Depositional environment and apparent age of the Fauske carbonate conglomerate, North Norwegian Caledonides

NGU-BULL436, 2000 -PAGE147

Depositional environment and apparent age of the Fauske carbonate conglomerate, North Norwegian Caledonides

VICTORA.MELEZHIK,TOMHELDAL,DAVIDROBERTS,IGOR M.GOROKHOV&ANTHONYE.FALLlCK

Melezhik,V.A.,Heldal,T., Roberts,D.,Gorokhov,I.M.&Fallick,A.E.2000:Depositio nalenviro nmentandap parentage oftheFauske carbo nateconglomerate,NorthNorw egian Caledo nides.Norges geologiskeuridersekelseBulletin 436, 147-168.

TheFauske conglomerate represents a rath errare caseof a mon omi ct carbo nate conglo merate in the Late Neo proterozoicto 5i1 urian, Iithostratigraph icsuccessions ofthe Norwegian Caledo nides.Lithologicalvarieties of this conglomerateunitfrom the Lovgavlen quarryhave ahighlydeco rative qualityand arewellknowninbot h domestic andinterna t ionalmarketsundertradin gnamessuchas'NorwegianRose', 'JauneRose', 'No rwegianGreen','Antique Fence'and'Hermelin'.The Fauskeconglomerate is a60m-thickunit whichrestsoneit her dark grey('blue')calcite marblesorwhitedolom itemarbles.Thelatt er are jointedandfragmented, andalso appearassedime ntarycollapse- breccia and debriswhere theyare in direct contactwit h the conglomerate.Althoug htheFauskeconglomeratehas beeninvolved intwomain pulsesofCaledoniantectonicdeform at ion,whichproducedanearly,syn-metamorphic flatt ening of thec1astsandalaterfoldin g orrot ation of c1astsinto aspaced cleavage,the overallsed imentary features arest illremarkably well preserved.

TheFauske conglomerate unitconsistsof25beds(5cm to3met res thick)comprisinglandslide,carbonat edebris andcarbonate breccia-con glom ero-breccias-g reywackelit hofacies.Blocks,fragm ents,cobb les,pebblesandsmaller c1asts are mainlyofwhite dolostone andpink,beige,whiteand'blue' calcite marbles.Themat rixhas agranoblastic texture andsimilarrange inlit hology wit hvariable amo untsof quartz,fuchsite,sericite,muscovite and chlorit e.

Withintheunit, an upw ardfinin g of thec1astsisfollow edbythe gradua l developm ent of calcareousgreywackelayers which show both cross beddin g and channelling.Thedepositional mod el involves: (i) a locally developed, tectonicallyunstable carbo nateshelf-margin,(ii)atem porarylow ering ofsealevel,(iii)for matio n ofahig h-relief, shore-to-basin fault scarp followed by(iv) the developme nt of a channel,wit h (v) subsequent,long-distance transport of c1asts of pink carbonates fromthe conti nent-basin margin, whichwere (vi) redepos ited togeth erwit h a carbo nate debris (white dolomite and'blue' calcitemarbles)onthe tectoni cally fragme nting edge ofacarbonate shelf.Bot h matrix andpebblesshow a sim ilar rangeinisotopi c values:-1.9to+0.6%0(vs. PDB)forOl3Cearb and 0.70896to0.709 46for875r/ 865r.Theleastalte red875r/865r(0.70896)isotopicvalue plottedon the calibration curve is consistentwit ha seawatercom posit ioncorrespondi ng to agesof470-475,505-510and520 ,whereastheleast alte redOl3Cearb(-0 .6%0)valuematches only520Ma.

Vict orA.Melezhik,To mHeldal&DavidRob erts,GeologicalSurveyof Norway,N-7491 Trondheim,Norwa y;IgorM.

Gorokhov,Institu teofPrecamb rianGeologyandGeochro nology,nab.Makaro va2,199034 St. Pet ersburq ,Russia;Antho ny E. Fall ick,Scottish UniversitiesEnvir onmental ResearchCentre,G75 OQFEast Kilb ride,Glasgow,Scotland.

Introduction

Polymict carbonate-silicat e conglomerates are abundant rocks in the Late Neoproterozoic to Siluria n, lith ostrati- graphic successionsofthe Norwegi an Caledon id es,inclu d- ing thoseknowninthe Fauskearea(Fig.1).Theconglo mer- at es occureither as clast- ormatr ix-supp ort edvarieties(Fig.

2a,b).Many of them have clasts ofschist, quartzi te, vein quartz and white doloston e, and some mayconta in large cobb lesofvolcanites(Fig. 2c)orrarefragme nts of pink mar- bles (Fig. 2d).Monomictcarbo nate conglome rates,how ever, represent a rat herrarecase.Inone unit of carbonatecon- glo merateexposednearFauske,inNordland ,nort hernNor- way - theFauske cong lome ra te - predominant lycarbonate materialcomposesboththeclasts and thematrix.Thispart ic- ularcong lomeratehasbeenexpl oited asa dimensionalstone since 1870from theLovgavlenquarry,and each of the main lit hologicalvarieti esis wellknownundercomm ercialnam es

(Heldal 1996) such as'Norw egian Rose' (pink and white), 'Jaune Rose' (pale pinkandwhite),'Norw egianGreen'(white wit hgreenpatches),'Antique Fence' (greywithwhiteveins) and 'Hermelin' (white wit h grey veins).Asthese different typesof cong lomerate havean economicsignif icance,there is apracticalreasonforcarry ingoutresearchontheirdep osi- tional environme ntand age.Results ofsucha st udysho uld hel p to providebettertheore ticalgrounds for future explo ra- tionofthisand similardeposits.

Geological setting

The Fauske conglomerateconstitutes ac.60 m-thick lensoid unit (Fig.1)withi nafor mation known from earlier lit erat ure asthe Fauske limeston e (Vogt 1927, Strand 1972) or the Fauskemarbles(Rut land & Nicho lson 1965).Thesecarb on- ates, both banded calcite marbl es and dolomite marbles, wereconside redtoform part of themiddleunit(t heFau ske

NGU-BULL436,2 0 00 - PAG E148 VICTORA. MELEZHIK,TOM HELDAL,DAVID ROBERTS, IGORM.GOROKHOV& ANTHONYE.FALLlCK

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VICTORA.MELEZHIK,TOM HELDAL,DAVIDROBERTS, IGORM. GOROKHOV& ANTHONYE.FALLlCK

NGU-BULL436,2000- PAGE 149

Fig . 2.Phot og raphsof naturalexposuresshowing typicalpolymict conglomeratesoftheRog nan Group:(a)Matrix-supportedconglomerate interbed- ded withgrittyandsilty greywacke;unsortedandunevenlydistributedc1astsarerep resent ed by arkosicand quartziticsandstones(pale grey)and do- lostones(palebrown).Inthisand the next photo, the c1astsareflattenedandelongat edwit hina schistosityat alow angletothe beddi ng. (b) Clast- suppo rtedconglomerate;c1astsare quartziticsandsto nes(p ale grey)and dolostones (palebrown)in greywackematrix. (c)(last- support ed conglomer- ate;unsort edc1astsarequartziticsandston es(palegrey ),interm ed iate volcanites(darkgreylanddolostones(pale brown)ina greywa cke matr ix.(d)Clast- supp ortedconglome rate;c1ast s are quartzitic sandsto nes(palegrey),am phibo lites(black) andpinkcalcitemarblesinan arkosicsandsto ne mat rix.

The photog raphsweretaken along theshoreofSaltd alsfjorden,eastof0ynes(Fig.2).Scale bars=10cm.

MarbleGroup of Nichol son & Rutla nd (1969))ofthreemain st ruct uraleleme nts inthe met amorphic alloc ht ho n ofthe Nordl and Caledo nides.The twomain carbo nate format io ns were laterplacedtog eth erund erthenam e Rogna nGroup (Kollung&Gustavson1995).Nichol son (1974,p.184)int ro- duced thetermFauskeNappeforthe mediu m-g rade,marble- rich successions lying st ruct urally above the high-grade GasakNappe and below rocks ofthe Rodlnqsfja llet Nappe Complex (including the Beiarn Nappe). The designation FauskeNappe¹has beenretained inmostrecent map compi- lations (Gust avson et al. 1995, 1999, Kollung & Gustavson 1995,Gust avson 1996).

Inacompilationof tectonostratigraphicunits in theScan- dinavian Caledonides carriedout in the early1980s (Gee et al.

1985,Robert s &Gee 1985).the Fauske Nappe was incorpo-

1. Alt hough useof the same geographical name for differ entgeologi- cal unitsisgenerally not acceptable (Norw egian Commi ttee on St ratigraphy;Nystuen1989),weretainthenameFauskeherepend- ing a fut ure decision onrevisionofnomen clature.

rated in theUp perm ostAllochth on.Latermapp ing showed, how ever,thattheFauske carbo nateswere morelikely corre- latabl e wit h rocks ofsimi lar metam or phic gradein,e.g.,the Hatt fj elld al andJofja llet Napp esfart her south, l.e.,the high- est tectoni cunitsinthe Upp er Koli Napp es,part ofthe Upper Allocht ho n.Subsequent map compilatio ns havefavou red thisaff iliat io n(e.g.Gustavson1996,Robert s etal. 1998).

Asnofossilshave been found in the carbonate forma- tions of the Rognan Grou p,the actual ages of the units are unknown.Earlier workers, e.g.Vogt(1927).considered that the Fauske limestones could be followed sout hw ards and theneastwardsalong the margin of theNasafje llet tectonic window into thePieskelimestone ofSweden,which Kulling (1972, p.263) considered to be of Middle Ordovician age.

Nicholson&Rutland (1969) did notbelievein thiscorrel at ion, and it hasnot been verified by lat er mapping.In another, longer distance correlation,Strand(1972) suggestedthatthe Fauske carbonate and its structurallyoverlying 0ynescon- glomerate may be equivalent to the Eveneslimestone and Even skjee rcongl om erat e,respecti vely,of the Ofoten district

NGU-BUL L 436.2000-PAGE150 VICTORA. MELEZ HIK,TOM HELDAL.DAVIDROBERTS, IGORM.GO RO KHOV&ANTHONYE.FALLlCK

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VICTORA.MELEZHIK,TOM HELDAL,DAVIDROBERTS, IGORM.GOROKHOV&ANTHONYE.FALLlCK

ofsout hern Trams.Thepossibleequivalenceof the Fauske andEvenes carbo nateswas alsosuggest ed by Nicholson &

Rutland(1969).

In this paper, our use ofthe name Fauske cong lom erate (FC) or Fauske carbonate conglomerate is strictly informal.

The lithofacialand bed-to -bed variations are such that we will alsooccasionallyusethe pluralform, Fauske conglo mer- ates(FCs),whenreferringcollectiv ely tothisintraformation al diversit y.

Local geology and tectonic deformation

TheRognanGroup carbonaterocks arecomp arativ elypoorly exposedin the wide valleyimmediately north ofFauske.In the l.evqavlen quarry,only the lower contact of the Fauske conglomerate is exposed,against subjacentdolomite marble (Fig. 3).Judging from the quarry exposuresand nearbyout-

NGU-BULL 436,2000 -PAGE15 1

craps, thelateral extensionoft he FC lens isatleast500 m,but itstruedimensions areunknown.

In general,theFe dip s atlowto moderateangles tothe sout heast,which contrastswit h the steep to int ermediat e northwesterlydips of most rockswithintheFauske Nappein this particular district (Gustavson 1996).Inthe quarry,the lower partsoftheFCtend todip at 20-30⁰to the SSEwhereas the highestexposed bedsdip at35-45⁰ totheSE.The clasts in the cong lomeratesshowclearsigns of tectonicdefor ma- tion,yet thereare interesting differences dependingon the c1ast lithology. White dolomite c1asts appear to have been largely mechanically rotated intoa prominent, tightly spaced cleavagedipping at low anglestothe NW,whereaspink,cal- cite marblec1asts areinmany cases tightlyfolded (Fig.4a) wit h the spacedcleavagefunctioni ng asthe axial planeto thesemesoscopic folds.Pebbleelongation lineationsplunge at very low angles tothesout hw est.

In addition to thisquite penetrativespaced cleavage,it is clear that the more duct ilecalcit e marbleclastsshow the

Fig.4.Phot og raph s of sawnsurfacesin the Lovgavlen quarry (Section5,Fig.3.Plate5) show ingthe typicalsty le of tectonic defor - mation in the Fauske conglomerate.(a) Tightlyfolded c1asts of beige-to red-col- oured,calcitemarble.Widt hofthephoto- graphis0.5m.(b)An inner corneroftwo wallsof thequarrydemon strating X:Zra- tiosofca.10:1in calcite marble c1astscom- paredwit honlyca.6:1indolomite c1asts (leftwatt; In theright wall, normaltothe c1astelongation trend,manyof the white dolomi tec1astsappeartohavebeenlarge- ly mechanically rotated into the second phase cleavage (top right to bottom left) whereas c1astsofpink,calcitemarb learein manycasesfolded.Heightofwalls

=

NGU-BULL 436,2000 -PAGE 152

effect ofanearlierdefo rmation which hashad only amin i- mumeffect on the much more compete nt dolom it e clast material.Inonebed,X:Z ratios of13:1 in calcitemarbleclasts comparewith only 6.5:1 in dolo mite clasts (Fig.4b).More importantly,theflattened calcite marb lec1astsdip atjusta slight lygreater angleto thatof beddi ng; and theplane of flattening parallelstheprincipalmetamorphic fabric in the rock. Thissyn-metamorphicflatte ning deform ation isthus presumed torepresenttheearliestCaledoniandeformati on intheRognanGroup.Theage ofthis earlie rdeformati on is not known.Whileonemig htinferittobeScand ian,i.e.Late Silurian toEarlyDevon ian, apossibleOrdovicianage cannot bedismissed at thepresent time.No pre-pebb lemetamor- phicfabricscould bedetect edinthepebblesand cob bles.

Thepro minentspacedcleavagewit hfolded marb leclastsis considered to belong toa secondmain deformation phase.

Inaddit io n to thesest ructures,excellentexamplesof NW- direct ed,meso-scale,ramp -and-f latthrusting can be seen in theLovgavlenquarry; andthesethrusts and the earlie r fab- ricspre-datethe spacedcleavage.Thethrusts are alsocut by afew NW-dipp ing mafic dykesandsubparallel,thinquartz veins.The struct uraland dyke-intr usivehistory oftheFCs is thus afascinati ngtop ic initself,but will notbeconside red furtherin thiscont ribution.

The Levqavlen quarry

IntheLovgavlenquarry,25bedswith thick nesses of5cmto 3met reshavebeen recordedin theFauske carbo natecon- glomerate unit. The FC is character ised by rapid facies changes,bot hverti callyand laterally.Four man-made chan- nels wit h near-vertical smooth wallscut through the con- glomerates provide excellent sectio ns throug h the litho- st ratigraphyandIit hofacies.These areherenumbered from 1 to 4.lnadd itio n,there arelong,near-vert icalquarryfaces cut approximately atrigh t-angles tothese channels.

Verticallithofaciescha nge

The vert icalfacieschange describedbelow relatesto oneof the profiles stretc hi ng from Channel 1towardsChanne l 3 (Fig.3).Thesetwo channels(Plates1and 2¹*),and part ly Chann el 2 (Plate 3) have been used as the basisfor the description.

Local basement

The'basement'orlocal su bstra tetotheFC unitin Channel1 is com posed of white dolomit e marbles (Plate 1).These rather massive rocksbecom e jointed closeto the contact wit h theconglomerates(Fig.Sa). Inplaces,the dolomitemar- blehasbeenbrokeninto blocks.Som e oftheblocks(upto 6 x4 minsize) im mediately beneat h the carbon ate conglom- erate-brecciasequence havebeenprized apartor arecom- pletelydet ached as aresult of gravitationalinstability ona steep slope,and the open spaces between the blocksare

1. The following abbreviat io nsare used inPlates1-5:PCM-pink cal- cite marble,WDM- whitedol omite marble,GDM-greydolom ite marbl e, BCM-'blue'calcite marble.

V/GORA.MELEZHIK,TOM HELDA L,DAVID ROBERTS, IGORM. GO RO KH O V&ANTHONYE.FA LLl CK

Fig.5.Thesubst rate totheFauske conglomerate.(a)Banded,white to palegrey,dol omite marblewithan irregularupper surface overlain by pink conglom erate s. Note that the irregu larpalaeorelief beneath the conglomerateis strong lyaffected by thetect onic deformation,l.e.,fold- ingwit ha spacedcleavageform ingtheaxialplanesto mesoscopic folds. (b) An'open'spacebetween tw o large blocks of white dolomite marble filledwit h fragment s of the samedolomit emarble.The dolomi temarble form sthe subst rate totheFauske conglomerates. The photograph is taken 6m below thecontactwith the cong lomera tes.Width of photo- graphs = 2.5m.Photogr aph stakenfromChannel 1,east face.

filledwit hangular fragme nts ofthe same dolomite(Fig. Sb).

Foreig nclasts havenot been observed here. The detached blocks of thebasement dolostones may be assigned to a landsl id efacies.Frag ment ation ofthe substrate was appar- ently caused by insta bi lity alo ng the edge of a carbonate shelf, wit h the blocksmoving under the force of gravity.

Jointing,fragmentation,detachm ent and initial movements occurred when the dolostone s were lithified but still remain eduncoveredby ot hersediments/rocks as indicated by the lackof for eignc1astsamong fragments fillingjoi nts, cavities andope nspaces.

Carbo natedebris litho facies

The first input of carbo nate clasts overlying the landslide faciesappears in theform ofcarbo natedebris which consti- tutesBeds2to5(Plate1).Eachbed in the carbonate debris lithofacies is characterised byrath er sharp boundaries due to differences in the mat rixand in the sizes of clasts.The thick- nessesof allthesebeds arehigh ly variab le.Thecarbonate

VICTORA.MELEZHIK,TOM HELDAL,DAVID ROBER TS, IGORM.GOROKHOV&ANTHONYE.FALL/CK

Fig.6.Chaoticallydeposited,unsort edblocksandang ular fragm ent s of pinkand palepinkcalcite marblesandwhitedolomitemarblesinadark calcareou sschist mat rix.Bed5, carbo natedebris,mass-flowfacies.Widt h ofphoto graph

=

debris faciesat the base of the FCis only locallydevelop ed and it is rapidly replacedby carbonatebrecciasandcong lom- erates.

Thebedsof carbonate debri s are composed ofang ular, unsort edblocks andfragments ofcarbonaterocks.Thec1asts are represente dby whitedolostones,whiteand pink calcite marbl es andsing le blocks ofwhite -rim med,dark calcite mar- bles ('blue'marbl es).The clasts rangeinsize fromlessthan1 cm to 3m. Althou ghthe majorityofthe white dolo ston e and 'blue' calcit e marblesappearas ang ularfragme nts,someof the pink marbles are rounded. In general, the carbonate deb ris is composedof largechaoticallyorganisedfragm ent s (Fig.6).However, afew channels filled wit h medium-size, mod erately sorte dc1asts have alsobeenrecognisedinChan- nel 1(Plate l).The maj orit y ofthe'blue'marbl ec1ast s and blocksare bleached around theirmargin s and along joi nts (Fig.la).Thebleaching was ap parent lycaused byoxidat io n wit h subsequent removal of organic material.This might havehapp enedina subaeria lenviro nme nt when the'b lue' carbonates were exposed to atmospheric oxygen.Alterna- tively,theloss of organic material could haveoccurreddur- ing fresh-waterdiagenesisinaphreati c zonewhere therocks mighthavebeen subjecte d to alterat ion by oxygen-contain- ingfluid s.Adetailed isotopic study is required before we may choose between these alternatives.

Beds3,4 and5 com pose thebulk ofthe carbo natedeb ris lithof aciesin Channell.At thesame tim eBed 2, consist ing of large blocks of wh ite dol omi t e marbleand white- rim med 'blue' marble,occursinChanne ll in a very abbreviatedform.

Incontrast,the sameBed 2 appearsinChannel2(80 m east of Chann ell,Fig. 3)asthemaj orunit inthecarbon atedebr is lithof acies (Plate 3).There, it is composedof largeblocks (:::;5 x1m insize) of stronglyjointed,white- rim med,'blue' mar- bles(Fig. Zb)andwhit eand palegrey dolostonesina'b lue' calcite matrix.Beds 3 and 4 are not present in Channel 2 (Plate 3).Bed 5mechanically 'int ruded' int o Bed 2from its surface and deformed it . Based on this relatio nship, and giventhe condition that Beds 3-5 and 2 are almostmutually exclusive,it is suggested that the attenuation of Bed 2 in

NGU-BULL436,2000 -PAGE 153

Fig.7.Photograph s illustra ting different stylesof bleachin gof'blue'cal- cite marblein Bed2. (a)Large rounde d blocksof'blue' calcitemarble bleachedaround their margins.Widthof phot ogr aph = 2.5m. (b)Large angularblockof'blue'calcitemarblebleachedarounditsmarginsand along lami nati o n surfaces.Ham merhead= 15cm.Both photog raphs takenfrom Channel2,eastface.

Chann ell mightbedueto aneffectoferosion.Anexte nsive erosionof previou sly deposite d bed sby newl ytransport ed debris flowsmigh t have caused very irregularcontact sur- faces,as such feat ures are seeninthe carbona tedebris litho- faciesinChannels l and 2. Addition al effectsmightalso have beencausedby syn-dep ositi onal deformati on.

Theoverallsedimen to logical featu res ofthis rock assem- blageindicate transportin and depositionfrom a massflow, in which ill-sorted masses ofsedi me nt moved dow n-slope dueto aloss ofinte rnalstre ngt hof the sedime nt mass. At leasttwomaj orpulsesof massflowhavebeenrecogni sedin the carbo nate debr islithofacies.The first is represented by Bed 2. The second phaseresulte dinpartia lerosion of Bed 2 and depositi on of Beds 3-5.Oast material wastransport ed from different sources. White doloston e and 'blue' calcite marblesarederivedfromalocal sourcewhich hasbeen iden- tified im mediately beneaththe carbonatedebris.Clastsof pink marbles, on the other hand,are comparatively long

NGU-BU LL436,2000-PAGE 154 VICTO RA. MELEZ HIK,TOM HELDAL,DAVIDROBERTS, IGOR M. GORO KHO V

s

Fig.8.Upwardfiningofclamwithinindividualbeds. (a) Bed 14 exhib its fourdistinctive unitswhichcorrespondto the A,B,Cand D unitsof a typ- ical Bouma sequ ence.Thebedstartswitha thickunit of conglomero- brecciaoverlainprogr essivelyby a fine-pebble conglomeratewithparal- lellamination,athin unitofcurrent-bedded gritstones ,and at thetop by asiltygreywacke wit h plane-parallel lamination.Heightof photograph = 1.2m. (b) Lowerpartof Bed18(abovethedarkgrey greywackelayer) ex- hibit inggradedbedd ing accompaniedby the developmentof aninter- nalplanar lamination. Height ofphotograph=2.5m.Both photographs taken fromChannel3,east face.

Fig.9.Originally horizonta llybedd edcarbo nate breccia showinga grad- ualupward decreasein fragm ent sizeaccompanied bythe gradualde- velopment ofan int ernalplanarlamination; Beds 8-12.Note that Beds 9 and11are distinguished inthe conglomeratesequencebytheir paler colours caused bya dominance ofwhitedolostonefragments in a pale grey calcarenite matrix.The c1asts are here(re)orient at edwithinthe D2 (52) schistosity. Fault-related, proxim al, submarine channel facies.

Height of photograph

=

VICTORA.MELEZHIK,TOMHELDAL,DAVIDROBERTS, IGORM.GOROKHOV&ANTHONYE.FALLlCK

NGU-BULL436,2000-PAGE 155

Fig.10.Upwardfining ofthe c1astswithinBeds4- 12 accompaniedbythe gradual developmentof an internal planar lamination.Heightof photo- graph

=

transported,asindicated primar ily by their more rounded shapes and theabsence of any definite source rockin the vicinity of Fauske (see discussion of geochemical data).

C arbonate breccia-conglomero-breccia-greywacke lithofacies

The carbonate debris lit hofacies is overlain with a sharp, straigh t contact byfragment-support ed carbo natebreccias repr esent edby Bed 6.High-anglecross-bedd ing has been

Fig.11.Combi nati on ofplanar andcross-laminationinBed 17.(a)Cross- laminatio n inthe channelfilled withcoarser greywacke sandstone(pale brown )appearing intheupperm ost partof Bed17;notethatthe channel thicknessgradu allyincreases down dip,and the cross-lami nate dsand- sto neis then abru pt ly replacedby siltygreywacke(to the right)which ex- hibit snovisibl elam inat ion.Height of photograph= 0.6 m. (b)Cross- lami nate dsandsto nechannel developed inthe middle part of Bed 17.

Height of phot ogr aph = 0.75 m.(clErosional channelin laminated dark greygreywackeofBed17.The former is composed ofcurrent-bedded, pink,carbonate gritsto nesand fine-pebble conglomerate;note that the cross-beddin g isemp hasised by a rhythmic repetitionof cross-bedded calcaren it e-greywacke couplets. Fault-related,distal,submarine channel fades.Heig ht ofphotograph

=

Fig.12.The 0.5m-th ick Bed 7(m iddle partofphotograph)showi ng alat- eralBouma sequence;thebedbegins as a bedded,fine- pebble, carbo n- ateconglomeratewhich is gradually rep laced down-dip by carbonate gritstones,carbo nat egrit ston es interbeddedwit hlaminatedgreywacke, and thenbyplane-lam inatedgreywacke and siltstonewitha massiveap- pearance.Height of phot ogr ap h = 1.7m.Phot og raph taken from Chan- nel 2, east face.

observed in Bed 6 as indicated by theimbricated distribution of predominantly white dolostonefragments(Plate 1).In the upperpart of Channel 1,Bed 6 has a thicknessof 2 mwhich increasesto 4 m dow n-dipwit hina distanceof 12 metres.The brecciasarecomposed of fragments of the same rocks as described in thedebrislithofacies.Thefragments,how ever,

NGU-BULL436,2000-PAGE156 VICTORA.MELEZHIK,TOM HELDA L,DA VIDROBE.'nS, IGO RM.GOROKHO V&ANTHONYE.FA LLlCK

Fig.13.Photograph s illustrati ngdifferentscales of channelling.(a) White,pale grey and pink,small- peb bleconglomeratesinterbeddedwithdark grey greyw ackes,thelatterbecom ing anessent ialcompo nentof the upper partofthe Fauskeconglomerateunit;not ethat carbo nategrit stone s andgrey- wackesusuallyformcouplets,andthatchannelling andlow-am p litude,long-w avelength currentripplesare verycharacteri stic featuresof the conglo m- ero-b reccia-greyw ackeIithofacies.Bed 18,fault -related,distal,submarinechannelfacies.Width of photograph = 5m.Phot ograp htakenfro m Channel 3,eastface.(b) Channel(righ t ofmeasuringtape)developed in small-pebble congl omeratebed sand infilledwithcoarsermaterial. Widthof photograph

=2m.Phot ographtaken from Section7,Fig . 3,Plate5.(c)Large -pebblecong lomerate s of Bed2f erode d and channelled,witha subsequentinfill of the channel consistingoffinely dispersedmaterial(black and dark greysil ty grey wac ke)of Beds 8-1O. Heig ht ofphotograph=2.7m.Photograph taken from Section 2,Fig. 3,Plate4.

are generally much smaller and 'blue' marbleshave never been observed among the c1asts. Althoug h the c1asts are poorly sortedand angular,manyof the pinkmarbles arerep- resent ed bywell rounded pebbles.Clastsize rangesfrom 0.5- 12cmin the low erpartofBed6to 0.2-7cm in itsupperpart . Upward fining isevident from systematic measureme nt s.

Howeve r,thisis almostacrypt icgradation asitisdiffi cultto detectvisually.The breccias are capp ed bya1-20 cm-t hick Bed 7 consisting of laminated, siltygreywacke.Thisiscom- posed of muscov ite, biotlte. quartz,plagioclaseand calcite.

Thebreccia-grey wackecoupletis overlain byaseriesof conglomero-brecciabeds(8to12inChannel 1,Plat e 1; 12 to 15in Channel3,Plate2) contai ni ng med iu m- to small-size fragments.The conglomero-breccias are inte rbed ded with thinbeds and layers ofwhit e and pink calcarenit e.Thecon- glome ro-breccia beds(12, 14 and 15)arecappedby bedsof siltygreywac ke(Plate 2).Thethicknessesofindivid ual con- glomero-brecciabeds range from 0.3mto more than 2.5 m (e.g.,Bed12)whereas calcarenitelenses are usuallylessthan 0.2m in thickness.Thethickn essesof Bed s12, 14 and 15are

almostuniformdow n dip,from 1.5 to 2.5 m.In general,the bed thicknesses in the conglomero-breccia sequence become ratherconstantdown dip as comparedtothe lower debrislithofacies.However,thegreywacke beds stillexhibit highly variab le thicknesses.

Conglomero-breccias are both matrix- and clast-sup- port ed.Fragments,cobbles,pebbles and smaller c1astsare mainlyofwhite dolost one and pink,beigeand white calcite marbles.The majority of the clasts are angular or poorly rounded.However, clasts of pinkcalcite marble aswellas a few ofthewhite dolomite marbl e are represented by well- roundedpebb les.Alt hou gh c1astsare poorly sorted,graded bedding has been observedin severalbeds(Fig.8a,b).Two late rally continu ous beds(9 and 11)arereadilydistingu ished in the conglomer ate sequence bytheirpaler colours caused by a dominanceofwhitedol ostonefrag ment s inapalegrey calcarenitematr ix(Fig. 9).Inot hercases,the matrix is com- posedof calcareous schist.Although the matrixshowsa sim- ilar range in lit ho logy,fuchsit e,sericite, muscovite,quartz and chlorite maybepresentin variableproportionsin addi-

VICTO RA.MELEZHIK,TOMHELD A L,DA VID ROBERTS, IGORM.GORO KH OV&ANTHONYE.FALLlCK

tion to finecarbonate clasts, afeature which givesthe differ- ent bedstheir slight ly variabl ecoloration.

Aseries of changesin terms of rock str uctureand litho- logy canbe detected in movingupwar ds in the stratigrap hy wit hin thecong lom ero-breccia sequenceexposedinChan- nel1.An upw ardfining of thec1asts is clearlyvisible wit hin both a sequence of beds (Beds8-12, Fig.9,Fig.10) and indi- vidualbeds(e.g.,Bed14,Fig. 8a). This isaccompanied bythe gradual developmentofaninterna l planar laminat ion inthe conglomero-breccia.

The str ucture of the silty greywacke,whichoverlies the conglo mero-breccia beds,changesupw ardsin the st rat ig ra- phy.Thelowe rsiltygreywacke, Bed7,hasan indistinctplanar laminationwhereas the uppermostand thethickestBed 17is characterisedby a combination of planar and cross-lamina- tion (Fig.11 a).Cross-laminat ion appears in channels filled wit hcoarsergreywacke. These 1to 15 cm-thick channelsare lessthan 1.5 m in length and havelow-angle erosional con- tacts wit h the silty greywacke.In thecross-sect ion s,therear parts of thechannels are only 1-2cm in thickness and are composed of massive palegrey sandsto ne, but the channel thickness gradually increases down dip. The thickness increaseis follow edbythedevelopm entof visible cross-lam- ination due to aheterogeneityin lithology resulting from an alte rnati on of sand- andsilt- rich lamin ae (Fig. 11a).Further down dip,cross-laminated sandst one is abrupt ly,though confo rmabl y replaced by siltygreywackewhic hexhibitsno visible lami natio n.This channel-gr eywacke then becom es indistinguishablefrom the maingreyw ackebody ,both con- sisting of muscovite, biotite,quartz,plagiocl ase and calcite (Fig.11a).Cross-lami nated sandstone channelshave been observedmainlyin theuppermost parts ofsilty greywacke bedsthoug h in afew casestheyhave been det ected inthe lower and middleparts (Fig. 11 b).

The appearanceofcross-lami nated sandstonechannels in the silty greywacke of Bed17 is accompanied by the devel- opmen t of numerou s 0.5-10cm-t hick layers of white and pink, cross-bedded carbonate gritstones and fine-pebble conglomerate lenses.Theselayers and lensesare irregu larly spaced in the silty greywackes aswellas inthesubjacentcon- glomero-b reccias.lnplaces,the cross-bedding is emphasised by arhythmi crepetiti on ofcross-bedde dconglo merate-ca1- carenit e andcalcarenite-greywackecouplets(Fig.11 c).

The upper parts ofthe carbonatebreccia-conglom ero- breccia-greywacke lithofacies exhibit a sequenceof sedi- ment ary str uct ureswhicharetypic al ofthose observedin tur- bidity current depo sits.Bed14,for example,exhibits fourdis- tinctiv e unit s (Fig.8a). Thebed starts wit h athick unit of massive orgraded conglomero-brecciawhich is overlainpro- gressivelyby a fine-pebble conglomerate with parallellami- nat ion, a thin unit of current-bedded gritstones,and is cappedby a siltygreywacke wit h plane-parallellamination.

Thesefour units appear tocorrespond totheA,B,Cand D units of atyp ical Bouma sequence.While Bed 17demon- strates a vertical Bouma sequence, Bed 7 in Channel 2 appearsto show a lateralBouma sequence (Fig.12).The 0.5 m-thickBed 7begi ns as a bedded, fine-pebble,carbonate conglo merateand thisis graduallyreplaceddown-dip over a

NGU-BULL436,2000-PAGE 157

distance of8m by carbon ategritston es,carbonategritstones interb edd ed wit h lam inatedgreywacke, and thenby plane- lami nat ed greywacke and siltsto ne wit ha massive appear- ance(Fig. 12,Plate 3).

Overall,the sedimen tolo gical features of the breccia- conglomero-breccia-g reywac ke lithofacies are comparabl e tothosefound insequences depositedfromdebri sflowfol- low edbyturbidity currents. Availabledatademon strate that manyofthe conglomero-brecciabeds and allthe conglom- ero-breccia-si lty greywackecoupletswere deposited from a sing le debris flow-turbid ity current pulse. The general upward fining of thec1astsindi cateseitherthat the c1asts were transport edfrom agreaterdistance as comparedwit h theclast sfromthecarbonatedebr islith ofacies orthatthere was a rise in sealevel. We suggest thatthe first optionwasthe more likely as it isconsist ent with the observed increased degr eeofround nessof thetransport ed c1asts.

Conglomero-breccia-greywacke lithofacies

Thislith ofacieslies wit harather subdued erosionalcontact on top of the channelled and cross-laminatedgreywackesof Bed 17.The Iit hofaciesis composedof pale pink carbonate grit stonesirregul arlyinterb edd ed wit h dark greygreywackes and subordinat e white calcarenit es.Carbonate gritstones and greywackesusuallyform couplets(Fig. 13a), whichstart wit ha 0.2-1.5m-th ick gritsto ne layer andendwit ha 0.1-0.5 m-thick greywacke layer.The contact betw een these two litholog ies iscommonly gradati onalwit hin adistance of1-2 cm.Both grit stones and greyw ackes exhibit planarand low- angle cross-lamination. Planar and cross-lamin ation is expressed bythedevelop ment of lamin ae wit heit hercoarse or finer c1ast s as well as by the appearan ceof thin greywacke laminae inthe gritty framework.Each carbonate gritstone- greywacke couplet exposesan erosional relationship with the underlying one.Clastsof rounded pink calcite marble andsemi-ro undedwhite dolomite marbleare poorly sort ed.

They exhibi t no gradatio nin sizewit hin layers.Small-scale channelsand pockets of fine-pebbl e conglomerate in the gritty framewo rk arecom mon phenome naof thislithofacies.

Some beds at thebaseof thecon glom ero-br eccia- grey- wacke lithofacies exhibit gradedbeddingresemblin gthatin Boumasequences.

Sedimentolo gical featu res of the conglo mero -b reccia- greywacke sandstone lith ofacies indicatethat both the clas- ticmaterial and thefin er sedi mentsweretransport ed inand depo sited from low-energ y current s on a gent ly inclined slope.

Lateral thickness, c1ast size and litho logical variations

All the 25bedsrecorded in theLovgavlenquarry showa cer- tain degree of lateral variation in litholog y, clast size and thickness.Bed thicknesshasbeenaffectedby tectonic st rain producing a general thinnin g of the sequence. How ever, signsofdifferential tecton ic thinningof diff erent lithologies, such as pinch-and-sw ell and boudinage, have only been detectedinafew,thin (2to10 cm thick), silty greyw ackelay- ers.Mostotherbedsseemtohave beensimila rlyaffected by

NGU-BULL436,2000 -PAGE 158 VICTO RA.MELEZ HIK,TOM HELDAI.,DAVIDROBERTS, IGORM.GORO KHO V

s

Fig.14.Substantialchang es in bothlithology andclastsizedocu- mentedinthe carbonate conglomer ates.(a)Finingin clastsizeac- companiedby the developmentof numerouslayers of greywack e (black and dark grey)in Bed s 8,10,13 and18.(b) Lateralfiningin c1astsizeaccompaniedbythe development ofgraded bedding.

Blocks,ang ular and roundedfragment s of'blue'andwhitecalcite marbl es(Bed2e)followed bycobblesofwhiteandgrey calcite anddolomite marbles(Bed Zf),which are in turn overlain bythe conglomerates(Beds8-10)showi ngwell-developedgradedbed- ding.The graded-beddedconglomeratesweredeposite d froma sing le turb idity current.Heig ht ofphotograph(a)=4.5m,height of phot og raph(b)

=

VICTO RA.MELEZHIK, TOM HELDAL,DAVID RO BERTS, IGOR M.GOROKHOV& ANTHONYE.FALLlCK

anoveralltectonic thinning.Thisis also clearlyindicat edby very well preserved sedime ntary featu res suchas sedime n- tary layering, graded bedd ing, cross-lami nation,erosional channels, etc. The measured thickness variations should therefore largely remai n comparable wit htheorigi nalvalues.

Pronoun ced thickness variat io nsof prim ary orig in may be observed inanyo ne bed over distancesof 10to 100m.

Themostremarkable change in thickness,wit h the com plete disappearanceofbedsinth ree directionswithina distanceof lessthan 100 m,is characteristicof Beds 3-6.This canbe dem- onstrated by comparing the cross-sectionsrecorded inChan- nels1and2 (Plates 1and 3).Beds3and 4 areobserved in Chann el1tbut theydonotreappearinChannel2, overadis- tance of only90 m.Onthecont rary, Bed 2 is aprom inent unit in Channel 2 but reappears in Channel 1 in a considerably attenuatedform.

Lessdramaticthou gh substan t ial thickness changeswit h associate d wedging -out eit her in two or three direct ions havebeendocum ent edinBeds 5-7,9,11-13,16 and25.This is demonstratedin thelong it ud inallith ologi cal secti ons(e.g., Plates4 and5).Fine-c1ast conglomerateof Bed16 andlarge- c1ast cong lo merate of Bed 25formmedium-scaleerosional chann els.Bed 25 has athicknessof 7 mwhereasthe lateral exte nsion of the channelislessthan50 m.Channellingon dif- ferent scalesis acommonfeatur e of manybeds and layers.In themost commoncases,chann els which develop edinsmall - pebb leconglo merate beds wereinfi lledwit hcoarser mate- rial(Fig.13b).Large-p ebbl econgl om erat eshave also been observed to be erodedand chann elled,witha subseq uent infillof the channel consist ing of finely dispersed material (silty greywacke) (Fig. 13c).Thisimpliesthe exist ence of high- energ y wate r current s developed on a st eep submar ine slop e.Gradually progressing down -slope erosion of grey- wackeand fine-pebbl e cong lomera te bedsmarkedbychan- nelling and low-amplitude, long-w ave current rippl es are very charact erist ic featur es of the conglomero-brecc ia- greyw ackelithofacies (Fig.13a).

Aconsidera b le lateralvariati oninc1astsize is com mo n ly observed in thosebeds which demonstrat ewell-pronou nced thickness variation s. A positive correlat ion bet ween bed thickn ess and clast size is a com monrulefor Beds 6, 12 and 14.Thesethreebeds exhi bit great lateralvariation in c1ast sizeand thicknesses whereas their lit ho logi cal composition s remainunchange d.In Bed 6, c1ast sizerangesfrom 10x30 cm (Secti on10,Plat e 4)to2x5 cm (Channel2, Plate 3) wit hina distance of 100m.

Substant ialchanges in both lit hol ogyand clast sizehave beendocum ent edinthecarbon atecon gl om erat es of Beds 8, 10,13 and18.In these cases the fining inc1astsize is acco m- paniedby thedevelo pmentofnumerous layers ofgreywacke (Fig 14a).As aresult , insomecasescarbon atecongl om erates are com plete ly rep laced by greyw acke (Bed 13, Sect ion 2, Plate 3;Bed18,Channel3,Plate 2).Lat eral fining in clastsize has also been observed tobe accompanied bythedevelop - mentof graded bedd ing(Fig.14b).

Variation s in lithology and c1astsize hamper correlatio n betw een sect io ns separate d by unexposed ground . Some beds, however,may serve as amarker.Two white-pebb le

NGU-BULL436,200 0 -PAGE 159

conglomeratebeds (9 and 11). whichare only0.1-0.5m thick, aredistingui shable in the cong lo merate sequence by their comparativelypalecolourpattern. Alt hough these beds are thin they are easy to detect and can be traced bothalong strike and down dip (e.g.,Plate 4).The pale coloration is exp ressedby adomin ance of whitedolosto nefragmen tsina palegreycalcarenite matr ix.

Theexamplesdescribed aboveserveto demonstratethat the high degree of variability in lithology,c1astsize and thick- nessisageneralcharacteristicof theFCs.This impliesunsta- bledepositio nalenvironments. The thicknessvariationshave apparent ly been caused by a num ber of fact ors, includ ing erosionaleffectsand chann ellin g,an irregularpalaeore liefof the deposit ional surfaceand a lateralrestriction ofturbidity currents.Tectonicfact ors have also played theirpartin mod- ifying bed thicknessand, as noted earlier,in causingflatten- ing ofthe calcitemarbleclastsin particular.

Clastcomposit ion

Lit ho logically, theFCsconsist ofblocks,fragments,cobbles, pebbles and smaller clasts mainly of white dolostone and pink,beige, whiteand dark grey('b lue') calcitemarbles (Fig.

16a).Clasts of quartzit es andveinquartzaresubordinate. A quantitative est imate of c1ast com posit io n shows that the clastsof'blue' calcit emarbles areexclusivelyassig ned to Bed 2 (Figs.15,16b)andthey have never been observed inany ot her bed.Clastsof quartzitesandvein quartzare also prefer- entia llyconcentra te dinBed 2.Onthe ot her hand,clastsof pinkcalcit emarblehaveneverbeenrecorded inBed 2. The fragm ent s of white and grey doloston e,and white calcite marble s are distributedthrough out theentiresequenceand neithe r thevertical northe lateral distributionshowsany vis- ibl eregulari ty(Fig.15).The mainmineral in the matrixis cal- cite, with minorquartz and muscov it e. Thematrixischarac- terised by a granoblastic texture and retains no primary sedime nta ry featur es. Measured clast-m atrix ratios range between 0.3 and4.6withanaveragevalueat1.5(n= 30).This ind icat es the presence of both c1ast-supported and matrix- supported conglo merates where the former are predomi- nant.However,thedata obtained mustbetreated with care as some clast-mat rix boundaries exhibit adiffuse,unclear appea rance dueto recrystallisati on.Althou gh the matrixhas asimilarrangein litholo gy,fuchsit e,sericite,muscoviteand chlorite may be present in variable proport ions as minor com ponentsinadditi on to fine carbo natec1asts.

Chemic ally, all thecarbon ate c1asts canbedivid ed into twogroups,namelydolomite andcalcite marbles (Table 1).

Dol omitemarbl esfromthelocal'basement' andin the c1asts are ide nt ical in terms of major and trace element abun- dances.Onvariousdiagrams theyare clusteredtogether (Fig.

17).clearly ind icatingthatthec1asts derived fro mthe under- lying dolomitemarbleunit. The Mg/Carati ofor theund er- lying doloston esrang esfrom0.58to 0.64 whichis closeto stoichiometric dolomit e (0.62)whereas the averageMg/Ca ratio for all the c1astsis 0.53.This apparent lypointsto a proc- ess ofdedolomitisatio n duringthe courseoftransportation andrede posit ion.

The overall bulk chem icalcomposit io nofot hercarbo n-

NGU- BULL436,2000-PAGE160 VICTORA.MELEZHIK,TOMHELDAL, DAVI DR0 8ERTS, IGORM.GOROKHOV&ANTHONYE.FALLlCK

Bed 12

Bed11

Bed 10

Beds 8+9+10

Bed8

Bed6

Cnl,Xl

Cn l,VI

Cnl,III Bed5

Cnl,VII

~ .J

CLAST·MATRIXDISTRIBUTION

I

LS2,X Bed2f

Bed2e

Bed2d

Bed2c

Bed2b

Bed 2a

Bed 1

I I i I I I I I

White dolomite marble Grey dolomitemarble Whitecalcitemarble Pinkcalcite marble 'Blue' calcite marble Mica-rich calcite marble Amphibole-rich calcite marble Quartzite

Veinquartz Matrix

Fig.15.Compositionof c1astsand matricesmeasuredfrom diff erent bed s.

The followingabbreviation sare used inthe figure :Ch1-Channe l1,Ch2-Channel2,LS1 - Longitudina lSection1,LS2 - Longitudi nalSectio n2.Roman numeralsindicatethe section numberwhichwasusedto count pebblecomposit io n;thesesections aremarkedon Plates1and2.Deta iled logsofLS1 andLS2arenot presentedin the article buttheymay be obtainedfrom thefirstaut ho ron requ est.