Chapter One: Introduction
1.3. Geological setting
The Faeroe Shetland Basin, geographically dem arcated by the Faeroe and Shetland Islands, is located on the N W European continental m argin and form s the study area for this project (Fig. 1.1) The Faeroe-Shetland Channel is the m odem bathym etric expression o f the Faeroe- Shetland Basin, w hich consists o f a series o f M esozoic tilted fault blocks overlain by a thick Cenozoic post rift sedim entary succession (Fig. 1.2, Bott et al., 1984; M udge and Rashid,
1987; Dore et al., 1999; Roberts et al., 1999). M ultiple rift episodes betw een the Triassic and the Palaeocene w ere responsible for generation o f the basin, w ith the final rift episode resulting in significant thinning o f the crust and generation o f a deep w ater m arine
basin prior to the opening o f the N orth A tlantic (Skogseid et al., 1992; D ean et al., 1999).
Structurally, the SE lim it o f the basin is defined by the Shetland Spine Fault w hich closely underlies the Shetland slope break, w hile the Faeroese m argin is defined by a thick basalt succession w hich has been folded b y com pressional forces to form a series o f large
anticlines including (from north to south) the F ugloy R idge , the East Faeroes Ridge, and the M unkagrunnar R idge am ong others (Figs. 1.1 & 1.2, W aagstein, 1988; H itchin and Ritchie, 1987; Boldreel and A ndersen, 1993; Boldreel and A ndersen, 1995; N adin et al., 1997;
N aylor et al., 1999).
A b rie f account o f the Cenozoic developm ent o f the basin is docum ented in order to sum m arise the geological evolution o f the basin that is relevant to this study. D uring the Palaeocene, thick sandstones w ere shed into the deep w ater Faeroe Shetland B asin from highlands to the south as a result o f tectonic uplift associated w ith the im pingem ent o f the proto-Iceland plum e at the base o f the cm st (W hite, 1989; M itchell et al., 1993; W hite and Lovell, 1997; Lam ers and Carm ichael, 1999; Jolley and Bell, 2002). Effusion o f volum inous flood basalts and intrusion o f igneous sills and dykes at this tim e associated w ith the m antle plum e resulted in creation o f the 5km thick Faeroese Platform , and definition o f the Faeroese m argin o f the basin, the lim it o f w hich is represented by the Faeroe-Shetland Escarpm ent (Fig. 1.1, W aagstein, 1988; N adin et al., 1997; N aylor et al., 1999). D uring the early Eocene, N-S oriented com pression associated w ith the initiation o f spreading on the A egir Ridge to the north o f the Faeroe Shetland Basin in association w ith opening o f the northern N orth A tlantic resulted in generation o f significant com pressional structures including the W yville Thom pson Ridge, w hich consists o f a ram p anticline underlain by a northerly dipping fault
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Chapter One Introduction
Continental crust beneath Faeroe
Westray Rona
Ridge Ridge
F aeroes Margin
East Faeroes Ridge
beneath basalts?
I 1 B asem ent M esozoic
Igneous Rocks 1 I P alaeocen e
E ocene-O ligocene N eogen e-R ecen t
Figure 1.2
Schematic cross section across the Faeroe Shetland Basin to illustrate the underlying structure of the basin and the nature o f the Cenozoic sediment fill (line location Figure 1.1). The basin is bounded by large NW dipping normal faults on the Shetland margin, and a combination of probable fault blocks combined with Palaeocene lavas on the Faeroese margin. The thick lava succession on the Faeroese margin hampers imaging o f underlying Mesozoic stratigraphy and structure. Figure modified from Dore et al. (1999).
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Chapter One Introduction
plane (Boldreel and A ndersen, 1993). W ithdraw al o f the plum e and associated subsidence o f the southern Faeroe Shetland Basin w as accom panied b y a m ajor southerly m arine
transgression and deposition o f the B alder Form ation, w hich records the transition from incised valley netw ork to delta top environm ent and finally establishm ent o f deep w ater m arine conditions (at least 300m) during the early Eocene (Y presian) (Ebdon et al., 1995;
Sm allw ood and Gill, 2002). The top B alder Form ation provides a regionally correlatable seism ic reflection w ithin the basin (Ebdon et al., 1995; Sm allw ood and Gill, 2002;
R obinson, 2004). The Eocene succession o f the Faeroe Shetland Basin is characterised by sh elf m argin progradation in the southern Faeroe Shetland B asin and m arine hem ipelagite deposition in the deep w ater (c. 1000m) northern Faeroe Shetland Basin (K iorboe, 1999;
Robinson, 2004). D uring the m iddle Eocene, three large clastic fans sourced from canyons on the Shetland slope w ere deposited into the basin axis, later to act as hydrocarbon
reservoirs sealed b y the associated hem ipelagite (Robinson, 2004).
In contrast to the early Palaeogene succession w ithin the basin, the O ligocene-R ecent succession is dom inated by contourite drift deposits (D am uth and O lsen 2001; D avies et al., 2001; Stoker, 2003; Stoker et al., 2005). The earliest contourite deposits w ithin the basin w ere identified using industrial seism ic profiles across the Faeroese slope and dated as early O ligocene by correlation to industry well data (D avies et al., 2001). D uring the O ligocene, com pression resulted in further developm ent o f the W yville Thom pson Ridge and associated folds (Boldreel and A ndersen, 1993). D uring the M iocene the basin w as characterised by w idespread contourite accum ulation resulting from a w ell established alongslope current regim e (Stoker, 2003; Laberg et al., 2005). E rosion by deep w ater currents is thought to have form ed deep w ater unconform ities during the m id M iocene, and is thought to be associated w ith the grow th o f N E/SW trending folds w hich form ed as a result o f m iddle M iocene com pression (Cloke et al., 1999; A ndersen et al., 2000; D avies and Cartwright, 2002; D avies et al., 2004). The form ation o f the Intra-N eogene U nconform ity during the late M iocene- early Pliocene represents the m ost significant deep w ater erosion event w ithin the Cenozoic succession, and is interpreted be the result o f deep w ater current erosion related to clim atic changes and tectonic adjustm ent (Stoker 1999; K nutz and Cartwright, 2003; Stoker, 2003;
Knutz and Cartw right, 2004; Stoker et al., 2005). D uring the Pliocene, contourite deposition continued, succeeded by form ation o f shelfal unconform ities and deposition o f large scale
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Chapter One Introduction
glacial prograding w edge deposits as a result o f progradation o f ice sheets onto the shelf during the Pleistocene (Stoker et al., 1998; D am uth and Olsen, 2001; K nutz and Cartwright, 2003, K nutz and Cartw right, 2004).