Monday, 6 February 2017

Ichnofossils of the Ballagan Formation

The TW:eed Team’s paper on ichnofossils from the Ballagan Formation has been published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology. The article is titled ‘Ichnofauna record cryptic marine incursions onto a coastal floodplain at a key Lower Mississippian tetrapod site’ and you can read the abstract online. Please contact me if you’d like me to send you a PDF of the paper.


Ichnofossils are burrows, tracks or traces in the sediment that are made by animals. The Ballagan Formation ichnofauna is dominated by Chondrites burrows, which occurs in 128 levels within the 500 metre thick Norham Core. Also present in lesser abundance are phycosiphoniform burrows, Diplocraterion, Rhizocorallium, Monocraterion, Asterosoma? and Zoophycos? Chondrites and most of the other burrows in the Ballagan Formation are thought to be made by marine animals. Chondrites burrows represent a branching network down into the sediment which the animal used to exploit food from the sediment. Without having the borehole core to study, this paper could not have been published, as these ichnofossils are hard to spot in the field: Chondrites burrows are on average 1 mm in diameter!
Chondrites burrows in the Norham Core, in a photograph (1), thin section scan (2) drawing of the thin section with burrow margins highlighted (3)

The paper also describes the presence of small microfossils found within palynology slides call scolecodonts. These are the mouth parts of polychaete worms that live in the sea. The ichnofauna contrasts with the more typical burrow types (Scoyenia Ichnofacies) of other Devonian-Carboniferous tetrapod sites, which are made by terrestrial or freshwater aquatic animals. Also unusual, is that most of the burrows occur within dolostone beds. We suggest that storm surge events transported animals from the sea into saline lakes on the floodplain, where they survived for a time. But the low diversity (only a few species) of burrows present indicates harsh environmental conditions.
Scolecodonts, the jaws of marine worms. Scale bars are 0.02 mm in length
Bioturbated levels within the Norham Core succession represent a total sediment thickness of 3%, so these were unusual. But because ichnofossil levels are much more common than marine body fossils or scolecodonts, they record cryptic marine incursions that might otherwise not be found. This study helps us to understand the complex mosaic of environments present when terrestrial tetrapods first appeared.

Until next time
Carys

Thursday, 22 December 2016

TW:eed Team Presents



Season’s Greetings to you all!

It’s been a busy two weeks for the team as we’ve just returned from two conferences! First we were in Lyon at the Annual Meeting of the Palaeontological Association. Jenny Clack presented on our new tetrapod species that have just been published in the Nature Ecology and Evolutionpaper. Tim Smithson spoke about where these fossils occur within the succession and what that means in terms of finding more fossils like these in the future. I presented a poster on the food web that we are now able to piece together due to all our detailed work. It was a great meeting with some spectacular talks in a truly wonderful city! 
 

Next it was the annual conference of the British Sedimentological Research Group, at Cambridge. I was fortunate enough to arrive in time to go on the fieldtrip, which visited the Oxford Clay and Red Crag sediments in Suffolk. It was a chilly day but wonderful to get outside after a full day travelling there by train from Lyon the day before. That evening we were hosted at the SedgwickMuseum for the Icebreaker and got to see some of the fossils from those sites in the museum, which was wonderful. At the conference Sarah Davies presented on the tetrapod habitats, while I talked about the taphonomy of the bone-bearing beds. Dave Millward presented on the evaporites, which are especially good in the Norham borehole.

 
BSRG participants study the London Clay
The Red Crag, Suffolk
Fossils from the Red Crag at the Sedgwick Museum
Sarah Davies at the BSRG meeting
 At both meetings, there was a lot of interest in the TW:eed Project, with many commenting that our project showcases just how successful interdisciplinary team research can be. We agree with that and our ethos has always been that cooperation, sharing knowledge and training the next generation of scientists is the way forward. On that note, Merry Christmas everyone!
 

Until next time
Carys