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Upper Triassic–Middle Jurassic) in Western Central Spitsbergen, Svalbard

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Upper Triassic–Middle Jurassic) in Western Central Spitsbergen, Svalbard NORWEGIAN JOURNAL OF GEOLOGY Vol 99 Nr. 2 https://dx.doi.org/10.17850/njg001 Facies, palynostratigraphy and sequence stratigraphy of the Wilhelmøya Subgroup (Upper Triassic–Middle Jurassic) in western central Spitsbergen, Svalbard Bjarte Rismyhr1,2, Tor Bjærke3, Snorre Olaussen2, Mark Joseph Mulrooney2,4 & Kim Senger2 1 Department of Earth Science, University of Bergen, P.O. Box 7803, N–5020 Bergen, Norway. 2Department of Arctic Geology, University Centre in Svalbard, P.O. Box 156, 9171 Longyearbyen, Norway. 3Applied Petroleum Technology AS, P.O. Box 173, Kalbakken, 0903 Oslo. 4Department of Geoscience, University of Oslo, P.O. Box 1047 Blindern, 0316 Oslo, Norway. E-mail corresponding author (Bjarte Rismyhr): [email protected] The Wilhelmøya Subgroup (Norian–Bathonian) is considered as the prime storage unit for locally produced CO2 in Longyearbyen on the Arctic archipelago of Svalbard. We here present new drillcore and outcrop data and refined sedimentological and sequence-stratigraphic interpretations from western central Spitsbergen in and around the main potential CO2-storage area. The Wilhelmøya Subgroup encompasses a relatively thin (15–24 m) siliciclastic succession of mudstones, sandstones and conglomerates and represents an unconventional potential reservoir unit due to its relatively poor reservoir properties, i.e., low-moderate porosity and low permeability. Thirteen sedimentary facies were identified in the succession and subsequently grouped into five facies associations, reflecting deposition in various marginal marine to partly sediment-starved, shallow shelf environments. Palynological analysis was performed to determine the age and aid in the correlation between outcrop and subsurface sections. The palynological data allow identification of three unconformity-bounded sequences (sequence 1–3). These sequences record intermittent deposition in the Early Norian, Early–Middle Toarcian, and Late Toarcian–Aalenian, interrupted by extended periods of erosion, bypass and/or non-deposition. The stratigraphically condensed development of the Wilhelmøya Subgroup in western central Spitsbergen is interpreted to be the result of very low subsidence rates coupled with a physiographic setting characterised by a very gentle depositional gradient. This facilitated rapid shoreline shifts in response to even relatively modest variations in relative sea level with considerable influence on the resulting depositional patterns. We present a revised depositional model for the regionally distinct Brentskardhaugen Bed at the top of the Wilhelmøya Subgroup involving condensation and partial reworking of a series of Upper Toarcian–Aalenian, high-frequency sequences. Coarse-grained extraformational fractions observed within conglomerates of the Wilhelmøya Subgroup are suggested to have been supplied from uplifted and exposed margins to the west (northern Greenland) and north (northern Svalbard). Keywords: Wilhelmøya Subgroup, Brentskardhaugen Bed, sequence stratigraphy, facies analysis, palynology, condensed unit Received 1. November 2017 / Accepted 15. April 2018 / Published online 19. October 2018 Introduction Senger et al., 2015). The prime source for the CO2 is the coal-fuelled power plant in Longyearbyen, emitting The Longyearbyen CO2 Lab (LYB CO2) project is a joint c. 70,000 tons of CO2 annually, and a suitable target ongoing effort by academic and industry partners to formation has been identified in the siliciclastic Kapp establish a test facility for the underground storage of Toscana Group at c. 670–970 m depth. To date, a diverse CO2 in the vicinity of Longyearbyen on the Norwegian collection of subsurface and field data have been acquired Arctic archipelago of Svalbard (e.g., Braathen et al., 2012; and analysed as part of the project, including more than Rismyhr, B., Bjærke, T., Olaussen, S., Mulrooney, M.J. & Senger, K. 2019: Facies, palynostratigraphy and sequence stratigraphy of the Wilhelmøya Subgroup (Upper Triassic–Middle Jurassic) in western central Spitsbergen, Svalbard. Norwegian Journal of Geology 99, 183–212. https://dx.doi.org/10.17850/njg001. © Copyright the authors. This work is licensed under a Creative Commons Attribution 4.0 International License. 183 184 B. Rismyhr et al. Stratigraphic Tectonic units in A 0 20 40 60 80 100 CANADA North Pole Sevarnaya Zemlya B Group RUSSIA Activity LYB CO2 km wells Arctic Ocean Age Lithology Q. Local Franz Josef Land volcanism RUSSIA Ma Mioc. Uplift and Greenland Svalbard 22.5 DENMARK NORWAY NEOG. erosion Oligo. Extension Greenland 38 Sea Kvitøya Novaya West Van Mijen- Eocen. Zemlya 55 ALEO Spitsbergen RUSSIA P fjorden 65 Pal. Orogeny Hinlopenstretet Compression Wijdefj. Barents Sea Uplift and NORWAY Upper erosion Isispynten RUSSIA Nordaust- ICELAND 100 ACEOUS Clastic landet SWEDEN wedges Volcanism, Carolinefjellet Lower CRET uplift and erosion in Helvetiafjellet Adventdalen Rurikfjellet 141 north 79° Upper Agardhfjellet 160 arls LandKongsøya Mid. Kong K 176 Condensed Wilhelmøya SG JURASSIC and hiatuses Lower Kapp Toscana Prins 195 De Geerdalen Karls Svenskøya Upper Clastic Spitsbergen 212 wedges TD Forland Mid. 223 Sassendalen Epicontinental sea/sag basin L. C Barentsøya 230 TRIASSIC WSFTB Isfjorden Upper Tempelfjorden 78° LYB 251 PERMIAN Lower Sedimentary/Metamorphic 280 290 Up. Gipsdalen Edgeøya Paleogene Bellsund CSB Jurassic-Cretaceous Middle Rifting 315 along fjorden Triassic Billefjorden Lineament Lower Billefjorden Stor Carboniferous-Permian 345 CARBONIFEROUS Devonian Svalbardian 77° 360 Upper Deformation Early Paleozoic- M. 369 Andree Land Hornsund Paleoproterozoic Lower Hecla Hoek east of DEVONIAN Billefjorden Fault Cretaceous 395 intrusions (dolerite) Hecla Hoek Hecla H. Hopen Cretaceous PreC-S basalt flows Sandstones Evaporites Basement Mudstones Carbonates Hiatus C Syltoppen Billefjorden Sassenfjorden Tempelfjorden ‘Criocerasdalen’ Konusdalen Marhøgda Billefjorden Fault Zone LYB CO2 a’ DH1, DH2 LYB CO2 DH3,DH4, DH5R,DH6, DH7A, DH8 LYB Isfjorden Advent- dalen Festningen Coles- bukta Grønfjorden a 0 km 10 D West Spitsbergen Fold and Thrust Belt Central Spitsbergen Basin Billefjorden Fault Zone 1000 a Grønfjorden Colesbukta Nordenskiöldfjellet Adventdalen a’ Festningen LYB CO2 DH4, DH5R,DH7A 0 -1000 Thrust fault -2000 Normal fault Angular unconformity Figure 1. Regional, geological and stratigraphic setting of Svalbard. (A) Simplified geological map of the Svalbard archipelago with the study area marked by a rectangle. Inset map shows the geographic location of Svalbard. Geological map modified from ©Norwegian Polar Institute, npolar.no. (B) Simplified stratigraphic column of Svalbard, drilled formations in the CO2 wells and overview of main tectonic phases since the Precambrian. Adapted from Nøttvedt et al. (1993b). (C) Close-up of study area with location of drill sites and investigated outcrop sections. Dashed line shows correlation line used in Fig. 11. Map modified from ©Norwegian Polar Institute, npolar.no. (D) Geological cross- section of the study area with projected position of wells and the Festningen outcrop section. Redrawn and modified from Dallmann (2015). Abbreviations: WSFTB – West Spitsbergen Fold and Thrust Belt, CSB – Central Spitsbergen Basin, LYB – Longyearbyen, TD – total depth. NORWEGIAN JOURNAL OF GEOLOGY Facies, palynostratigraphy and sequence stratigraphy of the Wilhelmøya Subgroup in Spitsbergen, Svalbard 185 4 km of drillcore from 8 onshore slimhole wells drilled the most promising reservoir interval (Braathen et al., near Longyearbyen (Fig. 1). Previous studies have shown 2012). Since both diagenetic effects and the intensity, that the targeted storage unit is underpressured and distribution and orientation of natural fractures have compartmentalised (Braathen et al., 2012; Senger et been shown to vary considerably with lithology and al., 2015; Mulrooney et al., 2019), and characterised by sedimentary facies (Ogata et al., 2012, 2014; Mørk, 2013), moderate porosities and low matrix permeabilities (i.e., determination of the internal facies distribution within unconventional reservoir) due to extensive mechanical the Wilhelmøya Subgroup is therefore of significant and chemical compaction (Farokhpoor et al., 2010; importance. This can subsequently be used as input into Mørk, 2013). Water injection tests and numerical increasingly more detailed reservoir models (Mulrooney simulations, however, indicate relatively good lateral et al., 2019), volumetric calculations and storage fluid flow facilitated by an extensive network of natural resource estimates (Senger et al., 2015), and contribute fractures (Braathen et al., 2012; Ogata et al., 2012, 2014; to improved predictions of CO2 injection behaviour and Van Stappen et al., 2014; Mulrooney et al., 2019) which subsequent migration trends. also contribute to the overall storage capacity (Senger et al., 2015). In this contribution, we refine the facies and sequence- stratigraphic interpretations of the Wilhelmøya Subgroup The upper part of the Kapp Toscana Group, comprising in and around the CO2 storage area based on extensive conglomerates, sandstones and mudstones of the new field and drillcore data. This was accomplished stratigraphically condensed, Early Norian–Bathonian, through detailed facies analysis of drillcores and outcrop Wilhelmøya Subgroup (Figs. 1B & 2; Mørk et al., 1999), material, with new palynological data from core samples offers the best reservoir properties and is considered providing a framework for sequence delineation and TVD MSL -2 m TVD MSL -20 m Drill
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