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Pleistocene till provenance in east Yorkshire Busfield, Marie E.; Lee, Jonathan R.; Riding, James B.; Zalasiewicz, Jan; Lee, Sarah V.

Published in: Proceedings of the Geologists' Association DOI: 10.1016/j.pgeola.2014.12.002 Publication date: 2015 Citation for published version (APA): Busfield, M. E., Lee, J. R., Riding, J. B., Zalasiewicz, J., & Lee, S. V. (2015). till provenance in east Yorkshire: Reconstructing ice flow of the British Lobe. Proceedings of the Geologists' Association, 126(1), 86-99. https://doi.org/10.1016/j.pgeola.2014.12.002

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Download date: 25. Sep. 2021 Elsevier Editorial System(tm) for Proceedings of the Geologists' Association Manuscript Draft

Manuscript Number: PGEOLA-D-14-00042R1

Title: Pleistocene till provenance in east Yorkshire: reconstructing ice flow of the British North Sea Lobe

Article Type: Research Paper

Keywords: North Sea Lobe; British-Irish Ice Sheet; Skipsea Till; Pleistocene; Provenance

Corresponding Author: Miss Marie Elen Busfield,

Corresponding Author's Institution: Royal Holloway

First Author: Marie Elen Busfield

Order of Authors: Marie Elen Busfield; Jonathan R Lee; James B Riding; Jan Zalasiewicz; Sarah V Lee

Abstract: The ice flow path and dynamic behaviour of the British-Irish Ice Sheet has been subject to renewed interest and controversy in recent years. Early studies in eastern England argued for interaction with Fennoscandian ice onshore in Britain, instigating re-examination of the sedimentology and provenance of many Pleistocene till successions. These studies instead supported an exclusively British provenance, and are used to predict southward advance of a broadly coast-parallel North Sea Lobe. Quantitative lithological and palynological analysis of the Pleistocene till succession in Holderness, East Yorkshire, however, remains to be carried out. We examined the lithologically diverse Skipsea Till in order to reconstruct ice flow pathways to the Holderness coast during the Pleistocene, thereby constraining which areas of substrate were subglacially eroded and entrained prior to deposition. The till yields a diverse range of soft, low-durability and uniquely British allochthonous material, including Magnesian Limestone, limestone and coal, and Carboniferous pollen and spore assemblages that would be unlikely to survive polyphase reworking. Ice extended southwards through southern Scotland, incorporating material in north ease England, north-east Yorkshire and the western margin of the North Sea Basin (NSB), supporting a recurrent ice flow pathway for the eastern margin of the British-Irish Ice Sheet during the Mid to Late Pleistocene.

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1 Pleistocene till provenance in east Yorkshire: reconstructing ice flow of the British 1 2 2 North Sea Lobe 3 4 3 5 6 7 4 Marie E. Busfield1*, Jonathan R. Lee2, James B. Riding2, Jan Zalasiewicz1, Sarah V. Lee1 8 9 1 10 5 Department of Geology, University of Leicester, University Road, Leicester LE1 7RH, UK 11 12 2 13 6 British Geological Survey, Environmental Science Centre, Keyworth, Nottingham NG12 14 7 5GG, UK 15 16 17 8 *Corresponding author. Current Address: Department of Earth Sciences, Royal Holloway, 18 19 9 University of London, Egham TW20 0EX, Surrey, UK. E-mail: 20 21 10 [email protected] 22 23 11 24 25 26 12 Abstract 27 28 29 13 The ice flow path and dynamic behaviour of the British-Irish Ice Sheet has been subject to 30 31 14 renewed interest and controversy in recent years. Early studies in eastern England argued for 32 33 15 interaction with Fennoscandian ice onshore in Britain, instigating re-examination of the 34 16 sedimentology and provenance of many Pleistocene till successions. These studies instead 35 36 17 supported an exclusively British provenance, and are used to predict southward advance of a 37 38 18 broadly coast-parallel North Sea Lobe. Quantitative lithological and palynological analysis of 39 40 19 the Pleistocene till succession in Holderness, East Yorkshire, however, remains to be carried 41 42 20 out. We examined the lithologically diverse Skipsea Till in order to reconstruct ice flow 43 44 21 pathways to the Holderness coast during the Pleistocene, thereby constraining which areas of 45 22 substrate were subglacially eroded and entrained prior to deposition. The till yields a diverse 46 47 23 range of soft, low-durability and uniquely British allochthonous material, including Permian 48 49 24 Magnesian Limestone, Carboniferous limestone and coal, and Carboniferous pollen and spore 50 51 25 assemblages that would be unlikely to survive polyphase reworking. Ice extended southwards 52 53 26 through southern Scotland, incorporating material in north ease England, north-east 54 27 Yorkshire and the western margin of the North Sea Basin (NSB), supporting a recurrent ice 55 56 28 flow pathway for the eastern margin of the British-Irish Ice Sheet during the Mid to Late 57 58 29 Pleistocene. 59 60 61 62 63 64 65 30 1. Introduction 1 2 3 31 Pleistocene glacial deposits and landforms along the eastern English coast are integral to 4 32 deciphering the dynamics and extent of the North Sea Lobe during expansion and retreat of 5 6 33 the last British-Irish Ice Sheet (BIIS). Onshore advance of the North Sea Lobe has been 7 8 34 demonstrated to occur during several different Mid and Late Pleistocene glaciations in 9 10 35 County Durham, north Yorkshire and north based upon detailed provenance analysis 11 12 36 (Lee et al., 2002; Davies et al., 2009, 2011, 2012; Roberts et al., 2013). Although subject to 13 14 37 recent geochemical, sedimentological and palaeontological assessment (Boston et al., 2010; 15 38 Evans & Thomson, 2010; Bateman et al., 2011), the Marine Isotope Stage (MIS) 2 stratotype 16 17 39 on the Holderness coast, east Yorkshire, is yet to yield systematic and quantitative erratic 18 19 40 clast and palynomorph provenance data. Holderness is of particular importance given its 20 21 41 chronostratigraphical significance, with Late Pleistocene glacial deposits overlying in situ 22 14 23 42 organic-rich silts (the „Dimlington Silts‟) which yield radiocarbon dates of 22.4-21.3 cal. C 24 14 25 43 ka BP (18.25±0.25 ka BP) and 23.3-21.2 cal. C ka BP (18.5±0.4ka BP) (Catt & Penny, 26 44 1966; Penny et al., 1969), constraining the earliest possible age for ice advance into this 27 28 45 region during the Late Devensian. 29 30 31 46 A for the Holderness coast has long been established (Catt & Penny, 1966; 32 33 47 Madgett & Catt, 1978; Bowen, 1999; Catt, 2007). However, recent studies focussing on the 34 35 48 3D geometry and geochemical composition of the major till units have raised significant 36 49 questions regarding their regional correlation (Boston et al., 2010; Evans & Thomson, 2010). 37 38 50 Reliable chronostratigraphical and lithological provenance constraints are therefore critical to 39 40 51 assess the significance of these units in the wider context of BIIS behaviour. In this study, we 41 42 52 examine the composition and provenance of the Skipsea Till which is commonly associated 43 44 53 with the first Late Devensian advance of North Sea ice into the region. This is to help 45 46 54 reconstruct: (1) the flow path of the North Sea ice lobe; (2) identify areas of substrate that 47 55 were being subglacially eroded and entrained. 48 49 50 56 51 52 53 57 2. Pleistocene deposits of the Holderness coast 54 55 58 The Pleistocene lithostratigraphy in Holderness has traditionally been subdivided into three 56 57 59 till members based principally upon lithological properties including colour, particle size 58 59 60 distribution, clast (qualitative) and heavy mineral composition, and matrix calcium carbonate 60 61 62 63 64 65 61 percentage (Catt & Penny, 1966; Madgett & Catt, 1978; Bowen, 1999; Catt, 2007). These are 1 2 62 termed the Basement Till, Skipsea Till and Withernsea Till members, and are separated by, 3 4 63 and in places inter-bedded with, stratified silts and (Catt, 2007). The lowermost 5 64 Basement Till rests on the underlying Chalk bedrock (Catt & Digby, 1988; Catt, 6 7 65 2007), and depending on its stratigraphical relationship to the Ipswichian Sewerby Raised 8 9 66 Beach is either pre-Ipswichian (Catt & Penny, 1966; Penny & Catt, 1967; Bateman & Catt, 10 11 67 1996; Catt, 2001, 2007) or Devensian in age (Eyles et al., 1994; Boston et al., 2010; Evans & 12 13 68 Thomson, 2010). At Dimlington, the stratotype for these glacial deposits, the Basement Till is 14 15 69 overlain by the Dimlington Silts (~18.5-18.2 ka) (Penny et al., 1969), and in turn by the 16 70 Skipsea and Withernsea tills (Rose, 1985; Evans & Thomson, 2010). Recent Optically 17 18 71 Stimulated Luminescence (OSL) age determinations of deposits between the Skipsea and 19 20 72 Withernsea Tills constrain the timing of initial advance (Skipsea Till) to ~21.7-16.2 ka, with 21 22 73 a second oscillation of the North Sea Lobe, and deposition of the Withernsea Till, occurring 23 24 74 between 16.2 ka and terminal retreat at ~15.5 ka (Bateman et al., 2011). 25 26 75 Between Withernsea and Bridlington the layer-cake lithostratigraphical arrangement of the 27 28 76 major till units identified by Catt & Penny (1966) further to the south at Dimlington is less 29 30 77 discernible. Evans & Thomson (2010) have argued that the till sequence here is 31 32 78 glacitectonically-deformed and thrust-thickened with deformation produced by a south to 33 34 79 south-eastwards advance of the North Sea ice lobe. Equally it is evident that the intra-till 35 variability is typically greater than the inter-till variability (Boston et al., 2010), and this is 36 80 37 81 especially applicable to the Skipsea Till (Catt, 2007). Recent unpublished studies recognise 38 39 82 potentially five distinct facies of Skipsea Till between Withernsea and Barmston based upon 40 41 83 matrix colour, matrix texture and clast content (British Geological Survey, unpublished data). 42 43 84 These include: (a) Chalk-rich facies as previously defined at Dimlington by Catt & Penny 44 45 85 (1966); (b) local Quaternary-rich facies; (c) Mercia Mudstone-rich facies; (d) Kimmeridge 46 86 Clay-rich facies; and (e) Lias-rich facies. 47 48 49 87 Various studies have debated the provenance of the Skipsea Till, with some authors 50 51 88 advocating west-east ice dispersal from the Lake District (Bisat, 1939; Foster, 1987), whilst 52 53 89 others favour erratic transport from northern Britain (Catt & Penny, 1966; Madgett & Catt, 54 55 90 1978; Catt, 2007). Whilst recent re-examination of deposits considered correlative in north 56 91 Yorkshire (Roberts et al., 2013), County Durham (Davies et al., 2009) and the North Sea 57 58 92 Basin (Davies et al., 2011) yield a predominantly northern British signature, quantitative 59 60 93 analysis of the clast lithology and palynomorph content of the Skipsea Till (and other 61 62 63 64 65 94 distinctive till units) in Holderness remains to be carried out. Previous quantitative studies of 1 2 95 the Skipsea Till have focussed upon the application of heavy mineralogy (Madgett and Catt, 3 4 96 1978) and geochemistry (Boston et al., 2010) to differentiate between different till units 5 97 within the region rather than reconstruct till provenance. This study represents the initial 6 7 98 findings of a major study examining the lithological and provenance variations within the 8 9 99 Skipsea Till. The focus of this paper is to examine the clast and micro- provenance from 10 11 100 the chalk-rich facies (A) of the Skipsea Till. This will facilitate comparison with other erratic 12 13 101 transport paths identified for the eastern British-Irish Ice Sheet, and thus contribute to our 14 15 102 understanding of the ice dispersal patterns which fed southwards advance of the North Sea 16 103 Lobe. 17 18 19 104 20 21 22 105 3. Methods 23 24 106 Multiple bulk samples of Skipsea Till (Facies E) were collected for the extraction of erratic 25 26 107 clast and palynomorph assemblages from the base of coastal cliff sections at Easington 27 28 108 (National Grid Reference TA 406 190), southern Holderness (Fig. 1). The sample site is 29 30 109 situated 3 km to the south-southeast of the stratotype sections at Dimlington with the chalk- 31 32 110 rich facies of the Skipsea Till being readily correlatable between the two based upon bulk 33 34 111 lithology and stratigraphical position. The unit sampled is a dark grey-brown (Munsell 35 112 Colour: 5Y 3/1) matrix-supported diamicton, with sub-angular to sub-rounded clast 36 37 113 morphologies alongside sparse glacially striated forms (Fig. 2). Samples were obtained from 38 39 114 a single section, with sampling restricted to freshly cleaned faces to minimise the effects of 40 41 115 weathering and surficial re-working, and thus ensure analysis of in situ material. 42 43 44 116 Erratic clasts were extracted by disaggregating bulk samples of the till in sodium 45 117 hexametaphosphate [(NaPO ) ] and wet-sieving through 16 mm, 8 mm, 4 mm and 2 mm 46 3 6 47 118 sieves. The 8-16 mm and >16 mm size fractions were categorised in terms of lithology and 48 49 119 stratigraphical age, and hence regions of likely provenance through correlation with reported 50 51 120 outcrop occurrences. The allochthonous palynomorph content was extracted from two 50 g 52 53 121 sub-samples of the bulk material through non-acid palynological preparation techniques 54 55 122 (Riding & Kyffin-Hughes, 2004, 2006). Three slide fractions were prepared from each 56 123 residue through swirling and heavy liquid separation (Riding & Kyffin-Hughes, 2004), 57 58 124 representing a light, heavy and centrifuged sub-sample. The palynomorphs were grouped 59 60 125 according to stratigraphical ranges, thus indicating their likely provenance. 61 62 63 64 65 126 1 2 3 127 4. Results 4 5 128 4.1. Clast Lithological Analysis 6 7 8 129 The total 8-16 mm and >16 mm erratic population of the Skipsea Till (Facies E) comprises a 9 10 130 diverse suite of locally-derived sedimentary lithologies (76.85%), alongside subsidiary far- 11 12 131 travelled sedimentary (4.18%) and crystalline components (13.53%) (Table 1, Fig. 3). The 13 14 132 remaining clasts (5.86%) represent erratic lithologies of indeterminate provenance, including 15 133 quartzo-feldspathic sandstone, fine-grained olive-green mudstone and intermediate igneous 16 17 134 lithologies, whose characteristics were not sufficiently diagnostic to discern a stratigraphical 18 19 135 association. 20 21 22 136 Clast lithologies derived from Pleistocene successions include reworked white-brown 23 24 137 (weathered) , Greensand chert and sandstone, and impure pebbles, constituting 25 138 10.32% of the sample population (Fig. 3). Cretaceous sedimentary lithologies are most 26 27 139 abundant (30.68%), consisting of chalk and black-grey (unweathered) flint (Table 1). The 28 29 140 assemblage (9.76%) consists of calcareous sandstone, silty micaceous limestone and 30 31 141 micaceous mudstone, alongside clasts of black bituminous mudstone (the Mulgrave Shale 32 33 142 Member of the Whitby Mudstone Formation or “Jet Rock”), ironstone, oolitic and/or shelly 34 limestone and allochthonous shell fragments. The Permo- fraction (12.83%) is 35 143 36 144 dominated by Magnesian Limestone, crystalline dolostone and dolomitic sandstone, with 37 38 145 subordinate quantities of brick-red Sherwood Sandstone, evaporite-bearing sandstone and 39 40 146 limestone, gypsum, and wind-faceted sandstone (dreikanter). Carboniferous erratic 41 42 147 lithologies (13.39%) include organic-rich sandstone, dark grey-brown and pink-red 43 44 148 (haematite stained) crystalline limestone, and single occurrences of coal and fossil material. 45 149 The remaining sedimentary constituent comprises minor, yet persistent populations of 46 47 150 „Old Red Sandstone‟ (1.95%) and Lower Palaeozoic greywacke and dark green 48 49 151 chert (2.23%). 50 51 52 152 Within the crystalline component (Table 1, Fig. 3), Devonian lithologies dominate (8.65%), 53 54 153 and include rhyolitic and andesitic porphyries, felsic intrusive material, and subsidiary 55 154 quantities of felsite, non-porphyritic andesite, volcaniclastic rock and quartzose metamorphic 56 57 155 lithologies. The Carboniferous fraction (4.18%) is dominated by mafic igneous lithologies, 58 59 156 alongside trace quantities of intermediate trachytic lava. Permian crystalline lithologies 60 61 62 63 64 65 157 (0.28%) are restricted to single occurrences of rhomb porphyry, and an unknown 1 2 158 microgranite. 3 4 159 5 6 7 160 4.2. Palynological Analysis 8 9 10 161 Facies E of the Skipsea Till contains a diverse association of allochthonous Carboniferous, 11 12 162 Jurassic, Cretaceous and Quaternary palynomorphs, in addition to abundant non-age 13 14 163 diagnostic forms (Table 2; Riding, 2012). Carboniferous spores predominate (51.84%), 15 164 including large populations of Densosporites spp. and Lycospora pusilla, alongside more 16 17 165 minor occurrences of Cirratriradites saturni, Radiizonates spp., Reticulatisporites spp., 18 19 166 Endosporites globiformis, Simzonotriletes intortus and Tripartites vetustus (Fig. 4). With the 20 21 167 exception of the latter, indicative of Late Mississippian (Viséan to Early Bashkirian) input 22 23 168 (Riding, 2012), the assemblage is characteristic of the Pennsylvanian (Late Bashkirian to 24 169 Kasimovian). Jurassic palynomorphs constitute 12.78% of the population (Table 2), including 25 26 170 pollen and spores, and rare cysts. Dinoflagellate cyst taxa recognised include 27 28 171 the Late Sinemurian marker Liasidium variabile, the characteristically Early Toarcian 29 30 172 Nannoceratopsis deflandrei subsp. senex and the Callovian to Middle Oxfordian index 31 32 173 Gonyaulacysta jurassica subsp. adecta, in addition to forms from the Kimmeridgian to 33 34 174 Tithonian such as Oligosphaeridium patulum, Perisseiasphaeridium panosum and 35 175 Systematophora spp. The Jurassic pollen assemblage contains the characteristically Early and 36 37 176 Mid Jurassic genus Chasmatosporites, and Callialasporites spp. which is typical of the Mid 38 39 177 and Late Jurassic, alongside minor occurrences of characteristically Jurassic spores such as 40 41 178 Ischyosporites variegatus (Riding, 2012). 42 43 44 179 The age-diagnostic palynomorph population with the lowest abundance are Cretaceous 45 180 palynomorphs (1.23%), with dinoflagellate cysts recognised including Cribroperidiium spp., 46 47 181 Odontochitina operculata, Hystrichodinium voigtii and ?Isabelidinium sp. With the exception 48 49 182 of the latter Late Cretaceous form, this assemblage is characteristic of the Early Cretaceous 50 51 183 (Riding, 2012). These occur alongside spores of the genus Cicatricosisporites, which is 52 53 184 typically Early Cretaceous. Palynomorphs derived from Quaternary deposits were found to be 54 55 185 low in abundance (6.65%); these include Pediastrum spp., Spiniferites spp and Tilia (Table 56 186 2). The remaining palynomorph population (27.50%) consists of long-ranging, and thus non- 57 58 187 age diagnostic forms such as acanthomorph acritarchs, bisaccate pollen and smooth fern 59 60 188 spores. 61 62 63 64 65 189 1 2 3 190 5. Discussion 4 5 191 5.1. Provenance of the erratic clast and palynomorph assemblages 6 7 8 192 The chalk-rich facies of Skipsea Till (Facies A) at Easington contains a diverse assemblage of 9 10 193 locally-derived and far-travelled erratic clasts and palynomorphs, incorporated through 11 12 194 erosion and entrainment of sedimentary and igneous strata in northern England, southern 13 14 195 Scotland and the western margin of the North Sea Basin (Fig. 5). The wide geological range 15 196 of lithologies present suggests that many of the major sedimentary bedrock units in eastern 16 17 197 England were not extensively buried beneath superficial deposits and thus were actively 18 19 198 eroded and being entrained subglacially. 20 21 22 199 Jurassic, Cretaceous and Quaternary sedimentary lithologies are considered to be locally 23 24 200 derived from the Cleveland Basin, southern Yorkshire, and adjacent offshore strata. These 25 201 include chalk and grey-black (fresh) flint from the Upper Cretaceous chalk bedrock (Kent, 26 27 202 1980; Cameron et al., 1992), immediately underlying the Pleistocene succession in 28 29 203 Holderness (Catt, 2007). Their local derivation, and hence minimal erosion during transport, 30 31 204 is consistent with the limited occurrence of Cretaceous spores and dinoflagellate cysts. Lower 32 33 205 Jurassic material, typical of the Cleveland Basin, include Liasidium variabile and 34 Nannoceratopsis deflandrei subsp. senex derived from the Redcar Mudstone and Whitby 35 206 36 207 Mudstone formations, respectively (Brittain et al., 2010; Bucefalo Palliani & Riding, 2000), 37 38 208 alongside trace quantities of the Mulgrave Shale Member (“Jet Rock”), which is unique to 39 40 209 Yorkshire. Oolitic and/or shelly limestones and allochthonous shell fragments are more 41 42 210 characteristic of the Mid to Late Jurassic strata of the northern Cleveland Basin (Fig. 5), 43 44 211 consistent with the occurrence of Gonyaulacysta jurassica subsp. adecta (see Riding & 45 212 Thomas, 1997), which was likely to have been eroded from the Callovian-Oxfordian 46 47 213 Osgodby Formation to Coralline Oolite Formation succession. White and brown (weathered) 48 49 214 flint and well rounded quartzite pebbles were provenanced to the locally widespread 50 51 215 and Pleistocene deposits, both on- and offshore (Lee et al., 2002). Trace quantities of 52 53 216 Cretaceous Greensand chert and glauconitic sandstone are likewise considered to be derived 54 55 217 through reworking within Quaternary deposits due to their lack of outcrop exposure north of 56 218 Holderness (Cameron et al., 1992; Mitchell, 1995; Hopson et al., 2008). 57 58 59 60 61 62 63 64 65 219 More far-travelled sedimentary lithologies include the Permian-Triassic Sherwood Sandstone 1 2 220 Group and Magnesian Limestone Formation, both of which outcrop extensively across 3 4 221 northern Yorkshire, southern County Durham and offshore (Fig. 5). Incorporation of 5 222 abundant Carboniferous material, including organic-rich sandstones and limestones, 6 7 223 alongside single occurrences of coal and thermally-matured coral, indicates derivation from 8 9 224 County Durham and Northumberland or the immediately adjacent offshore area, as 10 11 225 Carboniferous strata do not outcrop in the central North Sea (Cameron et al., 1992). Coal 12 13 226 material could arguably be derived from Jurassic strata in Yorkshire and the adjacent 14 15 227 offshore, but the greater outcrop occurrence of Carboniferous coal and the abundance of 16 228 Pennsylvanian „Coal Measures‟ palynoflora provides strong support for a Carboniferous age. 17 18 229 Pink-purple stained limestones of the Upper Coal Measures are considered more typical of 19 20 230 the Midland Valley strata, given their restricted extent in north-east England. Overall, 21 22 231 however, the low durability and large population of Carboniferous sedimentary lithologies 23 24 232 support a more proximal principal source region. 25 26 233 Rare far-travelled sedimentary clasts include lower Palaeozoic greywacke likely to have been 27 28 234 derived from the Southern Uplands (Greig, 1971), having only limited exposure in north-east 29 30 235 England (Taylor et al., 1971), alongside Devonian Old Red Sandstone clasts of southern 31 32 236 Scottish provenance (Greig, 1971; Cameron & Stephenson, 1985). In addition, crystalline 33 34 237 metamorphic lithologies characteristic of the Scottish Grampian Highlands (Johnstone, 1966) 35 are extremely low in abundance. Alternatively, theses erratics may be reworked clasts from 36 238 37 239 the widespread Dalradian-rich Old Red Sandstone conglomerates of the Midland Valley 38 39 240 (Cameron & Stephenson, 1985). 40 41 42 241 The far-travelled component is dominated by igneous lithologies typical of the Devonian 43 44 242 Cheviot Volcanic Complex (Fig. 5). These include characteristic purple to red-brown 45 46 243 rhyolitic and green to dark brown andesitic lavas and porphyries, alongside abundant 47 244 intrusive lithologies eroded from the main granitic pluton (Greig, 1971; Taylor et al., 1971; 48 49 245 Robson, 1980). This is established as the principal source of felsic intrusive material due to 50 51 246 its large extent and abundance of associated Cheviot lavas within the till. This is in contrast to 52 53 247 the paucity of erratic material derived from other major volcanic provinces, such as the Lake 54 55 248 District and the Grampian Highlands (Johnstone, 1966; Taylor et al., 1971). Basaltic erratic 56 249 lithologies may be provenanced to the extensive Carboniferous and Devonian lava 57 58 250 successions of north-east England (Taylor et al., 1971), and particularly southern and central 59 60 251 Scotland (Greig, 1971; Cameron & Stephenson, 1985). -dolerite erratics were likely to 61 62 63 64 65 252 have been incorporated through the erosion of mafic intrusions in northern Britain, including 1 2 253 the widespread Tertiary dyke swarm (Emeleus & Gyopari, 1992). However, the abundance of 3 4 254 Carboniferous sedimentary lithologies, and entrained erratics from the proximal Cheviot 5 255 volcanic complex provides support for derivation from the prominent Carboniferous Whin 6 7 256 Sill in northern England, and potentially from the coeval Midland Valley Sill in central 8 9 257 Scotland (Taylor et al., 1971; Dunham & Strasser-King, 1982; Bateson & Johnson, 1984; 10 11 258 Cameron & Stephenson, 1985). The single occurrence of volcaniclastic material within the 12 13 259 sample is considered to have been derived from the Devonian Ochil Hills Formation in the 14 15 260 Midland Valley (Cameron & Stephenson, 1985). The absence of extrusive volcanic 16 261 lithologies characteristic of north-west England, e.g. the fine-grained, pyroclastic material 17 18 262 and green-blue to grey andesitic lavas of the Borrowdale Volcanic District (Taylor et al., 19 20 263 1971), negates its inclusion as an erratic source region. 21 22 23 264 Only two clasts of probable Scandinavian provenance were recorded within the Skipsea Till 24 25 265 (Facies E), consisting of rhomb porphyry and an unknown microgranite. Possible correlatives 26 266 of the latter include the pyterlite variety of Rapakivi granite (Müller, 2007), sourced from the 27 28 267 Baltic sector of the Fennoscandian Shield (Fig. 5), or a microcrystalline form of the 29 30 268 Norwegian Drammensgranit (Lee et al., 2006). The latter may be more consistent with the 31 32 269 Oslofjord derivation of the rhomb porphyry erratic (Neumann et al., 2004; Larsen et al., 33 34 270 2008), although the granite clast is not a common constituent of Norwegian erratic 35 assemblages recognised elsewhere (Ehlers, 2011 pers. comm). The rare occurrence of these 36 271 37 272 clasts and the common occurrence of low-durability lithologies that are unique to eastern 38 39 273 England suggests that the Scandinavian erratics were reworked from pre-existing deposits 40 41 274 situated in the current offshore by the BIIS as opposed to direct derivation by Fennoscandian 42 43 275 ice (sensu Hoare & Connell, 2005; Lee et al., 2005). Possible sources include ice-rafted 44 45 276 erratics from Early Pleistocene coastal deposits (cf. Larkin et al., 2011; Hoare, 2012), or from 46 277 the reworking of older or contemporary deposits with reported Scandinavian input e.g. the 47 48 278 Basement Till on the Holderness coast (Catt, 2007) or the Fisher Formation offshore (Davies 49 50 279 et al., 2011). 51 52 53 280 Incorporation of some of the British lithologies through reworking of older glacigenic or non- 54 55 281 glacigenic strata is likely – especially robust and durable clast lithologies such as Greensand 56 282 chert, flint (white, brown and chatter-marked), vein quartz and quartzite. However, the 57 58 283 abundant occurrences of soft, non-durable sedimentary lithologies, including Jurassic 59 60 284 limestone, mudstone and the Mulgrave Shale Member (“Jet Rock”), Permian Magnesian 61 62 63 64 65 285 Limestone and Carboniferous limestone and coal, would be unlikely to have survived 1 2 286 multiple episodes of reworking, particularly in light of the evidence for highly-abrasive 3 4 287 subglacial conditions (e.g. striated clasts) (Lee et al., 2002). Similarly, during repeated 5 288 recycling, the Carboniferous palynomorph assemblage would likely have become 6 7 289 numerically diluted (e.g. Riding et al., 1997), rather than constituting approximately 52% of 8 9 290 the assemblage (Table 2), and would be unlikely to have preserved the abundant intact 10 11 291 palynomorphs (e.g. Fig. 4). The relative abundance of non-local erratic materials (e.g. 12 13 292 crystalline and sedimentary lithologies) and their grouping and attribution to specific 14 15 293 stratigraphical and geographical sources suggests that this component of the clast assemblage 16 294 is also of primary origin. 17 18 19 295 20 21 22 296 5.2. Erratic transport paths of the North Sea Lobe 23 24 297 The distinctive suite of lithologies and palynomorphs within Facies A of the Skipsea Till at 25 26 298 Easington supports transport of material sourced from ice dispersal centres situated over the 27 28 299 Midland Valley and southern central Scotland that fed into the Southern Uplands, and then 29 30 300 extended southwards entraining crystalline lithologies from the Cheviot Hills, and successive 31 32 301 Palaeozoic and Mesozoic strata along the east coast of England (see Fig. 6). This flow 33 34 302 trajectory is consistent with a range of Mid and Late Pleistocene tills in eastern England 35 303 attributed to derivation from the North Sea Lobe of the BIIS during several different Mid and 36 37 304 Late Pleistocene glaciations (e.g. Lee et al., 2002; Boston et al., 2010; Davies et al., 2012; 38 39 305 Roberts et al., 2013). Although these tills consistently record input from northern Britain 40 41 306 along a broadly southerly trajectory, the influence and activity of different ice dispersal 42 43 307 centres within the BIIS is variable. 44 45 308 Re-examination of Middle Pleistocene tills in County Durham (Davies et al., 2012) and north 46 47 309 Norfolk (Lee et al., 2002) reveals a broad suite of diagnostically British clast lithologies and 48 49 310 palynomorphs, rejecting earlier predictions of a Scandinavian provenance in these units 50 51 311 (Trechmann, 1915, 1931; Boswell, 1916; Bridge & Hopson, 1985; Ehlers et al., 1991). Rare 52 53 312 Scandinavian erratics, where present, are therefore considered to reflect reworking within the 54 55 313 North Sea Basin (Lee et al., 2002; Catt, 2007). Clast and palynomorph assemblages support 56 314 derivation from the Grampian Highlands, Midland Valley and Southern Uplands of Scotland, 57 58 315 as well as northern England and the adjacent North Sea. Material diagnostic of the north-west 59 60 316 of England, e.g. the Lake District, is not recorded, and curiously, compared to younger 61 62 63 64 65 317 (Devensian) tills, input from the extensive Carboniferous successions of Northumberland and 1 2 318 County Durham is minimal (Lee et al., 2002; Davies et al., 2011, 2012). 3 4 319 Initial Late Pleistocene (Devensian) re-advance in County Durham reflects similar erratic 5 6 320 transport paths from northern Britain, but with an additional input from north-western 7 8 321 England along the Tyne Gap (Davies et al., 2009). This is corroborated by clast fabrics and 9 10 322 striae which support west-east ice flow pathways. However, these deposits are immediately 11 12 323 overlain by till of exclusively eastern provenance such as the Horden Till (Davies et al., 13 14 324 2009), comprising the characteristic suite of material from the Midland Valley, Southern 15 325 Uplands, Cheviot Hills and north-eastern England, alongside north-south clast fabric 16 17 326 orientations. Further south at Upgang, on the North Yorkshire coast, basal deposits in the 18 19 327 Devensian succession reproduce this north-south erratic transport path, again incorporating 20 21 328 no material exclusively diagnostic of a Lake District input (Roberts et al., 2013). A striking 22 23 329 feature of the Devenisan till successions in both County Durham and North Yorkshire is a 24 25 330 notably increased input of low-durability Carboniferous erratic clasts and palynomorphs 26 331 compared to the pre-Devensian record. 27 28 29 332 Continuing southwards onto the Holderness coast, recent studies have corroborated the 30 31 333 dominance of a north-south ice flow pathway (e.g. Boston et al., 2010; Evans & Thomson, 32 33 334 2010), but lack the quantitative lithological and palynological analysis to facilitate 34 35 335 comparison with other erratic transport paths feeding the North Sea Lobe. This study 36 336 demonstrates that the Skipsea Till at Holderness records incorporation of material from 37 38 337 eastern Britain, eroding crystalline and sedimentary substrates from central and southern 39 40 338 Scotland, around the Cheviot Hills and southwards through north-east England and the North 41 42 339 Sea (Fig. 6). Similarly to the deposits of North Yorkshire and County Durham, the Skipsea 43 44 340 Till records an abundance of intact Carboniferous clasts and palynoflora, although is perhaps 45 46 341 unique within the Devensian tills for containing reworked Scandinavian erratics. However, 47 342 with a longer transport path, opportunity to rework erratics from older tills both on and 48 49 343 offshore is greatly increased. 50 51 52 344 53 54 55 345 5.3. Implications for the evolution of the British North Sea Lobe 56 57 346 Throughout the Mid to Late Pleistocene, till successions in eastern England recorded 58 59 347 deposition from a southerly extension of the British-Irish Ice Sheet, sourced to ice dispersal 60 61 62 63 64 65 348 centres in northern Britain. The persistent absence of material derived from north-western 1 2 349 Scotland is attributed to a well-established ice divide running broadly N-S across mainland 3 4 350 Scotland (e.g. Hughes et al., 2014). Any substrate east of this ice divide was potentially 5 351 subject to erosion and transport eastwards and southwards towards the North Sea Basin, thus 6 7 352 delivering erratic material from the Grampian Highlands, Midland Valley and Southern 8 9 353 Uplands to the eastern English coast (this study; Lee et el., 2002; Davies et al., 2009, 2012; 10 11 354 Roberts et al., 2013). Further south, ice is diverted along topographical corridors, flowing 12 13 355 westwards along the Solway Firth towards the Irish Sea (see Fig. 6), and deflected around the 14 15 356 Cheviot Hills to the east along the Tweed Ice Stream (e.g. Livingstone et al., 2012). This 16 357 dispersal path is supported by the orientation of drumlins and glacial lineations around the 17 18 358 Cheviot Massif (e.g. Everest et al., 2005), and clearly represents an important erratic transport 19 20 359 path given the recurrent Cheviot input within the Skipsea Till and other deposits of the North 21 22 360 Sea Lobe (Lee et al., 2002; Davies et al., 2009, 2011, 2012; Roberts et al., 2013). 23 24 25 361 During the Mid Pleistocene, west to east erratic transport across northern England appeared 26 362 inactive, and thus no material from north-western England e.g. the Lake District has been 27 28 363 observed within the tills of eastern England (e.g. Lee et al., 2002; Davies et al., 2012). By the 29 30 364 Late Pleistocene, however, ice was able to cross the Pennines via the Tyne and Stainmore 31 32 365 Gaps, generating west-east oriented streamlined bedforms (e.g. Livingstone et al., 2012), and 33 34 366 erratic transport pathways which fed Lake District material to ice in eastern Britain (Davies et 35 al., 2009). Expansion of the North Sea Lobe along the eastern English coast during the Last 36 367 37 368 Glacial Maximum effectively blocked trans-Pennine ice dispersal, and thus the termini of 38 39 369 these ice streams were dammed to form ice-marginal and proglacial lakes e.g. Glacial Lake 40 41 370 Wear, Glacial Lake Pickering and Glacial Lake Humber (Fig. 6; Livingstone et al., 2010; 42 43 371 2012). As a result, erratic transport paths from north-western England were abandoned, and 44 45 372 the glacial sediments recorded an exclusively eastern British provenance (e.g. Davies et al., 46 373 2009, 2011; Roberts et al., 2013). The Skipsea Till at Holderness recorded the initial southern 47 48 374 extension of the North Sea Lobe during the Late Devensian which can be constrained to 21.7- 49 50 375 16.2 ka based upon radiocarbon and OSL dating of immediately underlying and overlying 51 52 376 deposits (Penny et al., 1969; Bateman et al., 2011). This is further corroborated by high-level 53 54 377 lake deposits from palaeo-glacial Lake Humber with an OSL age of 16.6 ± 1.2 ka (Bateman 55 56 378 et al., 2008). 57 58 379 This southerly ice flow trajectory, though well constrained by geological evidence, is 59 60 380 enigmatic given that the more logical flow path would be for ice from the Midland Valley to 61 62 63 64 65 381 have continued eastwards over relatively soft, wet sediments towards the central axis of the 1 2 382 North Sea Basin. Significantly, this ice flow trajectory has been interpreted from several 3 4 383 different episodes of Mid and Late Pleistocene glaciation (Boulton et al., 1977, 2001; Lee et 5 384 al., 2002; Clark et al., 2012). Previous studies advocated the onshore (Perrin et al., 1979; 6 7 385 Bowen et al., 1986; Fish & Whiteman, 2001) or offshore (Boulton et al., 1991; Davies et al., 8 9 386 2009, 2011; Lee et al., 2012) presence of Fennoscandian ice deflecting British ice along its 10 11 387 southwards trajectory. The lack of evidence for Fennoscandian ice within mainland eastern 12 13 388 England appears to preclude the „onshore‟ scenario; however, its presence and interaction 14 15 389 with the central and northern North Sea is likely. For example, Graham et al. (2007) and 16 390 Bradwell et al. (2008) demonstrated that north-westward overspill of the Norwegian Channel 17 18 391 Ice Stream during the Late Weichselian enabled Fennoscandian ice to converge with the 19 20 392 British-Irish Ice Sheet to the southwest of Shetland (see Fig. 7a). Such an ice sheet 21 22 393 configuration could presumably have also occurred during older glaciations, however, the 23 24 394 offshore extent of both British and Fennoscandian ice masses remains largely unknown. 25 26 395 Conversely, Boulton et al. (1977, 1991) and Lee et al. (2002) have proposed models for 27 28 396 different Mid and Late Pleistocene glaciations whereby the British-Irish Ice Sheet spread and 29 30 397 extended across the floor of the North Sea Basin as a large piedmont lobe (Fig. 7b). The 31 32 398 advantage of these models is that they do not necessarily require the interaction of British 33 34 399 with Fennoscandian ice, and that ice extent was largely driven by unconstrained flow over a 35 soft and wet deformable substrate (Boulton et al., 1977, 1991; Lee, et al. 2002). 36 400 37 38 401 An alternative model was tentatively suggested by Clark et al. (2012), who proposed an ice 39 40 402 dome over part of the southern North Sea during the Late Weichselian which caused British 41 42 403 North Sea ice to be deflected southwards (Fig. 7c). Whilst such a model cannot be verified by 43 44 404 the currently available offshore data (Clark et al., 2012), the concept of a residual dome or 45 46 405 particularly a topographical rise (Clark et al., 2012) in the floor of the North Sea is 47 406 nevertheless worthy of further consideration because of its potential implications for ice 48 49 407 dynamics. Such a topographical rise (or a switch to a well-drained substrate) could form a 50 51 408 frictional „sticking-point‟ causing flow deceleration and ice thickening with enhanced areas 52 53 409 of basal sliding being directed into adjacent areas of lower relief and/or poorly-drained 54 55 410 substrate. Within the western part of the southern North Sea two obvious „frictional‟ areas 56 411 stand out: firstly, the north-south striking outcrop of Cretaceous Chalk that occurs along the 57 58 412 Yorkshire, Lincolnshire and western North Sea margins; and secondly, Dogger Bank, which 59 60 413 forms an extensive southwest-northeast trending bathymetric high to the north and northeast 61 62 63 64 65 414 (Fig. 7d). The zone between these two „frictional‟ areas, and the possible zone of enhanced 1 2 415 basal sliding, is characterised by a lower topography, with the geology composed of 3 4 416 extensive glacial lacustrine, meltwater and till deposits of Mid and Late Pleistocene age, 5 417 overlying Mesozoic mudstones (cf. Tappin et al., 2011). 6 7 8 418 The attraction of the various ice deflection hypotheses lies in the variation of erratic transport 9 10 419 paths during evolution of the British-Irish Ice Sheet. It is evident that Mid Pleistocene till 11 12 420 successions along the eastern English coast recorded significantly lower populations of 13 14 421 Carboniferous erratic material than their Late Pleistocene counterparts (Lee et al., 2002; 15 422 Davies et al., 2009, 2012; Roberts et al., 2013). This may reflect protection of the 16 17 423 Carboniferous substrate during earlier glacial episodes, e.g. by a blanket of older tills, or 18 19 424 alternatively enhanced erosion during the Late Pleistocene, potentially driven by switching 20 21 425 ice flow pathways. If ice in the North Sea Basin deflected the North Sea Lobe along its more 22 23 426 southerly trajectory, the prominent Tweed Ice Stream may have been similarly deflected, 24 25 427 arguments for which can be made based on the strike of drumlins and glacial lineations 26 428 (Raistrick, 1931; Everest et al., 2005; Mitchell, 2008). This is anticipated to have driven 27 28 429 greater subglacial erosion and entrainment of widespread Carboniferous bedrock throughout 29 30 430 north-east England, due south of the Tweed Ice Stream, as opposed to the considerably 31 32 431 younger Mesozoic and Quaternary deposits of the adjacent North Sea. 33 34 35 432 Currently, it is not possible to test these models further due to the lack of available offshore 36 433 data, and consequently they remain somewhat speculative. Nor is it currently possible to 37 38 434 accurately constrain the extents of the British or Fennoscandian ice sheets, except that 39 40 435 previous assertions for the presence of Fennoscandian ice in mainland eastern England during 41 42 436 various Mid and Late Pleistocene glaciations are not supported by geological evidence. It is 43 44 437 clear from the available geological evidence that the southwards flow of a British North Sea 45 46 438 lobe of ice broadly parallel to the trend of the modern coastline of eastern England was a 47 439 recurrent ice flow pattern, which logically was driven by broadly recurrent glaciological 48 49 440 processes and constraints during different Mid to Late Pleistocene glacial events. 50 51 52 441 53 54 55 442 6.1. Conclusions 56 57 443  Re-examination of the lithological and palynological content of the Skipsea Till (Facies 58 59 444 E) at Easington, East Yorkshire, confirms that the till was deposited by a lobe of British 60 61 62 63 64 65 445 ice as previously indicated by Catt (2001, 2007). Critical lithological evidence includes: 1 2 446 (1) the abundance of locally-derived and far-travelled erratic lithologies and 3 4 447 palynomorphs unique to the British geological record including Jurassic Mulgrave Shale 5 448 Member (“Jet Rock”), Permian Magnesian Limestone, Carboniferous limestone and coal; 6 7 449 (2) an extremely low abundance of Scandinavian erratic lithologies (0.28% of the sample 8 9 450 population) and a complete absence of characteristic high-grade metamorphic suites; (3) 10 11 451 predominance of low-durability sedimentary lithologies (e.g. Jurassic limestone and 12 13 452 mudstone, Permian Magnesian limestone) and numerically concentrated Carboniferous 14 15 453 palynoflora indicating direct incorporation from bedrock outcrops with minimal 16 454 reworking. 17 18 19 455  Erratic clast lithologies and palynomorphs suggest that ice was ultimately sourced from 20 21 456 central Scotland, before flowing through the Southern Uplands and northern England, 22 23 457 extending southwards across the floor of the North Sea into eastern England. 24 25 26 458  The diverse occurrence of lithologies indicate that during incorporation into this facies of 27 459 Skipsea Till, most major sedimentary bedrock units in eastern England were largely 28 29 460 devoid of Quaternary cover, and were actively eroded subglacially. Studies of other facies 30 31 461 of Skipsea Till are currently in progress and will determine whether the focus of 32 33 462 subglacial erosion and entrainment shifted either spatially or temporally during 34 35 463 emplacement of the till sheet. 36 37  This southwards ice flow trajectory is a recurrent ice flow path that can be replicated from 38 464 39 465 many Mid and Late Pleistocene tills in eastern England including a number that until 40 41 466 recently were thought to be of Fennoscandian origin. 42 43 44 467  The cause of this southwards ice flow has been debated over several decades and remains 45 46 468 ambiguous largely due to the paucity of available offshore evidence. However, the 47 48 469 repeated ice flow pattern reconstructed from several different glacial events suggests 49 470 common and recurrent glaciological constraints within the southern North Sea Basin. 50 51 52 471 53 54 55 472 Acknowledgements 56 57 58 473 This research was undertaken when the lead author was completing an MGeol at the 59 474 Department of Geology, University of Leicester. The authors wish to thank Jane Flint for 60 61 62 63 64 65 475 assistance with palynological sample preparation. Andy Saunders, Richard England, Colin 1 2 476 Cunningham and Nick Marsh are acknowledged for their advice on clast lithological analysis 3 4 477 and preparation. Jonathan Ford, Rodger Connell and John Catt are warmly thanked for their 5 478 comments and thoughts on the manuscript and aspects of the research, and the authors wish 6 7 479 to thank Bethan Davies and John Catt for informative and helpful reviews. 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Proceedings of the Geologists’ Association 108, 25-38. 58 59 60 61 62 63 64 65 651 Roberts, D.H., Evans, D.J.A., Lodwick, J. & Cox, N.J. 2013: The subglacial and ice-marginal 1 652 signature of the North Sea Lobe of the British-Irish Ice Sheet during the Last Glacial Maximum at 2 3 653 Upgang, North Yorkshire, UK. Proceedings of the Geologists’ Association 124, 503-519. 4 5 6 654 Robson, D.A. 1980: The Geology of North East England. Natural History Society of Northumbria 7 655 Special Publication, Newcastle Upon Tyne, 113 pp. 8 9 10 656 Tappin, D.R., Pearce, B., Fitch, S., Dove, D., Gearey, B., Hill, J.M., Chambers, C., Bates, R., Pinnion, 11 12 657 J., Diaz Doce, D., Green, M., Gallyot, J., Georgiou, L., Brutto, D., Marzialetti, S., Hopla, E., Ramsay, 13 658 E. & Fielding, H., 2011: The Humber Regional Environmental Characterisation British. Geological 14 15 659 Survey Open Report OR/10/54, 375pp. 16 17 18 660 Taylor, B.J., Burgess, I.C., Land, D.H., Mills, D.A.C. et al. 1971: British Regional Geology: Northern 19 661 England. British Geological Survey, HMSO, London, 121 pp. 20 21 22 662 Trechmann, C.T. 1915: The Scandinavian Drift of the Durham coast and the general glaciology of 23 663 south-east Durham. Quarterly Journal of the Geological Society 71, 53-83. 24 25 26 664 Trechmann, C.T. 1931: The Scandinavian Drift or Basement Clay on the Durham coast. Proceedings 27 28 665 of the Geologists Association 42, 292-294. 29 30 666 Woodcock, N. & Strachan, R. 2000: Geological History of Britain and Ireland. Blackwell Science 31 32 667 Ltd., Oxford, UK, 423 pp. 33 34 668 35 36 37 669 38 39 40 670 41 42 671 43 44 45 672 46 47 673 48 49 50 674 51 52 675 53 54 55 676 56 57 677 58 59 60 678 61 62 63 64 65 679 Figure captions 1 2 680 Fig. 1. Location map of north-west Europe showing the site studied and other locations referred to in 3 4 681 the text. Modified from Lee et al. (2002) and Woodcock & Strachan (2000). British county 5 6 682 boundaries reproduced from Ordnance Survey map data by permission of the Ordnance Survey © 7 683 Crown copyright 2010. 8 9 10 684 Fig. 2. Photographs of the sampled section of Skipsea Till at Easington (see Fig. 1). (A) Section 11 12 685 profile measures 2.82 m. Box (i) indicates example of sample section cleaned to minimise effect of 13 686 weathering. (B) Note the poorly sorted nature of the diamicton, and the sub-angular to sub-rounded 14 15 687 clast morphologies. Box (ii), re-drawn in (C), highlights the glacially striated chalk clast recovered 16 17 688 from the till. 18 19 689 Fig. 3. Population and lithostratigraphical association of 8-16 and >16mm clast assemblages within 20 21 690 each sample of the Skipsea Till studied. 22 23 691 Fig. 4. Carboniferous allochthonous palynomorphs extracted from two sub-samples of the Skipsea 24 25 692 Till. A-D) Densosporites spp.; E-H) Lycospora spp.; I) Tripartites spp.; J) Endosporites globiformis; 26 27 693 and K) Tripartites vetustus. The scale bar measures 10 μm. 28 29 694 Fig. 5. Bedrock geology map of northern Britain showing outcrop occurrences of lithostratigraphical 30 31 695 groups found within the Skipsea Till erratic clast and palynomorph assemblages. A-J indicate 32 33 696 geographical regions referred to in the text. Map modified from BGS DiGMapGB-625. Reproduced 34 697 with permission of the British Geological Survey © NERC. All rights reserved. 35 36 37 698 Fig. 6. Proposed ice flow path for the British-Irish Ice Sheet that deposited the Skipsea Till, overlain 38 39 699 onto outline bedrock geological boundaries (i), with corresponding bedrock geology map and key 40 700 inset (ii; see Fig. 5). Palaeo-ice marginal lakes and bedforms associated with advance of the North Sea 41 42 701 Lobe modified after the Britice Glacial Map of Britain (Clark et al. 2004). Geological map adapted 43 44 702 from BGS DiGMapGB-625. Reproduced with permission of the British Geological Survey © NERC. 45 703 All rights reserved. 46 47 48 704 Fig. 7. Hypothetical models for ice flow within the North Sea Basin to account for the development of 49 50 705 the southward-flowing North Sea lobe. (A) Southwards deflection of the North Sea lobe (NSL) by 51 706 Baltic ice (BI) and the overspill of the Norwegian Channel Ice Stream (NCIS) (cf. Fish and 52 53 707 Whiteman, 2001); (B) Piedmont-style lobe of British ice without necessary interaction with 54 55 708 Fennoscandian ice (cf. Boulton et al., 1977, 2001; Lee et al., 2002); (C) Southern flow path of North 56 709 Sea lobe driven by the development of an ice dome in the North Sea Basin (cf. Clark et al., 2012); (D) 57 58 710 Southern flow path of North Sea lobe driven by elevated or free-draining sticking-points within the 59 60 711 subglacial bed (this study). 61 62 63 64 65 712 Table 1. Lithostratigraphical association of the 8-16 mm and >16 mm erratic clast assemblages 1 713 extracted from the Skipsea Till. 2 3 4 714 Table 2. The distribution of palynomorphs in the two samples studied in eight age-related groups. The 5 6 715 numbers indicate the absolute numbers of palynomorphs in the grain count. An “X” indicates that the 7 716 respective palynomorph is present, but was not encountered in the count. An ellipsis (...) indicates that 8 9 717 the respective palynomorph is not represented. Full author citations are included for the taxa at and 10 11 718 below species level. 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 Table

Age Lithology 8-16mm >16mm Total (n=661) (n=56) Allochthonous sedimentary n n % Total Pleistocene 68 5 10.32 Quartzite 32 2 Weathered Flint 32 1 Greensand chert 4 1 Glauconitic sandstone 0 1 Total Cretaceous 198 22 30.68 Chalk, fresh flint 198 22 Total Jurassic 65 5 9.76 Grey/brown calcareous sandstone, grey-green micaceous limestone 27 3 Grey micaceous mudstone, black bituminous mudstone 15 0 Ferruginous sandstone, mudstone, ironstone 9 0 Shelly +/ oolitic limestone, shell material, Rhaxella chert 14 2 Total Permo-Triassic 85 7 12.83 Magnesian Limestone, crystalline dolostone, dolomitic sandstone 75 6 New Red Sandstone, wind-faceted sandstone (dreikanter) 3 0 Evaporitic sandstone/limestone, gypsum 7 1 Total Carboniferous 93 3 13.39 Quartzo-feldspathic, micaceous, calcareous organic-rich sandstone 55 1 Pink-red crystalline limestone 7 0 Dark grey-brown crystalline, crinoidal +/ shelly limestone 29 2 Coal, fossil material 2 0 Total Devonian 13 1 1.95 Old Red Sandstone 13 1 Total Lower Palaeozoic 16 0 2.23 Greywacke 10 0 Dark green chert 6 0 Total unknown provenance 36 3 5.30 Quartzo-feldspathic, polylithic, micaceous sandstone 35 3 Green mudstone 3 0 Allochthonous crystalline Total Permian 0 2 0.28 Microgranite 0 1 Rhomb porphyry 0 1 Total Carboniferous 24 6 4.18 Mafic quartz +/ olivine porphyry, basalt 11 2 Dolerite (+/ Tertiary?) 12 3 Trachyte 1 1 Total Devonian 60 2 8.65 Rhyolite porphyry, andesite porphyry, andesite, felsite 31 0 Granite, microgranite, granodiorite 24 1 Volcaniclastic sediment, red jasper 2 0 Quartzose schist, metapsammite 3 1 Total unknown provenance 3 0 0.42 Fine grained intermediate igneous with feldspathic phenocrysts 1 0 Ferruginous mafic-intermediate igneous 1 0 Grey-blue intermediate igneous with red crystals 1 0

Table

Palynomorphs Sample 1 Sample 2 (n) (n) Carboniferous pollen and spores Carboniferous spores - indeterminate 23 11 Cirratriradites saturni (Ibrahim 1932) Schopf et al. 1944 X X Densosporites spp. 45 26 Endosporites globiformis (Ibrahim 1932) Schopf et al. 1944 1 … Florinites spp. … 1 Lycospora pusilla (Ibrahim 1932) Schopf et al. 1944 104 82 Radiizonates sp. 1 X Reticulatisporites spp. 2 ?X Simozonotriletes intortus (Waltz 1938) Potonie & Kremp 1954 … X Tripartites vetustus Schemel 1950 X X Total Carboniferous palynomorphs 176 120 Jurassic pollen spores Callialasporites spp. 15 3 Cerebropollenites macroverrucosus (Thiergart 1949) Schulz 1967 … X Chasmatosporites spp. 1 1 Classopollis classoides (Pflug 1953) Pocock & Jansonius 1961 10 15 Classopollis meyeriana Klaus 1960 2 1 Dictyophyllidites sp. 1 9 Ischyosporites variegatus (Couper 1958) Schulz 1967 … X Perinopollenites elatoides Couper 1958 4 X Jurassic marine microplankton Gonyaulacysta jurassica (Deflandre 1939) Norris & Sarjeant 1965 X … subsp. adecta Sarjeant 1982 Halosphaeropsis liassica Mädler 1963 2 3 Hystrichosphaera orbifera (Klement 1960) Stover & Evitt 1978 X … Liasidium variabile Drugg 1978 1 1 Nannoceratopsis deflandrei Evitt 1961 subsp. senex (van Helden X 1 1977) Ilyina in Ilyina et al. 1994 Nannoceratopsis gracilis Alberti 1961 X … Oligosphaeridium patulum Riding & Thomas 1988 … 1 Pareodinia sp. 1 1 Perisseiasphaeridium pannosum Davey & Williams 1966 … X Systematophora sp. … X Total Jurassic palynomorphs 37 36 Cretaceous spore Cicatricosisporites sp. X X Cretaceous dinoflagellate cysts ?Isabelidinium sp. X 1 Cribroperidinium spp. 1 5 Hystrichodinium voigtii (Alberti 1961) Davey 1974 … X Hystrichodinium spp. X … Odontochitina operculata (Wetzel 1933) Deflandre & Cookson 1955 X … Oligosphaeridium complex (White 1842) Davey & Williams 1966 … X ?Phoberocysta sp. X … Wallodinium cylindricum (Habib 1970) Duxbury 1983 … X Total Cretaceous palynomorphs 1 6 Quaternary pollen Pinus 7 6 Quaternary pollen - indeterminate 2 X Tilia … X Quaternary dinoflagellate cysts Achomosphaera andalousiensis Jan du Chêne 1977 1 … Operculodinium centrocarpum (Deflandre & Cookson 1955) Wall … ?1 1967 Quaternary dinoflagellate cysts - indeterminate 2 6 Spiniferites spp. 11 2 Total Quaternary palynomorphs 23 15 Non-age diagnostic palynomorphs Botryococcus braunii Kützing 1849 0 1 chorate dinoflagellate cysts - indeterminate 0 1 dinoflagellate cysts - indeterminate 11 2 Micrhystridium spp. 12 3 Pediastrum spp. 1 1 prasinophytes 31 0 pre-Quaternary bisaccate pollen 2 0 smooth trilete spores 3 1 Total non-age diagnostic palynomorphs 62 95 Total 299 272

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