/T
boundaryhasbeenwell documented(e.g,reviewby Thientein,
1982;Keller,1988b;Smitandothers,1988);thesedata,in combination with dataon carbonisotopicratiosin surfaceand bottom dwellers (Arthur and others, 1987; Zachosand Arthur,
1986;Zachosandothers,1989),showthattheproductivityin the
surfacewaterscollapsedat the K/T boundary.Thebenthicforaminiferal faunalchangesat the K/T boundaryat Sites689 and
690 areexactlythe type ofchangesthat would be expectedto
of someinfaunal
result from such a collapse:a disappearance
(P.
(high carbonflux) species reussi C. incrassata),andan overall increasein relative abundanceof epifaunal(low nutrient)
just after the boundary.The lack of a massextinctionin
species
benthicorganismssuchasdeep-waterforaminifera,which prob-
Cylindrical species,o/o
Calcareous o ( , o ( J l
\lannolossilr )s
Cylindrical sp€cies, o/o
N
Cn
\|
O
;'q
d's
ds
;t
140m
200m
cP9
crou
b {; q N
U
z
u
o
o
u
cP 12
U
z
r
o
6
o
;s
N ( ,l {
Calcareous
{
/^--.-.---.--
g
160m
21Om
cP 8
cP8
U
L
o
-9
Szzom cP 6-7
180m
,( E
6
o
o
cP 6-7
o
o
* 200m
-9
o
u
-C P 2-?'
6 23Om
6
.o
u
cP 1b
E
U
=
o
J
cP5
.ct
E
CL
$zzom
o
a24Am
o
u
2
cP4
l
c
=cP 3cP2
240m
C. danlae
Zone
260m
u
250m
cP 1 b
aogl
o
c
N
o
.:
€
o
z
I
E
o
=
t
E
F
@
=
F
site'eo
Site 689
260m
The horizontal
in the asemblagethat belongto cylindricalspecies.
Figure7. Percentage
of specimens
(P/E) boundariesas
(K/T) and Paleocene/Eocene
linesmark the positionof the Cretaceous/Tertiary
nannofossilbiostratigraphy(PospichalandWise, 1989a,b, c) andplanktonic
by calcareous
established
foraminiferalbiostratigraphy(Huber,1990;StottandKennett,1990a);notethat thesectionofSite 689
is plottedat a differentdepthscale.
Late Cretaceous-earlyEocene mass.extinctionsin the deepsea
491
ably subsistlargelyas detritusfeeden,is in agreementwith the boundary(suchasG. beccariiformrs)becameextinctin thelar€sfi
theorythat detritusfeedingoffersa bufferto extinction(Sheehan Paleocene;
manyof the speciesthat becameextinctwereefihr
and Hansen,1986).In addition,bathyalto abysal benthicspe- nal species.Theseextinctions,however,have remainedunexciescommonlylive in an environmentof very low food supply, plained(e.g.,Culver, 1987).Thereis a maj61changein the
and thusarewell suitedto surviveperiodsof low productivity.
carbon isotoperecord at the sametime as the benthic fruml
In the interval below the K/T boundary,thereare fluctua- extinction (worldwide, Shackleton,1987; Miller and otherS
tions in ratio of infaunalto epifaunalspecies(Thomas,1990), 1987a;KaE and Miller, 1990),which had beeninterpretedas
suggesting
that fluctuationsin productivity were common,and pos.siblyresultingfrom a global decrease
in surfaceproductiviry
may have led to expansionand contractionof the oxygen- (Shackletonand others,1985).Miller and others(1987b)and
minimum zone.Therefore,many of the benthic foraminiferal Katz and Miller (1990),however,documentedthat the gradient
specieswere able to survivethe evengreaterfluctuationin pro. in 6l3C valuesbetweensurfaceand deepwaten did notchange
ductivity at the end of the Cretaceous.In my opinion, faunal significantlyduring this period(in contrastwith the situationat
changesof deepseabenthicforaminiferaat the end of the Cre- theK/T boundary;Zachos
andArthw, 1986),andthoughtthat a
taceous(smallincreasein relativeabundance
ofepifaunalspecies, decrease
in productivitycouldnot explainmorethana part of tbe
and minor extinction,mainly of infaunalspecies)canbe consid- observedchangesin the 613Crecords.They concludedthat th
ered to be secondary,resulting from the collapseof surface largechangesin the 6l3C recordin theupperPaleocene
probably
productivity. The causeof KlT extinctionwas thus a surface reflect(at leastpartially) a changein 6l3C of meanoceanwats
event,whetherit was a bolide impact (e.g.,Alvarez, 1986;this as a result of changesin the input or output ratio of organfo
volume)or relatedto large-scale
volcanism(Officer and others, carbonto carbonatecarbon(Miller and Fairbanks,1985).
1987;andthisvolume).Theeffecson thelowerbathyalfaunaon
Comparisonof thebenthicfaunaleventsat the K/T boundMaud Riseappearto be secondary,andthereis no evidenceof a ary with those in the latest Paleocenesuggeststhat the
major disturbanceof thedeep-waterenvironmentitself.
Paleocene/Eocene
extinctionof deep-seabenthic foraminiferal
The situationin the latestPaleocene
(planktonicforaminif- speciesdid not resultfrom a drop in surface-water
productivity.
eral ZonesP6t/b) wasvery different at that time therewasno The speciesthat becameextinct in the latestPaleocene
had surextinctionof planktonicspeciescomparablein sizeto the end- vived the collapseof productivity at the end of the Cretaceorq
Cretaceous
extinction,and diversitiesof calcareous
nannofossils, and thus it appearsunlikely that they would becomeextinct as
planktonic foraminifera, and dinoflagellateswere increasing the result of a much smallerdrop in productivity in the late
(Oberhaensliand flsti, 1986).At Maud Rise,calcareous
nanno- Paleocene:it has been well establishedthat the extinction of
fosils indicated maximum surface-watertemperaturesat the planktonic taxa at the end of the Cretac€ouswas much more
samelevelasthebenthicforaminiferalextinction(pospichal,per- severethan any decreasein divenity during the Cenozoic.In
sonalcommunication,1989).Thediversityof planktonicforami- addition,theMaudRisefaunalpatlernsof benthicforaminiferaat
niferal speciesat Maud Rise increaseddramaticallyduring the the time of Paleoceneextinctiondo not indicatea dccreasen
late Paleocene,and remainedhigh during the early and early productivity: there is an increasein the relative abundanceof
middle Eocene(Stott and Kennet! 1990a).Warm-waterindica- infaunal(highorganiccarbon)species,
suchasmightbe expected
tor speciespenetratedto high latitudesin the southernAtlantic from an increasein productivity,or a decrease
in oxygencontent
Ocean(Oberhanesliand llsii, 1986;Boersmaand othen, l98Z), of the deepwaters,resultingin lessoxidationof organicmaterial.
and oxygenisotopic recordsindicatethe strongestincreasein Thusit appeanthat the late Paleocene
eventwaslargelya deep
temperaturesof the Cenozoicfor bottom waters and surface waterevent(affectingwatersat lower bathyaldepthsor deeper),
water (Shackleton,1986;Oberhaensli
and Toumarkine,1985; in contrastwith the K/T boundaryevenLwhich was largelya
Oberhaensli,1986;CorlissandKeigwin,1986;Miller andothers, surface-water
event.Thissuggests
that thecauseof thelatePalo
1987a;Prenticeand Matthews,1988).In addition,it wasa pe- ceneextinctionshouldbe soughtin changesin the deepoceanic
riod of leasttemperaturedifferencebetweensurfaceandbottom environment,and such changesare most likely circulation
waters(Shackleton,1986).Thesecharacteristics
of the isotopic changes,
which occurin theright time range(lessthan25,000yr)
recordsare alsopresentin the isotopicrecordsfrom Maud Rise for the late Paleocene
extinction.
sites(KennettandStott,1990;Stottandothers,1990),with the
Many scientists,from Chamberlin (1906) through Hay
strongestincreasein temperatures
ofdeepandsurfacewaters,and (1988),havesuggested
that thedeepwatersof the oceansmayin
the lowestdeepto-surfacetemperaturegradientsat the time of thepasthaveformeddifferentlyfrom theway in which theyform
the benthicfaunalextinction.
now, i.e.,by sinkingof dense,cold,well-oxygenated
andnutrientThePaleocene/Eocene
benthicforaminiferalextinctionwas depletedwaten at highlatitudesin tle northernAtlantic (Worthglobal (Beckmann,1960; Braga and others, 1975; Schnitker, ington, 1972) andat high southernlatitudesin the WeddellSea
1979;ljalsma and Inhmann, 1983;Miller and others,1987b; (Fosterand Carmack,1976).In the absence
of largepolar ice
Katz and Miller, 1990),and represents
the largestCenozoicfau- caps,deepwatersmighthaveformedby evaporationand formanal turnover in deepseabenthic foraminifera,larger than the tion of dense,warm, salty deepwaters(Brassand othen, 1982;
K/T boundaryevent.Many speciesthat had survivedthe K/T Barron, 1987; Prenticeand Matthews,1988).Severallines of
492
E. Thomas
isotopic evidence,however,srggestthat deep to intermediate Eocene(Kennettand Stott, 1990).Miller and othen (1987b)
(Bar- suggested
that deepwatersformedat highlatitudesduringthelate
watersformedat high latitudesduringthe LateCretaceous
and that circulationmay havechangedin the early
rera and others,1987; Banera and Huber, 1990) and the late Paleocene,
boundary.More recentdata
Paleocene(Miller and others,1987b),even in the abseneeof Eoceneor at the Paleocene/Eocene
largeicecaps.A majorproblemin evaluatingtheevidencefor the (Katz and Miller, 1990;Miller and Katz, 1988)on materialreexistenceof largedeep-watermasses
of salty,warm wateris the coveredon ODP l-eg ll4 in tle southemmostAtlantic indicate
fact that the intermediatewaten (down to depthsof severalki- that during the late Paleoceneand early Eocenethe southern
lometen) may have formed by sinking at high latitudes,while oceanswere filled with nutrient-depleted(i.e., young) bottom
deeperwaten formedby evaporationandsinkingat low latitudes water, which presumablyformed by sinking at high southern
(e.g.,ManabeandBryan,1985;Hay, 1988,Fig. 5B).Thus,data latitudes.Theseauthorsalsoconcludedhowever,that the southfrom sitesat intermediatedepths(suchaslower bathyalSites689 ern supply of "young" deepwater was reducedor evenelimiboundary(58 to 57 Ma), and
and 690) might indicateformation of deepwatersby sinking, natednearthe Paleocene/Eocene
while deeperbasinswere filled with saltier, warmer bottom they agreedthat this circulation changecould have triggered
worldwidebenthicforaminiferalextinctions.
waters.
Maud Rise,however,is currentlynot in the path of newly
Deep-seabenthicfaunasat Sites689 and 690 were dominatedby epifaunalspecies
duringthelateMaastrichtianandearly formed Antarctic Bottom Water. becausethe site is too far toPaleocene,
suggesting
the existenceofwell-oxygenatedwatersat ward the east,and is bathedwith the relatively Warm Deep
lgwer bathyaldepthsin theMaud Risearea;preliminarydataon Water flowing into the Weddell Sea from the lndian Ocean
andothers,l97l; Anderson,1975;Pudseyandoththeostracodefaunasfrom Maud Risesupportthehypothesisthat (Seabrooke
the bathyal waterswere well oxygenated(P. Steineck,written en, 1988).Therefore,datafrom the Maud Risesitesmay not be
communication,1989). During the Paleocene,however,there indicative of conditionsat the hypotheticalPaleocene-Eocene
in whichtherelativeabundance
of infaunal sitesof formationof high-latitudedeepwaters;recentdeepwaten
wereseveralepisodes
speciesincreased,especiallyduring the late Paleocene(seee.g., riseup aroundMaud Risefrom depthsof 1,500to 2,000m to the
Fig.5, 210 mbsfat Site690,corresponding
to themiddlepartof surface.whereasbottom watersare formedin the northwestern
thelate Paleocene,
about6l Ma in thetime scaleof Berggrenand endof the WeddellSea(Comisoand Gordon,1987).More data
others, 1985). Theseeventsculminatedin the late Paleocene and precisestratigraphiccorrelationsareneededbeforethe exact
extinction event of deep-seabenlhic foraminifera,when many extentof oxygen-poordeepwaterscanbe evaluated.In my opinbecame ion, however,the largebenthicfaunal extinctionin the late Paepifaunalspeciesthat had survivedsincethe Cretaceous
extinct.Theseepisodescanbestbe explainedby eitherthebegin- leoceneis best explainedby a major changein deepwater
Formationof warm,saltydeepwatercan
ning of, or the strongincreasein, formationof warm salinebot- formationalprocesses.
provide
to causethe observed
the circulationchangenecessary
tom waters,so that the volumeof thesewarm and salinewaters
increaseduntil their upperlimit reached(at least)the levelsof faunalchanges.
Sites689 and 690. Thesewaterswould have a relativelyhigh
temperatureat their formation,andthusa low oxygencontent.In CONCLUSIONS
addition, cold oxygenatedwatersprobablyformed somewhere
and first appearances
l. The frequencyoflast appearances
closeto the Maud Rise sites,so that they would not havehad
foraminifera
from
Maud
Rise(WeddellSea,
of
deep-sea
benthic
time to becomemoredepletedin oxygenduringtheir shorttravel
patterns
indicate
that therewasno
Antarctica)
and the divenity
to the sites.Warm waiersformedat low latitudes,however,had
Cretaceous/Tertiary
mas
these
organisms
at
the
extinctionof
to travel a long distancebeforereachingMaud Rise,and thus
becameevenmore depletedin oxygenby the time they anived boundary.A short increasein relative abundanceof epifaunal
just after the boundarycan be explainedas a secondary
there.The faunasdominatedby the speciesTappaninaselmensis species
effect
of
the collapseof primaryproductivity.
canbe seenasthe Paleocene/Eocene
equivalentof morerecent
and first appearances,
2.
The
frequencyoflast appearances
faunasdominatedby bolivinidsor uvigerinids.Preliminarydata
patterns
for the latest
in
diversity
presence
combined
with
the
of
changes
of
on the ostracodefaunasfrom Maud Riseshow the
of deep-sea
Paleocene,
mass
extinction
show
that
there
was
a
lownon analogostracodefaunasduring the short interval of
(57.5
increasein
Ma).
A
large
foraminifera
benthic
at
that
time
faunas
rediversitybenthicforaminiferalfaunas;theseostracode
just
relative
infaunal
after
the
extinction
abundance
of
species
(on
generic
younger
level)
much
semble the
deep-thermospheric
in
(P.
by
a
change
deep-water
suggests
that
the
extinction
was
caused
from
Mediterranean
written
faunas
the
Steineck,
communicadeepwatersat lower bathcirculation,andthat moreoxygenated
tion, 1989).
Oxygenand carbonisotoperecordsfrom Maud Rise and yal depthswerereplacedwith warmer,lessoxygenatedwaters.[t
prothe southernOceansarein agreementwith this interpretationof is improbablethat the extinctionswerecausedby decreased
the benthicforaminiferaldata.The benthicforaminiferaloxygen ductivity, becausethe speciesthat becameextinct had survived
isotoperecordfrom the Maud Risesitessuggests
that production the almostcompletecollapseof primary productivityat the end
of warm deep watersincreasedduring the earliestpart of the ofthe Cretaceous.
Late Cretaceous-earl! Eocene mAssextinctions in the deepsea
3. Comparisonof the faunal recordsof deep-seabenthic
foraminiferaacrossthe Cretaceous/Tertiary
boundary(massextinction at the surface,not in the deepsea)and the uppermost
Paleocene(massextinctionin the deepsea"not at the surface)
srrggests
that eventhelargermass-extinction
periodsdo not influenceall the environments
on Earth,from the surfaceto the deep
waters.Massextinctions,in thesedifferentenvironmentsareapparentlynot related.
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