Lager Stat Ten, Cause and Classification

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Paleobiology,4(4), 1988,pp. 331-344

Konservat-Lagerstatten:ause and classification

Peter A. Allison

Abstract.-A review of the processes required for exceptional preservationof soft-bodiedfossilsdemonstrates hat anoxia does not significantlynhibit decay and emphasizes the importanceofearly diageneticmineralization.Early diagenesis is the principalfactor mongstthecomplex pro-cesses leading to soft-part reservation.The development of a particularpreservationalmineral scontrolledbyrate of burial, amount of organic detritus, nd salinity.A new causative classificationof soft-bodiedfossil biotas is presented based upon fossil mineralogy nd mineral paragenesis.

PeterA. Allison. Dept. of Geology, niversityf Bristol, ueensRoad, Bristol S6 5DS, UnitedKingdom.Currentddress: niversityfWashington,riday arbor aboratories,20Universityoad,Friday arbor,Washington8250

Accepted: August 10, 1988

Introduction

Exceptionallypreservedsoft-bodiedfossilbiotas, termedKonservat-Lagerstatteny Sei-lacher (1970), preserve invaluable evidenceof Phanerozoic metazoan diversity.For ex-ample,accordingto Sepkoski 1981: p. 39) ap-proximately 0% of marine metazoan cladesare known fromonly three Paleozoic Lager-stdtten: urgess Shale, Hunsriick Slate, andMazon Creek.

Seilacher's (1970) classification f suchde-posits recognized two types of occurrence:the Konzentrat,"rconcentration eposit, ndthe "Konservat," r conservationdeposit. Intheformer,rganic remains re concentratedbysedimentologicaland biological processeswhich generally exclude the preservation forganic softparts. n the latter,fossilization

isbrought boutbyunusual depositionalcon-ditionswhich lead to thepreservation f ex-ceptionaldetails such as softparts.Seilacher(1970) consideredthe mostcritical edimen-tological controlsfavoringexceptional pres-ervationtobe anoxia, rapid burial, earlydia-geneticconcretiongrowth, rthe occurrenceof a decay-inhibitorymedium such as tar,permafrost,ramber.Morerecently, eilach-er et al. (1985) refinedthe classificationofconservationdeposits.Obrution rapid buri-

al), stagnation, nd cyanobacterial overingswere considered the principal causes of ex-ceptional preservation.These classificationshighlightedthe importanceof depositional

conditionsto the development of particularlevels of preservation.Thus, obrutioncom-monly eads to the preservation f articulatedhard parts,but is rarelythe formative gentin the preservation of soft parts. Similarly,stagnation lone will notusually reservetheremainsofsoftparts; twill, however, nhibitscavengingandbioturbation,nd it thereforepromotes he preservation f articulatedhardparts. "Preservational traps," such as perma-frost,tarsands, and amber, may allow thepreservationof three-dimensional oftpartsand are associated with particular evels ofpreservation. For instance, permafrostmaypreserve oft issue nsuch fine onditionthatit sedible,and amber susuallycharacterizedby three-dimensionalpreservationof smallorganisms which lack internaldetail. Suchforms of preservation, however, are ex-

tremelyrare and rarelyencounteredby themajorityof paleontologists.The only long-termdecay-inhibitorymedium that s ofanyreal geological consequence is peat bogs. Ex-amples include the preservation f Iron Agehuman cadavers complete with flesh (Glob1969) and the preservationof three-dimen-sional plant organs (Scott 1979) and arthro-pods (Bartram t al. 1987) fromthe Carbon-iferouscoal depositsofEurope and America.The "cyanobacterial coverings" reported by

Seilacher et al. in 1985 have (to date) onlybeen reportedfrom a handful of localities,which include the Jurassic olnhofenLime-stone ofGermany Seilacher et al. 1985),the

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332 PETER A. ALLISON

Jurassic xfordClayofEngland Martill1986,1987), and the Eocene Messel Shale of Ger-many Wiittke 983). Byfar hegreatestnum-ber of Konservat-Lagerstdtten,owever, are

preserved s earlydiageneticmineralgrowths.The geochemical parameters for the forma-tion of such minerals have received muchattention n recent years (see Berner 1980,1981). Particular authigenic mineral speciesare indicative of specificdepositional condi-tions such as level of pH, Eh, organic content,rate of burial, salinity, nd degree ofoxygen-ation. The preservationalmineralogy f a fos-sil deposit is therefore valuable butunder-appreciated indication of the depositionalconditionsleading to fossil preservation. nthis study I review taphonomic conditionsrequired forsoft-part reservation nd pro-pose a new classification f Konservat-Lager-stdtten ased upon taphonomicfeatures uchas degree of compaction,level of soft-partpreservation, nd preservationalmineralogy.

Controls on the Formation ofKonservat-Lagersta ten

The salient characters hat define the oc-currence of a particulardeformational truc-tureare oftenreferred o as a structuraltyle.In a paleontological context, he term pres-ervational style" refersto the sum total oftaphonomic charactersexhibitedby a biotathat were produced during the fossilizationprocess. Thus, preservational tylewould de-scribecharacters uch as degree of fragmen-tation and disarticulation, extent of decaypriorto mineralization,preservationalmin-

eralogy,and mineral form.

Transport

Reduced transport as been cited as a con-tributary actor n the exceptional preserva-tion of theBurgess Shale (Whittington 971;ConwayMorris1979a)and theHunsriick late(Stiirmer nd Bergstrom 1973). In both ex-amples, the authors argued that minimaltransport educed the degree of disarticula-

tion and fragmentation f soft-bodied andlightlyskeletized organisms. Logically, thissuggeststhatexceptionally preservedbiotasareindicators f minimaltransportnd there-foreapplies certainconstraints o the spatial

relationship between depositional environ-ment and life habitat.

Actualisticexperimentation, owever,hasshown thatexceptional preservation s no in-

dication of duration or nature of transport(Allison 1986). Freshlykilled carcassesof oft-bodied and lightlyskeletized animals tum-bled in a rotating barrel for several hourssuffered eitherfragmentationorextensivedisarticulation. Conversely, carcasses en-tombed in a jar of seawaterwere buoyed upto the surface nd disarticulated uringdecaytoproducea carpet f skeletalfragments ponthe floorof the jar. Thus, it is extentof pre-burial decay, rather han natureor durationoftransport,which governstheoperationofthis process.

Decay: rate and inhibition

The decayoforganiccarbon nnatural ed-imentary equences is bestexpressed n termsof a half-life Berner 1985). The durationofthis half-life s dependent upon: a) natureofthedecomposing carbon; b) thesupplyofox-idants to bacteria involved in the decompo-

sition process; and c) sediment type.Natureof organic arbon.Organic carbonoccurs n a complexand variable form n as-sociation with other elements, principallyoxygen, nitrogen, nd phosphorus. Organicmolecules decay at different atesaccordingto their chemical formulae and molecularconfiguration. hose with the shortesthalf-lives maybe consideredvolatiles; those thatdemonstrate degree ofdecay-resistanceretermedrefractories. ellulose and chitin,for

example, belong to a groupofcarbohydratesknown as structuralolysaccharidesnd formcomplex biopolymers exhibiting consider-able decay resistance.

Oxidant supply.The depletion of pore-water oxygen forcesbacteria in sediment toutilize a series of alternative xidantsduringdecay (see Aller 1980;Allerand Yingst1980;Aller and Mackin1984;Berner1980;Westrichand Berner1984).Thepreferred onsumption

of these oxidants is governed by their free-energy yield during respiration. n ideal cir-cumstances, they are stratified n the sedi-mentprofile Fig. 1),withthose iberating hehighest free-energy ield occurring highest



KONSERVAT-LAGERSTATTEN 333

AEROBIC DECAY(CH2O)106(NH3)16H3P04 10602 o1 06C02 + 16NH3 + H3P04 + 106H20

ANAEROBIC DECAYManganese Reduction

(CH20)106(NH3)16H3PO4212MnO2+ 332C02 + 120H20O*438 HCO-3+ 16NH+4+ HPO2-4+ 212M&+4

Nitrate ReductionCH20)106(NH3)16H3PO484.8NO-3 .-.-7.2 C02 + 98.8HC0-3 + 16NH+4+ 42.4N2

+ HP024 + 49 2?

Iron Reduction

(CH20)106(NH3)16H3PO4424Fe(OH)3+ 756C02 o862 HC0-3+ 16NH+4 + HP02-4

+ 424Fe2+ + 304H20

Sulfate Reduction(CH20)106(NH3)16H3PO4 53S02-4 39 C02 + 67 HCO-3 + 16NH+4+ HP02-4+ 53 HS-

+ 39H20

Methanogenesis (Carbonate Reduction)

(CH20)106(NH3)16H3PO4 14H20 -39C02 + 14HCO-3 + 53CH4 + 16NH+4+ HPO2-4

FIGURE 1.

Stratified acterialreductionzones in "ideal" sediment.Reactions occurring t the top of the column

have a higherfree-energy ield. Reactions ower in the sediment profile ntyoperateafter he completereductionofions higher n the column (afterBerner 1981).

in thesequence (Redfield 1958; Berner 1981).Reactions ower nthesedimentprofilewouldonly operate after he completereductionofions required for the more efficient nes.However, the supply of these oxidants s notuniform.Nitrate-reductionnd methanogen-esis dominate in a freshwater nvironment,whereassulfate-reductionnd methanogene-sis dominate nmarineregimes Malcolm andStanley 1982). The depth to which these re-actions are active in the sediment dependsupon organic supply, temperature, nd sed-iment permeability.A greater input of or-ganic detritus ncreases demand for the ionsrequired for anaerobic respiration.Reducedpermeability mpedes the transfer f these

ions from heoverlyingwater olumn to pore-waters, nd temperaturencreases the rate ofdecay. In all situations, he reduction zonesin the chemicallystratified ediment will beattenuated. n the most extreme ase, the an-

oxic/oxic boundary is projected above thesediment/waternterface.

Prolonged exposure to oxygen can lead tothecompletedestruction forganic carbon nsedimentby aerobic bacteria. However, ac-cording to J0rgenson 1982, 1983) and Peckand Legall (1982), anaerobic bacteria are lessefficient iodegraders and may be unable tocompletely break down complex biopoly-mers.J0rgenson1982, 1983) suggested thatcompletebacterialutilizationofrefractoryr-ganic carbon in sedimentmay therefore e-quire the presenceofa bacterialcommunitycomposed of a complete range of reducingbacteria (e.g., aerobic bacteria, nitrate-re-ducers,manganese-reducers,tc.). n such an

environment, ach group of bacteria wouldpartiallydegrade the more complex mole-cules to produce by-products hatother bac-teria lower down in thechemically tratifiedcolumn) could use in therespiration rocess.




In this model, preservationof complex bio-polymerswould be favored in euxinic set-tings where the bacterialreduction ones areseverely attenuated and the microbial food

chain is broken.Aerobic respirationof organic carbon iscommonly considered to be a more rapidmeans ofbiodegradation than anaerobic de-cay. This is because aerobic decay processeshave a higher free-energy ield (Aller 1980)and may be able to supporta more diversebacterial community J0rgenson 982, 1983).Thus, anoxia is generally considered a pre-requisitefor preservation f soft-bodied ndlightly skeletized organisms (see Seilacher1970; Seilacher et al. 1985). However, the ac-tualisticexperiments f Allison (1988a) haveshown thatthe anaerobic decay of soft-bod-ied and lightly skeletized organismscan beextremelyrapid. The softparts of such or-ganisms can be considered volatiles and areeasily decayed. Anaerobic decay of such tis-sues is slower than aerobic decay, but, in ageological sense, t s notslow enoughtopro-motesoft-part reservation.

Sediment ype.Long-term decay inhibi-tion of organic softparts is an unusual oc-currenceand restricted o specific taphono-mic circumstances, such as low-pH peatswamps. Exceptionally preserved plant re-mains in calcareous concretionsfrom fossilpeats have been recordedfrommany locali-ties. Preservation s favoredbythe resistanceof cellulose to decay and the antibacterialqualitiesof tannic nd fulvic cids inthepeat.However, in additionto plants,a wide array

of invertebratesand vertebrates are pre-served in these peats. The best example isprovidedbythe so-called "bog people" fromthepeatsof northernGermany, candinavia,Britain, nd Ireland (Glob 1969). These IronAge human cadavers have been mistakenforrecentmurdervictims Glob 1969).Many pre-serve cellular detailofskin,hair, nd clothingfibers.However, preservation s solely due tothe tannic and fulvicacids produced by the

peat thatimpregnatethe carcasses and pre-serve it like tanned leather. The MiddleEocene GeiseltalesBrown Coal exposed nearHalle, in East Germany Voight 1935, 1957),is an older example of thistypeofpreserva-

tion. Preserved soft parts from this localityinclude muscle fibers nd epithelial cell struc-ture.

Fossil diagenesis

Although anoxia is ineffectives a preser-vational medium for organic soft parts, theremoval of oxygen leads to widespread re-ducing conditions and the production of re-active onic species (Fig. 1). This promotes heformation f early diagenetic mineral precip-itates Berner 1981) which can form duringthe first ew weeks of burial. Earlydiageneticmineral formation s theonly way to halt de-cay-induced nformationoss (Allison 1988a).

The most commonly occurring diageneticminerals associated with exceptional preser-vation are pyrite, arbonates such as calciteand siderite), phosphates (such as francoliteand vivianite),and silica. The minerals occurin a varietyofforms ontrolledby degree ofcrystallinity, rystal ize, and growth form.Mineral form s expressed taphonomically nthepreservation f soft-bodied iotasby threemodes of preservationwhich reflect ifferent

degrees of information loss. These threemodes of preservation are: permineralizedtissues, mineral coats or pseudomorphs, andmineral casts.

Permineralizedoft issues.In vivoprecipi-tationof authigenicmineralphases priortoorganic decay is rare. The mostfrequentoc-currenceof this typeof preservation s thatof permineralized refractoryissues such ascellulose and chitin.Thepreservation f morevolatile structures uch as muscle fibersre-

quires exceedingly rapidmineralization nd,as a result, s frequentlyrestricted o phos-phatic preservation refer osectionon phos-phates)sincephosphates mayform ery arlyin the diagenetic sequence of a deposit andmay pre-dateotherauthigenicmineralphas-es such as carbonates and pyrite (Allison1988b).

Mineral oats. The preservationf oft-partoutlines is the most frequentmode of occur-

rence of soft-bodied iotas. n thiscase, nvivoprecipitationof mineral phases is inhibited,and the internal structure fsoftparts s de-stroyed.However,theorganisms ctas a tem-plate for mineral formation, nd a soft-part




outline is preserved. Examples include: theMiddle CambrianBurgess hale of British o-lumbia (Conway Morris 1985); the UpperCambriananthraconites romVasterg6tland,

Sweden (Muller 1985; Muller and Wallosek1985);thepyritizedfaunasoftheOrdovicianBeecher's Trilobite Bed (Cisne 1973) and theDevonian HunsriickSlate (Stiirmer nd Berg-str6m1973; Stiirmer1985); and the EoceneMessel Oil Shale biota from Darmstadt inGermany Franzen 1985).

The Messel Shale contains flattenedbodyoutlinesofamphibians,flyingmammals, ndbirds (Franzen 1985). These outlines areformedbya permineralized ayerof bacteriawhich pseudomorph the original softparts(Wiittke 983) by promoting he precipitationof siderite. n this case, the bacteria respon-sible fordecay have initiated the precipita-tionresponsiblefor the mineral coat.

When bacteriadie, theyundergo autolysis,whereby enzymesand otherchemicalswith-in the bacterial cell corrode thebody wall ofthemicrobe nd cause ittoself-destruct.hisoccurswithinhours ordays.The presenceof

mineralizedbacteria thereforemplies fixingof the microbes priorto complete autolysis.Mineralization must occurvery rapidlyafterdeathor even duringthe lifeof the bacteria.It mayeven be a cause ofmortality.

The Orsten biota includes three-dimen-sional ostracodes nd crustaceans nclosed inconcretions of calcium carbonate (Muller1985). Preservationncludesfine oft-parte-tails such as limb morphology, yes, sex or-gans and possible guttraces MullerandWal-losek 1985). The animals are preserved incalciumphosphateand cantherefore e freedfrom heenclosing calcareous concretions ytreatmentwith acid and then examined un-der the SEM. Phosphate occurs as botha re-placementofcuticle and as a coat of euhedralcrystals.Very little s known of the mecha-nismof thistypeof mineralization, ut t mayhave been bacteriallymediated. Ennever etal. (1981) showed thatplaque bacteriaare re-

sponsible for the formation of phosphaticcoatson theteethof ivingmammals nd thatseveral strains f bacteriawerecapable ofpre-cipitatingphosphate in thisway. It is there-forepossible that thephosphate coats occur-

ring on the Orsten arthropods wereprecipitated by bacteria and subsequentlymodifiedduringdiagenesis.

Tissue asts ndmolds.Soft-tissue casts nd

molds only preservea two-or three-dimen-sional tissueoutlineand generally nvolve agreaterdegree of nformation oss than thosemineralogicalforms lready isted.Such bio-tas represent the lowest level of soft-tissuepreservation and have formed by the earlydiagenetic stabilization of sediment afteraperiod ofdecay, butpriorto lithificationndcompaction.Such stabilization s most com-monlya productofearly diagenetic mineralgrowth,butmayalso occur n the absence ofauthigenicmineral formation n naturalcast-ing sedimentssuch as fine sands and muds.

The Late PrecambrianPound Quartziteofthe Flinders Range of South Australia con-tains a varietyof soft-bodied asts which in-clude medusoids (Wade 1968). Preservationinvolved the deposition of fine-grainedrhythmiccasting" sands upon the carcassesshortly fterdeath.Organic decay continueduntil the organisms were destroyed. The

sands,being fine-grained, nderwent ittle rno compactionand retained the cast form fthe carcasses.

The Upper Carboniferous Mazon Creekbiotaoccurringwithin heFrancisCreekShaleof llinois has yieldeda variety fsoft-bodiedfossilspreservedwithin siderite nodules atthe base ofthe shale (Baird1979).Softtissuesare preservedsolely as casts and molds andas impressions with little or no internaldetail. Preservation occurredthrough earlydiageneticmineral formation round the de-cayingorganisms.Although decay has com-pletelydestroyedmostorganic tructures,helithification f sediment round theorganismcasta replicaofsoftparts.Thisreplicaformeda void in the subsequent concretion whichwas later infilledwith late-stagediageneticminerals, thus formingsoft-part asts andmolds.

Diagenetic Classification ofKonservat-Lagersta ten

Since diageneticmineral growthsare themost mportant actorn the formation f ex-ceptionallypreservedfossilbiotas, t slogical




to erect a causativeclassification ased uponmineral paragenesis. The following classifi-cationconcentrates pon theprincipalfactorscontrollingsedimentgeochemistry, amely

rate of burial, salinity, nd organic content,and how differentombinations fthese vari-ables function as a precipitation switch,thereby eading to mineral formation.Thisdiscussion concentrates on those mineralsmost commonly associated with the excep-tional preservation of macrofossils pyrite,phosphates, and carbonate).Silica is a valu-able source ofexceptionallypreservedmicro-organisms nd three-dimensional lants,butis rarelyassociatedwith the preservationofvolatilesoftpartsofmacrofossils. ilica is notreviewed here, but recent reviews includethose of Knauth (1979), Leo and Barghoorn(1976), and Ferriset al. (1988).

Certain compounds may function as pre-cipitation"poisons" (pore-water ompoundsthat nhibit heformation f certainminerals)and exert an as-yetunquantifiedeffect nmineralprecipitation.The existence of suchcompounds is acknowledged, but because

there s very ittle data on them,there s nodiscussion here on theirrole in earlydiage-neticmineralformation.The followingdis-cussion concentrates on the general geo-chemicalparameterspH, Eh,organic ontent,rateofburial, nd depositionalenvironment)requiredfor he mineralization fsoft-bodiedtissues.

Pyrite

Pyritized oftpartshave onlybeen record-ed from handful oflocalitiesincludingtheOrdovician Beecher's Trilobite Bed of NewYork State (Cisne 1973), the HunsriickSlateofthe Bundenbachdistrict fGermanyBerg-strom1989; Kott and Wiittke1987; Stiirmer1985; Stiirmer nd Bergstr6m 973),and theMiddle CambrianBurgess hale ofBritish o-lumbia (Conway Morris1986).

It has long been known that pyritemayformveryearly in the diagenetichistoryof

a sediment; ndeed, both pyrite nd its pre-cursors have been recorded in Recent sedi-ments Love 1967;Lein 1978)and around thebodies of living (Clark and Lutz 1980) anddead (Allison 1988a) animals. The occurrence

of authigenic pyrite n shales has been re-viewed by Brett nd Baird 1986), FisherandHudson (1985), and Hudson (1982). Theseworkersdemonstrated hat the morphology

and occurrence of pyrite was stronglycon-trolledby burial rate and geochemical con-ditions (such as organic and sulfatecontent)near the sediment/waternterface.

Authigenic pyriteforms s a result of theactionofanaerobicbacteriathatpromotere-ducing conditions. n such a system, etritaliron and bacterially educed ron)reactswithhydrogensulfide resultingfromthe reduc-tion of pore-water sulfates) to form ironmonosulfides such as greigite and mackina-wite Berner1970,1971). These mineralsreactin turn with bacterially iberatedhydrogensulfide o formuthigenicpyriteBerner1984,1985). Thus, formation fsedimentary yriteisfacilitated y theavailabilityoforganic car-bon (forbacterialrespiration),ron, nd pore-watersulfates forsulfatereduction) Bernerand Raiswell 1984) (Fig. 2). In mostmarinefine-grained lasticsediments, ronmineralsand pore-water ulfates re present n abun-

dance and theformation fpyrite s only im-ited by the availability of organic carbon.Freshwater nvironments, owever,are typ-ically low in sulfatecontent and pyritefor-mation is therefore ulfate-limited. uxinicmarine environments,however, are charac-terizedbyconcentrations fhydrogen ulfide(frombacterial ulfatereduction), huspyriteformationhere is determinedby the avail-abilityof reactive ron (Bernerand Raiswell1984). The conditionsrequired forpyritiza-tion of lightlyskeletized and softtissues inthese three freshwater,marine, nd euxinic)environments re discussed below.

Freshwater.Since iron is commonly vail-able in terrestrial eposits and sulfatecon-centrationsrelow, pyritizationsdependentupon the sulfate bank (Bernerand Raiswell1984). Depletion of this source is controlledbyrateofsedimentation nd organiccontent.In regardtothepreservation f softparts,we

can consider two geochemical extremes. nthe first ase,organiccontent s highand rateofburial is low. In such a system ulfate re-duction is uniform, nd thepyriteformed sdisseminated evenly throughout the sedi-




ment.The zone of bacterialsulfatereductionbecomes attenuated, and sulfate-reducingbacteriaaround decomposingorganicmatterare starvedofsulfate. n effect, carcasscan-

not function s a reducingprecipitation inkin suchan environment, ince it s surround-ed by decaying dispersed carbonin the sed-iment. n the second extreme, rganiccontentis low and burial rate is increased. In thissystem, widespread pyrite precipitationthroughout hesediment s inhibited, he sul-fate-reducing acteriaaround the carcassarenot limited by sulfate supply, and pyritiza-tion can occur. Burrowing nd scavenging nsuch an environmentwould be inhibitedbyrapid burial. Because of the low concentra-tionsof sulfate n freshwater eposits,pyrit-ization is rare.An example of such depositsisthe Lower DevonianGosslingialora f SouthWales (Kenrickand Edwards 1988).

Normalmarineanoxic/oxicnterfacet or be-low ediment/waterelvedge).-In a normalma-rine clastic setting,detrital iron and pore-water sulfates re present n abundance, andpyritizations only imitedby carboncontent

(Berner nd Raiswell 1984).We can thereforeconsidertheeffectsfburial and carboncon-tent. fburialrate s low,thenscavengers ndbioturbating rganismsmaydestroydelicatesoftparts.Rapid burial is therefore equiredto preventbioturbation. ellwood (1971) hasshownthatrapid catastrophic?) urialcan soimpede the diffusion f pore-watersulfatesfrom heoverlyingwatercolumnthatpyriteformationsslowed (i.e.,becomes sulfate-lim-iting).Thus carbon ontentwill exert he amecontrolover thepreservation fsoftpartsasit does in freshwater ystems i.e., a low car-bon content favorspyritizationof soft tis-sues). Pyritizationof softparts is thereforefavored by rapid burial and a low organiccontent.

Euxinic marine.-Euxinic marine environ-mentsoccur in stratified aters and result nwidespread sulfatereductionoforganicmat-ter nd theproduction f abundanthydrogen

sulfide.Pyriteformsby the reactionof hy-drogen sulfide with either reduced iron ordetrital ron mineralsand is limitedby thesupply of reactive ron (Bernerand Raiswell1984).What, hen, re the deal conditionsfor

U.ow

FIGURE 2. Depositional parameters stippled area) re-quiredforpyritizationf ightly keletizedand soft-bod-ied organisms.Earlydiageneticpyritization equiresrap-id (possibly catastrophic)burial, a low organic content,and the presenceof sulfates.

pyritization f softparts in this typeof en-vironment?Even thoughsuch basins are an-oxicand bioturbation nd scavengingarepre-vented, theymay still be swept by currents(Bairdand Brett 986)which could disaggre-gatea decomposingcarcass.Thusrapidburialwould stillfavor oft-partreservation.Over-all organicconcentrations re typicallyhighin euxinic environments, nd pyriteforma-tion may continue during burial to greatdepths (Hudson 1982). In localized areaswherecarboncontents low, pyritizationmaybe promotedby the migrationof hydrogensulfidefromorganic-rich reas (BernerandRiaswell 1984). What,then, s the role ofor-ganics in thepreservation fsoftparts? incepyritization s limited by the availabilityofiron, it is likely thata low (locally) organiccontentwill favorpreservation f softparts.Forexample, fcarboncontent s locally low,

then bacterial ronreductionwill be centeredupon decomposingcarcasses; heresultant e-duced ironwill rapidlyreact withmigratinghydrogen ulfide, nd pyritewill formn andaroundthecarcass. f,on the otherhand, car-




bon content shigh,thenbacteriallyiberatedreduced ironwill be rapidly depleted by or-ganic carbondispersedthroughout he sedi-ment, nd pyritization forganicconcentra-

tions, such as animal carcasses, will beimpeded. Earlydiagenetic pyritewill occuras disseminatedgrains and framboidsfromthe reaction of reduced iron (comparativelyreactive)and hydrogensulfide. Later in theburialhistory fthe equence,pyritewillformbythe reactionofhydrogen ulfidewith lessreactive) detrital ron-bearingminerals (forexample,see discussion of theJurassic osi-donia Shale in Hudson 1982).

Pyritizationof softparts is thereforefa-voredby rapidburial and a low organiccon-tent and is most likely o form n a marineenvironmentwhere sulfate oncentrationsrehighest Fig. 2).

Phosphates

Phosphatizedsoftpartsexhibit he highestquality of preservation, ncluding three-di-mensional preservation f softparts and the

retentionof cellularmorphology.Fossilizedmuscle fibers re morecommonly ssociatedwith phosphate replacementthan with anyothermineralizing agent. Examples includeconodont animals from the CarboniferousGranton hrimpbed ofScotland Briggs tal.1983; Aldridge etal. 1986),concavocarids bi-valved arthropods) rom heUpperDevonianof Australia (Briggs and Rolfe 1983), squid(Donovan 1983;Donovan and Crane in prep;Allison 1988c) fromthe OxfordClay of En-gland, crustaceans from he Jurassic f Italy(Pinna 1985),and fishfrom heCretaceous ofBrazil (Martill 1988). According to Zangerland Richardson (1963), Zangerl (1971), andConway Morris 1979b), compressionof de-cayingsoft issues s mainly the resultof col-lapse due to decomposition. Preservationofthree-dimensional ofttissues in the exam-ples cited above thereforemplies thatmin-eralizationwas initiatedpriorto appreciable

decay.In most freshwater nd marine settings,concentrations fthebicarbonate on exceedthose of the phosphate ion, and carbonate

mineralformation s favored. These circum-stances can be exacerbated n organic-rich e-quences where further icarbonate ions areproducedby anaerobic respiration.n such a

system,hecarbonate/ hosphate switch ssetat thedefaultposition Fig. 3) and favors ar-bonate precipitation. orphosphate mineralsto form,the solubility product of calciumphosphate must be exceeded. Gulbrandsen(1969) suggested thatthismay be achieved atsites of oceanic upwelling, where planktonand algae concentrate phosphates. Periodicblooms and subsequent decomposition ofthese organisms would liberate phosphatesto pore-water solution (Lucas and Prevot1984), thereby increasing concentrations.However, this process alone is not an ade-quate explanation,since the decompositionoforganicmatter iberatesfarmore bicarbon-ate ions than phosphate and mayeven leadto the calcium carbonate solubility productbeing exceeded. Benmore et al. (1983) sug-gested that phosphate liberated by the de-compositionoforganiccarbon would be ad-sorbed to ferric hydroxides within the

sediment.Upon the onset ofanoxia, and thereductionofferricron,phosphateswould beliberated to pore-water olutionat the anox-ic/oxic boundary,thereby roducinga phos-phateconcentration eak.Low burial rate in-creased residence time at this level) couldpromotephosphatization.Accordingto Gul-brandsen (1969), precipitationof phosphatewould be favoredbyan increasedpH. Thus,phosphatizationwould be promotedin thealkali reducing environmentformedby theamines and ammonia liberatedby thedecayof proteins n a carcass (Berner1968). How-ever, Coleman (1985) has shown thatphos-phates have a broaderstability ield withre-specttopH than do carbonates nd mayevenbe stable in mildlyacid environments.Witha low burial rate, ulfidesmaybe utilized bysulfide-oxidizing acteria,with a resultant e-duction in pH (Fig. 4). Coleman (1985) sug-gested that these circumstances ould favor

the formation f phosphate over carbonate.However,both models whethertheyrequirean acid or an alkali pH) requirea low rateofburial.In addition,Enneveret al. (1981) doc-




[ORGANIC RICH SEQUENCE |

normal pore waters

HCO' P04

P04adsorbed to ferrous

hydroxides

PRECIPITATION SWITCH ATDEFAULT POSITION

CARBONATE PHOSPHATE

OFF

BURIAL

RAPID EDUCED

residence time atLOW=anoxic/oxic boundary HIGH

LIBERATION OF P04 AT ANOXIC/OXIC INTERFACE

DISSEMINATED P04 within CONCENTRATED

THROUGHOUT sediment AT ANOXIC/OXICSEDIMENT INTER ACE

CARBONATE PHOSPHATE CARBONATE PHOSPHATE

OFF OFF

FIGuRE . Flow diagram ummarizing hedepositionalcontrols pon thecarbonate/phosphate recipitationwitch.High organic content and low rate of burial favorsphosphate formationwhilsthigh organic content with rapidburial favorscarbonate formation.

umentedthe n vivoformation fapatitecrys-tals nplaque bacteria, ndAllison 1987) sug-gestedthat imilar acteriamaybe responsibleforconcentrating hosphate in sediment.

However, t s clear that n some casesphos-phate levels only achieve a marginalconcen-trationwhere thesolubilityproduct s barelyexceeded and widespread phosphate precip-itation s inhibited.Allison (1988b) describedsuch a systemfrom heEocene London Clayof Kent, England, where phosphate forma-tionwas inhibitedand onlyoccurred round

phosphatic particles, uch as vertebrate ndarthropod fragments,which functioned asprecipitationnuclei.

In a marinesystem, uthigenicphosphates

normallyprecipitate s a sedimentaryfluor-apatite known as francolite. n freshwater,however, concentrations of iron ions arehigher, nd themost tablephosphatespeciesis usually vivianite Berner1981).

The fieldofsoft-partreservation orphos-phatic preservation s defined by a high or-ganic content and a low rate of burial (Fig.4). A high organic content supplies phos-phates to pore-water olutionduring thede-cayprocess.Phosphatizationofsoftpartswillbe favoredbya low rateof burial, as this will

increaseresidence timeattheanoxic/oxic n-terface,wherephosphateconcentrationsmaybe secondarilyenrichedby the reduction offerric ron (Benmoreet al. 1983).




_j~~~~~~~~~~~~~~~~~~~~~~~~~~~;a:

LL

4~~~~~t?~ ~ t

FIGuRE 4. Depositional parameters stippled area) re-quired forphosphatizationof softparts.Earlydiageneticphosphatizationrequires a low rate of burial and a highorganiccontent.

Carbonates

Preservation f softparts smore common-ly associated with carbonate mineralizationthanwith nyother uthigenicmineralphase.The carbonateoccurseither s concretions ras fine-grainedbedded limestone (oftenre-ferred o as Plattenkalk eposits).Concretion-arycarbonatespreserving oftpartsoccuras

sideriteor calcite and include the Carbonif-erous biotasofMazon Creek, llinois,and theMontceau les mines of France.

The decompositionoforganiccarbon n ananoxic environment eads tothe formation fthe bicarbonate on that, fproduced in suf-ficient uantity, an reactwith calciumor ronions present n pore-waters oexceedthe sol-ubilityproductofcalcium carbonate nd pro-duce authigenic carbonates (Raiswell 1971,

1976; Berner1981). In a marine system, al-cium is normally present n supersaturationlevels,and the ron reactspreferentially ithsulfide ons to formpyrite; hus calcite s themost likely mineral phase to form but see

Sellwood 1971). In a freshwaternvironment,.

cr.

FiGrEn 5.arpoitonalean parameter (stipldeariea)rei-qiredtfor presnervto fsftprt8iti1crontsField anitfxetoa brsraicroniscaraterizedbyerap-d

id (pssbl dcatasophc burialgofmarorganicihsequnce

irnsufioins o xdced theolubiit poducofetironararbonate ndspomoatederite prcipto-iation (Beerner1981). aiwll171 97)

Toeerheuantityen ofitilcarbonat-o ieaeinsufficientoi produceth olumedouctoncrse-d

crystalsfor continued carbonate formation.The preservationfield of organic soft partsbycarbonateminerals s therefore ontrolledby a high input of organic carbon.

Rapid burial of such organic-richsedi-ments would promote an anaerobic regime,

reducing he opportunityor ioturbationndinhibiting ron and sulfatereduction by re-movingdecaying carbonfrom he overlyingwaterbody. Moreimportantly,esidencetimeat the anoxic/Ioxicnterface s reduced, and




the precipitation witch s left at the defaultposition (i.e., carbonate on; phosphate off)(Fig.3). Salinity has littleeffect therthan asa control on the species of carbonate which

can form.The field of exceptionalpreserva-tion for carbonate mineralization Fig. 5) istherefore ontrolled by a high rateof burialand a high organic content.

The Mazon Creekbiota is preserved n sid-eriteconcretions n the Upper CarboniferousFrancisCreek Shale (Richardson nd Johnson1971; Baird 1979; Bairdetal. 1985).This shaleisa grey revasse-splay eposit Shabica 1979),which formspart of a cyclothemic equence.The shale is organic-poor, nd the fossil-bear-ing concretions re restricted o the owest10m overlying the Colchester (Number Two)Coal. The bicarbonate ons requiredfor sid-eriteformation riginatedfrom naerobic de-compositionof thepeatswhich nowform hiscoal. A scattereddistribution forganicmat-terpromotes this typeofpreservation.A re-duced number of precipitation nuclei cou-pled with increased supply of bicarbonateincreasesthe rateofprecipitationnd reduces

decay-induced nformation oss.Fine-grained, thinly bedded limestones,such as theJurassic olnhofen Limestone ofGermany, he Eocene Green River Formationof the central U.S. (Grande 1984), and theHaquel and Hjoula Limestones of Lebanon(Huckel 1970; Hemleben 1977),are oftenre-ferred oas Plattenkalkepositsor ithograph-ic limestones.Such deposits occur in lacus-trine as well as marine systemswhere thesupplyofterrigenous ediment s limited. nsuch a system, espiratory arbon dioxidepro-duced by bacteria, algae, and planktonachieves high levels of supersaturation ndpromotesthe precipitation f carbonatemin-erals (for review see Bathurst1975). Rapidburial in such fine-grained arbonatespro-motes the formationof exceptionally pre-served fossils. Further, rganicproductivitymaylead to the development of anoxic con-ditions which inhibit bioturbation nd scav-

enging. Fossils arecharacteristicallylattenedand eithercastbythe carbonatesor coatedbyother minerals. There has as yet been littlework on theirparagenesis or preservationalmineralogy.

Conclusion

Long-term ecay nhibitionon a geologicaltime-scaleis an unusual event and largely

restricted o refractory iological structuresand unique depositional systems peat bogs,amber, tarsands, alt deposits,etc.). In morecommon depositional settings, organic re-mains can be rapidlydestroyedby respiringmicrobes.Anoxia retardsdecay but does nothalt it.Different rganicmolecules have dif-ferentdecay rates;tissuessuch as muscle areextremely olatileand can be destroyedwith-in days or weeks of burial (Allison 1988a).Some compounds,however,are more decay-resistant and thereforehave a higher resi-dence time n the sediment.Thus,chitinwillpersist n sedimentlonger than muscle (Al-lison 1988a), although cellulose will persistforeven longer (Allison 1987),and lignifiedcellulose foreven longer still Leo and Barg-hoorn 1970; Stout et al. 1981). AccordingtoStoutet al. (1981), thehalf-life f cellulose isabout one-third hatof igninin aerobic con-ditions.By comparingthe relativedecay re-

sistanceof the tissueswhich formmostof thefossils hatpaleontologists ncounter,we cansee that fossil remainsat the outcrop repre-sent the end-product of the interplaybe-tween decay and diagenetic mineral forma-tion. If decay progresses aerobically, thendiagenetic mineral formationwill be hin-dered,and organictissues will be largelyde-stroyed. n such an instance, he sole remain-ing fossilswill be hard parts uch as bone andshell. Should decay progress anaerobically,then decay ratewill be reduced and the con-ditions requiredforearly diageneticmineralformationwill be enhanced. Were mineral-izationto occurshortly fter urial, thenvol-atile soft tissuesmay be preserved.If, h.low-ever,mineralization ccurs ater n the burialhistory f the sediment,then only themorerefractoryissues uchas chitin, ellulose,andligninwill be preserved. n the extreme ase,tissues are notmineralizedat all; then chitin

will be destroyed, uthighlyrefractoryissuesuchas lignin mayremain. t s therefore os-sible tocreate listofbiological tissuesbasedupon comparativedecay resistance see Fig.6). This listcanbe relatedto theform fpres-




l' ff p ~~~~~~SHELLYOSSILS|

Z INERALIZED_ UCLE \\\

EARLY LATE

MINERALIZATIONFIGURE 6. The relationship etweendecayand mineralization n thepreservation fexceptionally reservedfossils.Reduced decay and very early diagenetic mineralization re required for oft-tissue reservation. fmineralizationis impeded, decay will continue, nd only themorerefractorylements f biota will be preserved.Thepreservationalmineralogy of each tissuetype extends from he bottom eft-hand ornerof thebox to the boundaryfenceof thenext most refractoryissue type.

ervational mineral (permineralizations,tis-

sue imprints, ast/coats) nd plottedas pres-ervationalfieldsrelativeto rate ofdecay anddiagenetictimingFig.6). By consideringfos-sils as chemically xotic edimentary articlesin thisway, itmay be possible to isolate thedepositional circumstancesthat lead to ex-ceptionalpreservationn the fossilrecord ndthen go on to prospectforFossil-Lagerstitten.

Acknowledgments

D. E. G. Briggs,V. P. Wright,J.D. Hudson,and E. N. K. Clarksoncommentedon an ear-lier draft f themanuscript. amalso gratefulto the editorof this ournal and two anony-mous reviewersfor redpenning" a previousversion and providing useful and construc-tivecriticism. hisworkwas initiatedduringthe tenure of Natural EnvironmentalRe-search Council QuotaAwardno.GT4/84/GS/59 at theUniversity fBristol,England, and

completedduring a FridayHarbor Postdoc-toral Fellowship at the Universityof Wash-ington.

LiteratureCited

ALDRIDGE, . J., . E. G. BRIGGS,. N. K. CLARKSON,ND M. P.SMITH. 1986. The affinitiesf conodonts-new evidence fromthe Carboniferous fEdinburgh, cotland. Lethaia 19:279-291.

ALLER,R. C. 1980. Diageneticprocessesnear thesediment-waterinterface f Long Island Sound. I. Decompositionand nutrientelement geochemistry.Advances in Geophysics22:237-350.

ALLER, R. C. AND J. Y. YINGST. 1980. Relationships betweenmicrobialdistributions nd the anaerobic decomposition oforganic matter n surfacesediments of Long Island Sound,USA. Marine Biology56:29-42.

ALLER, R. C. AND J.E. MACKIN. 1984. Preservationof reactiveorganic matter n marine sediments.Earth and PlanetarySci-ence Letters70;260-266.

ALLISON, P. A. 1986. Soft-bodied nimals in the fossil record:

the role ofdecay in fragmentation uringtransport.Geology14:979-981.

ALLISON, P. A. 1987. The Taphonomy of Soft-Bodied ossil Bio-tas. Unpublished Ph.D. dissertation, niversity fBristol.Bris-tol, England. 198 pp.

ALLISON, P. A. 1988a. The decay and mineralization f protein-aceous macrofossils. aleobiology 14;139-154.

ALLISON,P. A. 1988b. Taphonomy nd diagenesis ofthe LondonClay (Eocene) biota. Palaeontology31(4):1079-1100.

ALLISON, P. A. 1988c. Soft-bodied quids from he Jurassic x-fordClay. Lethaia. 21(4):403-410.

BAIRD, G. C. 1979. Lithology and fossil distribution, rancisCreekShale in Northeastern llinois. Pp. 41-68. InNitecki,M.H. (ed.), Mazon Creek Fossils.Academic Press; London.

BAIRD,G. C., C. W. SHABICA,J.L. ANDERSON, AND E. S. RICHARD-SON, JR. 1985. The biota of a Pennsylvanianmuddy coast:habitatswithintheMazonian delta complex,northeasternl-linois. Journal f Paleontology 59:253-281.




BAIRD, G. C. AND C. E. BRETT. 1986. Erosion on an anaerobicseafloor: ignificance f reworkedpyrite eposits from he De-vonian of New York State.Palaeogeography,Palaeoclimatol-ogy,Palaeoecology 57:157-193.

BARTRAM,K. M., A. J. ERAM, ND P. A. SELDEN. 1987. Arthropodcuticles in coal. Journalof the Geological Societyof London

144:513-518.BATHURST,R. G. C. 1975. CarbonateSediments and Their Dia-

genesis. Developments in Sedimentology 12. Elsevier; Am-sterdam.620 pp.

BENMORE,R. A., M. L. COLEMAN, ND J.M. McARTHUR. 1983.Originof sedimentary rancolite rom tssulphurand carbonisotope composition.Nature 302:516-518.

BERGSTROM,J. 1989. Taphonomyof fossilLagerstatten:iinsruckSlate (Hi7nsruckschiefer).p. XXX-YYY. In Briggs,D. E. G., andP. R. Crowther eds.), Encyclopaedia of Palaeobiology. Black-well Scientific ress; Oxford. n press.

BERNER,R. A. 1968. Calcium carbonateconcretionsformedbythe decomposition oforganic matter. cience 159:195-197.

BERNER,R. A. 1970. Sedimentarypyriteformation.American

Journal f Science 268:1-23.BERNER, R. A. 1971. Principles of Chemical Sedimentology.

McGraw-Hill; New York. 240 pp.BERNER,R. A. 1980. EarlyDiagenesis: a theoretical pproach.

PrincetonUniversity ress; Princeton.241 pp.BERNER,R. A. 1981. Authigenicmineral formationresulting

from rganicmatter ecomposition nmodern ediments. ort-schritte er Mineralogie 59:117-135.

BERNER,R. A. 1984. Sedimentary yrite, n update.Geochimicaet Cosmochimica Acta 48:605-615.

BERNER,R. A. 1985. Sulphatereduction, rganicmatter ecom-position and pyriteformation. hilosophical TransactionsoftheRoyal SocietyofLondon 315A:25-37.

BERNER,R. A. AND R. RAISWELL. 1984. A new method for dis-

tinguishing freshwater rommarine sedimentaryrocks. Ge-ology 12:365-368.

BRETT,C. E. AND G. C. BAIRD. 1986. Comparativetaphonomy:key topaleoenvironmental nterpretationased on fossilpres-ervation.Palaois 1:207-227.

BRIGGS,D. E. G. AND W. D. I. ROLFE. 1983. New Concavocarida(new order ?Crustacea) from the Upper Devonian of Gogo,WesternAustralia, nd thepalaeoecology and affinitiesfthegroup. Special Papers in Palaeontology30:249-276.

BRIGGS,D. E. G., E. N. K. CLARKSON, AND R. J.ALDRIDGE. 1983.The conodont animal. Lethaia 16:1-14.

CISNE, J.L. 1973. AnatomyofTriarthrusnd therelationship ftheTrilobita.Fossils and Strata4:45-64.

CLARK,G. R. AND R.A. LUTZ. 1980. Pyritizationn the shells of

livingbivalves.Geology 8:268-271.COLEMAN, M. L. 1985. Geochemistry fdiageneticnon-silicate

minerals:kinetic onsiderations. hilosophicalTransactions ftheRoyal Societyof London 315A:39-54.

CONWAY MORmS, . 1979a. BurgessShale. Pp. 153-160. In Fair-bridge,R. W., and D. Jablonski eds.), The Encyclopaedia ofPaleontology. Dowden, Hutchinson and Ross; Stroudsberg,Pennsylvania.

CONWAY MORRIS, . 1979b. Middle Cambrianpolychaetesfromthe Burgess Shale of BritishColumbia. Philosophical Trans-actionsof the Royal Societyof London 285B:227-274.

CONWAY MoRms,S. 1985. Cambrian Lagerstdtten:heir distri-bution and significance. hilosophicalTransactions f theRoy-al SocietyofLondon 311B:49-67.

CONWAYMoRRis, . 1986. The community tructure fthe Mid-dle Cambrian phyllopod bed (BurgessShale). Palaeontology29:423-458.

DONOVAN, D. T. 1983. Mastigophorawen 1856, littleknown

genus ofJurassic oleoids. Neues Jahrbuch urGeologie undPalaontologie Abhandlungen 165:484-495.

DONOVAN, . T. AND M. CRANE. In prep. Type materialof Be-lemnotheutisnthePearceCollection at theBristolMuseumandArtGallery.

ENNEVER, ., . . STRECKFUSS,ND M. C. GOLDSCHMIDT. 1981.Calcifiabilitycomparison among selected micro-organisms.Journal fDental Research60:1793-1796.

FERRiS, . G., W. S. FYFE,AND T. J. EVERBRIDGE. 1988. Metallicionbindingby Bacillus ubtilus:mplications or hefossilizationofmicro-organisms. eology 16:149-152.

FISHER, I. ST. J.AND J.D. HUDSON. 1985. Pyritegeochemistryand fossilpreservation n shales. Philosophical Transactionsofthe Royal Society ofLondon 311B:167-169.

FRANZEN,J. L. 1985. Exceptionalpreservation of Eocene ver-tebrates n the lake deposit ofGriubeMessel (West Germany).PhilosophicalTransactions f theRoyalSociety fLondon 311B:181-186.

GLOB, . V. 1969. The Bog People. Faber; London. 200 pp.GRANDE, . 1984. Paleontology oftheGreen RiverFormation,

with a review of the fishfauna. Bulletin of the GeologicalSurveyofWyoming63:1-333.

GULBRANDSEN,R. A. 1969. Physicaland chemicalfactors n theformation fmarine apatite.EconomicGeology 64:365-382.

HEMLEBEN,C. 1977. RoteTiden und die Oberkretazischen lat-tenkalke im Libanon. Neues Jahrbuch urGeologie und Pa-l5ontologie,Monatshefte1977:135-113.

HUCKEL, . 1970. Die Fischenschiefer on Haqel and Hjoula inderOberkriededes Libanon.Neues Jarhbuch urGeologie undPalaontologie,Abhandlungen 135:113-149.

HUDSON, J.D. 1982. Pyrite n ammonite-bearing hales fromtheJurassic fEngland and Germany. edimentology27:639-667.

JORGENSON,B. B. 1982. Ecology of the bacteria of the sulphur

cyclewith special reference o anoxic-oxic nterface nviron-ments.Philosophical Transactions f theRoyal Society of Lon-don B298:543-561.

JORGENSON,B. B. 1983. Processes at the sediment-water nter-face.Pp. 477-561. In Bolin, B.,and R. B. Cook (eds.),The MajorBiochemicalCyclesand TheirInteractions.J.Wiley and Sons;Chichester.

KENRICK, P. AND D. EDWARDS. 1988. The anatomy of LowerDevonian Gosslingiareconensis eard based on pyritized xes,withsomecomments n thepermineralization rocess. Botan-ical Journal f the Linnean Society97:95-123.

KNAUTH,. P. 1979. Amodel for heoriginof chert n imestone.Geology 7:274-277.

KoTT, R. AND M. WUTTKE. 1987. Untersuchungenzur Mor-

phologie, Pala6kologie und Taphonomie von RetifungusudensReitschel 1970 aus dem HunsriuckschieferBundersrepublikDeutschland).GeologischesJahrbuchHessen 115:1-27.

LEIN, A. Y. 1978. Formationof carbonate and sulfide mineralsduring diagenesis of reduced sediment.Pp. 339-354. InKrum-bein, W. E. (ed.), EnvironmentalBiogeochemistrynd Geomi-crobiology.Ann ArborScience. Ann Arbor,Michigan.

LEO,R. F. AND E. S. BARGHOORN. 1970. Phenolic aldehydes:generationfromfossil woods and carbonaceous sedimentsbyoxidativedegradation.Science 168:582-584.

LEO,R. F. AND E. S. BARGHOORN. 1976. Silicification f wood.Botanical Museum LeafletsofHarvardUniversity 5:1-46.

LOVE, L. G. 1967. Earlydiagenetic ronsulphide in recent ed-iments of the Wash (England). Sedimentology9:327-352.

LUCAS,J. ANDL. PREVOT.1984. Apatite synthesisby bacterialactivityfromphosphaticorganicmatter nd several calciumcarbonates n natural freshwater nd seawater. Chemical Ge-ology42:101-118.




MALCOLM,. J.ANDS. 0. STANLEY.1982. The sedimentenvi-ronment.Pp. 1-14. InNedwell, D. B., and C. M. Brown eds.),SedimentMicrobiology.Academic Press; London.

MARTILL,D. M. 1986. The stratigraphic istribution nd pres-ervationof fossil vertebrates n the Oxford Clay of England.

MercianGeologist 10:161-188.MARTILL,D. M. 1987. A taphonomicand diageneticcase studyof a partiallyarticulated chthyosaur.Palaeontology 30:543-556.

MARTILL,D. M. 1988. The preservation f fishes n concretionsfrom he Santanna Formation Cretaceous) of Brazil.Palaeon-tology31:1-18.

MULLER,K. J. 1985. Exceptionalpreservationn calcareousnod-ules. PhilosophicalTransactions ftheRoyal Society f London311B:67-73.

MULLER, . J.ANDD. WALOSSEK. 985. Skaracarida, new orderofCrustaceafrom heUpper Cambrianof Vasterg6tland, we-den. Fossils and Strata17:1-65.

PECK,H. D. AND J.LEGALL.1982. Biochemistry fdissimilatory

sulphate reduction. Philosophical Transactions of the RoyalSocietyof London 298B:443-466.PINNA, G. 1985. Exceptionalpreservationn the Jurassic f Os-

teno. Philosophical Transactionsof the Royal Societyof Lon-don 311B:170-180.

RAIsWELL,R. 1971. The growthof Cambrian and Liassic con-cretions.Sedimentology17:147-171.

RAISWELL,. 1976. The microbiologicalformation f carbonateconcretions n theUpper Lias ofN. E. England.Chemical Ge-ology 18:227-244.

REDFIELD, . C. 1958. The biological controlofchemicalfactorsin the environment.American Scientist48:206-226.

RICHARDSON,. S.,JR.AND R. G. JOHNSON. 1971. Mazon Creekfaunas.Proceedingsofthe FirstNorthAmericanPaleontolog-

ical Convention 1:1222-1235.SCOTT, A. C. 1979. The ecology of Coal Measure florasfromnorthern ritain. roceedingsoftheGeologistsAssociation90:97-116.

SEILACHER, . 1970. Begriff nd bedeutung der Fossil-Lager-statten.Neues Jarhbuch urGeologie und Palaontologie Ab-handlungen 1970:34-39.

SEILACHER, ., W.-E.REIF,AND F. WESTPHAL. 985. Sedimento-logical, ecological and temporalpatterns fFossil-Lagerstatten.PhilosophicalTransactions f theRoyalSociety f London31 B:5-23.

SELLWOOD, . W. 1971. The genesis of some sideriticbeds inthe YorkshireLias (England). Journal f SedimentaryPetrol-ogy 38:854-858.

SEPKOSKI, .J., JR. 1981. A factor nalytic descriptionof thePhanerozoic marinefossil record. Paleobiology 7:36-53.

SHABICA, . W. 1979. Pennsylvanian edimentationn Northern

Illinois: examinatinofdelta models. Pp. 13-41. In Nitecki,M.H. (ed.), Mazon CreekFossils.AcademicPress; New York.

STOUT,J.D., K. M. GOH,AND T.A. RAFTER. 981. Chemistryndturnover f naturallyoccurringresistant rganiccompoundsin soil. Soil Biochemistry:1-73.

STORMER, . 1985. A small coleoid cephalopod with soft-partsfrom he Lower Devonian discovered using radiography.Na-ture 318:53-54.

STfJRMER,W. AND J. BERGSTR6M. 973. New discoverieson tri-lobitesby x-rays. alaontologischeZeitschrift7:104-141.

VOIGHT, . 1935. Die Erhaltungvon Epithelzellen mit Zell-kernen,von Chromatophorenund Corium in fossilerfrosch-haut aus der mitteleozanenBraunkohle das Geiseltales. Nova

ActaLeopoldina 3:339-360.VOIGHT, . 1957. Eine parasitischerNematode in fossiler Co-leopterenMuskulaturaus das eozanen Braunkohledes Gei-seltales bei Halle (Saare). Palaontologische Zeitschrift 1:35-39.

WADE,M. 1968. Preservationof soft-bodiedanimals in Pre-Cambriansandstonesat Ediacara,South Australia. Lethaia 1:238-267.

WESTRICH, .T. AND R. A. BERNER. 1984. The role of bacterialsulfatereduction:the G model tested. Limnologyand Ocean-ography29:236-249.

WHITTINGTON,H. B. 1971. TheBurgess hale: history fresearchand preservationof fossils. Proceedings of the FirstNorthAmericanPaleontologicalConvention 1:1176-1201.

WUrTKE,M. 1983. Weichteil-Erhaltung urch lithifizierteMi-croorganismenbei mittel-eozainenVertebraten us den 01-schiefernder Grube Messel bei Darmstadt. SenckenbergianaLethaea 64:509-527.

ZANGERL,R. 1971. On the geologic significanceof perfectlypreserved fossils. Proceedings of the FirstNorth AmericanPaleontological Convention 1:1207-1222.

ZANGERL,R. ANDE. S. RICHARDSON, JR. 1963. Thepaleoecologicalhistory ftwoPennsylvanianblack shales. Fieldianna GeologyMemoir4:1-132.

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