Attached you find some pictures of a fine grained sandstone/siltstone from the Buntsandstein in Germany. What are the bright pinkish, blobby structures? How do they form? They are calcreous.
Normally the sandstone has a red-brown colour. Around the blobby structures the sandstone is bleached which leads to the grey colour around the structures in question.
Hello, we can explore the properties of these inclusions with a new method. Patents RU 2721089 and BY 23260. Best regard Ihar Stepankin
I don't know a definitive answer but I can suggest a few things that might inspire discussion. Unfortunately, I am not familiar with the depositional environment of this rock so I am going to assume that the red coloration reflects a continental origin. Could the blobs have been evaporite nodules or rhizoliths? Could this be related to a paleosol?
it seems as load-cast stuctures, produced by density contrast in sedimentary materials.
https://i.ytimg.com/vi/VTPjagj4Pkk/maxresdefault.jpg
We can determine the mechanical properties (UCS, tdФ, BTS, Ck, YMS, PRS), and then determine mineralogical composition
To narrow down my field of speculation I have to raise some questions. What is the bedding relative to the drill string, what is the stratigraphically upward direction, what is the clay mineralogy of the encasing host rocks like ?
HGD
Harald G. Dill
Dear Mr. Dill,
the bedding relativ to the drill string is nearly horizontal, the stratigraphic upward direction is to the right. The clay minieralogy was not investigated.
Dear Mr. Ungewitter,
What is for sure is a reducing-upward physical-chemical regime with a sharp contact. So that between the two beds there is an abrupt change along a local disconformity. I have observed that from an outcrop in the Holy Cross Mts. It is a neptunian dike, in other words a fissure or vein-like undersea/water mineralization the process of which heralds a horizontal redox boundary with minor reaction with the footwall rocks (short-term) and intensive reaction (long-lasting) along the vertical boundary see also the convex reaction zones around the carbonate (could be a Fe calcite ?). As far as my knowledge of the Bunter Series is concerned ( I did my master thesis in this Triassic series), it could be an inland playa with alternating redox conditions typical of ephemeral lakes.
HGD
It might be instructive to see the core above this interval. If there is an abrupt change to a different redox environment (possibly marine?), the interval under discussion might be related to an exposure surface below a flooding surface. It should be easy to eliminate that hypothesis if this succession is actually completely continental. If there is a flooding surface, the implications would be important so it's worth investigating.
We encountered this type of mottling in the Bunt around a basement high, in NE France near Sierck, but the mottling was around fractures. The fractures were in coarse reddish sand, clay free or clay poor, and the mottling was white and occurred as a 'halo' around the fracture. (I'm afraid I forget if the fractures were open or filled, sorry.) The odd thing was that at the edge of the white halo (1-5 cm wide or so) was a concentrated hematite zone separating the white and the normal reddish background colour. It had the appearance of being 'bulldozed' away from the fracture to the edge of the white halo. My guess then was that there was natural gas from the Carboniferous below trapped around the basement high, and this reduced the hematite to its more soluble green counterpart, moving it outwards and then re-precipitating it along the more oxidized edge as a concentration. My guess for the present photograph is that it is a type of burrow filled with more porous material and has allowed some reductant like methane to reduce the hematite to green ferrous material. This Bunt is clearly more argillaceous than where we saw a similar chemical front.
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