What could be this structure? Appears like a trace fossil. The structure is seen on bed surface of silty sand lying above laminated Siltstones. Age of the host sediment late Carboniferous-early Permian. (Scale: Stick length: 4 cm)
I would suggest this is "only" a dewatering or "slump"-structure, not a trace fossil.
The second photograph seems to be affirmative for a slump structure.
Can you confirm the nature of these with respect to the surface - are they positive epi-relief on the surface of the bed or negative epi-relief on the bases? I doubt if water could do this by itself - and there may be a biofilm or algal mat involved in giving the surface the strength to hold together - check out Scieber et al 2007 Atlas of microbial mats in the clastic rock record - available online FoC....
Thanks to all for suggestions. I shall further work on it. Responding to Dr. Nicholls and Kietzmann, i would like to add that these are positive epirelief. Enlarged view in the bottom most picture shows faint yet regular annular traces.
As for the third photograph It seems to be a root structure. Horizontal root structures (rhizoliths, root traces, etc) are suggestive of a water table near the surface. Is it possible in the context of the sedimentary sequence?
Although I do not have first hand experience with Hillichnus, this interpretation seems less likely to me.
Heart-felt thanks to all my peers for suggestions. I understand, this is difficult to comment on this enigmatic structure based solely on photographs. From the close association with Kouphichnium isp., Diplichnites isp. and other ichnotaxa of cruziana ichnofacies, i cannot even rule out partially preserved Palmichnium undertracks, as an option. I guess i need to search for similar structures for confirmation.
Abhijit, is this structure found on a horizontal bedding plane, or is it a cross section of a vertical outcrop face?
Hi Steve! Thanks for your visit. Sure this is on a horizontal bedding plane of a low dipping silty sandstone strata within a ice-contact, deltaic-marginal marine Late Palaeozoic Talchir Formation (Gondwana). I am posting the field pic (Fig.A) of host sediment showing the fossil(?) position (arrow). The exposed bed surface initially revealed some enigmatic structure (Fig.B). Unraveling the top few cm (through chiseling), the referred structure (Fig.C) is found on the bed surface of underlying layer. I am not sure, whether this is part of a more exotic 3D structure (as Kietzmann indicated) or something exclusive, unrelated with the surface feature. We reported Kouphichnium isp. from thinner siltstone-shale layers underlying this unit. Associated ichnotaxa include varied tracks and trails, scolicia, diplichnites, rusophycus etc (see in the attached pics Fig.D).
Hillichnus shows more regular diameters of the branching tubes. Please find attached a picture (first picture) from a siliciclastic medium grained beach with similar structures.
For comparison with your plate D (lower right) I will attach a picture (second) from a pure sedimentological feature from the same setting, which is not a trace but an accumulation of a trace-like single wave ripple...
Please take in account, that a lot of anorganic or biomat related processes can result in "trace-like" sedimentary structures.
Best regards
Johannes
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