Sediment micro-fabric of oil rig drill spoil heaps: preliminary observations using low-temperature scanning electron microscopy

Low-temperature scanning electron microscopy is a specialized technique shown to be appropriate for the high-resolution examination of unconsolidated sea floor sediments. Newly developed cryogenic sediment sampling techniques combined with low-temperature scanning electron microscopy (LTSEM) protocols developed for the analysis of biological materials now permits the sampling of fully hydrated bottom sediments while preserving the structural integrity of the sampled material. This enables the direct observation of the sediment fabric as it exists at the seabed and the examination of delicate biological structures that are normally obliterated or distorted by the removal of water required for standard SEM preparation. This paper demonstrates the value of LTSEM and shows variation in microfabric structure between a station located on a spoil heap below an oil rig and a more remote (400 m distant) station. Energy-dispersive X-ray analysis (EDXA) was also conducted on the frozen samples and provided support for the qualitative differences found between the two sites. The results suggest that an organic film was more pervasive on the drill spoil heap and that biological activity in the form of foraminifera was much more extensive on the remote site. Insufficient data has yet been collected to allow statistical analysis of the results, but the paper provides the first microfabric analyses of submerged spoil sediments using LTSEM and confirms the potential of this technique in terms of environmental assessment and analysis of the nature of the sediment fabric of oily, drill spoil heaps from a location in the North Sea.