Journal of the Geological Society , London, Vol. 164, 2007, pp. 1–15. Printed in Great Britain. 1 1 Deformation bands in sandstone: a review 2 HAAKON FOSSEN 1 , RICHARD A. SCHULTZ 2 , ZOE K. SHIPTON 3 & KAREN MAIR 4 3 1 Centre of Integrated Petroleum Research, University of Bergen, Alle ´gaten 41, N-5007 Bergen, Norway 4 (e-mail: Haakon.Fossen@geo.uib.no) 5 2 Geomechanics–Rock Fracture Group, Department of Geological Sciences/172, Mackay School of Earth Sciences and 6 Engineering, University of Nevada, Reno NV 89557, USA 7 3 Department of Geographical and Earth Sciences, Gregory Building, University of Glasgow, Glasgow G12 8QQ, UK 8 4 Physics of Geological Processes, University of Oslo, PO 1048 Blindern, 0316 Oslo, Norway 9 Abstract: Deformation bands are the most common strain localization feature found in deformed porous 10 sandstones and sediments, including Quaternary deposits, soft gravity slides and tectonically affected 11 sandstones in hydrocarbon reservoirs and aquifers. They occur as various types of tabular deformation zones 12 where grain reorganization occurs by grain sliding, rotation and/or fracture during overall dilation, shearing, 13 and/or compaction. Deformation bands with a component of shear are most common and typically 14 accommodate shear offsets of millimetres to centimetres. They can occur as single structures or cluster zones, 15 and are the main deformation element of fault damage zones in porous rocks. Factors such as porosity, 16 mineralogy, grain size and shape, lithification, state of stress and burial depth control the type of deformation 17 band formed. Of the different types, phyllosilicate bands and most notably cataclastic deformation bands show 18 the largest reduction in permeability, and thus have the greatest potential to influence fluid flow. 19 Disaggregation bands, where non-cataclastic, granular flow is the dominant mechanism, show little influence 20 on fluid flow unless assisted by chemical compaction or cementation. 21 Deformation of stiff, low-porosity rock in the uppermost few 22 kilometres of the Earth’s crust occurs primarily by fracturing. 23 This can result in extensional fractures, such as joints and veins, 24 or shear fractures such as slip surfaces, which generally form the 25 primary deformation elements of faults in low-porosity rocks. 26 The process of fault formation and propagation in brittle low- 27 porosity rocks has been described in terms of linking of 28 microfractures and the reactivation or linking of mesoscopic 29 joints (e.g. Pollard & Fletcher 2005). The key element in a fault 30 is the slip surface, where the majority of offset has accumulated. 31 Surrounding fractures constitute an enveloping damage zone 32 (Caine et al. 1996). Slip surfaces and extension fractures, 33 structures that will be referred to in this paper as ordinary 34 fractures, typically represent mechanically weak structures that 35 are prone to reactivation and continued slip during subsequent 36 stress build-up. 37 Strain in highly porous rocks and sediments is not initially 38 accommodated by extensional fractures or slip surfaces. Instead, 39 strain localization occurs by the formation of deformation 40 structures commonly referred to as deformation bands. Localized 41 (higher offset) faults subsequently form by the failure of 42 deformation band zones. 43 Deformation bands in porous rocks are low-displacement 44 deformation zones of millimetres to centimetres thickness (Fig. 45 1) that tend to have enhanced cohesion and reduced permeability 46 compared with ordinary fractures. Quaternary geologists find 47 them in glacially or gravitationally deformed sand, where they 48 may reveal information on the local glacial history. Sedimentol- 49 ogists frequently encounter them in sandstones, where they may 50 be generated during soft-sediment deformation or post-burial 51 faulting. Petroleum geologists and hydrogeologists (should) look 52 for them in cores from clastic reservoirs and aquifers because of 53 their potential role as barriers or baffles to fluid flow (Pitman 54 1981; Jamison & Stearns 1982; Gabrielsen & Koestler 1987; 1 Antonellini & Aydin 1994, 1995; Beach et al. 1997; Knipe et al. 2 1997; Gibson 1998; Antonellini et al. 1999; Heynekamp et al. 3 1999; Hesthammer & Fossen 2000; Taylor & Pollard 2000; Lothe 4 et al. 2002; Shipton et al. 2002, 2005; Sample et al. 2006) and 5 because they commonly indicate proximity to a larger offset 6 fault. From an academic point of view, deformation bands 7 deserve attention because they provide important information on 8 the unique way that faults form in porous sandstones (e.g. Aydin 9 & Johnson 1978; Johnson 1995; Davis 1999) and on progressive 10 deformation in porous rocks in general (e.g. Wong et al. 2004; 11 Schultz & Siddharthan 2005). In this paper we review the 12 existing literature on deformation bands, present a classification 13 of deformation bands based on deformation mechanism and 14 discuss how the distinctive characteristics of deformation bands 15 relates to burial depth, lithology and fluid flow. 16 Characteristics of deformation bands 17 The term deformation band has long been used in different ways 18 in fields such as material science (e.g. Brown et al. 1968) and 19 crystal–plastic deformation of rock (e.g. Passchier & Trouw 20 1996); however, it was first applied in the context of sandstone 21 deformation by Aydin and co-workers (Aydin 1978; Aydin & 22 Johnson 1978, 1983). Since then, the term has gradually been 23 adopted to encompass terms such as microfaults (Jamison & 24 Stearns 1982), cataclastic faults (Fisher & Knipe 2001), faults 25 (Manzocchi et al. 1998; Fisher et al. 2003), (micro)fractures 26 (Borg et al. 1960; Dunn et al. 1973; Gabrielsen & Koestler 27 1987), shear bands (Meme ´ndez et al. 1996), deformation-band 28 shear zones (Davis 1999), Lu ¨ders’ bands (Friedman & Logan 29 1973; Olsson 2000), cataclastic slip bands (Fowles & Burley 30 1994), and granulation seams (Pittman 1981; Beach et al. 1999; 31 Du Bernard et al. 2002b). The most important characteristics of Article number = 06036 1 2