Friday, 7 June 2013

15 million years in 56 days.... by Tim Kearsey

Last week members of the TW:eed project completed a 501 metre deep borehole, just outside Berwick-upon-Tweed, Northumberland.  After eight weeks of drilling seven days a week, a near continuous run of core has been recovered from the Ballagan Formation representing approximately 15 million years of the rock record in which the earliest terrestrial fossils of our ancestral tetrapods, have been found. Dr Tim Kearsey explains all in his video and interview below:

How does drilling a hole in the ground help us understand the origin of vertebrate life on land?

The borehole is crucial in understanding how the different fossil locations in the Tweed area relate to each other in time. All the localities where tetrapod fossils have been found are in river beds where only a few tens of metres of Ballagan Formation are exposed. So it is impossible to correlate between the sites using the rocks exposed at the fossil sites.

What is needed is a continuous section of rocks through the sequence containing all the fossil localities to work out the order of evolution. A continuous section exists at Burnmouth, about 10km north of Berwick, but this is in a fault zone and at the coast which means we don’t know for certain how it relates to the fossil sites. By drilling the borehole inland, close to the fossil sites, we now have another continuous section and by comparing it with Burnmouth we can erect a time frame in which the fossil localities can be placed.

Crucially the core from the borehole also provides a continuous record of the climate and environmental change through the time that the tetrapods evolved. This will be created by assembling evidence from the sedimentary rocks in the borehole, along with geochemical information and the occurrence of fossil plant spores (palynology). Unlike the coastal outcrop at Burnmouth the borehole core is unaffected by weathering and erosion which can alter or destroy many of these types of evidence.

So what have you found?
Gypsum (pink) and anhydrite (white) in the core ; top/youngest rock is to the left
borehole is 7 inches (102mm) in diameter
On-site inspection of the core has found some interesting things. Some of the core contains plant fragments (see video), usually associated with the base of sandstone units. These are probably bits of tree and plant caught up in the rivers sediment in times of flood.
Also, we have found a lot of beds of gypsum and anhydrite (see above). These are tend get weathered way in the sections at the surface so the only preserved in the borehole. They are interesting as today they form in sabka environments in places like Persian Gulf and are formed by high rates of evaporation.

The carbonado diamond drill bit ; before (left) and after drilling the borehole (right)

What next?
Over the next few weeks the core will be shipped to BGS National Core Store in Keyworth, Nottingham. Once there it will be catalogued, split in half and photographed. Then, in the autumn, Dr Carys Bennett of Leicester University and I will spend over a month studying the core in great detail and taking samples for analysis.
We would like to thank our drilling partners Drilcorp of Seaham, County Durham, who drilled the high quality cores for us; also Alistair Berkett of John Wilson and Sons Farmers Ltd. for allowing is to drill the borehole on their farm.

by Tim

Catch up with past TW:eed posts here

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