Lower Greensand Cretaceous Ammonites

[TXV24]

Hi, 

 

Some of you may have seen my post yesterday about unexpectedly stumbling across some ammonites here in the Lower Cretaceous sandstones (Lower Greensand) on the SE Isle Of Wight, on a beach I would never have thought to look. Last night I headed back down there with the intention of properly collecting and testing how abundant this new site was. I was not disappointed. I scrambled along the rocks from Bonchurch and got down there around 7pm, (just a 10 minute walk from my house) and began to systematically scan the beach. Within about an hour I'd picked up more than 50 phragmocones and fragments of ammonites, some of which were a decent size. Phragmocones are by far the most common find, although why this is I'm not sure, possibly due to environmental energy breaking up the ammonites? As far as I can tell the ammonites are parts of nodules which are originating from a hard, glauconite rich bed at the base of the cliff meaning they seem to be from the upper most parts of the Sandrock fm. Some however also seem to come from the Monk's Bay Sandstone fm. (Carstone fm.) which overlays the Sandrock. These were laid down in a shallow sub-tropical shelf sea during the Albian stage (100-113mya), other formations of the Lower Greensand are estuarine/mud flats showing a cycle of sea level rise before the final marine incursion laid down in the Gault (which is also present here on top of the Lower Greensand). As far as species, most of the fragments seem to be members of the Hoplitidae, I've identified one as being Hoplites maritimus, although I think I'll post some up in the ID section as my ammonite knowledge isn't that great. There seems to be much larger ammonites present at the site too, as at the base of the cliff some large moulds could be seen (although the ammonites themselves were gone). There is also an abundance of large pieces of fossilised driftwood, which would likely have originated from land to NE. Needless to say it was a very productive trip (unfortunately the seal didn't return), and it's definitely rekindled my interest in the cretaceous strata here on the island and the fantastic finds it has to offer (I might even start pursuing the dinosaurs again!). If the weather holds I'll head back again this evening to continue investigating the site and the strata, I've also attached images of the finds below (including the larger moulds).   

 

The entire haul from the trip, lots of phragmocones

 

An example of the phragmocones

 

Some larger sections of ammonite, although I'm not sure on their ID's

[TXV24]

Hoplites maritimus ?

The large moulds in the base of the cliff. 

[Fossildude19]

Great report! 

Your knowledge of the local stratigraphy and lithology, as well as the paleo-environment, are impressive. 

I wish you luck with your further expeditions.  

Regards,

[Ludwigia]

Very interesting. What you are calling "phragmocones" is correct in a wider sense, since they are casts of the septal sections of the phragmocone. We call them "Katzenpfoten" in Germany, which means cat's paws, for obvious reasons. I'm no great expert on cretaceous ammonites, being confined mostly to Jurassic sediments where I collect, but I think you are on the right track with Hoplitidae, although I'm not so sure that it's possible to get the id down to a single species, especially if the exact horizon isn't known. Maybe a bit of digging and prying in the cliff exposure might reveal a few complete ones. Is that allowed there?

[TXV24]

@Fossildude19 Thank you! 

 

@Ludwigia Ah I see thank you for clearing that up as I'd seen them before but wasn't sure if that was the correct term for them. Yeah I've since been looking through more publications and books and it has characteristics from Euhoplites and Hoplites so I think H.maritimus may not be correct. As far as I'm aware (I'll double check) that should be allowed, I've started trying to make a note of the units in the cliff to help locate the horizon so I'll see what I can unearth. 

[Ludwigia]

12 hours ago, TXV24 said:

As far as I'm aware (I'll double check) that should be allowed, I've started trying to make a note of the units in the cliff to help locate the horizon so I'll see what I can unearth. 

 

Good luck!