煤沉积过程成煤构造环境中英文对照外文翻译文献.docx

煤沉积过程成煤构造环境中英文对照外文翻译文献.docx

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煤沉积过程成煤构造环境中英文对照外文翻译文献

中英文对照外文翻译

Coal-ProducingTectonicEnvironments

Thisfinalchapterintheinvestigationofcoalsedimentationisconcernedwithdepositionalaspectsofthehighestorderofmagnitude,namely,theinfluenceofthecrustalsettingonpeataccumulation.Thisisabroadandcomplexfieldwhichdrawsoninformation,gatheredfrommanydifferentdisciplinesoftheearthsciences.Someofthesearecurrentlyevolvingquiterapidly,whileothersreina“moppingup”stage,insensuKuhn（1970）andWalker（1973）,followingrecentscientificrevolutions.Anexampleofthelatteristhereplacementofthegeosynclinalhypothesisintheearly1970sbytheconceptofplatetectonics.Evenafteralifespanof20years,thisnewparadigmisstillintheprocessofbeingrefinedandfittedoutwithconceptualsubsets,asshownbythecurrentemphasisonterraneanalysis.Itisthereforenotpossibleatthisstagetomakeadefinitivestatementonthechosensubject,butmerelytooutlinetheprincipleonwhichamoderngeotectonicclassificationofcoalfieldscanbeestablished.Eventhismodestgoalisfraughtwithdifficulty,becausethechangefromthepredominantlystaticgeosynclinalviewofglobaltectonicstoitsmodern,largelymobilisticinterpretationhascomplicatedthetectonicclassificationofsomecoalfields.Whilethetectonicstatusofmanycoalfields,e.g.thoseinforedeepsorforelandbasinshaschangedrelativelylittle,thesettingofcoalsfoundininter-andintramontanetroughs,i.e.withinorogeniccordilleras,cannotbeproperlyassessedwithoutverycarefulstudy.Accordingtothegeosynclinalconcept,practicallyalloftheseintradeeps,togetherwithfore-andbackdeeps,theirextra-orogeniccounterparts,wereregardedaspartofagroupofmolassesbasins,thedevelopmentofwhichaccompaniesorfollows“terminalgeosynclinaltecto-orrgenic”（Aubouin1965）.Thisfixistandstrictlysequentialinterpretation（highlightedbytheterm“epieugeosyncline”ofKay1951）hasnoplaceinmoderngeotectonicanalysis,whichviewsmostorogenicbeltsascollagesofautochthonousandallochthonousterranes,i.e.astectono-stratigraphicassemblageswithpossiblycoevalbutheterogeneousstratigraphicrecordsreflectingtheiroriginindifferentgeologicalandgeographicaldomains（MongerandPrice1979,Mongeretal.1982）.Thetectonicsetting,whichinfluencedtheformationofanallochthonousterraneassemblagebeforeaccretion,mayhavebeenverydifferentinstyleandphysicallyfarremovedfromitsrestingplaceafterdocking.Itfollowsthatamulti-terraneorogenmaycontainavarietyofcoalsformedatdifferenttimesbeforeandafterterraneaccretion.Moreover,contemporaneouspre-accretionarycoaldepositsformedindifferentterranesarelikelytovaryincoaltypes,coalificationhistoriesandtectonicstyles,andallofthesewillinturndifferfromthepost-accretionarymolassescoals,whichalonereflecttheconditionaprevailingintheorogenitself.Indeed,thesituationmayevenbemorecomplex,aswillbediscussedinChap.9.3.2.2.

Platetectonicshascreateditsownnomenclature,ofwhichonlytheessentialtermswillbeusedhere.Theywillbesupplementedbytermswhichareeitherdescriptive,andthereforeindependentofgeotectonictheory,orwhichhavestoodthetestoftimebecausetheyareusefulinspiteoftheirgenericassociationwithnowobsoleteconcepts.Forexample,theexpressions“mio-”and“eugeosynclinalassemblage”havebeenkepthereasreferencetermforshallowwatermarine（mainlyshelf）,andoceanfloorpelagite,turbiditeandophioliteassociationa,respectively.Moreover,reducedtoa“miogeocline”,themiogeosynclinehasintheNorth-Americanliteraturebecomeastandardtermforautochthonous,sedimentaryterracewedgesonlappingcontinentalmargins.Alsotectonicattributesofsediments,suchas“synorogenic”flyschand“latesyn-（folded）topostorogenic（non-folded）”molasses,respectively,canstillbeusedinaplatetectoniccontextwithoutundulycorruptingtheirrelativelyloosedefinitions.Particularlyinthediscussionofcoalfieldssituatednearconvergentplateedges,theconceptofmolassesastheproductofthedestructionoftheupliftedorogenisveryuseful.Asinthepreviousdiscussion,itisnotthepurposeofthischaptertogivedetaileddescriptionsofalargenumberofcasesbuttoselectafewtypicalexamplesofcoalfieldsandrelatetheessenceoftheirarchitecturetotheirrespectiveplatetectonicsettings.

1EarlyExamplesofaTectonicClassificationofCoalfields

Large-scalecoalformationcantakeplaceonlyinactivelysubsidingregions,forexampleinsedimentarybasins.Itispossiblethereforetocharacterisethegeotectonicenvironmentoccupiedbyacoalmeasuresequenceinamannersimilartothatwhichisappliedtoothersedimentaryenvironments.Stutzer（1920）andStille（1926）wereamongthefirsttorecognisethegeneticlinksbetweentectonismandtheformationofcoal.Stille,inparticular,referredtothestrikingdifferenceintermsofbasinfill,numberofcoalseamspresent,theiraveragethicknessandproportioninrelationtototalcoalmeasurethickness,whichexistbetweentheCarboniferousandTertiarycoalmeasuresofEurope.HeattributedsuchdissimilaritiestocontrastingdegreesofcrustalmobilityintheareasaffectedbythetwomainEuropeancoal-formingperiods.HisresultsaresummarizedinTable9.1.EvenifdifferencesincompactionratiosbetweentheTertiarybrownandCarboniferousbituminouscoalsaretakenintoaccount（toalesserdegreethecompactionappliestointer-seamsediments）thecontrastisquiteremarkable.

LateritwasshownbyvonBubnoff（1937）thatthedistributionoftheworldreservesofcoalisalsorelatedtothegeotectonicsettingofcoalfields.HisconclusionsaresummarizedinTable9.2,whichindicatesthatofallcoaldepositsknownupto1937,some71%developedinformertectonicallyveryactiveenvironments,particularlyinthemolassesforedeepswhichdevelopadjacenttoorogenicbeltsandreceivemuchoftheweathereddebriswasheddownfromtheuplands.

CarboniferouscoalmeasuresinmobileVaricanbasins

TertiarycoalmeasuresincratonicbasinsofCentralEurope

Averagecoalmeasurethickness

3000m

150m

Averagenumberofcoalseams

200

2

Averageseamthickness

1m

15m

Cumulativethicknessofcoal

180m

25m

Proportionoftotalcoal

6%

16.7%

Proportionofeconomicinsitucoal

3.6%

12%

Table9.1.Stille’s（1926）comparison（slightlymodified）betweensomecharacteristicsofcoalmeasuresformedintectonicallymobileandcratonisedpartsofEurope,respectively

Table9.2.Thedistributionofworldreservesofcoalinreferencetothegeotectonicsettingofcoalfields.（AftervonBubnoff1937）

Foredeepsmarginaltoorogenicbelts70%

Intradeepswithinorogenicbelts1%

Shelfbasinsoncratonicmargins21%

Cratonicinterior8%

Theconcentrationofcoalintheregionsassociatedwithorogenicbeltsisevenmorehighlightedwhenthelateralextentofthedepositsisconsidered.Coalfieldssituatedwithinorontheshelfmarginsofcratonscoverawiderareathanthecomparativelynarrowforedeeps,butitsarealrestrictioniscompensatedbythefrequencyofcoalseamsoccurringinathickstackofcoalmeasures.Aswillbediscussedlater,thisisrelatedtothesubstantialandprolongedsubsidencethatthecontinentalmarginissubjectedtonearasubductioncomplex,asanorogenicbeltisaccretedontotheplateedge.Itisnotsurprising,therefore,thatvonBubnoff（1937）foundalsoaclosetemporalrelationshipbetweenorogeniesandcoalformationinNorthAmerica,Europe,AsiaandSouthernContinents.Ofcourse,therearemajororogeniesknownwhicharenotassociatedwithcoaldeposits.However,invariably,theirabsenceisrelatedtofactorsaffectingthevegetablesource.Forexample,allpre-Devonianorogeniesoccurredatatimewhentheplantkingdomwasstillinsufficientlyequippedbyevolutiontofulfilitsroleasaneffectiveproducerofpeat.

Thecontinentalshelfenvironment,beinglessmobile,hasproducedfewercoaldepositsthantheorogenicdomain.Inthiscontextitisimportanttodefinethetermshelf.Tothegeographer,theshelfregionisusuallythatpartoftheseawhichextendsbetweenthestrand-lineandthecontinentalslope.However,asvonBubnoff（1948a）noted,thepositionofthestrandlineisquiteincidentaldependingoncrustalmovementsandrelativesealevelpositions.Fromthegeologicalviewpoint,itappearsthereforeusefultoextendthedefinitionoftheshelfsothatthetimefactorcanbeaccommodated.Shelfregionsmaythenberegardedasthosemarginalbutfuullyintegratedzonesofcontinentswhichareoccasionallyaffectedbyshallowmarinetransgressions.Typicalareasarethetrailingedgesofcontinentalplatesandthecratonicmarginsofforedeeps.Commonlytwotypesofshelfenvironmentsaredistinguished,calledstableandunstable,respectively（vonBubnoff1948a;KrumbeinandSloss1963）.Themajorityfortheirassociatedcoalfieldsisparalicincharacter,whichishighlightedbytheintercalationofcoalmeasureswithmarinestrata,afeaturethatisalsocommontothemolassesforedeeps.However,marinestratamaynotalwaysberecognizedbecauseoflackoffossils,whichisrelatedtothedilutionofseawaterbyanexcessiveinfluxoffreshwaterfromthenearbycoastalswamps（DuffandWalton1962）.

Intracratoniccoalfieldsandthoseformedinintramontancbasinsarefrequentlylimnicincharacter,i.e.theyhavenohydrologicalconnectiontothesea,becausetheyhavebeenformedinland-lockedbasinsabovethethenprevailingsealevel.Aspectacularmodernexampleofintramontanepeatformationoccursinthereedmarshes