Bembridge Marls Late Eocene Micro-Vertebrates

[TXV24]

Hi, 

 

I thought I'd show some of my first micro-vertebrate fossils from the Bembridge Marls Mbr. of the Bouldnor Fm. I collected around 2kg of matrix from one of the 'shelly' estuarine horizons in the lower part of the member at Hamstead Ledge, and am really pleased the results so far!

 

The Bembridge Marls form the basal member of the Bouldnor Fm. and were deposited between 34.0 and 33.75 million years representing the final 250,000 years of the Eocene epoch. The depositional environment varies throughout the member and many beds are laterally discontinuous (like the Insect Bed, which produces finely preserved insects, feathers, leaves, and lizard skin impressions). Generally however, the Bembridge Marls were laid down in a sluggish lagoonal/estuarine environment with areas of wetland and adjacent sub-tropical/tropical forests, in the southern regions of the Hampshire Basin. To the south were forested chalk uplands that are now the downs of the Isle Of Wight. There was also some fluvial influence from rivers flowing from the west, draining the uplands around Dartmoor in Devon. Fauna-wise vertebrates like fish and freshwater turtles are common, and mammal remains are rarely found (in comparison to the overlying Hamstead members which are rich in post and pre-grande coupure mammals), these include palaeotheres, creodonts, rodents, anoplotheres, choeropotamids, xiphodonts, and primates. 

 

So far I've only searched through a small amount of the matrix but it has produced indeterminate teleost vertebra, Bowfin teeth, fin spines, indeterminate fish premaxillae, and a very nice crocodilian tooth.

 

(The quality of the images isn't always fantastic but I'm trying to find a way to work around it in the microscope's program) 

 

Isolated fish vertebra from teleosts are by far the most common micro-fossil, and I've collected more than 10 so far. Here's a nice example: 

 

Bowfin teeth are also quite common and vary in size from 2-7.5mm in length. Bowfins would have been ambush predators feeding on smaller fish and other vertebrates in the lagoons and estuaries. Based on vertebra I've found ex-situ on the beach it seems some of these fish were very large. 

 

(Close up of one the teeth)

 

These pre-maxillae also seem to turn up from time to time and appear to be from some form of teleost. The closest match I can find is with some kind of Gadiform? 

 

And finally the best find so far, a crocodilian tooth crown. I spotted this on the surface of one of the matrix blocks. It's most likely from the alligatoroid Diplocynodon which was very common in the wetlands and rivers of Europe from the Palaeocene to the Miocene. Diplocynodon has also been found in the early Eocene marine deposits of the London Clay suggesting that they frequented both freshwater and brackish/coastal habitats. 

 

The matrix is nowhere near fully sieved and sorted through yet so hopefully there's a lot more micro-vertebrates in there!

 

Hope this was of interest,

 

Theo 

[Brittle Star]

Great photos, I love the matrix from the IOW, staying in Bembridge in Feb for a few days so hoping I can pick up some more while I am there. I have examples of the same sort of things you are finding, I am sure I have found a name of the pre-maxillae on line somewhere but I can't recall what it was. Dmap has an example but the description is just fish upper jaw. That is going to bug me now. I have been hooked on micro fossils for years now. Well done.

[Tidgy's Dad]

A wonderfully informative insight into the final years of the Eocene in that region of England where I have been collecting briefly, but not microfossils. 

Great images, too. 

Thank you very much for sharing.

[ynot]

Nicely done!

 

Looking forward to seeing what You find in the future.

[Brittle Star]

Here I am again, pre-maxillae, look up drum. fish, it may be a match.

[TXV24]

@Brittle Star It's great isn't it! Bembridge should be really good matrix-wise, especially as you've got the fully marine Bembridge Oyster Bed over that way, and good exposures of the Bembridge Limestone with micro-mammals. Drum fish seems to be a very close match, I've found some 'Drum Fish style' teeth in the matrix so that could be where they are originating from. Thanks for your help!

 

@Tidgy's Dad Thank you! 

 

@ynot Thanks! I've got some early Oligocene coastal plain matrix on the go from the overlying Hamstead members so will post about that soon! 

 

 

[Brittle Star]

Last time I stayed at Bembridge it was hopeless as the day I chose to go on the beach could not have been any wetter so did not find anything really, plus not familiar with that beach it was my first time staying in the south, so need all the help I can get as to where to look, I did find some limestone and got an insect wing and insect debris right on the surface did not see that until I got it home under the microscope. Really lucky as I had already scrubbed it under the tap at the hotel. I have previously collected from Bouldnor to Hamstead Edge and Fort Victoria and down the west coast. Have visited Sandown the last couple of years as stayed near there and got some nice things. Thorness Bay sediments are really productive micro wise. Sandown is on my to do list next year also, only place I can get to on the bus as tides are bit early to go far. May be my last year of collecting as I am getting older it is getting too much due to health issues. So nice to see others interested in the tiny stuff.

[TXV24]

@Brittle Star I'm sorry to hear it might be your last year of collecting. My best advice for Bembridge would be to search the shingle for any fish vertebra etc. from the Bembridge Marls/Bembridge Limestone, although larger vertebrates are very rare, unlike in the west at Hamstead and Thorness. On the foreshore you've got very extensive exposures of the upper Bembridge Limestone and the lower beds of the Bembridge Marls so it would be worthwhile giving them a once over in case there's anything weathering out, as fish bones and a large snake vertebra have been found that way (usually in the thin white 'shelly' horizons of the Bembridge Marls). An insect is a really lucky find as the Insect Limestone is really patchy in terms of it's productiveness so congratulations! There's also a Pleistocene raised beach in the cliffs so pleistocene material is a possibility, hand axes have turned up from time to time. I've never really collected at Sandown myself as it's all cretaceous strata but it does produce some nice ammonites and bones etc. so hopefully you'll be in luck! 

[Brittle Star]

Thank you for the info, when there is a very low tide at Bembridge isn't there clay on the foreshore? was wondering whether or not that would be worth collecting a bag of. There is nothing I like best than sitting and searching shingle, get some very odd looks from dog walkers. I know a short cut to Hamstead that does not involve going down the landslip or the long walk from either end. Large turtle bits found there and lots of stuff from the shingle there, even when tide in still a bit of room and no chance of getting cut off.

After Feb will let you in to my secret collecting tips at Sandown. Have you trekked to the chalk, found a complete scale, only a small bit sticking out of a small piece of chalk so no idea what I had until I got it home. Also got a tiny piece of rib last year just lying on the beach, that was lucky as so over collected even at that time of year.

[TXV24]

@Brittle Star That would be the lagoonal clays from the Bembridge Marls. They don't tend to be that productive especially low down in the sequence like at Bembridge. Your best bet would be to search for one of the shelly beds (such as the Bembridge Oyster Bed) within the clay, they're often very rich in fish bones and can produce micro-mammals, although rarely. They were formed in brackish estuarine/marine conditions and are mix of shell fragments, sands, and clay with tiny black fish bones sometimes visible. Hamstead and Bouldnor are my main collecting sites and I think I know the shortcut you're referring to. No I've never been that far up Yaverland, but I've never heard of vertebrate material from the chalk there so that's fantastic, as is the rib! 

[Miocene_Mason]

Thanks for posting, very informative!

[Brittle Star]

I will remember to look for shelly bits in the clay foreshore and maybe scoop up a small bag to see what is in it. If successful just may visit Bembridge another year as will not be too strenuous or too far to walk. Guess you will be in work end of Feb if not your local knowledge would be really appreciated

[TXV24]

@Brittle Star It should be productive, especially as the Bembridge Marls in the east of the Island will have a lot more marine influence so shark teeth etc. should be in there. I might be but even so if you have any questions or want any tips for any of the localities just ask and I'll be happy to help.