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The Marine Transgression in the Middle Carboniferous of Broggerhalvoya (Svalbard)

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The Marine Transgression in the Middle Carboniferous of Broggerhalvoya (Svalbard) The marine transgression in the Middle Carboniferous of BrOggerhalvOya (Svalbard) PETRA LUDWIG Ludwig, Petra 1991: The marine transgression in the Middle Carboniferous of BrQggerhalvGya (Svalbard). Polar Research 9(1), 65-16. The change from continental to marine conditions in the Middle Carboniferous on Breggerhalv0ya started at the end of the Bashkirian with short-term transgressive events at the top of the Breggertinden Formation. Local basin subsidence was responsible for the pulsatory nature of the transgression. The establishment of a shallow marine carbonate-dominated environment is represented by the Moscovian Scheteligfjellet Member which overlies the post-Caledonian red beds of the Br~ggertindenFormation. The Scheteligfjellet Member is the lowermost member of the Nordenskioldbreen Formation and shows distinct lateral facies variations. Three facies associations can be distinguished: lagoonal facies, shoal facies and open marine facies. The succeeding two members were deposited in subtidal areas of the carbonate platform. A basin subsidence event at the Carboniferous/Permian boundary was responsible for a short shift into deeper depositional environments during a time of worldwide regression. After this a continuous regression led to supratidal conditions at the top of the Nordenskioldbreen Formation. Petra Ludwig, Spiegel-Verlag, Dokumentation, Brandstwiete 19, 0-2000 Hamburg 11, Germany Metamorphic rocks (Hecla Hoek), which were Upper Palaeozoic of Svalbard, will be described folded during the Caledonian orogenesis, are and interpreted in terms of their microfacies. unconformably overlaid by Upper Palaeozoic rocks on the Br~ggerhalvOyapeninsula, situated in the NW of Svalbard (Fig. 1). These post-Cale- donian sediments consist of a terrigenous redbed Stratigraphical setting succession overlaid by shallow marine platform The Upper Palaeozoic sediments on Brcdgger- carbonates. The carbonates, which mark the halvoya were first described by Holtedahl (1911, establishment of marine environment in the 1913) and in more detail by Orvin (1934). For the investigations presented in this paper the revision of the slratigraphical scheme by Cutbill & Chal- linor (1965) is used (Fig. 2). The base of the Upper Palaeozoic succession on Brcdggerhalv~yais mainly represented by the Middle Carboniferous Br~ggertindenFormation which rests unconformably on Hecla Hoek rocks. The presence of the Lower Carboniferous Orustdalen Formation on the SW coast of Brcdg- gerhalvcdya led Barbaroux (1966, fig. 4) to the incorrect assumption that the Orustdalen For- mation is present throughout the entire peninsula. The terrigenous red beds of the Br~ggertinden Formation, deposited in a local half-graben (Lud- wig 1989), are overlaid by the Nordenskioldbreen Formation which is of Moscovian to Sakmarian age and therefore spans the Carboniferous/ Permian boundary (Cutbill & Challinor 1965). II The Nordenskioldbreen Formation on Br~g- gerhalvcbya is about 370m in thickness and is Fig. I. Location of Breggerhalv0ya on Svalbard divided into three members: Scheteligfjellet 66 P. Ludwig Mitlrithecopora syrinx (Etheridge 1900; Oeken- Stage Croup Formation Member torp, pers. comm.) is defined as the boundary upper 1 1,prden] Kapp Starostin between the Broggertinden Formation and the Permian Kungur GrouD Formation I Scheteligfjellet Member in this investigation. This syringoporid coral (Oekentorp & Kaever 1970), Lower JArtinsk I Formation which occurs in situ, presumably was the fossil Tyrrellfjellei Permian Member identified by Holtedahl (1911) as Syringopora 1-1 1-1 Assel hordenskleld- parullefu Fischer. This limestone forms an easily breen Msrebreer Member perceptible marker horizon on Broggerhalv0ya, ferous CY- Formation .--_--__and after the recommendations of the Norwegian dalen Scheteligfjellet - Member Committee on Stratigraphy (Nystuen 1989), it is Croup Middle suggested as being an informal unit. Broggertinden Carbon11 The upper boundary of the Scheteligfjellet /Bashkir ferous , Formation Member corresponds to the top of the uppermost siliciclastic bed. Where these beds are missing, Lower the Scheteligfjellet Member consists solely of fos- ferous siliferous limestone, and the transition to the overlying Morebreen Member is gradual. In this case the base of the Morebreen Member is only FI,~.2. Stratigraphical scheme for the Permo-Carhomferoub indicated by the appearance of dolomites. Though succewon on Br~gpcrhdlvoya.Mgdificd after Cutbill 8; Chal- this might be a postdepositional characteristic, it linor {IW). is useful for mapping purposes. The thickness of Scheteligfjellet Member was estimated at 150 m by Challinor (1967) and 160m by Barbaroux Member. Morebreen Member. and Tyrrellfjellet (1967). This investigation shows lateral thickness Member (Cutbill & Challinor 1965; Challinor variations from a little over 10 m to 100 m. 1967). The type localities of the two lower members are situated on Broggerhalvoya. The Scheteligfjellet Member and the underlying Petrography and niicrofacies Broggertinden Formation together represent the The Scheteligfjellet Member displays significant Middle Carboniferous of Hrclggerhalvoya. facies variations between the different outcrops This investigation concentrates on the Schet- on Br@ggerhalv@ya. The successions can be eligfjellet Member and the establishment of mar- grouped into three facies associations: L, S, and ine environment on Broggerhalv~ya. 0 (Fig. 3). Their original relative position was changed by Tertiary thrust tectonics (Ludwig 1988). The Scheteligfjellet Member Facie5 associarion L. - This facies overlies a typi- cal succession of the uppermost Broggertinden L ith olog? Formation, which is characterized by alternating The Scheteligfjellet Member is a fossiliferous beds of bluegrey limestone, black calcrete - both limestone succession with locally intercalated sil- of intertidal origin (Ludwig 1989) - and coarse iciclastics and dolomites. alluvial fan conglomerates. Based on fossils Moscovian age was first pro- The Multithecopora Limestone forms the base posed for the Scheteligfjellet Member by Hol- of facies association L. This massive limestone is tedahl (1911. 1913). Challinor (1967) mapped characterized by layers with abundant Mu/- Broggerhalvoya using the stratigraphical scheme rirhecopora sp. (Fig. 4) and some single chal- of Cutbill & Challinor (1965) and described the cedony nodules with concentric structure and Scheteligfjellet Member. but he did not define its diameters of from 10 to 30 cm. Thin layers of red exact boundaries. jasper (4 to l0cm thick) with irregular lower For lithological and palaeoenvironmental and upper boundary surfaces occur between the reasons the base of a blue-grey limestone con- individual limestone banks. The Multithecopora taining abundant Multithecopora sp. probably Limestone shows the following microfacies: A The marine transgression in the Middle Carboniferous of BrgggerhalVQya (Svalbard) 67 1 Facies L Facies 5 Facies 0 Fig. 3. The three facies association of the Scheteligfjellet Member exemplified by three profiles of the Br~ggerhalv~ya crumbly micritic matrix containing echinoderms, In this facies association the Multithecopora brachiopods, bryozoans and corals (Multithec- Limestone is succeeded by thin dolomites and opora sp. and probably Caninia sp.) as coarse bituminous limestones, partly by a sparitic lime- sand-sized bioclasts (Fig. 5). The smaller-sized stone with fragments of echinoderms, bryozoans bioclasts are forams, pellets and Kamaena sp. and brachiopods that are well-rounded and (Buggisch, pers. comm.) (Fig. 6). Some whole sorted. The overlying laminated dark limestone ostracod shells also occur. contains a poor fauna dominated by ostracods. The brachiopods are dominated by productids Irregular laminae reflect the probable devel- which are mostly preserved as whole shells (Fig. opment of algal mats. The dark limestone is 7) which have been altered to red jasper. In overlaid by a massive arkosic litharenite showing addition the athyridine brachiopod Composita sp. thin layers with well-rounded sediment-pebbles. occurs (Fig. 8). It is succeeded by bituminous dolomitic mud- Most of the delicately branching multithec- stones with wavy lamination and with intercalated opores are altered to red jasper and are restricted red and green fine-grained sandstones (lithic to several intercalated thin horizons in the basal arkose). Silt-sized, angular quartz grains partly part of the Multithecopora Limestone. Small occur as thin layers in the laminated mudstone. sparitic particles with a lanceolate shape occur Besides scattered carbonaceous plant remnants, dispersed around their stems. These are probably ostracods and gastropods are the only fossils that calcitic elements into which the outer shells of the are found (Fig. 9). Irregular white nodules of multithecopores disintegrated. length-slow chalcedony are abundant. The multithecopores covered wide areas and Feldspars, though lacking in the underlying red built up colonies. They are associated with solitary beds of the Br~ggertindenFormation, make up a corals. No real bioherms are found, but small relatively high portion of the sandstones in the patch reefs, up to 20 cm in height, appear in thin Scheteligfjellet Member, and they show authi- horizons between the Multithecopora-bearing genic overgrowth. Facies association L shows layers. varying lithologies and its thickness varies from 68 P. Ludwig Fry J Bcds Hith .Llu/rirhPcoportr sp. in the lower part of the basal limestone (Multithecopora Limestone) of
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