Local geologists unsure: Is it a sea sponge?

[Johnny Fenton]

Found on a public footpath across a field near the town of Southam in the county of Warwickshire, United Kingdom. The area's geology is of lower Jurassic sediments, largely Blue Lias ('Rugby') limestone and Salford shale. There are a few limestone cement quarries nearby, some historic, one active. A whole ichthyosaur skeleton was found locally in one quarry in the C19th.

In this particular field, I have found ammonite fragments, a single ichthyosaur vertebra, a single gryphaea and a few large clam-like shells.

 

I initially thought this find was archaeology. But experts in mesolithic art at Leicester University, referencing my photos, concluded it was a fossil (or a fossil with grooves cut into it by human hand) and referred me to the Warwickshire Geological Conservation Society. From the photos, WGCS opinion was divided on whether it is manmade or a fossil. One expert has since inspected it physically under a microscope and concludes it is a mould-type fossil, of flint/silica: there is no evidence of human tooling. Of the WGCS and other experts he has been in touch with, the best suggestion he has received, in his opinion, is that it is from a sea sponge. But it isn't one that the group has seen before. Can anyone here positively identify it? 

 

The first photo, with grassy field edge background, is from moments after I found it.

 

 

[TqB]

Welcome to the forum.

Internal mould of a sponge is the only possibility I can think of at the moment but I've never seen one looking like that! 

If it's silica (and I agree it looks like it), it's probably an Upper Cretaceous flint erratic rather than from the Blue Lias. 

So no positive ID I'm afraid - it's really very unusual.

[Johnny Fenton]

8 minutes ago, TqB said:

Welcome to the forum.

Internal mould of a sponge is the only possibility I can think of at the moment but I've never seen one looking like that! 

If it's silica (and I agree it looks like it), it's probably an Upper Cretaceous flint erratic rather than from the Blue Lias. 

So no positive ID I'm afraid - it's really very unusual.

Thank you, TqB!

[Carl]

I'm completely getting an artificial vibe from this one. It definitely looks carved to me. If you look at the underlying colors you can see that they are not affected by the grooves, especially in the last photo, strongly suggesting a base material, seemingly rock, that was purposefully shaped. And I have a extremely broad familiarity with fossils of all types, ages, and preservations and have never seen anything like this in paleontology.