Clay mineralogy, strontium and neodymium isotope ratios in the sediments of two High Arctic catchments (Svalbard)

Ruth S Hindshaw,Edward T Tipper,Nicholas J Tosca,Alexander M Piotrowski

doi:10.5194/esurf-6-141-2018

Ruth S Hindshaw, Edward T Tipper + Show 2 more

Open Access

https://doi.org/10.5194/esurf-6-141-2018

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Abstract

Abstract. The identification of sediment sources to the ocean is a prerequisite to using marine sediment cores to extract information on past climate and ocean circulation. Sr and Nd isotopes are classical tools with which to trace source provenance. Despite considerable interest in the Arctic Ocean, the circum-Arctic source regions are poorly characterised in terms of their Sr and Nd isotopic compositions. In this study we present Sr and Nd isotope data from the Paleogene Central Basin sediments of Svalbard, including the first published data of stream suspended sediments from Svalbard. The stream suspended sediments exhibit considerable isotopic variation (εNd = −20.6 to −13.4; 87Sr ∕ 86Sr = 0.73421 to 0.74704) which can be related to the depositional history of the sedimentary formations from which they are derived. In combination with analysis of the clay mineralogy of catchment rocks and sediments, we suggest that the Central Basin sedimentary rocks were derived from two sources. One source is Proterozoic sediments derived from Greenlandic basement rocks which are rich in illite and have high 87Sr ∕ 86Sr and low εNd values. The second source is Carboniferous to Jurassic sediments derived from Siberian basalts which are rich in smectite and have low 87Sr ∕ 86Sr and high εNd values. Due to a change in depositional conditions throughout the Paleogene (from deep sea to continental) the relative proportions of these two sources vary in the Central Basin formations. The modern stream suspended sediment isotopic composition is then controlled by modern processes, in particular glaciation, which determines the present-day exposure of the formations and therefore the relative contribution of each formation to the stream suspended sediment load. This study demonstrates that the Nd isotopic composition of stream suspended sediments exhibits seasonal variation, which likely mirrors longer-term hydrological changes, with implications for source provenance studies based on fixed end-members through time.

Highlights

Since the Miocene, the Arctic has been subject to the repeated advance and retreat of ice sheets, a record of which is preserved in ocean sediments (Svendsen et al, 2004; Knies and Gaina, 2008)
The measured values are typical for shales (Taylor and McLennan, 1985) and the rare earth element (REE) chondrite normalised element profile of these samples closely follows that of the Post Archaean Australian Shale (PAAS, Table A2)
The large variations in 87Sr / 86Sr and εNd observed in sediments from two small catchments in Svalbard can be explained as a result of two isotopically and geochemically distinct sediment sources mixing during the Mesozoic and subsequently forming the Paleocene–Eocene sedimentary formations which are eroding today (Fig. 10)

Summary

Introduction

Since the Miocene, the Arctic has been subject to the repeated advance and retreat of ice sheets, a record of which is preserved in ocean sediments (Svendsen et al, 2004; Knies and Gaina, 2008). Vogt et al, 2001; Spielhagen et al, 2004; Knies and Gaina, 2008; Hillaire-Marcel et al, 2013; Fagel et al, 2014; Meinhardt et al, 2016). They provide information on past ocean chemistry through analysis of foraminifera (e.g. Knies et al, 2014), on iceberg abundance through analysis of ice-rafted debris Hindshaw et al.: The sediments of two High Arctic catchments

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