Foraminifera from Late Jurassic – Early Cretaceous Hydrocarbon Seep Carbonates, Central Spitsbergen 157

NORWEGIAN JOURNAL OF GEOLOGY Foraminifera from Late Jurassic – Early Cretaceous hydrocarbon seep carbonates, central Spitsbergen 157

Foraminifera from Late Jurassic – Early Cretaceous hydrocarbon seep carbonates, central Spitsbergen, Svalbard – preliminary results

Hanna Rósa Hjálmarsdóttir, Hans Arne Nakrem & Jeno’’ Nagy

Hjálmarsdóttir, H.R., Nakrem, H.A. & Nagy, J. Foraminifera from Late Jurassic – Early Cretaceous hydrocarbon seep carbonates, central Spitsber- gen, Svalbard – preliminary results. Norwegian Journal of Geology, Vol 92, pp. 157-165. Trondheim 2012, ISSN 029-196X.

Mixed calcareous-agglutinated benthic foraminiferal assemblages have been obtained from five hydrocarbon seep carbonate structures in the upper Slottsmøya Member (Agardhfjellet Formation) in central Spitsbergen, Svalbard. The composition of the agglutinated component is comparable to faunas previously described from the surrounding dark shales of the Slottsmøya Member, as well as from deposits of Arctic Russia and other areas of the Boreal Realm. Calcareous foraminifera are observed only in thin-sections. The foraminifera date the hydrocarbon seep bodies as Late Volgian – Late Ryazanian; an age determination in part slightly divergent from ammonite datings previously recorded from these carbonates. This is the first systematic report of foraminifera from seep structures developed at the Jurassic-Cretaceous transition.

Hanna Rósa Hjálmarsdóttir, Natural History Museum (Geology), University of Oslo, P.O. Box 1172 Blindern, NO-0318 Oslo, Norway. E-mail: hanna. [email protected]; Hans Arne Nakrem, Natural History Museum (Geology), University of Oslo, P.O. Box 1172 Blindern, NO-0318 Oslo, Norway. E-mail: [email protected]; Jenő Nagy, Department of Geosciences, University of Oslo, P.O.Box 1047, Blindern, NO 0316 Oslo, Norway. E-mail: [email protected].

Introduction The Slottsmøya Member consists of dark grey shales with local occurrences of black paper shales containing red to While excavating marine reptile skeletons from Upper yellowish siderite concretions, cold seep carbonate bod- Jurassic dark shales composing the Slottsmøya Mem- ies and siderite and dolomite interbeds. The top of the ber of the Agardhfjellet Formation, 15 carbonate bod- member forms a coarsening-upward shale-silt succession ies interpreted as fossil hydrocarbon seeps (Hammer with a gradational transition to the Myklegardfjellet Bed et al. 2011) were encountered. This fieldwork was done forming the base of the overlying Rurikfjellet Formation. through the years 2006-2010 in the Knorringfjellet- Janusfjellet area south of Sassenfjorden, central Spitsber- The Slottsmøya Member is locally rich in ammo- gen (Fig. 1). The age of the carbonate bodies as based on nites at some horizons (distinct beds with species of well preserved ammonite faunas varies from Late Vol- Dorsoplanites and well preserved ammonites in seep gian to Late Ryazanian (Wierzbowski et al. 2011) (Fig. 2). bodies) and bivalves (mainly species of Buchia) (Birken- The present paper is a preliminary account of the forami- majer et al.1982; Wierzbowski et al. 2011). In recent niferal content of the seep carbonates, with initial strati- years a rich Lagerstätte with well-preserved specimens of graphic information. More detailed analyses focusing on ichthyosaurs, plesiosaurs and pliosaurs has been docu depositional conditions, palaeoecology and taphonomy mented in these deposits (Hurum et al. 2010). Based on will be the topics of a forthcoming study including data sedimentological and micropalaeontological evidence, from the surrounding hypoxic shale facies. the member was deposited in restricted but open marine, shelf environments at water depths of 100-300 m. The Geological setting main restricting factor was hypoxia that alternated with more oxic conditions (Nagy et al. 1988, 2009; Dypvik et The Middle Jurassic to earliest Cretaceous Agardhfjellet al. 1991, 2002; Smelror et al. 2009: p.106). An upwards Formation is subdivided into four members in central- decreasing TOC coupled with an upwards increasing silt eastern Spitsbergen. The uppermost unit, the Slottsmøya content and foraminiferal diversity suggest a generally Member, is dated as Early Volgian to Late Ryazanian shallowing-upwards trend in the depositional environ- (Nagy & Basov 1998; Mørk et al. 1999; Wierzbowski et ment (Nagy et al. 1988; Nagy & Basov 1998). al. 2011) based on ammonites, agglutinated foraminifera and palynomorphs. 158 H.R. Hjálmarsdóttir et al. NORWEGIAN JOURNAL OF GEOLOGY

Figure 1: Geological map of the study area (modified from Dallmann et al. 2001) with inset map of Svalbard indicating the position of the study area.

Figure 2: Lithostratigraphic subdivision and age relationships of the Middle Jurassic to Early Cretaceous succession of central Spitsbergen. The black semi-hemispherical symbols indicate the position of the hydrocarbon seep carbonate bodies discussed in this paper.

Field relations of seep bodies slope. The other seep carbonate bodies are smaller, being The seep bodies were all found between the “Dorsopla- less than 2 m in diameter, and many also have downslope nites bed” and the Myklegardfjellet Bed in the upper part fields of scattered small carbonate blocks. of the Slottsmøya Member at Knorringfjellet and Janus- fjellet (Fig. 1). The largest seep carbonate body (2007- The macrofossils include benthic elements (sponges, 01) is c. 5 m in diameter, but has been fractured by frost bivalves, gastropods, scaphopods, brachiopods, echi- wedging, and thus some of their lateral extent may have noderms, and tube worms) and allochthonous ele- been extended by loose blocks that were sliding down ments from the water column (ammonites, belemnites NORWEGIAN JOURNAL OF GEOLOGY Foraminifera from Late Jurassic – Early Cretaceous hydrocarbon seep carbonates, central Spitsbergen 159 and pieces of wood) (Hammer et al. 2011). Micro shales, where tests are commonly compressed. The intact fossils include uncompressed agglutinated foraminifera, morphologies (e.g., visible apertural details) will provide calcareous foraminifera, ostracods, dinocysts, spores and new information about the test architecture of several pollen (Hammer et al. 2011; Nakrem, unpublished data). taxa in future revisions.

Material and methods The calcareous foraminifera were studied in conven- tional thin-sections of the seep carbonates. All illustrated Material from five seep carbonate bodies was selected for specimens are housed in the Palaeontological Collec- acetic acid treatment. The limestone samples, ranging tion of the Natural History Museum, University of Oslo in weight from 1.50 to 7.65 kilograms, were digested for (PMO). two weeks in 10% acetic acid and then wet sieved using sieves with a mesh diameter between 90 μm and 500 μm. Undissolved residue includes lumps of pyrite, siderite Foraminiferal assemblages and dolomite, as well as agglutinated foraminifera, pelo ids and siliciclastic grains. Fractions larger than 90 μm The agglutinated component were dried and picked for the fossil content including foraminifera. The minimum number of specimens In the five carbonate samples, a total of 35 agglutinated counted in each sample was c. 200. Varying amounts of species are recognised, 18 of which are cited under open the washed residue were used as a basis for the counting. nomenclature (Fig. 3). Some agglutinated genera can The preservation of the foraminiferal tests is excellent also be identified from thin-sections (Fig. 4). The num- due to authigenic precipitation of carbonate leading to ber of agglutinated species per sample varies from 14 to early cementation of the sediment, which has protected 20 (average 17). The most common species are Evoluti- the foraminiferal tests from compaction. This is in con- nella vallata Nagy & Basov and Recurvoides obskiensis trast to the state of preservation in the surrounding black Romanova, followed by Ammobaculites sp. 2, Labrospira

Figure 3: Range chart of foraminiferal taxa in the five sampled seep carbonate bodies presented in a stratigraphic framework based on ammonites. 160 H.R. Hjálmarsdóttir et al. NORWEGIAN JOURNAL OF GEOLOGY

Agardhfjellet Formation. The calcareous forms are only observable in thin-sections from the seep carbonates, and their determination at the species level is rather dif- ficult although their preservation is excellent. The faunas consist mainly of nodosariids including Lenticulina, Astacolus, Lingulina, Marginulina and Globulina. The ceratobuliminid genus Epistomina is in addition present in the youngest seep carbonates. The total range of this genus is Early Jurassic to Early Cretaceous, but it appears generally as common only in the Late Jurassic and Early Cretaceous (Williamson & Stam 1988).

Origin and age of assemblages

Biofacies aspects of seep carbonates and surrounding shales

The low diversity, entirely agglutinated nature of the foraminiferal succession in the shales of the Agardh- Figure 4: Selected agglutinated foraminiferal taxa in thin-sections fjellet Formation is documented in several papers (e.g., from seep carbonates, photographed in transmitted light (TL) and Løfaldli & Nagy 1983; Nagy & Basov 1998). Previous cross-polarised transmitted light (CPTL). Scale bar = 0.1 mm. studies (Nagy et al 1988; Dypvik et al. 1991) explain All from seep sample 2007-01, Knorringfjellet, Spitsbergen. Upper these faunal features by reduced oxygenation, also sug- part of the Slottsmøya Member, Late Ryazanian age. gested by the high to intermediate organic carbon con- A: Labrospira sp. TL, PMO 170.975 B: Labrospira sp. CPTL, PMO 170.975 tent of the Agardhfjellet shales. Hypoxic conditions were C: Recurvoides obskiensis Romanova. TL, PMO 170.976 apparently coupled with increased bottom water acid- D: Recurvoides obskiensis Romanova. CPTL, PMO 170.976 ity, which excluded calcareous taxa and favoured agglu- E: Recurvoides? sp. CPTL, PMO 170.973 tinated assemblages of commonly low diversity. At the present stage of research, however, it cannot be excluded that the absence of calcareous forms is a preservation artifact. Carbonate dissolution is demonstrated by mac- aff. goodenoughensis Chamney and Recurvoides cannin- rofossils such as bivalves and ammonites which are com- gensis (Tappan). The material contains some probable monly are found as internal moulds, without their exter- new species, which will be discussed in subsequent work. nal calcareous shells preserved (field observations).

The assemblages of the five seep samples reveal close Anoxic conditions have not been recognised within similarities to the faunas typical of foraminiferal zones the Agardhfjellet Formation of the Janusfjellet section F6, F7 and F8 recognised by Nagy & Basov (1998) in as shown by analysis of a set of densely-spaced samples the adjacent shale succession of the Slottsmøya Mem- covering the whole formation (Nagy & Basov 1998). ber. These zones are referred to the Upper Volgian – All of the samples contained agglutinated assemblages Upper Ryazanian interval. A marked difference is the although in varying diversities, showing minimum val- occurrence in the carbonates of Bulbobaculites elon- ues in the black paper shales with maximum TOC. gatulus Dain, Recurvoides canningensis and Trocham- mina praerosacea Nagy & Basov, which we consider to Recognition of the hydrocarbon seep carbonates (Ham- be redeposited specimens. The allochthonous nature mer et al. 2011) provides a new aspect to the previously of these occurrences is indicated by the fact that their published depositional model of the Agardhfjellet For- stratigraphic appearances in the Janusfjellet shale suc- mation. Of particular interest is the occurrence of the cession are located clearly below the stratigraphic level varied and rich calcareous faunas including several of the seeps. The previously documented range of these invertebrate groups and calcareous foraminifera (Fig. 5). supposed allochthonous components extends from Kim- meridgian to Middle Volgian (Nagy & Basov 1998). It cannot be excluded, however, that the total range of these Age relationships of seep assemblages species extends to higher stratigraphic levels. The following age assessments of the seep foraminiferal Calcareous assemblages assemblages are mainly based on comparisons with the species ranges reported by Nagy & Basov (1998) from the The seep samples contain a rather diversified calcare- Agardhfjellet Formation, which are correlated with the ous component in contrast to the virtually agglutinated standard boreal ammonite zones, and time-equivalent foraminiferal succession of the shales composing the sections in the Russian Arctic, e.g., the Western Siberian NORWEGIAN JOURNAL OF GEOLOGY Foraminifera from Late Jurassic – Early Cretaceous hydrocarbon seep carbonates, central Spitsbergen 161

Figure 5: Selected calcareous foraminiferal taxa in thin-sections from seep carbonates, photographed in transmitted light (TL) and cross-polarised transmitted light (CPTL). Scale bar = 0.1 mm. All from seep sample 2007-01, Knorringfjellet, Spitsbergen. Upper part of the Slottsmøya Member, Late Ryazanian age. A: Astacolus sp. 1. TL, PMO 214.744 B: Astacolus sp. 1. CPTL, PMO 214.744 C: Marginulina sp. 1. TL, PMO 214.737 D: Marginulinopsis sp. 1. CPTL, PMO 214.737 E: Astacolus sp. 2. TL, PMO 214.787 F: Lingulina sp. 1. TL, PMO 214.737 G: Lenticulina sp. 1. TL, PMO 170.958 H: Lenticulina sp. 1. CPTL, PMO 170.958 I: Epistomina sp. 1. TL, PMO 214.785 J: Epistomina sp. 1. CPTL, PMO 214.785 K: Epistomina sp. 2. CPTL, PMO 214.771 L: Bullopora? sp. 1. TL, PMO 214.778

succession (Bulynnikova et al. 1990) and the Northern are recognised in this sample (Fig. 3). Evolutinella emel- Siberian Nordvik sections (Marinov & Zakharov 2001). janzevi Schleifer has an Upper Volgian distribution in Species cited under open nomenclature are omitted from Spitsbergen (Nagy & Basov 1998), and Trochammina the following discussion, owing to their low stratigraphic annae Levina has previously been reported from Middle significance. Relevant species are illustrated in Figs. 6-8. Volgian deposits of Western and Northern Siberia (Dain 1972; Bulynnikova et al. 1990). Trochammina praerosa- Seep sample 2009-04 cea has a range from Lower Volgian to lowermost Upper Five species with well-defined stratigraphic distribution Volgian (Nagy & Basov 1998). 162 H.R. Hjálmarsdóttir et al. NORWEGIAN JOURNAL OF GEOLOGY

Figure 6: Agglutinated foraminiferal taxa from seep sample 2007-01, Knorring fjellet, Spitsbergen, photographed in reflected light. Upper part of the Slotts- møya Member, Late Ryazanian age. A-D: Evolutinella vallata Nagy & Basov. A: PMO 221.557, B-D: PMO 221.558 E,F: Bulbobaculites elongatulus (Dain). E: PMO 221.399, F: PMO 221.398 G,H,I: Recurvoides obskiensis Romanova. G,I: PMO 221.382, H: PMO 221.381 J,K,L: Labrospira aff. goodenoughensis (Chamney). J: PMO 221.396, K: PMO 221.395, L: PMO 221.394 M,N: Evolutinella emeljanzevi (Schleifer). M: PMO 221.385, N: PMO 221.384

(diachronous) stratigraphic ranges of agglutinated These ranges conflict with the appearances of both benthic foraminifera between basins are well known, Gaudryina rostellata Nagy & Basov and Gaudryina gerkei and many taxa have stratigraphic ranges that vary Vasilenko. Gaudryina rostellata is characteristic of the G. slightly or even markedly from basin to basin (Kaminski rostellata Zone in Nagy & Basov (1998), which is referred & Geroch 1992). The time gap between these last and to the Ryazanian in Spitsbergen, and Gaudryina gerkei is first appearances may also suggest a certain degree of a marker species for this zone. reworking of foraminifera from slightly older strata. The possibly reworked specimens show no sign of Recurvoides canningensis has a poorly defined strati- compression, indicating that the sediment in which they graphic range in Spitsbergen, but is reported to have a were originally embedded was not compacted at the time lower Oxfordian to Upper Kimmeridgian distribution of the seep development and thus reworking seems less in Siberia (Bulynnikova 1972). Evolutinella vallata has a likely to have taken place. Records of ammonites, e.g., long range in Spitsbergen (Middle Volgian – Late Ryaza- Kachpurites sp. (Wierzbowski et al. 2011), which occur nian (Nagy & Basov 1998)), and therefore is not useful in the Okensis Subzone of the Okensis Zone, lowermost for constraining the age. Upper Volgian on the Russian Platform (Zakharov & The above-mentioned foraminifera indicate a Mid Rogov 2008 and references therein) indicate that this is Volgian to Ryazanian age for this seep body. Deviating the oldest seep body which is within the Mid Volgian NORWEGIAN JOURNAL OF GEOLOGY Foraminifera from Late Jurassic – Early Cretaceous hydrocarbon seep carbonates, central Spitsbergen 163

Figure 7: Agglutinated foraminifera from seep sample 2007-01, Knorringfjellet, Spitsbergen, photographed in reflected light. Upper part of the Slottsmøya Mem- ber, Late Ryazanian age. A,B: Gaudryina rostellata Nagy & Basov. A: PMO 221.397, B: PMO 221.389 C,D: Gaudryina gerkei (Vasilenko). C: PMO 221.392, D: PMO 221.393 E,F,G: Recurvoides canningensis (Tappan). E: PMO 221.388, F: PMO 221.387, G: PMO 221.386 H,I: Recurvoides paucus Dubrovskaja. H: PMO 221.400, I: PMO 221.401 J,M: Evolutinella schleiferi (Sharovskaja). J: PMO 221.404, M: PMO 221.403 K,L: Trochammina praerosacea Nagy & Basov. K: Spiral view. PMO 221.390, L: Umbilical view. PMO 221.391 N,O: Ammobaculites sp. 1. N: PMO 221.406, O: PMO 221.405 P: Reophax aff. metensis (Franke). PMO 221.559

– Late Ryazanian time range implied by the foraminiferal The age indicated by Recurvoides obskiensis (Late Volgian occurrences. – Early Valanginian) is supported by the occurrence of Trochammina praerosacea, which has an Early Volgian Seep sample 2007-02 to lowermost Late Volgian range (Nagy & Basov 1998) Six, age-diagnostic, foraminiferal species are present in and Evolutinella vallata, which ranges from Mid Vol- this seep body (Fig. 3). gian to Ryazanian in Spitsbergen (Nagy & Basov 1998). Recurvoides obskiensis has its first appearance in the Trochammina rosacea Zaspelova has a Late Volgian age Upper Volgian in Spitsbergen (Nagy & Basov 1998), but in Western Siberia (Bulynnikova et al. 1990) and a Late has a higher Upper Ryazanian-Lower Valanginian distri- Kimmeridgian to Mid Volgian age in central Spitsbergen, bution in Northern Siberia (Marinov & Zakharov 2001). although it occurs sporadically in the Late Volgian (Nagy It has to be noted, however, that the Siberian range might et al. 1990). be extended upwards by a wide species concept of R. Gaudryina rostellata and Gaudryina gerkei have first obskiensis including transitional forms to the Valangin- occurrences in the Ryazanian which correspond to the ian R. excellens Rygina and other forms with increased age indicated by Recurvoides obskiensis and Evolutinella chamber numbers. Another complicating factor might vallata. Recurvoides canningensis has a deviating age as be the possible Early Valanginian hiatus at the Mykle- compared with Siberian occurrences (Bulynnikova et al. gardfjellet Bed. 1990). 164 H.R. Hjálmarsdóttir et al. NORWEGIAN JOURNAL OF GEOLOGY

the distribution of age-diagnostic species and are also similar to sample 2009-03 (Fig. 3). As in sample 2009-03, their age is limited by the presence of Gaudryina rostellata and Gaudryina gerkei to the Mid to Late Ryazanian. A rich occurrence of Recurvoides obskiensis in both samples supports this age, as do the occurrences of Evoluti- nella vallata, Evolutinella schleiferi, Orientalia baccula and Recurvoides paucus, which all extend into the Late Ryazanian. An interesting occurrence is that of Ammobaculites praegoodlandensis Bulynnikova. In Northern Siberia, it ranges from the Late Volgian to Ryazanian, and within the Ryazanian in Western Siberia (Bulynnikova et al. 1990). In Spitsbergen it has, however, previously been found in an interval correlated with the Mid to Late Volgian transition (Nagy & Basov 1998). As in sample 2009-03, Trochammina praerosacea, Recur- voides canningensis and Trochammina rosacea are also known from older units. Ammonites in seep body 2007-01, including Tollia (Tollia) tolli Pavlow and Surites (Bojarkia) tzikwinianus (Bogoslovsky) are indicative on an age close to the Ryaza- nian-Valanginian boundary, see e.g., Schulgina (1969), Figure 8: Agglutinated foraminifera from seep sample 2009-04, Surlyk (1978) and Mesezhnikov (1984), and thus indicate Janusfjellet, Spitsbergen, photographed in reflected light. Upper part that this is the youngest seep body. The foraminifera sup- of the Slottsmøya Member, Late Volgian age. port this age. A,B: Evolutinella emeljanzevi (Schleifer). A: PMO 221.409, B: PMO 221.408 C: Ammodiscus aff. uglicus (Ehremeeva). PMO 221.412 D,E: Textularia sp. 1. D: PMO 221.411, E: PMO 221.410 Conclusions

The recently discovered seep carbonate bodies of the Slottsmøya Member (Agardhfjellet Formation) contain The co-occurrence of the ammonites Craspedites mixed foraminiferal assemblages of agglutinated and cal- (Craspedites) okensis (d’Orbigny) and C. (Taimyroceras) careous species. originalis (Schulgina) in this seep body (Wierzbowski et al. 2011) is indicative of the Originalis Subzone of the These foraminifera are uniquely well preserved, espe- upper part of the Okensis Zone, earliest Late Volgian cially when compared to the assemblages reported from (Zakharov & Rogov 2008 and references therein). The the surrounding black shales. The excellent preservation foraminifera indicate a somewhat younger age than the in the seep bodies is due to authigenic precipitation of ammonites for this seep body. carbonate that led to early cementation of the sediment. No test deformation is observed, which is otherwise very Seep sample 2009-03 common in the shale assemblage consisting entirely of Stratigraphically important species in this carbonate agglutinated taxa. body include Recurvoides obskiensis, Trochammina rosacea and Evolutinella vallata. First occurrences of Orient The foraminifera extracted from the five analysed seep alia baccula Schleifer, Evolutinella schleiferi Sharovskaya bodies in general support the ages previously docu- and Recurvoides paucus Dubrovskaja are recorded here mented by ammonites. There are some discrepancies and according to Nagy & Basov (1998) all these species which may be attributed to reworking or mixing, includ- have a latest Volgian - Ryazanian age in Spitsbergen. ing the downward growth of seep carbonate into older The age of this sample is constrained by occurrence of sediments (maybe as much as a metre down) (Bayona Gaudryina rostellata and Gaudryina gerkei to the Mid to et al. 2009), extremely low sedimentation rates at seep Late Ryazanian. Trochammina praerosacea, Recurvoides sites as documented in Recent pockmarks, and gravity canningensis and Trochammina rosacea have deviating flows down pockmark slopes. It is also known (Kamin- older ranges, see discussion above. No ammonites have ski & Geroch 1992) that benthic foraminifera may have been found in this seep body. diachronous distribution between different sedimen- tary basins. The absence of compression or physical Seep samples 2007-01 and 2007-03 wear of the foraminiferal tests suggests that little or no These two samples are essentially identical concerning reworking processes have taken place. The foraminiferal NORWEGIAN JOURNAL OF GEOLOGY Foraminifera from Late Jurassic – Early Cretaceous hydrocarbon seep carbonates, central Spitsbergen 165 stratigraphy revealed for the seep carbonates gener- nated Foraminifera in correlating Lower Cretaceous pelagic and ally corresponds to the stratigraphy of Siberian succes- flysch sequences: current status and prospects for the future. Creta- ceous Research 13, 453-466. sions. There are some problems, however, because of Løfaldli, M. & Nagy, J. 1983: Agglutinating foraminifera in Jurassic inadequate stratigraphic stabilisation of a few species and Cretaceous dark shales in southern Spitsbergen. In: Verdenius, in Spitsbergen. Further adjustments and more precise J.G., van Hinte, J.E. & Fortuin, A.R. 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