The Geology of Jezero Crater, Observations & Findings Options

[nprev]

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!

[serpens]

From what we have seen of the delta front and Kodiak it seems to reflect delta growth into a lake under a stable flow regime with episodes of erosion reflecting dry periods and also a few periods of high intensity flow. My obviously deranged imagination pictures gently flowing river dominated deltas under cloudy skies at the edge of a choppy lake with an ocean visible to the East. In reality it was probably a more violent environment but I like the illusion.

Periodic high intensity flows transporting sizeable detritus both rounded and angular does not necessarily imply a desert flash flood or dry environment. It could reflect a gradual increase in flow to high intensity flood levels due to the progressive melting of abnormally large deposits of snow in the catchment or perhaps the collapse of obstructions at the crater inlet breach or the knickpoint further up the channel. Currently we are in the realm of hypothesis and dare I say imagination and Tim's last post highlights the fact that we have two plausible but opposed explanations for A2 from experts in the field although I don't believe they are mutually exclusive across the delta front.

For imagery of the watersheds try
https://www.arcgis.com/home/webmap/viewer.h...78.2144,20.7779

[JRehling]

Perhaps I'm wrong in associating wildly different phenomena with just one facet of similarity, but we've known for a long time that Mars had catastrophic, massive floods in its past, and then we had a long campaign of exploration that led us to discover and characterize these other kinds of water flow, due to climate, more typical of Earth, but should we then think of all of the water flow that took place in Jezero as the latter and not the former?

As Mars had (and has) massive deposits of crustal ice, this allowed volcanic activity to unleash massive floods that are endogenous in origin, not due to climate. Similarly, impact melt could accomplish the same result.

We know that the overall topography of Jezero was reworked by the rise of Syrtis Major to its immediate west. We moreover know from the eroded crater present on the delta that there was still significant impact cratering taking place after the time frame of the delta's formation; it's therefore plausible that as much or even (far?) more impact cratering took place during the time frame of the delta. The signs are abundant on Mars of lobate flows created by the impact melt of subsurface ice. For that matter, the kinetic (rather than thermal) result of an impact hitting a watershed would be yet another potential cause of catastrophic water flow.

It seems to me that it remains to be proven if any flash flooding was due to anything we'd associate with climate versus those two non-climate catastrophic scenarios.

In addition, we know that Mars has likely had cycles of axial tilt leading to climate changes wildly more catastrophic than what Earth has experienced which could have created climate epochs where ice would form locally, then other epochs in which there would be a lot of cumulative melt.

It seems to me that all of these and more are in play as potential explanations.

[tdemko]

It seems to me that all of these and more are in play as potential explanations.

I completely agree. However, the well-organized delta foreset strata at Kodiak, and the organization of channels and lobes from the orbital imagery suggest that sustained, or at least seasonal, flows probably built a significant volume of the deltaic deposits.

On the other hand, the catastrophic events like you've mentioned can also be important in shaping the geomorphology of lakes, and can produce significant deposits in lake basin fills.

Here is one of my favorite examples, from Lake Tahoe in the USA. A huge landslide deposited giant blocks on the lake floor, but also created tsunami and seiche flows which formed fields and channels of antidune and cyclic steps deposits around the lake margin as they returned back into the lake as supercritical flows. The point of my previous posts was that the authors of the Jezero paper don't seem to be familiar with these types of deposits, or even recognize that supercritical sediment gravity flows would also be expected in the types of short, steep, coarse-grained delta deposits that have been seen in Kodiak.

https://www.researchgate.net/publication/25...lifornia-Nevada

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