Figures/structures marks at the top of limestone bed, Palaeocene-Eocene deposits, Morocco
It is a network of cracks due to brittle deformation.
The network of cracks of the probably plate-shaped limestone shows sub-vertical dislocations. The margins of the fractures are outlined by subsequent solutions that have produced a faint relief (and may have healed by calcite again). The narrower the mesh size of the network of cracks, the more intense the brittle deformation.
Best regards,
Guenter Grundmann
Thanks for all answers. I agree with presence of fractures but figures with discoidal/circular shape are reminescent to rain-drops???
The roundish dimple-shaped depressions on the surface of the limestone are corrosion spots caused by lichen. The black spots are probably organic remnants of these lichen.
Best regards
Guenter Grundmann
Could you make a vertical section of the subcircular holes ??
if they give you I-shaped structure, they they are Skolithos, if they give you a simple U-shaped structure then they are Arenicolites, and if they are Connected U-shaped structures then Diplocraterion
bests
Abdel
I don't understand how roundish dimple-shaped depressions could be caused by lichen corrosion?. Are they fossil lichens? Thanks in advance@Guenter Grundmann
Abdel
Thanks for your suggestions. I will try them. @Abdelouahed Lagnaoui
I have another suggestion for the round pits:
Possibly, there were small pyrite aggregates, which were corroded and thereby developed sulfurous acid, which, in turn, dissolved the surrounding limestone. To test this, you would have to look around if there are some haematite, goethite or pyrite remains.
Alternatively, I have seen similar pits formed by ants in places where the limestone was in direct contact with the soil.
In any case, I think these are corrosional features rather than trace fossils.
Maybe this helps a bit.
I think the pits are only on the surface, not deep!. That is why I think they could be raindrops Christian Klug
hm, I've seen fossilized raindrop-imprints, but they looked quite differently.
Thanks for all answers. So now I think i will opt for the corrosion origin of subcircular pits ! @ Guenter Grundmann Christian Klug
I do not think they are raindrop marks, the rock seems dolomite or limestone deposited in high-water level environment, moreover they do not have overall form of raindrop marks.
this how a raindrop marks look like, with a sort of rim in the boudaries of circular structures
I have seen similar pits in the Cambrian limestones and in the Ordovician shells, there are usually associated with furrigenous microconcressions, they were probably resulted from disolution of these concretions. I think some pits contain remained iron-oxyds
Thanks my friend Abdelouahed for sharing the raindrop marks picture. I would thank also Azizi for his comment
Kind regards
Abdel
Ait,
can you really exclude that these are burrows? --> I have seen burrowed surfaces that look pretty similar. Very typical that the infill has a slightly different colour + is more grainy than the host rock. However, IF these were burrows, then you have of course be able to follow them in 3D...
Raindrop imprints that I have seen so far look different -- quite like the great pic that Abdelouahed shared.
Regards, N
Possible print of external mold of dissolved gyrogonites of charophytes and gastropods. Recently I have seen like this in an eocene lacustrine limestone
I don't think that due to theire size and shape. Thanks a lot for your answer Mr Khaled
Dear Niels,
They should be burrows but probably without infill! Also they're not deep prints. Thanks for answer.
Hello,
they look like sponge shallow borings, like Cliona or similar stuff, on a firm- or hard- ground surface.
Regards
I also have seen similar features (pits and cracks) in the Triassic carbonates of Alborz area, Iran. I think they are raindrop marks which are usually formed on the surface of very dense carbonates. Why are not these features seen within the rock? Pay attention to the climate of locality.
The cracks resemble leaf impression of monocotyledonous plant.
Obianuju P. Umeji
Rain prints are clear, Fine grain lime mudstone and wackstone are usually contain a small ratio of clay minerals which may expand at wet weather and shrink at dry hot weather leaving such shallow sun cracks. Tethys's Paleocene - Eocene limestones sedimentation is coincided with the thermal maximum (PETM) interval.
- Badges
- Science topic
- Similar topics
- Agricultural Science
- Soil Science
- Soil Analysis