| dc.description.abstract | Dust is a highly mobile and influential class of sediment. Dust influences the climate, biosphere, and soils, and holds information about Earth’s paleoclimate when preserved in the rock record. In this work we define dust as rock and mineral fragments, generally less than 100 µm, which are transported in suspension by the wind (Tsoar & Pye, 1987). We adopt size categories of dust proposed by Adebiyi et al. (2023, preprint) with fine dust 0-2.5 µm, coarse dust 2.5-10 µm, super coarse 10-62.5 µm, and giant dust >62.5 µm. When transported through the atmosphere, dust interacts with incoming solar radiation, outgoing infrared radiation, and clouds, altering the climate of the planet (Conen et al., 2011; Dufresne et al., 2002; 2023; Rosenfeld et al., 2001; Tang et al., 2016). The exact radiative effects are poorly understood and difficult to quantify and are the subject of ongoing research. One of the limitations in studying the radiative effects of dust is accurate particle size distributions (PSDs) for dust in the atmosphere (Kok et al., 2017). The effects of dust on the atmosphere depend on the composition, shape, and size of the dust particles. Fine dust (<2.5 µm) is assumed to scatter and reflect incoming shortwave solar radiation causing a cooling effect, while coarse dust (>2.5 µm) tends to have a warming effect by absorbing and reemitting longwave radiation (Adebiyi & Kok, 2020; Kok et al., 2023). Dust can influence cloud formation, precipitation, and nucleation of ice crystals, although the relationships are poorly understood (Kok et al., 2023).
When deposited in oceans or into soils, dust brings nutrients that promote biological productivity, which generally draws CO2 out of the atmosphere, causing cooling (Bristow et al., 2010; Mahowald et al., 2011; Okin et al., 2011; Skiles et al., 2018). When deposited on snow and ice it reduces albedo and the amount of solar radiation reflected from the surface. Dusty snow with its lower albedo is also easier to melt as it absorbs incoming solar radiation (Bristow et al., 2010; Mahowald et al., 2011; Okin et al., 2011; Skiles et al., 2018). Dust as a sediment in soils and the rock record preserves information about the climate and environment at the time of deposition (Jordanova et al., 2022; Daniel R. Muhs, 2013). For example, loess and paleosol sequences preserve intervals of aridity and rapid dust accumulation followed by stability and a low sedimentation rate where a soil horizon develops. If the source of dust is identified, then paleowind patterns can be determined, yielding information about the climate of the past.
Several processes have been proposed as mechanisms capable of producing dust including glacial grinding, aeolian saltation, explosive volcanism, high-altitude alpine weathering, chemical weathering, and biogenic siliceous diatoms (Aleinikoff et al., 1999, 2008; McTainsh, 1989; Nahon & Trompette, 1982; Smalley, 1995; Smalley, 1966; Smalley & Vita-Finzi, 1968). Not all of these processes have been thoroughly investigated, however. Many loess accumulations—structureless deposits of eolian silt—have been linked to glacial erosion by spatial proximity to the margins of former ice sheets. However not all loess deposits are geographically proximal to loess. For example, the Chinese Loess Plateau (CLP) is an immense loess deposit composed of silt-sized dust, but it is not proximal to any recently glaciated area (Muhs, 2013). This has led to speculation of other processes capable of producing dust. The CLP is downwind of a large desert and this has spurred debate about whether aeolian abrasion of sand grains in desert environments could produce abundant silt-sized dust. A series of experiments followed, attempting to replicate the process of aeolian saltation in the lab to determine if the mechanism was viable (Whalley et al. 1987; Wright et al. 1998; Bullard et al. 2004, 2007). Experiments have also been performed in the lab replicating glacial grinding. Initially, glacial grinding experiments did not produce abundant silt; however subsequent experiments determined that this was because crushed Brazilian vein quartz, which contained few crystal defects compared to plutonic quartz, was used in the experiments (Wright, 1995; Jefferson et al. 1997; Kumar et al., 2006). Experiments using sand from Cretaceous sandstones readily produced silt when ground in a ring-shear device, considered an analog for glacial grinding (Jefferson et al. 1997; Kumar et al., 2006).
While there have been several experiments exploring the physical abrasion processes capable of producing silt and dust, several knowledge gaps remain. Few studies have adequately investigated abrasion of basalt sands via aeolian abrasion and these previous results are not scalable to determine the geological significance. Most experiments have focused on the abrasion of quartz or granitic rocks, with few studies investigating the production of dust by abrading basalts, sedimentary rocks, or metamorphic rocks. Previous glacial grinding experiments that did not use ring shear devices used wheels of rock and sediment, ground against each other, rather than focusing on subglacial clasts and their shapes (Matthews, 1979; Lee and Rutter, 2004).
In this study two new experimental devices are used, which have been designed to better replicate aeolian abrasion and glacial grinding. The aeolian abrasion chamber is designed to simulate grain-on-grain collisions of sand saltating in a windstorm at high velocities (~40 m/s). The glacial grinding device abrades small rock fragments cut with flat and pyramidal (pointed) surfaces against a flat rock slab to emulate the grinding of clasts beneath a glacier. The aeolian abrasion experiment focuses on the abrasion of basalt sands from Hawaii and Iceland as analogs for Mars and compares them to results from quartzose sand from the Imperial Sand Dunes of southern California. The glacial grinding device abrades five basalts as analogs for Mars and eleven different rocks (granitoids, quartzites, a schist, sandstones, and limestones) as analogs for Earth-based glaciation.
We compare our results with previous dust production experiments and studies of dust to test two questions: (1) Do different abrasion mechanisms produce representative particle size distributions (PSDs) tied to the mechanism of production? (2) When abraded, do different lithological compositions produce dust at different rates and PSDs with defining traits based on composition? Results show that basaltic sand from Iceland produced 4 times more dust and 2.5 times more fine sand than Hawaiian samples. These experiments demonstrate the significance of dust production by aeolian saltation of basalt sand at the planetary scale and infer the possible influence of produced dust on the climate of early Mars. Results are scaled to determine dust production at the planetary level and suggest Mars would produce a geologically significant amount of dust capable of influencing the climate.
Results from experimental glacial grinding of small (~3 cm) clasts of varying lithologies (representing Earth and Mars) show that rock-on-rock abrasion produces sediment with PSDs containing silt modes (~30 µm). Pointed styluses generally produce more sediment than flat styluses. Pointed and flat styluses of the same lithologies generally produce similar PSDs. PSDs across all lithology and stylus types produce similar modes at 0.5 µm, 4-8 µm, 30 µm, and 100-300 µm. When our PSD results are compared to natural dust sources and previous experiments replicating a range of abrasion processes (e.g., volcanic dust, lunar dust, glacial grinding, aeolian abrasion, fluvial abrasion, mechanical crushing) the same modal ranges occur. Our study suggests an underlying physical process operating across abrasion mechanisms, varying mineralogical compositions, and clast shapes that limits PSD modes to specific ranges. | en_US |
