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The Bodélé Depression, Chad is the planet's largest single source of dust. Deflation from the Bodélé could be seen as a simple coincidence of two key prerequisites: strong surface winds and a large source of suitable sediment. But here we hypothesise that long term links between topography, winds, deflation and dust ensure the maintenance of the dust source such that these two apparently coincidental key ingredients are connected by land-atmosphere processes with topography acting as the overall controlling agent. We use a variety of observational and numerical techniques, including a regional climate model, to show that: 1) contemporary deflation from the Bodélé is delineated by topography and a surface wind stress maximum; 2) the Tibesti and Ennedi mountains play a key role in the generation of the erosive winds in the form of the Bodélé Low Level Jet (LLJ); 3) enhanced deflation from a stronger Bodélé LLJ during drier phases, for example, the Last Glacial Maximum, was probably sufficient to create the shallow lake in which diatoms lived during wetter phases, such as the Holocene pluvial. Winds may therefore have helped to create the depression in which erodible diatom material accumulated. Instead of a simple coincidence of nature, dust from the world's largest source may result from the operation of long term processes on paleo timescales which have led to ideal conditions for dust generation in the world's largest dust source. Similar processes plausibly operate in other dust hotspots in topographic depressions.

Author(s): C. S. Bristow (corresponding author) [1]; S. D. Bailey [1]; N. Lancaster [2] Linear sand dunes--dunes that extend parallel to each other rather than in star-like or crescentic forms--are [...]

Coastal dune accumulations at locations around the world have formed during sea-level highstands, rising sea levels, falling sea levels, and fluctuating sea levels. Initially, episodes of maximum Pleistocene dune activity in Bermuda, which is the type location for eolianite, were correlated with glacio-eustatic regressions. This model had been abandoned by the 1970s in favor of a rising sea-level model for Bermuda's north shore and autogenic sediment-supply model for the south shore. We report the results of a detailed investigation of the intercalated mid-late Pleistocene beach and coastal dune deposits on the islands of Bermuda, and we test the existing models for these deposits. We contend that the north shore model is invalidated by past misidentification of eoliandeposits as transgressive beach deposits. On the south shore, facies analysis of the marine isotope stage 7 (MIS 7) Belmont Formation reveals that coastal deposition was divided into two phases. S1, which includes foreshore and shoreface progradation, is predominantly marine and coincided with rising relative sea level. S2, which commenced with protosol development on top of the marine section prior to burial by advancing dunes, is nonmarine. We conclude that the two successions S1 and S2 resulted from forcing by glacio-hydro-isostatic relative sea-level change spanning a highstand (rising and then falling), rather than from transgressive or autogenic processes. The finding that, in Bermuda, the construction of protective coastal dunes depends on a falling relative sea level has potential implications for many vulnerable shorelines that face rising relative sea levels associated with climate change. [ABSTRACT FROM AUTHOR]

Ground-penetrating radar and luminescence dating studies of a large, complex, linear dune in the northern part of the Namib Sand Sea provide new information on the age and internal sedimentary structures of these dunes, with important implications for interpretations of paleoclimates and the rock record of eolian sandstones. The dune is a composite feature formed during several episodes of construction, including a hiatus of almost 2000 yr. The oldest sands within the dune are 5700 yr old, indicating complete turnover of sand during the Holocene. The dune has moved laterally by ∼300 m during the past 2500 yr, proving lateral migration of a large linear dune. Dune construction has been affected by climate change, and we attribute the hiatus to increased rainfall and vegetation, which largely halted sand movement and dune building in the Namib Desert during the middle Holocene. [ABSTRACT FROM AUTHOR]

Abstract The effectiveness of detrital zircon thermochronology as a means of linking hinterland evolution and continental basin sedimentation studies is assessed by using Mesozoic continental sediments from the poorly understood Khorat Plateau Basin in eastern Thailand. New uranium lead (U-Pb) and fission-track (FT) zircon data from the Phu Kradung Formation identify age modes at 141 ± 17 and 210 ± 24 Ma (FT) and 2456 ± 4, 2001 ± 4, 251 ± 3, and 168 ± 2 Ma (U-Pb), which are closely similar to data from the overlying formations. The FT data record post-metamorphic cooling, whereas the U-Pb data record zircon growth events in the hinterland. Comparison is made between detrital zircon U-Pb data from ancient and modern sources across Southeast Asia. The inherent stability of the zircon U-Pb system means that 250 Myr of post-orogenic sedimentary recycling fails to change the regional zircon U-Pb age signature and this precludes use of the U-Pb approach alone for providing unique provenance information. Although the U-Pb zircon results are consistent with (but not uniquely diagnostic of) the Qinling Orogenic Belt as the original source terrane for the Khorat Plateau Basin sediments, the zircon FT cooling data are more useful as they provide the key temporal link between basin and hinterland. The youngest zircon FT modes from the Khorat sequence range between 114 ± 6 (Phra Wihan Formation) and 141 ± 17 Ma (Phu Kradung Formation) that correspond to a Late Jurassic/Early Cretaceous reactivation event, which affected the Qinling Belt and adjacent foreland basins. The mechanism for regional Early Cretaceous erosion is identified as Cretaceous collision between the Lhasa Block and Eurasia. Thus, the Khorat Plateau Basin sediments might have originated from a reactivation event that affected a mature hinterland and not an active orogenic belt as postulated in previous models. [ABSTRACT FROM AUTHOR]