Aeolian sorting processes in the Ejina desert basin (China) and their response to depositional environment

Abstract

Granulometric analysis of Aeolian and fluvial sediments in a middle-latitude desert basin (Ejina) was conducted. Sediments were collected from four main geomorphological units (Gobi/foredune, interdune, dune crest and riverbed) which represent the typical surficial conditions. Dunes studied are relatively coarser and lie towards the worse-sorted end of the range in comparison with other deserts. Both the M-z values of aeolian and fluvial sediments tend to decrease as the distance increase toward the Langxin-shan but in different variational patterns for sorting parameters between them, indicating a regular change of grain size but different sorting processes in the regional scale between Aeolian and fluvial sediments. Dune sands become finer and better sorted and less positively skewed from dune crest to interdune and foredune. This sorting pattern in dune unit appears to follow those described from the Libya and Namib deserts. While, the Ejina dunefield is located close to its sand sources, which for the most part are believed in this study to be distal palaeo-alluvial fan deposits (Gobi sediments) rather than modern fluvial sediments. The Ejina dunes therefore contain significant amounts of coarse grains with weak sorting degree. This is unlike so-called mature sand seas (e.g., central Namib Sand Sea), which lie at some distance in time and space from the original sources of sediment, indicating that the availability of particle sizes in source area exerts a strong influence on the spatial patterns of particle size and sorting in the Ejina dunes. (C) 2013 Elsevier B.V. All rights reserved.