Downloaded from http://sp.lyellcollection.org/ by guest on October 1, 2021 Glaciogenic reservoirs and hydrocarbon systems: an introduction M. HUUSE1*, D. P. LE HERON2, R. DIXON3, J. REDFERN1, A. MOSCARIELLO4 & J. CRAIG5 1The University of Manchester, Manchester, UK 2Royal Holloway University of London, London, UK 3BP Exploration Operation Company Ltd, Sunbury on Thames, UK 4University of Geneva, Geneva, Switzerland 5Eni Exploration & Production, Milan, Italy *Corresponding author (e-mail: [email protected]) Abstract: Glaciogenic reservoirs host important hydrocarbon and groundwater resources across the globe. Their complexity and importance for exploration and palaeoclimate reconstruction have made glaciogenic successions popular subjects for study. In this paper we provide an over- view of the palaeoclimatic and tectonic setting for Earth glaciation and a chronological account of glaciogenic deposits since c. 750 Ma, with particular emphasis on their reservoir potential and associated hydrocarbon systems. Hydrocarbon accumulations within glaciogenic reservoirs occur principally in Palaeozoic (Late Ordovician and Permo-Carboniferous) sandstones in South America, Australia, North Africa and the Middle East, with relatively minor occurrences of shallow gas hosted in Pleistocene deposits in the North Sea and Canada. Groundwater reserves occur within glaciogenic sandstones across the northern European lowland and in North America. The main glaciogenic environments range from subglacial to glacier front to proglacial and deglacial. Rapidly changing environments, hydrodynamic regimes and glacier-front and sub- glacial deformation often result in very complex glaciogenic sequences with significant challenges for reconstruction of their origin and resource importance, which this volume seeks to address. Glaciogenic deposits constitute reservoirs for hydro- lake and continental shelf areas, as well as adjacent carbons in sedimentary basins across the globe, with continental slopes where large trough mouth fans reservoir ages ranging from Neoproterozoic to constitute volumetrically important deposits from Pleistocene (Fig. 1; Table 1). Onshore, Pleistocene Pleistocene glaciations (Sejrup et al. 2003; Ottesen glacial deposits are important reservoirs for ground- et al. 2012). In deep ocean settings, ice-rafted debris water in NW Europe and in North America, while provides the most important physical record of the offshore glacial deposits constitute potential drilling Pleistocene shelf glaciations (Hemming 2004). hazards and pose problems for deeper seismic The term ‘glaciogenic hydrocarbon systems’ can imaging due to their often anomalous infill litholo- be applied to any hydrocarbon system where at gies and pore fluids (in particular methane). Major least one part of that system is linked to glaciation. glaciations through Earth history appear on regular For example, we recognize glaciogenic reservoirs, 300–350 Myr cycles, with the Late Ordovician deglacial source rocks, glaciogenic seals, glacio- glaciation breaking this trend (Fig. 2; Page et al. genic deformation (glaciotectonics and glacial load- 2007). Important controls on glaciation include ing/unloading cycles), glacial sculpting of reservoir plate tectonic configuration (Fig. 3), ocean circula- rocks or cold climate conditions leading to gas tion and atmospheric CO2 pressure (Fig. 2; Craig hydrate formation. Source rock deposition linked et al. 2009). Growth of continental ice sheets leads with glaciation tends to be favoured by remnant topo- to global sea-level fall (Zachos et al. 2001; Miller graphic relief linked with glacial sculpting and et al. 2005), thus affecting depositional patterns transgressive and high sea-level stands causing con- worldwide, and also causes flexing of the litho- densed organic-rich sediment accumulation (Lu¨ning sphere within tens to a hundred kilometres from et al. 2000; Craig et al. 2009; Moreau 2011; Le the ice sheet margin and isostatic depression under Heron & Craig 2012). A common glaciogenic res- the ice sheet itself (e.g. Lambeck et al. 1998). ervoir and source rock system is deposited follow- Glaciogenic deposits are largely preserved in for- ing a glacial advance (lowstand), with subsequent merly glaciated lowland areas, including land, deposition of thick clastic reservoir systems during From:Huuse, M., Redfern, J., Le Heron, D. P., Dixon, R. J., Moscariello,A.&Craig, J. (eds) 2012. Glaciogenic Reservoirs and Hydrocarbon Systems. Geological Society, London, Special Publications, 368, 1–28. First published online November 19, 2012, http://dx.doi.org/10.1144/SP368.19 # The Geological Society of London 2012. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics Downloaded from http://sp.lyellcollection.org/ by guest on October 1, 2021 2 M. HUUSE ET AL. Fig. 1. Global distribution of glaciogenic reservoir and hydrocarbon system case studies (this volume). Cryogenian (c. 690 Ma): 1, Le Heron & Craig (2012). Ordovician (c. 444 Ma): 2, Hirst (2012); 3, Lang et al. (2012a, b); 4, Girard et al. (2012); 5, Douillet et al. (2012). Permo–Carboniferous: 6, Bache et al. (2012); 7, Martin et al. (2012). Oligo-Miocene: 8, Fielding et al. (2012). Pleistocene: 9–18. Key to case study numbers provided in Table 1. the ice retreat phase. Later during the deglacial contain structures formed by high-velocity jet-like transgression, the glaciogenic reservoirs are often water flows, not commonly observed with deposi- enhanced by transgressive reworking, and sub- tion under non-glacial hydrological conditions. In sequently overlain by sealing mudrocks, which, dur- many cases, associated larger-scale morphological ing the later stages of glaciation may be organic-rich features (observed at outcrop or in seismic data in source rocks. When more than one glacial cycle the subsurface), such as cross-shelf troughs, tunnel exists, intra-formational seals and possible source valleys, megascale glacial lineations (MSGLs), rock strata may also be found interbedded with the drumlins, iceberg scours, striations, moraines and reservoirs. The largest recorded transgression asso- glaciotectonics structures, allude to a likely glacio- ciated with rich post-glacial source rocks are found genic origin. in the early Silurian, following the Late Ordovician The specific origin of some glaciogenic features glacial interval (Fig. 2; Page et al. 2007). During the (e.g. cross shelf troughs, iceberg ploughmarks, drop- Pleistocene, numerous transgressive intervals are stones and moraines) is well documented, whereas recognized between glacial cycles (Zachos et al. others are being vigorously debated (e.g. tunnel val- 2001; Miller et al. 2005). leys, MSGLs, drumlins). Tunnel valleys, in particu- Glaciogenic sediments with reservoir potential lar, have been studied and debated for over a century may be deposited in a range of environments includ- (Ussing 1903; Ehlers et al. 1984; O’Cofaigh 1996; ing subaerial, subglacial, proglacial, lacustrine, shal- Huuse & Lykke-Andersen 2000a; van der Vegt low marine and deep offshore (Fig. 4). While some et al. 2012). Tunnel valleys can be hundreds of glaciogenic sediments may be difficult to distinguish metres deep, kilometres wide and many tens of kilo- from deposits not associated with glaciation, others metres long, incising lowland glacial and preglacial contain distinctive outsize clasts, large boulders substrates. They therefore represent huge reposi- and pebbles, sometimes striated, which are typical tories of glaciogenic (glacial, deglacial) and inter- of glacial environments. Glacial deposits are also glacial deposits in otherwise low-accommodation often associated with sandstone intrusions and other settings (e.g. Cummings et al. 2012). For this rea- soft-sediment deformation structures, produced son, an understanding of tunnel valley fill lithologies due to ice sheet loading, push or fluctuating water and facies variations would be a useful tool for reser- tables (Brodzikowski & van Loon 1991; Schack voir prediction. Unfortunately, to date, a consistent Pedersen 2012). Glaciogenic sandstones often model linking tunnel valley formation and infill Table 1. Summary of studies in this volume Downloaded from Authors* Region Area Age Case study/review Data & methods Significance Andersen et al. (9) NW Europe Denmark (on- & Pleistocene Tunnel valley 2D & 3D Seismic & EM Groundwater reservoir offshore) morphometrics Bache et al. (6) South America Bolivia (onshore) Permo-Carboniferous Glaciogenic valleys and 2D Seismic & Wireline Hydrocarbon reservoir fills logs Buckley (10) NW Europe North Sea (UK) Pleistocene Grounded ice evidence 2D & 3D Seismic Hazards & chronology http://sp.lyellcollection.org/ Douillet et al. (5) North Africa Jordan (onshore) Ordovician Tunnel valley fill Outcrop Hydrocarbon reservoir properties GLACIOGENIC RESERVOIRS: INTRODUCTION Fielding et al. (8) Antarctica McMurdo Sound Oligo-Miocene Glaciogenic Reservoir Subsurface Reservoir properties (offshore) Properties Girard et al. (2) North Africa Tassili N’Ajjer Ordovician Outwash channels Outcrop Hydrocarbon reservoir (Algeria/Libya) Hirst (3) North Africa Illizi Basin (Algeria) Ordovician Facies succession and Outcrop & Subsurface Hydrocarbon reservoir origin Kristensen & Huuse NW Europe North Sea (DK) Pleistocene Tunnel valley fills 3D & 2D seismic Hazards/imaging (11) Lang et al. (4) North Africa Illizi Basin (Algeria) Ordovician Sequence stratigraphy Core & wireline logs Hydrocarbon reservoir and facies Le Heron & Craig (1) Australia Centralian Superbasin Neo-Proterozoic