Morphometric analysis of channel networks suggests the Jezero system is a fluvial fan rather than a delta

Fluvial fans and river deltas are both fan-shaped landforms that contain complex channel networks. A critical difference between these landforms is that deltas form only along a standing body of water, whereas fluvial fans may form hundreds of kilometers from oceans or lakes. Accurately distinguishing between deltas and fluvial fans is thus critical for identifying paleo-shorelines on planetary bodies. Here we test an ensemble of quantitative methods to differentiate fluvial fans and deltas on Earth, and apply the methodology to Mars. We quantify differences in channel divergence angles, and in downstream changes of channel reach lengths and channel width between the divergence nodes. These differences in channel networks occur because fluvial fans build by channel avulsions, whereas delta build by avulsions as well as mouth bar growth and consequent bifurcations. Bifurcations in deltas form channel divergence angles of approximately 77° and cause a distinct downstream decrease in channel reach length and in channel width at bifurcation nodes. In contrast, avulsions in fluvial fans form considerably smaller channel divergence angles. Down-fan channel narrowing is also not linked to divergence nodes. This initial dataset shows that the methodology is applicable both on Earth and Mars, and that the Jezero system is likely a fluvial fan rather than a delta. These results indicate that channel networks need to be carefully assessed if used for the estimation of the location of paleo-shorelines on planetary bodies, as only deltas systematically occur at shorelines. Alternatively, additional evidence is needed for the presence of shorelines as fluvial fans may also occur at shorelines. On Earth, fluvial fans are less sensitive to sea-level rise and coastal hazards than deltas, due to upstream morphodynamic controls.