Μxrf INVESTIGATION OF RELATIONSHIPS BETWEEN GEOCHEMISTRY AND PHYSICAL GRAIN CHARACTERISTICS IN A GLACIO-FLUVIAL-AEOLIAN CATCHMENT IN ICELAND

Introduction: Iceland’s basaltic volcanic rocks, cool and wet climate, and fluvial and aeolian volcaniclastic sedimentary environments offer a unique opportunity to study physical and chemical changes to sediments along their transport pathways in a Marsanalog environment [1, 2]. Specifically, studying these changes can provide insights on how to evaluate the significance of weathering, alteration, and grain sorting in similar present and past environments on Mars. This project uses micro X-ray fluorescence (μXRF) to investigate how sediment geochemistry, grain size, and grain shape evolve along a glacio-fluvial-aeolian transport pathway with the aim to determine the propensity of minerals derived from volcanic source rocks to sort and weather during transport. We studied the Skjaldbreiðauhraun glacial outwash plain in SW Iceland, which sits at the base of Þórisjökull. The glacier caps intraglacial volcanic sequences which contribute the sediments to the outwash plain in addition to material derived from the postglacial Skjaldbreiður shield volcano which is situated further downstream. This area was used as the operations site for the SANDE: Semi-Autonomous Navigation for Detrital Environments project – a campaign-scale analog project that uses an autonomous rover and unmanned aerial system to investigate physical and chemical changes in sediment along a sediment transport pathway [3]. Methods: μXRF is a non-destructive technique to analyze minor and major geochemical concentrations in geological samples [4]. A μXRF instrument, PIXL (Planetary Instrument for X-ray Lithochemistry), will be deployed on the Mars2020 Perseverance rover [5]. We analyzed fluvial and aeolian samples from an 8 km transect that began proximal to the glacier and source material. Each sample is approximately 1 km apart along the transect. Samples were selected to capture the average fluvial and aeolian sediment at each location. Each sample was sieved into five grainsize separates at 710-1000 μ, 250-710 μ, 125-250 μ, 63-125 μ, and <63 μ in order to determine trends within each separate. To prepare each sample for μXRF, each grainsize separate was placed on a piece of glass (Fig. 1). Figure 1. A schematic of sediment sample layout is shown on the left for preparation of sand for μXRF analysis. Sand was evenly dispersed on tape, represented by the blue rectangles. Orange crosses are Ti tape used for correlation of the scan to the optical microscope images. There are 5 different grain size bins each classified by a number from finest (1) to coarsest (5). The right shows the medial fluvial sample ready for μXRF analysis. Pen tip is included for scale.