This paper employs a circularity function to quantify the internal morphology of
Martian watershed basins in Margaritifer Sinus region and to infer the primary erosional
processes that led to their current geomorphologic characteristics and possible climatic
conditions under which these processes operated. The circularity function describes the
elongation of a watershed basin at different elevations. We have used the circularity
functions of terrestrial basins that were interpreted as having been modified by (1) erosion
related to primarily groundwater sapping and (2) erosion related to primarily rainfall and
surface run-off, as well as the circularity functions of cratering basins on the Moon, in
order to formulate discriminant functions that are able to separate the three types of
landforms. The spatial pattern of the classification of Martian basins based on discriminant
functions shows that basins that look morphologically similar to terrestrial fluvial basins
are mostly clustered near the mainstream at low elevation, while those that look
morphologically similar to terrestrial basins interpreted as groundwater sapping origin are
located near the tributaries and at higher elevation. There are more of the latter than
the former. This spatial distribution is inconsistent with a continuous Earth-like warm and
wet climate for early Mars. Instead, it is more aligned with an overall early dry climate
punctuated with episodic wet periods. Alternatively, the concentrated erosion in the
mainstream could also be caused by a change of water source from rainfall to snowfall or
erosion cut through a duricrust layer