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Analysis of geologic materials at the microscale—where we use the term “microscale” to refer to features resolved approximately by a hand lens—has proven to be a powerful strategy to maximize the information gleaned from limited samples, such as on Mars. However, discrimination between processes that leave behind similar traces requires enlightened comparisons to well-characterized analogs. We characterized and imaged several terrestrial analogs of materials produced by volcanic, hydrovolcanic, or cryovolcanic Martian processes at the hand lens scale, and then we produced a convenient tool for the community to access those data for comparisons. We report on the preparation of this Mars-focused image atlas (the Mars Analog Handlens-Scale Image Database), using as an example analog studies of particles deposited by the 1996 Skeiđarársandur jökulhlaup (a jökulhlaup is a subglacially generated outwash flood resulting in a sandur, or sheet of outwash sands and gravel).

We imaged unconsolidated sediment particles in situ at about hand lens scale and documented their characteristics at six sites along the sandur. Average particle size and number of angular, very angular, and subangular particles decreased with distance from the source; the average sphericity of particles increased slightly; and the range of sphericity values present narrowed with distance. If observed in a region on Mars, this combination of characteristics would be one indicator that subglacially generated outwash flooding was the process responsible for deposition of sediment. The Mars Analog Handlens-Scale Image Database is searchable and can be found on the Geosciences Node of the Planetary Data System at http://an.rsl.wustl.edu/marsanalog/.

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