Multispectral Observations of Float Rocks Used to Investigate the Origin
of Boulders on the Western Jezero Fan Front, Mars
Abstract
The Mars 2020 Perseverance rover has explored the escarpment at the
front of the western fan in Jezero crater, Mars, where it encountered a
variety of rock units as in-place outcrops and as loose pieces of rock
separated from outcrops, or “float” rocks. Comparing float rocks to
in-place outcrops can provide key insights into the crater’s erosional
history and the diversity of units in the Jezero watershed that the
Perseverance rover cannot visit in-situ. Here, we used multispectral
observations from Perseverance’s Mastcam-Z instrument to investigate the
lithology and origin of float rocks found on the western Jezero fan
front (sols 415-707). We identified four textural classes of float rocks
(conglomerates, layered, massive, and light-toned) and investigated
their physical characteristics, spectral properties, and distribution to
interpret their source and constrain their mode of transport. We found
that the conglomerate and layered float rocks are highly spectrally
variable and altered with differing ferric and ferrous signatures, and
they likely derived from local sedimentary outcrops in the western fan
front. Massive float rocks are the least altered, exhibit ferrous
signatures, and could have derived from local outcrop sources or more
distal sources in the Jezero watershed. Massive float rocks separate
into two subclasses: massive olivine and massive pyroxene, which likely
derived from the regional olivine-carbonate-bearing watershed unit and
the crustal Noachian basement unit respectively. The unique light-toned
float rocks have variable hydration and low Fe-abundance, but there are
no local outcrop equivalent of these rocks in the western Jezero fan or
crater floor.