The K/T boundary of Gams (Eastern Alps, Austria) and the nature of terminal Cretaceous mass extinction

199 Pages·2009·9.56 MB·English

by  Grachev A.F.

THEK/TBOUNDARYOFGAMS(EASTERNALPS,AUSTRIA)
ANDTHENATUREOFTERMINALCRETACEOUSMASSEXTINCTION
The K/T boundary of Gams (Eastern Alps,
Austria) and the nature of terminal
Cretaceous mass extinction
Andrei F. Grachev
Editor
AttheendoftheCretaceous(65Maago)theEarthsufferedthegreatbiologicalcrisis
whenestimated60%oftheformerspecies,amongthemthedinosaurs,becameextinct.
Morethan3000paperswerepublishedforthelast30years,concerningthediscussion
thisquestionbutthedecisionremainsunresolved. Authorsproposethenewapproach
tothisproblembasedonthedetailedmicropalaeontological,lithological,geochemical,
nanomineralogical, isotopic and petromagnetic investigations of the unique sedimen-
tary sequence at the Cretaceous-Paleogene boundary in the Gams area, Eastern Alps,
Austria.
Theconclusionsdrawnfromtheresultsofanalysisprincipallydifferfromallpreex-
istingdataonthetransitionallayerbetweentheCretaceousandPaleogeneandprovide
another look at the reasons for the mass extinction of living organisms at 65 Ma ago.
These data eliminate the need for opposing volcanism to an impact event: both took
place,butthechangesinthebiotawereinducedbyvolcanism,asalsowastheappear-
anceoftheIranomalyitself,whereasthefallofacosmicbodyoccurredapproximately
500–800yearslater.
AmEndederKreidezeit,vor65MillionenJahren,erlebtedieErdeeinebedeutende
biologischeKrise: Gescha¨tzte60%derArtenstarbenaus, unterihnendieDinosaurier.
Obwohlu¨ber3000PublikationenzudiesemThemaindenletzten30Jahrenerschienen
sind,bliebdieUrsacheweiterimDunkeln. IndemvorliegendenBandwirddasThema
anhand mikropala¨ontologischer, lithologischer, geochemischer, nanomineralogischer,
isotopischer und petromagnetischer Untersuchungen neu beleuchtet. Grundlage ist
dieeinzigartigeAbfolgedesGrenzbereichsKreide/Pala¨ogennahedesindenOstalpen
(O¨sterreich)gelegenenOrtesGams.
DieSchlußfolgerungenausdenUntersuchungenunterscheidensichprinzipiellvon
fru¨heren Interpretationen der Genzschicht an der Kreide/Pala¨ogen-Grenze: Durch
die neuen Ergebnisse wird die Diskussion Vulkanismus oder Impakt obsolet: Beide
Vorga¨nge fanden statt, der große Einschnitt bei den Biota wurde so wie die Iridium-
AnomaliejedochdurchdenVulkanismusverursachtundnichtdurcheinenkosmischen
Ko¨rper. DieserhatseineSpurenerst500 800Jahrespa¨terhinterlassen.
DOI:10.2205/2009-GAMSbook
This book is published by The Geological Survey of Austria in cooperation with the Geophysical Center of
the Russian Academy of Sciences. The camera-ready copy of this book is produced from electronic version
composedusingLATEX2εtypesettingsystemundergamsbooktemplate.
Preface
Inmid-60softheXXcenturyIwasprivilegedtogetacquaintedwithLevGumiljevwho,at
thattime,wasoverwhelmedbytheinfluenceofgeographicalenvironmentonthedevelop-
ment of the society. His ideas, stating that such periodic catastrophes as sharp changes of
the climate, leading to drought and the disappearance of natural environment for planting
and breeding, had caused mass, up to the millions, migration of people, wars and changes
of state boundaries. These ideas were revolutionary: they neglected “the role of classes”
and“classstruggle”. WhiletalkingtoLevGumiljev,Iwasthinkingthatatimewouldcome
when I also get into studying a similar problem related to the influence of geographical
environmentonthebiosphereinthegeologicalPast.
My professional preferences, as a geologist, were related to tectonics and magmatism, as
wellasdisclosingtheevolutionoftheseprocessesinthehistoryoftheEarth. Inmylectures,
which I had been delivering for 20 years in the Leningrad University, I, quite naturally,
touchedupontheproblemofmassextinctionsinPhanerozoic. Theentiregeologicalchron-
icle is devoted to them. Nevertheless, I was not focussing on this problem, being of the
opinionthatthiswasapurelypalaeontologicalproblem.
I became intrigued by the problem of catastrophic events in the history of the Earth much
later, because of studying mantle plumes, especially one of its main manifestations – mag-
maticactivity. Once,inasecond-handbook-shop,IboughtabookbyGeorgesCuvier“Cat-
aclysmsonthesurfaceoftheEarth”(“Discourssurlesrevolutionsdelasurfaceduglobe”),
translatedintoRussianbythePublishingHouse“Academy”in1937. Theideaabouttherole
ofcatastrophicextinctionsinthehistoryoftheEarth,aspresentedbyG.Cuvier,stronglyop-
posedtheviewsofCh. Lyellandhissuccessorsonslow-pacechangesofthebiosphere.
Knowing that “Something is rotten in the state of Denmark,” I decided to find out how
mantle plume volcanism influences the bioshpere. But, by this time, the ideas of G. Cuvier
were unexpectedly supported by the study of L. Alvarez, Nobel prize-winner in physics.
L. Alvarez and his colleagues identified anomalous concentrations of iridium, clearly ex-
ceedingknownandmaximalpresencesoftheseelementsinthelithosphere,inthelayersof
themountainrockattheK/Tboundary(65Mayago)intheGubbio(Italy)andStevns-Klint
sections(Denmark). Theypresumedthatthoseanomalieswereconnectedtothecollisionof
a large-sized meteorite (or an asteroid) with the Earth which could have happened at that
time: suchbodieshavethesameamountofiridiumasthelayersattheK/Tboundary. Such
event could have caused the conditions of a “nuclear winter” as its consequence, within its
first days leading to the extinction of the majority of terrestrial and ocean organisms, and
theprocessofphotosynthesiswouldhavebeenceasedformanyyears.
ThereactionoftheglobalscientificcommunitytowardsthearticlepublishedbyL.Alvarez
et al. was unanimous: according to numerous follow-up publications, a high presence of
iridium was found in practically all cross-sections at the K/T boundary. Doubts expressed
by a number of scientists were not taken into account, though there were obvious grounds
forthem!
In 2000 I published an article in the magazine “Earth and Universe”, where I presented the
evidence of the connection between the volcanism of mantle plumes and mass extinctions
withinthelast540Mar: thosecouldnotbeexplainedeverytimebythefallofasteroids.
3
4
Thedesiretofindbymyselfthesolutiontothisproblemledtothedecisiontostudyacross-
section with a clearly expressed iridium anomaly. Inside Russia, after the collapse of the
SovietUnion,itwasimpossibletofindafullcross-sectionattheK/Tboundary,andacross-
section which was considered as closest to Moscow was located in Austria. In 2002, after
having discussed the problem with O. Korchagin, paleontologist from the Geological Insti-
tute of the Russian Academy of Sciences, and was specializing in studying of foraminifera
– leading one-cellar organisms, which permit to identify the age of marine sediments, we
decidedtocombineoureffortsinstudyingoneofsuchcross-sections.
Twoimportantcircumstancescontributedtotherealizationofthisidea.
The first one was of family nature. My wife, Vera, was a diplomat and worked at that time
in Vienna. She was very helpful in organizing “the base”, as geologists say, and in creating
ageneralatmospherefavorableforourwork.
The second one was related to the Natural History Museum in Vienna, which provided
us with a monolith cut out of a cross-section with an excellent and clearly expressed layer
at the K/T boundary of Gams (officially Gams bei Hieflau) in Austria for the research. In
the course of all those four years we have been enjoying the support and attention of our
Austrian colleagues – Dr. Herbert Summesberger, Dr. Mathias Harzhauser, and Dr. Heinz
Kollmann.
Having the monolith we could study the transitional layer like the surgeon in operating
theatre, that it was impossible to do at the outcrop. The first results presented to the wide
audienceattheMuseumofNaturalhistoryinViennaon6February2006,wereunexpected:
wefoundthatextinctionwasinducedbyvolcanismbeforeanimpactevent.
In following years we studied another two outcrops in Gams to be sure that our results are
correct. Allthesedataarepresentedinthisbook.
We have to mention that we enjoyed constant attention to our research paid by the lead-
erships of the National Park and European Geopark Eisenwurzen in St. Gallen: Reinhard
Mitterbaeck and Katharina Weiskopf and the Mayors of Gams: Hermann Lußmann and
ErichReiter.
We are grateful to S. Lyapunov, I. Kamensky, A. Kouchinsky, B. Krupskaya, N. Gorkova,
I. Ipat’eva, A. Savichev, V. Zlobin, N. Scherbatcheva, A. Nekrasov, A. Gorbunov from Geo-
logicalInstitute,RussianAcademyofSciences,fortheirhelpinthepreparationsofsamples
andthechemicalandisotopicalstudyoftheGamssectionsamples.
The electroinc version of this book was prepared at the Geophysical Center RAS by V. Ne-
chitailenko (developing of template and associated software and designing CD and online
versions) and T. Prisvetlaya (initial typesetting and technical proofreading). I greatly ap-
preciate to Vitaly Nechitailenko for his comments and advices related to publishing of this
book.
This study was financially supported by Program 5 “Interaction of a Mantle Plume with
the Lithosphere” of the Division of Earth Sciences, Russian Academy of Sciences, and
GrantRSH-1901.2003.5fromthePresidentoftheRussianFederationforsupportofresearch
schoolsandGrant030564303oftheRussianBasicResearchFoundation.
AndreiF.Grachev,Editor
February2009,Moscow–Vienna
Contents
TheK/TBoundaryofGams(EasternAlps,Austria)andtheNatureofTerminalCretaceousMassExtinc-
tion 1
Preface 3
Introduction byA.F.Grachev 7
Chapter 1. A Review of the Geology of the Late Cretaceous-Paleogene Basin of Gams (Eastern Alps,
Austria) byH.A.Kollmann 9
1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.2 OutlineoftheTectonicHistory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.3 TheCretaceous-PaleogeneBoundaryinAlpineDeposits . . . . . . . . . . . . . . . . . . . . . . . . 10
1.4 TheGosauGroupofGams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.5 TerminationoftheGosauCycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.6 LocationsofSectionsStudiedandSamplesPreparation . . . . . . . . . . . . . . . . . . . . . . . . . 13
Chapter2. Biostratigraphy byO.A.KorchaginandH.A.Kollmann 19
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.2 ForaminiferalAssemblages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.3 PreservationofForaminifera. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.4 TerminalMaastrichtian . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.5 LowerPaleogene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.6 AssociationofPlanktonicForaminifera . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Chapter3. GeochemistryofRocksintheGamsStratigraphicSequence byA.F.Grachev 39
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.2 MethodsofMaterialPreparationandStudying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.3 WholeRockChemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
3.4 TraceandRareEarthElements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
3.5 IsotopicCompositionofHelium,Carbon,andOxygen . . . . . . . . . . . . . . . . . . . . . . . . . 54
Chapter4. MineralsoftheTransitionalLayerinGamsSections byA.F.Grachev,
S.E.Borisovsky,andV.A.Tsel’movich 59
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
4.2 SamplingProcedure,SamplePreparationTechniques,andStudyMethods . . . . . . . . . . . . . . 59
4.3 MineralParagenesisintheGamsTransitionalLayer . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
4.3.1 Nativeelementsandmetallicalloys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
4.3.2 Sulfides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
4.3.3 Oxides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
4.3.4 Carbonates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
4.3.5 Sulphates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
4.3.6 Phosphates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
4.3.7 Silicates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
4.3.8 Vertical mineralogical zonation as an indicator of environments of the transitional layer
formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
4.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
5
Chapter5. MagneticPropertiesofRocksoftheGamsSection byD.M.Pechersky,
D.K.Nourgaliev,andZ.V.Sharonova 89
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
5.2 MethodsofPetromagneticStudies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
5.3 ResultsofPetromagneticStudiesoftheRocksFromGams-1Section . . . . . . . . . . . . . . . . . . 95
5.3.1 Paramagneticmagnetization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
5.3.2 Discussionofpetromagneticresults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
5.4 CharacterizationoftheBoundaryLayerintheGamsSections . . . . . . . . . . . . . . . . . . . . . 113
5.5 ComparativeCharacterizationofSectionsIncludingtheK/TBoundary. . . . . . . . . . . . . . . . 123
5.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
Chapter6. CosmicDustandMicrometeorites: MorphologyandChemicalComposition
byA.F.Grachev,O.A.Korchagin,andV.A.Tsel’movich 135
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
6.2 ResultsofInvestigations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
6.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
6.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
Chapter7. MantlePlumesandTheirInfluenceontheLithosphere,Sea-levelFluctuations
andatmosphere byA.F.Grachev 147
7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
7.2 MantlePlumesandLithosphere. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
7.3 Underplating,TopographyandSea-LevelChanges. . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
7.4 MantlePlumesandAtmosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
Chapter8. NatureoftheK/TBoundaryandMassExtinction byA.F.Grachev 165
8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
8.2 ATwo-StagesEvolutionoftheTransitionalLayer . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
8.3 MantlePlumesandMassExtinctions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
8.3.1 ArsenicattheCretaceous-Paleogeneboundary. . . . . . . . . . . . . . . . . . . . . . . . . . 169
8.3.2 PoisoningbytoxicelementsattheK/Tboundary: Thekillingmechanismsensustricto. . . 170
Conclusion byA.F.Grachev 173
References 175
ElectronicSupplement 188
AuthorIndex 189
SubjectIndex 195
6
THEK/TBOUNDARYOFGAMS(EASTERNALPS,AUSTRIA)ANDTHE
NATUREOFTERMINALCRETACEOUSMASSEXTINCTION
Thegreattragedyofscience–theslaying
ofabeautifulhypothesisbyanuglyfact.
(T.H.Huxley,1870)
Introduction
ThediscoveryofanomaliesofIrandotherplatinum- an almost unanimous consensus was distorted by
group elements in clays at the boundary between the some researchers who doubted the validity of the im-
Cretaceous and Paleogene (the so-called Cretaceous- pacthypothesisandputforthargumentsinsupportof
Tertiary, or K/T boundary) [Alvarez et al., 1980, 1984; magmatic (related to a mantle plume volcanism) rea-
Ganapathyetal.,1981;Preisingeretal.,1986;Smit,Herto- sonsforthedevelopmentofthetransitionallayer[Of-
gen, 1980] gave rise to the paradigm that the mass ex- ficer, Drake, 1985; Officer et al., 1987; Zoller et al., 1983].
tinction of the biota had been induced by an impact In particular, several scientists pointed to data on the
eventandgaveanimpetusforstudyingthisboundary multiplicity of Ir anomalies and the possibility of ex-
throughout the world (see A Rubey Colloquium, 2002). plaining the unusual geochemistry of the transitional
Thishypothesiswassupportedbythereasonableidea layerattheK/Tboundarybytheeffectofvolcanicac-
that high Ir concentrations, much higher than those tivity[Officeretal.,1987].
know in terrestrial rocks, were related to the fall of a Researchinearly1990sprovidednew,moredetailed
meteorite(oranasteroid)[Alvarezetal.,1980]. information on transitional layers at the K/T bound-
The establishment of the impact paradigm of the ary. Along with new finds of shocked quartz in the
massextinctionwasfacilitatedbythediscoveryofthe transitional layers of different regions of the world,
world’s largest Chicxulub crater in Yucatan, Mexico such high-pressure minerals as coesite and stishovite
[Hildebrand et al., 1991; Smith et al., 1992]. Moreover, werefound,aswellasspinelwithhigh(>5%)Nicon-
some rock units at the K/T boundary were found out centration and diamond [Leroux et al., 1995; Preisinger
to bear shocked quartz and coesite [Bohor et al., 1984; et al., 2002; Carlisle, Braman, 1991; Hough et al., 1997].
Koeberl,1997;Preisingeretal.,1986;ARubeyColloquium, Although all of these materials considered together
2002,andseveralothers]. provided irrefutable evidence of an impact event, the
Later papers by Alvarez et al. [1980] demonstrated mechanisms relating it to the mass extinction of the
thattheIranomalyinthetransitionallayerattheK/T biotaremaineduncertain.
boundary was present in virtually all of the inspected Meanwhile newly obtained data indicated that Ir
rocksequences,bothincontinentsandindeep-seadri- anomaliescouldoccurbothbelowandabovetheK/T
llingholesinoceans[Alvarezetal.,1992;Hsuetal.,1982; boundary[Ellwoodetal.,2003;Graup,Spettel,1989;Tan-
Kyte,Bostwick,1995;andseveralothers]. don, 2002; Zhao et al., 2002; and others]. Furthermore,
TheproblemofthemassextinctionattheCretaceous- Ir anomalies were found in rocks with no relation at
Paleogene boundary seemed to be resolved, although all to the Cretaceous-Paleogene boundary [Dolenec et
7
8
al.,2000;Keller,Stinnesbeck,2000;andothers]. AsKeller than670km,i.e.,fromthelowermantleor,moreproba-
hasrecentlyshown[Keller,2008],iridiumanomaliesare bly,fromthecore-mantleboundary(D”layer)[Grachev,
not unique and therefore not infallible K/T markers. 2000;andreferencestherein].
Hence,theIranomalyitself,whichwasoriginallycon- In the latter instance, perhaps because no scientifi-
sidered one of the milestone of the impact hypothesis cally plausible resolution of the mass extinction could
forthemassextinctionoflivingorganismsattheK/T be found, it was proposed to regard mass extinction
boundary [Alvarez et al., 1980], could not be anymore in the Phanerozoic as an accidental coincidence with
(in light of newly obtained data) regarded as a geo- coeval plume magmatism and impact events [White,
chemicalindicatorofsuchphenomena. Itisalsoperti- Saunders,2005].
nenttorecallthatdataonthePermian-Triassicbound-
Nevertheless, the problem remains unsettled as of
aryalsodidnotconfirmthatthereasonsfortheextinc-
yet. How can one explain the fact that the study of
tionofthatbiotawereofanimpact[Zhou,Kyte,1988].
the transitional layers at the K/T boundary over the
Theideathatthefundamentalchangesinthebiotaat
past25years,withtheuseofstate-of-the-artanalytical
the K/T boundary were related to volcanic processes
equipment and techniques, did not result in the solu-
became topical again [Grachev, 2000a, 2000b], particu-
tionofthisproblem?
larlyafterthedetailedstudyingofanomaliesofIrand
In our opinion, the answer to this question stems
otherPGEinplume-relatedbasaltsinGreenland,atthe
fromthemethodsemployedinthesestudies: thelayer
BritishIslands,andDeccan[Phillipetal.,2001;Poweret
wasinspectedasauniqueitem,anditscharacteristics
al.,2003;Crocket,Poul,2004],whichmadeitpossibleto
obtainedwithdifferenttechniqueswereascribedtothe
explainthehighIrconcentrationsinsedimentsbythe
whole thickness of this rock unit. Given the thickness
transportation of this element by aerosols during vol-
of the transitional layer at the K/T boundary varying
canic eruptions, as was earlier hypothesized in [Zoller
from 1 cm [Preisinger et al., 1986] to 20 cm [Luciani,
etal.,1983].
2002], sampling sites were commonly spaced 5–10 cm
AllofthesediscrepanciesbecamesoobviousthatW.
apart,or1–2cmapartneartheboundary[Gardin,2002;
Alvarez,oneofthemainproponentsoftheimpacthy-
Keller et al., 2002]. With regard for the known sedi-
pothesis,admittedthat“...althoughIhavelongbeena
mentation rates of about 2 cm per 1000 years [Stuben
proponent of impact at the K/T boundary, I hold no
etal.,2002andreferencestherein],thetransitionallay-
grief for all extinctions being caused by impact. If the
ers should have been produced over time spans from
evidence for a flood-extinction link is compelling, we
500to10,000years.
shouldacceptthatconclusion”[Alvarez,2002,p. 3]. He
also wrote: “It would be useful to the community of The time during which an impact event could af-
researchers to have a compilation of evidence for im- fect the character of sedimentation can be estimated
pactandforvolcanismatprominentextinctionlevels. from the numerical simulations of the nuclear win-
Thisisprobablysomethingthatshouldbepreparedby ter scenario, according to which the duration of this
a group of workers experienced in the field” [Alvarez, event at the Earth’s surface should range from 10 to
2002,p. 4]. 30days[Turkoetal.,1984]. Becauseofthis,evenifsuch
Itisalsoworthmentioningtwootherapproachesto eventstookplaceinthegeologicpast,andevenifsome
the problem of relations between impact events and records of them could be discerned in sediments, evi-
plumemagmatism. denceoftheseeventscannotbeidentifiedvisuallybut
Inoneofthem,anattemptwasundertakentorelate requireadetailedandscrupulousinvestigation.
the onset of plume magmatism to the decompression NearthebeginningofourinvestigationsintheGams
andmeltingofdeeplithosphericlayersundertheeffect section (Eastern Alps, Austria) we have provided an-
ofthedevelopmentofcratersofabout100kmdiame- other look at the reasons for the mass extinction at 65
ter. Here the impact itself is considered to be a trig- Ma [Grachev et al., 2005]. These first data rejected the
gering mechanism for the origin of a plume [Jones et needforopposingvolcanismtoanimpactevent: both
al.,2003;andothers]. Asidefromtheimplausibilityof took place, but the changes in the biota were induced
thisprocessfromthephysicalstandpoint[Molodenskii, byvolcanismbeforeanimpactevent. Infollowingpa-
2005], there is direct and only one evidence of the im- pers we adduced a new proof suggested the truth of
possibilityofthisprocess: theHeisotopicsignatureof suchpointofview[Grachevetal., 2006a, 2007a, 2007b,
plume basalts. As is well known, these basalts have 2008a, 2008b, 2008c; Pecherskyetal., 2006a, 2008]. This
a 3He/4He ratio more than 20×10−6, which could be monographsumsupallresultsofourinvestigationsof
causedbytheupriseofthemeltsfromdepthsofmore theK/TboundaryintheGamsstratigraphicsequence.
THEK/TBOUNDARYOFGAMS(EASTERNALPS,AUSTRIA)ANDTHE
NATUREOFTERMINALCRETACEOUSMASSEXTINCTION
Chapter 1. A Review of the Geology of the
Late Cretaceous-Paleogene Basin of Gams
(Eastern Alps, Austria)
1.1 Introduction croplate in the northwest of the Tethys Ocean [Mandl,
2000; Wagreich, 1993]. Deformation phases of folding
and thrusting have removed the series of its crustal
Gams,officiallybearingthesuffix“beiHieflau”(near
basement and have created a nappe complex of 20–
Hieflau)todistinguishitfromothercommunitieshav-
50 km in width and approximately 500 km in length.
ing the same name, is a village of approximately 600
In the north, it rests with overthrust contact on the
inhabitants. It is located in the north of the Austrian
Rhenodanubian Flysch which had been deposited in
provinceofStyriaamidtheNorthernCalcareousAlps
the northern segment of the Penninic Ocean trough.
which are rising in its surroundings up to 2600 m. To
In the south it overlies, mostly with tectonic contact,
ensure the protection of the area, Gams and other 5
the Variscan Greywacke Zone. A detailed description
communities have merged to the Nature Park Styr-
ofthecomplextectonicprocessesisgivenbyWagreich,
ian Eisenwurzen. Because of its exceptional geologi-
Decker[2002].
cal heritage and its public activities, the Nature Park
Late Cretaceous uplift followed by significant sub-
hasbeenacceptedasamemberoftheEuropeanGeop-
sidencehasledtotheformationoflimitedareasofin-
arksNetworkin2002andconsequentlyasamemberof
creased subsidence during late Cretaceous-Paleogene
the Global Geoparks Network of UNESCO. A perma-
times (Figure 1.1). After the community of Gosau in
nentexhibitionandtrailsinterpretingthelocalgeology
UpperAustriawhichislocatedonthelargestofthese
make Gams the centre of geological interpretation of
sediment traps they are traditionally called Gosau
thePark.
Basins. Their sediments are summarized under the
Ingeneral,thesignificanceofthegeologicalheritage
lithostratigraphic term Gosau Group (Gosau Beds or
becomes evident through scientific research. First ge-
Gosauschichtenoftheearlierliterature).Dependingon
ological explorations of the Park area date back to the
thesubsidencehistory, thesedimentcontentofthein-
firstquarterofthe19thcentury.Withtheaccumulation
dividualbasinsandthetimeslicerepresentedbythem
of knowledge, scientific methods and interpretations
variesandboundariesbetweenlithostratigraphicunits
havechangedalmostconstantly. Mostimpetuscomes
arediachronous.
from findings which contradict previous theories. We
Resting unconformly on sediments which have un-
believethattheobservationspresentedinthisvolume
dergone earlier tectonic deformations, the Gosau sed-
willstimulatethediscussionontheK/Tboundary.
imentary cycle began in the Late Turonian and ended
intheLowerEocene. TheGosauGroupissubdivided
intotheLowerandtheUpperGosausubgroups[Faupl
1.2 OutlineoftheTectonicHistory
et al., 1987; Piller et al., 2004]. The Lower Gosau Sub-
group comprises a succession of continental to shal-
The Northern Calcareous Alps extend from west to lowmarinesediments. Theywere depositedinsmall,
eastalmostthroughthewholeofAustriaandadjacent partly fault-bounded extensional and/or pull-apart
partsoftheGermanbundeslandBavaria. Theyforma basins [Sanders, 1998; Wagreich, 1993; Wagreich, Faupl,
thrust belt which is part of the Austroalpine unit and 1994]. Facies and thickness of units changes horizon-
hasoriginallybeendepositedontheAustroalpinemi- tallywithinshortdistances.
9
10 CHAPTER1
Figure 1.1. The distribution of Gosau Basins in the Eastern Alps [after Wagreich, Krenmayer,
1993].
TheUpperGosausubgroup(Santonian/Campanian boundary transition layer has been traced. From the
–LowerEocene)ischaracterizedbypelagicsediments name-giving Basin of Gosau, which extends over the
which indicate a general deepening [Wagreich, 1993, boundaries of the Austrian provinces Upper Austria
1995]. Thisresultedinanoversteppingoftheformerly and Salzburg, two sections have been described: the
isolated basins. Subsidence during the deposition of ElendgrabenclosetothevillageofRußbach[Preisinger
the Upper Gosau subgroup is explained with tectonic etal.,1986]andtheRotwandgraben[Perytetal.,1993].
erosion of the Austroalpine units as a consequence of Herm and others, provided a micro- and nannostrati-
subduction and/or underthrusting [Wagreich, Decker, graphical frame for the K/T boundary layers of the
2002]. WasserfallgrabenintheLattengebirge(BavarianAlps).
A study by Graup, Spettel, [1989], revealed three irid-
iumpeaksinthissection,ofwhichoneislocated16cm
1.3 TheCretaceous-PaleogeneBoundary
belowtheK/Tboundary.
inAlpineDeposits The third Gosau basin is that of Gams which is the
subject of this monograph. Lahodynsky [1988a, 1988b],
hasprovidedadetailedlithologicalsectionthroughthe
First indications on Paleogene in the Gosau Group
K/T boundary of the Knappengraben (Gams 1 in this
weregivenbyKu¨hn[1930]. HededucedaDanianage
monograph)whichhehadexcavatedtogetherwithH.
(consideredasterminalCretaceousatthattime)ofthe
Stradnerin1986. Stradner, Ro¨gl[1988], reportedabout
Zwieselalm Formation which forms the top of the se-
themicrofaunaandnannofloraofthissectionandem-
quence. Micropalaeontological studies in the Basin of
phasizedthecompletenessofthestratigraphicalrecord.
Gosau by Ganns, Knipscheer [1954], Ku¨pper [1956], and
onGamsbyWicher[1956],gaveamorecomprehensive
pictureofPaleogenedeposits. Byapplyingplanktonic
1.4 TheGosauGroupofGams
foraminifera in a large scale, this was confirmed later
byHerm[1962],andHillebrandt[1962],fortheLattenge-
birge (Bavaria), Kollmann [1963, 1964], for the Gams Becauseofitsgenerallysoftclasticrocks,theGosau
areaandbyWille-Janoschek[1996],forthewesternpart BasinofGams(forthelocationseeFigure1.1)formsa
oftheGosauarea. morphologicaldepressionwithincarbonatesofearlier
Stimulated by the world-wide discussion initiated Mesozoic age (Figure 1.2). The basin consists actually
by Alvarez et al. [1980], the nature of the K/T bound- of two sedimentary areas of different subsidence his-
ary was investigated in the Gosau Group in greater tory [Kollmann, 1963; Kollmann, Summesberger, 1982].
detail. There are three Gosau Basins where the K/T They are arranged in E-W direction and are sepa-