The Case for Barren Meanders in Earth’s Modern Endorheic Basins as Analogs to Early Mars’ Rivers

Abstract:

Through geological and historical times, vegetation and humans have successfully colonized most of Earth’s floodplains, so that barren fluvial systems are nowadays exceedingly rare and relegated to inhospitable niches such as polar and sub-tropical deserts. These environments have long been ignored by fluvial geomorphologists owing to their remote location, although advances in planetary geology revealed their potential as analogues to extra-terrestrial fluvial systems such as those observed on Mars. Many fluvial deposits on Mars consist of distributive systems (like fluvially dominated deltas) that abutted into the floor of inundated impact craters. These fluvial landforms have long been abandoned, and are the silent testimony of a once hydrologically active planets. Modern barren rivers in polar deserts often occupy steep, glaciated or recently deglaciated valleys, and although they may provide analogues to some ancient Martian rivers, their coarse-grained nature and braided planform makes them difficult to parallel with the many meandering systems recognized on Mars. In comparison, barren meandering systems found along fluvial fans that drain into modern hyper-arid endorheic basins in Earth’s sub-tropical belts constitute putative analogues to Mars’s ancient meandering streams. Here we summarize the findings of a recent worldwide remote-sensing analysis of barren meanders on Earth, and demonstrate how their migration sets them apart from vegetated rivers elsewhere. Focusing on key watercourses such as the Amargosa and Mojave rivers of California, we show that hydrologic analyses may elucidate the relationships between their flow intermittency, bankfull geometry, and stratigraphic records. We conclude by showing that, through simple assumptions related to bank erodibility and sediment transport, the results from Earth’s rivers can be scaled to Mars conditions – something that allows refined predictions of the pace of Mars’ ancestral rivers.