Rough bottoms on deep-water sandstones: using sole structures to improve flow and environmental prediction, and geohazard understanding — Featuring fieldwork in Canada/Poland, and experiments in Illinois, USA

Understanding geohazards in submarine systems is challenging because we can only measure the most dilute of flows, and even then we don’t have data close to the bed. In particular, the dynamics of the most powerful flows such as debris flows, slumps and slides, are largely known from very small scale subaqueous experiments, and larger, but not necessarily applicable subaerial experiments. Here we identify a new approach that can help us understand the dynamics of natural high-concentration sediment gravity flows. Sole structures provide a record of the flow processes at the bed itself, and understanding their formation, development and preservation provides us with an opportunity to look at bed processes, and identify the type and dynamics of the flows that formed them. The spatial distribution of sole structure also opens up new research potential in investigations of flow-substrate interactions, the recognition of different flow types and their transport processes in a range of natural flows.

Sole structures (flutes, tool marks, and a wide range of currently enigmatic features) are ubiquitous in deep-water clastic sediments, but at present geologists principally utilise them only as palaeocurrent indicators. This limited use is in sharp contrast with almost all other sedimentary structures, from which we interpret flow properties and thus help reconstruct ancient sedimentary environments. Indeed, it is astonishing that geologists have made such poor use of sole structures, given that other sedimentary structures are typically rare in deep-water sedimentary sequences, thus making environmental interpretations difficult, and limiting our ability to predict the character and spatial distribution of these sediments. This lack of progress in understanding sole structures reflects two key factors: a belief that they were all formed by low-concentration turbidity currents, and a near absence of research in this area since the early 1970s. However, since this time, our knowledge of deep-water sediment gravity flows (SGFs) has increased enormously, and we now recognise that there are a wide range of flows in these systems, from low-concentration, turbulent turbidity currents, through to high-concentration subaqueous debris flows, with a range of mud-rich transitional flows in between these end members.

Recent work by the supervisors has demonstrated that the underlying assumption of the past 65 years that all these sole structures are formed by classical low-concentration turbidity currents is fundamentally flawed. We have been able to show that different sole structures can be linked to different SGFs, enabling the use of these features to refine environmental interpretation and improve prediction of deep-water systems. Whilst we have demonstrated the greatly increased utility of sole structures, this has opened up an entirely new field that is ripe for further study, offering huge opportunities to explore the formative processes and utility of sole structures. For example, the spatial distribution of sole structure opens up new research potential in investigations of flow-substrate interactions, the recognition of different flow types and their transport processes in a range of natural flows, their use in resource exploration, and in the assessment of geohazards.

Aims and Objectives
This PhD project will investigate the formative processes of a range of sole structures, and determine how to interpret and utilise these within environmental interpretations and predictions. The objectives include:
• To understand the diversity of sole structures, their detailed morphology, and their spatial variability, in a range of deep-water settings. This will be achieved through fieldwork (Eastern Canada / Polish Carpathians), recording sole structure type, using photogrammetric and drone-based techniques to collect morphometric and spatial information on sole mark distribution, and sedimentary logging to record bed types, grain size / sorting, and enable environmental interpretations.
• To understand how a range of sole structures initiate and evolve, and the nature of flow dynamics across these bedforms. Laboratory experiments using modern measurement technologies will be utilised to study these processes. A wide range of different types of experiment can be used dependent on the sole structures of interest.
• To use the spatial and temporal relationships between different sole structures, to make big advances in understanding the processes operating in many subaqueous SGFs. In particular to examine the mechanics of debris flows, and the implications of this for geohazards.
• To combine these approaches to develop new process models for the formation and environmental distribution of different sole structures.