These are found on proterozoic sandy unit. I am unable to find them. Are they useful in interpretation of depositional environment. There role in basin modeling?
They appear as deformed cross stratification, deformed cross stratification have very diverse morphological preservation along with several other genetic origins. They might be useful only if you get a consistent layer or a mappable unit. One of the other explanation may be this might be a sandstone nodule, common in Mesozoic,( I am not sure of Proterozoic).
In the lower block the layering looks concentric - this would suggest that it is some unusually shaped concretion rather than a deformed cross bedding.
Test question: Is there really a grain size change related to that layer-like structure? If not it is unlikely to be some kind of deformed bedding (such as slumping structures).
Hi,
I agree with the comment of Michael. The problem is that it looks to be a block and not a real oucrop,isn't it? What is the true orientation?
One the hypothesis can be deformed bedding (liquefaction features) due to seismic shock, so called "seismite".
For me they are slumps! no doubt in we have same in deltaic facies of Triassic sandstone.
I agree with Riadh Ahmadi,
I have seen similar structures in the Pyrenees and in the Iberian massif
Well, they could well be slump structures as suggested by some folks above. Such "rolls" may be wrapped in undeformed strata (look above and below) and they can form on any unstable slope regardless of water depth - say on a delta front or in deep water or- even by a slide or tsunami ... caused by a jolt far far away.
I agree with the comment of Michael and Riadh Ahmadi. I think that is a slumping structure. In this photo, we can distinct two levels of slump separate by a thin layer undeformed. These structures are common were a sediment unstability exist (gravity, seismic activity,…) and are undependent to the age (we can fund it in the Proterozoic, Palaeozoic or Mesozoic belts).
I have a similar structures in the Carboniferous of Morocco.
Well, I will say that the strucure are "convolute bedding structures" as first diagnostic.
Neverthelles, it's hard to explain the genetic origin of these structures. Further investigation should be done. The genese can be gravity, seism, tsunami as expressed by my Ghulam and Mostafa.
Soft sediment slumps - almost certainly - will send you an image of similar things from the Ordovician of West Wales (shelf instability), and the Carboniferous in Scotland (seismic?)
I agree with Jerome - they look like convolute fold structure. However, the main problem is that to me it isn't clear whether this outcrop is in situ or a detached block which has moved and possibly re-orientated. I think the key to interpreting this is the true orientation of the fold axis relative to the bedding. If one assumes that this is in-situ and the fold axis are parallel to adjacent bedding then possibly slump structures....
As Jonathan says, these structures should be convolute fold structures, probably slumpings. Anyway, the first thing to be seen should be the attitude of the beds, if this outcrop is in situ. Judging by the orientation of the fold axes and the box shape of the folds, it seems that the stratification has currently a vertical arrangement, while the shear stress that has generated the folds should have acted in a horizontal or nearly horizontal direction. it would be interesting to know something by Veeru on the attitude of the beds. It would be interesting to know also the facies that are associated with these structures, stratigraphically above and below this layer.
Difficult to say on the basis of the photo and probably from the descriptive way we all can agree that it is a convolute bedding structure as suggested above. To say that it is a slump structure you need to look at around and establish the 3D relationship between various bedding planes, beds and their internal texture. Most importnatly I would look for features can be traced over at least outcrop-scale documenting their orientation etc, and their relationship with general structural and geological elements of the entire sedimentary successions this texture was identified. Good luck,
Possible water-escape structure and balling-up structure, especially in the upper part.
I am just wondering if what we are looking at, are not erosionally truncated simple recumbent folds. However it is important to know if the rock is in situ. Simple recumbent folds develop in response to horizontal stresses on planar cross-bedded sediments during liquefaction.
You might find this page and the paper they cite on "seismites" useful: http://www.habitas.org.uk/larne/seismite.html
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