Making loess-sized quartz silt: data from laboratory simulations and implications for sediment transport pathways and the formation of 'desert' loess deposits associated with the Sahara

Results from a series of laboratory simulations designed to investigate quartz silt generation by a number of geomorphic mechanisms are reviewed. These findings are then used to discuss potential sediment pathways involved in the formation of 'desert' loess deposits and a pathway is presented to show a proposed sequence of events involved in the formation of the loess deposits associated with the Sahara. The results indicate that both fluvial acid aeolian systems can be very effective at producing quartz silt. It is suggested that fluvial systems within hot desert environments may play a central role in both the production and distribution of loessic silt. First, the highly energetic but periodic fluvial regimes associated with arid and semi-arid environments may be responsible for considerable quantities of particle comminution. Second. the intermittent nature of these systems will help maintain geomorphologically active surfaces from which silt-sized material can be easily deflated. As well as fluvial comminution, a range of weathering mechanisms and aeolian abrasion may also be responsible for the generation of silts in 'desert' loess. Consequently, silt sources and mechanisms of silt generation are likely to be much more diverse for 'desert' loess than those associated with glacial loess. (C) 2001 Elsevier Science Ltd and INQUA. All rights reserved.