NGU-BULL 436, 2000 - PAGE 14 7. Depositional environment and apparent age
of the. Fauske carbonate conglomerate, North Norwegian. Caledonides.
NGU-BULL 436, 2000 - PAGE 14 7
Depositional environment and apparent age of the Fauske carbonate conglomerate, North Norwegian Caledonides VICTOR A. MELEZHIK, TOM HELDAL, DAVID ROBERTS, IGOR M. GOROKHOV& ANTHONY E. FALLlCK
Melezhik, V.A., Heldal, T., Roberts, D., Gorokhov, I.M. & Fallick, A.E. 2000: Depositio nal enviro nment and ap parent age of th e Fauske carbo nate cong lomerate, North Norw eg ian Caledo nides. Norges geo logiske uridersekelse Bulletin 436, 147-168. The Fauske co nglomerate represents a rath er rare case of a mon omi ct carbo nate conglo merate in t he Late Neo prot erozoic to 5i1 urian, Iith ostratigraph ic successions of t he Norwegian Caledo nides.Lith o logical variet ies of thi s cong lomera te unit fro m th e Lovgavlen qu arry have a highly deco rative q uality and are w ell known in bot h dom estic and interna t ional market s under t radin g names such as 'Norweg ian Rose', 'Jaune Rose', 'No rweg ian Green', 'Anti que Fence' and 'Hermelin'. The Fauske cong lomerate is a 60 m-t hick unit w hich rests o n eit her dark g rey (' blue') calcite marb les o r w hite do lomite marb les. The latt er are joi nted and fragm ent ed, and also appea r as sedime ntary collapsebreccia and de bris where th ey are in di rect contact wit h th e cong lom erate . Alt houg h t he Fauske cong lomerate has been invo lved in two main pulses of Caledonian tecto nic deform at ion, w hich prod uced an early, syn-metamorp hic flatt ening of th e c1 asts and a later folding or rot ation of c1 asts int o a spaced cleavage, the overall sed imentary featu res are st ill remarkab ly we ll preserved. The Fauske cong lomerate unit co nsists of 25 beds (5 cm to 3 met res t hick) comprising landslide, carbonat e debris and carbo nate breccia- con glom ero-breccias- g reywacke lit hofacies. Blocks,fragm ent s, cob b les, pebb lesand smaller c1asts are mainly of w hite dolostone and pink, beige, w hite and 'blue' calcite marbles. The mat rix has a granob last ic t exture and similar range in lit hology wit h variable amo unts of qu artz, fuchsite, sericite, muscovite and chlorit e. With in t he unit, an up w ard finin g of th e c1astsis follow ed by th e g radua l developm ent of calcareous g reywacke layers w hich show both cross beddin g and channelling. The depositional mod el invo lves: (i) a locally develop ed, t ecton ically unstable carbo nate shelf-margi n , (ii) a tem porary low ering of sea level, (iii) for matio n of a hig h-relief, shore-to -basin fault scarp fo llowed by (iv) th e deve lopme nt of a channel, wi t h (v) subsequent, long -di stance tr ansport of c1 asts of pink carbonates from th e conti nent-basin margin, w hich were (vi) redepos ited t ogeth er w it h a carbo nate deb ris (w hite dolom it e and 'blue' calcite ma rbles) on t he t ectoni cally fragme nt ing edge of a carbon ate shelf. Bot h matrix and peb bles show a sim ilar range in isotopi c values: -1.9 to +0.6%0 (vs. PDB) for Ol3Cearb and 0.70896 t o 0.7 09 46 for 875r/ 865r. The least alte red 875r/865r (0.70896) isotopic value plotted o n th e calibration curve is consistent wit h a seawater com posit ion correspondi ng to ages of 470 -475 , 505-510 and 520, wh ereas th e least alte red Ol3Cearb (-0.6%0) value matches only 520 Ma. Vict or A. Melezhik, Tom Heldal & David Rob erts, Geolog ica l Survey of Norway, N-7491 Trondheim, Nor wa y; Igor M. Goro khov, Institu te of Precamb rian Geology a nd Geochro no logy, nab . Ma karo va 2, 199034 St. Petersburq , Russia; Anthony E. Fall ick, Scottish Univ ersities Envir onmental Research Centre, G75 OQF East Kilb ride, Glasgow, Scotland.
Introduction Polymi ct carbo nat e-silicat e cong lomerates are ab und ant rock s in th e Late Neoprot erozo ic t o Siluria n, lith ostrat igrap hic successio ns of t he Norw egi an Caled on id es, in cluding th ose know n in t he Fauske area (Fig. 1). The conglo mer at es occur either as clast- or matr ix-supp ort ed varieties (Fig. 2a, b). Many of t hem have clasts of schist, qu artzi te, vein quartz and w hite do loston e, and some may contain large cobb les of vo lcanites (Fig. 2c) or rare fragme nt s of pink marbles (Fig. 2d). Mon omict carbo nate co nglome rates, how ever, rep resent a rat her rare case. In one unit of carbonate conglo merate exposed near Fauske, in Nordl and , nor t hern Norway - th e Fauske cong lomera te - predomi nant ly carbonate mat erial composes both t he clast s and t he matrix. This part icular cong lomerate has been expl oited asa dimensional stone since 1870 from t he Lovgavlen qu arry, and each of t he main lit hol ogical varieti es is we ll known und er comm ercial nam es
(Held al 1996) such as 'Norw egian Rose' (pin k and w hite), 'Jaune Rose' (pale pink and w hite), 'Norw egian Green' (w hite wit h green patches ), 'An tique Fence' (grey w it h w hite veins) and 'Hermelin ' (whi t e w it h grey vei ns). As the se different t ypes of cong lomerate have an economic signif icance, th ere is a practical reason for carrying ou t research on t heir dep ositi on al enviro nme nt and age. Result s of such a st udy sho uld help to provide better t heore tic al gr ound s fo r fut ure explo ratio n of th is and similar d eposits.
Geological setting The Fauske cong lo merate co nstitu tes a c. 60 m-thick lensoid unit (Fig . 1) withi n a for mation kno wn fr om earlier lit erat ure as t he Fau ske lim eston e (Vogt 1927, Strand 1972) or th e Fauske m arbl es (Rut land & Nicho lson 1965). These carb onates, both banded calcit e marbl es and do lomite marb les, we re co nside red to form part of t he middle unit (t he Fau ske
NGU- BULL 4 36,2 000 - PAG E 148
VICTOR A. M ELEZHIK, TOM HELDAL , DAVID ROBERTS, IGOR M. GOROKHOV & ANTHONY E. FALLlCK
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VICTOR A. MELEZHIK, TOM HELDAL, DAVID ROBERTS, IGORM. GOROKHOV & ANTHONY E. FALLlCK
NGU-BULL 436,2000 - PAGE 149
Fig. 2. Phot og raphs of natura l exposures showi ng typical polymict cong lomerates of t he Rog nan Group : (a) Matr ix-suppo rted conglomerate interbedded wi th gr itty and silty greywacke; unso rted and uneven ly distribu ted c1asts are rep resent ed by arkosic and q uartzitic sandstones (pale grey) and dolostones (pale bro wn ). In t his and the next photo, the c1asts are flattened and elongat ed wit hin a schistosity at a low angle to t he beddi ng. (b) Clastsuppo rted cong lomerate; c1a st s are qua rtzitic sandsto nes (pale grey ) and dolo stone s (pale brow n) in g reywacke matr ix. (c) (last- support ed conglomerate; unsort ed c1 astsare quartzitic sandston es (pale grey ), int erm ed iate volca nites (darkgreyl and do lostones (pale brown ) in a greywa cke matr ix. (d) Clastsupp orted cong lome rate; c1 ast s are quartzitic sand sto nes (pale grey), am phibo lites (black) and pink calcite marbles in an arkosic sandsto ne mat rix. The photog raphs were taken along th e sho re of Saltd alsfjord en, east of 0ynes (Fig. 2). Scale bars = 10 cm.
Marble Group of Nichol son & Rutla nd (1969)) of t hree main st ruct ural eleme nts in t he met amorphic alloc ht ho n of th e Nordl and Caledo nides. The two main carbo nate fo rmat io ns we re later placed t og eth er und er th e nam e Rogna n Group (Kollung & Gustavson 1995). Nichol son (1974, p. 184) int rod uced th e term Fauske Nappefor the mediu m-g rade, marble-
rich successions lyi ng st ruct urally above th e high-grade Gasak Nappe and below rocks of th e Rodlnqsfja llet Nappe Complex (including th e Beiarn Nappe). The designation Fauske Nappe 1 has been retained in most recent map compilation s (Gust avson et al. 1995, 1999, Kollung & Gustavson 1995, Gust avson 1996). In a comp ilation of tectonostratigraphic units in th e Scandinavian Caledonides carried out in the early 1980s (Gee et al. 1985, Robert s & Gee 1985). the Fauske Napp e was incorpo-
1.
Alt hough use of th e same geographical name for differ ent geolog ical unit s is gen erally not acceptable (Norw eg ian Commi ttee on St ratigr aphy; Nystuen 1989), w e retain th e name Fauske here pending a fut ure decision o n revision of nomen clatur e.
rated in th e Up perm ost All ochth on. Later mapp ing showed, however, th at th e Fauske carbo nates we re more likely corre latabl e w it h rocks of simi lar metamor phic grade in, e.g., t he Hatt fj elld al and Jofja llet Napp es fart her south, l.e., t he high est tectoni c units in t he Upp er Koli Napp es, part of t he Upper Allocht ho n. Subsequent map compilatio ns have favou red t his aff iliat io n (e.g. Gustavson 1996, Robert s et al. 1998). As no fossils have been found in t he carbonate forma tions of the Rognan Grou p, t he actual ages of the un its are unknown. Earlier workers, e.g. Vog t (1927). considered that th e Fauske limestones cou ld be fo llo wed sout hw ards and t hen eastwards along the margin of t he Nasafje llet tecton ic w indow into th e Pieske limestone of Swede n, which Kulling (1972, p. 263) con sidered to be of Middle Ordovician age. Nicho lson & Rutland (1969) did not believe in thi s correl at ion, and it has not been verified by lat er mapping. In another, longer distance corr elation , Strand (1972) suggested t hat the Fauske carbonate and its structura lly overlyi ng 0ynes con glomerate may be equiva lent to t he Evenes limestone and Even skjeer conglom erat e, respecti vely, of the Ofoten district
NG U-BUL L 436.2000 - PAGE 150
VICTOR A. M ELEZ HIK, TOM H ELDAL. DAVID ROBERTS, IGOR M. GOROKHO V & ANTHONY E. FALLlC K
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VICTORA. MELEZHIK, TOM HELDAL, DAVID ROBERTS, IGOR M. GOROKHOV & ANTHONY E. FALLlCK
of sout hern Trams. The possible equiva lence of the Fauske and Evenes carbo nates was also suggest ed by Nicho lson & Rutland (1969). In this paper, our use of th e name Fauske cong lom erate (FC) or Fauske carbonate conglomerate is strictly informal. The lithofacial and bed-to -bed variations are such t hat we will also occasionally use th e plura l form, Fauske conglo merates (FCs), w hen referring collectiv ely to th is intr afor mation al diversit y.
Local geology and tectonic deformation The Rog nan Group carbonate rocks are comp arativ ely poor ly expo sed in th e wide valley imme diately north of Fauske. In the l.evqavlen quarr y, only the lower contact of the Fauske conglomerate is exposed, against subjacen t dolomite marble (Fig. 3). Judging from the quarry exposures and nearby out-
NGU-BULL 436 ,2000 - PAGE 15 1
craps, t he lat eral extension oft he FC lens is at least 500 m, but it s tru e dim ensions are unknown. In general, t he Fe dip s at low to mo derate angles t o th e sout heast, which contrasts wi th th e steep to int ermediat e nor thwesterly dips of most rocks within the Fauske Nappe in this particular district (Gustavson 1996). In the quarry , th e lower parts of the FCtend to dip at 20-300 to the SSEwhereas t he highest exposed beds dip at 35-450 t o the SE. The clasts in th e cong lomerates show clear sig ns of t ectonic defor mation , yet there are interesting differences depe nding on the c1ast lithology. White dolom ite c1asts appear to have been largely mechanically rotated into a prominent, tightly spaced cleavage dipping at low ang les to th e NW, whereas pi nk, calcite marble c1asts are in many cases tightly folded (Fig. 4a) wi t h th e spaced cleavage functioni ng as t he axial plane to the se mesoscopic folds . Pebble elongation lineat ions plung e at very low angles to the southw est . In addition to th is quite penetrative spaced cleavage, it is clear th at th e more du ct ile calcit e marb le clasts show th e
Fig. 4. Phot og raph s of saw n surfaces in th e Lovgavlen quarry (Section 5, Fig. 3. Plate 5) showing th e typical style of t ectonic deformat ion in th e Fauske conglomerate. (a) Tightly folded c1a sts of beige- to red-coloured, calcit e marble. Widt h of t he photo grap h is 0.5 m. (b) An inn er corner of two walls of th e qu arry demon stratin g X:Z rati os of ca.10:1 in calcite marble c1 asts compared wi t h only ca. 6:1 in dolomite c1 asts (left watt; In th e right wall, norm al to th e c1 ast elongation trend , many of th e wh ite dolomi te c1 asts app ear to have been largely mechanically rot ated into th e second phase cleavage (top right to bottom left) whereas c1a sts of pin k, calcite marble are in many casesfo lded . Height of walls =2.5 m.
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effect of an earlier defo rmat ion w hich has had only a minimu m effect on t he mu ch more com pete nt dolom it e clast material. In one bed, X:Z rat ios of 13:1 in calcite marb le clasts comp are w it h only 6.5:1 in do lo mite clasts (Fig. 4b). More im port ant ly, t he flatt ened calcite marble c1 ast s di p at j ust a slight ly g reater angle to t hat of beddi ng; and th e plane of flatt ening parallels t he prin cipal met amorph ic fabric in th e rock. This syn-metamorph ic f latte ning def orm ation is t hus presumed to represent t he earliest Caledo nian defo rmati on in the Rog nan Group. The age of t his earlie r deformati on is not known . While one mig ht infer it to be Scand ian, i.e. Late Silurian t o Early Devon ian, a possibl e Ordo vician age cannot be dismi ssed at th e pr esent t ime. No pre-pebb le met amorphic fabrics could be detect ed in t he pebb les and cobbles. The prominent spaced cleavage wi t h fo lded marble clasts is consid ered to belong to a second main deformation phase. In addit ion t o t hese st ruct ures, excellent examples of NWdirected, meso-scale, ramp -and-f lat th rusting can be seen in t he Lovgavlen quarry; and t hese th rusts and th e earlie r fabrics pre-date t he spaced cleavage. The th rust s are also cut by a few NW-d ipp ing maf ic dykes and subparallel, t hin quartz veins. The st ruct ural and dyke-intr usive history of t he FCs is t hus a fascinati ng top ic in it self, but wi ll not be considered furth er in t his cont ribu ti on.
The Levqavlen quarry In t he Lovgavlen qu arry, 25 beds w ith t hick nesses of 5 cm t o 3 met res have been recorded in th e Fauske carbo nate conglomerate unit. The FC is character ised by rapid facies changes, bot h verti cally and laterally. Four man-m ade channels w it h near-vert ical smooth walls cut t hrough t he conglom erates provide excellent sectio ns t hroug h t he lit host ratig raphy and Iit hofacies. These are here numbered from 1 to 4.ln add itio n, th ere are long, near-vert ical quarry faces cut approximately at righ t-angles to th ese channels.
Verticallithofacies cha nge The vert ical facies change described below relates to one of t he profiles st retc hing from Chann el 1 towa rds Channe l 3 (Fig. 3). These two channels (Plat es 1 and 2 1 * ), and part ly Chann el 2 (Plat e 3) have been used as t he basis for th e descript ion.
Local basement The 'basement' or local substra te t o th e FC unit in Channe l 1 is composed of w hite dolomit e marbles (Plat e 1). These rath er massive rocks becom e jo inte d clo se to t he contac t w it h t he cong lomerates (Fig. Sa). In places, th e dolo mite marble has been broken into blocks. Som e of th e blocks (up to 6 x 4 m in size) immed iatel y beneat h the carbon ate cong lom erate-breccia sequence have been prized apart or are com pletely detached as a result of gravitat io nal inst ability on a st eep slope, and t he open spaces bet ween t he blocks are 1.
The follo w ing abbreviat io ns are used in Plates 1-5: PCM - pin k calcite marble, WDM - w hit e dol om ite mar ble, GDM - grey dolom ite marbl e, BCM - 'b lue' calcit e marb le.
Fig. 5. The subst rate t o t he Fauske conglomerate. (a) Banded, whi te to pale grey, dolomite marble wi th an irregular upper surface overlain by pink congl om erate s. Note th at t he irr egu lar palaeorelief beneath the cong lome rate is stro ng ly affected by the tect onic deformation, l.e., fold ing w it h a spaced cleavage form ing t he axial planes to mesoscopic folds . (b) An 'o pen' space between tw o large blocks of white dolomite marb le filled w it h frag ment s of t he same dolomit e marble . The do lomi te marble form s the subst rate to th e Fauske conglomerates. The photograph is taken 6 m below t he co ntact w ith t he cong lomera tes. Width of photograph s = 2.5 m. Phot ogr aph s taken from Channel 1, east face.
filled w it h angular fragme nts of t he same dolomite (Fig. Sb). Foreig n clasts have not been observed here. The detach ed blocks of th e basement dolostones may be assigned to a landsl id e facies. Fragment ation of th e substrate was apparent ly caused by insta bility along th e edge of a carbonate shelf, w it h t he blocks movi ng under t he force of gravity. Jointi ng, fragmentation, det achm ent and initial mov emen ts occur red w hen th e dolostone s were lithified but sti ll remain ed un covered by ot her sediments/rocks as indicated by th e lack of foreig n c1 asts amo ng fragments filling joi nt s, cavit ies and ope n spaces.
Carbo nate debris litho facies The fi rst input of carbo nate clasts overlying t he landslide facies appe ars in th e form of carbo nate debris which constit ute s Beds 2 to 5 (Plate 1). Each bed in the carbonate debris lithofacies is characterised by rath er sharp boundaries due to difference s in th e mat rix and in th e sizes of clasts. The thicknesses of all the se beds are high ly variab le. The carbona te
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Fig. 6. Chaot ically deposited , unsort ed block s and ang ular fragm ent s of pi nk and pale pink calcite marble s and w hite do lomi t e marbles in a dark calcareou sschist mat rix. Bed 5, carbo nate debris, mass-flow facies.Widt h of photo graph 2.5 m. Photograph t aken f rom Channel 1, w est face.
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debris facies at t he base of the FC is only locally develop ed and it is rapidly replaced by carbo nate breccia sand cong lomerates. The beds of carbonate debri s are composed of ang ular, unsort ed blocks and fragme nts of carbonate rocks. The c1a sts are represente d by whi te dolostones, whi te and pink calcite marbl es and sing le blocks of w hite-rim med , dark calcite marbles ('blue' marbl es). The clasts range in size from less th an 1 cm t o 3 m. Alth ou gh th e majority of th e w hite dolo ston e and 'blue' calcit e marb les appear as ang ular fragme nts, some of t he pink mar bles are rounded. In general, t he carbonate debris is composed of large chaotically organised fragm ent s (Fig. 6). However, a few channels filled wi t h medium-size, mod erately sorted c1asts have also been recognised in Channel 1 (Plate l ). The majorit y of t he 'blue' marbl e c1 ast s and blocks are bleached around th eir margin s and along j oi nts (Fig. l a). The bl eaching was apparent ly caused by oxi dat io n wit h subsequent removal of orga nic material. This might have happ ened in a subaeria l enviro nme nt w hen th e 'blue' carbonates were exposed to atmospheric oxygen . Alterna t ively, th e loss of organic material could have occurred during fresh-water diagenesis in a phr eati c zone w here th e rocks mi ght have been subjecte d t o alterat ion by oxygen-containing fl uids. A detailed isotopic study is required before we may choose bet ween these alternatives. Beds 3,4 and 5 compose th e bul k of th e carbo nate debris lith ofacies in Channell . At the same t im e Bed 2, consist ing of large blocks of w hite dolomi t e mar ble and w hite- rimmed 'blue' marble , occurs in Channe ll in a very abbr eviate d fo rm. In contra st, th e same Bed 2 appears in Channel 2 (80 m east of Chann ell , Fig. 3) as th e major unit in th e carbon ate debr is lith ofacies (Plate 3). There, it is compose d of large blocks (:::;5 x 1 m in size) of strong ly joint ed, w hite- rimmed, 'blue' marbles (Fig. Zb) and w hit e and pale grey dolos tone s in a 'blue' calcite matrix. Beds 3 and 4 are not pre sent in Channel 2 (Plate 3). Bed 5 mechanically 'int ruded' int o Bed 2 from it s surface and deformed it. Based on thi s relatio nship, and giv en the condition that Beds 3-5 and 2 are almo st mutua lly exclusive, it is sugge sted th at th e attenuation of Bed 2 in
Fig. 7. Photograph s illustra ting different style s of bleachin g of 'blue' calcite ma rble in Bed 2. (a) Large rounded blocks of 'blue' calcit e marble bleached around th eir margins. Width of ph ot ogr aph = 2.5 m. (b) Large angu lar block of 'blue' calcite marble bleached around it s margi ns and along lami nati o n surfaces. Ham mer head = 15 cm . Both ph otog raph s t aken from Channel 2, east face.
Chann ell might be du e to an effect of erosion. An exte nsive erosio n of previou sly deposited beds by newl y t ransport ed deb ris flows migh t have caused very irreg ular contac t surfaces, as such feat ures are seen in t he carbona te debris lithofacies in Channels l and 2. Additi on al effects mig ht also have been caused by syn-dep ositi onal deformati on. The overall sedimen to logical features of th is rock assemblage indicate trans port in and depos ition from a mass flow, in which ill -sorted masses of sedi me nt moved dow n-slope du e t o a loss of inte rnal stre ngt h of th e sedime nt mass. At least two major pul ses of mass flow have been recogni sed in t he carbo nate debr is lithofacies. The first is represen ted by Bed 2. The second phase resulte d in partia l erosion of Bed 2 and depositi on of Beds 3-5. Oast material was tr ansport ed from different sources. White doloston e and 'blue' calcite marbles are derived from a local source w hich has been identi fied immediately beneath t he carbona te debris . Clasts of pink marble s, on the other hand , are comparatively long
NGU-BU LL 436, 2000 - PAGE 154
VICTOR A. M ELEZ HIK, TOM H ELDAL, DAVID ROBERTS, IGOR M . GO RO KHO V ANTHONY E. FALLlC K
s
Fig. 8. Upward fin ing of clam wi thin individual beds. (a) Bed 14 exhib its four dist inctive uni ts whi ch correspon d to the A, B, Cand D uni ts of a typ ical Bouma sequ ence. The bed starts with a th ick unit of conglomerobreccia overlain progr essively by a fine-pebble cong lomerate with parallellamina tion , a t hin uni t of current-bedded gritstones , and at the top by a silty greywacke wi t h plane-parallel lamination . Heigh t of photograph = 1.2 m. (b) Lower part of Bed 18 (above the dark grey greywacke layer) exhibit ing graded bedd ing accompanied by the development of an internal planar laminat ion . Height of pho tograph = 2.5 m. Both photographs taken from Channel 3, east face.
Fig. 9. Originally horizonta lly bedd ed carbo nate breccia showing a grad ual upward decrease in fragment size accompanied by t he gradual development of an int ernal planar lamination; Beds 8-12. Note that Beds 9 and 11 are distingu ished in the conglomerate sequence by their paler colours caused by a do minance of wh ite dolostone fragmen ts in a pale grey calcarenite matr ix. The c1asts are here (re)orient at ed wi th in the D2 (52) schistosity . Fault-related, pro xim al, submarine channel facies. Height of pho tograph =2.5 m. Phot ograph s taken from Channel 1, east face.
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Fig. 10. Upwar d fining of t he c1asts withi n Beds 412 accompanied by th e gradual developmen t of an in ternal planar lamination. Heigh t of pho to graph 8.5 m . Photographs taken from Channel 1, west face.
=
Fig . 11. Combi nation of planar and cross-laminat io n in Bed 17. (a) Crosslam inat io n in t he channel filled w it h coarser g reywacke sandsto ne (pale brown ) appearing in th e upp erm ost part of Bed 17; note t hat t he channel t hickness g radu ally inc reases down dip, and t he cross-lami nate d sand sto ne is th en abru pt ly replaced by silty greywacke (to the right) which exhib it s no visibl e lam inat ion . Height of pho tograph = 0.6 m . (b) Crosslami nate d sandsto ne channel deve loped in t he middle part of Bed 17. Height of ph ot ogr aph = 0.75 m. (cl Erosional chann el in laminated dark g rey greywacke of Bed 17. The former is composed of cu rrent-bedded, pi nk, carbonat e gritsto nes and fine-pebble conglomerate; note that the cross-beddin g is emp hasised by a rhythmic repe tition of cross-bedded calcarenit e-greywacke couplets. Fault -related, distal , submarine channel fades . Heig ht of photograph 0.7 m . All photographs taken from Channel 3, east face.
=
tr ansported, as indicated primar ily by the ir mo re round ed shapes and t he absence of any definite source rock in the vicinity of Fauske (see d iscussion of geochemical data).
Carbonate breccia-conglomero-breccia-greywacke lithofacies The carbonate debris lit hofacies is overlain with a sharp, straigh t contact by fragment-supported carbo nate breccias repr esent ed by Bed 6. High-angle cross-bedd ing has been
Fig. 12. The 0.5 m-th ick Bed 7 (middle part of pho tograph ) showing a lateral Boum a sequence; th e bed begins as a bedded, fine- pebble, carbo nate co nglomerate which is g radually rep laced down-dip by carbona te g ritstones, carbo nat e g rit ston es interbedded wi t h laminated greywacke, and th en by plane-lam inated greywacke and siltstone wi th a massive appearance. Height of phot ogr aph = 1.7 m. Phot og raph taken from Channel 2, east face.
observed in Bed 6 as indicated by the imbricated distribution of predominantly white doloston e fragments (Plate 1). In th e upper part of Channel 1, Bed 6 has a t hickness of 2 m w hich increasesto 4 m dow n-dip wi t hin a distance of 12 metres .The breccias are comp osed of fragm ents of the same rocks as described in th e deb ris lithofacies. The fragme nts, how ever,
NG U-BULL 43 6, 2000 - PAGE 156
VICTOR A. M ELEZ HIK, TOM H ELDA L, DA VID ROBE.'nS, IGO R M . GO ROKHO V & ANTHONY E. FA LLlCK
Fig. 13. Phot ograph s illust rati ng different scales of channelling. (a) White, pale grey and pink, small- peb ble con glomerates interbedded w ith dark grey greyw ackes, t he latt er beco m ing an essent ial com po nent of t he up per part of t he Fauske conglomerate un it; not e that carbo nate g rit stone s and greywackes usually for m couplets, and t hat channelli ng and low-am p lit ude, long-w avelengt h curre nt ripp les are very characteri stic features of t he con glo mero-b reccia-greyw acke Iit hofacies. Bed 18, fault -relat ed, distal , subm arine channel facies.Width of photog raph = 5 m. Phot ograp h taken fro m Chann el 3, east face. (b) Chann el (righ t ofmeasuring tape ) developed in small-pebble congl omerate bed s and infilled wi th coarser material. Wid th of photograph = 2 m. Phot ograph taken from Section 7, Fig . 3, Plate 5. (c) Large-pebble cong lomerates of Bed 2f erode d and channelled, w ith a subsequent infill of the channel consisting of finely dispersed material (black and dark grey sil ty grey wacke) of Beds 8- 1O. Heig ht of pho tograph = 2.7 m. Photograph taken from Section 2, Fig. 3, Plate 4.
are generally much smaller and 'blue' marbles have never been ob served among the c1asts. Alth oug h th e c1 asts are poorly sorted and angular, man y of the pink marb les are represent ed by w ell rounded pebbles.Clast size range s from 0.512 cm in the low er part of Bed 6 to 0.2-7 cm in it s upp er part . Upward fin ing is evident from systematic measureme nt s. Howeve r, th is is almost a cryptic gradation as it is di ffi cult to detect visually. The breccias are capp ed by a 1-20 cm-t hick Bed 7 consisting of lam inated, silty greywacke. This is com posed of muscovite, biotlte. qua rtz, plagioclase and calcit e. The breccia-grey wacke couplet is overlain by a series of conglom ero-br eccia beds (8 to 12 in Channel 1, Plate 1; 12 to 15 in Channe l 3, Plate 2) contai ning medium- to small-size fragments. The cong lomero-breccias are inte rbed ded wi t h t hin beds and layers of w hit e and pink calcarenit e. The con glome ro-b reccia beds (12, 14 and 15) are cap ped by bed s of silty greywac ke (Plate 2). The thic knesses of indi vid ual con glomero-br eccia beds range f rom 0.3 m to more than 2.5 m (e.g., Bed 12) w hereas calcarenit e lenses are usually less t han 0.2 m in thickness. The th icknesses of Bed s 12, 14 and 15 are
almost un iform dow n di p, from 1.5 to 2.5 m. In general , the bed th icknesses in t he conglomero-breccia sequence become rath er constant down dip as compa red to t he lower debris lith ofacies. However, th e greywacke beds st ill exhi bit highly variab le th icknesses. Conglo mero-b reccias are bo th matr ix- and clast-support ed. Fragment s, cobb les, pe bbles and smaller c1a sts are main ly of whi te dolost one and pink, beig e and white calcite marb les. The majority of t he clasts are angular or poorly round ed. How ever, clasts of pink calcite marbl e as we ll as a few of th e w hite dolomite marbl e are represented by wellround ed pebb les. Alt hou gh c1asts are poorly sorted , graded bedd ing has been observed in several beds (Fig. 8a, b). Two late rally cont inu ous beds (9 and 11) are readil y dist ingu ished in the conglomerate sequence by t heir paler colours caused by a dominance of w hite dolostone frag ment s in a pale grey calcarenite matr ix (Fig. 9). In ot her cases, t he matrix is compo sed of calcareous schist. Although the matri x shows a sim ilar range in lit ho logy, fuchsit e, sericite, muscovite, quar tz and chlor ite may be present in variable proport ions in addi-
VICTO R A. MELEZHIK, TOM HELD A L, DA VID ROBERTS, IGO R M. GORO KH O V & ANTHON Y E. FALLlCK
tion to fine carbonate clasts, a feature which giv es the different beds th eir slightly variable coloration. A series of changes in t erms of rock str ucture and lithology can be detected in mov ing upwar ds in th e stratigrap hy wi t hin th e cong lom ero-breccia sequence exposed in Channel 1. An upw ard fining of th e c1asts is clearly visible within both a sequence of beds (Beds 8-12, Fig. 9, Fig. 10) and indi vid ual beds (e.g., Bed 14, Fig. 8a). This is accompanied by th e gradual deve lopment of an interna l planar lamina tion in th e conglomero-b reccia. The str ucture of the silty greywacke, which overlies th e conglo mero-breccia beds, changes upw ards in th e stratig raphy. The lowe r silty g reywacke, Bed 7, hasan indi stinct planar lamination whereas th e up permost and the t hickest Bed 17 is character ised by a combina tion of planar and cross-lamination (Fig. 11 a). Cross-lamination appears in channels filled wi t h coarser greywacke. These 1 t o 15 cm-thick channels are less than 1.5 m in length and have low-angle erosional contacts wi th th e silty greywacke. In th e cross-sect ion s, th e rear parts of th e channels are only 1-2 cm in thic kness and are composed of massive pale grey sandsto ne, but th e channel th ickness gradually increases down dip. The thic kness increase is fol low ed by th e developm ent of visible cross-lamination due to a het erogeneity in lithology resulting from an alte rnati on of sand- and silt- rich lamin ae (Fig. 11a). Furth er down dip, cross-laminated sandst one is abrupt ly, thou gh confo rmably replaced by silty greywacke whic h exhibits no visible lami natio n. This channel-gr eywacke th en becom es ind istinguishable from the main greyw acke body , both consisting of mu scovite, biotite, qu artz, plagiocl ase and calcit e (Fig. 11a). Cross-lami nated sandstone channels have been observed mainl y in th e upp ermost parts of silty greywacke beds t houg h in a few cases t hey have been det ected in the lower and middl e parts (Fig. 11 b). The appearance of cross-lami nated sandstone channels in th e silty greywacke of Bed 17 is accompanied by the developmen t of nu merous 0.5-10 cm-thick layers of white and pink, cross-bedded carbo nate gr itstones and fi ne-pebble congl omerate lenses. These layers and lenses are irregu larly spaced in th e silty greywackes aswe ll as in t he subjacent conglom ero-b reccias.ln places, th e cross-bedding is emphasised by a rhythmic repetiti on of cross-bedde d conglo merate -ca1carenite and calcarenite-greywacke couplets (Fig. 11 c). The upper parts of the carbona te breccia-conglom erobreccia-greywacke lit hofacies exhibi t a sequence of sediment ary str uct ures w hich are typic al of th ose observed in tu rbidity current depo sits. Bed 14, for example, exhibits four distinctiv e unit s (Fig. 8a). The bed starts wit h a thick unit of massive or graded conglomero-breccia which is overlain progressively by a fine-pebble conglomerate with parallel lamination, a th in unit of current-bedded gritstones, and is capped by a silty greywacke w it h plane-parallel lamination. These four units appear to correspond t o th e A, B, C and D units of a typ ical Bouma sequence. While Bed 17 demonstrates a vertical Bouma sequence, Bed 7 in Channel 2 appears to show a lateral Bouma sequence (Fig. 12). The 0.5 m-thick Bed 7 begi ns as a bedded, fine-pebble, carbonate conglo merate and thi s is gradually replaced down -di p over a
NGU-BULL 436,2000 - PAGE 157
distance of 8 m by carbon ate gritston es,carbonate gritstones interb edd ed wit h lam inated greywacke, and th en by planelami nat ed greywacke and siltsto ne wit h a massive appearance (Fig. 12, Plate 3). Overall, the sedimen tolo gical features of th e brecciaconglomero-breccia-g reywac ke lit hofacies are comparable t o those found in sequences dep osited fr om debri s flow follow ed by turbidity currents. Available data demon strate that many of t he conglomero-breccia beds and all th e conglomero-bre ccia-si lty greywacke couple ts were depos ited from a sing le debris flow -turbid ity current pulse. The general up ward fin ing of the c1asts indi cates eith er th at th e c1asts were tr ansport ed from a greater distance as compared wit h th e clast s from th e carbonate debr is lith ofacies or t hat t here was a rise in sea level. We suggest t hat the first option w asthe more likely as it is consist ent wi th the observed increased degr ee of round ness of th e tr ansported c1asts.
Conglomero-breccia-greywacke lithofacies This lith ofacies lies with a rather subdued erosional contact on top of t he channelled and cross-lamina ted greywacke s of Bed 17. The Iithofacies is com posed of pale pink carbonate grit stones irregul arly interb edd ed wi t h dark grey g reywackes and subordinat e w hite calcarenit es. Carbonate gritstones and greywackes usually form couplets (Fig. 13a), which start wit h a 0.2-1.5 m-th ick gri tsto ne layer and end wi t h a 0.1-0.5 m-th ick greywacke layer. The contact betw een these two lithologies is commonl y gradati onal wit hin a distance of 1-2 cm. Both grit stones and g reyw ackes exhibit planar and lowangle cross-lamination. Planar and cross-lamin ation is expressed by th e develop ment of lamin ae wi th eit her coarse or fi ner c1ast s as well as by the appearan ce of th in grey wacke laminae in the gritty framework. Each carbonate gritstonegreywacke coupl et exposes an erosional relatio nship wit h th e und erlying on e. Clasts of round ed pink calcite marble and semi-ro unded w hite dol omite marble are poorly sort ed. They exhibi t no gradatio n in size within layers. Small-scale channels and pockets of fine-pebble conglomerate in the gritty framewo rk are com mon phenome na of t his lit hofacies. Some beds at th e base of th e con glom ero-br eccia- greywacke lithofacies exhibit graded bedding resemblin g th at in Bouma sequences. Sedimentological featu res of th e conglo mero -b recciagreywacke sandstone lith ofacies indicate that both the clastic material and th e finer sedi ments were t ransported in and depo sited from low-energ y current s on a gent ly inclined slope.
Lateral thickness, c1ast size and litho logical variations All the 25 beds recorded in th e Lovgavlen quarry show a certain degr ee of lateral variation in lithology, clast size and thi ckness. Bed thi ckness has been affected by tectonic st rain producing a general th innin g of th e sequence. How ever, signs of differential t ecton ic thi nning of diff erent litholog ies, such as pi nch-and-sw ell and boud inage, have on ly been detected in a few, th in (2 t o 10 cm th ick), silty greyw acke layers. Mo st ot her beds seem to have been similarly affected by
NGU -BULL 43 6, 2000 - PAGE 158
VICTO R A. M ELEZ HIK, TOM H ELDAI., DAVID ROBERTS, IGOR M. GOROKHO V ANTHONY E. FALLlCK
s
Fig. 14. Substantial chang es in both lithology and clast size docu mented in t he carbonate cong lomer ates. (a) Fining in clast size accompa nied by the deve lopment of numerous layers of greywack e (black and dark grey) in Beds 8, 10, 13 and 18. (b) Lateral fining in c1ast size accompan ied by the development of g raded beddin g. Blocks, ang ular and rounded fragm ent s of 'blue' and w hit e calcite marbl es (Bed 2e) fo llowed by cobbles of w hite and g rey calcit e and dolom it e marbles (Bed Zf), wh ich are in t urn overlain by t he cong lomerates (Beds 8-10) showi ng w ell-deve lope d graded beddin g. The graded -bedd ed con glomerate s we re de posited from a sing le tu rb idit y current . Height of pho tograph (a) = 4.5 m, height of ph ot og raph (b) 2.5 m. Photograph (a) taken fro m Section 4, Fig. 3, Plate 4; ph ot og rap h (b) taken from Sect ion 1, Fig . 3, Plate 4.
=
NGU -BULL 43 6, 200 0 - PAGE 159
VICTO R A. MELEZHIK, TOM H ELDAL, DAVID RO BERTS, IGOR M . GO ROKHOV & ANTHONY E. FALLlCK
an overall t ectonic thi nning. This is also clearly indicated by very well preserved sedime ntary featu res such as sedime ntary layering, graded bedd ing, cross-lami nation, erosiona l channels, etc. The measured thickness variations should therefo re largely remai n comparable wi t h t he or igi nal values. Pronoun ced t hickness variat io ns of prim ary orig in may be observed in anyone bed over distances of 10 to 100 m. The most remarkab le change in thickness,wit h th e complete disappearan ce of beds in t hree direc t ions with in a distance of lessthan 100 m, is characteristic of Beds 3-6. This can be demonstrated by comparing t he cross-sections recorded in Channels 1 and 2 (Plates 1 and 3). Beds 3 and 4 are observed in Chann el 1t but th ey do not reappear in Channel 2, over a distance of only 90 m. On t he cont rary, Bed 2 is a prom inent unit in Channel 2 but reappears in Channel 1 in a considera bly att enuated form . Less dramatic t hou gh substan t ial thi ckness changes w it h associated w edging -out eit her in two or three di rect ions have been docum ent ed in Beds 5-7, 9, 11-13, 16 and 25. This is demonstrated in th e long it ud inal lith ological secti ons (e.g., Plates 4 and 5). Fine-c1ast cong lomerate of Bed 16 and largec1ast cong lomerate of Bed 25 for m med ium-scale erosio nal chann els. Bed 25 has a th ickness of 7 m w hereas t he lateral exte nsion of th e channel is lessth an 50 m. Channelling on different scales is a common featur e of many beds and layers. In th e most common cases, chann els w hich develop ed in small pebb le conglo merate beds we re infi lled w it h coarser material (Fig. 13b). Large-pebbl e congl om erat es have also been ob served to be eroded and chann elled, with a subseq uent infi ll of t he channel consist ing of fin ely dispersed mat erial (silty greywacke) (Fig. 13c). This implies th e exist ence of high energ y wate r cur rent s developed on a st eep submar ine slop e. Gradually progressing do wn -slope erosion of greywacke and fin e-pebbl e cong lomera te beds marked by channelling and low-amplitude, long -w ave current rippl es are very characterist ic featur es of the conglom ero-brecc iagreyw acke lithofacies (Fig. 13a). A considera ble lateral variati on in c1ast size is commo nly observed in those beds w hich demonstrate well -p ronou nced th ickness variation s. A po sitive correlat ion bet ween bed th ickness and clast size is a common rul e for Beds 6, 12 and 14. These three bed s exhibit great lateral variation in c1 ast size and thicknesses w hereas th eir lit ho logical comp osition s remain unchange d. In Bed 6, c1ast size ranges from 10 x 30 cm (Secti on 10, Plate 4) to 2 x 5 cm (Channel 2, Plate 3) w it hin a di stance of 100 m. Substant ial changes in both lit hology and clast size have been docum ent ed in th e carbon ate con glom erates of Beds 8, 10, 13 and 18. In th ese cases t he fi ning in c1ast size is accompanie d by t he deve lo pment of numerous layers of greywacke (Fig 14a). As a result, in some casescarbon ate con gl om erates are complete ly replaced by greyw acke (Bed 13, Sect ion 2, Plate 3; Bed 18, Channel 3, Plate 2). Lat eral fining in clast size has also been observed to be accompanied by th e dev elop men t of graded bedd ing (Fig. 14b). Variation s in lithology and c1a st size ham per correla tio n betw een sect ions separate d by unexposed g round . Some beds, however, may serve as a marker. Two w hite-pebble
cong lom erate beds (9 and 11 ). w hich are on ly 0.1 -0.5 m th ick, are distingui shable in th e cong lomerate sequence by t heir compara tively pale colour pattern. Alt hough these beds are thin t hey are easy to detect and can be traced both along strike and down dip (e.g., Plate 4). The pale coloration is expressed by a domin ance of w hite do losto ne fragmen ts in a pale g rey calcarenite matr ix. The examp les described above serve t o demonstrate that the high degree of variability in lithology, c1ast size and thic kness is a gene ral characterist ic of th e FCs. This impl ies un stable depositio nal environments. The t hickne ssvariation s have apparent ly been caused by a number of factors, includ ing erosional effects and chann ellin g, an irreg ular palaeore lief of t he deposit ional surface and a latera l restriction of turbid ity curre nts. Tectonic fact ors have also played the ir part in modifying bed thickness and, as noted earlier, in causing flattening of the calcite marble clasts in partic ular.
Clast composit ion Lit ho logically, th e FCs consist of blocks, fragmen ts, cobbles, pebbles and smaller clasts mainly of wh ite dolostone and pink, beige, w hite and dark grey ('blue') calcite marbl es (Fig. 16a). Clasts of qu artzit es and vein quartz are subord inate. A quan titative est imate of c1 ast composit ion shows th at th e clasts of 'blue' calcit e marbles are exclusively assig ned t o Bed 2 (Figs. 15, 16b) and t hey have never been observed in any ot her bed. Clasts of quartzitesand vein quartz are also preferentia lly concentra te d in Bed 2. On t he ot her hand, clasts of pin k calcit e marb le have never been recorded in Bed 2. The fragm ent s of white and grey doloston e, and w hite calcite marble s are distributed th rough out t he entire sequence and neithe r t he vertical nor t he lateral dist ribution shows any visibl e regulari ty (Fig. 15). The main mineral in the matrix is calcite, w ith minor qu artz and mu scov it e. The matrix is characterised by a granob lastic t exture and retains no prim ary sedime nta ry featur es. Measured clast-m atri x ratios range between 0.3 and 4.6 w ith an average value at 1.5 (n= 30). This ind icates the presence of both c1ast-sup ported and matrixsupport ed conglomerates where t he former are predom inant . However, th e data ob tained mu st be t reated with care as some clast-mat rix boundaries exhibit a d iffu se, un clear appea rance du e to recrystalli sati on . Alth ou gh t he matrix has a similar range in lith olo gy, fuch sit e, sericite, muscovite and chlorite may be present in variable proport ions as minor components in additi on t o fine carbo nate c1asts. Chemic ally, all th e carbon ate c1asts can be divid ed into two groups, namely dolomite and calcite marb les (Table 1). Dolomite marbl es from th e local 'basement ' and in th e c1a st s are ident ical in ter ms of major and t race element abu ndances. On various diagrams t hey are clustered together (Fig. 17). clearly ind icating th at th e c1 asts der ived from th e underlying dolomite marbl e unit. The Mg/ Ca rati o for th e underlying do loston es rang es fr om 0.58 to 0.64 which is close to stoichiomet ric dolom it e (0.62) w hereas th e average Mg /Ca ratio fo r all th e c1a sts is 0.53. This apparent ly poi nts to a process of dedolomitisatio n du ring t he course of tra nsportation and rede posit ion. The overa ll bul k chemical compo sit ion of ot her carbo n-
NGU- BULL 436, 2000 - PAGE 160
VICTOR A. MELEZHIK, TOM HELD AL, DAVI D R0 8ERTS, IGOR M. GOROKHOV &ANTHONY E. FALLlCK
Cnl, Xl
Bed12
Bed11
Bed10
Beds 8+9+10
Bed8
Cn l, VI
Bed 6
Cnl , III
Bed 5
Cnl, VII
~.J LS2, X
I
Bed 2f
Bed2e
CLAST·MATRIX DISTRIBUTION Bed2d
Bed2c
I I i
White dolomite marble Grey dolomite marble White calcite marble Pink calcite marble
Bed2b
Bed 2a
I I I
'Blue' calcite marble Mica-rich calcite marble Amphibole-rich calcite marble Quartzite
Bed1
I I
Vein quartz
Matrix
Fig. 15. Composition of c1asts and matric es measured from diff erent bed s. The following abbreviation s are used in the fig ure : Ch1 - Channe l 1, Ch2 - Channel 2, LS1 - Longitud ina l Section 1, LS2 - Longitu di nal Sect io n 2. Roman numerals indica te the section number w hich was used to cou nt pebb le composit io n; th ese sect ions are marked on Plates 1 and 2. Deta iled log s of LS1 and LS2are not presented in th e article but th ey may be obta ined from th e first aut ho r on requ est.
NGU-BULL4 36, 2000 - PAGE 161
VICTOR A. MELEZHIK, TOM H ELDAL, DAVID ROBERTS, IGOR M . GOROKHOV ANTHONY E. FALLlCK
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613 C (PDB) Fig. 16. Photog raph s illustrating th e variable c1 ast composit ion of t he FCs. (a) Carbon ate breccia composed of angu lar fragment s and subround ed pebbl es of pink , calcite marbl e, w hite, calcit e marb le wi th pink rim s, and white dolom it e marble in a dark calcarenite matrix. The initi al flatte ning and elongat ion of c1a sts is a Caledoni an D1 fabric. Clast reorientatio n and/ or fol ding relates to D2 deformation . Bed 10. Channel 1, east face. (b) Clasts of 'blue' calcite marbles. These are exclusively assigned to Bed 2. Width of phot og raphs = 0.8 m.
•
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MgO, wt%
Key Clasts ~
Wh ite calcite marble
• Pale calcite marble
+ White dolomite marble, basement
o White dolomite marble Matrix e White calcite marble o Pinkcalcite marble • 'Blue' calcite marble
• 'Blue' calcite marble ate c1asts approximates to that of a sandy calcite mar ble. The main siliciclast ic component is quartz t hou g h variable amou nts of mu scovit e may also be present . On a CaO-MgO diagram all t he calcit e marbles plot along a do lomite-calcit e mix t ure line (Fig. 17) indicati ng varyi ng degree of do lomit isation . The various calcit e marb le lit hologies are not disti nguished by major and t race element geoc hemistry. Even t ho ugh th is is the case, the clast provenance has to be different for th e 'b lue', w hite and pink calcite marbles. Whereasth e source for t he 'blue' marb les has been id entified, th e provenance of t he whi te, and in partic ular, of th e pin k calcite marbles remains enigmatic.
Isotope geochemistry and indirect age constraints Methods Oxyg en and carbon isotope analyses were carried out at the Scottish Universities Environm ent al Research Centre using the pho sphoric acid method of McCrea (1950) as modified by Rosenbaum & Sheppard (1986) for op eratio n at 100 "C. Car-
Fig. 17. Cross-plot sshow ing th e compos ition of different c1ast lith ologies and matrix. Samples in th e shaded areas are con sidered to have been subjected to alte rat ion, l.e., w it h a Mn/Sr ratio > 0.2. Arrows ind icate alt eration t rend caused by do lomit isation .
bon and oxygen isotope ratios in carbonate constituent s of t he who le-rock samples were measured on a VG SIRA 10 mass spectro mete r. Calibrat ion t o internati on al reference materi al was th roug h NBS 19 and precision (1o) for both isoto pe ratios is better t han ±0.20/00. Oxyge n isoto pe data w ere corrected using the fractionation factor 1.00913 recom mended by Rosenbaum & Sheppard (1986) for dolomites. The 13 C data are reporte d in per mil (%0) relative to V-PDB and th e 0180 data in %0 relativ e to V-SMOW. Rb-Sr analyseswe re carried out at th e Inst it ute of Precambrian Geology and Geochrono logy of t he Russian Academy of Sciences (St . Petersburg ) as specif ied in detail in Gorokhov et al. (1995). Prior to Rb-Sr isotope analysis, all t he samples were tr eated by 1N NH40 Ac to remove loosely bou nd chemical element s from t he silicate compon ents of th e rock. The
o
NGU-BULL43 6, 2000 - PAGE 162
V/U OR A. M ELEZ H/K, TOM H ELDAL, DAV/D ROBERTS, /GOR M. GOROKHO V ANTHONY E. FALLlC K
s
Tab le 1. Carbo n, oxyge n isoto pe and elem ent al composit ion of marbles from t he Fa uske conglome rate s. Sample
Lithology
No.
wt %
12.00
166
0.52
0.70
0.5
12.30
171
0.53
0.95
0.3
21.5
11.90
172
0.53
0.45
0.2
20.8
1.05
Uppermost conglomerate, Bed 25 0.037 18.37 29.79 0.213 0,01 5 0.05 0.120 0.021 0.06 0.01 9 19.1 6 30.62 0.026 18.50 29.66 0.177 0.010 0.04 0.035 15.99 25.48 0.289 0.018 0.03
10.00
144
0.53
0.96
0.6
21.2
0.56
0.33
0.031 4.26
49.23
0.184 0.013 0.07
11.90 342
0.07
0.29
0.03
22.4
Pink, banded calcite mar- 6.94 ble, cobble
0.76
0.51
0.048 4.64
46.82 0.16
0.258 0.01 5
11.60
328
0.08
035
0.2
22.3
0.15
An1
White dolostone, pebble
9.50
0.68
0.78
An2
White dolostone, pebble
7.11
0.39
0.49
An3
White dolostone, pebble
9.93
0.56
0.57
An4
White dolostone with pink 22.75 stripes, pebble
1.00
An5
Pinkcalcite marble,S cm- 5.81 thicklayer
An6
0.06
20.9
0.14
0.009
0.50
55.13
0.011
0.005 0.09
12.30 478
0.01
0.08
0.6
22.4
0.11
0.004 2.26
54.10
0.011
0.005 0.08
12.30
479
0.04
0.08
-0.2
22.4
0.27
0.022
1.56
53.25
0.091 0.007 0.08
12.20 380
0.02
0.14
-0.06
22.1
52.02 11.10 5.47
0.81
4.99
11.80
44.75
0.82
4.54
15.90
An7
Pa le calcite marble,pebble 1.50
An8
Palecalcite marble, pebble 0.97 with pinkrim
An9
Pinkcalcite marble, 6 cm- 3.02 thick layer
An 15a
Greywacke
An16a
Greywacke
An1 1
White, coarse-grained, cal- 0.52 cite marble, large cobble
An12
Light, medium-grained calcite marble, matrixfor An11
4.83
0.27
0.1 2
EX13
Pinkcalcite marble, 7cm- 2.44 thick layer
0.56
EX16
Whitecalcite marble, thin 0.64 outerrim ofcobble ofblue calcite marble
0.06
EX17
White dolostone, pebble
1.74
0.04
0.13
20.26
32.09
0.008 0.007 0.06
13.95
172
EX1 8c
Pinkcalcitemarble, coreof 0.34 pebble
0.1 2
0.09
0.008
0.79
55.14 0.24
0.015 0.010 0.11
13.18 295
EX1 8r
Pinkcalcite marble, rim of 1.12 pebble
0.44
0.21
0.032
2.08
53.1 6 0.19
0.108 0.026 0.10
13.04 227
0.26
10.39
5.56
0.15
1.88
0.06
0.22
2.70
216
n.d.
n.d.
1.42
0.07
0.24
3.70
298
n.d.
n.d.
Mass-flow Iithofacies, Beds 3-5 0.02
0.43
55.92
0.004
0.08
12.40
391
0.01
0.08
-0.5
-20.6
0.023
1.41
52.63
0.046 0.006
0.08
12.00
363
0.02
0.13
-1.2
22.1
0.30
0.043
3.47
50.44
0.095 0.022 0.10
12.94 175
0.06
0.97
0.6
20.8
0.03
0.007 0.65
54.93
0.013 0.006
13.07 426
0.01
0.11
-0.6
22.2
0.53
0.31
-0.4
21.6
0.01
0.26
-0.2
20.9
0.03
0.88
-0.1
21.5
0.11
'Blue' marbles, Bed 2 An13
'Blue' calcite marble, cob- 1.69 ble
0.18
0.15
0.021
2.98
52.33
0.044 0.005 0.06
12.40 467
0.05
0.08
-1.9
22.8
An14
Pale calcite marble, pebble
6.1 9
1.09
0.79
0.11 7 6.36
46.48
0.277 0.028 0.07
11.80
200
0.1 2
1.08
-0.4
223
An1 5
'Blue' calcite marble, matrixwith small fragments
1.97
0.28
0.15
0.024
2.99
52.80
-
0.068 0.008
0.08
12.30
483
0.05
0.13
-0.8
22.9
An 16
Greycalcite marble, matrix
1.01
0.06
0.05
0.009
3.40
53.06
-
0.030 0.002
0.07
12.40 374
0.05
0.04
-0.7
22.1
EX12
'Blue' calcite marble, matrixfrom 1m-thicklayer
5.38
0.25
0.14
0.020 2.72
50.75
0.11
0.057 0.005 0.09
12.60 376
0.05
0.10
-0.6
223
EX15
'Blue' calcite marble, cobble
0.80
0.05
0.02
0.005 0.67
54.74
-
0.008 0.005 0.10
13.09
422
0.01
0.09
-0.7
223
0.06
14.26
88
0.64
0.53
n.d.
n.d.
0.11 6 0.006 0.06
13.1 0
11 9
0.58
0.39
0.06
21.6
Local 'basement' for conglomerates EX14
White dolomite marble
0.17
0.09
0.14
An10
Whitedolomite marble
1.30
0.80
0.31
23.15 0.049
30.55
21.61 31.52
0.022 0.006
'Dashes' - be low detectio n lim its: 0.1% for AI20 3, a nd Na20 ; 0.02% for S; 0.003% for K20 ; 0.004 % for Ti0 2. 'n.d.' - not det e rmined.
VICTOR A. MELEZHIK, TOM HELDAL, DAVID ROBERTS, IGOR M. GOROKHOV & ANTHONY E. FALLlCK
Rb and Sr concentra ti ons we re det ermined by isoto pe dilut ion . The Rb isotopic composition was measured on a MI 1320 mass spect romet er. Strontium isot ope analyses were carried out in st at ic mode on a Finnigan MAT-261 mass spectrom eter. All 87 Sr/ 86Sr ratio s we re norm alised to a 86Sr/88Sr of 0.1194. Dur ing th e course of th e st udy th e valu e obtained for the 87Sr/ 86Sr rati o of t he NBS SRM-987 standard average d 0.710238±0.000012 (10 mean, n=2). The major and trace eleme nts we re analysed by X-ray fluorescence spect romet ry at NGU using a Philip s PW 1480 Xray spect romet er. The accur acy (1o) is typi cally around 2% of the oxide present (Si0 2, AIP3' MgO, CaO), even at the level of 0.05 wt %, and th e precision is almo st inv ariably better th an th e accuracy .
Data Twenty-four samples represent ing carbonate c1 asts, matr ix and th e im medi at e local 'basement' rocks (w hite dolomite marble) we re coll ected from th e quarry. The com plete sample collection was analysed fo r major and trace elements, twenty-three for oxyge n and carbon isotopes, and nine samples for strontium isotope compo sition (Tables 1 and 2). The 0 and C isoto pe measurements are sum marised in Figs. 17 and 18. The sp read of oxyg en and carbon isotop e values in th e data set is about 20.6-22.9.0%0 and -1.9 to +0.6%0, respectively. A 8 13C-8 180 cross-plot reveals no stat ist ically signif icant covari ation between oxygen and carbon isotopes (Fig. 17). However, all dolomite samples with one except ion exhibit positive 8 13C value s, th e pink calcite marble s all plot around zero, wh ereas th e 'b lue' and wh it e calcite marbl es have slight ly negative values (Fig. 17). The 'blue' marbl es are characterised by th e highe st 8 18 0 values, wh ile oth er lithologies have variable values. The pin k marbl es exhibit covaria tion between 8 13 C and Mn/Sr (r= 0.53), 8 18 0 and Mg /Ca (r=0.45), 8 13 C and Mg /Ca (r=0.56), and a negative corr elation between 8 18 0 and Mn /Sr (r=- 0.56) (Fig. 17). No cov ariations are observed for other lithologies. No reli able difference in elemental conc entrat ion and isot opic rati os has bee n detected between the c1 asts and their matrix (Fig. 17). The initial 87Sr/86Sr ratios in carbonate constituents range between 0.70896 and 0.70946, w ith th e least radiogen ic value measured from the 'blue' marbl e c1 ast (Fig. 18). The 'blue' calcite matrix and the clasts of the same rock are seen to ove rlap on the 87Sr/86Sr diagram (Fig. 18).
Evaluation of diagenesis and metamorphism and c1ast provenance Dolomite is gen erally considered as essentially a d iagenetic mineral. However, th ere is gro wing evid ence th at precipita tion of dolomite in the Precambrian was eit her coeval with calcite, or that dolomitisation wa s an early di agenetic phe nomenon caused by waters isotopically comparable to that of seawater (e.g. Veizer & Hoefs 1976; Veizer et al. 1992a, b). How ever, in th is study, for reasons of precaut ion , we exclude dolomite samples from exercises applied to th e reconstruct ion of the primary composition of seawate r. Several geoch em ical screening method s for pro viding evide nce of di agenetic and metamorphic alteration have
NGU-BULL 436, 2000 - PAGE 163
been devised. Hudson (1977) fo und th at oxyge n isotopes may be a sensiti ve indica tor of di agenetic alterati on. Diagenesis and met amorphi sm com monly cause a decrea se in 8180 value s and th e alte rat io n effe ct can be revealed by a 8' 3C and 8180 cro ss-pl ot . Oxyg en isotopes are co m mo nly much more easily aff ect ed by exchangeable oxyge n derived f rom either meteor ic water or intersti t ial fl uids at elevated temperat ures (e.g., Fairchild et al. 1990) w hereas 813C may be buffered by pre-exist ing carb onate . In general, depletion in bo th oxygen and carbon isotope values may be co nside rable du ring late diagene sis as well as in th e course of low-grade metam orphi sm accompanied by deformation (Guerrera et al. 1997). In t he stu died case no sig nificant covariation has been observed between oxyge n and carbon isotopes . How ever, t he covariation s between 8 18 0 and Mg /Ca, and 8 13C and Mg/ Ca obse rved in t he pink marbles can be attribu ted t o th e do lo mitisation. Th us, we suggest t hat slig ht ly elevat ed 813C and 8 180 values in some pink marbles were caused by diageneti c dolomitising fluid s. The least alte red sam ple is charact erised by 8 13 C and 818 0 values of - 0.2%0and 20.9%0, respect ively. The Mn /Sr rat io may serve as a t ool to discri mi nate between the alt ered and th e least altered samples . Fluids genera t ed d urin g th e co urse of diagenesis and me tamorphism commonly intro duce manganese and radio ge nic st ront ium, and decrease th e Sr co nt ent in carbo nate rocks (Brand & Veizer 1980, Derry et al. 1992, Kaufman & Kno ll 1995). Samples having a Mn /Sr rat io abo ve 0.2 should be tr eated as severely altere d and must not be used for reconst ructi on of seawate r composi tion (e.g., Kusnetzov et al. 1997). These sam ples wo ul d nor mally have lost Sr and t heir Rb-Sr isotope syst ems were distu rbed. Based on the Mn /Sr ratios the majo rity of th e pink marbl es and, ap parent ly, all dolomite marbl es (Figs. 17 and 18) should be excluded from further discu ssion. Based on th e limitati on crit erion , which includes Mn and Sr geochem istry, a 813c vs. 8 18 0 cross-plot and Mg /Ca ratio s, we sug gest th at t he best preserved Sr and oxygen isotope values for t he carbon at es st ud ied are 0.70897 and 22.9%0, respect ively (Fig. 18b, Tables 1 and 2). Both values have been measured from 'blue' marb le c1 asts. As far as th e carbon isotope compo sition is conc erned it is not clear whi ch of th e values reflect a primary signal. The least alt ered 813Ccarb value for th e 'b lue' marbles is -0.5%0 (Fig. 18a). How ever, as even non -di scrimin ated 813Ccarbvalues fo r all th e c1asts and matri ces of calcite marbles are closely clustered betw een -1.9 and +0.6%0, we may assume th at th e sou rce rocks were isotopically homog eneou s and apparently repr esent carb on ates of the same age precipitated from a norm al seawate r.
Implication for depositional age In general, d ating of non -fossil iferous carbon ates provides many probl ems regardle ss of th eir act ual age. In order to obtain an app arent d eposit ion al age for t he FC, t he measured 813Ccarb and Sr isotopic dat a have been used alo ng w it h 813Ccarb and 87Sr/ 86Sr calibration curve s. We exclude th e dolostone sam ples from our con sideration as isotopic values measured for dol oston es may not reflect th e isotopic com po-
NGU-BULL 436,2 000 - PAGE 164
VICTOR A. M ELEZ HIK, TOM HELD AL, DA VID ROBERTS, IGOR M. GOROKHO V & ANTHONY E. FALLlCK
Table 2. Strontium isoto pe and elemental com posit ion of marbles fro m th e Fauske cong lom erates. Insolubl e Sample No.
Mi ne ra ls in
resid ue
Rb
Sr*
wt%
ppm
ppm
Mg/Ca
Lithology
M n /S r
87Sr/86Sr
87Sr/8 6Sr
ins o lu b le
m easure d
i nitial * *
re si d u e
Uppermost conglom e ra t e, Bed 2 5 An7
Paleca lcite marble, pebble
1.7
0.031
481
0.01
0.08
0.70941
0.70941
Qu
An8
Palecalcite marble, pebblewith pinkrim
1.5
0.080
484
0.04
0.08
0.70947
0.70946
n.d.
Ma ss-flo w lithofaci es, Bed s 3-5 An11
White, coarsegrained, calcite marble, largecobble
1.1
0.031
401
0.01
0.08
0.709 16
0.70916
n.d.
EX13
Pink calcite marble, 7 cm-thicklayer
1.8
0.124
171
0.06
0.97
0.70944
0.70943
Qu, Ms, Chi
EX17
White dolomite marble, pebble
1.8
0.032
168
0.53
0.31
0.70921
0.7092 1
Qu
An13
'Blue'calcite marble, cobble
2.0
0.085
475
0.05
0.08
0.70922
0.70922
QU,Ms
An1 6
Grey calcite marble, matrix
2.6
0.050
379
0.05
0.04
0.70930
0.70929
Qu, Ms
EX12
'Blue'ca lcite marble, matrix from 1m-thick layer
5.5
0.323
433
0.05
0.10
0.70910
0.70908
QU,Ms
EX15
'Blue' calcite marble, cobble
0.6
0.104
408
0.01
0.09
0.70897
0.70896
n.d.
' Bl u e' mar b les, Bed 2
* Acid-soluble Sr analysed by standard isotope dilu t ion and solid-source mass spectromet ry.
** The initi al 87 Sr/86Sr ratios are calculated under t he assum ption that t he age of these rocks is equ al to 520 Ma. 'n.d,' - not determined . Abb reviat ions used: Ms - muscovite, Qu - qu artz, Chl - chlorite.
sit ion o f co ev al seawa t er. If we treat all th e carbo nat e c1 ast s as
least alt ered 8 13Ccarb va lue of -0.5%0 t o g et her wi t h the 87Sr/
if th ey hav e derive d from ca rbo na t e roc ks o f a sim ilar age,
86Sr of 0.70 9 16 o bta in ed fo r th e clas ts o f w hite calcit e m ar-
th en t h e b est-preser ve d 87Sr/86Sr va lue of 0.70896, w hich has
bl es w o uld g iv e an ap p arent age w hich is in d ist inguis hable
been obtain ed fo r th e clasts o f 'b lu e' m arb les, is co nsist e nt
fro m th at o f t h e 'b lue' marble s. The pin k an d p ale p in k car -
w it h ap pa re nt d ep osit ion al ag es of 47 0-475 , 505-5 10 an d 5 20
b on at es cann ot b e u sed for t h ese exerci ses as even the least
M a (Fig . 19). Ho w ev er, th e least alt er ed 813Ccarb va lue o f -
alt ered Sr iso to pe value s measu red f rom th em (0.70944 an d
0.6%0 m atc h es o n ly 52 0 Ma . St ric t ly sp eak in g, t he recon -
0.709 41 , resp ectiv ely) are highl y rad iogenic, and on th e dia -
st ructe d age s sho uld relat e t o the fo rm at ion of t h e carb o na t e
gram t he y p lo t abov e t h e 87Sr/86Sr refe re nce cu rv e w it hin
ro ck s b ef o re th ey w e re in co rp o rat ed into cong lom er at e
an y ap p rop riate t im e int erv al (Fig. 19).
c1 asts. Ho wever, av ailab le da t a su g g est th at th e co ng lom erates are intrafor m ati on al, an d t herefo re th ei r ti m e of d ep o siti on sh o u ld b e close t o th e ag e o f car bo na t es from w h ich
Depositional model
th ey form ed. If t h is w as t he case, th en th e obta ined ag e o f
Wil son (1975) defi ned th ree type s o f carb on at e pl at fo rm mar-
520 M a, Early Cambri an , i ndicate s the lo w er lim it for th e
gi n cor res p ondin g t o (1) ene rge t ical ly q u ie t, (2) moderate
appa re nt d ep o siti on al age of the Fau ske co ng lo m erat e.
an d (3) ro u g h seas. A ll t hr ee type s of env ironment usual ly
An oth er assum p t io n w h ic h can b ee n mad e is th at th e car-
produ ce t al us on a foreslo p e to th e carbona te p lat fo rm ma r-
b o nat es inco rp or at ed into t he clast s w ere of differe nt age s.
gin . Ho w ev er, t y p e 3 marg in s are ch aract er ised in particular
Then , th e least alte red 813Ccarb an d 87Sr/86Sr va lu es h ave t o
by th e d evel o p m ent o f wi de sp read g ian t talu s bl o cks, d ebris
be selec te d separat ely for di ff erent lit ho log ical gro u p s o f car-
flo w s an d t urb id it es on fo reslo p es and in d eep -she lf sett ing s
b on at es rep resented b y th e stu d ie d clast s. In t h is case, t he
(Wi lso n 1975, Leed er 198 2). A lth oug h t h e sedi m ent ol o gi ca l
NG U-BULL 436,2000 - PAGE 165
VICTOR A. MELEZHIK, TOM HELD AL, DAVID ROBERTS, IGOR M . GOROKHOV & ANTHONY E. FALLlC K
feat ur es of th e FCs are su pe rf icially co nsist ent wi t h a typ e 3 marg in , th e geolog ical d ata do not match th is type of envi-
0
ronment as th e Fau ske co ng lo m erate is only loc ally d ev elop ed . Such a lo cal d evelopm ent requ ire s th at a loc al fact or
c)
•
sho u ld be invo lved in the form ation of the conglom er ates,
0.1 ro
+ ++
U
Cl
breccia s and deb ris. Moreover, th e pre sence of foreign c1asts, i.e. fragments of t he pink calcite marb les, req uires a syst em
0
•
::2:
t hat could have tran sported such material to th e carbonate
(a) 0.01
p latform/ shelf marg in . Based on thi s, w e sugg est that the d epositiona l m od el sho u ld invo lve (Fig . 20): (i) a loc ally d ev el-
~
op ed , tecton ically un stabl e, carbon at e she lf margi n, (ii) a
--- - - -
ment of a ch annel w it h (v) su bseq ue nt, long-d istance tr ans-
~
... en
t emporary lo w erin g of sea lev el, (iit) format ion of a hig hrelief, sho re-t o-basi n fault scar p, fo llowed by (iv) th e d evel op-
~'"
~o -~ -
c:
::2:
~
~. +
0.1
+
20 ~
0 .....
6
0
8..... 6
N
gj
8.....
.....
6
6
(g
8..... 6
~
0 .....
6
0
8..... 6
port of c1asts of pin k carbonat es f ro m th e contin en t -b asin margin, w h ich we re (vi) redep osit ed t og ether with a car bo n-
••
~+
N
8..... 6
ate debris (w hite dolomite and 'b lue' calcite ma rb les) on the
(d)
gj
..... 6
(g
8..... 6
ro le both in exposing previously deposited carbonat es (w hit e dolomite and 'b lue' calcite carbonate rocks) and in the
Key
development of a chann el. The latter is cons id er ed as an
Glast ~
shelf.
A hig h-rel ief fault scarp ap pa re nt ly p layed an important
87Sr/86Sr
87Sr/86Sr
t ect o n ically fragme nting edg e of a shall ow ing carbonate
White calcite marble
• Pale calcite marble
essential feature fo r transport at ion of th e rela t ive ly far-trav-
o Pink calcite marble
el led (f ro m th e shoreli ne?) c1 asts of pin k carb on at es.
+ 'Blue' calcite marble
o White dolomite marble 'Blue' calcite marble, Matrix • the leastaltered sample + 'Blue' calcite marble
Depositional model and its application for exploitation and exploration
Fig. 18. Cross-plots showing 87Sr/86S r ratios in different c1 ast lithologies and mat rix.Sa mplesin the shaded area areconsidered to have beensubjected to alterati on, i.e., with a Mn/Sr ratio> 0.2. Arrows indicate alteration trend.
o.reso 0.7085
The depositiona l mode l has sev eral implications. First of all, th e data obtained may be used to qua ntify th e comm erc ial quality of the m arbles in the quarry. Thi s ap p lies espe cia lly for the pink and w hite cong lom ero-brecc ias, w hic h are cl early
l·m ··.·.· · · ·. .·
813 Ccarb, average spread
+8
I
0.7080
co
0.7075 0.7070
t-O
·4
0.7065 0.7060
-
+4 0 ~ 0 MU
1.,,,,' t~lt-- .- - .- -.- - - .- ~.- - .- - ~- - ,- - -,- -.- - .-~.- - - .- ~- - ,- -,--,--,--,--,--r-r-,.---,=
7055 0. Ma 400
450
500
550
o C ~L--_.l..--_.l..--
600
650
700
750
Neoproterozoic
800
850
_
The least altered strontium isotope value from Fauske conglomerate The least altered carbon isot ope v alue f rom Fauske conglomerate
Fig. 19. Apparent depositional age of the Fauske conglomerates (indicated by black arro w). The Sr- and C-isotope calibration curvesare based on data from Veizeret al. (1983), Asmeron et al.(1991), Derry et al. (1992, 1993), Gorokhov et al.(199S), Kaufman & Knoll (1995) and Azmy et al. (1998).
NGU -BULL 4 36.2000 - PAGE 166
VIGOR A. MELEZHIK, TOM HELDAL, DAVID ROBERTS, IGORM. GOROKHOV& ANTHONY E. FALLlCK
Fig. 20. Model for the depositional env ironments of the d ifferent facies of th e Fauske cong lom erates.
NGU-BU LL 436,2000 - PAGE 167
VICTOR A. M ELEZHIK, TOM HELD AL, DAVID ROBERTS, IGOR M. GOROKHOV ANTHONY E. FA LLlCK
s
th e most at tractive commercia l ty pes and t he basis for the com mercial value of th e de posit. To be of any value at all, th e conglomero-breccia beds should have at least a 0.5 m t hicknessof uniform marble . As shown above, there are significant lateral thickness variations of th e ind ividual beds and, in actual fact, all exp loitab le beds are show n t o thin out laterally wi thin the quarry area. Consequ entl y, t he com mercial part of the deposit occurs as a limited number of lenticular beds onla pping each other, and separated by non-commercial beds. The vast majority oftra ding blocks have in th e past, and wi ll in the futu re, come from t he lower, t hick, conglomerobreccia beds of the second lithofacies, mainl y Beds 8-1 1, 12, 14 and 15. For the future, Bed 25 may rep resent an additional pote ntial resource, altho ug h t he size of t he c1asts are generally larger than in th e currently exploited beds. In addit ion to t he th ickness variations, th e marble production is sensitive to the variations of quality within the beds. The pricing of marble depends tota lly on customer tastes, and in th e case of th e Fauske qu arry th ese tastes have deve loped t owards th e con glom erate sub- facies with small, sorte d pebbles as th e prime quality material. These types are essentially fo und in distal (thin) parts of t he beds and in the up per part of upward-finin g beds. The pink congl omero-breccias wit h large, sorte d pebbl es are considered t o be somew hat less att ractive in th e market than th e small-peb ble conglomerate, but still of considerable interest . Coarse, poorly sorted breccia (such as Bed 25) is, at the present time, not of any commercial value, but it might be used in th e fut ure as a separate sort ing. The pricin g of blocks is also dependent on th e compositio n of t he matrix . A pure carbo nate mat rix is preferab le, whilst t he value dro ps significantly and proportio nally with an increase in volume of dark silicate minera ls. In general, the commercial value of th e FCs is str ong ly linked t o even minor variatio ns in lith ofaciesand deposit ion al environment. Therefore, th e depositional model wi ll clearly cont ribute to our fu rt her understanding of such variations, and th us help in th e estimation of th e future reserves wi thin th e deposit . Anoth er app licatio n of th e mo del is th at of a prospect ing philosophy for deposits of similar quality. Two major components, namely pink and w hite marbles, make t he FCs com mercially att racti ve. These tw o compo nents derive from tw o different sources.The white do lomite marbles are from a very local source, whereas t he pink marbles we re transported fro m an unknown distant source. Moreover, for a commercially attrac tive rock, th e amou nt of ot her foreign c1asts mu st be very lim it ed.This combinatio n of factors highlig hts several strict limit ations on deposi tiona l enviro nmen ts: (l) a Fausketype cong lomera te may only form on the relative ly steep slope of a carbonate shelf; (2) a direct contact with whi te do lom ite is essential; (3) a high-relief fault scarp is considered t o play an impo rtant role both in exposi ng and fragm enting white dolomite and in t he develop ment of a channe l; (4) the channel is an essential feature for transportation of far-travelled clasts of pink carbonates. Thus, we suggest that a search for new deposi ts should be areally limited t o the development of relatively th ick unit s of w hite do lo mite marbles of
Early Cambr ian age; and a special att ent ion shou ld be paid to t he uppe r contacts of dol omite unit s wit h irregul ar surfaces indicating syndepositional faulting and fragmentation.
Conclusions The Fauske cong lomerate represent s a rather rare case of a monomict carbonate conglomerate in the Lat e Neoproterozoic to Silurian, lithos tratigrap hic successions of the Norwe gian Caledo nides. Lith ol ogical varieties of th is conglomerate uni t from t he Levqavlen quarry have a highl y decorat ive quality and are well known in both domestic and interna tional markets under trading names such as 'Norwegian Rose', 'Jaune Rose', 'Norwegia n Green', 'Antiq ue Fence' and 'Hermelin'. The Fauske conglo merate rests on dark grey ('b lue') calcite marb les and white dolomite marbles. The latter are jointed and fragmented, and also appear as sedimentary collapse-breccia and debr is w here th ey are in direct contact wi t h the cong lomerate. Alth ough th e Fauske cong lomerate has been invo lved in two main pu lses of Caledonian tectonic deformation, the overall sedimentary features are still remarkably well preserved. The Fauske co nglom erate is a 60 m-t hick unit consist ing of 25 beds w hich are from 3 to 5 metresth ick.The unit is composed of landslide, carbonate debris and carbonate brecciacong lomero-breccias - greywacke lithofacies. An upward fin ing of th e clasts is foll owed by th e gradual development of calcareous g reywacke layers which show both cross beddi ng and channelli ng. Blocks, frag ments, cob bles, pebb les and smaller c1asts are mainly of white dolostone and pink, beige, white and 'blue' calcite marbles. The matri x has a similar range in lith ology wit h variable amo unts of quartz, fuchsite, sericite, mu scovite and chlorite. Both matri x and pebbles show a similar range in isotopic values: -1.9 to +0 .6%0 (vs. V-PDB) for 1)13Ccarb and 0.70896 to 0.70946 for 87Sr/86Sr. The least altere d 87 Sr/ 86Sr (0.70897) isotopic value plotted on th e calibrat ion curve is consiste nt wit h appa rent deposit ional ages of 47 0-47 5, 505- 510 and 520 Ma 520 Ma, whe reas th e least altered 1)13Ccarb (-0.6%0) value matches only 520 Ma. The conglom erates were deposited on a tecto nically unstable carbon ate shelf margin . Clast of white do lomite and 'blue' calcite marbl es were locally derived. Clast s of pink carbon ates were transport ed from the continent - basin margin t o t he shelf margin through th e channel formed by a high relief, shore-to- basin fault sca rp. Both local and foreig n clasts were locally redeposited t ogeth er with a carbo nate deb ris (white dolomite and 'blue' calcite marbl es) on the tectonically fragmenti ng edge of a carbo nate shelf. The dep osit ion al mod el may by used to qu ant ify th e commercial qu alit y of th e marbl es in the qu arry. A search for new Fauske-typ e deposit s sho uld be areally lim ite d t o th e development of relati vely thick unit s of w hite dolomit e marbles of Early Cambrian age with an upper contact marked by irregular surfaces indicatin g syndepositional faulting and fragment ation.
NGU-BULL 436, 2000 - PAGE 168
Acknowledgements Access to rnininq property and the core material of the An kerske N S is acknowledged wi th thanks. The field and laboratory work has been sup' po rt ed by th e Geolog ical Survey of Norway, Proje ct 270509 . The carbon, oxygen and strontium isotope analyses were carried out at and partly supported by the Scottish Universi ties Environmental Research Centre, Glasgow, Scotland, and by the Institute of Precambrian Geology & Geochronolog y, St. Petersburg, Russia (Grant 99-05 -65181) . Leif Furuhaug partly assisted w ith drawings. We appreciate the critical reading of th e manuscript and suggested improvements by the referees, Knut BjorIykke and Robin Nicholson.
References Asmeron, Y., Jacobsen, S.B. Kno ll, A.H., Butterfield, NJ . & Swett, K. 199 1: Strontium iso topic variati on s of eoproterozo ic seaw ater : Irnplica t ions for crustal evo lut ion . Geochimica et Cosmochimica Acta SS, 2883 -2894 . Azmy , K., Veizer, J., Bassett, M.G. & Cooper, P. 1998. Oxygen and carb on isotopic composition of Silurian brach iopods: Implication for coeval seawater and glaciation. Geological Society of America Bulletin I /O, 1499-1512. Brand, U. & Veizer, J. 1980. Chem ical diagenesis of multicomponent carbonate system - 1. Trace elements. Journa l of Sedimentary Petrology 50, 1219-1250. Derry, L.A., Kaufm an, AJ. & Jacobsen, S.B.1992: Sedimentary cyclin g and environment al chang es in t he Late Proterozoic: evide nce from sta ble and radiogenic isoto pes. Geochimica et Cosmochimica Acta 56, 1379- 1329. Fairch ild , I.J., Marshall , J.D. & Bertrand-Sarafat i, J. 1990: Strat igraphic shifts in carbon isotop es from Proterozoic stromato lit ic carbonat es (Mauritania): Influences of primary m iner alogy and diagenesis. American Journal of Science 290-A, 46-79. Gee, D.G., Kumpulainen , R., Roberts, D., Stephens, M.B., Thon , A. & Zachr isson, E. 1985: Scandinavian Caledonides, Tectonostrat igraphic map, 1:2 mill ion . In Gee, D. G. & Sturt, B. A. (eds.) TheCaledonide orogen - Scandina via and related areas. John Wile y & Sons Ltd ., Chichester , England . Gorokhov, I.M., Semikhatov, MA, Baskakov, A.B., Kutya vin, E.P., Mel 'n ikov , N.N., Sochava, AV. & Turch en ko, T.L. 1995: Strontium isotope composit ion in Riphean, Vend ian and Lower Cambrian carbo nates. Stratigraph y and Geological Correlat ion 3, 3-33. Guerrera, A., Peacock, S.M. & Knauth, L.P. 1997: Large 18 0 and 13C deplet ion in greenschist facie s carbonate roc ks, w estern Arizona . Geology 25, 943-946 . Gustavson , M. 1996: Geologisk kart over Norge. Berggru nnskart SULlTJELM A, M 1:250 000. Norges geologiske undersokelse. Gustavson , M., Cooper, M. A., Kollung, S. & Tragh eim, D. G. 1995: Fauske 21291V. Berggrunnskart M 1:50 000. Forelopig utgave. Norges qeoiogiske undersokelse. Gustavson , M., Cooper , M. A., Kollung , S. & Traghe im , D. G. 1999: Bergg runnskart Fauske 2129 IV, M 1:50 000. Norges geologiske undersokelse. Helda l, T. 1996: Geolog isk un dersokel se av Lov gavlen marmo rbrudd , Fauske. Norges geologiske undersoketseRappor t 96.022, 36 pp . Hudson, J.D. 1977: Stable isotopes and lim eston e lithifi cati on. Journal of the Geological Society of London 133,637-660. Kaufman , AJ . & Kno ll, A.H. 1995: Neoproterozoic var iat ions in the Cv isotopic composit ion of seawater: stratigraph ic and biogeochemical im plicati ons. Precambrian Research 73, 27-49. Kaufman , AJ ., Jacobsen, S.B. & Knoll, A.H. 1993: The Vend ian record of Sr and C iso to pic var iat io ns in seawater: Im pli cati on s fo r tec to nics and paleocl imate. Earth & Planetary Science Letters /20, 409-430.
vicrc« A. M ELEZHIK, TOM HELDAL, DAVID ROBERTS, IGOR M. GOROKHOV s ANTHONY E. FALLlCK Kaufman , AJ ., Knoll, A.H. & Awrami , S.M. 1992: Biostratigraphic and che mos trat igra ph ic correlation of eoproterozo ic sedimentary successions : Upper Tindir Group, nor thwestern Canada, as a test case. Geology20, 181-185. Kollung, S. & Gustavson, M. 1995: Bergg runns kart ROGNAN 2129 Ill, M 1:50 000. Norges geologiske undetsokelse. Kulling , O. 1972: The Sw edish Caledonides. In Strand, T. & Kulling. O. (eds.) Scandinavian Caledonides. Wiley Interscience, New York, 147285. Kuznetsov, A.B., Goro kho v, I.M., Semikha tov, Mel'n ikov , . . & Kozlov , V.1. 1997: St ro nt ium isotope composit ion in lim est ones of the Inzer Format ion , Upper Riphean type section, Southern Urals. Transaction of the Russian Academy ofSciences, Section Geochemistry 353,3 19-324. Leeder , M.R. 1982: Sedimentology. Process and Product. George Alien & Unwin, London, 344 pp . M cCrea, J.M. 1950: On the isotopi c chem istry of carbonates and a paleo tem peratu re scale. Journal ofChemical Physics 18, 849-857. Melezhik, V.A, Roberts, D., Pokrovsky , B.G., Gorokhov, I.M. & Ovch inn ikova G.v. 1997: Prim ary isoto pic features in metamorphosed Caledonian carb on at es: impli cation s for depositional age. (Extended abstract ). Norgesgeologiske undersokelseBulletin 433,22-23. Nicho lson, R. 1974: The Scand inavian Caled onides. In Nairn, A. E. M. & Steh li, F. G. (eds.) The Ocean Basins and Marg ins, Vol. 2. The North Atlantic. Plenu s Press, New York, London, 161-203. Nicholson, R. & Rutland, R. W. R. 1969: A section across the orweg ian Caledon ides; Bodo to Sulitje lma . Norgesgeologis e underso else 260, 86 pp . ystuen. J. P. 1989: Rules and recommendations for nam ing geo log ical un its in Norway. Norsk Geologisk Tidsskriit 69, Supplement 2, 111 pp . Robert s, D., Gje lle, S. & Solli, A. 1998: Tektonostrat igrafiske enheter i den kaled onske fjell kjeden . Nordl and fylk e. (Dig it ised ma p). Norgesgeologiske undersokelse. Robert s, D. & Gee, D. 1985: An int roduct ion to the struc ture of the Scandinavian Caledo nides. ln Gee, D.G. & Sturt, BA (eds.): TheCaledonide Orogen - Scandinavia and Related Areas. John Wiley & Sons Ltd., Chichester, 55-68. Rosenbaum, J. M. & Sheppard, S.M.F. 1986: An isotopi c study of sider ites, dolomites and ankerites at high temperatures. Geochim ica et Cosmochimica Acta 50,1147 -1159. Rut land, R. W. R. & Nicholson, R. 1965: Tecton ics of the Caled on ides of par t of Nor dl and , Norway, Quarterly Journal of the Geological Society ofLondon /2/, 73-109 . Strand , T. 1972: The Norwegian Caledonides . ln Strand , T. & Kulli ng, O. (ed s.). Scandinavian Caledonides. Wiley Interscience, ew Yo rk, 1145. Veizer, J. & Hoefs, J., 1976: The nature of 160 /180 and 13(f 12C secular trends in sedimen tary carbona te rocks . Geochimica et Cosmochimica Acta 40, 1387-1395. Veizer, J., Clayton, R.N. & Hint on , RW . 1992a: Geochem istry of Precambr ian carbon ates: IV. Early Paleop rot erozoic (2.25 ± 0.25 Ga) seawater, Geochimica et Cosmochimica Acta 56, 875-885 . Veizer, J., Plumb , K.A., Clayton , R.N., Hinton, RW . & Grotzinger, J.P. 1992b: Geochemistry of Precambrian carbonates: V. Late Paleoproterozoic seawater (1.8± 0.25 Ga). Geochimica et Cosmochimica Acta 56, 24872501. Veizer, J., Com pston, W., C1auer, N. & Schidlowski, M. 1983: 87Sr/86Sr in Late Protero zoic carbona tes: evidence for a 'mant le' event at - 900 Ma ago. Geochimica et Cosmochimica Acta 47,295-302. Vogt , T. 1927: Sulitj elmafel tets geologi og petrografi. Norges geologiske undersokelse 12/, 560 pp . Wilson , J.L. 1975: Carbonate facies in geological history. Springer-Verlag , Berlin , 471 p p.
NW
Melezhik et al. - Plate 1
Lithological cross-suction, channull, Bast facB Srn
SE 8
--
an
-........~ ~
~ ~
~
~
,,-
---? -' ~
~
- ~-
......
"'-,-
/----
.J
(
r
)
\ 11L...-
11
'Landslide', white dolostone
Basement, white dolostone
---l
---l L...I
.
1
Carbonate breccia
Ca r bonate de bris
@ 11
I CID Carbonate debris
Carbonate cong lomerate Bed 12
U
Unso rt ed, " neul"r c las ts ofW » ;\( and ro unded clas ts of PC "I iu e ''l.'~' and pink matri x
Bed 10
Pink ca lca rcn lte
Un so rt ed, nn en1nr clas ts of W »M und rounded clasts of I' C I\I in en'\' mat ri x; la yers of pnl'l-
Banded en'~'wnl' kl' nnd sllty sa nds to ne
Bed 8 Un so rt ed, nne u1nr clas ts of \ V»I\I a n d round ed cln st s of PC I\I in e rl.'~· matri x
Bed 6
~
C ha n ncl of' mc di um -slze, u ns ort ed , " neul"r cla st s of PC" I " n d W»:\I in dark gl'l'y m a tri x
Bed 3
o
nsort cd cla sts of PC M, a nd W»I\I in pink matri x
Bed 2
Carbonate breccia
WI)i\1 and light PCM in white cnlcarcnite matri x (m a rk er laye r )
W»M und light PCM in white cnlc aren lte matrix (m a rker layer)
-
Bed 5a
Bed 7
Bed 9
Bed 11
o
Bed lOa
Basement
Hrecciu co ns isti nj; of In"gl', un sorted , nn guln,' clust s of PC"1 and WI)I\ I in pink matrlx
Bed 5 Block s uud un so rt ed , "neu l",' clas ts of PC I\I a nd W I)I\I in dark g "l'~' matri x
IJnsortcd clas ts of PCM, b locks of\V » M and whitc-rlmmed BC "I in pal e e '''~' m atri x
r:
I\lnssiw WDM
Symbols
[@J
Bed number
,Landslide'
Bed .. Un so rt ed nng ulm' clas ts of PC M a nd W»I\ I in d ark gn'~' ma t ri x
Deta ch ed a nd prl zerl bl ock s of W »:\ I
C lnst co un t sec tion a n d its numbe r re ferre d t o in Fie, 15
Uthological cross-section,channel 3,east face
NW
Melezhik et al. - Plate 2
5rn
SE
@ Legend
-
Bed 24
Beds 22-23
Bed 19
Bed 18
Bed 17
Unso rt ed ro unde d clns ts of PC \ l lllld a ng ular a nd round ed clnsts ofW I);\ 1 in pink , IIghl aud dark gre ~. matr i x
Bed 15
CI;] Bed 14
Silty lumlnut ed gn-~·wlI l· kt·, cha nne ls of' c ro ss-be dde d ca r bona te conglomeru tc a nd gritston~ Sm a ll-pe bble carbona te conglo me m tc with laye rs of silty g~~~"ac kt-, w h ite culca re n lte gr-u llng inl o cnrhona te gri lslo n~ : clasts of W I);\ 1 and I'C;\I in d a rk mat r ix
Sllty planar-la mi na ted an d cross-bed ded gr~~'",ack~, cha nne ls of cross -bed ded carbonate grilslon~ a nd con glo m~m l~ Car bo na te cong lomera te with lavers of' wh ltc calcarcnltc: urisurt ed round ...1 clas ts ofl'CM and a ng ular a nd round ed clas ts of WI);\I in pin k m ntrl x Unsort ed round ed clas ts of P C;\I and an gulal' a nd round ...1 clasts ofWI);\1 in pink m at ri x; laye rs of while ca lcaren lte
Bed 13
Bed 12
Bed 11
o
Bed 10
Silty gre-yw acke
Bed 8
~
;\ " 'diu m ,pl-bb ll'l'u ng luml'mll-: u n54111 ..1. angu lar clasts uf \\'I);\l lllld 1' (MIIIl"'" .-Iasl s ofl' C;\1 in gr('~' malrix
Bed 7
Bed 6 i\ll-d iu m - to sma ll-pe bble un sort ed , anor ular cla sts uf \\'I):\1 and round ... clas ts of I' C;\I in gl'e~' marri x
.
Sma ll-pe b ble l'O ng l()Jue l~tll' : un sorted , a ug ula l' cla sts of \\'1);\1 and round ed clnsts uf lig hl of I'Ci\ 1 in white ca learenite matrix (m a rk e r laye r)
~"SJ
Hrec cl n l'o nslsti n~ of' u n sorted
r ound ed cla st s o t I'CM and a ng ula r clusts ufW I):\ t in pink m nt ri x
CJ Bed 2f
Bed 2e
Lar~ , un sorted , an gul a r a nd ro u nde d clnst s a n d blo cks of GI);\llllld whi le -ri m med n CM in gre~' ca lcite ma t rix
Sym bols
Sma ll-pe b ble cong lomemle: un sort ed , _ ang ula l' cla st s of \\'1);\1 a nd ro und ...1 clusts uf I'C;\ I in whit e ca lca renitc m utrl x (m a rk e rlaye r)
l'unglo m~m te:
Bed 9
I
;\It-,lIum - tu sma ll-pebble l'ung lonll'mlt·: u nso rt ed , llllf ula r clusts uf \\'I):\llInd rou nd ... cla st s of I' C;\ I in pink -grvy m at ri x
ca
[S] Sma ll-pc h hle l'llng lunu'mlt' with la vers uf si lh ' gl'evwal'kt·: 11llllllll:d pchhl e» ;,fW1>:\ l a nd qu artz
[®~
Dyk e
Q ua rtz vein
T h rust
Hed num be r
Melezhik et al. - Plate 3
Lithological cross-sBction,channBI 2, east facB NW
Ca rbonate breccia
5m
SE Carbonate conglomerates
Ca r bonate debris
Legend Ca r bonate breccia Unsort ed, sma ll an gul a r clas ts ofWDM and ro unded clas ts of PCM in gn~y and pink m at ri x
Layel' 6 WDM a nd light PC M in wh ite ca lca re nl tc mat ri x (market' layer)
Layer 8
Layer 11
r.
.. Layer 9
WD M a n d light PC M in white cnlca re nlte matrix (marke r layer)
Uns orted, an gula r cla sts ofWDM and rounded clasts of r C M in grey matrix
Unsort ed , ang ular c1asts of \ VDM a nd ro u n de d c1asts of PCM in grey matri x
Layer 7 Carbo na te grits to ne gra ding into silty grey wacke
Symbols
Layer 21' Unsorted, sma ll angulat, clasts of rCM and W DM in pin k a nd gt'l.'J' matrix
Angula r; unsort ed d asts of G DM in pall' gl'l'y matr i x
Ca r bonate debris
Cong lome ra te
Layer 5
Layer I Unso rt ed , ro u n ded clasts ofWDM an d PC M in pink matri x
Layel' 2c-e ~ -~ ~
..
tfL-D -4
Unso rt ed , r'OIIIIIled c1 a sts of PC ;\! in pale gre y matrix
Layer la Block s a n d un sorted, ang ula r clasts of white- rimmed BCM a n d W DM in dark grey ma trix
Unso rt ed, round ed clasts ofW DM and light PC M in dar k gn.'y ma t ri x
La yer number
Clas t co un t sectio n and its number referred t o in Fig, 15
Me lezhik et al. - Plate 4
NE
Longitudinallithological section
Section 4
Sect ion 3
sw
Section 2 Section 1 Sect ion 2b Section I b
Sect ion la
Section 12
Sect ion 11
\6
Section 2a
12
Section 10
-
::.::-:-. -
2c
Srn
--
-:-
2
Legend C a r bonate breccia and con glom erate Bed 16
Unso rt ed ro unded c1ast s or
Bed 13
('C\ \ and a n/:u lar an d
ro unded clas ts orWI>~ \ in pin k a nd dark /: 1"(')' matr i x
Bed 15
Bed
Unsort ed rounded clast s or (' CM and a ng ular and 11111 ," I,'d clas ts orWI>~ [ in pin k ma t ri x Large to sma ll, un sort ed , rou nd ed clas ts or P C M a nd '1II11" lar clas ts or W I>M m pink matr t x
Bed 12
Fi ne-pe bble conelomc rn te gr.lding int o ca rbu nate gri tsto ne a nd laminat ed silt)' greywacke ~ [e di u m - pe b b lc hre ccia /:m di ng into sma ll-gcbbl" cOlI/:lo mcmt,'S wit I ch an ne ls a nd b eds or lam inat ed sill)'
gre,Ywarkc
Bed 11 Sma ll-pc bblc co nlilomc m t',: WDM a n d light I C M ill wh it e cal ca renite matrix (mu ..kcr layer)
Bed 10
E;J Bed 9
D Bed H
I}~
Br ec cla /:l1l1l1ng in to fin epeb ble con glome rute: lIIlS 0I1 l'( l , a ng ula r'dasts of W I>;'; [ a nd round ed c1asts of PC i\ [ in gre)"matrix
Sm a ll-pcbbl,' con/:lmncmtc: W I>1\ [ a nd II/:ht PC 1\[ in w hite ca leurcn ltc m atr i x (m a rke r la ye r) M edi u m -peh ble h re cc ia /:l':lIl1ng int o snm ll-gc bblc co ng lomc mtes wi t I cha nne ls and beds of lam inated s ilt~' /:re-ywackc
.. Bed 7
Bed 6
~ Bed 2f
~
Bed 2e La m ina te d s ilty g n') 'w;'H:k e•
Brcccia : la q.~ (·, UIl SOI1 1.'d , a ng ulal ' c1 ast s of W 1>;';[ and ro unde d ('Iast s of PC ;';[ in pin k mall '" i'h'lli u m to sm all, un so rt ed , an ~' lal' c1 as ts of(; Ul\[, BC l [ and s ma ll, ro u nded
clas ts or ,)" ,,, 't,, ill pa le gn') ' ('a l('lh' m a t l"ix
La .'gl.', un sort ed , a ng u lar c1asts a nd blocks orG I>M and IIC;';[ in d ark g l"(,~' culcit ..• m at ri x
Bed 2b
D
Bed 2d
§f~ ~ Bed 2c
Sm a ll, un sort ed , round ed clas ts orWI>;'; I, G I>~[ and qu art z in pal e /:I"cn ca lcite -sillciclas tic m at ri x
Bed 2a L," '/:c, un sorted , 'lII/:ular clas ts :tI1l1 block s or G I>M a nd IIC M in pal e /:1" )' calcltemutrl x I,a r ge-, un sorted , a ng u la r clas ts a nd block s o r GI>l\[ a nd I\ C\ [ ill d ark /: I"~' ca lcit ..• m ~ltl"i x
"- --- - ~ ;
...;;:.,,-... :.:::::.
"
La rge , un so rt ed , all 'iu hu ' clasts a nd blocks or ; 1>1\[ a nd IIC M in da rk /:1"(')' ca lcite m a t ri x
Bed 1
.. ~ ~
~
Large, un so rt ed , round ed clasts ofl'CM a nd " 'C M in da rk /: I"(,~' mat r ix
Dyke
Sym bols
0
Bed num her
Melezhik et al. - Plate 5
Longitudinallithological suction Section 13a
sw
NE
Section 13 24
24
Section 7
Section 6
22-23
20
19
5rn
18
Section 5 17
Legend Bed 24
Bed 20 Greywacke sandstone with layers and channels of carbonate small-pebble conglomerate
Beds 22-23 Unsorted rounded cIasts
Lm Bed 21
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of PCM and angular and rounded cIasts of WDM in pink, pale and dark grey matrix
Carbonate conglomerate, large to small unsorted, rounded cIasts ofPCM and angular cIasts ofWDM in pink matnx
Bed 19
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Bed 18
Fine-pebble COntlOmerate grading into car onate gritstone: rounded and angular, sorted cIasts ofWDM and PCM Silty laminated greywacke, channels of cross-bedded carbonate conglomerate and gritstone Small-pebble carbonate conglomerate with layers of silt); greywacke gradmg into car onate ~itstone: cIasts of WDM and CM in dark matrix
Bed 17
Bed 16
Bed 15
CJ -~
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Bed 14a Silty laminated greywacke, channels of cross-bedded carbonate gritstone
G
Unsorted rounded cIasts of PCM and angular and rounded cIasts of WDM in pink and dark grey matrix
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Unsorted rounded cIasts of PCM and angular and rounded cIasts of WDM in pink matrix
Small pebble conglomerate with layers of siltyAVtrvacke: rounded pebbles 0 M and quartz
Dyke
Symbols
0
Bed number
14a
