Chemical Geology 466 (2017) 199–218

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Chemical Geology

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Glacial erosion of East Antarctica in the Pliocene: A comparative study of MARK multiple 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, UK b Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, UK c Department of Earth and Environmental Sciences and Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964, USA d Lamont-Doherty Earth Observatory, Palisades, NY 10964, USA e Instituto Andaluz de Ciencias de la Tierra, CSIC-UGR, 18100 Armilla, Spain

ARTICLE INFO ABSTRACT

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

1. Introduction In the Southern Ocean, a number of studies have made composi- tional links between Holocene glaciomarine sediments surrounding the The ‘provenance’ of a detrital marine sediment assemblage describes its Antarctic continent, and distinct continental margin bedrock sources as components' derivation from erosion of their continental source rocks to constrained by sparse outcrops (Brachfeld et al., 2007; Cook et al., their subsequent burial at the ocean floor. Studying marine sediment pro- 2014, 2013; Farmer et al., 2006; Flowerdew et al., 2013, Flowerdew venance patterns has been recognised as a valuable approach in paleocli- et al., 2012; Hemming et al., 2007; Licht and Palmer, 2013; Licht et al., mate studies as they can provide information on a wide range of environ- 2014, Licht et al., 2005; Pierce et al., 2014, Pierce et al., 2011; Roy mental processes, such as atmospheric and ocean circulation patterns, et al., 2007; van de Flierdt et al., 2007; see also Farmer and Licht weathering style, changes in riverine discharge, ice sheet histories, and (2016), Palmer et al. (2012), and Welke et al. (2016) for work on nu- tectonics and crustal evolution on longer time scales (e.g., Goldstein and natak moraines, and review by Licht and Hemming (2017)). Extensive Hemming, 2003; Grousset and Biscaye, 2005; McLennan and Taylor, 1991). surveying work of this type can be coupled with results of airborne

⁎ Corresponding author. E-mail address: tina.vandefl[email protected] (T. van de Flierdt). 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. http://dx.doi.org/10.1016/j.chemgeo.2017.06.011 Received 8 January 2017; Received in revised form 18 May 2017; Accepted 6 June 2017 Available online 08 June 2017 0009-2541/ © 2017 Elsevier B.V. All rights reserved. C.P. Cook et al. Chemical Geology 466 (2017) 199–218 geophysical surveys (e.g. Aitken et al., 2014; Ferraccioli et al., 2009; components, in order to better identify the roles played by source rock Studinger et al., 2004) and tectonic reconstructions of conjugate mar- characteristics and depositional processes on controlling their delivery gins (e.g. Aitken et al., 2014; Collins and Pisarevsky, 2005; Fitzsimons, from source to sink. In detail, we used five different and widely used 2000a, 2000b, 2003; Harley et al., 2013; Li et al., 2008) to extend in- provenance approaches: (i), fine-grained (< 63 μm) detrital radiogenic ferred sub-ice geology inland of the continental margin. This informa- Sr isotopes (87Sr/86Sr), (ii) fine-grained (< 63 μm) detrital Nd isotopes tion in turn permits for reconstructions of buried landscapes (Cox et al., (expressed as ƐNd, which describes the deviation of a measured 2010; van de Flierdt et al., 2008), variations in glacial erosional pat- 143Nd/144Nd ratio from the Chondritic Uniform Reservoir in parts per terns (Thomson et al., 2013; Tochilin et al., 2012), and the locations of 10,000; Jacobsen and Wasserburg (1980)); (iii) fine-grained (< 2 μm) dynamic ice sheet behaviour in the past (e.g. Cook et al., 2014, 2013; clay mineralogy; (iv) sand-sized (> 150 μm, ice-rafted) hornblende Williams et al., 2010). grain 40Ar/39Ar ages, and (v) petrographic characterisation of ice-rafted However, a factor in sediment provenance studies that needs careful mineral grains (> 150 μm) and clasts (> 2 mm). Our results allow a consideration is the selection of appropriate tools, particularly when refined interpretation of the glacial history of an important sector of the studying a glaciated continent where a priori knowledge of the geolo- East Antarctic ice sheet. gical characteristics of hidden bedrock sources is limited. Additionally, multiple physical processes can act to modify a source rock signature in 1.2. Provenance tools derived sediments. To obtain a more holistic view of sediment sources and their implications for ice sheet dynamics, we use multiple prove- The long-lived radioactive decay systems of rubidium-strontium nance approaches on sediments drilled at Integrated Ocean Drilling (Rb-Sr) and samarium-neodymium (Sm-Nd) are widely used and very Program (IODP) Site U1361 (64°24′S, 143°53′E), located off the gla- useful tracers of fine-grained marine sediment provenance signatures ciated Adélie Land coast, East Antarctica (Fig. 1), and compare and (e.g. Bareille et al., 1994; Basak and Martin, 2013; Colville et al., 2011; contrast their strength and weaknesses. Cook et al., 2013; Dasch, 1969; Farmer et al., 2006; Jantschik and Grousset et al., 1998, 1988; Hemming et al., 2007, Hemming et al., 1.1. Controls on glaciomarine sediment provenance 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 can The complexities of studying sediment provenance patterns offshore therefore be used to trace supply from continental source areas (Taylor of a glaciated continent are illustrated in Fig. 2. For example, miner- and McLennan, 1995). The parent-daughter pairs Rb-Sr and Sm-Nd are alogical compositions, petrogenetic histories and grain-size character- fractionated during melting of mantle material, creating continental istics of different bedrock types, along with erosional patterns, play an crust reservoirs with high Rb/Sr ratios and low Sm/Nd ratios. Hence, important role in determining which detrital provenance tool may be bedrocks of different ages and lithologies can have characteristic Nd best suited to identify a specific on-land source terrane within a marine and Sr isotopic compositions. This approach has been used very suc- sediment assemblage (e.g., Taylor and McLennan, 1985). In addition, cessfully in glaciomarine sediments to reveal the provenance of fine- some mineral grains are more resistant to weathering than others (e.g. grained and bulk components, as it provides an integrated signal of all zircons [more resistant] vs. hornblendes [less resistant]; Kowalewski bedrock sources eroded within a glaciated catchment area (e.g. Farmer and Rimstidt, 2003), resulting in their preferential survival through et al., 2006; Colville et al., 2011; Cook et al., 2013; Hemming et al., numerous tectonic recycling events (e.g. Goodge and Fanning, 2010). 2007; Roy et al., 2007; Taylor and McLennan, 1995). Changes in the Sedimentary substrates are more likely to be physically eroded than depositional output of a glaciated terrane as recorded by changing Nd crystalline bedrock, and indeed ice streams often overlie subglacial and Sr isotopic signatures of glaciomarine sediments has been used to basins infilled with unconsolidated sediments (e.g. Studinger et al., indicate periods of major ice sheet change in both Antarctica (e.g. Cook 2001) suggesting their detrital outputs should contain a large compo- et al., 2013), and on continents surrounding the North Atlantic (e.g. nent of recycled sedimentary material. Rock texture also plays an im- Colville et al., 2011; Hemming et al., 1998). portant role, as finer-grained rock types such as shale are likely to be Clay minerals have traditionally been the most commonly used fine- under-represented in coarse-grained fractions of marine sediments. On grained marine sediment provenance tool in the Southern Ocean (e.g. the other hand, mineral grains from coarse-grained source rocks such as Diekmann and Kuhn, 1999; Ehrmann and Mackensen, 1992; Ehrmann plutonic rocks and high-grade metamorphic rocks will be represented in et al., 1992; Ehrmann et al., 1991; Hillenbrand et al., 2009; Petschick coarser fractions, but can also be found in glacial flour as a result of et al., 1996), and are a product of both the continental bedrock sources comminution. Additionally, subglacial erosional processes by melt- of detrital material, and the intensity of chemical weathering of those water and ice can integrate a diverse range of bedrock types over a sources (Biscaye, 1965; Robert and Kennett, 1994). A significant change large area. An excellent review on glacigenic sediment provenance has from smectite to illite dominated marine sediment facies around Ant- recently been provided by Licht and Hemming (2017). arctica marks glacial initiation in Antarctica (Ehrmann and Mackensen, Furthermore, different marine transport and depositional processes 1992; Robert and Kennett, 1994) caused by a large-scale change to have the potential to integrate marine sediments supplied from multiple pronounced physical weathering on the Antarctic continent. sources, and alter the distribution of different size fractions in the Although all grain sizes are represented in glaciomarine sediments, marine environment. For example, finer-grained detrital material can the only process that can deliver coarse-grained material to the deep be delivered to the deep ocean by turbidites, meltwater plumes and ocean beyond turbidite aprons and volcanic eruptions is rafting. Finer- contourites, surface and deep ocean currents, wind, iceberg and sea-ice grained material is likely to comprise a considerable proportion of an rafting. In contrast, beyond turbidite aprons, sand-sized and larger iceberg's sediment load (e.g. Ruddiman, 1977) but these size fractions detrital material can only be delivered to the deep ocean floor by ice- can be transported by a variety of processes. Therefore, coarse-sized rafting (both icebergs and sea-ice) and volcanic eruptions. Therefore, lithic material and mineral grains are best used to estimate sedi- studying one component of a particular glaciomarine sediment size- mentation from ice-rafting in distal locations. Mineral thermo- fraction may not fully capture the representative provenance signature chronometers applied to sand-sized grains (e.g. U-Pb ages of zircon, of that sediment's original source on land. Likewise fine grained sedi- garnet, rutile, monazite and sphere grains, 40Ar/39Ar ages of mica, ment may reflect multiple delivery mechanisms and thus a different feldspar, and amphibole grains) record information that can be used to aspect of the sedimentary provenance in addition to glacial processes. infer the magmatic and tectonothermal history of their original host We here present and discuss observations and interpretations of an rocks (e.g. Hodges et al., 2005; Reiners and Brandon, 2006). The tem- apparent inconsistency in the sediment sources at Site U1361. We perature at which a system such as a mineral grain becomes closed to present new data on a diverse range of tools from multiple sediment diffusive processes is its ‘closure’,or‘blocking’ temperature. 40Ar/39Ar

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

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 the continental 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 (offshore black 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 with direction 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; Pierce et 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 provenance sectors: 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 (east of 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 drainage catchments. NG: Ninnis Glacier, MG: Mertz Glacier, MSZ: Mertz Shear Zone. ages in hornblende grains reflect crystallisation and/or closure tem- Fanning, 2010; Hemming et al., 2007; Pant et al., 2013; Pierce et al., perature of ~500 °C (McDougall and Harrison, 1999), thus 40Ar/39Ar 2014, Pierce et al., 2011; Orejola and Passchier, 2014; Roy et al., 2007) hornblende grain ages record the timing of the last major tecto- demonstrate that the East Antarctic continent nearby to Site U1361 is nothermal event experienced by their host rock for fingerprinting ice- geologically heterogeneous and contains sedimentary, metamorphic rafted material sourced from continental terranes with complex tec- and extrusive and intrusive igneous rocks with ages spanning much of tono-metamorphic histories (e.g. Cook et al., 2014; Gwiazda et al., the last 3 billion years. Hence Site U1361 can receive sediments sup- 1996; Hemming et al., 2000; Hemming et al., 1998; Knutz et al., 2013; plied from a diverse range of rocks with a range of ages and lithologies. Peck et al., 2007; Pierce et al., 2014; Pierce et al., 2011; Roy et al., Here we focus on a well-defined Pliocene section (Escutia et al., 2007; Williams et al., 2010). While detrital zircons are a commonly 2011; Cook et al., 2013) between 45 and 125 mbsf (Fig. 3). Within this used circum-Antarctic sediment provenance tool (e.g. Fitzsimons, interval, five lithostratographic facies are identified: facies 1 (clays), 2000a, 2000b; Goodge and Fanning, 2010; Pierce et al., 2014; Veevers facies 2 (clays with dispersed clasts) and facies 3 (silty clays with dis- and Saeed, 2011), hornblendes were selected for this study. In addition, persed clasts) are dominated by terrigenous material and represent petrographic and lithological characterisation of ice-rafted mineral colder times during the Pliocene. Facies 4 (diatom-bearing silty clays) grains and lithic grains can provide information on source rocks and and facies 5 (diatom-rich silty clays) on the other hand contain more provenance of coarse-grained fractions (Anderson et al., 1992; Andrews significant biogenic opal components and were deposited during et al., 1995; Bond et al., 1992; Elverhøi et al., 1995; Licht et al., 2005; warmer intervals. Cook et al. (2013) investigated the provenance of Talarico et al., 2012; Thierens et al., 2012). fine-grained (< 63 μm) detrital sediments from Site U1361 between 75 and 125 mbsf using Nd and Sr isotopes and clay minerals, and found that diatom-poor sediments are characterised by distinct provenance 2. Study site and provenance background 87 86 signatures (ƐNd: −11.1 to −14.5; Sr/ Sr: 0.719 to 0.738; illite-rich) compared to diatom-rich sediments (Ɛ : −5.9 to −9.5; 87Sr/86Sr: IODP Site U1361 was drilled in 3466 m water depth, approximately Nd 0.712 to 0.719; smectite-rich). 315 km offshore of Adélie Land, East Antarctica, during Expedition 318 Here we supplement these existing data by extending the Nd and Sr (Escutia et al., 2011). Approximately 388 m of sediment were recovered isotope and clay mineral record up section to 47.25 mbsf (i.e. Late in total, and a chronology was compiled using palaeomagnetic in- Pliocene). To further investigate the provenance data presented by clination data and biostratigraphy (diatom and radiolarian datums) Cook et al. (2013), we present new ice-rafted mineral grain and clast (Escutia et al., 2011; Tauxe et al., 2012)(Fig. 3). Published onshore information, and the first ice-rafted hornblende grain 40Ar/39Ar age constraints (Fig. 1; Table S1) and existing marine sediment provenance data for this site. studies in the area (Cook et al., 2013; Domack, 1982; Goodge and

Onland Processes chemical and physical weathering; Marine Environment ice and meltwater drainage; ice-rafting; delivery and redistribution basal entrainment; supra-glacial via turbidity, contourite and bottom and aeolian deposition currents; meltwater plumes; aeolian deposition

East Antarctic volcanic/aeolian dust Ice Sheet material

Iceberg Sea ice

East Antarctic ice-rafted debris continent glacial sediments continental shelf continental SOURCE slope sea floor SINK turbidity and contourite currents/meltwater plume Source Rock Properties Syn- and Post- mineralogy; age; texture; grain depositional Processes size; susceptibility to authigenic precipitation; erosion/weathering diagenesis

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

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

Polarity Clast Count ε Inclination (clasts/10cm) Nd -100 100 05 -16 -12 -8 -4 2.6 45 2.7

50 2.8 6H 2.9 55 3.0 57.70 mbsf; n = 25 60 3.1 7H 62.27 mbsf; n = 24 3.2 65 65.69 mbsf; n = 17 3.3

3.4 70 8H 3.5

75 76.07 mbsf; n = 16 76.27 mbsf; n = 21 3.6 77.77 mbsf; n = 18 80 9H 3.7 3.8 Age (Ma) 85 3.9

4 10H Depth (mbsf) 90 92.07 mbsf; n = 17 4.1 92.95 mbsf; n = 1 94.03 mbsf; n = 7 95 4.2

4.3 100 11H 100.77 mbsf; n = 2 4.4

103.78 mbsf; n = 13 105 4.5

4.6 12H

110 Depth (mbsf) 109.76 mbsf; n = 9 4.7

4.8 115 115.47 mbsf; n=15 4.9 13H 120 5 Avg. facies1 to 3: ε Avg. facies Nd = -12.6 ε 5.1 125 4 & 5: Nd = -8.4 Facies 1: clay Facies 4: diatom-bearing silty clay Facies 2: clay with dispersed clasts Facies 5: diatom-rich silty clay Facies 3: silty clay with dispersed clasts

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 chron boundaries (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 clast counts (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 by arrows 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 4 and 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, the reader is referred to the web version of this article.)

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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 > 2 mm sediment fraction.

Sample Depth Grain count Quartz (%) Feldspar (%) Pyroxene (%) Garnet (%) Biotite (%) Magnetite (%) Hornblende (%) Glauconite Clasts (mbsf) (> 2 mm/g) (%) (> 2 mm)

Facies 1 8H 4W 117–119 cm 71.68 1.8 92.4 6.5 1.1 1 sand-stone, 1 siltstone

Facies 2 7H 7W 13–15 cm 65.65 0.8 83.3 6.3 6.3 2.1 2.1 2 siltstone 9H 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 4 7H 1W 120–122 cm 57.7 0.5 93.5 1.1 2.2 2.2 1.1 1 siltstone, 1 basalt 7H 1W 122–124 cm 57.72 2.1 91.9 3 1 4 1 schist, 2 siltstone, 1 sand-stone, 1 basalt

Facies 5 1H 1W 3–5 cm 0.03 1.4 86.5 2.7 2.7 5.4 2.7 7H 4W 127–129 cm 62.27 1.1 89.2 9.7 1.1 8H 3W 105–107 cm 70.06 3.5 95.3 2.3 2.3 8H 6W 27–29 cm 73.79 3.8 89.8 5.1 5.1 8H 6W 57–59 cm 74.09 2 94.2 4.7 1.2 9H 1W 57–59 cm 76.07 0.9 91.2 2.2 4.4 1.1 1.1 3 schist 9H 1W 77–79 cm 76.27 2 75.8 18.7 1.1 2.2 2.2 2 schist 10H 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 siltstone 10H 7W 3–5 cm 94.03 0.3 89.2 5.4 2.7 2.7 7 schist 11H 5W 25–27 cm 100.75 0.6 97.5 0.7 1.8 11H 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.

3. Samples and methods 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- 3.1. Petrographic characterisation and IRD counts of coarse-grained graphic content) to represent peaks in coarse-grained material in dif- sediment fractions ferent facies. Selection yielded samples from sedimentary facies 2 (clay with dispersed clasts; n = 3), facies 4 (diatom-bearing silty clays; The coarse-grained fractions (> 150 μm) of 19 samples from Site n = 2), and facies 5 (diatom-rich silty clays; n =9)(Table 2). U1361 were examined to characterise mineral grains, to count IRD 192 hornblende grains were hand-picked from the > 150 mm grains coarser than 2 mm (dropstones) and to identify their lithologies fraction and analysed for their 40Ar/39Ar ages at the AGES laboratory at (Table 1). Samples for characterisation were analysed from facies 1 Lamont-Doherty Earth Observatory of Columbia University (Fig. 5, see (n = 1), facies 2 (n = 3), facies 4 (n = 2) and facies 5 (n = 12). Pet- Table 2 for analytical information, and Table S2 for data). In most rographic characterisation of > 150 μm sediment fractions was based samples hornblende grains were very scarce. In order to improve grain on counts of 100 to 400 randomly distributed mineral grains in a counts and statistical confidence, the volume of bulk sample material picking tray and the relative abundances of different mineral types were processed was increased to 60 cm3 for nine samples. Larger sample assumed to be representative of the entire sample. In addition, all grains volumes however produced only limited success in increasing horn- coarser than 2 mm were counted from the entire sample, and all ob- blende grain yield. served clast lithologies were reported in order to constrain potential During picking for hornblende grains, it was noted that correlations between the amount of ice-rafted debris (IRD) present in the > 150 μm sediment fraction of one Pliocene sample (U1361 10H each sample and its provenance (Table 1; Fig. 4). 6W 35–37 cm, 92.95 mbsf) was composed of ~56% brown visually unaltered volcanic glass shards, containing occasional phenocrysts of 3.2. 40Ar/39Ar dating of ice-rafted hornblende grains biotite and hornblende. Eight fresh volcanic glass grains were selected from this sample and analysed for 40Ar/39Ar using either one-step or A total of 13 Pliocene samples (2 cm intervals, 20 cm3) from Site two-step laser fusion analysis (Fig. 6) in order to determine the absolute U1361, between 57.70 and 115.47 msbf, were selected for 40Ar/39Ar age of volcanic events and infer provenance (i.e. discriminate between dating of ice-rafted hornblende grains, and one Holocene sample (1H wind-blown ash and eroded bedrock). 1W 1–5 cm, 0.01 mbsf) (Fig. 3, Tables 2 and S2). Sample selection was To supplement existing provenance constraints on IODP Site U1361

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

Grain petrography Fig. 4. Petrographic and lithic grain summary of analysed > 150 μm fractions from (>150µm) Pliocene Site U1361 sediments. i) depth in mbsf; ii) lithostratigraphy; iii) ice-rafted debris 0.03 mbsf Clast lithology mass accumulation rates (IRD MAR; > 150 μm) from Patterson et al. (2014) and visual n=136; (>2mm) clast counts > 2 mm in diameter from Escutia et al. (2011); iv) pie charts showing re- IRD MAR 87% qtz lative abundance (%) of grain petrography; v) histograms showing number of lithic grains (g/cm3/kyr) 2 57.70 mbsf of different composition. Note that quartz grains are not included in the pie charts, due to 00.10.2 n=133; 1 the high content in all samples (provided in % next to the pie chart). The total number of

56 94% qtz grains number of number 0 non-quartz grains constituting each pie chart is between 5 and 24. 57.76 mbsf 2 58 n=77; 1 92% qtz grains

number of number 0 60 62.27 mbsf sediments and core-top surveys in the area (Roy et al., 2007; Pierce n=88; et al., 2011, 2014), we furthermore analysed hornblende grains from 62 89 % qtz core-top sediments from three additional sites located proximally to the 65.65 mbsf 2 40 39 64 n=44; 1 continent for their Ar/ Ar age populations: Deep Sea Drilling Pro- 83% qtz grains ′ ′ –

number of number 0 gram Site 274 (68°59 S, 173°25 E, 1R 5 W 110 111 cm; 12 grains), 66 70.06 mbsf IODP Site U1358 (66°05′S, 143°18′E; 1R 1 W 18–22 cm, 25 grains) and n=63; 95% qtz IODP Site U1360 (66°22′S, 142°44′E, 1R 1 W 0–18 cm, 21 grains) (see 68 2 71.68 mbsf Fig. 1 for locations; Fig. 5, Tables 2 and S2 for data). Core-top sediments n=107; 1 for the latter two sites have been dated to be Pliocene and Upper 70 92% qtz grains number of number 0 Pleistocene in age, respectively (Escutia et al., 2011). 73.79 mbsf 72 n=47; 90% qtz 3.3. Clay mineralogy 74 74.09 mbsf n=83; Clay mineral compositions were determined on the < 2 μm detrital 76 94% qtz 3 fractions of Pliocene sediments from IODP Site U1361, and were mea- 76.07 mbsf 2 78 n=88; 1 sured on 193 discrete samples between 47.46 and 75.00 mbsf. Samples grains

91% qtz of number 0 were taken from all identified Pliocene sedimentary facies (Figs. 7 and 80 76.27 mbsf 2 8, Table S3) and supplement existing data between 75.00 and n=88; 1 124.97 mbsf (Cook et al., 2013). Sample preparation and analysis was 76% qtz grains

82 of number 0 performed at the Instituto Andaluz de Ciencias de la Tierra (IACT, 2 84 84.95 mbsf Spain), following the same procedures as described by Cook et al. n=73; 1 (2013). 90% qtz grains 86 of number 0 3.4. Neodymium and Sr isotope compositions of fine-grained fractions 88 10 92.07 mbsf 8 6 n=47; 4 Depth (mbsf) Eleven Pliocene sediment samples were selected from IODP Site

90 76% qtz grains 2

number of number 0 2 U1361 between 47.25 and 73.79 mbsf for analysis of their Nd and Sr 92.95 mbsf isotopic compositions on the < 63 μm detrital fractions. Samples were 92 n=63; 1

90% qtz grains selected to represent a range of sedimentary facies 1 (n = 4), facies 2 number of number 0 94 10 (n = 1), facies 4 (n = 3) and facies 5 (n =3)(Table 3) and supplement 94.03 mbsf 8 6 n=53; 4 previously published early Pliocene data (Cook et al., 2013; Figs. 3 and 96 89% qtz grains 2 number of number 0 9; Table 3). Nine of the eleven samples, are identical to the ones utilised for > 150 μm hornblende 40Ar/39Ar analysis and had biogenic carbo- 98 100.75 mbsf n=146; nate and authigenic ferromanganese phases removed following the 100 98% qtz procedure outlined in Cook et al. (2013). Two samples were taken from

2 a smaller 1 cm interval, and were analysed for bulk (not sieved) Nd and 102 103.78 mbsf – – n=52; 1 Sr isotopes only (7H 5W 54 55 cm, 63.04 mbsf; 8H 3W 37 38 cm,

95% qtz grains 69.38 mbsf) (Table 3) in order to test for potential grain size effects. 104 of number 0 Sediments were acid digested on hotplates and target analytes were 106 separated by column chemistry, following the same procedures de- 109.74 mbsf n=120; scribed by Cook et al. (2013). Neodymium and Sr isotopes were ana- 108 88% qtz lysed by MC-ICP-MS and TIMS, respectively, in the MAGIC laboratories at Imperial College London, and analytical details are provided in Cook 110 et al. (2013) and in Table 3 footnotes. 4 112 115.49 mbsf n=53; 2 4. Results

90% qtz grains 114 of number 0 Feldspar Magnetite 4.1. Petrographic characterisation and IRD counts of coarse-grained

116 Shale Schist Pyroxene Hornblende Basalt sediment fractions Granite

0510 Siltstone

Clast Count Garnet Glauconite Sandstone (clasts/10cm) Biotite Pliocene mineral assemblages from coarse-grained sediment frac- tions (> 150 μm) from IODP Site U1361 (Table 1) are dominated by quartz (76–98%), with abundant feldspars (< 19%), pyroxenes (clino and ortho) (< 6%), biotite, garnet, magnetite, and hornblende (all < 7%), and trace amounts of glauconite (< 3%) (Fig. 4). Fifty-seven lithic clasts > 2 mm were found throughout the 19 samples. Lithic fragments are composed of siltstone, quartzose sandstone, shale, schist,

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

Table 2 40Ar/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 U1361 Facies 2 7H 7W 17–23 cma 65.69 0.8 4 3 0 8 1 1 17 9H 2W 77–83 cma 77.77 2.2 7 1 2 8 0 0 18 13H 2W 46–48 cm 115.47 12.6 4 0 0 10 0 0 15 Facies 4 7H 1W 120–122 cm 57.70 0.5 1 5 1 16 1 1 25 7H 4W 127–131 cma 62.27 1.1 1 5 1 15 1 0 24 Facies 5: 1H 1W 1–5cma 0.01 1.4 5 0 1 1 0 0 7 9H 1W 57–61 cma 76.07 0.9 5 1 1 8 0 0 16 9H 1W 77–79 cm 76.27 2.0 4 1 3 11 1 1 21 10H 5W 107–111 cma 92.07 2.4 4 2 1 8 1 1 17 10H 6W 35–37 cm 92.95 3.6 1 0 0 0 0 0 1 10H 7W 3–5 cm 94.03 0.3 3 1 0 3 0 0 7 11H 5W 27–29 cm 100.77 0.6 2 0 0 0 0 0 2 11H 7W 28–30 cm 103.78 1.0 9 2 0 2 0 0 13 12H 6W 51–53 cm 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 110–111 cm 7.10 0 0 1 9 0 2 12 IODP Site U1360 1R 1W 0–18 cm 0.00 0 0 0 0 0 21 21 IODP Site U1358 1R 1W 18–22 cm 0.18 0 0 0 0 0 38 38

40 39 Hornblende grains and monitor standards were irradiated at the TRIGA reactor at the USGS in Denver, with 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 < 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). basalt, granite, and abundant volcanic glass. No changes in abundance 1320 Ma (Fig. 5). of different ice-rafted mineral grains or lithic clasts were observed be- The number of ice-rafted grains > 2 mm per gram of sediment re- tween different facies. Particular mineralogies and lithologies show no veals no obvious correlation with hornblende 40Ar/39Ar ages (Table 2). correlation to the amount of IRD grains > 2 mm in size per gram of Furthermore, comparison of the different hornblende 40Ar/39Ar age sediment, although more data for facies 1 and 2 would be desirable. ranges identified in individual samples from different facies (Table 2) indicates only limited change in hornblende provenance with changing depositional conditions. A potentially significant exception to this ob- 40 39 4.2. Ar/ Ar dating of ice-rafted hornblende grains servation is that 18 of the 22 grains with a 40Ar/39Ar age between 90 and 290 Ma occur in samples from diatom-bearing facies 4 and 5 Hornblende is relatively scarce in these samples, with typical (Table 2), although more samples from facies 1 and 2 would be desir- abundances < 1% in the > 150 μm fractions and grain yields between able to confirm this observation. 3 1 and 25 for processing 20 to 60 cm of material (Table 2 and Fig. 3). Eight distinct volcanic glass grains were analysed for 40Ar/39Ar ages 40 39 Ar/ Ar ages from Pliocene and Holocene sediments at IODP Site from IODP Site U1361, sample 10H 6W 35–37 cm, in a two-step (n =7) U1361 yield two distinct populations: ~2 to 44 Ma (~28%; 54 out of or one-step (n = 1) heating procedure. Only one of seven grains pro- 192 grains analysed; Figs. 5 and 8, Tables 2 and S2), and 440–540 Ma duced results for both heating steps (6.0 ± 1.1 Ma and (~48%; 93 out of 192 grains analysed; Fig. 5, Tables 2 and S2). Within 5.1 ± 2.8 Ma), with all others samples yielding sufficient gas to cal- the younger population, 42% of hornblende grains have ages that culate ages only for the second step (2.1 ± 2.2 Ma, 3.7 ± 2.3 Ma, match, within error, the depositional age of the sediment from which 4.8 ± 0.6 Ma, 4.9 ± 2.6 Ma, 5.4 ± 2.8 Ma, 7.5 ± 0.8 Ma) they were extracted (~2 to 6 Ma) whereas 58% of hornblende grains (Fig. 6b). The single-step heated grain gave an age of 5.3 ± 2.8 Ma. are older (~6 to ~44 Ma) (Fig. 6). A minor bimodal age population Apart from the two glass grains with the oldest ages (6.0 ± 1.1 Ma and distribution can be identified within the 440 to 550 Ma population: one 7.5 ± 0.8 Ma), all ages are contemporaneous within error with the between 440 and 500 Ma (63 grains in total), and the other between estimated depositional age of the sample from which they were ex- 500 and 540 Ma (30 grains in total) (Fig. 5). Remaining hornblende tracted (~4 Ma). grains are found in minor numbers and are distributed over three broad Hornblende 40Ar/39Ar ages in the Holocene sediment sample from 40 39 Ar/ Ar age ranges (Fig. 5, Table 2): 90–290 Ma (~11%; 22 of 192 DSDP Site 274 (n = 12) (Fig. 1b for location, Fig. 5; Tables 2 and S2 for grains); 330–430 Ma (~6%; 11 grains of 192) and > 600 Ma (~6%; 11 data) predominantly fall between 476 and 524 Ma (9 grains in total), 40 39 of 192 grains). More than half of the grains with an Ar/ Ar age range with additional grains aged at 378 ± 5 Ma, 619 ± 36 Ma, and between 90 and 290 Ma fall between ~90 and ~130 Ma (n = 13; 1550 ± 9 Ma. Hornblende grains analysed from the Holocene marine Fig. 5, Table S2), while the remaining ages are distributed with no clear sediment sample from Site U1358 yield 40Ar/39Ar ages mainly between 40 39 sub-grouping. The oldest Ar/ Ar aged grains (> 600 Ma) represent a ~1420 and 1860 Ma (24 of 25 grains analysed), with one grain pro- wide range of ages between ~641 ± 8.7 Ma and 2339 ± 26 Ma, with ducing an age of 2250 ± 28 Ma (Fig. 1b for location, Fig. 5 and Tables more than half of these falling within an age range of ~1000 to

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

MVG Ross n=54 WA Orogeny n=13 n=93 50

40 a) Pliocene sediments from IODP Site U1361 (n=192) 30 (this study) Facies 1 & 2 20 Facies 4 & 5 Number of grains 10 0 30 b) Core-top sediments from Site 274 20 DSDP Site 274 (n=12), Site U1358 IODP Sites U1360 (n=21) Site U1360 10 and Site U1358 (n=25)

Number of grains 0 50

40 c) Regional core-top West Antarctica sediments from 22 sites Northern Victora Land 30 Adélie Land (n=578) Wilkes Land 20

Number of grains 10 0 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 Hornblende 40Ar/39Ar age (Ma)

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 data for 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-axis have 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 provenance sector (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 western Ross 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: Southern Victoria Land, TAM: Central Transantarctic Mountains, EPG: Early Palaeozoic Granites (near Ninnis Glacier). For definition of geographical sectors and locations see Fig. 1. Vertical grey bands 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.

2 and S2 for data). Similarly, core-top sediments sampled from Site ratios between 0.717 and 0.728. U1360 have hornblende 40Ar/39Ar ages that range from 1509 to 1736 Ma (17 of 21 grains analysed), with remaining grains producing 5. Discussion ages of 1988 ± 17 Ma, 2060 ± 9 Ma, 2514 ± 33 Ma, and 3944 ± 26 Ma (Fig. 1b for location, Fig. 5 and Tables 2 and S2 for In the following discussion we will first evaluate the provenance data). signatures of coarse and fine-grained Pliocene sediments from IODP Site U1361 separately, to then compare and contrast derived interpreta- 4.3. Clay mineralogy tions. We will show that robust provenance analysis of glaciomarine sediments is best achieved by combining various methodologies and Clay minerals in Pliocene sediments from IODP Site U1361 (Figs. 7 grain-sizes. In the particular case studied here, 40Ar/39Ar ages of and 8, Table S3) are dominated by illite (52–68%), smectite (11–33%), hornblende grains (> 150 μm) reveal erosion of regionally abundant with lesser amounts chlorite (5–19%) and kaolinite (7–16%, except for Palaeozoic granites emplaced during the Ross Orogeny (~440 to four samples with 29–33% kaolinite). Illite and smectite show a strong 540 Myrs; Figs. 1b and 5) as well as ages associated with more distal negative correlation (r2 = 0.8), which is significant despite relatively occurrences of McMurdo volcanics (< 44 Myrs; Figs. 1b and 5). The large analytical uncertainties (10–15%). In general, sediments from data furthermore hint at a far-travelled provenance component from facies 4 and 5 tend to contain slightly higher amounts of smectite and West Antarctica during warm Pliocene intervals (90–125 Myrs; Figs. 1b chlorite, while sediments from facies 1, 2 and 3 show a tendency for and 5). Warm intervals are furthermore characterised by quartz-rich higher illite contents. Smectite/illite ratios share a weak positive cor- mineralogies of the coarse fraction (Table 1) and a radiogenic detrital 2 relation with Nd isotopic compositions (r = 0.6; Fig. 8). Nd isotope signature of fine-grained sediments (εNd = −6.9 to −9.9), corroborating previous suggestions that Pliocene ice retreat led to 4.4. Neodymium and Sr isotope compositions of fine-grained fractions erosion of Ferrar Large Igneous Provenance (FLIP) and Beacon Super- group lithologies of Jurassic to Devonian ages, hidden today under- Neodymium and Sr isotope compositions of the < 63 μm fractions neath the East Antarctic ice sheet (cf. Cook et al., 2013). of Pliocene detrital sediments from Site U1361 display a large range of 87 86 values (ƐNd: −6.9 to −13.2; Sr/ Sr: 0.717 to 0.731) (Figs. 3 and 9, 5.1. Coarse-grained sediment provenance Table 3). Comparison of the Nd and Sr isotope results between the different facies reveals two distinct groups (Figs. 3, 9 and 10; Table 3). Hornblende grains extracted from the > 150 μm sediment fraction Samples analysed from clay-dominated facies 1 and 2 are characterised of marine sediments away from continental shelf areas are typically ice- 87 86 by ƐNd values between −11.2 and −13.2 and Sr/ Sr ratios between rafted in origin. However, in locations proximal to continents turbidity 0.723 and 0.731, whereas samples analysed from diatom-rich/bearing currents may play a role as well. In order to assess coarse-grained se- 87 86 facies 4 and 5 have ƐNd values between −6.9 and −9.2 and Sr/ Sr diment provenance offshore the Wilkes Subglacial basin during the

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

Marie Byrd Land – Erebus Province 1999) than those of Southern Victoria Land (480 550 Ma; Goodge, Mount Melbourne 2007; Wysoczanski and Allibone, 2004) and the Central Transantarctic Hallet Province Mountains (480–545 Ma; Goodge, 2007). According to our results, Contemporaneous with depositional age Older than depositional age DSDP Site 274 likely received IRD from proximal Northern Victoria Land source areas. 14 Ice-rafted hornblende 40Ar/39Ar ages in Holocene sediments at ff 12 (a) Adélie shelf sites U1360 and U1358 yield rather di erent ages of > 1420 Ma, clustering around 1600 to 1750 Ma (Table 2; middle 10 panel in Fig. 5). These ages agree well with onshore ages for the tec- 8 tonometamorphic overprint of the proximal Archean and Neoproter- 40 39 6 ozoic Adélie Craton ( Ar/ Ar argon ages ~1700 Ma (see Table S1 for references), and hornblende 40Ar/39Ar ages in Holocene sediments in 4 Number of grains the vicinity of the sites (Roy et al., 2007; Pierce et al., 2014, Pierce 2 et al., 2011)). Such a provenance also allows for the occurrence of Archean aged grains, which are found in small numbers at the Adélie 0 0 5 10 15 20 25 30 35 40 45 50 shelf sites (Table 2). Hornblende 40Ar/ 39Ar age (Ma) 5.1.2. Provenance of major age populations of ice-rafted hornblende grains in Pliocene-aged Site U1361 sediments 0.0030 (b) Despite high IRD depositional rates (Fig. 3; Escutia et al., 2011;

0.0025 Patterson et al., 2014) ice-rafted hornblende grain counts in Pliocene Site U1361 sediments are low (Table 2, Fig. 3), suggesting that horn- 0.0020 blendes are generally low in abundance in the predominant source Ar

40 0.0015 terranes. Ar/ 36 0.0010 5.1.2.1. Late Cambrian Ross Orogeny and Palaeozoic granites 40 39 Age = 6.9 ± 1.0 Ma (8.9 %) (440–540 Myrs). The most abundant hornblende grain Ar/ Ar age 0.0005 Age=6.9±1.0Ma(8.9%) 40 36 40Ar/ Ar/36ArInt.=302±3 Ar Int. = 302 ± 3 MSWD=2.5,P=0.00,n=30MSWD = 2.5, n = 30 population in Pliocene Site U1361 sediments has a range of 440 to 0 0 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 540 Myrs (Fig. 5 top panel, Table 2). Such ages were likely sourced from the high-grade Late Cambrian Ross Orogeny (Goodge, 2007 and 39Ar/ 40Ar references therein; Stump, 1995; see Fig. 1b for geographical extent). In 40 39 Fig. 6. a) Histogram of the youngest Cenozoic hornblende Ar/ Ar age population from Site U1361 sediments this population is comprised of two peaks, one Pliocene Site U1361 sediments. Also included are the known eruptive histories of the four between 440 and 500 Ma, and a secondary, smaller peak between 500 main volcanic provinces in the region (see text, and Table S1): HVP: Hallet Volcanic and 540 Ma (Fig. 5). Northern Victoria Land (460–550 Ma), Southern Province; MMVP: Mount Melbourne Volcanic Province; EVP: Erebus Volcanic Province; – MBLVP: Marie Byrd Land Volcanic Province. About half of the hornblende grains yield Victoria Land (480 550 Ma) and the Transantarctic Mountains ages older than the deposition age, indicating that they were transported to the site by (480–545 Ma) are potential sources for grains with such ages (see ice-rafting. b) Isochron plot of eight volcanic glass grains analysed from U1361 10H 6W discussion above for DSDP Site 274). The most likely source areas is 35–37 (depositional age of ~4.1 Ma). The syn-depositional age of these volcanic glass however located proximal to the drill site, where Early Palaeozoic grains with sediment depositional age points to aeolian supply to Site U1361. granites outcrop in the vicinity of the Ninnis Glacier (Goodge and Fanning, 2010; Fig. 1). This idea is supported by results from Holocene Pliocene we first evaluate our new 40Ar/39Ar data on regional core top marine sediments, located directly downstream of the Ninnis Glacier, 40 39 samples in the context of published on land thermochronology (Section which contain hornblende grains with Ar/ Ar ages between 480 and 5.1.1; Figs. 1b and 5). We selected three sites, covering distal source 560 Ma (Pierce et al., 2014, Pierce et al., 2011; Roy et al., 2007; areas from the Ross Sea (DSDP Site 274) and proximal source areas Fig. 1b). Indeed, the location of Site U1361 on the continental rise from the Adélie Shelf (IODP Sites U1358 and U1360) (Fig. 1a). We suggests that coarser-grained sediments derived from Early Palaeozoic subsequently compare these results with our new downcore record to terranes nearby could have been supplied to the site via downslope identify major (Section 5.1.2) and minor (Section 5.1.3) provenance processes such as turbidites Hence, the older sub-group within the Ross signatures observed. We finally elaborate on the exciting observation Orogeny population is likely derived from ice-rafting and turbidites that a small number of grains that were deposited during warm Plio- sourced from the proximal continental shelf and the Ninnis Glacier, cene intervals at IODP Site 1361 could have a West Antarctic origin and/or from ice-rafting from Southern Victoria Land and the (Section 5.1.4). Transantarctic Mountains, while the younger sub-group can be partially explained by derivation from Northern Victoria Land. However, seven grains aged between 440 and 460 Ma do not fit 5.1.1. Regional Holocene hornblende grain provenance: new results from documented ages from this region (Fig. 1b). Furthermore, a small DSDP Site 274, IODP Site U1358 and IODP Site U1360 number of grains have hornblende 40Ar/39Ar ages between 330 and The majority of hornblende 40Ar/39Ar ages of Holocene sediments at 430 Ma. While it is possible that a currently hidden terrane was the DSDP Site 274 (Ross Sea) fall within a range of 475 to 525 Ma (Table 2; source for these grains, these ages, although minor in number, can be middle panel in Fig. 5), which is within the metamorphic age range of matched well to the Bowers Terrane in Northern Victoria Land (e.g. the high-grade Late Cambrian Ross Orogeny (460 to 560 Ma; Boger, Borg et al., 1987; Rocchi et al., 2004; Weaver et al., 1984), which is 2011; Goodge, 2007 and references therein; Pierce et al., 2014, Pierce characterised by whole-rock K-Ar ages of between 320 and 450 Ma et al., 2011; Stump, 1995)(Fig. 1b). Despite the regional prevalence of (Adams, 2006). this high-grade metamorphic signature (Fig. 1b; see Goodge, 2007 for review), on land thermochronology suggests that the timing of peak 5.1.2.2. McMurdo Volcanics (< 44 Myrs). The youngest and second metamorphism of terranes in Northern Victoria Land can be identified most abundant hornblende 40Ar/39Ar age population identified in Site at slightly younger U-Pb ages (460–500 Ma; Dallmeyer and Wright, U1361 sediments shows ages < 44 Ma, and is most likely derived from 1992; Goodge and Dallmeyer, 1992; Klee et al., 1992; Schüssler et al., the Cenozoic McMurdo Volcanic Group (Harrington, 1958; Kyle, 1990;

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

Illite (%) Chlorite (%) Smectite/Illite 40 50 60 70 01020 01020 45

50

55

60

65

70

75

80

85 Depth (mbsf) 90

95

100

105

110

115

120

125 10 20 30 40 010203040 Smectite (%) Kaolinite (%)

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 orange horizontal 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 most pronouncedly 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 a corresponding 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 figure legend, the reader is referred to the web version of this article.)

0.8 Kyle and Cole, 1974; LeMasurier and Thomson, 1990; Figs. 5 and 6). The Hallet Volcanic Province, Mount Melbourne Volcanic Province and 0.7 Erebus Volcanic Province of the McMurdo Volcanic Group (Figs. 1 and 0.6 6) have well-documented eruptive histories spanning the last 26 million years (see Table S1 for references). Balleny Islands (Fig. 1) 0.5 constitute the volcanic edifice closest to Site U1361, and is believed to be no older than Miocene (Johnson et al., 1982). The islands are 0.4 however inaccessible and therefore poorly studied. The geochemical compositions of basalts from outcrops on these islands and volcanic ash 0.3 analysed from nearby marine sediments (Huang et al., 1975; Kyle and Smectite/Illite 0.2 Seward, 1984; Shane and Froggatt, 1992) suggest an intermediate geochemical composition between that of the Hallet Volcanic Province 0.1 y = 0.0409x + 0.8313 and Erebus Volcanic Province (Green, 1992; Johnson et al., 1982; Kyle 2 R = 0.6 and Cole, 1974), implying similar tectonic relationships and likely 0 similar ages for the initiation of their formation. It is hence feasible that -16 -15 -14 -13 -12 -11 -10 -9 -8 -7 -6 ε the Balleny Islands may be the source of some of the volcanic ash and Nd hornblendes younger than Miocene in age identified at Site U1361. Fig. 8. Neodymium isotope composition of < 63 μm detrital sediments at Site U1361 Three Eocene aged hornblende grains (35.9 ± 0.7 Ma, show a positive correlation with smectite/illite ratios. If data were not available from the 36.6 ± 1.4 Ma, 44.2 ± 0.25 Ma) may be sourced from even older exact same samples, samples were matched within 3 cm of core length. McMurdo Volcanic Group deposits currently undocumented in the Ross Sea. However, they could also have been supplied by icebergs sourced from Marie Byrd Land in West Antarctica, over 2000 km to the east of our study site, where Eocene volcanism has been dated to ~36 Ma, with the possibility of initial volcanism being even older (Wilch and

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Table 3 Strontium 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 U1361 sediments are available from Cook et al. (2013).

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

ODP Site U1361 Facies 1 6H 1W 25–27 cm 47.25 0.728823 ± 0.000010 0.512291 ± 0.000008 −11.7 ± 0.3 8H 3W 37–38 cmc 69.38 0.730877 ± 0.000008 0.511981 ± 0.000018 −12.8 ± 0.4 8H 3W 75–77 cm 69.76 0.728736 ± 0.000012 0.512060 ± 0.000010 −11.2 ± 0.3 8H 4W 117–119 cm 71.68 0.724040 ± 0.000008 0.511964 ± 0.000008 −13.2 ± 0.3 Facies 2 7H 7W 17–19 cm 65.69 0.723360 ± 0.000020 0.512058 ± 0.000018 −11.3 ± 0.4 Re-analysis 0.723367 ± 0.000016 Facies 4 7H 1W 120–122 cm 57.70 0.719666 ± 0.000014 0.512284 ± 0.000014 −6.9 ± 0.2 7H 4W 127–129 cm 62.27 0.721773 ± 0.000008 0.512185 ± 0.000012 −8.8 ± 0.2 7H 5W 54–55 cmc 63.04 0.728100 ± 0.000016 0.512164 ± 0.000008 −9.2 ± 0.2 Facies 5 8H 1W 115–117 cm 67.15 0.716570 ± 0.000012 0.512195 ± 0.000008 −8.6 ± 0.3 8H 3W 105–107 cm 70.06 0.717345 ± 0.000014 0.512192 ± 0.000008 −8.7 ± 0.3 8H 6W 27–29 cm 73.79 0.724461 ± 0.000022 0.512176 ± 0.000012 −9.0 ± 0.3 DSDP Site 274 1R 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 of 0.512646 ± 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 of 0.705018 ± 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.

McIntosh, 2000). grains were entrained glacially in the vicinity of their volcanic de- 58% of all hornblende grains from Pliocene sediments at Site positional centres before being transported to Site U1361 by icebergs. U1361, which are younger than 44 Ma, are older than the depositional In contrast, most of the volcanic glass grains analysed yield ages within age of the marine sediment itself (Fig. 6). It is hence likely that these error of the depositional age of the sediment sample from which they

10 East Antarctic Terranes IODP Site U1361: PrecambrianTerranes Facies 1-3 Adelie Craton 5 Facies 4 Wilkes Land, Holocene marine sediments Facies 5 0 PalaeozoicTerranes Wilson Group Granite Harbour Group -5 Robertson Bay Group

Nd Bowers Group Admirality Intrusives -10 MesozoicTerranes Ferrar Large Igneous Province

-15 Cenozoic McMurdo Volcanics Mt Melbourne Volcanic Province Erebus Volcanic Province -20 Hallet Volcanic Province Balleny Islands

-25 West Antarctic Terranes 0.70 0.71 0.72 0.73 0.74 0.75 0.76 Cenozoic Marie Byrd Volcanics Paleozoic and Mesozoic terranes 87Sr/86Sr

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 than symbols. 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 for references). 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., 87 86 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; Sr/ Sr: 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.)

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

-4 Ice-rafted hornblende (>150µm) 40 39 Ar/ Ar age populations Combined 25 <50 Ma (WA, TAM/SVL, NVL) age populations: -6 16 90-290 Ma (WA) 7 330-430 Ma (WA, NVL) 21 440-540 Ma (Ninnes glacier, 1 TAM/SVL, NVL) -8 9 >600 Ma (AL) 13 others

17 24 Diatom-rich/bearing -10 2 facies 4 and 5; 11 samples, 142 grains Nd (<63µm) 18 -12 7 17

Facies 4 and 5: -14 increased smectite/illite Facies 1 and 2: decreased smectite/illite 15 Clay facies 2; 3 samples, -16 50 grains 0.710 0.715 0.720 0.725 0.730 0.740 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 taken from 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 been performed 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 the different 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 samples from 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: Wilkes Subglacial Basin.

were extracted (Fig. 6), implying contemporaneous eruptive events. offshore of the Wilkes Land margin to the west of the Adélie Craton Volcanic glass and phenocrysts from the McMurdo Volcanic Group have (Cook et al., 2014; Pierce et al., 2014; Pierce et al., 2011; Roy et al., been identified in layers within existing continental ice in Northern 2007)(Fig. 1b), and thermochronological ages of on land exposures in Victoria Land and the Transantarctic Mountains (Narcisi et al., 2012; this region (Fitzsimons, 2003; Post, 2000; Post et al., 1997; Möller et al., Perchiazzi et al., 1999; Smellie et al., 2011), supplied by explosive 2002; Sheraton et al., 1992). This tectonometamorphic age range is volcanism from the Hallet Volcanic Province and Mount Melbourne inferred to be related to the Grenvillian Orogeny (Boger, 2011; Dalziel, Volcanic Province. This observation suggests that some of the sediment 1991; Fitzsimons, 2000a, 2000b). However, a supply of icebergs to Site load of regionally calved icebergs sourced from the continental interior U1361 from areas of the west of the Adélie Craton is unlikely, as this adjacent to Northern Victoria Land and Southern Victoria Land may would be opposite to the wind-driven iceberg trajectories around the contain a volcanic glass component – this could explain the un- continent (Fig. 1a), which was likely unaltered under Pliocene condi- weathered fresh appearance of the volcanic ash grains in Site U1361 tions (DeConto et al., 2007). The possibility of a Grenvillian-aged ig- sediments. An alternative source for volcanic glass could also be aeolian neous body, or at least crustal material with remnant Grenvillian sig- fallout from the Balleny Islands and/or delivery by sea-ice rafting. natures, located beneath the East Antarctic ice sheet to the west of the Transantarctic Mountains, has however been proposed in accordance 5.1.3. Provenance of minor age populations of ice-rafted hornblende grains with the SWEAT hypothesis (South-Western US and East Antarctica) in Pliocene U1361 sediments (Goodge et al., 2010; Goodge et al., 2008; Moores, 1991), as Grenvillian Four hornblende grains from Site U1361 sediments have 40Ar/39Ar U-Pb zircon ages have been identified in glacial sediments in the Ross ages that match the proximal Adélie Craton, which has well-constrained Sea area (Goodge et al., 2010). It is therefore possible that Mesopro- Proterozoic metamorphic age populations at ~1700 and ~2500 Ma (Di terozoic aged hornblende grains in Site U1361 may be related to a Vincenzo et al., 2007; Pierce et al., 2014; Roy et al., 2007)(Figs. 1b and continental interior source that is currently obscured by the ice sheet. 5). The scarcity of such ages in our core, despite its proximity to the Icebergs sourced from the Ross Sea and/or the Wilkes Subglacial Basin Adélie Craton, indicates only limited supply of coarse grained material may therefore have been a source for these grains. via downslope processes and ice-rafting to Site U1361 during the Pliocene. 5.1.4. Evidence for increased West Antarctic IRD in Pliocene U1361 A small Mesoproterozoic hornblende grain 40Ar/39Ar age popula- sediments during Pliocene warmth tion between 1000 and 1300 Ma can be seen in Pliocene sediments at A minor hornblende 40Ar/39Ar age population in Site U1361 Site U1361. Similar to Holocene sediments regionally (Pierce et al., Pliocene sediments is constituted by Mesozoic ages of ~90 to ~125 Ma 2011; Roy et al., 2007; this study; Figs. 1b and 5) and in Ross Sea se- (n = 13; Fig. 5). It is an intriguing observation that these grains pri- diments (Pierce et al., 2011; Roy et al., 2007), these ages occur in minor marily occur within diatom-bearing and diatom-rich sedimentary facies numbers in Site U1361 sediments (6 grains in total). This age range has 4 and 5, inferred to have been deposited during intervals of warmer- no known exposed analogues in East and West Antarctica to the east of than-present conditions (Cook et al., 2013). There are no known ex- the Adélie Craton. It does, however, match significant populations of posed rocks on the nearby East Antarctic continent with hornblende Proterozoic hornblende 40Ar/39Ar ages in Holocene marine sediments 40Ar/39Ar ages that lie in this age range (Fig. 1b). While it is impossible

211 C.P. Cook et al. Chemical Geology 466 (2017) 199–218 to rule out a bedrock source hidden within the East Antarctic con- climatic regimes, and radiogenic isotope compositions corroborate this tinental interior, there is no suggestion in the literature that rocks of finding. Proximal Palaeozoic granitoids can be inferred as an end- these ages could exist regionally. member for the fine-grained Nd and Sr isotope provenance signature Instead, the observed 90 to 125 Ma ages match very well with mi- during colder times. An additional endmember, or a mixture of sources, neral grain thermochronology identified in Holocene marine sediments is required to explain the fine-grained provenance signature at Site off the West Antarctic continental margin (hornblende 40Ar/39Ar ages, U1361 during warmer times, and likely involves Jurassic FLIP basalts 95 to 127 Ma; Roy et al., 2007), and downstream of West Antarctic ice and dolerites, and Devonian to Jurassic siliciclastic deposits of the streams that flow into the Ross Sea (U-Pb zircon, 100–110 Ma; Licht Beacon Supergroup. et al., 2014), > 2000 km to the east of Site U1361 (Fig. 1b). On land, this hornblende 40Ar/39Ar age population corresponds to the wide- 5.2.1. Clay mineral provenance spread occurrence of Cretaceous igneous rocks in West Antarctica Illite is the most common clay mineral in high latitude marine se- (Fig. 1b), where calc-alkaline and anorogenic granodiorites and gran- diments derived from physical weathering of plutonic and metamorphic ites were intruded between 95 and 125 Ma into metasedimentary and rocks (e.g. Biscaye, 1965) and is also the most abundant clay mineral in granodioritic basement rocks (Luyendyk et al., 1996; Mukasa and Pliocene sediment from Site U1361, particularly in those from facies 1, Dalziel, 2000; Pankhurst et al., 1998; Siddoway et al., 2005; Storey 2 and 3 (i.e. colder times during the Pliocene). Illites from Quaternary- et al., 1999; Weaver et al., 1992, 1994). Based on iceberg transport and Pliocene-aged channel levee sediments nearby to Site U1361 have pathways in the westward flowing coastal current (Fig. 1a), and the geochemical compositions that suggest sourcing from Early Palaeozoic excellent agreement with onshore and offshore West Antarctic con- granitoids found in the hinterland of the Ninnis Glacier (Fig. 1a) (be- straints, this age population is likely to have been sourced from this tween 64°17′S 143°22′E and 64°57′S 144°23′E: Damiani et al., 2006; distant region. Whether icebergs with these signatures were supplied Talarico and Kleinschmidt, 2003; Site U1359: Verma et al., 2014). from the Marie Byrd Land-Southern Ocean margin, or from icebergs Smectite is the second most abundant clay mineral in Pliocene marine calved from West Antarctica directly into the southern Ross Sea (Licht sediments at Site U1361and is typically interpreted as a weathering et al., 2014) is unknown, but their origin from West Antarctica seems a product of basic volcanic rocks (e.g. Biscaye, 1965). Smectite abun- robust finding. dances seem elevated in sediments from facies 4 and 5 (i.e. warmer Iceberg pathways are regionally constrained to follow an anti- times during the Pliocene). In detail, the two regional lithologies that clockwise, westward, direction around the East Antarctic continent are likely to produce smectites are the Cenozoic McMurdo Volcanic (Fig. 1a). Large modern tabular icebergs sourced from ice shelves have Group and the Jurassic volcanic terranes of the basaltic and doleritic lifetimes of several years, as observed from satellites (e.g. Tournadre FLIP rocks, which intruded ~180 Ma into the siliciclastic deposits of et al., 2015). For paleo-reconstructions, it is important to consider that the Beacon Supergroup (Damiani et al., 2006; Verma et al., 2014) sea surface temperatures of ocean waters near the Antarctic continent (Fig. 1a). Basalts of the FLIP group have been identified as a source of during the Pliocene were warmer than today (Cook et al., 2014). Pa- detrital smectite in the Ross Sea (Claridge and Campbell, 1989). On the laeothermometry indicators (TEX86: McKay et al., 2012) suggest sea- other hand, smectite associated with the McMurdo Volcanic Group is sonal temperatures up to 6 °C warmer than today during interglacials mainly authigenic in origin in the Ross Sea (Setti et al., 2000), and and prolonged Pliocene warm intervals in the Ross Sea area. Similarly derived from submarine weathering and hydrothermal alteration of warm temperatures have been identified in Pliocene sediments from volcanic material (Petschick et al., 1996; Setti et al., 2000). Despite the other locations around Antarctica (Bart and Iwai, 2012; Escutia et al., presence of volcanic ash in Site U1361 sediments, smectites in marine 2009; Whitehead and Bohaty, 2003; Whitehead et al., 2005). Based on sediments nearby to Site U1361 have been suggested to be detrital in iceberg survivability modelling in the Southern Ocean, the distance origin (Damiani et al., 2006). Hence, we rule out the McMurdo Volcanic icebergs could travel before melting during warm Pliocene intervals Group as a significant source of smectite and suggest that detrital was likely significantly reduced (Cook et al., 2014), suggesting that a smectite was instead supplied by FLIP terranes, which are exposed in considerable amount of icebergs must have been produced from the broad areas of the Transantarctic Mountains (Elliot and Fleming, 2008) West Antarctic ice sheet in order to travel over 2000 km to reach Site and inferred to occupy large areas underneath the ice in the Wilkes U1361. Additionally, sediments deposited in the Ross Sea have shown Subglacial Basin (Ferraccioli et al., 2009; Jordan et al., 2013; Studinger that the Ross Ice Shelf retreated repeatedly during the Pliocene (Naish et al., 2004; Fig. 1a). A strong negative correlation between the abun- et al., 2009), likely in response to warm Pliocene conditions. We dance of smectite and illites in Site U1361 sediments, combined with therefore propose that increased supply of West Antarctic IRD to Site positive correlations between smectite/illite and Nd isotope composi- U1361 was related to changes in ice sheet volume during particularly tions (Fig. 8; see also next section), suggests that provenance is an warm Pliocene intervals. This suggestion is in line with Pliocene IRD important control on smectite and illite contents. depositional patterns at the site (Patterson et al., 2014) and AND-1B Kaolinite and chlorite are less abundant in Pliocene Site 1361 se- results from the Ross Sea (Naish et al., 2009), indicating orbitally- diments. A possible continental source of kaolinite is the sedimentary modulated retreat of the WAIS during Pliocene interglacials. However, sequence of the Beacon Supergroup (Barrett, 1981; Piper and Brisco, higher resolution sampling of all facies in Site U1361 sediments, as well 1975; Fig. 1). These volcanoclastic to quartzo-feldspathic sediments can as improved statistical confidence in grain counts, would be required to be observed in many outcrops in the Transantarctic Mountains in as- substantiate this tentative interpretation. sociation with FLIP lithologies (e.g. Barrett et al., 1986). The most proximal known outcrops of Beacon Supergroup sediments to Site 5.2. Fine-grained sediment sources U1361 lie at the mouth of the Wilkes Subglacial Basin (Bushnell and Craddock, 1970). However, as indicated above, the association of FLIP To summarise above discussion, 40Ar/39Ar ages on ice-rafted horn- and Beacon lithologies probaly comprises a large part of the infill of the blende grains from Pliocene sediments at IODP Site U1361 show pre- Wilkes Subglacial basin (Ferraccioli et al., 2009). If the Beacon Super- dominant erosion from two major lithologies: (proximal) Ross Orogeny- group was the main source of kaolinite in Site U1361 sediments, its aged, Palaeozoic granitoids (~500 Ma), probably from around the abundance might be expected to correlate with smectite (and Nd iso- Ninnes Glacier and Southern Victoria Land, and more distal Cenozoic tope compositions), due to the inferred close association between FLIP McMurdo volcanics (< 44 Ma) (Fig. 1a). The following section will and Beacon Supergroup lithologies. No such trend is observed, and we explore the provenance of the < 63 μm fraction of the same marine hence consider it more likely for the kaolinite to be supplied from sediments. Clay mineralogy indicates crystalline and volcanic source weathering of granitic sources, such as the abundant Palaeozoic gran- areas, potentially contributing at different proportions during different ites in the area (Fig. 1a).

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

5.2.2. Neodymium and strontium isotope provenance 5.3. Fine-grained versus coarse-grained sediment provenance The Nd and Sr isotope compositions of fine-grained (< 63 μm) Site

U1361 detrital sediments are negatively correlated (ƐNd: −6.9 to Pliocene fine-grained sediments at Site U1361 were predominantly −13.2; 87Sr/86Sr: 0.717 to 0.729; Fig. 9) and fall into two distinct supplied from Early Palaeozoic granites in the nearby continental groups. Cook et al. (2013) found that clay-rich sediments of facies 1 to 3 margin, and from sources within the Wilkes Subglacial Basin, as con- Pliocene sediments, deposited during cooler climatic intervals, were strained by both Nd-Sr isotopes and clay mineralogy. Coarse-grained characterised by Nd isotope values of −11.2 to −13.2 and 87Sr/86Sr hornblende grains support an erosional source from local granites ex- isotope ratios of 0.723 to 0.730 (Fig. 9). They interpreted this signature posed on the proximal coast, but indicate in addition IRD supply from to be associated with erosion of Palaeozoic granitoids (ƐNd: −11.2 and multiple sources to the east, including Northern Victoria Land and West −19.8; 87Sr/86Sr: 0.714 to 0.753; Fig. 1a for exposures, Fig. 9, see Antarctica. In other words, there is no straight forward correlation of Table S1 for references). The most proximal outcrops of such rocks to provenance from coarse and fine grained sediments as illustrated in Site U1361 are located in the vicinity of the nearby Ninnis Glacier Fig. 10. Notably, ice-rafted hornblende grains extracted from Pliocene (Fig. 1a). Supply from this area is in accordance with modern deposi- sediments at Site U1361 lack any indication of erosion of FLIP lithol- tional patterns (Busetti et al., 2003; Donda et al., 2003; Escutia et al., ogies with typical emplacement ages around ~180 Ma (Duncan et al., 2003, Escutia et al., 2000) as well as with core-top sediment results 1997; Foland et al., 1993; Heimann et al., 1994; Minor and Mukasa, from the area (Cook et al., 2013; Pierce et al., 2014, Pierce et al., 2011). 1997)(Figs. 5 and 10). Conversely, diatom-rich/bearing sediments of facies 4 and 5, de- The Pliocene was a time of significant volumetric changes in the posited during warmer intervals, are characterised by ƐNd values of EAIS as indicated by IRD depositional patterns (Patterson et al., 2014) −6.9 to −9.9 and 87Sr/86Sr ratios of 0.716 to 0.728 (Figs. 3 and 9). and marine sediment provenance changes (Cook et al., 2013) at Site This signature requires input from a source lithology with a more U1361. It is likely that such dynamic ice sheet behaviour resulted in radiogenic Nd isotope fingerprint. We previously suggested (Cook et al., increased iceberg production from the Wilkes Subglacial Basin. We 2013) that the FLIP rocks make a good candidate for this endmember propose that the main differences between the provenance patterns of 87 86 (ƐNd: −3.5 and −6.9; Sr/ Sr: 0.709 to 0.719; Fig. 9, see Table S1 for fine-grained sediments and coarse-grained ice-rafted hornblende grains references). Ferrar dolerites were intruded as sills and dikes into De- from Site U1361 can be ascribed to delivery processes, and source rock vonian to early Jurassic sediments of the Beacon Supergroup and show characteristics. Sources within the Wilkes Subglacial Basin have low similar ages (~180 Ma) to extrusive basalts of the FLIP formation (e.g. hornblende concentrations (Hauptvogel and Passchier, 2012). Ad- Barrett, 1991; Elliot and Fleming, 2008). Furthermore, wherever ex- ditionally, existing grains may be subject to comminution and hence posed, FLIP and Beacon lithologies are closely associated (Fig. 1a). leave a fingerprint in the fine size fraction only. Detrital zircon analyses from the Beacon Supergroup in the Transan- tarctic Mountains and Northern Victoria Land yield a broad age spec- 5.3.1. Ice rafting versus down-slope sedimentation trum, reflecting deposition in a transantarctic sedimentary basin at the The apparent disparity between the provenance of fine-grained se- Panthalassan margin of Gondwana, situated between Precambrian diments and coarse (ice-rafted) hornblende grains used in this study cratonic terranes to the east and contemporaneous magmatic arc se- could be a product of variance in their delivery methods from source to quences to the west (~190–270 Ma: Early Triassic to early Jurassic sink (Fig. 2; see also Diekmann and Kuhn, 1999). Although it is ex- magmatic arc; ~470–545 Ma: Ross Orogeny granitoids; ~500–700 Ma: tremely difficult to reconstruct the dynamics of the glacial processes Pan-African Orogeny granitoids; ~800–1200 Ma: Grenville aged that initially resulted in the on land erosion of sediments supplied to crustal material; Elliot and Fanning, 2008; Elsner et al., 2013; Goodge Site U1361 during the Pliocene, we can nevertheless gain some insights and Fanning, 2010). The range of source lithologies and ages contained from considering modern processes and observations in the area. in the siliciclastic sediments of the Beacon Supergroup predicts a rather Today, detrital fine-grained sediments are supplied to Site U1361 by large range in radiogenic isotope compositions. To our knowledge there meltwater plumes and/or turbidity currents, which transport shelf se- are no published results on the Nd isotope composition of Beacon se- diments, initially derived from Early Palaeozoic bedrock in the coastal diments. Estimates can however be based on analyses of < 5 μm frac- hinterland (Pierce et al., 2011, 2014; Cook et al., 2013) downslope in tions of four dune samples with Beacon sandstone parent lithologies submarine channels orientated perpendicular to the coast (Busetti et al., from the Dry Valleys (Transantarctic Mountains), and one Beacon re- 2003; Donda et al., 2003; Escutia et al., 2003, Escutia et al., 2000; golith sample from Northern Victoria Land (Delmonte et al., 2010, Patterson et al., 2014). Site U1361 is located on the apex of a levee of

2013). The range of εNd values and Sr isotopic compositions in these one of these channels, with sediments deposited as non-erosional over- 87 86 samples (εNd = −5.6 to −8.1; Sr/ Sr = 0.7121 to 0.7182) overlaps spills (Escutia et al., 2011; Patterson et al., 2014). Therefore, both with the field shown for FLIP lithologies in Fig. 9. In contrary, Farmer coarse- and fine-grained sediments could be delivered to our site from and Licht (2016) estimated mixed Ferrar and Beacon compositions the shelf via downslope processes, a scenario that would explain the based on the < 63 mm fraction of glacial tills from the Byrd and presence of Early Palaeozoic hornblende grains, granite clasts, Nd-Sr Nimrod Glaciers in the central Transantarctic Mountains to be more isotope signatures suggestive of this endmember, and increased supply unradiogenic in Nd isotopes (εNd = −8.5 to −15.0) and more radio- of illites from Early Palaeozoic granites in facies 1, 2 and 3. genic in Sr isotopes (0.714–0.723), suggesting that at least some of the However, provenance constraints on facies 4 and 5, based on Nd-Sr

Beacon Supergroup must be characterised by εNd values as low as −15. isotope data and increased smectite contents, imply fine-grained sedi- Future work on Beacon Supergroup samples will have to show, ments were additionally supplied to the site from within the Wilkes which of these estimates is more applicable for provenance inter- Subglacial Basin during periods of ice sheet retreat, including a com- pretations at Site U1361. We can however conclude that a mixture of ponent of mafic FLIP lithologies (Cook et al., 2013; this study). One FLIP and Beacon rocks constitutes a viable endmember for eroded se- routing mechanism for the delivery of this material is via meltwater- diments during warm Pliocene intervals, and that such lithologies likely plume driven turbidity currents, which may have re-distributed mate- comprise a considerable component of the sedimentary infill of the rial deposited initially on the shelf at the mouth of the basin, to the east Wilkes Subglacial Basin (Ferraccioli et al., 2009; Jordan et al., 2013; of Site U1361. Gravity-density currents like turbidites are common Studinger et al., 2004; Fig. 1a), which would be more accessible during along glaciated margins (Dowdeswell et al., 1998; Hesse et al., 1997; warmer times in the Pliocene due to a retreated ice margin (Cook et al., Piper et al., 2007), and have been used as a proxy for past meltwater 2013). events associated with ice sheet deglaciation in the North Atlantic (e.g. Piper et al., 2007; Rashid et al., 2012). Subsequent westward deflection of these sediments injected into the Southern Ocean by surface (Fig. 1a)

213 C.P. Cook et al. Chemical Geology 466 (2017) 199–218 and bottom currents (Orsi et al., 1999) could carry clay and silt-sized U-Pb ages of detrital zircons, as well as zircons extracted from ice-rafted detrital material towards Site U1361, but discriminate against coarse- quartzite/sandstone clasts in Site U1361 sediments. grained material from the Wilkes Subglacial Basin. Instead, FLIP and Beacon Supergroup-derived lithic clasts and mineral grains, as well as 6. Conclusions coarse-grained hornblendes from sites to the east such as Victoria Land and the Ross Sea, must have been delivered to Site U1361 by ice- In this study we compared the provenance signatures of fine-grained rafting. Despite fine-grained sediments likely comprising some of this and coarse-grained detrital components in Pliocene sediments from distally sourced ice-rafted load, it appears that amounts are too minor IODP Site U1361, Wilkes Land, using clay minerals (< 2 μm), Nd and to dilute the signatures of locally supplied fine-grained sediments. A Sr isotopes (< 63 μm), hornblende grain 40Ar/39Ar ages (> 150 μm), corresponding decrease in the supply of more proximal Early Palaeo- and mineral grain (> 150 μm) and lithic clast (> 2 mm) petrography. zoic granitic derived sediments could be explained by contemporaneous Fine-grained signatures extend published provenance interpretations reduction in supply of sediments to the shelf edge, perhaps associated (Cook et al., 2013), whereby bedrock sources within the Wilkes Sub- with a regionally reduced ice sheet margin (Cook et al., 2013). How- glacial Basin (FLIP and Beacon Supergroup) and local Early Palaeozoic ever, this does not fully explain the absence of a 40Ar/39Ar age popu- terranes supplied fine-grained sediments to Site U1361 throughout the lations indicating FLIP origin in hornblende grains. Pliocene. Petrographic analyses of ice-rafted lithic clasts reveal that the FLIP and Beacon Supergroup lithologies were likely significant bedrock 5.3.2. Potential FLIP and Beacon Supergroup source rock bias sources for ice-rafted debris as well. Low amphibole contents within The FLIP is composed of dolerites and basalts (Elliot and Fleming, FLIP and Beacon bedrocks and/or comminution of such grains, how- 2008), with heavy minerals dominated by Mg-rich clinopyroxenes and ever, prevents us from tracing these particular lithologies by ice-rafted orthopyroxenes (Demarchi et al., 2001; Hauptvogel and Passchier, hornblende 40Ar/39Ar ages. On the other hand, ice-rafted hornblende 2012), a mineralogical feature common to rift-type volcanism (Nechaev 40Ar/39Ar ages reveal multiple erosional source areas along the con- and Isphording, 1993). The petrography of ice-rafted clasts and mineral tinental margins of East Antarctica, potentially even extending east- grains in coarse-grained fractions of Site U1361 sediments reveals sig- wards towards Marie Byrd Land (West Antarctica). West Antarctic nificant quantities of clinopyroxenes and orthopyroxenes (up to 4.3% of provenance of ice-rafted debris off the East Antarctic Wilkes Subglacial total detrital fraction > 150 μm, Table 1), suggesting that the FLIP was Basin occurred during warmer intervals, hinting at large-scale iceberg a viable source of ice-rafted material. This interpretation is validated by production events from the West Antarctic Ice Sheet. the presence of clasts of basalt in the same Pliocene sediments. Fur- Our study highlights the power of combining multiple provenance thermore, on land the FLIP is intimately associated with the Beacon tools within different grain-size fractions when studying marine sedi- Supergroup (Elliot and Fleming, 2008; Fig. 1a). Beacon Supergroup ments derived from a glaciated continent. Single provenance tools are lithologies are dominated by quartzites, sandstones and siltstones and less likely to capture the full spectrum of bedrock characteristics, in- contain very few heavy minerals (Hauptvogel and Passchier, 2012). formation vital for more accurate reconstructions of past ice sheet Their erosion is suggested by abundant clasts of quartzite in Site U1361 histories. sediments (Table 1). Whether the ice-rafted FLIP and Beacon Super- group mineral grains and lithic clasts were sourced from terranes in the Acknowledgments Wilkes Subglacial Basin, or from terranes in the Transantarctic Moun- tains, where they are commonly exposed (Fig. 1a), is difficult to con- C.P. Cook thanks the Grantham Institute for Climate Change at strain. What stands is the observation that FLIP lithologies are not Imperial College London for a PhD scholarship, K. Kreissig and B. Coles captured by hornblende 40Ar/39Ar age populations. This observation is for lab assistance, P. Simões Pereira and R. Bertram for discussion, and best explained by a source rock bias in the marine sediment record. IODP for providing materials. Ian Bailey and an anonymous reviewer Hornblende grains have been shown to be comparatively rare in heavy provided very insightful comments that helped improve the manuscript mineral assemblages derived from sediment sources dominated by FLIP a lot. Financial support for this study was provided by NERC UK IODP terranes (Hauptvogel and Passchier, 2012) and are unlikely to have to T.v.d.F. (NE/H014144/1, NE/H025162/1), by the European survived the multiple sedimentary cycles documented by zircon ages in Commission to T.v.d.F. (IRG 230828), by the National Science Beacon lithologies (Elliot and Fanning, 2008; Elsner et al., 2013; Foundation to T.W., T.v.d.F. and S.R.H. (ANT 0944489 and ANT Goodge and Fanning, 2010; see also discussion in Pierce et al., 2014). 1342213), and by the Royal Society to T.v.d.F. and S.R.H. (IE110878). Another possible explanation is that erosion of FLIP lithologies from within the Wilkes Subglacial basin was mainly happening subglacially Appendix A. Supplementary data and hence subject to comminution. Support for the latter idea, and the existence of a FLIP component in the fine-grained fraction of sediments Supplementary data to this article can be found online at http://dx. offshore the Wilkes Subglacial basin, comes from K-Ar analyses at Site doi.org/10.1016/j.chemgeo.2017.06.011. U1356, located to the west of site U1361. Johnson et al. (2012) found a strong correlation between the Nd isotope composition and K-Ar ages in References fine-grained (< 63 μm) Miocene sediments, extending from Palaeozoic ages to ages as young as the Jurassic intrusion ages of the FLIP Adams, C.J., 2006. Style of uplift of Paleozoic terranes in Northern Victoria Land, (~180 Ma). Antarctica: evidence from K-Ar age patterns. In: Fütterer, D.K., Damaske, D., Kleinschmidt, G., Miller, H., Tessensohn, F. (Eds.), Antarctica: Contributions to Hence we conclude that variable mineralogical compositions and Global Earth Sciences. Springer, Berlin, Heidelberg, New York, pp. 45–54. grain sizes in different bedrock types have produced the different pro- Aitken, A.R.A., Young, D.A., Ferraccioli, F., Betts, P.G., Greenbaum, J.S., Richter, T.G., venance signatures extracted from the Pliocene marine sediment as- Roberts, J.L., Blankenship, D.D., Siegert, M.J., 2014. The subglacial geology of Wilkes Land, East Antarctica. Geophys. Res. Lett. 41, 2390–2400. http://dx.doi.org/10. semblage at Site U1361. This interpretation could be tested with future 1002/2014GL059405. 40 39 analysis of Ar/ Ar ages of detrital plagioclase and basalt clasts Anderson, J.B., Shipp, S.S., Bartek, L.R., Reid, D.E., 1992. Evidence for a grounded ice identified in Site U1361 sediments, similar to existing thermo- sheet on the Ross Sea continental shelf during the Late Pleistocene and preliminary – chronological analyses of whole rock basalts and mineral grains from paleodrainage reconstruction. Ant. Res. Ser. 57, 39 62. 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