Marine Sediments

When I think of the floor of the deep sea, the single, overwhelming fact that possesses my imagination is the accumulation of sediments. I see always the steady, unremitting downward drift of material from above, flake upon flake, layer upon layer ….For the sediments are the material of the most stupendous snowfall the Earth has ever seen

Marine sediments - origin Eroded rock particles and fragments Biological Chemical Deposit by settling through water column Oceanographers decipher Earth history through studying sediments and sedimentary rock

Origen of sediments Lithogenous Biogenous Hydrogenous Cosmogenous

lithogenous Rock fragments Reflects the composition of the parent rock Continental margins Mostly silicate Coarser closer to shore Finer farther away

How do they get there? From where? How is this related to the watershed?

Biogeneous sediment Hard remains of once-living organisms Shells, bones, teeth Macroscopic (large remains) Microscopic (small remains) Tiny shells or tests settle through water column

Mainly algae and protozoans Ca CO3, silica From diatoms, radiolarians,

Siliceous ooze Seawater undersaturated with silica Siliceous ooze commonly associated with high biologic productivity in surface ocean When the ooze lithifies it turns into ‘diatomaceous earth’

To get Ca ooze deposits you need shallow depth To get Si ooze deposits you need really high production

Hydrogenous marine sediments Minerals precipitate directly from seawater. It used to be dissolved Manganese nodules Phosphates Carbonates Metal sulfides Small proportion

Distributed all around in diverse communities

Iron-manganese nodules Deep ocean floor Fist-sized lumps of manganese, iron, and other metals Very slow accumulation rates

Metal sulfides Contain iron, nickel, copper, zinc, silver, and other metals Associated with hydrothermal vents Evaporites Minerals that form when seawater evaporates…salts (not just NaCl) Restricted open ocean circulation High evaporation rates Halite (common table salt) and gypsum (drywall)

Cosmogenous marine sediments Macroscopic meteor debris Microscopic iron-nickel and silicate spherules Tektites Space dust Insignificant proportion

Mixtures of marine sediments Usually mixture of different sediment types For example, biogenic oozes can contain up to 70% non-biogenic components

Typically one sediment dominates a certain area

Distribution of neritic and pelagic marine sediments Neritic sediments cover about ¼ of sea floor and are composed of lithogenouse sediment almost exclusively Pelagic sediments cover about ¾ and can be made up of lithogenous (clays), biogenous, and hydrogenous

Distribution controlled by Proximity to sources of lithogenous sediments Productivity of microscopic marine organisms Depth of water Sea floor features

How do sea floor sediments ? represent surface ocean conditions Microscopic tests sink slowly from surface ocean to sea floor (10-50 years) Tests could be moved horizontally yet sediment deposits do reflect surface water conditions Most biogenous tests clump together in fecal pellets Fecal pellets large enough to sink quickly (1

Marine sediments often represent ocean surface conditions Temperature Nutrient supply Abundance of marine life Atmospheric winds Ocean current patterns Volcanic eruptions Major extinction events (K-T boundary) Changes in climate Movement of tectonic plates