Glacial Erosion of East Antarctica in the Pliocene a Comparative Study
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Chemical Geology 466 (2017) 199–218 Contents lists available at ScienceDirect Chemical Geology journal homepage: www.elsevier.com/locate/chemgeo 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