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Chemical Geology

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Glacial erosion of East Antarctica in the Pliocene: A comparative study ofmultiple marine sediment provenance tracers

Carys P. Cooka,b, Sidney R. Hemmingc,d, Tina van de Flierdtb,⁎, Elizabeth L. Pierce Davisc,Trevor Williamsd,1, Alberto Lopez Galindoe, Francisco J. Jiménez-Espejoe,2, Carlota Escutiae

a Grantham Institute for Climate Change and the Environment, Imperial College London, South Kensington Campus, London SW7 2AZ, UKb Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, UKc Department of Earth and Environmental Sciences and Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964, USAd Lamont-Doherty Earth Observatory, Palisades, NY 10964, USAe Instituto Andaluz de Ciencias de la Tierra, CSIC-UGR, 18100 Armilla, Spain

A R T I C L E I N F O

Keywords:East Antarctic ice sheetProvenanceMarine sedimentPliocene warmthRadiogenic isotopesThermochronology

A B S T R A C T

The history of the East Antarctic ice sheet provides important understanding of its potential future behaviour in awarming world. The provenance of glaciomarine sediments can provide insights into this history, if the un-derlying continent eroded by the ice sheet is made of distinct geological terranes that can be distinguished by themineralogy, petrology and/or geochemistry of the eroded sediment. We here present a multi-proxy provenanceinvestigation on Pliocene sediments from Integrated Ocean Drilling Program (IODP) Site U1361, located offshoreof the Wilkes Subglacial Basin, East Antarctica. We compare Nd and Sr isotopic compositions of< 63 μm detritalfractions, clay mineralogy of< 2 μm fractions, 40Ar/39Ar ages of> 150 μm ice-rafted hornblende grains, andpetrography of> 2 mm ice-rafted clasts and> 150 μm mineral grains. Pliocene fine-grained marine sedimentshave Nd and Sr isotopic compositions, clay mineralogy, and clast characteristics that can be explained by mixingof sediments eroded from predominantly proximal crystalline terranes with material derived from inland sourcesfrom within the currently glaciated Wilkes Subglacial Basin. Conversely, evidence for such an inland source isabsent from ice-rafted hornblende ages. We render a lithological bias against hornblende grains in the doleriticand sedimentary units within the basin the most likely explanation for this observation. 40Ar/39Ar hornblendeages however record additional provenance from the distal margins of the Ross Sea, and possibly even the WestAntarctic area of Marie Byrd Land. The latter lies> 2000 km to the east and hints at significant iceberg releasefrom the West Antarctic ice sheet during warm intervals of the Pliocene. Together our results make a strong casefor combining geochemical and mineralogical signatures of coarse- and fine-grained glaciomarine sedimentfractions in order to derive robust provenance interpretations in ice covered areas.

1. Introduction

The ‘provenance’ of a detrital marine sediment assemblage describes itscomponents' derivation from erosion of their continental source rocks totheir subsequent burial at the ocean floor. Studying marine sediment pro-venance patterns has been recognised as a valuable approach in paleocli-mate studies as they can provide information on a wide range of environ-mental processes, such as atmospheric and ocean circulation patterns,weathering style, changes in riverine discharge, ice sheet histories, andtectonics and crustal evolution on longer time scales (e.g., Goldstein andHemming, 2003; Grousset and Biscaye, 2005; McLennan and Taylor, 1991).

In the Southern Ocean, a number of studies have made composi-tional links between Holocene glaciomarine sediments surrounding theAntarctic continent, and distinct continental margin bedrock sources asconstrained by sparse outcrops (Brachfeld et al., 2007; Cook et al.,2014, 2013; Farmer et al., 2006; Flowerdew et al., 2013, Flowerdewet al., 2012; Hemming et al., 2007; Licht and Palmer, 2013; Licht et al.,2014, Licht et al., 2005; Pierce et al., 2014, Pierce et al., 2011; Royet al., 2007; van de Flierdt et al., 2007; see also Farmer and Licht(2016), Palmer et al. (2012), and Welke et al. (2016) for work on nu-natak moraines, and review by Licht and Hemming (2017)). Extensivesurveying work of this type can be coupled with results of airborne

http://dx.doi.org/10.1016/j.chemgeo.2017.06.011Received 8 January 2017; Received in revised form 18 May 2017; Accepted 6 June 2017

⁎ Corresponding author.

1 Present address: International Ocean Discovery Program, Texas A &M University, College Station, TX 77845, USA.2 Present address: Department of Biogeochemistry, Japan Agency for Marine-Earth Science and Technology, Yokosuka 237-0061, Japan.

E-mail address: tina.vandeflierdt@imperial.ac.uk (T. van de Flierdt).

Chemical Geology 466 (2017) 199–218

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geophysical surveys (e.g. Aitken et al., 2014; Ferraccioli et al., 2009;Studinger et al., 2004) and tectonic reconstructions of conjugate mar-gins (e.g. Aitken et al., 2014; Collins and Pisarevsky, 2005; Fitzsimons,2000a, 2000b, 2003; Harley et al., 2013; Li et al., 2008) to extend in-ferred sub-ice geology inland of the continental margin. This informa-tion in turn permits for reconstructions of buried landscapes (Cox et al.,2010; van de Flierdt et al., 2008), variations in glacial erosional pat-terns (Thomson et al., 2013; Tochilin et al., 2012), and the locations ofdynamic ice sheet behaviour in the past (e.g. Cook et al., 2014, 2013;Williams et al., 2010).

However, a factor in sediment provenance studies that needs carefulconsideration is the selection of appropriate tools, particularly whenstudying a glaciated continent where a priori knowledge of the geolo-gical characteristics of hidden bedrock sources is limited. Additionally,multiple physical processes can act to modify a source rock signature inderived sediments. To obtain a more holistic view of sediment sourcesand their implications for ice sheet dynamics, we use multiple prove-nance approaches on sediments drilled at Integrated Ocean DrillingProgram (IODP) Site U1361 (64°24′S, 143°53′E), located off the gla-ciated Adélie Land coast, East Antarctica (Fig. 1), and compare andcontrast their strength and weaknesses.

1.1. Controls on glaciomarine sediment provenance

The complexities of studying sediment provenance patterns offshoreof a glaciated continent are illustrated in Fig. 2. For example, miner-alogical compositions, petrogenetic histories and grain-size character-istics of different bedrock types, along with erosional patterns, play animportant role in determining which detrital provenance tool may bebest suited to identify a specific on-land source terrane within a marinesediment assemblage (e.g., Taylor and McLennan, 1985). In addition,some mineral grains are more resistant to weathering than others (e.g.zircons [more resistant] vs. hornblendes [less resistant]; Kowalewskiand Rimstidt, 2003), resulting in their preferential survival throughnumerous tectonic recycling events (e.g. Goodge and Fanning, 2010).Sedimentary substrates are more likely to be physically eroded thancrystalline bedrock, and indeed ice streams often overlie subglacialbasins infilled with unconsolidated sediments (e.g. Studinger et al.,2001) suggesting their detrital outputs should contain a large compo-nent of recycled sedimentary material. Rock texture also plays an im-portant role, as finer-grained rock types such as shale are likely to beunder-represented in coarse-grained fractions of marine sediments. Onthe other hand, mineral grains from coarse-grained source rocks such asplutonic rocks and high-grade metamorphic rocks will be represented incoarser fractions, but can also be found in glacial flour as a result ofcomminution. Additionally, subglacial erosional processes by melt-water and ice can integrate a diverse range of bedrock types over alarge area. An excellent review on glacigenic sediment provenance hasrecently been provided by Licht and Hemming (2017).

Furthermore, different marine transport and depositional processeshave the potential to integrate marine sediments supplied from multiplesources, and alter the distribution of different size fractions in themarine environment. For example, finer-grained detrital material canbe delivered to the deep ocean by turbidites, meltwater plumes andcontourites, surface and deep ocean currents, wind, iceberg and sea-icerafting. In contrast, beyond turbidite aprons, sand-sized and largerdetrital material can only be delivered to the deep ocean floor by ice-rafting (both icebergs and sea-ice) and volcanic eruptions. Therefore,studying one component of a particular glaciomarine sediment size-fraction may not fully capture the representative provenance signatureof that sediment's original source on land. Likewise fine grained sedi-ment may reflect multiple delivery mechanisms and thus a differentaspect of the sedimentary provenance in addition to glacial processes.

We here present and discuss observations and interpretations of anapparent inconsistency in the sediment sources at Site U1361. Wepresent new data on a diverse range of tools from multiple sediment

components, in order to better identify the roles played by source rockcharacteristics and depositional processes on controlling their deliveryfrom source to sink. In detail, we used five different and widely usedprovenance approaches: (i), fine-grained (< 63 μm) detrital radiogenicSr isotopes (87Sr/86Sr), (ii) fine-grained (< 63 μm) detrital Nd isotopes(expressed as ƐNd, which describes the deviation of a measured143Nd/144Nd ratio from the Chondritic Uniform Reservoir in parts per10,000; Jacobsen and Wasserburg (1980)); (iii) fine-grained (< 2 μm)clay mineralogy; (iv) sand-sized (> 150 μm, ice-rafted) hornblendegrain 40Ar/39Ar ages, and (v) petrographic characterisation of ice-raftedmineral grains (> 150 μm) and clasts (> 2 mm). Our results allow arefined interpretation of the glacial history of an important sector of theEast Antarctic ice sheet.

1.2. Provenance tools

The long-lived radioactive decay systems of rubidium-strontium(Rb-Sr) and samarium-neodymium (Sm-Nd) are widely used and veryuseful tracers of fine-grained marine sediment provenance signatures(e.g. Bareille et al., 1994; Basak and Martin, 2013; Colville et al., 2011;Cook et al., 2013; Dasch, 1969; Farmer et al., 2006; Jantschik andGrousset et al., 1998, 1988; Hemming et al., 2007, Hemming et al.,1998; Jantschik and Huon, 1992; Revel et al., 1996; Roy et al., 2007;van de Flierdt et al., 2007). They are present in all rock types and cantherefore be used to trace supply from continental source areas (Taylorand McLennan, 1995). The parent-daughter pairs Rb-Sr and Sm-Nd arefractionated during melting of mantle material, creating continentalcrust reservoirs with high Rb/Sr ratios and low Sm/Nd ratios. Hence,bedrocks of different ages and lithologies can have characteristic Ndand Sr isotopic compositions. This approach has been used very suc-cessfully in glaciomarine sediments to reveal the provenance of fine-grained and bulk components, as it provides an integrated signal of allbedrock sources eroded within a glaciated catchment area (e.g. Farmeret al., 2006; Colville et al., 2011; Cook et al., 2013; Hemming et al.,2007; Roy et al., 2007; Taylor and McLennan, 1995). Changes in thedepositional output of a glaciated terrane as recorded by changing Ndand Sr isotopic signatures of glaciomarine sediments has been used toindicate periods of major ice sheet change in both Antarctica (e.g. Cooket al., 2013), and on continents surrounding the North Atlantic (e.g.Colville et al., 2011; Hemming et al., 1998).

Clay minerals have traditionally been the most commonly used fine-grained marine sediment provenance tool in the Southern Ocean (e.g.Diekmann and Kuhn, 1999; Ehrmann and Mackensen, 1992; Ehrmannet al., 1992; Ehrmann et al., 1991; Hillenbrand et al., 2009; Petschicket al., 1996), and are a product of both the continental bedrock sourcesof detrital material, and the intensity of chemical weathering of thosesources (Biscaye, 1965; Robert and Kennett, 1994). A significant changefrom smectite to illite dominated marine sediment facies around Ant-arctica marks glacial initiation in Antarctica (Ehrmann and Mackensen,1992; Robert and Kennett, 1994) caused by a large-scale change topronounced physical weathering on the Antarctic continent.

Although all grain sizes are represented in glaciomarine sediments,the only process that can deliver coarse-grained material to the deepocean beyond turbidite aprons and volcanic eruptions is rafting. Finer-grained material is likely to comprise a considerable proportion of aniceberg's sediment load (e.g. Ruddiman, 1977) but these size fractionscan be transported by a variety of processes. Therefore, coarse-sizedlithic material and mineral grains are best used to estimate sedi-mentation from ice-rafting in distal locations. Mineral thermo-chronometers applied to sand-sized grains (e.g. U-Pb ages of zircon,garnet, rutile, monazite and sphere grains, 40Ar/39Ar ages of mica,feldspar, and amphibole grains) record information that can be used toinfer the magmatic and tectonothermal history of their original hostrocks (e.g. Hodges et al., 2005; Reiners and Brandon, 2006). The tem-perature at which a system such as a mineral grain becomes closed todiffusive processes is its ‘closure’, or ‘blocking’ temperature. 40Ar/39Ar

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(caption on next page)

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ages in hornblende grains reflect crystallisation and/or closure tem-perature of ~500 °C (McDougall and Harrison, 1999), thus 40Ar/39Arhornblende grain ages record the timing of the last major tecto-nothermal event experienced by their host rock for fingerprinting ice-rafted material sourced from continental terranes with complex tec-tono-metamorphic histories (e.g. Cook et al., 2014; Gwiazda et al.,1996; Hemming et al., 2000; Hemming et al., 1998; Knutz et al., 2013;Peck et al., 2007; Pierce et al., 2014; Pierce et al., 2011; Roy et al.,2007; Williams et al., 2010). While detrital zircons are a commonlyused circum-Antarctic sediment provenance tool (e.g. Fitzsimons,2000a, 2000b; Goodge and Fanning, 2010; Pierce et al., 2014; Veeversand Saeed, 2011), hornblendes were selected for this study. In addition,petrographic and lithological characterisation of ice-rafted mineralgrains and lithic grains can provide information on source rocks andprovenance of coarse-grained fractions (Anderson et al., 1992; Andrewset al., 1995; Bond et al., 1992; Elverhøi et al., 1995; Licht et al., 2005;Talarico et al., 2012; Thierens et al., 2012).

2. Study site and provenance background

IODP Site U1361 was drilled in 3466 m water depth, approximately315 km offshore of Adélie Land, East Antarctica, during Expedition 318(Escutia et al., 2011). Approximately 388 m of sediment were recoveredin total, and a chronology was compiled using palaeomagnetic in-clination data and biostratigraphy (diatom and radiolarian datums)(Escutia et al., 2011; Tauxe et al., 2012) (Fig. 3). Published onshoreconstraints (Fig. 1; Table S1) and existing marine sediment provenancestudies in the area (Cook et al., 2013; Domack, 1982; Goodge and

Fanning, 2010; Hemming et al., 2007; Pant et al., 2013; Pierce et al.,2014, Pierce et al., 2011; Orejola and Passchier, 2014; Roy et al., 2007)demonstrate that the East Antarctic continent nearby to Site U1361 isgeologically heterogeneous and contains sedimentary, metamorphicand extrusive and intrusive igneous rocks with ages spanning much ofthe last 3 billion years. Hence Site U1361 can receive sediments sup-plied from a diverse range of rocks with a range of ages and lithologies.

Here we focus on a well-defined Pliocene section (Escutia et al.,2011; Cook et al., 2013) between 45 and 125 mbsf (Fig. 3). Within thisinterval, five lithostratographic facies are identified: facies 1 (clays),facies 2 (clays with dispersed clasts) and facies 3 (silty clays with dis-persed clasts) are dominated by terrigenous material and representcolder times during the Pliocene. Facies 4 (diatom-bearing silty clays)and facies 5 (diatom-rich silty clays) on the other hand contain moresignificant biogenic opal components and were deposited duringwarmer intervals. Cook et al. (2013) investigated the provenance offine-grained (< 63 μm) detrital sediments from Site U1361 between 75and 125 mbsf using Nd and Sr isotopes and clay minerals, and foundthat diatom-poor sediments are characterised by distinct provenancesignatures (ƐNd: −11.1 to −14.5; 87Sr/86Sr: 0.719 to 0.738; illite-rich)compared to diatom-rich sediments (ƐNd: −5.9 to −9.5; 87Sr/86Sr:0.712 to 0.719; smectite-rich).

Here we supplement these existing data by extending the Nd and Srisotope and clay mineral record up section to 47.25 mbsf (i.e. LatePliocene). To further investigate the provenance data presented byCook et al. (2013), we present new ice-rafted mineral grain and clastinformation, and the first ice-rafted hornblende grain 40Ar/39Ar agedata for this site.

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

East Antarctic continent

continentalshelf

continentalslope sea floor

East Antarctic Ice Sheet

turbidity and contourite currents/meltwater plume

Iceberg

SO

UR

CE

SIN

K

ice-rafted debris

Onland Processeschemical and physical weathering;

ice and meltwater drainage; basal entrainment; supra-glacial

and aeolian deposition

Marine Environmentice-rafting; delivery and redistribution

via turbidity, contourite and bottom currents; meltwater plumes;

aeolian deposition

dust

Source Rock Propertiesmineralogy; age; texture; grain

size; susceptibility to erosion/weathering

Syn- and Post-depositional Processesauthigenic precipitation;

diagenesis

volcanic/aeolianmaterial

Sea ice

glacial sediments

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

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3.3

3.2

3.1

3.0

3.4

3.5

3.6

3.7

3.8

3.9

4

4.1

4.2

4.3

4.4

4.5

4.6

4.7

4.8

4.9

5

2.9

2.8

2.7

2.6

5.1

Age (M

a)D

epth

(mbs

f)

Dep

th (m

bsf)

Nd

45

50

55

60

65

70

75

80

85

90

95

100

105

110

115

120

125

0 5

Facies 4: diatom-bearing silty clayFacies 2: clay with dispersed clasts

Facies 3: silty clay with dispersed clastsFacies 5: diatom-rich silty clay

Facies 1: clay

7H

8H

9H

10H

6H

13H

11H

12H

Clast Count (clasts/10cm)

εInclination

Polarity

-100 100 -16 -12 -8 -4

57.70 mbsf; n = 25

62.27 mbsf; n = 24

65.69 mbsf; n = 17

76.27 mbsf; n = 2177.77 mbsf; n = 18

92.07 mbsf; n = 1792.95 mbsf; n = 1

94.03 mbsf; n = 7

100.77 mbsf; n = 2

103.78 mbsf; n = 13

115.47 mbsf; n=15

Avg. facies1 to 3: ε = -12.6

Avg. facies 4 & 5: ε = -8.4

76.07 mbsf; n = 16

109.76 mbsf;n = 9

NdNd

Fig. 3. Downcore summary of Pliocene sediments recovered from IODP Site U1361. From left to right: i) depth in meters below sea floor; ii) core intervals; iii) palaeomagnetic chronboundaries (Tauxe et al., 2012) with inclination data shown in red, and grey shading indicating areas with no data; iv) lithostratigraphy (modified after Escutia et al., 2011); v) visual clastcounts (Escutia et al., 2011)> 2 mm in diameter; vi) detrital Nd isotope composition (ƐNd) for Pliocene marine sediments from Site U1361; symbols represent new data from this study,and results taken from Cook et al. (2013); uncertainties are smaller than data points; depths of samples analysed for ice-rafted hornblende 40Ar/39Ar age populations are indicted byarrows with numbers representing number of grains analysed from each sample; vertical dashed lines denote average ƐNd values for samples measured from facies 1–3 (blue) and facies 4and 5 (red); vii) palaeomagnetic chron boundaries with extending blue dashed lines from Gradstein et al. (2012). (For interpretation of the references to colour in this figure legend, thereader is referred to the web version of this article.)

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3. Samples and methods

3.1. Petrographic characterisation and IRD counts of coarse-grainedsediment fractions

The coarse-grained fractions (> 150 μm) of 19 samples from SiteU1361 were examined to characterise mineral grains, to count IRDgrains coarser than 2 mm (dropstones) and to identify their lithologies(Table 1). Samples for characterisation were analysed from facies 1(n = 1), facies 2 (n= 3), facies 4 (n = 2) and facies 5 (n = 12). Pet-rographic characterisation of> 150 μm sediment fractions was basedon counts of 100 to 400 randomly distributed mineral grains in apicking tray and the relative abundances of different mineral types wereassumed to be representative of the entire sample. In addition, all grainscoarser than 2 mm were counted from the entire sample, and all ob-served clast lithologies were reported in order to constrain potentialcorrelations between the amount of ice-rafted debris (IRD) present ineach sample and its provenance (Table 1; Fig. 4).

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

A total of 13 Pliocene samples (2 cm intervals, 20 cm3) from SiteU1361, between 57.70 and 115.47 msbf, were selected for 40Ar/39Ardating of ice-rafted hornblende grains, and one Holocene sample (1H1W 1–5 cm, 0.01 mbsf) (Fig. 3, Tables 2 and S2). Sample selection was

based on the visual count of clasts> 2 mm on board the JOIDES Re-solution (Escutia et al., 2011; see Fig. 3 for sample locations in strati-graphic content) to represent peaks in coarse-grained material in dif-ferent facies. Selection yielded samples from sedimentary facies 2 (claywith dispersed clasts; n= 3), facies 4 (diatom-bearing silty clays;n = 2), and facies 5 (diatom-rich silty clays; n= 9) (Table 2).

192 hornblende grains were hand-picked from the> 150 mmfraction and analysed for their 40Ar/39Ar ages at the AGES laboratory atLamont-Doherty Earth Observatory of Columbia University (Fig. 5, seeTable 2 for analytical information, and Table S2 for data). In mostsamples hornblende grains were very scarce. In order to improve graincounts and statistical confidence, the volume of bulk sample materialprocessed was increased to 60 cm3 for nine samples. Larger samplevolumes however produced only limited success in increasing horn-blende grain yield.

During picking for hornblende grains, it was noted thatthe> 150 μm sediment fraction of one Pliocene sample (U1361 10H6W 35–37 cm, 92.95 mbsf) was composed of ~56% brown visuallyunaltered volcanic glass shards, containing occasional phenocrysts ofbiotite and hornblende. Eight fresh volcanic glass grains were selectedfrom this sample and analysed for 40Ar/39Ar using either one-step ortwo-step laser fusion analysis (Fig. 6) in order to determine the absoluteage of volcanic events and infer provenance (i.e. discriminate betweenwind-blown ash and eroded bedrock).

To supplement existing provenance constraints on IODP Site U1361

Table 1Relative 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 ofclasts found in the> 2 mm sediment fraction.

Sample Depth(mbsf)

Grain count(> 2mm/g)

Quartz (%) Feldspar (%) Pyroxene (%) Garnet (%) Biotite (%) Magnetite (%) Hornblende (%) Glauconite(%)

Clasts(> 2 mm)

Facies 18H 4W 117–119 cm 71.68 1.8 92.4 6.5 1.1 1 sand-stone,

1 siltstone

Facies 27H 7W 13–15 cm 65.65 0.8 83.3 6.3 6.3 2.1 2.1 2 siltstone9H 7W 45–47 cm 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 44–46 cm 115.49 4.2 90.1 1.5 4.2 2.7 1.5 4 schist,1 basalt

Facies 47H 1W 120–122 cm 57.7 0.5 93.5 1.1 2.2 2.2 1.1 1 siltstone,

1 basalt7H 1W 122–124 cm 57.72 2.1 91.9 3 1 4 1 schist,

2 siltstone,1 sand-stone,1 basalt

Facies 51H 1W 3–5 cm 0.03 1.4 86.5 2.7 2.7 5.4 2.77H 4W 127–129 cm 62.27 1.1 89.2 9.7 1.18H 3W 105–107 cm 70.06 3.5 95.3 2.3 2.38H 6W 27–29 cm 73.79 3.8 89.8 5.1 5.18H 6W 57–59 cm 74.09 2 94.2 4.7 1.29H 1W 57–59 cm 76.07 0.9 91.2 2.2 4.4 1.1 1.1 3 schist9H 1W 77–79 cm 76.27 2 75.8 18.7 1.1 2.2 2.2 2 schist10H 5W 107–109 cm 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 35–37 cm 92.95 3.6 90.4 2.7 1.4 4.1 1.4 1 siltstone10H 7W 3–5 cm 94.03 0.3 89.2 5.4 2.7 2.7 7 schist11H 5W 25–27 cm 100.75 0.6 97.5 0.7 1.811H 7W 28–30 cm 103.78 1 94.7 3.5 1.8 1 sand-stone,

2 schist,1 granite

12H 6W 49–51 cm 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.

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sediments and core-top surveys in the area (Roy et al., 2007; Pierceet al., 2011, 2014), we furthermore analysed hornblende grains fromcore-top sediments from three additional sites located proximally to thecontinent for their 40Ar/39Ar age populations: Deep Sea Drilling Pro-gram Site 274 (68°59′S, 173°25′E, 1R 5 W 110–111 cm; 12 grains),IODP Site U1358 (66°05′S, 143°18′E; 1R 1 W 18–22 cm, 25 grains) andIODP Site U1360 (66°22′S, 142°44′E, 1R 1 W 0–18 cm, 21 grains) (seeFig. 1 for locations; Fig. 5, Tables 2 and S2 for data). Core-top sedimentsfor the latter two sites have been dated to be Pliocene and UpperPleistocene in age, respectively (Escutia et al., 2011).

3.3. Clay mineralogy

Clay mineral compositions were determined on the< 2 μm detritalfractions of Pliocene sediments from IODP Site U1361, and were mea-sured on 193 discrete samples between 47.46 and 75.00 mbsf. Sampleswere taken from all identified Pliocene sedimentary facies (Figs. 7 and8, Table S3) and supplement existing data between 75.00 and124.97 mbsf (Cook et al., 2013). Sample preparation and analysis wasperformed at the Instituto Andaluz de Ciencias de la Tierra (IACT,Spain), following the same procedures as described by Cook et al.(2013).

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

Eleven Pliocene sediment samples were selected from IODP SiteU1361 between 47.25 and 73.79 mbsf for analysis of their Nd and Srisotopic compositions on the< 63 μm detrital fractions. Samples wereselected to represent a range of sedimentary facies 1 (n= 4), facies 2(n = 1), facies 4 (n= 3) and facies 5 (n= 3) (Table 3) and supplementpreviously published early Pliocene data (Cook et al., 2013; Figs. 3 and9; Table 3). Nine of the eleven samples, are identical to the ones utilisedfor> 150 μm hornblende 40Ar/39Ar analysis and had biogenic carbo-nate and authigenic ferromanganese phases removed following theprocedure outlined in Cook et al. (2013). Two samples were taken froma smaller 1 cm interval, and were analysed for bulk (not sieved) Nd andSr isotopes only (7H 5W 54–55 cm, 63.04 mbsf; 8H 3W 37–38 cm,69.38 mbsf) (Table 3) in order to test for potential grain size effects.Sediments were acid digested on hotplates and target analytes wereseparated by column chemistry, following the same procedures de-scribed by Cook et al. (2013). Neodymium and Sr isotopes were ana-lysed by MC-ICP-MS and TIMS, respectively, in the MAGIC laboratoriesat Imperial College London, and analytical details are provided in Cooket al. (2013) and in Table 3 footnotes.

4. Results

4.1. Petrographic characterisation and IRD counts of coarse-grainedsediment fractions

Pliocene mineral assemblages from coarse-grained sediment frac-tions (> 150 μm) from IODP Site U1361 (Table 1) are dominated byquartz (76–98%), with abundant feldspars (< 19%), pyroxenes (clinoand ortho) (< 6%), biotite, garnet, magnetite, and hornblende (all <7%), and trace amounts of glauconite (< 3%) (Fig. 4). Fifty-sevenlithic clasts> 2 mm were found throughout the 19 samples. Lithicfragments are composed of siltstone, quartzose sandstone, shale, schist,

0.03 mbsf n=136; 87% qtz

57.70 mbsfn=133; 94% qtz

57.76 mbsf n=77;92% qtz

62.27 mbsf n=88;89 % qtz

65.65 mbsfn=44;83% qtz

70.06 mbsf n=63;95% qtz

71.68 mbsf n=107;92% qtz

73.79 mbsfn=47;90% qtz

74.09 mbsf n=83;94% qtz

76.07 mbsf n=88;91% qtz

76.27 mbsf n=88;76% qtz

84.95 mbsf n=73;90% qtz

92.07 mbsf n=47;76% qtz

92.95 mbsf n=63;90% qtz

94.03 mbsf n=53;89% qtz

100.75 mbsf n=146;98% qtz

103.78 mbsf n=52;95% qtz

Clast Count (clasts/10cm)

IRD MAR (g/cm3/kyr)

0 5 10

0 0.1 0.256

58

60

62

64

66

68

70

72

74

76

78

80

82

84

86

88

90

92

94

96

98

100

102

104

106

108

110

112

114

116

Dep

th (

mbs

f)

Feldspar

Pyroxene

Garnet

Biotite

Magnetite

Hornblende

Glauconite

109.74 mbsfn=120;88% qtz

115.49 mbsfn=53;90% qtz

0

1

2

0

1

2

0

1

2

0

1

2

0

1

2

3

0

1

2

0

1

2

02468

10

0

1

2

02468

10

0

1

2

Grain petrography (>150µm)

Clast lithology (>2mm)

num

ber

of g

rain

snu

mbe

r of

gra

ins

num

ber

of g

rain

snu

mbe

r of

gra

ins

Sch

ist

Silt

ston

eS

ands

tone

Sha

leG

rani

teB

asal

t0

2

4

num

ber

of g

rain

snu

mbe

r of

gra

ins

num

ber

of g

rain

snu

mbe

r of

gra

ins

num

ber

of g

rain

snu

mbe

r of

gra

ins

num

ber

of g

rain

snu

mbe

r of

gra

ins

Fig. 4. Petrographic and lithic grain summary of analysed> 150 μm fractions fromPliocene Site U1361 sediments. i) depth in mbsf; ii) lithostratigraphy; iii) ice-rafted debrismass accumulation rates (IRD MAR;> 150 μm) from Patterson et al. (2014) and visualclast counts> 2 mm in diameter from Escutia et al. (2011); iv) pie charts showing re-lative abundance (%) of grain petrography; v) histograms showing number of lithic grainsof different composition. Note that quartz grains are not included in the pie charts, due tothe high content in all samples (provided in % next to the pie chart). The total number ofnon-quartz grains constituting each pie chart is between 5 and 24.

C.P. Cook et al. Chemical Geology 466 (2017) 199–218

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basalt, granite, and abundant volcanic glass. No changes in abundanceof different ice-rafted mineral grains or lithic clasts were observed be-tween different facies. Particular mineralogies and lithologies show nocorrelation to the amount of IRD grains> 2 mm in size per gram ofsediment, although more data for facies 1 and 2 would be desirable.

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

Hornblende is relatively scarce in these samples, with typicalabundances< 1% in the> 150 μm fractions and grain yields between1 and 25 for processing 20 to 60 cm3 of material (Table 2 and Fig. 3).40Ar/39Ar ages from Pliocene and Holocene sediments at IODP SiteU1361 yield two distinct populations: ~2 to 44 Ma (~28%; 54 out of192 grains analysed; Figs. 5 and 8, Tables 2 and S2), and 440–540 Ma(~48%; 93 out of 192 grains analysed; Fig. 5, Tables 2 and S2). Withinthe younger population, 42% of hornblende grains have ages thatmatch, within error, the depositional age of the sediment from whichthey were extracted (~2 to 6 Ma) whereas 58% of hornblende grainsare older (~6 to ~44 Ma) (Fig. 6). A minor bimodal age populationdistribution can be identified within the 440 to 550 Ma population: onebetween 440 and 500 Ma (63 grains in total), and the other between500 and 540 Ma (30 grains in total) (Fig. 5). Remaining hornblendegrains are found in minor numbers and are distributed over three broad40Ar/39Ar age ranges (Fig. 5, Table 2): 90–290 Ma (~11%; 22 of 192grains); 330–430 Ma (~6%; 11 grains of 192) and> 600 Ma (~6%; 11of 192 grains). More than half of the grains with an 40Ar/39Ar age rangebetween 90 and 290 Ma fall between ~90 and ~130 Ma (n= 13;Fig. 5, Table S2), while the remaining ages are distributed with no clearsub-grouping. The oldest 40Ar/39Ar aged grains (> 600 Ma) represent awide range of ages between ~641 ± 8.7 Ma and 2339 ± 26 Ma, withmore than half of these falling within an age range of ~1000 to

1320 Ma (Fig. 5).The number of ice-rafted grains> 2 mm per gram of sediment re-

veals no obvious correlation with hornblende 40Ar/39Ar ages (Table 2).Furthermore, comparison of the different hornblende 40Ar/39Ar ageranges identified in individual samples from different facies (Table 2)indicates only limited change in hornblende provenance with changingdepositional conditions. A potentially significant exception to this ob-servation is that 18 of the 22 grains with a 40Ar/39Ar age between 90and 290 Ma occur in samples from diatom-bearing facies 4 and 5(Table 2), although more samples from facies 1 and 2 would be desir-able to confirm this observation.

Eight distinct volcanic glass grains were analysed for 40Ar/39Ar agesfrom IODP Site U1361, sample 10H 6W 35–37 cm, in a two-step (n = 7)or one-step (n= 1) heating procedure. Only one of seven grains pro-duced results for both heating steps (6.0 ± 1.1 Ma and5.1 ± 2.8 Ma), with all others samples yielding sufficient gas to cal-culate ages only for the second step (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)(Fig. 6b). The single-step heated grain gave an age of 5.3 ± 2.8 Ma.Apart from the two glass grains with the oldest ages (6.0 ± 1.1 Ma and7.5 ± 0.8 Ma), all ages are contemporaneous within error with theestimated depositional age of the sample from which they were ex-tracted (~4 Ma).

Hornblende 40Ar/39Ar ages in the Holocene sediment sample fromDSDP Site 274 (n = 12) (Fig. 1b for location, Fig. 5; Tables 2 and S2 fordata) predominantly fall between 476 and 524 Ma (9 grains in total),with additional grains aged at 378 ± 5 Ma, 619 ± 36 Ma, and1550 ± 9 Ma. Hornblende grains analysed from the Holocene marinesediment sample from Site U1358 yield 40Ar/39Ar ages mainly between~1420 and 1860 Ma (24 of 25 grains analysed), with one grain pro-ducing an age of 2250 ± 28 Ma (Fig. 1b for location, Fig. 5 and Tables

Table 240Ar/39Ar ages of ice-rafted, detrital hornblende grains (> 150 μm) from cores tops and Pliocene sediments at IODP Sites U1358, U1360, U1361 and DSDP Site 274. Grain counts>2 mm/g indicate the general lack of coarse-grained material. Total hornblende grains picked and analysed are< 26 in all cases but the ice proximal Site U1358.

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

IODP Site U1361Facies 2

7H 7W 17–23 cma 65.69 0.8 4 3 0 8 1 1 179H 2W 77–83 cma 77.77 2.2 7 1 2 8 0 0 1813H 2W 46–48 cm 115.47 12.6 4 0 0 10 0 0 15

Facies 47H 1W 120–122 cm 57.70 0.5 1 5 1 16 1 1 257H 4W 127–131 cma 62.27 1.1 1 5 1 15 1 0 24

Facies 5:1H 1W 1–5 cma 0.01 1.4 5 0 1 1 0 0 79H 1W 57–61 cma 76.07 0.9 5 1 1 8 0 0 169H 1W 77–79 cm 76.27 2.0 4 1 3 11 1 1 2110H 5W 107–111 cma 92.07 2.4 4 2 1 8 1 1 1710H 6W 35–37 cm 92.95 3.6 1 0 0 0 0 0 110H 7W 3–5 cm 94.03 0.3 3 1 0 3 0 0 711H 5W 27–29 cm 100.77 0.6 2 0 0 0 0 0 211H 7W 28–30 cm 103.78 1.0 9 2 0 2 0 0 1312H 6W 51–53 cm 109.76 1.7 3 1 1 3 1 0 9

Total 54 22 11 93 6 3 192Regional dataDSDP Site 274

1R 5W 110–111 cm 7.10 0 0 1 9 0 2 12IODP Site U1360

1R 1W 0–18 cm 0.00 0 0 0 0 0 21 21IODP Site U1358

1R 1W 18–22 cm 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 cadmium shielding. 40Ar/39Ar ages were obtained using single-step CO2 laserfusion 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 calculatedusing 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 measurementsfrom 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 Mmhbvalues and are< 2%.Facies corresponds to lithostratigraphy description (see text): 2: clay with dispersed clasts; 4: diatom-bearing silty clay; 5: diatom-rich silty clay.

a Larger intervals (60 cm3 instead of 20 cm3 as for all other samples).

C.P. Cook et al. Chemical Geology 466 (2017) 199–218

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2 and S2 for data). Similarly, core-top sediments sampled from SiteU1360 have hornblende 40Ar/39Ar ages that range from 1509 to1736 Ma (17 of 21 grains analysed), with remaining grains producingages of 1988 ± 17 Ma, 2060 ± 9 Ma, 2514 ± 33 Ma, and3944 ± 26 Ma (Fig. 1b for location, Fig. 5 and Tables 2 and S2 fordata).

4.3. Clay mineralogy

Clay minerals in Pliocene sediments from IODP Site U1361 (Figs. 7and 8, Table S3) are dominated by illite (52–68%), smectite (11–33%),with lesser amounts chlorite (5–19%) and kaolinite (7–16%, except forfour samples with 29–33% kaolinite). Illite and smectite show a strongnegative correlation (r2 = 0.8), which is significant despite relativelylarge analytical uncertainties (10–15%). In general, sediments fromfacies 4 and 5 tend to contain slightly higher amounts of smectite andchlorite, while sediments from facies 1, 2 and 3 show a tendency forhigher illite contents. Smectite/illite ratios share a weak positive cor-relation with Nd isotopic compositions (r2 = 0.6; Fig. 8).

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

Neodymium and Sr isotope compositions of the< 63 μm fractionsof Pliocene detrital sediments from Site U1361 display a large range ofvalues (ƐNd: −6.9 to −13.2; 87Sr/86Sr: 0.717 to 0.731) (Figs. 3 and 9,Table 3). Comparison of the Nd and Sr isotope results between thedifferent facies reveals two distinct groups (Figs. 3, 9 and 10; Table 3).Samples analysed from clay-dominated facies 1 and 2 are characterisedby ƐNd values between −11.2 and −13.2 and 87Sr/86Sr ratios between0.723 and 0.731, whereas samples analysed from diatom-rich/bearingfacies 4 and 5 have ƐNd values between −6.9 and −9.2 and 87Sr/86Sr

ratios between 0.717 and 0.728.

5. Discussion

In the following discussion we will first evaluate the provenancesignatures of coarse and fine-grained Pliocene sediments from IODP SiteU1361 separately, to then compare and contrast derived interpreta-tions. We will show that robust provenance analysis of glaciomarinesediments is best achieved by combining various methodologies andgrain-sizes. In the particular case studied here, 40Ar/39Ar ages ofhornblende grains (> 150 μm) reveal erosion of regionally abundantPalaeozoic granites emplaced during the Ross Orogeny (~440 to540 Myrs; Figs. 1b and 5) as well as ages associated with more distaloccurrences of McMurdo volcanics (< 44 Myrs; Figs. 1b and 5). Thedata furthermore hint at a far-travelled provenance component fromWest Antarctica during warm Pliocene intervals (90–125 Myrs; Figs. 1band 5). Warm intervals are furthermore characterised by quartz-richmineralogies of the coarse fraction (Table 1) and a radiogenic detritalNd isotope signature of fine-grained sediments (εNd = −6.9 to −9.9),corroborating previous suggestions that Pliocene ice retreat led toerosion of Ferrar Large Igneous Provenance (FLIP) and Beacon Super-group lithologies of Jurassic to Devonian ages, hidden today under-neath the East Antarctic ice sheet (cf. Cook et al., 2013).

5.1. Coarse-grained sediment provenance

Hornblende grains extracted from the> 150 μm sediment fractionof marine sediments away from continental shelf areas are typically ice-rafted in origin. However, in locations proximal to continents turbiditycurrents may play a role as well. In order to assess coarse-grained se-diment provenance offshore the Wilkes Subglacial basin during the

Hornblende 40Ar/39Ar age (Ma)

Num

ber

of g

rain

sN

umbe

r of

gra

ins

a) Pliocene sediments fromIODP Site U1361 (n=192)

(this study)

c) Regional core-top sediments from 22 sites

(n=578)

b) Core-top sediments fromDSDP Site 274 (n=12),

IODP Sites U1360 (n=21) and Site U1358 (n=25)

Site 274Site U1358Site U1360

West AntarcticaNorthern Victora LandAdélie LandWilkes Land

Num

ber

of g

rain

s

n=54

n=13 n=93

MVG

WARoss

Orogeny

Facies 1 & 2Facies 4 & 5

0

10

20

30

40

50

0

10

20

30

0

10

20

30

40

50

0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000

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

C.P. Cook et al. Chemical Geology 466 (2017) 199–218

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Pliocene we first evaluate our new 40Ar/39Ar data on regional core topsamples in the context of published on land thermochronology (Section5.1.1; Figs. 1b and 5). We selected three sites, covering distal sourceareas from the Ross Sea (DSDP Site 274) and proximal source areasfrom the Adélie Shelf (IODP Sites U1358 and U1360) (Fig. 1a). Wesubsequently compare these results with our new downcore record toidentify major (Section 5.1.2) and minor (Section 5.1.3) provenancesignatures observed. We finally elaborate on the exciting observationthat a small number of grains that were deposited during warm Plio-cene intervals at IODP Site 1361 could have a West Antarctic origin(Section 5.1.4).

5.1.1. Regional Holocene hornblende grain provenance: new results fromDSDP Site 274, IODP Site U1358 and IODP Site U1360

The majority of hornblende 40Ar/39Ar ages of Holocene sediments atDSDP Site 274 (Ross Sea) fall within a range of 475 to 525 Ma (Table 2;middle panel in Fig. 5), which is within the metamorphic age range ofthe high-grade Late Cambrian Ross Orogeny (460 to 560 Ma; Boger,2011; Goodge, 2007 and references therein; Pierce et al., 2014, Pierceet al., 2011; Stump, 1995) (Fig. 1b). Despite the regional prevalence ofthis high-grade metamorphic signature (Fig. 1b; see Goodge, 2007 forreview), on land thermochronology suggests that the timing of peakmetamorphism of terranes in Northern Victoria Land can be identifiedat slightly younger U-Pb ages (460–500 Ma; Dallmeyer and Wright,1992; Goodge and Dallmeyer, 1992; Klee et al., 1992; Schüssler et al.,

1999) than those of Southern Victoria Land (480–550 Ma; Goodge,2007; Wysoczanski and Allibone, 2004) and the Central TransantarcticMountains (480–545 Ma; Goodge, 2007). According to our results,DSDP Site 274 likely received IRD from proximal Northern VictoriaLand source areas.

Ice-rafted hornblende 40Ar/39Ar ages in Holocene sediments atAdélie shelf sites U1360 and U1358 yield rather different agesof> 1420 Ma, clustering around 1600 to 1750 Ma (Table 2; middlepanel in Fig. 5). These ages agree well with onshore ages for the tec-tonometamorphic overprint of the proximal Archean and Neoproter-ozoic Adélie Craton (40Ar/39Ar argon ages ~1700 Ma (see Table S1 forreferences), and hornblende 40Ar/39Ar ages in Holocene sediments inthe vicinity of the sites (Roy et al., 2007; Pierce et al., 2014, Pierceet al., 2011)). Such a provenance also allows for the occurrence ofArchean aged grains, which are found in small numbers at the Adélieshelf sites (Table 2).

5.1.2. Provenance of major age populations of ice-rafted hornblende grainsin Pliocene-aged Site U1361 sediments

Despite high IRD depositional rates (Fig. 3; Escutia et al., 2011;Patterson et al., 2014) ice-rafted hornblende grain counts in PlioceneSite U1361 sediments are low (Table 2, Fig. 3), suggesting that horn-blendes are generally low in abundance in the predominant sourceterranes.

5.1.2.1. Late Cambrian Ross Orogeny and Palaeozoic granites(440–540 Myrs). The most abundant hornblende grain 40Ar/39Ar agepopulation in Pliocene Site U1361 sediments has a range of 440 to540 Myrs (Fig. 5 top panel, Table 2). Such ages were likely sourcedfrom the high-grade Late Cambrian Ross Orogeny (Goodge, 2007 andreferences therein; Stump, 1995; see Fig. 1b for geographical extent). InSite U1361 sediments this population is comprised of two peaks, onebetween 440 and 500 Ma, and a secondary, smaller peak between 500and 540 Ma (Fig. 5). Northern Victoria Land (460–550 Ma), SouthernVictoria Land (480–550 Ma) and the Transantarctic Mountains(480–545 Ma) are potential sources for grains with such ages (seediscussion above for DSDP Site 274). The most likely source areas ishowever located proximal to the drill site, where Early Palaeozoicgranites outcrop in the vicinity of the Ninnis Glacier (Goodge andFanning, 2010; Fig. 1). This idea is supported by results from Holocenemarine sediments, located directly downstream of the Ninnis Glacier,which contain hornblende grains with 40Ar/39Ar ages between 480 and560 Ma (Pierce et al., 2014, Pierce et al., 2011; Roy et al., 2007;Fig. 1b). Indeed, the location of Site U1361 on the continental risesuggests that coarser-grained sediments derived from Early Palaeozoicterranes nearby could have been supplied to the site via downslopeprocesses such as turbidites Hence, the older sub-group within the RossOrogeny population is likely derived from ice-rafting and turbiditessourced from the proximal continental shelf and the Ninnis Glacier,and/or from ice-rafting from Southern Victoria Land and theTransantarctic Mountains, while the younger sub-group can bepartially explained by derivation from Northern Victoria Land.However, seven grains aged between 440 and 460 Ma do not fitdocumented ages from this region (Fig. 1b). Furthermore, a smallnumber of grains have hornblende 40Ar/39Ar ages between 330 and430 Ma. While it is possible that a currently hidden terrane was thesource for these grains, these ages, although minor in number, can bematched well to the Bowers Terrane in Northern Victoria Land (e.g.Borg et al., 1987; Rocchi et al., 2004; Weaver et al., 1984), which ischaracterised by whole-rock K-Ar ages of between 320 and 450 Ma(Adams, 2006).

5.1.2.2. McMurdo Volcanics (< 44 Myrs). The youngest and secondmost abundant hornblende 40Ar/39Ar age population identified in SiteU1361 sediments shows ages< 44 Ma, and is most likely derived fromthe Cenozoic McMurdo Volcanic Group (Harrington, 1958; Kyle, 1990;

Num

ber

of g

rain

s

Hornblende 40Ar/ 39Ar age (Ma)

Contemporaneous with depositional age

Hallet ProvinceMount MelbourneErebus ProvinceMarie Byrd Land

Older than depositional age

0

2

4

6

8

10

12

14

0 5 10 15 20 25 30 35 40 45 50

(a)

0 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.450

0.0005

0.0010

0.0015

0.0020

0.0025

0.0030

Age=6.9±1.0Ma(8.9%)40Ar/36ArInt.=302±3MSWD=2.5,P=0.00,n=30

39Ar/ 40Ar

36A

r/ 40

Ar

(b)

40 36Age = 6.9 ± 1.0 Ma (8.9 %) Ar/ Ar Int. = 302 ± 3MSWD = 2.5, n = 30

Fig. 6. a) Histogram of the youngest Cenozoic hornblende 40Ar/39Ar age population fromPliocene Site U1361 sediments. Also included are the known eruptive histories of the fourmain volcanic provinces in the region (see text, and Table S1): HVP: Hallet VolcanicProvince; MMVP: Mount Melbourne Volcanic Province; EVP: Erebus Volcanic Province;MBLVP: Marie Byrd Land Volcanic Province. About half of the hornblende grains yieldages older than the deposition age, indicating that they were transported to the site byice-rafting. b) Isochron plot of eight volcanic glass grains analysed from U1361 10H 6W35–37 (depositional age of ~4.1 Ma). The syn-depositional age of these volcanic glassgrains with sediment depositional age points to aeolian supply to Site U1361.

C.P. Cook et al. Chemical Geology 466 (2017) 199–218

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Kyle and Cole, 1974; LeMasurier and Thomson, 1990; Figs. 5 and 6).The Hallet Volcanic Province, Mount Melbourne Volcanic Province andErebus Volcanic Province of the McMurdo Volcanic Group (Figs. 1 and6) have well-documented eruptive histories spanning the last26 million years (see Table S1 for references). Balleny Islands (Fig. 1)constitute the volcanic edifice closest to Site U1361, and is believed tobe no older than Miocene (Johnson et al., 1982). The islands arehowever inaccessible and therefore poorly studied. The geochemicalcompositions of basalts from outcrops on these islands and volcanic ashanalysed from nearby marine sediments (Huang et al., 1975; Kyle andSeward, 1984; Shane and Froggatt, 1992) suggest an intermediategeochemical composition between that of the Hallet Volcanic Provinceand Erebus Volcanic Province (Green, 1992; Johnson et al., 1982; Kyleand Cole, 1974), implying similar tectonic relationships and likelysimilar ages for the initiation of their formation. It is hence feasible thatthe Balleny Islands may be the source of some of the volcanic ash andhornblendes younger than Miocene in age identified at Site U1361.Three Eocene aged hornblende grains (35.9 ± 0.7 Ma,36.6 ± 1.4 Ma, 44.2 ± 0.25 Ma) may be sourced from even olderMcMurdo Volcanic Group deposits currently undocumented in the RossSea. However, they could also have been supplied by icebergs sourcedfrom Marie Byrd Land in West Antarctica, over 2000 km to the east ofour study site, where Eocene volcanism has been dated to ~36 Ma,with the possibility of initial volcanism being even older (Wilch and

45

50

55

60

65

70

75

80

85

90

95

100

105

110

115

120

125

40 50 60 70

Smectite (%)

Illite (%) Chlorite (%)

Kaolinite (%)

Dep

th (

mbs

f)

10 20 30 40

0 10 20

0 10 20 30 40

0 10 20

Smectite/Illite

Fig. 7. Clay mineralogy of Pliocene sediments from Site U1361. Shown are the relative abundances of illite, smectite, chlorite, kaolinite, and smectite/illite ratios. Yellow and orangehorizontal bands correspond to diatom-bearing silty clays (facies 4) and diatom-rich silty clays (facies 5) respectively. Relative illite and smectite abundances are anti-correlated mostpronouncedly in diatom-rich silty clays (facies 5) below 74.00 mbsf. A large pulse of kaolinite dominates the interval between 85.67 and 86.47 mbsf, which is accompanied by acorresponding decrease in illite. Samples from this interval have not been included in the data ranges cited in the main text. (For interpretation of the references to colour in this figurelegend, the reader is referred to the web version of this article.)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

-16 -15 -14 -13 -12 -11 -10 -9 -8 -7 -6

Nd

Sm

ectit

e/Ill

ite

y = 0.0409x + 0.8313

R2 = 0.6

ε

Fig. 8. Neodymium isotope composition of< 63 μm detrital sediments at Site U1361show a positive correlation with smectite/illite ratios. If data were not available from theexact same samples, samples were matched within 3 cm of core length.

C.P. Cook et al. Chemical Geology 466 (2017) 199–218

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McIntosh, 2000).58% of all hornblende grains from Pliocene sediments at Site

U1361, which are younger than 44 Ma, are older than the depositionalage of the marine sediment itself (Fig. 6). It is hence likely that these

grains were entrained glacially in the vicinity of their volcanic de-positional centres before being transported to Site U1361 by icebergs.In contrast, most of the volcanic glass grains analysed yield ages withinerror of the depositional age of the sediment sample from which they

Table 3Strontium and Nd isotope compositions of Pliocene detrital marine sediments (< 63 μm) from IODP Site U1361 and DSDP Site 274. Additional Sr and Nd isotope data for Site U1361sediments are available from Cook et al. (2013).

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

ODP Site U1361Facies 1

6H 1W 25–27 cm 47.25 0.728823 ± 0.000010 0.512291 ± 0.000008 −11.7 ± 0.38H 3W 37–38 cmc 69.38 0.730877 ± 0.000008 0.511981 ± 0.000018 −12.8 ± 0.48H 3W 75–77 cm 69.76 0.728736 ± 0.000012 0.512060 ± 0.000010 −11.2 ± 0.38H 4W 117–119 cm 71.68 0.724040 ± 0.000008 0.511964 ± 0.000008 −13.2 ± 0.3

Facies 27H 7W 17–19 cm 65.69 0.723360 ± 0.000020 0.512058 ± 0.000018 −11.3 ± 0.4Re-analysis 0.723367 ± 0.000016

Facies 47H 1W 120–122 cm 57.70 0.719666 ± 0.000014 0.512284 ± 0.000014 −6.9 ± 0.27H 4W 127–129 cm 62.27 0.721773 ± 0.000008 0.512185 ± 0.000012 −8.8 ± 0.27H 5W 54–55 cmc 63.04 0.728100 ± 0.000016 0.512164 ± 0.000008 −9.2 ± 0.2

Facies 58H 1W 115–117 cm 67.15 0.716570 ± 0.000012 0.512195 ± 0.000008 −8.6 ± 0.38H 3W 105–107 cm 70.06 0.717345 ± 0.000014 0.512192 ± 0.000008 −8.7 ± 0.38H 6W 27–29 cm 73.79 0.724461 ± 0.000022 0.512176 ± 0.000012 −9.0 ± 0.3

DSDP Site 2741R 5W 110–112 cm 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 of0.512646 ± 0.000016 (Weis et al., 2006). Total procedural blanks were consistently below 10 pg 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 of0.705018 ± 0.000013 (Weis et al., 2006). Procedural blanks were consistently< 300 pg, and usually< 30 pg.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.

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.c Bulk samples analysed. All other results are from< 63 μm detrital fractions.

87Sr/86Sr

-25

-20

-15

-10

-5

0

5

10

0.70 0.71 0.72 0.73 0.74 0.75 0.76 Cenozoic Marie Byrd Volcanics

Ferrar Large Igneous Province

Wilkes Land, Holocene marine sediments

Wilson Group

Granite Harbour Group

Robertson Bay Group

Bowers Group

Adelie Craton

East Antarctic Terranes

West Antarctic Terranes

Paleozoic and Mesozoic terranes

Admirality Intrusives

PalaeozoicTerranes

Facies 5

IODP Site U1361:

Facies 4

Facies 1-3

Nd

Cenozoic McMurdo Volcanics

Erebus Volcanic Province

Hallet Volcanic Province

Mt Melbourne Volcanic Province

Balleny Islands

PrecambrianTerranes

MesozoicTerranes

Fig. 9. Detrital Nd and Sr isotope compositions (< 63 μm) of different Pliocene sedimentary facies sediments at IODP Site U1361. Uncertainties for all data points are smaller thansymbols. Whole-rock Nd and Sr isotopic compositions of East and West Antarctic geological terranes are compiled from the literature (see Fig. 1 for lithologies and Table S1 forreferences). Due to limited outcrops in the Wilkes Land area, data from proximal Holocene marine sediments are plotted instead (Hemming et al., 2007; Pierce et al., 2011; Roy et al.,2007; van de Flierdt et al., 2007). The isotopic composition of the Adélie Craton (purple) primarily plots outside of the diagram space shown (ƐNd:−20 to−28; 87Sr/86Sr: 0.750 to 0.780;Borg and DePaolo, 1994; Peucat et al., 1999). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

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were extracted (Fig. 6), implying contemporaneous eruptive events.Volcanic glass and phenocrysts from the McMurdo Volcanic Group havebeen identified in layers within existing continental ice in NorthernVictoria Land and the Transantarctic Mountains (Narcisi et al., 2012;Perchiazzi et al., 1999; Smellie et al., 2011), supplied by explosivevolcanism from the Hallet Volcanic Province and Mount MelbourneVolcanic Province. This observation suggests that some of the sedimentload of regionally calved icebergs sourced from the continental interioradjacent to Northern Victoria Land and Southern Victoria Land maycontain a volcanic glass component – this could explain the un-weathered fresh appearance of the volcanic ash grains in Site U1361sediments. An alternative source for volcanic glass could also be aeolianfallout from the Balleny Islands and/or delivery by sea-ice rafting.

5.1.3. Provenance of minor age populations of ice-rafted hornblende grainsin Pliocene U1361 sediments

Four hornblende grains from Site U1361 sediments have 40Ar/39Arages that match the proximal Adélie Craton, which has well-constrainedProterozoic metamorphic age populations at ~1700 and ~2500 Ma (DiVincenzo et al., 2007; Pierce et al., 2014; Roy et al., 2007) (Figs. 1b and5). The scarcity of such ages in our core, despite its proximity to theAdélie Craton, indicates only limited supply of coarse grained materialvia downslope processes and ice-rafting to Site U1361 during thePliocene.

A small Mesoproterozoic hornblende grain 40Ar/39Ar age popula-tion between 1000 and 1300 Ma can be seen in Pliocene sediments atSite U1361. Similar to Holocene sediments regionally (Pierce et al.,2011; Roy et al., 2007; this study; Figs. 1b and 5) and in Ross Sea se-diments (Pierce et al., 2011; Roy et al., 2007), these ages occur in minornumbers in Site U1361 sediments (6 grains in total). This age range hasno known exposed analogues in East and West Antarctica to the east ofthe Adélie Craton. It does, however, match significant populations ofProterozoic hornblende 40Ar/39Ar ages in Holocene marine sediments

offshore of the Wilkes Land margin to the west of the Adélie Craton(Cook et al., 2014; Pierce et al., 2014; Pierce et al., 2011; Roy et al.,2007) (Fig. 1b), and thermochronological ages of on land exposures inthis region (Fitzsimons, 2003; Post, 2000; Post et al., 1997; Möller et al.,2002; Sheraton et al., 1992). This tectonometamorphic age range isinferred to be related to the Grenvillian Orogeny (Boger, 2011; Dalziel,1991; Fitzsimons, 2000a, 2000b). However, a supply of icebergs to SiteU1361 from areas of the west of the Adélie Craton is unlikely, as thiswould be opposite to the wind-driven iceberg trajectories around thecontinent (Fig. 1a), which was likely unaltered under Pliocene condi-tions (DeConto et al., 2007). The possibility of a Grenvillian-aged ig-neous body, or at least crustal material with remnant Grenvillian sig-natures, located beneath the East Antarctic ice sheet to the west of theTransantarctic Mountains, has however been proposed in accordancewith the SWEAT hypothesis (South-Western US and East Antarctica)(Goodge et al., 2010; Goodge et al., 2008; Moores, 1991), as GrenvillianU-Pb zircon ages have been identified in glacial sediments in the RossSea area (Goodge et al., 2010). It is therefore possible that Mesopro-terozoic aged hornblende grains in Site U1361 may be related to acontinental interior source that is currently obscured by the ice sheet.Icebergs sourced from the Ross Sea and/or the Wilkes Subglacial Basinmay therefore have been a source for these grains.

5.1.4. Evidence for increased West Antarctic IRD in Pliocene U1361sediments during Pliocene warmth

A minor hornblende 40Ar/39Ar age population in Site U1361Pliocene sediments is constituted by Mesozoic ages of ~90 to ~125 Ma(n = 13; Fig. 5). It is an intriguing observation that these grains pri-marily occur within diatom-bearing and diatom-rich sedimentary facies4 and 5, inferred to have been deposited during intervals of warmer-than-present conditions (Cook et al., 2013). There are no known ex-posed rocks on the nearby East Antarctic continent with hornblende40Ar/39Ar ages that lie in this age range (Fig. 1b). While it is impossible

Ice-rafted hornblende (>150µm)40Ar/39Ar age populations

<50 Ma (WA, TAM/SVL, NVL)90-290 Ma (WA)330-430 Ma (WA, NVL)440-540 Ma (Ninnes glacier, TAM/SVL, NVL)>600 Ma (AL)others

Facies 4 and 5: increased smectite/illiteFacies 1 and 2:decreased smectite/illite

Combined age populations:

Diatom-rich/bearing facies 4 and 5; 11 samples,

142 grains

Clay facies 2; 3 samples,

50 grains

15

7 1718

25

21

16

1

2

7

13

17

9

24

-16

-14

-12

-10

-8

-6

-4

0.710 0.715 0.720 0.725 0.730 0.740

Nd

(<63

µm)

87Sr/87Sr (<63µm)

Fig. 10. Comparison of Nd and Sr isotope compositions of fine-grained detrital sediments (< 63 μm) and 40Ar/39Ar age populations of ice-rafted hornblende grains (> 150 μm). Fine-grained fingerprint is plotted on x and y axis, while ages of ice-rafted hornblende grains are illustrated as coloured pie charts. Black central diamonds in pie charts mark samples takenfrom clay-rich facies (i.e. colder times), and diamonds in pie charts visualise samples taken from diatom-rich/bearing facies (i.e. warmer times). Note that all analyses have beenperformed on the exact same samples. The colour legend shows age ranges based on hornblende 40Ar/39Ar analyses. Numbers in brackets are potential geographic sources for each of thedifferent age groups. Combined age populations of all samples from different environmental conditions are shown to the right and illustrate that samples from colder facies 2 and samplesfrom warmer facies 4 and 5 show similar age populations, even though the fine-grained provenance indicates distinct source areas. WA: West Antarctica; NVL: Northern Victoria Land,SVL: Southern Victoria Land, TAM: Central Transantarctic Mountains, EPG: Early Palaeozoic Granites (near Ninnis Glacier; see Fig. 1 for location); AL: Adélie Land; WSB: WilkesSubglacial Basin.

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to rule out a bedrock source hidden within the East Antarctic con-tinental interior, there is no suggestion in the literature that rocks ofthese ages could exist regionally.

Instead, the observed 90 to 125 Ma ages match very well with mi-neral grain thermochronology identified in Holocene marine sedimentsoff the West Antarctic continental margin (hornblende 40Ar/39Ar ages,95 to 127 Ma; Roy et al., 2007), and downstream of West Antarctic icestreams that flow into the Ross Sea (U-Pb zircon, 100–110 Ma; Lichtet al., 2014),> 2000 km to the east of Site U1361 (Fig. 1b). On land,this hornblende 40Ar/39Ar age population corresponds to the wide-spread occurrence of Cretaceous igneous rocks in West Antarctica(Fig. 1b), where calc-alkaline and anorogenic granodiorites and gran-ites were intruded between 95 and 125 Ma into metasedimentary andgranodioritic basement rocks (Luyendyk et al., 1996; Mukasa andDalziel, 2000; Pankhurst et al., 1998; Siddoway et al., 2005; Storeyet al., 1999; Weaver et al., 1992, 1994). Based on iceberg transportpathways in the westward flowing coastal current (Fig. 1a), and theexcellent agreement with onshore and offshore West Antarctic con-straints, this age population is likely to have been sourced from thisdistant region. Whether icebergs with these signatures were suppliedfrom the Marie Byrd Land-Southern Ocean margin, or from icebergscalved from West Antarctica directly into the southern Ross Sea (Lichtet al., 2014) is unknown, but their origin from West Antarctica seems arobust finding.

Iceberg pathways are regionally constrained to follow an anti-clockwise, westward, direction around the East Antarctic continent(Fig. 1a). Large modern tabular icebergs sourced from ice shelves havelifetimes of several years, as observed from satellites (e.g. Tournadreet al., 2015). For paleo-reconstructions, it is important to consider thatsea surface temperatures of ocean waters near the Antarctic continentduring the Pliocene were warmer than today (Cook et al., 2014). Pa-laeothermometry indicators (TEX86: McKay et al., 2012) suggest sea-sonal temperatures up to 6 °C warmer than today during interglacialsand prolonged Pliocene warm intervals in the Ross Sea area. Similarlywarm temperatures have been identified in Pliocene sediments fromother locations around Antarctica (Bart and Iwai, 2012; Escutia et al.,2009; Whitehead and Bohaty, 2003; Whitehead et al., 2005). Based oniceberg survivability modelling in the Southern Ocean, the distanceicebergs could travel before melting during warm Pliocene intervalswas likely significantly reduced (Cook et al., 2014), suggesting that aconsiderable amount of icebergs must have been produced from theWest Antarctic ice sheet in order to travel over 2000 km to reach SiteU1361. Additionally, sediments deposited in the Ross Sea have shownthat the Ross Ice Shelf retreated repeatedly during the Pliocene (Naishet al., 2009), likely in response to warm Pliocene conditions. Wetherefore propose that increased supply of West Antarctic IRD to SiteU1361 was related to changes in ice sheet volume during particularlywarm Pliocene intervals. This suggestion is in line with Pliocene IRDdepositional patterns at the site (Patterson et al., 2014) and AND-1Bresults from the Ross Sea (Naish et al., 2009), indicating orbitally-modulated retreat of the WAIS during Pliocene interglacials. However,higher resolution sampling of all facies in Site U1361 sediments, as wellas improved statistical confidence in grain counts, would be required tosubstantiate this tentative interpretation.

5.2. Fine-grained sediment sources

To summarise above discussion, 40Ar/39Ar ages on ice-rafted horn-blende grains from Pliocene sediments at IODP Site U1361 show pre-dominant erosion from two major lithologies: (proximal) Ross Orogeny-aged, Palaeozoic granitoids (~500 Ma), probably from around theNinnes Glacier and Southern Victoria Land, and more distal CenozoicMcMurdo volcanics (< 44 Ma) (Fig. 1a). The following section willexplore the provenance of the< 63 μm fraction of the same marinesediments. Clay mineralogy indicates crystalline and volcanic sourceareas, potentially contributing at different proportions during different

climatic regimes, and radiogenic isotope compositions corroborate thisfinding. Proximal Palaeozoic granitoids can be inferred as an end-member for the fine-grained Nd and Sr isotope provenance signatureduring colder times. An additional endmember, or a mixture of sources,is required to explain the fine-grained provenance signature at SiteU1361 during warmer times, and likely involves Jurassic FLIP basaltsand dolerites, and Devonian to Jurassic siliciclastic deposits of theBeacon Supergroup.

5.2.1. Clay mineral provenanceIllite is the most common clay mineral in high latitude marine se-

diments derived from physical weathering of plutonic and metamorphicrocks (e.g. Biscaye, 1965) and is also the most abundant clay mineral inPliocene sediment from Site U1361, particularly in those from facies 1,2 and 3 (i.e. colder times during the Pliocene). Illites from Quaternary-and Pliocene-aged channel levee sediments nearby to Site U1361 havegeochemical compositions that suggest sourcing from Early Palaeozoicgranitoids found in the hinterland of the Ninnis Glacier (Fig. 1a) (be-tween 64°17′S 143°22′E and 64°57′S 144°23′E: Damiani et al., 2006;Talarico and Kleinschmidt, 2003; Site U1359: Verma et al., 2014).Smectite is the second most abundant clay mineral in Pliocene marinesediments at Site U1361and is typically interpreted as a weatheringproduct of basic volcanic rocks (e.g. Biscaye, 1965). Smectite abun-dances seem elevated in sediments from facies 4 and 5 (i.e. warmertimes during the Pliocene). In detail, the two regional lithologies thatare likely to produce smectites are the Cenozoic McMurdo VolcanicGroup and the Jurassic volcanic terranes of the basaltic and doleriticFLIP rocks, which intruded ~180 Ma into the siliciclastic deposits ofthe Beacon Supergroup (Damiani et al., 2006; Verma et al., 2014)(Fig. 1a). Basalts of the FLIP group have been identified as a source ofdetrital smectite in the Ross Sea (Claridge and Campbell, 1989). On theother hand, smectite associated with the McMurdo Volcanic Group ismainly authigenic in origin in the Ross Sea (Setti et al., 2000), andderived from submarine weathering and hydrothermal alteration ofvolcanic material (Petschick et al., 1996; Setti et al., 2000). Despite thepresence of volcanic ash in Site U1361 sediments, smectites in marinesediments nearby to Site U1361 have been suggested to be detrital inorigin (Damiani et al., 2006). Hence, we rule out the McMurdo VolcanicGroup as a significant source of smectite and suggest that detritalsmectite was instead supplied by FLIP terranes, which are exposed inbroad areas of the Transantarctic Mountains (Elliot and Fleming, 2008)and inferred to occupy large areas underneath the ice in the WilkesSubglacial Basin (Ferraccioli et al., 2009; Jordan et al., 2013; Studingeret al., 2004; Fig. 1a). A strong negative correlation between the abun-dance of smectite and illites in Site U1361 sediments, combined withpositive correlations between smectite/illite and Nd isotope composi-tions (Fig. 8; see also next section), suggests that provenance is animportant control on smectite and illite contents.

Kaolinite and chlorite are less abundant in Pliocene Site 1361 se-diments. A possible continental source of kaolinite is the sedimentarysequence of the Beacon Supergroup (Barrett, 1981; Piper and Brisco,1975; Fig. 1). These volcanoclastic to quartzo-feldspathic sediments canbe observed in many outcrops in the Transantarctic Mountains in as-sociation with FLIP lithologies (e.g. Barrett et al., 1986). The mostproximal known outcrops of Beacon Supergroup sediments to SiteU1361 lie at the mouth of the Wilkes Subglacial Basin (Bushnell andCraddock, 1970). However, as indicated above, the association of FLIPand Beacon lithologies probaly comprises a large part of the infill of theWilkes Subglacial basin (Ferraccioli et al., 2009). If the Beacon Super-group was the main source of kaolinite in Site U1361 sediments, itsabundance might be expected to correlate with smectite (and Nd iso-tope compositions), due to the inferred close association between FLIPand Beacon Supergroup lithologies. No such trend is observed, and wehence consider it more likely for the kaolinite to be supplied fromweathering of granitic sources, such as the abundant Palaeozoic gran-ites in the area (Fig. 1a).

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5.2.2. Neodymium and strontium isotope provenanceThe Nd and Sr isotope compositions of fine-grained (< 63 μm) Site

U1361 detrital sediments are negatively correlated (ƐNd: −6.9 to−13.2; 87Sr/86Sr: 0.717 to 0.729; Fig. 9) and fall into two distinctgroups. Cook et al. (2013) found that clay-rich sediments of facies 1 to 3Pliocene sediments, deposited during cooler climatic intervals, werecharacterised by Nd isotope values of −11.2 to −13.2 and 87Sr/86Srisotope ratios of 0.723 to 0.730 (Fig. 9). They interpreted this signatureto be associated with erosion of Palaeozoic granitoids (ƐNd: −11.2 and−19.8; 87Sr/86Sr: 0.714 to 0.753; Fig. 1a for exposures, Fig. 9, seeTable S1 for references). The most proximal outcrops of such rocks toSite U1361 are located in the vicinity of the nearby Ninnis Glacier(Fig. 1a). Supply from this area is in accordance with modern deposi-tional patterns (Busetti et al., 2003; Donda et al., 2003; Escutia et al.,2003, Escutia et al., 2000) as well as with core-top sediment resultsfrom the area (Cook et al., 2013; Pierce et al., 2014, Pierce et al., 2011).

Conversely, diatom-rich/bearing sediments of facies 4 and 5, de-posited during warmer intervals, are characterised by ƐNd values of−6.9 to −9.9 and 87Sr/86Sr ratios of 0.716 to 0.728 (Figs. 3 and 9).This signature requires input from a source lithology with a moreradiogenic Nd isotope fingerprint. We previously suggested (Cook et al.,2013) that the FLIP rocks make a good candidate for this endmember(ƐNd: −3.5 and −6.9; 87Sr/86Sr: 0.709 to 0.719; Fig. 9, see Table S1 forreferences). Ferrar dolerites were intruded as sills and dikes into De-vonian to early Jurassic sediments of the Beacon Supergroup and showsimilar ages (~180 Ma) to extrusive basalts of the FLIP formation (e.g.Barrett, 1991; Elliot and Fleming, 2008). Furthermore, wherever ex-posed, FLIP and Beacon lithologies are closely associated (Fig. 1a).Detrital zircon analyses from the Beacon Supergroup in the Transan-tarctic Mountains and Northern Victoria Land yield a broad age spec-trum, reflecting deposition in a transantarctic sedimentary basin at thePanthalassan margin of Gondwana, situated between Precambriancratonic terranes to the east and contemporaneous magmatic arc se-quences to the west (~190–270 Ma: Early Triassic to early Jurassicmagmatic arc; ~470–545 Ma: Ross Orogeny granitoids; ~500–700 Ma:Pan-African Orogeny granitoids; ~800–1200 Ma: Grenville agedcrustal material; Elliot and Fanning, 2008; Elsner et al., 2013; Goodgeand Fanning, 2010). The range of source lithologies and ages containedin the siliciclastic sediments of the Beacon Supergroup predicts a ratherlarge range in radiogenic isotope compositions. To our knowledge thereare no published results on the Nd isotope composition of Beacon se-diments. Estimates can however be based on analyses of< 5 μm frac-tions of four dune samples with Beacon sandstone parent lithologiesfrom the Dry Valleys (Transantarctic Mountains), and one Beacon re-golith sample from Northern Victoria Land (Delmonte et al., 2010,2013). The range of εNd values and Sr isotopic compositions in thesesamples (εNd = −5.6 to −8.1; 87Sr/86Sr = 0.7121 to 0.7182) overlapswith the field shown for FLIP lithologies in Fig. 9. In contrary, Farmerand Licht (2016) estimated mixed Ferrar and Beacon compositionsbased on the< 63 mm fraction of glacial tills from the Byrd andNimrod Glaciers in the central Transantarctic Mountains to be moreunradiogenic in Nd isotopes (εNd = −8.5 to −15.0) and more radio-genic in Sr isotopes (0.714–0.723), suggesting that at least some of theBeacon Supergroup must be characterised by εNd values as low as −15.

Future work on Beacon Supergroup samples will have to show,which of these estimates is more applicable for provenance inter-pretations at Site U1361. We can however conclude that a mixture ofFLIP and Beacon rocks constitutes a viable endmember for eroded se-diments during warm Pliocene intervals, and that such lithologies likelycomprise a considerable component of the sedimentary infill of theWilkes Subglacial Basin (Ferraccioli et al., 2009; Jordan et al., 2013;Studinger et al., 2004; Fig. 1a), which would be more accessible duringwarmer times in the Pliocene due to a retreated ice margin (Cook et al.,2013).

5.3. Fine-grained versus coarse-grained sediment provenance

Pliocene fine-grained sediments at Site U1361 were predominantlysupplied from Early Palaeozoic granites in the nearby continentalmargin, and from sources within the Wilkes Subglacial Basin, as con-strained by both Nd-Sr isotopes and clay mineralogy. Coarse-grainedhornblende grains support an erosional source from local granites ex-posed on the proximal coast, but indicate in addition IRD supply frommultiple sources to the east, including Northern Victoria Land and WestAntarctica. In other words, there is no straight forward correlation ofprovenance from coarse and fine grained sediments as illustrated inFig. 10. Notably, ice-rafted hornblende grains extracted from Pliocenesediments at Site U1361 lack any indication of erosion of FLIP lithol-ogies with typical emplacement ages around ~180 Ma (Duncan et al.,1997; Foland et al., 1993; Heimann et al., 1994; Minor and Mukasa,1997) (Figs. 5 and 10).

The Pliocene was a time of significant volumetric changes in theEAIS as indicated by IRD depositional patterns (Patterson et al., 2014)and marine sediment provenance changes (Cook et al., 2013) at SiteU1361. It is likely that such dynamic ice sheet behaviour resulted inincreased iceberg production from the Wilkes Subglacial Basin. Wepropose that the main differences between the provenance patterns offine-grained sediments and coarse-grained ice-rafted hornblende grainsfrom Site U1361 can be ascribed to delivery processes, and source rockcharacteristics. Sources within the Wilkes Subglacial Basin have lowhornblende concentrations (Hauptvogel and Passchier, 2012). Ad-ditionally, existing grains may be subject to comminution and henceleave a fingerprint in the fine size fraction only.

5.3.1. Ice rafting versus down-slope sedimentationThe apparent disparity between the provenance of fine-grained se-

diments and coarse (ice-rafted) hornblende grains used in this studycould be a product of variance in their delivery methods from source tosink (Fig. 2; see also Diekmann and Kuhn, 1999). Although it is ex-tremely difficult to reconstruct the dynamics of the glacial processesthat initially resulted in the on land erosion of sediments supplied toSite U1361 during the Pliocene, we can nevertheless gain some insightsfrom considering modern processes and observations in the area.Today, detrital fine-grained sediments are supplied to Site U1361 bymeltwater plumes and/or turbidity currents, which transport shelf se-diments, initially derived from Early Palaeozoic bedrock in the coastalhinterland (Pierce et al., 2011, 2014; Cook et al., 2013) downslope insubmarine channels orientated perpendicular to the coast (Busetti et al.,2003; Donda et al., 2003; Escutia et al., 2003, Escutia et al., 2000;Patterson et al., 2014). Site U1361 is located on the apex of a levee ofone of these channels, with sediments deposited as non-erosional over-spills (Escutia et al., 2011; Patterson et al., 2014). Therefore, bothcoarse- and fine-grained sediments could be delivered to our site fromthe shelf via downslope processes, a scenario that would explain thepresence of Early Palaeozoic hornblende grains, granite clasts, Nd-Srisotope signatures suggestive of this endmember, and increased supplyof illites from Early Palaeozoic granites in facies 1, 2 and 3.

However, provenance constraints on facies 4 and 5, based on Nd-Srisotope data and increased smectite contents, imply fine-grained sedi-ments were additionally supplied to the site from within the WilkesSubglacial Basin during periods of ice sheet retreat, including a com-ponent of mafic FLIP lithologies (Cook et al., 2013; this study). Onerouting mechanism for the delivery of this material is via meltwater-plume driven turbidity currents, which may have re-distributed mate-rial deposited initially on the shelf at the mouth of the basin, to the eastof Site U1361. Gravity-density currents like turbidites are commonalong glaciated margins (Dowdeswell et al., 1998; Hesse et al., 1997;Piper et al., 2007), and have been used as a proxy for past meltwaterevents associated with ice sheet deglaciation in the North Atlantic (e.g.Piper et al., 2007; Rashid et al., 2012). Subsequent westward deflectionof these sediments injected into the Southern Ocean by surface (Fig. 1a)

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and bottom currents (Orsi et al., 1999) could carry clay and silt-sizeddetrital material towards Site U1361, but discriminate against coarse-grained material from the Wilkes Subglacial Basin. Instead, FLIP andBeacon Supergroup-derived lithic clasts and mineral grains, as well ascoarse-grained hornblendes from sites to the east such as Victoria Landand the Ross Sea, must have been delivered to Site U1361 by ice-rafting. Despite fine-grained sediments likely comprising some of thisdistally sourced ice-rafted load, it appears that amounts are too minorto dilute the signatures of locally supplied fine-grained sediments. Acorresponding decrease in the supply of more proximal Early Palaeo-zoic granitic derived sediments could be explained by contemporaneousreduction in supply of sediments to the shelf edge, perhaps associatedwith a regionally reduced ice sheet margin (Cook et al., 2013). How-ever, this does not fully explain the absence of a 40Ar/39Ar age popu-lations indicating FLIP origin in hornblende grains.

5.3.2. Potential FLIP and Beacon Supergroup source rock biasThe FLIP is composed of dolerites and basalts (Elliot and Fleming,

2008), with heavy minerals dominated by Mg-rich clinopyroxenes andorthopyroxenes (Demarchi et al., 2001; Hauptvogel and Passchier,2012), a mineralogical feature common to rift-type volcanism (Nechaevand Isphording, 1993). The petrography of ice-rafted clasts and mineralgrains in coarse-grained fractions of Site U1361 sediments reveals sig-nificant quantities of clinopyroxenes and orthopyroxenes (up to 4.3% oftotal detrital fraction> 150 μm, Table 1), suggesting that the FLIP wasa viable source of ice-rafted material. This interpretation is validated bythe presence of clasts of basalt in the same Pliocene sediments. Fur-thermore, on land the FLIP is intimately associated with the BeaconSupergroup (Elliot and Fleming, 2008; Fig. 1a). Beacon Supergrouplithologies are dominated by quartzites, sandstones and siltstones andcontain very few heavy minerals (Hauptvogel and Passchier, 2012).Their erosion is suggested by abundant clasts of quartzite in Site U1361sediments (Table 1). Whether the ice-rafted FLIP and Beacon Super-group mineral grains and lithic clasts were sourced from terranes in theWilkes Subglacial Basin, or from terranes in the Transantarctic Moun-tains, where they are commonly exposed (Fig. 1a), is difficult to con-strain. What stands is the observation that FLIP lithologies are notcaptured by hornblende 40Ar/39Ar age populations. This observation isbest explained by a source rock bias in the marine sediment record.Hornblende grains have been shown to be comparatively rare in heavymineral assemblages derived from sediment sources dominated by FLIPterranes (Hauptvogel and Passchier, 2012) and are unlikely to havesurvived the multiple sedimentary cycles documented by zircon ages inBeacon lithologies (Elliot and Fanning, 2008; Elsner et al., 2013;Goodge and Fanning, 2010; see also discussion in Pierce et al., 2014).Another possible explanation is that erosion of FLIP lithologies fromwithin the Wilkes Subglacial basin was mainly happening subglaciallyand hence subject to comminution. Support for the latter idea, and theexistence of a FLIP component in the fine-grained fraction of sedimentsoffshore the Wilkes Subglacial basin, comes from K-Ar analyses at SiteU1356, located to the west of site U1361. Johnson et al. (2012) found astrong correlation between the Nd isotope composition and K-Ar ages infine-grained (< 63 μm) Miocene sediments, extending from Palaeozoicages to ages as young as the Jurassic intrusion ages of the FLIP(~180 Ma).

Hence we conclude that variable mineralogical compositions andgrain sizes in different bedrock types have produced the different pro-venance signatures extracted from the Pliocene marine sediment as-semblage at Site U1361. This interpretation could be tested with futureanalysis of 40Ar/39Ar ages of detrital plagioclase and basalt clastsidentified in Site U1361 sediments, similar to existing thermo-chronological analyses of whole rock basalts and mineral grains fromFLIP bedrock (Duncan et al., 1997; Fleming et al., 1997; Foland et al.,1993; Heimann et al., 1994). Investigation of the possibility of sedimentrecycling within the Beacon Supergroup and unconsolidated sedimentswithin the Wilkes Subglacial Basin could also be feasible via analysis of

U-Pb ages of detrital zircons, as well as zircons extracted from ice-raftedquartzite/sandstone clasts in Site U1361 sediments.

6. Conclusions

In this study we compared the provenance signatures of fine-grainedand coarse-grained detrital components in Pliocene sediments fromIODP Site U1361, Wilkes Land, using clay minerals (< 2 μm), Nd andSr isotopes (< 63 μm), hornblende grain 40Ar/39Ar ages (> 150 μm),and mineral grain (> 150 μm) and lithic clast (> 2 mm) petrography.Fine-grained signatures extend published provenance interpretations(Cook et al., 2013), whereby bedrock sources within the Wilkes Sub-glacial Basin (FLIP and Beacon Supergroup) and local Early Palaeozoicterranes supplied fine-grained sediments to Site U1361 throughout thePliocene. Petrographic analyses of ice-rafted lithic clasts reveal that theFLIP and Beacon Supergroup lithologies were likely significant bedrocksources for ice-rafted debris as well. Low amphibole contents withinFLIP and Beacon bedrocks and/or comminution of such grains, how-ever, prevents us from tracing these particular lithologies by ice-raftedhornblende 40Ar/39Ar ages. On the other hand, ice-rafted hornblende40Ar/39Ar ages reveal multiple erosional source areas along the con-tinental margins of East Antarctica, potentially even extending east-wards towards Marie Byrd Land (West Antarctica). West Antarcticprovenance of ice-rafted debris off the East Antarctic Wilkes SubglacialBasin occurred during warmer intervals, hinting at large-scale icebergproduction events from the West Antarctic Ice Sheet.

Our study highlights the power of combining multiple provenancetools within different grain-size fractions when studying marine sedi-ments derived from a glaciated continent. Single provenance tools areless likely to capture the full spectrum of bedrock characteristics, in-formation vital for more accurate reconstructions of past ice sheethistories.

Acknowledgments

C.P. Cook thanks the Grantham Institute for Climate Change atImperial College London for a PhD scholarship, K. Kreissig and B. Colesfor lab assistance, P. Simões Pereira and R. Bertram for discussion, andIODP for providing materials. Ian Bailey and an anonymous reviewerprovided very insightful comments that helped improve the manuscripta lot. Financial support for this study was provided by NERC UK IODPto T.v.d.F. (NE/H014144/1, NE/H025162/1), by the EuropeanCommission to T.v.d.F. (IRG 230828), by the National ScienceFoundation to T.W., T.v.d.F. and S.R.H. (ANT 0944489 and ANT1342213), and by the Royal Society to T.v.d.F. and S.R.H. (IE110878).

Appendix A. Supplementary data

Supplementary data to this article can be found online at http://dx.doi.org/10.1016/j.chemgeo.2017.06.011.

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