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Thinking outside of the burrow

Right from its earliest days as a modern scientific discipline, ichnology — the study of trace fossils — has bridged the gap between sedimentology and palae­ontology. As ichnologists we don’t generally have any clear idea of what made the burrows that are left in ancient sediments and bedding planes. The beauty of the discipline is in determining what the fossils can tell us — ‘sleuthing’ as one of my students dubbed it. To be a good ichnologist requires a broad knowledge base, of course, and plenty of imagination. And because it is an immature sci­ence, there is still a bewildering amount to see and do and learn.

Trace-makers are generally animals, so we need some biological background, particularly:

  • Biodiversity — what kinds of animals are there out there that might have made the trace fossil we are studying?
  • Biomechanics — what are those creatures capable of doing and how do they do it?
  • Functional morphology — how does an organism gain the necessities for life such as food and shelter?

Often the critical pieces of information that biology might provide for the ich­nologist, ‘What type of burrow does an animal make?’ and ‘What does the ani­mal do in its burrow?’, are unknowns. Biologists might at best know the shape of the open burrow an animal makes, but seldom do they consider the changes to the position of the burrow through the life of the animal. This opens up the important but underexplored discipline of ‘experimental neoichnology’ — the study of living trace-makers. There are few things that make this ichnologist happier than to be able to directly observe an animal in its burrow.

Even the most enthusiastic ichnologist will admit that the most important clues when interpreting a rock succession with trace fossils in it are actually sedi­mentological. Early in my career, my biggest shortcoming as an ichnologist was a poor knowledge of sedimentological processes. Only by understand­ing sedimentological context, is it possible to determine whether a trace fossil or assemblage of trace fossils is out of place. That kind of integrated sedimentological–ichnological approach to palaeoenvironmental ichnology had its greatest proponent in Roland Goldring. He devised the ichnofabric approach to ichnology which forces the user to take account of the sedimentological context of trace fossils. During my PhD, Roland was always harassing me to cut up my trace fossils. It was only after I had taken a 10-year hiatus from being a dedicated ichnologist to focus on sedimentology, sequence stratigraphy, and petroleum geology that I really began to appreciate ichnology. Now I cut up trace fossils all the time.

 The trace fossil  Diplocraterion  partially eroded by cross-bedded sandstones (Ordovician of Australia).

The trace fossil Diplocraterion partially eroded by cross-bedded sandstones (Ordovician of Australia).

This might seem extreme. The collecting, classifying, and care of beautiful fossils is something all palaeontologists love. To cut fossils up and destroy them still seems like a sin to the pure palaeontologist in me, but it yields so much insight. By relying on crack-out and bedding plane trace fossils, ichnologists often missed out on what the trace maker was actually doing. My current research focuses on three-dimensional digital reconstruction of trace fossils and their ichnofabric, employing serial grinding and photography, combined with petrography, geochemistry, and the measurement of porosity and permeability.

The future of ichnology is in understanding burrows in the context of the near-burrow environment, both ancient and modern. That those animal–sediment interactions also change the reservoir properties of hydrocarbon reservoirs is a bonus that makes our discipline increasingly relevant in the real world. If the next generation of ichnologists is to advance the science, we need biologists, sedimentologists, and palaeontologists capable of thinking outside the burrow.

Scaling the outcrop

The fine art of Mother Nature