The Last Glacial Maximum in the North Sea Basin

JOURNAL OF QUATERNARY SCIENCE (2006) 21(2) 131–153Copyright � 2006 John Wiley & Sons, Ltd.Published online 6 January 2006 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jqs.950

The Last Glacial Maximum in the North SeaBasin: micromorphological evidence ofextensive glaciationS. J. CARR,1* R. HOLMES,2 J. J. M. VAN DER MEER3 and J. ROSE41Department of Geography, Oxford Brookes University, Gipsy Lane, Oxford OX3 0BP, UK2British Geological Survey, Murchison House, West Mains Road, Edinburgh EH9 3LA, UK3Department of Geography, Queen Mary and Westfield College, University of London, Mile End, London, UK4Department of Geography, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK

Carr, S. J., Holmes, R., van der Meer, J. J. M. and Rose, J. 2006. The Last Glacial Maximum in the North Sea Basin: micromorphological evidence of extensive glaciation.J. Quaternary Sci., Vol. 21 pp. 131–153. ISSN 0267-8179.

Received 1 October 2004; Revised 24 April 2005; Accepted 3 May 2005

ABSTRACT: Despite a long history of investigation, critical issues regarding the last glacial cycle innorthwest Europe remain unresolved. One of these refers to the extent, timing and dynamics of LateDevensian/Weichselian glaciation of the North Sea Basin, and whether the British and Scandinavianice sheets were confluent at any time during this period. This has been the result of the lack of thedetailed sedimentological data required to reconstruct processes and environment of sedimentsrecovered through coring. This study presents the results of seismic, sedimentological and micromor-phological evidence used to reconstruct the depositional processes of regionally extensive seismicunits across the North Sea Basin. Thin section micromorphology is used here to provide an effectivemeans of discriminating between subglacial and glacimarine sediments from cored samples andderiving process-based interpretations from sediment cores. On the basis of micromorphology, cri-tical formations from the basin have been reinterpreted, with consequent stratigraphic implications.Within the current stratigraphic understanding of the North Sea Basin, a complex reconstruction issuggested, with a minimum of three major glacial episodes inferred. On at least two occasions duringthe Weichselian/Devensian, the British and Scandinavian ice sheets were confluent in the centralNorth Sea. Whilst micromorphology can provide much greater confidence in the interpretation ofLate Quaternary offshore stratigraphic sequences, it is noted that a much better geochronology isrequired to resolve key stratigraphic issues between the onshore and offshore stratigraphic records.Copyright � 2006 John Wiley & Sons, Ltd.

KEYWORDS: micromorphology; microfabric; Last Glacial Maximum; North Sea.

Introduction

The nature of Quaternary glaciation of the North Sea Basin(NSB) has been the subject of speculation since the earliestrecognition of lowland glaciation in Britain and Scandinavia(Geikie, 1873). While onshore ice limits have been definedwith some confidence in the British Isles (Rose, 1985; Clarket al., 2004) and northern Europe (Ehlers et al., 1984) for differ-ent Quaternary glacial periods, the offshore limits of the sameice sheets remain poorly understood. This is especially the casefor the Last Glacial Maximum (LGM), for which there is consid-erable confusion relating to the configuration, flow geometry

and dynamics of the British and Scandinavian ice sheets (Ehlerset al., 1991; Laban, 1995; McCabe, 1996; Peacock, 1997;Bowen et al., 2002).Initially, evidence for glaciation of the NSBwas based on infer-

ence from coastal sections in Britain and Denmark (Wood andRome, 1868; Geikie, 1873) or rare seabed sediment samplestrawled up in fishing nets (Tesch, 1942). The development of seis-mic profiling in the 1950s and 1960s allowed substantial expan-sion in the analysis of the bathymetry and the subsurfacesediment geometry of the NSB (Valentin, 1957; Kent, 1967;Caston, 1977; Fannin, 1989), resulting in more precisely definedice-sheet limits for the NSB during the LGM (Valentin, 1957;Hansen and Nielsen, 1960; Flinn, 1967; Jansen, 1976; Jansenet al., 1979; Long and Stoker, 1986; Wingfield, 1989, 1990;Ehlers and Wingfield, 1991; Laban, 1995; Huuse andLykke-Andersen, 2000) (Fig. 1). The reconstructed ice sheet limitshave been primarily based on two seismic approaches: the spa-tial extent of sediment packages ascribed seismostratigraphic

*Correspondence to: S. J. Carr, Department of Geography, Oxford Brookes Uni-versity, Gipsy Lane, Oxford OX3 0BP, UK. E-mail: [email protected]

formation status (Cameron et al., 1987; Cameron and Holmes,1999), and the extent and limits of elongate, sometimes infilleddepressions, termed ‘tunnel valleys’ (Wingfield, 1990; Ehlers andWingfield, 1991; Huuse and Lykke-Andersen, 2000). Much con-troversy exists regarding the origin and significance of tunnel val-leys as indicators of former ice sheet margins (O’Cofaigh, 1996).Whilst it is accepted that tunnel valleys reflect processes asso-ciated with Quaternary ice sheets (Boulton, 1996) there is littleagreement on the mode of origin of such features (Boulton andHindmarsh, 1987; Wingfield, 1989; Ehlers and Wingfield,1991; O’Cofaigh, 1996; Huuse and Lykke-Andersen, 2000;Kluiving et al., 2003).Additional evidence for Quaternary glaciation of the NSB

has been obtained from both deep (Sha, 1991) and shallowboreholes and long and short cores (Holmes, 1977; Flinn,1978; Rise and Rokoengen, 1984; Rise et al., 1984; Long andSkinner, 1985; Stoker et al., 1985; Stoker and Bent 1985; Bent,1986; Skinner et al., 1986; Cameron et al., 1987, 1992; Sejrupet al., 1987, 1991, 1994, 1995, 1996, 1998, 2000; Long et al.,1988;Wingfield, 1989, 1990; Andrews et al., 1990; Balson andJeffrey, 1991; Johnson et al., 1993; Gatliff et al., 1994; Laban,1995; Peacock, 1997; Carr, 1998, 1999; Cameron andHolmes, 1999; Carr et al., 2000).Existing models of ice sheet configuration during the LGM

vary, and there is no consensus on whether the British andScandinavian ice sheets were confluent during one or morestages of the Weichselian (Fig. 1). These contrasts arise fromsignificant problems associated with the interpretation of seis-mic data and limited investigation of sediments recovered incores and boreholes.The limited sample size available from sediment cores

restricts the analytical procedures available for interpreting gla-cigenic sediments recovered from the NSB. This has resulted infundamental problems in discriminating between in situwater-laid marine or glacimarine sediments from subglaciallydeformed sediments that have been reworked to produce tills(van der Meer and Laban, 1990; Carr et al., 2000; Carr, 2001).Recently, debate has focused on the timing and dynamics

of the LGMwithin the NSB. In the British Isles and Scandinavia,the LGM is traditionally attributed to the Dimlington Stadialof the Late Devensian/Weichselian, with a single phase of gla-ciation culminating at around 18 k 14C yr BP (Penny et al.,1969; Rose, 1985; Lundqvist, 1986). This ‘one-stage’ modelhas been criticised by Sejrup et al. (1994, 2000), who proposea more complex ‘two-stage’ glaciation of the NSB duringthe equivalent period of Late Devensian/Weichselian. Sejrupet al. (1994, 2000) suggest that the earlier phase of the LGM(22 k 14C yr BP) reflects glaciation of the NSB by confluentBritish and Scandinavian ice with a subsequent re-advance ataround 18k14Cyr BP of separate ice sheets.This paper presents the results of applying thin-section micro-

morphology to the sediments that constitute the established seis-mostratigraphic records from the North Sea Basin. This analysisaims to provide a more secure sedimentological framework bywhich the palaeogeography of the region during the Devensian/Weichselian glaciation may be established. This paper does notattempt to revise the current regional Late Quaternary stratigra-phy of the North Sea, although discussion of the stratigraphicimplications of the research findings will be noted.

Material and methods

Critical localities were selected for detailed investigation, eachtesting previous models of ice-sheet configuration in the NSB

(Fig. 1). Re-examination of BGS shallow reflection seismicrecords was used to check the existing Quaternary offshorestratigraphy for the locations under study (Fig. 2) to confirmthe character of seismostratigraphic units of interpreted Weich-selian age. This allowed regional correlation of each studylocality, permitting reconstruction of glacial episodes acrossthe entire NSB. Within each area, all available BGS vibrocoresand shallow boreholes were examined and used to tie seismicanalysis to specific lithofacies. On the basis of this reconnais-sance, cores were selected for further analysis and sampling forthin sections (Table 1, Fig. 1). Cores and boreholes wereselected to provide representative samples from different sedi-mentary facies constituting specific formations. In most cases,multiple cores within each seismostratigraphic formation weresampled to ensure representative micromorphological charac-terisation.Fifty-seven undisturbed samples were collected from BGS

cores and boreholes for thin-section production using theapproach of Lee and Kemp (1992) and Carr and Lee (1998),producing approximately 30-micrometre thickness thin sec-tions (80� 60mm). The majority of samples were aligned ver-tically in relation to the cores, although a few horizontal thinsections were prepared from selected samples. All preparedthin sections, as well as nine ‘mammoth’ (150� 80mm) thinsections obtained from the Dutch sector (see van der Meerand Laban, 1990) and 14 samples obtained from the Norwe-gian sector of the NSB (Carr et al., 2000) were examined usinga petroscope and petrological microscope under plane- andcross-polarised light, using the terms outlined by van der Meer(1993) and Carr (2004a).The structures defined by van der Meer (1993, 1997) are con-

sidered to be representative of deformation under high stressconditions typically found within a subglacial setting, withsome features, such as in situ crushed quartz grains, possiblydiagnostic of specific subglacial environments (Hiemstra andvan der Meer, 1997). The identification of reoriented domainsof fine silts and clays (plasmic fabric) under cross-polarisedlight is of importance in the investigation of fine-grained sedi-ments, in identifying evidence for deformation associated withpervasive or discrete shear (van der Meer, 1993).Analysis of structures indicative of glacimarine conditions

follows the scheme of Carr (2001, 2004a). Graded beddingassociated with dropstone structures and the widespread pre-sence of marine microfossils provide the strongest evidenceof glacimarine conditions (van der Meer, 1995), but Carr(2001) identifies associations of coarse, winnowed matrix tex-tures, absence of associated deformation structures and a lackof plasmic fabric development as good supportive indicators ofsuch conditions, although Carr (2001) expresses caution atbasing interpretations on individual features. Observation ofapparently in situ, undistributed marine microfossils alonemay be an unreliable indicator of marine conditions, owingto the potential for glacitectonic reworking, and theirpresence is extensively noted in glacial deposits (Boultonet al., 1996).Figure 3 summarises the key micro-scale features of subgla-

cial and glacimarine sediments that form the bulk of material inthis study; however, as noted by Carr (1998, 1999, 2001) inter-pretation of all thin sections in terms of processes and environ-ments requires the identification of an association of features,rather than dependence on a single ‘diagnostic’ feature.In this study, a simplified approach is used to present micro-

morphological data. The relevant micromorphology of physi-cal components, deformation structures, marine indicators,and plasmic fabric are plotted on a summary table allowingrapid comparison of a number of samples (Tables 2–4). Thisapproach is effective for discriminating well-developed and

132 JOURNAL OF QUATERNARY SCIENCE

Copyright � 2006 John Wiley & Sons, Ltd. J. Quaternary Sci., Vol. 21(2) 131–153 (2006)

common structures from rare or weakly developed features andhas been successfully applied to micromorphological data forregional stratigraphic and sedimentological reconstruction(Carr, 1999). It is also useful for providing a secure basis fromwhich more detailed analysis may be undertaken (Carr, 1999,2001; Carr et al., 2000; Lloyd Davies, 2004).The orientation of elongate quartz grains (microfabric) was

measured using a projection macroscope. Like larger clast fab-rics, microfabric is an excellent indicator of directional stresswithin a sediment. Work on till fabric has occasionally usedmicrofabric to demonstrate the stresses imparted (Glen et al.,1957; Ostry and Deane, 1963; Evenson, 1970; Johnson,1983; Carr and Rose, 2003). Within the current study, micro-fabric was primarily analysed in a vertical plane, with subgla-cially derived microfabrics expected to possess a unidirectionalor bimodal orientation pattern reflecting a lateral stress field(Carr, 1999; Carr et al., 2000), and distinct vertical patternsof grains deposited through suspension rain-out in proximal

to distal glacimarine sediments (Carr et al., 2000; Carr, 2001;Lee, 2001). Data were plotted using an Excel spreadsheet ashalf polar plots (right-hand side) of grain orientation in the ver-tical plane.

The stratigraphy of the North Seaduring the last glacial cycle

As stated above, the purpose of this paper is not to revise theLate Quaternary subdivision of the NSB, but to test the interpre-tation of critical sediment bodies within the established strati-graphic sequence. Accordingly, discussion here is restricted toa critique of the basis of the stratigraphy, highlighting some ofthe key issues relevant to this study. More general reviews ofthe Quaternary stratigraphy of the NSB may be found in

Figure 1 Overview of the different models of the extent of the LGM British and Scandinavian ice sheets in the North Sea Basin. The five study areasare highlighted. The scale of the map precludes showing the locations of individual cores and boreholes (see Table 1 for details)

LAST GLACIATION IN THE NORTH SEA 133


Andrews et al. (1990); Cameron et al. (1992); Johnson et al.(1993); Gatliff et al. (1994) and Sejrup et al. (1991, 1994,2000).The bathymetry of the NSB is such that the region may be

divided into three sectors. The southern NSB, south of 56 � N,is shallow, with present-day water depths typically less than40m. So it is likely that throughout much of the last glacialcycle, this region would have been above global eustatic sea

level, and thus was dry land. Conversely, in the central NSB,between 56 � N and 59 � N, water depths currently reach anaverage of 100–140m, with the present seafloor close to thelikely global eustatic sea level at the LGM (Fairbanks, 1989).North of approximately 59 � N, the NSB is around 140–200m depth, placing this part of the basin below globaleustatic sea level even at the peak of glaciation, implyingextensive and exclusively marine or glacimarine environments.

Figure 2 (A) Extracts of shallow seismic reflection data from the North Sea. Left: detail of seismic line 80, Dogger Bank area. This extract highlightsthe two-tier internal structure of the Dogger Bank Formation, with a lower, sub-horizontally layered unit overlain by a more chaotic unit preservingonly sporadic layering. Right: examples of Boomer and Sparker seismic lines from the same location, Fladen, central North Sea. (B) Interpreted seismiclines, Fladen area, Northern North Sea. In general, the original BGS interpretations were validated during the current research, allowing confidence inthe regional interpretation of the extent and geometry of key formations



Table 1 List of cores and boreholes sampled in this study, and the depths of specific samples within each core. The cores examined and sampledwere considered representative of specific facies of seismostratigraphic formations, and were selected after much broader examination of the BGScore and borehole archive

Core/borehole Latitude Longitude Depth below seabed (m) Sample

ve þ53 þ02 203 53 � 240 030 0 N 02 � 020 380 0 E 2.90 IND 1v/hve þ53 þ02 186 53 � 220 570 0 N 02 � 070 530 0 E 1.05 IND 2BH 79/08 53 � 210 200 0 N 02 � 250 440 0 E 21.8 IND 3ve þ54 þ02 135 54 � 140 160 0 N 02 � 250 520 0 E 3.82 BGS 1ve þ54 þ02 153 54 � 140 420 0 N 02 � 100 580 0 E 0.56 BGS 2

2.09 BGS 3ve þ54 þ02 218 54 � 410 300 0 N 02 � 080 260 0 E 3.09 BGS 4

2.20 BGS 5a/bve þ54 þ02 216 54 � 380 540 0 N 02 � 090 140 0 E 3.69 BGS 6

2.57 BGS 71.47 BGS8

ve þ54 þ02 223 54 � 570 590 0 N 02 � 370 580 0 E 5.00 BGS 94.16 BGS 102.79 BGS 11

ve þ54 þ02 220 54 � 520 580 0 N 02 � 170 390 0 E 1.66 BGS 122.75 BGS 13

ve 90 DW 538 1.20 Mi 839ve 90 DW 540 2.70 Mi 840

3.06 Mi 841ve 90 DW 542 1.30 Mi 842ve 90 DW 534

8>>>>>>>>>>>>>>>>><>>>>>>>>>>>>>>>>>:

All cores sampled in proximity to 54 � 150 N/03 �

9>>>>>>>>>>>>>>>>>=>>>>>>>>>>>>>>>>>;

1.97 Mi 843150 E

ve 90 DW 547 1.00 Mi 844ve 90 DW 548 1.00 Mi 846ve 90 DW 550 0.60 Mi 848ve 90 DW 552 1.55 Mi 849ve 90 DW 556 1.00 Mi 852ve 94 DW 08 54 � 420 500 N 03 � 130 050 0 E 3.90 C.65ve 94 DW 09 54 � 400 160 N 03 � 140 530 0 E 1.49 C.66

2.00 C.67BH 72/14 56 � 270 280 0 N 01 � 460 500 0 W 21.80 MAR 1

18.40 MAR 2BH 81/27 56 � 320 410 0 N 00 � 240 010 0 W 12.90 MAR 3

19.75 MAR 4BH 81/24 58 � 180 420 0 N 00 � 590 290 0 W 15.10 FLA 11

24.60 FLA 12BH 82/16 58 � 290 280 0 N 00 � 500 160 0 W 18.40 FLA 1

22.80 FLA 226.75 FLA 3

BH 81/26 58 � 080 200 0 N 00 � 100 460 0 W 34.10 FLA 430.80 FLA 5/5a25.12 FLA 612.24 FLA 7

BH 77/02 58 � 290 320 0 N 00 � 300 240 0 E 18.02 FLA 822.14 FLA 924.30 FLA 10

Sleipner B2001a 19.80 BER 914.45 BER 1013.20 BER 118.85 BER 12

BH 78/09 61 � 300 400 0 N 00 � 490 470 0 E 11.40 SHE 122.55 SHE 211.75 SHE 3

BH 80/01 61 � 060 210 0 N 00 � 210 280 0 E 22.74 SHE 418.02 SHE 5

BH 81/17 61 � 220 290 0 N 00 � 100 090 0 W 4.90 SHE 68.60 SHE 7

BH 84/08 61 � 040 120 0 N 00 � 320 150 0 W 4.65 SHE 86.96 SHE 9

ve þ61 �01 069 61 � 120 380 0 N 00 � 310 590 0 W 0.70 SHE 10ve þ61 þ01 161 61 � 290 020 0 N 01 � 430 390 0 E 0.70 SHE 11ve þ61 þ01 170 61 � 400 160 0 N 01 � 040 520 0 E n/a SHE 13ve þ61 þ01 174 61 � 270 400 0 N 01 � 120 310 0 E n/a SHE 12



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The northern margin of the NSB is delimited by the continentalshelf edge, where water depths rapidly increase from ca. 200mto> 1500m.The Quaternary subdivision of the NSB is primarily based on

seismic stratigraphy, using the approach of Mitchum et al.(1977) and Vail (1987) to divide the offshore deposits into seis-mostratigraphic units, each bounded by unconformities, andassigned formation status (Cameron et al., 1987; Cameronand Holmes, 1999). This seismostratigraphic framework is con-strained where possible by sedimentological and biostrati-graphic data from cores and boreholes, although the spatialand temporal quality of this data is extremely heterogeneous,as noted earlier. A generalised Late Quaternary seismic strati-graphy is presented in Fig. 4, based upon a review of the BGSand related Regional Mapping Programmes (Andrews et al.,1990; Cameron et al., 1992; Johnson et al., 1993; Gatliffet al., 1994; Holmes, 1997; Cameron and Holmes, 1999).Whilst seismostratigraphy may be an effective tool for discri-

minating the deposits associated with major environmentalshifts during the Quaternary, it is far from ideal at subdividingthe relatively thin and highly complex suites of glacigenicdeposits associated with the Mid–Late Quaternary of theNSB. Seismic profiling registers contrasts in acoustic impe-dance that may, or may not reflect lithostratigraphic bound-aries (Laban, 1995). This issue becomes more problematicgiven the inherent variability of glacigenic sediments, and thatthere is no simple stratigraphic sequence model associatedwith glaciation that can be applied on the scale of the NSB.Finally, the quality of seismic records from the NSB is highlyvariable, with environmental conditions at the time of surveya significant control over the quality of the resulting seismicprofiles obtained (Laban, 1995). This results in thinner seismos-tratigraphic formations (such as many of those in the southernNSB) being close to the practical resolution limits of the equip-ment being deployed.In Fig. 4, the key seismostratigraphic formations from the

NSB are loosely associated with marine isotope stages duringthe last glacial–interglacial cycle; however, the basis for thisis highly equivocal, derived from a limited and variably reliableradiometric dating of in situ or reworked marine bivalves or for-aminifera, and the speculative interpretation of palaeomag-netic horizons within formations as events such as the BlakeEvent (0.12Ma) (e.g. Skinner and Gregory, 1983). As a conse-quence, many formations have been interpreted to representmore than one stage of the Last Glaciation and in some casesare thought to reflect deposition through more than one gla-cial–interglacial cycle, which, given the range of potentialsedimentary processes operating over this cycle, is highlyimprobable.Up to three major episodes of glaciation have been inter-

preted for the NSB during the last glacial cycle reflected inthe stratigraphy summarised in Fig. 4. During the early part oftheWeichselian, tentatively associated with MIS 4, there is evi-dence of extensive glaciation of the North Sea within the FerderFormation (Skinner et al., 1986; Sejrup et al., 1989; Johnsonet al., 1993), during which time ice is considered to haveextended to the continental shelf break north and west of theShetland Isles. Much more controversial, however, is the evi-dence relating to Mid- and LateWeichselian/Devensian glacia-tion of the NSB. For this period, there are proponents of a one-stage LGM peaking at or around 18 k 14C yr BP (Cameron et al.,1987; Long et al., 1988) during which Scandinavian and Britishice sheets were separated by an ice-free corridor, and a con-strasting model for a two-stage LGM, with ice-sheet growthbetween 30 k and 22 k 14 C yr BP, peaking in confluent Britishand Scandinavian ice sheets, with retreat and a subsequentre-advance of separate ice masses after 18 k 14C yr BP (Sejrup

et al., 1994; Holmes, 1997; Sejrup et al., 2000; Wilson et al.,2002). These conflicting models each result in problems asso-ciated with the onshore lithostratigraphy of the British Isles dur-ing this period, where ice-free conditions persisted in Scotlanduntil ca. 26 k 14C yr BP (Rose, 1985; Boulton et al., 1991), andwith a distinct two-stage glaciation of western Scandinavia(Mangerud et al., 1991; Sejrup et al., 2000). While it is beyondthe scope of this paper, resolution of these stratigraphic issuesmay partly depend on the reliable genetic interpretations ofthe sediments comprising the interpreted seismostratigraphicformations.

Description of the micromorphology of keysediments in the North Sea Basin

Within the context of the regional stratigraphy outlined above,there are considered to be up to three major phases of glacia-tion in the NSB during the Last Glacial cycle. This is primarilybased on the evidence from the northern NSB, in which threeclear glacial episodes of either subglacial or glacimarine eventshave been identified by previous research (Table 4).

Early Weichselian glaciation: the Ferder glacialepisode

There is patchy evidence to support glacigenic sedimentationin the NSB during the early Weichselian, possibly at or aroundMIS 4, approximately 70 k yr BP (Stoker et al., 1985; Skinneret al., 1986; Sejrup et al., 1989). The evidence for regional gla-ciation during this time is primarily preserved in the Ferder For-mation, although it is likely that to the south, at least part of theCoal Pit Formation also reflects this period, and is laterally con-tiguous with the Ferder Formation.The Ferder Formation is thought to reflect sedimentation

from the Eemian through to the Mid-Weichselian (Skinneret al., 1986; Sejrup et al., 1989), although it is likely that suchsedimentation was concentrated in a few significant events,rather than being continuous throughout the period. Seismiclines identify that this formation extends from the NorwegianChannel to the continental shelf margin west of the ShetlandIsles as a continuous unit, up to 80m in thickness, which incores consists of fine-grained matrix supported diamictons,typically containing shell fragments (Johnson et al., 1993). Inseismic lines, the lower part of the Ferder Formation is charac-terised by subparallel layered reflectors, possibly indicatingsedimentary bedding; however, this has not been sampleddirectly from cores or boreholes in this study. The micromor-phology of the Ferder Formation is presented in Table 2. Allsamples preserve a suite of associated deformation features(rotation structures, crushed quartz grains, rotational plasmicfabrics; Fig. 6(A),(B)) and most preserve evidence for the canni-balisation of pre-existing sediments to produce rounded softsediment intraclasts. In samples SHE4 and SHE5 distinct gradedlaminations are identified within some intraclasts (Fig. 6(C)),possibly reflecting sediments derived from the lower, layeredpart of the formation (Table 2). Microfabric analysis ofboth vertical and horizontal sections indicates the appliedstress was unidirectional in nature (Fig. 5). On the basis ofthis micromorphological evidence and the spatial extent andgeometry of the formation, it is suggested that the Ferder For-mation reflects extensive glaciation across the northern NSB,with confluence of British and Scandinavian ice sheets, with



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the ice front terminating in a marine environment duringadvance.The Coal Pit Formation is an extensive seismostratigraphic

unit that is found across much of the central North Sea. In stra-tigraphic terms, the age of the Coal Pit Formation is unclear,although Stoker et al. (1985) suggest that it may span muchof the last glacial–interglacial cycle and is thought to be thesouthern equivalent of the Ferder Formation. Seismically, theCoal Pit Formation is complex, with reflectors indicating a mel-ange of chaotic and subparallel layering, as well as distinctiveintra-formational channel features, possibly representing a net-work of ‘tunnel’ valleys. The sediments of the Coal Pit Forma-tion have been sampled in many locations within the centralNorth Sea, focusing on the upper part of the formation, whichis typically identified as a shelly, fine-grained, dark olive-greymatrix supported diamicton (6Y 3/1), often displaying someevidence of stratification, as well as augen-shaped intraclasts.What is evident from all the thin sections of the Coal Pit For-

mation (Table 2) is that the sediment has undergone a signifi-cant degree of deformation under high confining stressregimes, with structures reflecting both planar and rotationaldeformation evident, and in situ crushed quartz grains (withevidence of displacement) present in all samples (Fig. 6(D)).Structural features indicating stratification (MAR4, FLA9v, 11and 12) are interpreted as pseudo-laminae or shear structures,displaying no internal grading or evidence of other primarysedimentary structures. The pseudo-laminae are typically asso-ciated with grain lineations, unistrial or masepic plasmic fab-rics (Fig. 6(E)), further demonstrating association with planardeformation. Microfabrics (Fig. 5) identify a unidirectional lat-eral applied stress field. This body of data strongly supports theinterpretation that at least the upper facies of the Coal Pit For-mation is a subglacial till, reflecting significant cannibalisationof pre-existing marine or glacimarine sediments. The evidencefor such cannibalisation of pre-existing sediments is particu-larly clear in borehole 81/26, where the upper contact betweenthe ‘Saalian age’ Ling Bank Formation (Stoker et al., 1985) andthe Coal Pit Formation is heavily deformed, with significant dis-turbance of the upper 9m of the Ling Bank Formation (Table 2).As the Coal Pit Formation is widespread across the central NSB,it is evident that this glacial event was widespread across theNSB.On the basis of the interpretation of a subglacial origin for

both the Ferder and Coal Pit Formations, it is possible to suggestextensive glaciation of the NSB during an early event within theWeichselian, possibly coinciding with MIS 4. Assuming thatboth the glacial evidence from each formation reflects the sameperiod of glaciation, the likely configuration of this ice sheet isdemonstrated in Fig. 7. During advance and at its maxima, it islikely that this ice sheet terminated in marine conditions to thenorth. It should be noted that as the stratigraphic status of theCoal Pit Formation is somewhat ambiguous, this reconstructionshould be considered tentative at best.

Mid- to Late Weichselian glaciation: the CapeShore glacial episode

It is increasingly likely that the growth of the LGM ice sheets inScandinavia and the British Isles is more complex than hasbeen previously considered. In this paper, a two-stage glacia-tion model is favoured, based on the discussion presented byCarr (2004b).The Cape Shore Formation extends across much of the north-

ern NSB, from the Norwegian Channel to, and just beyond, thecontinental shelf edge, and typically directly overlies the FerderT

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no.

size

ratio

type

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Formation. It is suggested by Johnson et al. (1993) that this for-mation is at least partly the lateral equivalent of the SwatchwayFormation in the central NSB. Whilst predominantly consistingof olive-grey (5Y 4/2) fine-grained massive or stratified shellydiamictons, observed in cores, it is evident from seismicrecords that the lower part of the Cape Shore Formation is dis-tinguished by sub-horizontal reflectors possibly indicative ofsedimentary bedding. The two-tier structure of the Cape ShoreFormation is evident in borehole 78/09, where the lower10–15m is a stratified facies, which in thin section (SHE2,Table 3) preserves some very faint sub-horizontal graded bed-ding (Fig. 8(A)), and a distinctly vertical microfabric arrange-ment (Fig. 5), suggestive of waterlain conditions, probablymarine given the presence of numerous marine bivalve shell-fragments. The upper facies of the formation (SHE1 and 3,Table 3) appears to be largely similar in macro-scale to the

lower facies, albeit with less well-defined stratification. How-ever, in thin section, the upper facies of the Cape Shore Forma-tion is typified by evidence of both planar and rotationaldeformation processes (notably associations of rotation struc-tures, pressure shadows, grain lineations), and related plasmicfabric development (Table 3). Once again, the presenceof crushed quartz grains and water escape structures inSHE1 imply a high confining pressure during deformation(Fig. 8(B)), suggestive of a subglacial glacitectonic origin. Themicrofabric of the upper facies of the Cape Shore Formation(Fig. 5) demonstrates a particle response to a unidirectional lat-eral stress field, rather than sediment settling out from suspen-sion. This combination of macro- and micro-scale analysis ofthe Cape Shore Formation suggests that the majority of the sedi-ments were laid down under marine conditions, with the upperpart of the deposit subsequently reworked and deformed under

Figure 5 Representative vertical microfabrics from samples in this study, highlighting the dips of individual sand-sized particles. The grey line in eachsample reflects a 0 � dip. Each sample is based on a random sampling of a minimum of 50 apparently elongate (a:b axes ratio > 1.5:1) sand-sizedquartz grains (250 micron metres to 1mm a axis)



Figure 6 Photomicrographs from samples related to the Ferder glacial episode. Each image is paired with an original and annotated version, and theblack bar reflects 5mm in each image. (A) Rotational pressure shadow, SHE9, Ferder Formation (plane-polarised light). (B) Skelsepic and lattisepicplasmic fabric, SHE9, Ferder Formation (cross-polarised light). (C) Laminated intraclast within deformed diamicton, SHE4, Ferder Formation (cross-polarised light). (D) Crushed quartz grains, FLA11, Coal Pit Formation (cross-polarised light). Samples outlined in a solid line reflect crushing thatoccurred during deposition/deformation, and reflect displacement of fractured grains and the ingress of ‘interstitial’ plasma material, while those out-lined in dashed lines reflect crushing during the polishing process during thin-section production, with no ‘interstitial’ plasma or evidence of displa-cement. (E) Grain lineation and associated unistrial plasmic fabric, FLA12, Coal Pit Formation (cross-polarised light)



subglacial conditions, during extensive glaciation across theentire northern NSB.Across much of the central NSB the Swatchway Formation

overlies the Coal Pit Formation, and is thought to be partly con-tiguous with the Cape Shore Formation (Johnson et al., 1993).The Swatchway Formation consists of an olive-grey (5Y 4/2)silty, matrix-supported diamicton with isolated, discontinuousbands of sorted silts and sands. Clast analysis reported fromborehole 77/02 by King (1991) identifies primarily subangularto sub-rounded igneous and metamorphic clasts, some ofwhich are striated, as well as less common sandstones, all ofwhich may be Scottish or Scandinavian in provenance. In bore-hole 77/02, a lower facies of the Swatchway Formation is iden-tified as a laminated silty-clay, in which complete marinebivalve shells are preserved (FLA8, Table 3). Elsewhere withinthe formation, there are very common marine shell-fragments,and occasional complete (though not paired) bivalve shells. Onseismic lines, the Swatchway Formation is identified as a seriesof transparent to chaotic reflectors, with a highly irregularupper surface, possibly reflecting the surface of a till sheet, ordisturbance through iceberg scour (Stoker and Long, 1984). Tothe east, the Swatchway Formation can be traced as a lateralequivalent of part of the Tampen Formation (Sejrup et al.,1991). The micromorphology of the Swatchway Formation(Table 3) identifies well-developed planar plasmic fabrics, rota-tion features and symmetrical pressure shadows in both sam-ples, as well as in situ crushed quartz grains, implying thatthe sediment has undergone deformation in a high confiningstress regime, under conditions of dilation and stiffening ofthe sediment body, resulting in brittle failure (Hiemstra andvan der Meer, 1997). In FLA8 (Table 3), it appears that shearingalong pre-existing boundaries of laminae has occurred, result-ing in the development of rotation features around completeshells and shell-fragments (Fig. 8(C)). The preservation of com-plete bivalve shells does not initially conform to the presence of

Figure 7 Palaeogeographic reconstruction of the Ferder glacial epi-sode in the North Sea Basin. This is based on the revised interpretationsof the relevant formations from this study in coordination with pre-viously published stratigraphic studies (for references see main text)

Tab

le3

Micromorphologica

lch

arac

teristicsofsamplessuggestedto

representtheCap

eSh

ore

glac

ialep

isode.

SeeheadingofTab

le2fordetails

Micromorphologica

lfeatures

Skeleton

Matrix

Voids

Deform

ationstructures

Marinefeatures

Plasm

icfabric

Shap

e

Form

ation

Sample

Grain

>500mm

<500mm

Tex

ture

Void

Void

Section

Rotation

Pressure

Crushed

Peb

ble

Peb

ble

Peb

ble

Water

Lineations

Dropstones

Microfossils

Skelsepic

Lattisep

icOmnisep

icMasep

icUnistrial

no.

size

ratio

type

elem

ents

shad

ow

grains

III

III

esca

pe

Dogg

erBan

kFo

rmation

BGS4

<250

SRSA

ML

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��

��

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BGS5a

250

RSA

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FBa

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250

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Cap

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ation

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250

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Form

ation

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9250

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fractured quartz grains, but it is likely from the suite of deforma-tion structures that deformation often occurred along discreteshear planes, rather than pervading through the entire sedimentpile, thus permitting complete shells to be preserved. Microfab-ric observations from both samples identify unidirectional ver-tical microfabrics, indicating the presence of a directionallateral stress field during deformation (Fig. 5). The consistencyof deformation between samples more than 60 km apart, aswell as the presence of features indicating deformation underhigh strain conditions would suggest a subglacial origin tothe Swatchway Formation.A similar tabular seismostratigraphic formation may be

traced within the Norwegian sector of the North Sea to the eastof the Swatchway Formation. This unit, known as the TampenFormation appears to be at least partly the lateral continuationof the Swatchway Formation. In borehole B2001a, the TampenFormation consists of two grey (2.5Y 5/1) fine grained matrix-supported diamictons, separated by a thin band of fine-grainedlaminated silts and clays. Whether the layer of laminated siltsand clays is stratigraphically significant is unclear, althoughCarr et al. (2000) suggest that this may imply the two diamic-tons reflect separate events, although the extent and geometryof the possible two units is not known, and the Tampen Forma-tion is typically mapped as one seismostratigraphic unit acrossmuch of the eastern part of the northern North Sea. The twodiamictons each preserve common sand and gravel lensesand intraclasts, and a moderate clast content, of which a num-ber of striated clasts may be identified, primarily of Norwegianorigin (Sejrup et al., 1987; Andrews et al., 1990). The micro-morphology of the Tampen Formation in the central NorthSea (Table 3) is dominated by rotation structures and skelsepicplasmic fabrics in all samples, while the rarity of crushed quartzgrains or unistrial plasmic fabrics suggests that deformation waspervasive through the entire sediment body, with little evi-dence for stress concentration under discrete shear sufficientto cause grain fracture. Microfabrics of both vertical and hori-zontal thin sections indicate well-developed unidirectionalparticle orientations, suggestive of a clear unidirectional lateralstress field (Fig. 5). It is notable, however, that the suite of defor-mation features in BER9 (lower diamict) differs slightly fromthat identified in the samples in the upper diamict, with ahigher presence of rotation structures and pressure shadows,and poorer plasmic fabric development in BER9 compared toBER11 and 12. This may support the suggestion that the condi-tions during deformation of the lower diamict were different tothose of the upper, reflecting stratigraphically discrete events.Sample BER10 differs significantly from the other Tampen

Formation sediments, in that it was sampled from a thin unitof silty-clay between two main diamicton facies. BER10 pre-serves sedimentary bedding, and rare, contorted dropstonestructures, associated with the formation of localised pressureshadows (Table 3). Throughout the sample, a well-developedmasepic plasmic fabric suggests pervasive re-orientation ofthe plasma through planar shear (Fig. 8(D)). This sample wasinterpreted by Carr et al. (2000) as reflecting initial glacimarine

deposition that was subsequently deformed through glacitec-tonic processes. However, the stratigraphic significance of thisis unclear: it is possible that the Tampen Formation reflects twostages of glaciation preserved within, separated by a short per-iod of glacimarine conditions; alternatively sample BER10 mayhave simply been recovered from a larger raft or intraclast ofglacimarine material during a single depositional/deforma-tional phase. The investigation of the Tampen Formation inborehole B2001a strongly supports the interpretation of Carret al. (2000) that the evidence reflects the extension of icebeyond the constraints of the Norwegian Channel during theLGM, and that this may possibly have occurred during morethan one phase.In the southern NSB, the Dogger Bank Formationmay at least

partly equate to the Swatchway Formation (Fig. 4). The DoggerBank Formation comprises mainly dark-grey to reddish-brown(10YR 6/4 to 7.5YR 6/4) fine-grained matrix supported diamic-tons, often containing pods and intraclasts of fine sands, and achalk and flint dominated clast content. Lower proportions ofclasts, and a generally finer grain-size, as well as the presenceof common shell fragments helps to discriminate the DoggerBank Formation from the Bolders Bank Formation, which itunderlies, or in part interdigitates with (Cameron et al.,1992). In seismic lines, the Dogger Bank Formation has a dis-tinctive structure, with layered seismic reflectors in the lowerportion of the formation becoming progressively more dis-turbed and acoustically chaotic in the top 10m of the formation(Fig. 9). At a regional scale, the Dogger Bank Formation forms apositive seafloor feature, and is analogous in geometry andscale to Denmark (Carr, 1998). Furthermore, Laban (1995)and the late Dr Robin Wingfield (pers. comm.) suggest thatsome seismic lines in the Dutch sector of the NSB identifylarge-scale thrusting of the Dogger Bank Formation occurringfrom the north. In thin section (Table 3), all samples displayat least some evidence of rotational deformation (Fig. 8(E)),

3————————————————————Figure 8 Photomicrographs from samples relating to the Cape Shoreglacial episode. Each image is paired with an original and annotatedversion, and the black bar reflects 5mm in each image (all imagesare in plane-polarised light). (A) Sands in glacimarine sediments mak-ing up the lower part of the Cape Shore Formation, SHE2, Cape ShoreFormation. (B) In situ crushed quartz grains, SHE1, Cape Shore Forma-tion. (C) Pressure shadow, FLA8, Swatchway Formation. (D) Rotationstructure, BGS5, Dogger Bank Formation. (E) Pebble Type III (see vander Meer, 1993), BGS8, Dogger Bank Formation

Figure 9 Palaeogeographic reconstruction of the Cape Shore glacialepisode in the North Sea Basin. The dashed lines reflect a suggestedretreat phase of this episode, during which Scandinavian ice retreatsto the Norwegian Channel, and Scottish ice terminates east of Buchanat the Bosies Bank moraine (Bent, 1986)



and many display plasmic fabrics that indicate discrete orpervasive shear of the sediment body. Microfabrics (Fig. 5) sug-gest that a unidirectional stress field with a significant lateralcomponent influenced almost all samples during deposition/deformation. However, some samples (BGS5b, BGS10, C.65,Table 3) display few deformation features, and preserve manyindications of true sedimentary bedding and abundant marinemicrofossils, and reflect waterlain deposition in a shallow gla-cimarine environment. Intraclasts (Pebble Type III in thescheme of van der Meer (1993)) of stratified sediments withsome sand-sized dropstone structures in BGS9 and BGS12(Fig. 8(F)) indicate the cannibalisation of pre-existing waterlaidsediments during the deposition of the Dogger Bank Formation.Carr (1999) suggests that these intraclasts, as well as the rela-tively undeformed samples noted above probably reflect thesediment characterising the lower (acoustically layered) faciesof the formation being progressively incorporated and homoge-nised during a subsequent deformation event.From the combination of the seismic, sedimentological and

micromorphological evidence, it is suggested that the DoggerBank Formation is in part shallow glacimarine in origin andthat, subsequent to deposition, at least the upper 10m of theformation underwent glacitectonic deformation. This involvedthe reworking of the in situ waterlain sediment as well as theaddition of allochthonous sediments. This conforms well tothe structure of the Dogger Bank itself, which Carr (1998,2004b) interprets as a large moraine belt comparable withthe Main Stationary Line of Denmark.The detailed stratigraphic status of the formations outlined

above is highly ambiguous, given the lack of reliable radio-metric ages for the region, although a broad classification ofthese formations as Mid–Late Weichselian is relatively secure.However, it is apparent from the micromorphology of the for-mations outlined above that during the Middle to Late Weich-selian, extensive glaciation occurred across much of the NSB,with confluent ice from Scotland and Scandinavia extendingnorthwards and westwards to the continental shelf edge, andsouthwards to produce the Dogger Bank (Fig. 9). LimitedAMS 14C dates from the central NSB (Sejrup et al., 1994) sug-gest that if the events identified in each of the formations werecontemporaneous, the peak of this glaciation was reachedsoon after 22 k 14C yr BP.

Late Weichselian glaciation: the BoldersBank glacial episode

Subsequent to the Cape Shore glacial episode, there is signifi-cant evidence of a third major advance of Scottish and Scandi-navian ice into the NSB. The evidence for this episode isprimarily in the form of diamictons with close association withrecognised tills from the onshore record of the east coast ofBritain.The Bolders Bank Formation consists of a dark reddish-

brown (7.5YR 4/2) over-consolidated fine-grained diamicton,with sub-rounded and subangular clasts mainly comprisingchalk, black flints and red sandstones. It has a massive struc-ture, with only occasional sand interbeds and intraclasts pre-sent, and has been mapped by Long et al. (1988) as a largelobe that extends up to 50 km offshore from the east coast ofnorthern England, before spreading across a large area ofthe southern North Sea, as far east as the Dutch Sector (seeFig. 1). Cameron et al. (1992) suggest that the Bolders BankFormation is the extension of the Skipsea and Withernsea Tillsof East Yorkshire (Catt, 1991), with which it shares manymacroscale similarities.

The micromorphology of the Bolders Bank Formation hasbeen described in detail by Carr (1999), and a summary is pre-sented in Table 4. All the samples investigated display manysimilar features, reflecting both planar and rotational deforma-tion regimes, with crushed quartz grains indicating a highdegree of normal stress exerted during sediment strain in manysamples (see Hiemstra and van der Meer, 1997). Microfabricanalysis (Fig. 5) illustrates that sand grains responded to astrong unidirectional lateral stress field. The micromorphologi-cal evidence, in combination with the macroscale descriptionsof cores suggests that the Bolders Bank Formation is a till of sub-glacial origin, reflecting an ice sheet extending from the eastcoast of Britain across the southern North Sea.The Wee Bankie Formation is a seismically chaotic forma-

tion that is laterally contiguous with the Bolders Bank Forma-tion to the south, and the Red Series tills in the Firth of Forth andonshore Scotland (Gostelow and Browne, 1986; Gatliff et al.,1994). The Wee Bankie Formation consists of dark reddish-brown (5YR 3/3), fine-grained, matrix-supported diamictons,with a high proportion of subangular and sub-rounded clastsreflecting a sediment source from the Midland Valley andHighlands of Scotland. The micromorphology of the WeeBankie Formation (Table 4, Fig. 5) includes a number ofsmall-scale deformation features, including boudins and intra-clasts, as well as moderately developed plasmic fabrics reflect-ing both rotational and planar mechanisms of deformation(Fig. 10(A)). It is apparent that as with the Bolders Bank Forma-tion, with which it is closely associated (Andrews et al.,1990), the Wee Bankie Formation is clearly a subglacial till,reflecting ice extending eastwards from the Midland Valley ofScotland.The eastern limit of the Wee Bankie Formation is distinctive,

with previous researchers interpreting a sequence of stackedmoraine ridges 50 km offshore (Stewart, 1991; Gatliff et al.,1994), interdigitating with an acoustically well-layered seis-mostratigraphic formation, termed the Marr Bank Formation.The sediments comprising the Marr Bank Formation range fromreddish-brown (5YR 4/3), moderately well-sorted sands in thewest to greyish-brown (10YR 5/2), well-sorted silts and clays inthe east, and have been interpreted by Holmes (1977) asreflecting glacimarine sedimentation contiguous with an icesheet terminating in a calving margin at the limit of the WeeBankie Formation. Micromorphological analysis of the MarrBank Formation (Table 4) indicates that there is significant spa-tial variation within the sediments that is not immediatelyobvious in macroscale. The suite of structures identified inMAR2 (Table 4) indicate a complex sediment evolution, inwhich laminated sediments were subsequently deformedthrough planar shear and rotation to produce a number of intra-clasts (Pebble Types II and III). These were finally reworkedunder aqueous conditions, producing a number of flow struc-tures (Carr, 1998; Fig. 10(B)). This suite of associated structuresand processes is consistent with sediment production in shal-low glacimarine or glacilacustrine conditions, associated witha fluctuating ice margin. To the east, the Marr Bank Formationchanges to a laminated silty-clay, within which lamination canclearly be seen in thin section (Table 4, Fig. 10(C)). This wouldseem to confirm the interpretation of Holmes (1977) of a signif-icant ice sheet margin some 50 km from the east coast of Scot-land during the Devensian.In the west of the northern North Sea, two seismostrati-

graphic ‘sequences’ are associated with renewed glaciationof the Shetland Isles. The Otter Bank sequence forms an arcuateband of mounded sediments with chaotic internal reflectorsaround the northern and eastern flank of the Shetland Ridge,whilst the Stormy Bank sequence appears to locally form amore seismically layered infill of topographic basins within





the Otter Bank Sequence. The Otter Bank sequence consists offine-grained diamictons with clasts of a largely Shetland prove-nance, whilst the Stormy Bank sequence is typified by fineshelly sands and silts, with a tendency to fine upwards. Singlethin sections were produced of the sediments making up eachsequence (Table 4). Both samples preserve a range of deforma-tion structures, including rotation structures (Fig. 10(D)) andpressure shadows indicative of rotational deformation, asso-ciated with rotational plasmic fabric development. It is appar-ent that such deformation occurred under high-stressconditions, with fracture of individual quartz grains. SampleSHE10, from the Otter Bank Formation also preserves well-developed grain lineations, indicating an element of planarshear during deformation, supported by the development of aweak masepic plasmic fabric. Development of boudinagestructures in SHE8 (Fig. 10(E)) indicates tensional stress appliedto the sediment during deformation. Microfabric analysis ofboth samples (Fig. 5) indicates the presence of a unidirectionallateral stress field during sediment deposition and deformationand, notably in SHE8, there is no evidence of depositionthrough rain-out from suspension. Given that only one samplefrom each formation was investigated in thin section, it isunclear how representative these samples are of eachsequence, but the data appears to confirm the previouslyreported presence of a local Shetland ice cap during a finalphase of glaciation of the northern North Sea (Ross, 1997).Whilst the overall seismic geometry of the Stormy Banksequence is suggestive of waterlaid deposition in shallow gla-cimarine conditions (Johnson et al., 1993), this is not confirmedby micromorphological analysis at this location.The Sperus Formation is a seismically layered unit that forms

an eastwards thickening wedge, beyond the limit of the OtterBank sequence, and is truncated in the east by the NorwegianChannel. The sediments of the Sperus Formation are dark grey(2.5Y 4/1), fine-grained, matrix-supported diamictons, com-monly containing complete bivalve shells. In thin section, theSperus Formation is generally structureless (Table 4), and thereis a notable absence of associated deformation features. Rare,isolated rotation structures, representing the rolling of indivi-dual grains, have produced weak skelsepic fabrics in SHE12,but reflect very localised deformation, probably produced dur-ing disturbance during a settling-out process. Microfabric ana-lysis of both samples identifies a well-developed verticalmicrofabric (Fig. 5), suggesting the absence of a unidirectionallateral stress field (Carr, 2001). These data suggest that theSperus Formation reflects deposition in low-energy conditions,probably within a glacimarine environment.

To the east, and partly overlying the Sperus Formation, asequence of diamictons, interpreted as the Norwegian Trenchand Tampen Formations (Rise et al., 1984) have been classi-cally associated with the Late Weichselian Scandinavian icesheet (Sejrup et al., 1987, 1991, 1995). The Norwegian TrenchFormation partly forms the lateral equivalent of the TampenFormation, and is found as a diamicton up to 40m thick, sug-gested to perhaps reflect up to three episodes of Mid–LateWeichselian glaciation (Sejrup et al., 1995, 2000) within theNorwegian Channel. At the northern edge of the NorwegianChannel, a series of glacimarine debris flow lobes have beendescribed by Carr et al. (2000) as the shelf-marginal equivalentof the Norwegian Trench Formation, reflecting sediment sup-ply at the grounding line of a tidewater calving ice sheet mar-gin. The micromorphology of the Tampen Formation in thenorthern North Sea (Table 4) is very similar to the upper partof the same formation further south (BER 11 and 12, Table 3),with rotation features, pressure shadows and crushed quartzgrains, as well as a distinct skelsepic and masepic plasmic fab-rics (Fig. 10(F)) and unidirectional microfabric (Fig. 5) support-ing a subglacial origin for the formation. However, as notedearlier, Carr (1998) suggests that the Tampen Formation mayreflect more than one stratigraphically significant glacial epi-sode, and it may be that these samples reflect earlier glaciationduring the ‘Cape Shore Episode’. However, it is clear from thesediments of the Norwegian Channel Formation and therelated debris flow deposits of the upper North Sea fan thatthere was clearly glaciation of the Norwegian Channel duringthis time, and potentially some extension of ice beyond, on tothe North Sea Plateau.The relative absence of post-depositional reworking of these

Late Weichselian formations by subsequent glaciation permitsquite detailed reconstruction of the palaeogeography of theNSB during the Bolders Bank glacial episode (Fig. 11). Whilethe quality of 14C AMS dating from the region is generally poor,the consensus view is that the Bolders Bank episode reflects re-advance of both the British and Scandinavian ice sheets afterapproximately 18 k 14C yr BP (Holmes, 1977; Rokoengenet al., 1982; Sejrup et al., 1994; Ross, 1997), and correlateswith the lithostratigraphic evidence of the Dimlington Stadialidentified in eastern Britain (Catt and Penny, 1966; Rose,1985; Boulton et al., 1991). However, this event is charac-terised by an ice-free shallow glacimarine corridor betweenboth ice sheets in the central and northern NSB, and terrestrialin the southern NSB.

Discussion

The role of micromorphology in examining offshoreQuaternary sediment sequences

The results of this research indicate that thin-section micromor-phology has a significant role to play in the examination of off-shore sediment sequences within Quaternary science. The dataoutlined above (Tables 2, 3 and 4) present a significant devel-opment in the level and quality of information that can beapplied in providing a genetic interpretation of the sedimentaryand deformational history of samples recovered from cores andboreholes. This permits rigorous testing of previous interpreta-tions, leading to some significant revision of the evolution ofcritical seismostratigraphic formations in the NSB (Table 5). Ithas been demonstrated that the identification of a suite ofassociated deformation structures in thin section can beused to identify subglacial conditions, and most importantly

3————————————————————Figure 10 Photomicrographs from sediments reflecting the BoldersBank glacial episode. Each image is paired with an original and anno-tated version, and the black bar reflects 5mm in each image. (A) Rota-tion structures and small pressure shadows around a micro-granitepebble, MAR 2, Marr Bank Formation (cross-polarised light) Note thestrong birefringence from a well-developed skelsepic plasmic fabric.(B) Water escape structure, MAR2, Marr Bank Formation (plane-polarised light). The arrow identifies the apparent initiation point ofthe structure. (C) True sedimentary lamination, MAR3, Marr Bank For-mation (cross-polarised light). (D) Rotation structures, SHE10, OtterBank Sequence (plane-polarised light). (E) Formation of boudins,SHE8, Stormy Bank Sequence (cross-polarised light) Note the well-developed unistrial plasmic fabric that identifies the developing bou-dins. (F) Development of masepic plasmic fabric, SHE11, Tampen For-mation (cross-polarised light). Rather than the discrete shearingidentified in 10(E), this masepic plasmic fabric reflects more pervasiveshear through the sediment body



Tab

le4

Micromorphologicalch

arac

teristicsofsamplessugg

estedto

representtheBoldersBan

kep

isode.

Seehea

dingofTab

le2fordetails

Micromorphologica

lfeatures

Skeleton

Matrix

Voids

Deform

ationstructures

Marinefeatures

Plasm

icfabric

Shap

e

Form

ation

Sample

Grain

>500mm

<500mm

Tex

ture

Void

Void

Section

Rotation

Pressure

Crushed

Peb

ble

Peb

ble

Peb

ble

Water

Linea

tions

Dropstones

Microfossils

Skelsepic

Lattisep

icOmnisep

icMasep

icUnistrial

no.

size

ratio

type

elem

ents

shad

ow

grains

III

III

esca

pe

BoldersBan

kFo

rmation

IND

1(H

)250

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discriminate between characteristics that can identify proximaland distal glacimarine environments. These data can be closelyrelated to the micromorphological structures identified inrecently deposited glacimarine and subglacial tills in reliableanalogue regions such as Svalbard and Alaska (Carr, 2001;Hiemstra, 2001) and provide an unprecedented degree of con-fidence in the interpretation of Quaternary glacial and glaci-marine sediments.From the present study, the identification of a series of asso-

ciated deformation features, unidirectional microfabrics andindications of deformation under high confining stress (crushedquartz grains) are used to infer subglacial conditions. However,it is currently unclear what the signature of iceberg ploughingcould be on pre-existing sediments. This may be of consider-able significance, given that formations such as the SwatchwayFormation have previously been interpreted as glacimarinesediments disturbed by extensive iceberg scour (Stoker et al.,1985; King, 1991). While it is likely that the effects of icebergploughing would be more variable and localised than subgla-cial processes, and therefore result in highly variable micro-morphological structures, this is yet to be tested at a reliableanalogue site. However, the consistency of sedimentologicalmicromorphological characteristics in repeat samples fromspatially widely separated samples suggests that in this study,there is little evidence to support extensive disturbance by ice-bergs in the formations under examination.

Regional reconstruction of glaciation

One of the key developments in this paper is the revision of theprocesses and environments of deposition of key sedimentaryformations within the NSB. It has proved possible to effectivelydiscriminate primary glacimarine sediments from those thathave been reworked or disturbed through processes of subgla-cial glacitectonism. This permits a robust interpretation and

Figure 11 Palaeogeographic reconstruction ofWeichselian glaciationof the North Sea basin during the Bolders Bank glacial episode

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testing of the depositional and deformation history of seismostra-tigraphic units from the NSB (Table 5). Taking the process-basedinterpretations obtained through micromorphology and apply-ing these to the existing Weichselian stratigraphy of the NSB,and incorporating previously published models of the palaeo-geography of the NSB (Fig. 1), three major phases ofWeichselian glaciation may be reconstructed (Table 5; Figs 7,10 and 12). The first two of these events (Ferder and Cape Shoreglacial episodes) reflect confluent glaciation of the Scandinavianand British ice sheets extending to the continental shelf edge,with the latter event conforming to the reconstruction of theLGM ice sheet in this region by Sejrup et al. (2000). The finalevent, termed here the Bolders Bank glacial episode, reflectsmore restricted glaciation of the region, with limited advanceof the Scandinavian ice sheet beyond the Norwegian Channel,and the extension of a tongue of ice from northeast England andScotland into the southern North Sea, with no evidence of icesheet confluence. An independent ice-cap developed over theShetland Isles, but it is unclear whether this was entirely sepa-rate (Sutherland, 1991), or partly contiguous with the main Brit-ish ice sheet (Hall and Bent, 1990; Stoker and Holmes, 1991).Application of thin-section micromorphology has provided areliable indication of the extent of the various ice sheets as theyextended into the NSB on different occasions, allowing greaterconfidence in the discussion of key stratigraphic and glaciolo-gical implications of such reconstructions.

Stratigraphic and chronological issues

While it is beyond the remit of this paper to revise the Late Qua-ternary stratigraphy of the NSB, it is clear that the findingsreported here have a fundamental impact on the current under-standing of glaciation in northwest Europe through the last gla-cial cycle, and therefore requires consideration. There are twoprincipal problems with attempts to reconstruct a detailedWeichselian glacial history for the NSB. Firstly, it is evident thatmuch of the stratigraphy for the last glacial cycle in the NSB isinadequately dated, and that the quality of 14C dating is con-strained by the quality of material available for dating. Otherapproaches to dating events in the NSB during the Weichselianthat have been attempted (AAR, palaeomagnetic analyses) donot provide anywhere near the temporal resolution necessaryin this context (see McCarroll, 2002). Secondly, it is apparentthat the relationship between individual formations in the NSBis not clearly identified by seismostratigraphy, and that a seriesof stratigraphic ambiguities limit the precision and confidencethat can be expressed in the correlations between formationsoutlined in Fig. 4 and described above. This results in great dif-ficulty in resolving key stratigraphic issues such as the numberof occasions during which the NSB was glaciated during theWeichselian. From the data outlined in this paper, it is clearthat there is evidence of multiple phases of glaciation, and thata number of these invoke confluent Scandinavian and Britishice sheets. The three stages of glaciation outlined above repre-sent a ‘best-fit’ of the stratigraphy as it currently stands in theNSB, but until improvements are made to the correlationsbetween specific formations (notably the Coal Pit, Swatchwayand Dogger Bank Formations), this model is subject to review.A host of stratigraphic issues arise from the three-phase

Weichselian glaciation model outlined above, relating to themanner in which the evidence in the NSB links the onshorerecords of the British Isles and Scandinavia. These problemsprimarily relate to the evidence for Middle to Late Weichselianglaciation. It is clear that both the Cape Shore and Bolders Bankepisodes reflect glaciation subsequent to MIS 3, during the tran-

sition from the Middle to Late Weichselian. The Cape Shoreglacial episode presents a range of stratigraphic and chronolo-gical problems, in that it is difficult to reconcile the onshoreand offshore records of glaciation, particularly with the Scottishonshore stratigraphy. Extremely limited 14C (bulk) radiometricages (Milling, 1975; Rise and Rokoengen, 1984; Johnson et al.,1993) suggest that the transition from glacimarine to subglacialconditions occurred in the Cape Shore Formation after approxi-mately 31–28k 14Cyr BP, reaching a peak of glaciation at oraround 22k 14Cyr BP (Sejrup et al., 1994). Whilst this chronol-ogy is largely compatible with the Weichselian glacial curve forWestern Scandinavia (Mangerud, 1991; Sejrup et al., 2000), itdoes not conform to the evidence from Scotland, from whichwell-constrained, high-quality 14C dated sites close to theLateWeichselian ice divide (Bishopriggs, Sourlie, Inchnadampf)identify cold, but ice-free conditions until approximately26 k 14C yr BP, with glaciation reaching a peak at or soon after18 k 14C yr BP (Rose, 1985; Boulton et al., 1991). However, it isnotable that in a recently recovered core from the Barra Fan,with a detailed 14C AMS chronology (Wilson et al., 2002),the British Ice Sheet is considered to have advanced to thecontinental shelf edge by 30 k 14C yr BP, suggesting that re-examination of the whole issue is required.Given that so few age estimates from the NSB can be consid-

ered reliable, in terms of the materials sampled for 14C dating(mainly marine shells or foraminifera samples), the over-dependence on a very limited number of dated cores, and inthe absence of new radiometric ages using 14C AMS and othertechniques (e.g. OSL dating), it is unlikely that this contradic-tion can be adequately resolved. However, it is interesting tonote that the recent compilation of data from the British Islesfor the Last Glaciation by Clark et al. (2004) recognise twostages of ice maxima in a number of locations across the BritishIsles, suggesting that there is further investigation to be done inthe onshore, as well as offshore records.

Conclusions

1 The investigation of thin-section micromorphology has pro-vided a significant improvement in the confidence by whichthe processes resulting in the deposition and deformation ofsediments recovered from offshore cores and boreholes fromthe NSB may be understood. Whilst it is apparent that furtherresearch is required to test micromorphological interpretationsin regions affected by iceberg scour, for example, thin-sectionexamination of offshore sediments shows great promise.

2 Within the constraints of the current seismostratigraphic fra-mework, three major glacial advances into the NSB havebeen reconstructed for theWeichselian/Devensian glaciation,two of which (Ferder and Cape Shore episodes) demonstrateconfluence between the British and Scandinavian ice sheets,supporting the ‘maximal’ model of the LGM in the NSBreported by Sejrup et al. (2000). A final, more restricted glacialadvance (Bolders Bank episode) reflects glaciation of the NSBwith an ice-free corridor between the two ice sheets.

3 The increased confidence in the genetic interpretation of thesediments of the NSB identifies significant problems withthe existing offshore seismostratigraphic framework for theDevensian/Weichselian glaciation. It is clear that there is aneed for fundamental re-examination of the geochronologyof the last glacial cycle in the region. This will be essential toresolve continuing controversy in understanding thedynamics of ice sheet development and the relationshipsbetween the onshore and offshore stratigraphic record inthe region.



Acknowledgements This research was funded as a NERC CASEresearch studentship GT4/94/364/G between Royal Holloway, Univer-sity of London, and BGS Edinburgh. Many thanks to Cees Labanfor access to cores and seismic lines held by the TNO/NITG, andto Hans-Petter Sejrup and Haflidi Haflidason for samples from theNorwegian Channel and North Sea Fan. Discussion with the lateRobin Wingfield was extremely useful in evaluating the status ofthe Dogger Bank, whilst Doug Peacock and Charles Harris helpedrefine many of the ideas forming the basis of this paper. S.J.C. wouldlike to acknowledge the significant assistance of Jerry Lee in makingthe thin sections. Reviews by John Hiemstra and Hans Petter Sejrupare gratefully acknowledged.

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The Last Glacial Maximum in the North Sea Basin