GEOLOGIC EVALUATION OF THE CITY "PYRAMID"

The third Cydonia high resolution image from the Mars Global Surveyor (MGS) included part of the area known as "The City" and the knobs known as the "City Square." This new image revealed a much clearer picture of one of the large "pyramidal" landforms at a resolution far exceeding that of the 1976 Viking images. Though a number of "interesting" landforms have been noted in the new image, this discussion will center on the "pyramidal" landform. See the accompanying image which has been annotated with letters to identify various features that have been noted during a preliminary geologic analysis.

I had been told, prior to viewing the image, that the landform was a three-sided pyramidal form. After seeing the image, I’m not sure about that. It is not clear if the landform is three- four- or five-sided. One face of the landform exists between letters C and H, but there is the suggestion of a ridge at A, bifurcating the continuity of that slope. Thus it is possible that the eastern side of the landform could be divided into two separate slopes, between C and A, and between A and H. More evaluation will be necessary to determine the authenticity of the perceived ridge at A. Subsequent images of this area would provide true stereoscopic analysis and would be of great value in determining the disposition of the landform’s eastern face.

A second slope face is apparent in the area to the west of B which is distinctly constrained by a sharp escarpment (cliff) to the north and the south-trending escarpment to its east. A third surface exists roughly between the letters B and G (west side of landform), but there is an expression of another ridge in the area of D, thus this surface may turn out to actually be two independently formed slopes rather than one. Whatever the case, the shape of the landform is certainly interesting in a geologic context.

Along the ridge located near B, there appears to be exposures of outcropping rock (darker areas). This suggests that most of this slope face is covered with loose sediment and talus (blocky material). The signature of the outcrops does not provide enough evidence to pinpoint what types of rocks may comprise the "pyramid", but they must be resistant to erosion in order to form the sharp ridges defining the landform’s shape. Resistant rocks on earth might include volcanics, sandstones, dolomites and some limestones depending upon environment. Still, unless there is an unrecognized structural component to the landform (for example, it’s a volcanic pile with radial dikes (conduit magma)), which is causing it to erode in a pyramidal form, it is difficult to envision a selectivity in water and wind processes which would degrade a preexisting landform into this particular shape. Such processes may have occurred in the Martian environment, but they are conjectural at best with the data at hand.

All of the slopes of the "pyramid" exhibit the same general pattern - the underlying rocks are covered with piles of loose sediment and debris. What is not clear is whether the loose sediment is a product of erosion of the landform or whether it has been transported by winds and piled up onto the landform - or both. At D and E (note the white lines), there are two scarps which seem to define the boundary between consolidated sediment (rock) and unconsolidated debris (talus and loose sediment). These scarps may indicate the boundary where active mass wasting (from gravity) is occurring. A sizeable amount of loose material appears to cover the slope from E to G and west of D. At F, it appears there is a partially filled-in impact? crater, but that interpretation is questionable because of the structure at H. At H, there is a sinuous escarpment (it is dark and looks like a wide, lower-case m) and the wall of the feature at F may be part of that escarpment. At G, it is possible that we have evidence of sheet runoff (water erosion). Interestingly, the form of the slope near G is somewhat reminiscent of alluvial fan deposits in the western U.S. Fractures may also play a role in the morphology of the slope at G. Still, the hints indicating water erosion of this landform are tantalizing to the history of the Cydonia area as well as Mars.

At C, we have an unusual feature which may indicate some underlying subsurface structure. It is a raised, elongated mound, which is topped by a series of parallel, bright forms. These may be dunes of some sort, but they do not have the character or the length of other undoubted dunes photographed on the surface of Mars. They may be representative of some type of dike deposits, volcanic joints or tension fractures, but the image resolution still does not allow for one to point to any of those with certainty. Perhaps they are even remnant structures from glacial activity, but that argument is speculative at this time.

In summary, the "pyramid" imaged in "The City" is a complex landform, which will certainly need more study to fully understand. It shows evidence of water erosion, slumping, wind erosion, and may exhibit evidence of a structural component which has determined its shape. The "pyramid’s" composition is indeterminate from the pattern of erosion, but nevertheless it must be composed of some highly resistant rock type. At this time, whether it is formed of volcanic rocks or sedimentary rocks can only be speculated.

ENIGMATIC MARTIAN FEATURES SOUTH OF "THE FACE"

The "Face" was captured in the first Cydonia image by MGS and lies about halfway down the long strip image. Just south of the "Face" is a mesa or hill (let’s call it Slippery Hill for this discussion, due to a large landslide of white sediment present on its southern slope (not pictured) which originates from an eroded summit crater). This hill contains some unusual features along its southeastern edge. In addition, more of these features are present to the south of Slippery Hill, just below a low-relief landform (see letter C in the accompanying image) that looks like a "coathanger. Let’s call this landform Coathanger Hill. The anomalous features in question are located at A and show as a series of bright, somewhat parallel "lines" which straddle the southeastern slope of Slippery Hill. The same feature is also located at B below Coathanger Hill. This feature is composed of about 25 to 30 bright, roughly parallel linear elements, all which seem to have about the same dimension in length and width.

These features, let’s call them Parallel Linear Elements or PLEs for short, are difficult to explain in light of the knowledge of the geology of this area. They seem to suggest some underlying structural component which has been exposed through the action of surface erosion and weathering. Their brightness may be due to their composition or it may be due to their relief in relation to the sediments they appear to sit on. Also, there are a number of low-relief mounds (letter D, for example) which have a similar brightness to the PLEs. Is this a reflection of composition similarities or a reflection of relief?

The eroded crater at E displays none of the brightness as do the mounds and the PLEs. One might conclude from this, that the PLEs and mounds may be composed of a different material than the crater. Some possible answers for the PLEs are ice, dunes, tension fractures (filled in) or volcanic joints. Unfortunately, none of these seem to explain them properly. Because the PLEs are present in a linear form near B and a curvilinear form at A (along the slope of Slippery Hill) that makes them all the more difficult to integrate into a geological picture based on ice, dunes, etc. At A, the PLEs are positioned on the slope of Slippery Hill and thus are at an angle in relation to the ground surface. That angle appears to be about 25-50 degrees. At B, the PLEs are situated along the surface and since the surface appears to have a low grade, the PLEs are generally horizontal in form. So similar yet so different. What does it mean?

My suggestion is for you to check out the PLEs yourself. Take a good look at them and see if you can come up with a satisfactory explanation - especially one based on natural events.

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