Thanks for the answers above, I will read around them and do some learning. Great detail as always!
In this small stream, there are clear pockets of shingle (not very wide or long) dotted along it. I was picking stones for my kids to throw into the stream when I noticed all the bivalves amongst the shingle and I’ve been going there once a month or so. (The initial sandstone Ammonite and Clay/mud nodule was from another location 20mins away). It runs along a forest on one side but the sides of the stream bank are near vertical and 2m deep, it looks like it gets cleared by machines but I would say not recently. I don’t know how the shingle pockets came to collect like this. The fossil explorer app gives this location as Kimmeridge Clay as the bedrock but being in a stream, I’m unsure what the geology is doing. It is definitely a natural stream as opposed to farm drainage ditch.
Yes I will keep going until I find that elusive ammonite, so far just segments. Also going to try Grafham water in the summer.
If I find another Ichthyosaur centrum I can make a set of earrings for my wife, she will be delighted.