QUANTIFICATION OF CHANNEL NETWORKS TO DIFFERENTIATE FLUVIAL FANS FROM DELTAS ON EARTH AND MARS

Fluvial fans and deltas are both fan-shaped landforms that contain complex channel networks. One difference between these landforms is that deltas form along shorelines of a standing body of water, whereas fluvial fans may or may not form along a standing body of water. Accurately identifying and distinguishing deltas from fluvial fans is crucial to understanding paleo-environments on Earth and Mars. The landform at Jezero crater on Mars is currently identified as a delta. Should this landform's geometry more closely resemble a fluvial fan, there would be alterations to current paleo-environment interpretations on Mars. As Jezero crater is the site of Mars Sample Return, there are also implications for the future analysis of these returned samples. Here we characterize multiple quantitative morphological characteristics to establish metrics differentiating fluvial fans from deltas. We quantify differences in channel divergence angles as well as downstream changes of channel lengths and widths between divergence nodes. Differences in channel networks occur because fluvial fans form by channel avulsions and sediment aggradation in channels, whereas deltas form by channel avulsions as well as mouth bar growth and consequent bifurcations. Published literature has shown delta bifurcation angles to be approximately 72° on Earth and 74° on Mars. Other studies have demonstrated a distinct downstream decrease in channel reach length and in channel width at bifurcation nodes. Fluvial forms form statistically significant smaller channel divergence angles. Down-fan channel narrowing also shows no association to the order of divergence nodes. Preliminary results from our analysis suggest the landform at Jezero crater closely resembles a fluvial fan, whereas the landform at Eberswalde crater more closely resembles a delta. These results indicate that channel networks need to be carefully assessed if used for estimation of the location of paleo-shorelines on planetary bodies, as only deltas systematically occur at shorelines. Additional evidence is also needed for the presence of shorelines as fluvial fans may also occur at shorelines.