Abstract
Cryogenic weathering is a key driver of periglacial sediment composition and properties. Selective mineral-grain weathering caused by freeze-thaw cycles in permafrost environments has the ability to dominate this process, leading to silt-rich grain-size distributions. The cryogenic weathering index (CWI) is a promising tool to quantify cryogenic weathering and freezing conditions. It considers the low resistance of quartz to freeze-thaw cycles compared to feldspars. Using this approach, this study aims to decipher post-depositional weathering by reconstructing cryogenic late Pleistocene Yedoma origins of the Yedoma stratotype exposure Duvanny Yar. To estimate the recent environmental endmember and to determine the initial mineral composition of sediment until freezing, the distribution of CWI in the active layer was studied. In addition to CWI, we studied mineral composition, heavy mineral distribution, grain size distribution and grain morphology. We suggest that cryogenic weathering likely altered polygenetic deposits (fluvial, nival, colluvial, lacustrine, alluvial, and aeolian processes) during sediment and ground ice accumulation. Moreover, we found two CWI distribution peaks in the late Pleistocene - Holocene sediments at the boundaries between glacial and interglacial ages. In conclusion, we see that the Duvanny Yar sediment facies varied by CWI, but also with grain-size distribution, suggesting environmental changes during formation. Nevertheless, post-depositional processes like cryogenic weathering have influenced sediment characteristics and should be considered in paleoenvironmental reconstructions.
Highlights
IntroductionThe permafrost region (including permafrost-free areas) of the Northern Hemisphere land area is estimated to be 21 million km (22% of the exposed land area), and modelling studies indicate that 13.9 million km are underlain by permafrost (Obu et al, 2019)
The permafrost region of the Northern Hemisphere land area is estimated to be 21 million km2 (22% of the exposed land area), and modelling studies indicate that 13.9 million km2 are underlain by permafrost (Obu et al, 2019)
Applying the cryogenic weathering index (CWI), the aim of this study is to decipher the Yedoma depositional environment and the post-depositional processes involved at the Duvanny Yar Yedoma stratotype by determining the role of cryogenic weathering in the formation of Yedoma deposits and the cover layers
Summary
The permafrost region (including permafrost-free areas) of the Northern Hemisphere land area is estimated to be 21 million km (22% of the exposed land area), and modelling studies indicate that 13.9 million km are underlain by permafrost (Obu et al, 2019). An accepted view is that quartz is more resistant than feldspar to chemical weathering, the process involving chemical reactions of minerals with water and acidity leading to the dissolution of the minerals. For cryogenic weathering, this is the opposite: quartz is less resistant than feldspar (Konishchev and Rogov, 1993; Schwamborn et al, 2012). Rogov (2000) suggested that when gas-liquid inclusions, generally containing salt, freeze, they create weak points, leading to the weathering of quartz minerals during freeze-thaw cycles Due to different surface energy (charge) quartz is assumed to have thicker water films compared to feldspar (Rogov, 2000). Rogov (2000) suggested that when gas-liquid inclusions, generally containing salt, freeze, they create weak points, leading to the weathering of quartz minerals during freeze-thaw cycles
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