Rover "Perseverance" on Mars
The new search of the "missing link" of life

Norbert Brügge, Germany

USGS prognostic geological map

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 volcanism."

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.
It is not uncommon assuming volcanic carbonatic material. Carbonate-bearing igneous rocks are known on Earth and could also occur on the Nili Fossae region in the form of this pumice deposits (also such in the Jezero 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.




Zoom view in direction Delta: Sandy elevation with boulders of unknown origin

First details from the surface of landing place


Earthly pumice