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What is this geomorphological form located at Vitrolles, France?

And how is it formed? It is like a 'raised flat land', or a base of a hill where the top 80% is cut, leaving only the wide, flat base.

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  • $\begingroup$ HI, are you asking about the separate chunk under the pin, or the whole plateau that extends east off the right edge of the photo? $\endgroup$ – Spencer Jul 19 at 19:52
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There are a couple of possibilities, depending on what you're paying the most attention to. This falls in an overlap area of terms that vary from region to region and even from person to person.

The key thing to notice in your photo is the whitish band running along the top of the escarpment that borders your landform. This shows that it's held up by a resistant, mostly horizontal, layer of sedimentary rock.

This French page refers to it as a cuesta; this is plausible, but the strata underlying cuestas usually slope more than what appears in your picture.

cuesta image from Wikipedia

(generalized cuesta image from Wikipedia)

"Plateau" is also plausible, but this is not very specific. The landform in your picture doesn't have quite the extent of the Colorado Plateau.

Tableland or table is probably the most generic name for the entire regional structure under the rock layer.

If you are talking about the remnant under the pin in your image (and especially if this were in America), then we'd have no trouble calling it a mesa or even a butte.

mesa

(Wikipedia image of a mesa in Monument Valley)

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  • $\begingroup$ I somewhere read something about the spanish adopted term cuesta on my quick research.The archeological paper I read of the site du griffon mentioned this as Plateau de Vitrolles. I did some geology at Perigaux on an Erasmus stance and I saw what french geologists describe as Cuesta. I left geomorpohology lessons some years ago, but I think the difference is if there is slope at the hard structure. $\endgroup$ – Universal_learner Jul 19 at 13:03
  • $\begingroup$ To see that Google is not enougth, an ortophoto and a sterescope is needed. Best option is to search for local studies on french journals. $\endgroup$ – Universal_learner Jul 19 at 13:05
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    $\begingroup$ @Universal_Learner "cuesta" is an elementary term taught to first-year undergraduates... $\endgroup$ – Spencer Jul 19 at 13:16
  • $\begingroup$ Spencer by curiosity. The term is strictly french or also used at US? I never heard the term on my spanish degree. Paradoxically being the term spaniard. $\endgroup$ – Universal_learner Jul 19 at 14:07
  • $\begingroup$ @Universal_Learner Used in the US. Since a lot of places in the Southwest US have Spanish-derived names, type names like 'cuesta' and 'mesa' (playa, arroyo, etc...) were adopted the into the technical lexicon. $\endgroup$ – Spencer Jul 19 at 15:45
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There is a similar and bigger chalk plateau at "plateau d'urle" in France.

That one looks like a "chalk plateau of continental shelf origin with straight channels eroded into the underlying clays", by it's flatness and proximity to the sea. The geologists write that the chalk is a freshwater lake chalk deposit due to it's fossils.

The sediments are layed down by different processes with different chemistries... Very tough pure chalk, softer chalk and silt deposits vary in bands, corresponding to underwater currents and rivers that vary over time.

The top layers erode away leaving a very tough protective chalk. The water flow at Vitrolles has stayed shallow, so that it has not tunneled deep under the chalk cap, it has burrowed straight channels just under and through it.

top layer (freshwater lake chalk) 60 million years... red stripes: Calcaires de Vitrolles (Montien-Tertiaire)

lower layer (clay and sandstone) 65-70 million years ... beige no stripes: Argiles et grès à lentilles calcaires (Rognacien-Secondaire)

enter image description here

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If the flat land formed as a river terrace, we could call it a raised terrace.

If the flat land is a resistant layer of rock, then we could call it a low plateau. (the thin layer of white rock immediately below the land surface might suggest this is the correct interpretation.)

If it formed by erosion in the past, it could be a peneplain.

The correct word depends on the origin of the feature.

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I couldn't find any paper describing the geomorphology of the zone, but this is refered as Plateau de Vitrolles; there is an archaeological deposit close to the point you marcked (source).

You can find a french geologic definition of plateu at this site. I guess the term is equivalent to plateau on US reference bibliography, but there migth be some little differences.

To shortly answer your question about how was it formed, the Ruisseau du Bondon excavated the plateau, forming the slopes and the valley.

To deeply answer a reference to a local geomorphologic study would be needed. There should be some study on geomorphology journals, as the zone looks interesting. If you are at University you could make a research for "Plateau de Vitrolles" and you migth find a complet explanation from local geologists.

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Your marker seems to indicate an escarpment, which is a long ridge where a cliff or a steep slope separates low ground from higher ground. These slopes or cliffs can have a number of different causes, but as I have never visited the one in your photo I wouldn't like to hazard a guess as to what caused this particular one.

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