|Joe in the field acquiring Bowland Shale samples from outcrop|
with the help of a hand-held core drill.
The Bowland Shale is of great interest to geologists because it was deposited during a time of change, during a major phase in the history of life. Vascular plants expanded across and colonised new lands in the Carboniferous, which ultimately increased the amount of organic matter entering the deep marine basins. Enhanced burial of organic matter in these basins acted to moderate the global carbon cycle by effectively sequestering CO2 out of the system on the geological timescale. Fundamental to understanding the organic matter burial efficiency of Carboniferous marine basins, is the environment of deposition, and how it evolved through time. We know the Bowland Shale comprises organic-rich sediments that were deposited as part of an epicontinental seaway that connected North America to central Europe. What we don’t understand particularly well is the distribution of organic matter this environment, and how sedimentological, chemical and biological processes influenced this distribution.
Some of the organic matter within the Bowland Shale comprises terrestrial particles such as wood, spores and pollen, which entered the sea via rivers that washed sediments off the land. Organic matter can also be marine in origin (ie algal). The origin of much of the organic matter in the Bowland Shale is not understood. By using a range of analytical techniques, such as palynology, geochemistry, thin section analysis, we can understand the processes that transported, deposited and preserved organic matter in the Bowland Shales. This will allow geologists to assess the shales as a potential gas resource as some types of organic matter have more potential gas than others.
|Core from the Bowland Shale.|
To begin this process, I need to get at the rocks. This can be achieved through drilling boreholes into the shales, or by studying the rocks where they outcrop in the landscape. There are many reasons to prefer borehole drillcore over outcrop, or vice versa. For me, outcrop is beneficial because I can see how deposits vary in three dimensions. In the absence of a close network of deep borehole drilling (such as in the UK), it provides an opportunity to study these deposits at a variety of scales from sub-millimetre to several kilometres. The ability to analyse shale at a range of scales is particularly relevant for the UK’s (possibly) emergent unconventional gas shale industry. By understanding the type and distribution of organic matter, this can enable better prediction of key prospective intervals for shale gas and could aid exploration process to be as selective and efficient as possible.
By Joe Emmings
Joe is a PhD student at the University of Leicester, his supervisors are Prof. Sarah Davies and Dr Gawen Jenkin (both University of Leicester) and at the British Geological Survey Prof. Melanie Leng, Prof. Mike Stephenson and Dr. Chris Vane.