[X] My Assistant

[dilo]

Short time to enjoy Eldorado images and now... just released picture of HomePlate, I know still hundred of meters away but seems so close!
stitch of two Sol712 NavCams:
It seems Spirit is now at the same level of HomePlate plateau!

Here I tried to identify some features seen from the summit... not totally sure on bright sand spots and rocks, any suggestion?

[ElkGroveDan]

I've been holding off on giving this little sedimentology lecture, but now seems like the appropriate time:

I tend to only use the term "festoon" for very large scale trough cross bedding, like you might find in eolian sanstones, where the cross bedding has recorded the migration of the foresets (the down-current face of a bedform) of very large dunes (m's to 10's m high). Large relief dune foresets can also form in subaqueous settings, like subtidal sandwaves or bars in deep river channels. I think the NASA/JPL guys use the term more generically for trough cross bedding and lamination.

The smaller-scale features that the rovers have been identifying would fit into what I would call "cross lamination". They have identified: 1) trough cross lamination, where the lamina foresets are curved and intersect the lower lamina set boundary at a low angle and may be truncated at a high angle at the upper lamina set boundary; 2) planar tabular cross lamination, where the foreset lamina are inclined, but parallel, and intersect the upper and lower lamina set boundaries at approximately the same angle; and 3) low angle inclined cross lamination, which is just what it sounds like. There is also plenty of horizontal planar lamination.

The difference between these lamination types has to do with the morphology of the bedform which migrated to form the strata type. When straight-crested subaqueous current ripples migrate, they produce planar tabular cross lamination. When sinuous-crested subaqueous current ripples migrate, they form trough cross lamination. Low-angle inclined cross lamination can form by migration or encroachment of a low-relief sand sheet, or a traction carpet, in either subaqueous or eolian settings. Horizontal planar lamination can form in a number of very different settings: 1) upper flow regime (fast current velocity and/or low water depth) plane beds, which can form in fluvial, tidal, and sediment gravity flow settings; 2) antidune migration, where the entire bed is in transport (the planar lamination forms down current from the up-current migrating antidune); and 3) settling out from suspension. Horizontal and low-angle inclined lamination can also form by the migration of wind ripples (also called ballistic ripples) in an eolian setting. This is sometimes called "wind ripple translatent strata". These features have distinctive alternations of coarse and fine fractions between lamina, which often results in a "pinstripe" appearance in outcrop, and they are then called pinstripe lamina.

Any oscillatory flow (influence of waves) either alone or combined with unidirectional flow, tends to make bedforms that leave trough cross lamination as they migrate (sometimes just vertically aggrading). This "wave-ripple cross lamination" exhibits curved foreset lamination, but they tend to have no preferential dip direction between lamina sets.

http://walrus.wr.usgs.gov/seds/

I was going to say that.

[RNeuhaus]

The other important criteria for describing cross bedding and lamination is the angle of climb... that will be Lecture #2!

Dave Rubin's site has many excellent examples of cross bedding and cross lamination and other resources:

http://walrus.wr.usgs.gov/seds/

Maybe he'll be kind enough to post it again. In the meantime, there are some pretty nice images and descriptions of several types at this site. Click on "Current bedforms" and "Waves and tides" in the frame on the left. You might also Google to find other sites.
http://www.ualberta.ca/~jwaldron/structurespage.html

Both references have helped me much to understand the bedorms and crossbedding. These references are a very useful geology sources since they will permit me, I have to practice it by observing during my hobby Truck 4x4 off road outdoor, to understand the formation of many places that I was not able to understand fully.

Again thanks to both!!!

Rodolfo

[CosmicRocker]

It's getting a bit hard to follow everything in the discussion here, and the mostly parallel one in "Home Sweet Home." Shouldn't we move this over there, since we are no longer "Going to Home Plate," but are actually there?

I've been holding off on giving this little sedimentology lecture, but now seems like the appropriate time:
...

That was quite informative. Thanks. It really pointed out just how complex the interpretation of crossbedding can be, be it aqueous or aeolian. Those movies that morphed into images of the outcrops were awesome. I think we'd all like to hear a few speculations from you about these HP rocks.

Several times on this forum its been mentioned the need for a drill core to piece together the geological history of the places we've seen on Mars, and here we have something that are
almost as good.
...

I'm all for drilling in a future mission. I'd like to ask Schlumberger to develop a borehole logging tool that could be included on a rover. Imagine running resistivity, SP, gamma ray, neutron porosity, and a dipmeter down a hole on Mars! It might be difficult to fill the hole with mud, though.

... I think we may be seeing more than one type of cross-lamination here.  Besides the abundant tabular stuff we have been seeing from the last two sols, there may be some that look like some kind of ripple cross-lamination, but the image contrast in the areas I am seeing it is very poor and I am not convinced yet.

I think I'll pull back on that for now, after looking more carefully at the images. I think I'm being misled by the nifty differential erosion we are seeing on these amazing rocks. I really want to see pancam closeups and MIs of the upper units. No, cancel that. I want to see more MI's of this lower section, first. Wait a minute, I'm not sure...

Is anyone having fun?

Edited to correct grammar.

[Shaka]

Is anyone having fun?

Edited to correct grammar.

HOOO...RAAHHH! (Insert emoticon for wild delirium)

P.S. "correct Grammar" ? What's wrong, she's all right isn't she? Let the Old Dear have her little say!