FALK FM
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Generell informasjon Attributt Verdi Litostrat. enhet Den litostratigrafiske enhetens offisielle navn.FALK FMNPDID for litostrat. enhet Sokkeldirektoratets entydige nøkkel for litostratigrafiske enheter.36Nivå Angir den litostratigrafiske enhetens nivå. Lovlige verdier: GROUP, FORMATION, MEMBER.FORMATIONLitostrat. enhet, forelder Den litostratigrafiske enhetens offisielle navn, refererer til forelder. Se også nivå. Vil være tom hvis Nivå = GROUP. -
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Falk Formation
NameFrom the Norwegian name for a falcon (4 species, all belonging to the genus Falco, are found in northern Norway).DefinitionThe type section is defined in the interval from 2221 m to 2024 m (log depth) in well 7120/2-1 , on the Loppa High (Fig 9.20) ; Table 9.1). The base corresponds to 2225, 7 m in core depth (Fig 9.24) . The formational base reflects an abrupt change from non-marine, reddish brown conglomerates of the Ugle Formation to dark grey, marine shales and marks the first marine transgression in the area; this gives a log response characterised by a change toward overall lower readings on the gamma ray log as a result of the transition into carbonates (Fig 9.20) . The formation otherwise shows a noisy log pattern, reflecting the intercalation of siliciclastics and carbonates.Reference sectionsReference sections are found from 2150 m to 2050 m in well 7128/6-1 (Fig 9.25) . 2058 m to 1952 m in 7128/4-1 (Fig 9.26) . 498.6 m to 363.5 m in core 7029/03-U-02 (Fig 9.27) . and from TD at 481.7 m to 458 m in 7030/03-U-01 (Fig 9.28) . all located on the Finnmark Platform. In 7029/03-U-02 the base also represents an abrupt change in both colour and overall lithofacies from non-marine, red and green mottled silty shales to marine, greenish-grey, bioturbated silty shales. In wells 7128/4-1 and 7128/6-1 the formation corresponds to units L1 and L2 of Ehrenberg et al. (1998a).ThicknessThe formation is thickest in the type well (201.7 m); it is 135 m thick in 7029/03-U-02 on the southern Finnmark Platform and thins northwards to 100 m in well 7128/6-1 and 58 m in 7128/4-1 (Fig 9.19) . The formation is missing in 7226/11-1 where carbonates of the overlying Ørn Formation rest directly on basement, while wells 7124/3-1 , 7121/1-1 R , 7228/9-1 S and 7229/11-1 reached TD higher in the Gipsdalen Group .LithologyThe formation consists of a mixture of shallow marine sandstones, marine siltstones and shallow marine carbonates. In 7120/2-1 , the lower 51 m consists of stacked, less than 5 m thick rhythms of coarse-grained pebbly sandstone with minor shale and dolomite (Fig 9.24) . Trough cross-bedding and horizontal lamination is common. This lower development is overlain by a 125 m thick unit of rhythmically interbedded shales, fossiliferous dolomitic mudstones to packstones (locally with anhydrite or chert nodules), and fine- to medium-grained sandstones with a few pebbly sandstone beds. Crinoids, brachiopods, fusulinids, small foraminifers and corals are the most abundant fossils, together with occasional phylloid algae and palaeoaplysinid plates. In the lower part of core 7029/03-U-02 and in 7030/03-U-01, the Falk Formation consists of 1 to 5 m thick fining upward units of light grey, medium- to coarse-grained, pebbly, trough cross-bedded to planar-laminated sandstones grading upwards into laminated greenish silty shales. Each unit has a sharp and erosive lower boundary. Marine fossils are limited to very rare brachiopods. The upper part of the formation in 7128/6-1 and 7029/03-U-02 consists of cycles of fine- to very fine-grained sandstone, green silty shale and carbonate wackestones to boundstones (Fig 9.25), (Fig 9.27), (Fig 9.29).Lateral extent and variationThe base of the formation represents a major transgression of the platform areas as seen in 7120/2-1 from the Loppa High and in the Finnmark Platform wells 7128/4-1 7128/6-1 , and 7029/03-U-02, where marine siliciclastics overlie continental deposits or basement. The top of the Falk Formation is likely to be highly diachronous as it reflects the differing times when local siliciclastic source areas were drowned and the mixed siliciclastic-carbonate depositional system was replaced by carbonates. The formation is accordingly expected to be thickest in proximal platform areas and around tectonically active highs; thinnest developments are expected distally on the platforms, and either highly condensed or missing in the basins; these prognoses are supported by the gross wedge-shaped geometry of the formation seen on the Finnmark Platform. The formation is missing in areas that have been sheltered from siliciclastic supply, like the local high on the southern Bjarmeland Platform where well 7226/11-1 was drilled: in this location carbonates of the overlying Ørn Formation rest directly on basement .AgeStemmerik et al. (1995, 1998) suggested a late Bashkirian to early-middle Gzelian age based on fusulinid data. The formation is of late Bashkirian to Moscovian age in 7120/2-1 , where the lower part of the overlying Ørn Formation is dated as being of late Moscovian age (Stemmerik et al. 1998). The top of the formation in 7030/03-U-01 apparently coincides with the Kasimovian-Gzelian boundary whereas an even younger age is indicated in 7029/03-U-02 where the uppermost part of the formation extends into the early to middle Gzelian (Stemmerik et al. 1995; Bugge et al. 1995). In 7128/6-1 , the formation is of late Moscovian to early Gzelian age (Ehrenberg et al. 1998a).Depositional environmentsThe Falk Formation is characterised by sediments deposited as a response to high frequency and high amplitude fluctuations in sea level (see e.g. Stemmerik et al. 1998; Stemmerik & Worsley 2000). Deposition also took place during an overall rise in relative sea level in shallow shelf environments ranging from offshore silt-dominated to shoreface sand-dominated lithofacies during deposition of the lower part of the formation. Sediments in the upper part of the formation suggest that the relative sea level rise had by then flooded most platform areas so that lithofacies there are characterised by more fine-grained siliciclastic input, deposited in offshore to lower shoreface environments, and by subtidal carbonates. The presence of caliche indicates periods of subaerial exposure of the carbonates, and during sea level lowstands the platform areas apparently formed vast lowlands.CorrelationMixed siliciclastics and shallow marine carbonates are common in the lower part of the Gipsdalen Group in the onshore areas of Svalbard. The formation correlates to the Kapp Kåre and Kapp Hanna formations on Bjørnøya (Worsley et al. 2001; Stemmerik & Worsley 2000), perhaps to the uppermost red-bed Hyrnefjellet Formation and lower Treskelodden Formation in Hornsund, the Tårnkanten/Schleteligfjellet and lower Wordiekamen formations of western Spitsbergen, and the Minkinfjellet, Malte Brunfjellet, Hårbardbreen and lowermost Wordiekammen formations of central to eastern Spitsbergen and Nordaustlandet (Dallmann et al. 1999: (Fig 9.6) . In contrast to the offshore and most onshore areas, both Bjørnøya and Hornsund were characterised by significant syndepositional tectonism at the time.Possible membersNo formal members are proposed herein, but the work of Ehrenberg et al. (1998a) and seismic mapping on the Finnmark Platform indicates that the formation in this area may comprise two distinctive units (“L-1” and “L-2”) separated by a hiatus spanning the lower Kasimovian in well 7128/6-1 . This corresponds to a period of tectonic activity on Bjørnøya (Worsley et al. 2001). On a seismic scale, however, these two informal units appear to be conformable on the Finnmark Platform.Source-
Larssen, G. B., Elvebakk, G., Henriksen, L. B., Kristensen, S. E., Nilsson, I., Samuelsberg, T. J., Svånå, T. A., Stemmerik, L. and Worsley, D. 2002: Upper Palaeozoic lithostratigraphy of the Southern Norwegian Barents Sea. NPD-Bulletin No. 9, 69 pp.
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