Thursday, 30 September 2010

An Introduction to the Oxford Clay - Part 1


Having written so many blog entries regarding the Oxford clay, I figured it was time to give a brief description and introduction to this important geological unit that has provided so many wonderful vertebrate specimens over the years and continues to do so. This is the first of a couple of blog entries describing the geology, palaeoecology and fossils of this important unit.

165 million years ago, at the end of the mid-Jurassic, the continents, as we like to think of them now, were part of the super-continent known as Pangaea. This enormous land mass was almost crescent shaped and the northern and southern arms were separated by the Tethys Ocean and it was here, in this shallow warm sea, that the Oxford Clay was deposited.

The Oxford Clay is a succession of mud rocks that lie above the sand dominated Kellaways formation. These clays are occasionally intersected by horizons of carbonate concretions and are overlain by various facies that are collectively known as the Corallian Beds. Quite often, and in many places, the upper limit of the clay is a disconformity. All of these mud rocks, and the fossils they contain, are typical of a warm shallow marine environment and, indeed, this is exactly the ecosystem that we find in locations such as Quarry 4.


This extraordinarily rich ecosystem was powered by the sun. Both free floating phytoplankton and bottom dwelling benthic microflora converted the sun’s energy into organic matter via photosynthesis and, indeed, the same process more or less continues in the shallow marine ecosystems of today. Various biological groups were represented by these micro organisms which included various types of bacteria and algae. They were incredibly abundant and their fossil remains are best observed in the sediment under the electron microscope. The fact that benthic microflora are here at all is clear evidence of shallow water since they must receive sunlight to enable them to utilise the process of photosynthesis.

From the smallest to the largest - the big carnivores of this shallow sea. Marine reptiles dominated and animals such as ichthyosaurs, plesiosaurs and marine crocodiles were the rulers of the Oxford Clay ecosystem. Linking these groups together are the other threads of this web of life including the fish and a plethora of invertebrates. When palaeontologists were piecing this astonishingly diverse ecosystem together, it became apparent that there were two distinct food webs. The first was in the upper reaches of the water column dominated by phytoplankton who were the primary food producers. The second was in the lower depths of the water column where the sea floor was covered by the benthic microflora and these were the primary food producers at this level. And, of course, an additional and an obviously major source of energy at this level came from dead organic matter that fell from the upper reaches of the sea.

Sunlight alone cannot maintain a healthy and complex web of life and this was supplemented by a rich source of nutrients. But where did this come from? Throughout the Oxford Clay you find fossils of plants and animals from the land. These fossils include an array of different plant species and trees and there have been a surprising amount of dinosaur bones recovered – remnants of bloated carcasses washed out to sea. Indeed the most complete theropod found in the UK (Eustreptospondylus) was recovered from the clay. Obviously this means that ancient shorelines were nearby and rivers would have provided a continual source of nutrients into the sea. And it is again worth pointing out that many fossils in the clay are from shallow water species.


Another source of nutrients is derived from recycling those nutrients that became available when other organisms died. Anybody familiar with the clay is aware how very productive this ecosystem really was and this is very evident from the amount of organic carbon residing within the sediment as a direct result of intense biological activity. It is this high organic volume material in the Oxford clay which made it so perfect for the brick making process. And it was the brick making industry that led to the uncovering of some of the best marine reptile fossils found anywhere in the world.

In part two, I’ll go into some more details about these animals, the quarries that they have been found in and some of the people involved with their discovery.

References

Calloman, J.H. 1968 The Kellaways Beds and the Oxford Clay; pp.264-290 in P. Sylvester Bradley and T.D. Ford (eds.), The Geology of the East Midlands. Leicester University Press, Leicester, UK.

Calloman, J.H., Dietl, G and Page, K.N. 1989. On the ammonite faunal horizons and standard zonation of the Lower Callovian stage in Europe; pp.359-376 in the 2nd International Symposium on Jurassic Statigraphy, Lisboa, 1988.

Cope, J.C.W., Duff, K.L., Parsons, C.F., Torrens, H.S., Wimbledon W.A. & Wright, J.K. 1980a. A correlation of Jurassic rocks in the British Isles, pt2, Middle and Upper Jurassic. Geological Society of London, Special Report, 15:1-109.

Martill, D.M & Hudson, J.D 1991. Introduction. Fossils of the Oxford Clay. The Palaeontological Association, London, UK, 1, 11-34.

Page, K. 1989 A stratigraphical revision for the English Lower Callovian. Proceedings of the Geologists’ Association, 100, 363-382.

Thursday, 23 September 2010

2010 - The Year of the Ceratopsia


I try not to jump on the paleo-blogosphere bandwagon when there is a media explosion regarding the announcement of new dinosaurian taxa. But this time I will make an exception and make no apologies for doing so!

Since I had the privilege of chatting to Scott Sampson over dinner at SVP in Bristol, I have been waiting for the official media and journal release of these spectacular chasmosaurines. I know I’ve blogged about it before, but I cannot emphasise enough how generous Scott was in revealing so much information to both myself and Scott Moore-Faye, then the senior preparator at the British Museum of Natural History.

At that time, the chasmosaurs were known as “Taxon A” and "Taxon B”. We now know that these are Kosmoceratops richardsoni and Utahceratops gettyi and what spectacular animals they are! I won’t go into great detail about them since there is a wealth of information on so many blogs, websites and forums already and the paper is freely available at PLoS ONE.

2010 is certainly the year of the ceratopsia. A multitude of new taxa announced, the magnificent tome that is New Perspectives on Horned Dinosaurs and I know of several other new taxa to be published in the next few years. Absolutely amazing. This highlights just how very little we do actually know about the dinosaurs as a whole but things are slowly coming together. It’s a great time to be involved in dinosaur palaeontology – especially for students of ceratopsians just now.

Congratulations must go to Scott and his team for a job well done and we all look forward to their next revelations.

Wednesday, 22 September 2010

Jurassic Bark


Towards the end of February a spring-like spell of weather meant that conditions at Quarry 4 were rapidly improving and it was obvious that the quarry floor would be drying out. It was time for a return visit.

Mark and I made quick arrangements and we were soon heading to the quarry on a bright Saturday morning. When we arrived the first topic of discussion was what to wear. We went for the compromise which involved mainly spring clothing with a sweater thrown in for good measure. It turned out to be a good decision.

The quarry itself had really dried out although there were still significant pools of water. The clay was really bright grey as opposed to the dark wet grey it was on our last visit. On the horizon we could see a great swathe of clay had been removed at the back of the quarry. We moved off to prospect.

This time the walk through the quarry was much easier. There were still some areas of soft clay to negotiate but now it was much firmer underfoot overall. As we approached the new scrape we came across a newly dug trench, perhaps 150 yards in length and we both dropped into it just about central to its total length. We both started to prospect – I went one way and Mark went the other.

It was much easier to discern this time and the trench looked good. However, the more I looked, the more I realised that this trench was obviously not in a very fossiliferous part of the quarry. This is something that we have now come to realise that, despite its apparent uniformity, Bed 10 can be remarkably zonal. Some parts have mainly belemnites, some are mainly Gryphea (although this is probably due to the fact that Bed 9 intersects now and then), and the best are a mixture of everything. All are dominated by the ammonite Kosmoceras.

But this trench was sparse except every now and then there would be huge blocks of mud shales that were like leaves of a book. All the layers are ultra thin but they all contain beautiful impressions of ammonites and bivalves. Their fragility makes them impossible to collect no matter how careful you try to be. Even if you managed to pick one up you would be certain to destroy them in transit, they are that fragile.

We met up and decided to move to the new scraping. To reach it we had to climb up an awkward spoil heap on the other side of the trench. As we reached the top we looked at each other, smiled and looked below us. The new scraping looked absolutely perfect, level and smack bang on Bed 10. As Mark said “If we don’t find anything here we want our butts kicking”. I knew what he meant.

We immediately began to prospect. Just where we entered the new scraping the digger had obviously gone a little deeper than intended and huge blocks of clay were upended and this was where we started. This was the first time in this quarry that I felt really at home and with the sun beating down on us, and the first warm temperatures for more than 5 months, we just had to find something.

After our initial excitement died down we looked intensively for any sign of bone that would lead to our first significant discovery of the year. This was the first time that we had the advantage of scouring a new face and we were intent on succeeding.

After about an hour we still had nothing to show for our efforts and we started to spread out a little bit more but still maintained our very slow, deliberate and methodical search for fossil bone. Eventually I came to a slight depression and noticed a high concentration of carbonised wood fragments covering a large area.

At the Bluff, wood and bone often go together, so I decided to spend some time here and began carefully scraping at the clay. I soon uncovered what I thought was an unusually large piece of wood and it appeared fairly solid. I began to brush away the clay from one end and the piece got bigger. So I brushed more clay away from the other end and still it got bigger. I called Mark for help.


As we uncovered more of the wood we both realised we had uncovered a really unusual fossil for these marine sediments. There, lying before us was a tree trunk, nearly 3 metres long and quite obviously part of a big tree. I know that you cannot compare it with some of the big trunks in, for instance, Arizona but never the less this was a big piece of wood.

Mark initially thought it may be a species of cypress. Personally, trees aren’t my strongpoint so I didn’t have a clue as to what it was. The immediate question was that now we had uncovered it, what on earth were we going to do with it? It was far too big for either of us to have and, besides, we would need the help of an excavator to remove it.

Eventually we decided to cover it over and mark the spot with a few rocks. Then we would later notify the local museum and see if they would be interested in taking it out. This particular museum had recovered many complete and partial skeletons from this quarry and others like it the area for many years and were very experienced and we felt that they would have the best chance of removing it – if it were required.

We carried on with our search but it became apparent that, despite the ideal conditions and situation, we were doomed to failure again. We both tried hard and I can honestly say that we covered the area with the proverbial fine tooth comb, methodically prospecting as we went. We were both certain that there was nothing to find and abandoned the new scrape for pastures new.

We carried on the search for some time afterward, concentrating our efforts in areas that were underwater from the previous trip but still there were no bones to be found. Quarry 4 and I just haven’t reached a compromise yet – but we will.

We eventually called it a day and walked back to the cars, boneless but in good spirits and, as usual, vowed that it would be our turn next time. I knew that, because of other commitments, it would be most likely May before we returned and, before then, a trip to Misty Bluff was next on the list. But return we would and try yet again to find that elusive marine reptile.

Footnote

A small group from the museum were going into Quarry 4 only 48 hours after our visit to see if the tree could be removed and conserved satisfactorily. They decided it wasn’t really suitable for preservation – besides, they said, where on earth would they put it? Understandable - but still a shame.

We uncovered a tree that hadn’t seen the light of day for 160 million years. When I next returned, it had disintegrated and the last remnants were blowing away in the wind…………

Monday, 13 September 2010

Stunning Skeletons but a Lesson is Learnt


During the autumn, Mark had managed to obtain for me a pass for Quarry 4 which would allow us to visit the quarry during any weekend we wanted, subject to the quarry owners’ approval and provided we always asked permission. This also allowed time for the security teams at the quarry to be alerted to our presence.

Prior to our first independent visit to the quarry, we were to be shown around the quarry by Cliff Nicklin, which was useful since we both knew Cliff well from previous visits. This was mainly for health and safety issues although we were both very familiar with Quarry 4.

As it turned out, for various reasons, Mark and I never seemed to be free at the same weekend and it seemed that the year would be over before we could get down there together since it was a cast iron never-to-be-broken rule that there is no lone prospecting or digging in the quarry. This is a bind, for both of us, since we are both seasoned workers in these quarries and you do feel like you are being treated a little like children sometimes. But if that is the price to pay for continued access to the quarries then so be it. Never the less, we stayed in touch trying to find this mutually convenient day.

During early November, I emailed Mark to see how he was and, when he replied, what he had written almost made me fall out of my chair! Cliff had told him that they had found two more or less complete very intact skeletons of a plesiosaur and a pliosaur, almost side by side. Not only that, but a third partial plesiosaur had also been exposed not too far away. A few of them were going in to uncover more of the in situ remains and decide on a plan of excavation.

Unfortunately I couldn’t make the following weekend since Chris and I were away for a pre-Christmas break. I was obviously a little disappointed but not that much since we always enjoy our short breaks and would still do a little fossil hunting at Bracklesham Bay, somewhere that I always fancied. But Mark was definitely going and would let me know the score when I got back.

We returned on the Monday and I checked my emails and I was not to be disappointed. Waiting for me was a short message and two attached images of a magnificent pliosaur paddle, virtually intact and complete. And it was big. I instantly picked up the phone and called Mark for the detail.

The skeletons appeared fairly complete and, most important of all, they both appeared to have the skulls preserved and encased in concretions. In fact the bulk of the skeletal remains were in concretions – not totally unexpected in this quarry. Cliff was in contact with the quarry owners to arrange the extraction of the remains before word got out and the local scavengers started to illegally remove the remains.

At this point I was surprised to hear that the exposed paddle was to be left in situ and covered over until the Tuesday when it would be removed, today being the Saturday as it was. On asking why, Mark revealed that he had offered to the others the necessary consolidant and bandaging to allow quarrying to begin but that it had been deemed sensible to leave it until Tuesday! I was perturbed and I knew that Mark was as well.

Later the following week, I again spoke to Mark about getting back to the quarry and asked if the paddle had been removed OK. I was crestfallen to hear that on their return the paddle had been illegally removed. It was at this point that we realised that the recent activity in the quarry had obviously been observed by others. Although strictly off limits to the public, a public footpath skirts Quarry 4 on its northern face and we know we have been watched before by others who also have an unethical interest in the quarry – one that involves profit. Mark also revealed that the NHM had even offered a team of five palaeontologists and students to take the remains out but this too had been declined – what an error to make!

Mark couldn’t make it at the weekend so we determined to return the following weekend at first light on the Saturday. During this time we were informed that the skeletons were to be dug out of their graves and removed by the quarry workers with Cliff and others in attendance. A couple of days later we heard that the fossils had indeed been removed.


A few days later we arrived at Quarry 4. Cliff was meant to meet us but didn’t show so we were on our own and apart from the security teams there we were to have the quarry to ourselves. Frustratingly, one of the security teams revealed that someone had been spotted in the quarry on the Friday afternoon and had appeared to remove yet more material before being challenged. This was getting to be quite distressing.

We soon arrived at the bone bearing horizon and there in front of us were the gaping holes where the skeletons had been removed. It was very obvious that huge blocks had been excavated and that there would be very little to retrieve. We set about the site, however, and started to prospect.

As it turned out, we were correct and only one small section of rib was found. Not keen to waste too much time we headed to the newly scraped corner of the quarry to see if anything had been uncovered. No bone was found but we started to find small pieces of fish “bone” which actually turned out to be a species of belemnite, Belemnopsis . Apart from these there appeared to be very little else.

We then decided to look at the third site where the partial plesiosaur was situated. Again this quarry had been excavated and nothing remained although the clay here was extraordinarily rich in fossils. Mark actually found a rare small ichthyosaur tooth and then promptly dropped it never to be found. Things were not good.

As if to compound our misery Mark then proceeded to find a cracking little “bone” weathering out of the clay until closer inspection revealed it to be some form of distorted metal tubing. We were not amused. Mark left shortly after to attend to some personal matters but I remained behind to continue the search.

I did find yet more wood but several small pieces of wood found in association do actually fit together and it appears to be a twig or a sapling. Unlike the usual bits of wood found, which need instant consolidation, these bits are well fossilised and will need minimum work to make them look good.

I left Quarry 4 about an hour and a half after Mark had gone. It was great to have such a huge quarry to yourself – very atmospheric. Indeed, the only movement to catch your eye, and occasionally make you jump, were the shadows from the vanes of the wind turbines located above the quarry.

We eventually found out that the two fairly complete specimens were taken for short term loan to two educational facilities allied with Peterborough museum until, when time and money permits, they can be prepared and studied properly. The whereabouts of the partial plesiosaur skeleton is still unknown to me but it is safe to assume that it is safe and residing in a correct repository. At time of writing this article, nobody knows where the missing pliosaur paddle eventually ended up – there was no trail to follow and no clues could be found. I find it deeply disturbing that this scientifically significant specimen, our nation’s inheritance, may have been sold off illegally into the private market. This is a shame since this Peloneustes skeleton looks as if it could be one of the most complete ever found.

During the second world war, there was a saying: “Careless talk costs lives”. Well it seems careless talk and actions also costs specimens. In the future, we will not be letting anyone know that we are going to Quarry 4, no advanced warning, except for, of course, the quarry owners and those in our immediate confidence. Hopefully when the next marine reptile puts in an appearance we will be able to notify the right people and, with a bit of luck, be able to get the remains out correctly and scientifically. To do this we will need the cooperation of the quarry owners and hopefully the Peterborough and/or the Natural History Museum will be on hand to excavate the specimens.

We must ensure that a repeat of this incident never happens again and that we never lose another specimen, important to science, to goodness knows where. My only concern is that these national treasures are preserved for the future and that everyone should be able to access them, whether that is for the general public to observe them or for scientists to study them. The battle to preserve our heritage starts now!

Monday, 6 September 2010

Marine Reptile Teeth From the Oxford Clay


A couple of days ago, I met up with Cliff and Carl and a small group from the University of Leicester for a field visit to Quarry 4. This was a bonus trip for me since we were originally planning to visit a few weeks ago but, due to various reasons and commitments, the trip couldn’t take place. When this opportunity arose, I was hardly going to miss it.

As mentioned previously, Quarry 4 is now not being worked and you are relying on rainy conditions to wash any new material out of the clay and reveal any new material in situ. A week previous to this visit there had been substantial rainfall, somewhere in the region of two inches had come down, and we were hopeful of finding a few bits and pieces. As usual there were some nice pieces recovered.

These included a few plesiosaur teeth, all Cryptoclidus, a Metriorhynchus tooth, a couple of Hypsocormus fish jaws complete with the caniniform teeth in the anterior part of the dentary, small fish vertebrae including a string of eight in articulation and a big bunch of lepidotid scales weathering through the surface of the clay. There were other pieces recovered including some interesting fish coprolites (complete with inclusions), a small marine reptile caudal vertebra and a few interesting bivalves.

There were also a few processes from crocodile vertebrae that turned up in one spoil heap. This pile of spoil keeps throwing bits of crocodile up and is gradually being worn away by both human activity and erosion and is likely to throw up a few more pieces yet. This spoil heap was obviously dragged or pushed from another part of the quarry that isn’t too far away and Cliff feels sure that the rest of this croc is waiting to be found.

As for me, I was lucky to find the above pictured pliosaur tooth which is in superb condition. It appears to be Peloneustes but I should be able to confirm that shortly once the tooth is cleaned and I can have a good look at the striations. I was also very fortunate to find a superb fully rooted Metriorhynchus tooth which is unfortunately missing the tip but this is still an excellent specimen and I was very lucky to find it.

Quarry 4 is still earmarked for flooding this November, so time here now is very limited. There is another group from the SVPCA meeting that is being held in Cambridge this month going in on September 18th. We will definitely be going in during October which will almost certainly be the last trip assuming that the flooding of the quarry will take place, as advertised, during November. We will see.

But, at last, there is some positive news on gaining access to Quarry 5 and it looks we will finally be approved for access in the New Year. I can hardly wait since this will be virginal clay with no backfill which is really going to help prospecting. I’m keeping everything crossed and not counting my dinosaurs just yet!!!