Steve Farrell

I was sat enjoying a pre-field day breakfast coffee on a sunny morning in Northern Ireland when I received the email from the BSRG saying I was to be the 2018 recipient of the Steve Farrell Memorial Fund. I excitedly told the other field trip staff that I’d won funding for my EGU trip. It wasn’t until we got back that the field trip leader, our head of school Simon Bottrell, found out it was in the memory of Steve Farrell. Simon told me that he and Steve were friends during their undergrad at Oxford.

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Stephen G. Farrell, 1960 – 1987. Photo used with permission of John Underhill.

When I was in the process of applying for the memorial fund, I quickly searched for some information on Steve but found it difficult to find anything. After Simon had told me he knew Steve, it reignited my curiosity in who Steve was, and why there was a memorial set up in his name.

“I remember Steve visiting Leeds just after I arrived here very vividly,” reminisced Professor Bottrell. “This would have been about 1986, not long before he died.” I told him about how I could find very little information on who Steve was, and he pointed me to Steve’s obituary from the AAPG Bulletin (Underhill, 1987).

Steve died tragically young, just two years after finishing his PhD, but had a huge impact on our understanding of the interplay between sedimentation and tectonics in such a short time. After his undergraduate degree at Oxford, Steve moved over to Cardiff to study the Ainsa Basin marine slope sediments for his Shell-sponsored PhD. Steve published numerous papers on this work, as well as subsequent research in Cyprus as he began working for BP.

Soft-sediment slumping due to gravity is a common feature of many basins, but in his first paper (Farrell, 1984), Steve concentrated on the ones exposed in the San Vincente Formation. He applied dislocation modelling to explain the complex relationships between compressional and extensional regimes within the slumps, and investigated the origins of overprinting of extensional regimes on top of compressional regimes. These somigliana dislocation models had typically been used at a larger, tectonic scale, but Steve applied the models at the slump scale to explain the complex relationships and how they could be distinguished as gravitationally-induced, as opposed to being related to the Pyrenean orogeny. The figures drawn by Steve in this paper evocatively capture the detail and complexity of the beautiful slumps, as well as showcasing Steve’s exquisite eye for detail.

 

 

Soft sediment slumps in the Labuerda Canyon, Ainsa Basin, which Steve studied extensively for his PhD. First image shows the complexity of folding in these slumps, displaying recumbent folds. The second image shows upright folding within the same outcrop. The third image is taken from a virtual outcrop model showing both of the previous features. All images courtesy of John Howell (@Virtualgeol) and the Virtual Outcrop Geology Group.

Steve blended sedimentology and structural geology seamlessly. A master of both, Steve’s next paper (Farrell et al., 1987) concentrated on constraining the sequence of thrusting during the Pyrenean orogeny through stratigraphic relationships. By studying folding and unconformities within the piggyback basins, he unravelled the complex faulting history within the foreland. Here, he showed that instead of the classic foreland-propagating thrust sequence, thin-skinned thrusting built up the Montsec thrust and constrained the Tremp-Graus basin. The northern edges of the Tremp-Graus basin were then deformed by thick-skinned, basement thrust sheet stacking in the axial zone to the north. This particular paper is especially poignant for me because we studied this area on an MSc field trip and saw for ourselves the stunning results of faulting and folding. The structural geology out there, such as the Mediano Anticline (below), is truly awe-inspiring.

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The breathtaking Mediano Anticline, Ainsa Basin, Spanish Pyrenees.

It wasn’t just the Pyrenees that Steve studied. Whilst working for BP, Steve was involved in the development of the booming North Sea plays. But Steve also studied in the field in Cyprus, resulting in his third (Farrell and Eaton, 1987) and fourth (Farrell and Eaton, 1988) papers, both published posthumously. In his third paper, Steve explored fold geometries in soft sediment slumps observed in the Khalassa and Maroni basins in Cyprus and compared them with those observed in the Ainsa Basin. Steve unpicked the complex folding styles, often folded then refolded, to determine models of slump translation distances. The more complex the folding, the higher the shear strain, and therefore the more complex the folding. Simple shear dominates during slump translation; once the slump begins to decelerate, pure shear can occur, resulting in beautiful sheath folds and refolded folds.

Deformation of sediments is not just related to palaeoslope-induced slumping, however, and Steve recognised this in his fourth paper (Farrell and Eaton, 1988). Here, again studying with Simon Eaton, Steve deconvolved the deformation that occurred due to slumping from ptygmatic folding occurring during compaction. Overprinting of later, diagenetically or compactionally-induced fabrics often occurs to complicate the stories of soft sediment deformation.

Steve’s career promised much but was tragically cut short. Steve’s research added valuable insights into soft sediment deformation processes and their relation to the tectonic evolution of sedimentary basins, paving the way for palaeoslope analyses through basins worldwide. Much of our understanding of the stratigraphic evolution of basins under active tectonics relies on detailed investigations of outcrops, and Steve’s brilliant mind was able to unravel these. In turn, these textbook examples of sedimentary and tectonic process interaction became invaluable as teaching tools for basin evolution. During my education, Steve’s research cropped up again and again – first at undergraduate level, studying the evolution of the sedimentary basins of Cyprus during the Tertiary in response to complex tectonics, then again at Masters level, on field work in the Pyrenees, studying complex tectonic and sedimentary interactions.

Despite his illness, Steve continued to pursue both sport and science with vigour. His squash prowess endured, reaching the finals of BP’s global squash tournaments even during his illness. Steve was committed to research and science all the way, too. Even during the infamous “Christmas conference season” of BSRG and TSG, December 1986 and early January 1987, Steve refused to let his illness beat him, and attended and contributed to both conferences. Steve died from cancer on 30th January 1987.

Steve was, and still is to this day, sorely missed by those who knew him. The BSRG decided to set up the Steve Farrell Memorial Fund in his name, in order to benefit scientists with even as much as half the vigour and enthusiasm that Steve displayed. I am hugely grateful and indebted to the BSRG for awarding me the Steve Farrell Memorial Fund in 2018 to aid my attendance to the EGU General Assembly in Vienna. Here, I was able to present the results of my own research. I feel privileged to have presented in the memory of Steve, and hope that I have honoured his name in the process.

Stephen G. Farrell, 1960 – 1987.

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Slumped Carboniferous deltaic sandstones near Greenhow Hill, Yorkshire, showing similar deformation characteristics to those studied in deepwater sediments by Steve. As well as dewatering structures, both upright and recumbent asymmetrical folds can be seen. These were induced by seismicity on the North Craven Fault, 2 km to the south.

References

Farrell, S.G. 1984. A dislocation model applied to slump structures, Ainsa Basin, South Central Pyrenees. Journal of Structural Geology. 6(6),pp.727–736.

Farrell, S.G. and Eaton, S. 1988. Foliations developed during slump deformation of Miocene marine sediments, Cyprus. Journal of Structural Geology. 10(6),pp.567–576.

Farrell, S.G. and Eaton, S. 1987. Slump strain in the Tertiary of Cyprus and the Spanish Pyrenees. Definition of palaeoslopes and models of soft-sediment deformation. Geological Society, London, Special Publications. [Online]. 29(1),pp.181–196. Available from: http://sp.lyellcollection.org/lookup/doi/10.1144/GSL.SP.1987.029.01.15.

Farrell, S.G., Williams, G.D. and Atkinson, C.D. 1987. Constraints on the age of movement of the Montsech and Cotiella Thrusts, south central Pyrenees, Spain. Journal of the Geological Society. [Online]. 144(6),pp.907–914. Available from: http://jgs.lyellcollection.org/cgi/doi/10.1144/gsjgs.144.6.0907.

Underhill, J.R. 1987. Memorial: Stephen G. Farrell (1960-1987). AAPG Bulletin. 71(7),p.901.

 

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