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 Figure B4-3 Sediment Cores 4-1 Sediment in the Sea

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 Figure 4-1 Hjulström’s Diagram 4-1 Sediment in the Sea

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

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. 4-2 Sedimentation in the Ocean

Shelf Sedimentation 4-2 Sedimentation in the Ocean Figure 4-2a Model Prediction of Shelf Sediments 4-2 Sedimentation in the Ocean

Sea Level Fluctuation and Coastlines 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

Shelf Sedimentation 4-2 Sedimentation in the Ocean Figure 4-3b Relict Sediment 4-2 Sedimentation in the Ocean

Calcareous biogenous sediments dominate tropical shelves. 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. 4-2 Sedimentation in the Ocean

Shelf Sedimentation Model Figure 4-4a Shelf Sedimentation Model 4-2 Sedimentation in the Ocean

Distribution of Shelf Deposits Figure 4-4b Relative Amounts of Shelf Sediments 4-2 Sedimentation in the Ocean

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. 4-2 Sedimentation in the Ocean

Paleogeography of North America Figure 4-5b Pangaea 100 MYBP Figure 4-5a North American Paleogeography 100 MYBP 4-2 Sedimentation in the Ocean

4-2 Sedimentation in the Ocean Figure 4-5c Western North American Tectonic Margin (Active Margin) Figure 4-5d Eastern North American Nontectonic Margin (Passive Margin) 4-2 Sedimentation in the Ocean

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

4-2 Sedimentation in the Ocean Figure 4-6c Present-Day Margin Southeast of Cape Cod 4-2 Sedimentation in the Ocean

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

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

If influx of terrigenous sediment is low and the water is warm, carbonate sediments and reefs will dominate. Figure 4-8 Distribution of Carbonate Shelves 4-2 Sedimentation in the Ocean

Deep-sea Sedimentation has two main sources of sediment: External – terrigenous material from the land Internal – biogenous and hydrogenous from the sea. 4-2 Sedimentation in the Ocean

Deep-Sea Sedimentation Figure 4-9a Sedimentation in the Deep Sea 4-2 Sedimentation in the Ocean

4-2 Sedimentation in the Ocean 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 4-2 Sedimentation in the Ocean

Bulk Emplacement of Sediment to the Deep Sea Figure 4-10b Turbidity Current 4-2 Sedimentation in the Ocean

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

Major pelagic sediments in the ocean are red clay and biogenic oozes. Figure 4-14b Foraminifera Figure 4-14e Diatoms 4-2 Sedimentation in the Ocean

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 Nodules 4-2 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. 4-2 Sedimentation in the Ocean

The Formation of Glacial-Marine Sediments Figure 4-12a Ice Rafting 4-2 Sedimentation in the Ocean

The Formation of Glacial-Marine Sediments Figure 4-12b Deep-Sea Deposits Around Antarctica 4-2 Sedimentation in the Ocean

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. 4-2 Sedimentation in the Ocean

The rate of sedimentation depends on the type of sediment in deep sea. Figure 4-13 Clays in Deep-Sea Muds 4-2 Sedimentation in the Ocean

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. 4-2 Sedimentation in the Ocean

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 4-2 Sedimentation in the Ocean

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 Ocean 4-2 Sedimentation in the Ocean

Stratigraphy of the Pacific Basin Figure 4-18b Stratigraphy of the Pacific Basin 4-2 Sedimentation in the Ocean

4-2 Sedimentation in the Ocean Figure 4-18c Model to Account for Pacific Stratigraphy 4-2 Sedimentation in the Ocean

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. 4-2 Sedimentation in the Ocean

The Drying Up of the Mediterranean Sea The “Drying-Out” Model The “Uplift” Model