Thursday, 31 March 2011

A Doorway into the Weald


It’s the eve of another field season and first up this year, as always, is Misty Bluff. Although there have been many blog entries regarding the Bluff, I thought it may be of interest to describe the quarry in some detail and put some meat on the bones as it were.

The quarry is situated in the south of England and is one of several that were once located around the area although the Bluff is now one of only two surviving brickworks and regular readers of this blog are aware that the Bluff is currently mothballed and no work is currently taking place although there is a small maintenance crew on site.

Exposures in the quarry are from the Weald Clay Group which, along with the Hastings Group, collectively forms the Wealden Supergroup. The clays and sandstones were deposited by rivers and lakes in a largely freshwater or brackish floodplain environment. These sediments in the Bluff are Early Cretaceous in age, Barremian and belong to the Upper Weald Clay Formation. The sediments exposed demonstrate a gradual shallowing from a lake or lagoon-like environment to a fluvial mud plain.

The Bluff has provided an extensive and diverse fossil record over the years and is an important mainland site. Although I primarily search for vertebrate fossils, the Bluff is renowned for its varied insect and plant faunas.

The insects are normally found in sideritic and mudstone lenses that crop out in various exposures. These include examples of termites, wasps, flies, beetles and lacewings. Other invertebrates found in these lenses include, ostracods, isopods and conchostracans, which are locally abundant in the light grey mottled silty clays, and the much rarer bivalve Filosina.

Filosina
Plant remains are relatively common at the Bluff. Marsh dwelling plants and ferns are those mostly recovered and are often found associated with insects in the aforementioned sideritic lenses as well as cropping out in other clay layers. Bevhalstia pebja is one of the earliest recorded flowering plants and is well known here. Other plants found include horsetails, club mosses and both conifer twigs and cones.

But for me, of course, it is the vertebrate fauna that is of the most interest. There have been some quite significant finds over the years – more than most people realise. By far the most commonly recovered remains are isolated elements and teeth. A lot of these can be quite scrappy and water worn but others are spectacularly well preserved. The bone can be either jet black or brown but is usually well mineralised and I haven’t seen a piece of bone yet that could be described as soft or flaky.

The earliest records of bone being excavated from the Bluff are from the 40’s and 50’s. Over a hundred bones belonging to multiple individuals of Iguanodon bernissartensis, Mantellisaurus atherfieldensis and also a titanosaurid sauropod were recovered. There were also many gastroliths found and all of these remains came from the sandstone exposures at the top of the Bluff and these are still producing today. The bones were often encrusted with pyrite and demonstrated both scuff marks and rounding off at the ends thus indicating probable fluvial transportation.

There have been at least three partial iguanodont skeletons excavated during the last 25 years. Two were recovered from the top of the northeast face and a third came from the southeast face and this specimen, which is a juvenile, has proven to be the most complete Mantellisaurus ever found in the UK.

The most famous discovery at the Bluff is, of course, that of Baryonyx walkeri in 1983. The story of its discovery has been well documented and continues to fascinate. To my knowledge there have been no further significant remains of Baryonyx found since then but teeth occasionally turn up and a few teeth were found in association with the Mantellisaurus skeleton mentioned above, which some workers have interpreted as evidence of scavenging. Baryonyx was also found on the southeast face and, indeed, the same horizon as Mantellisaurus. I am unaware of any other theropod remains but I imagine the chances are good of something showing up in the future.

Crocodile remains have turned up regularly over the years mainly attributable to Goniopholis sp. These are mainly teeth and osteoderms although there is also various postcrania found, including vertebrae, limb bones and ribs. Pterosaur remains are rarely found but they crop out every now and then and a phalanx bone was recovered last year.

Croc verts & osteoderm
Most dinosaurian and other reptilian remains are located in the clay and sandstone beds although Baryonyx was found in sideritic siltstone nodules. These nodules have also produced footprints and several have been found and excavated during the last few years in the southeast face but these appear to be isolated examples and a track way does not seem likely although there may be more to be found in the future.

Fish remains can be locally abundant and the most common fossils are those of Lepidotes mantelli and include scales, head plates, fin bones and teeth. Freshly exposed scales are beautiful and display a wonderful dark blue lustre. Occasional hybodont shark spines are found as well as Teleost fish and, back in 2005, an articulated pycnodont fish was found, the first ever recorded from the Wealden.

So it can be seen that the Bluff has been an important source of early Cretaceous Wealden fossils for many years now and will continue to be so as long as the quarry is worked. Before the site was mothballed we were informed that the next significant excavations were to be in the southeast face thus exposing more dinosaur bearing strata. Obviously, when this will take place is unclear but with an estimated supply of over 100 years of clay remaining, I think we can be fairly optimistic that new discoveries will continue throughout the 21st century.

Iguanodon caudal vertebra

A small croc tooth weathering out of the clay

Lepidotes scales

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