Unique on Mars: Spread of olivine/Mg-carbonate
"Jezero is a crater basin at the western edge of the Isidis Basin. It
is characterized by fluvial/deltaic sediment deposition into a paleolake.
A western and northern delta have been observed from orbit.The western
delta is dominated by Fe/Mg smectites
and exhibits well defined sedimentary layering, including bottomset deposits.
The northern delta is dominated by Mg-carbonates
and associated olivine, but is less well preserved than the
western delta. The basin fill is also dominated by olivine and Mg-carbonates,
though it is unclear whether this represents primary detrital deposition,
re-working of prelacustrine sediments, or exposure of the regional Mg-carbonate/olivine
unit observed more broadly in Nili Fossae (also of unknown origin). A
volcanic unit (~3.5 Ga) overlies most of the basin fill, embays the eroded
delta scarps, and surrounds deltaic remnants which have been separated
from the main delta bodies by aeolian deflation at some time prior to
The first photos
after landing on the planet on 02/18/2021 show a plain on which there
are debris of all sizes that are very similar to
volcanic pumice stone.
If it is actually pumice deposits, that's not good news. These pumice
deposits could have a significant thickness as the photos suggest. Aeolian
sands on the floor seem to be only a thin blanket.
The hoped-for sediments of a lake bottom would be difficult to find
because were blown out. Outcrops of (basaltic) pumice appear
to be very common in the crater, as seen in the video during the rover's
descent and in the landing zone. One stone is particularly interesting
because it has a peeled crust that could document smectite formation.
It could explain the previously measured slightly clayey portion in
the young aeolian sands.
It will be interesting whether such pumice deposits in the Jezero crater
can also be found in the deposits of the delta, and in what context
and conditions. According to the measurements, layered smectites are
also expected. Smectite are created by the weathering of basaltic material
on the earth (with atmospheric conditions and water). Smectites
are a mineral mixture of different layered silicates (phyllosilicates)
and belong to the clay minerals.
Measurements from orbit have found on the Nili Fossae region Mg-carbonates
with olivine on the surface (high terrain). Tectonic faults on the Nili
Fossae terrain are obious. Pumice material in the deposits of the delta
can come from higher elevations outside the crater.
At the moment, many scenarios are possible for the chronological sequence
of the filling in the Jezero crater. The great hope for trace of life
on Mars is in the delta. Some lander have found some prerequisites for
possible life on Mars, but the ultimate proof is lacking.