sedimentological ecological and temporal patterns of fossil lager stat ten

8/3/2019 Sedimentological Ecological and Temporal Patterns of Fossil Lager Stat Ten

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Phil. Trans. R. Soc. Lond. B 311, 5-23 (1985) [ 5 ]Printed n GreatBritainSedimentological,cological nd temporal atterns ffossil agerstaitten

BY A. SEILACHER, W.-E. REIF AND F. WESTPHALInstitut ndMuseum urGeologie ndPaldontologie,igwartstrasse0,D-7400 Tiubingen,.R.G.[Plate 1]

Preservation of non-mineralized structures including plants) and of articulatedskeletons results fromextraordinaryhydrographic, edimentational and early dia-genetic onditions.The corresponding hiefcausative ffectsstagnation, brution ndbacterial sealing) definea conceptual continuum nto which individual occurrencesmay be mapped. A more pragmatic, typological classification of conservationdeposits,usinga standard questionnaire,reveals ecological replacements, s well astrendsrelated to the evolution ofthebiosphere,throughgeological time.

The theme of thissymposium, extraordinary fossilbiotas: theirevolutionaryand ecologicalsignificance',recalls a project carried out some time ago in the Tubingen special researchdivision 53 on palaeoecology. Our term 'fossil Lagerstatten' (alternative spelling: Lager-staetten) is difficult o translate into English. Corresponding to economic Lagerstatten ofmineralsand ores,fossilLagerstattenwere defined as rock bodies unusuallyrich n palaeonto-logical information,either in a quantitative or qualitative sense. This means that thetermembraces not onlystratawith an unusual preservation,but also less spectaculardepositssuch as shell beds, bone beds and crinoidal limestones.The concept also implies that there sno sharp boundary with normal' fossiliferous ocks.Rather, the preservationofany fossil sto be consideredas an unusual accident thatdeservesattentionand questioning.The rationale behind such a broad approach is a sedimentologicalone. Fossil Lagerstattenare considered as end membersofordinary sedimentaryfacies, n which theunusual amountand qualityofthepalaeontological testbodies allows us to dentify etter hefactors esponsiblefor uch a faciesat all levelsof tsgenesis: biotope conditions (palaeobiology), fateofthesoftparts and organic skeletalmaterial (necrolysis), edimentary ransport nd burial (biostrati-nomy) and fate ofthe mineralized skeletons fossildiagenesis).On theotherhand thisapproach is based on thecontentionthat in spiteof all thepossiblecombinations and variations of biotic and abiotic factors nvolved there s a finitenumber ofsituationsthat lead to the formationof fossilLagerstattenand that prospectingfor them istherefore realisticobjective.A firsttep n thisdirectionwas a geneticclassificationfigure1),the broad outlines ofwhich are stillvalid.In themeantime,our understanding f concentrationepositsas been greatly mprovedby theconcepts ofdynamic and event stratigraphywith farreaching applications in basin analysis(see Einsele & Seilacher (I982) and Bayer & Seilacher (I985) forexamples and references).Withrespectto conservationeposits,n whichthis ymposium sfocused,manynew exampleshave been discoveredand old ones analysed in moredetail, including case historiespresentedin this ymposium.Each ofthemhas,- fcourse, ts merit s a peephole inthe screenof mperfect


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6 A. SEILACHER, W.-E. REIF AND F. WESTPHAL

Ad4&~ j tnon-marine

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PATTERNS OF FOSSIL LAGERSTATTEN 7overlain bya similarconglomeratic imestone.Palaeontological evidence, however, hows thatthis basal conglomerate of the Jurassic transgressionrepresents n fact a rather complexenvironmentalhistory.The erosional nature of the Triassic-Jurassic contact is shown first y the absence of theRhaetic, which in this area is usually representedby coal-bearing swamp deposits which passinto marine sands and clays farther o thewest. Second, the conglomerateconsists argely ofreworked calcareous concretions which are characteristicof the underlyingKeuper marls('Knollen-Mergel'). Third, the sole of the conglomeratic bed is covered by casts of verticalrhizocoralliid preiteburrows,whose perfectly reserved cratchmarks uggest hat the Keupermarl, into which theywere dug, was already well compacted and rather stiff. uch burrowsare characteristic ftheGlossifungiteschnofaciesofshallow marine firmgrounds.While otherspecies of the ichnogenus Glossifungitesre oblique and in the size-class of the relatedRhizocorallium,he smaller ones at the base of theJurassic can be compared to the verticalburrowsof the modern amphipod Corophiumnd may well be the works of related intertidalcrustaceans. In any case these burrows show that the conglomerate is not simply thedepositional phase of theeventthat made the erosion.Rather,the twoprocesseswereseparatedby a quiescent firmgroundperiod lasting long enough to allow the establishmentof theGlossifungitesommunity.Moreover,depositionoftheconglomeratebed at thisplace was notpreceded by major erosion, which would have destroyed the burrows.Nor does the conglomeratebed itselfrepresent simple sedimentationalprocess. Besideslithoclasts t contains many shells, predominantly fbyssateand cementedepifaunal bivalves(Plagiostoma, ima, Entolium,noceramus,iostrea).But poorly preservedspecimensof Cardiniaindicate that mud-burrowerswere also present originally,but were largely eliminated bydiageneticsolution of their ragoniticshells.Accordingly,we interpret his bed as a compositerecord of muddy periods interruptedby major stormevents. These winnowed the mud away,but their rosiveeffectwas stopped bythegrowing ag of hells nd pebbles,which aterallowedthe colonization by an epifaunal post-eventcommunityofepibyssateand cemented bivalvesbeforethemud tookover again.This interplay of sedimentation, shell production and stormreworking,comparable tosituations known from modern littoral environments (Seilacher I985), was periodicallyinterruptedby the deposition of black mud containing the echinoderms,which, unlike theprevious and followingmud-layers, ocally escaped subsequent storm erosion.The previous style of storm-winnowing, lus the lateral introductionof reworked Keupernodules, continued in the thicker onglomeraticbed overlyingthe echinoderm horizon. Butitstop is modelled by large oscillationripples, uggesting hattheeventual shift o themuddysedimentation fthe PsilonotusClays happened between the sand and the mud phase of singletempestite.

(b) Faunal spectrumndpreservationThe well preservedechinodermfauna (30 asteroid, 15 ophiuroid, 15 crinoid, 40 echinoid

specimens;Rosenkranz (I 97 )) isembedded in the ower1-2 cmof theclay lens (figure , 1-5).It represents n ordinary hellybottomcommunitywith respect to functional daptation, tro-phic diversity nd age structure. ts only unusual feature s thewell articulated preservation na muddy sedimentnot corresponding o the substrate n which such formswould normally ive.It is surprising, owever, that groups other than echinoderms re not equally well represented.


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8 A. SEILACHER, W.-E. REIF AND F. WESTPHAL'[ . pelagic 'S1>. washed-in | air ift*,> realm ,V> N benthos -.

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PATTERNS OF FOSSIL LAGERSTATTEN 9The only common non-echinoderm associate is a small oyster (Liostrea rregularis) hichencrustedpebblesas well as shellsof tsownkind.Such oyster lusters figure , 1) may compriseseveralgenerations, he changing orientationsof which attest to repeated overturnduringanextended exposure at the sediment surface.However, the generationscould also represent

differenthellyphases separated bymud-coveredperiods. Nevertheless,Rosenkranz foundthatabout 50 % oftheoysters n top of thebasal shellbed were double-valved and probably becamevictimsof the same event that killed the echinoderms.In contrast, pibyssalbivalves, being representedwithin hebasal shellbed, are conspicuouslylackingon itsechinoderm-bearing op.Rosenkranz'sexplanation is convincing: theshellybottomepifauna became buried alive byrapid mud sedimentation.Among the bivalves, this was fatal for the oysters,while pectinidsand limids could escape by swimming up. For the echinoderms,however,the fine sedimentalso had a smothering ffect ecause it blocked theirambulacral systems. t is this Achillesheel' that accounts for thehigh-leveltaxonomic selectivity ftheirpreservation.

(c) Other xamplesAs Rosenkranz (I971) has shown, many, ifnot themajorityofarticulatedechinoderms nthe fossilrecord are foundin a corresponding ituation: at the tops ofcondensed tempestitic

FIGURE 2. Ecological pectra frepresentativeurassic ossil agerstattennsouthern ermany.1, Reclining lusters f ystershow equences fgenerationseparated yoverturningand burial?) events.2-5,The exclusive,rticulatedreservationf cologicallyiversechinodermsuggestshat hey ell ictimstoa mud-smotheringvent.6-1l, Amongthevertebratess well as the nvertebratesheHolzmadenfauna s dominatedbypelagicorganisms.heirperfect reservationassociatedptychi, eriostracalilm ndzig-zag iphunclenammonites;ink ackspreservedn et andother oft artsncoleoids , 9) suggests apid ettlingfter eath ndthe bsenceofbenthic cavengers.n thebelemnites,nly arcasses unkby predator ites how oft arts including henon-calcifiedroostracum,), whichwereotherwiseostduring henecroplanktonicriftingtage 11).12-21, Normally enthic roups remainly epresented yformsttached ofloating bjects uch as driftwood 12-24) andbelemnitepecieswhosenon-calcifiedostrumermittedn extended ecroplanktonicrift(15), or to iveammonites16-21). Fordetails ee Seilacher I982).22-23, Crustaceans rerepresentednlyby very are pecimensf pparently enthic orms. he fact hatcorrespondingpecies re also found n deposits f theSolnhofenype 40-41; Osteno; Lebanon) suggests,however, hat heywerenot normalbenthos.24-30, Trulybenthic rganismsincluding oraminifersnd ostracods) recharacterized y small izeandmonotypicccurrence nparticular edding lanes.Thissuggestshat hey olonized hemud during enthicevents nd then becamesmotheredn an articulated ashion.Main representativesre epibyssate ivalverecliners24-26) andsmall,ong-spinedchinoids27). Endobenthossrepresentedytiered hondritesorizons(28) and very areburrowingivalves 29, 30 from iegraf1977)).31-36, In Solnhofen hepelagic guild s similar oHolzmaden,butcontains dditional lements uch ascrustaceanarvae 34), ellyfish35) and themicrocrinoidaccocoma36,reconstruction),hich nplaces s themost ommon ossil.37-39, Epiplanktons essdiverserarityf mmonites,bsence fdriftwood aybe a reason);but t ncludesfloats ssembled y byssate ivalves rom ecroplanktonichells fhibolitid elemnitesnd smallammonites(37). Overgrowneaweeds 39) wereprobablywashed nfromhe hore.40-41, Among hediverse rustacean auna, hecommon ccurrence fMecochirus40,with raceofdeathmarch) nd ofEryon41) is reminiscentfHolzmaden.42-49, In Solnhofenruly enthic rganismso notoccur s autochthonousenthic orizons, utas lateralimport y turbidityurrents.ome ofthemwere till live enough o eave a short rack 42-44), others ead,showingbelly-up andingmarks 5; figure ), current rientation46) orpostmortemontortion ossiblyindicative fhypersalineottomwaters. mmobile nd burrowingormsexcept rareSolemya,3) werenotimported.50-51, Rare, but extremely iverse nsects most commonly ragonflies),ike the flying eptiles ndArchaeopteryx,epresentmport y air or surfaceurrents.


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10 A. SEILACHER, W.-E. REIF AND F. WESTPHALshell beds. It could be added that this ituation s most ikely o occur in the transgressive hasesoflargeror smallercycles.In all cases, smothering y finer ediment s the dominating process,while oxygen deficiencyinthe pore water gyttja ondition) was either bsent or helpful nly n the sense that t nhibitedinfaunal scavengers or bulldozers that would have secondarily disarticulated the buriedskeletons.

2. THE BITUMINOUS POSIDONIA SHALES OF HOLZMADEN (L. TOARCIAN):A STAGNATION DEPOSIT

Since the famous fossil agerstatte of Holzmaden and its fossil ontenthave been adequatelydescribed (see Kauffman i98I; Riegraf I984), we can focus here on the points that areimportantfor a comparison with the other examples.(i) While the Gmund deposit is at the very base of theJurassic transgression, he Toarcianmarks its peak. This situation favours the establishment of anoxic conditions in manyepicontinental basins, whether this is due to changes in the hydrographic regime or to themobilization of brines fromunderlying alt deposits (Jordan I974).(ii) In contrastto the Gmund echinoderm bed, here we are dealing with an enormous rockbody that spreads over large parts of central Europe with a thickness f tens of metres andrepresenting time span of the order of millions of years. This difference s important to keepin mind in view of the neverending discussions as to whether we are dealing with a sapropelunderneath a stratified, xygen deficient water body or with a gyttja, in which oxygen

deficiencywas essentially estricted o thepore water. In such spatial and temporal dimensions,both conditionsmust be expectedat different imes nd places, as they re inmodern stagnantbasins (Savrda et al. I984). The question is simply, which situation dominated in space andtime and was responsible for the unusual preservation including softparts), with which weare concerned here.(iii) The ambiguity between the two alternative,or ratheralternating,models is expressedin contrasting edimentological s well as ecological evidence. Sedimentologically, he presenceofa millimetricamination that can be correlated over tens ofkilometres H. Roscher, personalcommunication) as well as landed ammonites that dropped theirovergrowthbefore theyeventuallytiltedover withoutchanging place or position (Seilacher I982) indicatevery quietwater.On the otherhand, the orientation nd linear accumulation of mmonite hells nd otherfossils tmany evels Brenner 1976; Seilacher I 982) record uniform urrents fup to 20 cm s-1.(iv) In the ecological spectrum figure2, 6-30) we observe thegeneral absence of benthicorganisms. Encrustingor reclining brachiopods, bivalves, serpulids and crinoids,otherwisestandard elements of Liassic softbottoms, are represented only as epiplanktonic float onammonite shells (figure2, 16-20), belemnite shellswitha non-calcifiedrostrum figure2, 15)or driftwood (figure , 12-14, Seilacher I982), while nektonic ormsammonites, oleoids, fish,ichthyosaurs nd plesiosaurs) are the dominant fossils.On the other hand there are individualhorizons covered by monotypic small epibenthics,such as diademoid echinoids or byssatebivalves (Posidonia, igure , 24-26), whosearticulatedstate ofpreservationwould be in conflictwith arge-scale ateral import.More common are horizons with abundant benthic microfauna(foraminifers,stracodes; Riegraf1985), while tiered bioturbationhorizons,dominated by thelow-oxygen race fossilChondritesfigure , 28; Bromley & Ekdale 1984) are restricted o a fewlevels, which become more numerous towards the margins of the basin.


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PATTERNS OF FOSSIL LAGERSTATTEN 11This picture s in accord withobservations nmodern stagnantbasins, wherebenthic faunasdecrease in body size and diversitywith decreasing oxygen levels and advance towards thecentre of the basin duringperiodsofreduced stagnation Savrda et al. I984). In theshallowerPosidonia shale basin, such benthic eventswere probably broughtabout by extremestorms,

but theyallowed only a fewgenerationsto flourish efore abiotic conditions tookover again.3. THE SOLNHOFEN LITHOGRAPHIC LIMESTONES (TITHONIAN):

AN OBRUTIONARY STAGNATION DEPOSIT(a) Stratigraphicndenvironmentaletting

This fossilLagerstatte,most famous for the preservationof featheredArchaeopteryxndmedusae, was formedust before the regressive nd of theJurassiccycle. With a thickness fup to 90 m it exceeds the southGerman Posidonia Shale, but both its lateral extent (basinsa fewkilometresn diameter n a buriedsponge-reef opography) as well as its timeequivalent(0.5 Ma) are considerablysmaller.Also differents the scarcityof fossils:had there been noquarries, theunit would have possiblybeen mapped as 'non-fossiliferous'.After ll the criteria foremergence (Limulus racks nterpreted s bird tracks,desiccationcracks,raindrop impressions, tc.) have been discredited, heold lagoonal model is no longerrelevant.Most authorsnow agree thatwe are dealing withpermanently ubmergedrestrictedbasins, in which stormwave action was confinedto a fewmetresofdepth and that therewassome kind ofstratificationn thewaterbody excludingmacrobenthos. This stratification adprobably the form fa halocline (Keupp 1977) and it is a secondary question,whetheror nottheresulting tagnationwas also expressedby an oxycline. In any case the bitumencontent,even if econdarily ostbyweathering,was originally ower than in thePosidonia Shales, owingto thehigherrate ofcarbonate mud sedimentation nd lowerproductivityn thesurfacewater.

(b) Ecological pectrumAs in the Posidonia Shales, the fauna (figure2, 31-51) is dominated by pelagic organisms.But instead of ammonites,the most common fossil s the minute stemlesscrinoid Saccocoma(figures , 36 and 3b), whose anatomy and preservation see below) suggests medusoid-likemode of life.There is also a large varietyoffish nd aquatic reptiles,but among these, and-

related forms re more common than theopen-ocean ichthyosaurs.Epiplanktonicfauna is also present,but on a broader spectrumof floats.Driftwood s hardlyeverfound, probably because in such small water bodies it would always be washed ashore.Since ammonites are rarer as a whole, thesmall percentageofovergrown hellsamounts onlyto a fewspecimens.Some of themcarryoysters, therlepadomorph barnacles (figure2, 38),which in Holzmaden occur only on wood (figure2, 13). Instead we findfouledbelemnites,not in the form f an encrustation hatoccurs when therostra ie at thebottom,but as a looseattachmentofbyssal bivalves thatprefer heconotheca ratherthan therostrum figure , 37).Obviously, the now dominant hibolitidbelemniteshad a longer necroplanktonicdriftingime,which made them more attractive for hitchhikers.The common association of severalbelemnites,or ofbelemnites and ammonites, n such clusters uggeststhat the bivalves couldactivelyenlarge their floatby byssal assemblage. Algal fronds re yet another kind offloat,but in thiscase we deal with seaweeds that were torn off heirrocky ittoralhabitat by stormsand washed into thebasin.Benthic elements are by no means missingin the Solnhofen limestones, but unlike the


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12 A. SEILACHER, W.-E. REIF AND F. WESTPHALHolzmaden situation they never represent utochthonous burrowor other benthic horizons(except perhaps ofForaminifera;Groiss I967). Instead we are dealing with nhabitantsoftheshallow marginsthat became accidentally washed-in. This view is supported by several linesof evidence. Most spectacular are the death marches recorded by tracks behind carcasses inan environment n which othertracks are never found. The lengthof these tracks relative tothe animal is largest in the low-oxygen bivalve Solemya figure 2, 43) and decreases (withdecreasing hardiness nLimulusfigure , 42), Mecochirusfigure , 40) and Eryon figure , 41).Other crustaceans are never found with a track,but the marks eftbythedorsal side ofPenaeus(figure , 45 and figure , plate 1), orbythe dorsal fins fvariousfish, howthat these wimmerswere already dead when they anded at the bottom (Mayr I967).A second indication is the selectivityof benthic import. With the exception of Solemya(figure , 43), no endobenthos (includingburrows) s represented, either s sessileepibenthos.Mobile epibenthic speciesare found,particularlyones that,on perturbation,would be able toswimup, such as Antedonfigure2, 47), Limulus figure2, 42) and a varietyof crustaceans. Itis also noteworthy hat almost all imported imulids are uvenilesnotadults,whose much largersizes can be reconstructedfrom tracks (not death marches) found in marginal areas ofSolnhofenbasins (Painten). This could be because juvenile limulidsmorereadilyswimup ondisturbanceand are thereforemore prone to be washed away than adults.

(c) NecrolyticeaturesA dorsal bend of the vertebralcolumn, comparable topostmortemeformations fdryingmodern carcasses (Schafer 1955) is a familiarfeature n SolnhofenArchaeopteryx,terodactylus

and Compsognathus,ut occursalso in fishes. n the attercase itcannot be a desiccationfeature,because associated belly-uplanding marks and tail finsdisruptedduring the bending of thevertebral olumn (figure ; Mayr I967) clearlyshowthatthe deformation ookplace onlyafterthe carcass had sunk to the bottom. Therefore tmay be assumed that the bottom water washypersaline to effect he necessary dehydration.Analogous necrolytic eformationsmaybe observed n articulated skeletons f nvertebrates.In a carcass of Penaeus figures and 5) witha belly-up landing mark,the ventral flexureofthe tail scraped off ediment after the body had tilted over. A possiblyrelated phenomenonis the contortion of Solnhofencrinoids. In Saccocoma, he feather-like orm of the arm tips(figure , 36) is invariablyobscuredby intense nward coiling (figure b). Antedon,n contrast,has the proximal parts of thearms ntensely oiled (figure c) and sometimes isrupted figure ,47), while thetipsare conspicuously traight. romsuchdeformationswe mayderiveflexibilitypatterns, nd hence the mode ofswimming n differentpecies (figure3d, e), but we may alsotake them as environmental ignals that seem to be lackingin Holzmaden-type deposits.

(d) BiostratinomiceaturesThe scarcity ffossilsn Solnhofenprecludesthestatisticalmeasurement fpreferred zimuthorientations.Strongcurrents re indicated, however, by tool and roll marks eftby ammonite

shells (Seilacher I963) and other objects. Their association with incipientflute casts furthersuggests hat thesecurrentsweresediment-loaded.This is in accord withthepreferred ositionof theSolnhofenfossils t the bases of beds and withtheoccurrence ofgradingin otherUpperJurassic occurrences (Nusplingen; Temmler I964). Turbidity currents re also indicated by


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PATTERNS OF FOSSIL LAGERSTATTEN 13Cenomanian,Haqel (Lebanon)

(d)1cm

Tithonian,Solnhofen X

Kimmeridgian,CerinFIGURE 3. Postmortemontortionof echinodermcarcasses in lithographic imestonesreveals flexibility atternsalongthe rms s wellas thedehydratingffectfhypersalineottomwaters.a) Antedonhiollieri,. Jurassic, erin.Dragmarksdotted) uggestecondaryontortionf he rm ipsna current-orientedarcass. b) In SolnhofenSaccocomaGPIT 1630/1)maximumontortionsinthepinnulatedrmtips see figure , 36) suggestinghatthesewere he ctivepartsnfilterwimming,hile he rmbaseswereheld out as an umbrella.c) Solnhofen'Antedon',n contrast ad stiffrmtipsmoved as oarsby the moreflexible roximalparts. d) This smallcomatulid asa style f ontortionimilar o c) (GPIT 1630/2). e) In the arger pecies, roximalrm ectionsare coiled ike n (c),whilethe distalportion eformednan arcuatefashionGPIT 1630/3).Scale barsareI cm.

theradialcurrent irections appedfrom ossilrientationsround hemuchmore ossiliferousand better xposed ithographicimestone asinsof theLebanese CretaceousHuickel 970,figure 3),which s nmarked ontrast otheuniformurrentirectionsf hePosidonia hales(Bre-nne-r TI976).


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14 A. SEILACHER, W.-E. REIF AND F. WESTPHAL(e) Diagenetic eatures

As to be expected in such different ithologies, certain biomaterials suffereddifferenttransformationsn bituminous shales and lithographic imestones. n Solnhofen,for nstance,both vertebrate coprolites and the ink sacks of coleoid cephalopods are phosphatic, while inHolzmaden only coprolites are phosphatized, while the ink is pr'es-erveds jet. In-both cases,however, mineralization happened so early that these originally oftmaterials did not becomedeformedby compaction.Aragonite olution eems to have been a similarly arlyprocess, s shown by thepreservationalhistory f ammonites (Seilacher et al. 1976). Their compactional deformation,varyingwithdifferenthellgeometries, hows that thearagonitewas dissolved notat thesurfacebut withinthe sediment.On the otherhand the plastic lateral deformation f Solnhofen ammonitesinslumped layers ('Krumme Lagen') indicates that the shells had already been reduced toperiostracalfilmswithina few metresbelow thesediment surface.The real problem is not the difference, ut the identityof diagenetic signaturesin theHolzmaden and Solnhofen cases in spite of their lithological differences.The flattenedperiostracalfoilpreservationof emptyammonite phragmocones that the two localitieshavein common contrasts harply with normal' situations, n which suchphragmocones are eitherlined with pyrite non-bituminousLiassic black shales; Hudson (I982)) or filledwithblockycalcite (micritic imestones f theUpperJurassic) and are thereforeittle ompacted. This indi-cates that thespecial conditionsresponsiblefor heexceptional preservation fotherfossilswerenot restricted o the open water,but had an effect lso on thepore water system.

(f) Prokaryoticcum:theneglectedfactorDiagenesis istraditionally iewedas the result fphysicochemicalprocesses.Withintheuppercentimetresfthe sediment olumn, however, nwhichthe observedsoft-part ermineralizationand aragonitesolutionappears to have takenplace, chemical conditionsare mainlycontrolledby microbiological activity.To reconstruct hemicrobiology f ancient mud bottoms s largelya geochemical task. Stillthere are a fewmorphologicalclues. Scanning electronmicroscopestudiesby Keupp (I977)have demonstratedthat, apart from occoliths (Hemleben 1977 b), coccoid cyanobacteria are

DESCRIPTION OF PLATE 1FIGURES 4-9. Cyanobacterialmats,probably most mportantactornpreservationalrocesses,an be inferredfromndirect vidence. n Solnhofen,heir resences indicatednotonlyby amination nd near-absenceferosion, ut alsobysurface eatures.FIGURE 4. Halo ofripped-upcum round waying ish ail from arthel1978), plate 61, figure ).FIGURE 5. Preservationf andingmarksrostral arina, ye tips, bdomen) besides fallen-overarcass fPenaeusand of crapemarkplusscumheap producedduring ostmortemnflectionftailend (GPIT 1630/4).FIGURE 6. Rufflingroundroll mark f an ammonite hell GPIT 1630/5) and drag marks EichstattMuseum).FIGURE 7. Cast ofreticulate idgepattern bottom urface, PIT 1630/6) aroundfishwith ostmortemontortionofvertebralolumn.FIGURE 8. Radial arrangement fsuchridges roundan ammonite hell,whose pedestal' elevation s a laterdiagenetic eature.FromJanicke I969), plate 6, figure .)FIGURE 9. Corresponding atternproduced by mechanical creasingof a depressurized lister. Courtesy fProfessor rei Otto, Universityf Stuttgart.)


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Phil.Trans.R. Soc.Lond. , volume1 Seilacher,t l.,plate7~~~~~~~~~~~~*,,K

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PATTERNS OF FOSSIL LAGERS TATTEN 15_ ~~~~~~~~~~~~(e)

. ~~~~~~~~~~~~~.(d) pelagic _(b) sessile,

FIGURE10.Stagnant asins f heHolzmaden ypemostly ituminoushalefacies) ndSolnhofenype lithographiccarbonates) oth ackautochthonousenthosexcept uringhort enthic vents) nd aredominated ydropfauna.The geometryfSolnhofen-typeasins,however, llows lso the ateral mport, y turbidityurrents,of ittoral enthos, referablyfvagileforms.a major constituent f the Solnhofenmuds. Their presenceis also expressedmacroscopicallybya scum on thebed surface.This scum allowed tracks nd roll marks tobe preserved, ausedtherufflingf roll and drag marks figure ; Mayr I967, plate 13, figures -3) and was visiblyripped off round a swayingfishbody (figure4). Its presence is also expressed by reticulateridgeson the tops ofSolnhofenbeds (figure7), which have been variously explained as raindrop impressions Mayr I967), syneresis racks (Janicke I969) or load casting.Their radialarrangement round an ammonite (figure ), however, uggests hat we deal with thecreasingof a filmsimilar to the tepee structures fmodern algal mats or the mechanical creasingofblistermembranes figure ). From otherevidence Hemleben & Freels I 977 a) have consideredsuch prokaryotic cum as the chief factor n the Cretaceous lithographic imestonesofHvar,Yugoslavia.Today, cyanobacterial films f this kindare largely restricted o hypersalineenvironments.But, likecyanobacterial stromatolites, hey ould have had a muchwiderdistributionnearliertimes,particularly n the Precambrian. Their effectwould be (Keupp I977): (i) toprotect oftsedimentsagainst erosion; (ii) to favour the preservationof tracks and othermarkings; (iii)to serve as food source duringbenthicevents; (iv) to protectcarcasses against decay; (v) toact as a 'carbonate pump' into the sediment Walker & Diehl, thissymposium); (vi) to sealtheparticular microenvironmentesponsiblefor he absence of bioturbation Krumbein I983)and for the unusual preservationalhistories fordinary fossils uch as ammonite shells.

As yet,thiseludes macroscopic investigation, ut itmay become more transparent hroughultramicroscopic studies in ancient rocks and particularly through microbiological andgeochemical analyses in adequate modern environments.


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16 A. SEILACHER, W.-E. REIF AND F. WESTPHAL4. OTHER EXAMPLES

As epitomized by the faunal spectra and modes of preservation,the Holzmaden and theSolnhofen deposits have obviously much in common. Differences are minor and largelyexplained by the different alaeogeographic frames figure11). On the one hand we have alarge stagnantbasin with ittle nflux rom he margins,butwith the possibility f torm-inducedwater-mixing nd the short-term stablishment fsmall-sized and monotypicbenthic faunas.In themuch smaller basins of the Solnhofentype, torms ould affect nly the shallow margins;but thesteeperslopes favouredtheepisodic introduction, y slumpingand turbidity urrents,of fine-grained ediment and transportablebenthic organisms fromthe more oxygenatednearshore environments.n such an event,the imported bodies (some still alive) would reachthebottom first,oon to be coveredbythe mud settling rom uspension.Therefore,we woulddefine heSolnhofen ithographic imestonesprimarily s a stagnationdeposit,butone inwhichobrutionwas also an importantfactor.There are many counterparts o these two types n thePhanerozoic record, each with minorbut significant ecularities.Thus thebituminous hales of theLower Lias of southernGermany(Olschiefer,Sinemurian) resemble Holzmaden except that,due to the thickness fonlya fewdecimetres nd poor outcrops,theirfauna is much lessspectacular; but theydo contain benthichorizonsof small echinoids ('Cidaris' olifex) s well as tiered bioturbation horizons. Equallycomparable are theUpper Triassic bituminousshales of southernSwitzerland,but the shalesthemselves ack periostracal mpressions f ammoniteshells,which are onlyfound n theharddolomitic layers,wheretheywerefixedby early diagenetic cementation(Rieber I973).

A less stagnantmodification fthe Holzmaden type s found nmarginalareas ofthe Toarcianbasin, where benthichorizonsare more common and the aragonitic ammonite shells are notdissolved.The same appears to be trueforpartsof theOxfordand Kimmeridge clays nBritain,where the benthic element includes reclining and bone-encrusting oysters (Martill, thissymposium; Aigner i 980). Nevertheless,the shales are bituminousand vertebrate skeletonshave remained articulated.The spongereef opography nd theregression ftheUpperJurassichas led totheformationof lithographiclimestonesin other parts of central Europe also. In Nusplingen (south ofTubingen) fauna and preservations re similar to Solnhofen except that Saccocomas lacking,some beds are clearly graded and the mud consists argelyofsponge spicules,indicating thatsponge reefs round the small basin were stillgrowing (Temmler I964, I966). The faunaldifferenceof the French locality of Cerin may be largely due to its slightlyolder age(Kimmeridgian, Bernieret al. I983). In thiscase, however,themuds did at timesemerge,asshownby horizonswith dinosaur tracks.The mostsimilarextra-Jurassic epresentatives f the Solnhofen typeare in the Cretaceousof Lebanon. These lithographic imestonesare associated and interbeddedwithhuge slumpmasses in what appear to be rhythmically ubsiding pull-apart basins related to the nearbyJordan rift ystem Huckel I970; Hemleben I977 a). Fossils are verycommon and diversified,with washed-in benthosdominatingover thepelagic rain. Post mortemontortions f fish ndechinoderm skeletons figure3) suggesta halocline. In themid-Triassic ithographicrocksofAlcover (Spain; Esteban Cerda et al. I977; Via Boada I977; Hemleben & Freels I977 b) therelation to an ancient reef topography in a regressingsea resembles Solnhofen. Minordifferences n preservation re due to the dolomitic nature of the rock, which,togetherwithgypsum crystals, lso suggests ncreased salinity n this case.


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PATTERNS OF FOSSIL LAGERSTATTEN 17Identification ecomes-more ifficult ith ncreasing emporaldistance from hejurassic-typeexamples. The lithographic limestonesof Monte Bolca (Eocene, N Italy; Sorbini I983),probably deposited in a volcanogenic topographyby graded turbidite edimentation, an stillbe compared to Solnhofen, although many index groups oforganismshave fallen victimsto

the Cretaceous extinction.But what about the lithographic' Green River Shales (Eocene) ofNorth America? Being deposited in a basin too large to produce turbidity urrents, re theyrather a stagnation deposit comparable to the Posidonia shales, but in a salinityregime thatfavoured bacteria-mediated carbonate precipitation?Similarly enigmatic is the case of thethin-beddedchalks of the Niobrara formation. n addition to thefamedvertebrate keletonsand the floating rinoid Uintacrinusheycontain Inoceramushells thatappear too large to havebeen epiplanktonic.However, the double-valved, closed preservationofthesegiant bivalves,equal encrustation n both valves and their yingalways on the same valve does not either fita recliningmode of ife.Also reclining ysters,which are such a regularelement notherchalks,are conspicuously absent. Could it be that the Niobrara chalks are the equivalent of a darkbituminous hale at a timewhenexcessiveplanktoniccarbonateproductiondiluted thesapropelinto a white mud without the necessity f lateral carbonate import?On the otherhand, the Lower Liassic depositsof Osteno (see Pinna, thissymposium)aredark-coloured, finelylaminated and bituminous. But they consist, like the lithographiclimestonesofNusplingen, largelyofsponge spicules. Also their faunal spectrumrelates themto SolnhofenratherthantoHolzmaden, withcrustaceans,worms and otherwashed-inbenthosdominatingover the pelagic guild and with benthic events (includingbioturbationhorizons)being completelyabsent. The preservationof the rare ammonites also resembles Solnhofen(flattened,non-pyritized, ig-zag siphuncle).What we can learn from hecomparisonsso far s that ithology, olour and bitumen contentshould not be taken as the primarycriteria n a genetic classificationof fossilLagerstatten,because they may change with the hydrographic situation and with shifts n biologicalcarbonate mud production.Nor should the salinityfactorbe rated too highly.The Jurassicdepositsof the Karatau (Kazakhstan), for xample, are a valid counterpartofthe Solnhofen ituationalthough theyweredepositedas dolomitic mudsin a tectonic,probablyhypersaline ake, inwhich the washed-inbenthos' ismainly replaced by river-importednsects.Also deposited in a tectonic ake are the Eocene shales ofMessel, Germany (Franzen, thissymposium).Their ecological spectrum fishes,washed-in and and flying ertebrates, nsects)resemblesKaratau, but this ediment s bituminous and non-calcareous without ndicationsofincreased salinity. Neverthelessthe complete absence ofautochthonous benthos suggeststhatthe stagnant condition was permanent and not interrupted by either storms (small basingeometry)or floods(thermocline).Environmental dentifications ecome stillmoredifficultfwe deal withPalaeozoic or evenPrecambrian examples because modes of lifeare increasinglydifficult o assess. There is noproblem in tracing back the obrution deposits of the Gmund type as long as we haveechinodermstogo by. The Holzmaden type s also well represented y bituminous hales suchas the Ohio shales oftheUpper Devonian and Lower Carboniferous ftheeasternUnited States(Barrow & Ettenson I980). But we do have problems to identify he Solnhofentype.The Silurian Mississinewashales of ndiana, for nstance,weredeposited n inter-reefasins,in which a turbiditicmode of sedimentation s indicated by grading and positionof thefossilsat the bases of the silty dolomite beds (Erdtmann & Prezbindowski I974~). But the fauna ismore diverse than in Solnhofen and includes such immobile benthic forms as sponges,

2 Vol. 3 II. B


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18 A. SEILACHER, W.-E. REIF AND F. WESTPHALbrachiopods and a large variety of dendroid graptolites. Also the beds are commonlybioturbated from the top, indicating a rather diversified utochth-onousbenthos. But thedominant dendroid graptolite genus is Dictyonema,enerally taken to have been pelagic. Alsothere are many kinds of cephalopods (little compacted, but not pyritized) and perfectly,three-dimensionally reservedcrinoid crowns,whose arms and pinnules are integrated nto anumbrellathat would fit pelagic mode of ifewell. Thus we are dealing witha simil-arituationto Solnhofen ombined witha benthic element unfamiliar nMesozoic lithographic imestones.There appears to be some similarity,however, to argillaceous dolomites of similar age inWisconsin (Mikulic etal., thissymposium).Also unfamiliar,from a Mesozoic point of view, are the Hunsruck Shales of the LowerDevonian of Germany (Kuhn i96I; Seilacher & Hemleben I966), because they combinesoft-part reservation non-mineralized keletons farthropods;articulation)withpyritizationand a diversebenthicfauna includinga variety fburrows.Siltymicroturbidites re a commonelement that also allows the preservationof various arthropodtracks. Current action is alsoindicated by sedimentary tructures nd fossil rientations,while wave ripples re conspicuouslyabsent. These features nd the predominance of echinoderms suggest that obrutionwas themajor factor;butoxygen deficiencymust also have been involved, fonly n theform fgyttja,to allow soft-part reservation. It is also noteworthy hat the echinoderms ack postmortemcontortions.Still strangerforms fconservationdepositsare representedn theCambrian. Among thesewe note the combination of a trilobite shell hash suggestiveof storm winnowing with abituminous ithology nd phosphatized arthropod softparts' in theUpper Cambrian AlumShales (Muller; this ymposium) and, ofcourse,thefamousBurgessShale (Collins et l. I983;Conway Morris,this ymposium).Here theproblematicnature ofmanyfossils nd the absenceofmore familiargroups such as echinoderms and molluscsmake it difficult o interpret heecological spectrum.As a whole,thebenthic element ppears to dominatein theBurgessShale,but in a washed-in rather than a benthic-eventfashion.However, there are some assumedpelagics such as Marrella,the most common faunal element. This looks like the Solnhofenspectrum,thougha non-carbonate version. The discoveryof new localities in addition to theclassical one suggests,however, that we deal not simplywith a unique physical setting,butthat a kind of timesignature s also involved.

The most challenging problem in this respect is the classification of the Ediacara-typeconservationdeposits of Vendian age (Fedonkin, this symposium): a task that is largelyindependent of the taxonomic problems involved (see Seilacher (I984) and thissymposium).There is no questionofdealing withtheimpressions fsoft-bodied rganisms n a sandy faciesthatcontrastswiththefine-grained edimentsdiscussed so far.It is truethat we do know sandy obrutiondepositsalso in the Phanerozoic. But theyreferto vertebrate keletons n continentalregimes,to exceptional turbiditeevents (fishdeposit ofSendenhorst; Siegfried 954) or to sand-smothered chinoderms Seilacher I968) and not tosoft-bodied rganisms.The Vendian fossiliferousandstones, n contrast, ppear to be largelystorm-generatedGoldring & Curnow I967), that is, depositionallysimilar to many shallowmarine sandstones in the Phanerozoic, in which such soft-bodympressionsnever occur. Toinvoke forthis unusual preservation unique physiographic onstellation s no more ustified,given that Ediacara-type fossilshave been found n more than 20 localitiesall over theworld(Glaessner 1984, figure .8) and also in sandstonesthat are claimed tobe deep-water turbidites


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PATTERNS OF FOSSIL LAGERSTATTEN 19(Anderson & Conway Morris I982). Clearly thispreservationmust be due to an 'anactualistic'factor in a Phanerozoic view) of a more global nature.It has been claimed that this actorwas a lack ofbioturbation.But burrowsmade by worm-likeorganisms and possiblycoelenterateshave been found n many Ediacaran fossil ocalities andwith surprisingly dvanced sediment feeding strategies. t should also be rememberedthatmicrobial degradation would destroy shallowly buried soft-bodied arcass. A more relevantcluemaycome from edimentologicaldata (J. Gehling,unpublished, nd personal observationsin the field). They suggest he presence of a ratherresistant yanobacterial scum thatprotectedthese sand surfaces gainst stormerosion and amalgamation and allowed flexible and-shardsto be ripped off.This would go along with the general impressionthat cyanobacterial mats(withor without stromatolitic tructures)were much morewidespread in Precambrian thanin later environments;but in exactlywhat way this non-uniformitarian eatureshould haveinfluencedthe preservationof soft-bodied rganismsstill remainsto be explained.

5. CONCEPTUAL FRAME AND CLASSIFICATIONOur shortreview ofconservationdeposits s admittedlyvery ncomplete.For instance tdoesnot covera group thatwe previously alled 'conservationtraps' (Seilacher & Westphal I 97 I),which is a holding bag forsuch differentases as mammoths in permafrost revices,amberinsects r bogs.Ofsignificancenourpresentdiscussion re onlytheearlydiageneticconcretionsin the formof coal balls (Scott & Rex, thissymposium), orsten' (Muller, thissymposium),Mazon Creek nodules (Baird etal., thissymposium)or the Lower Cretaceous fish oncretions

fromBrazil (Muller, thissymposium). Certainly, uch concretions re important n that theyfacilitate fossilhunting and that they provide, through the right preparation techniques,relativelyuncompacted fossils. ut in a genetic sense, they re onlya subset ofstagnation (andobrution?) deposits.In the Posidonia Shales, for instance, beautifully preserved reptiles, fish and coleoidcephalopods come from uch concretions;but most of the nodules are barren and most of thefossils re found n layersin which no such concretionsoccur.stagnation(hydrographicregime)

Holzmaden

SolnhofenSBundenbach Hvar

Gmund Ediacaraobrution bacterial(sedimentational regime) sealing(early diagenetic regime)

FIGURE 11. Among the many factors nvolved in the formationof conservationdeposits, stagnation, obrution andcyanobacterial sealing are considered the most dominant. They define a conceptual continuum, into whichparticular examples may be ' mapped'.2-2


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20 A. SEILACHER, W.-E. REIF AND F. WESTPHALTABLE 1. TENTATIVE QUESTIONNAIRE FOR CONSERVATION DEPOSITS

Tubingen questionnaireFossillagerstatten locality:Conservation eposits age:(1) basin situation (6) ecological pectrumsize (km): 10- 10?101102 103 burrowsepisodic, ontinuous):setting: trackswith r without odies):oceanic endobenthos:epicontinental hemisessileterrestrial vagileorigin: epibenthosepisodic, ontinuous):tectonic sessilevolcanic vagileastroblemic able to swimsubrosional pelagics:recifal nektonsedimentary floatersglacial epiplanktonon wood, cephalopodgeographic rame: shells,ive ordead)limestones terrestrialrganisms:clastics trackscrystalline skeletons(2) stratigraphy landplants twigs, eaves, runks)thickness m): 0.01 0.1 1 10 100 flyersdurationn absolute ime: (7) necrolyticriteriavertical ontext: death marches:transgressive landingmarks live,dead):peak transgression soft arts impressions,ilms):regressive organic uticles:fining-upycles articulationvertebrates,chinoderms,coarsening-upycles arthropods, ivalves, ptychi):lateral equence: (8) stratinomicriteria(3) sedimentology life ositions:lithology: rollmarks ofwhat?):biograins coccoliths, orams, convexup or down:radiolarians, picules, tc.): current rientationazimuth):sedimentarytructures: wave orientationazimuth):laminationvarves, lgal, etc.) (9) diagenetic riteriaslumphorizons aragonite reservationwhat?):gradedhorizons early ragonite olutioncurrent ipples (composite asts):waveripples pyritic teinkerns:

emersionmarks concretionaryementationnucleus,(tidal channels,mudcracks, tc.) pressure hadow,buckle, edestal):(4) geochemistry compactional eformationevaporitic recipitatesaragonite, incoalation:calcite, olomite, ypsum, alite): phosphatizationofwhat?):pyrite oncretionsglobular, iscoid): replacementshells, ones):isotopic deviations: General onclusions:Corg (particles, erogene, itumen): stagnation thermal rhalocline):(5) taxonomicpectrum obrution:dominated y (priority): algal sealing:echinodermscephalopodsvertebratescrustaceanstrilobitesothers:


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PATTERNS OF FOSSIL LAGERSTATTEN 21In spite of its incompleteness this review has shown, however, that, apart from the twoprincipal factorsof stagnation and obrution and their various combinations, a large numberof palaeogeographic, biological, sedimentological,diagenetic and time factorsmay contributeto the formation f conservationdeposits.The result s that each case has a 'personality' that

defies rigorous classification.Of course,there s some virtue n typologicalgroupings.Thus we may distinguishbetweenmarine, hypersaline, lacustrine and swamp deposits, or between vertebrate, echinoderm,arthropod and plant Lagerstatten.Or group into Solnhofen, Holzmaden, Bundenbach andBurgesstypes fdeposits. Grouping according toage (Conway Morris, this ymposium;Walker& Diehl, this ymposium) may also be revealing.Butwhile being useful o emphasize patterns,such classifications can never be binding, because unlike in taxonomy there will be noagreement as to which criteria should have primacy.Neverthelesswe should not be contentwithdescriptive registrations.nstead of expectingthe classification o provide a standard set ofpigeon holes, we should better considerit as aconceptual frameworkfor heuristicpurposes. In figure 11 we propose to use the criticalhydrographic, edimentationaland early diageneticexponentstodefine triangular pace intowhich each particularcase can be mapped. In addition,we presenta tentativequestionnaire(table 1) in order to standardize thismapping job, in which by necessity large number ofspecialistsmust be involved.What lies nfront fus, s morethanfossil unting, heunravelling ftaxonomicrelationshipsand facies analysis. Expanded over the whole fossilrecord, a comparative analysis of fossilLagerstatten could become a genuine contributionof palaeontologists to the integrated viewof Earth history.

REFERENCESAigner, . I980 BiofabricsndstratinomyftheLowerKimmeridge lay (U. Jurassic, orset, ngland).N. Jb.Geol. aldont. bh.159,324-338.Anderson,M. M. & ConwayMorris, . I982 A review,with escriptionsffour nusualforms,f he oft-bodiedfauna ofthe Conception nd StJohn'sGroups latePrecambrian), valonPeninsula,Newfoundland. hirdN. Am.Paleont. onv., roc. , 1-8.Barrow, . S. & Ettensohn, . R. I980 A bibliographyf he aleontologynd aleoecologyf he evonian-Missisippianblack-shaleequencen NorthAmerica. 6 pages. Morgantown,West Virginia: U.S. DepartmentEnergy,Informationenter.Barthel,K. W. 1978 Solnhofen.inBlick n dieErdgeschichte.93 pages.Thun: Ott-Verlag.Bayer,U. & Seilacher,A. I985 Sedimentarynd evolutionaryycles. n Friedmann, . M. (ed.) Lectureotesnearthciences,ol. 1,465 pages. Berlin,Heidelberg,NewYork,Tokyo: Springer.Bernier, .,Barale,G. & Bourseau, .-P. I983 Le chantier efouillesaleoecologiques e Kimmeridgienuperieurde Cerin Jura,France).Int. ongr.aleoecol.yon, uide xc. 1, 1-19.Brenner,K. 1976 Ammoniten-Gehausels Anzeigervon Palao-Stromungen. . Jb. Geol.Paldont., bh.151,101-118.Bromley, . G. & Ekdale,A. A. I984 Chondrites:trace ossilndicator f noxia nsediments.cience, ash. 24,- 872-873.Collins,D., Briggs, . & ConwayMorris, . I983 NewBurgess hale fossil ites evealMiddleCambrianfaunalcomplex. cience,Wash. 22, 163-167.Einsele, G. & Seilacher,A. (ed.) I982 Cyclic ndeventtratification.36 pages. Berlin,Heidelberg,New York:Springer.Erdtmann, .-E. & Prezbindowski,. 1974 Niagaran (Middle Silurian) nterreefossil urialenvironmentsnIndiana. N. Jb. Geol. aldont., bh. 44, 342-372.Esteban Cerda,M., Calzada, S. & Via Boada, L. 1977 Ambiente epositionaldeos yacimentos osiliferoselMuschelkalkuperior e Alcover-Mont-Ral. uadernoseol. berica , 189-200.Freels,D. 1975 Plattenkalk-Beckenei Pietraroia Prov.Benevento, -Italien) als VoraussetzunginerFossil-lagerstattenbildung.. Jb. Geol. aldont., bh. 48,320-352.


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22 A. SEILACHER, W.-E. REIF AND F. WESTPHALGlaessner,M. F. I984 Thedawn f nimalife.A biohistoricaltudy. 44 pages.Cambridge:University ress.Goldring,R. & Curnow,C. N. I967 The stratigraphynd facies fthe ate Precambrian t Ediacara, SouthAustralia.J. geol. oc.,Aust. 4, 195-.214.Groiss, . T. I967 Mikropalaontologischentersuchungener SolnhofenerchichtenmGebiet um Eichstiitt(SiidlicheFrankenalb). rlangereol.Abh. 6, 75-92.Hemleben,C. 1977a Rote Tiden und die oberkretazischenlattenkalkem Libanon. N. Jb.Geol.Pal., Mh.,pp. 239-255.Hemleben, . I977 b AutochthonendallochthoneedimentanteilendenSolnhofenerlattenkalken..Jb.Geol.Pal., Mh.,pp. 257-271.Hemleben,C. & Freels,D. 1977a Algen-laminiertend gradierte lattenkalken derOberkreide almatiens(Jugoslawien).N. Jb.Geol. aldont.,bh.154,61-93.Hemleben,C. & Freels, . 1977 b Fossilfuhrendeolomitisiertelattenkalkeus dem Muschelkalk uperior' eiMontral Prov.Tarragona,Spanien).N. Jb.Geol. aldont.,bh. 54, 186-212.Hudson,J.D. I982 Pyriten ammonite-bearinghalesfrom heJurassic fEnglandandGermany. edimentology29, 639-667.Huckel,U. 1970 Die FischschieferonHaqel and Hjoula inder Oberkreide es Libanon.N. Jb. Geol. aldont.,Abh. 35, 113-149.Janicke, . I969 UntersuchungenberdenBiotopderSolnhofenerlattenkalke. itt.bayer.taatssamml.alaont.

hist.Geol. , 117-181.Jordan,R. 1975 Salz- und Erdol/Erdgas-Austrittls Fazies bestimmende aktorenmMesozoikumNordwest-Deutschlands.Geol.Jb.,Reihe ,Heft13,64 pages.Kauffman,. G. I 98 I Ecological eappraisal f heGerman osidonienschieferToarcian)and the tagnant asinmodel. n Communitiesf he ast ed.J. Gray,A.J.Boucot & W. B. N. Berry);pp. 311-381. Stroudsburga:Dowden.Keupp,H. 1977 Ultrafaziesnd Geneseder SolnhofenerlattenkalkeObererMalm,sudliche rankenalb).Abh.naturhistor.es.Nurnberg7, 128pages.Krumbein,W. E. I983 Microbialhemistry.30 pages.Oxford:Blackwell.Kuhn,0. I96I Die Tierwelt er Bundenbacherchiefer. eue rehm-Bucherei74, 48 pages.Wittenberg.Mayr,F. X. I 967 Palaobiologie ndStratinomie er Plattenkalke erAltmuhlalb.rlangereol.Abh. 7,40pages.Rieber,H. I 973 Ergebnissealaontologisch-stratigraphischerntersuchungenn derGrenzbitumenzoneMittlereTrias) desMonte San Giorgio KantonTessin, chweiz).Ecl.geol.Helvetiae6, 667-685.Riegraf,W. 1977 GoniomyahombiferaGoldfuss)n the Posidonia hales (Lias epsilon).N. Jb.Geol. alaont.Mh.,pp. 446-448.Riegraf,W. I 984 DerPosidonienschiefer.iostratigraphie,aunaund aziesdes udwestdeutschenntertoarciums.95pages.Stuttgart:nke.Riegraf,W. I 985 Mikrofauna,iostratigraphiend Fazies munteren oarcium iiddeutschlandsndVergleichemitbenachbarten ebieten.Tubinger ikropal.Mitt. , 232 pages.Rosenkranz, . I97I Zur SedimentologiendOkologievonEchinodermen-Lagerstatten.. Jb.Geol.Paldont.,Abh.138,221-258.Savrda,C. E., Bottjer, . J. & Gorsline, . S. I984 Development f a comprehensivexygen-deficientarinebiofaciesmodel:evidence rom anta Monica,San Pedro, nd Santa Barbara Basins,California ontinentalBorderland. ull. Am.Ass.Petrol. eol. 8, 1179-1192.Seilacher,A. I963 Umlagerungund Rolltransport on Cephalopoden-Gehausen. . Jb. Geol.Paldont.,Mh.,pp. 593-619.Seilacher,A. I968 Origin nddiagenesisf heOriskany andstone LowerDevonian,Appalachians) s reflectedinits hellfossils. ecentevelopmentsncarbonateedimentologyn Centralurope, p. 175-185. Berlin,Heidelberg,NewYork:Springer.Seilacher,A. I982 Posidonia hales Toarcian,S. Germany) stagnant asinmodelrevalidated. n Paleontology,essentialfhistoricaleology,nternat.meeting enice 1981 (ed. E. Montanaro-Gallitelli),p. 25-55. Modena.Seilacher,A. I984 Late Precambrian nd earlyCambrianMetazoa: preservationalrrealextinction?n Patternsof changenearthvolution,ahlem-Konferenzen984 (ed. H. D. Holland & A. F. Trendall), pp. 159-168.Berlin,Heidelberg,NewYork,Tokyo: Springer.Seilacher,A. I985 TheJerammodel: event ondensationn a modernntertidalnvironment.n Sedimentaryndevolutionaryycles,ectureNotes nEarthSciences ed.G. M. Friedmann), ol.1,336-342. Berlin,Heidelberg,NewYork,Tokyo: Springer.Seilacher,A.,Andalib,F., Dietl,G. & Gocht,H. I976 Preservational istory fcompressed urassic mmonites

from outhernGermany.N. Jb. Geol. aldont., bh. 52,307-356.Seilacher,A. & Hemleben,C. I966 SpurenfaunandBildungstiefeerHunsruckschieferUnterdevon).Notizbl.hess. andesamtodenforsch4, 40-53.Seilacher,A. & Westphal, . I97i Fossil-Lagerstatten.n Sedimentologyf arts fCentralurope, uidebook . Int.Sediment. ongr.,pp. 327-335. Heidelberg.


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PATTERNS OF FOSSIL LAGERSTATTEN 23Siegfried,. 1954 Die Fisch.Faunadeswestfailischenber-Senons. alaeontographica106, 1-36.Sorbini, . I983 The fossil ish eposit fBolca (Verona), taly. nt.Congr. aleoecol.,yon, uide xc. llA, 23-33.Temmler,H. I964 Uberdie Schiefer- ndPlattenkalke es Weissen ura der Schwabischen lb (Wurttemberg).Arb.Geol.-Paldont.nst. erTH, N.F. 43, 107pages.Temmler, . I966 Uberdie Nusplinger azies desWeissenJuraer Schwabischen lb (Wiirttemberg).. deutsch.geol.Ges.116, 891-907.Via Boada, L., Villalta,J.F. & EstebanCerda, M. I977 Paleontologia paleoecologia e losyacimentososiliferosdel MuschelkalkuperiorntreAlcoveryMont-Ral.Cuadernoseol. berica , 247-256.

DiscussionR. RIDING (Departmentf Geology, niversityollege, ardifCF1XL, U.K.). I wish to query useof the termobrution. Reference to stagnation and smotheringobrution) as alternativemodesof formation fconservationLagerstatten s slightly onfusing ecause stagnation ndicates thenature ofthe environmentwhereas smotherings a typeofasphyxiation.It would be clearerin this ase to refer o rapid burial ratherthan tosmothering. tagnationand rapid burial couldthen be regarded as different rocesses, either of which can result in the asphyxiation oforganisms.Asphyxiation occurs above the substrate n the case ofstagnationand below it inthe case of smothering. This usage then clearly distinguishesenvironmental conditions(stagnation,rapid burial) from he actual mode ofdeath whichis, n bothcases, asphyxiation.E. N. K. CLARKsoN-(Grant InstitutefGeology, niversityfEdinburgh,WestMains Road, EdinburghEH9 3JW, U.K.). The Lower Lias obrution deposit at Gmund is, as Dr Seilacher has noted,dominated by echinodermsand he had suggestedthat in such a case the active elements nthe benthosmight have escaped, whereas the echinoderms could not.

Is it possible to distinguish uch an obrution deposit fromone in which the original faunawas dominated by echinoderms and littleelse? I ask thiswith particular reference o somehorizons richin intact echinoderms n the Scottish Silurian.H. B. WHITTINGTON, F.R.S. (DepartmentfEarthSciences, edgwickMuseum, UniversityfCam-bridge).The Burgess Shale fauna includes the hard parts of characteristicMiddle Cambriananimals - trilobites, ponges, brachiopods, molluscs, hyolithids nd echinoderms as well asa remarkable soft-bodied auna. I have argued in detail (Whittington 97I) that Marrellawasa benthicanimal, the thousands of specimens having been buried in varied orientations n thedepositresulting rom turbidity urrent.The highlyfossiliferousayers n thePhyllopod bedof theBurgessShale appear tooriginatefrom ucha mode oftransport nd burial (WhittingtonI980). Comparison with the Solnhofendeposit would thus involve consideration ofa similarmechanism for ts formation.ReferencesWhittington, . B. I97i RedescriptionfMarrella plendens,Trilobitoidea)from heBurgess hale, MiddleCambrian,British olumbia.Geol. urv. anadaBull.209, 19-20.Whittington,. B. I980 The significancefthefaunaoftheBurgess hale,MiddleCambrian,British olumbia.Proc.Geol.Ass.91, 129-132.A. SEILACHER. Obrution' means rapid burial, whetherthisprocess only preservedcarcassesor also killed theorganisms.But onlyin the latter case can we expect a selectivepreservation.In the meantime, theanalysis of clusteredtrilobites hat appear to have been selectivelykilled


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24 A. SEILACHER, W.-E. REIF AND F. WESTPHALand then buried bythemuddy clouds of stormevents has added another beautiful example ofsuch obrutiondeposits.Whether the striking bsence or under-representation fnon-trilobitesor non-echinoderms n these cases be consideredan originalfeatureor the outcome of betterresistivity o such accidents is a matterof ecological taste.ReferenceSpeyer, . E. & Brett, . E. 1985 Clusteredrilobitessemblagesn theMiddleDevonianHamiltonGroup.Lethaia18, 85-103.

sedimentological ecological and temporal patterns of fossil lager stat ten

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