Marine Sediments – Key Concepts for Exam

Sampling is performed from research vessels using a variety of instruments designed to collect sediments with different levels of disturbance and at different depths.
Grab sampler (aka dredge): locks itself when pulled; captures superficial mixed layer; used on small vessels.
Box corer: collects a square, relatively undisturbed block of sediment; sampled with acrylic tubes; requires a mid-sized vessel.
Multiple corer: retrieves several undisturbed cores simultaneously; preserves historical environmental conditions.
Gravity corer: penetrates to about 6 meters; penetration depends on sediment properties; launched from mid-sized research ships.
Piston corer: penetrates up to ~8 meters; piston mechanism gives better penetration; upper section may be disturbed.
Giant piston corer: can recover up to ~60 meters of undisturbed sediment; requires large, specialized vessels.
Drilling systems: obtain very long cores (>1000 m) but require drill ships, high costs, and international sponsorship (e.g., D/V Joides Resolution, D/V Chikyu).
Drill bits (on Chikyu): multiple types for boreholes and core sampling.
Sediment traps: collect settling particles over time; deployed for long periods and moored; each bottle represents a time interval.

Sediment cores reveal past environmental information: sea surface temperature, nutrient supply, abundance of marine life, atmospheric conditions, ocean current patterns, volcanic eruptions, extinction events, climate changes, tectonic movements.
Paleoceanography: study of past ocean–atmosphere–land interactions using seafloor sediments.
Cores are often divided into fragments or layers, with each layer recording a distinct event or condition in Earth’s history.

Major vessels: D/V JOIDES Resolution and D/V Chikyu.
Participating countries span many regions (Australia, Austria, Canada, China, Denmark, Finland, France, Germany, India, Ireland, Italy, Japan, Netherlands, New Zealand, Norway, Portugal, Spain, Sweden, Switzerland, United Kingdom, United States).
Programs apply paleoceanography to reconstruct past climate and global environmental changes.

Origin: derived from preexisting rocks; weathering and erosion produce sediment pieces.
Transport: moved by oceans, streams, wind, glaciers, gravity.
Composition: often quartz (SiO₂) due to resilience during transport.
Texture/shape: determined by energy of transport and erosion.

Origin: fragments of living organisms that reach the seabed; many are planktonic.
Size classes:
- Macroscopic: shells, bones, teeth (relatively rare).
- Microscopic: tests from diatoms, radiolarians, coccolithophores, foraminifers.
Oozes: deposits with at least 30% biogenous tests; rest lithogenous.
Silica vs calcium carbonate sources:
- Siliceous tests from diatoms (SiO₂) and radiolarians.
- Calcareous tests from coccolithophores and foraminifers (CaCO₃).

Neritic biogenous deposits near continents include carbonate deposits and stromatolites.
Pelagic biogenous deposits accumulate slowly on the deep ocean floor as siliceous ooze or calcareous ooze.
Key components: silica (SiO₂) from diatoms/radiolarians and calcium carbonate (CaCO₃) from coccolithophores/foraminifers.
Factors controlling accumulation: productivity, dissolution, and dilution by lithogenous material.
CCD: Carbonate Compensation Depth; depth at which CaCO₃ dissolves in seawater faster than it accumulates.

Siliceous ooze (pelagic): dominated by diatoms and radiolarians.
Calcareous ooze (pelagic): dominated by coccolithophores and foraminifers.
Neritic carbonate deposits include limestones, stromatolites, and related carbonates near shelves.

Origin: minerals precipitate directly from seawater (not from organisms).
Common types: manganese nodules, phosphates, carbonates, metal sulfides, evaporites.
Formation environments: can occur on seafloor away from terrigenous input or near hydrothermal systems.
Examples shown: manganese nodules, evaporite salts on basin floors.

Origin: materials from outer space (micrometeorites, space dust, and meteor debris).
Relative abundance is very low compared to other sediment types.
Includes cosmogenic spherules and other space-derived particles.

Sediments are typically a mix of lithogenous, biogenous, hydrogenous, and cosmogenous components depending on location.
Nearshore continental shelves (neritic zones): lithogenous materials dominate; carbonate-rich deposits and stromatolites common.
Deep-ocean pelagic zones: abyssal clay (lithogenous) common in the Pacific; biogenous ooze (siliceous and calcareous) found where productivity is high or conditions favor preservation.
Siliceous ooze tends to accumulate in areas of high productivity/low dissolution, calcareous ooze where CCD is deeper than the water depth.
Mid-ocean ridges tend to have higher calcareous ooze presence above the CCD due to shallower depths.

Energy resources: petroleum; gas hydrates (ice-like methane clathrates).
Other resources: sand and gravel; evaporative salts; phosphorite (phosphate minerals); manganese nodules and crusts; rare-earth elements.
Gas hydrates contain large amounts of organic carbon and can release methane when destabilized.
Sea salt production (evaporites) is a notable marine sediment-related resource.
Manganese nodules: extensive deep-sea coverage in parts of the Pacific and Atlantic; concentrations can be very high locally.

IODP Expedition 342 on the JOIDES Resolution and Expedition 370 on the Chikyu provide real-world drilling examples.
Drilling expeditions illustrate long cores, deep-water sampling, and international collaboration in understanding Earth history.