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A Glacial Origin of Polygonal Networks of Double-Ridged Grooves in Western Jezero Crater during the End of an Ice Age on Mars
  • Katya Yanez,
  • An Yin,
  • Travis Orloff
Katya Yanez
California State University, Northridge, California State University, Northridge

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An Yin
University of California Los Angeles, University of California Los Angeles
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Travis Orloff
Los Angeles Pierce College, Los Angeles Pierce College
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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.