Grain size and shape analysis of recent and paleo sediments along Poyang Lake with insight into its environmental significance

Abstract

Grain shape is a crucial sedimentological attribute commonly employed for reconstructing depositional environments and transport history. The new dynamic image analysis (DIA) techniques enable testing a large number of individual mineral grains simultaneously and overcomes many shortcomings of traditional visual evaluation. However, there is a relative dearth of comprehensive analysis on large quantities of sediments in recent and geological period to accurately document their grain shape properties and further evaluate their applicability in distinguishing sedimentary setting and its environmental significance. In this study, we measured the grain shape and size of 77 samples collected from modern surface sand (28 beach sand and 17 dune sand samples) and stratigraphic sediment (16 paleo-dunes sand and 16 paleo-lacustrine sand samples) along the Poyang Lake in southeastern China using the DIA method, and optically stimulated luminescence (OSL) dating was used to constrain the age of stratigraphic sediments from two sand hill sections. Also 217 published grain shape data from various sedimentary environments (coastal beach, desert dune and fluvial sand) were compiled as comprehensively assess the applicability of grain shape discrimination for sedimentary setting. Our results show the significant difference on grain shape feature among fluvial, coastal beach and dune sand. Dune sand exhibit the highest values for circularity (Ci), symmetry (Sy), aspect ratio (AR), and convexity (Cx), while fluvial sand displays high Ci, Sy, Cx value, and lowest AR value. This indicate that the grain shape can be a powerful tool for discriminating sedimentary setting. Principal component analysis shows that circularity and aspect ratio effectively describe the shape of the analyzed sediment and are decisive indicators for identification depositional environments, whereas the convexity has limited sensitivity in distinguishing grain edge roundness. The paleo-lacustrine sand (PLS) intercalated within the sand hill profiles returns OSL age of age of ∼ 26.5 ± 1.4 ka, which indicate the emergence of interdune lake rather than high lake level of Poyang Lake. PLS and modern beach sand (BS) exhibiting identical grain shape characteristics to those of modern aeolian dune sand (DS) suggested the occurrence of aeolian-fluvial interaction processes in our study area during the Last Glacial Maximum and present day. The paleo-dune sand (PDS) samples, yielding OSL age of 1.2 ± 0.1 ka, are characterized by higher Ci, Sy, and AR, indicating strong aeolian activity and dune reworking during the past two millennia along the Poyang Lake.