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

Attached thumbnail(s)

 

[Juramike]

I used the "ski tracks" feature in the T8 swath to attempt to speculate on the depth of the sediments in W Shangri-La.



The bright terrain Adiri appears to be an upwarped terrain that was left above sea level during the last major inundation. There is an interesting series of parallel ridges in the T8 swath that run predominantly E-W along the southern margin of the Shangri-La basin and continue across Adiri. These ridges have been upwarped across Adiri (or downwarped to form the Shangri-La basin). In Adiri, the ridges are coated in bright material, but as one tracks eastward, the ridges slope gently down below “sea level” and the bright material is no longer present. Entering the Shangri-La basin, the ridges can not be discerned by ISS, but still remain visible in RADAR images. As the ridges begin reemerge above "sea level" further E, the ridges reappear in ISS imagery in the area to the N of Perkunas Virgae. (The ridges (and valleys) themselves are parallel to Bacab Virgae).


Several of these ridges can be traced in the T8 swath. (I highlighted about 8 trending EW).
Interestingly, the fault highlighted by Soderblom et al. on the island next to the Huygens Landing Site runs parallel to these ridgelines. It seems likely the “island” closest to the Huygens Landing Site is an exposed section of one of these ridges.

Across the entire southern section of Shangri-La there are features that are oriented parallel to these ridges: these include Bacab Virgae, and the undersea parallel ridges S of Tortola Facula that were examined by altimetry.



It seem reasonable to estimate that the that the ridges and valleys in the parallel system have elevation differences of 200-300 m. (Based on Huygens Island topography analysis 250 m and the similar set of EW undersea parallel ridges S of Tortola Facula that varied by “several hundred meters”).

If we select one ridge in RADAR (green dashed line), we can follow it in ISS from the bright Adiri terrain into where it breaks up into exposed bright islands at the margin of Adiri (light blue line), until it disappears into Shangri-La (dark blue line), only to reemerge again into exposed bright islands (dark blue line). The light blue line shows where the valley was inundated (no more bright material on valley floor), and the dark blue line shows where the ridge tops were inundated (bright material removed even from ridgetops). Assuming the ridgeline to valley floor has an elevation difference of 200 m, the distance between the light blue line and the dark blue line can be used to derive the slope of the warp. This is approximately 200 m in 200 km, or 0.1%.




Extrapolating this slope into the "sea", we can estimate the depth of this section of Shangri-La basin. (In the slide, the red line is drawn in the valley just N and parallel to the ridgeline track in order to not obscure the ridge.) This would be estimated to be 100 m from sea level to ridgeline top. (Or 300 m from sea level to valley floor). An estimated (predicted) altimetry track is shown. [This track is close to the future T41 RADAR track]. These values are in the same ballpark as previously determined depths (above posts).

The area bounded by the dark blue lines and along the ridgeline is highlighted in yellow. By ISS, no bright ridges are observed. This makes sense: from the above analysis, the ridgetops would have been inundated (by 100 m of solvent) , and no bright coating would be expected. But in this same area, ridges can be observed by RADAR. This implies that the ridge tops are RADAR-visible above the lower level of sediment or loose dune sands. Since the ridge tops are 200 m above the valley floor, that implies that the sediment layer lying on the valley floor is less than 200 m thick.

(If the sediments were thicker than 200 m, the “undersea” ridges would not be visible by RADAR).



So the bottom line ( yup! I intened that! ) is that the Equatorial Sand Seas are relatively shallow (compared to Earth) but are not silted over.

-Mike