Depositional Environment and Apparent Age of the Fauske Carbonate Conglomerate, North Norwegian Caledonides
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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 ROB ERTS, IGOR M. GOROKHOV& ANTHONY E. FALLlCK Melezhik, V.A., Heldal, T., Roberts, D., Gorokhov, I.M. & Fallick, A.E. 2000: Depositio nal environment and apparent age of th e Fauske carbonate cong lomerate, North Norwegian Caledonides. Norges geologiske uridersekelse Bulletin 436, 147-168. The Fauske conglomerate represents a rather rare case of a monomi ct carbo nate conglo merate in the Late Neoprot erozoic to 5i1 urian, Iithostratigraphic successions of t he Norwegian Caledo nides.Lith ological variet ies of thi s conglomerate unit fro m th e Lovgavlen quarry have a highly decorative quality and are well known in both dom estic and interna tional market s under t radin g names such as 'Norwegian Rose', 'Jaune Rose','Norwegian Green', 'Antique Fence' and 'Hermelin'. The Fauske conglomerate is a 60 m-t hick unit which rests on either dark grey ('blue') calcite marbles or white do lomite marbles. The latter are joi nted and fragm ent ed, and also appear as sedimentary collapse breccia and debris where they are in direct contact wit h th e conglom erate. Althoug h t he Fauske cong lomerate has been involved in two main pulsesof Caledonian tecto nic deform ation, which prod uced an early, syn-metamorphic flatt ening of th e c1 asts and a later folding or rot ation of c1 astsint o a spaced cleavage, the overall sedimentary featu res are st ill remarkably well preserved. The Fauske cong lomerate unit consists of 25 beds (5 cm to 3 metres t hick) comprising landslide, carbonat e debris and carbonate breccia- conglom ero-breccias- greywacke lithofacies. Blocks,fragm ent s, cobbles, pebb lesand smaller c1 asts are mainly of white dolostone and pink, beige, white and 'blue' calcite marbles. The mat rix has a granob lastic texture and similar range in lit hology wit h variable amo unts of quartz, fuchsite, sericite, muscovite and chlorite. With in the unit, an upward finin g of th e c1 astsisfollowed by th e gradual developm ent of calcareous greywacke layers which show both cross beddin g and channelling. The depositional model involves: (i) a locally develop ed, tecton ically unstable carbonate shelf-margin , (ii) a temporary lowering of sea level, (iii) formation of a high-relief, shore-to -basin fault scarp followed by (iv) th e development of a channel, with (v) subsequent, long -distance transport of c1 asts of pink carbonates from the conti nent-basin margin, which were (vi) redepos ited togeth er wit h a carbonate debris (white dolom ite and 'blue' calcite marbles) on t he tectoni cally fragment ing edge of a carbon ate shelf. Bot h matrix and peb bles show a similar range in isotopi c values: -1.9 to +0.6%0 (vs. PDB) for Ol3Cea rb and 0.70896 to 0.70946 for 875r/865r.The least altered 875r/865r (0.70896) isotopic value plotted on the calibration curve is consistent with a seawater composition corresponding to ages of 470 -475 , 505-510 and 520, wh ereas the least altered Ol3Cearb (-0.6%0) value matches only 520 Ma. Victor A. Melezhik, Tom Heldal & David Rob erts, Geolog ical Survey of Norway, N-7491 Trondheim, Nor way; Igor M. Gorokhov, Instituteof Precambrian Geologyand 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. (Heldal 1996) such as 'Norwegian Rose' (pink and w hite), Introduction 'Jaune Rose' (pale pink and w hite), 'Norwegian Green' (white Polymi ct carbo nate-silicate cong lomerates are abundant wit h green patches), 'Antique Fence' (grey wit h w hite veins) rocks in th e Late Neoproterozoic to Siluria n, lith ostrati and 'Hermelin' (whi te w ith grey veins). As the se different grap hic successions of the Norwegi an Caledon ides, includ types of cong lomerate have an economic significance, th ere ing th ose know n in t he Fauske area (Fig. 1). The conglomer isa practical reason for carrying out research on their deposi ates occur either as clast- or matr ix-supp ort ed varieties (Fig. tional enviro nme nt and age. Results of such a study should 2a, b). Many of t hem have clasts of schist, qu artzite, vein help to provide better t heore tic al groundsfor future explora quartz and white do loston e, and some may contain large tio n of th is and similar deposits. cobb les of vo lcanites (Fig. 2c) or rare fragments of pink mar bles (Fig. 2d). Mon omict carbo nate conglomerates, however, represent a rat her rare case. In one unit of carbonate con Geological setting glo merate exposed near Fauske, in Nordl and, nor thern Nor The Fauske conglomerate constitu tes a c. 60 m-thick lensoid way - th e Fauske conglomera te - predominant ly carbonate unit (Fig. 1) within a formation known from earlier literat ure material composes both t he clast sand t he matrix.This part ic as the Fau ske lim eston e (Vogt 1927, Strand 1972) or th e ular cong lomerate has been exploited asa dimensional stone Fauske m arbl es (Rutland & Nicholson 1965). These carbon since 1870 from t he Lovgavlen qu arry, and each of t he main ates, both banded calcit e marbl es and do lomite marb les, lithological varieti es is well known und er commercial names were considered to form part of the middle unit (t he Fau ske NGU- BULL 436,2000 - PAG E 148 VICTOR A. M ELEZHIK, TOM HELDAL , DAVID ROBERTS, IGOR M. GOROKHOV & ANTHONY E. FALLlCK \ \ \ \ \ \ 15° 30 ' 1000 1000 o Ji--;r-U~..,.-,.-7:-;-;'hnir--===!--.:jS o -1000~/ ~="----"-'tL.-__-'IU«:l'-'-------'-_L.-.-~=--"--~ -1000 LEGEND Quaternary dep osit s GASAK :,\,\I'I'E Calcareou s D Mor ai ne mi ca schist • Mica schist Grey, banded, calcite • Cal c-silicute schist Caledo nian units marble IlEUR:,\ :'\AI'I'E • Mic a schis t with • Mica schist and gne iss do lost one boulders t· ~/~ 8 ~lica schist and ~n('iss Binti te-h ornblend e SEn:-KOLl • :,\,\PI'E CO'lPLEX D sra uro lite-mica schist IVDI:'\ GS F.L\LLET :'\AI'I'E CO ~ I I' LEX D Qu artzite • Calcite ma r ble Amphibolit e !:::: :',:i Qu artz-mlcu schist • Grey calcite marble Garnet-mi ca sc hist D Schist and gnei ss • LOWE R :,\,\PPES Calcite marble v / Mica schist • wit h bands of Leivset marble Mic a schisl a nd mctu-arkose Fuu ske co nu lomerure H:::::I Ba nded mct a- arkose Dolomite marble Polvm ict o 0 n n n n n l\1ica schist and gneiss cOllglOl11cl"ute + + + Granite gndss Fig. 1. Location map (a) and simplified geological map (b) of the Fauske area, modified afte r Gustavson (1996). VICTOR A. MELEZHIK, TOM HELDAL, DAVID ROBERTS, NGU-BULL 436,2000 - PAGE 149 IGORM. GOROKHOV& ANTHONY E. FALLlCK Fig. 2. Photographs of natura l exposures showi ng typical polymict cong lomerates of the Rognan Group : (a) Matr ix-suppo rted conglomerate interbed ded wi th gritty and silty greywacke; unso rted and uneven ly distributed c1a sts are represented by arkosic and quartzitic sandstones (pale grey) and do lostones (pale bro wn ). In this and the next photo, the c1a sts are flattened and elongat ed within a schistosity at a low angle to the beddi ng.(b) Clast suppo rted cong lomerate; c1a sts are quartzitic sandsto nes (palegrey) and dolo stone s (pale brown) in greywacke matr ix.(c) (last-support ed conglomer ate; unsort ed c1 astsare quartzitic sandston es (pale grey), int ermediate volcanites(darkgreyl and dolostones (pale brown) in a greywacke matrix. (d) Clast supp orted conglomerate; c1 asts are quartzitic sand sto nes (pale grey), amphibolites (black) and pink calcite marbles in an arkosic sandsto ne matrix. The photog raphs were taken along the shore of Saltd alsfjorden, east of 0ynes (Fig. 2). Scale bars = 10 cm. Marble Group of Nicholson & Rutla nd (1969)) of t hree main rated in th e Upperm ost Allochthon. Later mapp ing showed, st ruct ural eleme nts in t he metamorphic allochtho n of th e however, th at th e Fauske carbo nates we re more likely corre Nordl and Caledo nides. The two main carbo nate fo rmatio ns latable wit h rocks of simi lar metamorphic grade in, e.g., t he we re later placed togeth er under th e name Rogna n Group Hatt fjelld al and Jofjallet Napp es farther south, l.e., t he high (Kollung & Gustavson 1995). Nicholson (1974, p. 184) intro est tectoni c units in t he Upper Koli Napp es, part of the Upper duced th e term Fauske Nappefor the mediu m-g rade, marble Allocht ho n. Subsequent map compilations have favou red rich successions lyi ng structurally above th e high-grade t his affiliatio n (e.g. Gustavson 1996, Roberts et al. 1998). Gasak Nappe and below rocks of th e Rodlnqsfja llet Nappe As no fossils have been found in t he carbonate forma Complex (including th e Beiarn Nappe). The designation tions of the Rognan Grou p, t he actual ages of the un its are Fauske Nappe 1 has been retained in most recent map compi unknown. Earlier workers, e.g. Vogt (1927). considered that lations (Gustavson et al.