A Glacial Origin of Polygonal Networks of Double-Ridged Grooves in
Western Jezero Crater during the End of an Ice Age on Mars
Abstract
Western Jezero crater of Mars exposes smooth- and rough-surfaced plains
that bound a steep-sided fan-shaped plateau (i.e., western Jezero delta)
in the west. The two plain terrains have a gradational contact and their
end-member occurrences can be defined by the absence (smooth-surfaced)
and presence (rough-surfaced) of littered surficial boulders and
depressions. Early researchers interpret the plain terrains as
morphological expression of volcanic flow and aeolian, fluvial, or
lacustrine deposition, but these hypotheses have not been tested
rigorously via detailed mapping. Here we show results of HiRISE-based
mapping that reveals four landform units hosted by both smooth- and
rough-surfaced terrains: (1) polygonal networks of double-ridged grooves
that are 2-4 m wide, up to ~1700 m long, and spaced
> ~100 m, (2) reticulate networks of
grooves spaced mostly < ~10 m, (3) undulating
surfaces hosting variously shaped depressions, and (4) NE-trending
boulder-bearing ridges (~10 m wide and 70-300 m long)
locally displaying NE-pointing streamlined shapes. Our mapping shows
that the NE-trending boulder ridges formed first followed sequentially
by the formation of depressions, double-ridged grooves, and reticulate
grooves. None of the above observations can be explained as a whole by
volcanic emplacement and/or earlier proposed aeolian, fluvial, and
lacustrine depositional processes. Guided by Earth analogues, we
interpret the streamlined boulder ridges as subglacial flutes,
depressions including most circular pits with raised rims as kettle
holes and/or thermokarsts, polygonal networks of double-ridged grooves
as crevasse-filled ice-pressed moraine ridges and the polygonal pattern
was inherited from the fractured glacier, and reticulate grooves as
desiccation cracks during the final drying of glacial deposits at the
end of a martian ice age.