Sediment on the Sea Floor

The origins of sediment

I. Weathering

- breaking older rocks down into particle & solutions

*Two types.....1) mechanical, and 2) chemical

Controls on the rates of sediment production

• Topography

• Climate

2 types of sediment

• Clastic - particles

• Chemical - ions

Erosion & Transport

what moves sediment?

4 agents = 1. Gravity, 2. Wind, 3. Water, and 4. Ice

Deposition => occurs when transport ends

Sediments deposited within broad regional topographic low areas => Basins

Continental Margins - marine environments

Sediments on the Sea Floor

• Why are we interested in ocean sediments?

– History

– Resources

Location of Sediments

• 2 major types of marine sediments based on location

– Neritic

– Pelagic

Types of Sediment

• Classification - Based on Texture

– Grain size

– Shape

– Sorting

– genetic

Types of Sediment

• Terrigenous

• Biogenic

• Authigenic

• Volcanogenic

• cosmogenic

Deposition at Continental Margins

• Important Factors

• Margin Type - active versus passive

• Sediment Supply

• Climate

• Relative Sea Level History

– Eustasy versus subsidence

Shelf Sedimentation

• Profile - predicted distribution

• Why would we predict this distribution?

• Waves & tides

• Storms

Shelf Sedimentation

• Distribution and controls

• Glacio-eustatic S/L change

• Relict sediments

Carbonate Shelves

• Tropical Distribution

• Warm, clear water - lack terrigenous input

• Reefs = carbonate factories

• How do carbonate sediments get distributed on the shelf?

• Tropical storms

Deep-Sea Sedimentation

• Terrigenous versus Pelagic

• Terrigenous - bulk emplacement

• Deep-sea fans on rise

• Turbidity currents

•

• slumps

Deep-Sea Sedimentation

• Glacial Marine Sediments - bulk emplacement at high latitudes

• Why is this sediment very poorly sorted?

• Ice rafting

Deep-Sea Sedimentation

• Pelagic Sediments - pelagic clay

• Sources - terrigenous (fluvial and eolian)

• Why is the bulk of this sediment centered just north and south of the tropics?

Deep-Sea Sedimentation

• Pelagic Sediments - pelagic clay

• Chemical weathering in the tropics

• Eolian sources - deserts

Deep-Sea Sedimentation

• Volcanogenic Sediments

• Why is a large percentage of the terrigenous

sediments in the western pacific volcanogenic?

• “Ring of Fire”

Deep-Sea Sedimentation

• Pelagic Sediments - biogenic

• Ooze - distribution = supply - dissolution - dilution

• Settling rates = very low

• Why do oozes match what is living in the water column so well?

Deep-Sea Sedimentation

• Pelagic Sediments - biogenic

• Calcareous oozes

• Coccoliths, forams, pteropods

• CCD

Deep-Sea Sedimentation

• Pelagic Sediments - biogenic

• Siliceous ooze

• Diatoms and radiolarions

Deep-Sea Sedimentation

• Pelagic Sediments - authigenic

• Manganese and phosphate nodules

Deep Sea Stratigraphy

• Layers of sediment and sedimentary rock on the sea floor document the history of earth

• How do we study these layers?

• ODP cores

• Reflection seismic surveys

Deep Sea Stratigraphy

• Stratigraphy of the Pacific

Resources

• Petroleum

• Gas hydrates