Global documentation of overlapping lobate deposits in Martian gullies

Research areas:
  • Rishitosh K Sinha
  • Dwijesh Ray
  • Tjalling de Haas
  • Susan Conway
in review
Martian gullies are landforms comprising an alcove, channel and debris apron. In some gullies lobate deposits have
been observed, implying a debris-flow-like process, but uncertainty remains as to the importance of this process in the
gully-population and whether lobate deposits are related to a specific context. We document evidence of overlapping
lobate deposits on gully-fan surfaces within craters emplaced between 30˚-75˚ in both hemispheres. We have
identified 26 craters in which lobate deposits occur in gullies, of which 6 were previously reported. This corresponds to
3.39\% of the 765 gullied craters studied using 1004 HiRISE images. We show that gullies with lobate deposits (1) do
not show any location preference, (2) are poleward-facing, (3) are found in craters with and without latitude dependent
mantle (LDM) and/or glacier-like-forms, (4) are emplaced at slopes at the foot of the fans that range from 18-25° in the
northern and 7-19° in the southern hemisphere, and (5) form in craters of all ages. We infer that preservation of lobate
deposits in gullies is the main factor leading to their relative paucity within the gully-population. Further, we observe
morphological features associated with terrestrial wet-debris flows including: overlapping tongue-shaped terminal
lobes, levees, channel backfilling, plug formation and avulsion. We have not observed any significant present-day
changes in the morphology and topography of gullies and/or lobes. We conclude that a debris-flow-like process is
likely responsible for the majority of sediment transport in gully-landforms, but whether the fluidising agent is liquid
water or CO2 sublimation remains unknown.