Abstract
HiRISE-based mapping reveals five landform assemblages in western Jezero
crater, each defined by a landform association interpretable using
Earth-based landsystem models and well-understood Earth analogues. 1)
The northwestern assemblage hosts boulder hills rimmed by lobate ridges,
mounds and mesas on a valley floor, and valley-bounding ridges
superposed by striations (= parallel boulder-bearing ridges and
grooves). 2) A trough zone hosts variously shaped depressions,
intra-trough islands, linear and curvilinear boulder ridges, and
highland strips topped by striated surfaces and rimmed by
boulder-bearing ridges. 3) The steep-sided fan-shaped plateau (“western
Jezero delta”) hosts mesas, highland-rim boulder ridges, depressions,
linear and curvilinear ridges, and a plain superposed by radially
trending striations. 4) The crater-margin assemblage hosts a steep-sided
ridged and pitted hummocky terrain, a terrace-like capping surface, and
mounds surrounded by radially trending boulder ridges. 5) The
crater-floor assemblage hosts a polished and striated terrain that
displays fold-like and streamlined ridges, hummocky landforms dominated
by quasi-circular depressions with raised rims, mesas exposing
fold-thrust strata, flat-topped steep-sided ridges with U-shaped map
traces, polygonal-grooved plains, and unconsolidated boulder mounds and
ridges. Although any aforementioned landform unit could be explained by
multiple formative mechanisms, the spatiotemporal relationships mapped
in this study within and among the assemblages place stringent
constraints for any self-consistent interpretation. A model capable of
explaining the mapping results involves northeast-flowing glaciation,
ice-sheet collapse with ice-fracture patterns controlling the formation
of polygonal grooves via crevasse filling and ice pressing, and minor
aeolian modification. In the model, the plateau and crater-margin
assemblages were formed by ice-walled subglacial deposition, the trough
zone by subglacial flooding, the northwestern and basin-floor
assemblages by glacial deformation and deposition, circular depressions
with raised rims by melt out and down pressing of spherical dead-ice
blocks (i.e., thermal karsts and kettle holes), mesas by kame formation,
and striations by glacial fluting.