Mineral associations of late Quaternary permafrost deposits - Bol’shoy Lyakhovsky Island compared to other locations in northern Siberia.

Bol’shoy Lyakhovsky Island has been a major focus area in Yedoma research in course of joint Russian-German expeditions in 1999, 2007 and 2014 conducted by colleagues from the Mel’nikov Permafrost Institute Yakutsk and the Alfred Wegener Institute Potsdam [1,2]. However, origins and genesis of periglacial deposits such as the late Pleistocene Yedoma Ice Complex are still debated [3] and referred to by some researchers as pure windblown sediments, while other researchers suggest more local sediment sources from intense nivation and periglacial weathering, or even a polygenetic origin under comparable cold-climatic, highly continental conditions in different regions. To disentangle sources and potential transport pathways of sediments, mineral associations are useful indicators. Identifying linkages of mineral associations in sediments to local bedrock, fluvial sources, or fare ranging sources for potential eolian transport are therefore important. Various studies on palaeoecology [4,5], stable isotopy [6], geophysics [7], biogeochemistry [8] and palaeogenetics [9] have been carried out over the last more than 20 years. In the present study, we analyzed the mineral associations in sediments of one of the best-dated permafrost sequences including the Yedoma Ice Complex exposed at the southern coast of Bol’shoy Lyakhovsky Island near the Zimov’e River mouth. The permafrost record spans about 200 ka covering the Marine Isotope Stages (MIS) 6 to MIS 1 [10,11,12,13,15], although not continuously. From these deposits, exposed from sea level to about 35 m above sea level, we studied heavy and light minerals of 65 samples from different cryostratigraphic horizons in both the 63-125 µm and the 125-250 µm fractions. The studied mineral grains used are subangular to slightly rounded. The heavy mineral associations are dominated by amphibole, epidote, pyroxene, titanite, ilmenite, garnet, zircon, apatite, and rutile. Leucoxene is found in several samples as well as biotite, chlorite and weathered micas. The light mineral association is dominated by feldspar, quartz, and chlorites. Carbonates, muscovite, and broken mica are observed in some samples. Differences in the heavy and light mineral associations represent varying sediment sources and transport mechanisms of the deposits aligned to the distinct cryostratigraphic horizons (Fig. 1). Characteristic associations of the different horizons are assessed using variance analysis on the counted mineral grains. Statistically significant (at 95% confidence level) distinct mineral associations are found with ilmenite, garnet, zircon, tourmaline, titanite, and leucoxene in the heavy minerals and feldspar in the light minerals. MIS 1 (Holocene thermokarst deposits) is the least distinctly separable unit in the heavy minerals, MIS 4 (Zyryan stadial floodplain deposits) and MIS 6 (Yukagir interstadial Ice Complex) are the most distinctly separable units. In the light minerals, MIS 2 (stadial Sartan Yedoma Ice Complex) is the least and MIS 4 the most distinctly separable unit. The MIS 3 (interstadial Molotkov Yedoma Ice Complex) and the MIS 5 (interglacial Kazantsev thermokarst deposits) units show intermediate separability in both heavy and light minerals. The Bol’shoy Lyakhovsky mineral associations were compared with other permafrost exposures on the Siberian mainland along the Laptev Sea coast [15,16,17], in the Lena Delta [18], and on other islands of the New Siberian Archipelago. Our findings suggest that weathered bedrock from nearby ridges and hills was the most likely source material for the formation of late Quaternary permafrost deposits. The local sediment sources are more in line with hypotheses for Yedoma Ice Complex genesis [19] that involve largely local erosion, transport, and deposition processes as opposed to eolian deposition involving regional to panarctic-scale movement of dust and larger grainsize particles. A B Fig. 1 Averages of heavy (A) and light (B) mineral associations of the 63-125 µm fraction according to the stratigraphy References 1. Andreev, A. et al. Weichselian and Holocene palaeoenvironmental history of the Bol’shoy Lyakhovsky Island, New Siberian Archipelago, Arctic Siberia, Boreas, 2009, 38(1), 72–110. 2. Andreev, A. et al. Late Saalian and Eemian palaeoenvironmental history of the Bol'shoy Lyakhovsky Island (Laptev Sea region, Arctic Siberia), Boreas, 2004, 33(4), 319-348. 3. Schirrmeister, L. et al. Yedoma: Late Pleistocene ice-rich syngenetic permafrost of Beringia, Encyclopedia of Quaternary Science, 2nd edition, 2013, 3, 542-552. 4. Kienast, F. et al. Continental climate in the East Siberian Arctic during the last interglacial: implications from palaeobotanical records, Global Planet. Change, 2008, 60(3/4), 535-562. 5. Sher, A.V. et al. 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