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 clay 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

• 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
  • Red clay 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
  • Silt (0.004 - 0.0625 mm) intermediate size, often mixed with clay
  • Sand (0.0625 - 2 mm) visible grains, common on beaches and continental shelves
  • Gravel (> 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 turbidity currents
• 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 biogenous sediment 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
  • Carbonate compensation depth (CCD) marks dissolution of calcium carbonate
  • Lysocline zone of rapid increase in carbonate dissolution rate
• Seafloor topography influences sediment accumulation
  • Sediment focusing 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
  • Biostratigraphy 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 continental shelf 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