Search

As sand moves across Earth's landscapes, the shapes of individual grains evolve, and microscopic textures accumulate on their surfaces. Because transport processes vary between environments, the shape and suite of microtextures etched on sand grains provide insights into their transport histories. For example, previous efforts to link microtextures to transport environments have demonstrated that they can provide important information about the depositional environments of rocks with few other indicators. However, such analyses rely on 1) subjective human description of microtextures, which can yield biased, error-prone results; 2) nonstandard lists of microtextures; and 3) relatively large sample sizes (>20 grains) to obtain reliable results, the manual documentation of which is extremely labor intensive. These drawbacks have hindered broad adoption of the technique. We address these limitations by developing a deep neural network model, SandAI, that classifies scanning electron microscope images of modern sand grains by transport environment with high accuracy. The SandAI model was developed using images of sand grains from modern environments around the globe. Training data encompass the four most common terrestrial environments: fluvial, eolian, glacial, and beach. We validate the model on quartz grains from modern sites unknown to it, and Jurassic-Pliocene sandstones of known depositional environments. Next, the model is applied to two samples of the Cryogenian Bråvika Member (of contested origin), yielding insights into periglacial systems associated with Snowball Earth. Our results demonstrate the robustness and versatility of the model in quickly and automatically constraining the transport histories recorded in individual grains of quartz sand. [ABSTRACT FROM AUTHOR]

Dust dynamics influence planetary atmospheres. However, the settling velocity of dust—and thus its residence time in the atmosphere—is often mispredicted. Challenging, indirect experiments involving few ideal particles revealed that dust settling velocity deviates from Stokes' law under rarefied atmospheres. While useful, such experiments are inadequate to simulate more complex scenarios, including variable particles sizes and shapes. Here, we present direct measurements of settling velocity for spherical particles under Earth‐to‐Mars atmospheric pressures using time‐resolved particle image velocimetry (TR‐PIV), and validate their robustness with existing models. Our results demonstrate that TR‐PIV provides a relatively simple approach to quantifying dust settling velocity from direct observations of over 10,000 particles, enabling systematic investigations of dust settling under realistic scenarios. Such experiments will have significant implications for our understanding of Mars' past, present, and future ‐ from providing a tool to decipher its sedimentary record to enhancing predictive capabilities of atmospheric models. Plain Language Summary: Airborne dust strongly affects the environments and atmospheres of Earth and Mars. Knowing the speed at which dust settles is critical because it controls the time dust stays in the atmosphere. However, it is a difficult quantity to measure, and as a result, it is often poorly predicted by existing models. These models were built from experiments that did not match real‐world conditions and typically only considered few, idealized particles. Here, we propose a relatively simple approach to make direct measurements of dust settling under Earth‐to‐Mars atmospheric pressures. This technique, time‐resolved particle image velocimetry, allows us to directly measure the speed of over 10,000 particles. Using ideal particles, we show that our measurements align well with results from previously published models, validating the robustness of our procedure. The same experimental setup can be used to investigate dust settling under more realistic conditions, for example, varying the size distribution of dust particles, their shape, or dust concentration. Such measurements are a stepping stone toward accurate interpretations and predictions of dust dynamics on Earth and Mars. Key Points: Dust settling velocity controls residence time of dust in the atmosphere but is challenging to measure under low atmospheric densityWe measure dust settling velocity under Earth‐to‐Mars‐like conditions using time‐resolved particle image velocimetry (TR‐PIV)TR‐PIV enables systematic studies of dust settling on Mars and other bodies using realistic particles and varying dust concentrations [ABSTRACT FROM AUTHOR]

Candidate glaciovolcanic landforms have been identified across Mars, suggesting that volcano‐ice interactions may have been relatively widespread in areas that once contained extensive surface and near‐surface ice deposits. To better constrain the detection of glaciovolcanism in Mars' geological record, this study has investigated and characterized the petrology, geochemistry, and mineralogy of three intraglacial volcanoes and an interglacial volcano in the Þórisjökull area of southwest Iceland. Our results show that glaciovolcanism creates abundant, variably altered hyaloclastite and hyalotuff that is sufficiently geochemically and mineralogically distinctive from subaerially erupted lava for identification using instruments available on Mars rovers and landers. Due to the lower gravity and atmospheric pressure at the surface of Mars, hyaloclastite and hyalotuff are also more likely to form in greater abundance in Martian glaciovolcanoes. Our results support that magmatism following deglaciation likely triggers decompression melting of the shallow mantle beneath Iceland, creating systematic changes in geochemistry and mineralogy. Glaciation can also suppress magmatism at its peak, encouraging the formation of shallow fractionated magma chambers. As such, it is possible for the crustal loading of an ice cap to enhance igneous diversity on a planet without plate tectonism, creating glass‐rich, altered, and mineralogically diverse deposits such as those discovered in Gale crater by the Curiosity rover. However, as the eroded products of glaciovolcanism are similar to those formed through hydrovolcanism, the presence of a glaciovolcanic landform at the source is required to confirm whether volcano‐ice interactions occurred at the sediment source. Plain Language Summary: The ancient Martian climate has been long debated with scientists hypothesizing that the river channels and lake beds preserved on the surface today formed in either a warm and wet environment or a cold and icy environment, with heating events driving large‐scale melting. One such heating event includes volcanism. This study investigated the chemical and mineralogical impact of volcano‐ice interactions in Iceland using techniques available to Mars rovers and landers to improve the detection of these deposits on Mars. Our results show that deposits rich in glass and the early products of low temperature alteration (palagonite, clays, zeolites) are likely to be more prevalent on Mars compared to the Earth due to differences in gravity between the two planets. Furthermore, the presence of a thick ice cap on Mars may encourage a diversity of lava compositions to form in shallow magma chambers as the weight of a thick ice cap can suppress volcanism. These types of deposits are identifiable using Mars rover and lander techniques, but due to their similarities to other volcanic units that may have erupted in the presence of water, a candidate glaciovolcanic landform is needed to confirm that these deposits are from volcano‐ice interactions. Key Points: Glaciovolcanism creates large deposits of altered fragmented volcanic glass distinct from subaerial volcanismGlaciation can suppress magmatism, driving geochemical and mineralogical diversity in an area once deglaciation startsGlaciovolcanism may have occurred on Mars with explosive phreatomagmatic units more likely under Mars' planetary conditions [ABSTRACT FROM AUTHOR]

Windblown dunes are common features in our solar system, forming on planetary surfaces that span wide ranges in gravity and both atmospheric and sediment properties. The patterns formed by their crests, which are readily visible from orbital images, can record information about recent changes in boundary conditions, such as shifts in wind regime or varying sediment availability. Here, we demonstrate that the density of dune interactions (where neighboring crestlines are close to each other) within a dune field is an indicator of such changes. Using orbiter-based images of 46 dune fields on Earth and Mars, we compiled a database of pattern parameters including dune spacing, crestline orientation, and interaction density. Combined with sediment fluxes derived from ERA5-Land data and a martian global circulation model, we also compiled dune turnover time scales (the time it takes for a dune to migrate one dune length) for each investigated dune field. First, we show that dune fields undergoing changes in boundary conditions display higher than expected dimensionless interaction indices. Second, dune fields with longer turnover times display a wider range in interaction indices on both Earth and Mars because they are more likely to be observed while still adjusting to recent changes in boundary conditions. Thus, a dune field's interaction index offers a novel tool to detect and possibly quantify recent environmental change on planetary surfaces. [ABSTRACT FROM AUTHOR]

Loose sand, blown away from source regions by winds, is transported across Mars's surface into sand sheets and dunes and accumulates within topographic sinks. In the absence of plate tectonics, impact craters constitute a dominant sink for windblown sediments on Mars today. We analyzed the volume of all mapped eolian sands in martian craters >1 km in diameter to reveal spatiotemporal patterns of sediment accumulation on the planet's surface. We combined our results with global climate simulations, maps of depth to the ice table and dust cover, as well as lithologic and age information of the underlying geologic units, to better understand the controls on intracrater sand accumulation rates. We find that crater age, latitude, and lithology influence the accumulation rate of windblown sand and, notably, that it is enhanced in mechanically weaker substrates, high-latitude craters (suggesting that modern cryogenic processes may enhance sand production), and in Late Noachian and Early Hesperian craters (possibly hinting at increased erosion rates at that time). [ABSTRACT FROM AUTHOR]