© 2006 Jones and Bartlett Publishers Chapter 4 Marine Sedimentation

© 2006 Jones and Bartlett Publishers

Chapter 4

Marine Sedimentation

Classification of marine sediments can be based upon size or origin

• Size classification divides sediment by grain size into gravel, sand, silt and clay.– Mud is a mixture of silt and

clay.

• Origin classification divides sediment into five categories:– terrigenous sediments

– biogenous sediments

– hydrogenous sediments

– volcanogous sediments

– cosmogenous sediments

4-1 Sediment in the Sea

Figure B4-3 Sediment Cores

• Factors that control sedimentation include:– particle size

– the turbulence of the depositional environment

• Terrigenous sediments strongly reflect their source.– They are transported to the sea by wind, rivers and glaciers.

• Rate of erosion is important in determining nature of sediments.

• Average grain size reflects the energy of the depositional environment.

4-1 Sediment in the Sea

• Hjulström’s Diagram graphs the relationship between particle size and energy for – erosion– transportation – deposition

4-1 Sediment in the SeaFigure 4-1 Hjulström’s Diagram

• Based upon water depth, the ocean environment can be divided into:

– the shelf• shallow and near a terrigenous source

– the deep ocean basin• deep and far from a terrigenous source

4-2 Sedimentation in the Ocean

Review

• Shelf sedimentation is strongly controlled by:– Tides– Waves– Currents

• Their influence decreases with water depth.

• Shoreline turbulence prevents small particles from settling in the shallow water.

• Particle size decreases seaward for recent sediments.


Shelf Sedimentation


Figure 4-2a Model Prediction of Shelf Sediments

Past fluctuations of sea level have stranded coarse (relict) sediment across the shelf.– This includes most areas where only fine sediments are

deposited today.

Figure 4-2 Shelf Sedimentation

Sea Level Fluctuation and Coastlines

Shelf Sedimentation

Figure 4-3b Relict Sediment


• Worldwide distribution of recent shelf sediments by composition is strongly related to latitude and climate.

• Calcareous biogenous sediments dominate tropical shelves.

• River-supplied sands and muds dominate temperate shelves.

• Glacial till and ice-rafted sediments dominate polar shelves.


Shelf Sedimentation Model


Figure 4-4a Shelf Sedimentation Model

Distribution of Shelf Deposits

4-2 Sedimentation in the OceanFigure 4-4b Relative Amounts of Shelf Sediments

• Geologic controls of continental shelf sedimentation must be considered in terms of a time frame.

• For a time frame up to:

– 1000 years, waves, currents and tides control sedimentation.

– 1,000,000 years, sea level lowered by glaciation controls sedimentation and cause rivers to deposit their sediments at the shelf edge and onto the upper continental slope.

– 100,000,000 years, plate tectonics determines the type of margin that develops and controls sedimentation.


Paleogeography of North America

4-2 Sedimentation in the OceanFigure 4-5a North American Paleogeography 100 MYBP

Figure 4-5b Pangaea 100 MYBP


Figure 4-5c Western North American Tectonic Margin (Active Margin)

Figure 4-5d Eastern North American Nontectonic Margin (Passive Margin)

Development of a Passive Atlantic-type Margin

Figure 4-6a Initial Rifting (Triassic Period: 200 MYBP)

Figure 4-6b Jurassic Margin (150 MYBP) 4-2 Sedimentation in the Ocean

Figure 4-6c Present-Day Margin Southeast of Cape Cod


Subduction Tectonics and Sedimentation

Figure 4-7a Volcanic Arc-Trench System 4-2 Sedimentation in the Ocean

Figure 4-7b Accretionary Prism4-2 Sedimentation in the Ocean

If influx of terrigenous sediment is low and the water is warm, carbonate sediments and

reefs will dominate.

4-2 Sedimentation in the OceanFigure 4-8 Distribution of Carbonate Shelves

• Deep-sea Sedimentation has two main sources of sediment:

– External – terrigenous material from the land

– Internal – biogenous and hydrogenous from the sea.


Deep-Sea Sedimentation

4-2 Sedimentation in the OceanFigure 4-9a Sedimentation in the Deep Sea

Figure 4-9b River Input of Silt to Oceans 4-2 Sedimentation in the Ocean

• Major sedimentary processes in the deep sea include:– Bulk emplacement

– Debris flows

– Turbidity currents


Figure 4-10a Seismic-Reflection Profile

Bulk Emplacement of Sediment to the Deep Sea


Figure 4-10b Turbidity Current

Figure 4-10c Margin-Sedimentation Model 4-2 Sedimentation in the Ocean

Figure 4-10c Turbidite Beds

Major pelagic sediments in the ocean are red clay and biogenic oozes.


Figure 4-14b Foraminifera

Figure 4-14e Diatoms

• Hydrogenous deposits are chemical and biochemical precipitates that form on the sea floor. They include:– ferromanganese nodules – phosphorite

Figure 4-15b Global Distribution of Ferromanganese Nodules4-2 Sedimentation in the Ocean

• The distribution of sediments in the deep ocean reflects:– Latitude– distance from landmasses– the calcium carbonate compensation depth

• Glacial marine sediments occur in the high latitudes.

• Pelagic clays occur far from land and in the deepest water.


The Formation of Glacial-Marine Sediments

Figure 4-12a Ice Rafting


The Formation of Glacial-Marine Sediments

Figure 4-12b Deep-Sea Deposits Around Antarctica


• Calcareous oozes occur above the calcium carbonate composition depth.


The depth at which surface production of CaCO3 equals dissolution is called the calcium carbonate compensation depth (CCD) Figure 8.17 . Above this depth, carbonate oozes can accumulate, below the CCD only terrigenous sediments, oceanic clays, or siliceous oozes can accumulate. The calcium carbonate compensation depth beneath the temperate and tropical Atlantic is approximately 5,000 m deep, while in the Pacific, it is shallower, about 4,200-4,500 m, except beneath the equatorial upwelling zone, where the CCD is about 5,000 m. The CCD in the Indian Ocean is intermediate between the Atlantic and the Pacific. The CCD is relatively shallow in high latitudes.

http://www.log.furg.br/WEBens/morelock/8_image/17ccd.gif

• The rate of sedimentation depends on the type of sediment in deep sea.

4-2 Sedimentation in the OceanFigure 4-13 Clays in Deep-Sea Muds

Global Deep-Sea Deposits

Figure 4-16a Deep-Sea Sediment Distribution 4-2 Sedimentation in the Ocean

Global Deep-Sea Deposits

Figure 4-16b Sedimentation Rates 4-2 Sedimentation in the Ocean

• Deep-sea stratigraphy refers to the broad-scale layering of sediments that cover the basaltic crust.

• The stratigraphy of the deep sea is strongly influenced by sea-floor spreading.


• The Atlantic basin contains a “two-layer-cake” stratigraphy – a thick basal layer of carbonate ooze overlain by a layer of mud.

Figure 4-17 Stratigraphy of the Atlantic Basin


• The Pacific basin contains a “four-layer-cake” stratigraphy.• It crosses the equator where the CCD is lowered to the ocean bottom.

Figure 4-18a Pacific Ocean4-2 Sedimentation in the Ocean

Stratigraphy of the Pacific Basin

Figure 4-18b Stratigraphy of the Pacific Basin


Figure 4-18c Model to Account for Pacific Stratigraphy


• The Mediterranean basin is located where plates are colliding as Africa moves northward relative to Europe.

• Anhydrite and stromatolites of Miocene age indicate that the Mediterranean sea “dried” out between 5 and 25 million years ago.

• Two models have been suggested to account for this emptying of the Mediterranean Sea of its water.– The “Uplift” Model– The “Drying-Out” Model

• After drying out, seawater from the Atlantic Ocean cascaded down the face of the Gibraltar Sill, refilling it in about 100 years.


The Drying Up of the Mediterranean Sea

The “Uplift” Model The “Drying-Out” Model

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© 2006 Jones and Bartlett Publishers Chapter 4 Marine Sedimentation