FLUVIAL AND EOLIAN SEDIMENT SORTING AND ROUNDING IN A BASALTIC PRO-GLACIAL CATCHMENT: ÞÓRISJÖKULL GLACIER, ICELAND

The SAND-E: Semi-Autonomous Navigation for Detrital Environments planetary analog project examines physical and chemical changes in basaltic sediments from a glacio-fluvial-eolian environment and tests robotic and unmanned aerial systems technologies in planetary exploration operations. As a component of the SAND-E project, we examine fluvial sorting in a proglacial catchment and the contributions of fluvial sediment to the eolian system in the catchment.

We created a detailed surface geologic map to connect source rocks to sediments along a glacier-proximal-to-glacier-distal transect and characterize catchment geomorphology. Digital elevation models derived from TanDEM-X were used to identify stream order in the catchment and extract a channel long profile. We collected bulk sand and pebble samples of fluvial and eolian sediments every ~1 km along a ~8 km transect and measured their size and sphericity using a Camsizer. In addition, we measured the size of cobbles using the Wolman cobble-count method every 1 km along the transect. Cobble count data show a decrease in the length of the intermediate axis from 0.4 to 9 cm between the proximal and distal locations, respectively. In addition, cobble aspect ratios increased downstream. The general decrease in size and increase in aspect ratio observed for cobbles is expected for sediment travelling downstream a river. Cumulative size distribution curves of the bulk finer sediments show no significant trend, however fluvial samples were more poorly sorted than eolian samples. The lack of significant size variation in the finer-size fraction signals that winds in the catchment were capable of transporting the sand fraction of fluvial sediments. The lack of rounding variation may be due to the relative proximity of the investigated sites to the source rocks.