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Biogeography of the Late Paleocene Benthic Foraminiferal Extinction

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Biogeography of the Late Paleocene Benthic Foraminiferal Extinction t2 Biogeographyof the Late Paleocene Benthic ForaminiferalExtinction ELLENTHOIYAS ABSTRACT The latestPaleocene benthic extinction thus was corn- During the Late PaleoceneThermal Maximum (LPTM) plex.and factors such :is changes in deep-seacirculation, benthic fbraminif'era at rniddle bathl'al and greater increasedCaCO. corrosiveness.increased lemperatures, depthssuffered extinction of 30-507cof speciesduling a decreasedoxygenation. and changesin the patternsof lew thousandycars. Extinction was less sevcrc at neritic high productivitymay havecontributcd to its sevcrity. to upper bathyal depths, where temporary changc-sin launal compositionprevailed. Preextinction dcep-sea Environmental Setting taunaswere cosmopolitanand diverse.and contained heavilycalcified species. Imrnediate postextinction fau- The late Paleoceneand early Eocenewere the warmest naswere more variable geographically, exhibited low di- epochsof the CenozoicEra: polar ice capswere almost l'ersity.and were donrinatedby thin-walledcalcareous certainlyabsent. and shallowseas covered large parts of or agslutinatedtaxa, possibll, because CaCO, dissolu- all continents.During theseepochs, major changesoc- tion increasedglobally liom neritic to abyssaldcpths cured in climate and in the carbon cycle on -elobal just bcfbrethe extinction. Thcse assernbla-ges were dont- scalesof rnillions to thousandsof years. Long-term inatcd either by long-lived taxa sLrchas Nuttttllide.r warming of the deep oceansstarted in the mid-Pale- truerrtpt'iorby bulirninidtaxa. the latteraccompanicd by oceneEpoch (Miller et al. 1987a;Shackleton 1987; a-uglutinantsin somcareas. Kennettand Stott 1990;Zachos et al. 1992.19931 Seto Faunasdonrinated by N. tmentpri rverecontnton in the 199-5).Warm-water pelagic marine organismspene- Sor.rthAtlantic and at lower bathl'al through upper trated to polar latitudesby the end of the Paleocene abyssaldepth in the lndian Ocean.and might inclicate Epoch (Stott and Kennett 1990; Premoli Silva and oligotrophicconditions as well as incrcasedcorrr)si\L-- Boersma 1984: Boersmaet al. 1987: Aubry 1992; ness.Buliminid-dominated launas might indicatehigh Berg-{ren1992). Thermophilic vertebrates occurred in ratesof depositionof organicmatter or lor.l-oxygencon- theArctic (Estesand Hutchison1980: McKenna 1980t ditions.Such llunas werccommon globllly alongconti- Markr.r'ick1994). with vegetationand soil types indi- nentalrnargins. and locallv co-occun'edu'ith sedimcnto- cating warrn clirnates(Kemp 1978: Nilsen and Kerr logicor planktonictaunal indicators of high procluctivitr. 1978:Wolf'e1994: Basinger et al. 1994:Manum 199,1). In the bathyalcentral Pacific. however. buliminid-domi- Clay mineralassociations in oceanicsediments at high natedfaunas co-occun'ed with planktonicfaunas sug- to midlatitudes indicate high humidity and intensc- gestinsoli-sotl'ophi'. and thev could reflectlow-oxygen chemical weathering(Antarctic. Robert and Kennett conditiorrslesultin-u from sluggishocean circulation. ox- 1992;New Jerseymargin. Gibson et al. 1993;New idationof clissociatedmethanc hydrates. or rlarming ol' Zealand.Kaiho et al. 1996).Oxygen isotopeclata sug- bathl'al irbyssalwaters caused by a chan-gein deep-sea gest that latitudinal temperaturegradients were ver)/ circr.rlation.Alternatively, they could indicatethat thc shallow (Shackletonand Boersrna198 l: Stott et al. tiaction ol'organic matter rcaching the seafl(x)rin- 1990: Barreraand Huber 199l: Zachoset al. 199,1: creasedas a rcsult of decreasedoccanic oxygenf,tion. Braloweret al. 1995a,1995b; Lu andKeller 1995b). 214 The Late PaleoceneBenthic Foraminiferal Extinction 215 Ratesof speciesorigination and diversitywere high fbr and Miller 1992 Lu and Keller 1993. 1995a,1995b; ten'estrialvertebrates and flora (Hooker 1991;Collin- Canudo et al. 1995: Aubry et al. 1996: Thomas and son 1983:Reaet al. 1990:Winget al. 1991,1995; Maas Shackleton1996: Schmitz eL al. 1996).superimposed et al. 1995).as well as fbr pelagicoceanic organisms on a long-term decreasein values that startedin the (Romein1979: Boersma et al. 1987:Boersma and Pre- middle PaleoceneEpoch (Shackletonand Hall 1984; rnoli Silva 199l: Corfieldand Shackleton1988: Mc- Shackleton1986. 1987:Corfield et ai. l99l; Corfield Gowran 199l; Aubr1, 19921Berggren 1992: Corfield and Cartlidge 1992 Corfield 1995).An isotopeexcur- 1993:Kelly et al. 1996).The latePaleocene and earliest sion similar in magnitudeand estimatedduration oc- Eoceneepochs thus constitutea time of major innova- curredin the toothenamel of herbivoresand in carbon- tion of the biosphere(Briggs 1995 ). ateconcretions on land (Koch et al. 1992.1995: Stott et The unusualwarmth of theseepochs has beenconl- al. 1996).and in terrestrial-derivedorganic matter in a rnonlyexplained by high atmosphericpCO, concentra- New Zealandmarine section(Kaiho et al. 1996).The tions.probably ciiused by'plate tectonic processes such 'uvholeatmospheric-oceanic reservoir thus undervu'enta as massivevolcanism in the North Atlantic Volcanic rapid.negative shift in carbonisotope values during the Provinceduring initial openingof the North Atlantic. LPTM. the durationof which hasbeen estimated at be- decarbonationof limestoneor oxidationof organic-rich tween 50 kyr (Thornasand Shackleton1996) and 200 sedirnentsduring the beginningof the India-Asia conti- kyr (Kennettand Stott l99l ). ncntal collision. and high hydrothermalactivity along Massbalance equations show that this carbonisotope nridoceanicridges (see Thomas and Shackleton1996 ercursionwas so largethat it probablycould not have tbr a review). Proxy data for atmospheric7rCO. levels beencaused by transf'erof terrestrialbionlass into the tenttrtivelysupport higher values than todav (Cerling ocean-atmospheresystem or by eruption of volcano- 199l: Freernanand Hayes 1992). although this rematns genic CO.: it was so rapid that it probably could not debatable(Stott 1992).Clirnate modelin-e indicates that have beencaused by a changein depositionor eroslon at suchCO. lcvelstropical temperatures would be much ratesof carbon in carbonateas comparedto carbonin higher than deduced fiorn oxygen isotope data. and organicmatter (see Thomas and Shackleton1996. fbr a mechanismsfor highly incrensedheat transportfiorn review). This leaves f'ew explanationsopen. and re- krr,i,to high latitudesat the low latitudinaltemperature centlirit hasbeen speculated that this unusual,negative gradientsremain r.rnexplained (Sloan et al. 1995:Sloan carbon isotopeexcursion could have been causedby andRea 199-5). massivedissociation of (isotopicallyextremely lightt In the latestPaleocene Epoch the world warmedeven oceanicmethane hydrates as a resultof the deep-ocean more fbr a shorttime (Kennettand Stott 199l: Pak and warming(Dickens et al. 1995:Kaiho et al. 1996). Miller 1992:Thornas and Shackleton1996). which has the Late PaleoceneThermal Maximum been named Benthic Foraminifera TLPTM:Zachos et al. 1993).This eventoccurred rvithin paleomagneticChron C2:1r.in nannofbssilBiochron The latest Paleocenebenthic fbraminif'eralextinction NP9 (= Biochron CPt3),and befbrethe last appearance has been describedfrom land sectionsand at oceantc datur-n (LAD) of the planktonic fbraminif-er Mr.,rrr- drill sites. at depths ranging from outer neritic to .ot'ella veluscoen.si.s(Aubry et al. 19961Berggren and abyssal(appendices 12.1 and 12.2:figure l2.l). This Aubry 1996).Oxygen isotopedata indicatethat inter- extinction was rapid: it afl-ectedbenthic fbranlinif'eral mediateto deepocean waters globally warmedby'1 to faunascatastrophically worldwide. and it occurreddur- 6" C over lessthan a f'ewthousand years (Kennett and ing or close to the beginning of the LPTM and the Stott 199l: Thomasand Shackleton1996). but tropical ne-eatir,'eexcursion in carbon isotopes.just before the to subtropicalsurface to neritic temperaturesremained Paleocene/EoceneEpoch boundaryas most commonly constant(Stott 1992; Bralower et al. 1995a.1995b1 Lu defined(Thomas 1989.1990b: Stott and Kennett1990; and Keller 1995b:Schmitz et al. 1996).This rapid Nomura 199I in combinationwith Setoet al. 1991: Pak warming of the deep ocean has been explainedbi' a andMiller 1992;Bralower et al. 1995a,1995b; Canudo changein deep-to intermediate-watercirculation. dur- et al. 1995in combinationwith Ortiz 1995:Aubry et al. ing which the dominantsources of deepand interrnedi- 1996:Thomas and Shackleton 1996: Kaiho et al. 1996). ate waters shifted from high to subtropicallatitudes This major break in deep-seabenthic foraminiferal (Kennettand Stott 199l: Pak and Miller 1992:Thomas lbunas occuned between the Paleoceneand Eocene andShackleton 1996). epochsif Viewedat coarsetimescales. whereas plank- Coeval with this short-termwarming was a shifi in tonic foraminifera i.rnderu'enta major extinction at the carbon isotope values by about -2'/rr, in surfaceand endof theCretaceous Period (Cushman 1946; Beckmann deepwaters of all oceans(Kennett and Stott 199l: Pak 1960:von Hillebrandt1962). After the late Paleocene 215 THCI'1AS described [:1::':ii;i,,T::il]li:,:llljH;'il...,1jp,;T,i:::"""'as inappendices r2r and r2 2: nun,bers (driil sites)and rerters Thc paleoge ogr.phl rf thecon rine n r: in rhe,atr' pureue eneEpoch is aficrZach.s et al. ( I 99.r). benthic extinction faunaswere predominantlyof lclw (ODPI Sites 689 and 690 (Wed<tellSea: Thomas diversitythroughout the bathyaland abyssal and regronsof Shackleron1996). South Atlantic (Walvis the oceitns. whereas coeval planktonic Ridge) Deep organtsms Sea Drilling project (DSDp) showed high Sites 525 and 527 rates of speciesturnover. hi-eh
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