3.2 Marine sediment types and distribution
3 min read•july 24, 2024
Marine sediments are Earth's hidden history books, recording oceanic changes over millions of years. These underwater deposits come in various types, each telling a unique story about their origin, composition, and the forces that shaped them.
Understanding marine sediments is crucial for decoding past climates, ocean circulation patterns, and biological productivity. From tiny particles to coarse gravels, these sediments provide valuable clues about Earth's ever-changing marine environments and their global impacts.
Marine Sediment Classification and Distribution
Classification of marine sediments
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- Origin-based classification differentiates sediments by source
- Terrigenous sediments originate from land weathering and erosion transported to ocean (river sediment)
- Biogenous sediments form from remains of marine organisms (coral skeletons)
- Hydrogenous sediments precipitate directly from seawater (manganese nodules)
- Cosmogenous sediments come from extraterrestrial sources (micrometeorites)
- Composition-based classification groups sediments by chemical makeup
- Siliceous sediments contain silicon dioxide from diatoms and radiolarians
- Calcareous sediments rich in calcium carbonate from foraminifera and coccolithophores
- forms from fine terrigenous particles and authigenic minerals
- Grain size classification categorizes sediments by particle diameter
- Clay (< 0.004 mm) finest particles, stay suspended for long periods
- (0.004 - 0.0625 mm) intermediate size, often mixed with clay
- (0.0625 - 2 mm) visible grains, common on beaches and continental shelves
- (> 2 mm) largest particles, found near shorelines and in submarine canyons
Distribution patterns of sediment types
- Continental margins accumulate terrigenous sediments from land
- Coarser grain sizes near shore due to higher energy environments
- Finer sediments transported further offshore
- Abyssal plains covered in fine-grained sediments due to low energy
- Biogenous oozes dominate in high productivity areas (equatorial regions)
- Red clay prevalent in areas of low biological productivity
- Mid-ocean ridges have thin sediment cover due to young crust
- Hydrothermal deposits form near active vents (black smokers)
- Deep-sea trenches accumulate turbidites from submarine landslides
- Sediments transported by
- Polar regions contain ice-rafted debris from melting icebergs
- Coarse-grained sediments deposited far from shore
Factors in sediment distribution
- Ocean currents transport and sort sediments
- Strong currents carry particles further and keep them suspended
- Influence particle settling rates through turbulence and upwelling
- Biological productivity controls distribution
- Upwelling zones and equatorial regions have high productivity
- Siliceous oozes dominant in Southern Ocean due to diatom blooms
- Proximity to land affects terrigenous sediment input
- River discharge major source of sediments to continental margins
- Aeolian transport significant in arid regions (Saharan dust to Atlantic)
- Water depth impacts carbonate preservation
- (CCD) marks dissolution of calcium carbonate
- zone of rapid increase in carbonate dissolution rate
- Seafloor topography influences sediment accumulation
- occurs in basins and depressions
- Erosion prevalent on seamounts and ridges due to current scouring
- Climate zones affect weathering, erosion, and productivity
- Tropical regions have high chemical weathering rates
- Glacial environments produce large amounts of physical erosion
Sediments as environmental records
- Paleoceanographic proxies in sediments reveal past conditions
- Oxygen isotope ratios in foraminifera shells indicate past temperatures
- Trace element composition reflects ocean chemistry changes
- Sediment cores provide climate archives through time
- Stratigraphic analysis shows changes in sediment composition
- uses microfossil assemblages to date sediments
- Past ocean circulation patterns inferred from sediment properties
- Grain size distribution indicates current strength
- Sediment provenance studies track transport pathways
- Sea level changes recorded in sediments
- Shoreline deposits mark past sea levels during glacial periods
- Paleoproductivity indicators reflect past ecosystem changes
- Biogenic silica accumulation rates show diatom productivity
- Organic carbon content indicates overall marine productivity
- Ice sheet dynamics revealed through ice-rafted debris
- Coarse sediments in deep ocean indicate iceberg discharge events
- Anthropogenic impacts visible in recent sediments
- Microplastics accumulation shows increasing pollution
- Heavy metal concentrations reflect industrial activities
Key Terms to Review (21)
Abyssal plain: An abyssal plain is a flat, deep-sea floor area typically found at depths of 3,000 to 6,000 meters, characterized by its vast, smooth, and featureless expanse. These plains are significant components of the deep ocean basins and play a crucial role in understanding oceanic processes, marine life habitats, and sediment deposition patterns.
Biogenous Sediment: Biogenous sediment is a type of marine sediment that is primarily composed of the remains of living organisms, such as plankton, mollusks, and corals. This sediment forms when these organisms die and their hard parts accumulate on the ocean floor, contributing significantly to the overall composition of marine sediments. Understanding biogenous sediment is crucial for grasping the broader patterns of sediment types and their distribution in ocean environments.
Biostratigraphy: Biostratigraphy is a branch of stratigraphy that uses fossil organisms to date and correlate rock layers, helping to establish the relative ages of sedimentary deposits. This method relies on the distribution of fossils within sedimentary sequences, allowing scientists to reconstruct the geological history and understand the environmental conditions of past marine ecosystems. It plays a crucial role in studying marine sediment types and their distribution by providing insights into the biological activity at different geological times.
Calcareous Sediment: Calcareous sediment is a type of marine sediment primarily composed of calcium carbonate, originating from the skeletal remains of marine organisms such as corals, mollusks, and foraminifera. This sediment plays a crucial role in the carbon cycle and the formation of sedimentary rocks, influencing marine ecosystems and geological processes over time.
Carbonate compensation depth: The carbonate compensation depth (CCD) is the oceanic depth at which the rate of carbonate accumulation equals the rate of dissolution of calcium carbonate, leading to a net zero accumulation of carbonate sediments. This depth is crucial for understanding marine sediment types and distribution, as it marks the boundary where calcite and aragonite begin to dissolve in seawater due to increased pressure and lower temperatures, affecting the composition of sediments found on the ocean floor.
Clay: Clay is a fine-grained natural soil material that consists of very small particles and has plastic properties when wet, making it easily moldable. In marine environments, clay plays a significant role in the formation and distribution of marine sediments, often settling in deep ocean basins where it can accumulate over time and influence the geological features of the seabed.
Continental Shelf: The continental shelf is a submerged extension of a continent, characterized by its relatively shallow waters and gently sloping terrain that typically extends from the coastline to the shelf break, where it descends sharply into the deep ocean. This unique marine feature plays a vital role in marine ecosystems, sediment deposition, and the distribution of marine resources.
Cosmogenous sediment: Cosmogenous sediment refers to sediments that originate from extraterrestrial sources, primarily consisting of particles like meteorites, cosmic dust, and other materials that have fallen to Earth from space. These sediments are typically found in very small amounts within marine sediments and can provide valuable insights into the history of our planet and the universe, including information about impact events and the composition of cosmic materials.
Deep-sea trench: A deep-sea trench is a long, narrow, and steep-sided depression in the ocean floor, formed by the subduction of one tectonic plate beneath another. These trenches are the deepest parts of the ocean and play a crucial role in shaping oceanic features and processes. They are often associated with volcanic activity and seismic events, making them important for understanding plate tectonics and marine ecosystems.
Gravel: Gravel is a type of coarse sediment consisting of rock fragments that are larger than sand but smaller than boulders, typically ranging from 2 mm to 64 mm in diameter. It plays a crucial role in marine sediment dynamics, influencing seabed composition, habitat structures, and the transport of materials across ocean floors.
Holocene: The Holocene is the current geological epoch that began approximately 11,700 years ago, following the last Ice Age. It marks a significant period of climate stability and is characterized by the development of human civilization and major changes in marine sediment types and distribution due to rising sea levels and changes in ocean circulation patterns.
Hydrogenous Sediment: Hydrogenous sediment refers to sediment that precipitates directly from seawater through chemical processes. This type of sediment is typically formed when dissolved minerals in seawater crystallize and settle to the seafloor, contributing to the overall composition of marine sediments. Hydrogenous sediments are significant in understanding the chemical interactions in ocean water and can impact the distribution and types of marine sediments found on the ocean floor.
John Murray: John Murray was a prominent Scottish oceanographer and marine geologist, best known for his pioneering work in the study of marine sediments and their distribution on the ocean floor. His research significantly advanced the understanding of sediment types, processes, and their implications for marine environments, laying the groundwork for modern oceanography and sedimentology.
Lysocline: The lysocline is the depth in the ocean at which the rate of dissolution of calcium carbonate exceeds the rate of supply, leading to a rapid decrease in the concentration of calcium carbonate in the sediments. This depth is crucial for understanding how marine sediments are distributed and formed, as it marks the transition between areas where calcium carbonate can accumulate and those where it dissolves before reaching the seafloor.
Marie Tharp: Marie Tharp was an American geologist and oceanographic cartographer, best known for her groundbreaking work in mapping the ocean floor. Her maps revealed the existence of the Mid-Atlantic Ridge and helped reshape our understanding of plate tectonics, connecting sediment distribution and marine geology with her pioneering cartography.
Red clay: Red clay is a type of deep-sea sediment that primarily consists of fine particles and has a distinct reddish color due to the presence of iron oxides. This sediment is typically found in the ocean's abyssal plains and represents a significant part of the marine sediment types, particularly in areas that are far from land where other sediments like sand and mud are less prevalent. The unique characteristics of red clay provide insights into geological processes and historical climate conditions.
Sand: Sand is a granular material composed of finely divided rock and mineral particles that ranges in size from 0.0625 mm to 2 mm in diameter. It plays a crucial role in marine sediment types and distribution, as well as in coastal processes and landforms. The size, composition, and distribution of sand can significantly affect marine habitats, shoreline dynamics, and sediment transport mechanisms.
Sediment core analysis: Sediment core analysis is a scientific method used to study the physical, chemical, and biological properties of sediment layers collected from the seafloor or lakebeds. This technique provides valuable information about past environmental conditions, sedimentation rates, and geological events, allowing researchers to reconstruct historical climate changes and ecological shifts. The examination of sediment cores is crucial for understanding marine sediment types and their distribution over time, as well as the processes that shape these sediments.
Sediment focusing: Sediment focusing refers to the process by which sediments are redistributed and concentrated in certain areas of the ocean floor, often due to currents, biological activity, and topography. This phenomenon is crucial for understanding sediment types and their distribution, as it influences how and where different sediments accumulate, shaping the seafloor and impacting marine ecosystems. The interplay between sediment focusing and other factors, such as sediment supply and deposition rates, plays a significant role in the geochemical cycling of nutrients and contaminants in marine environments.
Silt: Silt is a fine-grained sediment that is smaller than sand but larger than clay, typically ranging from 0.002 to 0.05 millimeters in diameter. It plays a significant role in shaping marine environments and coastal landscapes due to its ability to retain water and nutrients, making it essential for various marine ecosystems. Its distribution and characteristics can influence sediment transport processes, sedimentation patterns, and the formation of coastal landforms.
Turbidity Currents: Turbidity currents are underwater flows of sediment-laden water that occur on the seafloor, driven by gravity. These currents can transport large volumes of sediments from continental shelves to deeper ocean basins, shaping marine sediment types and their distribution in the process. Their dynamic nature plays a crucial role in influencing sediment deposition, erosion, and overall seafloor morphology.