Knowing the camera lens (FOV etc) and the distance to the target, has anyone attempted to estimate the scale of this feature?

Using

http://www.unmannedspaceflight.com/index.p...st&p=251880

an estimate of the thickness of the clinoform is 8-9m. Single layers within the bed would be on the cm scale.

Andreas, I tuned in and it was a very good presentation. Thank you for sharing the link.

Here is a recent review of clinoforms:

https://doi.org/10.1016/j.earscirev.2018.05.016

According to this classification, the ca. 10m thickness, grain size distribution, and relative lack of topsets indicating erosion/non-deposition would place the Jezero clinoforms in the delta-scale shoreline class which fits the context well. On earth, this class is associated with fast progradation rates (meters/a), and geologically short (up to 1Ma, generally < 100K years) time scales for deposition of a complete sequence.

Charborob's mosaic is great. I could spend hours looking at it. Supercam rocks. LOL pun intended.

In the absence of any tectonic activity, what would explain the slumping of the median unit in the leftmost delta front do you think? There is a distinct margin between the horizontal upper strata and those tilted down 30 degrees. Below that unit there are again horizontal strata. Seems to be telling us something important.

Also on the right segment of the delta front there is some curvature to the downward sloping strata. Is there anything similar on Earth to compare to?

What appeared to me at first to disorganized loosely conglomerated large-scale clastic material seems to be stratified (to me at least) in this photo. It is hard to distinguish any clear difference among the clasts for my untrained eye.

It seems to be extremely crumbly as well with few visible clean fractures. Like you could easily dislodge chunks with a light tap of a hammer or trowel.

Fascinating. Lots yet to unmars ...

That is what is called a clinoform. The dipping beds are called foresets. Googling will bring up many examples and images. For a deeper review see https://doi.org/10.1016/j.earscirev.2018.05.016 .

On the right there are remnants of topsets so I feel the lack you refer to is due to erosion. On the left the foresets are somewhat higher indicating that the delta built up over a relatively short distance, possibly indicative of an increased sediment load.

Agreed, the sharp truncations look like an erosional top. Phases of erosion and retreat would be expected for a shoreline delta. To my eye, the right sequence projects underneath the left sequence, eg. these would be two sequences, separated by a quieter phase, and indicating, possibly subtle, dynamics in the sediment supply. It may be possible to estimate the overall basinward, gentle gradient and extrapolate a lateral extent of the full delta, after seeing the sequence from another angle.

It could also reflect an increasing water depth. It seems that this was a dynamic, warm, wet environment..

Thank you kindly Andreas. That is a helpful reference and a nice read.

What strikes me is clinothems/forms in lacustrine environments tend to be continuous and curvilinear giving evidence of the paleo-shoreline's geometry to depth. These though appear quite oblique/linear and demarked by very distinct horizontal boundaries. The strata on top and below are horizontal but section of (say) a few dm between them is markedly inclined. It seems to me these inclined beds may have been deposited horizontally and then shifted somehow. I would be interested to know more about the mechanics that would have caused this or if it is even a possibility.

Not sure what you mean MarkL. Topsets and bottomsets are pretty much parallel but may be inclined to a degree. For example on a sloping lake bottom the delta toe would tend to conform to the floor slope. Foresets have a slope similar to the leading section of sand dunes. While the imaged section of the delta has been subject to erosion it conforms to the classic delta configuration. To put this in perspective, at some time in the far past the water level would have been around the level of the topsets (upper horizontal deposits). At the edge of the delta sediment would have deposited at the delta front creating the dipping configuration and then remnant, sediment would create the horizontal bottomsets. So at the time of this deposition the lake depth at the point of deposition would have been some 7 metres

Remember, what we are seeing as clinoform surfaces (which bound the clinothem strata) are roughly 2D sections through 3D, most likely lobe-shaped, successions. Almost all deltas are constructed by prograding piles of sediment that build up at the mouths of the inlet channels. Mouthbar bodies form subaqueous in these areas by the drop in carrying capacity of discharge in the channel as it widens into the open basin. The mouthbar sediment fails as it reaches angle of repose, or is blown out by larger discharge events, and generates plunging sediment gravity flows that prograde out ahead of the mouthbar, creating the characteristic foreset geometry we see reflected in the clinothems. Larger gravitational failures will create slumps, which we have also seen. Delta lobes, and lobe elements, are typically paddle-shaped in plan view, and the outcrop sections we see in Jezero may be either stream-wise, in the major direction of flow and progradation, or span-wise sections oblique to perpendicular to flow. The angle and shape of the clinoforms will depend on the grain size and sorting of the sediment, and the apparent angle of the outcrop section with respect to the progradation direction.

Almost all the clinothems we have seen so far are characterized by high-angle truncation of the tops of the clinoforms by the topset strata. These are called top-truncated lobes, and the truncation could have been caused by a lake level fall, subsequent to lobe progradation, or by wave erosion during a later lake level rise. That they mostly are followed by topsets which dip at a much shallower angle than the foresets suggests the former.

Click to view attachment

This is the section of the delta front I have been wondering about. This is not a gradual curvilinear incline that you might equate to a paleo shoreline (and which is seen elsewhere nearby). It is a sharply delineated section of inclined strata - it seems to me to be sandwiched between two horizontal layers and does not continue down and to the left in a continuous slope along what would have been the old shoreline. Perhaps some catastrophic event like a break in the crater rim downstream could have caused a slump as Tim suggests. (Thank you Tim)

I guess a closer look will tell us more. The clastic material seems, at least color and grain-size to be very homogeneous in these adjacent sections of the delta.

This is from Thomas' supercam pano of the left side of Kodiak btw.

Really appreciate the geological insight. Thanks. It is a fascinating exploration.

Yes, this is what Tim explained so well as a truncation at the top. The idea is that there originally was a more sigmoidal clinothem the top of which must have been removed later by erosion to a somewhat lower, flat datum (by wave action or exposure). This in turn implies changes in lake water levels, from higher initially to a bit lower, and then back to higher, over time. To start the upper sequence, water levels would need to be high, but then not rise relative to sediment supply, to build out a new delta lobe into the lake. From a biosignature perspective, I think these variations are advantageous since they represent different potential habitats in terms of water depth and light intensity, potentially clay content or exposure to air, all of which could be studied.



Each of the many, many clinothems can be seen as a, perhaps annual, snapshot of the advancing shoreline at the top (some distance to the back), an incline towards a basin bottom (the main foreset) and a gradual transition to the very gently sloping floor. The lower, curved transition is well expressed in many places. The relative stratigraphic position of the conglomerate beds observed elsewhere is not clear at this point, I think. They may be related to these clinoforms, or be the result of a more substantial change, perhaps after a main deltaic phase.

In the right of Thomas' image (linked under), as Tim pointed out, the top of the foresets represents a deflationary surface, most likely following a decrease in the level of the lake. So what at a glance looked like remnant topsets are in fact bottomsets probably linked to a subsequent progration on the left of the image. This also seems to have a deflationary surface which may indicate that inflow from the catchment was cyclical with a reasonably lengthy period.

https://www.flickr.com/photos/thomasappere/51138790930/

Interesting rocks on the crater floor..any ideas as to the greyish greenish color on some of the white rocks?

Sol 65 had this interesting rock:

Click to view attachment

It appears to be stratified and I gently highlighted this texture. This points to a sedimentary origin. In addition, the stratification appears to be folded around a hinge zone which is brighter perhaps due to enhanced alteration. Slumping down a slope can generate such relatively tight folds.

https://mars.nasa.gov/mars2020-raw-images/p...9_110085J01.png

The angle of the image makes it difficult to see exactly if the strata were deposited in parallel layers. A higher angle may show they are not as folded as we see here.

It's perhaps a piece of the puzzle which will reveal what happened to the paleo-delta front and shoreline and why there are isolated remnants standing tall above the crater floor. It is still very mysterious to me why we see remnants at quite a distance from the front. The Kodiak feature is a good example. It is clearly related to the main delta front but why did it not erode like the rest of the front around it? Is this fluvial erosion carving out islands in a sometimes river sometimes lake?

The shape of the rock allows for tracing the stratification on the main top face and the two steep side faces where they are less apparent but still recognizable. That does not leave a lot of room for interpretation as I see it. If the folding can be confirmed, my guess is that it would be one of very few observations of such deformation anywhere. Are there other examples of relatively tight folding or slumping, perhaps at crater rims ?

Such remnants are a well known landform: http://www.unmannedspaceflight.com/index.p...st&p=250325

They typically become isolated from the main sequence long after formation, through gradual erosion around them and being protected by a more resistant unit on top. Today's shape and location of these remnants is not directly related to lake processes. Their location only can provide a minimum for the original extent of the delta. It is not unlikely that the landing location had been covered by more distal portions of the delta, now completely eroded, and such a sedimentary rock would be consistent with that idea.

Perhaps it is my tired old eyes Andreas but looking at the original image it looks more like weathered basalt to me. There doesn't seem to be any real indication of layering.

Well, thanks for giving it a try. I think there is at least an indication both in the left and in the right image. But I admit I am biased towards folding and faulting, and that basalt would be the safe bet. Remember to dare !

"Interesting rocks on the crater floor..any ideas as to the greyish greenish color on some of the white rocks?"
Don't trust anything relating to color in images like these - only real multispectral data are useful for analysis. If something looks green in one version of an image it might look very different in another processed version of the same image. So, if it really is green it might be olivine or serpentine, or a green impact glass like that from Apollo 15. But it's just as likely to be not green at all, a neutral shade looking a bit green because of the way it was processed.

Phil

Somehow I do not find that an entirely satisfying explanation, sorry Andreas. Do these have analogues on Earth?

Whatever eroded the rest of the delta front should have made just as quick work of the remnants. There must be something different about them beyond merely a hard top.

MarkL. After the lake dried up erosion would have been Aeolian; deflation and abrasion. The delta deposits would not have been homogenous and some would have been well indurated and resistant to erosion. If you look at the image below you may note the inverted channels where the more indurated beds of channels and possibly pools are raised above the more easily eroded delta material. As Mars lost atmosphere erosion would have effectively ceased. Andreas is spot on when he indicates that we cannot know the original size of the two deltas other than at a minimum it was far larger than the remnants and almost certainly once covered the current landing site.

Rephrasing -
The delta materials on mars would be a mix of everything from fine clays, silt, sand, grit, pebbles, cobbles, and stones.
The smaller they are, the further they move out into the lake; BUT then easier they are for winds to strip them away.
That means the area where the river meets the lake is the "sweet spot" where you have a mix of aggregate sizes, and you can expect a base flow of long-soaking / springs / mineral rich water which will evaporate in dry spells and help cement those varied aggregates together.

One of my favorite examples about 'grain size'. Gedanken experiment:
You can work your hand down to the bottom of a 5 gallon bucket filled with marbles, and then pull it back out easily.
You can work your hand down to the bottom of a 5 gallon bucket filled with bb shot and then pull it back out easily.
You can work your hand down to the bottom of a 5 gallon bucket filled with sand and then pull it back out easily.
You can work your hand down to the bottom of a 5 gallon bucket filled with flour and then pull it back out easily.

BUT- if you mix marbles, BBs, sand and flour, the intermixing of sizes create an extremely tough and resistant material.

Same thing happens at a the mouth of a delta, where you have sequential deposition of different sized aggregates.

There is a topographically lower lying unit between the current rover position and delta. I know it may be premature to comment but Is this unit thought to represent lake bed deposits or still representative of a volcanic unit?

From visual data it would appear that Perseverance landed close to a transition between Noachian deposits and the basaltic cover. Basalt is vulnerable to erosion and if the cover in the area was thin it could well have been removed. Alternatively a thin layer of lava could have embayed the seemingly old, etched terrain South of the landing site. (see image post #174).

Could the isolated Katmai butte be due to the effects of a meteor impact? Something like this...

- A meteorite strikes. The shock of the impact alters the underlying rock.
- The delta erodes. This impact-shocked rock, and possibly ejecta cover, makes it slightly more resistant to erosion.
- The spot becomes separated and isolated from the main eroding delta front as it continues to be eroded at a faster rate for various reasons, including variations in sediment types, and varying interaction of the slope/escarpment and wind-flow patterns.

Just spitballing here; I have no idea how to determine if any of this is actually possible.

Lots of rock imaging on sol 71 with a focus on the pebbles which are somewhat rounded but not spherical, in general. The imaging strengthens the idea that many pebbles are harder grains (concretions?, phenocrysts?) weathering out from the bright, platy pediment. This Watson image is maybe the best example of grains in various states of getting isolated from the bedrock to become pebbles:



There are a few multispectral images with six wavelength bands. Do we know the bands of the filters ? And what minerals they are designed to be sensitive for ?

See this filename description and Table 3 in Bell etal.

Thanks, very helpful. There is also a plot showing spectra of relevant minerals.

A new Supercam image zooms in to the previously recognized channel incision into the lower foresets at the delta remnant. Here is a quite heavily processed (sharpened, graded, somewhat devignetted, auto-balanced) version with the channel highlighted in an attempt to enable study:

Click to view attachment

The right boundary of the channel is less well defined. The highlight shows a maximum size.

The channel is crossing the apparent progradation gradient, and has relatively fine grained sands and shales, perhaps from a meandering portion of the channel. No signs of conglomerates. The channel formation would fall between delta progradation and a period of erosion of both, topsets and channels.

I guess that I have a predilection for seeking scour fill so that is what I lean towards. In the image we have clear foresets indicating that the view is reasonably perpendicular to the palaeo flow from right to left. These are seemingly truncated at the the top with an erosional contact as we have seen before. The shape of the deposit is classical scour but the interesting thing is for scour the steeper side would have been upstream with the tapering, low incline end pointed in the direction of flow. The view of this scour and fill if indeed it is such may be at a reasonable angle to the actual direction of flow at the time. The blocky deposition to the left transitioning to laminations downstream is also typical of scour fill. A change in direction of flow within the body of the delta is not contradictory if there was a hiatus in flow with aeolian erosion with changed surface contours.

Edit: As an example of changed flow direction the image of the delta at my post #174 on page 12 shows a significant raised river bed at right angles to the main channel that crosscuts previous streams.

Click to view attachment

I think what you've defined as a channel fill is a part of the outcrop that is expressing the bedding differently because of cementation and its relationship to the jointing/fracturing of the of the rocks, all subsequent to deposition and likely during burial and exhumation. The joints and fractures in the outcrop are shaped and spaced differently, presumably controlled by some aspect of the lithofacies (grain size, sorting, cement, bedding and lamination, etc.). The triangular/prismatic section you've highlighted coincides with a change in fracture orientation from curvilinear-near vertical to about 45 degrees and oblique to the bedding (highlighted in the attachment). You can see other fracture-bound areas where very thin bedding/cross bedding is obscured between closely spaced joints/fractures. You see this in terrestrial outcrops all the time, where one joint face may have very well-expressed internal bedding, while the conjugate face is completely obscured. There is a fluid flow and fracture timing story here, and it's mucking up our beautiful clinothems!

Thanks Tim. We defer to your logic and expertise.

On sol83 we had this Supercam zoom showing well layered sediments in outcrops peaking out of debris:

https://mars.nasa.gov/mars2020/multimedia/r...AM01083_0100I6J

The outcrop is located in front of the Mt. Zodiac outlier, here superimposed on a sol78 Zcam image:

Click to view attachment

The sediments are in a lower section of the delta, early or perhaps pre-delta, lake bottom. They may be an interesting target because they could be accessible, look to be low-energy/shaley, and can be clearly tied to the Lake history. Not very far below seem to be bright weathering, platy rocks, and it seems not unrealistic that it is possible to establish contact relationships to those.

Reworked Supercam photo from sol 83
Click to view attachment
Strange M-shaped stone with dimples in the foreground

The field of view of this photo
Click to view attachment
The area between the two blue lines was captured by the Supercam. The distance from the rover is about 600 to 700 m, and the distance from this area to the outlier in the background is about 1700 m.
Therefore, the layered outcrop and the debris belong to the lower etched unit in an erosional window.

Thanks for finding that spot. I have to admit it is closer than I thought it was. Alas, this location will not be visited. It does show that there are what are likely lake sediments preserved in that unit. Supercam could look at similar shale ridges to confirm, and perhaps start to map out their distribution.

Yes, without objects of known size in the landscape, the perspective impression can be deceptive.
Supercam sol 83 field of view (areas outlined in red) in a Mastcam-Z image of sol 69 (right eye, infrared filters 1 to 6 via PCA to RGB).
Geological units according to the Geologic Map of Jezero Crater by V. Z. Sun and K. M. Stack https://doi.org/10.3133/sim3464
Click to view attachment

Another layered outcrop of the lower etched unit was spotted on sol 69.
Mastcam-Z right eye, infrared filters 1 to 6 via PCA to RGB. The image is cropped to avoid flatfield inhomogeneities.
The field of view shown in the map belongs to the entire original photo.
I assume the prominent ridge in the Mastcam-Z photo is in the yellow circle.
Click to view attachmentClick to view attachmentClick to view attachment

Ahh, those false colour images take me back to the days of Spirit and Opportunity.

SuperCam image from Sol 94, and two older Mastcam Z images for context.
Click to view attachment Click to view attachment Click to view attachment
I wonder what those darker horizontal lines are on the slope of the crater wall.
Layered sediments deposited before the crater was formed? Ancient shorelines? Something else?

The horizontal lines in the background of the two SuperCam photos of Sol 94 are probably those elongated dunes on the slope of the crater wall.
The clearly layered sediments east of the circle are hidden behind small elevations between rover and outlier.
By the way: Does the prominent outlier/inselberg have an official name?
Click to view attachment

tau, nice work but could you clarify the designation NHjf2 please. It translates as Noachian, Hesperian, Jezero crater, fan, younger. Shouldn't the upper section of the unit be Hjf, overlying Njf1 which overlies Njfe2 (the Nle in your image).

*Edit: I appreciate that the designation you use is what appears on the map by Sun and Stack but the Hesperian deposits were evidently laid down as a separate event when the lake level had dropped. So Hesperian deposits should overlay Noachian. In fact the USGS map shows the NH fan deposits overlying Nue (Noachian upper). Does this mean that they believe the later deposition occurred across the Noachian/Hesperian transition? This would seem to imply an extremely long active period for the delta subsequent to the Noachian deposits.

QUOTE (serpens @ May 28 2021, 11:18 AM)

tau, nice work but could you clarify the designation NHjf2 please. It translates as Noachian, Hesperian, Jezero crater, fan, younger. Shouldn't the upper section of the unit be Hjf, overlying Njf1 which overlies Njfe2 (the Nle in your image).

*Edit: I appreciate that the designation you use is what appears on the map by Sun and Stack but the Hesperian deposits were evidently laid down as a separate event when the lake level had dropped. So Hesperian deposits should overlay Noachian. In fact the USGS map shows the NH fan deposits overlying Nue (Noachian upper). Does this mean that they believe the later deposition occurred across the Noachian/Hesperian transition? This would seem to imply an extremely long active period for the delta subsequent to the Noachian deposits.

Very specific questions - but sorry, I'm not a geologist. First I wondered because I could't find the designations Hjf, Njf1, and Njfe2 in the "Geologic map" by Sun and Stack. If I understand you correctly, you suggest to reinterpret the map. I just used it as it is.

NHjf2 means 'Noachian or Hesperian' Jezero fan 2 - its age is uncertain. It's not a Hesperian unit overlying a Noachian unit.

If the order of the units in my image looks odd (from bottom to top: Njf-Nle-NHjf2), it is an effect of perspective. My interpretation is the attached profile (not to scale). The elevated ridges of Nle just hid a part of the landscape between Perseverance and the outlier/inselberg, therefore NHjf2 only seeminly sits right on top of Nle. By the way: Does the outlier/inselberg have an official name?
Click to view attachment

Edit: Only few minutes later I found the answer in this post. The official name of the outlier/inselberg is "Kodiak". Many thanks to Saturns Moon Titan for his reference to Jim Bell's presentation.

Second edit: Profiles more credible than my amateurish one can be found on slide 12 of Jim Bell's presentation "Delta Bound: Early Exploits of the Mars 2020 Perseverance Rover in Jezero Crater".

Thanks Phil.

The sol 106 panorama of the rim of the small crater (I do not think it has a name yet) offers an opportunity to observe and interpret rock types encountered so far in isolation in closer context. Here is an annotated 'section':

Click to view attachment

There are massive rocks, some with weak internal layering and a rounded, smooth morphology of weathering, holey rocks, which seem often less rounded, and stratified, sedimentary rocks. All occur in an assemblage. Although the crater rim is disturbed and warped, a few contacts are preserved, and all units can be considered more or less in place. The most interesting observation is the contact between well stratified, seemingly immature sediments with an indication of (fluvial?) cross-bedding below a more homogeneous, massive unit. The massive units in turn seem associated with the holey rocks. As an assemblage, and in the geologic context, a volcaniclastic origin may explain best the sequence and the variety of rock types. The holey rocks could be gas-rich lava. They grade into lava/(hot)ash deposits which are often well amalgamated almost in a welded tuff fashion into a homogeneous, massive unit, and are intercalated with fluvio-lacustrine sediments of reworked basaltic flows and tuffs. From the outcrop, it is not clear if that sequence was deposited (or emplaced) before the deltaic phase or much later after delta and lake floor sediments had been deposited and then removed by erosion back down to a level close to the original crater floor. Speculating, the same assemblage may occur with the stratified rocks observed in Zcam images closer to the delta proper.

Andres, this ties into the interesting discussion on ejecta in the south from the landing site thread. The initial crater depth would have been on the order of 18 metres so ejecta would probably have included the eroded sedimentary layers and the proposed basaltic layer that covered them. Tau's supercam image of of one ejecta example, copied below, looks like vesicular basalt with a small possibility of phenocrysts. Fractured sedimentary ejecta would have eroded comparatively quickly.