Marine Geology

Abstract

The geology of the marine realm is fundamentally different from that of the continents. Marine geology requires specialized instrumentation, mostly deployed from ships, including acoustic devices for imaging the seabed and its subsurface geology. Seabed samples are collected using remotely operated tethered vehicles, corers and light drills, but samples deeper than 20m require a dedicated drillship. Oceanic crust underlies 60% of Earth's surface in the ocean basins. Their major bathymetric features are controlled by cooling of lithosphere away from spreading ridges, enhanced melt production in hot spots and the effects of subduction at trenches. Some 80% of oceanic crust is blanketed by pelagic sediments of biogenic carbonate and silica, and wind-blown abyssal red clays. Thinned continental crust underlies most continental margins and marginal seas. Margins comprise three main physiographic regions, where different sediment transport processes operate. The continental shelf is the shallow-water extension of the land surface, affected by waves, tides and sediment input directly from rivers. The steep continental slope separates the shelf from the deep ocean and is characterized by submarine canyons and large landslides, which supply shelf sediment to the continental rise by turbidity currents. On the rise, these currents build deep-sea fans, abyssal plains and fill some subduction trenches with terrigenous sediment. Oceanic circulation on the slope and rise reworks terrigenous sediments into contourite drifts. Landslides and currents are hazards to electricity and telecommunication cables and petroleum installations. Global climate change will result in rising sea level and disruptions of the oceanic carbon cycle.