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]

Delta erosion

At distances of a few hundered meters to a kilometer away from the current edge of the main delta deposits, there are a few isolated hills which could be classified as Inselbergs or outliers. Here is an example:

https://mars.nasa.gov/maps/location/?mission=M20&site=jez&mapLon=77.40930318832399&mapLat=18.444092466139594&mapZoom=15&globeLon=77.42958068847659&globeLat=18.463327291058505&globeZoom=12&globeCamera=0,-4882.8125,0,0,1,0&panePercents=0,100,0&on=Current Position$1.00,Waypoints$1.00,Surface View$1.00,Landing Ellipse$1.00,Rover Path$1.00,Labels$1.00,Basemap$1.00,North East Syrtis Base Map$1.00://https://mars.nasa.gov/maps/location...e Map$1.00

A typical, geological interpretation of such isolated hills is that they were once connected to a main, better preserved area, here the delta, and became disconnected by erosion. The Inselbergs would be therefore witnesses to a former, larger extent of the delta, and in german such features are called Zeugenberg (witness = Zeuge). Given the similar appearance in terms of height and a flat top and a spatial correlation with the edge of the delta, this to me would be the preferred interpretation of the formation of this hills. This could be tested by examining the local stratigraphy of the delta and the hills with the expectation that there should be a good match.

If this is the case, the delta was eroded back from its largest extent. This is to be expected during the time when the lake started to retreat to below delta levels. The current, abrupt edge of the delta is also more likely to have been shaped by erosion than being an original feature. Growing deltas tend to taper out into deeper water and transition into fans, leading to gentle slopes of a few degrees.

One question then becomes where did the significant mass of eroded delta sediments go ? Perhaps there have been mass balance studies but one possible candidate is the smoother appearing material covering the plane just below the slope of the delta in a ring a few km wide in places. This ring appears to be less cratered than the center of the crater.

Following the discussion it is also possible that the youngest sediments now are exclusively aeolian, and from impact dust and debris, and that eroded, reworked, and redeposited delta sediments are completely hidden below a top soil, accreted layer. And beneath both of those, there could be original lake bottom sediments. So it may make sense to investigate the craters closer to the rover which could have excavated deeper lake bottom sediments. But the safest place to get fluvial, water dominated, pristine material for sampling is probably right at the face of the current edge of the delta.

A few thoughts, mainly on the importance of the outliers surrounding the current delta.

[HSchirmer]

Delta erosion
...
A few thoughts, mainly on the importance of the outliers surrounding the current delta.

Excellent summary.

So, have any graduate students made a vacuum-formed crater and experimented with filling it with sediments and varying the water / sediment ratio to see what it takes to recreate the delta?
(Asking as "that kid" who filled the little red wagon with cement, sand & stone, dropped marbles to create craters for an "authentic" moonscape for the Mattel 'Space 1999 Eagle' to land on...)