POSSIBLE YOUNG LACUSTRINE DELTAS AND YARDANGS ON THE MARTIAN DICHOTOMY BOUNDARY

Here we investigate potentially young (~1.1 Ga) fluvial and lacustrine landforms mantled or reworked by aeolian processes in a 6,000 km² study area bordering the dichotomy in the Martian tropics ~600 km east of Gale crater. The dichotomy boundary is believed to be associated with ancient (>3.0 Ga) fluvial reworking and transport of material from the Martian highlands. The martian northern lowlands are thought to be an ancient ocean with deltaic forms, although arguments have been made suggesting a lacustrine environment.

We mapped and extracted morphometric information on deltas located below the dichotomy boundary using CTX and HiRISE imagery. Digital elevation models (DEMs) were created using the Aims Stereo Pipeline on four CTX stereopairs, which provided an 18 m/pixel DEM coverage. Crater statistics on six deltas indicate ages averaging to ~1.1 Ga. These dates suggest relatively near-term fluvial and lacustrine processes modified by aeolian processes.

These deltas were long thought to be interacting with a northern ocean. However, based on morphometric analysis they appear to be Gilbert deltas suggesting an interaction with freshwater lakes through hyperpycnal flow rather than marine deltas in a northern hemisphere ocean. Crater dating of these deltas suggests liquid water could have existed on the surface during the late Amazonian, possibly marking a brief period(s) of fluvial processes in a normally arid aeolian dominated environment. This evidence of such late-stage lacustrine environments points toward possible recent climate scenarios with warmer temperatures, a more active global water cycle, or equatorial glaciation and highlights the possible importance of recent high obliquity climate states. The Gilbert deltas are also associated with yardangs in lakebed deposits reworked by aeolian processes.