Wnt to lunch to day a friend and in the middle of my Rib eye- she dug out of her handbag the below stone object that she found in her backgasrdern and asked what I thought it was -'Look she said it looks like an embryo of some sort. Taking a close look at this curled object and the faint image inside- I said Its a Coprolite. Oh she said what that? A fossil Do Do- I think it put her right off her Half rack.
As the curator/manager is known to me from many years go[being a museum piece my self- I said it so you lot want have to] As FE said it is flint - but when carefully examined at the external shape it does seem have have formed around a clam shell. Flint is seems in its'forming state' is a sort of gel made up of decomposed organisms when then settled to a sea bed and then gets buried under the shell remains of smaller creatures and becomes flint over the time- some 60/70 m years- said the curator.
He's basing his explanation of the formation of flint nodules on the prevailing theory - that decomposing sea creatures (primarily sea sponges) form pockets of gel-like substance in layers of compressed sediment, and over very long periods of time the flint nodules form. In some flints you find minute fossilised sea creatures.
Nobody knows for sure, but the theory would certainly tend to explain the weird, irregular shapes of flint nodules, and the fact that they're embedded in sedimentary limestones - at least they are until they are eroded out by the action of the sea, or weather, or both.
The flint seems to be in regular layers indicating that is is a reoccurring event- like tree rings or the whirls on a shell- but I would think millions of years apart- Global warming and cooling perhaps- and it wasn't us that time.
I blame the Dinosaurs and piles of er coprolite myself
Thinking about that and using my normal 'out of my box' reasoning- concludes it has to be something else. The nodules are layered in chalk. Chalk Being the result of the remains of sea creatures deposited on the sea bed , suggests the sea itself was always there during the period and some other factors was at work when perhaps there were 'sterile' periods when no activity relating the flint nodule production. Temperature perhaps, variations in the constituents of the seawater[pollution] who knows or perhaps seabed 'heave' shallow to deep and back- who knows.