Marine Sediments

Chap 5

video

Lithogenous/Terrigenous Sediment

• Derived from land• Origin from weathering/erosion• Mainly quartz (SiO2) – resistant to abrasion• Main constituent of continental shelf

sediment can also be found in deep ocean

Sediment Texture

Big, cars go so slow, cool

Sediment Erosion, Transportation, Deposition

Sediment Maturity

Neretic Deposits(near shore lithogenous)

• found along continental margins and islands – mainly lithogenous

• Beach deposits – mainly quartz rich sands – but what ever is available

• Continental Shelf deposits – carried by rivers• Turbidite deposits due to underwater avalanches

– from turbidity currents –show graded bedding • Glacial Deposits – grinding by ice and trapped in

glacial ice

Pelagic Deposits(open water lithogenous)

• Fine grained material that accumulates on the ocean floor.

• Abyssal Clay >70% clay sized particles from continent- due to lack of other particles

• Contain oxidized iron making them red-brown or buff

Biogenous Sediment

• Derived from hard parts of once-living organisms – algae and protozoans.

• Macroscopic can be seen with eyes• Microscopic too small to be seen with unaided

eye• Microscopic organisms produce small shells

called tests and accumulates in the deep ocean to form ooze.

Composition

• Calcium Carbonate - CaCO3 (makes mineral calcite)

• Silica SiO2.

Calcium Carbonate forms Calcareous Ooze• Foraminiferans are protozoans

with porous CaCO3shells .• Coccolithophores are microalgae

that are 10-100 times smaller than diatoms, they are called nanoplankton. They have CaCO3 plates (cocoliths) that make up their shell. These decompose to form cocolith-rich CaCO3 ooze that can later lithify to form chalk and limestone.

Dover

Stromatolites• Lobate structures made of

layers of carbonate from cyanobacteria at particular shallow depth.

Silica forms Siliceous Ooze• Silica biogenous ooze made mainly

from planktonic algae called diatoms and a protozoans called radiolarians

• Diatomaceous earth used in filters, abrasives, absorbents, glass. Also diatoms have a droplet of oil in them that have accumulated into petroleum deposits (ex: off California)

• Silica dissolves is seawater and will only accumulate silica ooze where there is high production.

Calcite Compensation Depth -CCD• CaCO3 is saturate in warm shallow

waters and can form sediments.• At deeper cooler waters CaCO3 is

not saturated so does not form deposits after a certain depth – CCD.

• Average CCD is 4500 m• Below 5000 m, calcareous ooze not

usually found unless it was made at a higher depth and then covered before it’s present depth.

lysocline

Hydrogenous Sediment

• Derived from seawater• Chemical reaction cause minerals to

precipitate out of sea water usually when there is a temperature or pressure change

Manganese nodules

• 5-20 cm lumps of Mn, Fe and other metals• Found on deep ocean floor 100/m2

Phosphates

• Phosphate bearing compounds found on rocks and nodules on the continental shelf and banks at depths < 1000m.

• Used as fertilizer and other agricultural proposes

Carbonates• Aragonite and calcite are the two most

important carbonate sediments• Aragonite has a different crystalline structure

and is less stable and changes into calcite over time.

• Biogenous in origin, aragonite crstals can form hydrogenously by precipitating directly from seawater.

• Oolites are small calcite spheres that form in shallow tropical waters with high CaCO3 concentrations.

Metal Sulfides

• Made by black smokers at hydrothermal vents• Iron, nickel, copper, zinc, silver and other

metals.

Evaporites minerals

• In restricted circulation areas where evaporation is high – seawater becomes saturated with minerals and the minerals precipitate out.

• Collectively called salts, some evaporites may taste salty because of NaCl and other do not like calcium sulfate minerals anhydrite (CaSO4) amd gypsum (and H20)

Cosmogenous Sediment

• Extraterrestrial origin• Spherules = microscopic, usually once molten

basalt from impact events, forms tektites • Although 90% of tektites are destroyed by

frictional heating with the atmosphere, 300,000 metric tons/year reach Earth

• Meteor = macroscopic, impact material made of rock (chondrites) or iron and nickel (irons) settle out around impact sites.

% of Pelagic Sediments

• 47.7% Carbonate• 14.2% Siliceous• 38.1% Abyssal