Geological Techniques

In the previous chapters, the use of geophysical data for delineating the continental shelf has been discussed in some detail. But the determination of the case for any extension of the legal continental shelf beyond 200 nautical miles (M) from the territorial sea baseline may in some circumstances require a geological survey to confirm that a topographic or geophysical feature comprising what appears to be a natural prolongation of land territory is of continental or oceanic origin. A geological survey may also be necessary to determine the occurrence, thickness, and extent of sediments beyond the foot of the slope. Continental margins represent regions of transition from the landmass to the ocean basin and may be present-day areas of sediment erosion or deposition. Sediment supply to the continental shelf and slope, or the extent of erosion on the continental shelf and upper slope, is influenced by tectonic activity, sea-level fluctuations, climate change, variation in the wave or current regime, and various other processes. Bottom currents or gravity transport (turbidity) processes combine to varying degrees with pelagic sedimentation (the accumulation of the remains of marine organisms) to extend the supply of sediment well beyond the shelf and slope to the continental rise, ocean trench, or abyssal plain (Evans et al., 1998). In order to understand the geology of such areas, it is necessary to determine the structural setting, the tectonic and sedimentary evolution, the chrono-and lithostratigraphy, and the volcanic history. Understanding the ocean floor is a prerequisite for the determination of the extent of the continental shelf under UNCLOS. It is also highly relevant to the identification and delineation of mineral and energy resources, for determining the waste disposal potential of parts of the seafloor, and for undertaking an assessment of the risk of slope failure. None of these are directly relevant to establishing the new limits of the continental shelf, but they are highly relevant to its long-term exploitation. In order to achieve the necessary level of knowledge, the seafloor morphology and seabed character derived from bathymetric and sonar surveys (described in chapters 9 and 10) and the three-dimensional geology determined by geophysical surveys using seismic profiling, magnetometer, and gravity meter (discussed in chapters 12 and 13) need to be calibrated or "ground truthed" by sampling and coring (figure 14.1; Stoker et al., 1994).