Titan's Equatorial Sand Seas Options

[Juramike]

I’ve put together a sequence of events that could explain the morphology of the Equatorial Sand Seas. (An example basin similar to Shangri-La is shown)

This could explain the ria-like topography [http://en.wikipedia.org/wiki/Ria] on the Eastern shore, as well as the VIMS dark blue western parts of the Sand seas, and the placement of the dark brown unit on the Eastern parts of the sand seas.

1. Basin formation.
2. Water-ice sand deposition [slowly, suddenly?] forms an ice-sand margin
3. Mobile dark brown dune sands deposit on E side, depositing inland up W facing valleys.



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The dark brown sands will blow in following the predominantly W winds and make a dust coating on low-lying terrains on the eastern margins. This will be visible by VIMS and ISS as the dark-bright margin, placed “inland” from the "real margin" and will accentuate the local topography as seen by optical instruments. This accentuation on the E margin will make the Equatorial Sand Sea visible margin look “swoopy” and windblown (in effect, it is) from the dark basin. Similarly, the W margin will have a dark blue zone that appears blown from the western bright areas.

On the Eastern shore, the RADAR images will place the smooth-dark/mottled gray boundary far to the W of the VIMS brown dark-bright margin. (RADAR should be able to penetrate a thin coating of dark sands). The features in the limbo zone have been covered by dark sands, perhaps not enough to form dune structures, but enough to cover up the ice-sand margin, the near shore terrain, and perhaps even some of the underlying bright terrain.


This makes the deposition sequence in the Equatorial Sand Seas:
1: Basin formation
2. Major water ice sand emplacement
3. Dune sands cover up low-lying downwind valleys (enough to mask visible imagery)

Other Equatorial Sand Sea basins should look very similar around Titan: Shangri-La, Belet, Senkyo, Fensal and Quivra. Local winds may play a bonus role, but the overall trend of dark sand deposition up valley should be towards the E. For example: the false-color image in Figure 6 of the Soderblom paper seems to imply a predominant wind vector in Fensal and Quivra to the ESE.

[I’m pretty sure all this has been described in pieces before, but it gave me a really great excuse to play with PowerPoint. ]

-Mike

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[Juramike]

I’ve put together a hypothetical sequence that could explain the RADAR and VIMS appearance of the craters observed in the Equatorial Sand Seas. (Craters such as Sinlap, the T17 swath crater in W Fensal, and Guabonito). This sequence also explains the puzzling appearance of the bright material which highlights the crater rims and central peaks.






1. Crater forms, either before or after the Sand Sea basin forms or is partially filled in..
2. Water ice sand erodes on outside of crater, forming a debris apron or ice sand margin.
3. Bright material is deposited.
4. Liquid or fog percolates up to a set topographic level at the crater. All bright material below this line (“highest sea level”) is dissolved/modified/washed away.
5. The liquid (fog) level retreats, leaving crater high and dry and revealing previous units.
6. Mobile dark brown dune sands deposited on W side, but don’t fill in downwind (E) in the wind shadow of the crater.


Here are some examples of what we would expect to observe from this scenario, compared to actual VIMS and RADAR images:





This nicely explains the bright material deposited on the rim of the crater, but not on the blue ice sand margins (in some of the craters like Sinlap). It also explains the bright deposit on the central peaks of Sinlap, as well as on the central peak of the crater-shaped feature NE of the Huygens Landing Site (seen in ISS)..

The key to this sequence is that the bright material was deposited BEFORE the last major sea level rise.

It is possible that each item in the sequence is periodic, rather than a one time deal. So the deposition of bright material is episodic and rare, floods are less rare, and dune sands move quite often.

The bright/dark line around the Equatorial Dune Seas are fixed by the last major sea level height attained in that basin after bright material was deposited.

Craters that formed environments that were eventually deeply flooded will have a significant light blue and dark blue sand ice margin that extends outside the brightest material deposit (especially to the W). They will have a bulls-eye pattern in VIMS. Those craters that formed in areas that were only slightly covered in liquid at it’s highest point will have a very small blue ice sand margin that extends beyond the bright material – these will have a very asymmetric look in VIMS (strong trailing to the E). Some craters were never inundated and thus would only have bright material covering the entire crater complex – these may not show up by VIMS, only by RADAR.

Craters that formed in what was eventually a deep liquid environments include Sinlap, the Western T17 RADAR swath crater in Fensal, and Guabonito.
Craters that fomed in an enviroment that was eventually shallowly covered in liquid include Minerva, and the crater(?) that is on the W tip of Quivra (seen in the T25 RADAR swath)
Craters that formed in environments that were never inundated include the crater on the N end of Shikoku Faculae. (not obvious in ISS, but seen in RADAR).

By this analogy, Fensal is deeper than Aztlan. And Shangri-La nearest Xanadu is deep (subduction?) and Shangri La is very shallow near it’s contact with Adiri.

In general, areas with steep shorelines (“highest level attained after the last bright stuff deposition event”) will have fewer indentations and have a smoother light/dark border (i.e. Xanadu). Areas with shallow shores with relative highest topography closest to highest sea level height will have very jagged and irregular bright/dark borders (ancient bright stuff/liquid shorelines). From this we would predict that average elevation of Adiri is very close to the highest attained level. It may be an area that has been gently upwarped to a level just slightly above the highest attained sea level in Shangri-La basin after the last bright stuff deposition event.

The bright island at the Huygens Landing Site sits just above the level of the “highest level of liquid attained in Shangri-La after the last bright stuff deposition event”. The bright/dark contact line of the highland sits at the highest level of liquid attained in the Shangri-La basin. In the channel some of the sand bars have bright material deposited on them. This should allow us to link the two units. The bright stuff on the sand bars would also be just poking above the highest level of liquid attained in the Shangri-La basin after the last bright stuff deposition event..

The analogy of the Great Basin of North America, painted white, and then flooded with a Glacial Lake Bonneville amount of turpentine and then drained seems pretty close. (Possibly very close chemically).

-Mike