Glacial Erosion of East Antarctica in the Pliocene

1 Glacial erosion of East Antarctica in the Pliocene:

2 a comparative study of multiple marine sediment provenance tracers

3 Carys P. Cooka,b, Sidney R. Hemmingc,d, Tina van de Flierdtb*, Elizabeth L. Pierce Davisc,

4 Trevor Williamsd,1, Alberto Lopez Galindof, Francisco J. Jimenez-Espejof,2, Carlota Escutiaf

5 a Grantham Institute for Climate Change and the Environment, Imperial College London, South 6 Kensington Campus, London, SW7 2AZ, UK

7 b Department of Earth Science and Engineering, Imperial College London, South Kensington 8 Campus, London, SW7 2AZ, UK

9 c Department of Earth and Environmental Sciences, Columbia University, Lamont-Doherty Earth 10 Observatory, Palisades, New York, 10964, USA

11 d Lamont-Doherty Earth Observatory, Palisades, New York, 10964, USA

12 f Instituto Andaluz de Ciencias de la Tierra, CSIC-UGR, 18100 Armilla, Spain

13 1 present address: International Ocean Discovery Program, Texas A&M University, College Station, 14 TX 77845, USA

15 2 present address: Department of Biogeochemistry, Japan Agency for Marine-Earth Science and 16 Technology, Yokosuka, 237-0061, Japan

17 * Corresponding author: [email protected]

18 Abstract

19 The history of the East Antarctic Ice Sheet provides important understanding of its 20 potential future behaviour in a warming world. The provenance of glaciomarine sediments 21 can provide insights into this history, if the underlying continent eroded by the ice sheet is 22 made of distinct geological terranes that can be distinguished by the mineralogy, petrology 23 and/or geochemistry of the eroded sediment. We here present a multi-proxy provenance 24 investigation on Pliocene sediments from Integrated Ocean Drilling Program (IODP) Site 25 U1361, located offshore of the Wilkes Subglacial Basin, East Antarctica. We compare Nd 26 and Sr isotopic compositions of <63 µm detrital fractions, clay mineralogy of <2 µm 27 fractions, 40Ar/39Ar ages of >150µm ice-rafted hornblende grains, and petrography of >2mm 28 ice-rafted clasts and >150 µm mineral grains. Pliocene fine-grained marine sediments have 29 Nd and Sr isotopic compositions, clay mineralogy, and clast characteristics that can be 30 explained by mixing of sediments eroded from predominantly proximal crystalline terranes 31 with material derived from inland sources from within the currently glaciated Wilkes 32 Subglacial Basin. Conversely, evidence for such an inland source is absent from ice-rafted 33 hornblende ages. We render a lithological bias against hornblende grains in the doleritic and 34 sedimentary units within the basin the most likely explanation for this observation. 40Ar/39Ar 35 hornblende ages however record additional provenance from the distal margins of the Ross 36 Sea, and possibly even the West Antarctic area of Marie Byrd Land. The latter lies >2000km 37 to the east and hints at significant iceberg release from the West Antarctic ice sheet during 38 warm intervals of the Pliocene. Together our results make a strong case for combining 39 geochemical and mineralogical signatures of coarse- and fine-grained glaciomarine sediment 40 fractions in order to derive robust provenance interpretations in ice covered areas.

41 Keywords 42 East Antarctic ice sheet; provenance; marine sediment; Pliocene warmth; radiogenic isotopes; 43 thermochronology

44 1. Introduction

45 The ‘provenance’ of a detrital marine sediment assemblage describes its components’ 46 derivation from erosion of their continental source rocks to their subsequent burial at the 47 ocean floor. Studying marine sediment provenance patterns has been recognised as a valuable 48 approach in paleoclimate studies as they can provide information on a wide range of 49 environmental processes, such as atmospheric and ocean circulation patterns, weathering 50 style, changes in riverine discharge, ice sheet histories, and tectonics and crustal evolution on 51 longer time scales (e.g., Goldstein and Hemming, 2003; Grousset and Biscaye, 2005; 52 McLennan and Taylor, 1991). 53 In the Southern Ocean, a number of studies have made compositional links between 54 Holocene glaciomarine sediments surrounding the Antarctic continent, and distinct 55 continental margin bedrock sources as constrained by sparse outcrops (Brachfeld et al., 2008; 56 Cook et al., 2014, 2013; Farmer et al., 2006; Flowerdew et al., 2013, 2012; Hemming et al., 57 2007; Licht and Palmer, 2013; Licht et al., 2014, 2005; Pierce et al., 2014, 2011; Roy et al., 58 2007; van de Flierdt et al., 2007; see also Farmer et al. (2016), Palmer et al. (2012), and 59 Welke et al. (2016) for work on nunatak moraines, and review by Licht and Hemming 60 (2017)). Extensive surveying work of this type can be coupled with results of airborne 61 geophysical surveys (e.g. Aitken et al., 2014; Ferraccioli et al., 2009; Studinger et al., 2004) 62 and tectonic reconstructions of conjugate margins (e.g. Aitken et al., 2014; Collins and 63 Pisarvsky, 2005; Fitzsimons, 2000a,b, 2003; Harley et al., 2013; Li et al., 2008;) to extend 64 inferred sub-ice geology inland of the continental margin. This information in turn permits 65 for reconstructions of buried landscapes (Cox et al., 2010; van de Flierdt et al., 2008), 66 variations in glacial erosional patterns (Thomson et al., 2013; Tochilin et al., 2012), and the 67 locations of dynamic ice sheet behaviour in the past (e.g. Cook et al., 2014, 2013; Williams et 68 al., 2010). 69 However, a factor in sediment provenance studies that needs careful consideration is 70 the selection of appropriate tools, particularly when studying a glaciated continent where a 71 priori knowledge of the geological characteristics of hidden bedrock sources is limited. 72 Additionally, multiple physical processes can act to modify a source rock signature in derived 73 sediments. To obtain a more holistic view of sediment sources and their implications for ice 74 sheet dynamics, we use multiple provenance approaches on sediments drilled at Integrated 75 Ocean Drilling Program (IODP) Site U1361 (64°24’S, 143°53’E), located off the glaciated

76 Adélie Land coast, East Antarctica (Figure 1), and compare and contrast their strength and 77 weaknesses.

78 1.1 Controls on glaciomarine sediment provenance

79 The complexities of studying sediment provenance patterns offshore of a glaciated 80 continent are illustrated in Figure 2. For example, mineralogical compositions, petrogenetic 81 histories and grain-size characteristics of different bedrock types, along with erosional 82 patterns, play an important role in determining which detrital provenance tool may be best 83 suited to identify a specific on-land source terrane within a marine sediment assemblage (e.g., 84 Taylor and McLennan, 1985). In addition, some mineral grains are more resistant to 85 weathering than others (e.g. zircons [more resistant] vs. hornblendes [less resistant]l; 86 Kowalewski and Rimstidt, 2003), resulting in their preferential survival through numerous 87 tectonic recycling events (e.g. Goodge and Fanning, 2010). Sedimentary substrates are more 88 likely to be physically eroded than crystalline bedrock, and indeed ice streams often overlie 89 subglacial basins infilled with unconsolidated sediments (e.g. Studinger et al., 2001) 90 suggesting their detrital outputs should contain a large component of recycled sedimentary 91 material. Rock texture also plays an important role, as finer-grained rock types such as shale 92 are likely to be under-represented in coarse-grained fractions of marine sediments. On the 93 other hand, mineral grains from coarse-grained source rocks such as plutonic rocks and high- 94 grade metamorphic rocks will be represented in coarser fractions, but can also be found in 95 glacial flour as a result of comminution. Additionally, subglacial erosional processes by 96 meltwater and ice can integrate a diverse range of bedrock types over a large area. An 97 excellent review on glacigenic sediment provenance has recently been provided by Licht and 98 Hemming (2017). 99 Furthermore, different marine transport and depositional processes have the potential 100 to integrate marine sediments supplied from multiple sources, and alter the distribution of 101 different size fractions in the marine environment. For example, finer-grained detrital 102 material can be delivered to the deep ocean by turbidites, meltwater plumes and contourites, 103 surface and deep ocean currents, wind, iceberg and sea-ice rafting. In contrast, beyond 104 turbidite aprons, sand-sized and larger detrital material can only be delivered to the deep 105 ocean floor by ice-rafting (both icebergs and sea-ice) and volcanic eruptions. Therefore, 106 studying one component of a particular glaciomarine sediment size-fraction may not fully 107 capture the representative provenance signature of that sediment’s original source on land.

108 Likewise fine grained sediment may reflect multiple delivery mechanisms and thus a 109 different aspect of the sedimentary provenance in addition to glacial processes.

110 We here present and discuss observations and interpretations of an apparent 111 inconsistency in the sediment sources at Site U1361. We present new data on a diverse range 112 of tools from multiple sediment components, in order to better identify the roles played by 113 source rock characteristics and depositional processes on controlling their delivery from 114 source to sink. In detail, we used five different and widely used provenance approaches: (i), 115 fine-grained (<63µm) detrital radiogenic Sr isotopes (87Sr/86Sr), (ii) fine-grained (<63µm)

116 detrital Nd isotopes (expressed as ƐNd, which describes the deviation of a measured 117 143Nd/144Nd ratio from the Chondritic Uniform Reservoir in parts per 10,000; Jacobsen and 118 Wasserburg (1980); (iii), fine-grained (<2µm) clay mineralogy; (iv) sand-sized (>150µm, ice- 119 rafted) hornblende grain 40Ar/39Ar ages, and (v) petrographic characterisation of ice-rafted 120 mineral grains (>150µm) and clasts (>2mm). Our results allow a refined interpretation of the 121 glacial history of an important sector of the East Antarctic ice sheet.

122 1.2 Provenance tools

123 The long-lived radioactive decay systems of rubidium-strontium (Rb-Sr) and 124 samarium-neodymium (Sm-Nd) are widely used and very useful tracers of fine-grained 125 marine sediment provenance signatures (e.g. Bareille et al., 1994; Basak and Martin, 2013; 126 Colville et al., 2011; Cook et al,. 2013; Dasch, 1969; Farmer et al., 2006; Jantschik and 127 Grousset et al., 1998, 1988; Hemming et al., 2007, 1998; Huon, 1992; Revel et al., 1996; Roy 128 et al., 2007; van de Flierdt et al., 2007). They are present in all rock types and can therefore 129 be used to trace supply from continental source areas (Taylor and McLennan, 1995). The 130 parent-daughter pairs Rb-Sr and Sm-Nd are fractionated during melting of mantle material, 131 creating continental crust reservoirs with high Rb/Sr ratios and low Sm/Nd ratios. Hence, 132 bedrocks of different ages and lithologies can have characteristic Nd and Sr isotopic 133 compositions. This approach has been used very successfully in glaciomarine sediments to 134 reveal the provenance of fine-grained and bulk components, as it provides an integrated 135 signal of all bedrock sources eroded within a glaciated catchment area (e.g. Farmer et al., 136 2006; Colville et al., 2011; Cook et al., 2013; Hemming et al., 2007; Roy et al., 2007; Taylor 137 and McLennan, 1995). Changes in the depositional output of a glaciated terrane as recorded 138 by changing Nd and Sr isotopic signatures of glaciomarine sediments has been used to

139 indicate periods of major ice sheet change in both Antarctica (e.g. Cook et al., 2013), and on 140 continents surrounding the North Atlantic (e.g. Colville et al. 2011; Hemming et al., 1998). 141 Clay minerals have traditionally been the most commonly used fine-grained marine 142 sediment provenance tool in the Southern Ocean (e.g. Diekmann and Kuhn, 1999; Ehrmann 143 and Mackensen, 1992; Ehrmann et al., 1992, 1991; Hillenbrand et al., 2009; Petschick et al., 144 1996), and are a product of both the continental bedrock sources of detrital material, and the 145 intensity of chemical weathering of those sources (Biscaye, 1965; Robert and Kennett, 1994). 146 A significant change from smectite to illite dominated marine sediment facies around 147 Antarctica marks glacial initiation in Antarctica (Ehrmann and Mackensen, 1992; Robert and 148 Kennett, 1994) caused by a large-scale change to pronounced physical weathering on the 149 Antarctic continent. 150 Although all grain sizes are represented in glaciomarine sediments, the only process 151 that can deliver coarse-grained material to the deep ocean beyond turbidite aprons and 152 volcanic eruptions is rafting. Finer-grained material is likely to comprise a considerable 153 proportion of an iceberg’s sediment load (e.g. Ruddiman, 1977) but these size fractions can 154 be transported by a variety of processes. Therefore, coarse-sized lithic material and mineral 155 grains are best used to estimate sedimentation from ice-rafting in distal locations. Mineral 156 thermochronometers applied to sand-sized grains (e.g. U-Pb ages of zircon, garnet, rutile, 157 monazite and sphere grains, 40Ar/39Ar ages of mica, feldspar, and amphibole grains) record 158 information that can be used to infer the magmatic and tectonothermal history of their 159 original host rocks (e.g. Hodges et al., 2005; Reiners and Brandon, 2006). The temperature at 160 which a system such as a mineral grain becomes closed to diffusive processes is its ‘closure’, 161 or ‘blocking’ temperature. 40Ar/39Ar ages in hornblende grains reflect crystallisation and/or 162 closure temperature of ~500°C (McDougall and Harrison, 1999), thus 40Ar/39Ar hornblende 163 grain ages record the timing of the last major tectonothermal event experienced by their host 164 rock for fingerprinting ice-rafted material sourced from continental terranes with complex 165 tectono-metamorphic histories (e.g. Cook et al., 2014; Gwiazda et al., 1996; Hemming et al., 166 2000, 1998; Knutz et al., 2013; Peck et al., 2007; Pierce et al., 2014, 2011; Roy et al., 2007; 167 Williams et al., 2010). While detrital zircons are a commonly used circum-Antarctic sediment 168 provenance tool (e.g. Fitzsimmons, 2000; Goodge and Fanning; 2010; Pierce et al., 2014; 169 Veevers and Saeed, 2011), hornblendes were selected for this study. In addition, petrographic 170 and lithological characterisation of ice-rafted mineral grains and lithic grains can provide 171 information on source rocks and provenance of coarse-grained fractions (Anderson et al.,

172 1992; Andrews et al. 1995; Bond et al. 1992; Elverhoi et al. 1995; Licht et al. 2005; Talarico 173 et al. 2012; Thierens et al. 2012).

174 2. Study site and provenance background

175 IODP Site U1361 was drilled in 3466m water depth, approximately 315km offshore 176 of Adélie Land, East Antarctica, during Expedition 318 (Escutia et al., 2011). Approximately 177 388m of sediment were recovered in total, and a chronology was compiled using 178 palaeomagnetic inclination data and biostratigraphy (diatom and radiolarian datums) (Escutia 179 et al., 2011; Tauxe et al., 2012) (Figure 3). Published onshore constraints (Figure 1; Table S1) 180 and existing marine sediment provenance studies in the area (Cook et al., 2013; Domack et 181 al., 1982; Goodge and Fanning, 2010; Hemming et al., 2007; Pant et al. 2013; Pierce et al., 182 2014, 2011; Orejola and Passchier, 2014; Roy et al., 2007) demonstrate that the East 183 Antarctic continent nearby to Site U1361 is geologically heterogeneous and contains 184 sedimentary, metamorphic and extrusive and intrusive igneous rocks with ages spanning 185 much of the last 3 billion years. Hence Site U1361 can receive sediments supplied from a 186 diverse range of rocks with a range of ages and lithologies. 187 Here we focus on a well-defined Pliocene section (Escutia et al., 2011; Cook et al., 188 2013) between 45 and 125 mbsf (Figure 3). Within this interval, five lithostratographic facies 189 are identified: Facies 1 (clays), facies 2 (clays with dispersed clasts) and facies 3 (silty clays 190 with dispersed clasts) are dominated by terrigenous material and represent colder times 191 during the Pliocene. Facies 4 (diatom-bearing silty clays) and facies 5 (diatom-rich silty 192 clays) on the other hand contain more significant biogenic opal components and were 193 deposited during warmer intervals. Cook et al. (2013) investigated the provenance of fine- 194 grained (<63µm) detrital sediments from Site U1361 between 75 and 125 mbsf using Nd and 195 Sr isotopes and clay minerals, and found that diatom-poor sediments are characterised by 87 86 196 distinct provenance signatures (ƐNd: -11.1 to -14.5; Sr/ Sr: 0.719 to 0.738; illite-rich) 87 86 197 compared to diatom-rich sediments (ƐNd: -5.9 to -9.5; Sr/ Sr: 0.712 to 0.719; smectite-rich). 198 Here we supplement these existing data by extending the Nd and Sr isotope and clay 199 mineral record up section to 47.25 mbsf (i.e. Late Pliocene). To further investigate the 200 provenance data presented by Cook et al. (2013), we present new ice-rafted mineral grain and 201 clast information, and the first ice-rafted hornblende grain 40Ar/39Ar age data for this site.

202 3. Samples and Methods

203 3.1 Petrographic characterisation and IRD counts of coarse-grained sediment fractions

204 The coarse-grained fractions (>150µm) of 19 samples from Site U1361 were 205 examined to characterise mineral grains, to count IRD grains coarser than 2mm (dropstones) 206 and to identify their lithologies (Table 1). Samples for characterisation were analysed from 207 facies 1 (n=1), facies 2 (n=3), facies 4 (n=2) and facies 5 (n=12). Petrographic 208 characterisation of >150μm sediment fractions was based on counts of 100 to 400 randomly 209 distributed mineral grains in a picking tray and the relative abundances of different mineral 210 types were assumed to be representative of the entire sample. In addition, all grains coarser 211 than 2 mm were counted from the entire sample, and all observed clast lithologies were 212 reported in order to constrain potential correlations between the amount of ice-rafted debris 213 (IRD) present in each sample and its provenance (Table 1; Figure 4).

214 3.2 40Ar/39Ar dating of ice-rafted hornblende grains

215 A total of 13 Pliocene samples (2cm intervals, 20 cm3) from Site U1361, between 216 57.70 and 115.47 msbf, were selected for 40Ar/39Ar dating of ice-rafted hornblende grains, 217 and one Holocene sample (1H 1W 1-5cm, 0.01 mbsf) (Figure 3, Tables 2 and S2) . Sample 218 selection was based on the visual count of clasts >2mm on board the JOIDES Resolution 219 (Escutia et al., 2011; see Figure 3 for sample locations in stratigraphic content) to represent 220 peaks in coarse-grained material in different facies. Selection yielded samples from 221 sedimentary facies 2 (clay with dispersed clasts; n=3), facies 4 (diatom-bearing silty clays; 222 n=2), and facies 5 (diatom-rich silty clays; n=9) (Table 2). 223 192 hornblende grains were hand-picked from the >150 mm fraction and analysed for 224 their 40Ar/39Ar ages at the AGES laboratory at Lamont-Doherty Earth Observatory of 225 Columbia University (Figure 5, see Table 2 for analytical information, and Table S2 for 226 data). In most samples hornblende grains were very scarce. In order to improve grain counts 227 and statistical confidence, the volume of bulk sample material processed was increased to 228 60cm3 for nine samples. Larger sample volumes however produced only limited success in 229 increasing hornblende grain yield. 230 During picking for hornblende grains, it was noted that the >150µm sediment fraction 231 of one Pliocene sample (U1361 10H 6W 35-37cm, 92.95 mbsf) was composed of ~56% 232 brown visually unaltered volcanic glass shards , containing occasional phenocrysts of biotite 233 and hornblende. Eight fresh volcanic glass grains were selected from this sample and 234 analysed for 40Ar/39Ar using either one-step or two-step laser fusion analysis (Figure 6) in

235 order to determine the absolute age of volcanic events and infer provenance (i.e. discriminate 236 between wind-blown ash and eroded bedrock). 237 To supplement existing provenance constraints on IODP Site U1361 sediments and 238 core-top surveys in the area (Roy et al., 2007; Pierce et al., 2011, 2014), we furthermore 239 analysed hornblende grains from core-top sediments from three additional sites located 240 proximally to the continent for their 40Ar/39Ar age populations: Deep Sea Drilling Program 241 Site 274 (68°59’S, 173°25’E, 1R 5W 110-111cm; 12 grains), IODP Site U1358 (66°05’S, 242 143°18’E; 1R 1W 18-22cm, 25 grains) and IODP Site U1360 (66°22’S, 142°44’E, 1R 1W 0- 243 18cm, 21 grains) (see Figure 1 for locations; Figure 5, Tables 2 and S2 for data). Core-top 244 sediments for the latter two sites have been dated to be Pliocene and Upper Pleistocene in 245 age, respectively (Escutia et al., 2011).

246 3.3 Clay mineralogy

247 Clay mineral compositions were determined on the <2µm detrital fractions of 248 Pliocene sediments from IODP Site U1361, and were measured on 193 discrete samples 249 between 47.46 and 75.00 mbsf. Samples were taken from all identified Pliocene sedimentary 250 facies (Figures 7 and 8, Table S3) and supplement existing data between 75.00 and 124.97 251 mbsf (Cook et al., 2013). Sample preparation and analysis was performed at the Instituto 252 Andaluz de Ciencias de la Tierra (IACT, Spain), following the same procedures as described 253 by Cook et al. (2013).

254 3.4 Neodymium and Sr isotope compositions of fine-grained fractions

255 Eleven Pliocene sediment samples were selected from IODP Site U1361 between 256 47.25 and 73.79 mbsf for analysis of their Nd and Sr isotopic compositions on the <63µm 257 detrital fractions. Samples were selected to represent a range of sedimentary facies 1 (n=4), 258 facies 2 (n=1), facies 4 (n=3) and facies 5 (n=3) (Table 3) and supplement previously 259 published early Pliocene data (Cook et al., 2013; Figures 3 and 9; Table 3). Nine of the 260 eleven samples, are identical to the ones utilised for >150m hornblende 40Ar/39Ar analysis 261 and had biogenic carbonate and authigenic ferromanganese phases removed following the 262 procedure outlined in Cook et al. (2013). Two samples were taken from a smaller 1cm 263 interval, and were analysed for bulk (not sieved) Nd and Sr isotopes only (7H 5W 54-55cm, 264 63.04 mbsf; 8H 3W 37-38cm, 69.38 mbsf) (Table 3) in order to test for potential grain size 265 effects. Sediments were acid digested on hotplates and target analytes were separated by

266 column chemistry, following the same procedures described by Cook et al. (2013). 267 Neodymium and Sr isotopes were analysed by MC-ICP-MS and TIMS, respectively, in the 268 MAGIC laboratories at Imperial College London, and analytical details are provided in Cook 269 et al. (2013) and in Table 3 footnotes.

270 4. Results

271 4.1 Petrographic characterisation and IRD counts of coarse-grained sediment fractions

272 Pliocene mineral assemblages from coarse-grained sediment fractions (>150µm) from 273 IODP Site U1361 (Table 1) are dominated by quartz (76-98%), with abundant feldspars 274 (<19%), pyroxenes (clino- and ortho) (<6%), biotite, garnet, magnetite, and hornblende (all 275 <7%), and trace amounts of glauconite (<3%) (Figure 4). Fifty-seven lithic clasts >2mm were 276 found throughout the 19 samples. Lithic fragments are composed of siltstone, quartzose 277 sandstone, shale, schist, basalt, granite, and abundant volcanic glass. No changes in 278 abundance of different ice-rafted mineral grains or lithic clasts were observed between 279 different facies. Particular mineralogies and lithologies show no correlation to the amount of 280 IRD grains greater than 2mm in size per gram of sediment, although more data for facies 1 281 and 2 would be desirable.

282 4.2 40Ar/39Ar dating of ice-rafted hornblende grains

283 Hornblende is relatively scarce in these samples, with typical abundances <1% in the >150 284 µm fractions and grain yields between 1 and 25 for processing 20 to 60 cm3 of material 285 (Table 2 and Figure 3). 40Ar/39Ar ages from Pliocene and Holocene sediments at IODP Site 286 U1361 yield two distinct populations: ~2 to 44 Ma (~28%; 54 out of 192 grains analysed; 287 Figures 5 and 8, Tables 2 and S2), and 440-540 Ma (~48%; 93 out of 192 grains analysed; 288 Figure 5, Tables 2 and S2). Within the younger population, 42% of hornblende grains have 289 ages that match, within error, the depositional age of the sediment from which they were 290 extracted (~2 to 6 Ma) whereas 58% of hornblende grains are older (~6 to ~44 Ma) (Figure 291 6). A minor bimodal age population distribution can be identified within the 440 to 550 Ma 292 population: one between 440 and 500 Ma (63 grains in total), and the other between 500 and 293 540 Ma (30 grains in total) (Figure 5). Remaining hornblende grains are found in minor 294 numbers and are distributed over three broad 40Ar/39Ar age ranges (Figure 5, Table 2): 90-290 295 Ma (~11%; 22 of 192 grains); 330-430 Ma (~6%; 11 grains of 192) and >600 Ma (~6%; 11

296 of 192 grains). More than half of the grains with an 40Ar/39Ar age range between 90 and 290 297 Ma fall between ~90 and ~130 Ma (n = 13; Figure 5, Table S2), while the remaining ages are 298 distributed with no clear sub-grouping. The oldest 40Ar/39Ar aged grains (>600 Ma) represent 299 a wide range of ages between ~641 ± 8.7 Ma and 2339 ± 26 Ma, with more than half of these 300 falling within an age range of ~1000 to 1320 Ma (Figure 5). 301 The number of ice-rafted grains >2mm per gram of sediment reveals no obvious 302 correlation with hornblende 40Ar/39Ar ages (Table 2). Furthermore, comparison of the 303 different hornblende 40Ar/39Ar age ranges identified in individual samples from different 304 facies (Table 2) indicates only limited change in hornblende provenance with changing 305 depositional conditions. A potentially significant exception to this observation is that 18 of 306 the 22 grains with a 40Ar/39Ar age between 90 and 290 Ma occur in samples from diatom- 307 bearing facies 4 and 5 (Table 2), although more samples from facies 1 and 2 would be 308 desirable to confirm this observation. 309 Eight distinct volcanic glass grains were analysed for 40Ar/39Ar ages from IODP Site 310 U1361, sample 10H 6W 35-37cm, in a two-step (n=7) or one-step (n=1) heating procedure. 311 Only one of seven grains produced results for both heating steps (6.0 ± 1.1 Ma and 5.1 ± 2.8 312 Ma), with all others samples yielding sufficient gas to calculate ages only for the second step 313 (2.1± 2.2 Ma, 3.7 ± 2.3 Ma, 4.8 ± 0.6 Ma, 4.9 ± 2.6 Ma, 5.4 ± 2.8 Ma, 7.5 ± 0.8 Ma) (Figure 314 6b). The single-step heated grain gave an age of 5.3 ± 2.8 Ma. Apart from the two glass 315 grains with the oldest ages (6.0 ± 1.1 Ma and 7.5 ± 0.8 Ma), all ages are contemporaneous 316 within error with the estimated depositional age of the sample from which they were 317 extracted (~4 Ma). 318 Hornblende 40Ar/39Ar ages in the Holocene sediment sample from DSDP Site 274 (n 319 =12) (Figure 1b for location, Figure 5; Tables 2 and S2 for data) predominantly fall between 320 476 and 524 Ma (9 grains in total), with additional grains aged at 378 ± 5 Ma, 619 ± 36 Ma, 321 and 1550 ± 9 Ma. Hornblende grains analysed from the Holocene marine sediment sample 322 from Site U1358 yield 40Ar/39Ar ages mainly between ~1420 and 1860 Ma (24 of 25 grains 323 analysed), with one grain producing an age of 2250 ± 28 Ma (Figure 1b for location, Figure 5 324 and Tables 2 and S2 for data). Similarly, core-top sediments sampled from Site U1360 have 325 hornblende 40Ar/39Ar ages that range from 1509 to 1736 Ma (17 of 21 grains analysed), with 326 remaining grains producing ages of 1988 ± 17 Ma, 2060 ± 9 Ma, 2514 ± 33 Ma, and 3944 ± 327 26 Ma (Figure 1b for location, Figure 5 and Tables 2 and S2 for data).

328 4.3 Clay mineralogy

329 Clay minerals in Pliocene sediments from IODP Site U1361 (Figures 7 and 8, Table 330 S3) are dominated by illite (52-68%), smectite (11-33%), with lesser amounts chlorite (5- 331 19%) and kaolinite (7-16%, except for four samples with 29-33% kaolinite). Illite and 332 smectite show a strong negative correlation (r2 = 0.8), which is significant despite relatively 333 large analytical uncertainties (10-15%). In general, sediments from facies 4 and 5 tend to 334 contain slightly higher amounts of smectite and chlorite, while sediments from facies 1,2 and 335 3 show a tendency for higher illite contents. Smectite/illite ratios share a weak positive 336 correlation with Nd isotopic compositions (r2 = 0.6; Figure 8).

337 4.4 Neodymium and Sr isotope compositions of fine-grained fractions

338 Neodymium and Sr isotope compositions of the <63µm fractions of Pliocene detrital 87 86 339 sediments from Site U1361 display a large range of values (ƐNd: -6.9 to -13.2; Sr/ Sr: 0.717 340 to 0.731) (Figures 3 and 9, Table 3). Comparison of the Nd and Sr isotope results between the 341 different facies reveals two distinct groups (Figures 3, 9 and 10; Table 3). Samples analysed

342 from clay-dominated facies 1 and 2 are characterised by ƐNd values between -11.2 and -13.2 343 and 87Sr/86Sr ratios between 0.723 and 0.731, whereas samples analysed from diatom- 87 86 344 rich/bearing facies 4 and 5 have ƐNd values between -6.9 and -9.2 and Sr/ Sr ratios between 345 0.717 and 0.728.

346 5. Discussion

347 In the following discussion we will first evaluate the provenance signatures of coarse and 348 fine-grained Pliocene sediments from IODP Site U1361 separately, to then compare and 349 contrast derived interpretations. We will show that robust provenance analysis of 350 glaciomarine sediments is best achieved by combining various methodologies and grain- 351 sizes. In the particular case studied here, 40Ar/39Ar ages of hornblende grains (>150 m) 352 reveal erosion of regionally abundant Palaeozoic granites emplaced during the Ross Orogeny 353 (~440 to 540 Myrs; Figures 1b and 5) as well as ages associated with more distal occurrences 354 of McMurdo volcanics (<44 Myrs; Figures 1b and 5). The data furthermore hint at a far- 355 travelled provenance component from West Antarctica during warm Pliocene intervals (90 - 356 125 Myrs; Figures 1b and 5). Warm intervals are furthermore characterised by quartz-rich 357 mineralogies of the coarse fraction (Table 1) and a radiogenic detrital Nd isotope signature of

358 fine-grained sediments (Nd = -6.9 to -9.9), corroborating previous suggestions that Pliocene 359 ice retreat led to erosion of Ferrar Large Igneous Provenance (FLIP) and Beacon Supergroup

360 lithologies of Jurassic to Devonian ages, hidden today underneath the East Antarctic ice sheet 361 (cf. Cook et al., 2013).

362 5.1 Coarse-grained sediment provenance

363 Hornblende grains extracted from the >150 m sediment fraction of marine sediments 364 away from continental shelf areas are typically ice-rafted in origin. However, in locations 365 proximal to continents turbidity currents may play a role as well. In order to assess coarse- 366 grained sediment provenance offshore the Wilkes Subglacial basin during the Pliocene we 367 first evaluate our new 40Ar/39Ar data on regional core top samples in the context of published 368 onland thermochronology (section 5.1.1; Figures 1b and 5). We selected three sites, covering 369 distal source areas from the Ross Sea (DSDP Site 274) and proximal source areas from the 370 Adélie Shelf (IODP Sites U1358 and U1360) (Figure 1a). We subsequently compare these 371 results with our new downcore record to identify major (section 5.1.2) and minor (section 372 5.1.3) provenance signatures observed. We finally elaborate on the exciting observation that a 373 small number of grains that were deposited during warm Pliocene intervals at IODP Site 374 1361 could have a West Antarctic origin (section 5.1.4). 375 376 5.1.1 Regional Holocene hornblende grain provenance: new results from DSDP Site 274, 377 IODP Site U1358 and IODP Site U1360

378 The majority of hornblende 40Ar/39Ar ages of Holocene sediments at DSDP Site 274 379 (Ross Sea) fall within a range of 475 to 525 Ma (Table 2; middle panel in Figure 5), which is 380 within the metamorphic age range of the high-grade Late Cambrian Ross Orogeny (460 to 381 560 Ma; Boger, 2011; Goodge, 2007 and references therein; Pierce et al., 2014, 2011; Stump, 382 1995) (Figure 1b). Despite the regional prevalence of this high-grade metamorphic signature 383 (Figure 1b; see Goodge, 2007 for review), on land thermochronology suggests that the timing 384 of peak metamorphism of terranes in Northern Victoria Land can be identified at slightly 385 younger U-Pb ages (460-500 Ma; Dallmeyer and Wright, 1992; Goodge and Dallmeyer, 386 1992; Klee et al., 1992; Schussler et al., 1999) than those of Southern Victoria Land (480-550 387 Ma; Goodge, 2007; Wysoczanski and Allibone, 2004) and the Central Transantarctic 388 Mountains (480-545 Ma; Goodge, 2007). According to our results, DSDP Site 274 likely 389 received IRD from proximal Northern Victoria Land source areas. 390 Ice-rafted hornblende 40Ar/39Ar ages in Holocene sediments at Adélie shelf sites 391 U1360 and U1358 yield rather different ages of >1420 Ma, clustering around 1600 to 1750

392 Ma (Table 2; middle panel in Figure 5). These ages agree well with onshore ages for the 393 tectonometamorphic overprint of the proximal Archean and Neoproterozoic Adélie Craton 394 (40Ar/39Ar argon ages ~1700 Ma (see Table S1 for references), and hornblende 40Ar/39Ar ages 395 in Holocene sediments in the vicinity of the sites (Roy et al., 2007; Pierce et al., 2014, 2011). 396 Such a provenance also allows for the occurrence of Archean aged grains, which are found in 397 small numbers at the Adélie shelf sites (Table 2).

398 5.1.2 Provenance of major age populations of ice-rafted hornblende grains in Pliocene-aged 399 Site U1361 sediments

400 Despite high IRD depositional rates (Figures 3; Escutia et al., 2011; Patterson et al., 401 2014) ice-rafted hornblende grain counts in Pliocene Site U1361 sediments are low (Table 2, 402 Figure 3), suggesting that hornblendes are generally low in abundance in the predominant 403 source terranes.

404 Late Cambrian Ross Orogeny and Palaeozoic granites (440-540 Myrs) 405 The most abundant hornblende grain 40Ar/39Ar age population in Pliocene Site U1361 406 sediments has a range of 440 to 540 Myrs (Figure 5 top panel, Table 2). Such ages were 407 likely sourced from the high-grade Late Cambrian Ross Orogeny (Goodge, 2007 and 408 references therein; Stump, 1995; see Figure 1b for geographical extent). In Site U1361 409 sediments this population is comprised of two peaks, one between 440 and 500 Ma, and a 410 secondary, smaller peak between 500 and 540 Ma (Figure 5). Northern Victoria Land (460- 411 550 Ma), Southern Victoria Land (480-550 Ma) and the Transantarctic Mountains (480-545 412 Ma) are potential sources for grains with such ages (see discussion above for DSDP Site 413 274). The most likely source areas is however located proximal to the drill site, where Early 414 Palaeozoic granites outcrop in the vicinity of the Ninnis Glacier (Goodge and Fanning, 2010; 415 Figure 1). This idea is supported by results from Holocene marine sediments, located directly 416 downstream of the Ninnis Glacier, which contain hornblende grains with 40Ar/39Ar ages 417 between 480 and 560 Ma (Pierce et al. 2014, 2011; Roy et al. 2007; Figure 1b). Indeed, the 418 location of Site U1361 on the continental rise suggests that coarser-grained sediments derived 419 from Early Palaeozoic terranes nearby could have been supplied to the site via downslope 420 processes such as turbidites Hence, the older sub-group within the Ross Orogeny population 421 is likely derived from ice-rafting and turbidites sourced from the proximal continental shelf 422 and the Ninnis Glacier, and/or from ice-rafting from Southern Victoria Land and the 423 Transantarctic Mountains, while the younger sub-group can be partially explained by

424 derivation from Northern Victoria Land. However, seven grains aged between 440 and 460 425 Ma do not fit documented ages from this region (Figure 1b). Furthermore, a small number of 426 grains have hornblende 40Ar/39Ar ages between 330 and 430 Ma. While it is possible that a 427 currently hidden terrane was the source for these grains, these ages, although minor in 428 number, can be matched well to the Bowers Terrane in Northern Victoria Land (e.g. Borg et 429 al., 1987; Rocchi, 2004; Weaver et al., 1984), which is characterised by whole-rock K-Ar 430 ages of between 320 and 450 Ma (Adams, 2006).

431 McMurdo Volcanics (<44 Myrs) 432 The youngest and second most abundant hornblende 40Ar/39Ar age population 433 identified in Site U1361 sediments shows ages <44 Ma, and is most likely derived from the 434 Cenozoic McMurdo Volcanic Group (Harrington, 1958; Kyle, 1990; Kyle and Cole, 1974; 435 LeMasurier and Thomson, 1990; Figures 5 and 6). The Hallet Volcanic Province, Mount 436 Melbourne Volcanic Province and Erebus Volcanic Province of the McMurdo Volcanic 437 Group (Figures 1 and 6) have well-documented eruptive histories spanning the last 26 million 438 years (see Table S1 for references). Balleny Islands (Figure 1) constitute the volcanic edifice 439 closest to Site U1361, and is believed to be no older than Miocene (Johnson et al., 1982). The 440 islands are however inaccessible and therefore poorly studied. The geochemical compositions 441 of basalts from outcrops on these islands and volcanic ash analysed from nearby marine 442 sediments (Huang et al., 1975; Kyle and Seward, 1984; Shane and Froggatt, 1992) suggest an 443 intermediate geochemical composition between that of the Hallet Volcanic Province and 444 Erebus Volcanic Province (Green, 1992; Johnson et al., 1982; Kyle and Cole, 1974), 445 implying similar tectonic relationships and likely similar ages for the initiation of their 446 formation. It is hence feasible that the Balleny Islands may be the source of some of the 447 volcanic ash and hornblendes younger than Miocene in age identified at Site U1361. Three 448 Eocene aged hornblende grains (35.9 ± 0.7 Ma, 36.6 ± 1.4 Ma, 44.2 ± 0.25 Ma) may be 449 sourced from even older McMurdo Volcanic Group deposits currently undocumented in the 450 Ross Sea. However, they could also have been supplied by icebergs sourced from Marie Byrd 451 Land in West Antarctica, over 2000 km to the east of our study site, where Eocene volcanism 452 has been dated to ~36 Ma, with the possibility of initial volcanism being even older (Wilch 453 and McIntosh, 2000). 454 58% of all hornblende grains from Pliocene sediments at Site U1361, which are 455 younger than 44 Ma, are older than the depositional age of the marine sediment itself (Figure 456 6). It is hence likely that these grains were entrained glacially in the vicinity of their volcanic

457 depositional centres before being transported to Site U1361 by icebergs. In contrast, most of 458 the volcanic glass grains analysed yield ages within error of the depositional age of the 459 sediment sample from which they were extracted (Figure 6), implying contemporaneous 460 eruptive events. Volcanic glass and phenocrysts from the McMurdo Volcanic Group have 461 been identified in layers within existing continental ice in Northern Victoria Land and the 462 Transantarctic Mountains (Narcisi et al., 2012; Perchiazzi et al., 1999; Smellie et al., 2011), 463 supplied by explosive volcanism from the Hallet Volcanic Province and Mount Melbourne 464 Volcanic Province. This observation suggests that some of the sediment load of regionally 465 calved icebergs sourced from the continental interior adjacent to Northern Victoria Land and 466 Southern Victoria Land may contain a volcanic glass component – this could explain the 467 unweathered fresh appearance of the volcanic ash grains in Site U1361 sediments. An 468 alternative source for volcanic glass could also be aeolian fallout from the Balleny Islands 469 and/or delivery by sea-ice rafting.

470 5.1.3 Provenance of minor age populations of ice-rafted hornblende grains in Pliocene 471 U1361 sediments

472 Four hornblende grains from Site U1361 sediments have 40Ar/39Ar ages that match the 473 proximal Adélie Craton, which has well-constrained Proterozoic metamorphic age 474 populations at ~1700 and ~2500 Ma (Di Vincenzo et al., 2007; Pierce et al., 2014; Roy et al., 475 2007) (Figures 1b and 5). The scarcity of such ages in our core, despite its proximity to the 476 Adélie Craton, indicates only limited supply of coarse grained material via downslope 477 processes and ice-rafting to Site U1361 during the Pliocene. 478 A small Mesoproterozoic hornblende grain 40Ar/39Ar age population between 1000 479 and 1300 Ma can be seen in Pliocene sediments at Site U1361. Similar to Holocene 480 sediments regionally (Pierce et al., 2011; Roy et al., 2007; this study; Figures 1b and 5) and 481 in Ross Sea sediments (Pierce et al., 2011; Roy et al., 2007), these ages occur in minor 482 numbers in Site U1361 sediments (6 grains in total). This age range has no known exposed 483 analogues in East and West Antarctica to the east of the Adélie Craton. It does, however, 484 match significant populations of Proterozoic hornblende 40Ar/39Ar ages in Holocene marine 485 sediments offshore of the Wilkes Land margin to the west of the Adélie Craton (Cook et al., 486 2014; Pierce et al., 2014, 2011; Roy et al., 2007) (Figure 1b), and thermochronological ages 487 of on land exposures in this region (Fitzsimons, 2003; Post, 2000; Post et al., 1997; Möller et 488 al., 2002; Sheraton et al., 1992). This tectonometamorphic age range is inferred to be related 489 to the Grenvillian Orogeny (Boger, 2011; Dalziel, 1991; Fitzsimons, 2000a, 2000b).

490 However, a supply of icebergs to Site U1361 from areas of the west of the Adélie Craton is 491 unlikely, as this would be opposite to the wind-driven iceberg trajectories around the 492 continent (Figure 1a), which was likely unaltered under Pliocene conditions (DeConto et al., 493 2007). The possibility of a Grenvillian-aged igneous body, or at least crustal material with 494 remnant Grenvillian signatures, located beneath the East Antarctic ice sheet to the west of the 495 Transantarctic Mountains, has however been proposed in accordance with the SWEAT 496 hypothesis (South-Western US and East Antarctica) (Goodge et al., 2010, 2008; Moores, 497 1991), as Grenvillian U-Pb zircon ages have been identified in glacial sediments in the Ross 498 Sea area (Goodge et al., 2010). It is therefore possible that Mesoproterozoic aged hornblende 499 grains in Site U1361 may be related to a continental interior source that is currently obscured 500 by the ice sheet. Icebergs sourced from the Ross Sea and/or the Wilkes Subglacial Basin may 501 therefore have been a source for these grains.

502 5.1.4 Evidence for increased West Antarctic IRD in Pliocene U1361 sediments during 503 Pliocene Warmth

504 A minor hornblende 40Ar/39Ar age population in Site U1361 Pliocene sediments is 505 constituted by Mesozoic ages of ~90 to ~125 Ma (n=13; Figure 5). It is an intriguing 506 observation that these grains primarily occur within diatom-bearing and diatom-rich 507 sedimentary facies 4 and 5, inferred to have been deposited during intervals of warmer-than- 508 present conditions (Cook et al., 2013). There are no known exposed rocks on the nearby East 509 Antarctic continent with hornblende 40Ar/39Ar ages that lie in this age range (Figure 1b). 510 While it is impossible to rule out a bedrock source hidden within the East Antarctic 511 continental interior, there is no suggestion in the literature that rocks of these ages could exist 512 regionally. 513 Instead, the observed 90 to 125 Ma ages match very well with mineral grain 514 thermochronology identified in Holocene marine sediments off the West Antarctic 515 continental margin (hornblende 40Ar/39Ar ages, 95 to 127 Ma; Roy et al., 2007), and 516 downstream of West Antarctic ice streams that flow into the Ross Sea (U-Pb zircon, 100-110 517 Ma; Licht et al., 2014), more than 2000 km to the east of Site U1361 (Figure 1b). On land, 518 this hornblende 40Ar/39Ar age population corresponds to the widespread occurrence of 519 Cretaceous igneous rocks in West Antarctica (Figure 1b), where calc-alkaline and 520 anorogenic granodiorites and granites were intruded between 95 and 125 Ma into 521 metasedimentary and granodioritic basement rocks (Luyendyk et al., 1996; Mukasa and 522 Dalziel, 2000; Pankhurst et al., 1998; Siddoway et al., 2005; Storey et al., 1999; Weaver et

523 al., 1994). Based on iceberg transport pathways in the westward flowing coastal current 524 (Figure 1a), and the excellent agreement with onshore and offshore West Antarctic 525 constraints, this age population is likely to have been sourced from this distant region. 526 Whether icebergs with these signatures were supplied from the Marie Byrd Land-Southern 527 Ocean margin, or from icebergs calved from West Antarctica directly into the southern Ross 528 Sea (Licht et al., 2014) is unknown, but their origin from West Antarctica seems a robust 529 finding. 530 Iceberg pathways are regionally constrained to follow an anti-clockwise, westward, 531 direction around the East Antarctic continent (Figure 1a). Large modern tabular icebergs 532 sourced from ice shelves have lifetimes of several years, as observed from satellites (e.g. 533 Tournadre et al., 2015). For paleo-reconstructions, it is important to consider that sea surface 534 temperatures of ocean waters near the Antarctic continent during the Pliocene were warmer

535 than today (Cook et al., 2014). Palaeothermometry indicators (TEX86: McKay et al., 2012) 536 suggest seasonal temperatures up to 6°C warmer than today during interglacials and 537 prolonged Pliocene warm intervals in the Ross Sea area (e.g., Naish et al., 2009). Similarly 538 warm temperatures have been identified in Pliocene sediments from other locations around 539 Antarctica (Bart and Iwai, 2012; Escutia et al., 2009; Whitehead and Bohaty, 2003; 540 Whitehead et al., 2005). Based on iceberg survivability modelling in the Southern Ocean, the 541 distance icebergs could travel before melting during warm Pliocene intervals was likely 542 significantly reduced (Cook et al., 2014), suggesting that a considerable amount of icebergs 543 must have been produced from the West Antarctic ice sheet in order to travel over 2000 km 544 to reach Site U1361. Additionally, sediments deposited in the Ross Sea have shown that the 545 Ross Ice Shelf retreated repeatedly during the Pliocene (Naish et al., 2009), likely in response 546 to warm Pliocene conditions (McKay et al., 2012). We therefore propose that increased 547 supply of West Antarctic IRD to Site U1361 was related to changes in ice sheet volume 548 during particularly warm Pliocene intervals. This suggestion is in line with Pliocene IRD 549 depositional patterns at the site (Patterson et al., 2014) and AND-1B results from the Ross 550 Sea (Naish et al., 2009), indicating orbitally-modulated retreat of the WAIS during Pliocene 551 interglacials. However, higher resolution sampling of all facies in Site U1361 sediments, as 552 well as improved statistical confidence in grain counts, would be required to substantiate this 553 tentative interpretation.

554 5.2 Fine-grained sediment sources

555 To summarise above discussion, 40Ar/39Ar ages on ice-rafted hornblende grains from 556 Pliocene sediments at IODP Site U1361 show predominant erosion from two major 557 lithologies: (proximal) Ross Orogeny-aged, Palaeozoic granitoids (~500Ma), probably from 558 around the Ninnes Glacier and Southern Victoria Land, and more distal Cenozoic McMurdo 559 volcanics (<44 Ma) (Figure 1a). The following section will explore the provenance of the 560 <63m fraction of the same marine sediments. Clay mineralogy indicates crystalline and 561 volcanic source areas, potentially contributing at different proportions during different 562 climatic regimes, and radiogenic isotope compositions corroborate this finding. Proximal 563 Palaeozoic granitoids can be inferred as an endmember for the fine-grained Nd and Sr isotope 564 provenance signature during colder times. An additional endmember, or a mixture of sources, 565 is required to explain the fine-grained provenance signature at Site U1361 during warmer 566 times, and likely involves Jurassic FLIP basalts and dolerites, and Devonian to Jurassic 567 siliciclastic deposits of the Beacon Supergroup.

568 5.2.1 Clay mineral provenance

569 Illite is the most common clay mineral in high latitude marine sediments derived from 570 physical weathering of plutonic and metamorphic rocks (e.g. Biscaye et al., 1965) and is also 571 the most abundant clay mineral in Pliocene sediment from Site U1361, particularly in those 572 from facies 1,2 and 3 (i.e. colder times during the Pliocene). Illites from Quaternary- and 573 Pliocene-aged channel levee sediments nearby to Site U1361 have geochemical compositions 574 that suggest sourcing from Early Palaeozoic granitoids found in the hinterland of the Ninnis 575 Glacier (Figure 1a) (between 64°17’S 143°22’E and 64°57’S 144°23’E: Damiani et al., 2006; 576 Talarico and Kleinschmidt, 2003; Site U1359: Verma et al. 2014). Smectite is the second 577 most abundant clay mineral in Pliocene marine sediments at Site U1361and is typically 578 interpreted as a weathering product of basic volcanic rocks (e.g. Biscaye et al., 1965). 579 Smectite abundances seem elevated in sediments from Facies 4 and 5 (i.e. warmer times 580 during the Pliocene). In detail, the two regional lithologies that are likely to produce smectites 581 are the Cenozoic McMurdo Volcanic Group and the Jurassic volcanic terranes of the basaltic 582 and doleritic FLIP rocks, which intruded ~180 Ma into the siliciclastic deposits of the Beacon 583 Supergroup (Damiani et al. 2006; Verma et al. 2014) (Figure 1a). Basalts of the FLIP group 584 have been identified as a source of detrital smectite in the Ross Sea (Claridge and Campbell, 585 1989). On the other hand, smectite associated with the McMurdo Volcanic Group is mainly 586 authigenic in origin in the Ross Sea (Setti et al. 2000), and associated with submarine 587 weathering and hydrothermal alteration of volcanic material (Petschick et al. 1996; Setti et al.

588 2000). Despite the presence of volcanic ash in Site U1361 sediments, smectites in marine 589 sediments nearby to Site U1361 have been suggested to be detrital in origin (Damiani et al., 590 2006). Hence, we rule out the McMurdo Volcanic Group as a significant source of smectite 591 and suggest that detrital smectite was instead supplied by FLIP terranes, which are exposed in 592 broad areas of the Transantarctic Mountains (Elliot and Fleming, 2008) and inferred to 593 occupy large areas underneath the ice in the Wilkes Subglacial Basin (Ferraccioli et al., 2009; 594 Jordan et al. 2013; Studinger et al., 2004; Figure 1a). A strong negative correlation between 595 the abundance of smectite and illites in Site U1361 sediments, combined with positive 596 correlations between smectite/illite and Nd isotope compositions (Figure 8; see also next 597 section), suggests that provenance is an important control on smectite and illite contents. 598 Kaolinite and chlorite are less abundant in Pliocene Site 1361 sediments. A possible 599 continental source of kaolinite is the sedimentary sequence of the Beacon Supergroup 600 (Barrett, 1981; Piper and Brisco, 1975; Figure 1). These volcanoclastic to quartzo-feldspathic 601 sediments can be observed in many outcrops in the Transantarctic Mountains in association 602 with FLIP lithologies (e.g. Barrett et al., 1986). The most proximal known outcrops of 603 Beacon Supergroup sediments to Site U1361 lie at the mouth of the Wilkes Subglacial Basin 604 (Bushnell and Craddock, 1970). However, as indicated above, the association of FLIP and 605 Beacon lithologies probaly comprises a large part of the infill of the Wilkes Subglacial basin 606 (Ferraccioli et al., 2009). If the Beacon Supergroup was the main source of kaolinite in Site 607 U1361 sediments, its abundance might be expected to correlate with smectite (and Nd isotope 608 compositions), due to the inferred close association between FLIP and Beacon Supergroup 609 lithologies. No such trend is observed, and we hence consider it more likely for the kaolinite 610 to be supplied from weathering of granitic sources, such as the abundant Palaeozoic granites 611 in the area (Figure 1a).

612 5.2.2 Neodymium and strontium isotope provenance

613 The Nd and Sr isotope compositions of fine-grained (<63 m) Site U1361 detrital 87 86 614 sediments are negatively correlated (ƐNd: -6.9 to -13.2; Sr/ Sr: 0.717 to 0.729; Figure 9) 615 and fall into two distinct groups. Cook et al. (2013) found that clay-rich sediments of facies 1 616 to 3 Pliocene sediments, deposited during cooler climatic intervals, were characterised by Nd 617 isotope values of -11.2 to -13.2 and 87Sr/86Sr isotope ratios of 0.723 to 0.730 (Figure 9). They

618 interpreted this signature to be associated with erosion of Palaeozoic granitoids (ƐNd: -11.2 619 and -19.8; 87Sr/86Sr: 0.714 to 0.753; Figure 1a for exposures, Figure 9, see Table S1 for 620 references). The most proximal outcrops of such rocks to Site U1361 are located in the

621 vicinity of the nearby Ninnis Glacier (Figure 1a). Supply from this area is in accordance with 622 modern depositional patterns (Busetti et al., 2003; Donda et al., 2003; Escutia et al., 2003, 623 2000) as well as with core-top sediment results from the area (Cook et al., 2013; Pierce et al., 624 2014, 2011). 625 Conversely, diatom-rich/bearing sediments of facies 4 and 5, deposited during warmer 87 86 626 intervals, are characterised by ƐNd values of -6.9 to -9.9 and Sr/ Sr ratios of 0.716 to 0.728 627 (Figures 3 and 9). This signature requires input from a source lithology with a more 628 radiogenic Nd isotope fingerprint. We previously suggested (Cook et al., 2013) that the FLIP 87 86 629 rocks make a good candidate for this endmember (ƐNd: -3.5 and -6.9; Sr/ Sr: 0.709 to 0.719; 630 Figure 9, see Table S1 for references). Ferrar dolerites were intruded as sills and dikes into 631 Devonian to early Jurassic sediments of the Beacon Supergroup and show similar ages (~180 632 Ma) to extrusive basalts of the FLIP formation (e.g. Barrett, 1991; Elliot and Fleming, 2008). 633 Furthermore, wherever exposed, FLIP and Beacon lithologies are closely associated (Figure 634 1a). Detrital zircon analyses from the Beacon Supergroup in the Transantarctic Mountains 635 and Northern Victoria Land yield a broad age spectrum, reflecting deposition in a 636 transantarctic sedimentary basin at the Panthalassan margin of Gondwana, situated between 637 Precambrian cratonic terranes to the east and contemporaneous magmatic arc sequences to 638 the west (~190-270 Ma: Early Triassic to early Jurassic magmatic arc; ~470-545 Ma: Ross 639 Orogeny granitoids; ~500-700 Ma: Pan-African Orogeny granitoids; ~800-1200 Ma: 640 Grenville aged crustal material; Elliot and Fanning, 2008; Elsner et al., 2013; Goodge and 641 Fanning, 2010). The range of source lithologies and ages contained in the siliciclastic 642 sediments of the Beacon Supergroup predicts a rather large range in radiogenic isotope 643 compositions. To our knowledge there are no published results on the Nd isotope 644 composition of Beacon sediments. Estimates can however be based on analyses of <5 m 645 fractions of four dune samples with Beacon sandstone parent lithologies from the Dry 646 Valleys (Transantarctic Mountains), and one Beacon regolith sample from Northern Victoria

647 Land (Delmonte et al., 2010, 2013). The range of Nd values and Sr isotopic compositions in 87 86 648 these samples (Nd = -5.6 to -8.1; Sr/ Sr = 0.7121 to 0.7182) overlaps with the field shown 649 for FLIP lithologies in Figure 9. In contrary, Farmer and Licht (2016) estimated mixed Ferrar 650 and Beacon compositions based on the <63 mm fraction of glacial tills from the Byrd and 651 Nimrod Glaciers in the central Transantarctic Mountains to be more unradiogenic in Nd

652 isotopes (Nd = -8.5 to -15.0) and more radiogenic in Sr isotopes (0.714 – 0.723), suggesting

653 that at least some of the Beacon Supergroup must be characterised by Nd values as low as - 654 15. 655 Future work on Beacon Supergroup samples will have to show, which of these 656 estimates is more applicable for provenance interpretations at Site U1361. We can however 657 conclude that a mixture of FLIP and Beacon rocks constitutes a viable endmember for eroded 658 sediments during warm Pliocene intervals, and that such lithologies likely comprise a 659 considerable component of the sedimentary infill of the Wilkes Subglacial Basin (Ferraccioli 660 et al., 2009; Jordan et al. 2013; Studinger et al., 2004; Figure 1a), which would be more 661 accessible during warmer times in the Pliocene due to a retreated ice margin (Cook et al., 662 2013).

663 5.3 Fine-grained versus coarse-grained sediment provenance

664 Pliocene fine-grained sediments at Site U1361 were predominantly supplied from 665 Early Palaeozoic granites in the nearby continental margin, and from sources within the 666 Wilkes Subglacial Basin, as constrained by both Nd-Sr isotopes and clay mineralogy. Coarse- 667 grained hornblende grains support an erosional source from local granites exposed on the 668 proximal coast, but indicate in addition IRD supply from multiple sources to the east, 669 including Northern Victoria Land and West Antarctica. In other words, there is no straight 670 forward correlation of provenance from coarse and fine grained sediments as illustrated in 671 Figure 10. Notably, ice-rafted hornblende grains extracted from Pliocene sediments at Site 672 U1361 lack any indication of erosion of FLIP lithologies with typical emplacement ages 673 around ~180 Ma (Duncan et al., 1997; Foland et al., 1993; Heimann et al., 1994; Minor and 674 Mukasa, 1997) (Figures 5 and 10). 675 The Pliocene was a time of significant volumetric changes in the EAIS as indicated by 676 IRD depositional patterns (Patterson et al., 2014) and marine sediment provenance changes 677 (Cook et al., 2013) at Site U1361. It is likely that such dynamic ice sheet behaviour resulted 678 in increased iceberg production from the Wilkes Subglacial Basin. We propose that the main 679 differences between the provenance patterns of fine-grained sediments and coarse-grained 680 ice-rafted hornblende grains from Site U1361 can be ascribed to delivery processes, and 681 source rock characteristics. Sources within the Wilkes Subglacial Basin have low hornblende 682 concentrations (Hauptvogel and Passchier, 2012). Additionally, existing grains may be 683 subject to comminution and hence leave a fingerprint in the fine size fraction only.

684 5.3.1 Ice rafting versus down-slope sedimentation

685 The apparent disparity between the provenance of fine-grained sediments and coarse 686 (ice-rafted) hornblende grains used in this study could be a product of variance in their 687 delivery methods from source to sink (Figure 2; see also Diekmann and Kuhn, 1999). 688 Although it is extremely difficult to reconstruct the dynamics of the glacial processes that 689 initially resulted in the onland erosion of sediments supplied to Site U1361 during the 690 Pliocene, we can nevertheless gain some insights from considering modern processes and 691 observations in the area. Today, detrital fine-grained sediments are supplied to Site U1361 by 692 meltwater plumes and/or turbidity currents, which transport shelf sediments, initially derived 693 from Early Palaeozoic bedrock in the coastal hinterland (Pierce et al., 2011, 2014; Cook et 694 al., 2013) downslope in submarine channels orientated perpendicular to the coast (Busetti et 695 al. 2003; Donda et al. 2003; Escutia et al. 2003, 2000; Patterson et al., 2014). Site U1361 is 696 located on the apex of a levee of one of these channels, with sediments deposited as non- 697 erosional over-spills (Escutia et al., 2011; Patterson et al., 2014). Therefore, both coarse- and 698 fine-grained sediments could be delivered to our site from the shelf via downslope processes, 699 a scenario that would explain the presence of Early Palaeozoic hornblende grains, granite 700 clasts, Nd-Sr isotope signatures suggestive of this endmember, and increased supply of illites 701 from Early Palaeozoic granites in facies 1, 2 and 3. 702 However, provenance constraints on facies 4 and 5, based on Nd-Sr isotope data and 703 increased smectite contents, imply fine-grained sediments were additionally supplied to the 704 site from within the Wilkes Subglacial Basin during periods of ice sheet retreat, including a 705 component of mafic FLIP lithologies (Cook et al., 2013; this study). One routing mechanism 706 for the delivery of this material is via meltwater-plume driven turbidity currents, which may 707 have re-distributed material deposited initially on the shelf at the mouth of the basin, to the 708 east of Site U1361. Gravity-density currents like turbidites are common along glaciated 709 margins (Dowdeswell et at, 1998; Hesse et al., 1997; Piper et al., 2007), and have been used 710 as a proxy for past meltwater events associated with ice sheet deglaciation in the North 711 Atlantic (e.g. Piper et al., 2007; Rashid et al., 2012). Subsequent westward deflection of these 712 sediments injected into the Southern Ocean by surface (Figure 1a) and bottom currents (Orsi 713 et al., 1999) could carry clay and silt-sized detrital material towards Site U1361, but 714 discriminate against coarse-grained material from the Wilkes Subglacial Basin. Instead, FLIP 715 and Beacon Supergroup-derived lithic clasts and mineral grains, as well as coarse-grained 716 hornblendes from sites to the east such as Victoria Land and the Ross Sea, must have been 717 delivered to Site U1361 by ice-rafting. Despite fine-grained sediments likely comprising 718 some of this distally sourced ice-rafted load, it appears that amounts are too minor to dilute

719 the signatures of locally supplied fine-grained sediments. A corresponding decrease in the 720 supply of more proximal Early Palaeozoic granitic derived sediments could be explained by 721 contemporaneous reduction in supply of sediments to the shelf edge, perhaps associated with 722 a regionally reduced ice sheet margin (Cook et al., 2013). However, this does not fully 723 explain the absence of a 40Ar/39Ar age populations indicating FLIP origin in hornblende 724 grains.

725 5.3.2. Potential FLIP and Beacon Supergroup source rock bias

726 The FLIP is composed of dolerites and basalts (Elliot and Fleming, 2008), with heavy 727 minerals dominated by Mg-rich clinopyroxenes and orthopyroxenes (Demarchi et al., 2010; 728 Haban and Elliot, 1995; Hauptvogel and Passchier, 2012), a mineralogical feature common to 729 rift-type volcanism (Nechaev and Isphording, 1993). The petrography of ice-rafted clasts and 730 mineral grains in coarse-grained fractions of Site U1361 sediments reveals significant 731 quantities of clinopyroxenes and orthopyroxenes (up to 4.3% of total detrital fraction 732 >150µm, Table 1), suggesting that the FLIP was a viable source of ice-rafted material. This 733 interpretation is validated by the presence of clasts of basalt in the same Pliocene sediments. 734 Furthermore, on land the FLIP is intimately associated with the Beacon Supergroup (Elliot 735 and Fleming, 2008; Figure 1a). Beacon Supergroup lithologies are dominated by quartzites, 736 sandstones and siltstones and contain very few heavy minerals (Hauptvogel and Passchier, 737 2012). Their erosion is suggested by abundant clasts of quartzite in Site U1361 sediments 738 (Table 1). Whether the ice-rafted FLIP and Beacon Supergroup mineral grains and lithic 739 clasts were sourced from terranes in the Wilkes Subglacial Basin, or from terranes in the 740 Transantarctic Mountains, where they are commonly exposed (Figure 1a), is difficult to 741 constrain. What stands is the observation that FLIP lithologies are not captured by hornblende 742 40Ar/39Ar age populations. This observation is best explained by a source rock bias in the 743 marine sediment record. Hornblende grains have been shown to be comparatively rare in 744 heavy mineral assemblages derived from sediment sources dominated by FLIP terranes 745 (Hauptvogel and Passchier, 2012) and are unlikely to have survived the multiple sedimentary 746 cycles documented by zircon ages in Beacon lithologies (Elliot and Fanning, 2008; Elsner et 747 al., 2013; Goodge and Fanning, 2010; see also discussion in Pierce et al., 2014). Another 748 possible explanation is that erosion of FLIP lithologies from within the Wilkes Subglacial 749 basin was mainly happening subglacially and hence subject to comminution. Support for the 750 latter idea, and the existence of a FLIP component in the fine-grained fraction of sediments 751 offshore the Wilkes Subglacial basin, comes from K-Ar analyses at Site U1356, located to the

752 west of site U1361. Johnson et al. (2012) found a strong correlation between the Nd isotope 753 composition and K-Ar ages in fine-grained (<63 m) Miocene sediments, extending from 754 Palaeozoic ages to ages as young as the Jurassic intrusion ages of the FLIP (~180 Ma). 755 Hence we conclude that variable mineralogical compositions and grain sizes in 756 different bedrock types have produced the different provenance signatures extracted from the 757 Pliocene marine sediment assemblage at Site U1361. This interpretation could be tested with 758 future analysis of 40Ar/39Ar ages of detrital plagioclase and basalt clasts identified in Site 759 U1361 sediments, similar to existing thermochronological analyses of whole rock basalts and 760 mineral grains from FLIP bedrock (Duncan et al., 1997; Fleming et al., 1997; Foland et al., 761 1993; Heimann et al. 1994). Investigation of the possibility of sediment recycling within the 762 Beacon Supergroup and unconsolidated sediments within the Wilkes Subglacial Basin could 763 also be feasible via analysis of U-Pb ages of detrital zircons, as well as zircons extracted from 764 ice-rafted quartzite/sandstone clasts in Site U1361 sediments.

765 6. Conclusions

766 In this study we compared the provenance signatures of fine-grained and coarse- 767 grained detrital components in Pliocene sediments from IODP Site U1361, Wilkes Land, 768 using clay minerals (<2µm), Nd and Sr isotopes (<63µm), hornblende grain 40Ar/39Ar ages 769 (>150µm), and mineral grain (>150µm) and lithic clast (>2mm) petrography. Fine-grained 770 signatures extend published provenance interpretations (Cook et al., 2013), whereby bedrock 771 sources within the Wilkes Subglacial Basin (FLIP and Beacon Supergroup) and local Early 772 Palaeozoic terranes supplied fine-grained sediments to Site U1361 throughout the Pliocene. 773 Petrographic analyses of ice-rafted lithic clasts reveal that the FLIP and Beacon Supergroup 774 lithologies were likely significant bedrock sources for ice-rafted debris as well. Low 775 amphibole contents within FLIP and Beacon bedrocks and/or comminution of such grains, 776 however, prevents us from tracing these particular lithologies by ice-rafted hornblende 777 40Ar/39Ar ages. On the other hand, ice-rafted hornblende 40Ar/39Ar ages reveal multiple 778 erosional source areas along the continental margins of East Antarctica, potentially even 779 extending eastwards towards Marie Byrd Land (West Antarctica). West Antarctic provenance 780 of ice-rafted debris off the East Antarctic Wilkes Subglacial Basin occurred during warmer 781 intervals, hinting at large-scale iceberg production events from the West Antarctic Ice Sheet. 782 Our study highlights the power of combining multiple provenance tools within 783 different grain-size fractions when studying marine sediments derived from a glaciated

784 continent. Single provenance tools are less likely to capture the full spectrum of bedrock 785 characteristics, information vital for more accurate reconstructions of past ice sheet histories.

786 Acknowledgments: C.P. Cook thanks the Grantham Institute for Climate Change at Imperial 787 College London for a PhD scholarship, K. Kreissig and B. Coles for lab assistance, P. Simões 788 Pereira and R. Bertram for discussion, and IODP for providing materials. Ian Bailey and an 789 anonymous reviewer provided very insightful comments that helped improve the manuscript 790 a lot. Financial support for this study was provided by NERC UK IODP to T.v.d.F. 791 (NE/H014144/1, NE/H025162/1), by the European Commission to T.v.d.F. (IRG 230828), by 792 the National Science Foundation to T.W., T.v.d.F. and S.R.H. (ANT 0944489 and ANT 793 1342213), and by the Royal Society to T.v.d.F. and S.R.H. (IE110878).

794 Figure Captions

795 Figure 1 (a). Geological map of the study area, illustrating the diverse range of ages and 796 lithologies of exposed terranes (modified from Bushnell and Craddock, 1970). Also shown is 797 the continental subglacial topography (BEDMAP 2; Fretwell et al., 2013) with continental 798 regions below sea level to -2000m in light grey, and regions below -2000m in darker grey. 799 Black dashed lines refer to major structural features (Ferraccioli et al., 2009; Flottmann et al., 800 1993). Offshore, the star indicates the location of IODP Site U1361. Sites 1, 2 and 3 (offshore 801 black dots) refer to IODP Site U1358, IODP Site U1360 and DSDP Site 274 respectively. 802 Blue shading offshore represents the approximate transport region of modern icebergs with 803 direction of movement shown with small grey arrows (Tournadre et al., 2015). Larger dashed 804 arrows indicate the approximate flow direction of Antarctic Bottom Water (Orsi et al., 1999). 805 Inferred subglacial extent of the FLIP and Beacon groups in light green is from Ferraccioli et 806 al. (2009). NG: Ninnis Glacier, MG: Mertz Glacier, MSZ: Mertz Shear Zone. (b) 807 Thermochronological map of study area, illustrating the good agreement between detrital 808 hornblende 40Ar/39Ar age populations in Holocene marine sediments (Brachfeld et al., 2007; 809 Pierce et al., 2011; Roy et al., 2007; this study), and onshore ages (see Table S1). 810 Thermochronological ages correspond to colours shown in the scale bar and delineate four 811 distinct provenance sectors: a Wilkes Land sector to the west of 135°E, an Adélie Land sector 812 (135-142°E), a Northern Victoria Land and Ross Sea sector (~142°E to ~195°E), and a West 813 Antarctic sector (east of 195°E). Also shown are the locations of numerous Cenozoic 814 volcanic centres, shown as triangles. Red dashed lines denote the approximate positions of 815 major ice sheet drainage catchments. NG: Ninnis Glacier, MG: Mertz Glacier, MSZ: Mertz 816 Shear Zone.

817 Figure 2. Cartoon schematic for the East Antarctic margin illustrating the diverse range of 818 factors that can control a glaciomarine sediment provenance assemblage.

819 Figure 3. Downcore summary of Pliocene sediments recovered from IODP Site U1361. 820 From left to right: i) depth in meters below sea floor; ii) core intervals; iii) palaeomagnetic 821 chron boundaries (Tauxe et al., 2012) with inclination data shown in red, and grey shading 822 indicating areas with no data; iv) lithostratigraphy (modified after Escutia et al., 2011); v) 823 visual clast counts (Escutia et al., 2011) >2mm in diameter; vi) detrital Nd isotope

824 composition (ƐNd) for Pliocene marine sediments from Site U1361; symbols represent new 825 data from this study, and results taken from Cook et al. (2013); uncertainties are smaller than

826 data points; depths of samples analysed for ice-rafted hornblende 40Ar/39Ar age populations 827 are indicted by arrows with numbers representing number of grains analysed from each

828 sample; vertical dashed lines denote average ƐNd values for samples measured from facies 1-3 829 (blue) and facies 4 and 5 (red); vii) palaeomagnetic chron boundaries with extending blue 830 dashed lines from Gradstein et al. (2012).

831 Figure 4. Petrographic and lithic grain summary of analysed >150µm fractions from Pliocene 832 Site U1361 sediments. i) depth in mbsf; ii) lithostratigraphy; iii) ice-rafted debris mass 833 accumulation rates (IRD MAR; >150 µm) from Patterson et al. (2014) and visual clast counts 834 >2mm in diameter from Escutia et al. (2011); iv) pie charts showing relative abundance (%) 835 of grain petrography; v) histograms showing number of lithic grains of different composition. 836 Note that quartz grains are not included in the pie charts, due to the high content in all 837 samples (provided in % next to the pie chart). The total number of non-quartz grains 838 constituting each pie chart is between 5 and 24.

839 Figure 5. Comparison of hornblende 40Ar/39Ar ages from regional core-top marine sediments 840 (bottom panel; Brachfeld et al., 2008; Pierce et al., 2011; Roy et al., 2007), new core-top data 841 for DSDP Site 274, IODP Site U1358 and IODP Site U1360 (middle panel; this study), and 842 core-top and Pliocene sediments for IODP Site U1361 (top panel; this study). Ages on the x- 843 axis have been grouped in 50 million year bins. Core-top data in bottom panel are divided 844 into four populations compiled from 22 sites: dark grey corresponds to the Wilkes Land 845 provenance sector (west of 135°E; 7 sites in total), mid-grey represents the Adélie Land 846 provenance sector (135°E to 142°E; 7 sites in total), light-grey demarks Northern Victoria 847 Land and the western Ross Sea provenance sector (142°E to 195°E; 4 sites in total), and 848 white represents a West Antarctica source (east of 195°E; 4 sites in total). NVL: Northern 849 Victoria Land, SVL: Southern Victoria Land, TAM: Central Transantarctic Mountains, EPG: 850 Early Palaeozoic Granites (near Ninnis Glacier). For definition of geographical sectors and 851 locations see Figure 1. Vertical grey bands corresponding to the three most significant age 852 ranges identified in Site U1361 marine sediments, 0 to 50 Ma (McMurdo Volcanic Group, 853 MVG), 90-130 Ma (West Antarctica, WA) and 440-540 Ma (Ross Orogeny) from left to 854 right.

855 Figure 6. a) Histogram of the youngest Cenozoic hornblende 40Ar/39Ar age population from 856 Pliocene Site U1361 sediments. Also included are the known eruptive histories of the four 857 main volcanic provinces in the region (see text, and Table S1): HVP: Hallet Volcanic

858 Province; MMVP: Mount Melbourne Volcanic Province; EVP: Erebus Volcanic Province; 859 MBLVP: Marie Byrd Land Volcanic Province. About half of the hornblende grains yield 860 ages older than the deposition age, indicating that they were transported to the site by ice- 861 rafting. b) Isochron plot of eight volcanic glass grains analysed from U1361 10H 6W 35-37 862 (depositional age of ~4.1 Ma). The syn-depositional age of these volcanic glass grains with 863 sediment depositional age points to aeolian supply to Site U1361.

864 Figure 7. Clay mineralogy of Pliocene sediments from Site U1361. Shown are the relative 865 abundances of illite, smectite, chlorite, kaolinite, and smectite/illite ratios. Yellow and orange 866 horizontal bands correspond to diatom-bearing silty clays (facies 4) and diatom-rich silty 867 clays (facies 5) respectively. Relative illite and smectite abundances are anti-correlated most 868 pronouncedly in diatom-rich silty clays (facies 5) below 74.00mbsf. A large pulse of kaolinite 869 dominates the interval between 85.67 and 86.47 mbsf, which is accompanied by a 870 corresponding decrease in illite. Samples from this interval have not been included in the data 871 ranges cited in the main text.

872 Figure 8. Neodymium isotope composition of <63m detrital sediments at Site U1361 show 873 a positive correlation with smectite/illite ratios. If data were not available from the exact 874 same samples, samples were matched within 3 cm of core length.

875 Figure 9. Detrital Nd and Sr isotope compositions (<63 m) of different Pliocene 876 sedimentary facies sediments at IODP Site U1361. Uncertainties for all data points are 877 smaller than symbols. Whole-rock Nd and Sr isotopic compositions of East and West 878 Antarctic geological terranes are compiled from the literature (see Figure 1 for lithologies and 879 Table S1 for references). Due to limited outcrops in the Wilkes Land area, data from 880 proximal Holocene marine sediments are plotted instead (Hemming et al. 2007; Pierce et al., 881 2011; Roy et al., 2007; van de Flierdt et al., 2007). The isotopic composition of the Adélie 87 86 882 Craton (purple) primarily plots outside of the diagram space shown (ƐNd: -20 to -28; Sr/ Sr: 883 0.750 to 0.780; Borg and DePaolo, 1994; Peucat et al., 1999).

884 Figure 10. Comparison of Nd and Sr isotope compositions of fine-grained detrital sediments 885 (<63m) and 40Ar/39Ar age populations of ice-rafted hornblende grains (>150 m). Fine- 886 grained fingerprint is plotted on x and y axis, while ages of ice-rafted hornblende grains are 887 illustrated as coloured pie charts. Black central diamonds in pie charts mark samples taken 888 from clay-rich facies (i.e. colder times), and diamonds in pie charts visualise samples taken

889 from diatom-rich/bearing facies (i.e. warmer times). Note that all analyses have been 890 performed on the exact same samples. The colour legend shows age ranges based on 891 hornblende 40Ar/39Ar analyses. Numbers in brackets are potential geographic sources for each 892 of the different age groups. Combined age populations of all samples from different 893 environmental conditions are shown to the right and illustrate that samples from colder facies 894 2 and samples from warmer facies 4 and 5 show similar age populations, even though the 895 fine-grained provenance indicates distinct source areas. WA: West Antarctica; NVL: 896 Northern Victoria Land, SVL: Southern Victoria Land, TAM: Central Transantarctic 897 Mountains, EPG: Early Palaeozoic Granites (near Ninnis Glacier; see Figure 1 for location); 898 AL: Adélie Land; WSB: Wilkes Subglacial Basin.

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Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Table 1. Relative abundance of major detrital components in counted grains >150 µm from IODP Site U1361 sediments. Also reported is the absolute count of grains >2 mm and the

lithology of clasts found in the >2mm sediment fraction.

)

Depth count

Sample Clasts (>2mm)

(%) (%) (%) (%) (%) (%) (%)

(mbsf) (%)

2mm/g

Biotite Biotite

Quartz Garnet

Feldspar

Pyroxene Pyroxene

Magnetite

Glauconite Glauconite

Hornblende Hornblende

Grain

Facies 1: 8H 4W 117-119cm 71.68 1.8 92.4 6.5 1.1 1 sand-stone, 1 siltstone Facies 2: 7H 7W 13-15cm 65.65 0.8 83.3 6.3 6.3 2.1 2.1 2 siltstone 9H 7W 45-47cm 84.95 3.2 89.6 3.1 3.1 1 1 1 1 1 schist, 1 basalt, 1 siltstone, 1 shale, 1 granite 13H 2W 44-46cm 115.49 4.2 90.1 1.5 4.2 2.7 1.5 4 schist, 1 basalt Facies 4: 7H 1W 120-122cm 57.7 0.5 93.5 1.1 2.2 2.2 1.1 1 siltstone, 1 basalt 7H 1W 122-124cm 57.72 2.1 91.9 3 1 4 1 schist, 2 siltstone, 1 sand-stone, 1 basalt Facies 5: 1H 1W 3-5cm 0.03 1.4 86.5 2.7 2.7 5.4 2.7 7H 4W 127-129cm 62.27 1.1 89.2 9.7 1.1 8H 3W 105-107cm 70.06 3.5 95.3 2.3 2.3 8H 6W 27-29cm 73.79 3.8 89.8 5.1 5.1 8H 6W 57-59cm 74.09 2 94.2 4.7 1.2 9H 1W 57-59cm 76.07 0.9 91.2 2.2 4.4 1.1 1.1 3 schist 9H 1W 77-79cm 76.27 2 75.8 18.7 1.1 2.2 2.2 2 schist 10H 5W 107-109cm 92.07 2.4 75.6 6.7 6.7 4.4 2.2 4.4 10 schist, 7 granite, 1 basalt, 1 siltstone 10H 6W 35-37cm 92.95 3.6 90.4 2.7 1.4 4.1 1.4 1 siltstone 10H 7W 3-5cm 94.03 0.3 89.2 5.4 2.7 2.7 7 schist 11H 5W 25-27cm 100.75 0.6 97.5 0.7 1.8 11H 7W 28-30cm 103.78 1 94.7 3.5 1.8 1 sand-stone, 2 schist, 1 granite 12H 6W 49-51cm 109.74 1.7 88 8.4 0.9 0.9 0.9 0.9

Facies corresponds to lithostratigraphy description (see text): 1:clay; 2: clay with dispersed clasts; 4: diatom- bearing silty clay; 5: diatom-rich silty clay.

Table 2. 40Ar/39Ar ages of ice-rafted, detrital hornblende grains (>150m) from cores tops and Pliocene sediments at IODP Sites U1358, U1360, U1361 and DSDP Site 274. Grain counts >2mm/g indicate the general lack of coarse-grained material. Total hornblende grains picked and analysed are less than 26 in all cases but the ice proximal Site U1358.

Grain 90- 330- 440- 1000- Total Depth <44 Other Sample counts 290 430 540 1300 hbl (mbsf) Ma ages (>2mm/g) Ma Ma Ma Ma grains

IODP Site U1361 Facies 2: 7H 7W 17-23cm* 65.69 0.8 4 3 0 8 1 1 17 9H 2W 77-83cm* 77.77 2.2 7 1 2 8 0 0 18 13H 2W 46-48cm 115.47 12.6 4 0 0 10 0 0 15 Facies 4: 7H 1W 120-122cm 57.70 0.5 1 5 1 16 1 1 25 7H 4W 127-131cm* 62.27 1.1 1 5 1 15 1 0 24 Facies 5: 1H 1W 1-5cm* 0.01 1.4 5 0 1 1 0 0 7 9H 1W 57-61cm* 76.07 0.9 5 1 1 8 0 0 16 9H 1W 77-79cm 76.27 2.0 4 1 3 11 1 1 21 10H 5W 107-111cm* 92.07 2.4 4 2 1 8 1 1 17 10H 6W 35-37cm 92.95 3.6 1 0 0 0 0 0 1 10H 7W 3-5cm 94.03 0.3 3 1 0 3 0 0 7 11H 5W 27-29cm 100.77 0.6 2 0 0 0 0 0 2 11H 7W 28-30cm 103.78 1.0 9 2 0 2 0 0 13 12H 6W 51-53cm 109.76 1.7 3 1 1 3 1 0 9 Total 54 22 11 93 6 3 192

Regional Data DSDP Site 274 1R 5W 110-111cm 7.10 0 0 1 9 0 2 12 IODP Site U1360 1R 1W 0-18cm 0.00 0 0 0 0 0 21 21 IODP Site U1358 1R 1W 18-22cm 0.18 0 0 0 0 0 38 38

Hornblende grains and monitor standards were irradiated at the TRIGA reactor at the USGS in Denver, with 40 39 cadmium shielding. Ar/ Ar ages were obtained using single-step CO2 laser fusion at the Lamont-Doherty Earth Observatory argon geochronology lab (AGES: Argon Geochronology for the Earth Sciences). J values used to correct for neutron flux were calculated using the co-irradiated Mmhb-1 hornblende standard with an age of 525 Ma (Samson and Alexander, 1987). Measured values were corrected for background argon with measurements from an air pipette, and were also corrected for nuclear interferences (Renne et al., 1998). Analytical errors are based on the internal precision of measurements and variation of Mmhb values and are less than 2%.

Facies corresponds to lithostratigraphy description (see text): 2: clay with dispersed clasts; 4: diatom-bearing silty clay; 5: diatom-rich silty clay.

*larger intervals (60 cm3 instead of 20 cm3 as for all other samples)

Table 3. Strontium and Nd isotope compositions of Pliocene detrital marine sediments (<63 m) from IODP Site U1361 and DSDP Site 274. Additional Sr and Nd isotope data for Site U1361 sediments are available from Cook et al. (2013).

Depth Sample 87Sr/86Sr 2 SE 143Nd/144Nd 2 SE εNda 2 SDb (mbsf)

ODP Site U1361 Facies 1: 6H 1W 25-27cm 47.25 0.728823 ± 0.000010 0.512291 ± 0.000008 -11.7 ± 0.3 8H 3W 37-38cm* 69.38 0.730877 ± 0.000008 0.511981 ± 0.000018 -12.8 ± 0.4 8H 3W 75-77cm 69.76 0.728736 ± 0.000012 0.512060 ± 0.000010 -11.2 ± 0.3 8H 4W 117-119cm 71.68 0.724040 ± 0.000008 0.511964 ± 0.000008 -13.2 ± 0.3 Facies 2: 7H 7W 17-19cm 65.69 0.723360 ± 0.000020 0.512058 ± 0.000018 -11.3 ± 0.4 re-analysis 0.723367 ± 0.000016 Facies 4: 7H 1W 120-122cm 57.70 0.719666 ± 0.000014 0.512284 ± 0.000014 -6.9 ± 0.2 7H 4W 127-129cm 62.27 0.721773 ± 0.000008 0.512185 ± 0.000012 -8.8 ± 0.2 7H 5W 54-55cm* 63.04 0.728100 ± 0.000016 0.512164 ± 0.000008 -9.2 ± 0.2 Facies 5: 8H 1W 115-117cm 67.15 0.716570 ± 0.000012 0.512195 ± 0.000008 -8.6 ± 0.3 8H 3W 105-107cm 70.06 0.717345 ± 0.000014 0.512192 ± 0.000008 -8.7 ± 0.3 8H 6W 27-29cm 73.79 0.724461 ± 0.000022 0.512176 ± 0.000012 -9.0 ± 0.3

DSDP Site 274 1R 5W 110-112cm 7.10 0.717592 ± 0.000008 0.512506 ± 0.000008 -4.6 ± 0.3

Average 143Nd/144Nd JNdi values for ten analytical sessions over a sixteen month period were: 0.511979 ± 0.000028 (n=55); 0.512079 ± 0.000011 (n=22); 0.512138 ± 0.000020 (n=40); 0.512161 ± 0.000015 (n=30); 0.512153 ± 0.000012 (n=23); 0.512110 ± 0.000017 (n=33); 0.512093 ± 0.000014 (n=28); 0.512279 ± 0.000015 (n=18); 0.512254 ± 0.000015 (n=5); 0.512220 ± 0.000018 (n=18) (2 SD). All reported 143Nd/144Nd ratios are corrected to a JNdi value of 0.512115 (Tanaka et al., 2000). Inter-batch measurements of processing monitor standard BCR-1 yielded a 143Nd/144Nd of 0.512650 ±0.000021 (n=4), compared to the recommended value of 0.512646 ± 0.000016 (Weis et al., 2006). Total procedural blanks were consistently below 10pg Nd.

Repeated analyses of NBS987 standards (n = 71) yielded 87Sr/86Sr ratios of 0.710260 ± 0.000015 (2 SD), in agreement with published values for NBS987 (0.710252 ± 0.000013; n=88) (Weis et al., 2006). Repeated processing and analyses of BCR-1 yielded an 87Sr/86Sr ratio of 0.705025 ± 0.000018 (2 SD) (n=10), compared to the recommended value of 0.705018 ± 0.000013 (Weis et al., 2006). Procedural blanks were consistently less than 300pg, and usually less than 30pg. a Calculated using a present day 143Nd/144Nd (CHUR) of 0.512638 (Jacobsen and Wasserburg, 1980). b External uncertainty (2 sigma standard deviation) is based on the JNdi standard reproducibility of the analytical session. * Bulk samples analysed. All other results are from <63µm detrital fractions.

Re-analysis: Samples that were measured multiple times (same aliquot). Facies corresponds to lithostratigraphy description (see text): 1:clay; 2: clay with dispersed clasts; 4: diatom- bearing silty clay; 5: diatom-rich silty clay.