Clastic injection: process to product

Subsurface sediment remobilisation and subsequent extrusion records the release of overpressure through a sealing lithology by an injecting slurry. This investigation
focuses upon injections occurring in the shallow-subsurface and utilises a multidisciplinary approach to reappraise the dynamics of sand injections across a variety of scales. The study provides detailed analysis from the laboratory and field on three scale of form: centimetre-scale fluidisation pipes, metre-scale extrusions and decimetre-scale fluidisation pipes. The investigation has helped bridge the
knowledge-gap and converge ideas between traditional geologically-derived interpretations of sand injections and fluidisation pipes considered in chemical engineering. Laboratory modelling of fluidisation pipes provides the first processbased model of shallow sub-aqueous sand injection and extrusion in cohesionless sediments and recognises a series of processes hitherto unlinked to previously described internal sedimentary structures in fluidisation pipes. Fluidisation is shown to occur through a series of discrete phases and critically, the style, stability and temporal evolution of piping, along with flow velocity and concentration, are shown to exhibit considerable variability. The novel application of particle tracking velocimetry to active sand injections suggests that this technique could be invaluable in unravelling the flow dynamics in active injections. A process-based
mechanism of sand extrusion formation is proposed though investigation of the internal architecture of seismically-induced sub-aqueous sandstone extrusions. Sand sheets are shown to form through deposition from gravity currents when
multiple vents extrude coevally, whereas sand mounds or volcanoes will form from a single vent unless bypassing mechanisms such as channelisation influence sediment deposition. Previous estimate of flow velocity in sandstone intrusions and Reynolds numbers are shown to be inaccurate by up to two orders of magnitude. The investigation also demonstrates that sandstone-hosted intrusions exert control
on basinal fluid flow in a manner previously identified only in mudstone-hosted intrusions and proposes a new model of the formation of the sandstone intrusions in Kodachrome Basin State Park.