The Geology of Jezero Crater, Observations & Findings Options

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This thread is for those rockhounds among us to discuss the new terrain we'll see as Perseverance scoots around her new home. Let's get dirty & technical!

[Andreas Plesch]

There are sedimentologists specializing in landscape evolution and numerical modeling, see for example https://agupubs.onlinelibrary.wiley.com/doi...1002/jgrf.20031 . Consequently, there are a large number of models, based on diffusion or advection concepts. Unfortunately, I am not such a modeler and do not have that insight. My inclination would be to treat lower gravity similar to a change in slope both acting on the erosional effect at the river base in similar ways. Slope is just one parameter besides flow rate, sediment load or potentially tectonic uplift or subsidence.

With that in mind I would expect that 0.38g would require a much steeper slope for a stream to develop similar erosional characteristics, other parameters being equal (which would be difficult to establish). The 2km relief over 100km intuitively feels rather steep and it should be possible to find longitudinal river profiles of similar length, for a direct comparison. A main difference is that the profile does not look like a textbook river profile on earth which has a steep initial gradient, an intermediate section, and a very gentle final gradient before entering a base line (a lake or ocean) which is considered an equilibrium profile where erosion at the source and aggradation at the sink are in balance.

I suspect that there have been attempts to understand such profiles on Mars, after the idea of an early wet history was getting (more?) widely accepted.

Looking more closely along the stream, there are what could be rather short tributaries, and perhaps drainage from the Hargraves crater region to the north.

Proposing a secondary inlet at the northern crater rim clearly requires some interpretation since it would be not very well preserved. I do think there are markers of channeling and meandering further upstream which seem to connect to it.

[edit] ah Thanks serpens, yes that is what I see as well. It is just not much of a system of tributaries.

[serpens]

....It is just not much of a system of tributaries.

While the catchment as it stands can be reasonably constrained, as HSchirmer alludes to the area has been subject to tectonic activity, cratering and erosion that makes the accurate assessment of the ancient drainage area and tributary flows challenging to say the least. While there are traces of the tributaries much has been erased. As I understand it the mineralogy of the Northern and Southern deltas vary, reflecting the mineralogy of the two separate catchment areas. All in all it is a pretty impressive drainage area which I suspect would have hosted an extensive tributary network.

[HSchirmer]

While the catchment as it stands can be reasonably constrained, as HSchirmer alludes to the area has been subject to tectonic activity, cratering and erosion that makes the accurate assessment of the ancient drainage area and tributary flows challenging to say the least.

A follow up point - when tectonics tilts an entire river drainage network on 50, 200, 500, 1,000 km scale, you get paradoxes:
Example is the geology / biodiversity paradox for the US east coast: 500 MY old fish populations in 200 MY old rivers.

The main US coastal rivers: Hudson, Delaware, Susquehanna, Potomac, Cape Fear, Congaree & Savannah all run east from the Allegheny mountains to the Atlantic ocean. The Atlantic ocean opened up ~200 million years ago when Pangea broke up.
However, 500 MY old fossils of the same fish species that are in the river now indicates the rivers are over 500 million years old. At first glance would requires the east coast rivers to run UP HILL towards the central "Himalayan plateau" of Pangea.

The solution is that the river tributaries are older than the river & ocean they currently drain to, the large main stems have reversed course.
All the large east coast rivers USED to be small header tributaries that drained west to the proto-Mississippi.
Once the Atlantic opened, they had a steeper gradient heading east, which allowed quick erosion to gorges, which cut back to the west and captured more and more feeder rivers and streams, which accelerated erosion...
https://www.researchgate.net/figure/River-n..._fig1_327653964

Conversely, as the old western-draining network lost tributaries, reduced flow leads to silting up, which slows flow, dropping even more sediment: you get a series of lakes & wetlands, rising water levels, and eventually the water level over-tops the watershed divide and begins flowing east to the Atlantic instead of west to the Mississippi.

Repeat that process a few times for Jezro, add in 2 possible ocean shorelines, and you've got an idea of the scope of the question!

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