Sequence stratigraphy of the inner Finnmark carbonate platform (Upper Carboniferous-Permian), Barents Sea- correlation between well 7128/6-1 and the shallow IKU cores

STEPHEN N. EHRENBERG, NEIL A. H. PICKARD, TORE A. SV ÅNÅ, INGER NILSSON & VLADIMIR l. DA VYDOV

Ehrenberg, S. N., Pickard, N. A. H., Svånå, T. A., Nilsson, 1., Davydov, V. 1.: Sequence stratigraphy of the ioner Finnmark carbonate platforrn (Upper Carboniferous-Permian), Barents Sea - correlation between well 7 128/6-1 and the shallow IKU cores. Norsk Geologisk Tidsskrift, Vol. 80, pp. 129--162. Oslo 2000. ISSN 0029-196X.

A new set of descriptions has been prepared for five of the IKU cores, a series of shallow stratigraphic cores penetrating the Upper Carboniferous-Permian Finnmark carbonate platform succession near its southern erosional truncation against the Norwegian mainland. These data are compared with core descriptions previously published from the thicker 'stratigraphic reference section' of the exploration well 7128/6- 1 (Ehrenberg et al. 1 998a). New fusulinid datings from 7 128/6- 1 are correlated with existing fusulinid data from the IKU cores to provide a consistent time-stratigraphic frarnework for landward correlation of depositional sequences previously defined in the 7 128/6-1 reference section. These correlations reveal a limited two-dimensional image of depositional sequence geometry for the ioner platform. Of the 7 major sequences previously defined in the Kasimovian through Upper Permian section of well 7 1 28/6- 1 , 2 sequences are suggested to pinch out before reaching the IKU cores, while the remaining 5 sequences thin by 32-{)3% and show landward loss of lithologic resolution of systems tracts. Thinning is probably accomplished by increasing magnitude and frequency of hiatuses both within and bounding each sequence, reftecting gradual uplift of the Norwegian mainland and seaward tilting of the platform throughout the depositional history. Landward changes in lithology, dolomitization, and porosity are relatively subtle, suggesting that platform deposition extended well beyond the present southern termination of carbonate strata.

S. N. Ehrenberg, Statoil, N-4035 Stavanger, Norway (e-mail. sne@statoil.com); N. A. H. Pickard, Cambridge Carbonates Ltd.,

Clematis Cottage, 41 Linthurst Newtown, Blackwell, Bromsgrove, Worcestershire, B60 1BP, UK (e-mail. Neil_Pickard@email.msn.com); T. A. Svånå, Statoil, postboks 40, N-9481 Harstad, Norway (e-mail. tasv@statoil.com); l. Nilsson, Saga Petroleum a.s., Pb. 490, N-1301, Sandvika, Norway (e-mail. Inger.Nilsson@saga.com); V./. Darydov, Permian Research Institute, Department ofGeosciences, Boise State University, 1910 University Drive, Boise, ID 83725, USA (e-mail. VDA VYDOV@boisestate.edu)

Introduction

The Finnmark carbonate platform consists of gently north­dipping strata that thin southward and are erosionally truncated just before reaching the Norwegian coastline (Bugge et al. 1995; Ehrenberg et al. 1998a). Stratigraphic sections through these entirely subsurface strata have been studied in two areas: (l) from a series of eight shallow bore hoies drilled for stratigraphic information by IKU Petro­leum Research (renamed SINTEF Petroleum Research in 1999) near the present southern edge of the platform and (2) in exploration wells 7128/6-1 and 7128/4-1, approxi­mately 30 km north of the southern erosional truncation trend (Fig. 1). The IKU cores are numbered as follows (Fig. 1): 7127110-U-02, 7127/10-U-03, 7128/12-U-01, 7129/10-U-01, 7129/10-U-02, 7029/03-U-01, 7029/03-U-02, and 7030/03-U-01. Each core penetrates a different stratigraphic interval of the Upper Paleozoic succession, and these intervals have been assembled into a composite section using seismic, lithologic and biostratigraphic evidence (Elvebakk et al. 1990; Stemmerik et al. 1995;

Bugge et al. 1995). The same units have also been described in well 7128/6-1, where almost the entire platform stratigraphy was recovered by continuous coring (Fig. 2; Ehrenberg et al. 1998a). Supplementary core coverage has also been studied from well 7128/4-1, as described in Ehrenberg et al. (1998a, 1998b ).

These two near1y completely cored stratigraphic sec­tions represent considerable investments toward exploring one of Europe's major remaining frontier hydrocarbon provinces. The IKU cores were recovered in 1987-88 with funding from a consortium of oil companies to gain solid information about the then poorly known Upper Paleozoic rocks of the Barents Sea. The unusually comprehensive coring programme for Conoco's well 7128/6-1 was carried out in 1991 at the insistence of the Norwegian Petroleum Directorate, not just for the purpose of evaluating the PL 181 licence, but also to provide a stratigraphic reference section through the thicker platform strata further north of the IKU locations. Now, full y eight years after recovery of the Conoco cores, we present the first detailed correlation and comparison of these two core sets. However, this

130 S. N. Ehrenberg et al.

Fig. l. Map showing locations of cores studied and boundaries of present and former areas licenced for hydrocarbon exploration. Land areas are shown in black. Dashed lines are thickness contours (meters) for the carbonate platform succession (units L-l through L-9) interpreted from seismic data for part of the area shown. Zero-contour and fault trace mark southern termination of Paleo­zoic strata. Filled circles indicate cores in Upper Carboniferous-Permian carbo­nates. Open circles indicate cores in Lower Carboniferous siliciclastics.

report concems only the Upper Carboniferous-Pennian carbonate-dominated part of the succession. The under­lying Visean siliciclastic interval (cored in 7127/10-U-02, 7127/10-U-03, and 7029/03-U-01) is discussed only insofar as it is relevant to understanding porosity devel­opment in the carbonate strata.

Correlation and interpretation of the 7128/6-1 and IKU cores are important to hydrocarbon exploration for several reasons. Such extensive core coverage of potential reservoir and seal rocks is not available elsewhere in this province, and documentation of the relationship between these two sample sets is fundamental to their further utilization, for example, as a statistical basis for predicting porosity and permeability distributions within specific units or lithofacies. The most obvious use of the present investigation of stratal geometries is for evaluating the reservoir and seal potential for possible petroleum traps along the southward termination of the carbonate succes­sion against the Norwegian-Russian mainland. However, the present results should also be useful to seismic studies throughout the region. Detailed core information about lateral variability within specific depositional units repre­sents the only secure starting-point from which to approach the uncertainties involved in assigning geologic interpreta­tions to seismic images.

An improved basis for correlation was recently provided by a new fusulinid biostratigraphic study of well 7128/6-1, carried out by V. l. Davydov in 1998 for the recently

NORSK GEOLOGISK TIDSSKRIFT 80 (2000)

relinquished Norwegian production licence PL 181. The basis for correlation has been further strengthened by a new set of descriptions of the IKU cores, which are presented in Appendix l in the same format as that used for the 7128/6-1 core descriptions in Ehrenberg et al. (1998a). These core data panels are based on both macroscopic core descriptions and standardized descriptions of a set of thin sections and polished slabs prepared at fixed one-meter spacing throughout the IKU cores.

In this paper we present descriptive representations of the ioner platform stratigraphy at three different levels of geologic interpretation:

l. Appendix l shows data panels for the IKU cores, including gamma ray profile; fusulinid zones; micro­facies; high-frequency cycles; calcite/dolomite ratio; plug porosity measurements; and numerical scores for key bioclast abundances. Similar panels for the 7128/6-1 and 7 128/4-1 cores are found in Appendix l of Ehrenberg et al. (1998a).

2. Figures 3-7 show correlations between the core-data panels at reduced scale, each figure corresponding with one or two of the seven major depositional sequences interpreted to be present.

3. Figures 8-12 are schematic, dip-oriented cross-sections of the above sequences at an even more reduced scale, showing interpretations of facies relationships.

Based on these graphic representations, we compare the stratigraphy and porosity of the exploration cores and the IKU cores and discuss the causes and significance of the variations observed.

Setting The geological setting has been described in Ehrenberg et al. (1998a), but some additional information is necessary in order to characterize the relationship between the explora­tion wells and the IKU cores. Seismic data show that the carbonate platform strata thicken gradually northward from the IKU locations (Fig. 3 in Ehrenberg et al. 1998a). The Upper Carboniferous-Permian succession is 256 m thick in the IKU composite section (Figs. 3-7), 527 m thick in well 7128/6-1, and 1100-1300 m thick near the northem margin of the platform, adjacent to the Nordkapp Basin. At their southem limit, the platform strata are eroded and overlain by Pleistocene/Quatemary or locally tenninated by faulting (Fig. 1).

Because the IKU cores represent a range of locations spread over a subcrop trend some 85 km long (Fig. l), they show certain variability in structural and stratigraphic setting. In particular, the cores further to the southeast penetrate a thicker Gzhelian-Asselian carbonate section than is present due south of well 7128/6-1. A seismic line through the latter area is shown in Fig. 3 of Ehrenberg et al. (1998a), and seismic sections comparing the two areas are shown in Figs. 4 and 11 of Bugge et al. (1995).

NORSK GEOLOGISK TIDSSKRIFT 80 (2000)

7 1 28/6-1 Age

Griesbach.

Lt. Perm.­?Kung.

lt. Artinsk.

e. Artinsk.

Upper Paleozoic carbonates, Barents Sea 131

I KU Cores

?Tat.-Kaz. ?Kung.-Ufim. Artinsk. Sakmar.

lt. Assel.

It. Sakmar.

==�:.::.:.;��::....:..:.:.:..J.:=��;;;..:=.:..:.J J e. Sakmar.

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=--------k��=-----L-��:_J J m. Assel.

Lithostratigraphic unit boundary

Base-level rise

- Sequence boundary

Base-level fall

Maximum-flooding surface

Fig. 2. Corre1ation between well 7 128/6-1 and a composite stratigraphic section assemb1ed from 4 of the IKU cores. Previous1y defined sequence stratigraphy and age determinations are shown for well 7 1 28/6-1 (Ehrenberg et al. 1 998a).

In the present study, we follow the example of Bugge et al. (1995) in treating the IKU cores as a composite stratigraphic section (as if they were a single location), although we are well aware that there are significant variations along strike. This lateral variability is portrayed in Figs. 3-7 to the extent that the different IKU cores overlap stratigraphically, but the main component of stratigraphic variation is believed to be dip-oriented, as represented by comparison between 7128/6-1 and the individual IKU cores.

Biostratigraphy

The fusulinid zones recognized in well 7128/6-1 are listed in Appendix 2 and suggested correlations to Russian zones from the Ural Mountains and Moscow Basin and to previously reported zones in the IKU cores are noted (Nilsson 1993; Bugge et al. 1995). Appendix 2 is based on a new set of 79 fusulinid-bearing samples from well 7128/

6-1 which were collected by L Nilsson and analyzed by V. L Davydov. This represents a partial revision of previous 7128/6-1 fusulinid biostratigraphy by Nilsson (1992), Wahlman et al. ( 1995), and Groves & Wahlman ( 1997). Dating of the IKU cores is based on fusulinid biostrati­graphy by Nilsson (1993), which was summarized in Bugge et al. (1995). Nilsson defined seven fusulinid zones in the carbonate-dorninated Kasimovian-Artinskian suc­cession. Re-evaluation of these data during the present study shows that several of Nilsson's (1993) zones can be subdivided to provide more detailed correlation to the 7128/6-1 section. Individual fusulinid sample locations in the IKU cores are shown in Appendix l, and the extent of each zone is indicated in Figs. 3-6.

Lithostratigraphy

In well 7128/6-1 , Ehrenberg et al. (1998a) defined nine lithostratigraphic units (L-l to L-9) which were interpreted

132 S. N. Ehrenberg et al.

as comprising seven main depositional sequences (S-1 to S-7) and numerous smaller transgressive-regressive cycles. Based on the new biostratigraphic data from well 7128/6-1 (Appendix 2) and the new descriptions of the IKU cores (Appendix 1), this chapter discusses the probable correlations of the 7128/6-1 lithostratigraphic units to the IKU cores. New lithostratigraphic nomencla­ture has been proposed for these Upper Pa1eozoic strata by Larssen et al. (1999), including the Gipsdalen Group (units L-1 through L-7), the Bjarmeland Group (unit L-8), and the Tempelfjorden Group (unit L-9). The term 'buildup' is used in this paper to refer to Palaeoaplysina-phylloid algae-dorninated lithologies in the sense defined in Ehrenberg et al. (1998a).

L-1 (late Moscovian)

The correlative equivalent of this unit has not been identified in the IKU composite section. Unit L-1 may be represented in the IKU cores either by a hiatus or by the uppermost part of the poorly dated middle Carboniferous seisrnic unit (106--119 m in 7029/03-U-02; Bugge et al. 1995), consisting of nearshore-marine siltstones and sandstones. However, southward pinch-out of unit L-1 is supported by seisrnic data (see Fig. 3 in Ehrenberg et al. 1998a).

L-2 and L-3 (Kasimovian-late Gzhelian)

In well 7128/6-1, unit L-2 begins with a 25 m megacyc1e having a pronounced upward-decreasing GR profi1e and corresponding upward-shoaling facies progression (from basal shale, through bioclast-rich siltstones/silty wacke­stones, to a capping phylloid algae-Palaeoaplysina build­up ). This basal megacycle possibly correlates with the lowermost buildup interval and underlying siliciclastics in 7029/03-U-02 and 7030/03-U-01, as suggested in Fig. 3 by the first correlation line a bo ve the 'S-1' surface.

The upper part of unit L-2 in 7128/6-1 consists of 6 cycles of shale overlain by wackestone to calcareous siltstone. This interval is tentatively correlated with intervals of siltstone, dolomitic mudstone, and Palaeo­aplysina bui1dups in the two IKU cores which penetrate Gzhelian strata (Fig. 3). The marked lateral facies changes indicated by this correlation are suggested to reftect localized accumulation of lobate siliciclastic deposits around points of sediment inftux, as discussed further under sequence S-2 below.

Unit L-3 in 7128/6-1 consists of silty dolomitic mudstones with thin interbeds of various limestone lithologies. The general position of unit L-3 in the IKU cores is recognized based on lithology (thinly bedded siliciclastics and dolornitic mudstone) and GR profile (widely ftuctuating GR overlain by a blocky, low GR interval equivalent to L-4). The fusulinid assemblage at 66 m in 7029/03-U-02 indicates correlation of the buildup at 66--70 m with the lower part of unit L-3 in 7128/6-1, a possible seaward equivalent of the buildup being the thin

NORSK GEOLOGISK TIDSSKRIFT 80 (2000)

buildup and bryozoan wackestone beds at 2041-2044 m in 7128/6-1. Correlation of the lower contact of L-3 is suggested by the upper dashed line in Fig. 3.

L-4 (late Gzhelian-early Asselian)

Unit L-4 in well 7128/6-1 consists mainly of alternating buildups and dolornitic wackestones. The interval correla­tive with unit L-4 is identified in the IKU cores based on fusulinid zones 9-13. In 7128/6-1, the lower three of these fusulinid zones (9, 10 and 11) are recognized in samples from three successive intervals of high GR activity, corresponding with the transgressive bases of high­frequency cycles (Fig. 4). Sirnilar cyclic alternation of thin high-GR and thicker low-GR intervals is also apparent in the IKU cores, but exact correlation of these intervals to the 7128/6-1 cycles is uncertain.

The top of L-4 in the IKU cores is constrained by fusulinid zone 12, recognized as correlating 'exactly' between the uppermost L-4 buildup in 7128/6-1 and the second-to-uppermost buildup in 7030/03-U-01 (Fig. 4). Based on the above constraints, the lower part of L-4 in the IKU cores is seen to be buildup-rich, similar to its equivalent interval in 7128/6-1, while the upper part of L-4 (above the anhydrite bed) consists mainly of dolornitic wackestones with subordinate, thinner buildups.

Based on the evidence of fusulinid zone 10, which encloses the anhydrite bed in core 7030/03-U-01, the anhydrite is correlated to the interval of Palaeoaplysina buildups just above 1976 m in 7128/6-1 (Fig. 4). A possible explanation for this anhydrite bed is that it formed by restriction of a shallow lagoon behind a barrier formed by the 7128/6-1 buildups.

L-5 (middle Asselian)

Unit L-5, containing only fusulinid zone 13, corresponds to a relatively thin wackestonelbuildup interval in the IKU cores (Fig. 4). This interva1 lacks the thinly bedded dolornitic mudstones that characterize the upper part of unit L-5 in 7128/6-1, suggesting that these proximal shelf facies (hypersaline lagoon to sabkha) either terminate at a paleoshoreline or were erosionally truncated somewhere between the 7128/6-1 and IKU locations, as suggested by the dashed correlation line in Fig. 4.

L-6 (middle Asselian-early Sakmarian)

Unit L-6 of well 7128/6-1 is recognized in the IKU cores based on the occurrence of fusulinid zone 14 at the base of L-6 and the presence of the basal-L-7 calcareous shale beds immediately overlying the top of L-6 in 7129/10-U-02 (Fig. 5). As in the cores from 7128/6-1 and 7128/4-1, unit L-6 in the IKU cores is highly variable in composition, being made up mainly of packstones in 7030/03-U-01 and mainly of buildups, mudstones, and wackestones in 7129/ 10-U-02.

NORSK GEOLOGISK TIDSSKRIFT 80 (2000)

7128/6-1

7

5

l l

l

5-6 l

l l

l 4-5

l

Upper Paleozoic carbonates, Barents Sea 133

7029/03-U-02 7030/03-U-01

LEGEND:

Fig. 3. Stratigraphic correlations for cored intervals corresponding with sequence S-2. Inset shows column headings (see Appendix l for further details). Dashed

lines indicate suggested correlations consistent with lithology and dating constraints. The extent of 7128/6-1 fusulinid zones (Appendix 2) and probable equivalents in the IKU cores are shown by brackets and numbers along left side of each section.

L-7 (early-late Sakmarian) calcareous shales), overlain by a series of thin, poorly differentiated packstone/grainstone cycles. In 7129/10-U­

Unit L-7 in wells 7128/6-1 and 7128/4-1 consists of two 02, the two shale-rich basal cycles are clearly recognizable prominent basal cycles (major transgressions, expressed as based on both lithology and fusulinid zones 16 and 17, but

134 S. N. Ehrenberg et al. NORSK GEOLOGISK TIDSSKRIFT 80 (2000)

7030/03-U-01

15

-------------- S-3--�--------���--

----------

...............

7029/03-U-02

LEGEND:

Ill c. .8 +'

·c: :l

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Fig. 4. Stratigraphic correlations for cored intervals corresponding with sequence S-3. The three solid correlation lines between the S-2 and S-3 boundaries represent

correlations best consistent with fusulinid constraints. The dashed line suggests landward pinch-out of the dolomitic mudstone portion of unit L-5 of well 7128/6-l.

NORSK GEOLOGISK TIDSSKRIFT 80 (2000) Upper Paleozoic carbonates, Barents Sea 135

7128/6-1 7129/10-U-02

l

l

l l

l

l 16

LEGEND:

Fig. 5. Stratigraphic correlations for cored intervals corresponding with sequence S-4.

the upper packstone/grainstone portion of L-7 is entirely lacking (Fig. 5).

L-8 (late Sakmarian-late Artinskian/?Kungurian)

Unit L-8 in well 7128/6-1 consists of 89 m of bryozoan-echinoderm grainstone and packstone with subordinate wackestone, displaying a large-scale trans­gressive-regressive pattern. The lower part of L-8 has a distinctly transgressive development (upward-fining) in 7128/6-1, but consists entirely of grainstone with subordinate thin beds of shaly siltstone to sandstone in 7129/10-U-02, thus showing a more proximal develop­ment (Fig. 6). A thin shale at 1813 m in 7128/6-1 represents maximum flooding within unit L-8. This shale may correlate with siliciclastic-rich beds at either 36 m or 49 m in 7129/10-U-02.

There appears to be a major hiatus in core 7129110-U-02 somewhere between 30-36 m, as indicated by omission of the early Artinskian fusulinid zone 20 and possibly also 19. The upper 11-10 m of L-8 was cored in 7128/12-U-01 and 7129110-U-01 (fusulinid zone 21), where a darkened, pyrite-mineralized zone underlying the top surface is even more prominently and thickly deve1oped than in 7128/6-1. The thickness of the Sakmarian-Artinskian seismic unit in the area of the IKU cores (equivalent with unit L-8) is estimated by Bugge et al. (1995, p. 10) to be about 45 m, which is the thickness obtained by placing the cored intervals of 7129110-U-02 and 7128/12-U-01 on top of one another (Fig. 6).

L-9 (?Kungurian-Late Permian)

In cores 7128/12-U-01 and 7129/10-U-01, the equivalent

136 S. N. Ehrenberg et al. NORSK GEOLOGISK TIDSSKRIFr 80 (2000)

7128/6-1 7129/10-U-02 l 7128/12-U-01

L-

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o ' g:

>++-<-t-+1111fflffitt1t ;:::

LEGEND:

to the 7128/6-1 unit L-9 can be subdivided into four main lithologic zones (Appendix l, panels 8 and 9). These zones include three lithologies that were not previously described in the microfacies system of Ehrenberg et al. (1998a), necessitating the definition of new microfacies categories MF-13, MF-14, and MF-15 (Appendix l legend).

Zone l: silty shale with glauconite ooids. - Overlying the pyritized top of L-8, there is a basal zone (10-9 m thick) of silty, sandy shale containing a diverse

Fig. 6. Stratigraphic correlations for cored intervals corresponding with sequence S-5.

assemblage of horizontal burrows. In 7128/12-U-01, this zone contains a lower bed of glauconite-ooid sandstone (MF-14), and the ooids decrease in abundance upwards into the overlying silty shale. At the top of the silty shale (139.36 m), there is a thin conglomerate consisting of silty shale clasts in a shaly matrix. The conglomerate grades upwards into bioclast-rich silty shale and thence into the overlying limestone. In 7129/ 10-U-01, similar lithologies are present, except that the lower 1.5 m is a bed of shaly, fine-grained, sandstone

NORSK GEOLOGISK TIDSSKRIFT 80 (2000)

lacking ooids, and the top meter of the silty shale zone consists of glauconite ooids and large brachiopods in a silty shale matrix.

lime 2: bryozoan limestone. - The ooid-bearing siltstone is overlain by a zone (14-8 m thick) of coarse-grained bryozoan packstone and wackestone containing distinctive ramose bryozoans up to l cm in diameter (MF-13). Echinoderms and brachiopods are subordinate compo­nents, along with rninor calcite spicules and forarninifera. Most samples have a shale matrix containing rninor silt, but some samples have a matrix of silica-spicule pack­stone. This zone has an upward-decreasing GR profile indicative of progradational development.

lime 3: phosphorite. - In both cores, the limestone zone is sharply overlain by an extreme GR peak, which was cored only in 7129/10-U-01. Here the GR peak corresponds with an 0.8 m-thick bed of dark brown phosphorite (MF-15) overlain by a 1.2 m-thick bed of dark brown, collophane­cemented sandstone with sand grains consisting mainly of phosphorite, glauconite, and bioclasts (MF-14 ). The phosphorite has brecciated to nodular fabric and consists of large (0.05-0.4 mm diameter) spicule molds, variably oxidized glauconite ooids and pellets, and rninor quartz sand in a brown collophane matrix. The main part of this bed is phosphatized spiculite, but spicule molds become subordinate to glauconite ooids and pellets near the upper and lower boundaries.

lime 4: spiculite. - In 7129/10-U-01, the phosphorite bed is overlain by glauconite sandstone, presumed to mark the base of the Triassic siliciclastic interval. In 7128112-U -0 l, the extreme GR peak is overlain by a 6-m interval, the cored upper 3.4 m of which is pale grey to white, porous spiculite sirnilar to that cored in the upper L-9 cycle in 7128/4-1. The upper part of the cored interval (above 119.5 m) contains abundant glauconite pellets, rninor quartz sand, and phosphorite clasts and nodules.

In wells 7128/6-1 and 7128/4-1, unit L-9 is divisible into two cycles of upward-decreasing GR profile. The lower L-9 cycle consists of silty argillaceous mudstone overlain by calcareous, extremely fine-grained spiculite. The upper L-9 cycle consists of coarser-grained, nearly pure-silica spiculite containing major seisrnic anomalies interpreted as banks of coarse bioclastic limestone. One of these banks, 50 m thick, was penetrated in 7128/4-1 (Fig. 7), while 7128/6-1 is located off the margin of (but does not penetrate) another bank, as identified by seisrnic data.

Figure 7 illustrates one of several possible correlation solutions between the exploration wells and the IKU composite stratigraphic section. According to this model, the lower cycle of unit L-9 in the exploration wells pinches out before reaching the IKU core sites, where only the upper L-9 cycle is represented. The basal extreme GR peak of the exploration wells is suggested to thicken

Upper Paleozoic carbonates, Barents Sea 137

landward to correlate with lithologic zone l of the IKU cores, while the extreme GR peak of the IKU cores (phosphorite of Zone 3) is correlated with an assumed surface of submarine erosion or condensed sedimentation at the top of the limestone bank in 7128/4-1. An alternative viewpoint is that correlation should be based on assurning equivalence between the extreme GR peaks in the exploration wells and the IKU cores, in which case the bryozoan limestone of the IKU cores would be part of the lower L-9 cycle.

As in the exploration wells (Ehrenberg et al. 1998b ), an unresolved question is whether the top of unit L-9 in cores 7128112-U-01 and 7129110-U-01 was subaerially exposed before deposition of the overlying lowermost Triassic siliciclastics. The pronounced southward thinning of unit L-9 could result from either subaerial erosion or a combination of depositional condensation and submarine erosion. Fabrics observed in the IKU cores through this contact, described in the following paragraphs, are ambiguous regarding this question because they could indicate either meteoric or submarine diagenesis.

In 7128/12-U-01, the cored interval extends for 3.7 m into the spiculite underlying the basal Triassic silty shale. The color of the spiculite changes from pale grey in the lower 1.4 m of the core to light grey to green in the upper 2.3 m (the green color corresponding to clay-rich lenses and burrows). The uppermost 0.4 m of the spiculite was highly disrupted during coring, almost to rubble, possibly indicating a brecciated fabric. Except for this upper zone of questionable fabric, the underlying 3.3 m appears to be non-reworked spiculite with a nodular, deformed fabric refiecting early cementation and compaction.

In 7129/10-U -0 l, the base-Triassic contact is assumed to correspond with the top of a bed of dark brown, collophane-cemented sandstone 1.0 m thick, whose upper contact is thinly larninated and gradational over 0.2 m into the overlying medium-brown silty shale. Absence of the spiculite (Zone 4) above the phosphorite could indicate subaerial erosion or submarine erosionlcondensation. Bugge et al. (1995) interpret the top of the phosphorite as a subaerial exposure surface, but the large fissure in this surface and the reworking of phosphorite clasts into the overlying sandstone bed (64.5-65.7 m) could altematively be attributed to entirely submarine exposure.

Depositional sequences

Sequence stratigraphic terrninology used in this paper is the same as that explained in Ehrenberg et al. (1998a). In that paper, a one-dimensional sequence stratigraphic model (Fig. 2) was proposed for the Upper Carbonifer­ous-Perrnian succession, based on cyclic pattems of lithofacies variation observed in core and wireline logs from 7128/6-1 and 7128/4-1. In this section, we use this model as o ur frame of reference and attempt to identify the locations of the correlative sequence boundaries in the IKU cores based on a combination of biostratigraphic con-

138 S. N. Ehrenberg et al.

7128/4-1

L-9

\ \ \ \ \ \ \

L-

\ \ \

7128/6-1 7128/12-U-01

NORSK GEOLOGISK TIDSSKRIFT 80 (2000)

7129/10-U-01

Fig. 7. Stratigraphic correlations for cored intervals corresponding with sequences S-6 and S-7. Dashed correlation lines represent a suggested correlation sol uti on,

discussed in the text. Dashed portions of the lithology column in wells 7128/4-1 and 7128/6-1 (lower part of upper L-9 cycle) show lithology of uncored intervals,

as interpreted from side-wall cores. Circled numbers in the IKU sections indicate lithology zones defined in text.

NORSK GEOLOGISK TIDSSKRIFT 80 (2000)

straints and patterns of lithologic vanat10n. W e have considered whether revision of the previous sequence stratigraphic model is indicated by the IKU core data, but have found no obvious inconsistencies. Thus, the data from IKU cores do not seem to require the definition of any additional sequences not present in the 7128/6-1 section, although several of the sequences defined in 7128/6-1 may not be present in the IKU cores (S-1 and S-6). The alternative approach of attempting to define depositional sequences in the IKU cores independently of the 7128/6-1 data seems inadvisable because of the lesser stratigraphic resolution in the IKU cores. Furthermore, it is unlikely that the IKU cores contain any significant time-stratigraphic units not represented in the exploration wells, because a nearly complete and continuous record of Late Carboni­ferous to mid-Permian time is indicated in the 7128/6-1 cores by the technique of graphic correlation of fusulinid data (V. I. Davydov, unpublished results). A number of major hiatuses are, however, to be expected in the IKU composite section because of its landward position and lesser thickness.

In 7128/6-1, the carbonate platform (post-Visean) succession is divisible into two largest-scale depositional sequences (Fig. 2) spanning late Moscovian to Late Permian time (47-62 million years, according to the time-scale of Harland et al. 1990). These have individual age constraints indicating durations of 15-23 m.y. (late Moscovian-middle Asselian) and 28-43 m.y. (middle Asselian-Late Permian), respectively (see Table 4 in Ehrenberg et al. 1998a) and are thus 'second-order' (10-100 m.y. duration) 'supersequences' according to the terminology of Goldhammer et al. (1991). Each super­sequence includes 3-4 higher-order 'major sequences' (designated S-1 through S-7; Fig. 2) having average durations of 7-9 m.y., but with widely varying individual age constraints (<1-22 m.y.; Table 4 in Ehrenberg et al. 1998a). These are thus approximately 'third-order' sequences (1-10 m.y. duration; Goldhammer et al. 1991). However, it is debatable whether these 'major sequences' should be regarded as composite 'sequence sets', each including several component third-order sequences, or whether the higher-order cyclicity is best regarded as forming 'parasequence sets' (Van Wagoner et al. 1990).

The present interpretations of the locations of sequence boundaries in the IKU cores are based largely on the fusulinid correlations to the 7128/6-1 section. Facies relations and variations in cycle thickness in the IKU cores have been used to estimate the exact locations of these boundaries within the broader biostratigraphic constraints. It is not surprising that the sequence bound­aries of the present study differ from the five sequence boundaries defined by Stemmerik et al. (1995) for the Gzhelian-Asselian interval in 7030/03-U-01 and 7029/03-U-02, since the latter were based entirely on evidence from the IKU cores. Even so, SB l and SB4 from that study do coincide approximately with the tops of the present sequences S-2 and S-3, respectively.

Upper Paleozoic carbonates, Barents Sea 139

The obvious questions deriving from this work concern the nature of the sequences further seaward from the exploration well locations and indeed the fundamental characteristics of the platform profile and facies-belt structure during the successive stages of its evolution. The schematic facies pro files in the lower parts of Figs. 8, 9, 11, and 12 are intended to show general relationships between lithology, water depth, and landward proximity. However, the spatial dimensions of these proximal-to­distal transitions reflect the largely unknown paleotopo­graphic profile of the platform within any given time interval.

High-frequency cycles

In the present study, correlation of individual high­frequency cycles is not attempted between the 7128/6-1 and IKU sections, or even between different IKU cores, because of the considerable uncertainties involved. To begin with, experience from exposures of equivalent-age strata from Svalbard indicates that the number of high­frequency cycles recognizable in any one-dimensional ( core) view is a minimum compared to the number recognizable in outcrop. Thus lateral correlation of cycles, even between closely spaced sites, is likely to result in errors, because of missing or unrecognized cycles in each location.

A second uncertainty derives from the problem of identification of sedimentary cycles in core. Some of the cycles defined in Appendix l appear to be clearly developed and are readily recognized, while others are ambiguous owing to variations such as amalgamation or partial truncation. Ideally, cycles begin with a basal siliciclastic bed representing aeolian or fluvial transport of sand or silt across the exposed shelf during lowstand, followed by marine reworking during subsequent trans­gression. The overlying zone of carbonate to shale records the maximum water depth of the cycle and passes upwards into a top zone of shallower carbonate deposition representing highstand. The ideal cycle is then terminated by a surface of subaerial exposure, although compelling evidence for exposure is rarely available in the cores. For example, only a single occurrence of the soil feature Microcodium has been found in the IKU cores. This is, however, a very well-developed occurrence, with Micro­codium abundance increasing upwards toward the brec­ciated top surface of the Palaeoaplysina buildup at 98-100 m in 7129/10-U-02 (unit L-6).

Sequence S-1 (late Moscovian)

This interval (equivalent with unit L-1) is probably lost landward of 7128/6-1 because of erosion at the S-1 sequence boundary. This truncation reflects the waning tectonism following mid-Carboniferous (roughly Serpu­khovian-Bashkirian) rifting that is otherwise indicated by the pronounced thickness variations observed in the

140 S. N. Ehrenberg et al. NORSK GEOLOGISK TIDSSKRIFT 80 (2000)

o

L-

L-

L-1 100

distal shelf buildup hypersaline lagoon sabkha trend \\�� � � � Fig. 8. Facies model for sequence S-2

between well 7128/6-1 and the IKU

composite stratigraphic section,

represented by core 7029/03-U-02.

Calcareous

Silty shale siltstone and Silty Dolomitic

sandstone wackestone Buildup mudstone

V ertical scale is shown by tick marks at

l O m intervals along right edge. Horizontal distance between core sites is 77 km (Fig. l). However, insofar as these sites are regarded as representing

generalized distal and proximal positions on a dip-section of the inner platform, the lateral scale is roughly 30 km. The depositional profile below the geologic cross-section shows schematic relationships of facies beits to water depth and shoreline proximity. --�-

seismic unit equivalent to unit L-1 ( see Fig. 3 in Ehrenberg et al. 1998).

Sequence S-2 ( Kasimovian-middle Gzhelian)

S-2 is defined in well 7128/6-1 based on the transition from re1ative1y deep-water shale/silty-wackestone/buildup cycles (unit L-2) upward into thin, dolomitic-mudstone­dominated cycles (unit L-3). In the IKU cores, there is a similar upwards facies transition in the approximately age­equivalent section: from buildup-dominated cycles into an overlying zone of dolomitic mudstone and sandstone (Fig. 8). The base of sequence S-2 is placed at the erosional unconformity inferred by Bugge et al. (1995) to be at 106 m in 7029/03-U-02 based on seismic data and the presence of conglomerate beds. The top of S-2 is placed at the top of the dolomitic mudstone interval (54 m in 7029/ 03-U-02 and 122 m in 7030/03-U-01).

Sequence S-2 is approximately 32% thinner in the IKU locations, which could reftect both northward-increasing subsidence and strike-oriented variations in the continuity of local siliciclastic packages. S-2 is characterized by

mixed siliciclastic-carbonate sedimentation. Upwards­increasing carbonate content in the L-2 cycles is explained in terms of a system of deltaic siliciclastic lobes with intervening areas dominated by shallow-water carbonate production. Upon lobe abandonment, the carbonate envir­onments expanded across the tops of the upward-coarsen­ing siliciclastic intervals (Santisteban & Tabemer 1988). Grainstone shoals appear to have been poorly developed in this system, in contrast to the following (S-3) siliciclastic­poor deposits.

Sequence S-3 (late Gzhelian-middle Asselian)

In 7128/6-1, the base of sequence S-3 corresponds approximately with a marked decrease in siliciclastic supply and corresponding GR activity, reftecting termina­tion of local tectonism. This siliciclastic decrease is also evident in the GR profiles of the IKU cores (Fig. 2), where the S-2 sequence boundary has been correlated based on the transition from sandstone and dolomitic mudstone (unit L-3) into the overlying section of subtidal buildup/ wackestone cycles (Figs. 3, 4).

NORSK GEOLOGISK TIDSSKRIFT 80 (2000)

Fig. 9. Facies model for sequence S-3 between well 7128/6-1 and the IKU

composite stratigraphic section, represented by core 7030/03-U-01. Vertical scale is shown by tick marks at

10-m intervals along right edge. Horizontal distance between core sites is 105 km (Fig. l). However, insofar as !hese siles are regarded as representing generalized distal and proximal positions on a dip-section of the inner platform, the lateral scale is roughly 30 km. The three correlation lines between the S-2 and S-3 boundaries are supported by fusulinid datings (Fig. 4). The dashed

line suggests landward pinch-out of the upper, dolomitic mudstone portion of unit L-5. The depositional profile below

the geologic cross-section shows schematic relationships of facies beits to water depth and shoreline proximity.

distal shelf

Fusulinid wackstone

In well 7128/6-1, the aggradational (transgressive) and progradational (highstand) components of sequence S-3 are recognized based on the upward transition from buildup/wackestone cycles (unit L-4) first into packstone/ grainstone beds (lower L-5) and then finally into thin dolomitic-mudstone cycles (upper L-5). In the IKU cores, the base of S-3 is identified based on lithology, as described in the preceding paragraph, and the top of S-3 is constrained by biostratigraphy (it must Iie somewhere between fusulinid zones 13 and 15 in 7030/03-U-01; Fig. 4).

According to these correlations, S-3 thins by approxi­mately 33% toward the IKU locations. The lower part of S-3 contains thick Palaeoaplysina buildups in the IKU cores, while the central to upper portion consists mainly of dolomitized wackestone, probably representing lagoonal settings restricted by barriers formed by the buildups of the 7128/6-1 section (Figs. 4, 9). The upper dolomitic mud­stone interval of S-3 (upper unit L-5) is interpreted as pinching out landward of the 7128/6-1 location.

Upper Paleozoic carbonates, Barents Sea

buildup trend

sand shoal

Foram/algal Buildup packlgrainstone

� lill

Dolomitic mudstone

141

By middle Asselian time (unit L-5), grainstone shoals begin to be represented as a prominent component of the facies system. These may well have become prominent as early as in late Gzhelian (base of sequence S-3), but are poorly represented in the core locations because of the relative! y landward displacement of facies beits during the transgressive portion of S-3 development.

Sequence S-4 (middle Asselian-early Sakmarian)

S-4 is defined in well 7128/6-1 based on the transition from a mildly retrogradational interval of packstone/grainstone cycles (unit L-6) upward into two major shale-based cycles representing maximum flooding (lower L-7) and finally into a progradational series of grainstone-rich cycles with occasional buildups and sandstone beds (upper L-7). Information on the strike-oriented variability of S-4 is provided by 51 m of core, covering nearly all of units L-6 and L-7 in well 7128/4-1, 26 km west of well 7128/6-1, as described in Ehrenberg et al. (1998a, 1998b ).

142 S. N. Ehrenberg et al.

L·7

L·6

In the IKU cores, the base of S-4 is constrained by fusulinid zones 14 and 15, while the location of the top of S-4 is identified based on lithology (L-8 bryozoan­echinoderm grainstones at 64 m in 7129/10-U-02). Sequence S-4 thins landward by around 42%, owing to thinning and truncation of the packstone/grainstone inter­vals in both unit L-6 and upper L-7 (Fig. 10). However, two cycles of shale and silty wackestone in the lower part of unit L-7 thicken landward, reflecting landward-increas­ing siliciclastic supply during these two major transgres­sive episodes.

Sequence S-5 (late Sakmarian-?Kungurian)

In well 7128/6-1, the transgressive systems tract of sequence S-5 (unit L-8) consists of open-shelf, storm­influenced grainstones passing upwards into increasingly shaly wackestone/packstone beds. The highstand systems tract is thicker and consists mainly of grainstone-pack­stone beds. Similar bryozoan-echinoderm grainstone lithology also makes up the age-equivalent interval in the IKU cores (Fig. 11). Based on the thickness estimate of 45 m for this unit given in Bugge et al. (1995), S-5 thins by 49% landward. Absence of fusulinid zone 20 and possibly also 19 in the IKU section indicates that land­ward thinning results at least partly from an internat hiatus. It is uncertain whether S-5 has also been thinned by erosion of its top surface. The pyrite/glauconite-miner­alized top of L-8 is preserved in both 7128/6-1 and the IKU cores, indicating similar drowning and submarine exposure in both locations. Landward loss of lithologic resolution of the S-5 transgressive systems tract and maximum flooding surface (clearly recognizable in the 7128/6-1 section, but consisting mainly of grainstones in 7129/10-U-02) is a consequence of landward-decreasing accommodation.

NORSK GEOLOGISK TIDSSKR!Ff 80 (2000)

Fig. JO. Facies model for sequence S-4 between well 7128/6-1 and the IKU

composite stratigraphic section, represented by core 7129/10-U-02.

V ertical scale is shown by tick marks at l 0-m intervals along right edge. Horizontal distance between core sites is 45 km (Fig. 1). However, insofar as these sites are regarded as representing

generalized distal and proximal positions

on a dip-section of the inner platform,

the lateral scale is roughly 30 km. Lithology symbols and depositional profile are the same as those in Figs. 8 and 9.

Sequences S-6 and S-7 (?Kungurian-Late Permian)

Sequences S-6 and S-7 correspond with the lower and upper cycles of unit L-9. According to the interpretation in Figs. 7 and 12, S-6 pinches out before reaching the IKU core sites, while S-7 thins by 63%. The top surfaces of S-6 and S-7 may be either subaerial unconforrnities with substantial erosional truncation or drowning surfaces affected only by submarine erosion, bypass and condensa­tion.

In the area of the exploration wells, the distribution of limestone banks has been mapped based on their asso­ciated seismic anomalies (see Fig. 2 in Ehrenberg et al. 1998a and Fig. 9 in Bruce & Toomey 1993). The results show that the limestone banks occur in an east-west belt, approximately 25 km wide paralleling the Norwegian mainland and separated from the area of the IKU co res by a 25-30 km-wide gap containing no seismic anomalies. These limestones are assumed to have formed in a zone of favorable water depth during a period of rising relative sea level. The bryozoan limestones in the IKU cores are suggested to have formed during a subsequent pulse of relative sea-level rise, at which time the limestone banks around the exploration wells bad become drowned and were terrninated by a surface of condensation or submarine eros ion.

Landward thinning of sequences

The above results can be summarized as showing pronounced landward thinning of the seven major sequences defined by previous study of the 7128/6-1 cores, together with overall loss of lithologic resolution of systems tracts, but only subtle changes in gross lithology. Landward thinning must reflect some combination of: (l) southward-increasing erosion of the top of each unit soon after deposition, (2) multiple surfaces of erosion within each unit, or (3) southward-decreasing accommodation which was gradual enough to produce only subtle facies

NORSK GEOLOGISK TIDSSKR!Ff 80 (2000)

7128/6-1

L-B

Upper Paleozoic carbonates, Barents Sea

storm-influenced ramp

7129/1 0-U-02 7129/1 0-U-01 7128/12-U-01

143

Fig. 11. Facies model for sequence S-5 between well 7128/6-1 and the IKU composite stratigraphic section,

represented by cores 7129/10-U-02, 7129/10-U-01, and 7128/12-U-01. Vertical scale is shown by tick marks at l 0-m intervals along right edge. Horizontal distance between core sites is 30-45 km (Fig. l). The depositional

profile below the geologic cross-section shows schematic relationships of facies

beits to water depth and shoreline proximity.

Calcerous shale Shaly

bryozoan-echinoderm wackestone

Bryozoan-echinoderm grainstone

changes while still affecting relative accumulation rates. The biostratigraphic data, including particularly the pattern of correlation of multiple chronostratigraphic units within sequence S-3 (Fig. 9), support options (2) or (3), but do not exclude option (1).

Overall sirnilarity between lithofacies development within each of the five sequences which is preserved in both the exploration cores and the IKU cores implies that southward-decreasing accommodation was not expressed as systematically shallower water depths, since this would be expected to result in greater proportions of peritidal facies. Sirnilarity of water depths is also supported by comparison of thicknesses of Palaeoaplysina-phylloid algae buildups in the two areas (Fig. 13), which shows no obvious tendency toward thinner development in the IKU cores. As in the exploration wells, the IKU composite section consists almost entirely of subtidal facies bounded by surfaces of inferred subaerial exposure ('truncated catch-down cycles', in the terrninology of Soreghan & Dickinson (1994)). This style of cyclicity is typical of 'icc­house' times such as the Carboniferous-Early Perrnian, when glacially driven, high-amplitude eustatic ftuctuations tended to out-pace sedimentary response on carbonate platforms (Wright 1992). Under such a regime, lesser

� �g�

landward accommodation could be expressed by selective ornission of individual cycles and correspondingly longer exposure durations rather than by shallower water depths during periods of subtidal sediment accumulation.

There appears to be a trend toward upward increase in degree of landward thinning from sequences S-2, S-3, and S-4 (32, 33, and 42%, respectively) to the deeper-water facies of sequences S-5, S-6, and S-7 (49, 100, and 63%), which may reftect a trend toward increasing uplift of the Norwegian mainland and northward til ting of the platform beginning in rnid-Perrnian (Sakmarian) time.

Porosity and diagenesis

Porosity and permeability data for the IKU cores are taken from Elvebakk et al. (1988) and Bugge et al. (1989). All units, with the exception of L-7 and L-8, in the IKU cores contain zones of high porosity (15-30%), which tend to be thinly interbedded with zones of low porosity (Figs. 3-7). As in the exploration wells, high porosity in the IKU cores occurs in a range of different lithologies and facies, although the proportion of high-porosity samples varies with lithology (Fig. 14).

144 S. N. Ehrenberg et al.

7128/4-1

L-9

7128/12-U.01 7128/10-U.01

100

NORSK GEOLOGISK TIDSSKRIFf 80 (2000)

Maximum-ftooding surface • • • • • • • • • • • •• •

Silty shale

Bryozoan packl wackestone

-�

outerramp

Siltstone

[2] .

. .

. . .

.

Light�l�ed

-' '

'

Flooding surfaæ

limestone bank

Chamosite sand sto ne

Dark Calcareous

• A feeling for dip-oriented lateral variations in reservoir

quality and dolomitization can be obtained by comparing histograms of measurements between the exploration wells and the IKU cores (Figs. 14-17). Such comparisons should ideally be restricted to show individual lithostratigraphic units and lithofacies separately, but because of the limited number of porosity measurements for the IKU cores, we have combined data for units L-2 through L-7. The comparisons also show only the four lithologic categories having the most porosity data. Figure 14 demonstrates the overall similarity between the porosity distributions in the two areas. The only way in which the IKU cores appear significantly different is a tendency toward higher po­rosities in the fusulinid wackestone category. The perme­ability-porosity fields for different lithologies (Fig. 15) also show only minor differences from the trends observed

siliciclasti<XIominated innerramp

Phosphorite

� Silty

argillaceous mudstone

Fig. 12. Facies model for sequences S-6 and S-7 between well 7128/4-1 and the IKU composite stratigraphic section,

represented by cores 7128/12-U-01 and 7129110-U-01. Vertical scale is shown by tick marks at 10-m intervals along right edge. Horizontal distance between core sites is 42-62 km (Fig. l). However, insofar as these siles are regarded as representing generalized distal and proximal positions on a dip­section of the ioner platform, the lateral scale is roughly 30 km. The thick dotted lines represent flooding surfaces, which are expressed by condensed sedimentation or submarine erosion where they overlie limestone banks. The depositional profile below the geologic

cross-section shows schematic relationships of facies beits to water depth and shoreline proximity. The

bryozoan limestone banks in 7128/4-1

and the IKU cores are suggested to represent successive stages in the transgression overlying the S-6 sequence boundary.

in the exploration well cores (see Fig. 23 in Ehrenberg et al. 1998b).

Porosity types and cements in the IKU carbonate lithologies appear similar to those described in the exploration wells (Ehrenberg et al. 1998b ). Especially similar is the degree of porosity occlusion by coarse equant calcite cement, which is interpreted to have been generated mainly during burial. The extent and types of dolomitization of different lithologies also appear similar in the two areas, except that fusulinid wackestones are more extensively dolomitized in the IKU cores (Fig. 16), which may account for their higher porosity. In Fig. 17 it is shown that dolomitization has an overall positive relation­ship to porosity, with the more dolomitized microfacies MF-5 and MF-8 having higher porosity than MF-6 and MF-7. However, this correlation is not observed in the

NORSK GEOLOGISK TIDSSKRIFT 80 (2000)

5

Sequence S-4 o ��------��-----------------------

fl) Q) Q.

10

5

o

5

Sequence S-3 � o ����u_��---------------L-L fl) 10 o .... Q)

..0 E ::J

z 5

o

5

Sequence S-2 0 4-�����W--U�L------------------5

o o 2 3 4 5 6 7 . 8 9 10 11

Buildup thickness (m) Fig. 13. Histograms comparing thicknesses of Palaeoaplysina-phylloid algae buildups in the IKU cores (open symbol) and wells 7128/6-1 and 7128/4-1 (filled symbol) for sequences S-2, S-3, and S-4. (O= <0.5 m; l= 0.5-1.5 m; etc.)

exploration wells (Figs. 2 and 13 in Ehrenberg et al. 1998b).

A unique feature not observed in the 7 128/6- 1 and 7 128/

(/) Q) Q. E as (/) o .... Q)

..0

Upper Paleozoic carbonates, Barents Sea

5 MF- 5 ·fusulinid wackestone

5

o

5 i MF- 6 buildup

o- 1 OoOO O nO 10

5

o

145

5 MF- 7 foram grain/packstone

§ o z 15

10

5

o

5 MF- 8 dolomitic mudstone

0�----�����������--�

: l-•-•1•·••1·1 o 10 20

Porosity {%) • 30

Fig. 14. Histograms comparing porosity distributions (helium porosimetry of one-inch plugs) in four lithologic categories from units 2 through 7 in the IKU cores (open symbol) and wells 7128/6-1 and 7128/4-1 (filled symbol).

4- 1 cores is the development of coarse calcite spar and native sulfur filling vugs and replacing former anhydrite nodules throughout the 29 m interval underlying the anhydrite bed in 7029/03-U-02 (Appendix l, Panel 5). Elvebakk et al. ( 1990) suggested that these cements were

146

1000

-100 c E -

� � 10 m <C w � a: 1 w a..

0.1

0.01

S. N. Ehrenberg et al.

•

6

6

Eli 6 6

Sl 7Jæ •

o 5

o

6 o

6 7 • • o

• 7.

El • •

o o 7 7 6

•

o 7 • •

•

10 15 20 25 POROSITY (%)

6 o •

•

o

o

30 35

Fig. 15. Permeability versus porosity in units 2 through 7 of the IKU cores. Symbols indicate lithology: O = MF-5 fusulinid wackestone; 6 = MF-6 buildup; 7 = MF-7 foram packstonelgrainstone; • = MF-8 dolomitic mudstone.

formed by thermochemical sulfate reduction involving a paleo-hydrocarbon column trapped beneath the anhydrite. This process would imply diagenetic temperatures possi­bly in excess of 140°C (Worden et al. 1995) and at least higher than 100°C (Machel 1998), which seems incon­sistent with the vitrinite reflectance values around 0.3 reported from this core and the nearby 7029/03-U-01. Although Elvebakk et al. (1990) rejected bacterial sulfate reduction based on sulfur isotope data, this mechanism seems more plausible with regard to the probable temperature history of the strata.

In contrast to the overall similarity of porosity in carbonates from the exploration wells and the IKU cores, Visean sandstones have much higher porosity in the IKU cores than in either 7128/4-1 or 7128/6-1. A Visean-age unit of dean sandstone roughly l 00 m thick is present in both exploration wells (Ehrenberg et al. 1998a, 1998b ). This unit is uncored, but wireline log data indicate average porosity around 16% in 7128/6-1 and 8% in 7128/4-1, while cuttings samples show that porosity loss is largely due to quartz cementation. Visean sandstone cores in 7029/ 03-U-01, 7127/10-U-02, and 7127/10-U-03 have porosity in the range 27-36%, reflecting minor quartz cement development (Bugge et al. 1989). Higher porosity and lesser quartz cementation in the IKU cores indicates lesser thermal exposure, which is consistent with much shallower present burial depths and a lower vitrinite reflectance level (VR values of 0.33-0.45% reported in Bugge et al. (1989) and Elvebakk et al. (1988) versus around 0.8% at the depth of the Visean sandstone unit in the exploration wells; Fig. 3 in Ehrenberg et al. (1998b)). The VR data are consistent with the possibility of a thinner Triassic section overlying

30

20

10

NORSK GEOLOGISK TIDSSKRIFf 80 (2000)

MF- 5 fusulinid wackestone

oJL��L-L=��crL---------�� 10 i 0 -�

30

20

10

40

30

20

10

---·----111

MF- 6 buildup

MF- 7 foram grain/packstone

O ....L-.---'------�-...---

30

20

10

MF- 8 dolomitic mudstone

o��L-��==L--J��-----------.-30

20

10

o o 00 100

100 x calcite l (calcite + dolomite) Fig. 16. Histograms comparing degree of dolomitization in four lithologic cate­gories from units 2 through 7 in the IKU cores ( open symbol; values estima­ted from thin sections) and wells 7128/6-1 and 7128/4-1 (filled symbol; values measured by bulk XRD analysis).

the IKU locations at the time of maximum burial (probably Early-mid Tertiary).

Higher sandstone porosity in the IKU cores than in the exploration wells might be expected to correspond with

NORSK GEOLOGISK TIDSSKRIFf 80 (2000)

100

6 -Q) -·e 80 o o 6 7 77 "O + �60 (.) � • -

._ .S40 7 ·c::s cu (.) X

820 o 6 ,.... o o 7 o

• • • o

o 10 20 30 POROSilY (%)

Fig. 17. Degree of dolornitization (estimated from thin section) versus porosity in units 2 through 7 of the IKU cores. Symbols indicate lithology: O = MF-5 fusulinid wackestone; 6 = MF-6 buildup; 7 = MF-7 foram packstone/grainstone; • = MF-8 dolornitic mudstone.

high er carbonate porosity, since porosity loss in both lithologies is believed to have occurred mainly by burial cementation (Ehrenberg et al. 1998b ). Although VR level is lower in the exploration-well carbonate section (around 0.6%; Fig. 3 in Ehrenberg et al. (1998b)) than in the underlying Visean sandstones, VR leve1 of the exploration­well carbonates is still much higher than in the IKU cores. The apparently similar porosity development in both carbonate sections (Fig. 14) does not necessarily mean that thermal exposure is unrelated to degree of burial cementation, but implies that depositionaVearly diagenetic variations exert an overriding control on carbonate porosity, an observation that is already well established (Moore 1989; Ehrenberg et al. 1998b ).

Relevance for hydrocarbon exploration

This study provides specific information about the types and amounts of dip-oriented lateral variations in potential reservoir and seal units of the Finnmark Platform. These variations tend to be subtle, indicating that platform sedimentation throughout Upper Carboniferous-Permian time extended well southward of the present southem termination of the platform stratigraphy. During this long history, the shoreline retreated and transgressed many times across this area in response to eustacy (Ross & Ross 1995) and local tectonics. Despite similar facies develop­ment within each unit, the southward thinning indicates persistent uplift of the Norwegian mainland and northward

Upper Paleozoic carbonates, Barents Sea 147

tilting of the platform, either gradually or in a series of cumulative minor events.

Lateral variations in reservoir quality are also subtle. Although the degree of subaerial exposure is expected to increase southward from 7128/6-1, evidence for more extensive meteoric diagenesis in the IKU cores has not been observed. Possibly such evidence would be found, however, if more detailed observations were undertaken comparing specific units. In any case, the overall similarity in diagenesis and porosity development gives little support to the concept of stratigraphic trapping by changes in facies or cementation landward of the 7128/6-1 location.

The present observations can be helpful for under­standing lithological and geometric changes within indi­vidual lithostratigraphic units and sequences further seaward from the 7128/6-1 location. Such knowledge is relevant for evaluating dip-oriented lateral variations in seismic facies suspected to reftect differential development of reservoir and sealing facies. However, any such evaluations must also include information from the exploration wells 7229111-1, 7228/9-1, and 7226111-1, located nearer the platform margin (see Fig. 2 in Ehrenberg et al. 1998a). Another necessary component to this work is the results from outcrop studies of appropriate exposed analogs, such as the Upper Paleozoic strata of Svalbard, the Sverdrup Basin, and the mid-continental USA.

Acknowledgements. - This project was originally started in 1989 by Erik B. Nilsen (formerly with Statoil), who carried out the fixed-interval sampling of the IKU cores on which our work is based. The Barents Sea 'Area G' licence (Statoil, Saga, Norsk Hydro, and Agip) gave permission to use results of fusulinid dating by V. I. Davydov. We thank G. Elvebakk, N.-M. Hanken, A. Lønøy, T. J. Samuelsberg, S. K. Strømmen and editor M. B. E. Mørk for helpful suggestions for improving the manuscript.

Manuscript received March 1999

References

Atlas of Characteristic Assemblages of Permian Fauna and Flora of the Urals and Russian Platform 1986: Transactions of VSEGEI (AI1-Russian Geological Research Institute), new series, 331, 5-328 (in Russian).

Bruce, J. R. & Toomey, D. F. 1993: Late Paleozoic biotherm occurrences of the Finnmark Shelf, Norwegian Barents Sea: analogues and regional significance. In Vorren, T. O. et al. (eds.): Arctic Geology and Petroleum Potential.

Norwegian Petroleum Society (NPF), Special Publication No. 2, 377-392, Elsevier, Amsterdam.

Bugge, T., Elvebakk, G., Bakke, S., Fanavoll, S., Lippard, S., Leith, T. L., Mangerud, G., Moller, N., Nilsson, 1., Rømuld, A., Schou, L., Vigran, J. 0., Weiss, H. M. & Århus, N. 1989: Shallow drilling Barents Sea 1988 main report. !KU Report 89.022, 348 pp.

Bugge, T., Mangerud, G., Elvebakk, G., Mørk, A., Nilsson, 1., Fanavoll, S. & Vigran, J. O. 1995: The Upper Paleozoic succession on the Finnmark Platform, Barents Sea. Norsk Geologisk Tidsskrift 75, 3--30.

Chuvashov, B. I. 1993: General characteristics of the Permian deposits of the Urals and Povolzhie: Lower Permian. In Chuvashov, B. I. & Nairn, A. E. M. (eds.): Permian System: Guides to Geol. Excursions in the Uralian Type

Localities, 3-23. Occasional Publications of ESRI, New Series 10. Chuvashov, B. 1., Alksne, A. E. & Polozova, A. N. 1980: Zonal stratigraphy of

Artinskian of Western Urals and Preurals (based on fusulinids). In Rauser­Chemousova, D. M. & Chuvashov, B. I. (eds.): Biostratigraphy of Artinskian

and Kungurian of the Urals, 3-10. Acadamy of Sciences of the USSR, Uralian Science Center, Sverdlovsk, (in Russian).

Davydov, V. I. 1984: Zonal subdivisions of the Upper Carboniferous in Southwestem Darvas (Central Asia). Bulletin of Moscovian Society of Nature

(MO/P), Geology Series 59, 3, 41-57 (in Russian).

148 S. N. Ehrenberg et al.

Davydov, V. I. 1990: Zonal division of the Gzhelian in Donets Basin and Pre­Donets trough according to fusulinids. In Kolobova, l. M. & Modzalevskaya, T. L. (eds.): Problems of Modem Micropaleontology, 52-69. Transactions of the Paleontological Society, Leningrad, Session 34, (in Russian).

Davydov, V. l. 1992: Subdivision and correlation of the Donets Upper Carboniferous and Lower Perrnian deposits based on fusulinid data. Sovetskaya

Geologiya 5, 53-61 (In Russian). Davydov, V. I. 1993: Upper Paleozoic fusulinid stratigraphy from Kolguev Island

and Franz Josef Land, Arctic Russia. /KU report 23.1438.00111193 (Restricted), 122 pp.

Davydov, V. l. 1997: Middle/Upper Carboniferous Boundary: Problem of Definition and Correlation. Proceedings of the XIII International Congress

on the Carboniferous and Pennian, Warsaw, 113-122. Davydov, V. I. & Kozur, H. 1997: The position of the Carboniferous-Perrnian

boundary in the Carnic Alps compared with the stratotype region. Proceedings

of the XIII International Congress on the Carboniferous and Pennian, Warsaw, 123-130.

Ehrenberg, S. N., Nielsen, E. B., Svånå, T. A. & Stemmerik, L. 1998a: Depositional evolution of the Finnmark carbonate platform, Barents Sea: results from wells 7128/6-1 and 7128/4-1. Norsk Geologisk Tidsskrift 78, 185-224.

Ehrenberg, S. N., Nielsen, E. B., Svånå, T. A. & Stemmerik, L. 1998b: Diagenesis and reservoir quality of the Finnmark carbonate platform, Barents Sea: results from wells 7128/6-1 and 7128/4-1. Norsk Geologisk Tidsskrift 78, 225-251.

Elvebakk, G., Bugge, T., Eem, J. v. d., Fanavoll, S., Fjerdingstad, V., Haugane, E., Leith, T. L., Mørk, A., Rendal!, H., SkarbØ, 0., Smelror, M., Sættem, J., Vigran, J. 0., Weiss, H. M. & Århus, N. 1988: Shallow drilling Barents Sea 1987 main report. /KU Report 88.039, 311 pp.

Elvebakk, G., Fanavoll, S., Johansen, H. & Stemmerik, L. 1990: Sedimentology, stratigraphy, diagenesis, geochemistry and reservoir potential of Gzhelian­Asselian carbonates, Finnmark Platform. /KU Report 90.078, 76 pp.

Goldharnmer, R. K., Oswald, E. J. & Dunn, P. A. 1991: Hierarchy of stratigraphic forcing: example from Middle Pennsylvanian shelf carbonates of the Paradox basin. In Franseen, E. K., Watney, W. L., Kendall, C. G. & Ross, W. (eds.): Sedimentary Modeling: Computer Simulations and Methods for Improved

Parameter Dejinition, Kansas Geological Survey Bulletin 233, 361-413. Groves, J. R. & Wahlman, G. P. 1997: Biostratigraphy and evolution of Late

Carboniferous and Early Perrnian smaller forarninifers from the Barents Sea (offshore arctic Norway). Journal of Paleontology 71, 758-779.

Grozdilova, L. P. & Lebedeva, N. S. 1961: Lower Perrnian forarninifers of Northern Timan. Transactions VNIGRI 179, Microfauna USSR 13, 161-330(in Russian).

Harland, W. B., Armstrong, R. L., Cox, A. V., Craig, L. V., Smith, A. G. & Smith, D. G. 1990: A Geological Time Scale, 263 pp. Cambridge University Press, Cambridge.

Kireeva, G. D. 1949: Pseudofusulinids of Tastubian and Sterlitamakian Horizons of the burial reef massif of Bashkiriya. Transactions Geological Institute

Academy of Sciences of the USSR 105, Geology Series 35, 171-191 (in Russian).

Konovalova, M. V. 1991: Stratigraphy and fusulinids of Upper Carboniferous and Lower Perrnian of Timan-Pechora oil and gas bearing province. Ukhta

Geological Survey, Moscow, Nedra, 3-201 (in Russian). Krainer, K. & Davydov, V. I. 1998: Facies and biostratigraphy of the Late

Carboniferous/Early Permian sedimentary sequence in the Carnic Alps (Austria!Italy). Facies 40. In Crasquin-Soleau, S., Izart, D. & De Wever, P. (eds.): Peri-Tethys: Stratigraphic Correlation 2, 643-662. Geodiversitas 20.

Larssen, G. B., Elvebakk, G., Henriksen, L. B., Kristensen, S. E., Nilsson, 1., Samuelsberg, T. J. & Svånå, T. A. 1999: Lithostratigraphical nomenclature of the Upper Paleozoic rocks of the southwestern Barents Sea. Geonytt, January

issue, 65. Leven, E. Y a. & Davydov, V. I. 1991: The boundaries and the volume of the 1ower

Asselian fusulinid zone. News of Academy of Science of the USSR, Geological

Series 12, 61-73 (in Russian). Machel, H. G. 1998: Gas souring by thermochemical sulfate reduction at 140°C:

discussion. AAPG Bulletin 82, 187G--1873. Makhlina, M. Kh., Kulikova, A. M. & Nikitina, T. A. 1979: Sedimentology,

biostratigraphy and paleogeography of Upper Carboniferous of the Moscow syneclise. In Makhlina, M. Kh. & Shik, S. M. (eds.): Paleontology, stratigraphy

and paleogeography of Carboniferous of Moscow syneclise, 25-69. Geological Archives of RSFSR, (in Russian).

Makhlina, M. Kh., lsakova, T. N. & Zhulitova, V. E. 1984: Upper Carboniferous

NORSK GEOLOGISK TIDSSKRIFT 80 (2000)

in the Moscow Basin. In Menner, V. V. & Grigorieva, A. D. (eds.): Upper

Carboniferous of the USSR, 5-14. Transactions of the Stratigraphical Committee of the USSR 13, Nauka, Moscow, (in Russian).

Moore, C. H. 1989: Carbonate Diagenesis and Porosity. 338 pp. Elsevier, Amsterdam.

Nilsson, l. 1992: Fusulinider fra brønn 7128/06-0 l. unpublished IKU report 23.1681.00/01/92, 7 pp.

Nilsson, I. 1993: Upper Paleozoicfusulinid stratigraphy of the Barents Shelf and surrounding areas. unpublished Doctor Scient. dissertation, University of Tromsø.

Nilsson, I. & Davydov, V. I. 1992: Upper Carboniferous-Lower Perrnian fusulinid stratigraphy in Central Spitsbergen, Arctic Norway. /KU Report 23.1356.00/ 07192 ( restricted), 185 pp.

Rauser-Chernousova, D. M. 1940: Stratigraphy of Upper Carboniferous and Artinskian of western slope of the Urals and materials on fusulinids fauna. Transactions of the Geological Scientific Institute, Academy of Sciences of the

USSR 7, Geology Series 2, 37-101 (in Russian). Rauser-Chernousova, D. M. 1949: Stratigraphy of Upper Carboniferous and

Artinskian deposits of the Bashkirian Preurals. Transactions of the Geological

Scientific Institute, Academy of Sciences of the USSR, Issue 105, Geology

Series 35, 3-21 (in Russian). Rauser-Chernousova, D. M. 1960: Revision of Schwagerina genus and similar

genera and the Carboniferous!Perrnian boundary. Questions of Micropaleon­

tology 4, 3-32 (in Russian). Rauser-Chernousova, D. M., Gryzlova, N. D., Kireeva, G. D., Leontovich, G. E.,

Safonova, T. P. & Chernova, E. I. 1951: Middle Carboniferous fusulinids of the Russian Platform and adjacent regions. Academy of Sciences of the USSR,

Moscow, 1-380 (in Russian). Remizova, S. T. 1995: Foraminifers and biostratigraphy of Upper Carboniferous

of Northern Timan. Transactions of the Institute of Geology of Komi Scientific

Center of the Russian Academy of Sciences, 6-128 (in Russian). Rosovskaya, S. E. 1950: Triticites genus, its development and stratigraphic

significance. Transactions of the Paleontological Institute, Academy of

Sciences of the USSR 26, 5-78 (in Russian). Rosovskaya, S. E. 1958: Fusulinids and biostratigraphic subdivision of Upper

Carboniferous of Samarskaya Luka region. Transactions of the Geological

Institute, Academy of Sciences of the USSR 13, 57-120 (in Russian). Ross, C. A. & Ross, J. R.P. 1995: Perrnian sequence stratigraphy.1n Scholle, P.

A., Peryt, T. M. & Ulmer-Scholle, D. S. (eds.): The Pennian of Northem

Pangea Volume 1: Paleogeography, paleoclimates, stratigraphy, 98-123. Springer-Verlag, Berlin.

Santisteban, G. & Taberner, C. 1988: Sedimentary models of siliciclastic deposits and coral reefs interrelation. In Doyle, L. J. & Roberts, H. H. (eds.): Carbonate-Ciastic Transitions, 35-76. Developments in Sedimentology 42, Elsevier, Amsterdam.

Soreghan, G. S. & Dickinson, W. R. 1994: Generic types of stratigraphic cycles controlled by eustasy. Geology 22, 759-761.

Stemmerik, L., Nilsson, l. & Elvebakk, G. 1995: Gzhelian-Asselian depositional sequences in the western Barents Sea and North Greenland. In Steel, R. J. et al. (eds.): Sequence Stratigraphy on the Northwest European Margin, 529-544. Norwegian Petroleum Society (NPF), Special Publication, Elsevier, Amster­dam.

Van Wagoner, J. C., Mitchum, R. M., Campion, K. M. & Rahmanian, V. D. 1990: Siliciclastic sequence stratigraphy in well logs, cores, and outcrops: concepts for high-resolution correlation of time and facies. American Association of

Petroleum Geologists Methods in Exploration Series 7, 1-55. Wahlman, G. P., Davydov, V. I. & Nilsson, l. 1995: Fusulinid biostratigraphy of

subsurface cores from the Conoco 7128/6-1 well, offshore Barents Sea, Arctic Norway: XIII International Congress on Carboniferous-Pennian (XIII ICC-P),

Abstracts, Panstwowy lnstytut Geologiczny, Krakow, p. 150. Worden, R. H., Smalley, P. C. & Oxtoby, N. H. 1995: Gas souring by

therrnochemical sulfate reduction at l40°C. AAPG Bulletin 79, 854--863. Wright, V. P. 1992: Speculations on the controls of cyclic peritidal carbonates:

ice-house versus greenhouse eustatic controls. Sedimentary Geology 76, 1-5. Zolotova, V. P., Scherbakova, M. V., Ekhlakov, Y u. A., Kosheleva, V. F., Alksne,

A. E., Polozova, A. N. & Konovalova, M. V. 1977: Fusulinids from the Gzhelian and Asselian boundary beds of the Urals, Preurals and Tirnan. Questions of Micropaleontology 20, 93-120 (in Russian).

Zolotova, V. P. & Baryshnikov, B. B. 1978: Fusulinids of Kungurian of Kamskoe Preurals. Paleontological Journal 3, 22-30 (in Russian).

NORSK GEOLOGISK TIDSSKR!Ff 80 (2000) Upper Paleozoic carbonates, Barents Sea 149

Appendix l Core data profiles for 7030/03-U-01 (panels l through 3), 7029/03-U-02 (panels 4 and 5), 7129/10-U-02 (panels 6 and 7), 7128/12-U-01 (panel 8)

and 7129/1 0-U-01 (panel 9). Gamma ra y (GR) log scale is 0-300 API units for cores where wire line logs were run. For 7030/03-U-0 l, 7129/10-U-02, and 7129/10-U-01, core-surface GR logs (courtesy of Tom Bugge, IKU Petroleum Research) were normalized to approximately match the GR scale of the wireline logs. Numbers in the right-hand columns gi ve microfacies category and selected biological/petrographic abundance scores (O= none present; l = <2%; 2 = 2-5%; 3 = 5-20%; 4 = >20%) for samples at depths indicated by tick mark to teft of each row of numbers. 'Porosity' is helium porosity of plugs, from Elvebakk et al. (1988) and Bugge et al. (1989). 'CCD' = 100 calcite/(calcite + dolomite), estimated from thin-section observation. Width of lithology column indicates Dunham classification for carbonates and grain size for siliciclastics. Pattems indicate microfacies categories (see Table 3 in Ehrenberg et al. 1998a), plus four new lithologies not defined in that reference. Suggested locations of tops of lithostratigraphic units (L-2 through L-9) and sequences (S-1 through S-7) are indicated in the GR column.

Coarse spiculite

Bryozoan-ech i noderm wackestone

Bryozoan-echi noderm gra i nstone/packstone

Fusulinid/foraminifera wackestone/packstone

Buildups (plotted in "boundstone column", but including both boundstone and clastic fabrics). l Palaeoaplysina

Codeacean phylloid algea Encrusting forms (tubular foraminifera, algea, etc.) Coral

For am in ifera gra i nstone/packstone

MF-8 Dolomitic mudstone: o --barren

���� laminated

containing bioturbation and/or bioclasts

MF-9 Shale & silty shale (Lithology column width indicates silt content.)

Q MF-10 Calcareous siltstone

Q MF-11 Sandstone

Anhydrite

Bryozoan packstone/wackestone

Glauconite ooid/pellet sandstone

Phosphorite

Silicified zones

x x x x Microcodium

· ----- Shale layers (mainly 1-5 cm thick)

Glauconite: * minor ** abundant

Contacts between different lithologies: horizontal line =sharp, discontinuous no line = gradational

150 S. N. Ehrenberg et al.

Appendix 1, panel 1 of 9

~~ [Siliciclastic l~tho~ogy'

Gamma roy

~t1~~~te thGiog~ (counts/10min.l

[10k 30k [125

~"''"'"' p:l

130

1<::::>::

l> / 135-

l/<<:>? *

140-~~ L-2

~ 145-

r

1175

NORSK GEOLOGISK TIDSSKRIFf 80 (2000)

7030/03-U-01 " Porosity ., u (%) >-

CCD ~~ 12 ~ t~ 1<5 ~~ () [35 o dt ~o6

1

j [1-~ ~ i~ ~It l ~ 1\

.--~

.--1/

f-- f-f---, r--

r- f--

f-- f--

r-r-

r-r-

r-r-

r- f--.--r- f--

-f--

-f--

-r-

-r-I--

-f-f-

-f-f-

r---

8 o 2 o o o o o o 3

8 o 1 o o o o o o 2

5 o o 1 o o o o o o 8 o o o o o o o o 4

8 o o o o o o o o 3

8 o o o o o o o o 2

Cbl3~~~~~~~~: "IU 0 0 0 0 0 0 0 0 4

"IU 0 0 0 0 0 0 0 0 4

8 o o o o o o o o 4

ou000000004

8 o o o o o o o o 4

X O O O O O O O O O

-===== 9 o o o o o o o o 2

6 2 0 0 L 4 0 0 0

H+tt-H+tt-16200 21300

6 2 0 0 L 2 0 4 0

H-+++-IH+t+l 6 o o o ? 3 3 o 3 o 6 1 o o 2 4 o 2 o

1118000000000 8 o o o o o o o o o

~~~lii 8 o o o o o o o o 3 ~ 800000000;(

mm1 ~r~~6000L0 00 ut 6200 0000

Tf6200 03421

H-+++-lf-tt-UJit+f 6 1 o 1 ? o 3 2 4 o 116000L03022

11 o o o o o o o o 4

r---~~H mll8000000004

9 o o o o o o o o 3

1-t+t+1i'Ri3 gL o o o o o o'o 3

H+tt-H+t+l 9 o o o o o o o o 2

t+tt+i-+++t-1 9 o o o o o o o o 2

H+tt-H+t+l 11 2 o o o o o o o 4

~10 4 0 L 0 0 0 0 4

l+tt+-1-ttttl .l 4 0 L L 0 0 0 0 4

~10 2 1 3 o o o o 4

H+tt-f-tH-I"'r1o 3 o o o o o o o 4

~10 2 o 1 o o o o o 4 Htttttt++L.l"U 2 O O O O O O O 4

rm 3 o o o o o o o 4

t+t++t+H~:z::t.3 2 o o o o o o o 2

~rr~~~~~-'30oooooo3

HHHH~~~~~~10 000000004

m~10 2 o o o o o o o 4

1-+-+-+--+-+-+--t++t+++!l--t-HII

NORSK GEOLOGISK TIDSSKRIFT 80 (2000)

Appendix 1, panel 2 af 9

10k

Gamma ray Ccounts/10minol

!->iiiCiciOStiC hthalagy: ~~:" s,h sv,Sh ~; s,s c,9 :3~bar,~anate lithology:

30k 'l'WPGB

\

10 ~

10~

10 ~

10 :1

A

A

85 A

100~ 105-fZ»:~=

~

120

~~~ o o o

Upper Paleozoic carbonates, Barents Sea

., " u >. u 35

Porosity (;1.)

7030/03-U-01 t.J

CCD o

dol. col g o o 100 ~

1111ru ~

_HitttlH~~@~5 o o o o o o o o 3 ;rw::::s

1 {]5204000001 k----~+4~~4HttH~~~~

1---+--l-+-1--V) k---- ,

-

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V /

-~-l---+---1.1\

1-+--+-+--+17

~ 12000000000

u o o o o o o o o o 5 o o o o o o o o o

l~

~

u o o o o o o o o 1

u o o o o o o o o o u o o o o o o o o o u o o o o o o o o o 5 o o 2 o o o o o 1

u o o o o o o o o o

8 o o o o o o o o o

:!2 8 o 1 o o o o o o o Ht-t++l-tf'~ 5 o o 1 1 o o o o o

9 o o o 1 o o o o 1

3 1 o o 1 o o o o o

X O O O O O O O O 2

::;:::::6301231320

liil~8000000002 8 o 2 o o o o o o 1

6 o o o o o o o o o l~ 7 3 o 1 2 3 3 o o o ~6400111000

11m 6 o o o o o o o 4 o 5 o o o o o o o o o 5 o o o o o o o o o 8 o o o o o o o o o 8 o o o o o o o o 1

A O O O O O O O O 1

5 o o o o o o o o o 5 o o o o o o o o o 8 o 2 o o o o o o 1

n o o o o o o o o 4 A O O O O O O O O O

6 o o o o o o o o o 8 o o o o o o o o o 5 o o o o o o o o o 6 o o o 3 o o 4 o o 8 o o o o o o o o 1

5 o o o o o o o o 1

8 o 1 o o o o o o 1

8 o o o o o o o o 3

8 o o o o o o o o 4

8 o o o o o o o o 4 L TEK -GS/ A980331

151

152 S. N. Ehrenberg et al.

Appendix 1, panel 3 of 9 Sihciclosloc lithology :

Gamma ro y ~~ S1h Si/

1Sh ~i S

1s C

1g

<counts/10min.) ~;:;jcorbonote lithology : 10k 30k M W P G B

)

L-6 16 ._;,

16 ._;, 16 ._;,

25

lill

WJJ 16 ~ 30-#!/.""/~FFA

l

m 45

-H++++++t-H'rrnllll

11 ~ 65 li lllb c; ~

.. .. u "' u 35

Porosity (/.)

NORSK GEOLOGISK TIDSSKRIFf 80 (2000)

7030/03-U-01 gof/)-8 · _: g-~

CCD - 2 ~ ~ ·~ ~ v ~ g ~ L l col ~ 0 ~ ::J o L = o -o tJO . u ~· ·g In L g lg, E o 6

o o 100 '::1 .D l ~ -2 ~ Q) 'o o. Cl.. 1/)

rT~-H-+-+-+-H-+1f+l...f+l...f++.l7 3 o 1 3 o 2 o o o H-+-+-+-H-+1f+l...f+I...I-Hll.. 5 o o 2 3 o o o o o

7 002330002 LL-H-+-+-+-H-+1f+l...f+l...f-Hl7 o o o 3 4 3 o o O

7 000343021

1+++++++++16 000000000 l++i~+J.Ql7 200340001

r=z7 000332000

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~ ~~~j5 o o o o o o o o 3

1 1 ~5 104300002 ~5 303301002

8 000000000

1 Tf6 200222o4o ~6200210000

k---1-+-+--1-+-1-\. m~~~8 o o o o o o o o 1

1 mr..rm 6 o o 1 3 3 3 o 4 o

5 000000000

5 000000000

5 000000000

5 000000000

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m~~i5 o o o o o o o o o l~ 7 2 o 3 2 2 1 3 o o

8 o 2 o o o o o .o o 5 000000000

325 004000000 H~4-H~4+1++i~g lllll 5 2 o 4 o o o o o 1 H~4-H~4+1++i~~

11~ 7 1 o 3 2 o o o o o H-+-+-+-H-+I+t-1-l~~--~. 51: 7 2 o 2 1 2 o o o o

5 000000000

8 000000000

5 000000000 L.Ttk-GS/ Ata0l31

NORSK GEOLOGISK TIDSSKRIFf 80 (2000) Upper Paleozoic carbonates, Barents Sea 153

Appendix 1, panel 4 of 9 7029/03-U-02 pol.~·~·u~w .. lithology: .,

l~ 1111 ~~~ lill li Gamma ray ~LS/' Si Ss .. Porosity CCD l! CA Pl) ~år~ .Y!'. t'h9rcig~

o (1.) o~ol. ~;~ >.

l10k 30k (.J

1.1f li;

"&: 1\ l o l o o o o c o 9 c 1 o l o o o o o o 4

\ \ 9 c o!o o l o l o o l o 4

r ~.:q 8 c o o o l o l o o l o 2 ......

~1' c o o o l o o o l o 4 . .... . . . . . . . . \ . ... . .

• • o ••• •

2 o 1 1 1 2 o o 4 ••• • • o 1' 7-8~ . ' 1-- l\

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~ f\ 6 c o o 2 2 .1 o 1 o l 6 o o 1 3 2 4 14 o

1/ 6 c o o 21 3 l 4 2 l o o 1' o o o o 2 o o l o 4

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~ 1--

6 1 o o 1 2 2 2 l o o 6 o o 1 2 o o 4 o 6 2 o o 1 2 2 4 o o

~ ~6 o o o o o o o o o ~ 1 o o 1 2 1 2 4 o ~6

6 o o o o 4 o o o

~/c..(rLL' 6 o o o o o o 2 l o 2

><< 1C o o o o' o o o lo 4

on ... ov

/,t~~ 5-6~ i/;// r--5=~:::;

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4 5 ~

•• o •••• o o • • • •

o •••• •• • • • o. o

o . o • •••

95- .. .. .. • o ••• o •

. ::::-::::::::· f- f- vv

l .. f- f--1\ f- f-f-

lmn. 1\

k/7:7 V::H<

1--f------J

''. ·.· 1105

>l

110

li f:> <>

l.TEK GS/AI80324

154 S. N. Ehrenberg et al.

Appendix 1, panel 5 of 9

10k

~l

Gamma ray (AP Il

ISihclclastic lithology : ~~ s,h s;~sh ~i s,s c~ j3~ Carbonote lithology:

30k -o M W p G ~

9·10? ~

9·10? l~

(/)

<11 :; "O o c

l U

15 1\

45 V///Jl

~ 77=>

50~

~~~~~ c,c, = )C)(

55 c,c, /p

NORSK GEOLOGISK TIDSSKRIFf 80 (2000)

7029/03-U-02 "' ., o (J

35

Porosity (/.)

V

~::~V f-f-~ f-'--H

f-'---f-1\

1-+-+-tf, 1\

1---+--l-+-+-+17 y

l

r---~ \

'l

1----+-+-+-+11

n~---.---l-++-+-+-v)' J

-~/ ,_ __

[------___

do l. o o

5 1 o 4 2 o o o o 3 8 o o o o o o o o 4

1< o o o o o o o o o 1< o o o o o o o o o 1000000000

5 o o o o o o o o o 5 2 o 4 3 o 1 o o 1

5 o o o o o o o o o 5 o o o o o o o o o 5 o o o o o o o o o

5 o o 1 3 2 o o o o 6 o o o o 2 o o o o 6 o o 1 o o o o o o 6 o o o o o o o o 1 7 o o o o o o o o 2 5 o o o o o o o o o 5 o o o o o o o o 1 5 o o o o o o o o o 6 o o o o o o 1 o o 5 o o o o o o o o 1

H+++FK::s:~:zl- 6 1 o o 2 2 o o 3 o H+t-tl'~@~zt 5 1 o o 3 2 2 o 1 o H+t++~l-tPH- 6 o o o 3 2 1 o 4 o

~~~J5ooooooooo ~X300000000

5 o o o o o o o o o 5 o o o o o o o o o 5 o 3 o o o o o o 1

5 o o o o o o o o o 6 o o o o o o o o 1

8 o o o o o o o o 3 8 o o o o o o o o o 5 o o o o o o o o o 7 o o o o o 3 o o o 6 o o o o o o o o o 8 o 2 o o o o o o 2

11~ xooooooooo l~

5 o o o o o o o o o 5 o o o o o o o o o 8 o o o o o o o o 3 8 o o o o o o o o 4 8 o o o o o o o o 2

" o o o o o o o o 4 9 o o o o o o o o 4

5 o o o o o o o o o L TD<~OS/Ai!0324

NORSK GEOLOGISK TIDSSKRIFf 80 (2000)

Appendix 1, panel 6 of 9

16 -'.O

16[-i

5-3 14 :::: 14 '~' l 1110-

i~

~ 1115-

l

1125-

130

Upper Paleozoic carbonates, Barents Sea 155

7129/10-U-02

~--~--~~~~1~11~1~~~~ ~~~~~~~14 HHHH~~~k~lfflricoloocooololo HHHH~4W~~92Ioocooolol3

~~~~~~9 1looccoolol2 ~~++~#tt~g z lo2ocoolo13

~~~~~~91looccoolo2 ~~~~~~goloococolo z

I-I--HHHH~~~goloooaco!o2

H-~++++~~~s 1 lool2:z olo'o t'----1-+-++++~ 1+~-+-l--1+ 6 1 o o 3 2 2 o 3 o

V 1-1--HHI-1/

H++-1++++++- 6 2 o o ~ 2 1 o 3 o H++-l++++:lot-6 1 o a'' 1 z 2 o

~n7 5000000001 ~~~~~000000001

l< 1'000100004 1-1--~k 8000000002

\ ::=:.:8001010002 t""t-~++++--+. 1+1-+-+-l-1~ 6 2 o o 2 2 2 o 4 o

1-1--~++~ff*~s 10o32 040 ~~~~~~~6 00122040

~ ' o 2 2 o 1 o l o o msil' o 1ooo lo 1 ~~4444~~ ~ cooooooooo

~f--1----+---+--fj H++-1-+++1':;::::~ 7 o 2 4 2 1 o o o f--+--f--1----+----+-H H++1++++++ 7 o o o 4 3 1 o o o HHf-+--+---+--H 1-1-+-l-1-4-1-1-it::;~ 7 o o 3 o 1 o ' o 1

1-l-y ~---~

~7000201002 1.]:7001000040

~-+++-~~~::j. l3lo 12 c clolo ~ ,13lolo 1 o c c ela

1-l-p e,olololo o c c c iii ~ 1 o l o l o l o o c c c c

l-l-

l-""

e'clololo o o c o 1

e'clololo olo c o 2

~~· H++-1++++~6colo:oloooloo ~~~ 8colo

1oooaoo

156 S. N. Ehrenberg et al.

Appendix 1, panel 7 of 9

(

l l

J

l

18-19 ~

18·19 ~ 18-19 ~ 18·19 ~

17·184 17·184

17·18~

17·18 ::::;: 17·18 ,

17·18 -il

17·18 -il

17·18 ....,

16 ~

l~~

35

<n .

•

•

•

•

•

NORSK GEOLOGISK TIDSSKR!Ff 80 (2000)

7129/10-U-02 Por~sity CCO ~~ l§ Ill·~~ l1llci

(1.) 0~01. co\ l~~~ l] l~~ fg~~ l 111o 1 ~2o ~co

1-+-+-+-+-+-1' 1

4 41 o o ' a o o 2

~~ 4 4 O 2 1 a C OI O 1

~~++~r~~#440 1 1acolo!o ~~~ ~~#44lo 1 o oloio

1-++1--1-l~ 4 4 o 2 1 o c o[olo

1-++1--1-l~ 4 41 o 1 2 o 1 o l o: o 1-++1--1-lH--+--+-++ 4 4 o 1 o o o l o l o 1-++1--1-lH--+--+-++ 4 4! o 2 o 1 o o o l-t+l-l-l~4 4101 1 o o o o

~~~ ~~#44i021 12000 ~~~ ~~#4402 02001 ~~~~ffi#44 1 0200000 1 ~HHHH llilliilift44,02000000

100/. 44'01101001 calcite 4 41 o 3 o o o O 1

~~~ ~~~4402000001

~HH~ ~~#440220 101010 I--+---1HH-+---JI 1-++1--1-l-1+1-+l 4 4 O 2 O O O O O O

I--+---1HH--+---H ~-1-1-+-l-+4. 4 4 O Z O O O O 2

.~-1-1-+-l-+4- 4 4 o 2 o o o o 2 1---+---l---+----+---+---1-l ~-1-1-+-l-U- 4 4 o 2 1 o o o o 1 I--I-IHH-+--11 ~-1-1-+-l-+4. 4 4 O 2 1 O O O O 1

~~~ ~~4402 100001 ~~++~~~~4402 o 003

1-+--1---+----+-+-H ~~-U 4 4 o o o o o 2 1--+---1-+-+--+--+l ~~++- 4 4 o z o o o o 2 ~++++~~~~44'C< !c loloiL ~HH-+--f-j ~~ 4 41 o 1 1 c c o l o12 ~HH-+--tj I+++H++!# 4 41 O ' 1 C 1 O i O 1

~HH-+-+1 I+++H++!# 4 41 O 2 C C O l O l 2

~~ * .-- 44101 cc·olol2 ~ L.~~~H ~~~424' 1c cololz

;:::::: * -1C2a'ccclolol4 ) -1c2 1ccc c!olol4 / 1c de c;cololol4

1c 1 c.c1clc o ala 4 l-++l-l-l~9 1 c'clololo a a 4 1-++1--1-l~ 9 o c c, al o o o o 4

1-++1--1-l~ g a o, o[ al o o o o 3

~-+++H-1c 1 11 al o o a a o 4

1-++++l++++t- 9 1' o l o l o o a a o .~

l++++l~' 1 o:z zlo 1 o o 1

~+++~.u., 2 ol2 2lo 1 olol2 l++++l~1c o o 2 1!o o1 olol4

tttt6jjllll1cacCcccolo4 1CaCCCCC004

l~ 1C o o o o o o o o 4

NORSK GEOLOGISK TIDSSKR!Ff 80 (2000) Upper Paleozoic carbonates, Barents Sea 157

Appendix 1, panel 8 of 9 7128/12 -U-01 Gamma ray

~~ 1 ~",v, ,y~ si l~tho~gy = ., Porosity CCD J l! l l l ~ 11 l ~ i

<5 ~ en • .,

1 <APil lc~r~, . ~ ~~ ~ith~l~gr ~~g ( )( ) dol. cal ~ 10k 30k N 135 o 100 '

110

.• .• ·1 " y

• * L-9 **

- 2 o 4 o o o o o o 1 .. -. ',, -

* 2 o 4 o o o o o o 1 - . -'' . * 2 o 1 4 o o o o o o o

~ , - ' ,

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< colcite

135-

. ~~ ~ ~ ~ ~ ~ ~ ~ ~ o 1J 4 1 o 1 o o o o 2

13 4 o o 1 o o o o 2

** 9 o o o o o o o o 2

* 9 o o o o o o o o 3

• 9 o o o o o o o o 4

9 o o o o o o o o 4

9 o o o o o o o o 4

• CD 9 o o o o o o o o 4

* 9 o o o o o o o o 4

• 9 o o o o o o o o 4

• 9 o o o o o o o o 4

.•. ~·· 14 o o o o o o o o 3

L-8 r-- 4 3 o o 1 o o o ,o o

S-5 !150· 4 3 o o 1 o o o o o

4 4 o o o o o o o o 4 3 o 2 o o o o o o

21 ~ 4 4 o o o o o o o 2

1"'11 4 4 o o 1 o 1 o o o 4 4 o o o 1 1 o o o 4 4 o o o o o o o o

21 ~ 4 4 o o o o o o o 1

4 4 o 1 2 o o o o o 4 4 o o 1 o ~ ~ ~ ~ 21 ~

1160 n n ..

158 S. N. Ehrenberg et al. NORSK GEOLOGISK TIDSSKR!Ff 80 (2000)

Appendix 1, ponel 9 of 9 7129/10-U-01 Gamma ray

~ l~ihcic lostic lithal_ogy:

"' Parasity c CD li 1!11 111] Il~ ~i l~

l__51hSi/Sh Si ~J~3~~~: (]) . .,

<counts/10min.) l l 1:Sc (/.) ~o l. Il jcår$on~te f! l -.J~O co l l~ hok 30k N bo n bU

~~ L

!l li l

f--- !! ! l ill 65-~:~:=:::«~ •• ~

~ -.-.-.-.-.

1-

· 12 4 1 o o o C'C o 1

1~ 4 1 o o o o o o 1 ei)

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* 12 4 4 o o o ,o o 1

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** <D 1~ o o o c o o' o o 3

* 9 o o o a o o o o 4

* 9 o o o o o o o o 4

. . .. . . . . . . . . . . ... . . . . . . . . . . . . . 11 o o o o o o o o 4

5-5 L-B ~~ 1- 4 2 o o o o o o

85- ~ : : g g o ~ g ~ g g 21 ~ ~

1 ~ g g a z g g g g

• 21 ::j 4 4 o o 1 o o o o 4 4 o o o o o o

~u 4 4 c 1 l o l o l o a l o o

4 ~ c o l o l o l o o lo a 4i 4 i OI O al o o o l o o

95-

sa-

55-

60

NORSK GEOLOGISK TIDSSKRIFf 80 (2000) Upper Paleozoic carbonates, Barents Sea 159

Appendix 2. Fusulinid zones in we11 7128/6-l and suggested correlation to fusulinid zones in IKU cores (Nilsson 1993; Bugge et al. 1995). The extents of each zone in

well 7128/6-1 and its suggested correlative zones in the IKU cores are indicated in Figs. �. Sarnple locations in the IKU cores are indicated in Appendix l.

Depth

21 1749-1779

20 1783-1798

19 1799-1812.5

18 1813-1832

17 1844-1857

16 1862-1869

15 1875-1897

14 1902-1905

Age

late

Artinskian­

?Kungurian

earl y Artinskian

earl y

Artinskian

late Sakmarian

earl y

Sakmarian

earl y

Sakmarian

late Asselian

midd le

As se lian

Horizon*

Sarginian and Saranian (U)

Irginskian (U)

Burtsevian (U)

Sterlitarnakian

(U)

up per

Tastubian (U)

lower Tastubian (U)

Shikhanian (U)

upper

U skalikian (U)

Notes on 7128/6-1 zones

Occurrence of ParafusuliruJ solidissima, the index species of the late Artinskian fusulinid zone in the Urals (Rauser-Chemousova 1940; Chuvashov et al. 1980) clearly indicates late Artinskian age. This is

also supported by occurrence of Parafusulina

lajaensis and P. lwlviensis, which are cornrnon late

Artinskian spee i es in the Central Urals and Timan­Pechora Basin (Atlas 1986; Konovalova 1991).

PseudofusuliruJ shevelevi, described from Kungurian of the Urals (Zolotova & Baryshnikov 1978), and one

new species more advanced than ParafusuliruJ

solidissima are found at the very top of this interval. Thus, it is possible that beds beginning from leve!

1755 m may be Kungurian.

The assemblage is essentially the same as in the underlying beds, but occurrence of PseudofusuliruJ

pseudoconcavutas may indicate correspondence to

the Irginskian Horizon (Rauser-Chemousova 1949; Chuvashov et al. 1980).

Diagnostic taxa include PseudofusuliruJ kusjanovi,

Ps. concessa, Ps. jurjachaensis, Ps. Pashnjaensis, Ps.

mankomenensis.

Typical Sterlitarnakian taxa as Pseudofusulina

vicaria, Ps. longissima and Zigarella plicatissima

occur only in the uppermost part, but abundant Waeringella in the lower part is characteristic of

Sterlitarnakian in the Timan-Pechora Basin and

Kolguev Island (Konovalova 1991; Davydov 1992).

This zone contains abundant Waeringella and

Pseudofusulina and rare Schwagerina parajaponica

and Schw. aff. paraconfusa, the two latter species characteristic of the upper Tastubian in the Urals

(Rauser-Chemousova 1949; Kireeva 1949). In the

Timan-Pechora Basin and Kolguev Island,

Waeringe/la occurs in both upper Tastubian and Sterlitarnakian Horizons (Konovalova 1991,

Davydov 1992). PseudofusuliruJ sertchejuensis and

Ps. scheljarensis occur only in the upper Tastubian Horizon (Konovalova 1991).

Occurrence of EoparafusuliruJ? paraduplex, E?

tersus, E? duplex and real Eoparafusulina, such as E.

tchemyschevi memoranda and E. tchemyschevi

oblonga indicates correlation with the lower part of

the Tastubian Horizon of the Timan-Pechora Basin, Kolguev Island and Spitsbergen (Grozdilcrva & Lebedeva 1961; Konovalova 1991; Davydov 1992; Nilsson & Davydov 1992).

This zone is defined by the first occurrence of Schwagerina sphaeroidea, which is characteristic of the upper Asselian Shikhanian Horizon in the Central Urals, Timan-Pechora Basin and Spitsbergen (Rauser-Chemousova 1960; Konova1ova 1991; Nilsson & Davydov 1992; Remizova 1995). Other

characteristic species are: Schw. globulus, Schw.

exuberata, Schw. postsphaeroidea,

Sphaeroschwagerina sphaerica, S. sphaerica gigas,

S. kamica, and S. shamovi gerontica.

This zone contains more advanced species of

SphaeroschwageriruJ and Schwagerina similar to the

upper Uskalikian Horizon of the southem Urals.

Correlation to IKU cores

Probably correlates with the Pseudofusulina jenkinsi

zone (Biozone XIII of Bugge et al. 1995).

Not recorded from IKU cores.

The upper part of the EoparafusuliruJ paralinearis­

Schwagerina uralica zone (Biozone XII of Bugge et al. 1995) in 7129/10-U-02 (36-47 m) could be

equivalent with 7128/6-1 zones 18 to 19.

There are no data in the IKU cores providing good correlation with the Sterlitarnakian taxa in the 7128/

6-1 section. However, the EoparafusuliruJ parali­

nearis-Schwagerina uralica zone in 7129/10-U-02 (Biozone XII of Bugge et al. 1995) contains

fusulinids of the Schwagerina uralica group, which ranges into the upper Sakmarian of the central Urals.

May correlate with the lowermost sample from the

Eoparafusulina paralinearis-Schwagerina uralica zone (Biozone XII of Bugge et al. 1995) in 7129/10-

U-02 (74 m), where Schwagerina uralica longa and Schw. uralica volongaensis occur. Both species in

Timan-Pechora Basin first appear in upper Tastubian

and are characteristic of the PseudofusuliruJ vemeuili­

Schwagerina uralica zone (Grozdilova & Lebedeva 1961; Konovalova 1991).

Corre1ates with the upper part of the Sphaeroschwagerina sphaerica gigas zone (Biozone

XI of Bugge et al. 1995) in 7129110-U-02 (75-84 m) and 7030/03-U-01 (27-30 m), where

Eoparafusulina? domestica and Waeringe/la minima occur.

Correlates well with the upper part of the SchwageriruJ princeps-Sphaeroschwagerina moelleri zone through the lower part of the SphaeroschwageriruJ sphaerica gigas zone (Biozones X and XI, respectively, of Bugge et al. 1995) in

7129/10-U-02 (94-105 m) and 7030/03-U-01 (39 m).

The Jowermost beds of the Schwagerina princeps­

Sphaeroschwagerina moelleri zone (Biozone X of

Bugge et al. 1995) of 7129110-U-02 (108-109 m)

contain similar fusulinids (Schwagerina conspecta

and Biwaella omiensis).

160 S. N. Ehrenberg et al.

Appendix 2. (continued).

Depth

13 1926--1927

12 1939

Il 1955-1957

10 1975-1986

9 1995-1999.6

8 2020

7 2034-2043

6 2048-2051

Age

middle Asselian

early Asselian

early Asselian

late Orenburgian

late

Orenburgian

earl y

Orenburgian

earl y Orenburgian

late Gzhelian

Horizon*

lower U skalikian (U)

up per Sjurenian (U)

lower

Sjurenian (U)

upper Melekovskian (M)

lower

Melekovskian

(M)

upper

Noginskian (M)

Notes on 7128/6-1 zones

Schwagerina fecunda suleimanovi, Schw. parafe­

cunda, Schwagerina aff. nathorsti, Schw. nux, and

Schw. ivanovi indicate correlation to the lower Uskalikian Horizon of the southem Urals (Krainer & Davydov 1998). In the Central Urals and Timan­Pechora Basin most of these species characterize the

Schwagerina nux zone (the lower portion of middle

Asselian) (Leven & Davydov 1991; Chuvashov 1993).

This zone contains Sphaeroschwagerina shamovi

primitiva, S. ex gr. fusiformis, S. aff. moelleri, and Schwagerina krotowi, characteristic of the upper

Sjurenian Horizon in the southem Urals (Leven & Davydov 1991).

Species characteristic of the lower Asselian of Spitsbergen, Kolguev Island and Timan-Pechora

Basin (Konovalova 1991; Nilsson & Davydov 1992;

Davydov 1993) include Zigarella fumishi, Z. acuminulata, Z. subovata, Schellwienia

visotchnajaensis, Sch invisitata, Sch. kharjagaensis, and Sch. salebrosa. The assemblage is correlated to

the Sphaeroschwagerina vulgaris aktjubensis zone of

the southem Urals (Davydov 1997).

Species include Zigarella pseudoanderssoni, Z. narjanmarica, Z. grozdilovae, Schellwienia cognata, Sch. emaciata, Sch. grata, Sch. invisitata, and Schwagerina likharevi.

This interval contains diverse taxa of Schellwienia

and rare Daixina of the D. sokensis group. Based on

the occurrence of Schellwienia ulukensis, this interval

belongs to the Ultradaixina bosbytauensis­Schwagerina robusta zone of the southem Urals,

central Asia, Donets Basin, and Camic Alps

(Davydov 1984; Davydov 1990; Davydov 1993; Davydov & Kozur 1997).

This sample contains Daixina sokensis symmetrica, D. sokensis uchtaensis, D. naviculaeformis, D.

peifacilis, D. recava, which are described from the Daixina sokensis zone of the Russian Platforrn and

Urals (Zolotova et al. 1977). In the Southem Urals

these species occur in the Daixina vasylkovskyi zone, equivalent to the upper part of the Daixina sokensis ( sensu lata) zone.

lower Jigulites magnus, Jigulites pecularis, and J. Noginskian (M) fusiformis indicate correlation to the Daixina enormis

zone of the southem Urals.

Pavlovoposa­dian (M)

Jigulites longus longus, J. dagmara and J. jigulensis are characteristic of the Jigulites jigulensis zone of the Moscow Basin (Rosovskaya 1950; Makhlina et al. 1979, 1984).

NORSK GEOLOGISK TIDSSKRIFT 80 (2000)

Correlation to IKU cores

Corresponds to the lower part of the Schwagerina

princeps-Sphaeroschwagerina moelleri zone

(Biozone X of Bugge et al. 1995) of 7030/03-U-01

(50.3-52 m).

Correlates well with the lower Asselian

Sphaeroschwagerina vulgaris zone (Biozone IX of

Bugge et al. 1995) of 7030/03-U-01 (55 m).

Probably corresponds to the upperrnost portion of Zigarella paraanderssoni-Schellwienia arctica zone

(Biozone VIII of Bugge et al. 1995) where Zigarella

anderssoni and 'Schwagerina' sp. A. (probably

Zigarella aff. fumishi) occur.

Corresponds to the middle part of the the Zigarella

paraanderssoni-Schellwienia arctica zone (Biozone VIII of Bugge et al. 1995) in 7030/03-U-01 and

7029/03-U-02.

Apparently corresponds to the lowerrnost part of the

Zigarella paraanderssoni-Schellwienia arctica zone

(Biozone VIII of Bugge et al. 1995) in 7030/03-U-01

and 7029/03-U-02.

Occurrence of Schellwienia sp. B. at 66 m in 7029/03-U-02 suggests correlation with zones 7 and 8 of 7128/6-1.

No similar assemblages are recorded from the IKU cores. However, the Schellwienia sp. A. -

Rugosofusulina praevia zone (Biozone VIT of Bugge et al. 1995; except for the upperrnost sample from this

zone in 7029/03-U-02, at 66 m) corresponds

generally to zones 5 and 6 in 7128/6-1. The

Rugosofusulina ex gr. prisca-Pseudofusulinella

usvae zone (Biozone VI of Bugge et al. 1995) may

correspond to zones 4 and 5 of 7128/6-1.

Pseudofusulinella usvae, which occurs in the

Iowermost beds of the 7030/03-U-01 core, ranges

from Kasimovian through Late Permian, but in the

Arctic this species occurs only in the Gzhelian.

Moreover, the acme zone of Ps. usvae is in the early

Gzhelian. The Rugosofusulina ex gr. prisca -

Pseudofusulinella usvae zone in 7030/03-U-01

(161-166 m) and 7029/03-U-02 (93 m) is therefore

assigned to early Gzhelian age.

NORSK GEOLOGISK TIDSSKR!Ff 80 (2000) Upper Paleozoic carbonates, Barents Sea 16 1

Appendix 2. (continued).

Depth Age Horizon* Notes on 7128/6-1 zones Correlation to IKU cores

5 2055-2075 early Gzhelian Amerevian (M) This assemblage contains Rause rites stuckenbergi, R. postarcticus, and Jigulites procullomensis, which

characterize the Amerevian Horizon (Rosovskaya

1950; 1958; Makhlina et al. 1984; Krainer & Davydov 1998). Rugosofusulina triticitiformis and

Rugosofusulina sp. nov. 2 are also characteristic of this assemblage.

4 2087 early Gzhelian probably This zone comprises only Protonodosaria and Rechitsian (M) Pseudofusulinella species which are stratigraphically

widespread. However, Protonodosaria first appears at the beginning of the Gzhelian and ranges higher (Groves and W ahlman 1997).Because there is no

evidence of an unconforrnity and the succession

appears continous, the stratigraphic position between

upper Kasimovian and lower Gzhelian (Amerevian

Horizon) fusulinids suggests lowermost Gzhelian age.

3 2099 middle lower This sample contains Montiparsus paramontiparsus, Not recorded from IKU cores. Kasimovian Khamovniches- the index species of the Montiparsus

kian (M) paramontiparsus zone (Davydov 1997; Krainer &. Davydov 1998).

2 2100-2112 late upper Fusulinids of this assemblage are Fusiella Not recorded from IKU cores. Moscovian Myachkovian, lancetiformis, Pseudofusulinella eopulchra,

Peskovskaya Quasifusulinoides quasifusulinoides, Protriticites

Fm. (M) ovatus, Fusulinella helenae, characteristic only of the upper Myachkovian Horizon (Rauser-Chemousova et al. 1951; Davydov 1997).

2112.5-2125 late lower Occurrence of Hanostaffella paradoxa, Neostaffella Not recorded from IKU cores.

Moscovian Myachkovian, sphaeroidea, and Fusulinella cf. bocki indicate

Novlinskaya Myachkovian age (Rauser-Chemousova et al. 1951).

Fm. (M)

* (U) =Ural Mountains; (M) = Moscow Basin.